CN109361213B - Withdrawal device and method for series converter of hybrid direct-current power transmission system - Google Patents

Withdrawal device and method for series converter of hybrid direct-current power transmission system Download PDF

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CN109361213B
CN109361213B CN201811405436.3A CN201811405436A CN109361213B CN 109361213 B CN109361213 B CN 109361213B CN 201811405436 A CN201811405436 A CN 201811405436A CN 109361213 B CN109361213 B CN 109361213B
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converter
voltage source
direct
source type
parallel
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CN109361213A (en
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赵文强
王永平
黄志岭
俞翔
杨建明
卢宇
李海英
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NR Electric Co Ltd
NR Engineering Co Ltd
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NR Electric Co Ltd
NR Engineering Co Ltd
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    • H02J3/005—
    • 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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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Rectifiers (AREA)
  • Inverter Devices (AREA)

Abstract

The invention discloses a device and a method for withdrawing a series converter of a hybrid direct-current power transmission system, which comprise the following contents: controlling a thyristor converter needing to be withdrawn of the rectification converter station to switch on a direct-current side parallel bypass switch, locking the thyristor converter needing to be withdrawn, disconnecting a direct-current side isolation switch and disconnecting an alternating-current side incoming switch; controlling a voltage source type converter needing to be withdrawn from the inversion converter station to close the direct current side parallel bypass circuit, locking the voltage source type converter needing to be withdrawn, disconnecting the direct current side isolation disconnecting link and disconnecting the alternating current side incoming line switch; and finally, recovering the operating power of the hybrid direct-current transmission system. The invention can effectively solve the problem of online withdrawal of the hybrid converter, realize the online withdrawal of the series VSC converter, reduce the AC/DC current impact during withdrawal and better protect the safety of an AC/DC power transmission system.

Description

Withdrawal device and method for series converter of hybrid direct-current power transmission system
Technical Field
The invention belongs to the field of hybrid direct-current power transmission, and particularly relates to a device and a method for withdrawing a series converter of a hybrid direct-current power transmission system.
Background
High voltage direct current transmission systems can be divided into two types: conventional direct current transmission systems based on thyristor technology (LCC-HVDC) and flexible direct current transmission systems based on fully controlled voltage source converters (VSC-HVDC). The conventional direct current transmission system (LCC-HVDC) has the advantages of low cost, low loss and mature operation technology, and has the disadvantages of easy occurrence of commutation failure on an inversion side, strong dependence on an alternating current system, large reactive power absorption and large occupied area of a converter station. The new generation of flexible direct current transmission system has the advantages of capability of realizing active power and reactive power decoupling control, capability of supplying power to a passive network, compact structure, small occupied area, no problem of inversion side commutation failure and the like, but has the defects of high cost, large loss and the like. In recent years, a hybrid direct-current transmission technology integrating LCC-HVDC and VSC-HVDC technologies has a good engineering application prospect, the LCC-HVDC is adopted on the rectification side, the VSC-HVDC is adopted on the inversion side, the problem of phase commutation failure on the inversion side can be relieved or avoided, and meanwhile, the advantages of engineering cost are guaranteed to a certain extent.
In order to meet the requirement of long-distance large-capacity power transmission, a conventional direct-current power transmission system generally adopts a technology of connecting two or more converters in series to improve the direct-current voltage level and the transmission capacity of the system. Similarly, the current domestic hybrid direct-current transmission project adopts a topological structure that two thyristor converters are connected in series on the rectification side and two voltage source type converters are connected in series or one voltage source type converter and one thyristor converter are connected in series on the inversion side.
For a direct current power transmission system adopting a converter series connection technology, the on-line switching of the converter is a key technology. The online switching of the converters can ensure that the normal operation of the other series converter is not influenced by the switching-out and switching-out operation of the single converter, thereby ensuring the flexibility and the reliability of the operation of the series direct current transmission system. At present, the on-line switching technology of the thyristor type converter of the conventional direct current transmission system is mature, and the on-line switching technology of the voltage source type converter of the hybrid direct current transmission system is still under study. Patent CN106655125A proposes an online input and exit method based on a single valve bank in a hybrid dc system, in which the voltage source converter in the proposed method adopts a full-bridge submodule, is not suitable for a voltage source converter adopting a half-bridge submodule, and has no universality.
Therefore, the invention provides a withdrawal device and a withdrawal method for a series converter of a hybrid direct-current transmission system, which can effectively solve the problem of on-line withdrawal of the hybrid converter, realize the on-line withdrawal of the series VSC, reduce the impact of alternating current and direct current during withdrawal and better protect the safety of each transmission device.
Disclosure of Invention
In order to solve the problems, the invention provides a device and a method for withdrawing a series converter of a hybrid direct-current transmission system, which are applied to the hybrid direct-current transmission system formed by a rectification converter station with a thyristor converter at least at one end and an inverse conversion station with a voltage source converter at one end, can effectively solve the problem of online withdrawal of the hybrid converter, realize online withdrawal of a series VSC converter, reduce the impact of alternating current and direct current during withdrawal and better protect the safety of each transmission device.
In order to achieve the technical purpose and achieve the technical effect, the invention is realized by the following technical scheme:
a mixed direct current transmission system series converter exit device comprises a rectification converter station used for being connected with a transmitting end alternating current power grid, an inversion converter station used for being connected with a receiving end alternating current power grid and a direct current transmission line used for being connected with the rectification converter station and the inversion converter station, wherein the rectification converter station comprises at least one group of thyristor converter units, and the inversion converter station comprises at least one group of voltage source type converter units;
the thyristor converter unit comprises a thyristor converter and a bypass switch which are connected in parallel; or the thyristor converter, the bypass switch and the disconnecting link assembly are included, the thyristor converter is connected with the bypass switch in parallel, two ends of the parallel unit are respectively connected with one end of the connecting disconnecting link, and the other end of the connecting disconnecting link is connected with the bypass disconnecting link in parallel;
the alternating current side of the thyristor converter unit comprises an alternating current incoming line switch and a converter transformer which are connected in series;
the alternating current side of the voltage source type converter unit comprises an alternating current incoming line switch, a converter transformer and a charging resistor which are connected in series, and two ends of the charging resistor are also connected with a bypass switch in parallel;
the voltage source type converter unit comprises a voltage source type converter and a bypass circuit thereof; or the device comprises a voltage source type converter, a bypass circuit of the voltage source type converter and a disconnecting link assembly, wherein two ends of the voltage source type converter and the bypass circuit of the voltage source type converter are respectively connected with one end of a connecting disconnecting link, and the other end of the connecting disconnecting link is connected with the bypass disconnecting link in parallel;
the device for withdrawing the series current converter is used for withdrawing the series current converter on line and comprises a collecting unit, a judging unit and a control unit, wherein:
the acquisition unit is used for acquiring the direct-current voltage, the direct current and the position state of a direct-current field switch disconnecting link of the hybrid direct-current power transmission system, and the current converter quits the starting signal;
the judging unit is used for judging whether the hybrid direct current power transmission system performs the exit operation of the current converter or not according to the analog quantity signals and the digital quantity signals collected by the collecting unit;
the control unit is used for controlling the thyristor converter needing to be withdrawn of the rectification converter station to switch on the direct-current side parallel bypass switch, lock the thyristor converter needing to be withdrawn, switch off the direct-current side isolation switch and switch off the alternating-current side incoming switch when the judging unit detects that the converter withdrawing operation is needed in the hybrid direct-current power transmission system; controlling a voltage source type converter needing to be withdrawn from the inversion converter station to close the direct current side parallel bypass circuit, locking the voltage source type converter needing to be withdrawn, disconnecting the direct current side isolation disconnecting link and disconnecting the alternating current side incoming line switch; and finally, recovering the operating power of the hybrid direct-current transmission system.
Preferably, the control unit specifically executes the following steps when the determination unit detects that the hybrid dc power transmission system needs to perform the converter exiting operation:
(1) controlling the rectification converter station to increase a trigger angle, and controlling the direct-current voltage of the inversion converter station to be reduced to a range allowing the converter to exit;
(2) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a2) locking a voltage source type converter needing to be withdrawn from the inversion converter station;
(b2) a bypass circuit is connected in parallel at the closed direct current side;
(3) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a3) disconnecting the direct current side isolation disconnecting link;
(b3) disconnecting the AC side incoming line switch;
(4) controlling a thyristor converter needing to be exited of the rectification converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a4) closing the direct current side parallel bypass switch;
(b4) locking a thyristor converter which is required to be withdrawn from the rectification converter station;
(5) controlling a thyristor converter needing to be exited of the rectification converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a5) disconnecting the direct current side isolation disconnecting link;
(b5) disconnecting the AC side incoming line switch;
(6) and controlling the rectification converter station to reduce the trigger angle, controlling the inversion converter station to raise the direct-current voltage to a rated value, and recovering the operating power of the hybrid direct-current transmission system.
Preferably, the control unit specifically executes the following steps when the determination unit detects that the hybrid dc power transmission system needs to perform the converter exiting operation:
(21) controlling the rectifying converter station to increase the firing angle and controlling the DC voltage of the inverting converter station to decrease to a value that allows the converter to exit
Within the range;
(22) controlling a thyristor converter needing to be exited of the rectification converter station to operate according to the following two parts
The operation sequence of (A) is not in sequence:
(a22) closing the direct current side parallel bypass switch;
(b22) locking a thyristor converter which is required to be withdrawn from the rectification converter station;
(23) controlling a thyristor converter needing to be exited of the rectification converter station to operate according to the following two parts
The operation sequence of (A) is not in sequence:
(a23) disconnecting the direct current side isolation disconnecting link;
(b23) disconnecting the AC side incoming line switch;
(24) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a24) locking a voltage source type converter needing to be withdrawn from the inversion converter station;
(b24) a bypass circuit is connected in parallel at the closed direct current side;
(25) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a25) disconnecting the direct current side isolation disconnecting link;
(b25) disconnecting the AC side incoming line switch;
(26) and controlling the rectification converter station to reduce the trigger angle, controlling the inversion converter station to raise the direct-current voltage to a rated value, and recovering the operating power of the hybrid direct-current transmission system.
Preferably, the voltage source type converter and the bypass circuit thereof are that the direct current end of the voltage source type converter is connected with the bypass switch in parallel; or the direct current end of the voltage source type converter is connected with the bypass thyristor valve in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with the bypass switch in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with a bypass thyristor valve in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with a bypass switch in parallel, and meanwhile, two ends of the bypass switch are connected with a bypass thyristor valve in parallel; or after the direct current side of the voltage source type converter is connected with a diode valve in series, the direct current side of the voltage source type converter is connected with a bypass switch in parallel through a direct current circuit, and meanwhile, two ends of the bypass switch are connected with a bypass thyristor valve in parallel; or after the direct current side of the voltage source type converter is connected with a diode valve in series, the voltage source type converter is connected with the bypass switch in parallel and is connected with the bypass thyristor valve in parallel through a direct current line; or after the direct current side of the voltage source type converter is connected with the diode valve in series, the voltage source type converter is connected with the bypass thyristor valve in parallel and is connected with the bypass switch in parallel through a direct current circuit.
Preferably, the inverter exit enable signal is triggered by an operator or by a fault signal.
Preferably, the controlling of the rectification converter station to increase the firing angle and the controlling of the dc voltage of the inversion converter station to decrease to the range that allows the converter to exit means controlling the dc voltage of the hybrid dc power transmission system to be lower than a current threshold and controlling the dc voltage to be lower than a voltage threshold.
Preferably, the current threshold value range is 0-0.05 pu, wherein 1pu is rated direct current; the voltage threshold value range is 0-0.2 pu, wherein 1pu is rated direct current voltage.
The invention also provides a method for exiting the series converter of the hybrid direct-current transmission system, wherein the hybrid direct-current transmission system comprises a rectifying converter station for connecting a transmitting end alternating-current power grid, an inverting converter station for connecting a receiving end alternating-current power grid and a direct-current transmission line for connecting the rectifying converter station and the inverting converter station, the rectifying converter station comprises at least one group of thyristor converter units, and the inverting converter station comprises at least one group of voltage source type converter units;
the thyristor converter unit comprises a thyristor converter and a bypass switch which are connected in parallel; or the thyristor converter, the bypass switch and the disconnecting link assembly are included, the thyristor converter is connected with the bypass switch in parallel, two ends of the parallel unit are respectively connected with one end of the connecting disconnecting link, and the other end of the connecting disconnecting link is connected with the bypass disconnecting link in parallel;
the alternating current side of the thyristor converter unit comprises an alternating current incoming line switch and a converter transformer which are connected in series;
the alternating current side of the voltage source type converter unit comprises an alternating current incoming line switch, a converter transformer and a charging resistor which are connected in series, and two ends of the charging resistor are also connected with a bypass switch in parallel;
the voltage source type converter unit comprises a voltage source type converter and a bypass circuit thereof; or the device comprises a voltage source type converter, a bypass circuit of the voltage source type converter and a disconnecting link assembly, wherein two ends of the voltage source type converter and the bypass circuit of the voltage source type converter are respectively connected with one end of a connecting disconnecting link, and the other end of the connecting disconnecting link is connected with the bypass disconnecting link in parallel;
the converter withdrawing method comprises the steps of controlling a thyristor converter needing to be withdrawn of a rectification converter station to switch on a direct-current side parallel bypass switch, locking the thyristor converter needing to be withdrawn, disconnecting a direct-current side isolation switch and disconnecting an alternating-current side incoming switch when detecting that the mixed direct-current power transmission system needs to carry out converter withdrawing operation; controlling a voltage source type converter needing to be withdrawn from the inversion converter station to close the direct current side parallel bypass circuit, locking the voltage source type converter needing to be withdrawn, disconnecting the direct current side isolation disconnecting link and disconnecting the alternating current side incoming line switch; and finally, recovering the operating power of the hybrid direct-current transmission system.
Preferably, the converter exiting method specifically includes the following steps:
(1) controlling the rectification converter station to increase a trigger angle, and controlling the direct-current voltage of the inversion converter station to be reduced to a range allowing the converter to exit;
(2) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a2) locking a voltage source type converter needing to be withdrawn from the inversion converter station;
(b2) a bypass circuit is connected in parallel at the closed direct current side;
(3) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a3) disconnecting the direct current side isolation disconnecting link;
(b3) disconnecting the AC side incoming line switch;
(4) controlling a thyristor converter needing to be exited of the rectification converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a4) closing the direct current side parallel bypass switch;
(b4) locking a thyristor converter which is required to be withdrawn from the rectification converter station;
(5) controlling a thyristor converter needing to be exited of the rectification converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a5) disconnecting the direct current side isolation disconnecting link;
(b5) disconnecting the AC side incoming line switch;
(6) and controlling the rectification converter station to reduce the trigger angle, controlling the inversion converter station to raise the direct-current voltage to a rated value, and recovering the operating power of the hybrid direct-current transmission system.
Preferably, the converter exiting method specifically includes the following steps:
(21) controlling the rectifying converter station to increase the firing angle and controlling the DC voltage of the inverting converter station to decrease to a value that allows the converter to exit
Within the range;
(22) controlling a thyristor converter needing to be exited of the rectification converter station to operate according to the following two parts
The operation sequence of (A) is not in sequence:
(a22) closing the direct current side parallel bypass switch;
(b22) locking a thyristor converter which is required to be withdrawn from the rectification converter station;
(23) controlling a thyristor converter needing to be exited of the rectification converter station to operate according to the following two parts
The operation sequence of (A) is not in sequence:
(a23) disconnecting the direct current side isolation disconnecting link;
(b23) disconnecting the AC side incoming line switch;
(24) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a24) locking a voltage source type converter needing to be withdrawn from the inversion converter station;
(b24) a bypass circuit is connected in parallel at the closed direct current side;
(25) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a25) disconnecting the direct current side isolation disconnecting link;
(b25) disconnecting the AC side incoming line switch;
(26) and controlling the rectification converter station to reduce the trigger angle, controlling the inversion converter station to raise the direct-current voltage to a rated value, and recovering the operating power of the hybrid direct-current transmission system.
Preferably, the voltage source type converter and the bypass circuit thereof are that the direct current end of the voltage source type converter is connected with the bypass switch in parallel; or the direct current end of the voltage source type converter is connected with the bypass thyristor valve in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with the bypass switch in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with a bypass thyristor valve in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with a bypass switch in parallel, and meanwhile, two ends of the bypass switch are connected with a bypass thyristor valve in parallel; or after the direct current side of the voltage source type converter is connected with a diode valve in series, the direct current side of the voltage source type converter is connected with a bypass switch in parallel through a direct current circuit, and meanwhile, two ends of the bypass switch are connected with a bypass thyristor valve in parallel; or after the direct current side of the voltage source type converter is connected with a diode valve in series, the voltage source type converter is connected with the bypass switch in parallel and is connected with the bypass thyristor valve in parallel through a direct current line; or after the direct current side of the voltage source type converter is connected with the diode valve in series, the voltage source type converter is connected with the bypass thyristor valve in parallel and is connected with the bypass switch in parallel through a direct current circuit.
Preferably, the controlling of the rectification converter station to increase the firing angle and the controlling of the dc voltage of the inversion converter station to decrease to the range that allows the converter to exit means controlling the dc voltage of the hybrid dc power transmission system to be lower than a current threshold and controlling the dc voltage to be lower than a voltage threshold.
Preferably, the current threshold value range is 0-0.05 pu, wherein 1pu is rated direct current; the voltage threshold value range is 0-0.2 pu, wherein 1pu is rated direct current voltage.
The invention has the beneficial effects that:
the invention has simple structure and convenient operation, can effectively solve the problem of online withdrawal of the hybrid converter, realizes the online withdrawal of the series VSC converter, reduces the AC/DC current impact during withdrawal and better protects the safety of each device.
Drawings
Fig. 1 shows four topologies of thyristor converter cells and voltage source converter cells connected together;
fig. 2 is a diagram of four topologies of typical thyristor converter cell and voltage source converter cell connections;
FIG. 3 is a two-terminal hybrid ultra-high voltage DC transmission system with a rectification station composed of thyristor converters and an inversion station composed of two hybrid DC converters;
FIG. 4 is a hybrid cascade multi-terminal ultra-high voltage DC transmission system with a rectifying station composed of thyristor converters and an inverting station composed of two hybrid DC converters;
fig. 5 is a hybrid three-terminal dc transmission system in which the rectifying stations 1 and 2 are composed of thyristor converters and the inverting side is composed of a voltage source type converter;
FIG. 6 is a hybrid three-terminal DC transmission system composed of a rectifying station composed of a thyristor converter, an inverting station 1 composed of a thyristor converter, and an inverting station 2 composed of a voltage source type converter connected in parallel;
FIG. 7 is a hybrid three-terminal DC transmission system, in which the rectifying station is composed of a thyristor converter, and the inverting station 1 and the inverting station 2 are both composed of voltage source converters connected in parallel;
fig. 8 is an online exit device for a series converter of a hybrid dc power transmission system according to the present invention;
fig. 9 shows an online exit method for a series converter of a hybrid dc power transmission system according to the present invention.
Detailed Description
The present invention will be better understood and implemented by those skilled in the art by the following detailed description of the technical solution of the present invention with reference to the accompanying drawings and specific examples, which are not intended to limit the present invention. Wherein like components are given like reference numerals.
Fig. 1 shows four topologies of the thyristor converter cell and the voltage source converter cell of the present invention connected. Wherein, fig. 1(a) is a topological structure in which a cathode X1 of the thyristor converter unit is connected with a cathode X4 of the voltage source converter unit; fig. 1(b) is a topology in which the anode X2 of a thyristor converter cell is connected to the anode X3 of a voltage source converter cell; fig. 1(c) is a topology in which the cathode X1 of the thyristor converter cell and the anode X3 of the voltage source converter cell are connected; fig. 1(d) is a topology in which the anode X2 of the thyristor converter cell and the cathode X4 of the voltage source converter cell are connected.
Fig. 2 shows four topologies of the preferred thyristor converter cell and voltage source converter cell connection of the present invention. Wherein fig. 2(a) is a preferred topology in which the cathodes of the thyristor converter cells and the cathodes of the voltage source converter cells are connected; fig. 2(b) is a preferred topology where the anodes of the thyristor converter cells are connected to the anodes of the voltage source converter cells; fig. 2(c) is a preferred topology where the cathode of the thyristor converter cell is connected to the anode of the voltage source converter cell; fig. 2(d) is a preferred topology where the anodes of the thyristor converter cells are connected to the cathodes of the voltage source converter cells. The thyristor converter unit comprises a thyristor converter 1, a bypass switch and a disconnecting link assembly, the thyristor converter 1 is connected with the bypass switch 3 in parallel, two ends of the unit after being connected in parallel are respectively connected with one end of a connecting disconnecting link 5, and the other end of the connecting disconnecting link 5 is connected with the bypass switch or the disconnecting link 4 in parallel. The voltage source type converter unit comprises a voltage source converter 2, a bypass switch and a disconnecting link assembly, the voltage source converter 2 is connected with a current limiting reactor 61 and a blocking diode 32 in series and then is connected with a bypass power electronic switch 71 in parallel, two ends of the unit after being connected in parallel are respectively connected with one end of a valve group connecting line connecting switch or disconnecting link 5 and one end of a bus connecting switch or disconnecting link 5, and the other end of the valve group connecting line connecting switch or disconnecting link 5 and the other end of the bus connecting switch or disconnecting link 5 are connected with the bypass switch or disconnecting link 4 in parallel. In order to match the capacity of the thyristor converter 1, the voltage source converter 2 is a converter or a plurality of converters connected in parallel. Optionally, in order to better suppress the dc fault current, a dc breaker for breaking the dc fault current is added between the voltage source converter 2 and the current limiting reactor 61, or a blocking diode 32 is added in the same direction as the dc current.
The present invention is applicable to the hybrid dc transmission systems shown in fig. 3 and 4, but is not limited to these two transmission systems, and the hybrid three-terminal dc transmission systems shown in fig. 5, 6, and 7 are also applicable to the present invention. Fig. 3 is a specific example to explain the following.
As shown in fig. 3, the hybrid dc power transmission system includes: rectification current conversion station and contravariant current conversion station, both link to each other through two direct current transmission line, wherein: the rectification converter station 20 is used for converting three-phase alternating current of a sending end alternating current grid into direct current and then transmitting the direct current to the inversion converter station 21 through a direct current transmission line, a passive filter 23 can be connected to a bus 10 of the sending end alternating current grid, the bus may be absent, the determination needs to be carried out according to system engineering conditions, when the sending end is composed of a thyristor converter, the passive filter generally needs to be installed, and a reactive compensation capacitor needs to be installed in some cases. In fig. 3, the rectification converter station is formed by connecting two groups of thyristor converter units 1 in series, the series node of the rectification converter station is connected with a grounding electrode 7, and the positive end and the negative end of the rectification converter station after being connected in series are both connected with a direct current transmission line 15 through a smoothing reactor 13; and a DC filter 14 is provided between the DC line and the ground.
The thyristor converter unit adopts a twelve-pulse bridge circuit; each bridge arm is formed by connecting a plurality of thyristors in series, and the thyristor converters are controlled by a constant direct current control strategy. The thyristor converter is connected with a transmitting end alternating current network through a three-winding transformer 8 with the wiring mode of Y0/Y/delta, and the primary sides of the transformers are respectively provided with an alternating current breaker 11. The transformer can carry out voltage grade conversion on three-phase alternating current of a sending end alternating current system so as to adapt to required direct current voltage grade, and the difference of the secondary side wiring modes of the transformer is that upper and lower six-pulse converter bridges of the twelve-pulse bridge thyristor converter provide three-phase alternating current with a phase angle difference of 30 degrees so as to reduce harmonic current flowing into a power grid.
The inversion converter station is used for converting direct current into three-phase alternating current and then transmitting the three-phase alternating current to a receiving end alternating current power grid, and is formed by connecting two groups of voltage source type converters 2 and two groups of thyristor converters 1 in series, wherein the series node of the inversion converter station is connected with a grounding electrode 7, the voltage source type converters are connected with the receiving end alternating current power grid through a double-winding transformer 11 with a wiring mode of Y0/delta, an alternating current circuit breaker 11 is respectively arranged on the primary side of the transformer, the voltage source type converters are controlled by a constant direct current voltage and constant reactive power control strategy, and the thyristor converters are controlled by constant direct current voltage.
As shown in fig. 3, the voltage source converter unit includes a voltage source converter 2 and a bypass circuit 71 thereof, wherein the bypass circuit 71 is connected in parallel to two ends of the voltage source converter 2; or comprises a voltage source type current converter 2 and disconnecting link assemblies 4 and 5, wherein two ends of the voltage source type current converter 2 are respectively connected with one end of a connecting disconnecting link 5, and the other end of the connecting disconnecting link is connected with a bypass disconnecting link 4 in parallel; or the device comprises a voltage source type converter 2, a bypass circuit 71 of the voltage source type converter and disconnecting link assemblies 4 and 5, wherein two ends of the voltage source type converter 2 are connected with the bypass circuit 71 in parallel and then are respectively connected with one end of a connecting disconnecting link 5, and the other end of the connecting disconnecting link is connected with the bypass disconnecting link 4 in parallel; or the voltage source type converter 2 and a bypass circuit 71 thereof, a blocking diode 32 and the disconnecting link assemblies 4 and 5 are included, the voltage source type converter 2 is connected with the blocking diode 32 in series and then is connected with the bypass circuit 71 in parallel, two ends of the bypass circuit 71 are respectively connected with one end of the connecting disconnecting link 5, and the other end of the connecting disconnecting link is connected with the bypass disconnecting link 4 in parallel; or comprises a voltage source type converter 2 and a bypass circuit 71 thereof, a current-limiting reactance 61 and disconnecting link components 4 and 5, wherein the voltage source type converter 2 is connected in series with the current-limiting reactance 61 and then is connected in parallel with the bypass circuit 71, two ends of the bypass circuit 71 are respectively connected with one end of a connecting disconnecting link 5, and the other end of the connecting disconnecting link is connected in parallel with the bypass disconnecting link 4; or the voltage source type converter 2 is connected with the blocking diode 32 in series, the current-limiting reactance 61 is connected with the bypass circuit 71 in parallel after the current-limiting reactance 61, two ends of the bypass circuit 71 are respectively connected with one end of the connecting disconnecting link 5, and the other end of the connecting disconnecting link is connected with the bypass disconnecting link 4 in parallel.
The high-end converter and the low-end converter in the rectification converter station are both thyristor converters 1, the high-end converter in the inversion converter station is a thyristor converter 1, and the low-end converter is a voltage source type converter 2. For example, when the high-end converter and the low-end converter of the rectifying converter station are both in operation, and the high-end converter and the low-end converter of the inverting converter station are both in operation, the connecting switch or disconnecting link 11 of the alternating current bus of the rectifying converter station and the low-end converter are in on position, the bypass switch 3 is in off position, the connecting disconnecting link 5 is in on position, the bypass disconnecting link 4 is in off position, the connecting switch or disconnecting link 11 of the alternating current bus of the high-end converter of the inverting converter station is in on position, the bypass switch 3 is in off position, the connecting disconnecting link 5 is in on position, the bypass disconnecting link 4 is in off position, the connecting switch or disconnecting link 11 of the alternating current bus of the low-end converter of the inverting station is in on position, the bypass circuit 71 is in off position, the connecting disconnecting link 5 is in on position, and the bypass disconnecting link 4 is in off position. When a signal needing to quit the low-end converter is obtained, a trigger angle of a high-end converter and a low-end converter of the rectifying converter station is immediately increased to 164 degrees, so that direct current of a system is reduced to be close to zero, direct voltage of the inverter converter station is reduced to be close to zero, then the low-end thyristor converter 1 of the rectifying converter station is switched on by the bypass switch 3, then the low-end thyristor converter 1 is locked, finally the bypass knife switch 4 is switched on, the bypass switch 3 is disconnected, the connecting knife switch 5 is disconnected, the alternating current bus connecting switch or the knife switch 11 is disconnected, and the low-end thyristor converter 1 of the rectifying station is isolated. When the inversion converter station detects that the direct current is lower than the threshold, the bypass circuit 71 connected with the voltage source type converter in parallel is put into the inversion converter station, then the voltage source type converter 2 is locked, finally the bypass knife switch 4 is closed, the bypass circuit 71 is disconnected, the connecting knife switch 5 is disconnected, the alternating current bus connecting switch or knife switch 11 is disconnected, and the low-end voltage source type converter 2 of the inversion station is isolated. And finally, controlling the rectification converter station to reduce the trigger angle, controlling the inversion converter station to raise the direct-current voltage to a rated value, and recovering the operating power of the hybrid direct-current transmission system.
Fig. 8 shows a hybrid dc power transmission system series converter exit device of the present invention, which includes a collecting unit, a determining unit, and a control unit, and each unit is described in detail below:
the acquisition unit is used for acquiring the direct-current voltage, the direct current and the position state of a direct-current field switch disconnecting link of the hybrid direct-current power transmission system, and the current converter quits the starting signal;
the judging unit is used for judging whether the hybrid direct current power transmission system performs the exit operation of the current converter or not according to the analog quantity signals and the digital quantity signals collected by the collecting unit;
the control unit is used for controlling the thyristor converter needing to be withdrawn of the rectification converter station to switch on the direct-current side parallel bypass switch, lock the thyristor converter needing to be withdrawn, switch off the direct-current side isolation switch and switch off the alternating-current side incoming switch when the judging unit detects that the converter withdrawing operation is needed in the hybrid direct-current power transmission system; controlling a voltage source type converter needing to be withdrawn from the inversion converter station to close the direct current side parallel bypass circuit, locking the voltage source type converter needing to be withdrawn, disconnecting the direct current side isolation disconnecting link and disconnecting the alternating current side incoming line switch; and finally, recovering the operating power of the hybrid direct-current transmission system.
One preferred embodiment 1 is:
the control unit executes the following steps when the judging unit detects that the hybrid direct current power transmission system needs to perform converter quitting operation:
(1) controlling the rectification converter station to increase a trigger angle, and controlling the direct-current voltage of the inversion converter station to be reduced to a range allowing the converter to exit;
(2) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a2) locking a voltage source type converter needing to be withdrawn from the inversion converter station;
(b2) a bypass circuit is connected in parallel at the closed direct current side;
(3) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a3) disconnecting the direct current side isolation disconnecting link;
(b3) disconnecting the AC side incoming line switch;
(4) controlling a thyristor converter needing to be exited of the rectification converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a4) closing the direct current side parallel bypass switch;
(b4) locking a thyristor converter which is required to be withdrawn from the rectification converter station;
(5) controlling a thyristor converter needing to be exited of the rectification converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a5) disconnecting the direct current side isolation disconnecting link;
(b5) disconnecting the AC side incoming line switch;
(6) and controlling the rectification converter station to reduce the trigger angle, controlling the inversion converter station to raise the direct-current voltage to a rated value, and recovering the operating power of the hybrid direct-current transmission system.
A preferred embodiment 2 is:
the control unit executes the following steps when the judging unit detects that the hybrid direct current power transmission system needs to perform converter quitting operation:
(21) controlling the rectification converter station to increase a trigger angle, and controlling the direct-current voltage of the inversion converter station to be reduced to a range allowing the converter to exit;
(22) controlling a thyristor converter needing to be exited of the rectification converter station to operate according to the following two parts
The operation sequence of (A) is not in sequence:
(a22) closing the direct current side parallel bypass switch;
(b22) locking a thyristor converter which is required to be withdrawn from the rectification converter station;
(23) controlling a thyristor converter needing to be exited of the rectification converter station to operate according to the following two parts
The operation sequence of (A) is not in sequence:
(a23) disconnecting the direct current side isolation disconnecting link;
(b23) disconnecting the AC side incoming line switch;
(24) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a24) locking a voltage source type converter needing to be withdrawn from the inversion converter station;
(b24) a bypass circuit is connected in parallel at the closed direct current side;
(25) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a25) disconnecting the direct current side isolation disconnecting link;
(b25) disconnecting the AC side incoming line switch;
(26) and controlling the rectification converter station to reduce the trigger angle, controlling the inversion converter station to raise the direct-current voltage to a rated value, and recovering the operating power of the hybrid direct-current transmission system.
The voltage source type converter and the bypass circuit thereof are characterized in that the direct current end of the voltage source type converter is connected with the bypass switch in parallel; or the direct current end of the voltage source type converter is connected with the bypass thyristor valve in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with the bypass switch in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with a bypass thyristor valve in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with a bypass switch in parallel, and meanwhile, two ends of the bypass switch are connected with a bypass thyristor valve in parallel; or after the direct current side of the voltage source type converter is connected with a diode valve in series, the direct current side of the voltage source type converter is connected with a bypass switch in parallel through a direct current circuit, and meanwhile, two ends of the bypass switch are connected with a bypass thyristor valve in parallel; or after the direct current side of the voltage source type converter is connected with a diode valve in series, the voltage source type converter is connected with the bypass switch in parallel and is connected with the bypass thyristor valve in parallel through a direct current line; or after the direct current side of the voltage source type converter is connected with the diode valve in series, the voltage source type converter is connected with the bypass thyristor valve in parallel and is connected with the bypass switch in parallel through a direct current circuit.
Wherein the converter exit start signal is triggered by an operator or by a fault signal.
The control of the rectification converter station to increase the trigger angle and the control of the direct-current voltage of the inversion converter station to be reduced to the range allowing the converter to exit means that the direct-current voltage of the hybrid direct-current transmission system is controlled to be lower than a current threshold and the direct-current voltage is controlled to be lower than a voltage threshold; the current threshold value range is 0-0.05 pu, wherein 1pu is rated direct current; the voltage threshold value range is 0-0.2 pu, wherein 1pu is rated direct current voltage.
Fig. 9 illustrates a method for exiting a series converter of a hybrid dc power transmission system according to the present invention, where the hybrid dc power transmission system includes a rectifying converter station for connecting to a transmitting-end ac power grid, an inverting converter station for connecting to a receiving-end ac power grid, and a dc power transmission line for connecting the rectifying converter station and the inverting converter station, the rectifying converter station includes at least one set of thyristor converter units, and the inverting converter station includes at least one set of voltage source converter units;
the thyristor converter unit comprises a thyristor converter and a bypass switch which are connected in parallel; or the thyristor converter, the bypass switch and the disconnecting link assembly are included, the thyristor converter is connected with the bypass switch in parallel, two ends of the parallel unit are respectively connected with one end of the connecting disconnecting link, and the other end of the connecting disconnecting link is connected with the bypass disconnecting link in parallel;
the alternating current side of the thyristor converter unit comprises an alternating current incoming line switch and a converter transformer which are connected in series;
the alternating current side of the voltage source type converter unit comprises an alternating current incoming line switch, a converter transformer and a charging resistor which are connected in series, and two ends of the charging resistor are also connected with a bypass switch in parallel;
the voltage source type converter unit comprises a voltage source type converter and a bypass circuit thereof; or the device comprises a voltage source type converter, a bypass circuit of the voltage source type converter and a disconnecting link assembly, wherein two ends of the voltage source type converter and the bypass circuit of the voltage source type converter are respectively connected with one end of a connecting disconnecting link, and the other end of the connecting disconnecting link is connected with the bypass disconnecting link in parallel;
the converter withdrawing method comprises the steps of controlling a thyristor converter needing to be withdrawn of a rectification converter station to switch on a direct-current side parallel bypass switch, locking the thyristor converter needing to be withdrawn, disconnecting a direct-current side isolation switch and disconnecting an alternating-current side incoming switch when detecting that the mixed direct-current power transmission system needs to carry out converter withdrawing operation; controlling a voltage source type converter needing to be withdrawn from the inversion converter station to close the direct current side parallel bypass circuit, locking the voltage source type converter needing to be withdrawn, disconnecting the direct current side isolation disconnecting link and disconnecting the alternating current side incoming line switch; and finally, recovering the operating power of the hybrid direct-current transmission system.
A preferred embodiment 3 is:
the converter exiting method comprises the following steps:
(1) controlling the rectification converter station to increase a trigger angle, and controlling the direct-current voltage of the inversion converter station to be reduced to a range allowing the converter to exit;
(2) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a2) locking a voltage source type converter needing to be withdrawn from the inversion converter station;
(b2) a bypass circuit is connected in parallel at the closed direct current side;
(3) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a3) disconnecting the direct current side isolation disconnecting link;
(b3) disconnecting the AC side incoming line switch;
(4) controlling a thyristor converter needing to be exited of the rectification converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a4) closing the direct current side parallel bypass switch;
(b4) locking a thyristor converter which is required to be withdrawn from the rectification converter station;
(5) controlling a thyristor converter needing to be exited of the rectification converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a5) disconnecting the direct current side isolation disconnecting link;
(b5) disconnecting the AC side incoming line switch;
(6) and controlling the rectification converter station to reduce the trigger angle, controlling the inversion converter station to raise the direct-current voltage to a rated value, and recovering the operating power of the hybrid direct-current transmission system.
A preferred embodiment 4 is:
the converter exiting method comprises the following steps:
(21) controlling the rectifying converter station to increase the firing angle and controlling the DC voltage of the inverting converter station to decrease to a value that allows the converter to exit
Within the range;
(22) controlling a thyristor converter needing to be exited of the rectification converter station to operate according to the following two parts
The operation sequence of (A) is not in sequence:
(a22) closing the direct current side parallel bypass switch;
(b22) locking a thyristor converter which is required to be withdrawn from the rectification converter station;
(23) controlling a thyristor converter needing to be exited of the rectification converter station to operate according to the following two parts
The operation sequence of (A) is not in sequence:
(a23) disconnecting the direct current side isolation disconnecting link;
(b23) disconnecting the AC side incoming line switch;
(24) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a24) locking a voltage source type converter needing to be withdrawn from the inversion converter station;
(b24) a bypass circuit is connected in parallel at the closed direct current side;
(25) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a25) disconnecting the direct current side isolation disconnecting link;
(b25) disconnecting the AC side incoming line switch;
(26) and controlling the rectification converter station to reduce the trigger angle, controlling the inversion converter station to raise the direct-current voltage to a rated value, and recovering the operating power of the hybrid direct-current transmission system.
The voltage source type converter and the bypass circuit thereof are characterized in that the direct current end of the voltage source type converter is connected with the bypass switch in parallel; or the direct current end of the voltage source type converter is connected with the bypass thyristor valve in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with the bypass switch in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with a bypass thyristor valve in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with a bypass switch in parallel, and meanwhile, two ends of the bypass switch are connected with a bypass thyristor valve in parallel; or after the direct current side of the voltage source type converter is connected with a diode valve in series, the direct current side of the voltage source type converter is connected with a bypass switch in parallel through a direct current circuit, and meanwhile, two ends of the bypass switch are connected with a bypass thyristor valve in parallel; or after the direct current side of the voltage source type converter is connected with a diode valve in series, the voltage source type converter is connected with the bypass switch in parallel and is connected with the bypass thyristor valve in parallel through a direct current line; or after the direct current side of the voltage source type converter is connected with the diode valve in series, the voltage source type converter is connected with the bypass thyristor valve in parallel and is connected with the bypass switch in parallel through a direct current circuit.
The control of the rectification converter station to increase the trigger angle and the control of the direct-current voltage of the inversion converter station to be reduced to the range allowing the converter to exit means that the direct-current voltage of the hybrid direct-current transmission system is controlled to be lower than a current threshold and the direct-current voltage is controlled to be lower than a voltage threshold; the current threshold value range is 0-0.05 pu, wherein 1pu is rated direct current; the voltage threshold value range is 0-0.2 pu, wherein 1pu is rated direct current voltage.
The invention has the beneficial effects that:
the invention has simple structure and convenient operation, can effectively solve the problem of online withdrawal of the hybrid converter, realizes the online withdrawal of the series VSC converter, reduces the AC/DC current impact during withdrawal and better protects the safety of each device.
The above description is only a preferred embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by using the contents of the present specification and the accompanying drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims (13)

1. A mixed direct current transmission system series converter exit device comprises a rectification converter station used for being connected with a transmitting end alternating current power grid, an inversion converter station used for being connected with a receiving end alternating current power grid and a direct current transmission line used for being connected with the rectification converter station and the inversion converter station, wherein the rectification converter station comprises at least one group of thyristor converter units, and the inversion converter station comprises at least one group of voltage source type converter units;
the thyristor converter unit comprises a thyristor converter and a bypass switch which are connected in parallel; or the thyristor converter, the bypass switch and the disconnecting link assembly are included, the thyristor converter is connected with the bypass switch in parallel, two ends of the parallel unit are respectively connected with one end of the connecting disconnecting link, and the other end of the connecting disconnecting link is connected with the bypass disconnecting link in parallel;
the alternating current side of the thyristor converter unit comprises an alternating current incoming line switch and a converter transformer which are connected in series;
the alternating current side of the voltage source type converter unit comprises an alternating current incoming line switch, a converter transformer and a charging resistor which are connected in series, and two ends of the charging resistor are also connected with a bypass switch in parallel;
the voltage source type converter unit is characterized by comprising a voltage source type converter and a bypass circuit thereof; or the device comprises a voltage source type converter, a bypass circuit of the voltage source type converter and a disconnecting link assembly, wherein two ends of the voltage source type converter and the bypass circuit of the voltage source type converter are respectively connected with one end of a connecting disconnecting link, and the other end of the connecting disconnecting link is connected with the bypass disconnecting link in parallel;
the device for withdrawing the series current converter is used for withdrawing the series current converter on line and comprises a collecting unit, a judging unit and a control unit, wherein:
the acquisition unit is used for acquiring the direct-current voltage, the direct current and the position state of a direct-current field switch disconnecting link of the hybrid direct-current power transmission system, and the current converter quits the starting signal;
the judging unit is used for judging whether the hybrid direct current power transmission system performs the exit operation of the current converter or not according to the analog quantity signals and the digital quantity signals collected by the collecting unit;
the control unit is used for controlling the thyristor converter needing to be withdrawn of the rectification converter station to switch on the direct-current side parallel bypass switch, lock the thyristor converter needing to be withdrawn, switch off the direct-current side isolation switch and switch off the alternating-current side incoming switch when the judging unit detects that the converter withdrawing operation is needed in the hybrid direct-current power transmission system; controlling a voltage source type converter needing to be withdrawn from the inversion converter station to close the direct current side parallel bypass circuit, locking the voltage source type converter needing to be withdrawn, disconnecting the direct current side isolation disconnecting link and disconnecting the alternating current side incoming line switch; and finally, recovering the operating power of the hybrid direct-current transmission system.
2. The apparatus according to claim 1, wherein the control unit is configured to, when the determination unit detects that the hybrid dc power transmission system requires a converter exiting operation, specifically perform the following steps:
(1) controlling the rectification converter station to increase a trigger angle, and controlling the direct-current voltage of the inversion converter station to be reduced to a range allowing the converter to exit;
(2) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a2) locking a voltage source type converter needing to be withdrawn from the inversion converter station;
(b2) a bypass circuit is connected in parallel at the closed direct current side;
(3) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a3) disconnecting the direct current side isolation disconnecting link;
(b3) disconnecting the AC side incoming line switch;
(4) controlling a thyristor converter needing to be exited of the rectification converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a4) closing the direct current side parallel bypass switch;
(b4) locking a thyristor converter which is required to be withdrawn from the rectification converter station;
(5) controlling a thyristor converter needing to be exited of the rectification converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a5) disconnecting the direct current side isolation disconnecting link;
(b5) disconnecting the AC side incoming line switch;
(6) and controlling the rectification converter station to reduce the trigger angle, controlling the inversion converter station to raise the direct-current voltage to a rated value, and recovering the operating power of the hybrid direct-current transmission system.
3. The apparatus according to claim 1, wherein the control unit is configured to, when the determination unit detects that the hybrid dc power transmission system requires a converter exiting operation, specifically perform the following steps:
(21) controlling the rectification converter station to increase a trigger angle, and controlling the direct-current voltage of the inversion converter station to be reduced to a range allowing the converter to exit;
(22) controlling a thyristor converter needing to be exited of the rectification converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a22) closing the direct current side parallel bypass switch;
(b22) locking a thyristor converter which is required to be withdrawn from the rectification converter station;
(23) controlling a thyristor converter needing to be exited of the rectification converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a23) disconnecting the direct current side isolation disconnecting link;
(b23) disconnecting the AC side incoming line switch;
(24) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a24) locking a voltage source type converter needing to be withdrawn from the inversion converter station;
(b24) a bypass circuit is connected in parallel at the closed direct current side;
(25) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a25) disconnecting the direct current side isolation disconnecting link;
(b25) disconnecting the AC side incoming line switch;
(26) and controlling the rectification converter station to reduce the trigger angle, controlling the inversion converter station to raise the direct-current voltage to a rated value, and recovering the operating power of the hybrid direct-current transmission system.
4. A hybrid DC power transmission system series converter tie-out apparatus according to claim 1,
the voltage source type current converter and the bypass circuit thereof are characterized in that the direct current end of the voltage source type current converter is connected with the bypass switch in parallel; or the direct current end of the voltage source type converter is connected with the bypass thyristor valve in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with the bypass switch in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with a bypass thyristor valve in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with a bypass switch in parallel, and meanwhile, two ends of the bypass switch are connected with a bypass thyristor valve in parallel; or after the direct current side of the voltage source type converter is connected with a diode valve in series, the direct current side of the voltage source type converter is connected with a bypass switch in parallel through a direct current circuit, and meanwhile, two ends of the bypass switch are connected with a bypass thyristor valve in parallel; or after the direct current side of the voltage source type converter is connected with a diode valve in series, the voltage source type converter is connected with the bypass switch in parallel and is connected with the bypass thyristor valve in parallel through a direct current line; or after the direct current side of the voltage source type converter is connected with the diode valve in series, the voltage source type converter is connected with the bypass thyristor valve in parallel and is connected with the bypass switch in parallel through a direct current circuit.
5. A hybrid dc transmission system series converter tie-down apparatus according to claim 1 wherein the converter tie-down enabling signal is triggered by an operator or by a fault signal.
6. A hybrid DC power transmission system series converter tie-out apparatus according to claim 2 or 3,
the control of the rectification converter station to increase the trigger angle and the control of the direct-current voltage of the inversion converter station to be reduced to the range allowing the converter to exit means that the direct-current voltage of the hybrid direct-current transmission system is controlled to be lower than a current threshold and the direct-current voltage is controlled to be lower than a voltage threshold.
7. The hybrid direct current transmission system series converter exit device according to claim 6, wherein the current threshold value ranges from 0 to 0.05pu, where 1pu is a rated direct current; the voltage threshold value range is 0-0.2 pu, wherein 1pu is rated direct current voltage.
8. A method for exiting a series converter of a hybrid direct-current transmission system comprises a rectifying converter station for connecting a transmitting end alternating-current power grid, an inverting converter station for connecting a receiving end alternating-current power grid and a direct-current transmission line for connecting the rectifying converter station and the inverting converter station, wherein the rectifying converter station comprises at least one group of thyristor converter units, and the inverting converter station comprises at least one group of voltage source type converter units;
the thyristor converter unit comprises a thyristor converter and a bypass switch which are connected in parallel; or the thyristor converter, the bypass switch and the disconnecting link assembly are included, the thyristor converter is connected with the bypass switch in parallel, two ends of the parallel unit are respectively connected with one end of the connecting disconnecting link, and the other end of the connecting disconnecting link is connected with the bypass disconnecting link in parallel;
the alternating current side of the thyristor converter unit comprises an alternating current incoming line switch and a converter transformer which are connected in series;
the alternating current side of the voltage source type converter unit comprises an alternating current incoming line switch, a converter transformer and a charging resistor which are connected in series, and two ends of the charging resistor are also connected with a bypass switch in parallel;
the voltage source type converter unit is characterized by comprising a voltage source type converter and a bypass circuit thereof; or the device comprises a voltage source type converter, a bypass circuit of the voltage source type converter and a disconnecting link assembly, wherein two ends of the voltage source type converter and the bypass circuit of the voltage source type converter are respectively connected with one end of a connecting disconnecting link, and the other end of the connecting disconnecting link is connected with the bypass disconnecting link in parallel;
the converter withdrawing method comprises the steps of controlling a thyristor converter needing to be withdrawn of a rectification converter station to switch on a direct-current side parallel bypass switch, locking the thyristor converter needing to be withdrawn, disconnecting a direct-current side isolation switch and disconnecting an alternating-current side incoming switch when detecting that the mixed direct-current power transmission system needs to carry out converter withdrawing operation; controlling a voltage source type converter needing to be withdrawn from the inversion converter station to close the direct current side parallel bypass circuit, locking the voltage source type converter needing to be withdrawn, disconnecting the direct current side isolation disconnecting link and disconnecting the alternating current side incoming line switch; and finally, recovering the operating power of the hybrid direct-current transmission system.
9. A hybrid dc transmission system series converter tie-out method according to claim 8, characterized in that the converter tie-out method comprises the following steps:
(1) controlling the rectification converter station to increase a trigger angle, and controlling the direct-current voltage of the inversion converter station to be reduced to a range allowing the converter to exit;
(2) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a2) locking a voltage source type converter needing to be withdrawn from the inversion converter station;
(b2) a bypass circuit is connected in parallel at the closed direct current side;
(3) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a3) disconnecting the direct current side isolation disconnecting link;
(b3) disconnecting the AC side incoming line switch;
(4) controlling a thyristor converter needing to be exited of the rectification converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a4) closing the direct current side parallel bypass switch;
(b4) locking a thyristor converter which is required to be withdrawn from the rectification converter station;
(5) controlling a thyristor converter needing to be exited of the rectification converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a5) disconnecting the direct current side isolation disconnecting link;
(b5) disconnecting the AC side incoming line switch;
(6) and controlling the rectification converter station to reduce the trigger angle, controlling the inversion converter station to raise the direct-current voltage to a rated value, and recovering the operating power of the hybrid direct-current transmission system.
10. A hybrid dc transmission system series converter tie-out method according to claim 8, characterized in that the converter tie-out method comprises the following steps:
(21) controlling the rectification converter station to increase a trigger angle, and controlling the direct-current voltage of the inversion converter station to be reduced to a range allowing the converter to exit;
(22) controlling a thyristor converter needing to be exited of the rectification converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a22) closing the direct current side parallel bypass switch;
(b22) locking a thyristor converter which is required to be withdrawn from the rectification converter station;
(23) controlling a thyristor converter needing to be exited of the rectification converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a23) disconnecting the direct current side isolation disconnecting link;
(b23) disconnecting the AC side incoming line switch;
(24) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a24) locking a voltage source type converter needing to be withdrawn from the inversion converter station;
(b24) a bypass circuit is connected in parallel at the closed direct current side;
(25) controlling a voltage source type converter needing to exit from the inversion converter station to perform the following two parts of operations, wherein the two parts of operations are not in sequence:
(a25) disconnecting the direct current side isolation disconnecting link;
(b25) disconnecting the AC side incoming line switch;
(26) and controlling the rectification converter station to reduce the trigger angle, controlling the inversion converter station to raise the direct-current voltage to a rated value, and recovering the operating power of the hybrid direct-current transmission system.
11. A hybrid dc transmission system series converter exit method according to claim 8 wherein the voltage source converter and its bypass circuit are a voltage source converter with a dc terminal connected in parallel with a bypass switch; or the direct current end of the voltage source type converter is connected with the bypass thyristor valve in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with the bypass switch in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with a bypass thyristor valve in parallel; or the direct current side of the voltage source type converter is connected with a diode valve in series and then is connected with a bypass switch in parallel, and meanwhile, two ends of the bypass switch are connected with a bypass thyristor valve in parallel; or after the direct current side of the voltage source type converter is connected with a diode valve in series, the direct current side of the voltage source type converter is connected with a bypass switch in parallel through a direct current circuit, and meanwhile, two ends of the bypass switch are connected with a bypass thyristor valve in parallel; or after the direct current side of the voltage source type converter is connected with a diode valve in series, the voltage source type converter is connected with the bypass switch in parallel and is connected with the bypass thyristor valve in parallel through a direct current line; or after the direct current side of the voltage source type converter is connected with the diode valve in series, the voltage source type converter is connected with the bypass thyristor valve in parallel and is connected with the bypass switch in parallel through a direct current circuit.
12. A hybrid DC power transmission system series converter exit method according to claim 9 or 10,
the control of the rectification converter station to increase the trigger angle and the control of the direct-current voltage of the inversion converter station to be reduced to the range allowing the converter to exit means that the direct-current voltage of the hybrid direct-current transmission system is controlled to be lower than a current threshold and the direct-current voltage is controlled to be lower than a voltage threshold.
13. The hybrid direct current transmission system series converter exit method according to claim 12, wherein the current threshold value ranges from 0 pu to 0.05pu, where 1pu is a rated direct current; the voltage threshold value range is 0-0.2 pu, wherein 1pu is rated direct current voltage.
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