An Isolated Multilevel DC–DC Converter Topology With Hybrid Resonant Switching for EV Fast Charging Application

This article proposes a multilevel dc–dc converter topology for fast charging of electric and plug-in hybrid electric vehicles (EVs and PHEVs). The proposed dc–dc converter topology converts the front end ac–dc converter output and provides regulated supply to the EV propulsion battery. The proposed topology consists of full-bridge converter at the primary, while the secondary side consists of voltage doubler rectifier units and combination of diodes and mosfet for reconfiguration of the voltage doubler rectifiers to generate the multilevel voltage. The multilevel voltage at the output helps in reducing the output filter size and increases the power density of the converter. The topology utilizes the resonance between leakage inductor of high frequency transformer, parasitic output capacitors of full-bridge mosfets and voltage doubler capacitors to achieve soft switching (ZVS turn-on) for all the full-bridge devices and soft turn-offfor the rectifier diodes. The load limited ZVS turn on capability of conventional full-bridge topologies is mitigated through the use of resonance between magnetizing inductance of transformer and mosfet output capacitors. The converter is designed for 650 V dc bus input and 200–400 V EV battery output at 100 kW rated charging power. The analysis of the proposed converter in continuous and discontinuous modes of operation, soft switching operation, and the component design guidelines are presented in this article. The proposed converter is validated through detailed PLECS simulation results for 100 kW charging power. Experimental results from laboratory prototype of 500 W power are also presented to validate the design methodology and converter performance.