The WEG CFW500 drive has true Field Oriented Control. It’s also known as vector control
because the drive takes the current applied to the motor’s stator - which you can think of as
a vector - and breaks it up into two orthogonal components. One to directly control the rotor's
magnetic field and an orthogonal component to control the stator's magnetic field.
Keeping the stator's flux vector oriented 90 degrees relative to the rotor's flux vector
is what gives us the maximum torque per amp. So to change the torque, the drive’s job is to keep
those two vectors oriented at 90 degrees and just change the amplitude of the torque current vector.
Which is why we call it oriented or vector control. Now that’s complicated because this
whole thing is rotating at the speed of the motor. The drive can do that because it uses a feedback
sensor – usually, an encoder mounted on the shaft of the rotor – to tell it
exactly where the motor's rotor is. All of which means when using vector control,
the drive can accurately control the motor's speed and torque and it can provide full rated torque
all the way down to down to zero RPM. That’s something you can’t do with any other mode.
It turns out that with a little mathematical magic, the drive can also do vector control
without a sensor – we call that sensorless vector control. The limitation is it can only do it for
roughly the top 90% of the speed range. Below that and it falls apart. The drive needs that sensor to
do the slow speeds. That’s the bad news. The good news is that for the top 90% of the speed range,
you get fantastic accuracy and control over your motor for Free because it doesn’t require any
extra hardware. And for the vast majority of applications, sensorless vector control
is all you will ever need. So both are way better than the standard volts hertz,
and sensorless vector is Free, why wouldn’t you use them instead of volts hertz?
Well, there’s a slight downside. Both vector control and sensorless vector control require
that you tune the drive to the motor so the drive knows exactly how to manipulate the currents to
maximize the motor's performance. Volts hertz works right out of the box so it takes almost
no effort on your part to get things running. The good news is, the CFW500 drive makes tuning
super easy. And it only takes a couple minutes. So you might want to consider taking advantage
of one of the vector control modes if you want better control over your motor.
Let’s do a couple examples so you can see just how easy it is.
We’ll do vector control with the encoder in this video and then do sensorless vector in
the next video. And there’s a third video that gives you some helpful hints and covers things
we skipped in the first two videos. I’m using this single-phase input,
1 horsepower three-phase output drive, and this inverter duty motor that has a built-in encoder.
I can’t emphasize this enough. When doing vector control, you really-really-really need to use an
inverter duty motor. Because vector control is constantly manipulating the magnetic fields,
it places much more demand on the motor and especially if you plan to be operating at low
RPMs where the motor can get very hot. Inverter duty motors are designed to handle that. General
purpose motors aren’t, and you will actually see much shorter service life and in some cases,
the general purpose motor will even burn up. Can you get away with a general purpose motor while
learning about vector control? Sure. But in actual application, please do yourself a favor and use an
inverter duty motor. The initial cost is higher, but the long-term cost will be much, much lower.
Are all inverter duty motors created equal? Nope. But that’s a subject for another video.
Just know that a better motor will get you better results and that any of the “high performance,
inverter duty motors” at AutomationDirect.com will get you in the right ballpark.
The CFW500 drive comes with a standard I/O module under this cover which you need to
swap out with this encoder module. I wired the motors encoder to that module like this.
This is what the motor's built-in encoder looks like. Notice that we are using the encoder module's
supply to power the encoder – there’s no need for an extra supply! I love that. It is limited to
150mA and that is shared with all the other I/Os on the module. This encoder uses 100mA max so keep
that in mind and make sure your encoder plus any I/Os that you are using don’t exceed the 150mA.
You want to use a good shielded cable with twisted pairs that are individually shielded
and an outer shield around all of that. Connect all shields at the drive end only – that prevents
grounding issues especially if the motor is remote and possibly at a different potential.
And of course, keep the encoder cable as far away from the motor's power cables as you can.
Don’t run them in the same cable tray for example. This is the cable I’m using in this demo
simply because that’s what I had access to. it doesn’t have an outer shield which for our little
demo here in my electrically quiet office is fine. Here we go ... apply power to the drive.
This is a list of everything that needs to be done to tune a drive for vector control.
It looks kind of intimidating. The good news is most of this is read-only or default stuff.
So I’ll gray those out. Ahh, now we only have a couple parameters to set.
Let’s go to parameter 204 and set it to a 5 to reset the drive to 60Hz factory default
just so you know where I’m starting from. Go to parameter 27 and verify it’s
a 10 – that tells us the encoder module was installed correctly.
Parameter 39 shows us the encoder count. Is the encoder counting? Yep. Is it increasing
when rotating in the forward direction? Yep. Decreasing in the reverse direction? Yep.
Looks like we wired the encoder correctly. Notice that even though this is a 1024 PPR encoder,
the count we get is 4096 PPR which means the drive is using all 4 edges of the encoder cycle to get
four times the native resolution of the encoder. We can see it’s working correctly in Parameter
38 which shows us the rotation speed in RPM. If I rotate this at roughly one revolution
per second, yep we get roughly 60 revolutions per minute. Perfect.
If you forget to wire the encoder or it isn’t wired correctly, you will get an Alarm 79.
I love that the drive checks that for me. One last check before we start:
Hit Run. Is the shaft rotating in the same direction as this little arrow when looking
at the motor from the load? This one is so we are good to go. If not, then power down and swap any
two of the motor leads. Power back up and check it again. It should now be rotating correctly.
If changing the motor's direction is not an option – maybe your motor rotates backward
but is working great in an existing application for example - then swap the A and B wire pairs
on the encoder and then verify that the pulse count goes up when the arrow shows rotation to the right.
Great. We’re ready to start tuning. Drop into the parameter groups.
Here’s the good news: Scroll to the Startup menu and enter that. This is going to walk us through
everything we need to do in the order we need to do it to tune the motor. That makes tuning
super quick and easy. You don’t have to think – just follow the prompts.
It automatically drops us at Parameter 317
which we set to a 1 to tell the drive we want to configure it for vector or oriented control.
Config is now lit up on the display and will stay there until we are done.
That sends us to Parameter 202. Set it to a 4 to tell the drive we want it to use vector mode.
Parameter 296 is a read-only parameter that shows us the line voltage. It’s just a quick check to
make sure you have the drive you think you have. If this doesn’t match what you think you should
have then stop now and get the right drive. Service factor is fine and parameter 400 is
where we enter the exact line voltage we are using. The 220 default is what we are using.
Parameter 401 is the rated full load amps. If we look at the motor's faceplate, we see this motor
is rated for 3 amps, so we’ll enter that here. Frequency is 60 HZ – that’s fine.
According to the motor’s faceplate, its rated speed is 1725 so I’ll enter that here.
A five for this guy is 1 horsepower so that's good. We do have a 1024 PPR encoder so that’s good.
This is a self-ventilated motor. And we’re done! Now we just drop into Parameter 408
and set it to a 3 to do a full tuning with the load connected to the motor's shaft.
Beware – this is going to rotate the shaft. I’ll go ahead and start that along with a stopwatch
so we can see how long it actually takes. The bar graph down here shows us the progress.
If you are nervous about tuning with the motor driving your system, you can start with Mode 1
which doesn’t move the shaft, but also does the least tuning – it really just measures the
resistance. You could then try Mode 2 which does rotate the shaft, but with the motor not coupled
to your system. It will do a better job, but still won’t be optimized for your system. Then
when you do have the load connected you can run Mode 4 to update the mechanical time constant.
Or just run Mode 3 like we are doing here – it only takes a couple minutes.
If you have any of the tuning constants already from the motor's manufacturer, then use those.
These calculations are all based on WEG motors. I hear the motor thumping as the drive hits
the motor with current pulses. I’ll turn up the audio so you can hear it.
They are getting louder and louder as the drive issues larger and larger current pulses.
I’ll turn that back down so we don’t have to listen to it. Eventually, the shaft will spin
up a few times and tuning will be done. I’ll fast-forward the video so we
don’t have to wait. OK, looks like that took this much time. Not bad.
And that’s it! You are now ready to use this system and can expect to get
full-rated torque down to zero RPM. In fact, let’s go to Parameter 133 – the
minimum frequency – and set it to zero. Now if we run the motor, we see we can
actually run it down to zero Hz. Cool. You can’t do that with volts hertz!
I’m going to increase this to 2 Hz. The bar graph is showing us the percent of
rated current that we are using. Watch the bar graph as I grab the pulley. Did you see that?
The current increased as the drive tried to do everything it could to keep the shaft spinning.
The rated torque on this little motor is only 3-foot pounds so for this 4-inch pulley
I only needed to be able to hold 9 pounds so I could get away with this. Don’t just grab your
machine unless you know exactly what it’s capable of and you know it’s not going to hurt you.
Just for fun, let’s compare that with the exact same drive but set up with volts hertz
mode. This is what I did to get there. It’s definitely easier to set up. Now if I hit Run
and adjust the frequency, we see the motor struggles to run at anything below a couple hertz.
And that’s being generous. And notice the current – the drive is sending 100%
of rated current just in hopes of keeping the shaft spinning. If we wait long enough
we get a motor overload fault. Volts hertz does not like to operate at low frequencies.
Ok, I’m back in vector control mode. And if I drop to 0.1 hertz we see the current is modest,
so we don’t expect a motor overload fault. If I stop the motor ... there is something odd
here. If I reach up and try to spin this pulley ... yeah ... forget it. It doesn’t want to spin.
And look – the current bar graph tells us it’s injecting roughly 40% of rated current into the
motor. That explains the resistance I’m feeling, but why is the drive injecting current when the
motor is stopped? Well, when you are in vector control mode or even sensorless vector mode,
the magnetizing current is always active. But that means the motor is always burning power
even when it’s not running - which costs you money. If you don’t need that, then just go to
Parameter 181 and set it to a 1 to turn off the magnetization current when the motor is stopped.
It takes effect immediately. If I toggle it a few times you can see the current on the bar
graph come and go even though I haven’t hit Return yet. If I disable it, spin the pulley and quickly
enable it – you see the motor abruptly stops spinning. I’m going to disable it, and exit.
And again, when we see no bar graph current the motor is free to spin.
That ought to be enough to get you up and running with field oriented or vector control.
Join us in the next video where we will do the exact same example but without an encoder.
And be sure to watch Part 3 where we share some helpful hints and cover
the things we skipped in the first two videos. Meanwhile, click here to learn more about the WEG
CFW500 variable frequency drives. Click here to learn about AutomationDirect’s free award-winning
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