Digital Control Of A Bldc Motor - Motorola M68HC08 Manual

BLDC Motor Theory

3.1 Digital Control of a BLDC Motor

Designer Reference Manual
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The BLDC motor is driven by rectangular voltage strokes coupled with
the given rotor position (see Figure 3-2. Voltage Strokes Applied to
the 3-ph BLDC Motor). The generated stator flux interacts with the rotor
flux, which is generated by a rotor magnet, defines the torque and thus
the speed of the motor. The voltage strokes must be properly applied to
the two phases of the three-phase winding system so that the angle
between the stator flux and the rotor flux is kept close to 90°, to get the
maximum generated torque. Due to this fact, the motor requires
electronic control for proper operation.
Voltage
+U
DCB
Phase A
-U
DCB
+U
DCB
Phase B
-U
DCB
+U
DCB
Phase C
-U
DCB
30º 60º
Figure 3-2. Voltage Strokes Applied to the 3-ph BLDC Motor
For the common 3-phase BLDC motor a standard 3-phase power stage
is used, as is illustrated in
The power stage utilizes six power transistors with switching in either the
independent mode or complementary mode.
BLDC Motor Theory
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90º 120º 150º 180º 210º 240º
Figure 3-3. 3-phase BLDC Power
270º 300º 330º Electrical
angle
Stage.
DRM046 — Rev 0
MOTOROLA