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Reliability, efficiency, and cost comparisons of MW-scale photovoltaic inverters

This paper surveys the-state-of-the-art of high power photovoltaic (PV) inverters, and a novel quasi-Z source cascaded multilevel inverter (CMI) is proposed for application to MW-scale PV system. The proposed quasi-Z source CMI has a constant dc-link voltage and minimum KVA rating, compared to a traditional CMI with an unbalanced dc-link voltage and oversized KVA rating. Four MW-scale PV inverter topologies, including two 2-level inverters with and without transformer, traditional CMI, and quasi-Z source CMI, are compared in their reliability, power loss, and cost, by using an example of 1MW/4160V PV inverter. The quantified comparison shows that the traditional and quasi-Z source CMIs achieve better performance metrics in MW-scale PV inverter applications, than the 2-level inverters. Moreover, the quasi-Z source CMI is preponderant, when compared to traditional CMI, in its higher efficiency, lower cost, and one-third power modules saving. It is concluded that multilevel and modular topologies could become main structures for utility-scale PV inverters.