高压直流输电系统非线性定电流控制响应特性分析

Analysis of the Response Characteristics of HVDC Nonlinear Constant Current Control

由于换流器具有非线性特性,线性定电流控制无法满足高压直流输电系统暂态期间性能要求。为提高高压直流输电系统对交流系统扰动的耐受能力,并降低故障电流峰值,在线性定电流控制传递函数中加入非线性环节以补偿换流器的非线性特性,并通过仿真建模比较分析了两种不同作用范围的非线性定电流控制与线性定电流控制在线路故障、换相失败故障以及稳态运行时的响应特性。仿真结果表明,加入非线性环节的定电流控制具有控制策略简单、暂态特性良好的优点,但由于作用于全运行范围的非线性定电流控制在稳态运行时存在直流电流振荡现象,因此在实际工程中非线性定电流控制应避开稳态运行范围。

Because of the non-linear characteristic of the converter,the linear constant current control cannot meet the performance requirements of HVDC system during the transient period.In order to improve the tolerance capability of HVDC system against AC system disturbance and reduce the peak value of fault currents,a nonlinear element is added into the transfer function of linear constant current control to compensate the nonlinear characteristics of the converter.By modeling and simulation,response characteristics,commutation failure faults and steady state operation are analyzed and compared between the nonlinear constant current control and the linear constant current control in two different action ranges in the line fault.Simulation results show that the constant current control with the nonlinear element added has advantages including the simple control strategy and the better transient characteristics,but it should avoid the steady state operation range in practical cases because the nonlinear constant current control which acts on the full operation range will generate the DC current oscillation phenomenon in the steady sate operation.