Power Quality Enhancement Techniques in Hybrid AC DC Microgrid Analysis and Implementation

International Journal of Trend in Scientific Research and Development (IJTSRD)
Volume 6 Issue 6, September-October 2022 Available Online: www.ijtsrd.com e-ISSN: 2456 – 6470
@ IJTSRD | Unique Paper ID – IJTSRD52196 | Volume – 6 | Issue – 6 | September-October 2022 Page 1972
Power Quality Enhancement Techniques in Hybrid
AC/DC Microgrid Analysis and Implementation
Sumit Kumar1
, Ashish Bhargava2
1
Student, 2
Professor,
1,2
Bhabha Engineering Research Institute, Bhopal, Madhya Pradesh, India
ABSTRACT
Distributed generators (DGs) that rely on renewable energy sources
have become more important in the face of rising global
temperatures. Substantial impetus will soon be supplied by wind,
solar energy, biomass, mini-hydro, and the use of fuel cells and
microturbines. Distributed generation, where electricity is produced
by a number of different renewable and unconventional energy
sources, has emerged as a viable option for the construction of
modern electrical systems because to its low environmental impact,
scalability, and adaptability. A microgrid is a small-scale electrical
grid in which multiple loads and distributed generators are
coordinated under a single set of controls. Microgrids are a kind of
integrated energy delivery system that may either work in tandem
with the main power grid or operate autonomously. The concept of a
microgrid eliminates the need for several inverters in a single AC or
DC grid and simplifies the connection of intermittent, renewable AC
and DC power sources and loads. Equipment safety and security
issues have been brought to light by the power electronic converters
that link DGs to the utility/grid. Greater local dependability, lower
feeder losses, local voltage support, increased efficiency through
waste heat use, voltage sag correction, and uninterruptible power
supply are only some of the configuration options available to the
client for the microgrid. In this study, we analyse the functionality of
a hybrid AC/DC microgrid while connected to the mains power
supply. A solar array, a wind generator, and a battery are used to
build a microgrid. The converters can now properly coordinate the
AC and DC sub-grids thanks to the added control techniques. Results
were obtained by use of the MATLAB/SIMULINK software
environment.
How to cite this paper: Sumit Kumar |
Ashish Bhargava "Power Quality
Enhancement Techniques in Hybrid
AC/DC Microgrid Analysis and
Implementation" Published in
International Journal
of Trend in
Scientific Research
and Development
(ijtsrd), ISSN: 2456-
6470, Volume-6 |
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KEYWORDS: Solar (PV), Wind
Energy (WECS), Hybrid System,
AC/DC Microgrid, Distributed
Generators, Power Enhancement,
Stability, DFIG
1. INTRODUCTION:
There are a number of noteworthy changes in electric distribution technologies that will alter the needs of energy
delivery as we go into the next century. Both the demand and supply sides are pushing for these adjustments,
with the latter requiring changes to account for distributed generation and peak-shaving technology [1]. This is
because both the demand and supply sides want more reliable and efficient energy.
IJTSRD52196

International Journal of Trend in Scientific Research and Development @ www.ijtsrd.com eISSN: 2456-6470
Fig 1.1. Microgrid power system
As a consequence of deregulation and the
proliferation of distributed energy supplies, power
networks are undergoing profound changes in their
operational needs (DER). Many DERs take use of
RES like solar, wind, or hydro power, while others
rely on other technologies that allow for
microgeneration. Advantages include reducing
transmission losses and avoiding network congestion,
both of which are enhanced by placing micro sources
in close proximity to the load. Also, since
neighbouring micro sources, controllable loads, and
energy storage systems can run in the islanded mode
in the event of severe system disturbances, the
likelihood of end-customers connected to a low
voltage (LV) distribution grid (in Europe 230 V and
in the USA 110 V) losing power supply is reduced.
These systems are now known as microgrids.
Microgrids are shown in Figure 1.1. This unique
microgrid is about the same size as a low voltage
distribution feeder and has a maximum capacity of 1
MVA and a range of around 1 km. More than ninety
percent of low-voltage residential clients are typically
served by subterranean cable, with the remaining ten
percent provided via overhead lines. Microgrids often
use combined heat and power plants (CHP), gas
turbines, fuel cells, photovoltaic (PV) systems, wind
turbines, etc. to provide both electricity and heat to its
clients. Batteries and flywheels are common forms of
energy storage [2]. The microgrid's energy storage
system is analogous to the traditional grid's rotating
reserve of big generators in that it maintains power
stability, particularly at peak demand or when there
are sudden shifts in supply or demand [3].
Microgrids may benefit customers in a number of
ways, including meeting their thermal and electrical
needs, decreasing emissions, increasing power quality
by smoothing out voltage fluctuations, and decreasing
overall supply costs. From the perspective of utilities,
the use of decentralised energy sources has the
potential to lower the need for transmission and
distribution infrastructure. Distributed generation that
is geographically near to loads has two major
benefits: it may mitigate losses and it can possibly
replace infrastructure in the transmission and
distribution networks. Furthermore, having generation
near to demand might improve the quality of service
experienced by end users. Microgrids may help the
network out by reducing congestion and speeding up
the repair process after an outage. Emissions may be
reduced and climate change mitigated with the help of
newly developed microgrids. This is because
technologies based on renewable sources and micro
sources, which are characterised by extremely low
emissions, are readily available and are emerging for
distributed generating units [4].
Microgrids provide numerous benefits to consumers,
utilities, and society as a whole, including enhanced
energy efficiency, decreased overall energy
consumption, lower emissions of greenhouse gases
and other pollutants, higher service quality and
reliability, and lower replacement costs for electricity
infrastructure[2].
There are significant technical hurdles associated with
microgrid operation and controls. Improving complex
control techniques for microgrid inverters is
necessary to provide stable operation during network
disruptions, maintain stability and power quality in
the islanding mode of operation, and supply stable
frequency and voltage in the presence of arbitrarily
fluctuating loads [4]. Because of this, the idea of a
microgrid has piqued the interest of many scientists
and policymakers in the United States, Europe, and
Japan. Although microgrids hold great promise, their
integration and operation are fraught with challenges.
FEATURES OF MICROGRID THAT
REPRESENT TECHNICAL DIFFICULTIES
The protection mechanism for a microgrid, which
must respond to failures on both the main grid and the
microgrid, is a significant obstacle. To safeguard the
microgrid loads in the first scenario, the protection
system must quickly disconnect the microgrid from
the main grid; in the second scenario, the protection
system must isolate the tiniest possible section of the
microgrid after the fault is cleared [30]. Micro source
and load controllers are necessary for a microgrid's
segmentation, or the creation of several islands or
sub-microgrids. Selectivity (false, unneeded tripping)

and sensitivity (undetected faults or delayed tripping)
issues with the protection system may become
problematic under certain circumstances. There are
two primary concerns when it comes to microgrid
protection: the first involves the number of distributed
energy resource (DER) units installed in the
microgrid, and the second involves the availability of
a sufficient level of short-circuit current in the
islanded operating mode of microgrid, given that this
level may substantially drop down after a
disconnection from a rigid main grid. The authors of
[30] calculated short-circuit currents for radial feeders
equipped with DER and investigated the fact that the
short-circuit currents used by over-current (OC)
protection relays are location- and DER-specific. The
circumstances will create deviations in the short
circuit current's direction and magnitude. Given the
nature of micro sources (wind and sun) and periodic
demand change, the actual operating conditions of a
microgrid are dynamic and ever-changing. It is
possible to often alter the network's topology in an
effort to decrease loss or accomplish other financial
or operational goals. In addition, defects in such an in
grid or in side microgrid might cause the formation of
controlled islands of varying size and content. Since a
result, generic OC protection with a single setting
group may become inadequate, as it will no longer
ensure a selected operation for all conceivable faults,
and may cause a loss of relay coordination. Therefore,
it is crucial to make sure that the OC protection
relays' settings accommodate for the layout of the
grid and any shifts in the location, type, or quantity of
available generation. Otherwise, unintended
behaviour or failure could occur under required
circumstances. Microgrids dominated by micro
sources with power electronic interfaces necessitate a
new protection philosophy, where setting parameters
of relays must be checked/updated periodically to
ensure that they are still appropriate to deal with bi-
directional power flows and low short-circuit current
levels.
2. PHOTOVOLTAIC SYSTEM AND WIND
ENERGY SYSTEM (DFIG)
Photovoltaic system
The photoelectric effect was first noted by French
physicist Edmund Becquerel in 1839. He proposed
that certain materials have property of producing
small amounts of electric current when exposed to
sunlight. In 1905, Albert Einstein explained the nature
of light and the photoelectric effect which has become
the basic principle for photovoltaic technology. In
1954 the first photovoltaic module was built by Bell
Laboratories.
A photovoltaic system makes use of one or more solar
panels to convert solar energy into electricity. It
consists of various components which include the
photovoltaic modules, mechanical and electrical
connections and mountings and means of regulating
and/or modifying the electrical output.
Photovoltaic arrangements
Photovoltaic cell
Fig 2.1. Basic structure of PV Cell
The basic ingredients of PV cells are semiconductor
materials, such as silicon. For solar cells, a thin
semiconductor wafer creates an electric field, on one
side positive and negative on the other. When light
energy hits the solar cell, electrons are knocked loose
from the atoms in the semiconductor material. When
electrical conductors are connected to the positive and
negative sides an electrical circuit is formed and
electrons are captured in the form of an electric
current that is, electricity. This electricity is used to
power a load. A PV cell can either be circular or
square in construction.
Photovoltaic module
Because of the low voltage generation in a PV cell
(around 0.5V), several PV cells are connected in series
(for high voltage) and in parallel (for high current) to
form a PV module for desired output. In case of
partial or total shading, and at night there may be
requirement of separate diodes to avoid reverse
currents The p-n junctions of mono-crystalline silicon
cells mayhave adequate reverse current characteristics
and these are not necessary. There is wastage of power
because of reverse currents which directs to
overheating of shaded cells. At higher temperatures
solar cells provide less efficiency and installers aim to
offer good ventilation behind solar panel. Usually
there are of 36 or 72 cells in general PV modules. The
modules consist of transparent front side, encapsulated
PV cell and back side. The front side is usually made

up of low-iron and tempered glass material. The
efficiency of a PV module is less than a PV cell. This
is because of some radiation is reflected by the glass
cover and frame shadowing etc.
Photovoltaic array
A photovoltaic array (PV system) is an
interconnection of modules which in turn is made up
of many PV cells in series or parallel. The power
produced by single module is not enough to meet the
requirements of commercial applications, so modules
are connected to form array to supply the load. In an
array the connection of the modules is same as that of
cells in a module. The modules in a PV array are
usually first connected in series to obtain the desired
voltages; the individual modules are then connected in
parallel to allow the system to produce more current.
In urban uses, generally the arrays are mounted on a
rooftop. PV array output can directly feed to a DC
motor in agricultural applications.
Fig 2.2. Photovoltaic system
Working of PV cell
The basic principle behind the operation of a PV cell
is photoelectric effect. In this effect electron gets
ejected from the conduction band as a result of the
absorption of sunlight of a certain wavelength by the
matter (metallic or non-metallic solids, liquids or
gases). So, in a photovoltaic cell, when sunlight hits
its surface, some portion of the solar energy is
absorbed in the semiconductor material.
Fig 3.3. Working of PV cell
The electron from valence band jumps to the
conduction band when absorbed energyis greater than
the band gap energy of the semiconductor. By these
hole-electrons pairs are created in the illuminated
region of the semiconductor. The electrons created in
the conduction band are now free to move. These free
electrons are enforced to move in a particular direction
by the action of electric field present in the PV cells.
These electrons flowing comprise current and can be
drawn for external use by connecting a metal plate on
top and bottom of PV cell. This current and the
voltage produces required power.
Wind turbines
With the use of power of the wind, wind turbines
produce electricity to drive an electrical generator.
Usually wind passes over the blades, generating lift
and exerting a turning force. Inside the nacelle the
rotating blades turn a shaft then goes into a gearbox.
The gearbox helps in increasing the rotational speed
for the operation of the generator and utilizes
magnetic fields to convert the rotational energy into
electrical energy. Then the output electrical power
goes to a transformer, which converts the electricity to
the appropriate voltage for the power collection
system. A wind turbine extracts kinetic energy from
the swept area of the blades.
DFIG system
The doubly fed induction machine is the most widely
machine in these days. The induction machine can be
used as a generator or motor. Though demand in the
direction of motor is less because of its mechanical
wear at the slip rings but they have gained their
prominence for generator application in wind and
water power plant because of its obvious adoptability
capacity and nature of tractability. This section
describes the detail analysis of overall DFIG system
along with back-to-back PWM voltage source
converters.
3. SYSTEM DESIGN AND
IMPLEMENTATION AC/DC MICROGRID
The concept of microgrid is considered as a collection
of loads and micro sources which functions as a single
controllable system that provides both power and heat
to its local area. This idea offers a new paradigm for
the definition of the distributed generation operation.
To the utility the microgrid can be thought of as a
controlled cell of the power system. For example, this
cell could be measured as a single dispatch able load,
which can reply in seconds to meet the requirements
of the transmission system. To the customer the
microgrid can be planned to meet their special
requirements; such as, enhancement of local
reliability, reduction of feeder losses, local voltages
support, increased efficiency through use waste heat,

voltage sag correction [3]. The main purpose of this
concept is to accelerate the recognition of the
advantage offered by small scale distributed
generators like ability to supply waste heat during the
time of need [4]. The microgrid or distribution
network subsystem will create less trouble to the
utility network than the conventional microgeneration
if there is proper and intelligent coordination of micro
generation and loads [5]. Microgrid considered as a
‘grid friendly entity” and does not give undesirable
influences to the connecting distribution network i.e.
operation policy of distribution grid does not have to
be modified[7].
Configuration of the hybrid microgrid
Fig 3.1. A hybrid AC/DC microgrid system
The configuration of the hybrid system is shown in Figure 3.1 where various AC and DC sources and loads are
connected to the corresponding AC and DC networks. The AC and DC links are linked together through two
transformers and two four quadrant operating three- phase converters. The AC bus of the hybrid grid is tied to the
utility grid.
Figure 3.2 describes the hybrid system configuration which consists of AC and DC grid.
The AC and DC grids have their corresponding sources, loads and energy storage elements, and are
interconnected by a three phase converter. The AC bus is connected to the utility grid through a transformer and
circuit breaker.
In the proposed system, PV arrays are connected to the DC bus through boost converter to simulate DC sources.
A DFIG wind generation system is connected to AC bus to simulate AC sources. A battery with bidirectional
DC/DC converter is connected to DC bus as energy storage. A variable DC and AC load are connected to their
DC and AC buses to simulate various loads.
PV modules are connected in series and parallel. As solar radiation level and ambient temperature changes the
output power of the solar panel alters. A capacitor Cpv is added to the PV terminal in order to suppress high
frequency ripples of the PV output voltage. The bidirectional DC/DC converter is designed to maintain the stable
DC bus voltage through charging or discharging the battery when the system operates in the autonomous
operation mode. The three converters (boost converter, main converter, and bidirectional converter) share a

common DC bus. A wind generation system consists of doubly fed induction generator (DFIG) with back to back
AC/DC/AC PWM converter connected between the rotor through slip rings and AC bus. The AC and DC buses
are coupled through a three phase transformer and a main bidirectional power flow converter to exchange power
between DC and AC sides. The transformer helps to step up the AC voltage of the main converter to utility
voltage level and to isolate AC and DC grids.
Modeling and control of DFIG
This section explains the detailed modeling of DFIG. The state space equations are considered for induction
machine modeling. The parameters and specifications of the DFIG are given in table 3.1. Flux linkages are used
as the state variables in the model. Here two back to back converters are used in the rotor circuit. The main
purpose of the machine-side
converter is to control the active and reactive power by controlling the d-q components of rotor current, while the
grid-side converter controls the dc-link voltage and ensures the operation at unity power factor by making the
reactive power drawn by the system from the utility grid to zero.
Two back to back converters are connected to the rotor circuit is shown in Fig 3.3. The firing pulses are given to
the devices (IGBTs) using PWM techniques. Two converters are linked to each other by means of dc-link
capacitor.
Fig. 3.3. Overall DFIG system
4. RESULTS
A hybrid microgrid is simulated using MATLAB/SIMULINK environment. The operation is carried out for the
grid connected mode. Along with the hybrid microgrid, the performance of the doubly fed induction generator,
photovoltaic system is analyzed. The solar irradiation, cell temperature and wind speed are also taken into
consideration for the study of hybrid microgrid. The performance analysis is done using simulated results which
are found using MATLAB.
Hybrid AC/DC Microgrid

4.1. Simulation of PV array
Figure (4.1) -(4.6) represents I-V, P-V, P-I characteristics with variation in temperature and solar irradiation. The
nonlinear nature of PV cell is noticeable as shown in the figures, i.e., the output current and power of PV cell
depend on the cell’s terminal operating voltage and temperature, and solar irradiation as well.
Figures (4.1) and (4.2) verify that with increase of cell’s working temperature, the current output of PV module
increases, whereas the maximum power output reduces. Since the increase in the output current is much less than
the decrease in the voltage, the total power decreases at high temperatures.
Fig 4.1. I-V output characteristics of PV array for different temperatures
Fig 4.2. P-V output characteristics of PV array for different temperatures
Fig 4.3. P-I output characteristics of PV array for different temperatures

Fig 4.4. I-V output characteristics of PV array for different irradiance levels
Fig 4.5. P-V characteristics of PV array for different irradiance levels
Fig 4.6. P-I characteristics of PV array for different irradiance levels
Figures (4.4) and (4.5) show that with increase of solar irradiation, the current output of PV module increases
and also the maximum output power. The reason behind it is the open- circuit voltage is logarithmically
dependent on the solar irradiance, however the short-circuit current is directly proportional to the radiant
intensity.
4.2. Simulation of doubly fed induction generator
The response of wind speed, three phase stator voltage and three phase rotor voltage are shown in the figures
(4.7) - (4.9). Here the value of wind speed varies between 1.0 to 1.05 pu which is necessary for the study of the
performance of doubly fed induction generator. The phase-to-phase stator voltage is set to 300V whereas the
rotor voltage value is 150V.

Fig 4.7. Response of wind speed
Fig 4.8. Three phase stator voltage of DFIG
Fig 4.9. Three phase rotor voltage of DFIG
4.3. Simulation results of hybrid grid
The various characteristics of the hybrid microgrid are represented by the figures (4.10) – (4.25). Here the
microgrid operates in the grid tied mode. In this mode, the main converter operates in the PQ mode and power is
balanced by the utility grid. The battery is fully charged. AC bus voltage is maintained by the utility grid and DC
bus voltage is maintained by the main converter.
Figure (4.10) shows the curve of solar irradiation level which value is set as 950 W/sq.m from 0.0s to 0.1s,
increases linearly to 1300 W/sq.m from 0.1s to 0.2s, remains constant from 0.3s to 0.4s, decreases to 950
W/sq.m and keeps that value until 1s. Figures (4.11) – (4.13) signify output voltage, current and power with
respect to the solar irradiation signal. The output power of PV panel varies 11.25 kW to 13 kW, which closely
follows the solar irradiation when the ambient temperature is fixed.

Fig 4.10. Irradiation signal of the PV array
Fig 4.11. Output voltage of PV array
Fig 4.12. Output current of PV array
Fig 4.13. Output power of PV array

Fig 4.14. Generated PWM signal for the boost converter
Fig 4.15. Output voltage across DC load
Figure (4.14) shows the gate pulse signal which is fed to the switch of boost converter. The output voltage across
DC load is represented by figure (4.15) which is settled to around 820V.
Fig 4.16. State of charge of battery
Fig 4.17. Voltage of battery

Fig 4.18. Current of battery
Fig 4.19. Output voltage across AC load
Fig 4.20. Output current across AC load
Fig 4.21. AC side voltage of the main converter

Fig 4.22. AC side current of the main converter
The battery characteristics are shown in the figures (4.16) - (4.18). The state of charge of battery is set at 85%
whereas the battery current varies between -50 to 50A and the value of battery voltage is nearly 163.5. The
output characteristics of AC load voltage and current are represented by the figures (4.19) and (4.20). Phase to
phase voltage value of AC load is 300V and current value is 50A.Figure (4.21) and (4.22) shows the voltage and
current responses at the AC side of the main converter when the solar radiation value varies between 950-1300
W/sq.m with a fixed DC load of 25 kW.
Fig 4.23. Output power of DFIG
Fig 4.24. Three phase supply voltage of utility grid

Fig 4.25. Three phase PWM inverter voltage
Figure (4.23) shows the response of the DFIG power output which becomes a stable value 32kW due to
mechanical inertia. Figure (4.24) and (4.25) represents the three-phase supply voltage to the utility grid and three
phase PWM inverter output voltage respectively. In this chapter simulation results are discussed briefly. Also
various characteristics of PV array, doubly fed induction generator, battery and converters are studied in this
chapter and the waveforms are traced.
5. CONCLUSION & FUTURE SCOPE
Conclusion
The MATLAB/SIMULINK platform is used to
simulate the hybrid microgrid power system setup.
The focus of the current study is on the hybrid grid's
grid-tied mode of operation. In order to keep the
system stable under varying loads and resource
circumstances, models are created for each of the
converters, and their respective control mechanisms
are investigated. The maximum power point tracking
(MPPT) algorithm is used to get the most energy
possible out of DC sources and to regulate the flow of
electricity between the DC and AC grids. Although a
hybrid grid may reduce the need for DC/AC and
AC/DC converters within a single AC or DC grid,
implementing a hybrid grid based on the existing AC
dominant infrastructure presents a number of practical
challenges. Reducing conversion losses and adding an
additional DC connection will improve the overall
system's efficiency. Electricity from the hybrid grid is
more secure, of higher quality, and uses less resources
than traditional grids. For tiny, remotely located
manufacturing facilities, the hybrid grid might work if
the primary power source includes photovoltaic cells
and a wind turbine generator.
Future Scope
The control mechanism may be created for a
microgrid with unbalanced and nonlinear loads;
modelling can be done for the islanded mode of
operation.
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