DAB Converter with Q Capability for BESS/EV Applications to Allow V2H/V2G Services

This paper presents a dual active bridge (DAB) converter for a battery energy storage system (BESS) or an electric vehicle (EV) to deliver battery-to- home (B2H) and battery-to-grid (B2G) or vehicle-to-home (V2H) and vehicle-to-grid (V2G) services. The DAB topology is preferable for EV charging systems due to galvanic isolation and bidirectional power flow capabilities, however this topology increases reactive current peak and loses zero voltage switching (ZVS) operation at light loads if it is not controlled with improved modulation strategies and proper reactive power optimization (RPO) algorithm. This paper proposes a mixed modulation method and a RPO algorithm based on power system concepts that reduce the reactive power and provide ZVS operation over a wide voltage range. The mixed modulation allows one of the bridges of DAB converter to run with 2-level while and other to run with 3-level square wave modulation. Due to the complexities associated with the analytical solution using time domain analysis, this paper develops detailed universal expressions of a DAB converter using harmonic analysis method. Analytical identification of ZVS boundaries and DSP implementation of RPO algorithm become easier with these universal expressions. Multiple modes analysis for different operational states are no longer required. Simulation models of the DAB converters have been developed to show the results with different modulation strategies. The theoretical analysis of modulation strategies, RPO algorithm and ZVS operation are validated by experimental results on a laboratory scale prototype. Results show that the proposed mixed modulation with RPO algorithm improve the DAB converter performance.