This paper describes a brushless electrically excited synchronous machine with a distinctive rotor structure and additional harmonic field windings. Spatially distributed third harmonic magnetic fields will be created in the air gap by feeding the stator harmonic windings of a dc current. These harmonic MMFs will generate an induced voltage in the additional rotor harmonic coils, which can supply the field winding with a dc current after rectification. Based on this operation principle, distributions of harmonic windings and the stator harmonic magnetic fields are analyzed. The relationship between harmonic EMFs and rotor harmonic winding turns are studied. Mutual interference between the different magnetic fields and windings in the machine is discussed. The harmonic excitation fields and the air gap flux densities are then calculated by employing finite element methods, and the regulating characteristics of no-load EMF are analyzed and power losses of machine are discussed. Experimental results of one 1.0-kW prototype machine agree well with the theoretical analysis and finite element calculations, which helps to evaluate this type of synchronous machines having brushless electrical excitation.
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Yao et al. (2016) studied this question.
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