Wireless Power Transfer Solutions Research Articles

Wireless power transfer in space using flexible, lightweight, coherent arrays

Space solar power (SSP), envisioned for decades as a solution for continuous, stable, and dynamically dispatchable clean energy, has seen tremendous interest and a number of experimental demonstrations in the last few years. A practical implementation has been elusive to date, owing to the high launch costs associated with heavy, rigid photovoltaic and wireless power transfer (WPT) arrays. Lightweight and flexible solutions for WPT have been demonstrated terrestrially but, to date, have not been deployed and tested in space. In this paper, we present an experimental space demonstration of a lightweight, flexible WPT array powered by custom radio-frequency integrated circuits. The transmit arrays, receive arrays, and the rest of the system were operated and tested for eight months in Low Earth Orbit (LEO). Results from these experiments, including pointing of the array’s beam to Earth and its detection by a ground station, are presented and discussed in detail. Observations and results from this mission uncover existing strengths and weaknesses that inform future steps towards realizing SSP.

Long-Range Wireless Power Transfer for Moving Wireless IoT Devices

Wireless technologies are revolutionizing communications, with recent deployments, such as 5G, playing a key role in the future of the Internet of Things (IoT). Such progress is leading to an increasingly higher number of wirelessly connected devices. These require increased battery use and maintenance, consequently straining current powering solutions. Since most wireless systems rely on radiofrequency (RF) waves for communications and feature low-power technologies, it is increasingly feasible to develop and implement wireless power transfer solutions supported by RF. In this paper, a simultaneous wireless information and power transfer (SWIPT) solution targeting small mobile devices is presented. This solution uses beamforming to mitigate the path loss associated with the RF power propagation. It relies on an RF backscattering tracking algorithm to power moving devices. The feasibility to power wearable devices is demonstrated by tracking a walking individual (approximately 5 km/h) at a distance of 0.5 m while transferring a minimum of 6 dBm to a wearable device using 2 GHz RF signals. Simulations were used to determine the viability of such a solution to deliver useful power levels to a 1.2 × 1.4 m2 working area without exceeding specific absorption rate (SAR) limits.

Power boundaries in resonant electrodynamic wireless power transfer systems

This article focuses on deriving the maximum power that can be transmitted using recent wireless power transfer technology based on an electrodynamic receiver. Analytical derivations reveal two main constraints that can limit transmitted power: the magnetic field safety limit and the maximum stress before breaking the receiver. From these limits, expressions of maximum magnetic forces and power are derived, providing physical insights on how to optimize the transmitted power. Interestingly, the optimal electrical condition and the optimal electromechanical efficiency differ when maximizing the transmitted power under each constraint. In the final section of the paper, the proposed theoretical boundaries are applied to two types of receivers, based on either electromagnetic or piezoelectric transducers. The results demonstrate that the maximum power density achievable with both receivers is inherently limited (<10 mW/cm3) under realistic assumptions regarding electromechanical coupling and electrical circuitry. This value is smaller than some previously reported results involving rotating or magnetoelectric solutions, indicating that clamped-free beams are not the optimal solution for electrodynamic wireless power transfer. This analysis can be extended to other types of receivers and will be useful for optimizing, sizing, and assessing any technological solution for wireless power transfer.

Design and validation of a DC–DC converter-based inductive power transfer system with increased efficiency and reduced voltage stress across switches

Research in wireless power transfer(WPT) focuses on improving efficiency, reducing energy consumption, improving safety, and increasing sustainability. It prioritises developing more efficient transmission technologies, such as high-frequency switching and resonant coupling, to enhance the system’s overall performance. However, high voltage stress across the semiconductor devices during switching operations at high frequencies can result in increased switching loss, leading to decreased overall efficiency of the WPT system. The switching loss can be minimised by reducing voltage stress, resulting in higher efficiency and improved energy transfer performance. This leads to more cost-effective WPT solutions without compromising performance or reliability by using lower-rated components and reducing the need for elaborate voltage clamping and protection circuits. Lowering voltage stress across switches can also help WPT systems comply with industry standards and regulations related to electrical safety, electromagnetic compatibility (EMC), and energy efficiency. Meeting these standards is essential for ensuring the widespread adoption and commercial success of WPT technology. In this article, a class ø2 inverter and a modified class-E rectifier is integrated and applied in a WPT system. The benefits of a Resonant class ø2 inverter are zero voltage switching(ZVS) and lower switch voltage stress as compared to its predecessors. Also, a resonant class E/F3 rectifier inductively coupled in the receiving stage reduces the peak voltage stress across the diode. The system shown here is tuned to achieve maximum overall transfer efficiency. The proposed class ø2-E/F3 combined WPT system operating at 50 kHz simulated in PSIM software yielded a dc-dc efficiency of 94.56 percent, and the peak voltage stress across switches is found to reduced (2.4–2.7 times the input voltage as compared to the existing topologies where it surges upto 3.6–4 times the input voltage). These are also validated in Typhoon HIL’s Real-Time Emulator HIL402. In addition to that, a machine learning algorithm based on an Artificial Neural Network is used to generate a model to predict the switching frequency for a specified output voltage and efficiency.

Benchmarking of cutting-edge wireless power transfer for electric vehicles

Wireless power transfer (WPT), which can transfer energy though magnetic field, electronic field, laser beam, microwave and other methods without wire, provide electric vehicles (EVs) a better prospect. Compared to cars with internal combustion engines, Electric vehicles are more environmental-friendly, and do not need any fossil fuel, which is a ideal transportation in the future, however, for electric vehicles, battery technology is the major barrier: high cost, low energy density and large weight, which make electric vehicles very expensive and difficult to improve the endurance mileage, by applying wireless power transfer technology, using dynamic wireless charging can solve these problems perfectly. This paper reviews basic information of wireless power transfer technologies: four basic classification of WPT, basic compensation networks for inductive wireless power transfer, coil designs to improve the transferring efficiency, and wireless power transfer applications on EV charging, additionally, challenges and potential solutions for wireless power transfer of EV are presented.

An Integrated Three-Phase AC–DC Wireless-Power-Transfer Converter With Active Power Factor Correction Using Three Transmitter Coils

Three-phase AC-DC converters are more commonly used for high-power applications compared to single-phase converters. For high-power wireless power transfer (WPT) applications, such as wireless electric vehicle chargers, usually a two-stage topology is applied, which consists of a three-phase AC-DC rectifier with power factor correction and a DC-DC converter for WPT. Recently, there are several studies on three-phase single-stage WPT solutions being proposed to reduce power conversion stages, and furtherly increase overall efficiency and reduce system cost. In this paper, an integrated three-phase AC-DC WPT converter topology with active power factor correction is proposed. The count of power semiconductor devices is significantly reduced compared to state-of-the-art three-phase single-stage topologies. Moreover, three transmitter coils are used to enhance the system power capacity. Topology description, operation analysis, control method, power loss analysis, and reference design guideline of the proposed topology are presented in detail. Finally, a laboratory prototype is built and evaluated. The functionalities, performances, and advantages are demonstrated by the corresponding experimental results.

Investigation of wireless electrification for a reconfigurable manufacturing cell

Reconfigurable manufacturing systems (RMS) with a rearrangeable structure can quickly adjust their productivity to meet the dynamic market changes and the demand for high-variety products. Industry 4.0 technologies have enhanced the RMS flexibility and made the automation of the reconfiguration of the manufacturing system possible. As an Industry 4.0 technology, wireless power transfer (WPT) can further increase the flexibility of RMS by providing safe, reliable, and maintenance-free autonomous charging. This paper examines the wireless electrification of RMS by investigating different WPT configurations that increase flexibility and autonomy, creating a highly flexible RMS. It also proposes a battery charging platform for further enhancement of the flexibility of RMS. As a low-cost WPT solution, the paper tests capacitive charging systems. The proposed charging system has about 135 W power transfer capability at a 5 cm distance and about 84% efficiency.

Comparison of the Efficiency and Load Power in Periodic Wireless Power Transfer Systems with Circular and Square Planar Coils

In the article, a wireless charging system with the use of periodically arranged planar coils is presented. The efficiency of two wireless power transfer (WPT) systems with different types of inductors, i.e., circular and square planar coils is compared, and two models are proposed: analytical and numerical. With the appropriate selection of a load resistance, it is possible to obtain either the maximum efficiency or the maximum power of a receiver. Therefore, the system is analyzed at two optimum modes of operation: with the maximum possible efficiency and with the highest power transmitted to the load. The analysis of many variants of the proposed wireless power transfer solution was performed. The aim was to check the influence of the geometry of the coils and their type (circular or square) on the efficiency of the system. Changes in the number of turns, the distance between the coils (transmit and receive) as well as frequency are also taken into account. The results obtained from analytical and numerical analysis were consistent; thus, the correctness of the adopted circuit and numerical model (with periodic boundary conditions) was confirmed. The proposed circuit model and the presented numerical approach allow for a quick estimate of the electrical parameters of the wireless power transmission system. The proposed system can be used to charge many receivers, e.g., electrical cars on a parking or several electronic devices. Based on the results, it was found that the square coils provide lower load power and efficiency than compared to circular coils in the entire frequency range and regardless of the analyzed geometry variants. The results and discussion of the multivariate analysis allow for a better understanding of the influence of the coil geometry on the charging effectiveness. They can also be valuable knowledge when designing this type of system.

E-Textile Technology Review–From Materials to Application

Wearable devices are ideal for personalized electronic applications in several domains such as healthcare, entertainment, sports and military. Although wearable technology is a growing market, current wearable devices are predominantly battery powered accessory devices, whose form factors also preclude them from utilizing the large area of the human body for spatiotemporal sensing or energy harvesting from body movements. E-textiles provide an opportunity to expand on current wearables to enable such applications via the larger surface area offered by garments, but consumer devices have been few and far between because of the inherent challenges in replicating traditional manufacturing technologies (that have enabled these wearable accessories) on textiles. Also, the powering of e-textile devices with battery energy like in wearable accessories, has proven incompatible with textile requirements for flexibility and washing. Although current e-textile research has shown advances in materials, new processing techniques, and one-off e-textile prototype devices, the pathway to industry scale commercialization is still uncertain. This paper reports the progress on the current technologies enabling the fabrication of e-textile devices and their power supplies including textile-based energy harvesters, energy storage mechanisms, and wireless power transfer solutions. It identifies factors that limit the adoption of current reported fabrication processes and devices in the industry for mass-market commercialization.

Distributed beamforming based wireless power transfer: Analysis and realization

This paper presents a new Wireless Power Transfer (WPT) approach by aligning the phases of a group of spatially distributed Radio Frequency (RF) transmitters (TX) at the target receiver (RX) device. Our approach can transfer energy over tens of meters and even to targets blocked by obstacles. Compared to popular beamforming based WPTs, our approach leads to a drastically different energy density distribution: the energy density at the target receiver is much higher than the energy density at other locations. Due to this unique energy distribution pattern, our approach offers a safer WPT solution, which can be potentially scaled up to ship a higher level of energy over longer distances. Specifically, we model the energy density distribution and prove that our proposed system can create a high energy peak exactly at the target receiver. Then we conduct detailed simulation studies to investigate how the actual energy distribution is impacted by various important system parameters, including number/topology of transmitters, transmitter antenna directionality, the distance between receiver and transmitters, and environmental multipath. Finally, we build an actual prototype with 17 N210 and 4 B210 Universal Software Radio Peripheral (USRP) nodes, through which we validate the salient features and performance promises of the proposed system.

Miniaturised Wireless Power Transfer Systems for Neurostimulation: A Review.

In neurostimulation, wireless power transfer is an efficient technology to overcome several limitations affecting medical devices currently used in clinical practice. Several methods were developed over the years for wireless power transfer. In this review article, we report and discuss the three most relevant methodologies for extremely miniaturised implantable neurostimulators: ultrasound coupling, inductive coupling and capacitive coupling. For each powering method, the discussion starts describing the physical working principle. In particular, we focus on the challenges given by the miniaturisation of the implanted integrated circuits and the related ad-hoc solutions for wireless power transfer. Then, we present recent developments and progresses in wireless power transfer for biomedical applications. Last, we compare each technique based on key performance indicators to highlight the most relevant and innovative solutions suitable for neurostimulation, with the gaze turned towards miniaturisation.

A Multi-Tone Rectenna System for Wireless Power Transfer

Battery-less sensors need a fast and stable wireless charging mechanism to ensure that they are being correctly activated and properly working. The major drawback of state-of-the-art wireless power transfer solutions stands in the maximum Equivalent Isotropic Radiated Power (EIRP) established from local regulations, even using directional antennas. Indeed, the maximum transferred power to the load is limited, making the charging process slow. To overcome such limitation, a novel method for implementing an effective wireless charging system is described. The proposed solution is designed to guarantee many independent charging contributions, i.e., multiple tones are used to distribute power along transmitted carriers. The proposed rectenna system is composed by a set of narrow-band rectifiers resonating at specific target frequencies, while combining at DC. Such orthogonal frequency schema, providing independent charging contributions, is not affected by the phase shift of incident signals (i.e., each carrier is independently rectified). The design of the proposed wireless-powered system is presented. The main advantage of the solution is the voltage delivered to the load, which is directly proportional to the number of used carriers. This is fundamental to ensure fast sensor wakes-up and functioning. To demonstrate the feasibility of the proposed system, the work has been complemented with the manufacturing of two rectennas, and the analysis of experimental results, which also validated the linear relationship between the number of used carriers.

Channel-Dependent Scheduling in Wireless Energy Transfer for Mobile Devices

Resonant Beam Charging (RBC) is the Wireless Power Transfer (WPT) technology, which can provide high-power, long-distance, mobile, and safe wireless charging for Internet of Things (IoT) devices. Supporting multiple IoT devices charging simultaneously is a significant feature of the RBC system. To optimize the multi-user charging performance, the transmitting power should be scheduled for charging all IoT devices simultaneously. In order to keep all IoT devices working as long as possible for fairness, we propose the First Access First Charge (FAFC) scheduling algorithm. Then, we formulate the scheduling parameters quantitatively for algorithm implementation. Finally, we analyze the performance of FAFC scheduling algorithm considering the impacts of the receiver number, the transmitting power and the charging time. Based on the analysis, we summarize the methods of improving the WPT performance for multiple IoT devices, which include limiting the receiver number, increasing the transmitting power, prolonging the charging time and improving the single-user's charging efficiency. The FAFC scheduling algorithm design and analysis provide a fair WPT solution for the multi-user RBC system.

RF Wireless Power Transfer Using Integrated Inductor

Wireless power transfer (WPT) is an ideal power delivery solution for many light-load applications, such as for the Internet of Things. A regulated solution for WPT may utilize a power distribution unit (PDU). Previous works have designed planar inductors for integration with switched-inductor buck regulators, but these inductors will not be as efficient for light-load applications. This paper reevaluates the inductor loss for light-load applications by taking into account the frequency spectrum of the inductor current. Using this revised analysis, a planar inductor with screen printed NiZn ferrite epoxy composite magnetic core is designed for an RF near-field coupling system with 1–10-mW load power. In measurement with a 6-MHz buck converter, the PDU with designed inductor demonstrated up to 3% improved efficiency compared to surface-mount technology inductor in the pulse-frequency modulation mode and pulsewidth modulation mode. The designed embedded inductor was subsequently demonstrated in an integrated, compact RF near-field coupling system with peak 43% system efficiency.

Wireless Power Transfer Solutions and Their Effectiveness [Georgia Institute of Technology

My research focuses on the problems related to the creation of a wireless power transfer system designed for energy transmission at a distance of at least one meter. The project was created to provide data for the advancement of wireless power, specifically via radio frequency transmission. Previous research efforts that attempted to develop this technology have run into unforeseen obstacles that have hindered its consumer and commercial adoption. This research will yield more information into those barriers and what can be done to assist wireless power in its future development as an applied technology. To begin producing data, a wireless power system first must be created. The central design element of the transmitter was a Texas Instruments PLL and integrated VCO wideband frequency synthesizer programmed to output a 3.6GHz sine wave. That signal was then passed into a GaN amplifier integrated circuit from Analog Devices and finally transmitted via a wideband Molex antenna. The receiver circuit was much simpler, simply consisting of a second Molex antenna and a bridge rectifier circuit to convert the AC signal to DC. A multipurpose ATmega328 programs the frequency synthesizer on the transmitter and reads the voltage and current from the receiver with its integrated ADC. The research is currently still in progress, but the data that has been accumulated shows that transmission is possible but with lower power yields than initially expected. The maximum range of received power was one meter, but because the transmitted voltage and current did not meet the calculated values, the project must have reached one or more of the unknown obstacles in wireless power design. To isolate and learn more about them, the project will be revised to gather more data. It will change into different models of power transfer and be tested for their effectiveness for the benefit of future research in this topic.

Wireless Energy Transmission Channel Modeling in Resonant Beam Charging for IoT Devices

Power supply for Internet of Things (IoT) devices is one of the bottlenecks in IoT development. To provide perpetual power supply for IoT devices, resonant beam charging (RBC) is a promising safe, long-range, and high-power wireless power transfer solution. How long distance RBC can reach and how much power RBC can transfer? In this paper, we analyze the consistent and steady operational conditions of the RBC system, which determine the maximum power transmission distance. Then, we study the power transmission efficiency within the operational distance, which determines the deliverable power through the RBC energy transmission channel. Based on the theoretical model of the wireless energy transmission channel, we establish a testbed. According to the experimental measurement, we validate our theoretical model. The experiments verify that the output electrical power at the RBC receiver can be up to 2 W. The maximum energy transmission distance is 2.6 m. Both the experimental and theoretical performance of the RBC system are evaluated in terms of the transmission distance, the transmission efficiency, and the output electrical power. Our theoretical model and experimental testbed lead to the guidelines for the RBC system design and implementation in practice.

Fair Scheduling in Resonant Beam Charging for IoT Devices

Resonant Beam Charging (RBC) is the Wireless Power Transfer (WPT) technology, which can provide high-power, long-distance, mobile, and safe wireless charging for Internet of Things (IoT) devices. Supporting multiple IoT devices charging simultaneously is a significant feature of the RBC system. To optimize the multi-user charging performance, the transmitting power should be scheduled for charging all IoT devices simultaneously. In order to keep all IoT devices working as long as possible for fairness, we propose the First Access First Charge (FAFC) scheduling algorithm. Then, we formulate the scheduling parameters quantitatively for algorithm implementation. Finally, we analyze the performance of FAFC scheduling algorithm considering the impacts of the receiver number, the transmitting power and the charging time. Based on the analysis, we summarize the methods of improving the WPT performance for multiple IoT devices, which include limiting the receiver number, increasing the transmitting power, prolonging the charging time and improving the single-user's charging efficiency. The FAFC scheduling algorithm design and analysis provide a fair WPT solution for the multi-user RBC system.

Long-distance WPT unconventional arrays synthesis

Two innovative array concepts are introduced for the design of long-distance Wireless Power Transfer (WPT) radiating systems. The achievable tradeoffs between complexity/cost mitigation and power focusing capabilities of unconventional WPT architectures with respect to state-of-the-art optimal WPT solutions are investigated. To this end, clustered or sparse WPT arrangements are introduced by formulating their syntheses either as excitation or as pattern matching problems then solved by ad-hoc versions of the Contiguous Partition Method and Compressive Sensing algorithms. Selected numerical examples are presented to assess the features and the potentialities of unconventional WPT designs also in comparison with traditional state-of-the-art optimal methods.

High-Efficiency Millimeter-Wave Energy-Harvesting Systems With Milliwatt-Level Output Power

The output power level and the power conversion efficiency (PCE) rate of the energy-harvesting systems are vital factors in realizing effective millimeter-wave wireless power transfer solutions that can power battery-less and charge coil-free smart everyday objects. Two 60-GHz energy harvesters that use a tuned complementary cross-coupled oscillator-like rectifying circuitry in 40-nm digital CMOS process are presented. They harvest energy at power rates and peak PCE levels in excess of 1 mW and 30%. These figures are significantly higher than those of the prior art. In one design, two rectifier stages are in a cascode configuration to produce higher dc output voltage levels at the low-current regime. Novel theoretical analyses of the unique rectifying circuitry of the single-stage and two-stage cascode harvesters are presented, which formulate all of the key specifications.

Overview of wireless power transfer technologies for electric vehicle battery charging

In this study, a comprehensive review of existing technological solutions for wireless power transfer used in electric vehicle battery chargers is given. The concept of each solution is thoroughly reviewed and the feasibility is evaluated considering the present limitations in power electronics technology, cost and consumer acceptance. In addition, the challenges and advantages of each technology are discussed. Finally, a thorough comparison is made and a proposed mixed conductive/wireless charging system solution is suggested to solve the inherent existing problems.