IEEE Electrification Magazine - December 2019 - 44

Zonal
Operator

Zone
Communication
Interface

Loads

Z...

Communication Link

Electrical Connection

Zn-1

Main Energy
Sources

Energy
Storage

Remote Control
Center

Battery

Fuel Cell

Diesel Engine

SSCB

Figure 11. The layout diagrams of a ZEDS for a shipboard hybrid power system. Z: zone; SSCB: solid-state circuit breaker.

zonal operator (local controller). The main energy sources could be a fuel cell to achieve zero-emission operation or a small diesel engine. In ZEDS, several small
diesel engines can be used instead of a few big diesel
engines typically used in manned ships today. In this
case, a fault in one diesel engine will not have a significant effect on the ship's power system except for the
reduced redundancy. Hence, blackouts can be avoided,
which is essential for fully autonomous operation of
ships. Moreover, each small diesel engine can have an
integrated battery pack for operating at maximum efficiency with load smoothing. This will increase resilience and ensure that all of the small diesel engines can
be run at top efficiency. Moreover, a failed diesel engine
generator set (or another power unit) may then also be
quickly ejected and replaced at the harbor before a new
voyage is conducted. However, studies of life-cycle cost
and emissions are necessary to investigate the economic viability and environmental friendliness of replacing
a few big diesel engines with several small diesel
engines. Each zonal operator or local controller can be
regarded as an intelligent agent that controls its zone
and coordinates with other zones. Combined, these
agents form a multiagent system. The communication
interface enables system-level integration through communication among all zones and collects the systemlevel information required for optimization during
normal operation. Furthermore, during fault situations,
the system will be sectionalized for the isolation of fault
through a minimum isolation area, thereby avoiding
system failure. The advantages of using a ZEDS configuration include the following:
xx
Distributed coordinated control can be implemented
as a multiagent system that combines the advantages
of centralized coordinated control and decentralized
control.
xx
Self-healing is the most important requirement for
autonomous ships without a crew on board. In a ZEDS

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

configuration, self-healing can be achieved by isolating the faults through sectionalization. When a fault
occurs, the shipboard power system is sectionalized to
achieve isolation of the fault. When the fault is
cleared, the shipboard power system is reconstructed.
The sectionalizing aims to minimize the isolated area
while, at the same time, maintaining the power supply to healthy zones.
xx
Demonstrate and maintain improved resilience and
survivability.
xx
The design must be modular and scalable.
xx
It must allow for easier and quicker maintenance.
However, there are several challenges that need to be
addressed before the successful implementation of a
ZEDS configuration. The main challenge is that it
requires a communication interface for the coordination
of the local controllers, where communication time
delays and measurement errors may further hamper the
performance of the system-level optimization software
during normal operation and of the protection system
during faulty situations. Furthermore, in the case of shipboard dc power systems, protection is a challenging task
since it requires precise coordination between the solidstate circuit breakers (SSCBs) and the protective functions. Therefore, it is a protection system challenge to
achieve fast and efficient reconfiguration, during faulty
situations, and reconstruction, when the faults are
cleared. In recent years, a significant research effort has
been made to develop SSCBs using advanced widebandgap semiconductor materials (such as silicon carbide and
gallium nitride), new power electronic converter topologies, and advanced control techniques. Moreover, measurement errors can be overcome by using outliner data
detection and reconstruction algorithms.

Conclusions
In urban areas, increased population and economic activity are causing an exponential rise in congestion and

IEEE Electrification Magazine - December 2019

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