Wiener-Hopf approach to tradeoffs between stability margin and performance in two and three-degree-of-freedom multivariable control systems

In this paper, tradeoffs between stability margin and performance are considered. Maximum improvement in an approximate measure of stability margin is achieved at the expense of a prescribed increase in the quadratic cost functional measuring system performance. To attain an analytical solution to this fundamental tradeoff problem, the approximate measure of stability margin chosen is also a quadratic cost function. A novel approach is introduced which allows structured perturbations in the coprime polynomial matrix fraction description of the plant transfer matrix to be taken into account.