High efficiency wireless power transfer system design for circular magnetic structures

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.

The magnetic coupler plays an important role in wireless power transfer (WPT) system and concerns the transmission efficiency and output characteristic of system. The effects of asymmetric two-coil and three-coil magnetic couplers with a large intermediate coil on lateral misalignment tolerance for WPT system are studied. First, circuit models of two-coil and three-coil magnetic couplers are analyzed and the key parameters affecting the efficiency of two-coil and three-coil coupler are deduced. Then, a 3-D finite element model of the two-coil coupler is established, and the efficiency of WPT systems with two different structures is investigated while misaligning. Finally, the applicable conditions of two coil structures are discussed. The results show that when the maximum misalignment distance is reached, the misalignment tolerance effect of two-coil structures is weakened, and the system efficiency can be higher by using the three coils structure with a large intermediate coil.

Many researches have been carried out by previous researchers to get better performance of a wireless power transfer (WPT) system. This research uses a partitioned shielding made of metallic material to protect WPT system from electromagnetic interference (EMI). Also, a shielding material is connected to ground, so that it can reduce occurrence of stray/parasitic capacitance between electrodes of electronic components. Both the electromagnetic interference and the stray/parasitic capacitance can deteriorate performance of WPT system. In this research, the WPT system works at voltage 14.7V, frequency 56,298 Hz, distance coil to coil is 0 till 5 cm. The efficiency of WPT system is achieved until 14.9 % (without shielding) and until 17.9% (with partitioned shielding).

This paper presents a novel design concept for near-field wireless power transfer (WPT) systems that leverages the seamless integration of metamaterials (MTMs) into slotted resonators. This approach enhances magnetic field ( $$\textbf{B}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>B</mml:mi> </mml:math> ) distribution, strengthens evanescent wave coupling, and hence improves overall WPT performance. An MTM structure exhibiting negative permeability at the operating frequency of 433 MHz was designed and incorporated into a square-slot-based resonator. Electromagnetic (EM) analysis revealed increased current density and subsequently enlarged $$\textbf{B}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>B</mml:mi> </mml:math> around the resonator. Additionally, impedance matching, key parameter extraction, and equivalent circuit (EC) modeling were performed using the effective J-inverter method. The developed WPT system, with compact dimensions of 30 $$\times$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>×</mml:mo> </mml:math> 30 $$^{\text {2}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mtext>2</mml:mtext> </mml:mmultiscripts> </mml:math> , achieved a power transfer efficiency of 82% at 33 mm. The design was experimentally validated, showing excellent agreement among EM simulations, EC modeling, and measurement results. Finally, performance comparison with other reported systems confirmed the superiority and practical effectiveness of the proposed design in enabling compact and highly efficient WPT systems.

Wireless power transfer (WPT) system is an area where many studies have been conducted for electric vehicles (EV s) charging. Loosely coupled transformer with a wide range of coupling coefficient <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(k)$</tex> value is a main factor of WPT system. Coupling coefficient variation which is highly sensitive to the coil misalignment causes a change in overall system performance. Therefore, this paper introduces design method of WPT system insensitive to coupling coefficient variation depending on the coil misalignment. The actual coupling coefficient variation is discussed using the coils shown in SAE J2954 as standard for electric vehicle charging. Charging current <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(i_{\text{batt}})$</tex> control methods based on the connection of post-regulator and their effects on the system performance are also studied. Finally, efficiency analysis of designed WPT system from inverter to rectifier according to control methods is discussed.

Based on the magnetic coupling resonant wireless power transmission technology, how to improve the efficiency of the system under the condition of low voltage and high current input is studied. In this paper, a wireless power transfer system based on Z-source inverter is proposed. In the environment of low voltage and high current input, the input voltage is low, and the increase of DC-DC link will increase the loss of the system. Therefore, this paper analyzes the circuit of the magnetically coupled resonant wireless power transmission system in the low-voltage input and high-current output environment, and applies the Z-source inverter to the low-voltage and high-current input environment to improve the performance of the system.

A wireless power transfer (WPT) system via magnetic resonance coupling method is attracting attention to high convenience. A WPT system has problems such as power transmitting loss and output voltage fluctuation due to the change in the coupling coefficient and the load state. In previous method, sliding mode control system as a tracking controller considering nonlinearity and uncertainty has been proposed, but the output of this control system had bias and chattering. This paper proposes operator-based nonlinear sliding mode control system to reduce chattering and bias simultaneously for a WPT system using buck converter. First, the model of the WPT system using rectifier and buck converter is explained and dynamics formulas are derived. Next, the proposed operator-based nonlinear sliding mode control system design for the WPT system is described and tracking performance is confirmed. Finally, the result of simulation of constant voltage control and comparison with the previous method is shown.

Wireless power transfer (WPT) through magnetic resonance coupling (MRC) offers a safe and simple solution for underwater (UV) vehicles without being affected by water conductivity. Due to its ease of control in WPT systems, the most suitable topology is Serial-Serial (SS). In this study, square transmitting and receiving coils with dimensions of 40 cm - 40 cm were designed for 3.3 kW power transmission at 85 kHz. The design was studied in the air, pure water, and seawater environments. Three different cases were analyzed with ANSYS Maxwell 3D. The WPT system responded similarly in air and pure water environments. However, it was determined that the eddy current loss increased, the mutual inductance decreased, the coupling factor weakened, and the critical air gap decreased by about 0.2 cm in the seawater environment. The results showed that the WPT system's efficiency was similar for air and pure water but tolerably lower in the marine environment. Further, the health effects of the WPT design were examined through the ANSYS HFSS, in line with the IEEE standard and ICNIRP guidelines.

Wireless power transfer (WPT) systems are power electronic converters which can be installed under the road and charge the butteries of the electric vehicles. High total harmonic distortion (THD) of the input current is an important challenge in WPT system design. In this paper a new topology is proposed for WPT systems to reduce their input current THD. In the proposed topology, a quasi-Z-source inverter (QZSI) is used in series with a LLC resonant network. In addition to the DC voltage boosting, QZSI shapes the input current. The simulation results verify the performance of the proposed structure in THD reduction and power factor correction in comparison with the conventional Z-source resonant converter.

High Transmission Capacity P.U.A. Wireless Power Transfer for AUV Using an Optimized Magnetic Coupler

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.

This paper proposes double C-shaped reactive shielding coils to alleviate the efficiency degradation caused by the reactive shielding method. Using the proposed method, higher power transfer efficiency and EMF shielding performance than the conventional reactive shielding coil can be achieved. The main idea of the proposed shielding coils is to create an additional inner loop by making the shielding coil into two C-shaped loops. In the inner loop of the proposed shielding coils, current flows in the same direction as that of transmitting coil to amplify the magnetic field. In the outer loop, current flows in the opposite direction to cancel the leakage magnetic field. In this paper, the wireless power transfer system with the proposed shielding coils is designed and verified through 3D electromagnetic and circuit simulation.

Electric vehicles (EVs) with varying output power levels can be efficiently charged using wireless power transfer (WPT) systems. However, when there is a significant power class mismatch between vehicle assemblies (VAs) and ground assemblies (GAs) in charging stations, the overall WPT system efficiency can degrade substantially. To address this challenge, this article introduces a dc-link parallel ac-link series multi-inverter multirectifier architecture for high-power WPT systems. The design focuses on optimizing modulation, power transfer capability, and power sharing. A detailed analysis of power losses is conducted, and an effective control method based on mutual inductance identification is proposed to minimize losses. The proposed method is optimized using the Golden Jackal Optimization algorithm. The results of the simulation in MATLAB demonstrate the effectiveness of the proposed system in improving efficiency and reducing power losses. Simulation results show a significant reduction in system power losses, confirming the efficacy of the control strategy in enhancing the overall WPT performance

This paper presents a theoretical analysis, an optimal design method, and experimental results for a wireless power transfer (WPT) system with an intermediate coil. The analytical expression of the dc voltage transfer function is presented and discussed. In a two-coil WPT system, which has low coupling coefficient, the intermediate coil boosts the apparent self-inductance and magnetizing inductance of the primary side at around the resonance frequency of the intermediate coil, so that the apparent coupling coefficient is compensated. The coupling coefficient makes the system efficiency increase and induces bifurcation phenomenon. From the analysis, this paper proposes an optimal design method using the second resonance frequency operation with the bifurcation phenomenon and presents design procedure for high efficiency. A prototype of the WPT system with the intermediate coil is implemented and experimented to verify the validity of the analysis and the proposed design method. The prototype operates at 100 kHz switching frequency and has an air gap between primary and secondary side of 200 mm. An overall system efficiency of 95.57% has been achieved at 6.6 kW of output power.

To meet the regulations established to limit human exposure to time-varying electromagnetic fields (EMFs) such as the International Committee on Non-Ionizing Radiation Protection (ICNIRP) guidelines, thin metallic sheets are often used to shield magnetic field leakage in high power applications of wireless power transfer (WPT) systems based on magnetic field coupling. However, the metals in the vicinity of the WPT coils cause the decrease of self and mutual inductances and increase of effective series resistance; as such, the electric performance including transmission power and the efficiency of the system is affected. With the research objective of further investigating excellent shielding effectiveness associated with system performance, the utilization of the optimal magnetic field shielding method by metallic sheets in magnetic field coupling WPT is carried out in this paper. The circuit and 3D Finite Element Analysis (FEA) models are combined to predict the magnetic field distribution and electrical performance. Simulation and experiment results show that the method is very effective by obtaining the largest possible coupling coefficient of the WPT coils within the allowable range and then reducing the value nearest to and no smaller than the critical coupling coefficient via geometric unbroken metallic sheets. The optimal magnetic field shielding method which considers the system efficiency, transmission power, transmission distance, and system size is also achieved using the analytic hierarchy process (AHP). The results can benefit WPT by helping to achieve efficient energy transfer and safe use in metal shielded equipment.