A Cooperative Control Strategy for AC Fault Ride Through of Offshore Wind Power Based on AC Voltage Fluctuation

Abstract:
Aiming at the problem of low voltage ride through of offshore wind power through flexible direct transmission systems, a cooperative control strategy for AC fault ride through of offshore wind power based on AC voltage fluctuations is proposed, which monitors the AC voltage changes of onshore receiving converter stations in real time. When the bus voltage decreases due to AC faults, the reactive power control strategy of onshore receiving converter stations immediately adjusts the reactive power setting value, and the flexible direct system generates additional reactive power to maintain the AC bus voltage amplitude; At the same time, according to the low-voltage voltage limiting control strategy, the voltage amplitude of the AC bus of the offshore converter station is adjusted in real time, combined with the unique low voltage ride through capability of wind turbines, to achieve preliminary power balance of the flexible DC system. When the voltage amplitude of the AC bus of the offshore converter station is set to the low voltage ride through limit of the offshore wind turbine, the energy consumption resistor device is put into use to ab-sorb the excess active power that cannot be balanced by the flexible and straight system, and achieve AC fault ride through of the system. This method is based on the basic control strategy of the offshore wind power transmission system through flexible DC, and adds a low-voltage voltage limiting control and fixed reactive power correction strategy. It fully utilizes the low voltage ride through capability of the offshore wind turbine unit and the reactive voltage support capability of the flexible DC transmission system. Combined with the energy consumption resistor, it does not require fault detection, reduces the loss of the energy consumption resistor and its design parameter requirements. When the AC system at the onshore receiving end converter station fails, It can adjust the system power balance as much as possible and at the maximum speed per hour to ensure the safe and stable transmission of offshore wind power through flexible DC.