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Showing papers on "Electromagnetic coil published in 2019"


Journal ArticleDOI
01 Jun 2019-Nature
TL;DR: A copper oxide high-temperature superconductor magnet generates a direct-current magnetic field of 45.5 tesla—the highest value reported so far—using a design that enables operation at high current densities, validates predictions11 for high-field copper oxide super Conductor magnets by achieving a field twice as high as those generated by low-tem temperature superconducting magnets.
Abstract: Strong magnetic fields are required in many fields, such as medicine (magnetic resonance imaging), pharmacy (nuclear magnetic resonance), particle accelerators (such as the Large Hadron Collider) and fusion devices (for example, the International Thermonuclear Experimental Reactor, ITER), as well as for other diverse scientific and industrial uses. For almost two decades, 45 tesla has been the highest achievable direct-current (d.c.) magnetic field; however, such a field requires the use of a 31-megawatt, 33.6-tesla resistive magnet inside 11.4-tesla low-temperature superconductor coils1, and such high-power resistive magnets are available in only a few facilities worldwide2. By contrast, superconducting magnets are widespread owing to their low power requirements. Here we report a high-temperature superconductor coil that generates a magnetic field of 14.4 tesla inside a 31.1-tesla resistive background magnet to obtain a d.c. magnetic field of 45.5 tesla—the highest field achieved so far, to our knowledge. The magnet uses a conductor tape coated with REBCO (REBa2Cu3Ox, where RE = Y, Gd) on a 30-micrometre-thick substrate3, making the coil highly compact and capable of operating at the very high winding current density of 1,260 amperes per square millimetre. Operation at such a current density is possible only because the magnet is wound without insulation4, which allows rapid and safe quenching from the superconducting to the normal state5–10. The 45.5-tesla test magnet validates predictions11 for high-field copper oxide superconductor magnets by achieving a field twice as high as those generated by low-temperature superconducting magnets. A copper oxide high-temperature superconductor magnet generates a direct-current magnetic field of 45.5 tesla—the highest value reported so far—using a design that enables operation at high current densities.

370 citations


Journal ArticleDOI
Bin Li1, Qiang Li1, Fred C. Lee1
TL;DR: In this article, a novel PCB winding based magnetic structure is proposed to integrate both inductor and transformer into one component, which can be easily controlled by changing the cross-sectional area of the core or the length of the air gap.
Abstract: The momentum toward high power density high-efficiency power converters continues unabated. The key to reducing the size of power converters is high-frequency operation and the bottleneck is the magnetic components. With the emerging widebandgap devices, the switching frequency of power converters increases significantly, to hundreds of kilohertz, which provides us the opportunity to adopt printed circuit board (PCB) winding planar magnetics. Compared with the conventional litz-wire-based magnetics, planar magnetics can not only effectively reduce the converter size, but also offer improved reliability through automated manufacturing process with repeatable parasitics. Another way to reduce the number of magnetic components and shrink the size of power converters is through the magnetic integration. In this paper, a novel PCB winding based magnetic structure is proposed to integrate both inductor and transformer into one component. In this structure, the inductor value can be easily controlled by changing the cross-sectional area of the core or the length of the air gap. A 6.6-kW 500-kHz CLLC resonant converter prototype with 98% efficiency and 130-W/in3 (8 kW/L) power density is built to verify the feasibility of the proposed PCB winding based magnetic structure.

124 citations


Journal ArticleDOI
TL;DR: A novel long-distance wireless power transfer (WPT) system using repeater coils is proposed to provide power supplies for the driver circuits in high-voltage applications, such as flexible alternative current transmission systems.
Abstract: In this paper, a novel long-distance wireless power transfer (WPT) system using repeater coils is proposed to provide power supplies for the driver circuits in high-voltage applications, such as flexible alternative current transmission systems. Different from most of the existing wireless repeater systems where the load is only connected to the last coil and the repeater coils function solely as power relays, in the proposed system, multiple loads are powered by the repeaters. The repeater coils transfer power not only to the subsequent coils but also to the loads connected to them. Dual coil design is proposed for the repeaters with which load-independent characteristics are obtained with a suitable design of coupling coefficients. As a result, the load power can be easily adjusted without affecting each other. Load current characteristics and system efficiency have been analyzed in detail. The power transfer capability of the proposed system is illustrated for different coil quality factors and coupling coefficients. An experimental setup with 10 loads has been built to validate the effectiveness of the proposed long-distance WPT system. The maximum reachable system efficiency is about 84%.

116 citations


Journal ArticleDOI
TL;DR: In this paper, a novel wireless charging bowl with multiple transmitter coils is proposed to power portable devices, optimized to provide sufficiently strong and nearly uniform omnidirectional field distribution.
Abstract: Recently, omnidirectional wireless power transfer systems have been studied intensely due to their improved flexibility when compared with their planar counterparts. In this paper, a novel wireless charging bowl with multiple transmitter coils is proposed to power portable devices. The bowl-shaped transmitter coil is optimized to provide sufficiently strong and nearly uniform omnidirectional field distribution. Inside the bowl, a planar receiver coil can be charged with free-positioning and arbitrary orientation. This unique benefit is particularly attractive for low-power portable devices. In the experiment, the proposed transmitter coils are built and operated at 6.78 MHz. The magnetic field is measured to verify the uniform and omnidirectional magnetic field distribution. The coil to coil efficiency is 85% to 95%. A complete system including the inverter and rectifier stage is implemented. When charging a 5W smart phone receiver, the overall efficiency varies within a range from 68–80% for any possible position.

112 citations


Journal ArticleDOI
TL;DR: An underwater WPT prototype was built and the experimental results verified the theoretical analysis, finding that the optimum operating frequency is supposed to be larger than the resonant frequency to achieve the maximum dc–dc efficiency in the seawater.
Abstract: Wireless power transfer (WPT) has attracted much attention in recent years. In an underwater WPT system, the eddy current loss tends to be non-negligible as the frequency or the coil current increases. Thus, it is crucial to analyze the eddy current loss in an underwater WPT system. The analytical model of the eddy current loss of a coreless WPT system in the seawater is established with Maxwell's equations. The expressions of the electric field intensity and the eddy current loss are derived. The eddy current loss is analyzed in different circumstances to illustrate the impacts of related factors. For a WPT system in the air, there is an optimum resonant frequency, for a higher frequency leads to a larger induced voltage, but will result in larger coil losses simultaneously. However, the optimum resonant frequency will be shifted because of the eddy current loss in the seawater. Then, the optimum operating frequency is obtained based on the analytical model. It is found that the optimum operating frequency is supposed to be larger than the resonant frequency to achieve the maximum dc–dc efficiency in the seawater. An underwater WPT prototype was built and the experimental results verified the theoretical analysis.

107 citations


Journal ArticleDOI
15 Feb 2019-Energy
TL;DR: In this paper, a monostable electromagnetic energy harvester (EMEH) is presented, which is composed of a magnet-spring resonator encapsulated in a tube, a set of coil wrapped around the tube, and two endmost magnets affixed at the tube's two ends.

101 citations


Journal ArticleDOI
TL;DR: In this article, the authors presented the thermal hydraulic performance of TiO2-SiO2 nanofluids with wire coil inserts, which achieved the best condition for cooling system applications.

92 citations


Journal ArticleDOI
TL;DR: An interleaved converter that benefits the coupled inductor and built-in transformer voltage multiplier cell (VMC) and improves the efficiency of the proposed converter in high-current and high-voltage applications.
Abstract: This paper presents an interleaved converter that benefits the coupled inductor and built-in transformer voltage multiplier cell (VMC). Compared with the other converters with only a built-in transformer or only a coupled inductor, the combination of these techniques gives an extra degree of freedom to increase the voltage gain. The VMC is composed of the windings of the built-in transformer and coupled inductors, capacitors, and diodes. The voltage stress of MOSFETs is clamped at low values and can be controlled via the turns ratio of the built-in transformer and coupled inductor that increases the design flexibility. Moreover, the energy of the leakage inductances, is recycled to the clamp capacitors which avoids high voltage spikes across MOSFETs. In addition, the current falling rate of the diodes is controlled by the leakage inductances, and the reverse current recovery problem is alleviated. Meanwhile, due to the interleaved structure of the proposed converter, the input current ripple is minimized and the current stress of the power devices is decreased. All of these factors improve the efficiency of the proposed converter in high-current and high-voltage applications. The principle operation and steady-state analysis is given to explore the advantages of the proposed converter. Finally, a 1.3-kW prototype with 50–600 V voltage conversion is built to demonstrate the effectiveness of the proposed converter.

86 citations


Journal ArticleDOI
TL;DR: In this article, a metal object detection (MOD) system based on mistuned resonant circuits and utilizing the variation of self-inductance of a sensing pattern, is newly proposed for wireless electric vehicle (EV) chargers.
Abstract: In this paper, a metal object detection (MOD) system, a kind of foreign object detection (FOD), which is based on mistuned resonant circuits and utilizes the variation of self-inductance of a sensing pattern, is newly proposed for wireless electric vehicle (EV) chargers. The sensing pattern that consists of multiple loop coil sets is mounted on the transmitting (Tx) pad of an EV charger, where a loop coil set has two coils connected in series with the opposite polarity to cancel out the induced voltage generated by the Tx coil. Variation of self-inductance of the loop coil set is detected by a parallel-resonant circuit, driven by a current source and operating at near 1 MHz, in order to enhance the resolution of the proposed MOD system. To increase the detection sensitivity of the proposed MOD system, instead of an exact resonant frequency, a mistuned operating frequency near the –3 dB point is utilized for the parallel-resonant circuit. In this way, the proposed MOD system can detect very small metal objects regardless of their position and orientation on the Tx coil without any blind zone. Through simulations and experiments, it is found that the proposed MOD system detects not only horizontal but also standing upright metal objects. A prototype MOD system, operating at 85 kHz to satisfy the standard J2954, was fabricated to verify its feasibility. The results showed that output voltage change of the proposed MOD system becomes 22.7% for a piece of the aluminum foil of 3 × 3 cm2 and 40.9% for 100 Korean Won coin.

81 citations


Journal ArticleDOI
TL;DR: In this article, the authors present concepts for antennas that generate electromagnetic signals from mechanical motion, which can theoretically exceed the performance of conventional short dipole and coil transmitters by more than eight orders of magnitude for frequencies of 1 kHz and below.
Abstract: Antennas that operate in the very low frequency (LF) band and below are useful for a number of applications, including long-distance and underwater communication. When constrained in size, the antennas are electrically small and very inefficient. This has motivated the need for novel approaches to LF antenna design. Here, we present concepts for antennas that generate electromagnetic signals from mechanical motion. We first review the generated fields and efficiency of conventional magnetic and electric dipole transmitters. This is then extended to their mechanical counterparts for comparison. Our results show that the motion of magnets or electrets (the electrical analog of a magnet) can efficiently radiate electromagnetic energy when coupled to a low-loss electromechanical suspension. Mechanical antennas, with spatial dimensions on the order of a meter, can theoretically exceed the performance of conventional short dipole and coil transmitters by more than eight orders of magnitude for frequencies of 1 kHz and below. This paper is intended to lay the foundation for future development involving the implementation of efficient, small form-factor, mechanically actuated antennas.

79 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed a new method to create a larger resonant inductance by using a magnetic shunt integrated into planar windings, which reduces the whole converter's volume and thus increases the power density.
Abstract: Achieving high efficiency and high power density is emerging as a goal in many power electronics applications. LLC resonant converter has been proved as an excellent candidate to achieve this goal. To achieve smaller size of passive components, the resonant inductor in the LLC converter is usually integrated into the transformer by utilizing its leakage inductance. However, the leakage inductance of the transformer is usually insufficient and thus the LLC converter has to be operated in a limited frequency range (this limits the input voltage range accordingly), otherwise the power efficiency will drop dramatically. Therefore, a larger resonant inductance in the LLC converter is expected to operate in a wider input voltage range. This paper proposes a new method to create a larger resonant inductance by using a magnetic shunt integrated into planar windings. The accurate leakage inductance modeling, calculation, and optimal design guideline for LLC planar transformer, including optimal magnetic shunt selection and winding layout, are presented. A 280–380 V input and output 48 V–100 W half-bridge LLC resonant converter with 1 MHz resonant frequency is built to verify the design methodology. A comparison is made between two converters with the same parameters, one using magnetic shunt integrated transformer and the others using traditional planar transformer and external inductor. Experimental result shows the proposed converter with magnetic shunt is capable to achieve comparable high efficiency and regulation capability with the other under a wide input voltage, which verifies the optimal design methodology. Above all, this magnetics integration methodology reduces the whole converter's volume and thus increases the power density.

Journal ArticleDOI
TL;DR: Simulations show a degrading of field uniformity which was broadly consistent with measured values and should be incorporated into future designs, which should allow for greater take-up of this technology.
Abstract: To allow wearable magnetoencephalography (MEG) recordings to be made on unconstrained subjects the spatially inhomogeneous remnant magnetic field inside the magnetically shielded room (MSR) must be nulled. Previously, a large bi-planar coil system which produces uniform fields and field gradients was used for this purpose. Its construction presented a significant challenge, six distinct coils were wound on two 1.6 × 1.6 m2 planes. Here, we exploit shared coil symmetries to produce coils simultaneously optimised to generate homogenous fields and gradients. We show nulling performance comparable to that of a six-coil system is achieved with this three-coil system, decreasing the strongest field component Bx by a factor of 53, and the strongest gradient dBx/dz by a factor of 7. To allow the coils to be used in environments with temporally-varying magnetic interference a dynamic nulling system was developed with a shielding factor of 40 dB at 0.01 Hz. Reducing the number of coils required and incorporating dynamic nulling should allow for greater take-up of this technology. Interactions of the coils with the high-permeability walls of the MSR were investigated using a method of images approach. Simulations show a degrading of field uniformity which was broadly consistent with measured values. These effects should be incorporated into future designs.

Journal ArticleDOI
TL;DR: The proposed WPT technique developed in this study has been proven to solve the misalignment issue and offers a great opportunity as a key deployment component for the automation of farming practices toward the Internet of Farming applications.
Abstract: Drones can be used in agriculture applications to monitor crop yield and climate conditions and to extend the communication range of wireless sensor networks in monitoring areas. However, monitoring the climate conditions in agriculture applications faces challenges and limitations, such as drone flight time, power consumption, and communication distance, which are addressed in this study. Wireless power transfer (WPT) can be used to charge drone batteries. WPT using a magnetic resonant coupling (MRC) technique was considered in this study because it allows high transfer power and efficiency with tens of centimeters, power transfers can be achieved in misalignment situations, charging several devices simultaneously, and unaffected by weather conditions. WPT was practically implemented based on a solar cell using a proposed flat spiral coil (FSC) in the transmitter circuit and multiturn coil (MTC) in a receiver circuit (drone) for the alignment and misalignment of two coils at different distances. FSC and MTC improved power transfer and efficiency to 20.46 W and 85.25%, respectively, at 0 cm with the loaded system under alignment condition. In addition, the two coils achieved appropriate transfer efficiencies and power for charging the drone battery under misaligned conditions. The maximum power transfer and efficiency were 17.1 W and 71% for the misalignment condition, at an air gap of 1 cm between two coils when the system was loaded with the drone battery. Moreover, the battery life of the drone was extended to 851 minutes based on the proposed sleep/active strategy relative to the traditional operation (i.e., 25.84 minutes). Consequently, a 96.9% battery power saving was achieved based on this strategy. Comparison results showed that the proposed system outperformed some present techniques in terms of the transfer power, transfer efficiency, and drone battery life. The proposed WPT technique developed in this study has been proven to solve the misalignment issue. Thus it offers a great opportunity as a key deployment component for the automation of farming practices toward the Internet of Farming applications.

Journal ArticleDOI
TL;DR: Aiming at the problem of decrease in efficiency due to misalignment of wireless power transfer (WPT) coil, a novel coil was proposed in this article, where the authors analyzed the factors that affect the efficiency and the method of improving the efficiency of the coil.
Abstract: Aiming at the problem of decrease in efficiency due to misalignment of wireless power transfer (WPT) coil, a novel coil with high misalignment tolerance was proposed. First, the factors that affect the efficiency and the method of improving the efficiency and misalignment tolerance of the coil are analyzed. Second, the novel coil was set up through COMSOL simulation, which was compared with double-D (DD) coil and circular coil in misalignment tolerance. Finally, in order to verify the authenticity of theory and simulation, experiment device is implemented and experimental results show that the coupling coefficient changes affect coil efficiency, and the flat and high magnetic flux density can better maintain coil efficiency when lateral misalignment happened. This means that the novel coil has better misalignment tolerance, which can meet the demands of WPT system.

Journal ArticleDOI
TL;DR: Both the simulation and experimental results indicate that the proposed FOD method can effectively detect the presence and location of foreign objects.
Abstract: In this paper, a foreign object detection (FOD) method based on symmetrical coil sets is proposed to prevent wireless power transfer (WPT) systems from heating, which could possibly cause an accidental fire. First, the influence of a foreign metal object on the magnetic field distribution of the WPT system is analyzed. Then, a two-layer symmetrical detection coil set is proposed considering the magnetic field characteristics. This kind of FOD method can reduce the design complexity, and the detection strategy is easily realized. The mutual inductance variation patterns are used to detect the presence and location of metal objects. Four scenarios of foreign object intrusion, including one coin with different locations, a coin on top of two adjacent detection coils with the same cover area, different test bodies, and different numbers of coins, are taken into consideration for validating the effectiveness of the proposed FOD method. Finally, a WPT system prototype with symmetrical coil sets for FOD detection is established. Both the simulation and experimental results indicate that the proposed method can effectively detect the presence and location of foreign objects.

Journal ArticleDOI
22 Jul 2019
TL;DR: In this paper, a comprehensive and systematical overview on the rectangular wire windings AC electrical machine is introduced, based on the complex process craft and the electromagnetic performance, and the performance of rectangular wire-windings AC machine has been presented, with emphasis on the measure of improving the bigger AC copper losses.
Abstract: The rectangular wire winding AC electrical machine has drawn extensive attention due to their high slot fill factor, good heat dissipation, strong rigidity and short end-windings, which can be potential candidates for some traction application so as to enhance torque density, improve efficiency, decrease vibration and weaken noise, etc. In this paper, based on the complex process craft and the electromagnetic performance, a comprehensive and systematical overview on the rectangular wire windings AC electrical machine is introduced. According to the process craft, the different type of the rectangular wire windings, the different inserting direction of the rectangular wire windings and the insulation structure have been compared and analyzed. Furthermore, the detailed rectangular wire windings connection is researched and the general design guideline has been concluded. Especially, the performance of rectangular wire windings AC machine has been presented, with emphasis on the measure of improving the bigger AC copper losses at the high speed condition due to the distinguished proximity and skin effects. Finally, the future trend of the rectangular wire windings AC electrical machine is prospected.

Journal ArticleDOI
TL;DR: A compact battery charger based on wireless power transfer (WPT) technology without any communication requirement is proposed, which can achieve zero phase angle operation, fixed operating frequency, and zero-voltage switching, which not only can lower the power rating of power devices but also improve the efficiency.
Abstract: In this letter, a compact battery charger based on wireless power transfer (WPT) technology without any communication requirement is proposed. Here, a new intermediate coil is developed to achieve load-independent constant current (CC) and constant voltage (CV) outputs. The intermediate coil is split into two coils and is overlapped with the receiver coil to form a compact structure. Two switches on the receiver side are used to reconfigure the intermediate resonant circuit in order to select different charging modes, i.e., CC mode or CV mode. The communication between the transmitter side and the receiver side as well as complex control strategies is not needed in the proposed structure. Besides, the proposed system can achieve zero phase angle operation, fixed operating frequency, and zero-voltage switching, which not only can lower the power rating of power devices but also improve the efficiency. A laboratory prototype with a 3.6 A charging current and a 48 V charging voltage is built to verify the feasibility of the proposed method.

Journal ArticleDOI
TL;DR: A probabilistic model is introduced to improve the accuracy and to quantify the uncertainty in the prediction, based on Monte Carlo dropout, which establishes a basis for a fast and generalizable data-driven model used in the analysis, design, and optimization of EM devices.
Abstract: This paper investigates the feasibility of novel data-driven deep learning (DL) models to predict the solution of Maxwell’s equations for low-frequency electromagnetic (EM) devices. With ground truth (empirical evidence) data being generated from a finite-element analysis solver, a deep convolutional neural network is trained in a supervised manner to learn a mapping for magnetic field distribution for topologies of different complexities of geometry, material, and excitation, including a simple coil, a transformer, and a permanent magnet motor. Preliminary experiments show DL model predictions in close agreement with the ground truth. A probabilistic model is introduced to improve the accuracy and to quantify the uncertainty in the prediction, based on Monte Carlo dropout. This paper establishes a basis for a fast and generalizable data-driven model used in the analysis, design, and optimization of EM devices.

Journal ArticleDOI
TL;DR: In this article, a full-scale synchronous high-temperature superconducting (HTS) generator was successfully designed, built and field-tested in a 3.6 MW turbine.
Abstract: The main aim of the EU H2020 project EcoSwing was to demonstrate a technical readiness level of 6-7 for high-temperature superconducting (HTS) technology operating in a wind generator. To reach this goal, a full-scale synchronous HTS generator was successfully designed, built and field-tested in a 3.6 MW turbine. The generator has a rotor with 40 superconducting coils of 1.4 m long. The required >20 km of coated conductor was produced within the project's time schedule. All coils were tested prior to assembly, with >90% of them behaving as expected. The technical readiness level of HTS coils was thus increased to level 7. Simultaneously, the maturing of cryogenic cooling technology over the last decade was illustrated by the several Gifford-McMahon cold-heads that were installed on-board the rotor and connected with the stationary compressors through a rotating coupling. The cryogenic system outperformed design expectations, enabling stable coil temperatures far below the design temperature of 30 K after only 14 d of cool-down. After ground-based testing at the IWES facility in Bremerhaven, Germany, the generator was installed on an existing turbine in Thyboron, Denmark. Here, the generator reached the target power range and produced power for over 650 h of grid operation.

Journal ArticleDOI
TL;DR: The results indicate that the proposed structure is superior to others and that it shows better performance in power transfer efficiency and transfer distance, which is in good agreement with the theoretical and simulation analysis.
Abstract: To improve the power transfer efficiency in wireless power transfer systems, a novel configuration of a magnetic resonant structure is proposed in this paper. According to the analytical expression of mutual inductance, the magnetic field can be improved by weakening the demagnetizing factor for coils with a ferrite core. In this paper, the demagnetizing factors of a cylindrical ferrite core and a novel ferrite core are investigated. Compared with the cylindrical ferrite core, the proposed ferrite core has a smaller demagnetizing factor and an increased mutual inductance. In addition, the magnetic field through the receiving coil is enhanced due to the thin ferrite axis where the magnetic field is concentrated. The proposed ferrite core is designed and analyzed. Moreover, the effects of pitch and lateral misalignment, as well as the number of turns of the receiving coil, the core loss, and the load, are studied. Experimental prototypes are established to validate the performance of the wireless power transfer system with different types of receiving structures. The results indicate that the proposed structure is superior to others and that it shows better performance in power transfer efficiency and transfer distance, which is in good agreement with the theoretical and simulation analysis.

Journal ArticleDOI
TL;DR: An analytical approach is presented for the magnetic circuit design to minimize magnetic resistance in the motor core to improve the power density and energy efficiency of a wound-field synchronous motor using hairpin type rectangular wire for electric vehicle traction.
Abstract: This paper deals with a design method to improve the power density and energy efficiency of a wound-field synchronous motor (WFSM) using hairpin type rectangular wire for electric vehicle traction. First, the prototype is analyzed via experiments to come up with plans to improve it. In addition, mechanical loss of the prototype including the bearing and brush friction losses is obtained and used for designing the improved motor. After then, an analytical approach is presented for the magnetic circuit design to minimize magnetic resistance in the motor core. Also, the analytical methods are proposed to predict the resistance of the field and armature windings. At this step, rectangular wire is considered for the armature winding to reduce the copper loss. Moreover, the calculation process is presented to estimate the iron loss considering harmonics. The performances such as power density and efficiency of the improved WFSM are analyzed and compared with those of the prototype. In addition, the energy efficiency of the motors in the new European drive cycle (NEDC) is analyzed. Finally, the performances of the improved WFSM are compared with the experimental results to verify the validity of the proposed design process.

Journal ArticleDOI
TL;DR: In this article, an energy harvester using a rolling magnet is designed and fabricated, which can significantly increase the magnetic flux rate when cutting the coil compared to that using a sliding magnet.

Journal ArticleDOI
TL;DR: In this article, an improved analytical stray capacitance model for inductors is proposed, which considers the capacitances between the winding and the central limb, side limb, and yoke of the core.
Abstract: This paper proposes an improved analytical stray capacitance model for inductors. It considers the capacitances between the winding and the central limb, side limb, and yoke of the core. The latter two account for a significant proportion of the total capacitance with the increase of the core window utilization factor. The potential of the floating core/shield is derived analytically, which enables the model to apply not only for the grounded core/shield, but also for the floating core/shield cases. On the basis of the improved model, an analytical optimization method for the stray capacitance in inductors is proposed. Moreover, a global Pareto optimization is carried out to identify the tradeoffs between the stray capacitance and ac resistance in the winding design. Finally, the analysis and design are verified by finite element method simulations and experimental results on a 100-kHz dual active bridge converter.

Journal ArticleDOI
TL;DR: With the aid of the leakage inductances, zero-current switching of the active switches can be achieved and the reverse recovery problem of the diodes is alleviated.
Abstract: This paper proposes a new interleaved high step-up converter with coupled inductors. Interleaving configuration is employed at the input side to reduce the input current ripple and increase the power level. The series structure at the output side helps achieve a very high step-up voltage gain. Also, the proposed converter has very low switch voltage stress; thus, switching loss can be reduced and low-voltage-rating mosfet s with small on resistance are allowed to lower the conduction loss. Due to the passive clamp performance, the leakage energy of the coupled inductors can be recycled and large voltage spikes across the switches are alleviated. Furthermore, with the aid of the leakage inductances, zero-current switching of the active switches can be achieved and the reverse recovery problem of the diodes is alleviated. The operating principles, performance analysis, and design considerations of the proposed converter are discussed. A prototype with 20-V input and 400-V output is built, and experimental results are provided to verify the theoretical analysis.

Journal ArticleDOI
TL;DR: A metaheuristic optimization algorithm is used to minimize total harmonic distortion of the output signals, and consequently the estimated position error in concentrated coil wound field resolvers, and modified objective function and constraints are proposed.
Abstract: Among position sensors, resolvers are superior from reliability point of view. However, obtaining lower output voltage harmonics and simple manufacturing process is a challenge in the design and optimization of resolvers. In this paper, a metaheuristic optimization algorithm is used to minimize total harmonic distortion of the output signals, and consequently the estimated position error in concentrated coil wound field resolvers. Meanwhile, to minimize total coil numbers, manufacturing costs, and complexity of the winding process, modified objective function and constraints are proposed. In this way, a modified winding function method is employed for performance analysis of the axial flux resolver. Then, the merits of the optimized winding configuration with respect to fractional slot concentrated windings are shown. The results of the proposed configurations are verified with a three-dimensional time-stepping finite-element method. Finally, the prototype of the studied axial flux resolver is constructed and tested. Good agreement is obtained between simulation and experimental results, confirming the effectiveness of the optimization process.

Journal ArticleDOI
TL;DR: In this paper, a multiphase receiver for more steady output is proposed, including two-phase, three-phase and four-phase receivers, where the structure size of single-phase coil and distance between phases are optimized to improve the coupling coefficient and reduce cost, loss, and voltage level of resonator.
Abstract: The multiphase receiver for more steady output is proposed in this paper. The conventional power supply rail with multipole such as I-type, S-type, and n-type for dynamic wireless charging (DWC) system has a main drawback: the induced voltage of the double-D coil of receiver has a sinusoidal fluctuation along the driving direction and the fluctuation factor is 1.0. Therefore, the multiphase receivers including two-phase, three-phase, and four-phase receiver are proposed to solve the problem. The fluctuation factor, effective value (rms) of induced voltage and mutual inductance, cost, and loss of different numbers of phase in different connection modes are analyzed and compared. The applicable conditions of different types are given. The structure size of single-phase coil is optimized to achieve larger coupling coefficient. The influence of distance between phases on fluctuation factor and induced voltage (rms) are calculated and the design principle of the distance between phases is determined. Based on above research, design guideline for the multiphase receiver is proposed including the constraints of installation environment and the distribution of different phases. The structure size of single-phase coil and the distance between phases are optimized to improve the coupling coefficient and reduce cost, loss, and voltage level of resonator. Considering the practical application environment, a four-phase receiver of 10-kW DWC system is designed. A prototype system is also established and the analysis and simulation are verified. In the dynamic 10-kW experiment, the fluctuation factor is reduced to 0.146 from 0.3 of two-phase receiver and 1.0 of single-phase receiver.

Journal ArticleDOI
TL;DR: This paper designed and demonstrated a smartwatch strap wireless charging system using an LG Watch Urbane and achieved 30% dc–dc power transfer efficiency and exposed magnetic field of 270 mG, 1 cm away from the system through measurements.
Abstract: In this paper, we designed and demonstrated a smartwatch strap wireless charging system for the first time. First, we designed a flexible printed circuit board (PCB) coil, shielding material, and receiver (Rx) circuit in a watchstrap. In the design process, we proposed a model for the flexible PCB coil with a bending radius of 40 mm and shielding materials. We used a flexible PCB coil that has 215 μ m thickness with dimensions of 54.5 × 16 mm. In addition, ferrite core and sheet are applied on the transmitter (Tx) and Rx coils. We verified the proposed model through a three-dimensional (3-D) electromagnetic (EM) simulation and measurement in the frequency and time domains. The proposed flexible PCB coil inductance modeling results showed 7.5% and 3.4% errors when compared to the 3-D EM simulation and measurement results, respectively. Furthermore, we demonstrated the smartwatch strap wireless charging system using an LG Watch Urbane. A resonance frequency of 100 kHz with the series–series tuning topology is used in accordance with the Qi specifications. Finally, we achieved 30% dc–dc power transfer efficiency and exposed magnetic field of 270 mG, 1 cm away from the system through measurements.

Journal ArticleDOI
TL;DR: A novel parallel-hybrid dual permanent magnet (PM) machine topology with both enhanced torque density and improved flux weakening capability is proposed for electric vehicle propulsion in this paper.
Abstract: A novel parallel-hybrid dual permanent magnet (PM) machine topology with both enhanced torque density and improved flux weakening capability is proposed for electric vehicle propulsion in this paper. The key is to artificially construct the harmonics diversity with a single-layer concentrated armature winding in the stator and thus simultaneously couple the armature field with the excitation field produced by slot PM, rotor PM, and stator dc source, respectively. Enhanced torque density is obtained in this new topology due to the symmetrical flux-modulation effect between dual PM sources. Moreover, benefiting from a parallel excitation characteristic of hybrid magnetic circuit, the demagnetization risk is significantly mitigated for slot PM source and thus an extended flux weakening range is obtained. In this paper, the proposed new topology and its design mechanism are investigated, along with its electromagnetic performance evaluated based on finite-element analysis. Further, some leading design parameters are analyzed and determined to provide a design guideline for the proposed new topology. Finally, a prototype is built and fully tested. Relevant experimental results agree well with the finite-element predication.

Journal ArticleDOI
TL;DR: In this article, the failure and fatigue analysis results of a coil spring removed from a personal vehicle after having failed in service were analyzed using experimental procedures like visual observations, optical and scanning electron microscopy, the failed coil was examined in order to determine the causes of the fracture.

Journal ArticleDOI
TL;DR: In this article, a multi-purpose tunneling magnetoresistive (TMR) sensor matrix is proposed to measure the magnetic field distribution between coils to provide the critical information about charging performance, coil misalignment position, and the existence of metal objects.
Abstract: A cost-effective technology to monitor the charging performance and detect the coil misalignment and foreign metal objects is indispensable to the commercialization of wireless power transfer on electric vehicle (EV) charging. This paper presents a multi-purpose tunneling magnetoresistive (TMR) sensor matrix, which can monitor the charging performance as well as detect both the coil misalignment and metal objects for wireless EV charging. The magnetic field distribution between coils is measured by the TMR sensor matrix to provide the critical information about charging performance, coil misalignment position, and the existence of metal objects. The mutual inductance and charging power are derived from the measured z-components of the magnetic flux densities. Lateral misalignment position is determined by the symmetry coefficients of the time-varying magnetic field distribution in the range of ±150 mm. Metal objects are detected by the measured magnetic field offsets. In this paper, both 3D finite-element-method modeling and experimental results were presented to demonstrate the effectiveness of the proposed approach. A $14 \times 14$ TMR sensor matrix with high sensitivity of 80 mV/V/mT was designed and implemented to measure the magnetic field distribution in order to demonstrate the technology.