Bipolar dc microgrids have been increasingly adopted in different applications due to their versatility in scaling to higher power levels while maintaining the same safety requirements as lower voltage unipolar ones. On the other hand, power imbalance, commonly faced in bipolar systems, can lead to undesirable voltage deviations that may trigger protection devices, cause corrosion, and increase risks of electric shock. To address this issue, several voltage balancing solutions have been proposed, including self-balancing dc-dc converters, and others active balancers. Both approaches are different in terms of hardware implementation, efficiency, and complexity. In this paper, a two-switch buck/boost voltage balancer and a self-balanced current-fed dual active bridge (CF-DAB) converter are experimentally compared for applications in bipolar dc microgrids. Experimental results are presented using a 5-kW prototype. The results demonstrate that both solutions offer different opportunities for system optimization. However, the processed rms current analysis shows the self-balanced solution providing advantages in terms of efficiency, while the conventional buck/boost balancer offers a more cost-effective solution.

The isolated buck-boost current-fed (CF) series resonant converter with active clamping integrates low input current ripple, resonant soft-switching, and voltage spike suppression, thereby enhancing power conversion efficiency. While CF converters inherently operate in boost mode, achieving buck operation is crucial for applications that require a wide voltage gain range. To address this, various constant-frequency buck modulation methods have been proposed to regulate the step-down operation of CF-SRCs. This paper examines three buck control methods for an active-clamped CF series resonant converter: conventional Phase Shift Modulation (PSM), Hybrid Phase Shift Modulation (HPSM), and Single-Switch (1Sw) Buck Modulation. A comparative evaluation is conducted through theoretical analysis and experimental validation on a 350 W prototype, assessing efficiency, switching behavior, and voltage gain characteristics. The results confirm that 1Sw buck modulations achieve peak efficiencies while also highlighting key trade-offs in conduction losses and switching stress across the different modulation methods.

This paper presents a control strategy for Electric Vehicle (EV) battery charging that combines a soft-switched isolated dc-dc converter with a three-phase unfolding-based Power Factor Correction (PFC) topology and reduced number of inductors. The proposed system introduces a finite cycle-based model predictive control method, which regulates current by optimally allocating discrete switching cycles across multiple energy paths. For instance, operating at a 25 kHz sampling rate with 40 switching cycles per interval (enabling a 1 MHz switching frequency), the controller achieves 2.5% resolution in power delivery while maintaining sinusoidal grid currents and a high power factor. Unlike conventional designs that require three inductors and separate PFC stages, the proposed architecture uses only two inductors and shifts the PFC function to the high-frequency dc-dc stage, significantly enhancing power density and reducing system complexity. A soft-switching modulation strategy ensures that all GaN-based switches operate under zero voltage switching conditions at high switching frequencies (hundreds of kHz to several MHz), effectively minimizing switching losses. Simulation results show a total harmonic distortion below 3% and confirm the proposed system's ability to deliver high efficiency, compact design, and precise regulation across a wide output range making it well-suited for next-generation EV chargers.

Extensive use of electric vehicles (EVs) requires a wider availability of charging infrastructure. Together with the penetration of renewable sources, like PVs, and other dc-native technologies, this creates a demand for developments in the field of dc distribution grids. This paper presents the concept of a universal bidirectional dc-dc converter that can be used as an off-board charger for electric vehicles (EVs). Thanks to the reconfigurable input stage, it can be suited for various types of uni- and bi-polar dc grids. The possibility to operate in four different modes allows for the reduction of the stresses on the components while providing a wide output voltage range. The concept is verified with a simulation model of a 3.3 kW charger with an output voltage range of 150…1000 V.

Series-resonant converters (SRCs) have gained attention for many applications, including power supply units, data centers, and smart transformers, due to their high and very flat efficiency curve. However, ideally, SRCs operate without voltage regulation, as implementing phase shift or frequency control can penalize the converter efficiency. This presents a significant drawback for certain applications such as dc buildings, nanogrids, and dc microgrids, where such converters must operate under droop control, resulting in a variable output voltage. To address this limitation and enable SRCs to operate under variable output voltage, this paper proposes a bidirectional partial power converter as a post regulator stage (P3R). The proposed converter is based on a current-fed topology, featuring fully controlled switches to allow bidirectional power flow and the capability to step-up or down the output voltage. Experimental results, showcasing the converter waveforms for a 5-kW prototype, are presented to evaluate the converter's viability for this application.

Dual-active bridge (DAB) converters have gained significant attention in recent years, due to their high efficiency and excellent performance in medium and high-power applications. However, their performance is limited when a wide power and voltage range are required. One application example is the dc microgrid when DAB converters must operate with droop control to enable power balance and dc bus voltage regulation. When operating under droop control, the DAB converter efficiency can be penalized at low power, reducing the overall system efficiency. Being an open topic and not explained in current literature, this paper proposes for the first time to include the droop characteristic in the DAB converter analysis. The DAB converter efficiency is analyzed considering different factors, such as soft-switching conditions, circulating current, and dead-band insertion on droop control curves. Including the droop control as a new factor in the DAB converter design, a 5-kW prototype was built, and laboratory tested, evaluating different efficiency curves according to the selected droop curves.

Conventional full power dc-dc converters are processing the whole power flowing from the source to the load, which critically limits the overall efficiency of the system. Coming to the fact that the converter can perform the required functions by processing only the mandatory fraction of power, which is called power processing. In this paper, a Series Partial Power Converter (S-PPC). In order to get the full benefit of the S-PPC, the converter should process power less than 25% of the overall system power. Buck-Boost push-pull power converter is used in this paper with its modulation are proposed in this paper. The converter is modulated to ensure all switches are operating at soft-switching. Basic system analysis and system simulation are discussed in the paper

This paper compares the holdup time for different active-front end (AFE) dc grid-forming converters. AFE converters are required to perform an interface between the utility ac grid and dc microgrids in homes, offices, and other small-scale prosumer electrical installations (PEI). According to the current standards NPR 9090 and IEC 61000-4-11, AFE converters must provide isolation between ac and dc parts and ensure a minimum holdup time for the dc output side. Considering both requirements, two possible solutions are addressed and compared: a conventional dc-ac converter with a low-frequency isolation transformer and a two-stage ac-dc converter that includes a dc-dc stage with high-frequency isolation. To perform a comparative analysis of each solution, different scenarios are described and simulated in PSIM software.

This paper studies the transient behavior of a three-phase isolated bidirectional dc/ac converter operating as a rectifier. The purpose is to assess the viability of this converter for dc microgrid applications. A capacitor pre-charge method is developed to suppress inrush currents while charging the dc side capacitors during converter startup. The operation of the converter under grid fault transients is also studied, to assess the ability of the converter to maintain continuity of service to the dc microgrid in the case of grid undervoltage or loss of phase. A model of the converter was simulated on PSIM to validate the capacitor pre-charge method and grid fault responses.

A single-phase single-stage flying inductor based buck-boost inverter (S2FIB2I) is presented in this paper. Operation in buck, boost and buck-boost modes gives the proposed topology the ability to inject power into the grid at a wide range of input voltages. In other words, the proposed inverter has a dynamic voltage gain. The direct connection of the negative terminal of the input source with the neutral terminal of the power grid causes that in photovoltaic applications, the problem of injecting even harmonics into the grid is solved and the leakage current is completely eliminated. The absence of electrolytic capacitors in the proposed converter increases the life and reliability of the system. Also, the ability to operate at nonnity power factor allows the proposed inverter to control the reactive power at its output terminals. Theoretical analysis, design of passive elements and 1 kW simulation results are given to prove the accuracy of the proposed inverter performance.

This paper is presenting a new high-gain non-inverting buck-boost converter. The proposed converter has some distinct features such as high step up/down ability, low voltage and current stress on its switching devices. The voltage gain of the proposed converter is double of the traditional buck-boost converter and it is non-inverting. The three switches are operating synchronously. Although it has two inductors, the two inductors could be wounded on the same core due to similarity of the two inductors, and hence reduces the cost and size of the system. The overall efficiency of the system is promising due to the ability of selecting devices with low voltage drops. The steady state analysis of the system in both Continuous Conduction Mode (CCM) and discontinuous conduction mode (DCM) are presented in details. The system is simulated in MATLAB and results are discussed in detail through the paper. Experimental prototype is being build in the laboratory and hardware results will be presented in the final version.

Renewable energy sources like photovoltaic (PV) panels and battery energy storage are usually connected to the DC microgrids through dedicated full power DC/DC converters. Alternative to the conventional solutions is partial power converter (PPC) technology, where only a fraction of energy flow is handled by a DC/DC converter, and most of the energy flows from its source to a DC grid directly. PPC has several advantages over traditional full power converters: low power losses, lower cost, and higher power density. The proposed current-fed isolated full bridge buck-boost topology has shown excellent characteristics in PPC configuration, interfacing such nonlinear energy sources as PV panels. For experimental verification of PV partial power interface converter into a 350 V DC microgrid a 3.3 kW laboratory prototype with current-fed isolated full bridge buck-boost topology was designed, built, and tested. Experiments have proven the feasibility and benefits of PPC converter with proposed topology in DC microgrids.

In this paper, a new half-bridge inverter based on transformer-Z-network is proposed. The proposed Z-source inverter is suitable for applications which require dc/ac conversion with high voltage gain. The advantages of the proposed half-bridge inverter in comparison with classic half-bridge inverter are generating zero voltage level in the output and high boost factor at low value of the shoot-through duty cycle. In this paper, different operating modes of the proposed inverter are introduced and corresponding equations are derived. Logical diagram and waveforms of the switching pattern are presented. Moreover, design considerations for magnetizing inductors and capacitors are provided. Comparison of boost factor between the proposed and conventional inverters shows capability of the proposed inverter of generating high boost factor. To validate correct operation of the proposed half-bridge inverter, simulation results using PSCAD/EMTDC software and experimental results are provided.

Photovoltaic (PV) string converter for residential dc microgrids is presented. The concept of the converter is based on the interleaved buck-boost dc-dc converter with a wide input voltage range operation capability. The main control unit is a continuous control set model predictive control. The control system uses a simple droop control unit based on a proportional-integral regulator to ensure stability of the grid voltage. An experimental prototype based on a universal solar dc-dc/ac converter with the unfolding circuit was designed, featuring the MPPT voltage window from 150 V to 490 V and the nominal power of 3.6 kW. The efficiency benchmarking of a universal solar dc-dc/ac with connection to the dc microgrid is considered. Three real-world PV string profiles were considered during the experimental verification of the proposed approach. Based on the California Energy Commission (CEC) standard, the efficiency of the approach was well over 97 % in all selected case study scenarios.

This paper presents a detailed analysis of a series LC resonant isolated current source converter (SR-CSC) with the focus on a buck operation mode. Topologies of this type are generally proposed for PV, fuel cell, battery charging or DC microgrid applications. The switching processes on the example of the full-bridge topology are described and the corresponding mathematical equations derived. Further, the operational parameters of the converter, including switching frequency as well as transistor voltage and current stresses are estimated. The performed analysis is may be used to determine the component values for the optimal design of the DC-DC converter for a case study system. The obtained findings are verified with a simulation model of a 3.3 kVA SR-CSC.

This paper presents an improved modulation method for the cycloconverter stage of high frequency-link DC-AC inverters. By applying the quasi-resonant commutation mode during the entire operating period, the fast and reliable discharge of DC-side capacitances can be provided even if the output current is close to zero. This allows to ensure zero voltage switching (ZVS) conditions for the DC-side transistors, while applying small external snubber capacitors to reduce their turn-off losses. The proposed modulation strategy was significantly simplified and requires no external active auxiliary circuits or multi-mode operation. Moreover, two of the AC-side switches can operate at the fundamental frequency, while the rest operate with zero current switching (ZCS). The proposed modulation method is verified with mathematical analysis, simulation model and experimental prototype of full-bridge HF -link inverter.

Novel reconfigurable rectifier circuit is presented. It features three operating modes: full-bridge rectifier, voltage doubler rectifier, voltage quadrupler rectifier. After the rectifier topology is introduced, a case study dc-dc converter based on quasi-Z-source full-bridge topology is presented. An experimental prototype was assembled to verify concept feasibility. The assembled converter is suitable for the global maximum power point tracking owing to the wide input voltage range achieved. DC voltage gain theoretical expressions are verified experimentally, and measured efficiency is given.

An indirect model predictive control (iMPC) approach is proposed for regulating a grid current waveform provided by a single-phase inverter connected to a distorted grid. An algorithm implemented in the control system takes into account a significant computational delay. The distorted grid with the 5th harmonic is considered, which imposes additional restrictions on the iMPC and phase-locked loop utilization. Hardware setup involves a three-level neutral point clamped inverter and an inductive output filter. From a finite set of modulation index values, the iMPC current control selects one value for an external fixed switching frequency driver based on the LS-PWM strategy. Relevant cost function composition and modulation index regulation for improvements of transient and steady-state responses are discussed. Simulation and experimental verification is presented.

This paper describes a prototype of a solar inverter based on qZS network that is designed as a competitive solution to the available on the market commercial solutions. Passive and active components selection guidelines are analyzed. It is based on the target efficiency profile and theoretical losses model for active and passive components. Experimental results confirm theoretical predictions. The results and feasibility for commercial application of the proposed solution is discussed.

This paper presents a novel soft-switching technique for the galvanically isolated impedance-source full-bridge DC-DC converters. It allows reducing the turn off losses of the inverter switches, which otherwise represent a significant portion of the total power loss in such converters. Zero-current switching is achieved by the introduction of the additional energy return interval provided by the secondary side switches in addition to conventional synchronous rectification. This operation allows to redistribute the transformer current from one pair of switches to another, thus decreasing the current in the switch pair to be turned off. The paper presents the generalized operation principle corroborated with the simulation and experimental verification of the proposed modulation method.

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.

This paper presents a novel asymmetric bidirectional isolated DC-DC converter topology with current source and voltage source terminals. The topology can be implemented in renewable, supercapacitor, battery and de microgrid applications. It features two bidirectional and two reverse-conducting switches in the current-source bridge side. Thanks to special control algorithm it provides soft switching of all semiconductors under wide range of operating conditions with low energy circulation. This is achieved without any dedicated snubbers or clamp circuits. The converter theoretical performance at various operating conditions is assessed and compared with other competitive solutions in terms of rms current stress on the transformer and semiconductors. Steady-state operation and design aspects of the converter are presented and verified experimentally with 500 W prototype.

Focus is on the design of a multiphase galvanically isolated quasi-z-source dc-dc converter based on the single-switch topology. A novel control approach uses phase shedding for input-parallel-output-series architecture to achieve a wide input voltage regulation range. Current ripples are analyzed to implement the quasi-Z-source network with discrete and coupled inductors. Proposed approach provides for modeling of the latter taking into account leakage inductances of the coupled inductors and interactions between cells and the wiring inductance. An experimental prototype rated for 300 W, capable of delivering the rated power within the input voltage range of 10 V to 60 V was used. Experimental results demonstrate the performance of the developed concept implemented with resonant currents in the isolating transformer. Influence of the voltage-dependent resonant capacitance on the converter operation was analyzed.

In this paper buck-boost inverter based on unfolding circuit is discussed as novel solution for photovoltaic application. Simple control system is proposed and discussed for output voltage control in grid-off mode. Experimental results are presented for wide range of input voltage and power. The main advantage and potential problems are discussed in conclusions.

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.

This study proposes a simple digital control strategy for a single-phase interleaved quasi-z-source inverter (QZSI) with active-power decoupling (APD). Requirements for QZSI and APD passive elements are presented and discussed. The QZSI-APD with the applied control features low input current and power ripples. Firstly, it was achieved by an interleaved approach; as a result, high-frequency ripples are partly compensated. Secondly, APD with a multi-resonant controller allowed a decrease in low-frequency input ripple. Thus, the proposed topology and control reduced the QZSI capacitors significantly. In addition, as compared to a Z-source inverter, QZSI capacitor sizes could be significantly decreased due to lower voltage levels. The study assumed a 2 kW photovoltaic string inverter; our results proved that the interleaved QZSI-APD is a suitable solution for kW-scale photovoltaic systems.

This paper proposes a new modulation technique for an interleaved H-bridge qZS inverter that is intended for the single-phase photovoltaic systems. The potential benefits of this topology are reduced passive components and improved quality of energy generation. The modulation technique developed allows the maximum boost control for a better utilization of the dc-link. It is developed with the required phase-shifted carrier signals and wider shoot-through state generation than in simple boost control approach.

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.

This paper evaluates a modified single-switch galvanically isolated quasi-Z-source DC-DC converter intended as a topology for photovoltaic module-level power electronics applications. The operation principle of the converter is explained by the help of the steady-state analysis. To verify theoretical assumptions and evaluate the performance of the proposed concept, a 200 W experimental prototype of a photovoltaic microconverter was assembled and tested.

This paper discusses power losses in a current-fed DC/DC converter aimed for photovoltaic applications. Scenarios of the low voltage switch realization analyzed include a transistor with a series diode and two transistors in series. Both the high and the low voltage stage are designed with Si MOSFETs and GaN HEMTs to verify advantages of the new material in these applications. Semiconductor devices operate at soft-switching conditions, thus the study is focused on conduction and driving power losses. It appears from our calculations that GaN HEMTs show efficiency improvement of the soft-switching converter. Available GaN HEMTs belongs to the first generation of the commercially available devices. Future development of the GaN technology can greatly improve characteristics of the devices, which will result in superior performance over that of the Si.

This paper presents an evaluative comparison of Si- and SiC-based MOSFETs, operating in a qZS-derived step-up DC/DC converter. Special attention is paid to switching behaviour and power dissipation. A range of experiments was performed to determine an optimal di/dt value during transients to minimise overvoltages and dynamic losses. Additionally, some particular properties such as gate driver requirements, housing types and price are discussed.

Permanent magnet (PM) machines with tooth-coil windings are designed and analyzed. We study how the slot wedge material affects the behaviour of losses when using tooth-coil windings. The losses of an interior permanent magnet rotor are studied over a wide speed range. A finite element analysis applying Cedrat's Flux2D is made. Motors of this size can have high permanent magnet eddy current losses, and therefore, segmented magnets are often preferred even though interior magnets and semi-magnetic wedge materials are used. The study shows that tooth-coil windings may benefit from using a semi-magnetic material as a wedge material as it decreases the rotor iron losses and, especially, losses in the permanent magnets. The study shows also that wedges with relative permeabilities higher than 3 would not benefit this traction motor design, because of high losses and low maximum torque. Computations are compared to measurements of a 110 kW prototype traction motor.

This paper describes the operation of a grid-connected PV system based on a single-phase 3L-NPC qZSI using PSCAD as simulation tool for modelling the system: PV array, single-phase 3L-NPC qZSI, filter stage and electrical grid. The control system considers a maximum power point tracking algorithm, a phase loop locked for synchronization with the grid voltage, a control strategy to inject current in phase with the voltage at the point of common coupling and the modulation technique that also take into account shoot-through duty cycle. Simulation results are provided in order to show the viability of using this topology for PV energy systems connected to the electrical grid.

In this paper a low-power wind generation grid-connected system for domestic consumers with two control modes (Maximum Power Point Tracking (MPPT) and Power Control (PC)), will be presented. The MPPT mode will be active when the home's load is higher than the wind generator's maximum available power and the PC mode will be active when the home's load is lower than the wind generator's maximum available power. These two techniques will be adopted to both optimize the wind system performance and to prevent power injection into the electrical grid. Hence, the PC mode will be a particularly important part of this system. It will also be crucial to assure that the controller decides correctly on which control mode should be active, given the current grid supplying power.

Shoot-through control methods for qZSI-based dc/dc converters are presented and studied. The major goal was to increase efficiency. A new modulation technique, pulse width modulation (PWM) with shifted shoot-through, is compared with the conventional PWM shoot-through control method. The new method reduces switching frequency of bottom side transistors and inherently features partial soft switching. Previous studies have shown that the biggest drawback of PWM control with shoot-through is unequal switching frequencies of transistors. One solution to that problem could be signal swapping that has been proposed by the authors of this paper. All control methods are first simulated and then experimentally verified on a test prototype.

The half-bridge converter with a phase-shifted active rectifier bypasses the traditional hard-switched half-bridge converter with a diode rectifier regarding to high switching losses and parasitic oscillations in the inverter. The presented galvanically isolated step-down DC/DC converter with an improved control algorithm for the full-bridge active rectifier features reduced energy circulation and switching losses. The performance can be improved under wide input voltage and load variations. The advantages of the converter were verified with a 1 kW converter prototype and the test results were in full agreement with the expected waveforms. The presented steady-state operation principle and mathematical analysis of the converter based on the simulation and experimental results can be used as design guidelines for component and parameter estimation in practical applications.

This paper describes a new modulation technique for a single phase three-level neutral-point-clamped qZS inverter. The proposed converter is intended for applications that require input voltage gain and high quality of the output voltage. The simulation and experimental results are presented and discussed.