Design and implementation of three-level SiC interleaved boost converters for a grid connected multi-string PV inverter

Date

2023-9

Author

Altun, Ogün

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The popularity of solar power, which is an endless energy source for the world, increased in recent years. Developments in solar cells ensure higher efficiency at lower costs. Moreover, the advancements in power electronics also increased their popularity. In this thesis, the design of a 20 kW three-level boost converter is investigated. The designed converter is used for 1500 V multi-string photovoltaic inverters, which is the new trend in photovoltaic systems. The converter design is optimized so that the power conversion efficiency is higher than 99% for all conditions. The designed converter then implemented and verified experimentally. With the help of silicon carbide semiconductor devices, 80 kHz switching frequency is achieved. The implemented prototype is able to convert the input voltage of 850 - 1300 V to 1300 V at the output with the efficiency of 99.2% for worst case. The control algorithm provides maximum power point operation and balances the output capacitors even if the capacitor loads are not identical. The second design is implemented for multi-string operation where eight parallel converter is placed. For multi-input single output parallel converters, conventional interleaving does not result in the best operation. Hence, a novel algorithm is presented to find the optimum interleaving phase angle in order to minimize the capacitor current. Experimentally it is shown that proposed algorithm reduces the capacitor losses by 20% which extend the life-time of the capacitors and hence the designed converter.

Subject Keywords

Multi-string inverter, PV inverter, Multi-level converter, Silicon carbide, Interleaving, Capacitor current minimization

URI

https://hdl.handle.net/11511/105327

Collections

Graduate School of Natural and Applied Sciences, Thesis