In a low-voltage islanded microgrid powered by renewable energy sources, the energy storage systems (ESSs) are considered\nnecessary, in order to maintain the power balance. Since a microgrid can be composed of several distributed ESSs (DESSs), a\ncoordinated control of their state-of-charge (SoC) should be implemented, ensuring the prolonged lifespan. This paper proposes a\nnew decentralized control method for balancing the SoC of DESSs in islanded microgrids, without physical communication. Each\nDESS injects a current distortion at 175Hz, when its SoC changes by 10%. This distortion is recognized by every DESS, through\na phase-locked loop (PLL). In order to distinguish the origin of the distortion, each DESS injects a distortion of different time\nduration. This intermediate frequency has been selected in order to avoid the concurrence with the usual harmonics. The DESSs\ntake advantage of this information and inject a current proportional to the SoC. Implementing this strategy, a comparable number\nof charging/discharging cycles for each DESS are achieved. Furthermore, an active filter operation, implemented in the dq rotating\nframe for each individual harmonic, is integrated in the control of the distributed generation units, supplying nonlinear loads with\nhigh-quality voltage. The effectiveness of this method is verified by detailed simulation results
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