Effects of mismatched smith controller on stability in systems with time-delay

Abstract Stability of systems with a Smith controller is studied by taking into account the possibility of mismatch between plants and controllers. A necessary and sufficient condition for a system to maintain its stability in the presence of small mismatch is obtained. It follows from the condition that, depending on the growth rate of plant uncertainty towards high frequency, a Smith controller should be designed so that the control system has sufficiently steep high-cut-off frequency response.