Exact computation of the infimum in H∞-optimization via output feedback

The authors present a simple and noniterative procedure for the computation of the exact value of the infimum in the standard H_∞-optimal control with output feedback. The problem formulation is general and does not place any restrictions on the direct feedthrough terms between the control input and the controlled output variables, and between the disturbance input and the measurement output variables. The method is applicable to systems that satisfy the following conditions: (1) the transfer function from the control input to the controlled output is right-invertible and has no invariant zeros on the jω axis, and (2) the transfer function from the disturbance to the measurement output is left-invertible and has no invariant zeros on the jω axis