High Frequency Wireless Power Transfer Research Articles

Design of a Spiral Coil for High-Frequency Wireless Power Transfer Systems Using Machine Learning

Design of a Spiral Coil for High-Frequency Wireless Power Transfer Systems Using Machine Learning

A Bidirectional Autonomous High-Frequency Wireless Power Transfer System With Constant Voltage Output Against Load and Coupling Variations

A Bidirectional Autonomous High-Frequency Wireless Power Transfer System With Constant Voltage Output Against Load and Coupling Variations

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.

Analysis of Losses in Two Different Control Approaches for S-S Wireless Power Transfer Systems for Electric Vehicle

This paper presents the study and detailed analysis of converter losses at different stages together with the series-series (S-S) compensating coils in wireless power transfer (WPT) systems, via two distinct approaches to control the power converters. The two approaches towards wireless DC–DC power flow control are termed as the Single Active High-Frequency Wireless Power Transfer (SAHFWPT) system and the Dual Active High-Frequency Wireless Power Transfer (DAHFWPT) system. The operation of converters in SAHFWPT and DAHFWPT are controlled by the extended phase shift (EPS) and dual phase shift method respectively. The general schematic of the SAHFWPT system consists of an active bridge and a passive bridge, while the schematic of the DAHFWPT system consists of both active bridges. The efficiency evolutions of ideal SAHFWPT and DAHFWPT are far away from the real ones. Moreover, this article analyzes the operation and losses of the uni-directional power flow of the WPT system, i.e., from the DC bus in the primary side to the battery load in the secondary side. The loss estimation includes high-frequency switching losses, conduction losses, hard turn on and turn off coil losses, etc. Moreover, the efficiency of the WPT system depends on operation of the converter. A 50 W–3600 W Power range system at a resonant frequency of 85 kHz is implemented in MATLAB/SIMULATION to demonstrate the validity of the proposed method.

A 6.6-kW High-Frequency Wireless Power Transfer System for Electric Vehicle Charging Using Multilayer Nonuniform Self-Resonant Coil at MHz

A high-power, high-frequency wireless power transfer system for electric vehicles (EVs) is proposed in this article with lightweight and compact coil design. Leveraging a multilayer nonuniform self-resonant coil, no external capacitor is needed for compensation and the high-frequency conduction loss is mitigated by sharing current between multiple copper layers. The analytical model for the proposed coil is provided, and prototype coils with 200-mm radius are fabricated and tested, achieving a quality factor over 450 at 3 MHz. The optimized design for both coils and a GaN-based power stage are detailed and validated experimentally. Experimental tests show 95.2% dc–dc efficiency with 6.6-kW power transferred across a 100-mm coil-to-coil distance with 52.5 kW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> power density. The system demonstrates the first 6.6-kW wireless power transfer system for EV charging using compact self-resonant coils at MHz.

Scalable Architectures for High Frequency and Very High Frequency Wireless Power Transfer

Scalable Architectures for High Frequency and Very High Frequency Wireless Power Transfer

Coupled electromagnetic-thermal analysis of roadway inductive power transfer pads within a model pavement

Inductive Power Transfer (IPT) technology is a promising solution for wireless charging of Electric Vehicles (EVs). Given the expected uptake of IPT technology for both stationary and in motion in-road charging, many technical challenges regarding the electromagnetic field and thermal aspects need to be overcome to generate cost-effective and reliable solutions. One particular design constraint of in-road IPT systems is the occurrence of local increases in temperature during operation due to power losses in the wireless charging pads. In this paper, safe operating conditions of an enclosed wireless power transfer pad within a pavement model were identified. This aspect has been studied less rigorously compared with the electromagnetic design. This paper presents a numerical thermal analysis of a double-D (DD) prototype IPT primary pad based on two possible configurations; flush-mounted or buried, within a model pavement. A coupled electromagnetic-thermal simulation has been developed to aid in the development of thermally robust in-road IPT systems. In order to validate the proposed two-way coupled electromagnetic-thermal Finite Element (FE) simulations, experiments were performed to capture the evolving thermal field within an IPT primary pad under continuous and periodic duty cycles. This method made possible analysis of the heating patterns and so the identification of internal hotspots within an IPT pad in a roading structure. A thermal camera was used to provide detailed surface temperature distributions, while suitable application of non-metallic Fiber Bragg Grating (FBG) sensing technology enabled a robust technique to measure temperatures within the intense magnetic fields of a high frequency wireless power transfer system to be developed. Comparisons at steady state of the pavement surface temperature distribution, as well as point measurements with the pad and sand, demonstrate good accuracy. The maximum steady state surface temperature occurs at the centre of the sand surface where the IPT pad is placed and is approximately 87 °C and 100 °C for buried and flush-mounted pads, respectively. Moreover, for a 2/3 duty cycle loading, the maximum temperature of the pad tended to an average of approximately 76 °C, while at constant operation the average temperature is 105 °C. Therefore, a 5 min cooling period significantly reduced operating temperatures within the studied model IPT system. In the future, the methodologies proposed in this paper can also be used to improve the design of higher power IPT pads by identifying hotspots and maximum thermal stresses and determination of optimal charging patterns for heat dissipation.

On Using CNTFs-Based Wires for High Frequency Wireless Power Transfer Charging Systems

In many practical wireless power transfers (WPT) applications, such as cell phone wireless charger, electrical vehicles, and implantable cardiac pacemakers, the weight and power losses in the coupled coils are primary design issues. Currently, metallic wires are normally used to fabricate the WPT coils. The metallic wires have several problems, mainly involving large weight, poor mechanical performance, corrosion, and resistive losses (especially at high frequency due to both of skin and proximity effects). Carbon Nanotube Fibers (CNTFs)-based wire is a promising candidate to replace the conventional metallic wires in these applications. CNTFs-based wires have superior electrical properties at high frequencies. Furthermore, it shows high mechanical performance, light weight, and high thermal conductivity. This paper uses CNTF wires to investigate a planar spiral transformer suitable for WPT charging systems. Efficiency of the transformer is investigated theoretically and experimentally over several MHz frequencies and ampere currents. The CNTFs-based wireless transformer operation was compared with copper (Cu) based wireless transformer fabricated with similar dimensions and DC resistance values. The AC resistance of both transformers is calculated using the conventional model of solid round conductor and the FEM simulation. It is found that the calculated and the FEM AC resistance values are matched in case of Cu transformer with 4194A Impedance/Gain-Phase Analyzer measurements while they are mismatched in case of CNTFs one. Therefore, a correction factor for the AC resistance of CNTFs wire is proposed to match the calculated AC resistance with the measured one. Furthermore, both transformers were tested experimentally within 50 W/6.78 MHz WPT charging systems at different ampere currents. The charger efficiency measurements verify the analyzer results showing better efficiency with CNTF based transformer in comparing to copper one.

Isolated Gate Driver for Medium-Voltage SiC Power Devices Using High-Frequency Wireless Power Transfer for a Small Coupling Capacitance

A high-voltage operation and breakneck switching speed of medium-voltage (MV) silicon carbide (SiC) devices demand gate drivers (GDs) with high voltage withstanding capability, high common-mode (CM) transient immunity and a reliable short-circuit protection. An isolated GD to meet these challenging requirements is presented in this article. A novel isolated gate driver power supply using high-frequency wireless power transfer (WPT) with a nonoverlapped winding arrangement for a small coupling capacitance is proposed. Moreover, a grounded shield is added to further reduce the effective coupling capacitance and the CM current. The receiver (Rx) coil of the WPT system along with its power processing circuit have been epoxy encapsulated to achieve a very high breakdown voltage and an extremely small form factor without violating very demanding clearance and creepage distance requirements. The impact of epoxy, winding arrangement, Rx circuits, and the grounded shield on the coupling capacitance is analyzed in details. In addition, a sophisticated overcurrent protection (OCP) scheme with soft-turn-off capability for MV SiC devices is developed. The designed OCP scheme achieves fast protection and simultaneously avoids false tripping due to very high current overshoot associated with the MV SiC devices during turn-on transitions. An experimental prototype is developed and the performance of the proposed GD under various operating conditions is evaluated experimentally.

Gallium Nitride Inverter Design with Compatible Snubber Circuits for Implementing Wireless Charging of Electric Vehicle Batteries

High-frequency wireless power transfer (WPT) technology provides superior compatibility in the alignment with various WPT standards. However, high-efficiency and compact single-phase power switching systems with ideal snubber circuits are required for maximum power transfer capability. This research aims to develop an inverter using Gallium Nitride (GaN) power transistors, optimized RCD (resistor/capacitor/diode) snubber circuits, and gate drivers, each benefitting WPT technology by reducing the switching and conduction loss in charging electric vehicle batteries. A full-bridge GaN inverter was simulated and instituted as part of the wireless charging circuit design. The RCD circuits were adjusted by transferring maximum power from the power supply to the transmitter inductor. For verification of the simulated output, lab-scale experiments were implemented for two half-bridges controlled by gate drivers with corresponding snubber circuits. After authenticating the output results, the GaN inverter was tested with an input range of 30 V to deduce the success of charging electric vehicle batteries within an efficient time frame. The developed inverter, at 80 kHz frequency, was applied in place of a ready-to-use evaluation board, fully reducing less harmonic distortion and greatly increasing WPT system efficiency (~93%). In turn, the designed GaN inverter boasts considerable energy savings, resulting in a more cost-effective solution for manufacturers.

Reinforcements in europe

Inductive Power Transfer (IPT) technology is a promising solution for wireless charging of Electric Vehicles (EVs). Given the expected uptake of IPT technology for both stationary and in motion in-road charging, many technical challenges regarding the electromagnetic field and thermal aspects need to be overcome to generate cost-effective and reliable solutions. One particular design constraint of in-road IPT systems is the occurrence of local increases in temperature during operation due to power losses in the wireless charging pads. In this paper, safe operating conditions of an enclosed wireless power transfer pad within a pavement model were identified. This aspect has been studied less rigorously compared with the electromagnetic design. This paper presents a numerical thermal analysis of a double-D (DD) prototype IPT primary pad based on two possible configurations; flush-mounted or buried, within a model pavement. A coupled electromagnetic-thermal simulation has been developed to aid in the development of thermally robust in-road IPT systems. In order to validate the proposed two-way coupled electromagnetic-thermal Finite Element (FE) simulations, experiments were performed to capture the evolving thermal field within an IPT primary pad under continuous and periodic duty cycles. This method made possible analysis of the heating patterns and so the identification of internal hotspots within an IPT pad in a roading structure. A thermal camera was used to provide detailed surface temperature distributions, while suitable application of non-metallic Fiber Bragg Grating (FBG) sensing technology enabled a robust technique to measure temperatures within the intense magnetic fields of a high frequency wireless power transfer system to be developed. Comparisons at steady state of the pavement surface temperature distribution, as well as point measurements with the pad and sand, demonstrate good accuracy. The maximum steady state surface temperature occurs at the centre of the sand surface where the IPT pad is placed and is approximately 87 °C and 100 °C for buried and flush-mounted pads, respectively. Moreover, for a 2/3 duty cycle loading, the maximum temperature of the pad tended to an average of approximately 76 °C, while at constant operation the average temperature is 105 °C. Therefore, a 5 min cooling period significantly reduced operating temperatures within the studied model IPT system. In the future, the methodologies proposed in this paper can also be used to improve the design of higher power IPT pads by identifying hotspots and maximum thermal stresses and determination of optimal charging patterns for heat dissipation.