AN1915D Freescale Semiconductor / Motorola, AN1915D Datasheet - Page 9

• Manufacturer Part Number: AN1915D
• Description: 3-Phase BLDC Motor Control with Quadrature Encoder using DSP56F80x
• Manufacturer: Freescale Semiconductor / Motorola

MOTOROLA
3.1.3.1 Quadrature Encoder versus Hall Sensors
3.1.3.2 Commutation with Periodical Scanning of Quadrature Encoder
The BLDC motor application uses the Quadrature Encoder for rotor position sensing. The Quadrature
Encoder output consists of three signals. Two phases, A and B, represent the rotor position, and an
Index pulse defines the zero position. All Quadrature Encoder signals are depicted in
Compared with Hall Sensors, there are some differences, which affect the control algorithm. The main
differences are that the Quadrature Encoder does not give commutation moment and absolute position,
as do the Hall Sensors.
The differences between the Quadrature Encoder and Hall Sensors are summarized in
The two control algorithms are described later on with the Quadrature Encoder. The first solution is
commonly used and periodically scans the Quadrature Encoder. The second solution uses specific
advantages of DSP’s peripherals and translates the Quadrature Encoder outputs directly into Hall
Sensors signals. These internal signals are used as input for the commutation algorithm. This algorithm
is implemented in the presented application.
The commutation of the BLDC motor is performed in the six defined moments. Since the Quadrature
Encoder gives the precise position, the one electrical revolution is divided into six sectors (see
Figure
Table 3-3. Differences between Quadrature Encoder and Hall Sensors
3-10). To recognize the commutation moment, it is necessary to scan Quadrature Encoder
Table 3-2. Commutation Sequence for Counter Clockwise Rotation
does not give absolute position
Quadrature Encoder
give precise position
Figure 3-9. Quadrature Encoder output signals
3-Phase BLDC Motor Control with Quadrature Encoder
three outputs
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gives 6 events per electrical revolution
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gives absolute position
Hall Sensors
three outputs
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Target Motor Theory
Table
Figure
3-3.
3-9.
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