Torque Ripple Minimization Of PMSM Based On Hybrid Modulation Of Direct Torque Control System

Permanent magnet synchronous motor is widely used in industrial products dueto the high energy density, simple structure and good controllability. In order tomaking the Permanent magnet synchronous motor has a good dynamic performanceand fast torque response, the direct torque control is gradually paid people’s attention.But this control method is limited by many problems such as the torque ripple, theflux and torque observer that are inaccurate at low speed. All of these problems willdestroy the performance of the direct torque control and the scope of its applications.This paper firstly analyses the mathematical model of Permanent magnet synchronousmotor and basic principle of direct torque control, makes the derivation of theelectromagnetic torque expression and the direct reason of the torque ripple. Secondlybased on these conclusions, a new method of suppressing torque ripple is proposed.In this paper, a new direct torque control of combining discrete voltage vectorand duty ratio modulation for suppressing the torque ripple is presented according tothe characteristics of the torque ripple, and the whole motor speed range is dividedinto the low-speed area and the high speed area. This method will make up for theshortcoming of traditional direct torque control that the number of the voltage vectoris rare. At the same time, it also takes full advantage of the zero vectors that cansuppress torque ripple effectively at the high speed zone.Contrast to the traditional direct torque control’s results, these prove that theimpact of the new algorithm for the overall system performance is small and owesgood torque response. The capacity of the improved direct torque control to suppresstorque ripple is better, and the stator current harmonic distortion is improved by thehybrid method. This paper also designs the hardware and software system based ontraditional direct torque control and the algorithm of the software flow chart with thehybrid method is given, and it can be the foundation of subsequent experimentalresearch.