Research Of Direct Torque Control System Of Asynchronous Motor

Direct Torque Control (DTC) technology is a high-speed technology in the field of AC drive following the technique of vector control and it has rapid development in recent years. This control strategy attracts wide attention and research for its novel idea, simple structure and good performance. Differ from the vector control technologies, DTC technology uses the stator flux orientation and directly makes the flux and electromagnetic torque as the control volume, therefore the control of the electromagnetic torque is simple and fast, the system dynamic response capability is improved. Due to the inherent advantages of DTC technology, its theoretical research and technological development is receiving increasing attention, also the pace of progress faster and faster.In this article, we make direct torque control techniques applied to asynchronous motors. From a mathematical model of induction motor starting, introduced the basic theory of DTC technology. Based on depth analysis of the basis and principles, we module the DTC algorithm. In the Simulink environment, the asynchronous motor direct torque control system of quasi-circular flux simulation model is established. Simulation results show that the DTC technologies has fast dynamic response capability and directly control method, but the low-speed performance is poor, such as torque ripple is too large in low speed state and the stator current distortion is serious.In order to improve the low-speed performance of the asynchronous motor direct torque control system, a space vector pulse width modulation technology based on DTC scheme is presented, according to flux and torque deviation to predict the next sampling period required for the reference voltage vector and the use space vector modulation synthesis. We establish the simulation model in the Simulink environment, simulation results show that low-speed performance of DTC system is significantly improved, torque ripple and current distortion is decreased, system performance is effectively improved.Using speed sensorless technology to estimate the speed is an important trend in the AC drive field. Based on the analysis of several commonly used speed-sensor technology, an idea which can on-line identification speed and rotor resistance is presented, this strategy has an accurate identification of the motor speed. At last, we establish the model of speed sensorless DTC system of asynchronous motor, simulation results show the effectiveness of the program.