Disturbance Observer-Based Repetitive Control System With Nonminimal State-Space Realization and Experimental Evaluation

This brief develops a disturbance observer-based repetitive control system using a non-minimal state-space (NMSS) realization where all state variables correspond to the system’s input and output variables and past values. Tracking a periodic reference signal or rejection of a periodic disturbance signal is achieved by including a disturbance observer to estimate an input disturbance containing the same frequency characteristics. This new approach differs from previously published designs because it separates the design procedure into two tasks: first, stabilization via state feedback control; second, independent incorporation of the periodic modes via estimation of the disturbance. Moreover, the new design naturally contains an anti-windup mechanism when the control signal reaches its maximum or minimum value. Results from the experimental evaluation are given, including a comparison against a design that constructs a minimal state controller using an observer. These results demonstrate that the new method can deliver significant performance improvement, with excellent disturbance rejection and reference tracking.