Conventional Wireless Power Transfer System Research Articles

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

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

Helmholtz Coils Based WPT Coupling Analysis of Temporal Interference Electrical Stimulation System

Electrical nerve stimulation (ENS) is clinically important in treating neurological diseases. This paper proposes a novel temporally interfering wireless power transfer (WPT) system, based on Helmholtz coils, to address energy depletion and the miniaturization of wireless power transfer systems for implantable devices. Compared to conventional WPT systems, this paper uses Helmholtz coils with a centrosymmetric structure as the transmitting coils. A more uniform and stable magnetic field was obtained through structural improvements. It also improves the problem that changes in the receiving coil’s position affect the transmission power’s stability. Based on the principle of temporal interference (TI), two transmitting coils with a slight frequency difference generate a superposition of magnetic fields on the receiving coil and then induce a low-frequency electrical signal on it. The electrical stimulation system applies stimulation parameters of a specific intensity and frequency directly to the target nerve with electrodes connected to it. This eliminates the need for the conventional high-frequency signal to low-frequency signal processing circuitry and reduces the device’s size. In this paper, numerical calculations and an experimental verification of the proposed system are carried out. The magnetic field distribution and the receiving coil current waveform of the system were tested to verify the effectiveness and stability of the proposed design. The experimental results showed that the proposed wireless power transfer system can generate electrical signals of the desired waveform in the receiving coil. Its frequency of 10 Hz and amplitude of 42.4 mA meet the requirements for the electrical stimulation of the sciatic nerve.

Design and Analysis of Optimal Current Vector for HTS-Based Multi-Input Wireless Power Transfer Systems

This paper presents a newly-designed optimal current algorithm for high-temperature superconductor (HTS)-based multi-input wireless power transfer (WPT) systems. In this way, both high controllability and lower AC losses can be achieved in the proposed systems, and they are especially superior for long-range and long-time operations. Simplified AC loss modeling for HTS windings is developed for the designed transmitter coils. The accordant optimal current vector is derived and analyzed in order to achieve the highest output power and the lowest primary AC losses. With the proper current control of multiple transmitters and the use of a designed HTS coupler, the system controllability can be greatly improved compared with conventional WPT systems. Based on the information on the impedance characteristics on the primary side, the magnetic field generated by different transmitters can be maximized at the target position. Thus, the maximum output power tracking can be realized with a relatively long transmission distance and a low coupling coefficient. Both active and passive solutions are designed and presented to deal with the cross-coupling issue in multi-input WPT systems. For numerical validation, a practical prototype of the HTS couplers is fabricated. An experimental platform is established with a liquid nitrogen cooling system. The test results further validate the feasibility and the high controllability of the proposed system.

UAV-Enabled Wireless Power Transfer: A Tutorial Overview

Unmanned aerial vehicle (UAV)-enabled wireless power transfer (WPT) has recently emerged as a promising technique to provide sustainable energy supply for widely distributed low-power ground devices (GDs) in large-scale wireless networks. Compared with the energy transmitters (ETs) in conventional WPT systems which are deployed at fixed locations, UAV-mounted aerial ETs can fly flexibly in the three-dimensional (3D) space to charge nearby GDs more efficiently. This paper provides a tutorial overview on UAV-enabled WPT and its appealing applications, in particular focusing on how to exploit UAVs’ controllable mobility via their 3D trajectory design to maximize the amounts of energy transferred to all GDs in a wireless network with fairness. First, we consider the single-UAV-enabled WPT scenario with one UAV wirelessly charging multiple GDs at known locations. To solve the energy maximization problem in this case, we present a general trajectory design framework consisting of three innovative approaches to optimize the UAV trajectory, which are multi-location hovering, successive-hover-and-fly, and time-quantization-based optimization, respectively. Next, we consider the multi-UAV-enabled WPT scenario where multiple UAVs cooperatively charge many GDs in a large area. Building upon the single-UAV trajectory design, we propose two efficient schemes to jointly optimize multiple UAVs’ trajectories, based on the principles of UAV swarming and GD clustering, respectively. Furthermore, we consider two important extensions of UAV-enabled WPT, namely UAV-enabled wireless powered communication networks (WPCN) and UAV-enabled wireless powered mobile edge computing (MEC), by integrating the emerging WPCN and MEC techniques, respectively. For both cases, we investigate the UAV trajectory design jointly with communication/computation resource allocations to optimize the system performance, subject to the energy availability constraints at GDs. Finally, open problems in UAV-enabled WPT and promising directions for its future research are discussed.

Metal Surface Guided-Wireless Power Transfer System for Portable Applications With Multiple Receivers

Recently, research has been actively conducted to overcome various challenges observed in wireless power transfer (WPT) technology. However, as additional techniques are implemented, the complexity and cost of WPT systems increased. Therefore, there is a need for a new WPT method that can overcome the shortcomings of existing technology. This paper presents a metal surface guided-wireless power transfer (MSG-WPT) system for applications with multiple receivers (Rxs). First, a plate-wire propagation enhancer (PWPE) is shown to improve the power transfer efficiency (PTE). However, it is not suitable for portable receiving systems. Based on our analysis of the PWPE characteristics, applying an L-section lumped impedance-matching scheme instead of a PWPE can improve the portability of the Rx. A coil-based propagation enhancer (CPE), or a coil-based inductor (CI), can increase the power received if it replaces the lumped inductor in the L-section scheme. The MSG-WPT system does not experience the co-alignment issues that exist between a pair of transceivers (TRxs) in conventional WPT systems. It can also support multiple Rxs while ensuring that the PTE of each Rx is relatively unaffected. An electromagnetic simulation of the proposed MSG-WPT system is performed using a high-frequency structure simulator (HFSS), and measurements are conducted in a corresponding experimental environment. The system power efficiency is measured at −12 dB in the 4 MHz frequency band. The proposed MSG-WPT system with a CPE is adequately efficient and portable, while also allowing a more liberal arrangement of Rxs compared to other conventional WPT systems.

A High Efficiency LCC-S Compensated WPT System With Dual Decoupled Receive Coils and Cascaded PWM Regulator

A LCC-S compensated wireless power transfer (WPT) system with dual decoupled receive coils and a cascaded PWM regulator is proposed in this brief. The dual decoupled receive coils, comprising of bipolar coil and unipolar coil, provide two power paths. Most of input power is transferred to load directly through bipolar coil while only small portion of input power is transferred through unipolar coil and the cascaded PWM regulator, which can reduce power loss effectively. The output voltage of WPT system is regulated by the cascaded PWM regulator, thereby wireless communication links (WCLs) is not required in the feedback control loop, which leads to simple control circuits and good stability. Compared with conventional WPT system with two-stage power conversion, it is cost-effective as voltage/current stress of PWM regulator can be significantly alleviated. Besides, the LCC-S compensated WPT system can operate under zero phase angle (ZPA) condition with low voltage-ampere rating components. A 1.5kW prototype is built and experimental results show that the system efficiency up to 93% can be achieved under full load, which is 2.3% higher than that of conventional WPT system with two stage power conversion.

Scheme for providing parity-time symmetry for low-frequency wireless power transfer below 20 kHz

We provided parity-time symmetry (PT symmetry) for a magnetic resonance wireless power transfer (WPT) system designed to operate below 20 kHz. A lightweight coil having a mass of 39.1 g and consisting of a Mn–Zn ferrite core and 0.6-mm-diameter copper wire is considered herein. The coil had a Q factor of 111.5 at 16.5 kHz. The proposed system oscillated at 16.5 kHz for a transmission distance of 15 mm. A transmission power of 7.6 W was achieved when the DC power supply voltage was 100 V. Under these conditions, the power efficiency between the two coils was 92.1%. The oscillation frequency was automatically tuned to the optimal frequency for obtaining the maximum efficiency for a changing transmission distance. The relationship between the transmission power and the transmission distance was very different from that of a conventional WPT system, and an effect of PT symmetry clearly appeared.

Design and implementation of an efficient WPT system

Wireless power transfer (WPT) is a technique introduced to transfer power wirelessly. Generally, WPT systems are characterized by low efficiency and low output power. Since WPT process depends mainly on mutual coupling between transmitting and receiving coils in addition to load requirements, it is focused in this work toward enhancing the mutual coupling and conditioning the receiving circuit so as to optimally satisfy the load demand. The mutual coupling between transmitting and receiving nodes is enhanced via inserting three resonating circuits along with energy transmission path and conditioning the receiving circuit such that it accomplishes delivering maximum power to the load node. In this work, an adaptive efficient WPT system is introduced. This system is carried out on PSpice and validated experimentally. Both simulative and experimental WPT systems have accomplished significant enhancement in efficiency. The proposed WPT system has three resonators and three parallel connected identical receiving coils located at 6.61m from the power transmitter. The efficiency enhancement approaches thousands of times the efficiency of a conventional WPT system having similar power transmitter located at the same distance from the receiving circuit, which has a single coil identical to those in the proposed efficient WPT system.

Wireless Power Transfer System With High Misalignment Tolerance for Bio-Medical Implants

A hybrid array resonator structure for Wireless Power Transfer (WPT) is presented. The proposed structure exploits an array of four identical coils surrounded by a larger coil to generate uniform magnetic field. As a result, a nearly constant and high efficiency is achieved over a large misalignment region. The quasi-uniform magnetic field distribution of the proposed structure is analytically derived. For demonstration, one prototype operating at 40 MHz is designed for implantable medical devices (IMDs). According to experimental results, the developed WPT system exhibits an efficiency of 53% when the receiver and the transmitter are aligned, while the efficiency is 44% when they operate with a lateral misalignment of 10 mm. As per a conventional WPT system using a single spiral resonator as transmitter and receiver, the efficiency is 47.2% in aligned condition, while, it is 30.5% for a 10 mm lateral misalignment. The reported results demonstrate that the proposed design approach provides a high misalignment tolerance. This represents an attractive future for applications, such as the recharge of embedded devices, where the alignment between the transmitter and the receiver is difficult to guarantee.

Planar multiresonance reactive shield for reducing electromagnetic interference in portable wireless power charging application

Wireless power transfer (WPT) technologies are currently growing in popularity because of problems with batteries in portable devices, such as the added weight and the inconvenience of conventional wired charging methods. However, wireless charging systems generate leakage magnetic fields, causing malfunctions in adjacent electronic devices. Technologies to suppress electromagnetic interference (EMI) from portable WPT systems are required to prevent this problem. In this paper, we propose a topology design for a multiresonance reactive shield to suppress the EMI from WPT systems. The proposed shield employs closed loops, which are located peripheral to the WPT coil and resonance matching capacitor. The power efficiency and shielding performance of the proposed method were compared with those of the conventional WPT system coil shielding topologies. The proposed shield exhibited about 27.37 dB more 3rd harmonic EMI suppression than other methods while maintaining higher power transfer efficiency.

A compact module‐integrated wireless power transfer system with a square metal plate

AbstractIn this article, we propose a compact module‐integrated wireless power transfer (WPT) system for miniaturizing a WPT system and improving power transfer efficiency (PTE) within the operating distance. Using an eddy current (and its associated magnetic field) formed in a module‐integrated square metal plate, the proposed WPT system realizes a uniform mutual inductance between the coils within the operating distance and achieves an improved PTE of up to 54.7% at 6.78 MHz compared to the conventional WPT system.

On-Site Wireless Power Generation

Conventional wireless power transfer systems consist of a microwave power generator and a microwave power receiver separated by some distance. To realize efficient power transfer, the system is typically brought to resonance, and the coupled-antenna mode is optimized to reduce radiation into the surrounding space. In this scheme, any modification of the receiver position or of its electromagnetic properties results in the necessity of dynamically tuning the whole system to restore the resonant matching condition. It implies poor robustness to the receiver location and load impedance, as well as additional energy consumption in the control network. In this study, we introduce a new paradigm for wireless power delivery based on which the whole system, including transmitter and receiver and the space in between, forms a unified microwave power generator. In our proposed scenario the load itself becomes part of the generator. Microwave oscillations are created directly at the receiver location, eliminating the need for dynamical tuning of the system within the range of the self-oscillation regime. The proposed concept has relevant connections with the recent interest in parity-time symmetric systems, in which balanced loss and gain distributions enable unusual electromagnetic responses.

Z-Source Resonant Converter With Power Factor Correction for Wireless Power Transfer Applications

In this paper, the Z-source converter is introduced to power factor correction (PFC) applications. The concept is demonstrated through a wireless power transfer (WPT) system for electric vehicle battery charging, namely Z-source resonant converter (ZSRC). Due to the Z-source network (ZSN), the ZSRC inherently performs PFC and regulate the system output voltage simultaneously, without adding extra semiconductor devices and control circuitry to the conventional WPT system such as conventional PFC converters do. In other words, the ZSN can be categorized as a family of the single-stage PFC converters. In addition, the ZSN is suitable for high-power applications since it is immune to shoot-through states, which increases reliability and adds a boost feature to the system. The ZSRC-based WPT system operating principle is described and analyzed in this paper. Simulations and experimental results based on a 1-kW prototype with 20-cm air gap between the system primary and secondary sides are presented to validate the analysis and demonstrate the effectiveness of the ZSN in the PFC of the WPT system.

Wireless Power Transfer Using High Temperature Superconducting Pancake Coils

It is well known that the efficiency of a wireless power transfer (WPT) system depends on the resistance of the transmitting and receiving coils, especially for the case of low frequency. Since the ac loss of high temperature superconductors (HTS) is much lower than that of conventional conductors, using high temperature superconductors for WPT system is a good way to increase power transfer efficiency. Here, several kinds of WPT experiments were designed and conducted by use of HTS and conventional conductor (copper) coils, respectively. The results are presented and analyzed. It is shown that the behavior of HTS WPT system is similar to that of a conventional WPT system, but the efficiency of WPT system is much higher by use of HTS coils and HTS coil is more suitable for being as a transmitting coil than as a receiving one.

LOOP SWITCHING TECHNIQUE FOR WIRELESS POWER TRANSFER USING MAGNETIC RESONANCE COUPLING

We propose a loop switching technique to improve the e-ciency of wireless power transfer (WPT) systems using magnetic resonance coupling. The proposed system employs several loops with difierent sizes, one of which is connected to the system with various distances between the transmitter and the receiver. It enables the coupling coe-cient to be adjusted with the distance, which allows high e-ciency over a wide range of distances. The proposed system is analyzed using an equivalent circuit model, and electromagnetic (EM) simulation is performed to predict the performance. It is shown from the experimental results at 13.56MHz that the proposed loop switching technique can maintain high e-ciency over a wide range. The e-ciency is measured to be 50% at 100cm, which corresponds to a 46% increase compared to a conventional WPT system without the loop switching technique.