Fault judgment method and system for sea island micro-grid group based on satellite-ground network fusion

Abstract

The invention provides a satellite-ground network fusion island micro-grid group fault judgment method and system, and the method comprises the steps: obtaining a first three-phase current of a to-be-judged power grid node i at a current moment, and obtaining a second three-phase current of the to-be-judged power grid node i at a corresponding moment of a last period, obtaining a three-phase current fault component of the to-be-judged power grid node according to the first three-phase current and the second three-phase current; according to the three-phase current fault component, judging whether a to-be-judged island micro-grid group corresponding to the to-be-judged grid node i has a fault or not; if the fault is judged, extracting fault features according to the three-phase current fault component; constructing a fault coefficient vector according to the fault features; and obtaining a fault line and a fault phase of the island micro-grid group to be judged according to the fault coefficient vector. The position and the reason of the fault in the micro-grid can be rapidly obtained, and the fault can be rapidly and accurately repaired.

Description

Technical Field

[0001] The present application belongs to the field of electric power grid, and in particular, relates to a method and system for determining faults in an island microgrid group integrating satellite and ground networks. Background Art

[0002] Islands are rich in renewable energy. Microgrids are formed by integrating wind power, photovoltaic power and other new energy sources according to local conditions, and adjacent island microgrids are interconnected to form island microgrid groups. Through the coordinated operation and energy mutual assistance between sub-microgrids, the reliability of system power supply and the utilization rate of new energy are improved, which is an important way to achieve sustainable and high-quality power supply for offshore island groups. Compared with a single microgrid, a microgrid group has the following characteristics: First, there are multiple interconnection modes between microgrids, and the network topology changes frequently, resulting in bidirectional changes in system currents before faults and multiple system current flow paths after faults; second, the superposition of fault currents output by various types of micro-sources with different fault response processes leads to complex fault characteristics of microgrid groups and blurred fault boundaries inside and outside the area. Therefore, the design of an effective microgrid group protection scheme is the key to ensuring its safe and reliable operation. Summary of the invention

[0003] The main purpose of the embodiments of the present invention is to provide a method and system for fault judgment of an island microgrid group with integrated satellite and ground networks, which can quickly obtain the location and cause of the fault in the microgrid, and facilitate rapid and accurate fault repair.

[0004] In a first aspect, a method for determining faults in an island microgrid group with satellite-ground network integration is provided, the method comprising: Obtaining a first three-phase current of a to-be-judged grid node i at the current moment, and obtaining a second three-phase current of the to-be-judged grid node i at the corresponding moment of the previous cycle, and obtaining a three-phase current fault component of the to-be-judged grid node according to the first three-phase current and the second three-phase current; Judging whether the island microgrid group to be judged corresponding to the to-be-judged grid node i is faulty according to the three-phase current fault component; If the judgment is a fault, extracting fault features according to the three-phase current fault components; constructing a fault coefficient vector according to the fault characteristics; The fault line and the fault phase of the island microgrid group to be judged are obtained according to the fault coefficient vector.

[0005] In a possible implementation, the three-phase current fault component is calculated according to the formula Get, where is the first three-phase current, is the second three-phase current, n is the nth sampling point, N c is the number of sampling points in one cycle.

[0006] In another possible implementation, judging whether the island microgrid group to be judged corresponding to the to-be-judged grid node i is faulty according to the three-phase current fault component is specifically as follows: If the three-phase current fault component meets the preset fault judgment formula, then the island microgrid group to be judged has a fault.

[0007] Among them, the fault judgment formula is: or or , where I rat The fault judgment formula indicates that if the current sampling values ​​of any phase of the three-phase electricity in two adjacent power frequency cycles are different, it is judged that a fault occurs in the island microgrid group.

[0008] In another possible implementation, if the determination is a fault, extracting fault features according to the three-phase current fault component includes: Filtering out the high frequency component of the three-phase current fault component to obtain the fundamental frequency component of the three-phase current fault component; Obtaining a fault line fundamental frequency component from the fundamental frequency component; Filtering out the low-frequency component of the three-phase electrical fault component to obtain the high-frequency component of the three-phase current fault component; Acquire a fault line high frequency component from the high frequency component; The fault feature is obtained according to the fundamental frequency component of the fault line and the high frequency component of the fault line.

[0009] In a second aspect, a satellite-ground network integrated island microgrid group fault judgment system is provided, the system comprising: an acquisition module, configured to acquire a first three-phase current of a to-be-judged grid node i at a current moment, and acquire a second three-phase current of the to-be-judged grid node i at a corresponding moment in a previous cycle, and acquire a three-phase current fault component of the to-be-judged grid node according to the first three-phase current and the second three-phase current; A judgment module, used for judging whether the island microgrid group to be judged corresponding to the grid node i to be judged is faulty according to the three-phase current fault component; A fault feature extraction module, used for extracting fault features according to the three-phase current fault components if the fault is determined; A fault coefficient vector construction module, used to construct a fault coefficient vector according to the fault characteristics; The specific fault acquisition module is used to obtain the fault line and fault phase of the island microgrid group to be judged according to the fault coefficient vector.

[0010] In a possible implementation, the three-phase current fault component is calculated according to the formula Get, where is the first three-phase current, is the second three-phase current, n is the nth sampling point, N c is the number of sampling points in one cycle.

[0011] In another possible implementation, judging whether the island microgrid group to be judged corresponding to the to-be-judged grid node i is faulty according to the three-phase current fault component is specifically as follows: If the three-phase current fault component meets the preset fault judgment formula, then the island microgrid group to be judged has a fault.

[0012] Among them, the fault judgment formula is: or or , where I rat The fault judgment formula indicates that if the current sampling values ​​of any phase of the three-phase electricity in two adjacent power frequency cycles are different, it is judged that a fault occurs in the island microgrid group.

[0013] In another possible implementation, if the determination is a fault, extracting fault features according to the three-phase current fault component includes: Filtering out the high frequency component of the three-phase current fault component to obtain the fundamental frequency component of the three-phase current fault component; Obtaining a fault line fundamental frequency component from the fundamental frequency component; Filtering out the low-frequency component of the three-phase electrical fault component to obtain the high-frequency component of the three-phase current fault component; Acquire a fault line high frequency component from the high frequency component; The fault feature is obtained according to the fundamental frequency component of the fault line and the high frequency component of the fault line.

[0014] According to a third aspect, an electronic device is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, a method for determining faults of an island microgrid group integrating a satellite-ground network as provided in the first aspect is implemented.

[0015] In a fourth aspect, a non-transitory computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, a fault judgment method for an island microgrid group integrating a satellite and ground network is implemented as provided in the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in describing the embodiments of the present application are briefly introduced below.

[0017] Figure 1 A schematic diagram of the structure of an island microgrid cluster system integrating satellite and ground networks provided in an embodiment of the present invention; Figure 2 A flow chart of a method for determining faults in an island microgrid group with satellite-ground network integration provided by one embodiment of the present invention; FIG3( a ) is a schematic diagram of a fault component current at the time of a fault provided by an embodiment of the present invention; FIG. 3( b ) is a schematic diagram of a fault component current at a non-fault time provided by an embodiment of the present invention; FIG. 3( c ) is a schematic diagram of the current peak value extraction result of the fault component current at the time of the fault provided by an embodiment of the present invention; FIG. 3( d ) is a schematic diagram of the current peak value extraction result of the fault component current at the non-fault time provided by an embodiment of the present invention; FIG4( a ) is a schematic diagram of a high-frequency current flowing out of a node on one side of a fault line provided by an embodiment of the present invention; FIG4( b ) is a schematic diagram of a high-frequency current flowing out of a node on the other side of a fault line provided by an embodiment of the present invention; FIG. 4( c ) is a schematic diagram showing the processing result of a first-order accumulation generation operator of a high-frequency current flowing out of a node on one side of a fault line provided by an embodiment of the present invention; FIG4( d ) is a schematic diagram of the processing result of the first-order accumulation generation operator of the high-frequency current flowing out of the node on the other side of the fault line provided by an embodiment of the present invention; Figure 5 A structural diagram of a satellite-ground network integrated island microgrid group fault judgment system provided by an embodiment of the present invention; Figure 6 A schematic diagram of the physical structure of an electronic device provided by the present invention. DETAILED DESCRIPTION

[0018] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar modules or modules with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be interpreted as limiting the present invention.

[0019] It will be understood by those skilled in the art that, unless expressly stated, the singular forms "a", "an", "said" and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present application refers to the presence of the features, integers, steps, operations, modules and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, modules, components and / or groups thereof. It should be understood that when we refer to a module as being "connected" or "coupled" to another module, it may be directly connected or coupled to the other modules, or there may be intermediate modules. In addition, the "connection" or "coupling" used herein may include wireless connection or wireless coupling. The term "and / or" used herein includes all or any modules and all combinations of one or more associated listed items.

[0020] In order to make the objectives, technical solutions and advantages of the present application clearer, the implementation method of the present application will be further described in detail below in conjunction with the accompanying drawings.

[0021] The technical solution of the present application and how to solve the above-mentioned technical problems are described in detail below with specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0022] like Figure 1 Shown is a schematic diagram of the structure of an island microgrid cluster system integrating satellite and ground networks provided in an embodiment of the present invention.

[0023] like Figure 2 The figure is a flow chart of a method for determining faults in an island microgrid group with satellite-ground network integration provided by an embodiment of the present invention, the method comprising: Step S201, obtaining a first three-phase current of a to-be-judged grid node i at the current moment, and obtaining a second three-phase current of the to-be-judged grid node i at the corresponding moment of the previous cycle, and obtaining a three-phase current fault component of the to-be-judged grid node according to the first three-phase current and the second three-phase current; Step S202, judging whether the island microgrid group to be judged corresponding to the to-be-judged grid node i is faulty according to the three-phase current fault component; Step S203, if the fault is determined, extracting fault features according to the three-phase current fault components; Step S204, constructing a fault coefficient vector according to the fault characteristics; Step S205, obtaining the fault line and fault phase of the island microgrid group to be determined according to the fault coefficient vector.

[0024] In an embodiment of the present invention, the island microgrid group includes a physical layer, an information layer and a space layer. The microgrid group consists of three microgrids, MG-A, MG-B and MG-C, which are interconnected by submarine cables. The interconnection state is controlled by the interconnection switch. MG-A and MG-B are six-bus grid systems, consisting of photovoltaics, energy storage, interface transformers, power networks and loads. MG-C is a four-bus radial system, including wind turbines, interface transformers, power networks and loads. MG-B is a resource-rich microgrid, MG-A and MG-C are high-proportion load microgrids, and under normal circumstances, MG-B provides energy support to MG-A and MG-C. In addition, nodes in the system connected to three or more lines are called backbone nodes, and feeders with backbone nodes at both ends are called main feeders, otherwise they are branch feeders.

[0025] The information layer includes data acquisition system, time synchronization system, communication system and central protection unit.

[0026] (1) In the data acquisition system, the basic components are voltage transformers (PT) and current transformers (CT). On the one hand, the local control of the micro-source and the secondary control of the microgrid group collect the inverter port voltage and output current for system voltage and frequency regulation. On the other hand, the current of the main feeder and branch feeder connected to the backbone node is collected by the local intelligent protection equipment (IED), the required fault characteristics are extracted, and transmitted to the central protection unit for fault detection and location.

[0027] (2) In the time synchronization system, the basic component is the global positioning system (GPS) timing module, which is responsible for receiving satellite navigation signals and providing a unified time and frequency reference for the entire system. Each microgrid is equipped with a GPS time synchronization system, and data acquisition equipment and IEDs obtain time references through the precision time protocol (PTP) protocol or the network time protocol (NTP) protocol.

[0028] (3) The communication system includes ground networks (such as power grids, 5G, etc.) and low-orbit satellite networks. The two complement each other to ensure the uninterrupted transmission of power data within and between microgrids. In particular, due to the coupling of power transmission and fiber-optic communication packaging of interconnected submarine cables, power failures are usually accompanied by communication interruptions. At this time, low-orbit satellite communications will replace the ground network to support the operation control and decision-making of the microgrid group.

[0029] (4) Each microgrid is equipped with a central protection unit to collect relevant electrical data and control commands from the local IED, realize functions such as fault feature extraction and fault section identification, and send the protection results to the local IED for fault isolation and maintenance.

[0030] The space layer consists of the Global Navigation Satellite System (GNSS) and a low-orbit satellite network. GNSS is responsible for providing nanosecond or microsecond time references for data acquisition systems and communication systems, supporting the acquisition of high-availability electrical data with minimal time synchronization error and fast data transmission. Low-orbit satellite communications have the advantages of wide coverage, low latency, high bandwidth, and low cost. Starlink can provide global communication services with uplink speed of 10Mbps and downlink speed of 100Mbps, with a minimum delay of about 20ms, and is a high-quality supplement to the ground network. In addition, compared with medium and high-orbit satellites, low-orbit satellites have low signal attenuation and fast transmission rate. They can be used as space-based enhanced relays for GNSS, combining satellite-borne data with ground observation base stations to improve positioning, navigation, and timing accuracy. Therefore, the collaboration of high, medium, and low-orbit satellites can provide accurate time and frequency references for remote island microgrid groups.

[0031] The three-phase current fault components are calculated according to the formula Get, where is the first three-phase current, is the second three-phase current, n is the nth sampling point, N c is the number of sampling points in one cycle.

[0032] Among them, judging whether the island microgrid group to be judged corresponding to the to-be-judged grid node i is faulty according to the three-phase current fault component is specifically: If the three-phase current fault component meets the preset fault judgment formula, then the island microgrid group to be judged has a fault.

[0033] Among them, the fault judgment formula is: or or , where I rat The fault judgment formula indicates that if the current sampling values ​​of any phase of the three-phase electricity in two adjacent power frequency cycles are different, it is judged that a fault occurs in the island microgrid group.

[0034] If the judgment is a fault, extracting fault features according to the three-phase current fault component includes: Filtering out the high frequency component of the three-phase current fault component to obtain the fundamental frequency component of the three-phase current fault component; Obtaining a fault line fundamental frequency component from the fundamental frequency component; Filtering out the low-frequency component of the three-phase electrical fault component to obtain the high-frequency component of the three-phase current fault component; Acquire a fault line high frequency component from the high frequency component; The fault feature is obtained according to the fundamental frequency component of the fault line and the high frequency component of the fault line.

[0035] In this embodiment, to reflect the characteristics of the fundamental frequency current direction, first, a low-pass filter is used to filter out the high-frequency components to obtain the fundamental frequency components of the three-phase current fault components. Then, the opening and closing operators of the mathematical morphology algorithm are used to extract the first peak value of the fundamental frequency current fault components. The calculation formula is , where is the positive peak, is the negative peak, Peak ij,a (n), Peak ij,b (n), Peak ij,c (n) represent the peak values of the three-phase fundamental frequency current fault components, and g(m) (0 < m ≤ M) is the structuring element. 〇 and ● are the opening and closing operators respectively, which can eliminate noise, smooth pulses, and cut to obtain the positive and negative peak values of the current waveform, so as to obtain the first positive peak time T ij,a , T ij,b , T ij,c .

[0036] As shown in Figure 3(a), it is the current schematic diagram of the fault component current at the fault moment provided by the embodiment of the present invention. As shown in Figure 3(b), it is the current schematic diagram of the fault component current at the non-fault moment provided by the embodiment of the present invention. As shown in Figure 3(c), it is the schematic diagram of the current peak extraction result of the fault component current at the fault moment provided by the embodiment of the present invention. As shown in Figure 3(d), it is the schematic diagram of the current peak extraction result of the fault component current at the non-fault moment provided by the embodiment of the present invention. Since the short-circuit fault will cause jumps in the current amplitude and phase, the mathematical morphology algorithm can also detect the peak shape at the fault moment, which is called the pseudo-peak here. To avoid being misled by the pseudo-peak, it is stipulated that the first time value of the positive peak time series with a time interval greater than 10 ms is taken as the first positive peak time. It can be seen that the T ij of the power frequency fault component current of the fault line is less than 5 ms, while the T ij of the power frequency fault component current of the non-fault line is close to 10 ms.

[0037] To reflect the characteristics of the high-frequency current direction, a high-pass filter is used to filter out the low-frequency components to obtain the high-frequency components of the three-phase current , , . Since the high-frequency components are easily affected by background noise, fault resistance, and fault initial angle, a first-order accumulative generating operator (AGO) is used to amplify the high-frequency components. The calculation formula is , , , are respectively , , The first-order cumulative generator of .

[0038] Calculate separately , , The slope k of the first zero crossing zcs,a , k zcs,b , k zcs,c .definition , , The signed sum S ij,a , S ij,b , S ij,c , the calculation formula is , D w1 To calculate the data window length.

[0039] As shown in FIG4(a), a schematic diagram of the high-frequency current flowing out of a node on one side of a fault line according to an embodiment of the present invention is shown; as shown in FIG4(b), a schematic diagram of the high-frequency current flowing out of a node on the other side of a fault line according to an embodiment of the present invention is shown; as shown in FIG4(c), a schematic diagram of the processing result of the first-order accumulation generation operator of the high-frequency current flowing out of a node on one side of a fault line according to an embodiment of the present invention is shown; as shown in FIG4(d), a schematic diagram of the processing result of the first-order accumulation generation operator of the high-frequency current flowing out of a node on the other side of a fault line according to an embodiment of the present invention is shown. Compared with the original high-frequency current, the high-frequency current after first-order AGO processing is , , It presents a smoother and more regular waveform, and the fault line and non-fault line , , The differences in direction and magnitude are more obvious.

[0040] On a time scale, the voltage drop at the fault point at the time of the fault will introduce a sudden change in the current amplitude and phase. After the inverter-type micro-source detects a system fault, it will start the fault ride-through control, perform fault current limiting and reactive power support, and the current phase will change suddenly again. In order to characterize the current amplitude and phase jump caused by the voltage drop at the fault point and the micro-source fault ride-through control response, the current is reconstructed using Fourier-Taylor transform. The difference between the measured current and the reconstructed current is used to quantify the degree of current mutation before and after the fault.

[0041] First, measure the current i ij,a (n), i ij,b (n), i ij,c The discrete Fourier expansion of (n) is , T s is the sampling period, ω0 is the power frequency angular frequency, a 0,ijϕ 、a k,ijϕ , bk,ijϕ is the Fourier coefficient of the φ-phase current.

[0042] Since the measured current is a stable baseband signal under normal circumstances, the definition signal of the reconstructed current is also set to the baseband signal. When the calculation data window length is Dw2, the above formula is expressed as , using the least squares method, the Fourier coefficient matrix can be calculated , , , and then through the Fourier coefficient matrix, the reconstruction value of the three-phase current can be obtained as .

[0043] Finally, the sum of the actual value and the reconstructed value difference of all line currents connected to node i is calculated to obtain the three-phase current transient monitoring value TM of node i. ij,a ,TM ij,b ,TM ij,c , and its corresponding formula is , G is the number of nodes adjacent to node i, , , i ij,a (n), i ij,b (n), i ij,c (n) is the reconstructed value.

[0044] The fault characteristic data of all IED nodes in the microgrid and the fault characteristic data of remote IED nodes on the interconnection lines of adjacent microgrids are collected through ground network or satellite communication. i The data transmitted to the central protection unit mainly include the first positive peak moment of the power frequency current fault component, the signed cumulative value of the high frequency component of all line currents connected to node i, and the transient monitoring value of all line currents connected to node i. Since the delay required for the occurrence, calculation and ground network transmission of fault characteristics is less than 60ms, if the central protection unit does not receive the IED within 60ms after the fault, the fault will be detected. i When the fault data is i If the ground communication with the central protection unit fails, satellite communication will be used to transmit fault data.

[0045] The construction of the fault coefficient vector is as follows: Construction of the three-phase current direction mutation matrix: If there is no cable connection between node i and node j, the direction mutation characteristic of the fundamental frequency current fault component of line ij is D BF_ija , D BF_ijb , D BF_ijcIf there is a cable connection between node i and node j, and when the absolute value of the difference between the first positive peak moment of the fundamental frequency current fault component of phase A at both ends of the line |T ij,a -T ji,a |When it is less than 5ms, the directional mutation characteristics of the fundamental frequency current fault component of phase A on line ij are D BF_ija =1, otherwise 0. In summary, the fundamental frequency current fault component directional mutation characteristic matrix D of the microgrid system can be obtained. BF,a , D BF,b , D BF,c , whose formula is , N A is the number of nodes in the microgrid system.

[0046] Similarly, if there is no cable connection between node i and node j, the high-frequency current direction mutation characteristic of line ij is D HF_ija , D HF_ijb , D HF_ijc If there is a cable connection between node i and node j, taking phase A as an example, when the signed cumulative value of the high-frequency current of phase A at both ends of the line satisfies the formula When the direction of the high-frequency current of phase A on line ij is suddenly changed, D HF_ija is equal to 1, otherwise it is 0. Similarly, D HF_ijb , D HF_ijc In summary, the directional mutation characteristic matrix D of the high-frequency current of the microgrid system can be obtained: HF,a , D HF,b , D HF,c .

[0047] According to the formula and , the three-phase current direction mutation matrix of the microgrid system can be obtained as .

[0048] Construction of three-phase current transient monitoring vector: Based on the above formula, the three-phase current transient monitoring vector can be obtained as follows: .

[0049] Based on the directional mutation matrix and transient monitoring vector, the fault coefficient vector integrating the temporal and spatial characteristic information is constructed as follows: , F.I. ϕ represents the φ phase fault coefficient vector.

[0050] Furthermore, through the formula The fault coefficient vector is mean normalized.

[0051] Wherein, the obtaining of the fault line and the fault phase of the island microgrid group to be determined according to the fault coefficient vector includes: In the normalized fault coefficient vector, when the fault coefficient FI i,ϕ and FI j,ϕ When both are greater than 0, line ij is a fault line, phase φ is a fault phase, and a single-phase trip signal is sent to the IED protection devices at both ends of the line. i and IED j , isolate the faulty line and the faulty phase, otherwise the line ij is a non-faulty line and the φ phase is a non-faulty phase, and the protection does not operate.

[0052] In the embodiment of the present invention, the first three-phase current of the to-be-judged grid node i at the current moment is obtained, and the second three-phase current of the to-be-judged grid node i at the corresponding moment of the previous cycle is obtained, and the three-phase current fault component of the to-be-judged grid node is obtained according to the first three-phase current and the second three-phase current; whether the island microgrid group to be judged corresponding to the to-be-judged grid node i is faulty is determined according to the three-phase current fault component; if the judgment is a fault, the fault feature is extracted according to the three-phase current fault component; a fault coefficient vector is constructed according to the fault feature; and the fault line and fault phase of the island microgrid group to be judged are obtained according to the fault coefficient vector. The location and cause of the fault in the microgrid can be quickly obtained, which is convenient for fast and accurate fault repair.

[0053] like Figure 5 The figure shows a structural diagram of a satellite-ground network integrated island microgrid group fault judgment system provided by an embodiment of the present invention, the system comprising: An acquisition module 501 is used to acquire a first three-phase current of a to-be-judged grid node i at a current moment, and acquire a second three-phase current of the to-be-judged grid node i at a corresponding moment in a previous cycle, and acquire a three-phase current fault component of the to-be-judged grid node according to the first three-phase current and the second three-phase current; A judgment module 502 is used to judge whether the island microgrid group to be judged corresponding to the to-be-judged grid node i is faulty according to the three-phase current fault component; A fault feature extraction module 503 is used to extract fault features according to the three-phase current fault components if the fault is determined to be a fault; A fault coefficient vector construction module 504 is used to construct a fault coefficient vector according to the fault characteristics; The specific fault acquisition module 505 is used to obtain the fault line and fault phase of the island microgrid group to be judged according to the fault coefficient vector.

[0054] In an embodiment of the present invention, the island microgrid group includes a physical layer, an information layer and a space layer. The microgrid group consists of three microgrids, MG-A, MG-B and MG-C, which are interconnected by submarine cables. The interconnection state is controlled by the interconnection switch. MG-A and MG-B are six-bus grid systems, consisting of photovoltaics, energy storage, interface transformers, power networks and loads. MG-C is a four-bus radial system, including wind turbines, interface transformers, power networks and loads. MG-B is a resource-rich microgrid, MG-A and MG-C are high-proportion load microgrids, and under normal circumstances, MG-B provides energy support to MG-A and MG-C. In addition, nodes in the system connected to three or more lines are called backbone nodes, and feeders with backbone nodes at both ends are called main feeders, otherwise they are branch feeders.

[0055] The information layer includes data acquisition system, time synchronization system, communication system and central protection unit.

[0056] (1) In the data acquisition system, the basic components are voltage transformers (PT) and current transformers (CT). On the one hand, the micro-source local control and microgrid group secondary control collect the inverter port voltage and output current for system voltage and frequency regulation. On the other hand, the current of the main feeder and branch feeder connected to the backbone node is collected by the local IED, the required fault characteristics are extracted, and transmitted to the central protection unit for fault detection and location.

[0057] (2) In the time synchronization system, the basic component is the GPS timing module, which is responsible for receiving satellite navigation signals and providing a unified time and frequency reference for the entire system. Each microgrid is equipped with a GPS time synchronization system, and data acquisition equipment and IEDs obtain time references through the Precision Time Protocol (PTP) protocol or the Network Time Protocol (NTP) protocol.

[0058] (3) The communication system includes ground networks (such as power grids, 5G, etc.) and low-orbit satellite networks. The two complement each other to ensure the uninterrupted transmission of power data within and between microgrids. In particular, due to the coupling of power transmission and fiber-optic communication packaging of interconnected submarine cables, power failures are usually accompanied by communication interruptions. At this time, low-orbit satellite communications will replace the ground network to support the operation control and decision-making of the microgrid group.

[0059] (4) Each microgrid is equipped with a central protection unit to collect relevant electrical data and control commands from the local IED, realize functions such as fault feature extraction and fault section identification, and send the protection results to the local IED for fault isolation and maintenance.

[0060] The space layer consists of the Global Navigation Satellite System (GNSS) and a low-orbit satellite network. GNSS is responsible for providing nanosecond or microsecond time references for data acquisition systems and communication systems, supporting the acquisition of high-availability electrical data with minimal time synchronization error and fast data transmission. Low-orbit satellite communications have the advantages of wide coverage, low latency, high bandwidth, and low cost. Starlink can provide global communication services with uplink speed of 10Mbps and downlink speed of 100Mbps, with a minimum delay of about 20ms, and is a high-quality supplement to the ground network. In addition, compared with medium and high-orbit satellites, low-orbit satellites have low signal attenuation and fast transmission rate. They can be used as space-based enhanced relays for GNSS, combining satellite-borne data with ground observation base stations to improve positioning, navigation, and timing accuracy. Therefore, the collaboration of high, medium, and low-orbit satellites can provide accurate time and frequency references for remote island microgrid groups.

[0061] The three-phase current fault components are calculated according to the formula Get, where is the first three-phase current, is the second three-phase current, n is the nth sampling point, N c is the number of sampling points in one cycle.

[0062] Among them, judging whether the island microgrid group to be judged corresponding to the to-be-judged grid node i is faulty according to the three-phase current fault component is specifically: If the three-phase current fault component meets the preset fault judgment formula, then the island microgrid group to be judged has a fault.

[0063] Among them, the fault judgment formula is: or or , where I rat The fault judgment formula indicates that if the current sampling values ​​of any phase of the three-phase electricity in two adjacent power frequency cycles are different, it is judged that a fault occurs in the island microgrid group.

[0064] If the judgment is a fault, extracting fault features according to the three-phase current fault component includes: Filtering out the high frequency component of the three-phase current fault component to obtain the fundamental frequency component of the three-phase current fault component; Obtaining a fault line fundamental frequency component from the fundamental frequency component; Filtering out the low-frequency component of the three-phase electrical fault component to obtain the high-frequency component of the three-phase current fault component; Acquire a fault line high frequency component from the high frequency component; The fault feature is obtained according to the fundamental frequency component of the fault line and the high frequency component of the fault line.

[0065] In this embodiment, to reflect the characteristics of the fundamental frequency current direction, first, a low-pass filter is used to filter out the high-frequency components to obtain the fundamental frequency components of the three-phase current fault components. Then, the opening and closing operators of the mathematical morphology algorithm are used to extract the first peak value of the fundamental frequency current fault components. The calculation formula is , where is the positive peak, is the negative peak, Peak ij,a (n), Peak ij,b (n), Peak ij,c (n) represent the peak values of the three-phase fundamental frequency current fault components, and g(m) (0 < m ≤ M) is the structuring element. 〇 and ● are the opening and closing operators respectively, which can eliminate noise, smooth pulses, and cut to obtain the positive and negative peak values of the current waveform, so as to obtain the first positive peak time T ij,a , T ij,b , T ij,c .

[0066] Since a short-circuit fault will cause jumps in the current amplitude and phase, the mathematical morphology algorithm can also detect the peak shape at the fault moment, which is called a pseudo-peak here. To avoid being misled by the pseudo-peak, it is stipulated that the first time value of the positive peak time series with a time interval greater than 10 ms is taken as the first positive peak time. It can be seen that the T ij of the power frequency fault component current of the fault line is less than 5 ms, while the T ij of the power frequency fault component current of the non-fault line is close to 10 ms.

[0067] To reflect the characteristics of the high-frequency current direction, a high-pass filter is used to filter out the low-frequency components to obtain the high-frequency components of the three-phase current , , . Since the high-frequency components are easily affected by background noise, fault resistance, and fault initial angle, a first-order accumulation generation operator (AGO) is used to amplify the high-frequency components. The calculation formula is , , , are the first-order accumulation generation operators of , , respectively.

[0068] Calculate the slopes k , , of the first zero-crossing points of zcs,a , k zcs,b , k zcs,c respectively. Define , , The signed sum S ij,a , S ij,b , S ij,c , the calculation formula is , D w1 To calculate the data window length.

[0069] The high-frequency current flowing out of the nodes on both sides of the fault line and its first-order AGO processing results show that compared with the original high-frequency current, the first-order AGO processed , , It presents a smoother and more regular waveform, and the fault line and non-fault line , , The differences in direction and magnitude are more obvious.

[0070] On a time scale, the voltage drop at the fault point at the time of the fault will introduce a sudden change in the current amplitude and phase. After the inverter-type micro-source detects a system fault, it will start the fault ride-through control, perform fault current limiting and reactive power support, and the current phase will change suddenly again. In order to characterize the current amplitude and phase jump caused by the voltage drop at the fault point and the micro-source fault ride-through control response, the current is reconstructed using Fourier-Taylor transform. The difference between the measured current and the reconstructed current is used to quantify the degree of current mutation before and after the fault.

[0071] First, measure the current i ij,a (n), i ij,b (n), i ij,c The discrete Fourier expansion of (n) is , T s is the sampling period, ω0 is the power frequency angular frequency, a 0,ijϕ 、a k,ijϕ , b k,ijϕ is the Fourier coefficient of the φ-phase current.

[0072] Since the measured current is a stable baseband signal under normal circumstances, the definition signal of the reconstructed current is also set to the baseband signal. When the calculation data window length is Dw2, the above formula is expressed as , using the least squares method, the Fourier coefficient matrix can be calculated , , , and then through the Fourier coefficient matrix, the reconstruction value of the three-phase current can be obtained as .

[0073] Finally, the sum of the actual value and the reconstructed value difference of all line currents connected to node i is calculated to obtain the three-phase current transient monitoring value TM of node i.ij,a ,TM ij,b ,TM ij,c , and its corresponding formula is , G is the number of nodes adjacent to node i, , , i ij,a (n), i ij,b (n), i ij,c (n) is the reconstructed value.

[0074] The fault characteristic data of all IED nodes in the microgrid and the fault characteristic data of remote IED nodes on the interconnection lines of adjacent microgrids are collected through ground network or satellite communication. i The data transmitted to the central protection unit mainly include the first positive peak moment of the power frequency current fault component, the signed cumulative value of the high frequency component of all line currents connected to node i, and the transient monitoring value of all line currents connected to node i. Since the delay required for the occurrence, calculation and ground network transmission of fault characteristics is less than 60ms, if the central protection unit does not receive the IED within 60ms after the fault, the fault will be detected. i When the fault data is i If the ground communication with the central protection unit fails, satellite communication will be used to transmit fault data.

[0075] The construction of the fault coefficient vector is as follows: Construction of the three-phase current direction mutation matrix: If there is no cable connection between node i and node j, the direction mutation characteristic of the fundamental frequency current fault component of line ij is D BF_ija , D BF_ijb , D BF_ijc If there is a cable connection between node i and node j, and when the absolute value of the difference between the first positive peak moment of the fundamental frequency current fault component of phase A at both ends of the line |T ij,a -T ji,a |When it is less than 5ms, the directional mutation characteristics of the fundamental frequency current fault component of phase A on line ij are D BF_ija =1, otherwise 0. In summary, the fundamental frequency current fault component directional mutation characteristic matrix D of the microgrid system can be obtained. BF,a , D BF,b , D BF,c , whose formula is , NA is the number of nodes in the microgrid system.

[0076] Similarly, if there is no cable connection between node i and node j, the high-frequency current direction mutation characteristic of line ij is D HF_ija , D HF_ijb , D HF_ijcIf there is a cable connection between node i and node j, taking phase A as an example, when the signed cumulative value of the high-frequency current of phase A at both ends of the line satisfies the formula When the direction of the high-frequency current of phase A on line ij is suddenly changed, D HF_ija is equal to 1, otherwise it is 0. Similarly, D HF_ijb , D HF_ijc In summary, the directional mutation characteristic matrix D of the high-frequency current of the microgrid system can be obtained: HF,a , D HF,b , D HF,c .

[0077] According to the formula and , the three-phase current direction mutation matrix of the microgrid system can be obtained as .

[0078] Construction of three-phase current transient monitoring vector: Based on the above formula, the three-phase current transient monitoring vector can be obtained as follows: .

[0079] Based on the directional mutation matrix and transient monitoring vector, the fault coefficient vector integrating the temporal and spatial characteristic information is constructed as follows: , F.I. ϕ represents the φ phase fault coefficient vector.

[0080] Furthermore, through the formula The fault coefficient vector is mean normalized.

[0081] Wherein, the obtaining of the fault line and the fault phase of the island microgrid group to be determined according to the fault coefficient vector includes: In the normalized fault coefficient vector, when the fault coefficient FI i,ϕ and FI j,ϕ When both are greater than 0, line ij is a fault line, phase φ is a fault phase, and a single-phase trip signal is sent to the IED protection devices at both ends of the line. i and IED j , isolate the faulty line and the faulty phase, otherwise the line ij is a non-faulty line and the φ phase is a non-faulty phase, and the protection does not operate.

[0082] In the embodiment of the present invention, the first three-phase current of the to-be-judged grid node i at the current moment is obtained, and the second three-phase current of the to-be-judged grid node i at the corresponding moment of the previous cycle is obtained, and the three-phase current fault component of the to-be-judged grid node is obtained according to the first three-phase current and the second three-phase current; whether the island microgrid group to be judged corresponding to the to-be-judged grid node i is faulty is determined according to the three-phase current fault component; if the judgment is a fault, the fault feature is extracted according to the three-phase current fault component; a fault coefficient vector is constructed according to the fault feature; and the fault line and fault phase of the island microgrid group to be judged are obtained according to the fault coefficient vector. The location and cause of the fault in the microgrid can be quickly obtained, which is convenient for fast and accurate fault repair.

[0083] Figure 6 An example of a physical structure diagram of an electronic device is shown in FIG. Figure 6 As shown, the electronic device may include: a processor (processor) 601, a communication interface (Communications Interface) 602, a memory (memory) 603 and a communication bus 604, wherein the processor, the communication interface and the memory complete mutual communication through the communication bus. The processor may call the logic instructions in the memory to execute a method for fault judgment of an island microgrid group with satellite-ground network integration, the method comprising: obtaining the first three-phase current of the grid node i to be judged at the current moment, and obtaining the second three-phase current of the grid node i to be judged at the corresponding moment of the previous cycle, and obtaining the three-phase current fault component of the grid node to be judged according to the first three-phase current and the second three-phase current; judging whether the island microgrid group to be judged corresponding to the grid node i to be judged is faulty according to the three-phase current fault component; if the judgment is a fault, extracting fault features according to the three-phase current fault component; constructing a fault coefficient vector according to the fault feature; obtaining the fault line and fault phase of the island microgrid group to be judged according to the fault coefficient vector.

[0084] In addition, the logic instructions in the above-mentioned memory can be implemented in the form of software functional units and can be stored in a computer-readable storage medium when sold or used as an independent product. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program code.

[0085] On the other hand, an embodiment of the present invention further provides a computer program product, which includes a computer program stored on a non-transitory computer-readable storage medium, and the computer program includes program instructions. When the program instructions are executed by a computer, the computer can execute a method for fault judgment of an island microgrid group with satellite-ground network integration provided by the above-mentioned method embodiments, the method including: obtaining the first three-phase current of the grid node i to be judged at the current moment, and obtaining the second three-phase current of the grid node i to be judged at the corresponding moment of the previous cycle, and obtaining the three-phase current fault component of the grid node to be judged based on the first three-phase current and the second three-phase current; judging whether the island microgrid group to be judged corresponding to the grid node i to be judged is faulty based on the three-phase current fault component; if the judgment is a fault, extracting fault characteristics based on the three-phase current fault components; constructing a fault coefficient vector based on the fault characteristics; and obtaining the fault line and fault phase of the island microgrid group to be judged based on the fault coefficient vector.

[0086] On the other hand, an embodiment of the present invention further provides a non-transitory computer-readable storage medium having a computer program stored thereon, which is implemented when the processor executes a method for determining a fault of an island microgrid group integrating a satellite-ground network provided in the above-mentioned embodiments, the method comprising: obtaining a first three-phase current of the grid node i to be determined at the current moment, and obtaining a second three-phase current of the grid node i to be determined at the corresponding moment of the previous cycle, and obtaining a three-phase current fault component of the grid node to be determined based on the first three-phase current and the second three-phase current; determining whether the island microgrid group to be determined corresponding to the grid node i to be determined is faulty based on the three-phase current fault component; if the determination is a fault, extracting fault features based on the three-phase current fault components; constructing a fault coefficient vector based on the fault features; and obtaining the fault line and fault phase of the island microgrid group to be determined based on the fault coefficient vector.

[0087] It should be understood that, although the steps in the flowchart of the accompanying drawings are displayed in sequence as indicated by the arrows, these steps are not necessarily executed in sequence in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least a part of the steps in the flowchart of the accompanying drawings may include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be executed in turn or alternately with other steps or at least a part of the sub-steps or stages of other steps.

[0088] The above is only a partial implementation of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for fault judgment of an island microgrid group with satellite-ground network integration, characterized in that: The method comprises: Obtaining a first three-phase current of a to-be-judged grid node i at the current moment, and obtaining a second three-phase current of the to-be-judged grid node i at the corresponding moment of the previous cycle, and obtaining a three-phase current fault component of the to-be-judged grid node according to the first three-phase current and the second three-phase current; Judging whether the island microgrid group to be judged corresponding to the to-be-judged grid node i is faulty according to the three-phase current fault component; If the judgment is a fault, extracting fault features according to the three-phase current fault components; constructing a fault coefficient vector according to the fault characteristics; The fault line and the fault phase of the island microgrid group to be judged are obtained according to the fault coefficient vector.

2. The method according to claim 1, characterized in that The three-phase current fault component is calculated according to the formula Get, where is the first three-phase current, is the second three-phase current, n is the nth sampling point, N c is the number of sampling points in one cycle.

3. The method according to claim 1, characterized in that The method of judging whether the island microgrid group to be judged corresponding to the to-be-judged grid node i is faulty according to the three-phase current fault component is specifically as follows: If the three-phase current fault component meets the preset fault judgment formula, then the island microgrid group to be judged has a fault; Among them, the fault judgment formula is: or or , where I rat is the rated current; the fault judgment formula indicates that: if the current sampling values ​​of any phase of the three-phase electricity in two adjacent power frequency cycles are different, it is judged that a fault occurs in the island microgrid group.

4. The method according to claim 1, characterized in that If the judgment is a fault, extracting fault features according to the three-phase current fault component includes: Filtering out the high frequency component of the three-phase current fault component to obtain the fundamental frequency component of the three-phase current fault component; Obtaining a fault line fundamental frequency component from the fundamental frequency component; Filtering out the low-frequency component of the three-phase electrical fault component to obtain the high-frequency component of the three-phase current fault component; Acquire a fault line high frequency component from the high frequency component; The fault feature is obtained according to the fundamental frequency component of the fault line and the high frequency component of the fault line.

5. A satellite-ground network integrated island microgrid group fault diagnosis system, characterized in that: The system comprises: an acquisition module, configured to acquire a first three-phase current of a to-be-judged grid node i at a current moment, and acquire a second three-phase current of the to-be-judged grid node i at a corresponding moment in a previous cycle, and acquire a three-phase current fault component of the to-be-judged grid node according to the first three-phase current and the second three-phase current; A judgment module, used for judging whether the island microgrid group to be judged corresponding to the grid node i to be judged is faulty according to the three-phase current fault component; A fault feature extraction module, used for extracting fault features according to the three-phase current fault components if the fault is determined; A fault coefficient vector construction module, used to construct a fault coefficient vector according to the fault characteristics; The specific fault acquisition module is used to obtain the fault line and fault phase of the island microgrid group to be judged according to the fault coefficient vector.

6. The system according to claim 5, characterized in that The three-phase current fault component is calculated according to the formula Get, where is the first three-phase current, is the second three-phase current, n is the nth sampling point, N c is the number of sampling points in one cycle.

7. The system according to claim 5, characterized in that The method of judging whether the island microgrid group to be judged corresponding to the to-be-judged grid node i is faulty according to the three-phase current fault component is specifically as follows: If the three-phase current fault component meets the preset fault judgment formula, then the island microgrid group to be judged has a fault; Among them, the fault judgment formula is: or or , where I rat is the rated current; the fault judgment formula indicates that: if the current sampling values ​​of any phase of the three-phase electricity in two adjacent power frequency cycles are different, it is judged that a fault occurs in the island microgrid group.

8. The system according to claim 5, characterized in that If the judgment is a fault, extracting fault features according to the three-phase current fault component includes: Filtering out the high frequency component of the three-phase current fault component to obtain the fundamental frequency component of the three-phase current fault component; Obtaining a fault line fundamental frequency component from the fundamental frequency component; Filtering out the low-frequency component of the three-phase electrical fault component to obtain the high-frequency component of the three-phase current fault component; Acquire a fault line high frequency component from the high frequency component; The fault feature is obtained according to the fundamental frequency component of the fault line and the high frequency component of the fault line.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, it implements a method for determining faults in an island microgrid group with satellite-ground network integration as described in any one of claims 1 to 4.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by the processor, it implements a method for determining faults in an island microgrid group with satellite-ground network integration as described in any one of claims 1 to 4.

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