Multirate Fractional-Order Repetitive Control of Shunt Active Power Filter Suitable for Microgrid Applications

This paper presents a multirate fractional-order repetitive control (MRFORC) of three-phase shunt active power filter (APF) suitable for microgrid applications. The proposed APF control scheme includes an inner proportional-integral control loop with a sampling rate identical to switching frequency and an external plug-in repetitive control (RC) loop with a reduced sampling rate. The MRFORC loop is implemented in the dq-frame with interleaving for the reduction of computational burden in each control cycle. Moreover, in order to deal with the harmonics in the presence of wide grid frequency variations, FORC, which replaces the fractional-order elements with the Lagrange-interpolation-based finite impulse response filter, is adopted instead of the conventional RC. The synthesis, stability analysis, and parameter tuning criteria of the MRFORC system are derived in detail. A step-by-step design example of the proposed controller is also given in this paper. Finally, experiments are performed to validate the feasibility and effectiveness of the proposed scheme.