An Emergency Control Method of AC/DC Hybrid Power System Considering the Risk of DC Commutation Failure Under AC Fault

Abstract

DC commutation failure has become one of the key factors restricting the safe and stable operation of AC and DC hybrid power system. When an AC fault occurs in the power grid, the AC fault itself may cause rapid changes in the power angle, voltage, and frequency of the AC system. At the same time, if the AC fault also causes the DC commutation failure, the power impact of the DC system and the impact caused by the AC fault itself superposition makes the characteristics of the AC power grid more complicated and may cause more serious security and stability problems. However, the characteristics of the DC commutation is related to many factors such as the type of fault, the severity of the fault, the location of the fault, the degree of voltage asymmetry, the support capacity of the AC power grid, and the DC operating conditions. Usually, the control strategies are formulated by predictive fault simulation, it is not exactly the same as it is in the actual system, so the control strategy is formulated in accordance with the most conservative situation, which may cause unnecessary excessive control, and the economic cost is relatively high. An emergency control method is proposed, which is an additional control method based on the DC commutation failure signal under AC faults. When the commutation failure is detected, additional control is performed on the base of the original emergency control strategy, which can ensure system safety and re-duce control costs. Finally, based on a simulation case of Brazil's AC/DC hybrid power grid, the effectiveness of the proposed method is verified.