CN111371128A - Symmetrical single-pole flexible direct current converter station - Google Patents
Symmetrical single-pole flexible direct current converter station Download PDFInfo
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- CN111371128A CN111371128A CN202010192780.XA CN202010192780A CN111371128A CN 111371128 A CN111371128 A CN 111371128A CN 202010192780 A CN202010192780 A CN 202010192780A CN 111371128 A CN111371128 A CN 111371128A
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- transformer
- direct current
- converter station
- flexible direct
- neutral point
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J5/00—Circuit arrangements for transfer of electric power between ac networks and dc networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M7/219—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration
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Abstract
The invention relates to the technical field of flexible direct current transmission, and discloses a symmetrical single-pole flexible direct current converter station which comprises a modular multilevel converter, a transformer and a grounding module, wherein the input end of the transformer is used for being connected with an alternating current power grid, the output end of the transformer is connected with the input end of the modular multilevel converter, a neutral point of a valve side winding of the transformer is grounded through the grounding module, and a corresponding grounding mode is selected according to alternating current bus voltage of a back-to-back flexible direct current transmission system by the neutral point of a grid side winding of the transformer; the grounding module comprises a large resistance unit and a large inductance unit which are connected in series. The symmetrical unipolar flexible direct current converter station can adopt an optimized system design method such as zero sequence injection and the like to reduce equipment investment; and the number of used devices is relatively small, the structure is simpler, and the cost is reduced. In addition, the symmetrical unipolar flexible direct current converter station has a good grounding effect, and provides effective ground potential reference for total station equipment.
Description
Technical Field
The invention relates to the technical field of flexible direct current transmission, in particular to a symmetrical unipolar flexible direct current converter station.
Background
Compared with alternating current transmission and conventional direct current transmission, the flexible direct current transmission is used as a new generation of direct current transmission technology, can flexibly adjust the voltage of an alternating current system connected with the flexible direct current transmission while transmitting energy, has the remarkable advantages of better controllability, flexible operation mode and the like, and is widely applied to scenes of wind power integration, passive network power supply, asynchronous interconnection of power grids and the like.
At present, the existing flexible direct current converter station generally comprises a converter, a converter transformer device and the like. The flexible direct current converter station is mainly grounded in the following two ways; the first mode is as follows: a neutral point of a transformer valve side winding in the flexible direct current converter station is grounded through a large resistor, as shown in fig. 1; the second way is: the transformer valve side position in the flexible dc converter station is grounded via a star connection reactor as shown in fig. 2. However, in the process of implementing the present invention, the present inventors found that the prior art has at least the following technical problems: when the flexible direct current converter station is grounded in the first mode, although the grounding effect is good, the flexible direct current converter station cannot adopt optimized system design methods such as zero sequence injection and the like, so that the equipment investment is reduced; and when the flexible direct current converter station adopts the second middle mode grounding, the number of used equipment is large, and the cost of the flexible direct current converter station is increased.
Disclosure of Invention
The invention aims to provide a symmetrical unipolar flexible direct current converter station, which can adopt an optimized system design method such as zero sequence injection and the like to reduce equipment investment and uses relatively less equipment.
In order to solve the technical problem, the invention provides a symmetrical single-pole flexible direct current converter station, which comprises a modular multilevel converter, a transformer and a grounding module, wherein the input end of the transformer is used for being connected with an alternating current power grid, the output end of the transformer is connected with the input end of the modular multilevel converter, a neutral point of a valve side winding of the transformer is grounded through the grounding module, and a corresponding grounding mode is selected according to the alternating current bus voltage of a back-to-back flexible direct current transmission system by the neutral point of a grid side winding of the transformer; the grounding module comprises a large resistance unit and a large inductance unit which are connected in series.
As a preferred scheme, a neutral point of a valve side winding of the transformer is grounded through the grounding module, specifically:
the neutral point of the valve side winding of the transformer is connected with the first end of the large resistance unit, the second end of the large resistance unit is connected with the first end of the large inductance unit, and the second end of the large inductance unit is grounded.
As a preferred scheme, a neutral point of a valve side winding of the transformer is grounded through the grounding module, specifically:
the neutral point of the valve side winding of the transformer is connected with the first end of the large inductance unit, the second end of the large inductance unit is connected with the first end of the large resistance unit, and the second end of the large resistance unit is grounded.
Preferably, the large resistance unit is a resistor.
Preferably, the large inductance unit is a dry air core reactor or a voltage transformer.
Compared with the prior art, the invention provides the symmetrical unipolar type flexible direct current converter station, and the neutral point of the valve side winding of the transformer in the symmetrical unipolar type flexible direct current converter station is grounded through the large resistance unit and the large inductance unit which are connected in series, so that the symmetrical unipolar type flexible direct current converter station can adopt an optimized system design method such as zero sequence injection and the like, and the equipment investment is reduced; and the number of used equipment is relatively small, so that the structure of the symmetrical unipolar flexible direct current converter station is simpler, and the cost is reduced. In addition, the symmetrical unipolar flexible direct current converter station provided by the embodiment of the invention has a good grounding effect, and can provide effective ground potential reference for total station equipment.
Drawings
Fig. 1 is a schematic diagram of a grounding mode of a symmetrical unipolar type flexible dc converter station in the prior art;
fig. 2 is a schematic diagram of another grounding method of a symmetrical unipolar type flexible dc converter station in the prior art;
fig. 3 is a schematic structural diagram of a symmetrical unipolar type flexible dc converter station provided in an embodiment of the present invention;
fig. 4 is a schematic structural diagram of a modular multilevel converter provided in an embodiment of the present invention;
fig. 5 is a schematic structural diagram of a power unit according to an embodiment of the present invention;
fig. 6 is a schematic structural diagram of another power unit according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 3, a schematic structural diagram of a symmetric unipolar type flexible dc converter station according to an embodiment of the present invention is shown.
In the embodiment of the present invention, the symmetrical unipolar type flexible dc converter station includes a modular multilevel converter 1, a transformer 2, and a grounding module 3, an input end of the transformer 2 is used for being connected to an ac power grid, an output end of the transformer 2 is connected to an input end of the modular multilevel converter 1, a neutral point of a valve side winding of the transformer 2 is grounded through the grounding module 3, and a neutral point of a grid side winding of the transformer 2 selects a corresponding grounding mode according to an ac bus voltage of the back-to-back flexible dc transmission system; wherein the grounding module 3 comprises a large resistance unit 31 and a large inductance unit 32 connected in series.
Specifically, the input end of the transformer 2 is connected with the alternating current power grid through an alternating current bus; the neutral point of the valve side winding of the transformer 2 is grounded through the grounding module 3, which is embodied as follows: the neutral point of the valve side winding of the transformer 2 is connected with one end of the grounding module 3, and the other end of the grounding module 3 is grounded. The neutral point of the grid side winding of the transformer 2 can be grounded or ungrounded according to the alternating current bus voltage of the symmetrical unipolar flexible direct current converter station.
In the embodiment of the present invention, the working principle of the symmetrical unipolar flexible dc converter station specifically includes: alternating current output by the alternating current power grid is input through the alternating current bus, flows through the transformer 2, is converted into direct current through the modular multilevel converter 1 and is output.
In the embodiment of the present invention, the neutral point of the valve side winding of the transformer 2 in the symmetrical unipolar type flexible dc converter station is grounded through the large resistance unit 31 and the large inductance unit 32 connected in series, so that the symmetrical unipolar type flexible dc converter station can adopt an optimized system design method such as zero sequence injection to reduce the equipment investment; and the number of used equipment is relatively small, so that the structure of the symmetrical unipolar flexible direct current converter station is simpler, and the cost is reduced. In addition, the symmetrical unipolar flexible direct current converter station provided by the embodiment of the invention has a good grounding effect, and can provide effective ground potential reference for total station equipment.
It should be noted that the zero sequence injection design method specifically includes: certain zero sequence component (generally third harmonic) is injected into the output voltage of the flexible direct current converter station, so that a higher line voltage peak value is obtained under the condition of the same phase voltage peak value, and the direct current voltage utilization rate is improved.
In a preferred embodiment, the neutral point of the valve-side winding of the transformer 2 is grounded via the grounding module 3, specifically:
the neutral point of the valve side winding of the transformer 2 is connected to the first end of the large resistance unit 31, the second end of the large resistance unit 31 is connected to the first end of the large inductance unit 32, and the second end of the large inductance unit 32 is grounded.
In another preferred embodiment, a neutral point of a valve side winding of the transformer 2 is grounded through the grounding module 3, specifically:
the neutral point of the valve side winding of the transformer 2 is connected to the first end of the large inductance unit 32, the second end of the large inductance unit 32 is connected to the first end of the large resistance unit 31, and the second end of the large resistance unit 31 is grounded.
In the embodiment of the present invention, the type of the large resistance unit 31 may be set according to an actual use condition, and it is only necessary to ensure that the large resistance unit 31 has a large resistance value; the resistance value of the large resistance unit 31 is generally in the kilo-ohm range in engineering experience. In order to simplify the structure and reduce the cost, it is preferable that the large resistance unit 31 is a resistor in the present embodiment.
In addition, the type of the large inductance unit 32 may also be set according to the actual use condition, and it is only necessary to ensure that the large inductance unit 32 has a larger inductance value; the inductance value of the large inductance unit 32 is typically of the order of kilohents in engineering experience. In order to simplify the structure and reduce the cost, it is preferable that the large inductance unit 32 in this embodiment is a dry air core reactor or other devices capable of being equivalent to an inductance, such as a voltage transformer.
In the embodiment of the invention, the flexible direct current converter station has a zero sequence path, and under the condition that the flexible direct current converter station adopts a mode that the neutral point position of a winding on the transformer valve side is grounded through a large resistor, when the flexible direct current converter station adopts a zero sequence injection design method, the power consumption of the grounding resistor is large, so that the power consumption of the flexible direct current converter station is increased, and further, the equipment investment is increased. In the embodiment of the present invention, the neutral point of the valve side winding of the transformer 2 in the symmetrical unipolar flexible dc converter station is grounded through the large resistance unit 31 and the large inductance unit 32 connected in series, so that the problem of increased equipment investment after the symmetrical unipolar flexible dc converter station adopts a zero sequence injection design method is effectively solved, that is, the symmetrical unipolar flexible dc converter station can adopt an optimized system design method such as zero sequence injection to reduce the equipment investment.
In a preferred embodiment, the grid-side winding of the transformer 2 may select a corresponding grounding manner according to an ac bus voltage input to the symmetrical unipolar type flexible dc converter station, specifically:
when the alternating-current bus voltage of the symmetrical unipolar flexible direct-current converter station is greater than or equal to 220V, the neutral point of the network side winding of the transformer 2 is grounded;
when the alternating-current bus voltage of the symmetrical unipolar flexible direct-current converter station is less than or equal to 110V, the neutral point of the grid-side winding of the transformer 2 is grounded through the arc suppression coil, or the neutral point of the grid-side winding of the transformer 2 is not grounded.
In the embodiment of the present invention, when the ac bus voltage of the symmetrical unipolar type flexible dc converter station is greater than or equal to 220V, the neutral point of the grid side winding of the transformer 2 is directly grounded, and when the ac bus voltage of the symmetrical unipolar type flexible dc converter station is less than or equal to 110V, the neutral point of the grid side winding of the transformer 2 is grounded through an arc suppression coil, or the neutral point of the grid side winding of the transformer 2 is not grounded, so that the symmetrical unipolar type flexible dc converter station can be ensured to have a good grounding effect under different ac bus voltages, and the safety of the symmetrical unipolar type flexible dc converter station is further ensured.
In a preferred embodiment, as shown in fig. 4, the modular multilevel converter 1 comprises three legs 11, a first end of the leg 11 is a first output end of the modular multilevel converter 1, a second end of the leg 11 is a second output end of the modular multilevel converter 1, and a midpoint of the leg 11 is an input end of the modular multilevel converter 1;
the bridge arm 11 comprises two power modules 111 and a first bridge arm reactor L1And a second bridge arm reactor L2The first end of one power module 111 is the first end of the bridge arm 11, and the second end of the power module 111 and the first bridge arm reactor L1Is connected to the first end of the first leg reactor L1The second end of (a) is the midpoint of the bridge arm 11; the first bridge arm reactor L1And said second leg reactor L2Is connected to the first end of the second leg reactor L2Is connected to a first end of another power module 111, and a second end of the power module 111 is a second end of the bridge arm 11.
It can be understood that a first end of each of the bridge arms 11 is connected, a second end of each of the bridge arms 11 is connected, and a midpoint of one of the bridge arms 11 is correspondingly connected to an output end of the transformer 2.
Further, as shown in fig. 4 and 5, in a preferred embodiment, the power module 111 includes a plurality of power units, and the second terminal of one of the power units is connected to the first terminal of another one of the power units;
the power unit comprises a first insulated gate bipolar transistor VT1, a second insulated gate bipolar transistor VT2, a third insulated gate bipolar transistor VT3, a fourth insulated gate bipolar transistor VT4, a first capacitor C1, a first resistor R1 and a first switch W1, wherein a collector of the first insulated gate bipolar transistor VT1 is the first end of the power unit, a collector of the first insulated gate bipolar transistor VT1 is respectively connected with a collector of the third insulated gate bipolar transistor VT3, a first end of the first capacitor C1 and a first end of the first resistor R1, an emitter of the first insulated gate bipolar transistor VT1 is respectively connected with a collector of the second insulated gate bipolar transistor VT2 and a first end of the first switch W1, a second end of the first switch W1 is respectively connected with a collector of the second insulated gate bipolar transistor VT2 and a collector of the fourth insulated gate bipolar transistor VT4, an emitter of the second igbt VT2 is a second end of the power unit, an emitter of the second igbt VT2 is connected to an emitter of the fourth igbt VT4, a second end of the first capacitor C2, and a second end of the first resistor R2, respectively, and an emitter of the third igbt VT3 is connected to a collector of the fourth igbt VT 4.
It can be understood that, in the plurality of power units, the plurality of power units are connected in sequence, that is, the second end of one power unit is only connected to the first end of another power unit, and in the connected plurality of power units, the first end of the first power unit is the first end of the power module 111, and the second end of the last power unit is the second end of the power module 111.
In addition, the types of the first resistor R1 and the first capacitor C1 can be set according to actual use conditions; preferably, in this embodiment, the first resistor R1 is a voltage-sharing resistor; the first capacitor C1 is a power module capacitor.
In another preferred embodiment, as shown in fig. 4 and fig. 6, the power module 111 includes a plurality of power units, and the second terminal of one power unit is connected to the first terminal of another power unit;
the power unit comprises a fifth insulated gate bipolar transistor VT5, a sixth insulated gate bipolar transistor VT6, a second capacitor C2, a second resistor R2 and a second switch W2, the collector of the fifth igbt VT5 is the first terminal of the power cell, the collector of the fifth igbt VT5 is connected to the first terminal of the second capacitor C2 and the first terminal of the second resistor R2, the emitter of the fifth insulated gate bipolar transistor VT5 is connected to the collector of the sixth insulated gate bipolar transistor VT6 and to the first terminal of the second switch W2, the emitter of the sixth igbt VT6 is the second terminal of the power unit, an emitter of the sixth igbt VT6 is connected to the second terminal of the second switch W2, the second terminal of the second capacitor C2, and the second terminal of the second resistor R2, respectively.
It should be noted that the types of the second resistor R2 and the second capacitor C2 may be set according to actual use cases; preferably, in this embodiment, the second resistor R2 is a voltage-sharing resistor; the second capacitor C2 is a power module capacitor.
In addition, in the embodiment of the present invention, the symmetrical unipolar type flexible dc converter station further includes related devices for measurement and protection.
In summary, the present invention provides a symmetrical single-pole flexible dc converter station, including a modular multilevel converter 1, a transformer 2 and a grounding module 3, wherein an input end of the transformer 2 is connected to an ac bus, an output end of the transformer 2 is connected to an input end of the modular multilevel converter 1, a neutral point of a valve side winding of the transformer 2 is grounded through the grounding module 3, and a neutral point of a grid side winding of the transformer 2 selects a corresponding grounding manner according to an ac bus voltage of a back-to-back flexible dc transmission system; the grounding module 3 comprises a large resistance unit 31 and a large inductance unit 32 connected in series. The neutral point of the valve side winding of the transformer 2 in the symmetrical unipolar type flexible direct current converter station is grounded through the large resistance unit 31 and the large inductance unit 32 which are connected in series, so that the symmetrical unipolar type flexible direct current converter station can adopt an optimized system design method such as zero sequence injection and the like, and the equipment investment is reduced; and the number of used equipment is relatively small, so that the structure of the symmetrical unipolar flexible direct current converter station is simpler, and the cost is reduced. In addition, the symmetrical unipolar flexible direct current converter station provided by the embodiment of the invention has a good grounding effect, and can provide effective ground potential reference for total station equipment.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and substitutions can be made without departing from the technical principle of the present invention, and these modifications and substitutions should also be regarded as the protection scope of the present invention.
Claims (5)
1. A symmetrical single-pole flexible direct current converter station is characterized by comprising a modular multilevel converter, a transformer and a grounding module, wherein the input end of the transformer is used for being connected with an alternating current power grid, the output end of the transformer is connected with the input end of the modular multilevel converter, a neutral point of a valve side winding of the transformer is grounded through the grounding module, and a corresponding grounding mode is selected according to alternating current bus voltage of a back-to-back flexible direct current transmission system by the neutral point of a grid side winding of the transformer; the grounding module comprises a large resistance unit and a large inductance unit which are connected in series.
2. The symmetrical unipolar flexible dc converter station according to claim 1, wherein a neutral point of a valve-side winding of the transformer is grounded through the grounding module, specifically:
the neutral point of the valve side winding of the transformer is connected with the first end of the large resistance unit, the second end of the large resistance unit is connected with the first end of the large inductance unit, and the second end of the large inductance unit is grounded.
3. The symmetrical unipolar flexible dc converter station according to claim 1, wherein a neutral point of a valve-side winding of the transformer is grounded through the grounding module, specifically:
the neutral point of the valve side winding of the transformer is connected with the first end of the large inductance unit, the second end of the large inductance unit is connected with the first end of the large resistance unit, and the second end of the large resistance unit is grounded.
4. The symmetrical unipolar flexible direct current converter station according to any one of claims 1-3, wherein said high resistance units are resistors.
5. A symmetrical unipolar flexible dc converter station according to any one of claims 1 to 3, characterized in that said large inductance unit is a dry air reactor or a voltage transformer.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202010192780.XA CN111371128A (en) | 2020-03-18 | 2020-03-18 | Symmetrical single-pole flexible direct current converter station |
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| CN202010192780.XA CN111371128A (en) | 2020-03-18 | 2020-03-18 | Symmetrical single-pole flexible direct current converter station |
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| CN111371128A true CN111371128A (en) | 2020-07-03 |
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| CN202010192780.XA Pending CN111371128A (en) | 2020-03-18 | 2020-03-18 | Symmetrical single-pole flexible direct current converter station |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111614116A (en) * | 2020-06-18 | 2020-09-01 | 南方电网科学研究院有限责任公司 | Grounding method and device of flexible direct current system |
| CN112615360A (en) * | 2020-12-16 | 2021-04-06 | 全球能源互联网研究院有限公司 | Grounding device of flexible direct current transmission system |
-
2020
- 2020-03-18 CN CN202010192780.XA patent/CN111371128A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111614116A (en) * | 2020-06-18 | 2020-09-01 | 南方电网科学研究院有限责任公司 | Grounding method and device of flexible direct current system |
| CN112615360A (en) * | 2020-12-16 | 2021-04-06 | 全球能源互联网研究院有限公司 | Grounding device of flexible direct current transmission system |
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