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Special Issue "Wireless Power Transfer"

A special issue of Energies (ISSN 1996-1073).

Deadline for manuscript submissions: closed (31 July 2015)

Special Issue Editor

Guest Editor
Prof. Dr. K.T. Chau

Department of Electrical & Electronic Engineering, The University of Hong Kong, Pokfulam, Hong Kong
Website | E-Mail
Interests: electric and hybrid vehicles; machines and drives; renewable and clean energies; power electronics

Special Issue Information

Dear Colleagues,

In recent years, there has been increasing interest in the development of wireless power transfer technology. This disruptive technology enables new possibilities of supplying electric devices without using cables, connectors or slip rings, hence, increasing reliability and improving safety.

This Special Issue, entitled “Wireless Power Transfer”, invites articles that address state-of-the-art technologies and new developments for wireless power transfer (WPT), including, but not limited to, inductively coupled WPT and capacitively-coupled WPT. Articles which deal with the latest hot topics in WPT are particularly encouraged, such as resonance techniques, coupler designs, converter circuits, compensation networks, control strategies, and security considerations. In addition, articles which discuss WPT’s application to park-and-charge, move-and-charge, and vehicle-to-grid for electric vehicles, would be of particular interest. The discussion on the relationship between the use of WPT and electromagnetic field safety issues is most welcome.

Prof. Dr. K.T. Chau
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.


Keywords

  • wireless power transfer
  • inductive power transfer
  • capacitive power transfer
  • magnetic resonance
  • power electronics
  • energy encryption
  • battery charging
  • electric vehicle
  • vehicle-to-grid
  • electromagnetic compatibility

Published Papers (12 papers)

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Research

Open AccessArticle Autonomous Wireless Self-Charging for Multi-Rotor Unmanned Aerial Vehicles
Energies 2017, 10(6), 803; https://doi.org/10.3390/en10060803
Received: 25 April 2017 / Revised: 31 May 2017 / Accepted: 6 June 2017 / Published: 13 June 2017
Cited by 4 | PDF Full-text (2474 KB) | HTML Full-text | XML Full-text
Abstract
Rotary-wing unmanned aerial vehicles (UAVs) have the ability to operate in confined spaces and to hover over point of interest, but they have limited flight time and endurance. Conventional contact-based charging system for UAVs has been used, but it requires high landing accuracy
[...] Read more.
Rotary-wing unmanned aerial vehicles (UAVs) have the ability to operate in confined spaces and to hover over point of interest, but they have limited flight time and endurance. Conventional contact-based charging system for UAVs has been used, but it requires high landing accuracy for proper docking. Instead of the conventional system, autonomous wireless battery charging system for UAVs in outdoor conditions is proposed in this paper. UAVs can be wirelessly charged using the proposed charging system, regardless of yaw angle between UAVs and wireless charging pad, which can further reduce their control complexity for autonomous landing. The increased overall mission time eventually relaxes the limitations on payload and flight time. In this paper, a cost effective automatic recharging solution for UAVs in outdoor environments is proposed using wireless power transfer (WPT). This research proposes a global positioning system (GPS) and vision-based closed-loop target detection and a tracking system for precise landing of quadcopters in outdoor environments. The system uses the onboard camera to detect the shape, color and position of the defined target in image frame. Based on the offset of the target from the center of the image frame, control commands are generated to track and maintain the center position. Commercially available AR.Drone. was used to demonstrate the proposed concept which is equppied with bottom camera and GPS. Experiments and analyses showed good performance, and about 75% average WPT efficiency was achieved in this research. Full article
(This article belongs to the Special Issue Wireless Power Transfer)
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Open AccessArticle Economic Viability Study of an On-Road Wireless Charging System with a Generic Driving Range Estimation Method
Energies 2016, 9(2), 76; https://doi.org/10.3390/en9020076
Received: 4 September 2015 / Revised: 11 January 2016 / Accepted: 18 January 2016 / Published: 26 January 2016
Cited by 16 | PDF Full-text (4531 KB) | HTML Full-text | XML Full-text
Abstract
The economic viability of on-road wireless charging of electric vehicles (EVs) strongly depends on the choice of the inductive power transfer (IPT) system configuration (static or dynamic charging), charging power level and the percentage of road coverage of dynamic charging. In this paper,
[...] Read more.
The economic viability of on-road wireless charging of electric vehicles (EVs) strongly depends on the choice of the inductive power transfer (IPT) system configuration (static or dynamic charging), charging power level and the percentage of road coverage of dynamic charging. In this paper, a case study is carried out to determine the expected investment costs involved in installing the on-road charging infrastructure for an electric bus fleet. Firstly, a generic methodology is described to determine the driving range of any EV (including electric buses) with any gross mass and frontal area. A dynamic power consumption model is developed for the EV, taking into account the rolling friction, acceleration, deceleration, aerodynamic drag, regenerative braking and Li-ion battery behavior. Based on the simulation results, the linear dependence of the battery state of charge (SoC) on the distance traveled is proven. Further, the impact of different IPT system parameters on driving range is incorporated. Economic implications of a combination of different IPT system parameters are explored for achieving the required driving range of 400 km, and the cost optimized solution is presented for the case study of an electric bus fleet. It is shown that the choice of charging power level and road coverage are interrelated in the economic context. The economic viability of reducing the capacity of the on-board battery as a trade-off between higher transport efficiency and larger on-road charging infrastructure is presented. Finally, important considerations, like the number of average running buses, scheduled stoppage time and on-board battery size, that make on-road charging an attractive option are explored. The cost break-up of various system components of the on-road charging scheme is estimated, and the final project cost and parameters are summarized. The specific cost of the wireless on-road charging system is found to be more expensive than the conventional trolley system at this point in time. With decreasing battery costs and a higher number of running buses, a more economically-viable system can be realized. Full article
(This article belongs to the Special Issue Wireless Power Transfer)
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Open AccessArticle Expression of Heat Shock Proteins in Human Fibroblast Cells under Magnetic Resonant Coupling Wireless Power Transfer
Energies 2015, 8(10), 12020-12028; https://doi.org/10.3390/en81012020
Received: 27 July 2015 / Revised: 22 September 2015 / Accepted: 16 October 2015 / Published: 22 October 2015
Cited by 1 | PDF Full-text (681 KB) | HTML Full-text | XML Full-text
Abstract
Since 2007, resonant coupling wireless power transfer (WPT) technology has been attracting attention and has been widely researched for practical use. Moreover, dosimetric evaluation has also been discussed to evaluate the potential health risks of the electromagnetic field from this WPT technology based
[...] Read more.
Since 2007, resonant coupling wireless power transfer (WPT) technology has been attracting attention and has been widely researched for practical use. Moreover, dosimetric evaluation has also been discussed to evaluate the potential health risks of the electromagnetic field from this WPT technology based on the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines. However, there has not been much experimental evaluation of the potential health risks of this WPT technology. In this study, to evaluate whether magnetic resonant coupling WPT induces cellular stress, we focused on heat shock proteins (Hsps) and determined the expression level of Hsps 27, 70 and 90 in WI38VA13 subcloned 2RA human fibroblast cells using a western blotting method. The expression level of Hsps under conditions of magnetic resonant coupling WPT for 24 h was not significantly different compared with control cells, although the expression level of Hsps for cells exposed to heat stress conditions was significantly increased. These results suggested that exposure to magnetic resonant coupling WPT did not cause detectable cell stress. Full article
(This article belongs to the Special Issue Wireless Power Transfer)
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Open AccessArticle Investigation of High-Efficiency Wireless Power Transfer Criteria of Resonantly-Coupled Loops and Dipoles through Analysis of the Figure of Merit
Energies 2015, 8(10), 11342-11362; https://doi.org/10.3390/en81011342
Received: 31 July 2015 / Revised: 8 September 2015 / Accepted: 27 September 2015 / Published: 13 October 2015
Cited by 6 | PDF Full-text (1080 KB) | HTML Full-text | XML Full-text
Abstract
The efficiency of a Wireless Power Transfer (WPT) system is greatly dependent on both the geometry and operating frequency of the transmitting and receiving structures. By using Coupled Mode Theory (CMT), the figure of merit is calculated for resonantly-coupled loop and dipole systems.
[...] Read more.
The efficiency of a Wireless Power Transfer (WPT) system is greatly dependent on both the geometry and operating frequency of the transmitting and receiving structures. By using Coupled Mode Theory (CMT), the figure of merit is calculated for resonantly-coupled loop and dipole systems. An in-depth analysis of the figure of merit is performed with respect to the key geometric parameters of the loops and dipoles, along with the resonant frequency, in order to identify the key relationships leading to high-efficiency WPT. For systems consisting of two identical single-turn loops, it is shown that the choice of both the loop radius and resonant frequency are essential in achieving high-efficiency WPT. For the dipole geometries studied, it is shown that the choice of length is largely irrelevant and that as a result of their capacitive nature, low-MHz frequency dipoles are able to produce significantly higher figures of merit than those of the loops considered. The results of the figure of merit analysis are used to propose and subsequently compare two mid-range loop and dipole WPT systems of equal size and operating frequency, where it is shown that the dipole system is able to achieve higher efficiencies than the loop system of the distance range examined. Full article
(This article belongs to the Special Issue Wireless Power Transfer)
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Open AccessArticle Design Considerations for Wireless Charging Systems with an Analysis of Batteries
Energies 2015, 8(10), 10664-10683; https://doi.org/10.3390/en81010664
Received: 31 July 2015 / Revised: 27 August 2015 / Accepted: 22 September 2015 / Published: 25 September 2015
Cited by 3 | PDF Full-text (949 KB) | HTML Full-text | XML Full-text
Abstract
Three criteria, including charging time, effective charging capacity and charging energy efficiency, are introduced to evaluate the CC (constant current) and CC/CV (constant current/constant voltage) charging strategies. Because the CC strategy presents a better performance and most resonant topologies have the CC characteristic,
[...] Read more.
Three criteria, including charging time, effective charging capacity and charging energy efficiency, are introduced to evaluate the CC (constant current) and CC/CV (constant current/constant voltage) charging strategies. Because the CC strategy presents a better performance and most resonant topologies have the CC characteristic, the CC strategy is more suitable for the design of wireless charging systems than the CC/CV strategy. Then, the state space model of the receiver is built to study the system dynamic characteristics, and the design of nonuse output filter capacitors is proposed, which can improve the system power density and avoid the drop in efficiency caused by capacitor degradation. At last, an electrochemical impedance spectrum (EIS) based analysis method is introduced to validate that the design without output filter capacitors has no effects on the battery characteristics when the charging frequency is higher than 460 Hz. A prototype is fabricated to verify our research results. Full article
(This article belongs to the Special Issue Wireless Power Transfer)
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Open AccessArticle Inductive-Based Wireless Power Recharging System for an Innovative Endoscopic Capsule
Energies 2015, 8(9), 10315-10334; https://doi.org/10.3390/en80910315
Received: 3 August 2015 / Revised: 12 September 2015 / Accepted: 14 September 2015 / Published: 21 September 2015
Cited by 9 | PDF Full-text (2356 KB) | HTML Full-text | XML Full-text
Abstract
Wireless capsule endoscopic devices are adopted for painless diagnosis of cancer and other diseases affecting the gastrointestinal tract as an alternative to traditional endoscopy. Although much work has been done to improve capsule performance in terms of active navigation, a major drawback is
[...] Read more.
Wireless capsule endoscopic devices are adopted for painless diagnosis of cancer and other diseases affecting the gastrointestinal tract as an alternative to traditional endoscopy. Although much work has been done to improve capsule performance in terms of active navigation, a major drawback is the limited available energy on board the capsule, usually provided by a battery. Another key shortcoming of active capsules is their limitation in terms of active functionalities and related costs. An inductive-based wireless recharging system for the development of an innovative capsule for colonoscopy is proposed in this paper; the aim is to provide fast off-line battery recovery for improving capsule lifecycle and thus reducing the cost of a single endoscopic procedure. The wireless recharging system has been properly designed to fit the dimensions of a capsule for colonoscopy but it can be applied to any biomedical devices to increase the number of times it can be used after proper sterilization. The current system is able to provide about 1 W power and is able to recharge the battery capsule in 20 min which is a reasonable time considering capsule operation time (10–15 min). Full article
(This article belongs to the Special Issue Wireless Power Transfer)
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Open AccessArticle Determining the Frequency for Load-Independent Output Current in Three-Coil Wireless Power Transfer System
Energies 2015, 8(9), 9719-9730; https://doi.org/10.3390/en8099719
Received: 29 July 2015 / Revised: 25 August 2015 / Accepted: 31 August 2015 / Published: 9 September 2015
Cited by 7 | PDF Full-text (1184 KB) | HTML Full-text | XML Full-text
Abstract
Conditions for load-independent output voltage or current in two-coil wireless power transfer (WPT) systems have been studied. However, analysis of load-independent output current in three-coil WPT system is still lacking in previous studies. This paper investigates the output current characteristics of a three-coil
[...] Read more.
Conditions for load-independent output voltage or current in two-coil wireless power transfer (WPT) systems have been studied. However, analysis of load-independent output current in three-coil WPT system is still lacking in previous studies. This paper investigates the output current characteristics of a three-coil WPT system against load variations, and determines the operating frequency to achieve a constant output current. First, a three-coil WPT system is modeled by circuit theory, and the analytical expression of the root-mean-square of the output current is derived. By substituting the coupling coefficients, the quality factor, and the resonant frequency of each coil, we propose a method of calculating the frequency for load-independent output current in a three-coil WPT system, which indicates that there are two frequencies that can achieve load-independent output current. Experiments are conducted to validate these analytical results. Full article
(This article belongs to the Special Issue Wireless Power Transfer)
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Open AccessArticle A Uniform Voltage Gain Control for Alignment Robustness in Wireless EV Charging
Energies 2015, 8(8), 8355-8370; https://doi.org/10.3390/en8088355
Received: 2 July 2015 / Revised: 27 July 2015 / Accepted: 28 July 2015 / Published: 7 August 2015
Cited by 20 | PDF Full-text (2334 KB) | HTML Full-text | XML Full-text
Abstract
The efficiency of wireless power transfer is sensitive to the horizontal and vertical distances between the transmitter and receiver coils due to the magnetic coupling change. To address the output voltage variation and efficiency drop caused by misalignment, a uniform voltage gain frequency
[...] Read more.
The efficiency of wireless power transfer is sensitive to the horizontal and vertical distances between the transmitter and receiver coils due to the magnetic coupling change. To address the output voltage variation and efficiency drop caused by misalignment, a uniform voltage gain frequency control is implemented to improve the power delivery and efficiency of wireless power transfer under misalignment. The frequency is tuned according to the amplitude and phase-frequency characteristics of coupling variations in order to maintain a uniform output voltage in the receiver coil. Experimental comparison of three control methods, including fixed frequency control, resonant frequency control, and the proposed uniform gain control was conducted and demonstrated that the uniform voltage gain control is the most robust method for managing misalignment in wireless charging applications. Full article
(This article belongs to the Special Issue Wireless Power Transfer)
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Open AccessArticle Software-Based Wireless Power Transfer Platform for Various Power Control Experiments
Energies 2015, 8(8), 7677-7689; https://doi.org/10.3390/en8087677
Received: 19 May 2015 / Revised: 29 June 2015 / Accepted: 20 July 2015 / Published: 28 July 2015
Cited by 7 | PDF Full-text (655 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, we present the design and evaluation of a software-based wireless power transfer platform that enables the development of a prototype involving various open- and closed-loop power control functions. Our platform is based on a loosely coupled planar wireless power transfer
[...] Read more.
In this paper, we present the design and evaluation of a software-based wireless power transfer platform that enables the development of a prototype involving various open- and closed-loop power control functions. Our platform is based on a loosely coupled planar wireless power transfer circuit that uses a class-E power amplifier. In conjunction with this circuit, we implement flexible control functions using a National Instruments Data Acquisition (NI DAQ) board and algorithms in the MATLAB/Simulink. To verify the effectiveness of our platform, we conduct two types of power-control experiments: a no-load or metal detection using open-loop power control, and an output voltage regulation for different receiver positions using closed-loop power control. The use of the MATLAB/Simulink software as a part of the planar wireless power transfer platform for power control experiments is shown to serve as a useful and inexpensive alternative to conventional hardware-based platforms. Full article
(This article belongs to the Special Issue Wireless Power Transfer)
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Open AccessArticle A Dynamically Adaptable Impedance-Matching System for Midrange Wireless Power Transfer with Misalignment
Energies 2015, 8(8), 7593-7617; https://doi.org/10.3390/en8087593
Received: 8 June 2015 / Revised: 14 July 2015 / Accepted: 15 July 2015 / Published: 27 July 2015
Cited by 19 | PDF Full-text (1299 KB) | HTML Full-text | XML Full-text
Abstract
To enable the geometrical freedom envisioned for wireless power transfer (WPT), fast dynamic adaptation to unpredictable changes in receiver position is needed. In this paper, we propose an adaptive impedance-searching system that achieves good impedance matching quickly. For fast and robust operation, the
[...] Read more.
To enable the geometrical freedom envisioned for wireless power transfer (WPT), fast dynamic adaptation to unpredictable changes in receiver position is needed. In this paper, we propose an adaptive impedance-searching system that achieves good impedance matching quickly. For fast and robust operation, the proposed method consists of three steps: system calibration, coarse search, and fine search. The proposed WPT system is characterized using distance variation and lateral and angular misalignment between coils. The measured results indicate that the proposed method significantly reduces searching time from a few minutes to approximately one second. Furthermore, the proposed system achieves impedance matching with good accuracy. The robust impedance-searching capability of the proposed system significantly improves power transfer efficiency. At 6.78 MHz, we achieve a maximum efficiency of 89.7% and a high efficiency of >80% up to a distance of 50 cm. When the center-to-center misalignment is 35 cm, the efficiency is improved from 48.4% to 74.1% with the proposed method. At a distance of 40 cm, the efficiency is higher than 74% for up to 60° of angular rotation. These results agree well with the simulated results obtained using a lumped-element circuit model. Full article
(This article belongs to the Special Issue Wireless Power Transfer)
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Open AccessArticle An Integrated Chip High-Voltage Power Receiver for Wireless Biomedical Implants
Energies 2015, 8(6), 5467-5487; https://doi.org/10.3390/en8065467
Received: 4 May 2015 / Revised: 25 May 2015 / Accepted: 28 May 2015 / Published: 8 June 2015
Cited by 10 | PDF Full-text (2439 KB) | HTML Full-text | XML Full-text
Abstract
In near-field wireless-powered biomedical implants, the receiver voltage largely overrides the compliance of low-voltage power receiver systems. To limit the induced voltage, generally, low-voltage topologies utilize limiter circuits, voltage clippers or shunt regulators, which are power-inefficient methods. In order to overcome the voltage
[...] Read more.
In near-field wireless-powered biomedical implants, the receiver voltage largely overrides the compliance of low-voltage power receiver systems. To limit the induced voltage, generally, low-voltage topologies utilize limiter circuits, voltage clippers or shunt regulators, which are power-inefficient methods. In order to overcome the voltage limitation and improve power efficiency, we propose an integrated chip high-voltage power receiver based on the step down approach. The topology accommodates voltages as high as 30 V and comprises a high-voltage semi-active rectifier, a voltage reference generator and a series regulator. Further, a battery management circuit that enables safe and reliable implant battery charging based on analog control is proposed and realized. The power receiver is fabricated in 0.35-μm high-voltage Bipolar-CMOS-DMOStechnology based on the LOCOS0.35-μm CMOS process. Measurement results indicate 83.5% power conversion efficiency for a rectifier at 2.1 mA load current. The low drop-out regulator based on the current buffer compensation and buffer impedance attenuation scheme operates with low quiescent current, reduces the power consumption and provides good stability. The topology also provides good power supply rejection, which is adequate for the design application. Measurement results indicate regulator output of 4 ± 0.03 V for input from 5 to 30 V and 10 ± 0.05 V output for input from 11 to 30 V with load current 0.01–100 mA. The charger circuit manages the charging of the Li-ion battery through all if the typical stages of the Li-ion battery charging profile. Full article
(This article belongs to the Special Issue Wireless Power Transfer)
Open AccessArticle Experimental and Numerical Investigation of Termination Impedance Effects in Wireless Power Transfer via Metamaterial
Energies 2015, 8(3), 1882-1895; https://doi.org/10.3390/en8031882
Received: 8 December 2014 / Revised: 16 February 2015 / Accepted: 26 February 2015 / Published: 9 March 2015
Cited by 15 | PDF Full-text (16671 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents an investigation of the transmitted power in a wireless power transfer system that employs a metamaterial. Metamaterials are a good means to transfer power wirelessly, as they are composed of multiple inductively-coupled resonators. The system can be designed and matched
[...] Read more.
This paper presents an investigation of the transmitted power in a wireless power transfer system that employs a metamaterial. Metamaterials are a good means to transfer power wirelessly, as they are composed of multiple inductively-coupled resonators. The system can be designed and matched simply through magneto-inductive wave theory, particularly when the receiver inductor is located at the end of the metamaterial line. However, the power distribution changes significantly in terms of transmitted power, efficiency and frequency if the receiver inductor slides along the line. In this paper, the power distribution and transfer efficiency are analysed, studying the effects of a termination impedance in the last cell of the metamaterial and improving the system performance for the resonant frequency and for any position of the receiver inductor. Furthermore, a numerical characterisation is presented in order to support experimental tests and to predict the performance of a metamaterial composed of spiral inductor cells with very good accuracy. Full article
(This article belongs to the Special Issue Wireless Power Transfer)
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