Proposed Wireless Power Transfer System Research Articles

High efficiency three‐dimensional wireless power transfer system using cylindrical transmitting coil

AbstractThree‐dimensional (3D) wireless power transfer (WPT) is an attractive methodology to improve the charging safety and flexibility of portable electronic equipment and to meet the charging demand brought by the increase of electronic equipment. Herein a 3D WPT system using a cylindrical transmitting coil excited by a single power source is proposed to improve flexibility and efficiency. Specifically, the coil size is designed and the circuit model is analyzed. A method for determining inductor parameters of Inductor‐Capacity‐Capacity compensation is designed to achieve high efficiency. The power transmission performance of the WPT system is validated through an experimental platform. The measured maximum power is more than 50 W, and the maximum DC‐DC efficiency is up to 82.3%. The system can simultaneously charge multiple loads with different receiving coils at different positions. The proposed WPT system can improve the flexibility of equipment charging without control, and provide a reference for the design of portable equipment high efficiency wireless chargers.

Rotation insensitive implantable wireless power transfer system for medical devices using metamaterial-polarization converter

This article introduces an innovative approach for creating a circular polarization (CP) antenna-based rotation-insensitive implantable wireless power transfer (WPT) system for medical devices. The system is constructed to work in the industrial, scientific, and medical (ISM) frequency band of 902–928 MHz. Initially, a flexible, wide-band, and bio-compatible open-ended CP slot antenna is designed within a single-layer human skin tissue model to serve as the receiving (Rx) element. To form the implantable WPT link, a circular patch antenna is also constructed in the free-space to use as a transmitting (Tx) source. Further, a new metamaterial-polarization converter (MTM-PC) structure is developed and incorporated into the proposed system to enhance the power transfer efficiency (PTE). Furthermore, the rotational phenomenon of the Rx implant has been studied to show how the rotation affects the system’s performance. Moreover, a numerical analysis of the specific absorption rate (SAR) is conducted to confirm compliance with safety regulations and prioritize human safety from electromagnetic exposure. Finally, to validate the introduced concept, prototypes of the different elements of the proposed WPT system were fabricated and tested using skin-mimicking gel and porcine tissue. The measured results confirm the feasibility of the introduced approach, exhibiting improved efficiency due to use of the MTM-PC. The amplitude of the transmission coefficient (|S21|\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$|S_{21}|$$\\end{document}) has improved by 6.94 dB in the simulation, whereas the enhancement of 7.04 dB and 6.76 dB is obtained from the experimental study due to the integration of MTM-PC. As a result, the PTE of the proposed MTM-PC integrated implantable WPT system is increased significantly compared to the system without MTM-PC.

USING ARTIFICIAL NEURAL NETWORKS TO IMPROVE THE EFFICIENCY OF TRANSFORMERS USED IN WIRELESS POWER TRANSMISSION SYSTEMS FOR DIFFERENT COIL POSITIONS

This study uses magnetic resonance-based coupling theory to study the various placements of transmitter and receiver coils in wireless power transfer (WPT) systems. Various coil placements are examined to show where high efficiency can be achieved within the air gap. Basic characteristics such as self-inductance, mutual inductance, and coupling coefficient were calculated. Artificial neural networks (ANNs) in WPT are a powerful technique for predicting performance characteristics. Using ANNs provides an excellent method for streamlining the design process and reducing time-consuming calculations. To quickly determine and optimize coil design, this study compares recent research on ANN applications in WPT and the performance of different types of ANNs in WPT systems. An artificial neural network (ANN) was trained to predict the magnetic properties of a wireless power transfer (WPT) device. Appropriate cost functions have been implemented to train the ANN properly. It was shown that the trained ANN can effectively reproduce the data obtained by the finite element method (FEM). The results show an effective power transmission at different coil placements, with decreased efficiency observed after a certain distance. These data will help determine the proposed WPT system's air gap and angular limits.

A reconfigurable wireless power transfer system with constant exciting current for charging multiple batteries

At present, wireless power transfer (WPT) systems with constant current (CC) or constant voltage (CV) characteristics are typically achieved using a single transmitter and single pickup (STSP) configuration, which cannot transfer power to multiple battery loads simultaneously. In this paper, the LCC-LCC/S reconfigurable topology is proposed to realize the CC-to-CV transition for multiple battery loads. An LCC topology is designed on the primary side to achieve a constant current (0.362A) flowing through the transmitting coil to enable independent operation of power pickups. A reconfigurable LCC/S topology is designed on the secondary side to achieve the CC-to-CV transition of the battery loads. The received power from the pickups remains unaffected when pickups are moved in or out or are in different operating modes (CC or CV). The circuit can maintain zero phase angle (ZPA) operation, which greatly enhances the overall power density of the system. Additionally, detailed design process for the compensation parameters on both the primary and secondary sides are provided. Theoretical analysis proves that good system stability and robustness can be obtained in the case of variable quantity of pickups and quality factors of coils. The experimental prototype was built, with the CC value for the battery load designed at 0.7A and the CV value designed at 8 V. Experimental results demonstrate the smooth CC-to-CV transition of the proposed WPT system (with 3 pickups) at a power output of 15.4 W, and the system’s maximum efficiency can reach 75.5 %.

A Novel Impedance Matching of Class DE Inverter for High Efficiency, Wide Impedance WPT System

In high-frequency wireless power transfer (WPT) applications, Class D, E, and F inverters are most widely used. Class DE inverters combine the respective advantages of Class D and Class E inverters. However, the Class DE inverter is sensitive to changes in impedance, which can easily lead to the loss of soft switching characteristics, thereby reducing efficiency. In this paper, an impedance-matching compensation design method is proposed to expand the high-efficiency region of the Class DE inverter by matching impedance and parameters. The effect of the method on the zero-voltage switching (ZVS) characteristic of Class DE inverters is analyzed in detail. The proposed WPT system maintains a constant voltage and zero phase angle by employing PS/PS compensation topology. Theoretical analysis shows that the impedance can be compressed for the design of resonant network impedance, and the method can expand the high-efficiency region with a reasonable choice of parameters to match the phase. Finally, a 500 kHz, 1 kW WPT prototype was constructed with a coupling factor of 0.25–0.4 and a load range of 30–80 Ω. The inverter’s efficiency exceeds 95%, with optimal efficiency reaching 97.3%. The system efficiency is greater than 87%.

Implementation of the irregular pulse density modulation‐controlled wireless power transfer system for constant current and constant voltage output

SummaryIn this paper, irregular 32 pulse density modulation (PDM)‐controlled wireless power transfer (WPT) system is proposed for constant current (CC) and constant voltage (CV) outputs. The proposed WPT system has a load independent ZPA frequency characteristic with CC and CV outputs. Thus, soft switching conditions are achieved for both CC and CV outputs. An experimental prototype was prepared to validate the effectiveness of the proposed irregular 32 PDM‐controlled WPT system. WPT coil design parameters are presented and analyzed with lateral and rotational misalignment conditions in ANSYS. The experiments were determined as 3 A for CC output and 200 V for CV output. The maximum efficiency of the proposed system is measured (95.34%) at aligned coils with 100 mm air gap. In addition, the efficiency results are presented and evaluated by performing experimental studies under both lateral and rotational misalignment conditions.

Power Injection and Free Resonance Decoupled Wireless Power Transfer System with Double-Switch

This article presents a type of power injection and free resonance decoupled wireless power transfer (WPT) system, the double-switch independent power injection and free resonance wireless power transfer (IPIFR-WPT) system working in CCM. Based on the stroboscopic mapping model, the theoretical results show that the operation point of the proposed WPT system is determined by itself instead of the switching control strategy. Specifically, once the voltage on the primary capacitance does not decrease to the input voltage in the free-resonance process, the diode in series would not turn on and the system would not switch to the power injection process. Therefore, there is a wide soft-switching margin to ensure the system operating in soft-switching states. Another characteristic of the proposed WPT system is the monotonicity between output power and operation cycle, which presents a simple power control method. And since the soft-switching margin may have intersection under dynamic coupling coefficient, the proposed system maintains soft-switching states with a fixed switching strategy and presents advantage to resist the dynamic change of coupling coefficient. All the characteristics of the proposed WPT system mentioned above have been verified in both theory and experiment.

Technical and Ecological Limits of 2.45-GHz Wireless Power Transfer for Battery-Less Sensors

Wireless power transfer (WPT) is a possible alternative to batteries for supplying smart sensors. It is often described as “greener" because it avoids the use of batteries. However, this claim usually lacks the proper assessment of the environmental impacts of WPT and is particularly questionable given the poor efficiency of wirelessly transmitting power over a few meters of distance. In this paper, we design and thoroughly optimize a complete state-of-the-art WPT system and compare it to an equivalent battery-powered solution to assess whether it effectively represents an eco-friendly alternative. The proposed WPT system is a 2.45-GHz simultaneous wireless information and power transfer (SWIPT) system with beamforming and a high peak-to-average power ratio waveform for supplying a battery-less passive infrared sensor for room occupancy tracking. The final prototype of the smart sensor consumes 4and can operate in steady state at 5from the remote power head with an overall power transfer efficiency of 17/and can cold-start at 3.5. We carry out a life-cycle assessment (LCA) of the environmental impacts through four indicators, i.e., primary energy demand, global warming potential, terrestrial ecotoxicity, and freshwater consumption. Results show that for a 10-year lifetime, the WPT alternative has at least 5.5 to 10.3× higher environmental impacts than its battery-powered equivalent. This demonstrates the importance of LCA during the design of IoT smart sensors and shows that the use of meter-range 2.45¯/GHz SWIPT should be limited to applications where conventional battery-powered systems cannot be used.

Microwave wireless power transfer system using a dual-dielectric resonator oscillator

Non-radiating wireless power transfer (WPT) systems have found extensive applications in science and technology. This paper reports the design, simulation, and implementation of a compact single-port (DC to RF) WPT system composed of two coupled dielectric resonators (DR). The DR on the transmitter side, in combination with a transistor amplifier and a series feedback circuit, forms a dielectric resonator oscillator for microwave power generation. The DR on the receiver side is coupled to the transmitter DR such that the circuit can be considered as a dual-dielectric resonator oscillator or DDRO. The DDRO is designed for optimum power transfer to the output port. The measured RF output power of the proposed WPT system at 7.5 GHz for a 10 mm spacing between the transmitting and receiving DR is measured to be 13.07dBm at a DC voltage of 3.3 V and a supply current of 32.3 mA, which shows a good agreement with our proposed method of analysis. The available bandwidth at the operating frequency of 7.5 GHz is measured to be 150 MHz which provide a relatively wide bandwidth for simultaneous data transmission.

Wireless Power Transfer for Variable Load, Distance, and Power Division Ratio in a Loosely-Coupled Multiple-Receiver Relay System

This paper proposes a wireless power transfer (WPT) system for variant receiver (Rx) configuration, power distribution ratio, load and distance with multiple relays, each of which is connected to a resistive load. Each Rx relay transfers power to an adjacent Rx and acts as a relay while its local load consumes power. We develop a methodology for the design of wireless power transfer resonators that achieve optimum efficiency for multiple receivers with power distribution ratios, loads, and distances. The WPT configuration is extended to a general m×n, 2-dimensional grid for a large area coverage. A mathematical model of the proposed WPT system is provided, and a multiple-Rx wireless power network using a power inverter serves as a proof-of-concept. Following the design guidelines provided in this paper, experimental examples with variable parameters while delivering a total power of 100 W are discussed. To illustrate the practical applicability of this approach, a demonstration on a consumer display and speaker device is performed.

Concave Ferrite Core for Wireless Power Transfer (WPT)

High-efficiency wireless power transfer (WPT) systems can present a perfect solution for fast-charging autonomous guided vehicles (AGV) to improve working hours in high-tech warehouses. Stationary charging stations reduce separation distance, improving coupling factor and power transfer efficiency. Analysis and design of the WPT system focused on maximum power at the load with a SS compensation circuit to reach high efficiency while applying the theory of power transformers design to maximize the power handleability with the physical dimensions. The proposed concept fits small AGVs. This paper proposes a unique ferrite structure for the transmitter ferromagnetic core. This novel shape introduces horizontal angular misalignment resistance due to the transmitter’s omnidirectional concave disc ferrite core combined with an E-core ferrite at the receiver side. The proposed WPT system can output 200 W at 100 kHz. A realistic 3D model has been designed into a symmetrical equivalent to reducing complexity and computational effort. The visualization of the magnetic flux distribution demonstrated that the proposed design has a better path to flow without concentrating flux in small regions, reducing heating losses.

Semi-Implantable Wireless Power Transfer (WPT) System Integrated With On-Chip Power Management Unit (PMU) for Neuromodulation Application

Miniaturization of the neuromodulation system is important for non-invasive or sub-invasive optogenetic application. This work presents an optimized wireless power transfer (WPT) system integrated with an on-chip rectification circuitry and an off-chip stimulation circuitry for optogenetic stimulation of freely moving rodents. The proposed WPT system is built using parallel transmitter (TX) coils on printed circuit board (PCB) and wire-wound based receiver (RX) coil followed by a seven-stage voltage doubler and a low dropout regulator (LDO) circuit designed in 180 nm standard Complementary Metal Oxide Semiconductor (CMOS) process. A pulse stimulation is used to stimulate the neurons which is generated using a commercially available off-the-shelf (COTS) components based oscillator circuit. The intensity of the stimulation is controlled by using a COTS based LED driver circuit which controls the current through the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> LED. The total dimension of the RX coil is 8 mm × 3.4 mm. The maximum power transfer efficiency (PTE) of the proposed WPT system is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 35% and the power conversion efficiency (PCE) of the rectifier is 52%. The proposed system with reconfigurable stimulation frequency is suitable for exciting different brain areas for long-term health monitoring.

Three-Dimensional Wireless Power Transfer System Using Multiple Orthogonal Resonators for Spatial Freedom

In this paper, the three-dimensional (3D) wireless power transfer (WPT) system using multiple orthogonal resonators for spatial freedom is proposed. The proposed transmitter comprises three orthogonal resonators with a 3D structure. The three orthogonal resonators are positioned on top and bottom of the substrate, and the proposed system has an open box-shaped structure due to the 3D resonators. The proposed WPT system allows power transfer despite the receiver’s lateral and angular misalignment by generating magnetic fields in all directions generated by multiple resonators. For the performance verification, the operating principle of the proposed WPT system is theoretically calculated, and simulated. Also, the power transfer efficiency (PTE) under the lateral and angular misalignment is measured and is compared with the conventional WPT system and WPT system implemented on the two-dimensional plane using the multiple orthogonal resonators. The proposed WPT system achieves a PTE from 46.8% to 71.6% when the receiving resonator is set to 81×51 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> that can be built into the mobile phone, and the charging volume is 201×201×51 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .

A New Transmitting Coil for Powering Endoscopic Capsules Using Wireless Power Transfer

This study focuses on using wireless power transfer (WPT) technology based on magnetic resonant coupling (MRC) to supply electric power to an endoscopic capsule to be used for the direct feeding of specific functions or for battery charging. One of the main limitations of the diffusion of endoscopic capsules is the limited autonomy of the internal battery. The aim of the paper is to present an innovative system to wirelessly power capsules using inductive coupling. Here, a new transmitting coil architecture is proposed to allow the wireless charging of the capsule equipped with a monoaxial receiving coil for any possible geometric position and orientation. The new wearable transmitting coil consists of four rectangular coils with independent excitations, and it is capable of producing a magnetic field in any direction. The obtained results in terms of electrical performance of the proposed WPT system and in terms of in situ electromagnetic physical quantities are compared with the basic restrictions of electromagnetic field (EMF) safety guidelines. The results obtained are very promising, as the proposed WPT configuration can transfer at least 250 mW in a capsule that travels along the entire gastrointestinal tract.

Wirelessly Powered 3-D Printed Headstage Based Neural Stimulation System for Optogenetic Neuromodulation Application

This work presents a miniaturized wireless power transfer (WPT) system integrated with a neuromodulation headstage for duty-cycled optical stimulation of freely moving rodents. The proposed WPT system is built using the commercially available off-the-shelf components (COTS) for the optogenetic neuromodulation system consisting of a bridge rectifier, a DC-DC converter, an oscillator circuit, an LED driver, and a μLED. The total power consumption of the stimulation system is 14 mW which is provided using the WPT method. The WPT system includes a novel transmitter (TX) coil implemented on a printed circuit board (PCB), and a solenoid receiver (RX) coil wrapped around a customized 3-D printed headstage. The proposed TX coil is designed in such a way that the magnetic field all across the TX coil is sufficient to provide the required power to the optical stimulation system that is worn as a headstage by the freely moving rat. The headstage device's dimension is 18.75 mm × 21.95 mm, weighing 4.75 g. The ratio of the weight of the headstage and rat is 4.75:300. The proposed system is able to achieve a maximum overall efficiency of ∼63% at 5 cm separation between the TX and RX coils, where the maximum power transfer efficiency (PTE) of the WPT system is ∼88% and the power conversion efficiency (PCE) of the rectifier is 71.6%. The proposed system with reconfigurable stimulation frequency is suitable for exciting different brain areas for long-term health monitoring.

A Compact 3-D Multisector Orientation Insensitive Wireless Power Transfer System

The power conversion efficiency (PCE) in wireless power transfer (WPT) degrades due to angular misalignment between the transmitter (Tx) and the rectenna (Rx) along the azimuth plane. Therefore, a compact 3-D multisector orientation insensitive WPT system is proposed to address this problem. The optimal number of sectors ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N=8$ </tex-math></inline-formula> ) is determined analytically using patch antenna design equations to mitigate the effects of angular misalignment. In addition, conditions on the receiver antenna radiation pattern are investigated to enhance the performance of the WPT system. Furthermore, the observed conditions are utilized for designing a high gain WPT system at 5.8 GHz with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N=8$ </tex-math></inline-formula> sectors. The proposed WPT system provides uniform power harvesting capability in the azimuth plane and 51.2% higher power harvesting capacity than the patch antenna WPT system.

A Systematic Method for Efficient Wireless Powering to Implantable Biomedical Devices

Wireless power transfer (WPT) technology has played a vital role in the rapid development of biomedical devices. While several single methods to improve WPT efficiency have been reported, the lack of integrality in these single methods limits the effect of the improvements. In this investigation, we analyze the physical process of a typical WPT scenario and find that the high propagation loss consisting of in-tissue attenuation and interface reflection degrades the WPT performance. A systematic method to comprehensively improve WPT efficiency is then proposed. Specifically, a Fresnel zone plate (FZP) is applied against the attenuation of inner biological tissue, and a practical air layer-artificial matching layer (AL-AML) is applied to decrease the reflection on the surface of biological tissue. According to a simulation of possible analytical models, the efficiency is significantly improved when using the proposed method. In an experiment with an implant depth of 20 mm, the proposed systematic method is found to enhance maximum relative received power by 12 dB, with an almost 15-fold increase in efficiency over the conventional system with just a transmitter (Tx) and a receiver (Rx). It is also verified that the improvement in efficiency is greater in the systematic method than in single methods. Also, various misalignment tolerances between the proposed structures and the Rx are determined from the coupling strength of the proposed WPT system. The results of this investigation show the potential of the proposed systematic method for further improvements in WPT efficiency.

Three‐phase wireless power supply system using a matrix converter

AbstractThis paper proposes a three‐phase wireless power transfer (WPT) system with a three‐phase‐to‐three‐phase matrix converter. The proposed system directly converts power from an AC grid to high‐frequency AC for WPT. The three‐phase WPT system with the matrix converter is effectively expands the lifetime of the WPT system. A novel hybrid commutation method, which is suitable for the WPT system with a resonant characteristic, is proposed to avoid the commutation failure of the matrix converter. The strategy of the proposed hybrid commutation is based on an estimation of the current direction considering the resonant characteristics and elimination of commutation in the critical area. The proposed commutation method achieves an AC input‐current total harmonic distortion (THD) of 4.7% with the resonant three‐phase load without a current sensor on the high‐frequency side. Furthermore, the proposed WPT system achieves a system efficiency of 88.2% at a load of 4 kW.

Fine Beam Tracking Using Spatio–Temporal Interpolation in Wireless Power Transfer Systems

The use of transmit beamforming in a radio-frequency wireless power transfer (WPT) system can improve the energy transmission efficiency by concentrating the transmit power in the angle of departure (AoD). Optimal beamforming requires information regarding the AoD or the channel between the transmitter and receiver. A previously proposed WPT system continually estimates the optimal AoD using custom-designed pilot signals, which are known as beam-steered pilot signals and are transmitted periodically at every frame. Herein, we propose a spatio–temporal interpolation technique to improve the accuracy of beam tracking for such a WPT system. Specifically, thin-plate spline interpolation is adopted in the space domain to overcome the limited angular resolution of the beam-steered pilot signals in a three-dimensional channel. In the time domain, polynomial interpolation is performed to track the changing AoD during consecutive frames. Numerical results show that the proposed technique can improve the WPT efficiency as well as the mean square error performance of the beamforming weight vector.

Wireless Power and DATA Transfer to Deeply-Embedded Biosensors in Human Body

The process of transmitting power from one node to another via physical links without using wires is denoted as wireless power transfer (WPT). WPT plays an important role in medical applications for it offers the possibility of avoiding surgical operations during the replacement of embedded batteries in human body. In this paper, a WPT system for transferring power and DATA to deeply embedded biosensors is proposed. The system is designed such that it is capable of powering a biosensor simultaneously with DATA transmission from a transmitting coil located outside the human body at a distance of 100mm from the biosensor node. The simulation results have revealed the reception of a regulated DC voltage at the biosensor node of 1.2V, which is sufficient to charge a rechargeable embedded battery with an average DC current of 1.1mA. The results also reveal that the proposed system has succeeded in the extraction of the transmitted DATA at the biosensor side within a time of 30µs. The transmitter of the proposed WPT system is driven by a Class-E power source, which has accomplished a drain efficiency of 72% at an overall operating power of 6W. The proposed system is designed and verified on PSpice.