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Finite element models of electrical machines allow insights in electrothermal stresses which endanger the insulation system of the machine. This paper presents a thermal finite element model of a 3.7 kW squirrel-cage induction machine. The model resolves the conductors and the surrounding insulation materials in the stator slots. A set of transient thermal scenarios is defined and measured in the machine laboratory. These data are used to assess the finite element model. [ABSTRACT FROM AUTHOR]

In electric machine design, efficient methods for the optimization of the geometry and associated parameters are essential. Nowadays, it is necessary to address the uncertainty caused by manufacturing or material tolerances. This work presents a robust optimization strategy to address uncertainty in the design of a three-phase, six-pole permanent magnet synchronous motor (PMSM). The geometry is constructed in a two-dimensional framework within MATLAB®, employing isogeometric analysis (IGA) to enable flexible shape optimization. The main contributions of this research are twofold. First, we integrate shape optimization with parameter optimization to enhance the performance of PMSM designs. Second, we use robust optimization, which creates a min–max problem, to ensure that the motor maintains its performance when facing uncertainties. To solve this bilevel problem, we work with the maximal value functions of the lower-level maximization problems and apply a version of Danskin's theorem for the computation of generalized derivatives. Additionally, the adjoint method is employed to efficiently solve the lower-level problems with gradient-based optimization. The paper concludes by presenting numerical results showcasing the efficacy of the proposed robust optimization framework. The results indicate that the optimized PMSM designs not only perform competitively compared to their non-robust counterparts but also show resilience to operational and manufacturing uncertainties, making them attractive for industrial applications. [ABSTRACT FROM AUTHOR]

The development of monitoring and diagnostic methods for electrical machines requires the use of transient models capable of operating in real time and producing signal signatures with high precision. In this context, coupled-circuit models offer numerous advantages due to their speed of execution and accuracy. They have been successfully employed to create real-time digital twins of electrical machines. The main challenge of this modeling method lies in the preparation of the model, which involves numerous preliminary calculations and takes time to identify all its parameters. This is particularly due to the variation in inductances based on the rotor position. To determine these inductance values with great precision, the classical approach involves using finite-element field calculation software. However, the computation time quickly becomes an issue due to the large number of values to calculate and simulations to perform. This article introduces an innovative experimental approach to identify a coupled-circuit model and develop a digital twin of a wound-rotor induction machine. This method relies solely on simple electrical measurements and tests conducted at extremely low rotation speeds (1 rpm) to obtain inductance variations as a function of the rotor position. By employing this technique, the need for analytical models or finite-element field calculation simulations, which typically require precise knowledge of the machine's geometry and materials, is circumvented. The measurement processing employs optimization methods to extract the inductances as a function of the rotor position, which are then used as input data for the coupled-circuit model. The final parameters are specific to each machine and replicate all its manufacturing imperfections such as eccentricity and geometric or winding defects. This experimental identification method significantly enhances the model's accuracy and reduces the usually required preliminary calculation time in a finite-element-based identification process. [ABSTRACT FROM AUTHOR]

In Heating, Ventilation, and Air Conditioning (HVAC) systems, faults can be occurred due to various reasons such as drift deviation, valve/fan failure, water clogging, air filter obstruction, temperature sensor failure and so on. Similarly in electrical machineries faults can be occurred due to multiple causes such as phase reversal, over or under voltage, starter open/short circuit, bearing problems, insulation breakdown, overloading, thermal unbalance, environmental as well as other technical issues. The faults analysis at various stages of electrical systems are critically important for reliable operation of the system. In view of reliability and safety operations of modern sophisticated electrical systems, faults analysis and its diagnosis are necessary to avoid unaccountable losses. The faults at various stages, its causes, methods of detection and diagnosis, fault classifications are included in this work. The comment on effectiveness methods of detection of fault and diagnosis are included for electrical systems. In the industries, systems are incorporated with monitoring capacity for detection of faults at easy and early stage. This paper mainly focused on advancements in fault detection and diagnosis (FDD) methods with short review of various recent methods. This includes system information representation, methods of FDD, description of faults, fault classification, and decision actions related to maintenance, providing a systematic overview of the current state of FDD. Furthermore, the paper underscores the pivotal roles of FDD in electrical systems, emphasizing its effectiveness in identifying faulty states and taking pre-emptive actions against potential failures or accidents. The discussion extends to developments of current research in FDD approaches for electrical machineries with system monitoring, accompanied by short review of diverse and valuable FDD methodologies. The study concludes by addressing comments on recent trends, future directions, challenges, and prospective solutions in the hybrid and dynamic landscape of FDD. [ABSTRACT FROM AUTHOR]

The phrase "Multi-Power System (MPS)" refers to an application that combines different energy conversion technologies to meet a specific energy need. These integrated power systems are rapidly being lauded as essential for future decarbonized grids to achieve optimum efficiency and cost reduction. The fact that MPSs multiply several sources also multiplies their advantages to be environmentally friendly and increases the possibility of energy autonomy as they do not depend on a single source. Consequently, this increases the reliability and reduces the production costs and the size of the storage system. However, the main disadvantages of such a system are the complexity of its architecture and the difficulty in managing the power level, which leads the system to face many faults and sometimes failure. In this case, a fault-tolerant control (FTC) system can automatically adapt to component malfunctions while maintaining closed-loop system stability to achieve acceptable performance. However, on the way to build efficient FTC, one first needs to study the faults that may occur in the system in order to tolerate them. This review paper presents the faults of the MPS electrical sources used in a hybrid system, including a photovoltaic generator and a diesel generator, plus a lead–acid battery as a storage device. Only the most-encountered faults are treated. [ABSTRACT FROM AUTHOR]

Fault detection and diagnosis in electrical machines are periodical for preventing operational interruptions and unexpected shutdowns. However, a Wavelet Feature-dependent Clustering Technique (WFCT) is introduced to address the cyclic fault detection between successive operation intervals. This technique identifies override features from the time-frequency operational wavelets throughout the machine running time. This grouping binds time and operational frequency for identifying override exceeding shutdown/ failure instances. Based on their revamping time, the identified instances are further grouped to prevent overrides in successive operational hours. The fuzzy clustering prevents variation features based on conventional to high-fuzzified extractions. [ABSTRACT FROM AUTHOR]

The permanent magnet synchronous motor (PMSM) can be a suitable candidate for electrified propulsion in aviation. Despite the very high efficiency, heat dissipation during operation leads to performance limitations. Elevated temperatures in the electrical insulations and the magnets pose a potential safety risk that must be reduced by selective cooling. A comprehensive review is conducted to capture current research interests in cooling methods in PMSM. Cooling methods are described according to their heat transfer mechanism, grouped, and assigned to the components within the motor. Key findings of the literature reviewed are described in the context of PMSM cooling. Information on cooling media and potential combinations of cooling methods in components is gathered. Assessment parameters such as safety, weight, effectiveness, integrability, complexity and cost are defined to enable a subsequent qualitative analysis for six selected cooling methods. A point-weighted evaluation approach, according to VDI 2225, was applied to identify the most promising cooling approach for successful implementation in aviation. [ABSTRACT FROM AUTHOR]

Electrical machines are prone to various faults and require constant monitoring to ensure safe and dependable functioning. A potential fault in electrical machinery results in unscheduled downtime, necessitating the prompt assessment of any abnormal circumstances in rotating electrical machines. This paper provides an in-depth analysis as well as the most recent trends in the application of condition monitoring and fault detection techniques in the disciplines of electrical machinery. It first investigates the evolution of traditional monitoring techniques, followed by signal-based techniques such as spectrum, vibration, and temperature analysis, and the most recent trends in its signal processing techniques for assessing faults. Then, it investigates and details the implementation and evolution of modern approaches that employ intelligence-based techniques such as neural networks and support vector machines. All these applicable and state-of-art techniques in condition monitoring and fault diagnosis aid in predictive maintenance and identification and have the highly reliable operation of a motor drive system. Furthermore, this paper focuses on the possible transformational impact of electrical machine condition monitoring by thoroughly analyzing each of the monitoring techniques, their corresponding pros and cons, their approaches, and their applicability. It offers strong and useful insights into proactive maintenance measures, improved operating efficiency, and specific recommendations for future applications in the field of diagnostics. [ABSTRACT FROM AUTHOR]

The predictive maintenance of electrical machines is a critical issue for companies, as it can greatly reduce maintenance costs, increase efficiency, and minimize downtime. In this paper, the issue of predicting electrical machine failures by predicting possible anomalies in the data is addressed through time series analysis. The time series data are from a sensor attached to an electrical machine (motor) measuring vibration variations in three axes: X (axial), Y (radial), and Z (radial X). The dataset is used to train a hybrid convolutional neural network with long short-term memory (CNN-LSTM) architecture. By employing quantile regression at the network output, the proposed approach aims to manage the uncertainties present in the data. The application of the hybrid CNN-LSTM attention-based model, combined with the use of quantile regression to capture uncertainties, yielded superior results compared to traditional reference models. These results can benefit companies by optimizing their maintenance schedules and improving the overall performance of their electric machines. [ABSTRACT FROM AUTHOR]

The following paper presents an analytical study of the air-gap magnetic field distribution produced by the armature reaction of a linear machine. Based on the method of images, the magnetic field generated by a current carrying conductor inside the air-gap between two smooth infinitely permeable iron surfaces is modeled as a complex 2D function. The conductor model then becomes a current sheet model and horizontally oriented current sheets are used to model the magnetic field produced by the armature reaction for smooth ferromagnetic surfaces. Focus will be given to the study of the slot opening function in front of energized slots in comparison to the not energized ones of the classical theory pointing out some remarkable differences. Later, the model is extended to slotted geometries using a complex slotting function adapted for energized slots. At last, the Maxwell tensor expressed in complex formulation will be integrated to obtain the force components acting on the machine tooth tips, quantities that will be compared with FEM simulations in order to validate the proposed analytical model. [ABSTRACT FROM AUTHOR]

In three-phase AC motors, three-phase AC voltage system is essential to generate a rotating magnetic field. Three- phase AC motors also require a three-phase inverter for variable speed and torque operation. In general, the number of switching devices used in three-phase inverter is not less than six and decreasing its number is difficult. This paper focuses on an LC ladder circuit consisting of linear inductors and capacitors. This paper presents a new operating method of the AC motor based on a propagating magnetic field. It is successfully excited by connecting one single-phase AC power supply to the end of the LC ladder circuit. The induction motor operated by the presented method produces torque as in general induction motors. [ABSTRACT FROM AUTHOR]

Power-electronic-converter-induced motor bearing currents are a widespread problem in the field of electrical drives. Parasitic capacitances between the electrical machine's parts provide a path for leakage currents, which finally harm metallic ball bearings. Remembering that end-windings have a significant contribution in building up stray capacitances, a countermeasure affecting both the lamination stack and end-winding areas is needed. This article focuses on a countermeasure against the noncirculating bearing currents in the cluster of solutions at the motor side. The electrostatic shielding approach, which is a known principle to reduce capacitive couplings, is applied in electrical machines every now and then. In this article, the principle of slot-embedded grounded electrodes is extended to cover also the end-windings. Thus, the electrodes provide a better shaft-to-ground voltage mitigating effect compared to the case where electrodes are applied only in the lamination stack area. The feasibility and effectiveness of such a countermeasure are investigated. Different options in terms of scaling of both the machine size and diameter of the electrodes were analyzed and corresponding conclusions were pointed out. [ABSTRACT FROM AUTHOR]

The accurate measurement and modeling of ferromagnetic material losses are vital issues during the design and analysis of electrical machines. Higher loss values can describe the manufactured rotor and stator machine plates better than the catalog data obtained by standardized measurements using the Epstein frame. In this paper, different temperature-dependent models based on the loss-separation principle are introduced and compared with the measurements. The model parameters are computed from customized laboratory and standardized measurements. The customized measurements based on the stator part of an induction machine in the range of the automotive industry standard, i.e., in [−40 ° C, ⋯, 180 ° C]. The proposed model and measurement process can be used in the post-processing stage of numerical field analysis to obtain electromagnetic losses according to the agreement between measured and simulated results. During a numerically expensive optimization process, this model can be used to consider the temperature dependence of the losses more accurately. The study shows that more than 50% of loss increase can be measured, compared with the catalog data, if we use the manufactured, stator-based, customized measurements based on the estimation of the iron loss parameters. [ABSTRACT FROM AUTHOR]

This paper presents a practical thermal model of a synchronous generator for high-power applications. This model couples the lumped parameter thermal network and coolant network together to utilize the impact of the coolant's temperature rising over the machine. Furthermore, the advanced multi-planes technique provides a more precise and higher resolution temperature distribution of various machine sections. Therefore, the machines are divided into five planes; three belong to the active part, and two are added to model the machine's drive and non-drive end-regions. Furthermore, the paper pays special attention to describing the challenges and providing solutions to them during the heat transfer modeling and analysis. Finally, the analytical model is verified using experimental results on a synchronous generator with a salient pole rotor and an open self-ventilation (OSV) cooling system by comparing the analytical and experimental results. As a result, good correspondence between the estimated and measurement results is achieved. [ABSTRACT FROM AUTHOR]

Using the embedded onboard digital thermal model is an economical and effective way to monitor the rotor temperatures of the electric vehicle (EV) propulsion Permanent Magnet Synchronous Motor (PMSM) in real‐time. The onboard thermal model is generally in an analytical form with constant thermal resistances. However, in practical situations, the thermal convection intensities on the surfaces of the air gap and the end‐cavity vary significantly with the rotational speed, producing a non‐negligible influence on the estimation accuracy of the onboard thermal model. Aiming at eliminating this error and improving the accuracy, this paper explores the variation of the airflow's aerodynamics characteristics and the heat convection with the rotational speed through a syncretic study of theoretical, experimental, and numerical methods. It is found that the changing trend of the airflow presents a multi‐stage characteristic in the speed range of 0–12,000 rpm. The speed‐dependent convective thermal resistances are formulaically parameterised and then used to replace the related constant thermal resistances in the thermal model. The standard vehicle driving cycle test result shows that this optimisation brings a nearly 11% reduction of the overall estimation error. [ABSTRACT FROM AUTHOR]

Electric vehicles (EVs) are emerging as an alternative transportation system owing to a reduction in depleting lubricates usage and greenhouse gas emissions. This paper presents a technical review of each and every sub-system and its feasible control of battery EV (BEV) propulsion units. The study includes the possible combination of electrical machines (EMs), storage system, and power electronic converters and their associated control strategies. The primary unit, i.e., EM, is the heart of the EV, which is used to drive the vehicle at the desired speed as well as to restore the regenerative braking (RB) energy that is generated to enhance the overall system reliability. To electrify the transportation sector, it is necessary to include new options of power electronic converter topologies and their associated control strategies for numerous reasons, which include extracting maximum power from sources in case the EV is powered from renewable energy resources, boosting the energy storage capability for longer electric range, managing power flow from the source to battery or battery to vehicle or vehicle to battery, and regulating the speed of the vehicle and braking control. Based on the survey, the suitable combination of sub-systems and their control for three and four-wheeler EVs are summarized in this paper. [ABSTRACT FROM AUTHOR]

The presented article concerns issues related to the diagnostics of the technical condition of the insulation of electrical machines. It discusses the importance of the operational supervision, maintenance and diagnostics of electrical machine insulation systems. The structure of the insulation system is presented and known solutions for making winding insulation are described. The negative impact of conditions and various exposures on the technical condition of the insulation system is described. Special attention is focused on the review of available diagnostic methods for insulating systems of electrical machines. These methods have been arranged in a systematic order according to the type of tests to be carried out. [ABSTRACT FROM AUTHOR]

Although it is well known that the magnetic properties of electrical steel can be deeply affected by the cutting process, it is still not clear how to accurately evaluate these effects on a prototyped machine on its final shape, especially at a high frequency or a high power rating. This research provides a more practical method for accurate measurement of magnetic losses in electrical steel with consideration of material degradation effects due to the cutting process. Unlike other similar studies, these investigations are conducted not only on a few laminations but also on a complete electrical machine core. For a fair comparison between both cases, backlack bonding is used for lamination stacking since it is the most non-damaging joining technique. Two different test setups are used to measure the steel performance at a wide range of frequency and input power. Furthermore, a full axial length stator of a switched reluctance machine (SRM) is used as a case study to identify the magnetic properties of NO20 electrical steel. Additionally, by comparing the results obtained from the individual laminations and the assembled stator, the extra losses due to the cutting process and material degradation are extracted accurately. [ABSTRACT FROM AUTHOR]

This article proposes a hybrid evaluation method of electromagnetic force and vibration for electrical machines considering high-frequency current harmonics caused by the inverter. First, the permeance and armature magnetomotive force (MMF) is calculated based on the virtual MMF and the slot matrix. Then, the air-gap flux density and electromagnetic force construction process under arbitrary current is thoroughly studied. The vibration transfer function is obtained by utilizing the modal analysis and the modal test. Finally, the vibration can be calculated according to the modal superposition method. By applying this method to an interior permanent magnet machine, it can significantly reduce the computation efforts compared with the multiphysics procedure due to the extensive use of the finite-element method. In addition, the accuracy of this method is validated by conducting an experimental study. [ABSTRACT FROM AUTHOR]

Hybrid excitation is a technology that combines the advantages of field windings and permanent magnets for inducing magnetic flux. This article studies the benefits of hybrid excitation and provides an outlook on their possible applications, such as wind power generators and electric vehicle motors. Compared to permanent magnet-based machines, hybrid excitation gives a variable flux while still using the advantage of the permanent magnets for a portion of the flux. This article also looks into some different categories of machines developed for hybrid excitation. The categories are based on the reluctance circuit, the relative geometrical location of the field windings relative to the permanent magnets, or the placement of the excitation system. [ABSTRACT FROM AUTHOR]

To reduce the losses of the power electronic inverter, the voltage slew rate (du/dt) of the electric motors supplying voltage is increasing. As steep voltage slopes excite high frequencies in the megahertz range, transient phenomena in the winding of the electrical machine occur. To design the insulation system, the maximum electric potential difference between the conducting elements must be predicted. General design rules can lead to a significant overengineering of the interturn insulation, particularly when considering smaller stators with a known wire distribution. Therefore, two different winding topologies are studied comparing the voltage distribution in a round-wire winding and a winding with preformed coils. [ABSTRACT FROM AUTHOR]

This paper presents an experimental platform for regulating the DC motor angular speed powered by photovoltaic cells. The experimental platform comprises an Eco Green Energy EGE-260P-60 solar panel, DC/DC SEPIC converter, DC bus, DC/DC buck converter, DC motor and Nexys 4 board with an Artix-7 100T FPGA. The DC/DC SEPIC converter is used for harvesting the maximum amount of energy from the PV cells using the perturb and observe algorithm to track the maximum power point. The DC/DC buck converter is used as the motor drive using the active disturbance rejection control to regulate the angular speed of the DC motor. In addition, the FPGA architecture design is presented using a hierarchical top-down methodology with the VHDL hardware description language and Xilinx System Generator tool. The software takes advantage of the FPGA's concurrency to simultaneously evaluate the different processes, which is the main reason for choosing this digital device. Several tests were performed on the platform such as irradiance changes, DC bus variations, DC motor connection and load torque variations applied in the motor shaft. The results indicate that the maximum power is obtained from the photovoltaic cells, establishing the minimum operating conditions. In addition, the control approach estimates and cancels the effects of disturbances caused by variations in the environmental conditions, photovoltaic system, DC bus, and load changes in order to regulate DC motor speed. [ABSTRACT FROM AUTHOR]

This article presents a new variant of particle swarm optimization (PSO) algorithm, which was developed for a reliable parameter estimation in thermal analysis of electrical machines. The proposed algorithm uses a varied social network, where both number and size of the network (local neighborhoods) are randomly adjusted during the optimization process. Such approach has been introduced here to assure improved diversity of the PSO and consequently a more reliable and robust search of the solution space. A case study parameter estimation for a reduced-order thermal-equivalent-circuit (TEC) of an electrical machine has been used to demonstrate effectiveness of the proposed method. The analyzed black-box parameter estimation relies on the input and output data (demand data) from a short-transient finite-element-analysis (FEA) of a complete machine assembly. The proposed PSO variant has been benchmarked with a selection of the existing state-of-the-art PSO algorithms, which employ alternative social network schemes with the network parameters dynamically varied. The statistical data gathered from multiple runs of the PSO-based estimation suggests that the proposed new approach offers considerable improvements in terms of accuracy, efficiency, reliability, and robustness as compared with the alternative PSO algorithms. [ABSTRACT FROM AUTHOR]

In this paper, the authors propose a flexible automatic procedure for optimizing multiphase single-layer winding end-connections by the differential evolution algorithm. By using the winding distribution in slots as a predefined input, connections between phase conductors located in different slots are determined to minimize the winding average coil pitch and to simultaneously maximize the number of coils with identical coil pitch. For an adopted geometrical shape and number of turns of individual coils, minimization of winding average coil pitch results in minimized end-connection length, winding resistances, end-leakage inductances, winding mass and copper losses, while machine efficiency and power factor are maximized. However, maximizing the number of identical coils simplifies and speeds up the process of coil fabrication during machine assembly, but potentially leads to higher average coil pitch. The proposed method is applied to single-layer windings with different slot, pole and phase combinations, where it is proven that the method automatically provides end-connection arrangements which are better or equal in terms of copper usage and simplicity of fabrication than the ones found in the literature. Verification is conducted by comparing overall performance of several Rotor Permanent Magnet Flux Switching motors with different stack lengths, outer diameters and optimized end-windings by means of 2D finite element analysis and 3D analytical approach. The proposed method is conceived as an automatic tool for optimization of single-layer winding end-connections during comprehensive electrical machine design optimization. [ABSTRACT FROM AUTHOR]

This article presents the potential contribution of segmented stator magnetic circuits of rotating permanent magnet electrical machines with concentric winding. Two magnetic materials are mixed: FeSi non-oriented electrical steel and FeSi grain-oriented electrical steel (GOES). The choice of using GOES is based on the high performance it offers in terms of permeability and iron losses compared to conventional non-oriented grain electrical steel (NOES), particularly when GOES is magnetized in the rolling direction (RD). The goal is to analyze the contribution of the mixed magnetic circuit on the losses and electromagnetic torque but also the drawbacks due to the cut process and the assembly. The behavior of the magnetic field at the junction between the segments is studied by comparing different geometrical connection shapes and compared to a reference magnetic circuit fully made with NOES sheets. This comparison is experimentally made with a model representative of the existing phenomena in an electrical machine. In addition, numerical calculations using finite elements software are carried out by considering both the magnetic anisotropy and the saturation of the GOES. [ABSTRACT FROM AUTHOR]

The simulation of electrical machines at the first design stage requires efficient methods to characterize among other properties its vibrational behavior. Particularly when considering both designed and parasitic geometrical modifications, magnetic circuit calculations of large-dimensioned machines by finite-element methods (FEM) are cumbersome. Semi-analytical approaches by means of conformal mapping are therefore useful to estimate the impact of several effects, such as asymmetric stator laminations, rotor pole shapes and air gap imperfections. No-load operation is studied and the presented approach is validated by FEM simulations. The aim of this work is to study force excitations by the magnetic air gap field in salient multi-pole synchronous generators deviating from ideal and symmetrical geometrical conditions by using conformal maps. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is considered the enabling technology for topology optimized components, with its unparalleled, almost free-form design freedom. Over the past decade, AM of electromagnetic materials has evolved into a promising new area of research. Considerable efforts have also been invested by the electrical machine (EM) research community to develop and integrate novel additive components. Several challenges remain, however, in printing soft magnetic flux guides—most prominently, reducing the induced eddy currents to achieve competitive AM core efficiency. This paper demonstrates the workflow of laser additive manufacturing magnetic cores with superior magnetic properties to soft magnetic composites (at 50 Hz excitation): describing the workflow, parameter tuning for both printing and annealing, and shape optimization. Process optimization yielded the optimal energy density of 77 J/mm3 and annealing temperature of 1200 °C, applied to prepare the samples with the highest relative density (99.86%), lowest surface roughness Rz (0.041 mm), minimal hysteresis losses (0.8 W/kg at 1.0 T, 50 Hz), and ultimate yield strength of 420 MPa. For Eddy current suppression, the sample (5 × 5 × 60 mm toroid) with bi-directional grading reached specific core losses as low as 1.8 W/kg (W10,50). Based on the findings, the advantages and disadvantages of AM graded cores are discussed in detail. [ABSTRACT FROM AUTHOR]

Ferromagnetic materials may be affected by the presence of local losses due to defects or magnetic anomalies caused by machining processes. To highlight such anomalies is not easy; a noninvasive thermographic method has been refined to allow a proper comparison of different machining processes’ impact on the iron losses. Specimens obtained with punching, wire erosion, and laser cut have been analyzed using a high-speed IR camera when subjected to alternate magnetization at different frequencies. Also, the same technique has been adopted to the assembled stacks to investigate more simultaneous phenomena. The possibility to point out localized anomalies should be exploited to foresee and avoid electrical machines core faults. [ABSTRACT FROM AUTHOR]

A green revolution has accelerated over the recent decades with a look to replace existing transportation power solutions through the adoption of greener electrical alternatives. In parallel the digitisation of manufacturing has enabled progress in the tracking and traceability of processes and improvements in fault detection and classification. This paper explores electrical machine manufacture and the challenges faced in identifying failures modes during this life cycle through the demonstration of state-of-the-art machine vision methods for the classification of electrical coil winding defects. We demonstrate how recent generative adversarial networks can be used to augment training of these models to further improve their accuracy for this challenging task. Our approach utilises pre-processing and dimensionality reduction to boost performance of the model from a standard convolutional neural network (CNN) leading to a significant increase in accuracy. [ABSTRACT FROM AUTHOR]

The contemporary methodologies are focused in the students, who, in engineering programs, many times they are unmotivated by the lack of integration of practical content with attractive and experiential methods. In this paper, a design and implementation of a new teaching-learning method are presented. The proposed method here, called Integration practices of knowledge and resource articulation, seek the combination of different knowledge areas with laboratory resources, forming in the student a holistic vision of the electric energy systems. This method is composed of three sections: Prelaboratory, laboratory and poslaboratory, including in each of them, pedagogical moments who the student realize based in different teaching techniques, like active learning, affective teaching and gamification how learning experience. A meaningful and motivating experience is intended, using videos, didactic games, short reads, and activities that in innovative ways motivate students to continue their studies and do more research about the knowledge acquired, emulating the situations that can be found in the productive sectors. [ABSTRACT FROM AUTHOR]

This article presents a semi-analytical method for calculating ac copper loss of stator form-wound windings. The proposed method is capable of simulating circulating current effect between parallel strands with torsion transposition in the end region, as well as skin and proximity effect inside the strand. The solution model of circulating current is first derived, and the key parameter, namely the slot leakage inductance matrix, is also obtained by analytical method. Then, with the calculated current of each strand, the current density distribution inside the strand is induced. Finally, the calculated copper loss of a permanent magnet generator is compared with the finite element result, which validates the accuracy of the proposed model. [ABSTRACT FROM AUTHOR]

Robustness and reliability of modern synchronous motors require an accurate design of the permanent magnets (PMs) while accounting for the motor operating conditions (demagnetizing field and temperature). In this article, the important attribute of a PM non-linear demagnetization model within a finite element method (FEM) simulation environment is clearly emphasized. To do so, starting from the experimental measurement achieved on an NdFeB PM, a toolbox named “PM-Demag” has been developed. This toolbox manages the PM history and updates the PM $B(H)$ characteristics depending on the temperature and the PM working point. Finally, a relatively straightforward coupling is implemented with an FEM software and applied to a simple study case. The results show local magnetization loss in the PM due to the combination of both the temperature and the demagnetizing field. [ABSTRACT FROM AUTHOR]

Based exclusively on the exact subdomain (SD) technique and finite-difference method (FDM), this article proposes a 2-D hybrid model (HAM) for the semi-analytical magnetic field calculation in electrical machines at no-/on-load conditions. It is applied to dual-rotor permanent-magnet (PM) synchronous machines. The magnetic field is computed by solving Laplace’s and Poisson’s equations through exact SD technique in all regions at unitary relative permeability (i.e., PMs, air gap, and slots) with a numerical model based on FDM in ferromagnetic regions (i.e., teeth and rotor/stator yokes). These two models are specifically coupled in both directions (i.e., ${r}$ - and ${\theta }$ -edges) of the (non-)periodicity direction (i.e., in the interface between teeth regions and all its adjacent regions as slots and/or air gap). To provide accurate solutions, the current density distribution in slots regions is modeled by using Maxwell’s equations. The finite-element analysis (FEA) demonstrates highly accurate results of the developed technique. The 2-D HAM is ≈6 times faster than 2-D FEA. [ABSTRACT FROM AUTHOR]

Modern converter-supplied ac motors are exposed to bearing currents. Despite extensive research and development, the industry still does not have a final solution with acceptable cost and high efficiency. This article focuses on capacitive bearing currents. After a brief explanation of the phenomenon, an unconventional approach for effective mitigation of the capacitive bearing currents is proposed. The approach suggests using grounded electrodes in the slot openings to reduce the stator-winding-to-rotor-core capacitance and thereby the bearing currents. Different electrode diameters are considered and evaluated by a finite element method (FEM) analysis. The results are verified by laboratory tests. The bearing voltage ratios of the original and modified induction motor are compared. [ABSTRACT FROM AUTHOR]

The concept of self-healed permanent magnet (PM) machines is presented in this article. In order to demonstrate its technical feasibility, the remagnetization behavior of hard ferrite magnets in closed circuit as a function of temperature is initially discussed. Next, the experimental assessment of the remagnetization of engineered parts—with distinct geometry/dimensions from those of the material assessment—installed in an interior PM motor is addressed. Although the concept is agnostic regarding the PM material implemented, this study focused on ferrites since it explores best its benefits due to a unique combination of low criticality of elements, intrinsic physical properties, and cost accessibility. [ABSTRACT FROM AUTHOR]

The application of wide-band-gap-semiconductors in the power-electric circuit of future traction drives leads to an increased stress on the insulation system. This can cause partial discharge, which leads to a rapid breakdown of the insulation and must, therefore, be avoided. To enhance the durability of the insulation system and to fill up the air gaps between the enameled wires, impregnation material is applied. This leads to an increased partial discharge inception voltage between neighboring conductors as the discharge process only occurs in the remaining air enclosures. Due to the change of the electric field distribution, which is caused by the impregnation material, also the threshold voltage for partial discharge between the stator and the winding changes. While so-called twisted pairs are commonly applied to study the partial discharge behavior of the inter-turn insulation isolated from other effects, in this article a specimen that considers the phase-to-ground insulation is proposed. [ABSTRACT FROM AUTHOR]

Nowadays, one of the challenges in transport electrification is the reduction of the components’ size and weight in order to improve the power density. This is often achieved by designing electrical machines with higher rotational speeds and excitation frequencies. In addition, the converter needs to control the machine over a wide speed range given by the mission profile. Therefore, copper losses can significantly increase due to the combination of high frequency excitation and the harmonics introduced by the converter. The winding arrangement design plays a key role in the minimization of the copper losses, thus towards a higher efficiency and/or an improved power density. Different winding topologies can be adopted for high speed electrical machines and amongst them random windings are still one of the most widespread types. This paper presents an in depth study on AC losses in random windings for high frequency motor applications. An analytical method is compared against 2-D Finite Element (FE) simulation results. These are then compared to experimental measurements taken on a custom motorette. Importantly, in order to take into account the random positions of each strand within the machine slots, an Experimental Statistic Method (ESM) is proposed. The ESM allows to define the probability distribution which is useful to evaluate the winding copper losses at the design stage. The contribution of the Pulse Width Modulation (PWM) effect is also considered and experimentally evaluated. [ABSTRACT FROM AUTHOR]

Effective learning has many and different disciplines, one of them is the improvement of students' soft skills which include different abilities, such as presentation, communicating, teamwork, time/project management and effective writing. This paper addresses the improvement of writing skills, particularly when writing a technical laboratory or mini-project report is used. The report should contain all the factors that enhance students' writing using the appropriate language and conventions. Here, we investigate the students' performance and response when applying the proposed guidelines and recommendations for the suggested structure of mini-projects or laboratory reports. The analysis contains a discussion of a case study conducted over 12 consecutive terms to assess student performance in four different courses using the proposed report structure. Moreover, it includes a discussion about the students' response for the questionnaire which explores students' satisfaction with the assigned lab tasks and proposed structure for five consecutive terms for a specific course, namely electrical machines. [ABSTRACT FROM AUTHOR]

A method is proposed in this article to place sensors in an electrical machine in order to be able to reconstruct the magnetic field distribution. This method is based on the empirical interpolation method combined with the Maxvol technique. The results applied on a surface-mounted permanent magnet machine at no load show that the field distribution can be accurately reconstructed even when the sensor location is imposed in the airgap of the rotating machine. [ABSTRACT FROM AUTHOR]

Different mechanisms by which bearing currents flow inside the electrical machine are well studied. In contrast, investigation and development of different techniques to mitigate these currents remain a field for improvement, and the final common solution to the problem has not been provided yet. In pursuit of addressing the problem, this article deals with noncirculating (or capacitive) bearing currents. The circuit mechanism of capacitive currents is explained in brief, and an approach for their mitigation is introduced. This article studies the influence of the stator winding and the slot geometry and presents different geometries to modify the motor to reduce the capacitive bearing currents. The effectiveness of the proposed mitigation technique is shown by finite-element-based modeling and verified by laboratory tests with different induction motor designs, where the winding and magnetic circuit geometries are varied. The technique can be used, in particular, for the mitigation of noncirculating currents, but it also offers potential for further research. [ABSTRACT FROM AUTHOR]

In high power density applications, such as electric or hybrid electric vehicles, heat extraction is a crucial aspect of electrical machine design due to stringent volume specifications. In these cases, it is extremely difficult, if at all possible, to satisfy the maximum temperature requirement when using conventional cooling systems, such as housing fins, shaft-mounted fans or even water jackets. To this end, a novel direct oil cooling system conceived for Torus-type axial-flux permanent-magnet machines is proposed here. In order to demonstrate its effectiveness, lumped thermal equivalent circuit simulations, finite element analyses and experimental tests are presented. The expected performances of the machine using the proposed direct oil cooling are compared to those obtained using state of the art water cooling. [ABSTRACT FROM AUTHOR]

This work presents the study of the preparation routes of a soft magnetic composite (SMC), its electromagnetic properties and efficiency when applied to induction motors (low frequency magnetic fields), as an alternative to traditional electric steels. Thus, different SMCs (such as pure iron powder and ASC 100.29 iron powder, both with coating and isolation of the particles with phosphoric acid) have been studied in comparison with commercialized SMCs, such as Somaloy® 700 3P. In addition, methodologies for depositing the insulating layer, such as physical deposition, spraying and the Sol-Gel process were also studied. Initially, a commercial powder sample and another sample with a thin layer of phosphate were prepared. Sintered parts of these SMCs were then prepared and, subsequently, their electromagnetic parameters were acquired. From these data, an analysis of the magnetic flux in the engines built by these materials was made, in which it was observed that the sample of the composite material had properties compatible with conventional steels. It was also observed that, with the improvement of the SMC preparation routes, they can be used in the development of new engine topologies, for the most diverse applications, without loss of efficiency, mainly with regard to low frequency magnetic applications. [ABSTRACT FROM AUTHOR]

The magnetic field including tooth effect can be calculated by the tooth harmonic permeance. However, the mechanical pivot role of tooth is always neglected in vibration analysis and the slotted stator is considered as a simple cylinder. In this article, the mechanical pivot role that the tooth plays in vibration analysis is illustrated, where the transfer function of force is proposed to represent the process of force from the top of tooth to the yoke. First, the magnetic pivot role of tooth in magnetic field analysis is described by the tooth harmonic permeance. Then the force on the top of tooth is transferred to the yoke by the transfer function of force, after that the yoke can be considered as a cylinder. Based on the pivot role of tooth, the phenomenon that the high order force can cause the low mode vibration is explained and clarified straightforwardly. Not only the fractional slot permanent magnet synchronous motor (PMSM), but also the integer slot PMSM, are analyzed to demonstrate the universality of these methods. Finally, the finite element method simulation, and the experiments on one fractional slot PM motor and one integer slot PM motor, are applied to validate the theory. [ABSTRACT FROM AUTHOR]

This article presents a comparative study on different types of robust design optimization methods for electrical machines. Three robust design approaches, Taguchi parameter design, worst-case design and design for six-sigma, are compared for low-dimensional and high-dimensional design optimization scenarios, respectively. For the high-dimensional scenario, the computational burden is normally massive due to the robustness evaluation of a huge number of design candidates. To attempt this challenge, as the second aim of this paper, a space reduction optimization (SRO) strategy is proposed for these robust design approaches, yielding three new robust optimization methods. To illustrate and compare the performance of different robust design optimization methods, a permanent magnet motor with soft magnetic composite cores is investigated with the consideration of material diversities and manufacturing tolerances. 3-D finite element model and thermal network model are employed in the optimization process and the accuracy of both models has been verified by experimental results. Based on the theoretical analysis and optimization results, a detailed comparison is provided for all investigated and proposed robust design optimization methods in terms of different aspects. It shows that the proposed SRO strategy can greatly improve the design optimization effectiveness and efficiency of those three conventional robust design methods. [ABSTRACT FROM AUTHOR]

This article presents a new method for multi-objective robust design optimization of electrical machines and provides a detailed comparison with so far introduced techniques. First, two robust design approaches, worst-case design and design for six-sigma, are compared with the conventional deterministic approach for multi-objective optimization. Through a case study on a permanent magnet motor, it is found that the reliabilities of motors produced based on robust designs are 100% under the investigated constraints, while the reliabilities of deterministic designs can be lower than 30%. A major disadvantage of robust optimization is the huge computation cost, especially for high-dimensional problems. To attempt this problem, a new multi-objective sequential optimization method (MSOM) with an orthogonal design technique and hypervolume indicator (as a measure of convergence) is proposed for both deterministic and robust design optimization of electrical machines. Through another case study, it is found that the new MSOM can improve motor performance and greatly reduce the computational cost. For the robust optimization, the number of required finite element simulations can be reduced by more than 40%, compared with that required by the conventional approach. The proposed method can be applied to many-objective (robust) design optimization of electrical machines. [ABSTRACT FROM AUTHOR]

Thermal modeling and temperature assessment of electrical machines often rely on the use of lumped-parameter thermal networks. A historic limitation of analytical thermal models is their need for an experimental fine-tuning, necessary for selecting the appropriate values of thermal conductivity and convection heat transfer coefficients. This evaluation procedure is commonly carried out at the design stage of a new machine, by assuming that its thermal behavior will remain unchanged throughout its whole lifetime. This paper demonstrates, through an in-depth experimental investigation, how the capability of heat extraction from a machine's hot spot towards the coolant can be strongly affected by the level of thermal aging of its insulation system. Based on the experimental findings, a decrement of the winding equivalent thermal conductivity is noted as the thermal aging accumulates, with a corresponding progressive increment in hot-spot temperature. [ABSTRACT FROM AUTHOR]