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The Vernier machine can utilize magnetic-gear effect, which conspicuously improves the torque production over other type of synchronous machines. However, a dual-rotor/dual-stator structure enabled high torque density Vernier design is often unfavorable for industrial applications, due to manufacturing complexity and thermal management challenges. This article successfully addresses this problem, by building magnetic-gear effect into a consequent pole enabled alternating flux barrier structure with single-rotor single-stator (SRSS). In this way, the proposed machine can achieve a superior torque density as a Vernier machine does, while maintaining an equivalent manufacturing complexity as a conventional SRSS synchronous machine. This article begins with elaborating generic analytical equations, which can transform into a Vernier machine or an SRSS synchronous machine. More specifically, the magnetic-gear effect is manifested in the equations, via stator teeth originating flux modulation concept and resulting multiharmonic field coupling effects. An SRSS Vernier topology with consequent pole and V-shape magnet is then proposed. A considerable 52.6% improvement on the torque production with comparable efficiency is validated by experiments, where the comparison is made over that of a benchmark rare earth PM machine. Power factor would fall behind with increasing current load. Overall, this new design achieves an outstanding torque density, showing solid potential and feasibility for industry adoption. [ABSTRACT FROM AUTHOR]

This letter proposed a coupled resonant inductor structure for CLLC bidirectional converter, which can effectively reduce the number and volume of magnetic components and the oscillation caused by parasitic parameters. An optimized current detection method based on magnetic element voltage detection is also proposed to avoid the use of bulky and costly current sensors. Synchronous rectification is realized with the detection to improve efficiency. The effectiveness is verified by a 3 kW CLLC converter. [ABSTRACT FROM AUTHOR]

Magnetic components have become one of the primary barriers to high power density converters, especially to current-source converters (CSCs). In CSCs, the inductors/transformers have a predominantly dc flux to store energy, which can be offset by standard permanent magnets (PMs). However, eddy currents in standard PMs induce significant losses and thermal stress for medium-frequency applications. This article proposes using laminated PMs to offset the dc flux while reducing eddy currents, leading to significant reductions in the size, cost, and losses of inductors/transformers. Furthermore, the laminated PMs’ optimal location, orientation, and distribution are investigated to generalize this approach for maximum benefits. Three-dimensional finite-element analysis simulation and hardware experiments are presented to validate the effectiveness of the proposed approach in a medium-frequency transformer (MFT) for CSCs. Compared with standard PMs, the proposed use of laminated PMs reduces aggregate core-plus-PM losses by 85% in experiments, and thus, relaxes the MFT thermal design. Finally, the proposed approach is experimentally validated in a $\text{40}\,\text{kVA}$ flyback-type MFT for a soft-switching solid-state transformer. Compared to the traditional design without any PMs, the proposed design increases the saturation current by 46% while inducing only 5% more losses, leading to significant savings in magnetics cost and size. [ABSTRACT FROM AUTHOR]

This work couples a magnetic multi-stable mechanism to a pendulum vibration energy harvester so as to widen its bandwidth, especially in low-frequency operation. Multiple stable points are formed by a movable permanent magnet installed on the pendulum and two fixed permanent magnets installed symmetrically on the base of the energy harvester. Thus, the pendulum can swing between the stable points at two sides, which causes large motion amplitude and power generation. In designing the prototype of the energy harvester, dynamical modeling and potential energy analysis are carried out to achieve a low threshold for snap through. An experimental setup is developed and a series of comparative experiments are implemented to investigate prototype performance. It is shown that the energy harvester with the fixed magnets can generate a noticeable normalized induced voltage at 0.7 Hz, while the energy harvester without the fixed magnets requires the excitation frequency of 1.0 Hz to reach a similar level. The electrical outputs varying with vibration acceleration and load resistance are also examined. In general, the experimental results verify the effectiveness of the proposed structure on enlarging frequency bandwidth. This work can provide a promising candidate of energy harvesting for low-frequency applications such as ocean wave. [ABSTRACT FROM AUTHOR]

This work investigates a 2-D vector field behavioral model to describe the anisotropic magnetic permeability and losses in Grain-Oriented Electrical Steels (GOES) within quasi-static and magneto-harmonic working conditions. The model includes the an-hysteretic magnetic field driven by the total anisotropy, the coercive force responsible for the quasi-static hysteresis losses, and the dynamic damping eddy field responsible for the extra losses. Each field contribution requires the definition of a tensor property whose diagonal and non-diagonal coupling components are experimentally identified as a function of the flux density magnitude $B$ and its angle $\theta $ with the Rolling Direction (RD). The static behavior is identified at low frequency and the dynamic one takes the frequency-dependent field diffusion into account. Diagonalization tools reveal main characteristic magnetic axis for the separate properties with deflections at the macroscale. [ABSTRACT FROM AUTHOR]

This article proposes an improved tubular single-phase permanent magnet linear oscillation actuator (SP-PMLOA) considering eliminating detent force for direct drive compressor applications. First, the flux tube method and Maxwell stress tensor are used to derive the end force and cogging force formulations based on the magnetic flux leakage of the magnet rings. Then, a novel model with minimum detent force is presented by finite element parametric sweeping. Finally, the electromagnetic performance of the three SP-PMLOAs is compared using 2-D finite element analysis (FEA), whose merits are evaluated, and the thermal distribution of the optimal PMLOA is analyzed using 3-D FEA. The predicted results show that the proposed structure not only can significantly reduce the detent force and the mover axial length but also can increase the thrust force-moving magnet mass ratio. [ABSTRACT FROM AUTHOR]

Ac low voltage stabilizers with thyristor-based onload tap-changers are effective and cover 300 VA to 300 kVA applications. Among the solutions to reduce the internal short-circuit derived from the make-before-break changes, the multiwinding coil for years has proven to be reliable. This article shows a new operating mode of the coil that allows extra output voltages from every tap-switch using a magnetically coupled Nonius. The number of main taps is greatly reduced allowing, in a typical 10 MVA 34.5 kV line tap-changer, to save 33% of the cost of thyristors compared to the previous best solution without Nonius. In total, 29 voltage states can be obtained with only eight main taps and six auxiliary small Nonius taps per phase. Medium voltage stabilizers up to 36 MVA can be implemented using standard phase control thyristors with no series, nor parallel, association. Simulations and physical tests, controlled by digital signal processor, show that the new Nonius operating mode of the coil does not penalize the current rate of the switches, nor the flux of the coil core. Thus, magnetic-Nonius tap-changers achieve cost-effective stabilization with the fine regulation obtained by mechanical solutions with many taps. [ABSTRACT FROM AUTHOR]

This article presents a three degrees of freedom (3-DOF) permanent maglev platform for a cleanroom conveyor system supported by four magnetic poles that utilize a variable flux path mechanism. Since the magnetic force of poles is generated and controlled entirely by the rotation of disk-type permanent magnets (PMs), the system exhibits a quasi-zero power consumption and anti-adsorption capability. First, the system mechanism is illustrated, and the magnetic force of the variable flux path pole is measured. Then the mathematical model and state-space of the maglev platform are established based on dynamic analysis. Afterward, a double closed-loop controller is designed for stable levitation and motion control, and the coordinate transformation matrix is used to decouple the control system. Finally, the simulations and experiments were implemented, and stable levitation and 3-DOF motion control were realized with a remarkable positioning precision. The results indicate that the controller and decoupling strategy are effective. [ABSTRACT FROM AUTHOR]

As part of the European Strategy for Particle Physics there is an ongoing development towards a Future Circular Collider (FCC-ee) where electron-positron collisions could be used to study the entire electro-weak sector in a low background environment. Particle detectors are used to study these collisions and a strong magnetic field is required to measure the particles’ momenta. Currently, two detector concepts are being studied: the Innovative Detector for Electron-positron Accelerators (IDEA) and the CLIC-Like Detector (CLD). Both these detectors include a superconducting solenoid magnet with a central field of $2 \,\mathrm{T}$ of which the designs are presented here. The IDEA magnet has an stored magnetic energy density of 14 kJ/kg and in CLD this is 12 kJ/kg. Taking into account their respective free-bore diameters of $4.2 \,\mathrm{m}$ for IDEA and $7.2 \,\mathrm{m}$ for CLD this results in very challenging designs for which the mechanical and quench studies are presented. Their results are promising, but extensive R&D on these magnets would be needed in the future to reach the goals set out in the Conceptual Design Report (CDR). [ABSTRACT FROM AUTHOR]

A novel maglev wind yaw system (MWYS) based on the maglev technique and direct-drive structure was proposed to reduce the yaw power and failure rate. We first introduced the attraction force fluctuation and dynamic response time into the optimized design of axial flux motor, and constraints considering suspension startup, dc input voltage of suspension converter, and safe pitch limitation are given. Using multiobjective sequential quadratic programming technique, an optimization process is performed for minimizing the suspension losses, attraction force fluctuation, and the fastest attraction force dynamic response, considering the practical constraints. Ultra-low speed requirement makes the yaw motion easily vibrate with torque pulsation; we adopt the stator fractional slot structure and build stator slot permeance function and some constraints to perform the optimization of the stator construct parameters for minimizing cogging torque by the Lagrange function method. Finally, the design example is given and a prototype is manufactured. The experimental results show that the presented design method, structure, and the MWYS are feasible. [ABSTRACT FROM AUTHOR]

On the basis of prior research, a conceptual three-dimensional (3-D) configuration of a non-destructive two-layer magnet capable of generating megagauss-level magnetic field was developed. The design is based on the concept of quasi-force-free coils, in which conductors have a special shape tailored to minimize mechanical stresses caused by electromagnetic forces. Multivariate multi-physical finite element simulations were used as the main tool for developing the presented configuration. The magnetic system was analyzed for its ability to withstand Lorentz forces, and calculations demonstrate that the design ensures maximum stresses in the windings significantly less than the magnetic pressure of the generated field. That reveals a possibility of achieving a megagauss field in the system, provided that certain requirements are met for the used materials. Such requirements were formulated and are realistic (e.g., ultimate strength about 1 GPa for the conductors). Estimation of the possible pulse duration limited by the admissible temperature of the conductors allowed us to perform a transient electromagnetic analysis. Results highlight the importance of mitigating the skin effect in the system, and possible ways for that are proposed. The energy of the magnetic field in the proposed system is estimated to be about 1 MJ, which is significantly less than the energy in magnets of more conventional configurations with similar bore diameters. [ABSTRACT FROM AUTHOR]

This article presents the application of high-strength non-grain-oriented (NGO) silicon steel in the design of the rotor topology of a high-speed interior permanent magnet synchronous machine (IPMSM). By narrowing the magnetic bridges and center posts in the rotor, the purpose of reducing leakage flux and increasing output torque is achieved. Narrower magnetic bridge will cause electromagnetic loss concentration and tensile stress concentration, and tensile stress can effectively weaken the core loss at the part where the iron loss is concentrated. The high-strength NGO silicon steel used in this article is SW35YS600. This high-strength NGO adopts the method of increasing dislocations density to achieve the goal of increasing the structural strength while taking into account the electromagnetic properties at the same time. The electromagnetic properties of this high-strength NGO are less sensitive to tensile stress. As the frequency increases, the improvement of tensile stress on iron loss increases. However, after this material undergoes stress relief annealing, its electromagnetic and mechanical properties deteriorate significantly. Observing the grain structure, it was found that the grains of the high-strength NGO increased significantly after annealing. [ABSTRACT FROM AUTHOR]

Magneto-rheological elastomers (MREs) belong to the class of smart materials whose mechanical properties can be controlled by an external magnetic field. These materials can be integrated into mechatronic systems and submitted to multiple loadings such as temperature, mechanical stress, and magnetic field. Thus, this work is dedicated to the development of a magneto-mechanical bench and on first experimental characterizations of hard MREs taking multiphysics coupling into account. Regarding the mechanical loading, the experimental setup is able to create a uniaxial tensile stress in case of low strain (< 1%) without friction effect. In regards to the magnetic loading, a magnetic circuit made of a strong permanent magnet has been designed to impose a variable and a homogeneous magnetic field strength up to 41 kA/m. Experimental analysis has been performed on silicone rubber filled with 36%vol. of NdFeB particles. The purpose was first to investigate the evolution of the Young modulus with or without magnetic field. Results obtained from measurements show that the developed test bench is able to depict the mechanical behavior and phenomena linked to rubber-like material. [ABSTRACT FROM AUTHOR]

A novel stacked magnetic pendulum array (MPA) is proposed as an antenna for efficient transmission in ultralow frequencies (ULF). The MPA structure consists of an array of ${m\times n}$ magnets stacked in $n$ rows (m magnets of the same magnetization per row) and a solenoid that encompasses the array. The magnetic flux generated by the solenoid couples to the magnets through a mechanical motion and creates a strong time variant magnetic field at the resonance frequency of the array. The proposed MPA is developed utilizing bearings with extremely small damping which hold the magnets, enable efficient oscillation, and guarantees a high-quality factor ($Q$ -factor). A comprehensive analysis to study the performance of the MPA and a conventional solenoid will be provided and accordingly, characteristics of an arbitrary ${m\times n}$ array in terms of field strength, resonance frequency, transmission efficiency and inductance are studied. Furthermore, a figure of merit (FOM) is introduced as the ratio of efficiency to the maximum linear dimension of the antenna. The experimental results for a fabricated $5 \times 11$ array show a resonance frequency of 715 Hz and a Q-factor of 94 while the maximum linear dimension of the antenna is just 9 cm. Moreover, measurement results show 24.9 dB improvement in the transmission efficiency of the MPA compared to the efficiency of a single solenoid of the same dimensions. The MPA has the FOM of ${1.26\times 1}{0}^{{4}}$ which is noticeably higher than that of proposed antennas in the literature. To demonstrate broadband transmission with the MPA, a binary frequency shift keying (BFSK) signal is transmitted through the use of direct antenna modulation (DAM) at a rate of 18 bps. [ABSTRACT FROM AUTHOR]

This article re-examines the Brillouin flow solutions in crossed-field diodes, with applications to magnetrons, magnetically insulated line oscillators (MILOs), and magnetically insulated transmission lines (MITLs). The Brillouin flow solutions are constructed for various geometries, including planar magnetrons, MILOs, and MITLs, cylindrical magnetrons with electrons flowing in the azimuthal direction, cylindrical MITLs and MILOs with electrons flowing in the axial direction, and radial MITLs and MILOs with electrons flowing in the radial direction. A common theme of this analysis is that two main external parameters are used to characterize the Brillouin flow: the anode–cathode voltage ($V_{a}$) and the total magnetic flux within the crossed-field diodes ($A_{a}$). These two parameters are equivalent to the gap voltage and a specification of the degree of magnetic insulation, which is approximately equal to the ratio of the magnetic field to the Hull cutoff (HC) magnetic field. The magnetic flux may be provided externally by a magnet (as in a magnetron) or by the wall currents without an external magnet (as in a MILO or MITL), or by some combination of the two, as in the intermediate case of a magnetron–MILO hybrid. Once these two parameters are specified, the electron flow speed at the top of the Brillouin hub is uniquely determined. This immediately yields the Buneman–Hartree (BH) condition according to the Brillouin flow model, whether it be a planar magnetron or a cylindrical MILO. In so doing, we have obtained, for the first time using the Brillouin flow model, the BH condition for a cylindrical MILO, and we show that the same condition is obtained from the single-particle orbit model. We also found that, in general, the electron current within the Brillouin hub contributes only to a very small fraction of the magnetic flux $A_{a}$ , regardless of the gap voltage $V_{a}$ , thereby correcting an erroneous notion that the electron flow within the crossed-field gap could be responsible for the magnetic insulation. Another counter-intuitive finding is that, for a given degree of magnetic insulation, the Brillouin hub height decreases as the gap voltage $V_{a}$ increases. These conclusions, and other results, were based on the simple, explicit analytic expressions that we have obtained for the Brillouin flow profiles, including the velocity, electron density, as well as the self-magnetic field and the self-electric field profiles due to the Brillouin hub electrons. From these analytical expressions, we deduce useful scaling laws that are applicable to the prevailing cases where the magnetic field exceeds 1.5 times the HC magnetic field, and they are valid in both relativistic and non-relativistic regimes. Thus, these scaling laws show the contrast between magnetrons and MILOs, and a ready assessment of the viability of building a moderate-current MILO, a low-voltage MILO, and a magnetron–MILO hybrid which might combine the advantages of a magnetron and a MILO. The Brillouin flow profiles in a radial MITL are explicitly calculated. Additional issues are addressed. [ABSTRACT FROM AUTHOR]

In this article, a current balancing coupled inductor (CBCL) based asymmetrically configured quad-active-bridge (QAB) converter is proposed. The QAB converter provides high-frequency isolation for a dc–dc stage of a solid state transformer (SST), as well as provides a modular solution to the SST medium-voltage (MV) dc link. The proposed CBCL ensures current balancing among/three active H-bridges without using any dedicated controller and without expensive sensors when transferring equal power from MV to low-voltage side. The proposed CBCL is the integration of three inductors of the active H-bridges required for power transfer and zero-voltage-switching and does not require an extra magnetic volume. Experimental results are presented to validate the performance. [ABSTRACT FROM AUTHOR]

During electrical machine manufacturing, the process may induce plastic mechanical strains, especially in the magnetic core. However, magnetic properties are highly sensitive to the material mechanical state. Thus, the performances of electrical machines, which also rely on the magnetic material properties, are often deteriorated. This article proposes an approach to reduce the impact of the forming process on the magnetic core performances by creating high localized heterogeneous deformations instead of having a low homogeneous deformation distributed on the whole structure. A NO (non-oriented) FeSi (1.3%) electrical steel (M330-35A) is characterized after uniaxial tensile test. Samples are deformed either in heterogeneous or in homogeneous ways while keeping the same global deformation. Experimental measurements show that, for the same displacement value, the heterogeneous configuration, with localized strain, deteriorates less the global magnetic properties than the homogeneous configuration. These results are supported by a magneto-mechanical modeling approach that predicts accurately the physical behavior of the test samples. [ABSTRACT FROM AUTHOR]

This work studies the resonant frequency reduction of vibration energy harvesters so as to adapt low-frequency ambient vibrations. In a typical electromagnetic vibration energy harvester, it is common sense that the resonant frequency decreases with the spring stiffness. However, the mass gravity will result in a large initial deformation of the spring with small stiffness when the energy harvester is vertically installed. To solve the problem, this work proposes a method of resonant frequency reduction by adding a negative-stiffness magnetic spring which is arranged symmetrically at the two sides of the equilibrium point. The theoretical expression of resonant frequency is derived based on magnetic field calculation. Comparisons between the energy harvesters with and without negative-stiffness magnetic spring are implemented through simulations and experiments. The results show that the resonant frequency of the vertical energy harvester can be reduced as expected without an increase of initial spring deformation by using the negative-stiffness magnetic spring. This work can provide an effective approach to designing energy harvesters for applications with low-frequency vibrations. [ABSTRACT FROM AUTHOR]

An eddy current damper comprising a magnet and a conducting plate moving perpendicularly to it is called a perpendicular-motion-type eddy current damper, whereas one with a magnet and a conducting plate moving parallel to it is called a parallel-motion-type eddy current damper. In this article, a method of using magnetic vector potentials in a stationary-conductor coordinate system to obtain easily the damping coefficient (the A method) is proposed and applied to a perpendicular-motion-type eddy current damper comprising a ring magnet and conducting disk. The previously proposed coil method is also applied. Because both methods utilize the magnetic flux densities and magnetic vector potentials obtained using a circular current loop, they cannot be considered to be the effect of the magnetic field generated by eddy currents on the damping coefficients. However, the damping coefficients were in good agreement with those obtained using a 3-D finite element method (3-D-FEM). Hence, the effect of the secondary magnetic field can be ignored. Moreover, the A method is as precise as the 3-D-FEM, is less complicated, and does not require an air region and boundary conditions for computation. In addition, although the errors of the damping ratios calculated from measured data and the A method were 17%, the error of the modified damping ratios obtained by applying the equivalent mass of the disk to the A method decreased to 6%. [ABSTRACT FROM AUTHOR]

Induction machines have become one of the most widely used motor types due to their simple structure, stable operation, and relatively low cost. During operation, the problem of unbalanced magnetic pull (UMP) arising from uneven air gaps is very common, which endangers the safe and stable operation of the unit. In this article, a UMP reduction method is proposed using an active control method, which utilizes the non-linear relationship between UMP and rotor slip. Meanwhile, an analytical model to find the slip with the lowest UMP is presented, by which the UMP can be reduced by controlling the excitation voltage. In addition, the problem of UMP surge when controlling the slip during the transient state is discussed. [ABSTRACT FROM AUTHOR]

This article provides a novel approach for discriminating the interturn short circuit (ITSC) fault in a salient pole synchronous generator (SPSG) based on the use of noninvasive sensors. A stray magnetic field is used as a signal that can provide valuable data regarding the health condition of the SPSG. Generally, the captured signal under an ITSC fault is examined using a classical signal processing tool based on fast Fourier transforms (FFTs). The amplitude of the side-bands to the frequency spectrum is increased by ITSC, eccentricity, and broken damper-bar faults. Therefore, determining the type of fault is not possible by analyzing the FFT side-bands. A unique feature is introduced using a short-time Fourier transform to identify the ITSC in its early stage. The proposed feature can locate and recognize the ITSC fault with high accuracy in either the no-load or the full-load operation of the SPSG. This novel methodology is verified by applying an ITSC fault to a 100 $kVA$ custom-made SPSG. [ABSTRACT FROM AUTHOR]

The “Divertor Tokamak Test facility” (DTT) is an experimental fusion reactor being built in Frascati (IT) in the framework of the European Fusion Roadmap. The DTT Central Solenoid operates in a pulsed regime to generate the magnetic flux needed to induce the plasma current and is therefore subjected to burdensome load conditions. In DTT, this magnet will consist of a stack of six layer-wound independently energized modules, wound with Nb3Sn Cable-in-Conduit Conductors. Different layout solutions have been studied to improve the performance of the CS in terms of magnetic flux density and structural integrity. The design presented is the result of the “Design Explorer” algorithm that has been specifically developed for this purpose. This code investigates all possible configurations to find the optimum conductor geometry and winding solution by considering measurable physical quantities to maximize the magnetic flux density while maintaining mechanical stresses at an acceptable level. This manuscript includes the electromagnetic calculation related to the heterogeneous plasma scenarios of the machine, the static structural and the fatigue life assessment and the full set of in-depth analyses performed for the qualification of the main components of the CS structure. [ABSTRACT FROM AUTHOR]

In this article, the rotor stress is analysed for a high-speed permanent magnet (PM) machine (HSPMM) with segmented magnets retained by a carbon-fibre sleeve. The influence of rotor PM segmentation is firstly considered in the stress analysis. It is found that when the segmented magnets are under tensile stress, significant sleeve stress concentration will occur due to magnet edging effect. By contrast, the PMs will benefit from the segmentation with reduced tangential stress. This stress reduction effect is enhanced when the number of PM segments is larger. Furthermore, the influence of PM segmentation on the worst operating scenario is determined. In order to avoid stress concentration due to PM segmentation, the design guidelines are then given by investigating the influence of sleeve thickness and interference fit. A new design scheme of sleeve thickness is proposed based on the identified worst case scenarios. Finally, a 6-slot 4-pole high speed PM machine with segmented magnets retained by carbon-fibre sleeve is prototyped and tested at the speed of 90 krpm. The rotor stability indirectly indicts the validity of the theoretical analysis and design scheme. [ABSTRACT FROM AUTHOR]

A magnetization system with active compensation of unbalanced magnetic pull for synchronous machines with rotating exciters is demonstrated. The system used switched power electronics and a digital control system to control the currents in four rotor pole groups, each consisting of 3 poles. It was mounted on the shaft of a synchronous machine, providing an interface between a permanent magnet outer-pole brushless exciter and the segmented field winding. Measurements of magnetic flux density on each pole face and current control made it possible to control the airgap magnetic flux density to balance the machine magnetically, thus removing flux density space harmonics in the airgap and also the unbalanced magnetic pull. The construction of the system is presented along with results from experiments and simulations. Tests were performed with the stator winding both in series and with two parallel circuits. Approximately 80% reduction of static forces and 60% reduction of dynamic forces between the stator and rotor were observed when the system was running. [ABSTRACT FROM AUTHOR]

Magnetoelectric voltage tunable inductors (VTIs) offer a new paradigm for power electronics circuit design. Here, air-gapped VTIs are demonstrated exhibiting a large inductance tunability of 220% with applied fields under 20 kVcm−1 and operational stability up to 5 MHz that covers the full frequency range of the state-of-the-art power electronics. The design of air-gapped VTI comprises of two C-shaped ferrite cores, one permeability-variable magnetic flux valve (MFV) in between C-shaped cores, and slotted air gap between cores and MFV. The tunability of VTIs is achieved through the electric field modulation of permeability in the MFV based on the magnetoelectric effect. There is a tradeoff between the tunability and saturation current. The introduction of air gap significantly reduces the tunability but provides methodology toward increasing the saturation current and power handling capability due to the increased reluctance. The inductance and tunability reduces by 50% with increase in the air-gap width from 0.07 mm to infinity (condition with no C-shaped cores). Phase field simulations demonstrate that the air gap affects the magnetization, permeability, and tunability of VTIs by tailoring the demagnetization field that further influences the magnetic domain rotation process. VTIs with increased frequency range and saturation current will strengthen the continued development of tunable power electronics. [ABSTRACT FROM AUTHOR]

Magnetic gears realize the characteristics such as low acoustic noise and low vibration, maintenance-free by contact-less power transformation. However, conventional magnetic gears are not suitable for high-speed motor drive systems because of their low mechanical strength, which results from the permanent magnets of the input rotor. This article proposes a novel flux-switching magnetic gear for high-speed motor drive systems. The input rotor of the flux-switching magnetic gear consists of an iron core. Therefore, the structure is highly robust and can be driven in the high-speed region. Moreover, the flux-switching magnetic gears offer a high torque density by utilizing stationary field magnets arranged between the pole pieces. Through simulations and the experiments, parameters such as the torque density, mechanical strength, losses, and efficiency of the proposed gear are evaluated. [ABSTRACT FROM AUTHOR]

This article presents the rotor optimization in an interior permanent magnet synchronous machine (IPMSM) with high-strength non-grain-oriented (NGO) silicon steel material. Different from simple replacement with high-strength NGO, this article presents a customized design to make the best use of rotor iron core material. Specific optimization of the rotor topology is presented, followed with simulation verification by finite element method (FEM). Based on the simulation results, the benefits and limitations of the optimization design with the replacement of high-strength NGO are listed. In order to further overcome the limitations of the presented optimization design, magnetic characteristics of the high-strength NGO laminations subjected to various tensile stresses are measured in the experiment. Finally, experimental results are analyzed, and the conclusions to employ high-strength NGO for IPMSM are summarized. [ABSTRACT FROM AUTHOR]

This article investigates magnetic design aspects of the trans-rotary magnetic gear (TROMAG) that using a quasi-Halbach array. TROMAG is a magnetic gear that converts high-force, low-speed linear motion to low-torque, high-speed rotational motion and vice versa. It is shown that quasi-Halbach magnetization significantly improves the force capability of the device compared to that of radial magnetization. Finite element analysis is used to study several design aspects of the quasi-Halbach TROMAG, including optimization of magnet dimensions and core thickness, effect of air gap length, effect of magnet remanent flux density, and distribution of flux density in the air gap. Moreover, the possibility of demagnetization is studied, and it is shown that if the quasi-Halbach TROMAG becomes overloaded repeatedly, demagnetization of magnets can degrade its force performance down to that of a similar TROMAG with radial magnetization. A quasi-Halbach TROMAG is prototyped, and static force and flux measurements verify the theoretical results. [ABSTRACT FROM AUTHOR]

A vibration energy harvester (VEH) converts the kinetic energy of a moving source into electrical energy. In this article, we consider a 1-D electromagnetic vibration energy harvester (1-D EMVEH) that consists of three coaxial cylindrical permanent magnets enclosed in a tube such that the middle magnet is levitating. The resulting movement of the middle magnet can then induce an electromotive force (EMF) in one or more surrounding coils. Using an analytical model, we derive expressions for the 1-D-EMVEHs characteristic frequency and output power by using the Fourier space approach. First, the magnetostatic energy of the system as a function of the position of the levitating magnet is calculated. Its spatial gradient gives the force acting on a magnet, which drives its dynamics. Next, more accurate magnetic flux and EMF expressions are obtained. The results are compared with experimental measurements, revealing an excellent agreement. [ABSTRACT FROM AUTHOR]

This paper proposes a novel Bi-Magnet machine design concept in which ferrite and rare earth magnet materials are both utilized for torque production. The proposed design aims to reduce the cost of permanent magnet machines by minimizing the use of expensive high-grade rare earth magnet materials without compromising the high performance associated with them. The decreased performance due to the reduced rare earth magnet content can be compensated by adding inexpensive ferrite magnets. The design was optimized to achieve maximum cost-savings by minimizing the rare earth magnet content and improving the saliency of the rotor structure. A comparative study was conducted to highlight the advantages of the proposed concept using the Camry 2007 model as the baseline design. The results show that the proposed design is capable of achieving the same torque and power density as the baseline design using 30% less rare earth magnet materials, resulting in 20% active material cost reduction. The Bi-Magnet machine concept is shown to maintain the superior performance of conventional rare earth permanent magnet machines at a lower cost. [ABSTRACT FROM AUTHOR]

Although hybrid excitation synchronous machines (HESMs) can provide an attractive flux-regulating capability, the fabrication and mechanical strength of the complex rotor are with significant challenges and need great efforts especially for high torque machines. In this article, a modular fabrication method of the dual-end magnetic-shunting rotor is proposed for high torque hybrid excitation synchronous machine. Then, by using numerical methods, the thermal stress of the rotor is calculated and compared with the 3-D FEA methods. To improve the mechanical strength of the rotor, the size of the screw, lug boss and filler is optimized, meanwhile, the rotor loss is optimized and thermal stress is evaluated. The results show that the proposed modular fabrication method demonstrates the improved mechanical strength and material utilization rate compared with the conventional fabrication process. Based on the three-dimensional finite-element analysis (3-D FEA) results, a 100 kW HESM prototype is successfully designed and manufactured using the proposed modular magnetic-shunting rotor. The experimental tests validate the effectiveness of the modular fabrication method and mechanical strength analysis. [ABSTRACT FROM AUTHOR]

Magnetic shape memory alloy (MSMA), which has emerged in recent years, has been proven to have great potential for electromagnetic actuators due to the long life cycle, fast response, and relatively large load capacity. Current research on such material mainly focuses on the fundamentals, thermal effect, composition, and magnetic induction strain, but issues involved in its application to the industry are rarely addressed in detail. This article first analyzed the principle of magnetically induced strain and the corresponding constitutive equations, and investigated the magnetomechanical characteristics of the MSMA sample through measurement carried out on a specially designed experimental setup. Taking advantage of good drive performance, MSMA electromagnetic actuator with spring recovery was designed in detail. In order to resolve the contradiction between compactness and high magnetic field strength, a novel configuration with double-layered coils was proposed to achieve the required magnetic flux density. Influences of input current, prepressure, and spring stiffness on the dynamic response characteristics of the actuator excited by step signal and square wave signal input were analyzed by simulation. Finally, the experimental platform is built to verify the feasibility of the configuration and dynamic characteristics of the actuator. The experimental results show that the designed actuator has good output performance with a response time of 25 ms, demonstrating the superiority of MSMA in microdisplacement actuator with high dynamics. [ABSTRACT FROM AUTHOR]

The aim of the work is to try to separate two informations related to the magnetization of the material and the change in its magnetic permeability during the tensile test. These two parameters, in accordance with the adopted model, are associated with reversible and irreversible magnetomechanical effects present in the material degradation process. For extracting the material features, stimulation was performed using a slow-changing magnetic field with a value close to the natural field of the earth. For the observation field on the sample surface an original matrix of triaxial magnetic field sensors was used. Several measuring series were made for various construction steels for various load stages, both for the area of elastic and plastic deformation. The proposed approach together with the results from the conducted research allowed for a better identification of the magnetomechanical effects that carry diagnostic information about the material. [ABSTRACT FROM AUTHOR]

This article presents the design and validation of a lightweight magnetorheological (MR) clutch, called hybrid magnetorheological (HMR) clutch. The clutch utilizes a hybrid magnetization using an electromagnetic coil and a permanent magnet. The electromagnetic coil can adjust the magnetic field generated by the permanent magnet to a desired value and fully control the transmitted torque. To achieve the maximum torque-to-mass ratio, the design of the HMR clutch is formulated as a multiobjective optimization problem with three design objectives, namely the transmitted torque, the mass of the clutch, and the magnetic field strength within the clutch pack. A prototype of the HMR clutch is fabricated, and its dynamic performance is experimentally validated. Experimental results clearly demonstrate the advantages of the HMR clutch in applications requiring fast and precise motion and torque control. [ABSTRACT FROM AUTHOR]

The design of the first stage of a 59:1 multistage magnetic gearbox for a wind turbine demonstrator is presented. The multistage magnetic gearbox (MSMG) is composed of a two stage magnetic gearbox (MG). The first stage of the MSMG has a gear ratio of 6:45. A spoke type MG rotor typology is used with a unique segmented fully laminated rotor structure. Axially segmented magnets and a unique set of radial deflection rotor support rings are utilized. Design issues with respect to losses and torque ripple are highlighted. [ABSTRACT FROM AUTHOR]

In this paper, the main objective is to optimize permanent magnet synchronous generators for offshore direct drive wind turbine, examining the best choice of magnet grades, BHmax, and working temperature. A surface-mounted Nd–Fe–B generator is designed electromagnetically and structurally and optimized for different rated powers of 6, 8, and 10 MW. The results show that the cost of energy decreases as the wind turbine's rated power increases. Further optimizations were carried out using different neodymium magnet grades, and it was found that the higher magnet grades produce a lower cost of energy. In addition, steps were taken to estimate the effect of magnet temperature. A detailed thermal model is used to calculate the cooling airflow requirements to bring the magnet operating temperature from 120 to 80 °C. Allowing the use of cheaper temperature grades of magnets, the additional cooling reduces winding losses and improves the effective BHmax of the magnets. [ABSTRACT FROM AUTHOR]

In some wave energy converters, there is a need for linear electrical machines where all the active parts are mounted on the stator. For this reason the linear Vernier hybrid machine has been investigated. In other research, it is analyzed in 2D and assumed to have a flat cross section. In this paper a cylindrical version of the Vernier hybrid machine is presented and analyzed. A geometrical model is used to investigate potential mass savings of the cylindrical version, and a finite element analysis design study is used to demonstrate a potential improvement in performance. A proof of concept laboratory scale model has been built and tested to validate the predictions. [ABSTRACT FROM AUTHOR]

The driving coil, as a key element of synchronous induction coilgun, endures not only the radial expansionary force because of the magnetic flux compression but also the axial force due to the compressive force and counterforce of the armature. Dielectric breakdown and mechanical structure damage occurs frequently. Meanwhile, the driving coil should have high energy conversion efficiency as a pusher to accelerate the armature. Therefore, it is important to choose the appropriate structure and parameters in order to achieve a high launching performance. In this paper, the factors that influence the system efficiency are analyzed first. Different structure designs of the driving coil with the same inductance are evaluated. The effect of different calibers on the system efficiency is analyzed. The simulation result shows that the structure of the driving coil should be chosen according to the practical launching requirement while the magnetic coupling should be increased. Second, the electromagnetic force applied on the coil is calculated and the stress is analyzed. The thickness and displacement of the containment are calculated on the condition of unyielding. In order to validate the accuracy of the theoretical analysis, an electromagnetic-mechanical coupling finite element model is built. Comparing two calculation results, the error is small. Therefore, the method can be used to guide the design of the driving coil. Finally, a driving coil is fabricated according to the calculation results and experimented through static and dynamic tests. The experimental results show that the driving coil performs well and have high conversion efficiency. It provides a theoretical and experimental basis for the future design of multistage induction coilgun. [ABSTRACT FROM AUTHOR]

To decouple the multi-axis motion in the 6 degrees of freedom magnetically levitated actuators (MLAs), this paper introduces a numerical method to model the force and torque distribution. Taking advantage of the Gaussian quadrature, the concept of coil node is developed to simplify the Lorentz integral into the summation of the interaction between each magnetic node in the remanence region and each coil node in the coil region. Utilizing the coordinate transformation in the numerical method, the computation burden is independent of the position and the rotation angle of the moving part. Finally, the experimental results prove that the force and torque predicted by the numerical model are rigidly consistent with the measurement, and the force and torque in all directions are decoupled properly based on the numerical solution. Compared with the harmonic model, the numerical wrench model is more suitable for the MLAs undertaking both the translational and rotational displacements. [ABSTRACT FROM AUTHOR]

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

This paper compares the performance of inner-only and inner–outer type of magnetizing fixture designs to achieve the radial magnetization profile in an isotropic-bonded neo magnet. In inner-only fixture, the magnetization coils are located on only one side of the magnet circumference, and inner–outer fixture uses magnetization coils on either side of the magnet circumference. For both fixtures, the finite-element analysis (FEA)-based performance is presented and compared with the experimental validation. The effect of misalignment between the inner and outer coils in an inner–outer fixture is discussed using the FEA as well as experimental results, and a limit on the misalignment angle resulting in negligible reduction in mid-air-gap flux density integral per pole is arrived at. [ABSTRACT FROM AUTHOR]

This paper presents the performance comparison between a flux concentration (FC) and triple-permanent magnet (PM) consequent pole (CP) magnetic gear (MG) rotor typology with the same 7.5:1 gear ratio. The triple PM CP MG is unique in that it can create torque change through two field heterodyning pole combinations. The performance with respect to volumetric and mass torque density is considered. It is shown that the FC typology can operate with a higher mass and volumetric torque density, even when using a low FC ratio rotor. [ABSTRACT FROM AUTHOR]

There has been an increasing awareness of research on magnetic properties of soft magnetic materials. In reality, the soft magnetic materials are likely to be magnetized by 2-D rotating magnetic field. Moreover, the magnetic properties could be influenced by mechanical stress. In order to investigate the magnetic properties thoroughly, numerous measurement apparatuses have been developed, which could take rotating magnetic flux or mechanical stress into account. However, there is limited research on the investigation of 2-D magnetic properties affected by laminated direction mechanical stress, as few mature devices could be employed, since the traditional $B$ – $H$ sensing coils are easily damaged by laminated direction stress. Therefore, the sensing structure with cubic specimen is proposed for 2-D magnetic properties measurement considering laminated direction stress. The printed circuit board (PCB)-based $B$ – $H$ sensing coils, which are attached to the surrounding surface of the cubic specimen, could be free of the impact of the $z$ -direction mechanical stress. The accuracy of $B$ – $H$ sensing part is analyzed in detail by means of the finite-element method as well as experiments. And, more remarkable, the deficiency of the artificial $H$ -coils wound by enameled wire is presented. Hence, a modified $H$ -coil made of four layer PCBs is proposed in this paper, the measurement accuracy is proven through experiments. [ABSTRACT FROM AUTHOR]

A new flux-assisted consequent pole spoke-type permanent magnet (PM) synchronous torque motor is proposed in this paper. The proposed motor has fractional slot structure with a spoke-type rotor geometry and flux-assisted magnets. Initial design, rotor design optimization, detailed 2-D and 3-D finite-element analyses (FEAs), and structural and thermal simulations are all carried out. A prototype motor is built and tested. The optimized design is validated by 2-D/3-D FEA and experiments and compared with the reference conventional surface PM (SPM)-type torque motor. The results indicate that the proposed new motor has higher torque-to-magnet-weight ratio and wider constant power region than the conventional SPM synchronous torque motor. [ABSTRACT FROM AUTHOR]

Accurate evaluation of magnetic properties of a motor core under actual operating conditions is necessary for the design of efficient motors. To elucidate phenomena that occur in a motor core with high accuracy, we specifically examined visualization of the magnetic flux flow in the laminated core. Evaluations are usually conducted with a specimen of the electrical steel sheet, which is used for the motor core under a flux flow condition similar to that in an actual motor core. However, such simplistic methods cannot predict the actual magnetic phenomena occurring in the motor core under operating conditions. Therefore, we developed a measurement method using a magnetic flux sensor that is thinner than an electrical steel sheet. It can measure the 3-D magnetic flux flow in the motor core under operating conditions. This sensor can be placed in the narrow space of laminated electrical steel sheets and can be designed so that it does not disturb the magnetic flux flow in the motor core. Furthermore, the sensor has high electric noise tolerance in an operating motor. As described herein, we explain the development of an evaluation method for measuring the magnetic flux density inside the motor core in a rotation condition. Moreover, we compared results obtained from measurements and simulation. Results show that the proposed measurement method is useful for magnetic flux density measurements in a motor core under operating conditions. [ABSTRACT FROM AUTHOR]

On the macroscopic scale, mechanical and magnetic properties of ferromagnetics are closely related. Under mechanical stress, ferromagnetics are subject to deformations alongside the changes in magnetization. Stresses and strains lead to changes of interaction forces acting between adjacent atoms and lead to a change in the magnetization distribution in domains, which in turn results in a change of the magnetic properties. Generally, these phenomena are referred to as magnetomechanical effects. As a part of this research study, specimens of P91 steel were tested after being subjected to diverse heat treatment procedures affecting their microstructure. The samples were subjected to periodically pulsed tensile cyclic loads with different values of the active stress induced in the part of the sample used in the measurements. For each of the tested combinations of applied stresses and microstructures, the magnetization changes followed a different pattern although certain similarities were reported, too. The greatest changes in the value of the sample magnetization were registered in the initial load cycles. There were significant differences in the magnetization process between samples with a different microstructure. Potential applications of the self-magnetic flux leakage value to analyses of active stresses in the sample were explored. [ABSTRACT FROM AUTHOR]

Accurate measurements of magnetic losses in laminations are a prerequisite for their theoretical assessment, as well as for satisfying calculations of energy dissipation in engineering systems. The standardized and universally applied measurement method, used as a reference for the definition of the material quality in the specification standards, is based on the Epstein test frame magnetizer. Its success relies on the reproducibility of the performed measurements. Its limitations come, on the one hand, from cumbersome sample preparation and, on the other hand, from a certain divergence of the measured loss figures from the true loss figures. Similar systematic differences between measured and true loss values are also observed with the standard single-sheet tester (SST) method. In both cases, measurements under bidimensional induction are or cannot be envisaged. The design of new measurement setups and magnetizers overcoming the drawbacks of the Epstein and SST methods and possibly becoming recognized standards in the future is welcome, but challenging. This paper is devoted to a comprehensive discussion of the state of the art in the alternating and 2-D measurements of energy losses in soft magnetic materials for electrical applications. We will summarize, in particular, measuring solutions proposed in the current literature, and we will discuss in detail recent developments achieved in the authors’ laboratories regarding 1-D measurements with compensated permeameters and 2-D measurements at high inductions and high frequencies. [ABSTRACT FROM AUTHOR]

We demonstrate a full range rotational angle sensor system using two chemical etching intrinsic Fabry–Pérot interferometers (FPIs) fabricated by an electrical arc discharge technique. The use of magnetic scale, combined packaged FPI detectors, allows the exploration of position characteristic with direction discrimination. Numerical simulation is employed for optimizing the distance $(d)$ between the detector and the circle magnetic scale. Experiments and numerical simulation show the interference dip shifts of FPI have sinusoidal relation with the rotational angle, as d ranging from 1 to 2.5 mm. Measurements showed five times ( $d=1$ ) and four times ( $d=1.5$ ) of magnitude greater than FBG detectors, with the linearity of 0.993 and 0.999, respectively. The sinusoidal function variations are displayed by two detectors with a phase difference of 90 degrees, which help to discriminate rotational direction. Moreover, two detectors have a low temperature cross-sensitivity of 2.3 pm/C°. The important advantage of our rotational angle sensor is their angle measurement range without limitation. [ABSTRACT FROM AUTHOR]