Loss minimization of speed controlled induction machines in transient states considering system constraints

This paper proposes a new control scheme based on maximum torque-per-ampere (MTPA) for speed controlled induction machines. In the MTPA scheme the torque- and flux-generating currents are calculated from the reference torque. In order to attain the reference torque in the constrained regions, the loss minimization curve can not be guaranteed anymore. Instead of the optimum current, the boundary values are chosen. In the new approach the reference torque in transient states will be adapted dynamically in such a way, that the loss minimization is always pursued. To track this loss minimization trajectory exactly, especially in transient states, an optimum current control scheme with generalized predictive control is introduced. The simulation results show that the energy losses can be reduced significantly when compared to the steady state MTPA during the transient procedure in constrained regions without deterioration of drive dynamic.