An adaptive repetitive controller for three-phase PWM regenerative rectifiers

The frequency of the power system experiences variations due to various factors including intermittent renewable and distributed generators, and imbalance between generated and consumed power. This frequency variation may affect the operation of grid connected converters. For example, in case of repetitive control of grid connected converters, the grid electrical signal acts a reference signal and repetitive control requires exact knowledge of the reference signal. This paper contributes to the performance analysis of conventional repetitive controllers when the frequency of the reference signal is not fixed but is rather subjected to variations. It also proposes a novel method for making the repetitive controllers frequency adaptive i.e. the performance of the controller is not affected in variable frequency reference signal environments. The proposed scheme includes a Taylor Series expansion based fractional delay filter along with a typical repetitive controller. The proposed frequency-adaptive scheme enables the repetitive controller to maintain its good performance in both, fixed and variable frequency, environments. The novel frequency-adaptive controller offers fast on-line tuning and update of the controller when the frequency of the reference signal varies.