Research On Harmonic Detection And Current Tracking For Shunt Active Power Filter

With the power electronics technology and a variety of electronic devices being widely used in the power system,harmonic harm on the grid has become increasingly serious.Active power filter harmonic is one of the most effective method for harmonic elimination,which brings theories and technologies of several disciplines together.It has become a hot spot to be researched and developed.In order to enhance the harmonic current compensation effect,this paper studies harmonic current detection method and current tracking control method systematically.This paper analyzes and compares advantages and disadvantages of different harmonic current detection method and current tracking control method.Aiming at the structure of three-phase three-wire shunt active power filter,an combination scheme for harmonic current detection and harmonic current tracking control method is proposed.In this scheme,the harmonic current is detected based on Hopfield neural network,and the strategy of double hysteresis current comparison control based on voltage space vector modulation is used to tracking current.In respect of researching harmonic current detection method,this paper establishes a corresponding Hopfield neural network architecture,according to the form of the Fourier transform of each phase current real-time sampling data.Minimized objective function is established based on the output error between the current real-time sampling and neural network.According to each harmonic sine and cosine terms characteristics of each harmonic in Fourier transform expression,energy function stability theory is used to derive the recurrence formula between the fundamental amplitude and neural network weight.According to the fundamental amplitude and phase from neural network online learning,a fundamental current reconstruction and harmonic current calculation method is established.In respect of researching current tracking control method,harmonic current tracking and double hysteresis control system is established in this paper in order to current tracking rapidity and stability.According to different intervals of current output error,current tracking targets with different emphasis points are formulated.Depending on the current error,selection rules for voltage space vector under various operating state.The current tracking and double hysteresis control method not only has good dynamic and static performance,but also can reduce the switching frequency in steady state conditions.Finally,a simulation platform for three-phase three-wire shunt active power filter is constructed in MATLAB/Simulink.The performance difference of harmonic current detection and harmonic current tracking proposed in this paper and traditional method are compared.Simulation results show that dynamic and static performance of harmonic current detection and harmonic current tracking proposed in this paper are better than the combining scheme of traditional harmonic current detection method based on instantaneous reactive power theory and current comparison control method based on hysteresis.