CN112054551A - Hybrid two-end direct current transmission system and external characteristic test method thereof - Google Patents

Hybrid two-end direct current transmission system and external characteristic test method thereof Download PDF

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CN112054551A
CN112054551A CN202010960391.7A CN202010960391A CN112054551A CN 112054551 A CN112054551 A CN 112054551A CN 202010960391 A CN202010960391 A CN 202010960391A CN 112054551 A CN112054551 A CN 112054551A
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converter
direct
reference value
modular multilevel
power grid
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CN112054551B (en
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陈钦磊
林雪华
郭琦
饶宏
李书勇
陈德扬
罗超
曾冠铭
刘志江
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China South Power Grid International Co ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • Power Engineering (AREA)
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  • General Physics & Mathematics (AREA)
  • Inverter Devices (AREA)

Abstract

The application discloses a hybrid two-end direct current transmission system and an external characteristic test method thereof, aiming at LCC, on one hand, the application adopts a mode of maintaining the capacitance voltage of a modular multilevel converter and gradually increasing or decreasing the direct current voltage reference value of the modular multilevel converter to observe the corresponding electric quantity of a power grid phase change converter in real time; on the other hand, aiming at the MMC, the external characteristics of the hybrid two-end direct-current transmission system are tested by gradually increasing or decreasing the trigger angle reference value of the power grid commutation converter and observing the corresponding signal of the modular multilevel converter in real time, and the technical problem that the external characteristics of the hybrid two-end direct-current transmission system with one end adopting the LCC and the other end adopting the MMC are difficult to test in the prior art is solved.

Description

Hybrid two-end direct current transmission system and external characteristic test method thereof
Technical Field
The application relates to the technical field of high-voltage direct-current power transmission, in particular to a hybrid two-end direct-current power transmission system and an external characteristic testing method thereof.
Background
High voltage direct current transmission systems (LCC-HVDC) of grid commutation converters based on thyristor technology have matured very much after more than 40 years of development. At present, LCC-HVDC is widely applied to occasions of long-distance large-capacity power transmission, asynchronous power grid interconnection and the like. However, LCC-HVDC has high requirements on the connected AC power grid, cannot realize passive operation, and consumes a large amount of reactive power in the operation process, thereby restricting the further development of the LCC-HVDC to a certain extent.
Modular Multilevel Converters (MMC) have the advantages of modular design, strong expansibility, flexible power four-quadrant operation, less alternating voltage harmonic waves, small occupied area and the like, and are widely researched and utilized in the fields of asynchronous interconnection of alternating current power grids, wind power plant access and the like in recent years. However, compared with LCC-HVDC (Line Committed Converter high-voltage direct current, current source type high-voltage direct current transmission system), MMC-HVDC has poor economy.
Combining the economic advantages of LCC and the technical advantages of MMC, a hybrid dc transmission technology with LCC at one end and MMC at the other end has been called a research hotspot in recent years. The external characteristics of the direct current transmission system are characterized by direct current voltage Ud and direct current Id characteristics presented by a port of the converter to the outside, and are important bases for measuring the operation characteristics of the converter, evaluating the dynamic performance of the converter and analyzing the influence of the converter on an alternating current and direct current power grid. At present, a great deal of research on the external characteristics of the traditional conventional direct current has been conducted in the academic community, but the research on the external characteristics of the direct current at two mixed ends is less.
The prior art scheme aims at the traditional conventional direct current transmission system, and the current converters at two ends of the conventional direct current transmission system are all LCC current converters. One end of the direct current at the two mixed ends is LCC, and the other end of the direct current at the two mixed ends is MMC, and the external characteristics of the direct current are obviously different from those of the traditional direct current.
Disclosure of Invention
The embodiment of the application provides a hybrid two-end direct current transmission system and an external characteristic testing method thereof, and solves the technical problem that the external characteristic of the hybrid direct current transmission system with one end adopting LCC and the other end adopting MMC is difficult to test in the prior art.
In view of the above, a first aspect of the present application provides a hybrid two-terminal dc transmission system, where a transmitting terminal of the hybrid two-terminal dc transmission system is a grid commutation converter, and a receiving terminal of the hybrid two-terminal dc transmission system is a modular multilevel converter;
the power grid phase-change converter is used for converting alternating current into direct current to be output;
the modular multilevel converter is used for receiving direct current and converting the direct current into alternating current.
The second aspect of the present application provides a method for testing external characteristics of a hybrid two-terminal dc, the method comprising:
testing the power grid commutation converter:
operating a direct current system to a stable operation state, fixing the capacitor voltage of a modular multilevel converter to be a stable value, recording the direct current voltage reference value of the modular multilevel converter, and simultaneously recording a first signal of the power grid phase-change converter;
gradually increasing a direct-current voltage reference value of a modular multilevel converter, and recording the first signal of the power grid phase change converter when the direct current of the power grid phase change converter is 0;
restoring the direct-current system to a stable operation state before testing, gradually reducing a direct-current voltage reference value of the modular multilevel converter, and recording the first signal of the power grid phase change converter at the corresponding moment when the direct current of the power grid phase change converter begins to decline and when the direct-current voltage of the power grid phase change converter is reduced to 0;
testing the modular multilevel converter:
recording a trigger angle reference value of the power grid commutation converter and simultaneously recording a first signal of the power grid commutation converter under the stable operation state of the direct current system;
gradually increasing a firing angle reference value of the grid commutation converter, and recording a second signal of the modular multilevel converter when a direct current voltage of the modular multilevel converter starts to fall, when the direct current of the modular multilevel converter starts to fall and when the firing angle reference value of the grid commutation converter rises to a first preset angle, respectively;
and restoring the direct-current system to a stable running state before testing, gradually reducing the trigger angle reference value of the power grid phase change converter, and recording a second signal of the modular multilevel converter when the direct-current voltage of the power grid phase change converter starts to rise and the trigger angle reference value of the power grid phase change converter is reduced to a second preset angle.
Optionally, the step-by-step increasing the dc voltage reference value of the modular multilevel converter, and when the dc current of the grid commutation converter is 0, recording the first signal of the grid commutation converter at this time, specifically:
gradually increasing a direct-current voltage reference value of the modular multilevel converter, and observing a first signal of the power grid commutation converter corresponding to the direct-current voltage reference value in real time;
and when the direct current of the power grid phase change converter is 0, recording a first signal of the power grid phase change converter at the moment.
Optionally, the recovering the dc system to a stable operation state before testing, gradually decreasing a dc voltage reference value of the modular multilevel converter, and recording the first signal of the grid commutation converter at a corresponding time when the dc current of the grid commutation converter starts to decrease and when the dc current of the grid commutation converter decreases to 0, specifically:
restoring the direct-current system to a stable running state before testing, gradually reducing a direct-current voltage reference value of the modular multilevel converter, and observing a first signal of the power grid commutation converter corresponding to the direct-current voltage reference value in real time;
when the direct current of the power grid phase change converter begins to decline, recording a first signal of the power grid phase change converter at the moment;
continuously and gradually reducing the direct-current voltage reference value of the modular multilevel converter, and observing a first signal of the power grid commutation converter corresponding to the direct-current voltage reference value in real time;
when the direct-current voltage drop of the power grid phase change converter is 0, recording a first signal of the power grid phase change converter at the moment.
Optionally, the step-by-step increasing the firing angle reference value of the grid commutated converter, and recording a second signal of the modular multilevel converter when the dc voltage of the modular multilevel converter starts to decrease, when the dc current of the modular multilevel converter starts to decrease, and when the firing angle reference value of the grid commutated converter increases to a first preset angle, respectively, specifically:
gradually increasing a trigger angle reference value of the power grid commutation converter, and observing a second signal of the modular multilevel converter corresponding to the direct-current voltage reference value in real time;
recording a second signal of the modular multilevel converter when the direct-current voltage of the modular multilevel converter begins to drop;
when the direct current of the modular multilevel converter begins to fall, recording a second signal of the modular multilevel converter at the moment;
and when the trigger angle reference value of the power grid commutation converter is increased to a first preset angle, recording a second signal of the modular multilevel converter at the moment.
Optionally, the first preset angle is 90 °.
Optionally, the recovering the dc system to a stable operation state before the test, gradually decreasing the firing angle reference value of the grid commutation converter, and recording a second signal of the modular multilevel converter when the dc voltage of the grid commutation converter starts to increase and when the firing angle reference value of the grid commutation converter decreases to a second preset angle, specifically:
restoring the direct-current system to a stable running state before testing, gradually reducing a trigger angle reference value of the power grid commutation converter, and observing a second signal of the modular multilevel converter corresponding to the direct-current voltage reference value in real time;
when the direct-current voltage of the power grid commutation converter begins to rise, recording a second signal of the modular multilevel converter at the moment;
and when the trigger angle reference value of the power grid commutation converter is reduced to a second preset angle, recording a second signal of the modular multilevel converter at the moment.
Optionally, the second preset angle is 5 °.
Optionally, the first signal of the grid commutation converter is a direct current voltage, a direct current, a firing angle, a tap gear, and an ideal no-load voltage.
Optionally, the second signal of the modular multilevel converter is a direct current voltage, a direct current, a modulation ratio, a tap position, and a valve side voltage.
According to the technical scheme, the method has the following advantages:
the application provides a method for testing direct current external characteristics of two mixed ends, which comprises the following steps: testing the power grid commutation converter: gradually increasing the direct-current voltage reference value of the modular multilevel converter, and recording a power grid phase change converter signal when the direct-current voltage of the power grid phase change converter is 0; gradually reducing the direct-current voltage reference value of the modular multilevel converter, and recording a first signal of the power grid phase change converter when the direct current of the power grid phase change converter begins to drop and when the direct-current voltage of the power grid phase change converter is reduced to 0; testing the modular multilevel converter: gradually increasing the trigger angle reference value of the power grid phase change converter, and recording a second signal of the modular multilevel converter when the direct current voltage of the modular multilevel converter starts to fall, the direct current of the modular multilevel converter starts to fall and the trigger angle reference value of the power grid phase change converter is increased to a first preset angle respectively; and gradually reducing the trigger angle reference value of the power grid phase change converter, and recording a second signal of the modular multilevel converter when the direct-current voltage of the power grid phase change converter starts to rise and when the trigger angle reference value of the power grid phase change converter is reduced to a second preset angle.
Aiming at a hybrid direct-current power transmission system with one end adopting an LCC and the other end adopting an MMC, on one hand, aiming at the LCC, a mode of keeping the capacitance voltage of the modular multilevel converter and gradually increasing or decreasing the direct-current voltage reference value of the modular multilevel converter is adopted to observe the corresponding signal of the power grid phase-change converter in real time; on the other hand, aiming at the MMC, the external characteristics of the mixed direct-current two-end power transmission system with one end adopting the LCC and the other end adopting the MMC are tested in a mode of gradually increasing or decreasing the trigger angle reference value of the power grid phase-change converter and observing the corresponding signal of the modular multilevel converter in real time, and the technical problem that the external characteristics of the mixed direct-current two-end power transmission system with one end adopting the LCC and the other end adopting the MMC are difficult to test in the prior art is solved.
Drawings
Fig. 1 is a system topology diagram of an embodiment of a hybrid two-terminal dc power transmission system of the present application;
FIG. 2 is a flowchart of a method of one embodiment of a hybrid two-terminal DC external characteristic testing method of the present application;
fig. 3 is a graph of typical hybrid two-terminal dc external characteristics obtained by testing a hybrid two-terminal dc transmission system according to the present application.
Detailed Description
Referring to fig. 1, fig. 1 is a system topology diagram of an embodiment of a hybrid two-terminal dc transmission system, as shown in fig. 1, a transmitting terminal of the hybrid two-terminal dc transmission system in fig. 1 is a grid commutation converter, and a receiving terminal is a modular multilevel converter; the power grid phase-change converter is used for converting alternating current into direct current to output; the modular multilevel converter is used for receiving direct current and converting the direct current into alternating current.
For easy understanding, please refer to fig. 2, fig. 2 is a flowchart illustrating a method of an embodiment of a method for testing external characteristics of a hybrid dual-terminal dc device, as shown in fig. 2, which specifically includes:
testing the power grid commutation converter:
firstly, a direct current external characteristic test system at two mixed ends needs to be connected with a real-time simulation test platform, and test parameters are set on the real-time simulation test platform.
Specifically, before the hybrid multi-terminal direct current transmission system is subjected to characteristic test, the test parameters required to be set by the real-time simulation platform comprise that the hybrid direct current is operated to a single-pole earth return state (recommended to be operated to a rated power operation state), the voltage of an alternating current system at two ends is regulated to be rated voltage, a tap control mode at two ends is switched from an automatic mode to a manual mode, all protection and related trip outlet logics at two stations are quitted, a current margin compensation function is quitted, and upper and lower limit values of a voltage reference value of a fixed voltage station are released.
101. Operating a direct current system to a stable operation state, fixing the capacitor voltage of the modular multilevel converter to be a stable value, recording the direct current voltage reference value of the modular multilevel converter, and simultaneously recording a first signal of the power grid phase-change converter;
it should be noted that, in the present application, the sub-module capacitor voltage of the receiving-end MMC converter station may be fixed to be a steady-state value (generally, a rated value) of the current working condition, that is, when the dc system is in a stable operation state, the current reference value of the dc voltage of the receiving-end MMC converter station is obtained as an initial value; and simultaneously recording the initial signal of the sending end LCC converter station. The first signal in this application is dc voltage, dc current, firing angle, tap gear, ideal no-load voltage. Then the initial signals of the sending-end LCC converter station recorded at this time are the initial values of the dc voltage, the dc current, the firing angle, the tap shift, and the ideal no-load voltage.
102. Gradually increasing the direct-current voltage reference value of the modular multilevel converter, and recording a first signal of the power grid phase change converter when the direct current of the power grid phase change converter is 0;
it should be noted that, the reference value of the dc voltage of the receiving end MMC can be gradually increased, and the specific increasing method thereof is as follows: the MMC dc voltage reference value may be set as Udref, and then the kth dc voltage after boosting is:
Udrefk+1＝.Udrefk+△Udref(k＝0，1，……，N)
in the formula, Δ Udref may be set reasonably according to experimental needs, for example, Δ Udref may be set to 5 kV. After the direct current voltage reference value is increased once each time, the direct current power transmission systems at the two mixed ends are waited to enter a stable operation state, and the direct current voltage, the direct current, the trigger angle, the tap gear and the ideal no-load voltage of the LCC converter station at the transmitting end are observed in real time.
And when the direct current of the LCC converter station at the sending end is found to be reduced to 0, recording the direct current voltage, the direct current, the trigger angle, the tap gear and the ideal no-load voltage of the LCC converter station at the moment. Note that the first signal recorded at this time is the node (a in fig. 3) position in the outer characteristic curve of the LCC in the hybrid two-terminal dc power transmission system. Then, the curve (initial operating point to node a) obtained by the test at this time is the LCC in the typical mixed two-terminal dc external characteristic curve shown in fig. 3: first, the method comprises the following steps.
103. Restoring the direct current system to a stable running state before testing, gradually reducing the direct current voltage reference value of the modular multilevel converter, and recording a first signal of the power grid phase change converter at the corresponding moment when the direct current of the power grid phase change converter begins to drop and the direct current voltage of the power grid phase change converter is reduced to 0;
it should be noted that, the dc system is restored to the stable operation state before the test, the second-stage test of the LCC is started, and the dc voltage reference value of the receiving-end MMC can be gradually reduced, and the specific reducing method thereof is as follows: the MMC dc voltage reference value may be set to Udref, and then the j-th reduced dc voltage is:
Udrefj+1＝.Udrefj-△Udref(j＝0，1，……，N)
in the formula, Δ Udref may be set reasonably according to experimental needs, for example, Δ Udref may be set to 2 kV. After the direct current voltage reference value is reduced once each time, the direct current power transmission systems at the two mixed ends are waited to enter a stable operation state, and the direct current voltage, the direct current, the trigger angle, the tap gear and the ideal no-load voltage of the LCC converter station at the transmitting end are observed in real time.
And when the direct current of the LCC converter station at the sending end begins to drop, recording the direct current voltage, the direct current, the trigger angle, the tap gear and the ideal no-load voltage of the LCC converter station at the moment. Note that the first signal recorded at this time is the node (B in fig. 3) position in the outer characteristic curve of the LCC in the hybrid two-terminal dc power transmission system. Then, the curve (initial operating point to node B) obtained from the test at this time is the LCC in the typical mixed two-terminal dc external characteristic curve shown in fig. 3: and (II) performing secondary filtration.
And continuously and gradually reducing the direct-current voltage reference value of the MMC at the receiving end, and recording the direct-current voltage, the direct current, the trigger angle, the tap gear and the ideal no-load voltage of the LCC converter station at the moment when the direct-current voltage drop of the LCC converter station at the sending end is found to be 0. Note that the first signal recorded at this time is the node (C in fig. 3) position in the outer characteristic curve of the LCC in the hybrid two-terminal dc power transmission system. Then, the curve (node B to node C) obtained from the test at this time is the LCC in the typical mixed two-terminal dc external characteristic graph shown in fig. 3: and thirdly, performing a chemical reaction on the mixture.
Testing the modular multilevel converter:
104. recording a trigger angle reference value of the power grid commutation converter and simultaneously recording a first signal of the power grid commutation converter under the stable operation state of a direct current system;
it should be noted that, when the modular multilevel converter is started to be tested, at this time, the sub-module capacitor voltage of the receiving-end MMC converter station is not fixed to be a steady-state value any more, but in a stable operation state of the dc system, the trigger angle of the current sending-end LCC converter station is recorded as an initial value of the trigger angle, and at the same time, the dc voltage, the dc current, the trigger angle, the tap position, and the ideal no-load voltage of the grid phase-change converter are recorded.
105. Gradually increasing the trigger angle reference value of the power grid phase change converter, and recording a second signal of the modular multilevel converter when the direct current voltage of the modular multilevel converter starts to fall, the direct current of the modular multilevel converter starts to fall and the trigger angle reference value of the power grid phase change converter is increased to a first preset angle respectively;
it should be noted that the trigger angle reference value of the sending-end LCC converter station may be gradually increased, and the specific increasing method is as follows: the trigger angle reference value of the LCC converter station can be set to alpha0Then the firing angle reference value after the ith rise is:
αi+1＝.αi+△.α(i＝0，1，……，N)
in the formula, Δ α may be set appropriately according to experimental needs, and for example, Δ α may be set to 0.5 °. After the trigger angle reference value is raised once each time, waiting for the direct current transmission systems at the two mixed ends to enter a stable operation state, and starting to observe a second signal of the MMC converter station at the receiving end in real time, wherein the second signal specifically comprises direct current voltage, direct current, a modulation ratio, a tap gear and valve side voltage.
When the direct current voltage of the MMC converter station at the receiving end begins to drop, the direct current voltage, the direct current, the modulation ratio, the tap gear and the valve side voltage of the MMC converter station at the moment are recorded. Note that the second signal recorded at this time is the node (D in fig. 3) position in the outer characteristic curve of the MMC in the hybrid two-terminal dc power transmission system. Then, the curve (initial operating point to node D) obtained by the test at this time is the MMC in the typical mixed two-terminal dc external characteristic curve shown in fig. 3: first, the method comprises the following steps.
And continuously and gradually increasing the trigger angle reference value of the sending end LCC converter station until the direct current of the receiving end MMC converter station begins to decrease, and recording the direct current voltage, the direct current, the modulation ratio, the tap gear and the valve side voltage of the MMC converter station at the moment. Note that the second signal recorded at this time is the node (E in fig. 3) position in the outer characteristic curve of the MMC in the hybrid two-terminal dc power transmission system. Then, the curve (node D to node E) obtained by the test at this time is the MMC in the exemplary mixed two-terminal dc external characteristic diagram shown in fig. 3: and (II) performing secondary filtration.
And continuously and gradually increasing the reference value of the trigger angle of the sending-end LCC converter station until the trigger angle of the sending-end LCC converter station is increased to a first preset angle (the first preset angle can be reasonably set to a larger angle according to experimental needs, for example, the first preset angle can be set to 90 degrees), and recording the direct current voltage, the direct current, the modulation ratio, the tap gear and the valve side voltage of the MMC converter station at the moment. Note that the second signal recorded at this time is the node (F in fig. 3) position in the outer characteristic curve of the MMC in the hybrid two-terminal dc power transmission system. Then, the curve (node E to node F) obtained by the test at this time is the MMC in the exemplary mixed two-terminal dc external characteristic diagram shown in fig. 3: and thirdly, performing a chemical reaction on the mixture.
106. And restoring the direct current system to a stable operation state, gradually reducing the trigger angle reference value of the power grid commutation converter, and recording a second signal of the modular multilevel converter when the direct current voltage of the power grid commutation converter starts to rise and when the trigger angle reference value of the power grid commutation converter is reduced to a second preset angle.
It should be noted that, the dc system is restored to the stable operation state before the test, the second-stage test of the MMC is started, and at this time, the reference value of the trigger angle of the sending-end LCC converter station may be gradually reduced, and the specific reducing method thereof is as follows: the initial trigger angle reference value of the LCC converter station can be set to be alpha0Then the firing angle reference value after the nth rise is:
αn+1＝.αn-△.α(n＝0，1，……，N)
in the formula, Δ α may be set appropriately according to experimental needs, and for example, Δ α may be set to 0.5 °. After the trigger angle reference value is reduced once each time, waiting for the direct current transmission systems at the two mixed ends to enter a stable operation state, and observing the direct current voltage, the direct current, the modulation ratio, the tap gear and the valve side voltage of the MMC converter station at the receiving end in real time.
When the dc voltage of the MMC converter station starts to rise, the dc voltage, the dc current, the modulation ratio, the tap position and the valve side voltage of the MMC converter station at that moment are recorded. Note that the first signal recorded at this time is the node (G in fig. 3) position in the outer characteristic curve of the MMC in the hybrid two-terminal dc power transmission system. Then, the curve (initial operating point to node G) obtained by the test at this time is the MMC in the typical mixed two-terminal dc external characteristic curve shown in fig. 3: and fourthly, performing secondary filtration.
And continuously and gradually reducing the trigger angle reference value of the sending-end LCC converter station, and recording the direct current voltage, the direct current, the modulation ratio, the tap position and the valve side voltage of the MMC converter station at the moment when the trigger angle reference value of the sending-end LCC converter station is found to be reduced to a second preset angle (the second preset angle can be set to a reasonable small angle according to experimental needs, for example, the second preset angle can be set to 5 ℃). Note that the second signal recorded at this time is the node (H in fig. 3) position in the outer characteristic curve of the MMC in the hybrid two-terminal dc power transmission system. Then, the curve (node G to node H) obtained by the test at this time is the MMC in the exemplary mixed two-terminal dc external characteristic curve shown in fig. 3: fifthly.
The LCC: to LCC: ③ and linking the MMC: to MMC: fifthly, drawing in the same Ud/Id coordinate system, thus obtaining the direct current external characteristic curve chart of the typical mixing two ends shown in figure 3.
Aiming at a hybrid direct-current power transmission system with one end adopting an LCC and the other end adopting an MMC, on one hand, aiming at the LCC, a mode of keeping the capacitance voltage of the modular multilevel converter and gradually increasing or decreasing the direct-current voltage reference value of the modular multilevel converter is adopted to observe the corresponding signal of the power grid phase-change converter in real time; on the other hand, aiming at the MMC, the external characteristics of the mixed direct-current two-end power transmission system with one end adopting the LCC and the other end adopting the MMC are tested in a mode of gradually increasing or decreasing the trigger angle reference value of the power grid phase-change converter and observing the corresponding signal of the modular multilevel converter in real time, and the technical problem that the external characteristics of the mixed direct-current two-end power transmission system with one end adopting the LCC and the other end adopting the MMC are difficult to test in the prior art is solved.
It is clear to those skilled in the art that, for convenience and brevity of description, the specific working processes of the above-described systems, apparatuses and units may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.
The terms "first," "second," "third," "fourth," and the like in the description of the application and the above-described figures, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
It should be understood that in the present application, "at least one" means one or more, "a plurality" means two or more. "and/or" for describing an association relationship of associated objects, indicating that there may be three relationships, e.g., "a and/or B" may indicate: only A, only B and both A and B are present, wherein A and B may be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single item(s) or plural items. For example, at least one (one) of a, b, or c, may represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", wherein a, b, c may be single or plural.
The above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions in the embodiments of the present application.

Claims (10)

1. A hybrid two-end direct current transmission system is characterized in that a transmitting end of the hybrid two-end direct current transmission system is a power grid commutation converter, and a receiving end of the hybrid two-end direct current transmission system is a modular multilevel converter;
the power grid phase-change converter is used for converting alternating current into direct current to be output;
the modular multilevel converter is used for receiving direct current and converting the direct current into alternating current.
2. A method for testing the external characteristics of mixed two-end direct current is realized based on claim 1, and is characterized by comprising the following steps:
testing the power grid commutation converter:
operating a direct current system to a stable operation state, fixing the capacitor voltage of a modular multilevel converter to be a stable value, recording the direct current voltage reference value of the modular multilevel converter, and simultaneously recording a first signal of the power grid phase-change converter;
gradually increasing a direct-current voltage reference value of a modular multilevel converter, and recording the first signal of the power grid phase change converter when the direct current of the power grid phase change converter is 0;
restoring the direct-current system to a stable operation state before testing, gradually reducing a direct-current voltage reference value of the modular multilevel converter, and recording the first signal of the power grid phase change converter at the corresponding moment when the direct current of the power grid phase change converter begins to decline and when the direct-current voltage of the power grid phase change converter is reduced to 0;
testing the modular multilevel converter:
recording a trigger angle reference value of the power grid commutation converter and simultaneously recording a first signal of the power grid commutation converter under the stable operation state of the direct current system;
gradually increasing a firing angle reference value of the grid commutation converter, and recording a second signal of the modular multilevel converter when a direct current voltage of the modular multilevel converter starts to fall, when the direct current of the modular multilevel converter starts to fall and when the firing angle reference value of the grid commutation converter rises to a first preset angle, respectively;
and restoring the direct-current system to a stable running state before testing, gradually reducing the trigger angle reference value of the power grid phase change converter, and recording a second signal of the modular multilevel converter when the direct-current voltage of the power grid phase change converter starts to rise and the trigger angle reference value of the power grid phase change converter is reduced to a second preset angle.
3. The hybrid two-terminal dc external characteristic testing method according to claim 2, wherein the step-up of the dc voltage reference value of the modular multilevel converter is performed to record the first signal of the grid commutated converter when the dc current of the grid commutated converter is 0, specifically:
gradually increasing a direct-current voltage reference value of the modular multilevel converter, and observing a first signal of the power grid commutation converter corresponding to the direct-current voltage reference value in real time;
and when the direct current of the power grid phase change converter is 0, recording a first signal of the power grid phase change converter at the moment.
4. The method according to claim 2, wherein the step of restoring the dc system to a steady operation state before the test, the step of decreasing the dc voltage reference value of the modular multilevel converter, the step of recording the first signal of the grid commutated converter at the corresponding time when the dc current of the grid commutated converter starts to decrease and when the dc current of the grid commutated converter decreases to 0, specifically:
restoring the direct-current system to a stable running state before testing, gradually reducing a direct-current voltage reference value of the modular multilevel converter, and observing a first signal of the power grid commutation converter corresponding to the direct-current voltage reference value in real time;
when the direct current of the power grid phase change converter begins to decline, recording a first signal of the power grid phase change converter at the moment;
continuously and gradually reducing the direct-current voltage reference value of the modular multilevel converter, and observing a first signal of the power grid commutation converter corresponding to the direct-current voltage reference value in real time;
when the direct-current voltage drop of the power grid phase change converter is 0, recording a first signal of the power grid phase change converter at the moment.
5. The hybrid two-terminal dc external characteristic testing method according to claim 2, wherein the step-up of the firing angle reference value of the grid commutated converter records a second signal of the modular multilevel converter when the dc voltage of the modular multilevel converter starts to decrease, when the dc current of the modular multilevel converter starts to decrease, and when the firing angle reference value of the grid commutated converter increases to a first preset angle, respectively, and specifically:
gradually increasing a trigger angle reference value of the power grid commutation converter, and observing a second signal of the modular multilevel converter corresponding to the direct-current voltage reference value in real time;
recording a second signal of the modular multilevel converter when the direct-current voltage of the modular multilevel converter begins to drop;
when the direct current of the modular multilevel converter begins to fall, recording a second signal of the modular multilevel converter at the moment;
and when the trigger angle reference value of the power grid commutation converter is increased to a first preset angle, recording a second signal of the modular multilevel converter at the moment.
6. The hybrid two-terminal direct current external characteristic testing method according to claim 5, wherein the first preset angle is 90 °.
7. The hybrid two-terminal dc external characteristic testing method according to claim 2, wherein the dc system is restored to a steady operation state before testing, the firing angle reference value of the grid commutated converter is gradually decreased, and a second signal of the modular multilevel converter is recorded when the dc voltage of the grid commutated converter starts to increase and when the firing angle reference value of the grid commutated converter decreases to a second preset angle, respectively, specifically:
restoring the direct-current system to a stable running state before testing, gradually reducing a trigger angle reference value of the power grid commutation converter, and observing a second signal of the modular multilevel converter corresponding to the direct-current voltage reference value in real time;
when the direct-current voltage of the power grid commutation converter begins to rise, recording a second signal of the modular multilevel converter at the moment;
and when the trigger angle reference value of the power grid commutation converter is reduced to a second preset angle, recording a second signal of the modular multilevel converter at the moment.
8. The hybrid two-terminal direct current external characteristic testing method according to claim 7, wherein the second preset angle is 5 °.
9. The hybrid two-terminal direct current external characteristic testing method according to any one of claims 2 to 8, wherein the first signal of the grid commutated converter is a direct current voltage, a direct current, a firing angle, a tap position, an ideal no-load voltage.
10. The hybrid two-terminal direct current external characteristic testing method according to any one of claims 2 to 8, wherein the second signal of the modular multilevel converter is a direct current voltage, a direct current, a modulation ratio, a tap position and a valve side voltage.
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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6202041B1 (en) * 1998-04-29 2001-03-13 Hong Kong Polytechnic University Electrical power network modelling method
EP2975420A1 (en) * 2014-07-18 2016-01-20 Alstom Technology Ltd Synthetic test circuit
CN106160023A (en) * 2015-04-17 2016-11-23 华北电力大学 A kind of Hybrid HVDC receiving end weak mains frequency cooperative control method
CN106849148A (en) * 2017-03-10 2017-06-13 南方电网科学研究院有限责任公司 Alternating current fault ride-through control method for rectifying station of hybrid direct current transmission system

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6202041B1 (en) * 1998-04-29 2001-03-13 Hong Kong Polytechnic University Electrical power network modelling method
EP2975420A1 (en) * 2014-07-18 2016-01-20 Alstom Technology Ltd Synthetic test circuit
CN106160023A (en) * 2015-04-17 2016-11-23 华北电力大学 A kind of Hybrid HVDC receiving end weak mains frequency cooperative control method
CN106849148A (en) * 2017-03-10 2017-06-13 南方电网科学研究院有限责任公司 Alternating current fault ride-through control method for rectifying station of hybrid direct current transmission system

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