Motorola M68HC08 Reference Manual page 27

3.2.2 3-Phase BLDC Power Stage
3.2.3 Why Sensorless Control?
3.2.4 Power Stage — Motor System Model
DRM028 — Rev 0
MOTOROLA
Freescale Semiconductor, Inc.
The voltage for 3-phase BLDC motor is provided by a 3-phase power
stage controlled by digital signals. Its topology is the one as for the AC
induction motor (refer to
controlled by a dedicated microcontroller with on-chip PWM module.
As explained in the previous section, rotor position must be known in
order to drive a brushless dc motor. If any sensors are used to detect
rotor position, sensed information must be transferred to a control unit
(see Figure 3-4). Therefore, additional connections to the motor are
necessary. This may not be acceptable for some applications (see
Benefits of the Solution).
–
AC LINE VOLTAGE
=
CONTROL SIGNALS
SPEED
SETTING
Figure 3-4. Classical System
In order to explain and simulate the idea of back-EMF sensing
techniques a simplified mathematical model based on the basic circuit
topology has been created. See
BLDC Motor Control
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Brushless DC Motor Control Theory
Figure 3-5). The power stage is usually
POWER STAGE
POSITION FEEDBACK
CONTROL UNIT
MOTOR DRIVE
Figure 3-5.
BLDC Motor Control
1.3
POSITION
M
LOAD
SENSORS
Designer Reference Manual
27