Optimal rotor bars number in four pole cage induction motor with 36 stator slots - Part II: Results

The identification of the optimal number of rotor bars in grid-fed, four-poles, three-phase cage induction motor is addressed in this two-part work for the frequent case of 36 stator slots. The optimization criterion being adopted is the minimization of the electromagnetic torque pulsations in fullload steady-state conditions. In Part I of the work a parameterized winding function (PWF) model was successfully validated through commercially available finite element software. In this Part II of the work, electromagnetic torque is investigated using the validated PWF model as it allows for investigating a wide range of design alternatives in a very short time, taking into account the skewing of rotor bars. Electromagnetic pulsations for different continuously changed number of rotor bars in a rather wide range are numerically evaluated using the torque ripple factor as a performance index. The evaluation is applied to both possible practical cases of unskewed rotor bars and rotor bars that are skewed by one stator slot pitch.