Direct Torque Control Of Induction Motor Based On MRAS

Direct Torque Control (DTC) of induction motors, which has been developed in the recent decade, is a powerful control method for motor drives. Following the vector control technique, the quick development of DTC makes itself a new high performance AC driving technique paralleling to the vector control.In order to weaken the torque ripple and improved accuracy of the observation, the author changes the method of regulating stator flux, the machine parameters are adapted on-line and the method of speed estimate was improved. The works in this paper was listed as follow.According to the faults of traditional direct torque control and the requirement of an induction motor's control strategy. In this thesis, designs a new speed-adaptive flux observer which identifying stator flux and speed at the same time. The observed stator flux could be applied to direct torque system. The gain matrix is got by a new and convenient method. The reference observer is based on motor state space equation, which used stator current and stator flux as state variable, motor itself as reference model, the designed observer as modulation model, speed observer as modulation parameter.The speed estimation without speed sensor is an important trend of modem AC drive. The paper analyzes the method of speed estimate based on model reference adaptive system and compares their strengths and weaknesses. An improved mutual MRAS model which was built with variable parameters is presented.Based on the element of Simulink, the simulation former of speed sensorless direct torque control system was set up, and it discusses a scheme, which is the speed sensorless direct torque control system of asynchronous motor is digitized realization based on the controller's core is TMS320F2407A. The simulation results prove that the system has preferably observe precision of stator flux even in low speed, so the control character of motor can be improved, and the system based one MRAS has high performance.