The increasing penetration of wind power in the future smart grid may considerably affect the system frequency. Especially, the frequency fluctuation may be severe when the capacity of generators for load-frequency control (LFC) is insufficient in the nighttime. In general, the battery energy storage system (BESS) is used to alleviate the frequency fluctuation. Nevertheless, the installation cost
... [Show full abstract] of BESS with large capacity is very high. On the other hand, in the demand side, the installation of plug-in hybrid electric vehicles (PHEV) tends to increase significantly. The PHEV is normally plugged into the home outlet in the nighttime. Based on the vehicle-to-grid (V2G) control, the distributed batteries installed in PHEVs can be applied to LFC. As a result, the required capacity of BESS installed in the system can be reduced. This paper proposes the new contribution of the PHEV based on V2G control not only to alleviate frequency fluctuation in a smart grid with large wind farms, but also to reduce the BESS capacity. In the PHEV model, the charging schedule and battery state of charge are taken into account. To guarantee the well cooperative control of PHEV, BESS and conventional frequency controller, the proportionalintegral parameters of BESS and frequency controller are tuned by the particle swarm optimization while the V2G control of PHEV is performed. Simulation study confirms that the PHEV can effectively cooperate with BESS and frequency controller for alleviation of frequency fluctuation. Furthermore, it significantly reduces the required capacity of BESS.