Comparative Evaluation of Lifetime of Three-Level Inverters in Grid-Connected Photovoltaic Systems

Abstract

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...

Comparative Evaluation of Efficiency and Reliability of Single-Phase Five-Level NPC Inverters for Photovoltaic Systems

“…It can be seen from Fig. 13 It indicates that 1 % of the population is expected to fail after 20.5 years and 10 % of the population is forecasted to be failed after 40.5 years.…”

“…Accordingly, there are various attempts to improve the efficiency of PV inverters in different aspects such as inverter topologies, power device technology and pulse width modulation methods [6]- [11]. Furthermore, the reliability of PV inverters has been analyzed by considering the impact of various factors such as mission profile [12]- [16], inverter topology [12], [13], DC-to-AC ratio [14], [15], and panel degradation rate [16]. However, there is a still lack of study on more comprehensive analysis on both efficiency and reliability together including the impacts of various factors.…”

Thermal Cycling in Converter IGBT Modules with Different Cooling Systems in Pitch- and Active Stall-Controlled Tidal Turbines

“…In addition to cooling, the lifetime of converters can also be enhanced by using different converter topologies [15,23] in three-level converters. This paper, however, focuses on a two-level back-to-back converter.…”

Study on Effect of Installation Location on Lifetime of PV Inverter and DC-to-AC Ratio

“…Therefore, the lifetime of the power device is not the limiting factor to increase the R DC/AC in Aalborg and Iza. However, it is worthwhile mentioning that the R DC/AC is typically chosen between 1.0 and 1.6 since there is no benefit of the oversizing PV array on the Levelized Cost of Energy (LCOE) [14].…”

“…The mission profile based lifetime estimation of NPC inverter has been performed in the previous work in [14]. This study is extended from that approach to investigate the effect of the installation locations on the lifetime of the NPC inverter and DC/AC ratio selection.…”