Cliff P. White

A novel wireless power transfer for in-motion EV/PHEV charging

Wireless power transfer (WPT) is a convenient, safe, and autonomous means for electric and plug-in hybrid electric vehicle charging that has seen rapid growth in recent years for stationary applications. WPT does not require bulky contacts, plugs, and wires, is not affected by dirt or weather conditions, and is as efficient as conventional charging systems. When applied in-motion, WPT additionally relives range anxiety, adds further convenience, reduces battery size, and may help increase the battery life through charge sustaining approach. This study summarizes some of the recent activities of Oak Ridge National Laboratory (ORNL) in WPT charging of EV and PHEVs inmotion. Laboratory experimental results that highlight the wireless transfer of power to a moving receiver coil as it passes a pair of transmit coils and investigation of results of insertion loss due to roadway surfacing materials. Some of the experimental lessons learned are also included in this study.

Demonstrating Dynamic Wireless Charging of an Electric Vehicle: The Benefit of Electrochemical Capacitor Smoothing

The wireless charging of an electric vehicle (EV) while it is in motion presents challenges in terms of low-latency communications for roadway coil excitation sequencing and maintenance of lateral alignment, plus the need for power-flow smoothing. This article summarizes the experimental results on power smoothing of in-motion wireless EV charging performed at the Oak Ridge National Laboratory (ORNL) using various combinations of electrochemical capacitors at the grid side and in the vehicle. Electrochemical capacitors of the symmetric carbon-carbon type from Maxwell Technologies comprised the in-vehicle smoothing of wireless charging current to the EV battery pack. Electro Standards Laboratories (ESL) fabricated the passive and active parallel lithium-capacitor (LiC) unit used to smooth the grid-side power. The power pulsation reduction was 81% on the grid by the LiC, and 84% on the vehicle for both the LiC and the carbon ultracapacitors (UCs).

Oak Ridge National Laboratory Wireless Power Transfer Development for Sustainable Campus Initiative

Wireless power transfer (WPT) is a convenient, safe, and autonomous means for electric and plug-in hybrid electric vehicle charging that has seen rapid growth in recent years for stationary applications. WPT does not require bulky contacts, plugs, and wires, is not affected by dirt or weather conditions, and is as efficient as conventional charging systems. This study summarizes some of the recent Sustainable Campus Initiative activities of Oak Ridge National Laboratory (ORNL) in WPT charging of an on-campus vehicle (a Toyota Prius plug-in hybrid electric vehicle). Laboratory development of the WPT coils, high-frequency power inverter, and overall systems integration are discussed. Results cover the coil performance testing at different operating frequencies, airgaps, and misalignments. Some of the experimental results of insertion loss due to roadway surfacing materials in the air-gap are presented. Experimental lessons learned are also covered in this study.

Grid side regulation of wireless power charging of plug-in electric vehicles

Conductive charging of plug-in and battery electric vehicles (PEVs) is now well established and becoming more pervasive in the market. Conductive charger regulation of vehicle regenerative energy storage system (RESS), or battery pack charge rate is controlled by the dedicated on-board-charger (OBC) in coordination with the vehicles battery management system (BMS). Wireless Power Transfer (WPT) charging of PEVs is a relatively new and emerging technology that will not benefit from standardization work until 2014 or later. As such, various approaches are currently underway to manage the power flow from the grid-tied high frequency power inverter to the vehicle RESS. WPT regulation approaches can be secondary side only, primary side only or a combination of both. In this paper Oak Ridge National Laboratory (ORNL) envisions a system that is fast charge compatible and that minimizes the vehicle on board complexity by placing the burden of power regulation on the grid side converter. This paper summarizes the ORNL approach and experimental lessons learned at the National Transportation Research Center WPT laboratory1.

A bi-directional DC-DC converter with minimum energy storage elements

A proof-of-concept military advanced mobile generator set has been developed. The military generator set uses an internal combustion diesel engine to drive a radial-gap permanent magnet alternator at variable speed. The speed of the engine is determined from a user selectable interface that for a given load and ambient thermal conditions controls the engine to run at its most efficient operating point. The variable frequency, variable voltage produced by the permanent magnet alternator is diode-rectified to a high voltage (/spl sim/400 V) DC link, and an inverter is used to produce selectable frequency, controllable AC voltage. As part of the power electronics for this unit, a 7 kW bi-directional DC-DC converter has also been developed. The converter can charge 24 V batteries that are used to start the internal combustion engine and to power auxiliary low voltage DC loads. Additionally, the bi-directional converter can also draw power from the batteries to help maintain the high voltage DC link during severe load transients. Because of stringent weight and volume requirements for this application, the minimum in energy storage elements (high frequency transformers, capacitors, and inductors) was used. This paper presents a description and experimental analysis of this novel DC-DC converter design.

Electronic power conversion system for an advanced mobile generator set

The electronic power conversion system and control for an advanced mobile generator set is described. The military generator set uses an internal combustion diesel engine to drive a radial-gap permanent magnet alternator at variable speed. The speed of the engine is determined from a user selectable interface that for a given load and ambient thermal conditions controls the engine to run at its most efficient operating point. It is also possible to control the engine to run where it is most audibly quiet, at its least-polluting operating point, or at its most reliable, stiffest point such that it is less sensitive to load transients. The variable frequency, variable voltage produced by the permanent magnet alternator is diode-rectified to DC voltage, and an inverter is used to produce selectable frequency, controllable AC voltage. The power conversion system also incorporates a bi-directional DC-DC converter that can charge 24 V batteries that are used to start the IC engine and to power auxiliary loads. The bi-directional converter can also draw power from the batteries to help maintain the DC link during severe load transients. The design of this new generator set offers additional flexibility by being lighter, smaller, and more fuel efficient than a conventional fixed-speed gen-set.

A high-power wireless charging system development and integration for a Toyota RAV4 electric vehicle

Several wireless charging methods are under development or available as an aftermarket option in the light-duty automotive market. However, there are not many studies detailing the vehicle integrations, particularly a fully integrated vehicle application. This paper presents the development, implementation, and vehicle integration of a high-power (>10 kW) wireless power transfer (WPT)-based electric vehicle (EV) charging system for a Toyota RAV4 vehicle. The power stages of the system are introduced with the design specifications and control systems including the active front-end rectifier with power factor correction (PFC), high frequency power inverter, high frequency isolation transformer, coupling coils, vehicle side full-bridge rectifier and filter, and the vehicle battery. The operating principles of the overall wireless charging system as well as the control system are presented. The physical limitations of the system are also defined that would prevent the system from operating at higher levels. The system performance is shown for two cases including unmatched (interoperable) and matched coils. The experiments are carried out using the integrated vehicle and the results are obtained to demonstrate the system performance including the stage-by-stage efficiencies with matched and interoperable primary and secondary coils.

Vehicular integration of wireless power transfer systems and hardware interoperability case studies

Several wireless charging methods are under development or available as an aftermarket option in the light-duty automotive market. However, there are not a sufficient number of studies detailing the vehicle integration methods, particularly a complete vehicle integration with higher power levels. This paper presents the design, development, implementation, and vehicle integration of wireless power transfer (WPT)-based electric vehicle (EV) charging systems for various test vehicles. Before having the standards effective, it is expected that WPT technology first will be integrated as an aftermarket retrofitting approach. Inclusion of this technology on production vehicles is contingent upon the release of the international standards. The power stages of the system are introduced with the design specifications and control systems including the active front-end rectifier with power factor correction, high frequency power inverter, high frequency isolation transformer, coupling coils, vehicle side full-bridge rectifier and filter, and the vehicle battery. The operating principles of the control, and communications, systems are presented. Aftermarket conversion approaches including the WPT on-board charger (OBC) integration, WPT CHAdeMO integration, and WPT direct battery connection scenarios are described. The experiments are carried out using the integrated vehicles and the results obtained to demonstrate the system performance including the stage-by-stage efficiencies.

Design and evaluation of a 6.6 kW GaN converter for onboard charger applications

This paper presents a compact, lightweight, highly efficient, 6.6 kW isolated three-port dc-dc converter for onboard charger (OBC) applications. The converter was designed and fabricated using normally-off gallium nitride (GaN) transistors; a three-dimensional (3-D) printed cold plate; high-voltage heavy copper printed circuit board (PCB) power planes; low-voltage (14 V) and high-current PCB power planes; and a planar transformer. The prototype has a power density of 10.5 kW/L and specific power of 9.6 kW/kg. Test results show greater efficiency than a silicon-based counterpart, even at 2.5 times higher switching frequency. The isolated GaN converter was integrated with a 100 kW segmented traction inverter that uses silicon carbide MOSFETs and 3-D printed components to test the functionality as a level-2 OBC. Testing and evaluation of the integral onboard charging functionality was successfully completed at power levels up to 6.6 kW.