Remagnetization Strategies for Induction Machines Operating with Reduced Flux Levels

Induction Machines (IMs) drives are the preferred option for high-speed railway traction drives. Electric drives in this application can work for certain periods of time with light load levels. It is possible in this case to decrease the flux level to reduce the stator current and consequently both joule and hysteresis losses. A drawback of this approach is that if a torque increase is demanded, the machine must be firstly remagnetized. Remagnetization time is determined by the rotor time constant and the applied magnetizing current. Due to the relatively large values of the rotor time constant, fast torque changes are not feasible, which eventually penalizes the dynamic response of the drive. This paper presents strategies for the remagnetization of Induction Machines. Though proposed methods are primarily intended for railways traction, they can be easily extended to other uses of IM drives.