Abstract
There are many technical challenges associated with microgrid (MG) operation and reliability. A fast and reliable protection scheme is persistently needed either for a grid-connected or island mode of operation. This paper presents a novel communication-less directional protection scheme for a typical microgrid at the common bus (PCC) supplied by hybrid (AC/DC) renewable distributed generations (DGs). This protection scheme is based on the continuously measuring of each DG phase's current feeder and calculating the auto cosine similarity factors for the sampled current with movable window patterns concept. The selected window width is ¼ cycle and the proposed algorithm is applied between the measured window and its simultaneous stored previous cycle window. Using a movable pattern enables consideration of the intermittent generation of the different DG units. Applying the cosine similarity for the proposed relay action increases the MG reliability. The magnitudes indicate the fault incident while the sign is used for the fault feeder selection. The main advantages of the introduced technique are fast, sensitive and do not need any extra instruments or communication links for practical implementation. Besides, it eliminates the effects of fault impedance and loads changing on the digital relay efficiency.
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