Operation of a local alternating current network with a genset and a UPS

A method of operating a local AC power grid comprising a genset which includes a combustion engine and a generator, and an uninterruptable power supply (UPS) which includes an energy storage, the method comprising

• defining a frequency of an AC voltage of the AC power grid present at the genset by means of the UPS;
• altering the frequency of the AC voltage defined by means of the UPS in one direction away from a desired frequency, if a present power demand in the AC power grid increases beyond a present power supply in the AC power grid, and altering the frequency of the AC voltage defined by means of the UPS in the other direction away from the desired frequency, if the present power demand falls below the present power supply in the AC power grid;
• with increasing power demand of the AC power grid, limiting an alteration of the frequency of the AC voltage defined by means of the UPS in the one direction to a maximum value in that missing power is temporarily fed out of the energy storage into the AC power grid;
• keeping a shift of the frequency of the AC voltage defined by means of the UPS in the one direction away from the desired frequency until no more power flows out of the energy storage into the AC power grid;
• and
• responding to deviations of the frequency of the AC voltage of the AC power grid from the desired frequency in one direction by an increase of a genset power supplied by means of the genset, and responding to deviations of the frequency of the AC voltage of the AC power grid from the desired frequency in the other direction by a reduction of the genset power supplied by means of the genset.