A discrete continuous reactive source coordinated control method and device

Abstract

The present invention discloses a method and device for collaborative control of discrete and continuous reactive sources. The present invention predicts the future busbar node voltage of multiple sections continuously based on ultra-short-term load forecast information, ultra-short-term new energy forecast information, and power plant maintenance plans. On a regional scale, discrete quantity decisions at the gateway station are made at the gateway side to respond to the voltage situation of the entire region, and a regional gateway substation voltage control model is constructed. The calculation results of the regional gateway substation voltage control model and the predicted voltage fluctuations are combined to correct the standard regional voltage control model, coordinate continuous and discrete quantities in the region to make optimal decisions, reduce the risk of over-limit caused by random voltage fluctuations, improve the voltage quality of the regional power grid, reduce the cost of reactive adjustment, and enhance the level of new energy consumption, thereby providing an important technical means for reactive voltage decision-making in new power systems.

Description

Technical Field

[0001] The present invention relates to a discrete-continuous reactive source coordinated control method and device, belonging to the technical field of power system operation and control. Background Art

[0002] Automatic voltage control (AVC) is an important module for managing and controlling grid voltage. However, the large-scale integration of new energy sources into the distribution network has led to a sharp deterioration in the random fluctuations in grid voltage, creating the risk of exceeding the voltage limit. Summary of the Invention

[0003] The present invention provides a discrete-continuous reactive power source coordinated control method and device, which solves the problems disclosed in the background technology.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] A discrete continuous reactive power source coordinated control method, comprising:

[0006] Calculate the busbar node voltages at multiple consecutive sections in the future based on ultra-short-term load forecast information, ultra-short-term new energy forecast information, and power plant maintenance plans;

[0007] If the bus node voltage change trend direction is consistent and the change amount exceeds the threshold, a regional gateway substation voltage control model is constructed based on the bus node voltage change trend, and the regional gateway substation voltage control model is used to obtain the regional gateway discrete quantity control decision;

[0008] If a regional gateway discrete quantity control decision exists, the standard regional voltage control model is modified based on the gateway discrete quantity action and bus node voltage change trend corresponding to the regional gateway discrete quantity control decision, and the modified regional voltage control model is used to coordinate the regional continuous quantity and discrete quantity to make reactive power decision.

[0009] Based on ultra-short-term load forecast information, ultra-short-term renewable energy forecast information, and power plant maintenance plans, calculate the future busbar node voltages at multiple sections in the region, including:

[0010] Based on ultra-short-term load forecast information, ultra-short-term new energy forecast information, and power plant maintenance plans, obtain the active power of regional bus nodes at multiple consecutive sections;

[0011] According to the active power of regional bus nodes in multiple consecutive sections, the section power flow equation is constructed;

[0012] Based on the section's power flow equation, calculate the busbar node voltages of multiple sections in the region in the future.

[0013] The voltage control model of regional gateway substation is:

[0014]

[0015]

[0016]

[0017] Where m is the number of sections, s is the serial number of the continuous sections, s = 1, 2, 3…, m, i is the serial number of the busbar node, is the reactive power adjustment of the reactor in the regional gateway substation, is the voltage of the important busbar node at section s in the regional gateway substation, is the voltage target of the important busbar node at section s in the regional gateway substation, V i s is the voltage of the ith busbar node in the sth section, V i s V i s The lower limit of V i s The upper limit, is the voltage sensitivity of the reactor reactive power in the regional gateway substation to the important busbar in the region, is the voltage sensitivity of the reactor reactive power in the regional gateway substation to the i-th bus node, The reactive power of the reactor in the regional gateway substation, for The lower limit of for upper limit.

[0018] If the bus node voltage change trend direction is inconsistent, the bus node voltage change exceeds the threshold, or the regional gateway discrete quantity control decision does not exist, the standard regional voltage control model is modified based on the bus node voltage change trend.

[0019] Based on the discrete quantity actions of the regional discrete quantity control decisions and the bus node voltage change situation, or based on the bus node voltage change situation, the standard regional voltage control model is modified, including:

[0020] Calculate the upper and lower limit deviations of the bus node voltage based on the gateway discrete quantity action corresponding to the regional gateway discrete quantity control decision and the bus node voltage change situation, or based on the bus node voltage change situation;

[0021] The standard regional voltage control model is modified according to the upper and lower limit deviations of the bus node voltage.

[0022] The formula for calculating the upper and lower limit deviations of the bus node voltage is:

[0023]

[0024]

[0025] in, is the upper limit deviation of the voltage at the ith busbar node, are the lower limit deviation of the voltage of the ith bus node, V i is the current voltage of the i-th bus node, … are the voltages of the ith busbar node of the 1st, 2nd, ...mth sections, respectively. is the voltage sensitivity of the reactor reactive power in the regional gateway substation to the i-th bus node, is the reactive power adjustment of the reactor in the regional gateway substation, is a step function, and there is a discrete control decision at the regional threshold When it is 1, there is no discrete control decision at the regional gate is 0.

[0026] The revised regional voltage control model is:

[0027]

[0028] st

[0029]

[0030]

[0031] Among them, V p is the current voltage of important buses in the area, is the current voltage target of the important busbars in the area, Q c is the reactive power of the reactor in the region, Q c Q c The lower limit of Q c The upper limit of ΔQ g is the reactive power adjustment of the units / new energy equivalent units in the region, ΔQ c is the reactive power adjustment of the reactor in the region, C g is the voltage sensitivity of the regional units / new energy equivalent units to the regional important busbars by reactive power, C c is the sensitivity of the reactive power of the reactor in the region to the voltage of the important busbar in the region, C g,i is the voltage sensitivity of the reactive power of the units / new energy equivalent units in the region to the i-th bus node, C c,i is the voltage sensitivity of the reactor reactive power to the i-th bus node in the region, Vi V i The lower limit of V i The upper limit, Q g is the current reactive power of the units / new energy etc. in the area, Q g Q g The lower limit of Q g The upper limit, Q c is the current reactive power of the reactor in the area, Q c Q c The lower limit of Q c upper limit.

[0032] A discrete continuous reactive power source coordinated control device, comprising:

[0033] The future voltage calculation module calculates the busbar node voltages of multiple consecutive sections in the region in the future based on ultra-short-term load forecast information, ultra-short-term new energy forecast information, and power plant maintenance plans;

[0034] The regional gateway reactive power decision module, if the bus node voltage change trend direction is consistent and the change amount exceeds the threshold, builds a regional gateway substation voltage control model based on the bus node voltage change trend, and uses the regional gateway substation voltage control model to obtain the regional gateway discrete quantity control decision;

[0035] The regional coordinated reactive power decision-making module, if a regional gateway discrete quantity control decision exists, modifies the standard regional voltage control model based on the gateway discrete quantity action and bus node voltage change trend corresponding to the regional gateway discrete quantity control decision, and uses the modified regional voltage control model to coordinate regional continuous and discrete quantities for reactive power decision-making.

[0036] A computer-readable storage medium stores one or more programs, wherein the one or more programs include instructions that, when executed by a computing device, cause the computing device to perform a discrete-time continuous reactive power source coordinated control method.

[0037] A computing device includes one or more processors, one or more memories, and one or more programs, wherein the one or more programs are stored in the one or more memories and are configured to be executed by the one or more processors, and the one or more programs include instructions for executing a discrete continuous reactive source cooperative control method.

[0038] The beneficial effects achieved by the present invention are as follows: Based on ultra-short-term load forecast information, ultra-short-term new energy forecast information, and power plant maintenance plans, the present invention predicts the future bus node voltage of multiple continuous sections, responds to the voltage situation of the entire region on the gateway side through discrete quantity decisions of the gateway station on a regional scale, constructs a regional gateway substation voltage control model, combines the calculation results of the regional gateway substation voltage control model with the predicted voltage fluctuations, corrects the standard regional voltage control model, coordinates continuous and discrete quantities in the region to make optimal decisions, reduces the risk of over-limit caused by random voltage fluctuations, improves the voltage quality of the regional power grid, reduces the cost of reactive power adjustment, and improves the level of new energy consumption, providing an important technical means for reactive power and voltage decision-making in new power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Flowchart of the method of the present invention. DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0041] A discrete continuous reactive power source coordinated control method comprises the following steps:

[0042] Step 1: Calculate the busbar node voltages of multiple consecutive sections in the region in the future based on ultra-short-term load forecast information, ultra-short-term new energy forecast information, and power plant maintenance plans;

[0043] Step 2: If the bus node voltage change trends are consistent in direction and the change exceeds the threshold, a regional gateway substation voltage control model is constructed based on the bus node voltage change trends, and the regional gateway substation voltage control model is used to obtain the regional gateway discrete quantity control decision;

[0044] Step 3: If a regional gateway discrete quantity control decision exists, based on the gateway discrete quantity action corresponding to the regional gateway discrete quantity control decision and the bus node voltage change trend, the standard regional voltage control model is modified, and the modified regional voltage control model is used to coordinate the regional continuous quantity and discrete quantity to make reactive power decision.

[0045] The above method is based on ultra-short-term load forecast information, ultra-short-term new energy forecast information, and power plant maintenance plans to predict the future bus node voltage of multiple continuous sections. On the regional scale, the discrete quantity decision of the gateway station is used to respond to the voltage situation of the entire region on the gateway side, and a regional gateway substation voltage control model is constructed. Combined with the calculation results of the regional gateway substation voltage control model and the predicted voltage fluctuations, the standard regional voltage control model is modified, and the continuous and discrete quantities in the region are coordinated to make optimal decisions, reduce the risk of over-limit caused by random voltage fluctuations, improve the voltage quality of the regional power grid, reduce the cost of reactive power adjustment, and enhance the level of renewable energy consumption, providing an important technical means for reactive power and voltage decision-making in new power systems.

[0046] The specific process of the above method is as follows Figure 1 As shown in the figure, we first obtain highly accurate day-ahead forecast information, including ultra-short-term load forecast information, ultra-short-term new energy forecast information, and power plant maintenance plans. Based on the above information, we can obtain the active power of the regional bus node in multiple consecutive sections, which can be expressed as follows:

[0047]

[0048]

[0049] Where s is the serial number of the continuous section, s = 1, 2, 3…, m, m is the number of sections, i is the serial number of the busbar node, f is the future power flow function of the predicted load and power plant maintenance plan, P i s is the load of the s sections of the future busbar node i, is the predicted load of the sth section in the future, The predicted output of new energy in the sth section in the future, L is the set of load prediction bus nodes, W is the set of new energy / power plant prediction bus nodes, is the maintenance influencing factor of the s-section unit.

[0050] Furthermore, based on the active power of the regional busbar node in multiple consecutive sections, the section power flow equation can be constructed, which can be expressed as follows:

[0051]

[0052] Where n is the total number of busbar nodes in the power grid, P i s is the active power of the s-th section of the i-th busbar node, is the reactive power of the s-th section of the i-th busbar node, is the voltage value of the ith busbar node in the sth section, is the voltage value of the jth busbar node in the sth section, are the conductance, susceptance and phase angle difference between the i-th busbar node and the j-th busbar node in the s-th section respectively.

[0053] By solving the above equations, the bus node voltages at multiple sections in the future can be calculated. Based on the calculated bus node voltages, the bus node voltage change trend can be evaluated. If the bus node voltage change direction is consistent and the change exceeds the threshold, a regional gateway substation voltage control model is constructed based on the bus node voltage change trend. The regional gateway substation voltage control model is used to obtain the regional gateway discrete quantity control decision. The model aims to minimize the regional control cost. The formula can be expressed as:

[0054]

[0055] st

[0056]

[0057] Where m is the number of sections, s is the serial number of the continuous sections, s = 1, 2, 3…, m, i is the serial number of the busbar node, is the reactive power adjustment of the reactor in the regional gateway substation, is the voltage of the important busbar node at section s in the regional gateway substation, is the voltage target of the important busbar node at section s in the regional gateway substation, V i s is the voltage of the ith busbar node in the sth section, V i s V i s The lower limit of V i s The upper limit, is the voltage sensitivity of the reactor reactive power in the regional gateway substation to the important busbar in the region, is the voltage sensitivity of the reactor reactive power in the regional gateway substation to the i-th bus node, The reactive power of the reactor in the regional gateway substation, for The lower limit of for upper limit.

[0058] If there is a regional gateway discrete quantity control decision, the standard regional voltage control model is modified based on the gateway discrete quantity action and bus node voltage change trend corresponding to the regional gateway discrete quantity control decision (the standard regional voltage control model is an existing model and is not described in detail here).

[0059] If the bus node voltage change trend direction is inconsistent, the bus node voltage change exceeds the threshold, or the regional gateway discrete quantity control decision does not exist, the standard regional voltage control model is modified based on the bus node voltage change trend.

[0060] The modified standard regional voltage control model may specifically include: calculating the upper limit deviation and the lower limit deviation of the bus node voltage based on the gateway discrete quantity action corresponding to the regional gateway discrete quantity control decision and the bus node voltage change trend, or based on the bus node voltage change trend; and modifying the standard regional voltage control model according to the upper limit deviation and the lower limit deviation of the bus node voltage.

[0061] The correction process can be divided into two parts:

[0062] 1. First, calculate the upper and lower limit deviations of the bus node voltage according to the following formula;

[0063]

[0064] Among them, among them, is the upper limit deviation of the voltage at the ith busbar node, are the lower limit deviation of the voltage of the ith bus node, V i is the current voltage of the i-th bus node, … are the voltages of the ith busbar node of the 1st, 2nd, ...mth sections, respectively. is the voltage sensitivity of the reactor reactive power in the regional gateway substation to the i-th bus node, is the reactive power adjustment of the reactor in the regional gateway substation, is a step function, and there is a discrete control decision at the regional threshold When it is 1, there is no discrete control decision at the regional gate is 0.

[0065] 2. Then modify the regional coordinated secondary voltage control formula:

[0066] The revised regional voltage control model is:

[0067]

[0068] st

[0069]

[0070]

[0071] Among them, V p is the current voltage of important buses in the area, is the voltage target of the important busbars in the area, Q c is the reactive power of the reactor in the region, Q c Q c The lower limit of Q c The upper limit of ΔQ g is the reactive power adjustment of the units / new energy equivalent units in the region, C g is the voltage sensitivity of the regional units / new energy equivalent units to the regional important busbars by reactive power, C c is the sensitivity of the reactive power of the reactor in the region to the voltage of the important busbar in the region, C g,i is the voltage sensitivity of the reactive power of the units / new energy equivalent units in the region to the i-th bus node, V i V i The lower limit of V i The upper limit, Q g is the current reactive power of the units / new energy etc. in the area, Q g Q g The lower limit of Q g The upper limit, Q c is the current reactive power of the reactor in the area, Q c Q c The lower limit of Q c upper limit.

[0072] Finally, the modified regional voltage control model is used to coordinate regional continuous and discrete quantities to make reactive power decisions.

[0073] The above method evaluates the future voltage situation of the power grid bus nodes based on the day-ahead prediction, coordinates and optimizes continuous and discrete quantities at multiple times, improves the dynamic reactive power reserve level, reduces the number of discrete reactive source operations, improves the optimized operation level of the power grid on the entire time scale, and supports the safe absorption of new energy.

[0074] Based on the same technical solution, the present invention also discloses a software system of the above method, a discrete continuous reactive source cooperative control device, comprising:

[0075] The future voltage calculation module calculates the busbar node voltages of multiple consecutive sections in the region in the future based on ultra-short-term load forecast information, ultra-short-term new energy forecast information, and power plant maintenance plans;

[0076] The regional gateway reactive power decision module, if the bus node voltage change trend direction is consistent and the change amount exceeds the threshold, builds a regional gateway substation voltage control model based on the bus node voltage change trend, and uses the regional gateway substation voltage control model to obtain the regional gateway discrete quantity control decision;

[0077] The regional coordinated reactive power decision-making module, if a regional gateway discrete quantity control decision exists, modifies the standard regional voltage control model based on the gateway discrete quantity action and bus node voltage change trend corresponding to the regional gateway discrete quantity control decision, and uses the modified regional voltage control model to coordinate regional continuous and discrete quantities for reactive power decision-making.

[0078] In the above system, the data processing flow and method of each model are consistent and will not be repeated here.

[0079] Based on the same technical solution, the present invention also discloses a computer-readable storage medium storing one or more programs, wherein the one or more programs include instructions, which, when executed by a computing device, enable the computing device to perform a discrete continuous reactive source collaborative control method.

[0080] Based on the same technical solution, the present invention also discloses a computing device, including one or more processors, one or more memories and one or more programs, wherein the one or more programs are stored in the one or more memories and are configured to be executed by the one or more processors, and the one or more programs include instructions for executing a discrete continuous reactive source collaborative control method.

[0081] It will be understood by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0082] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0083] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0084] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0085] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of the claims of the present invention to be approved.

Claims

1. A discrete continuous reactive power source coordinated control method, characterized in that: include: Calculate the busbar node voltages at multiple consecutive sections in the future based on ultra-short-term load forecast information, ultra-short-term new energy forecast information, and power plant maintenance plans; If the bus node voltage change trend direction is consistent and the change amount exceeds the threshold, a regional gateway substation voltage control model is constructed based on the bus node voltage change trend, and the regional gateway substation voltage control model is used to obtain the regional gateway discrete quantity control decision; If a regional gateway discrete quantity control decision exists, the standard regional voltage control model is modified based on the gateway discrete quantity action and bus node voltage change trend corresponding to the regional gateway discrete quantity control decision, and the modified regional voltage control model is used to coordinate the regional continuous quantity and discrete quantity to make reactive power decision.

2. The discrete-continuous reactive source coordinated control method according to claim 1, characterized in that: Based on ultra-short-term load forecast information, ultra-short-term renewable energy forecast information, and power plant maintenance plans, calculate the future busbar node voltages at multiple sections in the region, including: Based on ultra-short-term load forecast information, ultra-short-term new energy forecast information, and power plant maintenance plans, obtain the active power of regional bus nodes at multiple consecutive sections; According to the active power of regional bus nodes in multiple consecutive sections, the section power flow equation is constructed; Based on the section's power flow equation, calculate the busbar node voltages of multiple sections in the region in the future.

3. The discrete-continuous reactive source coordinated control method according to claim 1, characterized in that: The voltage control model of regional gateway substation is: Where m is the number of sections, s is the serial number of the continuous sections, s = 1, 2, 3…, m, i is the serial number of the busbar node, is the reactive power adjustment of the reactor in the regional gateway substation, is the voltage of the important busbar node at section s in the regional gateway substation, is the voltage target of the important busbar node at section s in the regional gateway substation, V i s is the voltage of the ith busbar node in the sth section, V i s V i s The lower limit of V i s The upper limit, is the voltage sensitivity of the reactor reactive power in the regional gateway substation to the important busbar in the region, is the voltage sensitivity of the reactor reactive power in the regional gateway substation to the i-th bus node, The reactive power of the reactor in the regional gateway substation, for The lower limit of for upper limit.

4. The discrete-continuous reactive source coordinated control method according to claim 1, characterized in that: If the bus node voltage change trend direction is inconsistent, the bus node voltage change exceeds the threshold, or the regional gateway discrete quantity control decision does not exist, the standard regional voltage control model is modified based on the bus node voltage change trend.

5. A discrete-continuous reactive source coordinated control method according to claim 1 or 4, characterized in that: Based on the discrete quantity actions of the regional discrete quantity control decisions and the bus node voltage change situation, or based on the bus node voltage change situation, the standard regional voltage control model is modified, including: Calculate the upper and lower limit deviations of the bus node voltage based on the gateway discrete quantity action corresponding to the regional gateway discrete quantity control decision and the bus node voltage change situation, or based on the bus node voltage change situation; The standard regional voltage control model is modified according to the upper and lower limit deviations of the bus node voltage.

6. The discrete-continuous reactive source coordinated control method according to claim 5, characterized in that: The formula for calculating the upper and lower limit deviations of the bus node voltage is: Where, ΔV i + is the upper limit deviation of the voltage at the i-th bus node, ΔV i - are the lower limit deviation of the voltage of the ith bus node, V i is the current voltage of the ith bus node, V i 1 、V i 2 ,…V i m are the voltages of the ith busbar node of the 1st, 2nd, ...mth sections, respectively. is the voltage sensitivity of the reactor reactive power in the regional gateway substation to the i-th bus node, is the reactive power adjustment of the reactor in the regional gateway substation, is a step function, and there is a discrete control decision at the regional threshold When it is 1, there is no discrete control decision at the regional gate is 0.

7. The discrete-continuous reactive power source coordinated control method according to claim 6, characterized in that: The revised regional voltage control model is: Among them, V p is the current voltage of important buses in the area, is the current voltage target of the important busbars in the area, Q c is the reactive power of the reactor in the region, Q c Q c The lower limit of Q c The upper limit of ΔQ g is the reactive power adjustment of the units / new energy equivalent units in the region, ΔQ c is the reactive power adjustment of the reactor in the region, C g is the voltage sensitivity of the regional units / new energy equivalent units to the regional important busbars by reactive power, C c is the sensitivity of the reactive power of the reactor in the region to the voltage of the important busbar in the region, C g,i is the voltage sensitivity of the reactive power of the units / new energy equivalent units in the region to the i-th bus node, C c,i is the voltage sensitivity of the reactor reactive power to the i-th bus node in the region, V i V i The lower limit of V i The upper limit, Q g is the current reactive power of the units / new energy etc. in the area, Q g Q g The lower limit of Q g upper limit.

8. A discrete continuous reactive power source cooperative control device, characterized in that: include: The future voltage calculation module calculates the busbar node voltages of multiple consecutive sections in the region in the future based on ultra-short-term load forecast information, ultra-short-term new energy forecast information, and power plant maintenance plans; The regional gateway reactive power decision module, if the bus node voltage change trend direction is consistent and the change amount exceeds the threshold, builds a regional gateway substation voltage control model based on the bus node voltage change trend, and uses the regional gateway substation voltage control model to obtain the regional gateway discrete quantity control decision; The regional coordinated reactive power decision-making module, if a regional gateway discrete quantity control decision exists, modifies the standard regional voltage control model based on the gateway discrete quantity action and bus node voltage change trend corresponding to the regional gateway discrete quantity control decision, and uses the modified regional voltage control model to coordinate regional continuous and discrete quantities for reactive power decision-making.

9. A computer-readable storage medium storing one or more programs, characterized in that: The one or more programs include instructions that, when executed by a computing device, cause the computing device to perform any one of the methods according to claims 1 to 7.

10. A computing device, characterized in that include: One or more processors, one or more memories, and one or more programs, wherein the one or more programs are stored in the one or more memories and configured to be executed by the one or more processors, the one or more programs comprising instructions for performing any of the methods according to claims 1 to 7.

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