A method for simulating and calculating stray current of photovoltaic power station based on real topological structure

Abstract

This application discloses a method for simulating stray current in photovoltaic power plants based on real topology, belonging to the field of photovoltaic power generation system simulation modeling technology. The method first obtains the parameters of the photovoltaic modules, photovoltaic array, environment and operation, DC cable, grounding system, inverter, and ground fault detector of the photovoltaic power plant, and calculates the output current, DC leakage current, and equivalent resistance of the injection conductor of the photovoltaic array. Then, a three-dimensional simulation model is established based on the real spatial topological relationship of each conductor in the photovoltaic power plant, and soil parameters, conductor parameters, and cable coating parameters are set. Subsequently, a current source excitation determined by the output current of the photovoltaic array is applied to the DC positive and DC negative cables, causing the DC leakage current to enter the metal support through the injection conductor and naturally shunt between the metal support, equipment grounding conductor, grounding grid, and soil. Finally, the three-dimensional simulation model is run under DC steady-state conditions to obtain the longitudinal inflow current in each metal support, ground fault detector, and the connecting conductor between the equipment grounding conductor and the grounding grid, and calculates the total stray current. This invention can reflect the spatial distribution and flow path of stray current under the complex three-dimensional structure of a photovoltaic power plant, providing a quantitative basis for corrosion risk assessment of photovoltaic power plants and surrounding buried metal facilities.

Description

Technical Field

[0001] This application relates to the field of photovoltaic power generation system simulation modeling technology, and in particular to a method for simulating and calculating stray currents in photovoltaic power plants based on real topology. Background Technology

[0002] With the continuous expansion of photovoltaic power generation systems and the increasing complexity of their operating environments, the issues of DC leakage current and stray current under normal operating conditions have gradually attracted attention. In photovoltaic systems, although the conductors carrying DC current (photovoltaic modules, DC cables, etc.) are all equipped with insulation protection, under actual steady-state operating conditions, due to physical factors such as the inherent ground insulation resistance of the photovoltaic modules themselves and the inherent leakage conductivity of the insulation layer of buried DC cables, photovoltaic systems will inevitably continuously generate weak DC currents leaking from charged conductors to the ground.

[0003] Although the individual DC leakage current values ​​under normal steady-state operation are relatively small, its persistent and uninterrupted nature, coupled with the large area occupied by large photovoltaic power plants and the massive number of modules and cables, means that leakage current can accumulate at local underground nodes. When this leakage current is not completely captured by the equipment grounding conductor and instead seeks a return path through the ground and other low-resistance conductive paths (such as nearby buried pipelines), the long-term interference of DC stray currents can easily cause severe electrochemical corrosion damage to the metal structure of the photovoltaic power plant itself and surrounding third-party buried metal facilities.

[0004] However, current methods for assessing DC leakage current under normal operating conditions of photovoltaic (PV) systems still have significant limitations. Existing conventional analyses often rely on highly simplified lumped-parameter equivalent circuits, neglecting the vast and complex physical spatial distribution of the PV array. In reality, the magnitude and return path of the DC leakage current in a PV system are closely related to the actual relative spatial topology of all electrical components within the system. Traditional one-dimensional circuit models cannot accurately reflect the current flow direction and current density distribution of various metal conductors in three-dimensional physical space. Therefore, there is an urgent need to introduce a simulation calculation method for DC leakage current in PV systems that can accurately reflect the actual physical topology, thereby accurately assessing the spatial distribution of leakage current under normal steady-state operating conditions and providing guidance for the design optimization of PV power plants and the prevention and control of corrosion in underground metal structures. Summary of the Invention

[0005] This invention addresses the technical problems existing in the background art by proposing a stray current simulation calculation method for photovoltaic power plants based on real topology. This method can accurately calculate the spatial distribution and physical flow direction of stray current under steady-state operation of the system, providing a quantitative basis for assessing the DC interference and corrosion risks of photovoltaic power plants and surrounding buried metal facilities.

[0006] To solve the technical problem, the technical solution of the present invention is as follows:

[0007] A method for simulating stray current in a photovoltaic power plant based on a real topology includes the following steps:

[0008] S1. Obtain the basic parameters of the photovoltaic power station, including photovoltaic module parameters, photovoltaic array parameters, environmental and operating parameters, DC cable parameters, grounding system parameters, inverter parameters, and grounding fault detector parameters; calculate the output current, DC leakage current, and equivalent resistance of the injection conductor of the photovoltaic array based on the photovoltaic module parameters, photovoltaic array parameters, and environmental and operating parameters.

[0009] S2. Based on the DC cable parameters, grounding system parameters, inverter parameters, grounding fault detector parameters, DC leakage current, and equivalent resistance of the injected conductor, establish a three-dimensional simulation model of the photovoltaic power station according to the real spatial topology of each conductor in the photovoltaic power station.

[0010] S3. Set soil parameters, conductor parameters and cable coating parameters in the three-dimensional simulation model, and apply current source excitation determined by the output current of the photovoltaic array to the DC positive cable and DC negative cable, so that the DC leakage current enters the metal support through the injection conductor and is shunted between the metal support, the equipment grounding conductor, the grounding grid and the soil, forming a photovoltaic power station stray current simulation model under DC steady-state conditions.

[0011] S4. Run the photovoltaic power station stray current simulation model under DC steady-state conditions, obtain the longitudinal inflow current of each metal support, the longitudinal inflow current of the ground fault detector, and the longitudinal inflow current of the connecting wire between the equipment grounding conductor and the grounding grid, and calculate the total stray current based on the above currents.

[0012] Furthermore, the photovoltaic module parameters include the three-dimensional physical dimensions of a single photovoltaic module, operating voltage, insulation resistance to ground, short-circuit current and open-circuit voltage under standard test conditions, temperature coefficient of short-circuit current, internal equivalent series resistance, internal equivalent parallel resistance, diode ideality factor, and bandgap of semiconductor material; the photovoltaic array parameters include the number of photovoltaic modules constituting a single photovoltaic series circuit, operating voltage of a single photovoltaic array, and the relative position and orientation of each photovoltaic array in the spatial physical topology.

[0013] Furthermore, the environmental and operating parameters include the soil resistivity of the area where the photovoltaic power station is located, the coplanar irradiance of the photovoltaic modules, the backsheet temperature of the photovoltaic modules, the reference temperature under standard test conditions, the coplanar irradiance under standard test conditions, the charge constant, and the Boltzmann constant; the photogenerated current is determined based on the environmental and operating parameters, and the output current of the photovoltaic array is calculated based on the series topology of the photovoltaic modules.

[0014] Furthermore, the determination of the DC leakage current is based on the insulation resistance of the photovoltaic module to ground, and combined with the number of photovoltaic modules, the operating voltage of the photovoltaic modules, the DC voltage at the input of the inverter, and the insulation resistance of the photovoltaic modules, to determine the magnitude of the DC leakage current flowing into the injection conductor and the equivalent resistance of the injection conductor.

[0015] Furthermore, the DC cable parameters include the cross-sectional area of ​​the DC positive cable and the DC negative cable, the relative resistivity of the conductor, the resistivity and thickness of the coating material, the actual laying length and burial depth; the grounding system parameters include the three-dimensional dimensions, cross-sectional area and depth of the metal support driven into the soil, the cross-sectional area and laying route of the equipment grounding conductor, the grid size of the grounding grid, the burial depth and the equivalent cross-sectional area of ​​the conductor used in the grounding grid.

[0016] Furthermore, the three-dimensional simulation model includes a metal support, a grounding grid, a device grounding conductor, a DC positive cable, a DC negative cable, an inverter equivalent conductor, a grounding fault detector equivalent conductor, and an injection conductor;

[0017] The establishment of the three-dimensional simulation model includes: spatially positioning the metal support, grounding grid, buried metal piles, DC positive cable, DC negative cable, and equipment grounding conductor according to the actual construction layout of the photovoltaic power station, and constructing an electrical connection topology based on the connection relationship between each conductor; the electrical connection topology includes: setting an injection conductor between the beginning of the DC positive cable and the metal support, setting an inverter equivalent conductor between the end of the DC negative cable and the end of the DC positive cable, setting a ground fault detector equivalent conductor between the end of the DC negative cable and the grounding grid, and setting a connecting conductor between the equipment grounding conductor and the grounding grid.

[0018] Furthermore, the conductor parameter settings include determining the equivalent resistance and equivalent radius of the conductor based on the resistivity characteristics and cross-sectional area of ​​the conductor material, and assigning the equivalent resistance and equivalent radius of the conductor to the metal bracket, grounding grid, DC cable, equipment grounding conductor, inverter equivalent conductor, grounding fault detector equivalent conductor, and injection conductor, respectively; the cable coating parameters are used to characterize the electrical characteristics of the outer insulation layer of the DC positive cable and DC negative cable, and by setting the coating resistivity and coating thickness, the electrical characteristics of the outer insulation layer of the DC cable are characterized.

[0019] Furthermore, the soil parameters include soil resistivity, which is used to characterize the conductive environment of the area where the photovoltaic power station is located, and in the three-dimensional simulation model, it characterizes the conductive properties when current is discharged into the soil through the metal structure.

[0020] Furthermore, the current source excitation is used to simulate the normal operation of the DC side of the photovoltaic power station. By applying an equivalent current input to the DC positive cable and the DC negative cable, the current enters the metal support system through the injection conductor and is naturally shunted between the metal support, the equipment grounding conductor, the grounding grid and the soil.

[0021] Furthermore, the DC steady-state operating condition is characterized by setting the operating frequency of the simulation model to zero; the total stray current is determined based on the longitudinal current flowing into the ground fault detector branch and the longitudinal current flowing into the connecting wire between the equipment grounding conductor and the grounding grid; the three-dimensional simulation model is simulated and calculated using a software platform that supports three-dimensional conductor modeling and current distribution solution.

[0022] The present invention has the following advantages:

[0023] This invention employs a 3D object modeling method using the HIFREQ module, considering the actual spatial topology of the photovoltaic array metal frame, underground grounding grid, equipment grounding conductor, and buried cable. This simulation method can accurately reproduce the natural current distribution process between various metal conductors and the soil, thereby obtaining current flow and potential distribution data that more closely match actual physical conditions. This effectively overcomes the limitation of traditional two-dimensional equivalent circuit methods in reflecting the current distribution of complex three-dimensional grounding systems.

[0024] The simulation model parameters involved in this invention can all be directly obtained or calculated through engineering design drawings, conventional electrical tests, or on-site measurements. Compared with analytical methods that require complex derivations, the calculation process parameters provided by this invention are easy to obtain and more easily promoted and applied in the planning, design, operation and maintenance assessment, and safety protection engineering of photovoltaic power plants. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 The logic diagram of the stray current simulation model of a photovoltaic power station constructed for the embodiments of this application is shown.

[0027] Figure 2 A schematic diagram of a three-dimensional topology simulation model of a photovoltaic power station constructed for embodiments of this application;

[0028] Figure 3 A schematic diagram of the DC leakage current injection and stray current shunting path constructed for the embodiments of this application. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] Example 1:

[0031] like Figures 1-3 As shown, this embodiment takes a photovoltaic power station as an example to simulate and calculate the DC leakage current generated under normal steady-state operation of the photovoltaic power station and its current distribution law in the grounding system, metal support, buried cable and soil. The photovoltaic power station includes structures such as photovoltaic module array, metal support, DC positive cable, DC negative cable, equipment grounding conductor, grounding grid, inverter and grounding fault detector.

[0032] To accurately reflect the flow path of stray current in actual three-dimensional space, this embodiment establishes a simulation model based on photovoltaic power plant design drawings, construction drawings, and on-site environmental parameters, according to the actual spatial topology of each conductor. The HIFREQ module and SESCAD tool in CDEGS software are used as simulation platforms to complete three-dimensional conductor modeling, parameter assignment, current excitation setting, and simulation calculation.

[0033] Specifically, this embodiment first obtains basic parameters such as photovoltaic modules, photovoltaic arrays, DC cables, grounding systems, inverters, grounding fault detectors, and soil environment; then, based on the actual spatial arrangement of each component of the photovoltaic power station, a three-dimensional simulation model is established, including metal supports, grounding grids, equipment grounding conductors, DC positive cables, DC negative cables, and equivalent connecting wires; finally, by setting current source excitation, the process of DC leakage current entering the metal structure and naturally diverting through the equipment grounding conductors, grounding grids, and soil under normal operating conditions of the photovoltaic power station is simulated, thereby obtaining the spatial distribution characteristics of stray current in the metal structure, grounding system, and soil, and calculating the total stray current.

[0034] like Figure 1 As shown in the figure, this embodiment provides a method for simulating stray current in a photovoltaic power station based on a real topology. The specific steps include:

[0035] Step 1: Obtain the basic parameters of the photovoltaic power station based on the design drawings, construction drawings, and environmental meteorological data of the area. Specifically, these parameters include: photovoltaic module parameters, photovoltaic array parameters, environmental and operational parameters, DC cable parameters, grounding system parameters, inverter parameters, and grounding fault detector parameters.

[0036] The parameters of a photovoltaic module include: the three-dimensional physical dimensions of a single photovoltaic module, operating voltage, insulation resistance to ground, short-circuit current and open-circuit voltage under standard test conditions, temperature coefficient of short-circuit current, internal equivalent series resistance, internal equivalent parallel resistance, diode ideality factor, and bandgap of semiconductor materials.

[0037] Photovoltaic array parameters include: the number of photovoltaic modules that make up a single photovoltaic series circuit, the total operating voltage of a single photovoltaic array, and the relative position and orientation of each photovoltaic array in the spatial physical topology.

[0038] Environmental and operational parameters include: soil resistivity in the area where the photovoltaic power station is located, as well as historical coplanar irradiance of the photovoltaic modules, historical backsheet temperature, reference temperature under standard test conditions, coplanar irradiance under standard test conditions, charge constant, and Boltzmann constant.

[0039] The parameters of DC cables include: the cross-sectional area of ​​the DC positive and DC negative cables connecting the photovoltaic array and the inverter, the relative resistivity of the conductor, the resistivity and thickness of the coating material, and the actual laying length and burial depth.

[0040] Grounding system parameters include: the three-dimensional dimensions, cross-sectional area, and depth of the metal support that carries the photovoltaic modules; the cross-sectional area and laying route of the equipment grounding conductor (EGC) used for equipotential bonding of all metal supports; and the grid size, burial depth, and equivalent cross-sectional area of ​​the conductors used in the grounding grid.

[0041] Inverter parameters include: the equivalent load resistance on the inverter terminal side.

[0042] The parameters of the ground fault detector include: the equivalent load resistance of the ground fault detector. Step 2: Build a simulation model of the DC leakage current of the photovoltaic power station in CDEGS software:

[0043] 201: Using the photovoltaic module parameters and photovoltaic array parameters obtained in step 1, and based on the series topology of the photovoltaic module, calculate the output current of the photovoltaic array using the output current formula of the photovoltaic module. ,and ,in For photocurrent, This refers to the reverse saturation current of the PN junction in a photovoltaic module. The electron charge constant (with a value of 1.602 × 10⁻⁶) -19 C), For equivalent series resistance, For equivalent parallel resistance, The ideal coefficient for the diode. Boltzmann's constant (valued at 1.38065 × 10⁻⁶) -23J / K), where U is the operating voltage of a single photovoltaic module, U= The formula for calculating photocurrent is: ,in This refers to the short-circuit current under standard conditions for photovoltaic modules. The temperature coefficient of short-circuit current. For historical coplanar irradiance, Coplanar irradiance under standard test conditions. For the historical background temperature, This is the reference temperature under standard test conditions. The DC leakage current of the photovoltaic array is set to... The equivalent resistance of the injected wire is The formula for calculating DC leakage current is: The formula for calculating the equivalent resistance of the injected wire is: In the formula The number of photovoltaic modules connected in series. This refers to the operating voltage of a single photovoltaic module. This refers to the DC voltage at the inverter input terminal. This refers to the insulation resistance of the photovoltaic module.

[0044] 202: Set the soil type to uniform soil using the soil module in the HIFREQ module of the CDEGS software. The air resistivity in the soil properties is the system default, and the soil resistivity is the soil resistivity obtained in step 1.

[0045] 203: Using the SESCAD tool in the HIFREQ module of the CDEGS software, set the conductor types for each part of the photovoltaic power station. Using the conductor data obtained in step 1, first name each conductor and set the impedance specification to custom; then calculate the internal resistance of each conductor. ,and , The resistivity of the conductor material is given; based on the calculation results, fill in the internal resistance under the corresponding conductor type.

[0046] 204: Using the cable coating parameters obtained in step 1, use the SESCAD tool in the HIFREQ module of the CDEGS software to define the cable coating. The coating definition includes the coating name, coating resistivity, and coating thickness.

[0047] 205: Using the SESCAD tool in the HIFREQ module of CDEGS software, build a model of the photovoltaic power station according to the spatial topology order; first, draw the equivalent photovoltaic array metal grounding grid and buried metal piles underground; then draw the metal support above the ground; then draw the DC positive cable, DC negative cable and equipment grounding conductor in parallel at the corresponding depth underground; finally, connect the injection wire between the beginning of the DC positive cable and the horizontal beam node of the metal support, connect the inverter equivalent wire between the end of the DC negative cable and the end of the DC positive cable, connect the ground fault detector equivalent wire between the end of the DC negative cable and the grounding grid, and connect the wire between the equipment grounding conductor and the grounding grid.

[0048] 206: To bind physical properties to the conductors of each part in the completed 3D simulation model, select the corresponding conductor model and, according to the conductor types defined in step 203, set the corresponding conductor types for metal brackets, grounding grids, cables, equipment grounding conductors, inverters, grounding fault detectors, and injection wires; then, according to the formula... Calculate the equivalent radius of each conductor. ,in The cross-sectional area of ​​the conductor is specified. Enter the corresponding radius value for each conductor on this interface. Finally, set the coating for the cable according to the coating settings in step 204. The coating for other conductors is left as default.

[0049] 207: Use the SESCAD tool in the HIFREQ module of CDEGS software to add current excitation to the cable; set a current source excitation at the beginning of the DC positive cable conductor. A current source is installed at the beginning of the DC negative cable conductor for excitation. The magnitude of the excitation current is determined by the photovoltaic array output current calculated in step 201. The decision was made to energize the simulation model to simulate the process in which, under normal operating conditions, DC leakage current flows into the metal support through the injection wire and undergoes natural shunting through the equipment grounding conductor and soil in the real three-dimensional spatial topology.

[0050] Step 3: Simulation calculation of stray current:

[0051] Using the HIFREQ module in CDEGS software, the system frequency was set to 0, and the photovoltaic power station simulation model built in step 2 was run to obtain the longitudinal current flowing into each metal support. Where i = 1, 2, 3, ..., m, then the longitudinal inflow current of the ground fault detector is obtained. And the longitudinal current flowing into the connecting wire between the equipment grounding conductor and the grounding grid. Calculate stray current :

[0052]

[0053]

[0054] To further verify the accuracy and operability of the simulation calculation method of this invention, a specific photovoltaic power station was selected for simulation calculation verification. The specific parameters of the photovoltaic power station are shown in Table 1:

[0055] Table 1 Basic parameters of a photovoltaic power station simulation model

[0056] Parameter name numerical values unit Number of photovoltaic arrays 3 indivual Number of metal brackets 216 indivual Number of photovoltaic modules 576 piece Insulation resistance to ground of a single photovoltaic module 15.48 MΩ Photovoltaic module operating voltage 41.96 V Cable cross-sectional area 180 <![CDATA[mm 2 ]]> Cable burial depth 1 m Cable coating resistivity <![CDATA[1.0×10 14 ]]> Ω·m Cable coating thickness 0.0025 m Grounding grid size 15×15 m cross-sectional area of ​​metal support 141 <![CDATA[mm 2 ]]> Soil resistivity 1000 Ω·m

[0057] After theoretical conversion of the aforementioned formulas and solving the three-dimensional simulation model, the parameters and final simulation output results under the parameter settings described in this embodiment are shown in Table 2:

[0058] Table 2 Input and output parameters of a photovoltaic power station

[0059] Parameter name numerical values unit Photovoltaic array output current 12.87 A DC leakage current 0.813 mA Equivalent injection insulation resistance 1238400 Ω EGC longitudinal inflow current 19.60 mA GFDI longitudinal inflow current 19.61 mA Total stray current 0.01 mA

[0060] In this embodiment, the longitudinal inflow current can be obtained from the conductor current calculation results output by simulation software, preferably the current component along the conductor axial direction at the connection position of the conductor with other conductors or grounding structures, but it is not limited to this.

[0061] It should be noted that the technical concept of this invention lies in establishing a three-dimensional simulation model based on the actual spatial topological relationship of each conductor in a photovoltaic power station. This model can reflect the natural shunting process of DC leakage current among the metal support, equipment grounding conductor, grounding grid, and soil. The total stray current is then determined based on the simulation results. The use of the HIFREQ module and SESCAD tool in CDEGS software is merely a preferred embodiment for achieving the above-mentioned three-dimensional modeling, parameter assignment, current excitation setting, and simulation calculation, and should not be construed as limiting the scope of protection of this invention.

[0062] Those skilled in the art will understand that, without departing from the technical concept of this invention, other software platforms with functions such as three-dimensional conductor modeling, soil parameter setting, conductor electrical parameter assignment, cable coating equivalent setting, current source excitation setting, and current distribution solution can also be used to complete the stray current simulation calculation of photovoltaic power plants and obtain the same technical effects as this invention. Such implementation methods also belong to the implementation methods disclosed in this invention.

[0063] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0064] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for simulating stray current in photovoltaic power plants based on real topology, characterized in that, The steps include the following: S1. Obtain the basic parameters of the photovoltaic power station, including photovoltaic module parameters, photovoltaic array parameters, environmental and operating parameters, DC cable parameters, grounding system parameters, inverter parameters, and grounding fault detector parameters; calculate the output current, DC leakage current, and equivalent resistance of the injection conductor of the photovoltaic array based on the photovoltaic module parameters, photovoltaic array parameters, and environmental and operating parameters. S2. Based on the DC cable parameters, grounding system parameters, inverter parameters, grounding fault detector parameters, DC leakage current, and equivalent resistance of the injected conductor, establish a three-dimensional simulation model of the photovoltaic power station according to the real spatial topology of each conductor in the photovoltaic power station. S3. Set soil parameters, conductor parameters and cable coating parameters in the three-dimensional simulation model, and apply current source excitation determined by the output current of the photovoltaic array to the DC positive cable and DC negative cable, so that the DC leakage current enters the metal support through the injection conductor and is shunted between the metal support, the equipment grounding conductor, the grounding grid and the soil, forming a photovoltaic power station stray current simulation model under DC steady-state conditions. S4. Run the photovoltaic power station stray current simulation model under DC steady-state conditions, obtain the longitudinal inflow current of each metal support, the longitudinal inflow current of the ground fault detector, and the longitudinal inflow current of the connecting wire between the equipment grounding conductor and the grounding grid, and calculate the total stray current based on the above currents.

2. The simulation calculation method according to claim 1, characterized in that, The photovoltaic module parameters include the three-dimensional physical dimensions of a single photovoltaic module, operating voltage, insulation resistance to ground, short-circuit current and open-circuit voltage under standard test conditions, temperature coefficient of short-circuit current, internal equivalent series resistance, internal equivalent parallel resistance, diode ideality coefficient, and bandgap of semiconductor material; the photovoltaic array parameters include the number of photovoltaic modules constituting a single photovoltaic series circuit, operating voltage of a single photovoltaic array, and the relative position and orientation of each photovoltaic array in the spatial physical topology.

3. The simulation calculation method according to claim 1, characterized in that, The environmental and operating parameters include the soil resistivity of the area where the photovoltaic power station is located, the coplanar irradiance of the photovoltaic modules, the backsheet temperature of the photovoltaic modules, the reference temperature under standard test conditions, the coplanar irradiance under standard test conditions, the charge constant, and the Boltzmann constant; the photogenerated current is determined based on the environmental and operating parameters, and the output current of the photovoltaic array is calculated based on the series topology of the photovoltaic modules.

4. The simulation calculation method according to claim 1, characterized in that, The determination of the DC leakage current is based on the insulation resistance of the photovoltaic module to ground, and in combination with the number of photovoltaic modules, the operating voltage of the photovoltaic modules, the DC voltage at the inverter input terminal, and the insulation resistance of the photovoltaic modules, to determine the magnitude of the DC leakage current flowing into the injection conductor and the equivalent resistance of the injection conductor.

5. The simulation calculation method according to claim 1, characterized in that, The DC cable parameters include the cross-sectional area of ​​the DC positive and DC negative cables, the relative resistivity of the conductors, the resistivity and thickness of the coating material, the actual laying length and burial depth; the grounding system parameters include the three-dimensional dimensions, cross-sectional area and depth of the metal support driven into the soil, the cross-sectional area and laying route of the equipment grounding conductor, the grid size of the grounding grid, the burial depth and the equivalent cross-sectional area of ​​the conductor used in the grounding grid.

6. The simulation calculation method according to claim 1, characterized in that, The three-dimensional simulation model includes a metal support, a grounding grid, a device grounding conductor, a DC positive cable, a DC negative cable, an inverter equivalent conductor, a grounding fault detector equivalent conductor, and an injection conductor; The establishment of the three-dimensional simulation model includes: spatially positioning the metal support, grounding grid, buried metal piles, DC positive cable, DC negative cable, and equipment grounding conductor according to the actual construction layout of the photovoltaic power station, and constructing an electrical connection topology based on the connection relationship between each conductor; the electrical connection topology includes: setting an injection conductor between the beginning of the DC positive cable and the metal support, setting an inverter equivalent conductor between the end of the DC negative cable and the end of the DC positive cable, setting a ground fault detector equivalent conductor between the end of the DC negative cable and the grounding grid, and setting a connecting conductor between the equipment grounding conductor and the grounding grid.

7. The simulation calculation method according to claim 1, characterized in that, The conductor parameter setting includes determining the equivalent resistance and equivalent radius of the conductor based on the resistivity characteristics and cross-sectional area of ​​the conductor material, and assigning the equivalent resistance and equivalent radius of the conductor to the metal bracket, grounding grid, DC cable, equipment grounding conductor, inverter equivalent conductor, grounding fault detector equivalent conductor, and injection conductor, respectively. The cable coating parameters are used to characterize the electrical properties of the outer insulation layer of DC positive and DC negative cables. By setting the coating resistivity and coating thickness, the electrical properties of the outer insulation layer of DC cables are characterized.

8. The simulation calculation method according to claim 1, characterized in that, The soil parameters include soil resistivity, which is used to characterize the conductive environment of the area where the photovoltaic power station is located, and in the three-dimensional simulation model, it characterizes the conductivity of the current when it is released into the soil through the metal structure.

9. The simulation calculation method according to claim 1, characterized in that, The current source excitation is used to simulate the normal operation of the DC side of the photovoltaic power station. By applying an equivalent current input to the DC positive cable and DC negative cable, the current enters the metal support system through the injection conductor and is naturally shunted between the metal support, the equipment grounding conductor, the grounding grid and the soil.

10. The simulation calculation method according to claim 1, characterized in that, The DC steady-state condition is characterized by setting the operating frequency of the simulation model to zero; the total stray current is determined based on the longitudinal current flowing into the ground fault detector branch and the longitudinal current flowing into the connecting wire between the equipment grounding conductor and the grounding grid. The three-dimensional simulation model is performed using a software platform that supports three-dimensional conductor modeling and current distribution solving.

Images