1. A control system for controlling a non-linear process as a function of a process error signal, the non-linear process having a plurality of regions of operation, the control system comprising: means for producing an auxiliary variable signals which is indicative of an instantaneous region of operation for the non-linear process, the instantaneous region of operation being one of the plurality of regions of operation; and a fuzzy logic controller for producing a process control output signal for controlling the non-linear process in the instantaneous region of operation as a function of the process error signal and the auxiliary variable signal.