Power system transient stabilization determination method based on response relation curve

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 belongs to the field of power system transient stability identification technology, and particularly relates to a method for judging the transient stability of a power system based on a response relationship curve.

Background Art

[0002] With the widespread installation of synchronous phasor measurement devices in the Chinese power grid and the extensive deployment of wide-area measurement systems, it has become practical to monitor the dynamics of the power grid online and in real time, which is of great significance for transient stability analysis and its emergency control. Transient stability analysis and control based on response information rely on real-time measurement of response data, are not affected by the network structure, system parameters and models during operation, can reduce the dependence on the simulation model and pre-assumed operation mode for transient stability discrimination, and help to realize "real-time decision-making and real-time control", and it is expected to improve the accuracy of stability judgment results and the adaptability of emergency control strategies.

[0003] The response information of the generator, such as angular frequency and port current, contains important characteristic information that can reflect the transient stability level of the power system. Since the conventional transient stability discrimination method is greatly affected by changes in network structure and operation mode, it is difficult to solve or has a large computational amount, and it is difficult to meet the requirement of real-time transient stability discrimination. To overcome these problems, a method for discriminating the transient stability of a power system based on the response relationship curve is constructed. The port current and angular frequency of the generator after the power system is subjected to a large disturbance are measured in real time. Through theoretical derivation, the relationship between the two response electrical quantities is explored from the mechanism, and the functional relationship between the generator current and angular frequency is established. Based on the relationship between current and angular frequency, a relationship curve of current and angular frequency is plotted, the characteristics of the relationship curve are analyzed, and the important characteristics of the difference between transient power angle stability and transient power angle instability are extracted from it. Using the important characteristics of the relationship curves of the system current and angular frequency during stable and unstable states, the transient stability trend of the power system is discriminated, and the criteria for judging the transient power angle stability and instability of the power system based on the relationship curve of current and angular frequency are constructed, so that the transient power angle stability of the power system can be accurately and quickly discriminated.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The object of the present invention is to propose a method for simply and quickly identifying the transient power angle stability of a power system, avoiding problems such as the large computational amount faced by the conventional transient stability analysis method, the profound influence of changes in network structure, parameters and system operation mode, and the difficulty in meeting the requirement of real-time transient stability discrimination. By deeply exploring and establishing the relationship between the generator current and angular frequency, and introducing measurable and simple electrical quantities in the form of a relationship curve into the transient stability analysis of the power system, a method for discriminating the transient stability of the power system based on the response relationship curve is constructed. This method can be applied to traditional and new energy grid-connected power systems, and can guarantee and improve the transient stability of the power system.

Means for Solving the Problems

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

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

[0007] In a classical single-machine infinite-bus system with a second-order model, without considering damping, the motion equation of the generator rotor is

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[0008] Based on the motion equation of the generator rotor, theoretical derivation is carried out, the current quantity is introduced into the motion equation of the rotor, the relationship between the generator current and the angular frequency is explored, 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

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[0010] At the initial stage of the fault, the angular frequency deviation Δω of the generator is 0. Ignoring the change in the mechanical output of the generator, it is always

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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 equation, 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] The response information of a generator in a transient process usually contains rich transient stability information and can reflect the transient stability situation after the power system has suffered a major disturbance. Wide-area measurement technology is used to extract the real-time data of generator current and angular frequency in the system, and plot the relationship curve between current and angular frequency. When the system is stable, the relationship curve shows a "converging" trend; when the system becomes unstable, the relationship curve shows a "diverging" trend of collapse. This indicates that the relationship curve is closely related to the transient stability of the system and contains important information indicating the presence or absence of transient stability of the power system. Further analysis shows that whether the system is stable or unstable, an inflection point of angular frequency appears in the relationship curve in a relatively short time. During this period, the change in angular frequency first decreases and then increases. After passing through this inflection point of angular frequency, the convergence and divergence characteristics of the relationship curve gradually appear. At the same time, the current near this inflection point of angular frequency always shows an obvious difference between stable and unstable states, that is, the current near the inflection point of angular frequency when the system is stable continues to decrease, and the current near the inflection point of angular frequency when the system is unstable continues to increase.

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

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[0017] Utilize the significant differences existing in the relationship curves of current and angular frequency when the system is stable and unstable to judge the transient stability situation of the power system, and simplify the discrimination process of the transient power angle stability of the power system into the process of monitoring and identifying the important characteristics of stability and instability of the relationship curve.

[0018] 3) Proposal of the judgment criterion for the transient power angle stability of the power system based on the relationship curve between generator current and angular frequency

[0019] By identifying the important characteristics of system stability and instability in the relationship curve between generator current and angular frequency, quickly locate the inflection point of angular frequency, calculate the current change rate near the inflection point of angular frequency, judge the change trend of the current near the inflection point of angular frequency from the plus and minus signs, and construct the judgment criteria for transient power angle 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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Advantages of the Invention

[0020] The power system transient stability discrimination method based on the response relationship curve of the present invention has the following advantages. This method uses the generator current and angular frequency measured in real time as important electrical quantities for transient stability analysis, establishes the correlation between the two electrical quantities through theoretical derivation, plots the relationship curve between the current and the angular frequency, and intuitively and clearly reflects the transient stability situation of the power system. It constructs the judgment criterion for the transient power angle stability of the power system based on the relationship curve between the current and the angular frequency. This method can avoid problems such as the large amount of calculation faced by the conventional transient stability analysis method, the profound influence of changes in the network structure, parameters and system operation mode, and the difficulty in meeting the real-time requirement of transient stability discrimination. It can accurately and quickly identify the transient power angle stability situation of the power system and ensure the safe and stable operation of the power system.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0022] To better understand the purpose, configuration, and function of the present invention, the power system transient stability discrimination method based on the response relationship curve of the present invention will be further described in detail with reference to the drawings below.

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

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

[0025] In a classical single-machine infinite-bus system with a second-order model, without considering attenuation, the motion equation of the generator rotor is

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[0026] Based on the motion equation of the generator rotor, theoretical derivation is carried out, the current quantity is introduced into the motion equation of the rotor, the correlation between the generator current and the angular frequency is explored, and the generator current

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

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[0028] The general solution formula for Δω can be obtained from formula (5):

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[0029] At the initial time of the fault, the angular frequency deviation Δω of the generator is 0. Ignoring the change in the mechanical output of the generator, it is always

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[0030] Substituting Equation (2) into Equation (7), a correlation equation between current and angular frequency deviation can be obtained: [Number] 。

[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 obtain the rule of the real-time change of the current and angular frequency, it is necessary to simply process the angular frequency deviation. As can be seen from Equation (9), the term with the rated angular frequency ω0 is 0, so the change rate of the angular frequency deviation can be expressed by the change rate of the angular frequency itself, [Number] 、 and a correlation relationship between the change rate of the current and the angular frequency can be obtained: [Number] 。

[0032] Thus, not only the correlation relationship between the generator current and the angular frequency deviation is established, but also the correlation relationship between the current and the change rate of the angular frequency is established. From the analysis of the equation, it can be seen that the change trend of the angular frequency is determined by the current difference sign and [Number] the sign together. In this way, the change of the generator current is linked to the change of the angular frequency, providing a good theoretical basis for the analysis of the correlation characteristics of the relationship curve between the current and the angular frequency.

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

[0034] In the response information of the generator during the transient process, transient stability information is usually richly contained, and it can reflect the transient stability situation after the power system is subjected to a large disturbance. Using wide-area measurement technology to extract the real-time data of generator current and angular frequency in the system, and plot the relationship curve between current and angular frequency. When the system is stable, the relationship curve shows a "converging" trend, and when the system becomes unstable, the relationship curve shows a "diverging" trend of collapse. This indicates that the relationship curve is closely related to the transient stability of the system, and it contains important information indicating the presence or absence of transient stability of the power system. Further analysis shows that whether the system is stable or unstable, an inflection point of angular frequency appears in the relationship curve in a relatively short time. During this period, the change of angular frequency first decreases and then increases. After passing through this inflection point of angular frequency, the convergence and divergence characteristics of the relationship curve gradually appear. At the same time, the current near this inflection point of angular frequency always shows an obvious difference between stable and unstable states, that is, the current near the inflection point of angular frequency when the system is stable continues to decrease, and the current near the inflection point of angular frequency when the system is unstable continues to increase.

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

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[0036] Utilize the significant differences existing in the relationship curves of current and angular frequency when the system is stable and unstable to judge the transient stability state of the power system, and simplify the discrimination process of the transient power angle stability of the power system into the process of monitoring and identifying the important characteristics of stability and instability of the relationship curve.

[0037] 3) Proposal of the judgment criterion for the transient power angle stability of the power system based on the relationship curve between generator current and angular frequency

[0038] By identifying the important characteristics of system stability and instability in the relationship curve between generator current and angular frequency, quickly locate the inflection point of the angular frequency, calculate the current change rate near the inflection point of the angular frequency, judge the change trend of the current near the inflection point of the angular frequency from the plus and minus signs, and construct the judgment criteria for transient power angle 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] Specific example: To verify the effectiveness of this transient power angle stability discrimination method, as shown in FIG. 1, the present invention constructs a single-machine infinite bus system with a classical second-order model in the power system analysis integration program PSASP (Power System Analysis Software Package). A three-phase short-circuit ground fault is set in any one of the system's AC double-circuit lines, the fault location is set at 50% of the line, the fault is accessed at 0 s, and different fault severities are simulated by adjusting the fault clearing time. The fault is cleared at 0.15 s and 0.16 s respectively. When the fault is cleared at 0.15 s, the system is stable, and when the fault is cleared at 0.16 s, the system is unstable.

[0040] Using a wide-area measurement system, the current and angular frequency at the generator port of the system under two operating conditions are measured in real time. As shown in FIGS. 2 and 3, the relationship curves of the current and angular frequency after the fault under the stable and unstable operating conditions of the system are plotted respectively. Analysis is performed using the constructed power system transient power angle stability discrimination method. First, the inflection point of the angular frequency in the relationship curve is quickly located. The change in angular frequency first decreases and then increases. Next, the change rate of the current near the inflection point of the angular frequency is calculated. Finally, using the constructed transient power angle stability and instability criteria, the relationship curves of the current and angular frequency under the two operating conditions are judged to conclude whether the system is stable.

[0041] The relationship curve between current and angular frequency shown in Fig. 2 shows that the current continues to decrease near the inflection point of the angular frequency. From the stability judgment criterion, it can be seen that the system is stable under the operating conditions corresponding to Fig. 2. The relationship curve between current and angular frequency shown in Fig. 3 shows that the current continues to increase near the inflection point of the angular frequency. As can be seen from the instability judgment criterion, the system is unstable under the operating conditions corresponding to Fig. 3, and the effectiveness of the power system transient stability discrimination method based on the response relationship curve of the present invention is verified.

[0042] The present invention will be described with several embodiments. As is well known to those skilled in the art, without departing from the spirit and scope of the present invention, these features and embodiments can be variously changed or equivalently replaced. Further, these features and embodiments may be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention under the teaching of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments included within the scope of the claims of this application are within the scope protected by the present invention.

Claims

1. including the following steps, Step 1: Establish the relationship between generator current and angular frequency. In a single-machine infinite-bus system with a classical second-order model, without considering attenuation, the motion equation of the generator rotor is 【Number 1】 represented by 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 output of the generator, and P ｅ is the electromagnetic power of the generator, and generator current 【Number 2】 is considered to be composed of two parts: load current [Number 3] and additional current after a fault 【Number 4】 , 【Number 5】 、 the electromagnetic power represented by current is 【Number 6】 、 【Number 7】 where In the formula, Q ｅ is the reactive power of the generator, 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. 【Number 8】 and 【Number 9】 are the potential vector and amplitude inside the generator respectively, 【Number 10】 is 【Number 11】 and 【Number 12】 is the angle difference between the correlation equation between current and angular frequency deviation is 【Number 13】 where the rate of change of angular frequency deviation is represented by the rate of change of angular frequency itself, 【Number 14】 、 the relationship between current and the rate of change of angular frequency is 【Number 15】 where Step S2: Analyze the characteristics of the relationship curve between generator current and angular frequency. The current throughout the process shows the characteristic that the current continues to decrease as the angular frequency changes. The current throughout the process continues to increase as the angular frequency changes. Step S3: Propose 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 judging the transient stability of a power system based on a response relationship curve, characterized by quickly locating the inflection point of angular frequency by identifying the important characteristics of system stability and instability in the relationship curve between generator current and angular frequency, calculating the rate of change of current near the inflection point of angular frequency, and judging the change trend of current near the inflection point of angular frequency from the positive and negative signs.

2. In the step S2, near the stable equilibrium point 【Number 16】 where, in the process of decreasing angular frequency, 【Number 17】 、 【Number 18】 there is after passing through the inflection point of angular frequency, in the process of increasing angular frequency, 【Number 19】 、 【Number 20】 there is near the unstable equilibrium point 【Number 21】 where, in the process of decreasing angular frequency, 【Number 22】 、 【Number 23】 there is after passing through the inflection point of angular frequency, in the process of increasing angular frequency, 【24 Points】 、 【Number 25】 there is, which is characterized by the method for judging the transient stability of a power system based on the response relationship curve according to claim 1.

3. The step S3 i) system stability, 【Number 26】 and ii) system instability, 【Number 27】 including 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), which is characterized by the method for judging the transient stability of a power system based on the response relationship curve according to claim 1.

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