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.

The current source inverters (CSI) are considered more reliable than their voltage source counterparts due to the inherent current-limiting feature. This is particularly interesting for many applications, such as battery energy storage, where there is a possibility of very high short-circuit currents. In addition, CSI can provide an inherent voltage boost capability, allowing integration of extra-low voltage batteries with 230 Vac loads for standalone applications. For the past few years, CSI has not garnered much attention due to the unavailability of switches with reverse voltage blocking capability. However, with the emergence of new technologies based on wide bandgap materials and monolithic devices, CSI can potentially provide effective solutions for such applications. In this paper, a CSI is proposed as an interface between a ±48 V battery bank and a 230 Vacload. To minimize the forward voltage-drop across the switches of the current source inverter, silicon carbide MOSFETs-based four-quadrant switches are employed. In addition, a unipolar carrier-based modulation is proposed and implemented. This modulation technique facilitates easier control of overlap-time and minimizes its effect on the power quality output of the inverter. To validate this proposal, a 700 W prototype was built, and laboratory tested.

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.

This paper presents an analysis of a method for controlling power factor correction (PFC) rectifiers to achieve unity power factor and high quality of the input current. The duty cycle estimation is based on a combination of two terms: feedforward and PI. The feedforward term is calculated with a digital model of the converter using input voltage, input current and reference current values. The PI term is then added to compensate for non-idealities of the model including factors, like digital and sensing delays. The analytical equations and characteristics of the proposed combined method are derived and the performance is compared with a standard PI regulator. The results demonstrate that the combined method features significantly better phase margin and can provide unity power factor and low total harmonic distortion (THD) for wide range of load conditions even with significant digital delay.

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.

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.

Estonia is among the countries with the most energy-efficient Near Zero Energy Buildings (NZEBs) in Europe, i.e. their energy consumption is the lowest. From the energy management prospects, on one hand, the rising price of electricity and decreasing the feed-in prices, and on the other hand, the decreasing price of battery energy storage system (BESS) have made the self-consumption of NZEBs profitable. This paper develops a simple tool to study the optimal sizing of BESS and increase the profitability of NZEBs. The BESS sizing is done considering the installed PV capacity in the NZEB, the energy consumption profile, and the local electricity prices. The results of this paper demonstrate to the NZEB owner and planers that in case of self-consumption, investment in PV systems could be more profitable when it is combined with BESS. Simulation results are presented to validate the proposed BESS sizing tool and analyze the sensitivity of results to changes in electricity and battery system price.

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.

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 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.

This paper presents a novel bidirectional current-fed push-pull DC-DC converter topology with galvanic isolation. The control algorithm proposed enables full-soft-switching of all transistors in a wide range of input voltage and power with no requirement for snubbers or resonant switching. The converter features an active voltage doubler rectifier controlled by the switching sequence synchronous to that of the input-side switches. As a result, full-soft-switching operation at a fixed switching frequency is achieved. Operation principle for the energy transfer in both directions is described, followed by verification with a 300 W experimental prototype. The converter has considerably higher voltage step-up performance than traditional current-fed converters Experimental results obtained are in good agreement with the theoretical steady-state analysis.

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.

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.