Method and apparatus for determining safety inertia of power grid system, and computer device

Abstract

A method and apparatus for determining the safety inertia of a power grid system, and a computer device. The method comprises: determining a first safety inertia for ensuring safe operation of a power grid system when a frequency change rate after disturbance occurs in the power grid system exceeds a first threshold (S302); determining a second safety inertia for ensuring the safe operation of the power grid system when the frequency after the disturbance occurs in the power grid system is less than a second threshold (S304); and determining a target safety inertia according to the first safety inertia and the second safety inertia, wherein the target safety inertia is a safety inertia lower limit value for ensuring the safe operation of the power grid system (S306).

Description

Method, device and computer equipment for determining safe inertia of power grid system

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on June 20, 2023, with application number 202310739180.4, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of power system control, for example, to a method, device and computer equipment for determining the safety inertia of a power grid system. Background Art

[0003] A large number of renewable energy generators are connected to the grid through the use of power electronics, decoupling the transmission power of these generators from the grid frequency. Under conventional control mode, these generators are unable to provide inertia support to the grid during active power disturbances. This results in a decrease in system inertia when renewable energy generators outpace conventional synchronous generators or when renewable energy generators replace synchronous generators. However, after a disturbance, inertia in the grid system not only slows down rapid frequency changes, allowing for the system's primary frequency regulation, but also optimizes the system's frequency response, ensuring that the lowest frequency point after the disturbance does not exceed the limit. Therefore, when the system experiences an extreme disturbance, the reduction in inertia can cause the system frequency to rapidly spike or drop, deteriorating the system's frequency response and potentially exceeding the grid's third line of defense. This can expose the system to the risk of widespread generator and load shedding. Therefore, to avoid the system's operational dilemma of inertia shortage, it is necessary to calculate the minimum inertia required to ensure safe and stable system operation, providing a reference for operators to adjust inertia levels.

[0004] Most of the related technical studies on the minimum safe inertia of the system are obtained through a single constraint of the initial frequency change rate constraint and the lowest frequency point constraint, and the factors considered are not comprehensive; at the same time, there is a lack of consideration of the spatiotemporal distribution characteristics of the frequency.

[0005] Summary of the Invention

[0006] The embodiments of the present application provide a method, apparatus, and computer device for determining the safe inertia of a power grid system, so as to at least solve the technical problem of low accuracy of methods for determining the minimum safe inertia of a power grid system in related technologies.

[0007] According to one aspect of an embodiment of the present application, a method for determining a safe inertia of a power grid system is provided, comprising: determining a first safe inertia for ensuring safe operation of the power grid system when a frequency change rate exceeds a first threshold after a disturbance occurs in the power grid system; determining a second safe inertia for ensuring safe operation of the power grid system when a frequency is lower than a second threshold after a disturbance occurs in the power grid system; and determining a target safe inertia based on the first safe inertia and the second safe inertia, wherein the target safe inertia is a lower limit value of the safe inertia for ensuring safe operation of the power grid system.

[0008] In some embodiments, determining a first safety inertia for ensuring safe operation of the power grid system when the frequency change rate exceeds a first threshold after a disturbance occurs in the power grid system includes: obtaining the rated frequency of the power grid system; determining the frequency change rate of the power grid system near the disturbance point; determining the change in load power caused by the frequency change; and determining the first safety inertia based on the rated frequency, the frequency change rate of the near disturbance point, and the change in load power caused by the frequency change.

[0009] In some embodiments, determining the frequency change rate of a near-disturbance point of a power grid system includes: obtaining the frequency change rate of an inertia center of the power grid system; determining a proportional relationship between the frequency change rate of a near-disturbance point and the frequency change rate of the inertia center; and determining the frequency change rate of a near-disturbance point based on the proportional relationship and the frequency change rate of the inertia center.

[0010] In some embodiments, determining the change in load power due to frequency change includes: obtaining the active power of the load in the power grid system and the voltage of the load node before the disturbance occurs; determining a first power change based on the active power of the load and the voltage of the load node, wherein the first power change is the change in load power due to voltage change; determining the power change exceeding a third threshold generated by the power grid system under the influence of the disturbance as a second power change; and determining the change in load power due to frequency change as the difference between the first power change and the second power change.

[0011] In some embodiments, determining a second safety inertia that ensures safe operation of the power grid system when the frequency is lower than a second threshold after a disturbance occurs in the power grid system includes: obtaining a rated lower limit frequency of the power grid system; and in response to the frequency being the rated lower limit frequency after a disturbance occurs in the power grid system, determining that the inertia that ensures safe operation of the power grid system is the second safety inertia.

[0012] In some embodiments, in response to the frequency of the power grid system being the rated lower limit frequency after a disturbance occurs, determining the inertia for ensuring safe operation of the power grid system to be the second safety inertia includes: obtaining the rated frequency of the power grid system, the damping coefficient of the power grid system, the primary frequency modulation rate of the power grid system under the disturbance, and the primary frequency modulation action time; in response to the frequency of the power grid system being the rated lower limit frequency after a disturbance occurs, determining the inertia for ensuring safe operation of the power grid system to be the second safety inertia based on the rated frequency of the power grid system, the damping coefficient of the power grid system, the primary frequency modulation rate of the power grid system under the disturbance, and the primary frequency modulation action time.

[0013] In some embodiments, determining the target safety inertia according to the first safety inertia and the second safety inertia includes: determining the maximum value of the first safety inertia and the second safety inertia as the target safety inertia.

[0014] According to another aspect of an embodiment of the present application, a safety inertia determination device for a power grid system is further provided, including: a first determination module, configured to determine a first safety inertia for ensuring safe operation of the power grid system when the frequency change rate exceeds a first threshold after a disturbance occurs in the power grid system; a second determination module, configured to determine a second safety inertia for ensuring safe operation of the power grid system when the frequency is lower than a second threshold after a disturbance occurs in the power grid system; and a third determination module, configured to determine a target safety inertia based on the first safety inertia and the second safety inertia, wherein the target safety inertia is a lower limit value of the safety inertia for ensuring safe operation of the power grid system.

[0015] According to another aspect of an embodiment of the present application, a non-volatile storage medium is further provided, the non-volatile storage medium including a stored program, wherein when the program is running, the device where the non-volatile storage medium is located is controlled to execute any one of the above-mentioned methods for determining the safety inertia of the power grid system.

[0016] According to another aspect of the embodiments of the present application, a computer device is provided, including a processor, the processor being configured to run a program, wherein when the program is run, any one of the above-mentioned methods for determining the safe inertia of a power grid system is executed. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are used to provide an understanding of the present application and constitute a part of the present application. The exemplary embodiments of the present application and their descriptions are used to explain the present application. In the drawings:

[0018] FIG1 shows a hardware structure block diagram of a computer terminal for implementing a method for determining a safe inertia of a power grid system;

[0019] FIG2 shows a schematic diagram of a frequency domain response process of a power grid system;

[0020] 3 is a flow chart of a method for determining the safe inertia of a power grid system according to an embodiment of the present application;

[0021] FIG4 is a schematic diagram of a load voltage characteristic power response according to an embodiment of the present application;

[0022] FIG5 is a schematic diagram of a frequency response curve after linearization processing according to an embodiment of the present application;

[0023] FIG6 is a structural block diagram of a device for determining safety inertia of a power grid system according to an embodiment of the present application. DETAILED DESCRIPTION

[0024] The following describes the embodiments of the present application in conjunction with the accompanying drawings. The embodiments described are some related embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of this application.

[0025] The terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in a sequence other than those illustrated or described herein. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units listed, but may include other steps or units that are not listed or that are inherent to these processes, methods, products or devices.

[0026] According to an embodiment of the present application, an embodiment of a method for determining the safe inertia of a power grid system is provided. The steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0027] The method embodiment provided in the first embodiment of the present application can be executed in a mobile terminal, a computer terminal or a similar computing device. Figure 1 shows a hardware structure block diagram of a computer terminal for implementing a method for determining the safe inertia of a power grid system. As shown in Figure 1, the computer terminal 10 may include one or more (102a, 102b, ..., 102n are used in the figure to illustrate) processors (the processor may include a processing device such as a microprocessor MCU or a programmable logic device FPGA), and a memory 104 for storing data. In addition, the computer terminal 10 may also include: a display, an input / output interface (I / O interface), a universal serial bus (USB) port (which may be included as one of the ports of the BUS bus), a network interface, a power supply and / or a camera. It will be understood by those skilled in the art that the structure shown in Figure 1 is for reference only. For example, the computer terminal 10 may also include more or fewer components than those shown in Figure 1, or have a configuration different from that shown in Figure 1.

[0028] The one or more processors and / or other data processing circuits described above may generally be referred to herein as "data processing circuitry." The data processing circuitry may be embodied in whole or in part as software, hardware, firmware, or any other combination thereof. Furthermore, the data processing circuitry may be a single, independent processing module, or may be fully or partially integrated into any of the other components of the computer terminal 10. As described in the embodiments of the present application, the data processing circuitry functions as a processor control (e.g., selection of a variable resistor terminal path connected to an interface).

[0029] The memory 104 can be used to store software programs and modules of application software, such as the program instructions / data storage device corresponding to the method for determining the safe inertia of the power grid system in the embodiment of the present application. The processor executes the software programs and modules stored in the memory 104 to perform various functional applications and data processing, that is, to implement the method for determining the safe inertia of the power grid system of the above-mentioned application. The memory 104 may include a high-speed random access memory and may also include a non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memory. In some examples, the memory 104 may include a memory remotely located relative to the processor, and these remote memories may be connected to the computer terminal 10 via a network. Examples of the above-mentioned network include the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0030] The display may be, for example, a touch screen liquid crystal display (LCD), which enables a user to interact with a user interface of the computer terminal 10 .

[0031] When a disturbance occurs in the power system, the frequency regulation process involving generators can be divided into the inertia response phase, the primary frequency regulation phase, and the secondary frequency regulation phase, chronologically. Different frequency regulation methods are used in different response phases to adjust the unbalanced power generated by the grid. Figure 2 shows a schematic diagram of the frequency domain response process of a power grid system. As shown in Figure 2, the system's frequency response process can be divided into the following phases.

[0032] Phase 1: At the moment t1 when the disturbance occurs, there are two processes. One is the redistribution of the disturbance power. This process is actually the distribution of the disturbance power to each generator set according to the synchronous power coefficient, as shown in formula (1). It means that when the active disturbance ΔP occurs at the load k in the system, that is, when the power imbalance generated by the disturbance is ΔP, the output electromagnetic power P of the i-th generator is ei The second process is that the load voltage characteristics affect the operation of the power grid system. By changing the unbalanced power of the system after the disturbance, it plays a role similar to inertia in the system frequency response.

[0033] Where, E i and E j Represent the transient potential of the i-th and j-th generators, U k is the voltage across the load k, G ii is the diagonal element in the system node admittance matrix Y, that is, the self-admittance at node i, B ij is the mutual susceptance between node i and node j; B ik is the mutual susceptance between node i and node k; G ij is the mutual conductance between node i and node j; G ik is the mutual conductance between node i and node k. ij =δ i -δ j , δ i Represents the phase angle difference between the excitation potential and terminal voltage of the i-th generator in the system, that is, the power angle. j represents the phase angle difference between the excitation potential and terminal voltage of the jth generator in the system, δ ij Represents the power angle difference between the i-th generator and the j-th generator in the system. δ ik =δ i -δ k , δ k Represents the phase angle difference of load k in the system, δ ik Represents the power angle difference between the i-th generator and load k in the system.

[0034] Phase 2: Inertia response phase, from t1 to t2, after the disturbance occurs, the electromagnetic power of the synchronous generator increases suddenly, while the mechanical power remains unchanged, and the frequency is still in the dead zone of the speed regulator and has not yet taken action. At this time, since the rotor of the synchronous unit stores kinetic energy during the rotation process, it has a certain rotational inertia. After the power imbalance occurs, the rotor of the synchronous generator converts the stored kinetic energy into electromagnetic power through the power angle characteristics by accelerating or decelerating, and continues to maintain the active power supply and demand balance of the system. Since only inertia acts in the system at this time, the frequency change rate of the system is at its maximum value at this time, so constraints are generally set on the frequency change rate at this time, and then the minimum safe inertia of the system is solved. For a single synchronous generator, according to the rotor motion equation, it can be obtained:

[0035] Where: f n is the rated frequency of the power grid; H i is the inertia time constant of the i-th synchronous unit; S i is the rated capacity of the i-th synchronous machine; f(t) is the function of the frequency in the power grid with respect to time; ΔP i It is the deviation between the mechanical power and electromagnetic power of the synchronous generator, and is the disturbance power borne by the generator at the moment of disturbance.

[0036] Phase 3: At this point, the system's inertia response and primary frequency modulation response interact. At time t2, the system's frequency deviation exceeds the governor's frequency modulation deadband. After the governor issues a regulation signal, the prime mover's valve opening increases, increasing mechanical power output to the system. This reduces unbalanced power and gradually reduces the system's inertia support power. When the system's unbalanced power drops to zero, the system frequency reaches its lowest point.

[0037] Phase 4: After the frequency reaches the lowest point, the unit continues to increase power, making the system's mechanical power greater than the electromagnetic power. The synchronous generator rotor begins to absorb energy and recover part of the speed. At this time, the system's inertia response changes from positive to negative. The system frequency reaches a new balance at time t3 and remains at a low level. The system's mechanical power no longer increases.

[0038] Phase 5: After time t3, the secondary frequency regulation response phase begins. Because the primary frequency regulation is differential, when the steady-state frequency deviation is large, the secondary frequency regulation needs to be activated to increase the active power output within the frequency regulation plant and adjust the frequency to the rated system frequency.

[0039] Due to the frequency insensitivity and response delay of the speed regulator, the synchronous generator cannot immediately inject power into the system to eliminate the power imbalance when an active power disturbance occurs. Therefore, before the speed regulator is activated, the supply and demand balance can only be maintained by inertia. Inertia can be considered as stored energy in the generator rotor. Without additional power injection into the system, the system frequency will continue to decrease to zero at a constant rate after an active power disturbance, relying solely on inertia regulation.

[0040] In summary, when unbalanced power occurs in the system, it cannot be instantly balanced. Therefore, inertia plays a vital role in maintaining the balance between active power supply and demand. It provides an energy source for electromagnetic power, thereby maintaining the balance between active power supply and demand. It also slows the rate of change of the system frequency, buying time for the primary frequency regulation to take effect. It is an indispensable part of maintaining system frequency stability. Therefore, this application aims to solve the minimum safe inertia that meets the requirements for stable system operation.

[0041] Since the dynamic process of the frequency after the disturbance is related to factors such as the system operating state, the type, size and location of the active disturbance, when selecting the frequency index, typical characteristic indicators should be selected for constraint before calculating the inertia.

[0042] FIG3 is a flow chart of a method for determining the safe inertia of a power grid system according to an embodiment of the present application. As shown in FIG3 , the method includes the following steps:

[0043] Step S302 : determining a first safety inertia for ensuring safe operation of the power grid system when a frequency change rate exceeds a first threshold value after a disturbance occurs in the power grid system.

[0044] In this step, the frequency change rate can be selected as a characteristic indicator for constraint, and a first safety inertia is calculated to ensure safe operation of the power grid system when the frequency change rate exceeds a first threshold under the influence of a disturbance. For example, when a disturbance occurs in the power system, the frequency change rate is maximum at the initial moment of the disturbance. The safety inertia required when the frequency change rate of the power grid system is maximum can be calculated as the first safety inertia.

[0045] Step S304 : determining a second safety inertia for ensuring safe operation of the power grid system when the frequency is lower than a second threshold after a disturbance occurs in the power grid system.

[0046] In this step, frequency can be selected as a characteristic indicator for constraint. A second safety inertia is calculated to ensure safe operation of the power grid system when the frequency falls below a second threshold under the influence of a disturbance. For example, the frequency corresponding to the first time the rate of change of the frequency drops to zero after an active power disturbance occurs in the power grid system is the frequency extreme. Generally, it is assumed that the system frequency reaches its minimum value when the mechanical power input and electromagnetic power output are equal. The safety inertia required to achieve this minimum power grid system frequency can be calculated as the second safety inertia.

[0047] Step S306 : determining a target safety inertia based on the first safety inertia and the second safety inertia, wherein the target safety inertia is a lower limit of the safety inertia for ensuring safe operation of the power grid system.

[0048] In this step, the safety inertia required by the power grid system under the conditions of maximum frequency change rate and minimum frequency can be comprehensively considered to ultimately determine the minimum safety inertia for safe operation of the power grid system, that is, the lower limit of the safety inertia.

[0049] By respectively calculating the first safety inertia for ensuring the safe operation of the power grid system when the frequency change rate is the largest after a disturbance occurs in the power grid system, and the second safety inertia for ensuring the safe operation of the power grid system when the frequency is the lowest after a disturbance occurs in the power grid system, and comprehensively considering the first safety inertia and the second safety inertia, the minimum safety inertia for ensuring the safe operation of the power grid system in the process after the power grid is disturbed is determined. This achieves the effect of considering the minimum safety inertia required by the power grid in various situations and comprehensively determining the minimum safety inertia for ensuring the safe operation of the power grid system in the process after the power grid is disturbed, thereby achieving the technical effect of improving the accuracy of determining the minimum safety inertia of the power grid system, and further solving the technical problem of low accuracy of the method for determining the minimum safety inertia of the power grid system in the related art.

[0050] In some embodiments, determining a first safety inertia for ensuring safe operation of the power grid system when the frequency change rate exceeds a first threshold after a disturbance occurs in the power grid system includes: obtaining the rated frequency of the power grid system; determining the frequency change rate of the power grid system near the disturbance point; determining the change in load power caused by the frequency change; and determining the first safety inertia based on the rated frequency, the frequency change rate of the near disturbance point, and the change in load power caused by the frequency change.

[0051] In some embodiments, determining the frequency change rate of a near-disturbance point of a power grid system includes: obtaining the frequency change rate of an inertia center of the power grid system; determining a proportional relationship between the frequency change rate of a near-disturbance point and the frequency change rate of the inertia center; and determining the frequency change rate of a near-disturbance point based on the proportional relationship and the frequency change rate of the inertia center.

[0052] For example, the frequency change rate of the system is the largest at the moment the disturbance occurs. If the frequency change rate after the disturbance is constrained to not exceed a threshold value, the frequency change rate at the moment of the disturbance should be used as the benchmark. At this time, there is no frequency deviation, that is, there is no generator speed regulator and load frequency regulation effect. According to formula (3), the minimum safe inertia of the system based on the frequency change rate constraint H is min for:

[0053] Where ΔP max The maximum disturbance power that may occur in the system, generally refers to the disturbance power that occurs when the AC tie line is disconnected, the DC is blocked, or the largest generator set in the system stops operating. max Indicates the limit value of the frequency change rate of the center of inertia allowed by the system.

[0054] However, RoCoF in the above formula max It represents the frequency change rate of the system's inertia center, while the frequency constraint is usually based on the system's maximum bus frequency or a specific bus frequency, and is generally located near the disturbance point. For small systems, the frequency's spatiotemporal distribution characteristics are not obvious, and the frequency change rate near the disturbance point is approximately equal to the frequency change rate of the inertia center. However, for large systems, due to the influence of the frequency's spatiotemporal distribution characteristics, there is a significant difference between the frequency change rate near the disturbance point and the frequency change rate of the inertia center. Therefore, for large systems, it is necessary to quantify the relationship between the frequency change rate near the disturbance point and the inertia center, using the frequency change rate near the disturbance point to represent the frequency change rate of the inertia center, and using the frequency change rate near the disturbance point to calculate the first safety inertia.

[0055] In the inertia response stage, since the speed regulator has not yet been activated, it can be considered that the frequency change rate of the system is constant and the frequency shows a linear downward trend. Therefore, it can be considered that the system frequency deviation and the frequency change rate have an approximately equivalent relationship. The disturbance point and the area where the system inertia center is located are respectively equivalent to two units, and i is used as the power disturbance point, G i is the equivalent unit in the area near the disturbance point. We can get:

[0056] Where α represents the proportional coefficient of the frequency change rate of the equivalent unit in the area where the disturbance point and the system inertia center are located; RoCoF i It represents the frequency change rate of the equivalent unit in the area where the disturbance point is located; RoCoF coi It represents the frequency change rate of the equivalent unit in the area where the system inertia center is located; Δfi i It represents the frequency change of the equivalent unit in the area where the disturbance point is located; Δf coi It represents the frequency change of the equivalent unit in the area where the system inertia center is located.

[0057] Substituting (4) into (3), the frequency change rate constraint of the inertia center measured in the system can be transformed into the frequency change rate constraint of the near-disturbance point in the system, and the minimum safe inertia required for the system considering the frequency-space distribution characteristics is obtained as:

[0058] In some embodiments, determining the change in load power due to frequency change includes: obtaining the active power of the load in the power grid system and the voltage of the load node before the disturbance occurs; determining a first power change based on the active power of the load and the voltage of the load node, wherein the first power change is the change in load power due to voltage change; determining the power change exceeding a third threshold generated by the power grid system under the influence of the disturbance as a second power change; and determining the change in load power due to frequency change as the difference between the first power change and the second power change.

[0059] In some embodiments, the occurrence of disturbances will not only affect the system frequency, but also the system voltage. The change in voltage will cause the constant impedance and constant current load powers in the system to change accordingly, reducing the unbalanced power of the system and, in turn, reducing the rate of change of frequency after the disturbance. FIG4 is a schematic diagram of the load voltage characteristic power response provided according to an embodiment of the present application. As shown in FIG4 , its essence is to change the unbalanced power of the system. As the proportion of new energy in the power grid continues to increase, the role of the load voltage characteristic in slowing down the rate of change of the system frequency is becoming more and more obvious.

[0060] In Figure 4, ΔP is the power imbalance generated after the system is disturbed, ΔP L The power imbalance amount reduced due to the load voltage characteristics after the voltage changes, that is, the change in load power ΔP L for:

[0061] Where: P L is the active power of the load before the disturbance; U L0 is the voltage of the load node before the disturbance; U L is the voltage of the load node after the disturbance; l z 、l i 、l p They respectively represent the proportion of constant impedance load, constant current load and constant power load in the system to the total load.

[0062] Substituting (6) into (5), we can get the maximum power imbalance (i.e., ΔP) generated after the system disturbance. max ) to remove the power imbalance (i.e. ΔP L ), and obtain the part of the maximum power imbalance generated after the system disturbance that needs to be supported by the system's safety inertia (i.e. ΔP max -ΔP L ), and finally the minimum safety inertia required for the system considering the frequency-space distribution characteristics is obtained as:

[0063] In some embodiments, determining a second safety inertia that ensures safe operation of the power grid system when the frequency is lower than a second threshold after a disturbance occurs in the power grid system includes: obtaining the rated lower limit frequency of the power grid system; and determining that the inertia that ensures safe operation of the power grid system is the second safety inertia when the frequency is the rated lower limit frequency after a disturbance occurs in the power grid system.

[0064] In some embodiments, when the frequency of the power grid system is at the rated lower limit frequency after a disturbance occurs in the power grid system, determining the inertia for ensuring the safe operation of the power grid system to be the second safety inertia includes: obtaining the rated frequency of the power grid system, the damping coefficient of the power grid system, the primary frequency modulation rate of the power grid system under the disturbance, and the primary frequency modulation action time; when the frequency of the power grid system is at the rated lower limit frequency after a disturbance occurs in the power grid system, determining the inertia for ensuring the safe operation of the power grid system to be the second safety inertia based on the rated frequency of the power grid system, the damping coefficient of the power grid system, the primary frequency modulation rate of the power grid system under the disturbance, and the primary frequency modulation action time.

[0065] In some embodiments, when the frequency variation exceeds 0.033 Hz, it crosses the dead zone of the speed regulator. At this time, the speed regulator will increase the mechanical power input to reduce the system power deviation, thereby suppressing the frequency drop. Generally speaking, it is approximately believed that when the mechanical power input and the electromagnetic power output are equal, the system frequency reaches the minimum value f nadir In order to avoid triggering the low-frequency load reduction stabilization device, the lowest frequency point is also a key indicator for measuring the stability of the system frequency. It is necessary to meet the lowest system frequency value f nadir Greater than or equal to the system's rated minimum frequency f min :

[0066] f min ≤f nadir (8)

[0067] Since the frequency curves of the power grids in the same region tend to be consistent when reaching the lowest frequency point, the system can be regarded as a synchronous machine. The frequency response process of the system can be described using the rotor motion equation as follows:

[0068] Where: H sys is the overall inertia of the system; f(t) is the system frequency at time t; P m (t), P e (t) represent the total mechanical power and total electromagnetic power of the system respectively; D represents the damping effect during the system frequency response process; Δf(t) represents the deviation between the system frequency at time t and the rated frequency, where the rated frequency is generally 50 Hz.

[0069] As the frequency drops to its lowest point, the inertia response and the primary frequency modulation response interact, resulting in a nonlinear frequency response that presents a challenge. Figure 5 is a schematic diagram of a linearized frequency response curve according to an embodiment of the present application. To improve solution efficiency, the primary frequency modulation of the generator set is linearized as shown in Figure 5. By applying constraints to the lowest frequency point, the minimum safe inertia of the system is solved.

[0070] Assume that the system frequency is t nadir When it reaches the lowest point, the equation (9) from 0 to t nadir Integrating, we get:

[0071] After a disturbance occurs in the system, the system frequency begins to deviate from normal levels and quickly crosses the generator set's primary frequency regulation dead zone. The primary frequency regulation then begins to compensate for the system's unbalanced power. When the active power at the primary frequency regulation output equals the initial unbalanced power, the system frequency reaches its extreme value. The linearization technique used to simulate the system's frequency dynamic response after a disturbance ΔP occurs is shown in Figures 2 and 5. Under this disturbance, the system's primary frequency regulation rate is:

[0072] Where, T sys is the primary frequency modulation rate of the system under disturbance; t db It is the time for one frequency modulation action.

[0073] In 0~t db In the first stage, the primary frequency regulation has not yet started, and the power imbalance of the system remains unchanged. By integrating formula (9) in this stage, we can get:

[0074] Where, f db t db The frequency of the system at that moment.

[0075] After a frequency modulation starts, the time it takes for the frequency to reach the lowest point is:

[0076] For both sides of equation (9) from 0 to t nadir Points earned:

[0077] Substituting Equation (14) into the frequency constraint Equation (8), we can obtain the system safety inertia H that satisfies the lowest frequency point. sys for:

[0078] When the left and right sides of formula (15) are equal, the minimum safety inertia H required for the power system to meet the frequency minimum point constraint is obtained: sys,min .

[0079] In some embodiments, determining the target safety inertia according to the first safety inertia and the second safety inertia includes: determining the maximum value of the first safety inertia and the second safety inertia as the target safety inertia.

[0080] In some embodiments, after respectively solving for the minimum safe inertia of the power system that satisfies the frequency change rate constraint and the frequency minimum point constraint, it is necessary to comprehensively consider and solve for the minimum safe inertia H required for the power system:

[0081] H=max{H min , H sys，min} (16)

[0082] As an embodiment, simulation verification will be performed from two perspectives: an IEEE 10-machine 39-bus system and an actual power grid system.

[0083] 1. IEEE 10 machines and 39 nodes

[0084] The 10-machine 39-bus system includes 10 generators, 39 busbars, 19 loads and 34 transmission lines; the rated frequency is 50Hz, of which machine No. 1 is the external grid equivalent machine and machine No. 2 is the balancing machine.

[0085] Three scenarios are set in the above 10-machine 39-bus system. The minimum safe inertia requirement of the system under two frequency constraints is calculated in each scenario. The simulation is as follows:

[0086] Scenario 1: All generators in the system are synchronous units.

[0087] Scenario 2: The two synchronous units 5 and 6 in the system are replaced with wind turbines. At this time, the proportion of new energy in the system is 18.8%.

[0088] Scenario 3: The three synchronous units 5, 6 and 9 in the system are replaced with wind turbines. At this time, the proportion of new energy in the system is 32.2%.

[0089] Taking a sudden load increase event as an example, after the disturbance occurs, the system's frequency change rate and lowest frequency point at the initial disturbance moment are sampled to calculate the system's minimum safe inertia. Because this system is large, the frequency change rate near the disturbance point at the initial disturbance moment is more accurate than the frequency change rate at the inertia center. Therefore, when calculating the system's minimum safe inertia using the frequency change rate constraint, the frequency change rate near the disturbance point is required. Equations (7) and (15) can be used to calculate the system's minimum safe inertia for different frequency constraints. The calculation results of the system's minimum safe inertia under the three scenarios are shown in Table 1.

[0090] Table 1 Calculation results of minimum safe inertia constants for a 10-machine, 39-bus system

[0091] As shown in Table 1, in Scenario 1, when there are no renewable energy sources in the system, the results obtained using the proposed minimum safe inertia calculation method are close to the theoretical value. Furthermore, the closeness of the calculated minimum safe inertia values ​​to the theoretical values ​​after the proportion of renewable energy increases demonstrates that this method is applicable to both conventional power grids and those with a high proportion of renewable energy sources. Furthermore, a comparison shows that in large systems, calculating the minimum safe inertia using the initial rate of change of frequency near the disturbance point is more accurate than calculating the inertia at the center of the inertia.

[0092] 2. Actual high proportion of new energy systems

[0093] In order to analyze the applicability of the above-mentioned method for calculating the minimum safe inertia of the system in actual power grids, a provincial power grid J in my country was selected to calculate the minimum safe inertia that meets the conditions for stable operation of the system. The total installed capacity of the provincial power grid is 134.4091 million kilowatts, and the installed capacity of renewable energy accounts for about 14% of the total capacity of the province, of which the installed capacity of wind power accounts for about 8.26% of the total installed capacity of the entire network, and the installed capacity of photovoltaic power accounts for about 5.74% of the total installed capacity of the entire network. At the same time, the provincial power grid currently has four ultra-high voltage direct current transmission lines, and the DC feed-in power accounts for about 20.98% of the total installed capacity. In addition, according to the province's "14th Five-Year Plan", by 2025, the proportion of renewable energy installed capacity in the province will reach 30%.

[0094] This application takes the province's power grid's summer operation mode in 2019 as an example, and performs simulation calculations in the software. In systems where new energy accounts for 14% and 30%, respectively, taking a sudden load increase event as an example, after the disturbance occurs, the system's frequency change rate and the time of the lowest frequency point at the initial moment of the disturbance are sampled to calculate the system's minimum safe inertia.

[0095] Table 2 Calculation results of the minimum safe inertia constant of the actual power system

[0096] As can be seen from Table 2, after the disturbance, the method in this paper is used to calculate the minimum safe inertia of the system in the actual power system with high accuracy, which proves that the method of calculating the minimum safe inertia of the power system in this application is also applicable to the actual power system.

[0097] For the above-mentioned method embodiments, for the sake of simplicity, they are all expressed as a series of action combinations, but those skilled in the art should be aware that this application is not limited by the order of the actions described, because according to this application, some steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all exemplary embodiments, and the actions and modules involved are not necessarily required by this application.

[0098] Through the description of the above embodiments, those skilled in the art can understand that the method for determining the safe inertia of the power grid system of the above embodiment can be implemented by means of software plus a necessary general hardware platform, or of course by hardware, but in many cases the former is a better embodiment. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, can be embodied in the form of a software product, which is stored in a storage medium (such as a read-only memory ROM / random access memory RAM, a magnetic disk, or an optical disk), and includes at least one instruction for enabling a terminal device (which can be a mobile phone, a computer, a server, or a network device, etc.) to execute the method described in each embodiment of the present application.

[0099] According to an embodiment of the present application, a safe inertia determination device for a power grid system is further provided for implementing the above-mentioned safe inertia determination method for a power grid system. FIG6 is a structural block diagram of the safe inertia determination device for a power grid system provided according to an embodiment of the present application. As shown in FIG6 , the safe inertia determination device for a power grid system includes: a first determination module 72, a second determination module 74, and a third determination module 76. The safe inertia determination device for a power grid system is described below.

[0100] The first determining module 72 is configured to determine a first safety inertia for ensuring safe operation of the power grid system when a frequency change rate exceeds a first threshold after a disturbance occurs in the power grid system.

[0101] The second determining module 74 is connected to the first determining module 72 and is configured to determine a second safety inertia for ensuring safe operation of the power grid system when the frequency is lower than a second threshold after a disturbance occurs in the power grid system.

[0102] The third determination module 76 is connected to the second determination module 74 and is configured to determine a target safety inertia based on the first safety inertia and the second safety inertia, wherein the target safety inertia is a lower limit of the safety inertia to ensure safe operation of the power grid system.

[0103] The first determination module 72, the second determination module 74, and the third determination module 76 correspond to steps S302 to S306 in the embodiment. The examples and application scenarios implemented by the multiple modules and the corresponding steps are the same. It should be noted that the above modules, as part of the device, can be run in the computer terminal 10 provided in the embodiment.

[0104] An embodiment of the present application further provides a computer device, which may be located in at least one of a plurality of network devices in a computer network. The computer device includes a memory and a processor.

[0105] The memory can be used to store software programs and modules, such as the program instructions / modules corresponding to the method and apparatus for determining the safe inertia of a power grid system in the embodiments of the present application. The processor executes the software programs and modules stored in the memory to perform various functional applications and data processing, thereby implementing the above-mentioned method for determining the safe inertia of a power grid system. The memory can include high-speed random access memory and can also include non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memory. In some examples, the memory can include a memory remotely located relative to the processor, and these remote memories can be connected to the computer terminal via a network. Examples of the above-mentioned network include the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0106] The processor can call information and applications stored in the memory through the transmission device to perform the following steps: determining a first safety inertia that ensures the safe operation of the power grid system when the frequency change rate exceeds a first threshold after a disturbance occurs in the power grid system; determining a second safety inertia that ensures the safe operation of the power grid system when the frequency is lower than a second threshold after a disturbance occurs in the power grid system; and determining a target safety inertia based on the first safety inertia and the second safety inertia, wherein the target safety inertia is a lower limit value of the safety inertia that ensures the safe operation of the power grid system.

[0107] In some embodiments, the processor may also execute program code for the following steps: determining a first safety inertia for ensuring safe operation of the power grid system when the frequency change rate exceeds a first threshold after a disturbance occurs in the power grid system, including: obtaining the rated frequency of the power grid system; determining the frequency change rate of the power grid system near the disturbance point; determining the change in load power caused by the frequency change; determining the first safety inertia based on the rated frequency, the frequency change rate of the near disturbance point, and the change in load power caused by the frequency change.

[0108] In some embodiments, the processor may further execute program code for the following steps: determining the frequency change rate of a near-disturbance point of the power grid system, including: obtaining the frequency change rate of the inertia center of the power grid system; determining a proportional relationship between the frequency change rate of the near-disturbance point and the frequency change rate of the inertia center; and determining the frequency change rate of the near-disturbance point based on the proportional relationship and the frequency change rate of the inertia center.

[0109] In some embodiments, the processor may also execute program code for the following steps: determining the amount of change in load power due to frequency change, including: obtaining the active power of the load in the power grid system and the voltage of the load node before the disturbance occurs; determining a first power change based on the active power of the load and the voltage of the load node, wherein the first power change is the amount of change in load power due to voltage change; determining the amount of power change exceeding a third threshold generated by the power grid system under the influence of the disturbance as a second power change; and determining the amount of change in load power due to frequency change as the difference between the first power change and the second power change.

[0110] In some embodiments, the processor may also execute program code for the following steps: determining a second safety inertia to ensure safe operation of the power grid system when the frequency is lower than a second threshold after a disturbance occurs in the power grid system, including: obtaining the rated lower limit frequency of the power grid system; and determining that the inertia to ensure safe operation of the power grid system is the second safety inertia when the frequency is the rated lower limit frequency after a disturbance occurs in the power grid system.

[0111] In some embodiments, the processor may also execute program code for the following steps: when the frequency of the power grid system is at the rated lower limit frequency after a disturbance occurs in the power grid system, determining that the inertia for ensuring the safe operation of the power grid system is the second safety inertia, including: obtaining the rated frequency of the power grid system, the damping coefficient of the power grid system, the primary frequency modulation rate of the power grid system under the disturbance, and the primary frequency modulation action time; when the frequency of the power grid system is at the rated lower limit frequency after a disturbance occurs in the power grid system, determining that the inertia for ensuring the safe operation of the power grid system is the second safety inertia based on the rated frequency of the power grid system, the damping coefficient of the power grid system, the primary frequency modulation rate of the power grid system under the disturbance, and the primary frequency modulation action time.

[0112] In some embodiments, the processor may further execute program code of the following steps: determining a target safety inertia based on the first safety inertia and the second safety inertia, including: determining the maximum value of the first safety inertia and the second safety inertia as the target safety inertia.

[0113] An embodiment of the present application provides a method for determining the safe inertia of a power grid system. By separately calculating a first safe inertia for ensuring safe operation of the power grid system when the frequency change rate is the highest after a disturbance occurs, and a second safe inertia for ensuring safe operation of the power grid system when the frequency is the lowest after a disturbance occurs, and comprehensively considering the first and second safe inertias, a minimum safe inertia for ensuring safe operation of the power grid system during a disturbance is determined. This method achieves the effect of considering the minimum safe inertia required by the power grid in various situations and comprehensively determining the minimum safe inertia for ensuring safe operation of the power grid system during a disturbance, thereby achieving the technical effect of improving the accuracy of determining the minimum safe inertia of the power grid system, and further solving the technical problem of low accuracy of methods for determining the minimum safe inertia of the power grid system in related technologies.

[0114] A person skilled in the art will understand that all or part of the steps in the various methods of the above embodiments can be completed by instructing the hardware related to the terminal device through a program, and the program can be stored in a non-volatile storage medium, which may include: a flash drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, etc.

[0115] An embodiment of the present application further provides a non-volatile storage medium, which can be used to store program codes executed by the method for determining the safe inertia of a power grid system provided by the above embodiment.

[0116] In some embodiments, the non-volatile storage medium may be located in any computer terminal in a computer terminal group in a computer network, or in any mobile terminal in a mobile terminal group.

[0117] In some embodiments, the non-volatile storage medium is configured to store program code for performing the following steps: determining a first safety inertia that ensures safe operation of the power grid system when the frequency change rate exceeds a first threshold after a disturbance occurs in the power grid system; determining a second safety inertia that ensures safe operation of the power grid system when the frequency is lower than a second threshold after a disturbance occurs in the power grid system; and determining a target safety inertia based on the first safety inertia and the second safety inertia, wherein the target safety inertia is a lower limit value of the safety inertia that ensures safe operation of the power grid system.

[0118] In some embodiments, the non-volatile storage medium is configured to store program code for executing the following steps: determining a first safety inertia to ensure safe operation of the power grid system when the frequency change rate exceeds a first threshold after a disturbance occurs in the power grid system, including: obtaining the rated frequency of the power grid system; determining the frequency change rate of the power grid system near the disturbance point; determining the change in load power caused by the frequency change; determining the first safety inertia based on the rated frequency, the frequency change rate of the near disturbance point and the change in load power caused by the frequency change.

[0119] In some embodiments, the non-volatile storage medium is configured to store program code for executing the following steps: determining the frequency change rate of a near disturbance point of the power grid system, including: obtaining the frequency change rate of the inertia center of the power grid system; determining the proportional relationship between the frequency change rate of the near disturbance point and the frequency change rate of the inertia center; and determining the frequency change rate of the near disturbance point based on the proportional relationship and the frequency change rate of the inertia center.

[0120] In some embodiments, the non-volatile storage medium is configured to store program code for performing the following steps: determining the change in load power caused by frequency change, including: obtaining the active power of the load in the power grid system and the voltage of the load node before the disturbance occurs; determining a first power change based on the active power of the load and the voltage of the load node, wherein the first power change is the change in load power caused by voltage change; determining the power change generated by the power grid system under the influence of the disturbance that exceeds a third threshold as a second power change; determining the change in load power caused by the frequency change as the difference between the first power change and the second power change.

[0121] In some embodiments, the non-volatile storage medium is configured to store program code for executing the following steps: determining a second safety inertia to ensure safe operation of the power grid system when the frequency is lower than a second threshold after a disturbance occurs in the power grid system, including: obtaining the rated lower limit frequency of the power grid system; when the frequency is the rated lower limit frequency after a disturbance occurs in the power grid system, determining that the inertia to ensure safe operation of the power grid system is the second safety inertia.

[0122] In some embodiments, the non-volatile storage medium is configured to store program code for executing the following steps: when the frequency of the power grid system is at the rated lower limit frequency after a disturbance occurs in the power grid system, determining that the inertia for ensuring the safe operation of the power grid system is the second safety inertia, including: obtaining the rated frequency of the power grid system, the damping coefficient of the power grid system, the primary frequency modulation rate of the power grid system under the disturbance, and the primary frequency modulation action time; when the frequency of the power grid system is at the rated lower limit frequency after a disturbance occurs in the power grid system, determining that the inertia for ensuring the safe operation of the power grid system is the second safety inertia based on the rated frequency of the power grid system, the damping coefficient of the power grid system, the primary frequency modulation rate of the power grid system under the disturbance, and the primary frequency modulation action time.

[0123] In some embodiments, the non-volatile storage medium is configured to store program code for executing the following steps: determining a target safety inertia based on the first safety inertia and the second safety inertia, including: determining the maximum value of the first safety inertia and the second safety inertia as the target safety inertia.

[0124] The serial numbers of the above-mentioned embodiments of the present application are for description only and do not represent the advantages or disadvantages of the embodiments.

[0125] In the above embodiments of the present application, the description of each embodiment has its own focus. For parts that are not described in detail in one embodiment, please refer to the relevant descriptions of other embodiments.

[0126] In the several embodiments provided in this application, the disclosed technical content can be implemented in other ways. Among them, the device embodiments described above are schematic. For example, the division of the units can be a logical function division. In actual implementation, there can be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of units or modules, which can be electrical or other forms.

[0127] 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 units. Some or all of the units may be selected to implement this embodiment according to actual needs.

[0128] In addition, the functional units in the various embodiments of the present application may be integrated into a single processing unit, or each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0129] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a non-volatile storage medium. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes at least one instruction for enabling a computer device (which can be a personal computer, server or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a read-only memory, a random access memory, a mobile hard disk, a magnetic disk or an optical disk.

Claims

1. A method for determining the safety inertia of a power grid system, comprising: Determine a first safety inertia to ensure safe operation of the power grid system when a frequency change rate exceeds a first threshold after a disturbance occurs in the power grid system; Determine a second safety inertia for ensuring safe operation of the power grid system when the frequency is lower than a second threshold after the disturbance occurs in the power grid system; A target safety inertia is determined according to the first safety inertia and the second safety inertia, wherein the target safety inertia is a lower limit value of the safety inertia for ensuring safe operation of the power grid system.

2. The method according to claim 1, wherein: The determining of a first safety inertia to ensure safe operation of the power grid system when the frequency change rate exceeds a first threshold after a disturbance occurs in the power grid system comprises: Obtaining the rated frequency of the power grid system; Determining a frequency change rate of a near-disturbance point of the power grid system; Determine the amount of change in load power due to frequency changes; The first safety inertia is determined according to the rated frequency, the frequency change rate of the near-disturbance point, and the change in load power caused by the frequency change.

3. The method according to claim 2, wherein: Determining the frequency change rate of the near-disturbance point of the power grid system includes: Obtaining a frequency change rate of the inertia center of the power grid system; Determine a proportional relationship between the frequency change rate of the near disturbance point and the frequency change rate of the inertia center; The frequency change rate of the near-disturbance point is determined according to the proportional relationship and the frequency change rate of the inertia center.

4. The method according to claim 2, wherein: The determining of the change in load power caused by the frequency change comprises: Acquire the active power of the load in the power grid system and the voltage of the load node before the disturbance occurs; Determine a first power variation according to the active power of the load and the voltage of the load node, wherein the first power variation is a variation of the load power caused by the voltage variation; Determine a power variation exceeding a third threshold value generated by the power grid system under the influence of the disturbance as a second power variation; The load power change caused by the frequency change is determined as a difference between the first power change and the second power change.

5. The method according to claim 1, wherein: The determining of a second safety inertia to ensure safe operation of the power grid system when the frequency is lower than a second threshold after the disturbance occurs in the power grid system comprises: Obtaining a rated lower frequency limit of the power grid system; In response to the frequency of the power grid system being the rated lower limit frequency after the disturbance occurs, the inertia for ensuring safe operation of the power grid system is determined to be the second safety inertia.

6. The method according to claim 5, wherein: In response to the frequency of the power grid system being the rated lower limit frequency after the disturbance occurs, determining that the inertia for ensuring the safe operation of the power grid system is the second safety inertia, comprises: Acquire the rated frequency of the power grid system, the damping coefficient of the power grid system, the primary frequency regulation rate and the primary frequency regulation action time of the power grid system under the disturbance; In response to the frequency of the power grid system being the rated lower limit frequency after the disturbance occurs, the inertia for ensuring safe operation of the power grid system is determined to be the second safety inertia according to the rated frequency of the power grid system, the damping coefficient of the power grid system, the primary frequency regulation rate and the primary frequency regulation action time of the power grid system under the disturbance.

7. The method according to any one of claims 1 to 6, wherein: The step of determining a target safety inertia according to the first safety inertia and the second safety inertia includes: A maximum value of the first safety inertia and the second safety inertia is determined as the target safety inertia.

8. A safety inertia determination device for a power grid system, comprising: A first determination module is configured to determine a first safety inertia for ensuring safe operation of the power grid system when a frequency change rate exceeds a first threshold after a disturbance occurs in the power grid system; A second determination module is configured to determine a second safety inertia for ensuring safe operation of the power grid system when the frequency is lower than a second threshold after the disturbance occurs in the power grid system; The third determination module is configured to determine a target safety inertia according to the first safety inertia and the second safety inertia, wherein the target safety inertia is a lower limit value of the safety inertia to ensure safe operation of the power grid system.

9. A non-volatile storage medium, the non-volatile storage medium comprising a stored program, wherein: When the program is running, the device where the non-volatile storage medium is located is controlled to execute the method for determining the safe inertia of the power grid system as described in any one of claims 1 to 7.

10. A computer device comprising: Memory and processor, The memory stores a computer program; The processor is used to execute the computer program stored in the memory, and when the computer program is run, the processor executes the method for determining the safe inertia of the power grid system according to any one of claims 1 to 7.

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