A multi-level reactive power coordination optimization method for substation-line-transformer considering photovoltaic access

Abstract

This invention discloses a method for optimizing the multi-level reactive power coordination of a station, line, and transformer, taking into account photovoltaic access. This method constructs a multi-objective function for optimizing the multi-level reactive power coordination of a station, line, and transformer, based on the three aspects of photovoltaic absorption level, power supply reliability, and grid operation economy. This method uses the Delphi method to determine the weights of each objective function based on expert experience to obtain a comprehensive objective function. Based on the requirements for safe, stable, and economical grid operation, this method constructs constraint functions for a mathematical model for optimizing the multi-level reactive power coordination of a station, line, and transformer, taking into account photovoltaic access. This method optimizes the mathematical model for optimizing the multi-level reactive power coordination of a station, line, and transformer using a second-order cone relaxation method to obtain a strategy for optimizing the multi-level reactive power coordination of a station, line, and transformer.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution network loss reduction, and in particular to a station-line-transformer multi-level reactive power coordination optimization method considering photovoltaic access. Background Art

[0002] Under the "dual carbon" policy, a high proportion of distributed power sources are connected to the power grid, which has a significant impact on the stable operation of the power grid. The randomness and intermittent characteristics of photovoltaics increase the reactive power imbalance of the power grid. Relying on traditional voltage regulation and reactive power compensation methods is difficult to meet users' requirements for power quality. Therefore, a "station-line-transformer" multi-level reactive power coordination optimization method considering photovoltaic access is proposed.

[0003] Reactive power compensation plays a role in improving the power factor of the power grid in the power supply system, reducing the loss of power transformers and transmission lines, improving power supply efficiency, and improving the power supply environment. Commonly used reactive power compensation methods in power grids include:

[0004] (1) Centralized compensation: installing parallel capacitor banks in high and low voltage distribution lines;

[0005] (2) Group compensation: Install parallel compensation capacitors on the low-voltage side of the distribution transformer and the distribution panel in the user's workshop;

[0006] (3) On-site compensation of a single motor: Install a parallel capacitor at the single motor.

[0007] Reactive power optimization technology is a reactive power regulation method that can be used to optimize certain control variables when the system's structural parameters and load conditions are given, so as to achieve the optimal performance of one or more system performance indicators while satisfying all specified constraints.

[0008] The Delphi method is essentially a feedback-based anonymous inquiry method. Its general process is as follows: After obtaining expert opinions on the problem to be predicted, the opinions are collated, summarized, and compiled, and then anonymously fed back to the experts. Opinions are then solicited again, and the opinions are consolidated and fed back again until a consensus is reached.

[0009] Second-order cone programming (SOCP) is a problem that seeks to minimize a linear objective function at the intersection of a finite number of second-order cones and an affine subspace. Second-order cone programming is a branch of cone programming. It is both a generalization of linear programming and a special case of semidefinite programming. It is a symmetric cone programming with an elegant structure. This type of programming has a wide range of applications, such as facility site selection, graph-theoretic control optimization, antenna array design, investment portfolio problems, as well as in finance, engineering design, digital signal processing, acoustics, mechanics, civil aviation, and electrical engineering. Therefore, studying the theory and algorithms of second-order cone programming problems has important theoretical significance and practical value.

[0010] Publication number CN109672184B discloses a method and system for controlling the voltage of a photovoltaic distribution network. This system takes minimizing voltage deviation as the objective function, considers demand response and the reactive power regulation capability of the photovoltaic inverter, establishes a coordinated optimization model for the distribution network voltage, and uses an improved particle swarm algorithm based on distributed entropy to solve the model. The solution results in active control of the photovoltaic distribution network voltage.

[0011] Publication number: CN114629105A A distribution network voltage and reactive power optimization control method that considers the balance of interests of multiple parties. This control method comprehensively considers the voltage and reactive power optimization control of the distribution network's "source, grid, and storage" multiple entities, coordinates and optimizes the reactive power output of the three stakeholders: distributed photovoltaic power sources, distribution network (capacitor banks, static VAR compensators, and on-load tap-changing transformers), and energy storage systems, reduces line network losses, alleviates voltage over-limit problems caused by the access of photovoltaic and electric heating loads, and achieves safe and efficient operation of the distribution network. In addition, it plays a decisive role in resource allocation by the market, promotes a policy system that takes low-carbon development as the overall guide and matches the goals of energy conservation and efficiency improvement, promotes the orderly development of new energy sources such as wind power and photovoltaics, improves the capacity to absorb new energy, achieves coordinated coordination between power sources and grids, and between power generation and power consumption, and promotes the development of the electricity market.

[0012] With the access of a large number of distributed power sources, the current reactive power optimization strategy of the distribution network mainly focuses on the reactive power optimization at a single level of the distribution network. The reactive power optimization of substations and substations that are closely related to the distribution network has not been comprehensively considered. Both the reactive power compensation of the substation and the reactive power compensation on the substation side will have an impact on the reactive power flow of the distribution network. Therefore, it is necessary to comprehensively consider the reactive power optimization strategies at multiple levels of substations, lines, and substations. Summary of the Invention

[0013] The purpose of the present invention is to solve the shortcomings of the existing technology and propose a station-line-transformer multi-level reactive power coordination optimization method considering photovoltaic access. This method can better improve the voltage quality of the distribution network, and also take into account all reactive power optimization measures of substations, lines, and substations, so as to achieve multi-layer linkage and same-layer interaction of the "station-line-transformer" reactive power optimization strategy, improve the photovoltaic absorption capacity, and enhance the power supply quality of the power grid.

[0014] A station-line-transformer multi-level reactive power coordination optimization method considering photovoltaic access includes the following steps:

[0015] Step 1: Based on the three aspects of photovoltaic consumption level, power supply reliability, and grid operation economy, a multi-objective function for the coordinated optimization of reactive power at the “station-line-transformer” level is constructed;

[0016] Step 2: Among the three objective functions obtained in step 1, it is impossible for each objective to achieve the optimal value at the same time. Each objective must have its own weight. The Delphi method is used to determine the weight of each objective function based on the experience of experts to obtain the comprehensive objective function.

[0017] min F=ω1f1+ω2f2+ω3f3

[0018] Among them, ω1, ω2, and ω3 are the weight coefficients of photovoltaic absorption level, power supply reliability, and grid operation economy respectively;

[0019] Step 3: Based on the requirements for safe, stable, and economical operation of the power grid, a constraint function for the “station-line-transformer” multi-level reactive power coordination optimization mathematical model considering PV integration is constructed, specifically including:

[0020] 3.1 Node voltage upper and lower limit constraints:

[0021]

[0022] in, are the lower and upper limits of the voltage at node i, respectively; n is the set of network nodes;

[0023] 3.2 Branch current upper limit constraint:

[0024]

[0025] in, is the upper limit of the current in branch (i, j);

[0026] 3.3 Photovoltaic output constraints:

[0027]

[0028] Among them, Q i,DG is the actual reactive power of the i-th distributed photovoltaic; Q iN,DG is the rated reactive power of the i-th distributed photovoltaic;

[0029] 3.4 Reactive power compensation control constraints:

[0030] Continuous reactive power regulation, static VAR compensation device, namely SVC, has upper and lower limit constraints for switching:

[0031]

[0032] Discrete reactive power regulation mainly involves switching capacitor banks in groups;

[0033] Switching capacity constraints:

[0034] cast

[0035] Constraints on the number of cut groups:

[0036]

[0037] in, They are the upper and lower limits of reactive power emitted by SVC respectively; are the reactive powers connected to node j at time t; For single group capacity; They are the number of switching groups and the maximum number of switching groups respectively;

[0038] 3.5 Forward and backward substitution of power flow equation constraints for distribution network:

[0039]

[0040] Active power and reactive power of the load; are the active power and reactive power of the photovoltaic node j respectively; is the charging and discharging power of the energy storage device;

[0041] Transformer tap position constraints:

[0042] T min ≤T≤T max

[0043] Among them, T min 、T max The upper and lower limits of the transformer tap position;

[0044] Step 4: Optimize the mathematical model of the “station-line-transformer” multi-level reactive power coordination optimization through the second-order cone relaxation method, convert the original comprehensive objective function and constraints into linear functions, which become the general form of second-order cone programming, and obtain the “station-line-transformer” multi-level reactive power coordination optimization strategy.

[0045] Preferably, the photovoltaic absorption level in step 1 is expressed by the distributed photovoltaic utilization rate, which is expressed as follows:

[0046]

[0047] Preferably, the power supply reliability level in step 1 is expressed by measuring the power supply reliability level of the distribution network using the voltage deviation rate, and its expression is:

[0048]

[0049] Preferably, the economic operation level of the power grid in step 1 is expressed by measuring the economic operation level of the power grid with the minimum active power loss of the distribution network, and its expression is:

[0050]

[0051] Among them, α ij is the switch status of branch (i, j), 1 means the switch is closed, 0 means the switch is open; r ij is the resistance of branch (i, j); P ij , Q ij are the active power and reactive power at the head end of branch (i, j) respectively; V i is the voltage amplitude at node i.

[0052] The advantages and technical effects of the present invention are:

[0053] The present invention provides a station-line-transformer multi-level reactive power coordination optimization method that takes photovoltaic access into consideration. 1. Starting from the three aspects of photovoltaic absorption level, power supply reliability, and grid operation economy, a multi-objective function for the "station-line-transformer" multi-level reactive power coordination optimization is constructed. 2. The Delphi method is used to determine the weights of each objective function based on comprehensive expert experience to obtain a comprehensive objective function. 3. Based on the requirements of grid safety, stability, and economic operation, a constraint function for the "station-line-transformer" multi-level reactive power coordination optimization mathematical model that takes photovoltaic access into consideration is constructed. 4. The "station-line-transformer" multi-level reactive power coordination optimization mathematical model is optimized using a second-order cone relaxation method to obtain a "station-line-transformer" multi-level reactive power coordination optimization strategy.

[0054] The present invention's station-line-transformer multi-level reactive power coordination optimization method, which takes photovoltaic access into consideration, can comprehensively coordinate reactive power optimization measures at all levels of substations, lines, and substations. Vertically, it considers the multi-layer linkage of reactive power optimization measures at the substation, line, and substation levels to ensure voltage quality at each level. Horizontally, it considers the same-level interaction of reactive power optimization measures at the same voltage level to ensure optimal voltage quality at that level, while also taking into account the active-reactive coordination of distributed photovoltaics. This method can both ensure better grid power supply quality and improve the distributed photovoltaic absorption capacity, effectively contributing to improving the quality and efficiency of the grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0056] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0057] In the description of the present invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate description and simplify the description of the present invention. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation, and therefore should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0058] The present invention is a station-line-transformer multi-level reactive coordination optimization method that takes photovoltaic access into consideration. It mainly adopts a grid reactive compensation method. The grid reactive compensation method includes: substation reactive compensation, main transformer gear adjustment, line reactive compensation, substation reactive compensation, photovoltaic active-reactive coordination, and 10kV line voltage regulator. Vertically, it considers the multi-layer linkage of reactive optimization measures at the substation, line, and substation level to ensure the voltage quality of each level. Horizontally, it considers the same-level interaction of reactive optimization measures at the same voltage level to ensure the optimal voltage quality of this level. At the same time, it also takes into account the active-reactive coordination effect of distributed photovoltaics. First, starting from the three aspects of photovoltaic absorption level, power supply reliability, and grid operation economy, a multi-objective function of "station-line-transformer" multi-level reactive coordination optimization is constructed.

[0059] (1) Photovoltaic power consumption level: The photovoltaic power consumption level is measured by the utilization rate of distributed photovoltaic power.

[0060]

[0061] Among them, N DG is the number of photovoltaic cells in the distribution network; P iN,DG is the rated value of the active output of each distributed photovoltaic system; P i,DG is the actual value of the active power output of the i-th distributed photovoltaic system.

[0062] (2) Power supply reliability level: The power supply reliability level of the distribution network is measured by the voltage deviation rate.

[0063]

[0064] Where N is the number of distribution network nodes; U i,N is the rated voltage of node i; U i is the actual voltage at node i; U i,max is the maximum qualified voltage of node i; U i,min is the minimum qualified voltage of node i.

[0065] (3) Economic operation level of the power grid. The economic operation level of the power grid is measured by minimizing the active power loss of the distribution network.

[0066]

[0067] Among them, α ij is the switch status of branch (i, j), 1 means the switch is closed, and 0 means the switch is open. ij is the resistance of branch (i, j); P ij , Q ij are the active power and reactive power at the head end of branch (i, j) respectively; V i is the voltage amplitude at node i.

[0068] 1. For the three objective functions: photovoltaic consumption level, power supply reliability, and grid operation economy, it is impossible to achieve the optimal value for each objective at the same time. Each objective must have its own weight. The Delphi method is used to integrate expert experience to determine the weight of each objective function and obtain the comprehensive objective function.

[0069] min F=ω1f1+ω2f2+ω3f3 (4)

[0070] Among them, ω1, ω2, and ω3 are the weight coefficients of photovoltaic absorption level, power supply reliability, and grid operation economy, respectively.

[0071] 2. Based on the requirements of safe, stable and economical operation of the power grid, the constraint function of the "station-line-transformer" multi-level reactive power coordination optimization mathematical model considering photovoltaic access is constructed.

[0072] (1) Node voltage upper and lower limit constraints

[0073]

[0074] in, are the lower and upper limits of the voltage at node i, respectively; n A set of network nodes.

[0075] (2) Branch current upper limit constraint

[0076]

[0077] in, is the upper limit of the current in branch (i, j).

[0078] (3) Photovoltaic output constraints

[0079]

[0080] Among them, Q i,DG is the actual reactive power of the i-th distributed photovoltaic; Q iN,DG is the rated reactive power of the i-th distributed photovoltaic.

[0081] (4) Reactive power compensation control constraints

[0082] Continuous reactive power regulation, static var compensation (SVC), upper and lower limit constraints for switching

[0083]

[0084] Discrete reactive power regulation, mainly group switching capacitor banks

[0085] Switching capacity constraints

[0086]

[0087] Constraints on the number of switching groups:

[0088]

[0089] in, They are the upper and lower limits of reactive power emitted by SVC respectively; are the reactive powers connected to node j at time t; For single group capacity; They are the number of switching groups and the maximum number of switching groups respectively.

[0090] (5) Forward-backward power flow equation constraints for distribution networks

[0091]

[0092] Among them, P jk , Q jk are the active power and reactive power at the head end of branch (j, k) respectively; are the active power and reactive power of the load at node j respectively; are the active power and reactive power of the photovoltaic node j respectively; is the charging and discharging power of the energy storage device.

[0093] (6) Transformer tap position constraints

[0094] T min ≤T≤T max (11)

[0095] Among them, T min 、T max It is the upper and lower limits of the transformer tap position.

[0096] 3. The mathematical model of the multi-level reactive power coordination optimization of "station-line-transformer" is optimized through the second-order cone relaxation method, and the original comprehensive objective function and constraints are converted into linear functions, which become the general form of second-order cone programming, and the multi-level reactive power coordination optimization strategy of "station-line-transformer" is obtained.

[0097] Finally, all parts not fully described in the present invention adopt mature products and mature technical means in the existing technology.

[0098] In the description of this specification, reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in the embodiment or example of the present invention.

[0099] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A station-line-transformer multi-level reactive power coordination optimization method considering photovoltaic access, characterized in that: The following steps are involved: Step 1: Construct a multi-objective function for the coordinated optimization of reactive power at the "station-line-transformer" level, based on the three aspects of PV absorption level, power supply reliability, and grid operation economy. Step 2: Among the three objective functions obtained in step 1, it is impossible for each objective to achieve the optimal value at the same time. Each objective must have its own weight. The Delphi method is used to determine the weight of each objective function based on the experience of experts to obtain the comprehensive objective function. minF=ω1f1+ω2f2+ω3f3 Among them, ω1, ω2, and ω3 are the weight coefficients of photovoltaic absorption level, power supply reliability, and grid operation economy respectively; Step 3: Based on the requirements for safe, stable, and economical operation of the power grid, a constraint function for the "station-line-transformer" multi-level reactive power coordination optimization mathematical model considering PV integration is constructed, specifically including: 3.1 Node voltage upper and lower limit constraints: In i min ≤V i ≤V i max ,i∈ψ n Among them, V i min 、V i max are the lower and upper limits of the voltage at node i, respectively; n is the set of network nodes; 3.2 Branch current upper limit constraint: in, is the upper limit of the current in branch (i, j); 3.3 Photovoltaic output constraints: Among them, Q i,DG is the actual reactive power of the i-th distributed photovoltaic; Q iN,DG is the rated reactive power of the i-th distributed photovoltaic; 3.4 Reactive power compensation control constraints: Continuous reactive power regulation, static VAR compensation device, namely SVC, has upper and lower limit constraints for switching: Discrete reactive power regulation mainly involves switching capacitor banks in groups; Switching capacity constraints: cast Constraints on the number of cut groups: in, They are the upper and lower limits of reactive power generated by SVC respectively; are the reactive powers connected to node j at time t; For single group capacity; They are the number of switching groups and the maximum number of switching groups respectively; 3.5 Forward and backward substitution of power flow equation constraints for distribution network: Active power and reactive power of the load; are the active power and reactive power of the photovoltaic node j respectively; is the charging and discharging power of the energy storage device; Transformer tap position constraints: T min ≤T≤T max Among them, T min 、T max The upper and lower limits of the transformer tap position; Step 4: Optimize the mathematical model of the "station-line-transformer" multi-level reactive power coordination optimization using the second-order cone relaxation method. Convert the original comprehensive objective function and constraints into linear functions, which become the general form of second-order cone programming. Obtain the "station-line-transformer" multi-level reactive power coordination optimization strategy.

2. The method for multi-level reactive power coordination optimization of station-line-transformer considering photovoltaic access according to claim 1, characterized in that: The photovoltaic absorption level in step 1 is expressed by the distributed photovoltaic utilization rate, which is expressed as follows:

3. The station-line-transformer multi-level reactive power coordination optimization method considering photovoltaic access according to claim 1, characterized in that: The power supply reliability level in step 1 is expressed by measuring the power supply reliability level of the distribution network using the voltage deviation rate, and its expression is:

4. The station-line-transformer multi-level reactive power coordination optimization method considering photovoltaic access according to claim 1, characterized in that: The economic operation level of the power grid in step 1 is expressed by measuring the economic operation level of the power grid with the minimum active power loss of the distribution network, and its expression is: Among them, α ij is the switch status of branch (i, j), 1 means the switch is closed, 0 means the switch is open; r ij is the resistance of branch (i, j); P ij , Q ij are the active power and reactive power at the head end of branch (i, j) respectively; V i is the voltage amplitude at node i.

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