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Optimal Design of Medium Voltage Modular Multilevel Inverter with Reliability Consideration

Ghadrdan, Moein | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49841 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Zolghadri, Mohammad Reza
  7. Abstract:
  8. Modular multilevel converters provide higher output voltage levels than switches rated voltages by switching between cascaded modules. Increasing the number of modules might results in less reliability because of an increase in the number of elements. On the other hand, an increase in the number of modules decreases the semiconductors rated voltage, switches power losses and thermal stresses and consequently a lower switches failure rate is expected. Therefore the optimal number of modules, would minimize the failure rate. To investigate it, in this project, first fundamental elements of converter are designed for a MMC with different number of output levels, to drive a medium voltage medium power motor (1MVA, 3,3KV). In the following, designed topologies are simulated to find converter output specifications and sub-modules power losses. Using these losses, it is possible to calculate thermal stresses of switches. Using design results and calculated thermal stresses, converter total failure rate can be estimated and compared for structures with different number of modules. Economic analysis are done based on elements prices chosen from markets. Finally an optimization issue is formed to minimize an objective functions including output voltage THD, power loss, failure rate and total cost simultaneously for a limited number of levels for the converter. Optimization output determines optimal number of levels, converter can be built
  9. Keywords:
  10. Failure Rate ; Capacitive Voltage Transformer ; Modular Multilevel Converters (MMC) ; Reliability Oriented Design ; Voltage Sorting Algorithm ; Optimal Finding Levels Number

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