Comparison of harmonics in a microgrid when operating in island and mainland mode

A microgrid has been built on the island of Arholma in the archipelago of Stockholm, Sweden. The grid consists of two energy storage systems and solar photovoltaics. The microgrid is normally operated in mainland (grid connected) mode and the island operation is intended to be used only in case of grid outages at the mainland, meaning that it is not intended to be a stand-alone microgrid. The microgrid was installed in the spring of 2023 and has undergone several island operations for test purposes and data has been gathered since then. The voltage harmonics of the microgrid have therefore been investigated during several periods of island operations. These operations span over different time periods and different times of the year. Historically, the voltage harmonics on the island have been seen to be higher during summer and therefore different parts of the year have been investigated for more reliable results. Both Total Harmonic Distortion (THD) and individual harmonics are compared between different modes of operation and related to limits defined in the European standard EN 50160.