Reliability analysis method for distributed photovoltaic access railway through line power supply system

Abstract

The invention discloses a reliability analysis method for a distributed photovoltaic access railway through line power supply system, and the method comprises the steps: firstly, carrying out the theoretical analysis of the reason for the access of a photovoltaic power generation system to the railway through line power supply system to influence the electric energy quality; secondly, considering multiple power quality items such as voltage deviation, voltage fluctuation and waveform distortion, and designing a reliability comprehensive evaluation index based on entropy weight calculation; building a railway through line power supply system simulation model; then, the influence of the grid-connected capacity and the grid-connected position of a single distributed photovoltaic power generation system on the power supply reliability of the railway through line is researched; and finally, considering the large-scale development of the distributed photovoltaic power generation system, exploring the influence of multiple distributed photovoltaic accesses on the power supply reliability of the railway through line, and respectively analyzing the influence of multiple distributed access modes such as centralized tail end distribution, uniform distribution, progressive increase distribution and progressive decrease distribution on the power supply reliability of the power supply system of the railway through line.

Description

Technical Field

[0001] The invention belongs to the technical field of photovoltaic access to railway power supply, and in particular relates to a reliability analysis method for a distributed photovoltaic access to railway through-line power supply system. Background Art

[0002] Railways are an important mode of travel and freight transportation. With the development of the national economy, the scale of the railway system continues to expand. Against the background of continuous improvement in the level of electrification and the continuous development of high-speed and heavy-load rail transit, the railway system has gradually become a major energy consumer, and its energy consumption will continue to increase. In order to achieve my country's dual carbon goals of "carbon peak" and "carbon neutrality", it is urgent to strengthen energy conservation, emission reduction and pollution prevention in the railway field, optimize the transportation energy structure, promote the introduction of new energy into the railway power supply system, achieve energy conservation and emission reduction, green operation, and reduce carbon emissions.

[0003] In recent years, photovoltaic power generation technology and power electronics technology have been continuously developed and matured. Due to their own architectural layout and structural characteristics, high-speed rail stations and along the way have the advantage of laying photovoltaic panels on a large area. Domestic and foreign railway traction power supply systems and railway-related infrastructure systems have gradually begun to use photovoltaic power generation for power supply, achieving the purpose of energy conservation, emission reduction and optimization of energy structure. There are two main ways to connect photovoltaic power to the railway power supply system: connecting to the 27.5kV traction power supply system to supply power to train loads or connecting to the 10kV through-line power supply system to supply power to stations and basic equipment along the way. Although photovoltaic power generation has the advantages of flexibility, renewable, green and low-carbon, it is limited by uncontrollable natural factors, the output power fluctuates greatly, and the inverter in the photovoltaic power generation equipment contains a large number of power electronic equipment. Photovoltaic access will change the system flow and affect the power quality. Therefore, it is necessary to analyze the impact of distributed photovoltaic access to the railway through-line power supply system on power quality.

[0004] Photovoltaic access to distribution networks is one of the important research directions in the field of clean energy. Currently, a large amount of research work has been carried out worldwide, which can be roughly divided into four categories. The first is the access technology between photovoltaic power generation systems and distribution networks, mainly studying the design and control strategy of photovoltaic grid-connected inverters; the second is the site selection and capacity determination of photovoltaic power generation systems and the power management and coordinated control of multiple photovoltaic power stations; the third is the combination of energy storage technology and photovoltaic power generation systems, and the reasonable configuration of energy storage equipment; the fourth is the research on the safety and stability of photovoltaic power generation systems connected to distribution networks, focusing on the voltage and frequency control of photovoltaic power generation systems and the failure and recovery of power grids, power grid protection and other issues, to ensure that the intervention of photovoltaic power generation systems does not have an adverse impact on the operation of the power grid. The roadbed slopes, railway bridges, access roads, sound barriers, etc. unique to the railway system have created excellent conditions for the full utilization of photovoltaic power generation resources.

[0005] However, at present, these four types of research work are mostly used for civil purposes. Considering the relevant architectural features, transmission characteristics, energy demand, etc. of high-speed railways, there are relatively few studies on connecting photovoltaics to the railway through-line power supply system. In addition, the capacity, location and access methods of distributed photovoltaics to the railway power supply system rarely consider the impact of different access methods on power supply reliability, which is not conducive to the railway power supply system to select the optimal distributed photovoltaic access plan. There is a lack of research on the reliability evaluation indicators of distributed photovoltaic power generation systems connected to the railway power supply system, which is not conducive to the large-scale development of photovoltaics in the railway field. Summary of the invention

[0006] In order to solve the above problems, the present invention proposes a reliability analysis method for a distributed photovoltaic access to a railway through-line power supply system, which evaluates the impact of different large-scale photovoltaic access schemes on the power quality of the railway power supply system, and provides a reliable basis for the railway power supply system to select the capacity, location and access method of distributed photovoltaic access.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a reliability analysis method for a distributed photovoltaic access railway through-line power supply system, comprising the steps of:

[0008] S100, conduct theoretical analysis on the reasons why the photovoltaic power generation system connected to the railway through-line power supply system affects the power quality, and determine the characteristic parameters of power quality including voltage deviation, voltage fluctuation and waveform distortion rate;

[0009] S200, based on multiple power quality factors such as voltage deviation, voltage fluctuation and waveform distortion, establishes a comprehensive reliability evaluation index based on entropy weight calculation;

[0010] S300, builds a simulation model of the railway through-line power supply system and a photovoltaic power generation system model using maximum power point tracking;

[0011] S400, using the model to obtain the impact of the grid-connected capacity and grid-connected location of a single distributed photovoltaic power generation system on the power supply reliability of the railway through-line;

[0012] S500, based on the established comprehensive reliability evaluation index, uses the model to obtain the impact of multiple distributed photovoltaic access on the power supply reliability of the railway through-line, and analyzes the impact of multiple distributed intervention methods such as concentrated terminal distribution, uniform distribution, increasing distribution and decreasing distribution on the power supply reliability of the railway through-line power supply system.

[0013] Furthermore, in step S100, a theoretical analysis of the impact of photovoltaic power generation system access to the railway through-line power supply system on power quality is performed, including the increase in distribution network voltage caused by photovoltaic access, the impact of photovoltaic access on voltage before and after the access point, the impact of photovoltaic access on voltage fluctuations, and the impact of photovoltaic access on total harmonic distortion of voltage, so as to determine the power quality characteristic parameters including voltage deviation, voltage fluctuation and waveform distortion rate.

[0014] Furthermore, in step S200, the comprehensive reliability evaluation index calculated based on entropy weight includes multiple power quality indicators such as voltage deviation, voltage fluctuation and waveform distortion rate, and the weights of various power quality indicators in the comprehensive reliability evaluation index are determined by the entropy weight method in combination with industry-related national standards.

[0015] Furthermore, in the step S300, MATLAB / simulink is used to build a simulation model of the railway through-line power supply system, including a simulation model of the railway through-line power supply system and a simulation model of the photovoltaic power generation system; the railway through-line power supply system supplies power to the railway line through a box-type substation, and the box-type substation includes a transformer model and a load model connected to the low-voltage side; the photovoltaic power generation system achieves maximum power point tracking by dynamically matching the relationship between photovoltaic cells and loads.

[0016] Furthermore, in step S400, the impact of a single distributed photovoltaic access capacity and access location on the reliability of the railway through-line power supply system is achieved by setting different photovoltaic capacities or photovoltaic access location scenarios. The access of the photovoltaic power generation system reduces the power supply reliability of each node, wherein the larger the photovoltaic grid-connected capacity and the closer the distance, the greater the impact on the power supply reliability.

[0017] The access of a single distributed photovoltaic power generation system causes the voltage of each node to increase to a certain extent. When the access capacity is constant, the farther the distance from the access point, the less the voltage change is affected by photovoltaics; for the same node, the larger the access capacity, the greater the voltage deviation; the access of the photovoltaic power generation system will increase the total harmonic distortion rate of each node of the system. When the access photovoltaic capacity is constant, the total harmonic distortion rate of the access point is the largest. The closer to the photovoltaic access point, the larger the total harmonic distortion rate of the voltage. As the photovoltaic access capacity increases, the total harmonic distortion rate of the voltage at each node increases accordingly; the voltage fluctuation at the photovoltaic grid-connected point is the largest, and decreases with the increase of the distance from the access point, and increases with the increase of the photovoltaic grid-connected capacity.

[0018] Furthermore, in the step S500, the influence of multiple distributed photovoltaic access modes on the reliability of the railway through-line power supply system is achieved by setting multiple distributed photovoltaic power generation system distributed access mode scenarios. Multiple distributed photovoltaic access to the railway through-line power supply system will reduce the power supply reliability of the system compared with centralized access. Among the multiple distributed photovoltaic access system modes, the comprehensive index value of the decreasing distributed access is relatively small, that is, the power supply reliability of the decreasing decentralized distributed access railway through-line power supply system is relatively good.

[0019] Under the condition of a certain distributed photovoltaic access capacity, setting up distributed photovoltaic access scenarios will have an improvement effect on the feeder voltage, and the improvement effect is ranked as follows: concentrated terminal distribution > increasing distribution > uniform distribution > decreasing distribution. All four scenarios have changes in the direction of the power flow; the maximum voltage fluctuation of the system has the characteristics of concentrated terminal distribution > increasing distribution > uniform distribution > decreasing distribution; for the terminal distribution, due to the fluctuation of irradiation intensity, the output power of photovoltaic power sources is constantly changing, which has caused serious impact on the distribution network terminal. The photovoltaic grid-connected inverter will also be affected by the electric energy impact, which will lead to a significant increase in the terminal voltage waveform distortion rate. For the other three distributed access scenarios, the impact of irradiance changes on each node of the feeder is relatively evenly dispersed, showing a trend that the farther away from the bus, the greater the voltage fluctuation.

[0020] The beneficial effects of adopting this technical solution are:

[0021] The present invention uses a comprehensive evaluation index based on entropy weight calculation to evaluate and analyze the power supply reliability of the railway through-line power supply system, explores the impact of the photovoltaic power generation system connected to the railway through-line power supply system on its power supply reliability, and quantitatively analyzes the impact of distributed photovoltaic grid-connected capacity, grid-connected location and distributed access mode on power supply reliability. It summarizes the influence of photovoltaic access on the power quality of each node of the railway through-line, which can effectively improve the power supply reliability of the system;

[0022] The photovoltaic power generation system of the present invention adopts a maximum power point tracking model, and dynamically adjusts the working point of the photovoltaic power generation system by real-time monitoring of parameters such as light intensity and temperature, maximizes the system output power, and improves the power quality and reliability of the photovoltaic power generation system;

[0023] The present invention is easy to implement and provides a theoretical reference for large-scale access of distributed photovoltaic power generation systems to railway through-line power supply systems in the future while ensuring system power supply reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic flow chart of a reliability analysis method for a distributed photovoltaic access railway through-line power supply system according to the present invention;

[0025] Figure 2 A schematic diagram of a photovoltaic power generation system using maximum power point tracking in an embodiment of the present invention;

[0026] Figure 3 It is a simulation model diagram of the high-speed railway through-line power supply system in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described below with reference to the accompanying drawings.

[0028] In this embodiment, see Figure 1 As shown, the present invention proposes a reliability analysis method for a distributed photovoltaic access railway through-line power supply system, comprising the steps of:

[0029] S100, conduct theoretical analysis on the reasons why the photovoltaic power generation system connected to the railway through-line power supply system affects the power quality, and determine the characteristic parameters of power quality including voltage deviation, voltage fluctuation and waveform distortion rate;

[0030] S200, based on multiple power quality factors such as voltage deviation, voltage fluctuation and waveform distortion, establishes a comprehensive reliability evaluation index based on entropy weight calculation;

[0031] S300, builds a simulation model of the railway through-line power supply system and a photovoltaic power generation system model using maximum power point tracking;

[0032] S400, using the model to obtain the impact of the grid-connected capacity and grid-connected location of a single distributed photovoltaic power generation system on the power supply reliability of the railway through-line;

[0033] S500, based on the established comprehensive reliability evaluation index, uses the model to obtain the impact of multiple distributed photovoltaic access on the power supply reliability of the railway through-line, and analyzes the impact of multiple distributed intervention methods such as concentrated terminal distribution, uniform distribution, increasing distribution and decreasing distribution on the power supply reliability of the railway through-line power supply system.

[0034] As an optimization scheme for the above embodiment, in step S100, a theoretical analysis of the impact of the access of the photovoltaic power generation system to the railway through-line power supply system on the power quality is performed, including the increase in the voltage of the distribution network caused by photovoltaic access, the impact of the voltage before and after the photovoltaic access point, the impact of photovoltaic access on voltage fluctuations, and the impact of photovoltaic access on the total harmonic distortion rate of the voltage.

[0035] The purpose of analyzing the principle of the impact of photovoltaic power generation system connected to the railway through-line power supply system on power quality is to lay a theoretical foundation for the subsequent establishment of a comprehensive reliability evaluation system based on power quality.

[0036] For voltage deviation, due to the existence of impedance on the feeder, when the distributed photovoltaic is connected to the distribution network, the power flow changes, resulting in voltage offset. For voltage fluctuation, due to the serious uncertainty and volatility of light, temperature, etc., the photovoltaic power generation power is also greatly affected by them. After the photovoltaic is connected to the distribution network, it will cause power fluctuations in the system, thereby causing voltage fluctuations in the distribution network. For waveform distortion, photovoltaic power generation converts DC to AC through an inverter. Frequent use of power electronic devices will generate various harmonic components. During the photovoltaic injection process, the harmonic current flowing through the line impedance will generate a corresponding voltage drop, which will cause voltage distortion.

[0037] As an optimization scheme for the above embodiment, in step S200, the comprehensive reliability evaluation index calculated based on entropy weight includes multiple power quality indicators such as voltage deviation, voltage fluctuation and waveform distortion rate, and the weights of various power quality indicators in the comprehensive reliability evaluation index are determined by the entropy weight method in combination with industry-related national standards.

[0038] Voltage deviation, voltage fluctuation and waveform distortion are selected as the characteristic parameters of power quality to be evaluated. The hierarchical analysis method based on entropy value is used to analyze the location, capacity and distributed access mode of photovoltaic access to the railway distribution network. Entropy weight determination steps:

[0039] Step 1: De-dimensionalize and normalize each evaluation index. Let the sum of the three indicators be X 1 , X 2 , X 3 …X n , where X = {x 1 ,x 2 ,x 3 …x m}. The standardized value of each indicator data is Y 1 , Y 2 , Y 3 …Y n

[0040]

[0041] Step 2: Find the ratio of each indicator under each evaluation project, that is, the proportion of the jth indicator in the ith project, that is, calculate the variation of the indicator

[0042]

[0043] Step 3: Calculate the information entropy E of each indicator j

[0044]

[0045] Step 4: Calculate the weight Wj

[0046]

[0047] The specifications and standards related to the access of photovoltaic power generation systems to the power system and power quality mainly include the national standard "Technical Regulations for the Access of Photovoltaic Power Stations to the Power System" (GB / T19964-2012), "Technical Specifications for the Evaluation of Characteristics of Photovoltaic Power Generation Systems Accessed to Distribution Networks" (GB / T31999-2015) and the railway industry standard "Railway Power Design Specifications" (TB 10008-2015). The hierarchical analysis method described above designs various mandatory restrictions according to the provisions of the above standards to avoid damage to the system under extreme circumstances.

[0048] Voltage deviation, voltage fluctuation and waveform distortion are selected as characteristic parameters of power quality. The hierarchical analysis method based on entropy value to determine weights is used for analysis to evaluate the location, capacity and distributed access mode of photovoltaic access to the railway distribution network. The specifications and standards related to the access of photovoltaic power generation systems to the power system and power quality mainly include the national standard "Technical Regulations for the Access of Photovoltaic Power Stations to the Power System" (GB / T19964-2012), "Technical Specifications for the Evaluation of Characteristics of Photovoltaic Power Generation Systems Accessed to Distribution Networks" (GB / T31999-2015) and the railway industry standard "Railway Power Design Specifications" (TB10008-2015). The hierarchical analysis method described above designs various mandatory restrictions according to the provisions of the above standards to avoid damage to the system under extreme conditions.

[0049] As an optimization scheme for the above embodiment, in step S300, MATLAB / simulink is used to build a railway through-line power supply system simulation model, including a railway through-line power supply system simulation model and a photovoltaic power generation system simulation model; the railway through-line power supply system supplies power to the railway line through a box-type substation, and the box-type substation includes a transformer model and a load model connected to the low-voltage side; the photovoltaic power generation system achieves maximum power point tracking by dynamically matching the relationship between photovoltaic cells and loads.

[0050] The transformer model in the railway through-line power supply system uses a 10 / 0.4kV dry-type transformer. The primary side of the transformer is set to a delta connection mode, and the secondary side is set to a star connection mode. The load is represented by a three-phase parallel RLC load model, and the distribution feeder is represented by a three-phase series RLC branch model; the photovoltaic power generation system simulation model connects the output of the photovoltaic array through a cascaded DC / DC converter. The controller controls the on and off of the switch in the DC / DC converter by changing the duty cycle of the PWM pulse, thereby converting the fixed DC voltage into a variable DC voltage, thereby changing the characteristics of the load. Dynamically match the relationship between the photovoltaic cell and the load to achieve maximum power point tracking.

[0051] See also Figure 2 The figure shows a schematic diagram of a photovoltaic power generation system using maximum power point tracking, which consists of a photovoltaic cell array, a maximum power tracking device, a maximum power point tracking controller and a DC / DC converter. The photovoltaic cell array is used as the basic unit of energy conversion to convert solar radiation energy into DC power; the maximum power point tracking device monitors the voltage and current changes of the photovoltaic array in real time and transmits the changes to the controller. The PWM controller controls the on and off of the switch in the DC / DC converter by changing the duty cycle of the PWM pulse, thereby converting the fixed DC voltage into a variable DC voltage, thereby changing the characteristics of the load, dynamically matching the relationship between the photovoltaic cell and the load, and realizing maximum power point tracking.

[0052] See also Figure 3 As shown, it is a simulation model diagram of the power supply system of the high-speed railway through-line, which consists of a distribution station, a through-line, a box-type substation and a load model. The high-speed railway distribution station is a two-input and four-output model. The up and down lines are connected to a comprehensive through-line and a primary through-line respectively through a voltage regulator. The distribution station uses a transformer to supply power to its load, and the model is simplified into a power supply and a voltage regulator model; the transmission line model is mainly a concentrated parameter model and a distributed parameter model. The characteristics of the two types of line models are similar when the line is short. When the line is long, its distributed characteristics will increase significantly with the increase of length. The present invention uses a distributed parameter model for research; the high-speed railway through-line uses a box-type substation to supply power to the loads along the line. The box-type substation includes a transformer model and a load model connected to the low-voltage side. 10 / 0.4kV dry-type transformers are used in the box-type substations. The primary side adopts a triangle connection method, and the secondary side adopts a star connection method. The load is simulated by a power source in which the inductive reactive power and active power are connected in series.

[0053] As an optimization scheme for the above embodiment, in step S400, the model is used to obtain the influence of the grid-connected capacity and grid-connected location of a single distributed photovoltaic power generation system on the power supply reliability of the railway through-line; and simulation verification is performed by setting different grid-connected capacity and grid-connected location scenarios.

[0054] The impact of a single distributed photovoltaic access capacity and access location on the reliability of the railway through-line power supply system is achieved by setting different photovoltaic capacity or photovoltaic access location scenarios. The access of photovoltaic power generation systems reduces the power supply reliability of each node. The larger the photovoltaic grid-connected capacity and the closer the distance, the greater the impact on power supply reliability. The access of a single distributed photovoltaic power generation system increases the voltage of each node to a certain extent. When the access capacity is constant, the farther the distance from the access point, the less the voltage change is affected by photovoltaics; for the same node, the larger the access capacity, the greater the voltage deviation; the access of photovoltaic power generation systems will increase the total harmonic distortion rate of each node of the system. When the access photovoltaic capacity is constant, the total harmonic distortion rate of the access point is the largest. The closer the distance to the photovoltaic access point, the larger the total harmonic distortion rate of the voltage is. As the photovoltaic access capacity increases, the total harmonic distortion rate of the voltage at each node increases accordingly; the voltage fluctuation at the photovoltaic grid-connected location is the largest, and decreases with the increase of the distance from the access point, and increases with the increase of the photovoltaic grid-connected capacity.

[0055] As an optimization scheme for the above embodiment, in step S500, based on the established comprehensive reliability evaluation index, a model is used to obtain the impact of multiple distributed photovoltaic accesses on the power supply reliability of the railway through-line, and the impact of multiple distributed intervention methods such as concentrated terminal distribution, uniform distribution, increasing distribution and decreasing distribution on the power supply reliability of the railway through-line power supply system are analyzed respectively.

[0056] The impact of multiple distributed photovoltaic access modes on the reliability of the railway through-line power supply system is achieved by setting up multiple distributed photovoltaic power generation system distributed access mode scenarios. Compared with centralized access, multiple distributed photovoltaic access to the railway through-line power supply system will reduce the power supply reliability of the system. Among the multiple distributed photovoltaic access system modes, the comprehensive index value of the decreasing distributed access is relatively small, that is, the power supply reliability of the decreasing decentralized distributed access to the railway through-line power supply system is relatively good. Under the condition of a certain distributed photovoltaic access capacity, setting up distributed photovoltaic access scenarios will have an improvement effect on the feeder voltage, and the improvement effect is ranked as follows: concentrated terminal distribution > increasing distribution > uniform distribution > decreasing distribution. All four scenarios have changes in the direction of the power flow; the maximum voltage fluctuation of the system has the characteristics of concentrated terminal distribution > increasing distribution > uniform distribution > decreasing distribution; for the terminal distribution, due to the fluctuation of irradiation intensity, the output power of photovoltaic power sources is constantly changing, which has caused serious impact on the distribution network terminal. The photovoltaic grid-connected inverter will also be affected by the electric energy impact, which will lead to a significant increase in the terminal voltage waveform distortion rate. For the other three distributed access scenarios, the impact of irradiance changes on each node of the feeder is relatively evenly dispersed, showing a trend that the farther away from the bus, the greater the voltage fluctuation.

[0057] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A reliability analysis method for a distributed photovoltaic access railway through-line power supply system, characterized in that: Includes steps: S100, conduct theoretical analysis on the reasons why the photovoltaic power generation system connected to the railway through-line power supply system affects the power quality, and determine the characteristic parameters of power quality including voltage deviation, voltage fluctuation and waveform distortion rate; S200, based on multiple power quality factors such as voltage deviation, voltage fluctuation and waveform distortion, establishes a comprehensive reliability evaluation index based on entropy weight calculation; S300, builds a simulation model of the railway through-line power supply system and a photovoltaic power generation system model using maximum power point tracking; S400, using the model to obtain the impact of the grid-connected capacity and grid-connected location of a single distributed photovoltaic power generation system on the power supply reliability of the railway through-line; S500, based on the established comprehensive reliability evaluation index, uses the model to obtain the impact of multiple distributed photovoltaic access on the power supply reliability of the railway through-line, and analyzes the impact of multiple distributed intervention methods such as concentrated terminal distribution, uniform distribution, increasing distribution and decreasing distribution on the power supply reliability of the railway through-line power supply system.

2. According to claim 1, a reliability analysis method for a distributed photovoltaic access railway through-line power supply system is characterized in that: In step S100, a theoretical analysis of the impact of photovoltaic power generation system access to the railway through-line power supply system on power quality is performed, including the increase in distribution network voltage caused by photovoltaic access, the impact of photovoltaic access on voltage before and after the access point, the impact of photovoltaic access on voltage fluctuation, and the impact of photovoltaic access on voltage total harmonic distortion rate, so as to determine power quality characteristic parameters including voltage deviation, voltage fluctuation and waveform distortion rate.

3. According to claim 1, a reliability analysis method for a distributed photovoltaic access railway through-line power supply system is characterized in that: In step S200, the comprehensive reliability evaluation index calculated based on entropy weight includes multiple power quality indicators such as voltage deviation, voltage fluctuation and waveform distortion rate, and the weight of each power quality in the comprehensive reliability evaluation index is determined by the entropy weight method in combination with industry-related national standards.

4. According to claim 1, a reliability analysis method for a distributed photovoltaic access railway through-line power supply system is characterized in that: In the step S300, MATLAB / simulink is used to build a railway through-line power supply system simulation model, including a railway through-line power supply system simulation model and a photovoltaic power generation system simulation model; the railway through-line power supply system supplies power to the railway line through a box-type substation, and the box-type substation includes a transformer model and a load model connected to the low-voltage side; the photovoltaic power generation system achieves maximum power point tracking by dynamically matching the relationship between photovoltaic cells and loads.

5. According to claim 1, a reliability analysis method for a distributed photovoltaic access railway through-line power supply system is characterized in that: In step S400, the impact of a single distributed photovoltaic access capacity and access location on the reliability of the railway through-line power supply system is achieved by setting different photovoltaic capacities or photovoltaic access location scenarios. The access of the photovoltaic power generation system reduces the power supply reliability of each node. The larger the photovoltaic grid-connected capacity and the closer the distance, the greater the impact on the power supply reliability. The access of a single distributed photovoltaic power generation system causes the voltage of each node to increase to a certain extent. When the access capacity is constant, the farther the distance from the access point, the less the voltage change is affected by photovoltaics; for the same node, the larger the access capacity, the greater the voltage deviation; the access of the photovoltaic power generation system will increase the total harmonic distortion rate of each node of the system. When the access photovoltaic capacity is constant, the total harmonic distortion rate of the access point is the largest. The closer to the photovoltaic access point, the larger the total harmonic distortion rate of the voltage. As the photovoltaic access capacity increases, the total harmonic distortion rate of the voltage at each node increases accordingly; the voltage fluctuation at the photovoltaic grid-connected point is the largest, and decreases with the increase of the distance from the access point, and increases with the increase of the photovoltaic grid-connected capacity.

6. A reliability analysis method for a distributed photovoltaic access railway through-line power supply system according to claim 1, characterized in that: In the step S500, the influence of multiple distributed photovoltaic access modes on the reliability of the railway through-line power supply system is achieved by setting multiple distributed photovoltaic power generation system distributed access mode scenarios. Multiple distributed photovoltaic access to the railway through-line power supply system will reduce the power supply reliability of the system compared with centralized access. In the multiple distributed photovoltaic access system modes, the comprehensive index value of the decreasing distributed access is relatively small, that is, the power supply reliability of the decreasing decentralized distributed access railway through-line power supply system is relatively good. Under the condition of a certain distributed photovoltaic access capacity, setting up distributed photovoltaic access scenarios will have an improvement effect on the feeder voltage, and the improvement effect is ranked as follows: concentrated terminal distribution > increasing distribution > uniform distribution > decreasing distribution. All four scenarios have changes in the direction of the power flow; the maximum voltage fluctuation of the system has the characteristics of concentrated terminal distribution > increasing distribution > uniform distribution > decreasing distribution; for the terminal distribution, due to the fluctuation of irradiation intensity, the output power of photovoltaic power sources is constantly changing, which has caused serious impact on the distribution network terminal. The photovoltaic grid-connected inverter will also be affected by the electric energy impact, which will lead to a significant increase in the terminal voltage waveform distortion rate. For the other three distributed access scenarios, the impact of irradiance changes on each node of the feeder is relatively evenly dispersed, showing a trend that the farther away from the bus, the greater the voltage fluctuation.

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