Account for uncertainty with robust control design PART 2

Robust control can be applied to design controllers that can handle process uncertainty. The pH control problem exhibits several interesting characteristics that are associated with process nonlinearity and with the uncertainty (or complexity) in the description of the practical components, such as sensors and actuators. Experimental results show that the pH control performance degrades when the process operates away from its nominal design conditions. The process itself undergoes large gain variations, which means that simple controllers, such as a standard PI/PID system, would require either significant performance compromises or restriction to a tight operating range. The experimental results also show that when the process is operating in the vicinity of an operating point, the process model and the limitations on achievable closed-loop bandwidth can be identified with confidence and a systematic procedure can be used to design a controller to achieve this bandwidth. uniform performance can be achieved by using more sophisticated, nonlinear controller schemes.