IEEE Electrification Magazine - September 2017 - 86

GT
DG

Ship's Services
440 V
115 V

Frequency
Converter

Motor

Ship's Services
440 V
115 V

Figure 8. Shipboard power system.

generation, distribution, protection,
not been invented. Also, even if dc
and control were all copper based.
distribution is achieved at a given
Then the silicon-based converters
voltage level, several additional conand drives came onboard to supply
versions are required, because difelectronic loads and
ferent loads need
efficient motor loads
different voltage levSending and receiving
such as pumps, and
els. Generators and
on/off signals, i.e.,
efficient propulsion
circuit breakers may
digital signals, was
required electric drive
require 6.9 kV, pumps
for ships, which nefound to be much more may require 450 Vac,
cessitated that the
and the main propulefficient than sending
generated power onsion may require
analog signals over
board be conditioned
5-kV dc. Although the
long distances.
and controlled via silDina Star service ship
icon-based converters.
uses a dc architecture
Silicon-based converter
(ABB), generation and
penetration onboard the modern elecpropulsion are performed using actric ship is almost 100%.
rotating machines. Also, the system is
The binary framework of digital
limited to 20 MW, as power demand
power control, via PWM and other
growth challenges remain.
forms of modulation, is easy to
For decades, dc systems lagged
implement if the available source
behind ac systems; however, more
voltage begins in dc form. This is one
recently, a convergence of needs
of the primary reasons dc distribuexpressed by the renewable energy
tion is making a comeback. However,
sectors as well as information techac generation is still needed; hence,
nology data centers and the transthe rectification to dc. To date, effiportation sectors have led to an
cient brushless dc generators withaccelerated development in dc
out some form of rectification have
systems. These are mainly photo-

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

voltaic generating stations, offshore
wind-electric power collection and
transmission over long distances,
the electric car and the electric
train, and, finally, the oil and gas
pumping industry. These various
sectors contributed to the solution
of the various technical challenges
both at the device level as well as
the system controls level. For example, the solar energy industry had to
develop a cost-effective means of
connecting the dc solar panels to
the ac grid, and, hence, the grid-tie
inverter, which is essential to take
advantage of net metering. Also, collecting the dc energy from many
photovoltaic panels led to the need
for dc-dc converters, which allow
collection using higher voltages
and, hence, less losses. The same
can be said for the wind industry,
especially offshore where transmission cables are to be minimized due
to the high expense.
Future trends of power architectures onboard ships are pointing to
neither dc nor ac alone but rather an
optimum integration of both through
efficient digital power. This is obviously seen in modern PWM drives
that require both dc and ac in the
conversion process. The percentage of
ac to dc onboard will depend on the
platform and its mission requirements. Digital power will allow the
realization of the smart ship and the
remote-controlled ship but will also
bring new challenges such as the
resilient integration of stable and
secure networks of power and energy.

Biography
Mohamed Belkhayat (belkhayat@
email.gwu.edu) is an adjunct professor in marine power engineering
with George Washington University
and a senior research engineer with
Huntington Ingalls Inc.

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