Advanced digital repetitive control of shunt active power filter

Internal model principle based repetitive control is widely used in tracking sinusoidal periodic signals of known fixed frequency. The conventional repetitive control (CRC) offers a promising and accurate current control strategy to regulate the sinusoidal input currents at the grid side of shunt active power filters (SAPF) in the presence of fixed reference frequency of the system. However, in practical applications, the frequency of grid varies in limits (though very small) specified by the grid codes. This grid frequency variation causes degradation in the performance of the CRC controller & thus there is a need for a unified repetitive control algorithm to operate satisfactorily under fixed and variable frequency conditions. Lagrange interpolation based fractional order repetitive control provides frequency adaptive capability but it suffers from the online tuning and parameters updating issues. In this work, a Taylor Series expansion based advanced repetitive control (ARC) scheme for shunt active power filters is proposed, to deal with the issue of variable frequency arising in power systems due to a multitude of reasons such as the mismatch between source and load powers. The analysis and synthesis of the ARC system are also presented. The proposed ARC scheme offers optimal performance and thus maintains the grid currents sinusoidal with acceptable and very low total harmonic distortion (THD), in the presence of non-linear loads and variable frequency of the system. The proposed ARC has been applied to a three-phase SAPF. Simulation and experimental results are provided to demonstrate validity of the proposed ARC.