IEEE Power Electronics Magazine Compendium - March 2018 - 21

dynamically has been applied in factory automation using
buried cables for propulsion power, alignment, and communications. Implementing the same features into passenger
vehicles traveling at highway speeds exacerbates the challenges and illuminates the need for research on dynamic
wireless power transfer (WPT), whether based on continuous lengths of buried cables or a series of coils, appropriately energized by high-frequency (HF) current. The problem of coupling power over relatively large gaps, such as the
ground clearance of automobiles, has been solved using HF
magnetic resonance. For continuous spans of buried cable,
the power transfer will be smooth and the reactive power
burden will be high and manageable, but alignment may be
difficult to maintain without dynamic longitudinal stability
control of the vehicle. In the case of long tracts of buried
coils, the longitudinal stability may be less demanding and
the reactive burden will be lower, but the coil size and pitch
along the roadway will introduce a speed-dependent pulsating character to the both grid-side power supply and vehicle
charging power. This article addresses the issues of power
pulsation during dynamic charging on the roadway.
In 2011, the ORNL funded a development and demonstration project to showcase ORNL's WPT technology applied
to in-motion charging, as shown in Figure 1. Over the past
two years, the technology has been developed and demon-

strated, as recently reported in an internal press release by
the authors.
"ORNL dynamic wireless charging demonstrates gridside and in-vehicle power smoothing." In-motion wireless
charging of EVs can cause power pulsations in the vehicle battery and the grid supply. These pulsations are due
to the motion of the vehicle capture coil as it passes over
a series of roadway embedded coils and the resultant pattern of alignment and straddling of their magnetic fields.
It is well known that battery charging with a pulsating
current can deteriorate the battery service life, and
power pulsations to the utility are likewise detrimental
to power quality. The ORNL WPT team, in collaboration
with industry vendors, has now demonstrated for the
first time the benefits of using local power caches at the
trackside HF converter and in the vehicle, between the
secondary, or capture, coil and battery pack to mitigate
power pulsations.
Local power storage was implemented using two different high-power capacitor technologies: a pack of carbon
UCs fabricated at ORNL using cells produced by Maxwell
Technologies Inc. and operating in passive parallel with the
Global Electric Motors (GEM) EV battery pack and LiCs
operating in active parallel with the grid-side power supply.
The active parallel system was produced by ESL and loaned

The active parallel
combination of LiC
energy storage and the
grid supply resulted in
very uniform power
draw from the grid.

March 2014

z IEEE PowEr ElEctronIcs MagazInE

Table of Contents for the Digital Edition of IEEE Power Electronics Magazine Compendium - March 2018