Research On The Parallel Technology Of Modular Active Power Filter

With the growing maturity of electric power technology and the wide application of electric power equipment,the problem of harmonic pollution in power grid is becoming more and more serious.Active Power Filter(APF)can dynamically compensate for harmonic and reactive power,and it can solve harmonic pollution and improve power quality.Based on modular active power filter,the harmonic current detection algorithm,modular APF current sharing and current limiting control strategy,harmonic compensation current control strategy are studied in this paper.In this paper,harmonic detection method based on instantaneous reactive power theory,including p-q method and ip-iq method is first introduced.The method can achieve accurate harmonic compensation under ideal grid voltage condition,but it will bring detection error under non ideal grid voltage condition.Based on the instantaneous reactive power theory,the harmonic detection algorithm based on MAF-ANF is proposed in this chapter.The detection performance is not affected by the voltage distortion of the grid side,and has a high compensation accuracy under unbalanced grid voltage distortion.In this paper,three kinds of electric shunt schemes of modular active power filter are compared.The advantages and disadvantages of three current control schemes,including multistage current compensation,harmonic current frequency division compensation and capacity proportional distribution,are analyzed and compared,and the current sharing control strategy is expounded.This paper analyzes the cause of APF overcurrent,introduces the control strategy based on threshold current limiting and the control strategy based on proportional and current limiting,points out the shortcomings of the two current limiting control strategies,and puts forward a current limiting strategy combined with threshold current limiting method and proportional limiting method.The modular APF parallel system is modeled accurately,and the resonant problem of the modular APF parallel system is analyzed.In this paper,in the design of compensation current tracking controller,a double loop controller composed of the inner loop current loop is designed in detail,which consists of fast dynamic response and no static difference tracking complex harmonic current.The external voltage loop is composed of PI controller and the current loop is composed of PI controller and repetitive controller.The closed-loop stability and the harmonic compensation precision are effectively guaranteed.In this paper,a modular three-phase four wire APF main circuit parameter design,and set up the Simulink simulation model of the system,the system on load balanced and unbalanced load compensation effect were simulated,and the condition of non ideal grid voltage under unbalanced load is simulated,the simulation results verify the correctness of modular active power filter design and realization.