Investigate the influence of magnetic bridge design on mechanical strength and electromagnetic characteristics in high speed IPM machines

Interior permanent magnet (IPM) machines is a popular solution of high speed traction motor, since its advantages such as high efficiency, high power density, wide constant power range and so on. However, when the diameter of rotor of IPM machine is big enough, and the machine works too quickly, IPM machine may encounter too huge centrifugal force which will cause irreversible deformation in the thinner part of rotor. In this paper, the influence of magnetic bridge design on the mechanical stress and electromagnetic characteristics are investigated. During the investigation, the total width of bridges is constant, and with the variations of number, width, direction and position of bridges, the stress and electromagnetic characteristics are analyzed in details. By comprehensive simulations, the optimized design can have 5% stress less than conventional ones, and without the obviously negative effect on back-EMF and torque. However, unreasonable optimization will make the mechanical problem more seriously. In general, the bridge closer to the center of the magnet pole in the IPM machines will bear the centrifugal force more effectively.