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Performance Improvement of Grid-connected Quasi-Z-Source Photovoltaic Inverter to Reduce Leakage Currents

Noroozi, Negar | 2018

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 51437 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Zolghadri, Mohammad Reza
  7. Abstract:
  8. A quasi-Z-source inverter is a beneficial structure in photovoltaic applications. In a transformerless grid-connected inverter system, the common-mode voltage fluctuations cause the leakage current flow through the ground. The low-frequency harmonics of the common-mode voltage results in the malfunction of the residual current device. On the other hand, the high-frequency harmonics of the common-mode voltage cause EMI problems, additional loss and disturbance in the output currents. In this thesis, some methods are presented to reduce the leakage current in a three-phase quasi-Z-source inverter. First, different shoot-through implementation methods are investigated. By modifying the number of shoot-through intervals and their locations in a switching cycle, the shoot-through modulation methods with minimum common-mode voltage are identified. In this thesis, a reduced common-mode voltage method is also introduced which is based on using only the odd vectors in the three-phase quasi-Z-source inverter. By this method, the leakage current is nearly eliminated. The main disadvantage of this method is the limited linearity margin for the inverter operation. In addition, by using the harmonic analysis which is based on the Fourier transform, a novel modulation method is proposed to reduce the low-frequency harmonics of the common-mode voltage. In this method, the high-frequency harmonics are centered exactly at the switching frequencies in the frequency axis. The centered harmonics can be simply filtered
  9. Keywords:
  10. Common Mode Voltage ; Leakage Current ; Solar Inverter ; Three Phase Inverter ; Grid-Connected Photovoltaic System ; Quasi-Z-Source Inverter ; Three-Phase Transformerless Inverter

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