Comparative study of magnetic coupling for a doubly fed brushless machine with reluctance and cage rotors

The high costs of power electronic converters for adjustable speed drive and generating systems have prompted serious investigations of the doubly fed brushless machine (DFBM) systems yet much of the research has focused on developing the brushless doubly fed machine systems. However, the rotor structure basically determines the magnetic coupling between the two, primary and secondary, stator windings, which in turn, determines the machine power density, performance and required ratings of the power converter. This paper is intended to present a comparison study of the DFBM with different rotor structures, two reluctance and one cage rotors with a common stator. By analyzing the magnetic mutual coupling between the two sets of stator windings, the magnetizing characteristics with each rotor structure is evaluated and their differences are highlighted. The comparative study is carried out by using a unified approach-2D transient finite element analysis.