Fast Active Power Reduction Based Fault Ride-Through Control Strategy for VSC-HVDC Integrating Offshore Wind Farm Under Onshore Fault

The voltage source converter-based high voltage direct current (VSC-HVDC) integrating offshore wind farm (OWF) system suffers from direct current (DC) overvoltage under onshore grid fault. The existing methods mainly use DC chopper of VSC-HVDC or voltage drop control of the OWF to mitigate DC overvoltage, which lead to high costs or forced tripping of offshore wind turbine generators (WTGs). To suppress DC overvoltage and promote active power recovery, this paper proposes a two-stage fast active power reduction (FAPR) based fault ride-through control strategy. By mathematically clarifying the FAPR capacity of the WTG, the DC chopper resistances of the WTG and VSC-HVDC are economically designed. Then, during stage 1, a scheme that combines FAPR control of the OWF with DC chopper control of VSC-HVDC is proposed to suppresses DC overvoltage. During stage 2, considering the issue of electromagnetic torque saturation when offshore WTGs undergo fast active power recovery, a fast pitch angle reduction control scheme is proposed to facilitate the active power recovery. Simulations and experiments validate that the proposed method avoids DC overvoltage. Besides, the DC chopper resistors are reduced by 90% and 80% compared with DC chopper-based method and voltage drop-based method, respectively.