FUZZY CONTROLLER - DESIGN, EVALUATION, PARALLEL AND HIERARCHICAL COMBINATION WITH A PID CONTROLLER

Fuzzy techniques still remain ill-accepted in the control community. As a matter of fact, they rely on a new relation between the real world and the scientists. Whereas some theoretical studies are carried out on this subject, experiments on processes show what fuzzy techniques can bring to the control theory. This paper deals with some implementations of control structures using fuzzy techniques. Our goal is to study the ways to include fuzzy techniques into existing control tools in order to improve the closed-loop performances. The experiments are carried out on different processes with disturbances: a DC motor and industrial furnaces. They allow to study the design and properties of structures such as fuzzy control, commutation between fuzzy and PID controllers and fuzzy supervision of PID controller. After having described two fuzzy controller implementations (fuzzy proportional-derivative and fuzzy proportional-integral controllers), the comparison with a PID algorithm is a base for the design of the parallel PID-fuzzy controllers combination. Even though this strategy is interesting, another hierarchical combination of PID and fuzzy tools is considered. The proposed fuzzy supervisor leads to promising results concerning the development of combined control structures.