AN1915D Freescale Semiconductor / Motorola, AN1915D Datasheet - Page 4

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

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Target Motor Theory
3.
3.1 Digital Control of a BLDC Motor
The BLDC motor application utilizes the Quadrature Decoder connected to Quad Timer module A. It uses
the Decoder’s digital input filter, to filter the Encoder’s signals, but does not make use of its decoding
functions. So the decoder’s digital processing capabilities are free to be used by another application.
A brushless DC (BLDC) motor is a rotating electric machine, where the stator is a classic three-phase
stator like that of an induction motor, and the rotor has surface-mounted permanent magnets (see
Figure
In this respect, the BLDC motor is equivalent to an inverted DC commutator motor, in which the
magnet rotates while the conductors remain stationary. In the DC commutator motor, the current
polarity is reversed by the commutator and brushes. However, in the brushless DC motor, the polarity
reversal is performed by power transistors switched in synchronization with the rotor position.
Therefore, BLDC motors often incorporate either internal or external position sensors to sense the
actual rotor position, or the position can be detected without sensors.
The BLDC motor is driven by rectangular voltage strokes coupled with the given rotor position (see
Figure
magnet, defines the torque and thus the speed of the motor. To get the maximum generated torque, the
voltage strokes have to be applied to the three-phase winding system,
so that the angle between the stator flux and the rotor flux is kept close to 90°. To meet this criteria, the
motor requires electronic control for proper operation.
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Target Motor Theory
3-1).
3-2). The generated stator flux, together with the rotor flux, which is generated by a rotor
Includes logic to decode quadrature signals
Configurable digital filter for inputs
32-bit position counter
16-bit position difference counter
Maximum count frequency equals the peripheral clock rate
Position counter can be initialized by SW or external events
Preloadable 16-bit revolution counter
Inputs can be connected to a general purpose timer to aid low speed velocity.
3-Phase BLDC Motor Control with Quadrature Encoder
Freescale Semiconductor, Inc.
Figure 3-1. BLDC Motor - Cross Section
For More Information On This Product,
Go to: www.freescale.com
Stator
Stator winding
(in slots)
Shaft
Rotor
Air gap
Permanent magnets
MOTOROLA