Dynamic Voltage Stability of Distribution Grids with Fast Charging Stations for EV Units

The dynamics of EV chargers combined with that of induction motors and unique characteristics of distribution system could prove dynamic voltage stability a threat to secure operation of distribution systems. In previous studies, the dynamics of EV chargers and single-phase induction motors haven't been considered. EV chargers are new loads added to distribution grids which have unique properties, e.g., higher R/X ratio. In this paper, to capture and study the interactions between complex systems of a distribution network, detailed models of chargers and motors are used, and dynamic voltage stability effects of EV charging is studied in two different cases. First, with individual PFC quick chargers spread over the grid. Second, with multi-slot Fast Charging Stations able to dynamically maintain the PCC voltage. The results show that while uncoordinated EV charging might cause dynamic voltage instability, Fast Charging Stations can alleviate this problem by implementing an LVRT scheme, injecting reactive power into the grid and regulating the rate of EV charging.