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Introduction and Setup
Brushless dc motors are named in different ways:
• Permanent magnet synchronous motors
• Brushless permanent magnet
• Permanent magnet ac motors, etc.
A BLDC motor is equivalent to an inverted dc commutation motor, where
the magnet rotates while the conductors remain stationary. In the dc
commutation motor, the commutator and brushes reverse the current
polarity. But, in the brushless dc motor, a power transistor (which must
be switched in synchronization with the rotor position) performs the
polarity reversal. The BLDC motor often has either internal or external
position sensors to sense actual rotor position so that synchronization
can be performed.
The motor can have more than one pole-pair per phase. The pole-pair
per phase defines the ratio between the electrical revolution and the
mechanical revolution. For example, the BLDC motor shown in
Figure 1-3 has four pole-pairs per phase; which leads to four electrical
revolutions; per one mechanical revolution.
Advantages of the brushless dc motors are:
• No electrical noise due to brushes and commutator
• No tachometer needed for speed control
• High starting torque and high no load speed
• Good power output to size ratio
• Higher efficiency than ac induction motors
• Reversible
• Precise speed control
• Variable speed
• Oil-less operation
• Rapid acceleration and deceleration
• Very low torque ripple
DRM007
BLDC Motor Control Board for Industrial and Appliance Applications
26 Introduction and Setup MOTOROLA