Modulation Method for Improving Reliability of Multilevel T-Type Inverter in PV Systems

Multilevel inverters (MLIs) have proven superior performance in several applications, especially in photovoltaic (PV) applications. However, power switches in MLIs possess high failure rates due to unequal power losses distributions that shorten lifetime of the whole PV inverter. Therefore, a new pulsewidth modulation (PWM) methodology for loss balance in grid connected PV single-phase five-level inverters is presented in this paper. The proposed loss balance PWM (LBPWM) method is based on swapping the utilization of power switches through half or quarter of the fundamental line period based on the redundancies between the switching states in MLIs. In addition, the proposed LBPWM method achieves natural balance among voltages over the dc-link capacitors. The effectiveness and feasibility of the proposed LBPWM method are verified using the simulation environment and experimental prototype. Different operating conditions and points of PV inverters are investigated in addition to reliability evaluation of the PV inverter are provided. Moreover, the superior performance criterion of the proposed LBPWM methods are verified through comprehensive comparisons with the most prominent previously developed PWM methods in the literature. The generalization and implementation steps of the proposed LBPWM method are also provided.