多馈入直流系统换相失败分析

针对传统最小电压降落法在判断换相失败时准确性不高的问题，提出了新的换相失败判据。为了明确故障阻抗对换相失败的影响，分别通过两种方法：灵敏度分析法和节点阻抗矩阵法详细分析了故障阻抗与换相电压的数学关系。第一种方法能全面分析各种因素对换相电压的影响；第二种方法在一定的假设条件上得到了更为直观和简洁的换相电压表达式，可作为一种快速分析方法。基于两种换相电压分析方法，分别给出了当地换相失败和同时换相失败时的临界故障和临界耦合阻抗的求解方法。仿真分析表明，改进的换相失败判据准确度很高；同时由两种换相电压分析方法所得到的换相电压表达式也具有一定的准确性。最后，详细分析了交流故障、负荷特性以及系统参数对换相电压的影响，并得到了一些具有指导意义的普遍结论。

Study on the Commutation Failure in Multi-infeed HVDC System

Because the accuracy of the traditional minimum voltage drop method used to commutation failure is not high enough, a new commutation failure criterion was proposed. In order to clarify the effect of the fault impedance on the commutation failure, the mathematical relationship between the fault impedance and the commutation voltage was analyzed in detail by two methods of the sensitivity analysis and node impedance matrix. According to the two commutation voltage analysis methods, the critical fault and critical coupling impedance solving methods of local and simultaneous commutation failures were given, respectively. The simulation results showed that the accuracy of the new commutation failure criterion is very high, and two kinds of commutation voltage expressions deduced by the two analysis methods of commutation voltage have also a certain accuracy. At last, the effects of AC fault, load characteristics and system parameters on the commutation voltage were analyzed, and some useful and instrumental conclusions were obtained.