AN1913D Freescale Semiconductor / Motorola, AN1913D Datasheet - Page 5

• Manufacturer Part Number: AN1913D
• Description: 3-phase BLDC Motor Control with Sensorless Back-EMF ADC Zero Crossing Detection using DSP 56F80x
• Manufacturer: Freescale Semiconductor / Motorola

Figure 3-3
and the phase-to-phase Back-EMF voltage. The magnetic flux linkage was measured by calculating
the integration phase Back-EMF voltage, which was measured on the non-fed motor terminals of the
BLDC motor. As can be seen, the shape of the Back-EMF is approximately trapezoidal and the
amplitude is a function of the actual speed. During the speed reversal the amplitudeis changed and its
sign and the phase sequence change too.
The filled areas in the tops of the phase Back-EMF voltage waveforms indicate the intervals where the
particular phase power stage commutations are conducted. As can be seen, the power switches are
cyclically commutated through the six steps. The crossing points of the phase Back-EMF voltages
represent the natural commutation points. At the normal operation, the commutation is performed here.
Some control techniques lead the commutation by a defined angle in order to control the drive above
the PWM voltage control.
$WRS %WRS &WRS
&ERW $ERW %ERW
shows the number of waveforms, the magnetic flux linkage, the phase Back-EMF voltage
Ph. A Ph. B
Figure 3-3. BLDC Motor - Back-EMF and Magnetic Flux
A-A
BLDC control with BEMF Zero Crossing using ADC
Ph. A
Freescale Semiconductor, Inc.
For More Information On This Product,
B-B
Ph. B
Ph. C
Acting power switch in the power stage
Go to: www.freescale.com
C-C
Phase Magnetic Flux Linkage
Ph. C
Phase-Phase Back-EMF
Phase Back-EMF
Speed reversal
Target Motor Theory
3VLB$
3VLB%
3VLB&
8LB$%
8LB%&
8LB&$
8LB$
8LB%
8LB&
5