Power factor control using brushless doubly fed reluctance machines

The brushless doubly-fed machine (BDFM) allows the use of a partially rated inverter in many variable speed applications with limited speed variations. In its induction machine form (BDFIM), however, the BDFM has significant rotor losses and poor efficiency due to the cage rotor design. A reluctance version of the BDFM, the brushless doubly-fed reluctance machine (BDFRM), ideally has no rotor losses, and therefore offers the potential for greater efficiency and simpler control compared to the BDFIM. A theoretical study of this interesting machine is very important in order to gain a thorough understanding of its unusual operation, control features and compromises between optimal performance and the size of the inverter and the machine. This paper will specifically concentrate on power factor control properties of the machine and trade-offs with other control objectives such as maximum torque per inverter ampere and minimum copper losses. To date this kind of analysis has not appeared in the literature.