Commutation - Motorola M68HC08 Manual

3.4 Commutation

DRM046 — Rev 0
MOTOROLA
Freescale Semiconductor, Inc.
PWM
switching
ON
PWM Q1
OFF
ON
PWM Q2
OFF
ON
PWM Q3
OFF
ON
PWM Q4
OFF
ON
PWM Q5
OFF
ON
PWM Q6
OFF
10º 20º
Figure 3-5. Complementary Switching of Power Transistors
Commutation provides the creation of a rotation field. As was explained,
for the proper operation of a BLDC motor it is necessary to keep the
angle between the stator and rotor flux close to 90°. With six-step control
we get a total of six possible stator flux vectors. The stator flux vector
must be changed at a certain rotor position. The rotor position is usually
sensed by Hall sensors. The Hall sensors generate three signals that
also comprise six states. Each of the Hall sensors' states corresponds to
a certain stator flux vector. All of the Hall sensor states with
corresponding stator flux vectors are illustrated in Figure 3-6. Stator
Flux Vectors at Six-Step Control. The same figure is illustrated in
tables Table 3-1. Commutation Sequence for Counterclockwise
Rotation and Table 3-2. Commutation Sequence for Clockwise
Rotation.
BLDC Motor Theory
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Designer Reference Manual
BLDC Motor Theory
Commutation
80º 90º
Electrical
angle
21