Wireless Power Transfer For Electric Vehicles Research Articles

Sensitivity Analysis of a Double-Layer Coupling Structure for an Electric Vehicle Wireless Power Transfer System

This paper proposes a novel coupling structure wireless power transfer (WPT) technology for improving the charging and recharging efficiency between electric vehicles (EVs) in the case that the transmitting and receiving coils are not exactly aligned. During the process of wireless power transmission, if the relative position of the coils located on each objective is randomly changed, a change in the mutual inductance occurs, which critically leads to fluctuation in the WPT system output. In order to improve the tolerance of the EV WPT system, considering coupling structure misalignment and the deflection caused by relative location changes, a double-layer coupling structure with solenoid pads and double-D pads (SP-DDP coupling structure) is designed for deployment on the side of EVs. Then, the coupling structure is developed through parametrized optimization. Finally, the established coupling structure is evaluated through simulations and an experiment using a prototype, the results of which demonstrate that the proposed coupling structure can achieve good anti-misalignment and anti-deflection performance, realizing a system efficiency of 92.65% and an output power of 192.02 W for the designed EV WPT system.

Evaluation of Electromagnetic Exposure of the Human with a Coronary Stent Implant from an Electric Vehicle Wireless Power Transfer Device

The aim of this paper is to analyze in depth the coupling between leakage electromagnetic fields (EMFs) generated by an electric vehicle wireless power transfer (EV-WPT) device under misaligned operating conditions and metallic coronary stents, which could be potentially hazardous to human electromagnetic safety. In this paper, we established that a standing human with a coronary stent implant and a sitting human with a coronary stent implant are exposed to the leaked EMFs of an EV-WPT device with a transmission power of 11 kW and 22 kW and a transmission frequency of 85 kHz, and we quantified the induced E-field strength of the human body by considering the x- and z-axis misalignment ranges of the WPT device as [−75 mm, 75 mm]. The results showed that the enhancement of the induced E-field in the human tissues near the sharp edges of the implant is significant. Meanwhile, the larger the WPT device misalignment generated, the higher the transmission power, and the closer the human body is to the WPT device, the larger the induced E-fieldmax value of the human body is, which has the possibility of exceeding the ICNIRP safety limit, and there is a potential human body electromagnetic safety problem.

Uncertainty Quantification of Human Electromagnetic Exposure From Electric Vehicle Wireless Power Transfer System

With the rapid development of electric vehicles (EVs), the wireless power transfer (WPT) technology of EV is becoming more and more mature. The safety of human electromagnetic exposure caused by the WPT system of EV has become the focus of research. Considering the practical application of EV WPT system, this paper studies the electromagnetic exposure of human body based on the uncertainty quantification theory. A sparse polynomial chaos expansion method is used to establish the surrogate model of the mean value of some human organs’ SAR, and the probability distribution function of SAR is calculated. The Sobol is used to quantify the impact of relevant variables on SAR. The final calculation results show that when the person is on the side of the EV, the offset between the magnetic coupling coils of the WPT and the lateral displacement of the human body on the side of the EV have a greater impact; When a person is at the rear of the EV, the vertical displacement of the magnetic coupling coils of the WPT has a greater impact on the longitudinal displacement of the human body at the rear of the vehicle. Combined with the above analysis, this paper can provide reasonable suggestions for the safety protection of electromagnetic exposure of human body in the WPT of EVs.

Efficiency Optimization of Wireless Power Transfer System for Electric Vehicle Based on Improved Marine Predators Algorithm

Electric vehicle (EV) is the core part of future automobile technology, and safe and reliable wireless power transfer (WPT) technology is the key link to improve the intelligent driving technology of EV. In this paper, the uncertainty quantification method is proposed to guide the optimization design of WPT structure, so as to improve the efficiency of WPT. First this paper establishes a surrogate model of WPT efficiency based on the adaptive sparse polynomial chaos expansion, and the uncertainty of EVs WPT transmission efficiency is quantified, the computational efficiency is improved by about 8.4 times. Then the surrogate model is combined with the global sensitivity analysis method to quantify the impact of different variables in WPT on efficiency and screen out the variables with greater impact. Finally, this paper uses the improved marine predators algorithm to optimize the selected WPT system structure parameters. Considering the uncertainty, the average efficiency of the optimized WPT system is increased from 73.43% to 94.64%. Compared with other optimization methods, it proves that the method in this paper can optimize WPT more efficiently, and significantly improve the transmission efficiency.

Reconfigurable topology of electric vehicle wireless power transfer system to achieve constant-current and constant-voltage charging based on multiple windings

In the wireless charging system of electric vehicles, different charging stages have different charging requirements, namely constant-current (CC) charging mode and constant-voltage (CV) charging mode. The purpose of this paper is to provide a multi-winding wireless charging system with a reconfigurable topology to realize CC and CV charging with different optimal load resistances so that high efficiency can be achieved over a large load resistance range. The designed system can form different compensation topologies by switching on and off relays, such as the series–series topology and the inductor–capacitor–capacitor-series topology. Different topologies have different optimal load resistances, therefore, it can realize efficient transmission in a large load resistance range. In addition, the half-bridge scheme and the full-bridge scheme are the other two functioning modes for each topology. At the same time, the efficiency of the system can reach up to 94.34% and 95.13% in the half-bridge as well as full-bridge schemes under the CC mode. The highest transmission efficiency can reach 93.37% and 90.78% for the half-bridge as well as full-bridge schemes under the CC mode, respectively. Experiment results have validated the proposed method.

Shielding Design for High-Frequency Wireless Power Transfer System for EV Charging With Self-Resonant Coils

This paper provides a complete coil and shielding design solution for a 6.6 kW electric vehicle wireless power transfer system based on compact self-resonant (SR) coils. Due to the presence of a conductive vehicle body above the receiver coil, vertical fringing flux must be shielded in any electric vehicle wireless charger. Using high-frequency SR coils, parasitic capacitance introduced by standard shielding design approaches degrades the quality factor of the coils. In this work, the high-frequency parasitic capacitance introduced by the magnetic and conductive shielding materials is analyzed in detail, and a shielding geometry optimization method is proposed. Using ferrite and an additional dielectric spacer, prototype aluminum-backed SR coils are fabricated to validate the modeling. The total thicknesses of the transmitter and receiver coils are only 11.4 mm and 7.4 mm, respectively. The prototype coils achieve 92.3% DC-DC efficiency and 7.1 kW/dm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> volumetric power density. This paper demonstrates the first 6.6 kW WPT system for EV charging using compact megahertz-self-resonant coils including a complete magnetic and conductive shielding implementation.

Design of Electric Vehicle’s Wireless Power Transfer System Based on Deep Learning Combined With Multi-Objective Optimization

During the wireless power transmission of an electric vehicle (EV), due to the influence of the compensation circuit’s manufacturing process, the driver’s operating technique, and other factors, the wireless power transfer (WPT) efficiency features strong uncertainty. The article chooses the coil group’s spatial parameters as well as the compensation circuit’s parameters as input variables, and then builds the deep learning network as the framework of uncertainty quantification, so as to obtain the relevant statistical characteristic parameters of WPT efficiency, through comparing with the calculation results of classical Monte Carlo (MC), it can be verified that the uncertainty quantification based on deep learning has almost the same solution accuracy and higher computational efficiency. At the same time, the article adopts tent chaotic mapping and adaptive inertia weight strategy to improve the traditional Aquila Optimization (AO) algorithm, then uses the improved multiobjective AO algorithm to accomplish the optimization of the WPT system’s structure. Through the comparison of improved AO and other optimization algorithms, it can be concluded that the improved AO can search out the optimal design parameter group with faster speed and higher accuracy, which provides effective guidance for the actual optimized design of the EVs WPT system.

A Multimodal Modulation Scheme for Electric Vehicles’ Wireless Power Transfer Systems, Based on Secondary Impedance

This study aimed to investigate a multimodal modulation scheme that takes into account the wide range of output characteristics, numerous constraints, and complex working conditions in the wireless charging of electric vehicles. Key electrical parameters and variables in the secondary stages of electric vehicle wireless power transfer (EV-WPT) systems were evaluated based on capacitive, inductive, and resistive impedance working modes. The limiting duty cycle values, D, of the rectifier were derived by detecting the mutual inductance, M. This multimodal modulation was adopted, based on the secondary equivalent impedance phase, to control the impedance working condition and, hence, achieve optimal working performance. The proposed method can modulate the system performance before and during wireless transmission. The proposed control scheme was verified using a 10 kW EV-WPT experimental prototype under a capacitive impedance working mode with 8.5 kW power output. Our proposed method achieved full power output by modulating the impedance working conditions.

Wireless Power Transfer Positioning System with Wide Range Direction-Guided Based on Symmetrical Triple-U Auxiliary Pad

An important area of research in electric vehicle wireless power transfer systems is the detection of the secondary pad, which is vital evidence to determine whether the vehicle is in the effective charging area. However, the detection based on sensors mostly will reconstruct the vehicle structure and has a limit on versatility in all kinds of vehicles and the applicability of magnetic couplers and the influence on the primary pad. Therefore, an auxiliary pad structure and corresponding positioning method for offset estimation utilizing the existing inverter and secondary pad in the vehicle system are proposed. Firstly, to satisfy the needs of different positioning heights and avoid the effect on the primary pad, a triple-U positioning auxiliary pad is designed to assist positioning. Secondly, the direction-guided trajectory and detection algorithm are proposed to modify the vehicle location in real-time after analyzing the corresponding equivalent mutual inductance feature trajectory, according to the magnetic field characteristics of various typical magnetic couplers intervened by the proposed triple-U auxiliary pad. Finally, a prototype system is built to validate the applicability and feasibility of the triple-U auxiliary pad, where the positioning accuracy is within 10 mm, and the maximum recognizable recognition range can reach 300 mm × 300 mm, and the direction-guided trajectory is accurate, which can satisfy the actual positioning requirements of electric vehicles.

Stability Improvement and Overshoot Damping of SS-Compensated EV Wireless Charging Systems With User-End Buck Converters

The multiple fluctuations, such as grid DC input voltage, mutual inductance and the plug-in and plug-out of battery, may lead to instability and deterioration of dynamic performance of electric vehicle (EV) wireless power transfer (WPT) system. The overshoot issue can bring great current stress to EV WPT system, and may induce potential disastrous malfunction of the lithium-ion (Li-ion) battery. This study theoretically reveals the slow dynamic response and large overshoot of a traditional WPT system. For solving these issues, a reliable adaptive feedforward control scheme is proposed and applied in the user-side DC-DC converter, where the communication unit is eliminated. The feedforward loop is proved theoretically to suppress overshoot and system dynamic response. Besides, the feedforward control increases the selective range of control parameters, which can improve the system dynamics. Experiment results verifies that the proposed adaptive feedforward gain allows faster dynamics, and the aforementioned disturbances in EV WPT system can be solved while the system performance is not affected.

An Efficiency Optimization Method of Static Wireless Power Transfer Coreless Coils for Electric Vehicles in the 85 kHz Band Using Numerical Analysis

Wireless power transfer (WPT) has been attracting a lot of attention in recent years for its ability to greatly improve the convenience of our lives. Moreover, WPT for Electric Vehicles (EVs) has become an important key to the spread of EVs. The efficiency of WPT using magnetic field resonant coupling can be evaluated by the kQ product, but the optimal coil design method to maximize the kQ product at a specific frequency has not yet been established. In this paper, taking the Test station GA‐WPT1 and the Test station VA‐WPT1/Z3 of SAE J2954, which is officially defined as the standard for WPT while the electric vehicle is stationary in October 2020, as examples, the coil parameters that maximize the kQ product in the case of the coreless are determined according to the proposed method. An efficiency of 99.13% was obtained with a transmission distance of 200 mm and the number of turns of N1 = 34 and N2 = 30. Also, since all analyses can be derived immediately except for the analysis of the Litz wire to be used, the optimization time could be reduced significantly compared with the electromagnetic field analysis. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Analysis and design for constant current/constant voltage multi‐coil wireless power transfer system with high EMF reduction

The investigation on the constant current (CC)/constant voltage (CV) charging for the electric vehicle wireless power transfer (WPT) system has been widely conducted. However, the CC/CV performance under misalignment cases has been scarcely studied especially for the multi-coil WPT system. The resonant tank compensation methodology for the exciter-quadrature-repeaters (EQR) transmitter-based multi-coil WPT system is studied to achieve high power factor CC/CV charging with low leakage flux over ±150 mm lateral misalignment range. The EQR transmitter consists of one small exciter coil powered by a single full bridge inverter and two larger decoupled quadrature repeater coils which are magnetically coupled to the exciter coil. A variable switched capacitor is applied on the exciter side to maintain a high power factor in the CV mode. A 3-kW experimental setup with a 200 mm nominal vertical distance was built and a three-coil WPT system with a single large repeater coil is chosen as a comparison. Experimental results show that the EQR transmitter-based WPT system achieves 92% coil-to-coil efficiency and reduces the leakage flux density by 70% compared with the existing three-coil system in the CV mode at 150-mm lateral misalignment.

A Design Methodology for EV-WPT Systems to Resonate at Arbitrary Given Bands

Due to the effects of splitting frequency and cross coupling, the resonant frequency of the WPT system usually deviates from the given frequency band, and the system operating at the given frequency band suffers a very low output power. Ensuring that electric vehicle wireless power transfer (EV-WPT) systems operate at a resonant state is the prerequisite for efficient energy transfer. For this purpose, a novel design method by manipulating the eigenstate parameters is proposed in this paper. The proposed system can make a EV-WPT system with arbitrary coil successfully to resonate at any given bands, not just a single band. Therefore, the method designed in this article cannot only eliminate the problem of low power caused by frequency deviation, but also realize the application requirements of multiple frequency bands. Firstly, this article establishes an accurate state space model of an n-coil fully coupled EV-WPT system, and after that, the analytical current response on each circuit is derived. Based on that, a detailed frequency spectrum analysis is presented, along with several essential spectrum parameters’ derivations, including center frequencies and bandwidths. Then, with the center frequency and bandwidth as the design indexes, a novel methodology of designing to make EV-WPT systems achieve resonant-state at arbitrary given bands is derived. Finally, simulation and experimental verification are carried out. Simulation and experimental results show that whether it is a single-band or multi-band system, the accuracy of the value under designed resonant frequency is less than 0.01, which can effectively eliminate the frequency deviation phenomenon and obtain the maximum power output at the given frequency band.

Magnetic Force Calculation of Movable YBCO Superconducting Helical Coils Applicable to Electric Vehicles Wireless Power Transfer

Background and Objectives: Today, replacing gasoline-powered vehicles with electric vehicles (EVs) and connecting them to an electric power source have made the optimal usage of energy-saving resources. Therefore, wireless Power Transfer (WPT) outstands as an alternative technology to improve the user perception about the charging process of the EVs. Superconducting coils (SCs) with high-temperature have an applied feature in decreasing losses of wireless power transmission (WPT). The Magnetic force has effects of overall deformation modes between two current carrier superconducting coils, i.e. axial extension, torsion, and bending. Coil misalignment is a fundamental problem and its impact on wireless power transmission efficiency is very complex. The analysis of a magnetic force which is presented in this paper are beneficially for the design and application of the WPT systems. Here, a fast analytical solution is presented to obtain the magnetic force between the transmitter and receiver helical superconducting coils in different positions.Methods: In this paper, a new method applied to solve the numerically magnetic force solutions in different superconducting coils mismatch states for WPT. Finally, for improvement of efficiency, the WPT system has been designed on the basis of mutual inductance changes which receiving helical coil was moved inside the transmitting helical coil. Hence, the magnetic force calculation of movable YBCO superconducting helical coils inside each other is presented. These models have been compared with the FEM.Results: Results show that the presented equations are reliable as well. According to the comparing the analysis and FEM data, the obtained results indicated the errors with less than 0.0064%. Also, results show an excellent agreement with respect to the finite element method.Conclusion: In this paper, the numerical solutions of magnetic force in different superconducting coils mismatch states were solved by a new method. The magnetic force analysis basics introduced in this paper are useful to develop and apply for wireless power transmission system. The simulation results show that only by applying some constraints, the efficiency of the transmitted wireless power will be optimized. Then, analytical models have been presented which make it possible to calculate the axial force which was exerted between two axially Helical magnetized and two thin coils in air. Also, the analytical stiffness calculation applied between these distributions of magnetic source has been presented. These models have been compared with the FEM to show an appropriate consistency.

Parameter Optimization of Double LCC MCRWPT System Based on ZVS

At present, magnetically coupled resonance wireless power transfer (MCRWPT) is the main technology used in electric vehicle wireless power transfer (WPT) due to its advantages of high transmission power and high efficiency. The resonant compensation circuit of the system generally adopts the double LCC (DLCC) structure, which has many capacitor and inductor components. Therefore, it is necessary to optimize the circuit parameters to improve the transmission performance of the system. In this study, the DLCC compensation circuit was modeled and analyzed to lay the foundation for parameter optimization. Secondly, the size parameters of the energy transmitting and receiving coil were determined, and the influence of the change of the primary and secondary compensation inductance on the circuit element stress and output performance was analyzed to determine the optimal compensation inductance value. Thirdly, the realization condition of zero voltage switching (ZVS) was analyzed, the relationship between the input impedance angle of the compensation circuit and the component parameter value was obtained, and a parameter optimization control strategy for realizing ZVS was proposed. Finally, through simulation and experiment, it was concluded that under different power levels, the efficiency of the parameter optimization strategy proposed in this study is as high as 91.86%, increasing by about 1%. Therefore, the research undertaken in this study can promote the development of WPT technology and has certain practical significance.

Optimization of Ferrites Structure by Using a New Core-Less Design Algorithm for Electric Vehicle Wireless Power Transfer

In order to improve the customers’ continuous usage of electrical vehicles (EVs) and reduce the weight of the energy storage devices, wireless charging technology has been widely studied, updated, and commercialized in recent decades, regarding to its distinct superiority of great convenience and low risk. A higher coupling coefficient is the key factor that impacts the transmission efficiency, thus in most medium-power (hundreds of watts) to high-power (several kilowatts) wireless charging systems, ferrites are used to guide the magnetic flux and intensify the magnetic density. However, the weight of the ferrite itself puts an extra burden on the system, and the core loss during operation also reduces the total efficiency and output power. This paper proposes an optimized design algorithm based on a core-less method for the magnetic core, where the core loss and the coupling coefficient are consequently balanced, and the overall weight and efficiency of the system can be optimized. The iteration procedure is applied on the basis of removed ferrite length and thickness in the algorithm. In the simulation, a square coupler with a total volume of 300 mm × 150 mm, a circular coupler of 150 mm × 150 mm and a Double-D (DD) coupler of 300 mm × 150 mm are used to verify the advantages of the proposed method. The optimized ferrite structures are specific for each coupler shape, and the improvement is proved to be universal in current scale by means of 3-D finite element analysis.

Procedures for Identifying Mutual Inductance of Three-Coil Structure for Wireless Power Transfer in Electric Vehicles

Mutual inductance identification of the wireless power transfer (WPT) system is of great significance for improving the system performance. In this paper, a novel mutual inductance identification method for WPT in electric vehicles with three-coil structure is proposed based on the information measured from the primary and relay coils. The method deduces the influence of misalignment on mutual inductance of three-coil WPT system in electric vehicle application scenarios from a new perspective. The results show that the mutual inductance between primary and secondary coils, and the mutual inductance between relay and secondary coils can be estimated at one time by way of index according to the relationship between their ratio and themselves. Experimental results show the correctness of the proposed mutual inductance identification method.

Modelling and improvement of oscillation problem in a double-sided LCC compensation network for electric vehicle wireless power transfer

The double-sided LCC compensation network shows high performances in electric vehicle wireless power transfer (EV WPT) applications owing to its constant output current, low voltage stress and other good characteristics. In order to achieve full power and high-efficiency energy transmission within the specified range of coupling and battery voltage, a controlled rectification scheme became a trend in EVs manufacturers and standards. However, a current oscillation problem emerges in a double-sided LCC system when employing a circulating current control method for the controlled rectifier. This paper proposes a mechanism to understand the oscillation phenomenon caused by the inter-harmonics and a positive feedback scheme. The amplification effect of circuit admittance is believed to be the key cause of the inter-harmonics. Therefore, an oscillation improvement is proposed in this paper by adding an inductor and a capacitor to the secondary LCC network, minimizing the admittance amplification effect. A comprehensive simulation and experimental validations under different rectifier duty cycles, coupling positions and load resistances, confirmed the effectiveness of the proposed method. Interestingly, the optimized system expanded the safe operating region and reduced the oscillating operating points from 18 to 8 out of the 27 possible conditions. • This paper clearly reveals the cause of current oscillation in an EV-WPT system. • Interharmonics were grabbed and analyzed in an LCC-LCC circuit for the first time. • Additional LC is first introduced into the system, suppressing oscillation greatly.

Passivity-Based PI Control for Receiver Side of Dynamic Wireless Charging System in Electric Vehicles

The dynamic wireless charging for electric vehicles (EVs) is considered an efficient and practical choice to extend the driving range and reduce battery pack size. However, the coupling coefficient between transmitter coils and receiver coil varies rapidly on a large scale during the EVs moving, so it deteriorates the charging performance of dynamic wireless power transfer in EVs, such as the discontinuous charging for the lithium-ion batteries in EVs. Moreover, the charging power and efficiency of the system can also be affected. To solve these issues, a dc–dc converter is added to cascade on the receiver side to improve the output power and efficiency of the system. Furthermore, the passivity-based proportional-integral control is designed for the dc–dc on the receiver side of dynamic wireless charging system to improve the performance against the rapidly changing coupling coefficient. Finally, compared with the conventional proportional-integral-derivative controller, simulation and experimental results are given to show the performance and robustness of dynamic wireless charging system by the proposed method.

A Study on Precise Positioning for an Electric Vehicle Wireless Power Transfer System Using a Ferrite Antenna

In the last decade, engineers from automotive manufacturers and charging infrastructure suppliers have widely studied the application of wireless power transfer (WPT) technology to electric vehicles. Since this time, engineers from automotive manufacturers have studied precise positioning methods suitable for WPT using methods such as mechanical, communication-based or video-based. However, due to high costs, electromagnetic interference and environmental factors, the experts of the SAE J2954 was focused on the WPT’s precise positioning method by ferrite antennas and low power excitation. In this study, we present how to use the ferrite antennas to find a central alignment point between the primary and secondary units within the alignment tolerance area that requires the minimum power transfer efficiency of the EV WPT system. First, we analyze the ferrite antenna already applied in the automotive and verifies whether it is suitable for the precise positioning of the WPT system for EV. We use modeling and simulation to show that it is necessary to calculate all induced loop voltages in the relationship between incident magnetic field signal strength and induced loop voltage because of the short distance between the transmitter and receiver of the ferrite antenna in WPT. In addition, we also suggest a sequence to find the fitting location of the ferrite antenna, the number of antennas used and the center alignment point. After the simulation is performed on the suggestions, component-level and vehicle-level tests were conducted to verify the validity of the simulation results. As a result, it is shown that a ferrite antenna is suitable as a method for the secondary device to find the center alignment point of the primary device.