IMC-based PID control of servo motors with extended state observer

Abstract

In this paper, a simple and effective internal model control (IMC) with extended state observer (ESO) is presented for the position tracking control of servo motors perturbed by uncertainties and disturbances. Firstly, a linear feedback controller is directly derived from the standard IMC principle for a prescribed tracking performance. Then, a linear ESO is introduced into the IMC-based controller for active disturbance rejection control (ADRC). However, for the ESO with a limited bandwidth, there will exist state estimation errors, which limit the tracking accuracy. To overcome this drawback, 2-degree-of-freedom IMC-based PID controller with ESO is developed for further improvement of the control accuracy. The dynamics of the tracking error is analyzed based on an order reduction technique and the ultimately bounded stability of the control system can be guaranteed. Since the IMC scheme and the ESO can be designed separately and integrated effectively to attenuate the effect of disturbances, a simple, effective and intuitive framework can be given for the analysis and synthesis of the motion control system. Finally, the effectiveness of this novel control approach is validated by comparative simulations and experiments implemented on a practical servo motor system.