Mathworks SIMULINK 7 Installation Guide

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Simulink

Getting Started Guide

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Simulink

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Getting Started Guide

Revision History

September 2005 Online only New for Version 6.3 (Release 14SP3) March 2006 Online only Revised for Simulink September 2006 Online only Revised for Simulink March 2007 First printing Revised for Simulink September 2007 Second printing Revised for Simulink March 2008 Third printing Revised for Simulink October 2008 Fourth printing Revised for Simulink March 2009 Fifth printing Revised for Simulink September 2009 Online only Revised for Simulink March 2010 Online only Revised for Simulink

6.4 (Release 2006a)

6.5 (Release 2006b)

6.6 (Release 2007a)

7.0 (Release 2007b)

7.1 (Release 2008a)

7.2 (Release 2008b)

7.3 (Release 2009a)

7.4 (Release 2009b)

7.5 (Release 2010a)

Introduction

Product Overview ................................. 1-2

Overview Tool for Model-Based Design Tool for Simulation Tool for Analysis How Simulink Software Interacts with the MATLAB

Environment

........................................ 1-2

........................ 1-3

................................ 1-4

.................................. 1-4

................................... 1-4

Contents

What Is Model-Based Design?

Model-Based Design Modeling Process

Related Products

............................... 1-5

.................................. 1-6

.................................. 1-9

....................... 1-5

Simulink Software Basics

Starting Simulink Software ........................ 2-2

Opening the Simulink Library Browser Opening a Model

Simulink User Interface

Simulink Library Browser Simulink Model Window

Getting Help with Sim ulin k Software

Simulink Online Help Simulink Demo Models Web Site Resources

.................................. 2-4

............................ 2-6

.......................... 2-6

............................ 2-9

.............................. 2-10

............................. 2-11

................................ 2-14

............... 2-2

............... 2-10

Creating a Simulink Model

Overview ......................................... 3-2

Creating a Simple Model

Overview Creating a New Model Adding Blocks to Your Model Moving Blocks in the Model Window Connecting Blocks in the Model Window Saving the Model

Simulating the Model

Overview Setting Simulation Options Running the Simulation and Observing Results

........................................ 3-3

.................................. 3-13

........................................ 3-14

........................... 3-3

............................. 3-3

........................ 3-5

.................. 3-8

............... 3-9

.............................. 3-14

......................... 3-14

......... 3-16

Modeling a Dynamic Control System

Overview ......................................... 4-2

Understanding the Demo M odel

Opening the Demo Model Anatomy of the Demo Model Using Subsystems Masking Subsystems

................................. 4-6

........................... 4-3

.............................. 4-9

..................... 4-3

........................ 4-5

vi Contents

Simulating the Model

Running the Simulation Modifying Simulation Parameters Importing Data from the MATLAB Workspace Exporting Simulation Data to the MATLAB Workspace

.............................. 4-11

............................ 4-11

.................... 4-13

......... 4-20

.. 4-25

Index

vii

viii Contents

Introduction

• “Product Overview” on page 1-2

• “What Is Model-Based Design ?” on page 1-5

• “Related Products” on page 1-9

1 Introduction

Product Overview

Overview

Simulink®software models, simulates, and analyzes dynamic systems. It enables you to pose a question about a system, model the system, and see what happens.

In this section...

“Overview” on page 1-2

“Tool for Model-Based Design” on page 1-3

“Tool for Sim ulation” on page 1-4

“Tool for Analys is” on page 1-4

“How Simulink Software Interacts with the MATLAB Environment” on page 1-4

1-2

With Simulink, you can easily build models from scratch, or modify existing models to meet your needs. Simulink supports linear and nonlinear systems, modeled in continuous time, sampled time, or a hybrid of the two. Systems can also be multirate — having d ifferent parts that are sampled or updated at different rates.

Thousands of scientists and engineers around the world use Simulink to modelandsolverealproblemsinavariety o f industries, including:

• Aerospace and Defense

• Automotive

• Communications

• Electronics and Signal Processing

• Medical Instrumentation

Product Overview

Tool for Model-Based Design

With Simulink, you can move beyond idealized linear models to explore more realistic nonlinear models, f actori ng in friction, air resistance, gear slippage, hard stops, and the other things that describe real-world phenomena. Simulink turns your computer into a laboratory for modeling and analyzing systems that would not be possible or practical otherwise.

Whether you are interested in the behavior of an automotive clutch system, the flutter of an airplane wing, or the effect of the monetary supply on the economy, Simulink provides you with the tools to model and simulate almost any real-world problem. Simulink also provides demos that model a wide variety of real-world phenomena (see “Simulink Demo Models” on page 2-11).

Simulink provides a graphical user interface (GUI) for building models as block diagrams, allowing you to draw models as you would with pencil and paper. Simulink also includes a comprehensive block library of sinks, sources, linear and nonlinear components, and connectors. If these blocks do not meet your needs, however, you can also create your own blocks. The interactive graphical environment simplifies the modeling process, eliminating the need to formulate differential and difference equations in a language or program.

Models are hierarchical, so you can build models using both top-down and bottom-up approaches. You can view the system at a high level, then double-click blocks to see increasing levels of model detail. This approach provides insight into how a model is organized and how its parts interact.

1-3

1 Introduction

Tool for Simulation

After you define a model, you can simulate it, using a choice of mathematical integration methods, either from the Simulink menus or by entering commands in the MATLAB for interactive work, while the command line is useful for running a batch of simulations (for example, if you are doing Monte Carlo simulations or want to apply a parameter across a range of values).

Using scopes and other display blocks, you can see the simulation results while the simulation runs. You can then change many parameters and see what happens for “what if” exploration. The simulation results can be put in the MATLAB workspace for postprocessing and visualization.

Command Window. The menus are convenient

Tool for Analysis

Model analysis too ls include linearization and trimming tools, which can be accessed from the M ATLAB command line, plus the many tools in M ATLAB and its application toolboxes. Because MATLAB and Simulink are integrated, youcansimulate,analyze,andreviseyour models in either environment at any point.

1-4

How Simulink Software Interacts with the MATLAB Environment

Simulink software is tightly integrated with the MATLAB environment. It requires MATLAB to run, depending on it to define and evaluate model and block parameters. Simulink can also utilize many MATLAB features. For example, Simulink can use the MATLAB environment to:

• Define model inputs.

• Store model o utputs for analysis and visualization.

• Perform functions within a model, through integrated calls to MATLAB

operators and functions.

What Is Model-Based Design?

In this section...

“Model-Based Design” on page 1-5

“Modeling Process” o n page 1-6

Model-Based Design

Model-Based Design is a process that enables faster, more cost-effective development of dynamic systems, includin g control systems, signal processing, and communications systems. In Model-Based Design, a system model is at the center of the development process, from requirements development, through design, implementation, and testing. The model is an executable specification that is continually refined throughout the dev elo pment process. After model development, simulation shows whether the model works correctly.

When software a nd hardware implementation requirements are included, such as fixed-point and timing behavior, you can automatically generate code for embedded deployment and create tes t benches for system verification, saving time and avoiding the introduction of manually coded errors.

What Is Model-Based Design?

Model-Based Design allows you to improve efficiency by :

• Using a common design environment across project teams

• Linking designs directly to requirements

• Integrating testing with design to continuously identify and correct errors

• Refining algorithms through multidomain simulation

• Automatically generating embedded software code

• Developing and reusing test suites

• Autom atically generating documentation

• Reusing d esigns to deploy systems across multiple processors and hardware

targets

1-5

1 Introduction

Modeling Proces

There are six ste

1 Defining the Sy

2 Identifying System Components

3 Modeling the System with Equations

4 Building the

5 Running the Simulation

6 Validating the Simulation Results

You perform the first three steps of this process outside of the Simulink software before you begin building your model.

Defining

The first step in modeling a dynamic system is to fully define the system. If you are modeling a large system that can be broken into parts, you should model each subcomponent on its own. The n, after building each component, you can integrate them into a complete model of the system.

ps to modeling any system:

Simulink Block Diagram

the System

stem

1-6

For example, the demo model used l ater in th is guide models the heating system of a house. This system can be broken down into three m ain parts:

• Heater subsystem

• Thermostat subsystem

• Thermodynamic model subsystem

The most effective way to build a model of this system is to consider each of these subsystems independently.

ntifying System Components

Ide

The second step in the modeling process is to identify the system components. Three types of components define a system:

What Is Model-Based Design?

• Parameters — System values that remain constant unless you change

them

• States — Variables in the system that change over time

• Signals — Input and output values that change dynamically during the

simulation

In Simulink, parameters and states are represented by blocks, while signals are represented by the lines that connect blocks.

For each subsystem that you identified, ask yourself the fo ll owing questions:

• How many input signals does the subsystem have?

• How many output signals does the subsystem have?

• How many states (variables) does the subsystem have ?

• What are the parameters (constants) in the subsystem?

• Are there any intermediate (internal) s ignals in the subsystem?

Once you have answered these questions, you should have a comprehensive list of the system components, and are ready to begin modeling the system.

Modeling the System with Equations

The third step in modeling a system is to formu l ate the mathematical equations that describe the system.

For each subsystem, use the list of system compo nents you identified to describe the system mathematically. Your model may include:

• Algebraic equations

• Logical equations

• Differential equations, for continuous systems

• Difference equations, for discrete systems

You use these equations to create the block diagram in Simulink.

1-7

1 Introduction

Building the Simulink Block Diagram

After you have defined the mathematical equations that describe each subsystem, you can begin building a block diagram of your model in Simulink.

Build the block diagram for each of your subcomponents separately. After you have modeled each subcomponent, you can then integrate them into a complete model of the system.

See “Cre ating a S imple Model” on page 3-3 for more information on building the block diagram.

Running the Simulation

After you build the Simulink block diagram, you can simulate the m o del and analyze the results.

Simulink allows you to interactively define system inputs, simulate the model, and observe changes in behavior. This allows you to quickly evaluate your model.

1-8

See“SimulatingtheModel”onpage3-14formoreinformationonrunninga simulation.

Validating the Simulation Results

Finally, you must validate that the model accurately represents the physical characteristics of the system.

You can use the linearization and trimming tools available from the MATLAB command line, plus the many tools in MATLAB and its application toolboxes to analyze and validate your model.

Related Products

1-9

1 Introduction

1-10

Simulink Software Basics

• “Starting Simulink Software” on page 2-2

• “Simulink User Interface” on page 2-6

• “Getting Help w ith Simulink Software” on page 2-10

2 Simulink

Software Basics

Starting Simulink Software

In this section...

“Opening the Simulink Library Browser” on page 2-2

“Opening a M odel” on page 2-4

Opening the Simulink Library Browser

Your M ATLAB environment must be running before you can open Simulink software. You start Simulink from within MATLAB.

To start Simulink and open the Simulink Library Browser:

1 Start MATLAB. For more information, see “Starting a MATLAB Session”

in the MATLAB Getting Started Gu ide.

2 Enter simulink in the MATLAB Command Window.

2-2

The Simulink Library Browser opens.

Starting Simulink®Software

Note You can also start Simulink by:

• Clicking the Simulink icon

in the MATLAB toolbar

• Clicking the MATLAB Start button, then selecting Simulink > Library

Browser

2-3

2 Simulink

Software Basics

Opening a Model

You can open e xis Simulink Librar

ting Simulink models or create new models from the

yBrowser.

To create a new m

• Select File > N

Thesoftwareo

odel:

ew > Mode l in the Simulink Library Browser.

pens an empty model window.

2-4

Starting Simulink®Software

To open an existing model:

1 Select File > Open in the Simulink Library Browser.

The Open dialog box appears.

2 Select the model (.mdl file) you want to open, then click Open.

The software opens the selected model in the model window.

2-5

2 Simulink

Software Basics

Simulink User Interface

In this section...

“Simulink Library Browser” on page 2-6

“Simulink Model Window” on page 2-9

Simulink Library Browser

The Library Browser displays the Simulink block libraries installed on your system. You build models b y copying blocks from a library into a model window.

Block Search

2-6

Selected Library

Block Description

Simulink®Library Browser

Selected Block

Simulink®User Interface

Tips for Using the Library Browser

When using t h e Library Browser, note the following:

• You can view the blocks in a library by selecting the library name on the

left side of the Library Browser, or by double-clicking the library.

• When you select a block, a description of that block appears at the bottom

of the browser.

• For more information on a block, select the block, then select Help > Help

on the Selected Block to display the help page for the block.

• You can view the parameters for a block by right-clicking the block, then

selecting Block Parameters.

• You can search for a specific block by entering the name of the block in the

block search field, then clicking the Find block icon

Standard Block Libraries

Simulink software provides 16 standard block libraries. The following table describes each of these libraries.

Block Library

Commonly Used Blocks

Continuous Contains blocks that model linear functions, such as

Discontinuities

Discrete

Logic and Bit Operations

Description

Contains a group of the most commonly used blocks, such as the Constant, In1, Out1, Scope,andSum blocks. Each of the blocks in this library are also included in other libra ries.

the Derivative and Integrator blocks.

Contains blocks with outputs that are discontinuous functions of their inputs, such as the Saturation block.

Contains blocks that represent discrete time functions, such as the Unit Delay block.

Contains blocks that perform logic or bit operations, such as the Logical Operator and Relational

Operator blocks.

2-7

2 Simulink

Software Basics

Block Library

LookUp Tables

Description

Contains blocks that use lookup tables to determine their outputs from their inputs, such as the Cosine and Sine blocks.

Math Operations Contains blocks that perform mathematical and

logical functions, such as the Gain, Product,and

Sum blocks.

Model Verification

Contains blocks that enable you to create self-validating models, such as the Check Input

Resolution block.

Model-Wide Utilities

Ports & Subsystems

Contains blocks that provide information about the model, such as the Model Info block.

Contains blocks that allow you to create subsystems, such as the In1, Out1,andSubsystem blocks.

Signal Attributes Contains blocks that modify the attributes of signals,

such as the Data Type Conversion block.

Signal Routing Contains blocks that route signals from one point in

a block diagram to another, such as the Mux and

Switch blocks.

Sinks Contains blocks that display or export output, such

as the Out1 and Scope blocks.

2-8

Sources Contains blocks that generate or import system

inputs, such as the Constant, In1,andSine Wave blocks.

User-Defined Functions

Contains blocks that allow you to define custom functions, such as the Embedded MATLAB

Function block.

Additional Math &Discrete

Contains two additional libraries for mathematical and discrete function blocks.

Simulink®User Interface

Simulink Model W

The model window in the model wind each block, and

The model window also allows you to:

contains the block diagram of the model. You build models

ow by arranging blocks logically, setting the parameters for

then connecting the blocks with signal lines.

indow

• Set configuration parameters for the model, including the start and stop

time, type of solver to use, and data import/export settings.

• Start and stop simulation of the model.

• Save the model.

• Print the block diagram.

2-9

2 Simulink

Software Basics

Getting Help with Simulink Software

In this section...

“Simulink Online Help” on page 2-10

“Simulink Demo Models” on page 2-11

“Web Site Resources” on page 2-14

Simulink Online Help

Simulink software provides comprehensive o nline help that describes Simulink features, blocks, and functions, and provides detailed procedures for common tasks. The help includes online versions of all Simulink documentation, including:

• Simulink Getting Started Guide (this guide)

• Simulink User’s Guide

2-10

• Simulink Reference

• Writing S-Functions

• Simulink Release Notes

You access the online help from the Help menu of the Simulink Library Browser or model w indow .

Toaccesstheonlinehelp:

• From the Simulink Library Browser, select Help > Simulink Help.

• From the Simulink model window, select Help > Using Simulink.

Note To quickly access the help page for a specific block, right-click the

block and select Help.

Getting Help with Simulink®Software

Simulink Demo Mo

Simulink softwa modeling concep the MATLAB C omm

To access Simu

1 On the bottom l

Start button

The Start menu appears.

2 Select Simulink > Demos from the Start menu.

re provides a variety of demo models that illustrate key ts and Simulink features. You can access these dem os from

and Window.

link demos:

eft corner of the MATLAB Command Window, click the

dels

2-11

2 Simulink

Software Basics

2-12

Getting Help with Simulink®Software

3 From the Simulink demos page in the MATLAB Help browser, click the

demo model you want to open.

2-13

2 Simulink

Software Basics

Web Site Resourc

You can access ad site, including support.

To access the S

http://www.m

ditional Simulink resources on the MathWorks™ Web

Simulink related books, prerecorded webinars, and technical

imulink product page, go to:

athworks.com/products/simulink

2-14

Creating a Simulink Model

• “Overview” on page 3-2

• “Creating a Simple Model” on page 3-3

• “Simulating the Model” on page 3-14

3 Creating a Simulink

Overview

Model

This chapter describes how to create a simple model using Simulink software, and h ow to simulate that model. The basic techniques you use to create and simulate this simple model are the same as those for more complex models.

The model described in this chapter integrates a sine wave and displays the result along with the original w a ve. When completed, the block diagram of the model should look similar to this:

3-2

The instructions for constructing and simulating the example model are brief. However, each task is described in more detail in Simulink User’s Guide.

Creating a Simple Model

In this section...

“Overview” on page 3-3

“Creating a New Model” on page 3-3

“Adding Blocks to Your Model” on page 3-5

“Moving Blocks in the Model Window” on page 3-8

“Connecting B locks in the Model Window” on page 3-9

“Saving the Model” on page 3-13

Overview

This section describes how to model a simple dynamic system using Simulink software. A fter you create the model, you can simulate it as described in “Simulating the Model” on page 3-14.

Creating a Simple Model

Creating a New Model

Before you can begin building your model, you must start Simulink and create an empty model.

To create a new model:

1 If Simulink is not running, enter simulink in the MATLAB Command

Window to open the Simulink Library Browser.

2 Select File>New>Modelin the Simulink Library Browser to create a

new model.

software opens an empty model window.

The

3-3

3 Creating a Simulink

Model

3-4

Creating a Simple Model

Adding Blocks to

To construct a mo to the model wind four blocks:

• Sine Wave —Tog

• Integrator —T

• Scope —Tovis

• Mux —Tomulti

scope

To add block

1 Select the

The Simulink Library Browser displays the Sources library.

del, you first copy blocks from the Simulink Library Browser

ow. To create the simple model in this chapter, you need

o process the input signal

ualize the signals in the model

s to your model:

Sources library in the Simulink Library Browser.

Your Model

enerate an input signal for the model

plex the input signal and processed signal into a single

3-5

3 Creating a Simulink

Model

3-6

2 Select the Sine Wave block in the Simulink Library Browser, then drag it

to the model window.

A copy of the Sine Wave block appears in the model window.

3 Select the Sinks library in the Simulink Library Browser.

Creating a Simple Model

4 Select th

e Scope block from the Sinks library, then drag it to the model

window.

A Scope block appears in the model window.

5 Select the Continuous library in the Simulink Library Browser.

6 Select

the mod

the Integrator block from the Continuous library, then drag it to

el window.

An Integrator block appears in the model window.

7 Select the Signal Routing library in the Simulink Library Browser.

ct the Mux block from the Sinks library, then drag it to the model

8 Sele

ow.

wind

A Mux block appears in the model window.

3-7

3 Creating a Simulink

Model

Moving Blocks in

Before you conne logically to mak

To move a block i

• Drag the block

• Select the blo

Arrange the b

ct the blocks in your model, you should arrange them

e the signal connections as straightforward as possible.

n the model window, you can either:

ck, then press the arrow keys on the keyboard.

locks in the model to look like the following figure.

the Model Window

3-8

Creating a Simple Model

Connecting Bloc

After you add blo the signal conne

Notice that eac brackets repr

• The > symbol po

• The

Input port Output port

The following sections describe how to connect blocks by drawing lines from output ports to input ports:

• “Drawing Lines Between Blocks” on page 3-9

• “Drawing a Branch Line” on page 3-11

> symbol p

ctions within the model.

h block has angle brackets on one or both sides. These angle

esent input and output ports:

ks in the Model Window

cks to the model window, you must connect them to represent

inting into a block is an input port.

ointing out of a block is an output port.

Drawing Lines Between Blocks

You connect the blocks in your model by drawing lines betwee n output ports and input ports.

To draw a line between two blocks:

1 Position the mouse pointer over the output port on the right side of the

Sine Wave block.

Notethatthepointerchangestoacrosshairs(+)shapewhileovertheport.

3-9

3 Creating a Simulink

Model

2 Drag a line from the output port to the top input port of the Mux block.

Note that the that the poin input port o

3 Release the mouse button over the output port.

line is dashed while you hold the mouse button down, and

ter changes to a double-lined cross hairs as it approaches the

ftheMuxblock.

The software connects the blocks with an arrow that indicates the direction of signal flow.

3-10

4 Drag

a line from the output port of the Integrator block to the bottom input

tontheMuxblock.

por

The software connects the blocks.

Creating a Simple Model

5 Select the Mux block, then Ctrl+click the Scope block.

The softw are automatically draws the connection line between the blocks.

Note The Ctrl+click shortcut is especially useful w h en you are conn ecti n g widely separated blocks, or when working with complex models.

The model should now look similar to the following figure.

Drawing a Branch Line

The model is almost complete, but on e connection is missing. To finish th e model, you must connect the Sine Wave block to the Integrator block.

This final connection is somewhat different from the other three, which all connect output ports to input ports. Because the output port of the Sine Wave block already has a connection, you must connect this existing line to the input port of the Integrator block. The new line, called a branch line, carries the same signal that passes from the Sine Wave block to the Mux block.

Toweldaconnectiontoanexistingline:

1 Position the mouse pointer on the line between the Sine W ave and the

Mux block.

3-11

3 Creating a Simulink

Model

2 Press and hold the Ctrl key, then drag a line to the Integrator block’s

input port.

3-12

Thesoftwaredrawsalinebetweenthestartingpointandtheinputportof the Integrator block.

The m odel is now complete. It should look similar to the following figure.

Saving the Model

After you comple

te the model, you should save it for future use.

Creating a Simple Model

To save the mode

1 Select File > S

2 Specify the location in wh ich you want to save the model.

3 Enter simple_model in the File name field.

4 Click Save.

The softw are saves the model with the file name

ave in the model window.

simple_model.mdl.

3-13

3 Creating a Simulink

Model

Simulating the Model

In this section...

“Overview” on page 3-14

“Setting Simulation Options” on page 3-14

“Running the Simulation and Observing Results” on page 3-16

Overview

After you complete the model, you can simulate it and visualize the results. This section describes how to simulate the sample model you created in the previous section, “Creating a Simple Model” on page 3-3.

Setting Simulation Options

Before simulating a model, you can set simulation options such as the start andstoptime,andthetypeofsolverthat Simulink software uses to solve the model at each time step. You specify these options using the Configuration Parameters dialog box.

3-14

To specify simulation options for the sample model:

1 Select Simulation > Configuration Parameters in the model window.

The software displays the Configuration Param eters dialog box.

Simulating the Model

2 Enter 2

3 Click OK.

in the Stop time field.

Thesoftwareappliesyourchangestotheparametersandclosesthe Configuration Parameters dialog box.

Note For more information o n Simulink configuration parameters, see “Configuration Parameters Dialog Box” in the Simulink online documentation.

3-15

3 Creating a Simulink

Model

Running the Simu

Now you are ready simulation resu

To run the simul

1 Select Simula

Thesoftwarerunsthemodel,stopping when it reaches the stop time specified in the Configuration Parameters dialog box.

Tip On computers running the Microsoft®Windows®operating system, you

can click the Start simulation button

in the model w indow toolbar to start and stop a simulation.

2 Double-click the Scope block in the model window.

The Scope window displays the simulation results.

lts.

ation:

tion > Start in the model window.

lation and Observing Results

to simulate your example model and observe the

and Stop simulation button

3-16

Simulating the Model

3 Select Fi

le > Save in the model window.

Thesoftwaresavesthemodel.

4 Select File > Close in the model window.

The soft

ware closes the model.

3-17

3 Creating a Simulink

Model

3-18

Modeling a Dynamic Control System

• “Overview” on page 4-2

• “Understanding the Demo Model” on page 4-3

• “Simulating the Model” on page 4-11

4 Modeling a Dynamic Control System

Overview

This chapter illustrates how Simulink software can model a dynamic control system, using an example that simulates the thermodynamics of a house. The system models the outdoor environment, the thermal characteristics of the house, and the house heating system.

This chapter allows you to explore common Simulink modeling tasks, including:

• Grouping multiple blocks in a model into a single subsystem, simplifying

the block diagram

• Customizing the appearance of blocks using the masking feature

• Simulating a model and observing the results using a Scope block

• Changing the input parameters of the model to investigate how the system

responds

• Importing data from the MATLAB workspace into a model before

simulation

4-2

• Exporting simulation data from the model back to the MATLAB workspace

Understanding the Demo Model

In this section...

“Opening the Demo Model” on page 4-3

“Anatomy of the Demo Model” on page 4-5

“Using Subsystems” on page 4-6

“Masking Subsystems” on page 4-9

Opening the Demo Model

The demo model described in this chapter is called sldemo_househeat.You can open it from the MATLAB Command Window.

To open the demo model:

1 Ensure that MATLAB is open.

Understanding the Demo Model

2 Enter sldemo_househeat in the MATLAB Command Window.

The sof

tware starts and opens the

sldemo_househeat model.

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4 Modeling a Dynamic Control System

4-4

Understanding the Demo Model

Anatomy of the Demo Model

The demo system models the outdoor environment, the thermal characteristics ofthehouse,andthehouseheatingsystem.Itallowsyoutosimulatehowthe thermostat setting and outdoor environment affect the indoor temperature and cumulative heating costs.

The demo model includes many of the same blocks you used to create the simple model in Chapter 3, “Creating a Simulink Model”. These include:

• A Scope block (labeled

PlotResults) on the far right displays the

simulation results.

• A Mux block at the bottom right combines the indoor and outdoor

temperature signals for the Scope.

• A Sine Wave block (labeled

Daily Temp Variation) at the bottom left

provides one of three data sources for the model.

In the demo, the thermostat is set to 70 degrees Fahrenheit. The system models fluctuations in outdoor temperature by applying a sine wave with amplitude of 15 degrees to a base temperature of 50 degrees.

The three data inputs (sources) are provided by two Constant blocks (labeled

Set Point and Avg Outdoor Temp), and the Sine Wave block (labeled Daily Temp Variation

). The Scope block labeled PlotResults is the one output

(sink).

4-5

4 Modeling a Dynamic Control System

Using Subsystem

The sldemo_hous appearance of th the appearance encapsulated b

The demo model

• Thermostat

• Heater

• House

• Fahrenheit

• Celsius to

eheat

e block diagram, create reusable compon ents, a nd customize

of blocks. A subsystem is a hierarchical grouping of blocks

y a single Subsystem block.

uses the following subsystems:

to Celsius

Fahrenheit

demo model uses subsystems to simplify the

4-6

Understanding the Demo Model

Subsystems can be complex and contain many blocks that might otherwise clutter a diagram. For e xample, double-click the

House subsystem to open it.

Contents of House subsystem

You can see that the subsystem receives heat flow and external temperature as inputs, which it uses to compute the current room temperature. You could leave each of these blocks in the main model window, but combining them as a subsystem helps simplify the block diagram.

4-7

4 Modeling a Dynamic Control System

Subsystems can also be simple and contain only a few blocks. For example, double-click the

Contents of Thermostat subsystem

This subsys te m models the operation of a thermostat, determining when the heating system is on or off. It contains only one Relay block, but logically represents the thermostat in t h e block diagram.

Thermostat subsystem to open it.

4-8

Subsystems are also reusable, enabling you to implement an algorithm once and use it multiple tim es. F or example, the model contains two instances of identical subsystems named

Fahrenheit to Celsius. These subsystems

convert the inside and outside temperatures from degrees Fahrenheit to degrees Celsius.

Creating a Subsystem

Creating a subsystem allows you to group multiple related blocks into one subsystem block.

To create a subsystem:

1 Select the Thermostat block in the demo model.

2 Shift-click the Heater block in the demo model to select it.

3 Select Edit > Create Subsystem in the model window.

Understanding the Demo Model

The software creates a Subsystem block containing the Thermostat and Heater blocks.

4 Select Edit > Undo Create Subsystem to return the model to its original

configuration.

For more information about working with subsystems, see “Creating Subsystems” in the Simulink User’s Guide.

Masking Subsystems

You can customize the appearance of a subsystem by using a process known as masking. Masking a subsystem allows you to specify a unique icon and dialog box for the Subsystem block. For example, the subsystems display custom icons that depict physical objects, while the conversion subsystems display custom dialog bo xe s when you double-click them.

House and Thermostat

w the underlying blocks in the conversion subsystem, right-click the

To vie

ystem block, then select Look Under Mask.

subs

4-9

4 Modeling a Dynamic Control System

Contents of Fahrenheit to Celsius subsystem

Creating a Subsystem Mask

To mask a subsystem:

1 Select the Heater block in the demo model.

4-10

2 Select Edit > Mask Subsystem in the model window.

The Mask Editor dia log box a ppears.

3 Select disp (show text in center of block) in the Command

drop-down menu.

4 Enter disp('HEATER') in the Drawing commands field.

5 Click OK.

The software masks the subsystem block with the text you entered.

For more information about masking subsystems, see “Working with Block Masks” in the Simulink User’s Guide.

Simulating the Model

In this section...

“Running the Simulation” on page 4-11

“Modifying Simulation Parameters” on page 4-13

“Importing Data from the MATLAB Workspace” on page 4-20

“Exporting Simulation Data to the MATLAB Workspace” on page 4-25

Running the Simulation

Simulating the model allows you to observe how the thermostat setting and outdoor environment affect the indoor temperature and the cumulative heating cost.

To run the simulation:

1 In the demo model window, double-click the Scope block named

PlotResults.

Simulating the Model

ThesoftwareopensaScopewindowthat contains two axes with the labels “HeatCost” and “Temperatures.”

2 Selec

t Simulation > Start in the model w indow.

The software simulates the model. As the simulation runs, the cumulative heating cost appears on the “HeatCost” graph at the top of the Scope window. The indoor and outdoor temperatures appear on the “Temperatures” graph as yellow (top) and magenta (bottom) signals, respectively.

4-11

4 Modeling a Dynamic Control System

4-12

Simulating the Model

Modifying Simulation Parameters

One of the most powerful benefits of modeling a system with S imulink is the ability to interactively define the system inputs and observe changes in the behavior of your model. This allows you to quickly evaluate your model and validate the simulation results. This section describes:

• “Changing the Thermostat Setting” on page 4-13

• “Changing the Average Outdoor Temperature” on page 4-16

• “Changing the Daily Temperature Variation” on page 4-18

Changing the Thermostat Setting

Change the thermostat setting to 68 degrees Fahrenheit and observe how the model responds.

To change the thermostat setting:

1 Double-click the Set Point block in the model window.

4-13

4 Modeling a Dynamic Control System

The Source Block Parameters dialog box appears.

4-14

2 Enter 68 in the Constant value field.

3 Click OK.

The software applies your changes.

4 Select Simulation > Start to rerun the simulation.

The software simulates the model.

Simulating the Model

Notice that a lower thermostat setting reduces the cumulative heating cost.

4-15

4 Modeling a Dynamic Control System

Changing the Average Outdoor Temperature

Change the average outdoor temperature to 45 degrees Fahrenheit and observe how the model responds.

To change the average outdoor temperature:

1 Double-click the Avg Outdoor Temp block.

The Source Block Parameters dialog box appears.

4-16

2 Enter 45 in the Constant value field.

3 Click OK.

Thesoftwareappliesyourchangesandclosesthedialogbox.

4 Select Simulation > Start to rerun the simulation.

Simulating the Model

The software simulates the model.

Notice that a colder outdoor temperature increases the cumulative heating cost.

4-17

4 Modeling a Dynamic Control System

Changing the Daily Temperature Variation

Decreasethetemperaturevariationtoseehowthemodelresponds.

1 Double-click the Daily Temp Variation block.

The Source Block Parameters dialog box appears.

4-18

2 Enter 5 in the Amplitude field.

Simulating the Model

3 Click OK.

Thesoftwareappliesyourchangesandclosesthedialogbox.

4 Select Simulation > Start to rerun the simulation.

The software simulates the model.

IntheScopewindow,noticethatamorestable outdoor temperature alters the frequency with which the heater operates.

4-19

4 Modeling a Dynamic Control System

Importing Data from the MATLAB Workspace

Simulink also allows you to import data from the MATLAB workspace to the model’s input ports. This allows you to import actual physical data into your model. (For information about other data import capabilities, see “Importing Data from a Workspace” in the Simulink User’s Guide.)

Note In this example, you will create a vector of temperature data in MATLAB, and use that data as an input to the Simulink m od el.

To import data from the MATLAB workspace:

1 IntheMATLABCommandWindow,createtimeandtemperaturedataby

entering the following commands:

x = (0:0.01:4*pi)'; y = 32 + (5*sin(x)); z = linspace(0,48,1257)';

4-20

2 In the Simulink model window, select the Avg Outdoor Temp block, then

press the Delete key to delete it.

3 Delete the following items from the model in the same way:

Daily Temp Variation block

•

• Two input signal lines to the

Sum block

•

Sum block

The model should now look similar to the following figure. Notice that the output signal from the Sum block changes to a red, dotted line, indicating that it is not connected to a block.

Simulating the Model

4 If the Simulink Library Browser is not ope n, select View > Library

Browser in the model w indow to open it.

5 Selec

6 Select the In1 block in the Simulink Library Browser, then drag it to the

ttheSources library in the Simulink Library Browser.

model window.

In1 block appears in the model window.

nect the dotted line (originally connected to the

7 Con

ck.

blo

Sum block) to the In1

4-21

4 Modeling a Dynamic Control System

4-22

8 Select Simulation > Configuration Parameters in the model window.

The Co

9 Select Data Import/Export in the menu on the left sid e of the dialog box.

nfiguration Parameters dialog box appears.

The Data Import/Export pane appears.

Simulating the Model

10 Select the Input check box in the Load from workspace section.

11 Enter [z,y] in the Input field.

12 Click OK.

Thesoftwareappliesyourchangesandclosesthedialogbox.

13 Select Simulation > Start to rerun the simulation.

The software simulates the model.

4-23

4 Modeling a Dynamic Control System

In the Scope window, notice that the model ran using the imported data, showing colder temperatures and higher heat use.

4-24

Simulating the Model

Exporting Simul

Once you have com results to MATLA Data to the MATL export capabil

To export the

1 Select the Si

2 Select the Out1 block in the Simulink Library Browser, then drag it to

ities.)

eatCost

nks library in the Simulink Library Browser.

ation Data to the MATLAB Workspace

pleted a model, you may want to export your simulation

Bforfurtherdataanalysisorvisualization. (See“Exporting

AB Base Workspace” fo r information about additional data

data from the model to the MATLAB workspace:

the top right of the model window.

Out1 block appears in the model window.

3 Draw a bran

more infor

mation, see “Drawing a Branch Line” on page 3-11.

ch line from the

HeatCost signal line to the Out1 block. For

4-25

4 Modeling a Dynamic Control System

4 Select Simulation > Configuration Parameters in the model window.

The Configuration Parameters dialog box appears.

5 Select Data Import/Export in the men u on the left side of the dialog box.

The Data Import/Export pane appears.

4-26

6 Select the Time checkboxintheSavetoworkspacesection.

ct the Output check box in the Save to workspace section.

7 Sele

8 Click OK.

Thesoftwareappliesyourchangesandclosesthedialogbox.

9 Select Simulation > Start to rerun the simulation.

Simulating the Model

The software simulates the model and saves the time and to the M ATLA B workspace.

Notice that the

tout and yout va ri ables now appear in the MATLAB

workspace.

HeatCost data

4-27

4 Modeling a Dynamic Control System

4-28

Index

IndexA

adding blocks to a model 3-5

basics

Simulink 2-1

block libraries

descriptions 2-7

blocks

connecting 3-9 copying 3-5 masking 4-9 moving 3-8 ports 3-9 subsystems 4-6

browser

library 2-6

closing

model 3-17 Configuration Parameters dialog box 3-14 connecting

blocks 3-9

lines to input ports 3-9 control system

model overview 4-5

modeling 4-2 copying blocks to a model 3-5 creating

new model 2-4 3-3

subsystem 4-8

subsystem mask 4-10

data

exporting to MATLAB 4-25

importing from MATLAB 4-20

demo model

opening 4-3 overview 4-5 running 4-11

demos

accessing 2-11

example model 3-2 exporting

data from Simulink to MATLAB 4-25

help

Simulink 2-10

house model

overview 4-5

importing

MATLAB data to Simulink 4-20

input data

importing from MATLAB 4-20

input port 3-9

library

descriptions 2-7 searching 2-7 selecting 2-7 viewing 2-7

Library Browser

opening 2-2 overview 2-6 using 3-5

lines

Index-1

Index

branching a signal 3-11

carrying the same signal 3-9

connecting to input ports 3-9

masking

creating a mask 4-10

overview 4-9 MATLAB

exporting data from Simulink 4-25

importing data to Simulink 4-20

Simulink interaction 1-4 model window

moving blocks 3-8

overview 2-9 Model-Based Design

overview 1-5

process 1-6 modeling

control system 4-2

process 1-6 models

closing 3-17

control system example 4-5

creating new 2-4

creating simple 3-3

empty 3-3

opening 2-4

opening existing 2-5

saving 3-13

simple example 3-2

simulating 3-14 modifying

simulation parameters 4-13 moving

blocks in the model window 3-8

online help

accessing 2-10 Simulink 2-10

opening

demo model 4-3 existing model 2-5 model 2-4 Simulink 2-2

output data

exporting to MATLAB 4-25 output port 3-9 overview

demo model 4-5

Simulink 1-2

parameters

modifying 4-13 product overview 1-2 products

related 1-9

Mathworks SIMULINK 7 Installation Guide

Specifications and Main Features

Frequently Asked Questions

User Manual