A multilevel modular converter for a large, light weight wind turbine generator

Chong H. Ng, Max A. Parker, Li Ran, Peter J. Tavner, Jim R. Bumby, Ed Spooner

Research output: Contribution to journalArticlepeer-review

188 Citations (Scopus)

Abstract

In an onshore horizontal axis wind turbine, generator and converter are usually in the nacelle on the top of the tower, while the grid step-up transformer is placed at the bottom. Electric power is transmitted down through flexible cables of high current rating which are expensive and can suffer from large I2 R loss. An offshore wind turbine usually has to include the step-up transformer in the nacelle. This adds significantly to the mechanical loading of the tower even new designs aim to reduce the transformer size and weight. In either case, a transformer-less, high voltage, high reliability generating unit for nacelle installation would be an attractive technology for large wind turbines. This study presents a power electronic solution based on a permanent magnet generator design. A multilevel cascaded voltage source converter is developed to synthesize a high sinusoidal output voltage. The dc link voltages of inverter modules are balanced by rectifiers fed from isolated generator coils while the inverter switching strategy equalizes the power sharing between the modules. The switching strategy also reduces the low order harmonics to constrain the sizing of the dc link capacitors. The modulating effect between the ac and dc sides of the inverter is taken into account. This paper describes the generator-converter arrangement, analyzes the inverter switching effects and derives the switching strategy which is verified by simulation and laboratory experiment.
Original languageEnglish
Pages (from-to)1062-1074
Number of pages13
JournalIEEE Transactions on Power Electronics
Volume23
Issue number3
DOIs
Publication statusPublished - 2 May 2008

Keywords

  • DC link capacitor
  • grid connection
  • harmonics
  • multilevel inverter
  • power balance
  • wind power

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