Controller Order Reduction with Guaranteed Stability and Performance

In this paper we consider the problem of controller order reduction for control design for robust performance. In practical control design it may be important to have low order controllers. For example, one may want to gain schedule a series of LTI (linear, time invariant) controllers, or give simple physical interpretations to the control dynamics. When solving practical design problems using, say, H∞ software it is common to produce controllers of high order - equal to the sum of the order of the plant plus each of the weighting functions. However, there may be lower order controllers which stabilize the plant and provide satisfactory H∞ closed loop performance. The objectives of a method for controller order reduction within the H∞ framework, then, should be to find low order controllers which stabilize a given plant and provides satisfactory H∞ performance. Ideally, the method should apply to a large class of problems, be easy to implement and be guaranteed to work