Auto-Tuning and Variable Frequency Drives - 2

INTRODUCTION
An auto-tune helps
the VFD control the
motor with specific
motor settings
Variable Frequency Drives (VFDs)
make applications all over the world
work better, more efficiently, and
with their keypad displays, make the
equipment easier to interact with.
Almost to a tee, manufacturers of
these wonderful devices recommend
that you perform something called
an Auto-tune. Why is that? What
is that? It isn't anything scary or
complicated; it just helps the VFD
control the motor with specific motor
settings.
Just like the automotive companies
not knowing where to put the
adjustable seats in your brand new
car, the VFD manufacturer can't
guess the best default settings for
motor information, so they just use
some industry standard.
An example might be that the
manufacturer of a 40HP, 480volt
drive might default their motor full
load amp setting per NEC table
430.250 and set it at 52amps from
the factory. That would probably not
match your new premium efficiency
motor. Setting the amps correctly
is just the start to getting proper
performance.
Performing an auto-tune is easy, so
let's discuss the whats and whys of
auto-tuning for VFDs.
DIFFERENT THAN
SERVO TUNING
A VFD that is properly
auto-tuned will be
more efficient with
better performance.
Just to be clear, there are other
auto-tuning functions out there
in the world. As the name autotune
implies, any operation that
will calculate and adjust things
automatically at the user's behest,
can be called an auto-tune function.
In the world of servo motors and
amplifiers, close cousins of the VFD
and induction motor, the auto-tuning
function will probably have more to
do with tuning the servo pair to their
loads. The tuning will help adjust
gains for positioning and speed
loops.
The VFD auto-tuning asks specifically
that the load is totally detached from
the motor when the auto-tune is
performed.
The simple reason for the difference
is that servo motors and their
amplifiers are always bought
together from a single manufacturer.
A simple motor code is all that the
amplifier needs to know everything
about the motor that is attached to
it. Conversely, the VFD and motor
are only sometimes manufactured
by a common company. It is more
the norm that brand A motor will
probably be used with brand B
VFD. Because of this unfamiliarity
between the motor and the VFD that
auto-tuning becomes the bridge by
which good motor information can
be passed to the drive.
MONEY'S WORTH
Time really is money. Any time that
you " spend " on improving your VFD
performance better be worth the
time invested. So what is it that a
good auto-tune gets you?
If done correctly, a properly autotuned
VFD will be more efficient
(lower current for the same torque)
with better performance (more linear
and stable operation).
Just by giving the VFD the actual
electrical specifications from the
motor nameplate, the VFD will not
have to assume generic values and
produce excess motor flux and
possibly even saturate the motor's
magnetic field, which won't produce
more motor torque but probably will
produce more motor losses (heat).
The flipside of the equation is how
much time does it take to perform an
auto-tune? If you have a nice picture
of the motor's specs, say from the
motor nameplate, it will probably
take around 90 seconds to enter the
information and an additional minute
to run the auto-tuning. Of course,
these are estimates but we are
definitely in the neighborhood.
2 | Auto-tuning and Variable Frequency Drives

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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