Measurement Method Study Of Power System Harmonic Base On Wavelet Transform

With the development of modem industry, nonlinear loads of power system are greatly increased,which make electricity systems harmonics more, the parameter measure and analysis of power system gained more attention. Because of the nonlinearity, randomicity, distributing, and non-placidity, it is difficult to make a veracious measure of harmonics. Presently the main method to harmonics measure is the Fourier transforms and the wavelet transforms. Fourier transforms is the basic of modern harmonics measure, however this often brings frequency spectrum folding and frequency spectrum leaking。Wavelet transforms is the new method being researched nowadays, with this new method, the local characters of signals can be analyzed exactly, transient signals can be analyzed correctly, and the real-time and precision of harmonics measure can be improved too.The paper introduced the basic concept of harmonics, harmonic source and the harm of harmonics, analyzed and reviewed the method of power system harmonics measure. Researched the exiting reactive power theories, discussed the way and means of time domain and frequency domain analysis, analyzed the differences and application of time domain and frequency domain measures, and afforded some theory basic of harmonics survey and reactive power compensation. Discussed the transforms of vavelet theory such as continuous wavelet transform, discrete wavelet transform and wavelet packet transform and so on, offered the basic theory of harmonics measure using wavelet transform. Analyzed the time-frequency performance of wavelet transform, afforded several harmonics measure means of power system based on wavelet, and emulational experiments proved the feasibility and validity of the methods. A new method was proposed using synthesis algorithm on the basis of wavelet transforms and Fourier transforms to measure electricity parameter. Firstly use wavelet transforms to make pretreatment to the harmonics signal, in order to eliminate noise and detect and separate disturbances, then reconstruct signal and decompose it with Fourier transforms, separately figure out each harmonic parameter and electricity parameter. Numerical simulation proved the method proposed effective.