Wireless Charging Of Electric Vehicles Research Articles

Analysis and design of DD coupler for dynamic wireless charging of electric vehicles

In dynamic wireless charging (DWC) of battery-powered electric vehicles (BEVs), inductive power transfer takes place between two coils, one buried into the road and the other one installed onboard BEVs. This paper deals with the design of the coils of a lumped DWC system. At first, the concept of polarized coil is explicated and a DWC-suitable structure of polarized coil, namely the double-D (DD) coil, is illustrated. Then, the paper analyzes the inductive properties of a DD coupler and presents its design for a case study. The design embraces the dimensions of the coils and the magnetic cores, thickness included, and usage of bars instead of plates for the cores in order to save magnetic material. After developing closed-form expressions of the inductive parameters of the coils useful for their preliminary sizing, the analysis and design activities are carried out with the assistance of finite element method codes. Relevant results supporting the design are presented by help of tables, maps, and graphs.

3-D Coil Positioning Based on Magnetic Sensing for Wireless EV Charging

Wireless power transfer (WPT) via magnetic resonance coupling is considered a promising outlet for electric vehicle (EV) charging due to the noncontact method. Unlike a traditional transformer, with WPT, the relative spacing and lateral distance between the primary and secondary coils are highly variable, which can affect the wireless power delivery and lower the efficiency. A magnetic positioning approach that shares the wireless charging structure is proposed to solve the misalignment issue associated with wireless EV charging. The proposed alignment sensing system employs multiple auxiliary minor coils on the secondary side to position the charging pad. The positioning principle and equivalent circuit were analyzed. The 108 samples were tested and they were distributed throughout the detection range of 70 cm. The experimental results demonstrate that >92% of those samples have positioning errors of <2 cm and 98% of them have positioning errors of <3 cm.

Hybrid Bidirectional Wireless EV Charging System Tolerant to Pad Misalignment

Electric vehicles (EVs) are becoming increasingly popular as a means of future transport for sustainable living. However, wireless charging of EVs poses a number of challenges related to interoperability, safety, pad misalignment, etc. In particular, pad misalignments invariably cause changes in system parameters which in turn lead to increase in losses as well as reduction in power throughput, making the charging process long and inefficient. Consequently, wireless charging systems that are less sensitive to pad misalignments have become preferable. This paper, therefore, presents a hybrid wireless power transfer (WPT) system that charges EVs at constant rate despite large misalignments between charging pads. The proposed charging system uses a combination of two different resonant networks to realize a constant and efficient charging process. A mathematical model is also developed, showing as to how the two resonant networks can be combined to compensate for pad misalignments. To demonstrate the validity of the proposed concept as well as the accuracy of the mathematical model, theoretical performance is compared with both simulations and experimental results of a prototype 3.3 kW hybrid bidirectional WPT system. Results clearly indicate that the proposed hybrid WPT system is efficient and offers a constant charging profile over a wide range of spatial (three-dimensional) pad misalignments.

Comparative study of dynamic wireless charging of electric vehicles in motorway, highway and urban stretches

Electric vehicles are the most promising sustainable transport technology for solving problems linked to the internal combustion engine vehicles. Wireless charging reduce the main problems associated with electric vehicles, driving range, charging time and size and cost of the battery. Inductive power transfer is the most promising technology for dynamic wireless charging of electric vehicles, which can be used to supply the motors and charge the battery while moving. This paper presents a comparative study of a dynamic wireless power transfer system for charging electric vehicles driving on three stretches of traffic road (motorway, highway and urban stretch) in Cádiz (Spain). The study analyses the electricity consumption demanded by the dynamic wireless power transfer system and the battery state-of-charge of the electric vehicles that travel the stretch to evaluate the increase of autonomy, the length of the stretch or speed of the vehicle for achieving a specific increase of state-of-charge. The results show a great dependence on stretch of road, with large fluctuations in the urban stretch and more stability in the highway and motorway. This study could help to design stretches of roads with dynamic wireless power transfer and to quantify the power and energy demanded by the system.

Design Optimisation for an Efficient Wireless Power Transfer System for Electric Vehicles

Wireless Power Transfer (WPT) has been used to transfer small amounts of power over small distances to run smartphones, RFID tags, smart watches and even biomedical implants without any electrical contact. A popular application for this is the wireless charging of electric and hybrid electric vehicles. However, designing systems to send large amounts power over large distances while maintaining appreciable efficiency is hard to do. In this paper, an overview of a typical WPT system has been given. Simple design equations have been given to calculate inductance, capacitance, power, quality factor and coupling coefficient to optimise coil design for electric vehicle application. Further, a comparison has been made between the popular coil shapes and the effects of the change of coil parameters like number of turns, pitch and inner and outer radius on efficiency of the coil has been studied.

Robust wireless power transfer using a nonlinear parity-time-symmetric circuit.

Considerable progress in wireless power transfer has been made in the realm of non-radiative transfer, which employs magnetic-field coupling in the near field. A combination of circuit resonance and impedance transformation is often used to help to achieve efficient transfer of power over a predetermined distance of about the size of the resonators. The development of non-radiative wireless power transfer has paved the way towards real-world applications such as wireless powering of implantable medical devices and wireless charging of stationary electric vehicles. However, it remains a fundamental challenge to create a wireless power transfer system in which the transfer efficiency is robust against the variation of operating conditions. Here we propose theoretically and demonstrate experimentally that a parity-time-symmetric circuit incorporating a nonlinear gain saturation element provides robust wireless power transfer. Our results show that the transfer efficiency remains near unity over a distance variation of approximately one metre, without the need for any tuning. This is in contrast with conventional methods where high transfer efficiency can only be maintained by constantly tuning the frequency or the internal coupling parameters as the transfer distance or the relative orientation of the source and receiver units is varied. The use of a nonlinear parity-time-symmetric circuit should enable robust wireless power transfer to moving devices or vehicles.

Efficient Wireless Power Charging of Electric Vehicle by Modifying the Magnetic Characteristics of the Transmitting Medium

There is a developing enthusiasm for electric vehicle (EV) innovations because of their lower fuel utilization and greenhouse emission output. Integrating EVs with highway wireless power transfer (WPT) technology can appropriately reduce charging time and possibly expand their travel distance. There are several issues with the current WPT technology for EVs: 1) low efficiency due to large coil-coil distance and 2) slow charging time. Two ideas are proposed in this paper to increase system efficiency: 1) using a modified cement for covering the transmitting antenna area and 2) using high frequency wide bandgap switches, which can transfer a high amount of power in a short time. The optimization study of the receiving and transmitting coils is implemented with and without a core through 3-D finite-element analysis. The physics-based analysis is coupled with circuit-based analysis for utilizing high frequencies wide bandgap switch (SiC MOSFET). On the material side, the electromagnetic and mechanical properties of the modified cementitious composite are characterized and the results show significant improvement in the system efficiency.

An Integrated Characterization Model and Multiobjective Optimization for the Design of an EV Charger’s Circular Wireless Power Transfer Pads

A good magnetic design of a wireless electric vehicle (EV) charging system requires accurate characterization of the equivalent circuit parameters. This is while considering the effect of the magnetic core and the conductive shielding layers. In the literature, such an analysis is done using 3-D finite element analysis, which makes the design and optimization process time-consuming and computationally expensive. In this paper, an integrated analytical model for the characterization of a circular wireless power transfer EV pads is utilized. This analytical model provides a valuable tool to optimize the design process. This model is utilized when evaluating the objective function for each individual in the multiobjective Pareto Optimality optimization algorithm. The objective is optimizing the pads with three decision variables and four constraints.

Analysis and Control of Multiphase Inductively Coupled Resonant Converter for Wireless Electric Vehicle Charger Applications

In this paper, an inductively coupled multiphase resonant converter is presented for wireless electric vehicle charging applications. As an alternative to the traditional frequency and phase shift control methods, a hybrid phase-frequency control strategy is implemented to improve the system efficiency. A theoretical analysis of the proposed system is carried out considering a wide battery state-of-charging range. In order to confirm the proposed converter and control technique, a laboratory prototype wireless charger is designed using 8-in air-gap coreless transformer and rectifier. The proposed control is compared with the conventional control methods for various load conditions at the different power levels. In comparison results, the proposed hybrid control methodology demonstrates the efficiency improvements of 1.1% at the heaviest load condition and 5.7% at the lightest load condition.

A new integration method with minimized extra coupling effects using inductor and capacitor series-parallel compensation for wireless EV charger

Wireless electric vehicle charger has become increasingly popular because of its improved convenience and safety. The recently proposed inductor-capacitor-capacitor (LCC) compensated topology and bipolar magnetic coupler structure have promoted the comprehensive performance of the wireless power transfer (WPT) system. Furthermore, the idea of integrating the magnetic components in the LCC compensated WPT system has been proposed for reducing the bulk. However, the extra inter-couplings between the adjacent coils are also introduced, which complicates the parameters design and the characteristic analysis. In this paper, a new integration method is presented for wireless EV charger adopting LCC compensation networks along with bipolar coupler. The impact of the extra couplings is evaluated thoroughly through the circuit analysis and simulation. The finite element analysis (FEA) tool is utilized to evaluate the extra coupling effects of the compensated coils, which leads to the proposed integration coupler structure. The comparison of the unipolar and the bipolar as the compensated coils for the extra coupling minimizing is discussed considering the misalignment. At last, a prototype of the magnetic coupler with a size of 550mm×500mmhas been built and tested. A peak efficiency of 95% is achieved while transferring 6.6kW electric power from a DC power source to the load in the condition of 150mm vertical clearance.

Magnetic Integration of LCC Compensation Topology with Minimized Extra Coupling Effects for Wireless EV Charger

Abstract Wireless electric vehicle charger has become increasingly popular because of its improved convenience and safety. The recently proposed doubled-sided LCC compensated topology and bipolar magnetic coupler structure have promoted the comprehensive performance of the wireless power transfer (WPT) system. Furthermore, the idea of integrating the magnetic components in the LCC compensated WPT system has been proposed for reducing the bulk. However, the extra inter-couplings between the adjacent coils are also introduced, which complicates the parameters design and the characteristic analysis. In this paper, a new integration method is presented for wireless EV charger adopting LCC compensation networks along with bipolar coupler. The impact of the extra couplings is evaluated through circuit analysis and simulation. The finite element analysis (FEA) tool is utilized to simulate the extra coupling effects of the compensated coil, which leads to the proposed integration coupler structure. At last, a 550 mm × 500 mm with a nominal 150-mm-gap and 6.6-kW-power prototype, has been built and tested. A peak efficiency of 95% from a DC power source to the load is achieved.

A Witricity-Based High-Power Device for Wireless Charging of Electric Vehicles

In this paper, a Witricity-based high-power device is proposed for wireless charging of electric vehicles. According to the specific requirements of three-stage charging for electric vehicles, four compensation modes of the Witricity system are analyzed by the Loosely Coupled Theory among transformer coils and the Substitution Theorem in circuit theory. In addition, when combining voltage withstand levels, the current withstand capability, the switching frequency of electronic switching tubes, and the features of the resonant circuit, the series-parallel (SP) compensation mode is selected as the best compensation mode for matching the capacitor of the system. The performances of coils with different ferrite core arrangements are compared by simulations and models. The feasibility of the system is verified theoretically and the system functions are evaluated by the joint simulation of Simplorer and Maxwell. Finally, a Witricity-based high-power device is proposed as designed, and the correctness of theoretical analyses and simulation results are verified.

An Autonomous Coil Alignment System for the Dynamic Wireless Charging of Electric Vehicles to Minimize Lateral Misalignment

This paper proposes an autonomous coil alignment system (ACAS) for electric vehicles (EVs) with dynamic wireless charging (DWC) to mitigate the reduction in received power caused by lateral misalignment between the source and load coils. The key component of the ACAS is a novel sensor coil design, which can detect the load coil’s left or right position relative to the source coil by observing the change in voltage phase. This allows the lateral misalignment to be estimated through the wireless power transfer (WPT) system alone, which is a novel tracking method for vehicular applications. Once misalignment is detected, the vehicle’s lateral position is self-adjusted by an autonomous steering function. The feasibility of the overall operation of the ACAS was verified through simulation and experiments. In addition, an analysis based on experimental results was conducted, demonstrating that 26% more energy can be transferred during DWC with the ACAS, just by keeping the vehicle’s load coil aligned with the source coil.

High‐resolution magnetic‐field exposure simulations of automotive inductive power‐transfer systems using a scaled‐frequency finite difference time domain approach with multi‐GPU acceleration

AbstractInductive power transfer technology enables, eg, wireless charging of electric and hybrid vehicles. Proposed systems generally consist of at least 2 geometrically separated loosely coupled air‐cored coils. The charging process at operating frequencies from 80 to 140 kHz potentially exposes humans. The computational simulation of low frequency fields combined with lossy dielectric distributions in such scenarios requires nonstandard numerical approaches. As long as quasi‐static assumptions are valid, the scaled‐frequency finite difference time domain method is suitable for such problems. With additional considerations to the original approach from Gandhi and Chen, based on work from Kaune and Gilles, simulations may include anatomical body models as well as thin metallic sheets, which are quite common in automotive scenarios with thicknesses of 1 to 1.2 mm.

A New Integration Method for an Electric Vehicle Wireless Charging System Using LCC Compensation Topology: Analysis and Design

There is a need for charging electric vehicles (EVs) wirelessly since it provides a more convenient, reliable, and safer charging option for EV customers. A wireless charging system using a double-sided LCC compensation topology is proven to be highly efficient; however, the large volume induced by the compensation coils is a drawback. In order to make the system more compact, this paper proposes a new method to integrate the compensated coil into the main coil structure. With the proposed method, not only is the system more compact, but also the extra coupling effects resulting from the integration are either eliminated or minimized to a negligible level. Three-dimensional finite-element analysis tool ANSYS MAXWELL is employed to optimize the integrated coils, and detailed design procedures on improving system efficiency are also given in this paper. The wireless charging system with the proposed integration method is able to transfer 3.0 kW with 95.5% efficiency (overall dc to dc) at an air gap of 150 mm.

Design of In-Wheel Type Switched Reluctance Motor for Electric Vehicle Traction and Wireless Charging

Design of In-Wheel Type Switched Reluctance Motor for Electric Vehicle Traction and Wireless Charging

Privacy-Preserving Billing Scheme against Free-Riders for Wireless Charging Electric Vehicles

Recently, scientists in South Korea developed on-line electric vehicle (OLEV), which is a kind of electric vehicle that can be charged wirelessly while it is moving on the road. The battery in the vehicle can absorb electric energy from the power transmitters buried under the road without any contact with them. Several billing schemes have been presented to offer privacy-preserving billing for OLEV owners. However, they did not consider the existence of free-riders. When some vehicles are being charged after showing the tokens, vehicles that are running ahead or behind can switch on their systems and drive closely for a free charging. We describe a billing scheme against free-riders by using several cryptographic tools. Each vehicle should authenticate with a compensation-prepaid token before it can drive on the wireless-charging-enabled road. The service provider can obtain compensation if it can prove that certain vehicle is a free-rider. Our scheme is privacy-preserving so the charging will not disclose the locations and routine routes of each vehicle. In fact, our scheme is a fast authentication scheme that anonymously authenticates each user on accessing a sequence of services. Thus, it can be applied to sequential data delivering services in future 5G systems.

Analysis and optimization of a solenoid coupler for wireless electric vehicle charging

In light of the increased interest in e-mobility, comfortable, and safe charging systems, such as inductive charging systems, are gaining importance. Several standardization bodies develop guidelines and specifications for inductive power transfer systems in order to ensure a good interoperability between different coil architectures from the various car manufacturers, wireless power transfer suppliers, and infrastructure companies. A combination of a bipolar magnetic coil design on the primary side with a secondary solenoidal coil promises a good magnetic coupling and a high-transmitted power with small dimensions at the same time. In order to get a profound knowledge of the influence and behavior of the main variables on the coil system, a detailed parameter study is conducted in this paper. Based on these findings, a solenoid was designed for a specific case of application. Further, this design is optimized. The dimensions of the system could be reduced by 50% with a constant coupling factor at the same time. Besides the reduction of the dimensions and subsequently the costs of the systems, the stray field could be reduced significantly.

Power Stabilization Strategy of Random Access Loads in Electric Vehicles Wireless Charging System at Traffic Lights

An opportunity wireless charging system for electric vehicles when they stop and wait at traffic lights is proposed in this paper. In order to solve the serious power fluctuation caused by random access loads, this study presents a power stabilization strategy based on counting the number of electric vehicles in a designated area, including counting method, power source voltage adjustment strategy and choice of counting points. Firstly, the circuit model of a wireless power system with multi-loads is built and the equation of each load is obtained. Secondly, after the counting method of electric vehicles is stated, the voltage adjustment strategy, based on the number of electric vehicles when the system is at a steady state, is set out. Then, the counting points are chosen according to power curves when the voltage adjustment strategy is adopted. Finally, an experimental prototype is implemented to verify the power stabilization strategy. The experimental results show that, with the application of this strategy, the charging power is stabilized with the fluctuation of no more than 5% when loads access randomly.

Lumped Track Layout Design for Dynamic Wireless Charging of Electric Vehicles

Dynamic wireless charging (DWC) of electric vehicles (EVs) is an emerging technology that could lead to the breakthrough of EVs. The technology is based on the inductive coupling between an electrified track deployed under the road surface and a pickup coil fitted in EV. This paper refers to a lumped track made of DD coils and is concerned with the design of the track layout, namely coil dimension in the motion direction and track coil distance for a given energy requirement. This paper starts by comparing the coupling characteristics of DD coils with different dimensions by a finite-element method (FEM) analysis. Afterward, an analytical procedure is developed to establish the track coil distance able to transfer to a moving EV the propulsion energy required per unit of traveled space. The procedure utilizes the DD-coil coupling characteristics to calculate the power and, from it, the energy transferred from the track coils to the pickup coil along the track. Instrumental in the calculation is the definition of a parameter, denoted as track flux coverage, which gives the ratio between the dimension of the track coils in the motion direction and the coil distance; such a parameter corresponds to the percentage of road populated with track coils so that it is a cost index of the DWC system implementation. Effects of a lateral displacement of the EV motion from the line joining the track coil centers are also analyzed. Design findings are checked against the results obtained with a computer-assisted analysis.