研究目的
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. This paper comparatively evaluates the lifetime of NPC and T-type inverters, which are three-level inverter topologies that are widely used for PV systems, with a 30 kW grid-connected PV system.
研究成果
The NPC inverter has about 2.3 times a longer lifetime than the T-type inverter under the same mission profile of the PV system. The T-type inverter requires higher cooling capacity than the NPC inverter in order to have the same lifetime. The result emphasizes the importance of the reliability of PV inverters on the cost of PV energy.
研究不足
The study is limited to a 30 kW grid-connected PV system and focuses only on the power devices of NPC and T-type inverters. The lifetime models of the target IGBT modules are not available, so the estimated lifetime results should be considered only for the purpose of the lifetime comparison between the NPC and T-type inverters.
1：Experimental Design and Method Selection:
The study focuses on power devices since the power electronic components of both converters are the same except for the power devices. The power loss and temperature distributions of power devices are analyzed and their efficiencies are compared at different power levels with different switching frequencies.
2：Sample Selection and Data Sources:
A 30 kW grid-connected PV system is considered as a case study.
3：List of Experimental Equipment and Materials:
The study uses IGBT modules F3L75R07W2E3_B11 and F3L75R12W1H3_B11 from the same manufacturer for NPC and T-type inverters, respectively.
4：Experimental Procedures and Operational Workflow:
The power loss 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 with a one-year mission profile of the PV system.
5：Data Analysis Methods:
The junction temperature profiles of the power devices are obtained by using a look-up table, which is generated based on the information about the junction temperatures under the different input power levels and the ambient temperatures.
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