Feasibility Study of Wind Farm Grid-Connected Project in Algeria Under Grid Fault Conditions Using D-Facts Devices

applied sciences

Article Feasibility Study of Wind Farm Grid-Connected Project in Algeria under Grid Fault Conditions Using D-Facts Devices

Lina Wang 1 , Kamel Djamel Eddine Kerrouche 1,5,* , Abdelkader Mezouar 2, Alex Van Den Bossche 3 , Azzedine Draou 4 and Larbi Boumediene 2

1 School of Automation on Science and Electrical Engineering, Beihang University, Beijing 100191, China; [email protected] 2 Electro-Technical Engineering Lab, Faculty of Technology, Tahar Moulay University, Saida 20 000, Algeria; [email protected] (A.M.); [email protected] (L.B.) 3 Electrical Energy LAB EELAB Sint–Pietersnieuwstraat 41, B 9000 Ghent, Belgium; [email protected] 4 Department of Electrical Engineering, Madinah Mounawara University, Madinah 20012, Saudi Arabia; [email protected] 5 Satellite Development Center CDS, BP 4065 Ibn Rochd USTO, 31000 Oran, Algeria * Correspondence: [email protected]; Tel.: +86-131-2191-9077

Received: 21 October 2018; Accepted: 8 November 2018; Published: 15 November 2018

Abstract: The use of renewable energy such as wind power is one of the most affordable solutions to meet the basic demand for electricity because it is the cleanest and most efficient resource. In Algeria, the highland region has considerable wind potential. However, the electrical power system located is this region is generally not powerful enough to solve the problems of voltage instability during grid fault conditions. These problems can make the connection with the eventual installation of a wind farm very difficult and inefficient. Therefore, a wind farm project in this region may require dynamic compensation devices, such as a distributed-flexible AC transmission system (D-FACTS) to improve its fault ride through (FRT) capability. This paper investigates the implementation of shunt D-FACTS, under grid fault conditions, considering the grid requirements over FRT performance and the voltage stability issue for a wind farm connected to the distribution network in the Algerian highland region. Two types of D-FACTSs considered in this paper are the distribution static VAr compensator (D-SVC) and the distribution static synchronous compensator (D-STATCOM). Some simulation results show a comparative study between the D-SVC and D-STATCOM devices connected at the point of common coupling (PCC) to support a wind farm based on a doubly fed induction generator (DFIG) under grid fault conditions. Finally, an appropriate solution to this problem is presented by sizing and giving the suitable choice of D-FACTS, while offering a feasibility study of this wind farm project by economic analysis.

Keywords: wind farm; Fault Ride Through (FRT); Distributed-Flexible AC Transmission system (D-FACTS); Distribution Static VAr Compensator(D-SVC); Distribution Static Synchronous Compensator (D-STATCOM)

1. Introduction In Algeria, the ﬁrst attempt to connect the wind energy conversion system (WECS) to the electricity distribution network dates back to 1957, with the installation of a 100-kW wind turbine at the Grands Vents site (Algiers) by the French designer Andreau.

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Nowadays, the depletion of fossil fuels reserves in Algeria, ﬂuctuations in oil price and the locationAppl. ofSci. energy 2018, 8, x resources are causing instability in energy policy. 2 of 22 In addition, the use of fossil fuels for conventional power plants triggers alarms of an environmental disaster. Currently,In addition, to the reduce use of the fossil harmful fuels impactfor conven of conventionaltional power resourcesplants triggers and improvealarms of Algerian an environmental disaster. Currently, to reduce the harmful impact of conventional resources and energy efﬁciency, the energy policy program announced by the Ministry of Mines and Energy aims, improve Algerian energy efficiency, the energy policy program announced by the Ministry of Mines by 2030, to produce 40% electrical energy from renewable resources [1]. For WECS, the power to be and Energy aims, by 2030, to produce 40% electrical energy from renewable resources [1]. For WECS, producedthe power over to the be produced period 2012–2022 over the period is estimated 2012–2022 at is approximatelyestimated at approximately 516 MW, 516 ofwhich MW, of 10 which MW are installed10 MW at Kaberteneare installed (70 at kmKabertene from Adrar) (70 km infrom the Adrar) Algerian in the desert Algerian [1–4 ].desert This [1–4]. pilot This wind pilot farm wind consists of 12farm wind consists turbines of 12 with wind a unitturbines capacity with a of unit 0.85 capacity MW,the of 0.85 energy MW, produced the energy will produced be injected will be to the 30/220injected kV step to the up 30/220 transformer kV step up situated transformer in the situated same in locality the same [1], locality as shown [1], as in shown Figure in1 Figure. Currently, 1. the AlgerianCurrently, electrical the Algerian grid electrical code does grid not code consider does not WECS. consider In the WECS. region In ofthe Adrar, region theof Adrar, electrical the grid is notelectrical interconnected grid is not with interconnected the north; with it is the a local north; grid it is (ora local micro-grid). grid (or micro-grid). Therefore, Therefore, this program this of the energyprogram policy of the must energy be accompaniedpolicy must be by accompan continualied developmentby continual development of wind energy of wind technology energy and technology and optimization techniques, looking for better options concerning reduced costs, optimization techniques, looking for better options concerning reduced costs, improvement regarding improvement regarding wind turbine performances, reliability of electrical groups and electrical grid wind turbine performances, reliability of electrical groups and electrical grid integration. integration.

FigureFigure 1. Wind1. Wind farm farm at at Kabertene Kabertene in Adra Adrar.r. Reproduced Reproduced for for reference reference [5]. [5].

In theIn periodthe period of of 2009–2010, 2009–2010, SebaaSebaa Ben Ben Miloud Miloud F et F al. et [6] al. and [6] Himri and Himri et al. [7] et undertook al. [7] undertook the first the ﬁrst study to to identify identify a suitable a suitable site in site Adrar in region Adrar for region the wind for farm the installation. wind farm In installation. addition, Himri In et addition, al. [7] used data of wind speed over a period of nearly 10 years to assess the potential of wind power Himri et al.[7] used data of wind speed over a period of nearly 10 years to assess the potential of wind stations in two southern Algerian regions, namely, Timimoun and Tindouf. In [8], a study of the wind powerpotential stations in in seven two southern southern Algerian Algerian sites regions, was undert namely,aken, Timimoun from west to and east, Tindouf. Tindouf, In Bechar, [8], a study Adrar, of the windand potential Ghardaia, in sevenIn Amenas southern and In Algerian Salah (Tamanrasset). sites was undertaken, In [9] wind fromspeed west data towas east, collected Tindouf, over Bechar, a Adrar,period and of Ghardaia, almost 5 years, In Amenas from three and selected In Salah statio (Tamanrasset).ns in northern In Algeria. [9] wind Within speed this data context, was some collected overstudies a period in ofthe almost Algerian 5 years,high plat fromeau threeregion selected were performed stations in in [10 northern–12]. However, Algeria. the Withinauthors thisdid not context, someconsider studies the in theintegration Algerian issue high of the plateau wind regionfarm into were the performedelectrical grid in and [10 –it12 is]. well However, known that the the authors did notelectrical consider grid the influences integration greatly issue the of performa the windnce farm of wind into farm the electricalinstallation grid and and production. it is well known that the electricalAt the grid present inﬂuences time, doubly greatly fed the induction performance generato ofrs wind (DFIG) farm are installation the most used and in production.WECS [13,14] Atand the especially present in time, the Algerian doubly fedwind induction farm at Kabe generatorsrtene in Adrar. (DFIG) Simple are the induction most used generators in WECS have [13 ,14] some weaknesses such as reactive power absorption and uncontrolled voltage during variable rotor and especially in the Algerian wind farm at Kabertene in Adrar. Simple induction generators have speed. These complications are avoided by the installation of DFIG and power converters or power somedrives weaknesses [15,16]. The such particular as reactive feat powerure of the absorption DFIG is that and the uncontrolled injected power voltage by the duringrotor converter variable is rotor speed.only These a small complications part from the are total avoided provided by power the installation with its stator of DFIG directly and connected power converters to the electrical or power drivesgrid [15 [17–19].,16]. The Hence, particular the size, feature the cost ofand the losses DFIG of the is thatpower the converter injected are power optimized by the compared rotor converter to a is onlyfull-size a small power part converter from the of total the other provided generators. power with its stator directly connected to the electrical grid [17–19One]. Hence,of the most the size,important the cost considerations and losses ofin thea wind power farm converter grid-connected are optimized project is comparedfault ride- to a full-sizethrough power (FRT) converter capability, of thewhere other the generators.energy grid is often weak and the DFIG is frequently working Appl. Sci. 2018, 8, 2250 3 of 22

One of the most important considerations in a wind farm grid-connected project is fault ride-through (FRT) capability, where the energy grid is often weak and the DFIG is frequently working Appl. Sci. 2018, 8, x 3 of 22 under grid faults when the wind farm is located relatively far from this electrical grid [20]. Therefore, manyunder research grid faults works when focus the wind on studying farm is located the dynamic relatively behaviors far from of this wind electrical farms grid during [20]. andTherefore, after the clearancemany research of the gridworks fault focus conditions on studying without the dynami disconnectionc behaviors from of wind the electrical farms during grid. and In [ 21after], several the methodsclearance employed of the grid to fault improve conditions the FRT without capability disconnection of the fixed-speed from the electrical wind turbinesgrid. In [21], are several based on inductionmethods generators. employed to In [improve20], an enhanced the FRT capability application of tothe overcome fixed-speed grid wind fault turbines conditions are is based studied on for a windinduction farm generators. based on DFIG. In [20], FRT an control enhanced ofwind application turbines to withovercome DFIGs grid under fault symmetrical conditions is voltage studied dips is presentedfor a wind farm in [21 based]. In [ 22on] DFIG. a flexible FRT ACcontrol transmission of wind turbines system with (FACTS) DFIGs system under forsymmetrical DFIG toreduce voltage the dips is presented in [21]. In [22] a flexible AC transmission system (FACTS) system for DFIG to reduce effects of grid faults is proposed. the effects of grid faults is proposed. The present paper can extend the aforementioned research works. This paper, shows the feasibility The present paper can extend the aforementioned research works. This paper, shows the of installing a wind farm in an Algerian highland region, confirmed by some data of wind potential feasibility of installing a wind farm in an Algerian highland region, confirmed by some data of wind in the selected geographical location in the first part, which is an input for the wind power system. potential in the selected geographical location in the first part, which is an input for the wind power Onsystem. the other On the hand, other another hand, another important important aspect isaspect the weaknessis the weakness of the of electrical the electrical grid, grid, which which is often is anoften obstacle an obstacle in many in many countries countries that that have have established established wind wind energy energy projects. Consequently, Consequently, during during thethe feasibility feasibility study, study, some some techniques techniques toto identifyidentify the the cost-effectiveness cost-effectiveness of of areas areas for for the the wind wind farms farms installations,installations, the the possible possible electrical electrical pathpath ofof distributiondistribution lines, lines, and and their their corresponding corresponding estimated estimated cost cost areare used, used, and and the incorporationthe incorporation of electrical of electrical devices devices such assuch distributed as distributed FACTS (D-FACTS)FACTS (D-FACTS) technology is considered.technology is Furthermore, considered. Furthermore, the investors the may investor be confidents may be to confident fund this to possiblefund this project possible when project these technicalwhen these difficulties technical are difficulties taken into are consideration. taken into cons Then,ideration. in order Then, to in ensure order to the ensure economic the economic success of thesuccess future of wind the future farm wind project farm in theproject highland in the high region,land an region, accurate an accurate study bystudy some by simulationsome simulation results, showingresults, theshowing interaction the interaction between between wind turbine wind generatorsturbine generators and the and electrical the electrical grid in grid this in region this region with the impactwith the of theimpact D-FACTS of the D-FACTS systems, systems, is undertaken, is underta whichken, haswhich not has been not previouslybeen previously done. done. In this In this study, thestudy, Algerian the electricalAlgerian electrical grid code grid could code be consideredcould be considered in simulations in simulations similar to similar that of theto that Spanish of the grid codeSpanish as shown grid code in Figure as shown2. in Figure 2.

(pu) PCC V

Time (s)

FigureFigure 2. 2.Fault Fault ride-through ride-through (FRT)(FRT) proﬁleprofile according to to the the Spanish Spanish grid grid code. code. Reproduced Reproduced from from referencereference [23 [23].].

2.2. Algerian Algerian Wind Wind Potential Potential ThisThis section section discusses discusses a a method method forfor determining th thee production production of of wind wind energy energy at atdifferent different sites sites inin Algeria Algeria in in order order to to choose choose a a suitable suitable sitesite for a a cost-effective cost-effective energy energy installation. installation. Thus, Thus, we we have have both both thethe average average wind wind speed speed and and the the powerpower producedproduced by by wind wind turbines; turbines; we we can can combine combine them them to tocalculate calculate thethe energy energy produced produced by by these these wind wind turbines.turbines. Furtherm Furthermore,ore, in in this this paper, paper, five ﬁve selected selected geographical geographical locationslocations (altitude, (altitude, latitude latitude andand longitude)longitude) shown shown in in Table Table 1 andand Figure Figure 3 werewere obtained obtained from from the the National Meteorological Office (NMO) [24]. National Meteorological Ofﬁce (NMO) [24].

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TableTable 1. 1. Coordinates Coordinates of of stations stations at at different different Algerian Algerian sites. sites. Table 1. Coordinates of stations at different Algerian sites. Coordinates Station Coordinates Station Altitude (m) LatitudeCoordinates (deg) Longitude (deg) Station Altitude (m) Latitude (deg) Longitude (deg) SouthSouth region region (Sahara) (Sahara) Altitude (m) Latitude (deg) Longitude (deg) SouthAdrarAdrar region (Sahara) 263263 27°4927°49′ ′N N 00°17 00°17′ ′W W GhardaiaGhardaiaAdrar 468 468 263 27 32°24 32°24◦490′ N′N N 00◦17 03°48 03°480 W ′ ′E E ◦ 0 ◦ 0 CoastalCoastalGhardaia region region 468 32 24 N 03 48 E AlgiersCoastalAlgiers region 24 24 36°43 36°43′ ′N N 03°15 03°15′ ′E E OranOranAlgiers 9090 24 3635°3835°38◦430′ N′N N 03◦ 00°3715 00°370 E ′ ′W W HighlandHighland Oranregion region 90 35◦38 0 N 00◦370 W Tiaret 1080 35°37′ N 01°32′ E HighlandTiaret region 1080 35°37′ N 01°32′ E Tiaret 1080 35◦370 N 01◦320 E

77 66 55 44 33 22

Wind speed (m/s) Alger Oran Adrar Wind speed (m/s) 11 Alger Oran Adrar GhardaiaGhardaia TiaretTiaret 00 0.000.00 1.00 1.00 2.00 2.00 3.00 3.00 4.00 4.00 5.005.00 6.00 6.00 7.00 7.00 8.00 8.00 9.00 9.00 10.00 10.00 11.00 11.00 12.00 12.00

MonthsMonths

FigureFigure 3. 3. Wind WindWind speed speed variations variations at at different different locations locations in in Algeria. Algeria.

TheseThese wind windwind speed speedspeed data datadata are are collectedare collectedcollected only atonlyonly 10 m atat of 1010 altitude, mm ofof altitude, measuredaltitude, measuredmeasured using a type usingusing of anemometer aa typetype ofof anemometercupanemometer and vane. cup cup However, and and vane. vane. the However, However, action of thethe the windaction action speed of of th thee at wind wind the turbinespeed speed at at (tower the the turbine turbine height (tower (tower over 70 height height m) is over veryover 70complex,70 m)m) isis very andvery includes complex,complex, both andand deterministic includesincludes bothboth effects deterministicdeterministic (wind and effectseffects shadow (wind(wind average andand round), shadowshadow and averageaverage stochastic round),round), fast varyingandand stochastic stochastic wind speedfast fast varying varying is turbulent. wind wind speed Inspeed fact, is is windturbulent. turbulent. speed In In describing fact, fact, wind wind these speed speed variations describing describing is these usuallythese variations variations measured is is usuallyinusually the lower measuredmeasured atmosphere inin thethe using lowerlower either atmosphereatmosphere instrumented usingusing ei towerseitherther instrumentedinstrumented or tethered balloons, towerstowers or whichor tetheredtethered have balloons, notballoons, been whichavailablewhich have have in previousnotnot been been available stationsavailable [ 25in in, 26previous previous]. stations stations [25,26]. [25,26]. TheThe windwind speed speedspeed is isis the thethe most mostmost important importantimportant aspect aspectaspect of ofof wind wiwindnd potential; potential;potential; in infact,in fact,fact, the thethe annual annualannual variation variationvariation of the ofof thelong-termthe long-termlong-term average averageaverage wind windwind speed speedspeed provides providesprovides a good aa good understandinggood understandingunderstanding of the ofof long-term thethe long-termlong-term trend oftrendtrend wind ofof speed windwind speedandspeed gives andandconﬁdence givesgives confidenceconfidence to investors toto investorsinvestors on the availability onon thethe avavailabilityailability of wind of energyof windwind in energyenergy the years inin thethe ahead yearsyears [27 aheadahead]. Figure [27].[27].4 providesFigureFigure 4 4 provides theprovides average the the windaverage average speed wind wind during speed speed ﬁve during during years five offive data years years collection of of data data collection atcollection 5 stations at at in55 stations stations Algeria, in in which Algeria, Algeria, are whichconsideredwhich are are considered considered in this study in in [thisthis7,10 study –study34]. [7,10–33,34]. [7,10–33,34].

55 VV (m/s) (m/s) 44 V (m/s) V (m/s) 33

00 AlgerAlger Oran Oran Adrar Adrar Ghardaia Ghardaia Tiaret Tiaret

Figure 4. Annual wind speed in Algeria. FigureFigure 4. 4. Annual Annual wind wind speed speed in in Algeria. Algeria. Appl. Sci. 2018, 8, 2250 5 of 22

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3.3. Connection Connection Issue Issue of of a a Wind Wind Farm Farm to to the the Electrical Electrical Grid Grid InIn this this paper, paper, the proposed windwind farmfarm inin aa highlandhighland regionregion withwith average average power power is is considered considered as as a adecentralized decentralized generator generator unit, unit, which which is most is most often ofte connectedn connected to the to distribution the distribution network network and that and differs that differsfrom centralized from centralized generator generator units. In units. Algeria, In Algeri the electricala, the electrical distribution distribution grids are grids the most are importantthe most importantinfrastructure infrastructure of the whole of powerthe whole system, power which system, is considered which is asconsidered the final interface as the final that interface leads to mostthat leadsindustrial to most and industrial domestic and customers. domestic These customers. distribution These grids distribution are operated grids in are ranges operated of voltages in ranges below of voltages50 kV, which below is 50 the kV, voltage which level is the of thevoltage Medium level Voltage of the Medium (MV) and Voltage Low Voltage (MV) and (LV) Low ranges. Voltage Moreover, (LV) ranges.in the Algerian Moreover, distribution in the Algerian grid, thedistribution nominal voltagegrid, the of nominal the MV voltage is 10 kV of and the 30MV kV. is These10 kV voltageand 30 kV.levels These allow voltage a good levels compromise allow a good to limit compromise the voltage to drops, limit the minimizing voltage drops, the number minimizing of source thepositions number of(connecting source positions to High (connecting Voltage (HV)/MV to High powerVoltage station) (HV)/MV and power reduce station) the inherent and reduce constraints the inherent to high constraintsvoltages (investment to high voltages costs, protection (investment of property costs, andprotection persons). of Moreover,property Algerianand persons). distribution Moreover, grids Algerianare, in most distribution cases, radially grids are, networked. in most cases, The map radially of the networked. western Algerian The map electrical of the western grid is shownAlgerian in electricalFigure5. Thisgrid figureis shown shows in Figure the structure 5. This offigure the High shows Voltage the structure B 220 kV of transmission the High Voltage lines, whileB 220 thekV transmissionsubstations and lines, power while plants the aresubstations also shown and in power this figure plants [1]. are The also structure shown of in High this Voltagefigure [1]. A 60 The kV structuredistribution of High lines Voltage is shown A in 60 Figure kV distribution6. lines is shown in Figure 6.

FigureFigure 5. 5. MapMap of of the the western western Algerian Algerian electrical electrical grid. grid. Reproduced Reproduced from from reference reference [1]. [1]. Appl.Appl. Sci.Sci. 20182018,, 88,, xx 66 ofof 2222 Appl. Sci. 2018, 8, 2250 6 of 22 Appl. Sci. 2018, 8, x 6 of 22

FigureFigureFigure 6. 6.6.Western WesternWestern electrical electricalelectrical grid gridgrid near nearnear to toto the thethe proposed proposedproposed wind windwind farm. farm.farm. Figure 6. Western electrical grid near to the proposed wind farm. BasedBased onon thethe structurestructure ofof the the electrical electrical gridgrid onon the the west west side side near near the the proposed proposed wind wind farm farm (see (see BasedBased on on thethe structurestructure of thethe electricalelectrical grid grid on on the the west west side side near near the the proposed proposed wind wind farm farm (see (see FigureFigure6 ),6), this this radial radial electrical electrical grid grid of of 60 60 kV kV can can be be reconﬁgured; reconfigured; it it is is then then simulated simulated using using the the Power Power FigureFigure 6), 6), this this radial radial electrical gridgrid ofof 60 60 kV kV can can be be reconfigured; reconfigured; it isit thenis then simulated simulated using using the thePower Power SystemSystem Analysis Analysis Toolbox Toolbox (PSAT) (PSAT) software software with with actual actual electrical electrical grid parameters grid parameters and consumer and consumer proﬁles SystemSystem AnalysisAnalysis ToolboxToolbox (PSAT) softwaresoftware withwith actual actual electrical electrical grid grid parameters parameters and and consumer consumer atprofiles the peak at the load peak of each load bus,of each with bus, a centralized with a cent generationralized generation source Tiaretsource City Tiaret (TIARC) City (TIARC) power power plant. profilesprofiles at at the the peak peak loadload of each bus,bus, with with a a cent centralizedralized generation generation source source Tiaret Tiaret City City (TIARC) (TIARC) power power Simulation of the latter gives the results shown in Figures7 and8. More details on the overall plant.plant.plant. SimulationSimulation Simulation of ofof the the latterlatter givesgives thethe results resultsresults shown shownshown in inin Figures FiguresFigures 7 7and7 andand 8. 8.More8. MoreMore details detailsdetails on ontheon the theoverall overalloverall simulationsimulationsimulationsimulation of ofof of the thethe the west west westwest Algerian AlgerianAlgerian grid gridgrid can can cancan be be bebe foundfound foundfound in inin [34]. [ 34 [34].[34].].

Voltage Magnitude Profile VoltageVoltage Magnitude ProfileProfile RealRealReal Power PowerPower Profile ProfileProfile 1.5 1.51.5 0.60.60.6

0.40.40.4 111 0.20.20.2 [p.u.] [p.u.] [p.u.] L L L - P V [p.u.] - P V [p.u.] 0 0 - P V [p.u.] G 0 G

0.5 G 0.5 P 0.5 P P -0.2 -0.2-0.2

0 -0.4-0.4 00 1 2 3 4 5 6 7 -0.4 1 2 3 4 5 6 7 1 2 3 4 5 6 7 11 22 33 44 55 66 77 1 2 3 Bus4 # 5 6 7 Bus # Bus # Bus # Bus # Bus # Figure 7. In each bus of the 60-kV electrical grid in Tiaret region: (a) voltage amplitudes; (b) active FigureFigureFigure 7. 7.7.In InIn each eacheach bus busbus of ofof the thethe 60-kV 60-kV60-kV electrical electrelectricalical grid gridgrid in inin Tiaret TiaretTiaret region: region:region: ( a((a)a) voltage) voltagevoltage amplitudes; amplitudes;amplitudes; ( b((bb))) active activeactive powers. powers.powers.powers. Reactive Power Profile 0.2 ReactiveReactive PowerPower ProfileProfile 0.20.2 0.1 0.10.1 [p.u.]

L 0 [p.u.] [p.u.] L L - Q 00 G - Q Q

- Q -0.1 G G Q Q -0.1-0.1 -0.2 1 2 3 4 5 6 7 -0.2 -0.2 Bus # 11 22 33 44 55 66 77 Bus # Figure 8. Reactive power in each bus of the 60-kVBus # electrical grid in the Tiaret region. FigureFigureFigure 8. 8.8.Reactive ReactiveReactive power powerpower in inin each eacheach bus busbus of ofof the thethe 60-kV 60-kV60-kV electrical electricalelectricalgrid gridgrid in inin the thethe Tiaret TiaretTiaret region. region.region. Appl. Sci. 2018, 8, 2250 7 of 22 Appl. Sci. 2018, 8, x 7 of 22

The existence of an SNVI industrial site in the bu buss of N 2 between the city of Tiaret and the city of Tissemsilt can justify the presencepresence of the voltage drop across this line as shownshown in FigureFigure7 7a.a. ThisThis resulted in demand of an excessive reactive powerpower and active line losses due toto thethe high-ﬂuctuatedhigh-fluctuated demand of energy to the industrial site,site, asas shownshown inin FiguresFigures7 7b and and8. 8.

4. Distribution Flexible Alternative Current Transmission SystemSystem (D-FACTS)(D-FACTS) Shunt D-FACTSD-FACTS devices devices can can be classiﬁedbe classified into twointo main two categories, main categories, namely the namely variable the impedance variable typeimpedance such as type the distributionsuch as the distribution static var compensator static var compensator (D-SVC) and (D-SVC) the switching and the converter switching type converter such as thetype distribution such as the staticdistribution synchronous static synchronous compensator compensator (D-STATCOM). (D-STATCOM). The conﬁgurationconfiguration of the D-SVC connectedconnected toto thethe distributiondistribution gridgrid isis shownshown inin FigureFigure9 9..

Figure 9. Control conﬁgurationconfiguration of the distributiondistribution static var compensator (D-SVC) connected to the point of common coupling (PCC) withwith aa windwind farm.farm.

This figure figure shows shows a a D-SVC D-SVC consisting consisting of of a athyristor thyristor switched switched capacitor capacitor (TSC) (TSC) part part composed composed by by two switching thyristors connected with capacitive reactance X ; the other part is the two switching thyristors connected with capacitive reactance XTSC; the TSCother part is the thyristor- thyristor-controlledcontrolled reactor (TCR) reactor composed (TCR) composedby two thyristors by two connected thyristors with connected an impedance with an of impedance an inductive of an inductive reactance branch X . By controlling the angle thyristors (the angle with respect to the reactance branch XTCR. By controllingTCR the angle thyristors (the angle with respect to the zero crossing zeroof the crossing phase voltage), of the phase the device voltage), is able the to device control is the able amplitude to control of the the amplitudevoltage at the of thepoint voltage of common at the pointcoupling of common (PCC) due coupling to the changes (PCC) due in the to theangle changes resulting in themainly angle in resulting changes of mainly the current. in changes Therefore, of the current.the amount Therefore, of the reactive the amount power of consumed the reactive by powerthe inductor consumed L, for by an the angle inductor of α = L,90°, for the an inductive angle of α ◦ α ◦ circuit= 90 is, theactivated, inductive whereas circuit for is activated,α = 180°, this whereas inductive for circuit= 180 ,is this off. inductive circuit is off. The configurationconfiguration of the D-STATCOM connectedconnected toto thethe distributiondistribution gridgrid isis shownshown inin FigureFigure 10 10.. This figurefigure showsshows the the different different blocks blocks constituting constituti thisng this configuration configuration of the of control the control strategy, strategy, which consistswhich consists of: A phase of: A lock phase loop lock (PLL) loop for (PLL) synchronization for synchronization of the component of the component of the positive of the sequence positive voltagesequence with voltage the primary with the voltage primary of voltage the power of the distribution power distribution grid. An external grid. An control external loop control consists loop of controllingconsists of controlling the DC bus the voltage DC bus and voltage the grid and voltage. the grid Thevoltage. outputs The ofoutputs the voltage of the voltage controllers controllers are the currentare the current references references for the currentfor the current controllers. controllers. The internal The internal current current control loopcontrol consists loop consists of the current of the current controllers. The outputs of the current controllers consist in imposing the amplitude and phase of voltages of the D-STATCOM by generating Pulse Width Modulation (PWM) signals. Appl. Sci. 2018, 8, 2250 8 of 22 controllers. The outputs of the current controllers consist in imposing the amplitude and phase of voltages of the D-STATCOM by generating Pulse Width Modulation (PWM) signals. Appl. Sci. 2018, 8, x 8 of 22

Figure 10. Control conﬁguration of the distribution static synchronous compensator (D-STATCOM) connectedFigure 10. to theControl PCC configuration with a wind farm.of the distribution static synchronous compensator (D-STATCOM) 5. Constitutionconnected of to thethe PCC Wind with Farm a wind and farm. the Location of the Shunt D-FACTS 5. TheConstitution wind farm of connected the Wind toFarm the a distributionnd the Location system of the proposed Shunt inD-FACTS this section is shown in Figure 11, which consistsThe wind of farm eight connected DFIGs with to the 1.5 distribution MW of power system for proposed each wind in this turbine. section These is shown generators in Figure are connected11, which between consists them of eight to a DFIGs voltage with level 1.5 of MW 30 kVof power by a step-up for each transformer wind turbine. 690 These V/30 generators kV with 4 MVAare of powerconnected for eachbetween generator. them to Then a voltage a 45 km level line of that 30 iskV connected by a step-up to the transformer source substation 690 V/30 60 kV kV with through 4 anotherMVA step-upof power transformer for each generator. 30 kV/60 Then kV a 45 with km line 47 MVAthat is of connected power. to For the this source study, substation these lines 60 kV are modelledthrough with another the πstep-upmodel. transformer 30 kV/60 kV with 47 MVA of power. For this study, these lines areBased modelled on the with work the doneπ model. in [21 ,35] the simulation results obtained with a D-FACTS provides an effectiveBased support on the to work the bus done voltage in [21,35] to which the simulation it is connected. results obtained Therefore, with in a thisD-FACTS study, provides D-FACTS an is placedeffective at the support PCC for to twothe reasons:bus voltage to which it is connected. Therefore, in this study, D-FACTS is placed at the PCC for two reasons: • The location for the reactive power support should be as close as possible to the point at which • The location for the reactive power support should be as close as possible to the point at which the carrier is necessary because of the variation in the voltage and, therefore, power loss (Joule the carrier is necessary because of the variation in the voltage and, therefore, power loss (Joule loss) in the distribution line associated with reactive power ﬂow, loss) in the distribution line associated with reactive power flow, • • In theIn the studied studied system, system, the the effect effect of of the the change change inin voltagevoltage isis most common in in this this bus. bus. Appl. Sci. 2018, 8, 2250 9 of 22

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D − STATCOM / D − SVC

P1 P2 Line of 45km Line of 1 km ~

690V / 30 KV 30 KV / 60 KV Post source ~ ~ 4 MVA 47 MVA 60 KV 30 KV

PCC 4 MVA Line of 1 km Electrical distributi on grid

690V / 30KV ~ ~ 4 MVA

Line of 1 km

690V / 30 KV ~ ~ 4 MVA

Line of 1 km

690V / 30 KV ~ ~ 4 MVA

Wind farm ()12 MW : 8 wind turbine 1.5 MW (DFIG ) FigureFigure 11.11. Structure of the studied system based onon aa windwind farmfarm andand aa distributed-ﬂexibledistributed-flexible ACAC transmissiontransmission systemsystem (D-FACTS)(D-FACTS) connected connected to to the the Algerian Algerian distribution distribution grid. grid.

6.6. SimulationSimulation ResultsResults InIn thisthis section,section, simulationssimulations areare performedperformed onon Matlab/Simulink,Matlab/Simulink, to showshow thethe impactimpact ofof D-FACTSD-FACTS onon thethe abilityability toto controlcontrol thethe voltagevoltage atat thethe PCCPCC betweenbetween thethe electricelectric distributiondistribution gridgrid andand thethe windwind farm,farm, whichwhich isis describeddescribed inin thethe previousprevious sectionsection (Figure(Figure 1111).). AccordingAccording toto thethe previousprevious sectionsection ofof thethe windwind potentialpotential inin thethe AlgerianAlgerian highlandhighland region,region, thethe consideredconsidered windwind speedspeed inin thethe simulationsimulation startsstarts atat 88 m/sm/s and thenthen reachesreaches 99 m/s.m/s. The parameters of generators and D-FACTS are presentedpresented inin thethe AppendixAppendixA A.. ForFor thethe more more detailed detailed study, study, the proposedthe proposed system system devices, devices, the D-SVC the andD-SVC D-STATCOM and D-STATCOM structures usedstructures in the used context in the of context this paper of this are paper the sameare the as same the as SVC the and SVC STATCOM and STATCOM structures, structures, which which are presentedare presented in [36 in,37 [36,37],], giving giving their associatedtheir associated models models with their with appropriate their appropriate control schemes. control schemes. In addition, In theaddition, detailed the model detailed with model some simulationswith some simulati for WECSons based for WECS on DFIG based in power on DFIG system in power dynamics system are describeddynamics inare [38 described–41]. Generally, in [38–41]. a short-circuit Generally, faulta short-circuit has a signiﬁcant fault has effect a significant on the wind effect farm; on athe voltage wind dropfarm; is a causedvoltage even drop if is the caused fault iseven located if the near fault or is far located from the near PCC or orfar the from wind thefarm. PCC Thisor the voltage wind farm. drop atThis the voltage PCC leads drop to at an the over-current PCC leads into thean over-current rotor circuit of in DFIG, the rotor and circuit ﬂuctuations of DFIG, in theand DC fluctuations bus voltage. in Therefore,the DC bus the voltage. rotor sideTherefore, converter the (RSC)rotor side of the conver DFIGter should (RSC) beof the blocked DFIG to should avoid be being blocked damaged to avoid by overcurrentbeing damaged in the by rotor overcurrent circuit. in the rotor circuit. TheThe blockblock diagramdiagram ofof thethe simulatedsimulated windwind farmfarm connectedconnected toto thethe electricalelectrical distributiondistribution gridgrid isis shownshown inin FigureFigure 1212.. Appl.Appl. Sci. Sci. 20182018, ,88, ,x 2250 1010 of of 22 22

FigureFigure 12. 12. BlockBlock diagram diagram of of the the proposed proposed system system on Matlab/Simulink.

Appl. Sci. 2018, 8, 2250 11 of 22

In order to study the behavior and the impact of electrical faults in the distribution grid on the wind farm, worst-case scenarios of grid faults were assumed and included in the simulation. Therefore, the entire system was tested under two types of grid faults:

• Line to line electrical grid fault. • Voltage drop at the 60 kV bus.

The wind speed is considered as constant during the grid fault period, except for this disturbance; and generators and the electrical distribution grid are considered to be working in ideal conditions (no disturbances and no parameter variations in the studied system).

6.1. Simulation Results of the Line-to-Line Electrical Grid Fault In this section, we consider that the phases “b” and “c” at the PCC at P1 come into accidental contact. Then, the same grid fault is considered at a distance of 45 km from the PCC to the point P2 (Figure 11). Simulation results for this grid fault are shown in Figures 13–15. The active powers at the PCC with a short temporary grid fault of two-phase to ground are shown in Figure 14. The reactive powers at the PCC with a short temporary grid fault of two-phase to ground are shown in Figure 15. According to Figure 13, which reveals that without the use of D-FACTS systems the voltage at the PCC exceeds the acceptable voltage level 1 pu due to the voltage swell. However, using D-FACTS devices such as D-SVC and the D-STATCOM these undesirable effects are corrected. In addition, voltages at the PCC during a temporary grid fault presented in this ﬁgure show that, without the use of D-FACTS and when the grid fault is at the point P1, the voltage at the PCC drops to the value of 0.48 pu, which is less than the acceptable value. Thus, when the grid fault is at the point P2 without D-FACTS, the voltage drops to 0.52 pu. However, with the presence of D-FACTS devices, when this type of grid fault is at point P1, the voltage at the PCC drops to 0.63 with a slight ﬂuctuation. In addition, when the fault is at the point P2 with D-FACTS, the voltage is maintained at 0.71 pu. Moreover, it is noticed that the voltage at the PCC, when using D-STATCOM many oscillations are mitigated compared to using the D-SVC. According to Figure 14, which shows that during the occurrence of the same grid fault type in both points P1, P2 and without the presence of D-FACTS systems, no active power is supplied. Then, when the grid fault of 1000 ms duration exceeds the limit (see Figure2), the wind farm is disconnected from the grid. Moreover, the installation of D-FACTS systems at the PCC guarantees the wind farm commissioning during and after this type of grid fault at these points (P1, P2) without disconnecting from the electrical distribution grid, providing the active power of 10.6 MW. Therefore, in the presence of D-FACTS systems, production of active power by the wind farm is uninterrupted and in the absence of these systems the wind farm is disconnected from the grid by triggering the protection system. From Figure 15, it is noticed that in the absence of D-FACTS systems and when the grid fault is located at the points P1 and P2, no exchange of reactive power is provided to the electrical distribution grid. However, in the presence of D-FACTS systems, it provides almost the same amount of reactive power, 7.09 MVAr, when the grid fault is located at point P1 and 8.17 MVAr when the grid fault is located at point P2. Indeed, these injected reactive powers are required for compensation to maintain the stability of the wind farm with the voltage at the PCC around the acceptable value. Therefore, the wind farm is kept in service during and after this type of grid fault without disconnecting from the electrical distribution grid. Thus, the use of D-STATCOM has a capacity to compensate faster than using the D-SVC and the peaks of the injected reactive powers are eliminated. Appl. Sci. 2018, 8, 2250 12 of 22 Appl. Sci. 2018, 8, x 12 of 22 Voltages (pu)

Time (s) (a) Voltages (pu)

Time (s) (b)

Figure 13. (a) Voltage atat thethe PCCPCC duringduring line-to-lineline-to-line electrical grid fault; ( b) zoom of voltage at the PCC during line-to-line electrical grid fault. Appl. Sci. 2018, 8, 2250 13 of 22

Appl. Sci. 2018, 8, x 13 of 22 Active powers (MW) Active powers

Time (s) (a) Active powers (MW) Active powers

Time (s) (b)

FigureFigure 14. ( a14.) Active (a) Active power power at the at PCCthe PCC during during line-to-line line-to-line electrical electrical grid grid fault; fault; (b ()b zoom) zoom of of active active power at thepower PCC at during the PCC line-to-line during line-to-line electrical electrical grid fault. grid fault. Appl. Sci. 2018, 8, 2250 14 of 22 Appl. Sci. 2018, 8, x 14 of 22 Reactive powers (MVAr)

Time (s) (a) Reactive powers (MVAr)

Time (s) (b)

FigureFigure 15.15.( (aa)) ReactiveReactive powerpower atat thethe PCCPCC duringduring line-to-lineline-to-line electricalelectrical gridgrid fault;fault; ((bb)) zoomzoom ofof reactive reactive powerpower at at the the PCC PCC during during line-to-line line-to-line electrical electrical grid grid fault. fault.

6.2.6.2. SimulationSimulation ResultsResults ofof thethe VoltageVoltage DropDrop atat thethe 6060 kV kV BusBus TheThe mainmain purposepurpose ofof thisthis testtest isis toto studystudy howhow aa remoteremote gridgrid faultfault fromfrom thethe PCCPCC maymay affectaffect thethe operationoperation ofof aa windwind farm;farm; thisthis faultfault affectsaffects thethe sourcesource ofof 6060 kV,kV, whichwhich isis farfar fromfrom thethe PCCPCC wherewhere thethe windwind farmfarm basedbased onon thethe DFIGsDFIGs isis connectedconnected toto thethe grid.grid. Hence,Hence, aa temporarytemporary voltagevoltage dropdrop ofof 50%50% isis applied to the source for the duration of 500 ms at t = 10 s, and then the same grid fault for 1000 ms of duration. Appl. Sci. 2018, 8, 2250 15 of 22 applied to the source for the duration of 500 ms at t = 10 s, and then the same grid fault for 1000 ms Appl.of duration. Sci. 2018, 8, x 15 of 22 FigureFigure 16 16 shows shows that that during during this this type type of ofgrid grid fault fault and and without without the presence the presence of D-FACTS, of D-FACTS, the voltagethe voltage at the at PCC the PCCdrops drops to 0.44. to 0.44.Therefore, Therefore, the protection the protection system system will be will triggered be triggered and the and wind the farmwind will farm be will disconnected be disconnected if the fault if the duration fault duration exceeds exceeds the electrical the electrical interconnection interconnection grid gridcode codefor the for windthe wind turbine turbine systems systems (see (see Figure Figure 2). 2However,). However, in inthe the same same figure, ﬁgure, it itis is shown shown that that during during this this grid grid faultfault and and with with the the presence presence of of D-FACTS D-FACTS systems, systems, th thee voltage voltage at at the the PCC PCC is is maintained maintained around around 0.88 0.88 pupu with with a a transient transient peak peak without without triggering triggering the the protection protection system. system. Thus, Thus, by by using using the the D-STATCOM, D-STATCOM, transienttransient peaks peaks are are reduced reduced and and the the time time resp responseonse is is faster faster than than by by using using the the D-SVC. D-SVC. Voltages (pu)

Time (s)

FigureFigure 16. 16. VoltagesVoltages at at the the PCC PCC during during the the voltage voltage drop drop at at the the 60 60 kV kV bus. bus.

TheThe active active powers powers at at the the PCC PCC are are presented presented in in Figure Figure 17.17. FigureFigure 17 17 showsshows that, that, when when the the D-FACTS D-FACTS devices devices are are not not installed installed at at the the PCC, PCC, the the wind wind farm farm cannotcannot maintain itsits connection connection to to the the grid grid during during the gridthe faultgrid thatfault lasts that 1000 lasts ms 1000 because ms thebecause protection the protectionsystems are systems triggered are andtriggered the wind and farm the wind is disconnected. farm is disconnected. However, after However, the installation after the ofinstallation D-FACTS ofdevices D-FACTS and devices with the and same with grid the faultsame type grid andfault the type same and durationthe same ofduration grid fault, of grid the fault, wind the farm wind can farmreturn can to return the steady to the state steady and state inject and the inject active the power active of power 10.6 MW of 10.6 to the MW grid. to the grid. FromFrom the the results results shown shown in in Figure Figure 18, 18 ,it it is is noticed noticed that that without without the the presence presence of of a a compensation compensation system,system, the the wind wind farm is operating inin aa weakweak electricalelectrical grid grid due due to to its its normal normal behavior behavior and and there there is nois noreactive reactive power power exchange exchange with with the electricalthe electrical grid. grid. However, However, in the in same the same situation situation with thewith D-FACTS the D- FACTSdevices, devices, the necessary the necessary reactive reactive power ispower provided is prov to theided grid to the of 12.6 grid MVAr of 12.6 with MVAr D-SVC with and D-SVC 9.7 MVAr and 9.7with MVAr the D-STATCOM. with the D-STATCOM. Thus, a very Thus, fast a andvery signiﬁcant fast and significant ﬂuctuation fluctuation is observed is withobserved the usewith of the the useD-SVC of the compared D-SVC compared to the use to of the the use D-STATCOM. of the D-STATCOM. Appl. Sci. 2018, 8, 2250 16 of 22 Appl. Sci. 2018,, 8,, xx 16 of 22 Active powers (MW) Active powers Active powers (MW) Active powers

Time (s)

FigureFigure 17. 17. ActiveActive power power at at the the PCC PCC during during th thee voltage voltage drop drop at the 60 kV bus. Reactive powers (MVAr) Reactive powers (MVAr)

Time (s)

FigureFigure 18. 18. ReactiveReactive power power at at the the PCC PCC during during th thee voltage voltage drop drop at the 60 kV bus.

7.7. Economic Economic Analysis Analysis of of D-FACTS D-FACTS Systems TheThe global global market market for for FACTS FACTS and and D-FACTS D-FACTS systems systems is is expected expected to to reach reach $1,386,010,000 $1,386,010,000 in in 2018, 2018, itit had had already already reached reached $912,850,000 $912,850,000 in in 2012 2012 [12]. [12]. Th Thee D-SVC D-SVC is is the the most widely used solution in in the world market, followed by by fixed fixed capacitor banks. However, However, devices devices such such as as D-STATCOM D-STATCOM are are one customized solution for specific requirements of the distribution network. Obviously, some D- FACTSs are relatively expensive because they consist of many components such as advanced power electronics components, thyristors, reactors, capacitor banks, switches, protection systems and Appl. Sci. 2018, 8, 2250 17 of 22 customized solution for specific requirements of the distribution network. Obviously, some D-FACTSs Appl.are relativelySci. 2018, 8, expensivex because they consist of many components such as advanced power electronics17 of 22 controlcomponents, systems. thyristors, In this reactors,section, the capacitor range banks,of the cost switches, of the protection key features systems is often and taken control from systems. the companyIn this section, Siemens the and range the of Electric the cost Power of the keyResearch features Institute is often (EPRI) taken fromwith thethe companydatabase Siemensspecified and in [13],the Electricas shown Power in Figure Research 19. Institute (EPRI) with the database specified in [13], as shown in Figure 19.

140

120 100 STATCOM 80 60 SVC

Cost per kVAr 40

0 0 50 100 150 200 250 300 350 400 450

operating range (MVAr)

FigureFigure 19. Cost 19. Costof the of operation the operation range range for differen for differentt D-FACTS D-FACTS devices. devices. Reproduced Reproduced from from [14]. [14].

Generally,Generally, thethe costcost of of a D-FACTSa D-FACTS system system has twohas components:two components: the installation the installation costs and costs operating and operatingexpenses. expenses. The total costThe oftotal the cost entire of installedthe entire systems installed comprises systems thecomprises equipment the equipment price and the price delivery and theand delivery installation and ofinstallation these systems. of these The systems. operating The cost operating includes cost the includes cost of maintenancethe cost of maintenance and service. andSpeciﬁcally, service. theSpecifically, operating the cost operating of these devicescost of isthes approximatelye devices is approximately 5% to 10% of the 5% total to 10% installation of the total cost. installationTherefore, thecost. cost Therefore, functions the for cost theD-SVC function ands for D-STATCOM the D-SVC areand developed D-STATCOM as follows are developed [15]: as follows [15]:  2 CSVC = 0.0004 s − 0.262 s + 81.5  2 CC = =0.00040.0003ss2 −−00.305.262ss++127.3881.5 SVCSVC (1)  C = 0.00042 s2 − 0.3225 s + 128.75 C STATCOM= 0.0003 s − 0.305 s +127.38  SVC 2  CSTATCOM = −0.0008 s − 0.155 s + 120 (1) = 2 − + CSTATCOM 0.0004 s 0.3225 s 128.75 where s is the operating range of D-FACTS devices kVAr. The marginal cost per kVAr of the installed C = −0.0008 s 2 − 0.155 s +120 D-FACTS devices decreases asSTATCOM the operating rate of capacity increases. An overall cost for reactive wherepower s 100is the MVAr, operating D-SVC range ranges of D-FACTS from $60 devices to $100 kVAr. per kVAr. The Althoughmarginal cost the per D-SVC kVAr has ofsophisticated the installed D-FACTScomponents devices such decreases as thyristors, as the inductors operating and rate capacitors, of capacity it has increases. a control An structure overall cost that for is relatively reactive powersimple. 100 Similarly, MVAr, basedD-SVC on ranges Figure from 19, the$60 overallto $100 costper ofkVAr. a D-STATCOM Although the varies D-SVC from has $100 sophisticated to $130 per componentskVAr and 100 such MVAr as ofthyristors, operating inductors range. The and costs capacito of thers, installed it has a parallel control D-FACTS structure devices that is arerelatively shown simple.in the Table Similarly,2[16]: based on Figure 19, the overall cost of a D-STATCOM varies from $100 to $130 per kVAr and 100 MVAr of operating range. The costs of the installed parallel D-FACTS devices are Table 2. Costs of different reactive power compensators. shown in the Table 2 [16]: Parallel Reactive Compensator Cost (US $/kVar) Table 2. ShuntCosts of capacitor different reactive power compensators. 8/kVar D-SVC 60/kVar Parallel Reactive Compensator Cost (US $/kVar) D-STATCOM 100/kVar Shunt capacitor 8/kVar D-SVC 60/kVar From the above table, we seeD-STATCOM that the cost of D-FACTS devices100/kVar (D-SVC and D-STATCOM) is much more expensive compared to capacitors due to the cost of the control devices and the complexity of the designFrom the and above application table, we of D-FACTSsee that the systems. cost of TheD-FACTS D-STATCOM devices is(D-SVC the source and ofD-STATCOM) reactive power is much more expensive compared to capacitors due to the cost of the control devices and the complexity of the design and application of D-FACTS systems. The D-STATCOM is the source of reactive power compensation that is more expensive because of the used power electronics components like the Insolated Gate Bipolar Transistor (IGBT). Appl. Sci. 2018, 8, 2250 18 of 22

Appl. Sci. 2018, 8, x 18 of 22 compensationIn this study, that is the more Figure expensive 20 summarizes because the of performance the used power of both electronics D-FACTS types components (D-STATCOM like the Insolatedand D-SVC), Gate Bipolaralso by Transistorcomparing (IGBT).the amount of injected reactive power (MVAr) and the installation Appl. Sci. 2018, 8, x 18 of 22 costIn of this these study, devices the Figure($). This 20 comparison summarizes provides the performance a basis for system of both integration D-FACTS D-FACTS types (D-STATCOM in a wind andfarm D-SVC), consisting also by of comparing the DFIG the type amount of genera of injectedtor helping reactive to power achieve (MVAr) a better and thebalance installation between cost of theseperformance devices and ($). cost This in comparison the condition provides of specific a basis defects. for system integration D-FACTS in a wind farm consisting of the DFIG type of generator helping to achieve a better balance between performance and 12.6 cost in the condition13 of speciﬁc defects.

11 9.7 9 8.17 8.17 12.6 13 7.09 7.09 7 11 9.7 5 9 8.17 8.17 3 7.09 7.09

Reactive power (MVar) 7 1 5 Line to line fault (P1) Line to line fault (P2) 60 kV bus fault D-STATCOM D-SVC

3 Reactive power (MVar) Figure 20. Reactive power injected into the PCC by using D-SVC and D-STATCOM with different 1 types of grid faults.Line to line fault (P1) Line to line fault (P2) 60 kV bus fault D-STATCOM D-SVC The D-STATCOM provides a very effective reactive power compensation with respect to the D- SVC for all fault conditions. However, the D-SVC has a capacity option for a large amount of reactive Figure 20. ReactiveReactive power power injected injected into into the the PCC PCC by by using using D-SVC D-SVC and and D-STATCOM D-STATCOM with different power to be injected during a severe fault condition of the source. In the case of a two-phase ground typestypes of of grid grid faults. fault (worst event of the grid fault applied in this study), the cost of installation is an important factor to consider. Therefore, in this paper, the economic analysis aims to compare the total cost of two types The D-STATCOM D-STATCOM provides provides a a very very effective effective reacti reactiveve power power compensation compensation with with respect respect to the to theD- of parallel D-FACTS connected to a wind farm based on DFIGs, as presented in Figure 21. SVCD-SVC for for all allfault fault conditions. conditions. However, However, the the D-SVC D-SVC has has a acapacity capacity option option for for a alarge large amount amount of of reactive reactive According to Figure 21, it is clear that the use of D-STATCOM to maintain the wind farm in power to be injected during a severe fault conditio conditionn of the source. In the case of a two-phase ground service during grid fault conditions is an expensive application compared with D-SVC due to the use faultfault (worst (worst event event of of the the grid grid fault fault applied applied in in this this st study),udy), the the cost cost of of installation installation is is an an important important factor factor of the transformer and the cost of power electronics [17,18]. Consequently, one can conclude that the to consider. Therefore, in this paper, the economic analysis aims to compare the total cost of two types to consider.D-STATCOM Therefore, is more in cost-effective this paper, the compared economic to D-SVCanalysis for aims voltage to compare support theat the total PCC cost and of the two wind types of parallel D-FACTS connected to a wind farm based on DFIGs, as presented in Figure 21. of parallelfarm connection D-FACTS in connected the event of to the a wind most farmsevere based grid faulton DFIGs, conditions. as presented in Figure 21. According to Figure 21, it is clear that the use of D-STATCOM to maintain the wind farm in service during grid fault conditions is an expensive application compared with D-SVC970 due to the use 1000 of the transformer and the cost of power electronics [17,18]. Consequently, one can conclude that the 900 D-STATCOM is more cost-effective compared to D-SVC817 for voltage support at the PCC and the wind 756 farm connection800 in the event713 of the most severe grid fault conditions. 700 600 970 1000 500 500 413 900 400 817 800 756 300 713 700 200

Cost of D-FACTS (k$) (k$) Cost of D-FACTS 600 100 500 500 0 413 400 Line to line grid fault (P1) Line to line grid fault (P2) 60 kV bus fault D-STATCOM D-SVC 300

200

Cost of D-FACTS (k$) (k$) Cost of D-FACTS Figure 21. Cost of D-FACTS systems from different types of grid faults. 100 Figure 21. Cost of D-FACTS systems from different types of grid faults. According0 to Figure 21, it is clear that the use of D-STATCOM to maintain the wind farm in Line to line grid fault (P1) Line to line grid fault (P2) 60 kV bus fault service during grid fault conditions is an expensive application compared with D-SVC due to the use D-STATCOM D-SVC

Figure 21. Cost of D-FACTS systems from different types of grid faults. Appl. Sci. 2018, 8, x 19 of 22 Appl. Sci. 2018, 8, 2250 19 of 22 Figure 22 shows the cost breakdown of a proposed 12 MW wind farm installation. of theAccording transformer to andthis thefigure, cost it of can power be seen electronics that the [ 17proposed,18]. Consequently, solution based one on can a concludeD-FACTS that system the D-STATCOMrepresents only is more4% of cost-effective the overall cost compared of the wind to D-SVC turbine for installation. voltage support On the at other the PCC hand, and this the solution wind farmoffers connection good performance in the event at ofthe the wind most farm, severe ensuring grid fault its conditions.connection with the electrical grid and the reliabilityFigure of 22 the shows wind the energy cost breakdown conversion ofsystem. a proposed 12 MW wind farm installation.

Figure 22. Breakdown of the costs of the wind project. Figure 22. Breakdown of the costs of the wind project. According to this figure, it can be seen that the proposed solution based on a D-FACTS system represents8. Conclusions only 4% of the overall cost of the wind turbine installation. On the other hand, this solution offersThe good aim performance of this paper at is theto investigate wind farm, the ensuring feasibility its study connection of the withwind thefarm electrical project in grid an Algerian and the reliabilityhighland ofregion. the wind Nevertheless, energy conversion the study system.in this paper shows that Tiaret’s electrical grid is susceptible to host the proposed wind farm in order to benefit from the wind potential. Therefore, in this paper, 8. Conclusions the application of the D-FACTS systems as the appropriate solution for the electrical grid connection issueThe and aim to ofaccomplish this paper the isto uninterrupted investigate the operation feasibility of study a wind of farm the wind based farm on projectDFIG during in an Algerian the line- highlandto-line fault region. and Nevertheless,the voltage drop the studyat 60 kV inthis has paperbeen investigated. shows that Tiaret’s The D-FACTS electrical is grid connected is susceptible at the toPCC host where the proposed the wind wind farm farm is connected in order to to benefit the grid, from to the provide wind potential.necessary Therefore, reactive power in this for paper, voltage the applicationsupport of ofthe the wind D-FACTS farm. systemsBased on as the the appropriatesimulation results, solution the for stability the electrical improvement grid connection of the issuewind andfarm to through accomplish the theincorporation uninterrupted of the operation D-SVC or of ath winde D-STATCOM farm based has on DFIGbeen illustrated. during the In line-to-line addition, faultit can and be theconcluded voltage that drop using at 60 kVD-STATCOM has been investigated. reduces the The complexity D-FACTS of is controlling connected atthe the wind PCC turbine- where thegenerators, wind farm improves is connected the time to the response grid, to of provide reactive necessary power compensation, reactive power and for voltagecorrects support for the lack of the of winda wind farm. turbine. Based on the simulation results, the stability improvement of the wind farm through the incorporationFuture work of the will D-SVC evaluate or the the D-STATCOM impact of differe has beennt scenarios illustrated. for In wind addition, farms it integrated can be concluded into the thatAlgerian using electrical D-STATCOM grid reduceswith other the renewable complexity energy of controlling sources theand wind their turbine-generators,electricity price. improves the time response of reactive power compensation, and corrects for the lack of a wind turbine. AuthorFuture Contributions: work will L.W. evaluate and K.D.E.K. the impact contributed of different to thescenarios main idea forof this wind article. farms K.D.E.K integrated wrote the into paper. the AlgerianK.D.E.K. searched electrical literature. grid with K.D.E.K other renewablecollected data energy and performed sources and the theirsimulations. electricity L.W., price. A.V.D.B., A.M., A.D. and K.D.E.K. contributed to the analysis of data. L.W., K.D.E.K., A.V.D.B., A.M., A.D. and L.B. revised the paper Authorcritically. Contributions: All authors approvedL.W. and the K.D.E.K. final version contributed to be topublished. the main idea of this article. K.D.E.K wrote the paper. K.D.E.K. searched literature. K.D.E.K collected data and performed the simulations. L.W., A.V.D.B., A.M., A.D. andFunding: K.D.E.K. This contributed research towas the funded analysis by of data.the National L.W., K.D.E.K., Natural A.V.D.B., Science A.M.,Foundation A.D. and of L.B.China revised grant the number paper critically.51577005. All No. authors 51877005 approved and the the Aeronautical final version Science to be published.Foundation of China grant number 2015ZC51030. Funding:ConflictsThis of Interest: research The was authors funded declare by the Nationalno conflict Natural of interest. Science Foundation of China grant number 51577005. No. 51877005 and the Aeronautical Science Foundation of China grant number 2015ZC51030. ConflictsAppendix of Interest:A The authors declare no conflict of interest.

AppendixIn this A part, simulations are investigated with a 1.5 MW DFIG connected to a 690 V/50 Hz grid [28,40,42,43]. The parameters of the turbine and the generator are presented below: In this part, simulations are investigated with a 1.5 MW DFIG connected to a 690 V/50 Hz grid [28,40,42,43]. The parameters of the turbine and the generator are presented below: Appl. Sci. 2018, 8, 2250 20 of 22

Parameters Values Turbine Number of blades 3 Turbine radius 35.25 m Gear box ratio 90 DFIG Power 1.5 MW Nominal voltage 690 V Frequency 50 Hz Number of poles pair 2 Stator resistance 0.012 Ω Rotorique resistance 0.021 Ω Stator inductance 0.0137 H Rotor inductance 0.01367 H Mutual inductance 0.0135 H (Turbine + DFIG) Generator inertia 1000 Kg.m2 Friction factor 0.0024 Kg.m/s The parameters of the D-STATCOM are presented below [44]:

Parameters Values Transformer voltage 2.5/30 kV Nominal frequency 50 Hz Rated power 3–15 MVA Resistance 0.22/30 pu Inductance 0.22 pu DC-link voltage 4000 V The parameters of the D-SVC are presented below:

Parameters Values Transformer voltage 2.5/30 kV Nominal frequency 50 Hz Rated power 3–15 MVA Rated capacitor power 3–15 MVar Rated inductance power 1.5–10 MVar

References

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