Simulating Identified Model Output in Simulink

On this page…
When to Use Simulation Blocks Summary of Simulation Blocks Specifying Initial Conditions for Simulation

When to Use Simulation Blocks

Add model simulation blocks to your Simulink model from the System Identification Toolbox block library when you want to:

• Represent the dynamics of a physical component in a Simulink model using a data-based nonlinear model.

• Replace a complex Simulink subsystem with a simpler data-based nonlinear model.

You use the model simulation blocks to import the models you identified using System Identification Toolbox software from the MATLAB workspace into the Simulink environment. For a list of System Identification Toolbox simulation blocks, see Summary of Simulation Blocks.

Back to Top

Summary of Simulation Blocks

The following table summarizes the blocks you use to import models from the MATLAB environment into a Simulink model for simulation. Importing a model corresponds to entering the model variable name in the block parameter dialog box.

Block	Description
Idmodel	Simulate a linear identified model in Simulink, including process (idproc), linear polynomial (idpoly), state-space (idss), grey-box (idgrey) and transfer-function (idtf) models.
Nonlinear ARX Model	Simulate idnlarx model in Simulink.
Hammerstein-Wiener Model	Simulate idnlhw model in Simulink.
Nonlinear Grey-Box Model	Simulate nonlinear ODE (idnlgrey model object) in Simulink.

After you import the model into Simulink software, use the block parameter dialog box to specify the initial conditions for simulating that block. (See Specifying Initial Conditions for Simulation.) For information about configuring each block, see the corresponding reference pages.

Back to Top

Specifying Initial Conditions for Simulation

For accurate simulation of a linear or a nonlinear model, you can use default initial conditions or specify the initial conditions for simulation using the block parameters dialog box.

• Specifying Initial States of Linear Models

• Specifying Initial States of Nonlinear ARX Models

• Specifying Initial States of Hammerstein-Wiener Models

Specifying Initial States of Linear Models

For idss and idgrey models, specify the initial states for simulation in the Initial state field of the Function Block Parameters: Idmodel dialog box:

• To specify the initial states values as zero, use 'z'.

• To use the initial states values stored in the X0 property of the model, use 'm'.

• To match the simulated response of the model to a certain input/output data set, first use findstates(idParameteric) to estimate initial states values that maximize the fit. Specify the estimated initial states values in the Initial state field.

For idpoly, idtf and idproc models, the default initial states values are zero. If you want to specify different values, such as maximize fit to a given output data, convert the model to idss object, and then specify its initial states as described previously. For example, for the following idpoly model:

m1=idpoly([1 2 1],[2 2]);

the initial states correspond to those of the equivalent state-space model:

m2=idss(m1);

Specifying Initial States of Nonlinear ARX Models

The states of a nonlinear ARX model correspond to the dynamic elements of the nonlinear ARX model structure, which are the model regressors. Regressors can be the delayed input/output variables (standard regressors) or user-defined transformations of delayed input/output variables (custom regressors). For more information about the states of a nonlinear ARX model, see the idnlarx reference page.

For simulating nonlinear ARX models, you can specify the initial conditions as input/output values, or as a vector. For more information about specifying initial conditions for simulation, see the IDNLARX Model reference page.

Specifying Initial States of Hammerstein-Wiener Models

The states of a Hammerstein-Wiener model correspond to the states of the embedded linear (idpoly or idss) model. For more information about the states of a Hammerstein-Wiener model, see the idnlhw reference page.

The default initial state for simulating a Hammerstein-Wiener model is 0. For more information about specifying initial conditions for simulation, see the IDNLHW Model reference page.

Back to Top

Identifying Linear Models

Example – Simulating an Identified Model Using Simulink Software

© 1984-2012- The MathWorks, Inc.    -   Site Help   -   Patents   -   Trademarks   -   Privacy Policy   -   Preventing Piracy   -   RSS