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-to-battery 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-dual-phase-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.
Highlights
The conventional single-phase EV on-board charger usually adopts a multi-stage design shown in Fig.1, i.e., a front-end power factor correction(PFC) stage followed by an isolated DC/DC converter
In [2], a variable switching frequency(VSF) PWM was used for a three-phase motor control, which reduces the switching loss with the same current ripple requirement
Since simulation results show the three control algorithms do not have major differences in high-power applications, this paper focused on the light-load condition
Summary
The conventional single-phase EV on-board charger usually adopts a multi-stage design shown in Fig., i.e., a front-end power factor correction(PFC) stage followed by an isolated DC/DC converter. In [2], a variable switching frequency(VSF) PWM was used for a three-phase motor control, which reduces the switching loss with the same current ripple requirement. Even though such a control strategy is used for motor control, it could be directly used in the conventional PFC control. A less-stage-number isolated AC/DC converter was proposed in [6], which gets rid of the large DC link bus capacitor The problem of such topology lies on the utilization of the back-to-back connected switches, which increases the system and control complexity.
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Published Version
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