---

High reliability and system lifetimes in the range of 30 years are essential for renewable energy systems such as photovoltaic power plants to minimise costs for the generated electric energy. At the same time such systems are used in regions with high solar irradiance and also harsh environmental conditions. Therefore, designs for photovoltaic inverters need to meet not only the key design criteria of high conversion efficiency but also need to be very robust and at the same time meet challenging cost targets.

In this dissertation aspects concerning the lifetime and reliability of power semiconductors in photovoltaic central inverters are investigated. On key topic of the dissertation is the measurement of the voltage dependent failure rate due to cosmic radiation induced single-event-burnout of SiC and Si power semiconductors. The second topic is the development of a system level simulation to quantify the stress on the power semiconductors in a PV central inverters in various regions of the world. Further topics are the investigation of improved control concepts for the cooling system of PV central inverters and the monitoring of IGBT temperatures during converter operation.

---