ADAPTIVE REJECTION OF PERIODIC DISTURBANCES WITH UNKNOWN PERIOD

A disturbance cancellation extension by means of Youla parametrization to a stabilizing nominal controller is investigated. In the case of a known disturbance model, disturbance frequencies or period time, it m ay be implemented directly as an add-on device to the existing control system. The nominal control system may be designed without considerat ion of the deterministic disturbances. This way it may suffice with a PID controller. It may also be a more complex one e.g., designed to ob tain certain robustness properties. For known relation between the dis turbance frequencies (one or more periodic signal) but unknown fundame ntal frequency, a freguency shaped disturbance model estimation scheme is utilized. This makes it possible to e.g., adapt the disturbance mo del to minimize the error directly with respect to the output. For per iodic disturbances the scheme implements a self-tuning discrete time r epetitive controller. To illustrate the feasibility of the approach ta ken it is used for rejecting a periodic disturbance acting on a nonmin imum-phase plant.