Coordinated Grid-Forming Control Strategy for VSC-HVDC Integrating Offshore Wind Farms Based on Hybrid Energy

For integrating large-scale offshore wind farm system more effectively, issues as insufficient inertia energy and dc voltage variation caused by traditional grid-forming (GFM) control in voltage source converter based HVDC (VSC-HVDC) have to be settled urgently. This article proposes an improved coordinated GFM control strategy based on hybrid energy to improve grid frequency and dc voltage stability. In terms of grid-side VSC control, an improved virtual inertia control method consisting of additional capacitor structure and matching GFM control is proposed, which can decouple dc voltage and energy of dc capacitor in VSC-HVDC. By establishing coupling relationship between additional capacitor energy and grid frequency, the matching GFM control can fully utilize its energy and provide better inertia support. In terms of wind farm control, a three-stage coordinated control based on hybrid energy is designed. During stage1 and stage2, fast inertial support and primary frequency regulation are achieved through rotor kinetic energy. The supercapacitor is controlled to quickly increase or decrease active power to suppress sudden output power change caused by exiting rotor kinetic energy control in stage3. Finally, a comparative simulation is performed using MATLAB/Simulink to verify the effectiveness and advantages of the proposed strategy.