Free-chattering non-singular terminal sliding mode control of permanent-magnet synchronous motor with Luenberger observer

This paper presents a hybrid free-chattering non-singular terminal sliding mode (NTSM) control scheme for permanent-magnet synchronous motor (PMSM) speed vector system characterized by hierarchical speed/current structure and unknown load torque. A novel NTSM-like continuous sliding mode approach is proposed for desired finite-time convergence compared with that of super-twist and second-order NTSM approach. For the outer speed loop, second-order NTSM approach is utilized to eliminate static error and improve speed response in despite of asymptotic convergence; for the inner current loop, the proposed continuous NTSM approach is used to guarantee the rapidity of current tracking. Meanwhile, a Luenberger observer is designed to estimate the unknown load torque. Simulation results validate the proposed scheme.