A feedforward controller for a brushless excitation system during the diode open circuit fault operation

This study presents a control algorithm of the brushless excitation system for a synchronous machine during the failure of rotating diodes, specifically open circuit failure. Through the harmonic analysis of the exciter field current, the open circuit or short circuit diode fault can be detected. Also the FFT(fast fourier transformation) results of the exciter field current and the change ratio of the exciter field current to the dc link voltage of the 3-phase diode rectifier connected to the synchronous generator can be used as feedforward terms aiding the PI controller for the excitation system. The feedforward control can improve the system performance from that of the PI controller only and compensate the inaccuracy of the model of the system. The simulation results are presented to demonstrate the effectiveness of the proposed controller during the diode open circuit fault operations.