Wide speed range DTC drive performance with new flux weakening control [for induction motor drives]

The direct torque control (DTC) scheme is a dead-beat controller for the torque and stator flux magnitude. In the steady-state, the stator voltage vector driving the torque and the flux to their reference values is calculated during each fixed sampling period. Under transient or overmodulation conditions, an alternative switching algorithm must be used, since dead-beat control is no longer possible. In this paper, the performance of an induction motor drive with direct torque control, using two different flux weakening methods is compared. The first method is the standard one, where the flux magnitude, above the base speed, is proportional to the reciprocal of the rotor speed. The second one is a new method, which has been derived from the motor equations, when a limit is imposed to the stator voltages and the motor currents. The proposed method for the flux weakening has been experimentally tested and compared with the traditional one, showing that the torque that can be obtained from the motor can be increased by about 20%