Harmonic Analysis of a DFIG for a Wind Energy Conversion System

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Harmonic Analysis of a DFIG for a Wind Energy
Conversion System

• Lingling Fan, Ph.D., P.E.
• Assistant Professor
• Dept. Electrical Engineering
• University of South Florida
• Tampa, FL 33620
• Linglingfan_at_usf.edu
• April 20, 2010

2010 IEEE Transmission Distribution Conference
and Exhibition New Orleans, LA
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Outline

• Objective
• Principle
• Case studies
• Rotor injection
• Unbalanced stator conditions
• Conclusion

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Objective

• Develop a steady-state circuit to give
  quantitative analysis for harmonics in DFIG
• The work is useful for understanding of
• DFIG behavior during non-sinusoidal rotor
  injection
• DFIG under unbalanced grid conditions (fault ride
  through)

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Doubly Fed Induction Generator
Ps
RSC AC/DC
GSC DC/AC
Pr sPs
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A generalized circuit for harmonic analysis in
DFIG
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Case study 1 non-sinusoidal rotor injection
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Frequency components in rotor voltage and stator
current

• Stator currents
• (6n1)frfm, -(6n-1)frfm,

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Electromagnetic torque

• Interaction of stator and rotor currents

Stator Is1 (60 Hz) Is2(-245 36 Hz) Is3 (247 36 Hz)
Rotor Ir1(24 Hz) Ir2 (-245 Hz) Ir3 (247 Hz)
Ex Is1, Ir2 ? torque (60- (-120 36)) 144 Hz
624 Hz ? 6fr Is1, Ir3 ? torque (60- (168
36)) -144 Hz -624 Hz ? 6fr
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Torque

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Case study 2 unbalanced stator conditions

• Rotor injection programmable power source
  sinusoidal 3-phase
• Stator phase a resistance is reduced

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Analysis
Unbalanced stator currents
Positive sequence (fe)
Negative sequence (-fe)
Zero sequence
Rotor currents
Ir fe-fmsfe
Ir -fe-fm-(2-s)fe
s slip 1-fm/fe fm electric frequency
corresponding to rotating speed. fe nominal
frequency
60 Hz (stator) 50 Hz (rotating speed) 10 Hz
-60 Hz (stator) 50 Hz (rotating speed) -110 Hz
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Torque
Positive Negative
Stator Is1 (60 Hz) Is2 (-60 Hz)
Rotor Ir1 (10 Hz) Ir2 (-110 Hz)

1. Te1 Te2 dc components
2. Te3, Te4 pulsating components 120 Hz

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Reference frames
Pos. Neg. Sequences can be separated by a dc
filter!
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Extraction scheme
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Lab setup
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Case 3 Grid interconnected DFIG
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Simulation results
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Confirm simulation results with the analysis
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Conclusion

• This paper develops
• A generalized steady-state DFIG circuit for
  harmonic analysis
• A systematic method to compute torque by
  computing the interactions of stator and rotor
  currents
• The sequence network based on DFIG pos, neg
  circuits which facilitates the analysis under
  unbalanced stator conditions.