Robust Current Control of Voice Coil Motor in Tip-Tilt Mirror based on Disturbance Observer Framework

In this paper, a control methodology based on the disturbance observer (DOB) framework is proposed to improve the current dynamic characteristic and the robustness of the voice coil motor (VCM) in the tip-tilt mirror. It is shown that the open-loop current characteristic is a third-order plant, which is influenced obviously by both the electrical and mechanical uncertainties under different environment temperatures. Although the traditional PID control is helpful to improve the current dynamics, it is not able to provide enough robustness. Therefore, a new control methodology based on DOB is proposed. The plant model is simplified from third-order to first-order by considering the back-electromotive force (EMF) as the disturbance. The perturbation of the electrical parameters is compensated by the inner-loop of the DOB framework, and the perturbation of the mechanical parameters is compensated by suppressing the back-EMF. Moreover, new sufficient conditions for robust stability are presented in the control method based on ${H_\infty }$ algorithm. Compared with the traditional researches, the upper bound of the uncertainties is calculated directly in this paper. Therefore, the ranges of the electrical parameters are very clear according to the Q-filter. Based on the stability conditions, new design guidelines for the DOB-based robust current control for induction motor are also presented. Experiment results are given to show the design details and the superiority of the proposed control method.