Fault state load shedding optimization control method and system considering source load fluctuation

Abstract

The present invention provides a fault-condition load shedding optimization control method and system that considers source-load fluctuations. The method models the power uncertainty of renewable energy output on the power grid's generation side and load-side fluctuations; calculates the power distribution characteristics and overload probability of transmission lines using stochastic power flows; analyzes the impact of disconnecting overloaded lines exceeding a set value on the system topology; calibrates line power safety constraints based on the obtained line power distribution characteristics; and, combined with the analysis results of the impact of disconnecting overloaded lines, performs load shedding operations on the power grid with the goal of minimizing load shedding. This invention overcomes the problem that existing load shedding strategies fail to account for power uncertainty factors on both the generation and load sides.

Description

Technical Field

[0001] The present invention belongs to the field of steady-state safety analysis of power grids, and relates to a fault state load shedding optimization control method and system taking source load fluctuation into consideration. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] With the development of the economy and technology, electricity has become an essential secondary energy source for people's production and daily lives, bringing endless convenience to them. Therefore, ensuring a stable and reliable supply of electricity has become one of the most important tasks of power systems. When a power grid suffers a fault and an emergency occurs, load shedding, as a crucial emergency control measure to ensure safe grid operation, can prevent system voltage collapse, prevent line power from exceeding limits, and maintain steady-state and transient stability.

[0004] With the continuous integration of diverse renewable energy sources and loads, the volatility of the power system's source and load sides is increasing. The increasing output and determinism of wind and photovoltaic power, as well as the increasing load, present new challenges to the safe operation of the power grid. When the power grid is in emergency operation, the output of renewable energy is generally considered uncontrollable and its role is often overlooked.

[0005] The inventors understand that while existing load shedding strategies can solve the problem of power overload on transmission lines in emergency situations, they also have certain drawbacks:

[0006] (1) In the load shedding strategy based on power flow calculation, the values ​​of each state variable are deterministic, that is, expected values. This makes it difficult to take into account the uncertainties on the power generation side and the load side, and cannot fully reflect their impact on the system.

[0007] (2) In traditional load shedding calculations, the grid structure used only excludes lines that have been disconnected, but does not consider the probability of disconnection of high-risk overload lines, thereby reducing the accuracy of load shedding and easily obtaining overly optimistic evaluation results. It is not suitable for power grid systems with a high proportion of new energy access.

[0008] (3) In the current safety constraints for load shedding, the line safety constraints use the rated power constraints, which does not take into account the fluctuating characteristics of the line power. This can easily lead to an excessively large safety constraint range, making the load shedding measures inaccurate and creating new safety hazards. Summary of the Invention

[0009] In order to solve the above problems, the present invention proposes a fault state load shedding optimization control method and system considering source-load fluctuations. The present invention can overcome the problem that the existing load shedding strategy cannot consider the power uncertainty factors on the generation side and the load side.

[0010] According to some embodiments, the present invention adopts the following technical solutions:

[0011] A method for optimizing load shedding control in a fault state taking into account source load fluctuations comprises the following steps:

[0012] S1. Modeling the power uncertainty of renewable energy output on the power grid generation side and load side fluctuations;

[0013] S2. Calculate the power distribution characteristics and overload probability of transmission lines through random power flow;

[0014] S3. Analyze the impact of disconnecting overloaded lines whose overload probability exceeds a set value on the system topology;

[0015] S4. Correct the line power safety constraint according to the line power distribution characteristics obtained in step S2, and perform grid load shedding operation with the goal of minimizing load shedding in combination with the overload line disconnection impact analysis result in step S3.

[0016] As an optional implementation, the specific process of step S1 includes: establishing a wind power output model, a load model and a photovoltaic output model.

[0017] As an optional implementation, the specific process of step S1 includes: analyzing the output characteristics of the doubly-fed wind turbines in the wind farm, combining the wind speed statistics of the Weil distribution, and determining the wind farm output model under a constant power factor;

[0018] Analyze the normal distribution characteristics of load power based on the accuracy characteristics of load forecasting and determine the power model of load fluctuation;

[0019] Analyze the Beta distribution characteristics of light intensity and determine the output model of the photovoltaic field based on the characteristics of photoelectric conversion.

[0020] As an optional implementation, the specific process of step S2 is:

[0021] The stochastic power flow calculation of the current state of the system is carried out by using the semi-invariant method combined with the Gram-Charlier series expansion method, and the expected value and variance of the transmission line power and the corresponding probability density function are obtained.

[0022] The overload probability of the current line power distribution is calculated based on the rated power value of the line.

[0023] As an optional implementation, the specific process of step S3 is:

[0024] Based on the line overload probability, transmission lines with outage probability exceeding the set value are selected, and topology analysis is performed to determine whether the system should be decoupled.

[0025] As an optional implementation, in the correction of the line power security constraint in step S4, the mathematical model is: |P l | <T max -Aσ;

[0026] Among them, T max is the line rated power, σ is the standard deviation of line power fluctuation, and A is the safety factor.

[0027] As an optional implementation, in step S4, with the minimum load shedding as the goal, a load shedding mathematical model based on DC power flow is established as follows:

[0028]

[0029] Among them, P out,max The transmission line with the highest overload rate has the possibility of line disconnection. L is the number of load nodes, r i is the load removal amount of each load node.

[0030] As an optional implementation, the specific process of performing the grid load shedding operation with the goal of minimizing load shedding in step S4 is as follows: if the system is decoupled, the load shedding calculation is performed on each subsystem based on the result of the topology analysis in step S3, and finally the load shedding amount of the entire system is calculated.

[0031] A load shedding optimization control system in a fault state taking into account source load fluctuations, comprising:

[0032] a model building module configured to model power uncertainty of renewable energy output on the power grid generation side and fluctuations on the load side;

[0033] a calculation module configured to calculate power distribution characteristics and overload probability of a transmission line through random power flow;

[0034] An analysis module is configured to analyze the impact of disconnection of an overload line whose overload probability exceeds a set value on a system topology;

[0035] The optimization module is configured to correct the line power safety constraint according to the obtained line power distribution characteristics, and perform power grid load shedding operation with the goal of minimizing load shedding in combination with the analysis results of the impact of overload line disconnection.

[0036] A computer-readable storage medium stores a plurality of instructions, wherein the instructions are suitable for being loaded by a processor of a terminal device and executing the steps of a fault state load shedding optimization control method considering source load fluctuation.

[0037] A terminal device includes a processor and a computer-readable storage medium, wherein the processor is used to implement various instructions; the computer-readable storage medium is used to store multiple instructions, wherein the instructions are suitable for being loaded by the processor and executing the steps of a fault state load shedding optimization control method considering source load fluctuations.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The fault state load shedding optimization control method considering source-load fluctuations provided by the present invention fully considers the uncertainty of new energy and the load side, uses random power flow to analyze the distribution characteristics of transmission line power, uses topology analysis to study the impact of possible system outages, corrects the system's line rated power based on uncertain factors, and implements load shedding operation with the minimum load shedding amount as the optimization goal. Therefore, the method of the present invention is highly reliable, scientific and reasonable, and can effectively improve the stability of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0041] Figure 1 It is a flow chart of the control method of the present invention. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0043] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0044] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0045] The present invention uses the calculation process as a framework and combines the drawings of the invention book to introduce in detail the technical solution provided by the present invention, among which the load shedding optimization process in the fault state considering the source load fluctuation is introduced as the focus.

[0046] A fault state load shedding optimization control method considering source load fluctuation, such as Figure 1As shown, the following steps are included:

[0047] (1) Model the power uncertainty of renewable energy output on the power grid generation side and the power fluctuation on the load side.

[0048] First, model the uncertainty of the power system;

[0049] The wind power output model is:

[0050]

[0051] Where: v i is the cut-in wind speed; v r is the rated wind speed; v0 is the cut-out wind speed; P r is the rated active power of the fan; k1=P r / (v r -v i ); k2=-P r v i / (v r -v i ).

[0052] The load model is:

[0053]

[0054] Where: P L is the load active power, is the expected value of load active power; is the standard deviation of the load active power.

[0055] The photovoltaic output model is:

[0056] P S =r*A*η

[0057] in:

[0058]

[0059] Where: α and β are shape parameters, which can be obtained from the mean and variance of solar radiation in a short period of time; Γ is the Gamma function; r, r max is the actual irradiation intensity and maximum irradiation intensity in a short period of time, A is the total area of ​​the photovoltaic panel; η is the photoelectric conversion efficiency.

[0060] (2) Calculate the power distribution and overload probability of each transmission line:

[0061] In the present invention, the method of semi-invariant combined with Gram-Charlier series expansion can be used to perform random power flow calculation on the current state of the system to obtain the expected value and variance of the transmission line power and the corresponding probability density function;

[0062] The overload probability of the current line power distribution is calculated based on the rated power value of the line.

[0063] In this embodiment, the power distribution of the transmission line is:

[0064]

[0065] Where: represents the probability density function of the standard normal distribution, and H is the Emilian polynomial.

[0066] The line overload probability is:

[0067]

[0068] Where: P out is the line overload rate; T max is the rated capacity of the line; P l is the line active power.

[0069] (3) Minimum load shedding model and line rated power correction:

[0070] Objective function:

[0071]

[0072] Where: n L is the number of load nodes; r i is the load shedding of each load node, P out，max This is the line with the highest overload probability and there is a possibility of line disconnection.

[0073] Constraints:

[0074]

[0075] P S +P G +r+P W -P L =Bθ

[0076] P l =B f θ

[0077]

[0078] P l <T max

[0079]

[0080] Where: n G is the number of generators; Output power for the generator; n W is the number of wind farms; is the average output of wind power; n S is the number of photovoltaic power stations; is the average photovoltaic output; is the load power; B is the node admittance matrix; θ is the node voltage phase angle; P l is the branch active power; B f is the branch-node association matrix; They are the upper and lower limits of active power output of conventional units respectively.

[0081] Line power fluctuations are caused by wind, solar, and load fluctuations. When the variable models are determined, the line fluctuation value is a fixed value and cannot be controlled. Line power fluctuations within a small range can be considered to be approximately normally distributed, with a standard deviation P l，σ Therefore, in the process of load shedding optimization, the difference between the expected value of the line active power and the line rated power needs to be adjusted according to the standard deviation of the line active power flow:

[0082] |P l | <T max -Aσ

[0083] A is a coefficient indicating the magnitude of the line overload rate, representing the line capacity that should be reserved. A is a safety factor. Based on the "3σ" principle of the normal distribution curve, A can be selected based on actual needs.

[0084] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0085] The present invention also provides the following product embodiments:

[0086] A load shedding optimization control system in a fault state taking into account source load fluctuations, comprising:

[0087] a model building module configured to model power uncertainty of renewable energy output on the power grid generation side and fluctuations on the load side;

[0088] a calculation module configured to calculate power distribution characteristics and overload probability of a transmission line through random power flow;

[0089] An analysis module is configured to analyze the impact of disconnection of an overload line whose overload probability exceeds a set value on a system topology;

[0090] The optimization module is configured to correct the line power safety constraint according to the obtained line power distribution characteristics, and perform power grid load shedding operation with the goal of minimizing load shedding in combination with the analysis results of the impact of overload line disconnection.

[0091] A computer-readable storage medium stores a plurality of instructions, wherein the instructions are suitable for being loaded by a processor of a terminal device and executing the steps of a fault state load shedding optimization control method considering source load fluctuation.

[0092] A terminal device includes a processor and a computer-readable storage medium, wherein the processor is used to implement various instructions; the computer-readable storage medium is used to store multiple instructions, wherein the instructions are suitable for being loaded by the processor and executing the steps of a fault state load shedding optimization control method considering source load fluctuations.

[0093] It will be understood by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0094] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0095] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0096] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1A step that specifies a function in one or more boxes.

[0097] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

[0098] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. A method for optimizing load shedding control in a fault state taking into account source load fluctuations, characterized by: The following steps are involved: S1. Model the power uncertainty of renewable energy output on the power grid generation side and load side fluctuations; the wind power output model is: Where: is the cut-in wind speed; is the rated wind speed; To cut out wind speed; is the rated active power of the wind turbine; ; ; The load model is: Where: is the load active power, is the expected value of load active power; is the standard deviation of load active power; The photovoltaic output model is: in: Where: is the shape parameter, which can be obtained from the mean and variance of solar radiation in a short period of time; is the Gamma function; is the actual irradiation intensity and maximum irradiation intensity in a short period of time, is the total area of ​​photovoltaic panels; is the photoelectric conversion efficiency; S2. Calculate the power distribution characteristics and overload probability of the transmission line through random power flow. The power distribution of the transmission line is: Where: , represents the probability density function of the standard normal distribution, H is the Emilian polynomial; S3. Analyze the impact of disconnecting overloaded lines whose overload probability exceeds a set value on the system topology; S4. Correct the line power safety constraint according to the line power distribution characteristics obtained in step S2, and perform grid load shedding operation with the goal of minimizing load shedding in combination with the overload line disconnection impact analysis result in step S3.

2. The method for optimizing load shedding control in a fault state considering source load fluctuation according to claim 1, wherein: The specific process of step S1 includes: analyzing the output characteristics of the doubly-fed wind turbines in the wind farm, combining the wind speed statistics of the Will distribution, and determining the wind farm output model under a constant power factor; Analyze the normal distribution characteristics of load power based on the accuracy characteristics of load forecasting and determine the power model of load fluctuation; Analyze the Beta distribution characteristics of light intensity and determine the output model of the photovoltaic field based on the characteristics of photoelectric conversion.

3. The method for optimizing load shedding control in a fault state considering source load fluctuation according to claim 1, wherein: The specific process of step S2 is: The stochastic power flow calculation of the current state of the system is carried out by using the semi-invariant method combined with the Gram-Charlier series expansion method, and the expected value and variance of the transmission line power and the corresponding probability density function are obtained. The overload probability of the current line power distribution is calculated based on the rated power value of the line.

4. The method for optimizing load shedding control in a fault state considering source load fluctuation according to claim 1, wherein: The specific process of step S3 is: Based on the line overload probability, transmission lines with outage probability exceeding the set value are selected, and topology analysis is performed to determine whether the system should be decoupled.

5. The method for optimizing load shedding control in a fault state considering source load fluctuation according to claim 1, wherein: The mathematical model for correcting the line power security constraint in step S4 is: ; in, is the line rated power, is the standard deviation of line power fluctuation, is the safety factor.

6. The method for optimizing load shedding control in a fault state considering source load fluctuation according to claim 1, wherein: In step S4, the load shedding mathematical model based on DC power flow is established with the minimum load shedding as the goal: in, The transmission line with the highest overload rate has the possibility of line disconnection. is the number of load nodes, is the load removal amount of each load node.

7. The method for optimizing load shedding control in a fault state considering source load fluctuation according to claim 1, wherein: The specific process of performing the load shedding operation for the power grid with the goal of minimizing load shedding in step S4 is as follows: if the system is decoupled, the load shedding calculation is performed on each subsystem according to the result of the topology analysis in step S3, and finally the load shedding amount of the entire system is calculated.

8. A load shedding optimization control system for fault conditions taking into account source load fluctuations, characterized by: include: The model building module is configured to model the power uncertainty of renewable energy output on the power grid generation side and load side fluctuations; the wind power output model is: Where: is the cut-in wind speed; is the rated wind speed; To cut out wind speed; is the rated active power of the wind turbine; ; ; The load model is: Where: is the load active power, is the expected value of load active power; is the standard deviation of load active power; The photovoltaic output model is: in: Where: is the shape parameter, which can be obtained from the mean and variance of solar radiation in a short period of time; is the Gamma function; is the actual irradiation intensity and maximum irradiation intensity in a short period of time, is the total area of ​​photovoltaic panels; is the photoelectric conversion efficiency; The calculation module is configured to calculate the power distribution characteristics and overload probability of the transmission line through random power flow; the power distribution of the transmission line is: Where: , represents the probability density function of the standard normal distribution, H is the Emilian polynomial; An analysis module is configured to analyze the impact of disconnection of an overload line whose overload probability exceeds a set value on a system topology; The optimization module is configured to correct the line power safety constraint according to the obtained line power distribution characteristics, and perform power grid load shedding operation with the goal of minimizing load shedding in combination with the analysis results of the impact of overload line disconnection.

9. A computer-readable storage medium, characterized in that: There are multiple instructions, which are suitable for being loaded by a processor of a terminal device and executing the steps of a fault state load shedding optimization control method considering source load fluctuation according to any one of claims 1-7.

10. A terminal device, characterized in that: It includes a processor and a computer-readable storage medium, the processor is used to implement each instruction; the computer-readable storage medium is used to store multiple instructions, and the instructions are suitable for being loaded by the processor and executing the steps of a fault state load shedding optimization control method considering source load fluctuations according to any one of claims 1-7.

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