Research Of Permanent Magnet Synchronous Motor’s Direct Torque Control

Permanent magnet synchronous motors (PMSM) have many advantages, such as small size, simple structure, low weight, excellent energy efficiency and high power density. With the rapid development of permanent magnetic material, power electronic technology and modern control method, the PMSM’s application prospect would be broader. Direct torque control (DTC) is another high performance control theory after vector control (VC), but in traditional direct torque control system, the inverter’s switching frequency is not constant. And flux linkage and torque’s ripple is terrible.Firstly, the stator flux observation methods, speed control strategies and speed-sensorless techniques were summarized. Then the traditional direct torque control system, base on PMSM and DTC’s theory, was simulated. And its many defects were pointed out.Secondly, space vector pulse width modulation (SVPWM) was elaborated, and the traditional DTC system’s hysteresis comparator and selecting table were replaced by it. The simulation results showed that the flux linkage and torque’s ripple was reduced. According to the shortcomings, which were brought by the traditional DTC system’s voltage integrator, the extended kalman filter (EKF) was designed, which was used to observe the stator flux and rotor speed. Then through the contrastive analysis of simulation results, the flux linkage and torque’s ripple was further minimized and the estimated speed could accurately track the actual speed.In addition to, the traditional PI controller was sensitive to changes of environment and system parameters. So the active disturbance rejection controller (ADRC) was designed to control the speed loop in this article. And each component of ADRC was detailly analyzed. Through emulation results, it could be known that the ADRC not only inherited PI controller’s fast response characteristic, but also had enhanced anti-jamming ability, lower overshoot and steady-state error.Finally, the hardware circuit was designed and programming, compiling and debugging of the system was finished, which centered on DSP TMS320F2812. And the control strategies were proved based on the experimental platform.