| Direct Torque Control (DTC) of asynchronous motors, which has been developed in the recent decades, is a powerful 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. In this paper, a study of asynchronous motor model is made; 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 quickly torque control, a three-value regulator is adopted. To demonstrate the validity of the asynchronous motor's direct torque control system, a simulation system of DTC is designed through MATLAB; Moreover, the characteristics of the DTC and its existing problems are analyzed in detail.Stator resistance is a significant parameter in the system of DTC; Therefore, it is important to measure the stator resistance of asynchronous motors. Stator current can revise stator resistance, and any motor parameter can't change stator current expect stator resistance; So stator current error variation and stator current error variation rate are used to tune stator resistance. This paper presents a scheme of estimating the stator resistance on-line with fuzzy-neural network due to their complicated relations. After trained off-line, the network was used to measure the resistance. Simulation results show that this fuzzy-neural network estimator can precisely measure the value of resistance and improve the low-speed performances of DTC system efficiently.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. |
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