A New Mode-Switching Algorithm for the Line Commutated - Thyristor Bridge Emulated Rotating Power Electronic Converter for Brushless Exciter Applications

Conventional brushless exciters supply the field current to the wound-field synchronous machines through a diode bridge rectifier. Though these diode bridge-based exciters are more reliable compared to the static exciters which use brushes and slip rings, they can not produce a negative voltage across the field winding. This makes the rate of decay of the field current is very slow. To rapidly remove the field current in case of an internal fault in the synchronous machine, a thyristor emulated rotating power electronic converter (RPEC) has been proposed for brushless exciter applications. This paper shows the implementation of the gate pulse generation for the RPEC during both rectification mode as well as inversion mode. Also, the field winding current disruption issue has been analyzed while switching from rectification to inversion mode. To avoid this problem, a new algorithm has been introduced in this paper. Also, an analysis has been done on the maximum firing angle for the RPEC during the inversion mode to make sure the field current is not disrupted for the proposed converter. Finally, MATLAB-SIMULINK based simulation results are presented along with the experimental results.