On nonsingular value based design of controllers for robust stability

Measures of robustness based on singular values are known to be overly conservative and therefore can sometimes give misleading predictions of instability. It is desirable then to have alternative measures of robustness which are less conservative than singular values. Such a measure is given here, and leads to a design scheme that is a direct extension of the Rosenbrock Nyquist array design method, which has proved successful in a range of industrial applications. In this way, the generalised Nyquist array is reasserted as a viable scheme for the design of robust multivariable control systems.