IEEE Electrification Magazine - June 2016 - 51

Control and Coordination of the
Microgrid-Based Power System
Hierarchical Control: The Future
Smart Power System's Interface
Despite the benefits offered by the dc-based IPS, it is still
a challenging task to simultaneously achieve voltage

SFOC (g/kWh)

235
K=1
K=2
K=3
K=4

230
225
220
215
210
205
200
195
190

0

0.5

1

3
1.5
2
2.5
Load Condition (pu)

3.5

4

Figure 5. A schematic diagram of the fuel efficiency characteristic of diesel
generation (at a fixed speed). SFOC: specific fuel oil consumption.

Power Density (kW/kg)

power generation and power consumption, thus reducing fuel efficiency. The presence of the ESSs can inject
bidirectional, controllable power flow into the system to
achieve load conditioning. Such a fact enables modifying
fuel efficiency with the help of onboard ESSs. In this
way, it is possible for diesel generator sets to work constantly with the modified fuel efficiency.
Along with the development of energy storage
devices, a range of commercially available storage
device options for stationary or mobile terrestrial
applications have already appeared. A comparison of
their instantaneous power density and energy density
is shown in Figure 6. Heretofore, batteries, especially
lithium-ion batteries, became the preferred choice for
electric vehicles and hybrid electric vehicles. Electrical
double-layer capacitors [(EDLCs) or, informally, supercapacitors] have been applied for peak power shaving. Flywheels have found application in improving the
low-voltage ride-through ability for wind farms. Besides
that, there are several references involving sodium-sulfur
(Na-S) batteries and  superconducting magnetic energy
storage (SMES), even though they have extreme-temperature requirements. Since the AES IPS is a large-scale system with complex loads, one potential solution will be
distributed ESSs, which is based on a cluster of large or
small ESSs using different kinds of energy storage
devices. At present, the most promising, dominant
energy storage devices for maritime applications are
batteries, EDLCs, and flywheels. With proper allocation
and configuration, the onboard ESSs will be able to
enable multiple functions, such as power backup, peak
power shaving, and braking energy recovery.
From the perspective of control and decision making,
the integration of ESSs also introduces a new dimension
into the control and management of shipboard power
systems, where efficiency and the emissions from the
onboard generation could be actively optimized. By
cooperative control of onboard ESSs and generators
under the complex load conditions, the optimization
toward lowest fuel consumption and/or lowest emissions, as well as the need to service highly dynamic
load demands and pulsed energy requirements, can be
achieved simultaneously. Currently, a new trend of
installing PV panels and wind turbines on board vessels
to reduce the cost of sailing is drawing industrial attention. Such an optimization between ESSs and generational sources would be more effective and necessary
with the integration of onboard RESs in the near future.

6

EDLC

5

FW

Moltan Salt Battery

4
LTO

3
2

LPF
1
0

Lead NiCd
Acid
0

50

LMO

LCO

200
250
100
150
Energy Density (Wh/kg)

300

Figure 6. The power and energy densities of different energy storage
devices. FW: flywheel; NiCd: nickel-cadmium; LMO: lithium manganese oxide; LPF: lithium ferrophosphate; LCO: lithium cobalt oxide;
and LTO: lithium titanate.

regulation in a vessel's highly dynamic load condition
(especially in dynamic positioning operation) and realtime optimization of fuel economy. According to IEEE
Standard 1709-2010, the shipboard dc power system
needs to fulfill the following control objectives:
xx
power system stability: the ability to maintain autonomous equilibrium in normal conditions and regain a
state of operating equilibrium after being subjected to
a physical disturbance
xx
power quality: the ability to maintain or restore the
common dc buses at their nominal voltage with
acceptable voltage tolerance
xx
power management: the ability to optimize systemic
efficiency by intentional scheduling or intervention
without affecting the maximization of the power supply to the demand side.
In terrestrial applications, dc microgrids also face
similar challenges. According to the IEEE Standard
1547 series standards, microgrids should be able to
IEEE Electrific ation Magazine / j une 2 0 1 6

51



Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2016

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http://www.nxtbook.com/nxtbooks/pes/electrification_september2019
http://www.nxtbook.com/nxtbooks/pes/electrification_june2019
http://www.nxtbook.com/nxtbooks/pes/electrification_march2019
http://www.nxtbook.com/nxtbooks/pes/electrification_december2018
http://www.nxtbook.com/nxtbooks/pes/electrification_september2018
http://www.nxtbook.com/nxtbooks/pes/electrification_june2018
http://www.nxtbook.com/nxtbooks/pes/electrification_december2017
http://www.nxtbook.com/nxtbooks/pes/electrification_september2017
http://www.nxtbook.com/nxtbooks/pes/electrification_march2018
http://www.nxtbook.com/nxtbooks/pes/electrification_june2017
http://www.nxtbook.com/nxtbooks/pes/electrification_march2017
http://www.nxtbook.com/nxtbooks/pes/electrification_june2016
http://www.nxtbook.com/nxtbooks/pes/electrification_december2016
http://www.nxtbook.com/nxtbooks/pes/electrification_september2016
http://www.nxtbook.com/nxtbooks/pes/electrification_december2015
http://www.nxtbook.com/nxtbooks/pes/electrification_march2016
http://www.nxtbook.com/nxtbooks/pes/electrification_march2015
http://www.nxtbook.com/nxtbooks/pes/electrification_june2015
http://www.nxtbook.com/nxtbooks/pes/electrification_september2015
http://www.nxtbook.com/nxtbooks/pes/electrification_march2014
http://www.nxtbook.com/nxtbooks/pes/electrification_june2014
http://www.nxtbook.com/nxtbooks/pes/electrification_september2014
http://www.nxtbook.com/nxtbooks/pes/electrification_december2014
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