Beyond the small-gain paradigm: how to make use of the phase information of uncertainty

This paper tries to open a new field for robust control. The celebrated small-gain approach to robust control only makes use of the gain information of uncertainty. This results in a limitation on the achievable control bandwidth in system design. To relax this limitation associated with small-gain approach, we explore the possibility of utilizing the phase information of uncertainty in robust control. This paper discusses the modeling of uncertainty accounting for both gain and phase, robust stability conditions and their state space characterization.