A method and system for simulating power flow of a bidirectional converter-energy storage system

Abstract

The present invention relates to the field of subway power flow simulation calculation, and more specifically, to a method and system for simulating power flow of a bidirectional converter-energy storage combined system. The method for simulating power flow of a bidirectional converter-energy storage combined system proposed in the present invention comprises the following steps: step S1, inputting traction substation equipment information, train information, network parameters and simulation step size; step S2, calculating the node conductance matrix; step S3, iteratively calculating the network node voltage; step S4, iteratively calculating the traction substation operating condition; step S5, processing the critical point of the state of charge of the energy storage system and calculating the correction step size. The present invention establishes equivalent models of the voltage source and power source of the bidirectional converter and the energy storage system respectively based on the output characteristics of the bidirectional converter and the energy storage system, and considers the respective operating characteristics of the bidirectional converter and the energy storage system, and proposes a variety of operating condition switching strategies to enable the bidirectional converter and the energy storage system to work together, which is used for energy consumption analysis of the subway under the new power supply mode.

Description

Technical Field

[0001] The present invention relates to the field of subway power flow simulation calculation, and more particularly to a power flow simulation method and system for a bidirectional converter-energy storage combined system. Background Art

[0002] Smart urban rail transit is a crucial component of future smart city development. Bidirectional converters are the core equipment for active power supply and an effective way to achieve smart power supply.

[0003] At present, domestic and foreign universities and enterprises have conducted extensive research on bidirectional converters. Considering that directly feeding back regenerative braking energy to the medium-voltage ring network is not conducive to improving energy conservation and alleviating the pressure on traction substation output, many traction substations are equipped with energy storage systems.

[0004] Figure 1 The principle block diagram of a typical bidirectional converter-energy storage system is revealed, such as Figure 1 As shown, the traction substation 100 is equipped with a bidirectional converter 110 and an energy storage system 120. The energy storage system 120 is used to provide power support and energy storage to reduce the loss of braking energy in the intermediate flow link, while absorbing the peak power of the traction substation 100 to ensure a more stable rectifier output.

[0005] The bidirectional converter-energy storage system combines a bidirectional converter with energy storage. Its electrical wiring is similar to the existing subway system consisting of a 24-pulse uncontrolled rectifier and an energy feedback device (referred to as the existing system). The difference is that the bidirectional converter replaces the 24-pulse uncontrolled rectifier in the existing system, and the energy storage system replaces the energy feedback device in the existing system.

[0006] Power flow simulation calculation is an indispensable and important part in the field of power analysis, providing a data basis for quantitative data analysis.

[0007] Power flow calculation in DC traction systems is an important technical means to achieve smart power supply in smart urban rail. Currently, there is no power flow calculation that considers energy storage equipment in the full-line bidirectional converter active power supply system.

[0008] Currently, subway power flow simulations are performed only on combinations of 24-pulse rectifiers and inverter feedback devices or energy storage. Bidirectional converters are not included, nor is power flow simulation of a combined system of bidirectional converters and energy storage across the entire line.

[0009] With the development of smart urban rail and electronic devices, active power supply methods represented by bidirectional converters will inevitably become mainstream. Therefore, there is an urgent need for a power flow simulation method and system for a bidirectional converter-energy storage combined system to guide this new power supply method. Summary of the Invention

[0010] The purpose of the present invention is to provide a method and system for simulating power flow of a bidirectional converter-energy storage system, so as to solve the technical problem that it is difficult to perform power flow simulation on the bidirectional converter-energy storage system in the prior art.

[0011] To achieve the above objectives, the present invention provides a method for simulating power flow in a bidirectional converter-energy storage system, comprising the following steps:

[0012] Step S1: input traction substation equipment information, train information, network parameters and simulation step size;

[0013] Step S2: Calculate the node conductance matrix based on network parameters, train location, and traction substation location;

[0014] Step S3, iteratively calculating the network node voltage using the traction substation state and the node conductance matrix;

[0015] Step S4: iteratively calculating the traction substation operating condition based on the network node voltage and the traction substation status;

[0016] Step S5: Process the critical point of the state of charge of the energy storage system, calculate the correction step size, and enter step S3 until the correction step size is 0, ending the entire simulation calculation process.

[0017] In one embodiment, in step S1:

[0018] The traction substation equipment information includes the distance of the traction substation relative to the reference starting point, the total number of traction substations, the rated power of the bidirectional converter, the voltage regulation target value of the bidirectional converter, the minimum operating voltage threshold of the energy storage, the energy storage discharge voltage threshold, the energy storage charging voltage threshold, and the maximum operating voltage threshold of the energy storage;

[0019] The train information includes the distance of the up train relative to the reference starting point and the number of vehicles in the up train, and the distance of the down train relative to the reference starting point and the number of vehicles in the down train;

[0020] The network parameters include the contact network unit resistance, the running rail unit resistance and the track-to-ground leakage unit resistance;

[0021] The simulation step is the minimum duration of a single section and is used to describe the duration of a section.

[0022] In one embodiment, in step S2, the node conductance matrix Y corresponds to the expression:

[0023]

[0024] Where Y represents the node conductance matrix, subscript S represents the traction substation, subscript U represents the up train, subscript D represents the down train, and 0 represents the zero matrix.

[0025] In one embodiment, the step S3 further includes the following steps:

[0026] Step S31: Calculate the node injection current according to the traction substation status;

[0027] Step S32: Calculate the node voltage based on the node injection current, the traction substation state, and the node conductance matrix. Repeat the above steps iteratively until the difference between the two node voltages is less than the specified threshold, and then proceed to step S4.

[0028] In one embodiment, in step S31, when the traction substation equipment is in the power source mode, the node injection current is calculated according to the network node voltage and the train power. The node injection current I corresponds to the expression:

[0029]

[0030] Where P is the equipment power, U net is the grid voltage of the corresponding component.

[0031] In one embodiment, in step S31, when the traction substation equipment is in voltage source mode, the value of the node injection current I is a constant voltage value of the equipment.

[0032] In one embodiment, in step S32, the node voltage U corresponds to the expression:

[0033] U (k) =(Y) -1 I (k-1)

[0034] Where k is the number of iterations, I is the node injection current, and Y represents the node conductance matrix.

[0035] In one embodiment, the step S4 further includes the following steps:

[0036] Step S41: Calculate the current I of the bidirectional converter according to the state of the traction substation and the node voltage obtained in step S32. B and the current I of the energy storage system E , the corresponding expression is:

[0037]

[0038]

[0039] Where, I s is the total current of the traction substation, P BN and P EN are the rated output powers of the bidirectional conversion and energy storage systems respectively;

[0040] Step S42: Calculate the actual output power and state of charge of the bidirectional converter and the energy storage system;

[0041] Step S43: updating the traction substation operating condition according to the voltage, current, and output power of the bidirectional converter and the energy storage system and the traction substation grid voltage;

[0042] Step S44: If the operating condition of the traction substation after the update in step S43 is consistent with that in the last iteration, proceed to step S5; otherwise, proceed to step S3.

[0043] In one embodiment, the expression corresponding to the actual output power of the bidirectional converter and the energy storage system in step S42 is:

[0044] P B =U net I B

[0045] P E =U net I E

[0046] Where U net is the grid voltage of the traction substation, I B and I E are the currents of the bidirectional converter and the energy storage system, P B and P E are the output powers of the bidirectional converter and the energy storage system respectively.

[0047] In one embodiment, the state of charge corresponding to the charging and discharging behavior of the energy storage system in step S42 is expressed as follows:

[0048] SOC(t)=SOC(tT)+P c (t)*T*n c / W cn

[0049] SOC(t)=SOC(tT)-P d (t)*T / (n d *W cn )

[0050] Where t is the current calculation time, T is the time step, P c and P dare the energy storage charging power and discharging power respectively; n c and n d are the energy storage charging and discharging efficiency respectively; W cn is the capacity of the energy storage system.

[0051] In one embodiment, in step S43, the traction substation operating condition is switched according to a preset switching rule, and the traction substation operating condition further includes:

[0052] The first working condition is that only the bidirectional converter works, which is equivalent to power and absorbs electrical energy;

[0053] The second working condition is that both the bidirectional converter and the energy storage system are working, which is equivalent to a power source and absorbs electrical energy;

[0054] The third operating condition is that both the bidirectional converter and the energy storage system are working, which is equivalent to a voltage source and absorbs electrical energy;

[0055] The fourth working condition is that only the bidirectional converter works, which is equivalent to a voltage source;

[0056] The fifth working condition is that both the bidirectional converter and the energy storage system are working, which is equivalent to a voltage source and releases electrical energy;

[0057] The sixth operating condition is that both the bidirectional converter and the energy storage system are working, which are equivalent to power sources and release electrical energy;

[0058] The seventh working condition is that only the bidirectional converter works, which is equivalent to a power source and releases electrical energy.

[0059] In one embodiment, the step S5 further includes the following steps:

[0060] Step S51: If the difference between the state of charge value of the traction substation and the upper limit of the state of charge is within a specified threshold range, then calculating the time for all traction substation energy storage systems to reach the upper limit of the state of charge;

[0061] If the difference between the state of charge value of the traction substation and the lower limit of the state of charge is within the specified threshold, the time for the traction substation energy storage system to reach the lower limit of the state of charge is calculated;

[0062] Step S52: Take the minimum time Δt among all the times obtained in step S51 and calculate the correction step length Dt;

[0063] Step S53: If the correction step size Dt is equal to 0, then the entire simulation calculation process is terminated; otherwise, the state of charge of the energy storage system is updated according to the new calculation step size Dt, and the process proceeds to step S3.

[0064] In one embodiment, in step S51, the time when all traction substation energy storage systems reach the upper limit of the state of charge is expressed as follows:

[0065]

[0066] Where i is the number of the energy storage element, t is the current calculation time, T is the time step, P c is the energy storage charging power, n c is the energy storage charging efficiency, W cn is the energy storage system capacity, SOC max The upper limit of the state of charge.

[0067] In one embodiment, in step S51, the time when the energy storage of the traction substation reaches the lower limit of the state of charge is expressed as follows:

[0068]

[0069] Where i is the number of the energy storage element; t is the current calculation time, T is the time step, P d is the energy storage discharge power, n d is the energy storage discharge efficiency, W cn is the energy storage system capacity, SOC min It is the lower limit of the state of charge.

[0070] In one embodiment, in step S52, the corresponding expression of the modified step length Dt is as follows:

[0071] Dt=min(Δt1,Δt2,...,Δt n )

[0072] T=T-Dt

[0073] Where Dt is the correction step, i is the number of the energy storage element, t is the current calculation time, and T is the time step.

[0074] To achieve the above objectives, the present invention provides a bidirectional converter-energy storage system power flow simulation system, comprising:

[0075] a memory for storing instructions executable by the processor;

[0076] A processor is configured to execute the instructions to implement any of the methods described above.

[0077] In order to achieve the above object, the present invention provides a computer-readable medium having computer instructions stored thereon, wherein when the computer instructions are executed by a processor, any of the above methods is executed.

[0078] The present invention proposes a power flow simulation method and system for a bidirectional converter-energy storage system for energy consumption analysis in subways under new power supply modes. Based on the output characteristics of the bidirectional converter and energy storage system, equivalent models of their voltage source and power source are established, respectively. Taking into account the operating characteristics of each bidirectional converter and energy storage system, multiple operating condition switching strategies for the bidirectional converter and energy storage system are proposed. Furthermore, a critical point handling method is provided for the energy storage system's State of Charge (SOC). The power flow simulation method, which integrates the above strategies, enables the bidirectional converter and energy storage system to work together and better reflect actual operating conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] The above and other features, properties and advantages of the present invention will become more apparent through the following description in conjunction with the accompanying drawings and embodiments, in which like reference numerals represent like features throughout, wherein:

[0080] Figure 1 The principle block diagram of a typical bidirectional converter-energy storage system is revealed;

[0081] Figure 2 A flow chart of a method for simulating power flow in a bidirectional converter-energy storage system according to an embodiment of the present invention is disclosed;

[0082] Figure 3 A schematic diagram of the operating mode switching of a bidirectional converter-energy storage system according to an embodiment of the present invention is disclosed;

[0083] Figure 4 A principle block diagram of a power flow simulation system for a bidirectional converter-energy storage combined system according to an embodiment of the present invention is disclosed. DETAILED DESCRIPTION

[0084] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the invention and are not intended to limit the invention.

[0085] Figure 2 A flow chart of a method for simulating power flow of a bidirectional converter-energy storage system according to an embodiment of the present invention is disclosed. Figure 2 As shown, the present invention proposes a method for simulating power flow of a bidirectional converter-energy storage system, comprising the following steps:

[0086] Step S1: input traction substation equipment information, train information, network parameters and simulation step size;

[0087] Step S2: Calculate the node conductance matrix based on network parameters, train location, and traction substation location;

[0088] Step S3, iteratively calculating the network node voltage using the traction substation state and the node conductance matrix;

[0089] Step S4: iteratively calculating the traction substation operating condition based on the network node voltage and the traction substation status;

[0090] Step S5: Process the critical point of the state of charge of the energy storage system, calculate the correction step size, and enter step S3 until the correction step size is 0, ending the entire simulation calculation process.

[0091] Each step is described in detail below.

[0092] Step S1: Input traction substation equipment information, train information, network parameters and simulation step size.

[0093] The traction substation equipment information includes the distance of the traction substation relative to the reference starting point, the total number of traction substations, the rated power of the bidirectional converter, the voltage regulation target value of the bidirectional converter, the minimum operating voltage threshold of the energy storage, the energy storage discharge voltage threshold, the energy storage charging voltage threshold, and the maximum operating voltage threshold of the energy storage;

[0094] The train information includes the distance of the up train relative to the reference starting point and the number of vehicles in the up train, and the distance of the down train relative to the reference starting point and the number of vehicles in the down train;

[0095] The network parameters include the contact network unit resistance, the running rail unit resistance and the track-to-ground leakage unit resistance;

[0096] The simulation step is the minimum duration of a single section and is used to describe the duration of a section.

[0097] Step S2: Calculate the node conductance matrix Y based on network parameters, train location, and traction substation location.

[0098] Among them, the corresponding expression of the node conductance matrix Y is:

[0099]

[0100] Where Y represents the node conductance matrix, subscript S represents the traction substation, subscript U represents the up train, subscript D represents the down train, and 0 represents the zero matrix.

[0101] Step S3: Iteratively calculate the network node voltage using the traction substation state and the node conductance matrix.

[0102] The step S3 further comprises the following steps:

[0103] Step S31, calculating the node injection current I according to the traction substation status;

[0104] According to the output characteristics of the bidirectional converter and energy storage device, the equivalent models of their voltage source and power source are established respectively.

[0105] When the traction substation equipment is in power source mode, the node injection current is calculated based on the network node voltage and train power.

[0106] At this time, the node injection current I value is the rated power value of the bidirectional converter divided by the port voltage, that is, calculated according to formula (2);

[0107] The corresponding expression of the node injection current I is:

[0108]

[0109] Where P is the equipment power, and the equipment includes bidirectional converter, energy storage and train;

[0110] U net is the grid voltage of the corresponding component;

[0111] I is the node injection current, including the traction substation injection current and the train injection current;

[0112] When the traction substation equipment is in voltage source mode, the node injection current I value is the constant voltage value of the equipment.

[0113] Step S32: Calculate the node voltage based on the node injection current, the traction substation state, and the node conductance matrix. Repeat the above steps iteratively until the difference between the two node voltages is less than the specified threshold, and then proceed to step S4.

[0114] The corresponding expression of node voltage U is:

[0115] U (k) =(Y) -1 I (k-1) (3)

[0116] Where k is the number of iterations;

[0117] U is the node voltage vector, including the traction network node voltage and the rail node voltage;

[0118] I is the node injection current vector, including the traction substation injection current and the train injection current.

[0119] When U (k) with U (k+1) When the voltage difference is less than the specified threshold, it is considered that the voltage iterative calculation is completed and the process proceeds to step S4; otherwise, the process proceeds to step S31.

[0120] Step S4: Iteratively calculate the traction substation operating condition based on the network node voltage and the traction substation status.

[0121] The step S4 further comprises the following steps:

[0122] Step S41: Calculate the current I of the bidirectional converter according to (4) and (5) based on the state of the traction substation and the network node voltage obtained in step S32. B and the current I of the energy storage system E , the corresponding expression is:

[0123]

[0124]

[0125] Where, I s is the total current of the traction substation;

[0126] I B and I E are the currents of the bidirectional converter and the energy storage system respectively;

[0127] P BN and P EN are the rated output powers of the bidirectional conversion and energy storage systems respectively.

[0128] Step S42: Calculate the actual output power and SOC status of the bidirectional converter and the energy storage system.

[0129] The expression corresponding to the actual output power of the bidirectional converter and energy storage system is:

[0130] P B =U net I B (6)

[0131] P E =U net I E (7)

[0132] Where U net The grid voltage of the traction substation;

[0133] I B and I E are the currents of the bidirectional converter and the energy storage system respectively;

[0134] P B and P E are the output powers of the bidirectional converter and the energy storage system respectively.

[0135] The SOC corresponding to the charging and discharging behavior of the energy storage system is calculated by (8) and (9) respectively.

[0136] SOC(t)=SOC(tT)+P c (t)*T*nc / W cn (8)

[0137] SOC(t)=SOC(tT)-P d (t)*T / (n d *W cn ) (9)

[0138] Where t is the current calculation time;

[0139] T is the time step;

[0140] P c and P d are the energy storage charging power and discharging power respectively;

[0141] n c and n d are the energy storage charging and discharging efficiencies, respectively;

[0142] W cn is the capacity of the energy storage system.

[0143] Step S43: Update the traction substation operating condition according to the voltage, current and output power of the bidirectional converter and energy storage and the traction substation grid voltage.

[0144] Figure 3 The schematic diagram of the working state switching of the bidirectional converter-energy storage system according to an embodiment of the present invention is disclosed. Figure 3 As shown, the traction substation operating condition is switched according to the preset switching rules. The traction substation operating condition is defined as follows:

[0145] The first operating condition BPEC0 is when only the bidirectional converter works, which is equivalent to power and absorbs electric energy.

[0146] In the second operating condition, BPECP, both the bidirectional converter and the energy storage system are working, which are equivalent to power sources and absorb electrical energy.

[0147] In the third working condition, BUECU is in the state where both the bidirectional converter and the energy storage system are working, which is equivalent to a voltage source and absorbs electrical energy.

[0148] In the fourth operating condition BUE0, only the bidirectional converter works, which is equivalent to a voltage source.

[0149] The fifth operating condition BUEDU is when both the bidirectional converter and the energy storage system are working, which is equivalent to a voltage source and releases electrical energy.

[0150] In the sixth operating condition BPEDP, both the bidirectional converter and the energy storage system are working, which are equivalent to power sources and release electrical energy.

[0151] In the seventh operating condition, BPED0, only the bidirectional converter operates, acting as a power source and releasing electrical energy. Cflag and Dflag indicate whether the energy storage system can charge or discharge, depending on the SOC state.

[0152] P s and I s are the power and current of traction substation respectively, P BN and P EN are the rated powers of the bidirectional converter and energy storage system respectively, U e is the actual voltage of the energy storage system, U min and U max They are the minimum and maximum operating voltages of the energy storage system respectively, and “||” represents the logical “OR”.

[0153] like Figure 3 The switching principles of the bidirectional converter-energy storage system under various operating conditions are shown. The arrows above indicate the switching rules. Specifically:

[0154] If the current state is in the first operating condition BPEC0, and I s >0 and Cflag=1, then jump to the second working state BPECP;

[0155] If the current state is in the first operating condition BPEC0, and I s >0 and Cflag=0, then jump to the fourth working state BUE0;

[0156] If the current state is in the second operating condition BPECP, and U e >U max Or Cflag=0, then jump to the first working state BPEC0;

[0157] If the current state is in the second operating condition BPECP, and I s >0 and Cflag=1, then jump to the third working condition BUECU;

[0158] If the current state is in the third working state BUECU, and Cflag=0, then jump to the first working state BPEC0;

[0159] If the current state is in the third working condition BUECU, and Cflag=1 and I s >0 and P s >P BN +P EN , then jump to the second working condition BPECP;

[0160] If the current state is in the third working condition BUECU, and Cflag=1 and I s >0, jump to the fourth working state BUE0;

[0161] The switching rules for several working conditions of releasing electric energy on the other side are the same as Figure 3 As shown, no further details are given here.

[0162] Step S44: If the operating condition of the traction substation after the update in step S43 is consistent with that in the last iteration, proceed to step S5; otherwise, proceed to step S3.

[0163] Step S5: Process the critical point of the state of charge of the energy storage system, calculate the correction step size, and enter step S3 until the correction step size is 0, ending the entire simulation calculation process.

[0164] The step S5 further comprises the following steps:

[0165] Step S51: If the difference between the state of charge value of the traction substation and the SOC upper limit value is within the specified threshold range, that is, the traction substation is close to the SOC upper limit, then the time for the energy storage of all traction substations to reach the SOC upper limit is calculated using formula (10);

[0166] If the difference between the state of charge value of the traction substation and the SOC lower limit value is within the specified threshold, that is, the traction substation is close to the SOC lower limit, then (11) is used to calculate the time when the traction substation energy storage reaches the SOC lower limit.

[0167] The corresponding expressions are as follows:

[0168]

[0169]

[0170] Where i is the number of the energy storage element;

[0171] t is the current calculation time;

[0172] T is the time step;

[0173] P c and P d are the charging power and discharging power of the energy storage system respectively;

[0174] n d and n c are the discharge and charging efficiencies of the energy storage system, respectively;

[0175] W cn is the capacity of the energy storage system;

[0176] SOC max and SOC min are the upper and lower limits of SOC respectively.

[0177] Step S52: Take the minimum time Δt among all the times obtained in step S51, and use (12) to calculate the modified step length Dt. The corresponding expression is as follows:

[0178] Dt=min(Δt1,Δt2,...,Δt n ) (12)

[0179] T=T-Dt (13)

[0180] Where Dt is the correction step length;

[0181] i is the number of the energy storage element;

[0182] t is the current calculation time, and T is the time step.

[0183] Step S53: If Dt is equal to 0, the calculation is terminated; otherwise, the energy storage SOC is updated according to the new calculation step size, and the process goes to step S3 for iterative calculation.

[0184] Figure 4 A block diagram of a bidirectional converter-energy storage system power flow simulation system according to one embodiment of the present invention is disclosed. The bidirectional converter-energy storage system power flow simulation system may include an internal communication bus 401, a processor 402, a read-only memory (ROM) 403, a random access memory (RAM) 404, a communication port 405, and a hard disk 407. The internal communication bus 401 enables data communication between components of the bidirectional converter-energy storage system power flow simulation system. The processor 402 can make judgments and issue prompts. In some embodiments, the processor 402 may be composed of one or more processors.

[0185] Communication port 405 enables data transmission and communication between the bidirectional converter-energy storage system power flow simulation system and external input / output devices. In some embodiments, the bidirectional converter-energy storage system power flow simulation system can send and receive information and data from the network via communication port 405. In some embodiments, the bidirectional converter-energy storage system power flow simulation system can transmit and communicate with external input / output devices in a wired manner via input / output port 406.

[0186] The bidirectional converter-energy storage system power flow simulation system may also include various forms of program storage units and data storage units, such as a hard disk 407, a read-only memory (ROM) 403, and a random access memory (RAM) 404, capable of storing various data files used for computer processing and / or communication, as well as possible program instructions executed by the processor 402. The processor 402 executes these instructions to implement the main part of the method. The results processed by the processor 402 are transmitted to an external output device via a communication port 405 and displayed on the user interface of the output device.

[0187] For example, the implementation process file of the above-mentioned bidirectional converter-energy storage system power flow simulation method can be a computer program, stored in the hard disk 407, and can be recorded in the processor 402 for execution to implement the method of the present application.

[0188] When the implementation process file of the bidirectional converter-energy storage combined system power flow simulation method is a computer program, it can also be stored in a computer-readable storage medium as a product. For example, a computer-readable storage medium may include, but is not limited to, a magnetic storage device (e.g., a hard disk, a floppy disk, a magnetic strip), an optical disk (e.g., a compact disk (CD), a digital versatile disk (DVD)), a smart card, and a flash memory device (e.g., an electrically erasable programmable read-only memory (EPROM), a card, a stick, a key drive). In addition, the various storage media described herein can represent one or more devices and / or other machine-readable media for storing information. The term "machine-readable medium" may include, but is not limited to, wireless channels and various other media (and / or storage media) that can store, contain, and / or carry code and / or instructions and / or data.

[0189] The bidirectional converter-energy storage system power flow simulation method and system proposed in the present invention have the following beneficial effects:

[0190] 1) Based on the output characteristics of the bidirectional converter and energy storage device, their equivalent models are established respectively, and a power flow calculation model of the bidirectional converter-energy storage combined system is constructed. The power flow model is mainly composed of component models, and the calculation process involves the solution strategy of the present invention, which facilitates the energy consumption analysis and calculation of the bidirectional converter-energy storage combined system;

[0191] 2) Based on the operating conditions of the bidirectional converter and energy storage system, seven operating conditions of the traction substation are proposed, and switching strategies between different operating conditions are given to ensure the effective convergence of the algorithm proposed in this paper;

[0192] 3) A critical point simulation duration correction strategy for the energy storage system is proposed, which is not only applicable to the method proposed in this invention, but can also be used for reference in all simulation calculations involving energy storage SOC constraints.

[0193] Although the above methods are illustrated and described as a series of acts for simplicity of explanation, it is to be understood and appreciated that these methods are not limited by the order of the acts, as some acts may occur in a different order and / or concurrently with other acts from those illustrated and described herein or not illustrated and described herein but understandable to those skilled in the art according to one or more embodiments.

[0194] As used in this application and the claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" are not intended to refer to the singular but may include the plural. Generally speaking, the terms "comprises" and "include" only indicate the inclusion of the steps and elements specifically identified, and these steps and elements do not constitute an exclusive list. A method or apparatus may also include other steps or elements.

[0195] The above embodiments are provided to persons familiar with the art for implementing or using the present invention. Personnel familiar with the art may make various modifications or changes to the above embodiments without departing from the inventive concept of the present invention. Therefore, the scope of protection of the present invention is not limited to the above embodiments, but should be the maximum scope of the innovative features mentioned in the claims.

Claims

1. A method for simulating power flow of a bidirectional converter-energy storage system, characterized in that: The following steps are involved: Step S1: input traction substation equipment information, train information, network parameters and simulation step size; Step S2: Calculate the node conductance matrix based on network parameters, train location, and traction substation location; Step S3, iteratively calculating the network node voltage using the traction substation state and the node conductance matrix; Step S4: iteratively calculating the traction substation operating condition based on the network node voltage and the traction substation status; Step S5: Process the critical point of the state of charge of the energy storage system, calculate the correction step size, and enter step S3 until the correction step size is 0, ending the entire simulation calculation process; Wherein, the step S5 further includes the following steps: Step S51: If the difference between the state of charge value of the traction substation and the upper limit of the state of charge is within a specified threshold range, then calculating the time for all traction substation energy storage systems to reach the upper limit of the state of charge; If the difference between the state of charge value of the traction substation and the lower limit of the state of charge is within the specified threshold, the time for the traction substation energy storage system to reach the lower limit of the state of charge is calculated; Step S52: Take the minimum time Δt among all the times obtained in step S51 and calculate the correction step length Dt; Step S53: If the correction step size Dt is equal to 0, then the entire simulation calculation process is terminated; otherwise, the state of charge of the energy storage system is updated according to the new calculation step size Dt, and the process proceeds to step S3.

2. The method for simulating power flow of a bidirectional converter-energy storage system according to claim 1, wherein: In the step S1: The traction substation equipment information includes the distance of the traction substation relative to the reference starting point, the total number of traction substations, the rated power of the bidirectional converter, the voltage regulation target value of the bidirectional converter, the minimum operating voltage threshold of the energy storage, the energy storage discharge voltage threshold, the energy storage charging voltage threshold, and the maximum operating voltage threshold of the energy storage; The train information includes the distance of the up train relative to the reference starting point and the number of vehicles in the up train, and the distance of the down train relative to the reference starting point and the number of vehicles in the down train; The network parameters include the contact network unit resistance, the running rail unit resistance and the track-to-ground leakage unit resistance; The simulation step is the minimum duration of a single section and is used to describe the duration of a section.

3. The method for simulating power flow of a bidirectional converter-energy storage system according to claim 1, wherein: In step S2, the node conductance matrix Y corresponds to the expression: Where Y represents the node conductance matrix, subscript S represents the traction substation, subscript U represents the up train, subscript D represents the down train, and 0 represents the zero matrix.

4. The method for simulating power flow of a bidirectional converter-energy storage system according to claim 1, wherein: The step S3 further comprises the following steps: Step S31: Calculate the node injection current according to the traction substation status; Step S32: Calculate the node voltage based on the node injection current, the traction substation state, and the node conductance matrix. Repeat the above steps iteratively until the difference between the two node voltages is less than the specified threshold, and then proceed to step S4.

5. The method for simulating power flow of a bidirectional converter-energy storage system according to claim 4, characterized in that: In step S31, when the traction substation equipment is in the power source mode, the node injection current is calculated according to the network node voltage and the train power. The node injection current I corresponds to the expression: Where P is the equipment power, U net is the grid voltage of the corresponding component.

6. The method for simulating power flow of a bidirectional converter-energy storage system according to claim 4, characterized in that: In step S31, when the traction substation equipment is in voltage source mode, the node injection current I value is the constant voltage value of the equipment.

7. The method for simulating power flow of a bidirectional converter-energy storage system according to claim 4, characterized in that: In step S32, the node voltage U corresponds to the expression: U (k) =(Y) -1 I (k-1) Where k is the number of iterations, I is the node injection current, and Y represents the node conductance matrix.

8. The method for simulating power flow of a bidirectional converter-energy storage system according to claim 1, wherein: The step S4 further comprises the following steps: Step S41: Calculate the current I of the bidirectional converter according to the state of the traction substation and the node voltage obtained in step S32. B and the current I of the energy storage system E , the corresponding expression is: Where, I s is the total current of the traction substation, P BN and P EN are the rated output powers of the bidirectional conversion and energy storage systems respectively; Step S42: Calculate the actual output power and state of charge of the bidirectional converter and the energy storage system; Step S43: updating the traction substation operating condition according to the voltage, current, and output power of the bidirectional converter and the energy storage system and the traction substation grid voltage; Step S44: If the operating condition of the traction substation after the update in step S43 is consistent with that in the last iteration, proceed to step S5; otherwise, proceed to step S3.

9. The method for simulating power flow of a bidirectional converter-energy storage system according to claim 8, characterized in that: The expression corresponding to the actual output power of the bidirectional converter and the energy storage system in step S42 is: P B =U net AND B P E =U net AND E Where U net is the grid voltage of the traction substation, I B and I E are the currents of the bidirectional converter and the energy storage system, P B and P E are the output powers of the bidirectional converter and the energy storage system respectively.

10. The method for simulating power flow of a bidirectional converter-energy storage system according to claim 8, wherein: The state of charge corresponding to the charging and discharging behavior of the energy storage system in step S42 is expressed as follows: SOC(t)=SOC(t-T)+P c (t)*T*n c / W cn SOC(t)=SOC(t-T)-P d (t)*T / (n d *W cn ) Where t is the current calculation time, T is the time step, P c and P d are the energy storage charging power and discharging power respectively; n c and n d are the energy storage charging and discharging efficiency respectively; W cn is the capacity of the energy storage system.

11. The method for simulating power flow of a bidirectional converter-energy storage system according to claim 8, wherein: In step S43, the traction substation operating condition is switched according to a preset switching rule, and the traction substation operating condition further includes: The first working condition is that only the bidirectional converter works, which is equivalent to power and absorbs electrical energy; The second working condition is that both the bidirectional converter and the energy storage system are working, which is equivalent to a power source and absorbs electrical energy; The third operating condition is that both the bidirectional converter and the energy storage system are working, which is equivalent to a voltage source and absorbs electrical energy; The fourth working condition is that only the bidirectional converter works, which is equivalent to a voltage source; The fifth working condition is that both the bidirectional converter and the energy storage system are working, which is equivalent to a voltage source and releases electrical energy; The sixth operating condition is that both the bidirectional converter and the energy storage system are working, which are equivalent to power sources and release electrical energy; The seventh working condition is that only the bidirectional converter works, which is equivalent to a power source and releases electrical energy.

12. The method for simulating power flow of a bidirectional converter-energy storage system according to claim 1, wherein: In step S51, the time when all traction substation energy storage systems reach the upper limit of the state of charge is expressed as follows: Where i is the number of the energy storage element, t is the current calculation time, T is the time step, P c is the energy storage charging power, n c is the energy storage charging efficiency, W cn is the energy storage system capacity, SOC max The upper limit of the state of charge.

13. The method for simulating power flow of a bidirectional converter-energy storage system according to claim 1, wherein: In step S51, the time when the energy storage of the traction substation reaches the lower limit of the charge state is expressed as follows: Where i is the number of the energy storage element; t is the current calculation time, T is the time step, P d is the energy storage discharge power, n d is the energy storage discharge efficiency, W cn is the energy storage system capacity, SOC min It is the lower limit of the state of charge.

14. The method for simulating power flow of a bidirectional converter-energy storage system according to claim 1, wherein: In step S52, the corresponding expression of the modified step length Dt is as follows: Dt=min(Δt1,Δt2,...,Δt n ) T=T-Dt Where Dt is the correction step, i is the number of the energy storage element, t is the current calculation time, and T is the time step.

15. A bidirectional converter-energy storage system power flow simulation system, comprising: a memory for storing instructions executable by the processor; A processor, configured to execute the instructions to implement the method according to any one of claims 1 to 14.

16. A computer-readable medium having computer instructions stored thereon, wherein when the computer instructions are executed by a processor, the method according to any one of claims 1 to 14 is performed.

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