Robust Control of a Multivariable Experimental 4-Tank System

A multivariable laboratory process of four interconnected water tanks is considered for modeling and robust control. The objective of the current study is to design and implement a variety of control algorithms and present corresponding robust control analysis on a multivariable laboratory four tank process. The control methodologies considered are (i) decentralized PI control, (ii) “inner-outer” factorization based multivariable Internal Model Control, and (iii) μ-analysis based H∞ control. The three control algorithms are comparatively analyzed using standard robustness measures for stability and peformance. The algorithms are implemented on the four tank system and the performance is compared in reference tracking and disturbance rejection cases. Using experimental data, the process dynamics and disturbance effects are modeled. Inputoutput controllability analysis is performed to characterize achievable performance. A lumped unstructured uncertainty description is utilized to represent the variations ∗Author to whom correspondence should be addressed. Phone: (302) 831-0760. Fax: (302) 831-1048. E-mail: [email protected]. 1 in the system. The three controllers designed are implemented on the four tank experimental apparatus using a Bailey control system utilizing MATLAB and Freelance software interface. The controllers are shown to provide stable and acceptable performance for reference tracking and disturbance rejection experiments. The multivariable IMC and H∞ controllers performed similarly and provided better performance than the decentralized PI control.