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Performance Improvement of Cascaded H-bridge Multilevel Inverter under Faulty Conditions

Ouni, Saeed | 2017

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 50306 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Zolghadri, Mohammad Reza; Oraee Mirzamani, Hashem; Rodriguez, Jose
  7. Abstract:
  8. Fault-tolerant ability is more subjected in Cascaded H-Bridge Multilevel Inverter due to its high-power medium-voltage applications and large number of semiconductors switches used in its structure. In this thesis, the goal is performance improvement of Cascaded H-bridge Multilevel Inverter under faulty conditions. Since to achieve the post-fault ability two steps; fault detection and post-fault control are required, both steps are considered in the improving process. In this dissertation, first operation of Cascaded H-Bridge Multilevel Inverter in normal and faulty condition is surveyed. Then, the conventional fault detection methods are mentioned and post-fault control methods are categorized into two major groups. Afterwards, a fast and simple method is proposed to detect and diagnosis the faulty cell in Cascaded H-bridge Multilevel Inverter under switches short circuit and open circuit fault which is based on a comparison of the inverter output voltage and its reference value. The proposed method is not only fast and accurate, but also simple as well. After that, due to harmful effect of common mode voltage on electrical motors bearings, this work is focused on improving the post-fault performance of Cascaded H-bridge Multilevel Inverters by decreasing the common mode voltage. To achieve it two solution are proposed; Solution I and Solution II.
    In Solution I, a method is proposed to determine the optimal post-fault state among all possible states which have the same maximum available voltage. Furthermore, a modified technique is proposed to calculate the references of inverter phase voltages under faulty conditions. This technique leads to a decrease in the common mode voltage when the required output voltage is less than its maximum value. These solutions are mutually employed in the post-fault control system. Experimental results obtained by two prototypes in Universidad Federico Santa Maria and also Sharif University of Technology confirm the effectiveness of the proposed solutions in comparison with the existing methods in different cases
  9. Keywords:
  10. Common Mode Voltage ; Fault Tolerant Operation ; Fault Detection ; Fault Diagnosis ; Cascaded H Bridge Multilevel Inverter ; Performance Improvement

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