Repetitive Control Of Active Power Filter With LCL Filter

With the rapid development of power electronic technology and its application,a large number of harmonic current and reactive power have been injected into the power system,which is a severe problem to the quality and safe operation of the power system.The Active Power Filter(APF)is a kind of device which can control harmonic current and reactive power compensation efficiently.As a result,APF is used more and more widely,and the stability and reliability of APF get extensive attention.This paper focuses on filtering switching high frequency harmonics caused by APF and tracking compensation reference current of APF in fault-tolerant condition accurately and rapidly.For filtering switching high frequency harmonics,mathematical model of LCL-filter is established in order to analyze the filtering principle of LCL-filter.It is pointed out that the filtering effect of LCL-filter is better than traditional L-filter.The method of designing parameters for LCL-filter is provided,including the parameters of passive dampers when using the passive damping suppression method.Capacitor current feedback control strategy is proposed to suppress resonance of LCL-filter effectively,which overcomes the problems of heating generation,damping loss and weakening high frequency attenuation characteristic of traditional L-filter.For tracking compensation reference current of APF in fault-tolerant condition accurately and rapidly,the mechanism of fault-tolerant APF is studied and mathematical model of three-phase four-switch APF with LCL-filter is established.Based on the internal mode theory,by analyzing proportional resonant controller,the principle and structure of repetitive controller are elicited.The trantional repetitive controller is improved to enhance the dynamic response speed by designing a hybrid repetitive control method with PI controller.This hybrid repetitive control method is with both good steady-state characteristics and dynamic characteristics.The control system of TF-APF with LCL-filter is designed and MATLAB/Simulink is established.The simulation results show that LCL-filter with active damping is with good effect for filtering high frequency harmonics and good effect for suppressing resonance,as well as the hybrid repetitive control method is with both good steady-state characteristics and dynamic characteristics.