Study On Measurement Methods Of Parameters For Power Harmonic Based On Wavelet Transform

With the development of modern industry, nonlinear loads of power system are greatly increased. They absorb non-sine current waves form power network and result in voltage aberrance. Voltage aberrance makes power quality severely worsen, endangers power system safely and economically running and affects some users working normally. Harmonic content has become an important symbol of power quality. So, harmonic measurement in power system is of important significance.This paper introduces the concept of harmonic, harmonic mechanism of production, hazard of harmonic, harmonic source and deficiency of traditional harmonic measurement method. Moreover, it discusses several transform methods, such as continuous wavelet transform, discrete wavelet transform and wavelet packet transform of which characteristics are analyzed. Against the exiting question about which is hard to real-time analyze and measure speedy and exactly measurement of changing harmonic, this paper studys and realizes a harmonic analysis and measurement method based on reconstruction of wavelet packet decomposed coefficients. This paper puts forward a new concept of harmonic change rate. What's more, this paper studys, put forwards and builds a measurement method of harmonic change rate based on reconstruction of wavelet packet decomposed coefficients. According to this method, power system harmonic track can be realized. This method provides theory basis for taking an effective method for harmonic real-time compensate. This paper puts forward and builds a new measurement method based on reconstruction of wavelet packet decomposed coefficients. Emulator test shows the feasibility and correctness of this method. Using wavelet transform can make one voltage process decompose to a frequency band. According to sample frequency and decompose scale, frequency band can be confirmed. Harmonic content analysis is realized. All integral and non-integral harmonics are obtained. This method overcomes information missing resulting from spectrum leak, fence effect in traditional harmonic measurement. Reliability and accuracy of harmonic are improved.The method based on this paper has been successfully applied in XDZ-1 Virtual PowerParameter Measurement and Electric Measuring Instrument Meter Automatic Verification.The users and system verification have proved the advance and practicability of this method. The system has passed the expert authentication organized by Guangxi Power Company in January of 2004.