Electromagnetic Analysis Model Research Articles

Electrically Reconfigurable Metasurfaces for Frequency Selective Transmission via IPMC Kirigami

AbstractMetasurface with programmable configurations has attracted tremendous attention due to their exotic abilities to manipulate electromagnetic waves. Herein, an electrically reconfigurable metasurface for frequency selective transmission is developed based on ionic polymer–metal composite (IPMC) kirigami. First, low‐voltage driven IPMC actuators with stable actuation performance are realized, and then a thermomechanical equivalent model and a numerical electromagnetic analysis model are proposed for evaluating the deformation of the IPMC actuators and predicting the electromagnetic tunable properties of the IPMC kirigami metasurfaces, respectively. Subsequently, large‐area IPMC kirigami metasurfaces are proposed and produced by using programmable nanosecond laser micro‐processing technique that endows the uniformity of the kirigami units. Finally, the electromagnetic functionalities of these IPMC kirigami metasurfaces are researched and validated by experiments and numerical simulations. Both theoretical and experimental results demonstrate that the electromagnetic transmission frequency of the fabricated IPMC kirigami metasurface with 10 × 10 units can be tuned from 19.3 to 20.8 GHz by the application of a low voltage of 3 V. Compared with the existing reconfigurable metasurfaces, the proposed IPMC kirigami metasurface demonstrates clear advantages in its compact structure, lower driving‐voltage, low‐acoustic noise, and wide working frequency range.

Research on Temperature Distribution of Large Permanent Magnet Synchronous Direct Drive Wind Turbine

A wind turbine is a conversion mechanism that converts wind energy into electrical energy, but the conversion efficiency cannot reach 100%, so there is partial loss. These losses are converted into thermal energy, which in turn causes the wind turbine to heat up and affect generator performance. Therefore, the cooling and temperature field analysis of wind turbines is very important. In this paper, an electromagnetic analysis model is established by using the parameters of a 4 MW wind turbine; the losses of each part of the generator under rated load and three-phase short-circuit conditions are calculated, respectively; and the heat source is imported into the workbench fluent software to determine the cooling mode, so as to obtain the magnetic-thermal-flow field coupling model of permanent magnet synchronous direct drive wind turbine. The temperature distribution and temperature rise of the generator are obtained. Under the rated load condition, the overall maximum temperature rise of the wind turbine is 41.4 °C, about 180 mm near the fluid outlet side, which is as high as the winding temperature rises, because the winding is the main heating body. The maximum temperature rise of the rotor model and the permanent magnet model is about 36 °C. Under the three-phase short circuit condition, the temperature distribution of each component is similar to that under the rated load condition, and the temperature near the fluid inlet is low; the lowest is only 29.8 °C. The higher the temperature at the fluid’s outlet, but not close to it, the higher the temperature is when it is about 180 mm away from the fluid’s outlet side. The temperature difference in the same axial length is relatively large, with a maximum temperature difference of about 120 °C. The temperature distribution and temperature rise of the generator are independent of the operating conditions, which mainly affect the value. Additionally, through experimental verification, the minimum error under the rated load condition is 1.05%, the maximum error is 3.3%, and the average error is 2.30%. The minimum error under the three-phase short-circuit condition is 1.5%, the maximum error is 3.62%, and the average error is 2.26%. The difference with the engineering error range requirements is small, indicating the reasonable and effective effectiveness of this method. This study aims to provide a strong reference for analyzing the cooling and magnetic thermal flow field and a coupling analysis of direct drive wind turbines.

A new hybrid analytical model for electromagnetic analysis of wound rotor induction motors

AbstractAccurate modeling of slotting and magnetic saturation effects has been two main challenges for analytical modeling of electric machines. In this article, first, different techniques such as sub‐domain (S‐D) model, winding function theory, magnetic equivalent circuit (MEC) model, and conformal mapping (CM) method are introduced to analytical model and analysis of electric machines. These techniques are also compared in terms of their accuracy, and computational complexity. Second, with respect to the comparison results, a new hybrid analytical model is presented for electromagnetic modeling of wound rotor induction motors, which consider the modeling accuracy of slotting and magnetic saturation effect, simultaneously. In this way, the air‐gap region is modeled by using S‐D model, and the iron parts are considered by using MEC model assisted by CMs. In final, the analytical results are verified by comparing with corresponding results obtained through finite element method and experiment set‐up.

Study on Electromagnetic Structure Design of Electromagnetic Bearing Body for Control Rod Drive Mechanism

The electromagnetic structure design is the core of the design of electromagnetic bearing body for control rod drive mechanism (CRDM). In order to obtain a reasonable electromagnetic structure, a certain electromagnetic structure is selected according to different shapes of magnetic flux distribution, and used to build the analytical model and finite element model for electromagnetic analysis. Then, the working point of the electromagnetic bearing is determined by finite element simulation and analysis, and the key performance parameters, such as current stiffness and displacement stiffness, of the electromagnetic bearing are further analyzed and studied. Finally, cross verification is performed by comparison between the finite element simulation and analysis results and the analytical calculation results. The verification results show that the electromagnetic structure design of the CRDM electromagnetic bearing body is appropriate, and all performance indexes can meet the design requirements.

Comparative analysis of super high-speed permanent magnet generator electromagnetic and temperature fields with the PWM and uncontrolled rectifiers

ABSTRACT This paper presents a study on the influence of different rectifiers on a super-high-speed permanent magnet generator (SHSPMG), which is used in a micro-gas turbine distributed generation system. Taking a 117 kW, 60,000 r/min SHSPMG as an example, the influence of PWM and uncontrolled rectifiers on the generator performances were studied comparatively. The current harmonics and its total harmonic distortion were analysed firstly, and the variation characteristics of voltage and current harmonics were obtained. Based on the 2-D electromagnetic analysis model, the losses of the generator with different rectifier load were studied, especially for the rotor losses, and the mechanisms of the losses variation were determined. By using the method of the 3-D coupling field between fluid and temperature, the temperature distributions of the SHSPMG connected with the PWM and uncontrolled rectifiers were calculated, respectively, and the influences of the different rectifiers on the generator temperature field were studied. It could be found that the PWM rectifier has the advantages of reducing generator losses and optimizing temperature distribution.

Analytical 2-D Model of Slotted Brushless Machines With Cubic Spoke-Type Permanent Magnets

Brushless machines with interior permanent magnets (PMs) are mostly made with PM geometries inconsistent with the polar coordinates of the rotor cross section. Therefore, without any subdomain transformation, the analytical approaches cannot precisely model the interior PM machines in a single coordinate. This paper presents an accurate two-dimensional (2-D) analytical model for electromagnetic analysis of slotted brushless machines with rectangular spokePMs assisted by hub magnets. The slotting effect is modeled via subdomain technique. However, the spoke PM is not consistent enough with polar coordinates to be approximated by one subdomain. In order to map the spoke PMs in polar coordinates, herein, the rectangular geometry is approximated by a combination of arc shaped subdomains. On this basis, the 2-D analytic model is developed for M-fraction spoke PM. To verify the accuracy of the proposed 2-D approach, analytic results are compared with numeric results of finite elements method. It is revealed that by dividing the spoke PM into arc subdomains, the 2-D model achieves higher accuracy in calculation of electromagnetic quantities such as PM and armature reaction fields, electromagnetic torque, and back electromotive force.

Design optimization of high frequency transformer with controlled leakage inductance for current fed dual active bridge converter

Current fed dual active bridge converters for photovoltaic generation may typically require a given leakage or extra inductance in order to provide proper control of the currents. Therefore, the many researches have been focused on the leakage inductance control of high frequency transformer to integrate an extra inductor. In this paper, an asymmetric winding arrangement to get the controlled leakage inductance for the high frequency transformer is proposed to improve the efficiency of the current fed dual active bridge converter. In order to accurate analysis, a coupled electromagnetic analysis model of transformer connected with high frequency switching circuit is used. A design optimization procedure for high efficiency is also presented using design analysis model, and it is verified by the experimental result.

A study on thermal characteristics analysis model of high frequency switching transformer

Recently, interest has been shown in research on the module-integrated converter (MIC) in small-scale photovoltaic (PV) generation. In an MIC, the voltage boosting high frequency transformer should be designed to be compact in size and have high efficiency. In response to the need to satisfy these requirements, this paper presents a coupled electromagnetic analysis model of a transformer connected with a high frequency switching DC-DC converter circuit while considering thermal characteristics due to the copper and core losses. A design optimization procedure for high efficiency is also presented using this design analysis method, and it is verified by the experimental result.

MRI-Based Multiscale Model for Electromagnetic Analysis in the Human Head with Implanted DBS

Deep brain stimulation (DBS) is an established procedure for the treatment of movement and affective disorders. Patients with DBS may benefit from magnetic resonance imaging (MRI) to evaluate injuries or comorbidities. However, the MRI radio-frequency (RF) energy may cause excessive tissue heating particularly near the electrode. This paper studies how the accuracy of numerical modeling of the RF field inside a DBS patient varies with spatial resolution and corresponding anatomical detail of the volume surrounding the electrodes. A multiscale model (MS) was created by an atlas-based segmentation using a 1 mm3 head model (mRes) refined in the basal ganglia by a 200 μm2 ex-vivo dataset. Four DBS electrodes targeting the left globus pallidus internus were modeled. Electromagnetic simulations at 128 MHz showed that the peak of the electric field of the MS doubled (18.7 kV/m versus 9.33 kV/m) and shifted 6.4 mm compared to the mRes model. Additionally, the MS had a sixfold increase over the mRes model in peak-specific absorption rate (SAR of 43.9 kW/kg versus 7 kW/kg). The results suggest that submillimetric resolution and improved anatomical detail in the model may increase the accuracy of computed electric field and local SAR around the tip of the implant.

Improved Analytical Model for Electromagnetic Analysis of Axial Flux Machines With Double-Sided Permanent Magnet Rotor and Coreless Stator Windings

This paper deals with the experimental verification and electromagnetic analysis of an axial flux machine with a double-sided permanent magnet (PM) rotor and coreless stator windings, based on analytical field computation. Employing a magnetic vector potential and a 2-D analytical model, magnetic fields produced by PMs are obtained. The 3-D problem is solved by introducing a special function for the radial position. Then, the analytical solutions for back emf, electromagnetic torque, and efficiency of the PM-type axial flux machines are derived by using the magnetic field solutions and considering simple equivalent circuits. The analytical results are validated extensively by 3-D FE results. Test results such as back-emf, torque, and efficiency measurements are also presented to show the effectiveness of the analyses.

Analysis of a diffractive microlens using the finite-difference time-domain method

The finite-difference time-domain (FDTD) method is used as rigorous electromagnetic analysis model to calculate the field for a diffractive microlens (DML). The FDTD is used for the entire solution rather than using a near- to far-field propagation method to obtain the far-field energy distribution; thus, all the results are vector based. We derived a formula to calculate the magnitude of electric field, which is time dependent and can be used to graphically show the light wave propagation and focusing process through a DML. Both the comparison and the integral methods are presented to obtain wave amplitude in full solution space, and the distribution of light energy behind a DML is illustrated based on the wave amplitude. The formula of diffractive efficiency of the DML is derived from a time-averaged Ponyting vector, which can indicate the propagation direction of light energy. Application of these formulations in the analysis of a DML example demonstrates the high accuracy and efficiency of our method.

Electromagnetic wave radiated from an insulating spacer in gas insulated switchgear with partial discharge detection

As a means of diagnosing partial discharge (PD) signals propagate inside a gas insulated switchgear (GIS), a study for the leakage of electromagnetic waves (EM-waves) emitted from the insulating spacer was implemented. The EM-waves leaking out from the solid insulator have the resonance frequencies depend on the spacing between adjacent bolts in the direction of the flange circumference, because the leakage portion is the equivalent of a slot antenna. In this paper, using an electromagnetic analysis model which has a simulated spacer on a concentrically-shaped GIS tank, the output characteristics of the EM-waves that leaked out from the slit were analyzed under various conditions such as the spacing between adjacent bolts, the width of the spacer, the dielectric constant of the spacer and the form of the flange. Also the actual measurement by the experimental equipment used to simulate the model was implemented for comparison with the analytical results. Consequently, the optimal specifications of the sensor and the measurement method used to achieve highly-sensitive detection for practical use were summarized and proposed as well as evaluating the effectiveness of the electromagnetic analysis model adopted in this paper.

An improved finite-element model for electromagnetic analysis in aluminum cells

This article presents the use of an improved finite-element model to calculate the static electromagnetic field for an aluminum reduction cell. Consisting of three solid cells and their surrounding bus bars, the model can evaluate the non-uniformity of the current distribution in the inside conductors and bus bar system and couple the current into the sequential magnetic analysis through a conversion routine. Voltage potential distribution in the molten aluminum was investigated based on one industrial 320 kA aluminum cell with two designed bus bar arrangements. Characteristics of magnetic components’ distributions were also given.