A Medium Voltage Cascaded Multi-level Converter with Isolated High Frequency Link Using SiC Switching Devices



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In this thesis, a new medium voltage multi-level power converter using low voltage SiC devices that would result in an overall efficiency improvement in harnessing renewable energies was analyzed. The topology is based on cascading low voltage power stages that utilize isolated DC-DC converter. The units to be improved are the DC-DC converter, which was used in conjunction with a rectifier (depending on the nature of the renewable energy source- AC or DC power source) and an inverter at the output stage. The DC-DC converter is a Dual Active Bridge with a high frequency link; the high frequency link is possible based on the high-frequency transformer (HFT) and wide band gap switch (silicon carbide (SiC) MOSFET) that was adopted in this topology. Due to the inverse relationship between frequency and the size of magnetic components, the power density of the converter is high, which in-turn gives a higher efficiency. Apart from these benefits, there are a number of advantages in this topology such as the isolated link, the multilevel output, the variable frequency output, the compatibility with High Voltage Direct Current (HVDC) etc. In this case, the generation units could be offshore or in a remote on-shore area due to environmental or aesthetic reasons. One of the major factors that discourage harnessing of renewable energy is the initial cost involved; the topology chosen naturally minimizes the number of components involved and this, in turn, reduces the cost and the failure rate. The final output is a high power quality multilevel AC voltage with low concerns for electromagnetic compatibility. The Simulations were carried out using a library in MATLAB (Simelectronics/Simscape).



Multi-level, Silicon Carbide