对称故障下基于直流电流变化的后续换相失败风险预判及风险等级划分

在换流母线的不稳定电压作用下,高压直流输电系统发生多次换相失败造成的多次功率冲击对电网安全稳定运行影响很大.根据交直流系统实时运行状态对后续换相失败的风险进行预判是工程中迫切需要解决的问题.分析了高压直流输电系统换相失败的基本过程,根据高压直流输电系统准稳态方程推导了逆变侧关断角与直流电流变化的关系,提出一种基于直流电流变化的后续换相失败风险预判方法.选定前次换相失败后关断角重新恢复至参考值的时刻作为预判时刻,通过预估交流电压变化范围评估导致发生后续换相失败对应的直流电流上升区间,划分高压直流输电系统发生后续换相失败的风险等级,再根据预判时刻的直流电流大小确定发生后续换相失败的风险等级.通过PSCAD仿真软件中的Cigre高压直流标准测试模型,验证了所提方法的有效性.

Risk prediction and risk level classification of subsequent commutation failure under symmetrical fault based on change of DC current

Under the influence of the unstable voltage of the converter bus, continuous power shocks caused by multiple commutation failures of HVDC(High Voltage Direct Current) transmission system have a great impact on the safe and stable operation of power system. It is an urgent problem to predict the risk of subsequent commutation failure according to the real time operation status of AC/DC system. After analyzing the basic process of commutation failure of HVDC transmission system, the relationship between the arc extinction angle of inverter side and the change of DC current is deduced according to the quasi-steady-state equation of HVDC transmission system. A method to predict the risk of subsequent commutation failure based on the change of DC current is put forward. The time when the arc extinction angle recovers to the reference value after the previous commutation failure is selected as the pre-determined time. By estimating the change range of AC voltage, the DC current rising range corresponding to the subsequent commutation failure is evaluated, and the risk level of subsequent commutation failure is classified in HVDC transmission system. The risk level of subsequent commutation failure is determined according to the pre-determined time. The validity of the proposed method is verified by the standard testing model of the Cigre HVDC system in PSCAD simulation software.