You can use a priori knowledge of the expected transfer function
model structure to initialize the estimation. The
idtf model contains parameters
that allow you to specify the values and constraints for the numerator,
denominator and transport delays.
For example, specify a third-order transfer function model that contains an integrator and has a transport delay of at most 1.5 seconds:
init_sys = idtf([nan nan],[1 2 1 0]); init_sys.Structure.IODelay.Maximum = 1.5; init_sys.Structure.Denominator.Free(end) = false;
int_sys is an
with three poles and one zero. The denominator coefficient for the
is zero and implies that one of the poles is an integrator.
init_sys.Structure.IODelay.Maximum = 1.5 constrains
the transport delay to a maximum of 1.5 seconds. The last element
of the denominator coefficients (associated with the
is not a free estimation variable. This constraint forces one of the
estimated poles to be at
s = 0.
For more information regarding configuring the initial parameterization
of an estimated transfer function, see