Smart Grids (Sabonnadière/Smart Grids) || SmartGrids: Motivation, Stakes and Perspectives

Chapter 1

SmartGrids: Motivation, Stakes andPerspectives

1.1. Introduction

Power systems, after several decades of slow development, are experiencingtremendous changes due to several factors, such as the need for large-scaleintegration of renewable energies, aging assets, energy efficiency needs andincreasing concerns about system vulnerability in the context of the multiplication ofactors in free energy markets The complexity of operations is increasing, which willultimately require the introduction of more intelligence in the grid for the sake ofsecurity, economy and efficiency, thus allowing the emergence of the “SmartGrid”concept.

1.1.1. The new energy paradigm

The current operation of electrical networks is based on four levels resultingfrom the structure of the global electrical system:

– Power generation: most power is generated by large units installed in strategiclocations for operation with respect to the power grid.

– The transmission system, which allows power to be transferred from largepower plants to large consumption centers and other sub-transmission anddistribution systems. This is the backbone of the whole power system, whichcontains sophisticated equipment and has highly centralized management.

Chapter written by Nouredine HADJSAÏD and Jean-Claude SABONNADIÈRE.

SmartGrids Edited by Nouredine Hadjsaïd and Jean-Claude Sabonnadière© 2012 ISTE Ltd. Published 2012 by ISTE Ltd.

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– Distribution grids: these are at the interface between the transmission grid andthe end user (the customer). They are connected to the transmission grid through“interface buses” called “substations” via transformers and, for economic reasonsand simplicity of operation, are generally operated in radial structures. They are thuscharacterized, in the absence of significant local generation sources (interconnectedat the distribution level), by unidirectional energy flows (energy traditionally alwaysflows in the same direction, from the substation to the end user).

– End users are mostly passive customers characterized by “non-controllable”loads and do not contribute to system management.

The first three levels, although institutionally unbundled in a deregulatedenvironment with responsibility domains clearly defined, are closely interdependentand are governed by specific physical laws, related in particular to the generation–consumption balance or to respecting technical constraints. This system as a wholewas designed with the objective of generating, transmitting and distributingelectrical energy under the best conditions of quality and economy. Regarded as themost complex system ever built by man, it is made up of millions of kilometers oflines and cables, generators, transformers, connection points, etc. It also integratesseveral voltage levels, sophisticated protection and control equipment and centers.

On the level of the French electrical grid, for example, there are some1,300,000 km of electrical lines and cables. Moreover, most electrical systems onthe level of a continent are interconnected (such as in Europe or in North America),giving a “gigantic” dimension to this system, whereas its control still remainslimited in scale (performed on the level of each country, at best).

The control of this system is currently very centralized and arrangedhierarchically on the level of each electricity company or each network operator,whereas any disturbance can potentially result in a wide-spread impact (on the levelof the interconnected system). An example of this global disturbance effect is theoutage of November 4, 2006 in Europe, where a disconnection of an electrical linein the north of Germany resulted in a large disturbance across Europe (partition ofthe interconnected zone in three areas of different frequencies, with a load sheddingof 5,000 MW in France, etc.).

Similarly, in 2003 a line in Switzerland that was tripped resulted in a totalblackout in Italy. A similar incident that occurred a month earlier in the USA alsoaffected a large portion of the North-east US grid including Canada (about 50million customers lost power). The specific feature of these disturbances is that theyhave affected several states (or countries) and electricity companies that areinterconnected but do not have a global control system.

This system, which remained relatively stable for nearly a century, underwentsignificant changes at the end of the 20th Century. These changes were triggered bythe liberalization of energy markets and its consequences, in terms of the

SmartGrids: Motivation, Stakes and Perspectives 3

multiplication of actors, partitioning of responsibility, lack of cooperation betweensystem participants, etc.

Moreover, with the growing environmental concerns of our modern societies,building new electrical infrastructures such as overhead electrical lines and evengeneration units based on energy from fossil fuels has become increasingly difficult.Acceptance of such assets by local populations is decreasing (NIMBY or Not in MyBack Yard syndrome).

These concerns, combined with requirements for security of supply, have ledvarious institutional authorities to decide to set up regulatory incentives in favor ofrenewable energies, clean transportation facilities and energy efficiency, oftenlinked to ambitious objectives. Some renewable energy units will be connecteddirectly at the transmission system level, such as large wind farms. The smaller andmedium-sized ones (often below several dozen megawatts) will be integrated intodistribution systems. These last generation units are referred to as distributedgenerators.

The development of these energy sources has a strong impact on the traditionalfunctioning of electrical grids, at the transmission system level as well as at thedistribution system level.

Whereas transmission systems, considered to be the backbone of the electricalsystem due to their role in ensuring the generation–consumption balance and overallsystem security, are already well equipped with very sophisticated control andmonitoring systems. Distribution systems have been designed differently foreconomic reasons, particularly because of their wide-spread and distributed nature.Indeed, distribution systems have not historically been designed to integrate a largenumber of generation units, namely decentralized or distributed energy resources.

Moreover, distributed generators are often intermittent in nature (photovoltaicand wind energy, for example). This implies specific management if theirpenetration rate becomes significant (beyond a certain threshold).

The end-user segment has also considerably evolved. Consumers, who were“passive” and did not interact dynamically with the electrical system, are currentlyin a transformation process, thanks notably to the development of the “smart meter”and related energy boxes. They can, for example, offer load control and responseoptions, thus enabling them to participate in solving some network constraints,reducing peak demands or offering other services necessary to the system.

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Figure 1.1. Electric system organisation (Source: TI and IDEA)

Moreover, with the development of distributed generation the end user can,while being a consumer, become a producer or source of energy storage. Theconsumer thus becomes “active” or even “proactive”, when all the possibilities of“load control”, “local generation” or “energy storage” are included depending onregulations, market design or available technologies. Similarly the expecteddevelopment of the plug-in hybrid electric vehicle (PHEV) with its chargingcharacteristics and storage possibilities, will contribute to the complexity of systemmanagement. These changes encourage engineers and researchers to devise newsolutions to tackle the associated challenges while satisfying changing needs,avoiding over-investing in this system, while optimizing the whole energy chain.

Grid voltagemax

Grid voltagemin

1 year

Radial grid withoutwind turbines

Radial grid withwind turbines

1 year

Figure 1.2. Example of the interconnection impact of wind turbine generation onthe voltage profile of a distribution power grid


The electrical network is a facilitator for all electrical uses and allows the addedeconomic value to be increased for all components connected to it. This can beachieved thanks notably to the characteristics and capability of the power grid togeographically and temporally aggregate all different means of generation and wide-spread customers.

This power grid is now faced with an upheaval as significant as the advent ofelectricity. The solutions that will have to be imagined to tackle the challengesgenerated by these upheavals involve the introduction of more intelligence in thegrid while taking advantage of advanced information and communicationtechnologies (ICTs). All these considerations lead to the concept of an intelligentnetwork or SmartGrids.

Transmission

System operator

Water-heater

light

Household appliances

Central controlsystem

Audiovisualequipment

Fuel cell

Pomp swimming-ppol

heater

Air conditioning

Figure 1.3. SmartGrids from the power grid to the end user

It is important to note that in this chain, for the reasons explained above, thedistribution grids are in a particular position. They undergo a major paradigm shift,mainly because of their direct link with the traditional (end user) and new uses(PHEV). The advent of distributed generation, often of intermittent type, isincreasing the requirement for preserving or even improving the quality of supply,and integrating new technologies (metering, storage, sensors, ICT-based equipment,etc.) into the existing infrastructure. Distribution grids are thus at the forefront ofSmartGrid development to allow added value to be provided to all users who areconnected to it.

1.2. Information and communication technologies serving the electrical system

The recent development of ICTs at reasonable cost offers possible solutions forthe electrical system that were unimaginable only a few years ago. Thus, the

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possibility of installing meters with bidirectional communication with the network atthe site of the end user, even with embedded intelligence for energy management, ischanging the future vision of these networks. This interaction between the end userand the power system – whether it is through an energy supplier, an aggregator, acommercial broker or the distributor itself – can be done through variouscommunication media, but have a direct impact on the electric system.

Electrical networks are already equipped with various means of communicationas well as with sophisticated software for supervision and control centers. However,these technologies are usually dedicated to the transmission system, whoseimportance is predominant in overall security. There are also advanced technologiesat the level of substations, such as the French digital control-command station thathas a link to the transmission system. Likewise, one of the first applications of theInternet for business-to-business (b2b) use was in the field of electrical networks:namely to provide market participants with simultaneous and non-discriminatoryaccess to the same information on available transmission capabilities for example.Beyond this application, the potentialities offered by the Internet have been (and stillare) considered for various grid needs, such as Web-based services, applications notrequiring real-time control, observation and monitoring with no critical information,etc.

On the level of the distribution system, the penetration of these technologies ismuch less visible. We can always mention the French example of the tariff signalsthrough power line communications (PLCs) or the management of end users’subscriptions during peak/off-peak hours. The democratization of ICTs, withequipment such as asymmetric digital subscriber line or “ADSL” boxes that bringand gather several media services at the end-user side and bidirectionalcommunication possibilities offered by smart meters, however, has highlighted theopportunities that these technologies are able to bring to the flexibility of theelectrical system.

Figure 1.4. Communication and intelligence embedded into the grid


ICTs for power grids exist as embedded software, whether at the level ofcomponents or control centers, and means of physical communication (PLC,dedicated lines, fiber optics, wireless, WiFi, ADSL, etc.). A particular interest isassociated with the following functions:

– the smart meter with its different variants: broadband bidirectionalcommunication, with or without load control tools and energy service, offers(intelligence) using different communication media;

– advanced devices for energy management and energy services (often called“energy boxes”) at the point of the end-user, which are either linked to smart metersor take advantage of ADSL potentialities;

– the intelligence associated with various domestic, tertiary or industrialconsumption components, related to energy efficiency or the reliability of the powergrid itself. The typical example is the intelligent and decentralized load-shedding ofhome appliances that act on the fluctuation of the grid frequency or voltage;

– observability, supervisory control and network management linked withgeneration and consumption. This concerns intelligent sensors and theirmanagement, the transmission and processing of an increasingly large volume ofinformation, and the software-assisting grid operators for real-time application,including network security even at the level distribution systems (advanceddistribution management system or DMS);

– the intelligence carried by “objects” or “devices” within the electrical networkcharacterizing the following chain: measure, analyze, decide, act, communicate. Wecan find this chain on a set of applications, from protection and switching devices todecentralized voltage control and self-healing technologies. It is the concern of thewhole distribution automation, with more specific functions on distributed andautonomous control capabilities.

These developments thus relate to a large range of technologies and affect all theparticipants interacting within the electrical system. It thus implies that all thesepieces of equipment, actors and systems are interoperable.

1.3. Integration of advanced technologies

The paradigm shift set out above – particularly at the distribution grid, thedevelopment of information technology and communications (ITCs), the increasedmaturity of certain components of energy conversion (based on power electronics) –are some elements that have contributed to the emergence of new technologies thatwill influence the evolution of these power grids. Some particular examples arediscussed below:

– The smart or communicating meter: several countries have launched large-scale projects replacing conventional meters located with residential consumers with

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smart meters (this replacement operation involves tens of millions of meters,depending on the size of the network or the jurisdiction of the utility concerned). InFrance for example, a complete roll-out of 35 million of these smart meters isscheduled by 2018. Figure 1.5 depicts the structure of the French “LINKY” smartmeter. Among the reasons why this change has become necessary, we can mentionthe introduction of competition and the possibility for customers to choose theirenergy supplier. Currently, in some countries the development of these meters isalso linked to regulatory requirements (such as in Europe). This will allowresidential load curves or profiles to be known. Reading of the meter is processedremotely and may therefore serve as a portal linked to other purposes, with regardsto power quality and energy services for example. We can therefore expect someoptimization in the management of customer consumption (such demand–responseservices at the appliance level, optimization of energy bills, bundled home services,remote maintenance, security, etc.). Beyond these aspects, we understand thepotential of such devices for all value-chain stakeholders: consumers, energyproviders, aggregators, grid operators, balancing entities, etc.

– Actuators integrated into the power grid: these are generally devices that arebased on power electronics. They better manage power flows or other networkvariables, such as voltages or fault currents. Their use can also include thepossibility of managing grid architectures in emergency conditions (fast looping andunlooping devices for radial architectures, superconducting or static fault currentlimiters, adaptive medium and low voltage compensators and voltage regulators,etc.).

– Fast switching devices and intelligent protection: significant progress has beenmade in switching devices, such as frequent operation remotely-controlled switches.The costs have therefore been reduced and the lifespan of the equipment increasedwhich allows new network operating modes that were not previously possible. Suchprotections have also become more efficient and can self-adapt to their environment.Henceforth, we can envisage new patterns of grid operation enabling themanagement of a power system closer to its limits.

– High-performance and cost-effective sensors whether associated with existingdevices or not: the distribution networks are, for example, very weakly equipped interms of measurement devices, which poses the problem of observability. Theemergence of inexpensive sensors combined with adequate communicationpossibilities opens up additional opportunities in terms of observability. Thus,distribution grids can be better controlled in real time. There are some devices thatalready incorporate these measurement possibilities, such as communicating faultpassage indicators. Affordable sensors based on MEMS (micro electromechanicalsystems) technologies for distribution grids is an example of such advanced sensors.Affordable synchronized measurement units at the distribution level can also beincluded in the category of advanced sensors.

– Advanced energy management system and specifically DMS: these functionscan be located in the traditional control centers or distributed/decentralized into


distribution grids (intelligent substation or decentralized Supervisory Control AndData Acquisition [SCADA]). At the distribution level, for example, it allows thegathering of grid information at different locations and triggers real-time actions thatwere not possible until now.

– Energy storage devices: even though the potential for large-scale storage isnow extremely small and the overall cost relatively high, we can expect significantdevelopments in storage in the future, especially in relation to the development ofintermittent renewable energy sources;

– Etc.

One of the structuring elements for these new technologies in the distributionsystem consists of ICT contributions. These technologies may offer greatpossibilities for innovation and flexibility at very low cost. They do, however, havea negative side in terms of the risks associated with these technologies (from theaspect of security).

Figure 1.5. Structure of the French LINKY smart meter, courtesy of ERDF

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1.4. The European energy perspective

The development of the European energy landscape is primarily influenced byfactors such as:

– climate change and environmental concerns;– security of supply;– opening of the European domestic energy market and the integration of new

Member States;– aging infrastructures related to generation, transmission and distribution assets.

Thus, the European Union (EU) has recently adopted “the climate and energypackage”, with ambitious sustainable development objectives such as:

– 3 × 20% for 2020, indicating the aim to reduce CO2 emissions by 20%compared to 1990; and

– to increase energy efficiency by 20% and increase the share of renewableenergies to 20% (35% in the energy mix) within the existing electrical infrastructure.

This defines a way forward for the transition towards a more energy efficient andcarbon-free society. All stakeholders in the electricity sector are affected andsignificant evolution is underway in the electrical grid to accommodate the assignedtargets. This also implies heavy investment in low-carbon technologies and othertechnical innovations, which are seen as key enablers of this change.

Moreover, the EU generation assets need to be renewed, with an expectedreplacement (the retirement of about 300 GW) and expansion (of about 600 GW) ofcapacity by 2030, while consumption is expected to increase by an average of 2%per annum. The need for the renewal and expansion of transmission and distributioninfrastructure, including the accommodation of renewable energy sources anddistributed generation, is foreseen to represent about 850 billion euros by 2030(source IEA).

The EU is very active in adopting renewable energy sources, particularly solarand wind energies. Thus, in 2008, 80% of the worldwide photovoltaic capacitieswere installed in Europe, an increase of 92.9% between 2007 and 2008 (+ 4,592.6MWp). In 2010, the total EU-installed photovoltaic (PV) capacity has reached29,327.7 MWp (22.5 TWh generated energy), representing a growth rate of about120% on average [EUR 11].

Likewise, in 2008 the installed wind energy capacity of the EU reached65.933 GW, i.e. 54.6% of the world’s installed capacity in that year [EUR 11]. In2010, the capacity of wind power installed in EU countries reached 84,278 MW(about 10% of the total European electricity generation capacity) [EWE 11]. Thisrepresents an increase of 12.2% of installed cumulative capacity.


After being one of the most dynamic markets for wind generation (particularlydriven by Germany and Spain), the rate of market growth has slightly decreased inthe past couple of years (9,295 MW in 2010 compared to 10,486 MW in 2009).

Figure 1.6a. Cumulative worldwide installed wind power capacity from1990 to 2010 (Data sources: BTM, EWEA, GWEC and WWEA

[BTP 10], [EWE 10], [GWS 10], [WWE 10])

Figure 1.6b. Cumulated PV generation capacity installed inEU countries by 2010 (in MW) [EUR 11]

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Figure 1.6c. Evolution of the installed capacity of wind power (in GW) worldwide [EUR 11]

In this landscape, it is interesting to highlight the special case of Denmark, whichat an early stage faced the development of renewable energies, especially windturbines. Figure 1.7 is an illustration of this evolution from the 1980s and later1990s.

Système centralisé de production Système décentralise de production

Central production plantsOther plantsWind turbines

Central production plantsOther plantsWind turbines

Centralized generation system 1980s Decentralized generation system 1990s

Figure 1.7. Evolution of the distributed generation landscape in Denmark (source: Eltra)


On the left of Figure 1.7, we can see the situation of power generation in the1980s (centralized system).

On the right of Figure 1.7, we can see the power generation situation in the late1990s (multiplication of distributed generation). This has forced Denmark to comeup with innovative solutions for managing its electrical system beyond the back-upprovided by its neighbors via interconnections. The concept of cell structures forsystem operation or EDISON (electric vehicles in a distributed and integratedmarket using sustainable energy and open networks) experimentation (pilot project)dealing with synchronization of the availability of wind energy with electric vehiclesfor charging or injection processes can be mentioned here.

The French market also followed this development, more specifically from2005–2006, with improved regulatory inventive conditions. Figures 1.8 and 1.9illustrate the remarkable evolution of the installed capacity for both PV and windgeneration.

Thus, we can see the cumulated wind capacity installed multiplied by a factor ofapproximately 1,000 between 1996 and 2008. At the end of 2009, this capacityreached 4,400 MW (an increase of approximately 30% between 2008 and 2009).The installed PV capacity has more than doubled each year since 2006. However, ithas to be noted that the recent revised regulatory laws on feed-in tariffs for grid-interconnected PV cells have resulted in some slowing of the increase in PV powerbeing installed in the French market.

Evolution of wind parks in France

Figure 1.8. Evolution of the French cumulated and annualyl installedwind power capacity since 2000

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0

200

400

600

800

1000

1200

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010p

MW

Métropole DOMMainland IslandsYears

Figure 1.9. Evolution of the cumulated and annualyl installed PV capacity since 2000

These energies are characterized by their intermittency, which makes it difficultto guarantee the power produced with the necessary accuracy during preparatoryoperations or the day-ahead market, even with the sophisticated forecasts that wenow have. With the hypothesis of a lack of back-up generation (no sufficientreserves) with the required dynamics for system security and the current storagepossibilities, the development of these energies without controlling their outputpowers can jeopardize the production–consumption balance and thus the security ofthe electric system as a whole.

Date (January 1997)

Exportedpower(M

W)

Figure 1.10. Output power of a wind farm over a month (in the UK)


Figure 1.11. Output power of a PV farm atVinon sur Verdon-France, May 31, 2009

This variability and lack of control of these generation units considerably affectsthe traditional grid operation schemes. Up to now, conventional generation unitswere perfectly controlled and adapted to the fluctuation of consumption. It is only inextreme cases that load shedding is needed. A growing part of generation is notcurrently controlled and consumption is characterized by its increasing spatial andtemporal variability. Thus, the traditional solutions appear to be inappropriate toensure the security and energy efficiency requirement, particularly in an insecureeconomic context (there is the need for investment optimization).

This significant evolution of the EU energy landscape represents remarkabletechnical, economic and social challenges. In this context, the sustainability targetsissued by European policymakers cannot be achieved without a stepwisetransformation of the existing network infrastructure into a SmartGrid.

1.5. Shift to electricity as an energy carrier (vector)

The recent sharp increase in the price of oil and gas is a major concern forsociety. The case in France, for example, with regards to the share of electricity thatcomes from nuclear power argues for intensification of the electricity carrier as anenergy vector. Furthermore, the development of renewable energy and the expecteddevelopment of PHEVs favor this perspective. Some scenarios on the evolution ofdemand (consumption) in electrical networks in France show an average increase in

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consumption in the range of 1–2% per year, depending on the scenarios considered.In this forecast of consumption increase, despite the expected future gains in energyefficiency and conservation, the shift to electricity as an energy carrier is asignificant aspect.

1.6. Main triggers of the development of SmartGrids

The phenomena and drivers of the SmartGrids concept are various,encompassing technical, economic and regulation aspects. Taking into account theseelements, we can summarize the main triggers (a non-exhaustive list) leading to theconcept of SmartGrids, as being:

– change of the energy paradigm, notably characterized by the advent of freedomof the energy markets, the development of distributed generation and the advent ofrenewable energies and the multiplicity of actors in this landscape which require:

- non-discriminatory access to the grid,

- management of the intermittency of renewable energies,

- management of the observability and dispatchability of distributedgeneration,

- etc.;

– the aging of the existing electricity infrastructure;

– a need to adapt the network for large-scale integration of distributed generationunder the best security and economic conditions (the need for optimization ofinvestments). This adaptation requires a more flexible network and flexiblecomponents, including better automation;

– technological innovations in terms of ICT, power grid equipment (fast circuitbreakers/switch with frequent operations at affordable prices, protection, sensors,etc.) and smart meters that can embed intelligence for service offerings related to theoptimization of consumption (consumer–energy provider interaction);

– increased need for quality of supply (which may vary depending on theapplication or any other criterion) including the security of energy supply;

– the need to face the increasing complexity of the electrical system in its spatial(interconnections) and temporal (dynamic) dimensions.


1.7. Definitions of SmartGrids

There are many different views of the SmartGrid concept. This makes clear thefact that although the main drivers for SmartGrid development are relatively similarin different parts of the world, the priorities are different. For example, within theEU, the challenge of the integration of renewable energies, energy efficiency andEU market integration in the framework of a carbon-free economy are priorities. Inthe US, however, blackouts, peak-demand situations and aging assets are the mainpriorities.

In China, the fast development of the grid, the need to integrate large-scale windfarms in the north and interconnecting the different provinces are immediatepriorities, while the development of PHEV, PVs and microgrids are also fast-emerging issues. The EU Technology Platform1, for example, provides a verycomprehensive definition of the SmartGrids concept, encompassing technologicalsolutions, market issues, communication technology, standardization and regulatoryregimes. Referring to the EU SmartGrids Technology Platform, the concept ofSmartGrids is defined as an “electricity network which intelligently integrates theactions of generators and consumers connected to it in order to efficiently deliversustainable, economic and secure electricity supplies.”

The US Department of Energy gives a more detailed definition of SmartGrids. Itstates that “a smart grid is self healing, enables active participation of consumers,operates resiliently against attack and natural disasters, accommodates allgeneration and storage options, enables introduction of new products, services andmarkets, optimizes asset utilization and operates efficiently, provides power qualityfor the digital economy” (source: US DoE).

Although there are several definitions and descriptions of the SmartGrid concept,it can be summarized as an integration of electricity infrastructure and theembedded/decentralized ICT (software, automation and information processing).The coupling of the two infrastructures provides the required “intelligence”. Thisintelligence can be deployed at various levels of the network (generation, networkhardware, consumption, monitoring and control). In this context, the SmartGridconcept is a significant development that, from the existing network, can only beachieved in increments.

This development will most likely lead to major adjustments modifying the coremission of distribution system operators, for example, through moving from thetraditional model of delivering one-directional electricity to the active managementof grid flows and information.

1 European Technology Platform on SmartGrids.

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… intégration de deux infrastructures

« Infrastructure électrique »

« Infrastructure d’intelligence »

… intégration de deux infrastructures

« Infrastructure électrique »

« Infrastructure d’intelligence »

Electric infrastructure

... integration of two infrastructers

Information and infrastructure

Figure 1.12. SmartGrids: convergence of physical and digital infrastructures (source EPRI)

1.8. Objectives addressed by the SmartGrid concept

The SmartGrid concept must thus face the above-mentioned challenges. It ispossible to assign technical objectives related to innovations and solutions to theproblems raised and socioeconomic objectives presented by the integration of theactive consumer in his or her societal dimension. These objectives must also beassigned to the business models related to the necessary transitions of this systemtowards a more intelligent one.

As already indicated, transmission grids have historically integrated much moreintelligence and sophisticated equipment including ICTs than distribution grids inorder to manage the overall system security requirements. Thus, we can distinguishthe objectives addressed by transmission grids from those addressed by distributiongrids.

1.8.1. Specific case of transmission grids

The change in the energy paradigm has also affected transmission grids, namelythrough:

– Liberalization of energy markets and multiplicity of actors: this has resulted inresponsibility partitioning, the necessity to manage actors that may have divergentinterests including non-discriminatory treatment and motivation for any decisionwith an impact on these actors. Moreover, the management of information in thiscontext has become of paramount importance for the system operation.

– Large-scale development of renewable energies, such as large wind farmsexceeding some dozens of MW that are directly interconnected at the transmissionlevel (higher than 63 kV, for the French example). These energies are fastdeveloping, particularly for the offshore wind farms. However, as far astransmission grids are concerned, these energies have impacts on the whole


interconnected system (e.g. the large-scale development of wind farms in Germanyinevitably impacting the whole interconnected European electricity grid.

– Observation of distributed generation affecting the transmission grid at thelocal level and the traditional decoupling.

– Observation of distributed generation that may affect the transmission grid atthe local level specifically. The traditional decoupling of transmission anddistribution grids is being challenged by the development of distributed generation.Indeed, a large-scale development of distributed generation may cause reverseenergy flows for certain periods, from distribution to transmission, thus affectingupper voltage levels (transmission). However, these decentralized generation unitsare not currently observable in most cases and most are within the jurisdiction ofdistribution grids.

– European (or continental) integration: the multiplicity of transactions and thedevelopment of large-scale intermittent generation at a continental (European) levelrequire continental (European) observation of the entire network and a perfectcoordination of system operators. The first observation “bricks” have already beenlaunched between some countries in Europe, such as the CORESO platform.However, such cooperation and information sharing must be generalized to a largerscale (a whole “interconnected” grid) while addressing business (actors) andtechnical information on all generation means, especially on intermittent energyincluding real-time applications. The very large dimension of these interconnectedsystems combined with responsibility partitioning, however, means that this iscurrently a highly challenging task.

Furthermore, we can add to these factors – which are linked to each other – theincreasing difficulties of building new overhead lines or the need to operate powergrids ever closer to their security limit.

The intelligence objectives at the level of transmission grids are thereforestrongly associated with these factors in the view of maintaining the generation–consumption balance. It is therefore of paramount importance to preserve the overallsystem security in optimum economical conditions. The objectives are clearly of adifferent nature compared to those of distribution grids.

1.8.2. Specific case of distribution grids

Distribution grids are facing different challenges to those of transmission gridsbased at the interface between the transmission and end user. As such, the objectivesare those related to its evolution with respect to its link with the end user, distributedgeneration and new usages, such as PHEVs.

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In technical terms, the major objectives of the SmartGrid can be summarized asfollows:

– enabling large-scale integration of renewable energies including all storageoptions, facilitating PHEVs and increasing the participation of consumers (theconcept of the active consumer and optimization of consumption) under the bestpossible conditions of economy, energy of quality and security of supply;

– strengthening the overall energy efficiency, namely by significantly enhancingthe efficiency of the energy chain as a whole and reducing the environmental impactof the whole electricity supply system;

– allowing an easy and efficient management of the system, while facing theincreasing complexity of the system, including the management of a large amount ofdata; and

– developing interoperability between the various actors and stakeholders (e.g.between transmission and distribution systems).

1.8.3. The desired development of distribution networks: towards smarter grids

The expected operating modes of distribution grids in the up-coming years willdepend on the stakes they face and on the objectives that will be assigned.

The following four elements can characterize the expected qualities of thesenetworks:

– Accessible: the networks will accommodate all generation, storage andconsumption options required for connection.

– Economic: the focus will be put on grid investment and operations that give thegreatest advantage in the use of infrastructure, allowing costs to be optimized for thebenefit of all users.

– Flexible: redundancy of paths will be increased with respect to building up newgrid materials/equipment in order to optimize the efficiency of existing energy paths.This will allow the grid response to be optimized with respect to users’ needs as wellas to various disturbances affecting it while fulfilling system security, economicaland environmental requirements.

– Reliable: to ensure and increase the safety/security and quality of supply.

Given the challenges mentioned above, combined with various inherentconstraints of power grids (capital-intensive infrastructure, difficulties of buildingnew power lines, increasing complexity, interaction with the end user, etc.), theevolution of these grids must include the integration of some form of intelligence instructure and management. Many countries all over the world are now integratingthis dimension (SmartGrids in Europe, the US, China, Japan, etc.). The introductionof this “enhanced” intelligence in distribution networks, for example, is a challenge


in itself. It can help (in the more or less short- to medium- term) if we modernizethis infrastructure which, as we mentioned previously, had benefited less fromadvanced grid-embedded technologies when compared to transmission systems.

Obviously, this will require investments to achieve these “quality” goals becausethere is a significant “gap” between the current state of the grid and the targetrepresenting a more intelligent network.

1.9. Socio-economic and environmental objectives

Beyond the technical objectives, other objectives related to externalities can alsobe highlighted, such as the effect of innovations, the creation of value andemployment, the improvement of knowledge, the management of expertise, or theimprovement of carbon footprints.

SmartGrids are regarded as an “integrating and structuring concept”. They createvalue by intelligent system integration and can involve the development of othereconomic sectors (ICT infrastructure, electrical equipment, home automation,energy services, environment, etc.). Thus, structuring projects related to SmartGridsis likely to trigger large-scale innovations, not only in the electrical sector but also inother sectors linked with this concept.

Figure 1.13 comes from a study conducted by EPIC/SAIC, USA on the expectedbenefits of SmartGrid initiatives on technical issues (improving quality, solvingconstraints, etc.) as well as on environmental benefits and job creation issues.

Figure 1.13. Example of SmartGrid benefits distribution by value segment(source: EPIC/SAIC, USA)

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1.10. Stakeholders involved the implementation of the SmartGrid concept

Several actors are involved including all “stakeholders” who can interact with orbe integrated within the system vision of the SmartGrid concept:

– Consumers, whose expectations must be taken into account regarding thequality of energy supply, environmental concerns and the lowering of energy bills.The installation of smart energy meters will transform the nature of consumers byactively and simply affecting the consumption pattern while retaining consumers’comfort.

– System operators (transmission and distribution) in charge of system securityand energy quality under acceptable economical conditions will have increasedmeans of acting on the operation of the network while taking advantage of availableITCs.

– Manufacturers of electrical equipment who will develop and providecomponents and solutions that are intended to ensure the functioning and security ofthe network.

– ICT service providers who develop and deploy software and other informationequipment to support information, monitoring and control functions of the grid andits components; it also includes telecommunication systems providers.

– Centralized and decentralized energy producers, who are interested in networkdevelopment to prevent limitations of their integration into the grid.

– Energy and service providers including aggregators, who will thus take part inthe organization of the system and will be able to offer energy services.

– Research and innovation centers whose results will be implemented at a real-life scale on the network after having been tested in a laboratory.

– Education and training institutions such as universities who will have aprominent role in preparing the competences and capitalizing the expertise requiredfor the development of SmartGrids.

– Regulation authorities, such as the French Energy Regulatory Commission(CRE-Commission de Régulation de l’Energie), local authority and electricityorganizations representatives, such as Fédération Nationale des CollectivitésConcédantes et Régies, and energy agencies, such as the French Ademe.

– Standardization organizations.


Figure 1.14. Interaction of energy and information actors

1.11. Research and scientific aspects of the SmartGrid

In view of the drivers and objectives mentioned above, the SmartGrid concept isin itself an important and ambitious research program over different timescales(short-, medium- and long-term). It involves several stages including research,development, pilot demonstration, feedback and finally deployment processes.Several research projects are underway throughout the world. These projects areeither funded by government agencies or community organizations (such as theEuropean Commission in Europe or the Department of Energy in the US) orindustrial entities and consortia.

1.11.1. Examples of the development of innovative concepts

SmartGrid activity is carried out within the G2ELAB (Grenoble Institute ofTechnology, UJF and CNRS) and IDEA (a research center involving individualsfrom EDF, Schneider Electric and Grenoble Institute of Technology). The scientificorientation is based on achievements in the field of automation of grid functions, theintegration of renewable energy sources, the demand-side response, energy-flowoptimization and the coupling of electricity infrastructure with ITCs.

24 SmartGrids

This guideline specifically relates to the development of innovative concepts for:

– The distribution of intelligence (self-adaptive voltage controller, decentralizeddecision process and intelligent protection, for example). These kinds of devicesallow the insertion rate of distributed generators to be significantly increased withinthe existing network through solving specific distributed generator integrationconstraints for example. Study cases and achievements can be found in [RIC 05],[TRA 07], [KIE 09], [THA 06] including advanced decentralized or coordinatedcontrol function, such as voltage control per cell or islanding and automaticsynchronization of portions of the grid;

1.05 pu

1 pu

0.95 pu

Distance au poste source

V

Poste Source

Réseau de distribution sansGED

Problèmes de tension

But

1.05 pu

1 pu

0.95 pu

Distance au poste source

V

Poste Source

Réseau de distribution sansGED

Problèmes de tensionProblèmes de tension

But

Voltage constraint

Objective

Distribution grid without DG

Distance to substationSubstation

Figure 1.15a. Distributed generation and voltage profile in distribution systems

Contrôle centralisé régulation globale du réseau parcoordination des GED choix des consignes de régulationà adopter pour chaque GED

Nécessite organes de communication

Contrôle localisé régulation locale et autonome enfonction de l’état électrique du réseauau nœud de connexion de la GED

Participation intelligente de toutes lesGED à la sauvegarde du plan detension sans communication

GED

GED

Dispatchinglocal

P,Q,V..?HTA/BT

GEDGED

GEDGED

Dispatchinglocal

P,Q,V..?HTA/BT

GED

GED P,Q,V..?

HTA/BT

P,Q,V..? GEDGED

GEDGED P,Q,V..?

HTA/BT

P,Q,V..?

Coordinated control → global control of the gridby coordinating DGs → choice of control settings tobe implemented for each DG Requires communication infrastructure

Decentralized control → local and autonomouscontrol as a function of the network state at DG’sconnection bus Intelligent participation of all DGs to theregulation of voltage profile without communication

Decentralized control→ local and autonomouscontrol as a function of the network state at DG’sconnection bus.

MV/LV MV/LV

Figure 1.15b. Intelligent voltage control modes in distribution systemsin the presence of distributed generation


4 6 8 10 12 14 16 18 200.95

1

1.05

1.1

1.15

Time (H)

Volta

ge(pu)

V3/Vpu_aV3/Vpu_bV3/Vpu_cV4/Vpu_aV4/Vpu_bV4/Vpu_cV5/Vpu_aV5/Vpu_bV5/Vpu_c

4 6 8 10 12 14 16 18 200.95

1

1.05

1.1

1.15

Time (H)

Volta

ge(pu)

V3/Vpu_aV3/Vpu_bV3/Vpu_cV4/Vpu_aV4/Vpu_bV4/Vpu_cV5/Vpu_aV5/Vpu_bV5/Vpu_c

Figure 1.15c. Voltage management through conventional control(active/reactive or P/Q) on a test network

4 6 8 10 12 14 16 18 200.95

1

1.05

1.1

1.15

Time (H)

Volta

ge(pu)

V3/Vpu_aV3/Vpu_bV3/Vpu_cV4/Vpu_a

V4/Vpu_cV5/Vpu_aV5/Vpu_bV5/Vpu_c

Maximum admissible voltage (1.1 pu)V4/Vpu_b

4 6 8 10 12 14 16 18 200.95

1

1.05

1.1

1.15

Time (H)

Volta

ge(pu)

V3/Vpu_aV3/Vpu_bV3/Vpu_cV4/Vpu_a

V4/Vpu_cV5/Vpu_aV5/Vpu_bV5/Vpu_c

Maximum admissible voltage (1.1 pu)V4/Vpu_b

Figure 1.15d. Intelligent control of the voltage on a test network (source: IDEA athttp://www.leg.ensieg.inpg.fr/gie-idea)

– Self-healing power grids: this concept concerns distribution grids. The powergrid must quickly detect and even anticipate, isolate and restore safe operation in anoptimal and automated way after the occurrence of a fault. An example of thisachievement can be found in [HAD 10c].

26 SmartGrids

Substation

Cell level 1Intellegent Agent

Faulty zone beforerestoration process Faulty zone after

restoration process

Figure 1.16. Concept of the self-healing network: detect, locate, repair andre-energize the network after a fault (source: IDEA at http://www.leg.ensieg.inpg.fr/gie-idea)

– The virtual power plant: this is a concept that represents a set of methodologiesfor the connection and management of distributed energy resources at a large scalewhile taking account the intermittency. Figure 1.14 illustrates an aggregationpossibility of generation, storage and load control, as a single “virtual plant”allowing the power output of intermittent sources to be guaranteed or bettercontrolled. An example of this achievement is provided by [SUR 06] and the EUproject FENIX [KIE 09].

Réseau detransportRéseau detransport

Réseau deRéseau dedistributiondistribution

p p g qg

Prod.Prod. Cons.Cons.

GAZGAZGAZGAZGAZGAZ

Supervision/contrôle

Supervision/contrôle

Transmissiongrid

Distributiongrid

Monitorand control

Figure 1.17. The virtual power plant: energy mix management andgeneration aggregation tool (source: IDEA at http://www.leg.ensieg.inpg.fr/gie-idea)


– Observation of the power grid, particularly for distribution systems. Thetransmission grid is concerned with the interconnected system and large-scaleintermittent generation. The observation is an essential function for system controlpurposes. It can be viewed from the control center perspective and from sensors thatare coupled to components and system decision processes.

– Reconfigurable grid architectures that increase the acceptable generation rateor optimize the electrical losses in the presence of distributed generation (energyefficiency). An example of this achievement can be found in [HAD 09].

– Smart buildings and demand response/load control: this aspect can beextended to the convergence of the electrical grid with buildings, renewable energiesand PHEV. Figure 1.18 shows possible interactions between different appliances,storage devices, local generation units, PHEV, energy boxes within a house and theelectrical grid through a smart meter.

20

EnergyBox

CoffretélectriqueCoffret

électriqueCompteur

communicant

Terminaux decommunication

Appareils délestables

Stockage d’électricité

Production d’électricité

Appareils « prioritaires »

Flux d’informations

Flux d’électricité

Le smart Grid chez l’usager finalL’energy box comme « Energy Manager »

InternetBox

The SmartGrid and the end user

The energy box as an “Energy Manager”

Electricgrid

Smart meter

Electric board

Electricity generation

Electricity storage

Communicationterminals

Switchable appliances Priority appliances

Information flow

Electric flow

The SmartGrid and the end userThe energy box as an “Energy Manager”

Electricgrid

Figure 1.18. The smart house with its energy box and smart meter(source: H3C-Energies at www.h3c-energies.fr/)

28 SmartGrids

The structure of our energy supply, made increasingly complex by these newtypes of equipment, energy services and various tariff offers, will lead to thegeneralization of energy management systems, communicating with all installations.The house communicates and becomes intelligent, and the step towards integratedmanagement of all facilities (household appliances, telecommunication, electricity,safety, etc.) becomes smaller. Housing is connected, and energy efficiency becomesa fully-fledged parameter of the building management, on the same level as comfortor consumption.

1.11.2. Scientific, technological, commercial and sociological challenges

The SmartGrid concept provides a system vision encompassing research,development, testing, feedback and analysis of the innovative technologies involved.Its purpose is to achieve specific goals in terms of network management forimproved energy efficiency of the entire value chain, increased penetration ofrenewable energies and satisfying new needs such as PHEVs or the involvement ofthe end user in energy management, while taking advantage of ICTs. Theimplementation of this concept and the track of the SmartGrid objectives require thesame scientific breakthroughs that could lead to significant technologicalinnovations. Indeed, we recall that SmartGrids allow the convergence of physicalinfrastructure (the electrical system) and digital infrastructure (ICTs). It is wellknown that the meeting of two disciplines is a source of major innovations. Inaddition, although the electrical system is already equipped with ICTs, thesetechnologies have often been designed separately from the electrical system (asadditional layers), while being the property of the operator.

Nowadays, the cost of ICTs is relatively low, with strong penetration in modernsociety. In addition, the deregulation of the electricity market and the multiplicationof actors encourage the use of “on-the-shelf” technologies. This requiresinteroperability between the different “SmartGrid objects”, carrying an intrinsicsecurity, as well as between different grid participants. On the other hand, thedifference in lifespan between ICTs and energy infrastructure raises the question ofthe evolution process of the whole integrated system. Taking into account thesignificant investments necessary for the implementation of this concept, thequestion of technological risk involved in the evolution of the system, specificallywith respect to ICT, is of prime importance.

In this context, it is understood that the challenges are scientific, technological,commercial and sociological. They are remarkable challenges that can only be metwith the establishment of partnerships (and technological processes) involving allstakeholders in this chain (energy producers, system operators, energy serviceproviders, electrical equipment and ICT manufacturers, solution integrators,universities and research centers, standardization bodies, energy associations and


agencies). Of course, the final customer must also be included as an active entity andno longer as a passive consumer.

Some examples of the “locks” that need to be addressed at the research level,without being exhaustive, are discussed below.

1.11.2.1. Scientific and technological locks

These include:

– Integration of renewable energies and management of intermittency for aglobal system balance and economics, including the participation of these energysources in ancillary services.

– Integration of PHEVs on the grid, their various forms of load and interactionwith the system (injection, consumption, storage, control and services).

– Observability of the grid with a reduced set of sensors (with appropriateaccuracy) or on the basis of smart meters while taking into account real-timeconstraints. It also includes data processing and the management of large amount ofinformation with respect to a dynamic bidirectional communication “grid-smartmeter”. The issue of observability is also critical for interconnected transmissiongrids with large-scale intermittent generation as well as at the interface betweentransmission and distribution grids and operation.

– Development and implementation of “simple” and cost-effective self-healingtechnologies in the presence of distributed generation including at the low-voltagelevel.

– Protection/equipment with frequent switching capabilities, allowing multiplegrid reconfigurations for better flexibility and reduced losses (better energyefficiency).

– Coupling of load control with new usages (PHEVs) or intermittent generation(convergence of buildings, renewable energies, PHEVs and power grids) within celldistribution grids or “eco-smart cities”. This part includes coupled models andsimulation tools.

– Understanding the interdependency between the digital (virtual) and theelectrical power (physical) infrastructures. This aspect also falls within therequirement for coping with increased system complexity and ensuring systemsecurity (including cyber security) while embedding various “smart” technologiesinto the grid.

– Planning of SmartGrid investments in an uncertain environment (appropriatemodels, stochastic approaches, risk management, etc.) and evolution of power gridarchitectures.

30 SmartGrids

1.11.2.2. Commercial and sociological “locks”

These include:

– Business models for diffuse and efficient demand response, including valuecapturing and sharing, given the responsibility partitioning of the energy valuechain.

– Levels of technological deployment in an industry accustomed to slowevolution and transition.

– Acceptability to customers with respect to the intrusion of load controltechnologies and smart meters as well as to their “positive” behavior in participatingto demand response.

– Global optima with new usages.

1.12. Preparing the competences needed for the development of SmartGrids

These challenges, ambitious by nature, correspond to the stakes of the 21stCentury. Indeed, through the close entanglement between energy and intelligencethey realize the mindset of young engineers and technicians who were born in theage of ITCs. SmartGrids require cross-disciplinary competences as well as thecapitalization of expertise, since the future “smarter grid” will have to be built on thebasis of existing power infrastructures (evolution process). Thus, existing trainingprogrammes in power engineering need to incorporate knowledge on informationand communication science and vice versa. Currently, curricula addressingSmartGrid competences are emerging. The need for these competences is growingand the settling of these new (or evolutionary) training programmes has also to begeneralized. With this in mind, the investment in power grid equipment must beaccompanied by a serious modernization and an effort to recruit young engineersand technicians who are well armed and motivated to build the intelligent networksof the future.

1.13. Conclusion

We thus note an increase in complexity related to different parameters,institutional as well as technical, such as the increased share of intermittent energysources, the integration of the end user in energy management who becomes “pro-active”, the multiplication in the number of actors, the issues of interoperability, therequirement to maintain and even improve the quality of supply, the need to reachenergy efficiency and peak demand control objectives, etc. The implementation ofthe SmartGrid concept will thus induce a notable evolution of the entire energychain.


This concept will provide a technical framework for large-scale integration ofintermittent energy sources, enhanced energy efficiency, and better functioning of thenetwork, while tracking environmental targets and ensuring improved security andquality of supply under the best economic conditions.

The SmartGrid infrastructure will play a broader role than the specificmanagement of the electrical power grid:

− its functionalities will enable new energy services: smart energy managementof buildings and energy efficiency, security and monitoring services and other homeautomation related services;

− its infrastructure could be pooled together with other needs: development of jointmulti-utility SmartGrids (electricity, gas, water) and telecommunication networks byusing the densest network in the world.

Finally, like any technological adventure, “SmartGrids” will provide a source oftechnological and societal evolutions whose benefits cannot all be measured yet.They are likely to include technology transfer to other sectors (home automation andwhite goods, logistics, multi-fluid, application domains of artificial intelligence),catalysis of behavioral and societal evolutions (to support careful management ofenergy, other utilities, support to cooperation models and pooling of resources).

This SmartGrid potential must be preserved by a balanced consideration ofstakes and actors with effective and pragmatic management of the transitions froman economic and industrial viewpoint. Furthermore, it should not lose sight ofhuman, societal and environmental goals that are specific to energy in general and toelectricity in particular, as well as the need for cooperative operation modes.

1.14. Bibliography

[BTP 10] BTM Consult, World Market Update 2010, BTM Consult, 2010.

[EWE 10] EWEA, Wind in Power: 2010 European Statistics, European Wind EnergyAssociation, 2010, http://www.ewea.org.

[EUR 11a] www.eurobserv-er.org, 2011.

[EUR 11b] http://observer.cartajour-online.com, 2011.

[EU R12] Smart Grids European Technology Platform, http://www.SmartGrids.eu, 2012.

[GWS 10] GLOBAL WIND ENERGY COUNCIL, GLOBAL WIND STATISTICS, 2010; http://www.gwec.net.

[HAD 99] HADJSAÏD N., CANARD J-F., DUMAS F., “Dispersed generation impact ondistribution systems”, IEEE Computer Application of Power, pp. 23-28, 1999.

32 SmartGrids

[HAD 09] HADJSAÏD N., CAIRE R., RAISON B., “Decentralized operating modes for electricaldistribution systems with distributed energy resources”, Article (Panel), IEEE PESGM’2009, Alberta, Canada, July 26-30, 2009.

[HAD 10a] HADJSAÏD N., SABONNADIÈRE J-Cl., ANGELIER J-P., “Les réseaux électriques dedistribution: du patrimoine à l’innovation”, Repère REE, Revue REE, vol. 1 pp. 81-95,2010.

[HAD 10b] HADJSAÏD N., SABONNADIÈRE J-Cl., ANGELIER J-P., “Les systèmes électriques del’avenir: les SmartGrids”, Repère REE, Revue REE, vol. 1, pp. 96-110, 2010.

[HAD 10c] HADJSAÏD N., LE-THANH L., CAIRE R., RAISON B., BLACHE F., STÅHL B.,GUSTAVSSON R., “Integrated ICT framework for distribution network with decentralizedenergy resources: prototype, design and development”, Article (Panel) invite IEEE PESGM’2010, Minneapolis, MN, USA, July 24-29, 2010.

[KIE 09] KIENY C.H., BERSENEFF B., HADJSAÏD N., BESANGER Y., MAIRE J., “On theconcept and the interest of Virtual Power plant: some results from the European projectFENIX”, Article (Panel) invite, IEEE PES GM’2009, Alberta, Canada, July 26-30, 2009.

[RIC 05] RICHARDO O., VICIU A., BESANGER Y., HADJSAID N., KIENY Ch., “Coordinatedvoltage control in distribution networks using distributed generation”, IEEE/PESTransmission and Distribution Conference and Exposition, October 9-12, 2005, NewOrleans, USA.

[SER 09] Syndicat des énergies renouvelables, http://www.enr.fr, 2009.

[SUR 05] SURDU C., MANESCU L., BESANGER Y., HADJSAÏD N., KIENY Ch., “La centralevirtuelle: un nouveau concept pour favoriser l’insertion de la production décentraliséed’énergie dans les réseaux de distribution ”, Revue Enseigner l’Électrotechnique etl’Électronique Industrielle, vol. 3EI, no. 40, pp. 41-48, France 2005.

[SUR 06] SURDU C., MANESCU L., RICHARDOT O., BESANGER Y., HADJSAÏD N., KIENY Ch.,GEORGETTE F., MALARANGE G., MAIRE J., LAFARGUE J.P., “On the interest of the virtualpower plant concept in the distribution systems”, CIGRE 2006, Conseil International desGrands Réseaux Electriques, Paris, France, 2006.

[THA 06] HA PHAM T.T., BESANGER Y., HADJSAID N., “Intelligent distribution grid solutionto facilitate expanded use of dispersed generation potential in critical situation”,CRIS’2006, Alexandria, VA, USA, September 24-27, 2006,.

[TRA 07] TRAN-QUOC T., MONNOT E., RAMI G., ALMEIDA A., KIENY C., HADJSAID N.,“Intelligent voltage control in distribution network with distributed generation”,Conference Internationale CIRED, Vienna, Austria, May 2007.

[WWE 10] WWEA, World Wind Energy Report 2010, World Wind Energy Association,2010, http://www.wwindea.org.

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