Control and SRF-q based re-synchronization of a master DG for microgrids

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Primarily this paper investigates the key functions that should be carried out by a master distributed generator (DG) that adopts the master-slave control approach within a microgrid. Grid-connected operation, islanding detection, islanded operation, load shedding, phase locking and grid re-synchronization are key functions of the master DG that need to be executed in a logical and sequential manner. This sequence of tasks/functions are put together to develop a control flow chart called the master control algorithm. Secondarily, the investigation leads to the development of a simple SRF-q (synchronous reference frame quadrature component) based re-synchronization procedure. The proposed re-synchronization technique achieves a seamless re-synchronization which is of interest for microgrid-grid re-connection. This paper first details the control structure during the grid connected and islanded modes. Then, the proposed master control algorithm and the SRF-q re-synchronization procedures are verified by simulation as well as real-time hardware in the loop (HIL) experimental study.