CN113922406B - Control method of flexible direct current power grid - Google Patents
Control method of flexible direct current power grid Download PDFInfo
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- CN113922406B CN113922406B CN202010664206.XA CN202010664206A CN113922406B CN 113922406 B CN113922406 B CN 113922406B CN 202010664206 A CN202010664206 A CN 202010664206A CN 113922406 B CN113922406 B CN 113922406B
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- 230000006855 networking Effects 0.000 claims abstract description 59
- 230000005540 biological transmission Effects 0.000 claims abstract description 17
- 230000007935 neutral effect Effects 0.000 claims description 66
- 239000002184 metal Substances 0.000 claims description 24
- 238000002955 isolation Methods 0.000 claims description 9
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Classifications
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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
- H02J3/00—Circuit arrangements for AC mains or AC distribution networks
- H02J3/36—Arrangements for transfer of electric power between AC networks via a high-tension DC link
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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
- H02J1/00—Circuit arrangements for DC mains or DC distribution networks
-
- 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
- H02J3/00—Circuit arrangements for AC mains or AC distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
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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
- H02J3/00—Circuit arrangements for AC mains or AC distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/388—Islanding, i.e. disconnection of local power supply from the network
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
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Abstract
The application provides a control method of a flexible direct current power grid. The flexible direct current power grid comprises at least two flexible direct current power transmission converter stations, wherein the flexible direct current power transmission converter stations comprise networking fixed power converter stations or island converter stations and at least one fixed direct current voltage control converter station, at least one of the converter stations is a grounding converter station, and the control method comprises the following steps: when the flexible direct current power grid is started, the flexible direct current power grid is adjusted to a starting topology; preferentially starting the constant direct current voltage control converter station, and electrifying the flexible direct current power grid after starting; starting a networking constant-power converter station and/or an island converter station and integrating the networking constant-power converter station and/or the island converter station into a flexible direct current power grid to operate; the networking constant-power converter station is unlocked according to a constant-direct-current voltage control mode and then is connected with the grid, and the networking constant-power converter station is automatically switched from a constant-direct-current voltage control mode to a networking constant-power control mode after being connected with the grid; and adjusting the power of each converter station to respective target power to finish the starting of the flexible direct current power grid.
Description
Technical Field
The application relates to the technical field of flexible direct current transmission of power systems, in particular to a control method of a flexible direct current power grid.
Background
The direct current power grid is a power transmission system with 'meshes', and has the characteristics of more return connection lines between converters, redundant loops of the direct current lines and high reliability. The key equipment constituting the direct current power grid comprises: high voltage high power VSC converters, high voltage dc breakers, high voltage dc cables, overhead lines, and the like. The failure or maintenance of a single converter station does not affect the operation of other converter stations.
However, as the converter stations in the flexible direct current power grid adopt different control modes, the control method comprises the following steps: the starting and stopping processes of the converter stations in different control modes need to be designed in reasonable steps. So as to realize that the starting and stopping of each station does not cause large disturbance to the converter stations in other running of the direct current power grid.
Patent 201610530551.8 proposes a method for inputting a circuit into a dc network in a multi-terminal flexible dc power transmission system. The method aims at solving the problems that a certain line in the existing multi-terminal flexible direct current transmission system exits from a direct current network due to overhaul and the like, the direct current network is required to be put into operation again after the line is overhauled, and the input line can impact an alternating current-direct current system to cause that the direct current system cannot be put into operation in an electrified mode.
Patent 201910440394.5 describes a method, a device and equipment for starting and stopping a direct-current power distribution network of a star topology, which are used for improving the running stability and reliability of the direct-current power distribution network of the star topology.
Disclosure of Invention
The embodiment of the application provides a control method of a flexible direct current power grid, wherein the flexible direct current power grid comprises at least two flexible direct current power transmission converter stations, the flexible direct current power transmission converter stations comprise networking fixed power converter stations or island converter stations and at least one fixed direct current voltage control converter station, at least one of the converter stations is a grounding converter station, and the control method comprises the following steps: when the flexible direct current power grid is started, the flexible direct current power grid is adjusted to a starting topology; preferentially starting the constant direct current voltage control converter station, and electrifying the flexible direct current power grid after starting; starting a networking constant-power converter station and/or an island converter station and integrating the networking constant-power converter station and/or the island converter station into a flexible direct current power grid to operate; the networking constant-power converter station is unlocked according to a constant-direct-current voltage control mode and then is connected with the grid, and the networking constant-power converter station is automatically switched from a constant-direct-current voltage control mode to a networking constant-power control mode after being connected with the grid; and adjusting the power of each converter station to respective target power to finish the starting of the flexible direct current power grid.
According to some embodiments, the control method further comprises: when the flexible direct current power grid is out of operation, the power of each converter station is reduced to be below a specified threshold value; off-line non-constant direct current voltage control converter stations; after the non-constant direct-current voltage control converter station is completely stopped, stopping the constant direct-current voltage control converter station; and after all the converter stations exit and each voltage and current of the alternating-current and direct-current sides of each converter station are smaller than the corresponding threshold value, adjusting the flexible direct-current power grid to the shutdown topology to exit operation.
According to some embodiments, the networked fixed power converter station, the island converter station, the fixed direct current voltage control converter station and the grounding converter station all comprise an alternating current bus A1, a line incoming switch QF, a converter valve C1, a pole bus switch WPQ1, a pole bus P1, a neutral bus switch NBS and a neutral bus N1, wherein one end of the alternating current bus A1 is connected with an alternating current system; one end of the incoming line switch QF is connected with the other end of the alternating current bus A1; one end of the converter valve C1 is connected with the other end of the inlet wire switch QF; one end of the pole bus switch WPQ1 is connected with a first output end of the converter valve C1; the pole bus P1 is connected with the other end of the pole bus switch WPQ 1; one end of the neutral bus switch NBS is connected with the second output end of the converter valve C1; the neutral bus N1 is connected with the other end of the neutral bus switch NBS;
according to some embodiments, the ground converter station further comprises a station grounding switch NBGS arranged at the ground converter station, one side of the station grounding switch NBGS is grounded, and the other side is connected to the neutral bus N1.
According to some embodiments, the flexible direct current power grid further comprises metal loop switches mbs_1 to mbs_n, direct current line breakers dcb_1 to dcb_n, and a direct current charging resistance unit, wherein the metal loop switches mbs_1 to mbs_n are distributed on a metal loop, and the metal loop connects the flexible direct current power transmission converter station and a neutral bus of a counter station; the direct current pole line breakers DCB_1-DCB_n are distributed on direct current pole lines, and the direct current pole lines are connected with pole buses of the flexible direct current power transmission converter station and the opposite station; the direct-current charging resistance unit is connected with the pole bus switch WPQ1 in parallel, wherein the direct-current charging resistance unit comprises a direct-current charging resistance bypass isolation disconnecting link QS and a direct-current charging resistance Rdc which are connected in series.
According to some embodiments, the adjusting the flexible direct current power grid to a starting topology includes: selecting a grounded converter station; selecting a constant direct current voltage control converter station; selecting a networking fixed-power converter station and/or an island converter station; closing a grounding switch NBGS of the grounding converter station to enable a neutral bus of the flexible direct current power grid to be grounded; closing metal loop switches of all the converter stations to enable neutral buses of all the converter stations to be connected with neutral buses of opposite stations through metal loop; and closing a direct current polar circuit breaker of each converter station except the island converter station, and connecting a polar busbar of each converter station with a polar busbar of a counter station through a direct current polar line, wherein the counter station is the converter station except the island converter station.
According to some embodiments, the start-up dc voltage controlled converter station comprises: setting the selected constant direct current voltage control converter station to a constant direct current voltage control mode; closing a pole bus switch WPQ1 and a neutral bus switch NBS of the constant direct current voltage control converter station, wherein a converter valve C1 of the constant direct current voltage control converter station is reliably connected with a pole bus P1 and a neutral bus N1 respectively; closing an alternating current inlet switch QF, connecting the converter valve C1 with an alternating current bus A1, and charging the converter valve C1 through the alternating current bus A1; and unlocking the constant direct current voltage control converter station after the converter of the constant direct current voltage control converter station is charged, so that the constant direct current voltage control converter station keeps the constant direct current voltage grid-connected operation.
According to some embodiments, the networking fixed power converter station is unlocked according to a fixed direct current voltage control mode and then connected with the power network, and the method comprises the following steps: setting the selected networking constant-power converter station into a constant-direct-current voltage control mode; the method comprises the steps that a pole bus switch WPQ1 of the networking constant-power converter station is opened, a neutral bus switch NBS is closed, and a converter valve C1 of the networking constant-power converter station is isolated from a pole bus P1 and is reliably connected with a neutral bus N1; closing an alternating current inlet switch QF and charging a converter valve C1 of the networking constant-power converter station; unlocking after the charging of a converter valve C1 of the networking constant-power converter station is finished, and keeping the networking constant-power converter station to operate in a constant-direct-current voltage control mode; closing a pole bus switch WPQ1 of the networking constant-power converter station to enable a converter valve C1 of the networking constant-power converter station to be connected with a pole bus P1, wherein the networking constant-power converter station is integrated with a flexible direct-current power grid and is automatically converted from a constant-current voltage control mode to a networking constant-power control mode to operate; and setting an initial power reference value to enable the networking constant-power converter station to operate with power.
According to some embodiments, the incorporating island converter station startup into flexible dc grid operation includes: setting the selected island converter stations to an island control mode; closing a neutral bus switch NBS and a direct current charging resistor bypass isolation disconnecting link QS of the island converter station, wherein a converter valve C1 of the island converter station is reliably connected with a neutral bus N1, and the converter valve C1 of the island converter station is reliably connected with a pole bus P1 through a direct current charging resistor Rdc; closing the island converter station and direct current polar line breakers on two sides of a counter station, and charging the converter valve C1 of the island converter station by the counter station through a direct current charging resistor Rdc of the island converter station; after the converter valve C1 of the island converter station is stably charged, a pole bus switch WPQ1 is closed, the bypass isolation disconnecting link QS of the direct current charging resistor is disconnected, and the direct current charging resistor Rdc is withdrawn from operation; after the charging of the converter valve C1 of the island converter station is completed, the island converter station is unlocked in an island mode, and the alternating current inlet switch QF is closed, so that the island converter station is started.
According to some embodiments, the disabling the non-fixed direct voltage control converter station or disabling the fixed direct voltage control converter station comprises: locking all converters of the converter station to be shut down; opening an alternating current inlet switch QF of each converter station to isolate a converter valve C1 of each converter station from an alternating current bus A1; the pole bus bar switch WPQ1 and the neutral bus bar switch NBS of each of the converter stations are turned on, and the converter valve C1 is isolated from the pole bus bar P1 and the neutral bus bar N1.
According to some embodiments, the adjusting the flexible dc power grid to an off-stream topology out of operation includes: opening a direct current polar line breaker of a to-be-stopped converter station and a counter station, and isolating a neutral bus N1 of the to-be-stopped converter station and a polar bus P1 of the counter station; opening metal loop switches of the to-be-stopped converter station and the opposite station, and isolating a neutral bus N1 of the to-be-stopped converter station from a neutral bus N1 of the opposite station; the grounding point switch NBGS of the grounding converter station is opened to isolate the neutral bus N1 of the grounding converter station from the grounding point.
According to the technical scheme, after the networking fixed-power converter station is put into the direct-current power grid after being unlocked and operated in a fixed direct-current voltage operation mode, the control mode is automatically switched from the fixed direct-current voltage control mode to the fixed active power control mode and the power reference value is automatically set to be 0. The start-stop process of the flexible direct-current power grid defines the start-stop steps of the converter stations with different control modes and the start-up and stop sequences of the converter stations with different control modes in the flexible direct-current power grid, and provides a foundation for smooth implementation of flexible direct-current power grid engineering in the future.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic structural diagram of a flexible dc power grid according to an embodiment of the present application.
Fig. 2 is a schematic diagram of a unipolar structure of a modular multilevel converter according to an embodiment of the present application.
Fig. 3 is a schematic diagram of a starting process of each converter station of the flexible dc power grid according to an embodiment of the present application.
Fig. 4 is a schematic diagram of an outage process of each converter station of the flexible dc power grid according to an embodiment of the present application.
Detailed Description
The following description of the embodiments of the present application will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are some, but not all, of the embodiments of the present application. All other embodiments, which can be made by those skilled in the art based on the embodiments herein without making any inventive effort, are intended to be within the scope of the present application.
It should be understood that the terms "first," "second," and the like in the claims, specification, and drawings of this application are used for distinguishing between different objects and not for describing a particular sequential order. The terms "comprises" and "comprising," when used in the specification and claims of this application, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Fig. 1 is a schematic structural diagram of a flexible dc power grid according to an embodiment of the present application.
As shown in fig. 1, the flexible dc power grid comprises at least two flexible dc power transmission converter stations, including at least one constant dc voltage control converter station S1, a networked constant power converter station S2, S3 or an island converter station S4, at least one of which is a ground converter station.
The constant direct voltage control/ground converter station S1, the networked constant power converter stations S2, S3, the island converter station S4 in fig. 1 each include an ac bus A1, a line incoming switch QF, a converter valve C1, a pole bus switch WPQ1, a pole bus P1, a neutral bus switch NBS, and a neutral bus N1, as shown in fig. 2.
One end of the alternating current bus A1 is connected with an alternating current system. One end of the incoming line switch QF is connected with the other end of the alternating current bus A1. One end of the converter valve C1 is connected with the other end of the inlet wire switch QF. One end of the pole bus switch WPQ1 is connected to the first output end of the converter valve C1. The pole bus P1 is connected to the other end of the pole bus switch WPQ 1. One end of the neutral bus switch NBS is connected with a second output end of the converter valve C1. The neutral bus N1 is connected to the other end of the neutral bus switch NBS.
The ground converter station S1 further includes a station ground switch NBGS disposed in the ground converter station, one side of the station ground switch NBGS being grounded, and the other side being connected to the neutral bus.
The flexible direct current power grid also comprises metal loop switches MBS_1 to MBS_n, direct current line breakers DCB_1 to DCB_n and direct current charging resistor units.
The metal loop switches MBS_1-MBS_n are distributed on a metal loop, and the metal loop is connected with a neutral bus of the flexible direct current transmission converter station and the opposite station. The direct current pole line breakers DCB_1 to DCB_n are distributed on direct current pole lines, and the direct current pole lines are connected with pole buses of the flexible direct current transmission converter station and the opposite station. The direct-current charging resistance unit is connected with the pole bus switch WPQ1 in parallel, wherein the direct-current charging resistance unit comprises a direct-current charging resistance bypass isolation switch QS and a direct-current charging resistance Rdc which are connected in series.
Fig. 3 is a schematic diagram of a starting process of each converter station of the flexible dc power grid according to an embodiment of the present application.
In S110, when the flexible dc power grid is started, the flexible dc power grid is adjusted to a starting topology.
A constant direct voltage control converter station S1, a networked constant power converter station S2, a networked constant power converter station S3, and an island converter station S4 are selected. S1 is selected as the ground converter station.
The grounding switch NBGS of the grounding converter station S1 is closed to ground the neutral bus of the flexible direct current network.
Closing the metal loop switches of each converter station, such as the metal loop switches MBS12 and MBS14 of the grounding converter station S1, the metal loop switches MBS21 and MBS23 of the networking fixed power converter station S2, the metal loop switches MBS32 and MBS34 of the networking fixed power converter station S3 and the metal loop switches MBS41 and MBS43 of the island converter station S4, so that the neutral bus of each converter station is connected with the neutral bus of the opposite station through a metal loop.
The dc line breakers of the individual converter stations, such as dc line breakers DCB12 and DCB14 of the ground converter station S1, dc line breakers DCB21 and DCB23 of the networked fixed power converter station S2, dc line breakers DCB32 and DCB34 of the networked fixed power converter station S3, are closed, and dc line breakers DCB41 and DCB43 of the island converter station S4 are opened, so that the pole bus bars of the individual converter stations are connected with the pole bus bars of the counter stations by means of dc lines. The flexible direct current network is adjusted to the target starting topology.
In S120, the constant dc voltage control converter station S1 is preferentially started, and the flexible dc power grid is electrified after the start.
The selected constant direct voltage control converter station S1 is set to a constant direct voltage control mode. The pole bus bar switch wpq1_s1 and the neutral bus bar switch nbs_s1 of the constant direct current voltage control converter station S1 are closed, and the converter valve c1_s1 of the constant direct current voltage control converter station S1 is reliably connected to the pole bus bar p1_s1 and the neutral bus bar n1_s1, respectively. Closing ac line switch qf_s1, converter valve c1_s1 is connected to ac bus a1_s1, and converter valve c1_s1 is charged via ac bus a1_s1. After the converter of the constant direct voltage control converter station S1 is charged, unlocking operation is performed, so that the constant direct voltage control converter station S1 keeps constant direct voltage grid-connected operation, the direct voltage of the pole buses 1-3 reaches rated direct voltage, and the pole buses 1-3 are electrified and the pole bus 4 is not electrified.
In S130, starting and integrating the networking constant-power converter stations S2 and S3 and the island converter station S4 into a flexible direct-current power grid to operate; the networking constant-power converter stations S2 and S3 are unlocked in a constant-direct-current voltage control mode and then are connected with the power grid, and the networking constant-power converter stations are automatically switched from a constant-direct-current voltage control mode to a networking constant-power control mode after the power grid is connected with the power grid.
The selected networked fixed power converter station S2 is set to a fixed direct voltage control mode. The pole bus switch WPQ1_S2 of the networking fixed-power converter station S2 is opened, the neutral bus switch NBS_S2 is closed, and the converter valve C1_S2 of the networking fixed-power converter station S2 is isolated from the pole bus P1_S2 and is reliably connected with the neutral bus N1_S2. The ac line switch qf_s2 is closed and the converter valve c1_s2 of the networked fixed power converter station S2 is charged. And unlocking the converter valve C1_S2 of the networking constant-power converter station S2 after the charging is completed, and keeping the networking constant-power converter station S2 to operate in a constant-direct-current voltage control mode. Closing a pole bus switch WPQ1_S2 of the networking fixed-power converter station S2, enabling a converter valve C1_S2 of the networking fixed-power converter station S2 to be connected with the pole bus P1_S2, enabling the networking fixed-power converter station S2 to be integrated into a flexible direct-current power grid, and automatically converting from a fixed-direct-current voltage control mode to a networking fixed-power control mode for operation. An initial power reference value is set to cause the networked fixed power converter station S2 to operate with power.
The start-up mode of the networked fixed power converter station S3 is the same as that of the networked fixed power converter station S2.
The selected island converter station S4 is set to the island control mode. Closing a neutral bus switch NBS_S4 and a direct current charging resistor bypass isolation disconnecting link QS_S4 of the island converter station S4, reliably connecting a converter valve C1_S4 of the island converter station S4 with the neutral bus N1S 4, and reliably connecting a converter valve C1_S4 of the island converter station S4 with the pole bus P1_S4 through the direct current charging resistor R_S4. The island converter station S4 is closed, and the direct current line breakers on the two sides of the opposite station are closed, and the opposite station charges the converter valve C1_S4 of the island converter station S4 through the direct current charging resistor R_S4 of the island converter station S4. After the converter valve C1_S4 of the island converter station S4 is stable in charging, the pole bus switch WPQ1_S4 is closed, the direct-current charging resistor bypass isolation switch QS_S4 is opened, and the direct-current charging resistor R_S4 is withdrawn from operation. After the charging of the converter valve c1_s4 of the island converter station S4 is completed, the island converter station S4 is unlocked in an island mode, and the ac inlet switch qf_s4 is closed, so that the island converter station S4 is started.
After the operation is finished, the busbar voltage of each convertor station and the voltage of the direct current line reach rated direct current voltage level, and the direct current power grid is electrified.
In S140, the power of each converter station is adjusted to the respective target power, and the flexible dc grid start is completed.
Setting power reference values Pref of S2 and S3 respectively to transmit power; the power sent by the island station S4 is determined by the transmission power of the new energy source at the ac side, and the starting process is completed after the four stations of the flexible direct current power grid in fig. 1 are balanced.
According to the technical scheme, after the networking fixed-power converter station is put into the direct-current power grid after being unlocked and operated in a fixed-direct-current voltage operation mode, the control mode is automatically switched from the fixed-direct-current voltage control mode to the fixed-active power control mode and the power reference value is automatically set to be 0.
The soft direct power grid starting process defines the starting and stopping steps of the converter stations with different control modes and the starting sequence of the converter stations with different control modes in the soft direct power grid, and provides a foundation for smooth implementation of soft direct power grid engineering in the future.
And in the starting process of the flexible direct-current power grid, the direct-current charging resistor is connected in series into a loop when the island station is started and is charged through the direct-current circuit breaker, the direct-current charging resistor is isolated after the charging is completed, the direct-current circuit breaker is adopted for charging and is matched with the direct-current field series resistor, so that the electric impact during the charging of the island station can be reduced, and the safety of equipment such as valves is ensured.
Fig. 4 is a schematic diagram of an outage process of each converter station of the flexible dc power grid according to an embodiment of the present application.
Likewise, the shutdown process of the flexible direct current network is illustrated by taking fig. 1 as an example.
In S150, when the flexible dc network is shut down, the power of each converter station is reduced below a predetermined threshold.
The threshold may be set, for example, to be close to 0.
An off-stream non-constant direct voltage controlled converter station or an off-stream constant direct voltage controlled converter station comprising the following steps.
In S160, the converter station is controlled by the off-line ac voltage.
All converter valves C1 of the stations S2, S3, S4 to be shut down are blocked. The ac inlet switch QF of each converter station is turned on to isolate the converter valve C1 of each converter station from the ac busbar A1. The pole bus bar switch WPQ1 and the neutral bus bar switch NBS of each converter station are turned on, and the converter valve C1 is isolated from the pole bus bar P1 and the neutral bus bar N1. And each station S2, S3 and S4 exits the flexible direct current power grid.
In S170, the non-constant dc voltage controlled converter station is completely shut down, and then the constant dc voltage controlled converter station is shut down.
The station S1 to be shut down is blocked. The ac line switch qf_s1 is turned on to isolate the converter valve c1_s1 from the ac bus bar a1_s1. The pole bus switch wpq1_s1 and the neutral bus switch nbs_s1 are turned on, and the converter valve c1_s1 is isolated from the pole bus p1_s1 and the neutral bus n1_s1. So far S1 exits the grid.
In S180, after all the converter stations exit and each voltage and current on the ac-dc side of each converter station is smaller than the corresponding threshold, the flexible dc grid is adjusted to the shutdown topology to exit operation.
And opening a direct current polar line breaker DCB of the to-be-stopped converter station and the opposite station, and isolating a neutral bus of the to-be-stopped converter station and a polar bus of the opposite station. And opening a metal loop switch MBS of the to-be-stopped converter station and the opposite station, and isolating a neutral bus of the to-be-stopped converter station from a neutral bus of the opposite station. The ground point switch NBGS of the ground converter station is opened, isolating the neutral bus n1_s1 of the ground converter station S1 from the ground point. The dc grid in fig. 1 has thus far been tuned to a target off-stream topology.
After the shutdown operation is completed, the busbar voltage and the dc line voltage of each converter station in fig. 1 are reduced to approximately 0, and the dc grid in fig. 1 is not electrified.
According to the technical scheme, the start-stop process of the flexible direct-current power grid is provided, the start-stop steps of the converter stations with different control modes and the start-up and stop sequences of the converter stations with different control modes in the flexible direct-current power grid are defined, and a foundation is provided for smooth implementation of flexible direct-current power grid engineering in the future.
The foregoing has outlined rather broadly the more detailed description of embodiments of the present application, wherein specific examples have been provided herein to illustrate the principles and embodiments of the present application, and wherein the above examples are provided to assist in the understanding of the methods and concepts of the present application. Meanwhile, based on the ideas of the present application, those skilled in the art can make changes or modifications on the specific embodiments and application scope of the present application, which belong to the scope of the protection of the present application. In view of the foregoing, this description should not be construed as limiting the application.
Claims (10)
1. A control method of a flexible direct current power network comprising at least two flexible direct current power transmission converter stations including a networked fixed power converter station or island converter station, at least one fixed direct voltage control converter station, wherein at least one of the converter stations is a ground converter station, the control method comprising:
when the flexible direct current power grid is started, the flexible direct current power grid is adjusted to a starting topology;
preferentially starting the constant direct current voltage control converter station, and electrifying the flexible direct current power grid after starting;
starting a networking constant-power converter station and/or an island converter station and integrating the networking constant-power converter station and/or the island converter station into a flexible direct current power grid to operate; the networking constant-power converter station is unlocked according to a constant-direct-current voltage control mode and then is connected with the grid, and the networking constant-power converter station is automatically switched from a constant-direct-current voltage control mode to a networking constant-power control mode after being connected with the grid;
the networking constant-power converter station is unlocked according to a constant direct current voltage control mode and then connected with a network, and comprises:
setting the selected networking constant-power converter station into a constant-direct-current voltage control mode;
the method comprises the steps that a pole bus switch WPQ1 of the networking constant-power converter station is opened, a neutral bus switch NBS is closed, and a converter valve C1 of the networking constant-power converter station is isolated from a pole bus P1 and is reliably connected with a neutral bus N1;
closing an alternating current inlet switch QF and charging a converter valve C1 of the networking constant-power converter station;
unlocking after the charging of a converter valve C1 of the networking constant-power converter station is finished, and keeping the networking constant-power converter station to operate in a constant-direct-current voltage control mode;
closing a pole bus switch WPQ1 of the networking constant-power converter station to enable a converter valve C1 of the networking constant-power converter station to be connected with a pole bus P1, wherein the networking constant-power converter station is integrated with a flexible direct-current power grid and is automatically converted from a constant-current voltage control mode to a networking constant-power control mode to operate;
setting an initial power reference value to enable the networking constant-power converter station to operate with power; and adjusting the power of each converter station to respective target power to finish the starting of the flexible direct current power grid.
2. The control method according to claim 1, further comprising:
when the flexible direct current power grid is out of operation, the power of each converter station is reduced to be below a specified threshold value;
off-line non-constant direct current voltage control converter stations;
after the non-constant direct-current voltage control converter station is completely stopped, stopping the constant direct-current voltage control converter station;
and after all the converter stations exit and each voltage and current of the alternating-current and direct-current sides of each converter station are smaller than the corresponding threshold value, adjusting the flexible direct-current power grid to the shutdown topology to exit operation.
3. The control method of claim 1, wherein the networked fixed power converter station, the island converter station, the fixed dc voltage control converter station, and the ground converter station each comprise:
one end of the alternating current bus A1 is connected with an alternating current system;
one end of the incoming line switch QF is connected with the other end of the alternating current bus A1;
one end of the converter valve C1 is connected with the other end of the inlet wire switch QF;
one end of the pole bus switch WPQ1 is connected with the first output end of the converter valve C1;
a pole busbar P1 connected with the other end of the pole busbar switch WPQ 1;
one end of the neutral bus switch NBS is connected with the second output end of the converter valve C1;
and a neutral bus N1 connected with the other end of the neutral bus switch NBS.
4. A control method according to claim 3, wherein the ground converter station further comprises:
and a station grounding switch NBGS arranged at the grounding converter station, wherein one side of the station grounding switch NBGS is grounded, and the other side of the station grounding switch NBGS is connected with the neutral bus N1.
5. A control method according to claim 3, wherein the flexible direct current network further comprises:
metal loop switches MBS_1-MBS_n are distributed on a metal loop, and the metal loop is connected with a neutral bus of the flexible direct-current power transmission converter station and the opposite station;
the direct current pole line breakers DCB_1 to DCB_n are distributed on direct current pole lines, and the direct current pole lines are connected with pole buses of the flexible direct current transmission converter station and the opposite station;
and the direct-current charging resistance unit is connected with the pole bus switch WPQ1 in parallel, wherein the direct-current charging resistance unit comprises a direct-current charging resistance bypass isolation switch QS and a direct-current charging resistance Rdc which are connected in series.
6. The control method of claim 1, wherein said tuning the flexible dc power grid to a start-up topology comprises:
selecting a grounded converter station;
selecting a constant direct current voltage control converter station;
selecting a networking fixed-power converter station and/or an island converter station;
closing a station grounding switch NBGS of the grounding converter station to enable a neutral bus of the flexible direct current power grid to be grounded;
closing metal loop switches of all the converter stations to enable neutral buses of all the converter stations to be connected with neutral buses of opposite stations through metal loop;
and closing a direct current polar circuit breaker of each converter station except the island converter station, and connecting a polar busbar of each converter station with a polar busbar of a counter station through a direct current polar line, wherein the counter station is the converter station except the island converter station.
7. A control method according to claim 1, wherein the starting fixed dc voltage controlled converter station comprises:
setting the selected constant direct current voltage control converter station to a constant direct current voltage control mode;
closing a pole bus switch WPQ1 and a neutral bus switch NBS of the constant direct current voltage control converter station, wherein a converter valve C1 of the constant direct current voltage control converter station is reliably connected with a pole bus P1 and a neutral bus N1 respectively;
closing an alternating current inlet switch QF, connecting the converter valve C1 with an alternating current bus A1, and charging the converter valve C1 through the alternating current bus A1;
and unlocking the constant direct current voltage control converter station after the converter of the constant direct current voltage control converter station is charged, so that the constant direct current voltage control converter station keeps the constant direct current voltage grid-connected operation.
8. The control method of claim 1, wherein the incorporating island converter station start-up into flexible dc grid operation comprises:
setting the selected island converter stations to an island control mode;
closing a neutral bus switch NBS and a direct current charging resistor bypass isolation disconnecting link QS of the island converter station, wherein a converter valve C1 of the island converter station is reliably connected with a neutral bus N1, and the converter valve C1 of the island converter station is reliably connected with a pole bus P1 through a direct current charging resistor Rdc;
closing the island converter station and direct current polar line breakers on two sides of a counter station, and charging the converter valve C1 of the island converter station by the counter station through a direct current charging resistor Rdc of the island converter station;
after the converter valve C1 of the island converter station is stably charged, a pole bus switch WPQ1 is closed, the bypass isolation disconnecting link QS of the direct current charging resistor is disconnected, and the direct current charging resistor Rdc is withdrawn from operation;
after the charging of the converter valve C1 of the island converter station is completed, the island converter station is unlocked in an island mode, and the alternating current inlet switch QF is closed, so that the island converter station is started.
9. The control method according to claim 2, wherein the disabling the non-constant direct voltage control converter station or disabling the constant direct voltage control converter station comprises:
locking all converters of the converter station to be shut down;
opening an alternating current inlet switch QF of each converter station to isolate a converter valve C1 of each converter station from an alternating current bus A1;
the pole bus bar switch WPQ1 and the neutral bus bar switch NBS of each of the converter stations are turned on, and the converter valve C1 is isolated from the pole bus bar P1 and the neutral bus bar N1.
10. The control method of claim 2, wherein said adjusting the flexible dc grid to an off-stream topology out of operation comprises:
opening a direct current polar line breaker of a to-be-stopped converter station and a counter station, and isolating a neutral bus N1 of the to-be-stopped converter station and a polar bus P1 of the counter station;
opening metal loop switches of the to-be-stopped converter station and the opposite station, and isolating a neutral bus N1 of the to-be-stopped converter station from a neutral bus N1 of the opposite station;
the station grounding switch NBGS of the grounding converter station is opened to isolate the neutral bus N1 of the grounding converter station from the ground point.
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