For some really large size problems (states > 200),
modreal turns out to be the only way
to start the model reduction process. Because of the size and numerical properties
associated with those large size, and low damped dynamics, most Hankel based routines
can fail to produce a good reduced-order model.
modreal puts the large size dynamics
into the modal form, then truncates the dynamic model to an intermediate stage model
with a comfortable size of 50 or so states. From this point on, those more sophisticated
Hankel singular value based routines can further reduce this intermediate stage model,
in a much more accurate fashion, to a smaller size for final controller design.
For a typical 240-state flexible spacecraft model in the spacecraft industry, applying
bstmr (or any other additive routines) in sequence can reduce the
original 240-state plant dynamics to a seven-state three-axis model including rigid body
dynamics. Any modern robust control design technique mentioned in this toolbox can then
be easily applied to this smaller size plant for a controller design.