Study on digital control scheme of current loop in shunt Active Power Filter

Active Power Filter (APF) is usually used to compensate the harmonic and reactive currents which are generated by the nonlinear load, and its compensation performance mainly depends on the design of controller. This paper mainly analyzes that the compensation ability of digital Proportion-Integral (PI) controller cannot be used simply to control the output current without any steady error due to its limited current tracking capability. In order to improve the APF compensation performance, a new control method named as zero-steady-error control at the Synchronous rotating coordinate system is proposed. Through adding numbers of harmonic compensation to major harmonic currents, appointed order harmonic with outer control loop can achieve no offset regulation, meanwhile other harmonics without outer control loop remains the compensation of traditional PI controller. The feasibility of this output current controller architecture is verified completely by theoretic analysis and experimental results in detail.