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Offline Frequency Response Estimation

Estimate frequency response, examine frequency-domain characteristics, validate linearization of Simulink® model

Simulink Control Design™ software has both command-line tools and a graphical Linear Analysis Tool for estimating the frequency response of a system modeled in Simulink, without modifying the model. You can use the estimated response to validate exact linearization results, analyze linear model dynamics, or estimate parametric models. For more information about frequency response estimation, see Frequency Response Estimation Basics.

Frequency response estimation requires an input signal at the linearization input point to excite the model at the frequencies of interest. For more information, see Estimation Input Signals.

Graphical Tools

Linear Analysis ToolLinearize Simulink models


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frestimateFrequency response estimation of Simulink models
frestimateOptionsOptions for frequency response estimation

Input Signals

frest.SinestreamSignal containing series of sine waves
frest.createFixedTsSinestreamSinestream input signal with fixed sample time
frest.ChirpSwept-frequency cosine signal
frest.RandomRandom input signal for simulation
frest.createStepStep input signal
frest.simComparePlot time-domain simulation of nonlinear and linear models
frest.simViewPlot frequency response model in time- and frequency-domain
getSimulationTimeFinal time of simulation for frequency response estimation
frest.findSourcesIdentify time-varying source blocks
frest.findDependList of model path dependencies


Frequency Response Estimation Basics

Frequency Response Estimation Basics

A frequency response describes the steady-state response of a system to sinusoidal inputs. Simulink Control Design lets you estimate the frequency response of a model or perform online estimation of a physical plant.

Analyze Estimated Frequency Response

When you perform frequency response estimation, you can analyze the result by examining the raw simulated response and the FFT used to convert it to an estimated frequency response.

Estimation Input Signals

Estimation Input Signals

For frequency response estimation, the software injects an input signal and measures the response. You can use predefined signal types such as sinestream or chirp signals, or create an arbitrary input signal.

Noise and Time-Varying Inputs

Disable Noise Sources During Frequency Response Estimation

Noise sources can interfere with the signals at the linearization output points and produce inaccurate estimation results.

Estimate Frequency Response Models with Noise Using Signal Processing Toolbox

You can also estimate a frequency response model using Signal Processing Toolbox™ software, which includes windowing and averaging.

Estimate Frequency Response Models with Noise Using System Identification Toolbox

You can also estimate a frequency response model using System Identification Toolbox™ software.

Effects of Time-Varying Source Blocks on Frequency Response Estimation

Time-varying source blocks drive the model away from the operating point of the linearized system, which prevents the response from reaching steady state.

Validation of Linearization

Validate Linearization In Frequency Domain

You can assess the accuracy of your linearization results by estimating the frequency response of the nonlinear model and comparing the result with the response of the linearized model.

Linearization Validation in Frequency Domain Using FRESTIMATE

You can assess the accuracy of your linearization results at the command line by estimating the frequency response of the nonlinear model.

Validate Linearization In Time Domain

You can assess the accuracy of your linearization results by comparing the simulated output of the nonlinear model and the linearized model.

Code Generation

Generate MATLAB Code for Repeated or Batch Frequency Response Estimation

Generate MATLAB® scripts or functions for frequency response estimation using the Linear Analysis Tool.


Managing Estimation Speed and Memory

Improve frequency response estimation performance by reducing estimation time and memory requirements.

Troubleshooting Frequency Response Estimation

If your estimated frequency response does not match the expected behavior of your system, you can use the time-domain and frequency-domain response plots to help improve the results.

Featured Examples