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Analysis and Control of Circulating Current in High-Power Full Converter Wind Turbines with Modular Structure

Ravanji, Mohammad Hassan | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46458 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Parniani, Mostafa
  7. Abstract:
  8. This thesis aims at developing control system of a full converter wind turbine with modular and parallel back-to-back converters. Modular structures and paralleling of power electronic converters are the state-of-the-art methods for increasing their transferable power to the grid. Technological advances in high power wind turbines, especially for the offshore installations, which contain permanent magnet synchronous generators with back-to-back full converters, promote the use of modular structures.
    In addition to developing the regular control systems of wind turbines for modular structures, selection of appropriate structures, power sharing between parallel converters and mitigation of circulating current are new issues that emerge due to paralleling of power converters. Due to the breadth of these subjects, this thesis mainly focuses on the control of circulating current, which is less explored in the literature. For this purpose the hierarchical control system of PMSG-based wind turbines are described, and then causes of circulating current and its mitigation methods are presented.
    For the first time, this thesis relates the flow of circulating current to the third harmonic voltage generated with space vector modulation and the existence of this harmonic is demonstrated both analytically and by simulations. Then, suppression methods of circulating current are grouped in two categories: route incision methods and 3rd harmonic voltage reduction methods; and heuristic remedies are proposed for each one. Harmonic reduction methods are more beneficial and thus, they are studied with more details. In order to find the effects of other parameters on the magnitude of circulating current, a sensitivity analysis study is also done and the influences of various parameters on this current are compared.
  9. Keywords:
  10. Permanent Magnet Synchronous Generator (PMSG)Wind Turbine ; Back-to-Back Converter ; Modular Structure ; Circulating Current Control ; Hierarchical Control System for Wind Turbines

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