The use of doubly fed reluctance machines for large pumps and wind turbines

Brushless doubly-fed induction machines (BDFIMs) have been extensively researched over the last 15 years because of the possibility of using a partially rated inverter in many applications with limited speed variations. However, the special cage rotor construction and substantial rotor losses in one of the key deficiencies of these machines. A similar and extremely interesting machine, the brushless doubly-fed reluctance machine (BDFRM), has been largely ignored in comparison. This way mainly due to the fact that reluctance rotor designs were not capable of generating saliency ratios large enough to make the BDFRM competitive with other machines. However recent developments in reluctance rotors, spurred on by research into synchronous reluctance machines, have resulted in high saliency ratio cageless rotors that are economic to build. This, together with the promise of higher efficiency and simpler control compared to the BDFIM, means that further investigation of the BDFRM is warranted. This paper presents a comparative theoretical analysis of the important control properties and related machine performance/inverter size trade-offs for the BDFRM in the light of its most likely applications - large pump type adjustable speed drives and variable speed constant frequency wind power generation systems.