Reconnection of micro-grid from islanded mode to grid-connected mode used sliding Goertzel transform based filter

The micro-grid is a key interface between renewable energy sources and the utility. A micro-grid can work under islanded mode or grid-connected mode. To confirm the seamless transform of a micro-grid from islanded mode to grid-connected mode, synchronisation of the islanded micro-grid to the utility is an essential challenge. In this study, replacing first-order low-pass filter by sliding Goertzel transform based filter, a control strategy with an extended phase-locked loop is presented for the inverter applications in islanded micro-grids. It can ensure the synchronisation between the micro-grid voltage and the utility voltage, and guarantee the seamless reconnection of the micro-grid from islanded mode to grid-connected mode. Considering the influence of the voltage deviation between the micro-grid and the utility voltages in the synchronisation process, detailed analyses are proposed. Analytical non-linear model and small-signal model are presented to prove the fast and effective reconnect performance. Simulated and experimental results are provided to verify the validity and effectiveness of the proposed control strategy. This study is of interest for the seamless transform control of islanded micro-grids.