CN115622005A - High-permeability photovoltaic power distribution network relay protection device - Google Patents

High-permeability photovoltaic power distribution network relay protection device Download PDF

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Publication number
CN115622005A
CN115622005A CN202211291045.XA CN202211291045A CN115622005A CN 115622005 A CN115622005 A CN 115622005A CN 202211291045 A CN202211291045 A CN 202211291045A CN 115622005 A CN115622005 A CN 115622005A
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China
Prior art keywords
distribution network
power distribution
photovoltaic power
island
detection
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CN202211291045.XA
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Chinese (zh)
Inventor
柳青
谢灿明
谭文
张勇
杨先才
陈文�
徐凌
夏光辉
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HUBEI ELECTRIC POWER Co JINGZHOU POWER SUPPLY Co
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HUBEI ELECTRIC POWER Co JINGZHOU POWER SUPPLY Co
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Priority to CN202211291045.XA priority Critical patent/CN115622005A/en
Publication of CN115622005A publication Critical patent/CN115622005A/en
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/261—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations
    • H02H7/263—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations involving transmissions of measured values
    • 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
    • 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
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/261—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations
    • H02H7/262—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations involving transmissions of switching or blocking orders
    • 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
    • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
    • H02J13/00002—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by monitoring
    • 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
    • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
    • H02J13/00006—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment
    • H02J13/00022—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment using wireless data transmission
    • 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
    • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
    • H02J13/00032—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for
    • H02J13/00036—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for the elements or equipment being or involving switches, relays or circuit breakers
    • H02J13/0004—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for the elements or equipment being or involving switches, relays or circuit breakers involved in a protection system
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/388—Islanding, i.e. disconnection of local power supply from the network
    • 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]
    • 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
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • 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
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Abstract

The invention relates to the technical field of electronic power, and discloses a high-permeability photovoltaic power distribution network relay protection device. The device comprises an acquisition module, a storage module and a control module, wherein the acquisition module acquires the electrical characteristics of the photovoltaic power distribution network; the detection module performs island detection on the photovoltaic power distribution network according to the electrical characteristics based on a preset fault characteristic identification algorithm and a preset relay protection and island detection algorithm, and sends an island detection result of the photovoltaic power distribution network to the control module; the control module receives the island detection result based on the 5G wireless communication signal, determines the position information of the circuit breaker, and sends an island trip command to the execution module; and the execution module cuts off the tie line switch corresponding to the photovoltaic power supply in an island state so as to protect the photovoltaic power distribution network. According to the invention, by means of the electrical characteristics of island operation, island operation is detected within one hundred milliseconds based on 5G wireless communication, and island protection is realized by rapid tripping, so that the problems of low action speed, poor sensitivity and the like of island protection are avoided.

Description

High-permeability photovoltaic power distribution network relay protection device
Technical Field
The invention relates to the technical field of electronic power, in particular to a high-permeability photovoltaic power distribution network relay protection device.
Background
The development of economy and society promotes the continuous increase of the human demand for energy, and the development and the wide use of new energy become the hot spots of power grid energy development. For example, clean energy such as distribution network side distributed photovoltaic and the like is used for constructing a novel power system from the assistance of the distribution network side. The photovoltaic distributed power supply has the characteristics of less pollution, high reliability and energy utilization efficiency, flexible installation place and the like, and the characteristics of flexible position and dispersion of the distributed power supply are well suitable for the dispersed power demand and resource distribution, so that the photovoltaic distributed power supply is one of important measures for solving the contradiction between economic development, energy production and consumption and environment protection.
However, after the distributed Photovoltaic (PV) high permeability is connected to the power distribution network, great challenges are brought to the safe operation of the power distribution network, hidden dangers are caused to the safe and stable operation of the system, current quick-break and time-limited current quick-break protection may be caused to malfunction, and the safe reliability of the operation of the power distribution network is affected. Due to the adoption of a large number of power electronic technologies after the distributed power supplies such as a photovoltaic power supply are connected, equipment can be damaged, a fault line cannot be timely recovered to operate, the power failure time of a user is prolonged, and the operation reliability of a power distribution system is reduced. The deep research on the influence of a distributed power supply on a power distribution network and an improvement strategy become problems to be solved urgently.
The above is only for the purpose of assisting understanding of the technical solution of the present invention, and does not represent an admission that the above is the prior art.
Disclosure of Invention
The invention mainly aims to provide a high-permeability photovoltaic power distribution network relay protection device, and aims to solve the technical problem that the operation reliability of a power distribution network is reduced after an existing distributed power supply is connected to the power distribution network.
In order to achieve the above object, the present invention provides a high permeability photovoltaic power distribution network relay protection device, which comprises:
the acquisition module is used for acquiring the electrical characteristics of the photovoltaic power distribution network;
the detection module is used for carrying out island detection on the photovoltaic power distribution network according to the electrical characteristics based on a preset fault characteristic identification algorithm and a preset relay protection and island detection algorithm;
the detection module is also used for sending an island detection result of the photovoltaic power distribution network to the control module through a 5G wireless communication signal;
the control module is used for receiving the island detection result based on the 5G wireless communication signal and determining the position information of the circuit breaker of the photovoltaic power distribution network according to the island detection result;
the control module is also used for sending an island tripping command to the execution module according to the position information of the circuit breaker;
and the execution module is used for cutting off a tie line switch corresponding to the photovoltaic power supply in the island state according to the island trip command so as to protect the photovoltaic power distribution network.
In some embodiments, the detection module comprises: an island detection submodule; wherein the content of the first and second substances,
the acquisition module is further used for acquiring the difference characteristics of the electrical characteristics according to a preset distribution network topological graph and a preset distributed power supply nonlinear electrical model;
the island detection submodule is used for acquiring a detection signal in a characteristic mode of the difference characteristic based on a preset active detection method and generating a detection result according to the detection signal;
the island detection submodule is further used for performing weight correction and fusion on the detection result according to a preset information fusion method and a weight distribution method so as to obtain an optimized topological structure of the photovoltaic power distribution network;
the island detection submodule is also used for carrying out station domain side island judgment on the photovoltaic power distribution network through a preset tree-shaped search algorithm and the optimized topological structure based on 5G wireless communication so as to obtain a judgment result;
and the execution module is also used for executing alarm and locking and protecting the power distribution network when the judgment result determines that the position of the circuit breaker is abnormal or invalid.
In some embodiments, the island detection sub-module is further configured to optimize a number of a tree search algorithm according to a correlation property of the newly added branch and the factorization non-zero injection element, so as to obtain an initial tree search algorithm;
storing electrical primary wiring topological node information based on the adjacency matrix, and optimizing a tree-shaped search path of the initial tree-shaped search algorithm according to the voltage grade characteristics of the power system to obtain a preset tree-shaped search algorithm;
and based on 5G wireless communication, performing station domain side island judgment on the power distribution network through the preset tree-shaped search algorithm and the optimized topological structure to obtain a judgment result.
In some embodiments, the execution module is further configured to, when the determination result determines that the position of the circuit breaker is abnormal or invalid, determine, by using a fault tolerance check and error prevention mechanism of the circuit breaker position, whether to perform alarm and lock the power distribution network for protection.
In some embodiments, the detection module comprises: a fault detection submodule; wherein the content of the first and second substances,
the acquisition module is further used for acquiring the output characteristics of the photovoltaic power distribution network formed after the photovoltaic power supply is merged into the power grid in a preset interface mode according to the electrical characteristics;
the fault detection submodule is used for acquiring transient response characteristics of the photovoltaic power distribution network under a preset fault working condition;
the fault detection submodule is further used for establishing an electromagnetic transient analysis model of the photovoltaic power distribution network based on the output characteristic and the transient response characteristic;
the fault detection submodule is also used for monitoring the operation of the photovoltaic power distribution network and acquiring the current state information of the photovoltaic power distribution network;
the fault detection submodule is further used for analyzing the current state information based on the electromagnetic transient analysis model so as to judge whether the photovoltaic power distribution network has faults or not.
In some embodiments, the fault detection submodule is further configured to obtain a topology and a control strategy of the photovoltaic power supply access converter;
constructing a photovoltaic power supply accurate model for short-circuit current calculation analysis according to the topological structure and the control strategy;
and establishing an electromagnetic transient analysis model of the photovoltaic power distribution network based on the output characteristics, the transient response characteristics and the photovoltaic power supply accurate model.
In some embodiments, the detection module comprises: a relay protection detection submodule; wherein the content of the first and second substances,
the relay protection detection submodule is used for establishing a simplified model of the photovoltaic power distribution network based on the type, capacity and position of a photovoltaic power supply;
analyzing the simplified model according to a preset fault condition of the photovoltaic power distribution network to obtain an initial relay protection model of the photovoltaic power distribution network;
carrying out simulation test verification on the photovoltaic power distribution network through the initial relay protection model in a preset application scene to obtain an electromechanical transient simulation result;
optimizing the initial relay protection model according to the electromechanical transient simulation result to obtain a target relay protection model;
monitoring the operation of the photovoltaic power distribution network, and acquiring the current state information of the photovoltaic power distribution network;
and analyzing the current state information based on the target relay protection model to judge whether to execute relay protection on the photovoltaic power distribution network.
In some embodiments, the relay protection detection submodule is further configured to obtain a protection constant value setting calculation model of the photovoltaic power source accessed to the power distribution network under a preset working condition;
analyzing the setting of the fixed value under a preset operation mode and the adaptivity of the initial relay protection model in a preset application scene based on the protection fixed value setting calculation model to obtain the electromechanical transient simulation result; the electromechanical transient simulation result comprises online fixed value setting in a preset operation mode and the self-adaptive protection performance of the relay protection device.
In some embodiments, the electrical characteristics of the power distribution network include: microgrid voltage, frequency, power, and short circuit capacity.
In some embodiments, the photovoltaic power distribution grid includes a neutral point non-active grounding system.
The invention provides a high-permeability photovoltaic power distribution network relay protection device, which comprises: the acquisition module is used for acquiring the electrical characteristics of the photovoltaic power distribution network; the detection module is used for carrying out island detection on the photovoltaic power distribution network according to the electrical characteristics based on a preset fault characteristic identification algorithm and a preset relay protection and island detection algorithm; the detection module is also used for sending an island detection result of the photovoltaic power distribution network to the control module through a 5G wireless communication signal; the control module is used for receiving the island detection result based on the 5G wireless communication signal and determining the position information of the circuit breaker of the photovoltaic power distribution network according to the island detection result; the control module is also used for sending an island tripping command to the execution module according to the position information of the circuit breaker; and the execution module is used for cutting off a tie line switch corresponding to the photovoltaic power supply in the island state according to the island trip command so as to protect the photovoltaic power distribution network.
According to the island operation electrical characteristics, the island protection is carried out based on 5G wireless communication, the unplanned island operation state can be detected and tripping is carried out rapidly within hundred milliseconds by applying the island detection protection system to the two sides of the switching station and the photovoltaic power station, the problems of low action speed, poor sensitivity and the like of the existing island protection are solved, and the personal safety of power grid equipment and maintenance is guaranteed, so that the operation stability of the distributed power supply after being connected into a power distribution network is improved, and the technical problems that the operation reliability of the power distribution network is reduced after the existing distributed power supply is connected into the power distribution network and the accuracy and rapidity of the existing island detection algorithm are poor are solved.
Drawings
Fig. 1 is a schematic block diagram of a relay protection device for a photovoltaic power distribution network with high permeability according to a first embodiment of the present invention;
fig. 2 is a schematic block diagram of a relay protection device for a photovoltaic power distribution network with high permeability according to a second embodiment of the present invention.
The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive step based on the embodiments of the present invention, are within the scope of protection of the present invention.
It should be noted that all directional indicators (such as up, down, left, right, front, back \8230;) in the embodiments of the present invention are only used to explain the relative positional relationship between the components, the motion situation, etc. in a specific posture (as shown in the attached drawings), and if the specific posture is changed, the directional indicator is changed accordingly.
In addition, the descriptions related to "first", "second", etc. in the present invention are for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions in the embodiments may be combined with each other, but must be based on the realization of the technical solutions by those skilled in the art, and when the technical solutions are contradictory or cannot be realized, the technical solutions should be considered that the combination does not exist, and the technical solutions are not within the protection scope of the present invention. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
China needs to construct a novel power system with new energy as a main body.
The wide access of the distributed photovoltaic and other clean energy sources on the distribution network side is undoubtedly a loop with the vital goal of realizing the double-carbon goal, and is an important way for building a novel power system from the power assistance of the distribution network side. The photovoltaic distributed power supply has the characteristics of less pollution, high reliability and energy utilization efficiency, flexible installation place and the like, and the characteristics of flexible position and dispersion of the distributed power supply are well suitable for the dispersed power demand and resource distribution, so that the photovoltaic distributed power supply is one of important measures for solving the contradiction between economic development, energy production and consumption and environment protection.
However, after the distributed Photovoltaic (PV) high permeability is connected to the distribution network, a great challenge is brought to the safe operation of the distribution network, which is mainly reflected in the following aspects, namely: the photovoltaic output power highly depends on weather changes, natural changes such as solar radiation cause power fluctuation of a photovoltaic system, user load also changes in real time, and the change rule is asynchronous with the photovoltaic power generation change rule. Under the condition of high photovoltaic permeability, the power generated by the photovoltaic is larger than the power required by the load, reverse tide can occur along the feeder line, and the voltage of the feeder line is increased and even exceeds an upper limit value, so that hidden danger is caused to the safe and stable operation of the system. The continuous access of distributed energy such as photovoltaic and the like can affect the configuration and setting of a distribution network automation system and protection, and when the output power of a photovoltaic power supply is smaller than the rated power, the short-circuit current level of a distribution network can be larger than that of the photovoltaic power supply when the rated power is output. The method comprises the steps that the current quick-break and time-limited current quick-break protection of the power distribution network is set according to the existing setting scheme, and when the output power of a photovoltaic power supply is smaller than the rated power of the photovoltaic power supply, the current quick-break and time-limited current quick-break protection can be caused to generate misoperation. Considering the volatility of the output power of the photovoltaic power supply, the output power of the photovoltaic power supply is often smaller than the rated power of the photovoltaic power supply. Therefore, the current protection of the power distribution network is set according to the short-circuit current level of the power distribution network when the photovoltaic power supply outputs rated power, and the safety and reliability of the operation of the power distribution network are affected.
Therefore, the distributed power supply is connected to the power distribution network in a high-density and large-scale manner, so that the distribution of short-circuit current is changed, and the protection of correct action is greatly influenced. In addition, distributed power generation is generally connected to a medium-voltage or low-voltage distribution system, most of distribution networks are in single-power radial structures, and rapid disconnection and time-limited rapid disconnection protection modes are mostly adopted without directionality. The protection mode can effectively protect all lines on the existing radiation type power distribution network. However, when a distributed power supply is connected to a power distribution network, the injected power of the distributed power supply reduces the relay protection range, and the entire line cannot be reliably protected, and even when other parallel branches fail, a relay protection malfunction in which the distributed power supply is installed occurs. More importantly, due to the adoption of a large number of power electronic technologies after the distributed power supplies such as a photovoltaic power supply are connected, the fault characteristics of the power distribution system are fundamentally changed, and the fault current characteristics and the fault calculation model are not clear. After a line where a new energy power supply is located breaks down and the protection action of the new energy power supply trips, if the power supply is not disconnected to avoid reclosing, asynchronous reclosing of the faulty line can be caused, equipment can be damaged, the faulty line cannot be timely restored to operate, the power failure time of a user is prolonged, and the operation reliability of a power distribution system is reduced. In order to ensure the stable and efficient operation of the distributed power supply, the research on a new distribution network protection scheme and parameter setting specification of the applicability of the distributed power supply after the access is significant.
In a second aspect: in a power distribution network containing high-permeability photovoltaic, after a system breaks down, a distributed power supply and loads nearby the distributed power supply may form an electric power island, at the moment, the island network is difficult to keep a synchronous state with a large power grid, the phase angle difference between the distributed power supply and the large power grid is in any position between 0 and 360 degrees, if coincidence is carried out at the moment, the coincidence condition is difficult to meet, and the non-simultaneous reclosing can bring large impact current and transient overvoltage, so that a unit and power grid equipment are greatly damaged. When the islanding detection disconnection time of the photovoltaic power station is long, the action time sequence matching of the spare power automatic switching device is abnormal, and the spare power automatic switching device is too long and even fails. Therefore, when a distribution network accessed by the distributed power supply has a fault, isolated island operation of a local power grid is easily caused, and reliable actions of reclosing and automatic backup power switching of the regional power grid are influenced. More seriously, in an island operation state, the equipment is electrified abnormally, and even the life safety of operation and maintenance personnel can be endangered.
For the island detection method, the active detection method is widely researched and applied due to high detection precision and small blind area. However, due to the fact that the micro-grids are various in operation conditions and distributed power types, grid structures and load compositions of different micro-grids are different, the accuracy and the rapidity of active detection of all islanding micro-grids are still difficult to guarantee by a single method at present. At present, an island detection method mainly comprises a detection method based on communication, a passive detection method and an active detection method. Wherein the former has a greater dependence on the communication channel; the passive detection method is simple to realize, has little influence on the quality of electric energy, but has a detection blind area; most of active detection methods establish a positive feedback loop based on the positive feedback relation between reactive current and frequency, so that the frequency of a microgrid converter is changed to one direction quickly after voltage loss to realize island detection, and the method is expected to have good reliability, but currently, a single means is adopted to realize criteria. In fact, the micro-grid is complex in structure and large in operation change, and an island detection method based on a single criterion cannot always completely cover various operation conditions, so that a comprehensive judgment method based on various information quantities needs to be researched to reduce respective coverage blind areas to the maximum extent. Therefore, the research on the anti-islanding detection of the active power distribution network is carried out, and the research is very important for guaranteeing the reliability of the power distribution network comprising the photovoltaic distributed power sources and the like and guaranteeing the safety of operation and maintenance workers.
From the analysis, the influence of the distributed power supply on the relay protection of the power distribution network and the improvement strategy are urgently developed. In particular, in the conventional power grid fault analysis, the power supply model is mainly an alternating current synchronous motor. However, during a power grid fault, transient components, attenuation characteristics and the like of fault current fed into a power grid by a distributed power supply are greatly changed compared with a traditional alternating current synchronous motor, so that the traditional short-circuit current analysis theory and method based on a power supply of the alternating current synchronous motor are difficult to meet the requirement of power grid fault analysis after the distributed power supply is connected.
When the photovoltaic power generation stops due to a fault, the photovoltaic grid-connected power generation system installed at each user side cannot timely detect a power failure state and breaks away from the utility grid, the photovoltaic grid-connected power generation system supplies power to surrounding loads to form an island, and a power company cannot master the power supply state of the photovoltaic grid-connected power generation system. Islanding can adversely affect equipment operation, including: endangering the safety of line maintenance personnel of the power company; influencing the action program of a protection switch of the power distribution network; the power supply voltage and frequency of users in an island region are easy to be unstable; the problem of asynchronous phase caused by power supply restoration of a power company; the problem of phase failure power supply caused by single-phase power supply. The more the photovoltaic grid-connected system is connected to an alternating current power grid, the higher the probability of the occurrence of the islanding is, and therefore a proper strategy needs to be found to prevent the increasingly serious islanding problem. The accuracy and the rapidity of the existing island detection algorithm are poor, and an unplanned island is easy to cause. The research of distribution network protection control optimization strategies adapting to high-permeability photovoltaic access is a great technical requirement for building a novel power system and a national requirement for promoting the realization of a double-carbon target.
In view of the above problems, the present invention provides a relay protection device for a photovoltaic power distribution network with high permeability.
Referring to fig. 1, fig. 1 is a schematic block diagram of a relay protection device for a photovoltaic power distribution network with high permeability according to an embodiment of the present invention.
As shown in fig. 1, the relay protection device for a photovoltaic power distribution network with high permeability comprises:
the acquisition module 100 is used for acquiring the electrical characteristics of the photovoltaic power distribution network;
the detection module 200 is used for carrying out island detection on the photovoltaic power distribution network according to the electrical characteristics based on a preset fault characteristic identification algorithm and a preset relay protection and island detection algorithm;
the detection module 200 is further configured to send an island detection result of the photovoltaic power distribution network to a control module through a 5G wireless communication signal;
the control module 300 is configured to receive the island detection result based on a 5G wireless communication signal, and determine circuit breaker position information of the photovoltaic power distribution network according to the island detection result;
the control module 300 is further configured to send an island trip command to an execution module according to the circuit breaker position information;
the execution module 400 is configured to remove a tie line switch corresponding to the photovoltaic power source in the islanding state according to the islanding trip command, so as to protect the photovoltaic power distribution network.
It should be noted that, the photovoltaic power distribution network relay protection device with high permeability includes: the system includes an acquisition module 100, a detection module 200, a control module 300, and an execution module 400, and fig. 1 illustrates a connection manner of modules in a high-permeability photovoltaic power distribution network relay protection device, which is not limited in this embodiment. It can be understood that the relay protection device for the photovoltaic power distribution network with the high permeability can also comprise other modules. Distributed power sources include, but are not limited to, photovoltaics, wind turbines, and stored energy. In this embodiment, a distributed power source is a photovoltaic, and a distribution network is a distribution network including a distributed power source (distribution network including a photovoltaic).
Specifically, this embodiment provides the novel protection control device of active distribution network who contains 5G wireless communication function, and the function module of the new principle of integrated various fault characteristic identification algorithm and protection can realize the island detection based on 5G information, adopts 5G wireless communication signal to receive the relevant circuit breaker position information of system topology and sends island tripping operation GOOSE order, cuts off the junctor switch that distributed generator that is in island state corresponds to protection photovoltaic distribution network.
In the embodiment, aiming at the large-scale photovoltaic grid-connected condition, on-site practice is combined, island operation analysis under various working conditions is carried out, electrical characteristics of island operation are researched, an anti-island protection device based on 5G communication is developed, through application to two sides of a switching station and a photovoltaic power station, the fact that an unplanned island operation state is detected and tripping is carried out rapidly within one hundred milliseconds is achieved, the problems that existing anti-island protection is slow in action speed and poor in sensitivity are solved, safety of power grid equipment and overhaul personnel is guaranteed, the future power grid development trend that high-permeability photovoltaic power access and power electronization characteristics are increasingly prominent can be met, power grid relay protection and control are taken as the main points, adaptability of existing protection in a power distribution network with distributed power access such as photovoltaic power is researched, a new line rapid protection principle of transient characteristics when faults are fully discovered is developed, a safety defense system facing a future distributed power access distribution network complex power system is comprehensively constructed, and access of a distributed renewable power distribution network is promoted. The basic theory and the key technology for effectively avoiding the risk of the photovoltaic access distribution network are established and perfected, the technical level of relay protection is continuously improved, the difficulty in development of the distributed power supply access power grid is solved, and the realization of a double-carbon target is assisted.
According to the island operation electrical characteristic, island protection is prevented based on 5G wireless communication, through using in switch station and photovoltaic power plant both sides, can realize detecting unplanned island operating condition and tripping fast in hundred milliseconds, break through the current slow, the poor scheduling problem of sensitivity of island protection action speed of preventing, guarantee electric wire netting equipment, overhaul personal safety, thereby improve the operating stability behind the distributed generator inserts the distribution network, cause distribution network operational reliability to reduce and current island detection algorithm accuracy and the not good enough technical problem of rapidity after having solved current distributed generator inserts the distribution network.
In one embodiment, referring to fig. 2, the detection module 200 includes: an island detection sub-module 201; wherein, the first and the second end of the pipe are connected with each other,
the acquisition module 100 is further configured to acquire a difference characteristic of the electrical characteristic according to a preset distribution network topology diagram and a preset distributed power supply nonlinear electrical model;
the island detection submodule 201 is configured to obtain a detection signal in a characteristic mode of the difference characteristic based on a preset active detection method, and generate a detection result according to the detection signal;
the island detection submodule 201 is further configured to perform weight correction and fusion on the detection result according to a preset information fusion method and a weight distribution method to obtain an optimized topological structure of the photovoltaic power distribution network;
the island detection submodule 201 is further configured to perform station-side island judgment on the photovoltaic power distribution network through a preset tree search algorithm and the optimized topology structure based on 5G wireless communication to obtain a judgment result;
the execution module 400 is further configured to execute an alarm and lock and protect the power distribution network when the determination result determines that the position of the circuit breaker is abnormal or invalid.
Illustratively, aiming at the construction current situation, the existing problems, the development trend and the business requirements of a power distribution sensing system with a distributed power supply, the sensing information needs to be reviewed from the perspective of core assets, the power distribution sensing system architecture is optimized from the perspective of source end data uniqueness and information global sharing by fully using the industrial digital twin technology of data and model fusion, the decision-making capability of the power distribution data is reconstructed by light-weight and abundant distributed edge computing power, the power distribution digital-to-analog mapping capability is expanded and deepened, the key capabilities of power distribution sensing control, data integration and prediction analysis are driven, the long-standing difficult problems of business instantaneity, flexibility and diversity are solved, and the evolution route of a target architecture is realized from the perspectives of main station construction, terminal development, communication selection, model perfection and the like by researching the power distribution sensing system information architecture design of hierarchical domains. Aiming at the power distribution network topology containing various distributed power supplies, a complex power distribution network subgraph is detected based on a breadth-first search method, and a subgraph structure is judged according to a radial topology condition, so that the optimized expansion of the topological structure is realized, and the optimized expanded power distribution network topological graph is obtained.
Further, a state equation of the converter under different operating conditions in a voltage or current mode is deduced and analyzed by combining an optimized and expanded power distribution network topological graph (a preset power distribution network topological graph) and an electric model of a nonlinear power electronic element of the distributed energy grid-connected converter (a preset nonlinear electric model of a distributed power supply), and a chaos phenomenon, a bifurcation characteristic and a chaos generation mechanism in the converter are respectively analyzed from the aspects of time domain waveforms of a bifurcation graph, a phase graph, a Poincare section, an inductive current and an output voltage, so that a change rule of a chaos oscillation disturbance amplitude and frequency is obtained. According to the chaotic time series analysis and the phase space reconstruction technology, the difference characteristics of the electrical quantity in the chaotic oscillation process are obtained, wherein the difference characteristics of the electrical quantity include but are not limited to the voltage, the frequency, the power, the short-circuit capacity and the like of a micro-grid.
Exemplarily, the process of performing station domain side island judgment on the power distribution network through a preset tree-shaped search algorithm and the optimized topology structure based on 5G wireless communication to obtain a judgment result may include: optimizing the number of the tree-shaped search algorithm according to the correlation properties of the newly added branch and the factorization non-zero injection element to obtain an initial tree-shaped search algorithm; storing electrical primary wiring topological node information based on the adjacency matrix, and optimizing a tree-shaped search path of the initial tree-shaped search algorithm according to the voltage grade characteristics of the power system to obtain a preset tree-shaped search algorithm; and based on 5G wireless communication, performing station domain side island judgment on the power distribution network through the preset tree-shaped search algorithm and the optimized topological structure to obtain a judgment result.
Specifically, according to an active detection method (for example, frequency offset detection, sliding mode frequency drift detection, periodic current interference detection, and frequency mutation detection), detection signals (for example, frequency offset indexes, frequency shift threshold-crossing signals, and voltage fluctuation signals) with similar or different characteristic modes are obtained, a history of correct and incorrect information is judged according to a detection scheme, and data fusion and weight correction are performed on various pieces of criterion information by using information fusion methods such as D-S.
On the basis of a tree search algorithm, the station domain side island judgment based on 5G wireless communication is realized by a topology analysis method based on voltage grades. Aiming at the characteristic that an adjacency matrix of a storage network topological structure has high sparsity, the representation form of the adjacency matrix is improved, and the improved adjacency matrix is applied to node optimization numbering, advance determination of retrieval information and formation of a node admittance matrix. In the factorization process, in order to realize the non-zero retrieval in the column direction, the storage information in the column direction is added and a retrieval mode corresponding to the storage information in the column direction is formulated. According to the correlation property of newly added branches and factorization non-zero injection elements in the process of optimizing numbering, the positions of the newly added elements are recorded and a storage frame is formed while the numbering is optimized, then the electrical primary wiring topological node information is stored based on the adjacent matrix, and the tree-shaped search path is optimized by utilizing the voltage grade characteristics of the power system, so that the defects that the traditional full-matrix squaring algorithm is large in calculation amount and the tree-shaped search algorithm is low in search efficiency are effectively overcome.
In an embodiment, referring to fig. 2, the island detection sub-module 201 is further configured to optimize a number of a tree search algorithm according to a correlation property of a newly added branch and a factorization non-zero injection element, so as to obtain an initial tree search algorithm;
storing electrical primary wiring topological node information based on the adjacency matrix, and optimizing a tree-shaped search path of the initial tree-shaped search algorithm according to the voltage grade characteristics of the power system to obtain a preset tree-shaped search algorithm;
and based on 5G wireless communication, performing station domain side island judgment on the power distribution network through the preset tree-shaped search algorithm and the optimized topological structure to obtain a judgment result.
Illustratively, the process of optimizing the number of the tree search algorithm according to the correlation property of the newly added branch and the factorization non-zero injection element to obtain the initial tree search algorithm may include: based on the highly sparse characteristic of the adjacency matrix of the optimized topological structure, improving the expression form of the optimized topological structure to obtain an improved adjacency matrix; and optimizing the number of the tree-shaped search algorithm based on the improved adjacent matrix, the newly added branch and the correlation property of the factorization non-zero injection element to obtain an initial tree-shaped search algorithm.
Specifically, according to an active detection method (for example, frequency offset detection, sliding mode frequency drift detection, periodic current interference detection, and frequency mutation detection), detection signals (for example, frequency offset indexes, frequency shift threshold-crossing signals, and voltage fluctuation signals) with similar or different characteristic modes are obtained, a history of correct and incorrect information is judged according to a detection scheme, and data fusion and weight correction are performed on various pieces of criterion information by using information fusion methods such as D-S.
On the basis of a tree search algorithm, the station domain side island judgment based on 5G wireless communication is realized by a topology analysis method based on voltage grades. Aiming at the characteristic that an adjacency matrix of a storage network topological structure has high sparsity, the representation form of the adjacency matrix is improved, and the improved adjacency matrix is applied to node optimization numbering, advance determination of retrieval information and formation of a node admittance matrix. In the factorization process, in order to realize non-zero retrieval in the column direction, storage information in the column direction is added and a retrieval mode corresponding to the storage information in the column direction is formulated. According to the correlation property of newly added branches and factorization non-zero injection elements in the process of optimizing numbering, the positions of the newly added elements are recorded and a storage frame is formed while the numbering is optimized, then the electrical primary wiring topological node information is stored based on the adjacent matrix, and the tree-shaped search path is optimized by utilizing the voltage grade characteristics of the power system, so that the defects that the traditional full-matrix squaring algorithm is large in calculation amount and the tree-shaped search algorithm is low in search efficiency are effectively overcome.
It can be understood that, based on the 5G communication, the method for identifying the network topology of the active distribution network including the distributed photovoltaic (including the high-permeability photovoltaic relay protection device) of the active distribution network, specifically, the International Telecommunication Union (ITU) defines 3 main application scenarios for 5G, which are enhanced mobile broadband (eMBB), large-scale machine type communication (mtc), and ultra-reliable low-latency communication (rluclc), respectively. The eMB scene focuses on human-centered communication, entertainment, social contact and other consumption services, can meet the requirements of a user experience rate of 1 to 5Gbit/s and a time delay of 10 to 50ms, and partially needs large connection. The mMTC scene mainly aims at sensing and data acquisition of the Internet of things, supports transmission of mass data, packet data and universe data, and meets 100 ten thousand connection/km 2 Fingers with 1 to 100Mbit/s data rate and 50ms delayAnd (4) marking.
The topology identification method based on tree search is a basis of an anti-islanding protection technology based on 5G communication signals and suitable for various system structures, the tree search method converts power network topology into a graph, data structures such as an adjacency matrix or an adjacency list are adopted to store node connection information, a depth first search algorithm (DFS) or a breadth first search algorithm (BFS) is adopted to search the topological graph, and connectivity of DG nodes and a system power supply is judged. And searching the communication relation between the distributed power supply and the system power supply in real time by adopting a tree search method, thereby obtaining the island state of the distributed power supply.
Distributed power generation such as photovoltaic is generally connected to a medium-voltage or low-voltage distribution system, and a large number of distributed power sources connected to a low-voltage distribution network can have wide and profound influence on the distributed power generation system. For example, photovoltaic is mostly connected to an area power grid which is weak in connection with a main grid. After the regional power grid and the main grid are disconnected, the photovoltaic easily forms an island with the load in the regional power grid, so that the photovoltaic anti-island detection device cannot accurately and timely acquire island information, the passive island detection scheme of the distributed photovoltaic power supply generally has a large detection blind area (Non-detection zone, NDZ) under a power grid fault scene, and usually needs a long time to complete island detection and disconnect the photovoltaic power supply, so that the reliable action of reclosing or spare power automatic switching of the regional power grid and the life safety of operation and maintenance workers are seriously affected. In the aspect of the island detection technology of the power distribution network including the high-permeability distributed power supply, an Active island detection scheme such as an Active Frequency Shift method (Active Frequency Drift, AFD), a Sandia Frequency Shift method (SFS), a sliding Mode Frequency Shift Method (SMS), and the like may be adopted. The AFD method and the SFS method adopt a frequency offset perturbation-based strategy, and the SMS method adopts a phase offset perturbation-based strategy. By deeply analyzing the advantages and the disadvantages of various remote-form, passive and active microgrid island detection technologies, the island detection method of a multi-distributed power supply is discussed, and on the basis, a single inverter and multi-machine cluster-oriented multi-data comprehensive island detection method which is suitable for different control strategies is provided, so that the island detection method has better adaptability to actual operation conditions.
In the embodiment, according to advantages, disadvantages and applicability of traditional passive, active and remote island protection algorithms, aiming at the problems of tedious judgment, low efficiency and blind areas existing in the traditional island protection detection technology, a network topology identification method (including a high-permeability photovoltaic power distribution network relay protection device) of a distributed photovoltaic active power distribution network based on 5G communication is provided so as to adapt to multi-data comprehensive judgment island detection facing a single inverter and a multi-machine cluster with different control strategies. The island operation state judgment technology of the active distribution network based on different voltage level topologies is researched through power grid limited information rapidly acquired through 5G wireless communication, and a practical new island protection scheme is further researched and provided. When the photovoltaic is required to be operated in an island mode according to the regulation, the connection with a power grid must be cut off within 2s, and the rapid and reliable anti-island protection is configured, so that the safe operation of the power grid is very necessary. On the basis, a fault identification method and an anti-islanding protection technology are deeply researched, and the safe operation level of the power distribution network under the high-permeability photovoltaic access is further improved. By adopting the embodiment, the island protection action time of the high-permeability photovoltaic power distribution network relay protection device can be increased from less than 2 seconds to less than 200 milliseconds, which are required by the international standard.
For example, the island active detection method of the island microgrid is generally characterized in that an inverter is controlled to generate certain disturbance on the output power, frequency or phase of the inverter so as to trigger an island effect detection circuit. The method has higher detection precision and smaller non-detection area. The mainstream island microgrid active detection technology at present comprises frequency deviation detection, sliding mode frequency drift detection, periodic current interference detection, frequency mutation detection and the like. However, in the normal operation process of the microgrid, the operation modes are various, the distributed power supplies, grid structures and loads of different microgrids are different, the data information amount is large, and due to the limitation of the bandwidth and the transmission speed of the traditional communication method, the accuracy and the rapidity of the active detection of all the isolated island microgrids are difficult to guarantee. However, if panoramic collection is performed on real-time operation data in the microgrid, the problems can be solved well. Therefore, panoramic data which run in real time in each new energy station in the microgrid is collected by using a 5G communication technology, a set of multi-data comprehensive judgment method is designed to screen and use correct data, and further, according to results of active detection technologies based on different principles, a proper criterion fusion and weight distribution method is adopted to perform weight correction and fusion on results generated by each active detection technology, so that the accuracy of active rapid detection of the island microgrid is improved.
In an embodiment, the execution module 400 is further configured to, when the determination result determines that the position of the circuit breaker is abnormal or invalid, determine whether to perform an alarm and lock the power distribution network by combining a fault tolerance check and error prevention mechanism of the position of the circuit breaker.
For example, when the determination result determines that the position of the circuit breaker is abnormal or invalid, the process of performing an alarm and protecting the power distribution network in a locked mode may include: and when the judgment result determines that the position of the circuit breaker is abnormal or invalid, judging whether to alarm and lock and protect the power distribution network by combining a fault-tolerant check and error-proof mechanism of the position of the circuit breaker.
Specifically, when the position of the circuit breaker is abnormal or invalid, an island trip command is prevented from being mistakenly issued by means of alarming and locking protection and combining a fault-tolerant check and error prevention mechanism of the position of the circuit breaker, so that the reliability of a result of the relay protection device for the photovoltaic power distribution network with the high permeability is ensured.
In one embodiment, referring to fig. 2, the detection module 200 includes: a fault detection sub-module 202; wherein, the first and the second end of the pipe are connected with each other,
the acquisition module 100 is further configured to acquire, according to the electrical characteristics, an output characteristic of the photovoltaic power distribution network formed after the photovoltaic power supply is incorporated into the power grid in a preset interface manner;
the fault detection submodule 202 is configured to acquire a transient response characteristic of the photovoltaic power distribution network under a preset fault working condition;
the fault detection sub-module 202 is further configured to establish an electromagnetic transient analysis model of the photovoltaic power distribution network based on the output characteristics and the transient response characteristics;
the fault detection sub-module 202 is further configured to monitor operation of the photovoltaic power distribution network, and obtain current state information of the photovoltaic power distribution network;
the fault detection sub-module 202 is further configured to analyze the current state information based on the electromagnetic transient analysis model to determine whether the photovoltaic power distribution network has a fault.
Illustratively, by researching typical forms and characteristics of a hybrid active power distribution network formed by a new energy power supply (photovoltaic, energy storage and the like) which is merged into a power grid in a preset interface mode, an overall electromagnetic transient analysis model of the active power distribution network is established, and therefore the operation characteristics, the fault propagation characteristics and the fault characteristic extraction method of the distributed power supply under the condition of network faults (disturbance) on a direct current side and an alternating current side are analyzed. Wherein, the process of obtaining the output characteristics of the photovoltaic power distribution network formed after the new energy power supply is merged into the power grid in a preset interface mode can include: and acquiring the output characteristics of the new energy element converter under a grid-connected state, an island state, a preset control state and low voltage ride through respectively. New energy sources include, but are not limited to, photovoltaics, wind turbines, and stored energy. In this embodiment, a new energy is used as a photovoltaic, and a photovoltaic power distribution network is a power distribution network including a distributed power supply (a power distribution network including a photovoltaic) as an example. The predetermined control states include, but are not limited to, a PQ control state, a Vf control state, and a VSG control state.
Specifically, the output characteristics of the photovoltaic and other new energy element converters are researched and calculated under a grid-connected state, an isolated island state, a PQ control state, a Vf control state, a VSG control state and low-voltage ride-through respectively. The distributed power source plays an important role in a power distribution network system containing the distributed power source, and the fault characteristics of the distributed power source connected to a power grid are the primary problems needing to be analyzed. The DG may be divided into an asynchronous machine mainly based on a double-fed Induction Generator (DFIG) and an inverter mainly based on a direct-drive wind turbine and a photovoltaic power supply according to a difference in interface types. The preset interface mode includes but is not limited to an asynchronous machine mainly based on DFIG and an inverter mainly based on a direct-drive wind turbine generator and a photovoltaic power supply.
It should be noted that, in the process of researching the fault characteristics of the power grid including the distributed power supply, the distributed power supply is generally regarded as a constant current source or a davinan circuit which is equivalent to a voltage source and internal impedance. The analysis methods do not fully consider the influence of complex fault current characteristics of the distributed power supply under different fault conditions, so that the proposed power grid fault analysis method containing the distributed power supply and the result are not consistent with the actual conditions, and certain limitations exist. Photovoltaic, wind power and energy storage distributed power supplies are generally connected to the grid through a converter, and the converter adopts a double closed-loop decoupling control strategy of a voltage outer loop and a current inner loop. The voltage outer ring tracks a given voltage value in real time, an active current component and a reactive current component are obtained through a decoupling formula, and the current inner ring tracks the obtained active current component and reactive current component constantly, so that the active power output and the reactive power output of the photovoltaic power supply are controlled. However, compared with a normal working state, when the power transmission line has an asymmetric fault, the voltage of the common connection point may generate zero and negative sequence components, the three-phase symmetry affecting the output voltage of the inverter is a control method based on a positive sequence component by adopting a photovoltaic power generation system low voltage ride through control strategy, the zero and negative sequence components generated by the traditional control strategy are avoided, and the reactive power support can be provided by the power distribution network. Since the duration of the fault is generally short and the ambient temperature and light intensity changes little during the fault phase, it is generally considered that the maximum power obtained during the fault is substantially constant.
For example, the process of obtaining the transient response characteristic of the photovoltaic power distribution network under the preset fault condition may include: acquiring transient response characteristics of the photovoltaic power distribution network in the external faults of preset types, preset positions and preset degrees; and performing mathematical equivalence description on the transient response characteristics to obtain transient response characteristics. Specifically, transient response characteristics of new energy such as photovoltaic energy in external faults of different types, different positions and different degrees are obtained, mathematical equivalence description is carried out on the fault response characteristics, and therefore a quantitative analysis method of fault transient output is established to obtain the transient response characteristics.
The process of establishing an electromagnetic transient analysis model of the photovoltaic power distribution network based on the output characteristics and the transient response characteristics may include: acquiring a topological structure and a control strategy of a new energy power source access converter; constructing a distributed power supply accurate model for short-circuit current calculation analysis according to the topological structure and the control strategy; and establishing an electromagnetic transient analysis model of the photovoltaic power distribution network based on the output characteristics, the transient response characteristics and the accurate distributed power supply model. Exemplarily, a distributed power supply accurate model suitable for short-circuit current calculation and analysis is constructed according to a topological structure and a control strategy of a photovoltaic power supply access converter, and fault characteristics of converter PQ control, vf control, VSG control and low voltage ride through are deeply researched; based on the accurate distributed power supply model, an electromagnetic transient analysis model of the active power distribution network is built, the operating characteristics of the photovoltaic power supply in a fault (disturbance) scene are researched, the interaction characteristics of the network and the source fault (disturbance) and the influence on the original protection are analyzed, and an advanced signal processing tool is utilized to obtain a new method for fault identification and fault characteristic quantity extraction, namely the electromagnetic transient analysis model of the photovoltaic power distribution network.
Illustratively, the operation of the photovoltaic power distribution network is monitored, and the current state information of the photovoltaic power distribution network is obtained. Illustratively, the operation of a photovoltaic power distribution network power system is monitored, amplitude and phase information of three-phase voltage, current and zero-sequence current is acquired at regular time, and amplitude and phase information of positive and negative zero-sequence components is calculated. The current state information includes, but is not limited to, amplitude and phase information of the positive and negative zero sequence components. The present disclosure does not impose limitations on the current state information.
Illustratively, the current state information is analyzed based on the electromagnetic transient analysis model to determine whether the photovoltaic power distribution network fails. Illustratively, the amplitude and phase information of real-time three-phase voltage and current are used as input characteristics of an electromagnetic transient analysis model, whether the photovoltaic power distribution network fails or not is analyzed, or the specific fault type and/or fault area of the photovoltaic power distribution network are/is analyzed, and the like. In the embodiment, the distributed power supplies such as solar photovoltaic power generation and wind power generation are connected to the microgrid through the power electronic device, short-circuit current provided during fault is very small, so that the traditional relay protection device is difficult to detect, an accurate short-circuit current analysis model of the distributed photovoltaic power supplies, namely an electromagnetic transient analysis model of the photovoltaic power distribution network is established, the short-circuit current calculation error can be smaller than 10%, the fault identification accuracy under the distribution network scene of the distributed power supplies is improved, and the running stability of the distributed power supplies after being connected to the power distribution network is improved.
In this embodiment, an accurate distributed power model is established in consideration of the fault characteristics of distributed power supplies of different manufacturers. Due to the fact that the electromagnetic transient characteristics of the faults of the converter grid-connected power supply such as photovoltaic power, energy storage and the like are extremely complex, the diversity of the grid topology structure and the access elements is reflected, and particularly after the faults occur, the characteristics of being more complex compared with the traditional power distribution network are reflected. Therefore, the fault transient characteristic of various novel elements accessed to the power distribution network is built, an active power distribution network electromagnetic transient model which is attached to the actual engineering characteristics and contains high-permeability photovoltaic access is built, fault characteristic quantities are extracted based on the interaction of a system during the fault period, a fault identification method of a power distribution network containing high-permeability photovoltaic is formed, namely, fault information is deeply excavated through an electromagnetic transient analysis model when the photovoltaic power distribution network is monitored, and the fault identification accuracy of a distributed power supply under the power distribution network scene is improved. According to the embodiment, the accurate electromagnetic transient analysis model of the distributed power supply is established by researching the grid fault characteristics of the photovoltaic power distribution network formed after the new energy power supply is merged into the power grid in a preset interface mode. When monitoring the photovoltaic power distribution network, fault information is deeply excavated through the electromagnetic transient analysis model, and fault identification accuracy of the distributed power supply under a power distribution network scene is improved, so that operation stability of the distributed power supply after being connected to the power distribution network is improved, and the technical problem that operation reliability of the power distribution network is reduced after the existing distributed power supply is connected to the power distribution network is solved.
In an embodiment, the fault detection sub-module 202 is further configured to obtain a topology and a control strategy of the photovoltaic power supply access converter;
constructing a photovoltaic power supply accurate model for short-circuit current calculation analysis according to the topological structure and the control strategy;
and establishing an electromagnetic transient analysis model of the photovoltaic power distribution network based on the output characteristics, the transient response characteristics and the photovoltaic power supply accurate model.
Illustratively, the process of modeling an electromagnetic transient analysis model of the photovoltaic power distribution grid based on the output characteristics, the transient response characteristics, and the accurate distributed power source model may include: analyzing the topological structure of the photovoltaic power distribution network, and constructing a direct current side model by adopting a preset analytical method; constructing an alternating-current side model through the connectivity of a network and a minimum cut set theory; equivalently combining the direct current side model, the alternating current side model and the distributed power supply accurate model according to an alternating current and direct current wiring mode to obtain an initial electromagnetic transient analysis model; determining a preset time-frequency domain transient component algorithm according to the transient variation processes of the voltage and current time domain and the frequency domain under the preset condition; and optimizing the initial electromagnetic transient analysis model according to the preset time-frequency domain transient component algorithm to obtain an electromagnetic transient analysis model of the photovoltaic power distribution network. The preset time-frequency domain transient component algorithm comprises wavelet and wavelet packet transformation, hilbert transformation, variational modal decomposition and Hankel matrix transformation.
Specifically, the method is used for researching the output characteristics of the photovoltaic and energy storage new energy element converter in a grid-connected state and an isolated island state respectively, under PQ control, vf control, VSG control and low voltage ride through, and the transient response characteristics of the new energy in external faults of different types, different positions and different degrees and carrying out mathematical equivalence description on the fault response characteristics, so that the fault transient output quantitative analysis method is established. Secondly, reasonably equating the characteristics of the control system to each new energy power supply to form a power supply model for subsequent fault analysis; then, analyzing the topological structure of the hybrid active microgrid by adopting the concept of systematic recursion and gradual equivalence, constructing a direct current side model by adopting an FD analysis method, and constructing an interchange side model by adopting the network connectivity and the minimum cut-set theory; and (4) combining an alternating current and direct current wiring mode, equivalently combining the models, and building an active power distribution network electromagnetic transient analysis model, namely an initial electromagnetic transient analysis model.
The transient state change process of the voltage and current time domain and the frequency domain under the condition of multiple types, multiple positions and multiple ranges of faults of the power transmission network under the condition of access of new energy elements with multiple control strategies and under the condition of different types, different capacities and different access forms (centralized large scale and distributed) of new energy is further researched, and the time-frequency domain mathematical expression is obtained. And finally, verifying a short-circuit current calculation result of the distributed power supply simulation model based on an RTDS real-time digital distributed power supply active distribution network closed-loop simulation system, and ensuring that a short-circuit current calculation error is less than 10%.
Based on the distribution network model containing photovoltaic and other distributed power supplies, various different fault scenes are set, a multi-scale serial-parallel transient interaction mechanism formed by coupling multiple types of renewable energy sources and power electronic devices in a power electronic power system through a network and physical essence of the multi-scale serial-parallel transient interaction mechanism are considered, wavelet and wavelet packet transformation, hilbert transformation, variational modal decomposition and a characteristic decomposition and extraction method of time-domain transient components of Hankel matrix transformation and the like are utilized, and the advantages and disadvantages of speed, precision, sampling rate, data window requirements and the like during time-domain and frequency-domain processing of fault transient electric quantities are compared to realize deep excavation and multivariate fusion of fault information, so that a new algorithm for fault identification and fault characteristic quantity extraction under the distribution network scene containing the distributed power supplies is formed, namely, the initial electromagnetic transient analysis model is optimized through a preset time-domain transient component algorithm, and the electromagnetic transient analysis model of the photovoltaic distribution network is obtained.
It should be noted that in this embodiment, the initial electromagnetic transient analysis model is optimized by using wavelet and wavelet packet analysis, hilbert-yellow transform and Variable Mode Decomposition (VMD) isochronous/frequency fault feature analysis methods.
In one example, for wavelet and wavelet packet analysis, this application of wavelet transform to a signal processing method has the advantage of simultaneous localization of the time-frequency domain. The method is particularly suitable for analyzing transient mutation signals and has the properties of linearity, translation invariance, stretching co-variability, redundancy and the like. Wavelet packet analysis is an extension of wavelet analysis, which can further subdivide a high-frequency space that is not decomposed by wavelets, thereby extracting more accurate high-frequency components.
Figure BDA0003901360050000191
The continuous wavelet transform (sometimes also called integral wavelet transform) of f (t) is defined as:
Figure BDA0003901360050000192
when ψ (t) satisfies the permissivity condition, the inverse transform exists:
Figure BDA0003901360050000193
in the formula
Figure BDA0003901360050000194
Is Fourier transform of psi (t), inverse transform
Figure BDA0003901360050000195
C ψ Is a constant and psi is the base wavelet (or mother wavelet). The wavelet space can be decomposed into several small packet spaces:
Figure BDA0003901360050000196
Figure BDA0003901360050000197
j =1,2, \ 8230; p =1,2, \8230;, j, note n =2 p + q, with reference to the orthogonal wavelet formula, has a wavelet packet function:
wherein the content of the first and second substances,
Figure BDA0003901360050000201
in particular u 0 Phi (t) is a scaling function,u 1 (t) = ψ (t) is a wavelet function.
Both the wavelet packet function and the wavelet function have a scale parameter j and a translation parameter k, and the wavelet packet function has a frequency parameter n. Therefore, the wavelet packet has better frequency processing capability than the wavelet packet, and is more flexible and effective. The wavelet packet space can be further subdivided according to a wavelet packet decomposition algorithm to obtain wavelet packet coefficients in each space:
Figure BDA0003901360050000202
Figure BDA0003901360050000203
wherein h is k-21 For low-pass decomposition of the filter coefficients, g k-21 Are high pass decomposition filter coefficients. Each wavelet packet coefficient theoretically represents a characteristic of a signal component in each wavelet packet space, and wavelet packet analysis can be used to decompose the transient current in fault analysis into components of different frequencies, including high frequency components.
In one example, for a Hilbert-yellow transform (Hilbert-Huang transform), the Hilbert-Huang transform consists of an Empirical Mode Decomposition (EMD) and Hilbert transform, suitable for analyzing non-stationary, non-linear signals. The EMD decomposition can adaptively decompose the signal into a set of Intrinsic Mode functions (IMF-Intrinsic Mode functions) from high frequencies to low frequencies. And performing Hilbert transformation on each IMF to obtain the instantaneous frequency and the instantaneous amplitude of each IMF.
The EMD method decomposes a complex signal into a plurality of Intrinsic Mode Functions (IMFs), wherein each IMF satisfies the following two conditions: the number of the maximum values in the signal is equal to or different from the number of the zero-crossing points by one; the upper envelope formed by the signal maximum value points and the lower envelope formed by the minimum value points are symmetrical about a time axis.
In the EMD decomposition process, the IMF calculation needs to subtract the upper envelope line and the lower envelope line of all extreme points obtained by curve fitting from the original input signal s (t)Partial average value m i (t), solving repeatedly until m is reached i (t) shows a monotonous trend or r n (t) the loop ends when the IMF component is too small to extract from. The following can be obtained:
Figure BDA0003901360050000204
in the formula c j (t) the components of the signal under different time scales are arranged from small to large according to the time scales; r is a radical of hydrogen n And (t) is a residual term and represents the signal evaluation trend.
And solving the instantaneous frequency of each IMF of the fault signal through Hilbert transform:
Figure BDA0003901360050000205
wherein Re represents a real part, a i (t) denotes the magnitude of each IMF component, omitting the residual term r n (t) of (d). The right side of the above formula is a Hilbert-time frequency spectrum, called Hilbert spectrum for short, which represents the distribution of instantaneous amplitude on a frequency-time plane, can accurately describe the rule that the amplitude of a signal changes along with frequency and time on the whole frequency band, and can extract the instantaneous frequency of a fault signal to detect the type and the fault time of the fault signal by applying the method.
In an example, for a variational modal decomposition VMD, the overall framework of the VMD is a variational problem, with the goal of minimizing the sum of the estimated bandwidths of each modality. Assuming that each 'mode' is a limited bandwidth with different center frequencies, continuously updating each mode and the center frequency thereof by adopting an alternating direction multiplier method, gradually demodulating each mode to a corresponding base frequency band, and finally extracting each mode and the corresponding center frequency together.
For an original signal S, the corresponding constraint variation model expression is
Figure BDA0003901360050000211
Wherein, { u k Factorization into K modal components, { u } k }＝{u 1 ,…,u k }；{ω k Is the center frequency of each modal component, { ω } k }＝{ω 1 ,…,ω k }。
The Lagrange function is introduced to solve the optimal solution of the constraint variation problem, namely
Figure BDA0003901360050000212
In the formula, λ is a Lagrange operator indicating that the constraint condition strictness is maintained, and indicates a secondary penalty factor in the presence of gaussian noise, which is used to ensure the constraint condition strictness. And solving saddle points of the listed augmented Lagrange function by using the ADMM, namely solving the optimal solution of the formula constraint variation model. Determined modal component u k And center frequency omega k Are respectively as
Figure BDA0003901360050000213
Figure BDA0003901360050000214
In the formula (I), the compound is shown in the specification,
Figure BDA0003901360050000215
is the current residual amount
Figure BDA0003901360050000216
Wiener filtering of (2);
Figure BDA0003901360050000217
is the center frequency of the current mode function power spectrum;
Figure BDA0003901360050000218
representing an inverse Fourier transform whose real component is the time-domain modal component { u } k (t)}。
Compared with the recursion 'screening' mode of EMD and LMD, the VMD decomposes the transient signal into a non-recursion and variational mode decomposition mode, has a solid theoretical basis, is substantially provided with a plurality of self-adaptive wiener filtering groups, and shows better noise robustness.
In one embodiment, referring to fig. 2, the detection module 200 includes: a relay protection detection submodule 203; wherein the content of the first and second substances,
the relay protection detection submodule 203 is used for establishing a simplified model of the photovoltaic power distribution network based on the type, capacity and position of a photovoltaic power supply;
analyzing the simplified model according to a preset fault working condition of the photovoltaic power distribution network to obtain an initial relay protection model of the photovoltaic power distribution network;
carrying out simulation test verification on the photovoltaic power distribution network through the initial relay protection model in a preset application scene to obtain an electromechanical transient simulation result;
optimizing the initial relay protection model according to the electromechanical transient simulation result to obtain a target relay protection model;
monitoring the operation of the photovoltaic power distribution network, and acquiring the current state information of the photovoltaic power distribution network;
and analyzing the current state information based on the target relay protection model to judge whether to execute relay protection on the photovoltaic power distribution network.
Illustratively, the process of building a simplified model of a power distribution network based on the type, capacity and location of distributed power sources (photovoltaic power sources) in the power distribution network may include: establishing a protection configuration model of the distributed power supply with preset access capacity and position based on fault characteristics and bidirectional power flow of the distributed power supply; simplifying a protection configuration model of the distributed power source based on power electronics control characteristics to obtain a simplified model of the power distribution network. In one example, a typical form and characteristics of a hybrid active power distribution network formed by a photovoltaic power supply which is integrated into a power grid in a preset interface mode are researched, a protection configuration model of a distributed power supply is established, and therefore the operation characteristics and the fault propagation characteristics of the distributed power supply under the condition of network faults (disturbance) on a direct current side and an alternating current side are analyzed. Wherein, the new energy includes but not limited to photovoltaic, fan and energy storage. In this embodiment, a new energy source is a photovoltaic, and a power distribution network is a power distribution network including a distributed power source (a power distribution network adapted to photovoltaic access) as an example.
Specifically, aiming at the influences of the fault characteristics, the bidirectional power flow and the like of the distributed power supply such as photovoltaic and the like, protection configuration schemes and principles of the distributed power supply with different access capacities and positions are provided, the coordination and cooperation method of the existing protection and the distributed power supply network-related protection is analyzed, and the corresponding protection setting principle, technical specifications and the like are formulated so as to ensure that a protection device based on a target relay protection model can reliably and sensitively act when relay protection is performed on the power distribution network.
It should be noted that, in the process of researching the fault characteristics of the power grid including the distributed power supply, the distributed power supply is generally regarded as a constant current source or a Thevenin circuit equivalent to a voltage source and an internal impedance. The analysis methods do not fully consider the influence of complex fault current characteristics of the distributed power supply under different fault conditions, so that the proposed power grid fault analysis method containing the distributed power supply and the result are not consistent with the actual conditions, and certain limitations exist. Photovoltaic, wind power and energy storage distributed power supplies are generally connected to the grid through a converter, and the converter adopts a double closed-loop decoupling control strategy of a voltage outer loop and a current inner loop. The voltage outer ring tracks a given voltage value in real time, an active current component and a reactive current component are obtained through a decoupling formula, and the current inner ring tracks the obtained active current component and reactive current component constantly, so that the active power and reactive power output of the photovoltaic power supply is controlled. However, compared with a normal working state, when the power transmission line has an asymmetric fault, the voltage of the common connection point may generate zero and negative sequence components, the three-phase symmetry affecting the output voltage of the inverter is a control method based on a positive sequence component by adopting a photovoltaic power generation system low voltage ride through control strategy, the zero and negative sequence components generated by the traditional control strategy are avoided, and the reactive power support can be provided by the power distribution network. Since the duration of the fault is generally short and the ambient temperature and light intensity changes little during the fault phase, it is generally considered that the maximum power obtained during the fault is substantially constant.
The process of analyzing the simplified model according to the preset fault condition of the power distribution network to obtain the initial relay protection model of the power distribution network may include: acquiring a preset fault type of a current line protection mode; the current line protection mode comprises a three-section current protection mode and a differential protection mode; generating a preset fault working condition according to the error/refusal risk and mechanism of the protection criterion under the preset power distribution network access scene of the preset fault type; and providing a new relay protection criterion and a new relay protection scheme according to the preset fault working condition so as to analyze the simplified model and obtain an initial relay protection model of the power distribution network.
Specifically, the new energy element converter such as photovoltaic is calculated, and the like, under different fault types such as a grid-connected state, an isolated island state, a PQ control state, a Vf control state, a VSG control state, low voltage ride through and the like, the error/failure risk and mechanism of line protection (three-segment current protection, differential protection and the like) under the high-permeability photovoltaic access power distribution network scene are researched, and an analysis result, namely a preset fault working condition, is generated. And according to the analysis result, an improved new protection criterion and a new scheme are researched and provided, and the initial relay protection model is obtained. It can be understood that the method for simplifying fault modeling under the premise of keeping the control characteristics of the power electronic equipment comprehensively considers factors such as the fault type, the position and the short-circuit capacity of the power distribution network, determines the accuracy and the algorithm realizability of a centralized parameter model for protecting a renewable energy grid-connected line by analyzing the operation mechanism of new energy power generation equipment such as photovoltaic and the like during the fault ride-through period, the change rule and the mutual influence relation of various main electrical quantities and the contribution capacity of a renewable energy grid-connected control strategy to the short-circuit current, and then researches the fault/failure risk and the mechanism of the protection criterion of the line protection (three-section current protection, differential protection and the like) under the typical scene that a distributed power supply is connected to the power distribution network to obtain an analysis result.
Exemplarily, the process of performing simulation test verification on the power distribution network through the initial relay protection model in a preset application scenario to obtain an electromechanical transient simulation result may include: obtaining a protection constant value setting calculation model of a distributed power supply connected to a power distribution network under a preset working condition; analyzing the setting of the fixed value under a preset operation mode and the adaptivity of the initial relay protection model in a preset application scene based on the protection fixed value setting calculation model to obtain the electromechanical transient simulation result; the electromechanical transient simulation result comprises online fixed value setting in a preset operation mode and self-adaptive protection performance of the relay protection device.
Specifically, the error/rejection risk and mechanism of the protection criterion of line protection (three-section current protection, differential protection and the like) in the scene of high-permeability photovoltaic access power distribution network are researched under different fault types, an analysis result is obtained, and an improved new protection criterion and a new protection scheme are researched and proposed according to the analysis result, so that an initial relay protection model is obtained. And further, simulation test verification of a protection principle and a scheme of the initial relay protection model is developed in a typical application scene. Based on the implementation method (initial relay protection model) of the high-permeability photovoltaic access power distribution network protection configuration scheme, setting of the fixed value and the adaptability of the relay protection device in a complex and changeable operation mode are analyzed, and therefore the relay protection setting principle of the high-permeability distributed photovoltaic power distribution network is obtained based on the analysis.
Illustratively, the process of optimizing the initial relay protection model according to the electromechanical transient simulation result to obtain the target relay protection model may include: and according to the electromechanical transient simulation result, constructing a target relay protection model based on multi-terminal current amplitude comparison by utilizing the magnitude relation between the currents at two terminals and the comprehensive load current amplitude under the conditions of normal operation and internal and external faults.
Specifically, the method is characterized in that the wrong/refusal risk and mechanism of the protection criterion of the line protection (three-section current protection, differential protection and the like) under the typical scene of the distributed power supply connected to the power distribution network are researched to obtain an analysis result, and according to the analysis result, by utilizing different size relations of the current amplitude values of the two ends and the comprehensive load current under the conditions of normal operation and faults inside and outside the area, a new protection criterion based on multi-end current amplitude comparison, namely a target relay protection model based on the multi-end current amplitude comparison is constructed, fault occurrence areas can be accurately distinguished, and a novel unit type protection function independent of synchronous measurement is realized.
Illustratively, the operation of the power distribution network is monitored, and the current state information of the power distribution network is obtained. In one example, the operation of a power system of the power distribution network is monitored, amplitude and phase information of three-phase voltage, current and zero-sequence current is obtained regularly, and amplitude and phase information of positive and negative zero-sequence components is obtained through calculation. The current state information includes, but is not limited to, magnitude and phase information of positive and negative zero sequence components. The present disclosure does not impose limitations on the current state information.
Illustratively, the current state information is analyzed based on the target relay protection model to judge whether to perform relay protection on the power distribution network. Illustratively, the amplitude and phase information of real-time three-phase voltage and current are used as input characteristics of a target relay protection model, whether the power distribution network fails or not is analyzed, or specific fault types and/or fault areas of the power distribution network are analyzed, and whether relay protection is performed on the power distribution network is judged. In the embodiment, the distributed power supplies such as solar photovoltaic power generation and wind power generation are connected to the microgrid through the power electronic device, and single-stage differential protection of distribution network lines with different access capacities and positions of distributed photovoltaic can be realized through the target relay protection model, so that the problem that protection and reclosing are prone to malfunction or failure according to existing protection configuration and setting modes is avoided, and the operation stability of the distributed power supplies after being connected to the distribution network is improved.
This embodiment protects the distribution network through the target relay protection model after optimizing when monitoring the distribution network, ensures that relay protection is reliable, sensitive action to improve the operating stability after distributed generator inserts the distribution network, solved current relay protection mode after current distributed generator inserts the distribution network and had not enough, cause the technical problem that distribution network operational reliability reduces.
In an embodiment, the relay protection detection submodule 203 is further configured to obtain a protection fixed value setting calculation model of the photovoltaic power source accessed to the power distribution network under a preset working condition;
analyzing the setting of the protection setting value and the adaptivity of the initial relay protection model in a preset operation mode in a preset application scene based on the protection setting value setting calculation model to obtain an electromechanical transient simulation result; the electromechanical transient simulation result comprises online fixed value setting in a preset operation mode and the self-adaptive protection performance of the relay protection device.
It should be noted that the current protection and pilot current differential protection method is a line protection method in a conventional power distribution network. However, most of the distributed power supplies output direct current and then are inverted into alternating current to be connected to a power distribution network, so that the polymorphism of the fault current of the inverted distributed power supplies directly influences the construction of a protection system of the power distribution network. The protection designed based on the fault characteristics of the inverter type distributed power supply can better meet the safe operation requirement of the power grid. The current carrying capacity of the power electronics in the inverter is limited, and thus the inverter type distributed power supply is different from the fault current characteristic of a synchronous generator, which has a "polymorphic" characteristic and is influenced by many factors. From the perspective of relay protection, the following three aspects need to be noted when a protection system is constructed for a power distribution network including an inverter type distributed power supply.
In the first aspect, the action setting value of the protection needs to be determined according to the maximum short-circuit current of the inverter-type distributed power supply. The traditional extreme setting method according to the synchronous motor fault model enlarges the maximum fault current amplitude value provided by the inverter type distributed power supply, and is easy to cause the reduction of the protection range. Due to the near-end failure, the IGBT is turned off in order to prevent damage to the power electronics, resulting in a reduction in the fault current. Generally, the fault current of the inverter type distributed power supply is smaller than that of the traditional synchronous generator, and the fault current is mainly determined by the current carrying capacity of internal power electronic devices. The factors need to be considered in the setting calculation of the protection scheme of the target relay protection model based on the multi-terminal current amplitude comparison.
In the second aspect, a protection scheme (a target relay protection model based on multi-terminal current amplitude comparison) should have a strategy for dealing with the fault current 'multi-state' characteristic. The short-circuit current provided by the inverter type distributed power supply has the characteristic of polymorphism, and particularly after the protection action of a power electronic device, the amplitude of the short-circuit current is attenuated severely, and the steady state value of the short-circuit current is almost 0. If no measures are taken, the current protection has the condition of protection refusal. Therefore, in the protection scheme of the target relay protection model based on the multi-terminal current amplitude comparison, a coping strategy can be adopted in a self-adaptive manner according to the change of the power failure characteristics so as to ensure the reliable removal of the failure.
In a third aspect, the control characteristics of the distributed power supply enable the connected distribution network to have complex nonlinear characteristics. Fault analysis means such as a symmetrical classification method suitable for a linear system cannot objectively reflect fault transient characteristics of an active power distribution network including distributed power supply access. In the embodiment, the protection under the condition of high-permeability access of the distributed power supply is triggered from two angles of point-to-point protection and power distribution network protection, and relates to three levels of point, line and plane. The protection scheme of the target relay protection model based on multi-terminal current amplitude comparison meets the requirements of a relay protection principle and technology, and the grid-connected point protection can also meet the requirements of distributed autonomy of a micro-grid and flexible interaction with a power distribution network.
Illustratively, based on a protection constant value setting calculation model suitable for distributed power supplies with different working conditions to be connected to a power distribution network, a load flow calculation section is formed by inputting conventional parameters such as photovoltaic power and an upstream power supply, and an online constant value setting function and an adaptive protection function of a relay protection device in a complex and variable operation mode are realized according to an electromechanical transient simulation result, so that the online constant value setting result is cooperatively matched with a distributed power supply control strategy, a grid-connected or independent operation working condition, a distributed or centralized access mode and the like. Meanwhile, the fixed value online check of the self-adaptive protection of the improved line protection principle is completed by online updating input real-time data parameters, an actual control strategy and a real-time distribution network topology. Based on the work, based on the goals of considering the safety of the distributed renewable new energy and the reliability of the system and the coordination of the configuration and setting of the outgoing line protection, a distribution network relay protection setting principle and a distribution network relay protection setting technical specification containing the distributed power supply are formulated, and important standardized support is provided for the standard grid connection of the distributed power supply and the active management and control of the distribution network.
It should be noted that, in this embodiment, the following example may be adopted to implement the online fixed value setting in the complex variable operation mode and the adaptive protection function of the relay protection device.
In one example, adaptive protection, the setting of the protection is set online based on the local electrical information quantity. The protection on-line setting value can be modified along with the change of the system operation mode, the fault type and the load, so that the protection range is expanded, and the protection selectivity is improved. The following setting methods can be adopted, for example, a composite sequence network is adopted, and the voltage and current values detected at the protection installation position are utilized to obtain a current setting value; decomposing the fault model to obtain a fault additional network, and obtaining a real-time changing current setting value by using the equivalent potential and the equivalent impedance at the back side of the protection installation position; the distance between the protection installation position and a fault point is considered, a factor is multiplied for the voltage, different voltage factors are utilized to enable the voltage drop degrees measured at different protection installation positions of the same line to be different, and the protection action is completed according to the different voltage drop degrees; the method comprises the steps that analysis is carried out on the basis of two-phase current difference fault components, and the method is more sensitive than current quick-break protection under different operation modes and fault types; and analyzing the fault component by adopting a filtering algorithm to obtain a real-time setting value and the like.
In one example, the protection is constructed using a power frequency fault component. For example, power frequency fault component distance protection, the protection is configured by utilizing the proportional relation of the influence of the DG (distributed generation) auxiliary effect on the protection starting value and the action value; protection of negative sequence power frequency fault components, wherein when a negative sequence fault component is detected, a protection device is started, and only the protection of the maximum positive sequence fault component is detected, so that the fault range is judged; the direction overcurrent protection of the positive sequence current fault component is judged by the overcurrent protection, the protection is started, then the phase angle difference of the filtered positive sequence current fault component is calculated, and a fault line is disconnected after the fault direction is judged; the positive sequence fault component is combined with pilot direction protection, which utilizes the characteristic that the ring network of a double-ended power supply generally adopts an open-loop operation mode.
In one example, protection is based on multipoint information technology. The protection utilizes an intelligent electronic device, a distributed artificial intelligence technology, a multi-Agent system and a communication technology to classify the protection according to different fault isolation algorithms. Wide area protection, e.g., based on overcurrent protection; protection based on the maximum fault characteristic information quantity is carried out, and the protection is based on a wide area protection principle, and a protection algorithm supported by communication is adopted to judge the fault searching direction of the current quantity; searching a fault association section through cooperation between upper and lower level agents according to a multi-Agent system (MAS); exchanging protection information between different places by utilizing the cooperation between each Agent and the communication function of the SCADA system, and judging a fault section according to the comprehensive result of the information; based on the protection of the advanced feeder terminal unit, the fault area can be quickly positioned, and the fault can be isolated.
According to the above example, for the current situation of the change of the fault current characteristic after the intervention of the distributed power supply, a protection mode according to the conventional electric quantity information and multipoint information technology can be adopted, and the relay protection method provided by this embodiment is greatly improved compared with the three-stage current protection.
Exemplarily, after constructing a target relay protection model based on multi-terminal current amplitude comparison by using a magnitude relation between currents at two terminals and a magnitude relation between the currents at two terminals and the magnitude relation under normal operation and under the conditions of internal and external faults according to the electromechanical transient simulation result, the method further includes: and analyzing the application range of the target relay protection model based on the multi-terminal current amplitude comparison according to the running state of the distribution network, the initial fault angle, the fault type and the grounding impedance value condition, and determining the judgment dead zone of the target relay protection model based on the multi-terminal current amplitude comparison. Analyzing the current state information based on the target relay protection model to judge whether to execute relay protection on the power distribution network, including: when analyzing the current state information and determining that the fault point is positioned in the dead zone, adopting an overcurrent three-section protection mode with a direction judgment function, an overcurrent quick-break protection mode and the target relay protection model to form a target protection scheme; and executing relay protection on the power distribution network according to the target protection scheme.
Specifically, the application range of the new protection criterion based on multi-terminal current amplitude comparison is investigated by changing the conditions of the distribution network operation state, the fault initial angle, the fault type, the grounding impedance value and the like, and then the dead zone for distinguishing the slight fault and the special fault in the area by the criterion is determined. When a fault point falls in the dead zone, the original overcurrent three-section protection with the direction judgment function can still be used as backup protection to be matched with the new principle protection and the existing overcurrent quick-break protection, and a single-stage difference acceleration protection scheme is formed by communicating with an adjacent line protection unit while the current modulus differential criterion judges that the fault is positioned in the zone. Meanwhile, the influence of the control strategy switching on the system impedance characteristic and the output short-circuit current is analyzed based on the control strategy and the mode switching method of the renewable energy grid-connected operation and independent operation working conditions, and the adaptability of the power distribution network improvement protection criterion containing the distributed power supply under different working conditions is researched.
In one embodiment, the electrical characteristics of the power distribution network include: microgrid voltage, frequency, power, and short circuit capacity.
The method includes the steps of combining an optimized and expanded distribution network topology diagram (preset distribution network topology diagram) and an electrical model of a nonlinear power electronic component of a distributed energy grid-connected converter (preset distributed power nonlinear electrical model), deducing and analyzing state equations of a converter under different operating conditions in a voltage or current mode, and analyzing chaos phenomena, bifurcation characteristics and a chaos generation mechanism in the converter respectively from the aspects of bifurcation diagrams, phase diagrams, poincare sections, time-domain waveforms of inductive currents and output voltages to obtain a change rule of chaos oscillation disturbance amplitude and frequency. According to the chaotic time series analysis and the phase space reconstruction technology, the difference characteristics of the electrical quantity in the chaotic oscillation process are obtained, wherein the difference characteristics of the electrical quantity comprise but are not limited to microgrid voltage, frequency, power, short-circuit capacity and the like.
In an embodiment, the photovoltaic power distribution grid includes a neutral point non-active grounding system.
It should be noted that the distribution network includes a system of non-effective grounding of the neutral point. The photovoltaic power distribution network may also include a 24kV neutral grounding grid.
It should be understood that the above is only an example, and the technical solution of the present invention is not limited in any way, and in a specific application, a person skilled in the art may set the technical solution as needed, and the present invention is not limited in this respect.
It should be noted that the above-mentioned work flows are only illustrative and do not limit the scope of the present invention, and in practical applications, those skilled in the art may select some or all of them according to actual needs to implement the purpose of the solution of the present embodiment, and the present invention is not limited herein.
In addition, the technical details that are not elaborated in this embodiment can be referred to the image reconstruction method applied to the electrical impedance imaging system as described above provided by any embodiment of the present invention, and are not described herein again.
Further, it is to be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or system. Without further limitation, an element defined by the phrases "comprising a," "8230," "8230," or "comprising" does not exclude the presence of other like elements in a process, method, article, or system comprising the element.
The above-mentioned serial numbers of the embodiments of the present invention are merely for description and do not represent the merits of the embodiments.
Through the above description of the embodiments, those skilled in the art will clearly understand that the method of the above embodiments can be implemented by software plus a necessary general hardware platform, and certainly can also be implemented by hardware, but in many cases, the former is a better implementation manner. Based on such understanding, the technical solution of the present invention or portions thereof that contribute to the prior art may be embodied in the form of a software product, where the computer software product is stored in a storage medium (e.g. Read Only Memory (ROM)/RAM, magnetic disk, optical disk), and includes several instructions for enabling a terminal device (e.g. a mobile phone, a computer, a server, or a network device) to execute the method according to the embodiments of the present invention.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and all equivalent structures or equivalent processes performed by the present invention or directly or indirectly applied to other related technical fields are also included in the scope of the present invention.

Claims (10)

1. The utility model provides a contain high permeability photovoltaic distribution network relay protection device which characterized in that, contain high permeability photovoltaic distribution network relay protection device and include:
the acquisition module is used for acquiring the electrical characteristics of the photovoltaic power distribution network;
the detection module is used for carrying out island detection on the photovoltaic power distribution network according to the electrical characteristics based on a preset fault characteristic identification algorithm and a preset relay protection and island detection algorithm;
the detection module is also used for sending an island detection result of the photovoltaic power distribution network to the control module through a 5G wireless communication signal;
the control module is used for receiving the island detection result based on the 5G wireless communication signal and determining the position information of the circuit breaker of the photovoltaic power distribution network according to the island detection result;
the control module is also used for sending an island trip command to the execution module according to the position information of the circuit breaker;
and the execution module is used for cutting off a tie line switch corresponding to the photovoltaic power supply in the island state according to the island trip command so as to protect the photovoltaic power distribution network.
2. The relaying protection device for a photovoltaic power distribution network with high permeability according to claim 1, wherein said detection module comprises: an island detection submodule; wherein the content of the first and second substances,
the acquisition module is further used for acquiring the difference characteristics of the electrical characteristics according to a preset distribution network topological graph and a preset distributed power supply nonlinear electrical model;
the island detection submodule is used for acquiring a detection signal in a characteristic mode of the difference characteristic based on a preset active detection method and generating a detection result according to the detection signal;
the island detection submodule is further used for performing weight correction and fusion on the detection result according to a preset information fusion method and a weight distribution method so as to obtain an optimized topological structure of the photovoltaic power distribution network;
the island detection submodule is also used for carrying out station domain side island judgment on the photovoltaic power distribution network through a preset tree-shaped search algorithm and the optimized topological structure based on 5G wireless communication so as to obtain a judgment result;
and the execution module is also used for executing alarm and locking and protecting the power distribution network when the judgment result confirms that the position of the circuit breaker is abnormal or invalid.
3. The high-permeability photovoltaic power distribution network relay protection device of claim 2, wherein the island detection sub-module is further configured to optimize a number of a tree search algorithm according to a correlation property of the newly added branch and the factorization non-zero injection element to obtain an initial tree search algorithm;
storing electrical primary wiring topological node information based on the adjacency matrix, and optimizing a tree-shaped search path of the initial tree-shaped search algorithm according to the voltage grade characteristics of the power system to obtain a preset tree-shaped search algorithm;
and based on 5G wireless communication, performing station domain side island judgment on the power distribution network through the preset tree-shaped search algorithm and the optimized topological structure to obtain a judgment result.
4. The relaying protection device for a photovoltaic power distribution network with high permeability as set forth in claim 2, wherein said execution module is further configured to determine whether to execute an alarm and lock-protect said power distribution network in combination with a fault-tolerant check and error-proof mechanism of a breaker position when said determination result determines that the breaker position is abnormal or invalid.
5. The relaying protection device for a photovoltaic power distribution network with high permeability according to claim 1, wherein said detection module comprises: a fault detection submodule; wherein the content of the first and second substances,
the acquisition module is further used for acquiring the output characteristics of the photovoltaic power distribution network formed after the photovoltaic power supply is merged into the power grid in a preset interface mode according to the electrical characteristics;
the fault detection submodule is used for acquiring transient response characteristics of the photovoltaic power distribution network under a preset fault working condition;
the fault detection sub-module is further used for establishing an electromagnetic transient analysis model of the photovoltaic power distribution network based on the output characteristics and the transient response characteristics;
the fault detection submodule is also used for monitoring the operation of the photovoltaic power distribution network and acquiring the current state information of the photovoltaic power distribution network;
the fault detection submodule is further used for analyzing the current state information based on the electromagnetic transient analysis model so as to judge whether the photovoltaic power distribution network has faults or not.
6. The relaying protection device for a photovoltaic distribution network with high permeability as set forth in claim 5, wherein said fault detection sub-module is further configured to obtain topology and control strategy of the photovoltaic power access converter;
constructing a photovoltaic power supply accurate model for short-circuit current calculation analysis according to the topological structure and the control strategy;
and establishing an electromagnetic transient analysis model of the photovoltaic power distribution network based on the output characteristics, the transient response characteristics and the photovoltaic power supply accurate model.
7. The relaying protection device for a photovoltaic power distribution network with high permeability according to claim 1, wherein said detection module comprises: a relay protection detection submodule; wherein, the first and the second end of the pipe are connected with each other,
the relay protection detection submodule is used for establishing a simplified model of the photovoltaic power distribution network based on the type, the capacity and the position of a photovoltaic power supply;
analyzing the simplified model according to a preset fault condition of the photovoltaic power distribution network to obtain an initial relay protection model of the photovoltaic power distribution network;
carrying out simulation test verification on the photovoltaic power distribution network through the initial relay protection model in a preset application scene to obtain an electromechanical transient simulation result;
optimizing the initial relay protection model according to the electromechanical transient simulation result to obtain a target relay protection model;
monitoring the operation of the photovoltaic power distribution network, and acquiring the current state information of the photovoltaic power distribution network;
and analyzing the current state information based on the target relay protection model to judge whether to execute relay protection on the photovoltaic power distribution network.
8. The relay protection device for the photovoltaic power distribution network with the high permeability of claim 7, wherein the relay protection detection submodule is further used for obtaining a protection fixed value setting calculation model of the photovoltaic power source connected to the power distribution network under a preset working condition;
analyzing the setting of the protection setting value and the adaptivity of the initial relay protection model in a preset operation mode in a preset application scene based on the protection setting value setting calculation model to obtain an electromechanical transient simulation result; the electromechanical transient simulation result comprises online fixed value setting in a preset operation mode and the self-adaptive protection performance of the relay protection device.
9. The relay protection device for a distribution network including high permeability photovoltaics of any one of claims 1 to 8, wherein the electrical characteristics of the distribution network include: microgrid voltage, frequency, power, and short circuit capacity.
10. The relaying protection device for a distribution photovoltaic network according to any one of claims 1 to 8, wherein said distribution photovoltaic network comprises a neutral point non-active grounding system.
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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116169695A (en) * 2023-04-20 2023-05-26 新天绿色能源股份有限公司 VSG control method and system based on frequency-shift phasors
CN116388111A (en) * 2023-04-18 2023-07-04 杭州欣美成套电器制造有限公司 In-situ measurement and control protection integrated device of electric micro-grid
CN117458411A (en) * 2023-12-26 2024-01-26 四川迪思源科技有限公司 Distribution network protection self-adaptive system under power system

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116388111A (en) * 2023-04-18 2023-07-04 杭州欣美成套电器制造有限公司 In-situ measurement and control protection integrated device of electric micro-grid
CN116388111B (en) * 2023-04-18 2024-02-20 杭州欣美成套电器制造有限公司 In-situ measurement and control protection integrated device of electric micro-grid
CN116169695A (en) * 2023-04-20 2023-05-26 新天绿色能源股份有限公司 VSG control method and system based on frequency-shift phasors
CN117458411A (en) * 2023-12-26 2024-01-26 四川迪思源科技有限公司 Distribution network protection self-adaptive system under power system
CN117458411B (en) * 2023-12-26 2024-03-12 四川迪思源科技有限公司 Distribution network protection self-adaptive system under power system

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