Omnidirectional Wireless Power Transfer Research Articles

High-Efficiency Omnidirectional Wireless Power Transfer System

To achieve omnidirectional wireless power transfer (WPT), it is crucial to tune the direction of the total magnetic field from the transmitter (Tx) coils toward the receiver coil (Rx) that can be placed at different positions with respect to Tx. Several methods, such as amplitude modulation, phase-shifting, and frequency modulation, have been proposed to vary the Tx currents, depending on the angular position of Rx, but complex sensing and feedback control systems are required. In this article, we propose an efficient omnidirectional WPT system that is capable of self-tuning the power flow without any feedback from the Rx-side. It only requires a simple Tx current switching rather than complex feedback control system for detecting the Rx position. The proposed system consists of three orthogonal transmitter–repeater (Tx-Rp) channels that deliver power to Rx. In this configuration, the Tx currents are proportional to the mutual coupling between the Rp and Rx in the same channel, which ensures the self-tuning of the optimal power flow through channels. Both theoretical and experimental studies are performed to validate the proposed method. The prototype of the proposed approach enables the Rx to harvest power with almost uniform high efficiency (about 90%) regardless of its angular position.

Self-Tuning Omnidirectional Wireless Power Transfer Using Double-Toroidal Helix Coils

In this article, we suggest and study a novel omnidirectional wireless power transfer (WPT) system based on unusual double-toroidal helix coils. The suggested antenna is a double-helix coil wounded around a torus. It creates two mutually orthogonal magnetic fields. One is toroidal and confined inside the torus, and another one is poloidal and is distributed outside it. The intensities of these two fields can be independently tuned via the geometry of the turns. The coupling coefficients are tailored to ensure high efficiency regardless of the receiver position and orientation, without active circuitry for tuning or control. This topology provides self-tuning functionality which is achieved when the coupling between the transmitter and receiver is minimized while the coupling in the pairs transmitter–repeater and repeater–receiver is strong. The system consists of three transmitter–repeater pairs orthogonal to each other, ensuring omnidirectional functionality. Experimental results confirm self-tunability and high efficiency for any position and orientation of receivers. The proposed double-helix antenna is applicable to different WPT applications where the coupling/decoupling between coils can be freely controlled.

Power stability analysis of three-phase omnidirectional wireless power transfer system based on tripolar pad

Power stability analysis of three-phase omnidirectional wireless power transfer system based on tripolar pad

Planar Omnidirectional Wireless Power Transfer System Based on Novel Metasurface

In this article, we propose a novel metasurface-basedmagnetic coupling resonant wireless power transfer (MCR-WPT) system to realize planar omnidirectional WPT at a mid-range distance. The resonator devices—dielectric-constant disks or planar helixes—are located on both sides of the metasurface, which comprises conducting wires placed in a planar sunburst pattern. Transmission efficiency of >40% is achieved on a circular plane with a diameter of ∼40 cm. In addition, the transfer efficiency is insensitive to the placement of a human hand near the proposed MCR-WPT system. The maximum permissible input powers for the coil and dielectric resonator versions of the proposed MCR-WPT system are 0.83 and 2.56 W, respectively, in compliance with the limit prescribed in the International Commission of Non-Ionizing Radiation Protection guidelines. The proposed design may help realize many potential WPT applications, especially for the desktop wireless charging of household devices, such as mobile phones, tablets, and LED desk lamps.

A Tripolar Plane-Type Transmitter for Three-Dimensional Omnidirectional Wireless Power Transfer

This article proposes a tripolar plane-type (TPT) transmitter enabling three-dimensional (3-D) omnidirectional wireless power transfer (WPT) for consumer electronics, such as mobile phones and tablet computers. The proposed TPT transmitter is a 2-D plan-type structure, but it shows a 3-D omnidirectional power transmitting capability. This structure consists of two crossed bipolar coils and a unipolar circular coil, and the three coils are mutually decoupled naturally. By calculating the magnetic field distribution generated by the TPT transmitter, a 3-D omnidirectional magnetic field can be obtained. Then, a detailed circuit topology based on the inductor-capacitor-capacitor-series compensation networks and full-bridge inverters with phase-shift control is modeled and analyzed. On this base, an excitation current vector modulation strategy based on a targeting magnetic field is designed, which can improve and stabilize the system output power and efficiency. Finally, an experimental prototype is set up to verify the 3-D omnidirectional power transmitting capability of the proposed TPT transmitter and the effectiveness of the designed current vector modulation strategy. Besides, the superiority of the proposed 3-D omnidirectional WPT system is verified by comparison with other methodologies. The experimental results show that the system output power and efficiency are maintained at 61.4–80.6W and 80.7%–85.2% under arbitrary angular misalignment of the receiver.

A wearable metasurface for high efficiency, free-positioning omnidirectional wireless power transfer

We introduce a design principle of metasurfaces that can form any desired distribution of magnetic field for high-efficiency wireless power transfer centered at 200 kHz, which can be used to efficiently charge implanted medical devices. This metasurface can improve the power transfer efficiency for both single-user and multi-user cases by over tenfold compared to those without the metasurface. Our design enables a robust field distribution to the positions of the transmitting and receiving coils, as well as the geometric distortions of the metasurface itself, demonstrating its feasibility as a wearable device. With our design, the field distribution and subsequent power division among the multiple users can be readily controlled from equal distribution to any selective user(s). When incorporating a three-dimensional unit cell of the metasurface, we theoretically demonstrate an omnidirectional control of the field orientation to achieve a high-efficiency wireless power transfer for multiple users.

2D Omni-Directional Wireless Power Transfer Modeling for Unmanned Aerial Vehicles with Noncollaborative Charging System Control

Wireless power transfer (WPT) has been extensively studied from various aspects such as far field and near field, operating frequency, coil design, matched capacitance values, misaligned locations of transmitting and receiving coils, distance variance between them, target loads in the specific locations, environment, and operating conditions. This is due to the usefulness of WPT technology in many applications, including the revolutionary method of auto-recharging of unmanned aerial vehicles (UAVs). This paper presents analytical modeling of a WPT-link with two orthogonal transmitting coils arranged to produce an omnidirectional magnetic field suitable for charging a moving rotating load, maximizing energy transfer without any feedback from the receiving end. To achieve a suitable 2D WPT simulation system, as well as an accurate control design, the mutual coupling values in terms of receiver angular rotation are simulated using Ansys software. Power transfer is maximized by using extremum seeking control (ESC), making use of the input power as an objective function with specific parameter values that represent the WPT model to obtain the results. The results shown are those of the input power transmitted by the transmitting-end coils to a load of an orbiting mobile UAV. Based on the simulation results, the controller can achieve maximum power transfer in 100 µs of duration when the speed of the UAV is close to 314 rad/s.

Magnetic Field Analysis and Excitation Currents Optimization for an Omnidirectional WPT System Based on Three-Phase Tubular Coils

This article proposes an omnidirectional wireless power transfer system for powering up electronic devices inside a tubular structure, which has good received voltage stability (RVS) no matter how the receiving coil self-rotates on its own axis or revolves around the <i>z</i>-axis. Three-phase tubular coils are taken as the transmitter at the primary side, and a circular coil works as the receiver at the secondary side. Based on a three-phase half-bridge inverter and inductor capacitor capacitor-series (LCC-S) compensated topology, the expression of the received voltage is derived. To achieve the best RVS, the rotating magnetic field of the transmitter is modeled theoretically, and the essence of the RVS under angular misalignment of the receiver is analyzed. The phase difference of excitation currents is optimized to achieve the best RVS under two typical connection types of the transmitter. The finite-element method simulations are conducted to obtain the magnetic field distribution and the relationship between the received voltage and rotation angle. Finally, the experimental results show that the received voltage pulsation can be efficiently reduced within &#x00B1;15.6&#x0025; under arbitrary angular misalignment of the receiver.

Load Detection and Power Flow Control Algorithm For an Omnidirectional Wireless Power Transfer System

This article presents a control scheme for an omnidirectional wireless power transfer system. A system architecture is proposed to implement the current amplitude control. To focus power transfer towards targeted loads, a smart detection algorithm for identifying the positioning and orientation of receiver devices based on the input power information is presented. The system efficiency is further improved by a maximum efficiency point tracking function. A novel power flow control with a load combination strategy to charge multiple loads simultaneously is explained. Finally, the proposed control scheme is successfully applied to an example 6.78 MHz omnidirectional wireless charging bowl system. The experimental results confirm the accuracy of the load detection algorithm and validate the power flow control strategy.

Design of Magnetic Structure for Omnidirectional Wireless Power Transfer

Recently, an omnidirectional wireless power transfer (WPT) has attracted attention as a solution to the limitations of free-positioning and mobility of conventional WPT. However, the efficiency of the omnidirectional WPT is reduced due to the low mutual inductance relative to the transmitter size. Therefore, this article proposed an optimal magnetic structure to improve efficiency without increasing the size of the transmitter. Four magnetic structure candidates (spherical, cubical, crossed bar, three-orthogonal plane core) are presented and their performances are compared using finite element analysis software. A Pareto optimal set is selected using a multiobjective optimization design, and the optimal magnetic structure is determined considering the weight of the objective variable and the Tchebycheff distance. The optimal magnetic structure and omnidirectional WPT prototype are built for performance verification. The experimental results are consistent with the simulation results and demonstrate that the optimal magnetic structure improves the efficiency in the three-dimensional space. When the power transmission distance is 150 mm, the system efficiency is improved up to 18.6%.

Resonant Network Design Method to Reduce Influence of Mutual Inductance between Receivers in Multi-Output Omnidirectional Wireless Power Transfer Systems

Many studies have been conducted on multi-output systems that transfer power to multiple receivers in conventional planar-type wireless power transfer (WPT) systems; however, few studies and analyses have taken into account the mutual inductance between receivers in multi-output omnidirectional WPT systems. In this paper, the correlation between the mutual inductance between receivers and the power transfer efficiency (PTE) in a multi-output omnidirectional WPT system is analyzed, and a limitation in terms of a reduction in the PTE with an increase in the influence of the mutual inductance between the receivers is presented. To solve this problem, a resonant network design method is proposed to reduce the influence of mutual inductance between receivers, and appropriate canceling capacitor values are selected using the weighted sum method among multi-objective optimization methods. The proposed method is through simulations and experiments, and it presents the potential for improvement in the problems that occur when transferring power to multiple receivers.

LCCL-LC Resonant Converter and Its Soft Switching Realization for Omnidirectional Wireless Power Transfer Systems

Recently, omnidirectional wireless power transfer (WPT) systems have been studied intensely, due to their improved flexibility as compared to their planar counterparts. The LCCL-LC resonant converter topology is selected due to its current source characteristics in this article. The system frequency is pushed to megahertz (MHz) to increase the spatial charging freedom. In a megahertz WPT system, the reactance of the full bridge rectifier can no longer be neglected; therefore, an analytical model of the full bridge rectifier input impedance is built. Furthermore, zero-voltage switching (ZVS) of the switching devices is essential in reducing the switching loss and noise in a megahertz system. A design methodology of the LCCL-LC circuit is proposed to achieve the ZVS operation in the case of one transmitter and one receiver. Then, the ZVS analysis is extended to the scenario of multiple transmitter coils and one receiver coil. Finally, a 6.78-MHz wireless charging system is built according to the proposed design methodology. Experimental results validate the accuracy of the ZVS analysis, and the ZVS operation is well achieved under different coupling and load conditions. The peak system efficiency of 82% at 5-W output power is achieved.

Power stabilisation scheme design using spatial rotating coil based on magnetic field aggregation

The power fluctuation problem has been a key issue in dynamic wireless power transfer (WPT) systems. In the past research studies, the power fluctuation problem at low-transmission distance has been solved, but existing solutions often involve complex control strategies and cannot realise power stabilisation for dynamic WPT systems under high-transmission distance. As a remedy, the spatial rotating coil design scheme is proposed based on magnetic field aggregation to solve the power fluctuation problem without control strategy for high distance dynamic WPT system. Firstly, the crucial parameters affecting power fluctuations are analysed. Then the relative optimisation backgrounds are introduced. Afterwards, the mechanism of power sag is analysed based on magnetic field analysis. Subsequently, the spatial rotating double D (DD) coil design is proposed inspired by omnidirectional WPT coil, and various different DD coil schemes are optimised utilising magnetic field aggregation method to acquire the optimal scheme. Compared with the original coil scheme, the proposed design scheme improves fluctuation of system mutual inductance without complicated control strategies according to simulation results. Finally, a physical coil system consistent with the simulation system is constructed, which verifies the improvement effect of the proposed scheme and effectively confirm feasibility of the optimal scheme.

Omnidirectional wireless power transfer system with a multidirectional receiver inside a cubic transmitter

Omnidirectional wireless power transfer system with a multidirectional receiver inside a cubic transmitter

Plane-Type Receiving Coil With Minimum Number of Coils for Omnidirectional Wireless Power Transfer

In this article, a novel structure of a receiving (Rx) coil with only two coils, which enables omnidirectional wireless power transfer (WPT) for any type of transmitting (Tx) system, is proposed for the first time. The coil adopts each coils into plane cross-shaped ferrite core, with each leg of the ferrite core intersecting both coils. The intersecting direction of the ferrite core for one coil is identical to that of the other one when it is rotated 90 degrees. It is verified that voltage will be induced on at least one coil with any direction of magnetic flux. With an analysis of circuit diagram, it is shown that a high quality factor of each coil can guarantee an omnidirectional power transfer even when the coupling coefficient between two coils has a nonzero value. A simulation model and an experimental prototype is built to verify the omnidirectional WPT of the proposed Rx coil structure, with loop-type Tx coil as an example among various Tx types. Omnidirectional power transfer capability of the proposed coil was verified with a light emitting diode (LED) load. The superiority of the proposed coil was verified by comparison with other Rx coil structures also.

Analysis and Compensation of Incomplete Coupling for Omnidirectional Wireless Power Transfer

This paper proposes a detailed analysis of the incomplete coupling effect in omnidirectional wireless power transfer systems and a compensation method aiming to improve the transmission performance. Recently, omnidirectional wireless charging technologies have been gradually explored and studied. These charging technologies can transmit power to arbitrary directions in three-dimensional space. However, there are still specific regions where the transmitted power capability dramatically drops to an extremely low level due to the incomplete coupling effect. Accordingly, this paper provides a theoretical analysis and compensation of such an effect. The compensation effectiveness is validated by both a simulation and a 7 W experimental prototype. After the compensation, the transmitted power can be improved by 61% to drive the load in a full range of the space.

Transmitter Coils Design for Free-Positioning Omnidirectional Wireless Power Transfer System

Recently, omnidirectional wireless power transfer systems have been studied intensely due to their improved flexibility when compared with their planar counterparts. In this paper, a novel wireless charging bowl with multiple transmitter coils is proposed to power portable devices. The bowl-shaped transmitter coil is optimized to provide sufficiently strong and nearly uniform omnidirectional field distribution. Inside the bowl, a planar receiver coil can be charged with free-positioning and arbitrary orientation. This unique benefit is particularly attractive for low-power portable devices. In the experiment, the proposed transmitter coils are built and operated at 6.78 MHz. The magnetic field is measured to verify the uniform and omnidirectional magnetic field distribution. The coil to coil efficiency is 85% to 95%. A complete system including the inverter and rectifier stage is implemented. When charging a 5W smart phone receiver, the overall efficiency varies within a range from 68–80% for any possible position.

Design and Analysis of Quasi-Omnidirectional Dynamic Wireless Power Transfer for Fly-and-Charge

This paper proposes and implements a novel quasi-omnidirectional dynamic wireless power transfer (WPT) system using double 3-D coils for drone applications. In the traditional omnidirectional WPT system, the receiver direction is always facing the 3-D transmitter center to maximally pick up the magnetic flux. However, the on-drone receiver normally proceeds horizontal or vertical movements so that it is unable to fully utilize the magnetic flux and result in serious magnetic flux leakage. Thus, by newly proposing the 3-D intermediate coil and artfully aligning specific quadrant of double 3-D coils to the center of the flying area, the proposed WPT system can flexibly and efficiently power the drone in the specific space. Moreover, only one single power source is needed to drive the transmitter coil without using the sophisticated current phase control. Therefore, the proposed system can simultaneously achieve both quasi-omnidirectional WPT and dynamic WPT for the drone so that its flying time can be significantly extended. The theoretical, simulated, and experimental results are given to validate the feasibility of the proposed WPT system.

Angular-Misalignment Insensitive Omnidirectional Wireless Power Transfer

This paper proposes a quadrature-shaped pickup coil, which can realize an angular-misalignment insensitive omnidirectional wireless charging system. Recently, the three-dimensional wireless charging has shown promising prospects for removing the performance deterioration caused by the positional misalignment, which can transfer power to arbitrary spatial objectives. In the conventional design, the strength and the direction of the induced magnetic field can be adjusted by controlling the excitation currents of transmitting coils. However, the existence of angular misalignment caused by the self-rotation of the pickup unit still can result in a sharp decrease of the transmitted power. Accordingly, this paper proposes and implements a novel pickup coil topology to compensate such huge fluctuations in power transfer, which aims to ensure an angular misalignment insensitive omnidirectional wireless charging. Simulated and experimental results are both given to verify the feasibility of the proposed quadrature-shaped topology.

Energy Efficient Data Collection and Directional Wireless Power Transfer in Rechargeable Sensor Networks

This paper studies the scenario of data collection in a rechargeable sensor network (RSN), which is powered by directional wireless power transfer (DWPT). DWPT can overcome the limit of broadcast property of energy waves of omnidirectional wireless power transfer (WPT) by providing directional energy beams with higher antenna gain, therefore, help to promote energy efficiency. We formulate an energy efficiency maximization optimization problem, with buffer and delay constraints and propose a (M + 1)-approximation algorithm, where M is the number of sectors that a power beacon (PB)contains. Simulation results illustrate the benefit of our proposed scheme over the benchmark.