| With the application of the nonlinear power electronic devices, harmonicpollution caused by these devices is growing seriously. Harmonic elimination hasbeen paid much attention than ever before, and harmonic detection is the key ofharmonic elimination and reactive compensation. Owing to the inherentnonlinearity, randomness, distribution, nonstationarity and complexity ofinfluencing factor of harmonics, many conventional detection techniques can'tacquire accurate harmonic identification. Because of the excellent time-frequency localization characteristics, wavelet transform (WT) is a new researchdirection in harmonics detection of power system.Firstly, the concept, the appearance causation, the hazard of harmonic, thedeficiency of traditional harmonic and its detection method were introduced inthis dissertation, and then several transform methods, such as continuous wavelettransform, discrete wavelet transform and wavelet packet transform werediscussed, and the time-frequency characteristics of these methods were analyzed.Aiming at serious situation of harmonic in the distribution network of theSeventh Oil-producing factory of Daqing oil field, the harmonics were detected,and the harmonics of current were analyzed and simulated with Haar-waveletanalysis, dbN-wavelet analysis and wavelet packets analysis. According to theharmonic reconstruction and the error account, the results show that thefundamental can be seperated effectively;by wavelet analysis its characteristicsare rapidity and accuracy. The conclusion that wavelet packet transform candivide signals into multi-levels, and can also decompose the high-frequency partdeeply which can't be subdivided by the multi-resolution, and it can decomposefundamental wave, harmonic and other disturbance from harmonic signalseffectively were obtained. So wavelet transform has been used widely. Finally, a common scheme of harmonic's elimination has been proposed which is a goodbasis for harmonic's elimination.In a word, via the studies in this dissertation, not only the application effectof wavelet analysis of harmonic detection can be seen directly, but also a goodanalysis method for design and manufacturing of an active power filter based onwavelet transform was provided. |
