Design and Analysis of Asymmetric Electrical Machines for Automotive Applications

Abstract

Abstract The study has designed and optimised six different rotor topologies all with three different magnet grades with a common stator geometry. To first evaluate the maximum performance given the constrained volume and magnet mass for each topology and magnet grade with asymmetric magnet size and placement. Secondly the optimisation targets were changed from maximising performance to minimising cost and losses at two operating points important for WLTP efficiency. A brief analysis of the risk of demagnetisation during normal operation and ASC was also conducted. It was found that the asymmetric machine can deliver more torque per magnet mass and that the 3V N52 machine delivers the most torque for this size. In general, the V-rotors outperformed the U-rotors, and the V-rotors became more asymmetric from the optimisations. The asymmetric machines can not generate the same peak torque in both directions as a symmetric can and does therefore have a worse power factor in generator mode. Despite this the machines maintain a respectable WLTP efficiency at the same time as the material cost has greatly been reduced by the cost and efficiency optimisation.