Nonlinear disturbance observer-based model predictive control for magnetically levitated slice motor

Towards magnetically levitated slice motor (MLSM) which is a seriously coupled and nonlinear multi-input–multi-output system with fast dynamics, this paper proposes a novel nonlinear disturbance observer-based model predictive control scheme that decouples the outputs and enhances the system response speed and anti-disturbance capability while guaranteeing robustness and static performances. Based on the nominal mathematical model of MLSM, the closed-form MPC is employed to derive the optimal control inputs offline. With the derived inputs applied, the outputs are decoupled and meanwhile, a fast dynamic response is ensured. Nevertheless, the outputs suffer from various disturbances, including matching and mismatching ones. Aiming to eliminate disturbances from the outputs, a disturbance compensation matrix is deduced while a nonlinear disturbance observer is utilized to give the disturbance estimation. Finally, experiments together with simulations demonstrate that the proposed controller presents superiorities when compared to the dual-loop PID-PI controller. In the experiments, the settling times of speed step and displacement step are reduced by 54.5% and 95%, respectively and overshoots are avoided. Displacement deviation induced by speed step is 0 mm while it is an average of 0.27635 mm under PID-PI controller. Moreover, when disturbed, recovery time and deviation value of the system are reduced simultaneously by over 50%.