The Design of Squaring Compensators for the Feedback Control of Nonsquare Processes

An improved method to design control systems for nonsquare processes, processes in which the number of inputs and outputs are not equal, is presented. The control system utilizes squaring compensators that, when combined with the nonsquare process, form a square system that is decentrally controlled. The compensators are designed to reduce row and column interaction of the square system over a particular frequency range. The parameters of the squaring compensators can be determined analytically or by optimization. The design procedure is applied to the control of two distillation columns. The control systems are analyzed using modern analysis tools and tested by computer simulation.