Most photovoltaic (PV) generation systems are connected with a utility grid and recognized as supplemental generation resources; but in some applications such as microgrid concept, a PV system works as a main resource. To improve the availability of PV systems, technological development for higher less output fluctuation in normal condition, higher fault tolerance in fault occurrence, and power demand and supply balancing in isolated condition are required. For these reasons, hybridization of a PV system and an energy storage system (ESS) would become an important technology in the future. This paper presented two kinds of circuit models, conventional “ac-connected PV-ESS,” and proposed “dc-connected PV-ESS” in which ESS is inserted at the dc-side of PV system. This paper also investigated dc-link voltage controlled by dc-dc converter of ESS in dc-connected PV-ESS and suitable control systems are also discussed normal, during fault occurrence and isolated operation.
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