Stator Voltage Vector Direct Torque Control of induction machine

This paper presents improved high speed Induction Motor (IM) torque control algorithm that achieves full inverter voltage utilization in field weakening and smooth speed transition from the base speed to high speed region. The Stator Voltage Vector Direct Torque Control (SVV DTC) algorithm simultaneously controls IM torque and rotor flux by regulating stator voltage angle and amplitude in the base speed region, and by regulating only the voltage angle in the field weakening region. Fast torque dynamics is obtained in wide speed range by using torque regulator with variable gain. The main benefit from the proposed algorithm is in field weakening range, in which the machine is supplied by maximal available voltage without outer flux trajectory reference. This approach enables full utilisation of both magnetic material of the machine and power capabilities of the inverter, which is not possible with traditional vector drives with current regulators. Transition from base speed region to field weakening is obtained by simply limiting the output voltage. Experimental results gathered on the high speed low cost IM drive confirm the effectiveness of the proposed SVV DTC approach.