Design Of Repetitive Control For Systems With Actuator Nonlinearities Based On Equivalent Input Disturbance Compensation

Repetitive control (RC) is widely used in servo systems that exhibit repetitive control behavior, since it has distinguished control performance for periodic signals. It provides a simple and effective method to the high performance control of a class of periodic signals for many industrial systems. However, actuator nonlinearities can drastically affect the performance of the repetitive control system.This dissertation addresses the problem of compensating actuator nonlinearities in RC systems for systems subject to input actuator nonlinearities. A design method for RC systems based on equivalent input disturbance (EID) compensation is proposed, which effectively compensates the effect of actuator nonlinearities on the performance of the repetitive control system. It provides a new way for the design for nonlinear systems. It will broaden the application fields of repetitive control.Firstly, for a nominal system with actuator nonlinearities, a repetitive control system based on improved equivalent input disturbance (IEID) compensation is presented. The input actuator nonlinearities are taken to be an input-dependent disturbance. The EID method is used to estimate and compensate the effect on the output. The high accuracy tracking for period signals can be achieved by incorporating the estimate in the RC law. A system design algorithm is developed. This compensation method requires no precise model of the input nonlinearities. It has common applicability.Secondly, this method is used to solve the problem of tracking for period signals for uncertain systems with actuator nonlinearities based on the study mentioned above, thereby to broaden the application fields of RC. A plug-in repetitive control system based on EID compensation is established. The sufficient stability criterion and the system design algorithm are developed. The disturbance rejection performance and robust stability performance are then analyzed. Simulation results show that the proposed repetitive control system based on EID compensation effectively rejects non-periodic disturbances, and it is robust for plant with parameter uncertainties.Finally, experimental validation of nonlinear repetitive control is performed on a motor system. The proposed repetitive control method based on equivalent input disturbance compensation is applied to motor speed control for tracking period signals against actuator nonlinearities. The experiment results show that the proposed method is effective and feasible in practice.