Low-voltage distribution network voltage control method and device based on distributed photovoltaic inverters

Abstract

The present application belongs to the technical field of low-voltage distribution network distributed photovoltaic operation control, and discloses a low-voltage distribution network voltage control method and device based on a distributed photovoltaic inverter, wherein the method comprises: when the voltage of any node in a transformer area exceeds an upper limit value, solving the minimum reactive power output of the first-stage inverter; if there is a solution, executing the reactive power control instruction, otherwise entering the second stage, solving the minimum active power output reduction of the second-stage inverter; if there is a solution, executing the active power and reactive power control instruction, otherwise entering the third stage; solving the minimum active power output reduction of the third-stage inverter, and executing the active power and reactive power control instruction. The present application linearizes the distributed photovoltaic voltage regulation problem, reduces the calculation complexity of the global voltage optimization of the transformer area, and obtains the active power and reactive power regulation sensitivity matrix as the data support for the voltage regulation control by adjusting the photovoltaic output and recording the node voltage change, which is more practical and does not depend on the topology and line parameters.

Description

Technical Field

[0001] This invention relates to the field of distributed photovoltaic operation control technology in low-voltage distribution networks, and particularly to a voltage control method and device for low-voltage distribution networks based on distributed photovoltaic inverters. Background Technology

[0002] With increasing global concern over environmental protection and energy shortages, photovoltaic (PV) power generation has become a crucial measure for addressing energy and environmental issues, with distributed PV power generation forming a key component of smart distribution networks. Grid-connected PV power generation should adhere to the principles of decentralized development and localized consumption. Therefore, decentralized grid connection of PV at the user side is becoming a trend, with some regions fully utilizing rural rooftop resources to construct distributed PV systems and integrate them into low-voltage distribution networks. Rural areas have lower electricity loads, and the large-scale integration of distributed PV has caused severe mismatches between power supply and load in local low-voltage distribution networks. Power backflow has led to prominent voltage exceeding limits, with end-user voltages significantly exceeding national standards, posing a threat to user electricity safety.

[0003] Distributed photovoltaic (PV) inverters possess flexible active and reactive power output adjustment capabilities. By absorbing inductive reactive power, they can influence line power flow and reduce voltage. When necessary, they can also limit active power generation, thereby reducing backflow. Relying on the inverter's own regulation, voltage levels can be controlled without additional equipment investment. While inverters can limit local port voltage levels through built-in algorithms, this method cannot achieve global optimization of the entire distribution area and is prone to over-regulation. Excessive restriction of active power output increases line losses by introducing excessive reactive power flow.

[0004] By utilizing edge computing devices in low-voltage distribution substations, such as intelligent converged terminals, measurement information from the substations can be aggregated to globally optimize the output of all distributed photovoltaic inverters. However, this type of global optimization method currently faces two main problems that limit its practical application. First, global optimization methods require significant computing resources, making them difficult to implement given the limited computing capabilities of actual low-voltage distribution substations. Second, most global optimization methods require access to key data such as line topology, impedance parameters, and load power, which are difficult to obtain accurately due to the chaotic access of low-voltage distribution network equipment and the limited observability and measurability. Summary of the Invention

[0005] This invention provides a voltage control method and apparatus for low-voltage distribution networks based on distributed photovoltaic (PV) inverters. It performs coordinated global optimization of the active and reactive power outputs of all PV inverters within the distribution area, maximizing PV active power generation while effectively addressing voltage limit exceedance issues. Furthermore, it reduces reactive power output from PV inverters to minimize line losses while ensuring voltage quality and active power output. To provide a basic understanding of some aspects of the disclosed embodiments, a brief summary is provided below. This summary is not intended as a general commentary, nor is it intended to identify key / important components or describe the scope of protection of these embodiments. Its sole purpose is to present some concepts in a simple form as a prelude to the detailed description that follows.

[0006] According to a first aspect of the present invention, a low-voltage distribution network voltage control method based on a distributed photovoltaic inverter is provided, comprising:

[0007] When the voltage at any node in the distribution area exceeds the upper limit, and:

[0008] When the inverters in the distribution area are in the first stage, the minimum reactive power output of all inverters in the first stage in the distribution area is solved. The first stage is the stage where the current active and reactive power outputs have not reached the capacity constraint or the power factor constraint. If the minimum reactive power output of the inverters in the first stage has a solution, the reactive power control command is executed to complete the voltage control; otherwise, the second stage is entered.

[0009] The second stage is when the current active and reactive power output has reached the capacity constraint but not the power factor constraint. When the inverters in the distribution area are in the second stage, the minimum active power output reduction of all inverters in the second stage in the distribution area is solved. If the minimum active power output reduction of the inverters in the second stage has a solution, the active and reactive power control commands are executed to complete the voltage control; otherwise, the third stage is entered.

[0010] The third stage is when the current active and reactive power output has reached the power factor constraint. When the inverter in the distribution area is in the third stage, the minimum active power output reduction of all inverters in the third stage in the distribution area is calculated. After obtaining the minimum active power output reduction of the inverter in the third stage, active and reactive power control commands are executed to complete the voltage control.

[0011] When the voltage of all nodes in the transformer area is lower than the upper limit:

[0012] If the active power output of the inverter is limited, active power output recovery is performed to complete voltage control.

[0013] If the active power output of all inverters is unrestricted, then reactive power reduction is performed to complete voltage control.

[0014] In one embodiment, when the inverters within the distribution area are in the first stage, the step of minimizing the reactive power output of all inverters in the first stage within the distribution area further includes:

[0015] Solve the first-stage linear optimization problem:

[0016]

[0017] To determine the reactive power regulation of all inverters in the first stage within the distribution area, with the goal of minimizing reactive power output in the first stage;

[0018] In the formula, Φ AB For the first stage of inverter assembly, Q j Let Q be the reactive power output of inverter j, where j = 1, 2, ..., m, and m represents the number of inverters in the distribution area. j The inverter j absorbs the incremental inductive reactive power.

[0019] In one embodiment, the constraints of the first-stage linear optimization problem in this method include:

[0020] Capacity constraints:

[0021]

[0022] Power factor constraint:

[0023]

[0024] Overvoltage constraint:

[0025]

[0026] In the formula, S j P represents the capacity of inverter j. j For the active power output of inverter j, U is the angle of maximum power factor. i Let β be the effective value of the voltage at node i. i,j U represents the reactive power sensitivity of the voltage at node i to inverter j. max Let n be the upper limit of the node voltage, and n be the total number of nodes.

[0027] In one embodiment, when the inverters within the distribution area are in the second stage, the step of calculating the minimum active power output reduction for all second-stage inverters within the distribution area further includes:

[0028] Solve the second-stage linear optimization problem:

[0029]

[0030] To determine the active and reactive power regulation of all inverters in the second stage within the distribution area, with the goal of minimizing the reduction in active power output in the second stage.

[0031] In the formula, Φ BC For the second-stage inverter assembly, ΔP j This represents the change in the active power output of inverter j, with an increase in active power output being positive.

[0032] In one embodiment, the constraints of the second-stage linear optimization problem in this method include:

[0033] The second-stage boundary constraints for linearization:

[0034] ΔP j =a j ΔQ j ,j∈Φ BC

[0035] ΔP j ≤0,j∈Φ BC

[0036] Power factor constraint:

[0037]

[0038] Overvoltage constraint:

[0039]

[0040] In the formula, a j To linearize the active and reactive power relationship of inverter j in the second stage, α i,j Let be the voltage sensitivity of node i to the active power sensitivity of inverter j;

[0041] In the formula, a j The calculation method is as follows:

[0042]

[0043] In one embodiment, when the inverters within the distribution area are in the third stage, the step of calculating the minimum active power output reduction for all inverters in the third stage within the distribution area further includes:

[0044] Solve the third-stage linear optimization problem:

[0045]

[0046] To determine the active and reactive power regulation of all inverters in the third stage within the distribution area, with the goal of minimizing the reduction in active power output in the third stage.

[0047] In the formula, Φ CO This is the third-stage inverter assembly.

[0048] In one embodiment, the constraints of the third-stage linear optimization problem in this method include:

[0049] Third-stage boundary constraints:

[0050]

[0051] ΔP j ≤0,j∈Φ CO

[0052] Overvoltage constraint:

[0053]

[0054] In one embodiment, the step of performing active power recovery to complete voltage control when the active power output of the inverter is limited further includes:

[0055] When all node voltages are below the upper limit, an active power output recovery optimization algorithm is executed, aiming to maximize the increase in inverter active power output. The formula is as follows:

[0056]

[0057] In the formula, Φ set A collection of inverters whose active power output is limited.

[0058] In one embodiment, the formula for determining whether the work output is limited in this method is:

[0059] Φ set ={j|P j '-P j,fact <ε}

[0060] In the formula: P j ' represents the active power setpoint of inverter j, P j,fact This represents the actual active power of inverter j; ε is the power threshold.

[0061] The constraints include:

[0062] Inverter capacity constraints:

[0063]

[0064] Overvoltage constraint:

[0065]

[0066] In one embodiment, the power threshold ε in this method is 0.2KW.

[0067] In one embodiment, the step of performing reactive power reduction to achieve voltage control when the active power output of all inverters is unrestricted further includes:

[0068] When all node voltages are below the upper limit, a reactive power recovery optimization algorithm is executed, aiming to minimize the inverter's reactive power output. The formula is as follows:

[0069]

[0070] The constraints include:

[0071] Current unproductive output:

[0072] -Q i ≤ΔQ i ≤0, i=1,2,...,m

[0073] Overvoltage constraint:

[0074]

[0075] In one embodiment, the calculation of the active power sensitivity of the voltage at node i to inverter j in this method includes:

[0076] Perform the voltage-active power ratio calculation steps sequentially for the j-th inverter in the distribution area:

[0077] Reduced active power output ΔP test,j Record the voltage change ΔU at each node. test,ij , where i = 1, 2, ..., n;

[0078] Calculate the ratio of voltage change to reduction in active power output -ΔU test,ij / ΔP test,j ;

[0079] Restore inverter j to its natural power generation state;

[0080] The voltage-active power ratio calculation step is repeated a first preset number of times. The average value of all calculated voltage-active power ratios is taken as the voltage sensitivity α of node i to inverter j. i,j .

[0081] In one embodiment, the calculation of the voltage sensitivity of node i to the reactive power sensitivity of inverter j in this method includes:

[0082] Perform the voltage-reactive power ratio calculation steps sequentially on the j-th inverter within the distribution area:

[0083] Absorbing inductive reactive power ΔQ test,j Record the voltage change ΔU at each node. test,ij ;

[0084] Calculate the ratio ΔU of voltage change to absorbed inductive reactive power. test,ij / ΔQ test,j ;

[0085] Restore inverter j to pure active power generation state;

[0086] The voltage-reactive power ratio calculation step is repeated a second preset number of times. The average value of all calculated voltage-reactive power ratios is taken as the voltage sensitivity β of node i to inverter j. i,j .

[0087] According to a second aspect of the present invention, a low-voltage distribution network voltage control device based on a distributed photovoltaic inverter is provided.

[0088] In one embodiment, the device includes a first-stage control module, a second-stage control module, a third-stage control module, and a low-node voltage control module; wherein,

[0089] The first-stage control module is used to solve for the minimum reactive power output of all inverters in the first stage of the transformer area when the voltage of any node in the transformer area exceeds the upper limit and the inverters in the transformer area are in the first stage. The first stage is the stage where the current active and reactive power output has not reached the capacity constraint or the power factor constraint. If the minimum reactive power output of the inverters in the first stage has a solution, the reactive power control command is executed to complete the voltage control; otherwise, the second stage is entered.

[0090] The second-stage control module is used to solve for the minimum active power output reduction of all inverters in the second stage within the distribution area when the inverters are in the second stage. The second stage is the stage where the current active and reactive power output has reached the capacity constraint but has not reached the power factor constraint. If the minimum active power output reduction of the inverters in the second stage has a solution, then active and reactive power control commands are executed to complete voltage control; otherwise, the third stage is entered.

[0091] The third-stage control module calculates the minimum active power output reduction for all inverters in the third stage within the distribution area when the inverters are in the third stage. The third stage is the stage where the current active and reactive power outputs have reached the power factor constraint. After obtaining the minimum active power output reduction for the inverters in the third stage, it executes active and reactive power control commands to complete voltage control.

[0092] The low-node voltage control module is used to restore active power output to complete voltage control when the voltage of all nodes in the transformer area is lower than the upper limit. If the active power output of an inverter is limited, it will perform active power output reduction to complete voltage control.

[0093] According to a third aspect of the present invention, a computer device is provided.

[0094] In some embodiments, the computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the steps of the method as described in the first aspect.

[0095] According to a fourth aspect of the present invention, a computer-readable storage medium is provided.

[0096] In some embodiments, a computer program is stored on a computer-readable storage medium; the computer program is executed by a processor to implement the steps of the method as described in the first aspect.

[0097] The technical solutions provided by the embodiments of the present invention may include the following beneficial effects:

[0098] This invention proposes a global optimization method for voltage control in low-voltage distribution networks based on the active and reactive power regulation capabilities of distributed photovoltaic (PV) inverters. By linearizing the distributed PV voltage regulation problem through node voltage active and reactive power sensitivity, the computational complexity of global voltage optimization for the distribution area is reduced. Furthermore, by fully utilizing the regulation and measurement functions of the PV inverters themselves, the active and reactive power sensitivity of node voltages can be estimated without knowing the distribution area topology, line parameters, and load information. In addition, the optimization method proposed in this invention prioritizes reactive power regulation by the inverters when voltage exceeds limits in the low-voltage distribution area, and prioritizes restoring the active power output of the inverters when there are no voltage exceedances, effectively improving the utilization rate of PV power generation resources.

[0099] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Attached Figure Description

[0100] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0101] Figure 1 This is a flowchart of a low-voltage distribution network voltage control method based on distributed photovoltaic inverters provided in the embodiments of this application;

[0102] Figure 2 This is a schematic diagram of the three-stage voltage limiting control provided in the embodiments of this application;

[0103] Figure 3 This is a flowchart illustrating the specific implementation of the low-voltage distribution network voltage control method based on distributed photovoltaic inverters provided in this application embodiment;

[0104] Figure 4 This is a low-voltage power distribution system topology diagram provided in the embodiments of this application;

[0105] Figure 5 This is a diagram showing the load curves of each node in the example provided in this application.

[0106] Figure 6 This is a schematic diagram of the active power output of each photovoltaic inverter under natural power generation state provided in the embodiments of this application;

[0107] Figure 7 This is a schematic diagram of the voltage regulation results provided in the embodiments of this application;

[0108] Figure 8 This is a structural diagram of a low-voltage distribution network voltage control device based on a distributed photovoltaic inverter provided in an embodiment of this application;

[0109] Figure 9 This is a schematic diagram of the structure of a computer device according to an exemplary embodiment. Detailed Implementation

[0110] The following description and accompanying drawings fully illustrate specific embodiments described herein to enable those skilled in the art to practice them. Some embodiments may include or substitute parts and features of other embodiments. The scope of the embodiments herein encompasses the entire scope of the claims and all available equivalents thereof. Throughout this document, the terms “first,” “second,” etc., are used only to distinguish one element from another without requiring or implying any actual relationship or order between the elements. Indeed, a first element can also be referred to as a second element, and vice versa. Furthermore, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a structure, apparatus, or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a structure, apparatus, or device. Without further limitation, an element defined by the phrase “comprising one…” does not exclude the presence of other identical elements in the structure, apparatus, or device that includes said element. The various embodiments described herein are presented in a progressive manner, with each embodiment focusing on its differences from other embodiments; similar or identical parts between embodiments can be referred to interchangeably.

[0111] In this document, unless otherwise stated, the term "multiple" means two or more.

[0112] Those skilled in the art will know that in the field of distributed photovoltaic operation and control technology for low-voltage distribution networks, the active and reactive power sensitivities of node voltage are defined as the changes in node voltage caused by unit active and reactive power disturbances, respectively, as shown in equations (1) and (2):

[0113]

[0114]

[0115] In the formula: U i P represents the effective value of the voltage at node i; j Q j These represent the active and reactive power outputs of photovoltaic inverter j, respectively; α i,j β i,j These represent the active and reactive power sensitivities of the voltage at node i to the photovoltaic inverter j, respectively.

[0116] To linearize the distributed photovoltaic voltage regulation problem by utilizing the active and reactive power sensitivity of node voltages, thereby reducing the computational complexity of global voltage optimization for the distribution area, an active power-voltage sensitivity estimation process is provided in this application embodiment as follows:

[0117] a. Select a sunny midday period and sequentially perform the following steps on the j-th (j = 1, 2, ..., m, where m represents the number of inverters in the distribution area) inverter:

[0118] a1. Decrease in active power output ΔP test,j Record the voltage change ΔU at each node. test,ij (i = 1, 2, ..., n, where n represents the number of nodes in the transformer area where voltage can be measured);

[0119] a2. Calculate the ratio of voltage change to active power adjustment -ΔU test,ij / ΔP test,j ;

[0120] a3. Inverter j returns to its natural power generation state.

[0121] b. Repeat step a multiple times, and calculate the voltage-active power ratio - ΔU multiple times. test,ij / ΔP test,j The average value is taken to obtain an estimated value of the voltage-active power sensitivity, which is used as the voltage-active power sensitivity α in the embodiments of this application. i,j Specifically, the number of times step a is repeated can be set as needed; in this application, the first preset number of times is used as a reference.

[0122] Preferably, in some embodiments of this application, the multiple repetitions of step a above can be distributed over multiple days, with each repetition occurring once or multiple times. Specifically, each repetition of step a is performed during the midday period (12:00-14:00).

[0123] In some embodiments of this application, each time step a1 is performed, the amount of reduction in active power output is taken as the current active power output of inverter j.

[0124] In some embodiments of this application, considering that during the active power adjustment of a photovoltaic inverter, the active power output of other photovoltaic inverters may change due to the occasional changes in environmental factors such as light intensity and temperature, thereby affecting the node voltage, the voltage-active power ratio obtained in this calculation is valid and participates in the final average value calculation only if the change in active power output of other inverters except inverter j does not exceed 3% of its rated active power during the execution of steps a1-a3; otherwise, steps a1-a3 are re-executed for inverter j.

[0125] Furthermore, the reactive power-voltage sensitivity estimation process provided in this application embodiment is as follows:

[0126] c. Select a sunny midday period and sequentially perform the following steps on the j-th (j = 1, 2, ..., m, where m represents the number of inverters in the distribution area) inverter:

[0127] c1. Absorbing inductive reactive power ΔQ test,j Record the voltage change ΔU at each node. test,ij (i = 1, 2, ..., n, where n is the number of nodes in the low-voltage distribution radio area);

[0128] c2. Calculate the ratio ΔU of voltage change to reactive power adjustment. test,ij / ΔQ test,j ;

[0129] c3. Inverter J returns to pure active power generation state.

[0130] d. Repeat step c multiple times, and calculate the voltage-reactive power ratio ΔU multiple times. test,ij / ΔQ test,j The average value is taken to obtain an estimated value of the voltage-reactive power sensitivity, which is used as the voltage-reactive power sensitivity β in the embodiments of this application. i,j Specifically, the number of times step d is repeated can be set as needed; in this application, the first preset number of times is used as a reference.

[0131] Preferably, in some embodiments of this application, the multiple repetitions of step c can be distributed over multiple days, with each repetition occurring once or multiple times. Specifically, each repetition of step c is performed during the midday period (12:00-14:00).

[0132] In some embodiments of this application, each time step c1 is performed, the inductive reactive power ΔQ is absorbed. test,j The value is taken as the maximum value under the inverter capacity constraint and power factor constraint.

[0133] In some embodiments of this application, considering that during the reactive power adjustment period of a certain photovoltaic inverter, the active power output of other photovoltaic inverters may change due to occasional changes in environmental factors such as light intensity and temperature, thereby affecting the node voltage, the voltage-reactive power ratio ΔU is calculated only when the change in active power output of inverters other than inverter j does not exceed 3% of their rated active power during the execution of steps c1-c3. test,ij / ΔQ test,j If valid, participate in the final average value calculation; otherwise, repeat steps c1-c3 for inverter j.

[0134] Furthermore, Figure 1 A flowchart of the low-voltage distribution network voltage control method based on distributed photovoltaic inverters of the present invention is shown. After obtaining the estimated values ​​of the active and reactive power sensitivity of the photovoltaic inverter to the node voltage through the aforementioned method ad, the voltage level of the distribution area can be controlled by the following method. Figure 1 As shown:

[0135] S1: When the voltage of any node in the distribution area exceeds the upper limit, and the inverters in the distribution area are in the first stage, solve for the minimum reactive power output of all inverters in the first stage in the distribution area; if there is a solution for the minimum reactive power output of the inverters in the first stage, execute the reactive power control command to complete the voltage control, otherwise enter the second stage.

[0136] In practical implementation, when the voltage at any node in the transformer area exceeds the upper limit, such as Figure 2 As shown, voltage limiting control is performed in three stages.

[0137] Specifically, three types of inverters are defined as follows:

[0138] The first-stage inverter: The current active and reactive power output has not reached either the capacity constraint or the power factor constraint;

[0139] Second-stage inverter: The current active and reactive power output has reached the capacity constraint, but has not reached the power factor constraint;

[0140] The third-stage inverter: The current active and reactive power outputs have reached the power factor constraint.

[0141] Figure 2 In this context, S represents the inverter capacity. The inverter's maximum power factor angle is represented by the angle, both being built-in inverter settings; P represents the active power output by the inverter to the grid, and Q represents the inductive reactive power absorbed by the inverter. The first stage corresponds to line segment AB, where the inverter's operating state has neither reached the capacity limit nor the power factor limit; the second stage corresponds to line segment BC, where the inverter has reached the capacity limit but not the power factor limit; the third stage corresponds to line segment CO, where the inverter has reached the power factor limit. When the inverter's active power is low, points B and C coincide, and only the first and third stages exist. Figure 2 (a) converted to Figure 2 (b) Form.

[0142] In specific implementation, such as Figure 3 As shown, after detecting the voltage of each node, it is determined whether the voltage of any node in the distribution area exceeds the upper limit. If so, the first stage of reactive power regulation is executed. In specific implementation, the first stage linear optimization problem is first solved:

[0143]

[0144] To determine the reactive power regulation of all inverters in the first stage within the distribution area; specifically, the first stage aims to minimize reactive power output.

[0145] In the formula, Φ AB For the first stage of inverter assembly, Q j Let Q be the reactive power output of inverter j, where j = 1, 2, ..., m, and m represents the number of inverters in the distribution area. j The inverter j absorbs the incremental inductive reactive power.

[0146] The constraints of the first-stage linear optimization problem include:

[0147] Capacity constraints:

[0148]

[0149] Power factor constraint:

[0150]

[0151] Overvoltage constraint:

[0152]

[0153] In the formula, S j P represents the capacity of inverter j. j For the active power output of inverter j, U is the angle of maximum power factor. i Let β be the effective value of the voltage at node i. i,j U represents the reactive power sensitivity of the voltage at node i to inverter j.max Let n be the upper limit of the node voltage, and n be the total number of nodes.

[0154] Optional, node voltage upper limit U max It is 1.07 times the system's rated voltage.

[0155] In specific implementation, such as Figure 3 As shown, if a solution exists in this stage, the optimization process ends and the reactive power control command is executed; otherwise, all inverters in sections AB follow the... Figure 2 The reactive power at point B is set (absorbing inductive reactive power to the maximum extent under capacity and power reference constraints), and all current AB-segment inverters are thus converted into BC-segment inverters, entering the second stage.

[0156] Furthermore, the specific handling method for the unsolvable problem in the first stage is as follows:

[0157] All A and B segment inverters are in accordance with the attached... Figure 2 At point B, reactive power is set (to absorb inductive reactive power to the maximum extent under capacity and power reference constraints). This moves the inverters in section AB into section BC. With no inverters in section AB within the distribution area, the second stage begins. It's important to note that this only modifies inverter settings internally within the controller; no control commands are issued. Control commands are only issued when a solution is found for a particular stage.

[0158] Please continue reading Figure 1 :

[0159] S2: When the inverters in the distribution area are in the second stage, solve for the minimum active power output reduction of all inverters in the second stage in the distribution area; if there is a solution for the minimum active power output reduction of the inverters in the second stage, execute the active and reactive power control commands to complete the voltage control, otherwise enter the third stage.

[0160] In specific implementation, such as Figure 3 As shown, the second stage of active and reactive power coordinated regulation under capacity constraints is performed. Specifically, the second stage linear optimization problem is first solved:

[0161]

[0162] To determine the active and reactive power regulation of all inverters in the second stage within the distribution area, with the goal of minimizing the reduction in active power output in the second stage.

[0163] In the formula, Φ BC For the second-stage inverter assembly, ΔP j This represents the change in the active power output of inverter j, with an increase in active power output being positive.

[0164] The constraints for the second-stage linear optimization problem include:

[0165] The second stage of linearization (i.e., segment BC) boundary constraints:

[0166] ΔP j =a j ΔQ j ,j∈Φ BC (8)

[0167] ΔP j ≤0,j∈Φ BC (9)

[0168] Power factor constraint:

[0169]

[0170] Overvoltage constraint:

[0171]

[0172] In the formula, aj represents the linearized relationship between active and reactive power for inverter j in the second stage, and αi ,j Let be the voltage sensitivity of node i to the active power sensitivity of inverter j;

[0173] In the formula, a j The calculation method is as follows:

[0174]

[0175] In specific implementation, such as Figure 3 As shown, if a solution exists in this stage, the optimization process ends and active and reactive power control commands are executed; otherwise, all inverters in sections BC follow the... Figure 2 At point C, active and reactive power are set (active power is generated and inductive reactive power is absorbed, so that the inverter output simultaneously meets the inverter capacity constraint and power factor constraint). All current BC-segment inverters are thus transformed into CO-segment inverters, entering the third stage.

[0176] Furthermore, the specific handling method for the unsolvable second stage is as follows:

[0177] All BC section inverters are in accordance with the attached... Figure 2 Point C is configured with active and reactive power (generating active power and absorbing inductive reactive power, ensuring the inverter output simultaneously meets both inverter capacity and power factor constraints). This puts the inverters in section BC into section CO. With no inverters in section CO within the distribution area, the third stage begins. It's important to note that this only modifies the inverter settings internally within the controller; no control commands are issued until a solution is found for a given stage.

[0178] Please continue reading Figure 1 :

[0179] S3: When the inverters in the distribution area are in the third stage, calculate the minimum active power output reduction of all inverters in the third stage in the distribution area; after obtaining the minimum active power output reduction of the inverters in the third stage, execute active and reactive power control commands to complete voltage control.

[0180] In specific implementation, such as Figure 3 As shown, the second stage of active and reactive power coordinated regulation under power factor constraints is performed. Specifically, the third stage linear optimization problem is solved first:

[0181]

[0182] To determine the active and reactive power regulation of all inverters in the third stage within the distribution area, with the goal of minimizing the reduction in active power output in the third stage.

[0183] In the formula, Φ CO This is the third-stage inverter assembly.

[0184] The constraints for the third-stage linear optimization problem include:

[0185] Third-stage boundary constraints:

[0186]

[0187] ΔP j ≤0,j∈Φ CO (14)

[0188] Overvoltage constraint:

[0189]

[0190] In specific implementation, such as Figure 3 As shown, after solving the optimization model, active and reactive power control commands are executed.

[0191] Please continue reading Figure 1 :

[0192] S4: When the voltage of all nodes in the distribution area is lower than the upper limit: if the active power output of an inverter is limited, active power output recovery is performed to complete voltage control; if the active power output of all inverters is not limited, reactive power reduction is performed to complete voltage control.

[0193] In specific implementation, such as Figure 3 As shown, when the voltage of all nodes in the distribution area is lower than the upper limit, if the active power output of an inverter is limited (referred to as non-natural power generation state), the active power output is restored first; if all inverters are in natural power generation state, the reactive power output is reduced.

[0194] In practical implementation, when all node voltages are below the upper limit and not all inverters are in a natural power generation state, an active power output recovery optimization algorithm is executed, aiming to maximize the increase in active power output of the inverters. The formula is as follows:

[0195]

[0196] In the formula, Φ set This refers to a set of inverters whose active power output is limited, meaning that the photovoltaic inverters are currently operating with active power output equal to their set value.

[0197] Optionally, the formula for determining whether active power output is limited is as follows:

[0198] Φ set ={j|P j '-P j,fact <ε} (17)

[0199] In the formula: P j ' represents the active power setpoint of inverter j, P j,fact Let ε represent the actual active power of inverter j; ε is the power threshold. Specifically, ε is a small power threshold; specifically, when the active power setpoint is not greater than the actual value, the inverter is considered to be in a non-natural power generation state. To avoid repeated execution of the active power recovery algorithm due to measurement and control errors, a threshold is set to generate a certain control dead zone. Optionally, the power threshold in equation (17) is ε = 0.2kW.

[0200] The constraints include:

[0201] Inverter capacity constraints:

[0202]

[0203] Overvoltage constraint:

[0204]

[0205] like Figure 3 As shown, after solving the optimization model, the active power control command is executed.

[0206] In practical implementation, when all node voltages are below the upper limit and the active power output of all inverters is unrestricted (i.e., all are in a natural power generation state), a reactive power recovery optimization algorithm is executed, aiming to minimize the reactive power output of the inverters. The formula is as follows:

[0207]

[0208] The constraints include:

[0209] Current unproductive output:

[0210] -Q i ≤ΔQ i ≤0, i=1,2,...,m (21)

[0211] Overvoltage constraint:

[0212]

[0213] like Figure 3 As shown, after solving the optimization model, the reactive power control command is executed.

[0214] Optional, such as Figure 3 The inverter shown above performs active and reactive power coordinated voltage regulation once every 3 minutes.

[0215] In summary, the purpose of this invention is to propose a practical low-voltage distribution transformer area voltage control method. This method involves coordinated global optimization of the active and reactive power outputs of all photovoltaic inverters within the transformer area. While effectively addressing voltage limit exceedance issues, it maximizes the active power generation of the photovoltaic system. Furthermore, while ensuring voltage quality and active power output, it reduces the reactive power output of the photovoltaic inverters to minimize line losses.

[0216] This invention linearizes the distributed photovoltaic voltage regulation problem by considering the active and reactive power sensitivity of node voltages, thereby reducing the computational complexity of global voltage optimization in the distribution area and adapting to the computing capabilities of edge computing devices (such as intelligent converged terminals in distribution areas) in actual low-voltage distribution areas.

[0217] This invention fully utilizes the adjustment and measurement functions of the photovoltaic inverter itself to estimate the active and reactive power sensitivity of node voltage, thus solving the dependence of traditional low-voltage distribution network point voltage control global optimization methods on data such as transformer topology, line parameters, and load information.

[0218] This application provides further examples to illustrate the low-voltage distribution network voltage control based on distributed photovoltaic inverters proposed in this application, so as to further demonstrate the beneficial effects of this application.

[0219] Please see Figure 4 This application constructs a distributed photovoltaic voltage regulation simulation system based on the topology and line length of a rural distribution substation to verify the effectiveness of the present invention in controlling the voltage level of a low-voltage distribution network.

[0220] Specifically, the line impedance is (0.650 + j0.412) Ω / km; considering the peak and valley load characteristics of different users, three typical load curves are set for each node, such as... Figure 5 As shown.

[0221] Specifically, the rated power of the photovoltaic inverter is shown in the table below, and the rated capacity is 1.1 times the rated power:

[0222]

[0223] Specifically, the output curves of each inverter under natural power generation conditions are as follows: Figure 6 As shown, the inverter power factor limit is 0.9, and the node voltage limit is 235.4V.

[0224] Using MATLAB software, the low-voltage distribution network voltage control method described in this invention was simulated based on the above example. After executing the method described in this invention, the voltages of each node are as follows: Figure 7 As shown in (a), the voltages at the line's terminal nodes 9 and 16 are the highest, and even during midday, they do not exceed the upper voltage limit after voltage regulation. From 8:00 to 16:00, voltage fluctuations at each node are relatively gentle, especially at the terminal nodes where the voltage remains essentially constant. The control strategy effectively limits voltage rise, with minimal fluctuations. The highest voltage curves for each transformer area at different times are shown below. Figure 7 As shown in (b), it can be seen that the highest voltage of the transformer area exceeds 260V under natural power generation conditions. Relying solely on reactive power regulation cannot maintain the voltage level of the transformer area between 9 and 13. However, through the active and reactive power coordinated regulation described in this invention, the highest voltage of the transformer area is stabilized at the set upper limit of 235.4V.

[0225] It should be understood that although the steps in the flowchart are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order constraint on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the diagram may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the sub-steps or stages of other steps.

[0226] Please see Figure 8 One embodiment of this application provides a low-voltage distribution network voltage control device based on a distributed photovoltaic inverter, including a first-stage control module 10, a second-stage control module 20, a third-stage control module 30, and a low-node voltage control module 40; wherein,

[0227] The first-stage control module 10 is used to solve for the minimum reactive power output of all inverters in the first stage of the transformer area when the voltage of any node in the transformer area exceeds the upper limit and the inverters in the transformer area are in the first stage. The first stage is the stage where the current active and reactive power output has not reached the capacity constraint or the power factor constraint. If the minimum reactive power output of the inverters in the first stage has a solution, the reactive power control command is executed to complete the voltage control; otherwise, the second stage is entered.

[0228] The second-stage control module 20 is used to solve the minimum active power output reduction of all inverters in the second stage within the distribution area when the inverters are in the second stage. The second stage is the stage where the current active and reactive power output has reached the capacity constraint but has not reached the power factor constraint. If the minimum active power output reduction of the inverters in the second stage has a solution, then active and reactive power control commands are executed to complete voltage control; otherwise, the third stage is entered.

[0229] The third-stage control module 30 calculates the minimum active power output reduction for all inverters in the third stage within the distribution area when the inverters are in the third stage. The third stage is the stage where the current active and reactive power outputs have reached the power factor constraint. After obtaining the minimum active power output reduction for the inverters in the third stage, it executes active and reactive power control commands to complete voltage control.

[0230] The low node voltage control module 40 is used to perform active power recovery to complete voltage control when the active power output of an inverter is limited if all node voltages in the transformer area are lower than the upper limit; and to perform reactive power reduction to complete voltage control if the active power output of all inverters is not limited.

[0231] Specific limitations regarding the aforementioned low-voltage distribution network voltage control device based on distributed photovoltaic inverters can be found in the limitations of the low-voltage distribution network voltage control method based on distributed photovoltaic inverters mentioned above, and will not be repeated here. Each module in the aforementioned low-voltage distribution network voltage control device based on distributed photovoltaic inverters can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device in hardware form, or stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to each module.

[0232] In another embodiment of this application, a computer device is provided, which may be a server, and its internal structure diagram may be as follows. Figure 9As shown, the computer device includes a processor, memory, and a network interface connected via a system bus. The processor provides computing and control capabilities. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system, computer programs, and a database. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage medium. The database stores static and dynamic information data. The network interface communicates with external terminals via a network connection. When the computer program is executed by the processor, it implements the steps in the above method embodiments.

[0233] Those skilled in the art will understand that Figure 9 The structure shown is merely a block diagram of a portion of the structure related to the present invention and does not constitute a limitation on the computer device to which the present invention is applied. A specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0234] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon that, when executed by a processor, implements the steps in the method embodiments described above.

[0235] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the methods described above. Any references to memory, storage, databases, or other media used in the embodiments provided by this invention can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, or optical storage, etc. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0236] This invention is not limited to the structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this invention is limited only by the appended claims.

Claims

1. A low-voltage distribution network voltage control method based on distributed photovoltaic inverters, characterized in that, include: When the voltage at any node in the distribution area exceeds the upper limit, and: When the inverters in the distribution area are in the first stage, the minimum reactive power output of all the inverters in the first stage in the distribution area is solved; the first stage is the stage where the current active and reactive power outputs have not reached the capacity constraint or the power factor constraint; if the minimum reactive power output of the inverters in the first stage has a solution, then the reactive power control command is executed to complete the voltage control, otherwise the second stage is entered. The second stage is the stage where the current active and reactive power output has reached the capacity constraint but has not reached the power factor constraint. When the inverters in the distribution area are in the second stage, the minimum active power output reduction of all the inverters in the second stage in the distribution area is solved. If the minimum active power output reduction of the inverters in the second stage has a solution, then active and reactive power control commands are executed to complete voltage control; otherwise, the third stage is entered. The third stage is the stage where the current active and reactive power output has reached the power factor constraint; when the inverter in the distribution area is in the third stage, the minimum active power output reduction of all the inverters in the distribution area in the third stage is calculated; after obtaining the minimum active power output reduction of the inverter in the third stage, the active and reactive power control commands are executed to complete the voltage control. When the voltage of all nodes in the transformer area is lower than the upper limit value: If the active power output of the inverter is limited, active power output recovery is performed to complete voltage control; If the active power output of all the inverters is unrestricted, then reactive power reduction is performed to complete voltage control.

2. The low-voltage distribution network voltage control method based on distributed photovoltaic inverters according to claim 1, characterized in that, When the inverters in the distribution area are in the first stage, the step of minimizing the reactive power output of all inverters in the first stage within the distribution area further includes: Solve the first-stage linear optimization problem: To determine the reactive power regulation of all inverters in the first stage within the transformer area, the first stage aims to minimize reactive power output; In the formula, Φ AB For the first stage of inverter assembly, Q j Let Q be the reactive power output of inverter j, where j = 1, 2, ..., m, and m represents the number of inverters in the distribution area. j The inverter j absorbs the incremental inductive reactive power.

3. The low-voltage distribution network voltage control method based on distributed photovoltaic inverters according to claim 2, characterized in that, The constraints of the first-stage linear optimization problem include: Capacity constraints: Power factor constraint: Overvoltage constraint: In the formula, S j P represents the capacity of inverter j. j For the active power output of inverter j, U is the angle of maximum power factor. i Let β be the effective value of the voltage at node i. i,j U represents the reactive power sensitivity of the voltage at node i to inverter j. max Let n be the upper limit of the node voltage, and n be the total number of nodes.

4. The low-voltage distribution network voltage control method based on distributed photovoltaic inverters according to claim 3, characterized in that, When the inverters in the distribution area are in the second stage, the step of calculating the minimum active power output reduction of all inverters in the second stage within the distribution area further includes: Solve the second-stage linear optimization problem: To determine the active and reactive power regulation of all inverters in the second stage within the transformer area, with the second stage aiming to minimize the reduction in active power output; In the formula, Φ BC For the second-stage inverter set, ΔP j This represents the change in the active power output of inverter j, with an increase in active power output being positive.

5. The low-voltage distribution network voltage control method based on distributed photovoltaic inverters according to claim 4, characterized in that, The constraints of the second-stage linear optimization problem include: The second-stage boundary constraints for linearization: ΔP j =a j ΔQ j ,j∈Φ BC ΔP j ≤0,j∈Φ BC Power factor constraint: Overvoltage constraint: In the formula, a j To linearize the active and reactive power relationship of inverter j in the second stage, α i,j Let be the voltage sensitivity of node i to the active power sensitivity of inverter j; In the formula, a j The calculation method is as follows:

6. The low-voltage distribution network voltage control method based on distributed photovoltaic inverters according to claim 5, characterized in that, When the inverters in the distribution area are in the third stage, the step of calculating the minimum active power output reduction of all inverters in the third stage within the distribution area further includes: Solve the third-stage linear optimization problem: To determine the active and reactive power regulation of all inverters in the third stage within the transformer area, with the third stage aiming to minimize the reduction in active power output; In the formula, Φ CO This is the third-stage inverter assembly.

7. The low-voltage distribution network voltage control method based on distributed photovoltaic inverters according to claim 6, characterized in that, The constraints of the third-stage linear optimization problem include: Third-stage boundary constraints: ΔP j ≤0,j∈Φ CO Overvoltage constraint:

8. The low-voltage distribution network voltage control method based on distributed photovoltaic inverters according to claim 7, characterized in that, If the active power output of the inverter is limited, the step of performing active power output recovery to complete voltage control further includes: When all node voltages are below the upper limit, an active power output recovery optimization algorithm is executed, aiming to maximize the increase in active power output of the inverter. The formula is as follows: In the formula, Φ set A collection of inverters whose active power output is limited.

9. The low-voltage distribution network voltage control method based on distributed photovoltaic inverters according to claim 8, characterized in that, The formula for determining whether the active power output is limited is as follows: F set ={j|P j '-P j,fact <e} In the formula: P j ' represents the active power setpoint of inverter j, P j,fact This represents the actual active power of inverter j; ε is the power threshold; The constraints include: Inverter capacity constraints: Overvoltage constraint:

10. The low-voltage distribution network voltage control method based on distributed photovoltaic inverters according to claim 9, characterized in that, The power threshold ε is 0.2KW.

11. The low-voltage distribution network voltage control method based on distributed photovoltaic inverters according to claim 10, characterized in that, If the active power output of all the inverters is unrestricted, the step of performing reactive power reduction to complete voltage control further includes: When all node voltages are below the upper limit and all inverters are in natural power generation mode, a reactive power recovery optimization algorithm is executed, with the objective of minimizing the reactive power output of the inverters. The formula is as follows: The constraints include: Current unproductive output: -Q i ≤ΔQ i ≤0,i=1,2,...,m Overvoltage constraint:

12. The low-voltage distribution network voltage control method based on distributed photovoltaic inverters according to claim 11, characterized in that, The calculation of the voltage sensitivity of node i to the active power sensitivity of inverter j includes: The voltage-active power ratio calculation steps are performed sequentially on the j-th inverter within the transformer area: Reduced active power output ΔP test,j Record the voltage change ΔU at each node. test,ij , where i = 1, 2, ..., n; Calculate the ratio of voltage change to reduction in active power output -ΔU test,ij / ΔP test,j ; Let the inverter j return to its natural power generation state; The voltage-active power ratio calculation step is repeated a first preset number of times. The average value of all calculated voltage-active power ratios is taken as the voltage sensitivity α of node i to inverter j. i,j .

13. The low-voltage distribution network voltage control method based on distributed photovoltaic inverters according to claim 12, characterized in that, The calculation of the voltage at node i to the reactive power sensitivity of inverter j includes: The voltage-reactive power ratio calculation steps are performed sequentially on the j-th inverter within the transformer area: Absorbing inductive reactive power ΔQ test,j Record the voltage change ΔU at each node. test,ij ; Calculate the ratio ΔU of voltage change to absorbed inductive reactive power. test,ij / ΔQ test,j ; Restore the inverter j to its pure active power generation state; The voltage-reactive power ratio calculation step is repeated a second preset number of times. The average value of all calculated voltage-reactive power ratios is taken as the voltage-reactive power sensitivity β of node i to inverter j. i,j .

14. A low-voltage distribution network voltage control device based on a distributed photovoltaic inverter, characterized in that, It includes a first-stage control module, a second-stage control module, a third-stage control module, and a low-node voltage control module; among which, The first-stage control module is used to solve for the minimum reactive power output of all inverters in the first stage within the transformer substation when the voltage of any node in the substation exceeds the upper limit and the inverters in the substation are in the first stage. The first stage is the stage where the current active and reactive power outputs have not reached either the capacity constraint or the power factor constraint. If the minimum reactive power output of the inverters in the first stage has a solution, then the reactive power control command is executed to complete the voltage control; otherwise, the second stage is entered. The second-stage control module is used to solve for the minimum active power output reduction of all inverters in the second stage within the distribution area when the inverters are in the second stage. The second stage is the stage where the current active and reactive power output has reached the capacity constraint but has not reached the power factor constraint. If the minimum active power output reduction of the inverters in the second stage has a solution, then active and reactive power control commands are executed to complete voltage control; otherwise, the third stage is entered. The third-stage control module calculates the minimum active power output reduction for all inverters in the third stage within the distribution area when the inverters are in the third stage. The third stage is the stage where the current active and reactive power outputs have reached the power factor constraint. After obtaining the minimum active power output reduction for the inverters in the third stage, the module executes the active and reactive power control commands to complete voltage control. The low node voltage control module is used to perform active power recovery to complete voltage control when all node voltages in the transformer area are lower than the upper limit value, if the active power output of the inverter is limited; and to perform reactive power reduction to complete voltage control when the active power output of all inverters is unrestricted.

15. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1-13.

16. A computer-readable storage medium, characterized in that, It stores a computer program thereon; the computer program is executed by a processor to implement the method as described in any one of claims 1-13.

Images