Method for black starting a power station comprising a plurality of inverters connectable to an AC electrical grid

1. A method for black-starting a power station comprising a plurality of inverters connectable to a local AC grid, comprising:

building up a first AC voltage in the local AC grid by a first inverter of the plurality of inverters, and

connecting a second inverter of the plurality of inverters, after synchronization with the first AC voltage, to the local AC grid,

wherein the first AC voltage built up by the first inverter is reduced by at least a quarter with respect to a rated voltage of the local AC grid, and

wherein once the second inverter has been connected, a second AC voltage, which is increased with respect to the first AC voltage, is built up in the local AC grid.

2. The method as clamed in claim 1 , wherein the second AC voltage is 1.2 to 3 times the first AC voltage.

3. The method as claimed in claim 1 , further comprising connecting a third inverter, after synchronization with the second AC voltage to the local AC grid, wherein once the third inverter has been connected, a third AC voltage, which is increased with respect to the second AC voltage, is built up in the local AC grid.

4. The method as claimed in claim 1 , wherein a difference between successively built-up AC voltages is 0.2 to 2 times the first AC voltage.

5. The method as claimed in claim 1 , wherein a difference between successively built-up AC voltages remains the same.

6. The method as claimed in claim 1 , wherein the rated voltage in the local AC grid is built up in 3 to 10 stages.

7. The method as claimed in claim 1 , further comprising synchronizing the plurality of inverters with one of the AC voltages and then connecting the plurality of inverters to the local AC grid.

8. The method as claimed in claim 1 , wherein each inverter is connected powerlessly to the local AC grid.

9. The method as claimed in claim 8 , further comprising shifting a voltage droop and/or a frequency droop of an inverter to be connected in each case and/or of already connected inverters such that, on connection, no power flows into the local AC grid.

10. The method as claimed in claim 1 , further comprising, in order to distribute a load among all of the inverters connected to the local AC grid, matching a frequency droop and a voltage droop of a most recently connected inverter to the frequency droops and voltage droops of all of the inverters that have already previously been connected.

11. The method as claimed in claim 1 , wherein one of the AC voltages is built up in the local AC grid by the plurality of the inverters connected to the local AC grid up to that point.

12. The method as claimed in claim 11 , further comprising, in order to build up the next AC voltage, shifting voltage droops of a plurality of the inverters connected to the local AC grid in a direction of higher voltage values.

13. The method as claimed in claim 1 , further comprising, once one of the AC voltages has been built up, shifting frequency droops of a plurality of the inverters connected to the local AC grid in order to achieve a rated frequency of the local AC grid with the respective AC voltage in a direction of higher frequency values.

14. The method as claimed in claim 1 , wherein the first AC voltage in the local AC grid is built up by the first inverter beginning at a rated frequency of the local AC grid.

15. The method as claimed in claim 1 , wherein:

the first AC voltage built up by the first inverter in the local AC grid has a frequency which deviates from a rated frequency of the local AC grid by at least 10%, and

the second AC voltage built up once the second inverter in the local AC grid has been connected has a frequency which is closer to the rated frequency of the local AC grid.

16. A method for black-starting a power station comprising a plurality of inverters connectable to a local AC grid, comprising:

building up a first AC voltage in the local AC grid by a first inverter of the plurality of inverters, and

connecting a second inverter of the plurality of inverters, after synchronization with the first AC voltage to the local AC grid,

wherein the first AC voltage built up by the first inverter has a frequency which deviates from a rated frequency of the local AC grid by at least 10%, and

wherein once the second inverter has been connected, a second AC voltage, which has a frequency closer to the rated frequency of the local AC grid than the first AC voltage, is built up in the local AC grid.

17. The method as claimed in claim 16 , further comprising connecting a third inverter, after synchronization with the second AC voltage, to the local AC grid, wherein once the third inverter has been connected, a third AC voltage is built up in the local AC grid, which has a frequency closer to the rated frequency of the local AC grid than the second AC voltage.

18. The method as claimed in claim 16 , wherein the frequencies of two successively built-up AC voltages differ from one another by at least 10% of the frequency which is already closer to the rated frequency of the local AC grid.

19. A power station comprising a plurality of inverters connectable to a local AC grid and a superordinate control unit, which, during a black start, connects the inverters to the local AC grid in accordance with the method that comprises:

building up a first AC voltage in the local AC grid by a first inverter of the plurality of inverters, and

connecting a second inverter of the plurality of inverters, after synchronization with the first AC voltage, to the local AC grid,

wherein the first AC voltage built up by the first inverter is reduced by at least a quarter with respect to a rated voltage of the local AC grid, and

wherein once the second inverter has been connected, a second AC voltage, which is increased with respect to the first AC voltage, is built up in the local AC grid.

20. The power station as claimed in claim 19 , wherein the inverters are connected to photovoltaic generators on an input side.