Resonant Coupling Wireless Power Transfer Research Articles

Trends in Wireless Power Transfer: WPT Technology for Energy Harvesting, Mllimeter-Wave/THz Rectennas, MIMO-WPT, and Advances in Near-Field WPT Applications

Wireless power transfer (WPT) technology gained wide recognition over a decade ago following a resonance coupling WPT study conducted by a group at the Massachusetts Institute of Technology (MIT) [1]. WPT was originally proposed by Nicola Tesla at the end of the 19th century [2] based on a study of near-field inductive-coupling WPT and far-field WPT via radio waves. The first patent involving inductive WPT as a wireless charging system was granted in 1894 for the earliest electric vehicle (EV) [3]. Inductive WPT technology is based on a transformer and was commercialized as a wireless charger for an electric toothbrush in 1981 by Panasonic Corporation and as a power source for an integrated circuit (IC) card in 1995 by Sony Corporation. Daifuku Corporation produces many systems for material handling in stockroom and clean room applications [4]. From the 1970s through the 1990s, several research projects on wireless chargers for EVs were undertaken in New Zealand, the United States, and Europe. Advances in microwave technology led to improvements in WPT via radio waves, with many field experiments on microwave power transfer (MPT) conducted from the 1960s through the 1970s by William C. Brown in the United States [4]. The commercialization of RFID at the 920-MHz band started recently, and the proliferation of mobile rechargeable batteries since 2010 accentuates the need for a wireless charger in, e.g., mobile phones, EVs, and sensors for the Internet of Things (IoT).

Design and Implementation of Double‐Sided LCL Variable Compensation Topology of MCR‐WPT System

Aiming at the constant current charging and the constant voltage charging mode of the power battery pack in an electric vehicle, this paper proposes a double‐sided LCL variable compensation topology in a magnetically coupled resonance wireless power transfer system. With the proposed topology, the complexity of the circuit design and control will be simplified. The mathematical model for the double‐sided LCL topology is established using a two‐port network, and the output characteristics of constant current mode and constant voltage mode are studied on. By compensation analysis, the double‐sided LCL topology is improved and designed. The specific parameter configuration method and compensation conversion circuit are developed. Load characteristics analysis of variable compensation topology is given. A MATLAB Simulink simulation model and a prototype were built. Both the simulation results and the experiment results show the validity of the proposed variable compensation topology and parameter configuration method. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Operating characteristics of four‐coil magnetic resonant coupling wireless power transfer under different resonant states

SummaryIn wireless power transfer, the transfer efficiency decreases with the increase of the transfer distance. To improve the power transfer performance, the operating characteristics of a conformal coplanar four‐coil magnetic resonant coupling wireless power transfer system are investigated and analyzed under four different resonant states. Based on the complete equivalent circuit model, the transmission coefficient and the input impendence are calculated. The performance of the systems operated under four resonant states is studied and compared. Also, the origin of the difference is specifically analyzed. The simulation results indicate that the wireless power transfer system operated under State 1, the state where the compensated serial capacitance makes the coils work at the frequency of the maximum Q‐factor, shows the most excellent transfer characteristic among the four resonant states. The transmission coefficient can be well maintained above 0.8 within the transfer distance of 30 cm. Experiment has been carried out for validation, and the result indicates that more power can be delivered to the load for the system operated under State 1.

Research on the Characteristics of Wireless Power Transfer in Non-ferromagnetic Metal Pipe

With the development of various electronics, the way of transmitting energy by wire has brought increasingly negative effects on the operability and convenience of products. As wireless power transfer (WPT) technology requires no transmission lines, it has received increasingly wide attention. Most of the previous research on the technology of magnetic resonant coupling WPT mainly focused on the transmission of energy in the air. This paper establishes the wireless power transfer system model under non-ferromagnetic metallic environment and studies the effect of non-ferromagnetic metallic environment on coil self-inductance L, mutual inductance M and coil resistance R of WPT system. On this basis, the study on the relationship between coil diameter and mutual inductance is carried out for aluminium pipe, and the relationship between coil diameter and diameter of metal pipe at the maximum mutual inductance is fitted. Besides, experimental verification is conducted for the change of mutual inductance between the coils of WPT system in the aluminium pipe, presenting that the actual measurement results of mutual inductance in the aluminium pipe are consistent with the theory.

Adaptive Frequency Tracking Control with Fuzzy PI Compound Controller for Magnetically Coupled Resonant Wireless Power Transfer

Adaptive Frequency Tracking Control with Fuzzy PI Compound Controller for Magnetically Coupled Resonant Wireless Power Transfer

A Misalignment Resilient System for Magnetically Coupled Resonant Wireless Power Transfer

Misalignments between the transmitting and receiving coils of a wireless power system can significantly reduce power transfer efficiency (PTE). In this communication, we propose a novel magnetically coupled resonant wireless power transfer (MCR-WPT) system with good misalignment tolerance for wireless charging applications. Specifically, we employ three interconnected planar coils to form a transmitter that produce multiple paths of magnetic flux linkages and power to the receiver even in angular and lateral misalignment positions. Unlike other methods, no additional control circuits are needed so that the circuit can be easily realized and implemented. A prototype is simulated, fabricated, and tested. It has a wide angular misalignment range of 165° for the PTE of 20% or higher, which is 30% higher than 126° of the conventional system. It also has a wide lateral misalignment range of 180 mm for the PTE of 20% or higher, which is 73% higher than 104 mm of the conventional system. Thus, the proposed system presents a good and simple wireless power delivering system for practical applications in particular in the situations where angular and lateral misalignments occur in various degrees without prior acknowledge.

Frequency drift insensitive broadband wireless power transfer system

The resonant frequency of coils in a four-coil magnetic coupling resonance wireless power transfer (MCR-WPT) system has a direct impact on transfer coefficient. For efficient power transfer, most of the systems operate at high-Q resonant state, causing a narrow bandwidth and reducing the system tolerance to resonant frequency deviation. To deal with the problem, a four-coil MCR-WPT system characterized with broadband performance is investigated. Based on the equivalent circuit, the transfer coefficient and the input impedance are firstly calculated. The transfer characteristic at different resonant frequency under different transfer distances is discussed. By comparing the number and variance of the extreme values of transfer coefficient under different resonant frequencies, the resonant frequency for excellent broadband transmission is determined. To validate the broadband performance, frequency drift caused by capacitance variations is investigated at the resonant frequency of 19 MHz under the transfer distance of 45 mm. The results indicate that the MRC-WPT system generally maintains broadband transmission and the transfer coefficient at the excitation frequency of 19 MHz remains above 0.9 when the resonant frequency is deviated. Experiments have been performed to validate the excellent broadband performance. The results are generally consistent with the simulation analysis.

Frequency Splitting and Transmission Characteristics of MCR-WPT System Considering Non-Linearities of Compensation Capacitors

The frequency splitting phenomenon and transmission characteristics have been research hotspots in the field of magnetically coupled resonance wireless power transfer (MCR-WPT). In this paper, non-linear dynamics theory was innovatively introduced into the research, and non-linear coupled transmission dynamics modelling of the MCR-WPT system was established considering the non-linearities of the compensation capacitor. The mechanism of the frequency splitting phenomenon of the MCR-WPT system was revealed through systematic mathematical analyses based on the modelling. The analysis results showed that the system usually has dual natural frequencies which are low resonance frequency and high resonance frequency. Based on non-linear dynamics theory, the transmission characteristics of the system with different non-linear parameters were discussed comprehensively in relation to the modelling. The results of the numerical simulations and theoretical analyses showed that non-linear parameters can cause the jumping phenomena with the output responses, and the output responses in the vicinities of the lower resonance frequencies were extremely sensitive to changes in the coupling coefficient. According to analyses of the linear and non-linear systems, the energy transmissions performed in the vicinity of the high resonance frequency had a wider working frequency band and a better transmission stability under non-linear conditions.

Design and Optimization of Magnetic Coupled Resonant Wireless Power Transfer System at Weak - coupling Region

Frequency splitting is one of the hot topics in the research of magnetic coupling wireless power transfer technology. Its purpose is to improve the transmission efficiency by eliminating the frequency splitting at the over-coupled region of the system. Frequency splitting does not occur at the weak coupling region. The transmission characteristics of the system in weak-coupled region are also of research significance. The mathematical model of the system’s transmission characteristic was established by equivalent circuit theory. Several key factors that affect the transmission characteristics of the system, self-inductance of the coil, mutual inductance between the coils, load resistance and so on, were obtained. A magnetically coupled resonant wireless power transfer system is designed and A method of coil design is proposed. The transmission efficiency of the system at the weak-coupling region was improved by optimized the design of the coil. Simulation and experimental results had good consistency. The results show that the transmission performance of the system at the weak-coupling area was improved.

Design and development of wireless power transfer system for implantable cardioverter defibrillator

Wireless power transfer system is playing an important role in biomedical applications by transferring power wirelessly to the implants present in the body. In this paper, magnetic coupling resonance wireless power transfer system is used to recharge battery of implantable cardioverter defibrillator. The proposed system operates at 300 KHz frequency. The LCC-C compensation topology is used to tune the coils for operating the system at stable resonant frequency and to obtain higher efficiency. In this paper, we have investigated the performance of different coil structures in multiple layer configurations and we offer recommendations on the best suitable configuration for effective transfer of power.

Transfer characteristics of the MCR-WPT system using two series transmitting coils

PurposeThe impedance compensation approaches have been adopted to achieve the maximum output power and transfer efficiency in many magnetic coupling resonance wireless power transfer projects. However, it remains a challenge to obtain the constant output power and transfer efficiency in a fixed-frequency mode during variations in transfer distance and orientation of the coils. In this paper, using two series transmitting coils to achieve the constant output power and transfer efficiency is used.Design/methodology/approachFirst, the circuit model is established and transfer characteristics are studied. Second, using the two series transmitting coils to achieve the constant output power and transfer efficiency is investigated. Finally, the experimental system is designed; it can optimize the transfer performances by itself; the constant output power and transfer efficiency are achieved in the fixed-frequency mode.FindingsWhen the receiving coil moves between the two series transmitting coils, the tolerance of the output power and transfer efficiency is less than 5 per cent.Research limitations/implicationsWhen a receiving coil is placed between the two series transmitting coils, there are space limits. The receiving coil only shifts between the two transmitting coils.Practical implicationsHowever, the rail guide vehicle may achieve constant output power and transfer efficiency when it moves on the rail guide. So, this topology may provide a practical solution.Originality/valueIn this research, the three-coil MCR-WPT system including two series transmitting coils is presented. In a fixed-frequency mode, the constant output power and transfer efficiency is achieved in experiments during variations in transfer distance and orientation of the coils. The fluctuation of the output power and transfer efficiency is less than 5 per cent.

Strategy of Topology Selection Based on Quasi-Duality Between Series–Series and Series–Parallel Topologies of Resonant Inductive Coupling Wireless Power Transfer Systems

Series–series (SS) and series–parallel (SP) topologies are widely used in resonant inductive coupling wireless power transfer systems for various applications. However, the selection of an appropriate topology to achieve higher output power or higher efficiency is typically difficult because design optimization of the circuit parameters (e.g., characteristic impedance, load resistance, and mutual inductance) for each topology is generally separately discussed using different equivalent circuits with multiple resonance modes. Therefore, the purpose of this study involves proposing a simple strategy to select an appropriate topology. The proposed strategy is based on quasi-duality between the SS and SP topologies that are elucidated from the novel equivalent circuits derived using Lagrangian dynamics. Based on the quasi-duality, the output power and efficiency of the SP topology are calculated via the equivalent circuit of SS topology. Thus, the quasi-duality offers a simple comparison between the SS and SP topologies. The proposed strategy selects an appropriate topology by comparing only the equivalent ac load resistance, which is the ac resistance including the rectifying circuit and the load resistance, the characteristic impedance, and the ac load resistance that achieves the maximum efficiency or maximum output power of the SS topology. Experiments verify the appropriateness and effectiveness of the proposed strategy.

Robust beamforming optimization for magnetic resonance coupling wireless power transfer systems

Magnetic Resonance Coupling (MRC) wireless power transfer (WPT) is a promising technique for portable devices and Internet of Things applications, which can transfer power to energy-constrained terminals in mid-range with relatively high efficiency. To enhance the transfer performance, by applying more coils in transceivers, multiple-input single-output (MISO) MRC-WPT system has attracted much attention in recent years. In this paper, a MISO MRC-WPT system with multiple transmitters (TXs) and a single receiver (RX) is studied and its robust magnetic beamforming problem is investigated. The optimal robust beamforming design of the currents of TXs is investigated to maximize the power received by RX with the mutual inductance error between TXs and RX, whereas the total power required is less than a certain value and each TXs has a certain limited transmitting power. By using certain transformation techniques, the optimization problem is converted into a relaxed semidefinite programming (SDP) problem which can be solved efficiently. We further prove that the solution of the relaxed SDP problem is always rank-one, which indicates that the relaxation is tight, and the optimal solution for the problem was obtained. Numerical results demonstrate that the proposed beamforming design can achieve up to 97% transfer efficiency by reducing the measurement errors.

Optimal Position of the Intermediate Coils in a Magnetic Coupled Resonant Wireless Power Transfer System

Coaxial coil topology is used as the transfer medium in traditional MCR-WPT (Magnetic Coupled Resonant Wireless Power Transfer) systems to improve the transfer characteristics. The intermediate coils are added to extend the transmission distance, whose positions are critical. This paper focuses on the optimal intermediate coil positions for an MCR-WPT system with four coaxial planar circular spiral coils. By modeling the MCR-WPT system, the mathematical expression of the self-inductance and the mutual inductance are used to calculate the load power of the MCR-WPT system, which is composed of four planar circular spiral coaxial coils, and using MATLAB. The optimal distance ratio between the adjacent coils for maximizing the power of load is proposed. Furthermore, the experiments are implemented from the network analyzer and the experimental platform. In the platform, the load power is measured at the different intermediate coil positions, and the optimal position at which the load power is maximized is found. Both experimental results obtained by the network analyzer and the experimental platform have validated the theoretical and simulation results and provided the correctness of the suggested ratios.

Rotor Field Oriented Control of Resonant Wireless Electrically Excited Synchronous Motor

In order to solve the problems of wear and spark of the brush and slip ring in an electrically excited synchronous motor (EESM), based on the principle of magnetic resonance coupling wireless power transfer (MRC-WPT), a resonant wireless excitation system of EESM is designed. By modeling the EESM and analyzing the rotor field oriented control (RFOC) method, a control system of the resonant wireless EESM (RW-EESM) is established. Furthermore, the stator current distribution strategy is analyzed. Finally, a test of the RE-EESM prototype is carried out. The test results show that the motor can realize no-load stable operation, and the test speed is maintained at 85 r/min. The results show that the wireless excitation scheme of EESM is feasible, and the RFOC of RW-EESM motor is reasonable.

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.

Magnetic resonance coupling for 5G WPT applications

Inductive Wireless Power Transfer (IWPT) is the most popular and common technology for the resonance coupling power transfer. However, in 2007 it has experimentally demonstrated by a research group from Massachusets Institute of Technology (MIT) that WPT can be improved by using Magnetic Resonance Coupling Wireless Power Transfer (MRC WPT) in terms of the coupling distance and efficiency. Furthermore, by exploiting the unused, high-frequency mm-wave band which are ranging from 3~300 GHz frequency band, the next 5G generations of wireless networks will be able to support a higher number of devices with the increasing data rate, higher energy efficiency and also compatible with the previous technology. In this work, a square planar inductor with the dimension of 6.1 x 6.1 mm is designed, and the resonators have the same self-resonance frequency at 14 GHz. The coil resonators have been laid on Silicon and Oxide substrate to reduce the loss in the design. From the CST software simulation and the analytical model in MATLAB software, it has been shown that the MRC WPT design has improved the performance of IWPT design by 40% power transfer efficiency. MRC WPT design also has larger H-Field value which is 705.5 A/m, as compared to the IWPT design which has only 285.6 A/m when both Transmitter(Tx) and Reciever(RX) is at 0.3 mm coupling distance.

Receiving‐coil structure reducing stray AC resistance for resonant coupling wireless power transfer

Resonant inductive coupling wireless power transfer is widely known to be a possible convenient power supply method for the small mobile apparatus. However, the limited receiving-coil size tends to lower the efficiency and limit the output power owing to the small mutual inductance and comparatively large stray alternating current (AC) resistance of the receiving-coil. This study mitigates this issue by proposing a novel receiving-coil structure. This proposed structure comprises a coil and a drum core with a thin axis. The coil is wound on the axis to form a single winding layer. The proposed structure can reduce stray AC resistance by suppressing the proximity effect and reducing the wire length without deteriorating the mutual inductance significantly. Therefore, better efficiency and larger output power can be achieved. Simulations and experiments were performed to verify the proposed structure. Consequently, both simulations and experiments supported the reduction in AC resistance compared to the conventional structure. Furthermore, the experiment revealed improvements by the proposed structure in both efficiency and output power. These results support the effectiveness of the proposed structure for wireless power transfer to small mobile apparatus.

Omnidirectional magnetic resonant coupling wireless power transfer system with a cubic spiral transmitter

Though impressive advances of the extension of effective working distance for magnetic resonant coupling wireless power transfer system have been made over past decades, their applications have been severely limited by the requirement of unidirectional coaxial distribution for the transmitter and receiver. In this paper, an omnidirectional magnetic resonant coupling wireless power transfer system is proposed. The cubic spiral transmitter requires only a single power source, and the receiver receives power in all directions. The power transfer efficiency of the system is derived through an equivalent circuit model. And an impedance matching circuit which includes a pair of parallel and series capacitors is proposed for better stability and higher efficiency. In addition, geometrical parameters of the single power driven spiral transmitter structure are optimized to improve distribution uniformity for different directions. Thus the power transfer efficiency of the system, which depends on the distance between the transmitter and the receiver, is almost the same for different receiving angles. Finally, the theoretical analysis is verified by practical experimental results, which shows the power transfer efficiency of 60% at 150 mm.

A Resonant Capacitive Coupling WPT-Based Method to Power and Monitor Seat Belt Buckle Switch Status in Removable and Interchangeable Seats

<div class="section abstract"><div class="htmlview paragraph">In this study, we present an intelligent and wireless subsystem for powering and communicating with three sets of seat belt buckle sensors that are each installed on removable and interchangeable automobile seating. As automobile intelligence systems advance, a logical step is for the driver’s dashboard to display seat belt buckle indicators for rear seating in addition to the front seating. The problem encountered is that removable and interchangeable automobile seating outfitted with wired power and data links are inherently less reliable than rigidly fixed seating, as there is a risk of damage to the detachable power and data connectors throughout end-user seating removal/re-installation cycles. The present study tackles this issue through outfitting three removable and interchangeable rear seat assemblies with resonant capacitive coupling wireless power transfer as to power each rear seat across a variable gap between the interior paneling and that side of the seat closest to the interior paneling. A fundamental design challenge this system presented was the need to develop a rugged method to account for different sizes of seating, and hence to accommodate variable wireless power gaps. This issue was addressed via use of impedance matching technology to present a nearly constant load impedance to the dc-to-radiofrequency power inverter. The wirelessly received power enabled additional electronics added to the rear seat assemblies to wirelessly communicate the seat belt buckle states to a central hub where it was displayed via a custom graphical interface. Our approach involved the visibly imperceptible integration of resonant capacitively-coupled transmitting and receiving antennae behind the interior paneling for the transmitter and underneath the outer fabric of the rear seating. The resulting subsystem demonstrated the ability to power both the seat belt buckle switches and wireless communication over a range of wireless power gaps.</div></div>