AN1914 Freescale Semiconductor / Motorola, AN1914 Datasheet - Page 15

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

Freescale Semiconductor, Inc.
System Design Concept
4.2 Sensorless Drive Concept
The concept below was chosen. The sensorless rotor position technique developed detects the zero
crossing points of Back-EMF induced in the motor windings. The phase Back-EMF Zero Crossing
points are sensed while one of the three phase windings is not powered. The obtained information is
processed in order to commutate the energized phase pair and control the phase voltage, using Pulse
Width Modulation.
Figure 4-9. System Concept
The Back-EMF zero crossing detection enables position recognition. The resistor network is used to
divide sensed voltages down to a 0-3.3V voltage level. Zero Crossing detection is synchronized with
the center of center aligned PWM signal by the SW in order to filter high voltage spikes produced by
DSP56F80x MC PWM Module in Motor Control Applications
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