Development of multi-loop controller design tool for chemical processes

Abstract

Today, CAD(Computer Aided Design)is an indispensable tool for th fdve chemical engineering, especially for process design and control. Most chemical processes are multivariable systems that are much more difficult to design and operate than single-input/single-output processes, due to the interactions between the input/output variables. Those systems can be controlled by centralized controllers or by decentralized multi-loop controllers. Practically, multi-loop controllers are broadly used becaused they have the merits as hardware simplicity, design simplicity, and failure tolerance. However, we should solve both the loop pairing and controller tuning problems to use these multi-loop controllers. So far, the pairing and tuning problems are handled separately:the former was handled by interaction measures(steady state and/or frequency dependent measure) and the latter was hadled by tuning each controller based on Ziegler-Nichols method or IMC PID tuning method and detuning of the SISO controllers for system stability. Recently, a new approach to solve those problems using the linear quadratic optimal control (LQOC) theory was proposed (Lie and Balchen, 1991) to deal with the pairing and tuning problems simultaneously as well as to improve the closed loop performance. However, the solvability of the optimization problem is not guaranteed. The objective of this study is to develop a multi-loop controller design tool based on the closed-loop performance optimization method. The tool can be used for troubleshooting of existing controllers and/or designing a new controller. Our system has a well organized GUI(Graphic User Interface)which provides a convenient working environment.