This document summarizes a paper on developing a standalone microgrid powered by a hybrid renewable energy system. The microgrid was designed to provide reliable electricity to remote communities not connected to the main grid. It uses solar PV, wind turbines, and a diesel generator backed by batteries. The hybrid system was designed and implemented to meet technical challenges of remote operation and provide electricity comparable in quality to centralized grids. The microgrid concept and control strategies were applied to maximize efficiency and reliability of the off-grid renewable energy system.

1. Knowledge Institute of
Techhnology , Salem.
ISOLATED MICRO-GRIDS WITH RENEWABLE HYBRID
GENERATION
Submitted by:
p.lokesh
R.Gokul Raj
EEE-III-Year
Mail id:Tharaigokul@gmail.com
Mobile no:9677498664,

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ABSTRACT
Around 2, 00,000 families in INDIA have not been connected to an electricity grid yet. Out
of these, a significant number of villages may never be connected to the national grid due to
their remoteness. For the people living in these communities, access to renewable energy
sources is the only solution to meet their energy needs. In these communes, the electricity is
mainly used for household purposes such as lighting. There is little scope for the productive
use of energy. It is recognized that electric service contributes particularly to inclusive social
development and to a lesser extent to pro-poor growth as well as to environmental
sustainability. In this paper, we present the specification, design, and development of a
standalone micro-grid supplied by a hybrid generating source. The goal was to provide a
reliable, continuous, sustainable, and good-quality electricity service to users, as provided in
bigger cities. As a consequence, several technical challenges arose and were overcome
successfully as will be related in this paper, contributing to increase of confidence in
renewable systems to isolated applications.

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INTRODUCTION
Most small Island and remote communities
around the world today are dependent on
imported fossil fuels for most of their energy
requirements. These communities are
exposed to diesel fuel price volatility,
frequent fuel spills and high operation and
maintenance costs including fuel
transportation and bulk storage. In addition
to remote area power systems, commercial
and residential customers in urban areas are
also seeking new sources of back-up power
located on their premises. Diesel generators
are a major source of backup power due to
ease of transportation, installation and
removal, as well as the mature and stable
nature of the diesel industry with reliable
suppliers. In the past decade, diesel prices
have more than doubled. High fuel costs
have translated into tremendous increases in
the cost of energy generation. Diesel
generators are also a major source of
pollution. Renewable energy sources such
solar photovoltaic (PV) and wind power are
clean, affordable, readily available, and
sustainable and can supplement generators
in both grid connected and off-grid and
commercialapplications. The author has
been involved in the development of off-grid
remote area power systems over the past two
decades. This paper presents case studies of
micro-grid distributed generation systems
using photovoltaic modules and details how
an innovative variable speed diesel/biodiesel
generator) can be integrated into such
systems.
THE MICRO-GRID CONCEPT
A microgrid can be simply defined as an
aggregation of electrical generation, storages
and loads. The generators in the microgrid
may be microturbines, fuel cells,
reciprocating engines, or any of a number of
alternate power sources. A microgrid may
take the form of shopping center, industrial

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park or college campus. To the utility, a
microgrid is an electrical load that can be
controlled in magnitude. The load could be
constant, or the load could increase at night
when electricity is cheaper, or the load could
be held at zero during times of system stress.
Distributed Generation DG refers to the
numerous small, modular electricity
generators, preferably new and renewable
energy technologies which are located at LV
lines, often close to the point of end use.
Concept of Micro Grid supersedes all the
advantages of single source DG and hybrid
DG. Moreover, it also includes all the
advantages of networking, at mini scale. A
microgrid combined with power electronic
interface is a completely self-sufficient
network, with preferably autonomous
control, communication and protection. It is
capable of providing capacity support to the
transmission grid while in grid-connected
mode, and with capacity in excess of
coincident peak demand. So, the Micro grids
comprise low voltage LV distribution
systems with integration of Diverse Energy
Resources DER such as photovoltaic, wind,
bio-mass, bio fuel and fuel cell together with
Distributed storage DS like flywheels,
energy capacitors and batteries and
Controllable Loads that behave as a
coordinated entity networked by employing
advanced power electronic conversion and
control capabilities .
MICROGRID FEATURES
Micro grid is connected to the power
delivery system at a point of common
coupling PCC, thus appearing as a
controllable single subsystem to the utility
grid. The inter-connection switch is the
point of connection between the microgrid
and the rest of the distribution system.
The microgrid concept enables high
penetration of distributed generation without
requiring re-design of the distribution
system. A main feature of microgrid is to
ensure stable operation during faults and
various network disturbances.
Autonomous operation is realized by
opening the static switch, which disconnects
the microgrid from the main grid.
Distributed generations DG and
corresponding loads can be autonomously
separated from the distribution system to
isolate the micro grid’s load from the

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disturbance during faults. Also it will
intentionally disconnect when the quality of
power from the grid falls below certain
standard. Once the microgrid is isolated
from the main grid, the micro-sources
supplies to the system are responsible for
maintaining the voltage and frequency while
sharing the power.
Micro grids desired features may be listed as
follows:
 Accommodates a wide variety of
generation options –distributed,
intermittent and dispatch able.
 Empowers the consumer –
interconnects with energy
management systems in smart
buildings to enable customers to
manage their energy use and reduce
their energy costs.
 Plug and play functionality is the
features for switching to suitable
mode of operation either grid
connected or islanded operation,
provide voltage and frequency
protection during islanded operation
and capability to resynchronize
safely connect microgrid to the grid.
 Can independently operate without
connecting to the main distribution
grid during islanding mode, all loads
have to be supplied and shared by
distributed generations.
 Some micro-grids are equipped with
thermal power plants capable of
recovering the waste heat, which is
an inherent by-product of fissile-
based electricity generation called
combined heat and power (CHP),
these systems recycle the waste heat
in form of cooling or heating in the
immediate vicinity of the power
plant.
 It services a variety of loads
including residential, office,
industrial parks, commercial,
institutional campus.

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 Provides power quality needed by
21st century users
 provide good solution to supply
power in case of an emergency and
power shortage during power
interruption in the main grid,
 Self-healing – anticipates and
instantly responds to system
problems in order to avoid or
mitigate power outages and power
quality problems.
 Tolerant of attack – mitigates and
stands resilient to physical and cyber
attacks
Fully enables competitive energy markets –
real-time information, lower transaction
costs, available to everyone
 Optimizes assets – uses IT and
monitoring to continually optimize
its capital assets while minimizing
operations and maintenance costs –
more throughput per investment.
HYBRID SYSTEM
Is a term for new electricity supplied on
islands or to bring electricity to rural areas,
especially in developing countries. In the
future, several hybrid systems could be
connected and form micro grids which can
support the functions of the smart grid by,
for instance, enabling virtualpower plants
which can be used to firm up variable
generation.In developing countries, hybrid
systems can be built for remote locations or
island; they are simpler than micro grids but
they can be a step towards a micro grid,
when they are upgraded and get integrated
to a power system.
A. Power Center
The simplified block diagram of the
renewable hybrid generation system is
presented. The solar subsystem is composed
of 9 PV strings, in parallel, each formed by

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18 PV panel sin series. Each string has a
charge controller to provide the correct
changing of the battery bank. The total
maximum power of this subsystem is
approximately 21 kW. The wind sub system
is formed by three wind turbines, each with
nominal power of7.5 kW (at wind speed of
13.8 m/s). These turbines are placed
approximately 500 m from the power house
and are connected by three independent
three-phase underground cables. The wind
generators are the permanent magnet
synchronous type, and the generated ac
voltage is rectified to charge the battery
bank. These two subsystems work in parallel
to charge abank composed of 120 batteries,
arranged in six lines, each line formed by 20
batteries of 150 Ah in series. The nominal
voltage of the bank is 240 VDC.
There is a 53-kVA/48-kW diesel generator
as a backup unit to be used eventually
during the lack of each of the primary
sources of energy or in case of system
maintenance.
The dc bus is the input of the inverter
subsystem, which is formed by three
inverters configured to work in parallel,
sharing equally the load. In this early stage
of operation, just two inverters are necessary
for supplying the load. With this mode of
operation, the mean time before failure
(MTBF) of the overall system increases. The
supervisory control is done by a
programmable logic controller responsible
to coordinate the parallel operation of all
sources with special attention to efficiency,
the charge control of the battery bank; the
load control of the diesel generator
(eventually when it is turned ON), and the
measurement and transmission of all the
variables. The system will be monitored at
the university that is located several miles
away from island.
B. Monitoring and Control
Fig. 3 shows the monitoring and control
structure. A centralized control system

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monitors relevant ac/dc variables, making
decisions to provide reliable supply by using
efficiently the available resources and
preserving the useful life of battery bank.
All data are stored in the database system
with periodicity defined by the user. At the
SCADA system, relevant dc and ac
electrical variables are monitored and stored.
Current, voltage, and temperature
transducers at the dc side have been installed
to monitor the charge/discharge of battery
bank, to monitor the room temperature, and
to measure the contributions of the
photovoltaic system and wind turbines (after
rectifying) as well. This data is used by the
PLC in the charge control process (turn
ON/OFFPV rows), to startup/shutdown the
load transfer between the backup subsystem
and the inverter subsystem, to estimate the
state of charge of the batteries, etc. At the ac
side, three multivariable digital indicators
(MDIs)were used, measuring three-phase
demand, active and reactive powers, power
factor, etc., in all operating scenarios.
C. Criteria for Operation and Control
One of the features of standalone hybrid
renewable generation systems is its small
energy consumption motivatedmainly by the
low personal incoming/house. If the system
is projected to supply energy during, for
example, 20 years, it will be working a long
time at almost no-load condition. In this
scenario, the system’s efficiency will be
very low during the first years of operation.
Therefore, it is fundamental that the overall
generation plant works at its maximum
possible efficiency. Forexample, take a 20-
kVA inverter, with 88% efficiency (typical
for inverters of this size in Brazil). This
efficiency is measure data full load,
corresponding to 2.4 kW of power loss f or
this inverter. In the most optimistic situation,
the inverter no-load loss is in the range of 1
kW. Now, suppose that the wind speed is
1/3 of rated speed. At this operation point,
the wind turbine generated power would be
1/9 of rated value. With the windturbines
used in the project, this corresponds to
approximately0.833 kW. For this situation,
more than one wind turbine would be
necessary just to supply the inverter losses.
The same occurs to the diesel generator
backup. It should work only when there is a
complete lack of renewable energy.
Advantages

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In practice, reliability, cost, and
sustainability factors arestrongly linked.
Systems with low reliability are not
attractiveeither for consumers or investors.
This leads to stagnation ofthe economy in
places without electrical energy. Under
thismotivation, this paper presents the
design and implementationof a standalone
hybrid power generation system that meets
the following requirements:
 Provide electrical energy 24 hours a
day to consumers, with
 Reliabilityand quality similar (or
better than) to big cities.
 Robustness: the system must have
robust operation without
The intervention of specialized
people.
 Equipment must be designed to
operate in a centralizedway and in
adverse conditions (marine
environment and
High tropical temperatures).
 Remote monitoring: due to difficult
access, the systemshould be
designed to be remotely monitored,
by using
 Satellite communication service.
 Explore the available primary clean
energy resources.
 Efficiency: where energy is limited,
efficient proceduresand equipment
are required.
 Expansion flexibility: future
expansions must be allowed.
 Accomplish environmental pressure.
 Taking into account these
requirements, a robust renewable
 Energy-based standalone system to
bring electrical energy toisolated
communities has been developed.
 It is a hybrid systembased on solar
photovoltaic and wind energies,
conceived insuch a way to fully
provide electricity to the energy
demandwith quality, reliability,
sustainability, robustness, and
withoutdegrading the environment.
The main contributions of this work are:
1)To introduce micro-grid concepts in the
development of thiskind of application;
2)To include in the various critical stages of
the project,requirements to improve the
overall reliability of autonomoussystems
based on renewable energy;
3)Application of control and automation
technology to providea continuous energy
service, minimizing emissionsand
maximizing the trust and credibility of

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costumers andinvestors in the electric
service provided. The practical
resultsvalidate the proposal.
CHALLENGING ISSUES
SAMGs are associated to remote isolated
small communities, some geographically
concentrated, others spatially distributedin a
given region, with electrical service
provided by a single or
Several sources such as: diesel generators
photovoltaic systems,wind micro-turbines,
hybrid systems, etc., frequently
availableonly a few hours a day.
These communities are far from the
conventional electrical
grid due to the following reasons, among
others:
1)Natural obstacles, such as mountains,
rivers, natural reserves;
2)Communities located in islands;
3)Environmental constraints;
4)High distance from conventional
electricity networks.
The local weather, geographic location, and
environmentalcharacteristics of these small
isolated demands do not allow
theformulation of a unique technical
solution for any scenario. Rigorously, each
case is its own. Nevertheless, it is possible to
identifycritical issues with hard impact in
defining the most appropriated Solutions for
electrical service to a given isolated
community.
Some of these critical issues are as
follows.
• Poor communities: Small communities
with a lowdevelopmentindex are not
attractive for energy investments. Verylow
demand is critical for sustainability of
electrical service.
Usually, governmental actions have
subsidized initialinvestments in order to
promote economical evolution ofthese
communities and future sustainability of the
energyservice.
• Environmental and ecological issues:
Some communitiesare located in areas with
environmental constraints suchas reserves,
ecological parks, etc. In these cases,
pollutantgenerating sources are alternatives
to be excluded andclean primary sources
such as solar and wind, micro-hydro,tidal,
etc. are candidates to be considered.
• Weather issues: Weather includes
sunshine, rain, cloud cover, winds, hail,
snow, sleet, freezing rain,

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flooding,blizzards, ice storms,
thunderstorms, steady rains froma cold front
or warm front, excessive heat, heat
waves,and more. These issues determine
what kind of generatingsource is more
appropriate. Good and regular windspeed is
attractive for the exploration of wind
energy.Analogously, in case of good solar
incidence, the solarphotovoltaic energy
exploration is more appropriate.
• Hazardous environment: This term is
usually used to definethe destructive action
of the surrounding environment on
amaterial. For instance, exposed structures
and componentsin the marine environment
are subjected to several factorscausing or
conditioning mechanical, physical,
chemical, electrochemical and biological
breakdowns. This isthe case in islands and
the coast; the project must considerthese
issues in the development of the generating
system.
CONCLUSION
This paper reported the project and design of
a micro-gridwith a centralized renewable
hybrid generation system on solar
photovoltaic and wind energies. The
innovations introduced in this kind of
system are related to the requirements
imposed and adequately fulfilled, i.e.,
reliability of the service, adaptability to the
climate conditions, and high level of robust
automation in order to reduce maintenance
needs. Typical isolated communities have
low energy demand and difficult access.
These requirements are addressed to make
sustainable this kind of standalone energy
system. It was shown that part of these
requirements can be fulfilled with parallel
operations of inverters specially designed
for these applications. The system described
here definitely helps to bring energy to
isolated islands and to decrease the CO
emissions.