Selection of Rotor Slot Number in 3-phase and 5-phase Squirrel Cage Induction Motor; Analytic Calculation

With the spread of inverters, the attention of designers naturally turned to 5-phase motors, due to their advantageous properties. In this regard, perhaps the most important issue in the design of such machines is the selection of the correct rotor slot number. Many articles have been published on multiphase machines, however, only few of them deal with the rotor slot number. Although very useful results are achieved, the result is not comprehensive, systematic approach still awaits. In this paper, the behavior of the full range of 3-phase machines is calculated by using our formulas developed before, and then the method is simply transferred to 5-phase. The point is that relative rotor slot numbers are applied therefore the results are valid for any pole number on a comprehensive way. Detailed, well established design rules are provided. For better understanding of the process, the behavior of the oscillating torques generated by the synchronous parasitic torques during run-up and operation will be presented, using the equations of the unified electric machine theory. During the noise calculation, the concept of the Noise Component Equivalence Measure is introduced, which enables an accurate comparative calculation of the spectra of the radial force waves that excite the noise; it provides the final, comprehensive criteria for the selection of the right rotor slot number. With the study, the entire range of the slot number of any rotor mounted in any stator with any number of poles and number of slots is covered.