Linear system optimisation with prescribed degree of stability

The paper presents a scheme for obtaining a linear-feedback law for a linear system as a result of minimizing a quadratic-performance index; the resulting closed-loop system has the property that all its poles lie in a halfplane Re (s) < -a, where a >0 may be chosen by the designer. The advantages of this arrangement over conventional optimal design are considered. In particular, it is shown that the reduction of trajectory sensitivity to plant-parameter variations as a result of any closed-loop control is greater for a >0 than for a --0, that there is inherently a greater margin for tolerance of time delay in the closed loop when a >0, that there is greater tolerance of nonlinearity when a >>0, and that asymptotically stable bang-bang control may be achieved simply by inserting a relay in the closed loop when a > 0. The disadvantage of the scheme appears to be that, with a > 0, more severe requirements are put on the power level at which input transducers should operate than for a = O.