Analysis and weakening of radial electromagnetic forces in high-speed permanent magnet motors with external rotors based on shape functions

In this paper, a strategy of integrating direct-drive turbine compressors with high-speed permanent magnet external rotor motors is used to improve the problems of large footprint, low efficiency and high maintenance costs. The rotor of the motor will vibrate under the action of radial electromagnetic force when rotating, and under the action of high pressure and high speed gas, it may aggravate the rotor vibration. In the case of changing the original mechanical structure of the turbine, the vibration of the motor rotor needs to be analysed. In the paper, the radial electromagnetic force applied to the rotor is analysed. The influence of the order and size of the stator and rotor magnetic field harmonics on the size, frequency and order of the radial electromagnetic force wave is summarised. In order to weaken the radial electromagnetic force, this paper proposes a shape function about the magnetic pole size and designs a magnetic pole accordingly. The validity of the shape function was confirmed by comparing the radial electromagnetic force wave with a conventional, surface-mounted, built-in magnetic pole structure. Finally, based on the analysis of the rotor dynamics mode, the law of the effect of the change of the pole arc coefficient of the pole on the radial force was analysed using harmonic response, and reasonable conclusions were drawn.