Cogging torque, torque ripple and radial force analysis of permanent magnet synchronous machines

This dissertation presents a methodology for designing low noise small permanent magnet synchronous motor (PMSM) drives by addressing the issues of cogging torque, torque ripple, acoustic noise and vibration. The methodology incorporates several pole shaping and magnet skew schemes in different motor topologies with similar envelop dimensions and output characteristics intended for an automotive application. The developed methodology is verified with finite element analysis (FEA) and experiments.;A comprehensive design methodology has been developed for obtaining the analytical design of the machine for a given set of output characteristics. Using the FEA, the effects of various magnet shapes and skew arrangements on the machine performances (e.g. cogging torque, torque ripple etc.) have been analyzed. The FEA and experimental results show that for certain magnet designs and configurations the skewing does not necessarily reduce the ripple in the electromagnetic torque, but may cause it to increase. An analytical model to predict radial vibration due to magnetic radial pressure on the motor structure has also been developed. This model is used for predicting the noise power level for several motor topologies designed for similar power level applications.;The predicted noise levels are utilized to develop guidelines for selecting motor configurations, internal dimensions and winding types for a low-noise PMSM.;The selection of low-noise PMSM is not a straightforward one; rather it is a compromise between torque harmonics and radial vibration of the machine. Some PMSM configurations with less radial vibration might posses excessive torque ripples and thereby violate other requirements to be less noisy.;Experiments are conducted to record the torque ripple variation for different magnet shapes and skew in order to validate the results of FE models. The experimental results correlated well with the FE computations.