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In near future, it expects that the PV systems will be interconnected to the utility distribution lines with high density beyond the range dealt with by the current Japanese guideline for grid interconnection. As for islanding prevention under the high density interconnection, not only more reliable detection of islanding but also prevention of unnecessary detection in normality are strongly required to keep safety and stability of the grid. A new isanding prevention method of' Active/Passive Series Method' was designed in the study. The sequence of the method is; (a) Inverter current is made decrease a little when I" passive detective function operates., (b) Inverter operation is stopped when 2' passive detective function detects remarkable change of grid voltage, cased by a positive feed back effect of the current control inverter in islanding. As the results of a simulation using EMTP and an experiment, it is clear that islanding can be detected by enhancing the sensitivity of the 1 I passive detection and setting the current drop rate for 15% at most. The result also indicates that inverter current drop is restricted to less than 15% and the current can be recovered within I sec. by combination with the MPT control of inverter even when unnecessary operation of the 1I passive detective function occurs in normal condition. From above, applicability of the designed method to the high density interconnection is confirmed.

Islanding Prevention Technique by the Active/Passive Series Method Applied to PV Power Generation Systems Interconnected to The Grid with High Density