Multi-scale control scheme: Stabilization of a class of fourth-order integrating-unstable systems

Even when based on simple models, a fed-batch fermentation process can demonstrate several different forms of complex dynamic behaviours throughout the course of its operation. One of the most intriguing forms of dynamic behaviours that can occur at some points during the fed-batch operation is represented by a fourth-order integrating-unstable system with multiple RHP zeros. To deal with the stabilization of this complex dynamics, a new triple-loop multi-scale control (TL-MSC) scheme is proposed. This scheme aims to first decompose the complex dynamics into three simpler sub-systems which are then separately addressed in a multi-scale structure. This paper presents both the fundamental of TL-MSC scheme and the details of its design. A typical fed-batch alcoholic fermentation is shown as an example to demonstrate the applicability of the new scheme.