Optimum design of passive-adaptive, linear feedback systems with varying plants

In designing a feedback control system involving a variable (or incompletely known) plant the prime consideration, besides obtaining a satisfactory transfer function, is to specify a system which is insensitive to plant variations. Some procedures for obtaining insensitive designs have been described in the literature, but they all result in systems having large open loop bandwidths. In the presence of instrument noise such systems would tend to produce an excessive noise output. In this paper a minimization is carried out, where the conflicting requirements of small sensitivity to plant variations and insensitivity to instrument noise are satisfied simultaneously. The solution is approximate, but can be justified in most physical situations. A method for iterating the solution is also described.