Radial Flux Research Articles

Quantitative comparison of low-cost electrical machines with soft magnetic composite and ferrite magnet materials

Because of its special structure and manufacturing process, the soft magnetic composite (SMC) material has shown its advantages over silicon sheets, including magnetic and thermal isotropy, low high-frequency core loss, low material wastes during its manufacturing process, etc.. Considering the price of SMC raw material can be very cheap in the future, it is an ideal material for developing the low-cost electrical machine. Combined with SMC cores and low-cost ferrite magnets, some electrical machines with SMC and ferrite magnets for low-cost applications were developed in the past decades, which include the transverse flux flux switched permanent magnet motor (TFFSPMM), axial flux claw pole permanent magnet motor (AFCPM), axial flux vernier motor (AFVM), dual rotor axial flux permanent magnet motor (DRAFM) and axial radial flux permanent magnet motor (RAFM). To better utilize SMC material, all these machines are designed following the design guidelines of SMC machines. Though both of them with good performance for low-cost applications, it is necessary to know the main advantages of each machine. The main target of this paper is to compare these machines quantitatively. For obtaining the comparison results fairly all these machines are optimized by using the sequential robust Taguchi method. Finally, it can be seen that the AFVM and TFFSPMM are with relatively high torque ability and the DRAFM is with high efficiency and power factor ability.

Performance Analysis of HTS Armature Axial Flux Magnetic Field Modulation Direct Drive Wind Generator

Axial flux electrical machine has higher power density than the radial flux electrical machine, showing a promising application in the field of offshore wind power generation. However, the conventional copper armature winding will suffer from severe joule loss when improving the electrical loading, resulting in that the further improvement of the power density of axial flux electrical machine is limited. In order to overcome the limitation of the electrical loading improvement of the copper armature winding, this paper uses the high-temperature superconducting (HTS) armature winding instead of the conventional copper armature winding, proposes an HTS armature axial flux magnetic field modulation direct-drive wind generator (HTSAAFFM-DDG). In this paper, the topology and operational principle of the proposed HTSAAFFM-DDG is clearly demonstrated. Meanwhile, the electromagnetic performances are carefully analyzed, including airgap magnetic field, basic electromagnetic characteristics, and AC loss analysis of the HTS armature winding. The research results show that the torque density of the proposed HTS armature axial flux machine can be 24% higher than that of the copper armature axial flux machine with the same size and topology. Besides, the superconducting (SC) shielding layer used in the proposed HTSAAFFM-DDG exhibits an excellent inhibition effect on the PM excited field, and can reduce the AC loss of the armature winding obviously.

Implementation of Different 2D Finite Element Modeling Approaches in Axial Flux Induction Motors

Axial flux induction motors (AFIM) are gaining popularity due to their higher torque density than radial flux motors. However, axial flux motors have a more complex structure than radial flux motors due to their diameters expanding from the inside out. Before manufacturing, designers have two contradictory goals in the simulation phase. These are high accuracy and short analyses time. The finite element method is a commonly utilized technique for verifying designs. However, in the early stages of AFIM design, a 2D radial flux modeling approach can yield faster results. This approach is well-suited for radial motors, where 2D analysis is widely employed to achieve accurate designs within reasonable analysis times. However, for AFIM with a non-axisymmetric flux path, the application of 2D analysis poses some difficulties. This study compares three modeling approaches, linear, inner rotor and outer rotor modeling approaches to a 3D model and examines their steady-state performance. The results show compatibility in performance data, with some deviations in the torque-speed curve for inner rotor modeling and outer rotor modeling approach methods, which can be reduced by resizing the slots. Overall, acceptable errors and consistent results were achieved between the models.

Design, Modelling and Optimization of a High Power Density Axial Flux SRM with Reduced Torque Ripple for Electric Vehicles

Switched reluctance machines (SRMs) are potential candidates for use in the propulsion systems of electric vehicles. However, they suffer from low power density and high torque ripple. In this paper, a segmented rotor double-sided axial flux SRM (DSAFSRM) is chosen for detailed analysis. A hybrid design algorithm is proposed to take the effects of iron non-linearity into account. The proposed design procedure benefits from simplicity and high accuracy at the same time. A two-step optimization procedure is presented which minimizes the torque ripple of the DSAFSRM without jeopardizing its efficiency. The torque ripple is reduced from 120% to 35% after optimization. In the two-step optimization procedure, both geometrical and switching related parameters are investigated. Moreover, a double-sided radial flux SRM is designed and compared with the proposed DSAFSRM in terms of torque ripple, average torque, efficiency and power density. The results indicate superior performance of the optimized DSAFSRM, especially in terms of average torque, which is 26% higher than the torque produced by the double-sided radial flux SRM.

Measurements and modeling of type-I and type-II ELMs heat flux to the DIII-D divertor

Type-I and type-II edge-localized-modes (ELMs) heat flux profiles measured at the DIII-D divertor feature a peak in the vicinity of the strike-point and a plateau in the scrape-off-layer (SOL), which extends to the first wall. The plateau is present in attached and detached divertors and it is found to originate with plasma bursts upstream in the SOL. The integrated ELM heat flux is distributed at ∼65% in the peak and ∼35% in this plateau. The parallel loss model, currently used at ITER to predict power loads to the walls, is benchmarked using these results in the primary and secondary divertors with unprecedented constraints using experimental input data for ELM size, radial velocity, energy, electron temperature and density, heat flux footprints and number of filaments. The model can reproduce the experimental near-SOL peak within ∼20%, but cannot match the SOL plateau. Employing a two-component approach for the ELM radial velocity, as guided by intermittent data, the full radial heat flux profile can be well matched. The ELM-averaged radial velocity at the separatrix, which explains profile widening, increases from ∼0.2 km s−1 in attached to ∼0.8 km s−1 in detached scenarios, as the ELM filaments’ path becomes electrically disconnected from the sheath at the target. The results presented here indicate filaments fragmentation as a possible mechanism for ELM transport to the far-SOL and provide evidence on the beneficial role of detachment to mitigate ELM flux in the divertor far-SOL. However, these findings imply that wall regions far from the strike points in future machines should be designed to withstand significant heat flux, even for small-ELM regimes.

A Review of Axial Flux Permanent Magnet Machine Technology

Axial flux permanent magnet machines (AFPM) are popular for applications that benefit from high torque density and an axially compact form factor, such as in-wheel traction drives. Although the radial flux permanent magnet machine (RFPM) and the AFPM work based on the same underlying principle, the differences in their geometry introduce complexities in analysis of the AFPM. In this paper, the different AFPM design variants, their sizing approaches, computationally efficient design optimization techniques, and manufacturing techniques reported in literature are reviewed. In addition to classical AFPM machines, emerging variants and research opportunities with potential to push the boundaries of electric machine technology are reviewed. These include bearingless AFPMs, magnetically geared AFPMs, and combined radial-axial flux machines.

Research on a Novel High-Torque-Density Axial–Radial-Flux Permanent-Magnet Motor with Annular Winding for an Elevator-Traction Machine

The traditional radial flux PMSM and axial flux PMSM have an effective air gap on only one side, between the stator and rotor, and only the effective air gap generates electromagnetic torque. There are defects in the magnetic-field utilization, and it is difficult to improve the torque density. Therefore, this paper proposes an axial–radial-flux permanent-magnet synchronous motor (ARF-PMSM), which combines radial flux with axial flux, to be used in an elevator-traction machine-drive motor. The characteristics of the ARF-PMSM are that the stator core is made of a soft magnetic composite material and the winding is annular. The motor has three effective air gaps, which can achieve high torque density without increasing the overall dimensions. In this paper, the mechanical structure and operation mechanism of the ARF-PMSM are introduced, and the characteristics of its magnetic circuit structure are analyzed by using the equivalent magnetic circuit method. The torque characteristics and other electromagnetic characteristics of the ARF-PMSM, the traditional surface-mounted PMSM, and the spoke-type PMSM are compared and analyzed using the finite element method. The research results show that the proposed motor has high torque density, which provides a new design idea in the form of a high-torque-density PMSM for use in elevator-traction machines.

Thermal Optimization of a Radial Flux Permanent Magnet Synchronous Motor With Axial Division

Thermal Optimization of a Radial Flux Permanent Magnet Synchronous Motor With Axial Division

Research on distribution of winding leakage magnetic field of three-phase dry type transformer under short-circuit condition

Leakage flux magnitude and pattern greatly affect transformer short-circuit resistance. In this paper, finite element calculations and experimental measurements is used to calculate the leakage magnetic field of a transformer. This paper analyzed the radial and axial leakage flux distribution of each winding under different operating conditions to obtain a comprehensive view of the magnetic flux leakage distribution in all directions. This analysis can provide valuable insights for optimizing the anti-short-circuit ability of transformers.

Effect of a central barrier potential on asymmetry-induced transport in a coaxial Malmberg–Penning trap

Experiments are presented measuring the radial particle flux produced when a central barrier potential is applied to the central ring of a coaxial Malmberg–Penning trap at the same time as the voltages producing the main asymmetry potential ϕ1(r) cos (kz) cos (lθ−ωt). When a negative DC voltage is applied to the entire central ring, the peak flux produced by the main asymmetry is reduced by a factor e(Veff/1.2), where Veff is the effective applied potential in volts. This barrier potential also increases the frequency of this peak flux. When asymmetric ± voltages are applied to the two azimuthally divided halves of the central ring, DC voltages increase the radial flux while AC voltages decrease it. It is shown that these asymmetric barrier voltages produce their own transport and that the resulting modification of the plasma may be a factor in changing the observed flux.

High Integrated Methodology and Evaluation for Switched-Reluctance Type Bearingless Motors with Five Degree of Freedom Magnetic Levitation

To make bearingless motors more competitive in military and industrial applications, the volume and cost issues for the system need to be taken into account. In this paper, a series of highly integrated five degree of freedom (DOF) bearingless switched reluctance motors (BSRMs) without rare earth materials are proposed. The features of the novel topologies include the conical pole, the conical disk, the conical cylinder, and the thrust cylinder. The magnetization current is applied to generate the radial and axial fluxes based on these topologies. The axial levitation can be implemented by the two units without axial levitation windings. The two rotors are assembled on the shaft in parallel with 15 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> shifted for the torque compensation, and the four-DOF radial levitation can be implemented as well. According to the simulation and experiment results, the characteristics of the proposed topologies are evaluated. These novel topologies have a greater axial bearing capacity, and the capacities of the torque and the five-DOF levitation are guaranteed. In addition, the proposed topologies have broad application prospects in high-speed rotation and high-integration fields.

Hydraulic conductance and xylem vessel diameter of young maize roots subjected to sustained water‐deficit

AbstractWater deficit can have large impacts on plants, including likely alteration of root hydraulic conductance and root xylem vessel diameter, which can decrease crop productivity. No results, however, exist to assess possible linkages between these two variables as critical components contributing to plant water status. This linkage was investigated in three maize (Zea mays L.) cultivars. A stable water‐deficit treatment was established and maintained in pots by allowing soil drying to the point where transpiration rate was held constant at about 0.5 of well‐watered pots. Initially, the root hydraulic conductance of the water‐deficit plants was equivalent to that of well‐watered plants. Subsequently, however, hydraulic conductance decreased substantially. The results for xylem vessel diameter at 5 cm from the root tip exhibited a pattern similar to the decrease in root hydraulic conductance. A graph of root hydraulic conductance versus xylem vessel diameter at 5 cm showed a curvilinear response with lessening in the increase in hydraulic conductance with increasing xylem vessel diameter. The results indicate a possible link between root conductance and xylem diameter but the conductance is much less sensitive to vessel diameter than the fourth power of the radius predicted by Poiseuille's law. The association between conductance and xylem vessel diameter may reflect interaction of radial and axial water flux through the root system as indexed by vessel radius in the zone near the root tip.

An Analysis of the Design of a Low Rotational Speed Permanent Magnet Generator That Uses Radial Flux

A radial flux permanent magnet generator can be effectively used in generating wind power at low speeds. This generator uses a combination of permanent magnets and a stator to produce electricity from the wind’s kinetic energy. The permanent magnets are arranged in a radial pattern, which reduces the amount of heat lost and therefore increases the generator’s efficiency. This design allows for a low rotational speed, which makes it suitable for applications such as wind turbines. The air gap between the rotor and the stator affects the output voltage and power due to the decrease in magnetic flux. This study aims to increase the generator’s output voltage and output power by fitting stator teeth widths to the stator teeth. The stator teeth width fitting design method adjusts the air gap between the stator and the rotor to a uniform size. This helps to reduce the pulsating torque and ensure that the output voltage and power are maximized. The three variables are the stator slot width, the rotor slot width, and the air gap width. By adjusting these variables, the stator teeth width fitting design method can adjust the air gap between the stator and rotor.

Beyond 15 MW: A cost of energy perspective on the next generation of drivetrain technologies for offshore wind turbines

Leading wind turbine manufacturers are racing to build larger and more powerful offshore machines. Drivetrain configurations often use a permanent-magnet synchronous generator (PMSG), in either a direct-drive configuration or coupled to a gearbox. With increasing demand for critical rare-earth magnets, new generator technologies are emerging to ensure a stable and secure supply chain. We evaluate three different topologies of radial flux synchronous generators employing high field magnets with reduced or no rare-earth content: a direct-drive interior PMSG (DD-IPMSG), a geared drivetrain combining a medium speed gearbox with a PMSG (MS-PMSG), and a direct-drive low-temperature superconducting generator (DD-LTSG). We develop a conceptual design module for each of these technologies within a larger framework for full turbine design. This provides the fairest comparison between technologies at nominal power ratings from 15–25MW, which represent the next generation of offshore wind turbines. The analyses show that if operational expenditures (OpEx) are constant across the technologies, MS-PMSG results in the lowest LCOE with reductions of up to 7% relative to DD-IPMSG. DD-LTSG also yields lower LCOE values by 2%–3% for fixed-bottom turbines and 3%–5% with a floating platform. However, results are sensitive to OpEx assumptions, with a mere 10% increase causing the conclusions to shift.

Research on Electromagnetic Vibration Characteristics of a Permanent Magnet Synchronous Motor Based on Multi-Physical Field Coupling

Background and Purpose: The stator vibration characteristics are comprehensively mastered by considering the influence of winding and the housing structure on the stator modes. This effect is neglected in the research field of electromagnetic vibration of permanent magnet synchronous motors (PMSMs). Methods: The radial air-gap flux density equations and PMSM’s electromagnetic force density are derived, and then the harmonic characteristics of electromagnetic force density are studied. An equivalent finite element model of the stator is proposed that investigates the impacts of the winding and stator housing rules on the stator modal frequency. Finally, the harmonic response and acoustic analyses of electromagnetic vibration are carried out based on multi-physics field coupling. Results: The equivalent radiated power distribution laws and acoustic field of motor electromagnetic vibration under transient operating conditions are obtained. The theoretical analysis results are consistent with the experimental results. Conclusion: The obtained results show that the spatial order of the radial electromagnetic force is not equal to the order of the radial mode of the motor stator. The reason for this is that structural resonance is induced when the frequency components of the spatial radial electromagnetic force are coupled with the intrinsic frequency of the stator.

Condition Monitoring of Rotating Diodes in Synchronous Machines Through the Exciter Stray Flux Analysis

Brushless excitation systems have many advantages mainly related to the low maintenance. A failure in the rotating diodes leads to an increase in the exciter field current and an unbalance in the currents supplied by the exciter armature. This produces additional losses in the exciter and, in some cases, severe damage in the machine if operated for a long time under fault conditions. The supervision of the condition of the rotating diodes is, therefore, essential for the protection of the exciter and the machine. In this paper, monitoring of the diodes is carried out via the analysis of the exciter´s stray flux. Numerous experimental tests have been performed on a synchronous machine with axial and radial flux measurements under healthy condition, under one open diode fault and finally under a shorted diode. The experimental results prove that a failure in the diodes can be reliably detected due to the axial and radial stray flux signatures which significantly increase in comparison to the healthy condition.

Thermal Analysis for Improving the Design of Radial Flux Permanent Magnet Synchronous Generators

In this paper, the analytical thermal model of a radial flux permanent magnet synchronous generator (RF-PMSG) is developed for applications in variable speed direct-drive low-power wind turbines. The thermal model takes the form of a lumped parameter thermal network to estimate temperatures and heat fluxes for a wide operating range of the RF-PMSG. The proposed thermal model is fully coupled with the electromagnetic solution of a flexible analytical design methodology of RF-PMSGs and its algorithmic solution is coded in Matlab. The thermal analysis is an essential requirement for enhancing the design performance of radial flux permanent magnet synchronous generators. Finally, the performance of a 10 kW RF-PMSG is analyzed using the thermal model, for a wide steady-state operation range.

A direct numerical simulation study for confined non-isothermal jet impingement at moderate nozzle-to-plate distances: Capturing jet-to-ambient density effects

A direct numerical simulation (DNS) campaign is deployed for a series of confined downward oriented, non-isothermal turbulent impinging jet configurations. A baseline Reynolds number of 9960 is obtained through a precursor DNS pipe flow simulation (Reτ=505). Three jet temperature configurations (confinement height to nozzle diameter of three) enter a cylindrical domain that share ambient and impingement plate temperatures (298.15K). The range of jet temperatures are crafted such that the ratio of inlet to ambient density varies from unity to 0.52, showcasing the effect of density disparity on flow characteristics such as core collapse, radial mixing of momentum and energy, near-wall stagnation behavior, wall-jet profiles, and large-scale vortical structures. Surface quantities provided include mean radial heat flux and wall-shear stress profiles, and heat flux histograms at select radial stations. Results showcase increased radial normal stresses for higher temperature jets that support increased mixing, resulting in large-scale recirculation structures that are smaller, while retaining similar normalized radial wall profiles for shear stress, heat flux and pressure. Radial plots for wall shear stress and Nusselt number showcase strong radial decay as compared to previous configurations that share similar jet and ambient temperatures. For the 373.15 K case, a Gaussian-like histogram for heat fluxes at the impingement plate transitions to a log-normal profile as radial distances increase. In contrast, the 573.15 K configuration displays a bi-modal heat flux characteristic at the impingement plate, and in similar manner to the moderate temperature counterpart, transitions to a log-normal profile at larger radial distances.

Intensity fluctuations in Hurricane Irma (2017) during a period of rapid intensification

Abstract. This study aims to understand the fluctuations observed in Hurricane Irma (2017), which change the tangential wind speed and the size of the radius of maximum surface wind and therefore affect short-term destructive potential. Intensity fluctuations observed during a period of rapid intensification of Hurricane Irma between 4 and 6 September 2017 are investigated in a detailed modelling study using an ensemble of Met Office Unified Model (MetUM) convection-permitting forecasts. Although weakening and strengthening phases were defined using 10 m wind, structural changes in the storm were observed through the lower troposphere, with the most substantial changes just above the boundary layer (at around 1500 m). Isolated regions of rotating deep convection, coupled with outward propagating vortex Rossby waves, develop during the strengthening phases. Although these isolated convective structures initially contribute to the increase in azimuthally averaged tangential wind through positive radial eddy vorticity fluxes, the continued outward expansion of convection eventually leads to a negative radial eddy vorticity flux, which halts the strengthening of the tangential wind above the boundary layer at the start of the weakening phase. The outward expansion of the azimuthally averaged convection also enhances the outflow above the boundary layer in the eyewall region, as the convection is no longer strong enough to ventilate the mass inflow from the boundary layer in a process similar to one described in a recent idealised study.

Design and analysis of in-wheel motor with sinusoidal permanent magnet shape for electrical vehicles

This paper deals with the design and analysis of a surface-mounted outer rotor in-wheel motor (IWM) with the aim of reducing cogging torque and torque ripple for electric vehicles. The proposed IWM is equipped with axial sinusoidal surface-mounted permanent magnets (PMs), with the purpose of producing sinusoidal air gap flux density distribution, thus to realize sinusoidal back electromotive force (EMF) and smooth electromagnetic torque. To highlight the advantage of the proposed IWM, the conventional IWM with tile-shaped PMs and the IWM with stepwise-shaped PMs are also studied for comparison. The finite element method in the commercial software package is utilized to analyze the performance of the three motors, including the radial flux density of air gap, back EMF, cogging torque, and electromagnetic torque. Through the quantitative comparison, it is found that the proposed IWM greatly reduces the cogging torque, highly improves the sinusoidality of back EMF, and nearly eliminates the torque ripple.