Coreless Coil Research Articles

Design of Inductive Power Transfer Charging System with Weak Coupling Coefficient

Inductive power transfer (IPT) technology is used in various applications owing to its safety features, robust environmental adaptability, and convenience. In some special applications, the charging pads are required to be as compact as possible to accommodate practical spatial requirements, and even size requirements dictate that the diameter of the charging pad matches the air gap. However, such requirements bring about a decrease in the transmission efficiency, power, and tolerance to misalignment of the system. In this paper, by comparing a double-sided inductor–capacitor–capacitor (LCC), double-sided inductor–capacitor–inductor (LCL), series–series (SS), and inductor–capacitor–capacitor–series (LCC-S) compensation topologies in IPT systems, we identified a double-sided LCC compensation topology that is suitable for weak coupling coefficients. Furthermore, this study modeled and simulated the typical parameters of coreless coils in circular power pads, such as the number of coil layers, turns, wire diameter, and wire spacing, to enhance the mutual inductance of the magnetic coupler during misalignment and long-distance transmission. A wireless charging system with 640 W output power was built, and the experimental results show that a maximum dc-dc efficiency of over 86% is achieved across a 200 mm air gap when the circular power pad with a diameter of 200 mm is well aligned. The experimental results show that using a suitable compensation topology and optimizing the charging pad parameters enables efficient IPT system operation when the coupling coefficient is 0.02.

Coil Design Method Considering Power, Efficiency, and Magnetic Field Strength of Coreless Coils Using Numerical Analysis in Wireless Power Transfer

Wireless power transfer to electric vehicles while driving is a technology that is currently attracting attention as it has the potential to solve the problems faced by EVs that will become popular worldwide in the future. In the case of dynamic wireless power transfer (DWPT) to electric vehicles, it is necessary to transmit the required power with high efficiency and ensure safety. While there are multiple safety requirements, there are also regulatory values for the magnetic field strength emitted from the coil, which must be satisfied before it can be implemented in society. This research aims to speed up the design of coils by using only numerical analysis, in contrast to conventional coil design using electromagnetic field analysis. In the future construction of wireless power transfer systems, it is of great significance to discuss the design using only numerical analysis, as there are many design parameters. Experiments were carried out and compared with the numerical analysis and found to be in agreement. A power transmission of 20 kW converted value was carried out to verify the effect of the size, pitch, and number of turns of the transmission coils on the efficiency and magnetic field strength. The effect of input voltage was also discussed by simulation, and the optimum coil was derived. As a result, when the coil size was 800 × 600 mm, the number of turns was 46, the pitch was 6.1 mm and the input voltage was 1400 V, the analysis showed that a power transmission of 20 kW with an efficiency of 99.3% and a far magnetic field leakage strength of 81.6 dBμA/m could be achieved. Even with a coreless coil, the magnetic field strength could be below the regulation value. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

An Efficiency Optimization Method of Static Wireless Power Transfer Coreless Coils for Electric Vehicles in the 85 kHz Band Using Numerical Analysis

Wireless power transfer (WPT) has been attracting a lot of attention in recent years for its ability to greatly improve the convenience of our lives. Moreover, WPT for Electric Vehicles (EVs) has become an important key to the spread of EVs. The efficiency of WPT using magnetic field resonant coupling can be evaluated by the kQ product, but the optimal coil design method to maximize the kQ product at a specific frequency has not yet been established. In this paper, taking the Test station GA‐WPT1 and the Test station VA‐WPT1/Z3 of SAE J2954, which is officially defined as the standard for WPT while the electric vehicle is stationary in October 2020, as examples, the coil parameters that maximize the kQ product in the case of the coreless are determined according to the proposed method. An efficiency of 99.13% was obtained with a transmission distance of 200 mm and the number of turns of N1 = 34 and N2 = 30. Also, since all analyses can be derived immediately except for the analysis of the Litz wire to be used, the optimization time could be reduced significantly compared with the electromagnetic field analysis. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Thermally compensated inductive deformation sensor – Mathematical background and practical implementation

The article presents theoretical background and experimental verification of thermal compensation method of inductive displacement sensor. This sensor has the form of single-layer, coreless coil which is the inductance of a resonant LC circuit. Change of coil length causes change in oscillation frequency of Colpitts oscillator.Influence of the sensor temperature on the circuit oscillation frequency was significantly reduced. This was achieved by using the dependence of the sensor resistance on its temperature in a specially modified resonant circuit. The circuit was mathematically modeled. The detectors were made of various metals and their theoretical thermal characteristics were compared with the experimental ones.The sensor has successfully been used for years in rock samples’ deformations measurements during the compressibility test, at hydrostatic pressure up to 400 MPa with temperature changes of several dozen degrees. It replaced resistance strain gauges and LVDT sensors, that were unreliable at high pressures.

Development of Axial-Flux Single-Drive Bearingless Motor With One-Axis Active Positioning

This study proposes a novel axial-flux bearingless permanent magnet motor with one-axis active positioning. This bearingless motor consists of an axial-flux surface permanent magnet motor with coreless coils and a repulsive permanent magnet coupling located at its center. Therefore, it has a single three-phase winding and needs only one three-phase inverter for both rotation and magnetic suspension; it is, thus, referred to as a single-drive bearingless motor. The axial position of the rotor is actively controlled, whereas the radial and tilting motions are passively stabilized. The suspension force and torque are regulated by the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis currents, respectively. The structure of the proposed axial-flux single-drive bearingless motor is presented, and its torque and suspension force are obtained by both theoretical derivation and numerical modeling (using the finite-element method). A prototype machine is fabricated, and the obtained experimental results are presented and discussed.

Application of the mixing of the field of low amplitude AC bias with a strong field of linear slow varying to investigate the magnetic properties of materials

The paper presents a new experimental method of the magnetic hysteresis loop investigation and the constructed measurement instrument. The principle of operation is to mix two magnetic fields: the first of these fields has a very low amplitude, a shape of sine wave (AC bias) and the frequency range order of 10–104 Hz. The second field has a very low frequency (order 10−2 Hz), a high amplitude and forms approximately a triangle wave. The presented, dedicated system is different in comparison to commonly used hystographs and it consists of coreless coils only. The measurement method gives the opportunity of obtaining more detailed measurements of the initial cycles in the material magnetizing process. In a special case, the magnetic field strength changes in the B(H) curve can be stopped at any operating point and then it is possible to investigate local properties using AC bias field for various frequencies. The results revealed a successive displacement of the hysteresis loop and approaching to the steady state position.

Stray Flux Sensor Core Impact on the Condition Monitoring of Electrical Machines.

The analysis of the stray flux for electrical machine condition monitoring is a very modern and active research topic. Thanks to this technique, it is possible to detect several types of failures, including stator and rotor inter-turn faults, broken rotor bars and mechanical faults, among others. The main advantages are that it involves a non-invasive technique and low-cost monitoring equipment. The standard practice is to use coreless flux sensors, with which the stray flux of the machine is not perturbed and there are no problems due to saturation or nonlinear behavior of the iron. However, the induced voltage in the coreless coil sensor may be very low and even, in some cases, have a similar amplitude to the noise floor. This paper studies the use of iron core stray flux sensors for condition monitoring of electrical machines. The main advantage of iron core flux sensors is that the measured electromotive force is stronger. In the case of large machines in noisy environments, this can be crucial. Two different types of iron core stray flux sensors and a coreless flux sensor are tested. A comparison of the three sensors is presented. Extensive experimental testing with all sensors shows the superiority and greater sensitivity of sensors with core versus the coreless ones.

Inductive Energy Harvesting From Current-Carrying Structures

This article introduces an inductive method for harvesting energy from current-carrying structures. Numerical simulation of a structural beam shows that the skin effect can lead to significant current concentration at edges, providing a five-fold power benefit at such locations, even at frequencies below 1 kHz. The use of a rectangular ferrite core can provide a ×4 power density improvement. The adoption of funnel-like core shapes allows the reduction of core mass and coil frame size, leading to significant further power density enhancement. Magnetic field simulation and coil analysis demonstrate a power density increase of ×49 by ferrite funnels, in comparison to a coreless coil. Experimental results demonstrate rectified power over 1 mW delivered to a storage capacitor, from a 40 × 20 × 2 mm core-and-coil, in the vicinity of a spatially distributed 20 A current at 800 Hz. Rectification and impedance matching are studied experimentally using a voltage doubler circuit with input capacitor tuning to counteract the coil reactance. Experimental results from a spatially distributed 30 A current at 300 Hz and a 1:7 funnel core demonstrate power density of 36 μ W/g (103 μ W/cm3), opening up the way to noninvasive inductive powering of systems in the vicinity of current-carrying structures.

Design of an ICPT system for battery charging applied to underwater docking systems

High power consumption limits the endurance of autonomous underwater vehicles (AUVs). It’s necessary to build a docking station to recover and recharge AUVs underwater. Inductive coupling is a commonly used method for contactless power transmission, which demonstrates superiorities in an underwater environment. In this study, a pair of coaxial and coreless coil structure is proposed for battery charging of the AUV. The performance of an inductive contactless power transfer (ICPT) system in SP topology is analyzed considering the loss of eddy-current in sea water, switching elements and diode-bridge. An appropriate frequency is selected to realize a maximum system efficiency. In the laboratory experiment, the selected topology demonstrates stable properties and realizes a maximum charging power of approximately 300W. The efficiency of the ICPT system varies from 75% to 91% with a total efficiency of 63–77% during the entire charging period.

Wireless Power and Data Transfer via a Common Inductive Link Using Frequency Division Multiplexing

For wireless power transfer (WPT) systems, communication between the primary side and the pickup side is a challenge because of the large air gap and magnetic interferences. A novel method, which integrates bidirectional data communication into a high-power WPT system, is proposed in this paper. The power and data transfer share the same inductive link between coreless coils. Power/data frequency division multiplexing technique is applied, and the power and data are transmitted by employing different frequency carriers and controlled independently. The circuit model of the multiband system is provided to analyze the transmission gain of the communication channel, as well as the power delivery performance. The crosstalk interference between two carriers is discussed. In addition, the signal-to-noise ratios of the channels are also estimated, which gives a guideline for the design of mod/demod circuits. Finally, a 500-W WPT prototype has been built to demonstrate the effectiveness of the proposed WPT system.

Lumped Impedance Transformers for Compact and Robust Coupled Magnetic Resonance Systems

An innovative coupled magnetic resonance system (CMRS), introducing two lumped impedance transformers, is proposed. There are three major magnetic couplings between coils in CMRS: source-transmitter (Tx), Tx-receiver (Rx), and Rx-load couplings. Except for Tx-Rx coupling, other couplings do not directly contribute to wireless power transfer. Hence, in this paper, this miscellaneous coupling is replaced with a lumped transformer with ferrite core. Because there is only a Tx-Rx coupling, the CMRS becomes compact in size and robust to ambient changes. Moreover, the design of CMRS is drastically simplified without complicated multiresonance tunings due to little magnetic flux linkage from the source coil or load coil. Coreless coils are used for Tx and Rx coils to examine the characteristics of CMRS with lumped transformers. A detailed static analysis on the explicit circuit model of the proposed CMRS and design procedures are fully established. Experiments for 1- and 10-W prototype CMRSs with a class-E inverter at the switching frequency of 500 kHz, where the quality factors are less than 100, verified the usefulness of the proposed model, achieving 80% of the maximum Tx coil-to-load efficiency. It is concluded in this paper that the conventional CMRS, in general, is just a special form of an inductive power transfer system where the quality factor is extremely high.

Experimental study of thrusts of a cylindrical linear synchronous motor with an HTS coil magnet as the excitation system

The thrusts of a cylindrical linear synchronous motor with an HTS coil magnet as the excitation system were measured the first time and will be presented in this paper. The HTS coil magnet is made of second generation YBCO wire. The coil is a double pancake coil consisting of 34 turns wire. The inner diameter, outer diameter and height of the coil are 20, 30 and 13mm, respectively. The armature of the motor is three phases, and the inner diameter is 40mm. It is made of copper windings. With a direct current of 40A for the HTS coil magnet and a RMS current of 10A for the armature, a peak thrust of 3.8N was measured at the temperature of 77K and a radial gap of 5mm between the armature and the excitation system. Effects of armature current, coil current, running time, magnetizers and seams between magnetizers were also studied. In the experiments, the peak thrusts of different types of HTS coil magnets were about from 1.3 times to 8 times as strong as the peak thrust of the coreless coil magnet under the same conditions.

Non-dipole interaction of helix inclusions in metamaterials with artificial permeability

An analytic approach to calculate induced permeability of metamaterial filled with helix inclusions is developed. For an electrically small coil, the dynamic magnetization is determined by lumped inductance, capacitance, and resistance that are calculated from the coil design. The susceptibility of a coil is shown to be close to that of diamagnetic ellipsoid of the same elongation. Contrary to permeable particles in a composite, the coils screen each other thus decreasing the magnetic response of metamaterial compared to total response of comprised coils. The filling effect on magnetic spectrum of metamaterial is analyzed and verified by measurements for the case of identical coaxially placed coreless coils. The critical filling where magnetic response of metamaterial is maximal depends on coil shape and resistance. The coil-filled metamaterials may find applications as permeable EMI suppressors or microwave absorbers free of Snoek or Acher limitations on the high-frequency permeability, as well as of Curie limitation on the high-temperature magnetic performance.

Design and Test of a Long-Pulse Large Current Sensor With a Hall Probe Installed Inside

A high accuracy large current sensor which can directly output the current signal without integral has been designed, fabricated, and tested. It is composed of a coreless helix coil cut by pure copper tube and a hall probe installed inside. It has excellent linear performance due to the absence of iron core. The ability of resisting disturbance is much improved because the hall probe is installed inside. A calibrated prototype sensor has been applied on a 40 T long pulsed magnetic field system to output the current data as feedback signal. A long pulse magnetic field with 25.6 T/200 ms flat-top and ripples less than 0.02% was achieved.

The Development of a New Type Rooftop Ventilator Turbine

This paper presents a small power generation system motivated by a coreless stator AFPM (Axial Flux Permanent Magnet) generator which is driven by the rooftop ventilator. The generator consists of discs for the rotor and the stator geometry. The stator disc is sandwiched between two rotor discs and the magnets in the two opposite rotor discs may be placed N-S arrangements. Since there is no silicon steel inside the coils, we should eliminate the magnetic pulling force between the rotors and the stators. When the ventilator rotates, the flux of the permanent magnet rotors part move across the air gap and induces the emf in the coreless coils. After that, the ac voltage is rectified to dc voltage and finally charged to the 12 V 5 Ahr battery for household appliances. To analyze the magnetic circuit, the finite element analysis was used to simulate the magnetic flux density in the AFPM generator. The test is operated in electrical machines laboratory and essentially to determine the characteristics of prototype generator. Based on the experiments, the results of the output voltage can achieve 103 V with no-load, and 20 V on 100 Ω resistive loads at the speed of 200 rpm. For the results after installing the generator on the roof of a building to charge the 12 V battery, the minimum wind speed for enough charging to battery is at 10 rpm. Furthermore, the prototyped of the generator is relatively small and cheap. After the fabrication and testing of the prototype, this system has been proved feasible for practical application.

Design and Performance Evaluation of a Coreless Thrust Magnetic Bearing with a Cylindrical Permanent Magnet Mover

A thrust magnetic bearing using a magnetic disk with a large diameter is usually employed in five-degrees-of-freedom controlled magnetic bearings and bearingless drive systems. However, the large disk may result in a complicated assembly process and increased peripheral velocity, which results in the limitation of a maximum rotational speed. In this paper, a novel thrust magnetic bearing using a cylindrical permanent magnet (PM) mover without the large disk has been proposed, designed, and tested. Coreless coil stators are employed for the reduction of radial attractive force that may cause disturbance to the bearingless drive system. To enhance the thrust force, iron disks with the same diameter of the PM mover are attached to the rotor. The fabricated actuator can generate a desired thrust force with less disturbance to the bearingless motor.

コンパクト遠心血液ポンプの研究(第2報) : ビルトインモータ型遠心ポンプの性能(S64-2 生物医学工学における計測と制御(2),S64 生物医学工学における計測と制御)

This paper discusses miniaturization of a centrifugal blood pump with a magnetically levitated rotor. In the previous report, the fabricated centrifugal pump with the two-degrees-of-freedom controlled magnetic bearing was driven by the magnetically coupled brushless motor. In order to downsize the centrifugal pump, the motor should be incorporated into the centrifugal pump. A built-in motor consisting of a Halbach permanent magnet array .in a rotor and coreless coils in a stator is proposed. The advantage of the built-in motor is that unbalanced pull in the radial and axial directions of the rotor is not generated, and power consumption of the magnetic bearing to cancel the unbalanced force can be reduced. This report shows design, fabrication and performances of the centrifugal blood pump with the built-in motor.

2539 ジャイロタイプ風力発電機の風洞実験と発電機の性能

This report describes the development of small-sized wind power generators. The characteristics of the generator are rare-earth permanent magnets and core-less coils. We performed the wind tunnel experiment using the generator and Gyroscope-type wings. After obtaining the experimental results, some analytical works using IEM (Integral Element Method) software on dynamic magnetic field ware performed. We aim to obtain the way to the best design for the generator from experimental and analytical studies.

The Effect of Alternative Magnetic Field on the Pigment Ejection from Magnetic Anisotropic Gel Beads

Abstract Magnetic anisotropic gel beads (MA gel beads) were prepared by the gelation of a ferrite suspension in a static magnetic field. MA gel beads were found to oscillate in an alternating magnetic field. This oscillation can possibly reduce the thickness of the diffusion layer on the interface between the gel beads and the surrounding solution, so that the substance can be transferred more quickly across the gel–liquid interface. MA gel beads consisted of alginate gel containing ferrite powder and toluidine blue as a pigment. MA gel beads were loaded into a dual glass tube to make a column bed, which was inserted into a coreless coil which produced the alternating magnetic field. The concentration change of the pigment in the effluent from the column was measured during a lapse in time with repeating off and on the input of the alternating magnetic field. The pigment concentration in the effluent upon exposure to the alternating magnetic field increased to twice the maximum value obtained without a magnetic field. The stronger was the static magnetic field at the time of gelation and the alternating magnetic field, the larger was the increase in pigment concentration in the effluent. Also, the higher was the concentration of ferrite in gel beads, the larger was the increase in pigment concentration in the effluent.

High T/sub c/ superconducting quick response nonlinear inductances and magnetic modulators

Remarkable nonlinear inductances due to the soft magnetic BH hysteresis characteristics are obtained for YBa/sub 2/Cu/sub 3/O/sub 7-x/ disk-shaped cores at 77 K which are tightly wound with polyester-coated copper coils. The inductance changes from nearly zero due to the Meissner effect to that of an equivalent coreless coil as a result of the flux penetration effect due to increasing the exciting current or the applied external magnetic field. Values of inductances are almost constant from low frequency to at least 20 MHz, indicating that the high-T/sub c/ superconductor is a fast-response nonlinear inductor material. Fast-response magnetic modulators use one toroidal core or one pair of disk cores with a carrier frequency of more than 10 MHz and a signal frequency of 0 to 500 kHz. >