A new measure of process output controllability

A steady state, multivariable, and nonlinear measure is presented for assessing the input±output, open-loop controllability of a process. This measure ascertains the inherent controllability of the process, as it is calculated in the absence of any regulatory control structure. For the process examples utilized in this paper, it is also independent of the inventory control structure that might be assumed present in order to keep the inventory levels constant. This measure evaluates the ability of a design to reach all points of the desired output space and to reject the expected disturbances utilizing input action not exceeding the available input space. Besides being applicable to a SISO (Single Input, Signal Output) case, its multivariable character is shown to be more appropriate than existing measures such as RGA (Relative Gain Array), minimum singular value, and condition number.