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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。
As the main unbalanced load and harmonic load of electric power system, electric locomotive has three, five, seven high-frequency harmonic currents, which are the main characteristics of the electric locomotives. These high-frequency harmonic currents cause the safe and steady operation of electric locomotives A lot of harm. Taking the SS8 electric locomotive as an example, the working process of the rectification circuit is simulated. The characteristics of harmonics in the electric traction power supply system are analyzed. The harmonic current signals in the traction power supply system are decomposed by wavelet, thresholding and wavelet reconstruction, Power system harmonic current signal for noise reduction purposes. In order to find out the wavelet threshold which has a good effect on the noise reduction of the harmonic current signal in the traction power supply system, the adaptive threshold selection, heuristic threshold selection, sqrt (2log (length (X) Based on the different characteristics of the harmonic current signal, a variety of threshold processing methods are used to reduce or even eliminate the high-frequency harmonic current in the signal. The simulation results show that the optimal threshold of harmonic current signal in electric traction power supply system is sqrt (2log (length (X)) threshold, which can reduce the high frequency harmonic content in the signal significantly.