Operating area-dependent flexible ancillary service provision of electric vehicles: Capacity assessment and coordination

The vehicle-to-grid (V2G) technology enables electric vehicles (EVs) to provide ancillary services to the grid, but the service provision of EVs is challenged by the tradeoff between drivers’ traveling demands and the grid’s requirement for reliable support. Accurate assessment of schedulable capacities and grid requirement-adapted coordination of EVs has become a critical problem that needs to be addressed. This paper proposes an operating area-dependent capacity assessment and coordination strategy for EV clusters. First, considering the charging characteristics and traveling behavior of EVs, the state of charge (SOC)-time operating area of EVs is constructed. Based on the operating area, the schedulable capacity of EVs can be flexibly assessed under varying power amplitude and duration requirements. Then, a prioritization-based coordination strategy for EVs for ancillary service with certain power amplitude and duration is proposed with the objective of minimizing battery aging. To address the unexpected power deficit due to sudden disconnection of EVs during ancillary service, an emergency compensation strategy is proposed. The EVs outside the restricted boundaries are dispatched in such a case, and the stable and reliable ancillary service of EV cluster can be ensured. Case study results validate the proposed method in terms of ancillary service capacity estimation, battery aging reduction and stable service provision. In the studied case, the proposed method avoids a 13.3% decrease in the output power of the EV cluster due to inaccurate capacity estimation. Under the adopted aging assessment based on experimental degradation data, the proposed method substantially reduces battery aging costs compared with the conventional strategy. Furthermore, the proposed coordination strategy effectively maintains charging-discharging power stability during ancillary service provision.