Achieving robust stability and performance by augmenting the number of system inputs

In this paper we consider the problem of how to design compensators that guarantee robust stability and performance, in the context of linear time invariant multivariable systems, whose description involves structured parametric type uncertainty. We demonstrate that if the original system is modified appropriately by generating additional inputs, this allows for more flexibility in achieving robust stability and performance. This implies that in a physical implementation of the control law, more actuators will be needed. We motivate the discussion by considering a physical example. We first concentrate on robust stability, state conditions under which the procedure is possible and prove several general results. We then focus our attention on achieving robust stability and robust performance and suggest design procedures.