User Manual

Target Motor Theory
3-Phase BLDC Motor Control with Sensorless Back-EMF, ADC, Zero Crossing, Rev. 3
8 Freescale Semiconductor
Preliminary
Figure 3-5. Power Stage - Motor Topology
The 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 3-phase power stage plus a Brushless DC motor. The power for the
system is provided by a voltage source (U
d
). Six semiconductor switches (S
A/B/C t/b
), controlled elsewhere,
allow the rectangular voltage waveforms (see
Figure 3-2) to be applied. The semiconductor switches and
diodes are simulated as ideal devices. The natural voltage level of the whole model is applied at one half of the
DC-Bus voltage. This simplifies the mathematical expressions.