Efficiency Of Electrical Machines Research Articles

Electromagnetic Characterization of Silicon–Iron Additively Manufactured Cores for Electric Machines

This paper deals with the electromagnetic characterization of a laminated toroidal ferromagnetic core made through additive manufacturing, specifically using the laser powder bed fusion process. The continuing demand for increasingly efficient, lightweight, and higher performance electric machines is creating huge challenges in the design and realization of new electric motor solutions. The constant improvements in additive manufacturing technologies have prompted researchers to investigate the possibility of adopting these production techniques for the manufacture of high-value electric motors. For these reasons, this paper investigates the ferromagnetic characteristics of an additively manufactured core made with FeSi6.5 powder. The BH curve and the specific iron losses of the processed material have been measured so that they can be compared with a commercial lamination, and have the possibility of carrying out more precise finite element simulations.

Design Improvement of Permanent Magnet Motor Using Single- and Multi-Objective Approaches

Abstract Optimisation, or optimal design, has become a fundamental aspect of engineering across various domains, including power devices, power systems, and industrial systems. Engineers and academics have been actively involved in optimising these systems to achieve better performance, efficiency, and cost-effectiveness. Optimising electrical machines, including permanent magnet motors, is a complex task. It often involves solving intricate problems with various parameters and constraints. Engineers use different optimisation methods to tackle these challenges. Depending on the specific requirements and goals of a design project, engineers may employ either single-objective or multi-objective optimisation approaches. Single-objective optimisation focuses on optimising a single objective, while multi-objective optimisation considers multiple conflicting objectives. In optimisation, objective functions are mathematical representations of what needs to be optimised. In this case, optimising the efficiency of the motor, reducing cogging torque, and minimising the total weight of active materials are defined as possible objective functions. Genetic algorithms are nature based algorithms that are commonly used in engineering to find optimal solutions to complex problems, including those with multiple objectives. In this paper, after conducting optimisations using different objective functions and methods, a comparative analysis of the results is performed. This helps in understanding the trade-offs and benefits of different design choices. Finite element analysis (FEA) is a computational method used to analyse the physical properties and behaviours of complex structures and systems. In this case, FEA is used to validate and analyse selected optimisation solutions to ensure they meet the desired characteristics and parameters. Overall, this work demonstrates the interdisciplinary nature of engineering, where mathematics, computer science (for optimisation algorithms), and physics (for FEA) converge to improve the performance and efficiency of electrical machines. It also underscores the importance of considering multiple objectives in design processes to find optimal solutions that strike a balance between competing goals.

Research on the bending strategy for an innovative, ressource efficient stator design

Due to new requirements regarding the efficiency of electrical machines it is necessary to steadily improve machine concepts or create new ones. Therefore, manufacturing technology has to be continuously improved, adapted or developed new. Forming technology offers an excellent opportunity to implement components for highly efficient electrical machines through its advantages regarding high productivity and high degree of material usage. This paper presents a new method for bending complete stacks of grain oriented electric sheets for use as radially laminated modules in an innovative machine concept with flux barriers. First, the principle of electric drives with flux barriers and the arrangement of the new radial lamination are explained. Then, practical preliminary studies concerning the bending of single sheets are performed. Based on this, the process and tooling for bending of pre-stacked sheets is developed and analysed. Accordingly, an increase in material utilisation of about 30% can be expected compared to classically designed stators. Furthermore, the use of the radially laminated stator principle increases the slot area by about 20% which makes it possible to insert more copper into the slot and thus increase the efficiency of the machine during operation. After validation of the process chain with a demonstrator motor and description of several manufacturing and quality improvements, finally, an outlook is given, and possible further research approaches are discussed.

Comprehensive study on in‐plane eddy‐current loss in permanent‐magnet synchronous machines

AbstractIn‐plane eddy‐current loss in permanent‐magnet synchronous machines has been comprehensively and analytically studied by using three‐dimensional (3D) finite element method. Considering the accuracy and calculation time, the electrical conductivity in the stack direction should be set to zero in 3D analysis. Stacking factor is also an important analytical parameter in this kind of calculation. The influences of slot number and coil‐end height have been clarified. Harmonics caused by an inverter in pulse‐width‐modulation or one‐pulse mode result in additional in‐plane eddy‐current loss, which is independent of the slot number. This behaviour can be explained by a theoretical equation of the eddy‐current loss. These results are useful for the analysis and design of highly efficient electrical machines.

A novel framework based on adaptive Multi-Task learning for bearing fault diagnosis

Bearing fault diagnosis is very important for the security and efficiency of electric machines. In recent years, the newly emerging deep learning methods have risen bearing fault diagnosis as a research hotspot again. To achieve better performance and interpretability and absorb novel methods, this paper proposes a novel framework based on adaptive Multi-Task Learning for bearing fault diagnosis, Gramian Angular Fields - Markov Transition Fields - Convolutional Neural Network (GM-CNN), including data augmentation, image encoding methods and adaptive Multi-Task Learning (MTL). Firstly, data augmentation (DA) methods are applied in data preprocessing for tackling the problems of lack of data and weak generalization ability. They include cropping, flipping, and noise injection. Secondly, Gramian Angular Fields (GAF), Markov Transition Fields (MTF), and their combination GAF-MTF are used to encode time series into images which are more proper for convolutional neural network (CNN) to extract features and classify. Then, the processed data are fed into the proposed MTL framework, and tasks for classifying the fault type and severity are trained jointly as they share some general knowledge and this saves more time. Besides, attention is applied to make the MTL adaptive, which is helpful for more balanced training. Some experiments are carried out. And the experiment results show that the proposed framework is relatively simple but more effective, classifying the fault type and severity with high accuracy (basically higher than 99%). It is shown that every step of the framework is important and essential. This paper provides a reference for future studies on bearing fault diagnosis from the perspective of feature extraction and CNN. It could also be applied to other time series classification situations which could be promising directions.

Reluctance Network Model of IPM Motor Representing Dynamic Hysteresis Characteristics for High-Accuracy Iron Loss Calculation Considering Carrier Harmonics

It is essential to establish a simple and practical method for quantitatively estimating the iron loss considering the dynamic hysteresis behavior to further improve the efficiency of electric machines. In a previous study, a novel simple magnetic circuit model representing the dynamic hysteresis characteristics was presented by incorporating a play model, one of the phenomenological dc hysteresis models, and a Cauer circuit, which can consider the skin effect. It was demonstrated that this magnetic circuit model could accurately calculate the hysteresis loops and iron loss even under PMW excitation for magnetic reactors made of several types of core materials in a short time. However, this method can only be used for an object with a simple shape, such as a ring core. Hence, this paper describes that the previously proposed magnetic circuit model is extended to a reluctance network analysis (RNA) to expand the application range. Furthermore, the proposed method was experimentally validated using an interior permanent magnet (IPM) synchronous motor driven by a PWM converter as the examination target.

Stress-Dependent Magnetic Equivalent Circuit for Modeling Welding Effects in Electrical Steel Laminations

Welding has a severe impact on the efficiency of electrical machines. The heat added during the welding process affects the microstructure of the material and causes residual stress. This results in local degradation of the magnetic permeability and facilitates additional iron losses in the machine core. With the purpose of modeling and simulating welding effects in electric machines, this paper proposes a stress-dependent magnetic equivalent circuit (MEC) model for welded non-grain-oriented electrical steel laminations. A modified iron loss model is proposed to accommodate these welding effects. Furthermore, the proposed MEC model is applied to a M270-35A stator core as a case study. It was demonstrated that the core losses increase by 25% when four welding joints are applied. With a limited number of magnetic measurements on a welded and unwelded core, the model can be fully parametrized. Finally, the model was successfully validated on a core with eight welding seams at 100 Hz. The proposed model can be integrated into the design of electric machines to consider the welding effects.

Effects of pulsed laser ablation with various patterns on non-oriented electrical steels magnetic properties

Surface laser treatments can help improving soft magnetic materials properties through iron losses reduction which allows to increase the efficiency of electrical machines comprising Grain-Oriented Electrical Steels (GOES). What about surface laser treated Non-Grain-Oriented Electrical Steels (NOES) that remain very scarcely studied? In this work supported by experimental results, a laser process called ablation created with advanced Ultra-Short Pulse Laser (USPL) is studied and valued. Several sets of laser parameters and dot patterns are tested with the aim to investigate potential laser impacts unlocked by such technology on power losses and magnetic properties of a NOES grade. Experimental measurements are synthetized through a parametric study which led to find the optimized configuration amongst tested ones. The detailed analysis of the latter shows that improvement of magnetic properties of NOES using an USPL process is possible and may be compared to loss reductions obtained on laser treated GOES if absolute values are considered.

Electrical Conductivity of Additively Manufactured Copper and Silver for Electrical Winding Applications.

Efficient and power-dense electrical machines are critical in driving the next generation of green energy technologies for many industries including automotive, aerospace and energy. However, one of the primary requirements to enable this is the fabrication of compact custom windings with optimised materials and geometries. Electrical machine windings rely on highly electrically conductive materials, and therefore, the Additive Manufacturing (AM) of custom copper (Cu) and silver (Ag) windings offers opportunities to simultaneously improve efficiency through optimised materials, custom geometries and topology and thermal management through integrated cooling strategies. Laser Powder Bed Fusion (L-PBF) is the most mature AM technology for metals, however, laser processing highly reflective and conductive metals such as Cu and Ag is highly challenging due to insufficient energy absorption. In this regard, this study details the 400 W L-PBF processing of high-purity Cu, Ag and Cu-Ag alloys and the resultant electrical conductivity performance. Six Cu and Ag material variants are investigated in four comparative studies characterising the influence of material composition, powder recoating, laser exposure and electropolishing. The highest density and electrical conductivity achieved was 88% and 73% IACS, respectively. To aid in the application of electrical insulation coatings, electropolishing parameters are established to improve surface roughness. Finally, proof-of-concept electrical machine coils are fabricated, highlighting the potential for 400 W L-PBF processing of Cu and Ag, extending the current state of the art.

Synchronous Reluctance Machines: A Comprehensive Review and Technology Comparison

In the last decade, the trend toward higher efficiency and higher torque density electrical machines (EMs) without permanent magnets (PMs) for the industrial sector has rapidly increased. This work discusses the latest research and industrial advancements in synchronous reluctance machines (SynRMs), being the emergent motor topology gaining wide acceptance by many industries. This article presents an extensive literature review covering the background and evolvement of SynRM, including the most recent developments. Nowadays, SynRM has found its niche in the EM market, and the reasons for that are highlighted in this work together with its advantages and disadvantages. The key journal publications in SynRM topics are discussed presenting the biggest challenges and the latest advancements with particular regards to the design methodology. This article aims to provide a thorough overview to the research community and industry about SynRM. There is a clear potential for SynRM to take over a significant portion of the EM market in the near future to meet efficiency standards in industrial applications without the use of rare-Earth PM technology.

Common-Mode Voltage Elimination in Multilevel Power Inverter-Based Motor Drive Applications

The industry and academia are focusing their efforts on finding more efficient and reliable electrical machines and motor drives. However, many of the motors driven by pulse-width modulated converters face the recurring problem of common-mode voltage (CMV). In fact, this voltage leads to other problems such as bearing breakdown, deterioration of the stator winding insulation and electromagnetic interferences (EMI) that can affect the lifespan and correct operation of the motors. In this sense, multilevel converters have proven to be a useful tool for solving these problems and mitigating CMV over the past few decades. Among other reasons, because they provide additional degrees of freedom when comparing with two-level converters. However, although there are several proposals in the scientific literature on this topic, no complete information has been reviewed about the CMV issues and the different multilevel alternatives that can be used to solve it. In this context, the objective of this work is to determine how multilevel power converters provide additional degrees of freedom to make the reduction of the CMV possible by using specific modulation techniques, making it easier for engineers and scientists in this field to find solutions to this problem. This document consists of a descriptive study that collects the strengths and weaknesses of most important multilevel power converters, with special emphasis on how CMV affects each of them. In addition, the differences of modulation techniques aimed to the CMV reduction are explained in terms of output voltage, operating linear range, and generated CMV. Considering this last, it is recommended to use those modulation techniques that allow the generation of CMV levels of 0 V in order to be able to completely eliminate said voltage.

Controlling devitrification in the FeSiB system without alloying additions

Efficient electric machines require soft magnetic materials with superior properties, motivating research on the processing-structure-response correlation in Fe-based metallic glass systems. Here, significant differences in the primary devitrification process and the resulting microstructure of amorphous metallic Fe79Si11B10 alloys synthesized into two different forms by different rapid solidification methods are confirmed. Melt-spun ribbons and water-quenched microwires were investigated with calorimetric, structural, and magnetic probes. It is found that the primary devitrification process of the ribbons occurs at a higher temperature (by 80 K) with a faster exothermic heat release relative to that of the quenched microwires, despite their common chemical composition and fully devitrified structural state. Analysis of the primary devitrification reveals that the ribbons exhibit a ∼70% higher effective activation energy and a ∼110% larger value of Avrami exponent relative to those characterizing the microwires, indicating different devitrification routes taken by these two types of material. In specific, the ribbons crystallize via a continuous nucleation process that partly relies on pre-existing surface nuclei, with an interface-controlled growth mechanism. In contrast, the quenched microwires devitrify solely from pre-existing nuclei, with diffusion-controlled growth. These differences are attributed to unique quenched-in structures that are created by the specific rapid solidification conditions. These results suggest approaches to control the microstructure in FeSiB compositions without the need for non-magnetic alloying additions.

Liquid metal sliding contacts for electric machines

The electric sliding contact in the brush mechanism is one of the most unreliable components of electric machines of alternating and direct current and other electrical equipment in which the transmission of electric current is carried out using sliding contacts that require fairly frequent maintenance and can be a source of sparking. It is possible to increase the reliability and efficiency of electric machines with sliding electric contacts by replacing the dry friction mode with the liquid friction mode in the sliding electric contact. The most appropriate material for use in the construction of a liquid metal sliding contact is gallium. When replacing the sliding electrical contacts of asynchronous electric machines with a phase rotor from traditional solid to liquid metal gallium, it is possible to increase their power up to 1.4 times due to the availability of a higher thermal operating mode.

Determination of Eddy-Current and Hysteresis Losses in the Magnetic Circuits of Electrical Machines

We consider the problem of separation of the total losses in the electric steel of a magnetic circuit into two components: the losses caused by hysteresis and the losses caused by eddy currents. The solution of this technical problem would enable us to guarantee the possibility of efficient design and construction electric machines with magnetic circuits characterized by low magnetic losses. We deduce computational formulas for the hysteresis and eddy-current components of losses, which contain the levels of total losses measured in the open-circuit tests for two different frequencies of magnetization reversal and the ratio of these frequencies. It is shown that the optimal ratio of the frequencies of magnetization reversal is equal to 1.2. We also present the plots of dependences and the expressions aimed at finding the exponent of dependence of the frequency of magnetization reversal on the measured open-circuit losses and the values of frequency.

Thermal Management of Electrified Propulsion System for Low-Carbon Vehicles

An overview of current thermal challenges in transport electrification is introduced in order to underpin the research developments and trends of recent thermal management techniques. Currently, explorations of intelligent thermal management and control strategies prevail among car manufacturers in the context of climate change and global warming impacts. Therefore, major cutting-edge systematic approaches in electrified powertrain are summarized in the first place. In particular, the important role of heating, ventilation and air-condition system (HVAC) is emphasised. The trends in developing efficient HVAC system for future electrified powertrain are analysed. Then electric machine efficiency is under spotlight which could be improved by introducing new thermal management techniques and strengthening the efforts of driveline integrations. The demanded integration efforts are expected to provide better value per volume, or more power output/torque per unit with smaller form factor. Driven by demands, major thermal issues of high-power density machines are raised including the comprehensive understanding of thermal path, and multiphysics challenges are addressed whilst embedding power electronic semiconductors, non-isotropic electromagnetic materials and thermal insulation materials. Last but not least, the present review has listed several typical cooling techniques such as liquid cooling jacket, impingement/spray cooling and immersion cooling that could be applied to facilitate the development of integrated electric machine, and a mechanic-electric-thermal holistic approach is suggested at early design phase. Conclusively, a brief summary of the emerging new cooling techniques is presented and the keys to a successful integration are concluded.

Investigation of power split schemes for modern hybrid cars transmissions

The modes of operation of the transmissions for hybrid cars are studied in this work, using planetary gears for connecting the internal combustion engine (ICE) and the electric machines (motor-generators). The peculiarities of the two-stream variants with an electric branch – a closing block consisting of two electric machines is analysed. This achieves a stepless gear change and an increase in overall efficiency with respect to the efficiency of electrical machines. The theoretical formulation is based on the dependences between the losses of a two-stream circuit, which proves that this increase is a function of the relative share of power transmitted through the electrical branch. The characteristics of typical two-stream circuits with input differential and output differential with one mechanical and one electrical branch are determined. The aim is to evaluate not only the change in the total efficiency, but also the kinematic gear ratio and the ratio of the torques and their ranges for the whole circuit, as a function of the parameters of the electrical branch. The development of the schemes in order to improve their performance in different operating conditions is considered, which allows for combining the variants and modes of operation – serial hybrid and parallel hybrid in two variants, at low speed and high speed. Analytical and graphical methods are used to analyse and illustrate the results, which are more visual and suitable for composite planetary gears with more units. It is expected that cars with such transmissions will have better dynamics compared to conventional automatic transmissions and lower energy consumption or do less damage to the atmosphere, as a result of the optimal combination of the operating modes and dimensions of ICE and electric machines.

Magnetic Properties of Silicon Steel after Plastic Deformation.

The energy efficiency of electric machines can be improved by optimizing their manufacturing process. During the manufacturing of ferromagnetic cores, silicon steel sheets are cut and stacked. This process introduces large stresses near cutting edges. The steel near cutting edges is in a plastically deformed stress state without external mechanical load. The magnetic properties of the steel in this stress state are investigated using a custom magnetomechanical measurement setup, stress strain measurements, electrical resistance measurements, and transmission electron microscopic (TEM) measurements. Analysis of the core energy losses is done by means of the loss separation technique. The silicon steel used in this paper is non-grain oriented (NGO) steel grade M270-35A. Three differently cut sets of M270-35A are investigated, which differ in the direction they are cut with respect to the rolling direction. The effect of sample deformation was measured—both before and after mechanical load release—on the magnetization curve and total core energy losses. It is known that the magnetic properties dramatically degrade with increasing sample deformation under mechanical load. In this paper, it was found that when the mechanical load is released, the magnetic properties degrade even further. Loss separation analysis has shown that the hysteresis loss is the main contributor to the additional core losses due to sample deformation. Releasing the mechanical load increased the hysteresis loss up to 270% at 10.4% pre-release strain. At this level of strain, the relative magnetic permeability decreased up to 45% after mechanical load release. Manufacturing processes that introduce plastic deformation are detrimental to the local magnetic material properties.

INFORMATION TECHNOLOGIES IN IMPROVING ENERGY EFFICIENCY OF ELECTRIC MACHINES

The article provides results of research and suggestions for increasing energy efficiency of electric machines based of informational technologies in programming environment “КОМПАС-3D”. The article shows the relevance of resource saving for transport field where material, energetic, financial and human resources are being extensively used. Also, according to the statistical data almost 95% of electricity used by enterprises are being used to power transportation itself, hence power is used solemnly by electric vehicles – traction engines and auxiliary engines. Based on the analysis of research and their publications methods of increasing electric machines’ energy ef-ficiency were discovered. Usage of methodology of designing and manufacturing electric machines based on CAD/CAM systems gives ability to forecast their energy efficiency and solve a problem of resource storage, quality and competitiveness. Development of resource-efficient electric engine is a process of finding optimal parameters or structure. A choice of optimal engine structure lies in choosing design of each individual element, quantity of elements and relations between them, in defining spatial distribution of the elements. Built-in parameters of en-gine make it possible to conduct further development without using of mathematical apparatus, manufacturing engines of different configurations and calculation of technical and economical indicators, which evaluate effi-ciency of given solutions. On the example of the traction motor of the trolleybus the dependences of SEC on its geometrical parameters, properties of magnetic materials, power of the vehicle, and also speed of movement of the vehicle are resulted. The expediency of solving resource saving issues during the whole design process is shown. Keywords: resource saving, information technologies, energy efficiency, electric motor, computer-aided design systems, efficiency coefficient.

Analytical methods for the radial electromagnetic vibration of stator in permanent magnet motors with an amorphous alloy core

The urgent demand for high efficiency of electrical machines leads to the preliminary application of amorphous alloy, however the accompanying vibration problem becomes more complex. The radial electromagnetic vibration of the amorphous stator core in a permanent magnet motor is analytically investigated in this paper. The magnetic field distribution approach considering the slotted effects and eccentricity is proposed and the air-gap magnetic flux density is validated by the finite element method. The magnetization and magnetostriction characteristics of the amorphous alloy are obtained. The dynamic models for the stator core including yoke sections and the tooth-yoke sections are respectively established. The Maxwell stress and magnetostriction stress are integrated in the magneto-mechanical coupling model. Dynamic responses in the stator core for different radii, position angles and times are analyzed. Vibrations of conventional core with silicon steel and amorphous core are compared. The spatial and temporal characteristics of the dynamic responses in the stator core are explored. The origins and corresponding weights in the electromagnetic vibration at different rotating speeds are revealed. Experiments of a modified permanent magnet motor equipped with the amorphous core are conducted. The theoretical results are validated well by experiments. Results demonstrate that the vibration level of the amorphous core is larger than the silicon steel core when other conditions are the same. Radial vibrations of the stator core are caused by the Maxwell stress, magnetostriction stress and their interaction effects. The weight of magnetostriction effects is improved with the increasing rotating speed. These findings provide an insight into the mechanism of electromagnetic vibration in amorphous stator core and can be helpful for the design of high-efficiency electrical machines.

Investigation of a single-pulse electrical arc discharge in vacuum based on the crater morphology and discharge channel

To improve the machining efficiency of electric machining, a novel method, called electro-arc machining (EAM), was put forward and obtains a great machining efficiency. Afterwards, many researches were conducted to investigate the machining mechanism of EAM; however, up to now, the behaviors of EAM in vacuum had not been studied yet. Therefore, in order to improve the EAM theoretical system, an investigation about the behaviors of single-pulse electro-arc discharge in a negative pressure environment was designed and conducted. The crater morphology, including discolored area diameter (Dh), molten area diameter (Dm), crater diameter (Dc), crater depth (h), white layer thickness, molten volume (Vm), removal volume (Vr), and removal volume ratio, was studied with different discharge current, discharge time, and vacuum degree. The regular characteristics of electro-arc discharge in a negative pressure environment were obtained, and the theoretical model of arc column pressure was improved.