Design and implementation of brushless doubly fed induction machine with new stator winding configuration

Brushless doubly fed induction machine has acquired relevance as a wind electric generator because of its relative merits over doubly fed induction generator. However, the main drawback of brushless doubly fed induction machine is the presence of torque ripples due to spatial and time harmonics caused by two stator windings and complex rotor structure. In this article, a special design of brushless doubly fed induction machine using delta-star connection in one of the two stator windings is proposed to reduce the torque ripples. Simulation of the new brushless doubly fed induction machine design is performed in ANSYS Maxwell software, and the results when compared with the conventional winding design validated the effectiveness of the new design in minimizing the torque ripples. Prototype of the new brushless doubly fed induction machine has been fabricated and tested in laboratory. Tests have been conducted in both synchronous and asynchronous modes of brushless doubly fed induction machine. Simple induction and cascade connections have been tested in asynchronous motoring mode. Motoring as well as generating conditions have been tested in synchronous mode. Test results show that the new brushless doubly fed induction machine has not only the desired characteristics for wind turbine generator but also capabilities suited for variable torque–variable speed motor applications as well as constant speed applications.