AN1913D Freescale Semiconductor / Motorola, AN1913D Datasheet - Page 7

• 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

Freescale Semiconductor, Inc.
Target Motor Theory
3.4
Power Stage - Motor System Model
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
3-5), is provided.
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
). Six semiconductor switches (S
), controlled
d
A/B/C t/b
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.
BLDC control with BEMF Zero Crossing using ADC
7
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