Inertia Transmission Control of Full-Power Converter Variable-Speed Pumped Storage System for Grid Frequency Support

Full-power converter variable-speed pumped storage (FPC-VSPS) is a promising technique for flexible power regulation in small-scale distributed hydroelectric power plants. However, conventional vector control limits the synchronous motor of the FPC-VSPS from providing inertia support to the power grid. To overcome this limitation, this paper introduces an inertia transmission control for FPC-VSPS based on the concept of DC voltage synchronization. Firstly, the control incorporates the DC capacitor power equation into the GSC control. To enable inertia transmission from the FPC-VSPS synchronous machine, the DC capacitor dynamics are fed into both the speed and torque control of the MSC. Secondly, a torsion spring-rigid body equivalent model is introduced based on the inertia transmission process, analyzing the effects of physical parameters, control coefficients, and transmission delays on the inertia transmission performance. Theoretical analysis and simulation results reveal that the inherent physical differences and transmission delay have a negative impact on the effectiveness of the inertia transmission. Consequently, a DC capacitor design method based on inertia matching is proposed, accounting for the constraints of physical inertia matching, system stability, and operational security. Finally, simulations and experiments prove the necessity of inertia matching and verify the effectiveness of the proposed control to cope with frequency fluctuations in both pumping and generating modes.