Robust Beamforming for Secured Wireless Power Transfer in MIMO Magnetic Resonant Coupling System:A Probabilistic Approach

Wireless power transfer(WPT) to support mobile and portable devices is an emerging wireless technique.Among all kinds of approaches,magnetic resonance coupling(MRC) is an excellent one for mid-range WPT,which provides better mobility,flexibility,and convenience due to its simplicity in hardware implementation and longer transmission distances.In this paper,we consider an MRCWPT system with multiple power transmitters,one intended power receiver and multiple unintended power receivers.We investigate the probabilistic robust beamforming designs and provide efficient algorithms to achieve the local optimums under two different criteria,i.e.,total source power minimization problem and min-max unintended receiving power restriction problem.As the problems are quite typical in robust design situations,our proposed robust beamformers can be conveniently applied to other probabilistic robust design problems,thus reduce the complexity as well as improve the beamforming performance.Numerical results demonstrate that the proposed algorithms can significantly improve the performance as well as the robustness of the WPT system.

New Progress of Magnetically-coupled Resonant Wireless Power Transfer Technology

近些年,无线电能传输技术受到了越来越广泛的关注。作为一种中等距离无线电能传输技术,自从美国麻省理工学院于2007年发表其研究成果后,磁耦合谐振式无线电能传输技术就成为了研究热点问题。该文在对无线电能传输技术进行总体介绍的基础上,主要对磁耦合谐振式无线电能传输技术进行概括论述。首先分析了磁耦合谐振式无线电能传输技术的基本结构和工作原理,介绍了目前运用于分析该技术的主要理论;接着对该技术目前的传输水平和热点问题进行了分类阐释,主要分为传输特性、新材料的应用、干扰问题和实际应用,介绍了目前的研究现状;最后在当前研究热点问题的基础之上,对该技术有待研究的问题以及发展趋势进行了展望。

Theoretical Design of Energy Harvesting Module or Wireless Power Transmission Receiver Using Magnetic Field of 0.2 mT at 60 Hz

This paper presents a theoretical design method for a magnetic energy harvesting module. This module consists of an air-core coil and resonant capacitor. With a simple RLC circuit model, it can derive an equation of harvesting energy as a function of coil size. In order to demonstrate the magnetic field, a uniform magnetic field is generated by the developed coil system. From the experimented results, it is successfully demonstrated 100 mW of energy harvesting from a magnetic field of 0.09 mT at 60 Hz. This value is in good agreement with the estimated results. Harvested energy is proportional to the square of the magnetic flux density. However, ICNIRP2010 provides a guideline that an acceptable level for human health in a public space is 0.2 mT at power-line frequency. This paper also discuss the possibilities of several applications related with both magnetic energy harvesting and wireless power transmission.

Wireless Power Feeding with Strongly Coupled Magnetic Resonance for a Flying Object

Wireless power feeding was examined with strongly coupled magnetic resonance for an object moving in 3-D space. Electric power was transmitted from the ground to an electrically powered toy helicopter in the air. A lightweight receiver resonator was developed using copper foil. High Q of greater than 200 was obtained. One-side impedance matching the transmitter side was proposed to cope with high transmission efficiency and the receiver’s weight reduction. Results show that the efficiency drop near the ground was drastically improved. Moreover, the measured efficiency showed good agreement with theoretical predictions. A fully equipped helicopter of 6.56 g weight was lifted up with source power of about 5 W to an altitude of approximately 10 cm.

Intelligent Reflecting Surface Assisted Transmission Optimization Strategies in Wireless Networks

Wireless Power Transfer(WPT)technology can provide real-time power for many terminal devices in Internet of Things(IoT)through millimeterWave(mmWave)to support applications with large capacity and low latency.Although the intelligent reflecting surface(IRS)can be adopted to create effective virtual links to address the mmWave blockage problem,the conventional solutions only adopt IRS in the downlink from the Base Station(BS)to the users to enhance the received signal strength.In practice,the reflection of IRS is also applicable to the uplink to improve the spectral efficiency.It is a challenging to jointly optimize IRS beamforming and system resource allocation for wireless energy acquisition and information transmission.In this paper,we first design a Low-Energy Adaptive Clustering Hierarchy(LEACH)clustering protocol for clustering and data collection.Then,the problem of maximizing the minimum system spectral efficiency is constructed by jointly optimizing the transmit power of sensor devices,the uplink and downlink transmission times,the active beamforming at the BS,and the IRS dynamic beamforming.To solve this non-convex optimization problem,we propose an alternating optimization(AO)-based joint solution algorithm.Simulation results show that the use of IRS dynamic beamforming can significantly improve the spectral efficiency of the system,and ensure the reliability of equipment communication and the sustainability of energy supply under NLOS link.

Numerical Analysis of Magnetic-Shielding Effectiveness for Magnetic Resonant Wireless Power Transfer System

Magnetic radiation phenomena appear inevitably in the magnetic-resonance wireless power transfer （MR-WPT） system, and regarding this problem the magnetic-shielding scheme is applied to improve the electromagnetic performance in engineering. In this study, the shielding effectiveness of a two-coil MR-WPT system for different material shields is analyzed in theory using Moser＇s formula and Schelkunoff＇s formula. On this basis a candidate magnetic-shielding scheme with a double-layer structure is determined, which has better shielding effectiveness and coils coupling coefficient. Finally, some finite element simulation results validate the correctness of the theoretical analysis, and the shielding effectiveness with the double-layer shield in maximum is 30？dB larger than the one with the single-layer case.

Wireless Power Transmission into Metallic Tube Using Axial Slit for Infrastructure Diagnostics

Wireless power transfer (WPT) using a metallic tube with axial slits was attempted to demonstrate WPT using magnetic resonance coupling to the diagnostics infrastructure. The transmission efficiency was measured at various distances using the transmission and receiver resonator in the tube. Furthermore, the transmission and receiver resonator were set respectively outside and inside of the tube. Experiment results were assessed computationally using the finite-difference time-domain (FDTD) simulation. As a result, the transmission efficiency of the transmitter and receiver resonators in the metallic slit tube was higher than that of the case without a metallic tube in the range of the normalized transmission-distance of x/d > 0.4. In the simulation, the current density on the metallic tube around both transmitter and receiver coil were connected. These results reveal that the slit on the tube plays a role of the relay coil.

双耦合SP-S补偿紧凑型抗偏移WPT系统

在无线电能传输(wireless power transfer,WPT)系统中,偏移是不可避免的,偏移会引起系统参数的变化从而影响系统的传输性能。基于S-S和P-S补偿拓扑,提出一种具有抗偏移特性的双耦合SP-S补偿的紧凑型WPT系统。该系统采用两个同轴布置、相互解耦的圆角方形线圈作为能量的发射线圈,其与单一方形接收线圈均有耦合,提升了X方向和Y方向的抗偏移容忍度。通过谐振参数配置使接收线圈在偏移的过程中,一个线圈回路的输出增加,另一个线圈回路输出减少,从而使系统输出随接收线圈位置偏移波动平缓。提出方形解耦线圈结构参数的设计方法,并分析发射端并联补偿电容对输出抗偏移性能的影响。最后,搭建实验平台验证该方法的有效性与系统的抗偏移能力。

电动汽车多车位WPT下沉式磁屏蔽系统研究

在电动汽车无线电能传输系统中,实现高效传输的同时减少磁泄漏一直是一个技术挑战。针对这一问题,本文提出了一种应用于多无线电能传输系统的下沉式屏蔽线圈结构,该结构在减小目标面漏磁的同时不会影响系统的传输效率。首先,提出了一种基于矢量磁位的矩形线圈磁场计算方法,通过此方法对系统目标面漏磁进行分析,为后续的磁泄漏优化提供了理论依据;其次,介绍了一种漏磁优化的方法,运用该方法得到满足要求的各线圈参数,为实现高效的无线电能传输提供了关键支持;最后,根据得到的线圈参数,研制了一套带磁屏蔽结构的双车位电动汽车无线充电系统,通过仿真和实验,让提出的屏蔽结构和方法的有效性得到了充分证实。结果显示,当系统输出功率恒定在4 kW时,所提出的屏蔽结构不仅使目标区域最大泄漏磁场降低了25%,且传输效率高达95%。

基于交互式设计超材料建模与分析的MCR-WPT效率提升研究

超材料具有特殊的磁场调控能力,被广泛关注并应用于磁耦合谐振无线电能传输(MCR-WPT)领域,但寻求针对特定领域目标需求的超材料设计具有挑战性.目前,超材料的一般设计方法为S参数反演法和等效电路法,设计流程通常需要多次建模仿真得到目标参数,该过程较为繁琐耗时.对此,深入分析上述两种设计方法的特性并将二者结合,采用HFSS与MATLAB软件交互设计和优化用于MCR-WPT特性提升的超材料,有效简化了超材料的设计过程.以无线电能传输效率优化为目标设计方形和Koch两种超材料单元,分析对比两种单元的电磁特性.搭建工作频率为6.78 MHz的MCR-WPT系统实验平台,探究两种超材料对传输效率的影响.实验结果表明,方形超材料和Koch超材料分别实现了28.4%和24.6%的最大传输效率提升,证明了交互设计可以更简便地设计超材料并且用于无线电能传输系统传输效率的提升.

基于等效阻抗的分数阶RLC_(α)串联谐振BD-WPT系统传输特性分析

针对谐振式无线电能传输系统中分数阶电感、电容元件的仿真实现困难的问题,采用等效阻抗实现分数阶电容的等效.基于分数阶电容的阻抗特性,给出了一种分数阶RLC_(α)串联谐振双向无线电能传输(bidirectional wireless power transfer,BD-WPT)系统结构,通过建立含分数阶电容的串联谐振式双向无线电能传输系统的电路模型,推导了其传输功率和效率关系.仿真实验结果表明,与整数阶串联谐振系统相比,系统的输出功率提升了7.82%,传输效率提升了0.58个百分点.

基于SAR阻抗匹配的WPT最大效率跟踪控制方法

无线电能传输(WPT)技术因其安全、便捷、非接触等优点而备受关注。最大效率传输是WPT系统中一个重要课题。传统的最大效率跟踪方法通常设定系统在固定耦合条件进行负载阻抗匹配,然而,耦合系数会在初级和次级线圈相对位置变化时不可避免地发生变化。提出基于耦合系数辨识与半有源整流(SAR)阻抗匹配的最大效率跟踪控制方法,该方法利用SAR结合耦合系数识别进行阻抗匹配,开关控制电容(SCC)补偿其阻抗虚部,避免了整流电路中非线性因素的影响。同时系统响应较快且控制方法便于实现。仿真和实验结果表明,耦合系数和等效负载变化时,都可以准确估计耦合系数并跟踪至最大效率点和输出恒压。

Mid-Range Wireless Power Transfer and Its Application to Body Sensor Networks

It has been reported that, through the evanescent near fields, the strongly coupled magnetic resonance is able to achieve an efficient mid-range Wireless Power Transfer (WPT) beyond the characteristic size of the resonator. Recent studies on of the relay effect of the WPT allow more distant and flexible energy transmission. These new developments hold a promise to construct a fully wireless Body Sensor Network (wBSN) using the new mid-range WPT theory. In this paper, a general optimization strategy for a WPT network is presented by analysis and simulation using the coupled mode theory. Based on the results of theoretical and computational study, two types of thin-film resonators are designed and prototyped for the construction of wBSNs. These resonators and associated electronic components can be integrated into a WPT platform to permit wireless power delivery to multiple wearable sensors and medical implants on the surface and within the human body. Our experiments have demonstrated the feasibility of the WPT approach.

Advances in Inductively Coupled Power Transfer Technology for Rail Transit

Traditional power supply method for moving electric railway vehicles is based on contact type power collection technology.This sometimes cannot meet the requirements of modern rail transportation.A new wireless power transfer(WPT)technology can offer significant benefits in modern rail transportation particularly in some stringent environments.This paper reviews the status and the development of rail transit power supply technology,and introduces a new challenging technology--inductive power transfer(IPT)technology for rail transit.Tesla established the underpinning of IPT technology and creatively and significantly demonstrated power transfer by using highly resonant tuned coils long time ago.However,only in recent years the IPT technology has been significantly improved including the transfer air-gap length,transfer efficiency,coupling factor,power transfer capability and so on.This is mainly due to innovative semiconductor switches,higher control frequency,better coil designs and high performance material,new track and vehicle construction techniques.Recent advances in IPT for rail transit and major milestones of the developments are summarized in this paper.Some important technical issues such as coupling coil structures,power supply schemes,segmentation switching techniques for long-distance power supply,and bidirectional IPT systems for braking energy feedback are discussed.

基于平衡阻抗的MC-WPT系统传导干扰抑制方法

抑制电磁干扰(electromagnetic interference,EMI)以提升电磁兼容性是磁耦合无线电能传输系统推广应用中必须解决的关键问题。该文以传统LCC-S型磁耦合无线电能传为研究对象,针对阻抗不平衡和寄生参数造成的传导干扰问题,提出EMI滤波器和谐振补偿网络的融合拓扑。文中分析传统LCC-S型MC-WPT系统传导干扰的产生机理及传输通道特性,给出融合拓扑的设计方法,并通过实验验证该文所提出的拓扑对EMI抑制的有效性。在搭建的85 kHz/500 W实验系统中,该文提出的融合拓扑的线圈共模干扰电流相比于传统LCC-S型拓扑降低35.6 dB,在特定频率点的线圈差模干扰电流降低23.6 dB;在输入侧的共模和差模传导干扰分别降低约30 dB和10 dB。该文所提出的融合拓扑及其设计方法也可推广应用至其他谐振类型的MC-WPT系统中。

磁耦合WPT系统中的线圈特性仿真分析

针对磁耦合谐振无线电能传输系统的性能问题,提出利用互感耦合理论分析及Maxwell软件建模相结合的方法,探索线圈结构参数及位置对系统传输效率的影响。首先,运用互感耦合理论对磁耦合谐振无线电能传输系统进行理论分析,得到系统传输效率与耦合因数k的理论关系。然后利用Maxwell软件实现对互感线圈的建模与仿真,得到线圈结构参数以及一定范围内任意发射线圈的空间位置对系统传输性能的影响。根据仿真结果分析得出在一定范围内匝数、线径、内径的增加,系统的性能会得到幅度逐渐降低的提升。当线圈同时发生水平和垂直偏移时,较小偏移量情况下,垂直偏移对系统的性能影响更大。发生较大偏移量时,水平偏移对系统的性能影响更大。

全方向WPT系统磁耦合参数识别方法研究

全方位三激励WPT系统中接收端和发射端之间的磁耦合参数是影响系统传输效率的重要因素,对耦合参数进行有效地辨识是使全方位WPT系统达到最大效率的关键。在采用高频逆变器作为发射线圈激励源的情况下给出逆变输出电压各次谐波的数学描述,在移相角为π/3的条件下忽略谐波,将输出的方波电压用波形具有标准正弦形状的基波来近似替换。在此基础上推导出系统发射端电流有效值的数学模型,引入改进的遗传算法,将参数辨识问题转换为全局寻优问题,给出基于该模型的磁耦合参数辨识方法,并通过仿真及实验验证了所提方法的可行性及有效性。

基于WPT技术的超高压输电线路监测设备供电系统的研究

根据要求,500 kV及以上输电线路必须装设在线监测设备,从而很好地辅助维护人员及时了解输电线路的实时状态。为保证在线监测设备在各种情况下高效运行,需要配备一套稳定、可靠、抗干扰能力强的供电系统。立足无线电能传输(Wireless Power Transmission,WPT)技术,并遵循国家倡导的绿色电网理念,提出一种射频取电无线电能传输技术,并围绕该技术的原理、设计展开论述,以期优化超高压输电线路监测设备的供电方式,进一步保障对超高压输电线路的实时监测,推动超高压输电线路的稳定运行。

Transfer efficiency optimal control of magnetic resonance coupled system of wireless power transfer based on frequency control

In order to suppress the fast decrease of the transfer efficiency of magnetic resonance coupled wireless power transfer system(MRCWPTS) with distance increase,this paper investigates the impact factors of the system transfer efficiency and is,then formulates a new efficiency optimal control method based on frequency control.Based upon this control method two optimal control schemes are designed to achieve transfer efficiency control of the system.Simulations and experiments show that the proposed efficiency optimal control method can effectively stabilize the system transfer efficiency in a certain range so as to successfully solve the subtle issue of transfer efficiency variation with distance.

一种新型WPT二次侧谐振补偿拓扑

为了提高无线电能传输的距离,解决低耦合系数时传输功率、效率低的问题,提出一种新型二次侧谐振补偿拓扑。本文分析了系统交流阻抗特性与电路模型,采用该结构的二次侧等效为串联谐振,且具有更大的谐振Q值。给出了输出电压增益与效率的表达式,并与传统串联谐振结构进行对比。仿真和实验数据表明,相比较传统的二次侧串联谐振结构,本文所提出的结构在低耦合系数下传输增益和效率具有明显优势,更加适合于弱耦合应用。