sensorless ESC theory

3 phase V oltages,
DC Bus Current &
DC Bus Voltage
Sensing
ADC
Speed PI
Regulator
DSP56F80x
Pow er line
Actual Speed
PW M
3 Phase Voltages
D C -B us V oltage/C urrent
Tem perature
Three-Phase
Inverter
3-ph
BLDC
Motor
START
STOP
UP
DOWN
PW M
Generator
with
Dead Tim e
PC Master
SCI
3 phase BLDC
Power Stage
Commutation
Control
Zero Crossing
Period, Position
R ecognition
Zero
Crossing
Duty
Cycle
Required
Speed
1/T
Commutation
Period
Zero Crossing
Time moment
System Design Concept
3-Phase BLDC Motor Control with Sensorless Back-EMF, ADC, Zero Crossing, Rev. 3
14 Freescale Semiconductor
Preliminary
Figure 4-1. System Concept
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 software in order to filter high voltage
spikes produced by the switching of the IGBTs (MOSFETs).
The divided phase voltages are connected to the AD converter module on the controller and are processed in
order to get the Back-EMF Zero Crossing signal. The Back-EMF Zero Crossing detection enables position
recognition, as explained in previous sections. The software selects one of the phases which corresponds to the
present commutation step.