Fault RideThrough Strategies for VSCConnected Wind Parks

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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
Technical requirements

• 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

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Grid connection of wind power
Technical requirements

• 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!

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VSC transmission system overview

• 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

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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

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Fast power reduction
Communication

• Wind-park side VSC signals power reduction order
  to turbines through a communication link
• Only applicable for turbines with controllable
  converters
• Typical time delay 10100 ms
• Reliability is an issue

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Fast power reduction
Voltage 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

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Fast power reduction
Frequency droop

• 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

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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