A method and system for identifying the vertical foot voltage landing point corresponding to the out-of-step oscillation center

Abstract

The present invention discloses a method for identifying the vertical foot voltage drop point corresponding to the center of an out-of-step oscillation, and a system having the method. The method for identifying the vertical foot voltage drop point corresponding to the center of an out-of-step oscillation is based on the wide-area branch response and utilizes the reactive power flowing at the beginning and end of the branch to construct a vertical foot voltage drop point identification criterion. The obtained result can eliminate the risk of misjudgment caused by pseudo-vertical foot drop points in the selection of disconnection sections and the identification of dominant forms, thereby ensuring the accuracy of subsequent emergency control. The present invention only requires measurement at both ends of the branch, has good applicability, and has engineering application value.

Description

Technical Field

[0001] The present invention relates to the technical field of large power grid transient stability analysis and control applications, and in particular to a method and system for identifying a dropout voltage point corresponding to an out-of-step oscillation center. Background Art

[0002] During the out-of-step oscillation process of the power system, multiple vertical foot voltage drop points often appear at a certain moment. Some vertical foot voltage drop points will tend to drift toward the out-of-step oscillation center as the power angle continues to swing, until the voltage reaches zero and forms an out-of-step section. Such drop points can be defined as: the vertical foot voltage drop point corresponding to the out-of-step oscillation center (hereinafter referred to as the "true vertical foot drop point"); some vertical foot voltage drop points only appear on some branches for a short time, and then disappear as the power angle continues to swing, and will not tend to drift toward the out-of-step oscillation center and develop into a voltage reaching zero point. Such drop points can be defined as: the vertical foot voltage drop point corresponding to the non-out-of-step oscillation center (hereinafter referred to as the "pseudo vertical foot drop point").

[0003] False vertical foot landing points not only affect the accuracy of disconnection section selection but can also lead to misjudgment of the dominant instability pattern. Currently, most research on vertical foot voltage landing points focuses on locating multiple vertical foot voltage landing points, and no research has been found on distinguishing true and false vertical foot landing points. Therefore, it is urgent to identify the vertical foot voltage landing point corresponding to the out-of-step oscillation center to avoid the risk of stability failure accidents. Summary of the Invention

[0004] The present invention aims to address at least one of the technical problems existing in the prior art. To this end, the present invention proposes a method for identifying the vertical foot voltage drop point corresponding to the out-of-step oscillation center. This method, based on the wide-area branch response, utilizes the reactive power flowing at the beginning and end of the branch to construct a vertical foot voltage drop point identification criterion. The obtained result eliminates the risk of misjudgment caused by false vertical foot drop points in the selection of disconnection sections and the identification of dominant forms, thereby ensuring the accuracy of subsequent emergency control.

[0005] The present invention also provides a system having a method for selecting a controllable ratio of a controllable lightning arrester under the above-mentioned restricted conditions.

[0006] The method for identifying the vertical foot voltage landing point corresponding to the out-of-step oscillation center according to the first embodiment of the present invention is characterized by comprising the following steps:

[0007] Real-time acquisition of voltage and reactive power at the beginning and end of key tie lines;

[0008] Identify the vertical foot voltage location based on the voltage and phase difference at both ends of the line;

[0009] The relationship between the longitudinal and transverse components of the line voltage drop is obtained using the head-end power, and based on the head-end active power and the head-end reactive power, it is determined whether the base of the terminal voltage vector triangle is an acute angle.

[0010] The terminal power is used to obtain the relationship between the longitudinal and transverse components of the line voltage drop, and based on the terminal active power and terminal reactive power, it is determined whether the base of the terminal voltage vector triangle is an acute angle.

[0011] Based on the above judgment results, the constraints, numerical constraints and frequency of occurrence of the power flow scenarios at the beginning and end of the line are summarized.

[0012] Based on the reactive power flow direction at the head and end, the authenticity of the vertical foot landing point in different scenarios is judged.

[0013] The method for identifying the vertical foot voltage drop point corresponding to the out-of-step oscillation center according to an embodiment of the present invention has at least the following beneficial effects: Starting from the perspective of wide-area branch response, this method utilizes the reactive power flowing at the beginning and end of the branch to construct a vertical foot voltage drop point identification criterion. The obtained result can eliminate the risk of misjudgment caused by false vertical foot drops in the selection of disconnection sections and the identification of dominant forms, thereby ensuring the accuracy of subsequent emergency control. The present invention only requires measurement of quantities at both ends of the branch, has good applicability, and has engineering application value.

[0014] According to some embodiments of the present invention, after the step of combining and summarizing the constraints, numerical constraints, and frequency of occurrence of the power flow scenarios at the line headend and the line end based on the above-mentioned judgment results, the following step is further included:

[0015] Based on the electrical amplitude, potential power angle, node voltage and node voltage phase angle, and line impedance on both sides of the branch, the monotonicity of the active and reactive power of the branch during the out-of-step process is determined;

[0016] Based on the development trend of the voltage foot point in different scenarios and the monotonicity of power, the development trend of the voltage foot in the corresponding situation is analyzed to identify the authenticity of the voltage foot point in different scenarios.

[0017] According to some embodiments of the present invention, in the step of obtaining the voltage and reactive power of the key tie lines in real time, the flow reactive power is used instead of the reactive power as the input for subsequent judgment, and the formula is:

[0018]

[0019] Among them, Q AB , Q BA Respectively measure reactive power at the beginning and end, Q 1AB , Q 1BA are the reactive power flowing at the beginning and end, ΔQ yA , ΔQ yB are the reactive power of the first and the end charging, b yA 、b yB are the first and the end parallel susceptance to ground, UA 、U B are the voltages of the first and last nodes respectively.

[0020] According to some embodiments of the present invention, in the step of identifying the vertical foot voltage drop location based on the voltages and phase differences at both ends of the line, the formula for determining the voltage drop location criterion L is:

[0021] L=(|U1|cosθ-|U2|)(|U2|cosθ-|U1|)

[0022] Among them, U1 and U2 are the voltages at the two end points of the line respectively; θ is the phase difference of the line.

[0023] According to some embodiments of the present invention, the relationship between the longitudinal and transverse components of the line voltage drop obtained by using the head-end power is specifically:

[0024]

[0025] Among them, ΔU1 is the vertical component of the voltage drop at the first end, δU1 is the horizontal component of the voltage drop at the first end, P AB is the active power at the head end, R is the resistance of the transmission line, X is the reactance of the transmission line, U A 、U B are the voltage amplitudes at the beginning and end, Q AB is the reactive power at the head end.

[0026] According to some embodiments of the present invention, the relationship between the longitudinal and transverse components of the line voltage drop obtained by using the terminal power is specifically as follows:

[0027]

[0028] Among them, ΔU2 is the vertical component of the terminal voltage drop, δU2 is the horizontal component of the terminal voltage drop, P' AB is the active power flowing into the terminal, Q' AB is the reactive power flowing into the terminal.

[0029] According to some embodiments of the present invention, in the step of judging the authenticity of the vertical foot landing point in different scenarios based on the reactive power flow direction of the head and the end, the judgment is based on the following: if the actual flow directions of the reactive power at the head and the end are consistent, the vertical foot landing point is false; if the actual flow directions of the reactive power at the head and the end are both flowing from the two end points into the line, the vertical foot is true; the judgment is based on T>0 indicating that the vertical foot landing point existing inside the branch is true, and T<0 indicating that the existing vertical foot landing point is false. The specific formula is:

[0030] T=Q 1AB Q 1BA

[0031] Among them, Q 1AB , Q1BA are the reactive powers flowing at the beginning and end of the branch respectively.

[0032] The system for identifying the vertical foot voltage point corresponding to the out-of-step oscillation center according to the second embodiment of the present invention is characterized by comprising:

[0033] The data acquisition module can obtain the voltage and reactive power of the beginning and end of key tie lines in real time;

[0034] The vertical foot voltage point positioning module can identify the vertical foot voltage point based on the voltage and phase difference at both ends of the line;

[0035] The head-end voltage vector triangle simulation module can use the head-end power to calculate the relationship between the longitudinal and transverse components of the line voltage drop, and determine whether the base of the head-end voltage vector triangle is an acute angle based on the head-end active power and the head-end reactive power;

[0036] The terminal voltage vector triangle simulation module uses the terminal power to obtain the relationship between the longitudinal and transverse components of the line voltage drop, and determines whether the base of the terminal voltage vector triangle is an acute angle based on the terminal active power and terminal reactive power;

[0037] The scenario summarization module can combine the judgment results of the above modules to summarize the constraints, numerical constraints and frequency of scenario occurrence under the scenarios of power flow at the head end and the end end of the line;

[0038] The authenticity identification module can determine the authenticity of the vertical foot landing point in different scenarios based on the flow direction of reactive power flowing at the head and end.

[0039] According to some embodiments of the present invention, the system further comprises:

[0040] The out-of-step monotonicity analysis module can determine the monotonicity of the active and reactive power of the branch during the out-of-step process based on the electrical amplitude, potential power angle, node voltage and node voltage phase angle, and line impedance on both sides of the branch;

[0041] The module for distinguishing the true and false vertical foot landing points can analyze the development trend of the voltage vertical foot landing point in different scenarios based on the development trend of the voltage vertical foot landing point and the monotonicity of power in the corresponding situations, thereby distinguishing the authenticity of the voltage vertical foot landing point in different scenarios.

[0042] According to some embodiments of the present invention, the data acquisition module uses flow reactive power instead of reactive power as the input for subsequent judgment, and the formula is:

[0043]

[0044] Among them, Q AB , Q BA Respectively measure reactive power at the beginning and end, Q1AB , Q 1BA are the reactive power flowing at the beginning and end, ΔQ yA , ΔQ yB are the reactive power of the first and the end charging, b yA 、b yB are the first and the end parallel susceptance to ground, U A 、U B are the voltages of the first and last nodes respectively.

[0045] According to some embodiments of the present invention, the vertical foot voltage point location module determines the voltage point location using the formula L:

[0046] L=(|U1|cosθ-|U2|)(|U2|cosθ-|U1|)

[0047] Among them, U1 and U2 are the voltages at the two end points of the line respectively; θ is the phase difference of the line.

[0048] According to some embodiments of the present invention, in the head-end voltage vector triangle simulation module, the head-end power is used to obtain the relationship between the longitudinal and transverse components of the line voltage drop. The specific formula is:

[0049]

[0050] Among them, ΔU1 is the vertical component of the voltage drop at the first end, δU1 is the horizontal component of the voltage drop at the first end, P AB is the active power at the head end, R is the resistance of the transmission line, X is the reactance of the transmission line, U A 、U B are the voltage amplitudes at the beginning and end, Q AB is the reactive power at the head end.

[0051] According to some embodiments of the present invention, in the terminal voltage vector triangle simulation module, the terminal power is used to obtain the relationship between the longitudinal and transverse components of the line voltage drop. The specific formula is:

[0052]

[0053] Among them, ΔU2 is the vertical component of the terminal voltage drop, δU2 is the horizontal component of the terminal voltage drop, P' AB is the active power flowing into the terminal, Q' AB is the reactive power flowing into the terminal.

[0054] According to some embodiments of the present invention, in the authenticity identification module, the judgment basis T>0 indicates that the vertical foot landing point inside the branch is true, and T<0 indicates that the vertical foot landing point is false. The specific formula is:

[0055] T=Q 1ABQ 1BA

[0056] Among them, Q 1AB , Q 1BA are the reactive powers flowing at the beginning and end of the branch respectively.

[0057] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0059] Figure 1 Schematic diagram of a transmission line model taking into account ground capacitance according to an embodiment of the present invention;

[0060] Figure 2 A schematic diagram of a simple model of a power transmission line according to an embodiment of the present invention;

[0061] Figure 3 Schematic diagram of an endpoint voltage vector triangle according to an embodiment of the present invention; (a) and (b) represent voltage vector triangles under different scenarios;

[0062] Figure 4 Schematic diagram of the longitudinal and transverse components of the head-end voltage drop according to an embodiment of the present invention;

[0063] Figure 5 Schematic diagram of the longitudinal and transverse components of the terminal voltage drop according to an embodiment of the present invention;

[0064] Figure 6 This is a schematic diagram of an equivalent two-machine model according to an embodiment of the present invention;

[0065] Figure 7 Schematic diagram of the distribution of vertical foot voltage points according to an embodiment of the present invention;

[0066] Figure 8 is a voltage vector diagram according to an embodiment of the present invention;

[0067] Figure 9 Schematic diagram of the criterion T for an equivalent two-machine system according to an embodiment of the present invention;

[0068] Figure 10 This is a structural block diagram of a system for identifying the vertical foot voltage landing point corresponding to the out-of-step oscillation center provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0069] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0070] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention.

[0071] In the description of the present invention, "several" means one or more, "many" means more than two, "greater than," "less than," and "exceed" are understood to exclude the number itself, while "above," "below," and "within" are understood to include the number itself. The use of "first" and "second" in the description is solely for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance, implicitly specifying the number of the indicated technical features, or implicitly specifying the order of the indicated technical features.

[0072] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, and connecting should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0073] Example 1

[0074] The embodiment of the present application provides a method for identifying the vertical foot voltage drop point corresponding to the out-of-step oscillation center, the purpose of which is to identify the authenticity of the vertical foot voltage drop point and provide a basis for the stable operation of the power system. Specifically, the method includes at least the following steps:

[0075] Step S100: obtaining the voltage and reactive power of the beginning and end of the key tie line in real time.

[0076] Set the strategy delay start time T after the fault disappears delay , from the moment the fault disappears, after a time delay of T delay Finally, the real-time measuring device is used to obtain the voltage and reactive power at the beginning and end of the key interconnection lines.

[0077] by Figure 1 Taking the transmission line model shown in the figure as an example, b yA 、b yB are the first and the end parallel susceptance to ground, Q AB , Q BA Respectively measure reactive power at the beginning and end, Q 1AB, Q 1BA are the reactive power at the beginning and end, ΔQ yA , ΔQ yB The transmission distance of medium and long overhead lines is generally more than 100km. The ground capacitance of such lines is generally not negligible. The ground charging reactive power has a significant effect on the reactive power of the head and end, as well as the compensation effect on the terminal voltage. Even if the compensation effect weakens as the voltage along the line continues to drop, it is very easy to cause the measured reactive power Q to be higher in the early stage of out-of-step oscillation. AB and the flow reactive Q 1AB The flow direction is inconsistent, at this time Q AB Alternative Q 1AB It will have a significant impact on the subsequent identification method and may cause misjudgment. Therefore, it is necessary to correct the reactive measurement at the beginning and end of the branch, and calculate the earth impedance as the reactive load at the branch end to calculate the reactive load Q 1AB , Q 1BA Replace Q respectively AB , Q BA As the input quantity of the subsequent judgment, as shown in formula (1).

[0078]

[0079] Step S200 : Identify the vertical foot voltage landing point based on the voltages and phase differences at both ends of the line.

[0080] It is known that the two base angles of the triangle formed by the endpoint voltage vectors of the branch where the vertical foot voltage falls are both acute angles. Based on this feature, the vertical foot voltage falling point location criterion L is shown in Equation (2). The criterion L is used to screen and determine the vertical foot voltage falling point set at the current moment. If the criterion L is greater than 0, it means that the vertical foot voltage falling point is inside the line; if it is equal to 0, it means that it is at the line endpoint; and if it is less than 0, it means that it is outside the line.

[0081] L=(|U1|cosθ-|U2|)(|U2|cosθ-|U1|) (2)

[0082] Where: U1 and U2 are the voltages at the two end points of the line respectively; θ is the phase difference of the line.

[0083] Step S300: derive the relationship between the longitudinal and transverse components of the line voltage drop using the head-end power, and determine whether the base of the terminal voltage vector triangle is an acute angle based on the head-end active power and the head-end reactive power.

[0084] A simple model of a transmission line is Figure 2 As shown, U A 、U B are the voltage amplitudes at the beginning and end, θ A ,θ Bare the phase angles of the head and end voltages respectively, R + jX is the impedance of the transmission line, and it is agreed that P AB , P' AB are the active powers of the head and end respectively, and Q AB , Q' AB are the reactive powers of the head and end respectively. The power flow shown in the figure is the reference flow. The triangle formed by the voltage vectors at the endpoints of the transmission line is as Figure 3 shown. Only when the two base angles θ1 and θ2 of the triangle are both acute angles, will there be a foot voltage drop point inside the line. Analyze the relationship between the position of the foot voltage drop point and the branch power from this angle.

[0085] The relationships for obtaining the longitudinal and transverse components of the line voltage drop using the head power are shown in Equation (3), and the voltage vector is schematically shown as Figure 4 shown. To ensure that the base angle θ1 on the head side of the line is an acute angle, the longitudinal component of the voltage drop ΔU1 must be greater than zero. Therefore, the constraint on the foot voltage drop point located inside the line for the head power can be expressed as Equation (4).

[0086]

[0087] P AB R + Q AB X > 0 (4)

[0088] ① When P AB > 0, Q AB > 0

[0089] From Equation (4), the constraint relationship is obtained as shown in Equation (5). The actual flows of the head active and reactive powers are both consistent with the reference flow, which can make θ1 an acute angle. This constraint has nothing to do with the numerical value of the head power, that is, there is no numerical constraint.

[0090]

[0091] ② When P AB < 0, Q AB > 0

[0092] The actual flows of the head active and reactive powers are opposite, and their constraint relationship is shown in Equation (6). Given that R << X in the high-voltage transmission line, the numerical value of the head power must satisfy |Q AB / P AB | > (R / X) ≈ 0 to make θ1 an acute angle, and the condition is relatively loose.

[0093]

[0094] ③ When P AB < 0, Q AB < 0

[0095] The constraint relationship under this assumption is the same as formula (6). The power value at the head end satisfies (-Q AB / P AB )<0<(R / X), that is, Equation (6) cannot hold, indicating that under this assumption, there is no condition for θ1 to be an acute angle.

[0096] ④ When P AB >0,Q AB <0 hours

[0097] The constraint relationship under this assumption is the same as formula (5). The power value at the head end must satisfy |Q AB / P AB |<(R / X)≈0, meaning the reactive power is much smaller than the active power, makes θ1 an acute angle. Compared to cases 1 and 2, case 4 presents the most stringent conditions for making θ1 an acute angle.

[0098] Step S400: derive the relationship between the longitudinal and transverse components of the line voltage drop using the terminal power, and determine whether the base of the terminal voltage vector triangle is an acute angle based on the terminal active power and the terminal reactive power.

[0099] The vertical and horizontal components of the line voltage drop are obtained by using the terminal power, as shown in formula (7). The voltage vector is as follows: Figure 5 To ensure that θ2 is an acute angle, the longitudinal component ΔU2 must be less than zero, and the vertical foot voltage point is located inside the line. The constraint on the terminal power is expressed as formula (8).

[0100]

[0101] P′ AB R+Q′ AB X<0 (8)

[0102] ① When P' AB >0, Q' AB >0 hours

[0103] From formula (8), we can get formula (9), at this time the terminal power value satisfies (-Q' AB / P' AB )<0<(R / X), which contradicts Equation (9), indicating that under this assumption, there is no condition for θ2 to be an acute angle.

[0104]

[0105] ② When P' AB <0, Q' AB >0 hours

[0106] The constraint relationship under this assumption is shown in Equation (10). The actual flow directions of active and reactive power at the end are opposite, and the values ​​must satisfy |Q' AB / P' AB|<(R / X)≈0 can make θ2 an acute angle. Compared with cases ③ and ④, the condition for making θ2 an acute angle under the assumption of case ② is the most stringent.

[0107]

[0108] ③ When P' AB <0, Q' AB <0 hours

[0109] The constraint relationship under this assumption is the same as equation (10). The actual flow direction of the terminal active and reactive power is opposite to the reference flow direction, which makes θ2 an acute angle. This constraint is independent of the value of the terminal power, that is, there is no numerical constraint.

[0110] ④ When P' AB >0, Q' AB <0 hours

[0111] The constraint relationship under this assumption is the same as formula (9). The terminal power value must satisfy |Q' AB / P' AB Only when |>(R / X)≈0 can θ2 be an acute angle, and the condition is relatively loose.

[0112] Step S500: Based on the above judgment results, the constraint conditions, numerical constraints and frequency of occurrence of the scenarios of power flow at the head end and the end end of the line are combined and summarized.

[0113] Based on the above analysis, we can see that there are nine scenarios in which both base angles θ1 and θ2 of the line endpoint voltage vector triangle are acute angles (three head-end power constraints × three tail-end power constraints). The following will analyze the difficulty of different scenarios based on the looseness of the head-end and tail-end power numerical constraints. The scenario combinations are shown in Table 1.

[0114] Table 1 Scenario combination table

[0115]

[0116]

[0117] Note: The increasing numbers of the difficulty index represent the increasing difficulty of the scene

[0118] 1) Scenario b

[0119] When the actual flow direction of active and reactive power at the beginning and end points is from the two end points to the interior of the line, the conclusion that the two base angles θ1 and θ2 of the vector triangle are both acute angles does not constrain the values ​​of the power at the beginning and end. In other words, the validity of the conclusion depends only on the actual flow direction of power. Therefore, the difficulty index of this type of scenario is determined to be 0.

[0120] 2) Scenarios c and e

[0121] When the actual flow directions of active power at the beginning and end are the same, and the actual flow directions of reactive power at the beginning and end are from the two end points to the interior of the line, the double acute angle conclusion has no numerical constraints on the end where the actual flow directions of active and reactive power are the same, and only has loose numerical constraints on the end where the actual flow directions are opposite. Therefore, the difficulty index of this type of scenario is 1.

[0122] 3) Scenarios a and h

[0123] When the actual reactive power flows in the same direction at the beginning and end points, and the actual active power flows from the two end points toward the interior of the line, the double acute angle conclusion imposes stringent numerical constraints only on the end where the actual active and reactive power flows in opposite directions. The difficulty index for determining the occurrence of this scenario is 2.

[0124] 4) Scenario d and i

[0125] When the actual flow directions of active power at the beginning and end are the same, and the actual flow directions of reactive power are also the same, the double acute angle conclusion has loose numerical constraints on one end and more stringent numerical constraints on the other end. Therefore, the difficulty index of this scenario is 3.

[0126] 5) Scenes f and g

[0127] Scenario f, in which the actual flow of active power at the beginning and end of the line is from within the line to the two end points, does not exist because there is no active power source within the line. Considering the influence of the line charging power, scenario g, in which the actual flow of reactive power at the beginning and end of the line is from within the line to the two end points, may occur. However, in the π-type equivalent circuit of the line, the earth susceptance can be converted into the load at the node. After this conversion, scenario g does not exist.

[0128] Furthermore, according to some preferred embodiments of the present application, after step S500, the following steps are further included:

[0129] Step A100: Based on the electrical amplitude, potential power angle, node voltage and node voltage phase angle, and line impedance on both sides of the branch, determine the monotonicity of the active and reactive power of the branch during the out-of-step process.

[0130] by Figure 6 Taking the equivalent two-machine model of the power system as an example, E M 、E N are the internal potential amplitudes on both sides, δ is the internal potential angle of the sending end unit, U a 、U b are the voltages of two nodes along the line, θ a ,θ bare the voltage phase angles of the two nodes, and Z1, Z2, and Z3 are the impedances of the three segments along the line. When the system loses step oscillation, the power angle δ changes periodically within [0°, 360°], and the voltage on the line will reach zero (also known as the "out-of-step oscillation center", and its location is recorded as OC). The voltage amplitude and phase angle of observation point i are U i ,θ i , the impedance of this point from the first end potential is Z i , the current flowing from the observation point to the receiving end is I i , power is P i +jQ i .

[0131] In order to investigate the monotonicity of the power flowing from the observation point to the receiving end during the out-of-step process, let k = E M / E N , t∠θ t =Z i / Z ∑ , the system impedance angle is I i 、U i As shown in formula (11) and formula (12), P i , Q i As shown in formula (13) and (14) respectively.

[0132]

[0133]

[0134]

[0135]

[0136] because θ t ≈0°, and then we can get equations (15) and (16) by substituting them into equations (13) and (14) and taking the derivative of δ. From equation (15), we can see that when δ changes within [0°, 90°], P i As δ increases, P increases; when δ changes within [90°, 180°], i It decreases as δ increases. From formula (16), we can see that when t<1 / 2, the observation point is on the left side of the impedance midpoint, Q i It increases with the increase of δ; when t>1 / 2, the observation point is on the right side of the impedance midpoint, Q i It decreases as δ increases; by the same token, the monotonicity of the reactive power flowing from the observation point to the sending end is opposite to the monotonicity of the reactive power flowing to the receiving end; when k≈1, the voltage to zero point OC is located near the midpoint of the impedance, so it can be considered that the change of the reactive power on both sides of OC is monotonic, that is, the reactive power flowing from the nodes on both sides of OC to OC increases monotonically during the out-of-step process.

[0137]

[0138]

[0139] Step A200: Based on the development trend of the voltage footfall points in different scenarios and the monotonicity of the power, the development trend of the voltage footfall in corresponding situations is analyzed, thereby distinguishing the authenticity of the voltage footfall points in different scenarios.

[0140] Scenario i usually occurs on the right branch of the impedance midpoint, such as Figure 6 The line bN in the model shown. As δ gradually swings to more than 90°, |Q AB |Increment,|P AB |Decrement,|Q AB / P AB |Increases gradually. The vertical foot voltage drop point on such branches will be affected by the power value constraint |Q AB / P AB |<(R / X) cannot be satisfied and disappears; similarly, scenario d corresponds to the line Ma after δ is reversely swung to less than -90° ( Figure 6 The vertical foot voltage drop point on such a branch will be affected by the stringent numerical constraints |Q' AB / P' AB |<(R / X) cannot be satisfied and disappears. Therefore, the vertical foot voltage landing point in scenarios d and i will not develop into a voltage zero point, that is, a pseudo vertical foot landing point.

[0141] Scenario a(h) usually occurs in Figure 6 In the model shown, on the branches to the left (right) of the impedance midpoint, the reactive power at the head and tail ends, which actually flow in the same direction, is large, resulting in significant branch active power losses. This causes the actual flow of reactive power from the head and tail ends to the interior of the line. Similarly, the vertical foot voltage drop point in this scenario will disappear due to the inability to meet the stringent numerical constraints, resulting in a pseudo-vertical foot drop point.

[0142] Scenario c shows the situation where the vertical foot voltage point is located inside the OC point branch during the process of δ swinging forward to more than 90°. As δ gradually swings, |Q' AB |Increment,|P' AB |First increase and then decrease. In general, the numerical constraints of the vertical foot voltage drop point on the terminal power|Q' AB / P' AB |>(R / X)≈0 is continuously satisfied, and there is no numerical constraint on the head-end power. Scenario e corresponds to the situation where the vertical foot voltage landing point is inside the OC landing point branch during the reverse swing of δ to less than -90°. In general, the numerical constraint condition for the head-end power |Q AB / P AB|>(R / X)≈0 is consistently satisfied, with no numerical constraints on the terminal power. Scenario b corresponds to a situation where the vertical foot voltage dropout point is within the OC dropout point branch and the branch active power loss is significant. In this case, there are no numerical constraints on either the head or terminal power. Therefore, the vertical foot voltage dropout point in scenarios b, c, and e will develop into a voltage-zero point, i.e., a true vertical foot dropout point.

[0143] Step S600: judging the authenticity of the vertical foot landing point in different scenarios based on the reactive power flow direction of the head and terminal ends.

[0144] The actual flow directions of reactive power at the head and end of the pseudo-vertical foot landing scenarios a, h, d, and i remain consistent, while the actual flow directions of reactive power at the head and end of the true vertical foot landing scenarios b, c, and e all flow from the two end points into the line interior. Therefore, the reactive power flow directions at the head and end can be used as an important basis for distinguishing the authenticity of the vertical foot landing point. The true and false vertical foot landing point discrimination criterion T is constructed as shown in Equation (17). T>0 indicates that the vertical foot landing point inside the branch is true, and T<0 indicates that the vertical foot landing point is false.

[0145] T=Q 1AB Q 1BA (17)

[0146] Where Q 1AB , Q 1BA are the reactive powers flowing at the beginning and end of the branch respectively.

[0147] Example 2

[0148] Another embodiment of the present application provides a system for identifying the vertical foot voltage landing point corresponding to the out-of-step oscillation center, such as Figure 10 As shown, the system 10 includes:

[0149] Data acquisition module 101, capable of obtaining the voltage and reactive power of the key tie lines at the beginning and end in real time;

[0150] The vertical foot voltage point location module 102 can identify the vertical foot voltage point location based on the voltage and phase difference at both ends of the line;

[0151] The head-end voltage vector triangle simulation module 103 can use the head-end power to obtain the relationship between the longitudinal and transverse components of the line voltage drop, and determine whether the base of the head-end voltage vector triangle is an acute angle based on the head-end active power and the head-end reactive power;

[0152] The terminal voltage vector triangle simulation module 104 uses the terminal power to obtain the relationship between the longitudinal and transverse components of the line voltage drop, and determines whether the base of the terminal voltage vector triangle is an acute angle based on the terminal active power and terminal reactive power;

[0153] The scenario summarization module 105 can combine and summarize the constraints, numerical constraints and frequency of occurrence of the scenarios under the power flow direction of the line headend and the end end based on the judgment results of the above modules;

[0154] The authenticity identification module 106 can determine the authenticity of the vertical foot landing point in different scenarios based on the reactive power flow direction of the head and terminal ends.

[0155] Furthermore, the data acquisition module 101 uses flow reactive power instead of reactive power as the input for subsequent judgment, and the formula is:

[0156]

[0157] Among them, Q AB , Q BA Respectively measure reactive power at the beginning and end, Q 1AB , Q 1BA are the reactive power flowing at the beginning and end, ΔQ yA , ΔQ yB are the reactive power of the first and the end charging, b yA 、b yB are the first and the end parallel susceptance to ground, U A 、U B are the voltages of the first and last nodes respectively.

[0158] Furthermore, the vertical foot voltage point location module 102 determines the voltage point location using the following formula:

[0159] L=(|U1|cosθ-|U2|)(|U2|cosθ-|U1|)

[0160] Among them, U1 and U2 are the voltages at the two end points of the line respectively; θ is the phase difference of the line.

[0161] Furthermore, in the head-end voltage vector triangle simulation module 103, the head-end power is used to obtain the relationship between the longitudinal and transverse components of the line voltage drop. The specific formula is:

[0162]

[0163] Among them, ΔU1 is the vertical component of the voltage drop at the first end, δU1 is the horizontal component of the voltage drop at the first end, P AB is the active power at the head end, R is the resistance of the transmission line, X is the reactance of the transmission line, U A 、U B are the voltage amplitudes at the beginning and end, Q AB is the reactive power at the head end.

[0164] Furthermore, in the terminal voltage vector triangle simulation module 104, the terminal power is used to obtain the relationship between the longitudinal and transverse components of the line voltage drop. The specific formula is:

[0165]

[0166] Among them, ΔU2 is the vertical component of the terminal voltage drop, δU2 is the horizontal component of the terminal voltage drop, P' AB is the active power flowing into the terminal, Q' AB is the reactive power flowing into the terminal.

[0167] Furthermore, in the authenticity identification module 106, the judgment basis is that if T>0, the vertical foot landing point inside the branch is true, and if T<0, the vertical foot landing point is false. The specific formula is:

[0168] T=Q 1AB Q 1BA

[0169] Among them, Q 1AB , Q 1BA are the reactive powers flowing at the beginning and end of the branch respectively.

[0170] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, i.e., they may be located in one place or distributed across multiple network units. Some or all of the modules may be selected based on actual needs to achieve the objectives of this embodiment.

[0171] Those skilled in the art will appreciate that all or some of the steps and systems in the method disclosed above can be implemented as software, firmware, hardware, and appropriate combinations thereof. Some physical components or all physical components can be implemented as software executed by a processor, such as a central processing unit, a digital signal processor, or a microprocessor, or implemented as hardware, or implemented as an integrated circuit, such as an application-specific integrated circuit. Such software can be distributed on a computer-readable medium, and the computer-readable medium can include computer storage media (or non-transitory media) and communication media (or temporary media). As known to those skilled in the art, the term computer storage media is included in any method or technology for storing information (such as computer-readable instructions, data structures, program modules, or other data) and is volatile and non-volatile, removable, and non-removable. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory, or other memory technology, CD-ROM, digital versatile disks (DVD), or other optical disk storage, magnetic cassettes, magnetic tapes, disk storage, or other magnetic storage devices, or any other medium that can be used to store desired information and can be accessed by a computer. Furthermore, as is well known to those skilled in the art, communication media typically embodies computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism, and may include any information delivery media.

[0172] The above is a specific description of the preferred implementation of the present application, but the present application is not limited to the above implementation mode. Technical personnel familiar with the field can also make various equivalent modifications or substitutions without violating the spirit of the present application. These equivalent modifications or substitutions are all included in the scope defined by the claims of the present application.

Claims

1. A method for identifying the point of vertical foot voltage corresponding to the out-of-step oscillation center, characterized in that: The following steps are involved: Real-time acquisition of voltage and reactive power at the beginning and end of key tie lines; Identify the vertical foot voltage location based on the voltage and phase difference at both ends of the line; The relationship between the longitudinal and transverse components of the line voltage drop is obtained using the head-end power, and based on the head-end active power and the head-end reactive power, it is determined whether the base of the terminal voltage vector triangle is an acute angle. The terminal power is used to obtain the relationship between the longitudinal and transverse components of the line voltage drop, and based on the terminal active power and terminal reactive power, it is determined whether the base of the terminal voltage vector triangle is an acute angle. Based on the above judgment results, the constraints, numerical constraints and frequency of occurrence of the power flow scenarios at the beginning and end of the line are summarized. Based on the reactive power flow direction at the head and end, the authenticity of the vertical foot landing point in different scenarios is judged.

2. The method according to claim 1, characterized in that After the step of combining and summarizing the constraint conditions, numerical constraints, and frequency of occurrence of the power flow scenarios at the headend and the end of the line based on the above judgment results, the method further includes: Based on the electrical amplitude, potential power angle, node voltage and node voltage phase angle, and line impedance on both sides of the branch, the monotonicity of the active and reactive power of the branch during the out-of-step process is determined; Based on the development trend of the voltage foot point in different scenarios and the monotonicity of power, the development trend of the voltage foot in the corresponding situation is analyzed to identify the authenticity of the voltage foot point in different scenarios.

3. The method according to claim 1, characterized in that In the step of obtaining the voltage and reactive power of the key tie lines in real time, the flow reactive power is used instead of the reactive power as the input for subsequent judgment. The formula is: Among them, Q AB , Q BA Respectively measure reactive power at the beginning and end, Q 1AB , Q 1BA are the reactive power flowing at the beginning and end, ΔQ yA , ΔQ yB are the reactive power of the first and the end charging, b yA 、b yB are the first and the end parallel susceptance to ground, U A 、U B are the voltages of the first and last nodes respectively.

4. The method according to claim 1, wherein In the step of identifying the vertical foot voltage drop point location based on the voltages and phase differences at both ends of the line, the formula for determining the voltage drop point location criterion L is: L=(|U1|cosθ-|U2|)(|U2|cosθ-|U1|) Among them, U1 and U2 are the voltages at the two end points of the line respectively; θ is the phase difference of the line.

5. The method according to claim 2, characterized in that The relationship between the longitudinal and transverse components of the line voltage drop obtained by using the head-end power is specifically: Among them, ΔU1 is the vertical component of the voltage drop at the first end, δU1 is the horizontal component of the voltage drop at the first end, P AB is the active power at the head end, R is the resistance of the transmission line, X is the reactance of the transmission line, U A 、U B are the voltage amplitudes at the beginning and end, Q AB is the reactive power at the head end.

6. The method according to claim 2, characterized in that The relationship between the longitudinal and transverse components of the line voltage drop obtained by using the terminal power is specifically as follows: Among them, ΔU2 is the vertical component of the terminal voltage drop, δU2 is the horizontal component of the terminal voltage drop, P' AB is the active power flowing into the terminal, Q' AB is the reactive power flowing into the terminal.

7. The method according to claim 1, characterized in that In the step of judging the authenticity of the vertical foot landing point in different scenarios based on the reactive power flow direction of the head and the end, the judgment is based on the following: if the actual flow directions of the reactive power at the head and the end are consistent, the vertical foot landing point is false; if the actual flow directions of the reactive power at the head and the end are both flowing from the two end points into the line, the vertical foot landing point is true; the judgment is based on T>0 indicating that the vertical foot landing point inside the branch is true, and T<0 indicating that the existing vertical foot landing point is false. The specific formula is: T=Q 1AB ·Q 1BA Among them, Q 1AB , Q 1BA are the reactive powers flowing at the beginning and end of the branch respectively.

8. A system for identifying the vertical foot voltage point corresponding to the out-of-step oscillation center, characterized in that: include: The data acquisition module can obtain the voltage and reactive power of the beginning and end of key tie lines in real time; The vertical foot voltage point positioning module can identify the vertical foot voltage point based on the voltage and phase difference at both ends of the line; The head-end voltage vector triangle simulation module can use the head-end power to calculate the relationship between the longitudinal and transverse components of the line voltage drop, and determine whether the base of the head-end voltage vector triangle is an acute angle based on the head-end active power and the head-end reactive power; The terminal voltage vector triangle simulation module uses the terminal power to obtain the relationship between the longitudinal and transverse components of the line voltage drop, and determines whether the base of the terminal voltage vector triangle is an acute angle based on the terminal active power and terminal reactive power; The scenario summarization module can combine the judgment results of the above modules to summarize the constraints, numerical constraints and frequency of scenario occurrence under the scenarios of power flow at the head end and the end end of the line; The authenticity identification module can determine the authenticity of the vertical foot landing point in different scenarios based on the reactive power flow direction at the head and end terminals.

9. The system according to claim 8, characterized in that The system further comprises: The out-of-step monotonicity analysis module can determine the monotonicity of the active and reactive power of the branch during the out-of-step process based on the electrical amplitude, potential power angle, node voltage and node voltage phase angle, and line impedance on both sides of the branch; The module for distinguishing the true and false vertical foot landing points can analyze the development trend of the voltage vertical foot landing point in different scenarios based on the development trend of the voltage vertical foot landing point and the monotonicity of power in the corresponding situations, thereby distinguishing the authenticity of the voltage vertical foot landing point in different scenarios.

10. The system according to claim 8, wherein: The data acquisition module uses flow reactive power instead of reactive power as the input for subsequent judgment. The formula is: Among them, Q AB , Q BA Respectively measure reactive power at the beginning and end, Q 1AB , Q 1BA are the reactive power flowing at the beginning and end, ΔQ yA , ΔQ yB are the reactive power of the first and the end charging, b yA 、b yB are the first and the end parallel susceptance to ground, U A 、U B are the voltages of the first and last nodes respectively.

11. The system according to claim 8, wherein: The vertical foot voltage point positioning module determines the voltage point positioning criterion L by the formula: L=(|U1|cosθ-|U2|)(|U2|cosθ-|U1|) Among them, U1 and U2 are the voltages at the two end points of the line respectively; θ is the phase difference of the line.

12. The system according to claim 9, wherein: In the head-end voltage vector triangle simulation module, the head-end power is used to obtain the relationship between the longitudinal and transverse components of the line voltage drop. The specific formula is: Among them, ΔU1 is the vertical component of the voltage drop at the first end, δU1 is the horizontal component of the voltage drop at the first end, P AB is the active power at the head end, R is the resistance of the transmission line, X is the reactance of the transmission line, U A 、U B are the voltage amplitudes at the beginning and end, Q AB is the reactive power at the head end.

13. The system according to claim 12, wherein: In the terminal voltage vector triangle simulation module, the terminal power is used to obtain the relationship between the longitudinal and transverse components of the line voltage drop. The specific formula is: Among them, ΔU2 is the vertical component of the terminal voltage drop, δU2 is the horizontal component of the terminal voltage drop, P' AB is the active power flowing into the terminal, Q' AB is the reactive power flowing into the terminal.

14. The system according to claim 8, wherein: In the authenticity identification module, the judgment basis is that T>0 indicates that the vertical foot landing point inside the branch is true, and T<0 indicates that the vertical foot landing point is false. The specific formula is: T=Q 1AB ·Q 1BA Among them, Q 1AB , Q 1BA are the reactive powers flowing at the beginning and end of the branch respectively.

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