Narges Taran

Multilayer Concentrated Windings for Axial Flux PM Machines

Coreless axial flux machines are of interest because of the absence of stator core losses and cogging torque. These machines generally employ concentrated windings. One of the challenges with such a winding is that the torque producing MMF component that corresponds to the fundamental of the magnet excitation is accompanied by substantial asynchronous components. These harmonics cause losses in the rotor core and magnets, which can become significant at high speeds. This paper proposes a new multilayer winding arrangement to eliminate the non-torque producing MMF components. This winding is applied to a 12-coil 16-pole coreless axial flux machine. The efficacy of the winding is established by 3-D finite-element analysis.

On the feasibility of carbon nanotube windings for electrical machines — Case study for a coreless axial flux motor

The latest developments in carbon nanotube (CNT) wires and yarns attract great interest for potential application to electromagnetic devices, such as electrical machines and transformers. The CNT material properties are largely different from copper and aluminum in terms of electrical conductivity, mass density, and thermal transfer, creating a new design paradigm for which the traditional rules and device topologies no longer apply. This paper proposes a brushless permanent magnet multidisc axial flux construction with coreless stator and special windings and minimal rotor back iron, as a suitable topology for CNT winding application. Specific analytical closed-form sizing equations, as a function of winding electric conductivity, machine dimensions, and operating speed/frequency, are derived and employed in a systematic comparative study over a range of kW power ratings and speeds between 1,000 and 10,000 rpm. The numerical study is complemented by 3D and 2D electromagnetic FEA. The results show that the designs with CNT windings may have substantially higher specific power per mass, particularly at high rotational speeds and/or supply frequency, where the combined effect of DC and AC conduction losses in the windings is significant.

Axial-flux PM synchronous machines with air-gap profiling and very high ratio of spoke rotor poles to stator concentrated coils

Permanent magnet machines including a magnetic gearing effect are attractive for low-speed high-torque applications. This paper proposes a dual-stator axial-flux machine topology with a high ratio for the number of rotor poles to concentrated stator coils. The stator consists of a relatively small number of teeth, with each tooth including multiple smaller/auxiliary teeth. The rotor employs spoke-type permanent magnets, which result in high flux concentration, thereby further improving the torque density. The paper discusses the principle of operation of the proposed machine topology. Finite element results on example designs with 6 stator teeth, each having 2 and 3 auxiliary teeth, and with 20, 32, and 34 rotor poles are presented, respectively. Other feasible slot-pole combinations are also identified.

On the effect of design tolerances on the performance of synchronous PM machines evaluated according to the IEEE Std 1812

In the process of designing an electric machine, the systematic study of tolerances for the design variables and material properties is of the utmost importance. This paper proposes a method by which possible variations of the design variables and material properties can be distinguished. The design of experiments (DOE) technique, open-circuit and short-circuit tests, with minimum instrumentation requirements, have been employed. Virtual tests are conducted based on the recently approved IEEE 1812 testing guide for PM synchronous machines. As a case study, a 100 hp 16-pole 18-slot spoke-type PM machine is discussed. It is shown that variation in magnet remanence, steel grade, as well as dimensional tolerances, may be identified. The ratings and magnetic loading of the machine plays a critical role in identifying manufacturing tolerances.

A comparative study of conventional and coreless axial flux permanent magnet synchronous motors for solar cars

Axial Flux Permanent Magnet (AFPM) motors are suitable options for solar powered vehicles due to their compact structure and high torque density. Furthermore, in NS-type APFM machines, the magnetic stator core may be eliminated, which simplifies the manufacturing and assembly. This paper examines two different machine designs for use in the solar powered vehicle of the challenger class — a single rotor, single stator conventional AFPM machine, and a coreless AFPM machine with multiple stator and rotor discs. The conventional AFPM machine is designed for a one-wheel drive application, while the coreless one is intended for use in a vehicle with two driving wheels. Response surface methodology (RSM) is utilized to select among several hundreds of candidates, in both cases, the designs with minimum losses and mass while meeting the torque requirement. The performance of the selected designs have been studied via 3D finite element analysis (FEA).

Inductance testing according to the new IEEE Std 1812-application and possible extensions for IPM machines

Equivalent circuit parameters are very important for permanent magnet synchronous machines since they serve as the basis for performance estimation and implementation of power electronic drives controls. Specified in the newly approved IEEE Std 1812, a short-circuit test can be employed, in combination with an open-circuit measurement, in order to determine the back emf and the synchronous inductance. In this paper, it is shown that for interior permanent magnet (IPM) machines this approach can be used only to determine the d-axis inductance and additional and separate measurements are required for the q-axis inductance. In this respect, one method widely used in industry, which involves locked-rotor measurements at variable voltage and constant frequency supply, is studied in detail. Other lockedrotor methods based on DC current supply and static torque versus rotor position measurements are introduced for determining q-axis inductance in combination with the standardized open-circuit and short-circuit tests. Test results on an IPM motor design with non-sinusoidal back emf, relatively high torque ripple, and low leakage for the IEEE Std 1812 approach and the newly proposed method for inductance determination are both compared with those from finite element (FE) based simulations.

MAGNUS — An ultra-high specific torque PM axial flux type motor with flux focusing and modulation

Axial flux permanent magnet (AFPM) synchronous motors are attractive for low speed direct drive systems because of their high specific torque. The present paper proposes a novel axial flux machine topology, called MAGNUS, obtained by combining a yokeless central stator type NS arrangement with two external high polarity spoke-rotors, resulting in very high flux concentration. The stator, which includes main and auxiliary teeth for air-gap profiling has a small number of concentrated coils. Two stator configurations are discussed, the first, a yokeless construction with coils wound around the teeth, and the second with coils placed around the stator core in a Gramme ring arrangement. Feasible slot pole combinations are identified. High torque densities are achievable owing to torque magnification achieved by air-gap profiling as well as flux concentration. Initial analysis indicates that this machine presents higher torque than a YASA machine, which currently holds a record for torque density.

Multilayer concentrated windings for axial flux PM machines

Coreless axial flux machines with airgap concentrated windings are of interest due to their high torque density. One of the main challenges with such a winding is that the torque producing MMF component that corresponds to the fundamental of the permanent magnet excitation is accompanied by harmonics. At least one of them is of substantial amplitude. The other harmonics are asynchronous and cause losses in the rotor core and magnets. The lower order harmonics, due to their higher magnitude, are of especial harm. This paper proposes a new multilayer winding arrangement to reduce the non torque producing MMF harmonics. This winding is applied to a 12 coil 16 pole coreless axial flux machine. The efficacy of the winding is established by 3D finite element analysis.