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Wide Input Voltage Inverter Configurations and Control Systems for Renewable Energy Resources
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- Author / Creator
- Mehrabi Gohari, Zohre
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Nowadays, among renewable energy sources, PV systems are highly popular due to their easy installation and affordability. A key component of the PV system is the inverter, which can significantly affect the reliability, efficiency, and power quality of the system. The PV inverters are required to track the maximum power point (MPP) of the panel to maximize the production of the system. To achieve this goal, the inverter must be able to generate the required output waveforms for a wide range of input voltages. Normally, two-stage inverters are used to achieve this goal and produce high-quality output power; however, both stages process the full output power and have a high number of reactive components with high switching stress which can result in lower power density and higher losses of the converter. In this thesis, new topologies are proposed to reduce the required number of passive components for the inverter while allowing it to operate for a wide range of input voltages and maintain the power quality of the output.
The first proposed design features an extended input voltage range using a cascaded full-bridge inverter with a cascaded floating capacitor, leveraging low-frequency operation to generate fundamental output voltage components. It is coupled with low-voltage high-frequency operation to mitigate harmonics. A comprehensive control mechanism is used to regulate the modulation angle of the low-frequency full bridge. Additionally, a synchronous (or DQ) reference frame controller is used to regulate current and enable MPP tracking. To further reduce the blocking voltage of the capacitor-connected full bridge, the second structure replaces the PV-connected full bridge with a T-type inverter, halving the blocking voltage.
The flyback-assisted inverter is also proposed to further extend the inverter's operating input voltage range. This topology integrates cascaded full-bridge inverters with a flyback converter. This configuration allows the high-frequency full bridge to process a portion of the power based on input voltage. Precise control mechanisms for determining modulation angles and maximum power point tracking (MPP) in PV systems are implemented. Furthermore, the controller deactivates the flyback converter when the photovoltaic (PV) voltage reaches an optimal level for generating the desired output voltage. This reduces switching losses and can further improve converter efficiency.
Furthermore, a cascaded full-bridge converter with a single switching frequency is proposed to accommodate the broad voltage range of the flyback-assisted converter, while minimizing component count, and improving power density. A new control structure for the fast and robust operation of the inverter is proposed. These control mechanisms can independently regulate the power of each full bridge, allowing the converter to operate within a wide range of input voltages.
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- Subjects / Keywords
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- Graduation date
- Fall 2023
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.