Design of normalizing precompensators via alignment of output-input principal directions

Normalization is a crucial requirement for the effectiveness of multivariable control system design within the Characteristic Locus Method. Previous work addresses this problem by solving an optimization problem formulated in order to increase normality; its formulation, however, do not consider the closed-loop system robustness with respect to perturbations at the plant input. In this paper a different approach to the design of normalizing precompensators will be proposed. It is based on the minimization of a cost function representing the measure of misalignment between the output and input principal directions of the precompensated system. The main advantage of this approach is that, since normalization is obtained via alignment, the sensitivity of the characteristic loci to perturbations at both the plant input and output is reduced.