A Study on Passive Cooling in Subsea Power Electronics

This paper proposes a simplified approach to model the thermal behavior of the insulated-gate bipolar transistors (IGBTs) in a subsea power electronic converter. The models are based on empirical relations for natural convection in water, and IGBT datasheet values. The proposed model can be used in the design of subsea converters and in the reliability analysis of their IGBTs. Experimental results are provided to validate the proposed thermal model. Suggestions are made to minimize the net thermal resistance by introducing a high conductivity thermal material as a mounting plate between the IGBT and the cabinet walls. Impact of the mounting plate dimensions and material properties on the junction temperature of the IGBTs is studied. A case study analysis is made on a 100-kVA converter. Results indicate that the thermal spreading resistances in the mounting plate and the cabinet walls contribute significantly to the overall thermal resistance. Spreading resistances can be mitigated by appropriate design measures. Furthermore, it was observed that the passive cooling in water is not as effective as the forced water cooling. However, the low cost, simple design, and higher reliability of passive cooling systems might make them a favorable choice for subsea systems.