Study On Several Kinds Of Detecting Methods For Harmonic Current In Active Power Filters

In recent years, the electrical harmonic pollution is getting more and more serious with the far-ranging application of power electronics technologies. It has become a curse to power system, which deteriorates the quality of electric energy. Active power filter (APF) is an advanced power electric device, which can be used for integrated compensating harmonic. Compared with some conventional measures, active power filter has many advantages and favorable prospects.Harmonic current detection technology is one of the critical technologies of active power filters. The development of harmonic current detection technology has direct effects on the development of APF technology, improving the harmonic current detection technology is very significative to improving the property of APF. The paper primarily studies the harmonic detection methods in active power filters based on this.The theory of instantaneous reactive power has been applied in many fields since it was proposed in 1980s.Based on this theory, one harmonic real time detection method can be applied in active power filters. On the basis of analyzing the theory of instantaneous reactive power, this paper analyses the error factors in the harmonic current detection method based on the theory of instantaneous reactive power.Due to the powerful ability of dealing with nonlinear problems, the neural network has been applied in harmonic detection in APF in recent years. This paper analyzes the basic principles of the harmonic detection method based on multilayer feedforward neural networks, which has been studied extensively at present. By analyzing the deficiency in some present detection methods, this paper brings forward two new harmonic current detection methods according to the essence of thefunction of APF-improving the power quality and decreasing THD. One is themethod based on the BP network, the other is based on the ELMAN network .This paper studies the two new methods, comparing the detection effects of the two new methods. The Simulation shows that both of the two kinds of methods can be used in APF and the method which is based on the ELMAN network has the better effect.Due to the excellent time-frequency characteristic, wavelet transform has alsobeen applied to harmonic detection in recent years. On the basis of analyzing the theory of wavelet transform, this paper gives the method that the theory of wavelet transform is used in the harmonic current detection of APF, makes an analysis to the application, and illustrates the importance of the selection of wavelet function and wavelet scale in the harmonic current detection by the comparison of two kinds of wavelet function.