Comprehensive Analysis of Side-Placed Metamaterials in Wireless Power Transfer System

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.

The magnetic fields (MF) generated in close proximity to high power wireless power transfer (WPT) systems generally exceed exposure limits and might also violate basic restrictions (BR). However, there are as yet no available standards describing methods to measure the MF generated by WPT systems. In this study, a new method for demonstration of compliance with the BR in the close proximity to sources at frequencies from 3 kHz to 10 MHz is proposed. This approach mitigates overestimation by incident field assessment in strong field gradients close to WPT systems. The spatial peak MF amplitude and gradient generated by WPT systems are measured with a field gradient probe at the closest location to the source. The induced fields and absorbed power are then calculated on the basis of specific transformation functions for testing of compliance with the BR of all international safety guidelines.

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.

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.

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.

In the receiver-side of wireless power transfer (WPT) system, the two power stages such as rectifier and battery control converter have been widely used due to its easy implementation. However, since the two power stages cause many number of components on the conduction path, it degrades the efficiency and power density of WPT system. Also, in the WPT system, because the communication control between transmitter and receiver side have to be used due to its physical contactless structure, the transmitter-side cannot effectively control receiver-side rectifier outputs. To relieve these drawbacks, this paper proposes a new receiver-side integrated regulator. The proposed structure is based on the general full-wave rectifier diode structure, and a single-switch is integrated for output voltage regulation with phase-shift control strategy. The proposed structure can reduce the number of components on the conduction path, resulting in high power density. Moreover, the proposed method can remove communication control with stable receiver-side outputs. Theoretical analysis and simulation results verify that the proposed structure and control method enables stable output voltage regulation without communication control between transmitter and receiver side. The effectiveness of the proposed structure and control method is verified by a prototype with input 380V DC and 150W output.

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.

The defected ground structure (DGS) technique enables miniaturization of the resonator which leads to the development of the compact near-field wireless power transfer (WPT) systems. In general, numerous challenges are inherent in the design of the DGS-based WPT systems and, hence, appropriate trade-offs for achieving optimal performance are required. Furthermore, the design advancements have led to the development of the DGS-based multi-band WPT systems to fulfill the needs of simultaneous data and power transfer. The innovations in the DGS-based WPT systems have also resulted in the definition of more commonly used figures-of-merit for the benchmarking of various performance metrics. The literature is replete with the design schemes to address one or more associated design challenges and successful WPT system realizations with enhanced performance. With this in mind, this paper touches upon the DGS-based WPTs developments and presents a concise report on the current state-of-the-art and future directions.

Exploring Dielectric Resonator Antennas (DRAs) in Electric Vehicles (EVs) Wireless Power Transfer (WPT) systems is the focus of this study. DRA technology has gained prominence for its unique advantages, offering high efficiency and compact form factors in comparison to conventional antennas. In the context of EVs, the integration of DRAs in WPT systems has shown promising results in addressing challenges related to charging efficiency and spatial constraints. The resonant properties of DRAs enhance power transfer efficiency by mitigating impedance mismatches and reducing energy losses during transmission. Furthermore, the dielectric material properties of DRAs contribute to minimizing electromagnetic interference and enhancing the reliability of WPT in EV applications. This highlights the potential benefits of employing DRAs in achieving robust and efficient wireless charging solutions for electric vehicles. The study encompasses theoretical analysis, simulation studies, and practical implementations to validate the performance of DRAs in WPT systems. The findings suggest that DRA-based WPT systems present a compelling avenue for advancing the state-of-the-art in EV charging technology with efficiency of 84%, providing a more streamlined and effective approach to meet the growing demands of electric mobility in scooters.

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).

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.

The wireless power transfer (WPT) system for LED TVs could be adapted to transfer power to specific locations in luxury residences. However, at a resonant frequency, the output power of the WPT system is only able to provide maximum power at only a set distance. This article presents the adaption of mutual impedance for maximum power point tracking (MPPT) to vary the distance for LED TVs using the WPT system. To adapt the mutual impedance, the frequencies and the resonator capacitances are tuned to the required distance. In the experiment, the WPT system was loaded with a 30W LED TV and the input was through a full-bridge inverter to enable the input voltage and frequency to be varied. The computer simulation and the actual experiment on MPPT for the LED TV WPT system closely correlate. The result shows that when the LED TV WPT system input was 6.66 V, 3.01 kHz, C 16.8 F, the maximum output power was 30.1 W was achieved at a distance of only 10 cm. Significantly, when using the frequencies and resonator capacitances according to the mutual impedance adaption as proposed in this article, the LED TV WPT output power reached peak power at distances varying between 0-60 cm distances.

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.

ABSTRACTIn order to solve the problem that the automatic guided vehicle requires load‐independent constant current (CC) and constant voltage (CV) dual‐type outputs, it is necessary to design a dual‐output wireless power transfer (WPT) system with different output types. However, the existing dual‐output WPT systems have problems such as unnecessary cross‐coupling, limited space utilization, and complex control methods; therefore, this paper proposes a CC and CV dual‐output WPT system based on receiving side decoupling. In the system, the transmitting side coil uses a Q‐type coil and a solenoid coil that are connected in series and wound vertically, and the receiving side coil uses a Q‐type coil and a solenoid coil that are independent and perpendicular to each other; the mutually perpendicular Q‐coil and solenoid coils are naturally decoupled, thus eliminating the effects of cross coupling in the system. First, the decoupling characteristics of the proposed magnetic coupler are analyzed in detail. Second, a mathematical model is established based on the decoupling of the magnetic coupler, and the load‐independent output characteristics of the dual‐output WPT system and the input impedance showing pure resistance characteristics are derived in detail. Then, the output characteristics under ZPA conditions that can be achieved by the system are further verified through simulation analysis. In addition, in order to reduce the conduction loss of the switch tube in the system, the influence of the change of compensation component parameters on the realization of zero voltage switching is analyzed through normalized simulation. Finally, an experimental prototype is built, achieving CC output of 3.5 A and CV output of 70 V, verifying the correctness of the above theoretical analysis. In addition, when the first receiving side load is 30 and the second receiving side load is 19 , the peak efficiency can reach 92.6%.

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.