Impact of Electric and Magnetic Loading on the Electromagnetic Stress of PM Machines

The air-gap flux density distribution generates electromagnetic stress which acts on the machine bore. The variation in magnetic or electric loading alters the electromagnetic stress pattern in the air-gap. The air-gap magnetic field varies with the level of magnetic flux contribution from armature excitation and permanent magnets. The proportion of contribution from either sources of magnetic flux depends on machine configuration. In this paper, the impact of design configurations, magnetic and electric loading on the distortion of air-gap flux density distribution are analysed. The change in electromagnetic stress, acting on the stator bore, due to the air-gap flux density distribution is investigated. The level of distortion in the magnetic flux density distribution, due to permanent magnet and armature excitation and its subsequent effect on the electromagnetic stress distribution are analysed using finite element methods. The effect of change in machine configuration on the flux from armature excitation is investigated. The spatial components of stress, its temporal frequency of oscillation and effect on structural vibration are studied using modal and harmonic analysis.