A SELF-TUNING FUZZY PI CONTROLLER FOR PV-WIND-DIESEL-BATTERY HYBRID ENERGY SYSTEMS. Eng. Emad Sweelem* Electronics Research Institute NRC Buildings El-Tahrir St. Dokki, Giza Egypt Tel./Fax: 002023351631 email@example.com Dr. Abd-El shafy Nafeh Electronics Research Institute NRC Buildings El-Tahrir St. Dokki, Giza Egypt Tel./Fax: 002023351631 firstname.lastname@example.org Prof. Dr. Faten Hosney Electronics Research Institute NRC Buildings El-Tahrir St. Dokki, Giza Egypt Tel./Fax: 002023351631 email@example.com Abstract: An autonomous PV-Wind-Diesel-Battery (PVWDB) hybrid energy systems have many applications especially for sites which are far from conventional supply grid. But, the components of these systems are, usually, non-linear having a parameter variation problem. Therefore, this paper presents a robust self- tuning PI-type fuzzy logic controller (FLC). Depending on the process trend, the output scaling factor (SF) of the controller is modified on-line by an updating factor (r). The value of r is determined from a rule-base defined on error (E) and change of error (ΔE) of the controller variable. The proposed self- tuning controller is designed using a very simple control rule-base and the most natural and unbiased membership functions (MF). The proposed scheme is tested for a different numbers of membership functions with using Matlab-Simulink. Also, the compartive between FLC and the self-tuning fuzzy PI controller is cleared. The results show that our scheme gives results better than normal FLC with few trials of SF’s.