Electromagnetic Finite Element Method Research Articles

Design of 20 MW direct‐drive permanent magnet synchronous generators for wind turbines based on constrained many‐objective optimization

AbstractThis study introduces a constrained many‐objective optimization approach for the optimal design of 20 MW direct drive (DD) permanent magnet synchronous generators (PMSGs). Designing a high‐performance, competitive DD‐PMSG requires considering the generator's performance as well as its weight and material cost. Therefore, we focus on four main characteristics as our design objectives: (1) specific power (power per weight), (2) power‐per‐cost, (3) efficiency, and (4) power factor. To achieve this, we apply an advanced constrained nondominated sorting genetic algorithm III (NSGA‐III), a many‐objective optimization method utilizing evolutionary computation, capable of optimizing four or more objectives with constraints. Additionally, the electromagnetic finite element method is employed to evaluate the generator's characteristics. Through our proposed design process, we optimize three distinct 20 MW DD‐PMSG configurations: a 320‐pole/300‐slot, a 350‐pole/300‐slot, and a 350‐pole/336‐slot topology. Following this optimization, we perform additional multiphysics simulations (covering electromagnetic, structural, overload, and thermal aspects) and control response simulations on four selected models from the Pareto‐optimal solutions to validate their effectiveness as preliminary DD‐PMSG designs. Finally, we conduct a comprehensive analysis of all simulation results.

A Rigorous Code Verification Process of the Domain Decomposition Method in a Finite Element Method for Electromagnetics

A Rigorous Code Verification Process of the Domain Decomposition Method in a Finite Element Method for Electromagnetics

High-order cavity coupled plasmon polaritons in resonant cavity-monolayer MoS<sub>2</sub> system

Compared with graphene, two-dimensional (2D) transition metal sulfides, represented by mono-/few-layer MoS<sub>2</sub>, have tunable non-zero bandgap, and thus their applications in optoelectronic devices are more advantageous. By using classical electromagnetic theory and finite element method (FEM), we investigate the cavity coupled plasmon polaritons (CCPPs) formed through the coupling between cavity modes in a resonator and plasmons in monolayer MoS<sub>2</sub>, particularly calculate and verify the properties of the high-order CCPPs. In previous work, it was demonstrated that the substrates, defects, and polycrystalline grains of the CVD grown monolayer MoS<sub>2</sub> usually induce weak electron localization, which leads to the deviation from the Drude model based on the approximation of free electron gas. Therefore, here we use the Drude-Smith model with characteristic parameters obtained experimentally to describe the optical conductivity of monolayer MoS<sub>2</sub> in our theoretical calculation and simulation. Then, we not only derive and solve the dispersion equations of the high-order CCPPs, but also verify the existence and analyze the properties of these high-order modes. Specifically, there are three types of CCPPs in the asymmetric cavity-monolayer MoS<sub>2</sub> system, i.e. the FP-like-modes (FPLMs), the surface-plasmon-like modes (SPLMs), and the quasi-localized modes (QLMs). Among them, the FPLMs and QLMs can support high-order modes whereas the SPLMs only support the fundamental modes. According to our model, we calculate the wave localization properties for the 7th-order and 8th-order FPLM, the 3rd-order and 6th-order QLM, and the SPLM. These theoretical results are in good agreement with the simulation results. Moreover, the effects of weak electron localization are also shown by comparing the field distributions of the CCPPs based on the Drude model with those based on the Drude-Smith model. It is found that weak electron localization can reduce the coupling between the cavity modes and the plasmons in monolayer MoS<sub>2</sub>. These results can deepen our understanding of the excitation of plasmons in 2D materials as well as the modulation of their properties. Furthermore, the theoretical model can also be extended to other plasmonic systems related to low-dimensional and topological quantum materials.

Design and Analysis of Complex End Region of Pumped Storage Generator Motor Based on Novel Electromagnetic Vector Method

A very large end leakage flux is produced by the end winding of a pumped storage generator motor. It has a significant impact on the design, flux density, and temperature in the end region of the pumped storage generator motor. The high temperature makes it difficult to design pumped storage generator motors. To quickly and accurately obtain the flux density of end components, a novel electromagnetic vector method is proposed in this paper. A 300 MW pumped storage generator motor is designed. The electromagnetic vector method and finite element method are used to calculate the flux density of the end components, respectively. The obtained results are compared and analyzed. The results reveal that the novel method is more convenient and faster than the finite element method. The novel electromagnetic vector method reduces the design time and calculation time of the end flux density. The flux density and losses of the end components in the pumped storage generator motor are studied under different operating conditions. Three-dimensional fluid and thermal coupled field is calculated and analyzed. Moreover, the calculation results are verified by the experimental values.

Study on tide characteristics and mechanism of PSP in buried pipeline along the lake

The fluctuations of the Pipe-to-Soil Potential (PSP) in buried pipes are influenced by the geoelectric field induced by changes in the Earth's magnetic field, which can accelerate pipeline corrosion. Monitoring data of PSP along China's West–East Gas Pipeline near the lake indicates obvious tidal changes. This study proposes that the periodic movement of the conductivity boundary of the seepage area near the lake shore caused by tides is the fundamental cause of the tidal changes in PSP. The movement of the boundary changes the range of the H polarization of the geoelectric field, resulting in periodic changes in the PSP of the pipeline outside the seepage area. To investigate this mechanism, a dynamic boundary model of conductivity in the seepage area of Sailimu Lake in Xinjiang was established, and the characteristics of PSP at different distances from the boundary were analyzed using electromagnetic field finite element method and DSTL pipeline model. The study compared the simulation results of the model with the PSP data of the cathodic protection station and PSP monitoring station near Sailimu Lake, during a geomagnetic disturbance on September 23–24, 2016. The results of the study, as well as the corrosion of the test strips along the lake, verified the validity of the boundary change mechanism and model of the seepage zone. This study provides a theoretical basis for corrosion protection of pipelines near the lake’s edge.

Research on load circuit of medium frequency electromagnetic heat storage device

In order to improve the working efficiency of the electromagnetic heat storage device under high current and high frequency, the electromagnetic field finite element method is used to analyze and calculate the load circuit to make it in a suitable working state. Firstly, the circuit model of the energy storage device is built by using the field-circuit coupling method and the coil inductance is calculated. Secondly, the harmonic capacitor is analyzed and calculated, so that the load circuit works in a weak inductive state. On this basis, the variation law of loss on the inductor core and the distribution of water temperature rise flowing through the core at a certain water velocity are analyzed. A 50 kW prototype was built using the method proposed in this paper, and the experimental results show that the electro-thermal conversion efficiency of the electromagnetic thermal energy storage device reaches 93.39 %. The feasibility of the design method is proved by experiment and simulation, which has important guiding significance for the research and design of electromagnetic thermal energy storage device.

Simulating mechanical properties of human tissues or organs based on magnetorheological fluid for tactile display

Robot-assisted minimally invasive surgery enables surgeons to tele-perform elaborate surgical operations to patients with less damage and pain. Besides force feedback provided by the surgical robot to the surgeon, touching sensations are also important for the surgeon to acquire the complete conditions of the patient. Thus, tactile display devices are crucial elements in surgical robots. Meanwhile, various sensations of magnetorheological (MR) fluid can be provided to human fingers because its stiffness, elasticity, and viscosity can be controlled by applied magnetic field. Therefore, in this paper, a new tactile display device based on MR fluid is proposed. This device has high magnetic conduction efficiency, less magnetic leakage, no MR fluid leakage, and overcomes the major drawbacks of the existing tactile display devices based on MR fluid in literatures. Firstly, the design of the tactile display device is described in detail, followed by its fabrication and assembling methods. Secondly, the working current range of the tactile display device is determined by using electromagnetic finite element method (FEM) simulation. Thirdly, the mathematical model to characterize the compression and shear behaviors of the tactile display device is developed. Then, the tactile display device is tested in terms of normal and shear contact forces, followed by its elastic and shear moduli analysis. Finally, the unknown parameters in the mathematical model are figured out, and the model is validated by using structural FEM simulation. The experimental results show that the elastic and shear modulus range of the proposed tactile display device are respectively 3–7.5 kPa and 1.4–5.0 kPa, which can cover the mechanical properties of various human viscera.

Thermal and Electromagnetic Design of a Superconducting Coil

This article presents the methodology followed for the thermal and electromagnetic design of a superconducting coil at the University of Western Macedonia, Kozani, Greece, aimed to be used in a unique superconducting magnetic energy storage system for laboratory education and research purposes. First, we discuss the design constraints of the coil and select its dimensions using both the electromagnetic finite element method (FEM) and analytical equations based on the available length of a YBCO high-temperature superconductor. Then, we select the position of the coil inside a vacuum chamber. Then, an initial experiment without thermal load is performed to measure the cooling characteristics of the cryocooler. Using the results of the experiment and employing thermal FEM, we obtain an approximation of the cryocooler's cooling power versus time. After placing the coil and the thermal shield in the selected position inside the chamber, we carried out an experiment to measure the cooling curve with the load attached. The cryocooler's cooling power is approximated using the same FEM procedure. Thus, for this specific thermal load, the behavior of the apparatus is known. The methodology followed for the design of this unique system can be easily replicated by other researchers.

A Low-Loss, 77 GHz, 8 × 8 Microstrip Butler Matrix on a High-Purity Fused-Silica (HPFS) Glass Substrate.

A low-loss, compact, ultra-thin, passive, 77 GHz, 8 × 8 microstrip Butler matrix on a 200 μm thick high-purity fused-silica (HPFS) glass substrate embedded in 0.8 μm thick patterned gold conducting layers was developed for low power automotive radars. The first-of-its-kind, HPFS, glass-based Butler matrix comprised 12 hybrid couplers, 16 crossovers, and 8 phase shifters in a footprint area of 19.1 mm × 26.6 mm. The device and the corresponding building blocks were designed and optimized using 3D electromagnetic finite element method (FEM) simulations using the Advanced Design System (ADS) from Keysight™ Technologies. Due to the very-low-loss tangent of the HPFS glass substrate (0.0005 @77 GHz) compared to other common substrate materials and rigorous design optimization, the return loss and isolation of the input ports are both below -20 dB, respectively, as verified by 3D FEM simulations. Due to the absence of any published data on a 77 GHz 8 × 8 Butler matrix, the design was validated by developing a 4 × 4 version of the Butler matrix using the same building blocks and comparing the 3D simulation results in ADS with results published elsewhere that showed that the developed Butler matrix offers lower insertion loss in a 10% smaller footprint area. A low-cost microfabrication method has been developed to fabricate the devices using a standard lift-off process. A scaled version of the device can be used for 5G beamforming applications.

Comparative Design Study of HTS Synchronous Motor With Inner and Outer Rotor Type Based on Multi-Objective Optimization

In this paper, we report a design comparison between the inner and the outer rotor type for a partial high temperature superconductor (HTS) synchronous motor based on a multi-objective optimization. The partial HTS synchronous motors applied with no-insulation and multi-width winding technique are optimized by considering three characteristics; specific power (power per mass), power density (power per volume), and HTS tape consumption, simultaneously. The performance of each design is evaluated through the electromagnetic finite element method. Finally, the results obtained by optimization are compared between the inner and the outer rotor type.

Proposal of Inspection Method for Shrinkage Cavities in Spheroidal Graphite Cast Iron by Electromagnetic Force Vibration Using Differential Vibration Measurement

Spheroidal graphite cast iron is often used for machine parts that require high strength. A shrinkage cavity may be generated inside the cast iron during the manufacturing process. If there is a shrinkage cavity in the cast iron, the strength of the cast iron is significantly reduced. In this article, a non-destructive testing method for detection of shrinkage cavity inside the cast iron by constant frequency vibration measurement using electromagnetic force excitation at low frequency is proposed. In this method, the electromagnetic force vibration is generated inside the cast iron from the static magnetic field by a permanent magnet and the eddy current by an alternating exciting coil. Then, the vibration is measured by an accelerometer that is in contact with the surface of the cast iron material. If there is a shrinkage cavity inside the cast iron, since the vibration intensity is changed, the shrinkage cavity is estimated by the vibration measurement. In this method, the shrinkage cavities inside cast iron can be inspected at high speed with an inexpensive device. In this article, the electromagnetic force vibration is calculated using the 3-D nonlinear electromagnetic finite element method (FEM) analysis. The displacement due to vibration in the cast iron is calculated by the 3-D displacement FEM analysis. The phenomenon of electromagnetic force excitation is clarified using these FEM analysis methods. Then, the effectiveness of the proposed inspection method is investigated by comparing the results of the verification experiment and analysis.

SKIN – EFFECT LOSSES IN DIFFERENT LOADING CONDITIONS OF A POWER TRANSFORMER

The subject of the analysis is a 300 MVA auto-connected power transformer in different loading conditions with regard to the load losses. During the electrical design time, some operating points of the transformer were analyzed in more detail using 2D electromagnetic field finite element method (FEM) software. The models included 2D magnetic stray field calculation and covered a range of transformer loading cases that covered some that are more difficult to solve with traditional analytic methods based on the static magnetic field calculations. This is due to the presence of a phase shift between the currents through the windings. The results of the static magnetic Rabins’ method field calculation and the FEM method are compared and the best practice method is defined and determined accordingly.

Advanced Electrochemical Impedance Spectroscopy of Industrial Ni-Cd Batteries

Advanced electrochemical impedance spectroscopy (EIS) was applied to characterize industrial Ni-Cd batteries and to investigate the electrochemical redox processes. A two-term calibration workflow was used for accurate complex impedance measurements across a broad frequency range of 10 mHz to 2 kHz, resulting in calibrated resistance and reactance values. The EIS calibration significantly improved the measurements, particularly at high frequencies above 200 Hz, with differences of 6–8% to the uncalibrated impedance. With an electromagnetic finite element method (FEM) model, we showed that the impedance is strongly influenced by the cable fixturing and the self-inductance of the wire conductors due to alternating currents, which are efficiently removed by the proposed calibration workflow. For single cells, we measured the resistance and the reactance with respect to the state-of-charge (SoC) at different frequencies and a given rest period. For Ni-Cd blocks that include two cells in series, we found good agreement of EIS curves with single cells. As such, EIS can be used as a fast and reliable method to estimate the cell or block capacity status. For electrochemical interpretation, we used an equivalent electric circuit (EEC) model to fit the impedance spectra and to extract the main electrochemical parameters based on calibrated EIS, including charge-transfer kinetics, mass transport, and ohmic resistances. From the charge-transfer resistance, we computed the exchange current density, resulting in 0.23 A/cm2, reflecting high intrinsic rates of the redox electron transfer processes in Ni-Cd cells.

Analysis of Magnetic Field Characteristics of a Giant Magnetostrictive Actuator with a Semi-Closed Magnetic Circuit

The internal magnetic field characteristics of giant magnetostrictive actuators have an important influence on their output performance. Aiming at the deficiency of current scholars’ research, based on the electromagnetic theory and finite element method, this paper analyzes the magnetic field intensity on a giant magnetostrictive cylinder by using COMSOL Multiphysics software. Considering the inhomogeneity of magnetic field intensity along the radial direction of giant magnetostrictive cylinders, a new averaging method is introduced to calculate the magnetic field intensity in the axial section of the cylinder. The influence of the magnetic permeability of the displacement conversion mechanism (shell) and the size of the air gap inside the device on the magnetic field intensity of the giant magnetostrictive cylinder are analyzed. The prototype of the actuator is manufactured, and the correctness and accuracy of the simulation data are verified by experiments. In order to make the magnetic field on the cylinder strong and uniform, the displacement conversion mechanism and the shell should be made of low permeability and high permeability materials, respectively, and the air gap size should be reduced as much as possible under the condition of meeting the size requirement of the actuator pre-tightening force applying device.

Multifunctional antimony tin oxide/reduced graphene oxide aerogels with wideband microwave absorption and low infrared emissivity

The rapid development of high performance detection technology promotes the innovation of stealth technology moving towards the direction of multi-band compatibility, but suffers great challenges. Especially for the widely used radar detection and infrared detection, how to overcome the contradiction between their corresponding stealth materials and develop high-performance stealth materials with microwave-infrared compatible property is extremely urgent. Herein, flexible cellular reduced graphene oxide aerogels modulated by antimony tin oxide (ATO/rGO) have been synthesized by self-assembly, which demonstrate excellent microwave-infrared stealth compatibility. Remarkably, the aerogel exhibits dual-absorption in microwave stealth caused by strong interface polarization, achieving the maximum reflection loss (RL) of −40.92 dB at 11.36 GHz coupled with another absorption peak of −19.82 dB at 16.64 GHz and a broadest effective absorption bandwidth of 9.8 GHz covering the X band and Ku band, which can be verified by electromagnetic finite element method simulation. Moreover, trace amount of loss components ATO in conductive network structure guarantee the low infrared emissivity (0.383) and thermal insulation synchronously, which is the key to compatibility with infrared stealth. The light ATO/rGO aerogels demonstrate the great prospect for anti-detection and security protection, providing a novel approach for multispectral compatible stealth. • Synthesizing a new kind of ATO/rGO multifunctional flexible cellular aerogels. • Superior compatibility of microwave-infrared stealth was achieved. • Dual-absorption peaks extended absorption bandwidth to 9.8 GHz. • Absorption mechanism was firstly illustrated by SWR and electromagnetic simulation. • The aerogels exhibited low infrared emissivity and efficient thermal insulation.

A method to evaluate the plasma equivalent resistance of fusion relevant RF ion sources

To optimize the RF power transfer process for fusion relevant RF ion sources, the electric models evaluating the plasma equivalent resistance (PER) are used in engineering, such as the transformer model. This paper presents a method to evaluate the PER based on a FEM model, viz. the electromagnetic model describing the RF coupling and numerically solved by the finite element method (FEM). The inductively coupled plasma (ICP) is treated as a lossy dielectric. Then the ICP source loaded by the plasma is modeled in a generic electromagnetic FEM code. The method was applied to two fusion relevant ICP sources. The results showed that PER from the FEM model is quantitatively closer to PER from experiments than PER from other electrical models. Though the error in PER from the FEM model is still large, the method is an alternative to estimate the PER of fusion relevant RF ion sources. The error is mainly due to the stochastic heating model and the neglect of magnetization. Besides, for fusion relevant RF ion sources, the good-conductor approximation does not apply to the plasma and the plasma nonuniformity should be considered in electric models.

Analysis of the Influence of the Number of Coil Pairs Per Wing on Multiwing Reconnection Electromagnetic Launcher

The multiwing reconnection electromagnetic launcher is a variant of the plate reconnection device, and its working principle is the same as the reconnection device. The multiwing reconnection electromagnetic launcher is a geometrically complementary symmetrical mechanism, which can effectively improve the stability of the projectile. First, this article introduces the basic principle of one-stage plate reconnection electromagnetic launcher, and then focuses on the influence of the number of drive coil pairs per wing of the four-wing reconnection electromagnetic launcher on the launch performance. A four-wing reconnection electromagnetic launch model was established, the driving coil pairs of each wing are 1, 2, and 3, respectively, and the overall inductance of the coils of each wing consistent in three cases is ensured through the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> oscillation simulation. From the results of electromagnetic finite element method simulation, it is indicated that when the number of coil pairs per wing is 1, the projectile’s exit velocity is 474 m/s and the efficiency is 15.10%. This article shows that the most efficient acceleration of the projectile uses one driving coil pair per wing. More coil pairs per wing result in lower exit velocities and efficiencies. Finally, the phenomenon is explained from the perspective of the interaction between the magnetic field and the eddy current.

Design of an Integrated DC-Link Structure for Reconfigurable Integrated Modular Motor Drives

In this article, a dc-link structure feasible for integration with the circumscribing polygon modular integrated drives is proposed. The proposed dc-link structure combines both the dc-link capacitors and the bus-bar together and integrates them with the machine and the converter modules without increasing the outer diameter of the integrated machine/converter structure. A generic design methodology for the proposed dc-link structure is provided and applied on a reconfigurable 15 stator coils concentrated winding axial flux machine for all its possible phase configurations. The design methodology presented in this article involves the determination of the required dc-link capacitance and the multiphysics design of the bus-bar. The parasitics of the bus-bar part of the proposed dc-link structure are evaluated using electromagnetic finite element method (FEM) models and their influence on the dc-link waveforms is evaluated. Due to the expected high ambient temperature inside an integrated drive, electromagnetic and computational fluid dynamics (CFD) models are developed for the proposed dc-link structure to evaluate the loss density and the temperature distribution of the bus-bar to ensure reliable operation. An experimental setup is built to validate the design methodology.

Design of high-speed permanent magnet synchronous machines considering thermal demagnetization and mechanical characteristic of permanent magnet

This paper presents the design for a high-speed permanent magnet synchronous machine (PMSMs) considering the demagnetization and mechanical characteristics of rare-earth magnets based on the operating temperature. The TRV equation and plane stress analytical method are considered for the temperature, the rotor size is derived from the analysis results of the sleeve thickness, and the stator is designed on the basis of the results of the electromagnetic analysis method. The B–H curve of the permanent magnet (PM) changes with its operating temperature; thus, a thermal demagnetization analysis is conducted to verify the irreversible demagnetization caused by the operating temperature and armature reaction field using electromagnetic finite element method (FEM). It is necessary to consider the irreversible demagnetization with the operating temperature because it can decrease the electromagnetic performance. Therefore, the electromagnetic characteristics of high-speed machines using rare-earth PMs are analyzed to confirm irreversible demagnetization. The validity of the proposed design is confirmed via comparative verifications with the measured results from prototype models.

Multiplexed 16 × 16 Li-Ion Cell Measurements Including Internal Resistance for Quality Inspection and Classification

Characterization and classification of lithium-ion batteries (LIB) are of high relevance for cell and battery producers, especially with the rising demands on LIBs for electric vehicle applications. We present a compact measurement station with 256 multiplexed channels to measure the open-circuit voltage (OCV) and the alternating current internal resistance (ACIR) of a tray of 256 cylindrical cells. Four different cell types were distinguished based on the ACIR values ranging between 11 and 22 $\text{m}\Omega $ . The measurement station performance was assessed based on the cell-fixture recontacting error and the electronic noise of the channels. Several calibration workflows of different complexity were evaluated. Data correction for the measure station was done by a two-term calibration procedure, including a short and gain correction. This resulted in a 67% improvement on the real part of ACIR and 83% on the imaginary part both compared to a bench-top-based reference system. Electromagnetic finite element method (FEM) modeling was done to model the cables and the cell fixture, including different wire lengths. The state of health (SoH) of cycled cells was computed, and their correlation to ACIR was discussed, including the electrochemical interpretation based on an equivalent electric circuit model. Overall, we show how this multiplexed measurement station can be used for classification and LIB quality control in battery manufacturing.