Torque Pulsation Of Direct Torque Control Permanent Magnet Synchronous Motor

First of all, this thesis introduces the mathematic model of the permanent magnet synchronous motor (PMSM), then simply presents the history and improvement of the direct torque control (DTC). The simulation model for DTC PMSM is set up, and the simulation results show that it has the advantage of fast torque response and the robustness to the variable parameters of the rotor, but the disadvantages of big torque and flux ripples, low inverter's switching frequency at low speed hinder its development.In view of big torque and flux ripples of conventional DTC, this thesis presents two control methods based on space vector modulation (SVM). The first is predicting the next PWM period's flux amplitude and the rotate angle to control the torque and flux. The second uses the sliding mode variable structure controller (SMVSC) to control them. Three simulation systems are set up, which are the open loop SVPWM control system, the DTC system based on predictive thought and PI torque controller and the system based on SMVSC. The simulation results show that both systems using SVM can keep the fast response characteristic of the conventional DTC and apparently reduce the stator flux and torque ripples. Furthermore, under the same conditions, simulation results show that the system applied SMVSC can produce much smaller torque ripple than the other two DTC systems and is robust to the stator flux estimated angle error caused by stator resistance variation.At last, the control system including the drive and protect circuits of the IPM and the current sample circuits and so on are designed. Using assemble language to realize the conventional DTC system based on TMS320LF2407. The experiment results shows that the torque response is fast but the torque and flux ripples are large at the low speed.