高压直流输电系统换相失败的仿真研究

Simulation Study of Commutation Failure of HVDC Transmission System

换相失败是直流输电系统逆变器最常见的故障,当逆变器联接于弱交流系统时换相失败更容易发生,而以往的研究重点是换相失败的机理及数学推导,缺乏相应的仿真验证。为此,通过电磁暂态仿真研究了广泛使用的换相失败解析表达式及其不同短路情况下的误差。结果表明:三相短路时最小电压降的计算公式与仿真结果相吻合,而单相接地故障时最小电压降的计算结果与仿真有一定误差;理论计算结果稍偏保守,但是仍然能够作为反映换相失败的一个指标。在此基础上分析研究直流控制系统对连续换相失败影响的结果表明:增大逆变站控制器增益和减小其时间常数均可以抑制换相失败的发生,有利于逆变侧交流电压的恢复与维持。

The widely-used minimum voltage-drop analytic equation of commutation failure of HVDC based on the commutation area theory is tested with electro-magnetic transient simulation with EMTDC software, and its applicability in different fault conditions is analyzed in detail. Results based on CIGRE benchmark HVDC model show that for 3-phase short circuit fault, the analytic equation has a high simulation precision. However for single-phase short circuit fault, there are some errors between the theoretic analysis and the simulation. It can be concluded that the minimum voltage-drop analytic equation can be taken as an index which reflects the probability of commutation failure. Finally, the control ways influencing continuous commutation faihire are studied, and results show that the control system of inverter has more impact on commutation failure, the increase in the gain and the decrease in time constant of the control system can reduce the probability of commutation failure, while the increase of transferred power of HVDC can bring about an adverse effect on commutation. So reasonable parameters setting of control system is necessary for the operation of HVDC system.