Design of Electric Vehicle Battery Charger With Reduced Switching Frequency Variation

This article presents the design of an electric vehicle (EV) battery charger isolation stage for minimizing switching frequency variation with the proposed duplex control. Traditionally, the realization of an EV charger with a resonant power conversion stage involves extreme frequency variation in the constant voltage (CV) mode resulting in switching losses, imposes severe constraints on the optimal design of magnetics, and presents control complexities due to secondary resonance and degraded pulsewidth modulation resolution. In this context, reported hybrid control strategies are complex and entail the simultaneous variation of control variables. In order to simplify control complexity and design constraints, the EV charger isolation stage with the quadruple rectifier and employing the proposed duplex control is presented with notable frequency reduction. Furthermore, the effect of high-frequency transformer nonidealities on the soft-switching range is delineated. The proposed duplex control contributes to the efficiency enhancement of the EV charger over a comprehensive range during CV charging, ensures soft switching, and prevents secondary resonance. It also offers continuous resonant current to overcome the underutilization of the transformer arising from high-frequency distortions. To validate the presented analysis, a 1.25-kW hardware prototype is designed and tested in the laboratory, and experimental results are presented.