fault ride-through strategies for vsc-connected wind parks
DESCRIPTION
Fault Ride-Through Strategies for VSC-Connected Wind Parks. Ralph L. Hendriks, Ronald Völzke, Wil L. Kling. Contents. Introduction Technical requirements for grid connection VSC transmission system outline Influence of converter (de-)rating Energy dissipation Fast power reduction - PowerPoint PPT PresentationTRANSCRIPT
20-04-23
Challenge the future
DelftUniversity ofTechnology
Fault Ride-Through Strategies for VSC-Connected Wind Parks
Ralph L. Hendriks, Ronald Völzke, Wil L. Kling
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Contents
• Introduction• Technical requirements for grid connection• VSC transmission system outline• Influence of converter (de-)rating• Energy dissipation• Fast power reduction
• Direct communication• Voltage reduction• Frequency droop
• Design optimization• Conclusions
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Introduction
Future wind parks•will be situated far from load centres, long transmission
distances•will have high power ratings (hundreds of megawatt)
Application of HVAC transmission is limited by charging current of cables
HVDC transmission can overcome these limitations. Two types:•Current-source converter•Voltage-source converter
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Grid connection of wind power
Transmission system operators require well defined technical behaviour from wind power plants
During faults in the power system, wind power plants are usually required to:
•remain connected during and after the fault (fault ride through)
•support system restoration by supplying reactive current
Wind turbine generators have been further developed to comply to these requirements
Technical requirements
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Grid connection of wind power
Technical capabilities are required at the point of connection
For VSC-connected wind power plants, the behaviour during faults is completely determined by the properties of the VSC transmission system
Different types of wind turbines!
Technical requirements
U
t0 t1 t2
U0
Umin
Un
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VSC transmission system overview
BR
BR
WPVSC GSVSC
WP
• Two-terminal link connecting wind park to active network• WPVSC functions as a slack node, absorbs all power• GSVSC controls direct voltage• Converter type does not impact general applicability of
presented strategies
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Converter (de-)rating
Power electronic switches have hardly over-load capability
Current limit must be maintained at all times
De-rating could improve FRT performance
Q
P
Un = 1.1 p.u.
Un = 1.0 p.u.
Un = 0.9 p.u.
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Energy dissipation
• Control of the direct voltage during faults using a dissipative device• Power electronic control is required (chopper)• Power electronic switches will constitute a high price for this solution• Thermal aspects need to be considered
BR
BR
WPVSC GSVSC
WP
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Fast power reduction
Wind-park side VSC signals power reduction order to turbines through a communication link
Only applicable for turbines with controllable converters
Typical time delay 10–100 ms
Reliability is an issue
Communication
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Fast power reduction
Wind-park side VSC sinks the AC voltage to reduce the incoming power
Inherent reaction from directly coupled induction generators
The success for wind turbines with power electronic converters depends on the ratings and controls of the converters
Standard FRT methods need to be disabled
Voltage reduction
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Fast power reduction
The frequency in the wind park network is increased to signal power reduction
Inherent response from directly-coupled induction generators
Additional droop characteristic in turbine control necessary
Speed of frequency measurement is an issue, PLLs tend to be slow
Frequency droop
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Design optimization
Converter de-rating and dissipation load to higher investment costs
Strategies can (parly) be combined to realize reliable FRT solutions
System can be optimized by formulating boundary conditions and optimization methods, such as linear programming
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Conclusions
The FRT behaviour of VSC-connected wind parks is greatly determined by the design and control of the VSC-system
Grid-code compliance with respect to FRT could be achieved by de-rating, dissipation of excess energy and fast reduction of incoming wind power
Fast power reduction methods yield lowest additional costs
Optimized design could combine several FRT strategies