Fault feature calculation method and system for power distribution network containing distributed photovoltaic and energy storage

Abstract

The invention discloses a fault feature calculation method and system for a power distribution network containing distributed photovoltaic and energy storage, and the method comprises the steps: constructing a photovoltaic equivalent model and an energy storage equivalent model, and supporting the topology dynamic updating of the power distribution network containing distributed photovoltaic and energy storage and the combination of photovoltaic and energy storage control strategies. The method can better adapt to a complex operation scene of a distributed power supply access power distribution network, enhances engineering applicability, constructs a Jacobian matrix, can solve fault characteristics of asymmetric short circuit and symmetric short circuit, unifies symmetric and asymmetric fault calculation frameworks, improves fault calculation precision, and improves fault calculation efficiency. Fault feature automatic calculation is carried out in combination with multi-source data of the power distribution network, the workload of manual short circuit calculation and protection setting value setting is shortened, and the protection setting optimization efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system relay protection and distributed energy grid connection, and relates to a method and system for calculating fault characteristics of a distribution network containing distributed photovoltaic and energy storage. Background Art

[0002] With the advancement of the "dual carbon" goal, the penetration rate of distributed photovoltaic and energy storage in the distribution network continues to rise, and the distribution network has gradually evolved from a traditional one-way radial structure to a multi-power, multi-form active distribution system. However, the large-scale access of distributed power sources has led to fundamental changes in the fault characteristics of the distribution network, which are manifested as follows: (1) The uncertainty of the fault current amplitude and direction has increased. During the grid fault, the distributed photovoltaic is affected by the low voltage ride-through (LVRT) control strategy, and its output current switches from a constant power mode to a current source mode limited by the voltage drop depth. The current amplitude is no longer linearly related to the grid voltage. In addition, the energy storage system can be equivalent to a controlled voltage source in the discharge state. Its fault current is affected by the state of charge (SOC), charge and discharge control logic and inverter current limiting strategy, showing time-varying characteristics. (2) The dynamic reconstruction of the network topology changes frequently: The plug-and-play characteristics of distributed power sources, the switching of microgrids on and off the grid, and the network reconstruction operation make the equivalent topology of the distribution network change frequently. The traditional short-circuit calculation method based on fixed topology cannot adapt to such dynamic scenarios. (3) Complex coupling of asymmetric fault current sequence components: Under asymmetric faults such as single-phase grounding and two-phase short circuit, the negative-sequence and zero-sequence current characteristics of the distributed power supply are significantly affected by the inverter control strategy. For example, photovoltaic inverters usually do not have a zero-sequence current loop, and energy storage systems may adjust power balance through negative-sequence current in constant power control mode, resulting in calculation errors exceeding 30% using the traditional symmetrical component method.

[0003] At present, the following methods are mainly used for calculating short-circuit current of distributed power sources at home and abroad:

[0004] (1) Equivalent impedance model method: The distributed power source is simplified into a constant impedance, and its control strategy dynamics are ignored (such as the static model recommended by the IEEE 1547-2018 standard). This method has significant errors when the voltage drops deeply and cannot meet the protection setting requirements. (2) Iterative correction method: The distributed power source output constraint is introduced into the traditional Newton-Raphson algorithm, but no explicit association between the control strategy and the fault current is established. Existing methods also propose an iterative correction method based on the PQ node, but it does not consider the piecewise linear characteristics of the LVRT curve, resulting in a high risk of iterative divergence. (3) Real-time simulation method: The distributed power source fault response is simulated through hardware in the loop (HIL). Although it has high accuracy, it relies on dedicated equipment and is difficult to integrate into the distribution network management platform for online calculation.

[0005] The above methods generally have the following flaws: (1) Oversimplification of the model: The constraints of the PV LVRT curve and the energy storage charging and discharging switching logic on the fault current are not accurately represented. (2) Insufficient algorithm adaptability: The calculation framework for symmetric and asymmetric faults is not unified, and the sequence component coupling modeling is missing. (3) Poor engineering practicality: The calculation results are not directly linked to the protection setting process and lack an automatic output interface. Summary of the Invention

[0006] The purpose of the present invention is to solve the problems in the prior art of the lack of a unified framework for symmetric and asymmetric fault calculations, the lack of sequence component coupling modeling, which reduces the accuracy of fault calculations, the low adaptability of existing methods to complex operating scenarios where distributed power sources are connected to distribution networks, and the problems of false operation and refusal to operate caused by mismatch in protection setting values, and to provide a method and system for calculating the fault characteristics of a distribution network containing distributed photovoltaics and energy storage.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for calculating fault characteristics of a distribution network including distributed photovoltaics and energy storage includes the following steps:

[0009] Obtain multi-source data of the distribution network through the distribution network management platform PMS, analyze the multi-source data, and obtain the node-branch correlation matrix;

[0010] According to the node-branch correlation matrix, the photovoltaic equivalent model and the energy storage equivalent model are constructed;

[0011] The distributed power supply fault current constraint equation is formed based on the photovoltaic equivalent model and the energy storage equivalent model, and the Jacobian matrix is constructed based on the constraint equation;

[0012] Based on the Jacobian matrix, the fault characteristics of asymmetric short circuit and symmetric short circuit are solved respectively to obtain the fault characteristic solution results.

[0013] A further improvement of the present invention is:

[0014] The node-branch association matrix is obtained, including photovoltaic nodes PV, energy storage nodes VS, load nodes PQ and fault point locations.

[0015] The photovoltaic equivalent model is constructed, comprising:

[0016] When the operating conditions are normal, the equivalent node of the PV system is the load node PQ, which satisfies:

[0017]

[0018] Among them, Q0 and P0 are the reactive power per unit value and active power per unit value of the photovoltaic node PV output before short circuit, U PCCIndicates the per-unit voltage of the photovoltaic node PV grid connection point;

[0019] During a fault, the model switches to a controlled current source according to the LVRT curve of the distribution network:

[0020]

[0021] Among them, I PV It represents the output current of the photovoltaic system, and ΔV represents the voltage drop depth at the grid connection point.

[0022] The constructing of the energy storage equivalent model includes:

[0023] When the energy storage system is in the charging state, the energy storage system is equivalent to the load node PQ, satisfying:

[0024]

[0025] Among them, I c is the effective value of the converter output current;

[0026] When the energy storage system is in the discharging state, the energy storage system is equivalent to the energy storage node VS, satisfying:

[0027]

[0028] Wherein, ΔV represents the voltage drop depth at the grid connection point; I ESS Indicates the output current of the energy storage.

[0029] The constructing of the Jacobian matrix includes:

[0030]

[0031] Where ΔP represents the active power imbalance, ΔQ represents the reactive power imbalance, V and θ represent the node voltage amplitude and phase angle respectively, and I PV and I ESS Represent the output current of distributed photovoltaic and energy storage respectively.

[0032] The fault characteristics of symmetrical short circuit are solved by:

[0033] The sequence component of the symmetrical short-circuit fault is solved by the following formula:

[0034]

[0035] Among them, V pre-fault Indicates the voltage at the fault point before the fault; Z f Represents the ground impedance, Z (1) Represents the positive sequence impedance.

[0036] The fault characteristics of asymmetric short circuit are solved by:

[0037] When the fault is a single-phase grounding fault, the following formula is used to solve it:

[0038]

[0039] When the fault is a two-phase short circuit fault, the solution is obtained by the following formula:

[0040]

[0041] When the fault is a two-phase short-circuit grounding fault, the solution is obtained using the following formula:

[0042]

[0043] Among them, Z (1) , Z (2) and Z (0) are positive sequence impedance, negative sequence impedance and zero sequence impedance respectively, and are positive sequence current, negative sequence current and zero sequence current respectively, Z f is the grounding impedance of the fault point; V pre-fault Indicates the voltage at the fault point before the fault;

[0044] The fault current of each phase short circuit is obtained by superimposing each sequence component.

[0045] A distribution network fault characteristic calculation system including distributed photovoltaic and energy storage, comprising:

[0046] Multi-source data parsing module, used to obtain multi-source data of the distribution network, parse the multi-source data, and obtain the node-branch association matrix;

[0047] Equivalent model construction module, used to construct photovoltaic equivalent model and energy storage equivalent model according to the node-branch correlation matrix;

[0048] A Jacobian matrix construction module is used to form a distributed power supply fault current constraint equation based on the photovoltaic equivalent model and the energy storage equivalent model, and to construct a Jacobian matrix based on the constraint equation;

[0049] The solution module is used to solve the fault characteristics of asymmetric short circuit and symmetric short circuit respectively based on the Jacobian matrix to obtain the fault characteristic solution results.

[0050] A terminal device comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of any one of the methods of the present invention when executing the computer program.

[0051] A computer-readable storage medium stores a computer program, wherein the computer program, when executed by a processor, implements the steps of any method described in the present invention.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] The present invention discloses a method for calculating fault characteristics of a distribution network containing distributed photovoltaics and energy storage, constructs a photovoltaic equivalent model and an energy storage equivalent model, supports dynamic topological updating of the distribution network containing distributed photovoltaics and energy storage, and combines photovoltaic and energy storage control strategies, can better adapt to the complex operating scenarios of distributed power sources connected to the distribution network, enhances engineering applicability, constructs a Jacobian matrix, can solve the fault characteristics of asymmetric short circuits and symmetric short circuits, unifies the symmetric and asymmetric fault calculation frameworks, improves the accuracy of fault calculation, combines multi-source data of the distribution network to assist in fault calculation, shortens the workload of manual short circuit calculation and protection setting, and improves the protection setting optimization efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0055] Figure 1 Schematic diagram of the system architecture of the present invention;

[0056] Figure 2 This is a schematic diagram of a distribution network including distributed photovoltaics and energy storage;

[0057] Figure 3 Schematic diagram of the photovoltaic and energy storage low voltage ride-through LVRT curve and current limit of the present invention (where a represents photovoltaic LVRT control and b represents energy storage control strategy);

[0058] Figure 4 This is a logic diagram of energy storage charging and discharging state switching in the present invention. DETAILED DESCRIPTION

[0059] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0060] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0061] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0062] In the description of the embodiments of the present invention, it should be noted that if the terms "upper," "lower," "horizontal," "inner," etc. appear, the orientation or positional relationship indicated is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the inventive product is typically placed when in use. These terms are merely for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first," "second," etc. are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0063] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0064] In the description of the embodiments of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0065] The present invention is described in further detail below with reference to the accompanying drawings:

[0066] See also Figure 1 The embodiment of the present invention discloses a method for calculating the fault characteristics of a distribution network containing distributed photovoltaics and energy storage. By constructing a dynamic equivalent model of distributed power sources, improving the Jacobian matrix and sequence component coupling algorithm, it realizes the rapid calculation of symmetrical and asymmetrical short circuits in the distribution network containing photovoltaics and energy storage, provides the fault current calculation results required for protection setting, and improves the adaptive performance of relay protection setting in complex operating scenarios.

[0067] Step 1: Importing multi-source data of distribution network and dynamically analyzing topology

[0068] Step 1.1, data import

[0069] The PMS system, a distribution network management platform, provides real-time access to network topology, line parameters (R / X / B values), transformer tap locations, distributed PV capacity, LVRT curves (including voltage drop threshold, current limit, and recovery slope), energy storage system rated power, SOC range, and charge / discharge control mode (constant power / constant current / droop control). The system also receives real-time operational data from the PMS system, including node voltage, load power, distributed generation output, and energy storage SOC status.

[0070] Step 1.2, topology analysis

[0071] The fault modeling and automatic fault signature calculation system uses graph theory algorithms to generate a node-branch association matrix, labeling PV nodes (photovoltaic) as Type 1, VS nodes (energy storage) as Type 2 (charging) / Type 3 (discharging), PQ nodes (load) as Type 4, and fault points as Type 5. It dynamically identifies changes in network connectivity, such as topology reconfiguration during islanded operation, and updates equivalent model parameters.

[0072] Step 2: Dynamic equivalent modeling of distributed power generation

[0073] Step 2.1, Photovoltaic equivalent model:

[0074] Under normal operating conditions, it is equivalent to a PQ node, satisfying:

[0075]

[0076] Where Q0 and P0 are the reactive power per unit value and active power per unit value of PV output before short circuit, respectively. PCC Indicates the per-unit value of the PV grid-connected point voltage.

[0077] During a fault, the system switches to a controlled current source model and linearizes the LVRT curve piecewise based on the voltage drop depth (ΔV) at the grid connection point:

[0078]

[0079] Step 2.2, energy storage equivalent model:

[0080] When the SOC is greater than 80%, the energy storage unit will no longer be charged, but will be discharged instead to avoid damage to the energy storage system due to overcharging; when the SOC is less than 20%, the energy storage unit will no longer be discharged, but will be charged instead to avoid damage to the system due to overdischarge.

[0081] In the charging state, it is equivalent to a constant power load (PQ node), satisfying:

[0082]

[0083] Where, I c is the effective value of the converter output current.

[0084] In the discharge state, it is equivalent to a controlled voltage source (VS node), satisfying:

[0085]

[0086] Step 3: Improve the Jacobian matrix and sequence component coupling algorithm

[0087] Step 3.1, Improve the Jacobian matrix

[0088] On the basis of the traditional power flow calculation Jacobian matrix, the distributed power supply fault current constraint equation is added to form an extended Jacobian matrix:

[0089]

[0090] Where ΔP represents the active power imbalance, ΔQ represents the reactive power imbalance, V and θ represent the node voltage amplitude and phase angle respectively, and I PV , I ESS Represent the output current of distributed photovoltaic and energy storage respectively.

[0091] Step 3.2, sequence component coupling calculation

[0092] Symmetrical short circuit (three-phase short circuit):

[0093] Using the positive sequence network model, the fault point is equivalent to the ground impedance Z f , the fault current is solved iteratively by extending the Newton-Raphson method:

[0094]

[0095] Asymmetrical short circuit (single-phase to ground, two-phase short circuit, and two-phase short circuit to ground):

[0096] Decompose into positive sequence, negative sequence, and zero sequence networks, and construct a composite sequence network equation based on the fault type:

[0097] Single-phase ground fault:

[0098]

[0099] Two-phase short circuit fault:

[0100]

[0101] Two-phase short circuit grounding fault:

[0102]

[0103] Among them, Z (1) , Z (2) , Z (0) are positive sequence, negative sequence and zero sequence impedance respectively, are positive sequence, negative sequence, and zero sequence current respectively, Z f is the grounding impedance of the fault point.

[0104] Solve each sequence component jointly and superpose them to obtain the short-circuit current of each phase.

[0105] Step 3.3, Adaptive iterative calculation and result output

[0106] Based on the message information provided by the distribution network PMS system regarding possible mismatches of protection devices due to changes in operating mode and topology, the fault type and fault node conditions that require short-circuit calculation are determined, and automatic calculation of fault characteristics applicable to phase-to-phase protection and single-phase grounding protection is carried out. To ensure the stability of the calculation results, the convergence criterion shown in formula (10) is adopted:

[0107]

[0108] Based on the calculation results for phase-to-phase faults and single-phase-to-ground faults, a recommended protection setting scheme is generated based on the distribution network protection configuration plan. For example, current protection includes the operating current, operating time, and sensitivity verification results. The short-circuit characteristic calculation results and the recommended protection setting scheme are uploaded to the PMS system, which further verifies them according to operation and maintenance requirements and enables the download and update of protection settings.

[0109] Specifically, the present invention discloses an embodiment:

[0110] like Figure 1 As shown, the present invention provides a method and system for automatically calculating fault characteristics of a distribution network containing distributed photovoltaics and energy storage. The method includes a distribution network management platform (PMS) system and a fault modeling and fault characteristic automatic calculation system. The PMS system provides network topology, line parameters (R / X / B values), transformer tap location, distributed photovoltaic capacity and LVRT curve (including voltage drop threshold, current limit value, recovery slope), energy storage system rated power, SOC range, and charge and discharge control mode (constant power / constant current / droop control). The PMS system receives real-time operating data, including node voltage, load power, distributed power output, and energy storage SOC status. The fault modeling and fault characteristic automatic calculation system performs dynamic modeling of the distribution network containing distributed photovoltaics and energy storage, automatically calculates fault characteristics, and generates calculation results and protection setting recommendation schemes.

[0111] In this embodiment, the network topology, line parameters (R / X / B values), transformer tap position, distributed photovoltaic capacity and LVRT curve (including voltage drop threshold, current limit value, recovery slope), energy storage system rated power, SOC range, charge and discharge control mode (constant power / constant current / droop control) are obtained in real time from the distribution network management platform PMS system. Real-time operating data provided by the PMS system is received, including node voltage, load power, distributed power output, and energy storage SOC status. The PMS system includes a photovoltaic controller and an energy storage controller, which are configured through a JSON configuration file, and the photovoltaic controller and the energy storage controller respectively exchange information with the distributed photovoltaic and energy storage devices through the MODBUS protocol, DLT645 protocol, DLT698 protocol, and IEC104 protocol.

[0112] As Figure 2 As an example, a 10kV distribution network with photovoltaic and energy storage is shown. The topology includes two feeders, two photovoltaic power plants (total capacity 2MW), and two energy storage systems (total power 1MW / 2MWh). The fault point is a single-phase metallic ground fault at the end of the BC section of line L2. The main steps of the present invention are as follows:

[0113] Step 1: Import data from multiple sources through the PMS system

[0114] Distribution network structure: Dual-power 10kV distribution network, two feeders, two photovoltaic power stations (total capacity 2MW), and two energy storage systems (total power 1MW / 2MWh);

[0115] Switch status: Due to a change in operating mode, switch B3 on line 2 changes from closed to open, and tie switch KLL changes from open to closed. The end load of line 2 is transferred to S1 for power supply.

[0116] Protection configuration: The line is equipped with multi-stage phase-to-phase current protection;

[0117] Photovoltaic LVRT parameters: When the voltage drops ≤ 20%, the current limit is 1.2 times the rated value, and decreases linearly from 20% to 50%;

[0118] Energy storage control mode: constant power discharge, SOC lower limit 30%, maximum output current 500A;

[0119] Since the topology of line L1 has changed, for the phase-to-phase current protection of the switch, it is necessary to calculate the three-phase fault characteristics of the protection at the end of the BC section B2 of line 2 to further realize the correction of its action setting value.

[0120] Step 2: Analyze the distribution network topology:

[0121] PV node: The node connecting the PV inverter, marked as Type = 1;

[0122] VS node: The grid connection point of the energy storage system, and its charge and discharge status is determined by the SOC (charging: PQ node, marked as Type = 2; discharging: VS node, marked as Type = 3);

[0123] PQ node: The load node, marked as Type = 4;

[0124] Fault point: Marked as Type = 5, and record the fault phase (A / B / C) and impedance value.

[0125] The PMS system synchronizes the device status (such as energy storage SOC, PV output), and dynamically adjusts the node type.

[0126] Step 3: Calculation model construction

[0127] The PV LVRT control is as shown in Figure 3 (a):

[0128] When the voltage drop depth ΔV ≤ 0.2, the output current I PV =(1 + k1ΔV)I N ;

[0129] When the voltage drop depth 0.2 ≤ ΔV ≤ 0.5, the output current I PV =1.2I N ;

[0130] When the voltage drop depth ΔV < 0.5, the output current I PV =(1.2 - k2ΔV)I N , where k1 = 1, k2 = 1.5, and when the voltage < 0.2 p.u., the output is blocked and the current drops to 0.

[0131] The energy storage control strategy is as shown in Figure 3 (b): When 20% < SOC < 80%:

[0132] Charging mode (PQ node): When P PV >P load , charge at a constant power of 0.5 MW;

[0133] Discharging mode (controlled voltage source):

[0134] When P PV <P load , when the voltage drop depth ΔV ≤ 0.15, the output current I ESS =0;

[0135] When the voltage drop depth 0.15 ≤ ΔV ≤ 0.8, the output current I ESS=1.6(ΔV-0.15)I N ;

[0136] When the voltage drop depth ΔV>0.8, the output current I ESS =1.04I N .

[0137] The logic diagram of energy storage charging and discharging state switching is as follows Figure 4 As shown in the figure, when the SOC is greater than 80%, the energy storage unit will no longer be charged, but will be discharged to avoid damage to the energy storage system due to overcharging; when the SOC is less than 20%, the energy storage unit will no longer be discharged, but will be charged to avoid damage to the system due to overdischarging.

[0138] Step 4: Establish an extended short-circuit calculation Jacobian matrix, which includes the traditional power flow equation and the constraint equations of distributed photovoltaic PV1, PV2 and energy storage ESS1, ESS2:

[0139]

[0140] The expanded equations add four new distributed generation current constraint equations, expanding the matrix to a 12×12 size. Furthermore, the corresponding fault characteristics, namely the fault current, are automatically calculated. For example, the three-phase fault characteristics of the current protection terminal at B2 in the BC section of Line 2 are calculated.

[0141] According to the composite sequence network Perform coupling calculation, reference power S B =10MVA, reference voltage U B =10kV, positive sequence impedance Z (1) =0.12+j0.35p.u., negative sequence impedance Z (2) =0.15+j0.4p.u., zero sequence impedance Z (0) =0.3+j1.2p.u., we can get:

[0142]

[0143] Iterative calculation and result output:

[0144] Taking line L2 as an example, a multi-level phase-to-phase current protection scheme is configured, and a relaxation factor λ = 0.5 is introduced. After 6 iterations and convergence, the node power deviation and distributed power current deviation meet the following conditions:

[0145]

[0146] Total current at fault point: After superimposing the distributed power supply injection current, it is corrected to: I f =I f0 +I PV +IESS , the error is lower than that of traditional methods. Take the protection value as I set , set a 0.2s delay to ensure selectivity; after verification, pass the IEC 61850MMS protocol and set the fixed value I set , t delay Write protection device.

[0147] For single-phase grounding protection, since the medium-voltage side of the distribution network adopts an ungrounded method, the zero-sequence network of the single-phase grounding fault is not related to the distributed power supply. At this time, there is no need to calculate the single-phase grounding fault characteristics and perform online setting of the protection setting.

[0148] The method disclosed in this embodiment can better reflect the control characteristics of distributed photovoltaic and energy storage through the dynamic equivalent model and sequence component coupling algorithm, improve the calculation accuracy of fault characteristics, and provide a direct basis for the fine setting of protection settings. This embodiment supports the dynamic update of the topology of the distribution network containing distributed photovoltaic and energy storage and the combination of photovoltaic and energy storage control strategies, which can better adapt to the complex operating scenarios of distributed power sources connected to the distribution network and enhance the applicability of the project. This embodiment automatically carries out the calculation modeling of short-circuit fault characteristics and the protection setting recommendation scheme based on the multi-source data provided by the distribution network management platform PMS system, which greatly shortens the workload of manual short-circuit calculation and protection setting, and improves the protection setting optimization efficiency.

[0149] This embodiment also discloses a distribution network fault feature calculation system that includes distributed photovoltaics and energy storage. By acquiring network topology, main equipment parameters, operating parameters, and control strategies of distributed photovoltaic (PV) and energy storage systems (ESS) from the distribution network management resource service platform (PMS), the fault modeling and fault feature automatic calculation system establishes a dynamic equivalent modulus calculation model of the distribution network that includes distributed photovoltaics and energy storage, forms an improved Jacobian matrix, and uses a composite sequence network iterative algorithm. Based on the protection setting configuration scheme, the system accurately calculates short-circuit current fault features to meet the requirements of online protection setting settings in complex operating scenarios such as distribution network operation modes and topological structures. This system is suitable for distribution networks with a high proportion of distributed photovoltaics and energy storage. Specifically, the system includes:

[0150] Multi-source data parsing module, used to obtain multi-source data of the distribution network, parse the multi-source data, and obtain the node-branch association matrix;

[0151] Equivalent model construction module, used to construct photovoltaic equivalent model and energy storage equivalent model according to the node-branch correlation matrix;

[0152] A Jacobian matrix construction module is used to form a distributed power supply fault current constraint equation based on the photovoltaic equivalent model and the energy storage equivalent model, and to construct a Jacobian matrix based on the constraint equation;

[0153] The solution module is used to solve the fault characteristics of asymmetric short circuit and symmetric short circuit respectively based on the Jacobian matrix to obtain the fault characteristic solution results.

[0154] A schematic diagram of a terminal device provided in one embodiment of the present invention. The terminal device in this embodiment includes: a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of each of the aforementioned method embodiments are implemented. Alternatively, when the processor executes the computer program, the functions of each module / unit in each of the aforementioned device embodiments are implemented.

[0155] The computer program may be divided into one or more modules / units, which are stored in the memory and executed by the processor to accomplish the present invention.

[0156] The terminal device may be a computing device such as a desktop computer, a notebook computer, a PDA, a cloud server, etc. The terminal device may include, but is not limited to, a processor and a memory.

[0157] The processor can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0158] The memory may be used to store the computer programs and / or modules, and the processor implements various functions of the terminal device by running or executing the computer programs and / or modules stored in the memory and calling the data stored in the memory.

[0159] If the module / unit integrated in the terminal device is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the process in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, it can implement the steps of each of the above-mentioned method embodiments. The computer program includes computer program code, which can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal and software distribution medium. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals.

[0160] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for calculating fault characteristics of a distribution network containing distributed photovoltaics and energy storage, characterized in that: The following steps are involved: Obtain multi-source data of the distribution network, parse the multi-source data, and obtain the node-branch correlation matrix; According to the node-branch correlation matrix, the photovoltaic equivalent model and the energy storage equivalent model are constructed; The distributed power supply fault current constraint equation is formed based on the photovoltaic equivalent model and the energy storage equivalent model, and the Jacobian matrix is constructed based on the constraint equation; Based on the Jacobian matrix, the fault characteristics of asymmetric short circuit and symmetric short circuit are solved respectively to obtain the fault characteristic solution results.

2. A method for calculating fault characteristics of a distribution network containing distributed photovoltaics and energy storage according to claim 1, characterized in that: The node-branch association matrix is obtained, including photovoltaic nodes PV, energy storage nodes VS, load nodes PQ and fault point locations.

3. The method for calculating fault characteristics of a distribution network containing distributed photovoltaics and energy storage according to claim 1, characterized in that: The photovoltaic equivalent model is constructed, comprising: When the operating conditions are normal, the equivalent node of the PV system is the load node PQ, which satisfies: Among them, Q0 and P0 are the reactive power per unit value and active power per unit value of the photovoltaic node PV output before short circuit, U PCC Indicates the per-unit voltage of the photovoltaic node PV grid connection point; During a fault, the system switches to a controlled current source model according to the LVRT curve of the distribution network: Among them, I PV It represents the output current of the photovoltaic system, and ΔV represents the voltage drop depth at the grid connection point.

4. A method for calculating fault characteristics of a distribution network containing distributed photovoltaics and energy storage according to claim 3, characterized in that: The construction of the energy storage equivalent model includes: When the energy storage system is in the charging state, the energy storage system is equivalent to the load node PQ, satisfying: Among them, I c is the effective value of the converter output current; When the energy storage system is in the discharging state, the energy storage system is equivalent to the energy storage node VS, satisfying: Wherein, ΔV represents the voltage drop depth at the grid connection point; I ESS Indicates the output current of the energy storage.

5. The method for calculating fault characteristics of a distribution network containing distributed photovoltaics and energy storage according to claim 1, characterized in that: The constructing of the Jacobian matrix includes: Where ΔP represents the active power imbalance, ΔQ represents the reactive power imbalance, V and θ represent the node voltage amplitude and phase angle respectively, and I PV and I ESS Represent the output current of distributed photovoltaic and energy storage respectively.

6. A method for calculating fault characteristics of a distribution network containing distributed photovoltaics and energy storage according to claim 5, characterized in that: The fault characteristics of symmetrical short circuit are solved by: The sequence component of the symmetrical short-circuit fault is solved by the following formula: Among them, V pre-fault Indicates the voltage at the fault point before the fault; Z f Represents the ground impedance, Z (1) Represents the positive sequence impedance.

7. A method for calculating fault characteristics of a distribution network containing distributed photovoltaics and energy storage according to claim 6, characterized in that: The fault characteristics of asymmetric short circuit are solved by: When the fault is a single-phase grounding fault, the following formula is used to solve it: When the fault is a two-phase short circuit fault, the solution is obtained by the following formula: When the fault is a two-phase short-circuit grounding fault, the solution is obtained using the following formula: Among them, Z (1) , Z (2) and Z (0) are positive sequence impedance, negative sequence impedance and zero sequence impedance respectively, and are positive sequence current, negative sequence current and zero sequence current respectively, Z f is the grounding impedance of the fault point; V pre-fault Indicates the voltage at the fault point before the fault; The fault current of each phase short circuit is obtained by superimposing each sequence component.

8. A distribution network fault feature calculation system including distributed photovoltaic and energy storage, characterized in that: include: Multi-source data parsing module, used to obtain multi-source data of the distribution network, parse the multi-source data, and obtain the node-branch association matrix; Equivalent model construction module, used to construct photovoltaic equivalent model and energy storage equivalent model according to the node-branch correlation matrix; A Jacobian matrix construction module is used to form a distributed power supply fault current constraint equation based on the photovoltaic equivalent model and the energy storage equivalent model, and to construct a Jacobian matrix based on the constraint equation; The solution module is used to solve the fault characteristics of asymmetric short circuit and symmetric short circuit respectively based on the Jacobian matrix to obtain the fault characteristic solution results.

9. A terminal device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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