IEEE Power Electronics Magazine - June 2019 - 19

article provides a complete description of the main features and challenges of ac MGs and describes the hierarchical control architecture as an effective solution.
A detailed discussion of the control levels is presented
as well.

Microgrid Control Architecture

syst em con sider ations, communications, and model
predictive control (MPC) [6]-[10]. Decentralized control
consists of two major approaches: the optimal dispatch
approach and the multiagent approach [11], [12].
The highest level of grid control architecture is the tertiary control, which is responsible for managing the power
from an economic point of view, or economic dispatch.
There are two main categories of the techniques used in
tertiary control: centralized and decentralized [13], [14].
This article presents a comprehensive comparison of the
techniques that have been used in each control level, and
it focuses on the main advantages and challenges that face
each technique to achieve fully controlled, economically
dispatched, and reliable MGs.

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US$ (Million)

The conventional electric power grid is designed to generate, transmit, and distribute electrical energy in a secure,
reliable, and economical way. It is challenging for the current grid to maintain an electricity network able to
respond to changing generation and consumption
patterns. The MG is an emerging concept of a
future grid that is formed with DERs, energy storage, and various loads [1]. One of the advantages of
an MG is that it can operate either in grid-conMGs
nected or islanded mode. In the case of a fault in
MG deployment continues to grow worldwide. In recent
the main grid, the MG operates in islanded mode to
years, MGs have catered to various verticals, such as
maintain the energy supply and the stability of volteducational, military, government, utility, and healthage and frequency for the local loads [2], [3]. The
care insitutions. This growth contributed to increasing
greatest challenge in islanded mode is to ensure
annual MG capacity around the world. Navigant
system stability and reliability while meeting the
Research reported that the annual MG capacity and
power demand of the customer [4], [5].
spending by region increased from 2018 to the present
The hierarchical control consists of three levat a high rate across 123 countries globally. Also, the
els: primary, secondary, and tertiary. The primary
world market forecast for 2018-2027 predicts a capacity
control, known as local or field level, is adopted
of 33 GW by the end of 2027 (Figure 1) [15]. The MG
to ensure reliable operation through maintainconsists of various DERs using mainly renewable
ing the voltage and frequency stability to satisfy
energy sources. MGs can be described as intelligent dissome requirements, such as stabilizing the volttribution networks with the capacity for selling/buying
age and frequency [6], [7] and offering the plugpower to/from the utility grids or other MGs. MGs can
and-play capability for different DERs. Different
be disconnected completely from the main grid when
techniques used for the primary control level are
there is a need, such as a fault existing in the utility
based on the droop control method applied to
grid [16], [34]. Energy management systems in the MGs
various DERs. The secondary control, or manageplay a critical role in ensuring perfect coordination
ment level, is conceived to restore the voltage freamong DERs.
quency and amplitude deviations
produced inside the MG and manage the MG's communication. Two
35,000
18,000
main approaches have been devel16,000
30,000
oped in this level of control: cen14,000
tralized and decentralized. A cen25,000
12,000
tralized structure is considered
20,000
the conventional secondary con10,000
trol for MGs and requires a com8,000
15,000
plex, high-speed communication
6,000
10,000
network between the central con4,000
troller and local regulators. This
5,000
2,000
negatively affects system reliabil0
0
ity. Applying decentralized control
2018 2019 2020 2021 2022 2023 2024 2025 2026 2027
has become an attractive solution
Year
for reliability improvement and
simplicity in communication [8].
Annual MG Capacity
North America
Europe
Asia Pacific
Latin America
Middle East and Africa
Centralized secondar y control
Total Spending
consists of different approaches,
such as optimal dispatch, bidding,
nonmodel based, energy stora ge FIG 1 The annual MG capacity and world market forecast, 2018-2027.
June 2019

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IEEE Power Electronics Magazine - June 2019

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