Showing papers on "Electromagnetic coil published in 2016"

Modern Advances in Wireless Power Transfer Systems for Roadway Powered Electric Vehicles

Abstract: Wireless power transfer system (WPTS)-based wireless electric vehicles, classified into roadway-powered electric vehicles (RPEVs) and stationary charging electric vehicles (SCEVs), are in the spotlight as future mainstream transportations. RPEVs are free from serious battery problems such as large, heavy, and expensive battery packs and long charging time because they get power directly from the road while moving. The power transfer capacity, efficiency, lateral tolerance, electromagnetic field, air-gap, size, weight, and cost of the WPTSs have been improved by virtues of innovative semiconductor switches, better coil designs, roadway construction techniques, and higher operating frequency. Recent advances in WPTSs for RPEVs are summarized in this review paper. The fifth- and sixth-generation online electric vehicles, which reduce infrastructure cost for commercialization, and the interoperability between RPEVs and SCEVs are addressed in detail in this paper. Major milestones of the developments of other RPEVs are also summarized. The rest of this paper deals with a few important technical issues such as coil structures, power supply schemes, and segmentation switching techniques of a lumped inductive power transfer system for RPEVs.

Signal and power communication system positioned on a rotatable shaft

Abstract: A surgical instrument assembly can comprise a handle including an electric motor, a shaft assembly including a drive member, and a magnet configured to generate a magnetic field The surgical instrument assembly further comprises, one, a rotatable output shaft operably coupled with the electric motor and the drive member and, two, a wire coil wound around the output shaft which is positioned in the magnetic field The wire coil is rotated within the magnetic field when the output shaft is rotated about a longitudinal axis which induces a current in the wire coil The surgical instrument assembly further comprises a strain gauge mounted to the output shaft configured to detect strain created within the output shaft and, in addition, a circuit mounted to the output shaft, wherein the circuit and/or the strain gauge is powered by the current induced in the wire coil

Multi-Objective Optimization of 50 kW/85 kHz IPT System for Public Transport

Abstract: Inductive power transfer (IPT) is an attractive solution for the automated battery charging of public transport electric vehicles (EVs) with low maintenance requirements. This paper presents the design of a 50 kW/85 kHz contactless EV charger, with a focus on the IPT transmitter and receiver coils. The multi-objective magnetics optimization reveals the Pareto tradeoffs and performance limitations in terms of high efficiency, high power density, and low stray field for high-power IPT systems without moving mechanical parts. A full-scale hardware prototype is realized and experimentally investigated. The dc-dc conversion efficiency, including all the power electronics stages, is measured as 95.8% at 50 kW power transfer across an air gap of 160 mm (coil dimensions $410\times 760\times 60$ mm3). With 150 mm coil misalignment in the worst case direction, the dc-dc efficiency drops to 92%. The measurements of the magnetic stray field show compliance with ICNIRP 2010 at 800 mm distance from the IPT coil center.

A Dynamic Charging System With Reduced Output Power Pulsation for Electric Vehicles

Abstract: This paper proposes a continuous dynamic wireless power transfer system for electric vehicles that reduces power pulsations during the charging process. Multiple rectangular unipolar coils are used at the primary side as the transmitters, and another unipolar coil works as a receiver at the secondary side. The transmitters are placed closely together to reduce the variation of magnetic fields along the moving track of the receiver. This structure induces self-coupling between the adjacent transmitters. An LCC -compensated circuit topology is utilized, and a compensation parameter design is provided which considers self-coupling between the primary coils. Finite-element analysis of the dynamic charging system is performed using Maxwell. The receiver size is optimized to reduce the variation of the coupling coefficient. A 1.4-kW dynamic charging prototype is constructed according to the designed coil structure and circuit parameters. There are six transmitters, each with dimensions 388 mm×400 mm, and one receiver with dimensions 485 mm×400 mm. Experimental results show that the output power pulsation is within ±7.5% in the dynamic charging process, and the maximum efficiency is 89.78%. If the edge effects of the transmitters are neglected, then the power pulsation is within ±2.9%.

LC Passive Wireless Sensors Toward a Wireless Sensing Platform: Status, Prospects, and Challenges

Abstract: Inductor–capacitor ( $LC$ ) passive wireless sensors use a transformer with loose coupling between an external readout coil and an inductor that receives power through this inductive coupling. Changes in the sensor are wirelessly and remotely detected by the readout coil, which makes them highly useful in applications that require the sensor to be powered remotely and to occupy a small volume, such as harsh and sealed environments, where physical access to the sensor is difficult. Although the sensor to accomplish this function dates from the 1960’s, its rapid extension over the past decades has benefited from microelectromechanical systems. This paper provides an overview of the status and challenges in the $LC$ passive wireless sensor toward a wireless sensing platform. The basic sensing principles are first categorized into detecting changes of the sensor in response to the capacitance, resistance, inductance, or coupling distance due to the parameter of interest through monitoring the impedance magnitude and phase spectrum. The present state of the art in sensor applications for pressure, strain, temperature, humidity, biochemical, gas, and so on is then reviewed and compared. For emerging applications from many Internet of Things scenarios, geometrical constraints, such as small and non-invasive coils, reduce the magnetic coupling between the sensor and the readout coil, resulting in a limited interrogation distance. Furthermore, an increasing number of applications also require the simultaneous measurement of multiple parameters. Recent efforts to increase the interrogation distance and to extend the measurement of single parameter to multiple parameters are finally outlined. [2016-0093]

Wireless Power Transfer Charging System for AIMDs and Pacemakers

Abstract: This paper deals with the electric and magnetic field (EMF) safety aspects of a wireless power transfer (WPT) system based on magnetic resonant coupling between two coils. The primary coil is assumed to be on-body, while the secondary coil is assumed to be inside the human body and connected to a battery recharge system of an active implantable medical device such as a pacemaker. This study allows us to identify a good preliminary solution of the WPT coil configuration, compensation capacitor topology, and operational frequency. Demonstrative WPT systems operating at two different frequencies are proposed in order to verify the WPT performances. The EMF safety has been finally assessed by numerical dosimetry studies using anatomically realistic human body models revealing no particular concerns about this application.

20-T Dipole Magnet With Common-Coil Configuration: Main Characteristics and Challenges

Abstract: The Institute of High Energy Physics (Beijing, China) is pursuing R&D of high-field accelerator magnet technology for the recently proposed CEPC-SPPC project, which will need thousands of 20-T level accelerator magnets in 20 years. A long-term plan has been made aiming to realize the 20-T magnets in 15 years. The conceptual design study has been ongoing from 2014 based on the current J c level of superconductors. As both Nb 3 Sn and high-temperature superconductor superconducting materials are strain sensitive, the common-coil configuration has been chosen as the first option for the design study of the 20-T dipoles, to simplify the coil structure, raise the bending radius, and lower the strain level in superconducting coils. The magnetic analysis, mechanical analysis, and preliminary design study of the straight section and the coil ends have been completed for a 20-T common-coil dipole magnet. The main characteristics and challenges of this design concept will be presented in this paper.

Self-protection mechanisms in no-insulation (RE)Ba2Cu3Ox high temperature superconductor pancake coils

Abstract: No-insulation (NI) high temperature superconducting (HTS) coils possess much higher thermal stability than similar traditionally insulated HTS coils. Some NI coils are self-protecting in the sense that they fully recover after a quench without any external protection mechanism to dissipate the stored energy. The underlying mechanisms that make NI coils highly stable or even self-protecting, however, remain unclear. To answer this question, a numerical multiphysics quench model for NI pancake coils is built to study the electrical, thermal and magnetic behavior of NI coils subjected to local heat disturbances. The multiphysics model is built from an electric network model, tightly coupled to a two-dimensional thermal coil model and a three-dimensional magnetic field coil model. The results show that when heat disturbance initiates a local normal region on a turn, the transport current is redistributed not only from the local normal region, but also along the entire turn. The redistributed current flows in the form of radial current across the turn-to-turn contact resistance along the entire turn to the neighboring turns which are still in the superconducting state, driving these turns to an overcurrent state. This full-turn current sharing and overcurrent operation accelerate the redistribution of current away from the hot-spot, reducing localized Joule heating that would otherwise cause a sustainable quench. The results also show that the magnetic field generated at the coil center drops rapidly and the coil voltage changes dynamically during the early stage of normal zone formation. These phenomena can be utilized as effective methods for quench detection in NI coils by monitoring the magnetic field and coil voltage.

Comprehensive Evaluation of Rectangular and Double-D Coil Geometry for 50 kW/85 kHz IPT System

Abstract: In this paper, the influence of the inductive power transfer (IPT) coil geometry on the performance factors efficiency, power density, and stray field is studied for a public transport electric vehicle battery charging system. IPT coil geometries with rectangular winding and with double-D winding are compared based on the Pareto fronts obtained from a multi-objective optimization. In order to study the effect of the winding layout experimentally, two full-scale 50 kW/85 kHz hardware prototypes with the same outer coil dimensions ( $410\times 760\times 60$ mm3) and ferrite core structure are constructed. For both the prototypes, the measured dc–dc efficiency is approximately 95.5% at 50 kW with a 160 mm air gap and ideally positioned coils, which confirms the calculations. The positioning tolerance of the double-D prototype is inferior, because with coil misalignment the efficiency decays faster than for the rectangular winding prototype. Flux density measurements show that both the prototypes fulfill the ICNIRP 2010 standard at 800 mm lateral distance from the coil center. However, the measured magnetic stray field is a factor of two lower for the double-D prototype, which is a key advantage in high-power applications.

Multi-Paralleled LCC Reactive Power Compensation Networks and Their Tuning Method for Electric Vehicle Dynamic Wireless Charging

Abstract: Dynamic wireless power transfer (WPT) is a practical method to solve electric vehicle (EV) range anxiety and reduce the cost of on-board batteries. This paper presents a novel dynamic WPT system that combines the advantages of pads array and segmental long coils coupler. In the proposed circuit, several paralleled LCC reactive power compensation networks (RPCNs) in the primary side were excited by a sole inverter and the power distribution was realized automatically; an auxiliary LCC network was proposed to regulate current in the primary coil to minimize the electromagnetic interference (EMI) and reduce the system’s power loss. A scaled-down prototype of a dynamic wireless charging system was developed to prove the validity of the theoretical analysis.

A Flexible Integrated System Containing a Microsupercapacitor, a Photodetector, and a Wireless Charging Coil

Abstract: Nowadays, the integrated systems on a plane substrate containing energy harvesting, energy storing, and working units are strongly desired with the fast development of wearable and portable devices. Here, a simple, low cost, and scalable strategy involving ink printing and electrochemical deposition is proposed to fabricate a flexible integrated system on a plane substrate containing an all-solid-state asymmetric microsupercapacitor (MSC), a photoconduct-type photodetector of perovskite nanowires (NWs), and a wireless charging coil. In the asymmetric MSCs, MnO2-PPy and V2O5-PANI composites are used as positive and negative electrodes, respectively. Typical values of energy density in the range of 15–20 mWh cm–3 at power densities of 0.3–2.5 W cm–3 with an operation potential window of 1.6 V are achieved. In the system, the wireless charging coil receives energy from a wireless power transmitter, which then can be stored in the MSC to drive the photoconductive detector of perovskite NWs in sequence. The de...

Coil Design and Measurements of Automotive Magnetic Resonant Wireless Charging System for High-Efficiency and Low Magnetic Field Leakage

Abstract: For wireless charging of electric vehicle (EV) batteries, high-frequency magnetic fields are generated from magnetically coupled coils. The large air-gap between two coils may cause high leakage of magnetic fields and it may also lower the power transfer efficiency (PTE). For the first time, in this paper, we propose a new set of coil design formulas for high-efficiency and low harmonic currents and a new design procedure for low leakage of magnetic fields for high-power wireless power transfer (WPT) system. Based on the proposed design procedure, a pair of magnetically coupled coils with magnetic field shielding for a 1-kW-class golf-cart WPT system is optimized via finite-element simulation and the proposed design formulas. We built a 1-kW-class wireless EV charging system for practical measurements of the PTE, the magnetic field strength around the golf cart, and voltage/current spectrums. The fabricated system has achieved a PTE of 96% at the operating frequency of 20.15 kHz with a 156-mm air gap between the coils. At the same time, the highest magnetic field strength measured around the golf cart is 19.8 mG, which is far below the relevant electromagnetic field safety guidelines (ICNIRP 1998/2010). In addition, the third harmonic component of the measured magnetic field is 39 dB lower than the fundamental component. These practical measurement results prove the effectiveness of the proposed coil design formulas and procedure of a WPT system for high-efficiency and low magnetic field leakage.

Progress in the Development and Construction of a 32-T Superconducting Magnet

Abstract: The 32-T superconducting magnet is envisioned as a 15-T low-temperature superconductor (LTS) magnet combined with a separately powered REBCO high-temperature superconductor (HTS) insert configured as two coil stacks generating 17 T. Progress was made in all aspects of this project and is reported in this work. The design concept, which has been quite stable, is presented, as well as key elements from recent developments such as increased voltage standoff requirements. In both factory testing and installation at the NHMFL, the 15-T/250-mm-bore outer magnet built by Oxford Instruments met all specifications, including a ramp time of 1 h to full field. The test protocol included a deliberately induced full-field quench, releasing 7 MJ. After the helium level recovered, the magnet was ramped again in 1 h to full field, demonstrating full recovery. Helium boiloffs during normal operation and quench were observed, as well as the current and field decay during quench. The latter information serves as one of many inputs for the numerical quench code developed specifically to model quench in coupled LTS-HTS coils. Results from the 32-T quench analysis and implications for quench protection are summarized. All HTS conductor lengths were subjected to an extensive quality assurance (QA) protocol, and SuperPower has now delivered all required conductor lengths within specifications. A summary of the QA data and its implications are presented. The prototype coils, which are very similar in design to the 32-T REBCO coils but of reduced height, have now been impregnated with paraffin to address winding motion observed in previous testing. The prototype test protocol includes a study of the effectiveness of the quench heaters in the HTS coils in both a constant background field as provided by the actual 15-T LTS outer magnet for 32 T and, uniquely, in case the outer magnet is deliberately quenched.

Wireless Power Transfer System With an Asymmetric Four-Coil Resonator for Electric Vehicle Battery Chargers

Abstract: This paper proposes a high-efficiency wireless power transfer system with an asymmetric four-coil resonator. It presents a theoretical analysis, an optimal design method, and experimental results. Multicoil systems which have more than three coils between the primary and secondary side provide the benefits of a good coupling coefficient, a long transfer distance, and a wide operating frequency range. The conventional four-coil system has a symmetric coil configuration. In the primary side, there are source and transmitter coils, and the secondary side contains receiver and load coils. On the other hand, in the proposed asymmetric four-coil system, the primary side consists of a source coil and two transmitter coils which are called intermediate coils, and in the secondary side, a load coil serves as a receiver coil. In the primary side, two intermediate coils boost the apparent coupling coefficient at around the operating frequency. Because of this double boosting effect, the system with an asymmetric four-coil resonator has a higher efficiency than that of the conventional symmetric four-coil system. A prototype of the proposed system with the asymmetric four-coil resonator is implemented and experimented on to verify the validity of the proposed system. The prototype operates at 90 kHz of switching frequency and has 200 mm of the power transmission distance between the primary side and the secondary side. An ac–dc overall system efficiency of 96.56% has been achieved at 3.3 kW of output power.

A Triple-Loop Inductive Power Transmission System for Biomedical Applications

Abstract: A triple-loop wireless power transmission (WPT) system equipped with closed-loop global power control, adaptive transmitter (Tx) resonance compensation (TRC), and automatic receiver (Rx) resonance tuning (ART) is presented. This system not only opposes coupling and load variations but also compensates for changes in the environment surrounding the inductive link to enhance power transfer efficiency (PTE) in applications such as implantable medical devices (IMDs). The Tx was built around a commercial off-the-shelf (COTS) radio-frequency identification (RFID) reader, operating at 13.56 MHz. A local Tx loop finds the optimal capacitance in parallel with the Tx coil by adjusting a varactor. A global power control loop maintains the received power at a desired level in the presence of changes in coupling distance, coil misalignments, and loading. Moreover, a local Rx loop is implemented inside a power management integrated circuit (PMIC) to avoid PTE degradation due to the Rx coil surrounding environment and process variations. The PMIC was fabricated in a 0.35- $\mu{\rm m}$ 4M2P standard CMOS process with 2.54 ${\rm mm}^{2}$ active area. Measurement results show that the proposed triple-loop system improves the overall PTE by up to 10.5% and 4.7% compared to a similar open- and single closed-loop system, respectively, at nominal coil distance of 2 cm. The added TRC and ART loops contribute 2.3% and 1.4% to the overall PTE of 13.5%, respectively. This is the first WPT system to include three loops to dynamically compensate for environment and circuit variations and improve the overall power efficiency all the way from the driver output in Tx to the load in Rx.

Coil Design and Efficiency Analysis for Dynamic Wireless Charging System for Electric Vehicles

Abstract: Wireless charging electric vehicles (EV) is the development trend of EV. However, the battery taken by EVs has the disadvantages of big volume, long time to recharge, and limited driving distance. In this paper, an innovative dynamic wireless charging system based on magnetic coupled resonant power transmission is presented. The transmitting coil of this charging system can selectively turn ON/OFF for charging vehicles while driving. The structures of the transmitting coil and receiving coil are researched and improved. In addition, the dispersed coupling structure named grouped periodic series spiral coupler is proposed, and its characteristics are described. A simulation of coupling coefficients at different $D$ values is carried out. A prototype is built to experiment on the dynamic wireless charging process of EV. Meanwhile, the coil coupling and variation of transmission efficiency are analyzed. The comparison of the experiment indicated that the EV can obtain a stable charging process under 25 mm transmission distance using the improved receiving coil with $R$ : $H$ : $D=4:5:13$ . Moreover, the dynamic charging process is relatively stable without an obvious fluctuation while passing the interval between two transmitting coils, and the transmission efficiency is promoted by 50%.

Wireless Power Transfer With Automatic Feedback Control of Load Resistance Transformation

Abstract: This paper proposes a wireless power transfer with automatic feedback control of load resistance transformation to maintain high efficiency over wide variations of coupling current and load current. The receiver (Rx) first determines the desired current level of transmitter (Tx) coil such that the receiver-side converter can transform the load resistance into optimum effective resistance, based on load current and Tx-to-Rx distance information. The determined Tx coil current data are sent to the transmitter, which then adjusts the Tx coil current accordingly. In this way, the effective resistance transformed by the receiver-side converter remains optimum under the variations of distance and load current. One of the advantages of the proposed automatic feedback control is faster response and simple hardware because it does not use operating point sweep and observation. The receiver-side switching converter also incorporates the ability to send data from receiver to transmitter by modulating the duty cycle of converter at data frequency, eliminating the need for separate RF communication hardware. This proposed communication does not require shunt current dissipation from dc output to ground, resulting in low loss. Experimental result demonstrates that the system maintains high efficiency under wide variations of coupling and load current.

Six Degrees of Freedom Mobile Inductive Power Transfer by Crossed Dipole Tx and Rx Coils

Abstract: Crossed dipole coils for the wide-range 3-D omnidirectional inductive power transfer (IPT) are proposed. Free positioning of a plane receiving (Rx) coil is obtained for an arbitrary direction within 1m from a plane transmission (Tx) coil. Both the Tx and Rx coils consists of crossed dipole coils with an orthogonal phase difference; hence, a rotating magnetic field is generated from the Tx, which enables the Rx to receive power vertically or horizontally. Thus, the 3-D omnidirectional IPT is first realized for both the plate type Tx and Rx coils, which is crucial for practical applications, where volumetric coil structure is highly prohibited. This optimized configuration of coils has been obtained through a general classification of power transfer and searching for mathematical constraints on multi-D omnidirectional IPT. Conventional loop coils are thoroughly analyzed, and verified to be inadequate for the plate-type omnidirectional IPT in this paper. Simulation-based design of the proposed crossed dipole coils for a uniform magnetic field distribution is provided, and the 3-D omnidirectional IPT is experimentally verified by prototype Rx coils for a wireless power­ zone of 1 m3 with a prototype Tx coil of 1 m2 at an operating frequency of 280 kHz, meeting the power matters alliance. The maximum overall efficiency was 33.6% when the input power was 100 W.

Basic Control Principles of Omnidirectional Wireless Power Transfer

Abstract: This paper presents the basic control principles of omnidirectional wireless power transfer (WPT) based on the current amplitude control. The principles involve 1) an “omnidirectional” scanning process for detecting the power requirements in a 3-D space and 2) a “directional” power flow control for focusing the wireless power toward the targeted areas. Such principles apply to any WPT system comprising three orthogonal transmitter coils and multiple receivers with coil resonators. A current amplitude control method capable of generating a magnetic vector at a set of points evenly distributed on a spherical surface is explained. Based on the voltage and the current information in the transmitter circuit, the power involved in each vector over the spherical surface can be obtained. By scanning the vector over the spherical surface, the collective power flow requirements for the targeted loads can be determined. Based on the power requirements for the vectors over the spherical surface, a weighted time-sharing scheme is adopted to focus the wireless power toward the targeted areas. This method has been successfully applied to a hardware prototype. Both theoretical and experimental results are included to confirm these principles.

Lumped Track Layout Design for Dynamic Wireless Charging of Electric Vehicles

Abstract: Dynamic wireless charging (DWC) of electric vehicles (EVs) is an emerging technology that could lead to the breakthrough of EVs. The technology is based on the inductive coupling between an electrified track deployed under the road surface and a pickup coil fitted in EV. This paper refers to a lumped track made of DD coils and is concerned with the design of the track layout, namely coil dimension in the motion direction and track coil distance for a given energy requirement. This paper starts by comparing the coupling characteristics of DD coils with different dimensions by a finite-element method (FEM) analysis. Afterward, an analytical procedure is developed to establish the track coil distance able to transfer to a moving EV the propulsion energy required per unit of traveled space. The procedure utilizes the DD-coil coupling characteristics to calculate the power and, from it, the energy transferred from the track coils to the pickup coil along the track. Instrumental in the calculation is the definition of a parameter, denoted as track flux coverage, which gives the ratio between the dimension of the track coils in the motion direction and the coil distance; such a parameter corresponds to the percentage of road populated with track coils so that it is a cost index of the DWC system implementation. Effects of a lateral displacement of the EV motion from the line joining the track coil centers are also analyzed. Design findings are checked against the results obtained with a computer-assisted analysis.

Development of a brushless HTS exciter for a 10 kW HTS synchronous generator

Abstract: HTS synchronous generators, in which the rotor coils are wound from high-T c superconducting wire, are exciting attention due to their potential to deliver very high torque and power densities. However, injection of the large DC currents required by the HTS rotor coils presents a technical challenge. In this paper we discuss the development of a brushless HTS exciter which operates across the cryostat wall to inject a superconducting DC current into the rotor coil circuit. This approach fundamentally alters the thermal load upon the cryogenic system by removing the need for thermally inefficient normal-conducting current leads. We report results from an experimental laboratory device and show that it operates as a constant voltage source with an effective internal resistance. We then discuss the design of a prototype HTS-PM exciter based on our experimental device, and describe its integration with a demonstration HTS generator. This 200 RPM, 10 kW synchronous generator comprises eight double pancake HTS rotor coils which are operated at 30 K, and are energised to 1.5 T field through the injection of 85 A per pole. We show how this excitation can be achieved using an HTS-PM exciter consisting of 12 stator poles of 12 mm YBCO coated-conductor wire and an external permanent magnet rotor. We demonstrate that such an exciter can excite the rotor windings of this generator without forming a thermal-bridge across the cryostat wall. Finally, we provide estimates of the thermal load imposed by our prototype HTS-PM exciter on the rotor cryostat. We show that duty cycle operation of the device ensures that this heat load can be minimised, and that it is substantially lower than that of equivalently-rated conventional current leads.

Electronic device and method for controlling fan of electronic device

Abstract: According to various embodiments, an electronic device for charging a battery of an external device may include a coil and a first circuit configured to wirelessly transmit power to the external device through the coil. A second circuit may be configured to wirelessly receive information from the external device. A fan may be disposed adjacent to the coil to discharge heat to the exterior of the electronic device. A control circuit may adjust the driving speed of the fan based at least in part on the received information.

EMF Safety and Thermal Aspects in a Pacemaker Equipped With a Wireless Power Transfer System Working at Low Frequency

Abstract: A wireless power transfer (WPT) system based on magnetic resonant coupling is applied to a pacemaker for recharge its battery. The primary coil is assumed to be on-body, while the secondary coil is in-body. Three different configurations of the secondary coil are hereby investigated placing it inside the titanium case of the pacemaker, on the top surface of the case, or being part of the top surface case. The operational frequency is fixed to be at a relatively low frequency (20 kHz) in order to allow field penetration through the case and to limit the electric and magnetic field safety and thermal increase issues. For each examined configuration, these aspects are investigated by numerical and experimental techniques. The obtained results demonstrate the feasibility of the proposed solutions highlighting their advantages and disadvantages.

Quench detection for high temperature superconductor magnets: a novel technique based on Rayleigh-backscattering interrogated optical fibers

Abstract: High temperature superconducting materials are the only option for the generation of magnetic fields exceeding 25 T and for magnets operating over a broad range of temperature and magnetic field for power applications. One remaining obstacle for the implementation of high temperature superconductors magnets into systems, however, is the inability to rapidly detect a quench. In this letter we present a novel quench detection technique that has been investigated experimentally. Optical fibers are co-wound into two small Bi2Sr2Ca2Cu3O10+x superconducting coils and interrogated by Rayleigh-backscattering. Two different configurations are used, one with the fiber atop the conductor and the other with the fiber located as turn-to-turn insulation. Each coil is also instrumented with voltage taps (VTs) and thermocouples for comparison during heater-induced quenches. The results show that Rayleigh-backscattering interrogated optical fibers (RIOF) have significant advantages over traditional techniques, including very high spatial resolution and the ability to detect a hot-spot well before the peak local temperature exceeds the current sharing temperature. Thus, RIOF quench detection is intrinsically faster than VTs, and this intrinsic advantage is greater as the coil size and/or current margin increases.

Integrated Field and Armature Current Control Strategy for Variable Flux Reluctance Machine Using Open Winding

Abstract: This paper proposes an integrated field and armature current control strategy for a variable flux reluctance machine (VFRM) with an open-winding topology. By using an open-winding inverter, the field and armature currents can be injected into a single coil as a sinusoidal current biased by the dc offset rather than the separated field and armature windings. The integrated current control can reduce the copper loss to half and extend the operating speed range owing to the reduction in the winding resistance. In order to utilize the zero-sequence current as a field current, a zero-vector modification technique is proposed, in which the switching-on time of the zero vectors is modified to generate the constant zero-sequence voltage between two inverters. The proposed scheme is implemented in a synchronous $dq0$ -axis frame with space vector modulation. For the validation of the proposed method, a machine model of the VFRM is developed and implemented in MATLAB/Simulink. The simulation and experimental results verify that the proposed strategy can effectively reduce the copper loss and extend the operating speed range.

Frequency-Dependent Resistance of Litz-Wire Square Solenoid Coils and Quality Factor Optimization for Wireless Power Transfer

Abstract: In order to achieve the highest efficiency of wireless power transfer (WPT) systems, the quality factor of the resonant coil should be as high as possible. Due to the skin effect and the proximity effect, the coil resistance increases with the increase in the frequency. The highest quality factor exists for the optimal frequency together with the corresponding frequency-dependent inductor resistance. This paper employs the Biot–Savart law to calculate the magnetic field strength, which results in the proximity-effect resistance in single-layer litz-wire square solenoid coils without a magnetic core. A strand-number coefficient is introduced to reflect the influence of the strand number inside the wire bundle on the proximity-effect resistance. The coefficient is obtained through simple inductor resistance measurements for various numbers of litz-wire strands. The optimal frequency for the highest quality factor is derived based on the resistance evaluation. Several prototype coils were manufactured to verify the resistance analysis. Two $50\,\rm{cm}\times50\, {\rm cm}$ square coils were employed to construct a WPT prototype. The maximum dc–dc efficiency of this WPT was about 75% at 100-cm distance.

Wireless Power Transfer With Concurrent 200-kHz and 6.78-MHz Operation in a Single-Transmitter Device

Abstract: This paper proposes a wireless power transfer (WPT) transmitter that can concurrently operate at 200 kHz and 6.78 MHz in order to simultaneously power two receivers operating with different frequency standards. Unlike a dual-resonant single-coil design, the use of two separate coils decouples the design for one frequency from the other, enabling independent selection of inductance and Q -factor to simultaneously maximize efficiency at both frequencies. The two coils then support separate coil drivers, enabling concurrent multistandard operation. Dual-band operation is achieved in the same area as an equivalent single-band design by placing a low-frequency coil within the geometry of a high-frequency coil, where the outer diameter of inner coil is sacrificed only by 1.2 cm in a 12.5 × 8.9-cm2 design. Circuit analysis is presented to identify the eddy current between the two Tx coils and its associated loss, after which an eddy-current filter design is proposed. To validate the proposed design, a dual-mode transmitter, along with two receivers designed at 6.78 MHz and 200 kHz, respectively, have been fabricated. At 25-mm separation, the system is able to simultaneously deliver 9 and 7.4 W with efficiencies of 78% and 70.6% at 6.78 MHz and 200 kHz, respectively.

A high-speed, high-frequency, air-core PM machine for aircraft application

Abstract: High number of magnetic poles in an electric machine allows reduction in radial thickness of stator and rotor yoke and thus heavy alloy. If frequency is allowed to increase with pole-count (constant speed), power level can be maintained. Thus, high frequency, together with high pole count, can improve power density of rotating electric machines. The proposed high frequency concept is applied to designing a 1 MW motor, with power density and efficiency goals of > 13kW/kg and > 96%, respectively.

Numerical models for ac loss calculation in large-scale applications of HTS coated conductors

Abstract: Numerical models are powerful tools to predict the electromagnetic behavior of superconductors. In recent years, a variety of models have been successfully developed to simulate high-temperature-superconducting (HTS) coated conductor tapes. While the models work well for the simulation of individual tapes or relatively small assemblies, their direct applicability to devices involving hundreds or thousands of tapes, e.g., coils used in electrical machines, is questionable. Indeed, the simulation time and memory requirement can quickly become prohibitive. In this paper, we develop and compare two different models for simulating realistic HTS devices composed of a large number of tapes: (1) the homogenized model simulates the coil using an equivalent anisotropic homogeneous bulk with specifically developed current constraints to account for the fact that each turn carries the same current; (2) the multi-scale model parallelizes and reduces the computational problem by simulating only several individual tapes at significant positions of the coil's cross-section using appropriate boundary conditions to account for the field generated by the neighboring turns. Both methods are used to simulate a coil made of 2000 tapes, and compared against the widely used H-formulation finite-element model that includes all the tapes. Both approaches allow faster simulations of large number of HTS tapes by 1–3 orders of magnitudes, while maintaining good accuracy of the results. Both models can therefore be used to design and optimize large-scale HTS devices. This study provides key advancement with respect to previous versions of both models. The homogenized model is extended from simple stacks to large arrays of tapes. For the multi-scale model, the importance of the choice of the current distribution used to generate the background field is underlined; the error in ac loss estimation resulting from the most obvious choice of starting from a uniform current distribution is revealed.

Analysis and Optimization of the Efficiency of Induction Heating Applications With Litz-Wire Planar and Solenoidal Coils

Abstract: Optimization of the efficiency of an induction heating application is essential in order to improve both reliability and performance. For this purpose, multistranded cables with litz structure are often used in induction heating applications. This paper presents an analysis and optimization of the efficiency of induction heating systems focusing on the optimal copper volume of the winding with respect to different constraints. The analysis is based on the concept of a one-strand one-turn coil, which captures the dissipative effects of an induction heating system and reduces the number of variables of the analysis. An expression for the efficiency of the induction heating system is derived. It is found that, with the geometry and the other parameters of the system fixed, efficiency depends on the copper volume of the windings. In order to use this result to optimize the efficiency of an application, volume restrictions, the packing factor and the window utilization factor are also considered. The optimum frequency for an induction heating system is also studied in this study. An experimental verification for both planar and solenoidal cases is also presented.