Influence of rotor slot number on rotor bar current waveform and performance in induction machines

The effect of number of rotor slots on the stator and rotor current waveforms, slot and tooth flux densities and performance characteristics, such as torque, torque ripple, losses, electromagnetic force, power factor, and efficiency are numerically studied in case of a 3-phase, 8-pole squirrel-cage induction machine (IM). The IMs have been designed by using the same winding layout, stator outer diameter, stack length, stator current, and rated speed as the Toyota Prius 2010 interior permanent magnet machine. The designed IMs have 48 stator slots and the number of rotor slots is varied from 30 to 76. The geometry parameters of stator and rotor slots are kept at the same in all calculations. The harmonic content of each curve including the force and flux density curves are studied in detail. It has been revealed that the rotor slot number has a significant effect on the distortion level of the bar current and performance characteristics. It has also been shown that there is an optimal rotor slot number at which the maximum available power factor, torque, efficiency and minimum torque ripple are achieved.