Direct model predictive speed control strategy for a PMSM fed by a three-level NPC converter

This paper presents a direct predictive speed control strategy to control a permanent magnet synchronous motor (PMSM) fed by a three-level neutral-point clamped converter (NPC). A new cost function is proposed by incorporating the speed dynamic, the current dynamic and the system constraints to have a good performance without additional outer-loop PI speed controller. The current dynamic added to cost function is based on the concept of the sliding mode control (SMC). Moreover, a load torque observer is used for better performance of the proposed method and the stability of the observer is presented. By combining new reference value of the current into the cost function, the necessity to multiple horizon in the predictive speed control (PSC) is obviated, the effects of the current dynamic on the transient conditions is considered so current distortion and torque fluctuation is reduced considerably and the controller acts as fast as an original direct speed control without cascade structure. Simulation results using MATLAB/SIMULINK demonstrate the performance of the proposed scheme