Research On Techniques Of Three-level Active Power Filter

At present,the electricity is a kind of secondary energy that is the most widely used,has the minimum pollution and is the most convenient.With the development of power electronic technology,there are more and more power electronic devices in the grid.Lots of harmonic pollution cause voltage and current distortion.Now,using APF to compensate harmonic is the most effective method to solve the harmonic pollution of power quality.This paper investigates the harmonic compensation problem for a three-level APF.A split-phase dual control scheme is presented to harmonic compensation.By tracking harmonic current which is extracted from load-side current,a preliminary fast compensation is provided.In order to improve the compensation effect,compensation error is extracted from grid-side current and taken as a control variable to make it as small as possible.Different detection algorithms are used in the sampling current on both sides of load-side and grid-side.For the purpose of detecting primary instruction current rapidly,the i_p-i_q detection algorithm is adopted to extract harmonic current from load-side.While compensation error from grid-side is extracted by using Fourier analysis based detection algorithm.Combined with the strategy of each harmonic controlled individually,the harmonic compensation accuracy can be significantly improved.Since split-phase control of harmonic current is kept all the times during compensation control of the system,this control scheme is also applicable when the harmonic current of three phases is imbalance.Simulation results are given to illustrate the obvious advantages of the proposed split-phase control scheme.In addition,the working princi_ple,modulation method and neutral-point potential control strategy of three-level APF are introduced briefly.The design method for LCL parameters of the output filter of three-level APF is also proposed.Hardware design and test of the whole system are given finally.