In this paper, a new concept of variable impedance induction (Z) motor (VZIM) is introduced to combine high starting torque and high efficiency at nominal operation. The rotor is a sectionalized cage with different bar shapes for each sub-cage section. At the starting of the motor, sub-cages with high resistance are put inside the stator bore to increase the starting torque and reduce the starting current. By increasing the rotational speed, a centrifugal rotor shifter mechanism moves the rotor cage in the axial direction and brings the other sections of the rotor cage with low resistance inside the stator bore to reduce the rotor losses at the rated speed. Hence the efficiency of the motor is increased at the nominal operating point. A 5.5 kW, 4 pole prototype motor has been built and tested at our institute and the measurement results are presented in this paper.
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