The frequency response for a stable system describes the amplitude change and phase
shift as a function of frequency. If Y(s) and U(s) are the Laplace transforms of y(t) and
u(t), respectively, then G(s) is:
Gs =
Ys
Us,
where
Gs = Gjω =Ay
Au,
θ=∠
Y jω
X jω
= tan−^1
ImGjω
ReG jω.
The frd model that you get from frequency response estimation contains G(s) evaluated
at particular frequencies. Although your Simulink is usually nonlinear, you typically
perform estimation at a steady-state operating point. If the applied perturbation is small,
the resulting frd model is an approximation of the linearized response at that nominal
operating point.
Offline and Online Estimation
Simulink Control Design lets you: