Phase-Shift and Duty-Ratio Control Optimization of a 6 kW Three-Port Resonant DC–DC Converter for Dual Auxiliary Voltage EV Applications

Isolated three-port dc-dc converters (TPCs) facilitate integration of three voltage sources/loads in electric vehicle applications. Three-port resonant converter (TPRC) is an attractive TPC topology as it inherits the advantages of resonant converters. Phase-shift (PS) control applied to TPRCs enables independent power flow control among all ports. Phase-shift and duty-ratio (PSDR) control introduces three additional degrees of freedom providing the potential for improving the converter efficiency compared to PS control. This article presents a generalized harmonic approximation-based steady-state mathematical model for a TPRC with five-variable PSDR control. Mathematical solutions to the steady-state converter bridge voltages and the ac currents under PSDR control are provided. The proposed mathematical model is integrated with a TPRC power loss model and together are used to formulate a control optimization problem for evaluating the optimal control variables at maximum converter efficiency. The optimized five-variable PSDR control is compared against PS control using a 6 kW/100 kHz rated hardware demonstrator, with efficiency improvements as high as 12.4%.