Method for determining energy storage reactive power limit of transformer area and energy storage system

Abstract

The application discloses a kind of determination methods of district energy storage reactive power limit and energy storage system, it is related to power electronics field, the method comprises: obtaining the electrical operating data of energy storage grid-connected point;Obtain the impedance characteristic parameter of power grid line;According to the real-time voltage of energy storage grid-connected point and impedance characteristic parameter, determine the virtual voltage of grid-connected point in the state that energy storage is not put into operation;According to electrical operating data, virtual electrical parameter and virtual voltage, determine the first line loss value of power grid line after energy storage is put into operation and the second line loss value of power grid line when energy storage is not put into operation;With the second line loss value as reference, determine the upper limit value of reactive power that energy storage allows output, so that under the condition that active power of grid-connected point is maintained unchanged, after injecting the reactive power, the line loss of power grid line does not exceed the second line loss value.Therefore, the application can determine the reactive power output limit value for energy storage system under the premise of guaranteeing voltage control effect.

Description

Technical Field

[0001] This application relates to the field of power electronics, and in particular to a method for determining the reactive power limit of a transformer substation and an energy storage system. Background Technology

[0002] Distributed energy storage is widely used in the management of power supply quality in distribution areas. It can effectively alleviate problems such as weak distribution network structure and insufficient voltage regulation capacity by achieving peak shaving and valley filling and voltage support through charge and discharge control. However, due to project investment cost constraints, the rated power and rated capacity of energy storage systems often cannot be configured according to ideal voltage regulation conditions. Under extreme conditions such as high photovoltaic power generation and low load, the voltage regulation capacity relying solely on active power is insufficient, and reactive power needs to be used for auxiliary voltage regulation.

[0003] In related technologies, traditional voltage management for transformer substation energy storage typically employs a closed-loop control method that directly converts the deviation between the real-time voltage at the access point and the target voltage into active power output, relying on active power to maintain voltage compliance. When the active power regulation capability of energy storage is insufficient, existing solutions directly output reactive power based on the voltage deviation, lacking quantitative constraint logic for reactive power switching. While this method can achieve voltage regulation to some extent, it cannot quantify and limit the increase in line losses caused by reactive power injection.

[0004] Therefore, in the scenario of voltage management in distribution areas with limited energy storage capacity and power, how to determine the reactive power output limit for the energy storage system while ensuring the voltage management effect, so as to limit the new line losses caused by reactive power injection to not exceed a reasonable range, is an urgent technical problem to be solved. Summary of the Invention

[0005] The main purpose of this application is to provide a method for determining the reactive power limit of energy storage in a transformer substation and an energy storage system. Under the premise of ensuring the voltage control effect, the reactive power output limit of the energy storage system is determined so as to limit the new line losses caused by reactive power injection to not exceed a reasonable range.

[0006] To achieve the above objectives, this application provides a method for determining the reactive power limit of transformer substation energy storage, comprising: Acquire electrical operation data of the energy storage grid connection point and collect the real-time voltage of the grid connection point. Based on the electrical operation data, determine the virtual electrical parameters of the grid connection point under the condition that the energy storage is not in operation; wherein, the virtual electrical parameters reflect the power generated by the grid itself at the grid connection point assuming that the energy storage is not in operation. Obtain the impedance characteristic parameters of the power grid lines; Based on the real-time voltage of the energy storage grid connection point and the impedance characteristic parameters, determine the virtual voltage of the grid connection point when the energy storage is not in operation; Based on the electrical operation data, the virtual electrical parameters, and the virtual voltage, determine the first line loss value of the power grid line after the energy storage is put into operation and the second line loss value of the power grid line when the energy storage is not put into operation. Based on the second line loss value, the upper limit of reactive power that the energy storage can output is determined, so that after injecting this reactive power while maintaining the active power at the grid connection point, the line loss of the power grid line does not exceed the second line loss value.

[0007] Optionally, the electrical operation data includes the real-time active power P1, real-time reactive power Q1 of the grid connection point during energy storage operation, and the current active power output P_DES and current reactive power output Q_DES of the energy storage itself; the virtual electrical parameters include virtual active power P2 and virtual reactive power Q2, and satisfy: P2=P1 P_DES, Q2=Q1 Q_DES.

[0008] Optionally, obtaining the impedance characteristic parameters of the power grid line includes: A disturbance signal is applied to the power grid line using a periodic triggering method or an event triggering method. Based on the electrical response before and after the disturbance is applied, the impedance characteristic parameters of the power grid line are extracted. Specifically, when the event triggering method is used, if the voltage change rate at the grid connection point exceeds a preset change rate threshold or the load power change rate at the grid connection point exceeds a preset power change rate threshold, the operation of applying a disturbance signal to the power grid line is triggered.

[0009] Optionally, obtaining the impedance characteristic parameters of the power grid line includes: Obtain preset line impedance parameters, or measure the impedance characteristic parameters of the power grid line using a line parameter measuring device; wherein the impedance characteristic parameters include at least one of line resistance characteristic value and line reactance characteristic value.

[0010] Optionally, the impedance characteristic parameters include the line resistance characteristic value Rg and the line inductance characteristic value Lg; the step of applying a disturbance signal to the power grid line and extracting the impedance characteristic parameters of the power grid line based on the electrical response before and after the disturbance application includes: An active power step disturbance of a set amplitude is applied to the power grid line. The first voltage value of the grid connection point before the disturbance is applied is detected. When the voltage change rate of the grid connection point is less than a preset change rate threshold for a preset number of consecutive preset number of times after the disturbance is applied, the electrical parameters are determined to have reached a steady state and the second voltage value is recorded. A reactive power step disturbance of a set amplitude is applied to the power grid line. The third voltage value of the grid connection point before the disturbance is applied is detected. When the voltage change rate of the grid connection point is less than a preset change rate threshold for a preset number of consecutive preset number of times after the disturbance is applied, the electrical parameters are determined to have reached a steady state and the fourth voltage value is recorded.

[0011] Optionally, the line resistance characteristic value Rg satisfies Rg=ΔU1×Ub / ΔP, where ΔU1 is the absolute value of the difference between the first voltage value and the second voltage value, Ub is the second voltage value, and ΔP is the set amplitude of the active power step disturbance. The line inductance characteristic value Lg satisfies Lg=ΔU2×Ud / (ΔQ×2πf), where ΔU2 is the absolute value of the difference between the third voltage value and the fourth voltage value, Ud is the fourth voltage value, ΔQ is the set amplitude of the reactive power step disturbance, and f is the current grid frequency at the grid connection point.

[0012] Optionally, determining the virtual voltage of the grid connection point when the energy storage is not in operation includes: Obtain the line resistance characteristic value Rg and the line reactance characteristic value Xg from the impedance characteristic parameters, where Xg = 2πf·Lg, Lg is the line inductance characteristic value, and f is the power grid frequency; And U2 = U1 (P_DES×Rg) / U1 (Q_DES×Xg) / U1, where U1 is the real-time voltage value and U2 is the virtual voltage of the grid connection point.

[0013] Optionally, determining the first line loss value of the power grid line after the energy storage is put into operation and the second line loss value of the power grid line when the energy storage is not put into operation includes: The real-time current I1 = √(P1² + Q1²) / U1 is calculated based on the real-time active power P1, the real-time reactive power Q1 and the real-time voltage U1, and the line loss after the energy storage is put into operation is obtained from the first line loss value W1_loss = I1² × Rg. The virtual current I2 = √(P2² + Q2²) / U2 is calculated based on the virtual active power P2, the virtual reactive power Q2 and the virtual voltage U2, and the line loss when the energy storage is not in operation is obtained from the second line loss value W2_loss = I2² × Rg. Determine the increase in line loss before and after commissioning: ΔW = W1_loss W2_loss serves as an illustrative intermediate measure of the increase in losses caused by the commissioning of energy storage.

[0014] Optionally, determining the upper limit of the reactive power that the energy storage can output includes: Under the condition that it is determined that the real-time active power P₁ at the grid-connected point remains unchanged, set Q as the reactive power variable to be solved, obtain the line current I₃ after injecting the reactive power by I₃=√(P₁²+Q²) / U₃, and then obtain the third line loss value W₃_loss=I₃²×Rg, wherein U₃ is the energy storage control target voltage value; Establish a constraint W₃_loss≤W₂_loss, that is, the line loss of the power grid line after injecting the reactive power does not exceed the second line loss value when energy storage is not put into operation. If W₃_loss=W₂_loss, the upper limit of reactive power Q_lmt is obtained as: Q_lmt=√[((P₂²+Q₂²)×U₃²) / U₂² -P₁²]; wherein, the target voltage U₃ is set according to the voltage control scenario where the transformer district is located: When the real-time voltage of the grid-connected point is lower than the target voltage, that is U₁<U₃, it corresponds to a low-voltage control scenario; when the real-time voltage of the grid-connected point is higher than the target voltage, that is U₁>U₃, it corresponds to a high-voltage control scenario.

[0015] In addition, to achieve the above objective, the present application further provides an energy storage system, comprising: an energy storage unit and a controller; the controller is coupled to the energy storage unit, and the energy storage unit is connected to the distribution line of the transformer district; the energy storage unit is configured for charging or discharging, and the controller is configured to execute any one of the above methods for determining the reactive power limit of energy storage in a transformer district, so as to determine the upper limit of reactive power allowed to be output by energy storage.

[0016] The method for determining the reactive power limit of energy storage in a transformer district and the energy storage system proposed in the embodiments of the present application introduce the line loss difference before and after energy storage is put into operation as a hard constraint boundary for reactive power injection, and quantitatively incorporate the economic consideration in the voltage control process into the energy storage control strategy, so that the energy storage system has a clear quantifiable safety upper limit when outputting reactive power. Since the present application can automatically calculate the reactive power limit according to the real-time operation state of the power grid without relying on manual experience judgment, compared with traditional methods, the present application can effectively limit the new line loss caused by reactive power injection within a reasonable range on the premise of ensuring the voltage control effect, and avoid electric energy waste caused by blind switching of reactive power. Meanwhile, the present application takes the line loss when energy storage is not put into operation as the benchmark, which makes the determination result of the reactive power limit more in line with the actual operation condition of the transformer district, and can be deployed in the existing energy storage control system without additional hardware equipment. Therefore, the present application is especially suitable for transformer district scenarios with long power supply radius, weak grid structure, and energy storage capacity and power limited by investment. When the capacity of the energy storage system is limited and the voltage regulation capability relying only on active power is insufficient, the present application can provide a clear upper limit of reactive power output for the energy storage system, thereby solving the technical problem that the existing reactive power switching lacks quantitative constraints. Description of Drawings

[0017] Figure 1 This is a scenario example of the method for determining the reactive power limit of transformer area energy storage according to an embodiment of this application.

[0018] Figure 2 This is one of the flowcharts for a method to determine the reactive power limit of a transformer substation energy storage system, as described in this application.

[0019] Figure 3 This is the second flowchart of a method for determining the reactive power limit of a transformer substation energy storage system, as described in this application.

[0020] Figure 4 This is the third flowchart of a method for determining the reactive power limit of a transformer substation energy storage system, as described in this application.

[0021] Figure 5 This is the fourth flowchart of a method for determining the reactive power limit of a transformer substation energy storage system, which is an embodiment of this application.

[0022] Figure 6 This is the fifth flowchart of a method for determining the reactive power limit of a transformer substation energy storage system, which is an embodiment of this application.

[0023] Figure 7 This is the sixth flowchart of a method for determining the reactive power limit of a transformer substation energy storage system, which is an embodiment of this application.

[0024] Figure 8 This is the seventh flowchart of a method for determining the reactive power limit of a transformer substation energy storage system, which is an embodiment of this application.

[0025] Figure 9 This is a schematic diagram of the structure of an energy storage control device provided in an embodiment of this application.

[0026] In the diagram: 110, Transformer; 120, Transmission line; 130, Load unit; 140, Energy storage system; 910, Processor; 920, Communication interface; 930, Memory; 940, Communication bus.

[0027] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] Distributed energy storage is widely used in the management of power supply quality in distribution areas. It can effectively alleviate problems such as weak distribution network structure and insufficient voltage regulation capacity by achieving peak shaving and valley filling and voltage support through charge and discharge control. However, due to project investment cost constraints, the rated power and rated capacity of energy storage systems often cannot be configured according to ideal voltage regulation conditions. Under extreme conditions such as high photovoltaic power generation and low load, the voltage regulation capacity relying solely on active power is insufficient, and reactive power needs to be used for auxiliary voltage regulation.

[0030] Traditional voltage regulation methods for transformer substations typically employ closed-loop control that directly converts the deviation between the real-time voltage at the connection point and the target voltage into active power output, relying on active power to maintain voltage compliance. When the active power regulation capability of the energy storage is insufficient, existing solutions directly output reactive power based on the voltage deviation, lacking quantitative constraints on reactive power switching. While this approach can achieve voltage regulation to some extent, it cannot quantify and limit the increase in line losses caused by reactive power injection, easily leading to additional energy waste, especially in transformer substation scenarios with large power supply radii and weak grid structures.

[0031] Based on this, this application provides a method for determining the reactive power limit of energy storage in a distribution area. This method obtains electrical operation data and real-time voltage at the energy storage grid connection point to determine the virtual electrical parameters of the grid connection point when the energy storage is not in operation; obtains the impedance characteristic parameters of the power grid lines and determines the virtual voltage when the energy storage is not in operation by combining them with the real-time voltage; determines the first line loss value of the power grid lines after the energy storage is put into operation and the second line loss value of the power grid lines when the energy storage is not in operation based on the electrical operation data, virtual electrical parameters, and virtual voltage; and determines the upper limit of the reactive power that the energy storage can output, based on the second line loss value, such that after injecting this reactive power while maintaining the active power at the grid connection point unchanged, the line loss of the power grid lines does not exceed the second line loss value. Since this application uses the difference in line losses before and after the commissioning of energy storage as a hard constraint boundary for reactive power injection, it can determine the reactive power output limit for the energy storage system. Thus, while ensuring the voltage control effect, it limits the new line losses caused by reactive power injection to not exceed a reasonable range, realizes the quantitative control of reactive power output of the energy storage system, and solves the technical problem of lack of quantitative constraints on reactive power switching in scenarios where energy storage power and capacity are limited.

[0032] First, it should be noted that a distribution transformer area refers to a power supply zone that uses a distribution transformer as its power supply center and provides electricity to a specific area (such as a residential community, industrial park, or administrative village) through distribution lines. In distribution transformer area power supply systems, distributed energy storage systems are widely used to improve power quality, smooth load fluctuations, and support grid voltage. Figure 1 The image shown is a scenario example of the method for determining the reactive power limit of transformer area energy storage according to an embodiment of this application.

[0033] like Figure 1 As shown, the energy storage system is connected to the grid connection point of the distribution line in the transformer substation. The substation includes a transformer 110, a transmission line 120, load units 130, and an energy storage system 140. Load units 130 may include residential loads, commercial loads, and industrial loads. The energy storage system 140 is connected to the AC bus of the substation through the grid connection point, enabling it to both absorb (charge) and release (discharge) electrical energy from the grid, and also has the ability to independently regulate reactive power output.

[0034] The hardware structure of the energy storage system 140 includes energy storage units, a controller, and a converter unit. The energy storage units are connected to the AC bus of the distribution area via the converter unit (i.e., the energy storage converter, PCS). The converter unit enables bidirectional power conversion between the energy storage units and the AC grid. Its main circuit adopts a three-phase full-bridge voltage source converter topology and is connected to the AC bus of the distribution area through an LCL filter. Under the control of the controller, the converter unit can operate in rectification mode (charging the energy storage units) or inverter mode (discharging the energy storage units to output active power), and also has the ability to independently regulate reactive power output.

[0035] The energy storage unit is used to charge or discharge in response to charge / discharge power commands issued by the controller. The energy storage unit can use lithium iron phosphate battery packs, lead-carbon battery packs, or other forms of electrochemical energy storage media. The energy storage unit integrates a battery management system (BMS) to monitor parameters such as battery state of charge, state of health, temperature, and voltage, and reports these parameters to the controller in real time via an internal communication interface.

[0036] The controller is communicatively connected to both the converter unit and the energy storage unit, serving as the control core of the entire energy storage system 140. The controller can be set up independently, integrated within the energy storage converter, or installed in a power distribution intelligent terminal connected to a distribution box; this application does not limit this. The controller integrates a processor and a memory. The memory stores a computer program, and the processor executes this computer program to implement the method for determining the reactive power limit of the transformer area energy storage in the various method embodiments of this application. The specific hardware architecture of the controller can be implemented using industrial-grade control chips such as digital signal processors (DSPs), field-programmable gate arrays (FPGAs), or ARM processors.

[0037] At the grid connection point of the energy storage system 140 connected to the distribution line in the transformer substation, voltage transformers and current transformers are also installed to collect real-time voltage, real-time active power, and real-time reactive power at the grid connection point, respectively. The energy storage converter outputs the current active power output and current reactive power output to the controller through an internal communication interface. The controller is communicatively connected to the voltage transformer, current transformer, and energy storage converter to obtain the above data and use it as input parameters for method execution.

[0038] In actual operation, the controller, based on the acquired grid connection point electrical data and the energy storage's own operating data, executes the method for determining the reactive power limit of the energy storage area provided in this application embodiment to obtain the upper limit of the reactive power allowed to be output by the energy storage. The controller uses the determined upper limit of reactive power as the reactive power output limit command of the energy storage converter and sends it to the reactive power control loop of the energy storage converter to limit the reactive power output amplitude of the energy storage converter. The energy storage converter adjusts the reactive power output according to this command, ensuring voltage regulation while ensuring that the new line losses caused by reactive power injection do not exceed the line losses when the energy storage is not in operation.

[0039] In this embodiment, the controller of the energy storage system 140 executes the above method to determine the reactive power limit of energy storage based on the line loss difference constraint. Since this application uses the line loss difference before and after energy storage commissioning as a hard constraint boundary for reactive power injection, the energy storage system 140 can determine the reactive power output limit without increasing line losses, which is particularly suitable for transformer substation scenarios with large power supply radius, weak grid structure, and limited energy storage capacity and power due to investment constraints.

[0040] Figure 2 This is one of the flowcharts illustrating a method for determining the reactive power limit of energy storage in a distribution transformer area, according to an embodiment of this application. This method for determining the reactive power limit of energy storage in a distribution transformer area can be executed by a cloud platform, the control system of the distribution transformer area (such as the main controller of the energy storage system, the controller of the PCS), or by a processor of an electronic device, such as... Figure 2 As shown, the method for determining the reactive power limit of the energy storage area may include the following steps: Step 210: Obtain electrical operation data of the energy storage grid connection point and collect the real-time voltage of the grid connection point. Based on the electrical operation data, determine the virtual electrical parameters of the grid connection point under the condition that the energy storage is not in operation. Among them, the virtual electrical parameters reflect the power generated by the grid itself at the grid connection point assuming that the energy storage is not in operation.

[0041] In this implementation, the energy storage system acquires electrical operation data through acquisition devices at the grid connection point. Specifically, voltage transformers and current transformers are installed at the grid connection point to collect real-time voltage, real-time active power, and real-time reactive power, respectively. Simultaneously, the energy storage controller obtains its own current active and reactive power outputs through an internal communication interface. The energy storage converter, acting as a power conversion device between the energy storage unit and the grid, outputs power that represents the actual power injected into or absorbed from the grid by the energy storage system. This data can be directly obtained within the energy storage system without the need for additional sensors.

[0042] Optionally, virtual electrical parameters refer to the power value that should exist at the grid connection point when the energy storage device is not operating (i.e., the energy storage output is zero). Since energy storage injects power into or absorbs power from the grid when it is operating, the real-time power at the grid connection point is the sum of the grid's own power and the energy storage output. To restore the original grid power when the energy storage is not in operation, the energy storage's own output needs to be subtracted from the real-time power. In this way, the operating state of the grid when the energy storage is not in operation can be obtained without actually shutting down the energy storage device, avoiding interference with the normal power supply to the distribution area.

[0043] Step 220: Obtain the impedance characteristic parameters of the power grid line.

[0044] In this implementation, the impedance characteristic parameters of the power grid line where the energy storage connection point is located are obtained. The impedance characteristic parameters are used to describe the electrical characteristics of the line and are the basis for subsequent calculations of voltage drop and line losses.

[0045] Optionally, the impedance characteristic parameter reflects the line's obstruction of power transmission, and its accuracy directly affects the accuracy of virtual voltage and loss calculations in subsequent steps. By obtaining accurate line impedance, the calculation results in subsequent steps can more closely approximate actual operating conditions.

[0046] Step 230: Determine the virtual voltage of the grid connection point when the energy storage is not in operation, based on the real-time voltage and impedance characteristic parameters of the grid connection point.

[0047] In this implementation, after obtaining the real-time voltage of the grid connection point when the energy storage is in operation, the virtual voltage of the grid connection point when the energy storage is not in operation is calculated by combining the energy storage's own output and line impedance characteristic parameters.

[0048] Optionally, the physical meaning of virtual voltage is: the voltage value that should exist at the grid connection point assuming the energy storage is not in operation. When the energy storage is in operation, its output will cause a voltage drop across the line impedance, causing the real-time voltage at the grid connection point to deviate from the original voltage when the energy storage is not in operation. Therefore, by subtracting the voltage drop component caused by the energy storage output across the line impedance from the real-time voltage, the virtual voltage under the condition of the energy storage not being in operation can be restored.

[0049] Optionally, the virtual voltage reflects the original voltage level of the distribution area when energy storage is not in operation, and serves as a core reference for subsequently determining the degree of energy storage intervention. By inverting the virtual voltage, this method can determine the baseline voltage state of the distribution area without actually shutting down the energy storage equipment.

[0050] Step 240: Based on electrical operation data, virtual electrical parameters, and virtual voltage, determine the first line loss value of the power grid line after the energy storage is put into operation and the second line loss value of the power grid line when the energy storage is not put into operation.

[0051] In this implementation, line losses are calculated under two conditions. The first is the actual loss of the power grid lines after energy storage is put into operation, calculated based on real-time power data. The second is the virtual loss of the power grid lines before energy storage is put into operation, calculated based on virtual electrical parameters and virtual voltage. The difference between the two losses represents the change in line losses before and after energy storage is put into operation.

[0052] Optionally, line loss refers to the power consumed by current flowing through a power grid line, and its magnitude is related to both the current and the line impedance. In an AC circuit, the current is determined by both active and reactive power; therefore, both active and reactive power components must be considered when calculating the current. By calculating the line loss under both conditions, the impact of energy storage deployment on line loss can be quantified.

[0053] Optionally, the first line loss value reflects the actual power consumption of the grid lines under energy storage operation, while the second line loss value reflects the background power consumption of the grid lines when the energy storage is not in operation. Calculating both separately and using them as independent benchmark values ​​allows subsequent steps to directly use the line loss when the energy storage is not in operation as a constraint boundary to determine whether reactive power injection is reasonable, without introducing additional intermediate variables.

[0054] Step 250: Based on the second line loss value, determine the upper limit of the reactive power that the energy storage can output, so that after injecting this reactive power while maintaining the active power at the grid connection point, the line loss of the power grid line does not exceed the second line loss value.

[0055] In this implementation, under the condition of maintaining the active power at the grid connection point unchanged, the line loss corresponding to different reactive power injections is calculated based on the second line loss value. The maximum reactive power value that makes the line loss after reactive power injection not exceed the second line loss value is found, which is the upper limit of reactive power that the energy storage can output.

[0056] Optionally, the core of this step lies in establishing an equality relationship: ensuring that the line loss after reactive power injection equals the line loss before energy storage is put into operation. Since the active power remains constant before reactive power injection, and the line loss increases with the increase of reactive power injection, there exists a unique maximum reactive power value such that the loss just reaches the second line loss value. By solving this equality relationship, the upper limit of reactive power can be obtained.

[0057] Optionally, once the upper limit of reactive power is determined, the energy storage system outputs reactive power according to this limit, which can ensure voltage regulation while keeping line losses within a reasonable range. Compared with the existing technology that blindly outputs reactive power based on voltage deviation, this method provides a clear quantitative boundary for the reactive power output of energy storage.

[0058] In this embodiment, by acquiring the electrical operation data and real-time voltage of the energy storage grid connection point, the virtual electrical parameters of the grid connection point under the condition that the energy storage is not in operation are determined; the impedance characteristic parameters of the power grid line are acquired, and the virtual voltage under the condition that the energy storage is not in operation is determined in combination with the real-time voltage; based on the electrical operation data, virtual electrical parameters, and virtual voltage, the first line loss value of the power grid line after the energy storage is put into operation and the second line loss value of the power grid line when the energy storage is not in operation are determined; based on the second line loss value, the upper limit of the reactive power allowed to be output by the energy storage is determined, so that after injecting this reactive power while maintaining the active power of the grid connection point unchanged, the line loss of the power grid line does not exceed the second line loss value. Since this application uses the difference in line loss before and after the energy storage is put into operation as a hard constraint boundary for reactive power injection, it can determine the reactive power output limit for the energy storage system, thereby limiting the new line loss caused by reactive power injection to not exceed a reasonable range while ensuring the voltage control effect, realizing the quantitative control of the reactive power output of the energy storage system, and solving the technical problem of lack of quantitative constraints on reactive power switching in scenarios where energy storage power and capacity are limited.

[0059] The steps described above will be explained in detail below.

[0060] In step 210, the electrical operation data includes the real-time active power P1, real-time reactive power Q1 at the grid connection point during energy storage operation, and the current active power output P_DES and current reactive power output Q_DES of the energy storage itself; the virtual electrical parameters include virtual active power P2 and virtual reactive power Q2, and satisfy: P2=P1 P_DES, Q2=Q1 Q_DES.

[0061] In this implementation, the energy storage system acquires electrical operation data through acquisition devices at the grid connection point. Specifically, voltage transformers and current transformers are configured at the grid connection point to collect real-time voltage U1, real-time active power P1, and real-time reactive power Q1, respectively. Simultaneously, the energy storage controller acquires its own current active power output P_DES and current reactive power output Q_DES through an internal communication interface. The energy storage converter, acting as a power conversion device between the energy storage unit and the grid, outputs power that represents the actual power injected into or absorbed from the grid by the energy storage system. This data can be directly acquired within the energy storage system without the need for additional sensors.

[0062] Furthermore, based on the collected real-time active power P1 and the energy storage's current active power output P_DES, the virtual active power P2 is calculated; based on the collected real-time reactive power Q1 and the energy storage's current reactive power output Q_DES, the virtual reactive power Q2 is calculated. Specifically, the virtual active power P2 = P1. P_DES, virtual reactive power Q2=Q1 Q_DES. Virtual active power P2 reflects the active power generated by the power grid itself at the grid connection point assuming that the energy storage is not in operation, and virtual reactive power Q2 reflects the reactive power generated by the power grid itself at the grid connection point assuming that the energy storage is not in operation.

[0063] Optionally, the physical meaning of the virtual electrical parameters is the power value that should exist at the grid connection point when the energy storage device is not operating (i.e., the energy storage output is zero). Since the energy storage injects power into the grid or absorbs power from the grid when it is operating, the real-time power at the grid connection point is the result of the grid's own power and the energy storage output being superimposed. To restore the original grid power when the energy storage is not in operation, it is necessary to subtract the energy storage's own output from the real-time power. In this way, the operating state of the grid when the energy storage is not in operation can be obtained without actually shutting down the energy storage device, avoiding interference with the normal power supply to the distribution area.

[0064] Optionally, when the energy storage system is in discharge mode, the current active power output P_DES is positive, indicating that the energy storage is injecting active power into the grid. At this time, the virtual active power P2 = P1. P_DES is the real-time active power minus the active power injected by the energy storage system. When the energy storage system is in charging mode, the current active power output P_DES is negative, indicating that the energy storage absorbs active power from the grid. At this time, P2 = P1. P_DES is equivalent to the real-time active power plus the power absorbed by energy storage. Similarly, the virtual reactive power Q2 = Q1. Q_DES reflects the actual reactive power on the grid side when energy storage is not in operation.

[0065] Figure 3 This is the second flowchart of a method for determining the reactive power limit of a transformer substation energy storage system, according to an embodiment of this application. Figure 3 As shown, obtaining the impedance characteristic parameters of the power grid line in step 220 may include the following steps: Step 2211: Apply a disturbance signal to the power grid line using a periodic triggering method or an event triggering method, and extract the impedance characteristic parameters of the power grid line based on the electrical response before and after the disturbance is applied; When the event-triggered method is used, when the voltage change rate at the grid connection point exceeds the preset change rate threshold or the load power change rate at the grid connection point exceeds the preset power change rate threshold, the operation of applying a disturbance signal to the power grid line is triggered.

[0066] In this embodiment, the energy storage system calculates the impedance characteristic parameters of the power grid line by applying a power disturbance of known magnitude to the power grid line and detecting the voltage response at the grid connection point before and after the disturbance is applied.

[0067] Optionally, the periodic triggering method refers to periodically applying disturbances at preset time intervals. When using the periodic triggering method, the energy storage system applies a disturbance signal to the power grid line every fixed interval (e.g., every 5 minutes, every 15 minutes, or every hour), thereby periodically updating the impedance characteristic parameters. This method is suitable for scenarios where the power grid operation is relatively stable and the line impedance changes slowly, ensuring that the impedance parameters are updated promptly with environmental changes (such as temperature changes, line aging, etc.).

[0068] Optionally, the event-triggered method refers to initiating a disturbance application operation when a specific change in the grid operating state is detected. In the event-triggered mode, the energy storage system monitors the voltage change rate and load power change rate at the grid connection point in real time. When the voltage change rate or load power change rate at the grid connection point exceeds a preset threshold, the system triggers the application of a disturbance signal to the grid lines. This method can update impedance parameters promptly when significant changes occur in the grid state, while avoiding frequent disturbances during stable grid operation that could affect power supply quality.

[0069] Figure 4 This is the third flowchart of a method for determining the reactive power limit of a transformer substation energy storage system, according to an embodiment of this application. Figure 4 As shown, obtaining the impedance characteristic parameters of the power grid line in step 220 may include the following steps: Step 2221: Obtain the preset line impedance parameters, or measure the impedance characteristic parameters of the power grid line using a line parameter measuring device; wherein the impedance characteristic parameters include at least one of the line resistance characteristic value and the line reactance characteristic value.

[0070] In this embodiment, the energy storage system obtains the impedance characteristic parameters of the power grid line by acquiring preset line impedance parameters or by directly measuring them using a line parameter measuring device. The preset line impedance parameters refer to impedance values ​​pre-stored in a line parameter database. This database can be established based on parameters such as line type, length, and cross-sectional area, and can be directly queried and accessed by the energy storage system. The line parameter measuring device refers to a dedicated line impedance testing instrument, such as an impedance analyzer or multimeter, which can measure the resistance and reactance values ​​of the line on-site.

[0071] Optionally, when obtaining preset line impedance parameters, the energy storage system queries the corresponding impedance characteristic parameters from a preset line parameter database based on the model or identification information of the line where the current grid connection point is located. This database pre-stores the resistance and reactance characteristic values ​​corresponding to different line models and specifications, allowing for fast queries without additional operations. It is suitable for application scenarios where impedance accuracy requirements are not high or where line parameters are known.

[0072] Optionally, when the impedance characteristic parameters are obtained through the line parameter measuring device, the energy storage system, in conjunction with the measuring device, performs on-site testing of the power grid line to directly obtain the actual resistance and reactance characteristic values ​​of the line. This method can obtain the true impedance data of the line under its current operating condition and is suitable for scenarios with high accuracy requirements or where the line parameters are unknown or have changed.

[0073] Optionally, the impedance characteristic parameters obtained through the above method include at least one of the line resistance characteristic value and the line reactance characteristic value. The line resistance characteristic value is used for subsequent calculations of line losses and the active voltage drop component in the virtual voltage, while the line reactance characteristic value is used for subsequent calculations of the reactive voltage drop component in the virtual voltage. Step 2221, as an alternative to step 2211 (applying a disturbance signal to the power grid line to extract impedance characteristic parameters), provides a different path for obtaining impedance characteristic parameters, enabling this method to adapt to different application scenarios and accuracy requirements.

[0074] Figure 5 This is the fourth flowchart of a method for determining the reactive power limit of a transformer substation energy storage system according to an embodiment of this application. In step 2211, the impedance characteristic parameters include the line resistance characteristic value Rg and the line inductance characteristic value Lg, such as... Figure 5 As shown, step 2211, which involves applying a disturbance signal to the power grid line and extracting the impedance characteristic parameters of the power grid line based on the electrical response before and after the disturbance, may include the following steps: Step 22111: Apply an active power step disturbance of a set amplitude to the power grid line, detect the first voltage value of the grid connection point before the disturbance is applied, and when the voltage change rate of the grid connection point after the disturbance is applied is less than a preset change rate threshold for a preset number of consecutive preset number of times, determine that the electrical parameters have reached a steady state and record the second voltage value. Step 22112: Apply a reactive power step disturbance of a set amplitude to the power grid line, detect the third voltage value of the grid connection point before the disturbance is applied, and when the voltage change rate of the grid connection point after the disturbance is applied is less than the preset change rate threshold for a preset number of consecutive preset number of times, determine that the electrical parameters have reached a steady state and record the fourth voltage value.

[0075] In this embodiment, the energy storage system applies active power step disturbances and reactive power step disturbances of known amplitude to the power grid line respectively, and detects the voltage response before and after the disturbances are applied, providing a data basis for the subsequent extraction of line impedance characteristic parameters.

[0076] Optionally, in step 22111, before applying the active power step disturbance, the energy storage system first records the first voltage value at the grid connection point. Then, the energy storage system applies an active power step disturbance of a set amplitude to the grid line, which causes a change in the voltage at the grid connection point. After the disturbance is applied, the energy storage system continuously monitors the voltage change rate at the grid connection point. When the voltage change rate is less than a preset threshold for a preset number of consecutive preset number of times, it is determined that the electrical parameters at the grid connection point have entered a steady state, and at this time, a second voltage value is recorded. By calculating the difference between the first voltage value and the second voltage value, the voltage change caused by the active power disturbance can be obtained.

[0077] Optionally, in step 22112, the reactive power step disturbance is executed in a similar manner to the active power step disturbance. The energy storage system records a third voltage value before applying the reactive power step disturbance. After the disturbance is applied, it continuously monitors the voltage change rate. When the voltage change rate is less than a preset threshold for a preset number of consecutive preset cycles, it determines that a steady state has been reached and records a fourth voltage value. By calculating the difference between the third and fourth voltage values, the voltage change caused by the reactive power disturbance can be obtained.

[0078] Optionally, after applying an active power step disturbance and recording the voltage value, a reactive power step disturbance is applied, with the two processes executed in stages. This staged approach avoids the voltage response from overlapping when active and reactive disturbances act simultaneously, preventing the distinction between their individual contributions and ensuring the accuracy of subsequent identification of resistance and inductance characteristic values.

[0079] Optionally, the voltage change rate being less than a preset threshold for a preset number of consecutive preset number of times is used as a steady-state determination condition. The preset number of times and the preset threshold can be set according to the actual application scenario. By introducing a steady-state determination mechanism, it can be ensured that the voltage value recorded after the disturbance is applied is a stable electrical parameter, avoiding measurement errors introduced due to the transient process not being completed.

[0080] In step 22111, the characteristic value of line resistance Rg satisfies Rg=ΔU1×Ub / ΔP, where ΔU1 is the absolute value of the difference between the first voltage value and the second voltage value, Ub is the second voltage value, and ΔP is the set amplitude of the active power step disturbance. In step 22112, the line inductance characteristic value Lg satisfies Lg=ΔU2×Ud / (ΔQ×2πf), where ΔU2 is the absolute value of the difference between the third voltage value and the fourth voltage value, Ud is the fourth voltage value, ΔQ is the set amplitude of the reactive power step disturbance, and f is the current grid frequency at the grid connection point.

[0081] In this embodiment, the energy storage system calculates the line resistance characteristic value based on the voltage response before and after the application of an active power step disturbance, and calculates the line inductance characteristic value based on the voltage response before and after the application of a reactive power step disturbance.

[0082] Optionally, in step 22111, the first voltage value is the voltage value at the grid connection point before the active power step disturbance is applied, and the second voltage value is the voltage value at the grid connection point when it reaches steady state after the active power step disturbance is applied. ΔU1 is the absolute value of the difference between the two, reflecting the voltage change caused by the active power disturbance injection. Ub is the second voltage value, i.e., the voltage value after the active power disturbance is applied to the energy storage, serving as the voltage reference for calculating the current change. ΔP is the set amplitude of the active power step disturbance. Since the initial power is 0, Ub / ΔP reflects the current change, and the ratio of ΔU1 to the current change is the characteristic value of the line resistance.

[0083] Optionally, in step 22112, the third voltage value is the voltage value at the grid connection point before the reactive power step disturbance is applied, and the fourth voltage value is the voltage value at the grid connection point when it reaches steady state after the reactive power step disturbance is applied. ΔU2 is the absolute value of the difference between the two, reflecting the voltage change caused by the reactive power disturbance injection. Ud is the fourth voltage value, i.e., the voltage value after the energy storage is injected with reactive power disturbance, which serves as the voltage reference for calculating the current change. ΔQ is the set amplitude of the reactive power step disturbance, and f is the current grid frequency at the grid connection point. Since the initial power is 0, Ud / ΔQ reflects the current change, and the ratio of ΔU2 to the current change reflects the line reactance value. Dividing this by 2πf yields the line inductance characteristic value.

[0084] Optionally, the characteristic values ​​of line resistance and line inductance are fundamental electrical parameters of the power grid. The resistance characteristic value determines the magnitude of active power loss when active power flows through the line, while the inductance characteristic value, converted into a reactance characteristic value based on the grid frequency, determines the magnitude of voltage drop when reactive power flows through the line. The line resistance and line inductance characteristic values ​​extracted in this way will be used for calculating the virtual voltage and determining line losses in subsequent steps.

[0085] Figure 6 This is the fifth flowchart of a method for determining the reactive power limit of a transformer substation energy storage system, according to an embodiment of this application. Figure 6 As shown, determining the virtual voltage of the grid connection point in step 230 when the energy storage is not in operation may include the following steps: Step 231: Obtain the line resistance characteristic value Rg and the line reactance characteristic value Xg from the impedance characteristic parameters, where Xg = 2πf·Lg, Lg is the line inductance characteristic value, and f is the power grid frequency; And U2 = U1 (P_DES×Rg) / U1 (Q_DES×Xg) / U1, where U1 is the real-time voltage value and U2 is the virtual voltage at the grid connection point.

[0086] In this embodiment, the energy storage system uses the acquired line impedance characteristic parameters, combined with the current active power output P_DES and current reactive power output Q_DES of the energy storage itself, and the real-time voltage U1 of the grid connection point to infer the virtual voltage U2 of the grid connection point when the energy storage is not in operation.

[0087] Optionally, in step 231, the line reactance characteristic value Xg is determined by the product of the line inductance characteristic value Lg and the grid angular frequency 2πf. In an AC power grid, the impedance of an inductive element changes with frequency, therefore it is necessary to convert the inductance characteristic value into a reactance characteristic value according to the grid frequency for subsequent voltage drop calculations.

[0088] Optionally, the virtual voltage U2 is the physical meaning of the voltage value that should exist at the grid connection point if the energy storage is not in operation. When the energy storage is in operation, its active power output P_DES causes a voltage drop across the line resistance Rg, and its reactive power output Q_DES causes a voltage drop across the line reactance Xg. These two voltage drops cause the real-time voltage U1 at the grid connection point to deviate from the original voltage U2 when the energy storage is not in operation. Therefore, by subtracting the voltage drop component caused by active power output (P_DES×Rg) / U1 and the voltage drop component caused by reactive power output (Q_DES×Xg) / U1 from the real-time voltage U1, the virtual voltage U2 under the condition of the energy storage not being in operation can be restored.

[0089] Optionally, the first voltage drop contribution (P_DES×Rg) / U1 refers to the voltage drop generated across the line resistance by the active power output of the energy storage. When active current flows through the line resistance, a voltage drop occurs in the same direction as the active current, and its magnitude is related to the active power output and the characteristic value of the line resistance. The second voltage drop contribution (Q_DES×Xg) / U1 refers to the voltage drop generated across the line reactance by the reactive power output of the energy storage. When reactive current flows through the line reactance, a voltage drop occurs in the same direction as the reactive current, and its magnitude is related to the reactive power output and the characteristic value of the line reactance.

[0090] Optionally, the virtual voltage U2 determined in the above manner reflects the original voltage level of the distribution area when energy storage is not involved in operation, providing a benchmark reference for subsequently determining the upper limit of reactive power. By inverting the virtual voltage, this method can obtain the background voltage state of the distribution area without actually shutting down the energy storage equipment.

[0091] Figure 7 This is flowchart six of a method for determining the reactive power limit of a transformer substation energy storage system, according to an embodiment of this application. Figure 7 As shown, step 240, determining the first line loss value of the power grid line after the energy storage is put into operation and the second line loss value of the power grid line when the energy storage is not put into operation, may include the following steps: Step 241: Calculate the real-time current I1=√(P1²+Q1²) / U1 based on the real-time active power P1, real-time reactive power Q1 and real-time voltage U1, and obtain the line loss after the energy storage is put into operation from the first line loss value W1_loss=I1²×Rg. Step 242: Calculate the virtual current I2=√(P2²+Q2²) / U2 based on the virtual active power P2, virtual reactive power Q2 and virtual voltage U2, and obtain the line loss when energy storage is not in operation from the second line loss value W2_loss=I2²×Rg; Step 243: Determine the line loss increment ΔW = W1_loss before and after commissioning. W2_loss serves as an illustrative intermediate measure of the increase in losses caused by the commissioning of energy storage.

[0092] In this embodiment, the real-time current I1 refers to the current flowing through the power grid line after the energy storage is put into operation. In an AC circuit, the current is determined by both active and reactive power; therefore, both active and reactive power components need to be considered when calculating the current. Voltage transformers and current transformers collect the real-time voltage U1, real-time active power P1, and real-time reactive power Q1 at the grid connection point, respectively. The energy storage controller calculates the real-time current I1 based on these parameters. The first line loss value W1_loss reflects the active power loss on the power grid line after the energy storage is put into operation. This loss is generated when current flows through the line resistance, and its magnitude is proportional to the product of the square of the current and the characteristic value Rg of the line resistance.

[0093] The virtual current I2 refers to the current flowing through the power grid line when the energy storage is not operational, and is determined by the virtual active power P2, virtual reactive power Q2, and virtual voltage U2. The second line loss value W2_loss reflects the active power loss on the power grid line when the energy storage is not operational. It uses the same calculation logic as the first line loss value, i.e., the product of the square of the virtual current and the characteristic value of the line resistance Rg. The second line loss value represents the background power consumption of the power grid line when the energy storage is not operational and is an important benchmark for subsequently judging whether reactive power injection is reasonable.

[0094] The energy storage system calculates the change in grid line losses before and after energy storage commissioning, obtaining the loss increment ΔW. This loss increment reflects the increased grid line losses caused by energy storage commissioning, serving as an illustrative intermediate quantity for the loss increment caused by energy storage commissioning. In subsequent steps, by directly comparing the third line loss value after reactive power injection with the second line loss value, it can be determined whether the reactive power injection caused the line losses to exceed the baseline level before energy storage commissioning.

[0095] Optionally, the first line loss value W1_loss and the second line loss value W2_loss respectively represent the active power loss of the line in two different states. By separately calculating the line loss in these two states, the influence degree of energy storage putting into operation on line loss can be quantified, providing a data basis for determining the upper limit of reactive power.

[0096] Optionally, the loss increment ΔW is used as an explanatory intermediate variable to help understand the influence direction of energy storage putting into operation on line loss. When ΔW is a positive value, it indicates that putting energy storage into operation increases line loss; when ΔW is a negative value, it indicates that putting energy storage into operation reduces line loss. Since the present application takes the second line loss value as a reference, it is only necessary to ensure that the third line loss value after reactive power injection does not exceed the second line loss value when subsequently determining the upper limit of reactive power.

[0097] Figure 8 is the seventh flow chart of the method for determining the reactive power limit of district energy storage according to the embodiment of the present application. As Figure 8 shown, determining the upper limit of reactive power allowed to be output by energy storage in step 250 may include the following steps: Step 251: under the condition that the real-time active power P1 at the grid connection point is determined to be unchanged, set the reactive power to-be-solved variable Q, and obtain the third line loss value W3_loss=I3²×Rg from the line current after injecting the reactive power I3=√(P1²+Q²) / U3, wherein U3 is the target voltage for energy storage control; Step 252: establish a constraint W3_loss≤W2_loss, that is, the line loss of the power grid line after injecting the reactive power does not exceed the second line loss value when energy storage is not put into operation, and when W3_loss=W2_loss, the upper limit of reactive power Q_lmt=√[((P2²+Q2²)×U3²) / U2² −P1²]; wherein, the target voltage U3 is set according to the voltage governance scenario where the district is located: Step 253: when the real-time voltage at the grid connection point is lower than the target voltage U1<U3, it corresponds to a low-voltage governance scenario; when the real-time voltage at the grid connection point is higher than the target voltage U1>U3, it corresponds to a high-voltage governance scenario.

[0098] In this embodiment, under the condition that it is determined that the real-time active power P1 at the grid connection point remains unchanged, the energy storage system sets the reactive power to-be-solved variable Q. The constant active power means that the energy storage system does not change the active power output while outputting reactive power, so that the influence of reactive power change on line loss can be investigated separately. Under this condition, the line current I3 after injecting reactive power Q is jointly determined by the real-time active power P1, the reactive power to-be-solved variable Q and the energy storage control target voltage value U3. The third line loss value W3_loss reflects the active power loss on the power grid line after the energy storage injects reactive power, and its magnitude is proportional to the product of the square of the current and the line resistance characteristic value Rg.

[0099] Optionally, U3 is the energy storage control target voltage value, which is set according to the voltage control scenario where the transformer district is located. When the real-time voltage at the grid connection point is lower than the target voltage, U1<U3, which corresponds to a low-voltage control scenario, and the energy storage is required to inject reactive power to raise the voltage; when the real-time voltage at the grid connection point is higher than the target voltage, U1>U3, which corresponds to a high-voltage control scenario, and the energy storage is required to absorb reactive power to reduce the voltage.

[0100] The energy storage system takes the second line loss value W2_loss as a reference to establish a constraint condition for reactive power injection. The physical meaning of this constraint is that the loss of the power grid line after the energy storage injects reactive power shall not exceed the background loss of the power grid line when the energy storage is not put into operation. Through this constraint, it can be ensured that reactive power injection will not cause the line loss to exceed the level when the energy storage is not put into operation, so as to limit electric energy waste on the premise of ensuring the voltage control effect.

[0101] In this embodiment, the energy storage system makes the third line loss value W3_loss after injecting reactive power equal to the second line loss value W2_loss when the energy storage is not put into operation, and obtains the upper limit value of reactive power Q_lmt allowed to be output by the energy storage by solving this equivalent relation equation. Specifically: W3_loss=W2_loss, that is: (P1²+Q_lmt²) / U3²×Rg=(P2²+Q2²) / U2²×Rg. Since Rg exists on both sides of the equation and Rg≠0, after canceling Rg, we can obtain: (P1²+Q_lmt²) / U3²=(P2²+Q2²) / U2², and further obtain: Q_lmt=√[((P2²+Q2²)×U3²) / U2² -P1²]. This value is the upper limit value of reactive power allowed to be output by the energy storage. When the actually output reactive power of the energy storage does not exceed this limit value, the line loss of the power grid line will not exceed the background loss level when the energy storage is not put into operation.

[0102] Optionally, the third line loss value W3_loss is a mathematical expression with the reactive power variable Q as the independent variable, reflecting the trend of line loss changes corresponding to different reactive power injection amounts. Line loss increases with increasing injected reactive power; therefore, there exists a unique maximum reactive power value such that the loss just reaches the second line loss value. Since the expression for the third line loss value includes a squared term of the reactive power variable, the equation can be solved analytically without relying on empirical values ​​or manual judgment.

[0103] In this embodiment, by establishing the constraint W3_loss≤W2_loss based on the second line loss value, and setting W3_loss=W2_loss to solve for the upper limit value of reactive power Q_lmt, this application transforms the determination of the reactive power limit of energy storage into a mathematical problem with clear physical boundaries. This makes the determination of the reactive power limit independent of empirical values ​​or manual judgment, adaptable to the actual operating conditions of different transformer areas, and ensures that the determination result of the limit has a clear physical basis.

[0104] Based on the above embodiments, this application also provides a distributed energy storage system, which may include energy storage units and a controller. The controller is coupled to the energy storage units, and the energy storage units are connected to the power distribution lines of the transformer substation. The energy storage system may also include connections to a distribution box and an AC meter. Specific functions and connections are not detailed here.

[0105] The energy storage unit is used for charging or discharging. The controller can execute the method described above for determining the reactive power limit of the energy storage area to determine the upper limit of the reactive power that the energy storage can output. Furthermore, when the energy storage converter needs to output reactive power for voltage regulation, the controller sends the upper limit of reactive power as a limit to the reactive power control loop of the energy storage converter to limit the reactive power output amplitude of the energy storage converter.

[0106] Based on the above embodiments, this application also provides an energy storage control device, such as... Figure 9 As shown, the energy storage control device 900 may include a processor 910, a communication interface 920, a memory 930, and a communication bus 940, wherein the processor 910, the communication interface 920, and the memory 930 communicate with each other through the communication bus 940. The processor 910 may call logical instructions in the memory 930 to execute the above-described method.

[0107] Furthermore, the logical instructions in the aforementioned memory 930 can be implemented as software functional units and sold or used as independent products, and can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0108] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0109] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of various embodiments or some parts of embodiments.

Claims

1. A method for determining the reactive power limit of energy storage in a transformer substation, characterized in that, include: Acquire electrical operation data of the energy storage grid connection point and collect the real-time voltage of the grid connection point. Based on the electrical operation data, determine the virtual electrical parameters of the grid connection point under the condition that the energy storage is not in operation; wherein, the virtual electrical parameters reflect the power generated by the grid itself at the grid connection point assuming that the energy storage is not in operation. Obtain the impedance characteristic parameters of the power grid lines; Based on the real-time voltage of the energy storage grid connection point and the impedance characteristic parameters, determine the virtual voltage of the grid connection point when the energy storage is not in operation; Based on the electrical operation data, the virtual electrical parameters, and the virtual voltage, determine the first line loss value of the power grid line after the energy storage is put into operation and the second line loss value of the power grid line when the energy storage is not put into operation. Based on the second line loss value, the upper limit of reactive power that the energy storage can output is determined, so that after injecting this reactive power while maintaining the active power at the grid connection point, the line loss of the power grid line does not exceed the second line loss value.

2. The method for determining the reactive power limit of transformer area energy storage according to claim 1, characterized in that, The electrical operation data includes the real-time active power P1, real-time reactive power Q1 of the grid connection point during energy storage operation, and the current active power output P_DES and current reactive power output Q_DES of the energy storage itself; the virtual electrical parameters include virtual active power P2 and virtual reactive power Q2, and satisfy: P2=P1 P_DES, Q2=Q1 Q_DES.

3. The method for determining the reactive power limit of transformer area energy storage according to claim 1, characterized in that, The acquisition of impedance characteristic parameters of the power grid line includes: A disturbance signal is applied to the power grid line using a periodic triggering method or an event triggering method. Based on the electrical response before and after the disturbance is applied, the impedance characteristic parameters of the power grid line are extracted. Specifically, when the event triggering method is used, if the voltage change rate at the grid connection point exceeds a preset change rate threshold or the load power change rate at the grid connection point exceeds a preset power change rate threshold, the operation of applying a disturbance signal to the power grid line is triggered.

4. The method for determining the reactive power limit of transformer area energy storage according to claim 1, characterized in that, The acquisition of impedance characteristic parameters of the power grid line includes: Obtain preset line impedance parameters, or measure the impedance characteristic parameters of the power grid line using a line parameter measuring device; wherein the impedance characteristic parameters include at least one of line resistance characteristic value and line reactance characteristic value.

5. The method for determining the reactive power limit of transformer area energy storage according to claim 3, characterized in that, The impedance characteristic parameters include the line resistance characteristic value Rg and the line inductance characteristic value Lg; The step of applying a disturbance signal to the power grid line and extracting the impedance characteristic parameters of the power grid line based on the electrical response before and after the disturbance application includes: An active power step disturbance of a set amplitude is applied to the power grid line. The first voltage value of the grid connection point before the disturbance is applied is detected. When the voltage change rate of the grid connection point is less than a preset change rate threshold for a preset number of consecutive preset number of times after the disturbance is applied, the electrical parameters are determined to have reached a steady state and the second voltage value is recorded. A reactive power step disturbance of a set amplitude is applied to the power grid line. The third voltage value of the grid connection point before the disturbance is applied is detected. When the voltage change rate of the grid connection point is less than a preset change rate threshold for a preset number of consecutive preset number of times after the disturbance is applied, the electrical parameters are determined to have reached a steady state and the fourth voltage value is recorded.

6. The method for determining the reactive power limit of transformer area energy storage according to claim 5, characterized in that, The characteristic value of the line resistance Rg satisfies Rg=ΔU1×Ub / ΔP, where ΔU1 is the absolute value of the difference between the first voltage value and the second voltage value, Ub is the second voltage value, and ΔP is the set amplitude of the active power step disturbance. The characteristic line inductance value Lg satisfies Lg=ΔU2×Ud / (ΔQ×2πf), where ΔU2 is the absolute value of the difference between the third voltage value and the fourth voltage value, Ud is the fourth voltage value, ΔQ is the set amplitude of the reactive power step disturbance, and f is the current grid frequency at the grid-connected point.

7. The method for determining the reactive power limit of transformer area energy storage according to claim 2, characterized in that, The step of determining the virtual voltage at the grid-connected point in the state where the energy storage is not in operation comprises: acquiring the characteristic line resistance value Rg and the characteristic line reactance value Xg in the impedance characteristic parameters, where Xg=2πf·Lg, Lg is the characteristic line inductance value, and f is the grid frequency; And U2 = U1 (P_DES×Rg) / U1 (Q_DES×Xg) / U1, where U1 is the real-time voltage value and U2 is the virtual voltage of the grid connection point.

8. The method for determining the reactive power limit of transformer area energy storage according to claim 1, characterized in that, The step of determining the first line loss value of the power grid line after the energy storage is put into operation and the second line loss value of the power grid line when the energy storage is not put into operation comprises: calculating a real-time current I1=√(P1²+Q1²) / U1 according to the real-time active power P1, real-time reactive power Q1 and real-time voltage U1, and obtaining the line loss after the energy storage is put into operation from the first line loss value W1_loss=I1²×Rg; calculating a virtual current I2=√(P2²+Q2²) / U2 according to the virtual active power P2, virtual reactive power Q2 and virtual voltage U2, and obtaining the line loss when the energy storage is not put into operation from the second line loss value W2_loss=I2²×Rg; Determine the increase in line loss before and after commissioning: ΔW = W1_loss W2_loss serves as an illustrative intermediate measure of the increase in losses caused by the commissioning of energy storage.

9. The method for determining the reactive power limit of transformer area energy storage according to claim 8, characterized in that, The step of determining the upper limit value of the reactive power allowed to be output by the energy storage comprises: under the condition that the real-time active power P1 at the grid-connected point is determined to be unchanged, setting Q as a to-be-solved variable of reactive power, obtaining the third line loss value W3_loss=I3²×Rg from the line current I3=√(P1²+Q²) / U3 after injecting the reactive power, where U3 is the target voltage value for energy storage control; Establish the constraint W3_loss ≤ W2_loss, meaning that the line loss of the power grid after injecting this reactive power does not exceed the second line loss value when energy storage is not in operation. If W3_loss = W2_loss, then the upper limit of reactive power is Q_lmt = √[((P2² + Q2²) × U3²) / U2²] [P1²]; wherein, the target voltage U3 is set according to the voltage management scenario in which the transformer area is located: when the real-time voltage of the grid-connected point is lower than the target voltage, U1<U3, which corresponds to a low-voltage regulation scenario; when the real-time voltage of the grid-connected point is higher than the target voltage, U1>U3, which corresponds to a high-voltage regulation scenario.

10. An energy storage system, characterized in that, comprising: an energy storage unit and a controller; the controller is coupled to the energy storage unit, and the energy storage unit is connected to a distribution line of a transformer district; the energy storage unit is configured for charging or discharging, and the controller is configured to execute the method for determining the reactive power limit of energy storage in a transformer district according to any one of claims 1 to 9, so as to determine the upper limit value of the reactive power allowed to be output by the energy storage.

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