There will soon be a huge influx of EV chargers required in the coming years. Therefore it is important to find out the lifetime of EV chargers like the DC Fast Charger for business cases. These chargers are a combination of multiple power converters to help regulate the grid AC voltage to something that can be used to charge the battery. Multiple Industrial surveys have shown that the most vulnerable parts of power converters are the power semiconductors used inside them. Moreover, research shows that most of the failure in these EV chargers is due to thermal cycling which causes thermo-mechanical fatigue. While there are studies that estimate the lifetime of these semiconductors, it is seldom done in the context of EV charging load profiles. These EV charging load profiles are responsible for long-term power cycling contrary to short-term power cycling which is generally done to estimate the lifetime of the semiconductors. This thesis shall thus choose a popular DC Fast Charger power converter, feed in
a load profile and analyse the effects of thermal degradation of the switches and rectifier diodes present in the circuit. This data will then be used to make an estimate of how long the whole power converter will last thus leading to the lifetime of the DC Fast Charger.

The reliability of power semiconductor devices is an important feature when designing converter, since the semiconductors are prone to failure and a weak link in the system. Power semiconductor devices are susceptible to thermo-mechanical stresses, and should be investigated to make reliable semiconductors. The power losses inside the device resulting in thermal cycling and expanding and contracting the layers of the semiconductors with different rates, are the cause of the thermomechanical stresses. Thermo-mechanical fatigues are the most frequently encountered forms of failure in power devices, e.g. bond wire lift-off, solder cracks, and reconstruction of chip materialization. In this thesis, the end-of-life assessment of the silicon IGBT and silicon-carbide MOSFET are investigated. Specifically the power cycling test can replicate the thermo-mechanical stresses and wear out the device in a couple of weeks [8], [9]. Multple short power cycling tests are executed to find the relationship between the selected parameters and resulting thermal cycle. Furthermore, the thermal response measurements are used to study the thermal behaviour of the semiconductor devices and thermal fatigues. In addition, the thermal model for the test system is arrived, making it possible to create a testbed for the power cycling test for different thermal cycles. Lastly, the end-of-life assessment is executed for 23 days on eight silicon IGBTs.