© 2002 qxdesign, inc. building a pi controller this unit discusses installation of visual modelq...
TRANSCRIPT
© 2002 QxDesign, Inc.
Building a PI controller
This unit discusses• Installation of Visual ModelQ• The Visual ModelQ default model• Placing and configuring blocks• Wiring a model• Compiling and running a model
Visual ModelQ Training
© 2002 QxDesign, Inc.
Install Visual ModelQ
• Click here to visit www.QxDesign.com
**This unit can be completed with a free (unregistered) copy of Visual ModelQ
• Download Visual ModelQ**• Run Visual ModelQ installation• Launch Visual ModelQ using the Windows start
button or clicking on the icon
• The “default model” should appear
To run Visual ModelQ the first time:
© 2002 QxDesign, Inc.
The default model
• The default model has two required elements, a Solver and a Scope. It also includes a square-wave generator wired to a 1-Channel Live Scope. Click Run to compile and run this model.
Live Scope displays on model canvas
Square-wave generator
Wire connecting generator output to scope input
Run button
© 2002 QxDesign, Inc.
Modify the default model
• Stop the model using the stop button or the escape key.• Select (click on) and delete the 1-Channel Live Scope.
© 2002 QxDesign, Inc.
Move Wave Gen
• Move the waveform generator to the left to make room. We’ll use this block to generate the command.
© 2002 QxDesign, Inc.
Add 2-Channel Live Scope
• 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.
© 2002 QxDesign, Inc.
Add a subtraction block
• 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.
© 2002 QxDesign, Inc.
Add PI Control Law
• 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.
© 2002 QxDesign, Inc.
Add Power Converter Model
• 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.
© 2002 QxDesign, Inc.
Configure the Power Converter
• 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.
© 2002 QxDesign, Inc.
Add Plant Scaling
• 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.
© 2002 QxDesign, Inc.
Add Integral
• 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.
`
The plant model is a combination of a gain block and an integral.
© 2002 QxDesign, Inc.
Add Live Constants
• 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.
© 2002 QxDesign, Inc.
Flip Live Constants
• 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.
© 2002 QxDesign, Inc.
Initialize Live Constants
• 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.
© 2002 QxDesign, Inc.
Wire the Model
• 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.
© 2002 QxDesign, Inc.
Save the Model
• Click “File, Save…” or use the file save icon.• Save as “Building a PI Controller”
© 2002 QxDesign, Inc.
Compile the Model
• Click the compile button. When the model compiles, the button changes from red to green and a grid is drawn in the Live Scope.
© 2002 QxDesign, Inc.
Set the Scope Scaling
• Double-click on Live Scope for control panel. Set Channel 1 scaling to 0.5; repeat for Channel 2. Set Time to 0.01.
© 2002 QxDesign, Inc.
Set the Scope Trigger
• Select Trigger Tab of Live Scope control panel. Select Normal trigger.
© 2002 QxDesign, Inc.
Run the Model
• 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.
© 2002 QxDesign, Inc.
Visit www.QxDesign.com for information about software and
practical books on controls.
Click here for information on Visual
ModelQ
Click here for information on Observers in Control Systems,
published by Academic Press in 2002
Click here for information on Control System Design Guide (2nd Ed.), published by Academic Press in
2000