Distributed Control Design for V2G in DC Fast Charging Stations

In this paper, an SoC-based droop control design is proposed for the vehicle-to-grid (V2G) operating mode of electric vehicles (EVs) in a DC fast charging station (DCFCS). The proposed primary control design aggregates EVs in the V2G mode while balancing EV batteries SoCs during charge and discharge modes to protect EVs from overcharge/overdischarge and increase the time duration at which all connected EVs are able to operate in the V2G mode. The proposed controller employs the output of a sigmoid function as the droop coefficient to allocate power among EV batteries. EV batteries’ energy capacities and SoCs are the variables in the sigmoid function. Compared to the conventional methods, the proposed controller balances SoCs without using the average SoCs to provide complete independence among chargers, considers the effect of different EV batteries energy capacities on the SoC balancing, and balances SoCs faster. The effectiveness of the proposed controller is evaluated through steady-state and transient case studies in the DCFCS with three EVs connected to chargers.