Hybrid Distribution Transformers (HDTs) have been proposed as an alternative to conventional distribution transformers and Solid-State Transformers (SSTs), combining in a single solution a conventional Low-Frequency Transformer (LFT) with one or more power converter stages. Nonetheless, some HDT configurations exhibit a Circulating Active Power Flow (CAPF) while compensating for grid voltage disturbances. The CAPF increases the amount of power processed by the power converters, leading to reduced efficiency. The CAPF can be eliminated if the energy required to compensate for grid voltage disturbances is supplied by a DC source, such as a Battery Energy Storage System (BESS). Another alternative is to connect the DC stage of the HDT to a DC microgrid. In the context of a hybrid microgrid, the HDT can operate as an interlinking converter between both grids. The parallel-connected converter can manage energy flow between the AC and DC microgrids, while the series-connected converter can supply precise voltage regulation to the low-voltage AC grid. This work presents the model and control of an Interlinking Hybrid Distribution Transformer (IHDT) for a hybrid microgrid. A simple adaptive gain is employed to account for the distribution of the CAPF.

This paper presents a comparative study of modulation strategies for a full-bridge based unidirectional step-down partial power converter (PPC), focusing on a newly proposed Buck Modulation (BM) scheme. Unlike traditional Phase-Shift Modulation (PSM), BM disables transformer utilization by applying identical PWM signals to all switches in the converter’s full-bridge, effectively converting the topology into an equivalent buck converter. Thermal simulations were conducted to evaluate efficiency performance across different transformer turns ratios and load conditions. Results demonstrate that BM achieves superior efficiency at light loads when the transformer ratio is below unity, and consistently outperforms PSM across the entire power range when the ratio exceeds unity. Furthermore, BM offers a wider and more flexible operating voltage range.

This paper presents a Minimum Stress Factor Tracking (MSFT) algorithm designed for a T-Type Dual Active Bridge (DAB) DC-DC converter, aimed at electric vehicle (EV) charging applications. The proposed system dynamically selects among six different modulation configurations by evaluating a weighted combination of three normalized stress factors: Semiconductor Component Stress Factor (SCSF), Capacitor Component Stress Factor (CCSF), and Transformer Winding Component Stress Factor (WCSF). Each stress factor is mathematically modeled across the full operating range, allowing real-time optimization without dependency on runtime simulations. The weighting factors are user-defined and sum to unity, offering flexibility to adapt the stress minimization strategy according to specific reliability requirements. The results demonstrate that the proposed approach achieves significant stress reduction on critical components while maintaining full controllability and capacitor voltage balance. This methodology addresses a seldom-explored aspect in the current literature, opening a new path for reliability-oriented optimization in T-Type DAB converters for EV charging systems.

The high-voltage pulse generator is a crucial component for performing the electroporation process required in water treatment. This paper presents a three-state modulation for high-voltage pulse generator based on a modular converter structure. The converter consists of modular submodules connected in series, each comprising a half-bridge, a capacitor, and interconnecting diodes and inductors for series/parallel operation. The system eliminates the need for high-voltage switches and ensures a rapid dynamic response during the discharge process due to the absence of arm inductance. The proposal modulation allows to control the charging current, which is dependent on interconnecting inductors and switching frequency. The modulation technique is proposed, analyzed, and validated through simulation results.

This paper introduces a high-voltage pulse generator for water treatment, employing a multilevel modular converter structure. The pulse generator features completely modular submodules connected in series, each comprising a half-bridge, a capacitor, and interconnecting diodes for serial/parallel operation. It does not require high voltage switches and ensures a rapid dynamic response in output voltage because there is no arm inductance. The proposed converter provides flexibility, allowing configurable amplitudes and duration of the high voltage pulse. The power converter topology and a modulation technique are proposed, analyzed, and validated by simulation results.

This paper presents a simulation of a Maximum Power Point Tracking method applied to a point absorber Wave Energy Converter using a linear generator with three independent coils. Each of the three coils of the linear generator is individually connected to a submodule of the DC Modular Multilevel Converter. These submodules feature two stages with a capacitor DC-link between them. The first stage measures the current and voltage from each submodule. It applies the proposed MPPT method to calculate the reference current, which is then controlled with a PI controller to maximize the energy harvested. The second stage measures the output current and the voltage of each capacitor, applying a cascade control involving two loops. An outer loop controls the capacitor voltage using a reference current, while an inner loop employs a PI controller to regulate the output current. This MMC-DC topology is implemented in a simulation to maximize energy transfer.

Hybrid Distribution Transformers (HDTs) are a promising solution to power quality problems on distribution networks, allowing for precise voltage and current regulation. HDTs that connect the series converter on the primary side are subject to a Circulating Active Power Flow (CAPF) between the Low-Frequency Transformer (LFT) and the power converters that appear when compensating for voltage disturbances. This paper analyzes the cause of the CAPF and its behavior, considering varying grid conditions and the impact of the CAPF on the DC-Link ripple.

Power systems are experiencing a rapid and dramatic transformation driven by the massive integration of nondispatchable renewable energy sources, such as wind and solar, and highly variable loads, such as electric vehicles and air conditioning. This challenges existing grid assets, eventually leading to updating them, which, in turn, increases significantly the costs of sustainable technologies. Power electronics is a pivotal technology for electrical power processing for renewable energies and sustainable transportation. By means of “smart” functionalities, power electronics converters already embedded in such applications can also contribute to guaranteeing the overall system’s stable operation. Anyway, this cooperative contribution from distributed devices may be not enough leading to the need for the voltage transformation and power transmission of “system-level” power electronics solutions. In the case of large charging stations, a smart transformer (ST), while, in the case of large solar and wind parks, integration medium- or high-voltage direct current (HVdc) transmissions are system-level solutions. This article wants to review the potential of using such infrastructures to increase the capacity of existing grid assets, avoiding or deferring their upgrade and, hence, reducing the overall costs of renewables integration and the electrification of the transport sector. In fact, the power converters embedded in ST and HVdc can provide fast frequency and voltage response, and precise control of power flow acting at the system level much more effectively and feasibly for system operators as the distributed power converters embedded in several small sources and users. This article reviews, for the first time, these two key power electronics “system-level” solutions together—ST and HVdc—starting from their basic functionalities and showings how they can go beyond them, showing how, with grid-forming functionalities, they can offer new “smart grid” tools to enhance the capability of the existing electric grid infrastructures.

The wireless power transfer technology for electric vehicles charging has been largely improved during the last years in terms of system configurations, coil design, and control schemes with the aim to achieve higher power, higher efficiency, and longer transmission distance. The compensation stage is usually designed considering sinusoidal voltages and currents. However, the full-bridge converters used to generate the controlled voltage generate a square waveform, requiring design adjustments, reducing the efficiency of the compensation, and impacting the control performance. In this paper, a design guideline for the compensation stage and the evaluation of the performance of the wireless power sources system using power converters instead of sinusoidal sources is given.

The performance of model predictive control of power electronics converters depends upon an accurate discrete-time model to properly evaluate the effect of the control action over the controlled variables. One of the most used methods to obtain a discrete-time model from the continuous-time equations is to use an Euler approximation of the derivative. However, when sampling times are increased, an Euler discretized model may incur in error in the variables. This work presents an alternative discretization method based on the input-state linearization concept of nonlinear control. An auxiliary linear model is obtained which is then discretized by an exact linear approach. The method is illustrated using the dc-dc boost type converter as a case study showing improved results a compared with the Euler approximation.

Solid state transformers based on modular structures have become a suitable alternative to provide high voltage rating, reliability, and fault tolerance at the distribution level. Among them, the SST based on Modular Multilevel Converter with an input-series output-parallel interconnected by Dual Active Bridges configuration appears as a good solution to reach high voltage levels at the input and large currents at the output stage. However, the parallelization of SM generates cross-circulating currents among modules. In this paper, the cross-circulating currents are controlled and mitigated by a decoupled linear control. Simulation results shown the cross-circulating currents and their dependency under mismatches in both inductance and resistances.

Hybrid transformers are an attractive solution for improving power quality problems in distribution grids, due to the capability of power converters to provide precise current and voltage regulation. A hybrid transformer using a low-frequency transformer, which processes the biggest amount of power, and two converters connected in series and shunt, with an additional cascaded H-bridge converter connected in parallel, is presented. The use of a series converter on the primary side and a shunt converter on the secondary side allows to provide voltage regulation and load current compensation, respectively. Both converters improve the transformer power quality, extending its lifetime. Meanwhile, the cascaded H-bridge converter establishes a common DC-Link to support both converters operation. In this work, the model, control, and simulation results of the proposed configuration are presented, showing the improvement on the distribution transformer.

Future distribution grids will require to integrate renewable energies in higher penetration levels than we are used to today in conventional power systems. To make this possible, key aspects of their operation such as reliability and robustness must been in safe levels. To accomplish the latter, two different technologies have been proposed: (a) Virtual Synchronous Machines and (b) Smart Transformers. Despite all the benefits that each one of these technologies provide, solid-state transformers have not been very successful in operating as smart transformers. Then, hybrid transformers were proposed as a more feasible solution and with the capability of providing ancillary services to the distribution grid. In this paper, a new type of hybrid transformer that incorporate features of a virtual synchronous machine is proposed. The proposed transformer is capable of emulating virtual inertia as an ancillary service, and, at the same time, providing other basic services such as reactive power injection and voltage compensation. Simulation results provide evidence of the advantages of using this type of hybrid transformers in distribution grids.

Power quality has become a concern nowadays, due to the increasing and highly variable renewable energy systems connected to the distribution network and also due to the nonlinear loads that pollute the grid. A solution to this problem is the use of compensators to attenuate these disturbances. The use of a hybrid transformer composed by a conventional low-frequency transformer in conjunction with a power converter has become an interesting solution due to the high controllability and overall efficiency. In this paper, the model, control, and simulation of a hybrid transformer, where the converter is connected in series with the primary side and in parallel to the secondary side, is presented. Results show the correct operation of the converter in steady and transient state, successfully compensating grid voltage variations and load non-linear currents.

In this paper, a virtual synchronous generation (VSG) strategy is proposed for a three-phase quasi-impedance source inverter (qZSI). The main objective of the scheme is to provide inertia and damping to the inverter operation in order to add those characteristics to the system in the form of ancillary services, thus contributing a more stable operation of the microgrid where the inverter is operating. The generated references are received by linear control loops on the dc and ac sides of the three-phase qZSI. In the development of this work, the theoretical foundations of the proposal are shown. Also, to prove that the strategy helps to improve the response of the system, simulated results of the qZSI connected to a weak grid are displayed, showing data of the inverter operating in a traditional form (without inertia) and as a VSG, to make comparisons.

Increasing the amount of energy extracted from a large-scale photovoltaic (PV) plant directly impacts its profitability. Obtaining higher energy yields depends heavily on the efficiency of the power conversion stages, but also on the configuration of the PV plant. More distributed maximum power point tracking (MPPT) among PV modules, allows maximizing the amount of energy extracted, especially under non-uniform conditions. To deal with partial shading conditions at module level, a sub-module power optimizer based on partial power converters is proposed. The configuration employs an isolated partial DC-DC power converters allowing to decouple the shaded parts from the unshaded at PV module level, maximizing the energy extracted. The behavior of the proposed configuration is verified through simulation, which is compared with a classic string configuration through analysis based on performance, improvements, and drawbacks of the proposed structure under mismatching scenarios.

Inductors with soft saturation cores built on compressed iron powder have higher saturation flux densities in comparison to ferrite gapped inductors, exhibiting a gradual drop of permeability for increasing magnetic field strength. This behavior yields to a gradual drop of differential inductance for increasing current, which avoids sudden core saturation and overcurrent produced in hard saturation cores as the inductance plummets when the maximum flux density is reached. However, the inductance in soft saturation cores starts dropping in the wide range of nominal current operation, increasing the complexity of the converter model and the control scheme. In this work, an interleaved dc-dc converter for supercapacitor management is modeled in continuous and discontinuous conduction mode, considering an inductor core with a linear drop in the differential inductance. A suitable current control strategy is proposed. Analysis of the model is given and simulated results that confirm the performance of the proposed control strategy are shown.

Finite Control Set Model Predictive Control is an emerging alternative for the control of power converters. Its main advantages are its conceptual simplicity, fast control response, flexibility and direct consideration of non linearities as well as constraints. Due to computational constraints, short prediction horizons are usually desired in power converters. However, control issues may appear when applied in topologies that exhibit non-minimum phase behavior such as active front end rectifiers and boost dc-dc converters. This work proposes the use of the concept of statically equivalent outputs in order to control these systems with the shortest prediction horizon. The proposed predictive controller partially inverts the plant dynamics, determining an auxiliary output by means of nonlinear control tools. Theoretical and simulated results show the feasibility of the proposal.

This paper proposes a tubular permanent magnet linear generator (TPMLG) for a wave energy converter. The proposed TPMLG is built with an array of permanent magnets and independent coils. Advantages and disadvantages of the proposed device are determined with experimental and simulated results. A lumped parameter method is applied to analyze the amplitude of induced voltage and magnetic field mathematically. A finite element analysis is employed in the simulation software to obtain the dynamical behavior of these variables. The translator is tested at three different speeds. A prototype is built to confirm the theoretical analysis and simulations. Simulation and experimental results confirm the mathematical relationship between speed and the induced voltage.

Multilevel power converters are very attractive for medium- and high-voltage applications because they present some advantages compared with the traditional two-level converters. In this way, the multilevel technology is backed by the industry and academia support. Among multilevel converters, the modular multilevel converter (MMC) is very popular because it is well-suited for the high-voltage dc (HVDC) power transmission systems as well as it permits the connection of different nature ac grids. To operate the MMC power converter is required a proper modulation strategy. It can be based on carrier-less or pulse-width modulation (PWM) strategies. In order to determine the optimum modulation technique, several simulations have been performed in order to extract some conclusions related with the power losses and the power converter behavior.

Induction machines with double-star stator winding configuration, has extend the redundancy capability of the FEP based ship propulsion systems. However, under winding faulty conditions, the presence of negative sequence torque components introduce torque pulsations which are responsible for the torsional vibration stress. The classical Field Oriented Control (FOC) scheme approach, has a PI controller performance, because of the oscillating components, due to the development of negative sequence current components. On this matter, several approaches have been proposed, based on an alternative rotation matrix, which is dependant on the nature of the fault. In order to deal with this uncertainty, the present work presents a new approach, with the implementation of sliding current controllers in the synchronous reference frame.

Microgrids have become an alternative to increase the controlability and resilience of the electrical system due to the local and efficient energy management they provide. Additionally, when the microgrid has a main DC bus it does not require synchronization hence the control scheme is simplified allowing to improve the dynamics of currents and voltages. These DC microgrids are usually controlled using a three-level hierarchical scheme associated to different elements in the microgrid in which the third control level optimizes the operation of the whole microgrid in term of costs and efficiency. In this paper a tertiary control level is proposed for a DC microgrid which optimizes its operation in terms of costs but at the same time takes into account restrictions of the grid connection and battery state of charge. Simulation results with realistic operating conditions show a good performance in terms of dynamic response and steady state operation while an optimize economic operation is achieved.

Tow-stage configurations used in photovoltaic (PV) architectures (microinverter, string inverter or multistring inverter), are commonly used because of the advantages in front of mismatch conditions. In case of a partial shading scenario (produced by cloudy days and dust accumulation), two-stage architectures reach higher efficiencies compared with the traditional central inverter. It is because, the DC-stage allows a wide voltage range in order to perform maximum power point tracking (MPPT). On the other hand, the additional stage increase the component counts and the conversion losses, which leads to a reduced efficiency compared with the single-stage inverters. This work presents a solution for the traditional two-stage configurations, where the partial power conversion (PPC) concept is implemented in the DC-stage. In that way, the DC-DC converter handles a reduced power allowing a volume reduce and increased power density. Moreover, the AC-stage is made using a cascaded H-bridge topology, which improves the power quality and reduces the components size. Simulations are implemented in order to validate the proposed work.

Commercial photovoltaic microinverter topologies are normally composed of two stages: a step-up dc-dc stage and a step-down dc-ac stage. Nevertheless, to achieve high-ratio conversion, a high frequency transformer is used in the dc-dc stage, resulting in a bulky configuration with a high cost of implementation. To minimize these issues, a single stage boost inverter is proposed, composed by two bidirectional boost dc-dc converter. The control of this topology is complex due to its high non-linearity behaviour. Therefore, this paper presents a control methodology based on Finite Control Set Model Predictive Control (FCS-MP) algorithm with predictions of the system variables through the inverter model and an optimization process. Each boost dc-dc converter of the inverter is regulated to achieve an output signal composed of the sinusoidal wave with a dc bias. The main features of the boost inverter and predictive control are analysed. Simulations are shown in order to validate the proposed control and the converter for grid-connected PV applications.

In order to increase the conversion efficiency in photovoltaic (PV) systems, different configurations and topologies were developed. Depending on the application, the converters used for grid connection are built using one or two conversion stages. The advantages of the converters with a DC-stage are mainly the distributed maximum power point tracking algorithm per PV string or PV module and, when required for grid connection, the possibility of voltage elevation. However, the conversion efficiency is lower than configurations with a single-stage as the central inverter. Therefore, the proposed work presents a Partial Power DC-DC converter (PPC) which process part of the entire system power, and the remaining power is directly supplied to the output side. A topology is proposed and the details of its operation are explained based on the operating principle. Simulations are performed in order to evaluate the converter performance.

Solar photovoltaic (PV) energy has grown significantly during the last years. However, despite of the increase in installed capacity penetration, this energy source still arises important concerns due to the variability of power production. The short-term effects such as cloud shadowing and supply interruptions, as well as long-term effects such as dust accumulation, seasonal variation and ageing of PV modules can generate variability of power production. Therefore, the analysis of all the variability sources in order to provide a statistically consistent power production data represents an important challenge. This work presents a methodology to analyze data from a PV plant located in Chile by isolating the effect produced by soiling and, with this information a cost based cleaning program is proposed.

Current source converters (CSC) are used in AC-Drives and Electrochemical applications requiring large and controlled currents. Usually, a controller/modulating block using pulse width modulation is employed to provide current control. Although, several works describing predictive controllers have been presented for both two-level and multilevel voltage source converters. Only a few report predictive control in CSC This paper proposes a predictive control strategy for CSC. The performance of proposed controller is compared with linear PI controllers in terms of speed, harmonic distortion and switching frequency. It is shown that the proposed strategy is suitable for Modular CSC. Theoretical analysis and simulation results that validate the proposed controlled are shown.

Large-scale grid-connected photovoltaic (PV) energy conversion systems operate at low voltage and are interfaced to medium-voltage and high-voltage ac utility grids through one or two step-up voltage transformer stages. In addition, the power conversion is performed with either a single stage dc-ac converter (central inverter) or a two stage dc-dc/dc-ac (string or multi-string inverter). However, prime solar irradiation regions in the world are not always located close to available utility lines, and in some cases are far away from main consumption areas. Furthermore, long overhead transmissions lines (>400km) and underwater transmission lines above 70kM, HVDC has become the most cost-effective solution. Among HVDC technologies, voltage source converter based HVDC system, mainly based on the modular multilevel converter (MMC), have become popular due to smaller filters, multi-network connection and decoupling of active and reactive power. This paper explores a new large-scale PV plant configuration based on a dc-dc stage interfaced directly to an MMC based HVDC system. Since PV systems are dc by nature, the proposed solution has several advantages, particularly if combined directly with the HVDC power station. Some power circuit topologies are presented, including their corresponding control schemes. Simulation results are presented to provide a preliminary evaluation on the operation and performance of the proposed system.

This paper proposes a Machine Drive based on a Modular Multilevel Converter. The proposed converter uses current source cells with asymmetrical IGCTs as switching devices. A control scheme to manage the input and output current and, additionally, reduce the oscillations in the inductors currents is also proposed. The resulting machine drive will exhibit high power and high dynamical performance as shown in the simulation results.

Modular multilevel converter features high power quality and has high availability due to its inherent modularity. Those characteristics make this converter well suited for high voltage DC transmission applications. In this paper, a new application of modular multilevel converter in solar photovoltaic plants is proposed. The proposed structure can use higher voltages than standard photovoltaic plants, hence reducing internal losses. Additionally, an storage element can be integrated with the converter in order to perform peak shaving. The proposed topology and control strategy are shown and simulation results confirm their performance.

Direct matrix converter (DMC) is an AC-to-AC direct power conversion topology based on controlled bi-directional switches that can generate variable output voltages and sinusoidal source currents with variable power factor. Cascaded Matrix Converter (CMC) is a multilevel converter which combines the main characteristics of multi-cell power topologies and direct power conversion. The basic module is based on 3×2 direct matrix converter cell. This converter is fully regenerative, with multilevel output voltage and sinusoidal source current. In this work a reactive power control using a phase-shifted PWM scheme is presented. The modulation scheme can be developed using a simple digital logic and the results from open and closed loop tests are presented to evaluate the performance of proposed modulation.

This paper presents a new small-scale single-phase photovoltaic (PV) energy conversion system. The topology is based on the series connection of two three-level T-type converters, which form a 5-level converter with two independent maximum power point tracking (MPPT) string connections. The topology merges benefits of string and multi-string PV configurations. The operating principle, the switching states, modulation scheme and control method are addressed in the paper. Simulation results are presented under dynamic conditions and different operating points for the two PV strings, to provide a preliminary validation of the topology and its performance.

Large-scale photovoltaic energy conversion systems (LS-PECS) are currently well into the megawatt range. Therefore multilevel converters have been proposed as an attractive solution due to medium voltage operation, higher efficiency, power quality, and possibility to connect PV strings separately to each dc-link. However, the latter advantage makes the inverter susceptible to severe voltage unbalances due to the inherent power unbalance produced by the individual maximum power point tracking (MPPT) of the PV strings. This is particularly the case of the cascaded H-bridge inverter (CHB) where power cell and phase unbalances occur. In this work a new single dc-bus collector bus bar CHB is proposed for a multistring LS-PECS configuration. The operation with a single dc-bus is enabled by adding an isolation dc-dc converter stage to each power cell of the CHB. This allows inherent balanced operation of the CHB while fully decoupling the multistring PV-system from the grid tie inverter. This also greatly extends the operating range of the system compared to previous solutions. Simulation results for a 3.3kV 7-level CHB tested under dynamic conditions are presented and serve as a preliminary validation of the configuration and control schemes.

Modular multilevel cascaded converter offers several advantages for high voltage DC transmission systems such as high modularity and power quality. However, they also present an interesting challenge from the control point of view, due to its coupled current dynamics and the voltage balance of floating capacitors. This work presents a voltage balance scheme which does not affect the input nor the output voltages and currents, and its dynamics is independent on the power operating point. Simulations results show a good dynamic of the voltage balance under changes in the DC voltage reference and reversion on the power flow.

Modular multilevel cascaded converter emerges as an important alternative in high voltage DC transmission systems, due to its high reliability and power quality. This converter is composed by several identical cells whose are, in turn, composed by a chopper or an H-bridge and a floating DC capacitor. This paper proposes a modular multilevel converter with a novel cell topology based on a current source H-bridge. The use of this cell could improve the input and output power quality and, due to the IGCT current and voltage ratings, reduce the number of cells in series to achieve the required DC voltage and at the same time increase the transmitted power. Analysis and simulation of the proposed topology and its control are given.

Due to the increasing use of distributed and non-conventional power generation sources, grid synchronization and control of static power converters under variable grid frequency is of particular interest. This work develops a discrete-time phase locked loop (PLL) based on a rotating reference frame to be used in variable frequency systems. The PLL is used in combination with a time-varying transformation based on a rotating frame for control purposes. Finally, for a back-to-back static converter topology, linear and nonlinear control strategies are proposed and evaluated under frequency variations and different operating points. The results - including stability analysis - show their particular performance under frequency variations.

Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.