Bearing capacity calculation method for distributed power supply access power distribution network, medium and equipment

Abstract

The invention provides a bearing capacity calculation method for distributed power supply access to a power distribution network, which comprises the following steps of: 1) determining a target line, determining a set DG of grid-connected nodes of each distributed power supply in a line partition according to a topological relation of the line, and obtaining a maximum possible capacity value of each accessible distributed power supply, the value is the maximum rated output power of the distributed power supply; 2) electrical calculation is carried out, whether each point in the target line partition meets constraint conditions is checked, if all the constraint conditions are met, the step 6) is carried out, and if not, the step 3) is carried out to find a node with the most serious constraint out-of-limit condition, that is, the absolute value of the constraint index of the node deviates from the constraint conditions most mostly; and calculating the distributed power supply capacity value which has the most serious influence on the out-of-limit index of the node. And in combination with a multi-constraint condition, the real bearing capacity of the power grid is accurately calculated.

Description

Technical Field

[0001] The present invention belongs to the field of electric power technology, and in particular relates to a method, medium and equipment for calculating the carrying capacity of a multi-constrained distributed power source connected to a distribution network. Background Art

[0002] With the advancement of new power system construction, the widespread integration of distributed generation (DGs) has transformed distribution networks from simple radial networks into multi-terminal active networks. While DGs can supplement power supply, their integration can also impact the planning and operation of power distribution networks. These changes can alter the magnitude and direction of power flows, causing current and voltage distortion and rendering existing protection schemes ineffective. These impacts pose significant challenges to the distribution network's ability to fully accommodate and efficiently utilize DGs.

[0003] The existing methods for evaluating the maximum carrying capacity of distributed generation access to distribution networks mainly have the problem of single constraints. Most methods only consider a single constraint, such as voltage constraint or short-circuit current constraint, and fail to comprehensively and coordinately consider multiple types of constraints, resulting in a failure to reflect the true carrying capacity of the power grid.

[0004] Therefore, how to design an accurate calculation method for the carrying capacity of distributed power access to the distribution network based on multiple constraints has become a method that technicians in this field urgently need to solve. Summary of the Invention

[0005] In response to the above technical problems, the present invention provides a multi-constrained method for calculating the carrying capacity of distributed power sources connected to a distribution network, which combines multiple constraints to accurately calculate the actual carrying capacity of the power grid.

[0006] The technical solution of the present invention is: a method for calculating the carrying capacity of a distributed power source connected to a distribution network, comprising the following steps:

[0007] 1) Determine the target line, confirm the set DG of the distributed power grid connection nodes in the line partition according to the topological relationship of the line, and obtain the maximum possible capacity value SDG of each distributed power source that can be connected max , its value is the maximum rated output power of the distributed power supply;

[0008] Initialize, let lb m,i =50%*SDG max,i ;

[0009] Determine the carrying capacity of the distribution network connected to the distributed power generation: LB m =∑ i∈DG lb m,i ,

[0010] Where m represents the distribution operation mode; LB is the total carrying capacity of the distribution network connected to the distributed power source; LBm is the total carrying capacity of the distribution network connected to the distributed generation under the m operation mode; lb m,i is the maximum carrying capacity of node i connected to distributed generation under operating mode m; DG represents the set of nodes connected to the distribution network;

[0011] 2) Perform electrical calculations to check whether each point in the target line partition meets the constraints. If all constraints are met, go to step 6); if not, go to step 3);

[0012] 3) Find the node with the most serious constraint violation and calculate the distributed generation capacity value that most seriously affects the constraint violation index of this node;

[0013] 4) Find the target distributed power source with the largest improvement effect and non-zero capacity. The largest improvement effect means that after connecting to a certain distributed power source, simulation calculation is performed to make the constraint index value of each node change the most and be closest to the constraint condition, and increase its capacity by a step capacity △S=5%*SDG max,i ;

[0014] 5) Update the corresponding indicators of each node and each branch, and return to step 2);

[0015] 6) Solve all lb under the DG set m,i , by formula LB m =∑ i∈DG lb m,i Calculate the carrying capacity LB of the distribution network m .

[0016] Preferably, the constraints in step 2 include voltage constraints:

[0017] (1) Voltage offset:

[0018] (1-α)U i <(1+α)U

[0019] Where, U is the nominal voltage of the line, U i is the voltage of node i, α is the set voltage deviation percentage;

[0020] (2) Voltage fluctuation:

[0021] d m,i ≤d max

[0022] Among them, d i is the voltage fluctuation percentage of node i under operating mode m; d max The maximum permissible value of voltage fluctuation specified in the technical guidelines.

[0023] ​Preferably, the maximum allowable value of voltage fluctuation specified in the technical guidelines is:

[0024] When the fluctuation frequency is [0,1], the medium and low pressures are 4%, and the high pressure is 3%;

[0025] When the fluctuation frequency is (1,10], the medium and low pressures are 3%, and the high pressure is 2.5%;

[0026] When the fluctuation frequency is (10,100], the medium and low pressures are 2%, and the high pressure is 1.5%;

[0027] When the fluctuation frequency is (100,1000], the medium and low pressures are 1.25%, and the high pressure is 1%;

[0028] The low, medium and high voltages are 10kV and below, 10kV to 35kV, and 35kV to 110kV respectively.

[0029] Preferably, the constraints in step 2 include current constraints:

[0030] (1) Short-circuit current:

[0031] I i ≤I max

[0032] Among them, I i is the short-circuit current of node i; I max The maximum permissible short-circuit current specified in the technical guidelines;

[0033] (2) Maximum branch current:

[0034] |I b |≤I b,max

[0035] Among them, I b is the current on branch b; I b,max The maximum current that branch b can withstand is the maximum value of the current that the branch can withstand, which is the standard commonly used in the industry.

[0036] Preferably, the constraints in step 2 include circuit power balance constraints:

[0037] P DG,i =P L,i +U i ∑ j∈N U j (G ij cosθ ij +B ij sinθ ij )

[0038] Q DG,i =Q L,i +Ui ∑ j∈N U j (G ij sinθ ij -B ij cosθ ij )

[0039] P DG,i and Q DG,i are the maximum active power and reactive power injected by the distributed generation at node i under the corresponding operation mode; P L,i and Q L,i is the active power and reactive power of the load at node i under the corresponding operation mode; G ij 、B ij ,θ ij are the conductance, susceptance and phase angle difference between node i and node j respectively; N is the set of all nodes in the distribution network; U i , U j is the voltage amplitude of nodes i and j under the corresponding operating mode.

[0040] Preferably, the constraints in step 2 include voltage harmonic constraints:

[0041] THD V ≤THDV max ;

[0042] THD V and THDV max They are the total harmonic distortion rate of voltage and the maximum permissible value of voltage distortion rate specified in the technical guidelines;

[0043] Preferably, the maximum allowable value of voltage distortion rate specified in the technical guidelines is:

[0044] When the voltage level is 380V, THD Vmax ≤5%;

[0045] When the voltage level is 10kV, THD Vmax ≤4%;

[0046] When the voltage level is 35kV, THD Vmax ≤3%;

[0047] When the voltage level is 110kV, THD Vmax ≤2%.

[0048] Preferably, the constraint condition includes that the maximum carrying capacity of a node connected to the distributed power source satisfies the distributed power source output constraint: lb m,i ≤SDG max,i .

[0049] A computer device is provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the method for calculating the carrying capacity of a distributed power source connected to a distribution network is based on any one of the above-mentioned items.

[0050] A computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the method for calculating the carrying capacity of a distributed power source connected to a distribution network is based on any one of the above-mentioned methods.

[0051] The beneficial effects of the present invention are as follows: based on the grid structure and load conditions of the distribution network, a model for evaluating the carrying capacity of multiple distributed power sources connected to the distribution network is constructed, with the maximum grid-connected capacity of the distributed power sources as the objective function, and under multiple constraints of relevant standards such as voltage offset, voltage fluctuation, short-circuit current, and voltage harmonics, the carrying capacity of the distribution network connected to the distributed power sources is effectively evaluated, thereby providing guidance for the planning and construction of distributed power sources in the distribution network, and further reducing the risks to power quality brought about by the large-scale grid connection of distributed power sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 is a flow chart of the method of the present invention,

[0053] Figure 2 This is the distribution line network structure in the embodiment. DETAILED DESCRIPTION

[0054] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0055] This embodiment provides a method for calculating the carrying capacity of a distributed power source connected to a distribution network. Figure 1 , including the following steps:

[0056] 1) Determine the target line, confirm the set DG of the distributed power grid connection nodes in the line partition according to the topological relationship of the line, and obtain the maximum possible capacity value SDG of each distributed power source that can be connected max , its value is the maximum rated output power of the distributed power supply;

[0057] Initialize, let lb m,i =50%*SDG max,i ; that is, the capacity of a single node.

[0058] Determine the carrying capacity of the distribution network connected to the distributed power generation: LB m =∑i∈DG lb m,i , which is the sum of the capacities of all nodes in the target line partition.

[0059] Where m represents the distribution operation mode; LB is the total carrying capacity of the distribution network connected to the distributed power source; LB m is the total carrying capacity of the distribution network connected to the distributed generation under the m operation mode; lb m,i is the maximum carrying capacity of node i connected to distributed generation under operating mode m; DG represents the set of nodes connected to the distribution network;

[0060] 2) Perform electrical calculations, including power flow calculations and current short-circuit calculations, i.e., calculations related to constraints. Check whether each point in the target line partition meets the constraints. If all constraints are met, proceed to step 6); if not, proceed to step 3);

[0061] 3) Find the node with the most serious constraint violation, that is, the node whose absolute value of the constraint index deviates the most from the constraint condition, and calculate the distributed generation capacity value that has the most serious impact on the node's constraint violation;

[0062] 4) Find the target distributed power source with the largest improvement effect and non-zero capacity. The largest improvement effect means that after connecting to a certain distributed power source, simulation calculation is performed to make the constraint index value of each node change the most and be closest to the constraint condition, and increase its capacity by a step capacity △S=5%*SDG max,i The step size is a fixed value. During the optimization process, in one loop iteration, the node that needs to be optimized increases by a step size value so that the final result approaches the optimal solution. Finally, the maximum value that all nodes can access is obtained, which is the carrying capacity. The role of the step size is to add a fixed value to each node during the optimization process so that it approaches the optimal value.

[0063] 5) Update the corresponding indicators of each node and each branch, and return to step 2); 6) Solve all lb under the DG set m,i , by formula LB m =∑ i∈DG lb m,i Calculate the carrying capacity LB of the distribution network m .

[0064] In this embodiment, the constraints include voltage constraints to prevent the voltage at the feeder end from increasing when the DG output exceeds the local load, or from causing a voltage drop due to insufficient output. Specifically, they include:

[0065] (1) Voltage offset:

[0066] (1-α)U i <(1+α)U

[0067] ​Where, U is the nominal voltage of the line, U i is the voltage of node i, and α is the set voltage deviation percentage, which can be set as needed. For example, the maximum value for 20kV and below is 7%, and the maximum value for above 20kV is 8%;

[0068] (2) Voltage fluctuation:

[0069] d m,i ≤d max

[0070] Among them, d i is the voltage fluctuation percentage of node i under operating mode m; d max The maximum permissible value of voltage fluctuation specified in the technical guidelines.

[0071] In this embodiment, the maximum allowable voltage fluctuation value specified in the technical guidelines is:

[0072] When the fluctuation frequency is [0,1], the medium and low pressures are 4%, and the high pressure is 3%;

[0073] When the fluctuation frequency is (1,10], the medium and low pressures are 3%, and the high pressure is 2.5%;

[0074] When the fluctuation frequency is (10,100], the medium and low pressures are 2%, and the high pressure is 1.5%;

[0075] When the fluctuation frequency is (100,1000], the medium and low pressures are 1.25%, and the high pressure is 1%;

[0076] Low, medium and high voltage are 10kV and below, 10kV to 35kV, and 35kV to 110kV respectively.

[0077] Constraints include current constraints to prevent voltage increases at the feeder end when DG output exceeds local load, or voltage drops due to insufficient output. Specifically, they include:

[0078] (1) Short-circuit current:

[0079] I i ≤I max

[0080] Among them, I i is the short-circuit current of node i; I max The maximum permissible short-circuit current specified in the technical guidelines

[0081] The technical guideline parameters follow industry regulations as follows:

[0082] When the voltage level is 10kV and below, the maximum allowable short-circuit current is 40kA;

[0083] When the voltage level is 10kV to 35kV, the maximum allowable short-circuit current is 31.5kA;

[0084] When the voltage level is 35kV to 110kV, the maximum allowable short-circuit current is 20kA or 25kA, and the two values are selected according to the specific case.

[0085] (2) Maximum branch current:

[0086] |I b |≤I b,max

[0087] Among them, I b is the current on branch b; I b,max This is the maximum current that branch b can withstand. This maximum current is specified by industry standards. Typically, after a distribution network is constructed, the current ratings of all components in a branch (such as wires, fuses, circuit breakers, and switches) are finalized. All components in the branch are designed to withstand the expected maximum current.

[0088] In this embodiment, the constraints include circuit power balance constraints to prevent changes in active power output after DG connection, which could cause system frequency fluctuations; increase local reactive power shortages, which could lead to decreased voltage stability; and change in power factor regulation capability, which could affect reactive power flow and voltage stability in the distribution network. Specifically, the constraints include:

[0089] P DG,i =P L,i +U i ∑ j∈N U j (G ij cosθ ij +B ij sinθ ij )

[0090] Q DG,i =Q L,i +U i ∑ j∈N U j (G ij sinθ ij -B ij cosθ ij )

[0091] P DG,i and Q DG,i are the maximum active power and reactive power injected by the distributed generation at node i under the corresponding operation mode; P L,i and Q L,i is the active power and reactive power of the load at node i under the corresponding operation mode; G ij 、B ij ,θij are the conductance, susceptance and phase angle difference between node i and node j respectively; N is the set of all nodes in the distribution network; U i , U j is the voltage amplitude of nodes i and j under the corresponding operating mode.

[0092] Preferably, the constraints in step 2 include voltage harmonic constraints. Harmonics can interfere with precision electronic equipment and affect their normal operation. Reducing voltage harmonics can reduce this interference and ensure stable operation of the equipment:

[0093] THD V ≤THD Vmax ;

[0094] THD V and THD Vmax They are the total harmonic distortion rate of voltage and the maximum permissible value of voltage distortion rate specified in the technical guidelines;

[0095] Preferably, the maximum allowable value of voltage distortion rate specified in the technical guidelines is:

[0096] When the voltage level is 380V, THD Vmax ≤5%;

[0097] When the voltage level is 10kV, THD Vmax ≤4%;

[0098] When the voltage level is 35kV, THD Vmax ≤3%;

[0099] When the voltage level is 110kV, THD Vmax ≤2%.

[0100] In this embodiment, the constraint condition includes that the maximum carrying capacity of a node connected to the distributed power source satisfies the output constraint of the distributed power source: lb m,i ≤SDG max,i .

[0101] This embodiment provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the method for calculating the carrying capacity of a distributed power source connected to a distribution network is based on any one of the aforementioned items.

[0102] This embodiment provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the method for calculating the carrying capacity of a distributed power source connected to a distribution network is based on any of the aforementioned items.

[0103] Taking a 16-node dual-feeder radial 20kV distribution line as an example, its network structure is as shown in the attached figure. Figure 2There are 4 distributed power sources in this line section, including 2 wind turbines connected to nodes A1 and A6; and 2 photovoltaic units connected to nodes B7 and B8.

[0104] According to relevant technical guidelines, the voltage deviation α is taken as 7%, and the voltage fluctuation limit d max 3%, the maximum three-phase short-circuit current limit I max It is 20kA.

[0105] 1) Determine the set DG of the grid-connected nodes of each distributed generation in the line partition and the maximum possible capacity value of each distributed generation as shown in Table 1. Initialize the initial carrying capacity A1 = 4.55MVA, A6 = 3.9MVA, B7 = 5.07MVA, and B8 = 5.07MVA;

[0106] 2) Perform relevant electrical calculations such as power flow calculation and short-circuit calculation, check the constraints, and if all constraints are met, go to step 6);

[0107] 3) Find the node with the most serious constraint violation and calculate the distributed generation capacity value that most seriously affects the constraint violation index of this node;

[0108] 4) Find the target distributed power source with the largest over-limit improvement effect and non-zero capacity, and increase its capacity by one step capacity, with △S = 0.2MVA;

[0109] 5) Update the corresponding indicators of each node and each branch, and return to step 2);

[0110] 6) The final calculation results are shown in Table 1

[0111] Table 1 Calculation results of distributed power generation capacity in the example

[0112]

[0113] Table 1

[0114] Based on the grid structure and load conditions of the distribution network, the present invention constructs a model for evaluating the carrying capacity of multiple distributed power sources connected to the distribution network. Taking the maximum grid-connected capacity of distributed power sources as the objective function, the present invention effectively evaluates the carrying capacity of the distribution network connected to distributed power sources under multiple constraints of relevant standards such as voltage offset, voltage fluctuation, short-circuit current, and voltage harmonics. This model provides guidance for the planning and construction of distributed power sources in the distribution network, and further reduces the risks to power quality brought by the large-scale grid connection of distributed power sources.

[0115] The present invention is not limited to the above-mentioned embodiments. On the basis of the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and modifications to some of the technical features therein according to the disclosed technical content without creative labor, and these substitutions and modifications are all within the protection scope of the present invention.

Claims

1. A method for calculating the carrying capacity of a distributed power source connected to a distribution network, characterized in that: The following steps are involved: 1) Determine the target line, confirm the set DG of the distributed power grid connection nodes in the line partition according to the topological relationship of the line, and obtain the maximum possible capacity value SDG of each distributed power source that can be connected max , its value is the maximum rated output power of the distributed power supply; Initialize, let lb m,i =50%*SDG max,i ; Determine the carrying capacity of the distribution network connected to the distributed power generation: LB m =∑ i∈DG lb m,i , Where m represents the distribution operation mode; LB is the total carrying capacity of the distribution network connected to the distributed power source; LB m is the total carrying capacity of the distribution network connected to the distributed generation under the m operation mode; lb m,i is the maximum carrying capacity of the distributed power supply connected to node i under the m operation mode; DG represents the set of distributed generation nodes connected to the distribution network; 2) Perform electrical calculations to check whether each point in the target line partition meets the constraints. If all constraints are met, go to step 6); if not, go to step 3); 3) Find the node with the most serious constraint violation and calculate the distributed generation capacity value that most seriously affects the constraint violation index of this node; 4) Find the target distributed power source with the largest improvement effect and non-zero capacity. The largest improvement effect means that after connecting to a certain distributed power source, simulation calculation is performed to make the constraint index value of each node change the most and be closest to the constraint condition, and increase its capacity by a step capacity △S=5%*SDG max,i ; 5) Update the corresponding indicators of each node and each branch, and return to step 2); 6) Solve all lb under the DG set m,i , by the formula LBm=∑ i∈DG l bm,i Calculate the carrying capacity LB of the distribution network m .

2. A method for calculating the carrying capacity of a distributed power source connected to a distribution network according to claim 1, characterized in that: The constraints in step 2 include voltage constraints: (1) Voltage offset: (1-a)U i <(1+α)U​ Where, U is the nominal voltage of the line, U i is the voltage of node i, α is the set voltage deviation percentage; (2) Voltage fluctuation: d m,i ≤d max Among them, d i is the voltage fluctuation percentage of node i under operating mode m; d max The maximum permissible value of voltage fluctuation specified in the technical guidelines.

3. A method for calculating the carrying capacity of a distributed power source connected to a distribution network according to claim 2, characterized in that: The maximum permissible voltage fluctuations specified in the technical guidelines are: When the fluctuation frequency is [0,1], the medium and low pressures are 4%, and the high pressure is 3%; When the fluctuation frequency is (1,10], the medium and low pressures are 3%, and the high pressure is 2.5%; When the fluctuation frequency is (10,100], the medium and low pressures are 2%, and the high pressure is 1.5%; When the fluctuation frequency is (100,1000], the medium and low pressures are 1.25%, and the high pressure is 1%; The low, medium and high voltages are 10kV and below, 10kV to 35kV, and 35kV to 110kV respectively.

4. A method for calculating the carrying capacity of a distributed power source connected to a distribution network according to claim 1, characterized in that: The constraints in step 2 include current constraints: (1) Short-circuit current: I i ≤I max Among them, I i is the short-circuit current of node i; I max The maximum permissible short-circuit current specified in the technical guidelines; (2) Maximum branch current: |I b |≤I b,max Among them, I b is the current on branch b; I b,max is the maximum current that branch b can withstand.

5. A method for calculating the carrying capacity of a distributed power source connected to a distribution network according to claim 1, characterized in that: The constraints in step 2 include circuit power balance constraints: P DG,i =P L,i +U i ∑ j∈N U j (G ij cosθ ij +B ij sinθ ij ) Q DG,i =Q L,i +U i ∑ j∈N U j (G ij sinθ ij -B ij cosθ ij ) P DG,i and Q DG,i are the maximum active power and reactive power injected by the distributed generation at node i under the corresponding operation mode; P L,i and Q L,i is the active power and reactive power of the load at node i under the corresponding operation mode; G ij 、B ij ,θ ij are the conductance, susceptance and phase angle difference between node i and node j respectively; N is the set of all nodes in the distribution network; U i , U j is the voltage amplitude of nodes i and j under the corresponding operating mode.

6. A method for calculating the carrying capacity of a distributed power source connected to a distribution network according to claim 1, characterized in that: The constraints in step 2 include voltage harmonic constraints: THD V ≤THD Vmax ; THD V and THD Vmax They are the total harmonic distortion rate of voltage and the maximum allowable value of voltage distortion rate specified in the technical guidelines.

7. A method for calculating the carrying capacity of a distributed power source connected to a distribution network according to claim 6, characterized in that: The maximum allowable voltage distortion rate specified in the technical guidelines is: When the voltage level is 380V, THD Vmax ≤5%; When the voltage level is 10kV, THD Vmax ≤4%; When the voltage level is 35kV, THD Vmax ≤3%; When the voltage level is 110kV, THD Vmax ≤2%.

8. A method for calculating the carrying capacity of a distributed power source connected to a distribution network according to claim 1, characterized in that: The constraints in step 2 include the maximum load capacity of a node connected to the distributed power supply meeting the distributed power supply output constraint: lb m,i ≤SDG max,i .

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, it is based on the method for calculating the carrying capacity of distributed power sources connected to the distribution network according to any one of claims 1 to 8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, it is based on the method for calculating the carrying capacity of a distributed power source connected to a distribution network according to any one of claims 1 to 8.

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