Motorola M68HC08 manual 2 3-Phase Bldc Power Stage, Why Sensorless Control?

Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

BLDC Motor Control

Brushless DC Motor Control Theory

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).

	–	M	POSITION	LOAD
AC LINE VOLTAGE	POWER STAGE
			SENSORS
	=
	CONTROL SIGNALS

SPEED	CONTROL UNIT	POSITION FEEDBACK
SETTING

MOTOR DRIVE

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.

DRM028 — Rev 0		Designer Reference Manual
MOTOROLA	BLDC Motor Control	27
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