| The speed sensorless direct torque control system of asynchronous motor often experiences the operation of transient absence and reclosing of supply in the working process, because the system is speed sensorless, the accurate speed at the reclosing moment is unknown, if the identified speed is different from the actual speed greatly, it's likely to make the system fail to be magnetized, and then the whole system can't run.Based on the mathematic model of asynchronous motor, this paper makes a study of basic principle and structure of direct torque control which has circle stator flux curve, and then takes the identification method based on adaptive states observer to obtain speed, the adaptive law is deduced by Lyapunov stability theory, and the pole configuration method is taken to configure observer gain matrix to insure the system's stability. The stator flux obtained from the observer is utilized for direct torque control to improve the performance of system in low-speed area. The research of restarting with unknown speed control is carried out in this speed sensorless direct torque control system platform based on adaptive states observer, after analyzing the transient situation of absence and reclosing of supply, a restarting control method is introduced, this method is aimed at magnetizing to insure the system's transition at the transient moment of reclosing, it's simple and easy to be applied.In the Matlab/Simulink platform, the simulation is taken to analyze the the results of principle research. It can be shown that the speed identification method based on adaptive states observer has good performance, and the performance of system in low-speed area is better than system with conventional stator flux observing method. The transient situation analysis in the moment of absence and reclosing of supply and the validity of restarting control method are validated through simulation, the results are identical with the theory analysis. |
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