A grid-connected converter large-signal stability analysis method and device and storage medium

Abstract

The application discloses a grid-connected converter large-signal stability analysis method and device and a storage medium, wherein the method comprises the following steps: based on a system space model of the grid-connected converter, a system state space equation of the grid-connected converter is established; based on T-S fuzzy theory, a state space model of the grid-connected converter is established according to the system state space equation of the grid-connected converter; based on a stability theorem of the T-S fuzzy theory, a Lyapunov function of the grid-connected converter is constructed according to the state space model, each dimension of the Lyapunov function is projected to a two-dimensional state space plane, and a stable attractor domain of the Lyapunov large signal is obtained; an affine angle of the stable attractor domain is calculated, when the affine angle meets a preset condition, the stability strength of the grid-connected converter is calculated according to the affine angle, and a large-signal stability analysis result of the grid-connected converter is obtained according to the stability strength. The application can effectively improve the accuracy and reliability of the large-signal stability analysis of the grid-connected converter.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power systems, and particularly relates to a grid-connected converter large-signal stability analysis method and device and a storage medium. BACKGROUND

[0002] The progress of the two industrial revolutions is accompanied by not only rapid population growth and rapid economic development, but also intensified consumption of traditional primary energy such as coal, oil, and natural gas. At the same time, the environmental and energy problems brought about by this have become an obstacle to human sustainable development. According to statistics: in recent years, the average growth rate of primary energy consumption is 1.5%, but in 2018 it increased by 2.9%, and the growth rate of carbon emissions also reached the highest level. China, the United States, and India together contribute two-thirds of the global energy demand growth. Global power generation increased by 3.7%, of which China contributed more than half, and coal accounted for 38% of the power generation share, ranking first. Renewable energy increased by 14.5%. Although its 71 million tons of oil increment is very close to the record high of 2017, wind power generation increased by 32 million tons of oil equivalent, ranking first, and solar power generation increased by 30 million tons of oil equivalent, ranking second. This speed is still slightly lower than the historical average. China, as the largest energy consumer, has a much lower ratio of fossil energy reserves to production than the global average, which is worrying. Oil consumption grew by 1.5%, with China and the United States being the main sources of growth, exacerbating energy shortages. At the same time, environmental, smog, and other social problems have gradually become prominent, so the traditional development model based on fossil fuels cannot continue, and the development of clean and low-carbon renewable energy such as grid-connected wind power and grid-connected solar power is possible.

[0003] At present, wind power and photovoltaic power generation in China are developing rapidly. By the end of 2019, the installed capacity of wind power was 210 million kilowatts, and the installed capacity of photovoltaic power generation was 204 million kilowatts, with year-on-year growth of 14.0% and 17.3% respectively; wind power and photovoltaic power generation both broke through 200 million kilowatts for the first time, leading the world. In the field of wind power and photovoltaic power generation, three-phase grid-connected converters are a key component, which can be in the process of rectification or inversion, realizing energy transmission and conversion between the grid, and its stability is directly related to the reliable operation of the grid-connected system. However, with the large-scale access of large-scale power electronic devices such as wind power and photovoltaic power, the stability of the grid-connected converter system has been widely reported. At present, according to the fault mode, system stability analysis can be divided into two types: small-signal stability and large-signal stability. There are many studies on the small-signal stability of grid-connected converters, but even if the initial and terminal equilibrium points are small-signal stable, it does not mean that the system is large-signal stable in the transient process between the two equilibrium points, so it is necessary to study the large-signal stability of grid-connected converters.

[0004] The existing grid-connected converter large signal stability analysis method mainly includes: introducing T-S fuzzy model theory to construct Lyapunov function and calculate stability domain, and constructing Lyapunov function through system state space equation and calculating stability domain. However, different Lyapunov functions are constructed under each parameter and fault condition, and these functions can be hyperplanes in high-dimensional space, so that the accuracy of grid-connected converter large signal stability analysis is low.

[0005] The embodiment of the present application establishes a reliable state space model of the grid-connected converter based on T-S fuzzy theory, and projects the Lyapunov function of the grid-connected converter to the same space through affine transformation, realizes the equivalent mapping of the hyperplane in high-dimensional space to low-dimensional space, and can quickly and accurately analyze the large signal stability of the grid-connected converter under different parameters and fault conditions.

[0006] Further, the embodiment of the present application maps and decomposes the stability domain of the same high-dimensional space based on the energy function model, uses affine transformation and analytic geometry theory, so that the comparison of the elliptical area region can be realized with the origin as the center in the two-dimensional plane space, and the embodiment of the present application can effectively improve the accuracy and reliability of the large signal stability analysis of the grid-connected converter by defining two key performance indicators of stability strength and affine angle. SUMMARY

[0007] The present application provides a grid-connected converter large signal stability analysis method, device and storage medium to solve the technical problem of low accuracy of the existing grid-connected converter large signal stability analysis method.

[0008] The embodiment of the present application provides a grid-connected converter large signal stability analysis method, which comprises:

[0009] Based on the system space model of the grid-connected converter, the system state space equation of the grid-connected converter is established;

[0010] Based on T-S fuzzy theory, a state space model of the grid-connected converter is established according to the system state space equation of the grid-connected converter;

[0011] Based on the stability theorem of the T-S fuzzy theory, the Lyapunov function of the grid-connected converter is constructed according to the state space model, each dimension of the Lyapunov function is projected to a two-dimensional state space plane, and the stable attractor domain of the Lyapunov large signal is obtained;

[0012] The affine angle of the stable attractor domain is calculated, when the affine angle meets the preset condition, the stability strength of the grid-connected converter is calculated according to the affine angle, and the large signal stability analysis result of the grid-connected converter is obtained according to the stability strength.

[0013] Further, the system space model based on the grid-connected converter, the system state space equation of the grid-connected converter is established, including:

[0014] Based on the system space model of the grid-connected converter, the stable working point is defined as the coordinate origin, and 26 state variables of the grid-connected converter are calculated;

[0015] Assuming that the short-circuit ratio of the grid-connected converter on the power frequency side and the frequency division side is higher than the preset threshold, the influence of the phase-locked loop is ignored, and the nonlinear state variable is calculated according to the 26 state variables;

[0016] The nonlinear state variable is constructed as a nonlinear term to construct the system state space equation of the grid-connected converter.

[0017] Further, the T-S fuzzy theory is used to establish the state space model of the grid-connected converter according to the system state space equation of the grid-connected converter, including:

[0018] Based on the T-S fuzzy rule, the system fuzzy model is constructed;

[0019] According to the system fuzzy model, the stability theorem under the condition of continuous system is set;

[0020] According to the stability theorem, the nonlinear term in the system space equation corresponds to a plurality of fuzzy rules;

[0021] According to the minimum and maximum values of the state variables, the fuzzy set is constructed, the value of the nonlinear term is calculated, and the state space model of the grid-connected converter is established according to the value of the nonlinear term.

[0022] Further, the stability theorem based on the T-S fuzzy theory is used to construct the Lyapunov function of the grid-connected converter according to the state space model, including:

[0023] According to the stability theorem of the T-S fuzzy theory, the Lyapunov function of the grid-connected converter is constructed by solving the linear matrix inequality of the state space model of the grid-connected converter.

[0024] Further, the affine angle of the stable attraction domain is calculated, when the affine angle meets the preset condition, the stability strength of the grid-connected converter is calculated according to the affine angle, and the large signal stability analysis result of the grid-connected converter is obtained according to the stability strength, including:

[0025] The stable attraction domain is subjected to affine transformation, and different stable attraction domains are projected into the same space;

[0026] calculate an affine angle of the stable attraction domain through a geometric algorithm;

[0027] When the angle difference of the affine angles under the two conditions is less than the minimum affine angle, the stability strength of the grid-connected converter is calculated, and when the stability strength exceeds a preset range, it is judged that the large-signal stability of the grid-connected converter meets a preset condition.

[0028] The embodiment of the application provides a grid-connected converter large-signal stability analysis device, which comprises:

[0029] A system state space equation construction module is configured to establish a system state space equation of the grid-connected converter based on a system space model of the grid-connected converter.

[0030] A state space model construction module is configured to establish a state space model of the grid-connected converter based on a T-S fuzzy theory and the system state space equation of the grid-connected converter.

[0031] A stable attraction domain determination module is configured to construct a Lyapunov function of the grid-connected converter based on a stability theorem of the T-S fuzzy theory and the state space model, project each dimension of the Lyapunov function to a two-dimensional state space plane, and obtain a stable attraction domain of a large-signal Lyapunov function.

[0032] A large-signal stability analysis module is configured to calculate an affine angle of the stable attraction domain, calculate a stability strength of the grid-connected converter based on the affine angle when the affine angle meets a preset condition, and obtain a large-signal stability analysis result of the grid-connected converter based on the stability strength.

[0033] Further, the system state space equation construction module is specifically configured to:

[0034] Based on the system space model of the grid-connected converter, a stable operating point is defined as a coordinate origin, and 26 state variables of the grid-connected converter are calculated.

[0035] When the short-circuit ratios of the power frequency side and the frequency division side of the grid-connected converter are higher than a preset threshold, the influence of a phase-locked loop is ignored, and nonlinear state variables are calculated based on the 26 state variables.

[0036] The nonlinear state variables are taken as nonlinear terms to construct the system state space equation of the grid-connected converter.

[0037] Further, the state space model construction module is specifically configured to:

[0038] Based on a T-S fuzzy rule, a system fuzzy model is constructed.

[0039] According to the system fuzzy model, a stability theorem under continuous system conditions is set;

[0040] According to the stability theorem, the nonlinear terms in the system space equation are corresponded to a plurality of fuzzy rules;

[0041] According to the minimum and maximum values of the state variables, the values of the nonlinear terms are calculated, and the state space model of the grid-connected converter is established according to the values of the nonlinear terms.

[0042] Further, the large signal stability analysis module is specifically used for;

[0043] The stable attractor is subjected to affine transformation, and different stable attractors are projected into the same space;

[0044] The affine angle of the stable attractor is calculated by the analytic geometry algorithm;

[0045] When the angle difference of the affine angles under the two conditions is less than the minimum affine angle, the stability strength of the grid-connected converter is calculated, and when the stability strength exceeds the preset range, it is judged that the large signal stability of the grid-connected converter meets the preset condition.

[0046] An embodiment of the present application provides a computer readable storage medium, the computer readable storage medium comprises a stored computer program; wherein the computer program controls the device where the computer readable storage medium is located to execute the grid-connected converter large signal stability analysis method as described above when running.

[0047] The embodiment of the present application establishes a reliable state space model of the grid-connected converter based on the T-S fuzzy theory, and projects the Lyapunov function of the grid-connected converter into the same space by affine transformation, realizes the equivalent mapping of the hyperplane in high-dimensional space to low-dimensional space, and can quickly and accurately analyze the large signal stability of the grid-connected converter under different parameters and fault conditions.

[0048] Further, the embodiment of the present application maps and decomposes the stable domain of the same high-dimensional space by using affine transformation and analytic geometry theory based on the energy function model, so that it can realize the comparison of the elliptical area region with the origin as the center in the two-dimensional plane space, and the embodiment of the present application can effectively improve the accuracy and reliability of the large signal stability analysis of the grid-connected converter by defining the two key performance indexes of stability strength and affine angle. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 is a flowchart of a grid-connected converter large signal stability analysis method provided by the embodiment of the present application;

[0050] Figure 2 is a grid-connected converter topology schematic diagram based on M3C provided by an embodiment of the application;

[0051] Figure 3 is a structure schematic diagram of sub-converters A, B and C of the grid-connected converter power frequency (IF) side provided by an embodiment of the application;

[0052] Figure 4 is a structure schematic diagram of sub-converters U, V and W of the grid-connected converter frequency division (FF) side provided by an embodiment of the application

[0053] Figure 5 is a two-dimensional state space projection schematic diagram of LS-DOA provided by an embodiment of the application;

[0054] Figure 6 is an affine angle and stability strength definition schematic diagram provided by an embodiment of the application;

[0055] Figure 7 is a bridge arm inductance L parameter change stability margin comparison schematic diagram provided by an embodiment of the application

[0056] Figure 8 is a capacitance C parameter change stability margin comparison schematic diagram provided by an embodiment of the application

[0057] Figure 9 is a structure schematic diagram of a grid-connected converter large signal stability analysis device provided by an embodiment of the application. DETAILED DESCRIPTION

[0058] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0059] In the description of the present application, it should be understood that the terms "first", "second" are used only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0060] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integrally connected, it can be mechanical connection, or electrical connection, it can be directly connected, or indirectly connected through intermediate medium, or internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0061] Please refer to Figure 1 The embodiment of the present application provides a grid-connected converter large signal stability analysis method, comprising:

[0062] S1, based on the system space model of the grid-connected converter, the system state space equation of the grid-connected converter is established;

[0063] S2, based on T-S fuzzy theory, the state space model of the grid-connected converter is established according to the system state space equation of the grid-connected converter;

[0064] S3, based on the stability theorem of T-S fuzzy theory, the Lyapunov function of the grid-connected converter is constructed according to the state space model, each dimension of the Lyapunov function is projected to a two-dimensional state space plane, and a stable attractor of the Lyapunov large signal is obtained;

[0065] S4, the affine angle of the stable attractor is calculated, when the affine angle meets the preset condition, the stability strength of the grid-connected converter is calculated according to the affine angle, and the large signal stability analysis result of the grid-connected converter is obtained according to the stability strength.

[0066] The embodiment of the present application establishes a reliable state space model of the grid-connected converter based on T-S fuzzy theory, and projects the Lyapunov function of the grid-connected converter to the same space by using affine transformation, realizes the equivalent mapping of the hyperplane in high-dimensional space to low-dimensional space, and can quickly and accurately analyze the large signal stability of the grid-connected converter under different parameters and fault conditions.

[0067] In one embodiment, based on the system space model of the grid-connected converter, the system state space equation of the grid-connected converter is established, comprising:

[0068] Based on the system space model of the grid-connected converter, the stable working point is defined as the coordinate origin, and 26 state variables of the grid-connected converter are calculated;

[0069] Please refer to Figure 2 In the embodiment of the present application, e x e y i x i y v xyi xy (x = u, v, w; y = a, b, c) are defined as the voltages and currents of the nine bridge arms on both sides of the grid-connected converter, i.e. the power frequency side and the frequency-division side, respectively. Based on Kirchhoff's law and by taking as a differential operator, the voltage equation of the bridge arm can be expressed as:

[0070]

[0071]

[0072] Please refer to Figure 3 , Figure 3 The sub-converters on the intermediate frequency (IF) side are A, B and C. The relationship can be obtained by multiplying formula (1) by T abc / αβ0 and T αβ0 / dq (ωt) on the left. T abc / αβ0 and T αβ0 / dq (ωt) are the Clark and Park transformation matrices. The common-mode and differential-mode components on the power frequency side can be expressed as:

[0073]

[0074]

[0075] Please refer to Figure 4 , Figure 4 The sub-converters on the frequency-division (FF) side are U, V and W. The common-mode and differential-mode components can be expressed as:

[0076]

[0077]

[0078] The embodiment of the application assumes that all the unit capacitor voltages in the same bridge arm are equal for the module capacitor voltages of the nine bridge arms. The sub-module capacitor voltage of each bridge arm can be expressed as:

[0079]

[0080] In particular, the expressions of some important instantaneous power elements are as follows:

[0081]

[0082] It should be noted that the control system can be divided into two decoupled parts: the IF part and the FF part. The IF part is divided into an outer voltage loop SV and an inner current loop SI, and the expressions are as follows:

[0083]

[0084]

[0085] Similarly, the FF part can also be divided into voltage outer loop LV and current inner loop LI, and its expression is similar, which is not described here.

[0086] After the system space model of the grid-connected converter main circuit and the control system is established, in order to obtain the system state space equation, the 26 state variables of the grid-connected converter are calculated after the stable working point is defined as the coordinate origin:

[0087]

[0088] Wherein, the superscripts 0 and s i (i=1,2,…,13) represent the steady-state value and the integral part respectively. Rewrite s i As:

[0089]

[0090] Assuming that the short circuit ratio (SCR) of the power frequency side and the frequency division side of the grid-connected converter is higher than the preset threshold, the influence of the phase-locked loop (PLL) is ignored, and the nonlinear state variable is calculated according to the 26 state variables;

[0091] In the embodiment of the application, in order to avoid the curse of dimensionality for fault analysis, based on the above system state space equation, it is assumed that the short circuit ratio (SCR) of the power frequency side and the frequency division side of the grid-connected converter is higher than the preset threshold, that is, the influence of the phase-locked loop (PLL) can be ignored, and Y i (i=1,2,3,4,5) represents that the state space expression contains nonlinear terms, and the specific expression of the nonlinear term is as follows:

[0092]

[0093]

[0094]

[0095]

[0096]

[0097] Wherein, the expression of the nonlinear state variable multiplication part is:

[0098]

[0099] The nonlinear state variable is taken as a nonlinear term to construct the system state space equation of the grid-connected converter.

[0100] According to the nonlinear term expression of formula (14), the system state space equation of the grid-connected converter is constructed as:

[0101]

[0102] In this embodiment of the invention, after obtaining the system state-space equation, the system state-space equation is processed using TS fuzzy theory.

[0103] In one embodiment, based on TS fuzzy theory, a state-space model of the grid-connected converter is established according to the system state-space equations of the grid-connected converter, including:

[0104] Construct a fuzzy model of the system based on TS fuzzy rules;

[0105] It is understandable that the TS fuzzy model consists of an if-then rule base and a set of dependent functions. The i-th rule in this embodiment of the invention is described as follows:

[0106] Fuzzy rule i:

[0107] δx(t)=A i x(t)+B i u(t), i∈Γ r (16)

[0108] If the subordinate function M ij (z j (t) is z j Relative to fuzzy set M ij The system's fuzzy model is then expressed as: (The preceding component is then used to represent the system's fuzz

[0109]

[0110]

[0111] in:

[0112]

[0113]

[0114] φ i (z(t)) represents the subordinate function of the standardized fuzzy rule i, and satisfies the following mathematical relationship:

[0115]

[0116] Based on the fuzzy model of the system, a stability theorem is established under the condition of continuous system.

[0117] In this embodiment of the invention, due to the normalization of the dependency function, the TS fuzzy model is a combination of convex sets. This embodiment of the invention performs stability analysis by solving the LMI. The stability theorem under continuous system conditions is as follows:

[0118] If there exists a positive definite symmetric matrix P, then the following linear matrix inequality problem is feasible:

[0119]

[0120] where, denotes the symmetric part, i.e. and the system fuzzy model in equation (17) is globally asymptotically stable.

[0121] In summary, the essence of the stability criterion theorem is that if there exists a matrix P, then the alternative Lyapunov function that satisfies the following conditions can be explained:

[0122]

[0123] The stability criterion of the Lyapunov direct method based on the existence of energy function is a sufficient condition for determining the stability of the system.

[0124] According to the stability theorem, the nonlinear terms in the system space equation correspond to a plurality of fuzzy rules;

[0125] According to the minimum and maximum values of the state variables, the fuzzy set is constructed, the value of the nonlinear term is calculated, and the state space model of the grid-connected converter is established according to the value of the nonlinear term.

[0126] In an embodiment of the present application, based on the T-S fuzzy model theory, the six nonlinear terms of the system state space equation correspond to 26 fuzzy rules. According to the method of constructing a fuzzy set based on the minimum and maximum values of the state variables, the value of the nonlinear term can be represented as:

[0127]

[0128] The state space model of the grid-connected converter is finally obtained as:

[0129]

[0130]

[0131]

[0132] In one embodiment, based on the stability theorem of T-S fuzzy theory, the Lyapunov function of the grid-connected converter is constructed according to the state space model, including:

[0133] According to the stability theorem of T-S fuzzy theory, the Lyapunov function of the grid-connected converter is constructed by solving the linear matrix inequality of the state space model of the grid-connected converter.

[0134] Based on the above stability theorem, if the set of linear matrix inequalities of the state space expression is feasible, the Lyapunov stability of the M3C grid-connected converter is guaranteed. Finally, the Lyapunov function of the grid-connected converter can be derived by solving the linear matrix inequality and calculating the matrix P.

[0135]

[0136] Then the Lyapunov function based on the large signal stability of the grid-connected converter can be expressed as:

[0137] V(x)=x T ·P·x (28)

[0138] Where, it is assumed that V(x) min is the minimum value under the constraint of LMI. Specifically, if V(x)≤V(x) min , the system is globally asymptotically stable; however, when V(x)>V(x) min , the Lyapunov stability of the system cannot be guaranteed.

[0139] In one embodiment, the affine angle of the stable attractor domain is calculated, and when the affine angle meets a preset condition, the stability strength of the grid-connected converter is calculated according to the affine angle, and the large signal stability analysis result of the grid-connected converter is obtained according to the stability strength, including:

[0140] The stable attractor domain is subjected to affine transformation, and different stable attractor domains are projected into the same space;

[0141] Since V(x) has 26 dimensions, the geometric meaning of V(x)≤V(x) min describes a 26-dimensional hyperellipsoid. Therefore, the 26-dimensional hyperellipsoid is defined as the Lyapunov large signal stable attractor domain (LS-DOA) in the embodiment of the application.

[0142] In the LS-DOA, all initial states can converge to the coordinate origin after the transient process, where the coordinate origin is the equilibrium point. If the value of the state variable overflows from the LS-DOA during the transient process, Hopf bifurcation may occur, leading to instability of the system. Since the LS-DOA in the 26-dimensional space has non-intuitive problems, it is usually projected into a two-dimensional or three-dimensional state space plane for stability analysis. The LS-DOA determined by the quadratic function V(x) in the embodiment of the application is an elliptical region in the two-dimensional state space or the internal region of an ellipsoid in the three-dimensional state space, which can be described as:

[0143]

[0144]

[0145] Please refer to Figure 5 , LS-DOA is projected to 2D state space, which is composed of a plane of x Figure 5 The white area in the figure describes the LS-DOA of the equilibrium point O. The energy function value of the initial working point A is smaller than V(x) min , while that of B is larger. Considering condition 1: when large signal interference occurs, the system working point is suitable for transition from A to O, the analysis result will be stable because A is within the LS-DOA range of O. While for condition 2: transition from B to O, the analysis result will be the opposite because B is not in the LS-DOA of O. The embodiment of the present application can analyze the large signal stability of the system by calculating the LS-DOA of the target working point and the initial point position

[0146] In the embodiment of the present application, only the stability of the LS-DOA region can be qualitatively and approximately analyzed by the traditional T-S large signal stability analysis method. In order to quantitatively compare the stability under different conditions, the present embodiment introduces the affine angle and stability strength based on the least square-DODA. After affine transformation, different LS-DOA can be projected into the same space, and then the stability strength can be mathematically described based on the wide area of the hypersphere according to the analytic geometry algorithm.

[0147] The affine angle of the stable attractor domain is calculated by the analytic geometry algorithm;

[0148] In the embodiment of the present application, it can be deduced from formula (29) that the LS-DOA in the two-dimensional state space is an oval region of plane affine transformation. Compared with the standard equation, formula (29) does not have a first-order term, please refer to Figure 6 The center of the affine transformation is still located at the coordinate origin. The present embodiment establishes two key performance indicators: affine angle A and stability strength S. When adjusting the parameters or topology of the system, the two key performance indicators are defined as corresponding changes for quantitative description of stability. The affine angle A reflecting the offset degree of the standard ellipse can be expressed as:

[0149]

[0150] Where, x i = X i cos A + X j sin A; x j = -X i sin A + X j cos A.

[0151] When the angle difference of the affine angles under the two conditions is less than the minimum affine angle, the stability strength of the grid-connected converter is calculated, and when the stability strength exceeds the preset range, it is judged that the large signal stability of the grid-connected converter meets the preset condition.

[0152] The stable strength is defined to quantitatively represent the large signal stability margin, and the expression is as follows:

[0153]

[0154]

[0155] In the embodiment of the present application, only when the angle difference between the two conditions is less than or equal to A min , that is, ΔA≤A min , the stability strength of the grid-connected converter is calculated, and the large signal stability margin is quantitatively represented according to the stability strength.

[0156] Referring to Figures 7-8 , the embodiment of the present application compares the strengths of the stability of the grid-connected converter under different parameter conditions by using the affine transformation method through the change examples of the bridge arm inductance L and the capacitance C parameters of the grid-connected converter. Referring to Figure 7 , the embodiment of the present application displays all LS-DOAs in the same coordinate system by using the affine transformation, and compares them with the stability strength S, the minimum energy function value V and the affine angle A. Specifically, for LS-DOA, as the inductance value L increases, the elliptical area will be larger. Within the minimum angle difference A min , the large signal stability under different parameters can be quantitatively compared by the stability strength. Especially in the case where the LS-DOA elliptical area is close, the quantitative stability strength S performs better. Please continue to refer to Figures 7-8 , when L and C increase, LS-DOA expands.

[0157] The embodiment of the present application has the following beneficial effects:

[0158] The embodiment of the present application establishes a reliable state space model of the grid-connected converter based on the T-S fuzzy theory, and projects the Lyapunov function of the grid-connected converter to the same space by using the affine transformation, realizes the equivalent mapping of the hyperplane in the high-dimensional space to the low-dimensional space, and thus can quickly and accurately analyze the large signal stability of the grid-connected converter under different parameters and fault conditions.

[0159] Further, the embodiment of the present application maps and decomposes the stability domain of the same high-dimensional space by using the affine transformation and the analytic geometry theory based on the energy function model, so that it can realize the comparison of the elliptical area region with the origin as the center in the two-dimensional plane space, and the embodiment of the present application can effectively improve the accuracy and reliability of the large signal stability analysis of the grid-connected converter by defining the two key performance indexes of the stability strength and the affine angle.

[0160] Referring to Figure 9, based on the same inventive concept as the above embodiment, the present embodiment provides a grid-connected converter large signal stability analysis device, comprising:

[0161] The system state space equation construction module 10 is configured to establish a system state space equation of the grid-connected converter based on a system space model of the grid-connected converter.

[0162] The state space model construction module 20 is configured to establish a state space model of the grid-connected converter based on the T-S fuzzy theory and the system state space equation of the grid-connected converter.

[0163] The stable attractor determination module 30 is configured to establish a Lyapunov function of the grid-connected converter based on a stability theorem of the T-S fuzzy theory and the state space model, project each dimension of the Lyapunov function to a two-dimensional state space plane, and obtain a stable attractor of the Lyapunov large signal.

[0164] The large signal stability analysis module 40 is configured to calculate an affine angle of the stable attractor, calculate a stability strength of the grid-connected converter based on the affine angle when the affine angle meets a preset condition, and obtain a large signal stability analysis result of the grid-connected converter based on the stability strength.

[0165] In one embodiment, the system state space equation construction module 10 is specifically configured to:

[0166] Based on the system space model of the grid-connected converter, the stable working point is defined as the coordinate origin, and 26 state variables of the grid-connected converter are calculated.

[0167] Assuming that the short-circuit ratios of the power frequency side and the frequency division side of the grid-connected converter are higher than a preset threshold, the influence of the phase-locked loop is ignored, and nonlinear state variables are calculated based on the 26 state variables.

[0168] The nonlinear state variables are used as nonlinear terms to construct the system state space equation of the grid-connected converter.

[0169] In one embodiment, the state space model construction module 20 is specifically configured to:

[0170] Based on the T-S fuzzy rule, a system fuzzy model is constructed.

[0171] Based on the system fuzzy model, a stability theorem under the condition of a continuous system is set.

[0172] Based on the stability theorem, the nonlinear terms in the system space equation correspond to a plurality of fuzzy rules.

[0173] The fuzzy sets are constructed based on the minimum value and the maximum value of the state variables, the values of the nonlinear terms are calculated, and the state space model of the grid-connected converter is established based on the values of the nonlinear terms.

[0174] In one embodiment, the stable attraction domain determination module 30 is specifically used for:

[0175] According to the stability theorem of T-S fuzzy theory, the Lyapunov function of the grid-connected converter is constructed by solving the linear matrix inequality of the state space model of the grid-connected converter.

[0176] In one embodiment, the large signal stability analysis module 40 is specifically used for:

[0177] The stable attraction domain is subjected to affine transformation, and different stable attraction domains are projected into the same space;

[0178] The affine angle of the stable attraction domain is calculated by the analytic geometry algorithm;

[0179] When the angle difference of the affine angles under the two conditions is less than the minimum affine angle, the stability strength of the grid-connected converter is calculated, and when the stability strength exceeds the preset range, it is judged that the large signal stability of the grid-connected converter meets the preset condition.

[0180] One embodiment of the present application provides a computer readable storage medium, which comprises a stored computer program; wherein the computer program controls the device where the computer readable storage medium is located to execute the grid-connected converter large signal stability analysis method as described above when running.

[0181] The above is the preferred embodiment of the present application, it should be pointed out that, for those skilled in the art, without departing from the principles of the present application, can make a number of improvements and refinements, these improvements and refinements also regarded as the protection scope of the present application.

Claims

1. A method for analyzing large-signal stability of a grid-connected converter, characterized in that, The method comprises the following steps: establishing a system state space equation of the grid-connected converter based on a system space model of the grid-connected converter; establishing a state space model of the grid-connected converter based on T-S fuzzy theory and the system state space equation of the grid-connected converter; constructing a Lyapunov function of the grid-connected converter based on a stability theorem of the T-S fuzzy theory and the state space model, projecting each dimension of the Lyapunov function to a two-dimensional state space plane to obtain a stable attractor of the Lyapunov large signal; calculating an affine angle of the stable attractor, and when the affine angle meets a preset condition, calculating a stability strength of the grid-connected converter based on the affine angle, and obtaining a large signal stability analysis result of the grid-connected converter based on the stability strength; wherein the expression of the affine angle is as follows: wherein A is the affine angle; the expression of the stability strength is as follows: wherein S is the stability strength.

2. The grid-connected converter large-signal stability analysis method of claim 1, wherein, The system space model of the grid-connected converter is used to establish the system state space equation of the grid-connected converter, which comprises the following steps: defining a stable operating point as the coordinate origin based on the system space model of the grid-connected converter, and calculating 26 state variables of the grid-connected converter; assuming that the short-circuit ratios of the power frequency side and the frequency division side of the grid-connected converter are higher than a preset threshold, ignoring the influence of the phase-locked loop, and calculating nonlinear state variables based on the 26 state variables; constructing the system state space equation of the grid-connected converter by taking the nonlinear state variables as nonlinear terms.

3. The grid-connected converter large-signal stability analysis method of claim 1, wherein, The state space model of the grid-connected converter is established based on the T-S fuzzy theory and the system state space equation of the grid-connected converter, which comprises the following steps: constructing a system fuzzy model based on T-S fuzzy rules; setting a stability theorem under continuous system conditions based on the system fuzzy model; corresponding the nonlinear terms in the system state space equation to multiple fuzzy rules based on the stability theorem; constructing fuzzy sets based on the minimum and maximum values of the state variables, calculating the values of the nonlinear terms, and establishing the state space model of the grid-connected converter based on the values of the nonlinear terms.

4. The grid-connected converter large-signal stability analysis method of claim 1, wherein, The Lyapunov function of the grid-connected converter is constructed based on the stability theorem of the T-S fuzzy theory and the state space model, which comprises the following steps: the Lyapunov function of the grid-connected converter is constructed by solving the linear matrix inequality of the state space model of the grid-connected converter based on the stability theorem of the T-S fuzzy theory.

5. The grid-connected converter large-signal stability analysis method of claim 1, wherein, The affine angle of the stable attractor is calculated, and when the affine angle meets a preset condition, the stability strength of the grid-connected converter is calculated based on the affine angle, and the large signal stability analysis result of the grid-connected converter is obtained based on the stability strength, which comprises the following steps: affine transformation is performed on the stable attractor to project different stable attractors to the same space; the affine angle of the stable attractor is calculated by using an analytic geometry algorithm; when the angle difference between the affine angles under two conditions is less than a minimum affine angle, the stability strength of the grid-connected converter is calculated, and when the stability strength exceeds a preset range, it is judged that the large signal stability of the grid-connected converter meets a preset condition.

6. A grid-connected converter large-signal stability analysis device, characterized by, The method comprises the following steps: a system state space equation construction module is configured to construct a system state space equation of the grid-connected converter based on a system space model of the grid-connected converter; a state space model construction module is configured to construct a state space model of the grid-connected converter based on the T-S fuzzy theory and the system state space equation of the grid-connected converter; a stable attractor determination module is configured to construct a Lyapunov function of the grid-connected converter based on the state space model and the stability theorem of the T-S fuzzy theory, project each dimension of the Lyapunov function to a two-dimensional state space plane, and obtain a stable attractor of the Lyapunov large signal; a large signal stability analysis module is configured to calculate an affine angle of the stable attractor, calculate a stability strength of the grid-connected converter based on the affine angle when the affine angle meets a preset condition, and obtain a large signal stability analysis result of the grid-connected converter based on the stability strength; wherein the affine angle is expressed as follows: wherein A is the affine angle; the stability strength is expressed as follows: wherein S is the stability strength.

7. The grid-connected converter large-signal stability analysis apparatus of claim 6, wherein, The system state space equation construction module is specifically configured to: define a stable operating point as the coordinate origin based on the system space model of the grid-connected converter, and calculate 26 state variables of the grid-connected converter; ignore the influence of a phase-locked loop when assuming that the short-circuit ratios of the power frequency side and the frequency division side of the grid-connected converter are higher than a preset threshold, and calculate nonlinear state variables based on the 26 state variables; construct the system state space equation of the grid-connected converter by taking the nonlinear state variables as nonlinear terms.

8. The grid-connected converter large-signal stability analysis apparatus of claim 6, wherein, The state space model construction module is specifically configured to: construct a system fuzzy model based on T-S fuzzy rules; set a stability theorem under continuous system conditions based on the system fuzzy model; correspond the nonlinear terms in the system state space equation to multiple fuzzy rules based on the stability theorem; construct fuzzy sets based on the minimum and maximum values of the state variables, calculate the values of the nonlinear terms, and construct a state space model of the grid-connected converter based on the values of the nonlinear terms.

9. The grid-connected converter large-signal stability analysis apparatus of claim 6, wherein, The large signal stability analysis module is specifically configured to: perform affine transformation on the stable attractor, and project different stable attractors to the same space; calculate the affine angle of the stable attractor by using an analytic geometry algorithm; calculate the stability strength of the grid-connected converter when the angle difference between the affine angles under two conditions is less than a minimum affine angle, and determine that the large signal stability of the grid-connected converter meets a preset condition when the stability strength exceeds a preset range.

10. A computer-readable storage medium, characterized in that, The computer readable storage medium comprises a stored computer program; wherein the computer program controls a device where the computer readable storage medium is located to execute the grid-connected converter large signal stability analysis method according to any one of claims 1-5 when running.

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