The flux weakening up speed operation study for the direct torque control of induction motor

For the direct torque control of induction motor, the flux weakening operation is required when the motor speed beyond the rated speed. The determining of flux weakening operation point is the key of up speed control. In this paper, the definition of stator flux maximum average synchronous speed is introduced to the direct control algorithm and the estimation formula is given as well. On this basis, the torque-slip model of stator field-orientated control is established. The flux weakening operation region can be determined by two necessary conditions which are the maximum average synchronous speed and its torque must be more than the rated speed and the damping torque (damping torque and load torque when loaded) respectively, and the flux weakening operation point is determined according to the stator core utilization. The power and current formulas at flux weakening operation point are given respectively in order to check the security areas of operation. The experiment results demonstrate the correctness and effectiveness of the determined flux weakening operation point in this paper.