The disadvantages of the Brushless DC Motor over the AC motors are:
higher maintenance (due to brushes)
more expensive
In addition to the above the Brushless DC Motors have the same advantages over AC motors but they also have more advantages over Brushed DC Motors
lower maintenance (no brushes)
even higher starting torque ( Due to rare earth magnets)
even higher efficiency (over 90%) on sub fractional motors
even more compact design
better heat dissipation
lower noise
Magnetic characteristics of a brushless d.c. motor have been analyzed taking into account the magnetization distribution in the rotor magnet. The magnetization is calculated taking into account the magnetizing process of a magnet. This paper describes a method for calculating the magnetization in the magnet, and the effects of the pattern of magnetization distribution and the shape of the coil on torque ripples. The calculated results are in good agreement with the results measured. Because the flux distribution and the torque characteristics can be calculated, the optimum design of the brushless d.c. motor will be possible without repeating a trial manufacture.
