Dr. Omer Onar led a team at the Department of Energy’s Oak Ridge National Laboratory (ORNL) that demonstrated a 20-kilo-watt bi-directional charging system installed on a UPS hybrid electric delivery truck. The system enables electric vehicles to be charged while on the road.
Tech Briefs: What got you interested in wireless charging technology to begin with?Dr. Omer Onar led a team at The Department of Energy’s Oak Ridge National Laboratory (ORNL) that demonstrated a 20-kilowatt bi-directional charging system installed on a UPS hybrid electric delivery truck. It delivered that power across an 11-inch air gap.
Dr. Omer Onar: I got involved with the project in September of 2011. Soon after I started on it, I figured out this might be the way to go with electric vehicle charging because you could automate the charging process. Connected and automated vehicles can self-drive, self-park, and they can even make fuel- and time-saving decisions but they cannot currently self-charge. Because wireless charging can automate the charging process, it will be a key enabler for the transportation electrification.
Tech Briefs: Could you expand on the advantages of wireless over wired charging.
Dr. Onar: There are several benefits. One is that since the charging process is automated, when you get back to your home at the end of the day, you don’t have to plug in the vehicle — you won’t forget to plug it in and run out of charge the following day. Also, the process is completely safe because you don’t have to touch a cable or a high voltage connector. It also eliminates vandalism — you don’t need a pedestal with cables hanging around it because the transmitter can be embedded under the road or pavement. And it can be as efficient as the conductive charging solutions, so, it’s safe, highly efficient, flexible, and convenient.
Right now, many people don’t buy electric vehicles because most of the affordable ones have a limited range of around 50 to 100 miles. There is, however, a concept that we call in-motion, or dynamic wireless charging systems. If you electrify a portion of the roadway with this technology, a vehicle could pick up charge on the go and ideally have unlimited range.
Tech Briefs: I can’t picture picking up charge on the go. How would that work?
Dr. Onar: The transmitter pads could be embedded under the road-surfacing pavement. You would need to have a vehicle sensing system so once a vehicle approaches, you could energize a section of the roadway and then the vehicle’s receiver coil would pick up the magnetic field that comes from the transmitters. It could be transferred to the vehicle’s battery and maintain the state of charge of the battery while you are still driving. Initially, one might think that we would have to cover 100% of the roadways. But that’s not the case. Our studies show that you only need to cover 8% of the primary roadways and you could have unlimited range.
Tech Briefs: So, you would get just a little bit of charge as you were driving over each pad?
Dr. Onar: That’s right. Our idea is that you pick up more power than you spend as you are moving over the electrified section. You can kind of balance what goes out of the battery against what comes in. So, if you started your trip at roughly 80% of charge, you could have approximately the same level of charge at the end of your trip.
Tech Briefs: How would you signal the charging coils to go on when a car is coming and off when it is leaving the pad.
Dr. Onar: There are several methods. You could have pilot couplers or coils at the beginning of the electrified section. These could be operated at really low power in kind of a beaconing mode, so the standby power losses would be minimal. But it would be able to detect that a receiver coil is approaching. The approaching car will cause the pilot coil current to change, which generates a trigger to energize the whole section. Once the vehicle clears, the power in that section can be turned off.
Tech Briefs: What about stray fields when you’re charging?
Dr. Onar: We’ve measured the electric and magnetic field emissions in and around the system and have been able to determine that the field emissions are below the limits identified in international guidelines. The guidelines identify the maximum exposure levels to fields, including for people carrying medical implants or pacemakers. We are working to make sure that we confine the fields in between the transmitters and receivers and minimize or completely eliminate the stray fields around the coils. For the dynamic wireless charging systems, we are also designing advanced shielding technologies. It is important to eliminate interference with the vehicle-side electronic accessories and control systems or devices passengers might have with them.
Tech Briefs: What general range of frequencies are you using?
Dr. Onar: Right now, a lot of our systems operate at 85 kHz. There are four frequency bands available for wireless power transmission, that we could use for this application. The SAE J2954 standards development committee chose to move forward with an 85 kHz center operating frequency. The operating range can be from 79kHz to 90kHz.
Tech Briefs: You’ve said the process is bi-directional. You foresee being able to use stored energy in the batteries — How?
Dr. Onar: In our most recent project we’ve been working with United Parcel Service (UPS). A lot of large fleet owners like UPS, are electrifying their fleets because it’s more efficient and more cost effective for the same amount of distance that they travel — a lot more efficient than gas.
Think about 100 plug-in trucks; each using 20 kW from the facility, that’s a total of 2 MW of power. So, they’re trying to find a method to reduce their dependence on the grid and to reduce the demand charges they pay to utilities. A lot of facilities or campuses are targeting to have renewable energy integration, on-site energy storage systems, and the ability to provide power back to the grid or buildings with bidirectional electric vehicle charging systems. With a microgrid with these functionalities, facilities could accomplish peak shaving, time-of-use energy cost management, demand charge management, and several other grid support or ancillary services. With the bidirectional chargers, microgrid operations can be optimized, the effect of outages can be minimized, and cost of electricity for charging the vehicles can be reduced.
Tech Briefs: Could you convert existing electric vehicles to use this technology?
Dr. Onar: That’s what we’ve been doing. We integrate our technology into existing electric vehicles that have plug-in charging options and we enable them to use wireless charging.
As yet, there is no production vehicle that comes with this functionality. However, we’re trying to take this technology to the next level, so it can be integrated into production vehicles.
Tech Briefs: Do you have a rough timeline in mind in terms of commercialization?
Dr. Onar: Manufacturers are waiting for the standards to come out. Right now, we have a standards development committee within the SAE. We believe that within a year or two, a standard will be published and then manufacturers can start implementing this on their production vehicles.
Tech Briefs: How do the special facilities at Oak Ridge help you with your research?
Dr. Onar: We have state-of-the-art equipment including grid emulators, battery emulators, power supplies, measurement, testing, and instrumentation equipment. A lot of those facilities and equipment are excellent for working on our challenges. With our high-precision devices, we can accurately measure the efficiency, we can validate our designs, and do lots of rapid prototyping. We also have interdisciplinary facilities — for example, on material science, additive manufacturing, battery manufacturing, and vehicle systems testing and integration. We also have state-of-the-art high-performance computing facilities with the fastest computers in the world, enabling us to get rapid results and model very complex systems, which really accelerates our research.
Tech Briefs: What excites you about this project?
Dr. Onar: In our work on wireless power transfer, whenever we achieve a higher power level than before, or any improvement in efficiency — those two things really excite me. So far, the maximum power we’ve done so far is 120 kW. Our next target is 300 kW. When we get to that, I’ll be really excited because that means that for electric vehicle with 100 kWh battery capacity, we could have a 50% state of charge increase in about 10 minutes. And, right now, we have about 93% end-to-end efficiency, we would like to get to 95 – 97%.
An edited version of this interview appeared in the August 2020 issue of Tech Briefs.