AN1914 Freescale Semiconductor / Motorola, AN1914 Datasheet - Page 5

• Manufacturer Part Number: AN1914
• Description: 3-Phase BLDC Motor Control with Sensorless Back EMF Zero Crossing Detection Using DSP56F80x
• Manufacturer: Freescale Semiconductor / Motorola

The motor can have more then just one pole-pair per phase. This defines the ratio between the
electrical revolution and the mechanical revolution. The BLDC motor shown has three pole-pairs per
phase which represent three electrical revolutions per one mechanical revolution.
The rectangular, easy to create, shape of applied voltage ensures the simplicity of control and drive.
But the rotor position must be known at certain angles in order to align the applied voltage with the
Back-EMF. The alignment between Back-EMF and commutation events is very important. In this
condition the motor behaves as a DC motor and runs at the best working point. Thus simplicity of
control and good performance make this motor a natural choice for low-cost and high-efficiency
applications.
Figure 3-3
the phase-to-phase Back-EMF voltage. The magnetic flux linkage can be measured; however in this
case it was calculated by integrating the phase Back-EMF voltage, which was measured on the non-fed
shows number of waveforms: the magnetic flux linkage, the phase Back-EMF voltage and
DSP56F80x MC PWM Module in Motor Control Applications
Freescale Semiconductor, Inc.
Figure 3-2. Three Phase Voltage System
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
electrical
angle
Target Motor Theory
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