Triple Phase Shift Control of an LLL Tank Based Bidirectional Dual Active Bridge Converter

Isolated bidirectional dc-dc converters (IBDCs) with high efficiency and high power density demand for complete zero voltage switching (ZVS) of all active devices for its entire operating range. This paper presents a comprehensive analysis and optimization problem formulation of a triple phase shift (TPS)-controlled inductive link based voltage fed-dual active bridge (VF-DAB) converter. Limitation on natural ZVS range for the TPS-controlled inductive link based VF-DAB is presented. To extend the ZVS range in a TPS-controlled VF-DAB converter, passive auxiliary inductors are connected in parallel (LLL tank) to the primary and secondary sides of the high-frequency transformer. Analysis and subsequent numerical solutions for the TPS-controlled VF-DAB with auxiliary inductors show complete ZVS of all the mosfets for the entire operating range. Experimental results confirm complete ZVS of all mosfets under various voltage gains and load conditions. A comparative loss breakdown for the TPS-controlled LLL tank VF-DAB and the conventional inductive link VF-DAB at various operating conditions show the necessity of the additional auxiliary inductors in the conventional design for increasing optimal switching frequency of the IBDC.