Torque capability and control of a saturated induction motor over a wide range of flux weakening

The first part of this paper covers an investigation of the maximum torque which an induction motor with saturated air gap inductance can generate over its permitted speed range, when voltage as well as current are limited. From the investigation, three regions of operating speed are identified, based on limiting quantities which determine the maximum obtainable torque. In each of these regions a different control strategy must be applied. When maximum torque is not required, efficiency can be optimized but this strategy should not be applied at low torque levels when good dynamic performance is required. The second part illustrates how a modified rotor flux oriented control strategy is applied to achieve full utilization of the torque capability over the whole speed range. Several measures for improving dynamic and transient behavior of the drive in the flux weakening region are suggested. Performance of the new control strategy is verified by experiments