A power flow calculation method for a direct current traction power supply system based on a ground feedback device

Abstract

The application discloses a kind of based on ground feedback device's direct current traction power supply system power flow calculation method, the method comprises: reading the data file of t time, and sorting to all line nodes;Based on first basic configuration parameter, the first equivalent model of rectifier substation is established;Based on second basic configuration parameter, according to the working condition of ground feedback device, the second equivalent model of ground feedback device is obtained;Generation node admittance network equation, and carry out direct current traction power supply system power flow calculation, output t time direct current traction power supply system power flow calculation result.The direct current traction power supply system power flow calculation method proposed in the application fully considers the operating characteristics and limit working condition of ground feedback device, can adapt to the current engineering scene of widely used ground feedback device, has higher engineering guidance value and practical significance.

Description

Technical Field

[0001] This invention relates to the field of rail transit power supply technology, and in particular to a power flow calculation method for a DC traction power supply system based on a ground feedback device. Background Technology

[0002] The braking system of urban rail transit trains includes electric braking and mechanical braking. When a train begins to brake, electric braking is usually used. The traction motor switches from motor mode to generator mode, converting the kinetic energy of the vehicle into electrical energy to generate braking force. When the speed drops to a certain value, the electric braking switches back to mechanical braking. When using electric braking, the regenerated energy is fed back to the DC traction network for use by other trains; this is called regenerative braking. However, the electrical energy from regenerative braking is generally not completely absorbed by other trains running on the line, and it can cause an increase in the DC traction network voltage. If the DC traction network voltage rises above the safety threshold, it may cause overvoltage damage to equipment or even trigger a system-level failure. Therefore, it is necessary to install regenerative braking energy utilization devices to absorb or feed back excess regenerative braking energy, thereby controlling the grid voltage within the rated value.

[0003] Currently, there are three main types of devices for utilizing regenerative braking energy: braking resistors, ground-based energy storage devices, and ground-based feedback devices. Braking resistors dissipate excess regenerative braking energy as heat, which not only wastes a significant amount of energy but also increases the pressure on the environmental control system due to the heat trapped in the train or tunnel. Urban rail transit, with its large capacity, short station intervals, and frequent vehicle starts and stops, consumes a large amount of braking energy in braking resistors, resulting in significant energy waste. Ground-based energy storage devices use supercapacitor banks or energy storage components such as lithium batteries and nickel-metal hydride batteries connected in parallel with the traction network via a bidirectional DC / DC converter. These devices use the traction network voltage as a criterion, storing and reusing braking energy through charging and discharging to stabilize the traction network voltage. While utilizing excess regenerative braking energy on the DC traction side and stabilizing the traction network voltage, these devices are costly and bulky. The ground-based regenerative braking device is installed in the traction substation and connected to the DC traction network. It converts the remaining regenerative braking energy into AC, which is then input into the 35kV urban rail medium-voltage ring network or the 400V station power system via an isolation transformer. The energy from the ground-based regenerative braking device has the advantages of high feedback efficiency and reactive power compensation function, and its overall cost performance is higher than that of ground-based energy storage devices.

[0004] Current domestic research on ground-based power feedback devices mainly focuses on the device's control strategies, main circuit topology, transmission characteristics, and power quality control, while research on their modeling in traction power supply system power flow simulation analysis is relatively limited. With the increasing prevalence of ground-based power feedback devices in urban rail traction power supply systems, their system design has become a pressing issue in traction power supply design. Modeling and power flow analysis simulation of traction power supply systems incorporating ground-based power feedback devices are fundamental to completing related traction power supply calculations, optimizing the location, capacity, and quantity of ground-based power feedback devices, and evaluating the energy feedback effect. Therefore, fully considering the role of ground-based power feedback devices in traction power supply system power flow calculations is of significant value for system design and operational optimization. Summary of the Invention

[0005] The purpose of this invention is to provide a power flow calculation method for a DC traction power supply system based on a ground feedback device, so as to solve the problem that existing power flow calculation methods do not fully consider the ground feedback device and are difficult to adapt to the current widespread application scenarios of the ground feedback device.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a power flow calculation method for a DC traction power supply system based on a ground feedback device, the method comprising the following steps:

[0007] S1: Read the data file at time t and sort all the nodes. The data file at time t includes the first basic configuration parameters of the DC traction power supply system, the second basic configuration parameters of the ground feedback device, and the train operation parameters at time t.

[0008] S2: Based on the first basic configuration parameters, establish the first equivalent model of the rectifier substation; based on the second basic configuration parameters, obtain the second equivalent model of the ground feedback device according to the operating conditions of the ground feedback device;

[0009] S3: Based on the train operating parameters at time t, the initial current of each train car, the parameters of the first equivalent model, and the parameters of the second equivalent model, generate the nodal admittance network equation;

[0010] S4: Based on the node admittance network equation, perform power flow calculation of the DC traction power supply system and output the power flow calculation results of the DC traction power supply system at time t.

[0011] By reading system configuration parameters and real-time train operation data, equivalent models of the rectifier substation and ground feedback device are established respectively. Based on node information, train initial current and equivalent model parameters, node admittance network equations are constructed and power flow calculation is completed. Finally, the system power flow results are obtained through iteration.

[0012] Furthermore, in S1, the DC traction power supply system includes multiple rectifier substations and a DC traction network. Based on the number and location information of trains and rectifier substations, the nodes along the entire line are sorted, making the power flow calculation method of the present invention applicable to traction power supply systems with multiple power supply zones and complex topologies, which is more in line with actual engineering application scenarios.

[0013] Furthermore, in S2, a first equivalent model of the rectifier substation is established based on the external characteristic curve of the rectifier substation, which more accurately reflects the electrical output characteristics of the rectifier substation.

[0014] Furthermore, in S2, the process of establishing the first equivalent model of the rectifier substation includes: determining the equivalent DC voltage and equivalent internal resistance of the rectifier substation, wherein the initial operating range of each rectifier substation is set as the first operating range, and the equivalent voltage and equivalent internal resistance of the first operating range are calculated to provide initial calculation parameters for power flow calculation.

[0015] Furthermore, the process of obtaining the second equivalent model of the ground feedback device includes:

[0016] when or At that time, the rectifier unit is turned off, and the ground feedback device does not operate;

[0017] when and At that time, the rectifier unit is turned off, the ground feedback device is operated, and the voltage of the DC-side equivalent voltage source of the ground feedback device is... Power of the AC-side PQ node ;

[0018] when and At that time, the rectifier unit is turned off, the ground feedback device is operated, and the power of the DC-side equivalent power source of the ground feedback device is... Power of the AC-side PQ node ;

[0019] when At that time, the rectifier unit is turned off and the ground feedback device is disconnected;

[0020] when At that time, the rectifier unit is turned on, and the ground feedback device is in forward traction. The ground feedback device is equivalent to a voltage source, and the voltage of the voltage source is... ;

[0021] in, U d and P d These represent the DC bus voltage and power of the DC traction network, respectively. U dmaxand U dmin These are the upper and lower threshold values ​​for the DC traction network bus voltage, respectively. U on_hk , U off_hk , P s_hk , η These are the threshold voltage of the ground-based energy feedback device, the regeneration failure threshold voltage, the system capacity, and the energy feedback efficiency. P L The rated active power of the substation load, U qianyin This is the positive traction threshold voltage.

[0022] A second equivalent model is established based on the full-condition external characteristics of the ground feedback device. This eliminates the need for complex modeling, effectively reduces modeling complexity, and improves modeling and solution efficiency, making the model more suitable for power flow calculation.

[0023] Furthermore, in S3, the calculation process for the initial current of each train car includes: treating the train as a constant power source, setting the initial voltage of each train car to the rated voltage of the DC traction network, and calculating the initial current of each train car to provide initial current calculation parameters for power flow iteration.

[0024] Furthermore, in S4, the power flow calculation of the DC traction power supply system includes adaptively adjusting the first equivalent model of the rectifier substation. Specific steps include:

[0025] S4.1: Determine whether the DC voltage of each rectifier substation is within the corresponding threshold limit for that rectifier substation:

[0026] If the DC voltage of the rectifier substation exceeds the limit threshold, the first equivalent model is adjusted to the turn-off model, the node admittance network equations are regenerated, and power flow calculation is performed.

[0027] If the DC voltage of the rectifier substation is within the specified threshold, proceed to S4.2;

[0028] S4.2: Determine whether the load current of each rectifier substation corresponds to the current operating range; if they correspond, continue to the next rectifier substation; if they do not correspond, proceed to S4.3.

[0029] S4.3: Adjust the working range of the rectifier substation to the next working range, calculate the equivalent DC voltage and equivalent internal resistance of the adjusted working range, regenerate the nodal admittance network equations and perform power flow calculations;

[0030] S4.4: The online adaptive adjustment of the rectifier substation model ends when the load current of all rectifier substations corresponds to the current operating range.

[0031] By adaptively adjusting the first equivalent model of the rectifier substation, the equivalent voltage and equivalent internal resistance can be dynamically updated according to the real-time operating status of the system, effectively avoiding calculation errors caused by model mismatch and improving the reliability and engineering practicality of power flow calculation.

[0032] Furthermore, by redefining the second equivalent model before each power flow calculation, the model parameters can be matched with the current operating state of the system.

[0033] Furthermore, in S4, after the adaptive adjustment of the first equivalent model of the rectifier substation is completed, the train voltage iterative calculation is performed, specifically including the following steps:

[0034] 4.5.1: Determine if the train node voltage has converged; if it has converged, the train voltage iterative calculation ends; if it has not converged, proceed to 4.5.2.

[0035] 4.5.2: Based on the constant power principle, the train current is corrected using the current train node voltage, the node admittance network equations are regenerated, and power flow calculations are performed;

[0036] 4.5.3: Repeat step 4.5.1 until the train node voltage converges to ensure that the power flow calculation results are stable and accurate.

[0037] Furthermore, after S4, the data file at time t+Δt is read and transferred to S2 to realize the dynamic continuous simulation calculation of the DC traction power supply system.

[0038] Compared with existing technologies, the beneficial effects of this invention are as follows: By introducing an equivalent model of the ground feedback device into the power flow calculation of the DC traction power supply system, the power flow calculation method can be applied to the DC traction power supply system with a large number of ground feedback devices currently configured, effectively solving the problem that existing methods are difficult to adapt to changes in actual engineering scenarios; by establishing a second equivalent model based on the full-condition out-of-systems characteristics of the ground feedback device, the modeling complexity is reduced and the modeling and solution efficiency is improved, making the model more suitable for power flow calculation; by adaptively adjusting the first equivalent model of the rectifier substation, the equivalent voltage and equivalent internal resistance of the rectifier substation can be dynamically updated according to the real-time operating status of the system, effectively avoiding calculation errors caused by model mismatch, and improving the reliability and engineering practicality of the power flow calculation method. Attached Figure Description

[0039] To more clearly illustrate the technical solution of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only one embodiment of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a flowchart of the power flow calculation method for a DC traction power supply system based on a ground feedback device in an embodiment of the present invention;

[0041] Figure 2 This is a flowchart of the power flow calculation steps in an embodiment of the present invention;

[0042] Figure 3 This is a flowchart of the iterative calculation steps in an embodiment of the present invention. Detailed Implementation

[0043] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] To make the technical content of this invention easier to understand, the key technical terms in the solution are explained below:

[0045] Power flow analysis: Calculates the voltage and power distribution at various points and along various lines of an electrical network.

[0046] Regenerative braking: The energy generated during braking is fed back to the DC traction network for use by other trains starting or accelerating.

[0047] Currently, research on power flow simulation analysis methods for traction power supply systems rarely considers ground feedback devices. Research on ground feedback devices mainly focuses on their control strategies, main circuit topology, transmission characteristics, and power quality control. Therefore, this invention proposes a power flow calculation method for DC traction power supply systems that considers ground feedback devices, such as... Figure 1 As shown, the method includes the following steps:

[0048] S1: The simulation system reads the data file at time t and sorts all the nodes along the line. The data file at time t includes the first basic configuration parameters of the DC traction power supply system, the second basic configuration parameters of the ground feedback device, and the train operation parameters at time t.

[0049] First, input the basic configuration parameters of the DC traction power supply system into the human-machine interface, including the parameters of the rectifier traction substation (i.e., the rectifier substation) and the DC traction network line parameters. The rectifier substation parameters include: operating condition selection (normal operation or disconnection); the number and location of rectifier substations under different operating conditions; rectifier pulse count selection: 12 or 24; rectifier transformer primary side short-circuit capacity; rectifier unit rated capacity; rectifier transformer primary and secondary side rated voltages; rectifier transformer through-impedance voltage percentage; rectifier transformer half-through-impedance voltage percentage; rectifier substation rated voltage selection (consistent with the selected traction network rated voltage): 750V, 1500V, or 3000V, and corresponding limits. The DC traction network line parameters include: contact wire or contact rail unit length resistance; rail unit length resistance; and rail-to-ground leakage resistance. Then, input the second basic configuration parameters of the ground feedback device into the human-machine interface, including the location of the ground feedback device, threshold voltage, regenerative failure threshold voltage, system capacity, etc. The simulation system also collects train operation parameters at time t, including the number of trains going up and down at the sampling time, the train position, and the corresponding power of the train.

[0050] Based on the initial basic configuration parameters and the train operation parameters at time t, the simulation system sorts the nodes of the entire traction network according to the quantity and location information of trains, rectifier substations, and ground feedback devices. The sorting of nodes can be implemented as follows: following the route of the traction power supply system, rectifier substation nodes, ground feedback device nodes, traction network segment nodes, and train nodes are sequentially and uniformly numbered to form globally unique node serial numbers. This node sorting method can be flexibly adjusted according to the actual engineering scenario and the power supply system topology.

[0051] S2: Based on the first basic configuration parameters, establish the first equivalent model of the rectifier substation; based on the second basic configuration parameters, obtain the second equivalent model of the ground feedback device according to the operating conditions of the ground feedback device.

[0052] Based on the initial configuration parameters, an equivalent model of the rectifier substation is established according to its external characteristic curve. The initial operating range of each rectifier substation is set as the first operating range, and the equivalent voltage and equivalent internal resistance of this first operating range are calculated. For example, the operating range of the rectifier substation is divided into a constant voltage operating range, a current-limiting operating range, and a voltage-reducing protection range based on its external characteristic curve. The constant voltage operating range is the rated operating range of the rectifier substation, where the output voltage is constant and the current varies with the load. The current-limiting operating range is the overload protection range, where the output current is constant and the voltage decreases linearly. The voltage-reducing protection range is the extreme fault protection range, where the voltage drops rapidly and triggers protection action.

[0053] In this application, the specific modeling process of the first equivalent model of the rectifier substation is existing technology. Its modeling principles and methods can be found in existing publicly available literature, such as Liu Wei et al., "Cooperative Power Flow Calculation of Urban Rail Traction Power Supply System with Bidirectional Converter Device, Journal of Southwest Jiaotong University, 2023, Vol. 58, No. 5, pp. 1145-1153." This literature discloses the modeling ideas and power flow calculation methods for related equipment in the urban rail traction power supply system. The modeling process of the first equivalent model of the rectifier substation in this application can be implemented based on the existing technology disclosed in the aforementioned literature, without the need to propose a new modeling method.

[0054] Obtain the initial current of each train car: Treat the train as a constant power source. Based on the train power in the train operation parameters at time t and the rated voltage of the traction network in the second basic parameters, set the initial voltage of each train car as the rated voltage of the traction network, and calculate the initial current of each train car.

[0055] Based on the second basic configuration parameters, and according to the operating conditions of the ground feedback device, a second equivalent model of the ground feedback device is obtained. A key difference between the power flow calculation of urban rail DC traction power supply systems without ground feedback devices and the state transitions and corresponding equivalent modeling of the feedback device lies in the latter. Traditional mathematical modeling methods for ground feedback devices involve in-depth research into the electrical coupling relationships of the main circuit and control strategy, writing numerous calculus equations, deriving the mathematical model one by one, and finally selecting a suitable algorithm for solution. While this method produces relatively accurate models, it suffers from the following problems: it requires in-depth research into the coupling relationships of various electrical quantities in the ground feedback device, making modeling difficult; it requires a comprehensive understanding of the main circuit topology and control strategy, and obtaining detailed parameters; the algorithm organization is complex; the mathematical model derivation is tedious and labor-intensive; and the solution of nonlinear equations is prone to divergence and is time-consuming.

[0056] In power flow analysis and calculation of urban rail transit traction power supply systems that include ground feedback devices, the focus is usually only on the impact of the external characteristics of the ground feedback devices on the power flow distribution of the traction network. If traditional modeling methods are used in power flow calculations, the computational load per step of the power flow iteration will increase significantly, and the computation time will be greatly extended. Moreover, due to detailed modeling, a large amount of nonlinearity will be introduced, affecting the convergence of subsequent power flow iteration calculations. In addition, this type of modeling requires the configuration of a large number of fine parameters, which is difficult to calibrate and hard to adapt to actual engineering application scenarios.

[0057] Therefore, without affecting computational accuracy, and in order to reduce modeling difficulty and algorithm complexity, and improve modeling and solution efficiency, this embodiment of the invention performs equivalent modeling of the urban rail transit ground feedback device based on the external characteristics of the complete working process of each operating condition. The operating conditions include feedback operating conditions, traction operating conditions, and standby operating conditions. The specific process for obtaining the second equivalent model of the ground feedback device is as follows:

[0058] when or At that time, the rectifier unit is turned off, and the ground feedback device does not operate;

[0059] when and At that time, the rectifier unit is turned off, the ground feedback device is running, and the voltage of the DC side equivalent voltage source of the ground feedback device is... Power of the AC-side PQ node ;

[0060] when and At that time, the rectifier unit is turned off, the ground feedback device is running, and the power of the DC-side equivalent power source of the ground feedback device is... Power of the AC-side PQ node ;

[0061] when At that time, the rectifier unit is turned off and the ground feedback device is disconnected;

[0062] when At that time, the rectifier unit is turned on, and the ground feedback device is in forward traction. The ground feedback device is equivalent to a voltage source, and the voltage of the voltage source is... ;

[0063] in, U d and P d These represent the DC bus voltage and power of the traction network, respectively. U dmax and U dmin These are the upper and lower threshold values ​​for the traction network bus voltage, respectively. U on_hk , U off_hk , P s_hk , η These are the threshold voltage of the ground-based energy feedback device, the regeneration failure threshold voltage, the system capacity, and the energy feedback efficiency. P L The rated active power of the substation load, U qianyinThis is the positive traction threshold voltage. U d and P d The electrical quantities are calculated in real time for power flow iteration. The other parameters mentioned above are determined based on industry design specifications, equipment factory calibration data, and engineering design documents.

[0064] S3: Based on the train position and number of trains, the initial current of each train car, and the parameters of the first and second equivalent models in the train operation parameters at time t, generate the nodal admittance network equations. The generation, establishment, and solution calculation process of the nodal admittance network equations are existing technologies. For example, patent CN112966463B discloses an efficient simulation method for a distributed grid-connected system of converter groups, specifically disclosing the complete process in a power electronic converter grid-connected system, from calculating the equivalent admittance of equipment, constructing the nodal admittance matrix of a single equipment, assembling the system-level nodal admittance matrix, and then solving the nodal admittance network equations and obtaining the calculation results. The specific implementation principle and calculation method of the generation and calculation of the nodal admittance network equations in this application embodiment can refer to the above-mentioned existing technical solutions.

[0065] S4: Based on the node admittance network equation, perform power flow calculation of the DC traction power supply system and output the power flow calculation results of the DC traction power supply system at time t.

[0066] like Figure 2 As shown, the specific steps for power flow calculation are as follows:

[0067] S4.1: Determine whether the DC voltage of each rectifier substation is within the corresponding threshold limit for that rectifier substation:

[0068] If the DC voltage of the rectifier substation exceeds the limit threshold, the first equivalent model is adjusted to the turn-off model, the nodal admittance network equations are regenerated, and power flow calculation is performed.

[0069] If the DC voltage of the rectifier substation is within the specified threshold, proceed to S4.2;

[0070] S4.2: Determine whether the load current of each rectifier substation corresponds to the current operating range; if they correspond, continue to the next rectifier substation; if they do not correspond, proceed to S4.3.

[0071] S4.3: Adjust the working range of the rectifier substation to the next working range, calculate the equivalent DC voltage and equivalent internal resistance of the adjusted working range, regenerate the nodal admittance network equations and perform power flow calculations;

[0072] S4.4: Once the load current of all rectifier substations corresponds to the current operating range, the online adaptive adjustment of the rectifier substation model ends, and the train voltage iterative calculation phase begins.

[0073] Furthermore, the second equivalent model is redefined before each power flow calculation. The DC bus voltage of the traction network. U d Related to the DC output voltage of each rectifier substation, bus power P d It is determined by summing the output power of each operating rectifier substation and deducting line power losses.

[0074] like Figure 3 As shown, the specific process of train voltage iterative calculation includes the following steps:

[0075] 4.5.1: According to Determine if the train node voltage has converged; if it has converged, the train voltage iterative calculation ends; if it has not converged, proceed to 4.5.2.

[0076] 4.5.2: Based on the constant power principle, the train current is corrected using the current train node voltage, the node admittance network equations are regenerated, and power flow calculations are performed;

[0077] 4.5.3: Repeat step 4.5.1 until the train node voltage converges.

[0078] After the train node voltage converges, the output power flow calculation results of the DC traction power supply system at time t include the DC bus voltage of the traction network. U d Bus power P d The load current, DC output voltage, and operating range of the first equivalent model of each rectifier substation, as well as the operating status and actual feedback power of the ground feedback device.

[0079] After outputting the power flow calculation results of the DC traction power supply system at time t, the simulation system reads the data file at time t+Δt, obtains the dynamically updated train operation parameters at that time, and then switches to S2 to perform power flow calculation at time t+Δt.

[0080] This invention, in its embodiments, performs equivalent modeling of the AC and DC external characteristics of the entire working process based on the feedback, traction, and standby conditions of the ground feedback device. Furthermore, it integrates the equivalent model of the ground feedback device into the nodal admittance network equations of the large system, designing a power flow calculation process for an urban rail transit DC traction power supply system incorporating the ground feedback device.

[0081] Based on the external characteristics of the complete working process of the ground-based power feedback device under various operating conditions, this invention provides equivalent modeling for the device, offering advantages such as wide applicability and high scheme completeness. It also fully considers the extreme operating conditions where the ground-based power feedback device operates to its rated system capacity, i.e., reaching maximum feedback power or maximum traction power, thus better reflecting the actual operating conditions of the device and possessing higher engineering guidance value. Compared to traditional precise mathematical modeling methods for power feedback devices, the equivalent modeling method proposed in this invention effectively reduces modeling difficulty and algorithm complexity without affecting calculation accuracy, while improving modeling and solution efficiency. A power flow analysis process for a traction power supply system including the power feedback device is designed, providing important reference for power flow analysis software design.

[0082] The above embodiments should be understood as being used only to illustrate the present invention more clearly, and not to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

Claims

1. A method for power flow calculation of a DC traction power supply system based on ground feedback devices, characterized in that, The method comprises the following steps: S1: reading a data file at time t and sorting all line nodes, wherein the data file at time t comprises first basic configuration parameters of a direct-current traction power supply system, second basic configuration parameters of a ground feedback device, and train operation parameters at time t; S2: establishing a first equivalent model of a rectifier substation based on the first basic configuration parameters; and obtaining a second equivalent model of the ground feedback device according to a working condition of the ground feedback device based on the second basic configuration parameters; wherein the obtaining process of the second equivalent model of the ground feedback device comprises: When or the rectifier unit is switched off and the ground feedback device is not operated. When and the rectifier unit is turned off, the ground feedback device is operated, the voltage of the direct current side equivalent voltage source of the ground feedback device , the power of the alternating current side PQ node ; When and , the rectifier unit is turned off, the ground feedback device is operated, and the power of the equivalent power source on the DC side of the ground feedback device , the power of the AC side PQ node ; When the rectifier unit is turned off, the ground feedback device is disconnected. When the rectifier set is opened, the ground feedback device is forward traction, the ground feedback device is equivalent to a voltage source, the voltage ; wherein, U d with P d DC bus voltage and power of the DC traction network, respectively, U dmax and U dmin upper and lower threshold values of the DC bus voltage of the DC traction network, respectively, U on_hk , U off_hk , P s_hk , η threshold voltage of the ground feedback device, regenerative failure threshold voltage, system capacity and energy feedback efficiency, respectively, P L load rated active power of the substation, U qianyin forward traction threshold voltage; S3: generating a node admittance network equation based on the train operation parameters at time t, an initial current of each train, parameters of the first equivalent model and parameters of the second equivalent model; S4: performing direct-current traction power supply system power flow calculation based on the node admittance network equation, and outputting a direct-current traction power supply system power flow calculation result at time t.

2. The power flow calculation method of a DC traction power supply system based on a ground feedback device according to claim 1, characterized in that, In S1, the direct-current traction power supply system comprises a plurality of rectifier substations and a direct-current traction network, and all line nodes are sorted according to the number and position information of the trains and the rectifier substations.

3. The method of claim 1, wherein the method further comprises: In S2, the first equivalent model of the rectifier substation is established according to an external characteristic curve of the rectifier substation.

4. The method of claim 3, wherein the method further comprises: In S2, the establishing process of the first equivalent model of the rectifier substation comprises: determining an equivalent direct-current voltage and an equivalent internal resistance of the rectifier substation, wherein an initial working interval of each rectifier substation is set as a first working interval, and the equivalent voltage and the equivalent internal resistance of the first working interval are calculated.

5. The method of claim 1, wherein, In S3, the calculating process of the initial current of each train comprises: equivalent the train to a constant power source, and setting an initial voltage of each train as a rated voltage of the direct-current traction network, so as to calculate the initial current of each train.

6. The method of claim 1, wherein the method further comprises: In S4, the performing of the direct-current traction power supply system power flow calculation comprises adaptively adjusting the first equivalent model of the rectifier substation, and the specific steps comprise: S4.1: judging whether the direct-current voltage of each rectifier substation is within a limited threshold of the corresponding rectifier substation: If the direct-current voltage of the rectifier substation exceeds the limited threshold, the first equivalent model is adjusted to a shutdown model, the node admittance network equation is regenerated and the power flow calculation is performed again; If the direct-current voltage of the rectifier substation is within the limited threshold, S4.2 is entered; S4.2: judging whether the load current of each rectifier substation corresponds to the current working interval; if yes, the next rectifier substation is judged; if no, S4.3 is entered; S4.3: adjusting the working interval of the rectifier substation to a next working interval, calculating the equivalent direct-current voltage and the equivalent internal resistance of the adjusted working interval, regenerating the node admittance network equation and performing the power flow calculation again; S4.4: until the load currents of all rectifier substations correspond to the current working interval, the online adaptive adjustment of the rectifier substation model is ended.

7. The method of claim 6, wherein the method further comprises: Before each power flow calculation, the second equivalent model is determined again.

8. The method of claim 6, wherein the method further comprises: In S4, after the adaptive adjustment of the first equivalent model of the rectifier substation is ended, train voltage iterative calculation is performed, and the specific steps comprise: 4.5.1: Determine if the train node voltage has converged; if it has converged, the train voltage iterative calculation ends; if it has not converged, proceed to 4.5.

2. 4.5.2: Based on the constant power principle, the train current is corrected using the current train node voltage, the node admittance network equations are regenerated, and power flow calculations are performed; 4.5.3: Repeat step 4.5.1 until the train node voltage converges.

9. The method of claim 1, wherein the method further comprises: After S4, read the data file at time t+Δt and switch to S2.

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