Coordinated Interaction Between EV Charging Stations and Distribution Network via Stepwise Droop Control With SoC Interval Management

The flexible charging capability of electric vehicle charging stations (EVCSs) can improve distribution network (DN) operation with source-load uncertainties. To fully harness this potential, this paper proposes a three-stage coordinated interaction method between EVCSs and the DN, centered on a novel stepwise droop control function. In the first stage, a dynamic state of charge (SoC) interval management approach is introduced to determine the optimal SoC interval and the corresponding adjustable power interval for EVCSs, considering charging uncertainties and temporal coupling of energy. The second stage is implemented from the DN perspective using grid-wide information to optimize P-V stepwise droop control functions for EVCSs. To alleviate the computational burden from binary variables, a general binary reduction technique is adopted. In the last stage, each EVCS decomposes the obtained stepwise droop control function into multiple levels of charging power for individual EVs, considering the minimal changes in charging power and the satisfaction of target SoC. Consequently, in real time, the EVCS can self-regulate the charging power based on local voltage measurements. The simulation results verify the effectiveness of the proposed interaction method. Compared with the baseline method, it reduces the DN's average voltage deviation and power loss by 13.29% and 14.68%, respectively.