Speed ​​sensorless Induction Motor Direct Torque Control System

The direct torque control theory is a kind of new control theory followed the vector control theory in the field of alternating current drive. The method has the performance of quick reaction, simple structure, and easy design because it hasn't complicated vector transform. The speed sensorless method has been a focus in the field of alternating current drive since it came into being. Using speed sensor not only increases the cost, but also has the disadvan-tage of inconvenient fixing and maintenance. So using software instead of speed sensor, the speed sensorless method, has good application prospect.This paper makes a study of asynchronous motor model and the basic principle of direct torque control. The DTC system that has six-corner and the circle stator flux curve is analyzed in details. The torque ripple is weakened since the torque regulator of the control scheme which has circle stator flux curve. A new control scheme is proposed, which has eighteen-corner stator flux curve and better current curve. These control schemes are applied in different situation and speed range. This paper also makes a profound study of speed sensorless technique and analyzes emphatically the method of speed estimate based on model reference adaptive system. Three schemes of speed estimate are proposed. After applied in the direct torque control system, it seems that the scheme of speed estimate based on full-order flux observer is perfect. And the stator flux observed by the full-order flux observer can be directly applied in the direct torque control system.In this paper the DTC systems that have different stator flux curves are simulated detailedly by Matlab/Simulink. The simulation models of three speed estimate schemes are constituted and the speed sensorless direct torque control system of asynchronous motor is simulated. The simulation result accords with the analysis of theory.