Minimizing Leakage Magnetic Field of Wireless Power Transfer Systems Using Phase Difference Control

The power transfer efficiency of magnetic-resonance coupled wireless power transfer (WPT) systems is sensitive to the alignment of coils. In this paper, a novel multi-coil WPT system is proposed to enhance power transfer efficiency. It can overcome the misalignment problem and maintain high power transfer efficiency. The proposed coil loop structure can provide a strong magnetic resonance coupling between the Tx and Rx coils. There are four induvial resonators applied in the system and it demonstrates that at least a pair of coupled resonators in several misaligned conditions could realize high power transfer efficiency over a misaligned distance. The experimental results show that the proposed multi-loop WPT system can achieve 90.2% peak efficiency when the coils are well aligned. Mean-while, this WPT system maintains over 70% efficiency over a misalignment distance from 0 to 55 mm, which is about 66% of the length of the Rx board. The proposed WPT system could be used either in implant devices for biomedical healthcare and treatment or for electric vehicles charging systems.

It is well known that the power transfer efficiency (PTE) of a two-coil wireless power transfer (WPT) system is maximized at critical coupling under fixed system parameters. However, the two-coil WPT system is critical-coupled with a relatively short distance between the coils. To overcome the problem, a multicoil WPT system has been studied. In this paper, we review the impedance characteristics of the critical-coupled two-coil WPT system and reveal that the conventional three-coil WPT system cannot have the same impedance characteristics as critical coupling. Based on the impedance matching conditions with critical coupling of the two-coil WPT system, we propose a design method of a three-coil WPT system in which the free resonant frequencies of all resonators are changed. The proposed design method is successfully implemented at the operating frequency of 6.78 MHz. The experimental results are in good agreement with the simulated PTEs and show that by changing the free resonant frequencies, a higher PTE can be effectively achieved in comparison to the conventional two-coil and thee-coil WPT systems.

A Wireless Power Transfer (WPT) system, known for its contactless power delivery, is extensively used for power supply in spacecraft applications. Achieving efficient and stable power transfer necessitates the integration of DC/DC converters on both the primary and secondary sides of WPT systems for power conversion and control. Traditional efficiency optimization methods primarily focus on impedance matching within the wireless power resonance network, often neglecting the overall efficiency optimization of multi-stage DC-DC and WPT systems. This oversight results in suboptimal overall system efficiency despite optimal efficiency in the wireless transmission segment. Additionally, the time-varying nature of mutual inductance and load parameters during power transmission in WPT systems presents challenges for maximum efficiency tracking and power control. This paper introduces a multi-level coordinated control efficiency optimization method for WPT systems utilizing the particle swarm optimization (PSO) algorithm. This method takes into account the transmission losses across all power conversion units within the WPT system, establishing a mathematical model for the joint optimization of overall system transmission efficiency and power. The PSO algorithm is then employed to solve this optimization model using estimated mutual inductance and load values. By adjusting the DC/DC converters on both sides, the method ensures optimal overall system efficiency and consistent power transmission. Experimental results indicate that under varying load and mutual inductance conditions, a Series–Series (SS) compensated WPT system using this method achieves a 200 W power output with maximum efficiency tracking, a power output error of 0.63%, and an average transmission efficiency of 86.2%. This demonstrates superior power transmission stability and higher efficiency compared to traditional impedance matching methods.

Simultaneous power distribution to multiple loads using a single source in the wireless power transfer (WPT) system is a challenging issue due to cross-coupling between the load coils, which reduces the power transfer efficiency. In a resonant WPT system, when two or more coils operated under over coupled condition, the original operating resonant frequency gets bifurcated, and thereby reduction in the power transfer efficiency. Different techniques are investigated in the literature to mitigate the frequency bifurcation phenomena in the resonant WPT system. However, the utilization of frequency bifurcation approach for the simultaneous power transfer to multiple loads is not addressed. This paper proposes a simultaneous power transfer approach using frequency bifurcation for the multiple load system designed with different operating frequency. Mathematical, simulation, and experimental studies performed for dual, triple, and four coil WPT systems with multiple loads. In addition, an automatic power flow control method is implemented to estimate the load current from the source, which helps to select a new set of load coils to be charged. The experimental results confirm the proposed power transfer, helps to attain higher power transfer efficiency of 39.34%, 49.31%, 68.22% and cross interference of -31.2 dBV, -36.2 dBV, -41.2 dBV for dual, triple, and four coil WPT system, respectively.

The wireless power transfer (WPT) system based on parity-time (PT) symmetry has the advantages of robustness, stable, and efficient power transmission. However, the region of PT symmetry is limited, which cannot satisfy some practical requirements. Multiple transmitting coils have been shown to improve the misalignment tolerance of WPT systems. Towards this end, a parity-time-symmetric-based WPT (PT-based WPT) system with double-transmitting coil is presented in this article. First, an approximate equivalent circuit model of this PT-based WPT system was developed. Second, compared with the conventional single transmitting coil PT-based WPT system, the proposed system expands the PT symmetry region and provides higher output power and transmission efficiency. Furthermore, the mutual inductance between two transmitting coils can be designed to meet the requirements of different scenarios, which improves the freedom of system design. Finally, a 30 W prototype is designed to evaluate the proposed WPT system. Experimental results show that the critical coupling coefficient is reduced by about 12.5% at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> = 0.51, which implies a longer transmission distance. Moreover, the maximum output voltage fluctuation in the strongly coupled region is only 3.5%, while the transfer efficiency is approximately constant, which implies stable and efficient power transfer.

A highly efficient wireless power transfer (WPT) system is required in many applications to replace the conventional wired system. The high temperature superconducting (HTS) wires are examined in a WPT system to increase the power-transfer efficiency (PTE) as compared with the conventional copper/Litz conductor. The HTS conductors are naturally can produce higher amount of magnetic field with high induced voltage to the receiving coil. Moreover, the WPT systems are prone to misalignment, which can cause sudden variation in the induced voltage and lead to rapid damage of the resonant capacitors connected in the circuit. Hence, the protection or elimination of resonant capacitor is required to increase the longevity of WPT system, but both the adoptions will operate the system in nonresonance mode. The absence of resonance phenomena in the WPT system will drastically reduce the PTE and correspondingly the future commercialization. This paper proposes an open bifilar spiral coils based self-resonant WPT method without using resonant capacitors at both the sides. The mathematical modeling and circuit simulation of the proposed system is performed by designing the transmitter coil using HTS wire and the receiver with copper coil. The three-dimensional modeling and finite element simulation of the proposed system is performed to analyze the current density at different coupling distances between the coil. Furthermore, the experimental results show the PTE of 49.8% under critical coupling with the resonant frequency of 25 kHz.

Since the concept of wireless power transfer has been proposed and implemented by Tesla over a hundred years ago, it has obtained lots of breakthroughs and applied in many potential fields especially in implantable biomedical devices [1–2]. The implantable biomedical devices are surgically introduces into the human body to rebuild body function, achieve a better quality of life, and expand longevity. With the development of microelectronics, biotechnology, and materials, the industry of implantable biomedical devices grows up quickly. The researches show that in America 8% to 10% of the people have experienced an implantable medical device, while in industrialized countries 5% to 6% of population have consumption demand in implantable medical devices. How to provide a constant power supply, for implantable medical devices, becomes a restricted problem. In order to guarantee the implanted medical devices to work normally, the energy storage or harvesting components should be included in these devices. In the traditional implantable medical devices, there are two ways to provide power for the devices. The common method is the implantable batteries are used to be as a power supply, and the other method is to transfer the power in vitro to the devices with the lead wires through the skin. For implantable batteries, their lifetime, size and toxic composition will lead to potential hazard to the patients. The transcutaneous wires, as well, will bring infection and reliability problems. In order to address above problems, the technology of wireless power transfer is used in the biomedical devices. The system has two parts in which one part including power supply and the transmitter coil is placed outside the patients’ body, and the other part including the receiver coil is placed in the patients’ body. For this system, the receiver coil should be limited as small as possible and the power transfer efficiency should be as high as possible. Different from the traditional two-coil wireless power transfer system, a novel three-coil system is proposed in this paper. In the novel system, there are two rectangular transmitter coils and one circular receiver coil. To obtain the maximum power transfer efficiency, the system is optimal designed according to the following step as shown in Fig. 1. Firstly, the size and the geometry of the receiver coil are determined. A circular coil with a radius of 10mm is chosen as the receiver coil. Secondly, the distribution of the magnetic field generated by the rectangular coil is analyzed based on the Biot-Savart’s law. Then the relationship between the distance and the magnetic field intensity will be obtained and expressed as a formula according to the analysis result. Finally, the above formula is chosen as the optimization constrains and the power transfer efficiency is chosen as the optimization objective function. After the optimal designing, the optimal parameters of the transmitter coils are obtained and verified through the experimental system as shown in Fig. 2. The power transfer distance is about 30cm, and the power received by the receiver coil can achieve about 5W. The detailed results will be given in the full paper.

In previous researches, an operator-based sliding mode control design to achieve high power transfer efficiency of a wireless power transfer (WPT) system via magnetic resonance coupling were shown. However, it is difficult to reduce the steady-state error by using SMC-based tracking controller. In this paper, an operator-based integral sliding mode control method is adopted to reduce the steady-state error in the WPT system. Moreover, high power efficiency should be achieved in the WPT system by using an impedance matching control. The effectiveness of the proposed method is verified by simulation results.

Achieving high stable Power Transfer Efficiency (PTE) in Wireless Power Transfer (WPT) systems remains challenging due to the nonlinear, multimodal nature of the optimization space. Conventional algorithms such as Genetic Algorithms (GA), Differential Evolution (DE), and Simulated Annealing (SA) often face premature convergence, sensitivity to parameter settings, and inconsistent performance across runs. To overcome these issues, this study introduces the Evolutionary-Swarm Hybrid Algorithm (ESHA), which integrates DE for directional exploration, GA crossover for population diversity, SA for adaptive convergence, and Lévy Flights for stochastic global search. ESHA was implemented on a WPT system with a fixed 20 cm transmission distance and compared with GA, DE, and SA using three performance indicators: PTE, convergence speed, and computational efficiency. Results show that ESHA achieved a maximum PTE of 97.18%, surpassing GA (96.81%), DE (96.65%), and SA (96.19%), while maintaining zero variance across independent runs. It converged in an average of 31.2 iterations, slightly faster than GA (33.15) and SA (32.1), and comparable to DE (31.3). Execution time was 0.4738 s, close to GA (0.4654 s) and only marginally higher than DE (0.4262 s) and SA (0.4329 s). Statistical validation confirmed significant improvements in PTE (p &lt; 0.05).

In 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.

ABSTRACTThis paper proposes a new method to increase the transfer efficiency of a wireless power transfer (WPT) system, having a source coil, a sprial transmitter (Tx) coil, a load coil and a ground plane, by utilizing the ground plane itself. The creation of cross slits at the ground center and employment of a lumped capacitor on the ground plane transform the ground plane into an additional resonator, which makes the original WPT system work as a 4‐coil WPT system, producing a higher efficiency. By experiment, with an optimized capacitor on the ground plane of C = 2180 pF, the measurement of transfer efficiency shows a maximum improvement of 10% at a transfer distance of 40 cm, compared to the case without the ground plane. The transfer efficiency of the proposed system at transfer distance of 15 cm is 46%. Circuit theory and electromagnetic simulations are employed to analyze the proposed WPT system, giving results consistent with the measured ones. The operating frequency of the proposed system is 6.78 MHz. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:514–521, 2017

A method that efficiently calculates the Power Transfer Efficiency (PTE) of a Wireless Power Transfer (WPT) system is described in this paper. It allows for arbitrary relative positions and orientations between devices in the system, both in far-field and radiative near-field configurations. The method uses a single simulation or measurement of the radiation patterns of the antennas employed in the WPT system, from which the interaction between devices at any relative position and orientation can be modeled. A spherical harmonics decomposition, together with Wigner-D rotation matrices, is applied to perform efficient translations and rotations of the devices used in the WPT system.

Chronic neuropathic pain is one of the most debilitating medical conditions that impacts the lives of almost 20% of the population in the United States. Optogenetic neuromodulation is proven to be one of the possible cures for this chronic disease. To stimulate multiple neurons simultaneously, distributed miniaturized implants are needed to cover a wide range of areas. In this paper, an on-chip design of an inductively coupled wireless power transfer (WPT) system for an optogenetic implant is presented. A 0.3 mm × 0.3 mm on-chip spiral coil is designed using a standard 0.5 $\mu$ m CMOS process and characterized as the receiver of the WPT system. The electromagnetic (EM) field distribution through different tissue layers is investigated which helps to further evaluate the maximum specific absorption rate (SAR) and temperature through the brain tissue. The system achieves a measured power transfer efficiency (PTE) of 0.65% and 0.79% with matching networks through a 10 mm phantom tissue layer and air links respectively. At 10 dBm transmitted power, the maximum SAR value is simulated to be 1.53 W/kg with the maximum temperature increase of 0.73 $^{\circ }$ C through the skin layer due to the EM field exposure. A case study of the proposed on-chip coil-based WPT system shows the different light intensity levels that can be achieved for optogenetic neuromodulation application. Thus, the proposed miniaturized WPT system proves to be a good candidate for future distributive neuromodulation applications.

Dual-band coil modules facilitate efficient access to distinct-band, high-power, or rapid-charging wireless power transfer (WPT) systems. However, they do not function efficiently when the frequency ratio between two operating frequencies is large. To overcome this problem, we propose enhanced dual-band coil modules that adopt repeaters in the WPT system. We present a circuit-based analysis of repeaters in various dual-band coil modules compared with those in a single-band WPT system. The analytical results provide a design methodology applicable to diverse types of dual-band coil modules with a repeater in the WPT system. Our experimental results are consistent with the circuit-based analysis: coil power transfer efficiencies of 55% at 200 kHz and 74% at 6.78 MHz were obtained concurrently in the dual-band WPT system with a dual-band repeater. This paper reduced the application constraint of dual-band coil modules and facilitated the realization and application of multiband WPT systems.

Introduction. The system of delivering electricity without wires is known as wireless power transfer (WPT). The WPT system has been extensively used in a number of industries, health, telecommunications, and transportation. However, the distance between the transmitter and receiver coils has a significant impact on its efficiency. Lower power can be generated between coils the farther apart they are, and vice versa. The novelty of the proposed work is innovative in that it develops a multi-magnetic circular planar spiral relay to improve the WPT system’s performance and designs circular planar spiral coils to achieve an appropriate inductance value for the 5 kHz matching frequency. The goal of paper is to create a circular planar spiral coil with an appropriate inductance value for the 5 kHz matching frequency. Methods. The transmitter circuit, receiver circuit, and DC voltage source are parts of the WPT system. The inverter circuit uses the inductive coupling technique to transform the DC power source into AC voltage on the transmitter coil. The suggested coil is additionally employed as a multi-magnetic circular planar spiral relay in order to increase the mutual inductance between the receiver and transmitter coils. Results. To monitor the power improvement that results from adding a multi-magnetic relay to the system, the transmitter coil, receiver coil, and multi-magnetic relay are positioned at specific distances from each other. With Vdc = 30 V and dtr = 21 cm, the power received at the receiver coil can therefore be improved by up to 67 %. Practical value. The multi-magnetic circular planar spiral relay applied in the WPT system has been investigated in an experimental study and it can be applied for DC load. References 26, table 1, figure 18.