Study On The Measurement Of Harmonic Energy Based On Wavelet Packet Transform

With the development of modern industry, the nonlinear loads of power system are greatly increased. They absorb the non-sine current waves from power network and result in voltage aberrance. Voltage aberrance makes the power quality severely deteriorate, endangers the safe and economical running of power system and affects some users's normal work.The accurate measuring of harmonic energy may ensure power system to run in stable and economical state.The research purpose of this thesis is to realize the accurate measuring of harmonic energy and provide reliable evidence for scientific management on harmonic energy.This thesis introduces the fundamental concept of wave aberration and harmonic, and lists the main harmonic source and the hazard of harmonic in power system. Further more, it analyzes the distributing of power between power provider and user, expounds the social and economic values of the study on the technology for measuring harmonic energy, discusses several important transform methods, such as continuous wavelet transform, discrete wavelet transform and wavelet packet transform in wavelet theory, whose characteristics are analyzed, and disserts the fundamental principle of measuring harmonic energy.Against the exiting problem in the method to measure harmonic energy on the basis of FFT, which is hard to make an efficient, quick and accurate measurement of changing harmonic, this thesis presents a method to measure harmonic energy based on wavelet packet transform. The method has a good time and frequency characteristic, and it overcomes the abuse of Fourier Transform which can not analyse the signal in the time field. The analysis and measurement based on the method to the non-steady harmony signal have very good results. The emulation experiment has verified the validity and accuracy of this method.Following the hardware design principle of high capability and low cost, this thesis designs a system to measure harmonic energy based on wavelet packet transform. It may satisfy the running speed requirement of the algorithm which employs wavelet packet transform to measure harmonic energy. This thesis provides the circuit schematic of the unit for measuring harmonic energy and the flow chart for measuring harmonic active energy and harmonic reactive energy.This thesis discusses the error origin of the system for measuring harmonic energy based on wavelet packet transform, and set up the error model, and presents the...