An improved phase lead repetitive controller for a linear actuator

This paper presents an improved phase lead repetitive compensator (RC) for a linear actuator (LA) system. The linear phase lead compensation provided by the proposed compensator structure compensates the phase lag of the feedback system caused by payload variations and nonlinear friction present in the LA system. Unlike conventional phase lead RC structures which use a pure linear phase advance compensator z^m to cancel the phase lag of the uncertain system, the proposed phase lead structure incorporates a phase lag compensator to counterbalance and reduce the large fixed phase angle of z^m. This produces a control structure with a larger stability region and improved tracking performance in the presence of payload variations, and nonlinearities such as nonlinear friction. A comprehensive study and a detailed analysis of the proposed method are presented in this paper. Simulation results and a comparison study are also presented to support and verify the effectiveness of the proposed method when applied to a perturbed LA system.