Segmented Armature Axial Flux Research Articles

Anodized Aluminum Foil Winding Axial Flux Machine for Direct-Drive Robotic Applications

There is a need for higher specific torque electric actuators in novel direct-drive robotic applications. Since the specific torque is inherently limited by material properties, designers have to look at novel materials to push the specific torque limit further. In this article, anodised aluminium foil is considered as an alternative to enamelled copper wire in a yokeless and segmented armature axial flux machine. This machine topology has a high specific torque and is particularly suited for an anodised aluminium foil winding. The DC resistance, thermal properties and eventually the specific torque of a prototype test case machine are compared for both winding materials. A 3D thermal finite element model is used to analyse the influence of the thermal interface between winding body and housing, and the influence of the cooling performance on the specific torque. To conclude, anodised aluminium foil winding offers a higher specific torque in direct-drive yokeless and segmented armature axial flux actuators where the winding body thermal resistance is dominant in the thermal path from heat source to heat sink. It is experimentally shown that for the prototype machine, the torque per kg active stator mass increases 13% through the use of anodised aluminium foil.

Stall Torque Performance Analysis of a YASA Axial Flux Permanent Magnet Synchronous Machine

There is a trend to go towards low gear-ratio or even direct-drive actuators in novel robotic applications in which high-torque density electric motors are required. The Yokeless and Segmented Armature Axial Flux Permanent Magnet Synchronous Machine is therefore considered in this work. In these applications, the motors should be capable to deliver high torque at standstill for long periods of time. This can cause overheating of the motors due to a concentration of the losses in a single phase; hence, it becomes necessary to derate the motor torque. In this work the influence of the slot/pole combination, the addition of a thermal end-winding interconnection and the equivalent thermal conductivity of the winding body on the torque performance at standstill will be studied both experimentally via temperature measurements on a prototype stator, and via a calibrated 3D thermal Finite Element model. It was found that both a good choice of the slot/pole combination and the addition of a thermal end-winding interconnection have a significant influence on the torque performance at standstill, and allow up to 8% increase in torque at standstill in comparison to a reference design.

Electromagnetic thermal coupling analysis for a novel cooling system of an axial flux hub motor

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.

A Novel Stator Cooling Structure for Yokeless and Segmented Armature Axial Flux Machine with Heat Pipe

The yokeless and segmented armature axial flux machine is considered an excellent topology for electric vehicles application. However, its performance is severely limited by the stator cooling system. The heat pipe, as the small size, lightweight, but highly efficient passive phase-change cooling element, has been attracting more and more attention in the thermal management methods of electric motors. Therefore, the relationship between the thermal performance of the heat pipe with temperature is measured in detail through an experimental test platform in this paper. Further, a novel stator cooling structure that combines the heat pipe with the housing water-cooling method is introduced to improve the temperature distribution of the stator. Computational fluid dynamics (CFD) simulation verifies that the proposed cooling structure can accelerate the release of heat from the stator and reduce the temperature of the stator significantly.

Design of a new type yokeless and segmented armature axial flux machine

Design of a new type yokeless and segmented armature axial flux machine

A Yokeless and Segmented Armature Axial Flux Machine With Novel Cooling System for In-Wheel Traction Applications

This article proposes a new yokeless and segmented armature axial flux machine applied in-wheel traction. The loss analysis for the motor is performed based on finite-element method, 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 that 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 match well with the results of the electromagnetic and CFD analysis, and the peak power of the motor has been increased from 50 to 65 kW before and after improvement.

Multiphysics Analysis of a Stator Construction Method in Yokeless and Segmented Armature Axial Flux PM Machines

Increasing performance requirements for electrical machines such as energy efficiency and torque density require a multiphysics design approach. In these designs, many machine parts very often combine multiple functions, such as electromagnetic, thermal, and mechanical, to keep the design compact and reduce the overall weight, or introduce nonconventional materials in electrical machines. In this paper, epoxy potting techniques are used to keep the different stator parts of a yokeless and segmented armature axial flux PM machine together, and it focuses mainly on the multiphysics aspects of the epoxy resins as well as on their implications on the overall stator design. In this multiphysics design approach, the effect of specific epoxy resin parameters such as maximum service temperature, thermal conductivity, Brookfield viscosity, tensile strength, and coefficient of thermal expansion, on the electromagnetic, thermal and mechanical behavior of the stator are examined. Epoxy resin parameters are evaluated in detailed experiments on small test samples, and finally, measurements on a full prototype 4 kW, 2500 rpm stator are performed.

Parametric Studies for Combined Convective and Conductive Heat Transfer for YASA Axial Flux Permanent Magnet Synchronous Machines

In this paper, the effect of some geometrical parameters on the steady state average temperature of the stator core, the winding and the permanent magnets of the yokeless and segmented armature (YASA) axial flux permanent magnet synchronous machine (AFPMSM) is studied. The geometrical parameters selected for the study are the air gap length, the inward heat extraction fin thickness and the permanent magnet thickness. These parametric studies make it possible to obtain a better trade-off between power density and efficiency. These investigations are very helpful in correlating the values of the geometrical parameters to some specific desired performance criteria like not going below some desired minimum efficiency, limiting the temperature of specific part to some maximum value for maximization of lifetime and also determination of the allowed speed range to limit the temperatures lower than the critical values. This is important specifically for the synchronous machines due to the fact that the speed value affects both the losses and the heat transfer convection coefficients. The air gap length has a direct effect on the overall machine losses and the air gap convection coefficient and hence on the temperature of the machine. As the fins are between the stator windings, a thicker fin reduces the space for copper windings and hence increases the losses, but at the same time improves heat evacuation. In addition, the effect on the temperature is studied of the speed variation, which influences both the losses and the convection coefficients of the machine. Every study is made based on coupled electromagnetic and thermal models. The results are obtained from analytical electromagnetic and thermal models verified by finite element simulations and validated experimentally on a 4 kW yokeless and segmented armature axial flux machine.

Analysis and Optimization of Cogging Torque in Yokeless and Segmented Armature Axial-Flux Permanent-Magnet Machine With Soft Magnetic Composite Core

Analysis and Optimization of Cogging Torque in Yokeless and Segmented Armature Axial-Flux Permanent-Magnet Machine With Soft Magnetic Composite Core

Field-Weakening Performance Improvement of the Yokeless and Segmented Armature Axial Flux Motor for Electric Vehicles

In order to avoid the unsafe operation and raise efficiency of yokeless and segmented armature axial flux motors at high speed, the control current of air gap flux is expected to be as small as possible with the same field-weakening effect. To reduce the control complexity, a new structure of module poles with a combination of permanent magnet and soft magnetic material is proposed, which has the characteristics of lower d-axis reluctance and a higher performance of yokeless and segmented armature axial flux motor with surface mounted permanent magnet. According to finite element analysis (FEA), the flux distributions of a rotor pole in no-load and demagnetization condition are contrasted, and under this new configuration, the derivative analytical models of back electromotive-force (EMF), electromagnetic torque, and air gap flux are validated, moreover, the influence of soft magnetic material of rotor poles on controlling the air gap flux is investigated in different load. Based on a particular objective function, the combination of permanent magnet and soft magnetic material is optimized. The results show that optimal solution of field-weakening performance of yokeless and segmented armature axial flux motors can be improved effectively and legitimately.

Parasitic Currents in Structural Paths of YASA Axial Flux PM Machines: Estimation and Tests

This paper evaluates the parasitic currents that can occur in the structural part of some types of yokeless and segmented armature axial flux permanent magnet machines, where the frame-supporting stator floating teeth can originate stray paths. In this paper, these paths are defined and modeled, and the consequent effects (induced electro motive forces and currents) are estimated. The amount of these effects depends on the machine geometry, the magnetic circuit structure, and the winding layout. In this paper, the analysis is performed on two different rating machines, comparing their results. The model is validated by measurements on the corresponding prototypes.

Predicting the Temperature and Flow Distribution in a Direct Oil-Cooled Electrical Machine With Segmented Stator

This paper presents a computationally efficient thermo-fluid model to predict the temperature and flow distribution in an oil-cooled electrical machine with a segmented stator. The Yokeless and Segmented Armature axial flux machine was used as a case study in which a numerical model was set up and validated to within 6% of experimental results. The model was adapted to predict the temperature distribution of the segmented stator of a machine, identifying the hotspot temperatures and their location. Changes to the flow geometry on the stator temperature distribution were investigated. It was shown how by carefully controlling the flow distribution in the stator, the temperature distribution is improved and the hot spot temperature is reduced by 13 K. This benefits the machine by doubling the insulation lifetime or by increasing the current density by approximately 7%.

Development of a Yokeless and Segmented Armature Axial Flux Machine

This paper is about the mechanical design and analysis of a yokeless and segmented armature axial flux permanent-magnet (PM) synchronous machine, which consists of two external rotors and an inner stator. Although this new electrical machine has many advantages such as high torque density, shorter axial length, and high efficiency, its mechanical construction is yet challenging. This is mostly due to the high axial force between the stator and the two rotors, which can be further increased by the inevitable manufacturing and assembly tolerances. Based on the determined geometric dimensions of the electromagnetically relevant components, a reliable mechanical construction is developed in this paper. Subsequently, stress, deformation, thermal, and modal analyses are performed based on finite-element method (FEM). Finally, the first prototype is successfully manufactured and measured. It can be concluded that the proposed construction is reliable and the measured data match well with the results of the electromagnetic analysis.