A power distribution network voltage coordination control method and system based on light storage integrated power station

Abstract

This invention discloses a method and system for coordinated voltage control of a distribution network based on an integrated photovoltaic and energy storage power station. The method includes: establishing an optimized setting model for the reactive power operation threshold of the photovoltaic inverter, with the objective functions being minimizing the reactive power regulation of the photovoltaic inverter, minimizing the line loss of the entire network, and minimizing the voltage deviation of the entire network; when the voltage of a node within a feeder is greater than the upper limit of the reactive power operation threshold or less than the lower limit of the reactive power operation threshold, based on the reactive power operation threshold and reactive voltage sensitivity, implementing improved local reactive voltage droop control; when the voltage of the node is still greater than the upper voltage limit or less than the lower voltage limit, implementing coordinated reactive voltage control of the photovoltaic inverter within the feeder; after implementing coordinated reactive voltage control of the photovoltaic inverter within the feeder, when the voltage of the node is still greater than the upper voltage limit or less than the lower voltage limit, implementing local active voltage control of the energy storage device; this invention can reduce the reactive power regulation of the photovoltaic inverter, the line loss of the distribution network, and the node voltage deviation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power systems and their automation, and particularly relates to a power distribution network voltage coordination control method and system based on a light-storage integrated power station. BACKGROUND

[0002] With a large number of distributed photovoltaics connected to the power distribution network, the intermittency and volatility of the output thereof can easily lead to bidirectional flow of line power flow, causing node voltage to exceed the limit, and seriously affecting the safety of the power grid and the power quality. Traditional voltage regulation methods such as adjusting the transformer tap, grouping and switching the shunt capacitor, etc. have slow response speed and are difficult to adapt to the rapid changes in photovoltaic output.

[0003] The light-storage integrated power station provides a new idea for voltage regulation. The photovoltaic inverter has a fast reactive power regulation capability and can be used as the primary voltage regulation resource; the energy storage device has a flexible active power regulation capability, and when the reactive power capacity of the photovoltaic inverter is exhausted, the energy storage device can perform deep voltage regulation through active power "peak clipping and valley filling". At present, the photovoltaic inverter mostly uses fixed power factor control or traditional Q-V droop control, but the fixed power factor control greatly limits the reactive power regulation capability of the photovoltaic inverter, and the parameters (such as the action threshold and the slope) of the traditional droop control mostly depend on experience setting and are difficult to adapt to the dynamic changes in the system operating state, so the control effect is limited. In addition, each photovoltaic inverter in a single feeder often operates independently and lacks collaborative control capability, resulting in insufficient utilization of control resources and even possible control conflicts. SUMMARY

[0004] The purpose of the present application is to provide a power distribution network voltage coordination control method and system based on a light-storage integrated power station, which can reduce the reactive power regulation amount of the photovoltaic inverter.

[0005] Technical solution: The power distribution network voltage coordination control method based on a light-storage integrated power station provided by the present application comprises:

[0006] (1) An optimization setting model of the reactive power action threshold of the photovoltaic inverter is established, the minimum reactive power regulation amount of the photovoltaic inverter, the minimum active power loss of the line in the whole network and the minimum voltage deviation in the whole network are taken as the objective functions, the objective functions are converted into a single objective function through a weighting coefficient method, the single objective function is converted into a mixed integer second-order cone relaxation model with a voltage square term and a current square term through variable substitution and second-order cone relaxation, and the upper limit of the reactive power action threshold and the lower limit of the reactive power action threshold are obtained based on the converted model;

[0007] (2) When the voltage of a node in a feeder is greater than the upper limit of the reactive power action threshold or less than the lower limit of the reactive power action threshold, an improved local reactive power voltage droop control is executed based on the reactive power action threshold and reactive power voltage sensitivity. The improved local reactive power voltage droop control specifically means that when the node voltage is greater than the upper limit of the reactive power action threshold, a step-down control is started to increase the reactive power absorbed by the photovoltaic inverter; when the node voltage is less than the lower limit of the reactive power action threshold, a step-up control is started to increase the reactive power output of the photovoltaic inverter.

[0008] (3) After implementing the improved local reactive voltage droop control, when the voltage of the node is still greater than the upper voltage limit or less than the lower voltage limit, the photovoltaic inverter coordinated reactive voltage control in the feeder is implemented; the photovoltaic inverter coordinated reactive voltage control in the feeder specifically means that the photovoltaic inverters of all nodes in the feeder except the node assist the node in reactive power compensation based on the remaining reactive capacity and reactive voltage sensitivity.

[0009] (4) After the photovoltaic inverter in the feeder is coordinated to control the reactive voltage, if the voltage of the node is still greater than the upper voltage limit or less than the lower voltage limit, the local active voltage control of the energy storage device is executed.

[0010] Further, step (1) includes: establishing an objective function that minimizes the reactive power regulation of the photovoltaic inverter. The objective function is to minimize the active power loss of the entire network. The objective function is to minimize the voltage deviation of the entire network. :

[0011] ;

[0012] ;

[0013] ;

[0014] Using the weighted coefficient method , and Transform into a single objective function:

[0015] ;

[0016] In the formula: , and These represent the proportions of the reactive power regulation of the photovoltaic inverter, the active power loss of the entire grid lines, and the voltage deviation of the entire grid in the objective function, respectively. This represents the reactive power output of the photovoltaic inverter at node i at time t. This represents the reactive power baseline value, which is the sum of the upper limits of reactive power output from all photovoltaic inverters; Let be the resistance value of branch ij; Let be the current value of branch ij at time t; This represents the active power baseline value, which is the total grid line loss when the reactive power output of the photovoltaic inverter is 0. Let be the voltage amplitude at node i at time t; This is the reference voltage for the power distribution network. and These represent the number of distribution network nodes and the number of branches, respectively. The scheduling period is [number].

[0017] Furthermore, the optimized setting model for the reactive power action threshold also includes the following constraints: power flow balance constraint, voltage and current safe operation constraint, photovoltaic inverter reactive power regulation constraint, reactive power action threshold constraint, energy storage constraint, and substation gate power constraint.

[0018] The power flow balance constraint adopts the Distflow branch power flow form, selecting a certain node. :

[0019] ;

[0020] ;

[0021] ;

[0022] ;

[0023] In the formula: It is the set of the starting nodes of the branch with j as the ending node in the distribution network; It is the set of end nodes of the branch with j as the first end node; and Let be the active and reactive power at the beginning of branch ij at time t; and These are the active power and reactive power of the load at node j at time t, respectively. and Let be the active power and reactive power output of the photovoltaic inverter at node j at time t, respectively. and These represent the discharge power and charging power of energy storage at node j at time t, respectively. The reactance of branch ij; Let be the resistance value of branch ij; Let be the current value of branch ij at time t; Let be the voltage amplitude at node i at time t; and They are nodes The calculated active power and calculated reactive power; the voltage and current safe operation constraints are:

[0024] ;

[0025] ;

[0026] In the formula: and These are the upper and lower bounds of the voltage; and These are the upper and lower bounds of the current.

[0027] The reactive power regulation constraint of the photovoltaic inverter is:

[0028] ;

[0029] In the formula: The apparent power of the photovoltaic inverter connected to node i; and Let represent the active power and reactive power output of the photovoltaic inverter connected to node i at time t, respectively. and Let represent the maximum and minimum reactive power output of the photovoltaic inverter connected to node i at time t, respectively.

[0030] The reactive power threshold constraint is:

[0031] ;

[0032] ;

[0033] In the formula: and These are the upper limit and lower limit of the reactive power operation threshold for the photovoltaic inverter at access node i, respectively. This is the rated voltage of the power distribution network;

[0034] The energy storage constraints include charge / discharge power constraints, energy balance constraints, and remaining capacity constraints:

[0035] ;

[0036] In the formula: This is a binary variable representing the charging and discharging state of the energy stored at node j at time t, where 1 indicates discharging and 0 indicates charging. The maximum charge and discharge power for energy storage at node j; The remaining charge capacity of node j at time t; and These represent the minimum and maximum remaining capacity allowed for energy storage at node j during operation; Indicates a unit of time. Indicates charging efficiency;

[0037] The substation gate constraint is used to limit the switching power of the gate connecting the distribution network and the main grid within a certain range, specifically:

[0038] ;

[0039] In the formula: and These are the upper and lower bounds of the output power of the substation nodes. and The active power and reactive power output from the substation gate node;

[0040] The method of transforming the single objective function into a mixed integer second-order cone relaxation model with voltage square terms and current square terms using variable substitution and second-order cone relaxation is as follows:

[0041] make The tidal current balance can be simplified to the following formula:

[0042] ;

[0043] ;

[0044] ;

[0045] ;

[0046] And relax the last equation into an inequality:

[0047] ;

[0048] Then the inequality above is equivalently transformed into:

[0049] ;

[0050] The active power loss of the entire network lines is reduced by variable substitution. Transform into a linear form:

[0051] ;

[0052] Furthermore, for the objective function and Perform variable substitution, let:

[0053] ;

[0054] ;

[0055] for and Add additional constraints:

[0056] ;

[0057] ;

[0058] In the formula: and Maximum and minimum values ​​optimized for voltage; and The upper and lower limits for optimizing the reactive power regulation of photovoltaic inverters.

[0059] Further, step (2) includes:

[0060] Let the reciprocal of the reactive voltage sensitivity be taken as the slope of the reactive voltage droop curve, and assume... and These represent the changes in active power and reactive power injected into the nodes, respectively. and Let these be the changes in node voltage magnitude and phase angle, respectively. Based on the power flow equations in polar coordinates, the relationship between the changes in node injected power and node voltage is as follows:

[0061] ;

[0062] In the formula: , , and The Jacobian matrix of the distribution network;

[0063] make From the above formula, we get:

[0064] ;

[0065] In the formula: This is the reactive voltage sensitivity matrix. elements in Let be the reactive voltage sensitivity of node i to node j, representing the effect of a unit reactive power change at node j on the voltage amplitude at node i.

[0066] Improved local reactive power droop control is implemented: when the node voltage is greater than the upper limit of the reactive power activation threshold, buck control is activated to increase the reactive power absorbed by the photovoltaic inverter; when the node voltage is less than the lower limit of the reactive power activation threshold, boost control is activated to increase the output reactive power of the photovoltaic inverter. Specifically, the improved local reactive power droop control expression for the photovoltaic inverter is as follows:

[0067] ;

[0068] In the formula: The output reactive power of the photovoltaic inverter at node i after implementing improved local reactive voltage droop control; Let be the voltage of the photovoltaic inverter connected to node i at time t. Let i be the reactive voltage sensitivity of node i to itself. and Let represent the maximum and minimum reactive power outputs of the photovoltaic inverter connected to node i at time t, respectively. This represents the upper limit of the reactive action threshold. This is the lower limit of the reactive action threshold.

[0069] Further, step (3) includes:

[0070] When the voltage at node i exceeds the upper voltage limit after implementing improved local reactive voltage droop control, calculate the reactive power regulation amount that needs to be compensated. for:

[0071] ;

[0072] In the formula: The voltage of the photovoltaic inverter at node i after implementing improved local reactive voltage droop control. The reactive voltage sensitivity of node i to itself;

[0073] When the voltage at node i falls below the lower voltage limit after implementing improved local reactive power droop control, the required reactive power regulation is calculated as follows:

[0074] ;

[0075] in, and These are the upper and lower bounds of the voltage;

[0076] The photovoltaic inverters within the feeder coordinate reactive power and voltage control. When the voltage at node i is greater than the upper voltage limit, the photovoltaic inverter connected to node j within the feeder provides reactive power compensation to node i. As shown in the following formula:

[0077] ;

[0078] In the formula: Let be the reactive voltage sensitivity of node j to node i; Excluding nodes i and j, the sum of the reactive voltage sensitivities of other nodes in the feeder to node i; Minimum output reactive power after implementing improved local reactive voltage droop control for the photovoltaic inverter at node j; The output reactive power of the photovoltaic inverter at node j after implementing improved local reactive voltage droop control; The remaining reactive power capacity of the photovoltaic inverter connected to node j is the reactive power capacity that is discharged downwards. The sum of the remaining reactive power capacity of all other photovoltaic inverters in the feeder, excluding nodes i and j;

[0079] When the voltage at node i is less than the lower voltage limit, the reactive power compensation provided to node i by the photovoltaic inverter connected to node j within the feeder. for:

[0080] ;

[0081] In the formula: The maximum output reactive power after implementing improved local reactive voltage droop control for the photovoltaic inverter at node j; The remaining reactive power capacity of the photovoltaic inverter at node j is connected. This is the sum of the remaining reactive power capacity of all other photovoltaic inverters within the feeder, excluding nodes i and j.

[0082] Furthermore, step (3) also includes: verifying whether the sum of the current output reactive power and the reactive power compensation exceeds the upper and lower limits of the reactive power capacity of the photovoltaic inverter. After the photovoltaic inverter connected to node j performs the coordinated reactive voltage control of the photovoltaic inverter in the feeder, the actual output reactive power is as follows:

[0083] .

[0084] Further, step (4) includes:

[0085] When the voltage at node i is greater than the upper voltage limit, the active power increment of the energy storage device connected to node i... for:

[0086]

[0087] In the formula: The voltage of the photovoltaic inverter connected to node i after performing reactive power control coordination of the photovoltaic inverters in the feeder; The active voltage sensitivity of node i to itself;

[0088] When the voltage at node i is less than the lower voltage bound, the increase in active power of the energy storage device connected to node i is:

[0089]

[0090] In the formula: and These are the upper and lower bounds of the voltage;

[0091] Considering the maximum charge / discharge power constraints and remaining capacity constraints of the energy storage device, the actual output active power of the energy storage device connected to node i is... As shown in the following formula:

[0092] ;

[0093] In the formula: For nodes Maximum charge and discharge power of energy storage; For nodes Energy storage The remaining charge capacity at any given time; and They are nodes The minimum and maximum remaining capacity of energy storage during operation; For nodes where local active voltage control of energy storage devices is not implemented The output active power of the energy storage; Indicates a unit of time; and These are the upper and lower bounds of the voltage.

[0094] Based on the same inventive concept, the present invention also provides a distribution network voltage coordination control system based on a photovoltaic-storage integrated power station, comprising:

[0095] The model building module is used to establish an optimized tuning model for the reactive power operation threshold of the photovoltaic inverter. The objective functions are to minimize the reactive power regulation of the photovoltaic inverter, minimize the active power loss of the entire grid lines, and minimize the voltage deviation of the entire grid. The objective function is transformed into a single objective function by the weighted coefficient method. Then, the single objective function is transformed into a mixed integer second-order cone relaxation model with voltage square terms and current square terms by using variable substitution and second-order cone relaxation. Based on the transformed model, the upper limit and lower limit of the reactive power operation threshold are obtained.

[0096] The first control module is used to execute an improved local reactive voltage droop control based on the reactive voltage action threshold and reactive voltage sensitivity when the voltage of a node in a feeder is greater than the upper limit of the reactive voltage action threshold or less than the lower limit of the reactive voltage action threshold. Specifically, the improved local reactive voltage droop control is as follows: when the node voltage is greater than the upper limit of the reactive voltage action threshold, a step-down control is activated to increase the reactive power absorbed by the photovoltaic inverter; when the node voltage is less than the lower limit of the reactive voltage action threshold, a step-up control is activated to increase the reactive power output of the photovoltaic inverter.

[0097] The second control module is used to perform the improved local reactive voltage droop control. When the voltage of the node is still greater than the upper voltage limit or less than the lower voltage limit, the module performs the coordinated reactive voltage control of the photovoltaic inverters in the feeder. Specifically, the coordinated reactive voltage control of the photovoltaic inverters in the feeder involves the photovoltaic inverters of all nodes in the feeder except the node assisting the node in reactive power compensation based on the remaining reactive capacity and reactive voltage sensitivity.

[0098] The third control module is used to perform coordinated reactive voltage control of the photovoltaic inverter in the feeder, and when the voltage of the node is still greater than the upper voltage limit or less than the lower voltage limit, it performs local active voltage control of the energy storage device.

[0099] Based on the same inventive concept, the present invention also provides a computing device, comprising: one or more processors, one or more memories, and one or more programs, wherein the programs are stored in the memory and configured to be executed by the processor, and when the programs are loaded onto the processor, they implement the steps of the distribution network voltage coordination control method based on the photovoltaic-storage integrated power station as described in any of the preceding claims.

[0100] Based on the same inventive concept, the present invention also provides a storage medium storing a computer program, the computer program including program instructions, which, when executed by a processor, cause the processor to perform the steps of the distribution network voltage coordination control method based on the photovoltaic-storage integrated power station as described above.

[0101] Beneficial effects: Compared with the prior art, the present invention can effectively reduce the reactive power regulation of photovoltaic inverters, distribution network line losses and node voltage deviations by optimizing the reactive power action threshold of photovoltaic inverters. On the basis of local reactive power voltage droop control of photovoltaic inverters, the present invention effectively coordinates the reactive power compensation of each photovoltaic inverter in the feeder and gives full play to the active power regulation capability of energy storage devices. It can quickly and effectively deal with the voltage over-limit problem caused by distributed photovoltaic access and improve power supply quality. Attached Figure Description

[0102] Figure 1 This is a flowchart of a method according to an embodiment of the present invention;

[0103] Figure 2 This is a schematic diagram of the improved local reactive voltage droop control according to an embodiment of the present invention.

[0104] Figure 3 This is a schematic diagram of coordinated reactive power and voltage control of the photovoltaic inverter within the feeder according to an embodiment of the present invention. Detailed Implementation

[0105] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0106] like Figure 1 As shown in this embodiment, the distribution network voltage coordination control method based on the photovoltaic-storage integrated power station includes:

[0107] Step 1: Establish an optimization model for the reactive power operation threshold of the photovoltaic inverter. The objective functions are to minimize the reactive power regulation of the photovoltaic inverter, minimize the active power loss of the entire grid, and minimize the voltage deviation of the entire grid. The objective function is transformed into a single objective function by using the weighted coefficient method. Then, the single objective function is transformed into a mixed integer second-order cone relaxation model with voltage square terms and current square terms by using variable substitution and second-order cone relaxation. Based on the transformed model, the upper limit and lower limit of the reactive power operation threshold are obtained.

[0108] Step 2: When the voltage at a node within a feeder is greater than the upper limit of the reactive power action threshold or less than the lower limit of the reactive power action threshold, an improved local reactive power voltage droop control is executed based on the reactive power action threshold and reactive power voltage sensitivity. Specifically, the improved local reactive power voltage droop control involves: when the node voltage is greater than the upper limit of the reactive power action threshold, initiating buck control to increase the reactive power absorbed by the photovoltaic inverter; and when the node voltage is less than the lower limit of the reactive power action threshold, initiating boost control to increase the reactive power output of the photovoltaic inverter.

[0109] Step 3: After implementing the improved local reactive voltage droop control, when the voltage of the node is still greater than the upper voltage limit or less than the lower voltage limit, the photovoltaic inverter coordinated reactive voltage control within the feeder is implemented; the photovoltaic inverter coordinated reactive voltage control within the feeder specifically means that the photovoltaic inverters of all nodes in the feeder except the node assist the node in reactive power compensation based on the remaining reactive capacity and reactive voltage sensitivity.

[0110] Step 4: After implementing coordinated reactive voltage control of the photovoltaic inverter within the feeder, if the voltage at this node is still greater than the upper voltage limit or less than the lower voltage limit, implement local active voltage control of the energy storage device.

[0111] Step one includes:

[0112] The following three factors are mainly considered when setting the reactive action threshold:

[0113] (1) Photovoltaic inverters have the least reactive power regulation. The apparent power capacity of a photovoltaic inverter is fixed. Output reactive power will crowd out the capacity available for output active power, which may lead to "curtailment" of active power when there is sufficient sunlight. Therefore, the output reactive power of a photovoltaic inverter should not occupy too much inverter capacity. In addition, reactive power regulation of a photovoltaic inverter will increase its heat loss, so the inverter should not perform reactive power regulation multiple times.

[0114] ;

[0115] (2) Minimizes active power loss across the entire network. Distributed photovoltaic access points are generally located near the power load. Appropriate local reactive power compensation by the photovoltaic inverter can effectively reduce line losses. However, if the reactive power action threshold is not set appropriately, such as setting the upper limit of the reactive power action threshold too high or too low, there may be under-compensation or over-compensation of reactive power, which will lead to an increase in line losses instead of a decrease.

[0116] ;

[0117] (3) Minimum voltage deviation across the entire network. A good voltage level is a necessary condition for the normal operation of the distribution network. To ensure power supply quality, the voltage deviation of each node in the distribution network is used as one of the optimization objective functions.

[0118] ;

[0119] For three objective functions, the weighted coefficient method can be used to transform them into a single objective function. Therefore, the single objective function is:

[0120] ;

[0121] In the formula: , and These represent the proportions of reactive power regulation by the photovoltaic inverter, active power loss of the entire grid, and voltage deviation in the objective function, respectively. This represents the reactive power output of the photovoltaic inverter at node i at time t. This is the reactive power baseline value, which is the sum of the upper limits of reactive power output from all photovoltaic inverters; Let be the resistance value of branch ij; Let be the current value of branch ij at time t; This is the active power baseline value, which represents the total grid line loss when the reactive power output of the photovoltaic inverter is 0. Let be the voltage amplitude at node i at time t; This is the reference voltage for the power distribution network. and These represent the number of distribution network nodes and the number of branches, respectively. The scheduling period is [number].

[0122] The constraints for optimizing the reactive power action threshold setting include power flow balance constraints, voltage and current safe operation constraints, photovoltaic inverter reactive power regulation constraints, reactive power action threshold constraints, energy storage constraints, and substation gate power constraints.

[0123] 1) Power flow balance constraint

[0124] Distflow branch power flow pattern adopted:

[0125]

[0126]

[0127]

[0128]

[0129] In the formula: It is the set of the starting nodes of the branch with j as the ending node in the distribution network; It is the set of end nodes of the branch with j as the first end node; , Let be the active and reactive power at the beginning of branch ij at time t; , These are the active power and reactive power of the load at node j at time t, respectively. , Let be the active power and reactive power output of the photovoltaic inverter at node j at time t, respectively. , These represent the discharge power and charging power of energy storage at node j at time t, respectively. Let be the reactance of branch ij. The first two equations ensure active and reactive power balance, respectively; the latter two equations are voltage drop balance constraints.

[0130] 2) Voltage and current safety operation constraints

[0131] ;

[0132] ;

[0133] In the formula: , These are the upper and lower bounds of the voltage. , This represents the upper and lower bounds of the current.

[0134] 3) Reactive power regulation constraints of photovoltaic inverters

[0135] ;

[0136] In the formula: The apparent power of the photovoltaic inverter connected to node i; and Let represent the active power and reactive power output of the photovoltaic inverter connected to node i at time t, respectively. and Let represent the maximum and minimum reactive power outputs of the photovoltaic inverter connected to node i at time t, respectively.

[0137] 4) Reactive action threshold constraint

[0138] ;

[0139] ;

[0140] In the formula: and These are the upper limit and lower limit of the reactive power action threshold for the photovoltaic inverter at access node i, respectively. This is the rated voltage of the power distribution network.

[0141] 5) Energy storage constraints

[0142] This mainly includes charging and discharging power constraints, charge balance constraints, and remaining capacity constraints, namely...

[0143]

[0144] In the formula: This is a binary variable representing the charging and discharging state of the energy stored at node j at time t, where 1 indicates discharging and 0 indicates charging. The maximum charge / discharge power for energy storage at node j; The remaining charge capacity of node j at time t; , These represent the minimum and maximum remaining capacity allowed for energy storage at node j during operation; Indicates a unit of time. This indicates charging efficiency.

[0145] 6) Substation gate constraints

[0146] The switching power at the junction of the distribution network and the main grid should be limited to a certain range.

[0147]

[0148] In the formula: , These are the upper and lower bounds of the output power of a substation node. , This refers to the output active power and output reactive power from the substation gate node.

[0149] Based on the current load power forecast and photovoltaic power forecast, the above-mentioned reactive power action threshold optimization model is solved. Since the above model is a non-convex nonlinear optimization model, it can be transformed into a mixed integer second-order cone relaxation model with voltage square terms and current square terms by using variable substitution and second-order cone relaxation.

[0150] make Then the current equation becomes the following:

[0151]

[0152]

[0153]

[0154]

[0155] And relax the last equation into an inequality:

[0156]

[0157] Then it is equivalently transformed into:

[0158]

[0159] By substituting variables, the active power loss of the entire network can be transformed into a linear form:

[0160]

[0161] Furthermore, for the objective function and The value contains absolute values; process them as follows:

[0162]

[0163]

[0164] Add the following additional constraints:

[0165] ;

[0166] ;

[0167] In the formula: , Maximum and minimum values ​​optimized for voltage; , The upper and lower limits for optimizing the reactive power regulation of photovoltaic inverters.

[0168] Step two specifically includes:

[0169] Reactive voltage sensitivity reflects the magnitude of the impact of injected reactive power on node voltage; its reciprocal can be used as the slope of the reactive voltage droop curve. Let... and These represent the changes in active and reactive power injected into the nodes, respectively. and Let be the changes in node voltage magnitude and phase angle, respectively. Then, according to the power flow equations in polar coordinates, the relationship between the change in node injected power and the change in node voltage is:

[0170]

[0171] In the formula: , , and This is the Jacobian matrix of the distribution network. Under normal operating conditions, the voltage deviation between each node and the rated voltage is small, and the phase angle difference between each node is not large. Therefore, the Jacobian matrix is ​​approximately a constant matrix, and its elements are mainly determined by the distribution network parameters.

[0172] For photovoltaic inverters, to minimize curtailment, maximum power point tracking (MPPT) control is typically used, without reducing the active power output of the photovoltaic system. Therefore, let Therefore, the above equation can be rearranged to obtain:

[0173]

[0174] In the formula: This is the reactive voltage sensitivity matrix. elements in Let be the reactive voltage sensitivity of node i to node j, representing the effect of a unit change in reactive power at node j on the voltage amplitude at node i.

[0175] because When the distribution network is operating normally, it is approximately a constant matrix. It does not need to be updated when the distribution network topology does not change. Therefore, if the voltage of a certain node exceeds the limit, the photovoltaic inverter of the corresponding node can perform reactive power regulation based on the pre-calculated reactive voltage sensitivity, thereby suppressing the voltage exceeding the limit.

[0176] Based on the aforementioned reactive power action threshold and reactive power voltage sensitivity, an improved local reactive power voltage droop control strategy is proposed. (See attached...) Figure 2As shown, when the photovoltaic node voltage is greater than the upper limit of the set reactive power action threshold, buck control is activated to increase the reactive power absorbed by the photovoltaic inverter; when the photovoltaic node voltage is less than the lower limit of the set reactive power action threshold, boost control is activated to increase the output reactive power of the photovoltaic inverter; when the photovoltaic node voltage is within the normal operating range, the photovoltaic inverter does not perform reactive power regulation to avoid unnecessary reactive power flow and reduce the losses of the photovoltaic inverter.

[0177] The specific improved local reactive power droop control expression for the photovoltaic inverter is as follows:

[0178] ;

[0179] In the formula: The output reactive power of the photovoltaic inverter at node i after implementing improved local reactive voltage droop control; Let be the voltage of the photovoltaic inverter connected to node i at time t. Let be the reactive voltage sensitivity of node i to itself. This represents the upper limit of the reactive action threshold. This is the lower limit of the reactive action threshold.

[0180] Step three specifically includes:

[0181] When photovoltaic penetration is too high or load power increases sharply, the improved local reactive voltage droop control of a single photovoltaic inverter on a feeder may not be able to solve the problem of voltage exceeding the upper and lower voltage limits due to the limited reactive power regulation capacity of the photovoltaic inverter. Therefore, after implementing local reactive voltage droop control of the photovoltaic inverter failed to bring the voltage back to the normal operating range, a coordinated reactive voltage control strategy for photovoltaic inverters within the feeder was developed.

[0182] As attached Figure 3 As shown, to avoid large-scale reactive power flow, reactive power voltage control is only coordinated for the photovoltaic inverters within the feeder, and does not involve reactive power voltage control between feeders. When the voltage of a photovoltaic inverter node within a feeder is too high or too low, the photovoltaic inverters at other nodes within the feeder assist in reactive power compensation until the voltage returns to the normal operating range.

[0183] Assuming that the voltage at node i still exceeds the upper voltage limit after improved local voltage control, first calculate the reactive power regulation that needs to be compensated:

[0184] ;

[0185] In the formula: The voltage of the photovoltaic inverter at node i after implementing improved local reactive voltage droop control.

[0186] Similarly, the reactive power regulation amount that needs to be compensated when the voltage at node i crosses the lower voltage bound can be obtained:

[0187] ;

[0188] To utilize the remaining reactive power capacity of each photovoltaic inverter within the feeder more evenly, a reactive power regulation scheme that comprehensively considers both remaining reactive power capacity and reactive power voltage sensitivity is proposed: for photovoltaic inverters with sufficient remaining reactive power capacity and high reactive power voltage sensitivity to node i, the reactive power compensation provided to node i should be as large as possible; conversely, for photovoltaic inverters with insufficient remaining reactive power capacity and low reactive power voltage sensitivity to node i, the reactive power compensation provided to node i should be as small as possible. The reactive power compensation provided to node i by the photovoltaic inverter connected to node j within the feeder is shown in the following formula:

[0189]

[0190] In the formula: Let be the reactive voltage sensitivity of node j to node i; Excluding nodes i and j, the sum of the reactive voltage sensitivities of other nodes in the feeder to node i; Minimum output reactive power after implementing improved local reactive voltage droop control for the photovoltaic inverter at node j; The remaining reactive power capacity of the photovoltaic inverter connected to node j is the reactive power capacity that is discharged downwards. This is the sum of the remaining reactive power capacity of all other photovoltaic inverters within the feeder, excluding nodes i and j.

[0191] Similarly, when the voltage at node i exceeds the lower voltage bound, the reactive power compensation provided to node i by the photovoltaic inverter connected to node j within the feeder can be obtained as follows:

[0192]

[0193] In the formula: The maximum output reactive power after implementing improved local reactive voltage droop control for the photovoltaic inverter at node j; The remaining reactive power capacity of the photovoltaic inverter at node j is connected. This is the sum of the remaining reactive power capacity of all other photovoltaic inverters within the feeder, excluding nodes i and j.

[0194] The above two formulas can achieve a reasonable allocation of reactive power output of each photovoltaic inverter in the feeder. While making full use of the remaining reactive capacity, the photovoltaic inverters with more significant voltage regulation effect are given priority to participate in compensation, thereby improving the voltage regulation efficiency of the distribution network.

[0195] After determining the reactive power compensation amount that the photovoltaic inverters connected to each node within the feeder need to provide to node i locally, they also need to further verify whether the sum of the current output reactive power and the reactive power compensation amount exceeds the upper and lower limits of the photovoltaic inverter's reactive power capacity. After performing coordinated reactive voltage control within the feeder, the actual output reactive power of the photovoltaic inverter connected to node j is as follows:

[0196] .

[0197] Step four specifically includes the following process:

[0198] If the voltage at node i still exceeds the limit after reactive power voltage control coordinated by the photovoltaic inverter within the feeder, then local active power voltage control of the energy storage device is executed. Assuming the voltage at node i exceeds the upper limit, the active power increment of the energy storage device connected to node i is first calculated as follows:

[0199]

[0200] In the formula: The voltage of the photovoltaic inverter at node i after implementing coordinated reactive voltage control of photovoltaic inverters within the feeder; Let be the active voltage sensitivity of node i to itself.

[0201] Similarly, when the voltage at node i falls below the lower limit, the increase in active power of the energy storage device connected to node i can be obtained as follows:

[0202]

[0203] Considering the maximum charging and discharging power constraints and remaining capacity constraints of the energy storage device, the actual output active power of the energy storage device connected to node i is as follows:

[0204] .

[0205] Based on the same inventive concept, this embodiment also provides a distribution network voltage coordination control system based on an integrated photovoltaic and energy storage power station, comprising:

[0206] The model building module is used to establish an optimized tuning model for the reactive power operation threshold of the photovoltaic inverter. The objective functions are to minimize the reactive power regulation of the photovoltaic inverter, minimize the active power loss of the entire grid lines, and minimize the voltage deviation of the entire grid. The objective function is transformed into a single objective function by the weighted coefficient method. Then, the single objective function is transformed into a mixed integer second-order cone relaxation model with voltage square terms and current square terms by using variable substitution and second-order cone relaxation. Based on the transformed model, the upper limit and lower limit of the reactive power operation threshold are obtained.

[0207] The first control module is used to execute an improved local reactive voltage droop control based on the reactive voltage action threshold and reactive voltage sensitivity when the voltage of a node in a feeder is greater than the upper limit of the reactive voltage action threshold or less than the lower limit of the reactive voltage action threshold. Specifically, the improved local reactive voltage droop control is as follows: when the node voltage is greater than the upper limit of the reactive voltage action threshold, a step-down control is activated to increase the reactive power absorbed by the photovoltaic inverter; when the node voltage is less than the lower limit of the reactive voltage action threshold, a step-up control is activated to increase the reactive power output of the photovoltaic inverter.

[0208] The second control module is used to perform the improved local reactive voltage droop control. When the voltage of the node is still greater than the upper voltage limit or less than the lower voltage limit, the module performs the coordinated reactive voltage control of the photovoltaic inverters in the feeder. Specifically, the coordinated reactive voltage control of the photovoltaic inverters in the feeder involves the photovoltaic inverters of all nodes in the feeder except the node assisting the node in reactive power compensation based on the remaining reactive capacity and reactive voltage sensitivity.

[0209] The third control module is used to perform coordinated reactive voltage control of the photovoltaic inverter in the feeder, and when the voltage of the node is still greater than the upper voltage limit or less than the lower voltage limit, it performs local active voltage control of the energy storage device.

[0210] Based on the same inventive concept, this embodiment also provides a computing device, including: one or more processors, one or more memories, and one or more programs, wherein the programs are stored in the memory and configured to be executed by the processor, and when the programs are loaded onto the processor, they implement the steps of the distribution network voltage coordination control method based on the photovoltaic-storage integrated power station as described above.

[0211] Based on the same inventive concept, this embodiment also provides a storage medium storing a computer program, the computer program including program instructions, which, when executed by a processor, cause the processor to perform the steps of the distribution network voltage coordination control method based on the photovoltaic-storage integrated power station as described above.

Claims

1. A method for coordinated voltage control of a distribution network based on an integrated photovoltaic-storage power station, characterized in that, include: (1) Establish an optimization setting model for the reactive power operation threshold of the photovoltaic inverter. The objective functions are to minimize the reactive power regulation of the photovoltaic inverter, minimize the active power loss of the entire grid line, and minimize the voltage deviation of the entire grid. The objective function is transformed into a single objective function by weighting coefficient method. The single objective function is then transformed into a mixed integer second-order cone relaxation model with voltage square terms and current square terms by variable substitution and second-order cone relaxation. Based on the transformed model, the upper limit and lower limit of the reactive power operation threshold are obtained. (2) When the voltage of a node in a feeder is greater than the upper limit of the reactive power action threshold or less than the lower limit of the reactive power action threshold, an improved local reactive power voltage droop control is executed based on the reactive power action threshold and reactive power voltage sensitivity. The improved local reactive power voltage droop control specifically means that when the node voltage is greater than the upper limit of the reactive power action threshold, a step-down control is started to increase the reactive power absorbed by the photovoltaic inverter; when the node voltage is less than the lower limit of the reactive power action threshold, a step-up control is started to increase the reactive power output of the photovoltaic inverter. (3) After implementing the improved local reactive voltage droop control, when the voltage of the node is still greater than the upper voltage limit or less than the lower voltage limit, the photovoltaic inverter coordinated reactive voltage control in the feeder is implemented; the photovoltaic inverter coordinated reactive voltage control in the feeder specifically means that the photovoltaic inverters of all nodes in the feeder except the node assist the node in reactive power compensation based on the remaining reactive capacity and reactive voltage sensitivity. (4) After the photovoltaic inverter in the feeder is coordinated to control the reactive voltage, if the voltage of the node is still greater than the upper voltage limit or less than the lower voltage limit, the local active voltage control of the energy storage device is executed.

2. The distribution network voltage coordination control method based on integrated photovoltaic and energy storage power station according to claim 1, characterized in that, Step (1) includes: establishing an objective function that minimizes the reactive power regulation of the photovoltaic inverter. The objective function is to minimize the active power loss of the entire network. The objective function is to minimize the voltage deviation of the entire network. : ； ； ； Using the weighted coefficient method , and Transform into a single objective function: ； In the formula: , and These represent the proportions of the reactive power regulation of the photovoltaic inverter, the active power loss of the entire grid lines, and the voltage deviation of the entire grid in the objective function, respectively. This represents the reactive power output of the photovoltaic inverter at node i at time t. This represents the reactive power baseline value, which is the sum of the upper limits of reactive power output from all photovoltaic inverters; Let be the resistance value of branch ij; Let be the current value of branch ij at time t; This represents the active power baseline value, which is the total grid line loss when the reactive power output of the photovoltaic inverter is 0. Let be the voltage amplitude at node i at time t; This is the reference voltage for the power distribution network. and These represent the number of distribution network nodes and the number of branches, respectively. The scheduling period is [number].

3. The distribution network voltage coordination control method based on a photovoltaic-storage integrated power station according to claim 2, characterized in that, The optimized setting model for the reactive power action threshold also includes the following constraints: power flow balance constraint, voltage and current safe operation constraint, photovoltaic inverter reactive power regulation constraint, reactive power action threshold constraint, energy storage constraint, and substation gate power constraint. The power flow balance constraint adopts the Distflow branch power flow form, selecting a certain node. : ； ； ； ； In the formula: It is the set of the starting nodes of the branch with j as the ending node in the distribution network; It is the set of end nodes of the branch with j as the first end node; and Let be the active and reactive power at the beginning of branch ij at time t; and These are the active power and reactive power of the load at node j at time t, respectively. and Let be the active power and reactive power output of the photovoltaic inverter at node j at time t, respectively. and These represent the discharge power and charging power of energy storage at node j at time t, respectively. The reactance of branch ij; Let be the resistance value of branch ij; Let be the current value of branch ij at time t; Let be the voltage amplitude at node i at time t; and They are nodes The calculated active power and calculated reactive power; the voltage and current safe operation constraints are: ； ； In the formula: and These are the upper and lower bounds of the voltage; and These are the upper and lower bounds of the current. The reactive power regulation constraint of the photovoltaic inverter is: ； In the formula: The apparent power of the photovoltaic inverter connected to node i; and Let represent the active power and reactive power output of the photovoltaic inverter connected to node i at time t, respectively. and Let represent the maximum and minimum reactive power output of the photovoltaic inverter connected to node i at time t, respectively. The reactive power threshold constraint is: ； ； In the formula: and These are the upper limit and lower limit of the reactive power operation threshold for the photovoltaic inverter at access node i, respectively. This is the rated voltage of the power distribution network; The energy storage constraints include charge / discharge power constraints, energy balance constraints, and remaining capacity constraints: ； In the formula: This is a binary variable representing the charging and discharging state of the energy stored at node j at time t, where 1 indicates discharging and 0 indicates charging. The maximum charge and discharge power for energy storage at node j; The remaining charge capacity of node j at time t; and These represent the minimum and maximum remaining capacity allowed for energy storage at node j during operation; Indicates a unit of time. Indicates charging efficiency; The substation gate constraint is used to limit the switching power of the gate connecting the distribution network and the main grid within a certain range, specifically: ； In the formula: and These are the upper and lower bounds of the output power of the substation nodes. and The active power and reactive power output from the substation gate node; The method of transforming the single objective function into a mixed integer second-order cone relaxation model with voltage square terms and current square terms using variable substitution and second-order cone relaxation is as follows: make The tidal current balance can be simplified to the following formula: ； ； ； ； And relax the last equation into an inequality: ； Then the inequality above is equivalently transformed into: ； The active power loss of the entire network lines is reduced by variable substitution. Transform into a linear form: ； Furthermore, for the objective function and Perform variable substitution, let: ； ； for and Add additional constraints: ； ； In the formula: and Maximum and minimum values ​​optimized for voltage; and The upper and lower limits for optimizing the reactive power regulation of photovoltaic inverters.

4. The distribution network voltage coordination control method based on a photovoltaic-storage integrated power station according to claim 1, characterized in that, Step (2) includes: Let the reciprocal of the reactive voltage sensitivity be taken as the slope of the reactive voltage droop curve, and assume... and These represent the changes in active power and reactive power injected into the nodes, respectively. and Let these be the changes in node voltage magnitude and phase angle, respectively. Based on the power flow equations in polar coordinates, the relationship between the changes in node injected power and node voltage is as follows: ； In the formula: , , and The Jacobian matrix of the distribution network; make From the above formula, we get: ； In the formula: This is the reactive voltage sensitivity matrix. elements in Let be the reactive voltage sensitivity of node i to node j, representing the effect of a unit reactive power change at node j on the voltage amplitude at node i. Improved local reactive power droop control is implemented: when the node voltage is greater than the upper limit of the reactive power activation threshold, buck control is activated to increase the reactive power absorbed by the photovoltaic inverter; when the node voltage is less than the lower limit of the reactive power activation threshold, boost control is activated to increase the output reactive power of the photovoltaic inverter. Specifically, the improved local reactive power droop control expression for the photovoltaic inverter is as follows: ； In the formula: The output reactive power of the photovoltaic inverter at node i after implementing improved local reactive voltage droop control; Let be the voltage of the photovoltaic inverter connected to node i at time t. Let i be the reactive voltage sensitivity of node i to itself. and Let represent the maximum and minimum reactive power outputs of the photovoltaic inverter connected to node i at time t, respectively. This represents the upper limit of the reactive action threshold. This is the lower limit of the reactive action threshold.

5. The distribution network voltage coordination control method based on a photovoltaic-storage integrated power station according to claim 1, characterized in that, Step (3) includes: When the voltage at node i exceeds the upper voltage limit after implementing improved local reactive voltage droop control, calculate the reactive power regulation amount that needs to be compensated. for: ； In the formula: The voltage of the photovoltaic inverter at node i after implementing improved local reactive voltage droop control. The reactive voltage sensitivity of node i to itself; When the voltage at node i falls below the lower voltage limit after implementing improved local reactive power droop control, the required reactive power regulation is calculated as follows: ； in, and These are the upper and lower bounds of the voltage; The photovoltaic inverters within the feeder coordinate reactive power and voltage control. When the voltage at node i is greater than the upper voltage limit, the photovoltaic inverter connected to node j within the feeder provides reactive power compensation to node i. As shown in the following formula: ； In the formula: Let be the reactive voltage sensitivity of node j to node i; Excluding nodes i and j, the sum of the reactive voltage sensitivities of other nodes in the feeder to node i; Minimum output reactive power after implementing improved local reactive voltage droop control for the photovoltaic inverter at node j; The output reactive power of the photovoltaic inverter at node j after implementing improved local reactive voltage droop control; The remaining reactive power capacity of the photovoltaic inverter connected to node j is the reactive power capacity that is discharged downwards. The sum of the remaining reactive power capacity of all other photovoltaic inverters in the feeder, excluding nodes i and j; When the voltage at node i is less than the lower voltage limit, the reactive power compensation provided to node i by the photovoltaic inverter connected to node j within the feeder. for: ； In the formula: The maximum output reactive power after implementing improved local reactive voltage droop control for the photovoltaic inverter at node j; The remaining reactive power capacity of the photovoltaic inverter at node j is connected. This is the sum of the remaining reactive power capacity of all other photovoltaic inverters within the feeder, excluding nodes i and j.

6. The distribution network voltage coordination control method based on a photovoltaic-storage integrated power station according to claim 5, characterized in that, Step (3) further includes: verifying whether the sum of the current output reactive power and the reactive power compensation exceeds the upper and lower limits of the reactive power capacity of the photovoltaic inverter. After the photovoltaic inverter connected to node j performs the coordinated reactive voltage control of the photovoltaic inverter in the feeder, the actual output reactive power is as shown in the following formula: 。 7. The distribution network voltage coordination control method based on a photovoltaic-storage integrated power station according to claim 1, characterized in that, Step (4) includes: When the voltage at node i is greater than the upper voltage limit, the active power increment of the energy storage device connected to node i... for: ； In the formula: The voltage of the photovoltaic inverter connected to node i after performing reactive power control coordination of the photovoltaic inverters in the feeder; The active voltage sensitivity of node i to itself; When the voltage at node i is less than the lower voltage bound, the increase in active power of the energy storage device connected to node i is: ； In the formula: and These are the upper and lower bounds of the voltage; Considering the maximum charge / discharge power constraints and remaining capacity constraints of the energy storage device, the actual output active power of the energy storage device connected to node i is... As shown in the following formula: ； In the formula: For nodes Maximum charge and discharge power of energy storage; For nodes Energy storage The remaining charge capacity at any given time; and They are nodes The minimum and maximum remaining capacity of energy storage during operation; For nodes where local active voltage control of energy storage devices is not implemented The output active power of the energy storage; Indicates a unit of time; and These are the upper and lower bounds of the voltage.

8. A distribution network voltage coordination control system based on a photovoltaic-storage integrated power station, characterized in that, include: The model building module is used to establish an optimized tuning model for the reactive power operation threshold of the photovoltaic inverter. The objective functions are to minimize the reactive power regulation of the photovoltaic inverter, minimize the active power loss of the entire grid lines, and minimize the voltage deviation of the entire grid. The objective function is transformed into a single objective function by the weighted coefficient method. Then, the single objective function is transformed into a mixed integer second-order cone relaxation model with voltage square terms and current square terms by using variable substitution and second-order cone relaxation. Based on the transformed model, the upper limit and lower limit of the reactive power operation threshold are obtained. The first control module is used to execute an improved local reactive voltage droop control based on the reactive voltage action threshold and reactive voltage sensitivity when the voltage of a node in a feeder is greater than the upper limit of the reactive voltage action threshold or less than the lower limit of the reactive voltage action threshold. Specifically, the improved local reactive voltage droop control is as follows: when the node voltage is greater than the upper limit of the reactive voltage action threshold, a step-down control is activated to increase the reactive power absorbed by the photovoltaic inverter; when the node voltage is less than the lower limit of the reactive voltage action threshold, a step-up control is activated to increase the reactive power output of the photovoltaic inverter. The second control module is used to perform the improved local reactive voltage droop control. When the voltage of the node is still greater than the upper voltage limit or less than the lower voltage limit, the module performs the coordinated reactive voltage control of the photovoltaic inverters in the feeder. Specifically, the coordinated reactive voltage control of the photovoltaic inverters in the feeder involves the photovoltaic inverters of all nodes in the feeder except the node assisting the node in reactive power compensation based on the remaining reactive capacity and reactive voltage sensitivity. The third control module is used to perform coordinated reactive voltage control of the photovoltaic inverter in the feeder, and when the voltage of the node is still greater than the upper voltage limit or less than the lower voltage limit, it performs local active voltage control of the energy storage device.

9. A computing device, characterized in that, include: One or more processors, one or more memories, and one or more programs, said programs being stored in the memory and configured to be executed by the processor, said programs being loaded onto the processor to implement the steps of the distribution network voltage coordination control method based on any one of claims 1 to 7.

10. A storage medium, characterized in that, The storage medium stores a computer program, which includes program instructions that, when executed by a processor, cause the processor to perform the steps of the distribution network voltage coordination control method based on an integrated photovoltaic and energy storage power station according to any one of claims 1 to 7.

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