IEEE Electrification Magazine - September 2017 - 24

ferries with docking times that can
be as low as 4-5 min.
To improve the utilization of the
available docking time, specific
connection techniques have been
developed and tested on the first
battery-powered ferries. The MS
Ampere, which was the first fully battery-powered Norwegian motorcar
ferry to start regular operation, has,
for instance, been equipped with
two alternative, custom-designed
charging arrangements. One of the
solutions uses a gravity-based plug
Figure 1. Wärtsilä's concept for zero-emission ferries with inductive charging-the charging plate
can be seen at the middle of the ship side. (Photo courtesy of Wärtsilä Norway AS.)
that is dropped into a specially shaped
outlet, while the other solution relies
on a three-phase pantograph with a
years. The industrial development enabling this transition
design inspired by railroad systems.
toward zero-emission operation is also expected to find
The conventional approaches for battery charging that
widespread applications around the world.
can be applied to electrically operated ferries all depend
Although short-distance ferries can be operated with
on mechanical contacts or plugs. Thus, they will all be
batteries as the sole onboard energy source, this arrangeexposed to mechanical wear and tear and require relativement introduces unprecedented challenges to the techly precise positioning that might be hard to achieve during
nology for battery charging. In general, such vessels
operation in rough weather conditions. Furthermore,
operate on tight schedules with short docking times,
coastal ferries operate in a harsh and saline environment
meaning that the time available for charging is severely
that can be challenging for electrical safety. Reliable mechconstrained while the amount of energy to be supplied to
anisms for the quick and automatic disconnection of the
the battery at each stop must be sufficient for maintaining
charging system are also necessary to ensure safety in case
regular and continuous operation. This implies the need
the ferry urgently needs to leave the dock.
for high-power recharging. However, many Norwegian ferFor avoiding the challenges and limitations of mechanries operate in remote and rural areas where the local
ical connection systems for high-power battery charging
distribution grids have limited capacity. Therefore, local
in marine environments, a Norwegian industrial initiative
onshore energy storage may be required to supply the
has started the development of technology for contactless
necessary power during charging without overloading the
inductive power transfer to ships. Although wireless
available power supply or causing local voltage quality
inductive power transfer is well known and increasingly
problems. Considering a specified energy demand for batutilized in a wide range of applications, with rapid ongotery charging at each time-limited stop at a quay, it
ing developments for battery charging of electric cars,
becomes crucial to effectively utilize the available docking
buses, and rail vehicles, this is a new concept for marine
time for transferring power to the onboard batteries. The
high-power applications.
time spent for the connection and disconnection of chargThe motivation for utilizing inductive power transfer to
ing equipment will reduce the available time for transferachieve wireless battery charging is the same for ship
ring energy, and this will thus increase the required power
applications as it has been for the emerging applications
rating of onshore as well as onboard equipment. Higher
in electric vehicles. Indeed, inductive charging without
charging power requirements may also have detrimental
any mechanical contact is suitable for fully automated
effects on the battery life span.
operation without any need for electrical and mechanical
The established systems for electric power transfer to
interfaces that will be exposed to mechanical wear and
ships have been developed mainly for providing power
tear. Furthermore, inductive power transfer eliminates
from the shore to allow the onboard generators to stop
direct electrical contacts and challenges related to the
when the ships are staying in a harbor for periods of a
presence of large amounts of snow, ice, or other fouling as
few hours or more. In such applications, the time
well as the potential for leakage currents and corrosion in
required for the manual or automatic connection of
saline environments. This can improve safety and the relidynamic cables with mechanical plugs does not have
ability of charging solutions by avoiding position-sensitive
any significant influence on the overall operation, even if
moving parts. Galvanic isolation is also inherently providthe effective time required for connection and disconed between the charging equipment on land and the
nection could reach several minutes. However, conneconboard electrical system. Finally, one of the main advantion times of more than a minute are not acceptable for
tages is the possibility of transferring power without any

I E E E E l e c t r i f i c ati o n M agaz ine / SEPTEMBER 2017

Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2017