Restoration of Low-Voltage Distribution Systems With Inverter-Interfaced DG Units

The increasing share of distributed generation (DG) offers new chances in grid restoration of low-voltage distribution grids. Instead of relying on the transmission or high- and medium-voltage levels, establishing islanding operation in low-voltage grids might be a good option after a wide-area voltage collapse. This paper proposes a restoration strategy from zero-voltage conditions for inverter-interfaced DG under islanded conditions. In the approach, a flexible and scalable master DG inverter concept is introduced for DGs, where no communication is needed and an outage of the master can be balanced by other DG inverters. The control strategy ensures the tracking of nominal values of the system voltage and frequency without zero steady-state error. The influences of noncontrollable DG are also taken into account in the strategy with an effective countermeasure developed. Experimental results verify the effectiveness of the proposed approach.