Magnetic Gear Research Articles

Electromagnetic Analysis of Linear Magnetic Gears Based on the Characteristics of Their Flux-Modulation Poles

Magnetic gears (MGs) are energy converters that have recently received attention because of their advantages over conventional mechanical gears. Prior studies focused on MGs without mechanical losses, and research on linear MGs has focused on tubular structures. Therefore, in this study, we analyzed the electromagnetic characteristics of the materials used in flux-modulation poles. In addition to comparing the electromagnetic characteristics of each material, an equivalent stress analysis was performed. Finally, the proposed model was fabricated, and experimental verification was performed.

Comparison of Magnetic Gear Characteristics Using Different Permanent Magnet Materials

In the coaxial magnetic gear, the permanent magnets of each rotor face each other, and the driving frequency of each rotor has different values according to the gear ratio. The magnetic flux that changes with time is transmitted to each permanent magnet. If the permanent magnet has conductivity property, losses by eddy currents are occurred in the permanent magnet. It is a major loss of a magnetic gear. Because the loss causes demagnetization by heat, it is mentioned a fatal problem at high speed. In this paper, the characteristics were analyzed by applying permanent magnets without conductivity. In addition, the analysis of the electromagnetic field as well as the mechanical loss were also considered to show which magnet type is advantageous.

Design and Optimization of a Partitional Stator Flux-Modulated Memory Machine

In this article, a partitional stator flux-modulated memory machine (PS-FMMM) is proposed. Compared with a conventional variable-flux memory machine, it can significantly improve the torque density due to magnetic gear effect and PS, and can have good flux-regulating capability with AlNiCo magnets. First, the basic principle of the proposed PS-FMMM is introduced, and different combinations of stator poles and rotor poles are compared. Then, the torque-regulating characteristics of the proposed PS-FMMM under different magnetization levels of AlNiCo magnets are obtained. Finally, the pole-arc ratio of iron piece and parameters of AlNiCo magnets are optimized based on sensitivity analysis. Various finite-element analysis (FEA) simulation, optimization, and comparison studies of the proposed machine are performed. The results verified the effectiveness of the proposed structure.

Strucsture and Electromagnetic Characteristics of Pole-Piece Support Materials in Magnetic Gear

Studies on coaxial magnetic gears (CMGs) have been actively conducted. CMGs can replace mechanical gears because they can perform noncontact power transfer minimizing loss and damage from friction. In the design stage of a CMG, 2D electromagnetic finite element analysis (FEA), which is a highly reliable and cost-saving tool, is widely used. However, during prototyping and testing in the review phase of a project, the prototype's pull-out torque is lower than the pull-out torque predicted from 2D electromagnetic FEA, with up to a 40% difference. One explanation for this phenomenon is that the torsional stiffness of the pole-piece structure is low, causing the electrical angle to skew. There are high-frequency magnetic fluxes in the pole-piece structure in which magnetic losses are expected to be high. In many studies, non-metal pole-piece supports that can minimize this magnetic loss were used. The disagreement between analysis and experiment has been demonstrated, but no detailed examination of this effect has been conducted. In this study, metal pole-piece supports are used to remove the torsion possibility. Results from 3D-FEA and experiments are compared, and the results reveal that when torsion is accounted for, the analysis data can be reproduced the experimental data well or not. Furthermore, the magnetic loss on metal supports is analyzed in detail.

An Asymmetric Pole Coaxial Magnetic Gear With Unequal Halbach Arrays and Spoke Structure

In this paper, a novel asymmetric pole coaxial magnetic gear (CMG) with unequal Halbach arrays and spoke structure is proposed to improve the output torque of CMG. The inner rotor has an asymmetric N-S pole structure, the permanent magnets (PMs) on the inner rotor of the CMG are arranged in Halbach arrays with unequal magnetic poles, and PMs on the outer rotor are Spoke-type. According to the flux modulation effect, the contents of higher harmonics can be reduced and the output torque of the proposed CMG can be significantly improved compared to the conventional CMG with radial magnetization. The proposed CMG topology with 4 inner and 17 outer pole pairs is established. The proportional relationship between N pole and S pole is introduced. Then, the air gap flux density, electromagnetic torque, harmonic component of the CMG are investigated and verified by finite element analysis.

Development of spoke-type IPM magnetic gear

Magnetic gears can change output-torque and -speed without any mechanical contacts. Therefore, they have a low acoustic noise and vibration, and their maintainability and reliability are high. Especially, a flux-modulated type magnetic gear is expected to be put into practical use because its torque density is higher than that of other magnetic gears. For the practical use, further improvement of torque and losses is important, especially, reduction of eddy current loss in permanent magnets (PMs) due to asynchronous harmonic magnetic fluxes is necessary. This paper investigates an interior permanent magnet (IPM) structure to improve the efficiency by reducing the eddy current loss in PMs. In addition, this paper presents a method for increasing torque of the IPM magnetic gear by changing a position of magnetic-bridge.

Performance analysis of magnetic gear with Halbach array for high power and high speed

In this study, we propose a non-contact 80 kW, 60,000 rpm coaxial magnetic gear (CMG) model for high speed and high power applications. Two models with the same power but different radial and axial sizes were optimized using response surface methodology. Both models employed a Halbach array to increase torque. Also, an edge fillet was applied to the radial magnetized permanent magnet to reduce torque ripple, and an axial gap was applied to the permanent magnet with a radial gap to reduce eddy current loss. The models were analyzed using 2-D and 3-D finite element analysis. The torque, torque ripple and eddy current loss were compared in both models according to the materials used, including Sm2Co17, NdFeBs (N42SH, N48SH). Also, the structural stability of the pole piece structure was investigated by forced vibration analysis. Critical speed results from rotordynamics analysis are also presented.

Analytical Method for Magnetic Field of Eccentric Magnetic Harmonic Gear

Eccentric magnetic harmonic gears (EMHG) can achieve high speed ratio transmission and large torque output by modulating the air gap length between permanent magnets (PM). The analytical method is based on the boundary perturbation method. The vector magnetic potential perturbation equation in the air gap region is established, and the general solution is obtained using the boundary conditions. According to the superposition principle, the air gap flux density of stator and rotor PMs acting alone is synthesized, and the electromagnetic torque and unbalanced magnetic pull are calculated. Last, we compare magnetic field distributions, electromagnetic torque and unbalanced magnetic pull computed by the analytical method with those obtained from finite-element method (FEM).

Functional Analysis Diagram of a Flux Modulated Magnetic Gear

The reliability of a system is generally done by a functional analysis (FA), whose mission is to provide a deep understanding of the object to be designed, to discover all the valuable solutions, modes, and configurations, and finally to choose the best options for the system’s design. Functional analysis is then matched with a dysfunctional analysis, such as Failure Modes and Effects Analysis, to foresee and take measures to avoid the possible dysfunctionalities of the system and to determine the most suitable model. In this paper, the functional analysis diagram (FAD) is used in the conceptual phase of the design process of a Flux Modulated Magnetic Gear.

Improved design and experimental verification of linear magnetic gear using parametric analysis

This study aims at improving the design of a linear magnetic gear (LMG) and verifying its reliability using a fabricated prototype. LMGs represent electromechanical energy-conversion machines employing permanent magnets (PMs). However, given the linear structure of power-transmission devices, LMGs are difficult to manufacture. The proposed study presents an LMG-design aimed at facilitating ease of its manufacturing. To this end, the PM-ratio performance was first analyzed for selection of an appropriate basic model, which can be subsequently optimized by changing the PM-shape and flux-modulation poles to realize optimum electromagnetic characteristics. Moreover, mechanical characteristics of the optimized model were analyzed to aid fabrication. Results of finite-element analyses and experiments performed in this study on a fabricated prototype demonstrate the reliability of the proposed model.

Characteristics of Interior Permanent Magnet Magnetic Gear made of Amorphous Alloy

Characteristics of Interior Permanent Magnet Magnetic Gear made of Amorphous Alloy

Development and Testing of a Novel Cylindrical Permanent Magnet Linear Generator

Vernier hybrid machines (VHMs) are known for their simple salient translator structure and inherent magnetic gearing, making them a strong candidate for low-speed, high-force applications. As both the armature coils and the permanent magnets (PM) are mounted on the stator, linear versions of this machine are attractive for applications with a large stroke amplitude. In most configurations, single-sided or double-sided flat cross sections are utilized, giving a two-dimensional flux path. In this article, a cylindrical variant of the double-sided flat configuration is presented, where the flux path is now three dimensional. Three-dimensional finite-element analysis is used to design, analyze, and compare both flat and cylindrical topologies for a fixed PM mass and current density. Details and test results of a soft magnetic composite based laboratory prototype of the cylindrical VHM are given, which demonstrate the concept and validate the simulation results.

A new HTS dual stator linear permanent magnet Vernier machine with Halbach array for wave energy conversion

In this paper, a high-temperature superconductor-dual stator linear permanent magnet Vernier machine (HTS-DSLPMVM) with Halbach array has been proposed for wave energy conversion. In order to better investigate, this machine has been compared to the prototype double stator linear permanent magnet Vernier machine (DSLPMVM). Both of the machines operate based on magnetic gear effect. At lower speeds they have the ability to produce a high thrust force. DSLPMVM and HTS-DSLPMVM have the same structure. So that, DSLPMVM and HTS-DSLPMVM consist of two stators and one translator with a three-phase concentrated winding. Each phase has been located independently on the translator. Also, permanent magnet (PM) Halbach array with appropriate magnetic direction mounted among the slot of the translator. The innovation of the proposed machine is that HTS-Bulk is located between the slot of the stators to shield the leakage flux. The operation of the two machines has been compared and analysed using the finite element method (FEM). Results show that, HTS-Bulk makes back-EMF, air gap flux density, power factor and thrust force to increase significantly and inductance to decrease, which effectively improves the machine operation.

다상 전류 중첩을 이용한 기어비 가변 마그네틱 기어의 토크 조절

By controlling the speed of one layer of a concentric magnetic gear, we can change the ratio of the rotational speed between the other two layers, which are composed of permanent magnets and ferromagnetic steel. This results in torque ratio between the layers that is not the inverse of the speed, unlike in a general speed reducer. The value of the torque ratio is determined from the pole ratio of the permanent magnets and steel teeth constituting the layers. In this study, we propose experimentally verified method of varying the torque of the output layer of a variable speed magnetic gear by superimposing another polyphase power source on the control coil. By setting the torque ratio inversely to the speed, constant power can be maintained and some of the coil’s power can be supplied to the output side.

Design and analysis of a new partitioned stator flux‐modulation motor for direct drive applications

In this study, in order to improve the torque density of the conventional permanent magnet (PM) motor, a flux-modulation (FM) motor employing the magnetic gear effect is proposed. However, the FM motor has space conflict in the finite stator area, which limits the further improvement of torque density. Therefore, a new partitioned stator flux-modulation (PSFM) motor with separated PM excitation and armature windings is artfully proposed. The main design parameters influence on the average electromagnetic torque in the proposed PSFM motor is investigated, together with the proposed FM motor. Furthermore, based on the optimal designs for the highest average electromagnetic torque in this study, the electromagnetic performances of the three motors, including back-electromotive force performances, torque characteristics and several other performances with respect to speed are analysed by finite-element method. Additionally in the PSFM motor, torque generation mechanism and the reduction method of torque ripple are theoretically analysed. Results show that the proposed PSFM motor exhibits 29.1% higher torque density than the FM motor and 87.6% higher than the conventional PM motor with reduced torque ripple and superior loss performance. Finally, the proposed PSFM motor is prototyped for verification.

Magnetic Design Aspects of the Trans-Rotary Magnetic Gear Using Quasi-Halbach Arrays

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.

Investigation of Doubly Salient Structure for Permanent Magnet Vernier Machines Using Flux Modulation Effects

Recently, the permanent magnet vernier machine (PMVM) is studied extensively because of its merits such as the high torque density. Similar to the magnetic gears, the PMVM operates on the principle of flux modulation. However, there is a distinct difference in between the two as unlike the magnetic gear, in case of PMVM, the winding MMF harmonics rotates with different speed as that of the fundamental. As a result, these harmonics are capable of making a working magnetic field by interacting with different permeance harmonics. Therefore, this paper aims to provide an analytical explanation of this whole process, which is helpful to understand the effect of the flux modulation on the output torque. Furthermore, using the analytical formulation, this work finds the optimal geometric parameters which maximize the working magnetic field and hence the torque. A detailed analysis of the PMVM with the doubly salient structure is studied and the performance is analyzed using the finite element method (FEM) and the experimental setup. The FEM and experimental results verify the maximum torque production by using the optimal geometric parameters in the PMVM modeling, obtained using the analytical formulation.

Investigation on Magnetic Force of a Flux-Modulated Double-Rotor Permanent Magnet Synchronous Machine for Hybrid Electric Vehicle

Flux-modulated double-rotor (FMDR) machine topology has recently attracted much attention, particularly for the hybrid electric vehicle (HEV) propulsion. To maintain the driving stability and safety of the vehicle, the analysis of the magnetic force and the evaluation of the vibration performance for such kind of machine are indispensable. However, for the FMDR machine with the magnetic-gearing (MG) effect, there are at least two rotating magnetic fields with different speeds and frequencies. This leads to the complicated time harmonics of the radial force density. Actually, the publications on the FMDR machine hardly take into account the magnetic force or vibration characteristics. In this article, the sources, variations, and different kinds of magnetic forces are thoroughly investigated for a proposed FMDR machine. First, the machine topology and operation principle are introduced. Second, the theoretical analysis of the flux density and radial force density is implemented from the harmonic point of view, which is followed by the finite-element simulation, comparison, and validation. Also, an effective solution is proposed and discussed for the problem of different mixed electrical frequencies in the machine. Finally, the distributions of different kinds of magnetic forces appearing in the FMDR machine are concluded.

Design and Finite Element Analysis of Novel Two-Stage Magnetic Precession Gear

Design and Finite Element Analysis of Novel Two-Stage Magnetic Precession Gear

Rotor Pole Design of Radial Flux Magnetic Gear for Reduction of Flux Density Harmonics and Cogging Torque

This article focuses on a novel design of rotor topology for an interior permanent magnet superconductive radial flux magnetic gear to achieve sinusoidal air-gap flux density and lower cogging torque. The method is based on optimization of buried magnet's pole shape in a radial flux structure, modified by using a pulsewidth modulation technique and variable air-gap length applying the supershape formula on the iron core of the inner rotor. The unsatisfied harmonic contents of the air-gap flux density can be reduced with this technique while the main harmonic component and average torque can be maintained or enhanced. The key idea is to set the distribution of the air-gap flux density by segmenting the pole shoe into several elementary blocks and predetermined grooves based on a special curve. Superconductor bulks are placed between pole pieces of modulator ring to improve the flux-modulation effect and decrease cogging torque percentage. The computation of the block sizes and effects of variation of supershape formula parameters are performed by solving a constrained optimization problem. Results show that the radial air-gap flux density harmonics are eliminated, leading to almost sinusoidal air-gap flux density and lower level of cogging torque.