A special model reduction routine ncfmr produces a reduced-order model by truncating a balanced coprime set of a given model. It can directly simplify a modern controller with integrators to a smaller size by balanced truncation of the normalized coprime factors. It does not need modreal for pre-/postprocessing as the other routines do. However, any integrators in the model will not be preserved.
rng(89,'twister'); K= rss(30,4,3); [Kred,info2] = ncfmr(K);
Again, without specifying the size of the reduced-order model, any model reduction routine presented here will plot a Hankel singular value bar chart and prompt you for a reduced model size. In this case, enter 15.
Then, plot the singular values of the original and reduced-order models.
sigma(K,Kred) legend('Original (30-state)','Kred (15-state)')
If integral control is important, previously mentioned methods (except ncfmr) can nicely preserve the original integrator(s) in the model.