| The transmission of wind power via line commutated converter based high voltage direct current(LCC-HVDC)is one of the important ways for the development and utilization of large-scale new energy in our country.As a common fault of LCC-HVDC,commutation failure will lead to the decrease of the active power of the system and the surplus of reactive power at the sending end.There will be an AC overvoltage problem at the sending end.Due to the limited high voltage crossing capacity of the wind farm,serious overvoltage will cause the wind turbine to fall off the grid easily,which restricts the wind power consumption and LCC-HVDC transmission capacity.On the basis of existing research,this paper further studys the problem of AC overvoltage of HVDC transmission system integrated with wind power in the case of commutation failure.Firstly,the structure and basic control strategy of HVDC transmission system integrated with wind power are introduced;in the case of commutation failure on the inverter side of LCC-HVDC,the transient process is divided into several stages according to the AC voltage characteristics of the system,and the controller functions and transient characteristics of LCC and wind farm in each stage are analyzed respectively,and the contribution effects of HVDC rectifier station and wind farm station to different overvoltage stages are clarified.According to the power-voltage equations,the mathematical model of transient overvoltage degree and power variation is deduced,the relationship between relevant electrical quantities and overvoltage is compared and analyzed,and the key factors affecting overvoltage are extracted.Then,a delay compensation strategy to improve the reactive power response characteristics of wind farm is proposed,and the influence of the key parameters in the delay compensation model on the overvoltage characteristics is explored.At the same time,a decentralized cooperative control of reactive power based on the local power and voltage characteristics of LCC rectifier station and wind farm station is proposed.Based on the AC voltage and reactive power characteristics of the sending end,the reactive power coupling relationship and AC side power flow equation are used to determine the trigger angle of LCC rectifier station and the reactive power reference value of wind farm station.which are based on local power and voltage characteristics.The reactive power of the LCC rectifier station and the wind farm station are adjusted separately to reduce the reactive power surplus at the AC bus at the sending end.so as to realize the cooperative control of the overvoltage.Finally,based on the PSCAD/EMTDC simulation model,considering different fault types and different wind farm capacity,the effectiveness of the proposed control method to suppress overvoltage is verified.The results show that the proposed delay compensation strategy and decentralized cooperative control method can effectively reduce the transient overvoltage level caused by commutation failure. |
