Page 39 - Hybrid-Renewable Energy Systems in Microgrids

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Microgrid architecture, control, 2

and operation

,
Mekhilef Saad Bin Arif* **, M. Asif Hasan †
*Power Engineering Department, UTM, Johor Bahru, Malaysia; **Department of Electrical
†
Engineering, AMU, Aligarh, India; Department of Electrical and Electronics Engineering,
BIT Patna, Patna, India

1 Introduction

Charles Steinmetz, the famous electrical engineer, once said that the North American
interconnected power system is the largest and most complex machine ever devised
by man. A stable and reliable operation of such a big and complex system is really a
cumbersome task. However, it all started in September 1882 at New York City, where
Thomas Edison presented the world’s first complete electric power system with the
help of generator, cable, fuse, meter, and loads. Subsequently, the development of
electrical motor in 1884, as well as transformer and AC transmission in 1886, gave the
necessary wings to the power system engineering to widespread its span and take the
form it exists currently. As the power network spread into large geographical areas,
the problem of stability and reliability came into existence. Numerous research works
were carried out to address the stability- and reliability-related issues.
Technical development and environment-related concerns have led to the new phase
of power system architecture. In the new phase, microsources of electrical energy have
come into the picture, playing its role with significant footprint. Distributed energy
sources such as solar photovoltaics, wind energy generation unit, fuel cell, microtur-
bines, and gas turbines are providing clean energy. The concept of cluster of these
microsources and loads, operating as a single controllable unit and providing electrical
power to local area, has been given the name “microgrid” [1].
Most of these microsources that are renewable in nature are highly intermittent in
terms of the availability of power. Their independent operation depends upon the bal-
ance of generation and demand. Therefore two different operating modes are discussed
for a reliable operation of microgrid. One is autonomous mode, in which microsources
independently take care of connected loads, and necessary active and reactive power
balance is maintained by these sources through a centralized or decentralized control
unit. Second is the grid-tied mode, in which microsources operate in association with a
infinite grid [2,3]. In grid-tied mode, voltage stability and frequency stability are main-
tained by the infinite grid itself. The microsources act as single generating unit [4].
Because the nature of microsources is intermittent, and the quality of electrical out-
put power is not good enough to be fed to electrical loads directly, many semiconduc-
tor devices are employed to achieve the desired quality and control. Power electronic
interfacings such as AC/DC, DC/AC, AC/AC, and DC/DC converters are used in

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