Robust stabilization in the presence of coprime factor perturbations

The robust stabilization problem first suggested by M. Vidyasagar (1986) is considered. The authors examine uncertainty in the nominal system modeled by additive perturbations on the coprime factors of the system. It is demonstrated that the bound on the admissible uncertainty in D. McFarlane and K. Glover (1989) is restrictive in that there exist perturbations of larger size than this bound which are still stabilized. In the present work, the authors examine perturbations in certain `key´ directions whose sizes are larger than the robustness margin but do not destabilize the plant