基于小波变换的高压直流输电换相失败控制

Prevention Control of Commutation Faillure in HVDC Based on Wavelet Transform

换相失败是高压直流输电系统的常见故障之一。通过合理设计换相失败控制器,能够抑制换相失败故障发生的频率和减少相继换相失败的次数,从而降低换相失败对电力系统安全稳定运行的影响。本文基于小波分析方法,研究换相失败的控制方式,利用小波分析时频域分析的优点,对换相失败的进行实时控制。提取直流电压和交流电压并进行小波分析,计算信号小波系数d6的方差,能有效判断换相失败故障;通过移动窗口采样的方式,实现了故障的实时测量和控制;当判断发生换相失败故障时,及时提高熄弧角的给定值,能够有效防止严重故障引发的相继换相失败和控制方式不当引发的换相失败。仿真结果验证该控制策略的有效性和实时性。

Commutation failure is the common fault in HVDC systems. If the controller of commutation failure can be designed properly, commutation failure and successive commutation failure can be restrained. The impact of commutation failure on power system is lowered. Wavelet transform is a signal-processing method both in time and frequency. The application of wavelet transform can control commutation failure correctly in real-time. DC voltage and AC voltage in inverter side are the signals analyzed by wavelet. The variances of wavelet coefficient d~ are used to identify the fault. By moving sample windows, the measurement and classification of fault can be done online. When the controller identifies a fault, it can improve the desired value of distinguished angle and improve the margin of commutation. The control strategy prevents the successive commutation failure caused by AC three-phase short circuit fault and commutation failure caused by single-phase short circuit fault and improper control mode. The simulation results show that the controller is with well performance.