Fuzzy-PID controllers vs. fuzzy-PI controllers

The synthesis of a control system includes both the controller selection and the adjustment of its parameters. In some cases, the type of controller might be more complex or more general, like PID instead PI or PD, to improve the control system performance. In all cases, the tuning problem must be satisfactorily solved. On the other hand, fuzzy control has made possible the establishment of intelligent control. However, fuzzy logic controllers (FLC) are only used in simple configurations and their analytic knowledge is still poor. In this paper a quantitative and qualitative study of fuzzy controllers is done for the most complete case of a fuzzy-PID. The FLC-PID analytic performance is summarized in terms of its three input variables, which allows us to obtain initial values for the FLC-PID scale factors in terms of the classical PID parameters. This initial tuning has been tested for several systems and a qualitative tuning has also been established. The advantages of the derivative term are also examined.