This research investigates the modeling and control hardware-in-the-loop (HIL) implementation of a voltage source converter (VSC) with a medium voltage DC (MVDC) input and low voltage AC (LVAC) output in grid-forming mode. The system employs a step-down transformer between the L and C components of the converter output filter, enhancing cost-effectiveness and safety. However, this configuration presents challenges in modeling and control design due to the separation of feedback signals for the control system: the inverter current, used as the inner loop feedback signal, is measured on the primary side, while the capacitor voltage, used as the outer loop feedback signal, is measured on the secondary side. This paper addresses these challenges and presents a control strategy tailored for this configuration. The study utilizes a three-level converter with a Dyn11 transformer configuration. The validation process involves control hardware-in-the-loop (HIL) testing, using a Texas Instruments DSP F28379D for control implementation, MATLAB/Simulink for code generation, and Typhoon HIL for real-time simulation. The primary contribution is the development of a control strategy that effectively handles dual-sided feedback from the transformer, maintaining stable operation in grid-forming mode. This approach ensures low Total Harmonic Distortion (THD) and excellent dynamic response, enhancing the converter output voltage stability, and power quality.

With the development of artificial intelligence, the control strategies for critical power devices has a diversity such that more reliability solution can be guaranteed in diversity complicated working condition. LC-inverter is known as one of the most applied power conversion equipment nowadays due to the significantly increasing demand for more electrical transportation and multiple renewable energy source generation. To address the challenge of developing a degradation-aware control strategy, this paper intend to incorporates a novel degradation to the finite-set model predictive control for the LC inverter.

Increasing net profits and ensuring the comfort of the residents in community daily energy management is the primary mission of community power operators (CPOs). To reach these goals, the CPO may tailor a bidding strategy to pre-procure a portion of the cheaper power for the reservation to ensure a reliable power supply for scheduling programs. This paper develops a novel bi-level optimization model to resolve this challenge. In the upper level, the CPO aims to maximize net profits through customized power pre-procurement and real-time bi-directional power trading. The lower level focuses on minimizing the electricity costs of the buildings incorporating the building's thermal inertia depending on the real-time temperature variations. The proposed bi-level model presents an interdependent non-linear programming challenge. The instantiations indicate that setting different pre-order power levels for each time slot may improve net profitability for CPO.

A sudden change in loads creates troubles in grids/microgrids (MGs) such as frequency fluctuations. For balancing between generation and demand, a Doubly fed induction generator (DFIG) has been incorporated into the Egyptian power system (EG-EPS) to provide additional inertia. The studied EG-EPS consists of three conventional power plants (reheat, non-reheat, and hydro) as the main sources of generation, with 20% DFIG participation. The existing literature highlights that the control methods employ for LFC and DFIG in MGs are insufficiently coordinated for minimizing deviations in frequency and power. This limitation arises due to narrow control constraints and inadequate sensitivity to disturbances. To this regard, this paper proposes an adaptive control-based balloon effect modulation (BE) to tune the PID controller for the Automatic Generation Control (AGC) and to tune the PI controller of the DFIG speed controller. The balloon effect tool is used to minimize the impact of system load disturbance by increasing the optimizer sensitivity and traceability. The EG-EPS is examined under the influence of a 2% step load perturbation and random load variations using dSPACE DS1006 and real-time digital simulator (RTDS) as a Hard-In-Loop (HIL) test platform. The proposed controller demonstrates superior performance compared to the conventional one in terms of overshoot, undershoot, and stabilizing time.

This paper addresses the formulation problem of a power flow for controlled islanded microgrids including battery energy storage systems. The formulation considers droop-based primary controllers, probability-based wind distributions and power curves for the distributed generation units, and sigmoid-based models for the BESS operation and the load shedding. Two case studies are addressed where different BESS conditions are selected to highlight its role in the islanded microgrid, and its impact in the microgrid operative steady-state dynamics. The obtained results corroborate the proposed power flow formulation reliability for representing the controlled islanded microgrid and its usefulness for detailed operative planning and design.

This paper introduces a Power Electronic Converter (PEC) featuring a medium-frequency AC-link and a non-rectifier stage designed to connect photovoltaic (PV) modules to the grid while extracting the maximum power from the PV array. The proposed system incorporates a Battery Energy Storage System (BESS) to mitigate the effects of partial shading. A Three-Level Bidirectional Converter (3LBDC) has been adopted to facilitate battery charging. The 3LBDC converter exhibits minimal ripple in the inductor's current, maintaining the same inductance and frequency values consistent with a traditional boost converter. An Incremental Conductance algorithm is deployed as the Maximum Power Point Tracker (MPPT) on the boost converter, enabling the extraction of available power from the PV system and subsequent injection into either the grid or BESS as necessitated by the conditions. Simulated testing of the entire system indicates that it provides a viable solution for PV-ESS grid-tied applications.

This paper proposes distributed, event-triggered, power-sharing strategies to solve the economic power dispatch (EPD) problem for virtual energy storage systems (VESS) composed of smart homes in microgrids. Existing literature on this subject requires continuous or periodic communication. In this paper we propose a dynamic, event-triggered, information delivery strategy, combined with a weighted, distributed optimization algorithm. By inheriting economic parameters, the proposed algorithm guarantees power balance at each iteration, while power capacity constraints are guaranteed by deriving a virtual energy price for each smart home. These techniques enable the proposed resilient, distributed algorithm to solve EPD problem online with reduced communications. Theoretical analyses demonstrate the convergence and optimality of the proposed algorithm, which also excludes Zeno triggering behavior. Numerical analyses and simulations demonstrate the validity and effectiveness of the proposed strategies.

False data injection attacks (FDIA) in power systems involve intentionally injecting fabricated data to compromise system integrity, reliability, and functionality. These attacks have devastating consequences for power systems, particularly when they have the potential for sequential outages. To defend against these types of attacks, the implementation of an effective defense mechanism is crucial. The defense system should have advanced security measures, like encrypted phasor measurement units (PMU), to protect the integrity and reliability of the power system infrastructure from FDIA-caused outages that happen one after the other. In order to protect against sequential outages brought on by load redistribution attacks (LRA), this paper proposes a PMU placement optimization problem. In this study, we conduct an analysis of the susceptibility of the IEEE 30 bus standard system to LRA, resulting in sequential outages. Additionally, we explore the optimal placement of PMU as a means of improving the system's defense against such vulnerabilities.

For multibus wind power plants in microgrids, it is challenging to develop a reliable, effective, and robust harmonic suppression method for harmonic voltages and currents of all buses. This paper proposes a hierarchical harmonic control method to mitigate the harmonic voltages and currents of all buses in grid-forming wind power plants. The proposed method effectively reduces the terminal harmonic voltages and currents, PCC harmonic voltage, and grid harmonic current. It achieves adaptive harmonic mitigation and automatic harmonic current sharing between wind turbine units according to the rated capacity and feeder impedance of each unit. The effectiveness of the method is verified in the planned Turkish offshore wind power plant by simulation in Digsilent/PowerFactory.

Insulated Gate Bipolar Transistor modules, known as IGBT modules, play a critical and indispensable role in a wide range of power converter applications. However, IGBT modules are not immune to failures, which can have severe consequences such as system faults, downtime, and economic losses for industries relying on their functionality. Accurately estimating the junction temperature of IGBT modules is essential for managing their thermal characteristics, performing condition monitoring and lifetime prediction. Therefore, in this paper, recent IGBT junction temperature estimation methods of are summarized. First, the package, circuit principle and failure mode of IGBT module are introduced, followed by a discussion of various junction temperature estimation methods, including methods based on optical technologies, thermal network and Finite Element Analysis models, and temperature-sensitive electrical parameters (TSEPs). Finally, future research challenges and opportunities for implementing these technologies are presented.

A fuzzy logic based online energy management system (FLEMS) is designed in this paper to achieve the optimal electricity cost in a residential Microgrid (MG). The proposed FLEMS is combined by a local energy price model (LEPM) and a fuzzy-logic strategy. The LEPM will preprocess the sampling data to estimate the electricity market and local MG status. The fuzzy-logic mimics the artificial intelligent assessment to economic issues and make decision for the charging and discharging operation for energy storage system (ESS). In the FLEMS, not only electricity price and supply-demand balance, but also ESS state of charge are considered for the efficient and stable operations. The proposed method does not relay on the accurate prediction of renewable energy source and local loads. Historical experience of the system is involved by the LEPM and guides the ESS operation in the fuzzy-logic. A real-world data based household-level residential MG model is established to validate the performance of the FLEMS. A hourly-resolution-Particle swarm optimization (PSO) with perfect day-ahead prediction is implemented as the baseline to verify the superiority of the proposed method.

In this work, a comprehensive study on the dynamic modeling and control of the reformed methanol high-temperature proton exchange membrane fuel cell (HT-PEMFC) and battery system is presented for electrical applications. A more detailed mathematical model that considers the transient dynamics of the fuel cell is adopted, providing a simplified yet accurate solution for a wide range of fuel cell operational cases. The dynamic system model incorporates the FC, balance of plan (BoP) components, buck/boost converter, and battery. The buck/boost converter operation mode is automatically switched by power management rules according to the battery voltage, achieving coordination between the FC and the battery, stable DC bus voltage, and a healthy state-of-charge (SOC) level of the battery. Simulations are conduction on MATLAB/Simulink and the results validate the effectiveness of the proposed modeling approach and power sharing strategy in achieving enhanced performance and system stability under different load cases. The research contributes for integrating HT-PEMFC systems in future electrical applications.

Decarbonizing issues from ship transportation during visiting a port offer a few alternatives. Among them is the electrification onshore power system known as cold ironing that provides electric power from the shoreside to the visiting ship at port, replacing auxiliary engines-fossil fuel-based. This paper presents four different environmental dispatch strategies for cold ironing system to minimize both cost and environmental impact while meeting seaport operation constraints. The problem formulation was formulated as quadratic constrained programming (QCP) model and solved in GAMS optimization by using the CANOPT solver. The Pareto optimal front from the simulation offers port operators decision-making options that suit their priority objective function. Furthermore, sensitivity analysis for various load values in the optimization model gives insight into any changes in dispatching patterns as the load changes.

This paper offers a comparative analysis of Maximum Power Point Tracking (MPPTs) techniques under the spinning conditions for small satellite applications. The Nano Satellite (NanoSat) is constrained on volume and mass with body-mounted solar panels and where it is dedicated to some special orientation scenarios, depending on specific mission requirements. This results in irregular solar irradiance on the PV system; thus, it needs an efficient and effective strategy to extract the maximum power transferred to the loads in the NanoSat Electrical Power System (EPS). While the EPS can be regarded a space microgrid due to control and coordination in a small electric network of distributed generations (DGs), storage, and loads. Therefore, some well-known MPPT techniques are investigated where different scenarios are carried out among conventional Perturb and Observe (P&O), Incremental Conductance (IC), and Ripple Correlation Control (RCC) to highlight the optimal MPPT extractions for NanoSat applications. The system was developed and modeled in MATLAB/SIMULINK and the final findings demonstrate that the RCC provides smooth power compared to other ones, while the other ones offer an oscillated power under the effect of radiations change and spinning conditions for the system under test.

The virtual synchronous generator (VSG) has been extensively applied for the integration of distributed generators. For the benefit of analysis, both the reduced-order small-signal model (RSM) and full-order small-signal model (FSM) have been proposed; however, because of the different modeling approaches, the modeling accuracy may differ a lot. To provide a guideline for selecting a suitable model, an accuracy assessment has been conducted in this paper, where different grid strength cases and equilibrium points are considered. More specific, the eigenvalue analysis is adopted for comparing the dominant dynamics of the RSM and FSM. Afterwards, the responses of the RSM and FSM are compared with the nonlinear model (NM) in the Digsilent/Powerfactory to show the modeling accuracy. It has been found that the RSM is mainly suitable for the weak and relatively strong grids, while the FSM shows better accuracy in the case of an extremely strong grid and around the equilibrium point that is close to VSG's rated output.

Energy disaggregation is the process of disaggregating a household's total energy consumption into its appliance-level components. One of the limitations of energy disaggregation is its generalization capacity, which can be defined as the ability of the model to analyze new households. In this article, a new energy disaggregation approach based on adversarial autoencoder (AAE) is proposed to create a generative model and enhance the generalization capacity. The proposed method has a probabilistic structure to handle uncertainties in the unseen data. By transforming the latent space from a deterministic structure to a Gaussian prior distribution, AAEs decoder transforms into a generative model. The proposed approach is validated through experimental tests using two different datasets. The experimental results exhibit a 55% MAE performance increase compared to deterministic models and 7% compared to probabilistic models. In addition, considering the predictions made when the appliances areon, the AAE improves the performance by 16% for UKDALE and 36% for REDD dataset compared to the state-of-art models. Moreover, the online analysis performance of AAE is examined in detail, and the disadvantages of instant predictions and the possible solutions are extensively discussed.

Replacement of conventional generation units with a large number of renewable energy sources RESs causes an undesirable influence to the Egyptian power system EPS frequency stability, excessive supply due to full DGs generation due to the lack of system rotating inertia. The EPS consists of several conventional generation units (i.e., non-reheating, reheating, and hydraulic power plants) with inherent nonlinearities, and RESs (i.e., solar and wind energy). In order to solve this challenge, this paper provides a tertiary modified virtual inertia control loop-based energy storage system ESS as an active solution to improve the EPS stability during contingencies, and diminish the frequency deviations and regulate the power flow. In this method, the ability to imitate damping and inertia properties are presented based on the derivative technique. A comparative study between the conventional EPS with/without virtual (inertia + damping) is also presented. The constructed results using Matlab/Simulink software show the superior effectiveness and control effect of the proposed control method in terms of accurate tracking of the reference frequency and attenuating noise over the traditional one. Finally, it was verified that the auxiliary enhanced virtual inertia mechanism assisted the EPS by suppling further power inertia to robust the frequency against RESs and load demand penetrations.

As one of the vital load types in the military shipboard power system (SPS), the pulsed load normally features with the transient high power. Thus, in the case that the SPS has a small inertia constant, the operation of pulsed loads may heavily affects the voltage stability. Benefiting from various advantages of the DC microgrid in terms of the flexibility of power source connection, generator efficiency, and fuel consumption, the DC SPS is recognized as the next-generation solution. In order to assess the impact of pulsed loads in the future DC SPS, a comprehensive time-domain simulation study in Matlab/Simulink software has been conducted in this paper, where pulsed loads with two types of profiles, namely, single-pulse signal and multiple-pulses signal, have been included in the evaluation. Especially, the effect of pulse signal parameters, including the peak power, the pulse duration, the pulse interval time, and the pulse number has been simultaneously tested and analyzed. The DC bus voltage drop during the pulsed load operation has been taken as the index in the simulation. Key findings in the study have been summarized in detail, which leads to the final conclusions.

In order to emulate the frequency support characteristics of conventional synchronous generators (SGs), control algorithms based on the virtual synchronous generator (VSG) have been extensively applied to grid-tied converters. However, in the case that a large inertia is used in VSGs, active power oscillations can be introduced in the transients, due to the lack of enough damping effects. To avoid this phenomena, various solutions with additional damping terms have been proposed. This paper analyzes and compares six relevant fixed- parameter active-power-oscillation damping solutions in detail, where responses under set point and phase angle changes, the parameter sensitivity, and capabilities of limiting the rate of change of frequency (RoCoF) and attenuating power ripples are included. The results show the advantages and drawbacks of each solution, leading to the conclusion that extra damping terms may significantly degrade the inertial response of VSGs and have high dependency on the parameter estimation accuracy.

Wind turbine converters (WTCs) with grid forming (GFM) control can contribute to voltage and frequency support in the power system, by emulating synchronous machine (SM) dynamics, provided that there are sufficient buffers. Over the past few years, several control algorithms have been developed for the GFM operation of WTCs. This article investigates the state-of-the-art in the field of GFM control algorithms for WTCs, where the principle of each control algorithm is discussed in detail, and corresponding characteristics are summarized. Comparison results with respect to voltage build-up strategies, the synchronization of GFM WTCs, the interaction attenuation, the virtual inertia realization and the complexity of individual GFM algorithm are given in a table, which leads to the conclusion that mitigation of oscillations among WTCs, appropriate inertia emulation, and coordination with energy storage systems need to be further investigated in the future GFM WTCs.

The increase of green house gases (GHGs) emissions and depletion in fossil fuels have urged an extensive use of renewable energy resources (RESs) and energy storage systems (ESSs) in short route ferries and yachts. In current times, most of the smaller seaports are not equipped with the cold ironing facility, hence, when fossil fuel based SMGs are berthed at the port their auxiliary engines are kept on, which pollutes the seaport. In order to address this issue, RES and ESS equipped SMGs can be interconnected via DC bus to formulate a sea port microgrid. The Dc bus interfaced sea port microgrid can be used for providing mobile cold ironing facility to the nearby ships that are integrated with fossil fuels to minimize the emissions, vibrations, and noise pollution. Generally, power sharing among several mcicrogrids is achieved through a communication based control strategies that adds up complexity and the cost. This study, alternatively, proposes an adaptive droop based control algorithm, which is applied to DC SMGs for communication less power-sharing among hybrid energy resources (Battery, Photovoltaic and Fuel Cell). The proposed scheme further helps to charge the battery banks that are below the threshold limits by using the RES integrated in several SMGs.

A VICINITY platform-based load scheduling method by considering the smart parking and household smart appliances for renewable energy resources integrated residential microgrids is proposed in this paper. The proposed method can shift the local loads and publish the vacant number of parking slot with a real-time electric vehicle charging price to VICINITY platform according to the renewable energy generation and the usage of the parking spaces to reduce energy cost and increase resident's revenue. The experimental platform-based real-life cross domain lab testing verifies the effectiveness of the proposed control approach.

Grid-connected inverters with LCL filter work stable using active damping methods. However, stability can be threatened easily by grid impedance variation. Particularly, delay in digitally controlled systems has a negative effect on the stable region of grid-connected inverters and shrinks this region. Therefore, by variation of grid impedance, it is very probable that resonance frequency located in the unstable region. To address this problem, a delay compensation method based on converter-side current feedback is proposed in this paper, which tackles the negative impact of the delay. The proposed method expands the stable region using passivity-based stability and guarantees the stable operation of inverter against grid impedance variation. Also, it does not need any extra sensors for active damping, which reduces the cost and increases the reliability. It is shown that the proposed method is effective in case of multi-paralleled inverters whiles normally coupling effect among inverters makes the stability condition worse. The effectiveness of the proposed method is verified through various case studies.

This paper proposes the utilization of a bidirectional DC-DC converter with sliding mode control in a wind distributed system employing the switched reluctance generator (SRG). The SRG wind system is connected to a three-phase AC utility grid by means of a voltage source converter. The presented proposal employes the DC-DC converter to regulate the optimum excitation voltage at the SRG side, while the VSC is responsible to maintain the DC bus voltage in a fixed value to allow the DC-AC conversion with the required voltage level and frequency. To face the problem of wide voltage variations, sliding mode control is applied to ensure the desired PWM duty cycle to the bidirectional DC-DC converter. SRG control is implemented through direct power control by current hysteresis, for low speeds, and by voltage single pulse control, for high speeds of operation. A careful examination about the behavior of the system considering the whole SRG operating speed range is carried out. Simulation results show that the proposal system is applicable and the applied sliding mode controller has rapid an robust behavior, as desired.

The papers in this special section offer a collection of new and original papers that cover different aspects from architecture, scheme design, control strategy, optimization, application and deployment of energy Internet systems.

Maritime applications have found in the integration of the electric power system a way to further improve efficiency and reduce the weight of new electric ships. This movement has led scientists to integrate smart management systems to optimize the overall behavior of the grid. In this context, power electronics play a key role in linking the different elements of the power architecture. Moreover, the transition toward a dc distribution, which has already been established in other applications, is being regarded as a promising alternative to ease the integration of renewable sources, batteries, and the ever increasing number of dc loads. In this paper, blackbox models are proposed as a tool to foresee the effect of these complex interactions, overcoming the lack of detailed information about the power converters. Large-signal strategies are proposed in order to consider nonlinearities in the static and dynamic behavior of the converters. An accurate model of the physical layer is essential to allow intelligent systems to take the most out of the system performance. This approach offers the opportunity to study the dynamic response of complex interconnected systems, tune the system-level controllers, design protections, or assess the compliance of the system dynamics with the standards. Experimental results are included in order to validate the proposed method.

Fault current limiters (FCLs) are one class of solutions to cope with the upcoming challenges in microgrid protection. Considering high penetration of distributed generations (DGs) in microgrids, the necessity of designing cheap and effective FCL is getting higher. This paper attempts to fill this gap by proposing an embedded FCL operating based on modifying the secondary control of DGs. As this method is designed for four-wire system, besides cost-effectiveness, it has independency and flexibility to only limit the fault current of DG. In order to validate the proposed method, different types of faults are examined through an extensive simulation study.

Recently, DC distribution has been more and more considered in shipbuilding industry as an emerging solution due to its potential to enhance the system performance in terms of fuel economy, reliability, volume and weight. Moreover, there is a growing trend to integrate alternative power sources (APSs) and energy storage systems (ESSs) into next-generation ships, and thus reducing cost and emission. In this context, the future shipboard power systems (SPSs) are expected to be compatible with various generation methods and complex onboard power consumers, which can be naturally identified as islanding microgrids (MGs). In this paper, specialized hierarchical control strategy is proposed to coordinate the system operation and meet the requirement of shipboard applications. Several advantageous functions are achieved by proposed control strategy. A study case of DC SPS is modeled and simulations are carried out to verify the proposed control strategy.

In this paper a new method is presented to achieve economic exploitation and proper usage of network capacity by exerting controlling actions over flexible loads and energy storage (ES) equipment. Multi-objective planning for demand response programs (DRP) and battery management policies is carried out by considering energy not supplied (ENS). In order to achieve an optimal scheduling, charge/discharge control for batteries, demand response programs and dispatch of controllable distributed generations (DGs) are also considered. Then, the balanced cost and benefits of participants are evaluated. As a whole, the main objective of this paper is to manage the load and energy storage options in a smart grid to reduce ENS, to minimize overall operation cost and to maximize DG operators' (DGOs) profit. These goals are obtained by considering ENS cost in a multi-objective optimization problem. Distribution company (DisCo) modifies energy cost as a signal for DGO in order to coordinate with each other. So, behavior of DGO is based on modified energy price applied by upstream system considering ENS price.

In this paper, an improved grid voltage modulated control (GVM) with power compensation is proposed for grid-connected voltage inverters when the grid voltage is unbalanced. The objective of the proposed control is to remove the power ripple and to improve current quality. Three power compensation objectives are selected to eliminate the negative sequence components of currents. The modified GVM method is designed to obtain two separate second-order systems for not only the fast convergence rate of the instantaneous active and reactive powers but also the robust performance. In addition, this method converts the system into a linear invariant system though designing a new voltage input. Simulation results are presented to verify the correctness and validity of the proposed control strategy and power compensation method.

Voltage and frequency transient variations are the most common power quality issues in a ship microgrid system. In this paper, the impacts of the voltage dips induced by the sudden-load of ballast pump are analyzed in detail for the ship power systems. Several relevant ship power quality standards and potential solutions are introduced and discussed properly. The experimental tests from a real ship are presented to show the impact of moderate voltage dips on the selected working generator and bow thruster.

Microgrids rely on energy management levels to optimally schedule their components. Conventionally, the research in this field has been focused on the optimal formulation of the generation or the demand side management separately without considering real case scenarios and validated only by simulation. This paper presents the power scheduling of a real site microgrid under a price-based demand response program defined in Shanghai, China managing generation and demand simultaneously. The proposed optimization problem aims to minimize operating cost by managing renewable energy sources as well as shiftable loads considering the preferred time of use. The proposal has been tested experimentally in a laboratory prototype.

The external droop control loop of I-V droop control is designed as a voltage loop with embedded virtual impedance, so the internal current loop plays a major role in the system bandwidth. Thus, in this paper, the influence of internal current loop on transient response performance of I-V droop controlled paralleled dc-dc converters is analyzed, which is guided and significant for its industry application. The model which is used for dynamic analysis is built, and the root locus method is used based on the model to analyze the dynamic response of the system by shifting different control parameters. Analysis results show that any converter's inner current loop can influence all converters' dynamic responses in the system and the one with larger Virtual Resistance (VR) has greater effect. Increasing the proportional terms can decrease the fluctuations of current and voltage, and key parts of errors can be reduced more rapidly during dynamical process, but adverse effect on completely eliminating errors can be caused; increasing integral terms can enlarge current fluctuations during dynamical process, but the errors can be eliminated more rapidly. The experiments are performed to verify the analysis.

An average power sharing control strategy for parallel operation of voltage source inverter (VSI) based modular Uninterruptible Power Systems (UPSs) is proposed in this paper. The presented method is based on a modified droop control. The proposed method conquers the drawback of conventional droop plus virtual impedance control, and at the same time some challenges in the real applications have been considered. Such as the mismatch of output impedance of the parallel modules, the different calibration accuracy of the sample circuit, and the offset of the voltage reference from the control unit. Simulation has been presented in order to verify the effectiveness of the proposed control methodology under these three different conditions. The simulation results demonstrate that a better power sharing performance is obtained and successfully prevent of negative power which can protect the DC bus.

In order to suppress the zero sequence circulating currents (ZSCCs) between parallel operating three level voltage source inverters with common AC and DC buses, a common mode voltage reduction PWM (CMVR-PWM) technique and neural point potentials (NPPs) control based method is proposed in this paper. An equivalent model of ZSCC is developed, and two excitation sources of ZSCC, differences of common mode voltages (CMVs) and NPPs between paralleled inverters, are analyzed. A CMVR-PWM method is investigated to reduce the CMV, and a simple electric circuit is adopted to control the NPPs. With this two strategies, ZSCCs between parallel inverters can be eliminated effectively. This strategy has the advantage of without carrier synchronization and can be utilized to parallel operating inverters with different types of filter. Simulation result validate the proposed ZSCC elimination schemes.

During the past few years, microgrids (MGs) have been becoming more attractive as effective means to integrate different distributed energy resources (DERs). To coordinate active and reactive power sharing among DERs, conventional droop control method is widely used as a decentralized control scheme. However, sharing powers among the sources based on the units' rated capacities is not an optimal solution in terms of economy and efficiency. In this paper, a new adaptive droop-based control strategy is proposed for AC MGs to optimally share MG load between corresponding units. The mentioned control strategy is developed in two levels. The upper control level is a mixed-objective optimization algorithm that provides optimal set-points for power generations considering system's constraints and goals, while the lower control level is responsible for tracking the reference signals coming from the upper level. To demonstrate the effectiveness of the proposed control strategy under different operating scenarios, simulation results in a benchmark MG are also presented.

Based on the hierarchical control structure in islanded Micro-Grid (MG) systems, the coupling/tradeoff effects in different levels are analyzed in details. In the primary level, analyses of the coupling effects among droop control gains, line impedance differences, output reactive power and voltage magnitudes are provided specifically. In the secondary level, the tradeoffs between accurate reactive power sharing and voltage magnitudes regulation are further detailed. The analysis results can provide a guideline for the design of MG structure and its control parameters. In addition, novel containment-based controller is proposed to control the voltage into a reasonable range which is the first time to apply this algorithm in MG. Furthermore, dynamic-consensus-based controller is used to guarantee accurate reactive power sharing. The combination of controllers offers a coordinated distributed operation and enhanced system performance. Finally, experimental results are shown to validate the effectiveness of the proposed method.

Random fluctuation of PV power is becoming a more and more serious problem affecting the power quality and stability of grid as the PV penetration keeps increasing recent years. Aiming at this problem, this paper proposed a control strategy of energy storage system based on Model Predictive Control (MPC). By the continuous optimizing of MPC, we can obtain the system parameters accurately, and then calculate the energy storage power. At the same time, this control took state of charge (SOC) and other parameters into account to ensure the health and stability of the energy storage units. Finally, simulation results proved the proposed control strategy had good performance and robustness.

Microgrid is regarded as a new form to integrate the increasing penetration of distributed generation units (DGs) in the extensive distribution systems. This paper proposes an adaptive overcurrent protection strategy for a microgrid network. The protection coordination of the overcurrent relays is treated as a linear programming problem for the different operation states. In the control center, an artificial neural network (ANN) model is trained with real-time measurements to identify the states whether there is a fault on the line segment. Fault location is estimated further with the same measurements in another neural network model. Reconfigurations can be performed to modify the settings of the on-field relays to enhance the reliable operation for the different operational situations. The test results show that the adaptive overcurrent protection scheme with the assistance of estimation model can modify the protective settings for the new operation state accurately and intelligently.

This paper presents a linear active disturbance rejection control (LADRC) for grid-connected converter with LCL filter. The high rejection performance for external disturbance, internal decoupling, parameter variation is achieved by adopting extended state observer(ESO) and designing controller with direct pole placement. Robustness of parameter uncertainty and sensitivity of input disturbance are analyzed in frequency domain to demonstrate the superior characteristic in disturbance rejection. The theoretical analysis is verified in Matlab/Simulink. The simulation results show the excellent capability of rejection in grid voltage disturbance.

With penetration of plug-in electrical vehicles (PEV), fast charging stations (FCS) are expected to constitute be a considerable portion of total energy consumptions. This paper proposes a hybrid power coordinating control strategy implemented in a fast charging station equipped with flywheel energy storage system, in order to provide a comfortable charging circumstance for PEV as well as some ancillary services (active power and reactive power support) for grid by four-quadrate bidirectional operation. The distributed bus signaling (DBS) method is employed for coordinating the control between grid converter and flywheel converter to avoid the highly dependent on communication. Finally, the experimental results based on dSPACE1006 are presented to show the effectiveness of the proposed control structure.

In this paper, a novel control method was proposed for current source inverters under the grid-connected working mode. The control scheme is based on a modified droop control method, with an additional current reference signal that will be generated instead of the voltage reference. Hence, there is only a current control loop with droop control in the whole control scheme without voltage control loop. So it is very suitable for grid-connected current source inverter which will simplify the design of the control scheme and combine the advantage of droop control. The parallel configuration is widely used to acquire high power demand, but the circulating current problem is a key issue that should be considered. In this paper, a simulation based on parallel current source inverters using the proposed control scheme is provided. Simulation results showed that a good circulating current suppression capability of the proposed control scheme is obtained with a proper controller design.

The possibility of increasing penetration level of grid-interactive microgrids (MGs) has gained a great interest over the past decade. Thus, it is critical to investigate the performance of the MGs under voltage sags, since it may induce instability to the power grid. Negative sequence droop control based voltage support strategy has been proposed to aid MGs riding through three phase asymmetrical voltage sags. However, since the line impedance from each converter to the point of common coupling (PCC) is not identical, both positive sequence and negative sequence output current of the converters cannot be equally shared if no extra current balancing loop is added. Accordingly, a dynamic consensus algorithm (DCA) based negative/positive sequence current sharing scheme is proposed in this paper. Finally, a lab-scale AC microgrid was designed and tested in the lab to validate the feasibility of the proposed control method.

Synchronization techniques can be broadly classified into two major categories-closed-loop and open-loop methods. The open-loop synchronization (OLS) techniques, contrary to the closed-loop ones, are unconditionally stable and benefit from a fast dynamic response. Their performance, however, tends to worsen in the presence of frequency drifts. To deal with this problem, two approaches are often recommended in the literature-adapting OLS techniques to the grid frequency variations by feeding back the frequency estimated by them or using the frequency estimated by a secondary frequency detector in a parallel manner. In the presence of the frequency feedback loop, nevertheless, the OLS technique may not be truly open-loop, which makes a deep stability analysis necessary. Using the secondary frequency detector, on the other hand, increases the computational effort and implementation complexity. Another drawback of most of the available OLS techniques is that their implementation involves the computation of sine and cosine functions, which is undesirable from the computational standpoint, particularly when the implementation with low-cost digital signal processors is intended. The aim of this paper is to develop a true OLS (and therefore, unconditionally stable) technique without any need for the calculation of sine and cosine functions. The effectiveness of the proposed synchronization technique is confirmed through the simulation and experimental results.

In this paper, an intelligent energy management system based on energy saving and user's comfort is introduced and applied to a residential smart home as a case study. The proposed multi-objective mixed-integer nonlinear programming (MINLP)-based architecture takes the advantages of several key modeling aspects such as load shifting capability and domestic energy micro-generation characteristics. To demonstrate the efficiency and robustness of the proposed model, several computer simulations are carried out under different operating scenarios with real data and different system constraints. Moreover, the superior performance of the proposed energy management system is shown in comparison with the conventional models. The numerical results also indicate that through wise management of demand and generation sides, there is a possibility to reduce domestic energy use and improve the user's satisfaction degree.

In future, distributed energy resources (RESs) will be utilized at consumption points. As a consequence, power flow and fault current would be bidirectional and topology-dependent; and hence the conventional protection strategies would be inefficient. This paper categorizes the main challenges in AC and DC microgrids, and then investigates the existing and promising solutions for the corresponding challenges. To the authors' knowledge, three parts of smart grids are required to be developed to facilitate implementation of protection scheme in microgrids. The main requirements and open issues of these three parts are discussed at the end of this paper.

This paper presents a centralized strategy for equalizing the state of charge of distributed energy storage systems in an islanded ac microgrid. The strategy is based on a simple algorithm denoted as equalization algorithm, which modifies the charge or discharge ratio on the time, for distributed energy storage systems, within a determined period of time in order to equalize the state of charge. The proposed approach has been tested in a MATLAB/Simulink model of the microgrid where the performance of the proposed strategy was verified.

In this paper, an optimal power flow problem is formulated in order to minimize the total operation cost by considering real-time pricing in DC microgrids. Each generation resource in the system, including the utility grid, is modeled in terms of operation cost, which combines the cost-efficiency of the system with the demand response requirements of the utility. By considering the primary (local) control of the grid-forming converters of a microgrid, optimal parameters can be directly applied to the control of this level, thus achieving higher control accuracy and faster response. The optimization problem is solved in a heuristic way by using genetic algorithms. In order to test the proposed algorithm, a six-bus droop-controlled DC microgrid is used as a case-study. The obtained simulation results show that under variable renewable generation, load, and electricity prices, the proposed method can successfully dispatch the resources in the microgrid with lower total operation costs.

In this paper, a multiagent based distributed control is proposed for DC microgrid to minimize the operation cost. The power of each distributed generator (DG) is dispatched in a distributed manner in a multiagent system by means of voltage scheduling. Every DG unit is taken as an agent, and they share the load corresponding to the operation cost of all the units in the system with only communication with direct neighbors through incremental cost consensus. The power regulation according to the power reference generated by consensus is implemented through voltage scheduling in local primary controllers. Simulation verification shows that total operation cost of the DC microgrid is successfully reduced though the proposed method.

Due to the increasing penetration of distributed generation resources, more and more microgrids can be found in distribution systems. This paper proposes a phasor measurement unit based distance protection strategy for microgrids in distribution system. At the same time, transfer tripping scheme is adopted to accelerate the tripping speed of the relays on the weak lines. The protection methodology is tested on a mid-voltage microgrid network in Aalborg, Denmark. The results show that the adaptive distance protection methodology has good selectivity and sensitivity. What is more, this system also has a good capability on monitoring and control of the network.

Owing to the increasing penetration of distributed generation, there are some challenges for the conventional protection in distribution system. Bidirectional power flow and variable fault current because of the various operation modes may lead to the selectivity and sensitivity of the overcurrent protection decreased. This paper adopts distance protection for one mid-voltage level microgrid in Aalborg, Denmark. Different operation modes of the network are analyzed and tested in the paper. The simulation results show that the variations of the fault currents seen by the forward relays are much larger than the backward relays. Meanwhile, the fault currents change little with the randomness of renewable energy except the intermittence. Finally, it shows that the designed distance protection has satisfactory performance to clear the various faults.

Smart meters are the cornerstone in the new conception of the electrical network or Smart Grid (SG), providing detailed information about users' energy consumption and allowing the suppliers to remotely collect data for billing. Nevertheless, their features are not only useful for the energy suppliers, but they can also play a big role in the control of the Microgrid since the recorded power and energy profiles can be integrated in energy management systems (EMS). In addition, basic power quality (PQ) disturbances can be detected and reported by some advanced metering systems. Thus, this paper will expose an example of Smart Meters integration in a Microgrid scenario, which is the Intelligent Microgrid Lab of Aalborg Univeristy (AAU). To do this, first the installation available in the Microgrid Lab will be introduced. Then, three different test scenarios and their respective results will be presented, regarding the capabilities of this system and the advantages of integrating the Smart Meters information in the Microgrid control.

With the increasing penetration of renewable energy, microgrids (MGs) have gained a great attention over the past decade. However, a sudden cut out of the MGs due to grid fault may lead to adverse effects to the grid. As a consequence, reactive power injection provided by MGs is preferred since it can make the MG a contributor in smooth ride through the faults. In this paper, a reactive power support strategy using droop controlled converters is proposed to aid MG riding through three phase symmetrical voltage sags. In such a case, the MGs should inject reactive power to the grid to boost the voltage in all phases at AC common bus. However, since the line admittances from each converter to point of common coupling (PCC) are not identical, the injected reactive power may not be equally shared. In order to achieve low voltage ride through (LVRT) capability along with a good power sharing accuracy, a hierarchical control strategy is proposed in this paper. Droop control and virtual impedance is applied in primary control loop while secondary control loop is based on dynamic consensus algorithm (DCA). Experiments are conducted to verify the effectiveness of the proposed control strategy.

This document analyses the large-signal stability for an inverter-based generator such as photovoltaic and wind power sources. The objective of this study is to determine the stability region taking into account the electrical and control signal of the generator. The generator uses the concept of the electrostatic machine for the model of the generator. Finally, the applied procedure to find the Lyapunov's function is the Popov method, which not only permits to generate a valid function but also to determine the stability region of the system.

In this paper, a distributed multiagent based algorithm is proposed to achieve SoC balance for DES in the DC microgrid by means of voltage scheduling. Reference voltage given is adjusted instead of droop gain. Dynamic average consensus algorithm is explored in each agent to get the required information for scheduling voltage autonomously. State-space analysis on a single energy storage unit and simulation verification shows that the proposed method has two advantages. Firstly, modifying the reference voltage given has less impact on system stability compared to gain scheduling. Secondly, by adopting multiagent methodology, the proposed distributed control has less communication dependence and more reliable during communication topology changes.

This paper presents consensus-based distributed control strategies for voltage regulation and power flow control of dc microgrid (MG) clusters. In the proposed strategy, primary level of control is used to regulate the common bus voltage inside each MG locally. An SOC-based adaptive droop method is introduced for this level which determines droop coefficient automatically, thus equalizing SOC of batteries inside each MG. In the secondary level, a distributed consensus based voltage control strategy is proposed to eliminate the average voltage deviation while guaranteeing proper regulation of power flow among the MGs. Using the consensus protocol, the global information can be accurately shared in a distributed way. This allows the power flow control to be achieved at the same time as it can be accomplished only at the cost of having the voltage differences inside the system. Similarly, a consensus-based cooperative algorithm is employed at this stage to define appropriate reference for power flow between MGs according to their local SOCs. The effectiveness of proposed control scheme is verified through detailed hardware-in-the-loop (HIL) simulations.

Paralleled dc converter systems are widely used in distribution systems and uninterruptable power supplies. This paper implements a hierarchical control in a droop-controlled dc-dc conversion system with special focus on improving system efficiency which is dealt within the tertiary regulation. As the efficiency of each converter changes with output power, virtual resistances (VRs) are set as decision variables for adjusting power sharing proportion among converters. It is noteworthy that apart from restoring the voltage deviation, secondary control plays an important role to stabilize dc bus voltage when implementing tertiary regulation. Moreover, system dynamic is affected when shifting VRs. Therefore, the stability is considered in optimization by constraining the eigenvalues arising from dynamic state space model of the system. Genetic algorithm is used in searching for global efficiency optimum while keeping stable operation. Simulation results are shown to demonstrate the effectiveness of the method.

In this paper, a distributed coordinated control scheme based on frequency-bus-signaling (FBS) method for a low-voltage AC three phase microgrid is proposed. The control scheme is composed by two levels. Firstly a primary local control which is different for the DGs and the ESS is proposed. The ESS adopts FBS control which is based on changing slightly the bus frequency in the microgrid when the state-of-charge is near to the limit. This way, the DG controller when detecting that the frequency is increasing, will reduce the injected power by using a virtual inertia control loop. Then secondary control is implemented to restore the frequency deviation produced by the primary ESS controller while preserving the coordinated control performance. Real-time simulation results show the feasibility of the proposed approach by showing the operation of the microgrid in different scenarios.

This paper presents a novel approach to conceive the secondary control in droop-controlled MicroGrids. The conventional approach is based on restoring the frequency and amplitude deviations produced by the local droop controllers by using a MicroGrid Central Controller. A distributed networked control system is used in order to implement a distributed secondary control thus avoiding the use of a MicroGrid Central Control. The proposed approach is not only able to restore frequency and voltage of the MicroGrid but also ensures reactive power sharing. The distributed secondary control do not relies on a central control, so that the failure of a single unit will not produce the fail down of the whole system. Experimental results are presented to show the feasibility of the distributed control. The time latency limits of the communication systems are studied as well.