Application of dynamic flexibility index for evaluation of process control system designs

Traditionally, the process control systems have been evaluated on the basis of nominal model parameters and operating conditions. However, sole reliance on such criterion does not always guarantee operability if some uncertain parameters deviate from their assumed levels. Flexibility analysis has long been successfully adopted to quantify the ability of a given process to maintain its feasibility. This paper presents the use of the dynamic flexibility index (FI_d) for assessing the capability of PID controller of any given process system. In order to calculate FI_d efficiently, the computation strategy proposed by Ali et al. (2021) has been adopted. In particular, the dynamic flexibility index has been used as an additional criterion along with the integrated square of error, to determine suitable controller parameters. It has been shown in the case studies presented that FI_d can effectively complement the traditional tuning methods to enhance both operability and controllability in practical applications.