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 paper presents an AM for analyzing the electromagnetic performance of HIM. Firstly, the structure and operation principle of HIM are illustrated. Secondly, the equivalent magnetic circuit of HIM is built considering the saturation of stator and rotor core. Thirdly, 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 and inductances are calculated, then validated by 3-D FEM and corresponding experiments, which indicates that the proposed AM can provide reasonable results to estimate the electromagnetic performance of HIM, which would be helpful for the analysis of HIM.

The rotor topologies have a great influence on the vibration characteristics of permanent magnet assisted synchronous reluctance machines (PM-SynRMs). In this article, the vibrations of PM-SynRMs with different rotor topologies are studied and compared. First, the electromagnetic force harmonics of PM-SynRMs have been studied and the design rule about the combination of stator slots and “rotor virtual slots” is given to achieve low vibration. Then, a multiphysics model is established to calculate the vibration of the PM-SynRMs with different rotor topologies. The modal analysis is conducted through finite element method considering the orthotropic of materials and validated by the modal test. Besides, the prototype has been built and the vibration test is performed to confirm the accuracy of the vibration simulation. Based on the multiphysics model, the influence of the shapes of flux barriers and the number of “rotor virtual slots” is investigated. It proves that the design rule about the combination of stator slots and “rotor virtual slots” can achieve low vibration for PM-SynRMs.

Homopolar inductor machines (HIMs) are promising candidates of the pulsed alternator for the application of high power pulsed supplies. However, a single HIM can hardly serve as both a pulsed alternator and a motor, because the voltage and the frequency of the pulsed alternator are usually much larger than those of the motor. Thus, a prime motor is needed to drag the pulsed alternator, which complicates the pulsed alternator system. To simplify the structure of the system, this paper proposes a novel four-stator-core HIM (FSCHIM) consisting of an alternator and a motor. Firstly, both the configuration and operation principle of the FSCHIM are introduced. Secondly, the sizing equations of the FSCHIM are deduced to obtain its primary size parameters. Thirdly, the armature reaction is investigated and the influences of main structure parameters on key output indices are studied by using finite element analysis (FEA). Finally, the optimized scheme is validated by three dimensional FEA and experimental results on the sub electrical machines. The results demonstrate that the FSCHIM can serve as a combination of the motor and the pulsed alternator which enjoys the merits of high voltage and high-frequency discharge performance with a lower voltage and lower frequency driving system.

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.

To increase torque density, a combined-Halbach array for the axial flux permanent magnet machine (AFPMM) with a yokeless and segmented armature (YASA) is presented in this article. First, the YASA machine models with conventional axial magnets and combined-Halbach array magnets are established by using 3-D finite-element method (FEM). Then, the torque, torque per magnet-volume, and no-load back electromotive force (back EMF) are calculated, and the performance of the two machines is analyzed and compared. It is demonstrated that the combined-Halbach array can improve the torque density of the machine and the utilization rate of the magnets. Finally, the combined-Halbach array rotor is optimized, where the rotor with unequal-thickness magnets is established, and its torque density is calculated under different thickness. The results show that the combined-Halbach array with unequal-thickness magnets can decrease the amount of permanent magnet (PM) materials, thus improving the utilization of magnets and reducing the costs.