Integrated Modular Motor Drives Based on Multiphase Axial-Flux PM Machines with Fractional-Slot Concentrated Windings

The integrated motor drive (IMD) concept with possible modularization has attracted much attention in a broad spectrum of applications ranging from low-power general-purpose industrial drives to high-power electric propulsion. This paper presents the feasibility study and performance evaluation of using common axial-flux permanent-magnet (AFPM) machines with fractional-slot concentrated windings in IMDs, with the same diameter and a minimum increase in its axial length. Different winding configurations are compared in terms of the torque/power capability and fault tolerance without changing the winding current rating. The possibility of further torque improvement is discussed from the perspective of making full use of the air-gap field harmonics produced by PMs. An AFPM machine available in the lab has been dissembled and used to build the proof-of-concept design, to show the feasibility of the proposed design and benefits of the IMD

Systematically Exploring the Effects of Pole Count on the Performance and Cost Limits of UltraHigh Efficiency Fractional hp Axial Flux PM Machines

Optimizing the design of electric machines is a vital step in ensuring the economical use of active materials. The three-dimensional (3-D) flux paths in axial flux permanent magnet (AFPM) machines necessitate the use of computationally expensive 3-D electromagnetic analysis. Furthermore, a large number of design evaluations is required to find the optimum, causing the total computation time to be excessively long. In view of this, a two-level surrogate assisted algorithm capable of handling such expensive optimization problems is introduced, which substantially reduces the number of finite element analysis (FEA) evaluations to less than 200 while conventional algorithms require thousands of designs to be analyzed. The proposed algorithm is employed to optimally design an AFPM machine within a specified envelope, and to identify the limits of cost and efficiency. In order to obtain these limits, the variables\u27 ranges are assigned to be as wide as possible, resulting in a vast design space, the study of which was enabled by the developed special algorithm. Additionally, optimized designs with different rotor polarities are systematically compared in order to form the basis for a set of generalized design rules

Coreless and Conventional Axial Flux Permanent Magnet 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, certain types of AFPM machines may be configured without stator cores, which eliminates associated losses and cogging torque and simplifies the manufacturing and assembly. This paper examines two 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 disks. The response surface methodology (RSM) is utilized for the systematic comparison of the conventional and coreless topologies and to select the optimum designs among several hundreds of candidates. Designs with minimum losses and mass producing required torque with larger air-gap are favored. The performance of the selected designs has been studied via three-dimensional finite element analysis (FEA). The FEA parametric modeling methodology is validated by measurements on three AFPM machines of the conventional and coreless type

Exploring the Efficiency and Cost Limits of Fractional hp Axial Flux PM Machine Designs

Optimizing the design of electric machines is a vital step in ensuring the economical use of active materials. The three-dimensional flux paths in axial flux PM (AFPM) machines necessitate the use of computationally expensive 3D electromagnetic analysis. Furthermore, a large number of design evaluations is required to find the optimum, causing the total computation time to be excessively long. In view of this, a two-level surrogate assisted algorithm capable of handling such expensive optimization problems is introduced, which substantially reduces the number of FEA evaluations. The proposed algorithm is employed to optimally design an AFPM machine within a specified envelope, identifying the limits of cost and efficiency. Optimized designs with different rotor polarities are systematically compared in order to form the basis for a set of generalized design rules

Evaluating the Effects of Electric and Magnetic Loading on the Performance of Single and Double Rotor Axial Flux PM Machines

Axial flux PM (AFPM) machines are used particularly in applications requiring a compact structure. Their disc shape topology and axial air-gap have led to a variety of configurations including two popular ones: the yokeless and segmented armature (YASA), and the single-stator single rotor or single sided machine. In this study, a comprehensive comparative analysis of these configurations is conducted at different magnetic and electric loadings. It is found that at lower loadings, typically employed for air-cooled machines, the torque/ampere characteristics of the YASA machine are almost identical to those of a single sided machine constructed with half the magnet volume. On the other hand, the single sided machine outperforms the YASA machine when the magnet volumes in both machines are maintained equal. However, for higher electric loadings, the torque/ampere characteristics of the YASA machine droop significantly less than those of the single sided machine. The paper includes analytical estimations which are verified with experimentally validated FEA simulations. In addition, the impacts of the armature reaction on saturation and the magnetic flux linkage, the magnet losses and eddy current losses in both machines are also explored

Torque Production Capability of Axial Flux Machines with Single and Double Rotor Configurations

Axial flux PM (AFPM) machines are used particularly in applications requiring a compact structure. Their disc shape topology and axial air-gap have lead to a variety of configurations including two popular ones: the yokeless and segmented armature (YASA), and the single-stator single-rotor or single sided machine. In this study, a comprehensive comparative analysis of these configurations is conducted at different magnetic and electric loadings. It is found that at lower loadings, typically employed for air-cooled machines, the torque/ampere characteristics of the YASA machine are almost identical to those of a single sided machine constructed with half the magnet volume. On the other hand, the single sided machine outperforms the YASA machine when the magnet volumes in both machines are maintained equal. However, for higher electric loadings, the torque/ampere characteristics of the YASA machine droop significantly less than those of the single sided machine. The paper includes analytical estimations which are verified with experimentally validated FEA simulations. In addition, the impacts of the armature reaction on saturation and the magnetic flux linkage in both machines is also explored

Evaluation of Bearing Voltage Reduction in Electric Machines by Using Insulated Shaft and Bearings

Bearing voltages and corresponding currents in electric machines driven by pulse width modulation (PWM) converters with fast switching and high dv/dt can cause premature bearing failures. This paper evaluates the bearing voltage reduction by using insulated shafts and bearings. An equivalent circuit representation of electric machines taking into account high-frequency effects is developed to show the production mechanism of bearing voltage, based on which simulations are performed with detailed finite element models for transient and simplified equivalent circuit for steady-state analysis. The steady-state equivalent circuit is then calibrated, by combined numerical calculations and experimental measurements, and used to predict the bearing voltage for various scenarios, proving the effectiveness of using insulated shaft and bearings in reducing the steady-state bearing voltage

An Overview of Methods and a New Three-Dimensional FEA and Analytical Hybrid Technique for Calculating AC Winding Losses in PM Machines

This article proposes a new hybrid analytical and numerical finite element (FE) based method for calculating ac eddy current losses in wire windings and demonstrates its applicability for axial flux permanent magnet electric machines. The method takes into account three-dimensional (3-D) field effects in order to achieve accurate results and yet greatly reduce computational efforts. The new 3-D FE-based method is advantageous as it employs minimum simplifications and considers the end turns in the eddy current path, the magnetic flux density variation along the effective length of coils, and the field fringing and leakage, which ultimately increases the accuracy of simulations. This study is one of the first ones to compare meticulous 3-D finite element analysis (FEA) models with more approximate, but faster solution methods, which can be employed in the optimization process. The accuracy of the 3-D FEA calculations has been confirmed through tests on a prototype axial flux permanent magnet machine. The proposed method is applicable for cases with majority of ac copper losses induced due to external magnetic flux sources, such as permanent magnets. Examples of such machines designs are coreless or open slot PM machines with conductors sizes smaller than skin depth

Modeling of Bearing Voltage in Electric Machines Based on Electromagnetic FEA and Measured Bearing Capacitance

Bearing voltages and associated bearing currents in electric machines driven by pulsewidth modulation converters with high switching frequencies and high dv/dt can cause premature bearing failures. This article proposes a new modeling approach for the prediction of steady-state and transient bearing voltages based on two-dimensional (2-D) electromagnetic finite element analysis with coupled external circuits using measured bearing capacitance values. The distributed-element external circuit was employed mainly to take into account the influence of wire distribution and frequency dependency, which are typically neglected by traditional equivalent circuits. The developed model was then used to simulate bearing voltages for various scenarios and evaluate the effectiveness of several easy-to-implement bearing voltage reduction methods from the perspective of machine design and manufacturing, such as using the insulated shaft and/or bearings, introducing additional insulation in the rotor, and changing the material of machine components. Experimental measurements are also provided to facilitate the analysis and validate the proposed approach

Combined Numerical and Experimental Determination of Ball Bearing Capacitances for Bearing Current Prediction

High-frequency voltages across the steel ball bearings and the corresponding currents can cause premature bearing failures in electric machines driven by PWM converters. The bearing voltage, one of the most commonly-used failure indicators, depends heavily on the bearing capacitance. This paper presents a combined numerical and experimental approach for the calculation of ball bearing capacitances to address the uncertainty introduced by lubricant property, lubrication status and other metal parts, such as seals and ball retainers. Based on the obtained capacitance breakdown, the influences of temperature, speed and bearing load (radial, axial or combined) on the capacitance are studied. Measurements and associated results of bearing capacitances are provided to validate the proposed method