Transient dominant instability mode identification method and system, and readable storage medium

Abstract

The application discloses a transient dominant instability mode discrimination method and system, and a readable storage medium, and acquires a voltage phasor of a lowest node of a whole network voltage; whether a dominant instability mode discrimination algorithm is started is judged according to the voltage phasor of the lowest node of the whole network voltage, if the dominant instability mode discrimination algorithm is started, the next step is entered, otherwise the voltage phasor of the lowest node of the whole network voltage at the next time is acquired; a dominant instability mode combination criterion is calculated, and the dominant instability mode discrimination result is obtained by using the dominant instability mode combination criterion; and an emergency control strategy is generated according to the relationship between the voltage amplitude of the lowest node of the whole network voltage when the dominant instability mode discrimination result is obtained and the active splitting control threshold value. The application only needs single-end measurement, has better applicability and has engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of transient stability analysis and control applications of large power grids, specifically involving a method, system, and readable storage medium for identifying transient dominant instability modes. Background Technology

[0002] Under unforeseen disturbances, the evolution of transient instability in AC / DC hybrid power grids is complex and varied. Transient power angle instability and transient voltage instability often intertwine, making it difficult to identify the dominant characteristics. This restricts the formulation of effective emergency control strategies and seriously threatens the safe and stable operation of AC / DC hybrid power grids. Current research on the identification of the dominant characteristics of transient power angle instability and transient voltage instability is mainly divided into two categories: model-driven and response-driven.

[0003] Model-driven methods analyze instability mechanisms, identify dominant causes, and assess coupling strength based on system mathematical models. They are suitable for simulation analysis scenarios such as operation mode generation and safety control strategy formulation. When such studies analyze the correlation between power angle stability and voltage stability using methods such as energy functions, bifurcation theory, small disturbance analysis, and modal series, many constraints need to be set to establish an abstract mathematical model. It is difficult to fully consider the dynamic characteristics of the system, and the analysis results obtained are relatively conservative.

[0004] Response-driven methods, based on wide-area response information, identify dominant features, construct discriminant indicators, and make emergency control decisions. They aim to address the intertwined instability patterns caused by unforeseen events. Real-time dominant pattern identification provides a basis for emergency control decisions. These methods can effectively address sudden events beyond the "predicted fault set" and their corresponding instability patterns, supporting the formulation of emergency control strategies before instability and reducing the risk of system instability after large disturbances. However, existing response-driven methods suffer from difficulties in obtaining the required measurement information, identifying equivalent system parameters, and having poor timeliness in dominant pattern identification. The applicability and accuracy of the analysis results obtained from existing methods need improvement. Therefore, there is an urgent need to propose a transient dominant instability pattern identification method and system based on easily measurable response information that does not require system equivalence and has strong timeliness in discrimination. Summary of the Invention

[0005] The purpose of this invention is to provide a method, system and readable storage medium for identifying transient dominant instability modes, so as to overcome the defects of the existing technology. This invention only requires single-end measurement, has good applicability and has engineering application value.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] Methods for identifying transient dominant instability patterns include:

[0008] Obtain the voltage phasor of the node with the lowest voltage across the entire network;

[0009] Determine whether to activate the dominant instability mode discrimination algorithm based on the voltage phasor of the node with the lowest voltage in the entire network. If activated, proceed to the next step; otherwise, obtain the voltage phasor of the node with the lowest voltage in the entire network at the next moment.

[0010] Calculate the dominant instability pattern combination criterion and use the dominant instability pattern combination criterion to obtain the dominant instability pattern discrimination result;

[0011] An emergency control strategy is generated based on the relationship between the voltage amplitude of the node with the lowest voltage in the entire network when the dominant instability mode is determined and the active disconnection control threshold value. The voltage amplitude is the magnitude of the voltage phasor.

[0012] Furthermore, obtaining the voltage phasor of the node with the lowest voltage across the entire network specifically involves:

[0013] Starting from the moment the fault disappears, after a preset time delay, the voltage phasor of the node with the lowest voltage in the entire network is obtained using a measuring device.

[0014] Furthermore, the step of determining whether to activate the dominant instability mode discrimination algorithm based on the voltage phasor of the node with the lowest voltage in the entire network is as follows: if the voltage amplitude of the node with the lowest voltage in the entire network is less than the threshold value and shows a monotonically decreasing trend, then the dominant instability mode discrimination algorithm is activated.

[0015] Furthermore, the criteria for the dominant instability mode combination specifically include:

[0016]

[0017] Δt>T th (9)

[0018]

[0019] 0≤P≤1 (11)

[0020] P>1 (12)

[0021] in, From initial time t1 to final time t n The cumulative deflection angle γ of the voltage phasor trajectories between them. th The threshold value for the cumulative deflection angle ∑γ, where Δt is the duration, and T is the threshold value for the cumulative deflection angle ∑γ. th Δt is the threshold value for the duration, and P is the proportion of the distance from the point where the vertical voltage falls to the beginning of the line to the total length of the line.

[0022] Furthermore, the method for determining the deflection angle γ of the voltage phasor trajectories in two adjacent time periods in the dominant instability mode combination criterion is as follows:

[0023]

[0024]

[0025] Wherein, vector AB = (x2–x1, y2–y1), vector BC = (x3–x2, y3–y2), (x1, y1) are the coordinates of point A, (x2, y2) are the coordinates of point B, (x3, y3) are the coordinates of point C, and A, B, and C are any three ordered points in a rectangular coordinate system.

[0026] Furthermore, the method for determining the proportion of the distance from the point where the vertical voltage falls to the beginning of the line to the total length of the line is as follows:

[0027]

[0028] Among them, U A This refers to the voltage at the beginning of the AC line. X is the line power factor angle. AB I is the line reactance, and I is the line current.

[0029] Furthermore, the method of obtaining the dominant instability pattern discrimination result using the dominant instability pattern combination criterion is specifically as follows:

[0030] If equations (8), (9) and (11) are satisfied at the same time, it is determined to be a power angle instability mode; if equations (9) and (10) or equations (8), (9) and (12) are satisfied at the same time, it is determined to be a voltage instability mode.

[0031] Furthermore, the emergency control strategy generated based on the relationship between the voltage of the node with the lowest voltage across the entire network when the dominant instability mode determination result is obtained and the active disconnection control threshold value is as follows:

[0032] If the voltage of the node with the lowest voltage in the entire network when the dominant instability mode is determined is greater than or equal to the active disconnection control threshold, then the corresponding emergency control measures will be applied.

[0033] If the voltage of the node with the lowest voltage across the entire network when the dominant instability mode is determined is less than the active disconnection control threshold, the disconnection device will be directly triggered.

[0034] Furthermore, the specific implementation of the corresponding emergency control measures is as follows: if the problem is power angle instability, then the corresponding power angle stabilization emergency control will be implemented; if the problem is voltage instability, then the corresponding voltage stabilization emergency control will be implemented.

[0035] The direct-triggered disconnection device operates as follows: if the power angle is unstable, it triggers the corresponding out-of-step disconnection control; if the voltage is unstable, it triggers the corresponding low-voltage disconnection control.

[0036] The transient dominant instability pattern discrimination system includes:

[0037] Acquisition module: Used to acquire the voltage phasor of the node with the lowest voltage in the entire network;

[0038] Startup module: Used to determine whether to start the dominant instability mode discrimination algorithm based on the voltage phasor of the node with the lowest voltage in the entire network. If started, it enters the discrimination module; otherwise, it obtains the voltage phasor of the node with the lowest voltage in the entire network at the next moment.

[0039] Discrimination module: used to calculate the dominant instability mode combination criteria and obtain the dominant instability mode discrimination result using the dominant instability mode combination criteria;

[0040] Control module: Used to generate an emergency control strategy based on the relationship between the voltage of the node with the lowest voltage in the entire network when the dominant instability mode is determined and the active disconnection control threshold value, wherein the voltage amplitude is the magnitude of the voltage phasor.

[0041] Furthermore, in the startup module, the dominant instability mode discrimination algorithm is started based on the voltage phasor of the node with the lowest voltage in the entire network. Specifically, if the voltage amplitude of the node with the lowest voltage in the entire network is less than the threshold value and shows a monotonically decreasing trend, then the dominant instability mode discrimination algorithm is started.

[0042] Furthermore, in the startup module, the judgment module specifically includes the following criteria for determining the dominant instability mode combination:

[0043]

[0044] Δt>T th (9)

[0045]

[0046] 0≤P≤1 (11)

[0047] P>1 (12)

[0048] in, From initial time t1 to final time t n The cumulative deflection angle γ of the voltage phasor trajectories between them. th The threshold value for the cumulative deflection angle, Δt is the duration, and T is the threshold value for the cumulative deflection angle. th Δt is the threshold value for the duration, and P is the proportion of the distance from the point where the vertical voltage falls to the beginning of the line to the total length of the line.

[0049] The method of obtaining the dominant instability pattern discrimination result using the dominant instability pattern combination criterion is as follows:

[0050] If equations (8), (9) and (11) are satisfied at the same time, it is determined to be a power angle instability mode; if equations (9) and (10) or equations (8), (9) and (12) are satisfied at the same time, it is determined to be a voltage instability mode.

[0051] Furthermore, in the control module, an emergency control strategy is generated based on the relationship between the voltage of the node with the lowest voltage across the entire network when the dominant instability mode determination result is obtained and the active disconnection control threshold value, specifically:

[0052] If the voltage of the node with the lowest voltage in the entire network when the dominant instability mode is determined is greater than or equal to the active disconnection control threshold, then the corresponding emergency control measures will be applied.

[0053] If the voltage of the node with the lowest voltage across the entire network when the dominant instability mode is determined is less than the active disconnection control threshold, the disconnection device will be directly triggered.

[0054] Furthermore, in the control module, the handover to the corresponding emergency control is specifically as follows: if it is a power angle instability state, then the power angle instability state is handed over to the power angle stabilization emergency control; if it is a voltage instability state, then the voltage instability state is handed over to the voltage stabilization emergency control.

[0055] The direct-triggered disconnection device operates as follows: if the power angle is unstable, it triggers the corresponding out-of-step disconnection control; if the voltage is unstable, it triggers the corresponding low-voltage disconnection control.

[0056] A computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the transient dominant instability mode discrimination method.

[0057] Compared with the prior art, the present invention has the following beneficial technical effects:

[0058] This invention takes wide-area node response information as its starting point and utilizes single-ended measurements of the node with the lowest system voltage to propose a method for identifying dominant instability modes. From the perspective of voltage phasor trajectories, it proposes a cumulative deflection angle index representing the rotation direction of the ordered trajectory using the vector cross multiplication method, and constructs a combined criterion for dominant instability modes. The results can provide a decision-making basis for formulating emergency control strategies before instability, and further reduce the risk of system instability by implementing targeted proactive control. This invention is a powerful supplement to the existing three lines of defense for the safety and stability of large power grids. This invention only requires single-ended measurements, has good applicability, and has engineering application value. Attached Figure Description

[0059] The accompanying drawings are provided to further understand the invention and constitute a part of this invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0060] Figure 1 This is a diagram of the work angle stability analysis model.

[0061] Figure 2 This is a voltage stability analysis model diagram.

[0062] Figure 3 It is a vector cross product graph.

[0063] Figure 4 It is a voltage vector diagram of the voltage at the beginning and end of the line, where (a) is the voltage drop point inside the line and (b) is the voltage drop point outside the line.

[0064] Figure 5 It is the dominant strategy for identifying instability patterns and for emergency control.

[0065] Figure 6 It is a diagram of a 3-machine, 10-node system.

[0066] Figure 7 This is a transient response diagram of the system, where (a) is the unit power angle response and (b) is the voltage amplitude response.

[0067] Figure 8 It is a system dominant instability mode discrimination diagram, where (a) is the voltage phasor trajectory of Bus9 and (b) is the cumulative deflection angle ∑γ of the Bus9 trajectory.

[0068] Figure 9 The diagram shows the transient response after load shedding control, where (a) is the unit's power angle response and (b) is the voltage amplitude response.

[0069] Figure 10 This is the XJ AC / DC hybrid power grid diagram at the sending end.

[0070] Figure 11 This is a transient response diagram of the XJ power grid, where (a) is the unit power angle response and (b) is the voltage amplitude response.

[0071] Figure 12 This is a diagram of the dominant instability mode of the XJ power grid, where (a) is the voltage phasor trajectory of the CDM, (b) is the cumulative deflection angle ∑γ of the CDM trajectory, and (c) is the vertical voltage landing point on the YK-CDM.

[0072] Figure 13 The diagram shows the transient response after the generator tripping control, where (a) is the generator power angle response and (b) is the voltage amplitude response.

[0073] Figure 14 This is the HNYX AC / DC hybrid receiving-end power grid diagram.

[0074] Figure 15These are transient response diagrams of the HNYX power grid, where (a) is the unit power angle response, (b) is the voltage amplitude response, and (c) is a magnified view of the transient voltage response of the HNYX power grid.

[0075] Figure 16 This is a diagram of the dominant instability mode of the HNYX power grid, where (a) is the voltage phasor trajectory of YXH, (b) is the cumulative deflection angle ∑γ of the YXH trajectory, and (c) is the vertical voltage landing point on the branch connected to YXH.

[0076] Figure 17 These are transient response diagrams after voltage stabilization emergency control, where (a) is the power angle transient response after load shedding control, (b) is the voltage transient response after load shedding control, (c) is the power angle transient response after rapid DC reduction control, and (d) is the voltage transient response after rapid DC reduction control. Detailed Implementation

[0077] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0078] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0079] Example 1

[0080] A transient dominant instability mode discrimination method includes four steps: 1. Real-time measurement of voltage phasors of the node with the lowest voltage in the entire network; 2. Start judgment of dominant instability mode algorithm; 3. Real-time calculation of dominant instability mode combination criteria; 4. Generation of emergency control strategy.

[0081] Step 1: Real-time acquisition of voltage phasor measurements at the node with the lowest voltage across the entire network.

[0082] Set the sliding window size W, sliding step size S, and strategy startup delay T after the fault disappears. delay Continuous discrimination time threshold T th Cumulative deflection angle threshold γ th and voltage threshold value U th1 U th2 From the moment the fault disappears, after a time delay T delay Then, the voltage phasor of the node with the lowest voltage in the entire network is obtained using a measuring device.

[0083] Step 2: Determine if the dominant instability mode algorithm is activated.

[0084] The voltage amplitude U of the node with the lowest voltage in the entire network t Less than the voltage threshold value U th1 Furthermore, it exhibits a monotonically decreasing trend, meaning the voltage amplitude U at the current moment... t The voltage amplitude U is less than that of the previous moment. t-1 That is, when equations (1) and (2) are satisfied simultaneously, the dominant instability mode discrimination algorithm is activated. Equation (1) sets the voltage threshold value U. th1 The low voltage level of the system is defined as the threshold value for the start of the dominant mode discrimination algorithm; Equation (2) is used to identify the voltage drop and voltage recovery process.

[0085] U t th1 (1)

[0086] U t -U t-1 <0 (2)

[0087] Step 3: Real-time calculation of dominant instability mode combination criteria

[0088] 1) Voltage phasor trajectory under power angle instability

[0089] The voltage phasor locus is the directed trajectory of the bus voltage in the complex plane formed by its real and imaginary parts. The power angle stability analysis model is as follows: Figure 1 As shown, E1 and E2 are the potential amplitudes within the sending and receiving units, respectively, and the total AC reactance of the system is X. ∑ X oc U is the reactance from the point OC where the voltage drops to zero (also known as the "out-of-step oscillation center") on the tie line to the terminal potential E2. oc θ oc Let be the voltage amplitude and phase angle at the landing point OC, respectively. With the receiving-end unit as a reference, when the power angle δ changes periodically within [0°, 360°], the voltage phasor trajectories at each node are circular. The expression for the voltage phasor trajectory at the landing point OC where the voltage reaches zero is shown in equation (3). Where k... oc =X oc ​ / X ∑ This can represent the position OC where the voltage drops to zero, with the center coordinates being (E2–k). oc E2,0), radius k oc E1.

[0090] (x-(E2-k oc E2)) 2 +(y) 2 =(k oc E1) 2 (3)

[0091] Where x is the abscissa of the complex plane coordinate system composed of real and imaginary parts, and y is the ordinate of the plane coordinate system;

[0092] When the voltage reaches zero, the voltage amplitude at the point OC where it falls drops to zero, meaning the voltage phasor trajectory passes through the origin. Substituting the origin into equation (3) yields equation (4).

[0093]

[0094] In power angle instability scenarios with different values ​​of E1 / E2, OC is the point of most severe voltage drop in the system, U oc All are monotonically decreasing and tend to zero, θ oc All of them monotonically increase towards 90°; the voltage phasor trajector trajector trajectories at OC all tend counterclockwise towards the origin of the coordinate system along the circle, and the radius is largest when E1 / E2 is 1.00. However, the geometric relationship between each trajectory and the imaginary axis at the origin (corresponding to the moment when the voltage reaches zero) is independent of the value of E1 / E2. The occurrence of voltage reaching zero on the line is a typical feature of power angle instability, so the trajectory characteristics presented by its landing point position can be used to characterize power angle instability.

[0095] 2) Voltage phasor trajectory under voltage instability conditions

[0096] against Figure 1 The voltage stability analysis model can be obtained by performing Thevenin equivalents along a load node of the model shown. Figure 2 As shown, E eq Equivalent potential, δ eq For the equivalent work angle, X eq For equivalent reactance, U L θ L These represent the voltage amplitude and phase angle at the load node, respectively. L Q L These represent the active and reactive power of the load, respectively. An increase in either the active or reactive power demand can lead to voltage instability. Below, we simulate two typical scenarios of load node voltage instability by increasing the active power of the load while maintaining a constant power factor, and by increasing the reactive power demand while maintaining a constant active power factor:

[0097] ① To maintain power factor The load power increases in a constant manner, i.e., P L With Q L With proportional growth, the load can be considered as the impedance angle. The modulus Z remains unchanged L Gradually decreasing impedance Let k = Z L / X eq , k represents the ratio of the load impedance modulus to the equivalent reactance.

[0098] when At that time, the real and imaginary parts of the load node voltage satisfy equation (5). This trajectory is based on... With the center of the circle, A circle with radius and passing through the origin.

[0099]

[0100] when At this point, equation (6) can be derived, and the voltage phasor trajectory of the load node has a slope of tanδ. eq And a straight line passing through the origin of the coordinate system.

[0101] y = x · tanδ eq (6)

[0102] During the process of increasing load power, the voltage amplitude U L and phase angle θ L All are monotonically decreasing; E eq ∠δ eq For the common chord of circles with different trajectories, when At that time, the load node voltage phasor trajectory follows E eq ∠δ eq The line in question tends toward the origin, when At that time, the circle moves clockwise towards the origin along the trajectory, where Time E eq ∠δ eq The diameter of the trajectory circle is denoted as . When a load node becomes unstable due to heavy load, its trajectory characteristics can be used to characterize this typical voltage instability scenario.

[0103] ②Maintaining the active power P of the load L Constant, continuously increasing load reactive power Q L The real and imaginary parts of the load node voltage satisfy equation (7). The trajectory has a slope of tanδ. eq The ordinate intercept is –P L X eq / E eq cosδ eq A straight line.

[0104] y = x · tanδ eq -(P L X eq / E eq cosδ eq (7)

[0105] Reactive power Q under load L Increase to the maximum transmitted reactive power limit Q Max During the process, the voltage amplitude U at the load node L and phase angle θ L All are monotonically decreasing; the voltage phasor locus follows a slope of tanδ. eq The linear trend towards the voltage critical point (which corresponds to the maximum transmitted reactive power limit Q) Max The voltage instability caused by the surge in reactive power demand at load nodes can be characterized by its trajectory features.

[0106] 3) Criteria for the combination of dominant instability patterns

[0107] Through theoretical derivation and analysis, it can be seen that due to the different instability mechanisms of different instability modes, the phasor trajectory shape at the lowest voltage point exhibits different characteristics, which can be summarized as follows: 1) Under the power angle instability mode, the voltage phasor trajectory changes counterclockwise along a circle; 2) Under the voltage instability mode, the voltage phasor trajectory changes clockwise along a circle or along a straight line. Based on the above characteristics, the criteria are constructed as shown in equations (8), (9), and (10).

[0108]

[0109] Δt>T th (9)

[0110]

[0111] In equations (8) and (10) From initial time t1 to final time t n The cumulative deflection angle of the voltage phasor traject ... th This is used to mitigate the impact of the deviation between ideal assumptions and engineering reality on the determination of the dominant form. In equation (9), Δt represents the duration, and equation (9) sets a threshold value T for the duration Δt. th This is used to reduce the risk of misjudging the dominant pattern caused by short-term and drastic fluctuations in electrical quantities.

[0112] Considering that the closer the load node is to the out-of-step generator with leading power angle, the more similar the variation trend of the equivalent potential and the internal potential of the out-of-step generator will be, and the greater the influence of the time-varying characteristic of the equivalent potential on the voltage phasor locus of the load node will be. It may even cause the overall voltage phasor locus to present a clockwise variation trend, which is misjudged as the power angle instability pattern. At this time, other response electrical quantities need to be combined to further identify the dominant pattern. Since the occurrence of the foot point voltage drop point on the tie line is an important manifestation of the power angle instability pattern and a key feature different from the voltage instability pattern, whether there is a foot point voltage drop point near the lowest point of the system voltage can be used as an auxiliary criterion for the multi-instability pattern interleaving problem, as shown in Equations (11) and (12).

[0113] 0≤P≤1 (11)

[0114] P>1 (12)

[0115] In Equations (11) and (12), P is the ratio of the distance from the foot point voltage drop point to the line head end to the total length of the line. When 0<P<1, the foot point voltage drop point is located inside line AB; when P=0 or P=1, the foot point voltage drop point is located at the nodes at both ends of the line; when P>1, the foot point voltage drop point is located outside line AB.

[0116] The combined criterion for determining the dominant instability pattern is constructed as follows: if Equations (8), (9) and (11) are all satisfied, the pattern is determined as power angle instability; if Equations (9) and (10) are both satisfied, or Equations (8), (9) and (12) are all satisfied, the pattern is determined as voltage instability. For the locus that cannot complete criterion matching within a short period of time, it indicates that the dominant pattern is not yet clear, and continuous discrimination is required in subsequent time steps to monitor the change of dominance in real time.

[0117] The calculation method for the deflection angle γ of the voltage phasor locus in the combined criterion is as follows: the vector cross product method can be used to judge the rotation direction of any three ordered points in the Cartesian coordinate system, such as Figure 3 shown in the figure. The vector AB=(x2–x1, y2–y1), the vector BC=(x3–x2, y3–y2), and the vector cross product and the deflection angle γ are shown in Equations (13) and (14) respectively. The vector cross product is applied to the three coordinate points on the voltage phasor locus, and the rotation direction of the locus can be identified by calculating the deflection angle γ. To enhance the index sensitivity, the cumulative deflection angle ∑γ in a certain time interval is used to judge the rotation direction of the locus in that period.

[0118]

[0119]

[0120] The calculation method for P, which is the ratio of the distance from the foot point voltage drop point to the line head end to the total line length in the combined criterion of the dominant instability pattern, is as follows: the voltages U at the head and end of the AC lineA U B like Figure 4 As shown, the resistance of the high-voltage line is much smaller than its reactance and can be ignored. X AB U is the line reactance, I is the line current, and U is the line current. AB This is the voltage drop modulus of the line. Let P be the line power factor angle, and let P be the ratio of the distance from the point where the vertical voltage falls to the beginning of the line to the total length of the line, as shown in equation (15).

[0121]

[0122] Step 4: Emergency Control Strategy Generation

[0123] After obtaining the dominant instability mode discrimination result using the dominant instability mode combination criterion, if the voltage U of the node with the lowest voltage in the entire network at the time of determination is completed... t Greater than or equal to the active disconnection control threshold value U th2 The corresponding emergency control measures will be implemented (power angle instability corresponds to power angle stabilization emergency control, voltage instability corresponds to voltage stabilization emergency control); if the lowest voltage U t Less than U th2 This indicates that the system has reached the instability boundary and no longer requires emergency control; the tripping device can be directly triggered (power angle instability corresponds to out-of-step tripping control, voltage instability corresponds to low-voltage tripping control). The dominant instability mode identification and emergency control strategy are as follows: Figure 5 As shown.

[0124] Application Example 1: 3-machine 10-node system

[0125] W, S, T delay and T th A value that is too small will increase the risk of misjudging the dominant pattern caused by drastic fluctuations in electrical quantities, while a value that is too large may delay the control timing; γ th Values ​​that are too small or too large will increase the risk of misjudgment; U th1 U th2 Values ​​that are too small will increase the risk of system instability. th1 If the value is too large, it will lose its meaning in defining the low voltage level. th2 Excessively large values ​​will prematurely trigger the decoupling process, resulting in unnecessary control costs; therefore, the relevant parameters are set as follows: W = 0.03s, S = 0.01s, T delay =0.20s, T th =0.10s, γ th =5°, U th1 =0.80pu, U th2 =0.30pu.

[0126] 3-machine 10-node system, such as Figure 6As shown, Bus7 is a constant impedance load, and Bus10 is a motor load. At t = 0.20s, a three-phase short circuit occurs on one of the Bus5-Bus6 lines. The line trips 0.0058s later. The system power angle and voltage transient response are as follows. Figure 7 As shown.

[0127] The time after which the fault disappears is delayed by time T delay Then, at t = 0.4058s, the voltage phasors of all network nodes were collected. The Bus9 voltage was 0.7999 pu at t = 1.5658s, and it was the first to drop below U. th1 =0.80pu, and the voltage at t=1.5758s is 0.7997pu<0.7999pu, which simultaneously satisfies equations (1) and (2), thus initiating the dominant morphology discrimination algorithm. The voltage phasor trajectory of Bus9 and its cumulative deflection angle ∑γ are as follows: Figure 8 As shown.

[0128] Considering the sliding window size W is 0.03s, the initial calculation time for the cumulative deflection angle ∑γ is t = 1.5858s. Figure 8 The voltage phasor trajectory is displayed to rotate counterclockwise, and the cumulative deflection angle ∑γ is less than γ in the interval [1.5858s, 1.6858s]. th =5°, duration greater than T th =0.10s, which simultaneously satisfies equations (9) and (10), thus determining it as a voltage instability mode.

[0129] When t = 1.6858s, the voltage of Bus9 is 0.7955pu > U. th2 =0.30pu (active disconnection control threshold value), therefore, emergency voltage stabilization control is initiated. Considering a 100ms control delay, the 40MW motor load at Bus10 is disconnected at t=1.7858s. After load shedding control, the system power angle and voltage tend to stabilize, verifying the effectiveness of the invention. The transient response is as follows: Figure 9 As shown.

[0130] Application Example 2: XJ AC / DC hybrid power grid for external transmission.

[0131] The algorithm-related parameter settings are the same as above. A certain provincial XJ AC / DC hybrid power grid for external transmission is as follows: Figure 10 As shown, power is transmitted to the HZ power grid via TS-ZZ±800kV / 8000MW ultra-high voltage direct current, and to the XB power grid via two 750kV AC channels, HM-DH and TS-YD-SZ.

[0132] Under certain summer operating conditions, the TS-ZZ DC transmission line fed 6000MW into the HZ grid, and two 750kV AC transmission lines transmitted a total of 2700MW. At t=0.20s, the TS-ZZ DC line experienced a single-pole blockage, and the HM-DH single-circuit line experienced a fault-free interruption at t=0.20s. During this transient process, the XJ generating units lost synchronization with the XB main grid generating units, and the voltage in the SZ-YK-CDM area of ​​the transmission line dropped significantly, making it difficult to distinguish the dominant instability mode. Figure 11 As shown.

[0133] After time delay T delay Then, at t=0.40s, the voltage phasors of all 750kV nodes in the network were collected. When t=1.07s, the voltage of node CDM first dropped below 0.80pu, with a value of 0.799pu. At t=1.08s, the voltage of this node was 0.796pu < 0.799pu, satisfying both equations (1) and (2), and the dominant morphology discrimination algorithm was started. The voltage phasor trajectory of CDM, the cumulative deflection angle ∑γ, and the landing point of the vertical voltage on the YK-CDM branch are as follows: Figure 12 As shown.

[0134] Depend on Figure 12 It can be seen that the voltage phasor trajectory of the CDM rotates counterclockwise, and the cumulative deflection angle ∑γ is greater than γ in the interval [1.12s, 1.22s]. th =5°, simultaneously satisfying equations (8) and (9); the vertical voltage landing point index P value of the YK-CDM branch is located in the interval [0,1], satisfying equation (11), thus determining it as a power angle instability mode.

[0135] At t = 1.22s, the CDM voltage was 0.733pu > 0.30pu, triggering emergency power angle stabilization control. Considering a 100ms control delay, five 660MW units (total capacity cut off 3300MW) near the TS converter station were disconnected at t = 1.32s. After the disconnection control, the power angle and voltage of the XJ power grid stabilized, verifying the effectiveness of the invention. The transient response is as follows: Figure 13 As shown.

[0136] Application Example 3: HNYX AC / DC hybrid receiving-end power grid.

[0137] The algorithm-related parameter settings are the same as above. A certain provincial HNYX AC / DC hybrid receiving-end power grid is as follows: Figure 14 As shown, the plan is to construct an HM-YXH±800kV / 8000MW ultra-high voltage direct current transmission line, and transmit power to the HN power grid through three 500kV AC channels: MS-GY, LD-ZZ, and JH-RZ.

[0138] Under a certain year's Fengda operating mode, the DC feed-in power of HM-YXH was 7370MW, and the total power transmitted from the three 500kV AC channels was 3520MW. The load model was 40% static load + 60% induction motor load. A three-phase short circuit occurred at JH-RZ at t=0.20s, and both circuits were disconnected 0.10s later. During the transient process, the power angle fluctuation and voltage drop were intertwined, such as... Figure 15 As shown.

[0139] After time delay T delay Then, at t=0.50s, the voltage phasors of all 500kV nodes in the network were collected. At t=0.50s, node YXH had the minimum node voltage of the entire network, 0.654pu, and at t=0.51s, the voltage of this node was 0.652pu<0.654pu, satisfying both equations (1) and (2), and the dominant morphology discrimination algorithm was started. The voltage phasor trajectory of YXH, the cumulative deflection angle ∑γ, and the landing points of the vertical voltage on the LX-YXH and JH-YXH branches are as follows. Figure 16 As shown.

[0140] Depend on Figure 16 It can be seen that the voltage phasor trajectory of the CDM rotates counterclockwise, and the cumulative deflection angle ∑γ is greater than γ in the interval [0.59s, 0.69s]. th =5°, satisfying equations (8) and (9); the vertical voltage landing point index P of LX-YXH and JH-YXH are both greater than 1, satisfying equation (12), thus it is determined to be a voltage instability mode. When t = 0.69s, the voltage of YXH is 0.632pu>U th2 Emergency voltage stabilization control was initiated. Considering a 100ms control delay, 8% of the motor load (approximately 630MW) in the HNYX area was removed at t=0.79s. After the load shedding control, the system power angle stabilized, and the voltage returned to normal levels. The transient response was as follows: Figure 17 As shown in (a)(b).

[0141] DC droop control can reduce the reactive power demand of the inverter and facilitate the rapid recovery of voltage at nearby load nodes. It is another effective measure for emergency voltage stability control. Therefore, at t=0.79s, the HM-YXH DC droop power control command of 1400MW was executed. Afterwards, the voltage gradually recovered, and the command was withdrawn at t=1.79s. The HNYX generator group and the HN main grid generator group tended to synchronize, and the voltage stabilized. The transient response was as follows: Figure 17 As shown in (c) and (d), the transient responses following both types of emergency control verify the effectiveness of the present invention.

[0142] Example 2

[0143] The transient dominant instability pattern discrimination system includes:

[0144] Acquisition Module: Used to acquire the voltage phasor of the node with the lowest voltage in the entire network. Specifically, after a preset time delay from the moment the fault disappears, the voltage phasor of the node with the lowest voltage in the entire network is acquired using a measuring device.

[0145] Startup Module: Used to determine whether to start the dominant instability mode discrimination algorithm based on the voltage phasor of the node with the lowest voltage in the entire network. If started, it enters the discrimination module; otherwise, it obtains the voltage phasor of the node with the lowest voltage in the entire network at the next moment. Specifically: if the voltage amplitude of the node with the lowest voltage in the entire network is less than the threshold value and shows a monotonically decreasing trend, the dominant instability mode discrimination algorithm is started.

[0146] Discrimination module: used to calculate the dominant instability mode combination criteria and obtain the dominant instability mode discrimination result using the dominant instability mode combination criteria;

[0147] Specifically, the criteria for determining the dominant instability pattern combination include:

[0148]

[0149] Δt>T th (9)

[0150]

[0151] 0≤P≤1 (11)

[0152] P>1 (12)

[0153] In the formula, From initial time t1 to final time t n The cumulative deflection angle γ of the voltage phasor trajectories between them. th The threshold value for the cumulative deflection angle, Δt is the duration, and T is the threshold value for the cumulative deflection angle. th Δt is the threshold value for the duration, and P is the proportion of the distance from the point where the vertical voltage falls to the beginning of the line to the total length of the line.

[0154] If equations (8), (9) and (11) are satisfied simultaneously, it is determined to be a power angle instability mode; if equations (9) and (10) or equations (8), (9) and (12) are satisfied simultaneously, it is determined to be a voltage instability mode.

[0155] The method for determining the deflection angle γ of the voltage phasor trajectories between two adjacent time periods in the dominant instability mode combination criterion is as follows:

[0156]

[0157]

[0158] In the formula, vector AB = (x2–x1, y2–y1), vector BC = (x3–x2, y3–y2), (x1, y1) are the coordinates of point A, (x2, y2) are the coordinates of point B, (x3, y3) are the coordinates of point C, and A, B, and C are any three ordered points in a rectangular coordinate system;

[0159] The method for determining the proportion of the distance from the point where the vertical voltage falls to the beginning of the line to the total length of the line is as follows:

[0160]

[0161] In the formula, U A This refers to the voltage at the beginning of the AC line. X is the line power factor angle. AB I is the line reactance, and I is the line current.

[0162] Control module: used to generate an emergency control strategy based on the relationship between the voltage of the node with the lowest voltage in the entire network when the dominant instability mode is determined and the active disconnection control threshold value, wherein the voltage amplitude is the magnitude of the voltage phasor;

[0163] Specifically: if the voltage of the node with the lowest voltage in the entire network when the dominant instability mode is determined is greater than or equal to the active disconnection control threshold, then the corresponding emergency control is applied; the corresponding emergency control is applied as follows: if it is a power angle instability mode, then the power angle instability mode is applied to the corresponding power angle stabilization emergency control; if it is a voltage instability mode, then the voltage instability mode is applied to the corresponding voltage stabilization emergency control.

[0164] If the voltage of the node with the lowest voltage in the entire network when the dominant instability mode is determined is less than the threshold value of the active disconnection control, the disconnection device is directly triggered. Specifically, the disconnection device is triggered as follows: if it is a power angle instability mode, the corresponding out-of-step disconnection control is triggered; if it is a voltage instability mode, the corresponding low-voltage disconnection control is triggered.

[0165] Example 3

[0166] The present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the transient dominant instability mode discrimination method.

[0167] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention 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.

[0168] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations 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, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0169] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0170] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0171] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit its scope of protection. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that after reading the present invention, they can still make various changes, modifications or equivalent substitutions to the specific implementation of the invention, but these changes, modifications or equivalent substitutions are all within the scope of protection of the pending claims of the invention.

Claims

1. A method for identifying transient dominant instability patterns, characterized in that, include: Obtain the voltage phasor of the node with the lowest voltage across the entire network; Determine whether to activate the dominant instability mode discrimination algorithm based on the voltage phasor of the node with the lowest voltage in the entire network. If activated, proceed to the next step; otherwise, obtain the voltage phasor of the node with the lowest voltage in the entire network at the next moment. Calculate the dominant instability pattern combination criterion and use the dominant instability pattern combination criterion to obtain the dominant instability pattern discrimination result; The criteria for determining the dominant instability pattern combination specifically include: （8） （9） （10） （11） （12） in, Initial time t 1 to the end time t n The cumulative deflection angle of the voltage phasor trajectories between them. γ th Δ is the threshold value for accumulating deflection angle. t For duration, T th Duration Δ t The threshold value, P It is the proportion of the distance from the point where the vertical voltage falls to the beginning of the line to the total length of the line; An emergency control strategy is generated based on the relationship between the voltage amplitude of the node with the lowest voltage in the entire network when the dominant instability mode is determined and the active disconnection control threshold value. The voltage amplitude is the magnitude of the voltage phasor.

2. The transient dominant instability mode discrimination method according to claim 1, characterized in that, The specific steps for obtaining the voltage phasor of the node with the lowest voltage across the entire network are as follows: Starting from the moment the fault disappears, after a preset time delay, the voltage phasor of the node with the lowest voltage in the entire network is obtained using a measuring device.

3. The transient dominant instability mode discrimination method according to claim 1, characterized in that, The method of determining whether to activate the dominant instability mode discrimination algorithm based on the voltage phasor of the node with the lowest voltage in the entire network is as follows: if the voltage amplitude of the node with the lowest voltage in the entire network is less than the threshold value and shows a monotonically decreasing trend, then the dominant instability mode discrimination algorithm is activated.

4. The method for determining transient dominant instability patterns according to claim 1, characterized in that, The deflection angle of the voltage phasor trajectory between two adjacent time periods in the dominant instability mode combination criterion γ The method for obtaining this information is as follows: Where, vector AB = ( x 2– x 1, y 2– y 1), Vector BC = ( x 3– x 2, y 3– y 2), ( x 1, y 1) are the coordinates of point A, ( x 2, y 2) are the coordinates of point B, x 3, y 3) Let A, B, and C be the coordinates of point C, and let A, B, and C be any three ordered points in a rectangular coordinate system.

5. The method for determining transient dominant instability patterns according to claim 1, characterized in that, The method for determining the proportion of the distance from the point where the vertical voltage falls to the beginning of the line to the total length of the line is as follows: in, U A This refers to the voltage at the beginning of the AC line. φ AB The line power factor angle. X AB For line reactance, I This represents the line current.

6. The method for determining transient dominant instability patterns according to claim 1, characterized in that, The method of obtaining the dominant instability pattern discrimination result using the dominant instability pattern combination criterion is as follows: If equations (8), (9) and (11) are satisfied at the same time, it is determined to be a power angle instability mode; if equations (9) and (10) or equations (8), (9) and (12) are satisfied at the same time, it is determined to be a voltage instability mode.

7. The transient dominant instability mode discrimination method according to claim 6, characterized in that, The emergency control strategy is generated based on the relationship between the voltage amplitude of the node with the lowest voltage in the entire network when the dominant instability mode is determined and the active disconnection control threshold. Specifically: If the voltage of the node with the lowest voltage in the entire network when the dominant instability mode is determined is greater than or equal to the active disconnection control threshold, then the corresponding emergency control measures will be applied. If the voltage of the node with the lowest voltage across the entire network when the dominant instability mode is determined is less than the active disconnection control threshold, the disconnection device will be directly triggered.

8. The transient dominant instability mode discrimination method according to claim 7, characterized in that, The specific procedures for handing over the corresponding emergency control measures are as follows: if the problem is power angle instability, then the corresponding power angle stabilization emergency control will be applied; if the problem is voltage instability, then the corresponding voltage stabilization emergency control will be applied. The direct-triggered disconnection device operates as follows: if the power angle is unstable, it triggers the corresponding out-of-step disconnection control; if the voltage is unstable, it triggers the corresponding low-voltage disconnection control.

9. A transient dominant instability mode discrimination system, characterized in that, include: Acquisition module: Used to acquire the voltage phasor of the node with the lowest voltage in the entire network; Startup module: Used to determine whether to start the dominant instability mode discrimination algorithm based on the voltage phasor of the node with the lowest voltage in the entire network. If started, it enters the discrimination module; otherwise, it obtains the voltage phasor of the node with the lowest voltage in the entire network at the next moment. Discrimination module: used to calculate the dominant instability mode combination criteria and obtain the dominant instability mode discrimination result using the dominant instability mode combination criteria; The criteria for determining the dominant instability pattern combination specifically include: （8） （9） （10） （11） （12） in, Initial time t 1 to the end time t n The cumulative deflection angle of the voltage phasor trajectories between them. γ th Δ is the threshold value for accumulating deflection angle. t For duration, T th Duration Δ t The threshold value, P The ratio of the distance from the point where the vertical voltage falls to the beginning of the line to the total length of the line. Control module: Used to generate an emergency control strategy based on the relationship between the voltage of the node with the lowest voltage in the entire network when the dominant instability mode is determined and the active disconnection control threshold value, wherein the voltage amplitude is the magnitude of the voltage phasor.

10. The transient dominant instability mode discrimination system according to claim 9, characterized in that, In the startup module, the dominant instability mode discrimination algorithm is started based on the voltage phasor of the node with the lowest voltage in the entire network. Specifically, if the voltage amplitude of the node with the lowest voltage in the entire network is less than the threshold value and shows a monotonically decreasing trend, then the dominant instability mode discrimination algorithm is started.

11. The transient dominant instability mode discrimination system according to claim 9, characterized in that, The method of obtaining the dominant instability pattern discrimination result using the dominant instability pattern combination criterion is as follows: If equations (8), (9) and (11) are satisfied at the same time, it is determined to be a power angle instability mode; if equations (9) and (10) or equations (8), (9) and (12) are satisfied at the same time, it is determined to be a voltage instability mode.

12. The transient dominant instability mode discrimination system according to claim 11, characterized in that, In the control module, an emergency control strategy is generated based on the relationship between the voltage of the node with the lowest voltage across the entire network when the dominant instability mode is determined and the active disconnection control threshold value. Specifically: If the voltage of the node with the lowest voltage in the entire network when the dominant instability mode is determined is greater than or equal to the active disconnection control threshold, then the corresponding emergency control measures will be applied. If the voltage of the node with the lowest voltage across the entire network when the dominant instability mode is determined is less than the active disconnection control threshold, the disconnection device will be directly triggered.

13. The transient dominant instability mode discrimination system according to claim 12, characterized in that, In the control module, the handover to the corresponding emergency control is specifically as follows: if it is a power angle instability state, then the power angle instability state is handed over to the power angle stabilization emergency control; if it is a voltage instability state, then the voltage instability state is handed over to the voltage stabilization emergency control. The direct-triggered disconnection device operates as follows: if the power angle is unstable, it triggers the corresponding out-of-step disconnection control; if the voltage is unstable, it triggers the corresponding low-voltage disconnection control.

14. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of the transient dominant instability mode discrimination method as described in any one of claims 1 to 8.

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