Method for Determining Energy Storage Capacity of Traction Power Supply System Based on Comprehensive Utilization Rate

Abstract

This invention provides a method for determining the energy storage capacity of a traction power supply system based on comprehensive utilization rate, comprising the following steps: S1. Determining the operating conditions of the traction power supply system and the state of charge of the energy storage system under different operating conditions; S2. Determining the comprehensive utilization rate of regenerative braking energy of the traction power supply system under different operating conditions and different capacity configurations; S3. Fitting the comprehensive utilization rate of regenerative braking energy, the power of the energy storage system, and the rated capacity of the energy storage system to form a surface, finding the inflection point of the surface, and the capacity of the energy storage system corresponding to the inflection point is the optimal capacity; the capacity of the energy storage system is comprehensively determined based on multiple indicators such as the energy-saving effect of the traction substation, the energy recovery effect of the train's regenerative braking, and the charging and discharging utilization rate of the energy storage system, so that the capacity of the energy storage system can meet the needs of the traction power supply system.

Description

Technical Field

[0001] This invention relates to a method for determining the energy storage capacity of a power supply system, and more particularly to a method for determining the energy storage capacity of a traction power supply system based on comprehensive utilization rate. Background Technology

[0002] With the significant increase in energy consumption of the high-speed rail traction power supply system, and the fact that a large amount of regenerative braking energy is difficult to utilize effectively due to the complex operating conditions of the traction power supply system, it has to be sent back to the power grid or consumed in the braking resistor, resulting in low energy efficiency of high-speed rail station operation.

[0003] Currently, existing research typically uses technical indicators such as traction system energy saving rate, regenerative failure rate, and total system energy consumption as the basis for selecting energy storage capacity. However, these indicators only determine the energy storage system capacity from the perspective of the traction power supply system's operational performance, without considering the operational performance of the energy storage device itself. Although large-capacity energy storage systems can fully recover regenerative braking energy under high braking power conditions, the relatively short duration of this condition in the traction system means that the energy storage system is difficult to fully charge for a significant portion of the time, resulting in idle capacity and hindering the economical operation of the energy storage system.

[0004] Therefore, in order to solve the above-mentioned technical problems, it is urgent to propose a new technical approach. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for determining the energy storage capacity of a traction power supply system based on comprehensive utilization. The method comprehensively determines the capacity of the energy storage system based on multiple indicators, including the energy-saving effect of the traction substation, the energy recovery effect of the train regenerative braking, and the charging and discharging utilization rate of the energy storage system. This method ensures that the capacity of the energy storage system can meet the needs of the traction power supply system, make the energy storage system more economical, and achieve high efficiency and accuracy throughout the process.

[0006] This invention provides a method for determining the energy storage capacity of a traction power supply system based on comprehensive utilization rate, comprising the following steps:

[0007] S1. Determine the operating conditions of the traction power supply system and the state of charge of the energy storage system under different operating conditions;

[0008] S2. Determine the comprehensive utilization rate of regenerative braking energy of the traction power supply system under different operating conditions and different capacity configurations;

[0009] S3. Fit the comprehensive utilization rate of regenerative braking energy, the power of the energy storage system and the rated capacity of the energy storage system to form a surface, find the inflection point of the surface, and the capacity of the energy storage system corresponding to the inflection point is the optimal capacity.

[0010] Furthermore, in step S1, the state of charge of the energy storage system is determined using the following method:

[0011]

[0012] Among them: SOC es (k) represents the state of charge (SOCes(k-1)) of the energy storage system of the traction power supply system at time k, and SOCes(k-1) represents the state of charge (SOCes(k-1)) of the energy storage system of the traction power supply system at time k-1. s P represents the control period. es (k) represents the power of the energy storage system at time k, when P es (k) > 0 indicates a discharge state, when P es (k) < 0 indicates the charging state, Q es.n This is the rated power of the energy storage system.

[0013] Furthermore, in step S3, the overall utilization rate of regenerative braking energy is determined using the following method:

[0014]

[0015] in: To achieve the comprehensive utilization rate of regenerative braking energy, η TS η represents the energy saving rate of the substation for the traction power supply system. RBE η is the regenerative braking energy recovery rate of the train. ES η′ represents the average charge / discharge utilization rate of the energy storage system. RBE For the maximum recovery rate of regenerative braking energy, η′ TS η′ represents the maximum energy saving rate of the traction substation. ES This represents the maximum charge and discharge utilization rate of the energy storage system.

[0016] Furthermore, the energy-saving rate η of the traction substation is determined using the following method. TS :

[0017]

[0018] Where: n is the number of times the traction power supply system supplies power to the traction substation within a set period, P T.j E represents the j-th output power of the traction substation. T0 To determine the total traction energy consumption of the train within a set period, T s Indicates the control cycle.

[0019] Furthermore, the train regenerative braking energy recovery rate η is determined by the following method. RBE :

[0020]

[0021] Where: m is the number of times the energy storage system is charged within a set period, P es.i E is the power of the energy storage system during the i-th charge. z0 The total braking energy generated by the train within a set period.

[0022] Furthermore, the average charge-discharge utilization rate η of the energy storage system is determined using the following method. ES :

[0023]

[0024] Where: ΔSOC es.r This represents the difference in SOC (State of Charge) before and after the r-th charge or discharge of the energy storage system.

[0025] Furthermore, the operating conditions of the traction power supply system include full traction condition, full braking condition, equivalent traction condition, and equivalent braking condition.

[0026] The beneficial effects of this invention are as follows: By using this invention, the capacity of the energy storage system is determined comprehensively based on multiple indicators such as the energy-saving effect of the traction substation, the energy recovery effect of the train regenerative braking system, and the charging and discharging utilization rate of the energy storage system. This makes the capacity of the energy storage system not only meet the needs of the traction power supply system, but also make the energy storage system more economical. Moreover, the whole process is highly efficient and accurate. Attached Figure Description

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0028] Figure 1 This is a flowchart of the present invention.

[0029] Figure 2 This is a topology diagram of the high-speed railway station regenerative braking energy utilization system of the present invention.

[0030] Figure 3 This represents the power flow relationship under various operating conditions.

[0031] Figure 4 This refers to the regenerative braking energy recovery rate.

[0032] Figure 5 Energy saving rate of traction substation.

[0033] Figure 6 This refers to the average charge and discharge utilization rate of the energy storage system.

[0034] Figure 7 This refers to the comprehensive utilization rate of regenerative braking energy. Detailed Implementation

[0035] The present invention will be further described in detail below:

[0036] This invention provides a method for determining the energy storage capacity of a traction power supply system based on comprehensive utilization rate, comprising the following steps:

[0037] S1. Determine the operating conditions of the traction power supply system and the state of charge of the energy storage system under different operating conditions;

[0038] S2. Determine the comprehensive utilization rate of regenerative braking energy of the traction power supply system under different operating conditions and different capacity configurations;

[0039] S3. A surface is formed by fitting the comprehensive utilization rate of regenerative braking energy, the power of the energy storage system, and the rated capacity of the energy storage system. The inflection point of the surface is identified, and the capacity of the energy storage system corresponding to this inflection point is the optimal capacity. By continuously changing the capacity and power configuration of the energy storage system, the maximum capacity is reached based on the maximum daily braking power of the traction power supply system and the maximum recyclable braking energy configuration. Then, the corresponding comprehensive utilization rate is calculated, and a fitting is performed accordingly. MATLAB software is used for fitting. Through the above method, the capacity of the energy storage system is determined comprehensively based on multiple indicators such as the energy-saving effect of the traction substation, the regenerative braking energy recovery effect of the train, and the charging and discharging utilization rate of the energy storage system. This ensures that the capacity of the energy storage system can meet the needs of the traction power supply system, while also making the energy storage system more economical, and the entire process is highly efficient and accurate.

[0040] The operating conditions of the traction power supply system include full traction condition, full braking condition, equivalent traction condition, and equivalent braking condition, such as... Figure 2 As shown, the topology of the high-speed railway station regenerative braking energy utilization system is as follows: In step S1, the priority of regenerative braking energy recovery is set as follows: ① absorbed by the traction train on the other power supply arm; ② stored by the energy storage system; ③ consumed by the train braking resistor. In the regenerative braking energy utilization process, the priority of the traction power source required by the traction train is set as follows: ① regenerative braking energy generated by the braking train on the other power supply arm; ② regenerative braking energy stored in the energy storage system; ③ power supply from the public power grid via the traction transformer. Furthermore, the power flow relationship can be determined according to different operating conditions, such as... Figure 3 As shown:

[0041] In full traction mode, both the α and β phase power supply arms are in traction. At this time, the traction power supply system generates no regenerative braking energy. The energy storage system prioritizes providing energy to the traction trains on both power supply arms. When the energy storage system cannot meet the load demand, the traction substation supplements power from the public power grid.

[0042] In full braking mode, both the α and β phase power supply arms of the train are in braking condition. At this time, the regenerative braking energy generated by the train is first stored by the energy storage system. When the energy storage system reaches its upper charge limit, the remaining regenerative braking energy is consumed by the braking resistor.

[0043] In the equivalent traction condition, the trains of the α and β phase power supply arms are in traction and braking states respectively, and the power of the braking train is less than that of the traction train. The traction power supply system as a whole exhibits a traction energy consumption state. Among them, the braking power generated by the braking train is directly supplied to the traction train through the railway power regulator, and the surplus power required by the traction train is provided by the energy storage system and the traction substation.

[0044] In the equivalent braking condition, the trains in the α and β phase power supply arms are in traction and braking states respectively, and the braking train power is greater than the traction train power. The traction power supply system has residual regenerative braking energy. Therefore, the braking power generated by the braking train is preferentially used to power the traction train, and the remaining energy is stored by the energy storage system and consumed by the braking resistor.

[0045] In this embodiment, in step S1, the state of charge of the energy storage system is determined by the following method:

[0046]

[0047] Among them: SOC es (k) represents the state of charge (SOCes(k-1)) of the energy storage system of the traction power supply system at time k, and SOCes(k-1) represents the state of charge (SOCes(k-1)) of the energy storage system of the traction power supply system at time k-1. s P represents the control period. es (k) represents the power of the energy storage system at time k, when P es (k) > 0 indicates a discharge state, when P es (k) < 0 indicates the charging state, Q es.n The rated power of the energy storage system is given above. The relationship between the state of charge and the power is established. The state of charge is the ratio of the remaining capacity to the capacity in the fully charged state, thus obtaining the relationship between the capacity and the power of the energy storage system.

[0048] In this embodiment, in step S3, the overall utilization rate of regenerative braking energy is determined by the following method:

[0049]

[0050] in: To achieve the comprehensive utilization rate of regenerative braking energy, η TS η represents the energy saving rate of the substation for the traction power supply system. RBE η is the regenerative braking energy recovery rate of the train. ES η′ represents the average charge / discharge utilization rate of the energy storage system. RBE For the maximum recovery rate of regenerative braking energy, η′ TS η′ represents the maximum energy saving rate of the traction substation. ES This represents the maximum charge and discharge utilization rate of the energy storage system.

[0051] Specifically, the energy saving rate η of the traction substation is determined by the following method. TS :

[0052]

[0053] Where: n is the number of times the traction power supply system supplies power to the traction substation within a set period, P T.j E represents the j-th output power of the traction substation. T0 To determine the total traction energy consumption of the train within a set period, T s Indicates the control cycle.

[0054] The train regenerative braking energy recovery rate η is determined using the following method. RBE :

[0055]

[0056] Where: m is the number of times the energy storage system is charged within a set period, P es.i E is the power of the energy storage system during the i-th charge. z0 The total braking energy generated by the train within a set period.

[0057] The average charge / discharge utilization rate η of the energy storage system is determined using the following method. ES :

[0058]

[0059] Where: ΔSOC es.r This represents the difference in SOC (State of Charge) before and after the r-th charge or discharge of the energy storage system.

[0060] In this embodiment, Figure 4 The regenerative braking energy recovery rate of the train under different capacity configurations is shown. It can be seen that when the initial power and capacity configuration are 5MW and 0.5MWh, the system's regenerative braking energy recovery rate is 25.46%. As the rated energy storage power P... es.n With rated capacity Q es.n The increase of η RBE Rapidly increasing P significantly improves the regenerative braking energy recovery effect. es.n Increased to 29.5MW, Q es.n When increased to 3.12 MWh, η RBE It can reach 90%. Then, continue to increase energy storage power and capacity configuration, η RBE Growth is slow and gradually levels off, when P es.n Increase to P es.max For 55MW, Q es.n Increase to Q es.max When the value is 6MWh, η RBEIt can reach 99.92%. Therefore, as the capacity configuration increases, η... RBE After increasing to a certain extent, it will tend to level off.

[0061] In this embodiment Figure 5 The energy-saving rate of traction substations under different capacity configurations is shown, and it can be seen that, compared with... Figure 5 The changing trends are the same. Under the initial power and capacity configuration, the energy saving rate of the traction substation is 5.74%, and with P... es.n Q es.n Increased to 28MW, 3MWh, η TS Rapidly increase to 20%, then continue to increase power and capacity configuration, η TS The growth is slow. When the regenerative braking energy recovery rate is 99.92%, the maximum energy saving rate of the system is 22.53%. This indicates that the energy saving rate of the traction substation is closely related to the regenerative braking energy recovery rate. The more regenerative braking energy recovered by the energy storage system, the more traction load can be shared by the traction substation under traction conditions, thus achieving energy saving in the traction substation.

[0062] In this embodiment Figure 6 The average charge / discharge utilization rate of the energy storage system under different capacity configurations is shown. It can be seen that, under the initial configuration, the average charge / discharge utilization rate of the energy storage system is 54.08%, meaning that during the study period, the average charge / discharge capacity of the energy storage system per cycle is approximately 54% of its rated capacity. Q es.n Certainly, with P es.n Increased to 55MW, η ES It continued to increase to 78.22%; P es.n Certainly, with Q es.n Increased to 6MWh, η ES It continued to decrease to 12.78%. When Q es.n When the capacity is greater than 4MWh, the average charge and discharge utilization rate of the energy storage system is less than 30%, which means that the energy storage system is difficult to fully charge most of the time, and most of its capacity is idle, resulting in a waste of capacity.

[0063] In this embodiment Figure 7 This demonstrates the average charge and discharge utilization rate of energy storage systems under different capacity configurations, and the overall η under different capacity configurations. RBE η TS and η ES It is known that the higher the power and capacity of the energy storage system, the better the recovery of regenerative braking energy and the energy-saving effect of the traction substation. However, the operating characteristics of traction trains can also lead to idle capacity in large-capacity energy storage systems. Therefore, combining... Figure 7 The comprehensive utilization rate of regenerative braking energy determines the capacity of the energy storage system. The specific process is as follows: Q es.n At a certain time, With Pes.n The increase of P is rapid, but when P increases es.n When >27.5MW, The growth rate slows down and tends to stabilize; therefore, considering the cost-effectiveness of energy storage configuration, the rated power of the energy storage system can be determined to be 27.5MW. When P es.n At that time, by Figure 7 We can obtain, With Q es.n The increase of Q first increases and then decreases. es.n At 2.5MWh, The maximum value of 75.25% was reached, therefore the rated capacity of the energy storage system was determined to be 2.5 MWh.

[0064] Table 1 compares the evaluation indicators of each unit of the system under different capacity configurations. It can be seen that under the initial capacity configuration, the energy-saving effect of the traction substation and the regenerative braking energy recovery effect of the train are poor. Although the average charge-discharge utilization rate of the energy storage system is relatively high, it also means that the battery's charge-discharge depth is large, which will accelerate battery aging and capacity decay during long-term operation. Under the maximum capacity configuration, the energy-saving effect of the traction substation and the regenerative braking energy recovery effect of the train are the best, but the average charge-discharge utilization rate of the energy storage system is only 22.05%. Although the large capacity configuration reduces the depth of each charge-discharge cycle, the battery is difficult to fully charge most of the time, resulting in idle capacity. Therefore, compared with the initial capacity configuration and the maximum capacity configuration, the energy storage system capacity determined based on the comprehensive utilization rate can ensure that the working effect of each unit of the regenerative braking energy utilization system (source-load-storage) is better.

[0065] Table 1

[0066]

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for determining the energy storage capacity of a traction power supply system based on comprehensive utilization rate, characterized in that: Includes the following steps: S1. Determine the operating conditions of the traction power supply system and the state of charge of the energy storage system under different operating conditions; S2. Determine the comprehensive utilization rate of regenerative braking energy of the traction power supply system under different operating conditions and different capacity configurations; S3. Fit the comprehensive utilization rate of regenerative braking energy, the power of the energy storage system and the rated capacity of the energy storage system to form a surface, find the inflection point of the surface, and the capacity of the energy storage system corresponding to the inflection point is the optimal capacity. The overall utilization rate of regenerative braking energy is determined by the following method: in: To achieve the comprehensive utilization rate of regenerative braking energy, η TS η represents the energy saving rate of the substation for the traction power supply system. RBE η is the regenerative braking energy recovery rate of the train. ES η′ represents the average charge / discharge utilization rate of the energy storage system. RBE For the maximum recovery rate of regenerative braking energy, η′ TS η′ represents the maximum energy saving rate of the traction substation. ES To maximize the charge and discharge utilization rate of the energy storage system; The train regenerative braking energy recovery rate η is determined using the following method. RBE : Where: m is the number of times the energy storage system is charged within a set period, P es.i E is the power of the energy storage system during the i-th charge. z0 The total braking energy generated by the train within a set period; The average charge / discharge utilization rate η of the energy storage system is determined using the following method. ES : Where: △SOC es.r The difference in SOC before and after the r-th charge or discharge of the energy storage system; The energy-saving rate η of the traction substation is determined using the following method. TS : Where: n is the number of times the traction power supply system supplies power to the traction substation within a set period, P T.j E represents the j-th output power of the traction substation. T0 To determine the total traction energy consumption of the train within a set period, T s Indicates the control cycle.

2. The method for determining the energy storage capacity of a traction power supply system based on comprehensive utilization rate according to claim 1, characterized in that: In step S1, the state of charge of the energy storage system is determined using the following method: Among them: SOC es (k) represents the state of charge (SOC) of the energy storage system of the traction power supply system at time k. es (k-1) represents the state of charge of the energy storage system of the traction power supply system at time k-1, T s P represents the control period. es (k) represents the power of the energy storage system at time k, when P es (k)>0 indicates a discharge state, when P es (k) < 0 indicates the charging state, Q es.n This is the rated power of the energy storage system.

3. The method for determining the energy storage capacity of a traction power supply system based on comprehensive utilization rate according to claim 1, characterized in that: The operating conditions of the traction power supply system include full traction condition, full braking condition, equivalent traction condition, and equivalent braking condition.

Images