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MATLAB SIMULINK - Simulation andModel Based Design
http://www.mathworks.com
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Simulink runs under Matlab. Firststart Matlab, then type simulink at
the Matlab prompt.
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The first window that
pops up is the Library
Browser.
This is a library ofblocks that are
available for putting
into the Simulink blockdiagram.
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Simulink Help
Select Simulink
Help from thehelp menu in thelibrary browser.
Here you canfind tutorials,demos,information onavailable blocks,and so on.
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A Simulink model is a block diagram. ClickFile|New|Model in the Library Browser. An empty
block diagram will pop up. You can drag blocks intothe diagram from the library.
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Sources: Produce Signals
Select sources from the library.
Drag any block you want to useinto the model.
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Sinks: Terminate Signals
Select sinks from the library.
Drag any block you want to useinto the model.
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Connecting Blocks
Drag a signal line from the output
of a block to the input of anotherblock.
Ctrl-Click will automaticallyconnect.
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Running the Simulation
Change parameters under
Simulation | Configuration
Parameters.
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Running the Simulation
Set start and
stop time for thesimulation here.
I often change
from variable-stepto fixed-step to get
a smoother-lookingsolution.
Note: numericalsolution usingode45!
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Viewing Results: Scope
Double click on the scope icon to
open up the viewer. You oftenhave to zoom out using thebinocular icon if the curve doesntfit in the default axes.
You can save data from the scope to
the workspace using the Parameters,Data History tab.
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Modifying Block Properties
Double click on any block tobring up a properties box.
Here are the sine waveproperties. If you dont knowwhat something is leave italone!!!
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Adding Comments
You can add text commentsanywhere in the block diagramby double clicking and typing insome text.
You can change the defaultcomments under the blocks bydouble clicking and editing thetext.
Do In-Class Problem #1. Should be 2:00 at the end of
the problem.
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Signal Routing
Under the signal routing library,the MUX block can be used tobundle a group of signalstogether into a single line.
The DEMUX block does thereverse.
This can be useful to:
1. Clear up clutter in acomplicated block diagram.
2. Send multiple signals to thesame scope; then bothsignals will be displayed on
the same plot.
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Transfer Functions
U(s) = 1/s
X(s)=1/(s(s+1))=1/s-1/(s+1)
So x(t)=1-exp(-t)
Do In-Class Problem #2. It should be 2:20 by the end of the problem.
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Closed Loop Control System:
Here is an example of a closed-loop system
with an on-off controller. Notice theoscillations in the response.
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Integrators and Derivatives
Integrators and derivatives are available in
the continuous library.
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Integrators
For integrators, you can set theinitial condition and limit theoutput to not be allowed to goabove or below some value onthe properties for that block.
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Setting Up Systems with Integrators
If you have a nonlinear equation system, you cant describe it with a transferfunction. One option is to put all of the operations in as individual blocks:
i(t)
J(t)=ki(t)-f()
where f(w) is coulomb and viscous friction.
Use integrators rather
than derivatives, andput in as many
integrators as there arestates. Thenbootstrap!
Do in-class problem #3. It should be 2:40 at the end of the problem.
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Subsystems
You can group a set of blocks together into a subsystem, by selecting them
and right clicking and saying Create Subsystem. They will all go under asingle block. If you double click the subsystem, you can see what is underthe mask.
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Running Simulink Models from M-files
[T,X,Y] = SIM('model',TIMESPAN,OPTIONS,UT)
Here is the heartof the m-file.
Constants in the
simulink modelcan be defined inthe workspace.
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Running Simulink Models from M-files
The input and output of
the simulink model aredefined in the block
diagram using input andoutput sources andsinks.
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Control and Estimation Tool
Set input and output
points by right clickingon a signal, and
selecting LinearizationPoints.
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Control and Estimation Tool SelectTools:Control
Design: LinearAnalysis fromthe simulinkmenu.
The control and
estimation toolwill pop up.Select the type ofplot you want to
generate, andclick linearizemodel. Thesystem will belinearized about
the operatingpoint (see Ogata3-10 andSimulink Help)
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Control and Estimation ToolThe selected type of
plot will pop up foryour linearizedsystem. If you wanta different type of
plot, look underEdit:PlotConfigurations.
To export thelinearized system tothe Workspace soyou can use it withother design tools inMatlab, select File:
Export.
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Communicating with the WorkspaceAny constant or variable defined
in the Matlab workspace isavailable in the block diagram.
The simin and simout blocksallow you to pass signals in fromthe workspace, and out to theworkspace. Change the saveformat to Array for easiest use
(double click on the ToWorkspace block for options).
The clock source allows you togenerate a time signal if youwant to send that back to theworkspace.
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Other Useful Blocks
Under Discontinuous youwill find coulomb friction,dead zone, saturation, andrelay.
Under Continuous thereis a delay block.
Under Simulink Extrasthere is a PID controller,transfer function with non-
zero initial conditions,some useful sinks (suchas power spectraldensity), and radians-to-
degrees and Fahrenheit-to-Celsius converters.