Modeling and Control for VSG-Based Variable-Speed Pumped Storage Unit with Full-Size Converter

With the continuous decline of system inertia due to the large-scale integration of renewable energy sources, replacing the grid support functions of traditional synchronous machines has become increasingly critical. In this study, a modeling framework is proposed for a variable-speed pumped-storage unit (VSPSU) with the full-size converter (FSC) under virtual synchronous generator (VSG) control. The model incorporates hydraulic, mechanical, and electrical subsystems with coordination. Control strategies include optimal speed control for the governor, DC-link voltage control on the machine side, and VSG-based control on the grid side. Simulation results under islanded conditions demonstrate that the VSPSU can provide effective inertia support, primary frequency response, and voltage regulation. In particular, the proposed virtual hydraulic compensation strategy successfully eliminates the reverse power swing observed in conventional fixed-speed units, while achieving frequency regulation performance comparable to traditional systems.