Performance Of Wireless Power Transfer System Research Articles

Ferrite shielding thickness and its effect on electromagnetic parameters in wireless power transfer for electric vehicles (EVs)

Wireless power transfer (WPT) has become an increasingly popular technology for charging electronic devices wirelessly. One of the key challenges in WPT is increasing efficiency and reducing different losses in coils caused by the higher air gap and coil coupling between the primary and secondary coils. Ferrite shielding is a common technique used to reduce losses and increase the coupling in WPT systems. In this paper, we present an analysis and comparison study of the effect of ferrite shielding thickness (F_T) on the electromagnetic parameters of WPT systems. We investigate the impact of varying the ferrite shielding thickness on parameters such as power transfer efficiency, coupling coefficient (k), and magnetic field strength (B). Our results show that increasing the ferrite shielding thickness can significantly reduce losses and improve the performance of WPT systems. Also, analyze the trade-off between ferrite shielding thickness and power transfer efficiency and provide guidelines for selecting an optimal thickness for a given application. This study provides valuable insights into the design and optimization with weight vs. coupling comparison for WPT systems using ferrite shielding. It can help inform the development of future WPT technologies. The result obtained through simulation, i.e., coil-to-coil efficiency, is 98.88 to 99.7360% at 6.78MHz frequency for a 5-mm- to 50-mm-thick ferrite rectangular coupler using ANSYS Maxwell and ANSYS simplorer software.

Modeling of Litz-Wire DD Coil With Ferrite Core for Wireless Power Transfer System

DD planar coil with ferrite core is one popular coupling structure in wireless power transfer (WPT), especially for electric vehicle applications. The coil design is critical for improving the performance of WPT system. However, the coupler design purely relying on finite element analysis (FEA) software is time-consuming. And literature on the modeling of DD coil is lacking. Therefore, the model of DD coil with a ferrite core for calculating self-inductance, mutual inductance, and AC resistance is proposed in this paper. The condition when primary and secondary coils have different sizes is also considered. The case that there is misalignment is also analyzed. Meanwhile, a genetic algorithm based on the proposed coil mathematical model is proposed to optimize the coil structure. For verifying the accuracy of the proposed model, the simulation model based on the FEA and a 1.2-kW laboratory prototype are built simultaneously. The calculation values based on the proposed model is highly consistent with the simulation results and experimental values. Error for calculating self-inductance and mutual inductance is within 5% when coils on the primary side and secondary side are in alignment. The error for calculating the AC resistance of the coil is within 10% when the frequency range is 0-200kHz.

Novel Cuk-Based Bridgeless Rectifier of Wireless Power Transfer System With Wide Power Modulation Range and Low Current Ripple

A novel Cuk-based bridgeless rectifier is proposed for receiving side of wireless power transfer (WPT) system. The proposed converter can not only help improve overall efficiency but also is with features of wide power modulation range and very low output current ripple. In terms of the output current source characteristics of series-series-compensated WPT system, a bridgeless rectifier and a Cuk converter are combined and an input inductor of Cuk converter is cut down to form the proposed single-stage converter. Besides, a synchronization operation method is derived for the proposed converter to realize the optimal working point of transmission power and efficiency. Operation principles of the converter and its impact on performance of WPT system are analyzed. Also, design methods for system parameters are given. A prototype is built up to verify the feasibility of the proposed topology and the operation method. It is noted that the proposed converter can well adjust the output power of WPT system to realize the desired working point via adjusting the duty cycle at different transfer distances and loads.

Experimental Evaluation of Layered DD Coil Structure in a Wireless Power Transfer System

The transfer efficiency of a wireless power transfer system (WPT) is a critical and desired property for faster dynamic charging of electric vehicles, portable electronics, and battery powered medical devices. Mutual and self-inductance are two parameters that influence performance of the coil. To achieve an increase in inductance, coils are wound with more turns, therefore, making them bigger and not being able to fit into a fixed area. In this article, we have implemented a novel layered double D (LDD) coil with configuration that is optimized to create maximum constructive flux linkage between the transmitting and receiving coils. While also increasing the effective area of its parent double D (DD) coil, LDD still maintains the same lateral area. The inductances of both LDD and DD coil were measured alongside each other. LDD gave a significant increase in inductance comparison to the DD coil. Ferrite and aluminum shielding material are introduced to the coils to determine the effect on inductance. The coils had a more consistent performance when ferrite was used as a shield. By evaluating the WPT performance of various coil configurations, it was determined that the LDD coil with ferrite shield gave the best performance, making them very suitable for next generation WPT applications.

Position-Insensitive Wireless Power Transfer Based on Nonlinear Resonant Circuits

Near-field resonant-based wireless power transfer (WPT) technology has a significant impact in many applications ranging from charging of biomedical implants to electric vehicles (EVs). The design of robust WPT systems is challenging due to its position-dependent power transfer efficiency (PTE). In this paper, a new approach is presented to address WPT's strong sensitivity to the coupling factor variation between the transmit and receive coils. The introduced technique relies on harnessing the unique properties of a specific class of nonlinear resonant circuits to design position-insensitive WPT systems that maintain a high PTE over large transmission distances and misalignments without tuning the source's operating frequency or employing tunable matching networks, as well as any active feedback/control circuitry. A nonlinear-resonant-based WPT circuit capable of transmitting 60 W at 2.25 MHz is designed and fabricated. The circuit maintains a high PTE of 86% over a transmission distance variation of 20 cm. Furthermore, transmit power and PTE are maintained over a large lateral misalignment up to ±50% of the coil diameter and angular misalignment up to ±75°. The new design approach enhances the performance of WPT systems by significantly extending the range of coupling factors over which both load power and high PTE are maintained.

Design and analysis of 2-coil wireless power transfer (WPT) using magnetic coupling technique

2-coil non-radiative wireless power transfer (WPT) is studied to find the coil diameter ratio to effective distance of power transfer efficiency (PTE). Single circular coil and spiral coil are designed and simulated using CST software to compare the result of coil diameter versus effective distance of PTE by using S<sub>21</sub> value. Accordingly, the quality factor (Q) of both coils are presented as Q factor is one of the parameter that affect the performance of WPT system. The result is promising as the effective distance is more than the coil diameter with (PTE) more than 50% using spiral coil as compare to single coil design.

Implementing an Impedance Compression Network to Compensate for Misalignments in a Wireless Power Transfer System

This paper presents an impedance compression network (ICN) design in a wireless power transfer (WPT) system to compensate for distance or alignment variations between coils. In midrange WPT applications, magnetic resonant coupling coils are mainly implemented to achieve high efficiency for charging batteries. However, a distance or horizontal alignment variation between coils changes their coupling coefficient, and it decreases the overall performance of WPT systems because the zero voltage switching in a resonant inverter is lost. In order to reduce coil impedance variation, we propose an ICN that compresses variations in coil impedance. The ICN consists of a resistance compression network and a phase compression network to suppress magnitude and phase variations, respectively, in the coil impedance. Only passive components, such as inductors and capacitors, are used to implement an ICN.

S‐PS resonant topology of WPT system for implantable spinal cord stimulator

Magnetic resonance-based wireless power transfer (WPT) system offers a promising solution to provide power for implantable spinal cord stimulator (SCS). To meet with the clinical requirements, the SCS-WPT system should have high transfer efficiency and long transfer distance. As the topology of the resonant network will directly affect the transfer efficiency and output power of the WPT system, a new resonant network, series-parallel and series (S-PS), is selected in this work. The performance of WPT system with S-PS resonant network has been compared with those with the classic resonance networks, it is concluded that S-PS is the suitable resonant network for the WPT system in a wide range of load. Finally, an SCS-WPT prototype with S-PS resonant network is built with detailed parameter design to verify the correctness of theoretical analysis. The system efficiency is up to 68.4% at a coil separation of 50 mm.

Study of the Circular Flat Spiral Coil Structure Effect on Wireless Power Transfer System Performance

This paper analyses the relationship between the coil design parameters and the system performance, including power transfer efficiency and amount, when circular flat spiral coils are adopted in a wireless power transfer (WPT) system. Coil design variables including outer radius, inner radius, channel width and coil turns are thoroughly studied to improve the system performance with a limited maximum outer radius for practical purposes. A two-coil WPT system has been built to verify the analysis, and the experimental results show good consistency with the theoretical calculations and simulation results, which show that the coil design parameters have a significant impact on the system performance, even with the same coil size. In the experiments, the coil-to-coil distance is 150 mm, the maximum coil outer radius is limited in 300 mm, and the DC input voltage and the load resistance are 100 V and 5 Ω, respectively. When the coils are tightly-wound in the most traditional way to maximize the coil size, the coil-system efficiency is 62.6% with only 4.5 W load power. In contrast, the efficiency optimized coil can improve the coil-system efficiency to 91.2% with the outer radius stayed the same. Besides, when the power transfer efficiency and amount are considered simultaneously, the system can achieve 1279 W load power with 85.94% coil-system efficiency.

Effects of Foreign Metal Object on Soft-Switching Conditions of Class-E Inverter in WPT

A foreign metal object will deteriorate the performance of wireless power transfer (WPT) systems and cause insecurity issues. Therefore, the influence principles and rules of foreign metal objects on soft-switching conditions of Class-E inverters and the performance of WPT systems are developed in this paper. The effects of different metal materials on coil parameters at different frequencies and positions are analyzed first, then the effects of foreign metal objects on soft-switching conditions of Class-E inverters and the power transfer capability of WPT systems are investigated. Principle analyses and simulation results demonstrate that there are significantly different effects on the soft-switching conditions and power transfer when a foreign metal object is placed near the transmitter coil or the receiver coil. In addition, the monotonicity of the variation in power transfer also depends on the position of the foreign metal object. Finally, a WPT experimental prototype with a Class-E inverter is implemented to verify the influence principles and rules of foreign metal objects. The experimental results are highly consistent with the principle analyses and simulation results.

Field Orientation Based on Current Amplitude and Phase Angle Control for Wireless Power Transfer

The low coupling coefficient between the transmitter and receiver is the major constraint of a wireless power transfer (WPT) system. Although some approaches, such as increasing the quality factor and achieving precise impedance matching, can reduce the adverse impacts of the low coupling coefficient and improve the system performance, high leakage magnetic flux between the transmitter and receiver remains a problem. With the increase in transfer distance and the misalignment between the transmitter and receiver, the increasing leakage magnetic flux of nondirectional fields degrades the WPT system performance. This paper proposes an active field orientation method to shape the magnetic flux so as to minimize the leakage flux. The amplitude and phase angle of the magnetizing current are controlled, and a coil structure for minimizing the coupling among the transmitters and generating a three-dimensional magnetic field is proposed. This method realizes three-dimension full-range field orientation with adjustable magnitude and direction of B-field at an arbitrary point, and as a result the B-field is concentrated with reduced leakage magnetic flux. The proposed field orientation shaping technique is verified by theoretical analysis, simulation, and experimental results.

Optimisation analysis of coil configuration and circuit model for asymmetric wireless power transfer system

The authors present a new asymmetric structure using an optimisable coil configuration and circuit model to eliminate frequency splitting and increase high-efficiency transfer distance in wireless power transfer (WPT) via magnetic resonance coupling. A pair of non-identical coils is proved theoretically and optimised to limit the coupling coefficient. The series-shunt mixed-resonant circuit structure is adopted to promote the performance of WPT system. The advantages and characteristics of the asymmetric system using mixed-resonant circuit structure based on appropriate non-identical coils are depicted by numerical calculation and simulation. Moreover, the WPT system is finally set up to verify the theory prediction. All the calculated and experimental results show that frequency splitting is suppressed in close distance effectively. Moreover, the high-efficiency transfer distance is proved to exceed the triple diameter of receiving coil. Therefore, a relatively high-efficiency and long-distance WPT system, which can be a good candidate for charging portable electronics, is obtained by selecting suitable circuit parameters and appropriate non-identical coils.

A polygonal double-layer coil design for high-efficiency wireless power transfer

In this work, we present a novel coil structure for the design of Wireless Power Transfer (WPT) systems via magnetic resonant coupling. The new coil consists of two layers of flat polygonal windings in square, pentagonal and hexagonal shapes. The double-layer coil can be conveniently fabricated using the print circuit broad (PCB) technology. In our design, we include an angle between the two layers which can be adjusted to change the area of inter-layer overlap. This unique structure is thoroughly investigated with respect to the quality factor Q and the power transfer efficiency (PTE) using the finite element method (FEM). An equivalent circuit is derived and used to explain the properties of the angularly shifted double-layer coil theoretically. Comparative experiments are conducted from which the performance of the new coil is evaluated quantitatively. Our results have shown that an increased shift angle improves the Q-factor, and the optimal PTE is achieved when the angle reaches the maximum. When compared to the pentagonal and hexagonal coils, the square coil achieves the highest PTE due to its lowest parasitic capacitive effects. In summary, our new coil design improves the performance of WPT systems and allows a formal design procedure for optimization in a given application.

The Effect of Relay Coil in Four-coil Wireless Power Transfer System

Wireless power transfer (WPT) system based on magnetic resonant coupling can realize the mid-range wireless power transfer, but the efficiency will decrease rapidly with the transfer distance increasing to the long-range. In this letter, a relay coil is utilized to improve the performance of WPT system over a relative long distance. The circuit models of WPT system with or without relay coil are built and the scattering parameter is used to evaluate the transfer performance. In four-coil system, the frequency splitting is analyzed and the critical coefficient is given. In five-coil system, the positions of relay coil under different distances are investigated and using FEM software the model is corrected. Then, the design constraint of relay coil is derived. Based on the parameters used in model analysis, the simulations and experiments are carried out and the results confirm the model analysis, which indicate that the relay coil can effectively extend the transfer distance with a relative high efficiency or increase the transfer efficiency at a given distance.