An extra-high voltage flexible direct current power self-circulation system and a method of using the same

Abstract

The application relates to an extra-high voltage flexible direct-current power self-circulation system and a use method thereof, and the system comprises a first valve group, a second valve group, a polar line, a valve group connecting line, a neutral line and a grounding pole; the high-voltage end of the delta winding of the first valve group is connected with a station-outgoing transmission line through a first disconnecting switch, the polar line and a second disconnecting switch in sequence; the low-voltage end of the delta winding of the first valve group is connected with one end of the valve group connecting line through a third disconnecting switch; the high-voltage end of the delta winding of the second valve group is connected with the other end of the valve group connecting line through a fifth disconnecting switch, the low-voltage end of the delta winding of the second valve group is connected with the grounding pole through a sixth disconnecting switch, the neutral line and a seventh disconnecting switch in sequence, and the high-voltage end and the low-voltage end of the delta winding of the second valve group are connected through an eighth disconnecting switch; the application can meet different requirements of the operation and debugging of a converter station, and is widely applied in the electric power field.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electric power, in particular to a flexible HVDC power self-circulation system and a method for using the same. BACKGROUND

[0002] The UHV large-capacity flexible HVDC system is one of the key technologies for building future new power systems and is the only way for China to develop flexible HVDC technology. The technical advantages of flexible HVDC transmission are an effective solution for realizing the access and transmission of large-scale wind power, photovoltaic and other energy, multi-power supply and multi-drop wide-area coordinated complementary, which is conducive to the flexible energy interaction between renewable energy, pumped storage and load, the day-night complementary of large-scale photovoltaic and wind energy, the system peak shaving problem of large-scale renewable energy, the reduction of intermittent energy disturbance impact on the receiving end AC power grid, the improvement of clean energy access friendliness and the improvement of renewable energy utilization efficiency. It will promote the development of UHV flexible HVDC equipment and the construction of large-scale new energy transmission system through islands, including desert, deep sea and other scenarios, which is in line with the development scenarios of future new power systems and has strong adaptability.

[0003] At present, the UHV topology structure in China adopts high and low voltage double valve groups in series to form a single pole, and the bipolar ±800kV adopts the form of grounding electrode on the DC side. The flexible HVDC project has experienced the development of Shanghai Nanhui, Zhoushan five-end, Xiamen bipolar, Chongqing-Ezhou back-to-back, Zhangbei flexible HVDC grid, Wudongde three-end hybrid and Baijiang hybrid cascade projects, and its topology structure tends to be similar to the conventional UHV project. However, the Wudongde project has a long construction period, and the project adopts ±800kV / 5GW manufacturing level, and the high-end valve group of the Baijiang project is a conventional HVDC, and the low-end is a flexible HVDC, which is quite different from the UHV large-capacity flexible HVDC system.

[0004] In terms of building long-distance, UHV, large-capacity ±800kV / 8GW flexible HVDC system, there are often difficulties in equipment manufacturing and transportation, poor engineering implementation conditions, long construction period of long-distance DC lines, and other reasons, which require parallel development of production, debugging, construction and other tasks. The previous UHV DC projects, such as Figure 1As shown, the debugging task needs to be debugged by the double-end converter station and the DC line, and in the case of limited construction period, the debugging time and debugging items are compressed, which causes heavy debugging work and cannot effectively expose and solve hidden problems. Flexible DC has flexible control operation mode, and different power requirements can be met by controlling the amplitude and phase of the voltage. How to meet the requirements of UHV flexible DC single station single pole debugging through the flexible reliability of flexible DC is a key problem to be solved. In addition, due to the discrete type of debugging work, the power requirement of test items and the accommodation degree of local power grid, higher requirements are put forward for the power stability of the power grid, and another key problem to be solved is how to use the self-circulation strategy of the flexible DC system to stabilize the power of the AC section. The existing technical means does not involve the UHV flexible DC power self-circulation system. SUMMARY

[0005] In view of the above problems, the purpose of the present application is to provide a UHV flexible DC power self-circulation system and its use method, which can meet the requirements of flexible single converter station single pole full power debugging and operation, and ensure the power and voltage stability of the AC power grid section.

[0006] To achieve the above purpose, the present application adopts the following technical scheme: on the one hand, a UHV flexible DC power self-circulation system is provided, which comprises a first valve group, a second valve group, a pole line, a valve group connecting line, a neutral line and a grounding electrode;

[0007] The high voltage end of the delta winding of the first valve group is connected to the external power transmission line through the first disconnector, the pole line and the second disconnector in sequence; the low voltage end of the delta winding of the first valve group is connected to one end of the valve group connecting line through the third disconnector, and the high voltage end and the low voltage end of the delta winding of the first valve group are connected through the fourth disconnector;

[0008] The high voltage end of the delta winding of the second valve group is connected to the other end of the valve group connecting line through the fifth disconnector, the low voltage end of the delta winding of the second valve group is connected to the grounding electrode through the sixth disconnector, the neutral line and the seventh disconnector in sequence, and the high voltage end and the low voltage end of the delta winding of the second valve group are connected through the eighth disconnector;

[0009] The high voltage end of the delta winding of the first valve group and the high voltage end of the delta winding of the second valve group are connected through the ninth disconnector; the low voltage end of the delta winding of the first valve group and the low voltage end of the delta winding of the second valve group are connected through the tenth disconnector; the star windings of the first valve group and the second valve group are connected to the same AC power grid or different AC power grids;

[0010] The first valve group and the second valve group are in rectification operation or inversion operation respectively, and power is transmitted from the first valve group to the second valve group or from the second valve group to the first valve group by closing or opening of each disconnector.

[0011] Further, the sub-module types of the first valve group and the second valve group include half-bridge sub-modules, full-bridge sub-modules, full-bridge-like sub-modules, double-embedded sub-modules and hybrid sub-modules.

[0012] Further, the active-type control mode of the first valve group adopts constant DC voltage control, and the active-type control mode of the second valve group adopts constant DC power control or constant DC current control.

[0013] Further, the active-type control mode of the first valve group adopts constant DC power control or constant DC current control, and the active-type control mode of the second valve group adopts constant DC voltage control.

[0014] Further, the reactive-type control mode of the first valve group and the second valve group both adopts constant AC voltage control or constant reactive power control.

[0015] Further, when the first valve group is in rectification operation and the second valve group is in inversion operation, power is transmitted from the first valve group to the second valve group; when the first valve group is in inversion operation and the second valve group is in rectification operation, power is transmitted from the second valve group to the first valve group.

[0016] In another aspect, a use method of the UHV flexible DC power self-loop system is provided, comprising:

[0017] Isolating the self-loop system from the external transmission line of the station;

[0018] Connecting the high-voltage end and the low-voltage end of the first valve group delta winding and the second valve group delta winding respectively;

[0019] Connecting the self-loop system with the grounding electrode;

[0020] Making the first valve group and the second valve group be in rectification operation or inversion operation respectively, and realizing power transmission from the first valve group to the second valve group or from the second valve group to the first valve group.

[0021] Further, the active-type control mode of the first valve group adopts constant DC voltage control, and the active-type control mode of the second valve group adopts constant DC power control or constant DC current control.

[0022] Alternatively, the active-type control mode of the first valve group adopts constant DC power control or constant DC current control, and the active-type control mode of the second valve group adopts constant DC voltage control.

[0023] Further, the corresponding connection of the high-pressure end and the low-pressure end of the first valve group and the second valve group respectively comprises:

[0024] Close the ninth disconnector and the tenth disconnector.

[0025] Or, close the ninth disconnector, the third disconnector, the sixth disconnector and the eighth disconnector.

[0026] Or, close the first disconnector, the fourth disconnector, the fifth disconnector and the tenth disconnector.

[0027] Further, the connection of the self-circulation system and the grounding electrode comprises:

[0028] Disconnect the first disconnector, the third disconnector, the fourth disconnector, the fifth disconnector and the eighth disconnector, and close the sixth disconnector and the seventh disconnector.

[0029] Or, disconnect the first disconnector, the fourth disconnector and the fifth disconnector, and close the seventh disconnector.

[0030] Or, disconnect the third disconnector, the eighth disconnector and the ninth disconnector, and close the sixth disconnector and the seventh disconnector.

[0031] The present application has the following advantages due to the above technical solutions:

[0032] 1. The present application can realize power transmission between two flexible DC converter valves in a single pole, forming a self-circulation mode, while having less impact on the AC power grid section. Conventional extra-high voltage projects and HVDC projects do not have this design and have no operation experience.

[0033] 2. The present application can rely only on the equipment in a single converter station to carry out full-power debugging, and is also suitable for carrying out DC system debugging in advance during the stage when the DC line is not built. It can verify the maximum flow capacity of the equipment in the converter station, as well as the output characteristics of active power and reactive power.

[0034] 3. The present application can flexibly switch between two converter valve series operation and two converter valve back-to-back power transmission operation, which can meet different needs of converter station operation and debugging.

[0035] In summary, the present application can be widely used in the field of electric power. BRIEF DESCRIPTION OF DRAWINGS

[0036] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a description of the preferred embodiments and are not intended to limit the scope of the application. Throughout the drawings, the same reference numerals are used for the same components. In the drawings:

[0037] Figure 1 is a typical main wiring schematic diagram of the flexible HVDC provided by an embodiment of the present application;

[0038] Figure 2 is a self-circulation system structure schematic diagram provided by an embodiment of the present application;

[0039] Figure 3 is a first use method schematic diagram of the self-circulation system provided by an embodiment of the present application;

[0040] Figure 4 is a second use method schematic diagram of the self-circulation system provided by an embodiment of the present application;

[0041] Figure 5 is a third use method schematic diagram of the self-circulation system provided by an embodiment of the present application. DETAILED DESCRIPTION

[0042] Exemplary embodiments of the present application will be described herein below with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application can be embodied in various forms without being limited by the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art.

[0043] It should be understood that the terms used herein are merely for the purpose of describing particular example embodiments and are not intended to be limiting. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises," "comprising," "including," and "having" are inclusive and therefore specify the presence of stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order in which they are described, unless specifically indicated as such. It is also to be understood that additional or alternative steps can be employed.

[0044] Although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms can be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as "first," "second," and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

[0045] Due to the difficulties in equipment manufacturing and transportation, poor engineering implementation conditions, and long construction period of long-distance, extra-high voltage, and large-capacity ±800kV / 8GW flexible DC system, the production, debugging, construction, and other tasks need to be carried out in parallel. In the case of time limit, the debugging time and debugging items are compressed, resulting in heavy debugging work and problems that cannot be effectively exposed and solved. Flexible DC has flexible control operation mode, which meets different power requirements by controlling the amplitude and phase of voltage. How to meet the requirements of single station single pole debugging of extra-high voltage flexible DC through the flexibility and reliability of flexible DC is a key problem to be solved. In addition, due to the discrete type of debugging work, power requirement of test items, and local grid accommodation degree, higher requirements are put forward for the power stability of the grid, and another key problem to be solved is how to use the self-circulation strategy of the flexible DC system to stabilize the power of the AC section. The existing technical means does not involve the extra-high voltage flexible DC power self-circulation system. The extra-high voltage flexible DC power self-circulation system provided by the embodiment of the present application comprises a first valve group, a second valve group, a pole line, a valve group connecting line, a neutral line and a grounding electrode. The high voltage end of the delta winding of the first valve group is connected to the external power transmission line through the first disconnector, the pole line and the second disconnector in sequence. The low voltage end of the delta winding of the first valve group is connected to one end of the valve group connecting line through the third disconnector, and the high voltage end and the low voltage end of the delta winding of the first valve group are connected through the fourth disconnector. The high voltage end of the delta winding of the second valve group is connected to the other end of the valve group connecting line through the fifth disconnector, and the low voltage end of the delta winding of the second valve group is connected to the grounding electrode through the sixth disconnector, the neutral line and the seventh disconnector in sequence. The high voltage end and the low voltage end of the delta winding of the second valve group are connected through the eighth disconnector. The high voltage end of the delta winding of the first valve group and the high voltage end of the delta winding of the second valve group are connected through the ninth disconnector. The low voltage end of the delta winding of the first valve group and the low voltage end of the delta winding of the second valve group are connected through the tenth disconnector. The star windings of the first valve group and the second valve group are connected to the same AC power grid or different AC power grids. The first valve group and the second valve group are in rectifier operation or inverter operation respectively, and the power is transmitted from the first valve group to the second valve group or from the second valve group to the first valve group through the closing or opening of each disconnector. The present application can be self-debugged and power operated after the single station single pole construction is completed, and has little effect on the AC power grid section. There is no such design in conventional extra-high voltage projects, and there is no operation experience.

[0046] Embodiment 1

[0047] As shown in Figure 2 , the present embodiment provides an extra-high voltage flexible DC power self-circulation system, which comprises a first valve group 1, a second valve group 2, a pole line, a valve group connecting line, a neutral line and a grounding electrode.

[0048] The high voltage end of the delta winding of the first valve group 1 is connected to one end of a pole line through a first disconnector DS11, the other end of the pole line is connected to an external transmission line through a second disconnector DS3, the low voltage end of the delta winding of the first valve group 1 is connected to one end of a valve group connecting line through a third disconnector DS12, and the high voltage end and the low voltage end of the delta winding of the first valve group 1 are connected through a fourth disconnector DS13.

[0049] The high voltage end of the delta winding of the second valve group 2 is connected to the other end of the valve group connecting line through a fifth disconnector DS21, the low voltage end of the delta winding of the second valve group 2 is connected to one end of a neutral line through a sixth disconnector DS22, the other end of the neutral line is connected to a grounding pole through a seventh disconnector DS4, and the high voltage end and the low voltage end of the delta winding of the second valve group 2 are connected through an eighth disconnector DS23.

[0050] The high voltage end of the delta winding of the first valve group 1 and the high voltage end of the delta winding of the second valve group 2 are connected through a ninth disconnector DS1. The low voltage end of the delta winding of the first valve group 1 and the low voltage end of the delta winding of the second valve group 2 are connected through a tenth disconnector DS2. The star windings of the first valve group 1 and the second valve group 2 are connected to the same AC power grid or different AC power grids.

[0051] The first valve group 1 and the second valve group 2 are in rectification operation or inversion operation respectively, and by closing or opening of each disconnector, power is transmitted from the first valve group 1 to the second valve group 2 or from the second valve group 2 to the first valve group 1.

[0052] In a preferred embodiment, the sub-module types of the first valve group 1 and the second valve group 2 include but are not limited to half-bridge sub-modules, full-bridge sub-modules, full-bridge-like sub-modules, double-embedded sub-modules and hybrid sub-modules.

[0053] In a preferred embodiment, when the first valve group 1 is in rectification operation and the second valve group 2 is in inversion operation, power is transmitted from the first valve group 1 to the second valve group 2. When the first valve group 1 is in inversion operation and the second valve group 2 is in rectification operation, power is transmitted from the second valve group 2 to the first valve group 1.

[0054] In a preferred embodiment, the active type control mode of the first valve group 1 adopts constant DC voltage control, and the active type control mode of the second valve group 2 adopts constant DC power control or constant DC current control; or, the active type control mode of the first valve group 1 adopts constant DC power control or constant DC current control, and the active type control mode of the second valve group 2 adopts constant DC voltage control. The valve group with the active type control mode of constant DC voltage control can be used to stabilize the DC voltage; the valve group with the active type control mode of constant DC power control can be used to adjust the size of the self-circulation power. When the star windings of the first valve group 1 and the second valve group 2 are connected to the same AC power grid, the power transmission and reception of the node or bus connected to the AC power grid is substantially zero, and the AC cross-section power is stabilized.

[0055] In a preferred embodiment, the reactive type control mode of the first valve group 1 and the reactive type control mode of the second valve group 2 can both adopt constant AC voltage control or constant reactive power control. When the constant reactive power control is adopted and the AC power grid voltage is ensured to be stable, the reactive power instructions of the control systems of the corresponding DC converter stations of the first valve group 1 and the second valve group 2 can be set to be positive and negative and equal in absolute value, so as to ensure that the power grid absorbs zero reactive power.

[0056] Embodiment 2

[0057] As shown in Figure 3 , Figure 4 and Figure 5 , the embodiment provides a use method of the UHV flexible DC power self-circulation system, including the following steps:

[0058] 1) disconnect the second disconnector DS3, and isolate the self-circulation system of the embodiment 1 from the station external transmission line.

[0059] 2) correspondingly connect the high-voltage end and the low-voltage end of the delta windings of the first valve group 1 and the second valve group 2.

[0060] Specifically, as shown in Figure 3 , the ninth disconnector DS1 and the tenth disconnector DS2 can be closed, so that the high-voltage end and the low-voltage end of the first valve group 1 and the second valve group 2 are correspondingly connected.

[0061] Specifically, as shown in Figure 4 , the ninth disconnector DS1, the third disconnector DS12, the sixth disconnector DS22 and the eighth disconnector DS23 can be closed, so that the high-voltage end and the low-voltage end of the first valve group 1 and the second valve group 2 are correspondingly connected.

[0062] Specifically, as shown in Figure 5As shown, the first isolating switch DS11, the fourth isolating switch DS13, the fifth isolating switch DS21 and the tenth isolating switch DS2 can be closed, so that the high-pressure end and the low-pressure end of the first valve group 1 and the second valve group 2 are respectively connected.

[0063] 3) Connect the self-circulating system of Example 1 to the grounding electrode.

[0064] Specifically, such as Figure 3 As shown, the first disconnecting switch DS11, the third disconnecting switch DS12, the fourth disconnecting switch DS13, the fifth disconnecting switch DS21 and the eighth disconnecting switch DS23 can be disconnected, and the sixth disconnecting switch DS22 and the seventh disconnecting switch DS4 can be closed to connect the self-circulating system of Embodiment 1 to the ground electrode.

[0065] Specifically, such as Figure 4 As shown, the first isolating switch DS11, the fourth isolating switch DS13 and the fifth isolating switch DS21 can be disconnected, and the seventh isolating switch DS4 can be closed to connect the self-circulating system of Embodiment 1 to the ground electrode.

[0066] Specifically, such as Figure 5 As shown, the third isolating switch DS12, the eighth isolating switch DS23 and the ninth isolating switch DS1 can be disconnected, the sixth isolating switch DS22 and the seventh isolating switch DS4 can be closed, and the self-circulating system can be connected to the grounding electrode.

[0067] 4) Set the first valve group 1 and the second valve group 2 to rectifier operation and inverter operation respectively, so that power is transferred from the first valve group 1 to the second valve group 2; or set the first valve group 1 and the second valve group 2 to inverter operation and rectifier operation respectively, so that power is transferred from the second valve group 2 to the first valve group 1.

[0068] The above embodiments are only used to illustrate the present invention. The structure, connection method and manufacturing process of each component can be varied. All equivalent transformations and improvements made on the basis of the technical solution of the present invention should not be excluded from the protection scope of the present invention.

Claims

1. An extra-high voltage flexible direct current power self-circulation system, characterized in that, The first valve group, the second valve group, the polar line, the valve group connecting line, the neutral line and the grounding pole are included. The high-voltage end of the delta winding of the first valve group is connected to the station external power transmission line through the first disconnecting switch, the polar line and the second disconnecting switch in sequence; the low-voltage end of the delta winding of the first valve group is connected to one end of the valve group connecting line through the third disconnecting switch; and the high-voltage end and the low-voltage end of the delta winding of the first valve group are connected through the fourth disconnecting switch. The high-voltage end of the delta winding of the second valve group is connected to the other end of the valve group connecting line through the fifth disconnecting switch; the low-voltage end of the delta winding of the second valve group is connected to the grounding pole through the sixth disconnecting switch, the neutral line and the seventh disconnecting switch in sequence; and the high-voltage end and the low-voltage end of the delta winding of the second valve group are connected through the eighth disconnecting switch. The high-voltage end of the delta winding of the first valve group and the high-voltage end of the delta winding of the second valve group are connected through the ninth disconnecting switch; the low-voltage end of the delta winding of the first valve group and the low-voltage end of the delta winding of the second valve group are connected through the tenth disconnecting switch; and the star windings of the first valve group and the second valve group are connected to the same AC power grid or different AC power grids. The first valve group and the second valve group are respectively in rectification operation or inversion operation, and power is transmitted from the first valve group to the second valve group or from the second valve group to the first valve group through the closing or opening of the disconnecting switches.

2. The extra-high voltage flexible DC power self-circulation system according to claim 1, characterized in that, The types of the sub-modules of the first valve group and the second valve group include half-bridge sub-modules, full-bridge sub-modules, full-bridge-like sub-modules, double-embedded sub-modules and hybrid sub-modules.

3. The extra-high voltage flexible DC power self-circulation system according to claim 1, characterized in that, The active-type control mode of the first valve group adopts constant DC voltage control, and the active-type control mode of the second valve group adopts constant DC power control or constant DC current control.

4. The extra-high voltage flexible DC power self-circulation system of claim 1, wherein, The active-type control mode of the first valve group adopts constant DC power control or constant DC current control, and the active-type control mode of the second valve group adopts constant DC voltage control.

5. The extra-high voltage flexible DC power self-circulation system of claim 1, wherein, The reactive-type control mode of the first valve group and the second valve group both adopts constant AC voltage control or constant reactive power control.

6. The extra-high voltage flexible DC power self-circulation system of claim 1, wherein, When the first valve group is in rectification operation and the second valve group is in inversion operation, power is transmitted from the first valve group to the second valve group; when the first valve group is in inversion operation and the second valve group is in rectification operation, power is transmitted from the second valve group to the first valve group.

7. A method of using the extra-high voltage flexible DC power self-cycling system according to any one of claims 1 to 6, characterized in that, The first valve group, the second valve group, the polar line, the valve group connecting line, the neutral line and the grounding pole are included. The high-voltage end and the low-voltage end of the delta winding of the first valve group and the delta winding of the second valve group are connected in correspondence respectively; The self-circulation system and the grounding pole are connected. The first valve group and the second valve group are respectively in rectification operation or inversion operation, and power is transmitted from the first valve group to the second valve group or from the second valve group to the first valve group. The active-type control mode of the first valve group adopts constant DC voltage control, and the active-type control mode of the second valve group adopts constant DC power control or constant DC current control.

8. The method of claim 7, wherein, Alternatively, the active-type control mode of the first valve group adopts constant DC power control or constant DC current control, and the active-type control mode of the second valve group adopts constant DC voltage control. ​ 9. The method of claim 7, wherein, The high-pressure end and the low-pressure end of the first valve group and the second valve group are respectively connected in correspondence, comprising: closing the ninth disconnector and the tenth disconnector; or, closing the ninth disconnector, the third disconnector, the sixth disconnector and the eighth disconnector; or, closing the first disconnector, the fourth disconnector, the fifth disconnector and the tenth disconnector.

10. The method of claim 7, wherein, The connection of the self-circulation system and the grounding electrode comprises: opening the first disconnector, the third disconnector, the fourth disconnector, the fifth disconnector and the eighth disconnector, and closing the sixth disconnector and the seventh disconnector; or, opening the first disconnector, the fourth disconnector and the fifth disconnector, and closing the seventh disconnector; or, opening the third disconnector, the eighth disconnector and the ninth disconnector, and closing the sixth disconnector and the seventh disconnector.

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