Design and implementation of compound current control strategy for improved LCL-based Shunt Active Power Filter

Shunt Active Power Filters (APFs) are powerful in harmonic elimination and reactive power compensation in distribution network. The APF prototype discussed in this paper is based on conventional three-leg converter with an improved LCL filter in the ac side, which consists of a LC resonant branch and is tuned at switching frequency. It is helpful to suppress switching ripple injected to the grid and reduce the power loss in the damping resistor. What´s more, a compound current control strategy with an outer loop of repetitive control and an inner one of Proportional-Integral (PI) control is adopted. The inner loop is used to guarantee the dynamic response, and the outer one is designed to redeem the inherent phase lag of inner loop. Consequently, excellent harmonic current tracking performance both in steady-state and dynamical-state are achieved. Experimental results of the laboratory prototype prove its feasibility and efficiency.