Magnetic components in power electronic equipment usually suffer from nonsinusoidal excitations. In this paper, a brief description about the existing core loss calculation methods for nonsinusoidal excitations is given. Then calculation formulas of aforementioned methods for two typical excitation waveforms, that is, square and rectangular with variable duty cycle ${D}$ , are derived. Core loss of nanocrystalline FT-3KS, under above two nonsinusoidal excitations, is measured on an established test setup. The accuracy and applicability of each method are discussed theoretically and verified experimentally, especially in terms of different duty cycles and frequencies. It is found that the waveform coefficient Steinmetz equation (WcSE) is more applicable for the case of relatively small harmonics content of magnetic field intensity ${H}$ (normal duty cycle region), while the improved generalized Steinmetz equation (IGSE) has better precision where the harmonics count (extreme duty cycle region). In addition, the IGSE can better follow the changing trend of core loss with ${D}$ and have better frequency applicability than WcSE, which is proven to be not valid in low frequency (where the static hysteresis loss dominates). The results can provide reference for core loss prediction under nonsinusoidal excitations.

This paper proposes an analytical model for the prediction of airgap magnetic field distribution (MFD) for axial flux permanent magnet (AFPM) machine with various types of misalignments. The AFPM machine geometry is first transformed to a polar representation. Consequently, the sub-domain model based on current sheet technique is developed. Then the stator coordinate system is chosen as reference coordinate to consider both static/dynamic angular and axis misalignments. The back electro-magnetic forces and cogging torque are obtained accordingly based on Maxwell's equations. The results show that the proposed approach agrees with the finite element (FE) method. The model is further validated by experiments under healthy, dynamic angular and axis misalignment conditions, which can validate the proposed approach. It turns out that the proposed approach can predict the performance of AFPM machines with types of misalignment quickly and effectively, which is a great significant for the further fault detection.

The nanocrystalline alloys are gradually used as shielding materials in wireless power transfer (WPT) systems with the development of high power density. In this article, the system properties of WPT using ferrite and four types of nanocrystalline cores are simulated by 3-D finite element analysis (FEA). Based on this, a novel shielding pad composed of nanocrystalline alloy and ferrite is designed to improve the WPT system properties. The WPT systems are preliminarily compared with 3-D FEA when the different nanocrystalline alloys are used in the novel shielding pad. The experimental WPT system for 85 kHz and 1.5 kW with a 24 cm air gap between the primary and secondary coils is built to validate the simulation. The results show that significantly greater shielding can be realized for the novel pad at the price of a slight decrease of transmission efficiency than conventional ferrite core.

A series of high temperature superconducting (HTS) flux pumps have been developed to achieve the persistent current mode (PCM) operation for HTS magnets. However, most of the HTS flux pumps work with a small operating air gap, or with an iron core, the extra heat load brought by the conventional components deployed in the cryogenic environment is inevitable. To address this problem, in this study, in conjunction with the wireless power transfer (WPT) approach and transformer-rectifier type HTS flux pump, we have proposed a contactless self-regulating HTS flux pump. A circuit model and a 2D H-formulation finite-element model have been built for better understanding this system. Furthermore, a basic prototype was proposed to experimentally validate this concept. The measured results indicate that this method has the potential to charge the HTS magnet with all the conventional constituents outside the cryostat, and the operating frequency could be very low to evade inducing large eddy current as well as losses on the cryostat wall.

Three-dimensional (3-D) magnetic fluxes exist in rotating electric machines and T-joints of three-phase power transformers, and may cause local overheating in these devices. In this paper, 3-D magnetic properties of the core materials are measured by an improved 3-D magnetic property tester. First, the 3-D magnetization system is modeled by the voltage and flux linkage equations. Their parameters including the self and mutual inductances and nonlinear impedance are analyzed by the finite element analysis and measured by experiments. Second, a magnetic feedback method in the frequency domain is proposed to obtain the desired magnetization loci. Third, when the specimen is in deep magnetic saturation, the harmonics of magnetic flux density waveform would affect the shape of the corresponding magnetic field strength loci and the accuracy of loss computation. Thus, a waveform compensation method is proposed to eliminate the effects of harmonics. Fourth, the tensor effects of H coils are eliminated by averaging the results of clockwise and counterclockwise rotational experiments. Finally, the 3-D magnetic test system with feedback control, harmonics compensation, and automated data processing is developed. By using the 3-D magnetic tester, samples of nonoriented silicon sheet steel are measured with various excitation models and the results are more reliable than those obtained by experiments without feedback and harmonics compensation.

Based on thermoelectric analogy method, a thermal network model coupled with electromagnetic loss is presented. According to the actual structure of dry-type transformer windings, an accurate thermal network is established. Considering the distribution characteristics of heat source along cooling ducts inside the dry-type transformer, the thermal parameters such as heat flux and convective heat transfer coefficients are calculated by finite element method analysis (FEM) and computational fluid dynamics (CFD). Based on temperature rise experiment, the hottest spot located at the top of outmost high voltage winding is 151.8 °C, which verified the correctness of thermal network model.