Electromagnetic Finite Element Analysis Research Articles

Plasmonic gold nanojets fabricated by a femtosecond laser irradiation.

Gold nanojets with various morphologies, from nanopillar to nanotip with up to 800 nm height, and finally to nanotip with droplet, are fabricated on gold thin film by a femtosecond laser irradiation. The near-field localized surface plasmon resonance (LSPR) and photothermal effects of gold nanojets are studied through finite element electromagnetic (EM) analysis, supporting in nanojets design for potential applications of high-resolution imaging, nanomanipulation and sensing. For an individual nanotip, the confined electron oscillations in LSPR lead to an intense local EM field up to three orders of magnitude stronger than the incident field strength at the end of gold tip, where the vertical resolution for the field enhancement was improved down to nanoscale due to the small size of the sharp gold tip (5-nm-radius). At specific wavelength, nanopillar can serve as an effective light-to-heat converter and its heating can be fine-tuned by external irradiation, and its dimension. The long-range periodic nanojet arrays (periods from 1.5 µm to 2.5 µm) with different geometry were printed using several pulse energy levels. By confining more light into the tip (two orders of magnitude stronger than single tip), nanotip array shows more pronounced potential to serve as a refractometric sensor due to their high sensitivity and reproducibility. These results promote fs laser printing as a high-precision tool for nanoarchitecture in optical imaging, nanomanipulation and sensing application.

Comparison of Electrified Aircraft Propulsion Drive Systems with Different Electric Motor Topologies

Electric aircraft propulsion is a growing research area that looks into achieving propulsion through fully electric or hybrid electric systems while achieving low emissions. The system-level benefit gained by different electric and hybrid-electric propulsion schemes depends heavily on the performance of system-level components in the electric drive-train, including the electric motor, gear box, motor drive, protection systems, as well as the thermal management system. When comparing motor topologies, it is important to understand performance measures such as efficiency and specific power on a drive system level. Many different motor types have been qualitatively compared and can be found in the literature. To guide appropriate component selection, this paper presents details of a quantitative study for a given electric propulsion drive system. A Pareto optimal front for a notional drive system of a 1.5 MW electrical propulsor with different motor types is generated and compared. An optimization algorithm coupled with an electromagnetic finite element analysis software tool was used to optimize the induction motor, switched reluctance motor, wound rotor synchronous motor, permanent magnet synchronous motor (PMSM), slotless PMSM, permanent-magnet-assisted synchronous reluctance motor, brushless DC motor, and brushless doubly fed reluctance motor types for efficiency and specific power. Overall advantages considering system-level efficiency, specific power, and a few other key metrics such as origin of losses, cooling complexity, manufacturing tolerance, and fault tolerance are discussed. This gives an indication of the relative performance of different motor types and confirms the overall advantage of PM motor topologies in aircraft propulsion.

Coupled Electromagnetic-Thermal Analysis for Predicting Traction Motor Characteristics According to Electric Vehicle Driving Cycle

The accuracy of motor characteristics prediction according to driving cycle can be improved by taking temperature change of motor into account. From this point of view, this paper proposes a fast and accurate coupled analysis method. To calculate motor circuit parameters, electromagnetic finite element analysis (FEA) is used. The proposed method consists of two stages to exclude the time consuming FEA from repetitive process. In pre-process stage, the circuit parameters are stored as look-up tables (LUTs) considering motor temperature. Further, a technique that allows reducing the number of analyses is developed to consider a wide operating temperature range with less time consumption. In main process stage, the torque and voltage equations are solved using the circuit parameter LUTs. Among the solved motor characteristics, losses are applied to lumped parameter thermal network (LPTN) as heat sources to figure out thermal characteristics. Here, techniques including loss separation and thermal parameter tuning are introduced to improve both accuracy and speed of the LPTN. Since the computation of the characteristic equations and LPTN are fast, the iterative analysis at entire time steps of the driving cycle is facilitated. An example of the proposed method is presented using worldwide harmonized light vehicle test procedure (WLTP). Thereafter, the effectiveness of the method is discussed by comparison with conventional methods. Finally, the experimental verifications are conducted to validate the electromagnetic FEA and LPTN used in this study.

A Novel Meshing Method Based on Adaptive Size Function and Moving Mesh for Electromagnetic Finite Element Analysis

A moving meshing algorithm with mesh adaptive size function was proposed in this paper with regard to the modeling speed and solution accuracy of electromagnetic equipment in the optimization design process. In the proposed method, a mesh size function that considers curvature, feature size, and distance gradient restrictions is constructed, which can obtain high quality meshes and avoid excessive iteration; when the finite element mesh domain is deformed, only the mesh nodes close to the moving boundary are allowed to move, and the theory of force-balance is used combined with the second-order boundary projection algorithm to perform iterative optimization of the mesh node positions. The proposed method has the advantages of keeping the original mesh structure and minimum mesh deformation as well as speed up the convergence, save time in the finite element meshing, and ensure the quality of the generated mesh. Then, the proposed method was applied to a 37 kw motor for electromagnetic analysis, and the results obtained proved the accuracy of the algorithm; finally, the effectiveness of the mesh movement algorithm in three-dimensional space was tested by moving the sphere inside the cylinder.

Effects of stainless steel thickness and winding tension on electrical and thermal characteristics of metal insulation racetrack coils for 10-MW-class HTS wind generator

Experimental results on the electrical and thermal characteristics of GdBCO racetrack coils co-wound with stainless steel (SS) tapes of various thicknesses and winding tensions are presented in this paper. The SS thickness and winding tension are identified as the factors affecting the charging time and thermal stability of metal insulation (MI) coils. To verify these characteristics, three types of MI-SS racetrack coils were fabricated with various SS thicknesses and winding tensions: 100-μm SS thickness and 10-kgf winding tension; 100-μm SS thickness and 5-kgf winding tension; and 50-μm SS thickness and 10-kgf winding tension. Further, three MI-SS racetrack coils were characterized by sudden discharging, charging, and overcurrent tests. The sudden discharging and charging tests were performed in a steady state to investigate the decay time constant of the center magnetic field discharging the coils and the delay time of the magnetic field charging the test coils, respectively. To estimate the thermal stability of the three MI-SS coils, overcurrent tests were conducted in a transient state at 1.1 times the critical current (Ic) and 1.05 Ic. Based on the experimental results of three small-scale test coils, the total contact resistance between the layers of the test coils was calculated and applied to design a field winding using a second-generation high-temperature superconducting (HTS) tape for a 10-MW-class HTS generator used in an offshore wind turbine environment. Subsequently, an equivalent electrical circuit model was proposed to analyze the electromagnetic response and thermal stability characteristics of three HTS field coils of a 10-MW-class HTS generator with the key parameters of the HTS field coils, which were obtained using electromagnetic finite-element analysis. Finally, the charging delay time and thermal stability of the three HTS field coils were compared and analyzed in detail.

Open-Circuit Core Loss of Large Turbine Generators Considering the Influence of Key Bar Design

To provide power to electrical power distribution systems cost effectively, it is necessary to understand the efficiency of large turbine generators. Stator cores, which account for 10%–15% of total generator losses, are supported by a either a dovetail key bar or a square key bar. The dovetail key bar, mainly used in large turbine generators, has a shallow depth of penetration into the stator core; consequently, the need for research related to core loss has been limited in the case of dovetail key bars. By contrast, the square key bar, which is attracting attention owing to its ease of assembly, deeply penetrates the stator core, and thus has a greater effect on core loss than the dovetail key bar. However, core losses due to the key bar design have not been examined quantitatively in the literature. This paper analyzes the core-loss changes due to the key bar. Using electromagnetic finite-element analysis, we calculate the differences in core loss between the two aforenoted key bar types, which are commonly used in large turbine generators. In addition, we propose points for consideration when designing key bars for large-capacity generators.

Artificial Neural Network and Data Dimensionality Reduction Based on Machine Learning Methods for PMSM Model Order Reduction

The present paper targets a solution for permanent motor synchronous machine (PMSM) model order reduction (MOR) using artificial neural networks and machine learning techniques for data dimensionality reduction. The neural networks are trained using data obtained from a series of electromagnetic Finite Element Analysis (FEA), conducted in conditions imposed by the data dimensionality reduction method. The workflow proposed to build the PMSM MOR, starts with data generation, goes further to its post-processing, and finishes with the model training and experimental validation. In the study, data dimensionality reduction procedure (adaptive data generation) is performed to increase the computational efficiency, also maintaining the model accuracy. Different data reduction approaches are compared from the computational cost’s point of view and their ease of use. The obtained results are compared to those obtained from FEA seeking the best solution for building the dynamic model. The resulting ROM is included in a real-time control prototyping platform to characterize machine’s performances. The model accuracy and its usability are proved in a comparative analysis with simulated versus experimental measurements.

Analytical Calculation of Temporal and Circumferential Orders of Radial Force Density Harmonics in External-Rotor and Internal-Rotor Switched Reluctance Machines

This paper presents an analytical method to calculate the temporal and circumferential orders of the radial force density harmonics in switched reluctance machines (SRMs) without running the electromagnetic finite element analysis (FEA). The characteristics of the radial force density harmonics in several SRM topologies are investigated, including the 6/4, 24/16, and 6/14 internal-rotor (IR) SRMs, and 12/16 and 18/24 external-rotor (ER) SRM. The study shows that the temporal and circumferential orders of the radial force density harmonics depend on the pole configuration, the rotational directions of the rotor, the phase excitation sequence, and the rotor or stator radial force density waveform. The acoustic noise of a four-phase 8/6 internal-rotor SRM and a three-phase 12/16 external-rotor SRM was experimentally measured to validate the calculation of the temporal and circumferential orders of the radial force density harmonics. The proposed analytical method helps locate the possible radial force density harmonics of a given SRM configuration. In order to determine the dominant radial force harmonics, the proposed method should be complemented by analyzing the natural frequencies of the motor structure and the forcing frequencies of the radial force harmonics.

Acoustic Modeling and Prediction of Ultrahigh-Speed Switched Reluctance Machines Based on Multiphysics Finite Element Analysis

High-speed switched reluctance machines (SRMs) have been a timely topic recently. However, for ultrahigh-speed SRMs over 100,000 rpm, the acoustic noise is a significant issue in many applications such as high speed spindles, compressors/ turbochargers, flywheels, and etc. In this article, a multiphysics acoustic modeling of ultrahigh-speed SRMs is presented based on finite element analysis (FEA). First, a three-dimensional electromagnetic FEA is conducted to calculate the radial force on the stator teeth. Then, a modal analysis and a harmonic response analysis are shown in the frequency domain to estimate the natural frequencies and vibration of the whole motor. An acoustic response analysis is done to estimate the sound pressure level (SPL) using the superposition of the surface vibration. To verify the model, experiments are done to measure and compare the natural frequencies and the SPL of a 4/2 ultrahigh-speed SRM at 100,000 rpm. The results show that the SPL of the motor is as high as 115 dB at 10 mm away from the motor, which matches the simulation result (113 dB) well. The impact of the bearing is proven to be negligible compared with the noise generated by the radial force. Finally, a parametric study example of using the proposed model to guide the design of SRMs has been conducted. It is shown that “hot dog” shaped motors have less noise than “pancake” shaped motors under the same motor volume, speed, and power.

Convergence of Core Losses in a Permanent Magnet Machine, as Function of Mesh Density Distribution, a Case-Study Using Finite-Element Analysis

To limit numerical inaccuracies in electromagnetic finite element analysis, the mesh resolution needs to be set with care. Within electric vehicle propulsion, core losses are highly important while excessive simulation times should be avoided, due to the wide operating range. This paper investigates the procedure of achieving core loss convergence, in all parts of a permanent magnet synchronous machine, by varying mesh density. The finite element analysis is done in Ansys Maxwell and the core loss error is quantified by an estimated fully converged result. Two approaches to mesh tuning are compared. It is found that interdependence, between the mesh density in one part and the core loss in another, should be considered. The required mesh resolution is found to differ among operating points. Finally, the flexibility offered by this convergence method is shown. Once the convergence behaviour has been identified, a mesh can be found for any desired compromise of error and simulation time. For the investigated case, the estimated error in total core loss is below 1.2% when an angular machine segment covering one pole, is modelled with 15500 mesh elements. Reducing the number of mesh elements to 7200 gives an error below 3.3%.

Thermal and Electromagnetic Stator Vent Design Optimisation for Synchronous Generators

This article deals with the stator cooling of an air-cooled, synchronous generator with a power rating of 400 kVA, which has been improved by adding two radial vents to the stator. To ensure an optimal vent design, a novel combined thermal and electromagnetic modelling approach is developed. A parametric 3D Conjugate Heat Transfer Computational Fluid Dynamics (CFD) model is used for the thermal modelling. An electromagnetic 2D Finite Element Analysis determined the impact that venting the stator has on the loss distribution. The models are coupled by deriving analytical correlations between the combined vent width and rotor copper, rotor iron and stator iron losses. These correlations are implemented into the optimisation procedure of the parametric CFD model. Five design parameters are optimised simultaneously with the aim of minimising the peak stator winding temperature. The modeling approach was validated experimentally by thermal, torque and mass flow measurements on the benchmark machine, as well as the newly designed prototype.

Design and Analysis of HTS Rotor-Field Coils of a 10-MW-Class HTS Generator Considering Various Electric Insulation Techniques

This paper presents the results of an electromagnetic design and numerical analysis conducted on a 10-MW-class second-generation high-temperature superconducting generator (2G HTSG) used in an offshore wind power turbine. To report the operation reliability of 10-MW-class HTSGs employed in offshore environment, various electric insulation techniques (EITs) for HTS field coils (FCs), such as no-insulation, metal insulation, and metal-insulator transition insulation, are considered in this study. Using the time-transient solver of the three-dimensional (3D) electromagnetic finite element analysis (FEA), we investigated the electromagnetic characteristics of the HTSG with the three EITs in terms of the electrical output of the HTSG and the critical current of the FCs. To analyze the charging characteristic of the HTS FCs with the three EITs in steady-state operation as well as the electrical in transient-state operation, electric equivalent circuit models are built with key parameters based on the electromagnetic FEA results. Finally, the performances of the HTS FCs are discussed and evaluated in terms of the electromagnetic response and stability characteristics.

Development of a Novel Latching-Type Electromagnetic Actuator for Applications in Minimally Invasive Surgery

Single-port laparoscopic surgery (SLS), which utilises one major incision, has become increasingly popular in the healthcare sector in recent years. However, this technique suffers from several problems particularly the inability of current SLS instruments to provide the optimum angulation that is required during SLS operations. In this paper, the development of a novel latching-type electromagnetic actuator is reported, which is aimed to enhance the function of SLS instruments. This new actuator is designed to be embedded at selected joints along SLS instruments to enable the surgeon to transform them from their straight and slender shape to an articulated posture. The developed electromagnetic actuator is comprised of electromagnetic coil elements, a solid magnetic shell, and a permanent magnet used to enhance the magnetic field interaction along the force generation path and also to provide the latching effect. In this investigation, electromagnetic finite element analyses were conducted to design and optimise the actuator’s electromagnetic circuit. In addition, the performance of the new actuator was numerically and experimentally determined when output magnetic forces and torques in excess of 9 N and 45 mNm, respectively together with an angulation of 30° were achieved under a short pulse of current supply to the magnetic circuit of the actuator.

A Novel Hydraulic Actuation System Utilizing Magnetorheological Fluids for Single-Port Laparoscopic Surgery Applications.

Single-port laparoscopic surgery (SLS), which utilizes one major incision, can deliver favorable cosmetic outcomes with fewer patient hospitalization stays and less postoperative pain. However, current SLS instruments, which are rigid and slender, have been suffering from several drawbacks, including their inability to provide the optimum articulation required to complete certain SLS tasks. This paper reports on the development of a lightweight smart hydraulic actuation system that is proposed to be embedded at selected joints along current SLS instruments, in order to enhance their adaptability with a higher level of stiffness and degrees-of-freedom. The developed smart actuation system utilizes both conventional hydraulic and magnetorheological (MR) fluid actuation technologies. Electromagnetic finite element analyses were conducted to design the electromagnetic circuit of the smart actuator. A prototype of the developed actuation system was manufactured, and its performance was assessed using a dedicated experimental arrangement, which was found to agree well with the results obtained using a Bingham plastic theoretical model. Finally, the present design of the developed smart actuation system permits an angulation of about 90° and a maximum force output in excess of 100 N, generated under a magnetic excitation of about 1.2 Tesla, which should be sufficient to resist torques of up to 500 mNm.

Design of a Novel Modular Axial-Flux Double Rotor Switched Reluctance Drive

Nowadays, there is a renewed interest in switched reluctance machines and especially in axial-flux switched reluctance machines (AFSRM). This paper presents a comprehensive design procedure for modular AFSRM with an inner stator and two exterior rotors that have a new distribution of the stator and rotor poles, resulting in short magnetic paths with no flux reversal. After a description of the proposed machine, the output torque equation is derived from a simplified non-linear energy conversion loop and guidelines for its design are given. Once the preliminary sizing has been carried out the different modules of the AFSRM, the magnetically active parts made with SMC, are reshaped or refined using 3D printing and 3D electromagnetic finite element analysis until they reach their definitive shape and dimensions. Finally, an AFSRM has been built following the proposed design procedure and has been validated by experimental measurements.

Reliability-based robust design optimization for torque ripple reduction considering manufacturing uncertainty of interior permanent magnet synchronous motor

This study performed reliability-based robust design optimization (RBRDO) of stator and rotor shape of the IPM type electric motor to reduce the torque ripple considering uncertainties. A metamodel based on the design of experiments results, which was calculated by using 2-D electromagnetic finite element analysis, was used to calculate manufacturing uncertainties and material property distribution. As a result, the mean torque ripple of the optimum electric motor design was reduced by 56.4 % and the robustness was increased by 61.8 % compared with the initial design. The RBRDO design was compared with the designs of deterministic design optimization and reliability-based design optimization, and it was shown that, by using the RBRDO method, the optimum IPMSM can be designed to satisfying not only the minimum torque ripple but also the robustness and the reliability of output torque and torque ripple.

3D Finite Element Electromagnetic Analysis of a 14-Strand HTS Roebel Cable

Roebel cables with HTS strands exhibit reduced AC losses and possess large current carrying capacity. Even though works on several 2D and 3D numerical modelling and simulations are available, little efforts are made on computer-aided design (CAD) modelling, finite element analysis (FEA) and simulation of Roebel strands and cables. In this paper, finite element electromagnetic analysis and simulations of a 14-strand HTS Roebel cable is performed. The results obtained are then compared with another work which uses an H-formulation technique to model the problem. Although several numerical simulations have been carried out to optimise the HTS Roebel cable, no FEA work has yet been conducted on the complete 3D structure of Roebel cable. This work can therefore be considered as an initiator of the 3D finite element electromagnetic analysis of HTS Roebel cables.

A fully coreless Multi-Stator Multi-Rotor (MSMR) AFPM generator with combination of conventional and Halbach magnet arrays

An axial flux permanent magnet (AFPM) generator is known to be a good candidate for both low and high-speed application. In this paper, a new design of fully coreless multi-stator multi-rotor (MSMR) AFPM generator has been presented with conventional and Halbach magnet arrangement combined with an ironless (epoxy) rotor. For MSMR topology of AFPM machine, back iron is still present in the middle rotor and to maintain the same distribution of magnetic flux, magnets are using on both side of the middle rotor. This paper suggests replacing the middle iron rotors with a single epoxy rotor which reduces the weight of the machine, hence increase power density. On the other hand, for the elimination of iron and magnets in the middle rotor, conventional magnet arrays are used to maintain a continuous flux path. In addition, Halbach array is adopted on the external epoxy rotor to reduce flux leakage on the external sides of the machine. The performance of the proposed generator is investigated in terms of voltage, current, power, power density, and torque ripple. The analytical design approach is first presented and subsequently validated using ANSYS Maxwell® electromagnetic finite element analysis (FEA) software. It is found that a fully coreless MSMR AFPM generator with conventional and Halbach magnet arrays gives higher power density and lower torque ripple with a reduced axial length which is favorable in wind power and pico-hydro applications.

Strucsture and Electromagnetic Characteristics of Pole-Piece Support Materials in Magnetic Gear

Studies on coaxial magnetic gears (CMGs) have been actively conducted. CMGs can replace mechanical gears because they can perform noncontact power transfer minimizing loss and damage from friction. In the design stage of a CMG, 2D electromagnetic finite element analysis (FEA), which is a highly reliable and cost-saving tool, is widely used. However, during prototyping and testing in the review phase of a project, the prototype's pull-out torque is lower than the pull-out torque predicted from 2D electromagnetic FEA, with up to a 40% difference. One explanation for this phenomenon is that the torsional stiffness of the pole-piece structure is low, causing the electrical angle to skew. There are high-frequency magnetic fluxes in the pole-piece structure in which magnetic losses are expected to be high. In many studies, non-metal pole-piece supports that can minimize this magnetic loss were used. The disagreement between analysis and experiment has been demonstrated, but no detailed examination of this effect has been conducted. In this study, metal pole-piece supports are used to remove the torsion possibility. Results from 3D-FEA and experiments are compared, and the results reveal that when torsion is accounted for, the analysis data can be reproduced the experimental data well or not. Furthermore, the magnetic loss on metal supports is analyzed in detail.

Two-way controllable magnetorheological elastomer mount for shock and vibration mitigation

Current passive elastomeric mounts are designed to provide mitigation for a given shock and vibration exposure and are not capable of supporting variable payload systems, due to variation in the overall system dynamics. A novel magnetorheological elastomer (MRE) mount that can reduce or increase its stiffness based on payload and shock and vibration input is designed, fabricated, and tested to provide a wide controllable stiffness range for protecting sensitive systems that may require variable weight from external shock and vibration loading. A MRE is a field-controllable material in which the stiffness properties can be altered by changing the applied magnetic field. The two-way controllable MRE mount is designed by using three-dimensional electromagnetic finite element analysis. MRE mounts were developed by using relatively thick MRE layers and built-in electromagnets and permanent magnets. A two-layer MRE mount prototype is characterized by compression and shear tests. Control system hardware and software were developed to detect shock and vibration events, and activate the two-way controllable MRE mount, accordingly. The MRE mount and the control system were tested with variable representative weights. It was demonstrated that the designed control system can detect whether the incoming input is a shock event or a vibration event. The MRE mount demonstrated the ability to soften of stiffen based on the incoming input.