Closed-Form Solution for Efficient ZVS Modulation of DAB Converters

Abstract

A directly employable closed-form analytical solution for the calculation of an efficient, full-operating-range zero voltage switching (ZVS) modulation scheme for bidirectional dual active bridge (DAB) dc–dc converters is presented. Contrary to the analytical ZVS modulation schemes previously proposed in literature, the amount of charge that is required to charge the nonlinear parasitic output capacitances of the switches during commutation is incorporated, ensuring complete commutation of the bridge legs and ZVS of the switching devices. Besides quasi-lossless ZVS, the resulting modulation scheme leads to near-minimum high-frequency circulating currents and thus, minimum conduction losses under the condition of ZVS and for given values of the inductances and transformer turns ratio. Although modifiable for other implementations, the method is demonstrated for a full-bridge full-bridge DAB as a core part of a single-phase, single-stage, bidirectional, isolated ac–dc converter. The resulting modulation scheme is compared with a ZVS modulation scheme calculated using a previously published numerical approach, proving its effectiveness. Experimental results obtained from a state-of-the-art, $\text{3.7}\; \text{kW}$ converter prototype which interfaces a $\text{400}\; \text{V}$ battery with the $\text{230}\;\text{V}$ , $\text{50}\;\text{Hz}$ utility grid are given to validate the theoretical analysis and practical feasibility of the proposed strategy.