This paper proposes a new hybrid permanent magnet synchronous reluctance machine (HPM-SynRM) with axially sandwiched magnets for improving machine performance including airgap flux density, back electromotive force (EMF), torque, torque ripple, efficiency, and power factor. The significant feature of the proposed machine is the configuration of axially integrating two kinds of independent and symmetrical rotors with a specific assembling angle, such that it can make full use of the magnetic torque and the reluctance torque for efficient production of the total torque. Meanwhile, the proposed machine greatly improves the PM utilization for high magnetic torque, and releases the stress condition of SynRM rotors for more proper design of ribs, thus to further improve the torque, efficiency, and power factor, especially when compared to the conventional PM-SynRM with the same machine specifications and operating conditions. The design of the proposed machine, including the PM optimization using the Kriging method and genetic algorithm, rib width and assembling angle design using the finite element method (FEM), has been first discussed in detail. Then the advantages of the proposed machine is highlighted by quantitatively comparing to a conventional PMSynRM by the FEM. Finally, the proposed machine is manufactured to validate its high performance by experiments.

DC bias in power transformers leads to strong core saturation and thus nonlinearly inferior operation. This paper analyzes the ability of power transformers to withstand the dc bias by novel analytical criteria. The proposed criteria are obtained from the nonlinear equivalent circuit, which considers the effects of nonlinear inductances. The validity of the proposed analytical criteria is verified by the finite-element analysis results and experimental results, which indicates that the proposed analytical criteria are effective to evaluate the ability to withstand the dc bias of power transformers.

The AC copper loss of flat copper wire in axial flux permanent magnet (AFPM) motor can seriously affect the performance, so it cannot be ignored when optimizing the motor design. Accurate results can be obtained using 3-D transient field finite element (FE) to calculate AC copper loss. However, the calculation time is long, which is not conducive to the motor optimization design. In order to consider the effects of the external magnetic field, conductor arrangement mode, stator tooth-tip, skin effect, and proximity effect on AC copper loss and to balance the calculation accuracy and calculation time, the analytical calculation method and hybrid analytical calculation method are proposed. The analytical calculation method combines complex eddy current equation with the precise subdomain method, and the hybrid analytical calculation method combines three-dimensional FE with the analytical method. In order to comprehensively compare different calculation methods, the proposed methods are used to analyze the AC copper loss and motor efficiency under different conductor arrangement modes and working conditions, and the simulation verification is carried out by three-dimensional transient field. Finally, through the AC resistance experiment and prototype experiment, the accuracy of the proposed methods is verified, and the characteristics of different methods are summarized.

Power transformers play an important role in the safe and reliable operation of the whole power grid. Once a fault occurs, it will endanger the normal operation of the transformer, and even result in power grid accidents. Accurate and practical methods of transformer fault monitoring and type identification have attracted extensive attention in the field of electrical engineering. However, it is difficult to obtain a large number of measurement data for different fault types on a large power transformer. The vibroacoustic characteristics of transformer faults have significant asymmetry. For the power transformer in service, it is complex and uneconomic to obtain the vibroacoustic signals under different fault conditions. To handle this problem, this paper proposes simulation methods of several common transformer core faults, based on multi-physical field coupling, and then analyzes the vibroacoustic signals generated by the operating transformer. Finally, it verifies the results of acoustic and vibration signals under several faults, through physical experiments. The results show that the transformer fault simulation method is reasonable and accurate. Furthermore, a change in the transformer core state will cause a change in the transformer vibroacoustic characteristics, and different types of core faults can be distinguished by the analysis of vibroacoustic characteristics.

A shell-type medium frequency transformer (MFT) using amorphous alloy material is designed for high-power electronic applications. The optimal area product design method is adopted to design an MFT, which maximizes the high efficiency and power density, minimizes the loss and volume, and meets the limitations of insulation and temperature rise. Then, a 20 kVA/10 kHz MFT is designed. To ensure the rationality of the MFT design, the magnetic properties of the amorphous alloy material are measured, and finite element simulations are carried out based on measured magnetic properties. The magnetic flux density, loss, and temperature rise of the designed MFT are analyzed. Finally, a 20 kVA/10 kHz MFT prototype is fabricated, and experimental tests are carried out. The loss and temperature rise of the MFT prototype are within reason, which verifies the effectiveness of the proposed scheme.