Wireless Electric Vehicle Research Articles

Model Predictive Control to Maximize the Efficiency in EV Wireless Chargers

The automotive industry is undergoing a transition toward cleaner and more efficient technologies. Electric vehicles (EVs) play a relevant role in this scenario. However, these vehicles continue to suffer from limitations in terms of autonomy and charging times, which can be alleviated with wireless charging technology. This technology facilitates the charging process but has a lower efficiency when compared with conductive chargers. This effect is particularly severe under misalignment conditions and with the usual variations of the battery's electrical features. In order to avoid this disadvantage, this article presents a predictive control algorithm focused on maximizing the charging efficiency. As a novelty, the algorithm sets three configuration parameters in the power converters of the system. The main advantage lies in the fact that it does not need constant monitoring and offers very low response times. This control also improves compatibility with different automobile manufacturers, adding the capacity to work with receivers and batteries with diverse characteristics while complying with international standards. The validity of the proposal is verified by theoretical analysis, simulations, and the experimental results of a 2-kW prototype. The results show the feasibility of the proposed control and the improvement in the efficiency of the system.

Design of a High Power, LCC-Compensated, Dynamic, Wireless Electric Vehicle Charging System with Improved Misalignment Tolerance

Dynamic wireless power transfer (DWPT) systems are becoming increasingly important for on-the-move electric vehicle (EV) charging solutions, to overcome range anxiety and compensate for the consumed energy while the EV is in motion. In this work, a DWPT EV charging system is proposed to be implemented on a straight road stretch such that it provides the moving EV with energy at a rate of 308 Wh/km. This rate is expected to compensate for the vehicle’s average energy consumption and allow for additional energy storage in the EV battery. The proposed charging system operates at an average power transfer efficiency that is higher than 90% and provides good lateral misalignment tolerance up to ±200 mm. Details of the proposed system’s design are presented in this paper, including EV specifications, inductive link and compensation network design and power electronic circuitry.

Interoperability Improvement for Rectangular Pad and DD Pad of Wireless Electric Vehicle Charging System Based on Adaptive Position Adjustment

Wireless charging for electric vehicles has been investigated in recent years. One of the critical issues of the research is to improve the weak interoperability between two popular charging pads—rectangular pad (RCP) and double-D pad (DDP). This article intends to model the interoperability under pad misalignment and improve it by adjusting the pads’ relative position. First, the variation of interoperability with pad misalignment is analyzed by the flux model. Full output power and high transmission efficiency can be achieved when the two pads are misaligned to a certain distance. Second, the optimal misalignment is obtained by flux calculation and simulation. Third, an adaptive position adjustment method for the transmitting pad based on the variable-step perturbation and observation algorithm is proposed. By searching the maximum dc input current, the optimal position of the transmitting pad can be found. Finally, in the experiment, a 3.3 kW output with 95% coil-coil efficiency is realized when the RCP and DDP interoperate at the optimal position. Compared with the scenario without position adjustment, the improvement of output power and efficiency proves that the proposal can optimize the interoperability between the RCP and DDP.

Analysis and optimization of coil structure of magnetic circuit mechanism for electric vehicle wireless charging system

To improve the efficiency of the electric vehicle wireless charging system, an optimization design method for the number of coil layers is proposed and studied, which effectively improves the coupling coefficient of the magnetic circuit mechanism. This article first analyzes the energy efficiency characteristics of the wireless charging system for electric vehicles. Then, it analyzes the inductance value changes and magnetic field distribution characteristics of fixed turns coils under different layers. The finite element simulation results performed by MAXWELL show that inducing the number of primary coil layers and increasing the number of secondary coil layers are conducive to the improvement of the coupling coefficient between the coils. Then, based on the theoretical analysis results, the number of coil turns of each layer of the multilayer coil is analyzed and optimized, and a bowl-shaped pair multilayer coil winding method is proposed.

A Novel Misalignment Tolerant Magnetic Coupler for Electric Vehicle Wireless Charging

The lateral misalignment for static electric vehicle (EV) wireless charging could be much larger than 100 mm if the parking assistance systems are unavailable. This article proposes a split flat solenoid coupler (SFSC) to significantly extend the lateral misalignment and reduce the copper and ferrite usage. To obtain a good balance among coupling, misalignment tolerance, and cost, an optimization method for SFSC is proposed where the size limitations and ferrite tile specifications are considered. The optimized SFSC is compared with two magnetic couplers recommended in SAE J2954 in terms of coupling coefficient and misalignment tolerance. To eliminate the impact of coil size and make the comparison fair, the quantified misalignment tolerance is introduced. The proposed SFSC provides much better misalignment tolerance than the recommended couplers. A 1000-W prototype is built to show the advantages of the proposed coupler. The output current keeps unchanged when the lateral misalignment is as high as 400 mm. A highest power transfer efficiency, from dc input to dc output, of 89.12% is achieved when the output power is 1000 W.

Modeling and Analysis of Polarized Couplers under Misalignment for Electric Vehicle Wireless Charging Systems

Wireless power transfer (WPT) is becoming popular increasingly in stationary electric vehicle (EV) charging. Various coil structures were proposed to improve the coupling characteristics, and polarized couplers have been proven to have better performance. Considering the varying spatial scales of transmitting and receiving, coils will alter the mutual inductance, further affecting the output power and transmission efficiency; therefore, it is crucial to calculate the mutual inductance of polarized couplers with variable offset for WPT system design. However, given the complex structure and the various excitation conditions of polarized couplers, the solving process based on the finite element model is time-consuming and resource intensive, therefore it is necessary to develop analytical models of mutual inductance for polarized couplers under misalignment. In this paper, the analytical models of the two commonly used polarized couplers with a Double-D polarized coil (DDP) or a Bipolar polarized coil (BP) on both sides under misalignment along any direction under different excitation conditions are proposed based on dual Fourier transformation. The mutual inductance characteristics of the two polarized couplers under misalignment can be investigated based on the proposed analytical models and finite element models, respectively. The results show that the mutual inductance of BP-BP coupler with in-phase current excitation mode is greater and more stable, and the method based on the analytical model is timesaving. Finally, the prototype of the WPT system with the two polarized couplers has been built, and experiments have also been carried out to verify the accuracy of the analytical models.

A Fast Construction Method of Resonance Compensation Network for Electric Vehicle Wireless Charging System

When constructing an electric vehicle (EV) wireless charging system, limited by manufacturing technology and measurement errors, the capacitance and inductance in the impedance matching network will inevitably produce parameter deviations, which will cause tuning difficulties and even burn the power supply. In order to solve these problems, this article proposes a fast and accurate tuning technique based on a double-sided L3C compensation network with a capacitor matrix. The tuning method derived from theoretical analysis can be summarized as: tuning capacitor can achieve fast matching; fine adjusting the equivalent inductance can achieve precise matching and power zero-voltage switching. After resonance matching, the capacitors on the capacitor matrix can be removed and welded together, and an inductor can be used instead of equivalent inductance, so the technology is low cost, fast, and safe. In order to verify the tuning method, a 3-kW EV wireless charging system was developed. Experimental results show that the proposed method makes the system resonate rapidly and maintain stability, and the inverter is also easy to implement zero-voltage switching.

Simultaneous Metal Object Detection and Coil Alignment for Wireless EV Chargers Using Planar Coil Array

For the commercialization of wireless electric vehicle (EV) chargers, the metal object detection and coil alignment are needed for the safe and efficient operation of chargers. This paper proposes a dual-purpose method for the simultaneous metal object detection and coil alignment using a planar coil array before the start of wireless EV charging. Magnetic induction tomography is adopted to reconstruct the images of metal objects and the location of the objects is calculated using the image processing algorithms. The receiving coil in the EV is visualized using the induced voltage map from the coil array and the coil position is computed using characteristic points of the map. Firstly, the structure of the coil array is optimized using the finite element model (FEM) and 4×4 coil elements are used. Then the FEM simulation is conducted for the feasibility study of the proposed method. Finally, an experimental setup of the wireless charging is designed for further verification. For the metal object detection, eight experimental cases prove that the proposed method is able to detect and visualize metal objects with different numbers and different shapes. In addition, the maximum location error for all metal objects is 6.27 mm. For the coil alignment, the location error of the receiving coil is less than 2 cm. The proposed method can help to remove metal objects and assist the driver during the parking, which meets the requirement for the wireless EV charging.

Management of Charging Load of Electric Vehicles for Optimal Capacity Utilisation of Distribution Transformers

A de-centralised load management technique exploiting the flexibility in the charging of Electric Vehicles (EVs) is presented. Two charging regimes are assumed. The Controlled Charging Regime (CCR) between 16:30 hours and 06:00 hours of the next day and the Uncontrolled Charging Regime (UCR) between 06:00 hours and 16:30 hours of the same day. During the CCR, the charging of EVs is coordinated and controlled by means of a wireless two-way communication link between EV Smart Charge Controllers (EVSCCs) at EV owners’ premises and the EV Load Controller (EVLC) at the local LV distribution substation. The EVLC sorts the EVs batteries in ascending order of their states of charge (SoC) and sends command signals for charging to as many EVs as the transformer could allow at that interval based on the condition of the transformer as analysed by the Distribution Transformer Monitor (DTM). A real and typical urban LV area distribution network in Great Britain (GB) is used as the case study. The technique is applied on the LV area when its transformer is carrying the future load demand of the area on a typical winter weekday in the year 2050. To achieve the load management, load demand of the LV area network is decomposed into Non-EV load and EV load. The load on the transformer is managed by varying the EV load in an optimisation objective function which maximises the capacity utilisation of the transformer subject to operational constraints and non-disruption of daily trips of EV owners. Results show that with the proposed load management technique, LV distribution networks could accommodate high uptake of EVs without compromising the useful normal life expectancy of distribution transformers before the need for capacity reinforcement.

Experimental Study of Radiated Magnetic Field from Electric Vehicle Wireless Charging System

Wireless charging is an attractive option of energy replenishment for electric vehicles (EVs) as it does not require direct electrical contact to the EVs. However, the radiated magnetic field from the EV wireless charging system can be an electromagnetic compatibility (EMC) concern nearby electrical and electronic devices. This paper investigates the influence of the power level, the clearance, and offset between coils on the radiated magnetic field emitted from the wireless charging system. The experimental study shows that these variable parameters can affect the radiated magnetic field level and the field distribution, which provides valuable input for standardization of the test setup and working condition of the EV wireless charging system.

An Efficient PCB Based Magnetic Coupler Design for Electric Vehicle Wireless Charging

This paper proposes an efficient Printed Circuit Board (PCB) design of magnetic couplers for electric vehicle (EV) wireless power transfer (WPT) system. Since a WPT system operates at high frequency, Litz wire typically is used that can overcome high AC resistance, and improve overall efficiency. In EV wireless charging applications, the power level of the system is high, and therefore the magnetic pad size and copper cross-section of the Litz wire used in the magnetic couplers are large which increases the cost and weight. Besides, building the magnetic couplers using Litz wire requires excessive labor work, which causes fabrication errors. Replacing the Litz wire with PCB-based coils raises design and efficiency challenges. A new approach for designing the PCB-based magnetic couplers for high-power EV wireless charging applications is proposed to address the challenges associated with the PCB designs. In the proposed design, the efficiency of the PCB-based design is close to the Litz wire-based design. Moreover, machine assembly replaces the labor work and the magnetic coupler can be implemented with lower fabrication error, weight, and manufacturing cost. In this paper, a 3.3 kW PCB-based WPT system is designed, compared experimentally with the Litz wire setup which achieved a competitive efficiency profile.

RESEARCH ON SHIELDING AND ELECTROMAGNETIC EXPOSURE SAFETY OF AN ELECTRIC VEHICLE WIRELESS CHARGING COIL

RESEARCH ON SHIELDING AND ELECTROMAGNETIC EXPOSURE SAFETY OF AN ELECTRIC VEHICLE WIRELESS CHARGING COIL

A Technology Trend and Analysis of Electric Vehicle Wireless Charging System

A Technology Trend and Analysis of Electric Vehicle Wireless Charging System

Inductive Wireless Power Transfer Charging for Electric Vehicles–A Review

Considering a future scenario in which a driverless Electric Vehicle (EV) needs an automatic charging system without human intervention. In this regard, there is a requirement for a fully automatable, fast, safe, cost-effective, and reliable charging infrastructure that provides a profitable business model and fast adoption in the electrified transportation systems. These qualities can be comprehended through wireless charging systems. Wireless Power Transfer (WPT) is a futuristic technology with the advantage of flexibility, convenience, safety, and the capability of becoming fully automated. In WPT methods resonant inductive wireless charging has to gain more attention compared to other wireless power transfer methods due to high efficiency and easy maintenance. This literature presents a review of the status of Resonant Inductive Wireless Power Transfer Charging technology also highlighting the present status and its future of the wireless EV market. First, the paper delivers a brief history throw lights on wireless charging methods, highlighting the pros and cons. Then, the paper aids a comparative review of different type’s inductive pads, rails, and compensations technologies done so far. The static and dynamic charging techniques and their characteristics are also illustrated. The role and importance of power electronics and converter types used in various applications are discussed. The batteries and their management systems as well as various problems involved in WPT are also addressed. Different trades like cyber security economic effects, health and safety, foreign object detection, and the effect and impact on the distribution grid are explored. Prospects and challenges involved in wireless charging systems are also highlighting in this work. We believe that this work could help further the research and development of WPT systems.

Load Balancing of a Modular Multilevel Grid-Interface Converter for Transformer-Less Large-Scale Wireless Electric Vehicle Charging Infrastructure

This article analyzes the requirements for load balancing of a new transformer-less grid-interface topology for large-scale electric vehicle (EV) charging infrastructures. The proposed configuration utilizes a modular multilevel converter (MMC) to supply wireless EV chargers from each module. The inherent galvanic isolation provided by wireless inductive power transfer and the scalability of the MMC topology enable transformer-less connection to medium voltage (MV) distribution grids. This can reduce the footprint and copper volume of the internal power distribution for the parking infrastructure. The load distribution within the MMC topology depends on the location and power requirements of each EV to be charged. Requirements for load balancing by controlling the internal circulating currents of the proposed topology when supplying unevenly distributed loads are derived. It is also demonstrated how a second harmonic component of the circulating currents can be utilized to ensure balancing capability within each MMC arm, and how its required amplitude depends on the load distribution. The theoretical analysis and the performance of a corresponding control strategy are first verified by time-domain simulations of a large-scale infrastructure. Experimental results from a small-scale prototype based on an MMC where each arm has 12 modules with individual controllable loads are presented.

A Secondary-Side Controlled Electric Vehicle Wireless Charger

In this paper, the design procedure of an electric vehicle (EV) wireless charger is presented. Unlike most of the systems available in the literature, the proposed charging system is regulated from the vehicle side. The on-board electrical circuit automatically adapts the resonant compensation to guarantee compatibility with the primary inverter characteristics and achieve high transmission efficiency without communication between sides. Moreover, the proposed control strategy, used to regulate the secondary full active rectifier (FAR), allows the supply of the the EV battery, maximizing the efficiency during the whole charging process.

Crossed flat solenoid coupler for stationary electric vehicle wireless charging featuring high misalignment tolerance

This study proposes a crossed flat solenoid coupler (CFSC) for electric vehicle wireless charging. The impact of four size parameters of CFSCs on coupling coefficient and misalignment tolerance is studied using finite-element analysis. The optimisation methodology of CFSCs considering size constraints is given. The CFSC is compared with the planar square coupler (PSC) and double D coupler (DDC) from three aspects: coupling coefficient, misalignment tolerance, and copper usage. The CFSC performs the best in the three aspects, and the DDC performs the worst. Two wireless power transfer prototypes, one employing CFSCs and the other utilising PSCs, were built to demonstrate the superiority of the proposed coupler. Primary inductor-capacitor-capacitor secondary series compensation topologies were employed in the two prototypes. Experiments agree well with theoretical analysis and simulations. The power transfer efficiency of the CFSC-based prototype was 1.6% higher than the PSC-based prototype when the Z-axis displacement is 45 mm.

Optimized Electric Vehicle Wireless Chargers With Reduced Output Voltage Sensitivity to Misalignment

In this article, an optimized design of wireless charger for electric vehicle (EV) applications is presented to reduce the misalignment effect on the output voltage and efficiency of the wireless charger system. The existing methods to regulate the output voltage require either the communication link between the EV and charging station to control the charging station converter or a dc–dc converter on the EV. This article provides a solution to optimize compensation networks to reduce output voltage sensitivity with respect to misalignment and improve the efficiency of the overall system. Four topologies are studied in details, and the optimized compensation network is developed for each topology. The compensation networks are also designed to satisfy zero voltage switching (ZVS) for a wide range of misalignments. The performance of the optimized circuits is compared in detail in terms of efficiency, output voltage performance, size of the resonant network, and power loss distribution. This article also shows that LCC–LCC and LCC–series are the best candidates for operation in a wide range of misalignments. A 500-W/85-kHz prototype charger is built for each topology, and the performance of the optimized resonant networks is evaluated experimentally.

Research on the Topology of Wireless V2G for Electric Vehicle

Based on the circuit topology for the electric vehicle wireless V2G power transmission system, the boost circuit, wireless resonance circuit and grid-connected inverter circuit of the system were studied. According to the characteristics of the boost converter, a voltage feedback closed-loop control model based on PID and PWM was established. Since the excitation and magnetic leakage of the wireless transmission coil could not be ignored, the maximum transmission power model of the wireless resonance circuit was derived. Starting from the operation mode of the three-phase grid-connected inverter circuit, the control rules of the three-phase bridge arm that sent electrical energy back to the grid in a steady state were obtained. The simulation results showed that the maximum transmission power of the electric vehicle wireless V2G power transmission system was affected by the leakage magnetic field of the wireless transmission coil, and the maximum transmission power was inversely proportional to the leakage magnetic field. In addition, the boost circuit and grid-connected inverter circuit in the system were sources of harmonics, and a large amount of harmonic energy was sent to the grid during the operation process of the electric vehicle wireless V2G circuit.

Protection Strategy for Wireless Charging Electrical Vehicles

Wireless charging has become increasingly popular for electric vehicles (EVs) in recent years. However, possible device damage may happen because of the sharp variations of inverter output current and the ZVS angle due to the alignment variation between resonant coils especially while charging. To design a protection strategy, the characters of the inverter output current and phase angle are analyzed when the wireless charging EV leaves. The protection strategy is composed of the insufficient angle protection, overcurrent protection, and the excessive angle protection. A detection circuit is designed to measure the variation of inverter output current and phase angle. A wireless charging EV prototype is established to validate the proposed methods. The experimental results show that the designed detection circuit and protection strategy can catch the abnormal working state of the system when the wireless charged EV leaves and take measures immediately to protect the main circuit of the system from device damages.