In this video, we’ll point out a number of
things you might find helpful and fill out
some of the things we glossed over in the previous videos. This is a list of the topics
we will be covering – you can use that as an index if you just want to fast forward
to one of them. To get the most out of the vector control
modes – especially for applications requiring constant torque at low speeds - you really
need to be using a motor that is rated for VFD use. Why? Because those motors are designed
to handle the extra heat generated at low RPMs. Heat generated in general-purpose motors
reduces bearing and insulation life which causes the motors to fail. Inverter duty motors
are also designed to handle the voltage spikes created by the chopped waveform output by
the drive. In general-purpose motors those voltage spikes cause the wire insulation to
break down which causes the motor to fail. Did you notice in the previous videos that
the tuning setup asked us if the motor was self-ventilated in Parameter 406? Why does
that matter? The drive monitors how hard a motor is being driven and for how long. It
uses that to estimate when the motor is getting overloaded. This video does a really good
job of explaining how overloads work in the WEG drives. That video uses a WEG CFW300 drive,
but the exact same concepts apply to the WEG CFW500 drive. The bottom line is there are
overload protection levels defined by these three parameters. But, that’s all assuming
a motor that is not self-ventilated: that is, it does not have a cooling fan.
Self-ventilated motors do a better job of cooling themselves so the drive automatically
modifies these thresholds to take that into account. At low speeds the fan isn’t helping
much at all so there is no change. The faster the motor spins the more cooling it is going
to get so the drive raises the thresholds to account for that.
So if you have a self-ventilated motor, make sure you set Parameter 406 accordingly.
And make sure the motor’s faceplate full load amperage is greater than 1/3 of the drive's
rated output current. Why? Because if the motor is too small, it won’t draw enough
current for the drive’s algorithms to accurately measure.
And to get the best accuracy when doing torque control applications, make sure the drive’s
rated current matches the motor’s full load amperage as close as possible. The drive has
to make certain assumptions and the closer the motor is to the drive's rating the better
those assumptions will be. In the previous videos, we glossed over the
tuning modes and more importantly – how to choose the right one for the vector mode
you are using. Let’s take a closer look at that. Parameter 408 selects the tuning
mode. Tuning Mode 1 is for those times when you can’t run the motor while tuning. It
will be enough to get you started with any of the vector control modes and is the only
one that VVW can use. Mode 2 is the best you are going to do with
sensorless vector. It does spin the motor to measure the motor's magnetization current,
but the motors shaft should not be coupled to the load during this test. This mode does
a better job of estimating these parameters because it is dynamic.
Mode 3 is best for full vector mode because it estimates all the parameters with the motor
coupled to the load which is going to give you the best mechanical time constant estimation.
If your load isn’t available right now, run Mode 2 without a load then later when
you are connected to the load run Mode 4 to update just the mechanical time constant.
Mode 2 will generate a good enough estimate of all the tuning parameters to get you up
and running, and then Mode 4 will update just the mechanical parameters once you have access
to the actual load or if your load changes and you don’t want to re-run the full tuning.
Or when the load is available, just run Mode 3. It’s the best and quickest way to tune
for full vector control and it only takes a few minutes.
And if you want the best possible tuning results, tune with the motor warmed up. That will give
the drive the most accurate readings during tuning.
When using vector modes, the drive will use more power. Maintaining and controlling torque
takes a lot of manipulation of current, so expect
to see higher average current consumption
by the drive, which also means vector control modes also tend to give you higher power bills.
So you do get a lot better control over your motor, but it’s not free. I wish I could
give you a rule of thumb for how much, but that depends entirely on your application.
Try it. If you don’t like it, just turn it off.
I know we mentioned this in the previous videos, but it’s worth repeating: We saw in those
videos that when in any of the vector modes, by default, the drive continues to output
current even after the motor is stopped to maintain the magnetic flux. You can turn that
off if you don’t need it and that will help reduce your power bills.
In the previous videos, we assume a standard 4-pole motor which is the drive's default.
If you are using a 2-pole jet pump motor, for example, make sure you enter the motor's
poles before doing tuning. When using vector modes, you get an added
bonus – an additional braking mode. Because vector control modes do such a great job of
controlling torque, you can use that to your advantage to do braking that is 5 times
more effective than DC braking. Check out Chapter 12.5 in the user manual for details.
But beware, this kind of braking can cause increased vibration, increased acoustic noise,
and an increase in temperature. So make sure those don’t cause you any concerns.
Hopefully, this quick review gave you a little more insight into using the vector control
modes. Click here to learn more about the WEG CFW500
variable frequency drive. Click here to learn about AutomationDirect’s Free award-winning
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