一种基于自适应电压限值的换相失败抑制策略

A commutation failure suppression strategy based on adaptive voltage limits

为有效抑制高压直流输电系统在不同故障程度下的换相失败,提出了一种基于自适应电压限值的改进低压限流控制器(voltage dependent current order limiter,VDCOL)设计方案。首先,详细分析了包含传统VDCOL的直流输电系统在换相失败及恢复期间的运行特性,并提出VDCOL曲线在不同时间段下应具备的动态性能。然后,引入直流电流这一反映故障特性的时变电气量优化传统VDCOL的直流电压上下限值,从而在不同时间段自适应改变电流指令启动电压阈值与电压-电流指令变化趋势,以满足输电系统换相失败及恢复期间的有功与无功需求。同时考虑到VDCOL电压上下限值的过度变化会恶化系统运行特性,对其范围的设置进行了解析和合理选取。最后,在PSCAD/EMTDC中对所提方法进行仿真测试。结果表明,所提出的改进控制策略能在一定程度上抑制直流输电系统的连续换相失败,同时有效地改善换相失败各阶段直流输电系统的运行特性。

To effectively restrain a continuous commutation failure of an HVDC system at different degrees of fault,an improved voltage-dependent current order limiter(VDCOL)controller design scheme based on adaptive voltage limits is proposed.First,this paper makes a detailed analysis of operating characteristics of an HVDC system with VDCOL involved during commutation failure and recovery.At the same time,the dynamic performance of the VDCOL curve over different periods is proposed.Then,the time-varying DC current,which can reflect the fault characteristics,is introduced to optimize the upper and lower limits of the DC voltage of a conventional VDCOL.Thus,the starting voltage threshold and the variation trend between voltage and current instruction are adaptively changed in different periods,meeting the dynamic active and reactive power demand of the transmission system.Knowing that an excessive change of the voltage limits will deteriorate the system operational characteristics,its range is analyzed and rationally selected.Finally,the proposed method is simulated and tested in PSCAD/EMTD.The simulation results show that the improved control strategy can suppress the continuous commutation failure of the HVDC system to a certain extent and effectively improve the operation characteristics of the HVDC system at each fault stage.