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| R2011b Documentation → Simulink Control Design | |
Learn more about Simulink Control Design |
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Use the Simulation Results Viewer to analyze the results of your frequency response estimation, obtained by performing the steps in Estimating Frequency Response Using Linear Analysis Tool.
To open the Diagnostic Viewer in the Linear Analysis Tool:
In the Frequency Response Estimation tab, before performing the estimation task, select the Launch Diagnostic Viewer check box.
This action sets the Diagnostic Viewer to open when the frequency response estimation is performed.
Click
to estimate the frequency response of the model.
Tip To re-open the Diagnostic Viewer in the Linear Analysis Tool:
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Use the Simulation Results Viewer to analyze the results of your frequency response estimation, obtained by performing the steps in Estimating Frequency Response (MATLAB Code).
Open the Simulation Results Viewer using:
frest.simView(simout,input,sysest)
where simout is the simulated output, input is the input signal you created, and sysest is the estimated frequency response.
By default, the Simulation Results Viewer shows these plots:
To toggle the plots displayed in the Diagnostic Viewer using the Linear Analysis Tool:
Click the Diagnostic Viewer plot tab in the plot area of the Linear Analysis Tool.
In the Linear Analysis Tool, in the Plot tab > Plot Visibilities, select the check box for the plot that you want to toggle.
To modify plot settings, such as axis frequency units, right-click a plot, and select the corresponding option.
To toggle the plots displayed in the Simulation Results Viewer, select the corresponding plot from the Edit > Plots menu. To modify plot settings, such as axis frequency units, right-click a plot, and select the corresponding option.
Use the Bode plot to analyze the frequency response. If the frequency response does not match the dynamics of your system, see Troubleshooting Frequency Response Estimation for information about possible causes and solutions. While troubleshooting, you can use the Bode plot controls to view the time response at the problematic frequencies.
You can usually improve estimation results by either modifying your input signal or disabling the model blocks that drive your system away from the operating point, and repeating the estimation.
Use this plot to check whether the simulated output is at steady state at specific frequencies. If the response has not reached steady state, see Time Response Not at Steady State for possible causes and solutions.
If you used the sinestream input for estimation, check both the filtered and the unfiltered time response. You can toggle the display of filtered and unfiltered output by right-clicking the plot and selecting Show filtered steady state output only. If both the filtered and unfiltered response appear at steady state, then your model must be at steady state. You can explore other possible causes in Troubleshooting Frequency Response Estimation.
Note If you used the sinestream input for estimation, toggling the filtered and unfiltered display only updates the Time Response and FFT plots. This selection does not change estimation results. For more information about filtering during estimation, see How Frequency Response Estimation Treats Sinestream Inputs. |
Use this plot to analyze the spectrum of the simulated output.
For example, you can use the spectrum to identify strong nonlinearities. When the FFT plot shows large amplitudes at frequencies other than the input signal, your model is operating outside of linear range. If you are interested in analyzing the linear response of your system for small perturbations, explore possible solutions in FFT Contains Large Harmonics at Frequencies Other than the Input Signal Frequency.
To analyze the results in the Diagnostic Viewer, use the controls in the Plot tab of the Linear Analysis Tool.
Click Diagnostic Viewer in the plot area of the Linear Analysis Tool.
Click Plot in the Linear Analysis Tool. This action will open the Plot tab.
Enter the frequency range that you want to inspect in the From and To boxes of the Frequency Selector.
The units for frequency in the Frequency Selector match the units for the Bode plot in the Diagnostic Viewer.
In the Simulation Results Viewer, use Bode controls to display the simulated output and its spectrum at specific frequencies.
If you used the sinestream input signal in the estimation:
Drag arrows individually to display the time response and FFT at specific frequencies.
Drag the shaded region to shift the time response and FFT to a different frequency range.
If you used the chirp input signal in the estimation, drag the shaded region to increase or decrease the frequency range of the displayed time response and FFT.
You can display a data tip on the Time Response, FFT, and Bode plots in the Simulation Results Viewer by clicking the corresponding curve. Dragging the data tip updates the information.
Data tips are useful for correcting poor estimation results at a specific sinestream frequency, which requires you to modify the input at a specific frequency. You can use the data tip to identify the frequency index where the response does not match your system.
In the previous figure, the Time Response data tip shows that the frequency index is 11. You can use this frequency index to modify the corresponding portion of the input signal. For example, to modify the NumPeriods and SettlingPeriods properties of the sinestream signal, using MATLAB code:
input.NumPeriods(11) = 80; input.SettlingPeriods(11) = 75;
To modify the sinestream in the Linear Analysis Tool, see Modifying Sinestream Input Signal Using Linear Analysis Tool
For MIMO systems, view frequency response information for specific input and output channels:
In the Simulation Results Viewer, right-click any plot, and select I/O Selector.
Choose the input channel in the From list. Choose the output channel in the To list.
 | Estimating Frequency Response | Troubleshooting Frequency Response Estimation |  |
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