Showing papers in "IEEE Transactions on Magnetics in 2014"
TL;DR: In this article, the authors proposed a frequency tracking method to improve the power and efficiency of wireless power transfer via coupled magnetic resonance (MIMO) and showed that the proposed method is proved through the experiment, and it can provide an effective way to improve WPT.
Abstract: Wireless power transfer via coupled magnetic resonance has many merits, which has become one of the hot research spots in recent years. The progress of technology in the field of wireless power transfer is remarkable, but its power and efficiency vary with the impacts of the distance, orientation, and center deviation on transmission. To suppress the fast decrease of the transfer efficiency, the equivalent circuit model of wireless power transfer and mutual inductance theory were presented. The results provided critical insight into the design of improving efficiency using a novel method of frequency tracking. The measurement results showed that the efficiency decreased greatly with the distance, orientation and center deviation at fixed-resonance frequency, and the efficiency decreased slowly using adapted resonance frequency. The proposed method is proved through the experiment, and it can provide an effective way to improve the power and efficiency of wireless power transfer.
314 citations
TL;DR: In this paper, the authors discuss heat-assisted magnetic recording (HAMR) media requirements and challenges for areal densities (AD) beyond 1 Tb/in2, focusing on granular chemically ordered L10 FePtX-Y-perpendicular media with reduced average grain size.
Abstract: This paper discusses heat-assisted magnetic recording (HAMR) media requirements and challenges for areal densities (AD) beyond 1 Tb/in2. Based on recent roadmap discussions the focus is primarily on granular chemically ordered L10 FePtX-Y-perpendicular media with reduced average grain size down to 〈D〉 = 3-5 nm relative to current CoCrPt based perpendicular magnetic recording (PMR) media with average grain size 〈D〉 = 7-9 nm. In HAMR media the combination of thermal conductivity and Curie temperature TC determines the required laser power during recording. Key challenges are sigma variations of D and TC which need to be reduced to σD/D ~ 10-15% and σTC/TC ~ 2%. In addition AD is limited by switching field distribution (SFD) and thermal spot size. The key goal going forward is to optimize heads, media, head-media-spacing (HMS) and read-back channel technologies to extend AD to 4 Tb/in2 and beyond.
171 citations
TL;DR: In this paper, a new analytical calculation of the coaxial spiral rectangular coils is presented, which is simpler than the greenhouse method, and some guidelines for optimizing the coupling coefficient are given, when the received coil's size is limited by space constraints.
Abstract: The mutual inductance between two coils is a key parameter in the inductively coupled wireless power transmission. The spiral rectangular coils are easier to implement than the circular ones, but the study of the mutual inductance of the spiral rectangular coils is not enough. In this paper, a new analytical calculation of the coaxial spiral rectangular coils is presented, which is simpler than the greenhouse method. The impact of the track thickness and width is also analyzed. The calculation results are verified by the existing methods and the experimental results. Based on these results, some guidelines for optimizing the coupling coefficient are given, when the received coil's size is limited by space constraints.
157 citations
TL;DR: Using magnetic flux barriers in the stator yoke of electric machines with fractional slots, tooth-concentrated winding, it is possible to reduce or even to cancel some space harmonics of low order in the air-gap flux density resulting in lower rotor losses induced by the armature reaction field as mentioned in this paper.
Abstract: Using magnetic flux barriers in the stator yoke of electric machines with fractional slots, tooth-concentrated winding, it is possible to reduce or even to cancel some space harmonics of low order in the air-gap flux density resulting in lower rotor losses induced by the armature reaction field. In this paper, this new technique is applied during the design and analysis of two permanent magnet machines with different 12-teeth/10-poles concentrated windings. Considering the main machine performances, such as the electromagnetic torque, machine losses, and also the field-weakening capability, the new stator design shows significant advantages over the conventional design. According to the new technique, a prototype machine is built and some measurement results are given.
148 citations
TL;DR: In this article, a double-stator axial-flux spoke-type permanent magnet vernier machine was proposed, which has a high torque density feature as well as a high power factor at low speed.
Abstract: This paper proposes a novel double-stator axial-flux spoke-type permanent magnet vernier machine, which has a high torque density feature as well as a high-power factor at low speed for direct-drive systems. The operation principle and basic design procedure of the proposed machine are presented and discussed. The 3-D finite element method (3-D-FEM) is utilized to analyze its magnetic field and transient output performance. Furthermore, the analytical method and a simplified 2-D-FEM are also developed for the machine basic design and performance evaluation, which can effectively reduce the modeling and simulation time of the 3-D-FEM and achieve an adequate accuracy.
137 citations
TL;DR: In this article, a double main phase alloy method has been performed to adjust the composition and combination of main phases in the magnets and make a partial main phase without Ce, which can maintain higher remanence.
Abstract: Research on the application of the most abundant rare-earth elements for permanent magnetic materials has gained intense interest. However, the magnetic properties decrease dramatically with the increase of Ce content due to the traditional Ce substitute for Nd. A double main phase alloy method has been performed to adjust the composition and combination of main phases in the magnets and make a partial main phase without Ce, which can maintain higher remanence. The influence of Ce content on the rectangularity of demagnetization curves and magnetic properties of (Nd1-xCex)30 (Fe,TM)balB1 sintered by the double main phase alloy method has been investigated. When the Ce content was 30% of the total amounts of all the rare earth metals, the maximum energy product of the sintered magnet, was still over 43 MGOe.
122 citations
TL;DR: This paper proposes a method to minimize the cogging torque and torque ripple of an interior permanent magnet synchronous motor by adopting asymmetric barrier design and inverting lamination method, which has an advantage over skew design from a manufacturing point of view.
Abstract: This paper proposes a method to minimize the cogging torque and torque ripple of an interior permanent magnet synchronous motor by adopting asymmetric barrier design and inverting lamination method. The analysis method for cogging torque and torque ripple is suggested using finite-element method. An asymmetric barrier in a permanent magnet rotor is optimally designed without permanent magnet skew. This proposed design for low cogging torque and torque ripple has an advantage over skew design from a manufacturing point of view. The proposed model is compared with the skew model and nonskew model by calculating torque characteristics to determine the more effective method to reduce torque distortion.
118 citations
TL;DR: In this article, the frequency splitting of two-and three-coil wireless power transfer (WPT) systems is analyzed. But the authors mainly focus on the frequency split of two and three-and four-coils, respectively.
Abstract: In magnetic resonant coupling wireless power transfer (WPT) system, the frequency splitting phenomena have a vital influence on the output power. This paper mainly focuses on the frequency splitting of two-coil and three-coil WPT. First, the frequency characteristics of transfer power and system efficiency of the two-coil WPT are analyzed by circuit theory. In addition, the magnetic field distribution of the two splitting frequencies is simulated to analyze which frequency is better for the operating frequency. Second, considering the reference resistance of RF power, the frequency splitting of two-coil and three-coil WPT is analyzed. Finally, the critical coupling, which determines the over coupled region, of two-coil and three-coil WPT is derived. Meanwhile, we propose a tuned frequency method according to the numerical results. In addition, the transfer power can be kept at a relatively constant level in the over coupled region.
114 citations
TL;DR: In this paper, the effect of pole and slot combinations on force and vibration characteristics in low-speed generators is investigated using time-stepping finite-element analysis, including investigation on radial force density distribution, total forces on teeth, and timedependent force waveforms on a tooth.
Abstract: In this paper, radial forces and torque ripple characteristics are investigated in permanent magnet (PM) machines having different pole and slot combinations. Using the PM machines with concentrated windings could be beneficial in direct-drive wind generators since it is possible to reduce the size and weight of the generator. The PM machines with concentrated windings having a large number of poles are compared to investigate the effect of pole and slot combinations on force and vibration characteristics in low-speed generators. Cogging torque waveforms and torque ripple are investigated using time-stepping finite-element analysis. Analysis of radial forces is presented, including investigation on radial force density distribution, total forces on teeth, and time-dependent force waveforms on a tooth. Structural analysis and experimental modal analysis are performed on the prototype generator. The main mode of vibration in the prototype machine is observed experimentally and the results are in good agreement with the simulations.
114 citations
TL;DR: In this paper, the effect of cutting on the magnetic flux distribution for mechanical cutting as well as solid state laser cutting is calculated and analyzed space-resolved using the data obtained from investigations by neutron grating interferometry.
Abstract: It is well established that laser cutting or mechanical cutting of nonoriented electrical steel causes structural changes at the cutting edge, which finally affect the magnetic properties. During mechanical cutting, plastic deformation appears in the zone near the cutting edge. On the contrary, laser cutting induces thermal stress due to temperature gradients within the material during processing, which finally also results in deterioration of the magnetic properties. The knowledge of the type of the deterioration mechanism and the degree of the deterioration of magnetic property deterioration mechanisms is important for designing electrical machines in terms of magnetic field and loss calculations. In this paper, the effect of cutting on the magnetic flux distribution for mechanical cutting as well as solid state laser cutting is calculated and analyzed space-resolved using the data obtained from investigations by neutron grating interferometry. In addition, the resulting changes of magnetization behavior, i.e., the character of the $B$ versus $H$ curve, were studied. It will be demonstrated that the deterioration of the magnetic properties depends on the geometry of the parts at cutting. It is shown that the nature of the resulting spatial distribution of the magnetic flux is different for mechanical cutting and cutting by laser. By mechanical cutting, a drop of the magnetic flux in the region at the cutting edge appears. Through cutting by laser, the observed decrease of the magnetic flux $B$ is observed over the total width of the strip. The decrease of B at cutting of small parts by laser is remarkably different at the cutting edges, which are opposite to each other. Finally, the observed magnetic behavior is correlated to the different character of the induced residual stresses by mechanical cutting and cutting by laser.
112 citations
TL;DR: In this paper, Soft Magnetic Composite (SMC) powder coupled with the P/M production process open new possibilities in the design and manufacture of parts for electrical applications, which can contribute to a substantial decrease of specific core losses of the machine, simultaneously increasing its total efficiency.
Abstract: Powder metallurgical manufacture has the singular ability to produce net shaped products (gear box parts and motor parts) for the automobile industry. Soft magnetic composite (SMC) powder coupled with the P/M production process open new possibilities in the design and manufacture of parts for electrical applications. With increasing values of operating frequency, the use of SMC can contribute to a substantial decrease of specific core losses of the machine, simultaneously increasing its total efficiency. In contrast to laminated cores, the manufacturing process of SMCs does not influence their final magnetic properties. These properties are homogenous and do not change after assembly of the motor. New SMC materials can outperform current laminated steel materials when measurements are done in the same conditions with similar samples. Many of the existing prejudices about the magnetic properties of SMC can thus be eliminated or attenuated if we respect its optimal use in adequate applications.
TL;DR: The optimal VIPMM with assisted barriers shows the substantially improved performance compared with a conventional design, and is optimized by algorithms, such as the kriging method and genetic algorithm for improving the torque characteristics and efficiency.
Abstract: This paper performs a study on the optimal design of V-type interior permanent magnet motors (VIPMMs), in which the rotor is equipped with assisted barriers for the improvement of average torque and torque ripple. The approach differs from the conventional interior permanent magnet motors, in which the reluctance torque due to saliency reaches a maximum value at a current phase angle located 45 electrical degrees with respect to the maximum value obtained from the magnetic torque produced by the rotor magnets. The adoption of assisted barriers is employed to improve the torque production by creating rotor asymmetry to allow the reluctance torque and the magnetic torque reach a maximum value near or at the same current phase angle. To evaluate the contribution, the frozen permeability method is utilized to segregate the torque into its reluctance and magnetic torque components. First, an iterative optimization is performed on a concept design of a 6/4 VIPMM for demonstrating the design principle based on finite element method. Then, the VIPMM is further optimized by algorithms, such as the kriging method and genetic algorithm for improving the torque characteristics and efficiency. As a result, the optimal VIPMM with assisted barriers shows the substantially improved performance compared with a conventional design.
TL;DR: In this paper, a new type of vernier machine with permanent magnets (PMs) on both sides of rotor and stator was proposed, where the rotor is of the flux concentrating structure and the stator has also PMs between the flux modulation poles.
Abstract: This paper proposes a new type of vernier machine with permanent magnets (PMs) on both sides of rotor and stator. The rotor is of the flux concentrating structure and the stator has also PMs between the flux modulation poles. Compared with the other types of vernier machine, the proposed model has a huge increase in the induced voltage and developed torque at the same size. This shows the possibility of the new suggested machine to the direct-drive applications such as wind-power generators and in-wheel motors.
TL;DR: Novel circuits and architectures to build a 16 kb STT-MRAM design with low power and high reliability are presented, including the self-enable switching scheme, which reduces the power consumption effectively and the fore-placed sense amplifier improves the robustness to process variation.
Abstract: Spin-transfer torque magnetic random access memory (STT-MRAM) is considered one of the most promising non-volatile memory candidates thanks to its excellent performance in terms of access speed, endurance, and compatibility to CMOS. However, high power supply voltage is required in the conventional STT-MRAM writing circuit, which results in high power consumption (e.g., ${\sim}{10}~{\rm pJ}/{\rm bit}$ ). In addition, it suffers from stochastic switching behavior and process voltage temperature variations. These make power-efficient and reliable write/read circuits become critical challenges. In this paper, we present novel circuits and architectures to build a 16 kb STT-MRAM design with low power and high reliability. For example, the self-enable switching scheme reduces the power consumption effectively and the fore-placed sense amplifier improves the robustness to process variation. Using an accurate compact model of 65 nm STT-MRAM and a commercial CMOS design kit, mixed transient and statistical simulations have been performed to validate this design.
TL;DR: In this article, the authors proposed two novel traction motors with ferrite magnets for hybrid electric vehicles (HEVs), which have competitive torque density and efficiency as well as operating range with respect to a referenced rare earth magnet motor employed in the third generation Toyota Prius, a commercialized HEV.
Abstract: This paper proposes two novel traction motors with ferrite magnets for hybrid electric vehicles (HEVs), which have competitive torque density and efficiency as well as operating range with respect to a referenced rare earth magnet motor employed in the third-generation Toyota Prius, a commercialized HEV. The two proposed traction motors, named as dual stator radial flux permanent magnet motor (DSRFPMM) and dual stator axial flux permanent magnet motor (DSAFPMM), adopt the same design concept, which incorporates the unaligned arrangement of two stators together with the use of spoke-type magnet array and phase-group concentrated-coil windings for the purpose of increasing torque density and reducing torque ripple. A finite element method is utilized for predicting the main characteristics, such as back electromotive force, cogging torque, electromagnetic torque, iron loss, and efficiency in both of the proposed motors. Moreover, a comparative study between the proposed DSRFPMM and DSAFPMM is performed under the same operating condition. As a result, it is demonstrated that both of the proposed ferrite permanent magnet motors could be good alternatives for traction application, replacing the rare earth magnet motors.
TL;DR: In this article, an improved practical two-dimensional model for the analytical calculation of the magnetic field distributions in permanent magnet (PM) eddy current couplings is presented to obtain the torque characteristics.
Abstract: An improved practical two-dimensional model for the analytical calculation of the magnetic field distributions in permanent magnet (PM) eddy current couplings is presented to obtain the torque characteristics. By establishing the Cartesian coordinate reference system on the rotating conductor, the PM region is treated as a source of traveling wave magnetic field and then the multi-layer boundary value problem is solved. The formulation for the magnet blocks, the eddy current and saturation effects in the solid secondary back iron, and the equivalence relationships between typical PM shapes, are all reasonably taken into account. Calculation results produced by the proposed analytical model are compared with those from the nonlinear finite element method and experimental measurement.
TL;DR: In this paper, an annular permanent magnet is mounted on the exterior surface of a capsule, and the magnetic field can be measured and the capsule's 3D location and 3D orientation information can be estimated based on proposed closed-form analytical model of annular magnet and particle swarm optimization algorithm.
Abstract: Magnetic tracking technology is emerging to provide an occlusion-free tracking scheme for the estimation of full pose (position and orientation) of various instruments. This brings substantial benefits for intracorporeal applications, such as for tracking of flexible or wireless endoscopic devices, and thus is significant for further computer-assisted diagnosis, interventions, and surgeries. Toward efficient magnetic tracking, a 6-D magnetic localization and orientation method is proposed in this paper. An annular permanent magnet is mounted on the exterior surface of a capsule. With a magnetic sensor array, the magnetic field can be measured and the capsule's 3-D location and 3-D orientation information can be estimated based on proposed closed-form analytical model of annular magnet and particle swarm optimization algorithm. Magnetic dipole model and Levenberg-Marquardt algorithm are used to improve the speed and accuracy of estimation. Extensive simulation experiments show that the localization and orientation method works well with good position and orientation accuracy.
TL;DR: In this paper, the authors presented a permanent magnet (PM) shaping technique with optimal third harmonic to improve the output torque without deteriorating the torque ripple in surface-mounted PM (SPM) machines.
Abstract: This work presents a permanent magnet (PM) shaping technique with optimal third harmonic to improve the output torque without deteriorating the torque ripple in surface-mounted PM (SPM) machines. The optimal value of third harmonic injected into the sinusoidal PM shape for maximum torque improvement is analytically derived and confirmed by finite-element analysis. Further, the influence of magnet edge thickness on the airgap field distribution is investigated and utilized to compensate the inter-pole flux leakage and curvature effect. It is found that the optimal third harmonic is 1/6 of the fundamental one. For the SPM machines having rotors without shaping, Sine shaping, Sine shaping with third harmonic injected, the electromagnetic performance, including the back-EMF waveforms, cogging torque, average torque, and torque ripple are compared. It is demonstrated that the average torque in the machine of a Sine shaping with an optimal third harmonic injected can be improved by >9%, while the torque ripple remains similar to that of the one with Sine shaping. Finally, the machines with both conventional (without shaping) and optimal third harmonic PM rotors are prototyped and measured to validate the analyses.
TL;DR: In this article, a 2D analytical permanent-magnet (PM) eddy-current loss calculation for slotless PM synchronous machines with surface-inset PMs considering the current penetration effect is presented.
Abstract: Two-dimensional (2-D) analytical permanent-magnet (PM) eddy-current loss calculations are presented for slotless PM synchronous machines (PMSMs) with surface-inset PMs considering the current penetration effect. In this paper, the term slotless implies that either the stator is originally slotted but the slotting effects are neglected or the stator is originally slotless. The analytical magnetic field distribution is computed in polar coordinates from the 2-D subdomain method (i.e., based on formal resolution of Maxwell's equation applied in subdomain). Based on the predicted magnetic field distribution, the eddy-currents induced in the PMs are analytically obtained and the PM eddy-current losses considering eddy-current reaction field are calculated. The analytical expressions can be used for slotless PMSMs with any number of phases and any form of current and overlapping winding distribution. The effects of stator slotting are neglected and the current density distribution is modeled by equivalent current sheets located on the slot opening. To evaluate the efficacy of the proposed technique, the 2-D PM eddy-current losses for two slotless PMSMs are analytically calculated and compared with those obtained by 2-D finite-element analysis (FEA). The effects of the rotor rotational speed and the initial rotor mechanical angular position are investigated. The analytical results are in good agreement with those obtained by the 2-D FEA.
TL;DR: In this article, the structural behavior of a double-stator SRM and a conventional SRM was compared using a multi-physic analysis, where an electromagnetic finite element (FE) method was used to calculate force density at various parts of the stator surface in both machines.
Abstract: Vibration and acoustic noises are viewed as a drawback in switched reluctance machines (SRMs), which prohibit their widespread use in noise sensitive applications. Double-stator SRMs (DSSRMs) can be considered as a solution to this problem by incorporating an improved magnetic configuration, which reduces the radial forces in the machine. This paper compares structural behavior of a DSSRM and a conventional SRM using a multi-physic analysis. An electromagnetic finite-element (FE) method is used to calculate force density at various parts of the stator surface in both machines. These force densities are then used in a structural FE analysis to compute acceleration, deformation, and velocity of the vibrating surface at selected point on the outer surface of the machine.
TL;DR: The salient feature of the proposed designs is elimination and/or reduction of undesirable space harmonics which result from the existing fractional-slot per phase per pole permanent magnet machines with concentric windings.
Abstract: The paper is concerned with new winding configurations and associated pole-slot combinations for permanent magnet (PM) machines that lead to improved performance and facilitate cost reduction. Compared to the current state of the art, the salient feature of the proposed designs is elimination and/or reduction of undesirable space harmonics which result from the existing fractional-slot per phase per pole permanent magnet machines with concentric windings. This will bring the benefits of significant reduction of the eddy current loss in the rotor permanent magnets, short end-winding and hence reduced copper loss and copper usage, increased power/torque density, reduction in manufacturing cost, and improved energy efficiency. Although the proposed technique is primarily aimed for brushless permanent magnet machines, it is also applicable to synchronous reluctance machines, induction machines and synchronous wound field machines. The proposed technique is applied to the design of an interior mounted permanent magnet machine for electric vehicle traction applications, and demonstrated by the measurements on a prototype machine.
TL;DR: In this paper, the authors deal with modeling and power control methods of a switched reluctance generator (SRG) driven from the wind power generation system, where the flux linkage and torque of the designed generator computed by a finite element method are applied to the SRG model.
Abstract: This paper deals with modeling and power control methods of a switched reluctance generator (SRG) driven from the wind power generation system. To consider electromagnetic nonlinear characteristics of SRG, the flux linkage and torque of the designed generator computed by a finite element method (FEM) are applied to the SRG model. And the SRG model is controlled with a required output curve depending on the speed of the generator using optimized switching angle which has been analyzed in advance to maximize its efficiency. The power control algorithm is applied to a manufactured 3 kW prototype SRG. The simulation results are compared with the experimental ones for validation.
TL;DR: In this article, a complete analytical model for surface-mounted permanent magnet synchronous machines (PMSMs) is presented, which is based upon the combined solution of two models: the first model generates an exact solution of Maxwell's equations in the air gap area applied to a very simple geometry and the second model gives an accurate solution in the detailed parts with complex geometry, based on a magnetic equivalent circuit (MEC) to obtain fast and accurate results in a simple way.
Abstract: This paper presents a complete analytical model for surface-mounted permanent magnet synchronous machines (PMSMs). A new simple and fast technique was developed to obtain accurate results in the calculation of machine parameters electromotive force (EMF), torque, and losses. This technique is based upon the combined solution of two models. The first model generates an exact solution of Maxwell's equations in the air gap area applied to a very simple geometry. The second model gives an accurate solution in the detailed parts with complex geometry, based on a magnetic equivalent circuit (MEC) to obtain fast and accurate results in a simple way. The machine's global quantities are then obtained and validated using the results of a finite element model (FEM) for different loading conditions and geometries. Compared with FEM, the proposed combined solution has the advantage of flexibility in the geometrical machine parameters, significantly less CPU time and an accuracy for the considered PMSM up to 4.85% in the EMF, 4.41% in the torque, and 4.44% in the iron losses. Finally, the relation between grid refinement in the MEC (coarse or fine grid of reluctances) and accuracy is pointed out, showing that the EMF can be accurately computed with a rather coarse grid, while accurate loss computation requires a fine grid.
TL;DR: In this article, a method based on the Fresnel reflection at the fiber end face is presented to investigate the magnetic field (intensity and direction) and temperature-dependent refractive index of the magnetic fluid.
Abstract: The tunable refractive index of the magnetic fluid (MF) is a unique optical property, which has attracted a lot of research interest in recent years. In this paper, a method based on the Fresnel reflection at the fiber end face is presented. Experimental measurements are carried out to investigate the magnetic field (intensity and direction) and temperature-dependent refractive index of the MF. For a given concentration, with the increase of the magnetic field intensity, the nMF increases gradually when H//Light, while decreases when H⊥Light. The effect of temperature on nMF is relatively insignificant with the sensitivity of -8 × 10
-5
/°C. In addition, the mechanism is analyzed from the point of the microstructure by the Monte Carlo method.
TL;DR: In this article, the authors proposed a new design of SPOKE-type PM brushless direct current (BLDC) motor without using neodymium PM (Nd-PM).
Abstract: This paper proposes a new design of SPOKE-type PM brushless direct current (BLDC) motor without using neodymium PM (Nd-PM). The proposed model has an improved output characteristic as it uses the properties of the magnetic flux effect of the SPOKE-type motor with an additional pushing assistant magnet and subassistant magnet in the shape of spoke. In this paper, ferrite PM (Fe-PM) is used instead of Nd-PM. First, the air-gap flux density and backelectromotive force (BEMF) are obtained based on the field model. Second, the analytical expressions of magnet field strength and magnet flux density are obtained in the air gap produced by Fe-PM. The developed analytical model is obtained by solving the magnetic scalar potential. Finally, the air-gap field distribution and BEMF of SPOKE-type motor are analyzed. The analysis works for internal rotor motor topologies. This paper validates results of the analytical model by finite-element analysis for wing-shaped SPOKE-type BLDC motors.
TL;DR: The development of the smart grid and its correlation with magnetics, including electromagnetic compatibility issue, magnetic-field-based measurement/monitoring, and magnetic energy storage/conversion are reviewed.
Abstract: A revolution in power transmission and distribution, driven by environmental and economic considerations, is occurring all over the world. This revolution is spearheaded by the development of the smart grid. The smart grid is bringing profound change to both the power systems and many related industries. This paper reviews the development of the smart grid and its correlation with magnetics, including electromagnetic compatibility issue, magnetic-field-based measurement/monitoring, and magnetic energy storage/conversion. The challenge to the field of magnetics and the usage of the cutting edge magnetics technology in the development of the smart grid are discussed. This paper enables researchers in the magnetics community to be acquainted with the progress in the smart grid and inspires innovative applications of state-of-the-art magnetics technologies in the smart grid.
TL;DR: In this article, the losses of a high-speed permanent magnet motor were investigated by a model that can consider the skin effect and rotational loss, and the rotor eddy current losses were estimated by a fast hybrid method that could consider the end effect.
Abstract: This paper investigates the losses of a high-speed permanent magnet motor. The iron losses are calculated by a model that can consider the skin effect and rotational loss. The rotor eddy current losses are estimated by a fast hybrid method that can consider the end effect. Pulse-width modulation (PWM) harmonics brought by the voltage source inverter (VSI) are considered in the loss calculations. Then the temperature distribution of the motor is evaluated by using the calculated loss results and computational fluid dynamic (CFD) modeling. Finally, based on the CFD results, the motor structure is optimized to achieve better rotor cooling. The outer slots are closed to force the cooling air flow through the rotor surface. Calculated temperature distributions and optimization results are verified by measurements.
TL;DR: In this article, the difference between the exact piecewise linear and the sinusoidal course in terms of iron losses is discussed, and the measurements are validated using the improved generalized Steinmetz equation.
Abstract: The three-phase dual-active bridge is a dc-dc converter, which is highly suitable for high-power applications Among others, this is due to the medium-frequency transformer in the ac link, which provides galvanic isolation The transformer is operated with a square-shaped voltage waveform The flux density in the transformer core is piecewise linear However, for the sake of simplicity, the magnetic flux is often assumed sinusoidal Thereby, the actual iron losses generated in the core material are misinterpreted This paper discusses the difference between the exact piecewise linear and the sinusoidal course in terms of iron losses Silicon steel with a thickness of 018 mm is measured at a frequency of 1000 Hz, comparing the sinusoidal excitation with the actual one The measurements are validated using the improved generalized Steinmetz equation Finally, the transformer core losses are evaluated when the dc-dc converter is operated under load The results are confirmed through measurement
TL;DR: In this article, the authors presented a design method of broadband radar absorber (RA) combining together the features of frequency selective surfaces (FSSs), subwavelength hole array, and magnetic absorbing sheets.
Abstract: This paper presents a design method of broadband radar absorber (RA) combining together the features of frequency selective surfaces (FSSs), subwavelength hole array, and magnetic absorbing sheets. The absorber is constructed of a periodic array of square conducting patches embedded into a magnetic absorbing substrate perforated with circular hole arrays and backed by a metal ground. The absorption characteristics of the magnetic absorbing substrate are tuned and improved by means of perforating holes and embedding FSSs. After optimizing the dimensions of the holes and FSSs, the RA with a thickness of 2.4 mm achieves a reflection coefficient less than ${-}{\rm 10}~{\rm dB}$ from 6.3 to 17.3 GHz, which is nearly 3.6 times the bandwidth of the magnetic absorbing substrate. Meanwhile, the weight of the RA decreases by 15% due to the hole perforation, and the reflection coefficient is insensitive to incident angle from 0 $^{\circ}$ to 30 $^{\circ}$ for both TE and TM polarizations.
TL;DR: In this paper, the contribution of eddy currents to power losses in polycrystalline Mn-Zn ferrites and apply it to experimental results obtained on a broad frequency range in different commercial materials and differently sized ring samples.
Abstract: We predict the contribution of eddy currents to power losses in polycrystalline Mn-Zn ferrites and apply it to experimental results obtained on a broad frequency range in different commercial materials and differently sized ring samples. It is verified by theory and experiment that the eddy currents can, in sufficiently large specimens, measurably contribute to the energy dissipation, in conjunction with spin damping mechanisms. In this context, the direct role of the domain wall processes is shown to be negligible, with the so-called classical losses, chiefly associated with the rotations, accounting for all of the eddy-current losses. To predict the frequency dependent classical loss Weddy(cl)(f) in the actual heterogeneous material, the electromagnetic field equations are formulated under a variational multiscale approach, with fine and coarse scales identified with the thickness of grain boundary layers and grain size, respectively. The eddy-current patterns are correspondingly observed to evolve, on increasing the magnetizing frequency, from mostly grain-confined to circulating on the scale of the sample cross-section. Based on the measurement of the electrical resistivity versus frequency and knowledge of the average grain size, an overall frequency dependence of the classical loss Weddy(cl)(f) is formulated. With the energy loss W(f) measured from dc to 10 MHz in different types of commercial Mn-Zn ferrites having different cross-sectional areas, it is found that the W(f) behaviors in a given material all tend to fall onto a single W(f) curve once purged of the calculated Weddy(cl)(f). The residual size-independent loss is the one associated with the damping of the precessional spin motion, which can separately be accounted for.