Discrete repetitive controller with a non-integer number of samples per cycle and its application to an active power filter

Repetitive controllers are used to track periodic references or to reject periodic disturbances, exactly. When implementing this type of controllers digitally, the sampling period has to be chosen so that there is an integer number of samples within a period of the signal to be tracked or rejected. Otherwise, the controller performance deteriorates dramatically. This requirement is not always easy to fulfill when the signal period is not known exactly at the design stage or when it changes during operation. The robustness of the controller performance can be improved implementing higher-order repetitive controllers which require more memory allocation than the first-order type. This paper presents a simple addition for a first-order discrete repetitive controller to tackle applications in which the period of the reference signal or disturbance is not an exact multiple of the sampling period. petitive controller with a non-integer number of samples per cycle and its application to an active power filter of small errors in the mains frequency estimation for an active power filter to be used in an electrical-energy distribution system. The paper illustrates how the results of a previously-tested active power filter are improved with the addition proposed.