Very-low-frequency and low-frequency electric and magnetic fields associated with electric shuttle bus wireless charging

Abstract

Tests conducted to date at the University of Tennessee at Chattanooga (UTC) indicate that wireless charging of the Chattanooga Area Regional Transportation Authority's (CARTA) downtown shuttle bus, currently operating with off-board battery charging technology, offers significant improvements in performance and cost. The system operates at a frequency of 20 kHz and a peak power of 60 kW. Because the system's wireless charging is expected to occur during a nominal 3-min charging period with passengers on-board, the magnetic and electric fields associated with charging were characterised at UTC's Advanced Vehicle Test Facility and compared with established human exposure limits. The two most prominent exposure limits are those published by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the Institute for Electrical and Electronic Engineers (IEEE). Both organisations include limits for groups who are trained (workers in specific industries) to be aware of electromagnetic environments and their potential hazards, as well as a lower set of limits for the general public, who are assumed to lack such awareness. None of the magnetic or electric fields measured either within or outside the bus during charging exceeded either the ICNIRP or the IEEE exposure limits for the general public.

Elements of Wireless Power Transfer Essential to High Power Charging of Heavy Duty Vehicles

“…Most recently the authors in [39] explore this to some degree for an application that provides wireless power for vehicle in-wheel motors, and due to vehicle suspension system design the fully aligned case becomes the exception. More relevant information on EMF for the case of 60 kW charging of a city bus can be found in [40] where the authors carry out an extensive measurement program to fully characterize these fringe fields around and inside the bus.…”

ORNL Experience and Challenges Facing Dynamic Wireless Power Charging of EV's

“…ORNL researchers opted for photocells and these can be seen as the small bumps alongside the travel lane. The blue strip on the 10 driver side served as a manual lane keeping guide to hold lateral tolerance during in-motion power transfer. The two NEMA boxes alongside the track contain the WPT power inverter operating at approximately 22 kHz and the sequencing box that routed HF power to coil pairs in synchronism with vehicle passage.…”

“…Some controversy has arisen between the guideline and the standard in the case of individuals having implanted medical devices (IMD), such as a pacemaker, and the necessity for lower EMF levels that won't interfere with their sensing electronics. Examples of real world EMF measurements on a WPT charged EV transit bus was done by Tell, Kavet, Bailey, and Halliwell [10] that shows very low EMF inside the passenger cabin and around the perimeter of the bus during charging when coils are appropriately designed.…”

“…Kornbluth, Burke, Wardle, and Nickell [29] provide details for a variety of NLV's -narrow lane vehicles that are lightweight, 2 passenger in tandem seating, and 4 wheels. Table 1 provides representative specifications for an NLV and these values are used to compute the road load on level terrain and no headwind in (10).…”

Safety Assessment of Human Exposure to Intermediate Frequency Electromagnetic Fields

“…Especially, WPT systems used for charging electric vehicles (EVs) feature high output and large capacity transmitted via air gaps, and therefore leakage of electromagnetic field to environment has to be considered. Many WPT systems are based on electromagnetic induction schemes (including magnetic resonance coupling) using frequencies below 100 kHz (e.g., 85 kHz), and there are reports on evaluation of ambient magnetic field [49] and induced electric field using real machine of WPT [50]. According to these reports, basic restrictions are not violated even though ambient magnetic field of WPT exceeds reference levels [50].…”