ARRANGEMENT FOR REGULATING A POWER FLOW IN AN AC VOLTAGE GRID AND METHOD FOR PROTECTING THE ARRANGEMENT

Abstract

An arrangement for controlling a power flow in an AC voltage grid includes a converter arrangement having a first converter and a second converter. The converters are connectable to one another on the DC voltage side through a DC voltage link and are each connectable to the AC voltage grid on the AC voltage side. During the operation of the arrangement, the converters are correspondingly connected to the AC voltage grid. A switching branch is provided in the DC voltage link in parallel with the converters and at least one controllable switching element is provided in the switching branch. A method for protecting the arrangement in the case of an overload is also provided.

Claims

1. An arrangement for controlling a power flow in an AC voltage grid, the arrangement comprising: a DC voltage link; and a converter arrangement including a first converter and a second converter, said converters configured to be connected to one another on a DC voltage side through said DC voltage link and said converters each configured to be connected on an AC voltage side to the AC voltage grid; said DC voltage link containing a switching branch connected in parallel with said converters, said switching branch containing at least one controllable switching element.

2. The arrangement according to claim 1, wherein said at least one controllable switching element is configured for switching currents above 1 kA within less than 20 ms.

3. The arrangement according to claim 1, wherein said at least one controllable switching element is configured for switching currents above 1 kA within less than 10 ms.

4. The arrangement according to claim 1, wherein said at least one controllable switching element is a semiconductor switch.

5. The arrangement according to claim 3, wherein said semiconductor switch is a thyristor.

6. The arrangement according to claim 1, wherein said at least one controllable switching element includes a multiplicity of controllable switching elements connected to one another in a series circuit in said switching branch.

7. The arrangement according to claim 1, wherein at least one of said converters is a modular multilevel converter.

8. The arrangement according to claim 7, wherein said modular multilevel converter includes a number of series-connected switching modules, said number being dimensioned to cause said modular multilevel converter to generate a voltage being at least 5% greater than a predetermined rated voltage.

9. The arrangement according to claim 8, wherein said switching modules are half-bridge switching modules or full-bridge switching modules.

10. The arrangement according to claim 8, which further comprises protective circuit-breakers each being assigned to a respective one of said switching modules for limiting a current through said at least one controllable switching element.

11. The arrangement according to claim 1, which further comprises a matching transformer connecting said first converter to the AC voltage grid.

12. The arrangement according to claim 1, which further comprises a serial transformer connecting said second converter to the AC voltage grid.

13. The arrangement according to claim 1, which further comprises a bridging switch configured to bridge a connection of said first or second converter to the AC voltage grid.

14. A method for protecting an arrangement for controlling a power flow in an AC voltage grid, the method comprising: providing the arrangement according to claim 1; identifying an overload fault in at least one of the AC voltage grid or the arrangement; switching said at least one controllable switching element in said switching branch of the arrangement to enable a current flow through said switching branch; and using a bridging switch to bridge a connection of said first or second converter to the AC voltage grid.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0025] FIG. 1 is a schematic and block diagram showing one exemplary embodiment of an arrangement according to the invention;

[0026] FIG. 2 is a schematic and block diagram showing one example of an MMC for the arrangement of FIG. 1;

[0027] FIG. 3 is a schematic diagram showing a first example of a switching module for the MMC of FIG. 2; and

[0028] FIG. 4 is a schematic diagram showing a second example of a switching module for the MMC of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

[0029] Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen an arrangement 1 for controlling a power flow in an AC voltage grid. In the example shown in FIG. 1, an AC voltage grid 2 is represented by a transmission line between a first supply network 2a and a second supply network 2b. The arrangement 1 includes a first converter 3. The first converter 3 is connected to the AC voltage grid 2 on the AC voltage side by a parallel transformer 4. Furthermore, the first converter 3 is connected to a second converter 6 on the DC voltage side through a voltage link 5. The second converter 6 is connected to the AC voltage grid 2 on the AC voltage side by a series transformer 7. The connection of the second converter 6 to the AC voltage grid 2, in the example shown, in particular, the windings 8 of the series transformer 7 on the AC voltage side, can be bridged by a mechanical bridging switch 9.

[0030] A switching branch 10 extending between a first and a second DC voltage pole DC+, DC is disposed in the voltage link 5. A series circuit formed by switching elements in the form of thyristors 11 is disposed in the switching branch 10.

[0031] The arrangement 1 furthermore includes a regulating device or drive unit 12 configured for driving semiconductor switches of the converters 3, 6 and the thyristors 11. The regulating device 12 is connected to a current measuring device 14 for measuring a current through the first converter 3, to a voltage measuring device 13 for measuring terminal voltages of the first converter 3, to a further current measuring device 15 for measuring a current through the second converter 6, and to a further voltage measuring device 16 for measuring terminal voltages of the second converter 6.

[0032] The regulating device 12 is configured to detect a fault situation, for example an overload situation, on the basis of the current and voltage monitoring. To that end, a check is made, for example, to ascertain whether the measured current exceeds a predetermined current threshold. If such an overload fault is identified, then the switching units 11 in the switching branch are turned on by using corresponding driving signals, thereby enabling a current flow, in particular a short-circuit current, through the switching branch. At the same time or afterward, the bridging switch 9 is driven to turn on. Through the use of the bridging switch, the series transformer 7 and thus the connection of the second converter 6 to the AC voltage grid 2 are bridged, in such a way that the arrangement 1 overall is protected against overload.

[0033] FIG. 2 illustrates an MMC 20, which is useable as a first and/or a second converter 3, 6 of the arrangement 1 of FIG. 1. The MMC 20 is embodied in three-phase fashion and accordingly includes three AC voltage terminals A, B, C and also a first DC voltage terminal for connection to the first DC voltage pole DC+ and a second DC voltage terminal for connection to the second DC voltage pole DC. The MMC 20 includes six converter arms 21-26 extending in each case between one of the AC voltage terminals A-C and one of the DC voltage terminals. Each converter arm 21-26 has an arm inductance L and a series circuit formed by switching modules 27.

[0034] FIG. 3 illustrates a half-bridge switching module 30, which is useable as a switching module 27 in the MMC 20 of FIG. 2. The half-bridge switching module 30 includes a first semiconductor switch 31 and a second semiconductor switch 32, with a respective freewheeling diode D being connected antiparallel with each of the semiconductor switches. A capacitor C is disposed between a collector terminal of the first semiconductor switch 31 and an emitter terminal of the second semiconductor switch 32. A protective thyristor 33 is disposed between a first terminal X1 and a second terminal X2 of the half-bridge switching module 30 and can carry the short-circuit current in accordance with its forward direction in the case of a fault in order to relieve the load on the semiconductor switches 31, 32. A voltage meter 34 serves for monitoring a capacitor voltage Uzk across the capacitor C.

[0035] FIG. 4 illustrates a full-bridge switching module 40, which is useable as a switching module 27 in the MMC 20 of FIG. 2. The full-bridge switching module 40 includes a first semiconductor switch 41 and a second semiconductor switch 42, a third semiconductor switch 43 and a fourth semiconductor switch 44, with a respective freewheeling diode D being connected antiparallel with each of the semiconductor switches. A capacitor C is disposed between collector terminals of the first semiconductor switch 41 and the third semiconductor switch 43 and emitter terminals of the second semiconductor switch 42 and the fourth semiconductor switch 44. A first terminal X1 of the full-bridge switching module 40 is disposed between the first and second semiconductor switches 41, 42, and a second terminal X2 of the full-bridge switching module 40 is disposed between the third and fourth semiconductor switches 43, 44.