Electric Vehicles Wireless Charger Research Articles

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.

Quadruple-U Auxiliary Structure-Based Receiving Coil Positioning System for Electric Vehicle Wireless Charger

In order to strike a balance between economic development and green travel, electric vehicles with wireless charging have become one of the first choices for future transportation. Misalignment between the transmitting coil and receiving coil in wireless charging systems decreases power capacity and efficiency to a great extent. Hence, the detection of whether the electric vehicle enters the effective charging area is a hot issue in the current research. In this paper, a receiving coil positioning approach integrated with a quadruple-U auxiliary structure is proposed. The designed quadruple-U auxiliary structure with cruciform distribution consists of four U-shaped coils, which are inspired by the solenoid coil. Based on the symmetry of the auxiliary structure, a receiving coil positioning method is proposed by measuring the load voltages of each U-shaped coil working independently. Coordinates can be obtained by retrieving the measured results with the database established in advance. The positioning method has the advantages of wider positioning ranges, higher positioning accuracy, and not changing the structure of the receiving coil. Furthermore, the specific magnetic coupler is simulated by a three-dimensional finite element modeling tool and was verified by an experiment on a prototype. During the positioning process, the positions distributed throughout the ΔX ∈ [−300 mm, 0 mm]∩ΔY ∈ [−300 mm, 300 mm] positioning range were tested. The experimental results indicate that all of the tested positions are accurate to within 10 mm, with a 160 mm transfer distance. Meanwhile, combined with the symmetry of the auxiliary structure and the test results, it can be indicated that the positioning range can reach ΔX ∈ [−300 mm, 300 mm]∩ΔY ∈ [−300 mm, 300 mm].

A Self-Tuning LCC/SP System for Electric Vehicle Wireless Charging against Large Self- and Mutual Inductance Variations

An LCC/SP self-tuning wireless charging system is proposed herein for use in a wireless charging test bench. With different dislocations in addition to changes in the coil self-inductance and mutual inductance caused by different secondary magnetic shielding materials, the system can ensure that the high power factor of the primary side remains unchanged without changing the circuit topology. Based on this normalized detuning LCC/SP circuit model, a switch-controlled capacitor (SCC) self-tuning method based on PI control is proposed. The control scheme employs only two MOSFETs and capacitors, without WIFI communication or parameter identification. A 2 kW experimental device was set up in the laboratory, and experimental verification was carried out with large-scale dislocations and different secondary magnetic shielding materials. The experimental results confirm that the system can maintain a high power factor (&gt;0.9) under a system mutual inductance variation of 47.7% and secondary coil self-inductance variation of 12%, and that it can be applied in electric vehicle wireless chargers or high-power wireless charger test benches.

Frequency and Parameter Combined Tuning Method of LCC–LCC Compensated Resonant Converter With Wide Coupling Variation for EV Wireless Charger

The characteristics of inductive power-transfer (IPT) systems are sensitive to the variation of the coupling coefficient caused by misalignment conditions or different gaps. This results in a reduction in transferred power and efficiency. The output characteristics considering frequency modulation applied in series–series (SS), inductor–capacitor–capacitor (LCC)-S and LCC–LCC compensated IPT systems have been explored, revealing that high-order compensation topologies hold limited power regulation ability if coupling varies significantly. The parameter sensitivity of LCC–LCC-compensated topology is investigated through the singular values (SVs) analysis. It is found that the variation of the parallel-compensated capacitors has the greatest impact on the output power. Aiming at alleviating the power drop caused by the coupling variation, a parameter offline tuning method realized by switching the parallel-compensated capacitance for a detuned LCC–LCC resonant converter is proposed for electric vehicle (EV) wireless charging. Analytical expressions have been derived in aiding the design of modified value of capacitance ensuring primary zero voltage switching (ZVS) operation. Thus, the detuned parameter combinations, which deliver rated power even with the worst coupling, are obtained. Finally, a 6.6-kw prototype has been built to verify the validity of the proposed topology, which can deliver 6.1 kW with an efficiency of 94% even when the coupling drops from 0.3 to 0.15.

Magnetic Coupler Robust Optimization Design for Electric Vehicle Wireless Charger Based on Improved Simulated Annealing Algorithm

Fleets of autonomous vehicles including shuttle buses, freight trucks, and road sweepers will be deployed in the Olympic Village during Beijing 2022 Winter Olympics. This requires intelligent charging infrastructure based on wireless power transfer technology to be equipped. To increase the misalignment tolerance of a high-power wireless charger, the robustness of the magnetic coupler should be optimized. This paper presents a new type of unipolar coupler, which is composed of three connected coils in series. The dimensional configuration of the coils is analyzed by the finite element method. The characteristic parameters of the coil are identified with their influence on the self-inductance and coupling coefficient. An expert model is built, whose feasibility can be verified in the aimed design domain. Combined with the expert model, an improved simulated annealing algorithm with a backtracking mechanism is proposed. The primary coil can reach the expected characteristics from any starting parameter combination through the proposed optimization algorithm. Under the same conditions in terms of external circuit parameters, ferrite usage, and aluminum shielding, the offset sensitivity of the magnetic coupler can be reduced from 58.79% to 18.89%. A prototype is established, validating the feasibility of the proposed coil structure with the optimized parameter algorithm.

Optimal Design of Fully Integrated Magnetic Structure for Wireless Charging of Electric Vehicles

Optimal design of a fully integrated magnetic structure for electric vehicle (EV) wireless charging is proposed in this article. The proposed approach helps save ferrite material, reduce the implementation cost, shrink the size of the converter, and improve the cost and power density. Typically, in a wireless charging system, an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i> resonant network and the receiver dc–dc converter are used, which require a bulky inductor in their structures. The integration of resonant inductor with the transmitter-side coil has been studied in the literature to reduce the overall cost and improve the power density of an EV wireless charger. The integration of the dc–dc inductor with the vehicle-side receiver coil is also introduced in the literature. However, the full integration of both resonant inductor and dc–dc inductor into the transmitter and receiver coils of the wireless charging system creates new design challenges that have not been addressed before. In this article, the proposed fully integrated magnetic structure and its design challenges are studied in detail. A procedure for achieving the optimal design of the fully integrated structure is presented. An optimization problem is defined to design the best magnetic structure and select the best values for the resonant elements and dc–dc inductor. The outcome of this integration is an all-integrated magnetic structure, compact converter, and efficient wireless charger. A 2.2-kW/85-kHz system is built to verify the feasibility of the proposed integrated wireless charging system, and its performance is evaluated through the experiment.

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.

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.

Simulation and Optimal Design of Magnetic Coupler and its Shielding for EV Wireless Charger

This paper is focus on the coupler design of wireless power transfer (WPT) system for Electric Vehicle(EV). The author describes the coupler circuit model, design principles and steps, calibration methods and magnetic shielding methods for the coupler. Four shielding methods are simulated and compared in this paper. Through simulation, the author believes that aluminium plate shielding is the best for magnetic shielding, but it will cause more losses. Therefore, we need to do a more optimal design in the next study.

High Power Density Z-Source Resonant Wireless Charger With Line Frequency Sinusoidal Charging

Wireless charger for electric vehicles (EVs) is an offline application and it needs power factor correction (PFC) function, which usually consists of a front-end boost PFC and a cascaded dc–dc converter. Z-source resonant converter (ZSRC), a single-stage solution with low cost and high efficiency, was proposed for EV wireless charger lately. The Z-source capacitors in the ZSRC are designed to absorb the double-line frequency ripple in this single-phase application. Sinusoidal charging, which allows the double-line frequency ripple propagate to the output, is another solution aiming at reducing the bulky capacitors. Recently, a comparison of low-frequency (120 Hz) sinusoidal charging and dc charging shows a negligible impact on Li-ion batteries’ performance. Therefore, the ZSRC's capacitor, the biggest component, can be reduced dramatically from millifarad to several microfarads with a sinusoidal charging technique, which features the ZSRC high power density. Also, it keeps the Z-source's benefit of boost ability and being immune to shoot-through problems. In this paper, the sinusoidal charging behavior for the ZSRC is modeled, and a control scheme that has both PFC function and load regulation for sinusoidal charging is proposed. This control scheme can pass IEC61000-3-2 Class A criterion. Experimental results based on a 1-kW prototype with 20 cm air gap between the primary and secondary side are presented to illustrate the proposed control scheme.

Lateral Position Error Reduction Using Misalignment-Sensing Coils in Inductive Power Transfer Systems

Inductive power transfer (IPT) remains one of the most common ways to achieve wireless power transmission, operating on the same electromagnetic principle as electrical transformers but with an air core instead of an iron core. IPT has been implemented in many applications, including wireless charging of consumer products like smartphones and electric vehicles. However, one challenge with using IPT is ensuring precise alignment between the primary and secondary coils of the system so that maximum power transfer can take place. In this paper, the use of misalignment-sensing coils to detect and correct lateral misalignments in an IPT system is modeled and tested. The sensing coils exploit magnetic-field symmetry to give a nonlinear measurement of misalignment direction and magnitude. Experiments using such sensing coils give a misalignment sensing resolution better than 1 mm when applied to a commercial smartphone wireless charger. Voltage readings from the sensing coils are used for closed-loop control of an experimental two-dimensional coil positioner that can reduce lateral misalignments as large as 35 mm to less than 1.4 mm, allowing for effective power transfer. A similar sensing coil concept can be used to reduce lateral misalignments in scaled IPT systems, such as electric-vehicle wireless chargers.

Impact of Coil Misalignment in Data Transmission over the Inductive Link of an EV Wireless Charger

The penetration rate of electric vehicles (EVs) will experience a relative increment in the future, so easy to use ways to recharge will be demanded. In this sense, wireless charging represents a safe charging method that minimises user intervention. In a similar way to conductive charge, wireless charging requires some information exchange between the charger primary side and secondary side (battery) for safety and operational reasons. Thus, wireless chargers depend on a communication system for their controlled and correct operation. This paper analysed the communication performance of a wireless EV charger in which the communiction device is part of the wireless power transfer system. Particularly, this work studies how the communication system reacts to power coil displacements, which commonly occur in their conventional performance. The results show that the compensation topology selected to ensure the resonant operation clearly impacts on the communication performance. In particular, the theoretical model and the simulation results demonstrate that the asymmetrical compensation topologies are more stable in terms of the wireless communication channel capacity.

Comparison Study on SS and Double-Sided LCC Compensation Topologies for EV/PHEV Wireless Chargers

This paper compares the characteristics of the series–series and double-sided Inductor-Capacitor-Capacitor (LCC) compensation topologies for electric vehicle (EV) wireless chargers. Both the well-tuned and mistuned topologies for the two compensation methods are analyzed in detail. The mistuning considered here is mainly caused by the variations of the relative position between the primary and secondary sides. The output power displacements caused by mistuning are compared for both compensation topologies, as well as the impacts of the load variations on the performances of the mistuned topologies. The voltage and current stresses on components are also studied. The comparative result shows that the double-sided LCC compensation topology is less sensitive to mistuning. A double-sided LCC-compensated EV wireless charger system with up to 7.7-kW output power is built to verify the analysis results. A peak efficiency of 96% from dc power source to battery load is achieved.

Integrated ${LCC} $ Compensation Topology for Wireless Charger in Electric and Plug-in Electric Vehicles

This paper presents an integrated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LCC$</tex-math></inline-formula> compensation topology for electric vehicle/plug-in hybrid electric vehicle wireless chargers. The effect of the coupling between the additional coil and the main coil on the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LCC$</tex-math></inline-formula> compensation topology is studied. The proposed topology will reduce the size of the additional coil and make the system more compact with extremely high efficiency. The basic characteristics of the proposed topology are analyzed based on fundamental harmonic approximation. Furthermore, based on the steady-state model, three categories of operation modes are presented and analyzed. In order to realize zero-voltage switching, the series capacitor <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{2} $</tex-math></inline-formula> on the secondary side is tuned. A numerical method is used to analyze the impact of different values of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta C_{2}$</tex-math></inline-formula> on the turnoff current, and the best value of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{2}$</tex-math></inline-formula> is chosen to build a prototype to verify the analysis.