Minimum-RMS-Current Operation of Asymmetric Dual Active Half-Bridge Converters With and Without ZVS

This paper presents a comprehensive steady-state analysis of asymmetrically operated dual active half-bridge (DAHB) dc-dc converters, i.e, DAHB converters operated with a non 0.5 duty-ratio. Such asymmetric operation presents an additional control handle, which may be used to optimize converter performance. The different possible modes of operation are introduced followed by detailed analysis of active power and rms current variation and zero-voltage-switching (ZVS) performance in each mode. Using this information, closed-form expressions corresponding to two control strategies are derived which minimise rms value of transformer current at a given power with and without ZVS operation. The accuracy of the theoretical predictions are verified using numerical optimisation approaches and also through MATLAB Simulink-based simulations. Finally, experimental results on a 625W laboratory prototype are presented which validate the discussed ideas. Both simulation and experimental results indicate that the proposed strategies potentially offer significant efficiency advantages compared to simple square-wave control, especially under light-load conditions for converters operating with nonunity effective voltage conversion ratios.