Reliability analysis of IGBT Inverter for Wave Energy Converter with focus on thermal cycling

Power electronics and advanced motion control has allowed for creating Wave Energy Converters (WECs) with the generator directly coupled to the sinusoidal motions of the prime mover. However, this gives large fluctuations in output power, and the resulting peak to average power ratio exceeds most other energy producers. The typical cycle time of ocean waves is 5-7 seconds with subharmonic wave train fluctuations of 30-200 sec. These slow power fluctuations may cause significant thermal cycling of the IGBT powered inverter, with reduction in lifetime as result. In this work the Fred Olsen WEC system is used as a staring point, and a detailed thermal model for the inverter is implemented and simulated. Based on the study of earlier publications on IGBT reliability the resulting lifetime of the system is estimated. This study indicate that thermal cycling may impact on the system lifetime and that some oversizing is required.