Lifetime estimation of modular cascaded H-bridge MLPVI for grid-connected PV systems considering mission profile.

Recently, in grid-connected Photovoltaic (PV) systems, the modular cascaded H-bridge Multilevel PV Inverters (MLPVIs) has attracted many researchers because of high-quality output waveform with each semiconductor device operating at the lower switching frequency and a possibility to reach high-voltage without using the step-up transformer in high-voltage grid-connected PV systems, which reduce the system cost. The inverter is one of the most unreliable parts of the PV system operating in different environmental conditions, and the MLPVI requires more number of power semiconductor switches, which increases the probability of failure. In order to provide reliable operation, it is important to predict the lifetime of an inverter by considering the mission profile. This paper mainly concentrates on the lifetime estimation of the modular cascaded H-bridge MLPVI by considering the mission profile. The power loss calculation and electro-thermal analysis have been conducted to unveil the thermal loading of MLPVI. A cycle counting algorithm has been applied to recognize the mean junction temperature and amplitude of the temperature swings of each thermal cycle. A Monte Carlo analysis is used to obtain the lifetime distribution of the power devices by considering the parameter variation. At last, the lifetime of a 5-kW grid-connected 1-phase, 5-level modular cascaded H-bridge MLPVI is studied based on the lifetime models of power devices.