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Creating Operating Points

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Simulink Control Design Default Operating Point Computing Operating Points from Specifications Specifying Operating Points from Known Values Extracting Operating Points From Simulation Computing Equilibrium Operating Points

Simulink Control Design Default Operating Point

A default operating point is automatically created and stored in a node in the project tree every time you open the Control and Estimation Tools Manager unless you indicate otherwise. The default operating point consists of a snapshot of initial condition variables in the Simulink model. Initial condition variables are a special set of variables that can be set in the Simulink model. These variable include initial conditions for blocks with state, such as the integrator or state space blocks, and output values of root level inport blocks. For more information on setting these variables, see Importing and Exporting Data in the Simulink User's Guide.

By clicking on the Default Operating Point node, you can view these values and modify them for use in a linearization. The output levels for blocks like a constant block remain defined in the model.

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Computing Operating Points from Specifications

You can specify target values or constraints on a subset of the model's inputs, outputs, and states. The software uses numerical optimization methods to determine the full operating point based on this partial specification.

This section continues the magball example from Creating a Linearization Task. At this stage in the example, a linearization task has already been created for the model.

You compute the operating point from specifications when you only know partial or implicit information. Typical operating point specifications search for steady state or equilibrium operating points.

1. Create a new operating point by either:

   • Selecting the Operating Points node and then clicking the Compute Operating Points tab

   • Clicking the New Operating Point button on the Operating Points pane of the Linearization Task node

2. From the Compute new operating points using list, select operating specifications. The Control and Estimation Tools Manager window should now resemble the following figure.

   

3. Enter operating point specifications in the table, such as any known values or constraints on signal values. Switch between states, inputs, and outputs using the tabs on the left.

   A suitable set of specifications for the magball model is shown in the following figure. This model does not contain any root-level input or output ports and, as a result, the Inputs and Outputs panes are empty. You can still constrain the output signal of any block by adding an Output Constraint linearization point to the model. See Constraining Outputs for information about adding an output constraint to the specifications for an operating point.

   

   When you add states, inputs, or outputs to the model, or remove them from the model, click the Sync with Model button to update the operating point table to reflect these changes.

4. Click Compute Operating Points. The Simulink Control Design software finds an operating point that closely matches the specifications and adds the new operating point, labeled Operating Point, to the Operating Points node. Some specifications, even values specified as Known, may not be met exactly. Select the operating point in the project tree to view its contents and assess the results.

   

For information on options that you can set when finding operating points from partial specifications, see Changing Optimization Settings.

Note   Inputs and outputs for the operating point are not the same as the linearization input and output points, or analysis I/Os, used to define the inputs and outputs of the linearized model. Instead, operating-point inputs and outputs define the full operating point of a Simulink model, along with any additional, user-defined output constraints.

Tip   To automatically generate MATLAB code that computes operating points as specified in the Control and Estimation Tools Manager, click or select File > Generate MATLAB Code.

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Specifying Operating Points from Known Values

You can completely specify all inputs and states in the operating point.

This section continues the magball example from Computing Operating Points from Specifications. At this stage in the example, a linearization task has already been created for the model, and a steady state operating point has been computed from specifications.

When you know the values of all states and inputs at the operating point, you can create a new operating point in the Control and Estimation Tools Manager and manually edit the operating point values:

1. Select the Operating Points node in the left pane and then click the Operating Points tab in the right pane.

2. Click the New button in the bottom-right corner to create a new operating point under the Operating Points node. This new operating point is labeled Default Operating Point (2).

3. View the details of Default Operating Point (2) (shown in the following figure) by either:

   • Selecting it under the Operating Points node in the project tree

   • Selecting it in the Operating Points pane of the Linearization Task node, and then clicking View

     

4. Edit the operating point by entering new values in the table. Switch between state and input values using the tabs on the left.

   Change the value of State-1 of Controller to -14 and the value of Current to 7. The model does not contain any root-level input ports, and, as a result, the Inputs pane is empty.

   When you add states, inputs, or outputs to the model, or remove them from the model, click the Sync with Model button to update the operating point table to reflect these changes.

5. Rename the operating point by right-clicking Default Operating Point (2) under the Operating Points node, selecting Rename, and entering a new name in the dialog box.

   For example, label this operating condition Known Operating Conditions. The pane should now resemble the following figure.

   

Tip   To automatically generate MATLAB code that computes operating points as specified in the Control and Estimation Tools Manager, click or select File > Generate MATLAB Code.

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Extracting Operating Points From Simulation

You can create an operating point from a simulation of your model at the following simulation points:

• Specified simulation times, such as when the simulation reaches a steady state solution (see Creating Operating Points at Specified Simulations Timesexample in this section).

• Events during a specified simulation interval (see 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.

This section continues the magball example from Specifying Operating Points from Known Values. At this stage in the example, a linearization task has already been created for the model, a steady state operating point has been computed from specifications, and a completely known operating point has been specified.

To create operating points at specified simulation times:

1. Open the Compute Operating Points tab by either:

   • Selecting the Operating Points node in the project tree, and then clicking the Compute Operating Points tab

   • Clicking the New Operating Point button on the Operating Points pane of the Linearization Task node

2. From the Compute new operating points using list, select simulation snapshots. The window should now resemble the following figure.

   

3. Enter a vector of times in the Simulation snapshot times (sec) field. Enter [1,10] to compute operating points at t=1 and t=10.

4. Click Compute Operating Points. The Simulink Control Design software simulates the model, extracts operating points, labeled Operating Point at t=1 and Operating Point at t=10, and adds them to the Operating Points node in the project tree.

   To view the contents of the operating point you created, select the operating point in the project tree as shown in this figure.

   

   Note   When you add states, inputs, or outputs to the model, or remove them from the model, click the Sync with Model button to update the operating point table to reflect these changes.

Tip   To automatically generate MATLAB code that computes operating points as specified in the Control and Estimation Tools Manager, click or select File > Generate MATLAB Code.

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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Computing Equilibrium Operating Points

You can use the software to compute equilibrium operating points. Follow the basic instructions in Computing Operating Points from Specifications. 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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Ways to Create Operating Points

Working with Operating Points

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