Wireless Power Transfer Technology Research Articles

Uncertainty Quantification of Human Electromagnetic Exposure From Electric Vehicle Wireless Power Transfer System

With the rapid development of electric vehicles (EVs), the wireless power transfer (WPT) technology of EV is becoming more and more mature. The safety of human electromagnetic exposure caused by the WPT system of EV has become the focus of research. Considering the practical application of EV WPT system, this paper studies the electromagnetic exposure of human body based on the uncertainty quantification theory. A sparse polynomial chaos expansion method is used to establish the surrogate model of the mean value of some human organs’ SAR, and the probability distribution function of SAR is calculated. The Sobol is used to quantify the impact of relevant variables on SAR. The final calculation results show that when the person is on the side of the EV, the offset between the magnetic coupling coils of the WPT and the lateral displacement of the human body on the side of the EV have a greater impact; When a person is at the rear of the EV, the vertical displacement of the magnetic coupling coils of the WPT has a greater impact on the longitudinal displacement of the human body at the rear of the vehicle. Combined with the above analysis, this paper can provide reasonable suggestions for the safety protection of electromagnetic exposure of human body in the WPT of EVs.

Three-stage fuzzy-metaheuristic algorithm for smart cities: Scheduling mobile charging and automatic rule tuning in WRSNs

Recent breakthroughs in wireless power transfer technology have been promising for empowering and enabling seamless operation of wireless sensors and developing sustainable systems such as wireless rechargeable sensor networks (WRSNs). Relying on this technology and focusing on WRSNs, this paper proposes an adaptive charging scheduling algorithm called the three-stage fuzzy metaheuristic algorithm (TSFM) by using the whale optimization algorithm (WOA) and a multiobjective function designed to meet the application requirements of WRSNs in smart cities. The TSFM algorithm benefits from the WOA for the automated configuration and optimization of the fuzzy rule-base table in a three-stage fuzzy inference system for clustering, routing, and scheduling mobile charging simultaneously. Unlike the other methods, the TSFM algorithm determines the ratio of effect of fuzzy input parameters of every stage based on application and environment in addition to considering effective parameters for every stage, especially for charging scheduling (e.g., the energy of a charge-request node, the distance between a charge-request node and a mobile charging (MC), the density of a charge-request node, the average energy consumption rate of a charge-request node, and the time elapsed after a charge request). Furthermore, for the proper distribution of energy in a network, better responsiveness, and optimal use of a charging robot, two energy thresholds are defined in the TSFM algorithm, namely as the charging request issue threshold and the charging operation completion threshold. The TSFM algorithm is adaptable to applications, environments, and requirements of WRSNs not only by using the features of nodes (as the fuzzy input parameters) but also by considering the application-specific features, environments, and infrastructure (e.g., network size, number of nodes, base station (BS) positions, and designer’s goals) within the process of optimizing tunable parameters. The TSFM algorithm was evaluated and compared with some common methods such as FCFS, NJNP, and ESS in terms of functional metrics such as energy utility, charging latency, survival rate, death rate of nodes, system stability, number of packets received by BS, number of request nodes, number of alive nodes, average residual energy, adaptability analysis, and statistical validation in two scenarios and six applications. According to the simulation results, the proposed TSFM algorithm improved the performance criteria and outperformed the other methods by far in terms of application. For instance, the TSFM algorithm improved the minimum system stability rate by 167%, 0.73%, and 123% compared with FCFS, NJNP, and ESS methods, respectively.

Efficiency Optimization of Wireless Power Transfer System for Electric Vehicle Based on Improved Marine Predators Algorithm

Electric vehicle (EV) is the core part of future automobile technology, and safe and reliable wireless power transfer (WPT) technology is the key link to improve the intelligent driving technology of EV. In this paper, the uncertainty quantification method is proposed to guide the optimization design of WPT structure, so as to improve the efficiency of WPT. First this paper establishes a surrogate model of WPT efficiency based on the adaptive sparse polynomial chaos expansion, and the uncertainty of EVs WPT transmission efficiency is quantified, the computational efficiency is improved by about 8.4 times. Then the surrogate model is combined with the global sensitivity analysis method to quantify the impact of different variables in WPT on efficiency and screen out the variables with greater impact. Finally, this paper uses the improved marine predators algorithm to optimize the selected WPT system structure parameters. Considering the uncertainty, the average efficiency of the optimized WPT system is increased from 73.43% to 94.64%. Compared with other optimization methods, it proves that the method in this paper can optimize WPT more efficiently, and significantly improve the transmission efficiency.

A Double-Receiver Compact SCC-WPT System With CV/CC Output for Mobile Devices Charging/Supply

The single capacitance coupled wireless power transfer (SCC-WPT) technology facilitates improving the spatial freedom of the system to offer charging/supply services in two-dimensional planar. This paper proposes a double-receiver SCC-WPT system with three-plate compact coupler to achieve free-position charging and superior system performance. The system consists of two independent receivers: one receiver adopts the LCLC-S topology to achieve constant-voltage (CV) output, while the other adopts the LCLC-M topology to achieve constant-current (CC) output and did not affect each other. By circuit analysis, a simplified equivalent circuit of the three-plate coupler is established and, on this basis, the CV and CC characteristics are theoretically analyzed. The effectiveness of the proposed system is verified by building a prototype system, where the coupler and parameters are designed and optimized. The experimental results show that the two receivers can realize CV output and CC output, respectively. The output characteristic of each receiver is almost unchanged when another receiver is removed or moved in. The receiver can obtain stable output power at any position within the transmitting plate.

Load Current Control of One Pulsewidth Modulation for Dynamic Wireless Power Transfer System Using Vehicular AC Current Estimation

A wireless power transfer (WPT) system has been considered applicable to various charging applications. Dynamic WPT technology for EVs limits communication speed and capacity due to the separation of assemblies between the ground and vehicle sides. It is challenging to communicate signals synchronized with the transmission frequency at the same timing. Hence, the system that controls the power only by the vehicle itself is necessary for the sake of safety. This paper proposes a dynamic WPT system in which only the vehicle-side assembly acquires a synchronized signal and controls the load current to the battery. The theoretical analysis concludes that an input voltage derives an output ac current as a constant, and the one-pulse-width modulation for a converter changes a load current. A feed-forward control method of its current estimation is proposed. The bench system is designed, constructed, and tested to verify the effectiveness of the proposed method compared with the proportional-integral control in a static state. Furthermore, the system is also verified when in motion. The load current was limited to the maximum value of the system in areas where the coupling coefficient is high, while the current value was well controlled in the other areas.

Coil-based Wireless Power Transfer for Implanted Pacemakers: A Brief Review

Nowadays, implanted permanent pacemakers (PPM) users need to undergo periodic pacemaker replacement surgery. The surgery is needed since the pacemaker's battery is usually depleted in 5-10 years. This surgery, although poses relatively low health risks, is inconvenient for PPM users. Moreover, the surgery can still be dangerous for PPM users, especially considering that most of the users are elderly. PPM replacement surgery is also costly. In addition to the costs of the surgery itself, the PPM users need to bear the price of the new PPM every time they undergo surgery. Currently, when the PPM's battery runs out, the whole PPM needs to be replaced. This is conducted to prevent the possibility of a leak in the battery seal, which might allow the body fluids to enter the PPM. Typically, once a battery is inserted into the PPM, it will be permanently sealed along with all other electronic components, and thus, battery-only replacement is impossible. Thanks to the recent advancement of wireless power transfer (WPT) technology, a PPM replacement surgery might no longer be necessary in the near future. This article presents a brief review of the current state of coil-based WPT technology and its potential applications in pacemakers. Depending on the load and transmission distance, a recent WPT system for PPM could achieve WPT efficiency as high as 97.91% on air and 78% on pig tissue medium. In terms of output power, recent works that we have summarized showed that they are able to transmit power up to 5W on a WPT system implemented on a human phantom. We also discuss the challenges, limitations, and future prospects for WPT in the medical field, particularly for PPM applications.

Multi-Dimensional Resource Allocation for Throughput Maximization in CRIoT with SWIPT

To solve the power supply problem of battery-limited Internet of Things devices (IoDs) and the spectrum scarcity problem, simultaneous wireless information and power transfer (SWIPT) and cognitive radio (CR) technology were integrated into the Internet of Things (IoT) network to build a cognitive radio IoT (CRIoT) with SWIPT. In this network, secondary users (SUs) could adaptively switch between spectrum sensing, SWIPT, and information transmission to improve the total throughput. To solve the complicated multi-dimensional resource allocation problem in CRIoT with SWIPT, we propose a multi-dimensional resource allocation algorithm for maximizing the total throughput. Three-dimensional resources were jointly optimized, which are time resource (the duration of each process), power resource (the transmit power and the power splitting ratio of each node), and spectrum resource, under some constraints, such as maximum transmit power constraint and maximum permissible interference constraint. To solve this intractable mixed-integer nonlinear program (MINLP) problem, firstly, the sensing task assignment for cooperative spectrum sensing (CSS) was obtained by using a greedy sensing algorithm. Secondly, the original problem was transformed into a convex problem via some transformations with fixed-power splitting ratio and time switching. The Lagrange dual method and subgradient method were adopted to obtain the optimal power and channel allocation. Then, a one-dimensional search algorithm was used to obtain the optimal power splitting ratio and the time switching ratio. Finally, a heuristic algorithm was adopted to obtain the optimal sensing duration. The simulation results show that the proposed algorithm can achieve higher total system throughput than other benchmark algorithms, such as a greedy algorithm, an average algorithm, and the Kuhn–Munkres (KM) algorithm.

Frequency-hopping mechanism and control method for nonlinear parity-time-symmetric wireless power transfer systems

Nonlinear parity-time-symmetric wireless power transfer (NPTS-WPT) is a novel wireless power transfer technology. NPTS-WPT systems exhibit the resonant frequency bifurcation phenomenon in the strong coupling region. However, working frequency selection mechanisms and control methods for use in the bifurcation region remain unclear. In this study, the description function method was used to model and analyze the dynamics of NPTS-WPT systems. The frequency stability, evolution and convergence characteristics of resonant frequency bifurcation were studied for varying distances between the receiver (Rx) and transmitter circuits varies. In addition, the loop detuning characteristics and the mechanism by which the amplification factor of the operational amplifier influences the system’s frequency-hopping behavior were determined. The detuning rate must be greater than the detuning tolerance to cause resonant frequency-hopping. Moreover, we propose a method to induce changes in the natural frequency of the Rx circuit by adding a detuning control circuit at the Rx, thereby allowing the resonant frequency to be selected and controlled. Finally, the conclusions from the theoretical analysis and the feasibility of the proposed frequency control methods were validated using an experimental system. The proposed resonant frequency control methods offer a viable method for directional frequency selection and artificial frequency control in NPTS-WPT systems operating in the strong coupling region.

Level pinning of anti-PT-symmetric circuits for efficient wireless power transfer.

Wireless power transfer (WPT) technology based on magnetic resonance (a basic physical phenomenon) can directly transfer energy from the source to the load without wires and other physical contacts, and has been successfully applied to implantable medical devices, electric vehicles, robotic arms and other fields. However, due to the frequency splitting of near-field coupling, the resonant WPT system has some unique limitations, such as poor transmission stability and low efficiency. Here, we propose anti-resonance with level pinning for high-performance WPT. By introducing the anti-resonance mode into the basic WPT platform, we uncover the competition between dissipative coupling and coherent coupling to achieve novel level pinning, and construct an effective anti-parity-time (anti-PT)-symmetric non-Hermitian system that is superior to previous PT-symmetric WPT schemes. On the one hand, the eigenvalue of the anti-PT-symmetric system at resonance frequency is always pure real in both strong and weak coupling regions, and can be used to overcome the transmission efficiency decrease caused by weak coupling, as brought about by, for example, a large size ratio of the transmitter to receiver, or a long transmission distance. On the other hand, due to the level pinning effect of the two kinds of coupling mechanisms, the working frequency of the system is guaranteed to be locked, so frequency tracking is not required when the position and size of the receiver change. Even if the system deviates from the matching condition, an efficient WPT can be realized, thereby demonstrating the robustness of the level pinning. The experimental results show that when the size ratio of the transmitter coil to the receiver coil is 4.29 (which is in the weak coupling region), the transfer efficiency of the anti-PT-symmetric system is nearly 4.3 (3.2) times higher than that of the PT-symmetric system when the matching conditions are satisfied (deviated). With the miniaturization and integration of devices in mind, a synthetic anti-PT-symmetric system is used to realize a robust WPT. Anti-PT-symmetric WPT technology based on the synthetic dimension not only provides a good research platform for the study of abundant non-Hermitian physics, but also provides a means of going beyond traditional near-field applications with resonance mechanisms, such as resonance imaging, wireless sensing and photonic routing.

Wireless Power Transfer: A Review of Existing Technologies

Wireless Power Transfer (WPT) can be described as the processing of transmitting electricity without the use of wires. It has been increasingly used in places where battery depletion and replacement are major issues. WPT Technology are being used in different sectors. They include wireless charging, Electric vehicles, consumer electronics, etc. The paper describes the various types of WPT technologies; Inductive Coupling, Magnetic Resonance and Radio Frequency (RF) technology. It also discusses the advantages and shortfalls of each type. An extensive survey of past works was discussed. Results from the research findings showed that distance and conversion efficiency were limiting factors in implementing wireless transfer technology.

Design of a Highly Compatible Underwater Wireless Power Transfer Station for Seafloor Observation Equipment

Conventional cabled seafloor observatories (CSOs) power in-situ instruments via wet-mated or dry-mated direct electrical contact (DEC) connectors to achieve long-term and real-time observation. However, the DEC connectors have high risks of water leakage and short circuits in power feeding, especially under high water pressure. This paper proposes a highly compatible underwater station based on inductive wireless power transfer (IPT) technology to address the above reliability issue. A novel energy transmitter with runway-structure coils is applied to the proposed underwater station to cover a sufficient power feeding area so that various in-situ equipment can be powered with desirable misalignment tolerance. The magnetic field distribution is analyzed by both derivation and finite element analysis (FEA) methods, and the principal parameters of the transmitter are further optimized and compared with both the mixed-integer sequential quadratic programming (MISQP) algorithm and the evolutionary algorithm (EA) for better performance. The same results show a reliable optimization process. The WPT circuit characteristics are also investigated to power different loads and improve the power transmission efficiency. The output power decreases, and the transmission efficiency rises and then decreases as the load increases. In addition, receivers with higher mutual inductance have better transmission performance. A prototype of the underwater station has been tested both in air and in water, and the experimental results have proven it can power multiple seafloor observation instruments stably and achieve compatibility requirements. The maximum output power of the station prototype for testing is 100 W, and the maximum overall transmission efficiency is 61%.

Task-oriented Energy Scheduling in Wireless Rechargeable Sensor Networks

In recent years, the flourishing of Wireless Power Transfer (WPT) technology brings Wireless Sensor Networks (WSNs) a renewable, reliable, and controllable energy source. To achieve high efficiency, WPT and sensors both adopt directional antennas. Most previous works about directional charging optimize overall charging efficiency, but neglect energy scheduling on nodes for optimizing tasks. This disadvantage may cause a serious imbalance between the energy supply and task loads. This article takes both aspects into consideration. To achieve an overall performance improvement, we jointly schedule rotatable chargers and allocate tasks to nodes in a WSN powered by directional chargers. As far as we know, this is the first work to propose the Task-oriented Energy Scheduling (TOES) problem, i.e., given a set of rotatable directional chargers and some wireless rechargeable sensor nodes, scheduling chargers and nodes to maximize the total utility gained from a set of tasks. We prove the NP-Hardness of TOES. Then we design a 4-approximation algorithm for TOES by jointly solving two subproblems of the original one. We further extend this problem to the windowed task model and propose a \(\frac{4}{1-\gamma }\) approximation algorithm for it, where γ is the proportion of the rotating period. Finally, extensive simulation results show that our algorithms outperform baselines by at least 40.3%.

Robustness of Wireless Power Transfer Systems with Parity-Time Symmetry and Asymmetry

Recently, wireless power transfer (WPT) technology has attracted much attention and shown rapid development. However, a fundamental challenge emerges in practical applications: how to achieve robust power transfer against the variation of operating conditions, such as the fluctuation of transfer distance, as well as the relative orientation of resonant coils. In this article, we theoretically propose and experimentally demonstrate that the robustness of a parity-time (PT) asymmetric system with unbalanced gain-loss working in a weak coupling region can be improved significantly, compared with that of a PT-symmetric system with balanced gain-loss working in a strong coupling region under the premise that the system works at a fixed optimal frequency. A pure real mode known as bound state in the continuum (BIC) in the weak coupling region of the PT-asymmetric system is adopted to ensure the high efficiency and stability of the WPT and break the limitations of balanced gain-loss of the PT-symmetric system. The better robustness performance originates from the orthogonal state with a pure real eigenmode embedded in the weak coupling region. Further experiments also verify that the PT-asymmetric system can achieve higher efficiency than that of the PT-symmetric system. In addition, we discuss the performance of the WPT system based on the theories of coupled mode theory (CMT) and circuit theory (CT); the BIC in the framework of CMT and a perfect impedance matching condition in the framework of CT for efficient power transfer are consistent. We also conducted power experimental verification of 30 watts, and found the efficiency between the coils can reach over 90% in dynamic scenarios, which meets expectations. The presented framework extends the field of non-Hermitian physics, bridges the gap between the non-ideal PT-symmetric system and a practical engineering application, and introduces a novel WPT mechanism for flexible application scenarios. Our results could provide instructive significance for practical applications of the WPT system in the long term.

A Study on the Optimal Magnetic Beam Forming of Coil Arrays for Long Distance Wireless Power Transmission.

Multiple-input multiple-output (MIMO) wireless power transfer (WPT) technology which employs multiple transmitter (TX) coils to simultaneously couple power to the receiver (RX) coil has proved to be an effective technique to enhance power transfer efficiency (PTE). Conventional MIMO-WPT systems rely on the phase-calculation method based on the phased-array beam steering concept to constructively combine the magnetic fields induced by the multiple TX coils at the RX coil. However, increasing the number and distance of the TX coils in an attempt to enhance the PTE tends to deteriorate the received signal at the RX coil. In this paper, a phase-calculation method is presented that enhances the PTE of the MIMO-WPT system. The proposed phase-calculation method considers the coupling between the coils and applies the phase and amplitude to calculate the coil control data. From the experimental results, the transfer efficiency is enhanced as a result of the transmission coefficient improvement from a minimum of 2 dB to a maximum of 10 dB for the proposed method as compared to the conventional one. By implementing the proposed phase-control MIMO-WPT, high-efficiency wireless charging is realizable wherever electronic devices are located in a specific space.

Wireless Power Transfer: Principles and Applications [Book News

The book gives a comprehensive view of wireless power transfer (WPT) technologies, with a special emphasis on the multiple-pickup WPT. A number of applications is also described, including the systems employed in portable consumer electronics, in‐flight charging for unmanned aerial vehicles, underwater wireless charging, and the high‐power electrical vehicle (EV) wireless charging that has been already mentioned above. The book is organized in four parts, each one of them consisting of multiple chapters. The first part is divided into two chapters: an overview of several WPT technologies is given, but the main emphasis is given to inductive power transfer (IPT) technology. The second part of the book gives a view of the issues related to the design and optimization of coupled coils and power circuits.

Modeling and Analysis of Wireless Power Transfer System Via Unified Full-Load Discrete-Time Model

The wireless power transfer (WPT) technology has attracted more attention due to its convenience, electrocution-free, and safety. However, the current discontinuity characteristics of WPT systems are not sufficiently appreciated. In this paper, a unified full-load discrete-time (UFDT) model for the WPT system is established, which is both suitable for continuous conduction mode (CCM) and discontinuous conduction mode (DCM). The state-space equation in each state interval is derived according to the equivalent circuits, and then the UFDT model in one period is obtained by iteration. Meanwhile, a closed-loop solution is investigated to calculate the duration of each state interval for different conditions. Based on the UFDT model, characteristics of the series-series (SS) compensated WPT systems are analyzed and summarized among the full-load range, which provides a theoretical reference for solving the problems of WPT systems, especially in DCM with little theoretical basis so far. The state variables continuously change while the SS compensated WPT system enters DCM from CCM with load resistance increasing. And the boundary of CCM and DCM is a multi-peak function of operating frequency. Simulations and experiments are conducted to verify the UFDT model, and the full-load characteristics of the WPT system also match well with experimental results.

An On-/Off-Time Sensing-Based Load-Adaptive Mode Control of Triple Mode Buck Converter for Implantable Medical Devices.

Wireless power transfer (WPT) technology applied to implantable medical devices (IMDs) significantly reduces the need for battery replacement surgery health conditions. This paper presents an on-/off-time sensing-based load-adaptive mode control of triple mode buck converter for implantable medical devices; the converter can adjust the control mode for low power consumption and achieve high power conversion efficiency (PCE) under a small active area. The three modes in the proposed system are the pulse width modulation (PWM), pulse frequency modulation (PFM), and ultra-low power (ULP) modes. The on-time sensor can be used to adjust the system from PWM to PFM modes, and the off-time sensor can be used to adjust the system from PFM to ULP modes. It is fabricated using TSMC 0.18 µm CMOS technology. The input voltage lies in the range 2.2-5.0 V, the output voltage is 1.8 V, and the load current lies in the range 0.05-200 mA (x4000). The experimental results demonstrate the seamless mode transition under the step up/down load transient response. The peak PCE is approximately 94.3% at the 80 mA and the minimum PCE is approximately 65.4% within the load current range.

A comprehensive review of optical wireless power transfer technology

A comprehensive review of optical wireless power transfer technology

Robust Wireless Rechargeable Sensor Networks

Wireless rechargeable sensor networks have become a hot research issue as it can overcome the limited energy bottleneck of wireless sensor networks owing to the recent breakthrough of wireless power transfer technology. Though network lifetime is prolonged and sensor nodes can sustain immortally, the issue of network robustness is overlooked, yielding most theoretical work unsuitable for practical applications when confronting with unpredictable packet loss. In this paper, we address the network robustness issue by maximizing the charging utility in a risk-averse view. First, we build a risk-averse model based on the concept of CVaR (Conditional Value at Risk), which trades-off charging utility and risk aversion for quantifying robustness. Then, we propose a spatial discretization scheme to construct a charging route for mobile charger, which can reduce computational overhead. Afterwards, a path optimization scheme is designed to further improve the charging utility. We convert the original problem into the submodular function maximization problem and propose a method with a performance guarantee while maximizing the system robustness. Finally, testbed experiments and simulations are conducted, and the results demonstrate that our schemes outperform comparison algorithms by at least 22.4% in effective energy in the presence of risks to guarantee system robustness.

Remaining Opportunities in Capacitive Power Transfer Based on Duality With Inductive Power Transfer

Wireless power transfer (WPT) has proven to be an effective solution for electric vehicle charging. As two mainstream near-field WPT technologies, inductive and capacitive power transfer (IPT and CPT) have many similarities. This paper aims to explore the remaining opportunities in CPT systems, not yet reported in existing literature, based on duality with the mature IPT technology. First, a generic modeling method based on two-port network theory is proposed, which contributes to unified modeling and analysis for both inductive and capacitive couplings. Then, power transfer mechanism of IPT and CPT couplers is compared, and unified transfer efficiency is derived, promoting CPT theory developments. Last, the duality between existing IPT and CPT circuits is demonstrated in two aspects: compensation circuit configuration and resonant relationship. 14 CPT topologies are derived based on duality with the existing 7 mainstream IPT circuits, of which 11 circuits do not exist in literature, offering future opportunities in CPT. Detailed comparison and evaluation of the derived 14 CPT circuits are conducted, and high-performance circuits are recommended. As a demonstration, a case study of a 2.1kW 3MHz CPT system is implemented in hardware based on the newly proposed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> - <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SS</i> topology. This example system achieves a peak efficiency of 93.19% with the predicted circuit properties of load-independent constant-voltage (CV) output and zero-phase-angle (ZPA) property.