This paper presents a low-model-dependency adaptive droop control strategy for islanded direct current microgrids (DCMGs), integrating real-time state estimation and fuzzy logic-based damping. The decentralized approach combines an Extended Kalman Filter (EKF) for local estimation of output current and DC bus voltage, with a Fuzzy Logic Controller (FLC) that dynamically adjusts a virtual damping term to suppress low-frequency oscillations. Designed for buck-converter-based distributed generation (DG) units, the proposed method improves voltage stability and power sharing without requiring inter-unit communication. A detailed nonlinear model of the DCMG, incorporating converter dynamics and line impedances, is validated through MATLAB/Simulink simulations under two realistic scenarios: step load variation and plug-and-play DG reconnection. Results show an oscillation-free response, enhanced voltage regulation, and reduced power-sharing error compared to conventional droop control, confirming the method’s robustness and suitability for decentralized microgrid applications.

The operation of water electrolyzers with renewable energies means that long-term operation also involves several start-up/shut-down cycles of the system. In particular, for alkaline water electrolyzers (AWE) it is known that shut-down leads to reverse currents, which causes electrochemical degradation and thereby reducing the efficiency. In this work, a modeling framework is proposed and implemented for the electrochemical degradation of nickel electrodes in AWE stacks under start-up/shut-down (SU/SD) operation, and it is achieving good agreement with experiments. Such a model can be used for digital twins of electrolysis plants as well as optimizing its operation.

Power quality is a concern and more and more relevant due to the numerous technologies requiring an interface with the power grid through power electronics converters. Thus, efficient power factor correction (PFC) circuits, ensuring unitary power factor, sinusoidal AC currents, and controlled DC voltages, are of utmost importance. Aligned with such importance, a novel Single-phase Interleaved-based Three-level (SIT) PFC rectifier is proposed in this paper, which can be used in various applications for AC-DC conversion. A thorough explanation of the SIT PFC rectifier is given, supported by a comparison with the traditional solutions. Additionally, a predictive-based current control is discussed. The obtained simulations permit to examine the complete operation principle of the SIT PFC rectifier (i.e., sinusoidal AC current, interleaved-based mode, three levels of voltage, controlled DC voltage), revealing its accuracy even when operating in critical conditions of operation.

When it comes to integrating inverter-based resources (IBRs) into modern grids with varying characteristics like unbalanced systems, low-inertia networks, or very weak grids, synthesizing the synchronization control method (SCM) of the IBR’s phase-locked loop can be a challenging task. This paper provides a unique solution to enhance the three-phase IBR’s SCM using the adaptive dynamic programming (ADP) method based on reinforcement learning. By making the SCM more intelligent and self-learning, IBRs can be easily integrated into diverse grids. To this end, this article investigates the synchronization process’s detailed dynamics, including all incorporating disturbances and parameters required for the first step in designing the ADP method. Afterward, this research synthesizes an optimal controller using an ADP method. It is a data-driven and practically sound approach to the problem under investigation. The new methodology is based on the adaptive optimal control employing measurement feedback to control the output regulation problem of uncertain synchronization process dynamics via the internal model principle. The proposed SCM design deploys an ADP learning methodology to tackle uncertain parameters and unknown disturbance signals to synchronize IBRs during transients, thereby enhancing IBRs’ synchronization in challenging conditions of modern power systems with unbalanced, low-inertia, and very weak grids. For comparison purposes, this paper applies a robust controller based on the well-established$\mu$synthesis approach (benefiting from the well-known$D\text{-}K$iteration process). Comparative simulations are performed; experiments are conducted to reveal the effectiveness and practicality of the ADP-based optimal SCM proposed in this paper.Note to Practitioners—As different nations strive to combat global warming and accelerate decarbonization, power and energy systems are undergoing a significant shift. Inverter-based resources are being used as an essential component to achieve these goals. However, studies have revealed that designing synchronization control methods of the inverter-based resources’ phase-locked loop in unbalanced, low-inertia, and very weak grids is challenging due to the need for accurate dynamic models and other factors. This study revisits the synchronization process’s detailed dynamics. It also proposes a novel adaptive dynamic programming strategy using intelligent self-learning approaches to the synchronization control method associated with inverter-based resources. This method utilizes an optimal control to synthesize the adaptive dynamic programming control strategy for the inverter-based resources’ synchronization process. Besides, it employs measurement feedback to control the output regulation problem of uncertain dynamics of inverter-based resources’ synchronization process via the internal model principle. As a result, this paper makes this process data-driven. It utilizes a learning methodology using adaptive dynamic programming to address uncertain parameters and unknown disturbance signals associated with the dynamics derived and formulated for the problem under investigation. Thus, the proposed method applies to controlling inverter-based resources’ synchronization process even in cases with slow parameter variations caused by different factors. It can compensate for all functional disturbance signals affecting the dynamics of the systems. In fact, unlike traditional methods that need an exact dynamic model of the inverter-based resources’ synchronization process to design and tune the controller to achieve a proper transient response, the proposed control system trains itself and does so. This study’s simulations and experiments reveal that the above points give the proposed approach a competitive edge over the existing methodologies.

Grid-forming converters have demonstrated their ability to enhance the operation of renewable energy resources by providing essential grid voltage and frequency support. However, control delays can cause the output impedance of the converter having a negative-resistance region, which potentially leads to high-frequency instability in voltage control. While passivity-based design is typically employed to shape the output impedance, aspects such as ease of implementation, robustness, and constraints related to LC-filter design have not been fully explored. To address this gap, this paper examines four feedforward damping methods with varying sampling rates, ultimately recommending sixteen-sampling capacitor voltage feedforward as the optimal approach. The effectiveness of proposed approach is validated through experiments, with grid current feedforward used as a benchmark for comparison.

Grid modernization and large-scale integration of inverter-based resources (IBRs) into distribution systems have resulted in the development of new control strategies relying on information and communication technologies. To this end, this article proposes a distributed secondary control algorithm using an event-triggered mechanism for exchanging information among IBRs over digital communication channels in islanded modern microgrids. Unlike the existing event-triggered studies, the proposed method is based on a nonlinear mapping technique for encoding shared data over digital communication channels, making it suitable for real-world applications. It enables the control system to use digitized and encoded data instead of typical continuous analog information, resulting in the more efficient usage of communication infrastructures. As a result, it can be regarded as a practical algorithm for stabilizing voltage and frequency during the transient and steady-state response of autonomous modern microgrids considering computational constraints and the limited bandwidth of communication systems. Finally, comparative simulation studies and experimental results validate the performance and effectiveness of the proposed algorithm.

The control of heat–electricity-integrated multiple microgrid (MMG) systems is greatly challenged by anomalous measurements and inaccurate physical electricity and heat network models. Through the systematic integration of graph surrogate models, trajectory history information, and confederate image (CI) technology based distributed multiagent deep reinforcement learning (MADRL), we propose a robust coordinated control approach for the optimization of MMG systems. Each MG in the MMG system is first represented as a graph with tree topology that is processed by a graph neural network (GNN)-based module to produce robust representations of the measurements. Subsequently, the GNN-based module produces information that is fed into a fully connected layers module to model realistic power and thermal flow using historical data in a supervised manner, thereby forming the graph surrogate models. Before the MADRL training, the GNN-based module from trained surrogate models is embedded in the policy network of MADRL. With the support of CI, the state information and information from the GNN-based module are proceeded by the extracting trajectory history feature module. This process endows the MADRL-based controller with the ability to identify and correct anomalous measurements. The information from the GNN-based module further enhances the robustness against anomalous measurements. The trained surrogate models provide the reward signal to MADRL during MADRL training. It enables the proposed approach to be independent on accurate MMG parameter estimates. The effectiveness of the proposed approach is validated by the simulation results.

In this paper, a novel LLC-asymmetric half-bridge flyback converter (AHB) that can realize a wide range of voltage gains is proposed. This type of topology utilizes the idea of topology morphing to realize the mode transition between LLC mode and AHB mode by adding a switch. The sharing of the same set of resonant tank parameters for both LLC and AHB can be realized by suitable resonant tank parameter design, which allows this topology to use the AHB mode at low voltage gains and the full-bridge LLC mode (FBLLC) and half-bridge LLC (HBLLC) modes at higher voltage gains, and each topology operates in its more suitable operating range. The design considerations, design ideas of this topology are discussed in this paper. Finally, the performance and realizability of the proposed topology are confirmed by simulation results.

Grid-forming static synchronous compensator is an effective solution for inverter-based resources for reactive power support at the point of common coupling. However, the alternating voltage controller design is not fully investigated, and the potential high-frequency resonance may be triggered due to the control delay and the grid capacitive compensation. This paper mainly focuses on the virtual admittance-based voltage control, and the dissipative region of the converter output impedance in the high-frequency range is first discussed. Afterward, a passivity-based damping method is proposed using capacitor current feedforward and capacitor voltage feedforward, and the dissipative region can be optimized to the Nyquist frequency. Finally, the effectiveness of the proposed method is validated through the case study.

This paper proposes a novel single-stage single-phase transformerless topology based on a buck-boost converter for grid-connected photovoltaic (PV) inverters. The proposed inverter has a wide input voltage range, low total harmonic distortion of current, and effective suppression of common-mode leakage current. The single-input structure ensures that it does not suffer from energy imbalance problems. The new inverter utilizes dead beat control and refines the method of controlling the inverter when the input energy is insufficient. The simulation results verify that the proposed grid-connected PV inverter maintains high grid-connected power quality both during normal operation under conventional conditions and when operating under discontinuous conduction mode (DCM) during energy insufficiency. The simulation models the operating mode of the inverter under abnormal environments, such as load changes and grid voltage transients, which proves that the proposed inverter under dead beat control has a better dynamic performance.

This paper presents the design of an output-series active-clamp flyback high-voltage power supply. By utilizing an output-series connection, the voltage stress on rectifying diodes is reduced. Active-clamp technique is adopted to address issues such as reduced efficiency and high voltage stress on the main switch, which are caused by increased leakage inductance in the transformer due to insulation requirements of high-voltage outputs. The operational principles and design considerations of the converter are introduced, with particular attention given to the transformer's electric field distribution. A prototype is built to validate the feasibility of the system design.

As the search for sustainable, environmentally friendly energy sources continues, DC devices such as new energy-electric vehicles and energy-saving LED lights have been actively promoted. Consequently, the necessity for the DC microgrid in grid system development will become increasingly apparent, and the research on three-terminal output converters is increasing. Besides, double-frequency ripple power is an inherent problem in single-phase power electronic systems. This paper proposes a three-terminal output AC/DC converter with automatic power decoupling and common ground for the DC microgrid as a solution to the issues above. The equivalent circuit has been subjected to a detailed analysis to elucidate its underlying operating principles. Due to the structure of the common ground, the common mode leakage current can be eliminated in this converter. In addition, the implementation of automatic power decoupling enables the replacement of electrolytic capacitors with film capacitors, leading to higher power density and longer lifespan. Furthermore, the employed deadbeat control has a fast dynamic response capability. Finally, the simulation results are presented to verify the theoretical analysis and the performance of this converter.

This article presents a novel transformer-less single-stage buck-boost inverter (SSBBI) utilizing coupled inductors and its dual-mode time-sharing control method. The leakage current can be completely suppressed by connecting the neutral of the electrolytic capacitors to the common ground of the power grid. Besides, only one MOSFET operates at high-frequency in Buck and Boost mode. As a result, in theory, high conversion efficiency can be guaranteed for the proposed inverter. Moreover, compared with conventional Aalborg inverters, the number of switches, diodes, and inductors is further reduced to reduce cost and increase power density. In addition, the operating principle based on equivalent circuits and the control strategy of the proposed inverter are given in this article. As a proof of concept, the simulation results based on PSIM of the proposed SSBBI with different input voltages and output powers and a 110 V power grid are provided.

Virtual oscillator control (VOC) is a grid-forming controller designed for microgrids, where inverters are regulated to mimic the dynamics of weakly nonlinear oscillators. VOC operates in the time domain and offers a faster transient response compared to the virtual synchronous generator. However, conventional VOC implementations often result in reduced power system inertia, which poses a risk to frequency stability due to the lack of inertia. The inertial response is introduced into VOC by integrating the swing equation of a synchronous generator to represent virtual inertia and damping. Unlike real synchronous generators, the parameters of the swing equation can be adjusted in real time to support frequency stability. By employing varying levels of virtual inertia and damping during frequency deviation and recovery, improvements of 10.4% in frequency nadir and 4.9% in the rate of change of frequency are achieved compared to fixed inertia setups. Simulation results confirm the effectiveness of the proposed approach.

This paper proposes a multivariable, adaptive, robust (MAR) control strategy for islanded inverter-based resources (IBRs) operating as grid-forming inverters. The proposed method is employed in the inner control loop of the primary layer in the hierarchical or decentralized structures for the islanded operation of microgrids. The MAR control scheme is responsible for stabilizing IBRs’ output voltage in autonomous operations of microgrids, considering mismatched input voltage disturbances from the grid side and a large amount of system uncertainty. The control methodology introduced in this paper does not rely on the system’s physical parameters, such as microgrid topology, load dynamics, LCL filters, and output connectors. As a result, there is no need to know the nominal values or the bounds of uncertainties in system dynamics. The MAR control method uses online adaptation rules first to identify and then adjust the control parameters of the closed-loop system based on an arbitrary dynamic model. In other words, the MAR method replaces the actual dynamics of IBRs with predetermined dynamics of interest. Simulation results in the MATLAB/Simulink environment confirm the capability of the scheme introduced for the closed-loop stabilization and voltage regulation in the presence of disturbances and a significant amount of uncertainty under various case studies; moreover, comparative simulations by comparing the presented method with other studies using sliding mode control are provided. Finally, experiments verify the effectiveness and practicality of the proposed MAR control scheme.Note to Practitioners—Inverter-based resources are integral parts of current and especially future power and energy systems; with increasing concerns about carbon footprints, the tendency to substitute traditional synchronous generators with inverter-based resources increases. This transition towards the widespread use of power electronics devices needs careful studies regarding the stability and control of power converters. Although existing studies are addressing potential control system challenges, they suffer from complex mathematical computations and the need for the system’s preliminary information. With this in mind, this study proposes a multivariable, adaptive, robust control strategy for the inner voltage control loop of grid-forming inverters. This method utilizes online estimation algorithms to identify inverter-based resources’ parameters and tune control system parameters simultaneously, making it applicable even to cases with slow parameter variations caused by aging or environmental changes. It can compensate for potential voltage disturbances from the grid side and enable the designer to replace undesirable dynamics of inverter-based resource units with arbitrary and stable dynamics of interest. In fact, unlike traditional methods that need control parameters and gains to be tuned to achieve a proper dynamic response, the control system designer can choose reference dynamics and enforce the closed-loop system to imitate the dynamical model selected. This model is usually chosen based on established priorities, such as response time and other transient behaviors. Moreover, this method does not require complex mathematical and algebraic calculations to design and implement. It can be easily applied to inverter-based resource units after selecting the desired reference dynamics, as shown through this study’s experimental result. The above points give this method a competitive edge over the existing algorithms, especially in practical applications.

This article proposes a robust multiarea distribution system state estimation method for interval estimation of state variables based on a physics-informed decentralized graphical representation network and Gaussian process (GP)-aided multiarea state estimators. The real-time and pseudomeasurements are first cast to a graph with tree topology and a graph attention-based representation network is employed to capture the structural information between measurements from the historical data. A centralized pretraining and distributed inference framework is developed to extract essential global information from historical data and extend it to various subregions. Then, the robust nodal features extracted by the graphical network are fed into the GP with a multitask kernel for multiarea state estimation. The adopted kernel can find relevance between tasks for different subregions that are useful for the multiarea state estimation. The embedding of structural information in the representation network enables the proposed method to achieve robustness in the presence of outliers. The adopted kernel further allows us to reduce the reliance on network communication and achieve accurate multiarea state estimation. It also offers the ability to quantify the uncertainty of state variables, yielding more valuable estimation outcomes. Experimental results demonstrate the effectiveness of the proposed method in handling abnormal data and accurately quantifying the uncertainty of state variables.

The frequency and voltage stability of grid-forming virtual synchronous generator (GFM-VSG) grid-tied system becomes significant in inertia and damping support when GFM-VSG is attached to the power network. In this article, we propose a generic open-loop system model for the frequency–voltage induced-stability analysis, where the dynamics of rate of change of frequency (RoCoF) is a dynamic process that acts on the rate of change of voltage and then, in turn, reacts on RoCoF. In addition, frequency self-stability is evaluated by magnitude–phase feedback analytical model, where the frequency dynamics are identified by the interaction between RoCoF and frequency bias (FB). Also, it is found that inertia is the origin of occurrence of low-frequency oscillation, which induces a natural phase bias between RoCoF and FB. It is found that GFM-VSG can operate stably in weak grid but cannot operate well in ultrastrong grid condition. Finally, theoretical analysis is validated by simulations and experiments.

In high power application, a single active power filter (APF) limited by its capacity cannot compensate for whole harmonics. APF parallel system is thus adopted to solve this problem. Centralized control scheme for the parallel system features good current sharing ability, but subject to communication fault. On the other hand, decentralized control schemes cannot share current properly. This paper proposes a decentralized control scheme for modular APF parallel system in which all APF modules have equal status and share the current in proportion to their own capacities without central controller. What is more, plug and play of an APF is achieved, and current sharing can be done automatically. The correctness and effectiveness of the scheme have been testified by simulations.

Grid-side current feedforward has proven to be an effective approach in improving the dissipativity of dual-loop voltage control in grid-forming converters. However, due to the control delay, the dissipative characteristic of the converter output impedance can be significantly impacted by the designed resonance frequency of the designed LC-filter and any deviation in the filter parameters. To address this issue, the proposed method in this paper replaces grid-side current feedforward with capacitor current feedforward and capacitor voltage feedforward, resulting in enhanced dissipativity below the Nyquist frequency. Additionally, the proposed method improves the dissipativity robustness against deviation in the LC-filter parameters. Moreover, it allows for the LC-filter resonance frequency to be designed freely, without the need to consider the critical frequency. The effectiveness of this proposed method is validated through a case study.

In DC microgrid, the uncontrollable DC link short-circuit current seriously shortens the life of the electrolytic capacitors in conventional AC/DC converters. To solve the issue, a new AC/DC converter with controllable DC link short-circuit current is proposed. Simulation results have verified the performance of the proposed converter.

In order to mitigate the negative effect of multi-frequency ripple power, a non-isolated micro-inverter with active power decoupling has been proposed in recent years, which shows some potential advantages, in terms of low cost, fewer switches, high efficiency, and a brief system control strategy. However, it has two independent PV panel input dc sources, which may be asymmetrical in realistic PV systems, resulting in a decrease in the power generation capacity of the whole system. To address this problem, an improved non-isolated micro-inverter topology with active power decoupling is proposed in this paper. Similar to the conventional micro-inverter, it can effectively suppress the common-mode leakage current. Different from the conventional micro-inverter topology, it uses a single PV panel input dc source and achieves positive and negative half-line cycle equivalent dc sources through two split-bus capacitors. The simulation has validated the effectiveness of the proposed non-isolated micro-inverter.

Grid integration of renewable energy (REN) requires efficient and reliable power conversion stages, particularly with an increasing demand for high controllability and flexibility seen from the grid side. Underpinned by advanced control and information technologies, power electronics converters play an essential role in large-scale REN generation. However, the use of power converters has also exposed several challenges in conventional power grids, e.g., reducing the system inertia. In this article, grid integration using power electronics is presented for large-scale REN generation. Technical issues and requirements are discussed with a special focus on grid-connected wind, solar photovoltaic, and energy storage systems. In addition, the core of the energy generation and conversion—control for individual power converters (e.g., general current control) and for the system level (e.g., coordinated operation of large-scale energy systems)—is briefly discussed. Future research perspectives are then presented, which further advance large-scale REN generation technologies by incorporating more power electronics systems.

The articles in this month’s issue provide insight into the most important powerelectronics- based technologies for energy transition.

Effective detection of fault in rolling bearings with a limited amount of data is essential for the safe operation of electric machines. This article proposes a novel meta-learning-enabled method for the detection of fault in rolling bearings of electric machines under varying working conditions with limited data. The fault diagnosis under various working conditions is cast as a few-shot classification problem, which is solved using a model-agnostic meta-learning-based model. Specifically, a meta-learner is first trained using a series of interrelated fault-diagnosis tasks under various working conditions. During this stage, the gradient-by-gradient rule is utilized for parameter optimization to achieve an effective representation of these tasks. Then, the parameters of the meta-learner are refined on a new task. This technique can achieve fast adaptation to new tasks by utilizing only few-shot samples. The proposed method can obtain high fault-detection accuracy under various working conditions when only a limited amount of data is available. Comparative tests among various methods were carried out on the Case Western Reserve University Bearing Dataset and the Paderborn University Rolling Bearing Dataset. The results show that the proposed model performs better than other state-of-the-art methods under various working conditions; our method has stronger generalization ability and faster adaptation ability. The fault diagnosis accuracy for both datasets was at least 99%, which proves that the proposed strategy can be flexibly applied to various scenarios.

The active and reactive power controllers of grid-forming converters are traditionally designed separately, which relies on the assumption of loop decoupling. This paper proposes a full-state feedback control for the power loops of grid-forming converters. First, the power loops are modeled considering their natural coupling, which, therefore, can apply to all kinds of line impedance, i.e., resistive, inductive, or complex. Then a full-state feedback control design is used. By this way, the eigenvalues of the system can be arbitrarily placed to any positions in the timescale of power loops. Therefore, the parameters can be directly chosen by the predefined specifications. A step-by-step parameters design procedure is also given in this paper. Experimental results verify the proposed method.

This paper proposes an intelligent primary control strategy for voltage source converter (VSC)-based ac microgrid (MG). This is implemented by using a proportional resonant (PR) regulator adopted in the inner level of primary control of VSCs. An approach based on brain emotional learning (BEL) is proposed to provide an online and adaptive tuning of control coefficients of the PR regulator. The proposed BEL approach is fully model-free, indicating that the coefficients are regulated without previous knowledge of the system model and parameters. The outer level of primary control employs a droop control loop to regulate power-sharing among different distributed generators. Unlike the conventional control methods with constant coefficients, which are typically designed for a specified operating condition, the proposed approach avoids the dependency of the converter control system on the operating conditions and accommodates varying loading conditions. A sensitivity analysis is also performed to investigate the effects of PR coefficients on the system stability. Moreover, a Mesh analysis is carried out to examine the stability of dominant frequency modes of the whole AC-MG using the proposed control scheme. Simulations are provided to demonstrate the performance of the proposed control scheme.

In grid-connected inverter systems, the three-phase asymmetric LCL (A-LCL) filter has outstanding characteristics of simple structure, almost the smallest total inductance, and the strong resistance to the adverse effects of parameter shifts. Nevertheless, the order of this kind of power filter is high, and the control model is complicated due to its asymmetric structure. In this paper, a simplified modeling method, which effectively reduces the system order is proposed, without affecting the control performance. Then, the Kalman filter estimation (KF-estimation) is adopted to reconstruct the PCC voltage. A 380 V/50 Hz/6 kW three-phase laboratory setup has been developed to verify the correctness and effectiveness of the proposed control strategy.

Dual active bridge (DAB) converters are becoming one of the most reliable interfaces due to their high voltage range, easy realization of zero voltage switching (ZVS), galvanic isolation, etc. To meet specific consumer requirements in DC microgrids, DAB converters operate with different topologies. In this paper, a finite control set model predictive control (FCS-MPC)-based power sharing control is proposed when DAB converters are in different structures which are input series-output series, input parallel-output parallel, input parallel-output series, and input parallel-output parallel connecting structures. By analyzing the power balance relationship of the input port and output port, it determines the variable (input voltage/current or output voltage/current) which should be controlled to realize the power sharing. And then the cost function is designed based on the control strategy. Besides, this paper proposes a Kalman filter based parameter estimation method for the DAB converter. In this case, it guarantees the robustness of the MPC algorithm. Finally, the simulation results prove the effectiveness of the proposed method.

Utilizing energy storage systems (ESSs) to perform multiple grid supporting services is an effective way to rationalize the investment of ESS. It is crucial to choose the matching energy storage technologies (ESTs) for achieving the specific stackable services as well as reducing investment costs and increasing revenue. Therefore, the EST suitable for providing stackable services, which includes energy arbitrage and frequency regulation, is proposed in this paper based on a framework. The framework considers the influence of technical, economical, and lifetime parameters. It mainly consists of technical preselection and economic analysis. At first, the requirements of provided services to ESS are adopted as the hard constraints to select the technically feasible ESTs. For economic analysis, a cost-benefit evaluation model for stackable services is proposed. It can quantitatively describe the influence of ESS parameters on cost and revenue. The analysis is based on the estimated parameters of ESTs in 2022. The load data and frequency regulation data are from the IEEE 33-bus distribution system and the PJM market.

In recent years, the deadbeat-control-based MPC algorithm (DBC-MPC) has been widely studied because it can effectively reduce the number of candidate vectors. However, for the LCL-type grid-connected inverter, when calculating the reference value of the inverter output voltage, the control algorithm only addresses the influence of the current tracking error on the reference value of the output voltage of the inverter, and ignores the influence of the filter capacitor voltage, resulting in poor control performance. Therefore, in this paper an improved DBC-MPC is proposed for the LCL-type grid-connected inverter, where both effects of current and voltage tracking errors on the control performance are fully considered. Compared with the traditional DBC-MPC algorithm, the control performance of the system is greatly improved, while still effectively reducing the number of candidate voltage vectors. Finally, a three-phase simulation model is built to verify the control performance of the proposed algorithm.

This paper proposes a non-invasive fault location method for modular multilevel converters (MMC) considering light load conditions. The prior-art fault location methods of the MMC are mostly developed under full load conditions. However, it is revealed that the faulty arm current will be suppressed to be unipolar when the open-circuit fault happens on the submodule switch under a light load. This leads to the capacitor voltage of the healthy and faulty submodules rising or falling with the same variations, increasing the difficulty of fault location. The proposed approach of injecting the second-order circulating current will rebuild the bipolar arm current of the MMC and enlarge the capacitor voltage deviations between the healthy and faulty SMs. As a result, the fault location time is significantly shortened. The simulations are carried out to validate the effectiveness of the proposed approach, showing that the fault location time is reduced to 1/6 compared with the condition without second-order circulating current injection.

The abnormal events, such as the unprecedented COVID-19 pandemic, can significantly change the load behaviors, leading to huge challenges for traditional short-term forecasting methods. This article proposes a robust deep Gaussian processes (DGP)-based probabilistic load forecasting method using a limited number of data. Since the proposed method only requires a limited number of training samples for load forecasting, it allows us to deal with extreme scenarios that cause short-term load behavior changes. In particular, the load forecasting at the beginning of abnormal event is cast as a regression problem with limited training samples and solved by double stochastic variational inference DGP. The mobility data are also utilized to deal with the uncertainties and pattern changes and enhance the flexibility of the forecasting model. The proposed method can quantify the uncertainties of load forecasting outcomes, which would be essential under uncertain inputs. Extensive comparison results with other state-of-the-art point and probabilistic forecasting methods show that our proposed approach can achieve high forecasting accuracies with only a limited number of data while maintaining the excellent performance of capturing the forecasting uncertainties.

The uncertainties of charging behavior of electric vehicle (EV) owners have a negative impact on the loss of life (LOL) of distribution transformer. This article proposes a decentralized EV charging framework for optimization of the LOL of distribution transformer considering the dissatisfactions of EV owners. Specifically, long-short-term memory (LSTM) neural network is first utilized to capture the uncertainties caused by the load demand and electricity price. After that, each EV is modeled as an intelligent agent and a multiagent deep reinforcement learning approach is applied to solve the coordinated charging problem based on the forecasting information by the LSTM network. All the agents are trained in a centralized manner to develop coordinated control strategies while informing decisions based on local information when finishing the training process. The proposed approach can achieve coordinated charging management of EVs based on local information, which helps preserve the privacy of EV owners, reduce the cost induced by the deployment of communication devices, and avoid single-point failure. In addition, the parameter space noise and deep dense architecture in reinforcement learning are introduced to overcome premature convergence, training instability, and inefficiency due to the large action space of multiagent scenario. Comparative tests are carried out among several benchmarks utilizing real-world data to illustrate the effectiveness of the proposed approach.

The unbalance of the state-of-charges (SOCs) may be among paralleled energy storage systems (ESSs) is harmful for the system operation. This paper proposes an adaptive control strategy to achieve the balance of SOCs among the paralleled ESS-based virtual synchronous generators (VSGs) in a completely decentralized way. The parameters of the virtual governor are designed to change according to the local SOC taking the stability and steady-state frequency limitation into consideration. To realize the adaptive control, this paper starts with an analysis of the generalized requirements of the adaptive terms. Then linear relationships are chosen as an example to construct the adaptive controller. The IEEE 9-Bus system is used to verify that, with the proposed method, the SOC balancing can be gradually realized no matter the differences in the initial values and disturbances without the communication network.

The stability of frequency is at risk with increasing penetration of power electronic converters. In this case, the power grid will lack the moment of inertia to maintain a stable voltage and frequency in the event of a large disturbance. In order to improve the stability of the power grid, traditional grid-following control is needed to be transformed to grid-forming control. This paper analyzes the control structure of grid-following control and grid-forming control. Moreover, a case study is exemplified to compare the performance of two control strategies responding to frequency disturbances. Finally, a simulation model of 15 kW grid-connected converter is built in Matlab/Simulink to discuss the performance of the grid-following and grid-forming converters under different working conditions.

For the type-4 wind generation system, there is a dc link in the back-to-back converter. Whether the dc-link voltage should be controlled by the grid-side converter (GSC) or machine-side converter (MSC) is still an open question, although it is usually controlled by the GSC. Considering the stability of the system mainly depends on the GSC under weak grid conditions, two typical control methods on the GSC (i.e. power control and dc voltage control) are compared in this paper. It is found that the small-signal stability of these two control schemes are basically the same when choosing the same control loop bandwidths. Even so, the power control scheme is better than the dc voltage control scheme, because a wider range is available for tuning the power loop bandwidth to improve stability. Thus, the dc voltage control carried out on the MSC should be superior to the GSC under weak grid conditions.

Two-three (2/3)-level dual-active-bridge (DAB) DC-DC converters have high potential to be applied in the high-voltage (HV) applications due to their higher voltage blocking capability compared to the two-level DAB converters. However, capacitor voltage balancing will be a crucial issue for the neutral-point-clamped (NPC) bridge in the HV side. In order to regulate the capacitor voltages, this paper proposes a complementary-small-vector (CSV) balancing control scheme. According to the relationships among the polarity of the neutral-point current, the small vectors, and the polarity of the transformer current, two CSV pairs are obtained. In the proposed scheme, if a small vector is diagnosed as an adverse small vector for the capacitor voltage balance, it will be replaced by its CSV. After that, the polarity of the neutral-point current can be changed to increase the required charge injected into or drawn from the neutral point. Meanwhile, the waveforms of the current and voltage during the balancing process will remain unchanged. Therefore, the power fluctuation and current overshoot can be avoided. Furthermore, the implementation of the proposed scheme under different operating modes are demonstrated. Finally, the simulation results verify the performances of the proposed balancing control scheme.

The power supply system design of a marine data buoy system is a challenge. Due to cost reasons, it is difficult for marine buoys to obtain electricity directly from the power grid. At present, marine buoys use solar energy, wind energy or wave energy to supply power to sensors. Among them, the employment of wave energy and solar energy has broad application prospects due to the complementary power production of these sources. This paper presents a new wave energy conversion (WEC) device for a marine buoy, which is composed of a floating body and a power generation device. In addition, a three-dimensional finite element simulation model of the buoy movement is established, and the simulation is carried out using hydrodynamic software. On the basis of simulation, experiments are carried out on a 50 kg core power generation unit to estimate the power generation performance of the proposed WEC device.

This paper presents an IGBT open-circuit fault diagnosis method based on Kalman filter model and reconfiguration algorithm for H6 grid-tied inverter. This method can detect open-circuit fault by only sampling the inductor current through Kalman filter model. Then, through the reconfiguration algorithm, the H6 grid-tied inverter is reconfigured as a Boost-type converter to identify the faulty IGBT device. The Kalman filter model can also predict the grid voltage provided to the control loop, thus saving the ac voltage sensor for the system. This method does not require extra sensors and diagnostic circuits, so it can be easily embedded in the DC/AC inverter system.

The electrification of the transportation sector is moving on at a fast pace. All car manufacturers have strong programs to electrify their car fleet to fulfill the demands of society and customers by offering carbon-neutral technologies to bring goods and persons from one location to another. Power electronics technology is, in this evolution, essential and also in a rapid development technology-wise. Some of the introduced technologies are quite mature, and the systems designed must have high reliability as they can be quite complicated from an electrical perspective. Therefore, this article focuses on the reliability of the used power electronic systems applied in electric vehicles (EVs) and hybrid EVs (HEVs). It introduces the reliability requirements and challenges given for the power electronics applied in EV/HEV applications. Then, the advances in power electronic components to address the reliability challenges are introduced as they individually contribute to the overall system reliability. The reliability-oriented design methodology is also discussed, including two examples: an EV onboard charger and the drive train inverter. Finally, an outlook in terms of research opportunities in power electronics reliability related to EV/HEVs is provided. It can be concluded that many topics are already well handled in terms of reliability, but issues related to complete new technology introduction are important to keep the focus on.

The papers in this special section focus on applications of artificial intelligence in industrial power electronics and systems. The grid infrastructures and modernization, as well as the integration of renewable energies and using smart meters, can generate a large amount of data. These can lead to high complexity in the power system/electronics operation and control. Moreover, grid contingencies due to the natural disasters and cyber/physical attacks are highly unpredictable and costly preventable, which require fast and reliable data processing to preserve grid reliability and resiliency. Furthermore, the reliability of the power electronics devices and interfaces are very important, and can be improved by using the large data of measurements during long term operation. To this end, artificial intelligence (AI) techniques can potentially make it possible to provide new solutions to power electronics and power system operations and analysis. This special issue aims to investigate applications of AI in power system operation, analysis, planning, cybersecurity, as well as power electronics control, modulation techniques, reliability of the power electronics switches, and efficiency improvement in power electronics applications.

Integrated energy systems become more and more important to realize the energy complementary property. Micro-integrated energy system, served as the terminal integrated energy system, will have the electricity delivered directly to the local customers by energy hubs (EHs). Here, the data and information of the EHs during the operation are confidential and should be kept by each owner. Therefore, this article designs a dual-decomposition-based distributed algorithm to address this problem, where the optimal consensus problem is used for the dual problem to update the multipliers. The primary and dual problems are alternatively solved until the Karush-Kuhn-Tucher condition is satisfied. For the proposed distributed algorithm, the feasibility can be strictly guaranteed during the iteration process. Moreover, theorems and lemmas are proved for the linear convergence rate. The numerical results verify the effectiveness of the proposed algorithm.

In this period when the technology has been developing rapidly, resources are being exhausted as well conversely. Therefore, possible problems and the ways of handling them are changing and new problem-solving techniques are being tried. Due to the intermittent nature of photovoltaic (PV) systems, which have solar irradiance and temperature as a source, the problem of maximum power attaining arises. The solution to this problem aims to make optimal use of PV energy production. This study presents a metaheuristic algorithm to solve the problem of maximum power point tracking (MPPT) from PV systems which are an indispensable part of renewable energy technology. Symbiotic organisms search (SOS), a powerful and dynamic metaheuristic optimization algorithm, is adopted as a solution to this problem. The SOS algorithm has been inspired by the symbiotic interactions adopted their behavior to survive in the ecosystem, which has developed to solve optimization and engineering problems. The proposed algorithm, i.e., SOS, has been embedded in MATLAB/Simulink platform to test for accuracy and efficiency. From the obtained results, this evolutionary SOS algorithm is seen obviously to outperform in certain points more than the classical Perturb and Observe (P&O) and Incremental Conductance (INC) methods for the same system and conditions.

In grid-tied DC/AC inverter applications, the equivalent grid impedance often varies widely, which may limit the bandwidth of the inverter control system. This paper introduces a new method to perform the online estimation of the equivalent grid impedance with a Kalman filter by observing the grid voltage and grid current, as well as the voltage at the point of common coupling (PCC). With the estimated grid impedance, a high control bandwidth can be achieved for the grid-tied inverter through online regulation of the proportional coefficient of a current controller. A MATLAB/Simulink model of a grid-tied single-phase inverter has been setup to demonstrate the effectiveness of the proposed method. The simulation results show that the online estimated impedance is accurate enough and the inverter system can continuously maintain a high bandwidth, even under weak grid operating conditions.

Multi-sampling control provides an attractive way to reduce the control delays in LCL grid connected inverters, then the bandwidth and stability margin will be improved. However, high frequency switching harmonics (SHs) are introduced in the control loop, which may cause low frequency aliasing and deteriorate the power quality. In this paper, the multi-sampled currents are reconstructed through the double-sampled average currents, which is simple and easy to implement in a microprocessor. As a result, most of the SHs are removed and the power quality is better than the conventional multi-sampling control. Finally, a single-loop pseudo-derivative-feedback control with inverter current feedback is employed, and the effectiveness of the proposed method is verified through simulation.

Virtual oscillator control (VOC) has been proposed for Microgrids, since compared to the droop control method, VOC has a faster transient response. However, the output voltage of the conventional VOC always contains the third-harmonic. Thus, in the grid-connected mode, the third-harmonic voltage causes the generation of significant third-harmonic current which is injected into the power grid. In this paper, by analyzing the nonlinear oscillator and simplifying the nonlinear current source in the oscillator, a novel VOC for three-phase DC/AC inverter is proposed, where the third-harmonic of the oscillator output voltage can be successfully eliminated, whether in the islanded or grid-connected mode of operation. In addition, compared with the traditional VOC, the dynamic response of the proposed VOC-based inverter can be significantly improved, especially in the islanded mode. Experimental device designed on the DSPACE DS1202 is developed to verify the feasibility of the proposed strategy.

Thanks to the solid standards and principles of design and restoration planning after a blackout, power systems in developed economies generally show a high level of resiliency. Nevertheless, this power system restoration practice strongly relies on conventional power plants, e.g. large thermal power plants. As future global goals aim at reducing the use of fossil fuels and lowering carbon-dioxide emissions, conventional power plants are often taken out of operation. These are characterised by slow start-up times and considerable use of fossil fuels. In this context, large offshore wind farms (OWFs) show potential as renewable-based black start (BS) service providers. These can be equipped with a self-starter, e.g. synchronous generators or innovative power-electronic-based converters, such as battery energy storage systems (BESSs) and/or grid-forming wind turbines in order to BS the system. Additionally, state-of-the-art complementary devices such as STATCOMs or synchronous condensers can help with dynamic regulation and support the OWF both in island operation and BS. In this paper, an overview of different system configurations for OWF BS is presented. Firstly, the requirements for BS from non-conventional power plants are outlined. Afterwards, the challenges faced by OWFs to fulfil these requirements are identified. Finally, different solutions for system configuration to equip OWFs for BS are proposed.

This paper proposes an optimal modulation scheme for two-three (2/3)-level dual-active-bridge (DAB) DC-DC converters to guarantee zero-voltage-switching (ZVS) operation and minimize the current stress. Based on the unified ZVS principle, six operating modes are defined and constraints of each ZVS mode are then obtained. According to the operating modes, the power transmission model and current stress under all voltage conversion ratios are derived for optimization. The analytical solutions for minimum current stresses are obtained by using the Lagrange multiplier method with Karush-Kuhn-Tucker conditions. With the proposed modulation scheme, both the conduction and switching losses can be reduced, and thus, the entire efficiency can be improved. Finally, simulation results verify the theoretical analysis and the performance of the optimal modulation scheme.

In order to achieve low leakage currents, a symmetrical Z-source hybrid converter is proposed to simultaneously obtain a wide range of DC and AC output voltages. The proposed converter is derived from a traditional Z-source converter by replacing the control switch to a highly efficient and reliable inverter concept (HERIC) inverter. To be applied in PV applications, the impedance network is symmetrical, which can clamp the common-mode voltage of the proposed converter to be a constant (i.e., obtaining low leakage currents). A dedicated modulation scheme is introduced so that the symmetrical Z-source hybrid converter can achieve low leakage currents, a wide range of output voltages, high efficiency and reactive power injection. Simulations are performed on a 2-kW symmetrical Z-source hybrid converter to verify the effectiveness.

The Passivity-Based Control (PBC) has been adopted in LCL-filtered grid-tied inverter (GTI). However, the conventional PBC method depends much on accurate mathematical model, where zero steady-state error can't be realized when the accurate model parameters are not available or parameters drift occur. Furthermore, due to the utilizing of three state variables in the conventional PBC controller for LCL-filtered GTI, twelve sensors (voltage and current) must be used in a three phase system, which increase the costs and the failure rate of hardware. In order to handle the problems, a novel state observer based modified PBC (SOMPBC) controller for LCL-filtered GTI is proposed in this paper. Six sensors can be saved by the state observer and zero steady-state error can be easily realized by two modified control methods, where an integral regulator is insert into the conventional PBC controller with two different ways. Simulation platform is built in MATLAB/Simulink and a 3-kW experimental device is carried out with DS1202 to verify the correctness and effectiveness of proposed control method.

Nowadays, the entire world is facing challenges in energy and environment. To resolve these problems, the power systems are interconnected to promote the development of renewable energy sources (RESs). However, the economic dispatch (ED) problem for the global energy interconnection (GEI) should tackle two issues: 1) handle the uncertainty from RES and allocate the responsibility among the interconnected countries and 2) protect the information privacy through the dispatch. Motivated by the above, this article proposes a zonally adjustable robust decentralized ED model for the GEI. In the model, each country is only responsible for its own uncertainty, and tie-line power flows remain unchanged under uncertainties. Moreover, an alternating direction method of multipliers (ADMM)-based fully distributed algorithm is used, in which only limited information should be exchanged between neighboring countries. Finally, a case study on the Northeast Asian countries verifies the effectiveness of the proposed method. Note to Practitioners-Since the renewable energy generation has a spatial correlation among regional countries, global energy interconnection (GEI) aims to combine several power systems together to promote the renewable energy accommodation. However, two problems need to be considered: 1) Information Privacy: The information privacy of the power system in each country should be preserved, which prevents the GEI from conducting a centralized optimal dispatch framework and 2) Uncertainty: The uncertain output of renewable energy resources brings challenge to the power system secure operation. The main contribution of this article is to set up a zonally robust decentralized optimization for the GEI, where the zonally robust economic dispatch (ED) is conducted by the area control error (ACE) system to manage the difference between scheduled and actual generation under the uncertainties, and the alternating direction method of multipliers (ADMMs) algorithm is adopted for decentralizing the zonally adjustable robust ED model, which only needs limited information. In particular, this article uses a real-world example from Northeast Asian Countries to help engineers understand the advantages of the GEI and the new dispatch framework.

To increase the resilience of shipboard power systems, this paper presents an optimal defense strategy to protect critical lines against attacks. In the modeling, an attack is considered to destroy one critical bus, which may result in that all lines are connected to this bus will be out of service unless protection is enabled. Furthermore, after one true attack occurs, the network restoration is performed as soon as possible to pick up the critical loads and maintain system operation. To address the uncertain location of the attacks, a tri-level robust optimal defense strategy is set up to protect the critical lines under the worst attack. Moreover, a nested column-constraint generation method is employed to solve this model. A 60-bus shipboard power system is studied to demonstrate the effectiveness of the proposed model and the defense method.

In this article, a novel passivity-based control strategy is proposed for the exponentially stable tracking controller design of static synchronous compensator (STATCOM) system, which is a single input and single output. The STATCOM is not an input-affine system but a special port-controlled Hamiltonian system form. Hence, it is regularized by using a dynamic extension algorithm so that the proposed tracking control strategy is designed in an input-output linearization framework with a bounded solution to the driven zero dynamics equation. The proposed control strategy is proposed with consideration of the performance and stability of the input-output linearized dynamics. Simulation results show that the proposed control strategy improves the transient performance of the system compared to the previous results even in the lightly damped operating range.

Due to the increasing performance and decreasing price of microcontrollers, applying a high sampling frequency becomes more feasible in modern control. This approach is known as multisampling technology. This paper tries to give an overview of the multisampling application in power electronics converters as it enables a lot of opportunities. First, the multisampling can reduce control delays and thereby break bandwidth limitations in power electronic controllers. Secondly, a smarter control strategy can be realized with more current, voltage and system information acquired through multisampling techniques. However, this approach may also introduce two major drawbacks: risk of dead bands and high-frequency switching ripples, which may degrade the system stability margin. To address these issues, different solutions are explored and illustrated in this paper.

In this paper, an optimized topology for switched-capacitor (SC) multilevel inverter is proposed. The proposed topology, which is referred to as Optimized Switched-Capacitor Multilevel Inverter (OSC-MI), offers a boosted staircase voltage by using only one dc source and fewer switches count. Since each industrial load requires a specific power factor (PF), an optimal converter can be designated in a way that it both satisfies the required PF and employs fewer switches and gate drivers. Therefore, the main strategy of reducing switches count in the proposed topology is to design the converter according to the required PF value. In this paper, the theoretical analytics and comparison results are followed by MATLAB/SIMULINK simulation results to verify the inverter's capabilities.

This paper discusses reliability issues of three different types of capacitors (ceramic, electrolytic and film) applied in the input side of an impedance-source photovoltaic (PV) microconverter having an ultra-wide dc gain range. The study considers a wear-out failure analysis based on a daily PV mission profile. The general operation and control principle are first described. Then the selection criteria of the capacitors are analyzed. Experimental measurements of capacitors temperature are translated into accumulated damage using their corresponding lifetime models. Finally, conclusions are drawn regarding the applicability of different capacitor technologies in impedance-source PV microconverters, where the film capacitor has the lowest damage.

In this article, the conventional landsman DC-DC converter is modified to achieve the high inverting voltage conversion ratio for renewable energy applications. A new Switched Reactive Circuitry (SRC) made of one inductor, one capacitor, and two diodes are incorporated to lift the voltage conversion ratio. The characteristics waveform and operation of the proposed converter is discussed in detail. The proposed converter finds the major role in renewable energy integrated application where the high voltage demanded. The proposed landsman converter is compared with existing landsman converter and recently proposed converter in terms of voltage conversion ratio. The proposed configuration has higher voltage conversion ratio compared to conventional landsman converter. The simulation results match with theoretical analysis and validate the feasibility and functionality of the proposed converter.

This paper provides a small-signal model and stability analysis of interconnected AC microgrids (MGs) connected through back-to-back converters (BTBCs). The proposed modeling method of the networked microgrids (NMGs) is derived and it is generalized for any number of NMGs through BTBCs. Different BTBC control parts are analyzed to study their impact on the NMG stability. The eigenvalue analysis and participation matrix are employed to identify dynamic modes of BTBC DC voltage controller. For two NMGs, main participating state variables and corresponding parameters in the dominant low-frequency modes (LFMs) are recognized, then acceptable ranges of the parameters are calculated using the sensitivity analysis (SA). The contribution of the control BTBC parameters including PLL and DC voltage controller parameters in the small-signal stability margin are shown. In addition, to show the BTBC control impact on the NMGs stability in the time domain, simulation results are provided for the two NMGs in SimPowerSystems/Matlab environment.

In order to overcome the disadvantages of conventional DPC control, this paper proposes a combination of direct power control with space vector modulation used in shunt active power filter. For this reason, from the beginning, every efforts will be directed towards developing a control strategy that achieves the best results by reducing current THD and power ripple. The approach is based on the replacement of switching table and hysteresis controllers by a vector modulator and PI controllers to ensure operation at a constant switching frequency. A series of simulations under Matlab/Simulink environment, followed by a practical implementation using a Dspace 1104 are demonstrated.

Battery energy storage systems (BESS) have recently been widely integrated to photovoltaic (PV) systems with the aim of increasing the control flexibility. To ensure the profitability under long-term operation of PV-BESS, lifetime evaluation is necessary during the design stage. In PV-BESS, the battery and power converters are the reliability-critical components that are subjected to high stress during the operation. This paper proposes a systematic lifetime evaluation framework for the PV-BESS where a three-stage modeling approach is applied to the battery and power converter lifetime estimation. The proposed lifetime evaluation also includes the interaction between the operation of the battery and power converter and its impact on the lifetime, which is the key novelty of this work. The framework is demonstrated on a case study of the PV-BESS in Germany. It reveals that the battery is the most life-limiting component, where the deep cycles and high average state-of-charge are the main factors limiting the battery lifetime. Additionally, the thermal stress of the battery converter is higher than that of the PV converter due to the high loading dynamic resulting from the battery charging/discharaing.

In this paper, a new active neutral point clamped (ANPC) five-level (5L) inverter is proposed. The conventional ANPC output voltage is half of the input voltage. To rectify the above problem, a floating capacitor is used to boost the output voltage equal to the input voltage, which further reduces the size of the dc-link capacitors. In addition to this, the proposed topology does not need any sensors to balance the floating capacitor, which minimize the complexity of the inverter. Further, in the proposed topology, the neutral point is directly connected to the mid-point of dc-link capacitors, which reduces the leakage current and common mode voltage due to the presence of two clamping diodes. Moreover, a new carrier signal is introduced, and the advantages are discussed. The performance of proposed 5L inverter topology is analysed in terms of dynamic loading condition. To show the superiority of the proposed topology, it is simulated in MATLAB and results are discussed.

Increasing use of power electronic-based (PE-based) units has intensified the importance of the security scope of power systems. So far, the conventional security assessment approaches are used in the modern PE-based power system. It is not sufficient for the analysis of the system security. In this paper, a new scope of the PE-based power system security is proposed. To do so, the security assessment of PE-based units are involved in the general range of the system security assessment. More specifically, the transient stability and security of the grid-connected voltage source converters (VSCs) are studied in the scope of dynamic security of the PE-based power systems. Obtained results show that the new security scope gives a valuable viewpoint of the system security assessment in comparison with the conventional security schemes.

The wide utilization of power electronic converters causes the constant power load stability issue in DC microgrids. This paper proposes an offset-free model predictive controller for a DC/DC boost converter feeding constant power loads. First, a baseline nonlinear model predictive controller is designed by solving a receding horizon optimization problem explicitly. Then a higher-order sliding mode observer is utilized to estimate the unknown load variation and system uncertainties. Finally an offset-free controller is integrated by the baseline controller and observer. The proposed controller achieves optimized transient dynamics and accurate tracking with large signal stability. Simulation results are presented to verify the proposed approach.

As a promising new transmission device, the magnetic lead screw (MLS) is considered to have a huge potential for wave energy conversion (WEC). The wave power generation device which using MLS can well transfer low-speed linear motion into high-speed rotation and offer much higher force density than that using traditional linear permanent magnet generator. The MLS has the advantages of inherent overload capability, high force density, no mechanical friction, and low maintenance. Therefore, in this paper, a wave power generation system consists of MLS and a permanent magnet synchronous generator (PMSG) is proposed. And a linear motor is used to simulate the sea wave. To verity the system, the prototype is manufactured and tested in the laboratory. In addition, the MLS performance is evaluated by using the finite- element analysis (FEA).

Damping the LCL-filter resonance is an essential issue for grid-connected inverters. In most of the prior-art solutions, active damping focuses on a dual-loop architecture, e.g., using the capacitor-current to damp the resonance, thus complicating the entire control loop and/or increasing the cost. Digital filters (such as notch and all-pass filters) directly cascaded into the current controller, referred to as a single-loop scheme, are thus more economical, which feature no extra sensors and a simple open-loop scheme with easy parameter tuning. This paper proposes a practical single-loop damping method for grid-current feedback control (GCF) based on a first-order digital low-pass filter, which realizes damping by lagging the phase and meanwhile reducing the magnitude response for a sufficient gain margin. Simulations verify the proposed method.

This paper proposes an innovative active voltage control technique for flying-capacitor (FC) multilevel converters. The proposed active control method on the basis of the logic-equations exploits converter's measured variables including the capacitor voltages and output current to generate a switching state that regulates the FC voltages at reference values and also produces the commanded PWM voltage-level. Simulation results and experimental measurements are provided to confirm the introduced method and derived equations.

A modular-concatenated-cell (MCC) multilevel voltage-source converter topology is investigated in this paper, and its basic configurations are reviewed. A set of logic-equations are derived for control of the 1-cell 3-level and 4-cell 6-level MCC inverter topologies. Simulation results are provided to confirm the four-cell 6-level configuration and the proposed logic-equations. Furthermore, a 3-level MCC converter topology and its logic-equations-based modulation technique are experimentally verified using a 2 kW laboratory prototype.

A new concept of shade-tolerant PV microinverter named Optiverter is capable of operating with both 60- and 72-cell PV modules. In order to ensure highly reliable operation of the Optiverter, this paper analyzes the wear-out failures of the Optiverter considering both 60- and 72- cells Si crystalline PV modules. The lifetime evaluation of the Optiverter also considers the impact of module degradation rates and different mission profiles into consideration. The evaluation results reveal that operating the Optiverter with a high-power PV module (i.e., 72-cell) results in a lower reliability performance compared with 60-cell PV module. This is mainly due to the higher power and thermal loadings of the power devices in the Optiverter with a 72-cell PV module. When considering the effect of module degradation, using the 72-cell PV module also lead to a higher deviation in the reliability prediction compared to the case without considering the degradation.

The recently proposed current-fed trans-quasi-Z-source inverter (CF-trans-qZSI) can buck or boost voltage and provide a bidirectional power flow. Thus, it has received much attention. To minimize the current ripples and output harmonics, this paper presents a novel space vector pulse width modulation (SVPWM) strategy for the CF-trans-qZSI. The switching sequence in this SVPWM strategy for the boost mode is realized by partitioning equally the short zero state time into four parts; while, for the buck mode, it is implemented by dividing the short zero state time and open zero state time into more parts, where the time interval of each part is not equal. In both modes, the divided short zero state time, open zero state time, and two-active-state time are symmetrical in one switching cycle. Simulation and experiments are performed to validate the performance of the proposed strategy. The results show that the proposed SVPWM algorithm can improve the performance of the CF-trans-qZSI in terms of reducing the DC inductor current ripples and output current harmonics in both modes.

Quasi-Z-source cascaded H-bridge (qZS-CHB) inverters are one promising solution for high power photovoltaic (PV) systems. This type of topologies inherits the advantages of cascaded converters (i.e., multilevel outputs) and impedance-source inverters (i.e., high conversion ratios). In addition, it allows increasing the inverter reliability (with high redundancy). However, the modulation and control of qZS-CHB inverters are challenging to a certain extent. Thus, this paper proposes modified modulation techniques to increase the performances of qZS-CHB converters in terms of voltage gains and stresses. The novelty lies in the use of the switching frequency optimal as reference signals in the modulation techniques. A comparison in terms of harmonics with selected modulation techniques is performed.

The three level neutral-point clamped (3L-NPC) topology is one of the most widely used multilevel topologies in the low and medium voltage applications and also one of the most commercialized topologies. Although it offers many benefits compared to the conventional two level topology, it suffers from a considerable unequal loss distribution among the inner and outer switches and the clamping diodes. To solve this problem, we are proposing a control algorithm based on the finite control set model predictive control (FCS-MPC) that can provide a more balanced stress distribution. For implementing the proposed control algorithm no additional measurements are required nor thermal models of the semiconductor devices. The algorithm benefits are even more noticeable during low voltage ride through (LVRT) scenarios when the output voltage level of the converter is low and the current amplitude is high. Obtained simulation results confirm the positive effects on the thermal redistribution and also the junction temperatures of the most stressed devices are reduced. Effects of the algorithm are also verified on an experimental set-up.

This paper presents a new multilevel breed of XY converter family, called LY Multilevel Boost Converter (LY-MBC) topologies for renewable energy applications. Four LY-MBC topologies are designed to obtain a high voltage conversion ratio and which also offer an operative solution for renewable energy systems with minimal number of components. Existing LY converter topologies includes L-L, L-2L, L-2LC and L-2LCm converter topologies and LY converter is one of the breed of the XY converter family. The proposed LY-MBC topologies are derived by attaching the Cockcroft Walton (CW) multiplier to the Y converter of LY converter topologies. The proposed LY-MBC converter topologies are compared with existing LY converter topologies in terms of voltage conversion ratio and number of components. The noticeable features of the proposed LY-MBC topologies are also discussed in details. The working operation, feasibility, and design of the proposed LY-MBC topologies are verified by simulations.

This paper explores the fault tolerant capabilities of an Embedded Enhanced-Boost Z-Source Inverter (EEB-ZSI) for PV applications. Compared with the prior-art Embedded Source Inverters (E-ZSI) and Enhanced-Boost Z-Source Inverter (EB-ZSI), the proposed topology features that when one dc source (e.g., PV panel) is short-circuited (SC) or open-circuited (OC), the inverter can tolerate the faults and still operate with a compromised conversion ratio. However, the conversion ratio is still larger than the traditional E-ZSI. This topology can be further applied to the cascaded H-bridge inverter systems for multi-level applications with fault-handling capabilities. A detailed fault-tolerant analysis is conducted on the EEB-ZSI and simulations are provided to validate the analysis.

The lifetime prediction of LED lighting system is important to guide the designers to fulfill the design specifications and to benchmark the cost-competitiveness of different lighting technologies. Currently, the lifetime of LED system is usually predicted from the source part and the driver part separately, and then the thermal design is also optimized independently. In practice, the LED source and driver are usually compacted in a single fixture. The heat dissipated from LED source and driver will be coupled together and affect the heat transfer performance, which may degrade the whole system and accelerate the failure. In this paper, a new thermal model concerning the thermal coupling is proposed with Finite Element Method (FEM) simulation for parameter acquirement. The proposed model has a better estimation of the thermal stresses of key components in the LED lamps and therefore an improved lifetime prediction of the LED systems. Moreover, with a given lifetime requirements, this method can be used to guide the thermal design of the LED system. A case study of an outdoor lighting application is then demonstrated by both FEM simulations and experimental verifications in this digest.

Nowadays capacity of the photovoltaic systems in the grid is remarkable and provides a major part of energy in the grid. Therefore, an abruption of these systems from the grid can create a damage to the grid. Unlike in the past that PV systems disconnected from the grid when a voltage drop occurred, nowadays these systems should have Low Voltage Ride-Through (LVRT) capability. The PV system should stay connected to the grid at fault time and help to recover the grid voltage by injecting the reactive power like in a power plant or a custom power device. There are two important factors for single phase grid connected PV inverters. The first one is the structure of the inverter and the second one is the control part. In this regard, the HERIC inverter can be a good selection among the transformerless inverters for a PV system due to its high efficiency. For the control part, this paper presents a look-up table based Model Predictive Control (MPC) that is simple, fast and has soft behavior in tracking of the reference during LVRT. The proposed control method has been implemented in a 1 kW single-phase transformerless HERIC (Highly Efficient and Reliable Inverter Concept) inverter using an LCL filter.

A novel physics-based, electro-thermal model which is capable of estimating accurately the short-circuit behavior and thermal instabilities of silicon carbide MOSFET multi-chip power modules is proposed in this paper. The model has been implemented in PSpice and describes the internal structure of the module, including stray elements in the multi-chip layout, self-heating effect, drain leakage current and threshold voltage mismatch. A lumped-parameter thermal network is extracted in order to estimate the internal temperature of the chips. The case study is a half-bridge power module from CREE with 1.2 kV breakdown voltage and about 300 A rated current. The short-circuit behavior of the module is investigated experimentally through a non-destructive test setup and the model is validated. The estimation of overcurrent and temperature distribution among the chips can provide useful information for the reliability assessment and fault-mode analysis of a new-generation SiC high-power modules.

High-stiffness servo system is easy to cause mechanical resonance in elastic coupling servo system. Although on-line adaptive notch filter is effective in most cases, it will lead to a severer resonance when resonance frequency deviated from the natural torsional frequency. To explain this phenomenon, an improved discrete system model is proposed. This paper quantitatively analyzes the influence of damping, discretization and current loop time constant on mechanical oscillation frequency. A conclusion is drawn that the most effective notch frequency is the natural torsional frequency when resonant frequency is deviate. Simulation and experimental results verify the accuracy and effectiveness of the theoretical analysis.

For motor control applications, the speed loop performance is largely depended on the accuracy of speed feedback signal. M/T method, due to its high theoretical accuracy, is the most widely used in incremental encoder adopted speed measurement. However, the inherent encoder optical grating error and A/D conversion error make it hard to achieve theoretical speed measurement accuracy. In this paper, hardware caused speed measurement errors are analyzed and modeled in detail; a Single-Phase Self-adaptive M/T method is proposed to ideally suppress speed measurement error. In the end, simulation and experiment show the advantages and verify the validity of the proposed method.

In this paper, an eigenvalue-based harmonic stability analysis method for offshore wind farm is proposed. Considering the internal cable connection layout, a component connection method (CCM) is adopted to divide the system into individual blocks as current controller of converters, LCL filters, collection system cable impedance, transmission cable impedance and grid impedance. By using this method, each block can be modelled independently and then be integrated into a whole state space matrix which contains sparse and diagonal matrix. Compared with the traditional state space formulation process, this method is superior in reducing the computational cost. A 4 by 4 wind turbines wind farm is selected as the study case and the proposed method is validated by comparing the results obtained from time domain simulation software - Power System Computer Aided Design (PSCAD).

In this paper, magnetically-coupled impedance source (MCIS) three-phase four-switch inverters are introduced for renewable energy applications. This inverter utilizes two single-phase MCIS inverters to obtain a three-phase output, where less component-count is achieved in order to reduce the inverter volume. On the other hand, as a result of the reduced number of switches, the proposed inverter suffers from higher voltage stresses. The MCIS inverters are first reviewed. Then, the modulation and operation principle of the MCIS three-phase inverter topology are introduced before sizing the passive components. A comparison among the similar candidates is done. Finally, the analysis is verified by simulations.

This paper presents a family of cost-effective magnetically-coupled impedance source inverters for renewable energy systems. The inverters are derived from magnetically-coupled impedance source networks, featuring low cost and no ground leakage current when used in PV system. The numbers of required semi-conductor switches is reduced. More important, the elimination of leakage currents makes it particularly suitable for high-efficiency photovoltaic (PV) applications. A comparison among prior-art PV inverters is then performed. The Performances of the inverters are evaluated analytically as well as by simulations. The analysis and simulation show the superiority of the proposed inverter in terms of leakage current suppression and low cost.

Indirect rotor field oriented control (IRFOC) plays an important role in the high performance induction machine drives. In the indirect rotor field oriented control - based induction machine adjustable speed control system, the rotor field angle is usually obtained by the rotor angular velocity and the slip angular velocity. The rotor angular velocity can be sensed by an encoder with sufficient accuracy. However, the slip angular velocity is affected by the rotor parameters variations and the current control performance degradation especially in the field-weakening region. Therefore, the field angle used in the indirect rotor field oriented control may have considerable error. In the paper, the angle error caused by rotor resistance variation is analyzed and the impact on the output torque and the rotor field intensity of the induction machine is studied. Simulations and experimental verification in base-speed region and field-weakening region are presented.

The ship shaft power generation system based on a stand-alone brushless doubly-fed induction generator (BDFIG) have demonstrated excellent saving-energy performance. This paper presents a new control scheme of the stand-alone BDFIG for supplying unbalanced loads in the ship shaft power generation system. The positive-and negative-sequence components of the unbalanced power winding (PW) voltage caused by the unbalanced loads are regulated separately. Comprehensive experiments are carried out on a prototype BDFIG by employing the conventional and proposed control schemes. The experimental results verify the good performance of the proposed control scheme.

In this paper, a separation test method for eliminating the effects of different current densities on the bond wires is proposed. The separation test method makes it possible to study the effect of different current density on the fatigue damage of bond wires without changing the temperature swing and average temperature during the test. By analyzing the output characteristics of the linear region of MOSFET, the constraint relations among the gate voltage, on-state voltage drop and junction temperature are revealed in this paper. The one-to-one correspondence between gate voltage and conduction power loss can be used to adjust the current density under fixed temperature swing and average temperature. The commercial Silicon Carbide (SiC) MOSFET modules are tested to experimentally verify the proposed method. Finally, the effectiveness of proposed test method is validated by the experimental results.

In this paper, a novel single-stage single-phase transformer-less buck-boost inverter is proposed, in which a reduced number of passive components is used. The proposed inverter combines the conventional buck, boost, and buck-boost converters in one converter in order to obtain a sinusoidal output voltage. In the proposed inverter, the input DC source and the load or grid have the same ground. Therefore, the leakage current problem in photovoltaic (PV) systems is eliminated. Furthermore, the proposed inverter supports the bi-directional power flow capability and it can inject reactive power to the load or the grid. The analysis, principle of operation, and modulation of the proposed inverter are introduced in this paper, where simulation results using MATLAB/Simulink models in both islanded and grid-tied modes of operation are shown.

This paper proposes an Active Thermal Control (ATC) method for MOS-gated power switches aimed at reducing temperature swing amplitude during operation. It leverages on the fact that thermal cycle amplitude of many actuation system components (such as power devices) has a large impact on the system reliability and lifetime. These figures can then be improved, which eases the adoption of electrification in markets, such as transportation, where they are still below target values. The proposed ATC method leaves electric load parameters untouched, while acting dynamically on gate parameters, namely voltage and resistance. A model-predictive control (MPC) strategy is used to determine the most suitable parameters to use. Simulations of the control scheme are presented first, to predict the potential benefits on temperature swing amplitude, and the consequent improvements in terms of device lifetime are inferred, using literature models. Then, experimental proof of concept is presented and discussed, together with its limitations and drawbacks.

Active Thermal Control (ATC) consists in driving power switches in a less efficient way when low load conditions are present. The resulting wasted power is used to self-heat the device, reducing amplitude and occurrence of thermal cycles and hence improving the reliability. This paper presents a novel way to control losses, and hence temperature, of both positive- and negative-current devices in half-bridge topologies at various load conditions. The goal is achieved by means of a controlled shoot-through of the half-bridge leg.

Grid voltage unbalance, which is considered as most common disturbance in distribution networks, may significantly affect the normal operation of the grid-connected power electronics devices including Adjustable Speed Drives (ASD), and may result in a remarkable performance degradation. In this paper, the main aim is to analyze the effects of the grid unbalanced voltage on the multi-unit three-phase ASDs with the Silicon-Controlled Rectifier (SCR)-fed front-end rectifiers, where the DC-link current is controlled utilizing an Electronic Inductor (EI) technique. In this respect, the main effective factors on the drives harmonic performance are discussed. Moreover, the analysis is performed by considering an Equally-Pulse-Space (EPS) firing approach on the SCRs. Obtained simulation and experimental results verify the proposed theoretical analysis and mathematical modelling.

An energy management system of a microgrid (MG) has several basic objectives; e.g. to maximize the utilization of renewable energy resources (RES), to protect the internal components from overloading, and to ensure that the MG operates reliably under any operating conditions. Although many control techniques are available in the literature to monitor and control the energy flows among distributed RES in MGs, formal verification of those techniques was not proposed yet. The emphasis of this paper is to design and validate energy management system for a MG which consists of a solar photovoltaic (PV) array, a pair of battery energy storage systems (BESes), a diesel generator (DG) and a load (LD). The physics and dynamics of the MG are defined as energy flow invariants and the designed behaviours are abstracted, modelled and validated in this work. Therefore, we have considered an invariant based flow technique to manage the energy flow in an MG. The results are validated and verified with UPPAAL, a powerful industrial tool which is commonly used to verify the correctness of real-time systems like supervisory controllers, communication protocols and others.

Multi-modular converters have proven to be one of the most suitable topology to be used in high and power applications. The modularity of these configurations offer several advantages, such as: high quality voltage, redundancy and high efficiency. In these converters, the series connection of modules increase the number of voltage levels, but also the floating voltage of modules with respect the neutral point connection which may give rise to isolation issues at the DC side. Because of this, modules with two or more conversion stages are used to provide isolation and to prevent high floating voltages. However, increasing the number of conversion stages, increase also the losses and the implementation costs. In order to overcome these drawbacks, a new configuration of multi-modular converter is proposed in this paper. The proposed converter provides isolation with one conversion stage by means of using low frequency transformers in each module. The main principle behind this concept, the control structure and simulation results are presented to validate the proposed configuration.

In this paper magnetically integrated resonant single-switch quasi-Z-source DC-DC converter is evaluated as a candidate topology for the low-cost photovoltaic microconverter. The derivation of the topology and its basic operation principle are explained. Generalized design guidelines and experimental results of 250 W prototype are discussed for different realization approaches of the hybrid coupled inductor, which is the key component of the proposed topology.

A novel switching power loss estimation method for modular multilevel converters (MMCs) with the nearest level modulation (NLM) is introduced in this paper. It focuses on the switching actions caused only by change of the inserted submodule (SM) number per arm, named as the essential switching transitions. Every essential switching action can be identified under the assumption of ideal sinusoidal arm voltage reference. The corresponding arm current value determining the switching energy can be obtained with the exclusive use of the exact time of the switching action. Effects of the modulation index and the power factor on the power loss are also taken into account. Simulations have been performed on a 30-MVA three-phase grid-connected MMC system with 20 SMs per arm. The results have confirmed the effectiveness of the proposed method, where high estimation accuracy can be achieved under a range of operating conditions.

In this paper, the single-stage Maximum Power Point Tracking (MPPT) control strategy for the Aalborg photovoltaic inverter is presented. Aalborg inverter has many advantages, such as high efficiency, wide range of input voltage, minimum voltage drop of the filtering inductors, etc. Nevertheless, it is essentially a “half-bridge” inverter with two input sources, where one source works in MPPT mode, the other is out of control. If without the reasonable parameter design and the proper control, the bus-voltage of this inverter may change greatly, resulting in the serious power oscillation around maximum power point and the reduction of the energy utilization of PV array. In this paper, the MPPT algorithm of two independent PV arrays is proposed, and then the relation between ripple ratio and dc-link capacitance is analyzed. An 110V/50Hz prototype has been constructed. Simulations and experiments show that the proposed control strategy has good steady-state and dynamic performances.

The reliability aspect study of Modular Multilevel Converter (MMC) is of great interest in industry applications, such as offshore wind. Lifetime prediction of key components is an important tool to design MMC with fulfilled reliability specifications. While many efforts have been made to the lifetime prediction of IGBT modules in renewable energy applications by considering long-term varying operation conditions (i.e., mission profile), the justifications of using the associated mission profiles are still missed. This paper investigates the impact of mission profile data resolutions and electrical power modeling methods on the estimated lifetime of IGBT modules in an MMC for offshore wind power application. In a 30 MW MMC case study, an annual wind speed profile with a resolution of 1 s/data, 10 minute/data, and 1 hour/data are considered, respectively. A method to re-generate higher resolution wind speed data from lower resolution data is introduced as well. Based on the wind speed data, IEC 61400-12-1 power curve model and a wind speed-power stochastic model are compared as well. Five mission profile modeling scenarios are compared in terms of the predicted lifetime of the IGBT modules used in the MMC, resulting in significant differences. The study serves as a first step to quantify the impact of mission profile modeling on lifetime prediction, and to provide a guideline on mission profile collection for the presented application.

In order to reduce the Common-Mode Voltage (CMV) in three-to-five phase indirect matrix converters, three improved Space Vector Pulse Width Modulation (SVPWM) methods are proposed and discussed. The improved modulation schemes are achieved by reorganizing zero vectors from the inversion stage to the rectification stage. The proposed methods can not only theoretically reduce the CMV peak value by up to 47.1%, but also decrease the switching losses of the power devices. Moreover, comparisons show that a superior CMV reduction performance is achieved when only two large active voltage vectors (AVVs) in the inversion stage, which results in a large amount of third-order harmonics in output currents. In addition, the method that utilizes two adjacent active current vectors (ACVs) and the method that uses two non-adjacent ACVs in the rectification stage have the same CMV peak value. By contrast, the latter achieves a lower Total Harmonic Distortion (THD) level of the output currents. Simulation results verify the effectiveness of the proposed methods.

Continuously expanding deployments of distributed power-generation systems (DPGSs) are transforming the conventional centralized power grid into a mixed distributed electrical network. The modern power grid requires flexible energy utilization but presents challenges in the case of a high penetration degree of renewable energy, among which wind and solar photovoltaics are typical sources. The integration level of the DPGS into the grid plays a critical role in developing sustainable and resilient power systems, especially with highly intermittent renewable energy resources. To address the challenging issues and, more importantly, to leverage the energy generation, stringent demands from both utility operators and consumers have been imposed on the DPGS. Furthermore, as the core of energy conversion, numerous power electronic converters employing advanced control techniques have been developed for the DPGS to consolidate the integration. In light of the above, this paper reviews the power-conversion and control technologies used for DPGSs. The impacts of the DPGS on the distributed grid are also examined, and more importantly, strategies for enhancing the connection and protection of the DPGS are discussed.

A novel transformerless inverter for grid-tied PV systems is introduces with low leakage current in this paper. Four power switches, two capacitors, two diodes, and a LC filter are uses in this topology. The negative polarity of the PV panel is connected to the neutral of the utility grid with common line. Therefore, a common-mode voltage is constant and leakage current is nearly zero. A unipolar Sinusoidal Pulse-Width modulation (SPWM) method is utilized to reduce the output current ripple and requirements of filter. The major merits of this topology are compact size, low cost, flexible grounding configuration and higher efficiency. The operating principle and analysis of the proposed inverter are presented in details. Finally, a universal prototype rated 500 W are tested to validate the proposed topology and the overall concept. The results obtained clearly confirm the performance and practical application of the proposed topology for grid-connected PV systems.

Compared with conventional dc-link drive, slim dc-link drive is expected to achieve lower cost and longer life time. However, harmonics distortion problem may occur in such drive systems. This paper proposes to use an active damping control method to suppress the harmonic distortion with the benefit of low cost and also low loss. A new analysis method, based on the frequency domain impedance model, is presented to explore the mechanism of harmonics suppression. Also, a general method is presented to build the impedance model of a PMSM drive system using Field Oriented Control (FOC) method. Some design issues, including power levels, current control bandwidth and harmonic interaction, are discussed when the drive system is fed by a weak grid. Case studies on a two-drive system composed by two slim dc-link drive units are provided to verify the proposed analysis method.

This paper presents a new method to measure the phase dependent impedance from an experimental set up. Though most of power electronics based system is gradually migrating to IGBT based voltage source converter due to their controllability, the rectifier composed of diode or thyristor components are still widely used in AC-DC applications because of their cost effectiveness and reliability. However, these topologies generate harmonic problems in their network due to their switching instant variation caused by the frequency and phase of grid voltage. Hence, a lot of solutions have been proposed to provide an optimized solution for better power quality. However, the phase dependent impedance, which is driven by both switching instant variation and frequency coupling between ac and dc network, has not been treated in the design of passive filter or harmonic compensator design for power electronics application. It is found that the phase dependent impedance shows different properties with the impedance profiles, which have been proposed in the research. This paper explains a method to measure the phase dependent impedance profile from an experimental set up. Furthermore, the results are compared with results from time-domain simulations and results from an analytical model developed in the Harmonic State-Space (HSS).

The present paper addresses the AC microgrid control issue using the hierarchical control structure and droop controllers for load sharing. Once the droop controllers impose an operation with frequency and voltage deviations, depending on the load and droop parameters, a hierarchical control structure must be added to change the droop controller operating points. The hierarchical controllers operate with local measurements and shared signals from communication links among the distributed generation systems connected to the microgrid. Depending on the geographical size of the microgrid, the communication links can be economically unviable. This paper thus proposes a fuzzy secondary controller for AC microgrids to reduce the link communication dependency by using only local measurements. The simulation results show that the deviations as happened with the conventional secondary controllers can be compensated when the microgrid is operating as stand-alone mode, and can provide a certain amount of power to the connected utility bus when operating as grid-connected mode.

High Frequency (HF) voltage injection methods have been widely used in the low speed drive applications of Permanent Magnet Synchronous Machines (PMSMs). This paper compares two of the HF voltage injection methods, which are HF sinusoidal voltage injection method in the d-q reference frame and INdirect Flux detection by On-line Reactance Measurement (INFORM) method in the α-β reference frame. Implementation methods are deliberated in detail and the position estimation error caused by magnetic field distortion is also discussed. Experiments using a commercial PMSM are carried out for verifications.

The basic Zero-Voltage Switching (ZVS) three-level DC-DC converter has one clamping capacitor to realize the ZVS of the switches, and two clamping diodes to clamp the voltage of the clamping capacitor. In order to reduce the reverse recovery loss of the diode as well as its cost, this paper proposes to remove one of the clamping diodes in basic ZVS three-level DC-DC converter. With less components, the proposed converter can still have a stable clamping capacitor voltage, which is clamped at half of the dc link voltage. Moreover, the ZVS performance will be influenced by removing the clamping diode. But as long as the clamping capacitor is properly selected, the degradation of the ZVS performance can be neglected. The impact of the clamping capacitor on the ZVS performance is mathematically analyzed as well.

The control strategies of Doubly Fed Induction Generator (DFIG) system output current unbalance and distortion suppression have been well investigated in detail, with the implementation of two kinds of resonant regulators, i.e., conventional Resonance (R) regulator or Vector Proportional Integral (VPI) regulator. Nevertheless, these two resonance regulators have never been compared from the perspective of suppression capability of output current unbalance and distortion. In this paper, the impedance based analysis method is adopted to theoretically explain and compare the DFIG system impedance reshaping though the introduction of R and VPI regulator. It is pointed out that, when implemented in the DFIG system output current unbalance and distortion suppression, the VPI regulator (equivalent to the combination of virtual positive inductor and virtual positive resistor) has two advantages over R regulator (equivalent to the combination of virtual positive resistor and virtual negative inductor), i.e., better high order harmonic distortion suppression. The theoretical analysis and MATLAB simulation results have validated the correctness of this conclusion.

This paper addresses a state-space-based harmonic stability analysis of paralleled grid-connected inverters system. A small signal model of individual inverter is developed, where LCL filter, the equivalent delay of control system, and current controller are modeled. Then, the overall small signal model of paralleled grid-connected inverters is built. Finally, the state-space-based stability analysis approach is developed to explain the harmonic resonance phenomenon. The eigenvalue traces associated with time delay and coupled grid impedance are obtained, which accounts for how the unstable inverter produces the harmonic resonance and leads to the instability of whole paralleled system. The proposed approach reveals the contributions of the grid impedance as well as the coupled effect on other grid-connected inverters under different grid conditions. Simulation and experimental results are provided to verify the proposed harmonic stability assessment method.

The Doubly-Fed Induction Generator (DFIG) based wind turbine system is presently dominant in the wind turbine market. Due to heavy load switch-off and faults in the power grid, voltage swells may occur and this phenomenon is currently given sufficient insights. This paper starts to describe the DFIG modeling and challenges when facing the symmetrical voltage swell. Then, the High Voltage Ride-Through (HVRT) capability of the DFIG can be calculated by using the demagnetizing current control, and the stator current, rotor current as well as the electromagnetic toque can be deduced during the transient voltage swell and its recovery. It is concluded that although both higher swell level and higher rotor speed cause higher rotor electromotive force, the doubly-fed induction generator can successfully ride through the grid fault due to the relatively small swell level required by the modern grid codes. Additionally, the calculated maximum stresses of the DFIG can be verified by simulation results in terms of the rotor current, stator current, and the toque at various swell levels.

Power talk is a novel ultra narrow-band powerline communication (UNB-PLC) technique for communication among control units in MicroGrids (MGs). Unlike the existing UNB-PLC solutions, power talk does not require installation of additional dedicated communication hardware and, instead, uses only the power electronic converters through which the control units interface the common bus. This way the communication system has practically the same reliability as the power system. The information is transmitted by modulating the parameters of the primary control, incurring subtle power deviations that can be detected by other units. In this paper, we develop power talk communication strategies for direct-current (DC) MG systems with arbitrary number of control units that carry out all-to-all communication. We investigate two multiple access strategies: time-division multiple access, where only one unit transmits at a time, and full duplex, where all units transmit and receive simultaneously. We apply the concepts of signaling space, where the power talk symbol constellations are constructed, and detection space, where the demodulation of the symbols is performed. The proposed communication technique is challenged by the random changes of the bus parameters due to load variations. To this end, we investigate the performance of power talk when a solution based on training sequences that re-establishes detection spaces is employed. The presented evaluation shows that power talk has a potential to offer an effective and inexpensive solution for reliable communication among units in DC MGs.

We introduce a novel communication strategy for DC Micro Grids (MGs), termed power talk, in which the devices communicate by modulating the power levels in the DC bus. The information is transmitted by varying the parameters that the MG units use to control the level of the common bus voltage, while it is received by processing the bus measurements that units perform. This implies that the communication does not require a dedicated modem, but instead it is piggybacked on top of the power electronics. The communication is challenged by the random fluctuations of the voltage level due to the random load variations in the MG. We develop the corresponding communication model and address the random voltage fluctuations by using coding strategies that transform the MG into some well- known communication channels. The performance analysis shows that it is possible to mitigate the random voltage level variations and communicate reliably over the MG bus.

This paper presents guidelines for component design of the three-level three-phase T-source inverter with continuous input current under maximum boost control proposed recently. Steady state analysis under low-frequency current and voltage ripples in the dc side was made. Component sizes for both with and without low-frequency ripples are estimated and compared. Simulation results have confirmed most of theoretical predictions.

This paper presents an eigenvalue-based harmonic stability analysis method for inverter-fed power systems. A full-order small-signal model for a droop-controlled Distributed Generation (DG) inverter is built first, including the time delay of digital control system, inner current and voltage control loops, and outer droop-based power control loop. Based on the inverter model, an overall small-signal model of a two-inverter-fed system is then established, and the eigenvalue-based stability analysis is subsequently performed to assess the influence of controller parameters on the harmonic resonance and instability in the power system. Eigenvalues associated with time delay of inverter and inner controller parameters is obtained, which shows the time delay has an important effect on harmonic instability of inverter-fed power systems. Simulation results are given for validating the proposed harmonic stability analysis method.

In many important energy conversion systems, the power electronic converters are proven to have high failure rates. At the same time, the failures of the power electronics systems are becoming more and more unacceptable because of the high cost of failures and booming power capacity. As a consequence, an appropriate assessment of reliability performance for the power electronics is a crucial and emerging need, because it is the essential information for the design improvements as well as for the extension of converter lifetime, and reduction of the cost-of-energy. Unfortunately, there is still lack of suitable and cost-effective tools for the reliability assessment in power electronics. In this paper, an advanced design tool structure, which can acquire various reliability metrics of the power converters, is proposed. The proposed reliability design tool is based on the failure mechanisms in the critical components of the power electronics system, and the mission profiles in the converter applications are also taken into account. Finally, the potential methodologies, challenges and technology trends involved in this tool structure are also discussed.

In the wind power application, different asymmetrical types of the grid fault can be categorized after the Y/d transformer, and the positive and negative components of a single-phase fault, phase-to-phase fault, and two-phase fault can be summarized. Due to the newly introduced negative and even the natural component of the Doubly-Fed Induction Generator (DFIG) stator flux during the fault period, their effects on the rotor voltage can be investigated. It is concluded that the phase-to-phase fault has the worst scenario due to its highest introduction of the negative stator flux. Afterwards, the capability of a 2 MW DFIG to ride through asymmetrical grid faults can be estimated at the existing design of the power electronics converter. Finally, a control scheme aimed to improve the DFIG capability is proposed and the simulation results validate its feasibility.

The line current ripple and the size of the dc-link capacitor can be reduced by interleaving the carriers of the parallel connected Voltage Source Converters (VSCs). However, the interleaving of the carriers gives rise to the circulating current between the VSCs, and it should be suppressed. To limit the circulating current, magnetic coupling between the interleaved legs of the corresponding phase is provided by means of a Coupled Inductor (CI). The design of the CI is strongly influenced by the Pulsewidth Modulation (PWM) scheme used. The analytical model to evaluate the flux-linkage in the CI is presented in this paper. The maximum flux density and the core losses, being the most important parameters for the CI design, are evaluated for continuous PWM and discontinuous pulsewidth modulation (DPWM) schemes. The effect of these PWM schemes on the design of the CI is discussed. The simulation and the experimental results are finally presented to validate the analysis.

The power handling capability of the state-of-the-art semiconductor devices is limited. Therefore, the Voltage Source Converters (VSCs) are often connected in parallel to realize high power converter. The switching frequency semiconductor devices, used in the high power VSCs, is also limited. Therefore, large filter components are often required in order to meet the stringent grid code requirements imposed by the utility. As a result, the size, weight and cost of the overall system increase. The use of interleaved carriers of the parallel connected VSCs, along with the high order line filter, is proposed to reduce the value of the filter components. The theoretical harmonic spectrum of the average pole voltage of two interleaved VSCs is derived and the reduction in the magnitude of some of the harmonic components due to the carrier interleaving is demonstrated. A shunt LC trap branch is used to sink the dominant harmonic frequency components. The design procedure of the line filter is illustrated and the filter performance is also verified by performing the simulation and the experimental study.

This paper addresses the harmonic compensation error problem existing with parallel connected inverter in the same grid interface conditions by means of impedance-based analysis and modeling. Unlike the single grid connected inverter, it is found that multiple parallel connected inverters and grid impedance can make influence to each other if they each have a harmonic compensation function. The analysis method proposed in this paper is based on the relationship between the overall output impedance and input impedance of parallel connected inverter, where controller gain design method, which can minimize the compensation error under various conditions, is also proposed.

This paper presents the theoretical background and studies on the supply side current interharmonics in a double-stage Adjustable Speed Drive (ASD), when they are initiated by motor current imbalance. Some useful approaches are then proposed to compensate for these interharmonic currents in partially and/or fully controlled ASD, resulting in undistorted grid currents. The simulation studies verify the effectiveness of the proposed schemes.

This paper describes the design and development of a 6 kA/1.1 kV non-destructive testing system, which aims for short circuit testing of high-power IGBT modules. An ultra-low stray inductance of 37 nH is achieved in the implementation of the tester. An 100 MHz FPGA supervising unit enables 10 ns level control accuracy of the short-circuit duration, protection triggering, and acquisition of the electrical waveforms. Moreover, a protection circuit avoids explosions in case of failure, making the post-failure analysis possible. A case study has been carried out on an aged 1.7 kV IGBT power module. The case study shows the current and voltage waveforms during short-circuit, as well as the current mismatch among six inner sections, which demonstrate the capability and the effectiveness of the proposed setup in the short-circuit aspect reliability studies of MW-scale power modules.

A compact quasi-Z-source DC/DC converter is presented with high voltage gain, isolated output, and improved efficiency. The improvements in size and performance were achieved by using a square wave inverter with only two output switches driving an isolating transformer in push-pull mode, followed by a voltage doubling output rectifier. The converter is well-suited to applications requiring a high voltage gain, especially renewable energy sources such as photovoltaic and fuel-cell power supplies. To demonstrate the converter's performance a prototype designed to output 400 V at 500 W was constructed and tested. The efficiency at full load varied from 89.0% to 97.4% as the input voltage changed from 44 V to 82 V.

Grid-connected converters employ LCL-filters, instead of simple inductors, because they allow lower inductances while reducing cost and size. Active damping, without dissipative elements, is preferred to passive damping for solving the associated stability problems. However, large variations in the grid inductance may compromise system stability, and this problem is more severe for parallel converters. This situation, typical of rural areas with solar and wind resources, calls for robust LCL-filter design. This paper proposes a design procedure with remarkable results under severe grid inductance variation. The procedure considers active damping using lead-lag network and capacitor current feedback. Passive damping is also discussed. The design flow, with little iteration and no complex algorithms, selects the proper ratios between the switching and resonance frequency, the grid and converter inductance, and the filter capacitance and total inductance. An estimation for the grid current total harmonic distortion (THD) is also proposed. Simulation and experiments validate the proposals.

Three-phase active rectifiers guarantee sinusoidal input currents and unity power factor at the price of a high switching frequency ripple. To adopt an LCL-filter, instead of an L-filter, allows using reduced values for the inductances and so preserving dynamics. However, stability problems can arise in the current control loop if the present resonance is not properly damped. Passive damping simply adds resistors in series with the LCL-filter capacitors. This simplicity is at the expense of increased losses and encumbrances. Active damping modifies the control algorithm to attain stability without using dissipative elements but, sometimes, needing additional sensors. This solution has been addressed in many publications. The lead-lag network method is one of the first reported procedures and continues being in use. However, neither there is a direct tuning procedure (without trial and error) nor its rationale has been explained. Thus, in this paper a straightforward procedure is developed to tune the lead-lag network with the help of software tools. The rationale of this procedure, based on the capacitor current feedback, is elucidated. Stability is studied by means of the root locus analysis in z-plane. Selecting the lead-lag network for the maximum damping in the closed-loop poles uses a simple optimization algorithm. The robustness against the grid inductance variation is also analyzed. Simulations and experiments confirm the validity of the proposed design flow.

The thermal loading of power semiconductors is a crucial performance related to the reliability and cost of the wind power converter. However, the thermal loading impacts by the variation of wind speeds have not yet been clarified, especially when considering the aerodynamic behavior of the wind turbines. In this paper, the junction temperatures in the wind power converter are studied under not only steady state, but also turbulent wind speed conditions. The study is based on a 1.5 MW direct-driven turbine system with aerodynamic model described by Unsteady Blade Element Momentum Method (BEMM), and the thermal stress of power devices is investigated from the frequency spectrum point of view of wind speed. It is concluded that because of the strong inertia effects by the aerodynamic behavior of wind turbines, thermal stress of the semiconductors is relatively more stable and only influenced by the low band frequency of wind speed variations.

Thermal models are needed when designing power converters for Wind Turbines (WTs) in order to carry out thermal and reliability assessment of certain designs. Usually the thermal models of Insulated Gate Bipolar Transistors (IGBTs) are given in the datasheet in various forms at component-level, not taking into account the thermal distribution among the chips. This is especially relevant in the case of Press-Pack (PP) IGBTs because any non-uniformity of the clamping pressure can affect the chip-level thermal impedances. This happens because the contact thermal resistances in the thermal impedance chains are clamping pressure dependent. In this paper both component-level and chip-level dynamic thermal models for the PP IGBT under investigation are developed. Both models are developed using geometric parameters and material properties of the device. Using the thermal models, the thermal impedance curves under various mechanical clamping conditions are derived. Moreover, the deformation of the internal components of the PP IGBT under operating-like conditions is investigated with the help of the thermal models and the coefficient of thermal expansion (CTE) information.

This paper presents a series of current control strategies for the DFIG under symmetrical grid voltage dips. The controllable range, the damping time constant of the stator natural flux and the torque fluctuations of six control strategies are analyzed and compared. The control strategies which have the largest controllable range, the smallest damping time constant of the stator flux and the smallest torque fluctuation are listed, respectively. The comparison is verified by simulations.

Modern grid codes for interconnection of distributed energy resources have become more restrictive due to the massive integration of renewable energy sources. The interconnected renewable energy sources must operate accurately under normal and abnormal grid conditions in order to meet the grid requirements. In addition, the renewable energy systems require fault ride through capability in order to support the power grid under balanced or unbalanced low voltage grid faults. Therefore, the development of advanced current controller techniques is essential for the grid side power electronic converters in order to increase the renewable energy systems penetration and satisfy the grid codes. This paper proposes a current controller technique, which enables the appropriate operation of the grid side converter under unbalanced grid faults and harmonic distorted grid conditions. The proposed current controller is designed using multiple synchronous reference frames and can inject full positive or full negative sequence balanced sinusoidal currents under abnormal grid conditions. The accurate performance with robustness against unbalanced and harmonic distorted grid voltage indicates that the proposed current controller can be a useful tool in the fault ride through control of renewable energy systems.

Renewable energy sources require accurate and appropriate performance not only under normal grid operation but also under abnormal and faulty grid conditions according to the modern grid codes. This paper proposes a novel phase-locked loop algorithm (MSHDC-PLL), which can enable the fast and dynamic synchronization of the interconnected renewable energy system under unbalanced grid faults and under highly harmonic distorted voltage. The outstanding performance of the suggested PLL is achieved by implementing an innovative multi-sequence/harmonic decoupling cell in order to dynamically cancel out the oscillation of the positive sequence voltage vector, produced by the existence of unbalanced and harmonic distorted voltage. The fast and accurate response of the proposed PLL under abnormal grid conditions is very important for the appropriate synchronization and control of the interconnected renewable energy systems. Therefore, the performance of the new PLL can increase the quality of the injected power under abnormal conditions and in addition enable the renewable energy systems to provide the appropriate support to the grid under balanced and unbalanced grid faults.

Bi-directional Inductive Power Transfer (BDIPT) technique is suitable for renewable energy based applications such as electric vehicles (EVs), for the implementation of vehicle-to-grid (V2G) systems. Recently, more efforts have been made by researchers to improve both efficiency and reliability of renewable energy systems to further enhance their economical sustainability. This paper presents a comparative reliability study between a typical BDIPT system and an individually controlled segmented BDIPT system. Steady state thermal simulation results are provided for different output power levels for a 1.5 kW BDIPT system in a MATLAB/Simulink environment. Reliability parameters such as failure rate and mean time between failures (MTBF) are compared between the two systems. A nonlinear programming (NP) model is developed for optimizing charging schedule for a stationery EV. A case study of EV optimum charging is provided for a 24 hours period indicating minimum cost and higher reliability.

Three-phase three-wire shunt active power filters (APFs) usually employ very large electrolytic capacitors in the dc-link to mitigate utility side harmonics. These capacitors are however known to be bulky and of short operating lifetime, particularly for systems where high ripple currents exist. This paper presents the concept of dc-link compensator (DLC) that aims to decouple the harmonic power from the dc-link of APF. With proper system sizing and design, most of the harmonic power can be eliminated by this DLC circuit and very small electrolytic capacitors or even film type capacitors can be used instead. Moreover, DLC itself is constructed with small passive components and features very simple circuit configuration. Experimental results are provided to show its effectiveness.

This paper investigates a permanent magnet synchronous motor drive controlled by a second-order variable structure control technique, known as the super-twisting sliding modes (STSM) control. The STSM controller is designed as a direct torque and flux controller and it works in the stator flux reference frame, rather than the rotor frame, as a regular vector control scheme. Another second-order sliding mode controller (SMC) was developed and compared with the STSM controller. Also for comparison, a similar direct torque control scheme based on linear PI controllers was developed and tested. The tests show that the STSM controller displays very robust behavior, like any SMC, and it works without notable chattering, like the linear PI-based controller. The paper presents theoretical aspects for the STSM control, several design and implementation details, and comparative experimental results with all three schemes.

This review focuses on faults in Modular Multilevel Converter (MMC) for use in high voltage direct current (HVDC) systems by analyzing the vulnerable spots and failure mechanism from device to system and illustrating the control & protection methods under failure condition. At the beginning, several typical topologies of MMC-HVDC systems are presented. Then fault types such as capacitor voltage unbalance, unbalance between upper and lower arm voltage are analyzed and the corresponding fault detection and diagnosis approaches are explained. In addition, more attention is dedicated to control strategies, when running in MMC faults or grid faults. This paper ends up with a discussion of other opportunities for future development.

Converters with reduced switch counts usually face some performance tradeoffs, which make them suitable for some applications but not others. The same applies to the nine-switch converter, which is a reduced-switch version of the back-to-back twelve-switch converter. The nine-switch converter has since been shown to experience a higher voltage stress, which can be lowered in some cases. A corresponding evaluation of its current stress is however lacking, and is hence addressed now by computing its switch currents when used for ac-ac, ac-dc, dc-ac and dc-dc energy conversions. Relevant expressions, application requirements and simulation results are presented for identifying cases, where the nine-switch converter can have an improvement in performance despite its reduced switch count.

The electromagnets in modern particle accelerators require high performance power supply whose output is required to track the current reference with a very high accuracy (down to 50 ppm). This demands very high bandwidth controller design. A converter based on buck converter topology is used in this paper. The paper presents a model of the converter which enables the design of high performance controller using a proportional-integral controller and a feedforward gain. Experimental and simulation results are presented with resistive and inductive load which verify the system requirement using the proposed approach of the system model and controller design.

Silicon carbide (SiC) and other wide band gap devices are in these years undergoing a rapid development. The need for higher efficiency and smaller dimensions are forcing engineers to take these new devices in to considerations when choosing semiconductors for their converters. In this article a Si based converter and a SiC based converter is compared. Both converters are isolated DC/DC converters and were designed for 5 kW nominal outputs. Test setups for both converters were built and tested. The hardware differences between the two converters are described and performance is compared. An efficiency of above 97 % for the SiC JFET and over 90 % for the SI IGBT converter was measured. Cost differences between the two converters have been analyzed, showing that 772 days of operation are needed for the SiC converter costs to break even with the Si IGBT converter costs.

Grid converters require a simple inductor or an LCL-filter to limit the current ripples. The LCL-filter is nowadays the preferred solution as it allows lower inductance values. In order to solve the stability concerns, active damping is preferred to passive damping since it does not use dissipative elements. However, large variations in the grid inductance and resonances arising from parallel converters may still compromise the system stability. This calls for a robust design of LCL-filters with active damping. This paper proposes a design flow with little iteration for two well-known methods, namely lead-lag network and current capacitor feedback. The proposed formulas for the resonance frequency, grid and converter inductance ratio, and capacitance of the LCL-filter allow calculating all the LCL-filter parameters. An estimation for the achieved Total Harmonic Distortion (THD) of the grid current is also provided. Experimental results show very robust designs to the parameter variations.

The dual active bridge topology allows bidirectional power flow and galvanic isolation for DC/DC energy conversion. These features have made it the possible backbone of the future smart transformer for distribution. The different voltage drops and commutation dead-times of the semiconductor switches result in DC-voltage at the transformer terminals. Even small DC-voltage components produce large DC-bias currents as they are only limited by the transformer resistances. The DC-bias degrades the transformer performance by increasing the losses. If the core saturates the resulting current pulses can damage the converter. A typical approach to avoid the DC-bias is placing a capacitor in series with the transformer. This capacitor suffers large current variations, reducing its reliability, and complicates the control. The dual active bridge usually handles the power flow by modifying the phase-shift of the converter square waveforms. In this paper the duty-cycle of the converter waveforms is controlled to cancel the current DC-bias in both transformer sides. A formula relating the reference power and phase-shift is provided for the case of varying duty-cycle waveforms. The implementation with constant sampling frequency and its limitations are explained.

During last years an increasing attention has been paid to the efficiency of grid-connected PV inverters. They are manufactured from a number of discrete components and by using a certain topology and control strategy. Hence, the performance of a certain PV inverter not only depends on the selected topology and control strategy but also on the characteristics of the employed components. The aim of this paper is evaluate the effect of physical variations associated to the main components on the overall efficiency of PV inverters. It is concluded that a statistical evaluation of the power converter provides a better understanding of the PV inverter performance and, in this sense, the definition of the European Efficiency must be reviewed in order to show the quality of the manufactured product.

Wind speed variations make the power of wind turbine system to fluctuate, which could increase the thermal stress of the power converter and reduce its lifetime. In order to relieve this problem, short-term energy storage technologies are applied to improve the thermal performance of a 3 MW grid side wind power converter. The cost, weight and cycle life of the energy storage technologies are evaluated based on a typical low speed high turbulence wind profile. In detail, a wind turbine system model is established and its control strategy is illustrated, which is followed by the power control method of the energy storage system. Then the conventional thermal evaluation approach is simplified for evaluation with long term wind profile. The case studies are done to address the optimal power size and capacity of the energy storage system by comparing the improvement of the thermal performance. Also, the two promising candidates, ultracapacitors and batteries, are compared.

This paper deals with the design, control, efficiency and thermal cycling estimation of associated Si and SiC based three-phase PV-inverters. A novel Electro-Thermal Model able to consider the thermal coupling within the Transistor and Diode integrated on the same package is proposed. For each topology, three different cases study are simulated, according to the heatsink repartition: one-leg heatsink, shared heatsink and individual heatsink. Based on the model, it has been determined the minimum required heatsink thermal impedance in order not to overpass the device physically thermal limitations. Finally, simulation results are analyzed in order to decide which topology has a higher efficiency and a better thermal loading distribution within the devices.

Reliability is one of the key issues for the application of Insulated Gate Bipolar Transistors (IGBTs) in power electronic converters. Many efforts have been devoted to the reduction of IGBT wear out failure induced by accumulated degradation and catastrophic failure triggered by single-event overstress. The wear out failure under field operation could be mitigated by scheduled maintenances based on lifetime prediction and condition monitoring. However, the catastrophic failure is difficult to be predicted and thus may lead to serious consequence of power electronic converters. To obtain a better understanding of catastrophic failure of IGBTs, the state-of-the-art research on their failure behaviors and failure mechanisms is presented in this paper. Moreover, various fault-tolerant design methods, to prevent converter level malfunctions in the event of IGBT failure, are also reviewed.

In this paper, the case of symmetrical grid fault when using the multi-MW wind turbine of partial-scale and full-scale two-level power converter are designed and investigated. Firstly, the different operation behaviors of the relevant power converters under the voltage dip will be described and analyzed. Simulations of different configurations regarding the loss distribution and the junction temperature of the power device are presented in respect to the various voltage dips. It is concluded that for both systems the power loss will change dramatically during the Low-Voltage Ride Through (LVRT) condition as well as the junction temperature. For the full-scale wind turbine system, the most thermal stressed power device in the grid-side converter will appear at the grid voltage below 0.5 pu, and for the partial-scale wind turbine system, the most thermal stressed power device in the rotor-side converter will appear around 0.6 pu grid voltage.

This paper presents an efficiency improved single-phase power factor correction (PFC) converter with its target application to plug-in hybrid electric vehicle (PHEV) charging systems. The proposed PFC converter features sinusoidal input current, three-level output characteristic, and wide range of output DC voltage. Moreover, the involved DC/DC buck conversion stage may only need to convert partial input power rather than full scale of input power, and therefore the system overall efficiency can be much improved. Through proper control of the buck converter, it is also possible to mitigate the double-line frequency ripple power that is inherent in a single-phase AC/DC system. Both simulation and experimental results are presented to show the effectiveness of this converter.

Half-bridge inverters, full-bridge inverters and bidirectional buck converters share a common topological structure, in which two switches and two diodes are present. In such a topology, a dead time between the two signals controlling the switches is inserted. This influences the relationship between output voltage, input voltage and duty cycle as a function of the output current. In the literature, the dead-time effect has been studied in relation with inverters, active filters, voltage regulated modules and high-precision power amplifiers, and dead-time compensation techniques have been proposed. However, the measurement of the current is normally required for all dead-time compensation strategies, which can be a problem when the current approaches or crosses zero. In this paper, the operation of a bidirectional buck converter in the region around zero current has been analytically analyzed. It has been shown that in a region around zero there is no dead-time effect. The analytical expression of the borders between the areas where the dead-time effect is positive, zero or negative has been given. Moreover it has been shown that between these three areas, there are four other transitional areas. The analytical analysis has been confirmed by simulation and experimental results.

Advances in power electronics enable efficient and flexible processing of electric power in the application of renewable energy sources, electric vehicles, adjustable-speed drives, etc. More and more efforts are devoted to better power electronic systems in terms of reliability to ensure high availability, long lifetime, sufficient robustness, low maintenance cost and low cost of energy. However, the reliability predictions are still dominantly according to outdated models and terms, such as MIL-HDBK-217H handbook models, Mean-Time-To-Failure (MTTF), and Mean-Time-Between-Failures (MTBF). A collection of methodologies based on Physics-of-Failure (PoF) approach and mission profile analysis are presented in this paper to perform reliability-oriented design of power electronic systems. The corresponding design procedures and reliability prediction models are provided. Further on, a case study on a 2.3 MW wind power converter is discussed with emphasis on the reliability critical components IGBTs. Different aspects of improving the reliability of the power converter are mapped. Finally, the challenges and opportunities to achieve more reliable power electronic systems are addressed.

The increased penetration of renewable energy systems, like photovoltaic and wind power systems, rises the concern about the power quality and stability of the utility grid. Some regulations for Low Voltage Ride-Through (LVRT) for medium voltage or high voltage applications, are coming into force to guide these grid-connected distributed power generation systems. In order to verify the response of such systems for voltage disturbance, mainly for evaluation of voltage sags/dips, a Voltage Sag Generator (VSG) is needed. This paper evaluates such sag test devices according to IEC 61000 in order to provide cheaper solutions to test against voltage sags. Simulation and experimental results demonstrate that the shunt impedance based VSG solution is the easiest and cheapest one for laboratory test applications. The back-to-back fully controlled converter based VSG is the most flexible solution for the system test under grid faults but also the most expensive one.

In this paper, the multi-MW wind turbine of partial-scale and full-scale two-level power converter with DFIG and direct-drive PMSG are designed and compared in terms of their thermal performance. Simulations of different configurations regarding loss distribution and junction temperature in the power device in the whole range of wind speed are presented and analyzed. It is concluded that in both partial-scale and full-scale power converter the most thermal stressed power device in the generator-side converter will have higher mean junction temperature and larger junction temperature fluctuation compared to grid-side converter at the rated wind speed. Moreover, the thermal performance of the generator-side converter in the partial-scale power converter becomes crucial around the synchronous operating point and should be considered carefully.