Thermal Management Optimization of a 5 MW Power Electronic Converter

High Voltage Direct Current (HVDC) is a replacement of the existing Alternating Current (HVAC) solutions for the transport of electricity using underwater cables. An example is the connexion of off-shore wind turbines to the electrical network. The main consequence of chosing HVDC over HVAC is the need for large power electronic converters in place of standard low-frequency transformers. Here, we describe the system-level design of a 5 MW convert intended for HVDC connexion of large wind turbines. This converter is based on high voltage SiC transistors, which have a strong sensitivity to their junction temperature. Indeed, their on-state resistance is more than doubled between 25 and 125 °C. Although these devices are, in theory, capable to operate at higher junction temperature than silicon IGBTs, doing so results in a large drop in the efficiency of the converter. Here, we present the many parameters that must be taken into account for the thermal design of such a large converter: the cost and performance of the dies (including their variation of R DS on with temperature), the cost and performance of the cooling system and of the packaging (taking into consideration the high voltage isolation requirements), the mission profile of the wind turbine, the price of electricity. Our analysis demonstrates that there is a trade-off between the number of dies, the performance of the cooling system, and the price of electricity. Depending on the expected return on investment, it is therefore possible to optimize some key design parameters.