Auto-Tuning and Variable Frequency Drives - 5

AUTO-TUNE TYPES
FOR VFDS
Auto-tune types:
* Uncoupled rotational
auto-tune
* Stationary auto-tune
The most effective version of an
auto-tuning routine for VFDs and
motors requires the motor shaft to
be rotated while unloaded. This is
know as an Uncoupled Rotational
Auto-Tune.
If it is feasible,
always insist on
the uncoupled
rotational auto-tune.
There just isn't any replacement for
actual measurements that can be
made while the motor is actually
turning its own shaft.
However, not all applications
of VFDs and motors allow for
easy uncoupling. Using some
sophisticated calculations, some of
the motor model information can
be estimated using an auto-tune
method that does not require motor
shaft rotation. These non-rotational
auto-tunes are sometimes referred
to a Stationary Auto-tuning.
Finally, there are some auto-tunes
that are very basic and require little
information to be entered and take
only a few seconds.
For the most part, the auto-tune will
just measure the resistance that is
inherent in the windings of the stator
and the motor cable., basically the
line to line resistance mentioned
earlier. The advantage of such a
simple auto-tune is that the VFD can
then compensate for the reduced
magnetic field strength due to
voltage loss.
We won't cover it here but there are
also auto-tuning routines specifically
for permanent magnet motors in
many of the same VFDs. Some of
what the PM auto-tuning routines do
is common with what is done with
induction motors.
However, even more specific
information necessary for a proper
auto-tune of a PM motor and
wider variety of characteristics are
measured as well.
AUTO-TUNING TIPS
Most auto-tuning with VFDs is
pretty straightforward and nothing
that requires a PhD in electrical
engineering. However, there are
a couple of things that may make
things come out for the best.
First, some motor characteristics,
specifically, resistances, will change
as the temperature of the copper
windings increases. In other words,
a hot motor will measure differently
than a cold motor. Since during most
normal operation the motor will be
warm to hot, we would like our autotune
to reflect that state.
So the tip is to either run the autotune
multiple times or just run the
motor for a while, even unloaded,
before performing your rotational
auto-tune.
Second, because it is simpler to do
a stationary auto-tune, it is tempting
to settle for the stationary autotune.
That would be convenient but
a mistake.
Always insist on the uncoupled
rotational auto-tune. Often the
auto-tune can be run before the
application is fully assembled, like on
the build floor.
Sometimes it is easier to do the
full rotational auto-tune when the
motor are only 20ft apart and have a
relatively short motor cable.
Later when the application is fully
assembled and the motor is 75ft
away from the drive and already
coupled to the load, a simple Line-toLine
resistance can be run.
This non-rotational resistance
tune will not affect the motor
measurements but will re-test and
update the increased resistance due
to a longer motor cable. Viewing the
modified VFD settings can confirm
the new resistance measurement.
Auto-tuning and Variable Frequency Drives | 5

Auto-Tuning and Variable Frequency Drives

Table of Contents for the Digital Edition of Auto-Tuning and Variable Frequency Drives

Auto-Tuning and Variable Frequency Drives - 1
Auto-Tuning and Variable Frequency Drives - 2
Auto-Tuning and Variable Frequency Drives - 3
Auto-Tuning and Variable Frequency Drives - 4
Auto-Tuning and Variable Frequency Drives - 5
Auto-Tuning and Variable Frequency Drives - 6
Auto-Tuning and Variable Frequency Drives - 7
Auto-Tuning and Variable Frequency Drives - 8
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