Post on 07-Apr-2020
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
2Strictly Confidential. GAMESA CORPORACIÓN TECNOLÓGICA, S.A. (C)
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
3Strictly Confidential. GAMESA CORPORACIÓN TECNOLÓGICA, S.A. (C)
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