The Research And Simulation Of The Direct Torque Control For Permanent Magnet Synchronous Motor

Permanent magnet synchronous motor has been the development trends due to it has many advantages such as small size, light weight, wide speed range, high torque, high power density, stable in low-speed running, fast response time, high overload capacity and high reliability. Direct Torque Control (DTC) is an advanced AC motor control principle. DTC principle has been widely researched with its advantages such as simple structure, robustness, swift dynamic response and easy to realize algorithm. Therefore, the direct torque control in Permanent magnet synchronous motor has become the research focus in the field of AC drive.In this paper, the direct torque control strategy of Permanent magnet synchronous motor (PMSM) has been researched and implemented. The structure and classification of Permanent magnet synchronous motors is introduced, the development of its control technique is discussed. On the basis of analyze the coordinate transformation of PMSM under different coordinate systems and its mathematical models, research the control theory and basic principles of direct torque control. Focus on the role of the space voltage vector in the direct torque control, the determination of the stator flux and electromagnetic torque, and introduce the block diagram of direct torque control. Simulate the direct torque control system of PMSM in MATLAB/SIMULINK software environment and the results show that DTC has good control performance.To solve the problems such as high torque and flux ripple of traditional DTC, introduce a space vector modulated-direct torque control principle (SVM-DTC). Analyze the generation of reference space voltage vector and PWM modulation method. Establish a simulation of SVM-DTC control system. The simulation results show that the SVM-DTC control can greatly reduce the torque ripple and improve the system dynamic performance.To solve the drawback of use the optical encoder to detect the rotor position such as increasing the cost, reducing the reliability. Use high frequency injection method to implement a sensorless direct torque control system. In the sensorless control system, a specified high frequency signal is injected to PMSM in order to trace the magnetic anisotropy of the motor, by which we can get the value of rotor speed and position. The estimation of the rotor initialization position is also discussed and simulated. Results show that the system can achieve good accuracy with this technique.