Conference Paper

Analysis of the Yokeless And Segmented Armature Machine

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Abstract

This paper presents a new type of axial flux motor, the yokeless and segmented armature (YASA) topology. The YASA motor has no stator yoke, a high fill factor and short end windings which all increase torque density and efficiency of the machine. Thus, the topology is highly suited for high performance applications. The LIFEcar project is aimed at producing the world's first hydrogen sports car, and the first YASA motors have been developed specifically for the vehicle. The stator segments have been made using powdered iron material which enables the machine to be run up to 300 Hz. The iron in the stator of the YASA motor is dramatically reduced when compared to other axial flux motors, typically by 50%, causing an overall increase in torque density of around 20%. A detailed Finite Element analysis (FEA) analysis of the YASA machine is presented and it is shown that the motor has a peak efficiency of over 95%.

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... In recent years, Axial Flux (AF) machines gained much attention not only as a topic of research but commercially as well [1,2]. Interest in AF machines have been increased due to new and emerging environmentally-friendly technologies such as Electric Vehicles (EV). ...
... Dual air gap yokeless AF motors with Surface-Mounted Permanent Magnets (SPM) can exhibit increased torque [3] densities due to reduced mass and higher efficiency as magnetic flux paths through stator are shortened. [3] These properties of yokeless AF machines make them very attractive for Battery EVs [4,5,6] and Hybrid EVs [2], in which drives (especially direct) based on such high torque density machines can significantly reduce powertrain mass and volume. However, historically the AF machines were seldom used as they tend to be harder to manufacture and accurately analyze, requiring 3D models, as magnetic flux paths are more complex than in radial flux machines. ...
... No flux barriers representing laminations were added in the model because such stator cores would cause uneven flux densities at inner and outer radii, leading to magnetic saturation of the stator material at the inner radius (as visible at B field plot, Figure 3 b). This design can be realized using, for instance, Soft Magnetic Composite materials (SMCs) as the stator core material [2]. ...
Article
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The paper presents the results of a 3D FEA simulations series of a dual air gap Axial Flux (AF) electric machine with Surface-Mounted Permanent magnets (SPM) with parameterized rotor geometry. Pole number and pole span influence on back-emf, as well as cogging and ideal electromagnetic torques angular characteristics were investigated for each model with the common segmented yokeless stator with concentric windings. Synchronous and BLDC drives supply were used to estimate back-emf distortion. Ideal torque ripple and cogging torque spectra were analyzed. It was concluded that the number of poles closer to the number of slots with ~0.8 pole span tends to yield good torque density with the lowest cogging torque, back-emf distortion and ideal torque ripple.
... he ever increasing pressure on the global environment, has pushed electrical machines into new domains and applications, such as electrical and hybrid transportation, and the generation of alternative energy amongst others [1]- [3]. Electrical machines with high current densities, high efficiencies and a long life are desired. ...
... This increases the torque density by around 20% when compared to other axial flux machines. The peak efficiency can be maintained at over 95% [1]. Each stator pole piece of the YASA machine is made from concentrated windings of square cross section wire. ...
Article
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This paper re-evaluates flat windings to improve the current density of concentrated windings. The paper produces finite element and lumped parameter thermal models to compare the thermal profile of the new flat winding construction with traditional concentrated windings of square cross-sectional area. An experimental setup is developed to validate the models which are then used to establish the thermal profile and current density of the two constructions. Traditional concentrated windings are shown to have a number of thermal resistances across their inter winding layers. A hot spot temperature is therefore produced at the winding with the longest thermal path. Flat windings as proposed here eliminates this problem, leading to lower temperatures. As a result, higher current can be injected before the maximum allowed temperature is reached. The paper demonstrates that for a typical motor operating point of 300 Nm and 1500 rpm the maximum temperature is reduced by 97 K. For the same maximum temperature, the current density can be increased between 130-150%.
... By removing the stator yoke from the TORUS N-S type structure and adoption of the tooth-wound concentrated windings (CWs) for segmented stator construction, the Yokeless And Segmented Armature (YASA) AFPM machine topology is obtained, as shown in FIGURE 4. YASA motors are receiving more and more attention due to high torque density, compact structure and low weight, which makes them suitable for space-critical automotive, aerospace and marine applications. In [15], Woolmer and McCulloch designed and prototyped a YASA motor in which stator teeth are entirely made of soft magnetic composite (SMC) material, pressed to separately form the shoes and central part of the teeth, which can produce a nominal torque of 120 Nm, peak overload torque density of 10 Nm/kg and peak efficiency over 96% for high performance applications such as in-wheel direct drive light EVs. A number of electric motor manufacturers have developed mature YASA motor products with peak power higher than 200 kW and efficiency over 95%, for use in highperformance electric powertrains, e.g. ...
... YASA structure (from[15]). ...
Article
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Axial-flux (AF) permanent-magnet (PM) (AFPM) machine is a competent candidate for electric propulsion applications owing to its high power density, high efficiency and effective volume utilization. This paper reviews the progress of AFPM technology that has been made in recent years, especially for electric vehicle (EV) propulsions, with respect to the potential AFPM topologies, design methodologies and modeling, design considerations, thermal and mechanical analysis, as well as advanced material and construction aspects. The most promising AFPM motor structures and winding configurations, key design parameters, important design considerations and improvement methods, as well as construction techniques specified for EV motors are presented.
... The PMSM is classified in two types according to the direction of magnetic flux generated by PMs: Axial and radial flux type; the difference lies in crossing the air gap by magnetic flux in axial and radial direction consequently. The radial flux type is further categorized into two classes; SMPM and interior permanent magnet (IPM) motor with the main difference of magnets being mounted on the rotor in SMPM widely used in machinetools drives while in IPM, these are buried inside the rotor [7]. SMPMs have limited capabilities for high speed operation while IPMs have greater mechanical strength for high speed variable operation because of which are most commonly seen being used in automotive industry. ...
... The mathematical model of PMSM in d-q reference frame can be represented in form of voltage and flux linkage (1) to (7). In (7) the first term is magnetic torque while the second term represents the reluctance torque. ...
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The state-of-the-art robust H∞ linear parameter-varying controller is designed for wide speed operating range for non-linear mathematical model of permanent magnet synchronous machines (PMSM) in d-q reference frame for fully electric vehicle. This study propose polytopic approach using rotor speed as scheduling variable to reformulate mathematical model of PMSM into linear parameter varying (LPV) form. The weights were optimized for sensitivity and complementary sensitivity function. The simulation results illustrate fast tracking and enhanced performance of the proposed control technique over wide range of rotor speed. Moreover, as part of this work, the results of H∞ linear parameter varying controller is validated by comparing it with linear quadratic integrator and proportional integral derivative (PID) control techniques to show the effectiveness of the proposed control technique.
... Besides, too much stator space has been wasted and the output torque will be reduced compared with the conventional non-modular machines. For the modular machine shown in Fig. 1(b), it is yokeless and segmented armature (YASA) axial flux type [24]. The stator iron of this machine has been largely reduced and the torque density is consequently improved. ...
... (a) E-core modular stator and modular IPM machine[20]-[23]. (b) Modular stator YASA axial flux machine[24] ...
Article
This paper reviews the modularity techniques in the stator manufacture of permanent magnet machines for different applications. Some basic concepts of modular machines are firstly introduced. Modular machines for several typical applications are then described in details, including domestic appliances, automobiles and electric vehicles, more electric aircrafts and civic applications, wind power generators, etc. Besides, the influence of manufacture tolerance gaps and flux barriers on the electromagnetic performance is discussed.
... The characteristics required are strong, withstand high temperatures and uninfluential to the performance of the electric motor. Polyetheretherketone (PEEK) is a widely used material [8]. Nevertheless, high prices and complicated assembly processes become obstacles. ...
... The axial force is listed from 50 N to 450 N for the maximum. Paper [8] got the maximum axial force for 400 N, so the maximum value for 450 N is a proficient choice. The location and stable position are located on the inner diameter and outer diameter. ...
Article
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This paper deals with comparison and analysis of stator plate holder on Yokeless and segmented armature (YASA) machine. YASA topology consists of two rotors and one inner stator comprised of many independent segments. Core for stator uses Soft Magnetic Composite (SMC) to conduct the three-dimensional magnetic flux. All stator segments and concentrated winding are fixed with the aid of two annular plates. There are cavities on both plates which have the same shape as the shoe of the stator segment. Moreover, the deformation of the plates must be kept as low as possible and have very high yield strength because of stress from the bearing. A complex structure, high durability, and high electrical resistance are the challenges. Polyetheretherketone (PEEK) is usually used as the plates, however high price and manufacturing cost remain an issue. Some other materials have a possibility and approach to PEEK capability. In this paper, candidate materials will be developed as a specimen and tested on the BH - Curve meter. The BH-Curve data provide simulation on Finite Element Magnetic Method (FEMM). The advantages and disadvantages are discussed in this paper. The analysis result demonstrates that other materials possess a similar capability as PEEK related to YASA stator plate holder.
... To improve the force/torque density of PM machines, the dualrotor topologies are first applied for the rotary PM machines [26,27]. Similar to the dual-rotor PM machine, the double-sided design is further introduced into the flux-switching PMLM fields to improve the electromagnetic performance. ...
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A tubular flux-switching permanent-magnet linear machine (PMLM), which features unified magnetic field between the mover and two stators, is investigated for free-piston energy converter. The topology evolution, topology, operating principle and design considerations of the machine are thoroughly analysed. With the sinusoidal speed characteristic of free-piston Stirling engine considered, a tubular unified magnetic-field flux-switching PMLM is designed by finite-element analysis. Several main structural parameters, which include the outer and inner radius of the mover, the mover tooth width, the magnet thickness, the tooth widths of both the outer and inner stators and the widths of both the outer and inner stator yokes are studied to achieve high-force and mass-power density. Finally, the proposed machine is compared with two typical flux-switching PMLMs. The comparison results show that the unified magnetic-field flux-switching PMLM is suitable for applications which require high-power density, light mover structure and fast dynamic. © 2019 Institution of Engineering and Technology. All rights reserved.
... Internal stator AFPM machines have been developed for high performance applications. Among the internal stator AFPM machines, the yokeless and segmented armature (YASA) machine has a unique design which is distinguished by a modular stator construction and has shown to exhibit superior performance due to short end windings, high windings filling factor and reduced stator core [2], [3]. ...
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In this paper, a performance comparison between the novel axial flux magnetically geared machines (AFMG) and the conventional axial flux YASA machine is presented. The AFMG and YASA machines have the same stator construction in which segments are equipped with concentrated windings to form the stator. However, the AFMG machine has two rotors with different pole-pair numbers. Magnetic gear effect can be obtained to increase the torque density. The performance comparisons at no-load and on-load conditions are then studied by 3D-finite element analysis (FEM). Moreover, both machines are prototyped, tested and compared.
... In Figure 3, Ry is the equivalent reluctance of the stator yoke, Rt is the magnetic reluctance of the tooth, Fl is the magneto motive force generated by the stator winding, Rs is the slot reluctance, Rg is the air gap reluctance, and FPM is the magneto motive force generated by the permanent magnet. The AFPMSM is equivalent to a linear motor in this paper, and the magnetic circuit analysis method (MCAM) model was used to analyze the air gap magnetic density distribution of AFPMSM [25][26][27][28]: ...
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In order to provide a complete solution for designing and analyzing the axial flux permanent magnet synchronous motor (AFPMSM) for electric vehicles, this paper covers the electromagnetic design and multi-physics analysis technology of AFPMSM in depth. Firstly, an electromagnetic evaluation method based on an analytical algorithm for efficient evaluation of AFPMSM was studied. The simulation results were compared with the 3D electromagnetic field simulation results to verify the correctness of the analytical algorithm. Secondly, the stator core was used to open the auxiliary slot to optimize the torque ripple of the AFPMSM, which reduced the torque ripple peak-to-peak value by 2%. From the perspective of ensuring the reliability, safety, and driving comfort of the traction motor in-vehicle working conditions, multi-physics analysis software was used to analyze and check the vibration and noise characteristics and temperature rise of several key operating conditions of the automotive AFPMSM. The analysis results showed that the motor designed in this paper can operate reliably.
... In literature, several topologies of yokeless machines, including both the rotary type and linear type, have been investigated. A rotary version with axial-flux configuration is presented in [9] and [10], with yokeless and segmented armature. A novel topology of the yokeless PMLM is reported in [11], and it is shown that the absence of the yoke leads to 7.7% higher efficiency and 5.4% higher force density under the same volumetric and thermal constraints. ...
Article
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Permanent magnet linear motors (PMLM) have gained increased popularities in a wide range of applications. However, they generally suffer from considerably lower force densities. In this paper, a novel doubly yokeless PMLM equipped with quasi-Halbach trapezoidal-shape permanent magnets is presented to both increase the thrust force density and suppress the thrust ripple. Both the stator and the translator are yoke-free, and therefore, the increase of the installation space for the windings is conducive to enhancing the magneto-motive force and the thrust density of the motor. An analytical model is developed to predict the magnetic field distribution and electromagnetic performance of the doubly yokeless PMLM, and finite element computations are undertaken to validate the effectiveness and accuracy of the proposed model. The thrust performance is then optimized against magnet parameters under a specific set of volumetric constraints to the improve the thrust force quality. It is shown that the Halbach ratio and bottom angle of the trapezoidal magnets have significant impacts on the thrust force quality (in terms of both the average thrust and thrust ripple), and optimal values for the two parameters are obtained. The benefits of the doubly yokeless PMLM are highlighted by comparisons with a conventional PMLM with iron yokes.
... The YASA machine can be regarded as a next generation Torus type AFPM machine [1], [2] that combines winding arrangments of the NN and NS type Torus machines. The YASA structure has been proposed for traction application [3] and gained attention due to its high torque density and the segmented stator teeth structure that facilitates higher slot fill factor. On the other hand, the segmented structure adds to mechanical challenges [4], [5]. ...
... There are many different topologies of AFM. The Yokeless And Segmented Armature (YASA) machine is a new type of AFM that shows great improvement in torque density and efficiency which make it very suitable for the EV application [13], [14]. This topology comprises two external rotors and an inner stator which consists of many independent stator segments. ...
Article
Axial flux motor design is normally depended on a designer’s experience to adjust design parameters, which is vague and complex, for example, torque density and torque ripple are two key factors of a motor to restrain its development, since torque density dominates a motor’s volume and weight, while torque ripple determines its stability. Therefore, a general optimizations methodology is required in its design process. To realize this purpose, this paper proposes a general multi-objective optimization methodology for practical motor design. In detail, this methodology is based on Support Vector Machine-Chaotic Cultural Differential Evolution(SVM-CCDE) algorithm for both maximizing the torque density and minimizing the torque ripple, and Yokeless And Segmented Armature(YASA) motor of an electric vehicle(EV) considering practical constraints is presented as a typical example since it is a special topology of axial flux motor(AFM). A comparative analysis is presented in the paper to demonstrate the proposed method’s advanced features. Finally, the effectiveness of the optimization method is verified by finite element analysis (FEA) via Ansys software, the results well agree the analyses and further validate the proposed method. The proposed method is a potential feasible solution to improve the EV’s motor design in the coming future.
... Oxford YASA Motors Inc. developed a high power density AFPMSM with yokeless and segmented armature (YASA) topology, oil immersion cycle cooling, and soft magnetic composite (SMC) stator iron core. [2], [3]. Authors in [4]- [6] carried out important research in the aspects of magnetic flux density versus magnetic field intensity (B-H) curve characteristics of SMC material, comparison between Si steel core and SMC core, and its application in AFPMSM. ...
Article
This paper takes 12-slot/10-pole axial flux permanent magnet synchronous machine (AFPMSM) with fractional-slot-concentrated-windings (FSCW) and yokeless and armature (YASA) topology as the research object. Winding magnetic motive force (MMF) of three-phase double-layer (TP-DL) layout is analyzed by three kinds of methods, which are star diagram method (SDM), winding function method (WFM) and holographic spectrum method (HSM). The analysis results of finite element method (FEM) show that three methods is effective and consistent in analyzing winding MMF. Comparative analysis of iron loss density and B-H magnetizing curves of four typical iron materials are studied. B-H hysteresis loops of silicon steel sheet and soft magnetic composite (SMC) are measured by magnetizing and measuring equipment to validate iron core per unit mass. The 3D FEM is used for analyzing eddy-current loss in PMs considering radial segmentation. Finally, an AFPMSM prototype is manufactured adopting YASA topology and segmented PM. Load experiments show that solid-liquid coupling CFD model can precisely predict temperature distribution of AFPMSM. Improved cooling jacket is beneficial to afford large current load.
... "NS type" refers to north pole and south pole magnets facing each other at either side; thus, the flux can travel straight through this stator without any circumferential flow [4]. This type of DR-SS is more commonly known as a yokeless and segmented armature (YASA) motor or generator [5][6][7] and is often described as having a relatively high power density because it does not require a stator yoke. However, to be precise, a structure in the form of a 'stator yoke' is not required as a magnetic flux path, but is necessary to mechanically hold the teeth and coils of the stator [4]. ...
Article
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This paper presents the design of an axial-flux permanent-magnet (AFPM) generator used for hybrid electric propulsion drone applications. The design objectives of the AFPM generator are high power density, which is defined as output power per generator weight, and high efficiency. In order to satisfy the requirements for the target application and consider the practical problems in the manufacturing process, the structure of the AFPM generator comprising a double-rotor single-stator (DR-SS) was studied. In order to determine the rotor topology and stator winding specifications that had the greatest impact on performance in the DR-SS type design process, we selected three rotor models according to the arrangement of the magnetization direction and three stator models according to the coreless winding specifications. These models were first compared and analyzed. Then, a 3-D finite element method was performed to calculate the magnetic, mechanical, and thermal characteristics of the designed models. By consideration of the output power, efficiency, temperature, and mechanical stability, etc., a topology suitable for the design of generators for UAV systems was determined and manufactured. The reliability of the design result was confirmed through the test.
... The design in Fig. 1 is then simulated using 3-D Finite Element Analysis (FEA) [26]. The proposed motor is compared to three other PMSM configurations; an inner rotor radial flux motor in Fig. 2.a, a yokeless armature segmented axial flux motor (YASA) in Fig. 2.b [27] and a toroidal slotted armature axial flux motor (TORUS) in Fig. 2.c [28]. Table I shows the parameters and constraints of the four designs. ...
... In recent years, owing to the rapid development of highperformance materials and the continuous progress of the process level, some novel topologies of motors can be realised in the last decades [1][2][3]. Based on the comparison of different structures, it is pointed out that the yokeless and segmented armature axial flux machine (YASA) with double-layer concentrated winding is more suitable for the in-wheel propulsion system of the vehicle, as it has higher power density and torque density [4][5][6][7]. However, the axial force between the yokeless stator segmentation and rotors can increase the asymmetrical air gaps [8][9][10], and due to the absence of the stator yoke, it is difficult to integrate the cooling system, which limits the output power of the motor [11]. ...
Article
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Abstract In this paper, a novel cooling system of the yokeless and segmented armature axial flux machine (YASA) applied in‐wheel traction is presented. Although the cooling system has high cooling efficiency, it will deteriorate the electromagnetic characteristics of the motor. The eddy current analysis for the prototype is performed based on the 3‐D finite‐element method, and the distribution of eddy current in the cooling fins is presented. Through the 2‐D finite element analysis, the cause of the eddy current loss of the fin is revealed. In order to increase the output power of the motor, the height of the fin in the axial direction is optimised by the magneto‐thermal coupling method. And finally, the hub motor is manufactured and tested. It can be concluded that the measured data matched well with the analysis results.
... The shorter end windings in the YASA topology improve the torque density of the motor [6], [7]. Additionally, this topology reduces core losses by replacing the stator yoke with an additional rotor [5], [8], [9]. Grain-oriented electrical steel (GOES) is employed for the stator teeth, which primarily experience axially directed flux in the YASA topology. ...
Conference Paper
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This paper presents and evaluates a dual rotor axial flux permanent magnet motor for electric aircraft applications. Several features, including grain oriented electrical steel (GOES), magnet segmentation, and wires with rectangular cross-sections, are used to improve torque density and efficiency. Rather than simply optimizing the motor by itself, this paper evaluates the tradeoffs between motor performance and its interfaces with the drive, thermal management system (TMS), and mechanical structure. This information can be used along with similar analyses of the drive, TMS, and structure to select a design that achieves the system-level optimal performance. The paper uses finite element simulations to characterize tradeoffs between active mass, efficiency, fundamental frequency, power factor, axial forces on the rotors, and cooling surface area. Several designs exceed 95% efficiency at takeoff with less than 8 kg of active mass. While high pole counts, a large outer radius, and short stator teeth tend to optimize the magnetic performance at takeoff, this can reduce cruise efficiency, reduce the surface area through which the TMS can extract heat, increase the fundamental frequency the drive must supply, and increase the structural mass required to support the rotors. Additionally, designs with 20 °C cooler magnets were simulated to evaluate the impact of a more effective TMS, but the improvements in magnetic performance were relatively small.
... The stator is enclosed in a casing allowing liquid coolant to be injected into the stator, in direct contact with the windings, as shown in Figure 1. When compared to other axial flux machines, the YASA machine has its torque density increased by around 20%, with a peak efficiency over 95% [7]. Studies of the flow distribution and the convective heat transfer in this machine have been reported in [8,9], respectively. ...
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This paper proposes a new construction with a heat sink integrated into the concentrated wound coils of an axial flux, direct liquid cooled electrical machine. A preliminary assessment of the effectiveness of the heat sink and its position is made using computational fluid dynamics. Lumped-parameter thermal models are also developed, thus allowing accurate comparison of the thermal profile of the two constructions. Following experimental calibration of the model and thermal validation, the temperature profile of the new construction is compared to that from a traditional concentrated wound coil. The model is then used to estimate the effect of the new construction on the current density of the stator windings. The paper demonstrates that for an axial flux motor run at a typical operating point of 300 Nm and 1500 rpm, the maximum temperature is reduced by 87 K. The current density can be increased by 140% before the limiting maximum coil temperature is achieved.
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The yokeless and segmented armature axial-flux in-wheel motor with amorphous magnet metal (AMM) stator segment has the advantage of low iron losses, but its open-slot structure causes high eddy-current losses of the permanent magnet (PM), which reduces the efficiency and reliability of the in-wheel motor. To avoid the demagnetization caused by the heat generated by PM losses, the mechanism of PM eddy-current losses reduction for the axial-flux in-wheel motor is revealed by the calculation model. In this paper, the time-step three-dimensional finite-element method (3-D FEM) is used to analyze the PM eddy-current loss caused by slotting effects, spatial harmonics, and time harmonics at different speeds. The effect of PM skewing, PM segmentation, and soft magnetic composite (SMC) layer inserted on the top of PM on eddy-current losses are compared. These methods cannot simultaneously meet the requirements of PM losses reduction and the electromagnetic performance of the motor. A novel combined stator segment with the SMC brim arranged on the top of the AMM stator teeth is proposed to improve the amplitude and distribution of the PM eddy-current density. The analysis results show that the combined stator segment can significantly reduce the PM eddy-current loss and improve the electromagnetic performance of the in-wheel motor.
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Reduction of the cogging torque is preferred during design process of a PM synchronous machine, especially in the low speed traction applications. This paper presents a dual-skew magnet technique to minimize the cogging torque in the axial flux permanent magnet (AFPM) motor with yokeless and segmented armature (YASA). The theoretical expression of cogging torque of the AFPM machine is deduced, and the advantages of dual-skew magnet are verified by comparing with the sector shape magnet and conventional skew magnet using the 3D finite-element method (FEM). The simulation results show that compared with other two magnet topologies, the machine equipped with dual-skew magnet shows its advantages in reduction of cogging torque, torque ripple and magnet eddy current loss.
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Purpose Analysis of test data monitored for a number of electric machines from the low volume production line can lead to useful conclusions. The purpose of this paper is to trace the machine performance to find quality-related issues and/or identify assembly process ones. In this paper, the monitoring of experimental data is related to the axial flux motor (AFM) used in hybrid electric vehicle (HEV) and in electric vehicle (EV) traction motors in the global automobile market. Design/methodology/approach Extensive data analyses raised questions like what could be the causes of possible performance deterioration of the AFM and how many electric motors may not pass requirements during operation tests. In small and medium research units of AFM for HEV or EV, engineers came across a number of serious issues that must be resolved. A number of issues can be eliminated by implementing methods for reducing the number of failing AFMs. For example, improving the motor assembly precision leads to reduction of the machine parameters deterioration. Findings Assembly tolerances on electric motor characteristics should be investigated during motor design. The presented measurements can be usable and can point out the weakest parts of the motor that can be a reason for the reduced efficiency and/or lifetime of the AFM. Additionally, the paper is addressed to electric motor engineers designing and/or investigating electric AFMs. Originality/value Performance of AFM was monitored for a number of identical motors from low volume production line. All tested motors were operated continuously for a long period of time and the tests were repeated every few weeks for half a year to check the reliability of motor design and indicate how much the motor parameters may change. The final results point how many motors fail the requirements of motor performance. A few batches of AFM were selected for testing. Each batch represents a different size (nominal power) of the same type of AFM.
Article
A new axial flux permanent magnet machine (AFPM) with soft magnetic composited (SMC) cores is proposed for electric vehicle (EV) application in this paper. As its windings are wound on the stator ring core, it can be regarded as a toroidally wound internal stator (TORUS) machine. With the adopted SMC material for stator core, this machine has the benefits of 3-D magnetic flux properties. The windings and SMC cores can be designed to form a very compact structure, and thus, the torque density can be improved greatly. To obtain the a good flux concentrating ability, two TORUS machines are designed and analyzed, one is with NdFeB magnet for high-performance EV application and the other is with the cheap ferrite magnet for low-cost application. The 3-D finite-element method is used to analyze the electromagnetic parameter and performance. For performance comparison, a commercial AFPM with yokeless and segmented armature P400 is used.
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this paper proposed a new yokeless and segmented armature axial flux machine (YASA) applied in-wheel traction. The loss analysis for the motor is performed based on finite-element method (FEM), and several methods are adopted to increase the efficiency and the output power of the motor. Subsequently, a novel cooling system is proposed, and the thermal analysis of which is conducted. On this basis, computational fluid dynamics (CFD) is developed to investigate and optimize the cooling system to increase the heat transfer efficiency. And finally, the in-wheel motor is manufactured and tested. It can be concluded that the measured data matches well with the results of the electromagnetic and CFD analysis, and the peak power of the motor has been increased from 50kW to 65kW before and after improvement.
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Axial flux PM (AFPM) machines are used particularly in applications requiring a compact structure. Their disc shape topology and axial air-gap have led to a variety of configurations including two popular ones: the yokeless and segmented armature (YASA), and the single-stator single rotor or single sided machine. In this study, a comprehensive comparative analysis of these configurations is conducted at different magnetic and electric loadings. It is found that at lower loadings, typically employed for air-cooled machines, the torque/ampere characteristics of the YASA machine are almost identical to those of a single sided machine constructed with half the magnet volume. On the other hand, the single sided machine outperforms the YASA machine when the magnet volumes in both machines are maintained equal. However, for higher electric loadings, the torque/ampere characteristics of the YASA machine droop significantly less than those of the single sided machine. The paper includes analytical estimations which are verified with experimentally validated FEA simulations. In addition, the impacts of the armature reaction on saturation and the magnetic flux linkage, the magnet losses and eddy current losses in both machines are also explored.
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In this article, a fault tolerant deadbeat controller is proposed, which is able to compensate for both partial and uniform demagnetization faults in axial flux permanent magnet synchronous machines with double rotor, even with asymmetric defects in both rotors. For this purpose, the system model used by the deadbeat controller is equipped with a look-up table of the back-emf, in function of the mechanical rotor position. This look-up table is generated by means of an analytical model based on the magnetic vector potential. With this information, the deadbeat controller can eliminate both the additional bias and ripple in the stator current components caused by demagnetization faults. The proposed control strategy is validated on a 4 kW test set-up of an axial flux permanent magnet synchronous machine with yokeless and segmented armature topology fed by a three-phase two-level voltage source inverter, both by simulations and experiments. Key performance indicators concerning bias and ripple of the current components illustrate the superior performance of the proposed control strategy in comparison to a standard deadbeat controller without an up-to-date look-up table of the back-emf.
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This paper proposes a multi-stage axial flux permanent magnet machine (MAFPMM) and the properties with different stator core materials are analyzed. The mentioned MAFPMM has three rotor-disks and two stator-disks. As a key part of the flux path, stator core of silicon steel sheet, soft magnetic composite (SMC) and amorphous magnetic metal (AMM) are studied by three dimensional (3-D) finite element method (FEM), respectively. The performances such as flux density distribution, no-load back-electromotive force (EMF), cogging torque, output torque, and core loss are analyzed. FEM results indicate that the three materials have almost equal influence on flux density distribution, no-load back-EMF, cogging torque, and output torque. But in terms of core loss, difference appears between silicon steel sheet, SMC and AMM. Considering the disadvantages in mechanical property of AMM and silicon steel sheet, a prototype is fabricated using SMC stator core. The FEM results are verified by the experimental results of the prototype.
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Axial flux permanent magnet (AFPM) machines are promising for hybrid electric vehicles (HEVs) due to the compactness, high torque density and high efficiency. However, poor thermal characterization leads to an over-sizing of these machines which ultimately compromises overall system efficiency. In this paper, the transient thermal behavior of all the components in the single sided AFPM machine are characterized in an accurate but computationally efficient lumped parameter thermal model (LPTM). For the first time, contact measurements on the rotor have been used in AFPM machines to demonstrate the ability of the model to predict all component temperatures to within 4 °C for steady state. The mean temperature error over a load step transient was less than 5°C with a maximum error less than 13.5 °C which was for the winding. The model has a running time of approximately 1000 times faster than real time on a desktop machine and is suitable for integration into system simulation tools and predictive control strategies to avoid over-sizing of the motor and improve the usage of the electric machine in dynamic duty cycles.
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This book gathers selected papers from the 16th UK Heat Transfer Conference (UKHTC2019), which is organised every two years under the aegis of the UK National Heat Transfer Committee. It is the premier forum in the UK for the local and international heat transfer community to meet, disseminate ongoing work, and discuss the latest advances in the heat transfer field. Given the range of topics discussed, these proceedings offer a valuable asset for engineering researchers and postgraduate students alike.
Chapter
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This study aims to evaluate the performance and cooling effectiveness of both photovoltaic (PV) and hybrid PV/thermal systems under various ambient conditions. Two models, namely standard PV module subject to ambient conditions without active cooling and a single-pass hybrid PV/T air collector, have been designed and simulated using the CFD software of COMSOL Multiphysics V5.3a. The PV material used in our analysis is monocrystalline silicon with a power temperature coefficient of 0.41% ºC−1. The thermal and electrical performances of both systems are evaluated numerically and compared to experimental data for validation. The results predicted for cooling effects show noticeable enhancements in both the electrical and thermal efficiencies of the systems, with up to 44% compared to the PV module without active cooling. The electrical PV/T arrangement has increased the performance of air cooling in a laminar flow regime with up to 4%. A numerical-based design optimization is carried out to enhance the system performance.
Article
The segmented-stator dual-rotor axial flux permanent magnet motor (AFPMM) in this paper adopts two-segment Halbach permanent magnets (PMs) in the rotor and soft magnetic composite materials in the stator core, so it has the advantages of high torque density and high efficiency. This paper proposes an optimization method for AFPMMs combining analytical optimization and nonlinear optimization, based on the analytical calculation of the magnetic field and electromagnetic performance. To realize analytical calculations, the AFPMM is regarded as the superposition of equivalent linear PM motor slices at different radii. The magnetic field is calculated using the slotless 2D equivalent model and the slotted air gap relative permeability. Compared with finite element analysis (FEA), the analytical calculation of the electromagnetic characteristics has acceptable accuracy and faster speed. The multi-objective optimization program for the AFPMM aims at lighter motor mass and lower loss. In analytical optimization, the expression of the optimal axial magnetization coefficient of the two-segment Halbach array and the expression of the minimum rotor core thickness is deduced to improve the optimization speed and results. Then, the nonlinear optimization algorithm is used to solve the multi-objective optimization problem.
Article
In-wheel motors present a range of opportunities for innovation in electric vehicle design as the torque produced at each of two or four wheels can be controlled individually. A high aspect ratio (large radius, short axial length) motor is required to fit within the wheel. Due to its location, liquid cooling of the in-wheel motor is difficult and undesirable, but a high power density is required to reduce the mass---which is particularly important as it is unsprung---and fit the space envelope. Furthermore, a high torque density is required to eliminate the need for a gearbox. These constraints create a real challenge for the design of a machine for this application. An axial field machine using a Yokeless and Segmented Armature (YASA) topology is designed to fit these requirements as such a machine has clear advantages when considering the high aspect ratio. A soft magnetic composite (SMC) material is utilised to carry the flux in its non-planar path without incurring excessive losses or requiring a lamination design which is difficult and expensive to manufacture. A novel cooling arrangement involving heat-spreading elements on each armature segment is employed to improve heat dissipation and hence power density. The design, analysis, manufacturing, and testing of the motor is described in this paper to verify the concept against the requirements outlined above.
Article
A category of permanent-magnet-shield (PM-shield) axial-field dual-rotor segmented switched reluctance machines (ADS-SRMs) are presented in this paper. These topologies are featured by using the magnetic material to shield the flux leakage in the stator and rotor parts. Besides, the deployed magnets weaken the magnetic saturation in the iron core, thus increasing the main flux. Hence, the torque-production capability can be increased effectively. All the PM-shield topologies are proposed and designed based on the magnetic equivalent circuit (MEC) model of ADS-SRM, which is the original design deploying no magnet. The features of all the PM-shield topologies are compared with the original design in terms of the magnetic field distributions, flux linkages, phase inductances, torque components, and followed by their motion-coupled analyses on the torque-production capabilities, copper losses, and efficiencies. Considering the cost reduction and the stable ferrite-magnet supply, an alternative proposal using the ferrite magnets is applied to the magnetic shielding. The magnet demagnetization analysis incorporated with the thermal behavior is performed for further verification of the motor performance.
Article
Full-text available
Axial flux permanent magnet (PM) machines are being developed for many applications due to their attractive features. An extensive literature exists concerning the design of a variety of types of axial flux PM machines. An overview of axial flux, slotless and slotted various PM machines are presented in this paper. Machine structures, advantages and features of the Axial Flux PM machine (AFM) are clarified. Several interesting novel axial flux machine structures are also covered from a variety of perspectives.
Conference Paper
Full-text available
Two different external-rotor-internal-stator TORUS type axial flux PM machines can be derived based on the direction of the flux. In the first type of the TORUS machine, magnet driven flux enters the stator and travels circumferentially along the stator core while, in the second type, the flux enters the stator and travels axially along the machine axis of rotation. The major differences between the two topologies are the direction of the magnet driven flux, the winding arrangement and the thickness of the stator yoke. In this paper, the sizing equations are derived for both types of TORUS machines. Based on the sizing analysis, optimum design is achieved for minimum ripple torque and maximum torque density. Furthermore, finite element analysis (FEA) of both TORUS structures are investigated to get an insight in 3D field distribution, flux directions and paths in different parts of the machines for different load conditions. Minimization of the cogging and ripple torque components of the TORUS concept machines are displayed using 3D FEA for the insight in pulsating torques, ripple torques and cogging torques. Finally the comparison of the TORUS topologies are made in terms of flux densities, cogging and ripple torques and the results are illustrated in the paper.
Article
Purpose – To design a high power density machine, an automatic design method is proposed. Hopefully, automatic design method uses only the requirements (torque and speed) and the information about sources (voltage and current). Design/methodology/approach – To calculate the volume, a necessary flux density and an inductance are calculated by the permeance method. All mechanical parameters, stator diameter, teeth width, turn number and so on, realize the necessary flux density and an inductance, and these parameters are expressed as a function of a rotor diameter. By using both conditions of current density and copper loss, a rotor diameter which realizes the minimum volume can be obtained. Findings – As a result of an optimum design, 50 kW SPMSM is realized only into 2[L] spaces, which copper loss is only 500[W], 1 percent of the maximum output. Moreover, 50 kW axial flux type machine is realized only into 1.3[L] spaces. Accurate comparison is possible by only optimum designs because these have the solutions of the same conditions. In a comparison result, a volume of the axial flux machine is less than that of the radial flux machine, because the radial flux type cannot utilize the large rotor diameter. Thus the axial flux type motor is suitable to the high torque machine. Research limitations/implications – In this research, the length of the coil end and the iron loss, are ignored, because an axial length of stator is much longer than a coil end especially for the high power motor, and the iron loss estimation has not been established. Practical implications – By using this method, it is possible to perform the automatic design. If a designer inputs only the requested torque, speed and device information, an automatic calculation will be done, and a designer can automatically get a motor structure. Originality/value – Although some papers can calculate the mechanical parameters which realize only torque, all requirements, torque, speed and power are satisfied in this paper. In addition, an optimum point of the volume is theoretically obtained. In industrial applications, because the power range is very important, especially for electric vehicles and so on, this paper provides more compact and more powerful machines.
Article
This paper presents the design of two permanent magnet machines for a novel propulsion system for hybrid electric vehicles called the Four Quadrant Transducer (4QT). The presented machines are designed for a medium-sized passenger car with front wheel drive. It is therefore essential that the machines are compact, since the available space in the engine compartment is very limited. The first machine has a 3D-flux topology and uses Soft Magnetic Composites (SMC), i.e. iron powder, as the core material. The core is segmented in 48 parts, which individually consists of teeth and a rounded back. A rectangular conductor is toroidally wound around the back of each segment resulting in short end-windings and a high slot fill factor of 0,78. The second electrical machine design includes features that are unique for its power class, e.g. a segmented core with grain-oriented silicon iron teeth and rectangular copper conductors. The result is a slot fill factor of 0,74, a high fundamental winding factor for a tooth winding of 0,95, a cogging torque close to zero and high efficiency. Electromagnetic analyses of the proposed machines are performed with analytical calculations and by using the 3D-and the 2D-finite element methods, including torque ripple and eddy current calculations. A laboratory prototype has been built.
Conference Paper
This paper presents a new type of axial flux motor, the segmented armature torus (SAT) topology. The SAT motor has no stator yoke, a high fill factor and short end windings which all increase torque density and efficiency of the machine. Thus, the topology is highly suited for high performance applications. The LIFEcar project is aimed at producing the world's first hydrogen sports car, and the first SAT motors have been developed especially for the vehicle. A laboratory prototype has been built and some preliminary results presented. The peak torque density of the drive is 18 Nm/Kg