Power converter assembly with a line-commutated power converter and method for starting up the assembly

Abstract

A converter arrangement has a line-commutated converter with an AC voltage terminal to be connected to an AC voltage grid via at least one phase line. The converter arrangement has at least one switching module branch that is arranged in series in the at least one phase line and that includes a series connection of switching modules at whose terminals bipolar voltages that sum to give a branch voltage are in each case able to be generated. A bypass branch is arranged in a parallel connection to the switching module branch. At least one switching device is arranged in the bypass branch. The switching device includes activatable semiconductor switches that are connected in antiparallel. There is also described a method for starting up the converter arrangement.

Claims

1. A method of starting a converter arrangement, the method comprising: providing a converter arrangement having: a line-commutated converter having an AC voltage terminal for connection to an AC voltage grid via at least one phase line; at least one switching module branch connected in series in the at least one phase line, the at least one switching module branch having a series connection of switching modules with terminals configured to generate bipolar voltages that sum to give a branch voltage; a bypass branch connected in parallel with the at least one switching module branch, the bypass branch containing at least one switching device formed with activatable semiconductor switches that are connected in an antiparallel connection; blocking the switching modules in the switching branch; activating the semiconductor switches in the bypass branch with a predetermined delay; and commutating a branch current from the switching branch to the bypass branch through the delayed activation of the semiconductor switches.

2. The method according to claim 1, wherein the converter has an n-phase AC voltage terminal to be connected to the AC voltage grid via n phase lines, where n is at least 2, wherein a switching module branch is arranged in series in each of the phase lines, wherein a series connection of the switching modules is arranged in each switching module branch and a respective bypass branch having a respective switching device with semiconductor switches configured to be activated in antiparallel is arranged in parallel with each of the switching module branches.

3. The method according to claim 1, wherein the switching modules are full bridge switching modules.

4. The method according to claim 1, wherein the line-commutated converter is a thyristor-based converter.

5. The method according to claim 1, wherein the converter arrangement further comprises a mechanical bypass switch connected in parallel with the switching module branch and the bypass branch.

6. The method according to claim 1, wherein the converter arrangement further comprises a first inductance arranged in the switching module branch.

7. The method according to claim 1, wherein the converter arrangement further comprises a second inductance arranged in the bypass branch connected in parallel with each the switching module branch.

8. The method according to claim 1, wherein the bypass branch has a number Ah of antiparallel semiconductor switches and a respectively associated switching module branch has a number As of switching modules, and wherein Ah⇐As⇐3*Ah.

9. The method according to claim 1, wherein the converter arrangement further comprises a central actuation unit configured to activate the semiconductor switches in the bypass branch when a predetermined condition is present.

10. The method according to claim 1, wherein the semiconductor switches in the bypass branch are configured to be activated automatically when a predetermined condition is present.

11. The method according to claim 1, wherein the converter arrangement further comprises a controllable transformer arranged between the at least one switching module branch and the converter.

12. The method according to claim 1, which comprises switching the switching modules on a basis of a switching module voltage and a current direction of the branch current, to thereby charge the energy storage units of the switching modules to a predefined voltage level.

13. The method according to claim 1, which comprises, when the semiconductor switches in the bypass branch are activated, opening a mechanical bypass switch arranged in the parallel connection to the bypass branch, to thereby commutate the branch current to the bypass branch.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 shows a schematic illustration of an exemplary embodiment of a converter arrangement according to the invention;

(2) FIG. 2 shows a schematic illustration of an exemplary embodiment of an arrangement of parallel branches for a converter arrangement according to the invention;

(3) FIG. 3 shows a schematic illustration of a first vector diagram for branch current and branch voltage of a switching module branch; and

(4) FIG. 4 shows a schematic illustration of a second vector diagram for branch current and branch voltage of a switching module branch.

DETAILED DESCRIPTION OF THE INVENTION

(5) Referring now to the figures of the drawing in detail and first, in particular, to FIG. 1 thereof, there is shown a converter arrangement 1 that is connected, at a grid connection point 4, to a three-phase AC voltage grid 5. The converter arrangement 1 comprises a line-commutated converter 2. The converter 2 has a DC voltage side that is connected to a DC voltage grid or DC voltage line 3. A controllable transformer 26 comprising a step switch is arranged on the AC voltage side of the converter 2. The converter 2 comprises six converter arms or converter valves 6-11 that each extend between one of the DC voltage poles 12 or 13 of the converter 2 and one of the three AC voltage terminals 14-16. A series connection of thyristors 17 is arranged in each of the converter arms 6-11. The converter 2 is connected to the AC voltage grid 5 by way of the AC voltage terminals 14-16 via three phase lines 21-23.

(6) The converter arrangement 1 furthermore comprises a first switching module branch in a first arrangement of parallel branches 18, a second switching module branch in a second arrangement of parallel branches 19, and a third switching module branch in a third arrangement of parallel branches 20. The first branch arrangement 18 is introduced in series into a first phase line 21, the second branch arrangement 19 is introduced in series into a second phase line 22 and the third branch arrangement 20 is introduced in series into a third phase line 23. The three phase lines 21-23 extend between a connection point 25 to the transformer 26 and the grid connection point 4. In the example illustrated in FIG. 1, the three branch arrangements 18-20 are of identical design, but this does not generally have to be the case. The structure of the arrangements of parallel branches 18-20 and the structure of the switching module branches is discussed in more detail with reference to FIG. 2 below.

(7) A voltage dropped across the switching branches is denoted U.sub.c. The converter-side line-to-ground voltage is denoted U.sub.1, and the grid-side line-to-ground voltage is accordingly denoted U.sub.net. The branches 18-20 are used to compensate a line impedance X.sub.netz and/or a converter-side impedance X.sub.c and to stabilize a connection voltage U.sub.prim at the connection point 25 in order to guarantee stable and reliable operation of the converter arrangement 1, and in particular of the converter 2. The converter arrangement 1 for this purpose has a central actuation unit 24 that is designed to regulate the actuation of the switching module branches or to initiate the actuation of the semiconductor switches used there. The controllable transformer 26 is used to transform the connection voltage U.sub.prim into an output voltage U.sub.sec such that its amplitude is reduced.

(8) FIG. 2 shows an arrangement of parallel branches that is able to be used as one or more of the branches 18-20 in the converter arrangement from FIG. 1. A bypass branch 33 is arranged in a parallel connection to a switching module branch 31, and a bypass switch 35 is arranged in another parallel connection. The switching module branch 31 comprises a series connection 34 of switching modules 341, 342, these being full bridge switching modules known from the prior art (the figure illustrates only two switching modules 341, 342, but the number thereof may in principle be adjusted as desired and to the respective application). Each full bridge switching module comprises its own energy storage unit 38 in the form of a storage capacitor, as well as activatable and deactivatable semiconductor switches 41 in the form of (for example) IGBTs. A freewheeling diode is in this case connected in antiparallel with each IGBT. Bipolar voltages are able to be generated at the terminals of each full bridge switching module. A first inductance 40 is furthermore arranged in the switching module branch 31.

(9) The bypass branch 33 comprises a switching device 37. The switching device 37 has a first activatable semiconductor switch 36 in the form of a thyristor, and a second activatable semiconductor switch 42, likewise in the form of a thyristor. The forward directions of the two semiconductor switches 36 and 42 are in opposite directions. In this sense, the semiconductor switches 36 and 42 are connected in antiparallel. The bypass branch 33 furthermore comprises a second inductance 39. A further inductance of the arrangement is denoted by the reference sign 32. The difference between the voltages U.sub.1 and U.sub.2 corresponds to the branch voltage present on the switching module branch.

(10) FIG. 3 illustrates a vector diagram 50. The vector diagram 50 is a voltage/current diagram for the case of rectifier operation of a converter arrangement, which corresponds for example to the converter arrangement 1 of FIG. 1. The diagram 50 shows a primary-side voltage U.sub.prim on a primary side of a controllable transformer, for example the transformer 26 of FIG. 1, and a secondary-side voltage U.sub.sec on a secondary side of the transformer. The primary-side voltage U.sub.prim in this case corresponds to the connection voltage at the connection point between the switching module branches and the transformer. It may be seen that a branch voltage U.sub.FB applied to the switching module branches is phase-shifted by pi/2 in relation to a primary-side current i.sub.prim on the primary side of the transformer. At the same time, the primary-side current i.sub.prim is shifted by an angle φnet (phi.sub.net) in relation to a line voltage U.sub.net of an AC voltage grid connected to the converter arrangement. It may also be seen that the primary-side voltage U.sub.prim consists of the line voltage U.sub.net and the branch voltage U.sub.FB. The secondary-side voltage U.sub.sec is in phase with the primary-side voltage U.sub.prim, but has an amplitude that is reduced (by way of the transformer). The vector diagram 50 additionally shows that the reference system of the branch current i.sub.prim is selected for the regulation of the branch voltage U.sub.FB. The branch current i.sub.prim through the switching module branch or branches in this case corresponds to a line current i.sub.net. In the case that is illustrated in FIG. 3, the line voltage U.sub.net leads the primary-side voltage U.sub.prim by an angle Δφ (deltaphi).

(11) FIG. 4 illustrates a vector diagram 60. The vector diagram 60 is a voltage/current diagram for the case of inverter operation of a converter arrangement, which corresponds for example to the converter arrangement 1 of FIG. 1. The diagram 60 shows a primary-side voltage U.sub.prim on a primary side of a controllable transformer, for example the transformer 26 of FIG. 1, and a secondary-side voltage U.sub.sec on a secondary side of the transformer. The primary-side voltage U.sub.prim in this case corresponds to the connection voltage at the connection point between the switching module branches and the transformer. It may be seen that a branch voltage U.sub.FB applied to the switching module branches is phase-shifted by π/2 (pi/2) in relation to a primary-side current i.sub.prim on the primary side of the transformer. At the same time, the primary-side current i.sub.prim is shifted by an angle (net in relation to a line voltage U.sub.net of an AC voltage grid connected to the converter arrangement. It may also be seen that the primary-side voltage U.sub.prim consists of the line voltage U.sub.net and the branch voltage U.sub.FB. The secondary-side voltage U.sub.sec is in phase with the primary-side voltage U.sub.prim, but has an amplitude that is reduced (by way of the transformer). The vector diagram 50 additionally shows that the reference system of the branch current i.sub.prim is selected for the regulation of the branch voltage U.sub.FB. The branch current i.sub.prim through the switching module branch or branches in this case corresponds to a line current i.sub.net. In the case illustrated in FIG. 4, the line voltage U.sub.net lags the primary-side voltage U.sub.prim by an angle Δφ.