Converter arrangement having a star point reactor

Abstract

A converter arrangement has a converter which can be switched between an AC network and a DC voltage circuit and which has power semiconductor valves that extend between AC voltage connections and DC voltage connections. Each power semiconductor valve has a series connection of bipolar submodules that in turn include power semiconductor devices. The arrangement further includes a star point reactor which is arranged on the AC voltage side of the converter and has impedance coils that are connected to a grounded neutral point. In order to better balance the voltages in the DC circuit, the impedance coils have a common coil core.

Claims

1. A converter arrangement, comprising: a converter to be connected between an AC network and a DC voltage circuit; said converter having a plurality of power semiconductor valves each extending between an AC voltage connection and a DC voltage connection; each of said power semiconductor valves having a series circuit of two-pole submodules with power semiconductors; a star point reactor connected connected between a transformer, which is arranged on the AC-voltage side of said converter, and the AC voltage connection of said converter said star point reactor having inductor coils interconnected to form a grounded neutral point and said inductor coils having a common coil core and wherein a winding sense of said compensation windings and of said inductor coils is in a same direction; and a compensation winding assigned to each inductor coil of said star point reactor, wherein said compensation windings are arranged in an electrical series circuit between the neutral point and a link to ground, and wherein said compensation windings and said inductor coils have a common coil core; and said star point reactor includes a switching unit connected between said compensation windings and the link to ground.

2. The converter arrangement according to claim 1, wherein each inductor coil of said inductor coils has a sub core, assigned thereto, of said common coil core passing through it, and wherein each sub core delimits an air gap, wherein said air gap is in each case dimensioned such that each inductor coil has a predetermined inductance and a predetermined saturation point given a preset converter direct current.

3. The converter arrangement according to claim 1, further comprising a zero-sequence network inductor connected between the neutral point and a link to ground.

4. The converter arrangement according to claim 1, wherein said star point reactor is connected between a transformer, which is arranged on the AC-voltage side of said converter, and the AC voltage connection of said converter.

5. The converter arrangement according to claim 1, wherein said inductor coils of said star point reactor are converter-side windings of a transformer, which is arranged on the AC-voltage side of said converter, and said compensation windings are tertiary windings of said transformer, wherein a winding sense of said compensation windings is in an opposite direction to a winding sense of the assigned said inductor coils, and wherein said transformer and said star point reactor have a common coil core.

6. The converter arrangement according to claim 1, wherein said switching unit comprises at least one mechanical circuit breaker and/or at least one semiconductor switch.

7. The converter arrangement according to claim 1, wherein said star point reactor comprises a surge arrester connected in parallel with said compensation windings between the neutral point and the link to ground.

8. The converter arrangement according to claim 1, wherein each of said submodules has a full-bridge circuit with four power semiconductors capable of being turned off and an energy storage device, with said power semiconductors being interconnected with said energy storage device to enable each of said submodules to generate a voltage drop across said energy storage device, a zero-sequence voltage, or else an inverse energy storage device voltage at output terminals of said submodule.

9. The converter arrangement according to claim 1, wherein each of said submodules has a half-bridge circuit with two power semiconductors capable of being turned off and an energy storage device, with the power semiconductors being interconnected with said energy storage device to enable each of said submodules to generate an energy storage device voltage drop across said energy storage device or a zero-sequence voltage at output terminals of said submodule.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

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

(2) FIG. 2 shows a second exemplary embodiment of the converter arrangement according to the invention in a schematic illustration;

(3) FIG. 3 shows a third exemplary embodiment of the converter arrangement according to the invention in a schematic illustration;

(4) FIG. 4 shows an exemplary embodiment of a converter of the converter arrangement according to the invention in a schematic illustration.

DESCRIPTION OF THE INVENTION

(5) Specifically, FIG. 1 shows a converter arrangement 1. The converter arrangement 1 comprises a converter 2. The converter 2 has a DC-voltage side, which is connectable to a DC voltage circuit, for example a DC voltage link in an HVDC system or a DC voltage power supply system, by means of a DC voltage connection 3. In addition, the converter 2 has an AC-voltage side, which is connectable to an AC network 5 by means of AC voltage connection 4, said AC network being three-phase in the present example. In the exemplary embodiment illustrated in FIG. 1, the link to the AC network 5 takes place via a transformer 6. The transformer 6 comprises windings 61 on the power supply system side and windings 62 on the converter side on that side of the transformer 6 which faces the converter 2. Both the windings 61 on the power supply system side and the windings 62 on the converter side are each connected to one another in a star circuit.

(6) In principle, however, any other suitable configuration of the transformer is also possible, for example a star-delta configuration.

(7) A star point reactor 7 is arranged between the transformer 6 and the converter 2, said star point reactor being connected in parallel with the AC network 5, or between the phases of the AC network 5 and a connection to ground 8.

(8) The star point reactor 7 comprises a first inductor coil 9, a second inductor coil 10 and a third inductor coil 11. Each inductor coil 9-11 is connected to a phase, assigned thereto, of the AC network 5. The inductor coils 9-11 are connected to one another to form a common neutral point 12 on the side remote from the AC network 5. The three inductor coils 9-11 have a common coil core 13. In this case, each inductor coil 9, 10 or 11 has a subcore 14, 15 or 16, respectively, of the common coil core 13 passing through it. Each subcore 14, 15 or 16 has an air gap 17, 18 or 19, respectively, whose function has already been described above.

(9) A zero-sequence network inductor 20, which has a dedicated iron core 210 with an air gap, is arranged between the common neutral point 12 and the connection to ground or link to ground.

(10) The inductor coils 9-11 and the zero-sequence network inductor 20 are arranged in a common housing 21, which provides, for example, oil insulation, SF.sub.6 insulation, ester insulation or the like.

(11) A resistance element 22, which serves the purpose of current limitation, is located in a series circuit with the zero-sequence network inductor 20. A surge arrester 23 for voltage limitation is arranged in parallel with the series circuit comprising the zero-sequence network inductor 20 and the resistance element 22.

(12) FIG. 2 shows a second exemplary embodiment of a converter arrangement 25. Identical or similar elements of the converter arrangements 1 and 25 have been provided with the same reference symbols in FIGS. 1 and 2, respectively. For reasons of clarity, the air gaps of the subcores 14-16 are not explicitly illustrated in the illustration in FIG. 2. The design of the coil core 13 in this case corresponds in principle to that of the coil core 13 from FIG. 1, however.

(13) The converter arrangement 25 in FIG. 2 differs from the converter arrangement 1 in FIG. 1 in that a first compensation winding 26 is assigned to the first inductor coil 9, a second compensation winding 27 is assigned to the second inductor coil 10, and a third compensation winding 28 is assigned to the third inductor coil 11. The compensation windings 26-28 are arranged in a series circuit between the common neutral point 12 and the connection to ground 8. It can be seen that the common coil core 13 also passes through the compensation windings 26-28. The winding sense of the inductor coils 9-11 and of the compensation windings 26-28 is indicated in FIG. 2 by points 29. It can be seen that the winding sense of the compensation windings 26-28 is in the same direction as the winding sense of the inductor coils 9-11.

(14) In addition, the converter arrangement 25 comprises a switching unit 30, which is arranged between the compensation windings 26-28 and the connection to ground 8. The switching unit 30 comprises a parallel circuit comprising a switching element 31 and a nonlinear resistance element 32. In the present exemplary embodiment, the switching element 31 is a solid-state breaker comprising a series circuit of a plurality of power semiconductor switches. The direction of the direct currents in the star point reactor 7 is indicated by arrows 33.

(15) FIG. 3 shows a third exemplary embodiment of a converter arrangement 35. Identical or similar elements of the converter arrangements 1, 25 and 35 have been provided with the same reference symbols in FIGS. 1 and 2, respectively. For reasons of clarity, the air gaps in the subcores 14-16 are not explicitly illustrated in the illustration in FIG. 2. The design of the coil core 13 in this case corresponds in principle to that of the coil core 13 from FIG. 1, however. The inductor coils 9-11 of the converter arrangement 35 are embodied as the converter-side winding 62 of the transformer 6. For reasons of clarity, only one of the three windings 61, on the power supply system side, of the transformer 6 has been illustrated in the figure. However, it can be seen that the limbs or subcores 14-16 of the coil core 13 pass through both the inductor coils 9-11, the windings 61 on the power supply system side and the compensation windings 26-28. In contrast to the embodiment from FIG. 2, the winding sense of the compensation windings 26-28 of the converter arrangement 35 is in the opposite direction to the winding sense of the inductor coils 9-11. In this way, compensation of the magnetization of the coil core 13 is achieved, as a result of which premagnetization of the transformer 6 can be avoided. The corresponding direction of the resultant direct currents is indicated in FIG. 3 by the arrows 33.

(16) FIG. 4 shows a converter 2 for one of the converter arrangements from FIGS. 1 to 3. The converter 2 is connected between an AC voltage connection 4 and a DC voltage connection 3. Therefore, the converter 2 is connectable on the DC-voltage side to a DC voltage line or a DC voltage power supply system and on the AC-voltage side to an AC network. The converter 2 is a modular multi-level converter (MMC). The MMC has power semiconductor valves 121-126 arranged between the DC-voltage side and the AC-voltage side.

(17) Each power semiconductor valve 121-126 comprises a series circuit of two-pole submodules 127 and a smoothing inductor 128. In the exemplary embodiment illustrated in FIG. 2, all of the submodules 127 have an identical design, but this is not necessary in general. Interrupted lines 129 in FIG. 4 indicate that each power semiconductor valve 121-126 can have a greater number of submodules 127 than the two submodules 127 illustrated explicitly in FIG. 4.

(18) Each submodule 127 comprises two semiconductor switches 130, with one freewheeling diode 301 being connected back-to-back in parallel with each of said semiconductor switches, and an energy store in the form of a capacitor 131. The submodules 127 are therefore in the form of half-bridge circuits. The semiconductor switches 130 of the submodules 127 are controllable independently of one another.

(19) In place of the half-bridge circuits, the submodules can also be implemented, for example, as full-bridge circuits known to a person skilled in the art.

(20) In addition, the converter 2 comprises measuring devices 321-300, which are designed for measuring currents and/or voltages.

(21) In addition, a regulation unit for regulating the converter 2 is provided, but is not explicitly illustrated in FIG. 4.