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frest.findSources

Package: frest

Identify time-varying source blocks

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    Syntax

    blocks = frest.findSources(model)
    blocks = frest.findSources(model,io)

    Description

    Time-varying source blocks in a Simulink® model can interfere with frequency response estimation by driving the model away from the operating point of the linearized system. Using the frest.findSources function, you can identify such time-varying sources in your model. You can then 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 linearization output point marked in the Simulink model model.

    example

    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

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    Open Live Script

    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*')

    Figure contains an axes object. The axes object with title From: Ref To: Speed Output, ylabel Magnitude (dB) contains 2 objects of type line. One or more of the lines displays its values using only markers These objects represent sys, sysest.

    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*')

    Figure contains an axes object. The axes object with title From: Ref To: Speed Output, ylabel Magnitude (dB) contains 2 objects of type line. One or more of the lines displays its values using only markers These objects represent sys, sysest2.

    The estimated response matches the exact linearization.

    Input Arguments

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

    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

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    Time-varying source blocks, returned as a 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 Simulink Control Design Checks. 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

    See Also

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