Research And Implementation On Detection Algorithms Of Harmonics In Power System

With the rapid development of the power electronic technology and the broad application of electronic devices and nonlinear electric equipments, a lot of harmonics are injected into the power grid. Harmonic seriously affects the safe and stable operation of power system, it has become the network’s main pollution, so harmonic detection has become the important research subject.This thesis primarily studies the harmonic analysis algorithms and the design of harmonic detection system. This thesis firstly discusses the generation and harm of harmonic, then introduces the commonly used harmonic detection methods. This thesis focuses on the research about Fast Fourier transform (FFT) and Wavelet Transform (WT) in the application of harmonic detection, at last designs the harmonic detection system based on Digital Signal Processor (DSP) TMS320VC5402.At present the study of harmonic detection is very active. Harmonic analysis methods commonly used are mainly divided into the time domain methods and frequency domain methods. This thesis firstly studies harmonic detection method based on FFT. Because of spectral leakage and picket-fence effect of FFT, this thesis studies the improved FFT algorithms:the interpolating windowed FFT and all phase FFT. The interpolating windowed FFT can detect the amplitude and frequency accurately, and all phase FFT can realize phase invariance. Therefore, in the applications, these two methods are combined together for harmonic detection in order to improve the calculation precision effectively.Because FFT only analyze signal respectively from the time domain and frequency domain, this thesis then introduces WT which has localization in both time and frequency domain. This thesis discusses WT in the application of harmonic detection from the selection of wavelet function and decomposition level. According to the characteristics of FFT and WT, this thesis studies the combination of interpolating windowed FFT and WT for harmonic detection. Simulation results indicate that this method can not only calculate the parameters of steady-state harmonic, but also can detect unsteady-state harmonic.On the basis of algorithm research and simulation, this thesis designs harmonic detection system based on16fixed-point digital signal processor TMS320VC5402 produced by Texas Instruments. This thesis focuses on the design of analog input and A/D converting part, and the high-speed data acquisition circuit PCB is designed. The board is connected to the digital signal processor development system, and then uses the system to analyze the harmonic signal. Software design is based on the DSP integrated development environment CCS3.3, there are three parts including data acquisition, data processing and data transmission module in this detection system.The detection system can complete the data acquisition of grid voltage signal. A/D can convert an analog signal to a digital signal and then put into DSP, at last calculates the generic parameters of harmonics using the improved FFT algorithm, and then displays the results. The test shows that the design of harmonic detection circuit and the software processing method are effective; the detection system meets the requirements of relevant national standards.