Reliability evaluation and thermal design of medium-voltage converter for underwater long-distance high-voltage direct current transmission system

Underwater long-distance high-voltage direct current transmission system can provide long-term, reliable, and sustainable energy for ocean observatories system which has higher reliability requirement than onshore or conventional underwater equipment. As the main network point for high-voltage direct current transmission system, medium-voltage converter of the primary node is at the top layer of power supply chain and its reliability will directly affect the reliability of high-voltage direct current transmission system. Based on a 2.5kW medium-voltage converter, this study proposes a method to evaluate the reliability of medium-voltage converter with accuracy using the lifetime model of switch by analysis of component junction temperature providing theoretical foundation and technical guidance for medium-voltage converter design. Owing to the high power density of medium-voltage converter, the heat dissipation space is restricted to pressure vessel. This study proposes a thermal design method to ensure normal operation condition within appropriate temperature for medium-voltage converter and verified using ANSYS finite element analysis software.