A Perturbation Observer-Based Fast Frequency Support for Low-Inertia Power Grids Through VSC-HVDC Systems

Low-inertia power grids could suffer from large frequency excursions under even small power disturbances. When a voltage source converter-based high voltage direct current (VSC-HVDC) system is used to integrate a low-inertia grid into a main grid, an ancillary frequency support service can be provided to the low-inertia grid by the VSC-HVDC system. This paper proposes a perturbation observer-based fast frequency support controller (POFFS) of VSC-HVDC systems to improve the frequency stability of low-inertia power grids. According to the feedback linearization and the high gain observer technique, the perturbation observer of the inverter station is designed to estimate the comprehensive impact of multiple perturbations, including the power disturbances in low-inertia grids, the uncertainty of grid inertia, and unknown nonlinear dynamics. The estimate of the perturbations are further compensated by the feedback control loop to achieve robust frequency regulation. Compared with the conventional frequency controller, the proposed POFFS can provide better frequency support to low-inertia power grids, without requiring an accurate system model and parameters. Two test systems are used to verify the effectiveness of the proposed POFFS.