Study On Detection Methods Of Harmonic In Power Network

With the development of power electronics, the number of rectifier,frequency converter, arc furnace and all sorts of power electronics facility are continuously increasing. The electricity characteristic of nonlinear,impact and unbalance has seriously polluted power supply system. Active power filter (APF) is an advanced power electric device, which can be used for integrated compensating harmonic. 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, The paper primarily studies the harmonic detection methods in active power filters based on this.Firstly, the paper introduces the theory of instantaneous reactive power. On the basis of analyzing the theory of instantaneous reactive power, one harmonic real time detection method can be applied in active power filters. This paper analyses the error factors in the harmonic current detection method based on the theory of instantaneous reactive power.Secondly, 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 of the harmonic current detection method based on wavelet transform in the two different kinds of harmonic current, and illustrates the importance of the wavelet scale and wavelet function in the harmonic detection.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 feed forward neural networks, which has been studied extensively at present, and researches the simulation by Matlab software.Finally, using the theory of analogy paralleling filtration type of harmonic detecting equipment, the thesis constructs a new harmonic detecting method based on WNN.According to the characteristics of harmonic in power system and by means of analysis and research to the form approach of training samples, this paper has carried out simulation research to the proposed harmonic detecting method based on WNN by programming. The simulation result indicates that this new harmonic detecting approach is feasible and effective.