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Create Simple Model

You can use Simulink® to model a system and then simulate the dynamic behavior of that system. Simulink allows you to create block diagrams, where blocks you connect represent parts of a system, and signals represent input/output relationships between those blocks. The primary function of Simulink is to simulate behavior of system components over time. In its simplest form, this task involves keeping a clock, determining the order in which the blocks are to be simulated, and propagating the outputs, computed in the block diagram, to the next block. Consider a switch that turns on a heater. At each time step, Simulink must compute the output of the switch, propagate it to the heater, and then compute the heat output.

Often, the effect of a component's input on its output is not instantaneous. For example, turning on a heater does not result in an instant change in temperature. Rather, this action provides input to a differential equation, and the history of the temperature (a state) is also a factor. When the simulation of a block diagram requires solving a differential or difference equation, Simulink employs memory and numerical solvers to compute the state values for the time step.

Simulink handles data in three categories:

  • Signals — Block inputs and outputs, computed during simulation

  • States — Internal values, representing the dynamics of the block, computed during simulation

  • Parameters — Values that affect the behavior of a block, controlled by the user

At each time step, Simulink computes new values for signals and states. By contrast, you specify parameters when you build the model and can occasionally change them while simulation is running.

Model Overview

The basic techniques you use to create a simple model in this tutorial are the same techniques that you use for more complex models. This example simulates simplified motion of a car, after a brief press of the accelerator pedal.

A Simulink block is a model element that defines a mathematical relationship between its input and output. To create this simple model, you need four Simulink blocks.

Block nameBlock PurposeModel Purpose
Pulse GeneratorGenerate an input signal for the model Simulate the accelerator pedal
GainMultiply the input signal by a factorSimulate how pressing the accelerator affects the car's acceleration
Integrator, Second-OrderIntegrate input signal twiceObtain position from acceleration
OutportDesignate a signal as an output from the modelDesignate the position as an output from the model

Simulating this model integrates a brief pulse twice to get a ramp and then displays the result in a Scope window. The input pulse represents a press of the accelerator pedal in a car, and the output ramp represents the increasing distance from the starting point.

Open New Model

Use the Simulink Editor to build your models.

  1. Start MATLAB®. From the MATLAB Toolstrip, click the Simulink button .

  2. Click the Blank Model template.

    The Simulink Editor opens.

  3. From the File menu, select Save as. In the File name text box, enter a name for your model, For example, simple_model. Click Save. The model is saved with the file extension .slx.

Open Simulink Library Browser

Simulink provides a set of block libraries, organized by functionality in the Library Browser. The following libraries are common to most workflows:

  • Continuous — Building blocks for systems with continuous states

  • Discrete — Building blocks for systems with discrete states

  • Math Operations — Blocks that implement algebraic and logical equations

  • Sinks — Blocks that store and show the signals that connect to them

  • Sources — Blocks that generate the signal values that drive the model

  1. From the Simulink Editor toolbar, click the Library Browser button .

  2. Set the Library Browser to stay on top of the other desktop windows. On the Library Browser toolbar, select the Stay on top button .

To browse through the block libraries, select a MathWorks® product and then a functional area in the left pane. To search all of the available block libraries, enter a search term.

For example, find the Pulse Generator block. In the search box on the browser toolbar, enter pulse, and then press the Enter key. Simulink searches the libraries for blocks with pulse in their name or description, and then displays the blocks.

Get detailed information about a block. Right-click a block, and then select Help for the Pulse Generator block. The Help browser opens with the reference page for the block.

Blocks typically have several parameters. You can access all parameters by double-clicking the block.

Add Blocks to a Model

To start building the model, browse the library and add the blocks.

  1. From the Sources library, drag the Pulse Generator block to the Simulink Editor. A copy of the Pulse Generator block appears in your model with a text box for the value of the Amplitude parameter. Enter 1.

    Parameter values are held throughout the simulation.

  2. Add the following blocks to your model using the same approach.

    GainSimulink/Math Operations

    Gain: 2

    Integrator, Second OrderSimulink/Continuous

    Initial condition: 0


    Port number: 1

    Add a second Outport block right-clicking and dragging the existing one.

    Your model should now have the blocks you need.

  3. Arrange the blocks as follows by clicking and dragging each block. To resize a block, click and drag a corner.

Connect Blocks

Connect the blocks by creating lines between output ports and input ports.

  1. Click the output port on the right side of the Pulse Generator block.

    The output port, and all input ports suitable for a connection get highlighted.

  2. Click the input port of the Gain block.

    Simulink connects the blocks with a line and an arrow indicating the direction of signal flow.

  3. Connect the output port of the Gain block to the input port on the Integrator, Second Order block.

  4. Connect the two outputs of the Integrator, Second Order block to the two Outport blocks.

  5. Save your model. Select File > Save and provide a name.

Your model is complete.

Add Signal Viewer

To view the results, connect the first output to a Signal Viewer.

Access the context menu by right-clicking the signal. Select Create & Connect Viewer > Simulink > Scope. This creates a viewer icon on the signal, and opens a Viewer display.

You can open the viewer at any time by double-clicking the icon.

Run Simulation

After you define the configuration parameters, you are ready to simulate your model.

  1. On the model window, set the simulation stop time by changing the value at the toolbar.

    The default stop time of 10.0 is appropriate for this model. This time value has no unit. Time unit in Simulink depends on how the equations are constructed. This example simulates the simplified motion of a car for 10 seconds.

  2. To run the simulation, click the Run simulation button .

The simulation runs and produces the output on the Viewer.

See Also


Related Topics

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