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Permanent magnet synchronous motors (PMSMs) with non-concentric magnetic poles (NCMP) structure are widely used as high-precision servo motors. The current subdomain method mainly equates the NCMP to a rectangular magnet to make each subdomain boundaries of magnet parallel when calculating the magnet eddy current loss (ECL), which results in a lower accuracy of the calculation. This paper divides the NCMP into non-concentric region and concentric region along the radial direction. The non-concentric region is further divided along the circumferential direction, and each divided region has a single thickness. Based on the subdomain method, a novel analytical method of magnet ECL in PMSMs with NCMPs is proposed. Moreover, the 3-D distribution coefficient of ECL in the NCMP is derived by the equivalent impedance method. The effects of eddy current reaction and stator slotting are taken into account to improve the calculation accuracy. Then, through theoretical derivation, the relationship between the minimum magnet loss and the pole parameters is obtained, which provides a reference for the design of NCMPs. Finally, the loss separation experiment is performed on four prototypes with NCMPs. The experimental results, finite element method results and analytical results are compared to verify the correctness of the model.

This paper presents a novel configuration of the eddy current speed sensor to measure the rotating speed of iron rods and shafts up to 3000 rpm. The proposed eddy current speed sensor has an axial airgap structure with one excitation coil and two antiserially connected pick up coils. The speed sensor is mounted in the end shaft part region. Different solid iron materials for rotating shaft are considered in the measurements and calculations to evaluate solid iron material effect on the eddy current speed sensor performance. 2D and 3D finite element method is utilized for the performance analysis of the speed sensor. Also, a 2D analytical method is developed for parametric analysis. A copper rod is also used to compare the speed sensor with the rotating iron shaft and copper shaft. Finally, two thin copper discs with different diameters are mounted on the solid iron shaft and their influences on the eddy current speed sensor were evaluated and measured to increase sensitivity and decrease sensor dependency on the permeability of the solid iron shaft. The achieved nonlinearity errors are about 0.2%.

The rectangular profile conductor with a large cross-section requires less slot space and has better heat dissipation ability than the traditional round profile one. But its application in automotive propulsion electric machines is thwarted by high ac winding losses and temperature rise under high-speed operations. This paper proposes a novel stator winding topology with hybrid strands based on the ac losses' distribution characteristics and the theoretical relationship between the eddy current suppressing ability and the geometric parameters. The new winding can effectively reduce the ac loss and the peak temperature in the winding at high-speed operation. Meanwhile, it can maintain a high filling rate. Therefore, the machines maximum rotating speed and power density can be effectively improved. In experimental validation, a winding sample with this new topology is manufactured and compared with the conventional one formed by rectangular wires. It shows the proposed method can reduce the winding ac loss by up to 12% and the temperature rise by 10%~21%. It is validated to have considerable industrial potential in the future development of automotive motors.

The traditional remote field eddy current (RFEC) testing is a method widely applied for detecting the corrosion and wall thinning in a ferromagnetic pipe system and shows intrinsic deficiencies in axial defects quantification due to the distinct probe structure. A circumferential alignment probe structure is used to improve the sensitivity to axial defects of pipes. Meanwhile, current approaches typically are incapable of classifying inner diameter (ID) and outer diameter (OD) defects of the pipe, which brings difficulties to the formulation of strategies in pipe repair. An external pulsed RFEC method is proposed to address the issues in this paper. First, we give a thorough analysis of the effects of probe geometry and excitation parameters on the output signal, targeting parameters optimization. Secondly, the finite element model is built and used to analyze the relationships between the defect size and signal features under different excitation types. Finally, the improvements in probe performance and the ability to classify ID and OD defects are validated by measuring the defect depths of the pipe. Results showed the zero-crossing time feature can be used to distinguish ID from OD defects. Thus, the proposed method is an effective complementary measure for the existing RFEC tools.

This article proposes a mesh-based magneto-electric coupling network model for prediction and reduction of permanent magnet (PM) eddy current loss in a flux-switching permanent magnet machine. The key is to couple the electromagnetic inductions between the eddy current network and the equivalent magnetic network (EMN) in stator PMs dynamically. First, the eddy current networks of PMs are established with electric meshes. The electromotive forces of electric mesh are induced by considering double-side effects based on Maxwell's equations. Second, the stator meshing method is propose with PM segments, and combined in the EMN matching to the eddy current mesh. High efficiency and accuracy with detailed magnetic field distributions can be obtained. Then, the magnetic fields generated from EMN PM nodes are coupled in eddy current network to accurately predict the flow directions and density distributions. Finally, the original design and two other structures with rotor magnetic barriers are analyzed for reduction of eddy current losses. The effectiveness of the proposed model is verified by finite-element analyses and experimental results.

In this article, a new and general three-dimensional (3-D) analytical frame for evaluating the performance characteristics of the permanent magnet (PM) eddy-current coupling is presented using a magnetic vector potential formulation. Based on the 3-D Cartesian coordinate system, the actual coupling geometry is equated to a linear structure by applying the mean radius (for cylindrical conductor and PM rotors) and the equivalent cuboid (for PMs of various shapes) assumptions. The torque contribution from the overhangs of conductor back iron and the effects of PM and air gap thicknesses are all taken into considered. A verification process is implemented and it is shown that, in any case, the proposed 3-D analytical model can yield the results very close to those obtained by both the 3-D finite-element analysis and experimental measurement.

Most permanent magnet (PM) loss studies consider only eddy current loss and neglect hysteresis. In this article, the hysteresis behavior of two NdFeB PM grades with different magnetic properties is assessed when applied in a PMSM. Data from vibrating sample magnetometer measurements and hysteresis modeling are used as a base. In addition to the main magnetic phase, the samples contained magnetic phases with reduced coercivity. Such phases may contribute to hysteresis losses in a PM material. A new model is introduced to simulate the hysteresis of rare-earth magnets of any geometric shape in the second and first quadrants of the intrinsic BH -plane. The magnetic field strength distribution in the PM material of an electrical motor is analyzed by two-dimensional finite-element method. The results are used as the input data for an analytical hysteresis model. The results indicate that the hysteresis loss resulting from the structural imperfections and geometry of the magnet may introduce a considerable loss in NdFeB PMs applied in rotating electrical machines.

Real-time thermal capacity estimation is not only part of prognostics and health management (PHM) but also determines the dynamic loading capability of the traction transformer. The hot-spot temperature is the vital parameter for real-time thermal capacity estimation. In high-speed railway, the unbalanced loads of the two phases of the traction transformer cause unbalanced winding losses and therefore affect the top-oil temperature and further influence the hot-spot temperature in each phase. In order to explore the dynamic thermal performance of the transformer under unbalanced load (current), a thermal model for calculating the hot-spot temperature was proposed incorporating thermal interaction between two power supply phases. This model treats the winding loss of each phase independently, considering the temperature dependence of winding ohmic losses and eddy current losses. A thermal circuit topology was presented with independent phase windings sharing the same top-oil temperature, where an improved heat transfer correlation was used to account for the nonlinear thermal convection. The proposed model was verified by the factory temperature rise tests and field operation data for the same batch of transformers.

The linear motor system is normally a low-damping system to achieve high speed and high acceleration without mechanical transmission devices. Therefore, the vibration issue is serious especially in the high-speed start–stop motion process, which deteriorates the control precision and decreases work efficiency. This article proposes a dual-sided hybrid excitation eddy current damper (ECD) to suppress the vibration of the linear motor during decelerating and stopping stages. This ECD is composed of a copper plate and two E-shape hybrid excited electromagnets. The plate is sandwiched between these dual-sided electromagnets to generate the eddy current damping force when it moves and the ECD current is excited simultaneously. The analytical model of the ECD considering leakage flux is established and verified by FEA with the deviation less than 7%. Experiments are conducted on the prototype to verify the effectiveness of its vibration restraint performance. With the active damping, the peak amplitude of the position error and the settling time are reduced by 68.88% and 33.33%, respectively.

Currently, surface-mounted permanent-magnet (PM) rotors are more frequently employed than interior PM rotors in high-speed PM motors. It is mainly because the mechanical strengths of sleeve materials can be much higher than those of silicon steels. However, at high speeds, the current harmonics caused by pulsewidth modulation (PWM) converter induce high eddy current losses in PMs and sleeves when they are conductive. Moreover, because of the existence of nonmagnetic sleeves, the surface-mounted PM motors have very poor flux weakening abilities. Interior PM motors can not only avoid sleeves, but also reduce the influence of the PWM converters. Moreover, they can provide additional reluctance torque and have better flux-weakening abilities. A major drawback of interior PM rotors is their low mechanical strengths, which limit their surface velocities. In this article, high mechanical strength amorphous metal 2605SA1 is used to increase the surface velocity of an interior PM rotor. A surface-mounted PM rotor protected by carbon-fiber sleeve is designed to perform a comparison study. Both motors are built and tested. The advantages and disadvantages of the two motors in terms of mechanical, electromagnetic, and thermal behaviors are evaluated.

The article analyzes a high-speed solenoid valve (HSV) whose core and moving armature are massive elements characterized by strong eddy currents, hysteresis, and saturation. The feedback control employed in obtaining a predetermined nonsinusoidal current in the core coil necessitates the use of a high-frequency pulsewidth modulation (PWM)-like voltage with parameters varying in a manner unknown in advance during the uninterrupted transient. In view of the known difficulties in using finite-element solvers, physical Cauer circuits are found to be a reliable engineering alternative. The use of the duality transformation is proposed to obtain a pure electric model of the core and armature. As a preliminary result, it is found that a threefold reduction in eddy-current loss is achieved by using the slotted core. The results obtained with the model are in a reasonable agreement with the experimental magnetizing current and the armature movement during successive valve operations.

The ferrite core plays an essential role in coupling enhancement and magnetic shielding for the wireless power transfer of electric vehicles. However, ferrite has apparent defects, such as a low saturation and brittleness, especially at the vehicle side. Therefore, a novel flexible nanocrystalline core is proposed in this article, which has high flexibility and high saturation limits. However, the nanocrystalline core has a large eddy current under 85-kHz excitation, so the refinement crushing process and alternating seamless stitching process are adopted to reduce the eddy loss. The feasibility of the improvement process is preliminarily verified via finite element simulations, and four nanocrystalline cores with different permeabilities are obtained. Through static parameter measurements and 7.7-kW loading tests, the modified nanocrystalline cores achieve excellent results. Based on the above, the nanocrystalline core with the best performance is further selected for an anti-saturation test and leakage measurement at 11 kW. Even when the thickness is reduced to 2 mm, the ac–ac efficiency remains 97.408%. The maximum core temperature is only 80.9 °C, and the flux leakage completely satisfies the limit requirements of ICNIRP 2010. In contrast, the ferrite core cannot withstand the impact of a strong alternating field and fails.

Detecting defects in metal structures quickly and robustly is critical to maintaining safe operation in industry. This work discloses an eddy current (EC) testing probe with coils carrying three-phase currents as excitation and integrated array tunnel magnetoresistance (TMR) sensors measuring the magnetic field as receiver. The three-phase currents in the planar layout coils induce EC that migrates electrically in the material under test. This excitation method does not require multiplexing of the coils and is sensitive to defects of any orientations. The TMR array contains 64 sensors, which are microfabricated and packaged in a line. Within single probe pass, the sensors generate magnetic field image with high sensitivity ( $\text{1.99}\;\text{nT}/\sqrt {\text{Hz}} @\text{30}\;\text{kHz}$ ) and fine spatial resolution (0.5 mm pitch). By analyzing the output image, defects are identified and localized. The operating principle of the probe was investigated based on a finite-element method model. A prototype probe was developed and tested, with which machined defects in aluminum samples were inspected. Experimental results show that the probe has comparable sensitivity for horizontal and vertical defects, and it can recognize a small defect with length × width × depth = 1 × 0.2 × 1 mm3. The defects are located within 1 mm with an artificial neural network.

High-speed permanent magnet machine (HSPMM) design is considered with particular attention paid to machine electromagnetic, thermal, and mechanical analyses. In this article, a 140-kW, 15 000 r/min HSPMM is designed with its power losses evaluated at first. Afterward, the machine temperature distribution is obtained based on computational fluid dynamics modeling. HSPMM is prototyped with experimental tests conducted to verify the calculation results. Mechanical strength analysis is performed for the HSPMM rotor structure with pole filler by finite-element method for the rotor at three operational conditions, while the influences from sleeve parameters on rotor strength are comprehensively studied for the HSPMM rotor at the most challenging condition. In this article, stator auxiliary slotting is extensively researched to reduce the rotor eddy current loss with little effects on machine output torque. The air gap flux density for HSPMM with auxiliary slotting is analytically predicted, while the working mechanism is illustrated in-depth. The effects from auxiliary slot dimensions, numbers and positions, on machine performances are further proposed and investigated. The experimental tests also validate the reduction of HSPMM rotor eddy current loss by the application of auxiliary slotting.

Solid-rotor switched reluctance machines (SRM), having the rotor machined from a single piece of metal, are one of the few viable options for motoring and/or generation under harsh operating conditions, including high speeds, high shaft temperature, and corrosive environment. Apart from double saliency and high degree of magnetic saturation as in any SRM, significant core losses due to high eddy currents, even under static conditions, make the characterization and modeling of solid-rotor SRM challenging. The objective of this article is to understand the magnetic characteristics of a solid-rotor SRM through extensive experimental studies and to develop a stator-side model for the machine which adequately captures its magnetic behavior. First, the flux-linkage characteristics of the solid-rotor SRM under test are measured over a wide range of excitation conditions and rotor positions. Applying a computationally efficient decomposition technique on each set of experimental data, the measured winding current is resolved into magnetizing and core-loss components to obtain a stator-side model of the machine. The proposed model is useful to predict the winding current and core-loss under different excitation conditions, which is necessary for simulation and performance prediction. The proposed method is more accurate than the existing methods, while being simple and fast to implement.

Nondestructive detection of small fatigue cracks is a critical and challenging task in evaluating the properties of material. This article proposes a novel L-shaped ferrite magnetic open sensing structure of the eddy current pulsed thermography system for fatigue crack inspection on metallic materials with anomalistic geometry. The theoretical derivation model of the proposed structure is developed to generate a guided distribution of electromagnetic field for enhancing the weak thermal signal detection. The proposed detection model provides a region of interest that has relatively uniform magnetic field. This significantly enhances the detectability and thermal contrast of omnidirectional microfatigue cracks. In addition, the detection is completely in the open view of the infrared camera, and the configuration has advantages of dramatically increasing portability and efficiency for detecting complex workpiece. Experiments on natural cracks in several samples have been conducted to validate the reliability and efficiency of the proposed system.

This article proposes a self-temperature compensation method based on an analog multiplier, which reduces the circuit thermal drift by more than an order of magnitude. An ac bridge eddy current sensor (ECS) is used as an example to analyze the thermal drift of the circuit in detail, and the basic principle of the compensation method is expounded. A high-precision ECS prototype is manufactured and tested. Results show that the temperature coefficient of the circuit in the prototype is decreased from 243 to 5 ppm/°C with this technique. This self-compensation method is simple, effective, and universal. Furthermore, this technique has a unique advantage for high-bandwidth and high-precision sensors and can work efficiently in complex and harsh temperature environments.

Efficiency and multi-simultaneous-frequency (MSF) output capability are two major criteria characterising the performance of a power amplifier in the application of multi-frequency eddy current testing (MECT). Switch-mode power amplifiers are known to have very high efficiency, yet they have rarely been adopted in the instrumental development of MECT. In addition, switch-mode power amplifiers themselves are lacking in the research literature for MSF. In this paper, a Class D power amplifier is designed so as to address the two issues. An MSF selective harmonic elimination pulse width modulation (MSF-SHEPWM) method is proposed to generate alternating magnetic fields which are rich in selected harmonics. A field-programmable gate array (FPGA) based experimental system has been developed to verify the design. Results show that the proposed methodology is capable of generating high MSF currents in the transmitting coil with a low distortion of signal.

Speed sensing is an essential part in all closed-loop systems. There exist some situations in industry where the speed has to be measured without touching the target object, for example, the accurate speed measurement of the solid metal wheels with smooth surfaces of freight wagons. In this article, a contactless, eddy-current-based speed sensor is proposed for applications where the speed of a smooth conductive surface is to be measured; but contact to or modification of this target surface is prohibited. The proposed speed sensor is composed of a permanent magnet (PM) rotor that is free to rotate above the target surface. The relative motion of the surface with respect to the PM field induces eddy currents in the surface, which leads to a torque being applied on the rotor. Consequently, the PM rotor speeds up until it reaches a steady rotational speed that is proportional to the speed of the target surface. Three models are proposed. They are a two-dimensional (2-D) finite-element model, a 2-D analytical model, and a three-dimensional (3-D) combined numerical/analytical model. Measurements are taken on multiple hardware prototypes to validate the analysis. Finally, a multiobjective (PM volume vs. dynamic performance) Pareto optimization is conducted for the proposed speed sensing system. The results show that smaller rotors with lower pole-pair numbers generally have better dynamic performance as well as lower costs.

In this article, the permanent-magnet (PM) eddy current loss in a four-phase fault-tolerant flux-switching PM (FT-FSPM) machine is investigated from the perspective of air-gap magnetic field modulation. It can be found that the PM eddy current loss in FT-FSPM machines results from the relative motion between air-gap field space harmonics and PMs. Some effective working harmonics produce the major PM eddy current loss. The proportion of PM eddy current loss generated by each working harmonic is studied in detail, revealing that the low-order (third) harmonic is the main factor. Then, two new structures are proposed to reduce PM eddy current loss, in which magnetic flux barriers are designed by reducing low-order harmonics from the aspect of magnetic field modulation theory. Electromagnetic performance is investigated by finite element analysis. The results show that the proposed structure is effective to suppress PM eddy current loss. Finally, an experimental test platform is established to verify the theoretical analysis results.

For the high-speed permanent magnet synchronous motors (HSPMSMs), their magnetic fields are more complicated with the rotating magnetization and harmonics considered. Furthermore, there are interaction effects on motor iron loss from high frequency, temperature, and compressive stress. In order to obtain the accurate HSPMSM iron loss calculation model, different iron loss models are proposed, in this article, considering these physical factors, and the iron loss model considering the interaction effect of the multiphysics factors is given. The magnetic field, temperature field, and stress field are analyzed for HSPMSM by finite-element method (FEM). Then, the proposed models are employed to calculate the iron loss of the silicon steel sheet and the prototype. The accuracy of the proposed iron loss model, which can consider the interaction effect of the multiphysics factors, is verified by the experimental test measurements on the prototype.

Eddy current analysis is a key issue for large turbine generators. The finite-element method (FEM) is a computational tool for obtaining the electromagnetic characteristics of electrical machines. In this article, we propose a computer model of the eddy current losses of metal fasteners in the rotor slots of a large turbine generator. The electromagnetic properties of the rotor fasteners and the outer diameter of the rotor are taken as the input, and the eddy current loss of the rotor fasteners is taken as the output. A prediction model is constructed using the FEM and deep learning. The analysis results show that compared with the independent finite-element analysis, this method reduces the design cycle time and improves the design efficiency for a large-capacity turbine generator. Compared with other machine learning models, the error is smaller and the accuracy is higher. This method provides a new way to accurately predict the eddy current loss of a generator under complex nonlinear conditions.

Owing to the high-frequency and high-power requirements for communication integrated circuits (ICs) in today's rapid development of electronic technology, the intensity of electromagnetic field from the ICs can be significant. This article shows a failure due to this enhanced electromagnetic field in a gallium nitride based high electron mobility transistor high-frequency power amplifier. Inputs were provided as per the rated values and failures are observed on the drain and gate terminals. Detail failure analysis on the failed samples, using focus ion beam technique for cross sectioning the damaged area and examining under scanning electron microscopy/ energy dispersive X-ray spectroscopy, reveals the meltdown of the materials at the drain and gate terminals. Electromagnetic simulations and measurements are performed, and the failure mechanism is confirmed to be due to the magnetic field induced eddy current in the drain metal plate of the transistor, on top of the designed operating current in the metal plate.

Steel-reinforced concrete has been widely used in the construction of railways because of its robustness and low maintenance cost. This paper focuses on the analysis of unwanted losses in a reinforced concrete track when a high-power online wireless power transfer system is installed on it. Induced dielectric loss in the concrete, and eddy current and hysteresis losses in the reinforcing steel bar are calculated using analytic equations and finite-element analysis. Among the three sources of loss, a dominant one is identified in the first three sections of this paper. It is shown that the dielectric loss in the concrete and the hysteresis loss in the reinforcing bar do not have a critical impact on the efficiency. However, it is found that the eddy current loss of the reinforcing bar is dominant over the other two losses. Furthermore, the eddy current loss of the reinforcing bar overwhelmed the ohmic loss of a transmitter coil if the transmitter coil is not located in a proper position on the concrete track. The theoretical results are evaluated experimentally using a 7-m-long test bed. When the transmitter coil is located 0.14 m above the reinforcing bar, the measured eddy current loss of the steel bar is 3 kW while the Ohmic loss of the transmitter coil is 1.5 kW. As the distance between the transmitter coil and the steel bar increases, the eddy current loss of the bar decreases rapidly. From the simulation and the experimental evaluation of the loss, guidelines for installing a transmitter coil on a reinforcing bar for an in-motion wireless power transfer system are suggested in this paper.

Core-loss calculation is an important issue in the design and analysis of electric machines, especially in high-speed applications. However, because of the severe uneven distribution and local supersaturation of the flux density, in combination with the evident dc magnetic bias and the skin effect of the eddy current at a high frequency, it is difficult to estimate the core loss in a high-speed doubly salient electromagnetic machine. In this paper, two improved core-loss calculation methods are proposed. Additionally, an approach is established to determine the core-loss coefficients, which considers the influence of the frequency and amplitude of the flux density by adopting the function-fitting method. The change pattern of the core-loss coefficients is also investigated, together with the influence of the dc magnetic bias on the eddy-current loss. Finally, rotor-lock experiments and high-speed rotating experiments are both conducted. Additionally, two improved methods are used and compared for core-loss calculation.

© 2018 IEEE. In some special oscillatory applications, especially those operated at high speeds, the eddy current loss of a linear permanent-magnet (PM) synchronous machine (LPMSM) should be fully considered because the loss might be large and concentrated in PMs during the oscillation period. This paper presents a loss analysis method based on computationally efficient finite-element analysis (CE-FEA) for a 20-Hz oscillatory tubular LPMSM. Since the mover speed varies with time, an equally divided model in 1/4 period is introduced to calculate the average PM eddy current loss. The flux density curves in PMs are calculated at 18 intervals by the CE-FEA, through which the change rate of the magnetic flux density is analyzed, considering both the entering and leaving effects and coil end effects. The calculation results show that the eddy current loss is obviously concentrated in PMs near the two ends of coils. The calculation results at a speed of 3.6 m/s obtained by the CE-FEA and two-dimensional and three-dimensional time-stepping FEAs are compared to validate the accuracy. Finally, the proposed method is validated by the experimental test results on a prototype LPMSM.

The use of solid materials in tubular, linear machines has significant manufacturing benefits, as this removes the need for an axially laminated stator. However, this comes at the cost of extra eddy current losses. In this paper, a detailed analysis of the behavior of eddy currents in a tubular permanent magnet machine that comprises unconventional magnetic circuit is given, highlighting the importance of the field distribution and current directions, when compared with conventional magnetic circuits. This analysis is then used to identify and investigate the appropriate eddy current reduction methods for tubular machines, when a solid material stator is being used. Accurate three-dimensional models have been built and then validated on previously built testing setups. Different winding configurations have been accounted. Finally, considerations of these techniques are given when being implemented into an actual, tubular machine design, highlighting the improved performance and losses.

In this paper, the influence of the flat and cap secondary, which are usually applied in the linear metro system on transverse forces of linear induction motors, is calculated and analyzed. First, the cap-aluminum plate and lamination back iron of the cap secondary caused relative difficulty in the analytical calculation. Then, the equivalent of the cap-aluminum plate and lamination back iron is presented, and two equivalent coefficients are obtained. The two types of the asymmetry are discussed and the different magnetic motive forces are presented. Second, the analytical model and the method of the linear induction motor are presented. Third, for a cap secondary in practice, the two equivalent coefficients are calculated and discussed. Then, the flat and cap secondary are applied, and the different transverse forces are calculated and analyzed. For two types of the secondaries, the different eddy currents and air-gap flux densities are compared. Finally, the test workbench is built and the analytical result of the transverse force is experimentally validated. It shows that cap secondary has less influence on the railcar when the transverse displacement occurs.

Wireless power transfer (WPT) has attracted much attention in recent years. In an underwater WPT system, the eddy current loss tends to be non-negligible as the frequency or the coil current increases. Thus, it is crucial to analyze the eddy current loss in an underwater WPT system. The analytical model of the eddy current loss of a coreless WPT system in the seawater is established with Maxwell's equations. The expressions of the electric field intensity and the eddy current loss are derived. The eddy current loss is analyzed in different circumstances to illustrate the impacts of related factors. For a WPT system in the air, there is an optimum resonant frequency, for a higher frequency leads to a larger induced voltage, but will result in larger coil losses simultaneously. However, the optimum resonant frequency will be shifted because of the eddy current loss in the seawater. Then, the optimum operating frequency is obtained based on the analytical model. It is found that the optimum operating frequency is supposed to be larger than the resonant frequency to achieve the maximum dc–dc efficiency in the seawater. An underwater WPT prototype was built and the experimental results verified the theoretical analysis.

In this paper, the thermal analysis of a hybrid excitation linear eddy current brake is presented. The air gap flux of the hybrid excitation linear eddy current brake is provided by the excitation windings and the permanent magnets. Therefore, the braking force produced by the eddy current brake is large and controllable. But, on the other hand, there is a high heating value in the excitation windings and conductor plate; hence, it is necessary to analyze thermal characteristics of the eddy current brake to avoid the declination of braking performance or even damage of the device. First, the structure and working principle of the eddy current brake are described. Second, the analytical model of the eddy current brake is built, and then the thermal network model of the eddy current brake is built taking the actual airflow around the eddy current brake into consideration. Finally, the validity of the thermal network model is verified by steady and dynamic thermal experimental measurements.

Press plates are widely used in the end region of turbogenerators. However, due to the effect of magnetic field leakage from the end region, the eddy current losses of the copper screen and press plate will result in the copper screen and press plate having a high temperature under the rated load condition. In this paper, the influence of the magnetic permeability of the press plate on losses and temperature of the end region is researched in turbogenerators. Three-dimensional (3-D) fluid and thermal mathematic and physical models of the turbogenerator end region are established. Under different magnetic permeability values of the press plate, a 3-D transient electromagnetic field in the turbogenerator end region is calculated, and the obtained losses of the end parts are treated as heat sources. Fluid network equations are calculated, and the obtained fluid velocity and pressure values are applied to the end region as boundary conditions. After solving the fluid and thermal equations, fluid velocity around the surface of the end parts is obtained under the rated load condition. The temperature distribution of the end parts is determined for different magnetic permeability values of the press plate. The calculated temperature results agree well with the test data.

In this paper, a novel rotor design of claw-pole alternators for characteristics improvement is proposed from the results of both experiment and calculation. In the calculation, the magnetic field in the machine is separated into those produced by field current, armature current, and eddy current of the core by using the three-dimensional finite-element analysis with a frozen permeability technique in order to understand the main factor that determines the maximum output. From these results, a novel rotor design is proposed. The experimental verification is carried out by using the prototype machines. It is clarified that the output of the proposed machine increases, whereas the core loss decreases, as compared with the conventional machine.

An electrical machine applied as a hydraulic pump drive is featured by having a metallic can shield structure in airgap. Due to the eddy current induction on the can, electromagnetic features of a canned machine make a principal difference. Instead of the traditional canned induction machines, this paper analyzes the eddy current and loss due to the use of cans on a salient switched reluctance machine (SRM). First, at typical rotor positions, eddy current distribution on cans by a single phase followed by all phases is analyzed. Next, consequent ohmic loss on cans (can loss) is studied, which is extended to one stroke period and further to different control modes. Finally, compared to a standard SRM, the feature of airgap flux and eddy current loss due to the use of cans is shown. A three-dimensional finite-element method is used to show eddy current distribution, including end effect. The can loss simulation is verified by measurement.

Electromagnetic characteristics of single-sided linear induction motors (SLIMs) will be changed when the primary is displaced sideways from the symmetrical position in the metro. The transverse force will be produced, and edge effect will increase. In order to reduce the influence of the transverse force on the stability of the vehicle guidance system, the construction of the ladder-slit secondary, which consists of the slit aluminum and solid back-iron plates, is proposed and analyzed. A 3-D finite-element model (FEM) of the linear induction motor with the ladder-slit secondary is developed. With the different transverse displacements, the air-gap flux density, eddy currents, and forces are calculated and compared with the linear induction motor with the flat-solid secondary. It shows that the ladder-slit secondary can reduce the transverse force and edge effect, as well as is a good method to achieve the transversal stabilization of the rail vehicle.

This paper addresses the effect of rotor structure on the magnetic adjusting performance of an axial-radial permanent magnetic machine via the comparative performance investigation on the axial-radial flux type permanent magnet machines with three different structures. By using the three-dimensional time stepping finite-element method, the distributions of the air-gap flux density are obtained when the machine operates with different axial magnetomotive force, and the key factor that affects the magnetic adjusting ability is determined. The variation of the magnetic field is investigated, and the back electromotive forces of the three machines with different structures are also studied. Meanwhile, the eddy current distribution and the eddy current loss in machines with different structures during load operation are analyzed. The theoretical claims are verified by both numerical simulations and experimental tests.

The electromagnetic and heat issue is the core of the key problems for large synchronous generators. This paper presents a new method to account for the rotary excitation field of a large synchronous generator using a new 3-D static frequency-domain finite element to solve the end magnetic field and electromagnetic losses via phase transformation. The solution time is significantly reduced. Both magnetic flux leakage and temperature testing of the end structures are conducted. There is good consistency between the theoretical simulation and the experimental results for both magnetic and thermal fields. The regularity of the magnetic and thermal field distributions is studied drawing on the electromagnetic and heat transfer theories.

A large-capacity nominal-frequency (NF) power supply is required to measure the no-load characteristics of transformers, including the no-load loss, excitation current, and no-load current harmonic content for field and factory tests. The traditional NF method uses bulky test equipment and requires a highly complex test operation. This paper proposes an improved low-frequency (LF) method to reduce the capacity requirement of the testing power supply and make the test equipment portable. In this method, the core loss at LFs is first calculated by applying sinusoidal voltages at several LFs. The resultant core loss at LFs is then converted to core loss at NF based on the core loss separation and orthogonal least squares method. Finally, the excitation current, no-load loss and excitation voltage are determined by a corresponding eddy current compensation algorithm. In addition, experiments were conducted on a single-phase distribution transformer. The experimental results confirm that, compared to the traditional NF test, the proposed method possesses a similar measuring accuracy but reduces the capacity requirement of the testing power supply.