Design of multi-objective control systems with optimal failure tolerance

The selection of the control structure, which is a specification of the interconnection of measurements, exogenous inputs, and manipulated variables, is a critical step in the design of a control system. This paper presents a general internal model control structure with multiple degrees-of-freedom in which each controller can be independently designed for stable systems. The control system is shown to remain optimal when controllers are taken off-line due to component failures, without requiring re-design of any of the on-line controllers. The optimality of the proposed approach is demonstrated for the control of a simulated thin-film process for a variety of component failures.