Simulink Control Design™ - MathWorks

Experiment Parameters

The Frequency Response Estimator block is configured to run the experiment in

sinestream mode, which means that it injects a separate perturbation at each frequency.

The block is also configured to use the same amplitude, 1, for each frequency in the

perturbation signal.

The block is further configured to estimate frequency responses at the frequencies w =

logspace(0,2,20). To ensure that the experiment sampling rate is fast enough to

accommodate the highest frequency, it is a good practice to set the sampling time to

about 0.6 / wmax or faster, where wmax is the highest frequency in rad/s. For this example,

the experiment sample time is 0.005 seconds, is fast enough for the wmax of 100 rad/s.

Start/Stop Signal

The step blocks connected to the start/stop input port turn the experiment on with a

rising signal at t = 5, when the model is at steady state. The block provides a

recommended experiment length of about 174 s. This value is based on the specified

frequencies w, the number of settling periods to wait at each frequency, and the number

of periods to use for estimation. To ensure that the experiment runs long enough for a

good result, the start/stop signal stops the experiment at t = 180. (For details about

the recommended experiment length, see Frequency Response Estimator.)

Estimation Results

Simulate the model. You can use the scope to visualize the control signal, the perturbation

signal, and the plant output. Because the Display Bode Plot block parameter is selected,

the block automatically generates a plot of the specified baseline model and updates it

periodically with the estimated frequency response.

sim(mdl)

6 Online Frequency Response Estimation