Detection And Analysis Of Harmonic Based On Wavelet Transform

In recent years, with the development of power system, especially the excessive application of power electronic devices and other non-linear loads in power system, the problem of harmonic pollution has become increasingly serious. Harmonics not only seriously affect the power quality, being a threat to the security, stability and efficient operation of power grid, but also bring adverse effects on the user terminal equipment, increasing the transmission line loss and interference communication.Therefore, it is of great significance to detect and analyze harmonic accurately and rapidly. To this end, this paper makes a simulation analysis of harmonic detection.Firstly, the cause and harm of harmonic are analyzed, and the existing harmonic detection methods are introduced and compared.Then it focuses on the research status and basic theory of wavelet transform, the continuous wavelet transform, discrete wavelet transform and wavelet packet transform are introduced in detail.A harmonic detection method based on the combination of CWT and DWT is proposed in this paper. Firstly, the harmonic frequency of the signal is detected by the scale amplitude method based on CWT. Under the premise of the determination of harmonic components, using DWT to detect the harmonic amplitude. Simulation results show that the accuracy and reliability of this method.In the power sector, it is often essential to detect the fundamental component from the power signal. A simple algorithm for fundamental component detection based on discrete wavelet transform is presented. Two kinds of electric signal model are constructed and analysed, respectively. The simulation results show that this method can realize accurate detection(deviation approaches to 0) in one sampling period for signal with high frequency harmonics disturbances. But the mixed noise in signal will significantly reduce the fundamental component detection precision. Through the wavelet de-noising method can obviously improve the detection accuracy of the fundamental frequency component.Finally, the power quality disturbances in power system are modeled and simulated, and the starting and stopping time of power quality disturbances can be accurately detected by wavelet analysis.More over, wavelet packet is used to decompose and reconstruct the power harmonic signal, and the RMS value of each harmonic is obtained according to the wavelet packet decomposition coefficients. The results show that the error between the measured value and the actual value is very small, which provides an effective method for the analysis of harmonic parameters.