United States

INTRODUCTION&lt;br/&gt;The structure of doubly salient laminations and concentrated windings as well as the operation with unipolar rectangle currents and pulsating torques result in the significant radial magnetic force (RMF) in switched reluctance machines (SRMs), which contributes to the vibration and acoustic noise [1][2]. The analysis of the RMF plays an essential role in SRMs, in which the analytical method (AM) featuring with fast calculation and low computing loading, is helpful in the initial design. However, due to the severe nonlinearity of SRMs, it is of challenge to analytically predict the RMF [3]. Based on magneto-motive force (MMF)-permeance model [4], an AM is developed in this paper, and the saturations are considered via a rotor-position-independent magnetic equivalent circuit (MEC). The AM predictions will be validated by the finite element (FE) results and a prototype SRM.&lt;br/&gt;ANALYTICAL MODEL and RMF RESULTS&lt;br/&gt;The overall flowchart is shown in Fig. 1. The MMF distribution along air-gap periphery originated from the winding function and excitation, together with the air-gap permeance considering both stator/rotor saliency, are employed to predict the air-gap radial flux density. Then the RMF is calculated with Maxwell stress tensor. The magnetic saturation effect is included via a simplified MEC.&lt;br/&gt;The calculated RMFs along the air-gap periphery at one rotor position with single-phase excited are shown in Fig. 2(a), where both the linear and saturated conditions are included, and FE results are presented for the validation. The AM calculations agree well with FE results. Moreover, the AM-RMF waveform along the half air-gap periphery during one electric period is shown in Fig. 2(b).&lt;br/&gt;CONCLUSION&lt;br/&gt;An AM has been developed for predicting the RMF of SRMs, considering doubly salient laminations, unipolar rectangle currents and magnetic saturations. The calculation results are validated by the FE predictions. In the coming full paper, the details of the method, the flux tube of MEC and saturation factor, the validations on various SRMs with different excitations including overlapped currents, will be presented. A prototype SRM is to be tested.

![](https://assets.underline.io/uploads/markdown_image/1/image/824cbe0d375218c8beaf462fb166234b.jpg)

Fig. 1 Flowchart of AM of RMF.

![](https://assets.underline.io/uploads/markdown_image/1/image/f94362f2599ed11e8d796db183624985.jpg)

Fig. 2 RMF results along air-gap periphery.



2022 Joint MMM-INTERMAG

Analytical Model of Radial Magnetic Force in Switched Reluctance Machines with Consideration of Magnetic Saturations

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SGI 2021

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INTRODUCTION The structure of doubly salient laminations and concentrated windings as well as the operation with unipolar rectangle currents and pulsating torques result in the significant radial magnetic force (RMF) in switched reluctance machines (SRMs), which contributes to the vibration and acoustic noise [1][2]. The analysis of the RMF plays an essential role in SRMs, in which the analytical method (AM) featuring with fast calculation and low computing loading, is helpful in the initial design. However, due to the severe nonlinearity of SRMs, it is of challenge to analytically predict the RMF [3]. Based on magneto-motive force (MMF)-permeance model [4], an AM is developed in this paper, and the saturations are considered via a rotor-position-independent magnetic equivalent circuit (MEC). The AM predictions will be validated by the finite element (FE) results and a prototype SRM. ANALYTICAL MODEL and RMF RESULTS The overall flowchart is shown in Fig. 1. The MMF distribution along air-gap periphery originated from the winding function and excitation, together with the air-gap permeance considering both stator/rotor saliency, are employed to predict the air-gap radial flux density. Then the RMF is calculated with Maxwell stress tensor. The magnetic saturation effect is included via a simplified MEC. The calculated RMFs along the air-gap periphery at one rotor position with single-phase excited are shown in Fig. 2(a), where both the linear and saturated conditions are included, and FE results are presented for the validation. The AM calculations agree well with FE results. Moreover, the AM-RMF waveform along the half air-gap periphery during one electric period is shown in Fig. 2(b). CONCLUSION An AM has been developed for predicting the RMF of SRMs, considering doubly salient laminations, unipolar rectangle currents and magnetic saturations. The calculation results are validated by the FE predictions. In the coming full paper, the details of the method, the flux tube of MEC and saturation factor, the validations on various SRMs with different excitations including overlapped currents, will be presented. A prototype SRM is to be tested.

![](https://assets.underline.io/uploads/markdown_image/1/image/824cbe0d375218c8beaf462fb166234b.jpg)

Fig. 1 Flowchart of AM of RMF.

![](https://assets.underline.io/uploads/markdown_image/1/image/f94362f2599ed11e8d796db183624985.jpg)

Fig. 2 RMF results along air-gap periphery.

technical paper

The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

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Urban air mobility is expected to play a large part in future transportation, where conventional aircraft will be superseded by thousands of highly connected automated airborne vehicles [1]. One of the key barriers to success is the development of reliable lightweight propulsion motors. The conventional method of light-weighting motors uses mechanical gearing to increase motor speed and reduce torque output, however, in this sector the relatively low reliability of the gearbox and potential for catastrophic failure by jamming preclude this method. This paper describes the advances behind a special dual rotor, magnetically geared motor [2] designed for urban air mobility applications. The mechanical gearbox is replaced by a magnetic gearbox that is mechanically and magnetically integrated into the motor itself. The main motor operates at high speed and benefits from the low torque and low motor mass, the integrated magnetic gear reduces output rotor speed and provides a corresponding increase in output torque created by virtue of the extremely high airgap magnetic shear stress available. The magnetic design of this integrated motor is discussed and an exemplar 370Nm, 212mm OD machine is presented. The corresponding thermal design is discussed and loss models linking this with the electromagnetic design are detailed. The design is complimented with advances in mixed material structural design where composites are used within the non-magnetic structural parts. By combining the light-weighting gear effect without the adverse effect on reliability an air-cooled motor with a specific continuous torque density &gt;30Nm/kg is created which is ~30% improvement on the leading competing technology.

Ultra-Lightweight Motors for Urban Air Mobility Propulsion

Autonomous Guided Vehicles (AGVs) have been implemented in modern warehouse aiming for a full automation environment[1]. As any other electric vehicle, AGV requires fast charging of batteries to maintain the workflow on busy warehouses[2], especially when online sales have increased during the pandemic. Wireless charging systems (WCS) can be applied to recharge AGV with low maintenance cost while guarantying the safety of the workforce[3, 4]. However, wireless power transfer (WPT) loss efficiency on large air gaps due to leakage magnetic flux and to the increase of impedance on primary side[5], which require to apply a compensation circuit to optimize the power transfer[6]. This project proposes a novel model for WPT utilizing a DC motor of 2750 RPM and 300 W to spin a disc that has surface mounted permanent magnets (PMs), Figure 1. This disc is composed by 12 square and 12 circular PM, placed in pairs in the disc radius line, with the square PM near the end of the disc and the circular PM 5 mm from the square PM. The adjacent PM pairs have opposite polarity, so that when a coil is placed near this spinning PM disc, the magnetic field will oscillate inducing current on the receiver coil. An investigation on how much current can be harvest through this model is being conducted, also correlating the air gap between PM disc and receiver coils. In addition, the rotation of the PM disc and the induced current on receiver is being evaluated and an analysis of the optimum RPM speed for WPT is being conducted. Finite Element Method (FEM) simulations are being executed and analyzed, currently, a 2D model simulates the movement of the PMs over the coil, which resulted in an alternating induced current of 9A (peak). The main advantage of this model is utilizing the existing magnetic field of PM material, discarding the necessity of applying power to the transmitter, thus eliminating the parasite impedance losses. The system efficiency is expected to be improved in relation to existing WCS.

![](https://assets.underline.io/uploads/markdown_image/1/image/e666dee80dedf45884cc184098b7d1aa.jpg)

Schematic of proposed Rotating Wireless Power Transfer, utilizing a DC motor with a surface mounted magnetic disc coupled to the shaft.



Rotating Permanent Magnet Disc for Wireless Charging Autonomouns Guided Vehicles

Due to the merits of high power density and efficiency, surface-mounted high-speed permanent-magnet machine (HSPMM) is regarded as a competitive candidate for high-speed application of aviation. However, the rotor flux cannot be disengaged when a short circuit (SC) is initiated, so a large interturn SC current of more than ten times of the rated current is usually generated, which seriously threatens the reliability of motor[1]. Recently, numerous studies have been reported concerning the interturn SC fault suppression methods for concentrated winding fault-tolerance PMM[2]. The arrangement sequence of wires was optimized to make the back potential of each coil the same, so that the influence of the position of shorted turns on the value of interturn SC current was eliminated[3]. With use of a new vertical strip windings, the interturn SC current was restrained near rated current[4]. Besides, the typical control methods of injecting flux-weakening current and shorting winding terminals are also investigated to limit the interturn SC current[5]. However, the healthy windings will be sacrificed and a large phase SC current may also be introduced, if shorting all the winding terminals. And the effectiveness of injecting flux-weakening current is extremely dependent on the high-accuracy and rapid detection technology, which is also a great challenge for HSPMM[6,7]. This paper found the characteristic of strong interturn SC fault tolerance of the Gramme-ring-winding HSPMM, providing a solution for HSPMM to high-reliability application. The shorted turns wound around the stator yoke have a very large inductance, so the interturn SC current can be tremendously decreased. For this motor, the analytical models of the interturn SC current and inductance are established. And the principles for characteristic of strong interturn SC fault tolerance is revealed. Then the influences of the position and turns of interturn shorted coil are studied. The analytical models are finally verified by finite-element method. The figures show the cross section of Gramme-ring-winding HSPMSM with one turn of shorted coil and the waveform of winding current. As can been, the interturn SC current is just little higher than rated current.

![](https://assets.underline.io/uploads/markdown_image/1/image/f4f9034f42a5912822ac4f4afeff26cb.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/afe68871289d1d7811de006e539cab9b.jpg)

Research on Interturn Short-circuit Characteristic of the High-speed Permanent-magnet Machine with Gramme-ring Windings

Recently an increasing demand emerges for high-speed permanent magnet motor (HSPMM) in fuel cell compressor application. Overheating is thought as one of the biggest causes for the failure of HSPMM. This paper presents a slotless Gramme-ring-winding HSPMM, so as to reduce the rotor eddy-current loss caused by stator slotting. Besides, it is convenient to fix the slotless windings. However, exposed to the alternating magnetic field of airgap, large AC loss will be generated in the slotless windings. Litz wire, with a high number of individually insulated, small gauge strands separated into bundles and continuously transposed, is employed to control the AC losses associated with high-frequency operation in this paper. Considering the influence of magnetic field of airgap, the analytical model for losses of the litz wire was built based on an external-rotor motor [1]. The components of the losses for litz wire was analyzed in an air-core pulsed alternator, and the diameter was optimized to minimize the loss[2]. Besides, the pitch of litz wire was thought has a great influence on the loss, and the design method of pitch was provided[3]. In addition, the impacts of the litz wire strand shape, such as circular, square and rectangular, were compared on AC copper loss of the HSPMM[4]. Due to the complex structure of litz wire, the calculation method of the equivalent thermal conductivity was given, based on the Gasar porous metal materials. This paper first analyzes the loss of the litz-wire gramme-ring winding based on the FEA methods, considering the different magnetic field of airgap and the outer slots of stator. Then the analytical model for the loss of litz-wire gramme-ring winding is established, and the diameter and shape are optimized to minimize the loss. After that, the thermal analysis model of the litz-wire gramme-ring winding is investigated, and the temperature rise is calculated. Moreover, the influence of diameter and shape of litz wire is also studied. Through the above studies, the design of litz wire is finally provided for the slotless gramme-ring-winding HSPMSM. Fig.1 shows the configuration of the studied motor, and Fig.2 is the distribution of current density in litz wires on different positions.

![](https://assets.underline.io/uploads/markdown_image/1/image/c26e4d7be8939286475fc381ce3c6820.jpg)

Design of Litz Wires for a Slotless High-speed Permanent Magnet Motor with Gramme-ring Windings

Internet of Things devices prompt a rising demand for autonomous and compact power supply generators to sustain low-power wireless sensor nodes. Due to the ubiquity of waste heat in buildings and urban environments, low-grade heat sources are very attractive for applications. Thermomagnetic generators (TMG) can be small and autonomous. Ahmim’s TMG [1] produces 4.2 μW (0.24 mW/cm3 over a 35°C temperature difference. While this device exploits direct thermal contact with both reservoirs, a key element of a thermal device [2], the output power is penalized by a sub-Hertz working frequency. Khol’s TMG [3] produces 118 mW/cm3 at 84 Hz but over a larger temperature difference of 138°C. Their use of 5 μm thick Heusler Alloy films, compared to a 250 μm thick plate of LaFeSi by Ahmim, is an important factor to explain the different in the working frequency. We aim to explore the possibility to use thin films in Ahmim’s TMG while keeping its low temperature difference capability. Ahmim’s TMG has specific characteristics. Firstly, it needs to have a freestanding magnetocaloric film of several micrometers. Our recent work on Gd film deposition has shown a 17 μm film with significant magnetocaloric effect [4]. Secondly, it needs to have a magnetic field source that gives a maximum field variation but also confines the magnetic field in order to reduce the film displacement. By combining Gd films and high performance NdFeB micro-magnets [5], [6] with our design experience on macro devices (Fig.1), we will discuss the key steps of the design, e.g., the spring characteristics to achieve self-oscillating micro-devices. Several parameters need to be optimized, such as the micro-magnet pattern, the air gap and Gd film thickness. 3D numerical simulations of the magnetic force as a function of the material position and temperature (Fig. 2), which are being used to optimize the system design, will be discussed in detail. With our proposed design, if we assume a 50 Hz working frequency, there is 5mW of mechanical energy available.

![](https://assets.underline.io/uploads/markdown_image/1/image/6c8def3c8eadc39bbbf231f211465813.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/d44ec31fe73d8d8565d56c704b72f012.jpg)

Key steps in designing a micro thermomagnetic generator

Key steps in designing a micro thermomagnetic generator

I Introduction Due to the high-power density, simple structure and low cost, switched reluctance motors with amorphous alloy cores (SRMA) are widely applied in electric vehicles [1]. However, its development is limited by the vibration causing by the radial electromagnetic force. This paper proposes a new method to reduce the vibration of SRMA based on the inverse-magnetostriction effect. II Vibration reduction method based on inverse-magnetostriction effect The research in amorphous alloy motor is mainly about the evaluation of core loss and the literature involves vibration is rare [2]. The vibration mechanism of amorphous stator core was revealed through considering the Maxwell stress and magnetostriction stress [3]. However, the effective damping methods have not been involved and the inverse-magnetostriction effect was neglected. A method of vibration reduction for the SRMA is propose in this paper. First, compressive stress in the radial direction is applied to the stator teeth, because the magnetic permeability of the magnetic material will decrease under the action of compressive stress in the same direction. Then, the magnetic permeability is calculated by the nonlinear relationship with the stress. After the definition of the relative permeability of the stator core, the magnetic field distribution inside the motor is obtained. Second, the magneto-mechanical coupling model is established by combining the electromagnetic stiffness matrix and mechanical stiffness matrix to calculate the stress distribution of the stator core as shown in Fig.1(a-b). Third, the vibration reduction effect of the model is verified by the finite element simulation. III Results and discussion The simulation results of the sampling point of the stator teeth is calculated as shown in Fig.1(c-d). And the radial flux density of air gap (Bn) and radial electromagnetic force (Fn) is reduced by 13% and 20% respectively, which shows that the method can effectively reduce the radial electromagnetic force and has a certain damping effect.

![](https://assets.underline.io/uploads/markdown_image/1/image/b9b91cb059fef40d823d3087d758805e.jpg)

Research on vibration reduction method of switched reluctance motor with amorphous alloy cores based on inverse-magnetostriction effect

Research on vibration reduction method of switched reluctance motor with amorphous alloy cores based on inverse-magnetostriction effect

Permanent Magnet Linear Generators (PMLG) are currently studied as a main solution for the conversion of the energy contained in sea waves. Typically, a PMLG consists of an iron-made armature and a moving shaft. Magnets are usually installed on the shaft and the coils on the armature. The moving shaft generates an electromotive force in the coils. Such a machine suffers from a high level of cogging force due to the interfaces between air and iron impairing its overall performance. However, the function of iron in Permanent Magnet (PM) based machines is simply that of driving the flux along a predesigned path. No amplification of the magnetic flux is generated by iron because the flux is generated by the permanent magnet. As a result, a well-tailored design of a PM generator could avoid the use of iron avoiding any permeability difference along with its magnetic circuits and therefore cogging force is completely suppressed. Several questions remain open: how much is the performance of an ironless generator affected by the absence of iron? Which is the comparison between a traditional and an ironless generator? In this paper, we try to address experimentally these questions. We have built two prototypes of PM linear generators that share the same geometry: one of the two is a traditional generator the other is an ironless generator. At first, we have characterized the two machines by measuring the main electrical and mechanical parameters: resistance, reactance, mass, magnetic fields. Secondly, we have performed several open circuit measurements, by measuring cogging force, vibrations, electromotive force when the slider is moving at some given conditions. Finally, we have performed several load tests by measuring cogging force, vibrations, output voltage, current, and output power when the slider is moving at some given conditions. The comparison reported in the paper shows that the performance of the traditional machine is slightly superior in comparison with the ironless one, but an ironless machine does not present any cogging force and is lighter than the traditional one. These features can be a great advantage in the field of sea-wave energy conversion.

An Experimental Comparison Between an Ironless and a Traditional Permanent Magnet Linear Generator

Introduction - Flux-modulated type magnetic gears are expected to be applied as step-up gears for wind-power generation because of their advantages, including high torque density and maintenance-free operation [1]. Among them, an axial-flux magnetic gear (AFMG) has attracted great attention recently since it has a smaller axial length and is easy to assemble. In some cases, magnetic gears are required to have an integer gear ratio based on design requirements of the entire system, which results in larger cogging torque in the high-speed rotor that causes vibration and startup error. In addition, the conventional skew rotor structure is complicated and poor in assembling [2]. To solve the problems described above, this paper proposes two new types of pole-pieces, one is an unequal-width-type, another is an unequal-spacing-type. Two new types of pole-pieces – Fig. 1(a) shows the AFMG [3] investigated in this paper, while the (b) and (c) are the proposed unequal-width-type and unequal-spacing-type pole-pieces, respectively. The gear ratio of this AFMG is an integer of 10 given by the number of pole pairs of the high-speed and the low-speed rotors of 3 and 30, respectively. As shown in Fig. 1(b), pole-pieces with three different circumferential width ratios, which are 0.3, 0.8, and 0.7, are combined in the unequal-width-type, while as shown in Fig. 1(c), the relative position of the pole-pieces is adjusted which leads to an unequal interval structure. Both types are aimed at canceling the cogging torque. The cogging torque is calculated by the three-dimensional finite element method (3D-FEM). Fig. 2 shows the results of the high-speed rotor cogging torque of the two proposed new types, where (a) is of the unequal-width-type and (b) is of the unequal-spacing-type, respectively. As shown in the figure, it is clear that both proposed types can reduce the cogging torque significantly. This work was supported in part by the WISE Program for AI Electronics, Tohoku University.

![](https://assets.underline.io/uploads/markdown_image/1/image/eeec3ec6463607fb1bf5076d040b3ea8.jpg)

Fig. 1 The investigated AFMG and the proposed two types of pole-pieces; (b) unequal width, (c) unequal spacing.

![](https://assets.underline.io/uploads/markdown_image/1/image/9170e6aa71b8e0327dbcb0a6c124a106.jpg)

Fig. 2 The calculated high-speed rotor cogging torque of the two types of pole-pieces; (a) unequal width, (b) unequal spacing.

Cogging Torque Reduction of Integer Gear Ratio Axial-flux Magnetic Gear for Wind-Power Generation Application by Using Two New Types of Pole-Pieces

I. Introduction Stator-permanent magnet (PM) electrical machines are potential for developing as high-speed (HS) electrical machines, due to their advantages of high torque density and robust rotor structure. As one of the most promising stator-PM machines, flux-switching permanent magnet machine (FSPMM) has comparable torque density with the rotor-PM machines and easy thermal dissipation. However, the high fundamental frequency of conventional FSPMM is inevitable, making it difficult to be driven by the power electronics device. In this paper, a novel dual-step 2-phase 4/3 FSPMM is proposed and analyzed. Compared with the traditional FSPMM with the odd number of rotor poles, the proposed structure has good flux linkage waveform, non-UMF and high torque density. II. Design and Performance of the Proposed 4/3 FSPM Machine Fig. 1(a) shows the structure of the novel dual-step 4/3 FSPM machine. With using this structure, it can achieve the least number of rotor poles. The PMs have the same magnetization direction, whereas the winding directions are inverse, as shown in Fig. 1(b) and (c). The two set of windings can be connected in series, therefore it is convenient to drive the machine. The rear rotor is offset by 60° mechanically with respect to the corresponding front rotor. An appropriate gap distance between two stators is necessary to accommodate the end of inverse windings and avoid excessive magnet flux leakage. The flange and chamfering rotor is designed to reduce the cogging torque, as shown in Fig.2 (a). The performance of the novel 4/3 FSPM is obtained by using the finite element method and the parameters optimization method. Fig. 2(b) shows that the UMF of the proposed machine. It can be seen that the UMF of the proposed machine is relatively small. The peak-to-peak value of the cogging torque which varies with width of rotor flange is drawn in Fig.2 (c). The designed machine can obtain minimum cogging torque of 360.71 mNm.


![](https://assets.underline.io/uploads/markdown_image/1/image/cfeb923ad4dd15fdd6d408f889bdb4bb.jpg)

Design and Analysis of a Novel 2-Phase 4

![](https://assets.underline.io/uploads/markdown_image/1/image/c9e1a53d9fd13df6d0243077e46d6a55.jpg)

3 FSPMM with Chamfering and Flange Rotor Poles

Design and Analysis of a Novel 2-Phase 4/3 FSPMM with Chamfering and Flange Rotor Poles

Doubly salient brushless DC (DSBLDC) machine has been attracting much attention for aviation and vehicular applications, owing to its simple structure, adjustable flux, and reliability. Despite those merits, the torque ripple of DSBLDC machine limits its applications at medium-and-low speeds. The current harmonic injection (CHI) method has been proposed to reduce torque ripple, dealing with the subsequent issue, such as vibrations, acoustic noise, even starting failure. The traditional CHI choice of odd order harmonics to limit torque ripple is almost useless for the 3-phase 12/8-pole DSBLDC machine, due to the excitation and armature winding configurations, which generate its unique magnetic circuit and inductance characteristics. Firstly, A new instantaneous torque model from the perspective of harmonics has been derived. The main components of the excitation inductance are the 1st, 2nd and 4th harmonics. Only the armature current harmonics interact with the same-order inductance harmonics can contribute to the average torque, otherwise it will lead to torque harmonics. Thus, a harmonic injection algorithm based on the 2nd and 4th current harmonics is proposed to reduce the torque ripple. Fig.1(a) shows the topology of the DSBLDC machine, which is marked by the concentrated stator-field-winding and the absence of rotor excitation. Experiment platform is shown in Fig. 1(b). The instantaneous torque as shown in Fig. 1(c) can be divided into two parts: average torque and torque ripple, which is used to solve the current amplitude and phase parameters of injected current as shown in Fig.2(a). Fig.2 shows the solution based on the harmonic injection algorithm. Case I contains only the fundamental wave. The 2nd harmonic is added into Case II. Case III contains the 1st, 2nd and 4th harmonics, reducing the torque ripple from 54.84% to 44.28%. The torque waveform and its FFT results are shown in Fig. 2(b) and Fig. 2(c). Using the system diagram in Fig. 2(d) can experimentally validate the foregoing simulation, the partial result about Case I is given in Fig. 2(e).

![](https://assets.underline.io/uploads/markdown_image/1/image/06ff416686f82ddb1613b73f4d429ccc.png)

Fig.1 topology and torque model of the 12/8-pole DSBLDC machine.


![](https://assets.underline.io/uploads/markdown_image/1/image/9986831376a4f2901d749908e3201fc4.jpg)

Fig.2 simulation and experimental results based on the harmonic injection algorithm.

Analytical Model of Radial Magnetic Force in Switched Reluctance Machines with Consideration of Magnetic Saturations

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