A post-accident power flow transfer optimization control method for power system with energy storage

Abstract

The present invention relates to a post-accident power flow transfer optimization control method for an energy storage power system. After a power system accident is detected, the power flow transfer trend of the power grid is quickly estimated through the power flow to predict the overload line, and the adjustable generator sets, interruptible loads, and sound DC and energy storage power stations with good power flow control effects in the network are selected as control variables; based on the data of each meteorological observation station covered by the transmission channel corridor in the actual power grid, the line is gridded and segmented to form a line current-temperature grid estimation method considering the meteorological distribution, thereby improving the estimation accuracy of the line overload capacity; with the minimum control cost as the goal, a power flow transfer optimization model containing an energy storage system is established, and a control plan is quickly given to fully tap the energy storage regulation capacity and the line overload tolerance capacity, and effectively block the power flow transfer of the power grid and the spread of overload accidents; the power flow transfer optimization control method provides a new control means and decision-making plan basis for ensuring the safe operation of a new power system.

Description

Technical Field

[0001] The present invention belongs to the field of power system safety and stability control technology and application, and relates to a method for optimizing power flow transfer after an accident in a power system containing energy storage, and in particular to a method for optimizing power flow transfer after an accident in a power system containing energy storage based on gridded estimation of current temperature of a transmission line. Background Art

[0002] The grid structure with AC and DC coexistence has become the main structural form of my country's power grid. However, whether it is AC or DC transmission lines, the increase in their transmission capacity also brings new challenges to the safe operation of the power grid. As the power channel of the sending and receiving ends, the ultra-high voltage and extra-high voltage lines themselves have huge transmission power. After the fault of these lines is removed, large-scale power flow transfer will occur in the power grid, and some lines will be overloaded. If the power flow transfer phenomenon cannot be eliminated in time and effectively, in severe cases, chain tripping may even occur, causing large-scale power outages. In response to this problem, there are a large number of methods to avoid chain accidents in large power grids to a certain extent, but there is still a lack of in-depth analysis of the optimization and coordination of the controllable resources of the system. At the same time, the optimization control objects and optimization targets are relatively single, limited to traditional synchronous units or load resources, and lack of effective utilization of multiple control objects or new power grid resources.

[0003] Thanks to the continuous reduction in the cost of electric energy storage and its huge potential for rapid response, the number and scale of energy storage power stations used in power grids are also increasing significantly. The annual growth rate of my country's total installed capacity of energy storage put into operation is five times that of the global market. Therefore, flexibly controlled energy storage power stations provide a new control method to ensure the safe operation of the power system.

[0004] Energy storage currently used on the grid side is mainly installed in and near substations, providing services such as alleviating grid congestion, delaying transmission and distribution upgrades, and improving grid power supply safety, elasticity, flexibility, stability and reliability. However, the application of energy storage in the field of grid safety and stability control has just started. At present, the application of energy storage power stations is often limited to a few scenarios such as regional power grids (such as wind power and photovoltaic new energy consumption), and has not yet fully utilized its fast and flexible control capabilities.

[0005] At the same time, in actual grid power flow transfer emergencies, the allowable current of overloaded transmission lines is generally constrained by 1.2 to 2 times the rated current, which is too conservative. In fact, there is an electrothermal coupling relationship of "current-conductor temperature" in overloaded transmission lines. Affected by the thermal inertia of the conductor material, the conductor temperature change always lags behind the line operating current change, which makes the transmission lines under grid emergency operation have a certain degree of overload tolerance. At present, there is no relevant technology that considers solving the problem of grid power flow transfer overload safety by configuring energy storage and exploring and coordinating the energy storage control capability and the tolerance capacity of overloaded lines. Summary of the invention

[0006] In view of this, the present invention provides a method for optimizing control of power flow transfer after an accident in a power system containing energy storage in order to solve the problem of overload safety of power grid power flow transfer by configuring energy storage and exploring and coordinating the energy storage control capability and the tolerance capacity of overload lines, which is currently not considered in related technologies.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for optimizing power flow transfer after an accident in a power system containing energy storage comprises the following steps:

[0009] S1. Detect power system power flow transfer accidents, determine the overload line set and the non-overload line set, and select the adjustable generator sets, interruptible loads, sound DC and energy storage power stations with good power flow control effects in the network as control variables;

[0010] S2. Based on the data of each meteorological observation station covered by the transmission channel corridor in the actual power grid, the line is gridded and segmented to form a line current-temperature grid estimation method that considers meteorological distribution, thereby improving the estimation accuracy of line overload capacity;

[0011] S3. With the goal of minimizing the control cost, a power flow transfer optimization model including an energy storage system is established;

[0012] S4. Solve the power flow transfer optimization model, send power control instructions to implement optimization control, achieve optimal adjustment of power flow distribution, and effectively block the power flow transfer and the spread of overload accidents in the power grid.

[0013] Further, step S1 is specifically as follows:

[0014] When the AC / DC line in the AC / DC hybrid power grid is cut off for some reason, the current of the remaining normal lines in the network is estimated immediately through fast power flow, and compared with the rated current value of the own line to determine the overload line set and the non-overload line set; sensitivity analysis is carried out on the overload line set, and the adjustable generator sets, interruptible loads, sound DC and energy storage power stations with good power flow control effect on the overload line set are selected as control variables;

[0015]

[0016] Where I l Indicates the current magnitude of any line l in the network; I lmax represents the maximum normal operating current of the line l, i.e. the rated current; the optimized control variable u includes the adjustable generator set P Gn , interruptible load ΔP Lk, , sound DC P HVDC and energy storage power station PESm Four control methods; n, m, k represent the nodes where the corresponding adjustable generator sets, energy storage power stations and interruptible loads are located in the network respectively; S G , S ES and S L are the node sets of the generator sets, energy storage and interruptible loads involved in the control; S l Represents the entire network line set, S l1 and S l0 Represents the set of overloaded lines and the set of non-overloaded lines.

[0017] Further, step S2 performs gridded estimation of line current and temperature considering meteorological distribution, and the overloaded line set S l1 The line gridding segmentation considerations in the paper are as follows:

[0018] S21. Gridding of the area covered by the transmission line, extraction of the transmission line cell coordinate information

[0019] According to actual needs, the area covered by the transmission line corridor is divided into grids with a grid distance of τkm×τkm. The entire transmission line l is divided into N cells by the grid lines. The coordinate information of each cell is extracted. The i-th cell Q i The coordinates of the four vertices are A i (x ai ,y ai ), B i (x bi ,y bi ), C i (x ci ,y ci ) and D i (x di ,y di ), where i = 1, 2, ..., N; assuming that there are K meteorological observation stations along the divided area, the location coordinates of the jth meteorological observation station are P j (x pj ,y pj ), where j = 1, 2, …, K;

[0020] S22. Consider the impact of all meteorological observation stations along the transmission corridor

[0021] Given the coordinates of the vertices in each cell and the coordinates of the meteorological observation station, find the Q of the i-th cell i Vertex A i The distances to each meteorological observation station are Similarly, the distances of the other three vertices from each weather station are obtained; according to vertex A i The distance between the coordinates and each meteorological observation station is used to obtain the influence weight of each meteorological observation station on each meteorological parameter of the point, which is expressed as:

[0022]

[0023] In the formula Indicates the i-th cell Q of the network through which the transmission line passes i Vertex A i The weight of the meteorological parameter affected by the jth meteorological observation station; similarly, the distances and influence weights of the remaining three vertices from each meteorological station are obtained;

[0024] S23. Describe the meteorological parameters of each line segment

[0025] Obtain the four vertices of the network cell through weights and Meteorological parameters of this cell The average value of the four vertices represents the meteorological conditions of this section of the route:

[0026]

[0027] In the formula Indicates the meteorological observation station P j Measured meteorological data;

[0028] S24. Current temperature estimation of the entire transmission line

[0029] The current-temperature mapping equation of the transmission line is:

[0030]

[0031] Where q c (t), q s (t), q r (t), q l (t) are the convection heat dissipation power, radiation heat dissipation power, sunlight heat generation power and Joule heat power of line l at time t, W / m; T(t) is the temperature of line l at time t, ℃; m and c are the equivalent mass per unit length of the steel-core aluminum stranded wire composed of iron and aluminum materials, kg / m and equivalent specific heat capacity, J / (kg·℃);

[0032] Through the above gridding method, when a transmission line l is divided into N segments by network lines, the meteorological parameters of each segment of the transmission line l are obtained. Substituting it into equation (4), we can obtain the temperature matrix T of the entire transmission line l considering the influence of meteorological distribution: l (t) = [T l1 (t)T l2 (t)…T l i (t)…T l N (t)]T .

[0033] Further, step S3 establishes a power flow transfer optimization model including an energy storage system, specifically:

[0034] S31. Establishing the optimization control objective function:

[0035] The goal is to minimize the overall control cost, that is:

[0036]

[0037] Where P Gn,t P is the active output of the controllable generator set connected to node n at time t; ESm,t is the active output of energy storage access node m at time t; ΔP Lk,t is the active power removal amount of interruptible load node k at time t; a Gn , b Gn and c Gn is the active power control cost coefficient of different generator node n; d ESm is the active power control cost of different energy storage nodes m; e Lk is the equivalent cost of removing different interruptible load nodes k; t0 is the initial control time, t f is the end time of control, [t0,t f ] is the time domain of the optimization control process; F G 、F ES and F L They are the control costs of adjustable generator sets, energy storage and interruptible loads, and the weight factor λ of each control cost is introduced G , ES and λ L , weighted sum processing;

[0038] S32. Establish equality constraints:

[0039] The power balance of the power system with energy storage is:

[0040]

[0041] Where, node i includes the entire system network; P Gi,t , P ESi,t , P DCi,t , P Li,t , ΔP Li,t are the active power values ​​of the generator set, energy storage, sound DC, load and load shedding of node i at time t; Q represents the corresponding reactive power value; U i,t is the voltage amplitude of node i at time t; θ ij,t is the phase angle difference between node i and node j at time t;

[0042] Dynamic heat balance of overloaded transmission line: that is, the conductor electrothermal calculation equation, that is, equation (1) to equation (4), taking time t0 as the initial value of the variable according to meteorological conditions and power flow results, and estimating the control time domain [t0,t f ] Circuit temperature status within ;

[0043] S33, Inequality Constraints

[0044] System security constraints:

[0045]

[0046] Where U i,max and U i,min are the boundary values ​​of node voltage respectively; θ ij,min and θ ij,max is the boundary value of the phase angle difference. During the optimization control process, the node voltage and phase angle of the system should be ensured to be within a reasonable range.

[0047] Operation constraints of the electrothermal characteristics of transmission lines with energy storage: Introduce the estimated line temperature matrix T considering meteorological distribution l (t) is used as an indicator to characterize the safety of transmission line operation, and the conductor transient temperature limit is used as the safety boundary constraint of the line:

[0048] T l (t) ∞ ≤T max (8)

[0049] Where, T max The maximum allowable temperature of the transmission line, the transient temperature limit is usually 100℃;

[0050] Upper and lower limits of adjustable power: The active power output of the generator sets, energy storage and sound DC (if there is sound DC) involved in the control has boundary constraints:

[0051]

[0052] Active power removal constraints of loads involved in control:

[0053] 0≤ΔP Li,t ≤ΔP Li,max (10)

[0054] In the formula, the subscripts min and max correspond to the upper and lower limits of the variable respectively;

[0055] Adjustment rate constraints of adjustable power: Considering that too fast adjustment of power will have an impact on the power system, the power adjustment rate constraints of the generator sets and energy storage power stations involved in the control are introduced:

[0056]

[0057] In the formula, and They represent the maximum power adjustment rates of the generator access node n and the energy storage access node m respectively.

[0058] Further, step S4 is specifically as follows: solving the optimization model constructed above to obtain the optimization result, and the dispatching system immediately sends a power adjustment signal to the energy storage power source, the sound DC, the generator set and the load point to implement control, so as to achieve the optimization adjustment of the power flow distribution.

[0059] The beneficial effects of the present invention are:

[0060] 1. The present invention discloses a method for optimizing the power flow transfer after an accident in a power system containing energy storage. According to the parameters and geographical location information of the overhead transmission line, combined with the forecast data of the meteorological observation station within the spanning range, a real-time electrical quantity and meteorological quantity data grid of the entire transmission line corridor is formed. The difference in meteorological distribution along the entire length of the transmission line is considered, and the line is gridded and segmented to improve the accuracy of line overload capacity estimation. A power flow transfer optimization model containing an energy storage system is established to quickly give the optimal control amount and adjustment amount, so as to fully tap the energy storage regulation capability and the line overload tolerance capability, which can effectively block the power flow transfer of the power grid and the spread of overload accidents, and improve the reliable operation capability of the power grid.

[0061] 2. The present invention discloses a method for optimizing the control of power flow transfer after an accident in a power system containing energy storage. After detecting a power system accident, the power flow transfer trend of the power grid is quickly estimated through the power flow to predict the overloaded line, and the adjustable generator sets, interruptible loads, and sound DC and energy storage power stations with good power flow control effects in the network are selected as control variables; the lines are gridded and segmented based on the data of various meteorological observation stations covered by the transmission channel corridor in the actual power grid, forming a line current-temperature grid estimation method that considers the meteorological distribution, thereby improving the estimation accuracy of the line overload capacity; with the goal of minimizing the control cost, an optimization model for power flow transfer containing an energy storage system is established, and a control plan is quickly given to fully tap the energy storage regulation capability and the line overload tolerance capability, effectively blocking the power flow transfer of the power grid and the spread of overload accidents; the power flow transfer optimization control method provides a new control means and decision-making basis for ensuring the safe operation of new power systems.

[0062] 3. The present invention discloses a method for optimizing the control of power flow transfer after an accident in a power system containing energy storage. It considers configuring energy storage and exploring and coordinating the control capability of energy storage and the tolerance capability of overloaded lines, providing a new control method for ensuring the safe operation of the power system. Compared with the traditional machine shedding and load shedding control, it quickly gives the optimal control amount and adjustment amount, effectively blocking the power grid power flow transfer and the spread of overload accidents, solving the problem of power grid power flow transfer overload safety that no related technology has considered at present by configuring energy storage and exploring and coordinating the control capability of energy storage and the tolerance capability of overloaded lines.

[0063] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0065] Figure 1 It is a flow chart of the method for optimizing control of power flow transfer after an accident in a power system containing energy storage according to the present invention;

[0066] Figure 2 A grid division diagram of real-time electrical quantity and meteorological quantity data of the entire transmission line corridor of the present invention;

[0067] Figure 3 A typical wiring diagram of a power system including energy storage according to an embodiment of the present invention;

[0068] Figure 4 : is a comparison diagram of energy storage and interruptible load participation in control under different power flow transfer optimization control methods in the embodiment of the present invention, wherein Figure 4 (a) is the optimization method ② energy storage P ES1 and energy storage P ES2 Comparison chart of the change of adjustment value over time;

[0069] Figure 4 (b) Using the optimization method ③ Energy storage P ES1 and energy storage P ES2 Comparison chart of the change of adjustment value over time; Figure 4 (c) is a comparison chart of the change of load shedding value over time after different interruptible load variables are involved in the optimization method ①; Figure 4 (d) is a comparison chart of the change of load shedding value over time after different interruptible load variables are involved in the optimization method ②; Figure 4(e) is a comparison chart of the change of load shedding value over time after different interruptible load variables are involved in the optimization method ③;

[0070] Figure 5 This is a temperature state variation curve of the circuit during the control process using method ③ in the embodiment of the present invention. DETAILED DESCRIPTION

[0071] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0072] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0073] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0074] like Figure 1 A method for optimizing power flow transfer after an accident in a power system with energy storage is shown, comprising the following steps:

[0075] S1. Detect system power flow transfer accidents and determine control variables;

[0076] The detection power system can realize the prediction of overload lines of power flow transfer after an accident in the power system containing energy storage, and screen out the function of optimizing control variables.

[0077] Specifically: After the AC / DC line in the AC / DC hybrid power grid is cut off for some reason, the current size of the remaining normal lines in the network is estimated through fast power flow at the first time, and compared with the rated current value of the own line, to determine the overloaded line set and the non-overloaded line set; further sensitivity analysis is carried out on the overloaded line set, and the adjustable generator sets, interruptible loads, sound DC and energy storage power stations with good power flow control effect on the overloaded line set in the network are selected as control variables.

[0078]

[0079] In formula (1), I l Indicates the current magnitude of any line l in the network; I lmax represents the maximum normal operating current of the line l, i.e. the rated current; the optimized control variable u includes the adjustable generator set P Gn , interruptible load ΔP Lk, , sound DC P HVDC and energy storage power station P ESm Four control methods; n, m, k represent the nodes where the corresponding adjustable generator sets, energy storage power stations and interruptible loads are located in the network respectively; S G , S ES and S L are the node sets of the generator sets, energy storage and interruptible loads involved in the control; S l Represents the entire network line set, S l1 and S l0 Represents the set of overloaded lines and the set of non-overloaded lines.

[0080] S2, gridded estimation of transmission line current-temperature;

[0081] In the power system, the number of meteorological observation stations is limited and it is impossible for them to completely overlap with the transmission line corridor. High-voltage long-distance transmission lines pass through some areas with special climatic conditions, and their meteorological conditions may be significantly different from the surrounding environment. Therefore, the overload line set S in step S1 is l1 The grid-based segmentation of the lines in the grid can fully explore the impact of each meteorological observation station on each section of the power grid, and effectively improve the accuracy of line overload capacity estimation. Specifically:

[0082] S21. Gridding of the area covered by the transmission line, extraction of the transmission line cell coordinate information

[0083] like Figure 2 As shown in the figure, the area covered by the transmission line corridor is divided into grids with a grid distance of τkm×τkm according to actual needs. The entire transmission line l is divided into N cells by the grid lines. The coordinate information of each cell is extracted. The i-th cell Q i The coordinates of the four vertices are Ai (x ai ,y ai ), B i (x bi ,y bi ), C i (x ci ,y ci ) and D i (x di ,y di ), where i = 1, 2, ..., N; assuming that there are K meteorological observation stations along the divided area, the location coordinates of the jth meteorological observation station are P j (x pj ,y pj ), where j = 1, 2, …, K;

[0084] S22. Consider the impact of all meteorological observation stations along the transmission corridor

[0085] Given the coordinates of the vertices in each cell and the coordinates of the meteorological observation station, the i-th cell Q can be obtained i Vertex A i The distances to each meteorological observation station are Similarly, the distances from the other three vertices to each weather station can be obtained; according to vertex A i The distance between the coordinates and each meteorological observation station can be used to obtain the influence weight of each meteorological observation station on each meteorological parameter of the point, which can be expressed as:

[0086]

[0087] In formula (2) Indicates the i-th cell Q of the network through which the transmission line passes i Vertex A i Meteorological parameters are affected by j The weight of the influence of each meteorological observation station. Similarly, the distances and influence weights of the other three vertices from each meteorological station can be obtained;

[0088] S23. Describe the meteorological parameters of each line segment

[0089] The four vertices of the network cell can be obtained by the weights in step S22 and Meteorological parameters of this cell The average value of the four vertices can be taken to represent the meteorological conditions of this section of the line:

[0090]

[0091] In formula (3) Indicates the meteorological observation station P jThrough the above method, when a transmission line l is divided into N sections by network lines, the meteorological parameters of each section of the transmission line l are obtained.

[0092] S24. Current temperature estimation of the entire transmission line

[0093] For overhead transmission lines, the temperature change is mainly affected by factors such as current, wind speed, wind direction, sunshine, and temperature. The current-temperature mapping equation of the transmission line is:

[0094]

[0095] In formula (4), q c (t), q s (t), q r (t), q l (t) are the convective heat dissipation power, radiant heat dissipation power, solar heat generation power and Joule heat power of line l at time t, W / m; T(t) is the temperature of line l at time t, ℃; m and c are the equivalent mass per unit length of the steel-core aluminum stranded wire composed of iron, aluminum and other materials, kg / m and equivalent specific heat capacity, J / (kg·℃).

[0096] Through the above gridding method, when a transmission line l is divided into N segments by network lines, the meteorological parameters of each segment of the transmission line l are obtained. Substituting it into equation (4), we can obtain the temperature matrix T of the entire transmission line l considering the influence of meteorological distribution: l (t) = [T l1 (t)T l2 (t)…T l i (t)…T l N (t)] T .

[0097] S3. With the goal of minimizing the control cost, an optimization control model for power flow transfer including energy storage system is established;

[0098] S31. Establishing the optimization control objective function

[0099] The power flow transfer optimization control adopts energy storage to participate in power adjustment, cooperates with other means of sound DC, adjustable generator sets and interruptible loads to achieve power balance and ultimately block power flow transfer. Therefore, the model aims to minimize the overall control cost:

[0100]

[0101] In formula (5), P Gn,t P is the active output of the controllable generator set connected to node n at time t; ESm,tis the active output of energy storage access node m at time t; ΔP Lk,t is the active power removal amount of interruptible load node k at time t; a Gn , b Gn and c Gn is the active power control cost coefficient of different generator node n; d ESm is the active power control cost of different energy storage nodes m; e Lk is the equivalent cost of removing different interruptible load nodes k; t0 is the initial control time, t f is the end time of control, [t0,t f ] is the time domain of the optimization control process; F G 、F ES and F L They are the control costs of adjustable generator sets, energy storage and interruptible loads, and the weight factor λ of each control cost is introduced G , ES and λ L , weighted summation processing; different weight values ​​can be set in actual optimization operations to consider the degree of participation of different means. In addition, the active power control cost of a general sound DC is much smaller than the above three types, so the DC power adjustment cost is ignored in the proposed optimization model.

[0102] S32. Establishing equality constraints

[0103] ① Power balance of power system including energy storage:

[0104]

[0105] In formula (6), node i includes the entire system network; P Gi,t , P ESi,t , P DCi,t , P Li,t , ΔP Li,t are the active power values ​​of the generator set, energy storage, sound DC, load and load shedding of node i at time t; Q represents the corresponding reactive power value; U i,t is the voltage amplitude of node i at time t; θ ij,t is the phase angle difference between node i and node j at time t.

[0106] ② Dynamic thermal balance of overloaded transmission lines:

[0107] The conductor electrothermal calculation equations are as follows: (1) to (4); according to meteorological conditions and tidal flow results, the time t0 is taken as the initial value of the variable, and the control time domain [t0, t f ] circuit temperature status within.

[0108] S33, Inequality Constraints

[0109] ① System security constraints:

[0110]

[0111] In formula (7), U i,max and U i,min are the boundary values ​​of node voltage respectively; θ ij,min and θ ij,max is the boundary value of the phase angle difference. During the optimization control process, the system node voltage and phase angle should be ensured to be within a reasonable range.

[0112] ② Operation constraints of the electrothermal characteristics of transmission lines with energy storage:

[0113] Introduce the above estimated line temperature matrix T considering meteorological distribution l (t) is used as an indicator to characterize the safety of transmission line operation, and the conductor transient temperature limit is used as the safety boundary constraint of the line:

[0114] ‖T l (t) ∞ ≤T max (8)

[0115] In formula (8), T max It is the maximum allowable temperature of the transmission line. The transient temperature limit is usually 100°C, which will not affect its mechanical strength, life loss and sag change. It can tap a certain current tolerance while ensuring line safety.

[0116] ③Adjustable upper and lower limits of power:

[0117] There are boundary constraints on the active power output of the generator sets, energy storage and sound DC (if there is sound DC) involved in the control:

[0118]

[0119] ④ Constraints on active power removal of loads involved in control:

[0120] 0≤ΔP Li,t ≤ΔP Li ,max (10)

[0121] In equations (9) and (10), the subscripts min and max correspond to the upper and lower limits of the variables, respectively.

[0122] ⑤ Adjustment rate constraints of adjustable power:

[0123] Considering that adjusting the power too quickly will have an impact on the power system, the power adjustment rate constraints of the generator sets and energy storage power stations involved in the control are introduced:

[0124]

[0125] In formula (11), and They represent the maximum power adjustment rates of the generator access node n and the energy storage access node m respectively.

[0126] S4, step 4 sends power control instructions to implement optimized control

[0127] Solve the optimization model composed of equations (1) to (11) to obtain the optimization result. The dispatching system sends power adjustment signals to the energy storage power source, sound DC, generator set and load point to implement control and achieve optimal adjustment of power flow distribution.

[0128] Example

[0129] The process of the above method is described in detail below with a specific example. Figure 3 As shown in the figure, the original IEEE 39-bus system was modified: In order to effectively verify the effectiveness of the control method, the capacity and load of all generator sets in the original system were increased by 1.5 times, and the AC line L 26-37 Replaced with energy storage P ES1 and P ES2 , the capacity is 300MW, the AC line L 4-14 Replaced with DC lines, the improved 39-bus system forms a typical AC / DC power grid with energy storage.

[0130] Assuming that the DC line fault is locked at time t0, causing power flow transfer, the system implements overload optimization control to block the spread of the accident. Considering the thermal inertia of the conductor, the control step is selected as 2 minutes and the control time domain is 20 minutes. At the same time, in order to reflect the effect of energy storage and line electrothermal characteristics participating in power flow control, the following different optimization methods are set:

[0131] Method ①: Using the traditional overload control method, the control objects only include adjustable generator sets and interruptible loads, and the safety constraint of the overload line adopts the maximum allowable current (1.5 times the rated current).

[0132] Method ②: Add energy storage power station as a control variable, and keep the safety constraints consistent with those in solution ①.

[0133] Method ③: that is, the power flow transfer optimization method proposed in the present invention, which takes the comprehensive energy storage power station, adjustable generator set, sound DC and interruptible load as control variables, and the transient temperature limit of the conductor as the safety boundary constraint of the line, while considering the meteorological distribution of the overloaded transmission line.

[0134] After the DC is out of operation, the AC line L 9-39 and L 17-18When an overload occurs, a quick estimation of the power flow can determine whether the network is P G1 , P G8 , P G9 and P G10 Adjustable generator set variable, P L8 , P L16 and P L27 is the interruptible load variable, energy storage P ES1 and P ES2 Participates in control as an energy storage control variable.

[0135] Figure 4 It shows the comparison of energy storage and interruptible load participation in control under different power flow transfer optimization control methods. Figure 4 (a) is the optimization method ② energy storage P ES1 and energy storage P ES2 Comparison chart of the change of adjustment value over time; Figure 4 (b) Using the optimization method ③ Energy storage P ES1 and energy storage P ES2 Comparison chart of the change of adjustment value over time; Figure 4 (c) is a comparison chart of the change of load shedding value over time after different interruptible load variables are involved in the optimization method ①; Figure 4 (d) is a comparison chart of the change of load shedding value over time after different interruptible load variables are involved in the optimization method ②; Figure 4 (e) is a comparison chart of the change of load shedding value over time after different interruptible load variables are involved in the optimization method ③; it can be found that the load adjustment amount in method ① is obviously too high. During the control process, due to the overly conservative safety constraints of the overloaded line, a large number of machine shedding and load shedding are required to meet the control constraints; in method ②, due to the introduction of energy storage power stations to participate in power adjustment, the load shedding value is reduced; method ③, based on the electrothermal characteristics of the overloaded transmission line, expands the line safety constraints to a certain extent, and can give full play to the overload tolerance capacity of the line. In this example, only a small number of generator sets need to be adjusted, and the participation of interruptible loads is not required. Therefore, the actual overload optimization control process can reduce the impact on the power consumption of the load to a certain extent.

[0136] Figure 5 According to the meteorological characteristics, the overload line is gridded into 5 sections. Therefore, there are 5 different temperature rise curves in the corresponding figure. From top to bottom, the curves represent the line L during the overload control period. 9-39 The temperature change of the conductors in the first to fifth sections of the line. Under the control scheme of method ③, during the overload control period, the line L 9-39 The conductor temperature state change curve corresponding to each of the five segments after grid division shows that the maximum temperature parameter value does not exceed the transient critical temperature T of the conductor.max , can ensure the safety of the line.

[0137] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for optimizing power flow transfer after an accident in a power system containing energy storage, characterized in that: The steps include: S1. Detect power system power flow transfer accidents, determine the overload line set and the non-overload line set, and select the adjustable generator sets, interruptible loads, sound DC and energy storage power stations with good power flow control effects in the network as control variables; S2. Based on the data of each meteorological observation station covered by the transmission channel corridor in the actual power grid, the line is gridded and segmented to form a line current-temperature grid estimation method that considers meteorological distribution, thereby improving the estimation accuracy of line overload capacity; S3. With the goal of minimizing the control cost, a power flow transfer optimization model including an energy storage system is established; S4, solving the power flow transfer optimization model, sending power control instructions to implement optimization control, realizing the optimization adjustment of power flow distribution, and effectively blocking the power flow transfer of the power grid and the spread of overload accidents; The step S2 performs gridded estimation of line current and temperature considering meteorological distribution, and divides the overloaded line set S l1 The line gridding segmentation considerations in the paper are as follows: S21. Gridding of the area covered by the transmission line, extraction of the transmission line cell coordinate information According to actual needs, the area covered by the transmission line corridor is divided into grids with a grid distance of τkm×τkm. The entire transmission line l is divided into N cells by the grid lines. The coordinate information of each cell is extracted. The i-th cell Q i The coordinates of the four vertices are A i (x ai ,y ai ), B i (x bi ,y bi ), C i (x ci ,y ci ) and D i (x di ,y di ), where i = 1, 2, ..., N; assuming that there are K meteorological observation stations along the divided area, the location coordinates of the jth meteorological observation station are P j (x pj ,y pj ), where j = 1, 2, …, K; S22. Consider the impact of all meteorological observation stations in the transmission corridor Given the coordinates of the vertices in each cell and the coordinates of the meteorological observation station, find the Q of the i-th cell i Vertex A i The distances to each meteorological observation station are Similarly, the distances of the other three vertices from each weather station are obtained; according to vertex A i The distance between the coordinates and each meteorological observation station is used to obtain the influence weight of each meteorological observation station on each meteorological parameter of the point, which is expressed as: In the formula Indicates the i-th cell Q of the network through which the transmission line passes i Vertex A i The weight of the meteorological parameter affected by the jth meteorological observation station; similarly, the distances and influence weights of the remaining three vertices from each meteorological station are obtained; S23. Describe the meteorological parameters of each line segment Obtain the four vertices of the network cell through weights and Meteorological parameters of this cell The average value of the four vertices represents the meteorological conditions of this section of the route: In the formula Indicates the meteorological observation station P j Measured meteorological data; S24. Current temperature estimation of the entire transmission line The current-temperature mapping equation of the transmission line is: Where q c (t), q s (t), q r (t), q l (t) are the convection heat dissipation power, radiation heat dissipation power, sunlight heat generation power and Joule heat power of line l at time t, W / m; T(t) is the temperature of line l at time t, ℃; m and c are the equivalent mass per unit length of the steel-core aluminum stranded wire composed of iron and aluminum materials, kg / m and equivalent specific heat capacity, J / (kg·℃); Through the above gridding method, when a transmission line l is divided into N segments by network lines, the meteorological parameters of each segment of the transmission line l are obtained. Substituting it into equation (4), we can obtain the temperature matrix T of the entire transmission line l considering the influence of meteorological distribution: l (t) = [T l1 (t)T l2 (t)…T li (t)…T lN (t)] T ; The step S3 establishes a power flow transfer optimization model including an energy storage system, specifically: S31. Establishing the optimization control objective function: The goal is to minimize the overall control cost, that is: Where P Gn,t P is the active output of the controllable generator set connected to node n at time t; ESm,t is the active output of energy storage access node m at time t; ΔP Lk,t is the active power removal amount of interruptible load node k at time t; a Gn 、b Gn and c Gn is the active power control cost coefficient of different generator node n; d ESm is the active power control cost of different energy storage nodes m; e Lk is the equivalent cost of removing different interruptible load nodes k; t0 is the initial control time, t f is the end time of control, [t0,t f ] is the time domain of the optimization control process; F G 、F ES and F L They are the control costs of adjustable generator sets, energy storage and interruptible loads, and the weight factor λ of each control cost is introduced G , ES and λ L , weighted sum processing; S32. Establish equality constraints: The power balance of the power system with energy storage is: Where, node i includes the entire system network; P Gi,t , P ESi,t , P DCi,t , P Li,t , ΔP Li,t are the active power values ​​of the generator set, energy storage, sound DC, load and load shedding of node i at time t; Q represents the corresponding reactive power value; U i,t is the voltage amplitude of node i at time t; θ ij,t is the phase angle difference between node i and node j at time t; Dynamic heat balance of overloaded transmission line: that is, the conductor electrothermal calculation equation, that is, equation (1) to equation (4), taking time t0 as the initial value of the variable according to meteorological conditions and power flow results, and estimating the control time domain [t0,t f ] Circuit temperature status within ; S33, Inequality Constraints System security constraints: Where U i,max and U i,min are the boundary values ​​of node voltage respectively; θ ij,min and θ ij,max is the boundary value of the phase angle difference. During the optimization control process, the node voltage and phase angle of the system should be ensured to be within a reasonable range. Operation constraints of the electrothermal characteristics of transmission lines with energy storage: Introduce the estimated line temperature matrix T considering meteorological distribution l (t) is used as an indicator to characterize the safety of transmission line operation, and the conductor transient temperature limit is used as the safety boundary constraint of the line: ||T l (t)|| ∞ ≤T max (8) Where, T max The maximum allowable temperature of the transmission line, the transient temperature limit is usually 100℃; The upper and lower limits of adjustable power: If there is a sound DC, the active power output of the generator sets, energy storage and sound DC involved in the control has boundary constraints: Active power removal constraints of loads involved in control: 0≤ΔP Li,t ≤ΔP Li,max (10) In the formula, the subscripts min and max correspond to the upper and lower limits of the variable respectively; Adjustment rate constraints of adjustable power: Considering that too fast adjustment of power will have an impact on the power system, the power adjustment rate constraints of the generator sets and energy storage power stations involved in the control are introduced: In the formula, and They represent the maximum power adjustment rates of the generator access node n and the energy storage access node m respectively.

2. The method for optimizing power flow transfer after an accident in a power system with energy storage according to claim 1, characterized in that: Step S1 is specifically as follows: When the AC / DC line in the AC / DC hybrid power grid is cut off for some reason, the current of the remaining normal lines in the network is estimated through fast power flow immediately, and compared with the rated current value of the own line to determine the overload line set and the non-overload line set; sensitivity analysis is carried out on the overload line set, and the adjustable generator sets, interruptible loads, sound DC and energy storage power stations with good power flow control effect on the overload line set are selected as control variables; Where I l Indicates the current magnitude of any line l in the network; I lmax Indicates the maximum normal operating current of the line l, i.e. the rated current; The optimized control variable u includes the adjustable generator set P Gn , interruptible load ΔP Lk, , sound DC P HVDC and energy storage power station P ESm Four control methods; n, m, k represent the nodes where the corresponding adjustable generator sets, energy storage power stations and interruptible loads are located in the network respectively; S G , S ES and S L are the node sets of the generator sets, energy storage and interruptible loads involved in the control; S l Represents the entire network line set, S l1 and S l0 Represents the set of overloaded lines and the set of non-overloaded lines.

3. The method for optimizing power flow transfer after an accident in a power system with energy storage as claimed in claim 2, characterized in that: Step S4 is specifically as follows: solving the optimization model constructed above to obtain the optimization result, and the dispatching system immediately sends a power adjustment signal to the energy storage power source, sound DC, generator set and load point to implement control and realize the optimization adjustment of the power flow distribution.

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