IEEE Electrification Magazine - September 2017 - 25

Inductive Charging Technology for High-Power
Marine Applications
Significant research and development efforts have been
directed toward technology for contactless inductive
power transfer during the last few years. Wireless charging
systems for electric vehicles have been extensively studied by researchers in academia and industry. However, the
concepts intended for application in the automotive
industry have mainly been developed for improving user
convenience by allowing for wireless operation. Thus,
most of the attention of public and academic research has
been directed toward configurations that are intended for
replacing conventional plug-based chargers in the power
level of a few kilowatts.
At the same time, noticeable industrial development
efforts have been pursued for higher-power systems
intended for application in public transportation systems
like buses, trams, and trains. Conductix-Wampler (later IPT
Technology) has, for instance, provided technology for contactless inductive charging for electric buses, which was
demonstrated in Italy as early as 2002/2003. Bombardier
Primove later demonstrated inductive charging for buses
and trams with power levels reaching up to about 200 kW.
Similar developments have also been pursued by KAIST in
South Korea, where applications for buses and trains have
been considered. Based on the work at KAIST, the Korea
Railroad Research Institute has presented a design and a
full-scale demonstration of a system with a 1-MW transmitter and parallel operation of multiple receiver units in
the 200-kW range to obtain about 820-kW total power
transfer capacity. However, the specifications and designs
of these systems are not directly applicable to the particular challenges of high-power marine applications.

Bringing the inductive charging technology to the
marine sector introduces some specific challenges. The
first one is also the most obvious: ferries require significantly higher energy and power levels for operating
between two charging ports, as compared to city buses or
trams. The inductive charger must therefore be able to
deliver power in the megawatt power range, preferably in
one single unit.
Moreover, for point-based high-power battery charging,
road or rail vehicles are usually in a stationary position
while charging. By contrast, a docked ship can move with
respect to the fixed onshore charging structure during
charging operation due to the combined action of the
wind, waves, and draft of the vessel, as well as in response
to the change in tilt and draft that results from loading
and unloading. The charging system must be designed so
that the amount of power transferred, as well as efficiency
and safety in operation, are not compromised despite
such movements. This implies that the system should
have a high tolerance to misalignment and variations in
airgap distance and that it should be controlled to automatically compensate for the influence of such variations
in relative position.
In general, tolerance to large positional variations could
be addressed in two ways. A mechanical positioning system could be required for one of the inductive power
transfer system coils to keep the relative position of the
two coils fixed. Alternatively, the tolerance for variations in
relative position should be incorporated in the design and
control of the system. Such an approach with a static
arrangement of the coils, onboard as well as onshore, is
highly desirable for avoiding complex and bulky dynamic
positioning devices that have the six degrees of freedom
required for tracking the ship movements. This is especially important since the system should have high reliability
and the ability to operate under harsh weather conditions,
which may interfere with reliable, fast, and accurate position control. On the other hand, some demanding requirements are introduced on the maximum variations in

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Inductive
Coupler

mechanical connection procedure, allowing for better utilization of the limited docking time for battery charging.
Solutions for inductive power transfer can be designed for
immediately transferring power to the ship when it enters
its position in the dock and until the moment when it
starts its next trip.
An illustration of the initially envisioned system for
contactless inductive power transfer to a ship at quay is
shown in Figure 2. No mechanical connection should be
needed for the power transfer as long as the ship can be
kept within a reasonable range around its expected position. Thus, only a very slow mechanical positioning of the
onshore system would be necessary for operation in locations with large differences between low tide and high
tide. However, one of the challenges for developing such
technology is that the power level is significantly higher
than what is common for road or rail applications. Furthermore, the dynamic operating conditions of a system
for marine applications could be more challenging due to
the partially free-floating movement of the vessel with
respect to the dock, due to wind, waves, drafts, and loading/
unloading of the vessel.

Battery

Figure 2. The envisioned concept for the wireless inductive charging
of a battery-powered ship.

IEEE Elec trific ation Magazine / S EP T EM BE R 2 0 1 7

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