Low order robust H/sub infinity / controller synthesis

Robust stability of the closed-loop behavior of plants is investigated. It is shown that when the distance between the nominal plant model and the boundary of the nominal plant envelope is measured in the gap metric, a sufficient condition on the closed-loop stability can be given. Low-order controllers are derived using either model reduction or controller reduction techniques. It is shown that when using controller design followed by controller reduction techniques the size of the plant envelope is larger than if one is using plant model reduction followed by controller design.<>