Robust position control of linear brushless DC motor drive sytstem based on μ-synthesis

A robust position controller is proposed for the uncertainty rejection problem in a linear brushless DC motor (LBDCM) drive system. Friction and load variation are the main uncertainties in the LBDCM drive system; only viscous friction has been considered in previous work. Highly nonlinear friction in the system is measured and compensated by a radial basis function network. For solving the problem of load variation, three-controllers are proposed for different normalised payload conditions. Each has their own range of tolerable-load-variation; a mass estimator is developed to extend the tolerable load variation to the sum of three. In addition, mode-switching control is applied to achieve improved time-response. Both simulated and experimental results show that the proposed controller can suppress the influence of nonlinear friction and reduce the effect of large load variations; robust stability and robust performance are illustrated by corresponding μ-plots.