State-space formulas for the Nehari-Takagi problem for nonexponentially stable infinite-dimensional systems

We obtain state-space formulas for the solution of the Nehari--Takagi/suboptimal Hankel norm approximation problem for infinite-dimensional systems with a nonexponentially stable generator, via the method of J-spectral factorization. We make key use of a purely frequency-domain solution of the problem

H∞ Controller Design for Preview and Delayed Systems

The H∞ control problem of general preview/delayed systems is solved using analytic solutions of the corresponding operator Riccati equations. The solution to the problem can be applied to a broad range of input/output delayed systems and enables the handling of preview/delayed control problems. The solvability condition is characterized by the roots of the transcendental equations and the control law for the general problem is given based on a predictive compensation with an integro-differential observer. Some interpretations of typical control problems are presented based on the solvability condition and the resulting control law