A Compound Control Technology for The Current Loop of Shunt Active Power Filters

As the electric vehicle charging station generates a large amount of harmonic current, which reduces the power quality of the power system, active power filters are widely used to suppress harmonics and compensate reactive current due to their advantages of small steady-state error and fast dynamic response in electric vehicle charging facilities. This paper mainly studies the digital control strategy for the current loop of the three-phase three-wire shunt active power filters (SAPFs). Digital control is gradually replacing analog control in many fields with its many advantages such as more design flexibilities, easily realizing complicated and intelligent control methods. At the same time, traditional control methods still play an important role in digital control. As a result, the combination of advanced digital control algorithms and traditional control methods is the mainstream strategy. In order to improve the poor performance when the digital proportional-integral (PI) controller is used alone for compensation, a compound control method based on digital PI controller and digital repetitive controller is proposed where repetitive controller enhancing the performance of steady-state, PI controller improving the dynamic performance. Design method of two controllers, compensation performance, and stability judgment of compound control method are analyzed and deducted in detail. And the robustness of compound control method when system parameters are changed greatly is also analyzed. Simulation and experimental results verified that the compound control method can realize low steady-state error and quickly dynamic response.