CN113991623A - Flexible multi-terminal direct-current power transmission system, direct-current fault ride-through method and control device thereof - Google Patents
Flexible multi-terminal direct-current power transmission system, direct-current fault ride-through method and control device thereof Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/08—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current
- H02H3/087—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current for dc applications
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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
- 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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
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- 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 relates to a flexible multi-terminal direct-current power transmission system, a direct-current fault ride-through method, a control device and a storage medium thereof. The flexible multi-terminal direct-current transmission system comprises a plurality of converter stations, a direct-current transmission line is connected between the converter stations, direct-current conversion switches are arranged at two ends of the direct-current transmission line, and the direct-current fault ride-through method of the flexible multi-terminal direct-current transmission system comprises the following steps: responding to a direct current fault instruction, controlling each converter station to enter a voltage reduction and current limitation state so as to reduce fault current; if the current of the first target direct current transmission line is smaller than the maximum power-on/off current of the direct current change-over switch, controlling the direct current change-over switches at two ends of the first target direct current transmission line to be switched off so as to reduce the current of the first target direct current transmission line to zero; the first target direct current transmission line is a direct current transmission line corresponding to the direct current fault instruction; and restoring the working state of each converter station to the working state before entering the voltage reduction and current limiting state. The method can realize the DC fault ride-through quickly and reliably with low cost.
Description
Technical Field
The present disclosure relates to the field of flexible dc power transmission technologies, and in particular, to a flexible multi-terminal dc power transmission system, a dc fault ride-through method thereof, a control device, and a computer-readable storage medium.
Background
In the operation process of the flexible multi-terminal direct-current transmission system, the removal of direct-current faults and the change of the operation mode of the multi-terminal direct-current transmission system are indispensable operations. These operations involve the breaking of direct current. Switching off the dc current necessitates "forcing" the dc current to zero since the dc current has no natural zero crossing.
The direct current fault ride-through scheme of the flexible multi-terminal direct current transmission system in the prior art has the problems of high construction difficulty, complex structure and high cost.
Disclosure of Invention
In view of the foregoing, there is a need to provide a flexible multi-terminal dc power transmission system, a dc fault ride-through method, a control device and a computer-readable storage medium thereof, which can implement dc zero crossing and dc fault ride-through quickly at low cost.
On one hand, the embodiment of the invention provides a direct current fault ride-through method of a flexible multi-terminal direct current transmission system, the flexible multi-terminal direct current transmission system comprises a plurality of converter stations, direct current transmission lines are connected between the converter stations, direct current conversion switches are arranged at two ends of each direct current transmission line, and the direct current fault ride-through method of the flexible multi-terminal direct current transmission system comprises the following steps: responding to a direct current fault instruction, controlling each converter station to enter a voltage reduction and current limitation state so as to reduce fault current; if the current of the first target direct current transmission line is smaller than the maximum power-on/off current of the direct current change-over switch, controlling the direct current change-over switches at two ends of the first target direct current transmission line to be switched off so as to reduce the current of the first target direct current transmission line to zero; the first target direct current transmission line is a direct current transmission line corresponding to the direct current fault instruction; and restoring the working state of each converter station to the working state before entering the voltage reduction and current limiting state.
In one embodiment, two ends of each direct current change-over switch are provided with isolating switches; if the current of the first target direct current transmission line is smaller than the maximum power-on/off current of the direct current change-over switch, the direct current change-over switches at the two ends of the first target direct current transmission line are controlled to be switched off, so that the step of reducing the current of the first target direct current transmission line to zero further comprises the following steps: disconnecting the isolating switches on the two sides of the direct current change-over switch in the disconnected state.
In one embodiment, the submodule of the converter station is a half-bridge submodule, the submodule includes a first switch tube, a second switch tube, a first energy storage unit and an anti-parallel thyristor, the first switch tube is connected in parallel with the input and output ends of the submodule, the second switch tube is connected in series with the first energy storage unit and then connected in parallel with the input and output ends of the submodule, the anti-parallel thyristor is connected in parallel with the input and output ends of the submodule, and the step of controlling each converter station to enter the voltage reduction and current limiting state includes: and locking the first switching tube and the second switching tube and triggering the anti-parallel thyristor to be conducted so as to enable the converter station to enter a voltage reduction and current limiting state.
In one embodiment, the submodule of the converter station is a half-bridge submodule, the submodule includes a third switching tube, a fourth switching tube and a second energy storage unit, the third switching tube is connected with the input and output end of the submodule in parallel, the fourth switching tube is connected with the second energy storage unit in series and then connected with the input and output end of the submodule in parallel, the third switching tube is an anti-surge current switching tube, and the step of controlling each converter station to enter a voltage reduction and current limiting state includes: and triggering the third switching tube to conduct and locking the fourth switching tube so as to enable the converter station to enter a voltage reduction and current limiting state.
In another aspect, an embodiment of the present invention provides a flexible multi-terminal dc power transmission system, including: a plurality of converter stations; the direct current transmission lines are arranged among the converter stations; the plurality of direct current change-over switches are arranged at two ends of each direct current transmission line; and the control module is connected with each direct current change-over switch and comprises a memory and a processor, the memory stores a computer program, and the processor executes the computer program to realize the steps of the direct current fault ride-through method of the flexible multi-terminal direct current power transmission system.
In one embodiment, the control module is further configured to perform the following steps: responding to the maintenance instruction, and controlling the direct current change-over switches at two ends of the second target direct current transmission line to be switched off; the second target direct current transmission line is a direct current transmission line corresponding to the overhaul instruction.
In one embodiment, the sub-module of the converter station is a half-bridge sub-module, the sub-module includes a first switch tube, a second switch tube and a first energy storage unit, the first switch tube is connected in parallel with the input and output ends of the sub-module, the second switch tube is connected in series with the first energy storage unit and then connected in parallel with the input and output ends of the sub-module, and the first switch tube is an anti-surge current switch tube.
In one embodiment, the anti-surge current switch tube is an IGCT switch tube.
In another aspect, an embodiment of the present invention further provides a control device for a flexible multi-terminal dc power transmission system, where the flexible multi-terminal dc power transmission system includes a plurality of converter stations, a dc power transmission line is connected between the converter stations, dc transfer switches are disposed at two ends of the dc power transmission line, and the control device for the flexible multi-terminal dc power transmission system includes: the first control module is used for responding to a direct current fault instruction and controlling each converter station to enter a voltage reduction and current limitation state so as to reduce fault current; the second control module is used for controlling the direct current change-over switches at two ends of the first target direct current transmission line to be switched off if the current of the first target direct current transmission line is smaller than the maximum switchable current of the direct current change-over switches so as to reduce the current of the first target direct current transmission line to zero; the first target direct current transmission line is a direct current transmission line corresponding to the direct current fault instruction; and the third control module is used for recovering the working state of each converter station to the working state before entering the voltage reduction and current limiting state.
In still another aspect, an embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the steps of the dc fault ride-through method for a flexible multi-terminal dc power transmission system described above.
Based on any of the above embodiments, when a dc fault occurs, the dc transfer switch is used to force the fault current on the dc transmission line to zero, and since the current breaking capability of the dc transfer switch is weak, the converter station of the flexible dc transmission system needs to be controlled to enter the step-down current-limiting state first, so that the current breaking capability of the dc transfer switch is sufficient to cut off the fault current. And after the direct current fault is isolated by the direct current change-over switch, the working state of the converter station is recovered, and the direct current fault ride-through is realized. The direct current fault ride-through method is low in on-state loss, low in equipment investment, compact, light, passive and reliable, and has a good application prospect in a flexible multi-terminal direct current power transmission system, particularly a flexible offshore wind power direct current power grid.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments or the conventional technologies of the present application, the drawings used in the descriptions of the embodiments or the conventional technologies will be briefly introduced below, it is obvious that the drawings in the following descriptions are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a flexible multi-terminal direct-current transmission system in one embodiment;
fig. 2 is a schematic flow chart of a dc fault ride-through method of the flexible multi-terminal dc power transmission system according to an embodiment;
fig. 3 is a schematic structural diagram of a flexible multi-terminal direct-current transmission system in another embodiment;
fig. 4 is a schematic flow chart of a dc fault ride-through method of the flexible multi-terminal dc power transmission system according to another embodiment;
FIG. 5 is a block diagram of sub-modules of the converter station in one embodiment;
fig. 6 is a schematic structural diagram of a submodule of a converter station in another embodiment;
fig. 7 is a block diagram of a control device of the flexible multi-terminal dc power transmission system in one embodiment.
Detailed Description
To facilitate an understanding of the present application, the present application will now be described more fully with reference to the accompanying drawings. Embodiments of the present application are set forth in the accompanying drawings. This application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.
It will be understood that, as used herein, the terms "first," "second," and the like may be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another.
Spatial relational terms, such as "under," "below," "under," "over," and the like may be used herein to describe one element or feature's relationship to another element or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements or features described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary terms "under" and "under" can encompass both an orientation of above and below. In addition, the device may also include additional orientations (e.g., rotated 90 degrees or other orientations) and the spatial descriptors used herein interpreted accordingly.
It will be understood that when an element is referred to as being "connected" to another element, it can be directly connected to the other element or be connected to the other element through intervening elements. Further, "connection" in the following embodiments is understood to mean "electrical connection", "communication connection", or the like, if there is a transfer of electrical signals or data between the connected objects.
As used herein, the singular forms "a", "an" and "the" may include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises/comprising," "includes" or "including," etc., specify the presence of stated features, integers, steps, operations, components, parts, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof. Also, as used in this specification, the term "and/or" includes any and all combinations of the associated listed items.
As described in the background art, the existing dc fault ride-through scheme of the flexible multi-terminal dc transmission system has the problems of high construction difficulty, complex structure and high cost, and the inventor finds that the problem is caused by two technical routes for breaking the dc current. The first technical route is a current converter with fault ride-through capability, represented by full-bridge type, reverse-resistance type and mixed type current converters, the current converter needs to be locked in the direct-current switching-off process, the current converter is high in safety, but the structure of a current converter station is complex, the research on a control method is not mature, so that the investment and operation loss are too high, and the economy is not strong. The second technical route is to configure a dc circuit breaker, and when the forced dc current passes through zero, an auxiliary commutation switch is often used in conjunction with a switching-on/off mode of a power electronic conducting branch, that is, a hybrid dc circuit breaker is used to make the dc current pass through zero, or a high-frequency oscillating current is generated by capacitor pre-charging energy and is superimposed with the current of a through-current branch to generate a zero-crossing point, that is, a mechanical dc circuit breaker is used to make the dc current pass through zero. However, the hybrid dc circuit breaker has large on-state loss and high construction cost. The pre-charging system of the mechanical direct current breaker is difficult to build, and the quick secondary charging of the quick reclosing after the permanent fault is difficult to realize. More importantly, the price quoted by the existing direct-current circuit breaker is extremely expensive, the switching times of the direct-current circuit breaker are far less than those of the alternating-current circuit breaker, and the use cost of single switching is high. In conclusion, the fault ride-through cost of the two schemes is high, and the two schemes are mainly characterized by large increase of equipment investment, occupied area and loss. In a wind power scene of open sea, the problems of high platform construction difficulty, long construction period, high construction cost, trouble in maintenance and the like are faced, new requirements such as higher compactness, light weight, reliability and the like are provided for a current conversion station and switchgear, and the technical level of the existing current converter and switchgear cannot adapt to the new requirements.
Based on the above reasons, the embodiment of the invention provides a direct current fault ride-through method for a flexible multi-terminal direct current transmission system. The flexible multi-end (at least three-end) direct-current transmission system comprises a plurality of converter stations, a direct-current transmission line is connected between the converter stations, and direct-current change-over switches are arranged at two ends of the direct-current transmission line. Compared with a direct-current circuit breaker, the direct-current change-over switch has smaller switching-off current and slower action speed, is difficult to be directly used as direct-current fault switching-off equipment, but has the cost far lower than that of the direct-current circuit breaker and is widely applied to the operation mode switching of a flexible direct-current power transmission system. For example, a dc transfer Switch is used as a Neutral Switch (NBS), a Neutral Grounding Switch (NBGS), an Earth Return Transfer Breaker (ERTB), a Metal Return Transfer Breaker (MRTB), and the like. Taking the three-terminal flexible dc transmission system in fig. 1 as an example, the plurality of converter stations includes a converter station H1, a converter station H2, and a converter station H3. The direct-current transmission lines connected between the converter stations comprise a direct-current transmission line L1, a direct-current transmission line L2 and a direct-current transmission line L3. The direct current change-over switches arranged at two ends of each direct current transmission line comprise a direct current change-over switch SA1, a direct current change-over switch SA2, a direct current change-over switch SB1, a direct current change-over switch SB2, a direct current change-over switch SC1 and a direct current change-over switch SC 2.
As shown in fig. 2, the dc fault ride-through method of the flexible multi-terminal dc power transmission system includes steps S202 to S206.
And S202, responding to the direct current fault instruction, and controlling each converter station to enter a voltage reduction and current limitation state so as to reduce the fault current.
It can be understood that the dc fault command is used to indicate that a dc fault has occurred in the dc transmission line. The dc fault command may be generated after being detected by any dc fault detection method. Since the dc switching switch has a weak dc breaking capability, the fault current needs to be reduced to allow the dc current to pass through the dc switching switch. And because all the converter stations of the flexible multi-terminal direct-current transmission system are connected, the output current and voltage of each converter station will affect each other, so that the fault current can be reduced only by controlling all the converter stations of the flexible direct-current transmission system to enter a voltage reduction and current limitation state. And cutting off the energy storage module of the submodule of the converter station by controlling a switching tube of the converter station so as to enable the converter station to enter a voltage reduction and current limiting state. Specifically, when a dc short-circuit fault occurs in the dc transmission line L1, the converter station H1, the converter station H2, and the converter station H3 are all controlled to enter the step-down current limiting state.
And S204, if the current of the first target direct current transmission line is smaller than the maximum power-on/off current of the direct current change-over switch, controlling the direct current change-over switches at the two ends of the first target direct current transmission line to be switched off so as to reduce the current of the first target direct current transmission line to zero.
The first target direct current transmission line is a direct current transmission line corresponding to the direct current fault instruction. It can be understood that the first target dc transmission line is a dc transmission line with a dc fault, and when a fault current flowing through the first target dc transmission line is smaller than a maximum disconnectable current of the dc transfer switch, the fault current of the first target dc transmission line can be damped to zero by using an arc extinguishing capability of the dc transfer switch. Specifically, when the fault current of the dc conversion line L1 is smaller than the maximum switchable currents of the dc conversion switch SA1 and the dc conversion switch SA2, the dc conversion switch SA1 and the dc conversion switch SA2 are controlled to be switched off, so that the fault current of the dc transmission line L1 is reduced to zero.
And S206, restoring the working state of each converter station to the working state before entering the voltage reduction and current limiting state.
It can be understood that when the first target dc transmission line with the dc fault is isolated by the dc transfer switches on both sides, all the converter stations can exit the step-down current-limiting state and recover to the working state before entering the step-down current-limiting state, and due to the characteristic of interconnection of the flexible multi-terminal dc transmission systems, the load transmitted by the first target dc transmission line can be transferred by other converter stations, thereby reducing the influence on the flexible multi-terminal dc transmission system when the dc fault occurs. Specifically, when the dc transfer switch SA1 and the dc conversion switch SA2 are both off, the originally transmitted load of the dc transmission line L1 is transmitted between the converter station H1 and the converter station H2 through a transfer loop formed by the dc transmission line L2, the converter station H3, and the dc transmission line L3 after the converter station H1, the converter station H2, and the converter station H3 recover to the operating state before entering the step-down current-limiting state.
Based on the dc fault ride-through method of the flexible multi-terminal dc power transmission system in this embodiment, the dc transfer switch is utilized to force the fault current on the dc power transmission line to zero when the dc fault occurs, and since the current breaking capability of the dc transfer switch is weak, the converter station of the flexible dc power transmission system needs to be controlled first to enter the step-down current-limiting state, so that the current breaking capability of the dc transfer switch is sufficient to cut off the fault current. And after the direct current fault is isolated by the direct current change-over switch, the working state of the converter station is recovered, and the direct current fault ride-through is realized. The direct current fault ride-through method is low in on-state loss, low in equipment investment, compact, light, passive and reliable, and has a good application prospect in a flexible multi-terminal direct current power transmission system, particularly a flexible offshore wind power direct current power grid.
In one embodiment, two ends of each dc conversion switch are provided with a disconnecting switch, as shown in fig. 3, two sides of the dc conversion switch SA1 are provided with disconnecting switches QKA1 and QKA2, two sides of the dc conversion switch SA2 are provided with disconnecting switches QKA3 and QKA4, two sides of the dc conversion switch SB1 are provided with disconnecting switches QKB1 and QKB2, two sides of the dc conversion switch SB2 are provided with disconnecting switches QKB3 and QKB4, two sides of the dc conversion switch SC1 are provided with disconnecting switches QKC1 and QKC2, and two sides of the dc conversion switch SC2 are provided with disconnecting switches QKC3 and QKC 4. As shown in fig. 4, the dc fault ride-through method of the flexible multi-terminal dc power transmission system includes steps S402 to S408.
And S402, responding to the direct current fault instruction, and controlling each converter station to enter a voltage reduction and current limitation state so as to reduce the fault current.
Step S402 is the same as step S202, and the above can be referred to.
S404, if the current of the first target direct current transmission line is smaller than the maximum power-on/off current of the direct current change-over switch, the direct current change-over switches at the two ends of the first target direct current transmission line are controlled to be switched off so as to reduce the current of the first target direct current transmission line to zero.
Step S404 is the same as step S204, and the above can be referred to.
And S406, disconnecting the isolating switches on the two sides of the direct current change-over switch in the disconnected state.
It is understood that although the dc transfer switch has been configured to disconnect the dc fault, it is difficult to directly observe whether the dc transfer switch is in the open state or the closed state from the outside of the dc transfer switch due to structural limitations of the dc transfer switch, and it is difficult for a serviceman to determine whether a reliable insulation gap is formed when performing maintenance. Therefore, the isolating switches are arranged on two sides of each direct current change-over switch, obvious disconnection marks are formed when the isolating switches are disconnected, and maintenance personnel can easily judge whether the first target direct current transmission line has established a reliable insulation interval. Specifically, the dc transfer switches SA1 and SA2 are controlled to be turned off, and then the isolation switches QKA1, QKA2, QKA3, and QKA4 are also controlled to be turned off.
And S408, restoring the working state of each converter station to the working state before entering the voltage reduction and current limiting state.
Step S408 is the same as step S206, and the above can be referred to.
In one embodiment, the submodules of the converter station are half-bridge type submodules, as shown in fig. 5, the submodules include a first switch tube 501, a second switch tube 502, a first energy storage unit 503 and an anti-parallel thyristor 504. The first switch tube 501 and the second switch tube 502 have the same structure, and each of them includes a transistor and a diode connected in inverse parallel with the transistor. The transistors are often IGBT transistors. The first switch tube 501 is connected in parallel with the input and output ends of the sub-module, and the second switch tube 502 is connected in series with the first energy storage unit 503 and then connected in parallel with the input and output ends of the sub-module. When the sub-modules of the converter station work, the states of bypassing or charging the first energy storage unit can be switched by adjusting the control signals of the first switching tube and the second switching tube, so that the conversion is realized under the matching work of the sub-modules. The anti-parallel thyristor 504 is connected in parallel with the input and output terminals of the submodule. The step of controlling each converter station to enter a step-down current-limiting state comprises the following steps: and locking the first switching tube 501 and the second switching tube 502 and triggering the anti-parallel thyristor to conduct 504, so that the converter station enters a voltage reduction and current limiting state. It can be understood that when the first switch tube 501 and the second switch tube 502 are both locked and the anti-parallel thyristor 504 is turned on, the voltage at the input and output ends of the submodule is the on-state voltage drop of the anti-parallel thyristor 504, and can be regarded as zero, so as to implement voltage reduction of the submodule. Meanwhile, the first energy storage unit 503 cannot output current to the input and output ends of the sub-module through the second switching tube 502, so that current limitation of the sub-module is realized. The anti-parallel thyristor 504 receives a surge current generated when the converter station is switched to a state, and smoothly completes the state switching of the converter station.
In one embodiment, as shown in fig. 6, the sub-module of the converter station is a half-bridge sub-module, the sub-module includes a third switching tube 601, a fourth switching tube 602 and a second energy storage unit 603, the third switching tube 601 is connected in parallel with the input and output ends of the sub-module, the fourth switching tube 602 is connected in series with the second energy storage unit 603 and then connected in parallel with the input and output ends of the sub-module, and the fourth switching tube 602 is an anti-inrush current switching tube. The third switch 601 and the fourth switch 602 are similar in structure and each includes a transistor and a diode connected in anti-parallel with the transistor. The difference is that the third switching tube 601 is a switching tube with high surge current resistance. In a specific embodiment, the transistor of the third switch tube 601 is selected as an IGCT tube to improve the surge current resistance of the third switch tube 601. The step of controlling each converter station to enter a step-down current-limiting state comprises the following steps: and triggering the third switching tube 601 to conduct and lock the fourth switching tube 602, so that the converter station enters a voltage reduction and current limiting state. It can be understood that when the third switching tube 601 is turned on, the voltage at the input and output terminals of the sub-module is the conduction voltage drop of the third switching tube 601, and can be regarded as zero, so as to implement voltage reduction of the sub-module. Meanwhile, the second energy storage unit 603 cannot output current to the input and output ends of the sub-module through the fourth switching tube 602, so that current limitation of the sub-module is realized. By utilizing the characteristic that the third switching tube 601 has high surge resistance, the third switching tube 601 can bear surge current generated when the converter station is switched, and the state switching of the converter station is smoothly completed.
Regarding the parameter selection of the dc transfer switch, firstly, the transient on-off voltage of the dc transfer switch may be selected according to the parameters of the flexible multi-terminal dc transmission system and the requirement for the dc fault ride-through speed. The larger the equivalent inductance parameter of the flexible multi-terminal direct current transmission system is, the faster the fault ride-through speed requirement is, the higher the transient on-off voltage of the direct current conversion switch is, but the more generally the transient on-off voltage is smaller than the system voltage. Therefore, the on-off capacity of the direct current change-over switch can be ensured to be smaller than the on-off capacity requirement of the converter station in the conventional means of utilizing the direct current breaker to carry out forced zero crossing of direct current. Generally, the capacity of the dc transfer switch is less than one tenth of the capacity of the dc breaker. In addition, the voltage level of the direct current change-over switch can be adaptively selected according to the voltage level of the flexible multi-terminal direct current transmission system.
It should be understood that although the steps in the flowcharts of fig. 2 and 4 are shown in order as indicated by the arrows, the steps are not necessarily performed in order as indicated by the arrows. The steps are not performed in the exact order shown and described, and may be performed in other orders, unless explicitly stated otherwise. Moreover, at least some of the steps in fig. 2 and 4 may include multiple steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, which are not necessarily performed in sequence, but may be performed in turn or alternately with other steps or at least some of the other steps.
Referring to fig. 1, an embodiment of the present invention provides a flexible multi-terminal dc power transmission system, which includes a plurality of converter stations, a plurality of dc power transmission lines, a plurality of dc transfer switches, and a control module. A plurality of direct current transmission lines are arranged among the converter stations. The plurality of direct current change-over switches are arranged at two ends of each direct current transmission line. The control module is connected with each direct current transfer switch and comprises a memory and a processor, the memory stores a computer program, and the processor executes the computer program to realize the steps of the direct current fault ride-through method of the flexible multi-terminal direct current power transmission system in any embodiment.
In one embodiment, the control module is further configured to perform the steps of: and responding to the maintenance instruction, and controlling the direct current change-over switches at the two ends of the second target direct current transmission line to be switched off. The second target direct current transmission line is a direct current transmission line corresponding to the overhaul instruction. It can be understood that when the direct current transmission line needs to be overhauled, the direct current change-over switches at the two ends of the direct current transmission line needing to be overhauled are independently operated, and the original transmission power of the second target direct current transmission line is transferred by using other normally working direct current transmission lines and the converter station, so that the switching of the operation mode of the flexible multi-end direct current transmission system is realized. Specifically, taking the flexible multi-terminal dc transmission system in fig. 1 as an example, when the dc transmission line L1 needs to be overhauled, both the dc transfer switch SA1 and the dc conversion switch SA2 are controlled to be turned off, and the originally transmitted load of the dc transmission line L1 is transmitted between the converter station H1 and the converter station H2 through a transfer loop formed by the dc transmission line L2, the converter station H3, and the dc transmission line L3.
In one embodiment, the submodules of the converter station are half-bridge type submodules, as shown in fig. 5, the submodules include a first switch tube 501, a second switch tube 502, a first energy storage unit 503 and an anti-parallel thyristor 504. The first switch tube 501 and the second switch tube 502 have the same structure, and each of them includes a transistor and a diode connected in inverse parallel with the transistor. The transistors are often IGBT transistors. The first switch tube 501 is connected in parallel with the input and output ends of the sub-module, and the second switch tube 502 is connected in series with the first energy storage unit 503 and then connected in parallel with the input and output ends of the sub-module. When the sub-modules of the converter station work, the states of bypassing or charging the first energy storage unit can be switched by adjusting the control signals of the first switching tube and the second switching tube, so that the conversion is realized under the matching work of the sub-modules. The anti-parallel thyristor 504 is connected in parallel with the input and output terminals of the submodule.
In one embodiment, as shown in fig. 6, the sub-module of the converter station is a half-bridge sub-module, the sub-module includes a third switching tube 601, a fourth switching tube 602 and a second energy storage unit 603, the third switching tube 601 is connected in parallel with the input and output ends of the sub-module, the fourth switching tube 602 is connected in series with the second energy storage unit 603 and then connected in parallel with the input and output ends of the sub-module, and the fourth switching tube 602 is an anti-inrush current switching tube. The third switch 601 and the fourth switch 602 are similar in structure and each includes a transistor and a diode connected in anti-parallel with the transistor. The difference is that the third switching tube 601 is a switching tube with high surge current resistance. In a specific embodiment, the transistor of the third switch tube 601 is selected as an IGCT tube to improve the surge current resistance of the third switch tube 601.
The embodiment of the invention also provides a control device of the flexible multi-terminal direct-current transmission system, the flexible multi-terminal direct-current transmission system comprises a plurality of converter stations, a direct-current transmission line is connected between the converter stations, and direct-current change-over switches are arranged at two ends of the direct-current transmission line. Referring to fig. 7, the control apparatus of the flexible multi-terminal dc power transmission system includes a first control module 10, a second control module 30, and a third control module 50. The first control module is used for responding to a direct current fault instruction and controlling each converter station to enter a voltage reduction current limiting state so as to reduce fault current. The second control module is used for controlling the direct current change-over switches at two ends of the first target direct current transmission line to be switched off if the current of the first target direct current transmission line is smaller than the maximum switching-on/off current of the direct current change-over switches so as to reduce the current of the first target direct current transmission line to zero. The first target direct current transmission line is a direct current transmission line corresponding to the direct current fault instruction. And the third control module is used for recovering the working state of each converter station to the working state before entering the voltage reduction and current limitation state.
In one embodiment, two ends of the direct current transfer switch are provided with isolating switches, and the second control module is further used for disconnecting the isolating switches on the two sides of the direct current transfer switch in the disconnected state after controlling the direct current transfer switches on the two ends of the first target direct current transmission line to be disconnected.
In one embodiment, the submodule of the converter station is a half-bridge submodule, and the submodule comprises a first switching tube, a second switching tube, a first energy storage unit and an anti-parallel thyristor, wherein the first switching tube is connected with the input and output end of the submodule in parallel, the second switching tube is connected with the first energy storage unit in series and then connected with the input and output end of the submodule in parallel, and the anti-parallel thyristor is connected with the input and output end of the submodule in parallel. The first control module is used for locking the first switch tube and the second switch tube and triggering the anti-parallel thyristor to be conducted so as to enable the converter station to enter a voltage reduction and current limiting state.
In one embodiment, the submodule of the converter station is a half-bridge submodule, the submodule comprises a third switching tube, a fourth switching tube and a second energy storage unit, the third switching tube is connected with the input end and the output end of the submodule in parallel, the fourth switching tube is connected with the second energy storage unit in series and then connected with the input end and the output end of the submodule in parallel, and the third switching tube is an anti-surge current switching tube. The first control module is used for triggering the third switching tube to be conducted and locking the fourth switching tube so as to enable the converter station to enter a voltage reduction and current limiting state.
For specific limitations of the control device of the flexible multi-terminal dc power transmission system, reference may be made to the above limitations of the dc fault ride-through method of the flexible multi-terminal dc power transmission system, and details are not described herein again. All or part of each module in the control device of the flexible multi-terminal direct-current transmission system can be realized by software, hardware and a combination thereof. The modules can be embedded in a hardware form or independent from a processor in the computer device, and can also be stored in a memory in the computer device in a software form, so that the processor can call and execute operations corresponding to the modules. It should be noted that, in the embodiment of the present application, the division of the module is schematic, and is only one logic function division, and there may be another division manner in actual implementation.
In still another aspect, an embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the steps of the dc fault ride-through method for a flexible multi-terminal dc power transmission system described above.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by hardware related to instructions of a computer program, which can be stored in a non-volatile computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. Any reference to memory, storage, database or other medium used in the embodiments provided herein can include at least one of non-volatile and volatile memory. Non-volatile Memory may include Read-Only Memory (ROM), magnetic tape, floppy disk, flash Memory, optical storage, or the like. Volatile Memory can include Random Access Memory (RAM) or external cache Memory. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM), among others.
In the description herein, references to the description of "some embodiments," "other embodiments," "desired embodiments," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, a schematic description of the above terminology may not necessarily refer to the same embodiment or example.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above examples only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A DC fault ride-through method of a flexible multi-terminal DC power transmission system is characterized in that the flexible multi-terminal DC power transmission system comprises a plurality of converter stations, a DC power transmission line is connected between the converter stations, and DC change-over switches are arranged at two ends of the DC power transmission line, and the DC fault ride-through method of the flexible multi-terminal DC power transmission system comprises the following steps:
responding to a direct current fault instruction, controlling each converter station to enter a voltage reduction and current limitation state so as to reduce fault current;
if the current of a first target direct current transmission line is smaller than the maximum power-on/off current of the direct current change-over switch, controlling the direct current change-over switches at two ends of the first target direct current transmission line to be switched off so as to reduce the current of the first target direct current transmission line to zero; the first target direct current transmission line is the direct current transmission line corresponding to the direct current fault instruction;
and restoring the working state of each converter station to the working state before entering the voltage reduction and current limiting state.
2. The direct-current fault ride-through method of the flexible multi-terminal direct-current transmission system according to claim 1, wherein isolation switches are arranged at two ends of each direct-current change-over switch; if the current of the first target direct current transmission line is smaller than the maximum switchable current of the direct current change-over switch, the direct current change-over switches at the two ends of the first target direct current transmission line are controlled to be switched off, so that the step of reducing the current of the first target direct current transmission line to zero further comprises the following steps:
disconnecting the isolating switches on the two sides of the direct current change-over switch in the disconnected state.
3. The direct-current fault ride-through method for the flexible multi-terminal direct-current transmission system according to claim 1, wherein the submodule of the converter station is a half-bridge submodule, the submodule includes a first switching tube, a second switching tube, a first energy storage unit and an anti-parallel thyristor, the first switching tube is connected in parallel with an input/output end of the submodule, the second switching tube is connected in series with the first energy storage unit and then connected in parallel with an input/output end of the submodule, the anti-parallel thyristor is connected in parallel with an input/output end of the submodule, and the step of controlling each converter station to enter the voltage reduction and current limitation state includes:
and locking the first switch tube and the second switch tube and triggering the anti-parallel thyristor to be conducted so as to enable the converter station to enter the voltage reduction and current limiting state.
4. The direct-current fault ride-through method of the flexible multi-terminal direct-current transmission system according to claim 1, wherein a submodule of the converter station is a half-bridge submodule, the submodule includes a third switching tube, a fourth switching tube and a second energy storage unit, the third switching tube is connected in parallel with an input end and an output end of the submodule, the fourth switching tube is connected in series with the second energy storage unit and then connected in parallel with the input end and the output end of the submodule, the third switching tube is an anti-surge current switching tube, and the step of controlling each converter station to enter the voltage reduction and current limitation state includes:
and triggering the third switching tube to be conducted and locking the fourth switching tube so as to enable the converter station to enter the voltage reduction and current limiting state.
5. A flexible multi-terminal dc power transmission system, comprising:
a plurality of converter stations;
the direct current transmission lines are arranged among the converter stations;
the plurality of direct current change-over switches are arranged at two ends of each direct current transmission line;
a control module connected to each of the dc transfer switches, comprising a memory storing a computer program and a processor, the processor implementing the steps of the dc fault ride-through method of the flexible multi-terminal dc power transmission system according to any one of claims 1 to 4 when executing the computer program.
6. The flexible multi-terminal direct current transmission system according to claim 5, wherein the control module is further configured to perform the steps of:
responding to a maintenance instruction, and controlling the direct current change-over switches at two ends of a second target direct current transmission line to be switched off; the second target direct current transmission line is the direct current transmission line corresponding to the overhaul instruction.
7. The flexible multi-terminal direct-current transmission system according to claim 5, wherein the sub-module of the converter station is a half-bridge sub-module, the sub-module comprises a third switching tube, a fourth switching tube and a second energy storage unit, the third switching tube is connected with the input end and the output end of the sub-module in parallel, the fourth switching tube is connected with the input end and the output end of the sub-module in parallel after being connected with the second energy storage unit in series, and the third switching tube is an anti-surge current switching tube.
8. The flexible multi-terminal direct current transmission system according to claim 7, wherein the anti-surge current switching tube is an IGCT switching tube.
9. The utility model provides a controlling means of flexible multi-terminal direct current transmission system which characterized in that, flexible multi-terminal direct current transmission system includes a plurality of converter stations, be connected with direct current transmission line between the converter station, direct current transmission line both ends are provided with direct current change over switch, flexible multi-terminal direct current transmission system's controlling means includes:
the first control module is used for responding to a direct current fault instruction and controlling each converter station to enter a voltage reduction and current limitation state so as to reduce fault current;
the second control module is used for controlling the direct current change-over switches at two ends of the first target direct current transmission line to be switched off if the current of the first target direct current transmission line is smaller than the maximum switchable current of the direct current change-over switches so as to reduce the current of the first target direct current transmission line to zero; the first target direct current transmission line is the direct current transmission line corresponding to the direct current fault instruction;
and the third control module is used for recovering the working state of each converter station to the working state before entering the voltage reduction and current limiting state.
10. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out the steps of the dc fault ride-through method of the flexible multi-terminal dc power transmission system of any one of claims 1 to 4.
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