Comprehensive control method of energy storage system to participate in primary frequency regulation with adaptive state of charge recovery

This paper proposed a comprehensive control method for energy storage system (ESS) participating in primary frequency regulation (PFR). The integrated control strategy consists of PFR stage and "stage of charge" (SOC) recovery stage. In the PFR stage, the virtual droop control and virtual inertia control are combined and applied in the frequency deterioration phase to reduce the frequency deviation. The virtual negative inertia control coupled with virtual droop control is used in the frequency recovery phase to accelerate frequency recovery. In the SOC recovery stage, an adaptive SOC recovery control method is proposed. The SOC recovery control is performed while the frequency is within the dead zone, and the recovery power of ESS is based on the SOC to avoid overcharging and over-discharging. The proposed SOC recovery control can restore the SOC to a proper range which ensures the potential for ESS to participate in the next PFR process. It also reduces the number of SOC recovery starts compared with the fixed target SOC method and is beneficial to prolong the cycle life of ESS. Simulation outcomes demonstrate that the proposed comprehensive control method can efficiently enhance the frequency regulation performance and restore the SOC to the target range.