Estimation of valve stiction in control loops using separable least-squares and global search algorithms

• Published in: Journal of process control Vol. 18; no. 7; pp. 632 - 642
• Main Author: Jelali, Mohieddine
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.08.2008
• Subjects: Control performance monitoring; Control valve; Genetic algorithms; Hammerstein model; Oscillation detection; Pattern search; Stiction detection; Stiction estimation; stiction parameters; Pattern search; Hammerstein model; Oscillation detection; Stiction detection; Control performance monitoring; Stiction estimation; Control valve; Genetic algorithms
• ISSN: 0959-1524; 1873-2771
• DOI: 10.1016/j.jprocont.2007.12.007

This contribution presents a new procedure for quantifying valve stiction in control loops based on global optimisation. Measurements of the controlled variable (PV) and controller output (OP) are used to estimate the parameters of a Hammerstein system, consisting of a connection of a two-parameter stiction model and a linear low-order process model. As the objective function is non-smooth, gradient-free optimisation algorithms, i.e., pattern search (PS) methods or genetic algorithms (GA), are used for fixing the global minimum of the parameters of the stiction model, subordinated with a least-squares estimator for identifying the linear model parameters. Some approaches for selecting the model structure of the linear model part are discussed. Results show that this novel optimisation-based technique recovers accurate and reliable estimates of the stiction model parameters, dead-band plus stick band ( S) and slip jump ( J), from normal (closed-loop) operating data for self-regulating and integrating processes. The robustness of the proposed approach was proven considering a range of test conditions including different process types, controller settings and measurement noise. Numerous simulation and industrial case studies are described to demonstrate the applicability of the presented techniques for different loops and for different amounts of stiction.