Dynamic Stability Analysis and Grid Frequency Response of Adjustable Speed Pumped Storage Hydropower

Energy storage plays a crucial role in ensuring the reliability and stability of the power system. It remains an inevitable factor in the renewable energy portfolio. Pumped Storage Hydropower (PSH) is recognized for delivering power for prolonged periods facilitated by its extensive storage capacity. Adjustable Speed Pumped Storage Hydropower (AS-PSH) systems leverage advanced wind turbine technologies and power electronic converters to provide adjustable speed controls, operational flexibility, faster response, improved frequency regulation, better renewable energy integration, improved grid stability, and higher system reliability. Unlike conventional PSH, AS-PSH is distinguished for its capability to provide frequency regulation in pumping mode. Type-3 AS-PSH systems utilize doubly fed induction machines, and Type-4 AS-PSH employs full converter synchronous machines. This paper investigates performance of Type-3 AS-PSH and Type-4 AS-PSH. An IEEE 14-bus system and a real-world Western Interconnected power system model are used for this study, and the system is simulated with General Electric's Positive Sequence Load Flow (GE PSLF) software for various system disturbances under different operating conditions. The IEEE 14-bus system is studied for an under-frequency event in generating mode and over-frequency event in pumping mode. Western Interconnected system is studied for tripping of two large nuclear power plant units. The results are compared for both AS-PSH types, highlighting their frequency regulation performance and response characteristics.