Interview with Sheldon Williamson

Sheldon Sheldon S. Williamson (S’01–M’06–SM’13–F’20) received his Bachelors of Engineering (B.E.) degree in Electrical Engineering with high distinction from the University of Mumbai, Mumbai, India, in 1999. He received the Masters of Science (M.S.) degree in 2002, and the Doctor of Philosophy (Ph.D.) degree (with Honors) in 2006, both in Electrical Engineering, from the Illinois Institute of Technology, Chicago, IL, specializing in automotive power electronics and motor drives, at the Grainger Power Electronics and Motor Drives Laboratory. Currently, Dr. Williamson is a Professor at the Smart Transportation Electrification and Energy Research (STEER) group, within the Department of Electrical, Computer, and Software Engineering, at Ontario Tech University, in Oshawa, Ontario, Canada. He also holds the prestigious NSERC Canada Research Chair position in Electric Energy Storage Systems for Transportation Electrification. His main research interests include advanced power electronics and motor drives for transportation electrification, electric energy storage systems, and electric propulsion. Prof. Williamson is a Fellow of the IEEE.

In this interview, Sheldon answers questions from his webinar, Wireless Charging For Autonomous Electrified Micro-Mobility Devices: A Real-World Solution For Smart Cities To Be Pandemic-Ready, originally presented on June 30, 2020.

Question: What is the range of frequency and power levels for the combined far field and near field solution?

The power level depends on the application. You can have anywhere between 3.7 kW to 11.0 kW today, as per SAE J2954 standards. Frequency ranges for far-field WPT could be between 2.4–5.8 GHz, while for near field, as per standards, the range is 85 kHz.

Question: What is the range of frequency and power levels for the combined far-field and near field solution?

Question: What is frequency bifurcation in IPT system and how do you avoid it? What is the specification of Litz wire you have used for coil developed?

Get this question all the time. In IPT systems, when coils operate in an over-coupled mode, the resonant frequency tends to get split, which essentially leads to reduced power transfer efficiency. This is the infamous “bifurcation” phenomena in WPT. To avoid bifurcation, you can follow some simple, yet innovative analytical design procedures, which eliminate bifurcation for the entire range of load and coupling variations (see reference provided below). In the lab, Litz wire 90/38 SPN SN (90 strands, 38 AWG per strand) was used to build a 3.7 kW prototype.

See K. Aditya and S. S. Williamson, "Design Guidelines to Avoid Bifurcation in a Series–Series Compensated Inductive Power Transfer System," in IEEE Transactions on Industrial Electronics, vol. 66, no. 5, pp. 3973-3982, May 2019.

Question: Is there research ongoing in ferrite-less IPT?

Yes. “Parasitic Coils” have been looked at in literature (see reference below, as an example). Such technology could potentially replace ferrites in IPT systems. However, some key design parameters must be carefully selected, which could majorly affect overall performance, power transfer efficiency, and EMI shielding requirements.

See E. Noh, K. H. Ko, and K. Kim, "Transmitter coil system without ferrite in wireless power transfer," in Electronics Letters, vol. 52, no. 5, pp. 392-393, March 2016.

Question: Which one has the most potential for WPT – personal home charging or public charging?

Both scenarios are equally attractive moving forward. WPT primarily provides convenience and this is especially true during times when “physical distancing” and “non-contact” procedures are the need of the hour. Home chargers can be sized up to 7.7 kW and public charging could be built-in modules of 11.0 kW and 22.0 kW, when such standard becomes available.

Question: Is wireless power transfer possible in a country like India?

Absolutely. In fact, countries such as India, China, and other Asian nations are top markets for WPT usage in the next 5-10 years. It is a well-known fact that Asian cities prolifically use public transit, such as buses, trains, and streetcars. These public means of transportation make fixed stops during their routes, which makes wireless charging ideal. For one, the overall design of the charger can be easily optimized and made highly efficient (see reference provided below). Secondly, in the case of e-buses, using WPT will help reduce the gigantic on-board battery pack. In fact, irrespective of the WPT technology used, it is possible to quantify the effect of opportunity charging on public transit purely based on using energy calculations.

See L. Patnaik, P. S. Huynh, D. Vincent and S. S. Williamson, "Wireless Opportunity Charging as an Enabling Technology for EV Battery Size Reduction and Range Extension: Analysis of an Urban Drive Cycle Scenario," 2018 IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (Wow), Montréal, QC, 2018, pp. 1-5.