Research On Current Control Strategy Of Shunt Active Power Filter

In recent years,more and more non-linear loads are connected to the power grid,which brings serious harmonic pollution problems to the electric power system.Active power filter(APF)is widely used as an effective device to suppress harmonics.In order to improve the suppression effect of active power filter on harmonic current,the paper focused on current tracking control strategy,designed a current controller combining repetitive control(RC)and PI control and a current controller combining repetitive control and Linear Active Disturbance Rejection(LADRC).And the current controller combining repetitive control and PI control was optimized by the improved bat algorithm,in order to further improve its harmonic suppression performance.Firstly,the mathematical models of tri-level APF based on switching function,abc reference frame and dq reference frame were established.The diode clamp type tri-level converter was used as the main circuit of tri-level APF.The capacity of APF,DC bus voltage,DC side capacitance and parameters of LCL output filter were confirmed.Secondly,a current composite controller based on repetitive control and PI control was designed.Repetitive control can track the periodic instruction signal without static error and the dynamic response of PI control is excellent.The advantage of controller based on RC+PI is that it combines the advantages of RC and PI.That is to say,it ensured the accuracy of harmonic compensation and the speed of dynamic response.After the current controller,there was a state feedback realizing the decoupling control,which improved the harmonic suppression effect.Thirdly,RC+LADRC current controller was designed.Active disturbance rejection control(ADRC)has strong anti-jamming performance,but it's difficult to be designed because of its too many parameters.In order to reduce the number of parameters,ADRC was linearized.In this paper,LADRC was applied to tri-level APF.LADRC regards the disturbance including current coupling as a comprehensive disturbance,and observes it through linear extended state observer,then compensates it.It has strong robustness,but its compensation accuracy is lower than that of ADRC.In order to improve the compensation accuracy of LADRC,the repetitive control was introduced.RC+LADRC was applied to tri-level APF to enhance the anti-jamming ability and improved the harmonic suppression effect.Finally,the mechanism of variation and step are introduced into the basic bat algorithm,the effectiveness of the improved bat algorithm is verified by testing.And the improved bat algorithm is applied to the optimization of RC+PI controller,which improves the parameter performance of the controller and the harmonic suppression performance of tri-level APF.