A double-loop current control strategy for Shunt Active Power Filter with LCL filter

Shunt Active Power Filter (SAPF) is suitable to compensate current-type harmonics caused by nonlinear load, but high compensation precision is difficult to be obtained due to very high slew rate of harmonic current, output impendence of Voltage Source Converter (VSC) and control loop phase lag. LCL-filter with high attenuation ratio and small LC parameters is appropriate to be used as output filter considering the mentioned reasons. However, LCL-filter, as a third-order resonant circuit itself, is difficult to be stable. This paper proposes a novel control strategy for shunt active power filter with a LCL output switching filter. It integrates an outer loop of grid-side filter current regulator and an inner control loop of capacitor current feedback, which essentially imitates an active damper or a virtual resistor. Based on this double-loop control scheme, the SAPF can dramatically improve its efficiency and high quality steady-state grid current waveform and fast-dynamic response can be obtained even under the case of serious distorted grid voltage. Analysis and simulation results validate the correctness and feasibility of the proposed control strategy.