This paper presents the study of a high-voltage DC/DC resonant converter which has excellent behaviour to be used in applications with strong variations in output voltage and in output current, because it maintains high efficiency in these types of applications. To do so, the switching losses have been minimized by integrating all parasitic elements (leakage inductance, secondary side capacitance of the high-voltage transformer and parasitic capacitances of the power switches and diodes) into the power topology, and the conduction losses have been minimized by operating the converter in a special mode (optimum switching line) in which no reactive energy is returned from the resonant elements to the input voltage source. The type of control used (PWM phase-shifted) allows one to maintains these desirable characteristics even when the operating point suffers a very strong variation. The final power topology might be called a "full-bridge, clamped mode, LCC-type parallel resonant converter with capacitive output filter". >

An optimized DC-to-DC converter topology for high-voltage pulse-load applications

High frequency (HF) transformer isolated DC-DC converter is a part of a fuel cell inverter system for utility interface, required to translate the level of low fuel cell stack voltage to meet the peak utility line voltage and provides isolation between inverter and utility line. This paper presents a comparison of various soft-switched HF transformer isolated DC-DC converters for fuel cell to utility interface application. It is shown that due to wide variation in fuel cell voltage with load variation, none of the voltage-fed converters can maintain ZVS for the complete operating range. Active clamped two-inductor current-fed converter is able to maintain ZVS for wide load and fuel cell stack voltage variations and is suitable for the present application. Analytical and simulation results to evaluate the performance of the current-fed converter are presented.

A Comparison of Soft-Switched DC-DC Converters for Fuel Cell to Utility Interface Application

An electrolyzer is part of a renewable energy system and generates hydrogen from water electrolysis that is used in fuel cells. A dc-to-dc converter is required to couple the electrolyzer to the system dc bus. This paper presents the design of three soft-switched high-frequency transformer isolated dc-to-dc converters for this application based on the given specifications. It is shown that LCL-type series resonant converter (SRC) with capacitive output filter is suitable for this application. Detailed theoretical and simulation results are presented. Due to the wide variation in input voltage and load current, no converter can maintain zero-voltage switching (ZVS) for the complete operating range. Therefore, a two-stage converter (ZVT boost converter followed by LCL SRC with capacitive output filter) is found suitable for this application. Experimental results are presented for the two-stage approach which shows ZVS for the entire line and load range.

A Comparison of Soft-Switched DC-to-DC Converters for Electrolyzer Application

The analysis and design of an LCC resonant inverter for a 20 kHz AC distributed power system are presented. Several resonant converter topologies are assessed to determine their suitability for high efficiency power conversion, under resistive and reactive loads. Two LCC-resonant inverter designs were implemented. One with all switches operating with zero voltage switching (ZVS), and another with two switches operating with ZVS and two switches with zero current switching (ZCS). The experimental results are presented along with a performance comparison of the two versions. >

Analysis and design-optimization of LCC resonant inverter for high-frequency AC distributed power system

High frequency (HF) transformer isolated DC-DC converter is part of a fuel cell inverter system for utility interface, required to translate the level of low fuel cell stack voltage to meet the peak utility line voltage and provides isolation between inverter and utility line. This paper presents a comparison of various soft-switched HF transformer isolated DC-DC converters for fuel-cell to utility interface application. It is shown that due to wide variation in fuel cell voltage with load variation, none of the voltage-fed converters can maintain ZVS for the complete operating range. Active clamped two-inductor current-fed converter is able to maintain ZVS for wide load and fuel cell stack voltage variations and is suitable for the present application. Analytical, simulation and experimental results are presented to evaluate the performance of the current-fed converter.

http://www.jstage.jst.go.jp/article/ieejias/128/4/128_4_450/_pdf

The DC behavior of a constant-frequency, clamped-mode parallel-resonant converter operating above resonant frequency is characterized. The converter is shown to be able to operate with zero-voltage turn-on for all the switches from no load to full load over a wide input range. Various circuit operating modes are identified and their corresponding operating regions defined. DC characteristics for the converter design are derived. A 5 V, 50 W prototype converter operating at 104 kHz is breadboarded to show the feasibility of constant-frequency, zero-voltage-switching operation and to substantiate the analytical results. The converter is operated with zero-voltage switching from no load to full load over the entire input voltage range without any external antiparallel diodes and snubbers. The experimental results are in good agreement with the analytical predictions. An efficiency of 85% is achieved. >

F.-S. Tsai

Papers

Constant-frequency, zero-voltage-switched, clamped-mode parallel-resonant converter