Reduction of current distortions of VSI-fed induction machine controlled by DSC method-generalized approach

Possibilities of reduction of current distortions of an inverter-fed induction motor controlled using a direct self-control (DSC) method are considered. It is shown that these distortions are of a ´reactive type´ and for standard DSC they cannot be reduced. A simple method of reduction of these distortions for DSC with a free-running hysteresis torque controller is proposed. It is based on processing of not only the stator flux value, but also of the stator phase angle. By introducing phase sectors distributed symmetrically around the motor phase axis it is possible to form flux trajectories which are much closer to a circle than the original hexagon. As these trajectories have distinguishable corners, so the flux self-stabilization, which is essential in the case of the DSC method, works well in both static and dynamic conditions. Effectiveness of a similar approach to the reduction of the reactive current distortions of an induction machine fed from a three-level inverter is also shown. The proposed techniques are illustrated by results of simulation of a high power traction drive.