IEEE Electrification Magazine - September 2013 - 64

increased when the receiving coil becomes aligned with
that particular segment of the source coil. This way, the
field produced by the segmented source coil can be controlled by the position of the receiver.

Conclusions

Figure 8. A scaled-down testbed for dynamic wireless charging.

of the dynamic chargers could reach that of stationary
chargers if the optimized segmented source coils designed
for stationary charging are used, and the system transfers
power only when the misalignment is within prescribed
limits that guarantee 90% or higher efficiency.
Considering the segmented source coil design, the
issues of field containment, large source-coil self--
inductance, and difficulties with coil impedance compensation are easily addressed. However, developing a strategy
for powering the coupled segments is challenging, since it
requires complex receiver position feedback as well as a
method to energize and de-energize coils as needed. Further reduction in the size of each segment exacerbates
the issues and advantages associated with coil segmentation: small coils can further contain the leakage flux of
nonenergized coils, thus improving the coupling, but
result in a complicated design with many bypass switches and sensors.
Figure 8 shows a test-bench implementation of a
dynamic charging system, built in North Carolina. The
system consists of three source coils, identical to the
receiver coil, with small indicator receivers placed on each
segment of the source coil that are used as qualitative
gauges of the strength of the magnetic field present in the
coil. The source-coil segments are powered by a common
inverter, with the compensation capacitors located at the
inverter. The goal of the test-bench demonstration was to
show the ability of a novel method of focusing the field
produced by the source-coil underneath the receiver. The
system uses a single inverter to power multiple coil segments, by connecting each segment in parallel to the
inverter. The power is limited by compensating the coil
segments so that the coil resonance occurs at a frequency
offset from the system operating frequency. Because of
the large reactive impedance, the current in given coil segments is limited when the coil is uncoupled, resulting in a
relatively weak field in the uncoupled segments of the
sectionalized source coil. By designing the receiver to
reflect a large reactance back onto the source coil section,
the magnetic field of the source coil is automatically

I E E E E l e c t r i f i c atio n Magaz ine / september 2013

In this article, we have reviewed the state of the art of
IPT systems and have explored the suitability of the
technology to wirelessly charge battery powered vehicles.
The review shows that the IPT technology has merits
for stationary charging (when the vehicle is parked),
opportunity charging (when the vehicle is stopped for a
short period of time, for example, at a bus stop), and
dynamic charging (when the vehicle is moving along a
dedicated lane equipped with an IPT system). In the
case of stationary chargers, the products are reaching
maturity, with pertinent standardization initiatives taking place. The opportunity charging systems have also
been implemented in bus charging applications, with
systems installed on many commercial lines throughout
the world. Dynamic charging is a concept that is still in
its infancy, and there is a lot of work ahead that is needed for the systems to reach their full potential. The
main stumbling blocks for this technology, beyond the
technical challenges and efficiency concerns, are safety
and infrastructure costs.
On the other hand, dynamic wireless charging holds
promise to partially or completely eliminate the overnight
charging through a compact network of dynamic chargers
installed on the roads that would keep the vehicle batteries charged at all times, consequently reducing the range
anxiety and increasing the reliability of EVs. Dynamic
charging can help lower the price of EVs by reducing the
size of the battery pack. Indeed, if the recharging energy is
readily available, the batteries do not have to support the
whole driving range but only supply power when the IPT
system is not available. Depending on the power capability, the use of dynamic charging may increase driving
range and reduce the size of the -battery pack.

For Further Reading
Z. Pantic, S. Bai, and S. M. Lukic, "Inductively coupled
power transfer for continuously powered electric vehicles,"
in Proc. Vehicle Power and Propulsion Conf., 7-10 Sept.
2009, pp. 1271-1278.

Biographies
Srdjan Lukic (smlukic@ncsu.edu) is with the Department
of Electrical and Computer Engineering, North Carolina
State University, Raleigh.
Zeljko Pantic (zpantic@ncsu.edu) is with the Department of Electrical and Computer Engineering, North
-Carolina State University, Raleigh.

Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2013