Electrolytic capacitor-less PV converter for full lifetime guarantee interfaced with DC distribution

Abstract

Electrolytic capacitors to suppress the voltage and current fluctuation at PV side should be deployed in AC interface to ensure high harvest efficiency which makes it difficult to guarantee the lifetime of PV inverters due to the short lifetime electrolytic capacitors. This paper proposes an electrolytic capacitor-less photovoltaic (PV) micro-converter interfaced with DC distribution system. The short-lifetime capacitors can be eliminated in the proposed DC interfaced structure by using film capacitors which is helpful not only to fully guarantee the lifetime of PV generation system but also improve the system efficiency. Directly interfaced to DC distribution system, the proposed boost-type PV micro-converter features simple structure and high efficiency. In this paper, AC and DC interfaced systems are analyzed in view of PV converter lifetime. Different from conventional power converters, PV converters should keep high efficiency even under 50% load operation due to the solar irradiation profile normally below half of the full irradiation. Because the PV converters are operated by light load efficiency improvement technique such as burst mode method, voltage variation in light load range should be considered. Based on the analysis of voltage variation with respect to the light load efficiency improvement methods, PV micro-converter design guide is presented. 140W prototype PV converter shows maximum efficiency of 97.3% and European efficiency of 96.8% achieving light load efficiency higher than 93% as well as high MPPT efficiency is expected, without electrolytic capacitors which verifies the feasibility of this study.