Method for operating a converter circuit and apparatus for implementing the method

1. A method for operating a converter circuit, the converter circuit having a converter unit with a large number of drivable power semiconductor switches and with a three-phase electrical AC voltage system, the method comprising:

driving the drivable power semiconductor switches by means of a drive signal (S A ) formed from a control signal ((S R );

forming the control signal (S R ) by adjusting an H-th harmonic component of system currents (i NH ) to a system current setpoint value (i NHref ), where H=1, 2, 3, . . . ; and

forming the system current setpoint value (i NHref ) by adjusting an H-th harmonic component of system voltages (u NH ) to a predeterminable system voltage setpoint value (u NHref ), the control difference (u NHdiff ) from the H-th harmonic component of the system voltages (u NH ) and the system voltage setpoint value (u NHref ) being weighted by a system impedance (y NH ) determined with respect to the H-th harmonic component.

2. The method as claimed in claim 1 , wherein, with respect to the H-th harmonic component, the absolute value of the system voltage change (|Δu NH |) towards a threshold value (u NHTol ) is monitored, and wherein

each time the threshold value (u NHTol ) is exceeded, the system impedance (y NH ) is determined.

3. The method as claimed in claim 2 , wherein the system impedance (y NH ) is determined from the system voltage change (Δu NH ) with respect to the H-th harmonic component and from a system current change (Δi NH ).

4. The method as claimed in claim 3 , wherein the H-th harmonic component of the system voltages (u NH ) is formed from the Park-Clarke transformation of the system voltages (u Nd , u Nq ).

5. The method as claimed in claim 1 , wherein the H-th harmonic component of the system voltages (u NH ) is formed from the Park-Clarke transformation of the system voltages (u Nd , u Nq ).

6. The method as claimed in claim 5 , wherein the Park-Clarke transformation of the system voltages (u Nd , u Nq ) is formed from the space vector transformation of the system voltages (u Nα , u Nβ ).

7. The method as claimed in claim 6 , wherein the H-th harmonic component of the system currents (i NH ) is formed from the Park-Clarke transformation of the system currents (i Nd , i Nq ).

8. The method as claimed in claim 1 , wherein the H-th harmonic component of the system currents (i NH ) is formed from the Park-Clarke transformation of the system currents (i Nd , i Nq ).

9. The method as claimed in claim 8 , wherein the Park-Clarke transformation of the system currents (i Nd , i Nq ) is formed from the space vector transformation of the system currents (i Nα , i Nβ ).

10. The method as claimed in claim 9 , wherein the adjustment of the H-th harmonic component of the system voltages (u NH ) to the predeterminable system voltage setpoint value (u NHref ) takes place in accordance with a proportional/integral characteristic.

11. The method as claimed in claim 9 , wherein the adjustment of the H-th harmonic component of the system voltages (u NH ) to the predeterminable system voltage setpoint value (u NHref ) takes place in accordance with a dead-beat characteristic by means of iteration.

12. The method as claimed in claim 1 , wherein the adjustment of the H-th harmonic component of the system voltages (u NH ) to the predeterminable system voltage setpoint value (u NHref ) takes place in accordance with a proportional/integral characteristic.

13. The method as claimed in claim 1 , wherein the adjustment of the H-th harmonic component of the system voltages (u NH ) to the predeterminable system voltage setpoint value (u NHref ) takes place in accordance with a dead-beat characteristic by means of iteration.

14. An apparatus for implementing a method for operating a converter circuit, the converter circuit having a converter unit with a large number of drivable power semiconductor switches and being connected to a three-phase electrical AC voltage system,

with a control apparatus, which is used to generate a control signal (S R ) and is connected to the drivable power semiconductor switches via a drive circuit for forming a drive signal (S A ), the control apparatus ( 4 ) having a first controller unit for forming the control signal (S R ) by adjusting an H-th harmonic component of system currents (i NH ) to a system current setpoint value (i NHref ), where H=1, 2, 3, . . . , wherein

the control apparatus has a second controller unit for forming the system current setpoint value (i NHref ) by adjusting an H-th harmonic component of system voltages (u NH ) to a predeterminable system voltage setpoint value (u NHref ), the control difference (u NHdiff ) from the H-th harmonic component of the system voltages (u NH ) and the system voltage setpoint value (u NHref ) being weighted by a system impedance (y NH ) determined with respect to the H-th harmonic component.

15. The apparatus as claimed in claim 14 , wherein the control apparatus ( 4 ) has a first computation unit for forming the Park-Clarke transformation of the system voltages (u Nd , u Nq ) from the space vector transformation of the system voltages (u Nα , u Nβ ) and forming the H-th harmonic component of the system voltages (u NH ) from the Park-Clarke transformation of the system voltages (u Nd , u Nq ).

16. The apparatus as claimed in claim 15 , wherein the control apparatus has a second computation unit for forming the space vector transformation of the system voltages (u Nα , u Nβ ).

17. The apparatus as claimed in claim 16 , wherein the control apparatus has a third computation unit for forming the Park-Clarke transformation of the system currents (i Nd , i Nq ) from the space vector transformation of the system currents (i Nα , i Nβ ) and forming the H-th harmonic component of the system currents (i NH ) from the Park-Clarke transformation of the system currents (i Nd , i Nq ).

18. The apparatus as claimed in claim 14 , wherein the control apparatus has a third computation unit for forming the Park-Clarke transformation of the system currents (i Nd , i Nq ) from the space vector transformation of the system currents (i Nα , i Nβ ) and forming the H-th harmonic component of the system currents (i NH ) from the Park-Clarke transformation of the system currents (i Nd , i Nq ).

19. The apparatus as claimed in claim 18 , wherein the control apparatus has a fourth computation unit for forming the space vector transformation of the system currents (i Nα , i Nβ ).

20. The apparatus as claimed in claim 19 , wherein the second controller unit for adjusting the H-th harmonic component of the system voltages (u NH ) to the predeterminable system voltage setpoint value (u NHref ) comprises a controller.

21. The apparatus as claimed in claim 14 , wherein the second controller unit for adjusting the H-th harmonic component of the system voltages (u NH ) to the predeterminable system voltage setpoint value (u NHref ) comprises a controller.