Research On Three Phase Four Switch Shunt Active Power Filter Based On Repetitive Control

Active power filter (APF) in the treatment of harmonics control, reactive power compensation and power quality improvement achieves remarkable results. The research object of this paper is three-phase three-wire grid current, this paper analyzes the traditional APF circuit topology in detial, three-phase four-switch shunt active power filter (TFSSAPF) is proposed for small and medium capacity for harmonic control and reactive power compensation on the basis, this paper mainly analyzes its harmonic current detection method, Space Vector Pulse Width Modulation (SVPWM) algorithm, command current control strategy and DC side series double capacitor voltage control strategy and so on, the improvement of traditional repetitive controller is used in TFSSAPF system.Firstly, this paper introduces harmonic current detection algorithms of the traditional shunt active power filter, analyzes the implementation of ip-iq Harmonic Current Detection Algorithm in theoretical research and simulation. On the basis of the adaptive filtering’s principle, variable step size least mean square (LMS) algorithm proposed in this paper is applied to the harmonic current detection of TFSSAPF system. The simulation experiment tests that variable step size LMS harmonic detection algorithm is more accurate and fast, effectively solves the contradiction between steady-state error and convergence speed.Secondly, this paper finds that the traditional SVPWM algorithm does not apply to TFSSAPF systems, proposes a seven-segment SVPWM algorithm to achieve three phase compensating current output in TFSSAPF system. Then this paper studies the working principle of repetitive controller, and traditional repetitive controller is improved, finally it is combined with the traditional PI controller in parallel so as to compose instruction current control system, the instruction current control system effectively suppresses the periodic disturbance, makes the compensation current output be able to track and control instruction current.Moreover this paper analyzes the reasons of DC side voltage fluctuation and the traditional method of DC side voltage stability, on base of the conventional method, this paper proposes a DC side series dual capacitor voltage control strategy suited for the TFSSAPF system, with variable step size LMS harmonic current detection, effectively stabilizes the DC side series dual capacitor voltage so as to ensures the operation of the TFSSAPF system stablily.Finally, this paper uses MATLAB7.0/simulink to make simulation modeling of TFSSAPF system, through a comparative analysis, the result of TFSSAPF system simulation verifies that the TFSSAPF system achieve the purposes of harmonic suppression and reactive power compensation, the load current distortion rate is reduced from the initial 28.87% down to 3.13%, indicates that the proposed harmonic detection algorithm, seven-segment SVPWM algorithm and instruction current control system in the management harmonic current achieve remarkable results, the results of simulation shows that this method has a certain engineering value.