Relationship between homopolar inductor machine and wound-field synchronous machine

The homopolar inductor machine (HIM) has attracted recent interest in the field of flywheel energy storage system due to its merits of robust rotor and low idling losses. In some situations, the analytical methods of a conventional wound-field synchronous machine (WSM) can be used to analyze the HIM, but the clear explanation about why these can be done and the relationship between HIM and WSM were not given in the literature. To address these issues, this paper studies the HIM based on the basic theoretical model and equations. Firstly, the structure and magnetic circuit characteristics of HIM are introduced. Secondly, the mathematical model of HIM is derived and then decomposed, which indicates that the HIM can be seen as a WSM with large end leakage inductance when rotor tooth width θt≤π/p , or a combination of WSM and synchronous reluctance machine (SynRM) when θt>π/p Thirdly, the performance indexes of HIM and corresponding equivalent machines, including air-gap flux density, back electromotive force and inductance parameters, are analyzed and fully compared. Finally, an HIM is prototyped and tested on an experimental platform. The simulation and experiment results show that it is reasonable to regard the HIM as a WSM or a combination of WSM and SynRM. The conclusion gives a transparent explanation about the relationship between HIM and WSM, which helps to simplify the analysis of the HIM.