Modeling of polyphase brushless exciter behavior for failing diode operation

This paper describes an original numerical method for modeling rectified polyphase salient pole synchronous machines which are commonly utilized for large turbo-generator brushless excitation systems. Simulating this kind of system under normal (and especially abnormal) operating conditions, would be of great help for designers and operators in order to improve their reliability and availability. The proposed method is especially convenient to represent actual machines without almost any restrictive assumption. It makes possible the evaluation of the stress of semiconductors when diode failures occur. Results show that good operation of the exciter with short-circuited diodes is almost impossible since its output voltage and current are noticeably weakened. However, its operation can be acceptably maintained if one or more diodes are open.