Widen the zero-voltage-switching range and secure grid power quality for an ev charger using variable-switching-frequency single-dual-phase-shift control

Abstract

Compared to conventional electrical-vehicle(EV) on-board chargers utilizing a front-end Power-Factor-Correction(PFC) + an isolated DC/DC converter, which limits the wall-tobattery efficiency to ~94%, a new control strategy using variable switching frequency(VSF) and variable phase shifts frees the PFC stage thereby getting rid of the DC link capacitor and further increasing the system efficiency and power density. The challenge is to secure zero-voltage-switching (ZVS) turn-on for all switches within the full-power range. In this paper a novel VSF single-dualphase- shift(SDPS) control strategy is proposed, which consists of three control freedoms, i.e., two phase shifts and one variable switching frequency to secure ZVS and achieve PFC simultaneously. ZVS boundaries are pictured and compared among single-phase-shift(SPS), dual-phase-shift(DPS) and the proposed single-dual-phase-shift(SDPS) control. Simulation results and experimental validation through a level-2 EV on-board charger indicate that by using the proposed SDPS control, both ZVS and PFC are secured not only for the heavy load but also for the light load, without sacrificing the system efficiency.