Page 138 - Decision Making Applications in Modern Power Systems

Power quality issues of smart microgrids Chapter | 4 103

reactive power controllers that control the input voltage instead of output
voltage, but in contrary to other reactive power controllers, such as SVC and
flexible alternating current transmission system (FACTS), which only partici-
pate in reactive power compensating, ES is capable of compensating active
and reactive power. Recently, to take part in demand-side response of DC
microgrids, the concept of DC-ES has been proposed; it has the storage units
integrated and a bidirectional DC DC converter in the structure that makes
the DC-ES to perform the mentioned tasks in a DC microgrid [33].

4.3.4.3 Multifunctional distributed generations
The pioneer technology to improve the power quality in smart grids is the
use of MFDGs to enhance the power quality locally and globally. These
days the progress to a CO 2 -free world, cheap and clean energy sources would
accelerate the attention drawing to RESs. However, most of these energy
sources use power electronic based converters to output the desired AC
voltage to the main electricity grid, which makes these energy sources a
costly electricity generation. To make the technology more cost effective,
other functionalities could be added to the power electronic based interfac-
ing converters, such as power quality enhancement capabilities. These con-
verters could be used in harmonic compensation, voltage regulation, and as
an energy storage source for different smart grid applications. These features
could be empowered by means of several smart grid enabled tools such as
smart metering infrastructures and computational intelligence, and they will
have a big portion in smart grid power quality enhancement. These devices
could be categorized based on the controlled objects and the applied control
methods. Since a critical part of MFDGs is the applied advanced control
methods, it is worth dedicating a section to study the control methods and
their secondary applications in smart grids.

4.3.4.4 Applied control methods to multifunctional distributed
generations to enhance power quality
There are several control methods applied to MFDGs interfacing power elec-
tronic based converters in the case of harmonic compensation in the litera-
ture; the most relevant control methods are PR controller and model-based
predictive controller (MPC). Each of the mentioned methods has some
advantages to previously proposed methods; in the case of a PR controller,
the simplicity and the ability to control the voltage and current simulta-
neously are the advantages; and in the case of MPC, the advantages are
the flexibility of the control method, fast dynamic response, and acceptable
reference tracking operation in lower switching frequencies. The other merit
of the MPC method when applied to MFDG interfacing inverters is the capa-
bility of multiobjective operation, which means the ability to control several
objectives simultaneously regarding the priority of each objective; this would