Hi! In this video I will show you how to use our system to teach
permanent magnet DC motors, as well as DC motor drives.
The system will use the lead-acid battery pack
to power the motor. We will also use
the four-quadrant dynamometer / power supply, first,
to drive the generator, and then, when we study the motor, we will use it in the
power supply mode to be able to apply
a variable power supply to the motor itself.
The dynamometer will need to be mechanically coupled to the permanent magnet
machine,
using the supplied timing belt. To do that,
you will need to open the front panels, and place
a timing belt between the machines.
You will notice that, on the permanent magnet machine, the machine is not
centered:
this is because since the
shaft - the gear of the shaft - is smaller it needs to be to the right of the machine.
We will use this spring-loaded mechanism to put more tension on the belt itself.
So you will need to place your belt
between the machines, like this, and then make sure that your belt passes
between the tensioning bearings like this.
The student manuals are very important with that system.
They feature theory, as well as step-by-step procedures, in details.
"During the machine on", Connect this", "turn this to that amount",
and so on. It will also ask students to do measurements and explain
why they do get those measurements.
On top of the student manual you also have
an instructor guide that contains all of the answers to the questions
asked to the students, and a user guide that explains how to use the system in
general
and in detail, how you would use the data acquisition software.
The first exercise will explain to students the important concepts
of speed, torque, and mechanical power. To do so they will use the
four-quadrant dynamometer.
To use it you need to make sure that you are in a dynamometer mode,
then you can change the function by pressing on the function button.
For example now I see that it is
a 2-quadrant constant torque break, and the quantity that is blinking
is my actual quantity that I'm controlling, so in that case it would be the torque.
If I change it, for example, for a prime mover,
meaning that I want to drive my machine that would be
a generator, then I select that mode here.
If I control the speed, then I press Start
then the machine starts rotating.
I can stop them, I could go to counter-clockwise, I could go to constant-speed
prime mover,
and so on. Many modes are available and they're all explained in the student manuals.
In the second exercise they will study the permanent magnet DC machine as a
generator.
To do that they will use the dynamometer in prime mover mode
and change the speed of rotation. They would also need
a general-purpose multimeter, although they could also connect in the data acquisition
and they will use that to monitor the voltage
and the current that is available in the machine. So if I connect, for example,
directly on the machine here,
I put it in voltage mode, when I make
the machine turn I will see that the actual voltage
depends on the speed that my
motor goes to. So more speed basically gives me
more voltage. In the third exercise they will study the permanent magnet DC
machine
as a motor. To do that, in order to have a variable power supply to apply to it,
we will use the dynamometer in the Power supply mode.
We will use it as a voltage source so you can control your DC voltage here,
and we will connect the variable power supply directly on the
motor itself.
Since we will interested in knowing the actual speed of the machine when we
apply
more or less voltage to it, we will need
to connect the shaft encoder outputs
of the dynamometer directly into the data acquisition unit,
so we can, on the computer screen, see the actual
speed, torque, mechanical power,
and other interesting values.
Let's now check how to do the connections on the data acquisition unit.
So first I will need to bring the speed into
the data acquisition. In order to do that you will need a
smaller leads that are supplied with this system. They did supply smaller
leads so you cannot
by mistake connect power
leads into the lower voltage connections.
So the shaft encoder output A
will go into the encoder input A.
The digital ground needs to be connected
to the digital drowned,
and the shaft encoder B
is to be connected to B. If I wanted to see the
voltage and current of my motor, I could
take my power supply here and connect it
directly to a voltmeter, for example,
E1,
and to see the current, instead of going straight on my motor,
I would want to go through an ammeter so I would put
a jumper here, from my positive power supply,
into an ammeter,
and output of the ammeter
into my DC motor.
All of these steps are very well explained in the book,
don't hesitate to open the student manual and try the steps one by one.
You will also need to bring power to the data acquisition
and to connect a USB cable from your computer
into the data acquisition.
After that, you launch the LV-DAC Software.
When you launch the LV-DAC software it should
automatically detect what is connected on your USB port.
In that case I have a single data acquisition unit,
but mine has all of the currently available functions inside it.
Yours might be a bit smaller.
If you don't see a list here, you should double-check your connections
and click Refresh to make sure that you are effectively connected.
Otherwise you will see just a set
of fixed measurements - not your actual measurements.
So I click Okay, and now I can look at my actual measurements into the metering,
for example, here I would need to click on the continuous refresh to see
the actual values.
And if I start my system
I can see the actual voltages
and current, they should just be set to DC though,
I can also see the speed
that I would need to set
speed to the encoder A&B in that case.
I can also see the values on the oscilloscope,
phasor analyzer or harmonic analyzer but in this case it's not very useful
because we are all working in DC values.
The next book deals with DC motor drives.
You will study the basic PWM DC motor drives,
the bidirectional PWM motor drives with rich narrative breaking,
and the speed feedback and current control in PWM DC motor drives.
Basically, to connect the drives, you will need to connect
your battery pack into the IGBT pack,
so here I have my battery pack
into my IGBTs,
on the DC bus.
Depending on the exercise an additional smoothing inductor might
also be required. But for the basic ones
DC goes in, and the output will go into my
DC motors to output,
from the IGBT into the motor here.
I could go through switch, if I wanted do,
into the motor, and the return
would go to the negative of the battery.
Now to control the IGBT the
gate control will come from the data acquisition and control interface, and it
will be controlled through the
LV-DAC software. So I will need to connect the gates
on the data acquisition unit using one of
the special cables supplied with it,
which is just a 9 connector cable.
If I want to take a look at the voltages and currents
I can connect them directly on the power inputs here,
four volt meters, four ammeters, and if I want to look at the gate signal I can
use the smaller cables to go
into the analog inputs. All of the
nice pedagocial ways to look at that are explained in detail in the books.
Now let's try to take a look at what happens when I start the actual control.
After you launch the software you will need to go into the data acquisition
and control interface, and select the chopper inverter control.
In the case of the first exercise, the
chopper that I want to use, is a buck chopper, so I want
to reduce the voltage. Directly in the settings here
I can control the duty cycle, the switching frequency,
the acceleration and deceleration time as well.
So if i start this, and play with the duty cycle,
I'm sending a higher average value to my motor,
once the switch is on,
and I should be able to see the motor running,
but only if I also bring the 24-volt power supply to
the IGBT module.
As you see, if I had followed the steps
in the manuals, I would have seen that. So in that case
I will stop here the chopper,
do the connection, and start again.
The worst that could happen is that you would go into overcurrent if you try to
go to a high speed at once.
In that case I want to stop here, and maybe put some
acceleration time to avoid going into overcurrent, say I put five seconds
for acceleration, and
five for deceleration.
All you need to do is reset the unit,
and start again. We can see that
in the dynamometer mode, the actual speed is 254 rpm.
So if I put my four-quadrant dynamometer
into the dynamometer mode, into the break mode,
and I start my function here.
I will monitor the actual speed; I can also apply a breaking
torque, let's say I start to 0,
slowly increase that torque. I can see my mechanical power,
and I can also see that the torque changed and the speed changed
until a point where if I apply too much torque,
I should be able to go to overcurrent.
The other modes that the course will explore are the regenerative breaking by
using a buck boost chopper,
and also a drive that would
include feedback, so in that case I would want
a buck chopper with feedback,
and I have access to the various parameters:
the proportional gain, integral game filter, in so long.
I also have a four-quadrant DC motor drive
without current control and a four-quadrant DC motor drive that would
include current control as well,
which in fact is a PI that is controlling another PI
in cascade mode.
So, in summary, all of the connections and measurements are very easy to do if you
follow the steps in the books.
But if you try to just guess it by yourself
you will probably have a very hard time figuring it out.
So, at first, before students walk in, just take the time to try the exercise by
reading step-by-step
"1. Connect this 2. Turn the switch on.", and so on.
and you shouldn't have any problem with that. If you have
any additional questions
please don't hesitate to send us an email at services@labvolt.com.
Thanks!