Optimization of Youla-parametrized Controllers

The so-called Youla-parametrized controllers provide a special way todesign the best regulators for open-loop stable plants. The authorsformerly extended this parametrization for two-degree of freedom(TDOF) control systems. The control error in a generic TDOF controlsystem has three major parts: design-, realizability- and modeling-loss. This new decomposition opens useful ways for practical optimizationand the paper investigates the optimality of the second term.