Lightweight, compact and inexpensive DC permanent magnet motors are well suited for low cost high production use in industry. Unfortunately, the audible noise emanating from these motors can cause a false negative perception of the motor's quality. In cars, for example, fan motor noise can be a nuisance. The objective of this thesis is to examine the connection between motor noise and the line current wave form for a specific four pole DC permanent magnet motor. It is further concerned with identifying the underlying factors which influence the line current ripple. An audible noise to motor current transfer function is determined from test measurements and compared with a the mecllanical transfer function measured for the motor and for the motor in the fan scroll assembly. The inductance, which is a factor in the shape of the current ripple, is computed from theoretical and empirical inductance functions. Next a sequence of progressively more complex models is used to compute the current wave form. Arcing and commutation mechanisms are included in the most sophisticated of tbe models.
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