Axial-field Machine Research Articles

Modeling of an Axial Field Machine (AFM) With Superconducting Windings

The development of high-temperature superconducting (HTS) electrical machines results in applications of various fields, as they have higher efficiency and power density. Numerical modeling of superconducting electrical machines is usually performed by finite element method based their electrical behavior, and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> -Formulation of the Maxwell's equations is one of the models that are used tremendously due to its high flexibility and simplicity. Axial field machine (AFM) is a machine topology with higher efficiency and power density, but with more complexity when modeling. This paper proposed a new 2D model for the superconducting AFM, where the superconducting coil is simulated with a 2D infinitely long model, this model also divides the electrical machine into two parts: the superconducting parts (HTS coils, bulks, etc.) and non-superconducting parts (e.g., conventional conductors, machine structure). This paper compares the results of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H-A</i> Formulation and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T-A</i> Formulation with this approach, which requires appropriate boundary conditions and continuity between the two regions, along with correct modeling of fixed and moving parts of the electrical machine, where the geometry of this model is based on a linear synchronous machine, which means the rotor is moving linearly instead of rotation.

An Air-Cooled YASA Motor for in-Wheel Electric Vehicle Applications

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 material is utilized to carry the flux in its nonplanar 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 article to verify the concept against the requirements outlined earlier.

Analytical Model for the Magnetic Field Distribution in a Flux Modulation Superconducting Machine

This article presents a theoretical analysis of an axial field machine using high-temperature superconductors (HTSs) wires and bulks. The air-gap magnetic field obtained with the HTS coil and modulated by the HTS bulks is predicted by two 2-D axisymmetric models. Analytical models are based on the solution of Laplace’s equation by the separation of the variable method. The torque is obtained by a quick numerical integration of the Laplace force that acts on the armature winding. The proposed model is compared with 3-D finite-element simulations and good agreement is obtained. This model can be used with an optimization design procedure with a large reduction of the computational time.

Design procedure of coreless stator PM axial field synchronous machine for small-scale wind applications

Axial field machines are available in a wide range of configurations. It has flexible design restrictions. Several research efforts were performed to discover machine performance and design horizons. However, the common design process of axial field machines depends on numerical field analysis, due to the lack of trusted and generalized analytical and/or empirical formulas especially for field distribution. This paper aims to present the essential analytic formulation for dimension selection. In addition, it provides the normalized relations between dimensions and airgap flux density using 3D-FEM as an alternative for empirical formulas. The paper describes a design procedure for coreless stator axial flux permanent magnet synchronous machine. Definite equations are derived to help the designer select the proper number of PM poles and concentrated coils to get balanced multi-phase voltage out of the generator. Moreover, the paper defines the necessary limitations of the span of the concentrated coil for a certain pole pitch to reduce the harmonic content of the output voltage waveform. The paper proposes a new approach for selecting the dimensions of the magnetic circuit using proposed data curves instead of struggling with the 3D-FEM along with its high time consumption and the need for high computational power. The loss calculations and the armature reaction are also investigated as a performance analysis criteria for the designed generator. The paper investigates the design for small-scale wind applications. The design procedure is validated using both 3D-FEM simulations and experimental results. The results show the consistency of the proposed procedure. The procedure is described and applied for a certain configuration and materials. However, it is solely extendable to several other configurations.

ANALYSIS OF COGGING TORQUE REDUCTION TECHNIQUES IN AXIAL FIELD FLUX-SWITCHING PERMANENT MAGNET MACHINE

An axial-field flux-switching permanent-magnet machine (AFFSPMM) is suitable to be used in wind power generation and electric vehicles. However, the cogging torque (Tcog) is large. To obtain high-performance AFFSPMM, the reduction of Tcog in AFFSPMM is investigated. The theoretical Tcog expression is deduced. Based on a 3-D finite-element method, the influences of the design parameters on the Tcog and the reduction methods of Tcog, such as rotor tooth skewing (RTS), rotor tooth circumferential pairing (RTCP), and rotor tooth notching (RTN), are analyzed. The design parameters, except the axial length of rotor, have influences on Tcog, and optimizing the design parameters can decrease Tcog. Tcog can be greatly reduced by RTS for AFFSPMM with a parallel stator tooth and fan-shape permanent-magnet structure. However, RTS is not effective in reducing Tcog for AFFSPMM with a fan-shape stator tooth and parallel PM (FSST-PPM) structure. Tcog greatly decreases by RTN and RTCP for an FSST-PPM stator structure. Moreover, the reduction effect of Tcog with RTN is better than that with RTCP.

Toward Accurate Design of a Transverse Flux Machine Using an Analytical 3-D Magnetic Charge Model

Low-speed high-torque applications, e.g., wind energy generation, favor high number of pole solutions. This usually results in a dominating leakage flux in traditionally radial or axial field machines, while the output power remains constant. Within transverse flux machines (TFMs), an increase in output power proportional to the number of poles is achieved by traversing the flux direction. However, TFMs still suffer from a relatively large leakage, reducing their application in present industries. In order to research this leakage, fast and relatively accurate 3-D models are essential. To date, finite-element models (FEMs) have been dominantly used to calculate these 3-D magnetic fields. However, the FEM requires a large number of elements, hence it is very time consuming (hours for a single solution). A fast and more accurate parameterized model is essential to maximize the power factor while maintaining a high torque density. In this paper, the validity of a 3-D analytical magnetic charge model is used to investigate its applicability to model TFM topologies. As such, an automated parametric search has been undertaken to minimize machine volume, i.e., without considering power factor although with fixed constraints on magnetic flux density and slot leakage. Although this does not provide a global optimized minimum, it is surely interesting for the experienced machine designer who wants to further understand the physics of this machine. To illustrate the accuracy of the magnetic charge model, the error of the final result of such a parametric search is compared with a 3-D FEM, which shows an error in force prediction of only 8.9%.

A Novel Tapered Rotating Electrical Machine Topology Utilizing Cut Amorphous Magnetic Material

Amorphous magnetic materials (AMMs) have been used in low-frequency power transformer applications for more than two decades but not commercially utilized in high-frequency rotating electrical machines despite their low iron losses, which is an order of magnitude lower than conventional silicon iron. This was primarily due to the lack of a suitable handling method and an economical cutting technique. This paper reports a novel brushless synchronous permanent magnet rotating electrical machine that combines the benefits of the previous machine topologies while offering higher torque (due to the larger air-gap surface area compared with the flat axial-field machine) and ease of manufacturing from AMM material, which is suitable for a range of high-efficiency, high-power density, and high-speed machine applications. This paper provides the details and the performance characteristics of this novel tapered-field AMM machine as a generator at high speeds using a bonded rotor magnet topology.

Neuro fuzzy modeling of axial field machines behavior

PurposeThis paper aims to study modeling of the nonlinear behavior of the Torus machine back EMF using an adaptive networks fuzzy inference system (ANFIS). The model can be used to study the steady‐state as well as the dynamic performances of the machine operating as a motor or as a generator.Design/methodology/approachUsing the universal approximation capability of fuzzy systems the authors designed an ANFIS network to model the nonlinear behavior of the back EMF of the Torus motor. The ANFIS is trained using an actual set machine measurements data to generate the motor back EMF for different operating conditions.FindingsSimulation results of the ANFIS model of the Torus motor at different loads proved the ability of the algorithm to effectively model the complex electromagnetic behavior of the machine. Such efficient modeling can directly help in improving and optimizing the Torus motor drive system design.Originality/valueIt demonstrates that ANFIS can model the nonlinear behavior of the back EMF of the Torus motor with excellent accuracy.

Modeling of Axial Flux Permanent-Magnet Machines

In modeling axial field machines, three-dimensional (3-D) finite-element method (FEM) models are required in accurate computations. However, 3-D FEM analysis is generally too time consuming in industrial use. In order to evaluate the performance of the axial flux machine rapidly, an analytical design program that uses quasi-3-D computation is developed. In this paper the main features of the developed program are illustrated. Results given by the program are verified with two-dimensional and 3-D finite element computations and measurements. According to the results, it is possible to evaluate the performance of the surface-mounted axial flux PM machine with reasonable accuracy via an analytical model using quasi-3-D computation.

Evolution of Axial-Field Electrical Machines

This paper is a review of axial-field electrical machines, which were at the origin of the invention of electrical machines such as the famous Faraday’s disk. The different configurations of the axial-field machines are presented along with their advantageous key steady state characteristics such as high efficiency and high power to weight ratio. The differences between axial-field machines and conventional radial-field machines are discussed. The disc-type axial-field electrical machines with permanent-magnet excitation seem to be among the best designs in terms of compactness, suitable shape, robustness, and electric characteristics. Axial-field machines are expected to be used in a large number of applications in the future owing to their special features and distinct advantages compared to conventional radial-field machines.

Elimination of torque pulsations in a direct drive EV wheel motor

Double sided axial field machines are attractive for direct wheel drives in electric vehicles. This is due to the fact that stator/rotor misalignments can be accommodated. In this case the stator of the machine is envisaged mounted on the chassis of the car whilst the rotor directly drives the road wheel. Since the wheel is perturbed by the road surface the rotor will move vertically between the outside stator assemblies and thus give rise to torque pulsations. A vector control scheme has been implemented whereby the torque pulsations are eliminated by (i) calculation of the flux variation due to the rotor perturbation and (ii) using this signal for the modulation of the motor input current.

Analytic approach to magnetic circuit for saturated axial-field induction machines

Performance analysis for saturated axial-field induction machines is rather complicated due to their disc-shaped geometry and the saturation effect. A three-dimensional field computation is generally too expensive to predict their performance with engineering accuracy. To obtain the axial-field distribution in the disc-shaped planar airgap, a distributed magnetic circuit model, composed of a set of concentric ring circuit elements, is presented. By using the circuit model and an analytic method, the airgap flux and the axial-force density distributions in axial-field induction machines can be easily determined. Computed results obtained by the method are in excellent agreement with the measured results. Finally, several typical airgap field and axial force density patterns generally existing in axial-field induction machines are given.

Transient force calculations on a permanent magnet powder metallurgical cored machine

An alternative approach to the finite-element time-stepping procedure for transient force calculation is presented, in which the airgap field, force and power distribution are accurately obtained by acomputed tomography technique. Results are presented showing the true three-dimensional (3-D) variation of the axis components of the field, the derivative 3-D distribution of the Maxwell stress tensors, and the Poynting power flow conditions in the airgap of an electrical machine. The axial field machine used in the study uses powder core material instead of the conventional laminated steel.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Axial-Field Electrical Machines - Design and Applications

Axial-field electrical machines offer an alternative to the conventional machines. In the axial-field machine, the airgap flux is axial in direction and the active current carrying conductors are radially positioned. This paper presents the design characteristics, special features, manufacturing aspects and potential applications for axial-field electrical machines. The experimental results from several prototypes, including d.c. machines, synchronous machines and single-phase machines are given. The special features of the axial-field machine, such as its planar and adjustable airgap, flat shape, ease of diversification, etc., enable axial-field machines to have distinct advantages over conventional machines in certain applications, especially in special-purpose applications.

Axial-Field Electrical Machines???Design and Applications

Axial-field electrical machines (AFM's) offer an alternative to the conventional radial-field machines (RFM's). In the axial-field machine, the airgap flux is axial in direction and the active current-carrying conductors are radially positioned. This paper presents the design characteristics, special features, manufacturing aspects, and potential applications for axial-field electrical machines. The experimental results from several prototypes, including de machines, synchronous machines, and single-phase machines are given. The special features of the axial-field machine, such as its planar and adjustable airgap, flat shape, ease of diversification, etc., enable axial-field machines to have distinct advantages over conventional machines in certain applications, especially in special purpose applications.