frest.findSources

Namespace: frest

Identify time-varying source blocks

Syntax

blocks = frest.findSources(model)

blocks = frest.findSources(model,io)

Description

Use the frest.findSources function to identify such time-varying sources in your Simulink^® model. Time-varying source blocks can interfere with frequency response estimation by driving the model away from the operating point of the linearized system. You can disable the identified sources before estimating a frequency response using frestimate. For more information, see Effects of Time-Varying Source Blocks on Frequency Response Estimation.

blocks = frest.findSources(model) finds all time-varying source blocks in the signal path of any linear analysis output point marked in the Simulink model model.

blocks = frest.findSources(model,io) finds all time-varying source blocks in the signal path of any linearization output point specified in the array of linear analysis points io.

Examples

Disable Time-Varying Source Blocks for Frequency Response Estimation

Open a model that contains time-varying source blocks.

mdl = "scdspeed_ctrlloop";
open_system(mdl)

Set the engine reference model to normal simulation mode for accurate linearization.

set_param("scdspeed_ctrlloop/Engine Model",...
    "SimulationMode","Normal")

Obtain the linear analysis points that are defined in the model.

io = getlinio(mdl);

Estimate the frequency response of the model without disabling the time-varying source blocks. Define a sinestream input signal and obtain the estimated frequency response sysest.

in = frest.Sinestream(...
    "Frequency",logspace(1,2,10),...
    "NumPeriods",30,...
    "SettlingPeriods",25);
[sysest,simout] = frestimate(mdl,io,in);

To view the impact of the time-varying sources on the estimation result, compute an exact linearization of the model and compare it to the estimated response.

sys = linearize(mdl,io);
bodemag(sys,sysest,'r*')

The estimated frequency response does not match the exact linearization. The mismatch occurs because time-varying source blocks in the model prevent the response from reaching steady state.

Find the time-varying source blocks.

srcblks = frest.findSources(mdl); 

To disable the source blocks, first create an frestimateOptions object and set the BlocksToHoldConstant parameter to the time-varying source blocks.

opts = frestimateOptions("BlocksToHoldConstant",srcblks);

Estimate the frequency response with the time-varying source blocks disabled.

[sysest2,simout2] = frestimate(mdl,io,in,opts);

Compare the estimated response sysest2 with the exact linearization result.

bodemag(sys,sysest2,'r*')

The estimated response matches the exact linearization.

Input Arguments

model — Name of model

string | character vector

Name of the Simulink model for which you want to identify time-varying sources.

io — Linear analysis points

linearization I/O object | array of linearization I/O objects

Linear analysis points representing inputs, outputs, and loop openings, specified as a linearization I/O object or an array of such objects. The frest.findSources function uses only the linearization output points in io.

For more information on specifying linear analysis points, see Specify Portion of Model to Linearize and Specify Portion of Model to Linearize at Command Line.

Output Arguments

blocks — Time-varying source blocks

array of BlockPath objects

Time-varying source blocks, returned as an array of BlockPath objects. blocks includes time-varying source blocks inside subsystems and normal-mode referenced models.

If you specify io, blocks contains all time-varying source blocks contributing to the signal at the output analysis points in io.

If you do not specify io, blocks contains all time-varying source blocks contributing to the signals at the output analysis points marked in model. For more information on specifying analysis points in your model, see Specify Portion of Model to Linearize in Simulink Model.

Tips

• To disable time-varying source blocks during frequency response estimation, first create an frestimateOptions object and set its BlocksToHoldConstant property to blocks or a subset of blocks. Then, estimate the frequency response using frestimate.

• When model includes a reference model that contains a source block in the signal path of a linearization output point, set the reference model to normal simulation mode before finding sources using frest.findSources.

Alternative Functionality

• You can use the Simulink Model Advisor to determine whether time-varying source blocks exist in the signal path of output linear analysis points in your model. To do so, use the Model Advisor check Identify time-varying source blocks interfering with frequency response estimation. For more information about using the Model Advisor, see Check Your Model Using the Model Advisor.

• You can find and disable time-varying sources in your model when estimating frequency responses in the Model Linearizer app.

Version History

Introduced in R2010b