This paper describes the control of fully automatic fuzzy-based algorithm for rotating diode excitation system for steam turbogenerators. The fuzzy controller was designed by using microcontroller unit having the selectable voltage and power factor modes. The designed excitation control system has been used instead of the old conventional excitation system. As a case study, 6 MW steam turbogenerator has been controlled and protected according to the capability curve and limitation values supplied by the manufacturer.