Study On The Influence Of Commutation Failure On The Overvoltage Of AC/DC Hybrid Power System With Wind Farms

In recent years,China has made great efforts to develop new energy generation technology,in which wind power generation as the largest new energy generation mode has broad prospects of development.However,wind energy resources and load centers in China are inversely distributed,wind-fire bundled DC transmission becomes the most economical and effective transmission mode,which can not only meet the requirements of large-scale wind power centralized external transmission,but also improve the stability of transmission power.When the wind power is sent out by DC,the fault of AC system at the receiving end of DC leads to the commutation failure,and the AC bus at the sending end will have a large transient overvoltage,which will easily lead to the large area disconnection of the wind farm.Therefore,it is of great significance to study the mechanism of DC commutation failure affecting the transient overvoltage of AC/DC hybrid system with wind farms,and to put forward the method of restraining the transient overvoltage of AC/DC hybrid system.First of all,this paper builds the model of ac/dc hybrid system with wind power plant through PSCAD,and analyzes in detail the mechanism of transient overvoltage on the bus of AC/DC hybrid system twice after the dc system fails to convert phase.It is pointed out that the rapid decrease of DC current and the reduction of reactive power consumed by the converter station at the rectifier side are the main reasons for the transient overvoltage of the bus at the sending end.The influences of different fault types,different fault occurrence times and different AC system strength on the transient overvoltage of the bus at the transmitter side are analyzed and compared by simulation.Then,this paper studies the influence of condenser on the transient overvoltage of the bus at the sending end,and proposes a strategy to determine the capacity of condenser and suppress the transient overvoltage according to the magnitude of the transient overvoltage.The strategy can effectively suppress the transient overvoltage of the bus at the sending end caused by the commutation failure after the single-phase fault at the inverter side,and the correctness of the strategy is verified by simulation.Finally,the influence of Voltage Dependent Current Order Limiter parameter and PI parameter of Constant Current Controller on transient overvoltage of bus in AC/DC hybrid system is analyzed,and a PI parameter optimization method based on adaptive harmony search algorithm is proposed.After the PI parameter of the Constant Current Controller is optimized,the transient overvoltage of the bus at the sending end,which is caused by the commutation failure after the three-phase grounding fault at the end,can be further suppressed,and the effectiveness of the proposed method is verified by simulation.