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This paper focuses on a new three-phase high power current-fed dc/dc converter with an active clamp. A three-phase dc/dc converter with high efficiency and voltage boosting capability is designed for use in the interface between a low-voltage fuel-cell source and a high-voltage dc bus for inverters. Zero-voltage switching in all active switches is achieved through using a common active clamp branch, and zero current switching in the rectifier diodes is achieved through discontinuous current Conduction in the secondary side. Further, the converter is capable of increased power transfer due to its three-phase power configuration, and it reduces the rms current per phase, thus reducing conduction losses. Moreover, a delta-delta connection on the three-phase transformer provides parallel current paths and reduces conduction losses in the transformer windings. An efficiency of above 93% is achieved through both improvements in the switching and through reducing conduction losses. A high voltage ratio is achieved by combining inherent voltage boost characteristics of the current-fed converter and the transformer turns ratio. The proposed converter and three-phase PWM strategy is analyzed, simulated, and implemented in hardware. Experimental results are obtained on a 500-W prototype unit, with all of the design verified and analyzed. Index Terms--Active clamp, leakage inductance, three-phase dc-dc converter, three-phase pulsewidth modulation (PWM) strategy, voltage transfer ratio, zero-voltage switching (ZVS).

Abstract: In this paper, a three-phase current-fed dc/dc converter with an active clamp is introduced, and a new three-phase three-leg high frequency transformer is proposed for the converter. The three-phase dc/dc converter transfers power through transformer leakage inductances in the discontinuous current mode; a single common active clamp branch is employed for zero-voltage switching (ZVS) in all active switches. Further, the converter''s three-phase power configuration increases power transfer, and it reduces the rms current per phase, thus reduces conduction losses. Moreover, a delta–delta connection on the three-phase transformer provides parallel current paths and reduces conduction losses in the transformer windings. A three-phase transformer can be constructed by connecting three discrete single-phase transformers, but this process results in a higher volume and higher material costs. Therefore, a new three-phase three-leg high frequency transformer is designed with three discrete cores integrated into a single transformer core. The proposed transformer is analyzed according to the several operating modes of the converter, and its design rules are determined. Experimental results are obtained on a 500-W prototype unit; the design is fully verified and analyzed. [Copyright &y& Elsevier]