Design Methodology of a Three-Phase Four-Wire EV Charger Operated at the Autonomous Mode

Compared with grid to vehicle (G2V) and vehicle to grid (V2G) modes, electric vehicle (EV) battery chargers are more vulnerable to power quality problems at the autonomous mode, i.e., creating its own electric grid during the grid blackout while facing unbalanced and nonlinear loads. Active damping is another common challenge given most charger equip LC filters at grid-end voltage-source inverters (VSIs). In this article, an output-voltage control with harmonic compensation plus virtual impedance term is proposed to achieve high power quality and necessary damping, respectively. The physical meaning of the virtual impedance is further explained, and the voltage loop with PI plus multiresonant terms is analyzed in depth. More importantly, the analytical solutions and procedures to design such controllers considering the time delays are proposed. Finally, simulation results and experimental data on an EV battery charger prototype using SiC devices, which is made of one VSI and one isolated dc/dc converter, validate the effectiveness of the proposed design methodology.