Showing papers on "Electromagnetic coil published in 2020"

Conjunction of triboelectric nanogenerator with induction coils as wireless power sources and self-powered wireless sensors.

Abstract: Here we demonstrate a magnetic resonance coupling based wireless triboelectric nanogenerator (TENG) and fully self-powered wireless sensors. By integrating a microswitch and an inductor with the TENG, the pulsed voltage output is converted into a sinusoidal voltage signal with a fixed frequency. This can be transmitted wirelessly from the transmit coil to the resonant-coupled receiver coil with an efficiency of 73% for a 5 cm distance between the two coils (10 cm diameter). Analytic models of the oscillating and coupled voltage signals for the wireless energy transfer are developed, showing excellent agreement with the experimental results. A TENG of 40 × 50 mm2 can wirelessly light up 70 LEDs or charge up a 15 μF capacitor to 12.5 V in ~90 s. The system is further utilized for two types of fully self-powered wireless chipless sensors with no microelectronic components. The technologies demonstrate an innovative strategy for a wireless ‘green’ power source and sensing. Renewable energy based wireless power transfer is challenging. Here the authors show a resonant-coupled triboelectric nanogenerator as a wireless power source and have further utilized this system to explore two fully self-powered wireless chipless sensors.

A Load-Independent LCC-Compensated Wireless Power Transfer System for Multiple Loads With a Compact Coupler Design

Abstract: This article proposes a novel wireless power transfer (WPT) system for multiple loads. Multiple coils are used as power repeaters to enhance the power transfer capability over a long distance and each power repeater corresponds to a load. The inductor-capacitor-capacitor (LCC) compensation method is used for each repeater coil in the system, which ensures load-independent currents flowing through the loads. Thus, flexible power control can be achieved for all the loads without affecting each other. In order to save space, the compensation coil is integrated with the repeater coil to realize a compact design. Bipolar coils are used for both the repeater coil and compensation coil. The undesirable coupling coefficient between the repeater coil and its compensation coil can be eliminated by putting them perpendicularly. The compensation coil is not only used to achieve resonant condition for the system, but also transfers energy to the next repeater coil via the magnetic coupling between them. The operational principle has been explained in detail. An experiment platform with six loads has been built and the experimental results are provided to validate the effectiveness of the proposed WPT repeater system. The maximum efficiency can reach 86.6%.

Thermal Overload and Insulation Aging of Short Duty Cycle, Aerospace Motors

Abstract: Electrical machines for transportation applications need to be highly reliable, particularly if they drive safety-critical systems. At the same time, another main requirement is represented by the significant torque density, especially for aerospace, where weight constraints are extremely stringent. For achieving high peak torque, an effective strategy consists in supplying the windings with a current greater than the rated value; thus, thermally overloading the machine for limited time periods. However, if the insulation is overheated, the machine lifetime is shortened and reliability issues can arise. This paper experimentally investigates the influence of short-time thermal overload on the insulation lifetime for low voltage, random wound electrical machines. The analysis is performed on round enameled magnet wire coils, which are aged by accelerated thermal cycles. The obtained results are statistically processed through a two parameter Weibull distribution. According to the findings of the experimental data postprocessing, a lifetime prediction model is built. This model is employed for predicting the lifetime consumption of a motor embedded into an electromechanical actuator for aerospace application.

A High Step-Up Interleaved DC-DC Converter With Voltage Multiplier and Coupled Inductors for Renewable Energy Systems

Abstract: This paper proposes a new interleaved non-isolated high step-up dc-dc converter for interfacing renewable energy applications. The proposed converter achieves a very high step-up voltage gain by using two coupled inductors and a voltage multiplier cell. This topology utilizes the interleaved boost converter in the input side, and the input current is shared with low ripple. Moreover, a voltage multiplier cell with the secondary windings of the coupled inductors is employed in the output side to achieve the interleaved energy storage. The voltage stress on the semiconductor switches and the passive components is significantly reduced and lower than the output voltage. The aforementioned converter can be operated without an extreme duty cycle or a high turns ratio. The reverse recovery problem of the diodes is mitigated, and the leakage energy is recycled. Furthermore, by implementing low-voltage-rated MOSFETs with a small ON-resistance, the conduction losses can be reduced, and the efficiency can be improved. The topology is fed by a single input voltage, and the mathematical expression is methodically explored. The operation principle of the proposed converter and the comparison between the proposed converter with other topologies are discussed. The design, parameters selection, and experimental results are thoroughly introduced. A 32 to 800 V-dc is verified and simulated by using PLECS. Consequently, a 400 W hardware prototype is verified to validate the theory and the design.

A 50-kW Three-Phase Wireless Power Transfer System Using Bipolar Windings and Series Resonant Networks for Rotating Magnetic Fields

Abstract: The mass and volume of wireless power transfer (WPT) systems for charging electric vehicles are directly related to the rated power of the system. The difficulties of high-power wireless charging are exacerbated by the need to meet the same practical constraints associated with vehicle integration as lower power systems. Therefore, more advanced techniques are necessary to improve power density and specific power of wireless charging systems for high-power applications. This article presents theory and analysis of three-phase inductive WPT systems with bipolar phase windings. Magnetic coupler topologies and the theoretical and practical aspects of series three-phase resonant compensation networks are discussed. The systems under consideration are designed to utilize rotating magnetic fields to achieve a power transfer characteristic that is temporally smoother than single-phase systems. Other benefits associated with rotating magnetic field based WPT, including reduced ferrite mass, filter component requirements, and electromagnetic field emissions, are discussed. Experimental results of a prototype system are presented in both aligned and misaligned configurations. The system is demonstrated transferring 50 kW with 95% dc-to-dc efficiency over a 150-mm airgap in the aligned case. Onaper-pad basis, the magnetic couplers achieve a power density of 195 kW/m 2 and a specific power of 3.65 kW/kg. This article is accompanied by a video of the rotating magnetic field produced by a simulated three-phase WPT system.

Ferrofluid droplet manipulation using an adjustable alternating magnetic field

Abstract: Magnetically actuated droplet manipulation offers a promising tool for biomedical and engineering applications, such as drug delivery, biochemistry, sample handling in lab-on-chip devices and tissue engineering. In this study, characteristics of an adjustable alternating magnetic field generated by a magnetic coil for droplet manipulation was investigated which enables more control on droplet transport, and it can be considered as a suitable alternative for moving magnets or an array of micro-coils. By adjusting the magnetic flux density, the duty cycle and applied magnetic frequency, the manipulation of water-based ferrofluid droplets with a bio-compatible surfactant for different volumes was comprehensively examined. Also, the platform was able to manipulate the ferrofluid droplets completely immersed in oil. This solves the problem with droplet evaporation which has previously been reported for droplet manipulation on the surface. Furthermore, an analytical model is proposed for the movement of the ferrofluid droplet on the hydrophobic surface. The model predictions are in good agreement with experimental results. Also, the effects of magnetic flux density, duty cycle, frequency and the distance between the coils on the mixing process were studied. Results showed that the droplet movement on the hydrophobic surface was fully synchronized with the generated signal while the droplet moved backward in the oil after the magnetic field was turned off. By decreasing magnetic flux density, droplet volume, duty cycle, as well as increasing applied magnetic frequency, the step lengths become more uniform, the resolution of droplet displacement increases, but the average-velocity decreases.

Research on the Design Method of Uniform Magnetic Field Coil Based on the MSR

Abstract: The uniform magnetic field coil can be placed in the magnetic shielding room (MSR) to provide a more accurate magnetic source. The coil could generate a uniform magnetic field by the conventional design method, but when placed in the MSR, the uniformity of the field would be affected. The magnetic field analysis model of coil based on cuboid ferromagnetic boundary condition is constructed by the image method. This paper proposes a new design method of coil parameters based on the deviation of magnetic field distribution in volumes boundary. The coil system in the shield designed by the new method is compared with the conventional coil system, which not only solves the problem of uniformity reducing, but also further improves the uniformity of the magnetic field. The influence of the ratio kt of coil side length to MSR side length on coil parameters is found. The correspondence between the coil parameters and the kt can be used to guide the design of the coil system under the future ferromagnetic boundary conditions. The validity and significance of the analytical model as well as the new design method are proved by the results of finite-element software and experiments.

A Transformer Integrated Filtering System for Power Quality Improvement of Industrial DC Supply System

Abstract: This paper proposes a transformer integrated filtering system (TIFS) for harmonic suppression in the industrial dc supply system. Designed for the electric environment with large current and severe harmonic contamination and the installation space with restricted planning area, the proposed TIFS has the merits of lower transformer loss, stronger ability in harmonic elimination, and higher integration of the electric equipment in the high-power industrial applications. The winding arrangement of the inductive filtering transformer with integrated reactor is introduced. Considering the influence of the residual weak coupling, the electromagnetic decoupling model of TIFS is established. Then, the interaction between the zero-impedance designed filtering winding and the decoupled winding is analyzed to determine the restricted range of the design parameter. The control strategy together with the transformer design method is further illuminated. At last, the prototype of TIFS is established in the laboratory. The experimental results verify the feasibility and effectiveness of the proposed filtering method.

In vivo human head MRI at 10.5T: A radiofrequency safety study and preliminary imaging results.

Abstract: PURPOSE The purpose of this study is to safely acquire the first human head images at 10.5T. METHODS To ensure safety of subjects, we validated the electromagnetic simulation model of our coil. We obtained quantitative agreement between simulated and experimental B1+ and specific absorption rate (SAR). Using the validated coil model, we calculated radiofrequency power levels to safely image human subjects. We conducted all experiments and imaging sessions in a controlled radiofrequency safety lab and the whole-body 10.5T scanner in the Center for Magnetic Resonance Research. RESULTS Quantitative agreement between the simulated and experimental results was obtained including S-parameters, B1+ maps, and SAR. We calculated peak 10 g average SAR using 4 different realistic human body models for a quadrature excitation and demonstrated that the peak 10 g SAR variation between subjects was less than 30%. We calculated safe power limits based on this set and used those limits to acquire T2 - and T2∗ -weighted images of human subjects at 10.5T. CONCLUSIONS In this study, we acquired the first in vivo human head images at 10.5T using an 8-channel transmit/receive coil. We implemented and expanded a previously proposed workflow to validate the electromagnetic simulation model of the 8-channel transmit/receive coil. Using the validated coil model, we calculated radiofrequency power levels to safely image human subjects.

Zero-Phase-Angle Controlled Bidirectional Wireless EV Charging Systems for Large Coil Misalignments

Abstract: Misalignment between charging coils is an unavoidable problem in all electric vehicle (EV) charging systems that are based on wireless power transfer (WPT) technology. This is because variations in both self- and mutual inductances of charging coils due to coil misalignments significantly affect the charging rate and efficiency of the EV charger. As a solution, this article proposes a new control technique that maintains the rated charging power level at optimum efficiency in spite of large coil misalignments. To compensate for the variations in inductances, the technique uses the information extracted from input impedance to operate the system essentially at unique converter voltages with zero phase angle, ensuring that charging will take place at rated power with optimal efficiency despite any pad misalignments. The article presents a comprehensive mathematical model, describing the theoretical basis of the proposed control philosophy. To demonstrate the validity of the proposed control concept, a 1-kW bidirectional WPT EV charging system is built and results are presented under misaligned coil conditions. Results convincingly indicate that the proposed controller is efficient and capable of maintaining the rated charging rate despite large coil misalignments and without any dedicated wireless communication.

Asymmetric Bar Winding for High-Speed Traction Electric Machines

Abstract: A new asymmetric bar winding concept along with the analysis and benefits for high-speed traction electric machines is presented. The objective is to reduce the ac losses, especially at high speeds, utilizing optimized and asymmetric conductor heights within a slot for bar-wound stators. Detailed winding diagram, height optimization, ac loss analysis, and thermal performance are presented for both symmetric, i.e., conventional, and asymmetric bar windings. The proposed idea is validated using the closed-form analytical equation and 2-D time-stepped finite-element analysis (FEA). A substantial reduction of ac losses and improvement in continuous power over the wide operation range is achieved as demonstrated for a 12-pole, 100-kW high-speed (15 000 r/min) PM traction machine. Thermal performance analysis using forced liquid cooling is also included. The design and analysis methodology is presented to support high-speed traction electric machine designers meet the ever-increasing demand on efficiency and performance with bar-type windings.

Effective-Configuration WPT Systems for Drones Charging Area Extension Featuring Quasi-Uniform Magnetic Coupling

Abstract: This article presents a quasi-uniform magnetic coupling-based effective-configuration wireless power transfer (WPT) system for drones wider-area charging with multiple extended transmitter coils. The extended transmitter coil with two windings is proposed to cooperate with a small receiver coil for misalignment tolerance with efficient and quasi-uniform coupling. The extended coil is worked out by a simulation-based algorithm, which can be implemented by simple and low-cost procedures. Independent-operating multiple extended coils are designed with overlaps and a dynamic topology for low-cost and robust charging area extension according to performance analyses. Moreover, a novel landed position detection method based on the negative coupling characteristic of the extended coils is proposed for system configuration. The design enables cost-effective charging area extension and assists to sense the position of drones. A prototype is established with a charging area nearly 20 times the area of the receiver coil. Experimental results prove the feasibility of the design, which can be applied flexibly.

Reduction of Winding AC Losses by Accurate Conductor Placement in High Frequency Electrical Machines

Abstract: In the design of electrical machines, the increase in power density has become one of the main research themes. With most of the power loss in high power density electrical machines often being generated in the stator winding assembly, it is necessary to reduce these losses. The effects of strands and bundle positions in the slot on the ac losses in the winding are often overlooked. Taking as a case-study an existing high-frequency machine, this article analyzes and provides an in-depth insight into such effects. Exploiting the rapid advancements in precision three-dimensional printing, it is found and experimentally verified that by controlling the position of the conductors within the top of the slot the ac losses can be markedly reduced.

Symmetric Sensing Coil Design for the Blind-Zone Free Metal Object Detection of a Stationary Wireless Electric Vehicles Charger

Abstract: In this article, a simple and cost-effective symmetric sensing coil set to be used for the metal object detection (MOD) in a stationary wireless electric vehicle charger is newly proposed. Compared to the conventional nonoverlapping sensing coil using the magnetic field change detection method, the proposed symmetric sensing coil set design offers the considerable advantage of eliminating all blind zones, i.e., regions where metal is undetectable in the conventional method. Moreover, by reducing the number of layers to one, the fabrication of the proposed sensing coil is easier and more cost effective. The design of the proposed sensing coil is optimized for highly sensitive MOD based on a sensitivity equation and on the finite element method simulations. An experiment conducted with a metal object 40 × 40 mm2 in size and a 20 A transmitting (Tx) coil current verifies the reliability and the blind-zone elimination feature of the proposed sensing coil.

Estimating Power Transformer High Frequency Model Parameters Using Frequency Response Analysis

Abstract: Frequency response analysis (FRA) has become a widely accepted technique by worldwide utilities to detect winding and core deformations within power transformers. The main drawback of this technique is its reliance on the personnel level of expertise more than standard or automated codes. To establish reliable FRA interpretation codes, accurate high frequency transformer model that can emulate the frequency characteristics of real transformers in a wide frequency range is essential. The model can be used to investigate the impact of various winding and core deformations on the transformer FRA signature. The transformer equivalent high frequency electric circuit parameters can be calculated based on design data, which are rarely available, especially for old transformers. As such, this paper presents an artificial intelligence technique to estimate these parameters from the transformer FRA signature. The robustness of the proposed technique is assessed through its application on three, 3-phase power transformers of different ratings, sizes, and winding structures to estimate their high frequency electric circuit parameters during normal and fault conditions. Results show that the proposed technique can estimate equivalent circuit parameters with high accuracy and helps interpret the FRA signature based on the numerical changes of these parameters. The main advantage of this approach is the physical meaning of the model parameters facilitates reliable identification of various faults and hence aids in establishing reliable interpretation codes for transformer FRA signatures.

Highly efficient head-only magnetic field insert gradient coil for achieving simultaneous high gradient amplitude and slew rate at 3.0T (MAGNUS) for brain microstructure imaging.

Abstract: Purpose To develop a highly efficient magnetic field gradient coil for head imaging that achieves 200 mT/m and 500 T/m/s on each axis using a standard 1 MVA gradient driver in clinical whole-body 3.0T MR magnet. Methods A 42-cm inner diameter head-gradient used the available 89- to 91-cm warm bore space in a whole-body 3.0T magnet by increasing the radial separation between the primary and the shield coil windings to 18.6 cm. This required the removal of the standard whole-body gradient and radiofrequency coils. To achieve a coil efficiency ~4× that of whole-body gradients, a double-layer primary coil design with asymmetric x-y axes, and symmetric z-axis was used. The use of all-hollow conductor with direct fluid cooling of the gradient coil enabled ≥50 kW of total heat dissipation. Results This design achieved a coil efficiency of 0.32 mT/m/A, allowing 200 mT/m and 500 T/m/s for a 620 A/1500 V driver. The gradient coil yielded substantially reduced echo spacing, and minimum repetition time and echo time. In high b = 10,000 s/mm2 diffusion, echo time (TE) 50% reduction compared with whole-body gradients). The gradient coil passed the American College of Radiology tests for gradient linearity and distortion, and met acoustic requirements for nonsignificant risk operation. Conclusions Ultra-high gradient coil performance was achieved for head imaging without substantial increases in gradient driver power in a whole-body 3.0T magnet after removing the standard gradient coil. As such, any clinical whole-body 3.0T MR system could be upgraded with 3-4× improvement in gradient performance for brain imaging.

Eddy Current Loss and Detuning Effect of Seawater on Wireless Power Transfer

Abstract: Due to the conductivity of the seawater, the traditional mutual inductance circuit model in the air cannot be used directly to describe wireless power transfer (WPT) systems in seawater applications. This paper proposes a modified mutual inductance circuit model of an underwater WPT system to analyze the eddy current loss (ECL) and the detuning effect caused by the seawater. The time-harmonic electromagnetic field in the seawater and the air near the coil that carries a sinusoidal alternating current is analyzed. The root-mean-square (rms) value and phase angle of the induced voltage on the secondary coil can be obtained by the integral of the electric field intensity along the coil path. By introducing the equivalent ECL impedance at both the primary and secondary sides, a modified mutual inductance circuit model of an underwater WPT system was obtained. Through adding a compensation inductance to the primary circuit, the detuned system in the seawater is turned back to be resonant at the same frequency as in the air. A seawater WPT prototype was built and the experimental results verified the theoretical analysis.

Quarter-Turn Transformer Design and Optimization for High Power Density 1-MHz LLC Resonant Converter

Abstract: In this paper, quarter-turn planar transformer structure is proposed and implemented in an LLC resonant converter for server power supply applications. Main power losses of high-frequency resonant converters are secondary-side winding loss and transformer core loss. Conventional transformer winding structures limit the minimum number of turns on the primary and secondary sides, such that the core size and secondary-side conduction loss cannot be reduced by increasing the frequency. To achieve high efficiency and high power density, a fractional-turn transformer structure can reduce core volume and conduction loss in the windings. The optimized transformer design also enables the turn ratio of the fractional-turn to achieve normal coupling of primary and secondary sides without generating flux imbalance. The effects of different fractional-turn windings on efficiency are examined, and Maxwell simulation results are used to verify the structure and operation of the planar transformer. The printed circuit board layout is analyzed using Q3D Extractor to reduce the uneven current generated by parasitic components on the secondary-side windings. Wide-bandgap switches are utilized to implement a resonant converter with 1-MHz operating frequency, 380-V input voltage, 12-V output voltage, 1-kW output power, 37.6-W/cm3 power density, and 97% maximum efficiency.

Design of DD Coil With High Misalignment Tolerance and Low EMF Emissions for Wireless Electric Vehicle Charging Systems

Abstract: In this article, a design method of the double-D (DD) coil aiming at high misalignment tolerance is proposed, and the electromagnetic field (EMF) shielding of the system is considered. Inspired by the DD coil recommended in the standard J2954 published by the Society of Automotive Engineers, the novel structures of the transmitting (Tx) coil and the receiving (Rx) coil are designed, respectively. First, the standard DD coil is introduced as a reference. Second, for the Tx coil, the parameters, such as length, width, and coverage, are investigated in detail. For the Rx coil, the coil structure overlapped in the edge is optimized. The purpose is to obtain a higher coupling coefficient at the maximum offset. Third, considering EMF emissions exceeding the limit, the structure of the central-depressed coil with E-shaped cores is proposed in the Tx coil. The EMF emissions can be reduced to less than 27 μ T at the rated output power. Finally, a 6.6–kW experimental system of which the maximum transmission efficiency is higher than 94% is set up. The experimental results prove that the proposed structure is beneficial to maintain a higher coupling coefficient against misalignment and suppress EMF emissions.

Additive Manufacturing of Shaped Profile Windings for Minimal AC Loss in Electrical Machines

Abstract: Metal additive manufacturing enables production of copper and aluminium parts exhibiting unmatched geometric freedom, giving rise to new possibilities in the winding design of electrical machines and wound passive components. Early adopters of additive manufacturing are primarily concerned with improving power-density or efficiency by increasing slot fill-factor, optimizing end-winding topology or incorporating cooling channels into the conductors. In this article, a method of minimizing the elevated ac loss present in open slot electrical machine topologies is presented, in which individual conductor profiles are shaped according to their magnetic environment. Such shaped profile windings are shown to exhibit operating mode dependent loss behavior giving them potential for efficiency improvement in applications with a dominant operating mode such as electric vehicle traction, aerospace propulsion fans, and generators. For the first time, the conductor shaping method and associated benefits are demonstrated by the retrospective design, additive manufacture, and experimental test of a three-phase set of shaped profile windings for a concentrated wound, open slot, permanent magnet electrical machine.

Emergent electromagnetic induction in a helical-spin magnet

Abstract: An inductor, one of the most fundamental circuit elements in modern electronic devices, generates a voltage proportional to the time derivative of the input current1. Conventional inductors typically consist of a helical coil and induce a voltage as a counteraction to time-varying magnetic flux penetrating the coil, following Faraday’s law of electromagnetic induction. The magnitude of this conventional inductance is proportional to the volume of the inductor’s coil, which hinders the miniaturization of inductors2. Here, we demonstrate an inductance of quantum-mechanical origin3, generated by the emergent electric field induced by current-driven dynamics of spin helices in a magnet. In microscale rectangular magnetic devices with nanoscale spin helices, we observe a typical inductance as large as −400 nanohenry, comparable in magnitude to that of a commercial inductor, but in a volume about a million times smaller. The observed inductance is enhanced by nonlinearity in current and shows non-monotonous frequency dependence, both of which result from the current-driven dynamics of the spin-helix structures. The magnitude of the inductance rapidly increases with decreasing device cross-section, in contrast to conventional inductors. Our findings may pave the way to microscale, simple-shaped inductors based on emergent electromagnetism related to the quantum-mechanical Berry phase. Microscale magnetic devices containing nanoscale spin helices produce an inductance comparable in magnitude to that of a commercial inductor, in a volume about a million times smaller.

Hoop Stress Modification, Stress Hysteresis and Degradation of a REBCO Coil Due to the Screening Current Under External Magnetic Field Cycling

Abstract: Degradation of a REBCO coil under external magnetic fields is one of the major technical problems in the field of HTS magnet technology. A possible cause of such degradation is an inhomogeneous hoop stress distribution, or hoop stress modification (both increase and decrease), induced by the screening current. In this work, we investigate such a hoop stress modification by a small coil experiment with a strain measurement and a numerical simulation. An experimental result shows a very high stress increase factor of >4.1, defined by the maximum circumferential stress over BzJR stress, and the simulated result is in qualitative agreements. The strain (stress) shows a hysteresis effect corresponding to the screening current behavior. A large hoop stress modification causes not only a hoop stress increase, but also buckling of the conductor, which induces delamination and micro-clacks of the superconducting layer. We also show the stress modification can be reduced by bonding turns with epoxy.

A Hybrid Interleaved DC–DC Converter With a Wide Step-Up Regulation Range and Ultralow Voltage Stress

Abstract: In this article, a hybrid interleaved connecting boost converter (HIBC) with a wide step-up regulation range is proposed, which is suitable for the low-voltage distributed generation applications. In the input of the HIBC, the primary windings of the double-coupled inductors are interleaved parallel connection, inheriting shared current and reduced current ripples. Then, the lossless passive clamped circuits are used to recycle the leakage energy of the coupled inductor and to reduce the voltage stress on the semiconductor devices to a very low level. The secondary windings of the coupled inductors are, respectively, combined with a capacitor–diode to form the two voltage multiplier units, which are again, respectively, connected with an output capacitor for a voltage-doubling module. These two voltage-doubling modules are connected in interleaved series for supplying power to the output, whose structure enhances the voltage gain greatly without adopting an extreme duty cycle and reduces the output voltage ripples. In addition, the main switches of the proposed converter can be operated in zero-current switching and full duty cycle range in theory, achieving a wide step-up regulation range with the high efficiency. Finally, the theoretical behaviors of the presented converter are described in detail and some experimental results are also shown to demonstrate the effectiveness of the proposed converter.

T–A -Formulation to Model Electrical Machines With HTS Coated Conductor Coils

Abstract: Modeling high temperature superconductor (HTS) motors remains challenging mainly due to the high aspect ratio of these conductors but also because of the properties of the magnetic materials. This article presents a 2-D time dependent model to assess the ac losses of superconducting motors based on the new T-A-formulation, which by using the finite-element method, allows its implementation in commercial software. The T-A-formulation computes the magnetic flux density with different Maxwell's equations depending on the areas of the motor and makes it possible to use the thin strip approximation i.e., the HTS tapes are modeled as infinitely thin lines. The model is then expected to tackle the high aspect ratio of the HTS as well as decreasing both the mesh complexity and the computing time. The first objective of the article is to validate the method in 2-D by evaluating the ac losses of a specific synchronous motor called superconducting torque motor; the computed results are compared with good agreements to those assessed with the minimum electromagnetic entropy production method, already validated. In a second part, the same losses are computed, taking into account the field anisotropy of $J_{c}$ with the implementation of a dataset based on experimentally measured $I_{c}$ at 65 and 77 K. With the model proposed in this article, it is possible to calculate the magnetic field of a whole electrical machine cross section and compute the ac losses in the individual tapes of its windings within the same numerical model.

A High-Power Wireless Charging System Using LCL- N Topology to Achieve a Compact and Low-Cost Receiver

Abstract: In high-power electric vehicle wireless charging systems, the charging distance is short, and the coupling is strong in order to increase the power density and reduce the coil size and the system cost. With a strong coupling, the receiver-side compensation can be eliminated, and a high efficiency can still be obtained. The inductor-capacitor-inductor-none ( LCL -N) topology is formed with the LCL compensation on the primary side. The phase difference between the transmitter and receiver currents is larger than 90°, leading to the magnetic flux cancelation in the ferrites. Thus, the required ferrite thickness of the LCL- N topology is smaller than the fully-compensated topologies. Therefore, a compact, lightweight, and low-cost receiver structure is achieved with the omitted compensation and thinner ferrite. Moreover, the LCL- N topology can achieve zero voltage switching for all loading conditions, withstand open-circuit and short-circuit faults, and is suitable for constant-current and constant-voltage charging due to the fact that it has neither a CC nor a CV output characteristic. A 100-kW system is designed and simulated. A downscaled 1-kW system is implemented. The simulations and experimental results verify the effectiveness of the analysis.