The cost of the PV energy reduction is still required to increase the penetration level of PV systems in the energy market. The reliability of PV inverters is one of the important aspects to be enhanced in order to reduce the cost of PV energy, since it is closely related to the maintenance cost and the annual energy production. In this paper, the lifetime of NPC and T-type inverters, which are three-level inverter topologies that are widely used for PV systems, are comparatively evaluated with a 30 kW grid-connected PV system. It is performed by focusing on power devices since the power electronic components of both converters are the same except for the power devices. Therefore, this result can represent the comparison of the reliability performance of the NPC and T-type inverters. The power loss and temperature distributions of power devices are analyzed and their efficiencies are compared at different power levels with different switching frequencies. The lifetimes of the reliability-critical power devices in the NPC and T-type inverters are estimated, respectively with a one-year mission profile of the PV system, and the results are compared.Energies 2020, 13, 1227 2 of 14 and emphasized, since these aspects are closely related to the energy production as well as the volume and weight of the PV inverter [14]. In [14,15], the junction temperature profiles of the power devices in different single-phase PV inverter topologies are analyzed and compared. However, it is not enough to show the reliability of single-phase PV inverter topologies.The three-level inverters are attractive topologies for both high-power and low-power PV systems due to the outstanding efficiency and lower THD compared with the conventional two-level inverter [16,17]. The configurations of PV systems can be divided into an AC module, string, multi-string, and central configurations depending on the rated power of the PV system. Typically, neutral-point clamped (NPC) and T-type three-level inverter topologies are widely used for from a string inverter configuration of small power to a central inverter configuration of high power [18]. Previous research performed the evaluation of three-phase three-level inverter and converter topologies for a motor drive where the efficiency, semiconductor chip area, and harmonic machine losses were taken into account for the comparison factors of the three-level inverter and converter topologies, but the lifetime was not considered [17].In this paper, the comparative evaluation of the lifetime of three-phase NPC and T-type three-level inverters for the grid-connected PV systems is performed. Except for the power devices, the required power electronic components and applied stress on these components in both inverters are the same. Therefore, it can be expected that the lifetime of other components in both inverters are the same as each other. Therefore, the lifetime of the power device can represent the reliability comparison of the NPC and T-type inverter systems. A 30 kW grid-connected PV system is consi...