Native and Additional Cogging Torque Components of PM Synchronous Motors – Evaluation and Reduction

High performance motor drive applications require permanent–magnet synchronous motors that produce smooth torque with very low components of cogging torque. To fulfil such demands a variety of design techniques can be used to reduce or even eliminate cogging torque components. Rotor design techniques are in comparison to the stator ones much more effective, but their effectiveness depend considerably on the motor design parameters. Calculations have shown that the cogging torque can be significantly reduced while maintaining the output torque at the same level by the appropriate use of two or more presented techniques. However, the detailed analysis of cogging torque components has revealed that besides well-know native cogging torque components also additional cogging torque components exist which are provoked by assembly tolerances in mass–production. Since these two groups of cogging torque components are concerning design techniques mostly in contradiction, a minimization of the total cogging torque becomes a challenging task. A finite element method and Fast Fourier transformation were used to study the sensitivity of several motor simulation models with regard to manufacturing tolerances and assembly imperfections. On the bases of numerous simulations and analyses, it follows that manufacturing assembly tolerances and material imperfections cause the phenomena of additional cogging torque harmonic components, which are not present in the case of a perfect motor. The ascertainment that some permanent–magnet motor designs are more sensitive to the phenomenon of additional harmonic components in cogging torque than the others is an important fact for the producers of such motors, which must be seriously considered in the process of motor design optimization.