DFACTS-Based Mitigation of Power System Voltage Unbalance for Wide Adoption of EV Fast Charging Systems

This paper aims to investigate the unbalanced voltage effects of three-phase fast charging stations on power systems and devise an effective mitigation approach. A detailed three-phase fast charging system (FCS) with power factor correction capability is implemented in the EMTP-RV time-domain simulation environment and its operation characteristic is derived under unbalanced voltage conditions. This characteristic is employed in the power flow calculation and unbalanced voltage analysis. The results indicate that the FCS integration into the power system exacerbates the voltage unbalance if the system possesses a background unbalanced voltage. As a result, with a heavy adoption of the fast-charging systems, the system unbalanced voltage can exceed the standard limits. To mitigate the unbalanced voltage and accommodate higher capacity of FCSs in the system, PWM-based converters are employed as distributed flexible AC transmission system (DFACTS) to mitigate the negative-sequence voltage resulting from the FCSs. With such a mitigation approach, optimal charging capacity in the system under study is obtained such that the voltage and the unbalanced voltage standard limits are not violated. The simulation results demonstrate that the proposed method can effectively mitigate the unbalanced voltage impacts and enable the power system to accommodate more fast charging stations.