Modeling and estimation of core losses for doubly-fed wound rotor induction machine

Wound-rotor induction motor drive fed from inverters on both the stator and rotor side is discussed. The sensorless control scheme for the motor requires a V/f-type direct frequency control preferably on the rotor side, with either vector control or direct torque control on the stator side. Selection of any frequency for the rotor side inverter keeping the rotor flux constant is possible. This rotor frequency will decide the selection of the stator side frequency. In this paper, a study on core loss at different rotor injected frequencies is carried out at different loads. Also to operate the motor at an optimum efficiency during any loading condition, a method for correct selection of stator and rotor frequency is studied. It is also shown that core losses constitute a considerable amount of the total losses and hence should not be neglected for the sake of efficiency. Experimental results on a real machine are presented in support of the proposed concept.