Method for operating a converter in a system for generating electrical energy

1. A method for operating a converter, via a control unit, in a system used for generating electrical energy, the system including a generator operatively connected to the converter which, in tum, is operatively connected to an energy supply grid, the frequency of a voltage generated by the generator being variable and a plurality of different switch positions being realizable with the converter, the method comprising:

converting, in the control unit, voltages responsive to an output from the converter to respective d, q rotating coordinate system voltage trajectories, each being representative of a current voltage value and future voltage values;

specifying a desired voltage value matching a frequency of a voltage of the energy supply grid;

determining, from the d, q rotating coordinate system voltage trajectories, a closest trajectory having a current value closest to the desired voltage value and

switching the converter in dependence on the closest trajectory, the switching being based upon a frequency of the voltage of the energy supply grid;

wherein the specifying, the determining, and the switching are recomputed at predetermined time intervals.

2. The method to claim 1 , wherein the voltages responsive to an output from the converter are α,β coordinate system voltage values.

3. The method according to claim 1 , wherein the converter is switched to the position which allows generating an output voltage that is assigned to the closest trajectory.

4. The method according to claim 1 , wherein the desired voltage value is a desired output current value and wherein the future values are future output current values for different switch positions of the converter.

5. The method according to claim 4 , wherein the future output is determined which is relatively closest to the desired output current.

6. The method according to claim 5 , wherein the converter is switched to the position in which the output voltage is generateable that is assigned to the closest future output current.

7. The method according to claim 1 , wherein the desired voltage value represents a desired output current.

8. The method according to claim 1 , wherein the switching includes changing one or more converter switch positions to output the closest trajectory.

9. The method according to claim 1 , wherein the desired value is specified in dependence on the energy supply grid.

10. The method according to claim 1 , wherein the frequency of the voltage generated by the generator is relatively higher than the frequency of the voltage of the energy supply grid.

11. The method according to claim 1 , wherein the converter comprises a plurality of external commutating or self-commutating power semiconductor components, and wherein for external-commutating power semiconductor components, the converter is switchable to another switch position only if the power semiconductor components to be shut down in the process have a zero crossing for the current or if a counter voltage is generated by turning on a power semiconductor component.

12. A system, comprising:

a converter, operatively connected to an energy supply grid, useable to realize a plurality of different switching positions;

a generator, operatively connected to the converter, a frequency of a voltage produced by the generator being variable; and

a control unit configured to convert voltages responsive to an output from the converter to respective d, q rotating coordinate system voltage trajectories, each being representative of a current voltage value and future voltage values;

wherein the system is configured to:

specify a desired voltage value matching a frequency of a voltage of the energy supply grid;

determine, from the d, q rotating coordinate system voltage trajectories, a closest trajectory having a current value closest to the desired voltage value; and

switch the converter in dependence on the closest trajectory, the switching being based upon a frequency of the voltage of the energy supply grid;

wherein the specifying, the determining, and the switching are recomputed at predetermined time intervals.

13. The system according to claim 12 , wherein the generator is operatively connected to a electrical energy producer and is driven by the electrical energy producer.

14. The system according to claim 12 , wherein the generator is a n-phase polygonal generator and the converter is a direct converter or a matrix converter.

15. The method according to claim 2 , wherein output voltage is determined from voltage generated by the generator.

16. The method according to claim 2 , wherein the desired voltage value is a desired output current value and wherein the future values are future output current values for different switch positions of the converter.

17. The method according to claim 11 , wherein the plurality of external commutating or self-commutating power semiconductor components include at least one of insulated gate bipolar transistors (IGBTs) or integrated gate commutated thyristors (IGCT) or thyristors.

18. The system according to claim 13 , wherein the electrical energy producer is a gas turbine or a water turbine or a wind power plant.

19. The system according to claim 13 , wherein the generator is a n-phase polygonal generator and the converter is a direct converter or a matrix converter.