Research On DTC Of PMSM Based On Variable Structure Sliding Mode

Permanent magnet synchronous motors (PMSM) have been widely used in high-performance drive systems for its advantages, such as high torque-to-inertia ratio, high efficiency, compactness, high reliability and easy maintenance. Sensorless control of PMSM has become one of the hot research topics in the field of motor control, which not only reduces system cost, but also improves system reliability.Compared with vector control method, the direct torque control (DTC) has the advantages of simple configuration, fast torque control, and robust with respect to motor parameters. But the traditional DTC strategy has the drawback of serious current ripple, which is based on switch table, does not suitable for sensorless control of the motor. In this paper, a torque angle control strategy introduced into the PMSM direct torque control system improves the performance of the system greatly, and provides a good platform for the follow-up study of the sensorless control of the motor.Large chattering of the traditional sliding mode observer would result in poor static performance of the control system, and the phase lag caused by using the low-pass filter which cannot be exactly compensated delays the system response. So based on higher-order sliding mode control method, a higher-order nonsingular terminal-sliding-mode (NTSM) observer is presented by the nonlinear sliding hyperplane which is the extension of the traditional linear hyperplane, and the design of appropriate control rate. The stability and robustness of the system is proved by Lyapunov theory. The simulation results show that the proposed NTSM observer compared with the traditional sliding mode observe can effectively reduce the chattering, estimate motor speed more accurately and improve the static and dynamic performance of sensorless control system.Because of its parameter dependence and poor robustness, the conventional PI speed controller has been unable to content the high-performance requirements of motor control. So the NTSM control strategy is applied to design the speed controller, and the comprehensive simulation results show that the performance of the control system is further improved, and also has strong robustness.