Design of a DC excitation control for an autonomous wound-rotor induction generator in renewable-energy systems

This paper proposes the design of a novel DC excitation control for a wound-rotor induction generator (WRIG) under autonomous-generation mode using a micro controller 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 micro controller is properly designed and implemented. Due to high-speed modulation capability of the employed micro controller, the voltage variation of the studied autonomous WRIG under loading conditions can be effectively compensated. The proposed WRIG system with its DC excitation control is practically implemented in a laboratory 300-W wound-rotor induction machine driven by a DC motor of 500 W. From both experimental measurements and computer simulations, it can be concluded that the proposed isolated WRIG with its DC excitation controlled by the micro controller can provide better voltage profile than traditional self-excited induction generator (SEIG) containing only excitation capacitors under various loading and switching conditions.