High Power Transfer Efficiency Research Articles

Survey on magnetic resonant coupling wireless power transfer technology for electric vehicle charging

Wireless power transfer (WPT) technology makes it possible to supply power through an air-gap, without the need for current-carrying wires. One important technique of WPT technology is magnetic resonant coupling (MRC) WPT. Based on the advantages of MRC WPT, such as safety and high power transfer efficiency over a long transmit distance, there are many possible applications of MRC WPT. This study provides a comprehensive, state-of-the-art review of the MRC WPT technology and wireless charging for electric vehicle (EV). A comparative overview of MRC WPT system design which includes a detailed description of the prototypes, schematics, compensation circuit topologies (impedance matching), and international charging standards. In addition, this study provides an overview of wireless EV charging including the static wireless EV charging and the dynamic wireless EV charging, which focuses on the coil design, power transfer efficiency, and current research achievement in the literature.

Phase-Shift Modulation for a Current-Fed Isolated DC–DC Converter in More Electric Aircrafts

This paper discussed an active-bridge-active-clamp (ABAC) topology that is suitable for highpower more-electric-aircraft applications. Though conventional modulation techniques can be applied to ABAC converters, they present drawbacks, such as increased low-voltage (LV) current ripple and limited power transfer capability. To address these problems, a phase-shift-modulation (PSM) scheme is proposed to provide clean dc terminal current at the LV side while maintaining high power transfer capability and efficiency in a wide operating range. The proposed PSM has a complete switching harmonics cancellation on the LV terminals independent of the operating conditions. This results in high quality power without any ac components, thus minimizing passive filtering. In addition, when terminal voltages vary from their nominal values, the proposed PSM can improve the maximum power transfer capability of the ABAC converter compared to the conventional approach. The theoretical claims are validated by both simulation and experimental results on a 10-kW 270-V/28-V ABAC converter.

A Magnetic Resonance Wireless Power Transfer System Robust to Distance Variation Using Dual-Matching Scheme

A magnetic resonance wireless power transfer (WPT) system achieves maximum power transfer efficiency (PTE) at the position where critical coupling occurs, but the PTE degrades significantly off this position. In this paper, we propose a new design technique that can achieve high PTE over a wide range by generating critical coupling at two other positions by using a switchless passive dual-matching technique. We present a receiver (RX) and transmitter (TX) configuration implemented with lumped elements for dual-matching and derive the values of each device analytically. A RX part is constructed by connecting parallel LC and C in series to resonate at two frequencies. Considering the mutual inductances between the TX and RX coil at two distances, T-type TX matching is designed to achieve conjugate matching at two resonant frequencies for the source impedance simultaneously. To verify the performance of the proposed technique, a WPT system with critical coupling at 25 and 75 mm for two frequencies of 4 and 6.78 MHz was implemented, and the PTE was measured. The average PTE in the range of 20–80 mm is 70%, and it is verified that the proposed technique can achieve robust WPT system to distance variation.

Multiple-channel dynamic bandpass filter via radiation modes-assisted transparency in a side-coupled SNAP microcavity

We experimentally and theoretically demonstrate a tunable bandpass filter based on the optically induced transparency enabled by dynamical interference of continuous radiation modes and localized whispering gallery modes (WGMs) with a surface nanoscale axial photonics (SNAP) platform. The tunability in bandwidth and power transfer efficiency is achieved by scanning the microfiber which achieves a high power transfer efficiency up to 1.43, high out-of-band rejection of ∼31 dB, and bandwidth tunability of 30.6 MHz ∼ 2.32 GHz. The combination of easy alignment, fiber compatibility, high efficiency, and robust wide-range tunability facilitates applications ranging from quantum optics to photonic networks.

Modeling of Capacitive Resonant Wireless Power and Data Transfer to Deep Biomedical Implants

Neural implantable sensors require a harmless sustainable wireless power transfer technique for their lifetime operation. The capacitive-coupled (CC) power transfer method has proved to induce minimum electromagnetic interference as compared with inductive resonant power transfer. However, the CC method suffers from the limitation of low power transfer efficiency (PTE) and is suitable only for short-distance power transfer applications. In physical health-monitoring practices, the deep implants require high PTE with minimum electromagnetic interference. Similarly, the measured data need to be transmitted to the external world for remote monitoring and analysis. Nevertheless, the size and safety constraints limit the direct interfacing of the data communication module to implants. With this objective, this paper proposes a resonant capacitive-coupling (RCC) approach for wireless power transfer to brain implants. Moreover, to further improve the PTE, the proposed model is investigated with the additional intermediate plate capacitance between the transmitter (Tx) and the receiver (Rx). The analytical and experimental studies are carried out for intracranial pressure sensor (ICP) application and obtain the PTE of 24.2%, 34.14%, and 42.21% for CC, RCC, and RCC with an intermediate plate (RCCI) approaches, respectively. In addition, to eliminate the use of the antenna for data transfer, the same capacitive plates are used and tested with amplitude phase-shift keying (ASK) modulation technique for uplink communication. The proposed system is also integrated with the Internet of Things (IoT) module for the remote monitoring and analyses of patient health.

A Modified Wireless Power Transfer System for Medical Implants

Wireless Power Transfer (WPT) is a promising technique, yet still an experimental solution, to replace batteries in existing implants and overcome the related health complications. However, not all techniques are adequate to meet the safety requirements of medical implants for patients. Ensuring a compromise between a small form factor and a high Power Transfer Efficiency (PTE) for transcutaneous applications still remains a challenge. In this work, we have used a resonant inductive coupling for WPT and a coil geometry optimization approach to address constraints related to maintaining a small form factor and the efficiency of power transfer. Thus, we propose a WPT system for medical implants operating at 13.56 MHz using high-efficiency Complementary Metal Oxide-Semiconductor (CMOS) components and an optimized Printed Circuit Coil (PCC). It is divided into two main circuits, a transmitter circuit located outside the human body and a receiver circuit implanted inside the body. The transmitter circuit was designed with an oscillator, driver and a Class-E power amplifier. Experimental results acquired in the air medium show that the proposed system reaches a power transfer efficiency of 75.1% for 0.5 cm and reaches 5 cm as a maximum transfer distance for 10.67% of the efficiency, all of which holds promise for implementing WPT for medical implants that don’t require further medical intervention, and without taking up a lot of space.

A Novel Reluctance Magnetic Gear for High-Speed Motor

Magnetic gears are expected to be a maintenance-free system with low-noise and low-vibration characteristics by a noncontact power transmission. However, conventional magnetic gears are not suitable for use with high-speed motors because the mechanical strength is weak due to the use of permanent magnets in a high-speed rotor. Additionally, the magnet eddy current losses in the high-speed rotor seriously decrease the gear's efficiency during a high-speed operation. This paper presents a novel reluctance magnetic gear that can realize the high-speed drive and high efficiency. The high-speed rotor of the proposed magnetic gear is constructed by only an iron core. Therefore, the structure is very simple and robust, adding that it is possible to rotate in the high-speed region. Moreover, the proposed magnetic gear achieves high efficiency in the high-speed region because the magnet eddy current loss in the high-speed rotor is not generated because no magnets are used. The downsizing of the system and a high efficiency power transfer are realized by applying the proposed reluctance magnetic gear.

Design of Near-Field Focused Metasurface for High-Efficient Wireless Power Transfer With Multifocus Characteristics

This paper presents a new design of near-field focused metasurface for high-efficiency wireless power transfer with multifocus characteristics. A general synthesis procedure is outlined to design metasurfaces with desired multiple foci in the near-field zone. The unit cell of printed tridipole is used to realize the focused metasurface which has a large range of phase shift and is adapted to near-field focusing applications. Different feeding and focusing designs of the printed tridipole metasurfaces are proposed and analyzed. Two kinds of metasurfaces with 20×20 elements are designed, fabricated, and measured at 5.8 GHz. One is the single-feed and single-focus case, and the other is single-feed and two-focus case. Two-dimensional planar near-field scanning technique is implemented to measure the E -field focusing characteristics. Full-wave simulations and experiments demonstrate that the proposed focusing metasurfaces have a high wireless power transfer efficiency of 70%. The relative bandwidth with 50% power focusing efficiency is about 16%. The measured results are in good agreement with the theoretical designs and simulated results, which verify the feasibility and correctness of the proposed approach in this paper.

Highly Efficient, Flexible Wireless‐Powered Circuit Printed on a Moist, Soft Contact Lens

AbstractContact lens with built‐in electronics is a next‐generation wearable product with potential applications such as biomedical sensing and wearable displays. However, fabricating a wireless‐powered circuit on a moist, soft contact lens, via common dry lithography, makes producing smart contact lenses challenging. Here, electrochemically (EC) printing a wireless‐powered circuit onto a moist, soft contact lens is demonstrated. EC printing involves adding a conductive polymer at the interface between a metal contact and a hydrogel‐based contact lens, resulting in strong adhesion of the circuit to the lens without losing high power transfer efficiency (50%) from an eyeglass transmitter to the printed receiver lens. The energy transfer characteristics during eye movement are modeled using the Neumann equation and Kirchhoff's voltage law for wireless power transfer. The energy transfer efficiency between the eyeglass transmitter and the printed receiver lens is derived, and illumination of a wireless‐powered single light‐emitting diode display as a function of eye rotation angle is demonstrated. This work opens the door to integrating more complex circuits at soft contact lens interface to produce smart contact lens with increased functionality.

A Novel Approach to Reach Impedance Matching in Wireless Power Transfer Systems

Wireless power transfer (WPT) using magnetic resonant coupling technology, came into focus promptly by virtue of its long transfer distance, and its non-radiative and high-efficiency power transfer. The impedance matching has been studied in the literature in recent years. However, there is no suitable way to reach the optimum load in reality. In this paper, a new method is proposed to maximize the power transfer ability of a given pair of coupled coils. An analytical calculation of the mutual inductance is presented accurately with respect to the angled concentric multiple-turn printed spiral coils (PSC). In addition, the experimental results were in good agreement with the circuit simulation. Finally, a WPT experiment setup working at 3MHz resonance was established. The experiment results verified that the maximum transfer efficiency at fixed distances can be easily achieved by adjusting the angle to reach impedance matching. Compared to prior to optimization, the maximum improved efficiency was improved by 11%.

Investigation of magnetic resonance coupling circuit topologies for wireless power transmission

AbstractMagnetic resonance coupling circuits have four general topologies; however, there is a lack of comprehensive theoretical analysis with experimental verification for each of these topologies regarding their attractiveness for wireless power transfer (WPT). This article provides this for each of the four topologies to fully understand their differences and allow the selection of the most appropriate type based on system requirements. In addition, a problem associated with the resonance coupling method is the phenomenon of frequency splitting, which can lead to a high‐power transfer efficiency but low‐load power at the resonant frequency. Reasons for frequency splitting and methods of circumventing the problem will be illustrated in this article. Of the four topologies, the series‐parallel (SP) (input‐output) circuit configuration is the most efficient for the realization of a WPT system with a large load impedance, in terms of achieving both a high power transfer efficiency and high‐load power.

Distributed coordination control of hybrid energy resources for power sharing in coupled hybrid DC/AC microgrid using paralleled IFCs/ILCs

This study proposes flexible controllers for the interlinking converter (ILC) and interfacing converters (IFCs) used in coupled hybrid AC/DC microgrids (HMGs). Proposed controllers are specifically designed for the multiple stacked bidirectional DC–AC ILCs/IFCs based microgrid outlays, to omit the droop power flow and system stability issues. The ILC and IFC grid supportive converter controllers focus on the wide-spread AC/DC bus parameters control for both DC and AC bus voltage regulation and superfluous power sharing while operating in the grid forming and feeding modes. Proposed controllers minimise the need for the controller parameter tuning as opposed to the conventional controllers used in zonal HMG systems. This makes the system stable for a much wider operating conditions as opposed to the widely used higher-order PLL integrated PQ and dq 0 control algorithms. The proposed HMG also integrates the centralised battery energy stack through bidirectional dual active bridge DC–DC converter for achieving the high-power transfer efficiency and omitting the isolation issues between medium-voltage and low-voltage DC buses. The HMG system performance is evaluated using the simulation studies for various strategical operational modes. Further, the proposed controllers have also been tested individually on experimental platform.

Highly Efficient WPT System With Negative Impedance Converter for Q-factor Improvement

A negative impedance converter (NIC) has been combined with a wireless power transfer (WPT) system to maximize the system efficiency based on non-foster theory. The NIC is composed of transistor, voltage divider, capacitor, and inductor for impedance matching, and resonant circuit operating at 6.78 MHz. The desired negative impedance can be controlled by tunable impedance in the NIC. In this paper, the loss of the transmitting coil is reduced to 0.1 Ω, yielding a quality factor of 7,050, which is 19.1 times higher than that of the conventional coil. The WPT system with the NIC provides high power transfer efficiency (PTE) at various transmission distances. The experimental results are improved from 64% to 96% and from 5% to 55% at the transmission distances of 50 and 200 mm, respectively. Furthermore, the PTE is enhanced from 38% to 87% and from 2% to 38% at the diagonal misalignment distance of 0 and 150 mm, respectively, at a transmission distance of 100 mm. The proposed technology for increasing the receiving power in the receiving coil with a higher PTE can be utilized for numerous applications in the industrial, scientific, and medical band, with a restricted radio frequency power on the transmitter side.

A Tissue-Channel Transcutaneous Power Transfer Technique for Implantable Devices

For implantable devices, miniaturization is a key design consideration, which facilitates keyhole surgery and relieves the surgical pain. Wireless power transfer is a commonly used way for implants, and a high power transfer efficiency (PTE) could help to minimize or even remove the battery inside the human body. Conventionally, the required power is delivered transcutaneously to a medical implant by inductive coupling or capacitive coupling, but the PTE is extremely low when targeting at a very small implant through a thick tissue layer. In this paper, we propose a new technique by utilizing the body tissue as the power transfer channel, where a pair of medical electrodes are attached on the body surface to supply power to a miniaturized implant with a differential input. The PTE is remarkably improved by the current loop through the body tissue without violating the IEEE specific absorption rate standard. Measurement results show that the tissue-channel technique achieves 0.39% PTE for a 1-mm-sized implant locating 5 cm deep inside the tissue.

Efficiency Analysis of Multiple-Transmitter Wireless Power Transfer Systems

The range of the power transmission region can be effectively enlarged by a multiple-transmitter (TXs) and single-receiver (RX) magnetic wireless power transfer (WPT) system. However, the power transfer efficiency (PTE) of the WPT system with two TXs and a single RX has been intensively studied in the past few years. Therefore, a deep analysis of multiple-TX WPT systems needs to be implemented urgently to achieve the highest PTE in a wider range of power transmission. This paper analyzes a general multiple-TX single-RX system in detail based on the circuit model. Two optimal conditions, in which the feeding amplitude ratios need be equal to the mutual inductance ratios and the optimal load should be connected to RX, are derived to obtain the highest PTE. In the experiment part, the feeding amplitude ratios for multiple TXs are implemented by a proposed lumped transformer for the first time. The use of the lumped transformer reduces the complexity compared with the use of multiple inverters to achieve predetermined feeding amplitude ratios. Multiple-TX systems are designed and measured to validate the theoretical analysis. Experimental results agree very well with theoretical calculations.

Automatic Adaptation of Multi-Loop Wireless Power Transfer to Variable Coupling between Transmit and Receive Coils

In the conventional wireless power transfer (WPT) using magnetic resonance coupling, power transfer efficiency (PTE) exhibits a peak only at a matched distance between transmitter (Tx) and receiver (Rx). That is, it rapidly degrades if the distance deviates from the matched distance. In order to achieve high PTE over a wide range of the distance, automatic range-adaptation technique is proposed in this work by using multi-loop technique and tunable matching circuit with digital capacitors. For automatic range adaptation, the microcontroller unit (MCU) in Rx runs an algorithm to find optimum loop and capacitance for best PTE based on the received power. Tx and Rx are synchronized by using low power Bluetooth wireless communications. Instead of the conventional relays, microelectromechanical system (MEMS) switches with low loss and high isolation are employed to minimize the power dissipation. The entire WPT system automatically maximize PTE with the distance, achieving high PTE of 80.5% at 30 cm and 29.7% at 100 cm.

Coordinated Source Control for Output Power Stabilization and Efficiency Optimization in WPT Systems

This paper presents the framework for the applications of double-source wireless systems in charging for movable electronic devices. To acquire the real-time mutual inductances between the receiving coil and the transmitting coils, a detection strategy on the basis of primary parameters (currents and voltages) is introduced, which can replace the wireless communications between the receiving side and the transmitting side. Coordinated control of two source voltages is employed to deal with the power fluctuation of load, which is caused by load position variations. In specific, the constraint of two source voltages, which can maintain the output power stable, is derived. Based on these feasible combinations of source voltages, numerical calculations are further carried out to identify the optimized voltage combination, which can achieve high power transfer efficiency. Finally, an experimental prototype is built up and the results show that the proposed coordinated control strategy can minimize power fluctuation and maintain relative high efficiency at the same time.

Design Optimization of Multiple-Layer PSCs With Minimal Losses for Efficient and Robust Inductive Wireless Power Transfer

Inductive wireless Power Transfer (IPT) is a promising technology for remote powering of a wide variety of applications of electronic devices. To design IPT systems with the highest power transfer efficiency and the maximal robustness to coupling factor variations between transmitter and receiver of printed spiral coils (PSCs), high quality factors ( Q-Factor ) of the utilized PSCs are required. Designing PSCs with high Q-Factor is limited by the eddy current, the proximity effect, and parasitic losses. In this paper, PSC parasitic losses are carefully analyzed and specific design solutions are proposed. Genetic algorithm optimizations are developed to accommodate the proposed design solutions in minimizing losses. Single and multiple layer variable width PSCs are optimally designed with eddy current and proximity effect losses minimized. The designed PSCs are fabricated and experimental measurements are performed. The validity of the proposed approach to largely improve both IPT efficiency and robustness are confirmed. Using multiple coil layers, the robustness to axial and lateral coupling variations between coils is highly improved. For a triple-layer PSC design case, up to 3.5-fold improved robustness are obtained in reference to conventional IPT systems. Compared with the previous state of the art IPT topologies, the highest Figure-of-Merit value is obtained using the proposed design solutions.

Nearly Non-Coupling Coil Array Allowing Many Independent Channels for Magnetic Communication

Crosstalk between coil array components in magnetic systems has to be minimized to achieve enhanced performance, such as high data rate, high-power transfer efficiency, and simultaneous wireless information and power transfer. This paper presents a scalable non-coupling coil array composed of perpendicularly arranged quadrupole loop coils. The proposed coil array permits the number of fully or nearly independent channel streams to be increased to meet user’s requirements, unlike conventional coil arrays which have a limited number of channel streams. The proposed non-coupling coil array structure is investigated by theoretical analysis and 3-D electromagnetic simulation, and the performance of the proposed non-coupling coil array is verified with a prototype implementation. The proposed coil array shows relatively high signal-to-interference and noise power ratio of around 20 dB even at the three times further distance of a coil diameter.

Chip-Scale Near-Field Resonant Power Transfer via Elastic Waves

This paper reports on the proof-of-concept demonstration of an approach for the synthesis of a through package charging and authenticating communication link enabled by GHz-range aluminum nitride (AlN) piezoelectric transducers. The acoustic link is formed by two thickness-mode acoustic transducers placed on the two sides of a packaging substrate. The link leverages the enhancement of energy transfer that occurs at resonance; 1- $\mu \text{m}$ -thick (2.7 GHz) and 6- $\mu \text{m}$ -thick (500 MHz) AlN acoustic links are demonstrated showing substantial enhancement of power transfer efficiencies (PTE) when using thicker AlN substrates. PTEs of −8 dB at 2.7 GHz and −2 dB at 500 MHz are measured for transducers’ size of $1\times 100\times 100~\mu \text{m}^{3}$ and $6\times 100\times 100~\mu \text{m}^{3}$ through 700- and 500- $\mu \text{m}$ -thick silicon substrates, respectively. The experimental values are in very close agreement with the analytical model of the acoustic link. The potential misalignment between the two transducers is the main limitation of this approach. To overcome this challenge, acoustic phased arrays are devised to enable steering of the transmitted beam. Preliminary results on the steering capability demonstrate about 8 dB of improvement in PTE via a two-element array when dealing with a 100- $\mu \text{m}$ misalignment. This paper is the first step toward the development of next-generation high-efficiency and micro-scale power transfer units that could energize chips through packages. [2017-0010]