Method and system for carrying out flexibility evaluation on distributed photovoltaic and auxiliary equipment thereof based on projection method, and virtual power plant operator

Abstract

The invention discloses a method and a system for carrying out flexibility evaluation on distributed photovoltaic and auxiliary equipment based on a projection method, and a virtual power plant operator, relates to the field of electrical engineering, and is suitable for flexibility evaluation of any quantity and any type of distributed energy. All distributed energy sources are integrated into a power sub-grid which is connected with a superior power grid through a PCC (Personal Computer Controller). The method has the advantages of being high in solving precision, low in compromise degree and high in expansibility.

Description

Technical Field

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

[0002] Photovoltaic power generation, as a clean and renewable energy source, has received widespread attention and has developed rapidly. However, due to the influence of weather conditions and day and night changes, the output power of photovoltaic power generation has significant volatility and uncertainty, which poses a challenge to the stable operation of the power grid.

[0003] In order to solve the volatility problem of distributed photovoltaic power generation, there are currently two ways to deal with it. One is the traditional mode of abandoning light, which abandons part of the electricity when the photovoltaic power generation is too large. The other is the new method now - adding auxiliary energy storage equipment to photovoltaic power stations to play a buffering role between photovoltaics and the power grid. In order to make full use of photovoltaics, it is necessary to evaluate its flexibility. However, there is currently no unified flexibility evaluation plan for photovoltaics and their auxiliary equipment. Summary of the invention

[0004] Traditional photovoltaics, whether distributed or centralized, are considered as units that can provide unstable electricity in the power grid. However, the current high penetration of distributed photovoltaics means that photovoltaics cannot be simply regarded as a power supply unit, but a combination of a series of equipment - these equipment include all auxiliary equipment, such as energy storage units, energy storage converters, control equipment, communication equipment, etc. When considering distributed photovoltaics, the impact of these equipment cannot be ignored in order to evaluate the flexibility of photovoltaics as accurately as possible. Therefore, it is not accurate to simply add the upper and lower limits of the output of each distributed photovoltaic to obtain flexibility.

[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 trend of "large dispersion and small aggregation" 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] In order to achieve the above purpose, a method for evaluating the flexibility of distributed photovoltaics and its 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 The upper distance to the optimal flexibility domain boundary Ω best The farthest point

[0010] S4, point-based And 2 norm to shrink the boundary and get the point on the boundary of the optimal flexibility domain

[0011] S5. Base 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 is the amount of power that the distributed photovoltaic system can exchange with the outside world, D 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, solving 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, solving 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, solving 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, D is solved iteratively 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 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 abandoned light amount of each distributed photovoltaic to adjust the actual photovoltaic output power 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 dispatch center of the upper power grid and upload the calculated flexibility domain parameter D to the dispatch 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 is convenient for the upper power grid to make decisions and control.

[0045] 2. The present invention provides a flexibility assessment method based on projection method which is easy to expand and 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 of an embodiment provided by the present invention;

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

[0051] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain 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 can 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 assessment, the present invention provides a method for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on 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 The upper distance to the optimal flexibility domain boundary Ω best The farthest point Then based on the point And 2 norm to shrink the boundary and get the point 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 under the premise of low compromise and also has good scalability.

[0053] In order to achieve the above-mentioned purpose, an embodiment of the present invention provides a method for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on projection method, such as Figure 1 As 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 The upper distance to the optimal flexibility domain boundary Ω best The farthest point

[0057] S4, point-based And 2 norm to shrink the boundary and get the point on the boundary of the optimal flexibility domain

[0058] S5. Base 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 in the t-time period, and there are a total of T time periods. Formula (2-1) is the photovoltaic output constraint, formulas (2-2) and (2-3) are energy storage charging and discharging constraints, and formula (2-4) is 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 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, both 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 constitutes 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 obtained. Without loss of generality, "compromise degree" refers to the difference between the result obtained by the solution and the actual optimal result in order to ensure the feasibility of the solution. Specifically, in this patent, "compromise degree" refers to the area difference between the flexibility domain obtained by 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 is the power that the distributed photovoltaic system can exchange with the outside world, D 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 various constraints, the flexibility domain corresponding to the initial 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, formula (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". Formula (2-10) is equivalent to Formula (2-9).

[0083] Preferably, solving 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, solving 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, solving 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 A conceptual diagram of the iterative process is shown in Figure 3-2 As shown, with the iteration of, D K The outer blue area Keep shrinking.

[0090] Preferably, D is solved iteratively 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 is written on the computing software MATLAB R2024a, and the Yalmip solver equipped with gurobi is called to solve the problem. To solve the optimization problem, the computing device used is: a HUAWEI matebook laptop with an Intel Core i7-10510U processor, 16GB of running memory, and running the Windows 11 Professional operating system. The topology diagram used is as follows Figure 4 As shown, the solution result is Figure 5 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. 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] The embodiment of the present invention provides a distributed photovoltaic and auxiliary equipment flexibility assessment system based on 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 abandoned light amount of each distributed photovoltaic to adjust the actual photovoltaic output power 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 dispatch center of the upper power grid and upload the calculated flexibility domain parameter D to the dispatch 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, and all the 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 only 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 protection scope of the present invention.

Claims

1. A method for evaluating the flexibility of distributed photovoltaics and their auxiliary equipment based on the projection method. It is characterized in that The steps include: S1. At time t, obtain the output upper limit PV of each distributed photovoltaic at each time i max (t) and the maximum charging power P of its energy storage device i ch (t), maximum discharge power P i dis (t) and energy limit E max (t), and the upper power limit of each transmission line in the network topology S2. Get the initial technical constraints and network constraints AX≤B, the initial flexibility domain Constraint CP 总 ≤D 0 With the flexibility expression P 总 =EX+F; where matrix A is a constant coefficient matrix, vector B is a constant coefficient vector, and X is PE i (t), PV i (t), PL i (t) is a decision variable vector composed of 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 the t-th period. There are T periods in total. D 0 is the initial parameter vector obtained by the iterative method, D K is the parameter vector obtained in the Kth iteration, P 总 is the vector corresponding to the power value at the common coupling point PCC, that is, P 总 is the power size of the overall distributed photovoltaic that can be exchanged with the outside world, the matrix E is the summation coefficient matrix, and the vector F is the load coefficient matrix, both of which are constants; S3. Solve the min-max problem and obtain the current initial flexibility domain The upper distance to the optimal flexibility domain boundary Ω best The farthest point S4, based on Farthest point and 2 norm to perform boundary contraction and obtain the boundary of the optimal flexibility domain Boundary Points S5. Boundary Points Iteration D K And update the constraint CP 总 ≤D K ; The constant coefficient matrix C is as follows: C=[I T -I T L T -L T ] T (4) 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 .

2. The method for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on projection method as claimed in claim 1, It is characterized in that The technical constraints and network constraints are as follows: 0≤PV i (t)≤PV i max (t)(1) P i dis (t)≤PE i (t)≤P i ch (t)(2) 3. The method for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on projection method as claimed in claim 2, It is characterized in that Iterative solution of D K The first step is to find the farthest point The details are as follows: Solving equation (6) to obtain P 总 That is 4. The method for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on projection method as claimed in claim 3, It is characterized in that Iterative solution of D K The second step is to solve the boundary points The details are as follows: Solving equation (7) yields N 5. The method for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on projection method as claimed in claim 4, It is characterized in that Iterative solution of D K The third step is to solve the new D K , as follows: The M obtained by solving equation (8) is D K+1 .

6. The method for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on projection method as claimed in claim 5, It is characterized in that The iterative process is to update the constraint CP 总 ≤D K For CP 总 ≤D K+1 , 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 as claimed in claim 6, It is characterized in that The end mark of the iteration is that the solution result RES of equation (6) is 0, that is, the constraint condition corresponding to the equation has a solution.

8. A system for evaluating the flexibility of distributed photovoltaic and its auxiliary equipment based on projection method. It is characterized in that include: 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); Control module: used to control the charging and discharging PE of each energy storage unit i (t), and at the same time control the abandoned light amount of each distributed photovoltaic to adjust the actual photovoltaic output power PV i (t); 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 ; Communication module: used to communicate with the dispatch center of the upper power grid and upload the calculated flexibility domain parameter D to the dispatch center K , receiving instructions from the dispatch center and sending them to each module.

9. Virtual power plant operators, including multiple distributed photovoltaics, It is characterized in that All distributed photovoltaics under the virtual power plant operator are components of the system for flexibility assessment of distributed photovoltaics and their auxiliary equipment based on the projection method as described in claim 8.

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