Experimental Verification of a Flexible Vehicle-to-Grid Charger for Power Grid Load Variance Reduction

Abstract— This study designed a Vehicle-to-Grid (V2G) charger consisting of a three-phase AC/DC converter and a DC/DC buck-boost converter with various charger functions, such as charging/discharging, power factor and DC-link voltage controls. The highlight of this charger is its flexibility to accurately control the charging/discharging power of the Electric Vehicle (EV) battery to match the power grid reference targets to achieve a reduction of grid load variance. Moreover, the power factor control was employed to improve the overall charger efficiency through unity power factor operation. Meanwhile, the adopted DC-link voltage control smoothens the charging/discharging power transfer between the AC/DC and DC/DC converters. The control strategies of the proposed charger were successfully implemented via a double-layer PID controller. For practical validation purposes, a 1 kVA V2G charger prototype was constructed whereby the proposed control strategies were coded using the eZDSPF28335 development board. The experimental results revealed that the V2G charger prototype effectively managed the charging/discharging power of the EV battery to achieve a reduction in grid load variance through load leveling and peak load shaving operations. Moreover, the proposed control strategies prevented over-charging/discharging of the EV battery apart from regulating the DC-link voltage and maintaining the charger operation at unity power factor.