The%20Application%20of%20Three-level%20NPC%20Converter%20to%20WES

1
The Application of Three-level NPC Converter to
WES

• By Amir Yazdani
• yazdani_at_power.ele.utoronto.ca
• PhD candidate
• University of Toronto
• Feb. 20, 2004

2
Abbreviations

• NPC Neutral-Point diode Clamped converter
• WES Wind Energy System
• VSC Voltage-Sourced Converter
• BTB Back-To-Back (AC/DC/AC) converter system
• PWM Pulse Width Modulation
• THD Total Harmonic Distortion

3
Outline

• Wind turbine characteristics
• Variable-Speed technology
• Motivations for using the Three-Level NPC in WES
• Three-Level NPC circuit and operation
• Current research
• Conclusions

4
Wind Turbine Characteristics
5
Variable-Speed WES (General)

• Adjusts the generator speed to obtain the maximum
  power
• Optimized power capture
• Connects the generator to the grid via a
  two-level VSC BTB
• Decoupling of the grid and turbine
• Reactive-power/AC-voltage control
• Good power quality

6
Variable-Speed WES (Induction machine and
Two-Level BTB)

• Gearbox Wear

7
Variable-Speed WES (Synch. machine and Two-Level
BTB)

• No Gearbox

8
Why Three-Level NPC?
Demand for higher power WES

• Higher DC voltage by use of ordinary switches
  (lower current, higher efficiency)
• Faster dynamic response
• Superior power quality
• (lower THD, lower torque pulsations)
• Comparable switching losses with respect to
  Two-Level BTB

9
Three-Level NPC vs. Two-Level VSC
Two-Level VSC
Three-Level NPC
10
PWM Spectra
Three-Level NPC
Two-Level VSC
11
Waveforms of Three-Level NPC
12
Variable-Speed WES (Synch. machine and
Three-Level NPC BTB)
13
Demerits

• Higher component count
• Two capacitor banks
• More complicated PWM and control
• (e.g. C-voltage equalization issue)
• Mid-point current

14
Current research

• Mathematical modeling
• Control
• DC-voltage balancing
• DC-link voltage regulation of the BTB system
• Fault analysis

15
Conclusion

• The use of Three-Level NPC technology in WES
  offers
• More economical designs
• Lower THD waveforms
• Superior dynamic performance