Problems of application of direct flux and torque control methods to high power VSI-fed drives operating at low speed

In this paper, problems associated with the application of direct torque and flux control methods to medium and high power drives in the low motor speed range are discussed. A new strategy that allows avoidance of narrow semiconductor impulses is given. Another difficulty of direct flux and torque control methods is that they cannot operate with the reference torque equal zero. Here, a new technique that also allows flux self-control in zero speed and zero torque conditions is proposed by the author. The technique enables soft starting of a drive. With the proposed techniques, the direct flux and torque principle can be applied to medium and high power drives over the entire motor speed range. The proposed strategies are illustrated by results of simulation of a high power drive