IEEE Electrification Magazine - December 2019 - 99

General Overview

xx
There is no need for phase angle synchronization, and
Shipboard power systems are usually designed with an
thus, the generator's connection procedure is simplified.
xx
After faults, reconfiguration is enabled by using power
ac radial distribution system, as shown in Figure 1, and
electronics devices.
this still holds true for the majority of existing cruise
xx
Shipboard generators are no longer strictly coupled
ships and marine vessels. The radial power system
with the power system frequency (50 or 60 Hz), and
architecture usually involves up to three main generatherefore, high-speed generators can be used for reductors for each main busbar feeding all onboard loads
ing power system weight and volume.
through a medium-voltage ac (MVac) distribution sysxx
Prime movers can operate in variable speed mode, and
tem. In such an architecture, the frequency of the main
thus, fuel consumption can be reduced and optimized.
generators is strictly connected to the power system
xx
Energy storage can be directly connected to the
frequency (50 or 60 Hz). Thus, there are some MV loads
MVdc bus, thereby enhancing power availability
directly connected to the MVac through transformers
and overall system efficiency. Moreover, energy
and power electronics converters (e.g., the electrical
storage enables peak shaving, and thereby generapropulsion motors and thrusters), usually one per
tors and prime movers don't need to be sized for
main busbar, as depicted in Figure 1. Low-voltage (LV)
the load peak, resulting in reduced fuel consumpswitchboards supply all other ship loads and are fed
tion as well.
by the MVac distribution system through MV/LV
xx
In a naval application, the availability of a dc power
transformers. Considering that volume and weight
supply enables an easier integration of weapon sysimpose hard constraints in shipboard application,
tems and new sensors.
the cumbersome and heavy low-frequency voltage
xx
Finally, the power flow control is improved, particulartransformers can be replaced by lighter power elecly in emergency and transient conditions.
tronics devices. Moreover, in a shipboard power sysThanks to the listed advantages, the shipboard MVdc
tem, most of the loads are interfaced to the main
distribution system is a foreseeable design for the presbus through power converters, and therefore the
ent and future IPESs, not only for large merchant ships
MVdc distribution topology can improve the sysbut also for marine vessels. Many stakeholders are
tem's efficiency and controllability. It is one of the
investing in this research field, mainly attracted by the
main advantages offered by the MVdc distribution
possibility of cutting fuel consumption and increassystem, since the onboard space is very narrow and
ing ship payload by reducing the power system weight
shipowners demand higher payload (e.g., cabins in the
and volume.
cruise liners). Therefore, new power system architecOn the other hand, it is known that power electronics
tures have been developed in recent years exploiting
devices inject harmonic disturbances both on the supply
dc power system sections, as reported by IEEE Recomside and on the load side of the converter due to nonsinumended Practice for 1 kV to 35 kV Medium-Voltage DC
soidal currents and voltages-the first is absorbed on the
Power Systems on Ships, IEEE Standard 1709-2010. In
such a standard, two main architectures are mentioned: a radial-based architecture with MVdc
18 MVA
18 MVA
21 MVA
21 MVA
main busbars (Figure 2) and an
G
G
G
G
innovative zonal distribution system allowing bidirectional power
flow (Figure 3). Conversely, MVac
11 kV
11 kV
60 Hz
60 Hz
zonal distribution systems cannot
be affordable due to synchronization issues, since, for instance,
automatic system reconfiguration
M
M
M
M
can be difficult.
Other MV
Other MV
As shown in Figures 2 and 3,
Thruster
Thruster
Loads
Loads
the power electronics devices (in
LV
LV
2.5 MW
2.5 MW
Loads
Loads
green) are widely used in these
690 V
690 V
new distribution systems both on
230 V
230 V
M
M
the load and generation sides.
440 V
440 V
Above the aforementioned eli Main
Main
mination of large low-frequency
Propulsion
Propulsion
transformers, the most important
18 MW
18 MW
advantages of the MVdc distribuFigure 1. A shipboard IPES with a MVac radial distribution system. MVA: megavolt amperes.
tion are as follows:

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IEEE Electrification Magazine - December 2019

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