MC3PHAC Motorola, MC3PHAC Datasheet - Page 15

• Manufacturer Part Number: MC3PHAC
• Description: 3-Phase AC Motor Controller
• Manufacturer: Motorola

Freescale Semiconductor, Inc.
MC3PHAC/D
Features
Voltage Profile Generation — The MC3PHAC controls the motor voltage in
proportion to the specified frequency, as indicated in
Figure
5.
100%
VOLTAGE BOOST
FREQUENCY
BASE FREQUENCY
Figure 5. Voltage Profiling, Including Voltage Boost
An ac motor is designed to draw a specified amount of magnetizing current
when supplied with rated voltage at the base frequency. As the frequency
decreases, assuming no stator losses, the voltage must decrease in exact
proportion to maintain the required magnetizing current. In reality, as the
frequency decreases, the voltage drop in the series stator resistance increases
in proportion to the voltage across the magnetizing inductance. This has the
effect of further reducing the voltage across the magnetizing inductor, and
consequently, the magnetizing current. A schematic representation of this
effect is illustrated in
Figure
6. To compensate for this voltage loss, the voltage
profile is boosted over the normal voltage curve in
Figure
5, so that the
magnetizing current remains constant over the speed range.
PARASITICS
X
R
X
R
1
1
2
2
MAGNETIZING CURRENT
R2 (1 –s)
X
TORQUE CURRENT
M
(TRY TO KEEP CONSTANT)
s
Figure 6. AC Motor Single Phase Model
Showing Parasitic Stator Impedances
MOTOROLA
3-Phase AC Motor Controller
15
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