Power system restoration and operation of island grids with frequency dependent active power control of distributed generation

Distributed Generators (DGs), e.g. PV systems, connected to low voltage networks in Germany have to reduce their active power feed-in at over frequency with a gradient of 40 % per Hz starting at 50.2 Hz. In consequence, at 51.5 Hz there is still a feed-in of 48 % of their available power. Since all power plants (including conventional ones) are required to disconnect at 51.5 Hz, small island grids may collapse due to over frequency without the full potential of power reduction from DGs being realised. This is particularly relevant for power system restoration from small islands within the distribution system. This paper presents a simple island test system, consisting of a 50 MW gas turbine, some load and distributed generation. The new contribution of this work is an active power control scheme that provides an improved frequency behaviour in small island grids without any impact on the overall system behaviour in normal operation.