AN1931D Freescale Semiconductor / Motorola, AN1931D Datasheet - Page 27

• Manufacturer Part Number: AN1931D
• Description: 3-Phase PM Synchronous Motor Vector Control
• Manufacturer: Freescale Semiconductor / Motorola

MOTOROLA
Note:
4.3.3 Voltage Sensing
4.3.4 Power Module Temperature Sensing
Sectors 2 and 3:
Sectors 4 and 5:
The DCBus voltage sensor is represented by a simple voltage divider. The DCBus voltage does not
change rapidly. It is nearly constant, with the ripple given by the power supply structure. If a bridge
rectifier is used for rectification of the AC line voltage, the ripple frequency is twice the AC line
frequency. If the power stage is designed correctly, the ripple amplitude should not exceed 10% of the
nominal DCBus value.
The measured DCBus voltage must be filtered to eliminate noise. One of the easiest and fastest
techniques is the first order filter, which calculates the average filtered value recursively from the last
two samples and coefficient C:
To speed up the initialization of the voltage sensing (the filter has exponential dependency with
constant of 1/N samples), the moving average filter, which calculates the average value from the last N
samples, can be used for initialization:
The measured power module temperature is used for thermal protection The hardware realization is
shown in
noise suppression capacitor. The four diodes have a combined temperature coefficient of 8.8 mV/ C.
The resulting signal, Temp_sense, is fed back to an A/D input, where software can be used to set safe
operating limits. In this application, the temperature, in Celsius, is calculated according to the
conversion equation:
where:
temp
Temp_sense
a
b
u
DCBusFilt
The sector value is used for current calculation only, and has no other meaning in the sinewave
modulation. But if we use any type of space vector modulation, we can get the sector value as
part of space vector calculation.
Figure
n
+
Power module temperature in centigrades
Voltage drop on the diodes, which is measured by ADC [V]
Diodes-dependent conversion constant (a = -0.0073738)
Diodes-dependent conversion constant (b = 2.4596)
4-12. The circuit consists of four diodes connected in series, a bias resistor, and a
1
=
Freescale Semiconductor, Inc.
3-Phase PM Synchronous Motor Vector Control
Cu
For More Information On This Product,
u
DCBusFilt
temp
DCBusFilt
Go to: www.freescale.com
=
i
i
B
C
=
Temp_sense b
------------------------------------- -
n
=
=
+
–
–
1
–
n
i
i
N
=
A
B
a
–
1
–
–
u
Cu
i
i
DCBus
C
A
DCBusFilt
–
n
n
–
u
DCBusFilt
n
System Concept
(EQ 4-10.)
(EQ 4-6.)
(EQ 4-7.)
(EQ 4-8.)
(EQ 4-9.)
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