Optimal torque control of synchronous reluctance motor drive by predictive algorithm

Abstract

A predictive digital control of the synchronous reluctance motor drive is presented in this paper. The proposed control uses a recursive algorithm in which the reference values of d and q current components in rotor coordinates are imposed. The digital control system directly synthesizes the output vector which consists of the inverter on/off switches states. This technique results in avoiding the implementation of the traditional PI controllers and PWM technique. Under transient operation, the proposed algorithm allows the imposition of both the reference d-q current components, in order to achieve the maximum torque variation available during each sampling interval. The algorithm takes into account the magnetic cross saturation effects and the inverter voltage saturation constraint. So, the proposed control gets the fastest torque trajectory that can be exploited by the drive. Especially starting from rest, it can be shown that the proposed algorithm guarantees optimal torque step response. After the steady state torque is reached, the d-q current values, corresponding to the above torque, do not guarantee any further condition. Therefore, the proposed algorithm easily drives the above current components to the minimum Joule losses operating conditions, simultaneously keeping constant the torque value achieved. Hence, the proposed control algorithm gets the fastest start-up and the maximum efficiency, at the same time. A computer simulation study, using the Matlab Simulink tool, is conducted on the drive with the aim of highlighting the better performance of the proposed algorithm compared to the traditional and predictive (non optimal) ones.