AEE - SEMINAR ON GRID INTEGRATIONLas Palmas, 8 y 9 de Noviembre 2010
Strictly Confidential. GAMESA CORPORACIÓN TECNOLÓGICA, S.A. (C)
New Generators and Converters for Weak Grids
Andrés Agudo Araque
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Summary
1. Introduction
2. WTG Electrical System Evolution
3. Weak Grid Connection Requirements
4. Weak Grids Technical Conclusions
New Generators and Converters for Weak Grids
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Introduction
GAMESA Power Electronics Unit
o 45 engineers working on the Design, Industrialization and Validation of Power Converters and Control Panels for WTG.
o 3 Research Centers: Madrid, Bilbao and Pamplona
o 3 Factories: Valencia, Madrid and Tianjin (China)
o In-house design of:
• Power Converters for WTG from hundreds of kW to 5 MW.• Drives for DFIG, WRSG, PMSG (Geared and Direct Driven)• Inverters for Grid Connectivity from tens of kW to 50 MW.• Control Electronics for Power Converter and Auxiliary
Systems • Full Power Test Benches up to 5MW
New Generators and Converters for Weak Grids
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WTG Electrical System Evolution
FIXED SPEED WT DIRECTLY GRID CONNECTED
WITH SCIG
FIXED AND PARTIAL VARIABLE FIXED SPEED WT
Wind Fluctuations
PARTIAL VARIABLE FIXED SPEED (+10%)
WT DIRECTLY GRID CONNECTED WITH VRR SCIG
Mechanical Fluctuations
Electrical Power Fluctuations
PCC Voltage Fluctuations
Reactive Power Fluctuations (↑ line losses)
Capacitor Banks SVCs STATCOMs
Weak GridsWeak Grids
OptiSlipOptiSlip -- VestasVestas TMTM
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WTG Electrical System EvolutionVARIABLE SPEED WT WITH DOUBLY FED ASYNCHRONOUS GENERATOR
TECHNOLOGY IMPROVEMENTSo Variable speed: ± 20-30% around synch speed
o Power Control: P and Q
o High short-circuit current
o Power electronics: ± 20-30% Pn
Windturbine
control
AC, f = constant,n = semi - variabel
10 ... 34 kV, f = 50 Hz
line coupling
transformer
gearbox Brake
pitch driverotor bearing
main circuit breaker
converter
control
Medium voltageSwitchgear
generator converter
gridconverter
asynchronous generator with slip rings
Over sync
P
Q
P , Q
TECHNOLOGY DRAWBACKSo Need for extra protections for LVRT
(Crow-bar or oversized electronics)
o High complex control to achieve LVRT
o Necessity of slip-rings
Sub sync
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WTG Electrical System EvolutionVARIABLE SPEED WT WITH FULLY-RATING POWER CONVERTER
TECHNOLOGY IMPROVEMENTSo Generator uncoupled from the grid:
• same system for 50Hz & 60Hz
• avoid torque stress from grid disturbances
(increase drive train lifetime)
o Good tolerance to weak grids (LVRT, f,Vac)
o Qnom generation independent of wind
o Higher efficiency over wide power range
TECHNOLOGY DRAWBACKSo Power converter manage all the power:
• Big, heavy and costly
o Short-circuit current limited to nominal current.
o Need to have a reliable design (many components)
Windturbinecontrol
10 ... 34 kV,f = 50 Hz
line coupling transformer
Brake
pitch driverotor bearing
GeneratorRectifier
Converter Control
Medium voltage
Switchgear
PMSG, SCSG
GridInverter
Power
Control
Vdc Control
Q control
gearbox
Direct
Driven
P
Q
AVR
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WTG Electrical System EvolutionFULLY-RATING POWER CONVERTER TOPOLOGIES
o Rectifier very simple and cost effective
o There is no control over the generator excitation: need for a AVR for WRSG or a DC/DC converter for PMSG.
o High harmonic current content on the stator.
o The converter can not be used for motoring
T
=
WRSG
Unidirectional Power Converter
T
=
PMSG
=
=
AVR
P
PControl
Q
QControl
P
PControl
Q
QControl
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PMSG
WTG Electrical System EvolutionFULLY-RATING POWER CONVERTER TOPOLOGIES
o Rectifier more complex but with field controllability:
• Better generator voltage controllability during transients
• Generator improvement due to field reinforcement
o Better quality on generator current and possibility to cancel low order harmonics
o The converter can be used for motoring
Bidirectional Power Converter
WRSG
AVR
Q
QControl
Q
QControl
T
==
T
SCIG
==
PControl
P
P_controlField_control
P
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WTG Electrical System EvolutionFULLY-RATING POWER CONVERTER TOPOLOGIES
o System efficiency improvement due to progressive operation
o Availability improvement: degraded mode operation
o Grid side Quality IMPROVED
THD_I ~ 1%
Bidirectional Power Converter
PMSG
T
==
==
==
·········
Modular Systems
T
PMSG
=
=
Medium Voltage Converters
o Low harmonic distortion
o Improvement on system cabling & efficiency
o Higher cost & volume
o Specific training for maintenance operations
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Weak Grids Connection RequirementsElectrical System Impact
• Extending the limits implies new designs and cost increasement.
• IEC 61000–3–7
• Requires power active damping, done at WTG control level and helped with the use of full-converter topologies.
• IEC 61000–3–6
• DIFG & SCIG more sensible than WRSG & PMSG.
• Highly weak grids may need filtering (passive or active). Full-converter topologies enables current filtering
Voltage vs FrequencyFlickerVoltage unbalance & Harmonics
Power Quality & Operational Range
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Weak Grids Connection RequirementsElectrical System Impact
• May require external capacitor/reactance banks, SVCs or STATCOMs.
• At P<10%, Qmin not required
• Steady-state response
• Control done by the power converter
Q = F (Pn)Q = F (Vn)
Reactive Power Control
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Weak Grids Connection RequirementsElectrical System Impact
• 0% voltage dips implies transient electronics protection and advance control strategies for grid tracking
• Require big changes on HW to achieve transient demands.
• Current designs enables +10% permanent and +15% transient
• Limited to wind availability
• Need to include Delta control
V = F (t)V = F (t)P = F (frec)
Active Power Control & Voltage Control
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Summary. Weak grids technical conclusions
Generators and Converters for Weak Grids
o WTG manufacturers are improving the WT electrical system to better integrate Wind Energy into the grid
New Generators and Converters for Weak Grids
o At the same time, utilities are demanding tougher grid connection requirements, trying to achieve WTG the same response as the conventional power plants have.
o Commonly used WTG (DFIG & SG) have the capabilities to achieve the weak grid connection requirements demanded by the utilities, although HW and Control changes have to be done.
o Newly WT based on SG with Full Power converters enable flexible integration into the grid.
o New converters (Modular design & Medium Voltage) improve power quality and increase WTG availability.
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Thanks for your attention
New Generators and Converters for Weak Grids
