IEEE Electrification Magazine - September 2017 - 21

GL class rules require that the BMS be the master and
the battery charger the slave. This is because the BMS is
the main safety system.
The battery charger must be dimensioned for the maximum charge/discharge current and must be designed
such that it is not possible to overcharge or overdischarge
a battery system, i.e., it must be designed for over/undervoltage protection. Such a design acts as a second barrier
for voltage protection.
A Li battery might provide a short circuit power of
50-100 times its nominal rated power. The charger, or
the directly connected dc switchboard, must then be
designed to withstand this high short circuit power. In
a power network where the battery system is one of
the main sources of power for the ship (i.e., where the
battery is used for propulsion power), the DNV GL rules
require full selectivity between the breakers for all
important consumers. To achieve this, it is important to
remember that a traditional dc/dc or ac/dc converter
will limit the maximum short circuit power (typically
1.2-1.5 times the nominal power) and by doing so will
create some extra challenges in the relay coordination.
A battery system will always be alive, i.e., it will
always contain energy. For safe maintenance purposes,
the DNV GL rules require that the battery system be provided with an isolation switch in addition to short circuit
protection. Since the energy can flow in both directions
between the charger and the battery, both sides must
have short circuit protection installed. Overcurrent protection is sufficient to have in one end, normally the battery charger.
For ships with battery systems providing power to the
main and/or redundant propulsion or DP, the DNV GL
rules require that an energy management system (EMS)
be installed. The EMS must provide a reliable measure of
the available energy and power, taking into consideration
the battery's SOH and SOC. The available energy/power
and the remaining time/range that the battery can supply
energy must be presented and monitored at the navigation workstation.
Since Li battery technology is under constant development, the DNV GL class rules for battery-powered ships
provide for deviations from the requirements. Such deviations, however, must be based on a safety assessment in
which all hazards are identified, risk factors evaluated,
and risk control actions implemented.

DNV GL Battery-Related Activities
DNV GL will continue to support the drive toward a greener and cleaner maritime industry and to ensure that new
technological advancements are implemented in a safe
and sustainable manner. As the world's leading classification society, DNV GL strives to support all stakeholders
in the industry through state-of-the-art design rules,

G
=

~
~

Figure 15. A bidirectional converter for charging and discharging a
battery system. G: generator. (Image courtesy of DNV GL.)

spearheading initiatives like the Green Coastal Shipping
Programme (DNV GL 2017), and running joint industry
research projects like FellowSHIP.
Furthermore, DNV GL's Maritime Advisory provides
decision-making support to ship owners, designers,
yards, and vendors for making vessels ready for future
battery retrofit or battery operation today. DNV GL provides independent analysis, verification, and validation
services as well as training courses on maritime battery
systems. The DNV GL Handbook for Large Maritime Battery
Systems can be downloaded free of charge from www
.dnvgl.com.

For Further Reading
DNV GL. (2017). Green Coastal Shipping Programme with
futuristic projects that could transform our coastlines.
[Online]. Available: https://www.dnvgl.com/maritime/
research-and-development/futuristic-projects-transformcoastlines/index.html
Enova. (2017). [Online]. Available: https://www.enova.no/
bedrift/transport/energiogklimatiltakiskip/
NHO. (2017). NOx-fondet. (In Norwegian). [Online]. Available: https://www.nho.no/nox
Transport & Environment. (2017). Air pollution from ships.
[Online]. Available: https://www.transportenvironment.org/
what-we-do/shipping/air-pollution-ships

Biographies
Øystein Alnes (oystein.alnes@dnvgl.com) is with Group
Technology and Research, DNV GL AS, Bærum, Norway.
Sverre Eriksen (sverre.eriksen@dnvgl.com) is with Electrical Systems, DNV GL AS, Bærum, Norway.
Bjørn-Johan Vartdal (bjorn.johan.vartdal@dnvgl.com)
is with Group Technology and Research, DNV GL AS,
Bærum, Norway.

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

http://www.dnvgl.com https://www.dnvgl.com/maritime/ https://www.enova.no/ https://www.nho.no/nox https://www.transportenvironment.org/

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