LVRT Control Strategy Based on Supercapacitor for Offshore DFIG Wind Farm with HVDC-Grid

Offshore wind power is the focus of wind power development. The flexible HVDC power transmission system (HVDC-Flexible) will be an important power transmission mode for offshore wind power. Voltage drop in the DC grid will threaten the safe operation of the HVDC-Flexible system of the doubly-fed offshore wind farm (DFOWF-HVDC), so this paper proposes a LVRT scheme for DFOWF-HVDC based on supercapacitor. Utilizing the fast charge and discharge characteristics of supercapacitors, the transient stability of DFOWF-HVDC is guaranteed. The design scheme of the energy storage system based on supercapacitor is described. The control methods of the converter system during the LVRT process are given. The converter system consists of stator-side converter (SSC), rotor-side converter (RSC) of DFIG, and DC grid-side converter (GSC) and energy storage side converter (ESC). The simulation results verify the correctness of the proposed control strategy.