Effect of Magnetic Saturation on Performance of Series-Connected Wound-Rotor Induction Motors in Super-Synchronous Mode

Series-connected wound-rotor induction motor (SCWRIM) is capable of operation at two modes according to the rotor speed. In the first mode, the motor has a general behavior similar to that of the conventional induction motor, including running at a speed less than synchronous speed. So, it is called sub-synchronous mode. The second mode is called super-synchronous mode, in which the speed reaches twice the synchronous speed with the absence of inherent starting torque capability. In both modes, the stator and rotor windings of a slip-ring induction machine are connected in series with a proper phase sequence. This paper presents theoretical and experimental investigation of magnetic saturation effect on the steady state performance of SCWRIM in super-synchronous mode. The effect of saturation on both direct and quadrature axes inductances are considered. The motor starting to that mode has been achieved using scalar control technique via a variable voltage variable frequency (VVVF) supply. A laboratory set-up has been prepared and implemented to get experimental results that showed the applicability of the given analysis to obtain more accurate steady-state performance characteristics.