Calculation of negative torque caused by slot ripples of induction motors

A method to calculate the torque of induction motors considering the effects of harmonic core losses is proposed. The negative torque caused by the eddy current and the hysteresis phenomena in the stator and the rotor core is calculated from the time variation of the magnetic field distribution obtained by the nonlinear time-stepping finite element analysis. The calculated negative and total torques agree well with the experimental results. It is clarified that the negative torque is not negligible in the case of the motor with semiclosed slots and that the accuracy of the torque calculation is improved by the proposed method.