Research On Harmonic Detection And Simulation Of Active Power Filer Based On Empirical Mode Decom-Position

The harmonic pollution of power system is becoming more and more serious with the wide application of nonlinear equipment,especially the micro grid.Therefore,it is of great significance to study the performance of harmonic detection methods,and to take effective measures to restrain harmonics by analyzing the results.Compensating the grid current active filter is effective measures to restrain the harmonic current,the shunt active power filter as the research object,points out that the harmonic current detection affect the performance of shunt active power filter.The first of this paper,a method of harmonic detection based on empirical mode decomposition is proposed for the shortcomings of traditional detection methods.By using the empirical mode decomposition,sinusoidal signal containing harmonic is decomposed into intrinsic mode components of each order harmonic and the power frequency component,in order to detect the harmonic component of the grid.It carries on a simulation comparison with harmonic detection method based on the algorithm,shows that the empirical mode decomposition as an active power filter for harmonic detection has a certain advantage in the performance of harmonic detection accuracy.Secondly,some problems have been studied and improved,while the empirical mode decomposition is applied to harmonic detection.(a).In the original algorithm,the stop condition is too harsh to achieve.In this paper,the modal amplitude and the estimated function are regarded as the condition for the termination of component and the number of frequency about FFT analysis signal is treated as decomposition termination conditions.The stop condition in the foundation not only can meet the requirements of the algorithm,but also be easy to realize.(b).The problem of the end effect of the algorithm is improved by using the linear extrapolation method.Through the simulation study,the extension method can effectively restrain the end problem.(c).For empirical mode decomposition process,modal aliasing problem is inevitable.Simulation analysis shows that application of the method in harmonic detection is easy to occur in high frequency aliasing.It means high order harmonic is easily superimposed together,so in the low frequency component is detected out,we should minus the low frequency signal from original signal and the rest of the signal repeat cycle process of empirical mode decomposition until all frequency components are separated.The simulation results show that the method can effectively improve the phenomenon of mode mixing.Finally,a three-phase active power filter model is built in MATLAB/SIMULINK.The simulation results show that the harmonic detection of active power filter based on empirical mode decomposition is not only feasible,but also can improve the accuracy of harmonic detection,which can optimize the performance of the active power filter.