A method for determining transient stability of power systems based on response relationship curves

Abstract

To provide a method for simply and quickly recognizing the transient power angle stabilization of a power system.SOLUTION: A method includes steps of establishing an association relation between a power generator current and an angular frequency, analyzing characteristics of a relation curve between the power generator current and the angular frequency, and presenting a determination criterion of power system transient power angle stabilization based on the relation curve between the power generator current and the angular frequency. The present invention has advantages that: a transient power angle stabilization attitude of the power system can be accurately and quickly recognized; calculation is simple; there is no influence of changes in a network structure, parameters, and a system operation mode; requirements for a real-time property of a transient stabilization determination are easily satisfied; and applications for engineering are easy.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the field of power system transient stability identification technology, and more particularly to a power system transient stability determination method based on response relationship curves. [Background technology]

[0002] With the widespread installation of synchrophasor measurement devices on China's power grid and the widespread deployment of wide-area measurement systems, online real-time monitoring of power grid dynamics has become a reality, which is of great significance for transient stability analysis and its emergency control. Response-information-based transient stability analysis and control rely on real-time measurement of response data and are not affected by the network structure, system parameters, and models during operation. This reduces the reliance on simulation models and pre-determined operating modes for transient stability assessment, helping to achieve "real-time decision-making and real-time control," and is expected to improve the accuracy of stability assessment results and the adaptability of emergency control strategies.

[0003] Generator response information, such as angular frequency and port current, contains important characteristics that can reflect the transient stability level of a power system. To overcome these problems, traditional transient stability assessment methods are heavily affected by changes in network structure and operating mode, are difficult to solve, require high computational effort, and struggle to meet real-time transient stability assessment requirements. To address these issues, we develop a power system transient stability assessment method based on response relationship curves. We measure generator port current and angular frequency in real time after a power system experiences a large disturbance. Through theoretical derivation, we explore the relationship between the two response electrical quantities from a mechanistic perspective and establish a functional relationship between generator current and angular frequency. Based on the current-angular frequency relationship, we plot the current-angular frequency relationship curve and analyze its characteristics to extract key features that distinguish between transient power angular stability and transient power angular instability. The key features of the relationship curve between the current and angular frequency of the system during stability and instability can be used to determine the transient stability state of the power system, and a criterion for determining the transient power angle stability and instability of the power system based on the relationship curve between the current and angular frequency can be established, so that the transient power angle stability of the power system can be accurately and quickly determined. Summary of the Invention [Problem to be solved by the invention]

[0004] The purpose of this invention is to propose a simple and fast method for identifying the transient power angular stability of a power system, avoiding the problems faced by traditional transient stability analysis methods, such as the high computational complexity, the severe impact of changes in network structure, parameters, and system operation mode, and the difficulty of meeting the real-time requirements for transient stability identification. By deeply exploring and establishing the correlation between generator current and angular frequency and introducing measurable and simple electrical quantities into power system transient stability analysis in the form of a relationship curve, a power system transient stability identification method based on the response relationship curve is established. This method can be applied to both traditional and new energy grid-connected power systems, ensuring and improving the transient stability of power systems. [Means for solving the problem]

[0005] To achieve the above objectives, the specific technical solution of the power system transient stability determination method based on the response relationship curve of the present invention is as follows:

[0006] 1) Establishing the relationship between generator current and angular frequency

[0007] In the classical second-order model of a single-machine infinite bus system, the equation of motion of the generator rotor is given by:

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[0008] Based on the equation of motion of the generator rotor, a theoretical derivation is made, the amount of current is introduced into the equation of motion of the rotor, the relationship between the generator current and the angular frequency is explored, and the generator current is simply processed, and the generator current

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[0009] As can be seen from equation (1), the relationship between the angular frequency deviation and the electromagnetic power of the generator is as follows:

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[0010] If the angular frequency deviation of the generator at the initial point of the fault is Δω=0 and the change in the mechanical output of the generator is ignored,

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[0011] Substituting equation (2) into equation (7), we obtain the correlation between current and angular frequency deviation:

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[0012] Since the current and angular frequency change in real time during the transient process of the generator, in order to explore the transient stability information contained in the current and angular frequency after the system is subjected to a large disturbance, and to obtain the real-time change rules of the current and angular frequency, it is necessary to simply process the angular frequency deviation. As can be seen from equation (9), since the term with the rated angular frequency ω0 is 0, the change rate of the angular frequency deviation can be expressed as the change rate of the angular frequency itself,

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[0013] This establishes not only the correlation between the generator current and the angular frequency deviation, but also the correlation between the current and the rate of change of the angular frequency. From the analysis of the formula, the change trend of the angular frequency is related to the sign of the current difference.

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[0014] 2) Characteristic analysis of the relationship curve between generator current and angular frequency

[0015] Generator response information during transient processes typically contains a wealth of transient stability information and can reflect the transient stability of a power system after a large disturbance. Wide-area measurement techniques are used to extract real-time data on the generator current and angular frequency in the system, and a current-angular frequency relationship curve is plotted. When the system is stable, the relationship curve exhibits a "convergence" behavior; when the system becomes unstable, the relationship curve exhibits a "divergence" behavior. This indicates that the relationship curve is closely related to system transient stability and contains important information that indicates whether the power system is stable or unstable. Further analysis shows that, whether the system is stable or unstable, the relationship curve exhibits an angular frequency inflection point within a relatively short period of time. During this period, the angular frequency change first decreases, then increases. After passing this angular frequency inflection point, the relationship curve gradually exhibits convergence and divergence characteristics. At the same time, the current near the inflection point of this angular frequency always shows a clear difference between stable and unstable states; that is, the current near the inflection point of the angular frequency continues to decrease when the system is stable, and the current near the inflection point of the angular frequency continues to increase when the system is unstable.

[0016] Combined with generator power angle characteristic curve analysis, near the stable equilibrium point

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[0017] The significant difference between the current and angular frequency relationship curve when the system is stable and unstable is used to determine the transient stability state of the power system, and the process of determining the transient power angular stability of the power system is simplified to the process of monitoring and identifying the important features of stability and instability of the relationship curve.

[0018] 3) Proposal of criteria for determining transient power angular stability of power systems based on the relationship curve between generator current and angular frequency

[0019] By identifying the key features of system stability and instability in the relationship curve between generator current and angular frequency, we can quickly locate the inflection points of angular frequency, calculate the current change rate near the inflection points of angular frequency, and determine the change trend of the current near the inflection points of angular frequency from the plus or minus sign. We can then establish a criterion for judging the transient power angular stability and instability of the power system based on the relationship curve between generator current and angular frequency: i) System stability

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[0020] The power system transient stability determination method based on response relationship curves of the present invention has the following advantages: This method uses real-time measured generator current and angular frequency as key electrical quantities for transient stability analysis, establishes the correlation between the two electrical quantities through theoretical derivation, plots a current-angular frequency relationship curve to intuitively and clearly reflect the power system transient stability state, and establishes a power system transient power angle stability determination criterion based on the current-angular frequency relationship curve. This method avoids the problems faced by traditional transient stability analysis methods, such as high computational complexity, significant influences from changes in network structure, parameters, and system operating mode, and difficulty in meeting the real-time requirements for transient stability determination. It can accurately and quickly identify the power system transient power angle stability state and ensure the safe and stable operation of the power system. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic diagram of a classical quadratic model single-machine infinite bus system. [Figure 2] The relationship curve of current and angular frequency is shown under the operating condition of a single-machine infinite bus system with fault cleared in 0.15s. [Figure 3] The relationship curve of current and angular frequency is shown under the operating condition of single-machine infinite bus system after fault removal in 0.16s. DETAILED DESCRIPTION OF THE INVENTION

[0022] In order to better understand the purpose, configuration and function of the present invention, the transient stability determination method for a power system based on a response relationship curve of the present invention will be described in more detail below with reference to the accompanying drawings.

[0023] The power system transient stability determination method based on the response relationship curve includes the following steps.

[0024] 1) Establishing the relationship between generator current and angular frequency

[0025] In the classical second-order model of a single-machine infinite bus system, the equation of motion of the generator rotor is given by:

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[0026] Based on the equation of motion of the generator rotor, a theoretical derivation is made, the amount of current is introduced into the equation of motion of the rotor, the relationship between the generator current and the angular frequency is explored, and the generator current is simply processed, and the generator current

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[0027] As can be seen from equation (1), the relationship between the angular frequency deviation and the electromagnetic power of the generator is as follows:

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[0028] From equation (5) we obtain the general solution for Δω:

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[0029] If the angular frequency deviation of the generator at the initial point of the fault is Δω=0 and the change in the mechanical output of the generator is ignored,

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[0030] Substituting equation (2) into equation (7), we obtain the correlation between current and angular frequency deviation:

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[0031] Since the current and angular frequency change in real time during the transient process of the generator, in order to explore the transient stability information contained in the current and angular frequency after the system is subjected to a large disturbance, and to obtain the real-time change rules of the current and angular frequency, it is necessary to simply process the angular frequency deviation. As can be seen from equation (9), since the term with the rated angular frequency ω0 is 0, the change rate of the angular frequency deviation can be expressed as the change rate of the angular frequency itself,

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[0032] This establishes not only the correlation between the generator current and the angular frequency deviation, but also the correlation between the current and the rate of change of the angular frequency. From the analysis of the formula, the change trend of the angular frequency is related to the sign of the current difference.

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[0033] 2) Characteristic analysis of the relationship curve between generator current and angular frequency

[0034] Generator response information during transient processes typically contains a wealth of transient stability information and can reflect the transient stability of a power system after a large disturbance. Wide-area measurement techniques are used to extract real-time data on the generator current and angular frequency in the system, and a current-angular frequency relationship curve is plotted. When the system is stable, the relationship curve exhibits a "convergence" behavior; when the system becomes unstable, the relationship curve exhibits a "divergence" behavior. This indicates that the relationship curve is closely related to system transient stability and contains important information that indicates whether the power system is stable or unstable. Further analysis shows that, whether the system is stable or unstable, the relationship curve exhibits an angular frequency inflection point within a relatively short period of time. During this period, the angular frequency change first decreases, then increases. After passing this angular frequency inflection point, the relationship curve gradually exhibits convergence and divergence characteristics. At the same time, the current near the inflection point of this angular frequency always shows a clear difference between stable and unstable states; that is, the current near the inflection point of the angular frequency continues to decrease when the system is stable, and the current near the inflection point of the angular frequency continues to increase when the system is unstable.

[0035] Combined with generator power angle characteristic curve analysis, near the stable equilibrium point

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[0036] The significant difference between the current and angular frequency relationship curve when the system is stable and unstable is used to determine the transient stability state of the power system, and the process of determining the transient power angular stability of the power system is simplified to the process of monitoring and identifying the important features of stability and instability of the relationship curve.

[0037] 3) Proposal of criteria for determining transient power angular stability of power systems based on the relationship curve between generator current and angular frequency

[0038] By identifying the key features of system stability and instability in the relationship curve between generator current and angular frequency, we can quickly locate the inflection points of angular frequency, calculate the current change rate near the inflection points of angular frequency, and determine the change trend of the current near the inflection points of angular frequency from the plus or minus sign. We can then establish a criterion for judging the transient power angular stability and instability of the power system based on the relationship curve between generator current and angular frequency: i) System stability

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[0039] Examples: To verify the effectiveness of this transient power angle stability determination method, we constructed a classical second-order model single-machine infinite bus system in the Power System Analysis Software Package (PSASP), as shown in Figure 1. A three-phase short-circuit fault was placed on one of the system's dual AC circuits, with the fault location at 50% of the line. The fault was accessed at 0 seconds and different fault severity levels were simulated by adjusting the fault clearing time. The system was cleared at 0.15 seconds and 0.16 seconds, respectively. When the fault was cleared at 0.15 seconds, the system was stable, but when the fault was cleared at 0.16 seconds, the system was unstable.

[0040] A wide-area measurement system was used to measure the current and angular frequency of the system's generator port in real time under two operating conditions, and the relationship curves between current and angular frequency after a fault were plotted under stable and unstable operating conditions, respectively, as shown in Figures 2 and 3. The analysis was performed using the newly developed power system transient power angle stability judgment method, which first quickly located the angular frequency inflection point on the relationship curve, and determined that the angular frequency first decreased and then increased. Next, the rate of change of current near the angular frequency inflection point was calculated. Finally, the newly developed transient power angle stability and instability judgment criterion was used to judge the relationship curves between current and angular frequency under the two operating conditions and determine whether the system was stable.

[0041] In the relationship curve between current and angular frequency shown in Figure 2, the current continues to decrease near the inflection point of the angular frequency, and the stability criteria indicate that the system is stable under the operating conditions corresponding to Figure 2. In the relationship curve between current and angular frequency shown in Figure 3, the current continues to increase near the inflection point of the angular frequency, and as can be seen from the instability criteria, the system is unstable under the operating conditions corresponding to Figure 3, verifying the effectiveness of the power system transient stability determination method based on the response relationship curve of the present invention.

[0042] Although the present invention will be described with reference to several embodiments, those skilled in the art will recognize that various modifications and equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the present invention. Furthermore, these features and embodiments may be modified, under the teachings of the present invention, to adapt to particular situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the appended claims are within the scope of the present invention.

Claims

1. It includes the following steps: Step 1: Establishing the relationship between generator current and angular frequency; In the classical second-order model of a single-machine infinite bus system, the equation of motion of the generator rotor is given by: [Equation 1] is expressed as In the formula, Δω is the angular frequency deviation, δ is the power angle, M is the inertia coefficient, and P ｍ is the mechanical power of the generator, and P ｅ is the electromagnetic power of the generator, Generator Current [Equation 2] The load current [Equation 3] and additional current after the fault [Equation 4] It is considered to be composed of two parts: [Equation 5] 、 Electromagnetic power, expressed as a current, is [Equation 6] 、 [Equation 7] and In the formula, Q ｅ is the reactive power of the generator, and P ０ is the electromagnetic power during normal operation, j is the imaginary unit of a complex number, and real means taking the real part. [Equation 8] and [Equation 9] are the potential vector and amplitude in the generator, respectively, [Equation 10] teeth [0011] and [0012] is the angular difference between The correlation equation between current and angular frequency deviation is: [0013] and The rate of change of the angular frequency deviation is expressed as the rate of change of the angular frequency itself, [0014] 、 The relationship between current and rate of change of angular frequency is: [Equation 15] and Step S2: Characteristic analysis of the relationship curve between generator current and angular frequency; The current throughout the process continues to decrease as the angular frequency changes. The current in the whole process continues to increase with the change of angular frequency, Step S3: Submitting a criterion for judging the transient power angle stability of the power system based on the relationship curve between generator current and angular frequency; A method for determining transient stability of a power system based on a response relationship curve, characterized by quickly locating an inflection point of angular frequency by identifying important features of system stability and instability in the relationship curve between generator current and angular frequency, calculating the current change rate near the inflection point of angular frequency, and determining the change trend of the current near the inflection point of angular frequency from the plus or minus sign.

2. In step S2, Near the stable equilibrium point [0016] As the angular frequency decreases, [Equation 17] 、 [Equation 18] There are As the angular frequency increases after passing through the inflection point of the angular frequency, [Equation 19] 、 [Equation 20] There are Near the unstable equilibrium point [0000] As the angular frequency decreases, [Equation 22] 、 [Equation 23] There are As the angular frequency increases after passing through the inflection point of the angular frequency, [0000] 、 [Equation 25] 2. The method for determining transient stability of a power system based on a response relationship curve according to claim 1, wherein:

3. Step S3 i) system stability; [Equation 26] and, ii) system instability; [0000] and 2. The method for determining transient stability of a power system based on a response relationship curve according to claim 1, wherein in the formula, the angular frequency measured at time t is ω(t), the angular frequency measured at time t-τ is ω(t-τ), and the angular frequency measured at time t+τ is ω(t+τ).

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