Thermal analysis and reliability evaluation of cascaded H-bridge MLPVI for grid-connected applications

Nowadays, great progress has been made in the development of multilevel inverters (MLIs) in grid-connected photovoltaic (PV) energy systems, because of the advantages such as reduced voltage stress on the power semiconductor switches and having higher efficiency. Since the multilevel PV inverter (MLPVI) has been a critical part within the failures of a PV energy system, so it becomes important to predict the lifetime of the components and the MLPVI system. In this paper, a five-level modular cascaded H-bridge MLI is analyzed based on grid-connected application for PV energy system, and an independent dc-link voltage controller for each H-bridge is implemented by taking the reference value generated from the maximum power point tracking algorithm of each PV module. The loss and thermal distributions of the different power devices in the MLPVI system are investigated and illustrated for various pulse-width modulation (PWM) controllers. The junction temperature and power losses of the components in the MLPVI are simulated by MATLAB/Simulink and Piecewise Linear Electrical Circuit Simulation (PLECS) blockset, which validate the theoretical analysis. The reliability of the MLPVI is evaluated using parts stress method. It shows that the MLPVI has a good reliability when phase shift PWM control technique is used.