Effect of Magnetic Saturation and Iron Losses on Performance of Series-Connected Wound-Rotor Induction Motors in Sub-Synchronous Mode

Series-connected wound-rotor induction motor (SCWRIM) provides an electromechanical torque in two modes of operation. In the first mode, the rotor speed is exactly equal double the synchronous speed. With absence of inherent starting torque capability, the rotor speed in this mode only depends on supply frequency and number of poles for stable range of operation. In the second mode of operation, SCWRIM rotates at slightly less than the synchronous speed depending on the connected machine load. Therefore, this operation is known as sub-synchronous mode. In this mode, the motor has the capability of self-starting, and it runs in a similar manner to that of the conventional wound rotor induction motor operation. The influence of magnetic saturation and iron losses on steady-state performance of SCWRIM in sub-synchronous mode is examined theoretically and experimentally in this paper. The motor behavior has been investigated with considering magnetic saturation effect on both direct (d) and quadrature (q) axes flux linkages. The performance investigation has included the effect of magnetic saturation and iron losses at variable values of voltages and frequencies using scalar control technique via a variable voltage variable frequency (VVVF) supply. Finally, the simulation results are compared with experimental measured values to show the effectiveness and accuracy of the proposed approach of including magnetic saturation and iron losses effects.