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Analysis of the Yokeless And Segmented Armature Machine
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%.
... These articles also provide a means to extract trends in EM technology that migrate to the production of EVs. Research studies by [11][12][13][14][15][16][17][18][19] have focused on advanced new EM design, construction, and control strategies, enabling higher torque density, minimal to zero use of rare earth materials, and reduced torque ripple and/or improved torque delivery for drivability, respectively. The direction of magnetic flux, which is traditionally radial in PMSMs, has been shown analytically [18,20,21], experimentally [7], and in the production of EMs [22,23] to provide benefits in torque and packaging. ...
... The direction of magnetic flux, which is traditionally radial in PMSMs, has been shown analytically [18,20,21], experimentally [7], and in the production of EMs [22,23] to provide benefits in torque and packaging. Similar to studies by [5][6][7][8], a historical perspective, from the early 2000s to the present (2023), on EMs is provided in terms of performance and packaging [9,11,17,18,20,24,25], showing PMSMs to comprise a majority of the topology and yield the highest performance and smallest packaging, which are or attributes are provided for select EMs and TRMs, and the section is concluded with a high-level overview of TRM parasitic losses and the selection of power flow and torque transfer mechanisms for efficiency. ...
A review of past, current, and emerging electric vehicle (EV) propulsion system technologies and their integration is the focus of this paper, namely, the matching of electric motor (EM) and transmission (TRM) to meet basic requirements and performance targets. The fundaments of EM and TRM matching from a tractive effort and a vehicle dynamics perspective are provided as an introductory context to available or near-production propulsion system products available from OEM and Tier 1 suppliers. Engineering data and details regarding EM and TRM combinations are detailed with a specific focus on volumetric and mass density. Evolutionary trends in EM and TRM technologies have been highlighted and summarized through current and emerging products. The paper includes an overview of the initial EV propulsion system’s sizing and selection for a set of simple requirements that are provided through an examination of three light-duty EV applications. An enterprise approach to developing electrified propulsion modules with suitable applicability to a range of light-duty EVs from compact cars to full-size trucks concludes the paper.
... Specifically, Axial Flux Permanent Magnet (AFPM) machines have gained great interest because they have the advantages of PMSM with high levels of torque densities (Nm/m 3 ) and specific torque density (Nm/kg) [5]. Among AFPM machines, the YASA topology (Yokeless And Segmented Armature) stands out regarding high torque density and high efficiency [6]. ...
... With the voltage waveform, the FFT (Fast Fourier Transform) is performed in order to obtain the contribution of the fundamental component of the phase backemf E a1 . The ψ pm is then determined according to equation (6). ...
... 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]). ...
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.
... However, its torque density is affected by the ineffective end-windings, which occupy a considerable portion of the motor volume in shorter axial length designs with distributed windings. The axial flux machine has recently gained industrial interest [9][10][11][12][13], especially the Yokeless Armature Segmented (YASA) machine with no stator back iron and double-sided rotors that can enhance the motor torque density by reducing the magnetic material weight and increasing the electromagnetic interaction within the motor volume [10]. The transverse flux PMSM is also an interesting option for low speed applications [13][14][15][16], as it can achieve high torque density when high number of poles are adopted. ...
... However, its torque density is affected by the ineffective end-windings, which occupy a considerable portion of the motor volume in shorter axial length designs with distributed windings. The axial flux machine has recently gained industrial interest [9][10][11][12][13], especially the Yokeless Armature Segmented (YASA) machine with no stator back iron and double-sided rotors that can enhance the motor torque density by reducing the magnetic material weight and increasing the electromagnetic interaction within the motor volume [10]. The transverse flux PMSM is also an interesting option for low speed applications [13][14][15][16], as it can achieve high torque density when high number of poles are adopted. ...
... 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. ...
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.
... 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. ...
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%.
... The axial flux machines are categorized in numerous different topologies based on its stator and rotor arrangements. For example, dual rotor single stator [12], [13], dual stator single rotor [14], [15], multi stator multi rotor [16], [17], toroidal stator, NS and NN rotor [18], [19], Yokeless And Segmented Armature (YASA) etc [20]- [22]. Among them, the YASA stator machines are getting much attraction nowadays thanks to its high slot fill factor, short end winding, reduced joule losses and improved efficiency [23]- [25]. ...
The demand for Axial Flux Permanent Magnet(AFPM) brushless DC machine is expanding in electric mobility sector owing to its high power density and compact size. However, the axial flux PM machine requires the magnets to be inset on the rotor core for more robustness and reliability. In this paper, the effects of varying depth of the inset-magnet on the airgap magnetic flux density distribution and the dynamic torque response of the machine are analyzed. A parametric analysis is performed on the machine which leads to an optimum value of the inset-magnet depth for best dynamic performance. In order to carry out the analyses, a 1 kW AFPM BLDC machine with18-slot 20-pole combination is designed and investigated using3-D finite element analysis based software. Finally, the steady state performance of the designed machine is reported for the optimum inset-magnet depth
... Based on the traditional torus motor, the entire stator was replaced with segmented stators fixed on the casing, and the stator yoke was removed. Furthermore, as shown in Figure 13, square coils were used to efficiently utilize the slot space to achieve a high fill factor, shorten the axial length of the motor, and further reduce the weight [49]. Consequently, the YASA motor had approximately 50% less stator weight, exhibited a 20% increase in torque density, and reached 95% efficiency. ...
Axial flux permanent magnet synchronous motors (AFPMSMs) have been widely used in wind-power generation, electric vehicles, aircraft, and other renewable-energy applications owing to their high power density, operating efficiency, and integrability. To facilitate comprehensive research on AFPMSM, this article reviews the developments in the research on the design and control optimization of AFPMSMs. First, the basic topologies of AFPMSMs are introduced and classified. Second, the key points of the design optimization of core and coreless AFPMSMs are summarized from the aspects of parameter design, structure design, and material optimization. Third, because efficiency improvement is an issue that needs to be addressed when AFPMSMs are applied to electric or other vehicles, the development status of efficiency-optimization control strategies is reviewed. Moreover, control strategies proposed to suppress torque ripple caused by the small inductance of disc coreless permanent magnet synchronous motors (DCPMSMs) are summarized. An overview of the rotor-synchronization control strategies for disc contra-rotating permanent magnet synchronous motors (CRPMSMs) is presented. Finally, the current difficulties and development trends revealed in this review are discussed.
... The torus type includes popular AFPM variants, such as the coreless machine, yokeless and segmented armature (YASA) machine, as well as the toroidal winding machine. More information about these variants can be found in [13], [16]. ...
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.
... As shown in [49]- [52], SMC can offer significant improvements in performance and power density, given the possibilities for mass reduction, wide frequency range of application, low losses, among others features. The YASA topology, also referred to as Internal Segmented Armature (ISA), was first presented by [53] in 2007. The YASA topology is an enhancement of the SSDR machine type, where an attempt to optimize the N-N and N-S constructions led to a design where the stator yoke (back-iron) was completely removed, eliminating with it the re-circulation of magnetic flux between neighboring poles. ...
... This paper explained the importance of combined cooling to achieve the cooling requirements. Woolmer et al. [14] studied the yokeless motor and found it increased the torque density and overall performance of the motor. Lamperth et al. [15] developed technology based on axial flux topology. ...
The cooling of E-machines was investigated using phase change material (PCM). The PCM is widely used in the cooling of electronic components because of its heat-absorbing and cooling properties. In this study, PCM OM35 (50:50) and OM35 (60:40) were used for the cooling of E-Machines, which are commonly known as electric vehicle motors. Three different configurations, viz. no rib, two ribs, and four ribs, were studied to understand the impact of thermal behaviour on bracket cooling. The ribs were added in between the brackets to enhance the heat transfer. Numerical simulations were performed using the volume of fluid multiphase analysis approach to model the behaviour of phase change inside the brackets for 18 KW E-Machines. Based on the study, a four rib configuration showed good performance compared to no rib and two rib configurations, and heat transfer improved by 6%. Heat transfer is thus improved by increasing the number of ribs placed between the brackets. The cyclic heat load was applied to the best performing ribs to study the impact of different PCM materials OM35 (50:50) and OM35 (60:40).
... 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. ...
This paper presents and evaluates a dual rotor axial flux permanent magnet motor for electric aircraft applications. Several features, including grain oriented electrical steel, Halbach arrays, and wires with rectangular cross-sections, are used to improve torque density and efficiency. A novel winding arrangement is used to mitigate interturn short-circuit faults. 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 these subsystems to select the design with 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, increase the structural mass required to support the rotors, and introduce complexity to manufacturing process. Further analysis for a selected design reveals that the power factor can be significantly improved with a minimal torque penalty via field weakening, due to significant saturation in the stator teeth.
... The main advantage of multiphase machines is the improved fault tolerance, which is still today a relevant motivation for further research [22]. In contrast, little attention has been given to multiphase AFPM machines, once the majority of studies found in the literature address three-phase AFPM machines; except for [2], [3], which address a six-phase YASA machine, the other works cited so far address three-phase AFPM machines. Therefore, the sizing equations found in the literature have been almost exclusively applied to three-phase AFPM machines. ...
This work presents a theoretical and experimental study on the electromagnetic torque of multiphase axial-flux permanent-magnet (AFPM) machines. Initially, a torque equation is obtained through four different methods. The first method follows the definition of electromagnetic power, the second uses the magnetic shear stress, the third is based on the concept of co-energy, and the fourth applies the principle of Lorentz force. Although these methods are based on different assumptions, they lead to the same generalized torque equation, which depends on four parameters: i) the fundamental air gap induction; ii) the electrical loading defined for an arbitrary rotor radius; iii) the ratio of inner and outer rotor radius; iv) the cubic power of the outer rotor diameter. The torque equation is then validated using finite element (FE) analyses and experimental results obtained with a 32-pole/30-slot yokeless and segmented armature (YASA) machine. For this machine, the coils can be connected according to different arrangements so that the phase number can be chosen as three, five, or fifteen. The results show that the torque equation derived here provides sufficient accuracy in practical cases and that it can be applied to machines with phase numbers higher than three.
... 3. For the part of PM arrangements, the Halbach-array PM arrangement is adopted in [9], which can provide a higher flux density to increase torque density, and more sinusoidal air-gap field distribution to reduce eddy current loss. 4. For the part of stator core, the yokeless and segmented armature (YASA) single-stator dual-rotor AFPM machines are proposed in [10], [11]. It has the merits of high torque density and efficiency thanks to the high slot fill factor. ...
Axial-flux permanent magnet (AFPM) machines are gaining popularity in low speed and high torque applications due to their high torque density, high efficiency and compact structure. In this paper, a dual-rotor slotless (DRS) AFPM machine equipped with equidirectional toroidal winding (EDTW) is proposed and compared with that equipped with conventional single layer and double layer concentrated windings (SL and DLCWs). Firstly, the differences between the DRSAFPM machine with EDTW and that with conventional CWs in coil layout, electromotive force (EMF) and winding magnetomotive force (MMF) are revealed. Considering the special coil layout of the EDTW, the coil factor and size equations of the DRSAFPM machines with EDTW and conventional CWs are presented. Secondly, the electromagnetic performance including air-gap field, back-EMF, torque and efficiency of the DRSAFPM machines with EDTW and conventional CWs are analyzed based on the three-dimensional finite element method (3D-FEM). The simulation results validate the correctness of the coil factor and size equations and indicate the EDTW-DRSAFPM machine has superiority in back-EMF amplitude and torque density. Finally, a prototype of the EDTW-DRSAFPM machine is manufactured and tested, which validates the feasibility of the EDTW-DRSAFPM machine and the correctness of the analysis.
... 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]. ...
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.
... "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]. ...
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 torus type includes popular AFPM variants, such as the coreless machine, yokeless and segmented armature (YASA) machine, as well as the toroidal winding machine. More information about these variants can be found in [11], [12]. ...
... 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. ...
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.
... 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. ...
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 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. ...
Zusammenfassung
Axialflussmaschinen eignen sich mit ihrer scheibenförmigen Bauweise gut dazu, eine hohe Drehmomentausbeute in Bezug auf das eingesetzte Aktivmaterial zu realisieren. Gleichzeitig erlaubt es der planare Aufbau, den Eisenkreis modular und möglichst einfach herstellbar zu gestalten. In diesem Beitrag wird eine Maschinenvariante vorgestellt, deren Eisenkreis aus U‑Jochen mit UI-30-Kernblechen und Steckspulen aufgebaut ist. Solche genormten Bleche mit 30 × 40 mm Außenmaß und 30 $$\times$$ × 10 mm Nutausschnitt werden normalerweise zum Bau von Transformatoren eingesetzt. Vorteile dieses Maschinendesigns sind einfache Herstellbarkeit und Skalierbarkeit über die Anzahl der U‑Joche. Nachteile sind Wirbelstromverluste in den Magneten der Rotorscheibe, was den nutzbaren Drehzahlbereich aufgrund erhöhter Magnettemperaturen einschränkt. Da sich mit den UI-30-Kernblechen ebenso eine PMSM-Radialflussmaschine mit Außenläufer herstellen lässt, erfolgt ein direkter Vergleich der für beide Maschinenvarianten aufgebauten Prototypen anhand von Messdaten. In Bezug auf das Drehmoment ist die Radialflussmaschine im Vorteil, während die Axialflussmaschine in Bezug auf Rotorverluste, Materialbedarf und Herstellbarkeit besser abschneidet.
In this paper, electromagnetic performances of radial-flux dual-rotor (DR) fractional-slot concentrated-winding permanent magnet (PM) machines with series and parallel magnetic circuits are compared based on the optimised designs using finite-element analysis based genetic algorithm. It is found that under the same copper loss, the series magnetic circuit DRPM machine has higher output torque and lower iron loss due to yokeless structure. The influences of critical design parameters on both machines, e.g., PM thicknesses and pole arcs, inner and outer split ratios, and stator tooth width, are also investigated. It shows that both machines tend to sacrifice the inner rotor in order to enlarge the slot area, and the outer rotor makes a major contribution to the resultant torque.
Este trabalho desenvolveu a construção de geometrias modeladas através de Elementos Finitos (FEM) ante a construção dos núcleos do estator de um motor do tipo fluxo axial, este tipo de máquina que, compõe-se de materiais ferromagnéticos, produzidos a partir da metalurgia do pó. O núcleo, comumente construído de chapas laminadas, norteia a possibilidade dos materiais SMC’s (Soft Magnetic Composites) como alternativa ao laminado de grão não-orientado. Desta forma, o modelo computacional vem a levantar os comportamentos e geometria da máquina. Foi utilizado o software ANSYS ELETRONICS, de maneira a efetuar a simulação e, validar os parâmetros apurados das caracterizações, visando futura aplicação a uma máquina elétrica de fluxo axial do tipo YASA (Yokeless and Segmented Armature). Como resultados, desenvolveram-se núcleos e, demais geometrias visando-se a validação do uso da tecnologia e confirmação de parâmetros tridimensionais, a partir das caracterizações, o qual auxiliará na composição total do estator da máquina elétrica, tem-se que, para região de 7500 A/m as variações de B ficaram entre 1,5 e 1,42 T, para Somaloy® 1P, 1,55 e 1,25 T, para Somaloy® 3P, e, 1,42 e 1,35 T para Somaloy® 5P.
This study proposes a two-dimensional (2D) analytical model (AM) of slotless axial flux permanent magnet (AFPM) motor, which includes two submodels of armature winding (AW) and permanent magnet (PM) magnetic fields. It can reveal the operating mechanism of equidirectional toroidal winding (ETW) armature magnetic field in the theory and quantitatively analyze its AW and PM magnetic fields. The proposed AM is characterized in that AW magnetic field submodel is established only based on the current density distribution of the effective conductors on one side of a single toroidal coil considering its width and thickness. First, based on the proposed equivalence principle, the analytical submodels of AW and PM magnetic fields of AFPM motor with ETW are established separately, and the formulas of back EMF and torque of the motor are derived. Second, the electromagnetic performance of a slotless AFPM motor with ETW is studied by the proposed 2D AM, including the waveforms of AW and PM magnetic fields, phase back EMF and torque, which are verified by the finite element model. Finally, a prototype of AFPM motor with ETW is manufactured and tested in open-circuit and on-load conditions, which verifies the accuracy of the proposed AM.
In this paper a Lumped Parameter Thermal Network (LPTN) is proposed for a Yokeless and Segmented Armature (YASA) axial flux permanent magnet (AFPM) machine. A simulation model is used to examine the machine in isolation, with an Integrated Motor Drive (IMD), and the machine and IMD with a remote heat sink connected using heat pipes. Losses from electrical and magnetic Finite Element Modelling (FEM) are used as inputs to the model. Introduction of the IMD is found to reduce the power rating of the machine by 27%. This performance can be returned by utilising a remote heat sink configuration to enable enlargement of the heat sink by twice the original volume.
Due to the high-power density and compact structure, axial-flux permanent magnet (AFPM) machines have gradually received much attention with a view to researching breakthroughs in the next generation electric drive technology for electric vehicles in the recent decades. The AFPM machines with factional slot concentrated winding (FSCW) and yokeless stator, namely yokeless, and segmented armature (YASA) motors, have drawn much attention for its high-power density and potential manufacturability due to the concentrated winding and modular stator core configuration. However, the significant rotor loss resulting from the abundant armature reaction harmonics in FSCW machines imposes a great challenge to the rotor heat dissipation, especially when the pursuit of higher speed has become the trend for electric vehicle applications. On the other hand, distributed winding is widely used in high speed radial flux permanent magnet (PM) machines due to its low armature reaction harmonics. In order to figure out the advantages and disadvantages of various winding arrangement and rotor configuration of AFPM for electric vehicle applications, the comparative study of four AFPM machines with various winding configurations and rotor PM arrangements are comprehensively conducted in this article. First, the design and primary optimization of the four AFPM machines are conducted for the electric vehicle requirement specifications. Then, a comprehensive three-dimensional finite-element analysis (FEA) is employed to compare the electromagnetic performance including torque/power density, efficiency, and flux-weakening capacity. Furthermore, the guideline of winding selection of AFPM machines for electrical vehicle is given. Finally, a yokeless stator AFPM prototype with ISDW configuration is manufactured and tested to verify the validity of the FEA results, as well as confirm the comparison conclusion.
This paper systematically compares two axial flux permanent magnet (AFPM) machines designed for a university student racing car application: a doublerotor singlestator yokeless and segmented armature (YASA) structure, and a singlestator singlerotor configuration. Both machines are optimized for minimum loss and active weight using 3D finite element analysis and the highest performing candidate designs are compared in more detail. The studies indicate that the benefits offered by the YASA configuration over the singlestator singlerotor machine are achieved only for specific designs that are heavier. For the design space with lower mass, albeit with increased losses, the Pareto front designs overlap. In this envelope, the YASA configuration demonstrates higher efficiencies at higher speeds, whilst the single-stator single-rotor is more efficient in high torque duty cycles. This shows the performance of the two machines is very similar and the choice is application specific. To validate the Finite Element Analysis (FEA) used in the optimization, a prototype was built and tested. Results showed good alignment between simulation and experimental data.
The weight and volume of electric drive systems are of primary concern in aerospace applications. Here, a high power density axial-flux permanent magnet machine is developed. A compact stator winding with rectangular wire is proposed. The stator coils are connected along the machine inner diameter (ID). The ID connections help to reduce the machine weight and volume and meet the application targets. A detailed winding design procedure is presented considering manufacturing constraints. An electrostatic analysis is also performed to define the wire insulation thickness and the minimum spacing between conductors to assure the insulation system is free of partial discharges. Additional half turns are added to three coils of the winding to place the three-phase terminals at the machine outer diameter (OD). The resultant electromagnetic impact of these three coils is assessed.
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.
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.
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.
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.
This paper presents a new type of axial-field switched reluctance machine (AFSRM), axial-field dual-rotor segmented switched reluctance machine (ADS-SRM), along with its design methodology. The proposed ADS-SRM is featured by the segmental stator and rotor poles, the auxiliary flux-conductive rings, and the concentrated windings. The yokeless topology reduces the active length of the motor. Besides, the adopted shortend winding layout increases the slot fill factor and the motor’s reliability. First, the basic topology of ADS-SRM is introduced along with its operating principle and various stator/rotor pole combinations. The three-phase 12/8 configuration of ADS-SRM is chosen for further analysis. Then, the design methodology considering the fringing and leakage field effects through the magnetic equivalent circuit (MEC) method is developed, and the flowchart detailing the design procedure is presented. Through the comparison with the conventional yokeless and segmented armature (YASA) topology, ADS-SRM exhibits excellent performance at overload conditions. The prototype is designed and fabricated, and the experimental results verify the motor performance.
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.
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.
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.
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.
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.
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.
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