CORRECTION OF FLUX ERROR IN LOW SPEED RANGE OF DTC DRIVES OF INDUCTION MACHINES

The conventional direct torque control (DTC) method suffers a flux drop at low speeds, which is due to the long selection of zero (neutral) voltage vectors in these speed areas. Past studies with the continuous switch of direct and reverse active vectors to achieve proper flux adjustment, this procedure causes high and consecutive overshoots in the hysteresis band that causes a sharp increase in the switching frequency and increase in the torque and current ripple, which means decrease in the drive efficiency. In this article, a modified method for setting the standard DTC current is introduced, which can be achieved by controlling only one band (low or high band) at low speeds. The introduced method by reducing the selection of zero voltage vectors and at the same time minimizing the number of reverse voltage vectors prevents the loss of flux in low speed areas. In addition, it is effective in reducing torque ripple and current in low speed mode and a significant reduction in switching frequency will also be achieved. The effectiveness of the proposed method in the simulation which is done in MATLAB software will be proved.

Keywords:

Direct Torque Control , flux adjustment , Induction motor