Composite differential protection method, control device, storage medium and system

Abstract

The invention provides a composite differential protection method, a control device, a storage medium and a system, and belongs to the technical field of power distribution networks. The method comprises the following steps: after a power distribution network starts differential protection, exchanging electrical quantities measured by protection at two sides of a protected section; predicting the electrical quantities before and after the fault of the protected section by using the exchanged electrical quantities measured by the protectors at the two sides of the protected section; predicting the voltage of a fault point based on the predicted electrical quantities before and after the fault of the protected section, and calculating the action condition of differential protection; and when the calculated action condition of the differential protection meets the requirement, sending a tripping signal to realize composite differential protection. According to the method, the current and the active power of the T-connection DPV and the load branch under the fault are estimated by using the electrical data at the two ends of the protected section, and the protection principle is ensured to accord with the KCL and the active power conservation law, so that the problem of differential protection refusal or maloperation when the T-connection DPV and the load branch exist in the protected section at the same time is solved.

Description

Technical Field

[0001] This invention relates to the field of power distribution network technology, and more specifically to a composite differential protection method, control device, storage medium, and system. Background Technology

[0002] Differential protection treats the protected electrical equipment as a node. Under normal conditions, the current flowing into the protected equipment is equal to the current flowing out, and the differential current is zero. When a fault occurs, the current flowing into the protected equipment is not equal to the current flowing out, and the differential current is greater than zero. When the differential current exceeds the setting value of the differential protection device, the host computer alarm protection output will activate, tripping the circuit breakers on each side of the protected equipment, thus disconnecting the power supply to the faulty equipment. Current differential protection in distribution networks can only utilize the current phasors at both ends of the protected line to construct protection criteria. Taking the most common differential protection criterion with braking characteristics as an example, its operating conditions are as follows: ; ; ; ,in, This is the braking coefficient. The current measured by the M-side protection of the protected line. The current measured by the N-side protection of the protected line. Action threshold, For differential current, This is the braking current.

[0003] However, to prevent unexpected tripping during normal operation, the operating threshold must exceed the maximum steady-state unbalanced current. The operating threshold increases to varying degrees depending on the configuration of distributed photovoltaic (DPV) and loads in the T-branch, thus reducing the sensitivity of the current differential protection (CDP). Furthermore, the T-branch affects the differential current and restraint current, potentially causing the current differential protection to malfunction or fail to operate. Summary of the Invention

[0004] The purpose of this invention is to provide a composite differential protection method, control device, storage medium, and system to solve the problem of differential protection failure or maloperation when T-connected distributed photovoltaic and load branches exist simultaneously in the protected section.

[0005] To achieve the above objectives, embodiments of the present invention provide a composite differential protection method for T-connected branches. The composite differential protection method includes: after the differential protection of the distribution network is activated, exchanging the electrical quantities measured by the protection on both sides of the protected section; using the exchanged electrical quantities measured by the protection on both sides of the protected section, predicting the electrical quantities before and after a fault in the protected section; based on the predicted electrical quantities before and after a fault in the protected section, predicting the voltage at the fault point, and calculating the operating conditions of the differential protection; and when the calculated operating conditions of the differential protection meet the requirements, sending a trip signal to realize composite differential protection.

[0006] Optionally, the method of predicting the electrical quantities before and after a fault in the protected section by using the electrical quantities measured by the protection on both sides of the exchanged protected section includes: using the electrical quantities measured by the protection on both sides of the protected section before the fault, and combining them with the equivalent circuit during normal operation of the distribution network, to predict the active power captured per unit capacity and the load output factor of the photovoltaic branch of the T-connected branch; and using the electrical quantities measured by the protection on both sides of the protected section after the fault, and combining them with the positive sequence equivalent circuit during a fault in the distribution network, to predict the current and active power of the composite branch of the T-connected branch.

[0007] Optionally, the method of using the electrical quantities measured by the protection on both sides of the protected section before the fault, and combining them with the equivalent circuit during normal operation of the distribution network, to predict the active power captured per unit capacity and load output factor of the photovoltaic branch of the T-connection branch includes: the voltage measured by the protection on one side of the protected section. Convert to the corresponding equivalent voltage The voltage measured by the protection on the other side Convert to the corresponding equivalent voltage From voltage to voltage Iterative calculations are performed to obtain complex equations including real and imaginary parts; and the obtained complex equations are iteratively solved to obtain the active power captured per unit capacity of the photovoltaic branch of the T-junction and the load output factor.

[0008] Optionally, the method of using the electrical quantities measured by the protection on both sides of the protected section after the fault, and combining them with the positive sequence equivalent circuit during a distribution network fault, to predict the current and active power of the composite branch of the T-connection branch includes: the voltage measured by the protection on one side of the protected section. Convert to the corresponding equivalent voltage The voltage measured by the protection on the other side Convert to the corresponding equivalent voltage ; calculate the voltage at each common coupling point and T-junction point and determine the fault point; and based on the calculated voltage at each common coupling point and T-junction point, calculate the positive sequence voltage at each common coupling point and T-junction point to predict the current and active power of the composite branch of the T-junction branch.

[0009] Optionally, the fault point voltage can be predicted using the following formula. : in, Indicates the first i The voltage of the load node connected to the T-junction. Indicates the first i +1 voltage at common connection point, This represents the current measured by the M-side protection of the protected section. This represents the current measured by the N-side protection of the protected section. Indicates the first j The current of the load connected to the T-type connector. Indicates the first i The first T-connected load node and the first i +1 line impedance at common connection point Indicates the relative distance to the fault.

[0010] Optionally, the operating conditions of the differential protection can be represented by the following formula. and : in, Indicates the fault point f voltage, and These represent the setting values ​​for current differential protection and active power differential protection, respectively. This indicates the active power loss within the protected section. Indicates the first j The active power of each load. This represents the current measured by the M-side protection of the protected section. This represents the current measured by the N-side protection of the protected section. Indicates the first j The current of the load connected to the T-type connector. This represents the active power on the M side of the protected section. This indicates the active power on the N side of the protected section... Optionally, when the differential protection operates... When the calculated differential protection operating conditions are met, it indicates that the requirements are met.

[0011] This invention also provides a control device, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor. The processor executes the computer program to implement the above-described composite differential protection method.

[0012] This invention also provides a machine-readable storage medium storing instructions that cause a machine to execute the aforementioned composite differential protection method.

[0013] This invention also provides a composite differential protection system for a T-connected branch, the composite differential protection system including the above-mentioned control device and a distribution network including a T-connected branch.

[0014] The composite differential protection method for T-connected branches provided by the present invention, through the above technical solution, includes: after the differential protection of the distribution network is activated, exchanging the electrical quantities measured by the protection on both sides of the protected section; using the exchanged electrical quantities measured by the protection on both sides of the protected section, predicting the electrical quantities before and after the fault in the protected section; based on the predicted electrical quantities before and after the fault in the protected section, predicting the voltage at the fault point, and calculating the operating conditions of the differential protection; and when the calculated operating conditions of the differential protection meet the requirements, sending a trip signal to realize composite differential protection. The present invention utilizes electrical data at both ends of the protected section to estimate the current and active power of the T-connected distributed photovoltaic (DPV) and load branches under fault conditions, ensuring that the protection principle conforms to the KCL and the law of conservation of active power, thereby improving protection reliability and solving the problem of differential protection failure or maloperation when T-connected distributed photovoltaic and load branches exist simultaneously within the protected section.

[0015] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0016] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of a distribution network including T-junction branches; Figure 2 This is a schematic flowchart of a composite differential protection method for T-connected branches provided in an embodiment of the present invention; Figure 3 It is a schematic diagram of the equivalent circuit of a power distribution network during normal operation; and Figure 4 This is a schematic diagram of the positive sequence equivalent circuit during a power distribution network fault. Detailed Implementation

[0017] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0018] It should be noted that the acquisition, transmission, storage, use, and processing of data in the technical solution of this application all comply with the relevant provisions of national laws and regulations. In the embodiments of this application, certain existing industry solutions such as software, components, and models may be mentioned. These should be considered exemplary, intended only to illustrate the feasibility of implementing the technical solution of this application, and do not imply that the applicant has already used or necessarily used such solutions.

[0019] like Figure 1 As shown, when there are T-connected branches in the protected line (e.g., lines M to N), the differential current during normal operation or external faults... for Simultaneously, braking current for .in, This represents the sum of currents in the photovoltaic branches. This represents the sum of currents in the composite branches. The current measured by the M-side protection of the protected line.

[0020] However, to prevent unexpected tripping during normal operation, the operating threshold must exceed the maximum steady-state unbalanced current (i.e., The operating threshold will increase to varying degrees depending on the configuration of distributed photovoltaic and loads in the T-shaped branch, which will lead to a decrease in the sensitivity of the current differential protection; furthermore, the T-shaped branch will affect the differential current and braking current, which may cause the current differential protection to maloperate or fail to operate.

[0021] In response, this application provides a composite differential protection method for T-junction branches. Please refer to... Figure 2 The composite differential protection method may include the following steps: Step S110: After the differential protection of the distribution network is activated, the electrical quantities measured by the protection on both sides of the protected section are exchanged.

[0022] Please refer to Figure 1 The protected section is, for example, between line M and line N, where PV1 is a photovoltaic branch, and L (L1 to L) nThis is a composite branch. Relays R1 and R2 on one side (e.g., side M) and the other side (e.g., side N) of the protected section monitor corresponding electrical quantities (e.g., current, voltage, etc.). After the differential protection of the distribution network is activated, the electrical quantities measured by the protection devices on both sides of the protected section are exchanged. For example, after a fault occurs, the protection devices activate, and the two protection devices at both ends send the measured voltage and current to the other side via fiber optic or wireless communication (4G / 5G) channels. No shutdown is required; the measured electrical quantity information is exchanged only after a fault occurs. During normal operation, the two protection devices communicate to maintain synchronization.

[0023] Step S120: Using the electrical quantities measured by the protection on both sides of the exchanged protected section, predict the electrical quantities before and after the fault in the protected section.

[0024] In a preferred embodiment of the present invention, step S120 may include: step S121, using the electrical quantities measured by the protection on both sides of the protected section exchanged before the fault, and combining the equivalent circuit when the distribution network is operating normally, to predict the active power captured per unit capacity of the photovoltaic branch of the T-connected branch and the load output factor; step S122, using the electrical quantities measured by the protection on both sides of the protected section exchanged after the fault, and combining the positive sequence equivalent circuit when the distribution network is faulty, to predict the current and active power of the composite branch of the T-connected branch.

[0025] In this embodiment of the invention, step S121 can be understood as a steady-state prediction (or steady-state estimation) of the protected section of the distribution network. Please refer to... Figure 1 ,by This represents the active power captured per unit capacity of the photovoltaic branch (i.e., the DPV branch). Therefore, the current in a T-connected DPV branch can be expressed as: (1) in, This represents the output current of the j-th DPV branch. Indicates the first j The rated power of each DPV branch, Indicates the first j The voltage at each point of common coupling (PCC) This indicates the conjugate operation.

[0026] In this embodiment of the invention, the load output factor can also be predicted for the difference between the actual load power and the rated power (e.g., fluctuations in load power over time). This coefficient This represents the ratio of actual load power to rated load power. Furthermore, since the electricity consumption behavior of users in the same area during the same time period is similar, it can be predicted that the load output factor within the same area will remain basically consistent.

[0027] Therefore, the current in the load branch connected to T can be expressed as: (2) in, Indicates the first j The current output of each DPV branch, and They represent the first j The active and reactive power of each load. Indicates the first j The voltage at the load T contact point.

[0028] In a preferred embodiment of the present invention, step S121 may include: measuring the voltage measured on one side of the protected section. Convert to the corresponding equivalent voltage The voltage measured by the protection on the other side Convert to the corresponding equivalent voltage From voltage to voltage Iterative calculations are performed to obtain complex equations including real and imaginary parts; and the obtained complex equations are iteratively solved to obtain the active power captured per unit capacity of the photovoltaic branch of the T-junction and the load output factor.

[0029] Please refer to Figure 3 In this embodiment of the invention, let , ,according to Figure 3 It can be deduced that: (3) (4) in, Indicates the first j Voltage at each T-junction Indicates the first j-1 Voltage at each T-junction Indicates the first j Voltage at each PCC point This represents the current measured by the M-side protection of the protected section. Indicates the first k The current of the T connected to the PV, Indicates the first k The current of the load connected to the T-type connector. Indicates the first j The first T-connection node and the first jLine impedance between PCC nodes.

[0030] In this embodiment of the invention, equations (3) and (4) represent the voltage from bus M. to bus N voltage The iterative calculation process; by eliminating intermediate variables (i.e., and The equation can be obtained as follows: (5) in, This indicates the voltage measured by the N-side protection of the protected section. This indicates the voltage measured by the M-side protection of the protected section. This represents the current measured by the M-side protection of the protected section. Indicates the first j The current output of each DPV branch, Indicates the first j The current output of each DPV branch, Indicates the first j The current of the load connected to the T.

[0031] In an embodiment of the present invention, and They can be expressed by equations (1) and (2) respectively. Therefore, equation (5) includes two unknown variables. and Meanwhile, equation (5) is a complex equation consisting of two equations (real and imaginary parts). Equation (5) can then be solved iteratively using methods such as the Newton method, thus yielding the solution. and .

[0032] In this embodiment of the invention, step S122 can be understood as fault state prediction (or fault state estimation) for the protected section of the distribution network. Please refer to... Figure 1 ,by f Taking a point-to-point fault as an example, the corresponding positive-sequence equivalent circuit is as follows: Figure 4 As shown.

[0033] In a preferred embodiment of the present invention, step S122 may include: measuring the voltage measured on one side of the protected section. Convert to the corresponding equivalent voltage The voltage measured by the protection on the other side Convert to the corresponding equivalent voltage ; calculate the voltage at each common coupling point and T-junction point and determine the fault point; and based on the calculated voltage at each common coupling point and T-junction point, calculate the positive sequence voltage at each common coupling point and T-junction point to predict the current and active power of the composite branch of the T-junction branch.

[0034] In an embodiment of the present invention, let , The voltage at each PCC and T connection point can be derived and calculated from bus M and bus N respectively, as shown in the following formula: (6) (7) in, , , and These represent the first and second parts derived from the M-side or N-side of the busbar, respectively. j The voltage at each PCC point or load T contact.

[0035] Based on the fault point f The actual voltage value at the M-side PCC and T-junction is the dividing point. Voltage value calculated from bus M The same; similarly, the actual voltage values ​​of the N-side PCC and T-junction. Voltage value calculated from bus N The same applies. Therefore, regarding how to determine the fault point... f The location was not considered because the fault point was not taken into account. f The contribution of the fault current is such that the farther the PCC point or T connection point on the M side is from the bus N, the greater the difference between the voltage value calculated from the bus N and the actual value; the same applies to the N side. Based on the above analysis, the fault point can be determined using the following formula. f : (8) in, , , , These represent the corresponding voltage differences.

[0036] PCC point voltage and T-junction voltage It can be calculated using the following formula: (9) (10) By solving (9) and (10), all positive sequence voltages at the connection point of PCC and T can be determined, thereby determining the first positive sequence voltage. k The current output of each DPV branch and the k The current of the T-connected load Based on this, the active power of each T-connected branch can be calculated.

[0037] Step S130: Based on the predicted electrical quantities before and after the fault in the protected section, predict the voltage at the fault point and calculate the operating conditions of the differential protection.

[0038] In a preferred embodiment of the present invention, the fault point voltage can be predicted using the following formula. : (11) (12) in, Indicates the first i The voltage of the load node connected to the T-junction. Indicates the first i +1 voltage at common connection point, This represents the current measured by the M-side protection of the protected section. This represents the current measured by the N-side protection of the protected section. Indicates the first j The current of the load connected to the T-type connector. Indicates the first i The first T-connected load node and the first i +1 line impedance at common connection point For example, a coefficient between 0 and 1 represents the relative distance of the fault.

[0039] In an embodiment of the present invention, let , ,like Figure 3 As shown, the fault point f The voltage satisfies equations (11) and (12). Equations (11) and (12) are then transformed into the following matrix form: (13) Since the number of unknowns in the equation is less than the number of equations, the following formula can be used to find its least squares solution, thereby obtaining the fault point voltage. : (14) In a preferred embodiment of the present invention, the operating conditions of differential protection can be expressed by the following formula. and : (15) in, Indicates the fault point f voltage, and These represent the setting values ​​for current differential protection and active power differential protection, respectively. This indicates the active power loss within the protected section. Indicates the first jThe active power of each load. This represents the current measured by the M-side protection of the protected section. This represents the current measured by the N-side protection of the protected section. Indicates the first j The current of the load connected to the T-type connector. This represents the active power on the M side of the protected section. This indicates the active power on the N side of the protected section... Step S140: When the calculated differential protection operating conditions meet the requirements, a trip signal is sent to realize composite differential protection.

[0040] In a preferred embodiment of the present invention, when the differential protection operates... When the calculated differential protection operating conditions are met, it indicates that the requirements are met.

[0041] According to equation (15), the operating conditions (i.e., protection criteria) of the differential protection described in this embodiment of the invention include the current and active power of each branch, and therefore, it can comply with the KCL and the law of conservation of active power. Meanwhile, the provided protection criteria only require electrical quantities (i.e., electrical information) from both ends of the protected section, and can be implemented using a related two-end synchronous communication system, without requiring a multi-end synchronous communication system. Furthermore, the protection criteria include an estimated value of the fault point voltage to adaptively adjust the protection criteria according to the fault condition; fully utilizing the advantages of current differential protection and active power differential protection under different fault point voltages, it can include: when the fault point voltage is high, a more sensitive active power differential criterion can be used; when the fault point voltage is low, a better-performing current differential criterion can be used.

[0042] Accordingly, the composite differential protection method for T-connected branches provided by this invention includes: after the differential protection of the distribution network is activated, exchanging the electrical quantities measured by the protection on both sides of the protected section; using the exchanged electrical quantities measured by the protection on both sides of the protected section, predicting the electrical quantities before and after a fault in the protected section; based on the predicted electrical quantities before and after a fault in the protected section, predicting the voltage at the fault point, and calculating the operating conditions of the differential protection; and when the calculated operating conditions of the differential protection meet the requirements, sending a trip signal to realize composite differential protection. This invention utilizes electrical data at both ends of the protected section to estimate the current and active power of the T-connected distributed photovoltaic (DPV) and load branches under fault conditions, ensuring that the protection principle conforms to the KCL and the law of conservation of active power, thereby improving protection reliability and solving the problem of differential protection failure or maloperation when T-connected distributed photovoltaic and load branches exist simultaneously within the protected section.

[0043] Furthermore, this embodiment of the invention uses the least squares method to estimate the voltage level at the fault point, thereby enabling adaptive adjustment of the protection setting value and improving protection sensitivity. This embodiment of the invention only requires two-way communication, not multi-way communication (no need for information measurement of the T-connected line); compared to multi-way protection schemes, this embodiment of the invention does not require measurement information from the T-connected branch or multi-way synchronous communication system, greatly reducing communication costs.

[0044] Furthermore, related technical solutions have the risk of maloperation in T-connection situations, while the embodiments of the present invention can operate correctly even with T-connection branches, thereby further improving the reliability of active distribution network differential protection; it can adaptively adjust the protection setting value and can withstand phase-to-phase short-circuit faults of up to 60 ohms. Based on the embodiments of the present invention, the distribution network can be connected to distributed photovoltaic or loads in a T-connection form; at the same time, no additional modification or configuration of protection is required, making the expansion of the distribution network scale simpler and more economical.

[0045] This invention also provides a control device, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor. The processor executes the computer program to implement the aforementioned composite differential protection method.

[0046] This invention also provides a machine-readable storage medium storing instructions that cause a machine to execute the aforementioned composite differential protection method.

[0047] This invention also provides a composite differential protection system for a T-connected branch, which may include the control device described above and a distribution network including the T-connected branch.

[0048] It should be noted that the aforementioned control device, machine-readable storage medium, and composite differential protection system for T-junction branches can implement the composite differential protection method provided in the above embodiments. For specific implementation details, please refer to the description of the composite differential protection method in the above embodiments, which will not be repeated here.

[0049] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0050] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0051] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0052] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0053] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0054] Memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0055] Computer-readable media includes both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0056] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0057] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A composite differential protection method for T-connected branches, characterized in that, The composite differential protection method includes: After the differential protection of the distribution network is activated, the electrical quantities measured by the protection on both sides of the protected section are exchanged. By using the electrical quantities measured by the protection on both sides of the exchanged protected section, the electrical quantities before and after a fault in the protected section can be predicted. Based on the predicted electrical quantities before and after a fault in the protected section, the voltage at the fault point is predicted, and the operating conditions of the differential protection are calculated; and When the calculated operating conditions of the differential protection meet the requirements, a trip signal is sent to realize the composite differential protection.

2. The composite differential protection method according to claim 1, characterized in that, The method of predicting the electrical quantities before and after a fault in the protected section by using the electrical quantities measured by the protection on both sides of the exchanged protected section includes: By utilizing the electrical quantities measured by the protection devices on both sides of the protected section before the fault, and combining this with the equivalent circuit during normal operation of the distribution network, the active power captured per unit capacity and the load output factor of the photovoltaic branch of the T-connection branch are predicted; and By utilizing the electrical quantities measured by the protection devices on both sides of the protected section after the fault, and combining them with the positive sequence equivalent circuit during a distribution network fault, the current and active power of the composite branch of the T-connection branch can be predicted.

3. The composite differential protection method according to claim 2, characterized in that, The method utilizes the electrical quantities measured by the protection devices on both sides of the protected section before the fault, and combines them with the equivalent circuit during normal operation of the distribution network to predict the active power captured per unit capacity and the load output factor of the photovoltaic branch of the T-connection, including: The voltage measured on one side of the protected section Convert to the corresponding equivalent voltage The voltage measured by the protection on the other side Convert to the corresponding equivalent voltage ; From voltage to voltage Iterative calculations yield complex equations including both real and imaginary parts; and The obtained complex equations are solved iteratively to obtain the active power captured per unit capacity of the photovoltaic branch of the T-connection and the load output factor.

4. The composite differential protection method according to claim 2, characterized in that, The method of using the electrical quantities measured by the protection devices on both sides of the protected section after the fault, and combining them with the positive sequence equivalent circuit during a distribution network fault, to predict the current and active power of the composite branch of the T-connection branch includes: The voltage measured on one side of the protected section Convert to the corresponding equivalent voltage The voltage measured by the protection on the other side Convert to the corresponding equivalent voltage ; Calculate the voltage at each common coupling point and the T-junction point, and determine the fault location; and Based on the calculated voltages at each common coupling point and T-junction point, the positive sequence voltages at each common coupling point and T-junction point are calculated to predict the current and active power of the composite branch of the T-junction branch.

5. The composite differential protection method according to claim 1, characterized in that, The voltage at the fault point can be predicted using the following formula. : in, Indicates the first i The voltage of the load node connected to the T-connector. Indicates the first i +1 voltage at common connection point, This represents the current measured by the M-side protection of the protected section. This represents the current measured by the N-side protection of the protected section. Indicates the first j The current of the load connected to the T-type connector. Indicates the first i The first T-connected load node and the first i +1 line impedance at common connection point Indicates the relative distance to the fault.

6. The composite differential protection method according to claim 1, characterized in that, The operating conditions of the differential protection are expressed by the following formula. and : in, Indicates the fault point f voltage, and These represent the setting values ​​for current differential protection and active power differential protection, respectively. This indicates the active power loss within the protected section. Indicates the first j The active power of each load. This represents the current measured by the M-side protection of the protected section. This represents the current measured by the N-side protection of the protected section. Indicates the first j The current of the load connected to the T-type connector. This represents the active power on the M side of the protected section. This indicates the active power on the N side of the protected section...

7. The composite differential protection method according to claim 6, characterized in that, When the differential protection operates under the following conditions When the calculated differential protection operating conditions are met, it indicates that the requirements are met.

8. A control device, characterized in that, The control device includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the composite differential protection method according to any one of claims 1-7.

9. A machine-readable storage medium, characterized in that, The machine-readable storage medium stores instructions that cause the machine to perform the composite differential protection method according to any one of claims 1-7.

10. A composite differential protection system for T-connected branches, characterized in that, The composite differential protection system includes the control device as described in claim 8 and a distribution network including T-connected branches.

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