Reliability Study of SiC-Based Power Electronic Devices in DC-DC Converter Used in Heavy-Duty Electric and Hybrid Vehicles

Sammanfattning: A DC-DC converter is used in electrified and hybrid vehicles to supply powerto the low voltage (ex. 24V) system including headlights, horn, air conditioningsystem, wipers, radio, etc. The converter is fed from a high voltage (ex. 650V)battery, which is available in electric/hybrid vehicles, and transfers a relativelyhigh power. SCANIA’s conventional converters, used so far, have silicon-basedswitches, i.e., Si IGBT; and there is an intention to replace the converter with theupgraded counterpart in which SiC-based transistors (SiC-MOSFET) are usedinstead. Wide band-gap silicon carbide (SiC) semiconductor material offers possibilitiesof faster switching, high-temperature operation, and higher breakdownvoltage for power transistors. SCANIA is investigating the reliability of thesecond generation converter in which the Si IGBT transistors are replaced bySiC-MOSFET transistors. In this thesis, the reliability of a SiC-based switchesused in DC-DC converter of electrified trucks is investigated. The investigationis principally based on different reliability tests results carried out in both switchand converter levels.To investigate the reliability of SIC MOSFET transistors, first different failuremechanisms, such as gate oxide layer degradation, high-frequency side effects,etc., are introduced, and corresponding test results are presented and discussed.On converter level, the reliability study of SCANIA’s first generation converteris considered, and the weak components in the converter are identified.In this thesis, the test results provided by SiC-MOSFET and converter suppliersare analyzed and compared with the similar test results conducted on the Sibasedconverter. In additions, SCANIA performs some particular tests based onits own standardization related to different environmental working conditions,such as high ambient temperature and high vibration situation, to assure thematurity and robustness of the SiC-based converter. These test results arepresented and discussed.By comparing investigation outcomes acquired from different suppliers and customers,it is shown that the SiC MOSFET transistor is more efficient that Sibasedtransistor. It is also demonstrated that SiC MOSFET is more robust andreliable in high power, high voltage, and high switching frequency applications.The SCANIA’s second generation DC-DC converter has shown advantages overthe first generation; it is more efficient, lighter, and more compact. From thereliability point of view, the second generation has passed almost all relevanttests.