Simulation Of Direct Torque Control System On Speed Sensor-less Asynchronous Motor

Induction motor has been used everywhere in industry. The improving of the automatic technology in industry brings the stricter requirement to the motor control system. To certain extent, whether the development of motor control system can keep up with the pace of the industrialization will affect the whole domestic economy.The highest precision, shortest response time and simplest computing are the eternal destination of motor control system. Direct Torque Control (DTC) was advanced and developed based on these objects by western country -Germany. Nowadays, it has become the most important control theory in induction motor control system just because of its characteristics such as simple computing, low reliability to motor parameter and good dynamic and statistic characteristic. At first this thesis introduces the basic principle of direct torque control on asynchronous motor. Through mathematics model of asynchronous motor stator flux and torque can be got. After the analysis of the state of converter switches, the voltage space vector is received. On the basis of hexagon stator flux trace method of traditional direct torque control, by changing the regulation of stator flux, hexagon and approximate round trace of stator flux can be got when using different voltage space vector. The fast regulation is realized when three-value regulator is used to adjust torque.Because in U-I model flux observation pure integration element is adopted, it brings about two problems of DC drift error and initial integration error. These errors will produce alternating component on the amplitude of stator flux to cause stator flux circle deformation, and increase torque ripple and motor produce vibration noise. A new stator flux observer based on the low-pass filter is designed in the paper. The flux observer with close-loop amplitude compensation can eliminate DC drift and integration error. It can not only improve the accuracy of flux observation, but also show higher robustness for motor stator resistance.