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| This paper provides a comprehensive comparison of three primary modern brushless doubly-fed machines (BDFMs), namely, cascaded doubly-fed induction machine (CDFIM), brushless doubly-fed induction machine (BDFIM) and brushless doubly-fed reluctance machine (BDFRM) in terms of design-related issues, such as cross-coupling capability and torque density, as the antecedence of the companion paper dealing with modeling and control aspects. The definition of specific electric loading, specific magnetic loading and efficiency in conventional single-fed ac machine design are discussed and extended so as to be suitable for doubly-fed ac machines. A generaltorquedensity equationsubject to electromagnetic loading constraints is developed and then applied tothe three topological variations for initial sizing and torque density comparison.Three typical BDFM prototypes from existing literatures are employed to validate the effectiveness of the general torque density equation. The comparison establishes a solid foundation for the proper utilization and further development of the BDFMs. |
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| Keywords:Electric machines and electric apparatus; brushless doubly-fed machine (BDFM); general torque density equation; specific electromagnetic loadings |
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