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Introduction and Setup
Brief Overview to Brushless DC Motors
Simply forcing the two PWMs to be inversions of each other is not always
sufficient. Since a time delay is associated with turning off the transistors
in the motor drive, there must be a “deadtime” between the deactivation
of one PWM power transistor and the activation of the opposite transistor
in a top and bottom pair. Deadtime can be specified in the deadtime
write-once register. This 8-bit value specifies the number of CPU clock
cycles to use for the deadtime.
1.5 Brief Overview to Brushless DC Motors
A brushless dc motor is a rotating electric machine where the stator is a
classic 3-phase stator like that of an induction motor and the rotor has
surface-mounted permanent magnets. There are no brushes on the
rotor and the commutation is performed electronically at certain rotor
positions. The stator is usually made from magnetic steel sheets. The
stator phase windings are inserted in the slots (distributed winding) as
shown on Figure 1-3.
Stator
Stator windings
in slots
Shaft
Rotor
Air gaps
Permanent
magnets
Figure 1-3. BLDC Motor – Cross Section
BLDC Motor Control Board for Industrial and Appliance Applications
DRM007
MOTOROLA Introduction and Setup 25