Robust Controller Design for Uncertain Systems

This paper proposes a simple approach to design a PID controller for an uncertain SISO system that will guarantee closed loop stability when the input is varied between 0 and 60 % of its working range. The Robust Controller design method used here is based on Small Gain theorem. A family of transfer functions corresponding to different working ranges is used to describe the uncertain plant for which the controller is to be designed. In this paper, the controller is designed for a warm air-drying chamber which is a good example for an uncertain system. The design is carried out considering the plant behaviour at 3 working points. The closed loop step responses obtained, prove the robust operation of the designed controller for the plant under the considered working range. Keywords— Robust controller, Uncertain model, Small gain theorem, Closed loop stability.