Repetitive control implementation with frequency adaptive algorithm for shunt active power filter

Shunt active power filter (APF), as parallel part of unified power quality modulation (UPQC), has been proved as a flexible solution for compensating the harmonic distortion caused by nonlinear loads in power distribution power systems. Digital repetitive control can achieve zero steady-state tracking error of any periodic signal under the sampling points within one repetitive cycle that must be a specific integer. However, the compensation performances of the APF would be degradation when the grid frequency varies. In this paper, an improved repetitive control scheme with frequency adaptive capability is presented to track any periodic signal with variable grid frequency, and then the variable delay items caused by time-varying grid frequency are approximated with Pade approximants. Additionally, the stability criterion of proposed repetitive control scheme is given. A three-phase shunt APF experimental platform with proposed repetitive control scheme is built in our laboratory. Simulation and experimental results demonstrate the effectiveness of the proposed repetitive control scheme.