Mission profile based multi-disciplinary analysis of power modules in single-phase transformerless photovoltaic inverters

The popularity of transformerless photovoltaic (PV) inverters in Europe proves that these topologies can achieve higher efficiency (e.g., ≥ 98% has been reported). Along with the advanced power electronics technology and the booming development of PV power systems, a long service time (e.g. 25 years) has been set as a main target and an emerging demand from the customers, which imposes a new challenge on grid-connected transformerless inverters. In order to reduce maintenance cost, it is essential to predict the lifetime of the transformerless PV inverter and its components based on the mission profiles — solar irradiance and ambient temperature. In this paper, a mission profile based analysis approach is proposed and it is demonstrated by three main single-phase transformerless PV inverters — Full-Bridge (FB) with bipolar modulation scheme, the FB inverter with DC bypass (FB-DCBP) topology and the FB inverter with AC bypass leg (highly efficient and reliable inverter concept, HERIC inverter). Since the thermal stress is one of the most critical factors that induce failures, the junction temperatures on the power devices of the three topologies are analyzed and compared by considering the mission profiles. The lifetimes of these topologies are discussed according to the thermal performance and the power losses on the switching devices are also compared.