Magnetic Gear Research Articles

Design, Fabrication, Test, and Benchmark of a Magnetically Geared Permanent Magnet Generator for Wind Power Generation

Magnetic gears with an integrated permanent magnet machine provides advantages within the field of wind turbine drive trains compared to both mechanically geared generators due to non physical contact between rotors as well as direct driven generators where size and weight can be reduced. Theoretical and practical benchmark of the technology against commercial direct drive generators with regards to material use and performance is yet to be found in the literature. In this article, a magnetically geared permanent magnet generator is designed with operational specifications based on a commercial 3.5 kW permanent magnet generator designed for direct drive wind turbines. A demonstrator is fabricated and the design models are validated experimentally. Performance and material use for both the demonstrator and the direct drive generator is mapped. The experimentally verified results are used for benchmarking and the comparison shows promising results as both size and weight is significantly reduced for similar performance. It is also found that the material consumption is reduced, and contrary to popular belief, the use of magnet material in the magnetically geared machine is actually less than that of the benchmark generator.

Loss estimation of magnetic gears

Reduction in losses is essential for the efficiency enhancement of magnetic gears. In this paper, the power losses of a coaxial magnetic gear are estimated, based on a developed convenient approach for loss analysis using a time-dependent finite element model. The results are confirmed by a sophisticated measurement system for magnetic gear testing. Eddy current losses in permanent magnets and magnetic cores, magnetic flux reluctance and harmonic distortion in magnetic materials during magnetic gear operation are determined. The output torque reduction, especially at high rotational speeds and high gear ratios caused by losses, is analyzed. Different permanent magnet material grades are utilized in order to evaluate the eddy currents and the torque transmission losses during the magnetic gear performance.

Magnetic Loss Analysis in Coaxial Magnetic Gears

This paper proposes a procedure for computing magnetic losses in coaxial magnetic gears. These magnetic structures are made of permanent magnets and ferromagnetic poles in relative motion transferring torque between two shafts in a contactless way. The loss computation in magnetic materials is crucial to define the system performance. The flux distribution inside the iron parts is computed by means of the finite element method and a model of iron losses taking into account the rotational nature of the flux loci is applied. The procedure highlights where the major loss sources are present and gives the opportunity to evaluate some corrective measures to reduce their effects. Particular attention is devoted to the 2D modeling in presence of permanent magnets segmentation.

Design and analysis of a two‐stage transmission magnetic‐geared machine

The purpose of this paper is to realize a two‐stage transmission magnetic‐geared (2‐STMG) machine with high gear ratio. The proposed machine contains a concentric magnetic gear (CMG) and a Vernier machine (VM). Both the components meet the magnetic gearing effect and share a common high‐speed rotor (HSR). The VM is the first stage, and the CMG is the second stage. The designed gear ratio of the proposed 2‐STMG is 34. The magnetic flux is partially coupled to the HSR yoke. The cogging torque on the HSR is slightly higher than that on the low‐speed rotor (LSR). A method is presented to detect the gear ratio of magnetic geared machines with the back‐electromotive force (back‐EMF). And the evaluated gear ratio of the prototype is found to be close to the design value. The amplitude of the fundamental back‐EMF is nearly linear with the LSR speed, and the slope of the fitting curve is ∼0.16 V/rpm. The peak static torques on both rotors are positively correlated with the DC currents applied to windings but limited by saturation when current is larger than 4A. The 2‐STMG machine is controllable, and the speed ratio of HSR to LSR is close to the gear ratio of the outer CMG. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Design and Analysis of Coaxial Magnetic Gear Mechanism with Halbach Permanent-Magnet Array

The disadvantages of mechanical gear can be replaced by the advantages of magnetic gear related to transferring torque without mechanical touch, no gear lubrication, low mechanical loss, low vibration, and intrinsic overload protection. From the types of magnetic gear, coaxial magnetic gear is the most developed type. Halbach permanent-magnet arrangement in coaxial magnetic gear mechanism can offer higher on transmitted torque and also capable of increasing the magnetic field compared to radially magnetized. Then this paper aims to carry out the characteristic of coaxial magnetic gear with Halbach magnetized in steady-state condition. Furthermore, magnetic field and transmitted torque were investigated by commercial software ANSYS/Maxwell. Finally, by using 2D finite element method, the result shows the maximum torque with 2150.76 Nm.

An Axial Flux Focusing Magnetically Geared Generator for Low Input Speed Applications

An axial-flux magnetic gear (MG) is integrated into a radial field stator to construct a unique magnetically geared generator for low input speed applications. The high-speed rotor of the axial-flux MG uses a flux-focusing typology. This article presents the stator design and experimental testing of this unique proof-of-principle axial-flux focusing MG generator. The peak torque and active region torque density were measured to be 473 N m and 94.4 N m/L, respectively. The stator of the proposed machine shares the high-speed rotor with the axial-flux MG. Therefore, there is no need for a separate rotor. It is shown that the stator can also be used to provide additional flux into the MG in order to boost torque during transient overshoots.

Design and Characteristics Analysis of Coaxial Magnetic Gear for Contra-Rotating Propeller in Yacht

In this article, the design and characteristic research of the coaxial magnetic gear for the contra-rotating propeller in the premium yacht are presented. The scale-down model of 1/25 is reviewed as the research of the applicability of the coaxial magnetic gear. The space harmonic characteristics of the magnetic field in the coaxial magnetic gear with the low gear ratio from 1 to 2 are investigated, and the optimized models with the surface-mounted permanent magnet and quasi-Halbach array are obtained using the response surface method. In the several operating points of the diesel engine, the magnetic loss and the resultant thermal characteristics are analyzed and compared in each model. Finally, the desired coaxial magnetic for the contra-rotating propeller in the premium yacht is achieved.

Equivalent Circuit for the Trans-Rotary Magnetic Gear

This letter proposes an equivalent circuit for the trans-rotary magnetic gear. The circuit is presented for both impedance and admittance analogies. In both analogies, the gearing effect is modeled by a transformer. The gear's compliance is modeled by a parallel capacitor in the impedance analogy and by a series inductor in the admittance analogy. As an example, the proposed equivalent circuit is coupled to the equivalent circuit of a backpack energy-harvesting system to create an all-electric equivalent for the energy-harvesting system. The resulting all-electric equivalent circuit provides insight into system dynamics and control strategies. Moreover, the proposed circuit can be readily extended to other types of magnetic gears.

Influence of Gear Ratio on the Performance of Fractional Slot Concentrated Winding Permanent Magnet Machines

Fractional slot concentrated winding (FSCW) permanent magnet synchronous machines (PMSMs) have been a research hotspot over the past few decades. Recently, the magnetic gearing effect in FSCW PMSMs is revealed along with its gear ratio, which is a function of slot/pole number combination. At the design stage of FSCW PMSMs, one of the key issues is the selection of the slot/pole number combination. This paper shows that the gear ratio can contribute to a proper slot/pole number selection in any multiphase FSCW PMSMs by acting as a unified index for a quick overall performance comparison. In this paper, first, the magnetic gearing effect in FSCW PMSMs is explained and the gear ratio is further discussed. The advantages of adopting gear ratio as the overall performance index over other indices are revealed. The influence of the gear ratio on the winding factor, torque output, cogging torque, inductance, and rotor losses of three- and six-phase FSCW PMSMs is analyzed and validated by experiments, thus proving the analyses.

A Review on Magnetic Gears: Topologies, Computational Models, and Design Aspects

Geared devices are commonly used to match the operating speed and torque of the power source with the second mover. Such geared devices are usually mechanical gears. As counterparts of the conventional mechanical gears, magnetic gears (MGs) are becoming promising devices, mainly due to the merits of physical isolation between moving parts, no gear lubrication, no mechanical fatigue, inherent overload protection and reduced maintenance, etc. Recently, several new topologies have been proposed to achieve better performances. In this paper, a general review of MGs is presented, including a discussion of the most common and upcoming topologies and a description of the working principle. A comparison of different topologies is carried out in terms of gear ratio and torque density. The main computational techniques generally adopted for coaxial MGs are listed and described. Some key aspects concerning the design, the existed challenges, and potential applications are also discussed. This paper aims to provide a comprehensive overview of the MG for readers working in this field.

Electromagnetic Analysis and Experimental Testing of a Flux Focusing Wind Turbine Magnetic Gearbox

The electromagnetic design of the second stage of a 59:1 multistage magnetic gearbox for a wind turbine demonstrator is presented. The multistage series connected magnetic gearbox is composed of a 6.45:1 first stage and 9.14:1 second stage magnetic gear. The magnetic gears utilize a flux focusing spoke type rotor typology with a unique segmented fully laminated design. The electromagnetic impact of structural design changes on the second stage gearbox is considered with respect to torque density. Severe three-dimensional edge effects were encountered that greatly reduced the expect torque density of the second stage magnetic gear. Experimental testing of the multistage magnetic gear highlights unexpected problems associated with eddy current loss and torque ripple.

In-tube condensation heat transfer characteristics of CO2 with N2 at near critical pressure

The condensation heat-transfer coefficient and pressure drop for pure CO2 and CO2 + N2 mixtures were investigated under the near-critical condition, which simulates the CO2 transporting conditions under Carbon Capture, Transportation, and Storage (CCS). The experimental apparatus consists of a test section, heat exchangers, mass flow meters, temperature sensors, a magnetic gear pump, and a differential pressure transducer. The test section made with a copper tube was assembled with Polyvinyl Chloride (PVC) pipe to form a double tube. The condensation temperature and mole fraction of N2 of the CO2 mixtures ranged from 20 °C to 30 °C, and 1 to 5%, respectively. The mass flux was changed from 500, 600 and 700 kg·m−2s−1. The average heat transfer coefficient of the CO2 + N2 mixtures decreased by 2.23 to 15.9% based on the average heat transfer coefficient of pure CO2, and the pressure drop decreased by 53.4 to 77.3% at the condensation temperature of 25 °C with increase of the mole fraction of N2.

Intelligent Maximum Power Tracking Control For a Wind Energy System Based on Magnetic Gear Generator

This paper studies maximum wind power extraction from magnetic gear generator using an artificial neural network for the wind energy system. High speed can be reached with this representation either with magnetic gear generator, under low wind conditions often found inland, or without mechanical gear. In order to track maximum power, the artificial neural network controller adjusts the outer rotor speed, and thus, inner rotor speed. The proposed system is supported by simulation results.

Design and Analysis of a Novel Dual-Stator Cylindrical Linear Vernier Machine With LTS Field Windings

The cylindrical linear vernier machine (CLVM), in which the magnetic gearing effect is adopted, is a specific kind of the linear vernier machines (LVMs) and is suitable for the direct-drive applications that both low speed and high thrust are demanded at the same time. In order to further improve the thrust density of the LVMs, a novel dual-stator CLVM with low-temperature superconducting field windings (DCLVM-LTS) is proposed and analyzed in this paper. The operation principles of the DCLVM-LTS will be introduced in the paper by the analysis of the air-gap flux density. The superiorities of the proposed DCLVM-LTS are calculated by the finite element method. Compared to a DCLVM with PM arrays, the thrust density of the proposed DCLVM-LTS exhibits a considerable improvement in terms of thrust density, power factor, and economy efficiency.

A Novel HTS Modulated Coaxial Magnetic Gear With Eccentric Structure and Halbach Arrays

In order to improve the high torque density of coaxial magnetic gear, a novel high temperature superconducting (HTS) bulks coaxial magnetic gear (CMG) with an eccentric pole of inner rotor and Halbach arrays of outer rotor is proposed in this paper. According to the Meissner effect, the HTS bulks replace the traditional epoxy resin to improve the flux-modulation effect. Moreover, the HTS bulks CMG has an eccentric structure of permanent magnets (PMs) on inner rotor and has Halbach PMs arrays on the outer rotor. The proposed HTS bulks CMG topology with 4 inner and 23 outer pole pairs is established. The topology performance is assessed and verified by finite element analysis.

A Novel HTS Claw-Pole Vernier Machine Using Single Excitation Unit With Stationary Seal

This paper proposes a novel high-temperature super-conducting (HTS) claw-pole vernier machine, which combines the merits of stator HTS-excitation machine with the “magnetic gearing effect” designed for direct-drive applications. The key is to adopt claw-pole stator structure to realize the multi-pole pattern using single HTS-excitation unit with stationary seal, thus greatly simplifying the cooling Dewar architecture as well as improving the structural compactness. Moreover, the armature windings are wound around the split-teeth which are set on the surface of claw poles to achieve the physical separation from the HTS-excitation coil, thus reducing their space conflicts and impact with each other. The operation principle analysis and the initial machine design are conducted in details. By using the three-dimensional finite element analysis, the machine performances are evaluated, and its validity is verified.

Linear magnetic gear with HTS bulks for wave energy conversion

This study proposes a linear magnetic gear (LMG). Unlike conventional LMGs, the proposed one purposely uses high-temperature superconducting (HTS) bulks replace permanent magnets (PMs). The high-speed mover of the magnetic gear is connected to the secondary of the linear permanent magnet generator (LPMG), which constitutes a direct-drive wave power system that converts wave energy into electrical energy. First, the LMG structure is presented according to the principle of magnetic field modulation, and the authors briefly analyzed the number of pole pairs of inner, outer, and ferromagnetic modulators. Second, they also established a finite element analysis model to analyze the performance of magnetic gear, including magnetic field distribution, radial air gap magnetic flux density, and force characteristic. An LMG with HTS bulks not only increased the radial air gap magnetic flux density but also improved the speed of LPMG. In conclusion, this experiment verifies the efficacy of direct-drive wave power take-off system and effectively converts wave energy into electrical energy.

Parametric Design and Optimization of Magnetic Gears With Differential Evolution Method

Recently, magnetic gears have drawn wide attention due to their inherent merits, such as noncontact operation, high torque density, and intrinsic overload protection. In this paper, an analytical calculation based on magnet magnetomotive force permeance theory is adopted to analyze the modulation effect in a magnetic gear. After that, the effects of some key parameters on magnetic gear performance are investigated, including the air-slot-opening-to-pole-pitch ratio $c_0$ , the magnet-arc-to-permanent-magnet-pole-pitch ratio $\alpha$ , and the permanent magnet thickness $h_m$ . In particular, three types of steel pole pieces are considered: radial slots, parallel teeth, and parallel slots. A global optimization design is then carried out by using the differential evolution algorithm, and some useful suggestions are derived from the optimal Pareto range. Finally, the determination of outer rotor yoke thickness is discussed considering the iron saturation, and the iron loss distribution is investigated. This paper will be helpful for the design and optimization of a coaxial magnetic gear.

Leakage Flux of the Trans-Rotary Magnetic Gear

This paper investigates the leakage flux of the trans-rotary magnetic gear (TROMAG). TROMAG is a magnetic gear that converts a high-force low-speed linear motion to a low-torque high-speed rotation and vice versa. TROMAG is tailored to force-intensive linear motion applications such as backpack energy harvesting and artificial heart in which the gear is positioned close to the human body and/or electronic devices. In such applications, it is critical to ensure the TROMAG’s magnetic field penetrating the surrounding environment (referred to as the leakage flux hereafter) is below the limits permitted by standards. This paper employs 3-D finite-element analysis (FEA) to study spatial distribution and magnitude of the leakage flux. The FEA calculations of magnetic field are verified by experimental measurements. Both radial and quasi-Halbach configurations are investigated, and it is revealed that the quasi-Halbach configuration exhibits less leakage flux. Moreover, it is shown that the use of a thin iron shield surrounding the TROMAG can effectively reduce the leakage down to permissible values.

Investigation into linear generators with integrated magnetic gear for wave energy power take off

This work presents a new wave energy converter power take off (PTO) system that combines two recent developments in drive train technology, the consequent pole linear vernier hybrid permanent magnet machine and the linear magnetic gear. The combined system is fully realised in three-dimensional finite element method and compared to a similar direct drive machine. While the resulting system is lighter, reducing the active material mass by 30%, and more efficient, the system requires larger amounts of high cost permanent magnet material and increased PTO complexity. It is summarised that while such a system could be recommended in certain conditions, it is not viable for general application.