High Performance Electrical Machines Research Articles

Analysis of a New Asymmetric Biased-Flux Operation for an Inter-Modular Permanent Magnet Motor

Net zero and electrification targets are continuing to enforce a need for the development of high-performance electrical machines, increasingly based on the use of rare earth permanent magnets. Biased flux motors have the potential to overcome some of the disadvantages associated with more conventional electrical machines. Since their introduction, there has been a consistent trend towards new and improved topologies, all relying on the same principles of operation. In this paper, a new alternative operation is proposed where the magnetic flux density offset of each module is different. The resulting asymmetric biased excitations of the magnets leads to a flux concentration in the air gap. Placement of magnets in the slot-opening area is shown to produce a higher average torque at a higher power factor. It is mathematically shown that the conventional methods used to investigate the effect of each group of magnets separately cannot be used for the explanation of this operation principle. Therefore, it is necessary to simultaneously consider both groups of magnets in the magnetic equivalent circuit. Due to the use of magnets in these motors, thermal conditions are also investigated. Finally, a comprehensive comparison between several stator-situated-magnet motors is presented. The performance of the proposed motor is improved in terms of average torque, torque density, PM torque density, power factor, and overload capability. The torque density specifically has increased by 9%. Moreover, both motors have suitable thermal behaviour which confirms the validity of the demagnetization analysis.

Unraveling the role of the BCC-B2 transition and V occupancies in the contradictory magnetism-ductility relationship of FeCoV alloys

The contradictory relationship between magnetism and ductility restricts further applications of FeCoV alloys in high-performance electrical machines. The role of the BCC-B2 transition, accompanied by vanadium (V) site occupancies, in magnetic moments and ductility has been explored using first-principles calculations. The variations in magnetism and ductility of FeCoV alloys are attributed to the coupling of the BCC-B2 transition and V occupancies. When V replaces Fe atoms in the equiatomic B2-FeCo alloy, the superior magnetism observed in B2-Fe50-cCo50Vc alloys is a consequence of the enhanced local magnetic moment of Fe and the ferrimagnetic-ferromagnetic transition in the magnetic state. Moreover, due to the preferential V occupancy in the B2 phase, the B2-Fe46Co50V4 alloy exhibits comparable ductility to the BCC-Fe50Co46V4 alloy. The results indicate that the increased brittleness in the B2 phase arises from the raised Peierls stress and the enhanced covalent component in interatomic bonding, which is caused by the strong hybridization between Fe and Co atoms. Pearson correlation analysis illustrates that valence electron concentration (VEC) and V content are significant factors in the contradictory relationship between magnetization and ductility. The theoretical results demonstrate that tuning the V content and atomic occupancies is helpful to achieve a trade-off between magnetization and ductility in B2-FeCoV alloys.

Frequency- and Temperature-Dependent Uncertainties in Hysteresis Measurements of a 3D-Printed FeSi wt6.5% Material.

Additive manufacturing of soft magnetic materials is a promising technology for creating topologically optimized electrical machines. High-performance electrical machines can be made from high-silicon-content FeSi alloys. Fe-6.5wt%Si material has exceptional magnetic properties; however, manufacturing this steel with the classical cold rolling methodology is not possible due to the brittleness of this material. Laser powder bed fusion technology (L-PBF) offers a solution to this problem. Finding the optimal printing parameters is a challenging task. Nevertheless, it is crucial to resolve the brittleness of the created materials so they can be used in commercial applications. The temperature dependence of magnetic hysteresis properties of Fe-6.5wt%Si materials is presented in this paper. The magnetic hysteresis properties were examined from 20 °C to 120 °C. The hysteresis measurements were made by a precision current generator-based hysteresis measurement tool, which uses fast Fourier transformation-based filtering techniques to increase the accuracy of the measurements. The details of the applied scalar hysteresis sensor and the measurement uncertainties were discussed first in the paper; then, three characteristic points of the static hysteresis curve of the ten L-PBF-manufactured identical toroidal cores were investigated and compared at different temperatures. These measurements show that, despite the volumetric ratio of the porosities being below 0.5%, the mean crack length in the samples is not significant for the examined samples. These small defects can cause a significant 5% decrement in some characteristic values of the examined hysteresis curve.

A physics-informed Bayesian optimization method for rapid development of electrical machines

Advanced slot and winding designs are imperative to create future high performance electrical machines (EM). As a result, the development of methods to design and improve slot filling factor (SFF) has attracted considerable research. Recent developments in manufacturing processes, such as additive manufacturing and alternative materials, has also highlighted a need for novel high-fidelity design techniques to develop high performance complex geometries and topologies. This study therefore introduces a novel physics-informed machine learning (PIML) design optimization process for improving SFF in traction electrical machines used in electric vehicles. A maximum entropy sampling algorithm (MESA) is used to seed a physics-informed Bayesian optimization (PIBO) algorithm, where the target function and its approximations are produced by Gaussian processes (GP)s. The proposed PIBO-MESA is coupled with a 2D finite element model (FEM) to perform a GP-based surrogate and provide the first demonstration of the optimal combination of complex design variables for an electrical machine. Significant computational gains were achieved using the new PIBO-MESA approach, which is 45% faster than existing stochastic methods, such as the non-dominated sorting genetic algorithm II (NSGA-II). The FEM results confirm that the new design optimization process and keystone shaped wires lead to a higher SFF (i.e. by 20%) and electromagnetic improvements (e.g. maximum torque by 12%) with similar resistivity. The newly developed PIBO-MESA design optimization process therefore presents significant benefits in the design of high-performance electric machines, with reduced development time and costs.

Blue laser welding of laminated electrical steels: Dynamic process, weld bead characteristics, mechanical and magnetic properties

Laminated electrical steels are the key material structure of the stator and rotator of a motor, where high-quality welding is crucial for improving the performance of the electric machine. However, it is challenging to achieve a desired balance among the magnetic properties, mechanical properties, and welding efficiency for the laminated electrical steels at present. This work first adopted a 450 nm flat-top blue laser with a maximum power of 2000 W, which has a higher primary absorption rate to Fe compared to that of the conventionally used 980-1080 nm infrared laser, to join the laminated electrical steels. The dynamic process, weld bead characteristics, mechanical properties, and magnetic properties of the blue laser welding of laminated electric steels were investigated. The results show that a flat-top and large-spot blue laser can make the molten pool have a self-stabilizing ability to keep the continuity when encountering the gap and unsmooth surface. Moreover, a further improved self-stabilizing ability is observed for a small welding speed. The largest depth and width of the blue laser weld bead in this work are 2.30 and 0.57 mm, respectively, with a shear strength of up to 1700 N, which are achieved at the laser power of 1500 W and welding speed of 10 mm/s. In addition, the work also validated that the blue laser could significantly reduce the splashing in welding of electrical steel laminations and improve the welding efficiency, which provides a promising solution for high-performance electrical machine manufacturing.

New design of electric vehicle motor based on high-strength soft magnetic materials

PurposeThe purpose of the paper is to make a high speed motor based on the characteristics of high strength silicon steel. With the higher requirements for torque density and power density of the driving system of electric vehicles (EV), conventional magnetic materials have been difficult to meet the demands in the future. In this paper, a new type of high-strength non-grain-oriented (NGO)material is tested.Design/methodology/approachThrough analyzing the characteristic of high strength silicon steel, it is applied to the rotor part of a high-speed motor. A topological optimization is applied to achieve higher power density and higher efficiency of the motor.FindingsThe feasibility of the scheme was analyzed by the finite element method, and a prototype was also fabricated to verify the analysis.Originality/valueIn this paper, the characteristics of new soft magnetic materials as a breakthrough to manufacture a new generation of high-performance electrical machine (EM) are discussed. Consequently, the presented work greatly facilitates further explorations and guides the innovative application of soft magnetic materials and the iterative optimization of motor structure.

Comparison of AC Losses in the Winding of Electrical Machines with Fixed Strands Positions, Fixed Conductor Shapes and Random Winding

In high performance electric machines, the increase of fundamental frequency leads to additional losses in the winding due to parasitic effects such as the associated skin and proximity effects. In the first part, this paper presents an investigation into accurate modelling of AC losses in the winding using numerical methods and their experimental verification. Then, using experimental motorette setups, this research provides a comparative study between fixed strand positioning and fixed conductor shapes on the AC losses in the winding. It is shown that the exact position of strands in the conductor is not a critical factor; however, it is very important to control the conductor shape inside the slot. In the final section of this paper, an investigation into the relationship between AC losses in the winding and copper filling factor is presented. It is shown experimentally that counter-intuitive design choices such as using a lower copper fill factor and thicker strand diameters may be beneficial in achieving the highest overall efficiency.

Comparison between Space Mapping and Direct FEA Optimizations for the Design of Halbach Array PM Motor

Effective methods for the design of high-performance electrical machines must use optimization techniques and precise and fast physical models. Convergence, precision and speed of execution are important issues, in addition to the ability to explore the entire domain of solutions. The finite element method (FEM) presents a high accuracy in the results but with high computational costs. Analytical models, on the other hand, solve the problem quickly but compromise the accuracy of the results. This work shows a comparison between an optimization made with an analytical electromagnetic model and a direct optimization with finite element field calculation for the optimal design of a Halbach array permanent magnet synchronous motor (PMSM). In the case of the analytical model, it is necessary to use an iterative method of correcting the model to obtain a valid solution. This method is known as Space Mapping (SM) and the analytical model can be improved with a reduced number of iterations with the FEM. The results show a rapid convergence towards an optimal solution for the SM, with more than 78% reduction in computational cost compared to a Direct FEM optimization. Both solutions have only a difference of 3% on the power density, which indicates that FEM does not improve the results obtained by SM. This represents a great advantage that allows for the consideration of a large amount of designs to analyze the domain of solutions in more detail. This study also shows that SM is a powerful method to optimize the power density or torque density of electrical machines.

The effect of grain size on the internal oxidation of Sm2Co17-type permanent magnets

This work has examined the influence of grain size in sintered Sm2(Co,Fe,Cu,Zr)17-type permanent magnets on the growth of an internal oxidation zone (IOZ). Two magnets of similar composition but with average grain sizes of 46 μm and 170 μm respectively, were exposed to temperatures of 500 °C in air for times up to 1000 h. Overall, the smaller grained magnet showed a reduced growth rate of the IOZ (∼39.01 μm2h−1) compared to the larger grained magnet (∼48.95 μm2h−1) and a smaller irredeemable loss in Br (3.11%) after 1000 h. However, growth rate of the IOZ is shown to depend on the growth direction, in respect to the crystallographic c-axis of the matrix phase. The smaller grain size was shown to be most effective at retarding the growth of IOZ under surfaces parallel to the c-axis. It is proposed therefore, that a smaller grained sintered magnet may be the microstructure of choice for use in demanding, high temperature applications, where a protective coating is not always a possibility, such as a high-performance electrical machine with a surface mount PM rotor. Orientation of the exposed face must also be considered to minimise the resultant magnetic induction loss caused by oxidation.

Electrical Machine Slot Thermal Condition Effects on Back-Iron Extension Thermal Benefits

The slot thermal condition is critical for thermal management of high-performance electrical machines, due to the high heat losses and poor heat transfer ability within the slot. With a part of the back iron projected radially downward into the slot, back-iron extension (BIE) shortens the heat dissipation path from the slot coil to the back iron and was proved to be an effective thermal improvement technique. The relationship between BIE thermal benefits and various electrical machines’ parameters remains to be investigated. Based on an existing concentrated-wound machine, the relationship between the equivalent slot thermal conductivity (ESTC) and the BIE effectiveness is researched in this article. Utilizing a developed 3-D thermal model, the ESTC effects on the temperature reduction with BIE are indicated with simulation results and verified with experimental tests. BIE is reported to provide temperature reductions ranging from 48 °C down to 18 °C across the plausible range of ESTC values considered. Guidelines are given in the final part to suggest the situations under which BIE is more effective.

Effect of Laminate Cutting and Annealing Treatment on the Magnetic Properties of Fe49Co49V2 Alloy

The Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">49</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">49</sub> V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> alloy is a soft magnetic material commonly used in high-performance electrical machines in form of a laminate made of stacked thin sheets. Laminate preparation inevitably induces defects along the cut edge, which will deteriorate the magnetic properties of the alloy. Three laminate cutting methods, namely, punching, electrical discharge machining (EDM), and laser cutting, have been assessed for their impact on the magnetic properties of the laminates. The effect of annealing treatment before and after the cutting process was also studied. The magnetic properties of the ring laminate samples were measured under a frequency of 400 Hz at room temperature. The grain size and local misorientation were evaluated by electron backscattering diffraction (EBSD). Our study indicates that grain boundary and local misorientation within the grains are key considerations when assessing the deterioration of the soft magnetic properties. The mean grain size along the edge of laser-cut laminates with a post-annealing treatment was about 29.3 μm, larger than that in the center area of about 24 μm. This process route also exhibited the lowest fraction of local misorientation of greater than 0.5° along the edge area. As a result, laminates produced by laser cutting followed by a post-annealing treatment displayed the best magnetic performance among all investigated manufacturing routes.

Reliability-Oriented Design of Inverter-Fed Low-Voltage Electrical Machines: Potential Solutions

Transportation electrification has kept pushing low-voltage inverter-fed electrical machines to reach a higher power density while guaranteeing appropriate reliability levels. Methods commonly adopted to boost power density (i.e., higher current density, faster switching frequency for high speed, and higher DC link voltage) will unavoidably increase the stress to the insulation system which leads to a decrease in reliability. Thus, a trade-off is required between power density and reliability during the machine design. Currently, it is a challenging task to evaluate reliability during the design stage and the over-engineering approach is applied. To solve this problem, physics of failure (POF) is introduced and its feasibility for electrical machine (EM) design is discussed through reviewing past work on insulation investigation. Then the special focus is given to partial discharge (PD) whose occurrence means the end-of-life of low-voltage EMs. The PD-free design methodology based on understanding the physics of PD is presented to substitute the over-engineering approach. Finally, a comprehensive reliability-oriented design (ROD) approach adopting POF and PD-free design strategy is given as a potential solution for reliable and high-performance inverter-fed low-voltage EM design.

Estimation of Oil Spray Cooling Heat Transfer Coefficients on Hairpin Windings With Reduced-Parameter Models

Hairpin windings and spray cooling are becoming an increasingly popular combination in the field of high-performance electrical machine design. Machines adopting hairpin windings can achieve higher torque and power densities while enabling them to be manufactured automatically on a large scale to meet the rapid market growth of electric transport. Spray cooling is an effective way for high heat flux removal, which has shown great potentials in electrical machine applications. Although spray cooling has been studied for decades in different engineering applications, the focus had been on investigating its performance on regular surfaces using low-viscosity liquids, such as water. In addition, many existing models for spray cooling heat transfer were built on spray parameters that are difficult to obtain without specialist equipment. Thus, most results from previous studies are difficult to be interpreted and directly applied to electrical machine applications. Practical and economical approaches for estimating the heat transfer coefficients (HTCs) of spray cooling on hairpin windings are needed. This article proposes and validates an experimental approach based on reduced-parameter models that can be applied to predict the HTC of spray cooling setups on hairpin windings.

Multiload Point Optimization of Interior Permanent Magnet Synchronous Machines for High-Performance Variable-Speed Drives

Multiobjective and multiload point design optimization of an interior permanent magnet (IPM) synchronous machine using a global response surface method to achieve low torque ripple with high average torque over the entire speed range is presented in this article. The approach consisting of a set of design steps and multiobjective optimization to obtain high-performance electric machines with optimum usage of rare-earth materials for mass production is presented. The design optimization has been applied to a 12-slot eight-pole IPM machine with two different rotor structures to arrive at the optimized design for a variable-speed high-performance application. Motor parameters are extracted under different load conditions to predict the torque/speed performance of the motors. The proposed design approach provides a machine design with maximized output torque, improved torque density, lower torque ripple, and optimum usage of rare-earth materials. Finally, the finite-element-based modeling results are validated with the experimental results.

Surface Roughness and Surface Topography of Inconel 718 in Powder Mixed Dielectric Electrical Discharge Machining (PMEDM)

In high speed EDM, maximum material removal rate (MRR) is a desirable to increase productivity rate and reducing production cost to the need of industry. However, the surface finish of the machined surface also cannot be neglected since it related to product quality and safety factor especially when to cut difficult to machine material such Inconel 718, which is widely used in aerospace industry. Surface roughness as one of the surface integrity criteria was choose as a response in this research. High discharge current from 20A to 40A, longer pulse on-time (pulse duration) from 200µs to 400µs and the different concentration of the nano Alumina powder were selected as the main parameters, respectively. The effect of powder mixed dielectric in EDM performance in terms of surface roughness was evaluated. The dielectric circulating system known as High Performance Electrical Discharge Machine (HPEDM) was attached to the conventional EDM machine to run the experiments involving powder mixed dielectric. The experiment results shows that, the highest peak current deteriorated the surface roughness. The surface roughness, Ra was increased with the increasing of the peak current. The result also shows that an increasing of the pulse duration the surface roughness was slightly improved. It is observed that, the value of Ra was closely related to the surface topography characteristic of the machined surfaces and directly depends on the applied discharge energy. There is no improvement in surface roughness when powder additive was mixed in a dielectric fluid.

Design and fabrication of morphologically controlled carbon nanotube/polyamide-6-based composites as electrically insulating materials having enhanced thermal conductivity and elastic modulus

Electrically insulating polymer materials having high thermal conductivity and elastic modulus are in high demand for next-generation electric machines and electronic devices. Carbon nanotubes (CNTs) show extremely high thermal conductivity and elastic modulus; however, even the addition of a few CNTs to polymers leads to them losing their electrically insulating properties. Herein, morphologically controlled multiwalled CNT (MWCNT)/polyamide-6 (PA6)/poly(p-phenylene sulfide) (PPS) composites, having high thermal conductivity, electrical insulation and elastic modulus, were designed and fabricated. First, MWCNT/PA6/PPS/EGMA composites comprising a PA6 matrix and MWCNT-localized PPS domains surrounded by shell-layers formed from poly(ethylene-co-glycidyl methacrylate) (EGMA) were prepared. The thermal conductivity of the composites was improved without losing the volume resistivity. However, these composites showed low elastic modulus, especially at high temperature, due to MWCNT localization and the existence of EGMA. Therefore, MWCNT/PA6/PPS/(3-glycidyloxypropyl)trimethoxysilane (GOPTS) composites having a novel morphology were designed and fabricated using GOPTS as a highly reactive shell-forming agent. In this composite, the MWCNT ends were capped with nano-sized PPS domains (MWCNT-PPS nanodomain-linked structure) to prevent electrically conductive paths forming, and MWCNT-PPS nanodomain-linked structures were uniformly dispersed in the PA6 matrix, leading to much enhanced elastic modulus and heat resistance in addition to improved thermal conductivity and electrically insulating properties. These composites containing CNT-nanodomain-linked structures are promising as electrically insulating materials for various applications including high-performance electric machines and electronic devices.

Performance Improvement of Ferrite-Assisted Synchronous Reluctance Machines Using Asymmetrical Rotor Configurations

Recently, the demand for developing high performance electric machines which are free of rare earth magnets are becoming more and more attractive since the raw materials in the rare earth magnets suffer the challenge of increased price and limited supply [1]. In particular, the ferrite-assisted synchronous reluctance machines (FA SynRMs) are regarded as one competitive candidate which incorporate the advantages of the permanent magnet synchronous machines (PMSMs) and synchronous reluctance machines (SynRMs) [2]-[3]. However, all the reported research for FA SynRMs is performed on a fact that the magnets are inserted in the central rotor flux barriers. Thus the rotor shape maintains circumferential symmetry such that the magnetic torque and the reluctance torque obtained from an d-q rotor frame equivalent circuit reach the maximum value at different current phase angles theoretically by 45° (elec.) with each other. Hence, only a portion of each torque component is effectively utilized. Nevertheless, the situation can be improved by taking advantage of the design concept in [4], in which the maximum values of torque components can meet near or at the same current phase angle by flux barrier design in a V-type IPM machine.

Research of Highly Effective Magnetoelectric Disc Type Synchronous Motor

The electrical and magnetic materials development, as well as the electrical machines principles of design, prepared the base for the research and new designs of high-performance disk-type electric machines development for use, for example, as a high-performance valve gearless electric drive part.

Electric drive systems are constantly evolving and key to defining future hybrid and electric vehicle trends

Hybrid electric vehicles (HEVs) and full electric vehicles (EVs) are the fastest growing part of the passenger car market. These vehicles rely on high-performance electric machines and power electronics to drive them resulting in exciting and novel advancements in design and manufacturing. System level attributes and architecture selections provide a clear drive on the component level designs and overall vehicle performance. It is the intention of this article to provide an overview of the numerous HEV topologies including full EV approaches and the types of electric machines they use.

A multiscale model for magneto-elastic behaviour including hysteresis effects

Magnetic and mechanical behaviour are strongly coupled: an applied stress modifies the magnetic behaviour, and on the other hand, magnetic materials undergo a magnetisation-induced strain known as the magnetostriction strain. These coupling effects play a significant role on the overall performance of electromagnetic devices such as magnetostrictive transducers or high-performance electric machines. In order to provide engineers with accurate design tools, magneto-elastic effects must be included into constitutive laws for magnetic materials. The origin of the magneto-elastic coupling lies in the competitive contributions of stress and magnetic field to the definition of magnetic domain configurations in magnetic materials. The magnetic domain scale is then suitable to describe magneto-elastic interactions, and this is the reason why multiscale approaches based on a micro-mechanical description of magnetic domain structures have been developed in the last decades. We propose in this paper an extension of a previous anhysteretic multiscale model in order to consider hysteresis effects. This new irreversible model is fully multiaxial and allows the description of typical hysteresis and butterfly loops and the calculation of magnetic losses as a function of external magneto-mechanical loadings. It is notably shown that the use of a configuration demagnetising effect related to the initial domain configuration enables to capture the non-monotony of the effect of stress on the magnetic susceptibility. This configuration demagnetising effect is also relevant to describe the effects of stress on hysteresis losses and coercive field.