Frequency Control in Hydro Power Systems with High Penetration of Inverter-Based Resources

In power systems with high penetration of inverter-based resources (IBRs), maintaining stable frequency has become increasingly challenging. This paper investigates the performance of hydropower, with a focus on variable-speed (VS) pumped storage, as the primary source of frequency control in high IBR penetration systems. Dynamic models, incorporating a Francis turbine, penstock, synchronous machine, converter, and relevant standard control systems, are developed to represent multiple traditional fixed-speed (FS) units and VS units in a power system study. Their performance is assessed in a system resembling the Tasmanian power system, which relies on wind power and High Voltage Direct Current (HVDC) transmission, with local hydro generation regulating system frequency. Case studies involving large active power shortages demonstrate that VS units can provide controlled and sustained release of kinetic energy, highlighting the benefits of VS pumped storage technology in providing primary frequency response. This study demonstrates that the effectiveness of VS units in primary frequency control is closely tied to the system's available inertia, thereby necessitating the coordination of VS frequency response with system inertia levels.