Repetitive control for systems with nonzero relative degree

Repetitive control is considered for linear time-invariant plants with nonzero relative degree. The main objective is to clarify the property of reference signals which the plant can follow, and present conditions on the plant for achieving repetitive control. It is shown that, if a plant with the same number of inputs and outputs is minimum-phase and of relative degree one, a repetitive control system for any periodic reference signal with bounded time-derivative can be constructed. The square integral of the tracking error computed for the repetitive period tends to zero as time goes to infinity. Simulation results are presented