The Research On H_∞ Control And Fuzzy Control In Shunt Active Power Filter

With the development of society, the demand of"green power"is increasing. Active power filter is an effective method to improve power quality. It can dynamically compensate the harmonic whose amplitude and frequency is changing and the variable reactive power. The control system of APF includes two parts: tracking control of the reference current and stability control of the DC-link capacitor voltage. Compensating results of traditional control methods are bad and the robustness of system is weak, so the advanced control method is introduced to the design of APF controller.Firstly, the parameters of the main circuit are designed based on three-phase three-wire shunt APF and the simulation model of this typical architecture is established using Simulink. The compensating current control uses the instantaneous value comparing method and DC-link voltage control uses PI control. This model is the basis of following research work.Secondly, H_∞control theory is studied and it is applied in the current control of APF. The first order state-space model of shunt APF is established. Taking errors as external disturbance to the system, an H_∞robustness controller is designed. Simulation results certify that this controller reduces the total harmonic distortion of source current, improves the compensating effect and increases the stability as well as the robustness of system. But it has little effect on the stability of DC-link voltage.Thirdly, the basic principles of fuzzy control are studied and the fuzzy control with self-adjustable factor is applied in the DC-link voltage PI control of APF. Taking the error between actual value and reference value of DC-link voltage and its change rate as inputs, the self-adjustable factor can regulate in the whole region according to error absolute value and the outputs of system are the correction of scale factor and integrating factor. Simulation results certify that this controller can improve the stability of capacitor voltage, but it has little effect on the improvement of source current.Finally, H_∞control and fuzzy control are applied in the simulation of APF simultaneously. This synthetical control improves the control effect of source current and capacitor voltage and increases the robustness and dynamic response characteristics.