Brushless DC Motor Control
The permanent magnet brushless DC motor is identical to the synchronous machine and indeed with ac polyphase windings on the stator it can act as such, if the phase currents are sinusoidal and the windings are approximately sinusoidally distributed. It is more common, however for the currents to be switched DC. In this form it is truly an inside-out d.c. commutator motor with the mechanical commutator replaced with an electronic switching circuit.
The most obvious advantage of the brushless DC motor is the removal of the brushes. Brush maintanence is no longer required and problems associated with brushes are eliminated. These motors have a high torque/inertia ratio. They can be used in hazardous environments or even under-water applications.
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