  Electric Vehicles (EVs) are promising to provide frequency regulation
services due to their fast regulating characteristics. However, when EVs
participate in Supplementary Frequency Regulation (SFR), it is challenging to
simultaneously achieve the dispatch of the control center and the expected
State of Charge (SOC) levels of EV batteries. To solve this problem, in this
paper we propose a Vehicle-to-Grid (V2G) control strategy, in which an
uncertain dispatch is implemented in the control center without detailed EV
charging/discharging information. The regulation from the control center is
achieved by allocating the regulation task within the frequency regulation
capacity (FRC) of EVs. The expected SOC levels of EV batteries are guaranteed
by a real-time correction of their scheduled V2G power in EV charging stations.
Simulations on an interconnected two-area power system validate the
effectiveness of the proposed V2G control in achieving both the frequency
regulation and the expected SOC levels of EVs.
