Resonant Wireless Power Transfer Research Articles

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.

A Fractional-Order Resonant Wireless Power Transfer System With Inherently Constant Current Output

Wireless power transfer (WPT) using magnetic-coupling resonant has been proved to be a promising transmission method. At present, most of the existing resonant WPT systems adopt integer-order inductors and capacitors. In fact, in addition to integer-order components, there also exists fractional-order inductors and capacitors, which possess richer characteristics than integral-order inductors and capacitors. However, there are few studies on the application of fractional-order components in resonant WPT system. Therefore, this paper proposes a fractional-order resonant WPT system, which is based on a fractional-order resonant circuit only incorporating a fractional-order capacitor. The coupled-mode theory model of the proposed WPT system is established, and the impact of different loads and orders on transfer characteristics is explored. The theoretical analysis demonstrates that the proposed system can achieve constant current output that is independent of load, just by choosing appropriate parameters of the fractional-order capacitor. Finally, an experimental prototype of the fractional-order resonant WPT system is built, and the experiment results verify the correctness of the theoretical analysis.

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.

Energy-Concentrating Optimization Based on Energy Distribution Characteristics of MCR WPT Systems With SS/PS Compensation

Spatial energy distribution characteristics (EDCs) as well as power and efficiency should be considered to ensure the electromagnetic safety of people nearby when analyzing some magnetically coupled resonant wireless power transfer systems, which is difficult for circuit theory. In this article, we first propose an energy-concentrating effect (ECE) of unit transmitting active power (TAP) based on the EDCs of the system with series-series/parallel-series compensation, and we find that the area integral of the active power density on the infinite plane perpendicular to the transmission direction between the coils equals the TAP of the system, which is consistent with the result obtained by circuit theory. Several couplers are designed and optimized based on the ECE. Simulation and experimental results reveal that the optimized inner-outer ring (IOR) and disc-coil couplers increase the ECE by 10% and 32%, respectively, compared with the original spiral-coil coupler. Furthermore, the electromagnetic exposure of the human body in the same position around the three couplers indicates that the maximum induced electric field and specific absorption rate in the human body around the optimized IOR and disc-coil couplers are substantially decreased, and thus the two couplers increase the maximum allowable TAP of the system from 297 to 379 W and to 700 W.

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.

Single-Stage Regulated Resonant WPT Receiver With Low Input Harmonic Distortion

Resonant rectifier topologies would be a promising candidate for achieving simple, compact, and reliable single-stage wireless power transfer (WPT) receiver if not for the lack of good DC regulation capability. This paper investigates the problems that prevent the feasibility of single-stage DC regulation in resonant rectifier topologies. A possible solution is the proposed differential resonant rectifier topology, of which the rectifier is designed to have a relatively constant AC voltage, and that phase shift control is used to achieve relatively good output regulation. Design considerations on the reactive component sizing, magnetic component design, frequency and phase synchronization, small signal modelling, and closed-loop feedback control design, are discussed. Experimental results verified that the proposed WPT receiver system can achieve single-stage AC rectification and DC regulation while attaining the key features of low harmonic distortion in its AC output voltage, continuous DC current, and zero-voltage-switching (ZVS) operation over a wide operating range.

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.

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

Green wireless power transfer system for a drone fleet managed by reinforcement learning in smart industry

The optimal management of a fleet of drones is proposed in this paper for providing connectivity to sensors and actuators in Industrial Internet of Things (IIoT) scenarios. The persistent mission without any human intervention on the battery charge is obtained by means of an on-field wind generator supplying a charge station that adopts resonant wireless power transfer. The objective of the fleet management is to provide the best connectivity over the time considering the variability of both the bandwidth request and the wind energy availability. The optimal management is performed by a system controller adopting reinforcement learning (RL) for deciding the number of drones to take off and, consequently, the instantaneous provided bandwidth. A constant charge time of drone battery represents a key element of the system because this enables to strongly reduce the complexity of the system controller task. To this purpose, an adaptive current control for the charge station is introduced to compensate charge time variabilities due to the coupling factor changes caused by misalignments that can occur between a pad and a drone. The results have highlighted that the RL provides good performance improvement in case of green generation. An important aspect arose from this study is the ability of RL to increase the saved energy even if it is not considered as a target of the controller.

Output Voltage Range of a Power-Loaded Series–Series Compensated Inductive Wireless Power Transfer Link Operating in Load-Independent Regime

The article proposes an in-depth analysis of a series-series compensated resonant inductive wireless power transfer (WPT) link, operating at load-independent frequency while feeding a power load. It is shown that due to the presence of equivalent series resistances in practical systems, a load-independent operation point is only an approximation. The output voltage is still affected by the load, obtaining minimum and maximum values under rated load and no-load operation, respectively. While the output voltage value under rated load is typically well predicted by the commonly used first-harmonic-approximation-based equivalent circuit, the latter is unsuitable for obtaining the output voltage value under light loading due to nonlinearity caused by the discontinuous conduction mode of the secondary. Time-domain analysis is, therefore, used to accurately predict the WPT output voltage value under zero-load operation and accurately derive the expected WPT output voltage range in the load-independent regime. Simulations and experiments based on a 400-V 1-kW WPT link demonstrate excellent matching, validating the proposed analysis.

Patterned Magnetic Fields for Remote Steering and Wireless Powering to a Swimming Microrobot

Common digestive and lung disorders such as stomach problems and pleural emission pose serious difficulties for patients who undergo open surgeries wherein a wirelessly powered swimming microrobot has the potential for minimally invasive missions from diagnosis to drug delivery and surgery. However, remote steering toward an arbitrary destination is yet a challenge to existing microrobots. Here, a resonant wireless power transfer system is incorporated into an array of planar coils to generate spatio-temporal patterns of magnetic fields on an untethered swimming microrobot. As shown, this generates an effective Lorentz force on the microrobot's power receptor coil. Automated switching of the array current creates a traveling magnetic pattern that enables smooth microrobot steering and controls its velocity. This eliminates the need for embedded magnets and shielding materials that suffer from nonlinear characteristics. The microrobot's function is validated by an in vitro experiment that mimics the anatomy of the stomach filled with fluid at a centimeter range underneath the skin. Our microrobot with a mass of 7 g is able to reach the velocity of 0.45 mm/s in a controlled direction by applying a small peak magnetic field of 2.15 mT at 96 kHz. The propelling force is proportional to the square of the total magnetic field's intensity and can be enormously increased depending on the application. Compared to microrobots with similar dimensions, this method results in a 50-fold increased ratio of propelling force to applied magnetic energy, which is suitable for carrying heavier payloads to farther locations.

Using uniform magnetic field to obtain the constant output power and transfer efficiency for MCR-WPT

Purpose This paper aims to find an approach that achieves constant output power and transfer efficiency in an open space, such as charging pads. Design/methodology/approach In this study, a topology of the five-coil system including two transmitting coils is presented. Also, in a fixed-frequency mode and an open space, this study focuses on the two transmitting coils to achieve the uniform magnetic field and ultimately, attain the constant output power and transfer efficiency. Findings In a fixed-frequency mode and an open space, the constant output power and transfer efficiency is then achieved in experiments by inserting the relay loop into the uniform magnetic field. Practical implications An approach that achieves constant output power and transfer efficiency in an open space. The topology of the five-coil magnetically coupled resonant-wireless power transfer (MCR-WPT) system shows prospective value for various applications, which could be used at designing of wireless battery charger dedicated for cars or mobile phones. Originality/value By comparing the simulation and experimental results, the topology can be optimized in the transmission performance by itself. By doing so, the constant output power and transfer ef?ciency are achieved in the constant frequency mode.

Text Mining for Patent Analysis to Forecast Emerging Technologies in Wireless Power Transfer

Governments around the world are planning to ban sales of vehicles running on petroleum-based fuels as an effort to reduce greenhouse gas emissions, and electric vehicles surfaced as a solution to decrease pollutants produced by the transportation sector. As a result, wireless power transfer technology has recently gained much attention as a convenient and practical method for charging electric vehicles. In this paper, patent analysis is conducted to identify emerging and vacant technology areas of wireless power transfer. Topics are first extracted from patents by text mining, and the topics with similar semantics are grouped together to form clusters. Then, the process of identifying emerging and vacant technology areas is improved by applying a time series analysis and innovation cycle of technology to the clustering result. Lastly, the results of clustering, time series, and innovation cycle are compared to minimize the possibility of misidentifying emerging and vacant technology areas, thus improving the accuracy of the identification process and the validity of the identified technology areas. The analysis results revealed that one emerging technology area and two vacant technology areas exist in wireless power transfer. The emerging technology area identified is circuitries consisting of transmitter coils and receiver coils for wireless power transfer, and the two vacant technology areas identified are wireless charging methods based on resonant inductive coupling and wireless power transfer condition monitoring methods or devices.

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.

Single-Switch-Regulated Resonant WPT Receiver

A single-switch-regulated wireless power transfer (WPT) receiver is presented in this letter. Aiming at low-cost applications, the system involves only a single-switch class-E resonant rectifier, a frequency synchronization circuit, and a microcontroller. The number of power semiconductor devices required in this circuit is minimal. Only one active switch is used and no diode is required. As a single-switch solution, this simplifies circuit implementation, improves reliability, and lowers hardware cost. The single-switch resonant rectifier provides a relatively constant quasi-sinusoidal voltage waveform to pick up the wireless power from the receiver coil. Due to the resonant nature of the rectifier, ZVS turn on and turn off are achieved. The steady-state analysis and discussions on the component sizing and the control design are provided. A prototype is built and experimental works are performed to verify the features.

Cross Interference Minimization and Simultaneous Wireless Power Transfer to Multiple Frequency Loads Using Frequency Bifurcation Approach

Simultaneous power distribution to multiple loads using a single source in the wireless power transfer (WPT) system is a challenging issue due to cross-coupling between the load coils, which reduces the power transfer efficiency. In a resonant WPT system, when two or more coils operated under over coupled condition, the original operating resonant frequency gets bifurcated, and thereby reduction in the power transfer efficiency. Different techniques are investigated in the literature to mitigate the frequency bifurcation phenomena in the resonant WPT system. However, the utilization of frequency bifurcation approach for the simultaneous power transfer to multiple loads is not addressed. This paper proposes a simultaneous power transfer approach using frequency bifurcation for the multiple load system designed with different operating frequency. Mathematical, simulation, and experimental studies performed for dual, triple, and four coil WPT systems with multiple loads. In addition, an automatic power flow control method is implemented to estimate the load current from the source, which helps to select a new set of load coils to be charged. The experimental results confirm the proposed power transfer, helps to attain higher power transfer efficiency of 39.34%, 49.31%, 68.22% and cross interference of −31.2 dBV, −36.2 dBV, −41.2 dBV for dual, triple, and four coil WPT system, respectively.

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.