Control of uncertain systems using nonlinear feedback

Robust control theory attempts to provide systematic techniques and methods to solve control problems where uncertainty is a dominant issue. Often, a linear time-invariant fixed controller is designed for a given robust linear multivariable control problem. The authors have recently explored the question of what advantages nonlinear time-varying controllers have over their linear counterparts. This has led them to formulate a qualitative principle, called the plant uncertainty principle, which captures all the results known so far. The authors present some of the results as evidence of the usefulness of this principle