Study On Active Power Filter Based On Internal Model Principle

With more and more serious harmonic pollution, active power filters are playing an increasingly important role. Since the level of harmonic compensation is greatly affected by the current-tracking control method of APF, how to improve the steady-state accuracy and dynamic response of a system is the key issue in the realm of active power filter.Traditional PI current control is not able to perform non-static-error tracking towards sinusoidal signal. On the other hand, increasing the bandwidth of the system brings stability problems. However, resonant control and repetitive control can increase on a certain frequency with a significantly decreasing steady-state error. Currently, there are many studies on resonant current control and repetitive control, but few papers analyze the relationship between internal model control and repetitive control and the differences between resonant control and repetitive control.This study starts from the typical principle of deriving repetitive control methods from internal model, and then analyzes the relationship between resonant control and repetitive control. Finally, it applies this two control methods in active power filter in order to improve the compensation. The main contents include:The first chapter introduces the background information of this study, including the generation of harmonic and its harm as well as current study achievement of APF. The importance of this study is given as well.The second chapter deals with the circuit structure and working principle of three-phase four-wire shunt active power filter. The mathematical model of this system is established and the steady-state error and dynamic characteristics are analyzed. In addition, the theoretical analysis is verified in a20kVA active power filter prototype.Chapter three describes the implementation mechanism of internal model principle. The mathematical process is derived from the internal model principle to repetitive control. Also, the relationship between resonance control and repetitive control is analyzed.Chapter four is the application of the two methods, resonant control and repetitive control, in the APF control. Then I analyze the stability of the system and the design of two controller parameters, as well as the analysis of the steady-state error and dynamic characteristics. In a20kVA active power filter, the steady-state error and dynamic characteristics of the system using the two methods is verified, and the results are compared with that of the traditional PI current control.Chapter five is the conclusion of this study and the prospects of future research.