CN110912175A - Hybrid four-terminal high-voltage direct-current transmission system - Google Patents
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/261—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations
- H02H7/262—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations involving transmissions of switching or blocking orders
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J1/00—Circuit arrangements for dc mains or dc distribution networks
- H02J1/10—Parallel operation of dc sources
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/48—Controlling the sharing of the in-phase component
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/50—Controlling the sharing of the out-of-phase component
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
Abstract
The application relates to a four mixed end HVDC system, include: a first converter station and a second converter station on a rectifying side, and a third converter station and a fourth converter station on an inverting side; and when the transmission line of the direct current transmission system has a fault, the corresponding hybrid direct current circuit breaker acts to transfer the power flow of the direct current transmission system, and the direct current transmission system maintains normal operation. The problem of among the prior art direct current transmission system when taking place direct current trouble, can't be by sending end to receiving end normal transmission power to influence system reliability is solved.
Description
Technical Field
The application belongs to the technical field of direct current transmission, and particularly relates to a hybrid four-terminal high-voltage direct current transmission system.
Background
In recent years, with the increasing prominence of environmental problems, in order to reduce carbon emission and the proportion of coal-fired power generation, the national energy structure is optimized, and renewable energy sources need to be developed and utilized on a large scale. With the rapid development of renewable energy power integration, high-voltage direct-current power transmission is widely applied in China to transmit a large amount of new energy power to a remote load center.
For high capacity transmission, hybrid hvdc transmission systems (including grid commutated converters (LCCs) and Modular Multilevel Converters (MMCs)) have become the most compatible candidate for future transmission systems, since such a configuration will combine the advantages of LCCs and MMCs.
The grid commutation converter needs a receiving-end alternating-current grid to provide enough reactive power and commutation voltage, and needs to absorb more reactive power in the power recovery process after commutation failure. Therefore, when an ac fault occurs at a certain point of the receiving-end system, a phase commutation failure may occur simultaneously on multiple dc lines, which may cause a temporary interruption of the transmission power of the multiple dc lines, and pose a serious threat to the safety and stability of the transmitting-receiving-end ac system.
At present, in order to solve the above problems, the adopted scheme is as follows: a Voltage Source Converter (VSC) is adopted as a receiving end converter, and a modularized multi-level converter (MMC) is preferably adopted to replace a conventional power grid phase-change converter. The modularized multi-level converter has a dq decoupling controller and has the advantages of self-conversion and the like, so that the problem of reactive power support can be effectively solved.
Hybrid high-voltage direct-current transmission (Hybrid-HVDC) can realize advantage complementation between LCC and MMC, and fully exerts respective advantages of a conventional direct-current technology and a flexible direct-current technology. Yuan Xuan Peak et al propose to use MMC instead of LCC as the receiver to form a hybrid DC power transmission system, thereby avoiding the problem of commutation failure caused by conventional DC power transmission techniques, and having weak AC system access capability. (Yuan Xuan Peak, Cheng Time Jie, Wenjuyu. CSC and VSC based hybrid multi-terminal DC Transmission System and its simulation [ J ] Power System Automation, 2006(20):32-36+ 76.). Tang-Heng et al propose that MMC is adopted at the receiving end and a high-power diode valve bank is connected in series at the direct current side to block direct current fault current, and make up for the defect that MMC can not process direct current fault. (Tang-G, Xuxu-Zheng, Xue Ying Lin. LCC-MMC hybrid HVDC Transmission System [ J ]. Electrical and technical bulletin, 2013,33(10):301-
However, when a dc fault occurs, the dc transmission system cannot normally transmit power from the transmitting end to the receiving end, which affects the reliability of the system.
Therefore, the application of the point-to-point hybrid high-voltage transmission system based on the LCC and the MMC in the ultra-high voltage transmission faces many technical problems. Meanwhile, for existing hybrid dc power transmission systems and flexible dc power transmission systems, improvement of a system structure is required to improve system stability.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the problem that in the prior art, when a direct current fault occurs in a direct current transmission system, power cannot be normally transmitted from a sending end to a receiving end, and therefore system reliability is affected is solved.
In order to solve the technical problems, the invention provides a hybrid four-terminal direct-current power transmission system and a control strategy suitable for long-distance power transmission of multiple energy bases, which realize power transmission of the multiple energy bases to multiple load centers and have the capability of uninterrupted operation of direct-current faults.
The technical scheme adopted by the invention for solving the technical problems is as follows: a hybrid four-terminal high voltage direct current transmission system comprising: a first converter station and a second converter station on a rectifying side, and a third converter station and a fourth converter station on an inverting side; the direct current side of the first converter station is connected with the direct current side of the third converter station, and the direct current side of the second converter station is connected with the direct current side of the fourth converter station; the method is characterized in that:
the first converter station is connected in parallel with the second converter station, and the third converter station is connected in parallel with the fourth converter station;
and when the transmission line of the direct current transmission system has a fault, the corresponding hybrid direct current circuit breaker acts to transfer the power flow of the direct current transmission system and maintain the normal operation of the direct current transmission system.
Further, according to the hybrid four-terminal high-voltage direct-current transmission system, when the power transmission line of the direct-current transmission system has a pole-to-ground fault, the hybrid direct-current circuit breakers on two sides of the fault point are disconnected, and when the power transmission line of the direct-current transmission system has a pole-to-pole fault, all the hybrid circuit breakers on the power transmission line with the fault are disconnected.
Further, according to the hybrid four-terminal high-voltage direct-current transmission system, the hybrid direct-current circuit breaker comprises a main branch, a transfer branch and an energy consumption branch which are connected in parallel; the main branch circuit comprises a mechanical switch and an auxiliary direct current switch which are connected in series, and the auxiliary direct current switch and the transfer branch circuit are both composed of fully-controlled power electronic devices which are connected in series.
Further, according to the hybrid four-terminal high-voltage direct-current transmission system, the hybrid direct-current circuit breaker further comprises isolating switches, and the isolating switches are respectively connected with the current input sides of the main branch, the transfer branch and the energy consumption branch in series.
Further, according to the hybrid four-terminal high-voltage direct-current transmission system, the auxiliary direct-current switch is formed by connecting two IGBTs with anti-parallel diodes in series; the transfer branch circuit is formed by connecting more than two IGBTs with anti-parallel diodes in series.
Further, according to the hybrid four-terminal high-voltage direct-current transmission system, a current-limiting inductor is further arranged on the direct-current side of each converter station, and the current-limiting inductor is connected with the hybrid high-voltage direct-current circuit breaker in series.
Further, according to the hybrid four-terminal high-voltage direct-current transmission system, the first converter station adopts a 12-pulse power grid commutation converter, and the second converter station, the third converter station and the fourth converter station all adopt half-bridge modular multilevel converters.
Further, according to the hybrid four-terminal high-voltage direct-current transmission system, the first converter station adopts constant-current control to cooperate with low-voltage current-limiting control; the second converter station adopts constant active power control and constant reactive power control; the third converter station adopts constant direct current voltage control; and the fourth converter station adopts constant active power and constant reactive power control.
Further, according to the hybrid four-terminal high-voltage direct-current transmission system, the third converter station and the fourth converter station on the inverting side adopt an independent control mechanism of alternating current and direct current decoupling for independently controlling direct current and alternating current.
Further, according to the hybrid four-terminal high-voltage direct-current transmission system provided by the invention, the direct-current transmission lines among the converter stations comprise direct-current cables, overhead lines and hybrid transmission lines of the overhead lines and cable lines.
The invention has the beneficial effects that: (1) the direct current transmission system can transmit the power of a plurality of energy bases to a plurality of load centers at the same time.
(2) Compared with a point-to-point high-voltage direct-current transmission system, the direct-current transmission system can timely cut off a fault line and transfer power flow when the direct-current line fails, and power of each transmitting end and each receiving end can be kept at rated values under the fault condition.
(3) According to the method, the starting stage is divided into an uncontrolled rectifying charging stage and a controllable charging stage. The voltage and the current of the system are maintained in a safe range during the starting process.
Drawings
The technical solution of the present application is further explained below with reference to the drawings and the embodiments.
Fig. 1 is a schematic diagram of a hybrid four-terminal dc transmission system according to an embodiment of the present application;
FIG. 2 is a power grid commutation converter topology of an embodiment of the application;
fig. 3 is a modular multilevel converter topology of an embodiment of the present application;
fig. 4 is a circuit configuration diagram of a hybrid dc circuit breaker according to an embodiment of the present application;
fig. 5(a) is a current flow situation in a dc transmission system in normal operation according to an embodiment of the present application;
FIG. 5(b) is a current flow condition in the case of a pole-to-pole fault in an embodiment of the present application;
fig. 5(c) shows the current flow after the pole-to-pole fault line is cut off according to the embodiment of the present application.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.
The technical solutions of the present application will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.
The application provides a four mixed end high voltage direct current transmission system, its direct current transmission line can adopt forms such as direct current cable, overhead line and cable run mix. The system adopts a true bipolar wiring mode, and the DC voltage grade is +/-500 kV.
Examples
As shown in fig. 1, the hybrid four-terminal high-voltage direct-current transmission system of the present embodiment includes: a first converter station C1 and a second converter station C2 on the rectifying side, a third converter station C3 and a fourth converter station C4 on the inverting side.
Wherein the first converter station C1 is connected to the dc side of the third converter station C3, the second converter station C2 is connected to the dc side of the fourth converter station C4, the first converter station C1 is connected in parallel with the second converter station C2, and the third converter station C3 is connected in parallel with the fourth converter station. Meanwhile, the AC sides of the first converter station C1 and the second converter station C2 are connected to the energy bases AC1 and AC2 for outputting AC respectively, and the AC sides of the third converter station C3 and the fourth converter station C4 are connected to the load centers AC3 and AC4 respectively.
The direct current side neutral points of the converter stations are connected through a neutral line and grounded through a resistor R at the third converter station C3, and meanwhile, in consideration of the condition of large-scale and long-distance power transmission, the converter stations are connected through a long-distance overhead line.
In this embodiment, the first converter station C1 employs a 12-pulse grid commutation converter LCC, as shown in fig. 2; the second converter station C2, the third converter station C3 and the fourth converter station C4 all employ half-bridge modular multilevel converters MMC as shown in fig. 3. In a further embodiment the ac side of the grid commutated converter LCC is provided with an ac filter and reactive compensation equipment for filtering ac harmonics and providing reactive power, and the dc side of the grid commutated converter LCC is provided with a dc filter and a smoothing reactor for filtering harmonics generated at the dc side.
As shown in fig. 1, the energy base AC1 outputs AC power to the first converter station C1, the first converter station C1 is configured to rectify AC power output from the energy base S1 into dc power and output the dc power to the third converter station C3, and the third converter station C3 inverts the input dc power into AC power and outputs the AC power to the load center AC 3.
The energy base AC2 outputs AC power to the second converter station C2, the second converter station C2 is configured to ballast the AC power output from the energy base C2 to dc power and output the dc power to the fourth converter station C4, and the fourth converter station C4 inverts the input dc power to AC power and outputs the AC power to the load center AC 4.
Furthermore, in this embodiment, hybrid dc circuit breakers CB are disposed on the dc sides of the first converter station C1, the second converter station C2, the third converter station C3, and the fourth converter station C4, and when an electrode-to-electrode fault occurs in a transmission line of a dc transmission system, 4 hybrid dc circuit breakers on positive and negative transmission lines between two converter stations are all turned off; when a pole-to-ground fault occurs in a power transmission line of a direct current power transmission system, the hybrid direct current circuit breakers on two sides of a fault point are turned off; therefore, the power flow of the direct current transmission system is transferred, and the direct current transmission system is ensured to maintain normal operation.
As shown in fig. 4, the hybrid dc circuit breaker of this embodiment includes a disconnecting switch K2, and a main branch 1, a transfer branch 2, and an energy consumption branch 3 connected in parallel, where the disconnecting switch K2 is connected in series with the main branch 1, the transfer branch 2, and the energy consumption branch 3, respectively.
In the embodiment, the mechanical switch K1 adopts a high-speed repulsion switch based on an electromagnetic repulsion mechanism, the auxiliary direct-current switch and the transfer branch are both formed by connecting fully-controlled power electronic devices in series, and the fully-controlled power electronic devices can be insulated gate bipolar transistors, integrated gate commutated thyristors or gate turn-off thyristors. The energy consumption branch is composed of lightning arresters.
As shown in fig. 4, as a preferred embodiment, the auxiliary dc switch is composed of T1 and T2 two IGBTs with anti-parallel diodes connected in series; the transfer branch is formed by connecting a large number of IGBTs (T3-Tn) in series, and each IGBT is provided with an anti-parallel diode.
When the hybrid direct current circuit breaker CB normally operates, the hybrid direct current circuit breaker CB is in a closing state, the mechanical switch is closed, the auxiliary direct current switch is triggered, current in the direct current transmission system flows through the main branch circuit and supplies power to the load center, and current in the transfer branch circuit is zero.
When a short-circuit fault occurs on the direct-current side of the direct-current power transmission system, the hybrid direct-current circuit breaker CB is in an on-off state, the current flowing through the main branch circuit rapidly rises, when the current exceeds a protection fixed value, the auxiliary direct-current switch is triggered to be turned off, the IGBT in the transfer branch circuit is triggered to be turned on, the current is converted into the transfer branch circuit, and the mechanical switch K1 is switched off;
the mechanical switch K1 is switched off to a safe open distance without electric arc, and does not bear large current, the main branch is switched off, fault current is cut off, and the isolating switch is switched off to cut off smaller residual current, so that the fault circuit is isolated.
And (4) fault current transfer, IGBT in the transfer branch circuit is locked, the lightning arrester is conducted, and the current is transferred to the lightning arrester and attenuated. The energy consumption branch circuit is used for preventing the IGBT from being broken down by overvoltage and is beneficial to protecting the IGBT.
Further, this embodiment has still set up current-limiting inductance L, and this current-limiting inductance L establishes ties with hybrid dc circuit breaker for the rate of rise of restriction fault current reduces the requirement to the fault judgement sensitivity and the requirement to the switching speed mobility. The circuit breaker is advantageous in that rapid arc-free commutation can be achieved by turning off the auxiliary dc switch.
Fig. 5(a) shows the current flow in the dc transmission system during normal operation, in which the converter stations are in normal operation, and the arrows in the figure show the current flow direction during normal operation of the converter stations. Fig. 5(b) shows the current flowing in the dc power transmission system after the pole-to-pole fault occurs at the midpoint of the power transmission line between C1 and C3, and at this time, the fault current is fed to the fault point by both the first converter station C1 on the rectification side and the third converter station C3 on the inversion side. Fig. 5(C) shows the situation where the current flows in the dc transmission system after the hybrid dc breaker on the fault line in the fault situation shown in fig. 5(b) is operated, and at this time, the positive and negative transmission lines between C1 and C3 are both cut off, and the operation mode of the dc transmission system is changed, but the energy can still be transmitted normally.
When the direct current transmission system of this embodiment is in normal operation, the first converter station C1 on the rectification side adopts constant-direct current control and low-voltage current-limiting control, and the low-voltage current-limiting control is beneficial to recovery of alternating current voltage and avoids instability of alternating current voltage when an alternating current system of the first converter station is disturbed or failed. The second converter station C2 on the rectifying side adopts constant active power control and constant reactive power control.
The third converter station C3 on the inverting side is configured with constant dc voltage control, and the fourth converter station C4 on the inverting side adopts constant active power control and constant reactive power control. Furthermore, for the third converter station C3 and the fourth converter station C4(MMC) which adopt an inversion side on the inversion side, an independent control mechanism of alternating current and direct current decoupling is adopted, the control mechanism is divided into an alternating current control loop and a direct current control loop, and direct current and alternating current can be independently controlled.
Furthermore, the alternating current control loop is based on decoupling control under a rotating coordinate system, three-phase alternating current is decoupled into d-axis current and q-axis current in the rotating coordinate system, and the alternating current control loop is decoupled into active current control and reactive current control according to the d-axis current and the q-axis current. The d-axis active control is constant direct-current voltage control, so that the direct-current voltage of the system is maintained; the q-axis reactive current control ensures that the transmitted reactive power remains constant.
In light of the foregoing description of the preferred embodiments according to the present application, it is to be understood that various changes and modifications may be made without departing from the spirit and scope of the invention. The technical scope of the present application is not limited to the contents of the specification, and must be determined according to the scope of the claims.
Claims (10)
1. A hybrid four-terminal high voltage direct current transmission system comprising: a first converter station and a second converter station on a rectifying side, and a third converter station and a fourth converter station on an inverting side; the direct current side of the first converter station is connected with the direct current side of the third converter station, and the direct current side of the second converter station is connected with the direct current side of the fourth converter station; the method is characterized in that:
the first converter station is connected in parallel with the second converter station, and the third converter station is connected in parallel with the fourth converter station;
and when the transmission line of the direct current transmission system has a fault, the corresponding hybrid direct current circuit breaker acts to transfer the power flow of the direct current transmission system and maintain the normal operation of the direct current transmission system.
2. The hybrid four-terminal hvdc transmission system in accordance with claim 1, wherein the hybrid dc breakers on both sides of the fault point are opened when a pole-to-ground fault occurs in the transmission line of the dc transmission system, and all the hybrid breakers on the transmission line that has failed are opened when a pole-to-pole fault occurs in the transmission line of the dc transmission system.
3. The hybrid four-terminal hvdc transmission system in accordance with claim 1, wherein said hybrid dc breaker comprises a main branch, a transfer branch, and a dissipation branch connected in parallel; the main branch circuit comprises a mechanical switch and an auxiliary direct current switch which are connected in series, and the auxiliary direct current switch and the transfer branch circuit are both composed of fully-controlled power electronic devices which are connected in series.
4. The hybrid four-terminal hvdc transmission system in accordance with claim 1, further comprising disconnectors connected in series with the current input sides of the main, transfer and dissipation branches, respectively.
5. The hybrid four-terminal hvdc transmission system in accordance with claim 4, wherein said auxiliary dc switch is comprised of two IGBTs with anti-parallel diodes connected in series; the transfer branch circuit is formed by connecting more than two IGBTs with anti-parallel diodes in series.
6. A hybrid four-terminal HVDC transmission system according to claim 5, characterized in that the DC side of each converter station is further provided with a current limiting inductor, which is connected in series with the hybrid HVDC breaker.
7. The hybrid four-terminal hvdc transmission system in accordance with claim 1, wherein the first converter station employs a 12-pulse grid commutated converter and the second, third and fourth converter stations each employ a half-bridge modular multilevel converter.
8. The hybrid four-terminal hvdc transmission system in accordance with claim 7, wherein the first converter station employs dc-dc current control in conjunction with low voltage current limiting control; the second converter station adopts constant active power control and constant reactive power control; the third converter station adopts constant direct current voltage control; and the fourth converter station adopts constant active power and constant reactive power control.
9. The hybrid four-terminal hvdc transmission system in accordance with claim 8, wherein the third and fourth stations on the inverting side employ an independent control mechanism of ac/dc decoupling for independent control of dc and ac currents.
10. The hybrid four-terminal hvdc transmission system in accordance with claim 1, wherein the dc transmission lines between the converter stations comprise dc cables, overhead lines, and hybrid overhead and cable lines.
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|---|---|---|---|---|
| CN111521908A (en) * | 2020-04-30 | 2020-08-11 | 华中科技大学 | Alternating current fault positioning method applied to four-end wind power direct current power grid |
| CN114285066A (en) * | 2021-12-28 | 2022-04-05 | 国网北京市电力公司 | Power balance coordination control method and system for multi-terminal flexible interconnection power distribution system |
| CN115241964A (en) * | 2021-04-23 | 2022-10-25 | 中电普瑞电力工程有限公司 | Power supply system of offshore platform and fault protection method thereof |
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