Simulink® Control Design™

Creating Operating Points

Role of Operating Points in Linearization

Before linearizing the model, you must choose an operating point about which to linearize the system. This operating point is often a steady state value. Refer to What Are Operating Points? and Why Are Operating Points Important? in the Simulink^® Control Design™ getting started documentation for more information on the role of operating points in linearization.

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Creating Operating Points from Specification

You can specify target values or constraints on a subset of the model's inputs, outputs, and states (see Creating Operating Points from Specifications in the Simulink Control Design getting started documentation). The software uses numerical optimization methods to determine the full operating point based on this partial specification.

For example, when you know that:

• The height of the ball in magball should be 0.05

• The rate of change of the height is small

• The current should be positive

• Your initial guess for the states in the Controller is 0

then, you can compute an operating point that closely matches the specifications.

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Creating Operating Points from Known Values

You can completely specify all inputs and states in the operating point (see Creating Operating Points from Known Values in the Simulink Control Design getting started documentation).

For example, when you know that:

• The height of the ball in magball should be 0.05

• The rate of change of the height should be 0

• The current should be 7.0036

• You also know the values of the states in the Controller

then, this information completely specifies the operating point.

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Creating Operating Points From Simulation

You can use the following methods for creating an operating point from a simulation of your model:

• Creating Operating Points at Specified Simulations Times

• Creating Operating Points at Simulation Events

Creating Operating Points at Specified Simulations Times

You can extract an operating point at specified times during a simulation of the model (see Creating Operating Points from Simulation in the Simulink Control Design getting started documentation).

For example, you run a simulation of a model and use the values of the states and inputs at time 10 as the operating point values. This approach is especially useful when the simulation has reached a steady state.

Creating Operating Points at Simulation Events

You can create an operating point from a simulation of your model at one or more of the following simulation events:

• Trigger-based events

• Function-call events

For more information about modeling events in Simulink^® models, see Creating Conditional Subsystems in the Simulink User's Guide.

The Simulink Control Design software creates operating points at all simulation events within a specified simulation time.

To create operating points at one or more simulation events:

1. Add a Trigger-Based Operating Point Snapshot block to your model. This block is in the Simulink Control Design block library.

   The model in the Trigger-Based Operating Point Snapshot demo shows the use of this block.

2. Select the Compute Operating Points tab in the Operating Points node.

3. From the Compute new operating points using list, select simulation snapshots.

4. Enter a scalar value that specifies the simulation end time in the Simulation snapshot times (sec.) field, shown in the following figure.

   

5. Click Compute Operating Points. The software simulates the model, extracts operating points, and adds them to the Operating Points node in the project tree. Select an operating point to view its contents and assess the results.

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Using the Default Operating Point

You can choose to accept the default operating point in the Simulink Control Design software. The initial values of the states, inputs, and outputs, define this operating point. For more information on using the Default Operating Point see Simulink^® Control Design™ Default Operating Point in the Simulink Control Design getting started documentation. Only use the default operating point when the initial values are very close to the operating point of interest.

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Importing Operating Points

This section continues the example from Example Model: The Magnetic Ball System. At this stage in the example, a linearization project has already been created for the model, and linearization points have been inserted, and operating points have been created from specifications, known values, and simulation.

To import operating points from the MATLAB^® workspace or from a MAT-file.

1. To import a new operating point, select the Operating Points node in the project tree and then select the Operating Points tab on the right. Click the Import button at the bottom of the pane. This displays the Operating Point Import dialog box.

   

2. Click Workspace or MAT-file as the location to import the operating point from, select an operating point from the list below, and then click Import. For this example, two operating points are loaded into the MATLAB workspace when you open the magball model.

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Computing Equilibrium Operating Points

You can use the software to compute equilibrium operating points. Follow the basic instructions in Creating Operating Points from Specifications in the Simulink Control Design getting started documentation. When you enter specifications in the States pane, select the Steady State check box at the top of the table. Selecting this check box causes the algorithm to look for an operating point in which all states are at equilibrium, or steady state.

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Specifying Operating Points

Working with Operating Points