Research on LCL filter applied to shunt active power filter

Based on the maximal allowable current ripple, the switching frequency and the damping characteristic, a novel design method of the LCL filter applied to the three-phase shunt APF (Active Power Filter) is proposed. The LCL filter is effective in eliminating switching harmonics of VSI, which has better performance than LC filter and can overcome the influence of the grid parameter uncertainty. With the detail introduction of design process, an example is presented. To avoid the current resonance caused by LCL filter, damping resistance is usually needed, which increases wastage and reduces system efficiency. A novel control strategy is proposed, in which the capacity current feedback is used as damping resistance to strengthen the damp and effectively suppress the resonance of low harmonics by regulating the feedback coefficient with unchanging system resonance frequency. Simulation and experiment validate the design of LCL as well as the control strategy.