AN1911 Freescale Semiconductor / Motorola, AN1911 Datasheet - Page 3

• Manufacturer Part Number: AN1911
• Description: 3-Phase AC Motor Control with V/Hz Speed Open Loop Using DSP56F80X
• Manufacturer: Freescale Semiconductor / Motorola

3.
3.1 3-Phase AC Induction Motors Drives
The PWM block has the following features:
The AC Motor control utilizes the PWM block set in the complementary PWM mode, which
configures the PWM output as a pair of complimentary channels.
The AC induction motor is the workhorse in adjustable speed drive systems. The most popular type is
a 3-phase squirrel-cage AC induction motor that is an efficient, low-cost, maintenance-free, low noise
motor. The stator is supplied by a balanced three phase AC power source. The synchronous speed of
the motor (n
where f
induction motor produces zero torque at the synchronous frequency and therefore must run at the
speed given by a load torque. The motor speed is characterized by a slip s
where n
torque characteristics and corresponding slip. As can be seen from
speed is controlled by variation of a stator frequency with influence of the load torque.
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Target Motor Theory
s
r
Three complementary PWM signal pairs, or six independent PWM signals
Features of complementary channel operation
Deadtime insertion
Separate top and bottom pulse width correction via current status inputs or software
Separate top and bottom polarity control
Edge-aligned or center-aligned PWM signals
15-bits of resolution
Half-cycle reload capability
Integral reload rates from one to 16
Individual software-controlled PWM output
Programmable fault protection
Polarity control
20-mA current sink capability on PWM pins
Write-protectable registers
is the rotor mechanical speed and n
is the synchronous stator frequency in Hz, and p is the number of stator poles. The AC
s)
is given by
Indirect Power Factor Correction Using DSP56F80X
Freescale Semiconductor, Inc.
For More Information On This Product,
s
n
r
s
=
=
--------------------
120 f
------------------ -
n
Go to: www.freescale.com
s
n
p
–
s
n
r
s
=
sl
n
----- -
n
sl
s
is the slip speed, both in rpm.
rpm
-
EQ 3-1
r
:
Figure 3-1
and
Target Motor Theory
EQ
3-2, the motor
(EQ 3-1.)
(EQ 3-2.)
illustrates the
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