CN117200224A - Three-phase fault ride-through method for continuous low voltage of hybrid cascade direct current system - Google Patents
Three-phase fault ride-through method for continuous low voltage of hybrid cascade direct current system Download PDFInfo
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Abstract
The application relates to a three-phase fault ride-through method for continuous low voltage of a hybrid cascade direct current system, which comprises the following steps: according to the three-phase alternating voltage of the soft direct current converter transformer network side of the soft direct current converter station in the mixed cascade direct current system, calculating the alternating voltage amplitude of the receiving end of the mixed cascade direct current system and detecting the three-phase fault of the near-area alternating current system of the soft direct current converter transformer; when detecting that the soft direct current converter transformer has three-phase faults of the near-area alternating current system, the phase shifting of the transmitting end of the hybrid cascade direct current system is carried out, the phase shifting is released after the set phase shifting time is kept, and the alternating current fault recovery process is carried out; in the alternating current fault recovery process, according to the continuous low-voltage state and alternating current voltage amplitude of the receiving end of the hybrid cascade direct current system, the transmitting end of the hybrid cascade direct current system adopts a square wave type power limiting mode or a slope type power limiting mode, so that the frequency stability, the voltage stability and the power angle stability of the transmitting end and the receiving end of the hybrid cascade direct current system are ensured, and the method can be widely applied to the field of direct current transmission.
Description
Technical Field
The application relates to the field of direct current transmission, in particular to a three-phase fault ride-through method for continuous low voltage of a hybrid cascade direct current system.
Background
The energy resources in China are reversely distributed with the load center, the construction of the extra-high voltage backbone power grid needs to be steadily promoted, and the conveying capacity of the extra-high voltage large power grid is exerted. The direct current feed-in demand of the part load center of China, such as the eastern China, is continuously increased, but the dense feed-in of direct current outside the area can cause the reduction of the electric distance between the converter stations, the multi-feed-in short-circuit ratio is reduced, the risk of multi-circuit direct current commutation failure is gradually increased, and the power grid is caused to face serious safety and stability problems. In order to realize long-distance large-capacity power transmission and multi-drop point power supply and solve the problem of short-circuit ratio reduction of the receiving end multi-feed-in, a mixed cascade extra-high voltage direct current power transmission mode, namely a technical scheme of cascade connection of a conventional direct current converter and a plurality of flexible direct current converters, is adopted, combines the advantages of the conventional direct current and the flexible direct current, can effectively improve the stability of the receiving end alternating current power grid, is high in reliability, flexible in operation mode, has wide application prospect, and is a key technology for constructing the future energy Internet.
LCC (grid commutation converter) is adopted at the transmitting end of the hybrid cascade extra-high voltage direct current system, different alternating current falling points are connected in a scattered mode through LCC and VSC (voltage source converter) at the receiving end, but because the receiving end is usually a developed area, the falling points are still close to each other, different degrees of electric coupling still exist between the alternating current falling points, when a single converter breaks down in a near-area three-phase alternating current system, the voltages of alternating current buses at the network sides of the other converters are simultaneously caused to fall in different degrees, the condition that the alternating current buses continuously run low voltage is easy to occur is caused, so that high-end LCC commutation failure and cascading failure reactions of the VSC with long-time limited output power are caused, serious surplus of the direct current power of the VSC is continuously injected at the transmitting end, and serious overvoltage or energy-dissipating device energy out of the VSC is finally caused, and the operation is seriously caused.
Therefore, how to reduce the surplus power of the direct current side of the VSC converter after the three-phase fault of the near-area alternating current system at the receiving end of the hybrid cascade direct current system, and ensure that the system can realize the three-phase fault ride-through of the near-area alternating current system when the continuous low voltage occurs in various operation modes is a key problem of safe and reliable operation of the hybrid cascade direct current system, but the prior art has not been related yet.
Disclosure of Invention
Aiming at the problems, the application aims to provide a three-phase fault ride-through method for continuous low voltage of a hybrid cascade direct current system, which can ensure that the system realizes three-phase fault ride-through of a near-area alternating current system when continuous low voltage occurs in various operation modes.
In order to achieve the above purpose, the present application adopts the following technical scheme: in a first aspect, a three-phase fault ride through method for continuous low voltage of a hybrid cascading direct current system is provided, including:
according to the three-phase alternating voltage of the soft direct current converter transformer network side of the soft direct current converter station in the mixed cascade direct current system, calculating the alternating voltage amplitude of the receiving end of the mixed cascade direct current system and detecting the three-phase fault of the near-area alternating current system of the soft direct current converter transformer;
when detecting that the soft direct current converter transformer has three-phase faults of the near-area alternating current system, the phase shifting of the transmitting end of the hybrid cascade direct current system is carried out, the phase shifting is released after the set phase shifting time is kept, and the alternating current fault recovery process is carried out;
in the alternating current fault recovery process, according to the continuous low-voltage state and alternating current voltage amplitude of the receiving end of the hybrid cascade direct current system, the sending end of the hybrid cascade direct current system adopts a square wave type power limiting mode or a slope type power limiting mode, and the frequency stability, the voltage stability and the power angle stability of the sending end and the receiving end of the hybrid cascade direct current system are ensured.
Further, the calculating the ac voltage amplitude of the receiving end of the hybrid cascade dc system and detecting the three-phase fault of the near-area ac system of the soft dc converter transformer according to the three-phase ac voltage of the soft dc converter transformer network side of the soft dc converter in the hybrid cascade dc system includes:
collecting three-phase alternating current voltage at the net side of a soft direct converter transformer of a soft direct converter station in a mixed cascade direct current system in real time;
according to the three-phase alternating voltage at the net side of the flexible direct current converter transformer acquired in real time, calculating the alternating voltage amplitude of the receiving end of the hybrid cascade direct current system;
and detecting a three-phase fault of the near-area alternating current system of the soft direct current converter transformer according to the three-phase alternating current voltage of the net side of the soft direct current converter transformer acquired in real time.
Further, the calculating the ac voltage amplitude of the receiving end of the hybrid cascade dc system according to the three-phase ac voltage of the net side of the soft dc converter transformer acquired in real time includes:
CLARK conversion is carried out on three-phase alternating voltage at the net side of the flexible direct current converter transformer acquired in real time to obtain two-phase componentsAnd->The amplitude of the alternating voltage +.>The method comprises the following steps:
。
further, according to the real-time collected three-phase ac voltage at the net side of the soft direct converter transformer, detecting a three-phase fault of the near-zone ac system of the soft direct converter transformer includes:
the three-phase alternating voltage at the net side of the flexible direct current converter transformer acquired in real time is subjected to positive and negative sequence PARK conversion to obtain dq positive sequence voltage component、/>And dq negative sequence voltage component +.>、/>；
According to dq positive sequence voltage component、/>And dq negative sequence voltage component +.>、/>Respectively calculating positive sequence voltage component amplitude +.>And negative sequence voltage component amplitude +.>：
When meeting the requirementsAnd->When the soft direct current converter transformer is in the near zone alternating current system three-phase fault, judging that the soft direct current converter transformer is in the near zone alternating current system three-phase fault, wherein ∈>Judging threshold value for positive sequence voltage component amplitude, +.>A threshold is determined for the negative sequence voltage component amplitude.
Further, in the ac fault recovery process, according to the state of the continuous low voltage of the receiving end of the hybrid cascade dc system and the ac voltage amplitude, the transmitting end of the hybrid cascade dc system adopts a square wave power limiting mode or a slope power limiting mode, so as to ensure stable frequency, stable voltage and stable power angle of the transmitting end and the receiving end of the hybrid cascade dc system, including:
in the alternating current fault recovery process, according to the state that the receiving end of the hybrid cascade direct current system continuously has low voltage, the transmitting end of the hybrid cascade direct current system enters a power limit recovery mode, wherein the power limit recovery mode comprises a square wave type power limit mode and a slope type power limit mode;
the method comprises the steps that a square wave type power limiting mode is preferentially adopted by a sending end of a hybrid cascading direct current system, electromechanical-electromagnetic transient joint simulation is carried out on the hybrid cascading direct current system when a near-area alternating current system three-phase fault occurs on the basis of alternating voltage amplitude of a receiving end of the hybrid cascading direct current system, and whether the square wave type power limiting mode can ensure stable frequency, stable voltage and stable power angle of the sending end and the receiving end of the alternating current system is determined;
when the square wave type power limiting mode is adopted, the stability of the alternating current system at the transmitting end and the receiving end cannot be guaranteed, and the slope type power limiting mode is adopted, so that the frequency stability, the voltage stability and the power angle stability of the transmitting end and the receiving end are guaranteed based on the alternating voltage amplitude of the receiving end of the mixed cascade direct current system.
Further, the square wave type power limiting mode is as follows: setting a maximum recovery power limit value when the power is recovered after the phase shift of the transmitting end of the hybrid cascade direct current systemLimiting the maximum recovery power of the transmitting end of the hybrid cascade direct current system to +.>And maintain time->Then, the system is restored to the level before failure;
the slope type power limiting mode is as follows: alternating current voltage amplitude of receiving end of mixed cascade direct current systemReal-time communication is carried out to a transmitting end, the transmitting end carries out station low-voltage current limiting according to the alternating current bus voltage of a receiving end, and a low-voltage current limiting curve of a hybrid cascade direct current system is set up +.>Wherein->For the current running mode of the mixed cascade direct current systemRated power of system>Is a margin coefficient.
Further, the method further comprises:
scanning a near-zone alternating current system three-phase fault of a soft direct current converter station in a hybrid cascade direct current system, acquiring alternating current low voltage amplitude and low voltage duration under a continuous low voltage working condition that energy absorption of an energy dissipation device is maximum in a near-zone alternating current system three-phase fault recovery process of recovery voltage over a plurality of milliseconds, and judging the maximum recovery power limiting value and the maintenance time in a square wave power limiting mode by the acquired alternating current low voltage amplitude and low voltage duration.
In a second aspect, a three-phase fault ride through method for continuous low voltage of a hybrid cascading direct current system is provided, including:
the near-zone alternating current system three-phase fault detection module is used for calculating the alternating current voltage amplitude of the receiving end of the hybrid cascading direct current system and detecting the near-zone alternating current system three-phase fault of the soft direct current converter according to the three-phase alternating current voltage of the soft direct current converter network side of the soft direct current converter in the hybrid cascading direct current system;
the alternating current fault recovery module is used for removing the phase shift after the phase shift of the transmitting end of the hybrid cascade direct current system is maintained for a set phase shift time after detecting that the soft direct current converter transformer has a near-zone alternating current system three-phase fault, and entering an alternating current fault recovery process;
and the power limit recovery module is used for ensuring stable frequency, stable voltage and stable power angle of the transmitting end and the receiving end of the hybrid cascade direct current system according to the continuous low voltage state and the alternating voltage amplitude of the receiving end of the hybrid cascade direct current system in the alternating current fault recovery process.
In a third aspect, a processing device is provided, including computer program instructions, where the computer program instructions, when executed by the processing device, are configured to implement steps corresponding to the three-phase fault ride through method for continuous low voltage of the hybrid cascaded direct current system described above.
In a fourth aspect, a computer readable storage medium is provided, where the computer readable storage medium stores computer program instructions, where the computer program instructions are executed by a processor to implement steps corresponding to the three-phase fault ride through method for continuous low voltage of the hybrid cascade direct current system.
Due to the adoption of the technical scheme, the application has the following advantages:
1. the application provides a complete set of fault ride-through method and process under continuous low voltage of alternating current, which effectively solve the problem of energy out-of-limit of a direct current side energy dissipation device when the continuous low voltage is long time caused by the fault of a flexible direct current alternating current system, reduce the surplus power of the direct current side of a VSC, limit the energy of the energy dissipation device within an allowable range, avoid the investment of primary equipment of the energy dissipation device, and ensure that three-phase fault ride-through of a near-zone alternating current system under continuous low voltage can be realized under various running modes of the system.
2. The square wave type power limiting mode provided by the application does not need inter-station communication, and can ensure the fault ride-through capability in various operation modes; the proposed slope type power limiting mode depends on inter-station communication, but can reserve power transmission capacity to the maximum extent, reduce power loss, and the two schemes can be selected according to system requirements.
In summary, the application can be widely applied to the field of direct current transmission.
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Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the application. Like parts are designated with like reference numerals throughout the drawings. In the drawings:
FIG. 1 is a schematic diagram of a hybrid cascaded DC system topology according to an embodiment of the present application;
FIG. 2 is a flow chart of a method according to an embodiment of the present application;
fig. 3 is a schematic diagram of VSC ac voltage amplitude calculation of a hybrid cascading dc system according to an embodiment of the present application;
fig. 4 is a flow chart of a three-phase fault detection method of a VSC near-zone ac system of a hybrid cascading dc system according to an embodiment of the present application.
Detailed Description
Exemplary embodiments of the present application will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art.
It is to be understood that the terminology used herein is for the purpose of describing particular example embodiments only, and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises," "comprising," "includes," "including," and "having" are inclusive and therefore specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order described or illustrated, unless an order of performance is explicitly stated. It should also be appreciated that additional or alternative steps may be used.
Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as "first," "second," and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.
As shown in fig. 1, the transmitting end of the hybrid cascade direct current system adopts a conventional extra-high voltage direct current topological structure, and each pole is formed by cascade connection of 2 twelve-pulse conventional direct current converters; the receiving end of the hybrid cascade direct current system adopts a hybrid cascade direct current system topological structure, each pole is formed by cascading a plurality of (3 in the drawing) parallel flexible direct current converters of a high-voltage end (namely 800 kV-400 kV) twelve-pulse conventional direct current converter and a low-voltage end (400 kV-neutral line), the flexible direct current converters adopt half-bridge modularized multi-level converters, and the receiving end conventional direct current converter and each flexible direct current converter are fed into different alternating current buses. The three-phase fault ride-through method for the continuous low voltage of the hybrid cascade direct current system provided by the embodiment of the application can effectively reduce the surplus power of the direct current side of the VSC converter under the continuous low voltage after the three-phase fault of the system receiving end near-zone alternating current system, and ensure that the system can realize alternating current fault ride-through under various operation modes.
Example 1
As shown in fig. 2, the embodiment provides a three-phase fault ride-through method for continuous low voltage of a hybrid cascading dc system, which includes the following steps:
1) Scanning a near-area alternating current system three-phase fault of a soft direct current converter station in a hybrid cascade direct current system to obtain alternating current low-voltage amplitude under a continuous low-voltage working condition that energy absorption device absorbs energy maximally in a near-area alternating current system three-phase fault recovery process with recovery voltage of more than 100 millisecondsAnd low voltage duration +.>。
Specifically, the process of the three-phase fault scanning method of the near-zone alternating current system is as follows: an electromechanical-electromagnetic hybrid simulation model of a hybrid cascade direct current system is established, and the hybrid cascade direct current system is based on a severe mode of an alternating current system in a hybrid stageUnder the combination of different direct current operation modes and various VSC inputs of the direct current system, the three-phase fault of the near-area alternating current system is subjected to global scanning, and the alternating current low-voltage amplitude value under the continuous low-voltage working condition that the energy dissipation device absorbs the energy most in the process of recovering the three-phase fault of the near-area alternating current system with the recovery voltage of more than 100 milliseconds is obtainedAnd low voltage duration +.>The severe mode of the alternating current system refers to different wiring and different operation powers of the alternating current system, the severe mode refers to that the energy absorption device absorbs large energy in the mode, the direct current operation mode of the hybrid cascade direct current system comprises 7 types of bipolar full-voltage operation, monopolar earth return operation, monopolar metal return operation, bipolar mixed voltage operation, monopolar half-voltage earth return operation, monopolar half-voltage metal return operation and the like, the VSC input combination refers to the number of VSCs respectively input by the positive electrode and the negative electrode, and each pole can be input by 1 to 3 VSCs.
2) According to the three-phase alternating voltage of the soft direct current converter transformer network side of the soft direct current converter station in the mixed cascade direct current system, calculating the alternating voltage amplitude of the receiving end of the mixed cascade direct current systemAnd detecting three-phase faults of a near-zone alternating current system of the soft direct current converter transformer, which specifically comprises the following steps:
2.1 The method comprises the steps of) collecting three-phase alternating current voltage at the net side of a soft direct current converter transformer of a soft direct current converter station in a mixed cascade direct current system in real time.
2.2 According to the three-phase alternating voltage at the net side of the flexible direct current converter transformer acquired in real time, calculating the alternating voltage amplitude of the receiving end of the mixed cascade direct current system。
Specifically, as shown in fig. 3, the three-phase ac voltage on the net side of the flexible direct current converter transformer collected in real time is subjected to CLARK conversion to obtain two-phase componentsAnd->The amplitude of the alternating voltage +.>The method comprises the following steps:
（1）
2.3 As shown in fig. 4, according to the three-phase ac voltage on the net side of the soft direct converter transformer acquired in real time, detecting the three-phase fault of the near-zone ac system of the soft direct converter transformer:
2.3.1 Positive and negative sequence PARK conversion is carried out on three-phase alternating voltage at the net side of the flexible direct current converter transformer acquired in real time to obtain dq positive sequence voltage component、/>And dq negative sequence voltage component +.>、/>。
2.3.2 According to dq positive sequence voltage component、/>And dq negative sequence voltage component +.>、/>Respectively calculating positive sequence voltage component amplitude +.>And negative sequence voltage component amplitude +.>：
（2）
（3）
2.3.3 Setting a positive sequence voltage component amplitude judgment thresholdAnd a negative sequence voltage component amplitude determination threshold。
2.3.4 When meeting(s)And->And when the soft direct current converter transformer is in the short-range alternating current system three-phase fault, judging that the soft direct current converter transformer has the short-range alternating current system three-phase fault.
3) When detecting that the soft direct current converter transformer has three-phase faults of the near-zone alternating current system, the transmitting end of the hybrid cascade direct current system shifts the phase and keeps the set phase shifting timeAnd then the phase shift is released, and the alternating current fault recovery process is carried out.
4) In the AC fault recovery process, according to the state of continuous low voltage of the receiving end of the hybrid cascade DC system and the amplitude of the AC voltageThe transmitting end of the hybrid cascade direct current system adopts a square wave type power limiting mode or a slope type power limiting mode, so that the transmitting end and the receiving end of the hybrid cascade direct current system are ensuredEnd frequency stability, voltage stability and power angle stability (frequency stability, voltage stability and power angle stability are terms and refer to the ability of recovering to a specific state within a certain time after disturbance occurs), and specifically include:
4.1 In the alternating current fault recovery process, according to the state that the receiving end of the hybrid cascade direct current system continuously has low voltage, the transmitting end of the hybrid cascade direct current system enters a power limit recovery mode, wherein the power limit recovery mode comprises a square wave type power limit mode and a slope type power limit mode.
4.2 Square wave type power limiting mode is adopted for the transmitting end of the hybrid cascade direct current system, and the alternating current voltage amplitude value of the receiving end of the hybrid cascade direct current system is basedThe mode is adopted to perform electromechanical-electromagnetic transient joint simulation when the three-phase fault of the near-area alternating current system occurs in the mixed cascade direct current system, and whether the square wave type power limiting mode is adopted can ensure stable frequency, stable voltage and stable power angle of the alternating current system at the transmitting end and the receiving end.
Specifically, the square wave power limiting mode is: setting a maximum recovery power limit value when the power is recovered after the phase shift of the transmitting end of the hybrid cascade direct current systemLimiting the maximum recovery power of the transmitting end of the hybrid cascade direct current system to +.>And maintain time->After that, the pre-failure level is restored.
More specifically, the maximum recovered power limit value in square wave power limit modeAnd a maintenance timeThe method meets the following conditions: />，/>Wherein->For the nominal operating power of the system, +.>The AC voltage is rated for the network side of the soft DC converter transformer.
4.3 When the square wave type power limiting mode is adopted and the stability of the sending end alternating current system and the receiving end alternating current system cannot be ensured, the alternating current voltage amplitude of the receiving end based on the mixed cascade direct current systemAnd a slope type power limiting mode is adopted, so that the frequency stability, the voltage stability and the power angle stability of the transmitting end and the receiving end are ensured.
Specifically, the slope power limit mode is: alternating current voltage amplitude of receiving end of mixed cascade direct current systemReal-time communication is carried out to a transmitting end, the transmitting end carries out station low-voltage current limiting according to the alternating current bus voltage of a receiving end, and a low-voltage current limiting curve of a hybrid cascade direct current system is set up +.>Wherein->For the rated power of the hybrid cascade DC system in the current operating mode,/-for>As a margin coefficient, the coefficient is set to ensure that the power of the direct current side sent by the sending end is smaller than the power capability which can be consumed by the receiving end, surplus power is avoided, and 0.9-1 is recommended.
The method of the application is described in further detail below by taking a three-phase fault ride-through of a continuous low-voltage near-zone alternating current system of a hybrid cascade direct current system with +/-800 kV/8000MW and a single LCC and 3 VSCs at the receiving end as an example.
1) And establishing an electromechanical-electromagnetic hybrid simulation model of the hybrid cascade direct current system, and performing global scanning on three-phase faults of the near-area alternating current system under various operation modes of the hybrid cascade direct current system and various VSC input combinations based on a severe mode of the alternating current system. In this embodiment, by using an electromechanical-electromagnetic hybrid simulation (adcsp, PSASP) platform, direct current modes such as bipolar full voltage, bipolar half voltage, unipolar full voltage, unipolar half voltage, metal loop and the like are completed, and each input VSC combination (123, 12, 23, 13 and the like) is considered, three-phase fault global scanning of the VSC near-area ac system is performed under the most severe winter peak mode, so that a 1+2 low voltage operation mode (high voltage end LCC input operation, low voltage end 2 VSCs input operation) of the three-phase fault of the dc system is obtained, and in this operation mode, the most severe low voltage amplitude in the three-phase fault recovery process of the VSC near-area ac system is 0.72pu (per unit base value is rated ac voltage amplitude), and the low voltage duration is 0.9s at the most.
2) According to the three-phase alternating voltage of the soft direct current converter transformer network side of the soft direct current converter station in the mixed cascade direct current system, calculating the alternating voltage amplitude of the receiving end of the mixed cascade direct current systemAnd detecting a three-phase fault of a near-zone alternating current system of the soft direct current converter transformer. In this embodiment, the positive sequence voltage component amplitude judgment threshold +.>And a negative sequence voltage component amplitude determination thresholdTaken as 0.8pu, 0.2pu, respectively, when the positive sequence voltage component amplitude +.>And negative sequence voltage component amplitude +.>Satisfy the following requirementsAnd->And when the soft direct current converter transformer is in the short-range alternating current system three-phase fault, judging that the soft direct current converter transformer has the short-range alternating current system three-phase fault.
3) When detecting that the soft direct current converter transformer has three-phase faults of the near-zone alternating current system, the transmitting end of the hybrid cascade direct current system shifts and maintains the phaseAnd after the time, the phase shift is released, and the alternating current fault recovery process is carried out. In this embodiment, <' > a->Set to 70ms.
4) In the AC fault recovery process, according to the state of continuous low voltage of the receiving end of the hybrid cascade DC system and the amplitude of the AC voltage of the receiving end of the hybrid cascade DC system, and the obtained amplitude of the AC low voltage and the duration of the low voltageThe transmitting end of the hybrid cascade direct current system adopts a square wave type power limiting mode or a slope type power limiting mode, so that the frequency stability, the voltage stability and the power angle stability of the transmitting end and the receiving end of the hybrid cascade direct current system are ensured. In this embodiment, the square wave power limiting mode is adopted to ensure the stable frequency, stable voltage and stable power angle of the transmitting end and the receiving end of the hybrid cascade direct current system, so that the power limiting recovery mode is adopted, wherein the maximum recovery power limiting value +.>Set to 0.7pu (per unit basis value +.>) Maintenance time->Set to 1s. Finally, after adopting the square wave type power limiting mode, scanning and finding out the three-phase fault of the near-area alternating current system of the soft direct current converter station of the hybrid cascading direct current system again, the method effectively reduces the power surplus of the direct current side of the VSC, limits the energy of the energy dissipation device of the direct current side of the VSC within the allowable range, and ensures that the three-phase fault ride-through of the near-area alternating current system under continuous low voltage can be realized under various running modes of the system.
Example 2
The embodiment provides a three-phase fault ride through method for continuous low voltage of a hybrid cascade direct current system, which comprises the following steps:
the fault scanning module is used for scanning the three-phase faults of the near-area alternating current system of the soft direct current converter station in the hybrid cascade direct current system and obtaining alternating current low-voltage amplitude and low-voltage duration under the continuous low-voltage working condition that the energy dissipation device absorbs energy most in the process of recovering the three-phase faults of the near-area alternating current system with recovery voltage of more than a plurality of milliseconds.
And the near-zone alternating current system three-phase fault detection module is used for calculating the alternating current voltage amplitude of the receiving end of the hybrid cascade direct current system according to the three-phase alternating current voltage of the soft direct current converter transformer network side of the soft direct current converter station in the hybrid cascade direct current system and detecting the near-zone alternating current system three-phase fault of the soft direct current converter.
And the alternating current fault recovery module is used for removing the phase shift after the phase shift of the transmitting end of the hybrid cascade direct current system is maintained for a set phase shift time after detecting that the soft direct current converter transformer has a near-zone alternating current system three-phase fault, and entering an alternating current fault recovery process.
And the power limit recovery module is used for ensuring stable frequency, stable voltage and stable power angle of the transmitting end and the receiving end of the hybrid cascade direct current system according to the continuous low voltage state and the alternating voltage amplitude of the receiving end of the hybrid cascade direct current system in the alternating current fault recovery process.
The system provided in this embodiment is used to execute the above method embodiments, and specific flow and details refer to the above embodiments, which are not repeated herein.
Example 3
The present embodiment provides a processing device corresponding to the continuous low-voltage three-phase fault ride-through method of the hybrid cascade direct current system provided in embodiment 1, where the processing device may be applied to a processing device of a client, for example, a mobile phone, a notebook computer, a tablet computer, a desktop computer, etc., to execute the method of embodiment 1.
The processing device comprises a processor, a memory, a communication interface and a bus, wherein the processor, the memory and the communication interface are connected through the bus so as to complete communication among each other. The memory stores a computer program that can be run on the processing device, and when the processing device runs the computer program, the three-phase fault ride-through method for continuous low voltage of the hybrid cascade direct current system provided in this embodiment 1 is executed.
In some implementations, the memory may be high-speed random access memory (RAM: random Access Memory), and may also include non-volatile memory (non-volatile memory), such as at least one disk memory.
In other implementations, the processor may be a Central Processing Unit (CPU), a Digital Signal Processor (DSP), or other general-purpose processor, which is not limited herein.
Further, the logic instructions in the memory described above may be implemented in the form of software functional units and stored in a computer-readable storage medium when sold or used as a stand-alone product. Based on this understanding, the technical solution of the present application may be embodied essentially or in a part contributing to the prior art or in a part of the technical solution, in the form of a software product stored in a storage medium, comprising several instructions for causing a computer device (which may be a personal computer, a server, a network device, etc.) to perform all or part of the steps of the method according to the embodiments of the present application. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a random access Memory (RAM, random Access Memory), a magnetic disk, or an optical disk, or other various media capable of storing program codes.
It will be appreciated by those skilled in the art that the structures of the computing devices described above are merely partial structures related to the present inventive arrangements and do not constitute limitations of the computing devices to which the present inventive arrangements are applied, and that a particular computing device may include more or fewer components, or may combine certain components, or have a different arrangement of components.
Example 4
The present embodiment provides a computer program product corresponding to the method for continuous low-voltage three-phase fault ride-through of a hybrid cascading dc system provided in the present embodiment 1, where the computer program product may include a computer readable storage medium having computer readable program instructions for executing the method for continuous low-voltage three-phase fault ride-through of a hybrid cascading dc system described in the present embodiment 1.
The computer readable storage medium may be a tangible device that retains and stores instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination of the preceding.
The foregoing embodiment provides a computer readable storage medium, which has similar principles and technical effects to those of the foregoing method embodiment, and will not be described herein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The foregoing embodiments are only for illustrating the present application, wherein the structures, connection modes, manufacturing processes, etc. of the components may be changed, and all equivalent changes and modifications performed on the basis of the technical solutions of the present application should not be excluded from the protection scope of the present application.
Claims (10)
1. The three-phase fault ride through method for continuous low voltage of the hybrid cascade direct current system is characterized by comprising the following steps of:
according to the three-phase alternating voltage of the soft direct current converter transformer network side of the soft direct current converter station in the mixed cascade direct current system, calculating the alternating voltage amplitude of the receiving end of the mixed cascade direct current system and detecting the three-phase fault of the near-area alternating current system of the soft direct current converter transformer;
when detecting that the soft direct current converter transformer has three-phase faults of the near-area alternating current system, the phase shifting of the transmitting end of the hybrid cascade direct current system is carried out, the phase shifting is released after the set phase shifting time is kept, and the alternating current fault recovery process is carried out;
in the alternating current fault recovery process, according to the continuous low-voltage state and alternating current voltage amplitude of the receiving end of the hybrid cascade direct current system, the sending end of the hybrid cascade direct current system adopts a square wave type power limiting mode or a slope type power limiting mode, and the frequency stability, the voltage stability and the power angle stability of the sending end and the receiving end of the hybrid cascade direct current system are ensured.
2. The method for three-phase fault ride-through of continuous low voltage of a hybrid cascading dc system according to claim 1, wherein the calculating the ac voltage amplitude of the receiving end of the hybrid cascading dc system and detecting the three-phase fault of the near-zone ac system of the soft dc converter transformer according to the three-phase ac voltage of the soft dc converter transformer network side of the soft dc converter in the hybrid cascading dc system comprises:
collecting three-phase alternating current voltage at the net side of a soft direct converter transformer of a soft direct converter station in a mixed cascade direct current system in real time;
according to the three-phase alternating voltage at the net side of the flexible direct current converter transformer acquired in real time, calculating the alternating voltage amplitude of the receiving end of the hybrid cascade direct current system;
and detecting a three-phase fault of the near-area alternating current system of the soft direct current converter transformer according to the three-phase alternating current voltage of the net side of the soft direct current converter transformer acquired in real time.
3. The method for three-phase fault ride through of continuous low voltage of hybrid cascading direct current system according to claim 2, wherein the calculating the alternating voltage amplitude of the receiving end of the hybrid cascading direct current system according to the three-phase alternating voltage of the network side of the soft direct current converter transformer collected in real time comprises:
CLARK conversion is carried out on three-phase alternating voltage at the net side of the flexible direct current converter transformer acquired in real time to obtain two-phase componentsAnd->The amplitude of the alternating voltage +.>The method comprises the following steps:
。
4. the method for three-phase fault ride-through of continuous low voltage in a hybrid cascade direct current system according to claim 2, wherein the detecting the three-phase fault of the near-zone alternating current system of the soft direct current converter according to the three-phase alternating current voltage at the net side of the soft direct current converter acquired in real time comprises:
the three-phase alternating voltage at the net side of the flexible direct current converter transformer acquired in real time is subjected to positive and negative sequence PARK conversion to obtain dq positive sequence voltage component、/>And dq negative sequence voltage component +.>、/>；
According to dq positive sequence voltage component、/>And dq negative sequence voltage component +.>、/>Respectively calculating positive sequence voltage component amplitude +.>And negative sequence voltage component amplitude +.>：
；
When meeting the requirementsAnd->When the soft direct current converter transformer is in the near zone alternating current system three-phase fault, judging that the soft direct current converter transformer is in the near zone alternating current system three-phase fault, wherein ∈>Judging threshold value for positive sequence voltage component amplitude, +.>A threshold is determined for the negative sequence voltage component amplitude.
5. The method for three-phase fault ride-through of continuous low voltage of hybrid cascading direct current system according to claim 1, wherein in the process of ac fault recovery, according to the state of continuous low voltage of the receiving end of the hybrid cascading direct current system and the amplitude of ac voltage, the transmitting end of the hybrid cascading direct current system adopts square wave power limiting mode or slope power limiting mode, so as to ensure stable frequency, stable voltage and stable power angle of the transmitting end and the receiving end of the hybrid cascading direct current system, comprising:
in the alternating current fault recovery process, according to the state that the receiving end of the hybrid cascade direct current system continuously has low voltage, the transmitting end of the hybrid cascade direct current system enters a power limit recovery mode, wherein the power limit recovery mode comprises a square wave type power limit mode and a slope type power limit mode;
the method comprises the steps that a square wave type power limiting mode is preferentially adopted by a sending end of a hybrid cascading direct current system, electromechanical-electromagnetic transient joint simulation is carried out on the hybrid cascading direct current system when a near-area alternating current system three-phase fault occurs on the basis of alternating voltage amplitude of a receiving end of the hybrid cascading direct current system, and whether the square wave type power limiting mode can ensure stable frequency, stable voltage and stable power angle of the sending end and the receiving end of the alternating current system is determined;
when the square wave type power limiting mode is adopted, the stability of the alternating current system at the transmitting end and the receiving end cannot be guaranteed, and the slope type power limiting mode is adopted, so that the frequency stability, the voltage stability and the power angle stability of the transmitting end and the receiving end are guaranteed based on the alternating voltage amplitude of the receiving end of the mixed cascade direct current system.
6. The method for three-phase fault ride-through for continuous low voltage in a hybrid cascading dc system as claimed in claim 5, wherein said square wave power limiting mode is: setting a maximum recovery power limit value when the power is recovered after the phase shift of the transmitting end of the hybrid cascade direct current systemLimiting the maximum recovery power of the transmitting end of the hybrid cascade direct current system to +.>And maintain time->Then, the system is restored to the level before failure;
the slope type power limiting mode is as follows: alternating current voltage amplitude of receiving end of mixed cascade direct current systemReal-time communication is carried out to a transmitting end, the transmitting end carries out station low-voltage current limiting according to the alternating current bus voltage of a receiving end, and a low-voltage current limiting curve of a hybrid cascade direct current system is set up +.>Wherein->For the rated power of the hybrid cascade DC system in the current operating mode,/-for>Is a margin coefficient.
7. The method for three-phase fault ride-through for a continuous low voltage in a hybrid cascading dc system of claim 1, further comprising:
scanning a near-zone alternating current system three-phase fault of a soft direct current converter station in a hybrid cascade direct current system, acquiring alternating current low voltage amplitude and low voltage duration under a continuous low voltage working condition that energy absorption of an energy dissipation device is maximum in a near-zone alternating current system three-phase fault recovery process of recovery voltage over a plurality of milliseconds, and judging the maximum recovery power limiting value and the maintenance time in a square wave power limiting mode by the acquired alternating current low voltage amplitude and low voltage duration.
8. The three-phase fault ride through method for continuous low voltage of the hybrid cascade direct current system is characterized by comprising the following steps of:
the near-zone alternating current system three-phase fault detection module is used for calculating the alternating current voltage amplitude of the receiving end of the hybrid cascading direct current system and detecting the near-zone alternating current system three-phase fault of the soft direct current converter according to the three-phase alternating current voltage of the soft direct current converter network side of the soft direct current converter in the hybrid cascading direct current system;
the alternating current fault recovery module is used for removing the phase shift after the phase shift of the transmitting end of the hybrid cascade direct current system is maintained for a set phase shift time after detecting that the soft direct current converter transformer has a near-zone alternating current system three-phase fault, and entering an alternating current fault recovery process;
and the power limit recovery module is used for ensuring stable frequency, stable voltage and stable power angle of the transmitting end and the receiving end of the hybrid cascade direct current system according to the continuous low voltage state and the alternating voltage amplitude of the receiving end of the hybrid cascade direct current system in the alternating current fault recovery process.
9. A processing device comprising computer program instructions, wherein the computer program instructions, when executed by the processing device, are configured to implement the steps corresponding to the method for three-phase fault ride-through for continuous low voltage in a hybrid cascading dc system according to any one of claims 1-7.
10. A computer readable storage medium, wherein computer program instructions are stored on the computer readable storage medium, wherein the computer program instructions, when executed by a processor, are configured to implement the steps corresponding to the three-phase fault ride-through method for continuous low voltage of a hybrid cascading dc system according to any one of claims 1-7.
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