Optimal Operation Trajectory Control of Variable Speed Pumped Storage for Power System Frequency Regulation

Variable speed pumped storage (VSPS) possesses significant potential for power system frequency regulation. This paper proposes a novel optimal trajectory control for VSPS to enhance power system frequency response (FR) by fully leveraging its regulation potential, while maintaining its rotor speed stability. First, the speed stability of VSPS during FR process in both turbine and pump modes is investigated. Following this, an analytical expression for the rotor speed is derived, specifically for the turbine mode, given its susceptibility to speed instability. This expression enables not only an efficient assessment of rotor overspeed risks but also a precise characterization of critical points along the operational trajectory. Then, the design principles of additional power control for VSPS are proposed to achieve a smooth switch of operation stages. Based on these principles and derived expressions, the optimal operation trajectory of VSPS is determined by system disturbances and the unit's operating conditions. This adaptability of the proposed strategy optimizes power response and strengthens FR capability. Furthermore, an overspeed control is developed to ensure rotor speed stability. Finally, the IEEE 39-bus system is utilized to test the proposed strategy under various operating conditions, demonstrating its superior performance in improving power system FR.