an integrated hybrid power supply for dg

5/19/2018 An Integrated Hybrid Power Supply for Dg

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POWER-MANAGEMENT STRATEGIES FOR A

GRID-CONNECTED PV-FC HYBRID SYSTEM

ABSTRACT

This paper presents a method to operate a grid connected hybrid system. The hybrid

system composed of a Photovoltaic (PV) array and a Proton exchange membrane fuel cell

(PEMF) is considered. T!o operation modes" the unit#po!er control ($P) mode and the

feeder#flo! control (FF) mode" can be applied to the hybrid system. %n the $P mode"

variations of load demand are compensated by the main grid because the hybrid source output is

regulated to reference po!er. &ene!able energy is currently !idely used. 'ne of these resources

is solar energy. The photovoltaic (PV) array normally uses a maximum po!er point tracing

(MPPT) techniue to continuously deliver the highest po!er to the load !hen there are

variations in irradiation and temperature. The disadvantage of PV energy is that the PV output

po!er depends on !eather conditions and cell temperature" maing it an uncontrollable source.

Furthermore" it is not available during the night.

%n order to overcome these inherent dra!bacs" alternative sources" such as PEMF"

should be installed in the hybrid system. *y changing the F output po!er" the hybrid source

output becomes controllable.Therefore" the reference value of the hybrid source output must be

determined. %n the FF mode" the feeder flo! is regulated to a constant" the extra load demand is

piced up by the hybrid source" and" hence" the feeder reference po!er must be no!n. he

system can maximi+e the generated po!er !hen load is heavy and minimi+es the load shedding

area. ,hen load is light" the $P mode is selected and" thus" the hybrid source !ors more

stably. The changes in operating mode only occur !hen the load demand is at the boundary of

mode change- other!ise" the operating mode is either $P mode or FF mode. *esides" the

variation of hybrid source reference po!er is eliminated by means of hysteresis. The proposed

operating strategy !ith a flexible operation mode change al!ays operates the PV array at

maximum output po!er and the PEMF in its high efficiency performance band" thus improving

the performance of system operation" enhancing system stability" and decreasing the number of

operating mode changes.


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INTRODUCTION

&ene!able energy is currently !idely used. 'ne of these resources is solar energy. The

photovoltaic (PV) array normally uses a maximum po!er point tracing (MPPT) techniue to

continuously deliver the highest po!er to the load !hen there are variations in irradiation and

temperature. The disadvantage of PV energy is that the PV output po!er depends on !eather

conditions and cell temperature" maing it an uncontrollable source. Furthermore" it is not

available during the night. %n order to overcome these inherent dra!bacs" alternative sources"

such as PEMF" should be installed in the hybrid system. *y changing the F output po!er" the

hybrid source output becomes controllable. o!ever" PEMF" in its turn" !ors only at a high

efficiency !ithin a specific po!er range .

The hybrid system can either be connected to the main grid or !or autonomously !ith

respect to the grid#connected mode or islanded mode" respectively. %n the grid#connected mode"

the hybrid source is connected to the main grid at the point of common coupling (P) to deliver

po!er to the load. ,hen load demand changes" the po!er supplied by the main grid and hybrid

system must be properly changed.

The po!er delivered from the main grid and PV array as !ell as PEMF must be

coordinated to meet load demand. The hybrid source has t!o control modes/ 0) unit#po!er

control ($P) mode and feeder#flo! control (FF) mode. %n the $P mode" variations of load

demand are compensated by the main grid because the hybrid source output is regulated to

reference po!er. Therefore" the reference value of the hybrid source output must be

determined. %n the FF mode" the feeder flo! is regulated to a constant" the extra load demand is

piced up by the hybrid source" and" hence" the feeder reference po!er must be no!n.

The proposed operating strategy is to coordinate the t!o control modes and determine the

reference values of the $P mode and FF mode so that all constraints are satisfied. This

operating strategy !ill minimi+e the number of operating mode changes" improve performance

of the system operation" and enhance system stability.


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DISTRIBUTED GENERATION

1istributed generation" also called on#site 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(coal" gas

po!ered) nuclearor hydropo!er plants. These plants have excellent economies of scale" but

usually transmit electricity long distances and negatively affect the environment.

Most plants are built this !ay due to a number of economic" health2safety" logistical"

environmental" geographical andgeologicalfactors. For example" coal po!er plants are built

a!ay from cities to prevent their heavy air pollution from affecting the populace. %n addition"

such plants are often built near collieriesto minimi+e the cost of transporting

coal. ydroelectricplants are by their nature limited to operating at sites !ith sufficient !ater

flo!. Most po!er plants are often considered to be too far a!ay for their !aste heat to be used

for heating buildings.

3o! pollution is a crucial advantage of combined cycleplants that burn natural gas. The

lo! pollution permits the plants to be near enough to a city to be used for district heatingand

cooling.

1istributed generation is another approach. %t reduces the amount of energy lost in

transmitting electricity because the electricity is generated very near !here it is used" perhaps

even in the same building. This also reduces the si+e and number of po!er lines that must be

constructed. Typical distributed po!er sources in a Feed#in Tariff (F%T) scheme have lo!

maintenance" lo! pollution and high efficiencies. %n the past" these traits reuired dedicated

operating engineers and large complex plants to reduce pollution. o!ever" modern embedded

systemscan provide these traits !ith automated operation and rene!ables"such as sunlight" !ind

andgeothermal. This reduces the si+e of po!er plant that can sho! a profit.
http://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Coalhttp://en.wikipedia.org/wiki/Combined_cyclehttp://en.wikipedia.org/wiki/Combined_cyclehttp://en.wikipedia.org/wiki/Nuclear_reactorhttp://en.wikipedia.org/wiki/Economyhttp://en.wikipedia.org/wiki/Healthhttp://en.wikipedia.org/wiki/Safetyhttp://en.wikipedia.org/wiki/Logisticshttp://en.wikipedia.org/wiki/Geographyhttp://en.wikipedia.org/wiki/Geologyhttp://en.wikipedia.org/wiki/Collieryhttp://en.wikipedia.org/wiki/Hydroelectricityhttp://en.wikipedia.org/wiki/Combined_cyclehttp://en.wikipedia.org/wiki/Natural_gashttp://en.wikipedia.org/wiki/District_heatinghttp://en.wikipedia.org/wiki/Feed-in_Tariffhttp://en.wikipedia.org/wiki/Embedded_systemhttp://en.wikipedia.org/wiki/Embedded_systemhttp://en.wikipedia.org/wiki/Renewable_energyhttp://en.wikipedia.org/wiki/Geothermalhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Coalhttp://en.wikipedia.org/wiki/Combined_cyclehttp://en.wikipedia.org/wiki/Combined_cyclehttp://en.wikipedia.org/wiki/Nuclear_reactorhttp://en.wikipedia.org/wiki/Economyhttp://en.wikipedia.org/wiki/Healthhttp://en.wikipedia.org/wiki/Safetyhttp://en.wikipedia.org/wiki/Logisticshttp://en.wikipedia.org/wiki/Geographyhttp://en.wikipedia.org/wiki/Geologyhttp://en.wikipedia.org/wiki/Collieryhttp://en.wikipedia.org/wiki/Hydroelectricityhttp://en.wikipedia.org/wiki/Combined_cyclehttp://en.wikipedia.org/wiki/Natural_gashttp://en.wikipedia.org/wiki/District_heatinghttp://en.wikipedia.org/wiki/Feed-in_Tariffhttp://en.wikipedia.org/wiki/Embedded_systemhttp://en.wikipedia.org/wiki/Embedded_systemhttp://en.wikipedia.org/wiki/Renewable_energyhttp://en.wikipedia.org/wiki/Geothermal


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Distributed ener! res"ur#e

1istributed energy resource (1E&) systems are small#scale po!er generation

technologies (typically in the range of 4 , to 05"555 ,) used to provide an alternative to or

an enhancement of the traditional electric po!er system. The usual problems !ith distributed

generators are their high costs.

'ne popular source is solar panelson the roofs of buildings. The production cost is 65.77 to

8.559, (855:) plus installation and supporting euipment unless the installation is1o it

yourself(1%;) bringing the cost to 68 to 5.75


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pollution.1esignscurrently have uneven reliability" !ith some maes having excellent

maintenance costs" and others being unacceptable.

o#generators are also more expensive per !att than central generators. They find favor

because most buildings already burn fuels" and the cogeneration can extract more value from thefuel.

Dome larger installations utili+e combined cyclegeneration. $sually this consists of a gas

turbine!hose exhaust boils !aterfor a steam turbinein a &anin cycle. The condenser of the

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

!ith cogeneration have the highest no!n thermal efficiencies" often exceeding >=H.

%n countries !ith high pressure gas distribution" small turbines can be used to bring the

gas pressure to domestic levels !hilst extracting useful energy. %f the $I !ere to implement this

country!ide an additional 8#B ,e !ould become available. (@ote that the energy is already

being generated else!here to provide the high initial gas pressure # this method simply

distributes the energy via a different route.)

Future generations of electric vehicles !ill have the ability to deliver po!er from the

battery into the grid !hen needed. This could also be an important distributed generation

resource. &ecently interest in 1istributed Energy Dystems (1ED) is increasing" particularly onsite

generation. This interest is because larger po!er plants are economically unfeasible in many

regions due to increasing system and fuel costs" and more strict environmental regulations. %n

addition" recent technological advances in small generators" Po!er Electronics" and energy

storage devices have provided a ne! opportunity for distributed energy resources at the

distribution level" and especially" the incentive la!s to utili+e rene!able energies has also

encouraged a more decentrali+ed approach to po!er delivery.

There are many generation sources for 1ED/ conventional technologies (diesel or natural

gas engines)" emerging technologies (micro turbines or fuel cells or energy storage devices)" andrene!able technologies (small !ind turbines or solar9photovoltaicJs or small hydro turbines).

These 1ED are used for applications to a standalone" a standby" a grid#interconnected" a

cogeneration" pea shavings" etc. and have many advantages such as environmental#friendly and

modular electric generation" increased reliability" high po!er uality" uninterruptible service" cost

savings" on#site generation" expandability" etc. Do many utility companies are trying to construct
http://en.wikipedia.org/wiki/Micro_combined_heat_and_powerhttp://en.wikipedia.org/wiki/Combined_cyclehttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Rankine_cyclehttp://en.wikipedia.org/wiki/Micro_combined_heat_and_powerhttp://en.wikipedia.org/wiki/Combined_cyclehttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Rankine_cycle


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small distribution stations combined !ith several 1ED available at the regions" instead of large

po!er plants.

*asically" these technologies are based on notably advanced Po!er Electronics because

all 1ED reuire Po!er onverters" interconnection techniues" and electronic control units. That

is" all po!er generated by 1ED is generated as 1 Po!er" and then all the po!er fed to the 1

distribution bus is again converted into an G po!er !ith fixed magnitude and freuency by

control units using 1igital Dignal Processor (1DP). Do improved po!er electronic technologies

that permit grid interconnection of asynchronous generation sources are definitely reuired to

support distributed generation resources

The research !ors in the recent papers about 1ED focus on being utili+ed directly to a

standalone G system or fed bac to the utility mains. That is" !hen in normal operation or main

failures" 1ED directly supply loads !ith po!er (standalone mode or standby mode)" !hile" !hen

1ED have surplus po!er or need more po!er" this system operates in parallel mode to the mains.

Therefore" in order to permit to connect more generators on the net!or in good conditions" a

good techniue about interconnection !ith the grid and voltage regulations should overcome the

problems due to parallel operation of Po!er onverter for applications to 1ED.

DISTRIBUTED ENERGY SYSTEMSToday" ne! advances in technology and ne! directions in electricity regulation encourage a

significant increase of distributed generation resources around the !orld. Gs sho!n in Fig. the

currently competitive small generation units and the incentive la!s to use rene!able energies

force electric utility companies to construct an increasing number of distributed generation units

on its distribution net!or" instead of large central po!er plants. Moreover" 1ED can offer

improved service reliability" better economics and a reduced dependence on the local utility.

1istributed eneration Dystems have mainly been used as a standby po!er source for critical

businesses. For example" most hospitals and office buildings had stand#by diesel generation as an

emergency po!er source for use only during outages. o!ever" the diesel generators !ere not

inherently cost#effective" and produce noise and exhaust that !ould be ob?ectionable on anything

except for an emergency basis.


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Fig. G large central po!er plant and distributed energy systems

Mean!hile" recently" the use of 1istributed Energy Dystems under the =55 , level is

rapidly increasing due to recent technology improvements in small generators" po!er electronics"

and energy storage devices. Efficient clean fossil fuels technologies such as micro#turbines andfuel cells" and environmentally friendly rene!able energy technologies such as solar9photo

voltaic" small !ind and hydro are increasingly used for ne! distributed generation systems.

These 1ED are applied to a standalone" a standby" a grid#interconnected" a cogeneration" pea

shavings" etc. and have a lot of benefits such as environmental#friendly and modular electric

generation" increased reliability" high po!er uality" uninterruptible service" cost savings" on#site

generation"

Expandability" etc. The ma?or 1istributed eneration technologies that !ill be discussed in this

section are as follo!s/ micro#turbines" fuel cells" solar9photovoltaic systems" and energy storage

devices.

Micro#turbines" especially the small gas fired micro turbines in the 8=#055 , that can be

mass#produced at lo! cost have been more attractive due to the competitive price of natural gas"

lo! installation and maintenance costs. %t taes very clever engineering and use of innovative

design (e.g. air bearing" recuperation) to achieve reasonable efficiency and costs in machines of

lo!er output" and a big advantage of these systems is small because these mainly use high#speed

turbines (=5"555#75"555 &PM) !ith air foil bearings. Therefore" micro turbines hold the most

promise of any of the 1ED technologies today. Fuel cells are also !ell used for distributed

generation applications" and can essentially be described as batteries !hich never become

discharged as long as hydrogen and oxygen are continuously provided.


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The hydrogen can be supplied directly" or produced from natural gas" or liuid fuels such

as alcohols" or gasoline. Each unit ranges in si+e from 4 K 8=5 , or larger M, si+e. Even if

they offer high efficiency and lo! emissions" todayJs costs are high. Phosphoric acid cell are

commercially available in the range of the 855 ," !hile solid oxide and molten carbonate cell

are in a pre#commercial stage of development.

The possibility of using gasoline as a fuel for cells has resulted in a ma?or development

effort by the automotive companies. The recent research !or about fuel cells is focused to!ards

the polymer electrolyte membrane (PEM) fuel cells. Fuel cells in si+es greater than 855 ," hold

promise beyond 855=" but residential si+e fuel cells are unliely to have any significant maret

impact any time soon.

Mixed micro#turbine and fuel cell systems !ill also be available as a distributed

generation source. &ecently" a solid oxide fuel cell has been combined !ith a gas micro#turbine

creating a combined cycle po!er plant. %t has expected electrical efficiency of greater than :5 H"

and the expected po!er levels range from 8=5 , to 8.= M,. Dolar9photovoltaic systems may

be used in a variety of si+es" but the installation of large numbers of photovoltaic systems is

undesirable due to high land costs and in many geographic areas !ith poor intensity and

reliability of sunlight.

%n general" almost one acre of land !ould be needed to provide 0=5 , of electricity" so

solar9photovoltaic systems !ill continue to have limited applications in the future. Energystorage devices such as ultra capacitors" batteries" and fly!heels are one of the most critical

technologies for 1ED. %n general" the electrochemical capacitor has high po!er density as !ell as

good energy density. %n particular" ultra capacitors have several benefits such as high pulse po!er

capacity" long lifetime" high po!er density" lo! ED&" and very thin and tight.

%n contrast" batteries have higher energy density" but lo!er po!er density and short

lifetime relative to ultra#capacitor. Do hybrid Po!er Dystem" a combination of ultra#capacitor and

battery" is strongly recommended to satisfy several reuirements and to optimi+e system

performance. &ecently storage systems are much more efficient" cheaper" and longer than five

years ago. %n particular" fly!heel systems can generate :55 , for = seconds" !hile 8>#cell ultra

capacitors can provide up to 08.= , for a fe! seconds.


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%n the past" the electric utility industry did not offer various options that !ere suited for a

!ide range of consumer needs" and most utilities offered at best t!o or three combinations of

reliability#price. o!ever" the types of modern 1ED give commercial electric consumers various

options in a !ider range of reliability#price combinations. For these reasons" 1ED !ill be very

liely to thrive in the next 85 years" and especially" distributed generation technologies !ill have

a much greater maret potential in areas !ith high electricity costs and lo! reliability such as in

developing countries

PROB$EM STATEMENTS

1ED technologies have very different issues compared !ith traditional centrali+ed po!er

sources. For example" they are applied to the mains or the loads !ith voltage of B>5 volts or less-

and reuire po!er converters and different strategies of control and dispatch. Gll of these energy

technologies provide a 1 output !hich reuires po!er electronic interfaces !ith the

distribution po!er net!ors and its loads. %n most cases the conversion is performed by using a

voltage source inverter (VD%) !ith a possibility of pulse !idth modulation (P,M) that provides

fast regulation for voltage magnitude.

Po!er electronic interfaces introduce ne! control issues" but at the same time" ne!

possibilities. For example" a system !hich consists of micro#generators and storage devices

could be designed to operate in both an autonomous mode and connected to the po!er grid. 'ne

large class of problems is related to the fact that the po!er sources such as microturbines and

fuel cell have slo! response and their inertia is much less. %t must be remembered that the

current po!er systems have storage in generatorsJ inertia" and this may result in a slight

reduction in system freuency. Gs these generators become more compact" the need to lin them

to lo!er net!or voltage is significantly increasing.

o!ever" !ithout any medium voltage net!ors adaptation" this fast expansion can

affect the uality of supply as !ell as the public and euipment safety because distribution

net!ors have not been designed to connect a significant amount of generation. Therefore" a ne!

voltage control system to facilitate the connection of distributed generation resources to

distribution net!ors should be developed.


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%n many cases there are also ma?or technical barriers to operating independently in a

standalone G system" or to connecting small generation systems to the electrical distribution

net!or !ith lo!er voltage" and the recent research issues includes/

0. ontrol strategy to facilitate the connection of distributed generation resources to distribution

net!ors.

8. Efficient battery control.

4. %nverter control based on only local information.

B. Dynchroni+ation !ith the utility mains.

=. ompensation of the reactive po!er and higher harmonic components.

. 3oad sharing.

7. &eliability of communication.

05. &euirements of the customer.

1ED offers significant research and engineering challenges in solving these problems.

Moreover" the electrical and economic relationships bet!een customers and the distribution

utility and among customers may tae forms uite distinct from those !e no! today. Forexample" rather than devices being individually interconnected in parallel !ith the grid" they may

be grouped !ith loads in a semi#autonomous neighborhood that could be termed a micro grid is a

cluster of small sources" storage systems" and loads !hich presents itself to the grid as a

legitimate single entity. ence" future research !or !ill focus on solving the above issues so

that 1ED !ith more advantages compared !ith tradition large po!er plants can thrive in electric

po!er industry.


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PROB$EM DESCRIPTION

These ne! distributed generations interconnected to the lo! grid voltage or lo! load voltage

cause ne! problems !hich reuire innovative approaches to managing and operating the

distributed resources. %n the fields of Po!er Electronics" the recent papers have focused on

applications of a standby generation" a standalone G system" a combined heat and po!er

(cogeneration) system" and interconnection !ith the grid of distribution generations on the

distribution net!or" and have suggested technical solutions !hich !ould permit to connect

more generators on the net!or in good conditions and to perform a good voltage regulation.

1epending on the load" generation level" and local connection conditions" each generator can

cause the problems described in the previous chapter. The main goals !hich should be achieved

!ill thus be/ to increase the net!or connection capacity by allo!ing more consumers and

producer customers connection !ithout creating ne! reinforcement costs" to enhance the

reliability of the systems by the protections" to improve the overall uality of supply !ith a best

voltage control.

A% C"n&iur'ti"ns &"r DES

() C'se I/ G Po!er onverter connected in a Dtandalone G Dystem or in Parallel !ith the

$tility Mains

Fig. sho! a distributed po!er system !hich is connected to directly load or in parallel !ith

utility mains" according to its mode. This system consists of a generator" an input filter" an

G9G po!er converter" an output filter" an isolation transformer" output sensor (V" %" P)" and a

1DP controller. %n the Figures" a distributed generator may operate as one of three modes/ a

standby" a pea shaving" and a standalone po!er source. %n a standby mode sho!n in Fig. a

generator set serves as a $PD system operating during mains failures. %t is used to increase the

reliability of the energy supply and to enhance the overall performance of the system. The static

s!itch D, 0 is closed in normal operation and D, 8 is open" !hile in case of mains failures or

excessive voltage drop detection D, 0 is open and D, 8 is simultaneously closed.

%n this case" control techniues of 1ED are very similar to those of $PD. %f a transient

load increases" the output voltage has relatively large drops due to the internal impedance of the

inverter and filter stage" !hich freuently result in malfunction of sensitive load. Fig.


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an serves as a pea shaving or interconnection !ith the grid to feed po!er bac to

mains. %n both modes" the generator is connected in parallel !ith the main grids. %n a pea

shaving mode" this generator is running as fe! as several hundred hours annually because the

D, 0 is only closed during the limited periods.

Mean!hile" in an interconnection !ith the grid" D, 0 is al!ays closed and this system

provides the grid !ith continuous electric po!er. %n addition" the converter connected in parallel

to the mains can serve also as a source of reactive po!er and higher harmonic current

components. %n a standalone G system sho!n in Fig. the generator is directly connected to the

load lines !ithout being connected to the mains and it !ill operate independently. %n this case"

the operations of this system are similar to a standby mode" and it serves continuously unlie a

standby mode and a pea shaving mode.

Fig. *loc diagram of a standby mode

Fig. *loc diagram of a pea shaving mode


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Fig. *loc diagram of a standalone mode

Gs sho!n in Fig. the output voltage of the generator is fed to a 19G converter that

converts a 1 output of the generator to be fixed voltage and freuency for utility mains or

loads. The 1DP controller monitors multiple system variables on a real time basis and executes

control routines to optimi+e the operation of the individual subsystems in response to measured

variables. %t also provides all necessary functions to sense output voltages" current" and po!er" to

operate protections" and to give reference signals to regulators.

The output po!er of the converter is controlled according to the reference signal of the

control unit. Gs described above" in order to compensate for reactive po!er and higher harmoniccomponents or to improve po!er factor" the active po!er (P) and reactive po!er (L) should be

controlled independently. Moreover" the above system needs over#dimensioning some parts of

the po!er converter in order to produce reactive po!er by the converter at rated active po!er.

*ecause a po!er converter dimensioned for rated current can supply reactive po!er only if the

active component is less than rated. Therefore" a control strategy easy to implement is reuired to

ensure closed loop control of the po!er factor and to provide a good po!er uality. %n case that a

generator is used for distributed generation systems" the recent research focuses are summari+ed

as follo!s/

0. ontrol strategy !hich permits to connect more generators on the net!or

8. ompensation of the reactive po!er and higher harmonic components

4. Gn active po!er (P) and a reactive po!er control (L) independently

B. Po!er factor correction


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=. Dynchroni+ation !ith the utility mains


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Fig.*loc diagram of po!er converters connected in parallel

Do the above issues can be applied to distributed po!er systems similarly" and the recent research

focuses are summari+ed as follo!s/

0. Dtandardi+ed 1ED modeling using the soft!are tools

8. Eual load sharing such as the real and reactive po!er" the load harmonic current among the

parallel connected inverters.

4. onnection capability of more 1ED to the utility mains in best conditionsB. %ndependent P" L control of the inverters

=. Po!er factor correction


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E+AMP$ES

C'se ( , Eeren#!.Te/"r'r! P"0er A//1i#'ti"n

%n mid#@ovember 855:" the to!n of hester" alifornia" !as preparing to undergo a :8#

hour po!er shutdo!n. This !as reuired to improve the service reliability in hester after past

sustained outages due to circuit configuration" condition and exposure. For that reason" Pacific

as and Electric (P2E) !ould replace B0 po!er poles and their cross#arms on its amilton

*ranch transmission line. This line serves the hester community !ith 0"


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C'se * , O/en-M'r2et Pri#e Hedin

The volatility in the energy maret !as greatly affecting the po!er department budget in

the city of urricane" $tah. %ts population surged from >"8=5 in 8555 to 08"5>B in 855< K an

increase of B


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Fig. # 1 in urricane ity Po!er Plant

C'se 3 , C"bined CHP 'nd St'ndb! P"0er &"r H"s/it'1

G cost effective combined heat and po!er (P) and standby po!er generation pacage

!as reuired for the @orfol and @or!ich ospital being built by 'ctagon ealthcare in the$nited Iingdom. %n addition" tariff uality metering !as necessary to ualify the P as eligible

for payment under the limate hange 3evy ood Luality PQ scheme. &ather than the usual

basement plant room" a stand#alone energy center !as built to give better access for servicing

and supplies.

The P system prime mover is a at 4=0< leanburn gas engine. eat is recovered

from the engine exhaust" ?acet !ater and oil cooler circuits" to provide 040B ,. %t is

used heat the returning medium#pressure hot !ater before it re#enters the boiler" so the P acts

as lead boiler. ,hen thermal demand is lo! excess heat is dumped to a remote radiator. G at

D&B generator directly lined to the engine provides B55 volts at =5 +. This feeds a

synchroni+ing circuit breaer inside a control panel" in turn connected to the hospitalJs V line

via a step#up transformer. The complete system is displayed on a graphical overvie!- a simple

touch of the screen is all that is reuired for an operator to interact !ith the system.


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The standby generation system comprises four 88=5 VG (0>55 ,) aterpillar 4


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3andfill gas (3F) is produced naturally as organic !aste decomposes in landfills. 3F

is composed of about =5 percent methane" about =5 percent carbon dioxide and small amounts of

non#methane organic compounds. Gt most municipal solid#!aste landfills" the methane and

carbon dioxide are destroyed in a gas collection and control system or utility flare. o!ever" to

use 3F as an alternative fuel" the gas is extracted from landfills using a series of !ells and a

vacuum system. Pipes are inserted deep into the landfill to provide a point of release for the

landfill gases. G slight vacuum is then applied in the pipe to dra! the gases into and through it to

a central point" !here it can be processed and treated for use in generating electricity" replacing

the need for conventional fossil fuels. ere are a fe! examples from around the !orld of ho!

3F is used to produce electric po!er through engine generator sets in landfill configurations.

Fig.# 3andfill as Engine enerator Det

Deneca Meado!s 3andfill" Deneca Falls" @e! ;or This energy system" o!ned by

%nnovative Energy Dystems of 'afield" @;" began operation in 077< and has been expanded

three times to its current 00.8 M, capacity. The system (see Fig.) uses fourteen atO 4=05 percent) and carbon dioxide (85#=5 percent). *iogas can be extracted for commercial use

from almost any of its sources. For example" some livestoc farms or large feeder operations use

a lagoon to store the manure generated by their livestoc.

%nstead of releasing the methane and carbon dioxide generated by the decomposition of

this manure into the atmosphere" the methane can be extracted and burned at the farm in biogas#

fueled boilers" heaters or other gas consuming devices" including gas engines.


23/97

%n addition to livestoc farms" other agricultural operations afford opportunities for

biogas productions. For example" cassava#processing plants" !hich produce starch" are common

in hina" %ndia and %ndonesia and may utili+e biogas for electric po!er. *y tapping their biogas

resources" these plants not only avoid the cost of purchasing heavy fuel oil and electricity but

also reclaim valuable land that !ould other!ise have to be used to purify the factoryJs

!aste!ater" and virtually eliminating odor and pest issues caused by large#scale decomposition

of organic material.

Gs an example of this type of 1 application" let us consider the @ong &ai Farm" in

&aying" Thailand. The farm partners !ith the P roup" one of the largest food suppliers in

Thailand" and runs a feeder operation for more than 45"555 hogs. @ong &ai Farms consumes

approximately 855 , of po!er for blo!ers" drying systems and other auxiliary needs

associated !ith its operations. The manure produced by its hogs is piped into a digester pond (see

Fig. >)" !here it generates biogas that is used to fuel the generator sets" !hich produce sufficient

po!er for all of @ong &ai FarmJs electric po!er reuirements.

Fig. # *uffer Tan and 1igestion Process in Thailand

C'se 6 , C"'1 Mine Met7'ne 8CMM) G's A//1i#'ti"ns

The anthropogenic release of methane (B) into the environment and its global !arming

potential continues to dra! attention globally. Methane can be released into the atmosphere

through sources !here it naturally occurs/ landfill decomposition" agriculture" gas and oil

extraction systems" and coal mining activities. Gbout >H of total anthropogenic methane

emissions come from coal mines.


24/97

lobally" coal mines emit approximately B55 million metric tons or 8> billion cubic

meters of carbon dioxide euivalent annually. This amount is euivalent to consumption of >0>

million barrels of oil or the carbon dioxide emissions of


25/97

G circuit model of a three#phase 1 to G inverter !ith 3 output filter is further

described in Figure Gs sho!n in the figure" the system consists of a 1 voltage source (Vdc)" a

three# phase P,M inverter" an output filter (3f and !ith considering parasitic resistance of

filter# &f). Dometimes a transformer may be used for stepping up the output voltage and hence 3f

can be transformer inductance.

Figure P,M inverter diagram

There are t!o !ays for controlling an inverter in a distributed generation system

A% P9 In:erter C"ntr"1

This type of control is adopted !hen the 1 unit system is connected to an external grid

or to an island of loads and more generators. %n this situation" the variables controlled by the

inverter are the active and reactive po!er in?ected into the grid" !hich have to follo! the set

points Pref and Lref" respectively. These set points can be chosen by the customer or by a central

controller. The PL control of an inverter can be performed using a current control techniue in

d reference frame !hich the inverter current is controlled in amplitude and phase to meet the

desired set#points of active and reactive po!er.

,ith the aim of Par transform and euations bet!een inverter input and output" the

inverter controller bloc diagram for supplying reference value of Pref and Lref is as figures. For

the current controller" t!o Proportional#%ntegral (P%) regulators have been chosen in order to

meet the reuirements of stability of the system and to mae the steady state error be +ero. ,ith

this control scheme" it is possible to control the inverter in such !ay that in?ects reference value

of Pref" Lref into other part of stand#alone net!or.


26/97

,hen the output voltage is needed to be regulated" the PV control scheme that is similar

to PL mode !ith feedbac of voltage used to ad?ust Lref.

Figure / PL control scheme of inverter

B% V& In:erter C"ntr"1

This controller has to act on the inverter !henever the system is in stand#alone mode of

operation. %n fact in this case it must regulate the voltage value at a reference bus bar and the

freuency of the !hole grid. G regulators !or in order to eep the measured voltages upon the

set points. Moreover the freuency is imposed through the modulating signals of the inverter

P,M control by mean of an oscillator. G simple P% controller can regulate bus voltage in

reference value !ith getting feedbac of real bus voltage. Figure outlines this control strategy. %n

this case it is obvious that the 1 unit should have storage device in order to regulate the po!er

and voltage.


27/97

Figure/ Vf control scheme of inverter

FUE$ CE$$

Intr"du#ti"n;

G fuel cell is an electrochemical cellthat converts a source fuel into an electrical current.

%t generates electricity inside a cell through reactions bet!een a fuel and an oxidant" triggered in

the presence of an electrolyte. The reactants flo! into the cell" and the reaction products flo! out

of it" !hile the electrolyte remains !ithin it. Fuel cells can operate continuously as long as the

necessary reactant and oxidant flo!s are maintained.

Fuel cells are different from conventional electrochemical cell batteries in that they

consume reactant from an external source" !hich must be replenished a thermodynamically open

system. *y contrast" batteries store electrical energy chemically and hence represent a

thermodynamically closed system. Many combinations of fuels and oxidants are possible. G

hydrogen fuel cell uses hydrogenas its fuel and oxygen(usually from air) as its oxidant. 'ther

fuels include hydro carbonsand alcohols.'ther oxidants includechlorineand chlorine dioxide.
http://en.wikipedia.org/wiki/Electrochemical_cellhttp://en.wikipedia.org/wiki/Battery_(electricity)http://en.wikipedia.org/wiki/Thermodynamic_systemhttp://en.wikipedia.org/wiki/Thermodynamic_systemhttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Hydrocarbonhttp://en.wikipedia.org/wiki/Alcoholhttp://en.wikipedia.org/wiki/Chlorinehttp://en.wikipedia.org/wiki/Chlorine_dioxidehttp://en.wikipedia.org/wiki/Electrochemical_cellhttp://en.wikipedia.org/wiki/Battery_(electricity)http://en.wikipedia.org/wiki/Thermodynamic_systemhttp://en.wikipedia.org/wiki/Thermodynamic_systemhttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Hydrocarbonhttp://en.wikipedia.org/wiki/Alcoholhttp://en.wikipedia.org/wiki/Chlorinehttp://en.wikipedia.org/wiki/Chlorine_dioxide


28/97

Fuel cells come in many varieties- ho!ever" they all !or in the same general manner.

They are made up of three segments !hich are sand!iched together/ the anode" the electrolyte"

and the cathode. T!o chemical reactions occur at the interfaces of the three different segments.

The net result of the t!o reactions is that fuel is consumed" !ater or carbon dioxide is created"

and an electrical current is created" !hich can be used to po!er electrical devices" normally

referred to as the load.

Gt the anode a catalyst oxidi+es the fuel" usually hydrogen" turning the fuel into a

positively charged ion and a negatively charged electron. The electrolyte is a substance

specifically designed so ions can pass through it" but the electrons cannot. The freed electrons

travel through a !ire creating the electrical current. The ions travel through the electrolyte to the

cathode. 'nce reaching the cathode" the ions are reunited !ith the electrons and the t!o react!ith a third chemical" usually oxygen" to create !ater or carbon dioxide.

DESIGN FEATURES IN A FUE$ CE$$ ARE;

The electrolyte substance. The electrolyte substance usually defines the type of fuel cell.

The fuel that is used. The most common fuel is hydrogen.

The anode catalyst" !hich breas do!n the fuel into electrons and ions. The anode

catalyst is usually made up of very fine platinum po!der.

The cathode catalyst" !hich turns the ions into the !aste chemicals lie !ater or carbon

dioxide. The cathode catalyst is often made up of nicel.

G typical fuel cell produces a voltage from 5.< V to 5.: V at full rated load. Voltage decreases

as current increases" due to several factors/

Gctivation loss

'hmic loss (voltage dropdue to resistance of the cell components and interconnects)

Mass transport loss (depletion of reactants at catalyst sites under high loads" causing rapid

loss of voltage).
http://en.wikipedia.org/wiki/Anodehttp://en.wikipedia.org/wiki/Electrolytehttp://en.wikipedia.org/wiki/Cathodehttp://en.wikipedia.org/wiki/Nickelhttp://en.wikipedia.org/wiki/Nickelhttp://en.wikipedia.org/wiki/Overpotentialhttp://en.wikipedia.org/wiki/Overpotentialhttp://en.wikipedia.org/wiki/Voltage_drophttp://en.wikipedia.org/wiki/Anodehttp://en.wikipedia.org/wiki/Electrolytehttp://en.wikipedia.org/wiki/Cathodehttp://en.wikipedia.org/wiki/Nickelhttp://en.wikipedia.org/wiki/Overpotentialhttp://en.wikipedia.org/wiki/Voltage_drop


29/97

To deliver the desired amount of energy" the fuel cells can be combined in series and parallel

circuits"!here series yields higher voltage" and parallel allo!s a higher currentto be supplied.

Duch a design is called a fuel cell stac. The cell surface area can be increased" to allo! stronger

currentfrom each cell.

T!/es "& &ue1 #e11s;

Pr"t"n e


30/97

system costs in volume production (pro?ected to =55"555 units per year) are 6 $T Po!er has B55 , stationary fuel cells for

60"555"555 per B55 , installed costs. The goal is to reduce the cost in order to compete

!ith current maret technologies including gasoline internal combustion engines. Many

companies are !oring on techniues to reduce cost in a variety of !ays including

reducing the amount of platinum needed in each individual cell. *allard Po!er Dystems

have experiments !ith a catalyst enhanced !ith carbon sil !hich allo!s a 45H

reduction (0 mg9cm to 5.: mg9cm) in platinum usage !ithout reduction in performance.

Monish $niversity"Melbourneuses PE1'Tas acathode.

The production costs of the PEM (proton exchange membrane). The@ationmembrane

currently costs 6=


31/97

1urability" service life" and special reuirements for some type of cells. Dtationary fuel

cell applications typically reuire more than B5"555 hours of reliable operation at a

temperature of #4= N to B5 N (#40 NF to 05B NF)" !hile automotive fuel cells reuire a

="555 hour lifespan (the euivalent of 0=5"555 miles) under extreme temperatures.

urrent service lifeis :"455 hours under cycling conditions.

Gutomotive engines must also be able to start reliably at #45 N (#88 NF) and have a high

po!er to volume ratio (typically 8.= , per liter).

3imited carbon monoxidetolerance of the cathode.

Hi7 te/er'ture &ue1 #e11s;

As"1id "


32/97

electrolyte. 3ie all fuel cell electrolytes ;DX is conductive to ions" allo!ing them to pass from

the anode to cathode" but is non#conductive to electrons. ;DX is a durable solid and is

advantageous in large industrial systems. Glthough ;DX is a good ion conductor" it only !ors at

very high temperatures.

The standard operating temperature is about 7=5o. &unning the fuel cell at such a high

temperature easily breas do!n the methane and oxygen into ions. G ma?or disadvantage of the

D'F" as a result of the high heat" is that it places considerable constraints on the materials

!hich can be used for interconnectionsQ. Gnother disadvantage of running the cell at such a high

temperature is that other un!anted reactions may occur inside the fuel cell. %t is common for

carbon dust" graphite" to build up on the anode" preventing the fuel from reaching the catalyst.

Much research is currently being done to find alternatives to ;DX that !ill carry ions at a lo!ertemperature.

MCFC;

Molten#carbonate fuel cells (MFs) are high#temperature fuel cells" That operate at

temperaturesof


33/97

acid fuel cell plant. ,hen the !aste heat is captured and used" overall fuel efficiencies can be as

high as >= percent.

$nlie alaline" phosphoric acid" andpolymer electrolyte membrane fuel cells" MFs

donYt reuire an external reformer to convert more energy#dense fuels to hydrogen.

1ue to the high temperatures at !hich MFs operate" these fuels are converted to

hydrogen !ithin the fuel cell itself by a process called internal reforming" !hich also reduces

cost.

Molten carbonate fuel cells are not prone to poisoning by carbon monoxide or carbon

dioxideZthey can even use carbon oxides as fuelZ maing them more attractive for fueling

!ith gases made from coal. *ecause they are more resistant to impurities than other fuel cell

types" scientists believe that they could even be capable of internal reforming of coal" assuming

they can be made resistant to impurities such as sulfur and particulates that result from

converting coal" a dirtier fossil fuelsource than many others" into hydrogen.

The primary disadvantage of current MF technology is durability. The high

temperatures at !hich these cells operate and the corrosive electrolyte used accelerate

component breado!n and corrosion" decreasing cell life. Dcientists are currently exploring

corrosion#resistant materials for components as !ell as fuel cell designs that increase cell life

!ithout decreasing performance.

Fue1 #e11 e&&i#ien#!;

The efficiency of a fuel cell is dependent on the amount of po!er dra!n from it. 1ra!ing

more po!er means dra!ing more current" !hich increases the losses in the fuel cell. Gs a general

rule" the more po!er (current) dra!n" the lo!er the efficiency. Most losses manifest themselves

as a voltage drop in the cell" so the efficiency of a cell is almost proportional to its voltage. For

this reason" it is common to sho! graphs of voltage versus current (so#called polari+ation curves)

for fuel cells. G typical cell running at 5.: V has an efficiency of about =5H" meaning that =5H

of the energy content of the hydrogen is converted into electrical energy- the remaining =5H !ill
http://en.wikipedia.org/wiki/Cogenerationhttp://en.wikipedia.org/wiki/Alkalinehttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Catalyst#Inhibitors.2C_poisons_and_promotershttp://en.wikipedia.org/wiki/Carbon_monoxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Cogenerationhttp://en.wikipedia.org/wiki/Alkalinehttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Catalyst#Inhibitors.2C_poisons_and_promotershttp://en.wikipedia.org/wiki/Carbon_monoxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Fossil_fuel


34/97

be converted into heat. (1epending on the fuel cell system design" some fuel might leave the

system unreacted" constituting an additional loss.)

For a hydrogen cell operating at standard conditions !ith no reactant leas" the efficiency

is eual to the cell voltage divided by 0.B> V" based on the enthalpy" or heating value" of the

reaction. For the same cell" the second la! efficiency is eual to cell voltage divided by 0.84 V.

(This voltage varies !ith fuel used" and uality and temperature of the cell.)

The difference bet!een these numbers represents the difference bet!een the reactionYs

enthalpy and ibbs free energy. This difference al!ays appears as heat" along !ith any losses in

electrical conversion efficiency.

Fuel cells do not operate on a thermal cycle. Gs such" they are not constrained" as

combustion engines are" in the same !ay by thermodynamic limits" such as arnot cycle

efficiency. Gt times this is misrepresented by saying that fuel cells are exempt from the la!s of

thermodynamics" because most people thin of thermodynamics in terms of combustion

processes (enthalpy of formation). The la!s of thermodynamics also hold for chemical processes

(ibbs free energy) lie fuel cells" but the maximum theoretical efficiency is higher (>4H

efficient at 87>I in the case of hydrogen9oxygen reaction) than the 'tto cyclethermal efficiency

(


35/97

In /r'#ti#e;

For a fuel cell operating on air" losses due to the air supply system must also be taen into

account. This refers to the pressuri+ation of the air and dehumidifying it. This reduces the

efficiency significantly and brings it near to that of a compression ignition engine. Furthermore"

fuel cell efficiency decreases as load increases.

The tan#to#!heel efficiency of a fuel cell vehicleis greater than B=H at lo! loads and

sho!s average values of about 4 onda released a fuel cell electric vehicle (the onda F larity) !ith fuel stac

claiming a 55 degrees elsius. This heat can be captured and used

to heat !ater in a micro combined heat and po!er (m#P) application. ,hen the heat is

captured" total efficiency can reach >5#75H at the unit" but does not consider production and

distribution losses. P units are being developed today for the European home maret.
http://en.wikipedia.org/wiki/Fuel_cell_vehiclehttp://en.wikipedia.org/wiki/New_European_Driving_Cyclehttp://en.wikipedia.org/wiki/New_European_Driving_Cyclehttp://en.wikipedia.org/wiki/Honda_FCX_Clarityhttp://en.wikipedia.org/wiki/Liquid_hydrogenhttp://en.wikipedia.org/wiki/Liquid_hydrogenhttp://en.wikipedia.org/wiki/Fuel_cell#cite_note-28http://en.wikipedia.org/wiki/Fuel_cell#cite_note-28http://en.wikipedia.org/wiki/Thermal_powerhttp://en.wikipedia.org/wiki/Solar_energyhttp://en.wikipedia.org/wiki/Wind_powerhttp://en.wikipedia.org/wiki/Electrolysishttp://en.wikipedia.org/wiki/Lead-acid_batteryhttp://en.wikipedia.org/wiki/Micro_combined_heat_and_powerhttp://en.wikipedia.org/wiki/Fuel_cell_vehiclehttp://en.wikipedia.org/wiki/New_European_Driving_Cyclehttp://en.wikipedia.org/wiki/New_European_Driving_Cyclehttp://en.wikipedia.org/wiki/Honda_FCX_Clarityhttp://en.wikipedia.org/wiki/Liquid_hydrogenhttp://en.wikipedia.org/wiki/Liquid_hydrogenhttp://en.wikipedia.org/wiki/Fuel_cell#cite_note-28http://en.wikipedia.org/wiki/Thermal_powerhttp://en.wikipedia.org/wiki/Solar_energyhttp://en.wikipedia.org/wiki/Wind_powerhttp://en.wikipedia.org/wiki/Electrolysishttp://en.wikipedia.org/wiki/Lead-acid_batteryhttp://en.wikipedia.org/wiki/Micro_combined_heat_and_power


36/97

Dtationary fuel cell applications (or stationary fuel cell po!er systems) are stationarythat

are either connected to the electric grid(distributed generation) to provide supplemental po!er

and as emergency po!er system for critical areas" or installed as a grid#independent generator for

on#site service.

C"des 'nd st'nd'rds Dtationary fuel cell applications is a classification in F

H!dr"en #"des 'nd st'nd'rdsand&ue1 #e11codes and standards. The other main standards are

P"rt'b1e &ue1 #e11 '//1i#'ti"nsand Fue1 #e11 :e7i#1e.

Fuel cell gas appliances up to :5 ,

%nstallation permitting guidance for hydrogen and fuel cells stationary applications

Dtandard for the installation of stationary fuel cell po!er systems

Eeren#! /"0er s!stes;

Emergency po!er systems are a type fuel cell system" !hich may include lighting"

generators and other apparatus" to provide bacup resources in a crisis or !hen regular systems

fail. They find uses in a !ide variety of settings from residential homes to hospitals" scientific

laboratories" data centers"telecommunicationeuipment and modern naval ships.

Uninterru/ted /"0er su//1!;

Gn uninterrupted po!er supply ($PD) provides emergency po!er and" depending on the

topology" provide line regulation as !ell to connected euipment by supplying po!er from a

separate source !hen utility po!er is not available. %t differs from an auxiliary po!ersupply or

standby generator" !hich does not provide instant protection from a momentary po!er

interruption.

C"ener'ti"n
http://en.wikipedia.org/wiki/Stationaryhttp://en.wikipedia.org/wiki/Electric_gridhttp://en.wikipedia.org/wiki/Distributed_generationhttp://en.wikipedia.org/wiki/Emergency_power_systemhttp://en.wikipedia.org/wiki/Hydrogen_codes_and_standardshttp://en.wikipedia.org/wiki/Fuel_cellhttp://en.wikipedia.org/wiki/Fuel_cellhttp://en.wikipedia.org/wiki/Portable_fuel_cell_applicationshttp://en.wikipedia.org/wiki/Fuel_cell_vehiclehttp://en.wikipedia.org/wiki/Fuel_cell_vehiclehttp://en.wikipedia.org/wiki/Fuel_cell_gas_appliances_up_to_70_kWhttp://en.wikipedia.org/w/index.php?title=Installation_permitting_guidance_for_hydrogen_and_fuel_cells_stationary_applications&action=edit&redlink=1http://en.wikipedia.org/wiki/Standard_for_the_installation_of_stationary_fuel_cell_power_systemshttp://en.wikipedia.org/wiki/Emergency_power_systemshttp://en.wikipedia.org/wiki/Hospitalhttp://en.wikipedia.org/wiki/Data_centerhttp://en.wikipedia.org/wiki/Telecommunicationhttp://en.wikipedia.org/wiki/Uninterrupted_power_supplyhttp://en.wikipedia.org/wiki/Auxiliary_powerhttp://en.wikipedia.org/wiki/Stationaryhttp://en.wikipedia.org/wiki/Electric_gridhttp://en.wikipedia.org/wiki/Distributed_generationhttp://en.wikipedia.org/wiki/Emergency_power_systemhttp://en.wikipedia.org/wiki/Hydrogen_codes_and_standardshttp://en.wikipedia.org/wiki/Fuel_cellhttp://en.wikipedia.org/wiki/Portable_fuel_cell_applicationshttp://en.wikipedia.org/wiki/Fuel_cell_vehiclehttp://en.wikipedia.org/wiki/Fuel_cell_gas_appliances_up_to_70_kWhttp://en.wikipedia.org/w/index.php?title=Installation_permitting_guidance_for_hydrogen_and_fuel_cells_stationary_applications&action=edit&redlink=1http://en.wikipedia.org/wiki/Standard_for_the_installation_of_stationary_fuel_cell_power_systemshttp://en.wikipedia.org/wiki/Emergency_power_systemshttp://en.wikipedia.org/wiki/Hospitalhttp://en.wikipedia.org/wiki/Data_centerhttp://en.wikipedia.org/wiki/Telecommunicationhttp://en.wikipedia.org/wiki/Uninterrupted_power_supplyhttp://en.wikipedia.org/wiki/Auxiliary_power


37/97

C"ener'ti"ncan be used !hen the fuel cell is sited near the point of use" its !aste heat

can be captured for beneficial purposes. Mi#r" #"bined 7e't 'nd /"0er (MicroP) is

usually less than = ,e for a 7"e &ue1 #e11or small business.

Fue1 #e11 '//1i#'ti"ns;

POWER;

Fuel cells are very useful as po!er sources in remote locations" such as spacecraft"remote !eather stations" large pars" rural locations" and in certain military applications. G fuel

cell system running on hydrogen can be compact and light!eight" and have no ma?or moving

parts. *ecause fuel cells have no moving parts and do not involve combustion" in ideal

conditions they can achieve up to 77.7777H reliability. This euates to around one minute of

do!n time in a t!o year period.

Dince electrolyses systems do not store fuel in themselves" but rather rely on external

storage units" they can be successfully applied in large#scale energy storage" rural areas being

one example. %n this application" batteries !ould have to be largely oversi+ed to meet the storage

demand" but fuel cells only need a larger storage unit (typically cheaper than an electrochemical

device).

'ne such pilot program is operating on Dtuart %sland in ,ashington Dtate. There the

Dtuart %sland Energy %nitiative has built a complete" closed#loop system/ Dolar panels po!er an

electroly+er !hich maes hydrogen. The hydrogen is stored in a =55 gallon tan at 855 PD%" and

runs a &eli 'n fuel cell to provide full electric bac#up to the off#the#grid residence.

C"ener'ti"n;

Micro combined heat and po!er (MicroP) systems such as home fuel cells and

cogenerationfor office buildings and factories are in the mass production phase. The system
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generates constant electric po!er (selling excess po!er bac to the grid !hen it is not

consumed)" and at the same time produces hot air and !ater from the !aste heat. MicroP is

usually less than = ,e for a home fuel cellor small business. G lo!er fuel#to#electricity

conversion efficiency is tolerated (typically 0=#85H)" because most of the energy not converted

into electricity is utili+ed as heat.

Dome heat is lost !ith the exhaust gas ?ust as in a normal furnace" so the combined heat

and po!er efficiency is still lo!er than 055H" typically around >5H. %n terms of energy

ho!ever" the process is inefficient" and one could do better by maximi+ing the electricity

generated and then using the electricity to drive a heat pump.Phosphoric#acid fuel cells(PGF)

comprise the largest segment of existing P products !orld!ide and can provide combined

efficiencies close to 75H (4=#=5H electric R remainder as thermal) Molten#carbonate fuel cellshave also been installed in these applications" andsolid#oxide fuel cellprototypes exist.

Ot7er '//1i#'ti"ns;

Providing po!er forbase stationsor cell sites

'ff#gridpo!er supply

1istributed generation

For 3ifts

Emergency po!er systemsare a type of fuel cell system" !hich may include lighting"

generators and other apparatus" to provide bacup resources in a crisis or !hen regular

systems fail. They find uses in a !ide variety of settings from residential homes to

hospitals" scientific laboratories" data centers"telecommunicationeuipment and modern

naval ships.

Gn uninterrupted po!er supply($PD) provides emergency po!er and" depending on the

topology" provide line regulation as !ell to connected euipment by supplying po!er

from a separate source !hen utility po!er is not available. $nlie a standby generator" it

can provide instant protection from a momentary po!er interruption.

*ase load po!er plants
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Electricand hybrid vehicles.

@oteboo computersfor applications !here Gcharging may not be available for !ees

at a time.

Portable charging docs for small electronics (e.g. a belt clip that charges your cell phone

or P1G).

Dmartphone!ith high po!er consumption due to large displays and additional features

lie PD might be euipped !ith micro fuel cells.

Dmall heating appliances.

Fuel cells are a technology that both the public and private sectors are increasinglyturning to for both primary and bac#up po!er needs. Glthough the understanding of the

chemistry of fuel cells goes bac more than a century" they are very much a 80st century

technology. The basic design and electrochemical principle behind fuel cells is straightfor!ard. G

fuel cell stac reuires only hydrogen (or a similar energy carrier)" oxygen" and an electrolytic

solution.

ydrogen and ambient air flo! into the fuel cell" !hich contains an anode and a cathode.

Gt the anode" the hydrogen separates into a proton and an electron. The proton migrates to the

cathode" !here it reacts !ith the oxygen to form !ater. The electrons" !hich cannot pass through

the membrane" flo! from the cell to provide useful electrical po!er. Fuel cells are uiet" have no

moving parts" and produce no particulate emissions. They are virtually maintenance free and can

be both tested and operated remotely. *ecause they are modular" they can be configured for any

si+e po!er needs" from a fe! ilo!atts for a remote telecommunications to!er to mega!att#

scale for hospitals and airports. ydrogen is safely stored on#site or produced !ithin the fuel cell

itself.

SO$ID O+IDE FUE$ CE$$S

Dolid oxide fuel cells (D'Fs) offer a clean" lo!#pollution technology to

electrochemically generate electricity at high efficiencies- since their efficiencies are not limited
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the !ay conventional heat engineYs is. These fuel cells provide many advantages over traditional

energy conversion systems including high efficiency" reliability" modularity" fuel adaptability"

and very lo! levels of polluting emissions. Luiet" vibration#free operation of D'Fs also

eliminates noise usually associated !ith conventional po!er generation systems.

$p until about six years ago" D'Fs !ere being developed for operation primarily in the

temperature range of 755 to 0555o (048oF)- in addition to the capability of internally

reforminghydrocarbon fuels (for example" natural gas)" such high temperature D'Fs provide

high uality exhaust heat for cogeneration" and !hen pressuri+ed" can be integrated !ith a gas

turbine to further increase the overall efficiency of the po!er system.

o!ever" reduction of the D'F operating temperature by 855o (478oF) or more allo!s

use of a broader set of materials" is less demanding on the seals and the balance#of#plant

components" simplifies thermal management" aids in faster start up and cool do!n" and results in

less degradation of cell and stac components. *ecause of these advantages" activity in the

development of D'Fs capable of operating in the temperature range of 55o (0858 to

0B:8oF) has increased dramatically in the last fe! years. o!ever" at lo!er temperatures"

electrolyte conductivity and electrode inetics decrease significantly- to overcome these

dra!bacs" alternative cell materials and designs are being extensively investigated.
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Fig.0. operating principle of solid oxide fuel cell

Gn D'F essentially consists of t!o porous electrodesseparated by a dense" oxide ion

conductingelectrolyte. The operating principle of such a cell is illustrated in Figure 0. 'xygen

supplied at the cathode(air electrode) reacts !ith incoming electronsfrom the external circuit to

form oxide ions" !hich migrateto the anode(fuel electrode) through the oxide ion conducting

electrolyte. Gt the anode" oxide ions combine !ith hydrogen (and9or carbon monoxide) in the

fuel to form !ater (and9or carbon dioxide)" liberating electrons. Electrons (electricity) flo! from

the anode through the external circuit to the cathode.

The materials for the cell components are selected based on suitable electrical conducting

properties reuired of these components to perform their intended cell functions- adeuate

chemical and structural stability at high temperatures encountered during cell operation as !ell

as during cell fabrication- minimal reactivity and inter diffusion among different components-

and matching thermal expansion among different components.

M'teri'1s 'nd #e11 desins

E1e#tr"1!te

;ttrium#doped +irconium oxide (;DX) remains the most !idely used material for the electrolyte

in D'Fs because of its sufficient ionic conductivity" chemical stability" and mechanical

strength. The only dra!bac of stabili+ed ;DX is the lo! ionic conductivity in the lo!er cell

operation temperature regime" belo! about :=5o (04>8oF). T!o solutions that have been tried to

resolve this problem are to decrease the thicness of the ;DX electrolyte and to find other

materials to replace the yttrium. Dcandium#doped +irconium oxide has higher conductivity than

;DX but high cost of scandium and detrimental ageing effects in scandium doped +irconium

oxide mae it less attractive in commerciali+ing D'Fs.

adolinium# or samarium#doped cerium oxide materials possess higher oxide ion

conductivity compared to +irconium based materials. o!ever" cerium oxide based materials"

under reducing conditions at high temperatures" exhibit significant electronic conductivity and
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dimensional change. 'peration at temperatures belo! about


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and9or nicel" have been developed and optimi+ed for better performance. %n general" these

materials offer higher oxide iondiffusion rates and exhibit faster oxygen reduction ineticsat the

cathode9electrolyte interface compared !ith lanthanum manganite. o!ever" the thermal

expansion coefficient of cobaltites is much higher than that of the ;DX electrolyte" and the

electrical conductivities of ferrites and nicelites are lo!.

@evertheless" promising results have been reported using these materials" though in many

cases the improved cathodic performance is found to decrease during the cell lifetime as a result

of chemical or microstructural instability. Minimi+ation of cathodicpolari+ationlosses is one of

the biggest challenges to be overcome in obtaining high" stable po!er densities from lo!er

temperature D'Fs. o!ever" these materials are very reactive to!ard ;DX.

Therefore" a thin layer" generally of a cerium oxide based material" is used to reduce the

chemical reaction bet!een the cathode and ;DX. Microstructure also plays a ma?or role in the

cathode polari+ation- this is particularly true !hen a composite cathode" !hich sho!s a better

performance compared to a single composition cathode" is used. %t has been sho!n that

polari+ation resistance depends upon the grain si+e of the ionic conductor in the composite

electrodeand the volume fraction of porosity.

An"de

The anodemust be an excellent catalystfor the oxidationof fuel (hydrogen" carbon dioxide)"

stable in the reducing environment of the fuel" electronically conducting" and must have

sufficient porosity to allo! the transport of the fuel to and the transport of the products of fuel

oxidation a!ay from the electrolyte9anode interface !here the fuel oxidation reaction taes

place. The other reuirements include matching of its thermal expansion coefficient !ith that of

the electrolyteand interconnect- integrity of porosity for gas permeation- chemical stability !ith

the electrolyte and interconnect- and applicability to use !ith versatile fuels and impurities. %n

addition" cost effectiveness is al!ays a factor for commerciali+ation.

@icel#;DX composites are the most commonly used anode materials for D'Fs. @icel

is an excellent catalyst for fuel oxidation- ho!ever" it possesses a high thermal expansion

coefficient" and exhibits coarsening of microstructure due to metal aggregation through grain
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gro!th at cell operation temperatures. ;DX in the anode constrains nicel aggregation and

prevents sintering of the nicel particles" decreases the effective thermal expansion coefficient

bringing it closer to that of the electrolyte" and provides better adhesion of the anode !ith the

electrolyte. %n these anodes" nicel has dual roles of the catalyst for hydrogen oxidation and the

electrical current conductor.

%n addition" it is also highly active for the steam reformingof methane. This catalytic

property is exploited in the so#called internal reforming D'Fs that can operate on fuels

composed of mixtures of methane and !ater. Glthough nicel is an excellent hydrogen oxidation

and methane#steam reforming catalyst" it also cataly+es the formation of carbon from

hydrocarbons under reducing conditions.

$nless sufficient amounts of steam are present along !ith the hydrocarbon to remove

carbon from the nicel surface" the anode may be destroyed. Gs a result" even !hen using

methane as the fuel" relatively high steam#to#carbon ratios are needed to suppress this deleterious

reaction. $nfortunately" due to the high catalytic activity of nicel for hydrocarbon cracing" this

approach does not !or for higher hydrocarbons" and it is generally not possible to operate

nicel#based anodes on higher hydrocarbon#containing fuels !ithout pre#reforming !ith steam

or oxygen. %n spite of this dra!bac" nicel# ;DX composite remains the most commonly

utili+ed anode material for D'Fs and is satisfactory for cells operating on clean" reformed fuel.

o!ever" advanced D'F designs place additional constraints on the anode" such as

tolerance of oxidi+ing environments and9or the ability to tolerate significant uantities of sulphur

and9or hydrocarbon species in the fuel stream. Glternative materials" such as cerium oxide or

strontium titanate9cerium oxide mixtures" have yielded some promising results in these designs"

but the benefits obtained in terms of sulphur" hydrocarbon and9or redox tolerance are

counterbalanced by other limitations (such as the difficulty of integrating such materials !ith

existing cell and stac fabrication processes and materials). opper based anodes have also been

proposed for intermediate temperature ([>55o- [0B:8oF) D'Fs intended to operate directly on

hydrocarbon fuels !ithout prior reformation" but the lac of catalytic activity for oxidation of

fuel in copper and sintering of copper at the cell operating temperatures have limited their use in

practical D'Fs.
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Inter#"nne#t

Dince a single cell only produces voltageless than 0 Vandpo!eraround 0 ,9cm8" many

cells are electrically connected together in a cell stac to obtain higher voltage and po!er. To

connect multiple cells together" an interconnection is used in D'F stacs. The reuirements of

the interconnection are the most severe of all cell components and include/ nearly 055 percent

electronic conductivity- stability in both oxidi+ing and reducingatmospheres at the cell operating

temperature since it is exposed to air (or oxygen) on the cathodeside and fuel on the anodeside-

lo! permeability for oxygen and hydrogen to minimi+e direct combination of oxidantand fuel

during cell operation- a thermal expansion coefficient close to that of the cathode and the

electrolyte- and non#reactivity !ith other cell materials.

To satisfy these reuirements" doped lanthanum chromite is used as the interconnection

for cells intended for operation at about 0555o (0>48oF).

%n cells intended for operation at lo!er temperatures ([>55o- [0B08oF)" it is possible to

use oxidation#resistant metallic materials for the interconnection. ompared to lanthanum

chromite ceramic interconnects" metallic alloys offer advantages such as improved

manufacturability" significantly lo!er ra! material and fabrication costs" and higher electrical

and thermal conductivity. *ut to be useful for the interconnect application" the metallic alloys

must satisfy additional reuirements" including resistance to surface oxidation and corrosionin a

dual atmosphere (simultaneous exposure to oxidi+ing and reducing atmospheres)" thermal

expansion matching to other stac components (particularly for stacs using a rigid seal design)"

chemical compatibility !ith other materials in contact !ith the interconnect" such as seals and

cell materials" high electrical conductivity not only through the bul material but also in in#situ#

formed oxide scales" mechanical reliability and durability at the cell operating temperature" and

strong adhesion bet!een the as#formed oxide scale and the underlying alloy substrate.

Ferritic stainless steels are the most promising candidates" o!ing to the fact that some

alloys in this family offer a protective and conductive chromium#based oxide scale" appropriate

thermal expansion behavior" ease of manufacturing and lo! cost. Deveral ne! ferritic stainless

steels have been developed specifically for D'F interconnects. Glthough these alloys

demonstrate improved performance over traditional compositions" several critical issues remain-
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among these are chromium oxide scale evaporation and subseuent poisoning of cathodes-scale

electrical resistivity in the long term- corrosion and spalling under interconnect exposure

conditions- and compatibility !ith the ad?acent components such as seals and electrical contact

layers. To overcome some of these problems" some surface coatings can be applied onto metallic

interconnects to minimi+e scale gro!th" electrical resistance and chromium volatility.

St'#2 desin

%n terms of stac design" most development has focused on planar and tubular design cells" each

of these designs having a number of interesting variants- for example" the planar D'F may be

in the form of a circular dis fed !ith fuel from the central axis" or it may be in the form of a

suare plate fed from the edges. The tubular D'F may be of a large diameter (0= mm)" or of

much smaller diameter ([= mm)" the so#called micro tubular cells. Glso" the tubes may be flat

and ?oined together to give higher po!er density and easily printable surfaces for depositing the

electrode layers. Figure 8 illustrates typical planar cell stacs and a tubular cell bundle. 'ne of

the inherent advantages of tubular cell bundles is that the air and the fuel are naturally isolated

because the tubes are closed at one end.

o!ever" in the case of planar cell stacs" an effective seal must be provided to isolate air

from the fuel. The seal must have a thermal expansion match to the fuel cell components" must

be electrically insulatingand must be chemically stable under the operational conditions of the

stac. Glso" the seal should exhibit no deleterious interfacial reactions !ith other cell

components" should be stable under both the high temperature oxidi+ing and reducing

operational conditions" should be created at a lo! enough temperature to avoid damaging cell

components (under >=5o or 0=


47/97

%n addition" the sealing system should be able to !ithstand thermal cycling bet!een the

cell operation temperature and room temperature. G number of different sealing approaches are

under development" including rigid" bonded seals (for example" glass#ceramics and bra+es)"

compliant seals (for example viscous glasses) and compressive seals (for example" mica#based

composites)- multiple sealants may also be used in any given stac design bet!een different cell

components. Duccessful development of sealing materials and concepts for planar D'Fs is

probably the most important issue for the long#term performance stability and lifetime of planar

D'F stacs and hence for their eventual commerciali+ation at competitive costs.

Glternate tubular geometry cells being developed by Diemens.

A//1i#'ti"ns
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G Diemens ,estinghouse 055 ilo!att D'F po!er system.

$sing planar D'Fs" stationary po!er generation systems of from 0#,to 8=#, si+e

have been fabricated and tested by several organi+ations. Deveral hundred 0#, si+e combined

heat and po!er units for residential application !ere field tested by Dul+er exis- ho!ever" theircost and performance degradation !as high and stac lifetime too short. ,ith improved sealing

materials and sealing concepts" planar D'F prototype systems in the 0# to =#, si+es have

recently been developed and are being tested by various organi+ations !ith greater success.

$sing tubular (cylindrical) D'Fs" Diemens9 ,estinghouse fabricated a 055#,

atmospheric po!er generation system (Figure B). The system !as successfully operated for t!o

years in the @etherlands on desulfuri+ed natural gas !ithout any detectable performance

d

an integrated hybrid power supply for dg

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