Seamless Transition Between Interconnected and Islanded Operation of DC Microgrids

In this paper, a seamless interchange method between interconnected and islanded operational mode of a DC Microgrid is presented. The DC Microgrid examined consists of photovoltaic generation, batteries, and loads. A novel islanding detection method is presented ensuring fast detection of the islanding condition. The proposed detection method is based on the insertion of a controllable load in parallel with the DC Microgrid central switch. To achieve seamless interconnection to the utility grid, a proportional-integral (PI) regulator is installed in the Microgrid central controller. The PI regulator sends to the voltage forming unit (batteries) the appropriate setpoint, in order to align the voltage of the DC Microgrid to the utility network voltage during reconnection. The performance of the proposed control strategy is evaluated through simulations and Control Hardware-in-the-loop experiments performed at the Electric Energy Systems Laboratory, National Technical University of Athens.