Vibration Characteristics of Modular Permanent Magnet Brushless AC Machines

The radial force density harmonics and vibration characteristics of three-phase modular permanent magnet brushless AC machines, in which the coils that belong to each phase are concentrated and wound on adjacent or alternative teeth, are analysed. It is shown that, due to the presence of a large number of low and high order space harmonic magnetomotive forces, it is more likely that low frequency modes of vibration are excited in modular machines. Consequently, modular machines are more susceptible to low frequency resonant vibrations. Experimental results validate the analysis and its findings