Calculation method of the nearest voltage stability critical point based on continuation power flow method and direct method

Abstract

A method for calculating the nearest voltage stability critical point based on a continuous power flow method and a direct method. In step S1, the voltage stability critical point in a predetermined power growth direction is obtained using a single continuous power flow method, and a normal vector is obtained as the new power growth direction. In step S2, the power flow equation is solved using the optimal multiplier method to estimate the critical point in the new power growth direction. In step S3, the estimated result is used as the initial value to solve the nonlinear equations satisfied by the critical point in the new power growth direction using the Newton-Raphson method to obtain the nearest voltage stability critical point. This method not only calculates the nearest voltage stability critical point using a single continuous power flow method and two direct method calculations, effectively reducing the amount of calculation, but also performs a secondary solution using the Newton-Raphson method, effectively improving calculation accuracy.

Description

Technical Field

[0001] The present invention relates to a method for calculating a nearest voltage stability critical point based on a continuous power flow method and a direct method, and in particular to a method for calculating a nearest voltage stability critical point based on a continuous power flow method and a direct method. Background Art

[0002] With the increase in the penetration rate of new energy and the increasingly prominent nonlinear characteristics of load components, the issue of voltage stability has gradually attracted attention. At present, the industry has developed a variety of methods for obtaining the critical point of system voltage stability, such as the continuous power flow method and the direct method. The continuous power flow method calculates the voltage stability critical point through multiple continuous power flow calculations, and the direct method directly calculates the voltage stability critical point after determining the initial value. These methods generally assume that the system injection power grows in a predetermined direction, and different growth directions will lead to different stability limits.

[0003] Although both methods can obtain the critical point of voltage stability, they still have the following defects:

[0004] 1. The continuous power flow method requires iterative calculations, so the amount of calculation is large.

[0005] 2. It is difficult to determine the initial value in the direct method.

[0006] The information disclosed in this background technology section is only intended to increase understanding of the overall background of the application and should not be considered as an admission or any form of suggestion that the information constitutes the prior art already known to ordinary technicians in this field. Summary of the Invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art of large amount of calculation or difficulty in determining the initial value, and to provide a method for calculating the nearest voltage stability critical point based on the continuous power flow method and the direct method, which has a small amount of calculation and can quickly and accurately determine the initial value.

[0008] To achieve the above objectives, the technical solution of the present invention is:

[0009] In a first aspect, the present invention proposes a method for calculating the nearest voltage stability critical point based on a continuation power flow method and a direct method, comprising:

[0010] The calculation method includes:

[0011] S1, from the initial operating point (x 0 ,μ 0 )Departure, x 0 is the initial state variable, μ 0 is the initial system parameter, given the injection power growth direction μ d0The voltage stability critical point (x 1 ,μ 1 ), and calculate the critical point f x The left eigenvector w corresponding to the zero eigenvalue 1 , construct the singular surface S and calculate the normal vector η 1 ;

[0012] S2. According to the calculation results of the continuous power flow method in S1, we can get μ 0 Start along η 1 Direction of the ray and μ 1 The intersection of the tangent plane T Solving the power flow equation using the optimal multiplier method Get estimated values ​​of system state variables

[0013] S3, is the initial value, the injection power growth direction μ d =η 1 Finally, the Newton-Raphson method is used to solve (x 2 ,w 2 ,λ 2 ), the new critical point is (x 2 ,μ 2 =μ 0 +λ 2 η 1 );

[0014] S4, note (x 2 ,w 2 ,μ 2 ,α 2 ) is the initial value, and the Newton-Raphson method is used to solve it again to obtain the nearest voltage stability critical point.

[0015] In S1, the tidal current equation used in the continuous tidal current method is:

[0016] f(x,μ)=0;

[0017] In the above formula, x is the system state variable, its elements are the amplitude and phase angle of the node voltage, and μ is the system parameter;

[0018] make When the parameter μ is along a certain direction μ d Change until f x Singular, at this time the system reaches the critical point of voltage stability, the expression of the critical point is:

[0019] f(x,μ 0 +λμ d )=0

[0020] f x T w 1 =0

[0021] w T w 1 -1=0;

[0022] In the above formula, the variables to be solved are (x,w 1 ,λ), the coefficient λ is the stability margin, w T is the transpose of w, w 1 f x The left eigenvector corresponding to the zero eigenvalue of .

[0023] In the S1, the singular surface S is formed by making f x The singular point set is composed of the singular surface S, the expression of which is S = {μ:f(x,μ) = 0, det(f x )=0}, the initial operating point (x 0 ,μ 0 ) is a point μ on the singular surface S. * , when μ * and μ 0 The distance between ||μ * -μ 0 When || reaches the minimum, at the nearest voltage stability critical point, the direction μ * -μ 0 coincides with the normal vector of the singular surface at that point;

[0024] Singular surface S in μ 1 Normal vector η at the point 1 The expression is:

[0025] η 1 =f μ T w 1

[0026] In the above formula, f μ T For the trend solution, w 1 f x The left eigenvector corresponding to the zero eigenvalue of ;

[0027] The singular surface S is placed in μ 1 Normal vector η at the point 1 Substitute into the following formula:

[0028]

[0029] In the above formula, μ 2The estimated value of for and μ 0 The distance between them.

[0030] In S2, when the power flow equation has a solution, is the solution of the equation. When the tidal current equation has no solution, is the least squares solution of the power flow equation, set is x 2 estimated value.

[0031] In S3, the expression of the nearest voltage stability critical point is:

[0032] f(x,μ)=0

[0033] f x T w=0

[0034] (μ-μ 0 )-α(f μ T w)=0

[0035] w T w-1=0;

[0036] In the above formula, (x, w, μ, α) are the variables to be solved, and α is a constant term used to compare || μ * -μ 0 || and ||η * ||, the size of the nearest voltage stability critical point μ * -μ 0 coincides with the normal vector.

[0037] In a second aspect, the present invention proposes a system for calculating the nearest voltage stability critical point based on a continuous power flow method and a direct method, comprising:

[0038] The system includes a power growth direction calculation module, a critical point estimation module and a recent voltage stability critical point calculation module;

[0039] The power growth direction calculation module is used to obtain the voltage stability critical point in the predetermined power growth direction by a continuous power flow method, and obtain the normal vector as the new power growth direction;

[0040] The critical point estimation module solves the power flow equation by the optimal multiplier method to estimate the critical point in the new power growth direction;

[0041] The nearest voltage stability critical point calculation module is used to use the estimated result as the initial value to solve the nonlinear equation group satisfied by the critical point in the new power growth direction using the Newton-Raphson method to obtain a new critical point, and perform a secondary solution using the Newton-Raphson method to obtain the nearest voltage stability critical point.

[0042] The specific steps of the power growth direction calculation module include:

[0043] From the initial operating point (x 0 ,μ 0 )Departure, x 0 is the initial state variable, μ 0 is the initial system parameter, given the injection power growth direction μ d0 The voltage stability critical point (x 1 ,μ 1 ), and calculate the critical point f x The left eigenvector w corresponding to the zero eigenvalue 1 , construct the singular surface S and calculate the normal vector η 1 ;

[0044] The tidal flow equation used in the continuous tidal flow method is:

[0045] f(x,μ)=0;

[0046] In the above formula, x is the system state variable, its elements are the amplitude and phase angle of the node voltage, and μ is the system parameter;

[0047] make When the parameter μ is along a certain direction μ d Change until f x Singular, at this time the system reaches the critical point of voltage stability, the expression of the critical point is:

[0048] f(x,μ 0 +λμ d )=0

[0049] f x T w 1 =0

[0050] w T w 1 -1=0;

[0051] In the above formula, the variables to be solved are (x,w 1 ,λ), the coefficient λ is the stability margin, w T is the transpose of w, w 1 f x The left eigenvector corresponding to the zero eigenvalue of .

[0052] The specific steps of the power growth direction calculation module also include:

[0053] The singular surface S is formed by making f x The singular point set is composed of the singular surface S, the expression of which is S = {μ:f(x,μ) = 0, det(f x )=0}, the initial operating point (x 0 ,μ 0 ) is a point μ on the singular surface S. * , when μ * and μ 0 The distance between ||μ * -μ 0 When || reaches the minimum, at the nearest voltage stability critical point, the direction μ * -μ 0 coincides with the normal vector of the singular surface at that point;

[0054] Singular surface S in μ 1 Normal vector η at the point 1 The expression is:

[0055] η 1 =f μ T w 1

[0056] In the above formula, f μ T For the trend solution, w 1 f x The left eigenvector corresponding to the zero eigenvalue of ;

[0057] The singular surface S is placed in μ 1 Normal vector η at the point 1 Substitute into the following formula:

[0058]

[0059] In the above formula, μ 2 The estimated value of for and μ 0 The distance between them.

[0060] The specific steps of the power growth direction calculation module include:

[0061] According to the calculation results of the power growth direction calculation module, we can get 0 Start along η 1 Direction of the ray and μ 1 The intersection of the tangent plane T Solving the power flow equation using the optimal multiplier method Get estimated values ​​of system state variables When the power flow equation has a solution, is the solution of the equation. When the tidal current equation has no solution, is the least squares solution of the power flow equation, set is x 2 estimated value.

[0062] The specific steps of the module for calculating the most recent voltage stability critical point include:

[0063] by is the initial value, the injection power growth direction μ d =η 1 Finally, the Newton-Raphson method is used to solve (x 2 ,w 2 ,λ 2 ), the new critical point is (x 2 ,μ 2 =μ 0 +λ 2 η 1 ),remember (x 2 ,w 2 ,μ 2 ,α 2 ) is the initial value, and the Newton-Raphson method is used to solve it again to obtain the nearest voltage stability critical point;

[0064] The expression of the nearest voltage stability critical point is:

[0065] f(x,μ)=0

[0066] f x T w=0

[0067] (μ-μ 0 )-α(f μ T w)=0

[0068] w T w-1=0;

[0069] In the above formula, (x, w, μ, α) is the variable to be solved, and α is a constant term used to compare ‖μ * -μ 0 || and ||η * ||, the size of the nearest voltage stability critical point μ * -μ 0 coincides with the normal vector.

[0070] Compared with the prior art, the present invention has the following beneficial effects:

[0071] 1. In the present invention's method for calculating the nearest voltage stability critical point based on the continuous power flow method and the direct method, in step S1, the voltage stability critical point in a predetermined power growth direction is obtained using a single continuous power flow method, and the normal vector is obtained as the new power growth direction. In step S2, the power flow equation is solved using the optimal multiplier method to estimate the critical point in the new power growth direction. In step S3, the Newton-Raphson method is used to solve the nonlinear equations satisfied by the critical point in the new power growth direction using the estimated result as the initial value to obtain the nearest voltage stability critical point. Therefore, this design can calculate the nearest voltage stability critical point using a single continuous power flow method calculation and two direct method calculations, effectively reducing the amount of calculations.

[0072] 2. In the method for calculating the nearest voltage stability critical point based on the continuous power flow method and the direct method of the present invention, in S4, since at the nearest voltage stability critical point, the direction μ * -μ 0 It coincides with the normal vector of the singular surface at this point, so the coefficient α is introduced so that (μ * -μ 0 )-α(f μ T w) = 0, a new parameter α is introduced. The size of α affects the convergence of the power flow equation and the calculation error. The Newton-Raphson method is then used to perform a secondary solution on the calculation results of S3, thereby more accurately calculating the nearest voltage stability critical point. Therefore, this design effectively improves the calculation accuracy by introducing new parameters and then performing a secondary solution using the Newton-Raphson method.

[0073] 3. In the method for calculating the nearest voltage stability critical point based on the continuous power flow method and the direct method of the present invention, the power flow equation is solved in S2 by the optimal multiplier method to obtain When the power flow equation has a solution, is the solution of the equation. When the tidal current equation has no solution, It can be considered as the least squares solution of the tidal flow equation. That is x 2 The estimated value of and μ 0 The distance between Get initial value quickly and accurately Therefore, this design can solve the tidal current equation by the optimal multiplier method to obtain the solution of the tidal current equation or the least squares solution, and then quickly and accurately obtain the initial value.

[0074] 4. In the present invention's method for calculating the nearest voltage stability critical point based on the continuous power flow method and the direct method, the target voltage stability critical point is the closest to the current operating point. The stability margin at the nearest critical point is typically smaller than the stability margin in the predetermined growth direction, and the corresponding injected power change direction exhibits the most dangerous variation pattern. Therefore, this design avoids inaccurate results caused by the randomness of the injected power growth direction, effectively improving the accuracy of the nearest voltage stability critical point calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 is a flow chart of the method of the present invention.

[0076] Figure 2 It is a structural diagram of the system of the present invention.

[0077] Figure 3 Schematic diagram of parameter space and voltage stability critical point in the method of the present invention.

[0078] Figure 4 This is a schematic diagram of the equipment structure in Example 3. DETAILED DESCRIPTION

[0079] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0080] Example 1:

[0081] See also Figure 1 A method for calculating the nearest voltage stability critical point based on a continuation power flow method and a direct method, the method comprising:

[0082] S1, from the initial operating point (x 0 ,μ 0 )Departure, x 0 is the initial state variable, μ 0 is the initial system parameter, given the injection power growth direction μ d0 The voltage stability critical point (x 1 ,μ 1 ), and calculate the critical point f x The left eigenvector w corresponding to the zero eigenvalue 1 , construct the singular surface S and calculate the normal vector η 1 ;

[0083] S2. According to the calculation results of the continuous power flow method in S1, we can get μ 0 Start along η 1 Direction of the ray and μ 1 The intersection of the tangent plane T Solving the power flow equation using the optimal multiplier method Get estimated values ​​of system state variables

[0084] S3, is the initial value, the injection power growth direction μ d =η 1 Finally, the Newton-Raphson method is used to solve (x 2 ,w 2 ,λ 2 ), the new critical point is (x 2 ,μ 2 =μ 0 +λ 2 η 1 );

[0085] S4, note (x 2 ,w 2 ,μ 2 ,α 2 ) is the initial value, and the Newton-Raphson method is used to solve it again to obtain the nearest voltage stability critical point.

[0086] In S1, the tidal current equation used in the continuous tidal current method is:

[0087] f(x,μ)=0;

[0088] In the above formula, x is the system state variable, its elements are the amplitude and phase angle of the node voltage, and μ is the system parameter;

[0089] make When the parameter μ is along a certain direction μ d Change until f x Singular, at this time the system reaches the critical point of voltage stability, the expression of the critical point is:

[0090] f(x,μ 0 +λμ d )=0

[0091] f x T w 1 =0

[0092] w T w 1 -1=0;

[0093] In the above formula, the variables to be solved are (x,w 1 ,λ), the coefficient λ is the stability margin, w T is the transpose of w, w 1 f x The left eigenvector corresponding to the zero eigenvalue of .

[0094] In the S1, the singular surface S is formed by making f x The singular point set is composed of the singular surface S, the expression of which is S = {μ:f(x,μ) = 0, det(f x )=0}, the initial operating point (x 0 ,μ 0 ) is a point μ on the singular surface S. * , when μ * and μ 0 The distance between ||μ * -μ 0 When || reaches the minimum, at the nearest voltage stability critical point, the direction μ * -μ 0 coincides with the normal vector of the singular surface at that point;

[0095] Singular surface S in μ 1 Normal vector η at the point 1 The expression is:

[0096] η 1 =f μ T w 1

[0097] In the above formula, f μ T For the trend solution, w 1 f x The left eigenvector corresponding to the zero eigenvalue of ;

[0098] The singular surface S is placed in μ 1 Normal vector η at the point 1 Substitute into the following formula:

[0099]

[0100] In the above formula, μ 2 The estimated value of for and μ 0 The distance between them.

[0101] In S2, when the power flow equation has a solution, is the solution of the equation. When the tidal current equation has no solution, is the least squares solution of the power flow equation, set is x 2 estimated value.

[0102] In the above S3, in the space of μ, f x The set of singular points constitutes a singular surface S, that is, S={μ:f(x,μ)=0,det(f x)=0}, the singular surface is the set of critical points of voltage stability in different directions. Given an initial operating point (x 0 ,μ 0 ), the nearest voltage stability critical point is a point μ on S * , so that μ * and μ 0 The distance between ||μ * -μ 0 || reaches the minimum, at the nearest voltage stability critical point, direction μ * -μ 0 Coincident with the normal vector of the singular surface at that point. The normal vector of S at a point is

[0103] η=f μ T w;

[0104] where w is f x The left eigenvector corresponding to the zero eigenvalue of . The equation for calculating the nearest voltage stability critical point is:

[0105] f(x,μ)=0

[0106] f x T w=0

[0107] (μ-μ 0 )-α(f μ T w)=0

[0108] w T w-1=0;

[0109] In the above formula, (x, w, μ, α) are the variables to be solved, and α is a constant term used to compare || μ * -μ 0 || and ||η * ||, the size of the nearest voltage stability critical point μ * -μ 0 coincides with the normal vector.

[0110] This embodiment uses the IEEE 57-node test system for simulation verification and compares it with the traditional master-slave iteration method:

[0111] The parameters used in this embodiment are: the active load and reactive load of all load nodes are increased with the power factor unchanged, and the power output is increased proportionally to the initial value;

[0112] The following table lists the spatial distances between the voltage stability critical point and the initial operating point obtained in each step of the two methods:

[0113]

[0114] This embodiment iterates three times to obtain the nearest voltage stability critical point, while the traditional master-slave iteration method requires multiple iterations to obtain a result that is sufficiently close to the nearest voltage stability critical point. From the calculation results, the nearest voltage stability critical point obtained by the two methods is relatively close;

[0115] Under the same running and computing conditions, this method takes 0.841s, while the traditional master-slave iteration method takes 2.307s. This method is faster.

[0116] Example 2:

[0117] A system for calculating the nearest voltage stability critical point based on a continuous power flow method and a direct method, the system comprising a power growth direction calculation module, a critical point estimation module, and a nearest voltage stability critical point calculation module;

[0118] The power growth direction calculation module is used to obtain the voltage stability critical point in the predetermined power growth direction by a continuous power flow method, and obtain the normal vector as the new power growth direction;

[0119] The critical point estimation module solves the power flow equation by the optimal multiplier method to estimate the critical point in the new power growth direction;

[0120] The nearest voltage stability critical point calculation module is used to use the estimated result as the initial value to solve the nonlinear equation group satisfied by the critical point in the new power growth direction using the Newton-Raphson method to obtain a new critical point, and perform a secondary solution using the Newton-Raphson method to obtain the nearest voltage stability critical point.

[0121] The specific steps of the power growth direction calculation module include:

[0122] From the initial operating point (x 0 ,μ 0 )Departure, x 0 is the initial state variable, μ 0 is the initial system parameter, given the injection power growth direction μ d0 The voltage stability critical point (x 1 ,μ 1 ), and calculate the critical point f x The left eigenvector w corresponding to the zero eigenvalue 1 , construct the singular surface S and calculate the normal vector η 1 ;

[0123] The tidal flow equation used in the continuous tidal flow method is:

[0124] f(x,μ)=0;

[0125] In the above formula, x is the system state variable, its elements are the amplitude and phase angle of the node voltage, and μ is the system parameter;

[0126] make When the parameter μ is along a certain direction μ d Change until f x Singular, at this time the system reaches the critical point of voltage stability, the expression of the critical point is:

[0127] f(x,μ 0 +λμ d )=0

[0128] f x T w 1 =0

[0129] w T w 1 -1=0;

[0130] In the above formula, the variables to be solved are (x,w 1 ,λ), the coefficient λ is the stability margin, w T is the transpose of w, w 1 f x The left eigenvector corresponding to the zero eigenvalue of .

[0131] The specific steps of the power growth direction calculation module also include:

[0132] The singular surface S is formed by making f x The singular point set is composed of the singular surface S, the expression of which is S = {μ:f(x,μ) = 0, det(f x )=0}, the initial operating point (x 0 ,μ 0 ) is a point μ on the singular surface S. * , when μ * and μ 0 The distance between ||μ * -μ 0 When || reaches the minimum, at the nearest voltage stability critical point, the direction μ * -μ 0 coincides with the normal vector of the singular surface at that point;

[0133] Singular surface S in μ 1 Normal vector η at the point 1 The expression is:

[0134] η 1 =f μ T w 1

[0135] In the above formula, f μ T For the trend solution, w 1 f x The left eigenvector corresponding to the zero eigenvalue of ;

[0136] The singular surface S is placed in μ 1 Normal vector η at the point 1 Substitute into the following formula:

[0137]

[0138] In the above formula, μ 2 The estimated value of for and μ 0 The distance between them.

[0139] The specific steps of the power growth direction calculation module include:

[0140] According to the calculation results of the power growth direction calculation module, we can get 0 Start along η 1 Direction of the ray and μ 1 The intersection of the tangent plane T Solving the power flow equation using the optimal multiplier method Get estimated values ​​of system state variables When the power flow equation has a solution, is the solution of the equation. When the tidal current equation has no solution, is the least squares solution of the power flow equation, set is x 2 estimated value.

[0141] The specific steps of the module for calculating the most recent voltage stability critical point include:

[0142] by is the initial value, the injection power growth direction μ d =η 1 Finally, the Newton-Raphson method is used to solve (x 2 ,w 2 ,λ 2 ), the new critical point is (x 2 ,μ 2 =μ 0 +λ 2 η 1 ),remember (x 2 ,w 2 ,μ 2 ,α 2) is the initial value, and the Newton-Raphson method is used to solve it again to obtain the nearest voltage stability critical point;

[0143] The expression of the nearest voltage stability critical point is:

[0144] f(x,μ)=0

[0145] f x T w=0

[0146] (μ-μ 0 )-α(f μ T w)=0

[0147] w T w-1=0;

[0148] In the above formula, (x, w, μ, α) are the variables to be solved, and α is a constant term used to compare || μ * -μ 0 || and ||η * ||, the size of the nearest voltage stability critical point μ * -μ 0 coincides with the normal vector.

[0149] Example 3:

[0150] A device for calculating the nearest voltage stability critical point based on a continuation power flow method and a direct method, the device comprising a processor and a memory;

[0151] The memory is used to store computer program code and transmit the computer program code to the processor;

[0152] The processor is configured to execute the method for calculating the nearest voltage stability critical point based on the continuation power flow method and the direct method as described in Example 1 according to the instructions in the computer program code.

[0153] A power balancing storage medium for distributed resources stores a computer program, which, when executed by a processor, implements the method for calculating the nearest voltage stability critical point based on the continuous power flow method and the direct method as described in Example 1.

[0154] The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiment. Any equivalent modifications or changes made by ordinary technicians in this field based on the contents disclosed in the present invention should be included in the protection scope recorded in the claims.

Claims

1. A method for calculating the nearest voltage stability critical point based on the continuation power flow method and the direct method, characterized by: The calculation method includes: S1, from the initial operating point Set off, is the initial state variable, is the initial system parameter, given the injection power growth direction , the voltage stability critical point is calculated by the continuous power flow method , and calculate the critical point Left eigenvector corresponding to zero eigenvalue , constructing singular surfaces , and calculate the normal vector ; S2. According to the calculation results of the continuous power flow method in S1, we can get Departure along Directional rays and Tangent plane The intersection of , , for and The distance between them is calculated by the optimal multiplier method to solve the tidal current equation. , get the estimated value of the system state variable ; S3, is the initial value, the direction of injection power growth , and finally the Newton-Raphson method is used to solve , the new critical point is ; S4, note , To solve the trend, As the initial value, the Newton-Raphson method is used to solve again to obtain the nearest voltage stability critical point.

2. The method for calculating the nearest voltage stability critical point based on the continuation power flow method and the direct method according to claim 1, characterized in that: In S1, the tidal current equation used in the continuous tidal current method is: ； In the above formula, is the system state variable, whose elements are the amplitude and phase angle of the node voltage, are the parameters of the system; make , when the parameter Along a certain direction Change until Singular, at this time the system reaches the critical point of voltage stability, the expression of the critical point is: ； In the above formula, the variables to be solved are , The coefficient is the stability margin, for The transpose of for The left eigenvector corresponding to the zero eigenvalue of .

3. The method for calculating the nearest voltage stability critical point based on the continuation power flow method and the direct method according to claim 2, characterized in that: In S1, the singular surface Depend on in the space The set of singular points constitutes the singular surface The expression is , the initial operating point The nearest voltage stability critical point is the singular surface Previous point ,when and The distance between When it reaches the minimum, at the nearest voltage stability critical point, the direction coincides with the normal vector of the singular surface at that point; Strange Face exist Normal vector at the point The expression is: ； In the above formula, for The left eigenvector corresponding to the zero eigenvalue of ; The strange face exist Normal vector at the point Substitute into the following formula: ； In the above formula, for estimated value.

4. The method for calculating the nearest voltage stability critical point based on the continuation power flow method and the direct method according to claim 3, characterized in that: In S2, when the power flow equation has a solution, is the solution of the equation. When the tidal current equation has no solution, is the least squares solution of the power flow equation, set for estimated value.

5. The method for calculating the nearest voltage stability critical point based on the continuation power flow method and the direct method according to claim 4, characterized in that: In S4, the expression of the nearest voltage stability critical point is: ； In the above formula, is the variable to be solved, is a constant term used for comparison and The size between the nearest voltage stability critical point coincides with the normal vector.

6. A system for calculating the nearest voltage stability critical point based on the continuation power flow method and the direct method, characterized by: The system includes a power growth direction calculation module, a critical point estimation module and a recent voltage stability critical point calculation module; The power growth direction calculation module is used to obtain the voltage stability critical point in the predetermined power growth direction by a continuous power flow method, and obtain the normal vector as the new power growth direction; The critical point estimation module solves the power flow equation by the optimal multiplier method to estimate the critical point in the new power growth direction; The nearest voltage stability critical point calculation module is used to use the estimated result as the initial value to solve the nonlinear equation group satisfied by the critical point in the new power growth direction using the Newton-Raphson method to obtain a new critical point, and perform a secondary solution using the Newton-Raphson method to obtain the nearest voltage stability critical point.

7. The system for calculating the nearest voltage stability critical point based on the continuation power flow method and the direct method according to claim 6, characterized in that: The specific steps of the power growth direction calculation module include: From the initial operating point Set off, is the initial state variable, is the initial system parameter, given the injection power growth direction , the voltage stability critical point is calculated by the continuous power flow method , and calculate the critical point Left eigenvector corresponding to zero eigenvalue , constructing singular surfaces , and calculate the normal vector ; The tidal flow equation used in the continuous tidal flow method is: ； In the above formula, is the system state variable, whose elements are the amplitude and phase angle of the node voltage, are the parameters of the system; make , when the parameter Along a certain direction Change until Singular, at this time the system reaches the critical point of voltage stability, the expression of the critical point is: ； In the above formula, the variables to be solved are , The coefficient is the stability margin, for The transpose of for The left eigenvector corresponding to the zero eigenvalue of .

8. The system for calculating the nearest voltage stability critical point based on the continuation power flow method and the direct method according to claim 7, characterized in that: The specific steps of the power growth direction calculation module also include: The singular surface Depend on in the space The set of singular points constitutes the singular surface The expression is , the initial operating point The nearest voltage stability critical point is the singular surface Previous point ,when and The distance between When it reaches the minimum, at the nearest voltage stability critical point, the direction coincides with the normal vector of the singular surface at that point; Strange Face exist Normal vector at the point The expression is: ； In the above formula, To solve the trend, for The left eigenvector corresponding to the zero eigenvalue of ; The strange face exist Normal vector at the point Substitute into the following formula: ； In the above formula, for The estimated value of for and The distance between them.

9. The system for calculating the nearest voltage stability critical point based on the continuation power flow method and the direct method according to claim 8, characterized in that: The specific steps of the power growth direction calculation module include: According to the calculation results of the power growth direction calculation module, we can get Departure along Directional rays and Tangent plane The intersection of , , for and The distance between them is calculated by the optimal multiplier method to solve the tidal current equation. , get the estimated value of the system state variable , when the tidal current equation has a solution, is the solution of the equation. When the tidal current equation has no solution, is the least squares solution of the power flow equation, set for estimated value.

10. The system for calculating the nearest voltage stability critical point based on the continuation power flow method and the direct method according to claim 9, characterized in that: The specific steps of the module for calculating the most recent voltage stability critical point include: by is the initial value, the direction of injection power growth , and finally the Newton-Raphson method is used to solve , the new critical point is ,remember ,by As the initial value, the Newton-Raphson method is used to solve again to obtain the nearest voltage stability critical point; The expression of the nearest voltage stability critical point is: ； In the above formula, is the variable to be solved, is a constant term used for comparison and The size between the nearest voltage stability critical point coincides with the normal vector.

Images