IEEE Electrification Magazine - December 2019 - 8

TECHNOLOGY LEADERS

to their elevated thermal conductivity
and melting point. At the same time,
they offer high switching frequencies
because of their significant electron
velocity. As the switching frequency
rises, the size of the power converter
and passive filters diminishes. The
benefits of WBG switches support the
continued development of efficient
converters where the power rating,
frequency, size and weight, and losses
are important considerations. The
higher power rating makes those

converters suitable for shipboard
applications that have a steep de-
mand for energy. On the other hand,
a ship's space constraints have always
been a crucial part of a vessel's design.
WBG-based high-frequency convert-
ers may significantly enhance mari-
time design flexibility by replacing
bulky components.

Power Converters
Power converters that have the afore-
mentioned switches are widely used

100,000,000
GTO

10,000,000

IEGT

Power (W)

1,000,000
100,000

Thyristor

10,000

IGBT
IEGT
Module

SiC
GaN

1,000
100
10
10

Discrete
IGBT
Discrete MOSFET
100

1,000

10,000
100,000 1,000,000
Frequency (Hz)

Figure 1. The semiconductor switches' capacity. IEGT: injection-enhanced gate transistor.

Shipboard Converter

Rectifier

VSD

dc to dc

Diode Rectifier

Voltage Source
Converter

Buck

Active Front End
Rectifier

Current Source
Converter

Boost

Cycloconverter

Bidirectional

Figure 2. The power converters that are commonly used in electrified ships.

8

I E E E E l e c t r i f i cati o n M agaz ine / DECEMBER 2019

in marine electrification. With their
high efficiency, light weight, and low
fault-occurrence probability, they
form an integral part of the power
grid topologies of the ac and dc sys-
tems in marine power plants. From
the design perspective, the mission is
always to maximize efficiency and
reliability while minimizing size,
weight, and cost. By increasing the
commutation frequency, the size of
the converters can be decreased at
the cost of elevated switching losses.
Solid-state devices' switching behav-
ior is highly nonlinear. In addition,
their saturation, hysteresis, and bounds
intensify the challenges for achieving
the control, prediction, and estima-
tion of the converters' status.
Figure 2 presents the basic types
of converters that are used in ship-
board power systems, including recti-
fiers, VSDs, and dc-to-dc converters.
Uncontrolled (diode) rectifiers are
mostly used in VSDs, whereas con-
trolled rectifiers are employed to
level the alternator's voltage output.
Uncontrolled rectifiers also find appli-
cations as generator power convert-
ers in onboard dc power systems.
Controlled rectification is achieved by
using an emerging active front-end
rectifier, which incorporates fully
controllable IGBT switches and anti-
parallel diodes for shaping the ac
voltage. Voltage-source converters
(VSCs) have many onboard applica-
tions, mainly in the propulsion-motor
drives, uninterruptible power sup-
plies, and so on. Current-source con-
verters (CSC) are primarily used for
high-power applications and perma-
nent-magnet synchronous machines.
Cycloconverters control the speed
of the onboard synchronous motors
by converting the supply frequency.
They are mostly found in ice-break-
ing and ice-going vessels for which
low-speed operation and perfor-
mance are essential. They can also be
used in dynamic positioning- and
passenger vessels if those require
agile maneuverability. Buck and
boost converters level dc voltages. A
IEEE Electrification Magazine - December 2019

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