AN1627 Freescale Semiconductor / Motorola, AN1627 Datasheet - Page 3

• Manufacturer Part Number: AN1627
• Description: Low Cost High Efficiency Sensorless Drive for Brushless dc Motor Using MC68HC (7)05MC4
• Manufacturer: Freescale Semiconductor / Motorola

2
2.1
In order to explain and simulate the idea of Back-EMF sensing techniques a simplified mathematical
model, based on the basic circuit topology (see Figure 2-1.), has been created.
The second goal of the model is to find how the motor characteristics depend on the switching angle.
The switching angle is the angular difference between a real switching event and an ideal one (at the
point where the phase to phase Back-EMF crosses zero).
The motor-drive model consists of a normal three phase power stage plus a Brushless DC motor. The
power for the system is provided by a voltage source (U
controlled elsewhere, allow the rectangular voltage waveforms (see Figure 1-1.) to be applied. The
semiconductor switches and diodes are simulated as ideal devices. The zero voltage level of the whole
model is put at one half of the DC-Bus voltage. This simplifies the mathematical expressions when
output waveforms from the power stage are calculated.
AN1627
REV 0.2
THEORY
Power Stage - Motor System Model
Freescale Semiconductor, Inc.
For More Information On This Product,
Figure 2-1.
Go to: www.freescale.com
Power Stage - Motor Topology
d
). Six semiconductor switches (S
MOTOROLA
A/B/C t/b
),
3