Robust Model Predictive Speed Control of Induction Motors Using a Constrained Disturbance Observer

This paper proposes an offset-free speed control method for induction motors using a model predictive control and disturbance observer. The proposed method has cascade control loops i.e. inner-loop model predictive torque control and outer-loop robust speed control. The outer-loop robust speed controller is composed of a stabilizing MPC and a discrete-time disturbance observer. The disturbance observer estimates the effects of the parameter uncertainties and the load torque to yield an offset free speed tracking, while taking the torque limit of the motor into account. This speed controller generates the reference torque for the inner-loop torque controller. A loss-minimizing continuous control set model predictive torque controller(CCS-MPTC) considering the current and voltage constraints of the motor is used as the inner-loop torque controller. Experimental results show a significant performance improvement when the torque constraints are considered in the DOB design.