Performance of the brushless doubly-fed machine under normal and fault conditions

In this study, the steady-state operation of the brushless doubly-fed machine (BDFM) in various modes is physically elaborated and the active power flow and torque analysis are presented for each operating mode alongside confirmatory experimental results on a 4/8 pole D160 size machine. The machine behaviour in asynchronous operating modes is described similar to the conventional induction machines with corresponding pole numbers. Moreover, its performance in synchronous mode is shown to be similar to synchronous machines. On the basis of the above, the BDFM performance is further analysed under two possible fault conditions: first, a controller or converter fault leading to loss of synchronism is considered, where the asynchronous, double-cascade mode must be introduced to describe the machine performance. Second, a voltage dip at the mains terminal is considered. The simplistic behaviour of the BDFM during this fault, including the operation of a converter protective crowbar, is investigated using steady-state torque-speed curves to obtain a general view of the machine performance.