with the actual responses. The results of the simulations
are given in Figures 28–35.
In the SISO case, all of the controllers perform
equally well, with the main difference being that the
DOFC and IDC methods have a pure exponential convergence.
In the MIMO case, the IHC and DOFC
methods have a similar performance, converging to
zero in both channels. The FSCF, IDC and SFSCF
methods have equally poor convergence, resulting in a
significant steady-state deviation from zero. This is an
interesting result, proving the need for the time-domain
analysis, as the performance analysis carried out in the
preceding section suggested similar performance for all
methods, which is a direct result of the conservativity of
the analyses based on the singular values. The impact of
the conservativity is the most visible in MIMO systems,
where the net output of the process is considered,
allowing a very poor control performance in a single
channel without affecting the analysis thereof. In the
MISO case, all controllers provide good convergence
when only a single disturbance tone is present. The initial
convergence rate of the FSCF and SFSCF methods
is faster than that of the others. However, due to the
nonminimum phase-like behavior, the final convergence
time is approximately the same. The perceived
‘‘ballooning’’ effect gets worse if the allowed convergence
time is reduced, resulting in potential problems
in certain processes. In the presence of two disturbance
tones, the performance is similar except for the IHC
method, which actually amplifies the disturbances, as
was perceived in the sensitivity analysis earlier. The
inferior performance of the IHC method is due to the