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Classical system – Motorola M68HC08 User Manual

Page 27

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BLDC Motor Control

Brushless DC Motor Control Theory

DRM028 — Rev 0

Designer Reference Manual

MOTOROLA

BLDC Motor Control

27

3.2.2 3-Phase BLDC Power Stage

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

Figure 3-5

). The power stage is usually

controlled by a dedicated microcontroller with on-chip PWM module.

3.2.3 Why Sensorless Control?

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

1.3

Benefits of the Solution

).

Figure 3-4. Classical System

3.2.4 Power Stage — Motor System Model

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

Figure 3-5

.

AC LINE VOLTAGE

=

POWER STAGE

POSITION

SENSORS

LOAD

CONTROL UNIT

CONTROL SIGNALS

POSITION FEEDBACK

SPEED

SETTING

M

MOTOR DRIVE

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Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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