Abstract
This paper investigates the ripple phenomena in digital repetitive control systems, where the plant to be controlled is a continuous-time system while the controller to be designed is a discrete-time system and reference and/or disturbance inputs are periodic. We can see from the Internal Model Principle that the steady-state error is zero at sampling instants if we implement a model of generator for the periodic signals in the feedback loop and stabilize it. However, there may exist undesired phenomena or ripple behaviors between sample instants.
It is shown that the larger ripple is mainly caused by the larger level of steady-state control input based on the steady-state analysis. We introduce an index for the level of the ripple which is related to the level of the steady-state control input and uniquely determined by discretized plant. We also proposed a design method using asynchronized sampling for the attenuation of the ripple.
