A multi-state control strategy for battery energy storage based on the state-of-charge and frequency disturbance conditions

With the large-scale penetration of renewable generation, many power systems face increasing frequency deterioration issues. Because of the fast response capability, battery energy storage (BES) has become an essential flexible resource to maintain the system frequency stability. This paper investigates how the state of charge (SOC) of a BES could be effectively managed while guaranteeing the frequency control service. A novel multistate control strategy is proposed to adaptively control the active power of a BES for various frequency disturbance scenarios. This control strategy explicitly takes into account the interdependency between the BES's SOC, lifetime, and frequency regulation performance. A finite state machine is implemented to divide the frequency and the SOC into multiple states to set diverse control objectives and constraints for a BES under different operating conditions. By simultaneously considering the SOC/frequency states, the initial SOC-recovery power, and the overload capacity of inverters, three sub-strategies are designed in the multi-state framework to control the BES in any feasible state. Case studies on a modified IEEE RTS-79 system verify the effectiveness of the proposed control strategy. Leveraging the proposed strategy, the BES can provide better frequency control effect as compared to the conventional droop control.