Online regulation and control method for improving transient stability of weak sending end system

Abstract

The invention provides an online regulation and control method for improving transient stability of a weak sending end system, and relates to the technical field of power systems and automation thereof. The online regulation and control method comprises the following steps: determining the equivalent impedance of a weak sending end system at the current moment; the weak transmission end system comprises a new energy station and network construction energy storage; based on the equivalent impedance at the current moment, determining a short-circuit ratio of the weak sending end system at the current moment; if the short-circuit ratio at the current moment is smaller than a preset threshold value, determining the output adjustment amount of the new energy station at the next moment and the output adjustment amount of network construction energy storage at the next moment based on the equivalent impedance at the current moment; and on the basis of the output adjustment amount of the new energy station and the output adjustment amount of network construction energy storage, carrying out online regulation and control on the weak transmission end system so as to improve the transient stability of the weak transmission end system. Through the method, online regulation and control of output of the new energy station and output of network construction energy storage can be realized, so that the transient stability of a weak transmission end system is improved, and the instability risk of the system is reduced.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field, in particular to an online regulation method for improving transient stability of a weak sending-end system. BACKGROUND

[0002] Traditional power grids are dominated by synchronous generators. Synchronous generators naturally provide the strength, inertia and voltage regulation capability of the power grid through their huge rotating mass and inherent physical characteristics (excitation system, speed regulation system), making the power grid "rigid".

[0003] However, new power systems, due to the participation of new energy and energy storage connected to the grid through power electronic converters, weaken the strength of the sending-end power grid, forming a weak sending-end system, which increases the risk of system transient instability. SUMMARY

[0004] The present disclosure provides an online regulation method for improving transient stability of a weak sending-end system to solve the technical problem of increased risk of system transient instability due to the participation of new energy and energy storage.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present disclosure is as follows: The first aspect of the present disclosure provides an online regulation method for improving transient stability of a weak sending-end system, comprising: determining the equivalent impedance of the weak sending-end system at the current time; the weak sending-end system comprising a new energy station and a grid-forming energy storage; based on the equivalent impedance at the current time, determining the short-circuit ratio of the weak sending-end system at the current time; if the short-circuit ratio at the current time is less than a preset threshold, based on the equivalent impedance at the current time, determining the output adjustment amount of the new energy station at the next time and the output adjustment amount of the grid-forming energy storage at the next time; based on the output adjustment amount of the new energy station and the output adjustment amount of the grid-forming energy storage, performing online regulation on the weak sending-end system to improve the transient stability of the weak sending-end system.

[0006] In some embodiments of the present disclosure, the output adjustment amount comprises an output power adjustment amount; based on the equivalent impedance at the current time, determining the output adjustment amount of the new energy station at the next time and the output adjustment amount of the grid-forming energy storage at the next time, comprising: obtaining the rated voltage of the weak sending-end system and the lower limit of the short-circuit ratio of the weak sending-end system; based on the equivalent impedance at the current time, the rated voltage and the lower limit of the short-circuit ratio, determining the target output power of the new energy station at the next time; obtaining the output power of the new energy station at the current time, and determining the difference between the output power of the new energy station at the current time and the target output power of the new energy station at the next time as the output power adjustment amount of the new energy station at the next time; based on the output power adjustment amount of the new energy station at the next time, determining the output power adjustment amount of the grid-forming energy storage at the next time; the output power adjustment amount of the grid-forming energy storage is equal in amplitude and opposite in direction to the output power adjustment amount of the new energy station.

[0007] In some embodiments of the present disclosure, the formula for determining the target output power of the new energy station at the next time point comprises: , wherein, V nom is the rated voltage of the weak sending system, Z_th is the equivalent impedance of the weak sending system at the current time point, SCR_dn is the short-circuit ratio lower limit of the weak sending system.

[0008] In some embodiments of the present disclosure, the short-circuit ratio lower limit comprises any value in the range of 1.0-1.5.

[0009] In some embodiments of the present disclosure, the equivalent impedance at the current time point is determined by using recursive least squares; the equivalent impedance at the current time point is determined by using recursive least squares, comprising: obtaining the equivalent impedance of the weak sending system at the previous time point; obtaining the grid-connected point voltage and the grid-connected point current of the weak sending system at the current time point; based on the equivalent impedance at the previous time point, the grid-connected point voltage at the current time point and the grid-connected point current at the current time point, performing recursive least squares update to obtain the equivalent impedance at the current time point, so as to realize online estimation of the equivalent impedance at the current time point.

[0010] In some embodiments of the present disclosure, the formula of the recursive least squares comprises: , wherein, θ k is the parameter estimation value at the current time point, comprising the equivalent impedance at the current time point, k k is the parameter estimation value at the previous time point k-1, comprising the equivalent impedance at the previous time point k-1, θ k is the gain matrix at the current time point, k k is the prediction error at the current time point, k k is the grid-connected point voltage at the current time point, y k φ k θ k-1 k y k k V pcc k φ k θ k-1 φ k ​​​​​​​​​​​​​​​​​​​​​​​​) is predicted based on a regression vector of a current time point k and a parameter estimation value of a previous time point φ -1 k ) and a grid-connected point voltage predicted based on the regression vector of the current time point k and the parameter estimation value of the previous time point θ -1 k , φ , k ) = [1, - I _ pcc , k ], I _ pcc , k a grid-connected point current of the current time point k .

[0011] In some embodiments of the present disclosure, the short-circuit ratio of the weak sending end system at the current time point is determined based on the equivalent impedance at the current time point, including: obtaining a rated voltage of the weak sending end system; determining a short-circuit capacity of the weak sending end system at the current time point based on the equivalent impedance at the current time point and the rated voltage; the short-circuit capacity is a ratio of the square of the rated voltage to the equivalent impedance; obtaining an output power of the new energy station at the current time point; determining the short-circuit ratio of the weak sending end system at the current time point based on the short-circuit capacity at the current time point and the output power of the new energy station at the current time point; the short-circuit ratio is a ratio of the short-circuit capacity to the output power of the new energy station.

[0012] In some embodiments of the present disclosure, the preset threshold value includes any value in the range of 2.0-3.0.

[0013] In a second aspect of the present disclosure, an online regulation device for improving transient stability of a weak sending end system is provided, including: a first determination unit configured to determine an equivalent impedance of the weak sending end system at a current time point; the weak sending end system including a new energy station and a grid-forming energy storage; a second determination unit configured to determine a short-circuit ratio of the weak sending end system at the current time point based on the equivalent impedance at the current time point; a third determination unit configured to, if the short-circuit ratio at the current time point is less than a preset threshold value, determine an output adjustment amount of the new energy station at a next time point and an output adjustment amount of the grid-forming energy storage at the next time point based on the equivalent impedance at the current time point; and an online regulation unit configured to perform online regulation on the weak sending end system based on the output adjustment amount of the new energy station and the output adjustment amount of the grid-forming energy storage, so as to improve the transient stability of the weak sending end system.

[0014] The present disclosure also provides an electronic device, including: a memory configured to store at least one instruction; and a processor configured to invoke the instruction stored in the memory to execute the online regulation method for improving the transient stability of the weak sending end system in the first aspect and any one of the embodiments of the first aspect.

[0015] The present disclosure also provides a computer-readable storage medium, which stores at least one executable instruction, the executable instruction is loaded and executed by a processor to implement the online regulation method for improving transient stability of a weak sending-end system in the first aspect and any one of the embodiments of the first aspect.

[0016] The present disclosure also provides a computer program product, which comprises computer program code, when the computer program code is run by a computer, the computer program code causes the computer to execute the online regulation method for improving transient stability of a weak sending-end system in the first aspect and any one of the embodiments of the first aspect.

[0017] Compared with the prior art, the present disclosure has the following beneficial effects: The present disclosure determines the equivalent impedance of the weak sending-end system online, and then determines the short-circuit ratio of the weak sending-end system online. In the case that the short-circuit ratio is less than a preset threshold, the output of the new energy station and the output of the network-forming energy storage are adjusted online to improve the transient stability of the weak sending-end system. The above method can effectively adapt to the real-time changes of the operating state of the weak sending-end system, avoid the errors caused by fixed parameters or offline calculation in the traditional method, ensure the accuracy of risk identification, and effectively prevent system instability. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a flowchart of an online regulation method for improving transient stability of a weak sending-end system provided by an embodiment of the present disclosure; Figure 2 is a flowchart of a method for determining the equivalent impedance of the weak sending-end system at the current time provided by an embodiment of the present disclosure; Figure 3 is a flowchart of a method for determining the short-circuit ratio of the weak sending-end system at the current time provided by an embodiment of the present disclosure; Figure 4 is a flowchart of a method for determining the output adjustment amount of the new energy station at the next time and the output adjustment amount of the network-forming energy storage at the next time provided by an embodiment of the present disclosure; Figure 5 is a structural schematic diagram of a weak sending-end system provided by an embodiment of the present disclosure; Figure 6 is a schematic diagram of the convergence state of an RLS algorithm provided by an embodiment of the present disclosure; Figure 7 is a schematic diagram of a power regulation result provided by an embodiment of the present disclosure; Figure 8 is a schematic diagram of a short-circuit ratio monitoring result provided by an embodiment of the present disclosure; Figure 9 is a structural block diagram of an online regulation device for improving transient stability of a weak sending-end system provided by an embodiment of the present disclosure. Detailed Implementation

[0019] The present disclosure will now be further described with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present disclosure and should not be construed as limiting the scope of protection of the present disclosure. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application.

[0020] The acquisition, transmission, storage, use, and processing of data in this disclosed technical solution comply with relevant national laws and regulations. In the embodiments of this disclosure, certain existing industry solutions such as software, components, and models may be mentioned. These should be considered exemplary, intended only to illustrate the feasibility of implementing the technical solution of this disclosure, and do not imply that the applicant has already used or necessarily used such solutions.

[0021] All terms used in this disclosure have the same meaning as understood by one of ordinary skill in the art to which this disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant art, and not as idealized or highly formalized, unless expressly defined herein.

[0022] Traditional power grids are dominated by synchronous generators. Synchronous generators, through their enormous rotating mass and inherent physical characteristics (excitation system, speed regulation system), naturally provide the grid with strength, inertia, and voltage regulation capabilities. The power grid is "rigid." However, new power systems involve new energy sources and energy storage connected to the grid via power electronic converters. These devices themselves lack support capabilities, and some are located far from the main grid, forming a weak sending-end system, increasing the risk of system transient instability.

[0023] Based on this, embodiments of this disclosure provide an online control method for improving the transient stability of a weak-end system, such as... Figure 1 As shown, the specific steps may include S11 to S14.

[0024] Step S11: Determine the equivalent impedance of the weak-sending system at the current moment.

[0025] It should be noted that the weak-sending system in this embodiment refers to a power system where the grid strength is insufficient due to the connection of new energy power plants and grid-connected energy storage through the same grid connection point. In other words, the weak-sending system includes new energy power plants and grid-connected energy storage.

[0026] Additionally, it should be noted that the equivalent impedance of the weak transmitting end system at the current moment in this embodiment refers to the comprehensive impedance viewed from the grid connection point towards the weak transmitting end system at the current sampling moment. Z_thAn impedance equivalent to the system part other than the point of common coupling, which comprehensively reflects the electrical characteristics of the system at the point of common coupling, contains a resistance component R_th and a reactance component X_th .

[0027] In a possible implementation, the system can determine the equivalent impedance by using Thevenin theorem and update the equivalent impedance at the current time by using recursive least squares.

[0028] As shown in Figure 2 , the equivalent impedance at the current time is determined by using recursive least squares, which can specifically include the following steps S101 to S103.

[0029] Step S101, obtain the equivalent impedance of the weak sending end system at the previous time.

[0030] It should be noted that in the embodiments of the present disclosure, the equivalent impedance of the weak sending end system at the previous time refers to the comprehensive impedance of the weak sending end system from the point of common coupling obtained by the same or similar online estimation method at the time immediately before the current time, which is used as the initial value or the previous value of the recursive least squares algorithm, and provides basic data for updating the equivalent impedance at the current time. It can be understood that under the initial condition, the operator can set an iterative initial value according to experience.

[0031] By obtaining the equivalent impedance of the weak sending end system at the previous time, a historical reference value is provided for the iterative update of the recursive least squares, so as to ensure the continuity and accuracy of the algorithm. The system can retrieve the equivalent impedance data calculated and saved at the previous time through the storage module. In a possible implementation, the system can store the result in a specific database or cache after completing the equivalent impedance estimation each time, so as to quickly obtain the equivalent impedance at the previous time at the subsequent time.

[0032] Step S102, obtain the point of common coupling voltage and the point of common coupling current of the weak sending end system at the current time.

[0033] In a possible implementation, the system uses high-precision voltage and current measuring devices to collect the instantaneous values of the point of common coupling voltage and current at a high sampling frequency, and then processes the data to obtain the voltage and current phasor or effective value for the recursive least squares calculation.

[0034] By obtaining the point of common coupling voltage and the point of common coupling current of the weak sending end system at the current time, the measured electrical quantities at the current time are provided for the recursive least squares algorithm, which are used as the input data for updating the equivalent impedance.

[0035] Step S103: Based on the equivalent impedance of the previous moment, the grid connection point voltage and grid connection point current of the current moment, perform recursive least squares update to obtain the equivalent impedance of the current moment, so as to realize the online estimation of the equivalent impedance of the current moment.

[0036] It should be noted that, in the embodiments of this disclosure, recursive least squares update refers to an algorithm process that uses recursion to iteratively update the equivalent impedance based on historical estimates (equivalent impedance at the previous moment) and measured data at the current moment (grid connection point voltage and grid connection point current); online estimation refers to the ability to estimate the equivalent impedance in real time and continuously to adapt to the dynamic changes in the system's operating state.

[0037] In some embodiments of this disclosure, the formula for recursive least squares includes: In the formula, θ ( k (This refers to the current time) k The parameter estimates, including the current time. k The equivalent impedance, θ ( k -1) represents the previous time step. k -1 parameter estimates, including those from the previous time step. k The equivalent impedance of -1, K( k (This refers to the current time) k The gain matrix, [ y ( k ) - φ ( k ) * θ ( k-1 [] represents the current time. k The prediction error y ( k (This refers to the current time) k Grid connection point voltage V _ pcc ( k ), φ ( k ) * θ ( k-1 )for φ ( k (Using the current time) k regression vector φ ( k ) and the previous moment k -1 parameter estimate θ ( k -1) Predicted grid connection point voltage, φ ( k ) = [1, - I _ pcc (k )], I _ pcc k current time k of the point of common coupling.

[0038] In a possible implementation, the system can employ a recursive least square algorithm with a forgetting factor to enhance the weight of the latest data and improve the real-time performance and accuracy of the equivalent impedance estimation. In addition, it should be noted that when performing the recursive least square update, the convergence and stability of the algorithm also need to be considered to ensure that the equivalent impedance after each update can reasonably reflect the system state.

[0039] Through recursive iteration, the estimated value of the equivalent impedance is continuously corrected to accurately reflect the electrical characteristics of the weak sending end system at the current time, thereby providing accurate parameters for subsequent short circuit ratio calculation and output adjustment.

[0040] Step S12, based on the equivalent impedance at the current time, determining the short circuit ratio of the weak sending end system at the current time.

[0041] It should be noted that in the embodiments of the present disclosure, the short circuit ratio is an important indicator for measuring the strength of the system power grid.

[0042] In some embodiments of the present disclosure, based on the equivalent impedance at the current time, the short circuit ratio of the weak sending end system at the current time is determined, which can specifically include the following steps S201 to S204 as shown in Figure 3

[0043] Step S201, obtaining the rated voltage of the weak sending end system.

[0044] It should be noted that in the embodiments of the present disclosure, the rated voltage of the weak sending end system refers to the standard voltage value specified when the system is normally running. In a possible implementation, the system pre-stores the rated voltage of the weak sending end system in the parameter library, and directly reads it from the parameter library when needed. For example, in a specific embodiment, the system reads the rated voltage V_nom= 230e 3 V.

[0045] By obtaining the rated voltage of the weak sending end system, necessary voltage parameters are provided for subsequent calculation of short circuit capacity.

[0046] Step S202, based on the equivalent impedance at the current time and the rated voltage, determining the short circuit capacity of the weak sending end system at the current time.

[0047] ​​It should be noted that in the embodiments of the present disclosure, the short-circuit capacity refers to the size of the short-circuit power that the system can provide when the system has a short-circuit fault. In some embodiments of the present disclosure, the short-circuit capacity is the ratio of the square of the rated voltage to the equivalent impedance. For example, the short-circuit capacity , wherein, V nom| is the amplitude of the rated voltage, Z_th| is the amplitude of the equivalent impedance (the modulus of the resistance and the reactance).

[0048] In a possible implementation, the system can first convert the rated voltage into a per-unit value or other convenient form for calculation, and then calculate the short-circuit capacity in combination with the equivalent impedance.

[0049] Step S203, acquiring the output power of the new energy station at the current moment.

[0050] It should be noted that in the embodiments of the present disclosure, the output power of the new energy station at the current moment refers to the active power or apparent power delivered by the new energy station (such as a wind power station, a photovoltaic station, etc.) in the weak sending end system to the system at the current moment, which reflects the power generation output of the new energy station at the current moment.

[0051] The system can collect the output power data of the new energy station in real time through the monitoring system of the new energy station. In a possible implementation, the system interacts with the Supervisory Control and Data Acquisition (SCADA) of the new energy station to acquire the output power at the current moment.

[0052] By acquiring the output power of the new energy station at the current moment, the parameter of the output of the new energy station is provided for calculating the short-circuit ratio.

[0053] Step S204, determining the short-circuit ratio of the weak sending end system at the current moment based on the short-circuit capacity at the current moment and the output power of the new energy station at the current moment.

[0054] It should be noted that in the embodiments of the present disclosure, the short-circuit ratio refers to the ratio of the short-circuit capacity of the weak sending end system to the output power of the new energy station connected to the system, which is a key indicator for measuring the strength of the system and the matching degree of the output of the new energy station. For example, the short-circuit ratio , wherein, S_sc P wind is the short-circuit capacity,

[0055] By determining the short-circuit ratio of the weak sending end system at the current moment, it is judged whether the strength of the current system meets the requirements, which provides a basis for whether the output needs to be adjusted subsequently.​​​

[0056] In step S13, if the short-circuit ratio at the current moment is less than the preset threshold, the output adjustment amount of the new energy station at the next moment and the output adjustment amount of the grid-forming energy storage at the next moment are determined based on the equivalent impedance at the current moment.

[0057] It should be noted that in the embodiments of the present disclosure, the preset threshold is a short-circuit ratio value preset according to the operation requirements and transient stability standards of the weak sending end system, which is used to determine whether the system needs to adjust the output; the output adjustment amount of the new energy station refers to the power size (including direction) that needs to be adjusted by the new energy station on the basis of the original output; and the output adjustment amount of the grid-forming energy storage refers to the power size (including direction) that needs to be adjusted by the grid-forming energy storage on the basis of the original output. If the short-circuit ratio at the current moment is less than the preset threshold, it indicates that the system grid strength is insufficient, and the technical scheme of the present disclosure can enhance the system grid strength and improve the system transient stability by adjusting the output of the new energy station and the grid-forming energy storage.

[0058] In addition, it should be noted that when calculating the output adjustment amount, the output limit of the new energy station and the grid-forming energy storage also needs to be considered, such as the maximum and minimum output of the new energy station, the charge and discharge power limit of the grid-forming energy storage, and the like.

[0059] In some embodiments of the present disclosure, the preset threshold includes any value in the range of 2.0-3.0. For example, in a specific embodiment, the preset threshold is 2.0.

[0060] In some embodiments of the present disclosure, the output adjustment amount includes an output power adjustment amount; and the output adjustment amount of the new energy station at the next moment and the output adjustment amount of the grid-forming energy storage at the next moment are determined based on the equivalent impedance at the current moment, as shown in FIG. 3, specifically including the following steps S301-S304. Figure 4

[0061] In step S301, the rated voltage of the weak sending end system and the lower limit of the short-circuit ratio of the weak sending end system are obtained.

[0062] In some embodiments of the present disclosure, the lower limit of the short-circuit ratio includes any value in the range of 1.0-1.5.

[0063] In step S302, the target output power of the new energy station at the next moment is determined based on the equivalent impedance at the current moment, the rated voltage, and the lower limit of the short-circuit ratio.

[0064] It should be noted that in the embodiments of the present disclosure, the target output power of the new energy station at the next moment refers to the output power value that the new energy station should reach at the next operating moment immediately after the current moment, which is preset or calculated according to factors such as the transient stability demand of the weak sending end system and the current short-circuit ratio state.

[0065] ​In some embodiments of the present disclosure, the formula for determining the target output power of the new energy plant at the next time point comprises: , wherein, V nom is the rated voltage of the weak sending end system, Z_th is the equivalent impedance of the weak sending end system at the current time point, SCR_dn is the short-circuit ratio lower limit of the weak sending end system.

[0066] Step S303, obtain the output power of the new energy plant at the current time point, and determine the difference between the output power of the new energy plant at the current time point and the target output power of the new energy plant at the next time point as the output power adjustment amount of the new energy plant at the next time point.

[0067] It should be noted that in the embodiments of the present disclosure, the output power adjustment amount of the new energy plant at the next time point refers to the power size and direction (increase or decrease) required to transition the new energy plant from the current output power to the target output power at the next time point.

[0068] By determining the output power adjustment amount of the new energy plant, the output adjustment range of the new energy plant is further determined, which provides a basis for subsequent power compensation of the grid-forming energy storage.

[0069] Step S304, determine the output power adjustment amount of the grid-forming energy storage at the next time point based on the output power adjustment amount of the new energy plant at the next time point.

[0070] It should be noted that in the embodiments of the present disclosure, the output power adjustment amount of the grid-forming energy storage at the next time point refers to the output power size and direction required for the grid-forming energy storage to respond to the output adjustment of the new energy plant and maintain the power balance of the weak sending end system at the next operating time point immediately after the current time point.

[0071] Through the power compensation of the grid-forming energy storage, the influence of the output adjustment of the new energy plant on the system power balance is offset, and the system voltage and frequency fluctuations caused by the output change of the new energy plant are avoided, thereby ensuring the transient stability of the system.

[0072] ​It should be noted that in some embodiments of this disclosure, the output power adjustment of the grid-connected energy storage is equal in magnitude and opposite in direction to the output power adjustment of the renewable energy power station. This enables real-time power balance of the system; that is, the reduced output of the renewable energy power station is compensated by the grid-connected energy storage through discharge, and the increased output of the renewable energy power station is absorbed by the grid-connected energy storage through charging, ensuring that the total system output remains stable. In one possible implementation, the system directly calculates the output power adjustment of the grid-connected energy storage through the power balance equation, i.e., the output power adjustment of the grid-connected energy storage = - the output power adjustment of the renewable energy power station. Simultaneously, the calculation results need to be verified in conjunction with constraints such as the current state of charge (SOC) and charging / discharging power limits of the grid-connected energy storage to ensure that the adjustment is within the safe operating range of the grid-connected energy storage. Additionally, it should be noted that when the output power adjustment of the new energy power station is positive (i.e., increasing output), the output power adjustment of the grid-connected energy storage is negative (i.e., absorbing power for charging); when the output power adjustment of the new energy power station is negative (i.e., decreasing output), the output power adjustment of the grid-connected energy storage is positive (i.e., releasing power for discharging).

[0073] Step S14: Based on the output adjustment of new energy power plants and the output adjustment of grid-connected energy storage, online control is performed on the weak-sending system to improve the transient stability of the weak-sending system.

[0074] It should be noted that, in this embodiment of the disclosure, online control refers to the operation of adjusting the output of the renewable energy power plants and grid-connected energy storage in the weak-send system in real time based on the calculated output adjustment amount. The system converts the calculated output adjustment amount into control commands and sends them to the control modules of the renewable energy power plants and grid-connected energy storage respectively. The control modules adjust their respective outputs according to the commands.

[0075] In addition, it should be noted that when conducting online control, the real-time nature and accuracy of the control must also be considered to ensure that the adjusted output can respond in a timely and accurate manner, thereby effectively improving transient stability.

[0076] In this embodiment, the weak-sending system is controlled online based on the output adjustment of the new energy power station and the output adjustment of the grid-connected energy storage. By adjusting the output of the two, the electrical characteristics of the system are changed, thereby improving the transient stability of the weak-sending system.

[0077] The online regulation method for improving transient stability of a weak sending end system provided by the embodiments of the present disclosure calculates the equivalent impedance of the weak sending end online, calculates the short-circuit ratio in real time, and compares it with a preset threshold. Once the short-circuit ratio is lower than the preset threshold, the regulation mechanism is triggered immediately to adjust the output of the new energy station and the grid-forming energy storage. This evaluation method based on real-time data avoids the errors caused by fixed parameters or offline calculation in traditional methods, ensures the accuracy of risk identification, and effectively prevents system instability.

[0078] For the convenience of understanding, the online regulation method for improving transient stability of a weak sending end system provided by the embodiments of the present disclosure is explained and described as a whole in combination with the specific structure of the weak sending end system.

[0079] As shown in Figure 5 , in a possible implementation, the weak sending end system can include multiple thermal power generating units, a grid-following device (such as a wind power station, i.e., a new energy station), a grid-forming energy storage, and an alternating current system (i.e., an external power grid). Among them, the multiple thermal power generating units are connected to the alternating current system through their own transformers and line impedance 2; the grid-following device and the grid-forming energy storage are connected to the alternating current system through a booster transformer and line impedance 1. The grid-following device and the grid-forming energy storage have the same grid connection point, and in the figure I pcc For the grid connection point current, V pcc For the grid connection point voltage. The thermal power generating unit can provide stable active and reactive power support as a traditional power source; the grid-following device usually follows the grid voltage / frequency operation and does not actively provide voltage / frequency support, but relies on the stable operation conditions of the external power grid; the grid-forming energy storage has the ability to actively build grid voltage and frequency. That is, the core power grid structure of the weak sending end system includes traditional thermal power, grid-following new energy stations, and grid-forming energy storage. The thermal power generating unit provides basic inertia, the grid-following device (such as wind power) realizes new energy grid connection, and the grid-forming energy storage actively supports voltage / frequency in transient state to solve the problem of transient stability of the weak sending end system.

[0080] The online regulation method for improving transient stability of a weak sending end system provided by the embodiments of the present disclosure includes the following steps.

[0081] Step one: online calculation of system impedance using real-time measurement information.

[0082] The recursive least squares algorithm (Recursive Least Squares, RLS) is used to calculate the system impedance online, and the specific process is as follows: According to Kirchhoff's voltage law, there is the following relationship: (1), In the formula, _th : is the equivalent Thevenin voltage source of the power grid,Z_th Z is the equivalent impedance of the power grid, V_pcc V is the voltage measured at the grid-connection point of the new energy station, i.e. grid-connection point voltage, I_pcc I is the current measured at the grid-connection point of the new energy station, i.e. grid-connection point current.

[0083] Equation (1) can be rewritten as: (2), Let the output be: y ( k ) = Z(k) V _ pcc ( k ) = V(k) - Z(k) * I(k), the regression vector be: φ ( k ) = [1, - I _ pcc ( k )], and the parameter vector to be estimated be: θ = [ _th; Z_th]^T,^T represents matrix transposition. Equation (2) can be written as: (3), For each data measurement point k , the gain matrix L(k) is calculated: (4), In the equation, P ( k ) is the covariance matrix of the estimation error, is a forgetting factor, usually taking a value of 0.95~0.99, and^H represents conjugate transposition.

[0084] For each newly obtained measurement data, the parameter estimation θ ( k ) is updated: (5), In the equation, [ y ( k ) - φ ( k ) * θ ( k-1 )] is the prediction error at the current time.

[0085] The covariance matrix P ( k ) is updated: (6), In the equation, I is an identity matrix.

[0086] In the calculation process,θ ( 0 ) requires the operator to set the initial grid impedance value according to experience. P ( 0 ) is initialized as a large diagonal matrix δI , satisfying δ>10.

[0087] The convergence precision is set as E, which is preferably 0.02; when the algorithm satisfies the following condition after the mth iteration: (7), the current system impedance is obtained: (8), wherein, θ ( m ) is the second element of θ ( m ).

[0088] Step two: calculate the short-circuit ratio based on the system impedance and the output power of the new energy station.

[0089] The system short-circuit capacity S_sc is: (9), wherein, V_nom is the rated voltage of the system.

[0090] The short-circuit ratio SCR is: (10), wherein, P_wind is the output power of the new energy station.

[0091] Step three: if the short-circuit ratio is lower than the preset threshold, it means that there is a risk of instability between the new energy station and the system, and at this time, the output of the new energy station and the grid-forming energy storage is adjusted.

[0092] The lower limit of the short-circuit ratio is set as SCR_dn . The expected output of the new energy station P_pre is calculated by the following formula: (11), The output reduction of the new energy station is P_ctl : (12), At the same time, the output of the grid-forming energy storage is adjusted, and the increase is P_ctl .

[0093] In order to verify the beneficial effects of the online regulation method for improving the transient stability of the weak sending-end system provided by the embodiments of the present disclosure, the following simulation verification is performed.

[0094] Simulation verification was performed in MATLAB, with the rated voltage set to 230e. 3 V, a fault is set at 100ms. The control parameters of the online control algorithm are as follows: the preset threshold for the short-circuit ratio is set to 2.0, and the RLS forgetting factor is set. Set the RLS convergence accuracy to E = 0.02.

[0095] Simulations yielded the convergence state of the RLS algorithm as follows: Figure 6 As shown, the horizontal axis represents time (unit: ms), and the vertical axis represents the convergence indicator. Observation Figure 6 It can be seen that the algorithm does not converge for a period of time at the beginning. This is because when the fault occurs, the system impedance suddenly increases, affecting the control parameters in the algorithm. This means that historical data still has a large weight, which slows down the algorithm's response to mutations. Temporarily reducing the forgetting factor when a mutation is detected can help the algorithm converge faster.

[0096] After the RLS algorithm converges, as Figure 7 As shown, the power regulation mechanism begins to take effect, and the power of renewable energy decreases, meaning the output power of renewable energy power plants decreases. In order to maintain the overall output power unchanged, grid-connected energy storage needs to fill the power gap. After regulation, the sum of renewable energy power and grid-connected energy storage power is basically equivalent to the original renewable energy power.

[0097] As can be seen from equation (10), the short-circuit ratio is inversely proportional to the output power of the new energy source. Observation Figure 8 It can be seen that after adjustment, the short-circuit ratio increases, and the short-circuit ratio value is basically maintained at the short-circuit ratio threshold (i.e., the preset threshold).

[0098] In combination with the above Figure 6 to Figure 8 Simulation results show that when the short-circuit ratio is detected to be lower than a preset threshold, this disclosure achieves rapid power redistribution by reducing the output of new energy power plants (such as wind farms) and simultaneously increasing the output of grid-connected energy storage. This control method ensures the stability of the system's total output power and enhances the system's ability to resist disturbances by increasing the short-circuit ratio. After a fault occurs, the control system can quickly pull the system back from its extreme operating state to a safe area, significantly reducing the risk of transient instability.

[0099] Based on this, embodiments of this disclosure also provide an online control device for improving the transient stability of a weak-end system, such as... Figure 9 As shown, the online control device 100 may specifically include a first determining unit 110, a second determining unit 120, a third determining unit 130, and an online control unit 140.

[0100] The first determining unit 110 is used to determine the equivalent impedance of the weak-sending system at the current moment. The weak-sending system includes renewable energy power plants and grid-connected energy storage.

[0101] The second determining unit 120 is used to determine the short-circuit ratio of the weak sending end system at the current time based on the equivalent impedance at the current time.

[0102] The third determining unit 130 is used to determine the output adjustment amount of the new energy power station and the output adjustment amount of the grid-connected energy storage in the next moment based on the equivalent impedance at the current moment if the short-circuit ratio at the current moment is less than a preset threshold.

[0103] The online control unit is used to perform online control of the weak-supply system based on the output adjustment of the new energy power station and the output adjustment of the grid-connected energy storage, so as to improve the transient stability of the weak-supply system.

[0104] For details and benefits of the online control device for improving the transient stability of a weak-feeding-end system provided in the embodiments of this disclosure, please refer to the above description of the online control method for improving the transient stability of a weak-feeding-end system, which will not be repeated here.

[0105] This disclosure also provides an electronic device, comprising: a memory for storing at least one instruction; and a processor for calling the instruction stored in the memory to execute the online control method for improving the transient stability of a weak-end system in any of the above embodiments.

[0106] This disclosure also provides a computer-readable storage medium storing at least one executable instruction, which is loaded and executed by a processor to implement the online control method for improving the transient stability of a weak-end system in any of the above embodiments.

[0107] This disclosure also provides a computer program product, which includes computer program code. When the computer program code is run by a computer, it causes the computer to execute the online control method for improving the transient stability of the weak-end system in any of the above embodiments.

[0108] Those skilled in the art will understand that embodiments of this disclosure can be provided as methods, systems, or computer program products. Therefore, this disclosure can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this disclosure can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0109] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure One one or more flow or blocks Figure One means for functionally implementing the steps listed in the flowchart block or blocks.

[0110] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instructions which implement the function specified in the flowchart block or blocks. Figure One one or more flow or blocks Figure One means for functionally implementing the steps listed in the flowchart block or blocks.

[0111] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure One one or more flow or blocks Figure One means for functionally implementing the steps listed in the flowchart block or blocks.

[0112] In one typical configuration, the computing device includes one or more processors (CPUs), input / output interfaces, network interfaces, and memory.

[0113] The memory can include non-persistent memory and / or volatile memory, such as random access memory (RAM) and / or cache memory, for storing instructions and data used and / or generated by the computing device. The memory can also include non-volatile memory, such as read-only memory (ROM), electrically programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory, or nonvolatile random access memory (RAM) (e.g., fault tolerant RAM), for storing instructions and data used and / or generated by the computing device. The memory is an example of computer-readable media.

[0114] Computer-readable media includes permanent and non-permanent, movable and non-movable media that can be implemented by any method or technology to store information. The information can be computer-readable instructions, data structures, program modules or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transmission medium that can be used to store information accessible to a computing device. According to the definition herein, computer-readable media does not include transitory media such as modulated data signals and carriers.

[0115] It should also be noted that the "first", "second", and similar words used in the present disclosure do not represent any order, number or importance, but are only used to distinguish different parts. "Include" or "contain" and similar words mean that the elements before the word cover the elements listed after the word, and do not exclude the possibility of also covering other elements.

[0116] Although the operations in the embodiments of the present disclosure are described in a specific order in the accompanying drawings, it should not be understood as requiring the operations to be performed in the specific order or serial order shown, or requiring all the operations to be performed to obtain the desired results. In a specific environment, multitasking and parallel processing can be advantageous.

[0117] Finally, it should be noted that the above content is only used to illustrate the technical solutions of the present disclosure, and is not a limitation on the protection scope of the present disclosure. Simple modifications or equivalent replacements of the technical solutions of the present disclosure made by those skilled in the art do not deviate from the essence and scope of the technical solutions of the present disclosure.

Claims

1. An online control method for improving the transient stability of a weak-end system, characterized in that, include: Determine the equivalent impedance of the weak-sending system at the current moment; The weak-end transmission system includes new energy power stations and grid-connected energy storage; Based on the equivalent impedance at the current moment, determine the short-circuit ratio of the weak-sending end system at the current moment; If the short-circuit ratio at the current moment is less than a preset threshold, then based on the equivalent impedance at the current moment, the output adjustment amount of the new energy power station and the output adjustment amount of the grid-connected energy storage at the next moment are determined. Based on the output adjustment of the new energy power station and the output adjustment of the grid-connected energy storage, the weak-sending system is controlled online to improve the transient stability of the weak-sending system.

2. The online control method as described in claim 1, characterized in that, The output adjustment amount includes the output power adjustment amount; determining the output adjustment amount of the new energy power station and the output adjustment amount of the grid-connected energy storage at the next moment based on the equivalent impedance at the current moment includes: Obtain the rated voltage of the weak-feeding end system and the lower limit of the short-circuit ratio of the weak-feeding end system; Based on the equivalent impedance at the current moment, the rated voltage, and the lower limit of the short-circuit ratio, determine the target output power of the new energy power station at the next moment; The output power of the new energy power station at the current moment is obtained, and the difference between the output power of the new energy power station at the current moment and the target output power of the new energy power station at the next moment is determined as the output power adjustment amount of the new energy power station at the next moment. Based on the output power adjustment of the new energy power station at the next moment, the output power adjustment of the grid-connected energy storage at the next moment is determined; the output power adjustment of the grid-connected energy storage is equal in magnitude and opposite in direction to the output power adjustment of the new energy power station.

3. The online control method as described in claim 2, characterized in that, The formula for determining the target output power of the new energy power station at the next moment includes: ， In the formula, V _ nom The rated voltage for the weak-feeding end system. Z_th Let be the equivalent impedance of the weak-feeding system at the current moment. SCR_dn This is the lower limit of the short-circuit ratio for the weak-sending system.

4. The online control method as described in claim 2 or 3, characterized in that, The lower limit of the short-circuit ratio includes any value in the range of 1.0 to 1.

5.

5. The online control method as described in any one of claims 1-3, characterized in that, The equivalent impedance at the current moment is determined by recursive least squares. The method of determining the equivalent impedance at the current moment using recursive least squares includes: Obtain the equivalent impedance of the weak-sending system at the previous moment; Obtain the grid connection point voltage and grid connection point current of the weak transmitting end system at the current moment; Based on the equivalent impedance at the previous moment, the grid connection point voltage and grid connection point current at the current moment, a recursive least squares update is performed to obtain the equivalent impedance at the current moment, so as to realize the online estimation of the equivalent impedance at the current moment.

6. The online control method as described in claim 5, characterized in that, The formula for recursive least squares includes: ， In the formula, θ ( k (This refers to the current time) k The parameter estimates, including the current time. k The equivalent impedance, θ ( k -1) represents the previous time step. k -1 parameter estimates, including those from the previous time step. k The equivalent impedance of -1, K( k (This refers to the current time) k The gain matrix, [ y ( k ) - φ ( k ) * θ ( k-1 [] represents the current time. k The prediction error y ( k (This refers to the current time) k Grid connection point voltage V _ pcc ( k ), φ ( k ) * θ ( k-1 )for φ ( k (Using the current time) k regression vector φ ( k ) and the previous moment k -1 parameter estimate θ ( k -1) Predicted grid connection point voltage, φ ( k ) = [1, - I _ pcc ( k )], I _ pcc ( k Current moment k The grid connection point current.

7. The online control method according to any one of claims 1-3, characterized in that, Determining the short-circuit ratio of the weak-sending system at the current moment based on the equivalent impedance at the current moment includes: Obtain the rated voltage of the weak-feeding end system; Based on the equivalent impedance at the current moment and the rated voltage, determine the short-circuit capacity of the weak-sending system at the current moment; the short-circuit capacity is the ratio of the square of the rated voltage to the equivalent impedance; Obtain the output power of the new energy power station at the current moment; Based on the short-circuit capacity at the current moment and the output power of the new energy power station at the current moment, the short-circuit ratio of the weak transmission end system at the current moment is determined; the short-circuit ratio is the ratio of the short-circuit capacity to the output power of the new energy power station.

8. The online control method as described in claim 1, characterized in that, The preset threshold includes any value within the range of 2.0 to 3.

0.

9. An online control device for improving the transient stability of a weak-end system, characterized in that, include: The first determining unit is used to determine the equivalent impedance of the weak sending-end system at the current moment; The weak-end transmission system includes new energy power stations and grid-connected energy storage; The second determining unit is used to determine the short-circuit ratio of the weak transmitting end system at the current time based on the equivalent impedance at the current time. The third determining unit is used to determine the output adjustment amount of the new energy power station and the output adjustment amount of the grid-connected energy storage at the next moment based on the equivalent impedance at the current moment if the short-circuit ratio at the current moment is less than a preset threshold. The online control unit is used to perform online control of the weak-sending system based on the output adjustment of the new energy power station and the output adjustment of the grid-connected energy storage, so as to improve the transient stability of the weak-sending system.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores at least one executable instruction, which is loaded and executed by a processor to implement the online control method as described in any one of claims 1-8.

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