Magnetic Resonance Wireless Power Transfer Research Articles

Research on Frequency Tracking of Magnetic Coupled Resonant wireless Power Transmission System

In order to solve the problem that the magnetic coupling resonant WPT system with SS compensation structure causes a decrease in transmission efficiency when it is detuned, the resonant state of the system is tracked by detecting the output voltage of the transmitting coil inverter and the coil current of the receiving coil. Phase difference is converted into dc voltage signal with phase discriminator, ADC module is used to sample dc signal, PID algorithm is used to track resonance frequency of the system, 90° phase difference is taken as expected value of PID algorithm, and 90° phase shift is indirectly realized by digital method. The experiment shows that the resonant frequency tracking method is effective.

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.

Effects of Number of Relays on Achievable Efficiency of Magnetic Resonant Wireless Power Transfer

In magnetic resonant wireless power transfer (WPT), relays are placed between a transmitter and a receiver as a means of increasing both the operating distance and the power transfer efficiency, but this makes the analysis of the WPT system more complicated. In this letter, we derive a mathematical expression for the power transfer efficiency with an optimal load resistance based on an equivalent circuit model, and analyze the effects of varying the number of relays on the power transfer efficiency that can be achieved. By means of circuit-level simulations and experiments under a variety of scenarios, we verify the accuracy of our analysis, and we also confirm that there is an optimal number of relays for maximizing the achievable power transfer efficiency for a given end-to-end distance.

Optimal Design of a 3-Coil Wireless Power Transfer System for Deep Micro-Implants

This paper presents a design methodology for a 3-coil magnetic resonance wireless power transfer (WPT) system with a long transfer distance (up to 20 cm) and a small implanted receiver (RX) (2mm in diameter) at a specific frequency. The methodology aims to find out the optimal value of dimensional parameters (i.e., coil diameter, gap interval and coil turn number) of the transmitter (TX) coils to maximize the magnetic field strength at the target distance while keeping the coil self-resonant frequency (SRF) twice of the target operational frequency. Firstly, the circuit model of the TX circuits is developed, which include a single-turn coupling coil and a multi-turn primary coil. Secondly, the co-dependences between the dimensional parameters are analyzed, which shows the dominant factors and secondary factors of each dimensional parameter, and how the optimal values of dimensional parameters are changed by these factors. Based on the analysis, design flow of the TX circuit is proposed to decide the optimal values of dimensional parameters given the transfer distance, source voltage, operational frequency and wire diameter. Using the design flow, optimal values of dimensional parameters are predicted for 20-cm transfer distance and 16-cm transfer distance and are verified with finite element analysis (FEA) software COMSOL Multiphysics. With the optimal TX design, the power received by a 2-mm ferrite core solenoid RX is calculated. At 20 cm transfer distance, up to 4.3 mW can be achieved in air, and 0.8 mW can be achieved in conductive human tissue.

무선전력 전송효율 음영영역 제거와 최대효율 전송을 위한 3D 스캐닝 MR-WPT 시스템

This paper proposes a 3D scanning magnetic resonance wireless power transfer system to eliminate dead-zones and improve transmission efficiency. This system consists of an oscillator, power amplifier, microcontroller unit, personal computer, pan-tilt motor, transceiver coil, rectifier, and wireless communication units. This system provides the maximum voltage to the receiver within a short timeframe using the zone-based maximal transmission efficiency searching process algorithm. From the measurement results, it can be observed that the time to find the maximum transmission efficiency with this algorithm is 11 times faster than that of the full scan by 5° and that the position error of maximum transmission efficiency is less significant.

Modeling and Design of a Transmission Coil and Four Cascaded Receiving Coils Wireless Charging Structure With Lateral Misalignments

Magnetic resonance wireless power transfer (WPT) is an emerging technology that may create new applications for wireless power charging. However, the mutual inductance fluctuations resulting from lateral misalignments are the major factors hindering the promotion of this technology. In this paper, a structure of a transmission coil and four cascaded receiving coils for wireless charging systems is proposed to suppress fluctuations in mutual inductance with lateral misalignments. The mathematical model of the proposed structure with lateral misalignments is built based on the equivalent circuit method. The expressions of the output voltage and the efficiency are then derived by solving the system equivalent equations. In addition, a method of compensation capacitance is proposed to suppress the effect of the cross-coupling mutual inductance on the voltage and efficiency. The primary advantage of the proposed structure is that the sum of the mutual inductances between the receiving coils and the transmission coil is nearly constant with lateral misalignments. Therefore, the output voltage and efficiency can also be kept nearly constant by using the proposed structure with lateral misalignments. Simulation and experimental results validating the proposed method are shown.

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.

Simultaneous Magnetic Resonance Wireless Power and High-Speed Data Transfer System With Cascaded Equalizer for Variable Channel Compensation

Wireless power transfer (WPT) systems can potentially provide simultaneous power and data transfer for Internet-of-Things devices, such as smart speakers, glasses, and watches. However, due to the high quality factor of coils, the intrinsically narrow WPT channel bandwidth severely limits the data transmission capability of the system, especially for data downloading links requiring higher data rates. In addition, the channel bandwidth varies with power transfer distances, which is also undesirable for wireless communication. In this study, the channel features of a two-coil series–series matching magnetic resonance wireless power and data transfer (MWPDT) system, including the bandwidth and the roll-off slope are characterized analytically. Based on the characterization results, a receiver front-end circuit with a three-stage cascaded equalizer (EQ) is proposed and implemented to extend the bandwidth of a MWPDT system at different distances. The proposed EQ can provide a frequency response with a variable roll-up slope from 10 to 45 dB/dec to compensate for the distance-dependent channel response of an MWPDT system. A complete MWPDT system is built and tested to verify the performance of the proposed method. Experimental results demonstrate that the data rates can be extended from 650, 500, and 350 kbps to 850, 700, and 650 kbps at 0.4, 0.5, and 0.6-m distances, respectively. The highest data rate extension ratio is 85% at a transmission distance of 0.6 m, which is 2.4 times the radii of the coil employed in the system.

자기공진 무선전력전송 수신부용 이중 대역 CMOS 정류기 IC 설계

자기공진 무선전력전송 수신부용 이중 대역 CMOS 정류기 IC 설계

Magnetic Resonance Wireless Power Transfer Over 10 m With Multiple Coils Immersed in Seawater

An autonomous underwater vehicle (AUV) is used for exploring marine resources and monitoring infrastructure facilities. Because an AUV is powered by batteries, it needs to be lifted out of the water to have them replaced or recharged. Thus, wirelessly feeding power to an AUV under the sea would improve the efficiency of marine activities. However, it is difficult to wirelessly power an object under the sea because seawater has high conductivity. We examine the electromagnetic field in lossy materials such as a conductor, a coil cover, and seawater. We design a wireless magnetic resonance-based power transfer system with multiple coils using bandpass filter (BPF) theory. The coil structure is sealed so that water cannot enter it. We perform experiments on this system completely immersed in seawater and measure the coil coupling coefficient, efficiency, and wattage. The results confirm wireless power transfer exceeding a distance of 10 m in an undersea setting. We verify the transmission efficiency by changing the receiving-coil position on the central axis of the transfer coils. Furthermore, we confirm a dependence on transfer on the order of 1 to 100 W.

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.

Comparative Analysis of Frequency-Selective Wireless Power Transfer for Multiple-Rx Systems

In this article we describe a comparative study of the frequency-selective wireless power transfer (WPT) by considering two different configurations, Tx-Rx-Rx and Rx-Tx-Rx, in a multiple-receiver system. In this system, the receivers have different resonant frequencies and a transmitter can select a driving frequency to transfer power. Using an ECM, we analyze the power transfer efficiency (PTE) and the power distribution according to the variation of the driving frequency. We also find the achievable PTE (η max ) and the maximum power division ratio (α max ) in numerical terms for both configurations. The analysis and experimental results provide insightful information for understanding the effects of the arrangement of the resonators on η max and α max by comparison with the magnetic-resonant WPT, where the resonant frequencies of all the receivers are the same as the driving frequency. We find that the Rx-Tx-Rx configuration is generally more useful for distributing the power to the receivers than the Tx-Rx-Rx configuration, for both frequency-selective and magnetic-resonant WPT. In addition, the frequency-selective WPT enables a more adaptive power distribution than the magneticresonant WPT in the Rx-Tx-Rx configuration while maintaining η max . We further verify that the results of the analysis are in accordance with the measured values, by means of experiments conducted in a variety of environments.

Effect of Vertical Metal Plate on Transfer Efficiency of the Wireless Power Transfer System

Power transfer efficiency is an important issue in wireless power transfer (WPT). In actual applications, the WPT system may be exposed to a complex electromagnetic environment. The metal which is inevitably or accidentally close to the system will impact the power transfer efficiency. Most previous research has aimed at the effect of the metallic sheet paralleled to the resonant coil. This paper focuses on the effect of the metallic plate perpendicular to the resonant coils. Firstly, based on the theoretical analysis, a simulation model is setup using COMSOL Multiphysics. The efficiencies of the double-coils magnetic resonant WPT system with the presence of the parallel and vertical aluminum plate are studied comparatively. Efficiency improvement is observed with the vertical plate while the reduction appeared with the presence of the parallel plate. The vertical metallic plate has shown a magnetic field shielding effect according to the magnetic field distribution. It can reduce the radial magnetic field and enhance the axial magnetic field. Then, the effects of the position and size of the vertical plate are studied. It is found that the transfer efficiency has a preferable improvement when the vertical aluminum plate with a larger size is placed between the resonant coils and near outer edge of the windings. Finally, the experiment is carried out to verify the effect of the vertical aluminum plate on the WPT system.

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.

Impact of non-ideal waveforms on GaN power FET in magnetic resonant wireless power transfer system

GaN field-effect transistors (FET) have low conduction and switching losses in high-frequency (>MHz) resonant wireless power transfer systems. Nevertheless, such systems impose a unique stress on GaN FETs owing to their non-ideal voltage waveforms. In this work, we report the observed non-ideal behavior in a 6.78 MHz magnetic resonant wireless transfer system that employs class-D GaN power amplifiers. The non-ideal waveform phenomenon existing at the output of the power amplifier is explained. The study analyzes the causes of this phenomenon, including the coupling coefficient k of the coil, the DC input voltage of the amplifier, and the load on the receiver. Each parameter is simulated and analyzed using LTspice. The influence of the phenomenon on the on-state resistance of the GaN device is proved in an experimental measurement, and the cause of the phenomenon is explained. The study combines a theoretical simulation and an experimental test to discuss the effect of this phenomenon on GaN power devices and proposes the corresponding solutions, which include the limitation of voltage, current, and power of the system, thermal management, and other protection measures.

Maximizing Received Energy in Magnetic Resonance Wireless Power Transfer Using Feedback

This paper considers the effect of variation of load resistance, as a function of the amount of charged energy in battery, in magnetic wireless power transfer. We calculate load resistance as a function of time, and show that load resistance increases as the receiver acquires energy over time. Unlike the previous studies that considered the resonance frequency of transmitter and receiver as a fixed value, so that it remains unchanged once it has been set, it is shown that the resonance frequency changes as load resistance varies. To avoid performance degradation due to the unmatched resonance frequencies between transmitter and receiver, we employ feedback from the receiver. Considering the cost of feedback, there is a trade-off between the number of feedbacks that the receiver sends and the collected energy at the receiver. For a point-to-point system model, the optimal feedback interval that maximizes the received energy is found. The numerical results show that the proposed protocol collect more energy compared to the conventional magnetic wireless power transfer systems.

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.

Nonlinear Modeling and Harmonic Analysis of Magnetic Resonant WPT System Based on Equivalent Small Parameter Method

The magnetic resonant wireless power transfer (WPT) system with a class E inverter has wide application in mid-range power transmission, especially for several megahertz scenario. However, it is cumbersome for the existing modeling and analysis methods to obtain the analytical solution to the system variables, which limits the evaluation of system characteristic. This paper proposes a nonlinear mathematical model for the WPT system with a class E inverter. The equivalent small parameter method (ESPM) is first adopted to solve the proposed six-order nonlinear model, and symbolic-form steady-state periodic solutions are yielded. During the whole solving process, only three iteration steps are needed for the proposed method. Compared with other existing modeling and analysis methods, the symbolic periodic results acquired by the ESPM exhibit sufficient accuracy by virtue of the combination of more higher harmonics. Meanwhile, the calculation complexity is simplified remarkably. Simulation and available experiments validate the effectiveness and accuracy of the proposed method.