Speed ​​sensorless Induction Motor Direct Torque Control

Direct Torque Control(DTC) of asynchronous motors, which has been developed in the recent decades, is a power control method for motor drives. Following the vector control technique, the quick development of DTC makes itself a new high-powered Alternating Current(AC) driving technique paralleling to the vector control. The DTC is good at its robust characteristics, simple realization and excellent dynamic response.In this thesis, the author made a study of asynchronous motor model ; according to the faults of traditional direct torque control and the requirement of an asynchronous motor's control strategy, the author changes the method of regulating stator flux to make its track approximate to a circle as possible as could. To get quick torque control, a three-value regulator is adopted. To demonstrate the validity of the asynchronous motor's direct control system, a simulation system of DTC is designed through MATLAB; Moreover, the characteristics of the DTC and its existing problem are analyzed in detail.The speed estimation without speed sensor is an important trend of modern AC drive. This thesis has discussed several primary algorithm of speed estimation and emphasized on the algorithm of speed estimate based on model reference adaptive system(MRAS). The results of simulation prove its feasibility. Due to the torque ripple of asynchronous motor in DTC system, especially in low speed, the author proposes a new, simple and effective control strategy to over this drawback by the torque-tracking method.Finally, the direct torque system without speed senor is designed using digital signal processor(DSP).