Reduction of torque ripple in synchronous machines by quasi-skew-asymmetric rotor

Torque ripple and cogging torque are thoroughly studied phenomena that occur in permanent magnet synchronous machines (PMSM). They are highly unwanted because they cause extra vibrations and noise in the system. Therefore, special design methods of PMSMs are used to reduce the torque ripple and cogging torque. This paper introduces and discovers a new method for the reduction of the torque ripple and cogging torque by applying so called quasi-skew-asymmetric rotor structure. In the paper it is shown that this method achieves similar performance advantages as of the traditional stepped skewing method and can apply several quasi-skew steps without need to apply actual skewing. This helps to avoid extra complicity of the rotor structure and extra costs related to the skewing. Further, the proposed method is very robust in terms of appearing of unwanted torque ripple and cogging torque components if some motor parameters are changed (e.g. pole geometry, stator geometry or air gap flux density harmonics), compensating all the possible torque ripples and cogging torque in a similar manner as in a traditionally skewed machine.