The Application of Three-level NPC Converter to

WES

By: Amir Yazdaniyazdani@power.ele.utoronto.ca

PhD candidateUniversity of Toronto

Feb. 20, 2004

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

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

Wind Turbine Characteristics

Variable-Speed WES (General)

1. Adjusts the generator speed to obtain the maximum power

Optimized power capture

2. 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

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

Gearbox Wear

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

No Gearbox

Why Three-Level NPC?

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

Demand for higher power WES

Three-Level NPC vs. Two-Level VSC

Two-Level VSC Three-Level NPC

PWM Spectra

Three-Level NPC

Two-Level VSC

Waveforms of Three-Level NPC

Variable-Speed WES (Synch. machine and Three-Level NPC BTB)

Demerits

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

Current research

Mathematical modeling Control DC-voltage balancing DC-link voltage regulation of the BTB

system Fault analysis

Conclusion

The use of Three-Level NPC technology in WES offers:

More economical designs Lower THD waveforms Superior dynamic performance