Reactive Power Management in Islanded

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Reactive Power Management in Islanded Micro grid—Proportional

Power Sharing in Hierarchical Droop Control

Abstract

In this project A micro grid (MG) is a local energy system consisting of a number of energy

sources (e.g., wind turbine or solar panels among others), energy storage units, and loads that

operate connected to the main electrical grid or autonomously. MGs provide fleibility, reduce

the main electricity grid dependence, and contribute to changing large centrali!ed production

paradigm to local and distributed generation. "owever, such energy systems re#uire comple

management, advanced control, and optimi!ation. Moreover, the power electronics converters

have to be used to correct energy conversion and be interconnected through common control

structure is necessary. $lassical droop control system is often implemented in MG. It allows

correct operation of parallel voltage source converters in grid connection, as well as islanded

mode of operation. "owever, it re#uires comple power management algorithms, especially in

islanded MGs, which balance the system and improves reliability. %he novel reactive power

sharing algorithm is developed, which ta&es into account the converters parameters as apparent

power limit and maimum active power.


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INTRD!CTIN

Micro grid (MG) is a separate system that produces and storages electrical energy, which consists

of renewable energy sources ('), local loads, and energy storage based on batteries or super

capacitors. It is inherent part of modern and popular smart grids which includes also intelligent

buildings, electrical car stations, etc. All ' are using power electronics devices (e.g.,

converters), which number significantly increasing and costs decreasing in range *+-+ every

year. ' are usually connected to the grid and many installations cause the parallel operation of

' close to each other. %his is one of reasons to future change of the classical structure of

electrical power systems, toward new solution containing distributed generation, energy storage,

protection and control technologies, and improving their performances.

MG is highly advanced system from control and communication point of view. It has to manage

power for local loads as well as control all converters with high efficiency and accuracy,

especially when MG operates as islanded system. Islanding mode of operation provide the

uninterruptible power supply for local loads during grid faults. %he performances of islanded

MG are specified according to I. ith increasing number of ' applications, operating

parallel, close to each other (few &m) and with developed islanded mode of operation, the MGs

are become perfect solution for ' integration.

/undamental algorithms of ac MGs, are based on masterslave control or hierarchical droop

control. %he first solution includes only one converter with voltage control loop (0$1),operating as a master, and others operating in current control loop ($$1)2slaves. %he produced

power is controlled by sources with $$1 and the voltage amplitude and fre#uency is &eeping in

point of common coupling (3$$) by master unit. 4isadvantage of this solution is no possibility

to connect other 0$1 sources to MG, which are the most popular and used ' solutions. %he

second control solution, called droop control, includes many 0$1 sources and provides

possibility to many different ' interconnection. %he idea of droop control is based on active

and reactive power related to voltage fre#uency and amplitude droop on coupled impedances.

5nfortunately, classical droop control method with proportional droop coefficients does not

provides proper reactive power sharing between converters connected to common ac bus. In

classical approach, the e#ual reactive power sharing ('3) can be obtained only when active

powers are e#ual and droop coefficients are well chosen. hen active powers are changing, the

reactive power sharing cannot be controlled causing overload or reactive power circulation


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between converters. Moreover, the important issue in droop control is static trade6off between

voltage regulation and reactive power. /or increasing reactive power, the voltage droop on

converter7s output impedance also increase, what may cause overvoltage. In order to provide

appropriate power sharing and minimi!e the ris& of converter damage the many additional

aspects (e.g., nominal apparent power, instantaneous active power, nominal voltage of converter)

/ig. *. #uivalent circuit of parallel connected 0Is.

%here are only few papers describing reactive power sharing between parallel operating

converters in islanded ac MGs. %he researchers focused on '3 between all ' usually

controlled by MG central control unit or implemented as virtual impedances. /rom the other

hand, researches consider reactive power sharing in order to optimi!e transmission power losses

by appropriate optimi!ation algorithm (e.g., particle swarm optimi!ation), which can be

neglected in MGs, hence the short distances and the line impedances are low.

"owever, algorithms described in literature are not considering capabilities of single ', which

have limited apparent power. If active power, usually calculated from maimum pea& power

trac&ing (M33%) algorithms, obtain almost nominal apparent converter limit the e#ual power sharing algorithms cannot be used, because the overload can occur, what leads to damage or

eclusion from operation of ' unit. %he new reactive power sharing algorithm is developed

And presented in this project. In ection I, the current solutions and problems of reactive power

sharing are described.

"#isting method

%he first solution includes only one converter with voltage control loop (0$1), operating

as a master, and others operating in current control loop ($$1) slaves. %he produced

power is controlled by sources with $$1 and the voltage amplitude and fre#uency is &eeping in

point of common coupling (3$$) by master unit. 4isadvantage of this solution is

no possibility to connect other 0$1 sources to MG, which are the most popular and used '

solutions. %he second control solution, called droop control, includes many 0$1 sources and

provides possibility to many different ' interconnection.


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Proposed method

%he proposed method describes MGs provide fleibility, reduce the main electricity grid

dependence, and contribute to changing large centrali!ed production paradigm to local and

distributed generation. "owever, such energy systems re#uire comple management, advanced

control, and optimi!ation. Moreover, the power electronics converters have to be used to correct

energy conversion and be interconnected through common control structure is necessary.

$lassical droop control system is often implemented in MG. It allows correct operation of

parallel voltage source converters in grid connection, as well as islanded mode of operation.

Distributed generation

4istributed energy, also on6site generation (8G) or district9decentrali!ed

energy is generated or stored by a variety of small, grid6connected devices referred toas distributed energy resources (4') or distributed energy resource systems.

$onventional power stations, such as coal6fired, gas and nuclear powered plants, as well

as hydroelectric dams and large6scale solar power stations, are centrali!ed and often

re#uire electricity to be transmitted over long distances. :y contrast, 4' systems are

decentrali!ed, modular and more fleible technologies, that are located close to the load they

serve, albeit having capacities of only *;megawatts (M) or less.

4' systems typically use renewable energy sources, including smallhydro, biomass, biogas, solar power , wind power , and geothermal power , and increasingly play

an important role for the electric power distribution system. A grid6connected device

for electricity storage can also be classified as a 4' system, and is often called a distributed

energy storage system (4). :y means of an interface, 4' systems can be managed and

coordinated within a smart grid. 4istributed generation and storage enables collection of energy

from many sources and may lower environmental impacts and improve security of supply.

Micro grids are modern, locali!ed, small6scale grids, contrary to the traditional,centrali!ed electricity grid (macro grid). Micro grids can disconnect from the centrali!ed grid and

operate autonomously, strengthen grid resilience and help mitigate grid disturbances. %hey are

typically low6voltage A$ grids, often use diesel generators, and are installed by the community

they serve. Micro grids increasingly employ a miture of different distributed energy resources,

such as solar hybrid power systems, which reduce the amount of emitted carbon significantly.

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verview

"istorically, central plants have been an integral part of the electric grid, in which large

generating facilities are specifically located either close to resources or otherwise located far

from populated load centers. %hese, in turn, supply the traditional transmission and distribution(%


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C. the increasing relative economy of mass production of smaller appliances over heavy

manufacturing of larger units and on6site constructionB

D. Along with higher relative prices for energy, higher overall compleity and total costs for

regulatory oversight, tariff administration, and metering and billing.

$apital mar&ets have come to reali!e that right6si!ed resources, for individual customers,

distribution substations, or micro grids, are able to offer important but little6&nown economic

advantages over central plants. maller units offered greater economies from mass6production

than big ones could gain through unit si!e. %hese increased value2due to improvements in

financial ris&, engineering fleibility, security, and environmental #uality2of these resources can

often more than offset their apparent cost disadvantages. 4G, vis6E6vis central plants, must be

justified on a life6cycle basis. 5nfortunately, many of the direct, and virtually all of the indirect,

benefits of 4G are not captured within traditional utility cash6flow accounting.

hile the leveli!ed cost of distributed generation (4G) is typically more epensive than

conventional, centrali!ed sources on a &ilowatt6hour basis, this does not consider negative

aspects of conventional fuels. %he additional premium for 4G is rapidly declining as demand

increases and technology progresses, and sufficient and reliable demand may bring economies of

scale, innovation, competition, and more fleible financing, that could ma&e 4G clean energy

part of a more diversified future.

4istributed generation reduces the amount of energy lost in transmitting electricity because the

electricity is generated very near where it is used, perhaps even in the same building. %his also

reduces the si!e and number of power lines that must be constructed.

%ypical 4' systems in a feed6in tariff (/I%) scheme have low maintenance, low pollution and

high efficiencies. In the past, these traits re#uired dedicated operating engineers and large

comple plants to reduce pollution. "owever, modern embedded systems can provide these traits

with automated operation and renewables, such as sunlight, wind and geothermal. %his reduces

the si!e of power plant that can show a profit.

$rid parit%

Grid parity occurs when an alternative energy source can generate electricity at a leveli!ed cost

(1$8) that is less than or e#ual to the end consumerFs retail price. 'eaching grid parity is

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considered to be the point at which an energy source becomes a contender for widespread

development without subsidies or government support. ince the @;*;s, grid parity for solar and

wind has become a reality in a growing number of mar&ets, including Australia, several

uropean countries, and some states in the 5..

Technologies

4istributed energy resource (D"R ) systems are small6scale power generation or storage

technologies (typically in the range of * & to *;,;;; &) used to provide an alternative to or

an enhancement of the traditional electric power system. 4' systems typically are

characteri!ed by high initial capital costs per &ilowatt. 4' systems also serve as storage device

and are often called 4istributed energy storage systems (4).

4' systems may include the following devices9technologies

• $ombined heat power ($"3), also &nown as cogeneration or trigeneration

• /uel cells

• "ybrid power systems (solar hybrid and wind hybrid systems)

•Micro combined heat and power (Micro $"3)

• Micro turbines

• 3hotovoltaic systems (typically rooftop solar 30)

• 'eciprocating engines

•

mall wind power systems

• tirling engines

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• 8r a combination of the above. /or eample, hybrid photovoltaic, $"3

and battery systems can provide full electric power for single family residences without

etreme storage epenses.

Cogeneration

4istributed cogeneration sources use steam turbines, natural gas6fired fuel cells, micro

turbines or reciprocating engines to turn generators. %he hot ehaust is then used for space or

water heating, or to drive an absorptive chiller for cooling such as air6conditioning. In addition

to natural gas6based schemes, distributed energy projects can also include other renewable or low

carbon fuels including biofuels, biogas, landfill gas, sewage gas, coal bed

methane, syngas and associated petroleum gas.

4elta6ee consultants stated in @;*C that with ?D+ of global sales the fuel cell micro combined

heat and power passed the conventional systems in sales in @;*@. @;.;;; units were sold

in apan in @;*@ overall within the ne /arm project. ith a 1ifetime of around ?;,;;; hours.

/or 3M fuel cell units, which shut down at night, this e#uates to an estimated lifetime of

between ten and fifteen years. /or a price of H@@,?;; before installation. /or @;*C a state subsidy

for -;,;;; units is in place.

In addition, molten carbonate fuel cell and solid oide fuel cells using natural gas, such as the

ones from /uel $ell nergy and the :loom energy server , or waste6to6energy processes such as

the Gate - nergy ystem are used as a distributed energy resource.

Solar power

3hotovoltaics, by far the most important solar technology for distributed generation of solar

power , uses solar cells assembled into solar panels to convert sunlight into electricity. It is a fast6

growing technology doubling its worldwide installed capacity every couple of years. 30

systems range from distributed, residential, and commercial rooftop or building

integrated installations, to large, centrali!ed utility6scale photovoltaic power stations.

%he predominant 30 technology is crystalline silicon, while thin6film solar cell technology

accounts for about *; percent of global photovoltaic deployment. In recent years, 30 technology

has improved its sunlight to electricity conversion efficiency, reduced the installation cost per

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watt as well as its energy paybac& time (3:%) and levelised cost of electricity (1$8), and has

reached grid parity in at least *> different mar&ets in @;*D.

As most renewable energy sources and unli&e coal and nuclear, solar 30 is variable and non6

dispatch able, but has no fuel costs, operating pollution, as well as greatly reduced mining6safetyand operating6safety issues. It produces pea& power around local noon each day and its capacity

factor is around @; percent.

&ind power

ind turbines can be distributed energy resources or they can be built at utility scale. %hese have

low maintenance and low pollution, but distributed wind unli&e utility6scale wind has much

higher costs than other sources of energy. As with solar, wind energy is variable and non6

dispatch able. ind towers and generators have substantial insurable liabilities caused by high

winds, but good operating safety. 4istributed generation from wind hybrid power

systems combines wind power with other 4' systems. 8ne such eample is the integration of

wind turbines into solar hybrid power systems, as wind tends to complement solar because the

pea& operating times for each system occur at different times of the day and year.

H%dro power

Main articles mall hydro and ave power

"ydroelectricity is the most widely used form of renewable energy and its potential has already

been eplored to a large etent or is compromised due to issues such as environmental impacts

on fisheries, and increased demand for recreational access. "owever, using modern @*st century

technology, such as wave power , can ma&e large amounts of new hydropower capacity available,

with minor environmental impact.

Modular and scalable et generation &inetic energy turbines can be deployed in arrays to serve

the needs on a residential, commercial, industrial, municipal or even regional scale. Micro hydro

&inetic generators neither re#uire dams nor impoundments, as they utili!e the &inetic energy of

water motion, either waves or flow. o construction is needed on the shoreline or sea bed, which

minimi!es environmental impacts to habitats and simplifies the permitting process. uch power

generation also has minimal environmental impact and non6traditional micro hydro applications

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can be tethered to eisting construction such as doc&s, piers, bridge abutments, or similar

structures.

&aste'to'energ%

Municipal solid waste (M) and natural waste, such as sewage sludge, food waste and animal

manure will decompose and discharge methane6containing gas that can be collected and used as

fuel in gas turbines or micro turbines to produce electricity as a distributed energy resource.

Additionally, a $alifornia6based company, Gate - nergy 3artners, Inc. has developed a process

that transforms natural waste materials, such as sewage sludge, into biofuel that can be

combusted to power a steam turbine that produces power. %his power can be used in lieu of grid6

power at the waste source (such as a treatment plant, farm or dairy).

"nerg% storage

Main article Grid energy storage

A distributed energy resource is not limited to the generation of electricity but may also include a

device to store distributed energy (4). 4istributed energy storage systems (4) applications

include several types of battery, pumped hydro, compressed air , and thermal energy storage.

P( storage

ArtistFs image of the %esla 3ower wall

$ommon rechargeable battery technologies used in todayFs 30 systems include, the valve

regulated lead6acid battery (leadacid battery), nic&elcadmium and lithium6ion batteries.

$ompared to the other types, lead6acid batteries have a shorter lifetime and lower energy density.

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"owever, due to their high reliability, low self6discharge (D?+ per year) as well as low

investment and maintenance costs, they are currently the predominant technology used in small6

scale, residential 30 systems, as lithium6ion batteries are still being developed and about C.-

times as epensive as lead6acid batteries. /urthermore, as storage devices for 30 systems are

stationary, the lower energy and power density and therefore higher weight of lead6acid batteries

are not as critical as for electric vehicles.

"owever, lithium6ion batteries, such as the %esla 3ower wall, have the potential to replace lead6

acid batteries in the near future, as they are being intensively developed and lower prices are

epected due to economies of scale provided by large production facilities such as

the Gigafactory *. In addition, the 1i6ion batteries of plug6in electric cars may serve as future

storage devices, since most vehicles are par&ed an average of >- percent of the time, their

batteries could be used to let electricity flow from the car to the power lines and bac&. 8ther

rechargeable batteries that are considered for distributed 30 systems include, sodiumsulfur and

vanadium batteries, two prominent types of a molten salt and a flow battery, respectively.

(ehicle'to'grid

/uture generations of electric vehicles may have the ability to deliver power from the battery in

a vehicle6to6grid into the grid when needed. An electric vehicle networ& has the potential to

serve as a 4.

)l%wheels

An advanced flywheel energy storage (/) stores the electricity generated from distributed

resources in the form of angular &inetic energy by accelerating a rotor (flywheel) to a very high

speed of about @;,;;; to over -;,;;; rpm in a vacuum enclosure. /lywheels can respond #uic&ly

as they store and feedbac& electricity into the grid in a matter of seconds.

Integration with the grid

/or reasons of reliability, distributed generation resources would be interconnected to the same

transmission grid as central stations. 0arious technical and economic issues occur in the

integration of these resources into a grid. %echnical problems arise in the areas of power #uality,

voltage stability, harmonics, reliability, protection, and control. :ehavior of protective devices on

the grid must be eamined for all combinations of distributed and central station generation. A

large scale deployment of distributed generation may affect grid6wide functions such as

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fre#uency control and allocation of reserves. As a result smart grid functions, virtual power

plants and grid energy storage such as power to gas stations are added to the grid.

ach distributed generation resource has its own integration issues. olar 30 and wind power

both have intermittent and unpredictable generation, so they create many stability issues for voltage and fre#uency. %hese voltage issues affect mechanical grid e#uipment, such as load tap

changers, which respond too often and wear out much more #uic&ly than utilities

anticipated. Also, without any form of energy storage during times of high solar generation,

companies must rapidly increase generation around the time of sunset to compensate for the loss

of solar generation. %his high ramp rate produces what the industry terms the =duc& curve= that is

a major concern for grid operators in the future. torage can fi these issues if it can be

implemented. /lywheels have shown to provide ecellent fre#uency regulation. hort term use

batteries, at a large enough scale of use, can help to flatten the duc& curve and prevent generator

use fluctuation and can help to maintain voltage profile. "owever, cost is a major limiting factor

for energy storage as each techni#ue is prohibitively epensive to produce at scale and

comparatively not energy dense compared to li#uid fossil fuels finally, another necessary method

of aiding in integration of photovoltaics for proper distributed generation is in the use

of intelligent hybrid inverters.

Cost *actors

$o generators are also more epensive per watt than central generators. %hey find favor because

most buildings already burn fuels, and the cogeneration can etract more value from the fuel .

1ocal production has no electricity transmission losses on long distance power lines or energy

losses from the oule effect in transformers where in general J6*-+ of the energy is lost (see

also cost of electricity by source).

ome larger installations utili!e combined cycle generation. 5sually this consists of a gas

turbine whose ehaust boils water for a steam turbine in a 'an&ine cycle. %he condenser of the

steam cycle provides the heat for space heating or an absorptive chiller . $ombined cycle plants

with cogeneration have the highest &nown thermal efficiencies, often eceeding J-+.

In countries with high pressure gas distribution, small turbines can be used to bring the gas

pressure to domestic levels whilst etracting useful energy. If the 5K were to implement this

countrywide an additional @6D Ge would become available. (ote that the energy is already

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being generated elsewhere to provide the high initial gas pressure 6 this method simply

distributes the energy via a different route.)

Micro grid

3icture of a local micro grid, the endai Micro grid, located on the campus of %oho&u /u&ushi

5niversity in endai $ity in the %oho&u district in apan

A micro grid is a locali!ed grouping of electricity generation, energy storage, and loads that

normally operate connected to a traditional centrali!ed grid (macro grid). %his single point of common coupling with the macro grid can be disconnected. %he micro grid can then function

autonomously. Generation and loads in a micro grid are usually interconnected at low voltage

and it can operate in 4$, A$ or the combination of both. According to the recent developments

in renewable energy systems, storage systems, and the nature of newly emerging loads, there

have been some researches for comparing the efficiency and performance of A$ and 4$ micro

grids. /rom the point of view of the grid operator, a connected micro grid can be controlled as if

it were one entity.

Micro grid generation resources can include stationary batteries, fuel cells, solar, wind, or other

energy sources. %he multiple dispersed generation sources and ability to isolate the micro grid

from a larger networ& would provide highly reliable electric power. 3roduced heat from

generation sources such as micro turbines could be used for local process heating or space

heating, allowing fleible tradeoff between the needs for heat and electric power.

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Micro6grids were proposed in the wa&e of the uly @;*@ India blac&out

mall micro6grids covering C;-; &m radius

mall power stations of -*; M to serve the micro6grids

Generate power locally to reduce dependence on long distance transmission lines and cut

transmission losses.

G%M 'esearch forecasts micro grid capacity in the 5nited tates will eceed *.J gigawatts by

@;*J.

Comm+nication in D"R s%stems

I$ ?*J-;6L6D@; is under development as a part of I$ ?*J-; standards, which deals with the

complete object models as re#uired for 4' systems. It uses communication services mapped

to MM as per I$ ?*J-;6J6* standard.

83$ is also used for the communication between different entities of 4' system.

4istributed generation (4G) refers to power generation at the point of consumption. Generating

power on6site, rather than centrally, eliminates the cost, compleity, interdependencies, andinefficiencies associated with transmission and distribution. 1i&e distributed computing (i.e. the

3$) and distributed telephony (i.e. the mobile phone), distributed generation shifts control to the

consumer.

The &orld Needs Distrib+ted $eneration that is Clean and Contin+o+s

"istorically, distributed generation meant combustion generators (e.g. diesel gensets). %hey were

affordable, and in some cases reliable, but they were not clean. hile many people will toleratedirty generation thousands of miles away from them, they thin& twice when it is outside their

bedroom window or office door.

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'ecently, solar has become a popular distributed generation option. Although the output is clean

it is also intermittent, ma&ing it an incomplete strategy for businesses that need power around the

cloc&, including when the sun is not shining.

The ,ene*its o* ,loom "nerg%

:loom nergy is a 4istributed Generation solution that is clean and reliable and affordable all at

the same time .:loomFs nergy ervers can produce clean energy @D hours per day, C?- days per

year, generating more electrons than intermittent solutions, and delivering faster

paybac& and greater environmental benefits for the customer. And while other 4G systems may

re#uire lengthy installations, sunny locations, or demand for consistent @D9L9C?- heat load,

:loomFs systems are easy and fast to install, practically anywhere.

As 4istributed Generation moves to the forefront of corporate consciousness, :loom nergy

ervers are perfectly designed to meet the demanding needs of todays economically and

environmentally minded companies.

4istributed generation is an approach that employs small6scale technologies to produce

electricity close to the end users of power. 4G technologies often consist of modular (and

sometimes renewable6energy) generators, and they offer a number of potential benefits. In many

cases, distributed generators can provide lower6cost electricity and higher power reliability and

security with fewer environmental conse#uences than can traditional power generators.

In contrast to the use of a few large6scale generating stations located far from load centers66the

approach used in the traditional electric power paradigm664G systems employ numerous, but

small plants and can provide power onsite with little reliance on the distribution and transmission

grid. 4G technologies yield power in capacities that range from a fraction of a &ilowatt &N to

about *;; megawatts MN. 5tility6scale generation units generate power in capacities thatoften reach beyond *,;;; M.

Classic "lectricit% Paradigm66$entral 3ower tation Model

http://www.bloomenergy.com/fuel-cell/energy-server/http://www.bloomenergy.com/customer-fuel-cell/walmart-renewable-energy/http://www.bloomenergy.com/customer-fuel-cell/walmart-renewable-energy/http://www.bloomenergy.com/customer-fuel-cell/staples-environmental-impact/http://www.bloomenergy.com/fuel-cell/energy-server/http://www.bloomenergy.com/customer-fuel-cell/walmart-renewable-energy/http://www.bloomenergy.com/customer-fuel-cell/walmart-renewable-energy/http://www.bloomenergy.com/customer-fuel-cell/staples-environmental-impact/


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%he current model for electricity generation and distribution in the 5nited tates is dominated by

centrali!ed power plants. %he power at these plants is typically combustion (coal, oil, and

natural) or nuclear generated. $entrali!ed power models, li&e this, re#uire distribution from the

center to outlying consumers. $urrent substations can be anywhere from *;s to *;;s of miles

away from the actual users of the power generated. %his re#uires transmission across the

distance.

%his system of centrali!ed power plants has many disadvantages. In addition to the transmission

distance issues, these systems contribute to greenhouse gas emission, the production of nuclear

waste, inefficiencies and power loss over the lengthy transmission lines, environmental

distribution where the power lines are constructed, and security related issues.

Many of these issues can be mediated through distributed energies. :y locating, the source near

or at the end6user location the transmission line issues are rendered obsolete. 4istributed

generation (4G) is often produced by small modular energy conversion units li&e solar panels.

As has been demonstrated by solar panel use in the 5nited tates, these units can be stand6alone

or integrated into the eisting energy grid. /re#uently, consumers who have installed solar panels

will contribute more to the grid than they ta&e out resulting in a win6win situation for both the

power grid and the end6user.


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Classic "lectricit% Paradigm

Distrib+ted $eneration -D$. "lectricit% Paradigm

&hat are Some "#amples o* Distrib+ted $eneration Technologies/

4istributed generation ta&es place on two6levels the local level and the end6point level. 1ocal

level power generation plants often include renewable energy technologies that are site specific,

such as wind turbines, geothermal energy production, solar systems (photovoltaic and

combustion), and some hydro6thermal plants. %hese plants tend to be smaller and less centrali!ed

than the traditional model plants. %hey also are fre#uently more energy and cost efficient and

more reliable. ince these local level 4G producers often ta&e into account the local contet, the

usually produce less environmentally damaging or disrupting energy than the larger central

model plants.


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&ind T+rbines at ,+**alo Mo+ntain0 TN

Photovoltaic -Solar. Panels help Power this "lementar% School in )airban1s0 Alas1a


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A 233 1& Capstone Micro t+rbine at a Demonstration Pro4ect at the a1 Ridge National

5aborator% in a1 Ridge0 TN

3hosphorus fuel cells also provide an alternative route to a 4G technology. %hese are not asenvironmentally reliant as the previously mentioned technologies. %hese fuel cells are able to

provide electricity through a chemical process rather than a combustion process. %his process

produces little particulate waste.

At the end6point level the individual energy consumer can apply many of these same

technologies with similar effects. 8ne 4G technology fre#uently employed by end6point users is

the modular internal combustion engine. /or eample, some departments here at 0irginia %ech

use these power generators as a bac&up to the normal power grid. %hese modular internal

combustion engines can also be used to bac&up '0s and homes. As many of these familiar

eamples show 4G technologies can operate as isolated =islands= of electric energy production

or they can serve as small contributors to the power grid.


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Droop control

In electrical power generation, 4roop peed $ontrol is a speed control mode of a prime

mover driving a generator connected to an electrical grid. %his mode allows synchronous

generators to run in parallel, so that loads are shared among generators in proportion to their

power rating.

%he fre#uency of a synchronous generator is given by

where

/ O /re#uency (in "!),

3 O number of poles,

O peed of generator (in '3M)

%he fre#uency (/) of a synchronous generator is directly proportional to its speed (). hen

multiple synchronous generators are connected in parallel to electrical grid, the fre#uency is

fied by the grid, since individual power output of each generator will be small compared to theload on a large grid. ynchronous generators connected to the grid run at various speeds but they

all run at the same fre#uency because they differ in the number of poles (3).

A speed reference as percentage of actual speed is set in this mode. As the generator is loaded

from no load to base load, the actual speed of the prime mover tend to decrease. In order to

increase the power output in this mode, the prime mover speed reference is increased. :ecause

the actual prime mover speed is fied by the grid, this difference in speed reference and actual

speed of the prime mover is used to increase the flow of wor&ing fluid (fuel, steam, etc.) to the prime mover, and hence power output is increased. %he reverse will be true for decreasing power

output. %he prime mover speed reference is always greater than actual speed of the prime mover.

%he actual speed of the prime mover is allowed to =droop= or decrease with respect to the

reference, and so the name.

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/or eample, if the turbine is rated at C;;; rpm, and the machine speed reduces from C;;; rpm

to @JJ; rpm when it is loaded from no load to base load, then the droop + is given by

O(C;;; C*@;) 9 C;;;

O D+

O (C;;; @JJ;) 9 C;;;

O D+

In this case, speed reference will be *;D+ and actual speed will be *;;+. /or every *+ change

in the turbine speed reference, the power output of the turbine will change by @-+ of rated for a

unit with a D+ droop setting.

4roop is therefore epressed as the percentage change in (design) speed re#uired for *;;+

governor action.

/or eample, how fuel flow is increased or decreased in a G6design heavy duty gas turbine can

be given by the formula,

/' O (/K'@ P (%'6%")) Q /K'*

here,

/' O /uel tro&e 'eference (/uel supplied to Gas %urbine) for droop mode

%' O %urbine peed 'eference

%" O Actual %urbine peed

/K'@ O $onstant

/K'* O $onstant

As fre#uency is fied on the grid, and so actual turbine speed is also fied, the increase in turbine

speed reference will increase the error between reference and actual speed. As the difference


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increases, fuel flow is increased to increase power output, and vice versa. %his type of control is

referred to as =straight proportional= control. If the entire grid tends to be overloaded, the grid

fre#uency and hence actual speed of generator will decrease. All units will see an increase in the

speed error, and so increase fuel flow to their prime movers and power output. In this way droop

speed control mode also helps to hold a stable grid fre#uency. %he amount of power produced is

strictly proportional to the error between the actual turbine speed and speed reference. %he above

formula is nothing but the e#uation of a straight line -% 6 m# 7 8..

Multiple synchronous generators having e#ual + droop setting connected to a grid will share the

change in grid load in proportion of their base load.

/or stable operation of the electrical grid of orth America, power plants typically operate with a

four or five percent speed droop. ith -+ droop the full6load speed is *;;+ and the no6load

speed is *;-+. %his is re#uired for the stable operation of the net without hunting and dropouts

of power plants. ormally the changes in speed are minor due to inertia of the total rotating mass

of all generators and motors running in the net. Adjustments in power output are made by slowly

raising the droop curve by increasing the spring pressure on a centrifugal governor or by

an engine control unit adjustment. Generally this is a basic system re#uirement for all power

plants because the older and newer plants have to be compatible in response to the instantaneous

changes in fre#uency without depending on outside communication. 0oltage control of several

power sources is not practical because there would not be any independent feedbac&, resulting in

the total load being put on one power plant.

$ontiguous 5nited tates power transmission grid consists of C;;,;;; &m of lines operated by

-;; companies.

It can be mathematically shown that if all machines synchroni!ed to a system have the same

droop speed control, they will share load proportionate to the machine ratings.DN

%he thousands of A$ generators are running synchronously with the power grid which acts li&e

an infinite sin&. et to the inertia given by the parallel operation of synchronous generators,

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-N the fre#uency speed droop is the primary instantaneous parameter in control of an individual

power plantFs power output (&).

S is the ratio of fre#uency deviation when comparing the load versus the nominal fre#uency.

4roop control is a control strategy commonly applied to generators for primary fre#uency

control (and occasionally voltage control) to allow parallel generator operation (e.g. load

:ac&ground

'ecall that the active and reactive power transmitted across a lossless line are

ince the power angle is typically small, we can simplify this further by using the

approimations and

/rom the above, we can see that active power has a large influence on the power angle and

reactive power has a large influence on the voltage difference. 'estated, by controlling active

and reactive power, we can also control the power angle and voltage. e also &now from

the swing e#uation that fre#uency is related to the power angle, so by controlling active power,

we can therefore control fre#uency.

%his forms the basis of fre#uency and voltage droop control where active and reactive power are

adjusted according to linear characteristics, based on the following control e#uations

https://en.wikipedia.org/wiki/Droop_speed_control#cite_note-5https://en.wikipedia.org/wiki/KWhttp://www.openelectrical.org/wiki/index.php?title=Frequency_Control&action=edit&redlink=1http://www.openelectrical.org/wiki/index.php?title=Frequency_Control&action=edit&redlink=1http://www.openelectrical.org/wiki/index.php?title=AC_Power_Transmission#Lossless_Line_.28Classical_Approach.29http://www.openelectrical.org/wiki/index.php?title=Swing_Equation&action=edit&redlink=1https://en.wikipedia.org/wiki/Droop_speed_control#cite_note-5https://en.wikipedia.org/wiki/KWhttp://www.openelectrical.org/wiki/index.php?title=Frequency_Control&action=edit&redlink=1http://www.openelectrical.org/wiki/index.php?title=Frequency_Control&action=edit&redlink=1http://www.openelectrical.org/wiki/index.php?title=AC_Power_Transmission#Lossless_Line_.28Classical_Approach.29http://www.openelectrical.org/wiki/index.php?title=Swing_Equation&action=edit&redlink=1


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here is the system fre#uency

is the base fre#uency

is the fre#uency droop control setting

is the active power of the unit

is the base active power of the unit

is the voltage at the measurement location

is the base voltage

is the reactive power of the unit

is the base reactive power of the unit

is the voltage droop control setting

%hese two e#uations are plotted in the characteristics below

0oltage droop characteristic

%he fre#uency droop characteristic above can be interpreted as follows when fre#uency falls

from f ; to f , the power output of the generating unit is allowed to increase from P ; to P . A falling

fre#uency indicates an increase in loading and a re#uirement for more active power. Multiple

parallel units with the same droop characteristic can respond to the fall in fre#uency by

increasing their active power outputs simultaneously. %he increase in active power output will

counteract the reduction in fre#uency and the units will settle at active power outputs and

fre#uency at a steady6state point on the droop characteristic. %he droop characteristic therefore


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allows multiple units to share load without the units fighting each other to control the load

(called =hunting=).

%he same logic above can be applied to the voltage droop characteristic.

Droop Control Set points

4roop settings are normally #uoted in + droop. %he setting indicates the percentage amount the

measured #uantity must change to cause a *;;+ change in the controlled #uantity. /or eample,

a -+ fre#uency droop setting means that for a -+ change in fre#uency, the unitFs power output

changes by *;;+. %his means that if the fre#uency falls by *+, the unit with a -+ droop setting

will increase its power output by @;+.

%he short video below shows some eamples of fre#uency (speed) droop

5imitations o* Droop Control

/re#uency droop control is useful for allowing multiple generating units to automatically change

their power outputs based on dynamically changing loads. "owever, consider what happens

when there is a significant contingency such as the loss of a large generating unit. If the system

remains stable, all the other units would pic& up the slac&, but the droop characteristic allows the

fre#uency to settle at a steady6state value below its nominal value (for eample, D>.L"! or

->.L"!). $onversely, if a large load is tripped, then the fre#uency will settle at a steady6statevalue above its nominal value (for eample, -;.-"! or ?;.-"!).

8ther controllers are therefore necessary to bring the fre#uency bac& to its nominal value (i.e.

-;"! or ?; "!), which are called secondary and tertiary fre#uency controllers.

%he micro sources can not only provide A$ power in grid6connected mode, but also control the

fre#uency and voltage for the micro grid load in island mode. :y using the voltage and

fre#uency droop control method, the micro sources can reali!e the Rplug6and6playS concept

share the load automatically by using only the local information, i.e. the voltage, fre#uency,

instead of the communications with the other micro sources or the micro grid central control

system. %he micro sources can wor& in parallel to the grid or as an island. hen the micro grid

system disconnects from the grid, caused by the gridFs short current or power failure, the micro

sources can &eep on wor&ing for the micro grid loads, without restart process.


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Micro grid -M$.

What is a micro grid?

A micro grid is a local energy grid with control capability, which means it can disconnect from

the traditional grid and operate autonomously.

How does a micro grid work?

%o understand how a micro grid wor&s, you first have to understand how the grid wor&s.

%he grid connects homes, businesses and other buildings to central power sources, which allow

us to use appliances, heating9cooling systems and electronics. :ut this interconnectedness means

that when part of the grid needs to be repaired, everyone is affected.

%his is where a micro grid can help. A micro grid generally operates while connected to the grid,

but importantly, it can brea& off and operate on its own using local energy generation in times of

crisis li&e storms or power outages, or for other reasons.

A micro grid can be powered by distributed generators, batteries, and9or renewable resources li&e

solar panels. 4epending on how it7s fueled and how its re#uirements are managed, a microgrid

might run indefinitely.

How does a micro grid connect to the grid?

A micro grid connects to the grid at a point of common coupling that maintains voltage at the

same level as the main grid unless there is some sort of problem on the grid or other reason to

disconnect. A switch can separate the micro grid from the main grid automatically or manually,

and it then functions as an island.

Why would a community choose to connect to micro grids?

A micro grid not only provides bac&up for the grid in case of emergencies, but can also be used

to cut costs, or connect to a local resource that is too small or unreliable for traditional grid use.

A micro grid allows communities to be more energy independent and, in some cases, more

environmentally friendly.


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How much can a micro grid power?

A micro grid comes in a variety of designs and si!es. A micro grid can power a single facility li&e

the anta 'ita ail micro grid in 4ublin, $alifornia. 8r a micro grid can power a larger area. /or

eample, in /ort $ollins, $olorado, a micro grid is part of a larger goal to create an entire districtthat produces the same amount of energy it consumes.

A micro grid is an electrical system that includes multiple loads and distributed energy resources

that can be operated in parallel with the broader utility grid or as an electrical island.

4istributed generation, also called on6site generation, dispersed generation, embedded

generation, decentrali!ed generation, decentrali!ed energy, distributed energy or district energy,

generates electricity from many small energy sources. Most countries generate electricity in large

centrali!ed facilities, such as fossil fuel (coal, gas powered), nuclear, large solar power plants or

hydropower plants. %hese plants have ecellent economies of scale, but usually transmit

electricity long distances and can negatively affect the environment. 4istributed generation

allows collection of energy from many sources and may give lower environmental impacts and

improved security of supply., 4istributed energy, also district or decentrali!ed energy is

generated or stored by a variety of small, grid6connected devices referred to as distributed energy

resources (4') or distributed energy resource systems. $onventional power stations, such as

coal6fired, gas and nuclear powered plants, as well as hydroelectric dams and large6scale solar

power stations, are centrali!ed and often re#uire electricity to be transmitted over long distances.

:y contrast, 4' systems are decentrali!ed, modular and more fleible technologies, that are

located close to the load they serve, albeit having capacities of only *; megawatts (M) or

less.4' systems typically use renewable energy sources, including, but not limited to, biomass,

biogas, solar power, wind power, geothermal power and increasingly play an important role for

the electric power distribution system. A grid6connected device for electricity storage can also be

classified as a 4' system, and is often called a distributed energy storage system (4). :y

means of an interface, 4' systems can be managed and coordinated within a smart grid.

4istributed generation and storage enables collection of energy from many sources and may

lower environmental impacts and improve security of supply.

Reegle De*inition

http://building-microgrid.lbl.gov/santa-rita-jailhttp://building-microgrid.lbl.gov/fort-collinshttp://building-microgrid.lbl.gov/santa-rita-jailhttp://building-microgrid.lbl.gov/fort-collins


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o reegle definition available, o reegle definition available., 4istributed generation, also called

on6site generation, dispersed generation, embedded generation, decentrali!ed generation,

decentrali!ed energy or distributed energy, generates electricity from many small energy sources.

$urrently, industrial countries generate most of their electricity in large centrali!ed facilities,

such as fossil fuel nuclear or hydropower plants. %hese plants have ecellent economies of scale,

but usually transmit electricity long distances and negatively affect the environment. Most plants

are built this way due to a number of economic, health < safety, logistical, environmental,

geographical and geological factors. /or eample, coal power plants are built away from cities to

prevent their heavy air pollution from affecting the populace. In addition, such plants are often

built near collieries to minimi!e the cost of transporting coal. "ydroelectric plants are by their

nature limited to operating at sites with sufficient water flow. Most power plants are often

considered to be too far away for their waste heat to be used for heating buildings. 1ow pollution

is a crucial advantage of combined cycle plants that burn natural gas. %he low pollution permits

the plants to be near enough to a city to be used for district heating and cooling. 4istributed

generation is another approach. It reduces the amount of energy lost in transmitting electricity

because the electricity is generated very near where it is used, perhaps even in the same building.

%his also reduces the si!e and number of power lines that must be constructed. %ypical

distributed power sources in a /eed6in %ariff (/I%) scheme have low maintenance, low pollution

and high efficiencies. In the past, these traits re#uired dedicated operating engineers and large

comple plants to reduce pollution. "owever, modern embedded systems can provide these traits

with automated operation and renewables, such as sunlight, wind and geothermal. %his reduces

the si!e of power plant that can show a profit.

A micro grid is a discrete energy system consisting of distributed energy sources (including

demand management, storage, and generation) and loads capable of operating in parallel with, or

independently from, the main power grid. %he primary purpose is to ensure local, reliable, and

affordable energy security for urban and rural communities, while also providing solutions for

commercial, industrial, and federal government consumers. :enefits that etend to utilities and

the community at large include lowering greenhouse gas (G"G) emissions and lowering stress

on the transmission and distribution system.


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In many respects, micro grids are smaller versions of the traditional power grid. 1i&e current

electrical grids, they consist of power generation, distribution, and controls such as voltage

regulation and switch gears. "owever, micro grids differ from traditional electrical grids by

providing a closer proimity between power generation and power use, resulting in efficiency

increases and transmission reductions. Micro grids also integrate with renewable energy sources

such as solar, wind power, small hydro, geothermal, waste6to6energy, and combined heat and

power ($"3) systems.

Micro grids perform dynamic control over energy sources, enabling autonomous and automatic

self6healing operations. 4uring normal or pea& usage, or at times of the primary power grid

failure, a micro grid can operate independently of the larger grid and isolate its generation nodes

and power loads from disturbance without affecting the larger gridFs integrity. Micro gridsinteroperate with eisting power systems, information systems, and networ& infrastructure, and

are capable of feeding power bac& to the larger grid during times of grid failure or power

outages.

hat are mart Micro gridsT

Micro grids are modern, small6scale versions of the centrali!ed electricity system. %hey achieve

specific local goals, such as reliability, carbon emission reduction, diversification of energy

sources, and cost reduction, established by the community being served. 1i&e the bul& power

grid, smart micro grids generate, distribute, and regulate the flow of electricity to consumers, but

do so locally. mart micro grids are an ideal way to integrate renewable resources on the

community level and allow for customer participation in the electricity enterprise. %hey form the

building bloc&s of the 3erfect 3ower ystem.

http://galvinpower.org/state-activities/illinoishttp://galvinpower.org/state-activities/illinoishttp://galvinpower.org/resources/microgrid-workshophttp://galvinpower.org/resources/microgrid-workshophttp://galvinpower.org/about-perfect-power/introduction-perfect-power-fact-sheethttp://galvinpower.org/state-activities/illinoishttp://galvinpower.org/state-activities/illinoishttp://galvinpower.org/resources/microgrid-workshophttp://galvinpower.org/resources/microgrid-workshophttp://galvinpower.org/about-perfect-power/introduction-perfect-power-fact-sheet


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"ere at the Galvin lectricity InitiativeFs Micro grid "ub, you will find a comprehensive set of

resources on micro grids, collected from our partners and from across the web. 5se the

navigation system at the left to browse through all of our micro grid materials, and if you have

suggestions for additional content, please let us &now. If you are a member of the media see&ing

information on micro grids, be sure to view our press &itin addition to the other resources.

Power converters

In electrical engineering, power engineering and the electric power industry, power conversion is

converting electric energy from one form to another, converting between A$ and 4$, or just

changing the voltage or fre#uency, or some combination of these. A power converter is an

electrical or electro6mechanical device for converting electrical energy. %his could be as simple

as a transformer to change the voltage of A$ power, but also includes far more comple systems.

%he term can also refer to a class of electrical machinery that is used to convert

one fre#uency of alternating current into another fre#uency.

3ower conversion systems often incorporate redundancy and voltage regulation.

8ne way of classifying power conversion systems is according to whether the input and output

are alternating current (A$) or direct current(4$), thus

• 4$ to 4$

• 4$6to64$ converter

• 0oltage regulator

• 1inear regulator

• A$ to 4$

• 'ectifier

• Mains power supply unit (35)

• 4$ to A$

• Inverter

• A$ to A$

• %ransformer 9autotran

• 0oltage converter

• 0oltage regulator

• $ycloconverter

http://www.galvinpower.org/microgrid-press-kithttps://en.wikipedia.org/wiki/Electrical_engineeringhttps://en.wikipedia.org/wiki/Power_engineeringhttps://en.wikipedia.org/wiki/Electric_power_industryhttps://en.wikipedia.org/wiki/Electric_energyhttps://en.wikipedia.org/wiki/Alternating_currenthttps://en.wikipedia.org/wiki/Direct_currenthttps://en.wikipedia.org/wiki/Voltagehttps://en.wikipedia.org/wiki/Voltagehttps://en.wikipedia.org/wiki/Frequencyhttps://en.wikipedia.org/wiki/Electro-mechanicalhttps://en.wikipedia.org/wiki/Electro-mechanicalhttps://en.wikipedia.org/wiki/Transformerhttps://en.wikipedia.org/wiki/Transformerhttps://en.wikipedia.org/wiki/Voltagehttps://en.wikipedia.org/wiki/Voltagehttps://en.wikipedia.org/wiki/Alternating_currenthttps://en.wikipedia.org/wiki/Utility_frequencyhttps://en.wikipedia.org/wiki/Utility_frequencyhttps://en.wikipedia.org/wiki/Alternating_currenthttps://en.wikipedia.org/wiki/Alternating_currenthttps://en.wikipedia.org/wiki/Redundancy_(engineering)https://en.wikipedia.org/wiki/Redundancy_(engineering)https://en.wikipedia.org/wiki/Voltage_regulationhttps://en.wikipedia.org/wiki/Alternating_currenthttps://en.wikipedia.org/wiki/Direct_currenthttps://en.wikipedia.org/wiki/Direct_currenthttps://en.wikipedia.org/wiki/DC-to-DC_converterhttps://en.wikipedia.org/wiki/Voltage_regulatorhttps://en.wikipedia.org/wiki/Linear_regulatorhttps://en.wikipedia.org/wiki/Rectifierhttps://en.wikipedia.org/wiki/Power_supplyhttps://en.wikipedia.org/wiki/Power_inverterhttps://en.wikipedia.org/wiki/AC/AC_Converterhttps://en.wikipedia.org/wiki/Transformerhttps://en.wikipedia.org/wiki/Autotransformerhttps://en.wikipedia.org/wiki/Voltage_converterhttps://en.wikipedia.org/wiki/Voltage_regulatorhttps://en.wikipedia.org/wiki/Cycloconverterhttp://www.galvinpower.org/microgrid-press-kithttps://en.wikipedia.org/wiki/Electrical_engineeringhttps://en.wikipedia.org/wiki/Power_engineeringhttps://en.wikipedia.org/wiki/Electric_power_industryhttps://en.wikipedia.org/wiki/Electric_energyhttps://en.wikipedia.org/wiki/Alternating_currenthttps://en.wikipedia.org/wiki/Direct_currenthttps://en.wikipedia.org/wiki/Voltagehttps://en.wikipedia.org/wiki/Frequencyhttps://en.wikipedia.org/wiki/Electro-mechanicalhttps://en.wikipedia.org/wiki/Transformerhttps://en.wikipedia.org/wiki/Voltagehttps://en.wikipedia.org/wiki/Alternating_currenthttps://en.wikipedia.org/wiki/Utility_frequencyhttps://en.wikipedia.org/wiki/Alternating_currenthttps://en.wikipedia.org/wiki/Redundancy_(engineering)https://en.wikipedia.org/wiki/Voltage_regulationhttps://en.wikipedia.org/wiki/Alternating_currenthttps://en.wikipedia.org/wiki/Direct_currenthttps://en.wikipedia.org/wiki/DC-to-DC_converterhttps://en.wikipedia.org/wiki/Voltage_regulatorhttps://en.wikipedia.org/wiki/Linear_regulatorhttps://en.wikipedia.org/wiki/Rectifierhttps://en.wikipedia.org/wiki/Power_supplyhttps://en.wikipedia.org/wiki/Power_inverterhttps://en.wikipedia.org/wiki/AC/AC_Converterhttps://en.wikipedia.org/wiki/Transformerhttps://en.wikipedia.org/wiki/Autotransformerhttps://en.wikipedia.org/wiki/Voltage_converterhttps://en.wikipedia.org/wiki/Voltage_regulatorhttps://en.wikipedia.org/wiki/Cycloconverter


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• witched6mode power supply • 0ariable6fre#uency tr

%here are also devices and methods to convert between power systems designed for single and

three6phase operation.

%he standard power fre#uency varies from country to country, and sometimes within a country.

In orth America and northern outh America it is usually ?; hert! ("!), but in many other parts

of the world, is usually -; "!. Aircraft often use D;; "! power, so -; "! or ?; "! to D;; "!

fre#uency conversion is needed for use in the ground power unit used to power the airplane

while it is on the ground.

$ertain speciali!ed circuits, such as the fly bac& transformer for a $'%, can also be considered

power converters.

$onsumer electronics usually include an A$ adapter (a type of power supply) to convert mains6

voltage A$ current to low6voltage 4$ suitable for consumption by microchips.

$onsumer voltage converters (also &nown as =travel converters=) are used when travelling

between countries that use U*@; 0 vs. U@D; 0 A$ mains power. (%here are also consumer

=adapters= which merely form an electrical connection between two differently shaped A$

power plugs and soc&ets, but these change neither voltage nor fre#uency.)

%he tas& of a power converter is to process and control the flow of electric energy by supplying

voltages and currents in a form that is optimally suited for the user loads. nergy was initially

converted in electromechanical converters (mostly rotating machines). %oday, with the

development and the mass production of power semiconductors, static power converters find

applications in numerous domains and especially in particle accelerators. %hey are smaller and

lighter and their static and dynamic performances are better.

Reactive power sharing

/or a coordinated integration of the increasing amount of distributed generators in the

distribution networ&, the micro grid has been presented. /or the islanded operating condition of

the micro grid, the conventional approaches for grid control are no longer applicable as the micro

grid characteristics differ significantly from those of conventional power systems. %herefore, in

https://en.wikipedia.org/wiki/Switched-mode_power_supplyhttps://en.wikipedia.org/wiki/Variable-frequency_transformerhttps://en.wikipedia.org/wiki/Hertzhttps://en.wikipedia.org/wiki/Flyback_transformerhttps://en.wikipedia.org/wiki/Flyback_transformerhttps://en.wikipedia.org/wiki/Cathode_ray_tubehttps://en.wikipedia.org/wiki/Cathode_ray_tubehttps://en.wikipedia.org/wiki/AC_adapterhttps://en.wikipedia.org/wiki/Power_supplyhttps://en.wikipedia.org/wiki/Voltage_converterhttps://en.wikipedia.org/wiki/Voltage_converterhttps://en.wikipedia.org/wiki/AC_power_plugs_and_socketshttps://en.wikipedia.org/wiki/AC_power_plugs_and_socketshttps://en.wikipedia.org/wiki/AC_power_plugs_and_socketshttps://en.wikipedia.org/wiki/Switched-mode_power_supplyhttps://en.wikipedia.org/wiki/Variable-frequency_transformerhttps://en.wikipedia.org/wiki/Hertzhttps://en.wikipedia.org/wiki/Flyback_transformerhttps://en.wikipedia.org/wiki/Cathode_ray_tubehttps://en.wikipedia.org/wiki/AC_adapterhttps://en.wikipedia.org/wiki/Power_supplyhttps://en.wikipedia.org/wiki/Voltage_converterhttps://en.wikipedia.org/wiki/AC_power_plugs_and_socketshttps://en.wikipedia.org/wiki/AC_power_plugs_and_sockets


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this paper, the reactive power control by means of a reactive power9fre#uency droop control

strategy is studied in an islanded micro grid. %he active power on the other hand, is controlled by

using a droop control strategy of the dc6bus voltage to the grid voltage amplitude. It is shown

that the combination of the aforementioned control methods gives good results concerning

reactive power sharing and avoidance of circulating currents. Also, a reactive power limiting

procedure is incorporated in the droop controller.

hen paralleling multiple inverters that are capable of operating as an island, the inverters

typically employ the droop control scheme. %raditional droop control enables the decentrali!ed

regulation of the local voltage and fre#uency of the micro grid by the inverters. %he droop

method also enables the inverters to share the real and reactive power re#uired by the loads. %his

paper focuses on some of the limitations of parallel islanded single phase inverters using droopcontrol. Algorithms with the aim to address the following limitations in islanded operation were

proposed reactive power sharing and reduction of the voltage harmonic distortion at the point of

common coupling (3$$).

A distributed power system consisting of two uninterrupted power supplies (53) is investigated

in this paper. 3arallel operation of the two sources increases the established power rating of the

system. 8ne of the sources can supply the system even when the other system is disconnected

due to some faults, and this is an important feature. %he control algorithm ma&es sure that the

total load is shared between the supplies in accordance with their rated power levels, and the

fre#uency of the supplies is restored to the rated values after the transitions. As the 53s operate

at an optimum power level, losses and faults due to overloading are prevented. %he units safely

operate without any means of communication between each other.

Control o* S%nchrono+s $enerators with Droop and Cross'C+rrent Compensation9

%he ecitation of a synchronous generator is usually done by an A0' (Automatic 0oltage

'egulator) that uses generator voltage and9or current as inputs in order to control its output to a

pre6set value.

A0's include different control modes to optimise performance depending on whether the


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generator is connected to the grid, or in island mode. %herefore, they can be set to maintain the

voltage, the 3/ or the reactive power.

In this report, we will analyse the principle of operation of the voltage control mode of the A0',

&nown as droop compensation, when one or more generators operate in island mode or are

connected to the grid. :ased on droop control limitations, we will study techni#ues to improve

its performance, and compare it with the cross6current compensation method.

:9 (oltage control mode ; Droop Compensation

In the voltage control or droop mode, the A0' is regulated by a droop characteristic, which is

shown in the following drawing.

/igure *. A0' et6point 0 vs reactive power V

%he droop characteristic represents a graph of the A0' voltage set6point 0 as a function of the

generator reactive power produced. %his set6point regulates the generator terminal voltage when

in island mode.

%he interpretation of the above graph is that as the reactive power demand from the generator


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increases, the generator terminal voltage decreases. %he set6point in the A0' is chosen so that

when the generator reactive power V supplied is !ero, the generator 0 is e#ual to the nominal

voltage. If the initial A0' set6point

Reactive Power Management in Islanded

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