Possible Cause Action
Model is unstable. You cannot estimate the frequency response using
frestimate. Instead, use exact linearization to get a
linear representation of your model. See “Linearize
Simulink Model at Model Operating Point” on page 2-
74 or the linearize reference page.
Stable model is not at steady
state.Disable all source blocks in your model, and repeat the
estimation using a steady-state operating point. See
“Compute Steady-State Operating Points” on page 1-6.
Stable model captures a
growing transient.If the model captures a growing transient, increase the
number of periods in the input signal by changing
NumPeriods. Repeat the estimation using a steady-
state operating point.Time Response Is Discontinuous or Zero
What Does This Mean?
Discontinuities or noise in the time response indicate that the amplitude of your input
signal is too small to overcome the effects of the discontinuous blocks in your model.
Examples of discontinuous blocks include Quantizer, Backlash, and Dead Zones.
If you used a sinestream input signal and estimated with filtering, turn filtering off in the
Simulation Results Viewer to see the unfiltered time response.
The following model with a Quantizer block shows an example of the impact of an input
signal that is too small. When you estimate this model, the unfiltered simulation output
includes discontinuities.
Troubleshooting Frequency Response Estimation