An Improved Modulation Scheme of Active Commutated Current-Fed Bidirectional dc/dc Converter

Active commutated or naturally clamped techniques have emerged as a new solution to achieve wide range soft-switching and eliminate the necessity of active clamping circuit of current-fed bidirectional dc/dc converter. Multiple typical modulation schemes have been proposed, which include single phase-shift (SPS) modulation, dual phase-shift (DPS) modulation, and discontinuous current SPS (DCSPS) modulation. DCSPS provides the lowest circulating current compared with prior two modulations, but it suffers from the problem of resonance and high peak current at partial loads. This article proposes a DCDPS modulation based on the existing modulations. The duty cycles of the two legs on the high-voltage side are controlled to be unsymmetrical to solve the current resonance problem in DCSPS. Extra phase shift is introduced to achieve much lower circulating current at wide range load conditions. Zero current switching (ZCS) of primary switches and zero voltage switching (ZVS) of secondary switches can be achieved over wide input range and wide load range. A 250-W laboratory converter prototype has been built. Experimental results are presented to validate the analysis and design.