An Adaptive Frequency Regulation Method With Grid-Friendly Restoration for VSC-HVDC Integrated Offshore Wind Farms

With the rapid growth of voltage source converter based high-voltage direct current (VSC-HVdc)-integrated offshore wind farms, wind turbines (WTs), and VSC stations are required to provide frequency regulation to maintain the onshore system frequency stability. However, after a temporary power increase during the initial period of a disturbance, WTs and VSC stations must reduce their output power to restore their own initial operating states. If there is no other power injection to offset the corresponding power shortage, a significant second frequency drop (SFD) may occur. To address this issue, this paper proposes an adaptive frequency regulation method with grid-friendly restoration. Different frequency regulation strategies are designed to adaptively use the releasable kinetic energy inWTs or the electrostatic energy in VSC stations according to their own real-time operating status. In addition, a system-level grid-friendly coordination is proposed to use the persistent energy reserves of WTs with a deloading strategy to increase the instantaneous power injection and avoid a significant SFD while otherWTs or VSC stations restore their operating states. The quantitative calculation and switching mechanism of the additional power injections of deloading WTs are highlighted, and the effectiveness of the proposed method is verified in a case study.