Design of a DC excitation control for an autonomous wound-rotor induction generator

This paper proposes the design of a novel dc excitation control for a wound-rotor induction generator (WRIG) under autonomous-generation mode using a microcontroller based on a reduced instruction set chip (RISC). The source of the dc excitation control for the studied WRIG is obtained from its generated ac voltage through a step-down transformer, a bridge rectifier, and a dc-to-dc buck converter. In order to effectively modulate the desired dc voltage for controlling the generated voltage of the WRIG, a fuzzy controller embedded in the RISC-based microcontroller is properly designed and implemented using the PIC 8-bit microcontroller under voltage variations. The calculation results are sent to the pulsewidth-modulation ports to drive the power MOSFET switch of the dc-to-dc buck converter. The proposed WRIG system with its dc excitation control is practically implemented in a laboratory wound-rotor induction machine driven by a dc motor. From both experimental measurements and computer simulations, it can be concluded that the proposed isolated WRIG with its dc excitation controlled by the microcontroller can provide better voltage profile than a self-excited induction generator containing only excitation capacitors under various loading and switching conditions.