小波降噪在电力牵引供电系统谐波分析中的应用

Application of Wavelet Denoise in the Harmonic Analysis of Electrical Traction Power Supply System

电力机车作为电力系统的主要不平衡负荷、谐波源负荷,其特征谐波电流主要为3,5,7次高频谐波电流,这些高频谐波电流对电力机车的安全、稳定运行造成了很大的危害。以SS8型电力机车为例,仿真其整流电路工作过程,分析电力牵引供电系统谐波的特征,对牵引供电系统中的谐波电流信号进行小波分解、阈值处理和小波重构,以达到对牵引供电系统谐波电流信号进行降噪处理的目的。为寻找对牵引供电系统谐波电流信号降噪效果较好的小波阈值,仿真中分别采用Stein的无偏似然估计原理进行自适应阈值选择、启发式阈值选择、sqrt(2log(length(X)))阈值选择和极大极小原理阈值选择,根据谐波电流信号的不同特征,采用多种阈值处理方法使信号中的高频谐波电流含量减少甚至消除。仿真结果表明:电力牵引供电系统谐波电流信号的最优阈值为sqrt(2log(length(X)))阈值,用它降噪后可使信号中的高频谐波含量明显降低。

Electric locomotive is the main unbalance load and harmonic source load of power system, whose typieal harmonie eurrent mainly are 3, 5, 7 times high frequeney harmonie currents. These high frequeney harmonie eurrents will do great harm to the safe and stable operation of eleetrie loeomotive. Taking type SS8 eleetrie loeomotive as an example, the working proeess of its reetifying cireuits were simulated, and the harmonie eurrent eharaeteristies of the eleetric traetion power supply system were analyzed. Wavelet deeomposition, threshold disposal and wavelet reconstruetion were earried through on the harmonic current signal of electrie traction power supply system for the purpose of denoising its harmonic currents. In order to seareh the best wavelet threshold for the better denoise of the harmonie signal in electric traction power supply system, adaptive threshold selection based on Stein unbiased likelihood estimation theory, heuristic threshold selection, sqrt（2log（length（X））） threshold selection and minimax threshold selection were adopted in simulation. Various wavelet denoise thresholds were used to reduee and eliminate high frequency harmonic eurrent eontent of signal aeeording to different charaeteristies of harmonic signal. Simulation results show that the best threshold of the harmonie eurrent signal in eleetrie traction power supply system is sqrt（2log（length（X） ）） and it can reduce high frequency harmonic currents of signal obviously after its denoising.