SOC Consistency Optimization Control Strategy of Flywheel Array Energy Storage System for Grid Primary Frequency Regulation

Aiming at the state of charge (SOC) imbalance of flywheel array energy storage system (FAESS) when it participates in primary frequency regulation (PFR), a SOC consistency optimization control strategy based on hierarchical architecture is proposed. Firstly, the lower controller is designed based on the principle of vector control strategy, and the flywheel charge and discharge control strategy is divided into emergency recovery mode and normal working mode according to SOC to avoid overcharge or over-discharge of flywheel unit. Due to SOC differences among flywheel units participating in primary frequency regulation, some flywheel units will withdraw from operation in advance during charging and discharging, resulting in secondary drop of power grid frequency. To solve this problem, the upper controller is optimized, and an improved equal time allocation strategy is proposed to adjust the output power in real time according to the SOC of each flywheel unit, so that the SOC of the flywheel array gradually becomes consistent during the charging and discharging process, and the balance of the remaining energy of the flywheel array is guaranteed. Finally, a simulation model is built in Matlab/Simulink to simulate two typical working conditions of small load disturbance and large load disturbance respectively and compare with the conventional power allocation strategies to verify the effectiveness and feasibility of the proposed control strategy.