The Simulation Study On Speed Sensorless Direct Torque Control System

In the field of AC drive field, direct torque control (DTC) theory is a kind of newly control one which follows the vector control theory. The method has the performance of quick dynamical response, simple structure, and easy design because it hasn't complicated vector transform. The speed sensorless method is a heated-spot in the field of AC drive nowadays. Mechanical speed sensor not only increases the cost, but also has the disadvantage of inconvenient fixing and maintenance. The speed sensorless method, that is, application to software instead of mechanical speed sensor, has good prospects.This paper builds a mathematic model for asynchronous motor and tells the basic principle of direct torque control. In oval stator flux control scheme of DTC system, the flux linkage regulator and the torque regulator are elaborated in detail. This paper studies speed sensorless techniques and analyzes emphatically of speed identification method based on model reference adaptive system. The mathematic models of speed identification schemes respectively based on rotor flux linkage and counter-electromotive force are given and the two speed identification schemes are applied in DTC system. In the range of middle and high speed range the scheme based on rotor flux linkage works well; but in the range of low speed range the scheme based on counter-electromotive force does better. In order to enhance speed dentification's precision in the whole range of speed, switching between two models is done while system's speed goes through from high speed to low speed, in the meantime GA optimizes adaptive law on line to reduce ripple of torque. The simulation shows the effects of changeable-structure speed identification is very ideal.The paper uses Matlab/Simulink to simulate oval flux linkage DTC system, and constructs different simulation models in various speed range and simulates. The simulation results prove the scheme of combination of changeable-structure and parameters intelligent optimization can enlarge speed regulative range availably.