voltage source converters in wind turbines. - saaei algorithms have to be added to the wind turbine...

25/06/2009

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Alcala University Department of Electronics

Section IV:Section IV:

Voltage source converters in wind turbines.

1


1. Overview of wind turbine topologies.

Agenda

2. Low voltage ride through (LVRT).

3. Reactive power compensation.

4. Participation in the ancillary services.

5 Detection and operation in islanding mode5. Detection and operation in islanding mode.

6. References.

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Overview of wind turbines

Fixed speed with capacitor bank (reactive power)

Variable speed shifting between number of poles

Overview of topologies (1/2)

( )

Inductiongenerator

Variable speed with rotor resistance rotor

Inductiongenerator

3

Gear

Pitch

Grid

Reactivecompensator

Resistancecontrol


Overview of wind turbines

Variable speed: Induction generator –Squirrel cage rotor

Doubly fed

Variable speed: Doubly-fed inductor generator-wounded rotor

Overview of topologies (2/2)

Gear

Doubly-fedinduction generator

Pitch

Grid

DC

AC

AC

DC

Pref Qref

Variable speed: Synchronous generator –V i bl d S h t

4

y gExternal magnetized Variable speed: Synchronous generator –

Permanent magnets

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Evolución anual y acumulada de la potencia eólica 1997-2008

Overview of wind turbinesProduction of wind energy in Spain (1/2)

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Overview of wind turbinesProduction of wind energy in Spain (2/2)

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Source: Red Eléctrica Española.Avance del informe 2008 http://www.ree.es

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Overview of wind turbinesResearching topics to increase the grid integration of wind power

The high penetration of wind parks in the power system can seriously damage the grid stability. The ambitious objectives of the Spanish and European governments will not be affordable if novel solutions are not proposed in the next years.

The correct operation and the stability in the steady and transient states of the power system with high wind power penetration has to be assured.

The power system stability margins has to be studied rigorously.

N l l ith h t b dd d t th i d t bi t ll th t th

7

Novel algorithms have to be added to the wind turbine controllers, so that they :participate in the ancillary services, contributing actively to the system dynamic stability; andcollaborate to mitigate the power quality events.

In the future, to include storage elements in the wind turbines will contribute to increase their participation in the ancillary services.


Overview of wind turbinesWind Turbine generator system model

8Source: Z. Lubosny, “Wind Turbine Operation in Electric Power Systems. Advanced Modelling” Springer, 2007. ISBN: 3-540-40340-X

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Overview of wind turbinesBlock diagram of the controller

VSC1 PiDC1 iDC2Grid VSC2

Wind Turbine(WT)

Power Electronic System

ii2AC generatorCDC2

NP

N

PCC

CDC1

( )tig

r

G

( )te gr 2DCu1DCu

4500μF

4500μF

i1i2

uc

uDC meas.NP Voltage Balancing

Controller

)(ku)(* kur

PWMgenerator

)(* kur

12 pulses

Machine measurements

( )trω

( )kki θ)(r

( )k ( )kP

PWMgenerator

12 pulses

Grid current meas.

Grid voltages meas.

DSC-SRF-PLL

( )timr

9

uDCcontroller

)(kuDC

)(kuDC∗

Current controller

)(kid∗

)(kiq∗

)(ku)(kig

r

( )kek gr),(1θ

Control of VSC connected to the grid Control of VSC connected to the AC generator

High level controller

References from the grid operator

)(Current

controller Machine controller

)(kim∗r

)(kr∗ω)(kd

∗λ

( )kki rm θ),( ( )krω

MPPT

( )kPw

Information fromWT Controller


Agenda





5 Detection and operation in islanding mode

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5. Detection and operation in islanding mode.

6. References.

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Voltage dips – effect in distributed power generation systemsLow-voltage ride through

0.7 0.8 0.9 1600700800900

1000

x104

u DC(V

)

Solutions to avoid the converter switch-off

Under fault Pg< PW.It produces an energyexcess that should bedissipated or storage.

11

Hardware:Rotor energy storage.Braking chopper.DC-bus energy storage.Oversize.Active crowbar.

Software:Generation of new reference currents

Solutions to avoid the converter switch-off


Low-voltage ride throughDFIG-system with “ride-through”

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DC crowbar is based on a chopper with a resistor in order to limit the DC voltage from exceeding safe range.The rotor side converter has to be over dimensioned to handle the high current transients in

addition to the normal load.

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AC crowbarFor a successful ride through the short-circuit made by the crowbar

has to be removed before the rotor side converter can start.

Low-voltage ride through

(a)

This is a problem for the crowbar Fig. (b), where the current through

the thyristor is continuous and does not allow the turn-off.

The crowbar of Fig. (a) may have some problems as well because the

rotor currents may have significant DC component and thus the zero

crossings that would turn the thyristors off do not exit when they would

be needed.

(b)

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The snubber design for the thyristor of the crowbar of Fig. b may be

problematic.

Fig. b has only one controlled component and thus is optimal in this

respect.


Voltage dip ride-throughDFIG-system with “ride-through”

Simulation results under unbalanced voltage grid

0.7 0.72 0.74 0.76 0.78 0.8 0.82 0.84 0.86 0.88700

720

740

760

780

800

time (s)

u DC

(V)

300300

400

0.7 0.72 0.74 0.76 0.78 0.8 0.82 0.84 0.86 0.88700

720

740

760

780

800

time (s)

u DC

(V)

( )Non-compensation Compensation

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0.7 0.72 0.74 0.76 0.78 0.8 0.82 0.84 0.86 0.88

-300

-200

-100

0

100

200

time (s)

i grid

(A)

0.7 0.72 0.74 0.76 0.78 0.8 0.82 0.84 0.86 0.88-400

-300

-200

-100

0

100

200

time (s)

i grid

(A)

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Agenda





5 Deteccion and operation in islanding mode

15

5. Deteccion and operation in islanding mode.

6. References.


Reactive power compensationReactive power ability suggested by the E.ON code

Upper Limit of voltage

Lower Limit of voltage

Ireactive/In

U/Un

1.0

0.5

-1.0

Generation of reactive current

Normal operation area(variable power factor)

16

Reactive current output from the WF to increase 2% for a 1% voltage decrease, to have 100% rated capacity of the converter utilized at 50% voltage at the WT terminal

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Reactive power compensation( ) ( ) ( ) ( )

( )( ) ( )δ

αδ

i33

cos3sin3 11

1

UEEUE

Q

UEXUE

P

g

gL

gg ==( ) ( ) ( ) ( )( )g

L

g

L

gggg EU

XE

jXUE

jQPS −+=+= δδ cos3sin3 11

11

r

Grid-converter limitation to compensate the reactive power

( ) ( )( ) ( ) ( )αδ sin3cos3 111

UEEUX

Q ggL

gg =−=

gE

( )11 gL IjX

α

δ

( )1gI

( )1U

( )13 UEg

α

δ

( )1gI

( )11

3U

XE

L

g

gP

gQ

α

OMg

L

g EXE

1

3

6 x 105

Pg (W)

22⎞⎛

17-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

x 105

-6

-4

-2

0

2

4

Qq (VAr)Sn=Pmáx

2222

11

225.13⎟⎟⎠

⎞⎜⎜⎝

⎛=⎟

⎟⎠

⎞⎜⎜⎝

⎛++

L

DCg

L

ggg X

uEXE

QP

( )( )2122 3 máxggg IEQP =+


Agenda






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6. References.

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The angle δ can be controlled regulating the active power P whereas the inverter

voltage VA is controllable through the reactive power Q.

Participation in the ancillary servicesDroop control

voltage VA is controllable through the reactive power Q.

Control of the frequency dynamically controls the power angle and, thus, the real

power flow.

Thus by adjusting P and Q independendently, frequency and amplitude of the grid

voltage are determined

Hovewer, low voltage distributio lines have a mainly resistive nature.19


Agenda






20


6. Conclusions.

7. References.

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Detection and operation in islanding mode Anti-islanding methods overview

Passive methods, based on the detection ofOver/under voltage (OUV) and Over/Under frequency (OUF)Voltage harmonicsgPhase jump

Active methodsPositive Feedback in the inverter controlInjection of harmonics via the PV inverterActive frequency driftSlip-mode Phase Shift (SMS)

Detection methods at the grid levelImpedance connection methodMethods based on the communication between the grid and photovoltaic inverter

Every method has a NDZ (Non Detection Zone)

In stand-alone control mode, no grid exists so the output voltages need to be controlled in terms of amplitude and frequency and thus, the reactive and, respectively, active power flow is controlled.In the case of unbalance between the generated and the load-required power, adjustment of the speed of the generator can regulate the produced power in a limited range. The potential excess of power will be quickly dissipated in the damp resistor by starting the chopper control.

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Every method has a NDZ (Non Detection Zone)

Stand-alone control mode


Agenda





5 Detection and operation in island mode

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5. Detection and operation in island mode.

6. Conclusions.

7. References.

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IEEE Std 929-2000 – IEEE Recommended Practice for Utility Interface of Photovoltaic (PV) Systems,2000, ISBN 0-7381-1934-2IEC 61727 CDV Ed.2 – Characteristics of the Utility Interface for Photovoltaic (PV) Systems, 2002IEEE Std 1547 – IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems,2003, ISBN 0-7381-3720 0

References

3720-0EN 50330-1 – Utility Interactive Faile Save Protective Interface for PV-Line Commutated Converters, Copyright OVE/ON, 1999Evaluation of Islanding Detection Methods for Photovoltaic Utility Interactive Power Systems - Task V, Report IEA-PVPS T5-09: 2002 March 2002, www.iea.orgG.A.Smith, lA.Onions and D.G. Infield, "Predicting islanding operation of grid connected PV inverters", IEE Proc.-Electr. Power Appl., Vol. 147, No. 1. January 2000Asiminoaie L.,Teodorescu,R., Blaabjerg,F., Borup,U. – “A Digital Controlled PV-Inverter with Grid Impedance Estimation for ENS Detection ” IEEE Trans on PE 2005.F. De Mango, M. Liserre, A. Dell’Aquila and A. Pigazo “Overview of anti-islanding algorithms for PV systems. Part I: passive methods ” EPE PEMC 2006methods EPE-PEMC 2006.F. De Mango, M. Liserre, A. Dell’Aquila“Overview of anti-islanding algorithms for PV systems. Part II: active methods ” EPE-PEMC 2006.R. Teodorescu, F. Blaabjerg, “Flexible Control of Small Wind Turbines With Grid Failure Detecction Operating in Stand-Alone and Grid-Connected Mode”, IEEE Trans. on Power Electronics, vol. 19, no. 5, September 2004, pp. 1323-1332.Z. Lubosny, “Wind Turbine Operation in Electric Power Systems. Advanced Modelling” Springer, 2007. ISBN: 3-540-40340-XRed Eléctrica Española.Avance del informe 2008 http://www.ree.esSpanish Wind Energy Association. http://www.aeeolica.esR.Teodorescu, M.Liserre, P.Rodríguez. “Power Electronics for Renewable Energy Systems – in theory and practice (PERES course)”. May 2007. Aalborg University. Institute of Energy Technology. http://www.iet.aau.dk/ 23


Thank you for your kind attention!!!!!

Emilio Bueno [email protected]

Research group “Electronics Engineering Applied to the Renewable Energies” (GEISER)http://geiser.depeca.uah.es/

Department of Electronics. http://www.depeca.uah.esAlcalá University. http://www.uah.esAlcalá de Henares (Madrid). Spain.

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voltage source converters in wind turbines. - saaei algorithms have to be added to the wind turbine...

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