Modulation Method of Series-Resonant Dual-Active Half-Bridge Converter for ZVS and Minimum RMS Current

This article presents a modulation method for the series-resonant dual-active half-bridge (SR-DAHB) converter. The proposed method employs four control degrees of freedom: primary- and secondary-side duty ratios, voltage phase shift angle, and switching frequency. The proposed modulation method minimizes the rms current of the resonant tank while achieving complete zero-voltage switching of all primary and secondary switches for all operational ranges. Time-domain analysis of the SR-DAHB converter, which takes into account every harmonic, has been performed to obtain control value sets. Accurate steady-state values, such as half-bridge inverter switching current/voltage, output current, and rms current of the resonant tank, are derived in closed-form expressions. The derived expressions are utilized in numerical optimization algorithms to calculate optimal control value sets. Since closed-form equations are used, the computational burden of the numerical solver is relieved. The effectiveness of the proposed modulation method is verified through simulations and experiments on a 9.0 kW, 600 V full-SiC converter prototype. Compared to existing modulation methods, it is advantageous when primary- and secondary-side dc-link voltages have a large voltage difference. Particularly, in 0.25 voltage conversion ratio operation, the proposed modulation method presents an efficiency boost of up to 2% compared to the existing modulation methods.