Accurate ZVS Boundary Analysis for Bidirectional Dual-Bridge Series Resonant dc-dc Converters

Analysis of zero-voltage switching (ZVS) range is critical to the design and control of bidirectional dc-dc converters. This paper discusses the derivation of the accurate ZVS boundary for bidirectional dual-bridge series resonant converter (DBSRC) based on state-plane analysis. First, the closed-form solution of ZVS boundary for pure phase shift modulation is derived. Next, the analysis is extended to the case of phase shift plus pulse width modulation, and an implicit function expressing the ZVS boundary of all switches is deduced in closed form. Through this function, the hard switching and ZVS regions under any voltage conversion ratio and resonant-to-switching frequency ratio can be easily derived numerically using mathematical software. Compared with the fundamental harmonic approximation (FHA) method, the ZVS boundary obtained in this paper shows higher accuracy. Furthermore, the generality of the state-plane approach maintains its validity also with small resonant-to-switching frequency ratios, in which the converter behavior becomes that of a dual active bridge topology with a large dc-blocking capacitor. The analysis is validated via computer simulations and verified on an 800W experimental DBSRC prototype.