Reduction of synchronous torques in induction machines using asymmetrical rotor slots

Removing the rotor skew in induction machines reduces the negative effects created by inter-bar currents. On the other hand, synchronous torques at low rotor speeds may appear, this can prevent the rotor to reach its rated speed. This paper presents a new method for the reduction of synchronous torques in unskewed induction machines. By introducing modulated rotors, having an asymmetrical rotor slot distribution, these parasitic torques can be suppressed. A simple numerical model is used to find suitable modulation coefficients for an efficient reduction of synchronous torques. This method is verified by FEM-simulations of different rotor designs. The results show that the synchronous torques can be controlled by the modulation coefficients used.