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Fast Failure Detection in Modular Multilevel Converter Power Switches for Fault Tolerant Operation

Haghnazari, Saeed | 2017

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 50037 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Zolghadri, Mohammad Reza
  7. Abstract:
  8. Multilevel converters are the best solution in medium and high voltage applications because of their better output votage quality, redundant structure, less power semiconductor losses and common-mode voltages. Modular multilevel converters (MMCs) have additional advantages such as higher degree of modularity, transformerless operation capability and using a single common DC-bus. All these useful features make MMC the first alternative for HVDC systems. Fault detection, defected cells insulation and post fault operation control are necessary to ensure MMC continouse service. A simple, fast and accurate fault detection method is proposed for MMC semiconductor power switches in this thesis. Simulations and experiments results show that open and short circuit faulty cells are determined less than one switching period after effect on MMC normal operation.Then, a MMC post fault operation strategy is introduced which does not require redundant cells in cold and spinnig reserve schemes. This new post fault operation method offers two outlines in MMC design stage. In first outline, redundant cells are used as main cells increasing converter reliability and quality improvement of output voltage waveform during normal operation. In second outline, redundant cells are removed from modular multilevel converter structure leading converter cost, volume and weight reduction
  9. Keywords:
  10. Modular Multilevel Converters (MMC) ; Post Fault Operation ; Circuit Breakers (CBs) ; Fast Fault Detection ; Fault Tolerant Operation

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