Weak node detection and instability index establishment method and system of novel power system

Abstract

According to the novel weak node detection and instability index establishment method and system for the electric power system, the linkage relation between oscillation characteristic samples is mapped into different value ranges of the equivalent impedance angle of an inverter, and the actual value of the equivalent impedance angle of the inverter is calculated according to the relation between the actual value of the equivalent impedance angle of the inverter and the different value ranges, obtained through mapping, of the equivalent impedance angle of the inverter. Forming a novel power system stability criterion; taking the nodes of which the load flow entropy weakness indexes are not less than a set threshold value as weak nodes; under the constraint conditions of the power angle, the voltage, the frequency and the impedance angle, establishing a multi-dimensional stability margin space by using the coupling relationship among the power angle stability margin, the voltage stability margin, the frequency stability margin and the impedance angle stability margin; constructing a stability margin index of the weak node by using the equivalent impedance angle actual value of the inverter and the equivalent output impedance amplitude of the inverter; and when the stability margin index of the weak node exceeds the multi-dimensional stability margin space, determining that the novel power system is unstable.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system stability detection, and in particular, relates to a novel method and system for weak node detection and instability index establishment of a power system. Background Art

[0002] In recent years, the technology for determining the instability conditions of new power systems has received increasing attention. Since new power systems have the characteristics of a high proportion of new energy and a high proportion of power electronic equipment, they have the characteristics of multiple types of disturbances in actual operation, which always affect their stability. Various disturbances have an impact on new power systems and their stability. In the prior art, the determination of instability conditions of new power systems mainly starts from the structure, load characteristics, power electronic equipment and other aspects of new power systems, and a series of instability condition determination methods are proposed. For example, the instability condition determination method of new power systems based on complex network theory quickly determines whether the new power system has instability by analyzing the complex structure of the new power system and the correlation between nodes. In addition, the instability condition determination method based on load characteristics determines whether the new power system has instability risks by analyzing the law of load changes. In addition, there is also a method for determining whether the new power system has instability by analyzing the working status and control strategy of power electronic equipment. In terms of determining the instability conditions of new power systems, different types of evaluation indicators are proposed for network structures with different characteristics. The current evaluation method mainly starts from the stability analysis and control strategy of new power systems, and proposes a variety of instability condition determination methods and algorithms. For example, the instability condition identification method based on frequency domain analysis can determine whether the new power system has instability by analyzing the frequency response characteristics of the new power system. The voltage-power angle-frequency stability of the traditional power system is combined with the broadband oscillation stability, and the dominant factors of instability are coupled with each other, making it difficult to effectively identify them. The stability analysis in the prior art mainly starts from the stability analysis and control strategy of the new power system, and proposes a variety of instability condition identification methods and algorithms. For example, the instability condition identification method based on frequency domain analysis, the instability condition identification method based on control strategy, and the instability condition identification method based on model predictive control. However, the existing models and methods cannot meet the needs of comprehensive analysis of the dominant factors of instability in such new power systems in terms of the coverage of the research object, the multidimensionality of the time scale of the model, the effectiveness of the calculation method, and the accuracy of the evaluation index. Since the dominant factors of instability are coupled with each other, it is difficult to effectively identify them, so effective instability identification technology is more needed. In terms of weak node identification, among the current identification methods, the reliability tracking method can identify the weak nodes in the system from the perspective of reliability. In terms of identification, the reliability tracking method can point out that a component is weak, but it cannot point out which specific aspect of the component (capacity, failure rate, repair rate, etc.) is the main cause of the node weakness. Summary of the invention

[0003] In order to solve the deficiencies in the prior art, the present invention provides a method and system for detecting weak nodes and establishing instability indicators of a new type of power system, so as to realize quantitative identification of weak links in the new type of power system, analyze the instability relationship between the system's voltage-frequency-power angle and dynamic impedance based on the transient and stable energy transfer laws of the system, and propose an analytical strategy for the dominant factors of instability in the new type of power system.

[0004] The present invention adopts the following technical solution.

[0005] The present invention proposes a novel method for detecting weak nodes and establishing instability indexes of a power system, comprising:

[0006] Obtain oscillation feature samples of historical oscillation accidents, map the linkage relationship between the oscillation feature samples into different value ranges of the equivalent impedance angle of the inverter, and form a new power system stability criterion based on the relationship between the actual value of the equivalent impedance angle of the inverter and the different value ranges of the equivalent impedance angle of the mapped inverter;

[0007] Based on the new power system stability criterion, when the system is judged to be in an unstable state, the proportion of the flow impact on a branch connected to a node in the total flow impact received by the node is obtained as the flow transfer ratio of a node to a branch; based on the information entropy model, the flow transfer ratio of a node to each branch is used to determine the flow distribution entropy of a node; the node branch flow channel variable is introduced, and the total flow impact received by a node and the flow distribution entropy of a node are used to determine the node's flow entropy weakness index; the node whose flow entropy weakness index is not less than the set threshold is regarded as a weak node;

[0008] Based on the generator rotor motion equation and the inverter equivalent power angle / frequency second-order equation, an energy mapping model of the system's power angle, voltage, frequency, and impedance angle is established, and the constraints of the power angle, voltage, frequency, and impedance angle are determined using oscillation characteristic samples; under the constraints of the power angle, voltage, frequency, and impedance angle, a multi-dimensional stability margin space is established using the coupling relationship between the power angle stability margin, voltage stability margin, frequency stability margin, and impedance angle stability margin;

[0009] The stability margin index of the weak node is constructed by using the actual value of the equivalent impedance angle of the inverter and the equivalent output impedance amplitude of the inverter;

[0010] When the stability margin index of the weak node exceeds the multi-dimensional stability margin space, the new power system is determined to be unstable.

[0011] Preferably, the oscillation characteristic samples include: active power and reactive power output by the inverter, output voltage and current, and a composite impedance angle of the inverter and the line;

[0012] The phase angle of the sum of the equivalent output impedance of the inverter and the line impedance is taken as the composite impedance angle of the inverter and the line, which satisfies the following relationship:

[0013]

[0014] Where θ is the composite impedance angle of the inverter and the line, R is the sum of the inverter equivalent output resistance and the line resistance; X is the sum of the inverter equivalent output reactance and the line reactance.

[0015] Preferably, according to the oscillation characteristic sample, the linkage relationship between the active power P and reactive power Q output by the inverter, the output voltage U1 and current I1, and the synthetic impedance angle θ between the inverter and the line is mapped into different value ranges of the equivalent impedance angle of the inverter, with the actual value of the equivalent impedance angle of the inverter The relationship between the different value ranges of the equivalent impedance angle of the mapped inverter constitutes a new power system stability criterion, including:

[0016] 1) When the linkage relationship is P↑→Q↓→U1↑→I1↓→θ↑→Q↑, if When the linkage relationship is P↓→Q↑→U1↓→I1↑→θ↓→Q↓, if When , the new power system is determined to be stable;

[0017] 2) When the linkage relationship is P↑→Q↓→U1↑→I1↓→θ↓→Q↓, if When the linkage relationship is P↓→Q↑→U1↓→I1↑→θ↑→Q↑, if When , the new power system is determined to be unstable;

[0018] 3) When the linkage relationship is P↑→Q↓→U1↑→I1↓→θ↓→Q↑, if When the linkage relationship is P↓→Q↑→U1↓→I1↑→θ↑→Q↓, if When , the new power system is determined to be stable;

[0019] 4) When the linkage relationship is P↑→Q↓→U1↓→I1↑→θ↑→Q↓, if When , the new power system is determined to be unstable; when the linkage relationship is P↓→Q↑→U1↑→I1↓→θ↓→Q↑, if When , the new power system is determined to be unstable;

[0020] 5) When the linkage relationship is P↑→Q↓→U1↓→I1↑→θ↓→Q↑, if When the linkage relationship is P↓→Q↑→U1↑→I1↓→θ↑→Q↓, if When , the new power system is determined to be stable;

[0021] 6) When the linkage relationship is P↑→Q↓→U1↓→I1↑→θ↓→Q↓, if When , the new power system is determined to be unstable; when the linkage relationship is P↓→Q↑→U1↑→I1↓→θ↑→Q↑, if When , the new power system is determined to be unstable;

[0022] Among them, the symbol ↑ indicates that the oscillation characteristic sample increases, the symbol ↓ indicates that the oscillation characteristic sample decreases, and when the oscillation characteristic sample on the left side of the symbol → changes, the oscillation characteristic sample on the right side of the symbol → will change.

[0023] Preferably, the power flow transfer ratio of node a to branch i satisfies the following relationship:

[0024]

[0025] In the formula, is the power transfer ratio of node a to branch i, ΔP i is the flow impulse on branch i connected to node a, i = 1, 2, 3, ..., N, N is the total number of branches, ΔP a is the total flow impact on node a;

[0026] The power flow distribution entropy of node a satisfies the following relationship:

[0027]

[0028] In the formula, is the power flow distribution entropy of node a;

[0029] The power flow entropy weakness index of node a satisfies the following relationship:

[0030]

[0031] In the formula, H P (a) is the power flow entropy weakness index of node a, C n is the node branch power flow channel variable.

[0032] Preferably, the threshold value range is set to [0,1]; the power entropy weakness index of all nodes in the system is calculated and compared with the set threshold. When the number of nodes whose power entropy weakness index is greater than the set threshold accounts for 10% of the total number of nodes in the system, the optimal set threshold is obtained, and these 10% nodes are regarded as weak nodes.

[0033] Preferably, based on the generator rotor motion equation and the inverter equivalent power angle / frequency second-order equation, it is determined that the active power model of node a satisfies the following relationship:

[0034] P e =ΔP δ (V a ,δ a )+ΔP θ (V a ,θ a )+ΔP δ,θ (V a ,δ a ,θ a )

[0035] In the formula, ΔP δ (V a ,δ a ) is the voltage V at node a a and power angle δ a The power change caused by θ (V a ,θ a ) is the voltage V at node a a and impedance angle θ a The power change caused by δ,θ (V a ,δ a ,θ a ) is the voltage V at node a a , power angle δ a and impedance angle θ a The amount of power change caused;

[0036] Based on the active power of node a, the Popov method is used to establish the energy mapping model of the system's power angle, voltage, frequency, and impedance angle, satisfying the following relationship:

[0037] V=ΔV m (δ m ,V m ,f m ,θ m )+ΔV r (δ r ,V r ,f r ,θ r )+ΔV e (δe ,V e ,f e ,θ e )+ΔV L (δ L ,V L ,f L ,θ L )

[0038] Where V is the energy mapping function of the new power system, ΔV m (δ m ,V m ,f m ,θ m ) is the synchronous generator m with respect to the power angle δ m , voltage V m , frequency f m , impedance angle θ m Energy mapping function, m = 1, 2, ..., N m , N m is the total number of synchronous generators in the system; ΔV r (δ r ,V r ,f r ,θ r ) is the inverter r with respect to the power angle δ r , voltage V r , frequency f r , impedance angle θ r Energy mapping function, r = 1, 2, ..., N r , N r is the total number of inverters in the system; ΔV e (δ e ,V e ,f e ,θ e ) is the power angle of the system network δ e , voltage V e , frequency f e , impedance angle θ e Energy mapping function; ΔV L (δ L ,V L ,f L ,θ L ) is the load L with respect to the power angle δ L , voltage V L , frequency f L , impedance angle θ L Energy mapping function, L = 1, 2, ..., N L , N L is the total number of loads in the system.

[0039] Preferably, based on the energy mapping model of the power angle, voltage, frequency and impedance angle of the system, the constraints of the power angle, voltage, frequency and impedance angle are obtained by using the oscillation characteristic samples, including:

[0040] 1) Nonlinear constraints between the power angle and the synchronous generator rotor angle potential energy, inverter equivalent potential energy, line inductance and / or capacitance potential energy;

[0041] 2) Nonlinear constraints between voltage and line inductance and / or capacitance potential energy, resistance dissipation energy, constant power and / or constant impedance load potential energy;

[0042] 3) Nonlinear constraints between frequency and synchronous generator rotor kinetic energy, inverter equivalent kinetic energy, constant power and / or constant impedance load potential energy;

[0043] 4) Nonlinear constraints between the impedance angle and the inverter filter inductance and / or capacitance potential energy, line inductance and / or capacitance potential energy, and resistance dissipation energy.

[0044] Preferably, under the constraints of power angle, voltage, frequency and impedance angle, a multi-dimensional stability margin space is established by utilizing the coupling relationship between the power angle stability margin, voltage stability margin, frequency stability margin and impedance angle stability margin, satisfying the following relationship:

[0045] SP(δ,V,f,θ)=P{SP(δ),SP(V),SP(f),SP(θ)}

[0046] Wherein, SP(δ,V,f,θ) is the multi-dimensional stability margin space of the new power system, P{} is the coupling relationship function between the power angle stability margin SP(δ), voltage stability margin SP(V), frequency stability margin SP(f) and impedance angle stability margin SP(θ);

[0047] The constraints of the multi-dimensional stability margin space of the new power system satisfy the following relationship:

[0048] δ min ≤δ≤δ max

[0049] V min ≤V≤V max

[0050] f min ≤f≤f max

[0051] θ∈{[θ down - τ ,θ up-τ ]}

[0052] In the formula, δ min , δmax are the lower and upper limits of the power angle δ, V min 、V max are the lower and upper limits of voltage V, respectively, and f min 、f max are the lower and upper limits of the frequency f, respectively. The subscript τ is the number of the different value ranges of the equivalent impedance angle of the inverter obtained by mapping. The value range of τ = 1 corresponds to The value range of τ=2 corresponds to The value range of τ=3 corresponds to The value range of τ=4 corresponds to The value range of τ=5 corresponds to The value range of τ=6 corresponds to θ down-τ is the lower limit of the value range τ, θ up-τ is the upper limit of the value range τ.

[0053] Preferably, the stability margin index of the weak node is constructed using the actual value of the equivalent impedance angle of the inverter and the equivalent output impedance amplitude of the inverter, satisfying the following relationship:

[0054]

[0055] In the formula, SM(θ c ,a c ) is the stability margin index of the weak node, where θ c is the stability margin of the equivalent impedance angle of the inverter, a c is the stability margin of the equivalent impedance amplitude of the inverter, the subscript τ is the number of the different value ranges of the equivalent impedance angle of the inverter obtained by mapping, and the value range of τ = 1 corresponds to The value range of τ=2 corresponds to The value range of τ=3 corresponds to The value range of τ=4 corresponds to The value range of τ=5 corresponds to The value range of τ=6 corresponds to k cτ is the stability margin coefficient of the equivalent impedance angle within the value range τ, According to the oscillation characteristic samples, the boundaries of the stable range under the constraints of power angle, voltage, frequency and impedance angle are obtained. is the actual value of the equivalent impedance angle of the inverter, a cτ is the equivalent output impedance amplitude of the inverter within the value range τ, f cτ It is a quantization factor between the actual value of the equivalent impedance angle of the inverter and the equivalent output impedance amplitude within the value range τ. The value range is (0,1), and the value is determined according to the composite impedance angle of the inverter and the line within the value range τ.

[0056] Preferably, when the calculated stability margin index of the weak node exceeds a certain boundary of the multi-dimensional stability margin space, the new power system is determined to be unstable; and the type of power system instability is confirmed by comparing the stability classification proposed in the "Definition and Classification of Power System Stability" report released by IEEE / CIGRE to determine the dominant factors of instability of the new power system.

[0057] The present invention also proposes a novel weak node detection and instability index establishment system for a power system, comprising:

[0058] A stability criterion establishment module is used to obtain oscillation characteristic samples of historical oscillation accidents, map the linkage relationship between the oscillation characteristic samples into different value ranges of the equivalent impedance angle of the inverter, and form a new power system stability criterion based on the relationship between the actual value of the equivalent impedance angle of the inverter and the different value ranges of the equivalent impedance angle of the mapped inverter;

[0059] The weak node detection module is used to obtain the proportion of the flow impact on a branch connected to a certain node in the total flow impact received by a certain node based on the new power system stability criterion when the system is determined to be in an unstable state, as the flow transfer ratio of a certain node to a branch; based on the information entropy model, the flow transfer ratio of a certain node to each branch is used to determine the flow distribution entropy of a certain node; introduce the node branch flow channel variable, use the total flow impact received by a certain node and the flow distribution entropy of a certain node to determine the node flow entropy weakness index; the node whose flow entropy weakness index is not less than the set threshold is regarded as a weak node;

[0060] The stability margin index system establishment module is used to establish the energy mapping model of the system's power angle, voltage, frequency, and impedance angle based on the generator rotor motion equation and the inverter's equivalent power angle / frequency second-order equation, and use the oscillation characteristic samples to determine the constraints of the power angle, voltage, frequency, and impedance angle; under the constraints of the power angle, voltage, frequency, and impedance angle, use the coupling relationship between the power angle stability margin, voltage stability margin, frequency stability margin, and impedance angle stability margin to establish a multi-dimensional stability margin space; use the actual value of the inverter's equivalent impedance angle and the inverter's equivalent output impedance amplitude to construct the stability margin index of the weak node;

[0061] The instability detection module is used to determine whether the new power system is unstable when the stability margin index of the weak node exceeds the multi-dimensional stability margin space.

[0062] It also includes: an instability dominant factor detection module, which is used to confirm the type of power system instability by comparing the stability classification proposed in the "Definition and Classification of Power System Stability" report released by IEEE / CIGRE, so as to identify new power systems.

[0063] A terminal comprises a processor and a storage medium; the storage medium is used to store instructions; the processor is used to operate according to the instructions to execute the steps of the method.

[0064] A computer-readable storage medium stores a computer program, which implements the steps of the method when executed by a processor.

[0065] The beneficial effects of the present invention are that, compared with the prior art, at least the method proposed by the present invention aims at the problem of variable network energy transmission law and unclear dominant factors of instability caused by random access of distributed renewable energy to the new power system, realizes quantitative identification of weak links in the new power system, analyzes the instability relationship between the system's voltage-frequency-power angle and dynamic impedance based on the transient and stable energy transfer laws of the system, proposes a strategy for analyzing the dominant factors of instability in the new power system, and guides the planning and transformation of the power system. The present invention realizes the mapping relationship between the broadband oscillation stability criterion of the new power system and the three major stability criteria of voltage, frequency, and power angle of the traditional power system, realizes the construction of factors affecting the stability of the new power system and stability conditions, and can accurately analyze the relationship between different influencing factors and different types of stability, thereby identifying the main influencing factors of system stability and the type of system instability. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 The present invention proposes a flow chart of a novel method for detecting weak nodes and establishing instability indexes of a power system;

[0067] Figure 2 It is the equivalent circuit of the grid-type inverter in the embodiment of the present invention. DETAILED DESCRIPTION

[0068] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only embodiments of a part of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0069] The present invention proposes a novel method for detecting weak nodes and establishing instability indexes of power systems. Figure 1 As shown, including:

[0070] Step 1: Obtain oscillation feature samples of historical oscillation accidents, map the linkage relationship between the oscillation feature samples into different value ranges of the equivalent impedance angle of the inverter, and form a new power system stability criterion based on the relationship between the actual value of the equivalent impedance angle of the inverter and the different value ranges of the equivalent impedance angle of the mapped inverter.

[0071] Obtain historical oscillation accidents of power electronic equipment in the system, and use common factors that lead to historical oscillation accidents of power electronic equipment as oscillation feature samples; oscillation feature samples include: active power and reactive power output by the inverter, output voltage and current, and synthetic impedance angle of the inverter and the line; in the embodiment, by summarizing and analyzing the broadband oscillation phenomenon that has occurred, oscillation feature samples are extracted, and the main features of such phenomena are summarized. Among them, some typical oscillation accidents that have occurred in reality, such as oscillation accidents in Guyuan, Hebei, oscillation accidents in Texas, the United States, oscillation accidents in Hami, Xinjiang, offshore oscillation accidents in the North Sea of ​​Germany, etc., the common factors that lead to such oscillation accidents are oscillation feature samples, specifically:

[0072] 1) The main participants of the oscillation are power electronic equipment and their control systems, as well as traditional electrical equipment and transmission networks. For this type of new power system dominated by a high proportion of power electronic equipment, the source side is connected to the grid through an energy router, which can be regarded as a grid-building inverter or a grid-following inverter to provide sufficient voltage and power support for the system, and can further increase the utilization ratio of renewable energy; while the load side is connected to the grid through an energy router, which can usually be regarded as a combination of constant impedance load and constant power load. This constant power characteristic makes the entire power system prone to instability;

[0073] 2) Its oscillation form often starts with small signal negative damping instability, and then diverges and continues to oscillate in a wide frequency range, ranging from a few Hz to several thousand Hz;

[0074] 3) This type of power system involves multiple units and multiple electrical equipment in multiple regions, and the oscillation frequency will change with the change of the topological structure of the power electronic equipment, showing a multi-modal form of expression, that is, a multi-source, multi-type, and multi-structure form of expression. For the mode with a lower oscillation frequency, its oscillation energy is large and the impact range is wide. This is because the interaction between a single mode of oscillation and power electronic equipment may stimulate a new oscillation mode, causing the oscillation energy to propagate over a large range in the power grid, causing the oscillation to develop from a local to a global direction, so that the broadband oscillation exhibits a time-varying characteristic that the oscillation frequency changes with the time change of the power electronic equipment, and also exhibits the characteristic that the broadband oscillation energy has a wide-area propagation in the power grid;

[0075] In order to improve the detection efficiency, it is necessary to select a type of representative indicators such as the equivalent impedance angle of the inverter based on the oscillation characteristic samples of typical accidents, and establish a connection between the equivalent impedance angle of the inverter and the oscillation characteristic samples in a mapping manner, so as to comprehensively consider the oscillation characteristic factors and establish a new type of instability indicator.

[0076] The impedance angle characteristics are analyzed, and the impedance angle model is constructed for the small sample data or zero sample data of the system. Such small sample or zero sample data is generally an equivalent model mapped by the oscillation feature sample extracted from the oscillation sample, that is, the oscillation of the oscillation sample is mostly broadband oscillation. In the broadband oscillation section, the main participants are all power electronic equipment, which can be equivalent to a power system with a grid-type inverter as the source side input. The impedance angle model is established using the equivalent model of the grid-type inverter;

[0077] 1) Impedance angle characteristic analysis

[0078] Based on the characteristics of the new power system, when new energy is connected to the weak power grid system, the new energy grid-connected converter with the grid-building and grid-following control strategies is generally used to connect to the weak power grid. In the wide-band oscillation frequency band of the system, the equivalent impedance of the grid-building inverter will change with the change of current. The equivalent circuit of the grid-building inverter is as follows: Figure 2 shown.

[0079] Figure 2 In the figure, U1 and U2 are the output voltage and bus voltage of the grid-type inverter; Z=R+jX is the sum of the inverter equivalent output impedance Z1 and the line impedance Z2; Z=Z1+Z2, Z1=R1+jX1, Z2=R2+jX2; R1 and X1 are the inverter equivalent output resistance and reactance, respectively; R2 and X2 are the resistance and reactance of the line, respectively; δ is the angular deviation between the inverter output voltage and the bus voltage.

[0080] according to Figure 2 , the inverter output apparent power is expressed as:

[0081]

[0082] Where P is the active power output by the inverter; Q is the reactive power output by the inverter.

[0083]

[0084] In the formula, θ is the phase angle of the sum of the inverter equivalent output impedance and the line impedance Z, which becomes the synthetic impedance angle of the inverter; R is the sum of the inverter equivalent output resistance and the line resistance; X is the sum of the inverter equivalent output reactance and the line reactance;

[0085] Therefore, the active power and reactive power can be expressed as:

[0086]

[0087] In the actual system, since the angle deviation δ between the inverter output voltage and the bus voltage is very small, assuming that δ is approximately equal to 0, Q can be equivalent to:

[0088]

[0089] Due to the existence of the equivalent negative impedance of the inverter, the synthetic impedance angle will be expanded from the conventional range [-π / 2,π / 2] to [-π,π]. In order to facilitate the analysis of the impedance angle characteristics, it is assumed that the equivalent output impedance of the grid-type inverter takes a fixed value in the third quadrant. At this time, since the line impedance remains fixed in the first quadrant, the equivalent impedance of the inverter takes the third quadrant to facilitate the synthesis of the impedance angle, which is more conducive to the analysis of the impedance angle characteristics by changing the line impedance Z2 so that the equivalent impedance is located in different intervals. At the same time, θ1 is taken as the angle of the equivalent output impedance Z1 of the inverter.

[0090] Using the relationship between the system output active power and reactive power:

[0091] P 2 +Q 2 =K1

[0092] Among them, K1 is a constant.

[0093] According to the oscillation characteristic samples, the linkage relationship between the active power P and reactive power Q output by the inverter, the output voltage U1 and current I1, and the synthetic impedance angle θ between the inverter and the line is mapped to different value ranges of the equivalent impedance angle of the inverter, forming a new power system stability criterion, which is convenient for analyzing and judging the stability performance of the power system under load disturbance. The stability performance criterion of the power system is shown in Table 1:

[0094] Table 1 Stability performance criteria of power system

[0095]

[0096] When determining whether a power system is unstable, it is necessary to determine the specific type of instability by combining the coupling relationship between the impedance angle stability margin and other margins.

[0097] Since impedance angle stability involves a dynamic process, its stability type cannot be simply defined by voltage stability or frequency stability. It is mainly affected by the equivalent impedance of the grid-connected converter and the grid-side impedance. The equivalent impedance of the grid-connected converter is related to its internal inductance, capacitance and control parameters. It manifests as internal potential energy in the dynamic process, and the grid-side inductance and capacitance parameters manifest as external potential energy in the dynamic process. In the dynamic process, impedance angle stability is mainly affected by the mutual conversion between the internal potential energy of the converter itself and the external potential energy on the grid side. Impedance angle stability reflects the system's ability to stabilize oscillations at the power balance point. Therefore, this type of stability is a type of stability that converts potential energy into a dominant power oscillation.

[0098] In the embodiment, small sample data or zero sample data of the system is collected to obtain the inverter equivalent output impedance Z1, and the line impedance Z2 is connected at 0.1s after the system is running stably. This will be more in line with the impedance angle stabilization process and better demonstrate the change of system stability after the system reactive power changes. Finally, the difference in the stability performance of the power system obtained in Table 1 is used to establish the impedance angle model for the specific power system case to be analyzed.

[0099] Utilizing the impedance angle characteristics of the system model with small samples or zero samples, according to the relationship between the system impedance angle and stability, a self-evolving data model of small sample data or zero sample data of the power system to be analyzed is constructed corresponding to the specific analysis case, that is, the power system stability performance of the specific power system under the impedance angle range is obtained.

[0100] The present invention maps the linkage relationship between oscillation feature samples into different value ranges of the equivalent impedance angle of the inverter to form a new power system stability criterion, which realizes the organic combination of the new power system wide-band oscillation stability criterion and the three major stability criteria of voltage, frequency and power angle of the traditional power system, and can be applied to the analysis of factors affecting system stability and stability conditions. Moreover, the new power system stability criterion not only characterizes the change trend of the physical quantity itself, but also characterizes the influence relationship and influence direction between the changes of various physical quantities, so that the relationship between different influencing factors and the new power stability can be determined more accurately.

[0101] Step 2, based on the new power system stability criterion, when it is determined that the system is in an unstable state, obtain the proportion of the flow impact on a branch connected to a certain node in the total flow impact received by a certain node, as the flow transfer ratio of a certain node to a branch; based on the information entropy model, use the flow transfer ratio of a certain node to each branch to determine the flow distribution entropy of a certain node; introduce the node branch flow channel variable, use the total flow impact received by a certain node and the flow distribution entropy of a certain node to determine the node's flow entropy weakness index; the node whose flow entropy weakness index is not less than the set threshold is regarded as a weak node.

[0102] The potential instability and the causes of instability are analyzed, and the possibility of instability at each node of the system and the possible causes of instability are analyzed, including: instability is mainly due to the application of a high proportion of renewable energy in the new power system accompanied by the use of a high proportion of power electronic equipment. The main cause of instability is the negative resistance effect of the inverter, that is, the real part of the system impedance (the sum of the equivalent impedance of the energy router and the grid-side impedance) is negative, and after exceeding a certain value, the system becomes unstable. The subsynchronous resonance generated when the grid-connected converter is connected to the grid is related to the connection impedance between it and the grid. Different control methods will change the output impedance characteristics of the energy router. For the control equipment in the new power system, taking the doubly fed wind turbine as an example, when the active power is constantly output, it can be equivalent to a constant negative resistance. During the fault period, it can be equivalent to a variable negative resistance and a variable negative reactance in parallel, and the impedance value is closely related to the voltage and active and reactive power at the grid connection point. The equivalent resistance of the doubly fed wind turbine is negative at the subsynchronous resonance frequency, and this negative value is related to the rotor itself and the control parameters. Its inductive negative resistance characteristics in the subsynchronous frequency band interact with the capacitive characteristics of the grid to cause oscillation. In addition, the direct-drive wind turbine exhibits "negative resistance and capacitance" at the subsynchronous oscillation frequency, and forms a second-order negative damping oscillation loop with the inductive reactance of the power grid to cause oscillation. The reason for the oscillation of the wind farm is that the wind turbine controller presents a negative equivalent conductance (resistance), and when its value increases to a certain value, the system becomes unstable.

[0103] Determine the instability boundary of the system's broadband oscillation according to the system's oscillation mechanism, conditions, and criteria, use entropy theory to determine whether the system has instability risks and the causes of instability, obtain the system's nodes prone to oscillation, analyze the oscillation conditions of each node in the new power system, and evaluate the weak nodes in the system;

[0104] Information entropy, also known as Shannon entropy, is used to measure the information uncertainty of discrete systems and characterizes the degree of order and disorder of the system. When the n states of the system appear with equal probability, the system has the lowest degree of order and the highest information entropy; when the system is in a unique state, the system has the highest degree of order and the lowest information entropy. Information entropy can be used to judge the stability of a system's state. Specifically, for a certain system, if the more possible operating states it has and the more average the probability of their occurrence, the higher the degree of disorder of the system, and the greater its entropy value; conversely, if the fewer operating states a system has and the more concentrated the probability of their occurrence is in a few states, the higher the degree of stability of the system and the smaller its entropy value. The entropy function of a general system is as follows:

[0105]

[0106] In the formula, H is the entropy function of the system, ω is a constant; M e is the total number of operating states of the entropy system; X is the probability that the corresponding operating state may occur.

[0107] Corresponding to the power system, the power system is an energy balance system, and its internal stable balance can be described by the entropy change process of the energy distribution inside the system. The energy entropy H in the power system is defined as the energy increment θ flowing through branch i i As pheromone, the total number of system branches N is taken as the total number of states, then:

[0108]

[0109] Where N is the total number of branches;

[0110] At this time, energy entropy H represents the distribution law of energy flowing through a certain node under a certain operating state of the system. The more uniform the distribution, the more stable the system. Considering the influence of the branch, the branch variable C is introduced to satisfy the following relationship:

[0111]

[0112] Then the energy entropy of the power system is:

[0113]

[0114] Corresponding to the power flow distribution of the power system, assuming that when the power flow through a certain node a of the system changes, the power flow impact ΔP on the branch i (i = 1, 2, 3, ..., N) connected to node a i for:

[0115] ΔP i =|P i -P i 0 |

[0116] Where P i 0 is the power flow of branch i in the initial state; P i is the power flow of branch i after node a is impacted by the power flow;

[0117] Therefore, the total power flow impact on node a is:

[0118]

[0119] In the formula, ΔP a is the total flow impact on node a, ΔP i is the flow impact on branch i (i=1, 2, 3,…, N) connected to node a.

[0120] Based on the new power system stability criterion, when the system is judged to be in an unstable state, the proportion of the flow impact on a branch connected to a certain node in the total flow impact on the certain node is obtained as the flow transfer ratio of a certain node to a branch. In the embodiment, the flow transfer ratio of node a to branch i is Satisfies the following relationship:

[0121]

[0122] In the formula, is the power transfer ratio of node a to branch i, ΔP i is the flow impulse on branch i connected to node a, i = 1, 2, 3, ..., N, N is the total number of branches, ΔP a is the total flow impact on node a.

[0123] Based on the information entropy model, the power distribution entropy of a node is determined by using the power transfer ratio of a node to each branch. In the embodiment, the power distribution entropy of node a satisfies the following relationship:

[0124]

[0125] In the formula, is the power flow distribution entropy of node a, is the power transfer ratio of node a to branch i.

[0126] The node branch flow channel variable is introduced, and the total flow impact amount received by a node and the flow distribution entropy of a node are used to determine the flow entropy weakness index of the node; in the embodiment, the flow entropy weakness index of node a satisfies the following relationship:

[0127]

[0128] In the formula, H P (a) is the power flow entropy weakness index of node a, C n is the node branch power flow channel variable;

[0129] The size of the power flow distribution entropy of the defined node reflects the distribution characteristics of the power flow in the system after different nodes are subjected to power flow impact. If the entropy value is larger, it means that the power flow impact suffered by the node is more evenly distributed in each line; conversely, if the entropy value is smaller, it means that the power flow impact is more concentratedly distributed on a few lines, which can easily cause the lines carrying most of the power flow impact to be overloaded or overloaded.

[0130] The nodes whose power entropy weakness index is not less than the set threshold are regarded as weak nodes, where the set threshold value range is [0,1]. The larger the power entropy weakness index of the nodes exceeding this range is, the more likely this node area is to have overload, overload and other faults. The power entropy weakness index of all nodes in the system is calculated and compared with the set threshold. When the number of nodes whose power entropy weakness index is greater than the set threshold accounts for 10% of the total number of nodes in the system, the optimal set threshold is obtained, and these 10% nodes are regarded as weak nodes.

[0131] According to its power flow entropy weakness index, the greater the power flow impact on the node, and the more uneven the impact is distributed in the adjacent lines, the more likely the area where the node is located will experience line power flow overload and overload failure, so it is identified as a weak node; conversely, the impact of power flow impact on the system in this area is smaller. The power flow entropy weakness index is constructed using entropy theory to complete the quantitative evaluation of weak nodes in the power system.

[0132] A high proportion of new energy and power electronic equipment are connected to the power system, and the system oscillation frequency range is wider. Analyze the reasons why the system is instability due to broadband oscillations in the system when the system is in a specific working condition or fault disturbance. The principle of identifying weak links in new power systems is to determine the instability boundary of the system broadband oscillation based on the system oscillation mechanism, conditions, and criteria, so as to determine whether there are hidden dangers of instability in the system and the causes of instability, and obtain the links in the system that are prone to oscillation. By analyzing the failure rate, maintenance history, and availability of each key equipment in the power system, the weak links in the system are evaluated. Analyze the performance of the system under different working conditions, especially the operation under weak link conditions, and use entropy theory to quantitatively evaluate the weak links of the system.

[0133] Step 3, based on the generator rotor motion equation and the inverter equivalent power angle / frequency second-order equation, establish the system's power angle, voltage, frequency, and impedance angle energy mapping model, and use the oscillation characteristic samples to determine the power angle, voltage, frequency, and impedance angle constraints; under the power angle, voltage, frequency, and impedance angle constraints, use the coupling relationship between the power angle stability margin, voltage stability margin, frequency stability margin, and impedance angle stability margin to establish a multi-dimensional stability margin space.

[0134] Specifically, step 3 includes:

[0135] Step 3.1, based on the generator rotor motion equation and the inverter equivalent power angle / frequency second-order equation, establish the energy mapping model of the system's power angle, voltage, frequency, and impedance angle, and use the oscillation characteristic samples to determine the constraints of the power angle, voltage, frequency, and impedance angle.

[0136] The nodes included in the power system include "source-grid-load", that is, power source, power grid and power load. The three involve energy conversion and transmission. We can analyze the essential relationship between power angle stability, voltage stability, frequency stability, impedance angle stability and energy conversion through the conversion law of kinetic energy / potential energy among the three, so as to achieve the purpose of analyzing the possibility of instability of each node in the power system; by using the system motion equation and network topology to construct a new power system power angle, voltage, frequency, impedance angle and energy mapping relationship. The source side system motion equation is established by the generator rotor motion equation and the inverter equivalent power angle / frequency second-order equation:

[0137]

[0138] Where T is the generator inertia time constant, is the first derivative of the electrical angular velocity, P M is the rotor mechanical power, P e is the active power of the system, D is the damping coefficient, for ω0 is the electrical angular velocity under rated working conditions.

[0139] Considering the system impedance angle as a variable, the grid-side energy will be expanded from the energy caused by the node voltage power angle to the energy caused by the power angle and impedance angle changes. Based on the generator rotor motion equation and the inverter equivalent power angle / frequency second-order equation, the active power model of node a is determined to satisfy the following relationship:

[0140] P e =ΔP δ (V a ,δ a )+ΔP θ (V a ,θ a )+ΔP δ,θ (V a ,δ a ,θ a )

[0141] In the formula, ΔP δ (V a ,δ a ) is the voltage V at node a a and power angle δ a The power change caused by θ (V a ,θ a ) is the voltage V at node a a and impedance angle θ a The power change caused by δ,θ (V a ,δ a ,θa ) is the voltage V at node a a , power angle δ a and impedance angle θ a The amount of power change caused.

[0142] Based on the active power model of node a, the Popov method is used to establish the energy mapping model of the system's power angle, voltage, frequency, and impedance angle, satisfying the following relationship:

[0143] V=ΔV m (δ m ,V m ,f m ,θ m )+ΔV r (δ r ,V r ,f r ,θ r )+ΔV e (δ e ,V e ,f e ,θ e )+ΔV L (δ L ,V L ,f L ,θ L )

[0144] Where V is the energy mapping function of the new power system, ΔV m (δ m ,V m ,f m ,θ m ) is the synchronous generator m with respect to the power angle δ m , voltage V m , frequency f m , impedance angle θ m Energy mapping function, m = 1, 2, ..., N m , N m is the total number of synchronous generators in the system; ΔV r (δ r ,V r ,f r ,θ r ) is the inverter r with respect to the power angle δ r , voltage V r , frequency f r , impedance angle θ r Energy mapping function, r = 1, 2, ..., N r , N r is the total number of inverters in the system; ΔV e (δ e ,V e ,fe ,θ e ) is the power angle of the system network δ e , voltage V e , frequency f e , impedance angle θ e Energy mapping function; ΔV L (δ L ,V L ,f L ,θ L ) is the load L with respect to the power angle δ L , voltage V L , frequency f L , impedance angle θ L Energy mapping function, L = 1, 2, ..., N L , N L is the total number of loads in the system.

[0145] Based on the energy mapping model of the system's power angle, voltage, frequency, and impedance angle, the constraints of the power angle, voltage, frequency, and impedance angle are obtained using oscillation feature samples, including:

[0146] 1) Nonlinear constraints between the power angle and the synchronous generator rotor angle potential energy, inverter equivalent potential energy, line inductance and / or capacitance potential energy;

[0147] 2) Nonlinear constraints between voltage and line inductance and / or capacitance potential energy, resistance dissipation energy, constant power and / or constant impedance load potential energy;

[0148] 3) Nonlinear constraints between frequency and synchronous generator rotor kinetic energy, inverter equivalent kinetic energy, constant power and / or constant impedance load potential energy;

[0149] 4) Nonlinear constraints between the impedance angle and the inverter filter inductance and / or capacitance potential energy, line inductance and / or capacitance potential energy, and resistance dissipation energy.

[0150] In the embodiment, when establishing the mapping relationship, characteristic parameters of the system when power angle stability problems, voltage stability problems, frequency stability problems and impedance angle stability problems occur are extracted from the oscillation characteristic samples.

[0151] Step 3.2, under the constraints of power angle, voltage, frequency, and impedance angle, a multi-dimensional stability margin space is established by utilizing the coupling relationship between the power angle stability margin, voltage stability margin, frequency stability margin, and impedance angle stability margin to satisfy the following relationship:

[0152] SP(δ,V,f,θ)=P{SP(δ),SP(V),SP(f),SP(θ)}

[0153] Wherein, SP(δ,V,f,θ) is the multi-dimensional stability margin space of the new power system, P{} is the coupling relationship function between the power angle stability margin SP(δ), voltage stability margin SP(V), frequency stability margin SP(f) and impedance angle stability margin SP(θ);

[0154] The constraints of the multi-dimensional stability margin space of the new power system satisfy the following relationship:

[0155] δ min ≤δ≤δ max

[0156] V min ≤V≤V max

[0157] f min ≤f≤f max

[0158] θ∈{[θ down - τ ,θ up-τ ]}

[0159] In the formula, δ min , δ max are the lower and upper limits of the power angle δ, V min 、V max are the lower and upper limits of voltage V, respectively, and f min 、f max are the lower and upper limits of the frequency f, respectively. The subscript τ is the number of the different value ranges of the equivalent impedance angle of the inverter obtained by mapping. The value range of τ = 1 corresponds to The value range of τ=2 corresponds to The value range of τ=3 corresponds to The value range of τ=4 corresponds to The value range of τ=5 corresponds to The value range of τ=6 corresponds to θ down-τ is the lower limit of the value range τ, θ up-τ is the upper limit of the value range τ.

[0160] Instability of new power systems is often characterized by supply-demand mismatch and increasing kinetic / potential energy coupling, and it is difficult to determine the conditions for system instability only from the instability manifestations. Current impedance technology and state equation technology have the defects of high computational complexity, weak engineering practicality and low judgment accuracy, so it is difficult to accurately and efficiently judge the stability of the system. A more optimized analytical strategy is needed. Therefore, based on the energy mapping relationship, the present invention constructs a multi-dimensional stability margin space that comprehensively reflects the energy mapping relationship between the power angle, voltage, frequency, impedance angle and the stability margin, thereby effectively improving the reliability of the stability judgment results of the new power system.

[0161] Step 4: Use the actual value of the equivalent impedance angle of the inverter and the equivalent output impedance amplitude of the inverter to construct the stability margin index of the weak node, which satisfies the following relationship:

[0162]

[0163] In the formula, SM(θ c ,a c ) is the stability margin index of the weak node, where θ c is the stability margin of the equivalent impedance angle of the inverter, a c is the stability margin of the equivalent impedance amplitude of the inverter, the subscript τ is the number of the different value ranges of the equivalent impedance angle of the inverter obtained by mapping, and the value range of τ = 1 corresponds to The value range of τ=2 corresponds to The value range of τ=3 corresponds to The value range of τ=4 corresponds to The value range of τ=5 corresponds to The value range of τ=6 corresponds to k cτ is the stability margin coefficient of the equivalent impedance angle within the value range τ, According to the oscillation characteristic samples, the boundary of the stable range under the constraints of power angle, voltage, frequency and impedance angle is obtained, and k cτ The larger the value, the wider the stability margin of the equivalent impedance angle within the value range τ. Usually, k cτ Take 1, is the actual value of the equivalent impedance angle of the inverter, a cτ is the equivalent output impedance amplitude of the inverter within the value range τ, f cτ It is a quantization factor between the actual value of the equivalent impedance angle of the inverter and the equivalent output impedance amplitude within the value range τ. The value range is (0,1), and the value is determined according to the composite impedance angle of the inverter and the line within the value range τ. The quantization factor establishes a connection between the equivalent impedance angle of the inverter and the composite impedance angle of the inverter and the line, so as to make it easier and more intuitive to judge the system stability.

[0164] The random access of renewable energy to the new power system results in the changeable law of network energy transmission and the unknown dominant factors of instability. The method proposed in the present invention is used to realize a self-evolutionary learning of small sample data or zero sample data of an autonomous analysis system. The existing sample data is analyzed, its features are extracted and summarized, its impedance angle characteristics are analyzed, and an impedance angle model is constructed for the small sample data or zero sample data of the system. The impedance angle of the system model of the small sample or zero sample is obtained, and the self-evolution data of the small sample data or zero sample data of the system is obtained according to the relationship between the system impedance angle and stability.

[0165] Step 5: When the stability margin index of the weak node exceeds the multi-dimensional stability margin space, the new power system is determined to be unstable.

[0166] The stability criterion of the new power system shown in Table 1 is to judge the stability performance of the system from the factor of the equivalent impedance angle of the inverter, and the multi-dimensional stability margin space realizes the combination of the equivalent impedance angle of the inverter that can judge the stability performance of the system with the power angle, voltage and frequency in the traditional power system, and takes the coupling index between the power angle stability margin, voltage stability margin, frequency stability margin and impedance angle stability margin as the comprehensive stability margin index, so as to associate the constructed impedance angle margin with the traditional existing power angle stability margin, voltage stability margin and frequency stability margin through mapping to establish a multi-dimensional stability margin space, so as to realize the quantitative evaluation of the multi-dimensional stability margin of the new power system.

[0167] When the calculated stability margin index of the weak node exceeds a certain boundary of the multi-dimensional stability margin space, the new power system is determined to be unstable; and the stability classification proposed in the "Definition and Classification of Power System Stability" report released by IEEE / CIGRE is compared to confirm the type of power system instability, so as to determine the dominant factor of instability of the new power system, that is, to achieve the identification of instability type, including:

[0168] ① The stability margin of the grid-connected converter decreases as the strength of the grid increases.

[0169] The greater the grid strength, the smaller the amplitude of the line impedance, the smaller the phase angle difference between the system impedance and Z, that is, the closer Z is. When the converter is running, it exhibits a negative impedance characteristic. When the system impedance is in this range, the system is more likely to become unstable than stable. However, when the grid strength is weaker, it means that the amplitude of the line impedance is larger, the system impedance Z is closer, and is less susceptible to changes. At this time, the system is more likely to be stable;

[0170] ② The stability margin of the grid-following converter increases as the strength of the grid increases.

[0171] The greater the grid strength, the smaller the amplitude of the line impedance, the easier it is for the system impedance Z to fall into the stable zone, and the stronger the system stability;

[0172] ③ The stability of the purely inductive power grid is the worst

[0173] The smaller the phase angle difference between and , the faster the amplitude of increases with the increase of impedance angle, the greater the change of reactive power emitted or absorbed by new energy, and the easier it is for the system reactive power to lose balance. When the inductive component of is larger, the smaller the phase angle difference between and , according to the above analysis, the easier it is for the system to lose stability;

[0174] ④ The oscillation problem of the inverter connected to the grid increases with the increase of its output active power

[0175] When the active power output of renewable energy increases, the power angle increases, the stability range decreases, and the risk of oscillation in the new power system increases.

[0176] The present invention also proposes a novel weak node detection and instability index establishment system for a power system, comprising:

[0177] A stability criterion establishment module is used to obtain oscillation characteristic samples of historical oscillation accidents, map the linkage relationship between the oscillation characteristic samples into different value ranges of the equivalent impedance angle of the inverter, and form a new power system stability criterion based on the relationship between the actual value of the equivalent impedance angle of the inverter and the different value ranges of the equivalent impedance angle of the mapped inverter;

[0178] The weak node detection module is used to obtain the proportion of the flow impact on a branch connected to a certain node in the total flow impact received by a certain node based on the new power system stability criterion when the system is determined to be in an unstable state, as the flow transfer ratio of a certain node to a branch; based on the information entropy model, the flow transfer ratio of a certain node to each branch is used to determine the flow distribution entropy of a certain node; introduce the node branch flow channel variable, use the total flow impact received by a certain node and the flow distribution entropy of a certain node to determine the node flow entropy weakness index; the node whose flow entropy weakness index is not less than the set threshold is regarded as a weak node;

[0179] The stability margin index system establishment module is used to establish the energy mapping model of the system's power angle, voltage, frequency, and impedance angle based on the generator rotor motion equation and the inverter's equivalent power angle / frequency second-order equation, and use the oscillation characteristic samples to determine the constraints of the power angle, voltage, frequency, and impedance angle; under the constraints of the power angle, voltage, frequency, and impedance angle, use the coupling relationship between the power angle stability margin, voltage stability margin, frequency stability margin, and impedance angle stability margin to establish a multi-dimensional stability margin space; use the actual value of the inverter's equivalent impedance angle and the inverter's equivalent output impedance amplitude to construct the stability margin index of the weak node;

[0180] The instability detection module is used to determine whether the new power system is unstable when the stability margin index of the weak node exceeds the multi-dimensional stability margin space.

[0181] It also includes: an instability dominant factor detection module, which is used to confirm the type of power system instability by comparing the stability classification proposed in the "Definition and Classification of Power System Stability" report released by IEEE / CIGRE, so as to identify new power systems.

[0182] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0183] A computer-readable storage medium may be a tangible device that can hold and store instructions used by an instruction execution device. A computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples of computer-readable storage media (a non-exhaustive list) include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure in a groove on which instructions are stored, and any suitable combination of the foregoing. As used herein, a computer-readable storage medium is not to be interpreted as a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted through a wire.

[0184] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0185] The computer program instructions for performing the operation of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-related instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages-such as Smalltalk, C++, etc., and conventional procedural programming languages-such as "C" language or similar programming languages. Computer-readable program instructions may be executed completely on a user's computer, partially on a user's computer, as an independent software package, partially on a user's computer, partially on a remote computer, or completely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network-including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., using an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA) may be personalized by utilizing the state information of a computer-readable program instruction, and the electronic circuit may execute a computer-readable program instruction, thereby realizing various aspects of the present disclosure.

[0186] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A novel method for detecting weak nodes and establishing instability indexes of a power system, characterized in that: include: Obtain oscillation feature samples of historical oscillation accidents, map the linkage relationship between the oscillation feature samples into different value ranges of the equivalent impedance angle of the inverter, and form a new power system stability criterion based on the relationship between the actual value of the equivalent impedance angle of the inverter and the different value ranges of the equivalent impedance angle of the mapped inverter; Based on the new power system stability criterion, when the system is judged to be in an unstable state, the proportion of the flow impact on a branch connected to a certain node in the total flow impact on the certain node is obtained as the flow transfer ratio of a certain node to a branch. Based on the information entropy model, the power flow distribution entropy of a node is determined by using the power flow transfer ratio of a node to each branch. The node branch power flow channel variable is introduced, and the power flow entropy weakness index of the node is determined by using the total power flow impact amount received by the node and the power flow distribution entropy of the node. The node whose power flow entropy weakness index is not less than the set threshold is regarded as a weak node. Based on the generator rotor motion equation and the inverter equivalent power angle / frequency second-order equation, an energy mapping model of the system's power angle, voltage, frequency, and impedance angle is established, and the constraints of the power angle, voltage, frequency, and impedance angle are determined using oscillation characteristic samples; under the constraints of the power angle, voltage, frequency, and impedance angle, a multi-dimensional stability margin space is established using the coupling relationship between the power angle stability margin, voltage stability margin, frequency stability margin, and impedance angle stability margin; The stability margin index of the weak node is constructed by using the actual value of the equivalent impedance angle of the inverter and the equivalent output impedance amplitude of the inverter; When the stability margin index of the weak node exceeds the multi-dimensional stability margin space, the new power system is determined to be unstable.

2. The method for detecting weak nodes and establishing instability indexes of a novel power system according to claim 1 is characterized in that: The oscillation characteristic samples include: active power and reactive power output by the inverter, output voltage and current, and the composite impedance angle of the inverter and the line; The phase angle of the sum of the equivalent output impedance of the inverter and the line impedance is taken as the composite impedance angle of the inverter and the line, which satisfies the following relationship: Where θ is the composite impedance angle of the inverter and the line, R is the sum of the inverter equivalent output resistance and the line resistance; X is the sum of the inverter equivalent output reactance and the line reactance.

3. The method for detecting weak nodes and establishing instability indexes of a novel power system according to claim 2 is characterized in that: According to the oscillation characteristic samples, the linkage relationship between the active power P and reactive power Q output by the inverter, the output voltage U1 and current I1, and the synthetic impedance angle θ between the inverter and the line is mapped into different value ranges of the equivalent impedance angle of the inverter, with the actual value of the equivalent impedance angle of the inverter as the value. The relationship between the different value ranges of the equivalent impedance angle of the mapped inverter constitutes a new power system stability criterion, including: 1) When the linkage relationship is P↑→Q↓→U1↑→I1↓→θ↑→Q↑, if When the linkage relationship is P↓→Q↑→U1↓→I1↑→θ↓→Q↓, if When , the new power system is determined to be stable; 2) When the linkage relationship is P↑→Q↓→U1↑→I1↓→θ↓→Q↓, if When the linkage relationship is P↓→Q↑→U1↓→I1↑→θ↑→Q↑, if When , the new power system is determined to be unstable; 3) When the linkage relationship is P↑→Q↓→U1↑→I1↓→θ↓→Q↑, if When the linkage relationship is P↓→Q↑→U1↓→I1↑→θ↑→Q↓, if When , the new power system is determined to be stable; 4) When the linkage relationship is P↑→Q↓→U1↓→I1↑→θ↑→Q↓, if When , the new power system is determined to be unstable; when the linkage relationship is P↓→Q↑→U1↑→I1↓→θ↓→Q↑, if When , the new power system is determined to be unstable; 5) When the linkage relationship is P↑→Q↓→U1↓→I1↑→θ↓→Q↑, if When the linkage relationship is P↓→Q↑→U1↑→I1↓→θ↑→Q↓, if When , the new power system is determined to be stable; 6) When the linkage relationship is P↑→Q↓→U1↓→I1↑→θ↓→Q↓, if When , the new power system is determined to be unstable; when the linkage relationship is P↓→Q↑→U1↑→I1↓→θ↑→Q↑, if When , the new power system is determined to be unstable; Among them, the symbol ↑ indicates that the oscillation characteristic sample increases, the symbol ↓ indicates that the oscillation characteristic sample decreases, and when the oscillation characteristic sample on the left side of the symbol → changes, the oscillation characteristic sample on the right side of the symbol → will change.

4. The method for detecting weak nodes and establishing instability indexes of a novel power system according to claim 1 is characterized in that: The power transfer ratio of node a to branch i satisfies the following relationship: In the formula, is the power transfer ratio of node a to branch i, ΔP i is the flow impulse on branch i connected to node a, i = 1, 2, 3, ..., N, N is the total number of branches, ΔP a is the total flow impact on node a; The power flow distribution entropy of node a satisfies the following relationship: In the formula, is the power flow distribution entropy of node a; The power flow entropy weakness index of node a satisfies the following relationship: In the formula, H P (a) is the power flow entropy weakness index of node a, C n is the node branch power flow channel variable.

5. The method for detecting weak nodes and establishing instability indexes of a novel power system according to claim 1 is characterized in that: The threshold value range is set to [0,1]; the power flow entropy weakness index of all nodes in the system is calculated and compared with the set threshold. When the number of nodes with power flow entropy weakness index greater than the set threshold accounts for 10% of the total number of nodes in the system, the optimal set threshold is obtained, and these 10% nodes are regarded as weak nodes.

6. The method for detecting weak nodes and establishing instability indexes of a novel power system according to claim 3 is characterized in that: Based on the generator rotor motion equation and the inverter equivalent power angle / frequency second-order equation, the active power model of node a is determined to satisfy the following relationship: P e =ΔP δ (V a ,d a )+ΔP θ (V a ,i a )+ΔP δ,θ (V a ,d a ,i a ) In the formula, ΔP δ (V a ,δ a ) is the voltage V at node a a and power angle δ a The power change caused by θ (V a ,θ a ) is the voltage V at node a a and impedance angle θ a The power change caused by δ,θ (V a ,δ a ,θ a ) is the voltage V at node a a , power angle δ a and impedance angle θ a The amount of power change caused; Based on the active power of node a, the Popov method is used to establish the energy mapping model of the system's power angle, voltage, frequency, and impedance angle, satisfying the following relationship: V=ΔV m (d m ,V m ,f m ,i m )+ΔV r (d r ,V r ,f r ,i r )+ΔV e (d e ,V e ,f e ,i e )+ΔV L (d L ,V L ,f L ,i L ) Where V is the energy mapping function of the new power system, ΔV m (δ m ,V m ,f m ,θ m ) is the synchronous generator m with respect to the power angle δ m , voltage V m , frequency f m , impedance angle θ m Energy mapping function, m=1,2,…,N m , N m is the total number of synchronous generators in the system; ΔV r (δ r ,V r ,f r ,θ r ) is the inverter r with respect to the power angle δ r , voltage V r , frequency f r , impedance angle θ r Energy mapping function, r = 1, 2, ..., N r , N r is the total number of inverters in the system; ΔV e (δ e ,V e ,f e ,θ e ) is the power angle of the system network δ e , voltage V e , frequency f e , impedance angle θ e Energy mapping function; ΔV L (δ L ,V L ,f L ,θ L ) is the load L with respect to the power angle δ L , voltage V L , frequency f L , impedance angle θ L Energy mapping function, L = 1, 2, ..., N L , N L is the total number of loads in the system.

7. The method for detecting weak nodes and establishing instability indexes of a novel power system according to claim 6 is characterized in that: Based on the energy mapping model of the system's power angle, voltage, frequency, and impedance angle, the constraints of the power angle, voltage, frequency, and impedance angle are obtained using oscillation feature samples, including: 1) Nonlinear constraints between the power angle and the synchronous generator rotor angle potential energy, inverter equivalent potential energy, line inductance and / or capacitance potential energy; 2) Nonlinear constraints between voltage and line inductance and / or capacitance potential energy, resistance dissipation energy, constant power and / or constant impedance load potential energy; 3) Nonlinear constraints between frequency and synchronous generator rotor kinetic energy, inverter equivalent kinetic energy, constant power and / or constant impedance load potential energy; 4) Nonlinear constraints between the impedance angle and the inverter filter inductance and / or capacitance potential energy, line inductance and / or capacitance potential energy, and resistance dissipation energy.

8. The method for detecting weak nodes and establishing instability indexes of a novel power system according to claim 7 is characterized in that: Under the constraints of power angle, voltage, frequency and impedance angle, a multi-dimensional stability margin space is established by utilizing the coupling relationship between the power angle stability margin, voltage stability margin, frequency stability margin and impedance angle stability margin, satisfying the following relationship: SP(δ,V,f,θ)=P{SP(δ),SP(V),SP(f),SP(θ)} Wherein, SP(δ,V,f,θ) is the multi-dimensional stability margin space of the new power system, P{} is the coupling relationship function between the power angle stability margin SP(δ), voltage stability margin SP(V), frequency stability margin SP(f) and impedance angle stability margin SP(θ); The constraints of the multi-dimensional stability margin space of the new power system satisfy the following relationship: d min ≤δ≤δ max In min ≤V≤V max f min ≤f≤f max In the formula, δ min , δ max are the lower and upper limits of the power angle δ, V min 、V max are the lower and upper limits of voltage V, respectively, and f min 、f max are the lower and upper limits of the frequency f, respectively. The subscript τ is the number of the different value ranges of the equivalent impedance angle of the inverter obtained by mapping. The value range of τ = 1 corresponds to The value range of τ=2 corresponds to The value range of τ=3 corresponds to The value range of τ=4 corresponds to The value range of τ=5 corresponds to The value range of τ=6 corresponds to θ down-τ is the lower limit of the value range τ, θ up-τ is the upper limit of the value range τ.

9. The method for detecting weak nodes and establishing instability indexes of a novel power system according to claim 3 is characterized in that: The stability margin index of the weak node is constructed by using the actual value of the equivalent impedance angle of the inverter and the equivalent output impedance amplitude of the inverter, which satisfies the following relationship: In the formula, SM(θ c ,a c ) is the stability margin index of the weak node, where θ c is the stability margin of the equivalent impedance angle of the inverter, a c is the stability margin of the equivalent impedance amplitude of the inverter, the subscript τ is the number of the different value ranges of the equivalent impedance angle of the inverter obtained by mapping, and the value range of τ = 1 corresponds to The value range of τ=2 corresponds to The value range of τ=3 corresponds to The value range of τ=4 corresponds to The value range of τ=5 corresponds to The value range of τ=6 corresponds to k cτ is the stability margin coefficient of the equivalent impedance angle within the value range τ, According to the oscillation characteristic samples, the boundaries of the stable range under the constraints of power angle, voltage, frequency and impedance angle are obtained. is the actual value of the equivalent impedance angle of the inverter, a cτ is the equivalent output impedance amplitude of the inverter within the value range τ, f cτ It is a quantization factor between the actual value of the equivalent impedance angle of the inverter and the equivalent output impedance amplitude within the value range τ. The value range is (0,1), and the value is determined according to the composite impedance angle of the inverter and the line within the value range τ.

10. The novel method for detecting weak nodes and establishing instability indexes of a power system according to claim 1, characterized in that: When the calculated stability margin index of the weak node exceeds a certain boundary of the multi-dimensional stability margin space, the new power system is determined to be unstable; and the type of power system instability is confirmed by comparing the stability classification proposed in the "Definition and Classification of Power System Stability" report released by IEEE / CIGRE to determine the dominant factor of instability of the new power system.

11. A new type of weak node detection and instability index establishment system for power system, characterized in that: include: A stability criterion establishment module is used to obtain oscillation characteristic samples of historical oscillation accidents, map the linkage relationship between the oscillation characteristic samples into different value ranges of the equivalent impedance angle of the inverter, and form a new power system stability criterion based on the relationship between the actual value of the equivalent impedance angle of the inverter and the different value ranges of the equivalent impedance angle of the mapped inverter; The weak node detection module is used to obtain the proportion of the flow impact on a branch connected to a certain node in the total flow impact received by the certain node based on the new power system stability criterion, when the system is determined to be in an unstable state, as the flow transfer ratio of a certain node to a branch; Based on the information entropy model, the power flow distribution entropy of a node is determined by using the power flow transfer ratio of a node to each branch. The node branch power flow channel variable is introduced, and the power flow entropy weakness index of the node is determined by using the total power flow impact amount received by the node and the power flow distribution entropy of the node. The node whose power flow entropy weakness index is not less than the set threshold is regarded as a weak node. The stability margin index system establishment module is used to establish the energy mapping model of the system's power angle, voltage, frequency, and impedance angle based on the generator rotor motion equation and the inverter's equivalent power angle / frequency second-order equation, and use the oscillation characteristic samples to determine the constraints of the power angle, voltage, frequency, and impedance angle; under the constraints of the power angle, voltage, frequency, and impedance angle, use the coupling relationship between the power angle stability margin, voltage stability margin, frequency stability margin, and impedance angle stability margin to establish a multi-dimensional stability margin space; use the actual value of the inverter's equivalent impedance angle and the inverter's equivalent output impedance amplitude to construct the stability margin index of the weak node; The instability detection module is used to determine whether the new power system is unstable when the stability margin index of the weak node exceeds the multi-dimensional stability margin space.

12. The novel power system weak node detection and instability index establishment system according to claim 1 is characterized in that: Also includes: The instability dominant factor detection module is used to confirm the instability type of the power system by comparing the stability classification proposed in the "Definition and Classification of Power System Stability" report released by IEEE / CIGRE, so as to determine the instability of the new power system.

13. A terminal comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method according to any one of claims 1 to 10.

14. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 10 are implemented.

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