Flywheel energy storage optimal configuration method for urban rail transit regenerative braking energy recovery

Abstract

The invention provides a flywheel energy storage optimal configuration method for regenerative braking energy recovery of urban rail transit, which comprises the following steps of: S1, modeling a traction power supply system according to a fixed energy-saving traction strategy, and constructing a load flow calculation model of a direct-current traction power supply system of a whole line; s2, under the condition that a flywheel energy storage unit is added, a flywheel energy storage economical model is constructed; and S3, on the basis of the flywheel energy storage economic model, solving the load flow calculation model to obtain a configuration scheme of the flywheel energy storage unit. According to the method, the economic model of flywheel energy storage is constructed, optimization solution is performed in combination with the load flow calculation model, the optimal energy storage configuration scheme can be determined, and on the premise that the performance requirement of the system is met, the investment and operation cost is minimized, and the overall economic benefit of the project is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of urban rail transit traction power supply, and particularly relates to an optimized configuration method for flywheel energy storage of regenerative braking energy recovery in urban rail transit. Background Art

[0002] Urban rail transit has the characteristics of short inter-station distances and high vehicle operation densities. The braking energy generated during frequent starts and stops is 30% or more of the traction energy. Under the existing uncontrolled rectifier power supply mode, part of the energy of the train's regenerative braking is absorbed by adjacent trains, while the unabsorbed part is consumed by the braking resistor, resulting in waste of regenerative braking energy. Therefore, recycling the regenerative braking energy of urban rail trains plays an important role in reducing energy consumption, suppressing the voltage fluctuation of the catenary, and improving the stability of the power supply system.

[0003] Compared with electrochemical energy storage and supercapacitor energy storage, the flywheel energy storage system has a long service life, the stored energy does not decrease during the whole life cycle, is safe and environmentally friendly, and is very suitable for the recovery of regenerative braking energy in the application scenarios of frequent acceleration and deceleration of urban rail transit.

[0004] The subway traction system contains the energy interaction relationship between multiple vehicles - multiple stations - multiple storages, showing strong non-linear time-varying characteristics in terms of time and space. Using a mature commercial software to establish a detailed power flow model to calculate the network voltage and power changes, the interface is not flexible, and it is difficult to carry out the comparative analysis and optimization solution of different energy storage capacity configurations. Summary of the Invention

[0005] The present invention proposes an optimized configuration method for flywheel energy storage of regenerative braking energy recovery in urban rail transit to solve the technical problems that the existing optimized configuration methods are not flexible in interface and difficult to carry out comparative analysis of capacity configurations during optimization.

[0006] To solve the above technical problems, the present invention provides an optimized configuration method for flywheel energy storage of regenerative braking energy recovery in urban rail transit, including the following steps: Step S1: According to the fixed-form energy-saving traction strategy, model the traction power supply system and construct a power flow calculation model of the DC traction power supply system for the whole line; Step S2: Construct a flywheel energy storage economic model under the condition of adding a flywheel energy storage unit; Step S3: Based on the flywheel energy storage economic model, solve the power flow calculation model to obtain the configuration scheme of the flywheel energy storage unit.

[0007] Preferably, in step S1, the expression for modeling the traction power supply system is: ; ; ; ; In the formula, represents the train traction energy consumption, represents the train traction power, represents the train departure time, represents the train traction end time, represents the train arrival time, represents the train speed, represents the station spacing, represents the running time between stations under the train operation diagram, represents the maximum allowable train running speed between stations.

[0008] Preferably, in step S1, the method for constructing the power flow calculation model of the DC traction power supply system for the whole line includes: equivalent the rectifier unit to a voltage source with unidirectional current flow; equivalent the flywheel energy storage unit to two voltage sources with unidirectional current flow; parallel the rectifier unit and the flywheel energy storage unit to construct a simplified substation model; equivalent the train to a current source; correlate the magnitudes of the up / down variable resistances and the rail resistance with the distances between the up / down trains and the substation.

[0009] Preferably, the charging resistance of the flywheel energy storage unit after equivalent processing ; In the formula, represents the rectifier unit output voltage; represents the charging threshold voltage of the flywheel energy storage unit; represents the charging power of the flywheel energy storage unit.

[0010] Preferably, the discharging resistance of the flywheel energy storage unit after equivalent processing ; In the formula, represents the rectifier unit output voltage; represents the discharging threshold voltage of the flywheel energy storage unit; represents the discharging power of the flywheel energy storage unit.

[0011] Preferably, the expression of the train current after equivalent processing is: ; In the formula, represents the train traction power, represents the train traction voltage.

[0012] Preferably, in step S2, the expression of the flywheel energy storage economy model includes: Cost recovery rate :

[0013] Static recovery period F : ; Total revenue model : ; Objective function: ; ; The constraint conditions include: The number of flywheel units at each site is an integer; Flywheel SOC Value range: ; Static recovery period: not greater than ; In the formula, represents the annual income of reducing the total power grid purchase cost; represents the investment cost; represents the designed life of the flywheel; and represent the weight coefficients; represents the flywheel SOC lower limit of the value; represents the flywheel SOC upper limit of the value; represents the maximum static recovery period.

[0014] Preferably, when solving in step S3, the sites are clustered and grouped according to the site spacing and the energy to be absorbed; then grouped solving is carried out to obtain the flywheel configuration scheme.

[0015] Preferably, when clustering and grouping, through the energy transfer matrix between sites, analyze the energy transfer matrix, and obtain the number of adjacent sites with energy transfer greater than the set threshold as the number of each group during clustering.

[0016] Preferably, the method for grouped solving includes: in the first round, parallel optimization is carried out for each group, and the Pareto optimal frontiers of each group are respectively selected. On this basis, one flywheel energy storage unit is deleted from the selected sites of each group, and the second-round optimization calculation is carried out to gradually obtain the frontier solution set, and finally the configuration scheme of the optimal flywheel energy storage unit is obtained.

[0017] The beneficial effects of the present invention at least include: The flywheel energy storage unit has a fast response ability and can provide or absorb power within milliseconds to adjust the voltage fluctuations in the traction power supply system in real time, enhancing the stability and reliability of the system and ensuring the safety of train operation. The high-efficiency energy recovery and reuse ability of the flywheel energy storage system helps to reduce the power procurement cost and lower the operation cost. By constructing an economic model of the flywheel energy storage and combining it with a power flow calculation model for optimization, the optimal energy storage configuration plan can be determined to minimize the investment and operation costs on the premise of meeting the system performance requirements and improve the overall economic benefits of the project. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic flowchart of the method according to an embodiment of the present invention; Figure 2 It is a schematic diagram of the urban rail transit power supply system according to an embodiment of the present invention; Figure 3 It is a schematic diagram of the power flow calculation simulation model according to an embodiment of the present invention; Figure 4 It is a schematic diagram of the simplified model of the traction power supply system according to an embodiment of the present invention; Figure 5 It is a schematic diagram of the economic model of the flywheel energy storage according to an embodiment of the present invention; Figure 6 It is a schematic diagram of the site grouping based on the K-means clustering algorithm according to Embodiment 2 of the present invention; Figure 7 It is a schematic flowchart of the solution according to Embodiment 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] Next, with reference to the accompanying drawings in the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] Embodiment 1 As Figure 1 shown, an embodiment of the present invention provides a flywheel energy storage optimization configuration method for regenerative braking energy recovery in urban rail transit, including the following steps: Step S1: According to the fixed-form energy-saving traction strategy, model the traction power supply system and construct a power flow calculation model for the DC traction power supply system of the whole line.

[0021] As Figure 2As shown in the figure, the subway power supply system can be divided into two parts: the AC power supply network and the DC traction network. The AC power supply network mainly includes switchgear, traction and step-down substations, and step-down substations. The switchgear introduces medium-voltage AC power from the previous-stage medium-voltage AC substation. Usually, one switchgear is arranged at each head and tail of each line. Each station is equipped with a traction and step-down substation or a step-down substation. The traction and step-down substation includes a traction substation and a step-down substation. The traction substation rectifies the medium-voltage AC power into DC traction network voltage through a rectifier transformer and a rectifier device and then supplies power to the DC traction network. The step-down substation steps down the medium-voltage AC power to low-voltage AC voltage through a transformer and then supplies power to low-voltage loads such as lighting, elevators, and air conditioners. It can be seen that the urban rail transit power supply system has typical distributed characteristics.

[0022] As Figure 3 shown in (a) of the figure, the rectifier unit can be equivalent to a voltage source with unidirectional current flow, where is the no-load voltage of the rectifier unit, is the output current, is the equivalent resistance of the rectifier unit; the flywheel energy storage is equivalent to two voltage sources with unidirectional current flow, is the charging threshold voltage, is the charging resistance, is the discharging threshold voltage, is the discharging resistance; the train can be equivalent to a current source, is the train current, is the braking resistance action threshold, is the equivalent resistance of auxiliary energy consumption. Figure 3 Shown in (b) of the figure is the overall model of the urban rail transit traction power supply system. The rectifier unit is connected in parallel with the flywheel energy storage to form a simplified substation model. The sizes of the up / down variable resistances and the rail resistance depend on the distances between the up / down trains and the substation.

[0023] As Figure 4 shown, the rectifier unit provides energy, and the power P Si of each station can be simulated by a voltage node with internal resistance. When the train starts, for a certain train load P Ti >0, the equivalent circuit is as shown in (a) of the figure; when the train brakes, for a certain train load Figure 4 Ti <0, the equivalent circuit is as shown in (b) of the figure. P <0, the equivalent circuit is as shown in (b) of the figure. Figure 4 in the figure.

[0024] To carry out the modeling and analysis of the traction power supply system, traction calculation is first required to obtain the power curve during the train operation. Adopting the timed energy-saving traction strategy, the trajectory planning mathematical model during the single-train interval operation can be expressed as: ; ; ; ; Among them, represents the train traction energy consumption, represents the train traction power, represents the train departure time, represents the end time of train traction, represents the train arrival time, represents the train speed, represents the station spacing, represents the running time between stations under the train operation diagram, represents the maximum allowable train speed between stations.

[0025] The specific solution process can adopt a hierarchical optimization method: the first layer solves the qualified solution with mileage, time, and terminal speed as the constraint objectives. On this basis, in the second layer of the calculation process, the minimum traction energy is used as the objective to find the optimal solution among the qualified solutions.

[0026] After that, according to the port characteristics of the main equipment such as rectifier units, trains, and flywheel energy storage in the line, their respective equivalent circuit models are established, and a single-station - single-train - single-storage model is constructed first.

[0027] The rectifier unit can be equivalent to a voltage source with unidirectional current flow, where is the no-load voltage of the rectifier unit, is the output current, is the equivalent resistance of the rectifier unit; the flywheel energy storage is equivalent to two voltage sources with unidirectional current flow, is the charging threshold, is the charging resistance, the output voltage of the rectifier unit is and when the flywheel charging power is , satisfies the following formula: ; is the discharging threshold, is the discharging resistance, the output voltage of the rectifier unit is and when the flywheel discharging power is , satisfies the following formula: ; The rectifier unit and the flywheel energy storage are connected in parallel to form a simplified model of the substation.

[0028] The train can be equivalent to a current source, is the train current, is the braking resistor operation threshold, is the equivalent resistor for auxiliary energy consumption, satisfies the following formula: ; In the formula, represents the train traction power, represents the train traction voltage.

[0029] After verification and analysis, based on the modular modeling method, a power flow calculation model of the DC traction power supply system for the entire line is formed. The magnitudes of the variable resistors for the up / down lines and the rail resistance depend on the distances between the up / down trains and the substation.

[0030] Step S2: Construct a flywheel energy storage economic model under the condition of adding a flywheel energy storage unit.

[0031] Specifically, as Figure 5 shown, establish a flywheel energy storage economic model, which mainly includes three parts: a cost model, an income model, and a profit model. Among them, the cost model takes the rated power of the flywheel energy storage unit as P N , the rated capacity as W N , and the unit cost is denoted as ; configure m flywheel units, then the flywheel investment cost is: ; In addition, relevant investment costs such as supporting switchgear, secondary control, engineering design, construction, and control system access need to be considered, as well as operation and maintenance costs. The total cost is denoted as .

[0032] Compared with the original system solution without flywheel energy storage, the annual income of flywheel energy storage mainly includes reducing the total grid power purchase cost. The annual income is denoted as .

[0033] Annual cost recovery rate model, denote the annual cost recovery rate as : ; Denote the static recovery period (unit: year) as F : ; Total income model, the designed life of the flywheel is years, and the total income is denoted as : ; The objective function is: ; ; Among them, and are weight coefficients.

[0034] Constraint conditions: The number of flywheel units at each site is an integer, and the value is less than num ; Flywheel SOC Value range: ; Static recovery period: not greater than .

[0035] Among them, represents the lower limit of the flywheel SOC value; represents the upper limit of the flywheel SOC value; represents the maximum static recovery period.

[0036] Step S3: Based on the flywheel energy storage economy model, solve the power flow calculation model to obtain the configuration scheme of the flywheel energy storage unit.

[0037] Specifically, according to the objective function of the flywheel energy storage economy model, comprehensively consider the static recovery period and total income of each scheme, calculate the Pareto front, and select the scheme that takes both into account.

[0038] Embodiment 2 In this embodiment, on the basis of Embodiment 1, after clustering and grouping the sites, solve again to obtain the configuration scheme of the flywheel energy storage unit.

[0039] Specifically, according to the site spacing and the energy to be absorbed at each site without flywheel energy storage units, divide the sites into several groups as Figure 6 shown. When solving, as Figure 7 shown, adopt a step-by-step optimization solution method combining parallel and series to optimize the scheme in multiple steps, obtain the static recovery period and total income results of each scheme, and comprehensively select the optimized configuration scheme based on the static recovery period and total income. In the first round, carry out parallel optimization for each group, respectively select the Pareto optimal front of each group. On this basis, delete one unit from the selected sites in each group, carry out the second-round optimization calculation, gradually obtain the front solution set, and finally obtain the comparison results of the static recovery period and total income of each scheme.

[0040] Embodiment 3 In this embodiment, on the basis of Embodiment 2, in order to reduce the overall computational amount of this optimization problem, set the size of the grouping through the energy transfer matrix.

[0041] Specifically, based on the power flow calculation model, the energy transfer matrix between stations can be further extracted. For a certain station in the middle of a line, there are oncoming trains in the upward and downward directions at the same time. Within the scope of this station, the track impedance between the two trains is ignored. During the deceleration process of the incoming train and the acceleration process of the outgoing train, the power time series of the two trains are added to obtain the total power time series, that is: the i train power at station ; In the formula, represents the power of the upward train, represents the power of the downward train, and the powers of the upward and downward trains can be solved separately through the model in step S1 .

[0042] Specifically, the power interaction relationship between stations is represented by matrix A, and the power P S of each station can be expressed as: P S =A P T ; Among them, P S = P S1 P S2 …P SN T , P T = P T1 P T2 …P TN T .

[0043] Among them, P Si represents the output power of the rectifier unit at the i-th station. Since the rectifier unit of the traction power supply system has a unidirectional conduction characteristic, it is discussed in two cases: train starting and train braking: 1) P Ti >0, that is, the train starts The rectifier unit provides energy, and each station P Si can be simulated by a voltage node with internal resistance, and the node voltage is the voltage of the rectifier unit, is the equivalent internal resistance of the rectifier unit.

[0044] The solution is obtained: ​​ ; Apply them separately in sequence , calculate the elements of each column, and then obtain the elements of the energy transfer matrix. Each station mainly has a relatively close energy transfer relationship with 2 to 3 adjacent stations. As the distance increases, the energy transfer relationship between stations weakens significantly.

[0045] 2) P Ti <0, that is, the train brakes When the train brakes, energy is fed into the traction network, the diodes of the rectifier unit are cut off, and the energy storage or braking resistor operates. P Si It can be simulated by the available voltage node, and the node voltage is the action threshold of the braking resistor.

[0046] Apply them separately in sequence , calculate the elements of each column, and then obtain the elements of the energy transfer matrix.

[0047] The finally obtained energy transfer matrix is shown in Table 1.

[0048] Table 1

[0049] It can be seen from Table 1 that each station mainly has a relatively close energy transfer relationship with 2 to 3 adjacent stations, that is, the value is greater than the set threshold. As the distance increases, the energy transfer relationship between stations weakens significantly. According to the energy transfer relationship between stations, the stations are classified. Therefore, in this embodiment, the number of groups is 22 / 3 = 7.3, so 8 groups are divided using clustering.

[0050] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. Only the preferred embodiments of the present invention are expressed. The description is relatively specific and detailed, but it cannot be understood as a limitation to the scope of the present invention. As long as the combination of these technical features does not conflict, it should be considered as the scope recorded in this specification.

[0051] It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. A flywheel energy storage optimization configuration method for regenerative braking energy recovery in urban rail transit, characterized in that: It includes the following steps: Step S1: Model the traction power supply system according to the fixed-form energy-saving traction strategy, and construct a power flow calculation model for the DC traction power supply system of the entire line; Step S2: Construct a flywheel energy storage economy model under the condition of adding a flywheel energy storage unit; Step S3: Based on the flywheel energy storage economy model, solve the power flow calculation model to obtain the configuration scheme of the flywheel energy storage unit.

2. The optimized configuration method of flywheel energy storage for regenerative braking energy recovery in urban rail transit according to claim 1, characterized in that: In Step S1, the expression for modeling the traction power supply system is: ； ； ； ； Wherein, represents the train traction energy consumption, represents the train traction power, represents the train departure time, represents the train traction end time, represents the train arrival time at the station, represents the train speed, represents the station spacing, represents the running time between stations under the train operation diagram, represents the maximum allowable train running speed between stations.

3. An optimization configuration method for flywheel energy storage of regenerative braking energy recovery in urban rail transit according to claim 2, characterized in that: In Step S1, the method for constructing the power flow calculation model of the DC traction power supply system of the entire line includes: equivalent the rectifier unit to a voltage source with unidirectional current flow; equivalent the flywheel energy storage unit to two voltage sources with unidirectional current flow; parallel the rectifier unit and the flywheel energy storage unit to construct a simplified substation model; equivalent the train to a current source; associate the up / down variable resistance and the rail resistance with the distance between the up / down trains and the substation.

4. An optimized configuration method for flywheel energy storage of regenerative braking energy recovery in urban rail transit according to claim 3, characterized in that: Charging resistance of the flywheel energy storage unit after equivalent processing Satisfies the following expression: ； Wherein, represents the output voltage of the rectifier unit; represents the charging threshold voltage of the flywheel energy storage unit; represents the charging power of the flywheel energy storage unit.

5. An optimized configuration method of flywheel energy storage for regenerative braking energy recovery in urban rail transit according to claim 4, characterized in that: Discharge resistance of the flywheel energy storage unit after equivalent processing Satisfies the following expression: ； Wherein, represents the output voltage of the rectifier unit; represents the discharge threshold voltage of the flywheel energy storage unit; represents the discharge power of the flywheel energy storage unit.

6. The flywheel energy storage optimal configuration method for regenerative braking energy recovery of urban rail transit according to claim 5, characterized in that: Train current after equivalent processing The expression is as follows: ； In the formula, represents the train traction power, represents the train traction voltage.

7. An optimized configuration method of flywheel energy storage for regenerative braking energy recovery in urban rail transit according to claim 1, characterized in that: In Step S2, the expression of the flywheel energy storage economy model includes: Cost recovery rate : Static recycling period F : ； Total Revenue Model : ； Objective function: ； ； The constraint conditions include: The number of flywheel units at each site is an integer; Flywheel SOC Value range: ; Static recycling period: not greater than ; Wherein, represents the annual income for reducing the total grid power purchase cost; represents the investment cost; represents the designed life of the flywheel; and represent the weight coefficients; represents the flywheel SOC lower limit of the value; represents the flywheel SOC upper limit of the value; represents the maximum static recovery period.

8. An optimized configuration method of flywheel energy storage for regenerative braking energy recovery in urban rail transit according to claim 1, characterized in that: When solving in Step S3, cluster and group the sites according to the site spacing and the energy to be absorbed; then perform grouped solution to obtain the flywheel configuration scheme.

9. The flywheel energy storage optimal configuration method for regenerative braking energy recovery of urban rail transit according to claim 8, characterized in that: When performing clustering and grouping, analyze the energy transfer matrix through the energy transfer matrix between sites, and obtain the number of adjacent sites with energy transfer greater than the set threshold as the number of each group during clustering.

10. An optimized configuration method of flywheel energy storage for regenerative braking energy recovery in urban rail transit according to claim 8, characterized in that: The method for performing grouped solution includes: in the first round, carry out parallel optimization for each group, respectively select the Pareto optimal front of each group, on this basis, delete one flywheel energy storage unit from the selected sites of each group, perform the second-round optimization calculation, gradually obtain the front solution set, and finally obtain the optimal configuration scheme of the flywheel energy storage unit.

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