Axial Flux Permanent Magnet Machine Research Articles

Cogging Torque Reduction Techniques in Axial Flux Permanent Magnet Machines: A Review

Axial flux permanent magnet machines have garnered significant attention in recent years due to their numerous advantages in various applications, including electric vehicles, wind turbines, and robotics. However, one of the critical challenges associated with these machines is the presence of cogging torque, which can hinder their efficiency and performance. This review article provides a comprehensive overview of the state-of-the-art techniques employed for cogging torque reduction in Axial Flux Permanent Magnet Machines. Different techniques are described, encompassing geometric optimization, magnet placement, and skewing methods. Firstly, the significance of Axial Flux Permanent Magnet Machines is described, as well as the issue of the cogging torque. In the methods section, a review of the strategies for the reduction of cogging torque is described from various articles, and finally, in the discussion section, a list of actions is presented for cogging torque reduction for different topologies. The novelty of the study is that it combines strategies for cogging torque reduction in a single article.

Modeling and Analysis of Axial Flux Permanent Magnet Machines with Stator Module Misalignment

Modeling and Analysis of Axial Flux Permanent Magnet Machines with Stator Module Misalignment

Computation and Design of Detailed Sizing of Stator Slot Types Utilized in Axial Flux Permanent Magnet Machines

Computation and Design of Detailed Sizing of Stator Slot Types Utilized in Axial Flux Permanent Magnet Machines

Multi-Objective Optimization with Hybrid 2-D Equivalent Model on Axial Flux Permanent Magnet Machine for Special Electric Vehicles

Multi-Objective Optimization with Hybrid 2-D Equivalent Model on Axial Flux Permanent Magnet Machine for Special Electric Vehicles

Evolution and Comparison of Two Axial–Flux PM Machines for All–Electric Aircraft Propulsion

Evolution and Comparison of Two Axial–Flux PM Machines for All–Electric Aircraft Propulsion

Analysis of AC Losses in Flat-Wire Windings of Dual-Rotor Axial-Flux PM Machines with Segmented Stators

Analysis of AC Losses in Flat-Wire Windings of Dual-Rotor Axial-Flux PM Machines with Segmented Stators

Research on the Axial Stability of Large-Capacity Magnetic Levitation Flywheel Driven by Axial-Flux Permanent Magnet Machine Based on Runge-Kutta Method

Research on the Axial Stability of Large-Capacity Magnetic Levitation Flywheel Driven by Axial-Flux Permanent Magnet Machine Based on Runge-Kutta Method

A New Concept of Direct Oil Cooling System for AFPM Machines, Numerical Analysis and Optimization

Given the strong growth of the electric drive industry, the automotive sector needs to increase the power density of its motors, leading to a size decrease and, consequently, to economic savings. The increase in power density brings with itself the consequence of increasing the Joule effect losses in the active conductors of the machine. For this reason, the problem of cooling turns out to be of utmost importance precisely because of its direct coupling with mechanical and electromagnetic design. This paper has the aim to perform a CFD analysis concerning the cooling system of a permanent magnet axial flux electric machine. The innovative cooling system studied is a direct one which takes advantage of oil to cool down the DC powered coils. The innovation brought by the present research lays in both the direct axial ejection and the use of oil as coolant. At the current state of art, the coolant flows tangentially and, moreover, water is usually employed instead of oil. The main aim of this analysis will be, after a validation of the numerical code by comparison of the literature data, to minimize the maximum temperature of the coil by means of the proper positioning of the nozzle.

Torque Improvement of Dual-Rotor Coreless Stator AFPM Machine With Non-Overlapping Concentrated Winding for Counter-Rotating Ducted Fan Application

Torque Improvement of Dual-Rotor Coreless Stator AFPM Machine With Non-Overlapping Concentrated Winding for Counter-Rotating Ducted Fan Application

Analyzing heat transfer in Axial Flux Permanent Magnet electrical machines: A literature review on the discretization methods-FVM and FDM

Axial Flux Permanent Magnet (AFPM) machines have gained significant attention due to their high power density, efficiency, and compact design. However, effective heat transfer analysis is critical for optimizing their performance and reliability. This paper presents a comprehensive literature review on the application of discretization methods, specifically the Finite Volume Method (FVM) and Finite Difference Method (FDM), in the thermal analysis of AFPM machines. The fundamentals of FVM and FDM are briefly explained, followed by an exploration of their applications in AFPM machine thermal analysis. The advantages and limitations of using these methods are discussed, and a comparison between FVM and FDM is provided. Advanced discretization techniques, such as the Finite Element Method (FEM), and coupled thermal-electromagnetic analyses are also examined. The paper highlights studies that have utilized FVM or FDM in developing optimized designs and effective thermal management strategies for AFPM machines. Lastly, potential future research directions are identified, including the development of more efficient discretization methods, the incorporation of advanced materials, and the investigation of novel cooling techniques. This review offers valuable insights into the current state of research and potential future directions in the thermal analysis of AFPM machines using discretization methods.

PM Eddy-Current Loss Reduction of Axial Flux PM Wheel Motor With Arc Incompletion Segmentation

The high permanent magnet (PM) eddy-current loss will inevitably cause the risk of irreversible demagnetization, and the PM complete segmentation (CS) method is a common method to reduce the PM eddy-current loss. However, PM CS design will increase the cost and difficulty of assembly process, especially for axial flux PM (AFPM) machines. To address this issue, a new arc incompletion segmentation (AIS) method is proposed to reduce the PM eddy current loss and cost, including double-side AIS and single-side AIS designs. Then, some of the key parameters are optimized. In addition, the PM eddy current loss, cost, and torque performance are studied and compared with different segmentation methods under different conditions based on 3-D finite element method (FEM). Finally, two different 25kW prototypes are manufactured and tested to validate the proposed method and analysis.

Design and Analysis of a Rotor Air-Cooling Enhanced Method for Axial Flux Permanent Magnet Machine With Housing-Cooling

The temperature of axial flux motor components directly affects the performance of machine. The cooling design for the rotor is obviously difficult because of its inherent rotation characteristic. A rotor air-cooling enhanced method for axial flux machines with housing-cooling is proposed in this article. In order to improve the air-cooling performance of the rotor, tile-shaped fins are mounted to the inner wall of the housing taking into account the fluid flow characteristics of axial flux motors in a cavity. The impact of the key parameters on the thermal performance are investigated by the theoretical analysis and computational fluid dynamics. In addition, the thermal model of the tile-shaped fin is derived, and the thermal network of the rotor is constructed accordingly. Finally, two prototype motors are manufactured to evaluate the viability of the proposed approach. The results of theoretical and experimental studies show good agreement.

A Review of Axial Flux Permanent Magnet Machine Technology

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

Circulating and Eddy Current Losses in Coreless Axial Flux PM Machine Stators With PCB Windings

Printed circuit board (PCB) stators in coreless axial flux permanent magnet (AFPM) machines have been proposed, designed, and studied for use in multiple industries due to their design flexibility and reduction of manufacturing costs, volume, and weight compared to conventional stators. This paper investigates mechanisms and methods of approximating open circuit losses in PCB stators within example wave and spiral winding topologies for a dual rotor, single stator configuration using 3D FEA, analytical hybrid techniques and experiments. The effect of rotor magnet shape, end winding, and active conductor geometry on eddy currents is studied, and some mitigation techniques are proposed. Through stator equivalent circuit analysis, circulating current losses caused by mechanical abnormalities and magnetic circuit asymmetry are assessed. Possible strategies and schemes to minimize circulating current losses are also described. The trade-off between stator loss components and some practical design considerations are outlined in detail. The open circuit power losses of a prototype coreless AFPM motor were experimentally tested using multiple example PCB stators and emulated rotor asymmetries, with the findings being comparable to the FEA and hybrid analytical methods results.

Equivalent Transformation Between Axial- and Radial-Flux Permanent-Magnet Machines

In this paper, an equivalent transformation approach for permanent-magnet (PM) electrical machines using coordinate transformation theory is presented. With the proposed method, an axial-flux PM (AFPM) machine can be transformed to an equivalent radial-flux PM (RFPM) machine or vice versa. The main purpose of proposing such a transformation method is to simplify the design of AFPM for specific applications. Besides, according to the working space requirement, the shape of PM machines can be changed while maintaining magnetic performances. The proposed transformation theory is based on the basic magnetic theory and the theoretical derivation is presented in detail. The resulted transformation equations for RFPM and AFPM machines with surface-mounted PMs are friendly to engineers. Moreover, an AFPM machine is used to validate the proposed theory, both FEM and experimental results have good agreement with the results of the proposed method. With the equivalent transformation theory, engineers could design, simulate and evaluate the AFPM machines with an exist well-developed machines.

An Improved Magnetic Equivalent Circuit Method for Segmented-Halbach Axial-Flux Permanent Magnet Machines

Much attention is paid to axial-flux permanent magnet (AFPM) machines thanks to the compactness and high torque density. However, the finite element method (FEM) for AFPM machines will cause a large computational burden during simulation. Thus, this paper proposes an improved magnetic equivalent circuit method (MECM) to predict the performances of segmented-Halbach AFPM machines, which can consider the different magnetization directions of Halbach PMs. Magnetic circuit is built in the whole machine. Besides, the air gap is treated as a slide layer to avoid the additional models for position-dependent permeances. Then, the predicted performances are compared with those calculated by FEM and measured in an experiment. As a quasi 3D analytical method, it predicts the same air-gap flux density as the FEM. The only errors are due to the serious flux leakage caused by opening slots. The predicted back EMF is consistent with the measurement in the experiment. The electromagnetic torque is affected by the errors of air-gap flux density, which results in large ripples. However, the trend of torque with current coincides with the measurement. It means the proposed MECM is effective for the segmented-Halbach AFPM machine.

Improved Coreless Axial Flux Permanent-Magnet Machine With Nonuniformly Distributed Winding

The windings of coreless axial flux permanent-magnet machine (CAFPM) are exposed to the rotor magnetic field, where each back electromotive force (EMF) harmonic is induced not only by several different spatial field harmonics but also by the winding distribution. In order to reduce the time harmonics of back EMF for CAFPM with non-overlapping winding, one new winding structure with non-uniform distributed coils is proposed in this paper, in which the coils are arranged in a non-uniform way with annular distribution in the stator. Firstly, the relationship between uniform and non-uniform distributed windings is analyzed based on the phasor diagram of each coil EMF, and the analytical expression of back EMF under non-uniform distributed windings is established. Secondly, key performance indexes under different working states, like no-load, are investigated by three dimensional (3-D) finite element analysis (FEA). Finally, comprehensive experiments are carried out to verify related theoretical analysis, which demonstrate that the non-uniform distributed windings can effectively reduce the time harmonics and increase the working efficiency.

Impact of Manufacturing Tolerances on Axial Flux Permanent Magnet Machines with Ironless Rotor Core: A Statistical Approach

Axial Flux Permanent Magnet (AFPM) machines with ironless rotors are an attractive and recently studied solution in low-speed applications, due to their potentially high power/weight ratio, high aspect ratio, and high efficiency. Nevertheless, these machines are prone to be affected by manufacturing tolerance during its fabrication process and consequently, the magnets may move freely inside the rotor structure. This work presents a statistical analysis of manufacturing tolerances of an AFPM machine with an ironless rotor, considering several magnet fault types. A computationally efficient superposition method is developed and implemented to obtain both the cogging torque and rated torque considering several tolerance combinations with acceptable accuracy. The results obtained from a statistical analysis of 10,000 designs of a two-stator one rotor tooth coil winding AFPM (TCW-AFPM) machine allowed us to identify the parameters with the most impact on relevant performance indicators and disclosed a substantial increase in cogging and ripple torque when unavoidable combined tolerances are present.

Comparison of Thermal Characteristics in Various Aspect Ratios for Radial-Flux and Axial-Flux Permanent Magnet Machines

This paper proposes an axial-flux permanent magnet machine (AFPM) that uses a neodymium-bonded permanent magnet (Nd-bonded PM) and a coreless rotor structure and assesses how it performs in industrial applications requiring high efficiency and low cost. The AFPM is able to achieve high efficiency in high-speed regions because its Nd-bonded PM can restrain eddy current loss. Additionally, the AFPM can continuously function at the rated operating point without a cooling system, so the expenses for one can be eliminated. Hence, the AFPM can simultaneously achieve high efficiency and low-cost mass production. In this paper, a comprehensive comparison including the thermal characteristics of the proposed AFPM and a conventional radial-flux permanent magnet machine (RFPM) is shown. Furthermore, this paper also focuses on how the aspect ratio influences the thermal characteristics of both machines. Finally, the effectiveness of the proposed AFPM in industrial applications is assessed using 3D-FEA and experimental results.

Novel Multiphysics Design Methodology for Coreless Axial Flux Permanent Magnet Machines

This work is devoted to multiphysics design of coreless axial flux permanent magnet machines with concentrated coils. Recently, these machines have been proposed for the propulsion of civil miniature electric unmanned aerial vehicles, which need very high torque and power densities. Such requirements tend to be in contrast with other important features such as high efficiency and resilience, making the design quite challenging. Among the various geometrical parameters, the rotor poles to stator coils ratio plays a key role in their performance. The main contribution of this paper is the development of an original design method hinging upon the said ratio. The 2D electromagnetic model at the heart of the approach is derived at the average radius and accounts for multi-layer and axially thick stator coils. Additional contributions include the concurrent use of thermal modelling in the preliminary design stage and mechanical analyses in the design refinement stage aimed at optimizing torque density and guaranteeing rotor integrity at maximum speed. Comprehensive experimental tests on a full-scale prototype are reported and help build confidence in the proposed methodology.