Transcript Visual ModelQ

Visual ModelQ Training
Building a PI controller
This unit discusses
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Installation of Visual ModelQ
The Visual ModelQ default model
Placing and configuring blocks
Wiring a model
Compiling and running a model
Install Visual ModelQ
To run Visual ModelQ the first time:
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Click here to visit www.QxDesign.com
Download Visual ModelQ**
Run Visual ModelQ installation
Launch Visual ModelQ using the Windows start
button or clicking on the icon
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The “default model”
should appear
**This unit can be completed with a free (unregistered) copy of Visual ModelQ
The default model
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The default model has two required elements, a Solver and a
Scope. It also includes a square-wave generator wired to a 1Channel Live Scope. Click Run to compile and run this model.
Square-wave
generator
Run
button
Wire connecting generator
output to scope input
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Live Scope
displays on
model canvas
Modify the default model
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Stop the model using the stop button or the escape key.
Select (click on) and delete the 1-Channel Live Scope.
Move Wave Gen
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Move the waveform generator to the left to make room. We’ll
use this block to generate the command.
Add 2-Channel Live Scope
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Add a 2-Channel Live Scope. We’ll use this to compare the
command and feedback signals. Click on the icon in the circle;
place as indicated by the arrow.
Add a subtraction block
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Place a subtraction block on the model canvas. We’ll use this
block to form the error, the difference between the command and
the feedback signals.
Add PI Control Law
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Add a PI (Proportional-Integral) Control Law from the “Analog”
tab. The PI controller is popular in industry because it’s simple
and it provides good performance in most systems.
Add Power Converter Model
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Add a 2-pole low-pass filter from the “Analog” tab to simulate the
effect of power conversion. All control systems have power
converters and a low-pass filter is often a good model.
Configure the Power Converter
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Set the frequency of the low-pass filter to 800 Hz to simulate an
800 Hz bandwidth converter. Double-click on the Frequency
node of the filter (in red circle) to view adjustment window.
Add Plant Scaling
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Add a “Scale-by” block from the “Math” tab to simulate the gain
of the “plant.” All plants have gain. Examples of plant gain are
inertia of a motor and inductance of a coil.
Add Integral
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Add an integral from the “Analog” tab to simulate an integrator in
the plant. The integrating plant is the most common plant in
industrial control systems.
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The plant model is a
combination of a gain
block and an integral.
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Add Live Constants
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Add 3 Live Constants from the “Constants” tab; these gains will
be easy to change while the model runs. Change the names to
KP, KI, and System Gain (double-click in strings under blocks).
Double-click
in this area to
change name.
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Flip Live Constants
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Flip the constants KI and System Gain; this will make wiring
more convenient. Right click inside each block and select “Flip
Horizontal” from the pop-up menu.
Initialize Live Constants
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Set initial gains as KP = 2, KI = 100, and System Gain = 500.
Set these gains by double-clicking on the diamond in the upper
left corner (shown by red circles) to get initialization window.
Wire the Model
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Select the wiring icon.
Connect 11 wires as below. Move mouse over a node and click
to start a wire; move to second node and click again to finish.
Example: move mouse to
one end and click to start
a wire; move to the other
end and click again.
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Save the Model
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Click “File, Save…” or use the file save icon.
Save as “Building a PI Controller”
Compile the Model
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Click the compile button. When the model compiles, the button
changes from red to green and a grid is drawn in the Live Scope.
Set the Scope Scaling
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Double-click on Live Scope for control panel. Set Channel 1
scaling to 0.5; repeat for Channel 2. Set Time to 0.01.
Set the Scope Trigger
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Select Trigger Tab of Live Scope control panel. Select Normal
trigger.
Run the Model
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Click the run button. The Live Scope compares command (blue)
to feedback (red). The values of KP(2) and KI (100) provide
good performance; settling time is ~15 mSec with little overshoot.
Visit www.QxDesign.com for
information about software and
practical books on controls.
Click here for information on Control
System Design Guide (2nd Ed.),
published by Academic Press in
2000
© 2002
QxDesign, Inc.
Click here for
information on Visual
ModelQ
Click here for information on
Observers in Control Systems,
published by Academic Press in
2002