A distributed energy storage system for low voltage distribution areas

Abstract

The application discloses a kind of distributed energy storage systems for low-voltage distribution area, including site selection unit and control unit, site selection unit is used to site selection and capacity configuration in energy storage system in energy storage node, control unit is used to adjust the output current of each energy storage node according to the number of energy storage node and the power to be compensated in low-voltage distribution area, wherein, site selection unit is specifically used to determine pre-energy storage node according to the voltage stability margin index of all nodes in low-voltage distribution area, then determine the number of energy storage nodes based on objective function and constraint condition;Again, determine the total capacity of energy storage system based on the number of energy storage nodes, finally determine at least one energy storage node.The application first addresses the energy storage node reasonably, then adjusts the output current of each energy storage node according to the number of energy storage node and the power to be compensated, improves the stability of energy storage system in distribution network.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electric power, in particular to a distributed energy storage system for low-voltage distribution area. BACKGROUND

[0002] Electric energy is an important support for social and economic activities and an important foundation for the development of modern society. With the continuous development of modern society, the demand for electric energy is on the rise. However, the power generation on the power generation side is constant, while the power consumption on the power consumption side is in a changing state, and there is a significant peak and valley every day. Therefore, the current practice is to set up an energy storage system in the power distribution network to shave the peak and fill the valley for the power consumption side.

[0003] The access and exit of the energy storage system in the prior art have the characteristics of decentralized layout and poor controllability, which is not conducive to the scheduling of the energy storage system. Its disordered operation does not help to improve the power grid frequency, voltage and power quality, resulting in a large waste of energy storage resources.

[0004] Therefore, how to improve the stability of the energy storage system in the power distribution network and thus improve the safety level and operation efficiency of the power grid is a technical problem to be solved by those skilled in the art. SUMMARY

[0005] The technical purpose of the present application is to improve the stability of the energy storage system in the power distribution network and thus improve the safety level and operation efficiency of the power grid. To achieve the above purpose, the present application provides a distributed energy storage system for low-voltage distribution area, which comprises:

[0006] A site selection unit for site selection and capacity configuration of energy storage nodes in the energy storage system;

[0007] A control unit for adjusting the output current of the energy storage nodes according to the number of energy storage nodes and the power to be compensated in the low-voltage distribution area.

[0008] Further, the site selection unit is specifically used for:

[0009] Determining a set of pre-energy storage nodes according to the voltage stability margin index of all nodes in the low-voltage distribution area;

[0010] Determining the number of energy storage nodes based on the objective function and the constraint condition;

[0011] Determining the total capacity of the energy storage system and at least one energy storage node in the set of pre-energy storage nodes based on the number of energy storage nodes.

[0012] Further, the voltage stability margin index is specifically as follows:

[0013]

[0014] In the formula, U m (i) is the voltage stability margin index of the i-th node in the low-voltage power distribution area, U0(i) is the current voltage value of the i-th node, U cr (i) is the critical voltage value of the i-th node.

[0015] Further, the objective function is specifically as follows:

[0016]

[0017] In the formula, P l ′ oss P is the total active network loss of the low-voltage power distribution area system within a preset time period T, P loss (k) is the active network loss of the low-voltage power distribution area system at time k.

[0018] Further, the constraint conditions specifically include node voltage constraints, energy storage power constraints, and energy storage quantity constraints.

[0019] Further, the control unit is specifically configured to:

[0020] determine the to-be-compensated power in the low-voltage power distribution area;

[0021] determine the shared power of each energy storage node based on the to-be-compensated power and the number of energy storage nodes;

[0022] determine the output current of the corresponding energy storage node based on the shared power of each energy storage node.

[0023] Further, the control unit is specifically configured to:

[0024] determine the voltage offset of the low-voltage power distribution area;

[0025] determine the current droop coefficient of the corresponding energy storage node based on the shared power of each energy storage node;

[0026] determine the output current of the corresponding energy storage node based on the voltage offset and the current droop coefficient.

[0027] Further, the current droop coefficient of the corresponding energy storage node is specifically determined by the following formula:

[0028]

[0029] In the formula, R i is the equivalent line impedance of the i-th energy storage node, K i is the current droop coefficient of the i-th energy storage node, and N is the power ratio between the energy storage nodes, P maxU is the low-voltage distribution area load voltage, and ΔU is the maximum value of the voltage offset max U is the low-voltage distribution area load voltage, and ΔU is the maximum value of the voltage offset

[0030] Compared with the prior art, the application has the beneficial effects that:

[0031] The embodiment of the application provides a distributed energy storage system for a low-voltage distribution area, which comprises a site selection unit and a control unit, the site selection unit is used for site selection and capacity configuration of energy storage nodes in the energy storage system, and the control unit is used for adjusting output currents of the energy storage nodes according to the number of the energy storage nodes and the power to be compensated in the low-voltage distribution area, wherein the site selection unit is specifically used for determining a pre-energy storage node according to a voltage stability margin index of all nodes in the low-voltage distribution area, then determining the number of the energy storage nodes based on a target function and a constraint condition, determining the total capacity of the energy storage system based on the number of the energy storage nodes, and finally determining at least one energy storage node. The application first reasonably addresses the energy storage nodes, and then adjusts the output currents of the energy storage nodes according to the number of the energy storage nodes and the power to be compensated, so that the stability of the energy storage system in the power distribution network is improved. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor. In the drawings:

[0033] Figure 1 The structure schematic diagram of the distributed energy storage system for the low-voltage distribution area provided by the embodiment of the application. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should be within the protection scope of the present application.

[0035] It should be understood that, although the terms first, second, third, etc. can be employed in this application to describe various information, the information should not be limited to these terms. These terms are only used to differentiate one piece of information from another piece of information of the same type. For example, without departing from the scope of the application, the first information can also be referred to as the second information, and similarly, the second information can also be referred to as the first information. Depending on the context, the word "if" as used herein can be interpreted as "when" or "upon determination" or "in response to a determination".

[0036] In order to avoid waste of energy storage resources, improve the stability of the energy storage system in the distribution network, and further improve the safety level and operation efficiency of the power grid, the present application proposes a distributed energy storage system for low-voltage distribution area, as shown in the figure, the system comprises: Figure 1

[0037] a site selection unit for site selection and capacity configuration of energy storage nodes in the energy storage system;

[0038] a control unit for adjusting the output current of each energy storage node according to the number of energy storage nodes and the power to be compensated in the low-voltage distribution area.

[0039] Specifically, the system proposed in the present application includes a site selection unit and a control unit. The distributed energy storage arranged at multiple points on the power grid has the characteristics of high energy utilization rate, small environmental pollution and flexible installation. However, the distributed energy storage system will affect the network power flow, power quality and system reliability when it is connected to the low-voltage distribution area network. Therefore, reasonable site selection and capacity planning of the energy storage nodes of the distributed energy storage system can effectively improve the working efficiency of the energy storage system.

[0040] In the embodiments of the present application, the site selection unit is specifically used for:

[0041] determining a pre-energy storage node set according to the voltage stability margin index of all nodes in the low-voltage distribution area;

[0042] determining the number of energy storage nodes based on the objective function and the constraint condition;

[0043] determining the total capacity of the energy storage system and at least one energy storage node in the pre-energy storage node set based on the number of energy storage nodes.

[0044] The voltage stability margin index is specifically as follows:

[0045]

[0046] In the formula, U m (i) is the voltage stability margin index of the i th node in the low-voltage distribution area, U0(i) is the current voltage value of the i th node, U cr (i) is the critical voltage value of the i th node.​

[0047] Specifically, the voltage stability margin refers to that a node in a power grid is started from a current state, power or load is continuously increased until a critical point of voltage collapse is reached, and a distance between a running voltage value in the current state and a critical voltage value is used to measure a level of voltage stability. In a low-voltage distribution substation power grid system, a load change rate corresponding to a voltage critical value of each node is the same, and a node with a larger change amount of voltage amplitude is more likely to have voltage out-of-limit at the same load change rate. The node is a node prone to voltage instability.

[0048] According to the voltage stability margin index formula, the voltage stability margins of all nodes in the low-voltage distribution substation are determined, and the nodes are arranged in descending order of the voltage stability margin. The nodes with a specified number or greater than a specified threshold are taken as a pre-energy storage node set.

[0049] Since the energy storage system has two states of charging and discharging in the entire low-voltage distribution substation power grid system, the energy storage system is charged at the electricity trough, and the line current is increased. The line current is reduced when discharging at the electricity peak, so it is necessary to install the energy storage node at a reasonable number position, which can play a role in loss reduction.

[0050] In the embodiment of the application, the objective function is specifically as follows:

[0051]

[0052] In the formula, P' loss is the total active network loss of the low-voltage distribution substation system in the preset time period T, P loss (k) is the active network loss of the low-voltage distribution substation system at time k.

[0053] In the embodiment of the application, the constraint condition specifically includes a node voltage constraint, an energy storage power constraint, and an energy storage number constraint.

[0054] Specifically, the minimum network loss of the low-voltage distribution substation system as a whole is taken as the objective function, and the number of energy storage nodes is determined based on the constraint conditions. The node voltage constraint is specifically that the corresponding node voltage is within the upper and lower limit intervals, the energy storage power constraint is specifically that the single charging and discharging power of the energy storage node is within the upper and lower limit intervals of the energy storage power, and the energy storage number constraint is specifically that the number of energy storage nodes is within the specified number interval.

[0055] After the number of energy storage nodes is determined, the total capacity of the energy storage system is further determined according to the capacity of the energy storage equipment that can be installed in each energy storage node.

[0056] In the embodiment of the application, the control unit is specifically used for:

[0057] determining the to-be-compensated power in the low-voltage distribution substation;

[0058] determine the shared power of each energy storage node based on the power to be compensated and the number of energy storage nodes;

[0059] determine the output current of the corresponding energy storage node based on the shared power of each energy storage node.

[0060] In the embodiments of the present application, the control unit is specifically configured to:

[0061] determine the voltage offset of the low-voltage distribution area;

[0062] determine the current droop coefficient of the corresponding energy storage node based on the shared power of each energy storage node;

[0063] determine the output current of the corresponding energy storage node based on the voltage offset and the current droop coefficient.

[0064] Specifically, taking an example of two energy storage nodes in the energy storage system, the power to be compensated P is equal to the first energy storage node shared power P1 plus the second energy storage node shared power P2, and the ratio of the first energy storage node shared power to the second energy storage node shared power is N, and the following formula can be obtained:

[0065] P1 = (U r -ΔU) * ΔU * K1

[0066] P2 = (U r -ΔU) * ΔU * K2

[0067] In the formula, U r is the offset voltage reference value, i.e., the standard voltage value, ΔU is the voltage offset, K2 is the current droop coefficient of the second energy storage node, and K1 is the current droop coefficient of the first energy storage node.

[0068] In a specific application scenario, the current of the energy storage node and the voltage offset have a droop characteristic, that is, when the voltage offset is positive and larger, the output current of the energy storage node is larger, and when the voltage offset is negative and smaller, the output current of the energy storage node is larger. According to this characteristic, the load distribution between the energy storage nodes can be realized.

[0069] In the embodiments of the present application, the current droop coefficient of the corresponding energy storage node is determined by the following formula:

[0070]

[0071] In the formula, R i is the equivalent line impedance of the i-th energy storage node, K i is the current droop coefficient of the i-th energy storage node, N is the power ratio between the energy storage nodes, P max is the maximum value of the power to be compensated, U is the load voltage of the low-voltage distribution area, and ΔU maxThe maximum value of the voltage offset.

[0072] Based on the above scheme, an experiment is carried out using a simulation experiment platform. When a low-voltage distribution area system adopts a traditional voltage-type droop strategy, the output currents of the energy storage nodes in the distributed energy storage system are consistent at the beginning, and the loads are evenly distributed. Subsequently, due to the change of line impedance between the energy storage nodes, the output currents between the energy storage nodes begin to change and have a large deviation, and the system power distribution effect becomes poor. When the technical scheme of the application is adopted, the output current deviation between the energy storage nodes is small, and the control effect is obviously improved.

[0073] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present application, which are used to illustrate the technical solutions of the present application, but not to limit them. The protection scope of the present application is not limited thereto. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can modify or easily think of changes to the technical solutions recorded in the foregoing embodiments, or make equivalent replacements to some technical features, within the technical scope disclosed by the present application. Such modifications, changes or replacements do not cause the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be covered within the protection scope of the present application.

Claims

1. A distributed energy storage system for low-voltage distribution substations, characterized in that, The system includes: The location unit is used for the location and capacity configuration of energy storage nodes in the energy storage system; The control unit is used to adjust the output current of each energy storage node according to the number of energy storage nodes and the power to be compensated in the low-voltage distribution area. The addressing unit is specifically used for: The pre-storage node set is determined based on the voltage stability margin index of all nodes in the low-voltage distribution area. The number of energy storage nodes is determined based on the objective function and constraints. The total capacity of the energy storage system is determined based on the number of energy storage nodes, and at least one energy storage node is identified from the pre-energy storage node set. The voltage stability margin index is specifically shown in the following formula: In the formula, U m (i) represents the voltage stability margin index of the i-th node in the low-voltage distribution substation area, and U0(i) represents the current voltage value of the i-th node. cr (i) represents the critical voltage value of the i-th node; The objective function is shown in the following formula: In the formula, P′ loss For the total active power loss of the low-voltage distribution substation system within a preset time period T, P loss (k) represents the active power loss of the low-voltage distribution substation system at time k; The constraints specifically include node voltage constraints, energy storage power constraints, and energy storage quantity constraints. The control unit is specifically used for: Determine the power to be compensated in the low-voltage distribution area; The power sharing of each energy storage node is determined based on the power to be compensated and the number of energy storage nodes. The output current of the corresponding energy storage node is determined based on the power shared by each energy storage node. The control unit is specifically used for: Determine the voltage offset of the low-voltage distribution station area; The current droop coefficient of the corresponding energy storage node is determined based on the power shared by each energy storage node. The output current of the corresponding energy storage node is determined based on the voltage offset and the current droop coefficient. The current droop coefficient for the corresponding energy storage node is determined using the following formula: In the formula, R i Let K be the equivalent line impedance of the i-th energy storage node. i Let P be the current droop factor of the i-th energy storage node, N be the power ratio between energy storage nodes, and P be the current droop factor. max The maximum value of the power to be compensated is given by ΔU, where U is the load voltage of the low-voltage distribution substation. max This represents the maximum voltage offset.

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