The Stability of mxm Multivariable Process Control System

A technique is described for the investigation of conditions of stability of a mxm multivariable process controlled by m independent controllers in terms of the parameters of the m uncoupled control systems and the transfer functions of the cross-coupling elements. The method is an extension of a similar result for 2×2 systems [2]. The analytical results are given convenient graphical representations by means of standard frequency response techniques yielding a simple, but powerful tool for synthesis of multiple controllers for multivariable processes.