IEEE Electrification - September 2020 - 31

isolation transformer is much smaller than the transformers used in ac bus systems as only a fraction of bus power
is used by hotel loads.
The dc bus system significantly reduces the complexity
of the IEP system because the essential, intermediate dc
voltage of each ac drive is unified and connected as the
common dc bus, therefore, the large and costly rectifying
transformer and ac-dc rectifier at each drive are eliminated. The absence of frequency and phase angle of the dc
bus enables fast interconnection of DGs and ac drives for a
more flexible and configurable system.
The dc bus IEP system is a high semiconductor power
system using more silicon to replace steel and copper
than is found in the ac bus system. In contrast to the ac
bus IEP system, power in the dc bus is entirely generated
and consumed by power electronic converters, and each
supply and consumption unit can be independently controlled. The modular and granular controls of the converters unlock the full potential configuration and
operation of the dc bus, that is, there is more flexibility
related to interconnecting of the loads or supplies to the
dc bus for maximizing system-level efficiency and

G

G

ac/dc

ac/dc

DG

reliability, which also enables high penetration of new
energy storage and sources such as shipboard batteries
and solar power generation directly to the dc bus. The
power electronic converters have higher power density
than the ferromagnetic devices. The cost of power electronic converters is destined to decrease due to the rapid
decline in the cost of the power semiconductor manufacturing process and the low cost and large reserves of the
raw material, silicon.

Power-Conversion Converters in dc Systems
Modularity and Scalability of Converters
in dc Bus IEP Systems
To streamline the design and implementation of the
increased number of converters used in dc bus systems, a
versatile building block using the common power electronic circuit can be used in both ac-dc and dc-dc conversions, as depicted in Figure 3. This modular design is
becoming popular in both dc bus IEP systems to reduce
both capital and maintenance costs. The power modules
can be connected in parallel as multiple channels for

Solar
Panel

G

G

ac/dc

ac/dc

Contactor
Digital dc and Drive
Semiconductor Power System
(High Silicon)
1,000-V dc Bus

Fast Fuse

Link Converter

dc/dc

Bus Tie
dc/ac

dc/ac

M

Propulsion
Motor

dc/ac

dc/ac

dc/ac

M

M

M

dc/dc

Energy Storage

Hotel Loads
Figure 2. The dc bus IEP system schematic, using more silicon for semiconductor devices. The bus, propulsion drives, and hotel loads
are digital.

	

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

31



IEEE Electrification - September 2020

Table of Contents for the Digital Edition of IEEE Electrification - September 2020

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