Based On Fourier - Wavelet Transform Shunt Active Power Filter

Electricity is essential and vital energy in the development of modernsociety. But in recent years, with the wide application of power electronicdevices in the power system and the presence of nonlinear loads, the resultingharmonics, seriously affect the normal operation of the equipment and thequality of the power supply grid. So, that, how to further improve power qualityand effective suppression of harmonics current and voltage and reactive power,has caused widespread concern of the community.With the emergence of controllable Self-turn-off power devices and thedevelopment of control theory, the Active Power Filter (Active Power Filter,APF) is an important trend in the current harmonic control. APF is a new type ofpower electronic devices.It's main function is to existing in the real-timetracking of the harmonic compensation. As the most effective means ofcomprehensively control grid pollution, APF has good prospect, extensiveresearch and application.Active power filter system consists by the current detection circuit, controlcircuit and the compensation current generating circuit. The key to the activepower filter compensation performance is the harmonic current detectionprocess and system control strategy. This paper mainly makes a deep research inthe harmonic detection and control strategies to provide a theoretical basis andreference value for the future development of Active Power Filter. This papermainly studies the content as follows:1, For harmonic current detection link, Fourier transform analysiscommonly used for steady-state signal has significant advantages. But fortime-varying signal, there are some certain limitations. So an analysis methodwith rising time-frequency is introduced-the wavelet transform. Wavelettransform has good frequency domain band-pass characteristics and goodsensitivity of the mutant signal, which can accurately determine the mutatedmoment and filter out interfering signals. But it can't accurately and easilydistinguish every harmonic. On the basis of a detailed study of the characteristics and analysis methods of power system harmonics, this paperproposes the Fourier-wavelet transform method with advantages combinationwith Fourier transform and wavelet transform. This harmonic detection methodis well suited to all types of harmonic signals for accurate analysis.2, In the control strategy, analysis of the traditional hysterics controlmethod can identify the strengths and weaknesses of the control method. On thisbasis, certain improvements are made to the traditional hysterics control, whichcan effectively solve the unfavorable impact of too high switch frequency of theIGBT and make compensation effect more perfect.3,This paper establishes the simulation model of shunt active power filteron the basis of MATLAB. Through the research of simulation model and results,it proves that the program can track and compensate harmonic in real-time withthe grid current distortion. With the advantages of good dynamic response, highdetection precision and fast compensation harmonic etc, it can finally optimizeof power quality.