Increasing the dynamic torque per ampere capability of induction machines

The objective of this paper is to present a novel means of increasing the dynamic torque per ampere capability of induction machines. The method developed is based on use of an indirect field oriented controller (IFOC) for the induction machine. It is well known that IFOC allows the rotor flux amplitude to be controlled by the d-axis component of stator current. It is also well established that the flux-producing component of the stator current may be controlled independent of the torque-producing component of the stator current. The principal constraint, however, is that the amplitude of the peak current (the vector amplitude) is limited by the power electronic switch ratings. This constraint implies that optimal partitioning of the current components should be possible. Previously used methods have optimized steady state efficiency or steady state torque per ampere. This paper identifies a dynamic method which achieves transient torques over 35% greater than the prior methods. The limitations of the method and its sensitivity to detuning is also examined