Interaction between process design and process control: the impact of disturbances and uncertainty on estimates of achievable economic performance

Abstract Model-based controllers permit existing processes to be operated close to their economically optimal conditions at all times. At the process design stage, however, a choice must often be made between alternatives with little information available as to the final form (or likely performance) of any control scheme. In this paper, a quick methodology is presented for examining the likely economic impact of disturbances and model uncertainty on the achievable optimal performance of a process. The resulting algorithm is based on a consideration of the amount the optimal operating point has to be ‘backed-off’ from the active constraint set to ensure no operational constraints are violated. This algorithm was implemented within Matlab, a commercial numerical analysis package. The algorithm is applied to an illustrative single-input single-output example. Extensions to multivariable systems are discussed.