Grid Code Requirements for Wind Power Integration in Europe

8/21/2019 Grid Code Requirements for Wind Power Integration in Europe

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Hindawi Publishing CorporationConerence Papers in EnergyVolume , Article ID ,pageshttp://dx.doi.org/.//

Conference PaperGrid Code Requirements for Wind Power Integration in Europe

Constantinos Sourkounis and Pavlos Tourou

Institute for Power System Technology and Power Mechatronics, Ruhr-University Bochum, Germany

Correspondence should be addressed to Pavlos ourou; [email protected]

Received December ; Accepted March

Academic Editors: Y. Al-Assa, P. Demokritou, and A. Poullikkas

Tis Conerence Paper is based on a presentationgiven by Pavlos ourou at Power Options or the Eastern Mediterranean Regionheld rom November to November in Limassol, Cyprus.

Copyright C. Sourkounis and P. ourou. Tis is an open access article distributed under the Creative Commons AttributionLicense, whichpermits unrestricted use, distribution, andreproduction in anymedium, providedthe original workis properlycited.

As the capacity o wind power continues to increase globally, stricter requirements regarding grid connection o wind generatorsare introduced by system operators. Te development o wind turbine technology is inevitably affected by the new grid codes, andwind power plants are expected to support the grid and provide ancillary services much like conventional power plants. Te mostdemanding regulations are ound in Europe where wind penetration levels are higher. Tis paper presents the main aspects ocurrent grid code requirements or the integration o wind power in European countries and suggests perormance characteristicsin order to satisy the most demanding requirements. Te dynamic behavior o wind turbines with doubly ed inductiongeneratorsis investigated and a solution or low voltage ride through compliance is presented.

1. Introduction

WIND power installations continue to increase worldwide,with a total installed capacity o GW by the end o ,which meets about % o the global electricity demand, andan expected capacity o GW by [, ]. In Europe,wind power generation is expected to contribute to EUs targets or reduction o carbon dioxide emissions bymore than % and to supply at least %% o Europeselectricity []. Te penetration o wind power in the electrical

grids increases steadily in many European countries, withthe highest percentage ound in Denmark (%), a countrythat has recently set the ambitious target to produce %o its electricity rom wind turbines by the end o . Inorder to maintain reliable grid perormance with increasingwind penetration, transmission system operators (SOs)update their grid connection codes with specic require-ments regarding the operation o wind generators and windarms. In general, wind arms are expected to support thegrid and to provide ancillary services much like conventionalpower plants (e.g., active power control, requency regulationand dynamic voltage control, and low voltage ride through(LVR)).

Te requirementsvary between countries andtheir sever-ity usually depends on the wind power penetration level aswell as on the robustness o the national or regional powernetwork. Grid code requirements have been a drive or thedevelopment o wind turbine technology. Manuacturers inthe wind energy sector are constantly trying to improve windturbines, mainly in the area o wind turbine control andelectrical system design, in order to meet the new grid coderequirements. Tis can ofen imply higher costs, as moreadvanced powerelectronic designs and morecomplex control

systems have to be utilized.Tis paper discusses the inuence o wind power on

the operation o existing power systems and presents themain aspects o the latest grid code requirements or theintegration o wind power in several European countries.Te different requirements are analyzed and compared, andthe most demanding are highlighted. Te ability o differentwind turbine technologies to meet these requirements isalso discussed. Te low voltage ride through, one o themost important requirements or the dynamic perormanceo wind turbines during network ailures, is considered indetail. Simulation studies are conducted to study the behav-ior o wind turbines equipped with doubly-ed induction


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Conerence Papers in Energy

generators (DFIGs) during severe voltage dips caused bygrid aults. Control strategies and hardware that improve theLVR capability o the wind turbines during the ault arepresented.

2. Frequency and Voltage Operating Range

.. Importance for Power System Operation. Te powersystem requency is an indication o the balance betweenpower generation and load consumption. Any deviation romthe planned production or consumption moves the systemrequency away rom its nominal value. In the case o asudden increase in the load, the requency o the produced

voltage decreases and it is restored back to the nominal whenpower production is increased by primary control. Under-requency can also occur as a result o an unexpected losso generation units. On the other hand, over-requency canoccur with a sudden decrease in load or an unexpectedincrease in generation (e.g., wind gusts) [].

Grid codes require that wind arms must be capableo operating continuously within the voltage and requency

variation limits encountered in normal operating conditions.In addition, they should remain in operation in case orequency deviations outside the normal operating limits ora specied time and in some cases with a specic activepower output. By having the ability to remain connected tothe grid or a wider requency range, wind arms support thesystem during abnormal operating conditions and allow ora ast system requency restoration. Wind turbines must bedesigned appropriately, as abnormal requencies can overheatgenerator windings, degrade insulation material, and damagepower electronic devices.

.. Grid Code Requirements. Te requency ranges requiredby the various grid codes are presented in Figure . In thegreen requency ranges, the wind turbines must remainconnected and operate continuously at ull power output. Inthe white ranges, they must remain connected at least or theminimum time specied, usually at a lower power output, inorder to support the grid during requency restoration. Inmany cases the active power reduction must be controlledproportionally with the requency deviation rom the nom-inal. In the extreme grey requency ranges, wind turbinesare allowed to disconnect rom the grid. Te active powerrequirements at different requencies, i specied in the grid

code, are also shown inFigure .

.. Comparison and Capability to Fulll All Requirements.Wind turbines are now required to remain connected in thecase o large requency deviations, with the most extremerequencies being Hz and Hz. As the requency devia-tion increases, the minimum connection time and minimumactive power conditions are relaxed. In the case o under-requencies wind turbines must remain connected to thegrid or longer periods beore they are allowed to trip. Telargest requency ranges o mandatory continuous operation,in which the wind turbines must never trip, are seen inthe UK, Romania (. Hz Hz), and Italy (. Hz.).

Large requency ranges are expected in isolated systems withweak interconnections where the system stability is more

vulnerable to disturbances compared to large interconnectedsystems (e.g., UCE).

Te most extreme requirements, taking also into accountthe voltage range level at which the requency range is

required, were combined to produce the requency-voltageprole shown inFigure . I a wind turbine has the capabilityto operate within the area shown in Figure , then itcan meetall the different requirements specied in the European gridcodes.

3. Active Power Control

.. Importance for Power System Operation. Active powercontrol is the ability o wind power plants to regulate theiractive power output to a dened level and at a dened ramprate (e.g., in the case o active power curtailment requests bySOs). Tese requirements aim to ensure a stable requency

in the system, to prevent overloading o transmission linesand to minimize the effect o the dynamic operation o windturbines on the grid (e.g., during extreme wind conditions, atstartup/shutdown).

Te ability o wind turbines to control their active poweris also important or transient stability during aults. I thepower can be controlled effectively as soon as a ault occurs,the turbine can be prevented rom overspeeding. Hence, thereactive power needed or remagnetization o the generatorsis less afer the ault is cleared, which helps reestablishingthe grid voltage. Ofen, active power generation is reducedtemporarily by the control system during the low voltageperiod []. Tis allows the increase o reactive power gener-

ation without exceeding the rated current o the converters.Afer the ault period, a ast return to normal active powergeneration is essential to ensure the power balance andstability o the grid.

.. Grid Code Requirements. Most grid codes demand activepower curtailment upon request rom the network operator,at a specied set-point. Tis is done either by disconnectingwind turbines or by controlling the pitch angle o the bladesinorder to limit the power extracted rom the wind. Some gridcodes also impose limitations on the rate o change o activepower, with maximum and minimum ramp-up and ramp-down rates. Tese limitations aim to suppress large requency

uctuations caused by extreme wind conditions and to avoidlarge voltage steps and in-rush currents during wind armstartup and shutdown.

.. Comparison and Capability to Fulll All Requirements.Te most demanding requirements or active power controlare presented inable .

Under normal conditions many grid codes require aramp-down rate o


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England and Wales Scotland Romania Denmark

Disconnection

2% active powerreduction per Hz

Max 5% linear

active power

reduction

20 s

Max 5% linear

active power

reduction

20 s 20 s

Disconnectionwithin1 s

Continuous with 20%

max power losses

Continuous-linear

proportional to

20 s, 80% power

Frequency

53.5

5352.5

52

51.5

51

50.5

50

49.5

49

48.5

48

47.5

47

46.5

46

Frequency

53.5

53

52.5

52

51.5

51

50.550

49.5

49

48.5

48

47.5

47

46.5

46

Germany

Fast automaticdisconnection

Fast automatic

disconnection

30 min

30 min

20 min

10 min

30 min at reducedpower output

Nominal power

Nominal power

SpainFrance Cyprus

Time by

agreement

Time by

agreement

20 s, power set by TSO

15 min, power set by TSO

60 min, 90% power

5 hrs, 90% power

3 min, 90% power

3 min, 85% power

20 s, 80% power

3 s5 s

60 min

60 min

30 min%oav/s), where due to the isolated nature o their electricalgrids the wind arms must provide ast active power supportto assist in the grid voltage recovery.

In general, the most demanding requirements regardingactive power control are ound in the Danish grid code wherewind arms must be equipped with and apply active powercontrol unctions with set-points and ramp-rates set by thesystem operator as shown in Figure . Te Delta controlunction is particularly demanding, as the active poweroutput o wind arms with capacity greater than MW mustbe constrained to a required constant value in proportion to

the available active power. Tis reserve power can be used inast grid requency control, similar to the spinning reservesin conventional power plants.

4. Reactive Power Control

.. Importance for Power System Operation. Te voltagelevels in a power system must be maintained constant (within

a very narrow range) because equipment o the utility andconsumers are designed to operate at specic voltage levels.Recent adaptations to national grid codes demand rom windarms to contribute to voltage regulation in the system, asconventional power plants do. Tey must have the ability togenerate or absorb reactive power in order to inuence the

voltage level at the point o common coupling (PCC). Undernormal operation the voltage at the PCC can be increased byinjecting reactive power to the grid and can be decreased byabsorbing reacting power. Wind arms should have reactivepower capabilities in order to support the PCC voltage during

voltage uctuations and to assist in balancing the reactivepower demand in the grid.


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53

52

51

50

49

48

47

8590 95

100105110

115115.8

/(%)

Frequency(H

z)

50.3

49.7

>30 minno

restriction

Continuous

operation

=

Continuous

operation

for>20 s

1hour

=90%

P > 80%PN

P > 80%

F : Most extreme requirements or wind arm operation atdeviations rom nominal grid voltage and requency.

Activepower

Possible active power

Activation of active powerproduction constraint

Activation of deltaproduction constraint

Activation of gradientproduction constraint

Activation of delta and

deactivationgradient production constraint

Deactivation of absoluteproduction constraint

Spinning

Time

reserve

F : Active power control unctions required in Denmark [].

.. Grid Code Requirements. Te reactive power require-ments are usually expressed with - diagrams (availableactive power versus available reactive power). Te requiredamount o reactive power compensation varies with differentpower system congurations. Te effect o injected/absorbed

reactive power on the PCC voltage level depends on thegrid impedance, grid short-circuit capacity, as well as on anyconnectedload near the point o connection []. Te differentreactive power requirements are summarized inFigure .

.. Comparison and Capability to Fulll All Requirements.Te widest ranges are ound in Germany where one o thethree variants must be chosen in agreement with the gridoperator. In order to ulll all gridcode requirementsin termso reactive power capability, a wind turbine or arm mustoperate in the whole area shown in the / prole oFigure .At ull active power the wind turbine must be capable osupplying reactive power in the range . p.u. inductive

Inductive Capacitive

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

0.5 0.4 0.3 0.2 0.1 0 0.1 0.2 0.3 0.4 0.5

/

/

Germany variant 1

Denmark1.525 MW

Germany variant 2Germany variant 3

Ireland

UK

Denmark25 MW

F : Reactive power requirements o various grid codes.

1.0

0.2

0

Powerfactor =0.925

Powerfactor =0.44

Power

factor =0.9

Powerfactor =0.38

0.41 0.1 0 0.1 0.48

Q/PN(p.u.)

P/PN

(p.u.)

Inductive Capacitive

F : - prole to satisy all grid codes.

to . p.u. capacitive which corresponds to a power actorrange . lagging to . leading. Tis reactive power rangemust be maintained with active power down to . p.u. andor lower active power output the reactive power can be

decreased proportionally.

5. Low Voltage Ride Through (LVRT)

.. Importance for Power System Operation. Te low voltageride through is the most important requirement regardingwind arm operation that has been recently introduced inthe grid codes. It is vital or a stable and reliable operationo power supply networks, especially in regions with highpenetration o wind power generation. Faults in the gridcan cause large voltage dips across wide regions and somegeneration units can be lost as a consequence. In the past,during grid disturbances and low grid voltages the wind


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0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200

05

10152025303540455055

6065707580859095

100

Time (ms)

Germany

Germany/Greece STI

Greece

SpainBelgium

Denmark

Ireland/Romania

ItalyPoland

CyprusUK

Turkey

Finland, Sweden

U/UN

(%)

France400 kV

France63225 kV

F : LVR requirements in various grid codes.

turbines and arms were allowed to disconnect rom the grid.But i there is a large amount o wind generation in thenetwork, the simultaneous disconnection o wind generatingunits and arms can cause larger voltage depression and even-tually collapse o voltage in the affected region. Furthermore,

the additional loss o power generation as a result o thedisconnection can cause a greater generation/consumptionimbalance andthus drop in the system requency in the widerregion [].

.. Grid Code Requirements. Recent grid codes require windarms to remain connected and support the grid during andafer a ault. Tey must withstand voltage dips o a certainpercentage o the nominal voltage or the specied timedurations, as shown in the LVR voltage-time proles oFigure . Disconnection is not allowed above the borderline.Below the borderline wind turbines are not required to

contribute to the grid and they can be tripped by circuitbreakers.

Furthermore, in some countries voltage control isrequired during the low voltage aults as shown inFigure .Wind arms must supply reactive current to the grid basedon the depth o the voltage dip, in order to support thelocal voltage and thus limit the geographical low voltage areacaused by the grid ault. During this low voltage period theactive current can be decreased and priority should be givento the reactive current in order to back up the grid voltage.Te German grid code asks or a constant o proportionality between the voltage deviation and the required reactivecurrent that can be set in the range = 010 afer an

agreement with the network operator, with a deault value = 2.

.. Comparison and Capability to Fulll All Requirements.

Te most severe requirements or LVR were combined tocreate the LVR prole shown in Figure . Wind turbinesand arms must remain connected to the grid above thesolid line. Below the solid line and until . seconds afer thestart o the ault, wind turbines can disconnect only i theycan resynchronize with the grid within seconds. I voltageremains below % o the nominal afer . seconds, windturbine are allowed to disconnect unconditionally.

Regarding the contribution o the wind arms to gridvoltage support, the German grid code is the most demandingas it can require rated reactive current at % voltage decreasewith very ast step response characteristics (rise time = ms,transient time = ms). Afer ault clearance, the steepestincrease o active power is ound in the UK, according towhich theactive power must be increasedto thepreaultvaluewith a rate equal to p.u. per second. In the next sections,the response o DFIG-based wind turbines in the case o low

voltage grid aults is analyzed, and their capability to meet theLVR requirements is examined.

6. LVRT Capability of DFIG-BasedWind Turbines with Doubly FedInduction Generators

Fixed-speed wind turbines with squirrel cage inductiongenerators have a very limited LVR capability. Tey are


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Germanyk = 2,rise time= 30 ms, settling time= 60 msGermanyk = 10,rise time= 30 ms, settling time= 60 ms

Denmark, settling time= 100 ms

Spain, settling time= 150 ms

1

0.8

0.6

0.4

0.2

00 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Reactivecurrentdeli

vere

dtothegrid(p.u.)

Voltage decrease (dU/Unom ) at the PCC (p.u.)

F : Reactive current requirements with grid voltage decrease.

U/UN

(%)

100

80

39.5

156.6

0

0 250 375 625 1500 3000

Time (ms)

Disconnectionis not permitted

Disconnection

possible

Short-time disconnection allowed

F : Fault ride through prole to satisy all grid codes.

constantly absorbing reactive power rom the grid or theirmagnetization. During low voltage aults they tend to over-speed and they can become unstable, suppressing urther thegrid voltage. Te LVR capability o wind arms with xed-speed turbines can be improved by retrotting reactive powercompensation equipment such as static Var compensators

(SVCs) and static synchronous compensators (SACOMs)[]. Variable-speed wind turbines with ull rated converterscan ride through the aults without signicant problems andthey candeliver reactive power orvoltage support. Te LVRcapability o variable-speed wind turbines equipped withdoubly-ed induction generators is studied in the ollowingsections.

.. Doubly Fed Induction Generators. Te doubly-ed induc-tion generators (DFIGs) are currently the most widely usedtype o electrical generators or wind turbine systems inthe Megawatt range []. Te DFIG technology has provento be an efficient and cost-effective solution or variable

speed wind turbines. An important disadvantage o this typeo generators is its behavior during signicant voltage dipsat their stator terminals. Beore the introduction o LVRrequirementsin the nationalgrid codes,wind arms equippedwith DFIG wind turbines were allowed to disconnect romthe grid in the case o signicant grid voltage deviations.

In order or the wind turbines to remain connected andsupport the grid during low voltage periods, enhancementsare required in the hardware and control o these windturbines.

.. Description of a DFIG-Based Wind Turbine System.Te wind rotor is in most cases connected to the rotorshaf o the generator through a gearbox that increases therotational speed at the generator side as shown inFigure .Te stator windings are directly connected to the grid. Terotor windings are connected to the grid through two voltagesource converters connected back-to-back. Tis converterconguration decouples the rotor electrical requency rom

the grid requency, and as a result the rotor can havea variable speed, normally in a range % around thesynchronous speed. Variable-speed wind turbines can harvestmuch more energy compared to xed-speed wind turbinesbecause depending on the wind speed, they can operate atthe optimum rotational speed at which the aerodynamicefficiency o the wind rotor is maximum [].

During normal operation the stator power ows romthe stator to the grid, while the ow o rotor power overthe DC-link is bidirectional; current ows rom the grid tothe rotor at undersynchronous speeds (n

r < n

s) and in the

opposite direction at oversynchronous speeds (nr

> ns).

Te maximum rotor power depends on the slip, and since

the rotational speed range is limited, the rotor power is onlya raction o the stator power. Tis allows signicant costsavings as the power electronic converters can be partiallyrated to only %% o the total power o the generator.Furthermore, the power efficiency is higher because thereare lower switching and conduction losses in the powerelectronics due to the partial rating o the back-to-backconverter.

.. Control System. Te operation management controls therotational speed o the wind turbine in order to capturemaximum wind power []. It provides the active powerreerenceto the rotorside converter (RSC) andthe pitch angle

to the pitch actuator system. Pitch control is used to limitthe power output o the wind rotor in the case o very highwind speeds, by decreasing the aerodynamic efficiency o therotor blades. Additionally the operation management limitsthe active power reerence in the case o grid aults and aferinstructions rom the network operator.

Te RSC controller is responsible or providing decoupledcontrol o the active and reactive power at the stator. Tetask o the grid side converter (GSC) controller is to keepthe DC-link voltage constant, irrespective o the rotor powerow direction while maintaining unity power actor at theGSC terminals. A vector control approach is adopted or theRSC and GSC, and the resulting reerence voltages are ed


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Wind

DFIG

RSC GSC

Wind rotor

Gearbox

Filter

TSO

management

RSCcontrol

Gridtransformer

GSCcontrol

Wind speedPitch angle

Control system

Operation

IGSC

VRSC VGSC VDC

VDC QSPS

3

=3

=

nr

nr

QGSC Igrid

VgridQgrid

Pgrid

IRSC

F : DFIG-based wind turbine system.

to space vector modulators to create the switching signalor the respective converters. By applying -phase voltageswith the appropriate amplitude, phase, and requency, theow o currents and consequently the active and reactivepower exchange with the grid at both the stator and the GSCterminals can be controlled.

7. Investigations on the DFIG Response toSevere Grid Faults

.. Response to Severe Voltage Dips. A detailed model othe DFIG-based wind turbine system was developed inMatlab/Simulink in order to investigate its behavior in thecase o severelow voltage aults. In this paper, the worst case isconsidered: an instantaneous voltage drop down to zero voltsor a time duration o ms while the generator operatesat maximum rotational speed and power output. Te aultoccurs at the grid-side o the transormer, and the voltagedrop experienced by the wind turbine terminals is shown inFigure .

At the start o the ault very high transient currents aredeveloped at the rotor and the RSC reaching times therated value o the converter. Furthermore, the voltage on

the DC-link rises to . p.u. Tese effects arise due to theinstantaneous collapse o the stator voltage. Te stator uxspace vector, which beore the ault rotates synchronouslywith a magnitude proportional to the stator voltage, stopsrotating and its magnitude decays exponentially with time.Similarly, DC stator currents with a decaying magnitude startto ow in the stator. Due to the electromagnetic couplingbetween the stator and the rotor circuits, the DC stator uxand currents induce a high requency component in therotor voltages, that is, superimposed on the normal voltagethat has a low slip requency. Te magnitude o the inducedrotor voltage is higher at the beginning o the ault and itcan be greater than the stator voltage i the rotor speed at

the time o the ault is oversynchronous []. Te RSC, dueto its partial rating, cannot produce such high voltages tomatch the induced rotor voltages, the control o current islost, and very high currents result in the rotor and the RSC.Tese highcurrentsow into the DC-link, increasing theDC-link voltage. Te GSC cannot balance the DC-link voltageby dissipating this energy to the grid, because its power islimited due to the low residual voltage and its rated current.As result the DC-link voltage rises much higher than the rated

voltage o the capacitor. Similarly, high rotor currents are also

induced at the instantaneous return o the grid voltage. Inthis case the GSC can operate at its maximum power output,balancing the DC-link voltage aster.

Tese very high currents and the signicant DC-linkovervoltage are unacceptable because they can damage theDC-link capacitor and the power electronic switches o theRSC. In order to protect themselves against these effectsduring severe grid voltage aults, the DFIG-based windturbines must disconnect rom the grid, violating the LVRgrid code regulations. Appropriate countermeasures must beadopted in order to protect the sensitive devices o the windturbine system and to meet the LVR requirements.

.. Response to Voltage Dips with a LVRT-Enhanced System.In order to mitigate the effects o severe grid aults on theDFIG, the rating o the power electronic converters can beincreased, so that it is possible to control the high transientcurrents at the beginning and end o the voltage dip. Tissolution is undesirable, as it eliminates the partial-ratingadvantage o the DFIG concept, increasing signicantly theoverall cost o the system. A more cost-effective solution is touse an active crowbar circuit between the rotor and the RSCas shown inFigure []. Tis consists o a ull-wave bridgerectier, a power resistor, andan IGB switch. During normaloperation the switch is open. Te switch can be activatedon detection o rotor overcurrents or DC-link overvoltage in


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0 0.1 0.2 0.3 0.4 0.5 0.6

Time (s)

0

2

4 Reactive current (p.u.)

01

2 Active power (green), reactive power (p.u.)

00.5

11.5

22.5

3 DC-link voltage (p.u.)

0

24

RSC currents (p.u.)

0

1PCC voltage (p.u.)

4

2

1

4

2

1

F : Response o a DFIG-based wind turbine during a msgrid voltage dip.

order to redirect the rotor currents in the crowbar circuit,where the energy is dissipated in the resistor.

Te behavior o the DFIG wind turbine equipped with acrowbar during a severevoltage dip is shown in Figure . Tecrowbar is activated with rotor overcurrent at the beginningand end o the voltage dip, and the high current peaks aresuccessully redirected away rom the RSC. Te DC-link

voltage is limited below . p.u. during the ault. Te crowbarremains connected to the rotor or about ms to allow or

the decay o the initial high transient currents. Afer thisperiod the crowbar is disconnected and the RSC ramps upthe reactive current to the rated value. A moderate increase inthe local grid voltage is observed during the reactive currentinjection. During the ault the active power reerence is keptto zero. Te active power is increased back to the preault

value and the reactive power back to zero about ms aferclearance o the ault. In the case o longer voltage dipsat higher residual voltage, sufficient active power must bedelivered to the grid in combination with blade pitch controlin order to prevent overspeeding o the wind rotor.

DC-link

DFIGCrowbar

Rotor-sideconverter

Rcb

F : DFIG with an active crowbar circuit.

Reactive current (p.u.)

Active power (green), reactive power (p.u.)

DC-link voltage (p.u.)

RSC currents (p.u.)

PCC voltage (p.u.)

0123

Crowbar currents (p.u.)

0 0.1 0.2 0.3 0.4 0.5 0.6

Time (s)

1

2

0

1

2

00.5

11.5

22.5

3

0

2

4

0

1

4

2

1

2

1

1

0

321

F : Response o a DFIG-based wind turbine with an activecrowbar during a ms grid voltage dip.


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.. Fullling the LVRT Requirements of Grid Codes. TeDFIG wind turbines, enhanced with a crowbar and a ded-icated control during the ault, can meet all the LVRrequirements ound in the European grid codes. Simulationstudies have shown that the wind turbines can ride through

voltage dips down to zero voltage or ms. During the

ault, they can provide voltage support by supplying ratedreactive current to the grid and they can restore their activepower very ast back to the preault active power. In general,the crowbar solution can protect sensitive components odoubly ed inductiongenerators and LVRcompliance can beachieved without the need or oversizing the expensive powerelectronic converters.

8. Conclusion

Te main aspects o current grid code requirements regard-ing wind power integration in European grids have beenpresented. Perormance characteristics in order to satisy all

the grid codes examined have also been suggested. As windpenetration increases, wind turbines and wind arms areexpected to be more tolerant to abnormal conditions andto contribute to grid stability during normal operation, aswell as during and afer grid aults. Te behavior o DFIG-based wind turbines during grid aults was investigated anda low cost solution or ullling the LVR requirements waspresented. Complying with grid code regulations is vital orgrid stability and the improved wind turbine perormancewill allow or larger wind power penetration in electricalpower grids.

References

[] World Wind Energy Association, World wind energy report, May , http://www.wwindea.org/webimages/World-WindEnergyReport.pd.

[] Global Wind Energy Council, Global Wind Report: Annualmarket update , March , http://gwec.net/wp-con-tent/uploads///Annual report lowres.pd.

[] European Wind Energy Association, Wind energy and EUclimate policy, October , http://www.ewea.org/lead-min/ewea documents/documents/publications/reports/ ClimateReport.pd.

[] . Ackermann, Wind Power in Power Systems, John Wiley &Sons, .

[] I. Erlich, W. Winter, and A. Dittrich, Advanced grid require-

ments or the integration o wind turbines into the Germantransmission system, in Proceedings of the IEEE Power Engi-neering Society General Meeting (PES ), p. , June .

[] M. Molinas, J. A. Suul, and . Undeland, Low voltage ridethrough o wind arms with cage generators: SACOM versusSVC,IEEE Transactions on Power Electronics, vol. , no. , pp., .

[] S. Muller, M. Deicke, and R. W. De Doncker, Doubly edinduction generator systems or wind turbines,IEEE IndustryApplications Magazine, vol. , no. , pp. , .

[] C. Sourkounis and B. Ni, Inuence o wind-energy-convertercontrol methods on the output requency components,IEEETransactions on Industry Applications, vol. , no. , pp. , .

[] J. Lopez, P. Sanchis, X. Roboam, and L. Marroyo, Dynamicbehavior o the doubly ed induction generator during three-phase voltage dips, IEEE Transactions on Energy Conversion,vol. , no. , pp. , .

[] G. Pannell, D. J. Atkinson, and B. Zahawi, Minimum-thresholdcrowbar or a ault-ride-through grid-code-compliant DFIGwind turbine,IEEE Transactions on Energy Conversion, vol. ,no. , pp. , .


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Grid Code Requirements for Wind Power Integration in Europe