Frequency response estimation uses either sinestream or chirp input signals.
|Sinusoidal Signal||When to Use|
|Sinestream||Recommended for most situations. Especially useful when:|
A sinestream signal consists of several adjacent sine waves of varying frequencies. Each frequency excites the system for a period of time.
Frequency response estimation using
the following operations on a sinestream input signal:
Injects the sinestream input signal you design, uest(t), at the linearization input point.
Simulates the output at the linearization output point.
frestimate adds the
signal you design to existing Simulink® signals at the linearization
of the output (and the corresponding input) at each frequency.
simulated output at each frequency has a transient portion and steady
SettlingPeriods corresponds to the
transient components of the output and input signals. The periods
SettlingPeriods are considered to be
at steady state.
Filters the remaining portion of the output and the corresponding input signals at each input frequency using a bandpass filter.
When a model is not at steady state, the response contains low-frequency transient behavior. Filtering typically improves the accuracy of your model by removing the effects of frequencies other than the input frequencies. These frequencies are problematic when your sampled data has finite length. These effects are called spectral leakage.
frestimate uses a finite
impulse response (FIR) filter. The software sets the filter order
to match the number of samples in a period such that any transients
associated with filtering appear only in the first period of the filtered
steady-state output. After filtering,
the first period of the input and output signals.
You can specify to disable filtering
during estimation using the signal
Estimates the frequency response of the processed signal by computing the ratio of the fast Fourier transform of the filtered steady-state portion of the output signal yest(t) and the fast Fourier transform of the filtered input signal uest(t):
To compute the response at each frequency,
only the simulation output at that frequency.
The swept-frequency cosine (chirp) input signal excites your system at a range of frequencies, such that the input frequency changes instantaneously.
Alternatively, you can use the sinestream signal, which excites the system at each frequency for several periods.