A Simple Control Technique for Distributed Generations in Grid-Connected and Islanded Modes

This paper presents a control technique for the seamless transfer of AC microgrid between grid-connected and islanded modes of operation. When a fault occurs in the utility grid, microgrid should be disconnected from the utility grid to protect its components and continuously supply the local loads in the microgrid. In the opposite case, if the utility grid is in normal condition, the microgrid should be connected to the utility grid. To fulfilling these control objectives, the proposed control technique handles two transfer modes: grid-connected to islanded mode and vice versa. Each distributed generation (DG) unit is controlled by the voltage control technique in islanded mode whereas the DG is controlled by feed-forward based control technique in grid-connected mode so as to ensure the seamless transition. Furthermore, parallel converters have been controlled by droop control technique in order to deliver desired power to the local loads in the islanded mode. The general operation principle is analyzed and demonstrated by means of simulation.

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