Method, system and virtual power plant operator for flexibility evaluation of distributed photovoltaic and its auxiliary equipment based on projection method

Abstract

This invention discloses a method, system, and virtual power plant operator for evaluating the flexibility of distributed photovoltaic (PV) and its auxiliary equipment using a projection method. The method relates to the field of electrical engineering and is applicable to evaluating the flexibility of any number of distributed energy resources of any type, as long as all distributed energy resources are integrated into a power subgrid connected to a higher-level power grid via a PCC. This method offers high accuracy, minimal tradeoffs, and strong scalability.

Description

Technical Field

[0001] The present invention belongs to the field of electrical engineering technology. More specifically, the method is applicable to distributed photovoltaic power stations. Background Art

[0002] Photovoltaic power generation, as a clean, renewable energy source, has received widespread attention and is experiencing rapid development. However, due to the influence of weather conditions and day-night variations, the output power of photovoltaic power generation exhibits significant fluctuations and uncertainties, which poses challenges to the stable operation of the power grid.

[0003] To address the volatility of distributed photovoltaic power generation, there are currently two approaches. One is the traditional approach of curtailing solar power, which discards some of the electricity when photovoltaic power generation is excessive. The other is a newer approach: adding auxiliary energy storage devices to photovoltaic power plants to act as a buffer between the photovoltaic power plant and the grid. To fully utilize photovoltaic power, it is necessary to assess its flexibility. However, there is currently no unified flexibility assessment scheme for photovoltaic power plants and their auxiliary equipment. Summary of the Invention

[0004] Traditional photovoltaic systems, whether distributed or centralized, are designed to provide unstable power to the grid. However, the current high penetration of distributed photovoltaics means that photovoltaics cannot be viewed simply as a power supply unit, but rather as a combination of various devices—including all auxiliary equipment such as energy storage units, energy storage inverters, control devices, and communications equipment. When considering distributed photovoltaics, the impact of these devices must be considered to ensure the most accurate assessment of photovoltaic flexibility. Therefore, simply adding the upper and lower output limits of each distributed photovoltaic system to calculate flexibility is inaccurate.

[0005] "Flexibility" refers to the size and changing trend of active power. If we only look at a single distributed photovoltaic and its auxiliary equipment, the volume is too small, and the distribution of distributed photovoltaics has a "large dispersion and small aggregation" trend in space, that is, it is distributed as a whole, but it will be more dense in certain areas (such as villages, industrial parks, etc.), so it is necessary to consider the flexibility of distributed photovoltaics as a whole.

[0006] To achieve the above objectives, a method for evaluating the flexibility of distributed photovoltaics and their auxiliary equipment based on the projection method is provided, comprising:

[0007] S1. At time t, obtain the output upper limit PV of each distributed photovoltaic at each time i max (t) and the maximum charge and discharge power P of its energy storage device i ch (t), P idis (t) and energy limit E max (t), and the upper power limit of each transmission line in the network topology

[0008] S2. Get the initial technical constraints and network constraints AX≤B, the initial flexibility domain Constraint CP 总 ≤D0 and flexibility expression P 总 =EX+F; where D0 is the initial parameter vector obtained by the iterative method, D K is the parameter vector obtained at the Kth iteration.

[0009] S3. Solve the min-max problem and obtain the current initial flexibility domain Upper distance optimal flexibility domain boundary Ω best The farthest point

[0010] S4, point-based and 2 norm to perform boundary contraction and obtain points on the boundary of the optimal flexibility domain

[0011] S5, Stronghold Iteration D K And update the constraint CP 总 ≤D K .

[0012] S6. Continue to repeat the above steps S3-S5 until the min-max solution is 0, that is, stop the iteration and output the Kth iteration result D K .

[0013] Preferably, the specific form of the network constraint is:

[0014] 0≤PV i (t)≤PV i max (t)(1-1)

[0015] P i dis (t)≤PE i (t)≤P i ch (t)(1-2)

[0016]

[0017] Among them, PE i (t) is the external power exchange value of the i-th energy storage unit in period t, PV i (t) is the output value of the i-th distributed photovoltaic in period t, PL i(t) is the power flowing through the i-th line in time period t, and there are T time periods in total.

[0018] Preferably, the decision variable of the network constraint is X, and it is:

[0019] X=[PE i (t),PV i (t),PL i (t)] T (1-5)

[0020] Preferably, specifically, matrix A is a constant coefficient matrix, vector B is a constant coefficient vector, matrix E is a summation coefficient matrix, and vector F is a load coefficient matrix, all of which are constants.

[0021] Preferably, considering that distributed photovoltaics are integrated into a subgrid connected to the upper grid through a common coupling point PCC, P 总 is the vector corresponding to the power value at the common coupling point PCC, that is, P 总 D is the amount of power that the distributed photovoltaic system can exchange with the outside world. K is the parameter of the projection domain, that is, the object to be solved, and the constant coefficient matrix C is as follows:

[0022] C=[I T -I T Λ T -Λ T ] T (1-6)

[0023]

[0024] Specifically, all constraints are as follows:

[0025]

[0026] Preferably, the ultimate goal of solving the flexibility domain is to solve D K The first step is to find the farthest point The details are as follows:

[0027]

[0028] Specifically, solving equation (8) yields P 总 That is

[0029] Preferably, solve D K The second step is to solve the boundary points The details are as follows:

[0030]

[0031] Specifically, N obtained by solving equation (9) is

[0032] Preferably, solve D K The third step is to solve the new D K , as follows:

[0033]

[0034] Specifically, the M obtained by solving equation (10) is D K+1 , sum(·) means to sum the vectors in the brackets.

[0035] Preferably, solve D K It is an iterative process. Specifically, it repeatedly solves equations (1-9)-(1-11) and updates the constraint CP in the process. 总 ≤D K For CP 总 ≤D K+1 .

[0036] Preferably, iteratively solve D K The end mark is that the solution result RES of formula (8) is 0. Specifically, the constraint condition corresponding to formula (1-8) has a solution.

[0037] Furthermore, the present invention also provides a system for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on the projection method, comprising:

[0038] Measurement module: used to measure the PV of each distributed photovoltaic i max (t) and P of the energy storage unit i ch (t), P i dis (t) and E max (t).

[0039] Control module: used to control the charging and discharging PE of each energy storage unit i (t), and at the same time control the amount of abandoned light in each distributed photovoltaic to adjust the actual photovoltaic output PV i (t).

[0040] Edge computing module: receives the measured parameters from the measurement module and calculates the flexibility domain parameter D through the algorithm installed K and output the calculated D to the communication module K .

[0041] Communication module: used to communicate with the dispatching center of the upper power grid and upload the calculated flexibility domain parameter D to the dispatching center KIf necessary, it can also receive instructions from the dispatch center and send them to each module.

[0042] Furthermore, the present invention also provides a virtual power plant operator, including multiple distributed photovoltaics, and all distributed photovoltaics under the virtual power plant operator are components of a system for flexibility assessment of distributed photovoltaics and their auxiliary equipment based on the projection method as described in the present invention.

[0043] The present invention has the following beneficial effects:

[0044] 1. The evaluation method provided by the present invention accurately describes the coupling relationship of distributed photovoltaic flexibility between adjacent time periods, which facilitates decision-making and control by the upper power grid.

[0045] 2. The present invention provides an easily scalable flexibility assessment method based on projection method, which can also be applied to the flexibility assessment of any number of distributed energy sources of any type, as long as all distributed energy sources are integrated into a power subgrid connected to the upper power grid through PCC. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A flow chart of a method for aggregating and regulating distributed photovoltaics based on an analytical approach;

[0047] Figure 2 Conceptual diagram of the projection method for evaluating distributed photovoltaic flexibility provided by the present invention;

[0048] Figure 3-1 , 3-2, 3-3 are conceptual diagrams of iterative solutions for evaluating distributed photovoltaic flexibility provided by the present invention; wherein, the blue area is the flexibility domain of the iterative solution, and the area within the red border is the optimal flexibility domain. Figure 3-1 are the initial flexibility domain and the optimal flexibility domain, Figure 3-2 is the flexibility domain after the first iteration, Figure 3-3 The flexibility domain for when the iteration is completed;

[0049] Figure 4 An improved IEEE-13 node feeder diagram according to an embodiment of the present invention;

[0050] Figure 5 This is a simulation verification result diagram provided by the present invention on the IEEE-13 node feeder diagram; DETAILED DESCRIPTION

[0051] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0052] In order to solve the current problem of distributed photovoltaic flexibility evaluation, the present invention provides a method for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on the projection method. The overall idea is to obtain the output upper limit PV of each distributed photovoltaic at each moment. i max (t) and the maximum charge and discharge power P of its energy storage device i ch (t), P i dis (t) and energy limit E max (t), and consider the power limit of each transmission line in the network topology Get the initial technical constraints and network constraints AX≤B, the initial flexibility domain Constraint CP 总 ≤D0 and flexibility expression P 总 =EX+F; where D0 is the initial parameter vector obtained by the iterative method, D K is the parameter vector obtained at the Kth iteration. Then, solve the min-max problem and obtain the current initial flexibility domain Upper distance optimal flexibility domain boundary Ω best The farthest point Then based on the point and 2 norm to perform boundary contraction and obtain points on the boundary of the optimal flexibility domain And based on this point Iteration D K And update the constraint CP 总 ≤D K , continue to repeat the above steps until the min-max solution is 0, that is, stop the iteration and output the Kth iteration result D K This method can ensure the accuracy of flexibility domain estimation with a low degree of compromise and also has good scalability.

[0053] In order to achieve the above objectives, the embodiment of the present invention provides a method for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on the projection method, such as Figure 1 Shown, including:

[0054] S1. At time t, obtain the output upper limit PV of each distributed photovoltaic at each time imax (t) and the maximum charge and discharge power P of its energy storage device i ch (t), P i dis (t) and energy limit E max (t), and the upper power limit of each transmission line in the network topology

[0055] S2. Get the initial technical constraints and network constraints AX≤B, the initial flexibility domain Constraint CP 总 ≤D0 and flexibility expression P 总 =EX+F; where D0 is the initial parameter vector obtained by the iterative method, D K is the parameter vector obtained at the Kth iteration.

[0056] S3. Solve the min-max problem and obtain the current initial flexibility domain Upper distance optimal flexibility domain boundary Ω best The farthest point

[0057] S4, point-based and 2 norm to perform boundary contraction and obtain points on the boundary of the optimal flexibility domain

[0058] S5, Stronghold Iteration D K And update the constraint CP 总 ≤D K .

[0059] S6. Continue to repeat the above steps S3-S5 until the min-max solution is 0, that is, stop the iteration and output the Kth iteration result D K .

[0060] Preferably, the specific form of the network constraint is:

[0061] 0≤PV i (t)≤PV i max (t)(2-1)

[0062] P i dis (t)≤PE i (t)≤P i ch (t)(2-2)

[0063]

[0064] Among them, PEi (t) is the external power exchange value of the i-th energy storage unit in period t, PV i (t) is the output value of the i-th distributed photovoltaic in period t, PL i (t) is the power flowing through the i-th line during time period t, with a total of T time periods. Equation (2-1) represents the PV output constraint, Equations (2-2) and (2-3) represent the energy storage charge and discharge constraints, and Equation (2-4) represents the transmission line constraint.

[0065] Preferably, the decision variable of the network constraint is X, which is the value of all PE i (t), PV i (t) and PL i (t) The set of all time periods, which is:

[0066] X=[PE i ,PV i ,PL i ] T (2-5)

[0067] Specifically, matrix A is a constant coefficient matrix, vector B is a constant coefficient vector, matrix E is a summation coefficient matrix, and vector F is a load coefficient matrix, all of which are constants.

[0068] Preferably, the original high-dimensional polyhedron is determined by the constraint AX≤B. Specifically, each element in the decision variable X corresponds to a dimension, which together constitute the high-dimensional polyhedron Ω original , and the optimal flexibility domain Ω best is a high-dimensional polyhedron Ω original The concept of projection method is as follows: Figure 2 shown.

[0069] Since solving this problem is an NP-hard problem, we can only solve the flexibility domain Ω best An approximate solution is obtained but the exact value cannot be determined. Without loss of generality, "compromise" refers to the difference between the solution obtained and the actual optimal solution in order to ensure the feasibility of the solution. Specifically, in this patent, "compromise" refers to the area difference between the flexibility domain obtained using the projection method and the actual optimal flexibility domain.

[0070] Preferably, P 总 is the vector corresponding to the power value at the common coupling point PCC, that is, P 总 D is the power that can be exchanged between the distributed photovoltaic system and the outside world. K is the parameter of the projection domain, that is, the object to be solved, and the constant coefficient matrix C is as follows:

[0071] C=[I T -I T Λ T-Λ T ] T (2-6)

[0072]

[0073] Preferably, D K An initial value D0 needs to be given. Due to the existence of various constraints, the flexibility domain corresponding to the initially given D0 must be infeasible, such as Figure 3-1 As shown, the blue area Completely in Ω best External. The purpose of iteration is to change D0→D K , so that the new flexibility domain satisfies all constraints. The specific method to obtain D0 is as follows:

[0074]

[0075] Specifically, all constraints are as follows. If it is the first iteration, the D used in the solution is K For D0:

[0076]

[0077] Preferably, the ultimate goal of solving the flexibility domain is to solve D K The first step is to find the farthest point The details are as follows:

[0078]

[0079] Specifically, solving equation (8) yields P 总 That is

[0080] Preferably, Equation (2-9) is a linear optimization problem, so it can be transformed into an equivalent problem that is easy to solve using the dual method, as follows:

[0081]

[0082] Specifically, α and β are the dual variables corresponding to the decision variable X, χ is the Lagrange multiplier, and δ is the auxiliary Boolean variable of the "Big M method". Equation (2-10) is equivalent to Equation (2-9).

[0083] Preferably, solve D K The second step is to solve the boundary points The details are as follows:

[0084]

[0085] Specifically, N obtained by solving equation (9) is

[0086] Preferably, solve D K The third step is to solve the new D K , as follows:

[0087]

[0088] Specifically, the M obtained by solving equation (2-14) is D K+1 , sum(·) means to sum the vectors in the brackets.

[0089] Preferably, solve D K It is an iterative process. Specifically, it repeatedly solves equations (2-12)-(2-14) and updates the constraint CP in the process. 总 ≤D K For CP 总 ≤D K+1 , D K is the parameter obtained in the Kth iteration, and the obtained projection domain is The conceptual diagram of the iterative process is as follows Figure 3-2 As shown, with the iteration of, D K The outer blue area Keep shrinking.

[0090] Preferably, iteratively solve D K The end mark is that the solution result RES of formula (2-11) is 0. Specifically, the constraint condition corresponding to formula (2-10) has a solution. The conceptual diagram of the completed iteration is as follows Figure 3-3 As shown, the blue area Completely in Ω best internal.

[0091] The corresponding program was written in the computing software MATLAB R2024a, and the Yalmip solver equipped with gurobi was used to solve the optimization problem. The computing device used was: a HUAWEI matebook laptop with an Intel Core i7-10510U processor, 16GB of RAM, and running the Windows 11 Professional operating system. The topology diagram used is as follows: Figure 4 As shown, the solution results are as follows Figure 5 As shown. The solution is P 总 The upper and lower bounds of the selection area are 7h-12h in a day.

[0092] The present invention provides a system for evaluating the flexibility of distributed photovoltaics and their auxiliary equipment based on a projection method below. The system for evaluating the flexibility of distributed photovoltaics and their auxiliary equipment based on a projection method described below and the method for evaluating the flexibility of distributed photovoltaics and their auxiliary equipment based on a projection method described above can be referenced to each other.

[0093] An embodiment of the present invention provides a distributed photovoltaic and auxiliary equipment flexibility assessment system based on a projection method, comprising:

[0094] Measurement module: used to measure the PV of each distributed photovoltaic i max (t) and P of the energy storage unit i ch (t), P i dis (t) and E max (t).

[0095] Control module: used to control the charging and discharging PE of each energy storage unit i (t), and at the same time control the amount of abandoned light in each distributed photovoltaic to adjust the actual photovoltaic output PV i (t).

[0096] Edge computing module: receives the measured parameters from the measurement module and calculates the flexibility domain parameter D through the algorithm installed K and output the calculated D to the communication module K

[0097] Communication module: used to communicate with the dispatching center of the upper power grid and upload the calculated flexibility domain parameter D to the dispatching center K If necessary, it can also receive instructions from the dispatch center and send them to each module.

[0098] The present invention provides a virtual power plant operator, including multiple distributed photovoltaics. All distributed photovoltaics under the virtual power plant operator are components of a system for flexibility assessment of distributed photovoltaics and their auxiliary equipment based on the projection method as described in the above embodiment.

[0099] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for evaluating the flexibility of distributed photovoltaics and their auxiliary equipment based on a projection method, characterized in that: The steps include: S1. At the moment t , obtain the output limit of each distributed photovoltaic at each moment and the maximum charging power of its energy storage equipment , Maximum discharge power and energy limit , and the upper power limit of each transmission line in the network topology ; S2. Obtain initial technical constraints and network constraints , initial flexibility domain Constraints Expressions with flexibility ; Among them, the matrix is a constant coefficient matrix, vector is a constant coefficient vector, yes , , The decision variable vector composed of For the Energy storage units in External power exchange value of the time period, For the Distributed photovoltaic Output value of the period, For the On the line The power flow during the period is Periods, is the initial parameter vector obtained by the iterative method, is the vector corresponding to the power value at the common coupling point PCC, that is, The power size of the distributed photovoltaic system that can be exchanged with the outside world, the matrix is the sum coefficient matrix, vector is the load factor matrix, all of which are constants; S3. Solve the min-max problem and obtain the current initial flexibility domain Upper distance to the optimal flexibility domain boundary The farthest point ; S4, based on the farthest point And 2 norm to perform boundary contraction and obtain the boundary points on the boundary of the optimal flexibility domain ; S5, according to the border point Iteration and update the constraints , For the The parameter vector obtained by the iteration; Constant coefficient matrix as follows: （4） （5） S6. Continue to repeat the above steps S3-S5 until the min-max solution is 0, that is, stop the iteration and output the Iteration results .

2. The method for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on the projection method according to claim 1, characterized in that: The technical and network constraints are as follows: （1） （2） （3）。 3. The method for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on the projection method according to claim 2, characterized in that: Iterative solution The first step is to find the farthest point , as follows: （6） Solving equation (6) yields That is .

4. The method for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on the projection method according to claim 3, characterized in that: Iterative solution The second step is to solve the boundary points , as follows: （7） Solving equation (7) yields That is .

5. The method for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on the projection method according to claim 4, characterized in that: Iterative solution The third step is to solve the new , as follows: （8） Solving equation (8) yields That is .

6. The method for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on projection method according to claim 5, characterized in that: The iterative process is to update the constraints for , and repeat the steps as described in claims 3-5.

7. The method for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on projection method according to claim 6, characterized in that: The end mark of the iteration is the solution of formula (6) is 0, that is, the constraint condition corresponding to the formula has a solution.

8. A system for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on the projection method according to any one of claims 1 to 7, characterized in that: include: Measurement module: used to measure the and energy storage units , and ; Control module: used to control the charging and discharging of each energy storage unit , and at the same time control the amount of abandoned light in each distributed photovoltaic system to adjust the actual photovoltaic output power ; Edge computing module: receives the measured parameters from the measurement module and calculates the flexibility domain parameters through the algorithm installed , and output the calculated ; Communication module: used to communicate with the dispatch center of the upper power grid and upload the calculated flexibility domain parameters to the dispatch center , receive instructions from the dispatch center and send them to each module.

9. A virtual power plant operator, comprising multiple distributed photovoltaics, characterized in that: All distributed photovoltaics under the virtual power plant operator are composed of the flexibility assessment system for distributed photovoltaics and their auxiliary equipment based on the projection method as described in claim 8.

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