CN108429278B - LCC-MMC system single valve bank input control method and DC power transmission system - Google Patents

LCC-MMC system single valve bank input control method and DC power transmission system Download PDF

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CN108429278B
CN108429278B CN201810168351.1A CN201810168351A CN108429278B CN 108429278 B CN108429278 B CN 108429278B CN 201810168351 A CN201810168351 A CN 201810168351A CN 108429278 B CN108429278 B CN 108429278B
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direct current
disconnecting link
valve
mmc
lcc
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CN108429278A (en
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杨美娟
王先为
吴金龙
马焕
张�浩
刘永慧
姚为正
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Xuji Group Co Ltd
State Grid Zhejiang Electric Power Co Ltd
XJ Electric Co Ltd
Electric Power Research Institute of State Grid Zhejiang Electric Power Co Ltd
Xian XJ Power Electronics Technology Co Ltd
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Xuji Group Co Ltd
State Grid Zhejiang Electric Power Co Ltd
XJ Electric Co Ltd
Electric Power Research Institute of State Grid Zhejiang Electric Power Co Ltd
Xian XJ Power Electronics Technology Co Ltd
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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
    • 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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  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)
  • Control Of Electrical Variables (AREA)

Abstract

The invention provides a single valve bank input control method of an LCC-MMC system and a direct current transmission system, wherein the LCC valve bank is input after the MMC valve bank is input, and finally, the time sequence setting of the direct current voltage lifting of the valve bank is carried out, so that the ordered online input of the single valve bank of the LCC-MMC system adopting a high-low valve bank series connection type is realized, the normal operation of other valve banks is not influenced, and the method has good application value. The MMC is firstly put into a direct current system, because if the LCC is put into the direct current system firstly, the LCC needs to operate for a long time in a state of being close to zero direct current voltage in the MMC starting charging process, the trigger angle of the LCC is close to 90 degrees, the harmonic wave of an alternating current system is large, the requirement on reactive power support of the system is high, and the system is very unfavorable for the operation stability of the system. And the MMC has good harmonic characteristics and no reactive support requirement, and can not influence the stability of an alternating current system even if the MMC runs in a zero direct current voltage state for a long time.

Description

LCC-MMC system single valve bank input control method and DC power transmission system
Technical Field
The invention belongs to the technical field of direct-current power transmission of a power system, and particularly relates to a single-valve-set input control method of an LCC-MMC system and a direct-current power transmission system.
Background
The hybrid direct-current transmission system combines the advantages of mature traditional direct-current transmission (LCC-HVDC) technology, high transmission capacity, low cost, flexible control of flexible direct-current transmission (VSC-HVDC), independent active and reactive decoupling, no commutation failure and the like, and becomes a research hotspot at the present stage. The modular multilevel converter MMC adopts a submodule cascading technology, has the advantages of strong expansion performance, low harmonic level, small switching loss and the like, is more suitable for matching with the high-voltage large-capacity characteristics of LCC, and forms a hybrid direct-current power transmission system. The sending end adopts the LCC transverter, and the receiving end adopts the LCC-MMC type hybrid direct current transmission system of MMC transverter mainly is applicable to the system that has many conventional direct current feedings in receiving end, can effectively improve the secondary commutation failure scheduling problem of conventional direct current through the introduction of MMC, improves system operating stability.
When the direct-current system is applied to an extra-high voltage high-capacity power transmission field, the LCC converter station mostly adopts a topological structure that two double 12-pulse valve banks are connected in series for operation, the MMC is limited by the pressure resistance level of a switch device, the design difficulty of a control system and the like, and when the direct-current system is applied to extra-high voltage LCC-MMC type mixed direct-current power transmission, the structural form that the two valve banks are connected in series is also considered. In order to increase the flexibility and reliability of system operation, when a single LCC or MMC valve bank needs to be withdrawn due to maintenance or failure, the LCC valve bank and the MMC valve bank in the same position are usually withdrawn at the same time, so that the rest valve banks continue to operate, and the power loss of a direct-current system is reduced. And when the valve bank is overhauled or the fault is cleared, the withdrawn valve bank needs to be put into the on-line state, and the full-pressure running state of the direct-current system is recovered. Therefore, in the extra-high voltage direct current project, the on-line input control of the single valve bank becomes one of important control links, and in the input process of the single valve bank, the normal operation of the other valve banks is not required to be influenced.
At present, research on ultra-high voltage flexible direct current and ultra-high voltage hybrid direct current transmission technologies is still in an initial stage, and few reports are made on the aspect of online investment of single valve banks of a flexible direct current converter station. Although the single valve bank online investment technology of the conventional extra-high voltage direct current system has been researched, due to the difference of the control characteristics of the LCC converter and the MMC converter, the advantages of flexibility in MMC control, good harmonic characteristics and the like, and the characteristics of large harmonic and high reactive power requirements and the like during low-voltage operation of the LCC converter are necessarily combined at the same time, and a more reasonable and ordered single valve bank online investment scheme is made for the LCC-MMC hybrid direct current system.
Disclosure of Invention
The invention aims to provide a single valve bank input control method of an LCC-MMC system and a direct-current power transmission system, which are used for solving the problem of single valve bank on-line input of the LCC-MMC hybrid direct-current power transmission system.
In order to achieve the purpose, the invention provides a single valve bank input control method of an LCC-MMC system, which comprises the following technical scheme:
the method comprises a sending end converter station and a receiving end converter station, wherein the sending end converter station comprises at least two LCC valve sets, the receiving end converter station comprises at least two MMC valve sets, one of the LCC valve sets and one of the MMC valve sets form a group of valve sets, when the valve sets need to be put into, the MMC valve sets to be put into are controlled to be put into, after the MMC valve sets are put into, the LCC valve sets corresponding to the MMC valve sets to be put into are controlled to be put into, and after the LCC valve sets are put into, the direct-current voltage instruction value of the MMC valve sets is controlled to be increased to a rated value.
And in the second method scheme, on the basis of the first method scheme, when the valve banks needing to be put into the first method scheme are at least two groups of valve banks, after one group of valve banks is controlled to be put into the second method scheme, the other valve banks are controlled to be put into the first method scheme in sequence.
In the third method scheme, on the basis of the second method scheme, the input process of the MMC valve group is as follows: the method comprises the steps of charging an MMC valve set, unlocking after charging is finished to conduct fixed direct current control, giving a direct current instruction to be zero, converting the fixed direct current control into fixed direct current voltage control when the direct current instruction of the MMC valve set rises from zero to be the same as the direct current line current, and giving the direct current voltage instruction to be zero.
And on the basis of the second method scheme, the input process of the LCC valve bank is as follows: and when the direct current instruction of the LCC valve bank rises from zero to be the same as the current of the direct current line, the constant direct current control is still adopted for the LCC valve bank, and the direct current instruction is given as the current of the direct current line.
On the basis of the third method scheme, each MMC valve group is respectively provided with a first direct current field switch for controlling the corresponding valve group to be switched in or switched off, a direct current side positive port of each MMC valve group is connected with a positive wire inlet end of the corresponding direct current field switch, and a direct current side negative port of each MMC valve group is connected with a negative wire inlet end of the corresponding direct current field switch; the first direct current field switch comprises a first bypass disconnecting link, a first bypass switch, a first isolation disconnecting link and a second isolation disconnecting link, one end of the first bypass disconnecting link is connected with one end of the first isolation disconnecting link to form a positive outlet terminal of the first direct current field switch, the other end of the first bypass disconnecting link is connected with one end of the second isolation disconnecting link to form a negative outlet terminal of the first direct current field switch, one end of the first bypass switch is connected with the other end of the first isolation disconnecting link to form a positive inlet terminal of the first direct current field switch, and the other end of the first bypass switch is connected with the other end of the second isolation disconnecting link to form a negative inlet terminal of the first direct current field switch; after the MMC valve bank is subjected to constant direct current control, the MMC valve bank is controlled to be in a half-input operation state, wherein the half-input operation state refers to that a first bypass disconnecting link is disconnected, and a first bypass switch, a first isolation disconnecting link and a second isolation disconnecting link are closed; when the direct current instruction of the MMC valve bank rises to the current of the direct current line, the MMC valve bank is controlled to be in an input state, the input state refers to the disconnection of the first bypass disconnecting link and the first bypass switch, and the connection of the first isolation disconnecting link and the second isolation disconnecting link.
On the basis of the fourth method scheme, each LCC valve bank is respectively provided with a second direct current field switch for controlling the corresponding valve bank to be switched on or switched off, a direct current side positive port of each LCC valve bank is connected with a positive incoming line end of the corresponding direct current field switch, and a direct current side negative port of each LCC valve bank is connected with a negative incoming line end of the corresponding direct current field switch; the second direct-current field switch comprises a second bypass disconnecting link, a second bypass switch, a third isolation disconnecting link and a fourth isolation disconnecting link, one end of the second bypass disconnecting link is connected with one end of the third isolation disconnecting link to form a positive wire outlet end of the second direct-current field switch, the other end of the second bypass disconnecting link is connected with one end of the fourth isolation disconnecting link to form a negative wire outlet end of the second direct-current field switch, one end of the second bypass switch is connected with the other end of the third isolation disconnecting link to form a positive wire inlet end of the second direct-current field switch, and the other end of the second bypass switch is connected with the other end of the fourth isolation disconnecting link to form a negative wire inlet end of the second direct-current field switch; before the LCC valve bank is controlled by constant direct current, the LCC valve bank is controlled to be in a half-input operation state, wherein the half-input operation state refers to that a second bypass disconnecting link is disconnected, and a second bypass switch, a third isolation disconnecting link and a fourth isolation disconnecting link are closed; and when the direct current instruction of the LCC valve bank rises to the current of the direct current line, controlling the LCC valve bank to be in an input state, wherein the input state refers to that the second bypass disconnecting link and the second bypass switch are disconnected, and the third isolation disconnecting link and the fourth isolation disconnecting link are closed.
The invention also provides a direct current transmission system, which comprises the following technical scheme:
the first system scheme is that the direct-current transmission system comprises a sending end converter station, a receiving end converter station and a controller, wherein the sending end converter station comprises at least two LCC valve banks, the receiving end converter station comprises at least two MMC valve banks, one of the LCC valve banks and one of the MMC valve banks form a group of valve banks, when the valve banks need to be put into, the controller is used for controlling the MMC valve banks to be put into, after the MMC valve banks are put into and completed, the LCC valve banks corresponding to the MMC valve banks to be put into are controlled to be put into, and after the LCC valve banks are put into and completed, the direct-current voltage instruction value of the MMC valve banks is controlled to rise to a rated value.
And in the second system scheme, on the basis of the first system scheme, when the valve banks needing to be put into the system are at least two groups of valve banks, after one group of valve banks is controlled to be put into the system, the other valve banks are controlled to be put into the system in sequence.
And on the basis of the second system scheme, the input process of the MMC valve group is as follows: the method comprises the steps of charging an MMC valve set, unlocking after charging is finished to conduct fixed direct current control, giving a direct current instruction to be zero, converting the fixed direct current control into fixed direct current voltage control when the direct current instruction of the MMC valve set rises from zero to be the same as the direct current line current, and giving the direct current voltage instruction to be zero.
And on the basis of the second system scheme, the input process of the LCC valve bank is as follows: and when the direct current instruction of the LCC valve bank rises from zero to be the same as the current of the direct current line, the constant direct current control is still adopted for the LCC valve bank, and the direct current instruction is given as the current of the direct current line.
In the fifth system scheme, on the basis of the third system scheme, each MMC valve group is respectively provided with a first direct current field switch for controlling the corresponding valve group to be switched in or switched off, a direct current side positive port of each MMC valve group is connected with a positive inlet wire end of the corresponding direct current field switch, and a direct current side negative port of each MMC valve group is connected with a negative inlet wire end of the corresponding direct current field switch; the first direct current field switch comprises a first bypass disconnecting link, a first bypass switch, a first isolation disconnecting link and a second isolation disconnecting link, one end of the first bypass disconnecting link is connected with one end of the first isolation disconnecting link to form a positive outlet terminal of the first direct current field switch, the other end of the first bypass disconnecting link is connected with one end of the second isolation disconnecting link to form a negative outlet terminal of the first direct current field switch, one end of the first bypass switch is connected with the other end of the first isolation disconnecting link to form a positive inlet terminal of the first direct current field switch, and the other end of the first bypass switch is connected with the other end of the second isolation disconnecting link to form a negative inlet terminal of the first direct current field switch; after the MMC valve bank is subjected to constant direct current control, the MMC valve bank is controlled to be in a half-input operation state, wherein the half-input operation state refers to that a first bypass disconnecting link is disconnected, and a first bypass switch, a first isolation disconnecting link and a second isolation disconnecting link are closed; when the direct current instruction of the MMC valve bank rises to the current of the direct current line, the MMC valve bank is controlled to be in an input state, the input state refers to the disconnection of the first bypass disconnecting link and the first bypass switch, and the connection of the first isolation disconnecting link and the second isolation disconnecting link.
On the basis of the fourth system scheme, each LCC valve bank is respectively provided with a second direct current field switch for controlling the corresponding valve bank to be switched on or switched off, a direct current side positive port of each LCC valve bank is connected with a positive inlet wire end of the corresponding direct current field switch, and a direct current side negative port of each LCC valve bank is connected with a negative inlet wire end of the corresponding direct current field switch; the second direct-current field switch comprises a second bypass disconnecting link, a second bypass switch, a third isolation disconnecting link and a fourth isolation disconnecting link, one end of the second bypass disconnecting link is connected with one end of the third isolation disconnecting link to form a positive wire outlet end of the second direct-current field switch, the other end of the second bypass disconnecting link is connected with one end of the fourth isolation disconnecting link to form a negative wire outlet end of the second direct-current field switch, one end of the second bypass switch is connected with the other end of the third isolation disconnecting link to form a positive wire inlet end of the second direct-current field switch, and the other end of the second bypass switch is connected with the other end of the fourth isolation disconnecting link to form a negative wire inlet end of the second direct-current field switch; before the LCC valve bank is controlled by constant direct current, the LCC valve bank is controlled to be in a half-input operation state, wherein the half-input operation state refers to that a second bypass disconnecting link is disconnected, and a second bypass switch, a third isolation disconnecting link and a fourth isolation disconnecting link are closed; and when the direct current instruction of the LCC valve bank rises to the current of the direct current line, controlling the LCC valve bank to be in an input state, wherein the input state refers to that the second bypass disconnecting link and the second bypass switch are disconnected, and the third isolation disconnecting link and the fourth isolation disconnecting link are closed.
The invention has the beneficial effects that:
the LCC-MMC mixed direct-current power transmission system considers the difference of the control characteristics of the LCC converter and the MMC converter, combines the advantages of flexible control, good harmonic characteristic and the like of the MMC and the characteristics of large harmonic wave, high reactive power demand and the like when the LCC is operated at low voltage, puts the LCC valve bank into the MMC valve bank after putting the LCC valve bank into the MMC valve bank, and finally sets the time sequence for improving the direct-current voltage of the valve bank, thereby realizing the ordered online putting of the single valve bank of the LCC-MMC system adopting a high-low valve bank series connection type, not influencing the normal operation of other valve banks, and having good application value. The MMC is firstly put into a direct current system, because if the LCC is put into the direct current system firstly, the LCC needs to operate for a long time in a state of being close to zero direct current voltage in the MMC starting charging process, the trigger angle of the LCC is close to 90 degrees, the harmonic wave of an alternating current system is large, the requirement on reactive power support of the system is high, and the system is very unfavorable for the operation stability of the system. And the MMC has good harmonic characteristics and no reactive support requirement, and can not influence the stability of an alternating current system even if the MMC runs in a zero direct current voltage state for a long time.
Drawings
FIG. 1 is a schematic diagram of an LCC-MMC single pole system with two valve banks in series;
FIG. 2 is a flow chart of a single valve bank online input control method of the present invention.
Detailed Description
The following further describes embodiments of the present invention with reference to the drawings:
a kind of LCC-MMC mixed direct current transmission system, including sending end electric wire netting, sending end converter station, receiving end electric wire netting and control device, the alternating current side of the sending end converter station is connected with sending end electric wire netting, the alternating current side of the receiving end converter station is connected with receiving end electric wire netting, the sending end converter station includes at least two LCC valves, the receiving end converter station includes at least two MMC valves, the said sending end converter station includes at least two LCC valves, the direct current side cascade connection of each LCC valve sets, each LCC valve set disposes the second direct current field switch which controls the corresponding valve set to put into or cut off separately, the direct current side positive port of each LCC valve set connects with positive inlet wire end of the corresponding direct current field switch, the direct current side negative port of each LCC valve set connects with negative inlet wire end of the corresponding direct current field switch; the receiving end converter station comprises at least two MMC valve groups, each MMC valve group is respectively provided with a first direct current field switch for controlling the corresponding valve group to be switched in or switched off, a direct current side positive port of each MMC valve group is connected with a positive wire inlet end of the corresponding direct current field switch, and a direct current side negative port of each MMC valve group is connected with a negative wire inlet end of the corresponding direct current field switch; and the positive and negative line end of the first LCC valve bank is connected with the positive and negative line end of the first MMC valve bank through a direct-current line. One of them LCC valves and an MMC valves constitute a set of valves, when needs drop into the valves, the controller is used for controlling the MMC valves to be dropped into, after the MMC valves drop into and accomplish, the LCC valves corresponding to the MMC valves to be dropped into are controlled to drop into, after the LCC valves drop into and accomplish, the direct voltage instruction value of the MMC valves is controlled to rise to the rated value.
In this embodiment, when the valve banks to be put into operation are at least two groups of valve banks, after one group of valve banks is controlled to be put into operation, the other valve banks are controlled to be put into operation in sequence.
Specifically, an example of an LCC-MMC unipolar system using a two-valve-block series configuration is shown in fig. 1. The sending end is an LCC converter station, and the receiving end is an MMC converter station. Each end constitutes high low valves topological type by two valves series connection, wherein LCC1, LCC2 is LCC end height respectively, the low-voltage valves, MMC1, MMC2 is MMC end height respectively, the low-voltage valves, the interchange side of LCC1 valves is connected with the send end electric wire netting through first transformer, the interchange side of LCC2 valves passes through the second transformer and is connected with the send end electric wire netting, the interchange side of MMC1 valves passes through the third transformer and is connected with the receive end electric wire netting, the interchange side of MMC2 valves passes through the fourth transformer and is connected with the receive end electric wire netting.
Each valve group direct current side comprises a set of direct current field switch used for switching in or switching off the valve group. The first dc field switch of the MMC1 valve bank includes a first bypass switch BPI1, a first high speed bypass switch BPS1, and first and second isolation switches Q1, Q2. One end of the BPI1 is connected with one end of the Q1 and serves as a positive wire outlet end of the first direct current field switch, the other end of the BPI1 is connected with one end of the Q2 and serves as a negative wire outlet end of the first direct current field switch, one end of the BPS1 is connected with the other end of the Q1 and serves as a positive wire inlet end of the first direct current field switch, and the other end of the BPS1 is connected with the other end of the Q2 and serves as a negative wire inlet end of the first direct current field switch. The second direct current field switch of the LCC1 valve group comprises a second bypass knife switch BPI2, a first high-speed bypass switch BPS2, a first isolation knife switch Q3 and a second isolation knife switch Q4. One end of the BPI2 is connected with one end of the Q3 and serves as a positive wire outlet end of the second direct current field switch, the other end of the BPI2 is connected with one end of the Q4 and serves as a negative wire outlet end of the second direct current field switch, one end of the BPS2 is connected with the other end of the Q3 and serves as a positive wire inlet end of the second direct current field switch, and the other end of the BPS2 is connected with the other end of the Q4 and serves as a negative wire inlet end of the second direct current field switch. Similarly, the structures of the dc field switches corresponding to the other valve banks and the dc field switches of the MMC1 and the LCC1 are the same, and are not described herein again.
The direct current positive and negative ports of the LCC1, the LCC2, the MMC1 and the MMC2 are respectively connected with the positive and negative inlet terminals of the direct current field switch. The negative outlet end of the LCC1 direct-current field switch is connected with the positive outlet end of the LCC2 direct-current field switch, the positive outlet end of the LCC1 direct-current field switch is connected with the positive line of the direct-current circuit, and the negative outlet end of the LCC2 direct-current field switch is grounded. The connection method of the direct current field switch outlet terminal of the MMC valve group is similar to that of the direct current long switch outlet terminal of the LCC valve group.
The working condition that the MMC1 needs to be put into service again after the service of the LCC1 and the MMC1 form a group of valve banks, and the LCC2 and the MMC2 form another group of valve banks is taken as an example for explanation (or the LCC1 and the MMC2, the LCC2 and the MMC1 form a group of valve banks respectively, and the putting strategies are consistent). Before the MMC1 is put into operation, the hybrid system is operated by two valve banks of LCC2 and MMC2 under half-pressure, and direct-current field switches of the LCC1 and the MMC1 are in an exit state; the direct current field switches of the LCC2 and the MMC2 are both in an on state.
Fig. 2 is a flow chart of an online input control scheme of valve groups to be input at each end. When the direct current field switch of each end valve group to be input is in an exit state, firstly, the MMC valve group to be input is input, then the LCC valve group to be input is input, and finally, the direct current voltage of the valve group is increased. In this embodiment, for the MMC1 valve bank, the dc field switch in the exit state means that BPI1 is closed, and BPS1, Q1, and Q2 are all opened; the direct current field switch is in a half-input state, namely BPI1 is disconnected, and BPS1, Q1 and Q2 are all closed; the direct current field switch is in an on state, namely BPI1 and BPS1 are disconnected, and Q1 and Q2 are both closed. Wherein, when the quit state is converted into the half-input state, the operation sequence of each switch is as follows: q1, Q2 are closed first, followed by BPS1 and then by BPI 1.
The process of controlling the valve groups to be put into each end when the direct current field switches of the valve groups to be put into each end are in the running quitting state and the direct current field switches of the other valve groups are in the putting state comprises the following steps, taking an MMC1 valve group and an LCC1 valve group as examples:
A. starting the MMC1 to charge the sub-module capacitor, unlocking after charging, and performing constant direct current control, wherein the direct current instruction is zero;
B. sequentially closing Q1 and Q2 of the MMC1, closing the BPS1, and then opening the BPI1 to convert the direct-current field switch of the MMC1 into a half-input state;
C. the MMC1 dc command gradually increases from zero to the current dc line current level, at which time the current flowing through BPS1 of MMC1 gradually decreases until it is zero, so that BPS1 has a turn-off condition;
D. the BPS1 of the MMC1 is disconnected, so that a direct current field switch of the MMC1 is switched to be in an on state, the MMC1 is switched to be controlled by constant direct current voltage, and a direct current voltage command is given to be zero so as to maintain the original operating voltage and current level of a direct current system;
E. sequentially closing Q3 and Q4 of the LCC1, closing the BPS2, and then opening the BPI2 to enable the direct-current field switch of the LCC1 to be in a half-input state;
F. unlocking the LCC1 by a trigger angle of 90 degrees and adopting constant direct current control, wherein a direct current instruction is gradually increased from zero to the current direct current line current level, and at the moment, the current flowing through the BPS2 of the LCC1 is gradually reduced to zero, so that the BPS2 has a turn-off condition;
G. the BPS2 of the LCC1 is disconnected, so that a direct current field switch of the LCC1 is switched to an on state, the LCC1 keeps constant direct current control, and a direct current command is given to the current level on a current direct current line so as to maintain the original operating voltage and current level of a direct current system;
H. through the operation, the LCC1 and the MMC1 can realize undisturbed online input, but the operating voltage and the power of the LCC1 and the MMC1 are zero at the moment, and the voltage is required to be raised to enable the direct current system to recover full-voltage operation, so that the transmission capacity is improved. For this reason, the MMC1 valve pack should eventually gradually increase the dc voltage command value to the rated value. In the process, the trigger angle of the LCC1 is necessarily reduced by the action of the constant-current controller at the LCC1 end, so that the direct-current voltage of the LCC1 is increased along with the voltage of the MMC1, and the power of the LCC1 and the MMC1 is gradually increased along with the voltage increase.
At this point, the LCC1 and MMC1 are put into service on-line and the dc voltage and power return to normal levels.
The reason why the MMC1 is firstly put into the dc system is that if the LCC1 is put into the dc system firstly, during the starting and charging process of the MMC1, the LCC1 needs to operate for a long time in a state close to zero dc voltage, and at this time, the trigger angle is close to 90 degrees, the harmonic of the ac system is large, the requirement for the reactive support of the system is high, and the operation stability of the system is not very favorable. And the MMC has good harmonic characteristics and no reactive support requirement, and can not influence the stability of an alternating current system even if the MMC runs in a zero direct current voltage state for a long time.
The specific embodiments are given above, but the present invention is not limited to the above-described embodiments. The basic idea of the present invention lies in the above basic scheme, and it is obvious to those skilled in the art that no creative effort is needed to design various modified models, formulas and parameters according to the teaching of the present invention. Variations, modifications, substitutions and alterations may be made to the embodiments without departing from the principles and spirit of the invention, and still fall within the scope of the invention.

Claims (8)

1. The single valve group input control method of the LCC-MMC system is characterized by comprising a sending end converter station and a receiving end converter station, wherein the sending end converter station comprises at least two LCC valve groups, the receiving end converter station comprises at least two MMC valve groups, one of the LCC valve groups and one of the MMC valve groups form a group of valve groups, when the valve groups are required to be input, the input of the MMC valve group to be input is controlled, after the input of the MMC valve groups is finished, the input of the LCC valve group corresponding to the MMC valve group to be input is controlled, and after the input of the LCC valve groups is finished, the direct-current voltage instruction value of the MMC valve group is controlled to rise to a rated value;
the input process of the MMC valve group is as follows: charging the MMC valve bank, unlocking after charging, and performing constant direct current control, wherein a direct current instruction is given to be zero, when the direct current instruction of the MMC valve bank rises from zero to be the same as the direct current of a direct current line, the constant direct current control is converted into constant direct current voltage control, and the direct current voltage instruction is given to be zero;
each MMC valve group is respectively provided with a first direct current field switch for controlling the corresponding valve group to be switched in or cut off, a direct current side positive port of each MMC valve group is connected with a positive wire inlet end of the corresponding direct current field switch, and a direct current side negative port of each MMC valve group is connected with a negative wire inlet end of the corresponding direct current field switch; the first direct current field switch comprises a first bypass disconnecting link, a first bypass switch, a first isolation disconnecting link and a second isolation disconnecting link, one end of the first bypass disconnecting link is connected with one end of the first isolation disconnecting link to form a positive outlet terminal of the first direct current field switch, the other end of the first bypass disconnecting link is connected with one end of the second isolation disconnecting link to form a negative outlet terminal of the first direct current field switch, one end of the first bypass switch is connected with the other end of the first isolation disconnecting link to form a positive inlet terminal of the first direct current field switch, and the other end of the first bypass switch is connected with the other end of the second isolation disconnecting link to form a negative inlet terminal of the first direct current field switch; after the MMC valve bank is subjected to constant direct current control, the MMC valve bank is controlled to be in a half-input operation state, wherein the half-input operation state refers to that a first bypass disconnecting link is disconnected, and a first bypass switch, a first isolation disconnecting link and a second isolation disconnecting link are closed; when the direct current instruction of the MMC valve bank rises to the current of the direct current line, the MMC valve bank is controlled to be in an input state, the input state refers to the disconnection of the first bypass disconnecting link and the first bypass switch, and the connection of the first isolation disconnecting link and the second isolation disconnecting link.
2. The LCC-MMC system single-valve-block putting-in control method of claim 1, wherein when the valve blocks to be put in are at least two groups of valve blocks, after one group of valve blocks is put in, the other valve blocks are put in sequence.
3. The LCC-MMC system single-valve-pack input control method of claim 2, wherein the input process of the LCC valve pack is as follows: and when the direct current instruction of the LCC valve bank rises from zero to be the same as the current of the direct current line, the constant direct current control is still adopted for the LCC valve bank, and the direct current instruction is given as the current of the direct current line.
4. The LCC-MMC system single-valve-bank switching control method of claim 3, wherein each LCC valve bank is configured with a second DC field switch for controlling the switching-in or switching-off of the corresponding valve bank, the DC-side positive port of each LCC valve bank is connected with the positive inlet line end of the corresponding DC field switch, and the DC-side negative port of each LCC valve bank is connected with the negative inlet line end of the corresponding DC field switch; the second direct-current field switch comprises a second bypass disconnecting link, a second bypass switch, a third isolation disconnecting link and a fourth isolation disconnecting link, one end of the second bypass disconnecting link is connected with one end of the third isolation disconnecting link to form a positive wire outlet end of the second direct-current field switch, the other end of the second bypass disconnecting link is connected with one end of the fourth isolation disconnecting link to form a negative wire outlet end of the second direct-current field switch, one end of the second bypass switch is connected with the other end of the third isolation disconnecting link to form a positive wire inlet end of the second direct-current field switch, and the other end of the second bypass switch is connected with the other end of the fourth isolation disconnecting link to form a negative wire inlet end of the second direct-current field switch; before the LCC valve bank is controlled by constant direct current, the LCC valve bank is controlled to be in a half-input operation state, wherein the half-input operation state refers to that a second bypass disconnecting link is disconnected, and a second bypass switch, a third isolation disconnecting link and a fourth isolation disconnecting link are closed; and when the direct current instruction of the LCC valve bank rises to the current of the direct current line, controlling the LCC valve bank to be in an input state, wherein the input state refers to that the second bypass disconnecting link and the second bypass switch are disconnected, and the third isolation disconnecting link and the fourth isolation disconnecting link are closed.
5. A direct current transmission system is characterized by comprising a sending end converter station, a receiving end converter station and a controller, wherein the sending end converter station comprises at least two LCC valve banks, the receiving end converter station comprises at least two MMC valve banks, one of the LCC valve banks and one of the MMC valve banks form a group of valve banks, when the valve banks need to be put into, the controller is used for controlling the MMC valve banks to be put into, after the MMC valve banks are put into, the LCC valve banks corresponding to the MMC valve banks to be put into are controlled to be put into, and after the LCC valve banks are put into, the direct current voltage instruction value of the MMC valve banks is controlled to rise to a rated value;
the input process of the MMC valve group is as follows: charging the MMC valve bank, unlocking after charging, and performing constant direct current control, wherein a direct current instruction is given to be zero, when the direct current instruction of the MMC valve bank rises from zero to be the same as the direct current of a direct current line, the constant direct current control is converted into constant direct current voltage control, and the direct current voltage instruction is given to be zero;
each MMC valve group is respectively provided with a first direct current field switch for controlling the corresponding valve group to be switched in or cut off, a direct current side positive port of each MMC valve group is connected with a positive wire inlet end of the corresponding direct current field switch, and a direct current side negative port of each MMC valve group is connected with a negative wire inlet end of the corresponding direct current field switch; the first direct current field switch comprises a first bypass disconnecting link, a first bypass switch, a first isolation disconnecting link and a second isolation disconnecting link, one end of the first bypass disconnecting link is connected with one end of the first isolation disconnecting link to form a positive outlet terminal of the first direct current field switch, the other end of the first bypass disconnecting link is connected with one end of the second isolation disconnecting link to form a negative outlet terminal of the first direct current field switch, one end of the first bypass switch is connected with the other end of the first isolation disconnecting link to form a positive inlet terminal of the first direct current field switch, and the other end of the first bypass switch is connected with the other end of the second isolation disconnecting link to form a negative inlet terminal of the first direct current field switch; after the MMC valve bank is subjected to constant direct current control, the MMC valve bank is controlled to be in a half-input operation state, wherein the half-input operation state refers to that a first bypass disconnecting link is disconnected, and a first bypass switch, a first isolation disconnecting link and a second isolation disconnecting link are closed; when the direct current instruction of the MMC valve bank rises to the current of the direct current line, the MMC valve bank is controlled to be in an input state, the input state refers to the disconnection of the first bypass disconnecting link and the first bypass switch, and the connection of the first isolation disconnecting link and the second isolation disconnecting link.
6. The direct current transmission system according to claim 5, wherein when the valve banks to be put into use are at least two groups of valve banks, after one group of valve banks is put into use, the other valve banks are put into use in sequence.
7. The direct current transmission system of claim 6, wherein the LCC valve packs are placed into service by: and when the direct current instruction of the LCC valve bank rises from zero to be the same as the current of the direct current line, the constant direct current control is still adopted for the LCC valve bank, and the direct current instruction is given as the current of the direct current line.
8. The direct-current transmission system according to claim 7, wherein each LCC valve bank is provided with a second direct-current field switch for controlling the switching-in or switching-out of the corresponding valve bank, a direct-current side positive port of each LCC valve bank is connected with a positive inlet end of the corresponding direct-current field switch, and a direct-current side negative port of each LCC valve bank is connected with a negative inlet end of the corresponding direct-current field switch; the second direct-current field switch comprises a second bypass disconnecting link, a second bypass switch, a third isolation disconnecting link and a fourth isolation disconnecting link, one end of the second bypass disconnecting link is connected with one end of the third isolation disconnecting link to form a positive wire outlet end of the second direct-current field switch, the other end of the second bypass disconnecting link is connected with one end of the fourth isolation disconnecting link to form a negative wire outlet end of the second direct-current field switch, one end of the second bypass switch is connected with the other end of the third isolation disconnecting link to form a positive wire inlet end of the second direct-current field switch, and the other end of the second bypass switch is connected with the other end of the fourth isolation disconnecting link to form a negative wire inlet end of the second direct-current field switch; before the LCC valve bank is controlled by constant direct current, the LCC valve bank is controlled to be in a half-input operation state, wherein the half-input operation state refers to that a second bypass disconnecting link is disconnected, and a second bypass switch, a third isolation disconnecting link and a fourth isolation disconnecting link are closed; and when the direct current instruction of the LCC valve bank rises to the current of the direct current line, controlling the LCC valve bank to be in an input state, wherein the input state refers to that the second bypass disconnecting link and the second bypass switch are disconnected, and the third isolation disconnecting link and the fourth isolation disconnecting link are closed.
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