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25/06/2009
1
Alcala University Department of Electronics
Section IV:Section IV:
Voltage source converters in wind turbines.
1
Alcala University Department of Electronics
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.
2
25/06/2009
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Alcala University Department of Electronics
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
Alcala University Department of Electronics
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
25/06/2009
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Alcala University Department of Electronics
Evolución anual y acumulada de la potencia eólica 1997-2008
Overview of wind turbinesProduction of wind energy in Spain (1/2)
5
Alcala University Department of Electronics
Overview of wind turbinesProduction of wind energy in Spain (2/2)
6
Source: Red Eléctrica Española.Avance del informe 2008 http://www.ree.es
25/06/2009
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Alcala University Department of Electronics
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.
Alcala University Department of Electronics
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
25/06/2009
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Alcala University Department of Electronics
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
Alcala University Department of Electronics
Agenda
1. Overview of wind turbine topologies.
2. Low voltage ride through (LVRT).
3. Reactive power compensation.
4. Participation in the ancillary services.
5 Detection and operation in islanding mode
10
5. Detection and operation in islanding mode.
6. References.
25/06/2009
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Alcala University Department of Electronics
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
Alcala University Department of Electronics
Low-voltage ride throughDFIG-system with “ride-through”
12
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.
25/06/2009
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Alcala University Department of Electronics
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)
13
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.
Alcala University Department of Electronics
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
14
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)
25/06/2009
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Alcala University Department of Electronics
Agenda
1. Overview of wind turbine topologies.
2. Low voltage ride through (LVRT).
3. Reactive power compensation.
4. Participation in the ancillary services.
5 Deteccion and operation in islanding mode
15
5. Deteccion and operation in islanding mode.
6. References.
Alcala University Department of Electronics
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
25/06/2009
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Alcala University Department of Electronics
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 =+
Alcala University Department of Electronics
Agenda
1. Overview of wind turbine topologies.
2. Low voltage ride through (LVRT).
3. Reactive power compensation.
4. Participation in the ancillary services.
5 Detection and operation in islanding mode
18
5. Detection and operation in islanding mode.
6. References.
25/06/2009
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Alcala University Department of Electronics
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
Alcala University Department of Electronics
Agenda
1. Overview of wind turbine topologies.
2. Low voltage ride through (LVRT).
3. Reactive power compensation.
4. Participation in the ancillary services.
5 Detection and operation in islanding mode
20
5. Detection and operation in islanding mode.
6. Conclusions.
7. References.
25/06/2009
11
Alcala University Department of Electronics
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.
21
Every method has a NDZ (Non Detection Zone)
Stand-alone control mode
Alcala University Department of Electronics
Agenda
1. Overview of wind turbine topologies.
2. Low voltage ride through (LVRT).
3. Reactive power compensation.
4. Participation in the ancillary services.
5 Detection and operation in island mode
22
5. Detection and operation in island mode.
6. Conclusions.
7. References.
25/06/2009
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Alcala University Department of Electronics
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
Alcala University Department of Electronics
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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