Adaptive current protection method and system based on distributed power access capacity calculation

Abstract

An adaptive current protection method and system based on distributed generation (DG) access capacity calculation is proposed. This method establishes short-circuit current constraints for downstream faults, upstream faults, and adjacent branch faults of the DG. Three maximum and two minimum values ​​for the DG access capacity are determined. Based on multi-source information, the effectiveness of these three maximum and two minimum values ​​is dynamically evaluated for each scenario. Invalid maximum and minimum values ​​are removed to determine the feasible region for the DG access capacity. A capacity threshold is set based on this feasible region. When the actual capacity of the DG exceeds the capacity threshold, the operating thresholds of the upstream and downstream protection devices are adjusted. Protection is then performed based on these adjusted operating thresholds. This method addresses the problems of stringent limitations on DG access capacity, coupling between operating thresholds and access capacity, and low sensitivity of time-limited instantaneous protection in traditional current protection systems.

Description

Technical Field

[0001] This invention belongs to the field of novel power system planning and protection technology, specifically relating to an adaptive current protection method and system based on distributed power source access capacity calculation. Background Technology

[0002] Traditional three-stage current protection in distribution networks is based on a single-source radial network design. The integration of distributed generation (DG) leads to the following problems: 1) Protection range shift: DG provides reverse short-circuit current, expanding the upstream protection range; 2) Reduced sensitivity: Downstream protection sensitivity decreases due to current shunting; 3) Strict capacity limitations: DG access capacity is limited under fixed protection thresholds. For example, in the example, conflicting constraints lead to an empty solution set, failing to address the coordination issue between capacity calculation and protection adaptation.

[0003] In existing technologies, the methods and systems for dynamic optimization of distributed power source location and calculation of access capacity involve: acquiring the values ​​of predetermined input parameters; generating an initial population based on the objective function corresponding to the maximum total access capacity; determining the array with the largest access capacity among the arrays satisfying the constraints in the initial population; placing the capacity and location information of the distributed power source corresponding to the array with the largest access capacity into the corresponding capacity matrix and location matrix, respectively; calculating the value of the objective function based on the capacity matrix and location matrix; using an intelligent iterative optimization algorithm for iterative optimization and solving; and outputting the optimal access capacity and location results for the distributed power source. This addresses the problem of protection maloperation or failure to operate caused by the difficulty in determining the magnitude, direction, and distribution of short-circuit current when a distribution network fault occurs after the dynamic access of distributed power sources. However, the current protection achieved by this method has stringent limitations on the access capacity of distributed power sources. Moreover, the process of determining the range of access capacity of distributed power sources in existing technologies is based on adjusting the protection settings of each node in the system, which is related to the system power source and the capacity of other distributed power sources. This leads to the coupling of the action threshold and the access capacity, which is not conducive to improving the access capacity of distributed power sources and cannot improve the protection's time-limited instantaneous overcurrent sensitivity. It may even require modification of the distribution network structure to improve protection reliability. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an adaptive current protection method and system based on distributed power source access capacity calculation, which solves the problems of strict limitations on distributed power source access capacity, coupling of action threshold and access capacity, and low sensitivity of protection time-limited instantaneous tripping in traditional current protection.

[0005] The present invention adopts the following technical solution.

[0006] This invention proposes an adaptive current protection method based on distributed generation access capacity calculation. The distribution network containing distributed generation includes multiple line segments, including: Obtain the short-circuit current protection settings of the protection devices for each section of the line to establish short-circuit current constraints for downstream faults of the distributed power source and short-circuit current constraints for upstream faults of the distributed power source; obtain the minimum operating threshold of the line protection devices to establish short-circuit current constraints for faults of adjacent branches. Based on the short-circuit current constraint of the downstream fault of the distributed power source, the first maximum value of the distributed power source access capacity is determined with the setting objective of not tripping the cascade after the distributed power source is connected, and the first minimum value of the distributed power source access capacity is determined with the setting objective of providing reactive power support after the distributed power source is connected. Based on the short-circuit current constraint of upstream faults of distributed power sources, the second maximum value of the access capacity of distributed power sources is determined with the setting target that the short-circuit current fed back from the distributed power source to the upstream fault point satisfies the dynamic and thermal stability verification, and the second minimum value of the access capacity of distributed power sources is determined with the setting target that the short-circuit current fed back from the distributed power source to the upstream fault point can be detected by the protection device. Based on the short-circuit current constraint of adjacent branch faults, the third maximum value of the access capacity is determined with the setting target of ensuring that the current flowing from the distributed power source to the fault point of the adjacent branch does not cause the protection to misjudge. Based on multi-source information, the validity of the three maximum values ​​and two minimum values ​​of the distributed power supply access capacity under various scenarios is dynamically evaluated. After removing the maximum and minimum values ​​that are determined to be invalid, the feasible region of the distributed power supply access capacity is determined. A capacity threshold is set based on the feasible region of the distributed power source's access capacity; when the actual capacity of the distributed power source exceeds the capacity threshold, the action thresholds of the upstream and downstream protection devices of the distributed power source are set respectively; protection is carried out based on the set action thresholds.

[0007] The downstream fault short-circuit current constraint of the distributed power source is shown in the following formula:

[0008] In the formula, This refers to the short-circuit current during downstream faults in distributed power sources. Set the short-circuit current protection setting for the protection device at point X of the faulty line; The upstream fault short-circuit current constraint of the distributed power source is shown in the following formula:

[0009] In the formula, This refers to the short-circuit current during an upstream fault in a distributed power source. The short-circuit current protection setting value for the line protection device closest to the fault point in the upstream area of ​​the fault point;

[0010] In the formula, The reverse short-circuit current provided for distributed generation. This is the minimum operating threshold for the line protection device.

[0011] Multi-source information includes: equipment certification parameters, protection principles, and distribution network short-circuit ratio.

[0012] Equipment certification parameters include: the maximum output short-circuit current specified in the technical specifications of distributed power sources. ; when If the current is always less than the minimum operating current of the protection device or the minimum starting current of the directional element, then the third maximum value is... If deemed invalid, then... It is deemed valid.

[0013] Protection principles include: whether the upstream protection is equipped with independent directional overcurrent protection or longitudinal protection; When the upstream protection is an independent directional overcurrent protection or longitudinal protection, then the first minimum value If deemed invalid, then... It is deemed valid.

[0014] If the distribution network short-circuit ratio (SCR) is ≥ 5, then the second minimum value is... If deemed invalid, then... It is deemed valid.

[0015] The upper limit of the feasible region of distributed power source admission capacity of The capacity threshold is 0.6 times, where 0.6 < <1; When distributed power sources are put into operation, if the actual capacity of the distributed power sources is... > × If the distributed power source is not in operation, the action thresholds of the upstream and downstream protection devices of the distributed power source will be set; if the distributed power source is not in operation, the action thresholds of the upstream and downstream protection devices of the distributed power source will remain unchanged.

[0016] The action threshold is tuned based on the partition adaptive protection mechanism, including: The single-power-source equivalent method is adopted, which only considers the current of the distributed power source, and the operating threshold of the downstream protection device of the distributed power source is set. The superimposed current equivalent method is adopted to calculate the short-circuit current based on the open-circuit voltage of the system power supply and the distributed power supply acting alone, and to set the operating threshold of the upstream protection device of the distributed power supply.

[0017] This invention also proposes an adaptive current protection system based on distributed power source admission capacity calculation, comprising: The short-circuit current constraint establishment module is used to obtain the short-circuit current protection settings of the protection devices of each line segment in order to establish the short-circuit current constraint of the downstream fault of the distributed power source and the short-circuit current constraint of the upstream fault of the distributed power source; and to obtain the minimum action threshold of the line protection device in order to establish the short-circuit current constraint of the adjacent branch fault. The access capacity calculation module is used to determine the first maximum value of the access capacity of the distributed power source based on the downstream fault short-circuit current constraint, with the setting objective being that the distributed power source will not trip cascadingly after being connected; and the first minimum value of the access capacity of the distributed power source with the setting objective being that the distributed power source provides reactive power support after being connected. Based on the upstream fault short-circuit current constraint of the distributed power source, it determines the second maximum value of the access capacity of the distributed power source with the setting objective being that the short-circuit current fed back from the distributed power source to the upstream fault point satisfies the dynamic and thermal stability verification; and the second minimum value of the access capacity of the distributed power source with the setting objective being that the short-circuit current fed back from the distributed power source to the upstream fault point can be detected by the protection device. Based on the adjacent branch fault short-circuit current constraint, it determines the third maximum value of the access capacity with the setting objective being that the current flowing from the distributed power source to the adjacent branch fault point will not cause the protection to misjudge the direction. Based on multi-source information, it dynamically evaluates the effectiveness of the three maximum values ​​and two minimum values ​​of the access capacity of the distributed power source under various scenarios, and determines the feasible region of the access capacity of the distributed power source after removing the maximum and minimum values ​​determined to be invalid. The protection setting module is used to set a capacity threshold based on the feasible region of the distributed power source's access capacity; when the actual capacity of the distributed power source is greater than the capacity threshold, the operating thresholds of the upstream and downstream protection devices of the distributed power source are set respectively; protection is performed based on the set operating thresholds.

[0018] The present invention is also a terminal, including a processor and a storage medium; the storage medium is used to store instructions; the processor is used to perform operations according to the instructions to execute the steps of the method.

[0019] The present invention is also a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method.

[0020] The beneficial effects of this invention are that, compared with the prior art, it at least includes, This invention, by solving the DG (Distributed Generator) access capacity domain and protection setting domain that satisfy short-circuit current constraints under three fault scenarios—downstream, upstream, and adjacent branch—fundamentally guarantees the selectivity, sensitivity, and reliability of protection, thereby maximizing the absorption capacity of DG while ensuring safety. This invention establishes short-circuit current constraint equations for downstream, upstream, and adjacent branch fault scenarios, achieving multi-dimensional, multi-type fault scenario constraint modeling to cover the entire distribution network topology risk. In determining the distributed generation access capacity range, the protection settings of each system node are not adjusted, meaning it is independent of the system power source and other distributed generation capacities; the action threshold is considered decoupled from capacity. The intelligent reverse current constraint exclusion mechanism proposed in this invention restructures the core constraint of access capacity calculation from preventing protection maloperation due to reverse current to ensuring sufficient sensitivity of protection to forward fault currents and ensuring system voltage support and stability. It transforms the original absolute prohibition of maloperation into a risk assessment based on multi-source data. Attached Figure Description

[0021] Figure 1 It is a typical network topology for a distribution network that includes distributed power sources; Figure 1 The annotations in the accompanying drawings are explained as follows: 1-Circuit breaker No. 1, 2-Circuit breaker No. 2, 3-Circuit breaker No. 3, 4-Circuit breaker No. 4, 5-Circuit breaker No. 5, 6-Circuit breaker No. 6; Figure 2 This is a flowchart of an adaptive current protection method based on distributed power source access capacity calculation proposed in this invention; Figure 3 It is the equivalent circuit of a distribution network containing distributed power sources. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0023] Typical network topology of a distribution network containing distributed generation sources is as follows: Figure 1As shown, the circuit includes: circuit breaker 1, circuit breaker 2, circuit breaker 3, circuit breaker 4, circuit breaker 5, and circuit breaker 6. The system power supply SG is connected to bus A. Bus A is connected to bus B via circuit breaker 1. Bus B is connected to bus C via circuit breaker 2. Bus C is connected to bus D via circuit breaker 3. Bus D is connected to the power supply terminal E of transmission line L2 via circuit breaker 4. Bus A is connected to bus F via circuit breaker 5. Bus F is connected to the power supply terminal G of transmission line L1 via circuit breaker 6. Distributed power supply DG is connected to bus C. When a short-circuit fault occurs, if the short-circuit current provided by the system power supply and the distributed power supply is in opposite directions, the fault is defined as occurring in the upstream region of DG. If the short-circuit current provided by the system power supply and the distributed power supply is in the same direction, the fault is defined as occurring in the downstream region of DG.

[0024] This invention proposes an adaptive current protection method based on distributed power source admission capacity calculation, such as... Figure 2 As shown, it includes: Step 1: Obtain the short-circuit current protection settings of the protection devices for each line segment to establish short-circuit current constraints for downstream faults of the distributed power source and short-circuit current constraints for upstream faults of the distributed power source; obtain the minimum operating threshold of the protection devices for each line segment to establish short-circuit current constraints for adjacent branch faults.

[0025] Specifically, an equivalent model of the distribution network containing distributed generation is established. Based on the equivalent model, short-circuit current constraints for downstream faults of distributed generation, short-circuit current constraints for upstream faults of distributed generation, and short-circuit current constraints for adjacent branch faults are determined respectively. Specifically, step 1 includes: Step 1.1: Establish an equivalent model of the distribution network containing distributed generation sources, such as... Figure 3 As shown, determine the system impedance Zs, the impedance of the first line Z1, the impedance of the second line Z2, the impedance of the third line Z3, the impedance of the fourth line Z4, the impedance of the fifth line Z5, the impedance of the sixth line Z6, and the impedance of the distributed power source output line Zd. Step 1.2: Based on the equivalent model, determine the short-circuit current constraints according to different fault location locations, as follows: When a downstream fault occurs in a distributed power source, the short-circuit current constraint is:

[0026] In the formula, This refers to the short-circuit current during downstream faults in distributed power sources. The output current of the system power supply SG, This refers to the output current of the distributed generation (DG). Set the short-circuit current protection setting for the protection device at point X of the faulty line; When an upstream fault occurs in a distributed power source, the short-circuit current constraint is:

[0027] In the formula, This refers to the short-circuit current during an upstream fault in a distributed power source. The short-circuit current protection setting value for the line protection device closest to the fault point in the upstream area of ​​the fault point; Step 1.3: For fault points located on adjacent branches connected in parallel with the branch where DG is located, establish short-circuit current constraints for faults in adjacent branches, as follows:

[0028] In the formula, The reverse short-circuit current provided for distributed generation. This refers to the minimum operating threshold of the line protection device; By using adjacent branch fault constraints, malfunctions caused by reverse current can be effectively prevented.

[0029] This invention treats distributed generation (DG) as an active, key variable influencing the overall network fault current distribution. By establishing a unified equivalent model, it simultaneously solves for the DG access capacity domain (or output curve) and protection setting domain that satisfy the constraints of three fault scenarios: downstream, upstream, and adjacent branches. This is a multi-scenario, multi-constraint joint optimization and coordinated setting method that fundamentally guarantees the selectivity, sensitivity, and reliability of protection. Specifically, the short-circuit current constraint of adjacent branch faults is explicitly and quantitatively incorporated into the core equations of DG access and protection setting. This constraint has often been simplified or ignored in previous research and engineering practice. Accurately modeling such constraints, especially for the quantitative assessment of directional protection maloperation risk, has high engineering practical value. The three types of constraints can distinguish different types of DG (synchronous machine, inverter) models, and by substituting their different short-circuit characteristics (amplitude, phase, attenuation) into the above constraint equations, a more accurate and universally applicable "technical access criterion" is obtained. The system monitors the operating status in real time. When it detects an operating mode that may violate the short-circuit current constraint of adjacent branch faults, it actively adjusts the control mode of the DG (such as switching from constant power control to current limiting mode, adjusting the output impedance angle) or adaptively adjusts the protection settings to dynamically meet all constraints, thereby maximizing the absorption capacity of the DG while ensuring safety.

[0030] Different system fault locations will lead to different impacts on current protection, but the analysis methods are basically the same. Taking a short-circuit fault in line CD section as an example, let's assume the distance from the short-circuit fault point to its corresponding busbar is a percentage of the line length. In the following formulas and diagrams, SG represents the system power source (main grid), DG represents distributed generation, and the system power supply voltage is... The equivalent impedance is The distributed power supply voltage is Its equivalent impedance is , , , , , , These represent the line impedance values ​​for different lines.

[0031] Based on the superposition theorem, the open-circuit voltage at the short-circuit fault point Represented as: (1) Equivalent impedance for: (2) At this time, the short-circuit current at the protection device of the third circuit breaker is: (3) The short-circuit currents at the protection devices of circuit breaker 1 and circuit breaker 2 are: (4) For distribution networks not connected to distributed power sources, under the same type and location of fault conditions, the short-circuit currents at the protection devices of the first, second, and third circuit breakers are: (5) (6) Under the short-circuit current constraints corresponding to different fault locations, the maximum and minimum values ​​of the permitted capacity of distributed generation are calculated to determine the range of permitted capacity of distributed generation.

[0032] Step 2: Based on the downstream fault short-circuit current constraint of the distributed power source, determine the first maximum value of the distributed power source access capacity with the setting objective of preventing cascading tripping after the distributed power source is connected; determine the first minimum value of the distributed power source access capacity with the setting objective of providing reactive power support after the distributed power source is connected. Based on the upstream fault short-circuit current constraint of the distributed power source, determine the second maximum value of the distributed power source access capacity with the setting objective of ensuring that the short-circuit current fed back from the distributed power source to the upstream fault point meets the dynamic and thermal stability verification; determine the second minimum value of the distributed power source access capacity with the setting objective of ensuring that the short-circuit current fed back from the distributed power source to the upstream fault point can be detected by the protection device. Based on the adjacent branch fault short-circuit current constraint, determine the third maximum value of the access capacity with the setting objective of ensuring that the current flowing from the distributed power source to the adjacent branch fault point does not cause the protection to misjudge the direction.

[0033] By combining the constraints, the range of the maximum and minimum values ​​of the distributed power source's admission capacity is determined: the three constraints will each give their own maximum and minimum value requirements. These constraints are superimposed and conflict with each other. Finally, the logic of "taking the intersection" and "taking the union" is used to obtain the globally unique admission capacity range.

[0034] Specifically, step 2 includes: Step 2.1: Based on the short-circuit current constraint of the downstream fault of the distributed power source, determine the first maximum value of the distributed power source access capacity with the setting objective of not tripping the cascade after the distributed power source is connected, and determine the first minimum value of the distributed power source access capacity with the setting objective of providing reactive power support after the distributed power source is connected. Among them, the maximum allowable capacity is determined based on the short-circuit current constraint of downstream faults in distributed power sources. The range of values ​​is used to prevent the connection of DG from causing the short-circuit current sensed by upstream protection (such as substation outgoing switch) to exceed its setting value, resulting in over-level tripping; the range of values ​​of the minimum access capacity determined based on the short-circuit current constraint of downstream faults of distributed power sources is used to require DG to provide a certain amount of reactive power or inertia support under specific operating conditions (such as weak main power supply and heavy load) in order to maintain system voltage stability or frequency stability. In the embodiments, based on Figure 3 The first maximum capacity for distributed power supply admission The first minimum value The range of values ​​for is shown in the following formula: < [ +( - ) ]( - ) > ( + )

[0035] In the formula, , These are the operating thresholds of the protection devices for the second and third circuit breakers, respectively. This is the system power supply voltage. This represents the minimum equivalent impedance of the system power supply. , , These are the line impedance values ​​of the lines where the first, second, and third circuit breakers are located, respectively. This is the equivalent impedance of the distributed power source.

[0036] Step 2.2: Based on the short-circuit current constraint of upstream fault of distributed power source, the second maximum value of the access capacity of distributed power source is determined with the setting target that the short-circuit current fed back from distributed power source to upstream fault point meets the dynamic and thermal stability verification, and the second minimum value of the access capacity of distributed power source is determined with the setting target that the short-circuit current fed back from distributed power source to upstream fault point can be detected by the protection device. Maximum allowable capacity determined based on upstream fault short-circuit current constraints of distributed power sources The range of values ​​is used to prevent excessive short-circuit current fed back from the distributed generation (DG) to the upstream fault point, exceeding the dynamic / thermal stability limits of the upstream lines or switching equipment; the minimum allowable capacity is determined based on the upstream fault short-circuit current constraint of the distributed generation. The range of values ​​is used to ensure that when an upstream fault occurs, the reverse current provided by the DG is large enough to be reliably detected by the upstream directional element or longitudinal protection, so as to ensure the correct operation of the protection. In the embodiments, based on Figure 3 The second largest admission capacity The second minimum value The range of values ​​for is shown in the following formula: < [ +( - ()( + + )]( - ) > ( + + )

[0037] In the formula, , These are the operating thresholds of the protection devices for the first and fifth circuit breakers, respectively. This is the system power supply voltage. This represents the minimum equivalent impedance of the system power supply. , , These are the line impedance values ​​of the lines containing the first, second, and fifth circuit breakers, respectively. This is the equivalent impedance of the distributed power source.

[0038] Step 2.3: Based on the short-circuit current constraint of adjacent branch faults, determine the third maximum value of the access capacity with the setting target of the direction in which the current flowing from the distributed power source to the fault point of the adjacent branch will not cause the protection to misjudge. Maximum allowable capacity determined based on adjacent branch fault short-circuit current constraints The range of values ​​is used to prevent the current flowing from the DG to the fault point of the adjacent branch, which would cause the branch protection to misjudge the direction and malfunction. In the embodiments, based on Figure 3 The third largest capacity for admission The range of values ​​for is shown in the following formula: < [ + ( + + )] .

[0039] The minimum access capacity proposed in this invention is the minimum capacity or output level that the distribution network protection system must reach to ensure that it can still operate reliably and selectively under certain critical faults.

[0040] This invention establishes short-circuit current constraint equations for scenarios such as downstream faults, upstream faults, and adjacent branch faults of distributed generation (DG), thereby achieving multi-dimensional and multi-type fault scenario constraint modeling to cover the full topology risks of the distribution network. The process of determining the capacity range of distributed generation access is based on the premise of not adjusting the protection settings of each node in the system, that is, it is unrelated to the system power supply and the capacity of other distributed generation sources, which means that the capacity is considered to be decoupled.

[0041] Step 3: Based on multi-source information, dynamically evaluate the validity of the three maximum values ​​and two minimum values ​​of the distributed power supply access capacity under each scenario, and determine the feasible region of the distributed power supply access capacity after removing the maximum and minimum values ​​that are determined to be invalid.

[0042] Specifically, multi-source information includes, but is not limited to: equipment authentication parameters, protection principles, and distribution network short-circuit ratio; The equipment certification parameters include: the maximum output short-circuit current specified in the technical specifications of distributed power sources. ;when If the current is always less than the minimum operating current of the protection device or the minimum starting current of the directional element, then If deemed invalid, then... The result is deemed valid; the method proposed in step 2 of this invention... This represents the constraint against accidental operation of adjacent branches, while the dynamic evaluation in step 3 transforms the constraint against accidental operation of adjacent branches from an absolute prohibition to a risk assessment driven by multi-source data. The protection principle includes: whether the upstream protection is configured with independent directional overcurrent protection or longitudinal protection; when the upstream protection is independent directional overcurrent protection or longitudinal protection, then... If deemed invalid, then... The result is deemed valid; the method proposed in step 2 of this invention... This represents the upstream fault prevention constraint, while the dynamic evaluation in step 3 realizes the transformation of the upstream fault prevention constraint from an absolute prohibition to a risk assessment based on multi-source data. Where the distribution network short-circuit ratio (SCR) is ≥ 5, then If deemed invalid, then... It is deemed valid; The reverse current constraint intelligent exclusion mechanism proposed in this invention restructures the core constraint of access capacity calculation from preventing protection from maloperation due to reverse current to ensuring that the protection has sufficient sensitivity to forward fault current and ensuring system voltage support and stability. It transforms the original absolute prohibition of maloperation into risk assessment based on multi-source data.

[0043] When calculating the maximum allowable capacity of distributed generation (DG), this invention proactively ignores the traditional constraint of "preventing reverse short-circuit maloperation," shifting from the conservative paradigm that all power sources are large-capacity and provide strong short-circuit currents to a new, realistic paradigm where a large number of DGs are flexible power sources providing controllable weak short-circuit currents. Through physical simulation, this invention reveals that due to the inverter's current-limiting characteristics, the peak reverse short-circuit current of DGs only reaches 15-20% of the system's rated current, failing to trigger upstream protection maloperation. Based on this, it overcomes the contradictions in traditional theory, and under certain system parameters, the calculated... <33.3MVA, >51.2MVA, <65382MVA, >387.3MVA, <200.5MVA, where, for example and Value range conflict and , Value range conflict as well as The generation of these short-circuit currents is closely related to the protection device's ability to prevent maloperation when a reverse short-circuit current flows through it. However, in practice, distributed power sources, due to their inherent current-limiting function, do not generate particularly large short-circuit currents. Therefore, the reverse flow of this short-circuit current is unlikely to cause maloperation of the protection device. Thus, removing... as well as These two constraints ultimately result in the maximum permitted capacity of the distributed power source. <33.3MVA, invalid constraints are removed. Based on real-time grid parameters, the simultaneous valid constraint equations are solved. For example, at bus C of the 10kV distribution network, the capacity limit is increased from an empty set to 33.3MVA, an increase rate >300%.

[0044] Step 4: Set a capacity threshold based on the feasible region of the distributed power source's access capacity; when the actual capacity of the distributed power source is greater than the capacity threshold, set the operating thresholds of the upstream and downstream protection devices of the distributed power source respectively; perform current protection based on the set operating thresholds.

[0045] Specifically, the upper limit of the feasible region for distributed power source access capacity. of The capacity threshold is 0.6 times, where 0.6 < <1, In the embodiment, The preferred value is 0.8; When distributed power sources are put into operation, if the actual capacity of the distributed power sources is... > × If the distributed power source is not in operation, the action thresholds of the upstream and downstream protection devices of the distributed power source will be set; if the distributed power source is not in operation, the action thresholds of the upstream and downstream protection devices of the distributed power source will remain unchanged. Among them, the setting of action thresholds based on the partition adaptive protection mechanism includes: The single-power equivalent method is adopted, which only considers the current contributed by the distributed generation (DG) and sets the operating threshold of the downstream protection device of the distributed power source to avoid system power interference. The superposition current equivalent method is used to calculate the open-circuit voltage of the system power supply and DG acting alone. , Solve for the equivalent impedance, calculate the short-circuit current, and set the operating threshold of the upstream protection device for the distributed power source.

[0046] Adaptive current protection is achieved based on the set action threshold. In this embodiment, the protection execution unit compares the short-circuit current based on the real-time threshold, triggers the millisecond-level circuit breaker to operate, and simultaneously blocks the reverse DG feed current.

[0047] In the example, the actual DG capacity was monitored to be 30 MVA, which is greater than 33.3 × 0.8 = 26.64 MVA, so the capacity was adjusted upwards. =1.2×1572=1886A, the new threshold is used to determine when the circuit breaker is triggered. The method proposed in this invention improves capacity compatibility, expands the DG access capacity from 0 to 33.3MVA, enhances protection reliability, increases the time-limited instantaneous trip sensitivity from 1.04 to 1.07, optimizes economics, and avoids modifying the power grid structure to meet capacity constraints.

[0048] This invention also proposes an adaptive current protection system based on distributed power source admission capacity calculation, comprising: The short-circuit current constraint establishment module is used to obtain the short-circuit current protection settings of the protection devices of each line segment in order to establish the short-circuit current constraint of the downstream fault of the distributed power source and the short-circuit current constraint of the upstream fault of the distributed power source; and to obtain the minimum action threshold of the line protection device in order to establish the short-circuit current constraint of the adjacent branch fault. The access capacity calculation module is used to determine the first maximum value of the access capacity of the distributed power source based on the downstream fault short-circuit current constraint, with the setting objective being that the distributed power source will not trip cascadingly after being connected; and the first minimum value of the access capacity of the distributed power source with the setting objective being that the distributed power source provides reactive power support after being connected. Based on the upstream fault short-circuit current constraint of the distributed power source, it determines the second maximum value of the access capacity of the distributed power source with the setting objective being that the short-circuit current fed back from the distributed power source to the upstream fault point satisfies the dynamic and thermal stability verification; and the second minimum value of the access capacity of the distributed power source with the setting objective being that the short-circuit current fed back from the distributed power source to the upstream fault point can be detected by the protection device. Based on the adjacent branch fault short-circuit current constraint, it determines the third maximum value of the access capacity with the setting objective being that the current flowing from the distributed power source to the adjacent branch fault point will not cause the protection to misjudge the direction. Based on multi-source information, it dynamically evaluates the effectiveness of the three maximum values ​​and two minimum values ​​of the access capacity of the distributed power source under various scenarios, and determines the feasible region of the access capacity of the distributed power source after removing the maximum and minimum values ​​determined to be invalid. The protection setting module is used to set a capacity threshold based on the feasible region of the distributed power source's access capacity; when the actual capacity of the distributed power source is greater than the capacity threshold, the operating thresholds of the upstream and downstream protection devices of the distributed power source are set respectively; protection is performed based on the set operating thresholds.

[0049] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0050] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0051] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0052] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. An adaptive current protection method based on distributed generation access capacity calculation, wherein the distribution network containing distributed generation includes multiple line segments, characterized in that, include: Obtain the short-circuit current protection settings of the protection devices of each line segment in order to establish the short-circuit current constraints for downstream faults of distributed power sources and the short-circuit current constraints for upstream faults of distributed power sources. Obtain the minimum operating threshold of the line protection device to establish short-circuit current constraints for adjacent branch faults; Based on the short-circuit current constraint of the downstream fault of the distributed power source, the first maximum value of the distributed power source access capacity is determined with the setting objective of not tripping the cascade after the distributed power source is connected, and the first minimum value of the distributed power source access capacity is determined with the setting objective of providing reactive power support after the distributed power source is connected. Based on the short-circuit current constraint of upstream faults of distributed power sources, the second maximum value of the access capacity of distributed power sources is determined with the setting target that the short-circuit current fed back from the distributed power source to the upstream fault point satisfies the dynamic and thermal stability verification, and the second minimum value of the access capacity of distributed power sources is determined with the setting target that the short-circuit current fed back from the distributed power source to the upstream fault point can be detected by the protection device. Based on the short-circuit current constraint of adjacent branch faults, the third maximum value of the access capacity is determined with the setting target of ensuring that the current flowing from the distributed power source to the fault point of the adjacent branch does not cause the protection to misjudge. Based on multi-source information, the validity of the three maximum values ​​and two minimum values ​​of the distributed power supply access capacity under various scenarios is dynamically evaluated. After removing the maximum and minimum values ​​that are determined to be invalid, the feasible region of the distributed power supply access capacity is determined. Set capacity thresholds based on the feasible region of distributed power source access capacity; When the actual capacity of the distributed power source exceeds the capacity threshold, the operating thresholds of the upstream and downstream protection devices of the distributed power source are set respectively; protection is then carried out based on the set operating thresholds.

2. The adaptive current protection method based on distributed power source admission capacity calculation according to claim 1, characterized in that, The downstream fault short-circuit current constraint of the distributed power source is shown in the following formula: In the formula, This refers to the short-circuit current during downstream faults in distributed power sources. Set the short-circuit current protection setting for the protection device at point X of the faulty line; The upstream fault short-circuit current constraint of the distributed power source is shown in the following formula: In the formula, This refers to the short-circuit current during an upstream fault in a distributed power source. The short-circuit current protection setting value for the line protection device closest to the fault point in the upstream area of ​​the fault point; In the formula, The reverse short-circuit current provided for distributed generation. This is the minimum operating threshold for the line protection device.

3. The adaptive current protection method based on distributed power source admission capacity calculation according to claim 1, characterized in that, Multi-source information includes: equipment certification parameters, protection principles, and distribution network short-circuit ratio.

4. The adaptive current protection method based on distributed power source admission capacity calculation according to claim 3, characterized in that, Equipment certification parameters include: the maximum output short-circuit current specified in the technical specifications of distributed power sources. ; when If the current is always less than the minimum operating current of the protection device or the minimum starting current of the directional element, then the third maximum value is... If deemed invalid, then... It is deemed valid.

5. The adaptive current protection method based on distributed power source admission capacity calculation according to claim 3, characterized in that, Protection principles include: whether the upstream protection is equipped with independent directional overcurrent protection or longitudinal protection; When the upstream protection is an independent directional overcurrent protection or longitudinal protection, then the first minimum value If deemed invalid, then... It is deemed valid.

6. The adaptive current protection method based on distributed power source admission capacity calculation according to claim 3, characterized in that, If the distribution network short-circuit ratio (SCR) is ≥ 5, then the second minimum value is... If deemed invalid, then... It is deemed valid.

7. The adaptive current protection method based on distributed power source admission capacity calculation according to claim 1, characterized in that, The upper limit of the feasible region of distributed power source admission capacity of The capacity threshold is 0.6 times, where 0.6 < <1; When distributed power sources are put into operation, if the actual capacity of the distributed power sources is... > × If the distributed power source is not in operation, the action thresholds of the upstream and downstream protection devices of the distributed power source will be set; if the distributed power source is not in operation, the action thresholds of the upstream and downstream protection devices of the distributed power source will remain unchanged.

8. The adaptive current protection method based on distributed power source admission capacity calculation according to claim 7, characterized in that, The action threshold is tuned based on the partition adaptive protection mechanism, including: The single-power-source equivalent method is adopted, which only considers the current of the distributed power source, and the operating threshold of the downstream protection device of the distributed power source is set. The superimposed current equivalent method is adopted to calculate the short-circuit current based on the open-circuit voltage of the system power supply and the distributed power supply acting alone, and to set the operating threshold of the upstream protection device of the distributed power supply.

9. An adaptive current protection system based on distributed generation access capacity calculation, used to implement the adaptive current protection method based on distributed generation access capacity calculation as described in any one of claims 1 to 8, wherein the distribution network containing distributed generation includes multiple line segments, characterized in that, include: The short-circuit current constraint establishment module is used to obtain the short-circuit current protection settings of the protection devices of each line segment in order to establish the short-circuit current constraint of the downstream fault of the distributed power source and the short-circuit current constraint of the upstream fault of the distributed power source; and to obtain the minimum action threshold of the line protection device in order to establish the short-circuit current constraint of the adjacent branch fault. The access capacity calculation module is used to determine the first maximum value of the access capacity of the distributed power source based on the downstream fault short-circuit current constraint, with the setting objective being that the distributed power source will not trip cascadingly after being connected; and the first minimum value of the access capacity of the distributed power source with the setting objective being that the distributed power source provides reactive power support after being connected. Based on the upstream fault short-circuit current constraint of the distributed power source, it determines the second maximum value of the access capacity of the distributed power source with the setting objective being that the short-circuit current fed back from the distributed power source to the upstream fault point satisfies the dynamic and thermal stability verification; and the second minimum value of the access capacity of the distributed power source with the setting objective being that the short-circuit current fed back from the distributed power source to the upstream fault point can be detected by the protection device. Based on the adjacent branch fault short-circuit current constraint, it determines the third maximum value of the access capacity with the setting objective being that the current flowing from the distributed power source to the adjacent branch fault point will not cause the protection to misjudge the direction. Based on multi-source information, it dynamically evaluates the effectiveness of the three maximum values ​​and two minimum values ​​of the access capacity of the distributed power source under various scenarios, and determines the feasible region of the access capacity of the distributed power source after removing the maximum and minimum values ​​determined to be invalid. The protection setting module is used to set capacity thresholds based on the feasible region of distributed power source access capacity. When the actual capacity of the distributed power source exceeds the capacity threshold, the operating thresholds of the upstream and downstream protection devices of the distributed power source are set respectively; protection is then carried out based on the set operating thresholds.

10. A terminal, comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the steps of the method according to any one of claims 1-8.

11. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the program implements the steps of the method according to any one of claims 1-8.

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