Showing papers in "IEEE Transactions on Magnetics in 2015"

Bit-Patterned Magnetic Recording: Theory, Media Fabrication, and Recording Performance

Abstract: Bit-patterned media (BPM) for magnetic recording provides a route to thermally stable data recording at >1 Tb/in 2 and circumvents many of the challenges associated with extending conventional granular media technology. Instead of recording a bit on an ensemble of random grains, BPM comprises a well-ordered array of lithographically patterned isolated magnetic islands, each of which stores 1 bit. Fabrication of BPM is viewed as the greatest challenge for its commercialization. In this paper, we describe a BPM fabrication method that combines rotary-stage e-beam lithography, directed self-assembly of block copolymers, self-aligned double patterning, nanoimprint lithography, and ion milling to generate BPM based on CoCrPt alloy materials at densities up to 1.6 Td/in 2 . This combination of novel fabrication technologies achieves feature sizes of 2 (roughly equivalent to 1.3 Tb/in 2 ) demonstrate a raw error rate -2 , which is consistent with the recording system requirements of modern hard drives. Extendibility of BPM to higher densities and its eventual combination with energy-assisted recording are explored.

Analysis of Air-Gap Field Modulation and Magnetic Gearing Effects in Switched Flux Permanent Magnet Machines

Abstract: In this paper, switched flux permanent magnet (SFPM) machines are analyzed from the perspective of the air-gap field harmonics. It is found that the modulation of the salient rotor to PM and armature reaction fields in SFPM machines is similar to that of the iron pieces to those fields in the magnetic gear and magnetically geared machine. The magnetic gearing effect is analyzed in SFPM machines with different stator/rotor pole combinations, winding configurations, and stator lamination segment types by a simple magnetomotive force-permeance model, and validated by finite-element (FE) analysis. Different from fractional-slot surface-mounted PM machines in which the working air-gap field harmonic generates 95% of the average electromagnetic torque, 95% of the average electromagnetic torque in SFPM machines having ps stator pole pairs and n r rotor poles are contributed by several dominating field harmonics, i.e., rotating ones with |kn r ± (2i - 1)p s | pole pair (k = 1, i = 1, 2, 3) and static ones with (2i - 1)ps pole pair (i = 1, 2, 3). The FE predicted average static torques in SFPM machines are validated by measurements on prototype machines.

Roadmap for Emerging Materials for Spintronic Device Applications

Abstract: The Technical Committee of the IEEE Magnetics Society has selected seven research topics to develop their roadmaps, where major developments should be listed alongside expected timelines: 1) hard disk drives; 2) magnetic random access memories; 3) domain-wall devices; 4) permanent magnets; 5) sensors and actuators; 6) magnetic materials; and 7) organic devices. Among them, magnetic materials for spintronic devices have been surveyed as the first exercise. In this roadmap exercise, we have targeted magnetic tunnel and spin-valve junctions as spintronic devices. These can be used, for example, as a cell for a magnetic random access memory and a spin-torque oscillator in their vertical form as well as a spin transistor and a spin Hall device in their lateral form. In these devices, the critical role of magnetic materials is to inject spin-polarized electrons efficiently into a nonmagnet. We have accordingly identified two key properties to be achieved by developing new magnetic materials for future spintronic devices: 1) half-metallicity at room temperature (RT) and 2) perpendicular anisotropy in nanoscale devices at RT. For the first property, five major magnetic materials are selected for their evaluation for future magnetic/spintronic device applications: 1) Heusler alloys; 2) ferrites; 3) rutiles; 4) perovskites; and 5) dilute magnetic semiconductors. These alloys have been reported or predicted to be half-metallic ferromagnets at RT. They possess a bandgap at the Fermi level $E_{F}$ only for its minority spins, achieving 100% spin polarization at $E_{F}$ . We have also evaluated $\text{L1}_{0}$ alloys and $D0_{22}$ –Mn alloys for the development of a perpendicularly anisotropic ferromagnet with large spin polarization. We have listed several key milestones for each material on their functionality improvements, property achievements, device implementations, and interdisciplinary applications within 35 years time scale. The individual analyses and the projections are discussed in the following sections.

Novel Partitioned Stator Switched Flux Permanent Magnet Machines

Abstract: A novel switched flux permanent magnet (PM) machine with a partitioned stator structure is proposed, consisting of a conventional switched flux machine with the PMs removed from the stator teeth and placed on a secondary stator within a salient rotor. This novel machine harnesses two distinct synergies in machine design: magnetically geared and switched flux machines. The machine is optimized and the performance is compared with different numbers of rotor poles and validated by experiment. This machine benefits from reduced copper loss, improved torque density, and torque per magnetic volume, compared with conventional switched flux machines.

Electric-Field-Controlled Magnetoelectric RAM: Progress, Challenges, and Scaling

Abstract: We review the recent progress in the development of magnetoelectric RAM (MeRAM) based on electric-field-controlled writing in magnetic tunnel junctions (MTJs). MeRAM uses the tunneling magnetoresistance effect for readout in a two-terminal memory element, similar to other types of magnetic RAM. However, the writing of information is performed by voltage control of magnetic anisotropy (VCMA) at the interface of an MgO tunnel barrier and the CoFeB-based free layer, as opposed to current-controlled (e.g., spin-transfer torque or spin-orbit torque) mechanisms. We present results on voltage-induced switching of MTJs in both resonant (precessional) and thermally activated regimes, which demonstrate fast ( $\sim 1.5{-}2~{\rm V}$ . We also discuss the implications of the VCMA-based write mechanism on memory array design, highlighting the possibility of crossbar implementation for high bit density. Results are presented from a 1 kbit MeRAM test array. Endurance and voltage scaling data are presented. The scaling behavior is analyzed, and material-level requirements are discussed for the translation of MeRAM into mainstream memory applications.

Multimaterial Topology Optimization of Electric Machines Based on Normalized Gaussian Network

Abstract: This paper presents a topology optimization method for multimaterial models based on the normalized Gaussian network. In this method, one can determine optimal shapes of machines that are composed of various materials, such as iron, magnetic, and non-magnetic material. The present method is applied to the optimization of the average torque for interior permanent magnet motor to determine the distributions of magnetic core and flux barrier as well as magnets. The optimization results show that average torque can be improved using as small amount of magnet as possible. In addition, the characteristic of the present method is discussed in detail.

Design and Loss Analysis of Loosely Coupled Transformer for an Underwater High-Power Inductive Power Transfer System

Abstract: To prevent magnetic flux leakage to the maximal extent, increase the coupling coefficient of high-power inductive power transfer (IPT) system, and reduce the electromagnetic radiation in water medium, a novel underwater loosely coupled transformer (LCT) based on the semiclosed magnetic core structure is proposed in this paper. Power loss of the devised LCT is investigated comparatively in three media including air, freshwater, and seawater. It is shown that winding loss and core loss in the three media are basically identical. However, additional eddy current (AEC) loss in various water media is different for the sake of the difference in conductivity. In particular, AEC loss is extremely low in freshwater and relatively significant in seawater. Furthermore, when the operating frequency exceeds a certain value, AEC loss will be greater than core loss and winding loss, and become the major factor in restricting transmission efficiency of LCT in seawater. Finally, theoretical analysis and simulation are demonstrated by the underwater experiment on an IPT prototype system, which can transfer 10 kW at 91% maximal transmission efficiency and over a 25 mm air gap.

Magnonic Waveguides Studied by Microfocus Brillouin Light Scattering

Abstract: The paradigm of magnonics is based on utilization of propagating spin waves (or their quanta—magnons) for signal transmission and processing in magnetic-field-controlled devices. Implementation of magnonic devices for future-generation microelectronics requires the use of spin-wave guiding structures with micrometer- to nanometer-sized dimensions. Therefore, the deep understanding of propagation, excitation, and control of spin waves in microscopic waveguides is an absolute prerequisite for further developments in the field. Here we review recent experiments on spin-wave propagation in microscopic magnonic waveguides utilizing high-resolution Brillouin light-scattering spectroscopy enabling 2-D visualization of spin waves on the nanoscale.

29.5- $\hbox{Gb/in}^{2}$ Recording Areal Density on Barium Ferrite Tape

Abstract: The recording performance of a new magnetic tape based on perpendicularly oriented barium ferrite particles was investigated using a 90-nm-wide giant-magnetoresistive reader and a prototype enhanced-field write head. A linear density of 600 kb/in with a postdetection byte-error rate $ was demonstrated based on measured recording data and a software read channel that used a noise-predictive maximum likelihood detection scheme. Using a new iterative decoding architecture, a user bit-error rate of $ can be achieved at this operating point. To facilitate aggressive scaling of the track density, we made several advances in the area of the track-following servo. First, we developed an experimental low-noise tape transport. Second, we implemented an optimized servo channel that together with an experimental timing-based servo pattern enables the generation of position estimates with nanoscale resolution at a high update rate. Third, we developed a field-programmable gate array-based prototyping platform in which we have implemented the servo channel and an $H_{\infty }$ -based track-following controller, enabling real-time closed-loop track-following experiments. Combining these technologies, we achieved a position-error signal (PES) with a standard deviation of 10.3 nm. This magnitude of PES in combination with a 90-nm-wide reader allows the writing and reading of 177-nm-wide tracks at 600 kb/in, for an equivalent areal density of 85.9 Gb/in $^{2}$ . This paper clearly demonstrates the continued scaling potential of tape technologies based on low-cost particulate media.

Investigation of Skewing Effects on the Vibration Reduction of Three-Phase Switched Reluctance Motors

Abstract: Switched reluctance motors (SRMs) are gaining in popularity because of their robustness, low cost, and excellent high-speed characteristics. However, they are known to cause vibration and noise primarily due to the radial pulsating force resulting from their double-saliency structure. This paper investigates the effect of skewing the stator and/or rotor on the vibration reduction of the three-phase SRMs by developing four 12/8-pole SRMs, including a conventional SRM, a skewed rotor-SRM (SR-SRM), a skewed stator-SRM (SS-SRM), and a skewed stator and rotor-SRM (SSR-SRM). The radial force distributed on the stator yoke under different skewing angles is extensively studied by the finite-element method and experimental tests on the four prototypes. The inductance and torque characteristics of the four motors are also compared, and a control strategy by modulating the turn-ON and turn-OFF angles for the SR-SRM and the SS-SRM are also presented. Furthermore, experimental results validate the numerical models and the effectiveness of the skewing in reducing the motor vibration. Test results also suggest that skewing the stator is more effective than skewing the rotor in the SRMs.

Low Space Harmonics Cancelation in Double-Layer Fractional Slot Winding Using Dual Multiphase Winding

Abstract: One of the main drawbacks of nonoverlapped coils in fractional slot concentrated winding permanent magnet (PM) machines are the high eddy current losses in both rotor core and permanent magnets induced by the asynchronous harmonics of the armature reaction field. It has been shown in the literature that the reduction of low space harmonics can effectively reduce the rotor eddy current losses. This paper shows that employing a combined star-delta winding to a three-phase PM machine with fractional slot windings and with a number of slots equal to 12, or its multiples, yields a complete cancellation to the fundamental magneto-motive force (MMF) component, which significantly reduces the induced rotor eddy current. Besides, it offers a slight increase in machine torque density. A case study on the well-known 12-slot/10-pole PM machine is conducted to explore the proposed approach. With the same concept, the general n-phase PM machine occupying 4n slots and with a dual n-phase winding is then proposed. This configuration offers a complete cancelation of all harmonics below the torque producing MMF component. Hence, the induced eddy currents in both rotor core and magnets are significantly reduced. The winding connection and the required number of turns for both winding groups are also given. The concept is applied to a 20-slot/18-pole stator with a dual five-phase winding, where the stator winding is connected as a combined star/pentagon connection. The proposed concept is assessed through a simulation study based on 2-D finite element analysis.

Demagnetization Assessment of Fractional-Slot and Distributed Wound 6-Phase Permanent Magnet Machines

Abstract: A 6-phase fractional-slot-per-pole-per-phase interior permanent magnet (IPM) machine having a novel topology of 18-slot, 8-pole and a 6-phase, 48-slot, 8-pole IPM with distributed windings, both designed for a segment-A electric vehicle, are assessed for the risk of partial irreversible demagnetization under various fault conditions. This paper describes a more accurate approach of demagnetization assessment based on 2-D transient finite-element analysis. It is shown that due to the presence of low-order space harmonics in the fractional-slot IPM machine, the demagnetization risks across all pole pairs are different. Compared with the distributed wound machine, the fraction-slot machine is less vulnerable to demagnetization due to relatively high winding inductance, although its demagnetized regions are not uniform in each pole. It is also shown that although the demagnetizing current of one 3-phase short-circuit (SC) is greater than that of 6-phase SC, the resultant demagnetization risk is lower than that of 6-phase SC in the fractional-slotmachine.

Design of a Resonant Reactive Shield With Double Coils and a Phase Shifter for Wireless Charging of Electric Vehicles

Abstract: In this paper, a novel resonant reactive shield using a double-shield coil and phase-shift circuit is proposed to reduce magnetic field leakage in electric vehicle wireless charging applications. The double-reactive shield with a four-capacitor phase shifter generates a canceling magnetic field, the phase of which is perfectly opposite to that of the incident magnetic field, effectively reducing the leakage magnetic field as a result. The concept and structure, and an equivalent-circuit model analysis of the double-reactive shield are explained and discussed. The shielding effectiveness of the double-reactive shield is compared with that of a conventional reactive shield with a single-shield coil by a simulation and is verified by experiments.

Hybrid-Excited Doubly Salient Synchronous Machine With Permanent Magnets Between Adjacent Salient Stator Poles

Abstract: A novel stator hybrid-excited, parallel flux path, synchronous machine of doubly salient topology is proposed. It has the novel features of: 1) hybrid dc field and permanent magnet (PM) excitation in the stator; 2) magnets placed in the slots between adjacent salient stator poles; and 3) the magnetic poles of PMs arranged, such that the flux premagnetizes the stator, but it is in a direction to oppose the dc excitation flux. The electromagnetic characteristics of the machine are analyzed on open-circuit and load. Since the new machine topology is developed from the variable-flux machine (VFM), a comparison of their electromagnetic torque and machine losses is conducted. The average electromagnetic torque of the hybrid-excited machine can be increased by 18% for fixed copper loss in comparison with the VFM due to the reduction of magnetic saturation in the stator. It is also shown that at high temperatures some risk of PM demagnetization exists when excited with dc and armature currents due to fringing flux that exists between the stator and the rotor poles. However, this affects only a very small area of the PMs. The performance of the hybrid-excited machine is predicted by a 2-D finite-element analysis and experimentally validated.

Design of Ferrite–Graphene-Based Thin Broadband Radar Wave Absorber for Stealth Application

Abstract: Currently, a wide range of materials are used for radar wave absorption. But it is still a very challenging task to develop a thin radar wave absorber that operates for a wide range of frequencies. The main objective of this paper was to achieve good absorption with wide bandwidth corresponding to reflection loss (RL) ≤−10 dB for lower thickness (≤2 mm) by developing ferrite–graphene (FG) composites. A critical study has been carried out by varying the composition of FG to obtain wideband absorption with lower thickness. The effective complex dielectric permittivity ( $\varepsilon '$ , $\varepsilon ''$ ) and effective complex magnetic permeability ( $\mu '$ , $\mu ''$ ) of composites were measured using transmission/reflection waveguide method in the range of 8.2–12.4 GHz. These measured $\varepsilon '$ , $\varepsilon ''$ , $\mu '$ , and $\mu ''$ values have been used for the design of single- and double-layer absorber. Increasing the graphene content in FG composites resulted in a reduction of thickness and wide absorption bandwidth. Furthermore, a multilayer approach is adopted to enhance the radar wave absorption with broad bandwidth at a lower absorber layer thickness. The double-layer absorber shows a strong RL of −55.28 dB at 10.2 GHz with broad bandwidth of 3.1 GHz in the frequency range of 8.6–11.7 GHz. The multilayering approach facilitated to attain a lower absorber layer thickness of 1.7 mm. Findings provide an effective and feasible way to develop a thin and broadband absorber, which may be utilized for stealth applications.

Comparison of Iron Loss Models for Electrical Machines With Different Frequency Domain and Time Domain Methods for Excess Loss Prediction

Abstract: The goal of this paper is to investigate the accuracy of modeling the excess loss in electrical steels using a time domain model with Bertotti's loss model parameters n 0 and V 0 fitted in the frequency domain. Three variants of iron loss models based on Bertotti's theory are compared for the prediction of iron losses under sinusoidal and non-sinusoidal flux conditions. The non-sinusoidal waveforms are based on the realistic time variation of the magnetic induction in the stator core of an electrical machine, obtained from a finite element-based machine model.

3-D Analytical Model for Axial-Flux Eddy-Current Couplings and Brakes Under Steady-State Conditions

Abstract: This paper presents a 3-D analytical model for axial-flux eddy-current couplings and brakes, leading to closed-form expressions for the torque and the axial force. The proposed model is valid under a steady-state condition (constant speed operation). It takes into account the reaction field due to induced currents in the moving conducting part. In order to simplify the analysis, we adopt the assumption of linearization at the mean radius, and the problem is then solved in 3-D Cartesian coordinates (curvature effects are neglected). The solution is obtained by solving the Maxwell equations with a magnetic scalar potential formulation in the nonconductive regions (magnets and air gap) and a magnetic field strength formulation in the conductive region (copper). Magnetic field distribution, axial force, and torque computed with the 3-D analytical model are compared with those obtained from the 3-D finite-element simulations and experimental results.

Unequal Teeth Widths for Torque Ripple Reduction in Permanent Magnet Synchronous Machines With Fractional-Slot Non-Overlapping Windings

Abstract: Permanent magnet synchronous machines (PMSMs) with fractional-slot non-overlapping windings, also known as tooth-coil winding PMSMs (TCW PMSM), have been under intensive research during the latest decade. There are many optimization routines explained and implemented in the literature to improve the characteristics of this machine type. This paper introduces a new technique for torque ripple minimization in TCW PMSM. The source of torque harmonics is also described. The low-order torque harmonics can be harmful for a variety of applications, such as direct drive wind generators, direct drive light vehicle electrical motors, and for some high-precision servo applications. The reduction of the torque ripple harmonics with the lowest orders (6th and 12th) is realized by machine geometry optimization technique using finite element analysis. The presented optimization technique includes the stator geometry adjustment in TCW PMSMs with rotor surface permanent magnets and with rotor embedded permanent magnets. Influence of the permanent magnet skewing on the torque ripple reduction and cogging torque elimination was also investigated. It was implemented separately and together with the stator optimization technique. As a result, the reduction of some torque ripple harmonics was attained.

Novel Electrical Machines Having Separate PM Excitation Stator

Abstract: In this paper, novel electrical machines having a separate permanent magnet (PM) excitation stator are proposed based on a partitioned stator (PS) flux reversal (FR) PM (FRPM) machine. Different from the conventional FRPM machines with a single stator, the PS-FRPM machines have two stators with PMs surface mounted in one stator and the armature windings located in another stator. This paper investigates the electromagnetic performance of PS-FRPM machines with 12/10, 12/11, 12/13, and 12/14 stator/rotor-pole, together with the influence of leading design parameters. The torque characteristics of PS-FRPM machines are quantitatively compared with the conventional FRPM machines based on their globally optimized designs. It shows that the PS-FRPM machines can generally produce higher torque when the PMs are thicker and exhibit >56% higher torque density than that of the conventional FRPM machines. Even compared under the same PM volume, the proposed PS-FRPM machines can have larger torque due to better utilization of the inner space. The investigation is validated by both finite-element and experimental results.

Vibroacoustic Analysis of Radial and Tangential Air-Gap Magnetic Forces in Permanent Magnet Synchronous Machines

Abstract: This paper analyzes Maxwell tensor tangential and radial magnetic forces in permanent magnet synchronous machines in the no-load case. Using matrix notation in the complex domain, a simple expression of the Fourier harmonics of both radial and tangential forces is derived, including all space and time harmonics. These expressions prove that both the frequency content of cogging torque and zeroth-order radial forces are linked to the least common multiple between the stator slot number and the rotor poles number, and that the optimal pole arc to pole pitch ratio to reduce cogging torque is also optimal for the reduction of average radial magnetic forces. It is also shown that both the smallest non-zero spatial order of tangential and radial force harmonics are given by the greatest common divider of the number of slots and the number of poles. These results can be used during the design stage when choosing the pole and slot numbers combination. These analytical results are then compared with calculations using MANATEE vibroacoustic and electromagnetic simulation software. Finally, some variable speed acoustic noise simulations are carried out on three different designs to analyze the efficiency of different vibroacoustic design rules on the slot and pole numbers combination. An attempt to formulate a new vibroacoustic design rule choice is detailed. It is concluded that no simple analytical design rule can be used to evaluate noise and vibrations induced by magnetic forces, and that numerical simulation is necessary.

Design and Analysis of a Double-Sided Linear Induction Motor for Transportation

Abstract: An air-bus system is proposed as one alternative to urban mass transportation. The propulsive force of this system is generated by a linear motor. Several single- or double-sided linear motor topologies could be employed, but a double-sided linear induction motor (LIM) is preferred due to its simple passive track and high value of force density. Several research works were carried out to develop analytical models for the analysis of LIM performance. In this paper, a quasi-1-D analytical method is proposed to analyze motor performance, and the longitudinal and transversal edge effects are considered as well. Accuracy of the proposed method is evaluated by comparing the analytical results with the experimental data, which shows acceptable conformity. Then, the motor design for the desired application is presented and its performance is evaluated by both finite-element method and analytical modeling. Derivations of major equations are given as well.

Investigation and Design of a High-Power Flux-Switching Permanent Magnet Machine for Hybrid Electric Vehicles

Abstract: Flux-switching permanent magnet (FSPM) machines exhibit high torque density, high efficiency, and robust rotor structure. In this paper, a prototype of a high-power three-phase 12-stator-slot/10-rotor-pole FSPM motor used for hybrid electric vehicles (HEVs) is designed by finite-element analysis (FEA). First, the initial FEA model is improved by gradually taking into account lamination ${B}$ – ${H}$ curves due to different electrical frequencies, operation temperatures, 3-D end effect, and rotor eccentric. Thereafter, a modular manufacture method of the FSPM motor is discussed with the improved FEA model and validated by experimental measurements. Then, the measured overload capability of the FSPM motor is compared with that of an interior permanent magnet (IPM) motor used in Honda Civic, and the results indicate that the IPM motor exhibits significantly stronger overload capability, which is analyzed in depth from soft-iron materials, cooling conditions, and and so on. Finally, both the merits and demerits of FSPM motor employed for low-voltage and high-current HEV applications are highlighted.

Coupled Spin Torque Nano Oscillators for Low Power Neural Computation

Abstract: We present coupled spin torque nano oscillators (STNOs) as electronic neurons for efficient brain-inspired computation. The coupled STNOs show two distinct outputs, depending on whether the frequencies are locked or not. The locking mechanisms are based on magnetic coupling or injection locking. The neuron firing threshold can be set by tuning the locking range of the coupled STNOs. We employ a crossbar array of programmable memory devices like memristors to implement electronic synapses that work seamlessly with the coupled STNOs for hardware implementation of neural networks. Results show that injection locking-based neuron model can be attractive from scaling point of view and computation like character recognition can be performed with energy consumption per neuron of $\sim $ 1.8X and $\sim $ 3X lower than the digital and the analog CMOS counterpart, respectively.

Impact of Pole and Slot Combination on Vibrations and Noise of Electromagnetic Origins in Permanent Magnet Synchronous Motors

Abstract: In low- to medium-power-rated brushless machines, noise of electromagnetic origin is generally prevailing over mechanical and aerodynamic sources. The appropriate combination of pole and slot of a permanent magnet synchronous motor is one of the keys to its performances among which stands noise reduction. This paper investigates configurations regarding this aspect for distributed overlapping and single-layer concentrated nonoverlapping winding configurations. Chosen combinations are 8 poles 48 slots (8p48s), 8p72s, 46p48s and 50p48s. The air-gap flux density is obtained by 2-D finite element analysis (FEA), allowing to compute the electromagnetic pressure. It then serves as input of mechanical and acoustical 3-D FEA models of the stator with carter.

Investigation on Operational Envelops and Efficiency Maps of Electrically Excited Machines for Electrical Vehicle Applications

Abstract: In this paper, the operational envelops and efficiency maps of an electrically excited (EE) machine with/without employing flux weakening control via armature current and/or with/without the field excitation regulating are obtained and comprehensively compared for electric vehicle applications. It shows that even in EE machines, only using the field excitation regulating but without the flux weakening armature current control, the maximum power at high speed is not constant but inversely proportional to the machine speed. Only by employing the flux weakening armature current control, the maximum constant power operation at high-speed region can be achieved while the operational high-speed region can be greatly extended. The maximum efficiency in this extended high-speed region can be achieved when both the field excitation and flux weakening ${d}$ -axis armature current change proportionally. The main benefit of the field excitation regulating is that the efficiency in low-torque region can be significantly improved. All the analyses are validated analytically.

Partial Irreversible Demagnetization Assessment of Flux-Switching Permanent Magnet Machine Using Ferrite Permanent Magnet Material

Abstract: This paper investigates the partial irreversible demagnetization characteristics of magnets in flux-switching permanent magnet (FSPM) machines. Two different partial demagnetization mechanisms in the FSPM machines are modeled and demonstrated. The 2-D finite-element analysis (FEA) results for a baseline 10 kW 15 kr/min ferrite FSPM machine verify the validity of the proposed partial demagnetization model. Performance degradation due to demagnetization is evaluated for the baseline machine based on the FEA results. This paper also proposes a novel design to enhance the demagnetization withstand capability. This research reveals the most vulnerable region of the magnet to irreversible demagnetization in the FSPM machines. It also provides a guideline for developing demagnetization withstand capability improvement techniques.

Analysis of Windings in Variable Reluctance Resolver

Abstract: In this paper, the relationship between the numbers of stator slots, winding polarities, and rotor poles for variable reluctance resolvers is derived and verified, which makes it possible for the same stator and winding to be shared by the rotors with different poles. Based on the established relationship, a simple factor is introduced to evaluate the level of voltage harmonics as an index for choosing appropriate stator slot and rotor pole combinations. With due account for easy manufacturing, alternate windings are proposed without apparent deterioration in voltage harmonics of a resolver. In particular, alternate windings with nonoverlapping uniform coils are proved to be possible for output windings in some stator slot and rotor pole combinations, which further simplify the manufacture process. Finite element method is adopted to verify the proposed design, together with experiments on the prototypes.

Topology Optimization of Synchronous Reluctance Motor Using Normalized Gaussian Network

Abstract: This paper presents the topology optimization of a synchronous reluctance motor using the normalized Gaussian network. In the optimization, the average torque and iron loss are considered. In the resultant motor, the area of the rotor surface adjacent to the stator is found to be reduced when the weight for the iron loss is sufficiently large. On the other hand, large flux barriers are present in the rotor when the average torque is maximized without considering the iron loss.

Analytical Analysis of Cage Rotor Induction Motors in Healthy, Defective, and Broken Bars Conditions

Abstract: This paper presents a 2-D static analytical method in the frequency domain for the calculation of magnetic field distribution, eddy-currents, circuit model parameters, and steady-state performances in multiphase/multipole cage rotor induction motors with integer and fractional stator winding. The complex model allows to study the healthy, defective, and broken bars conditions in these electrical machines. The proposed static analytical model considers stator and rotor slotting with tooth-tips. The method is based on the resolution of Poisson’s, Laplace’s, and Helmholtz’s equations in stator slots, air-gap, and rotor bars regions, respectively. The electromagnetic torque is obtained from both the electrical equivalent circuit and Maxwell stress tensor that is given by the magnetic field calculation. The analytical results are validated by those issued from time harmonic finite-element method.

Effect of Stress on Magnetic Hysteresis Losses in a Switched Reluctance Motor: Application to Stator and Rotor Shrink Fitting

Abstract: A magnetic hysteresis model is developed based on the vector generalization of Jiles–Atherton (JA) model combined with a simplified multiscale approach to take into account the effect of mechanical stress on the magnetic behavior. The model aims at representing electrical steel behavior under any loading configuration considering the magnetic field vector and the mechanical stress second-order tensor. Mechanical stress is introduced in the JA hysteresis model through the anhysteretic magnetization and a modified pinning parameter. The main properties of the model are shown under alternating and rotating applied induction, especially in terms of hysteresis losses. The differential magnetic susceptibility is derived from the model, and the implementation into a time-stepping finite-element method is detailed. Finally, a quasi-statically rotating switched reluctance motor is studied: considering different shrink-fitting conditions, the resulting stress is shown to have a significant effect on both distribution and global value of hysteresis losses.