A new approach to phase cancellation in repetitive control

Effective repetitive control requires that the q-filter, placed within the internal model loop for robustness, have zero phase shift and that the phase shift of the plant be cancelled in the feedforward loop. Previously reported methods of phase cancellation use a moving average q-filter and zero-phase error tracking techniques for plant phase cancellation and are memory and processor intensive. The theory and methods of using a new method to cancel plant and filter phase shift in a repetitive control system are described. This method uses a tunable time advance and enables an analog/digital repetitive control loop to be used. Comparison with previously reported methods shows that it provides good phase cancellation, reduces low frequency repetitive disturbances, is easily tunable based on the closed-loop frequency response of the system without repetitive control, is less memory intensive, and is more easily implemented