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Homopolar inductor machine (HIM) has caught much attention in the field of flywheel energy storage system (FESS) due to its merits of robust rotor, brushless exciting, and high reliability. Compared with permanent magnet HIM (PM-HIM), the HIM with field winding (FW-HIM) can effectively eliminate the idling loss caused by the no-load magnetic field by cutting off the excitation current, while the charge/discharge efficiency of the HIM would be decreased due to the copper loss of field winding. To address this contradiction, a novel PM-HIM with a mechanical flux modulator (MFM-HIM) is proposed to achieve low idling loss and high charge/discharge efficiency. First, the special structure and operation principle of the MFM-HIM are investigated. Afterwards, the characteristic of the equivalent magnetic circuit of the MFM-HIM is analyzed and the key structure parameters of it are derived and optimized. Moreover, the electromagnetic performance indexes of the MFM-HIM, including back electromotive force, flux weakening ability, losses, etc. are fully analyzed. Finally, a prototype of the MFM-HIM is designed, manufactured, and tested. Experiment results confirm those obtained by simulations. Results show that the proposed MFM-HIM inherits the merits of high charge/discharge efficiency of PM-HIM and almost no idling electromagnetic loss of FW-HIM. The MFM-HIM could be a promising candidate for the application of FESS. [ABSTRACT FROM AUTHOR]

Homopolar inductor machine (HIM) has been applied in the field of flywheel energy storage system (FESS) due to its merits of simple structure, high reliability, and low idling losses. However, the HIM features unipolar air-gap flux density, which makes its power density lower than that of the electrical machine with bipolar air-gap flux density. Addressing this issue, a novel outer rotor homopolar inductor machine (OR-HIM) is proposed in this article. First, the special structure and operation principle of the OR-HIM are illustrated. Then, the unit motors of the OR-HIM are obtained and investigated based on the magnetic equivalent circuit method to facilitate the design. Moreover, the performance indexes, including power density, output characteristics, losses, and rotor stress of the OR-HIM, are fully analyzed. Finally, a 13-kW prototype is designed, manufactured, and tested. The back electromotive force, load voltage, output torque, and efficiency are measured and compared with those obtained by the finite element analysis. The results indicate that the proposed OR-HIM is a promising candidate for the application of FESS. [ABSTRACT FROM AUTHOR]

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. First, the structure and magnetic circuit characteristics of HIM are introduced. Second, 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 $ {\theta _t} \leq \pi /p$ , or a combination of WSM and synchronous reluctance machine (SynRM) when ${\theta _t} > \pi /p$. Third, 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. [ABSTRACT FROM AUTHOR]

Homopolar inductor machine (HIM) has a wide range of applications in the field of flywheel energy storage system and ship propulsion due to its merits of simple structure, brushless exciting, and low idling losses. However, the three-dimensional finite element method (3-D FEM) is mainly used to investigate the electromagnetic performance indexes of HIM due to its intrinsic 3-D flux density distribution, which is time-consuming. To facilitate the analysis of HIM, an analytical method (AM) is necessary, especially in the initial design stage. Hence, this article presents an AM for analyzing the electromagnetic performance of HIM. First, the structure and operation principle of HIM are illustrated. Second, the magnetic equivalent circuit of HIM is built considering the saturation of stator and rotor core. Third, the air-gap permeance function is obtained considering the affection of stator and rotor slots. Finally, the magnetomotive force, air-gap flux density, back electromotive force, inductances and electromagnetic torque of HIM are calculated, then validated by 3-D FEM and corresponding experiments. The results indicate that the proposed AM can provide reasonable results to estimate the electromagnetic performance of HIM, which would be helpful for the analysis of HIM. [ABSTRACT FROM AUTHOR]

An axial-flux permanent-magnet (PM)-assisted claw-pole generator (APCG) is designed based on an equivalent magnetic circuit model (EMCM). It is designed for generating power in vehicle with the merits of high power density, no brush, and wide airgap flux density modulation range. This paper mainly focuses on establishing the EMCM of the APCG and designing a set of optimal structure parameters. First, the topology and operation principle of the APCG are introduced in detail, including material, fabrication, and magnetic flux distribution. Second, the magnetic circuits in claw poles are simplified and the relationships among the key parameters are discussed. Finally, based on the simplified model and the relationships among the key parameters, the EMCMs of current and PM excitation are established, respectively. According to the EMCM, a scheme of a 4 kW APCG is carried out. Comprehensive investigations demonstrate that the EMCM is time-saving and relatively accurate when compared with a finite element method. [ABSTRACT FROM AUTHOR]

The homopolar inductor machine (HIM) is of particular interest in the field of flywheel energy storage system, where it has the potential to significantly reduce self-discharge associated with magnetic losses. However, the conventional HIM suffers from low power and torque density due to its unipolar air-gap flux density. Besides, the air-gap flux density of HIM is limited by the cross section of rotor, and the rotor diameter is limited by the maximum tip speed of the rotor. Thus, the maximum effective length and diameter of rotor should be within a certain range, which constrains the output power and stored energy of the HIM. To solve these problems, a novel multi-unit out-rotor HIM (MO-HIM) with bipolar air-gap flux density is proposed in this paper. First, the structure and operating principle of MO-HIM is illustrated. Then, the characteristics of the proposed machine are analyzed, indicating that MO-HIM can be regarded as a superposition of multiple unit machines. Finally, to verify the superior performances of the proposed MO-HIM, it is compared with a unipolar out-rotor HIM with multi-segment stator cores in terms of air-gap flux density, back electromotive force, and output torque. Results show that the proposed MO-HIM has larger fundamental air-gap flux density, higher power, and torque density. [ABSTRACT FROM AUTHOR]

An automobile generator has stringent requirements on its weight and volume. As a combination of permanent magnet and electric excitation motor, hybrid excitation machine has the merits of small size, lightweight, and adjustable output voltage, which can meet the requirements of the vehicular generator. In this paper, a novel axial flux stator partition hybrid excitation brushless synchronous generator (ASHG) is proposed. First, the structure and the operating principle of ASHG is illustrated. Afterward, the shape of the magnetic pole is optimized to obtain the air-gap flux density with low harmonic component. Finally, the regulation performance of the magnetic field and output voltage are investigated by using the 3-D finite-element analysis method. The result indicates that the ASHG has a good ability to adjust the terminal voltage. [ABSTRACT FROM AUTHOR]