IEEE Electrification Magazine - December 2019 - 43

Remote Control
Center
(a)

Remote Control
Center

(b)

(c)

Figure 9. An illustration of autonomous ship operation modes. (a) Fully autonomous operation. (b) Semiautonomous operation. (c) Remote-controlled operation. Dotted lines indicate that a selected set of signals is included in the communication. Solid lines indicate that all the signals are
included in the communication. Red signifies communication from the vessel. Green signifies communication to the vessel.

intelligent algorithms in computers. Semi- or fully autonomous operation can be conducted with or without onboard
crewmembers, who typically have other duties (e.g., passenger comfort) or more supervisory tasks.
In most of the shipboard power systems, hierarchical
control is used since different levels of the control system are
decoupled from each other. However, in hierarchical control,
though the low-level real-time control of components is
handled by independent local controllers, the system-wide
real-time control and online optimization rely on the coordination of many local controllers. Based on the coordination
among local controllers, hierarchical control can be classified
into three categories (Figure 10), described as follows:
1) centralized coordination control: This is implemented
through a central controller and a communication
network [Figure 10(a)]. Centralized control enables
system-level optimization, which means the whole
system fails if the centralized control fails. Furthermore, during autonomous operation, the ships are
vulnerable to malicious cyberattacks with centralized
coordination. Therefore, this is not very suitable for
fully autonomous operation of ships.
2) decentralized control: This is achieved through independent local controllers without any coordination [Figure
10(b)]. The main advantage of decentralized control is
that it offers independence from the communication
link and the central controller, so the system can continue to operate during a single-point failure. The
main drawback of decentralized control is the limitation on system-level performance since system-level
optimization is not possible due to the lack of systemlevel integration/information.
3) distributed coordination control: This combines the advantages of centralized coordination control and decentralized control. In distributed coordination control, the
central controller does not exist, but local controllers
communicate to perform system-level optimization as
well as to maintain system operation during singlepoint failures, thereby avoiding system-level failure.

Fully autonomous operation of ships, without a crew
on board, could significantly reduce the total weight
and the space requirement of the vessel. However, this
presents some challenges, chiefly the issue of designing
all of the ship's systems to operate with fault-tolerant
capabilities. Resilience and survivability are the most
important factors to be considered during the design
and operation of the shipboard hybrid power system. A
zonal electrical distribution system (ZEDS) architecture could be used (Figure 11) to maximize resilience
and survivability. Here, the shipboard hybrid power
system is divided into several zones interconnected
through a physical electrical connection to exchange
power and a communication interface to exchange
information. Each individual zone is a minigrid with
main energy sources, energy storage, loads, and its own

Central
Controller
Controller 1 Controller 2

Controller n

(a)
Controller 1 Controller 2

Controller n

(b)

Controller 1 Controller 2

Controller n

(c)
Figure 10. A diagram indicating (a) centralized coordination control,
(b) decentralized control, (c) and distributed coordination control.

IEEE Elec trific ation Magazine / D EC EM BE R 2 0 1 9

IEEE Electrification Magazine - December 2019

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