Broadband oscillation analysis method and device for network-forming photovoltaic grid-connected system, and medium

Abstract

The invention discloses a broadband oscillation analysis method, device and medium for a network-forming type photovoltaic grid-connected system, and relates to the field of stability analysis of power systems, and the method comprises the steps: discretizing electromagnetic transient continuous state space models of all elements in the network-forming type photovoltaic grid-connected system to obtain electromagnetic transient discrete state space models; further determining an electromagnetic transient discrete equivalent circuit; an adjoint circuit method is adopted, an electromagnetic transient discrete state space model of the system is determined according to the electromagnetic transient discrete equivalent circuit and the electromagnetic transient discrete state space model of each element in the system, then characteristic value modal analysis is carried out, and a characteristic value, modal frequency, a damping ratio and a participation factor are obtained through calculation; the characteristic value, the modal frequency and the damping ratio represent the stability of the grid-forming type photovoltaic grid-connected system, and the participation factor is used for positioning a characteristic state variable which causes modal instability in the grid-forming type photovoltaic grid-connected system. According to the invention, broadband oscillation analysis of the grid-forming type photovoltaic grid-connected system can be rapidly and accurately realized.

Description

Technical Field

[0001] The present application relates to the field of power system stability analysis, and in particular to a method, device and medium for analyzing broadband oscillations of a grid-connected photovoltaic grid-connected system. Background Art

[0002] With the transformation of energy structure and the large-scale access of new energy sources such as wind power and photovoltaics, new energy is gradually becoming the main form of energy supply for the future "new power system". The power electronic characteristics of the power system are becoming more and more prominent, and the application of power electronic converters in the power system is becoming more and more extensive. However, due to the multi-time scale control characteristics of power electronic equipment and the uncertainty of new energy sources themselves, the safe and stable operation of the "new power system" faces new threats and challenges. In contrast, the core of the traditional power system is synchronous generators and the oscillation problem is mainly concentrated in the low frequency band, while the broadband oscillation phenomenon in the "new power system" covers a very wide range of frequencies, from low frequency to high frequency, and its oscillation form shows rich and diverse characteristics. These broadband oscillations also show significant time-varying and wide-area propagation characteristics, posing a complex and severe challenge to the stability of the power system. Summary of the invention

[0003] The purpose of this application is to provide a method, device and medium for analyzing broadband oscillations of a grid-connected photovoltaic system, which can quickly and accurately realize broadband oscillation analysis of a grid-connected photovoltaic system.

[0004] To achieve the above objectives, this application provides the following solutions:

[0005] In a first aspect, the present application provides a method for analyzing broadband oscillations of a grid-connected photovoltaic system, comprising:

[0006] Constructing an electromagnetic transient continuous state space model of each component in a grid-connected photovoltaic grid-connected system; the grid-connected photovoltaic grid-connected system comprises a power supply side component unit and an AC side component unit; the power supply side component unit and the AC side component unit each comprise a plurality of components;

[0007] Based on bilinear transformation, the electromagnetic transient continuous state space model of each component is discretized to obtain the corresponding electromagnetic transient discrete state space model;

[0008] Based on the electromagnetic transient discrete state space model of each component, determine the corresponding electromagnetic transient discrete equivalent circuit;

[0009] Adopting the adjoint circuit method, according to the electromagnetic transient discrete equivalent circuit and electromagnetic transient discrete state space model of each component in the grid-connected photovoltaic grid-connected system, the electromagnetic transient discrete state space model of the grid-connected photovoltaic grid-connected system is determined;

[0010] An eigenvalue modal analysis is performed on the electromagnetic transient discrete state space model of the grid-connected photovoltaic system to calculate the eigenvalue, modal frequency, damping ratio and participation factor; the eigenvalue, modal frequency and damping ratio are all used to characterize the stability of the grid-connected photovoltaic system, and the participation factor is used to locate the characteristic state variables that cause modal instability in the grid-connected photovoltaic system.

[0011] In a second aspect, the present application provides a computer device, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement a method for analyzing wide-band oscillations of a grid-connected photovoltaic system.

[0012] In a third aspect, the present application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements a method for analyzing broadband oscillations of a grid-connected photovoltaic system.

[0013] According to the specific embodiments provided by the present application, the present application has the following technical effects: the present application provides a method, device and medium for analyzing broadband oscillation of a grid-connected photovoltaic grid-connected system, establishes an electromagnetic transient continuous state space model of each component in the grid-connected photovoltaic grid-connected system, and then discretizes based on bilinear transformation to form an electromagnetic transient discrete state space model and an electromagnetic transient discrete equivalent circuit of each component, and adopts the adjoint circuit method to form an electromagnetic transient discrete state space model of the grid-connected photovoltaic grid-connected system, and obtains the eigenvalue, modal frequency, damping ratio and participation factor in the discrete domain based on the model, analyzes the stability of the system and locates the dominant influencing factors of the unstable mode. The above-mentioned overall process provided by the present application can provide an accurate electromagnetic transient discrete state space model of the grid-connected photovoltaic grid-connected system for the broadband oscillation characteristic analysis of the "new power system" of large-scale power electronics, and simplify the selection process of its state variables, so as to quickly and accurately realize the broadband oscillation analysis of the grid-connected photovoltaic grid-connected system. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0015] Figure 1 A schematic flow chart of a method for analyzing broadband oscillations of a grid-connected photovoltaic system provided in one embodiment of the present application.

[0016] Figure 2A schematic diagram of the structure of a single-stage grid-connected photovoltaic system provided in one embodiment of the present application.

[0017] Figure 3 A control block diagram of a DC voltage matching control link provided in one embodiment of the present application.

[0018] Figure 4 A block diagram of the droop control link and the voltage and current inner loop control link of a grid-connected photovoltaic system provided in one embodiment of the present application.

[0019] Figure 5 A schematic diagram of an electromagnetic transient discrete equivalent circuit of a photovoltaic power generation unit provided in one embodiment of the present application.

[0020] Figure 6 A schematic diagram of an electromagnetic transient discrete equivalent circuit of an inductor branch provided in one embodiment of the present application.

[0021] Figure 7 A schematic diagram of an electromagnetic transient discrete equivalent circuit of a capacitor branch provided in an embodiment of the present application.

[0022] Figure 8 A schematic diagram of an electromagnetic transient discrete equivalent circuit of a resistance branch provided in an embodiment of the present application.

[0023] Fig. 9 A schematic diagram of an initial system electromagnetic transient discrete equivalent circuit provided in an embodiment of the present application.

[0024] Fig.10 A schematic diagram of a discrete time-domain eigenvalue stability region provided in an embodiment of the present application.

[0025] Fig.11 A schematic diagram of the structure of a computer device provided in one embodiment of the present application. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0027] Eigenvalue analysis is a commonly used tool for assessing the stability of power systems. This method establishes a state space model of the system and then calculates the eigenvalues ​​of the state matrix to assess the dynamic stability of the power system and identify possible oscillation modes. These eigenvalues ​​reveal the response characteristics of the power system at different frequencies, including the frequency, attenuation rate and stability of the oscillation. Based on modal analysis, the dominant influencing factors related to the oscillation mode can be obtained, providing key information for in-depth understanding of the dynamic behavior of power system oscillations and designing effective control strategies. Therefore, the "eigenvalue analysis method" can be used to perform broadband oscillation analysis of the "new power system".

[0028] In view of the complexity of the large-scale "new power system", a discrete state space modeling strategy can be introduced. This strategy draws on the core concept of EMTP (Electro-Magnetic Transient Program) modeling and converts the system components into a parallel model of conductivity and historical current source. In this framework, the historical current source term is selected as the key state variable. This selection is based on the linear independence between them, which fully meets the strict conditions for state variable selection. The discrete state space modeling method effectively simplifies the complex process of state variable selection when performing state space modeling for large-scale systems, providing a more efficient and accurate approach for power system analysis.

[0029] As an important part of the "new power system", it is necessary to establish a discrete state space model for grid-connected photovoltaic power generation. Based on the above analysis, this application provides a method, device and medium for analyzing broadband oscillations of a grid-connected photovoltaic grid-connected system, and constructs an electromagnetic transient discrete state space model of a grid-connected photovoltaic grid-connected system suitable for analyzing broadband oscillation characteristics of the "new power system" of large-scale power electronics. This model can deeply analyze the oscillation characteristics of the grid-connected photovoltaic grid-connected system within a wide frequency range. Through this model, not only can a comprehensive broadband oscillation analysis of the grid-connected photovoltaic grid-connected system be performed, but also the dominant factors affecting the stability of the system can be effectively identified, thereby providing an important basis for the stable operation and optimal design of the system.

[0030] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0031] In an exemplary embodiment, Figure 1 As shown, a method for analyzing wide-band oscillation of a grid-connected photovoltaic grid-connected system is provided. The method is executed by a computer device, and can be executed by a computer device such as a terminal or a server alone, or by a terminal and a server together. In an embodiment of the present application, the method includes the following steps 101 to 105.

[0032] Step 101, constructing an electromagnetic transient continuous state space model of each component in a grid-connected photovoltaic grid-connected system; the grid-connected photovoltaic grid-connected system includes a power supply side component unit and an AC side component unit; the power supply side component unit and the AC side component unit each include multiple components.

[0033] Specifically, the power supply side component unit is a photovoltaic power generation unit, including a photovoltaic array, a DC capacitor, a three-phase single-stage inverter and an output filter; wherein the control of the three-phase single-stage inverter is jointly realized by a DC voltage matching control link, a reactive power droop control link and a voltage and current inner loop control link.

[0034] The DC voltage matching control link realizes the self-synchronization function between the inverter and the power grid by accurately utilizing the dynamic characteristics of the DC capacitor, ensuring that the inverter can seamlessly access the power grid. The droop control link provides the inverter with dynamic voltage support capability through the reactive power-voltage droop control strategy, enabling it to adjust the output voltage according to the power grid demand and enhance the stability and flexibility of the system; the voltage and current inner loop control link, as the core control part, is responsible for quickly and accurately adjusting the output voltage and current of the inverter to achieve accurate tracking and response to the power grid, further improving the dynamic performance and power quality of the system.

[0035] Figure 2 This is a schematic diagram of a single-stage grid-connected photovoltaic grid-connected system. The DC capacitor is connected in parallel with the photovoltaic array. The DC capacitor is used to smooth the DC power generated by the photovoltaic array and then send it to the three-phase single-stage inverter. DC-AC conversion is performed in the three-phase single-stage inverter to convert the DC power into AC power with the same frequency and phase as the power grid. The output end of the three-phase single-stage inverter is connected to the input end of the output filter to suppress harmonics and filter the AC power output by the three-phase single-stage inverter through the LCL filter to ensure that the power quality meets the requirements of the power grid and is finally safely and efficiently connected to the power grid; the output end of the output filter is connected to the power grid. Figure 2 In, C dc is the DC capacitance, L C1 , L C2 It is divided into inverter side filter inductor and grid side filter inductor, C f is the filter capacitor, R g and L g are the equivalent resistance and inductance of the circuit respectively; I pv ,I dc 、i k 、i g It is divided into the current emitted by the photovoltaic array, the current flowing to the inverter, the current flowing out of the inverter, and the grid-connected current; U dc 、u k 、u cf 、u g、u s They are DC voltage, inverter output voltage, filter capacitor parallel point voltage, grid connection point voltage, and AC grid voltage.

[0036] (11) When the component is a photovoltaic array, the engineering model of the photovoltaic cell is used to calculate the standard operating conditions (e.g., T ref =25℃、S ref =1000W / m 2 ) under four electrical performance parameters (including short-circuit current I scref , Maximum power point current I mref , open circuit voltage U ocref , Maximum power point voltage U mref ), the UI characteristic equation of photovoltaic cells under non-standard conditions is derived:

[0037]

[0038]

[0039] Electrical parameters corresponding to non-standard battery temperature and light intensity I sc ,I m , U oc , U m , can be derived using the following formula based on the parameters under standard test conditions.

[0040]

[0041] Among them, S is the actual light intensity; T air is the actual air temperature; T ref is the reference value of air temperature; S ref is the reference value of light intensity; k is the temperature coefficient, usually 0.03℃·m 2 / W; a, b, c are compensation coefficients, usually 0.0025 / ℃, 0.5, 0.00288 / ℃ respectively; e is the base of the natural logarithm, usually approximately 2.71828.

[0042] Assume that the number of photovoltaic cells connected in series in the photovoltaic array is N s , the number of parallel connections is N p , using the engineering model of photovoltaic cells, the UI characteristic equation of the photovoltaic array under standard working conditions is:

[0043]

[0044] After linearizing the UI characteristic equation of the photovoltaic array and combining it with Figure 2 The small signal equation of the photovoltaic array can be obtained, that is, the electromagnetic transient continuous state space model corresponding to the photovoltaic array is:

[0045]

[0046] Among them, I pv is the output current of the photovoltaic array, V pv is the output voltage of the photovoltaic array, Δ represents the change of each variable, ΔI pv , ΔV pv are all algebraic variables. The subscript 0 indicates the steady-state value of each variable. Specifically, I sc0 is the short-circuit current of the photovoltaic cell in steady state, V pv0 is the output voltage of the photovoltaic array in steady state, U oc0 is the open circuit voltage of the photovoltaic cell in steady state. C1 and C2 are intermediate parameters.

[0047] (12) When the element is a DC capacitor, KCL, the basic characteristics of the capacitor element and the Figure 2 The characteristic equation of DC capacitance can be derived:

[0048]

[0049] Considering that the switching loss of the inverter is small, this factor can be ignored in the modeling process. Therefore, the sum of the power added by the DC capacitor and the power output by the inverter is equal to the output power of the photovoltaic array. It can be deduced from the instantaneous power theory (the coordinate transformation adopts equal amplitude transformation):

[0050]

[0051] Substitute the formula derived from the instantaneous power theory into the characteristic equation of the DC capacitor and substitute i qg =0,u qg =0, we get:

[0052]

[0053] After linearizing the above equation, the small signal model of the DC side filter capacitor can be obtained, that is, the electromagnetic transient continuous state space model corresponding to the DC capacitor is:

[0054]

[0055] Where, ΔV pv =ΔU dc ; C dc is the capacitance value of the DC capacitor, U dc is the DC voltage, u dg is the d-axis component of the grid connection point voltage, i dg is the d-axis component of the grid-connected current.

[0056] (13) When the component is an output filter, the basic characteristics of KCL, KVL, capacitors and inductors are combined Figure 2 The filter characteristic equation can be deduced as:

[0057]

[0058] By performing abc / dq coordinate transformation and linearizing the above equation, the small signal equation of the output filter in the dq coordinate system can be obtained, that is, the electromagnetic transient continuous state space model corresponding to the output filter is:

[0059]

[0060] Among them, i dk is the d-axis component of the current flowing out of the three-phase single-stage inverter, i qk is the q-axis component of the current flowing out of the three-phase single-stage inverter, i dg is the d-axis component of the grid-connected current, i qg is the q-axis component of the grid-connected current, u dcf is the d-axis component of the voltage at the filter capacitor parallel connection point, u qcf is the q-axis component of the voltage at the parallel point of the filter capacitor, u dk is the d-axis component of the output voltage of the three-phase single-stage inverter, u qk is the q-axis component of the output voltage of the three-phase single-stage inverter, u dg is the d-axis component of the grid connection point voltage, u qg is the q-axis component of the grid connection point voltage, ω is the AC side angular frequency of the grid-connected photovoltaic system, C f is the filter capacitor, L C1 , L C2 It is divided into inverter side filter inductor and grid side filter inductor.

[0061] (14) When the component is a three-phase single-stage inverter, such as Figure 3 As shown, it is a control block diagram of the DC voltage matching control link, wherein the following equation can be written according to the block diagram of the DC voltage matching control link:

[0062]

[0063] ω=x1+ω0.

[0064] Linearize the above two equations and substitute ΔU dcref =0, the small signal equation of the DC voltage matching control link can be obtained as follows:

[0065]

[0066] like Figure 4As shown in the figure, the block diagram of the droop control link and the voltage and current inner loop control link of the grid-connected photovoltaic grid-connected system can be written into the following equations according to the block diagram of the droop control link and the voltage and current inner loop control link:

[0067]

[0068]

[0069] Linearize the above two equations and substitute them into ΔU g =0, ΔQ ref =0,u qgref =0, Q = 1.5 × (u qg i dg -u dg i qg ),i qg0 =0,u qg0 = 0, the small signal equations of the droop control link and the voltage and current inner loop control link can be obtained as follows:

[0070]

[0071]

[0072] Among them, x1, x2, x3, x4, x5, θ P is the state variable, u dk 、u qk is an algebraic variable; M Q is the droop coefficient of QV reactive power droop control, M T is the tracking factor of the DC voltage, M D is the damping coefficient of inertial synchronization equivalent, M J is the inertia coefficient of inertial synchronization equivalent, Q is the reactive power generated by the inverter, Q ref is the reference value of reactive power generated by the inverter, U gref is the reference value of the grid-connected point voltage amplitude, U dc is the DC voltage, U dcref is the reference value of DC voltage, k pud is the d-axis voltage inner loop PI proportional coefficient, k iud is the d-axis voltage inner loop PI integral coefficient, k puq is the PI proportional coefficient of the inner loop of the q-axis voltage, k iuq is the q-axis voltage inner loop PI integral coefficient, k pid is the inner loop proportional coefficient of the d-axis current, k iid is the d-axis current inner loop integral coefficient, k piq is the q-axis current inner loop proportional coefficient, k iiq is the integral coefficient of the inner loop of the q-axis current.

[0073] The small signal differential equations and algebraic equations of each component of the photovoltaic power generation unit are arranged into the following matrix form:

[0074]

[0075] Among them, A1, B1, C1, A2, B2, C2 are all coefficient matrices, x pv is the state variable column vector; u inter is the intermediate variable column vector, u gdq is the terminal voltage column vector of the photovoltaic power generation unit.

[0076] x pv =[U dc ,i dk ,i qk ,i dg ,i qg ,u dcf ,u qcf ,x1,x2,x3,x4,x5,θ P ].

[0077] u inter =[I pv ,ω,u dk ,u qk ].

[0078] u gdq =[u dg ,u qg ].

[0079] Substitute the algebraic equations of each component of the photovoltaic power generation unit into the small signal differential equation and eliminate the intermediate variable u inter The following equation can be obtained:

[0080]

[0081] Among them, the expressions of the state matrix and input matrix are:

[0082]

[0083] The current expression of the photovoltaic power generation unit output to the network is:

[0084] i gdq =C pv x pv .

[0085] Among them, C pv is the coefficient matrix, i gdq =[i dg ,i qg ], eliminating the intermediate variable u interThe equation after that and the current expression of the photovoltaic power generation unit output to the network can be used to obtain the electromagnetic transient continuous state space model corresponding to the power supply side component unit:

[0086]

[0087] Among them, A pv , B pv are coefficient matrices; i gdq It is the current output by the photovoltaic power generation unit to the network.

[0088] In an application example, the AC side element unit includes an inductor branch, a capacitor branch and a resistor branch, and all are connected to the power grid. Specifically, common components on the AC side (transformer, transmission line, etc.) can usually be simulated by three-phase RLC parallel or series branches. In view of the wide application and basic status of the electromagnetic transient continuous state space model of the inductor, capacitor and resistor branches in the power system, its detailed construction process will not be repeated here.

[0089] Step 102 : discretize the electromagnetic transient continuous state space model of each component based on bilinear transformation to obtain a corresponding electromagnetic transient discrete state space model.

[0090] Specifically, the electromagnetic transient discrete state space expressions of the photovoltaic power generation unit, the inductance branch, and the capacitance branch are respectively expressed as follows:

[0091]

[0092]

[0093] Among them, h pv 、h L 、h C are the historical current items of the photovoltaic power generation unit, the inductor branch, and the capacitor branch respectively; i gdq 、i Ldq 、i Cdq are the terminal current, inductor branch current, and capacitor branch current of the photovoltaic power generation unit in the dq coordinate system; u gdq 、u Ldq 、u Cdq They are the terminal voltage, inductor branch voltage, and capacitor branch voltage of the photovoltaic power generation unit in the dq coordinate system; the rest are coefficient matrices.

[0094] Step 103, based on the electromagnetic transient discrete state space model of each component, determine the corresponding electromagnetic transient discrete equivalent circuit; specifically, the photovoltaic power generation unit is integrated into a single-port component, and the inductance branch, the capacitance branch, and the resistance branch are integrated into a two-port component. The electromagnetic transient discrete equivalent circuits of the photovoltaic power generation unit, the inductance branch, the capacitance branch, and the resistance branch are respectively as follows: Figure 5-Figure 8 As shown, where g pv =D pv , g L =D L , g C =D C , g R =1 / R.

[0095] Step 104, using the adjoint circuit method, according to the electromagnetic transient discrete equivalent circuit and electromagnetic transient discrete state space model of each component in the grid-connected photovoltaic grid-connected system, determine the electromagnetic transient discrete state space model of the grid-connected photovoltaic grid-connected system.

[0096] Specifically, step 104 includes:

[0097] (41) The system topology is determined according to the grid-connected photovoltaic system, and the main circuit of the grid-connected photovoltaic system can be obtained.

[0098] (42) Adopting the adjoint circuit method, according to the system topology and the electromagnetic transient discrete equivalent circuit of each component, the electromagnetic transient discrete equivalent circuit of the initial system is determined, such as Fig. 9 shown.

[0099] (43) According to the electromagnetic transient discrete equivalent circuit of the initial system, a branch-node association matrix and a conductance matrix are determined; wherein the branch-node association matrix L is:

[0100]

[0101] The conductivity matrix G is:

[0102]

[0103] (44) Adopting the adjoint circuit method, according to the branch-node association matrix, the conductance matrix and the electromagnetic transient discrete state space model of each element, the electromagnetic transient discrete state space model of the grid-connected photovoltaic system is determined. According to the model, the oscillation characteristics and stability of the system can be deeply analyzed, and an accurate model basis can be provided for the oscillation characteristics analysis of the large-scale power electronics "new power system", simplifying its state variable selection process.

[0104] Firstly, the historical current source iteration formula and output current expression of each component in the grid-connected photovoltaic system are sorted out as follows:

[0105]

[0106] Based on the relationship between branch current and voltage and node current and voltage, combined with the branch-node association matrix and the conductivity matrix, by eliminating the intermediate variables in the historical current source iteration formula in the above equation, the electromagnetic transient discrete state space model of the grid-connected photovoltaic system can be obtained as follows:

[0107]

[0108] Among them, I 2×2 is a 2-row 2-column identity matrix, g pv is the conductance corresponding to the power supply side element unit in the initial system electromagnetic transient discrete equivalent circuit, g line-L is the conductance corresponding to the line inductance in the initial system electromagnetic transient discrete equivalent circuit, is the conductance corresponding to the line resistance in the initial system electromagnetic transient discrete equivalent circuit, h sys (t) is the current source at time t, A dsys is the electromagnetic transient discrete state matrix, h sys (t-Δt) is the current source at time t-Δt, A sys , B sys , C sys are coefficient matrices, () T Represents the transpose of a matrix.

[0109] Step 105, performing eigenvalue modal analysis on the electromagnetic transient discrete state space model of the grid-connected photovoltaic system to calculate eigenvalues, modal frequencies, damping ratios and participation factors; the eigenvalues, modal frequencies and damping ratios are used to characterize the stability of the grid-connected photovoltaic system, and the participation factors are used to locate characteristic state variables that cause modal instability in the grid-connected photovoltaic system.

[0110] The eigenvalue modal analysis of the electromagnetic transient discrete state space model of the grid-connected photovoltaic system includes:

[0111] (51) According to the electromagnetic transient discrete state space model of the grid-connected photovoltaic system, the electromagnetic transient discrete state matrix is ​​solved; the electromagnetic transient discrete state matrix contains multiple discrete eigenvalues ​​z i (i=1,2...n); such as Fig.10 As shown, the stability of the grid-connected photovoltaic system is determined by the position of the discrete eigenvalues ​​on the z plane. When the amplitudes of all discrete eigenvalues ​​in the polar coordinate system are less than 1, the grid-connected photovoltaic system is in a stable state, otherwise it is unstable.

[0112] (52) According to the eigenvalues ​​in the electromagnetic transient discrete state matrix, the modal frequency and the damping ratio are calculated. In the discrete domain, the modal frequency can be expressed by the ratio of the phase angle of the discrete eigenvalue to the discrete step length, and the damping ratio is used to describe the distance of the discrete eigenvalue relative to the stable boundary (i.e., the unit circle) on the z plane. Based on this, the calculation formulas of the modal frequency and the damping ratio are:

[0113]

[0114] Among them, f d represents the frequency of the mode, α d is the damping ratio, is the phase angle of the discrete eigenvalue in polar coordinates, |λ d | represents the amplitude of the discrete eigenvalue, Δt d represents the discrete step length, X d is the horizontal axis coordinate of the discrete eigenvalue in the polar coordinate system, Y d is the vertical axis coordinate of the discrete eigenvalue in the polar coordinate system.

[0115] like Fig.10 As shown, when α d >0, the discrete eigenvalues ​​are located within the unit circle on the z plane, and the system is stable; when α d When <0, the discrete eigenvalue is outside the unit circle on the z plane, and the system is unstable. By calculating the modal frequency and damping ratio in the discrete domain, the broadband oscillation stability of the grid-connected photovoltaic system can be quantitatively analyzed.

[0116] (53) According to matrix theory, the electromagnetic transient discrete state matrix is ​​diagonally decomposed to obtain a left eigenvector matrix and a right eigenvector matrix.

[0117] Specifically, in the characteristic mode analysis of the discrete domain, the concept of participation factor similar to that of the continuous domain analysis is used to quantify the degree of influence of the system characteristic variables on the characteristic modes. The mathematical principles of these two analysis methods are consistent, both of which are based on the modal decomposition principle of the state matrix. Based on this, this application uses the following formula in the process of diagonal decomposition of the electromagnetic transient discrete state matrix according to matrix theory:

[0118] P T A dsys Q=Λ dsys .

[0119] Among them, A dsys is the electromagnetic transient discrete state matrix, P is the left eigenvector matrix, Q is the right eigenvector matrix, P T Q=I, I is the unit matrix; Λ dsysis a diagonal matrix, and the elements in the diagonal matrix are all eigenvalues ​​of the electromagnetic transient discrete state matrix.

[0120] Make the following linear transformation to obtain several new state variables Z sys (t), these variables are called modal quantities.

[0121] h sys (t) = QZ sys (t).

[0122] Substituting the above modal quantity equation and the diagonal decomposition formula into the electromagnetic transient discrete state space model of the grid-connected photovoltaic system, the electromagnetic transient discrete state space equation based on the modal quantity can be obtained as shown below:

[0123] Z sys (t) = Λ dsys Z sys (t-Δt).

[0124] Given that dsys The diagonal characteristics of the matrix can achieve the decoupling of the characteristic modes in the system electromagnetic transient discrete state space constructed using modal quantities. On this basis, when performing modal analysis on the system, each different eigenvalue can be expanded separately.

[0125] (54) Based on the left eigenvector matrix and the right eigenvector matrix, a participation matrix is ​​determined; the participation matrix includes a plurality of participation factors; the participation factors are used to quantify the influence of characteristic state variables on characteristic modes, and then locate the characteristic state variables that cause modal instability in the grid-connected photovoltaic system.

[0126] Similar to the method of continuous eigenmode analysis, the right eigenvector matrix in the diagonal decomposition formula reveals the contribution of n independent modes to the dynamic behavior of discrete state variables in the grid-connected photovoltaic grid-connected system, while the left eigenvector matrix reveals the controllability of discrete state variables to each mode. In order to further reveal the intrinsic connection between state variables and modal quantities, the concept of participation matrix is ​​introduced, where the formula for determining the participation factor is:

[0127] C (m,n) =P (m,n) Q (m,n) .

[0128] The subscript (m,n) is the value of the element in the mth row and nth column of the matrix; C is the participation matrix, C (m,,n)is a participation factor, a dimensionless constant used to measure the degree of correlation between the nth eigenmode and the mth eigenstate variable. By analyzing the size of the participation factor, the state variable most closely associated with the dominant instability mode can be effectively identified, that is, the larger the absolute value of the participation factor, the closer the corresponding state variable is to the dominant instability eigenmode. Furthermore, by examining the physical position or control link of the state variable, the key factors that cause modal instability can be located, thereby providing valuable reference for revealing the mechanism of system oscillation.

[0129] In an exemplary embodiment, a computer device is provided. The computer device may be a server or a terminal. The internal structure diagram thereof may be as follows: Fig.11 As shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, referred to as I / O) and a communication interface. Among them, the processor, the memory and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The input / output interface of the computer device is used to exchange information between the processor and an external device. The communication interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, a broadband oscillation analysis method for a grid-connected photovoltaic grid-connected system is implemented.

[0130] Those skilled in the art will understand that Fig.11 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components. In an exemplary embodiment, a computer device is provided, including a memory and a processor, wherein a computer program is stored in the memory, and the processor implements the steps in the above-mentioned method embodiments when executing the computer program.

[0131] In an exemplary embodiment, a computer-readable storage medium is provided, storing a computer program, and when the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0132] In an exemplary embodiment, a computer program product is provided, including a computer program, and when the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0133] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant regulations.

[0134] Those of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM may be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM).

[0135] The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. The non-relational database may include a distributed database based on blockchain, etc., but is not limited thereto. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but is not limited thereto.

[0136] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0137] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for analyzing broadband oscillation of a grid-connected photovoltaic system, characterized in that: The broadband oscillation analysis method of the grid-connected photovoltaic system comprises: Constructing an electromagnetic transient continuous state space model of each component in a grid-connected photovoltaic grid-connected system; the grid-connected photovoltaic grid-connected system comprises a power supply side component unit and an AC side component unit; the power supply side component unit and the AC side component unit each comprise a plurality of components; Based on bilinear transformation, the electromagnetic transient continuous state space model of each component is discretized to obtain the corresponding electromagnetic transient discrete state space model; Based on the electromagnetic transient discrete state space model of each component, determine the corresponding electromagnetic transient discrete equivalent circuit; Adopting the adjoint circuit method, according to the electromagnetic transient discrete equivalent circuit and electromagnetic transient discrete state space model of each component in the grid-connected photovoltaic grid-connected system, the electromagnetic transient discrete state space model of the grid-connected photovoltaic grid-connected system is determined; An eigenvalue modal analysis is performed on the electromagnetic transient discrete state space model of the grid-connected photovoltaic system to calculate the eigenvalue, modal frequency, damping ratio and participation factor; the eigenvalue, modal frequency and damping ratio are all used to characterize the stability of the grid-connected photovoltaic system, and the participation factor is used to locate the characteristic state variables that cause modal instability in the grid-connected photovoltaic system.

2. The method for analyzing broadband oscillation of a grid-connected photovoltaic system according to claim 1, characterized in that: The power supply side component unit is a photovoltaic power generation unit, including a photovoltaic array, a DC capacitor, a three-phase single-stage inverter and an output filter; wherein the control of the three-phase single-stage inverter is jointly realized by a DC voltage matching control link, a reactive power droop control link and a voltage and current inner loop control link; The DC capacitor is connected in parallel with the photovoltaic array, and the DC capacitor is used to smooth the DC power generated by the photovoltaic array and then send it to the three-phase single-stage inverter; the output end of the three-phase single-stage inverter is connected to the input end of the output filter; the output end of the output filter is connected to the power grid; The AC side element unit includes an inductor branch, a capacitor branch and a resistor branch.

3. The method for analyzing broadband oscillation of a grid-connected photovoltaic system according to claim 1, characterized in that: Adopting the adjoint circuit method, according to the electromagnetic transient discrete equivalent circuit and electromagnetic transient discrete state space model of each component in the grid-connected photovoltaic grid-connected system, the electromagnetic transient discrete state space model of the grid-connected photovoltaic grid-connected system is determined, including: Determining a system topology according to the grid-connected photovoltaic system; Adopting the adjoint circuit method, according to the system topology and the electromagnetic transient discrete equivalent circuit of each component, determining the electromagnetic transient discrete equivalent circuit of the initial system; Determine a branch-node association matrix and a conductance matrix according to the initial system electromagnetic transient discrete equivalent circuit; The electromagnetic transient discrete state space model of the grid-connected photovoltaic system is determined by using the adjoint circuit method according to the branch-node association matrix, the conductance matrix and the electromagnetic transient discrete state space model of each element.

4. The method for analyzing broadband oscillation of a grid-connected photovoltaic system according to claim 1, characterized in that: The eigenvalue modal analysis is performed on the electromagnetic transient discrete state space model of the grid-connected photovoltaic system, including: According to the electromagnetic transient discrete state space model of the grid-connected photovoltaic grid-connected system, the electromagnetic transient discrete state matrix is ​​solved; the electromagnetic transient discrete state matrix contains multiple discrete eigenvalues; when the amplitudes of all discrete eigenvalues ​​in the polar coordinate system are less than 1, the grid-connected photovoltaic grid-connected system is in a stable state; Calculating the modal frequency and damping ratio according to the eigenvalues ​​in the electromagnetic transient discrete state matrix; According to matrix theory, the electromagnetic transient discrete state matrix is ​​diagonally decomposed to obtain a left eigenvector matrix and a right eigenvector matrix; Based on the left eigenvector matrix and the right eigenvector matrix, a participation matrix is ​​determined; the participation matrix includes multiple participation factors; the participation factors are used to quantify the influence of characteristic state variables on characteristic modes, and then locate the characteristic state variables that cause modal instability in the grid-connected photovoltaic system.

5. The method for analyzing broadband oscillation of a grid-connected photovoltaic system according to claim 4, characterized in that: The calculation formula of the modal frequency and the damping ratio is: Among them, f d represents the frequency of the mode, α d is the damping ratio, is the phase angle of the discrete eigenvalue in polar coordinates, |λ d | represents the amplitude of the discrete eigenvalue, Δt d represents the discrete step length, X d is the horizontal axis coordinate of the discrete eigenvalue in the polar coordinate system, Y d is the vertical axis coordinate of the discrete eigenvalue in the polar coordinate system; According to matrix theory, the formula used in the process of diagonal decomposition of the electromagnetic transient discrete state matrix is: P T From dsys Q=Λ dsys ; Among them, A dsys is the electromagnetic transient discrete state matrix, P is the left eigenvector matrix, Q is the right eigenvector matrix, P T Q=I, I is the unit matrix; Λ dsys is a diagonal matrix, the elements of which are all eigenvalues ​​of the electromagnetic transient discrete state matrix; The formula for determining the participation factor is: C (m,n) =P (m,n) Q (m,n) ; The subscript (m,n) is the value of the element in the mth row and nth column of the matrix; C is the participation matrix, C (m,,n) is a participation factor.

6. The method for analyzing broadband oscillation of a grid-connected photovoltaic system according to claim 3, characterized in that: The branch-node association matrix L is: The conductivity matrix G is: The electromagnetic transient discrete state space model of the grid-connected photovoltaic system is: Among them, I 2×2 is a 2-row 2-column identity matrix, g pv is the conductance corresponding to the power supply side element unit in the initial system electromagnetic transient discrete equivalent circuit, g line-L is the conductance corresponding to the line inductance in the initial system electromagnetic transient discrete equivalent circuit, is the conductance corresponding to the line resistance in the initial system electromagnetic transient discrete equivalent circuit, h sys (t) is the current source at time t, A dsys is the electromagnetic transient discrete state matrix, h sys (t-Δt) is the current source at time t-Δt, A sys , B sys , C sys are coefficient matrices, () T Represents the transpose of a matrix.

7. The method for analyzing broadband oscillation of a grid-connected photovoltaic system according to claim 2, characterized in that: When the element is a photovoltaic array, the corresponding electromagnetic transient continuous state space model is: Among them, I pv is the output current of the photovoltaic array, V pv is the output voltage of the photovoltaic array, Δ represents the change of each variable; N p is the number of photovoltaic cells in parallel in the photovoltaic array, N s is the number of photovoltaic cells in series in the photovoltaic array, C1 and C2 are intermediate parameters, and e is the base of the natural logarithm; subscript 0 represents the steady-state value of each variable, I sc0 is the short-circuit current of the photovoltaic cell in steady state, U oc0 is the open circuit voltage of the photovoltaic cell in steady state; I mref is the maximum power point current of the photovoltaic cell under standard working conditions, I scref is the short-circuit current of the photovoltaic cell under standard working conditions, U mref is the maximum power point voltage of the photovoltaic cell under standard working conditions, U ocref is the open circuit voltage of the photovoltaic cell under standard working conditions; When the component is a DC capacitor, the corresponding electromagnetic transient continuous state space model is: Where, ΔV pv =ΔU dc ; C dc is the capacitance value of the DC capacitor, U dc is the DC voltage, u dg is the d-axis component of the grid connection point voltage, i dg is the d-axis component of the grid-connected current; When the component is an output filter, the corresponding electromagnetic transient continuous state space model is: Among them, i dk is the d-axis component of the current flowing out of the three-phase single-stage inverter, i qk is the q-axis component of the current flowing out of the three-phase single-stage inverter, i dg is the d-axis component of the grid-connected current, i qg is the q-axis component of the grid-connected current, u dcf is the d-axis component of the voltage at the parallel point of the filter capacitor, u qcf is the q-axis component of the voltage at the parallel point of the filter capacitor, u dk is the d-axis component of the output voltage of the three-phase single-stage inverter, u qk is the q-axis component of the output voltage of the three-phase single-stage inverter, u dg is the d-axis component of the grid connection point voltage, u qg is the q-axis component of the grid connection point voltage, ω is the AC side angular frequency of the grid-connected photovoltaic system, C f is the filter capacitor, L C1 , L C2 It is divided into inverter side filter inductor and grid side filter inductor; When the component is a three-phase single-stage inverter, the corresponding electromagnetic transient continuous state space model includes: The small signal equation of the DC voltage matching control link is: Δω=Δx1; The small signal equations of the reactive power droop control link and the voltage and current inner loop control link are: Among them, x1, x2, x3, x4, x5, θ P is the state variable; M Q is the droop coefficient of reactive power droop control, M T is the tracking factor of the DC voltage, M D is the damping coefficient of inertial synchronization equivalent, M J is the inertia coefficient of inertial synchronization equivalent, k pud is the d-axis voltage inner loop PI proportional coefficient, k iud is the d-axis voltage inner loop PI integral coefficient, k puq is the PI proportional coefficient of the inner loop of the q-axis voltage, k iuq is the q-axis voltage inner loop PI integral coefficient, k pid is the inner loop proportional coefficient of the d-axis current, k iid is the d-axis current inner loop integral coefficient, k piq is the q-axis current inner loop proportional coefficient, k iiq is the integral coefficient of the inner loop of the q-axis current.

8. The method for analyzing broadband oscillation of a grid-connected photovoltaic system according to claim 7, characterized in that: The electromagnetic transient continuous state space model corresponding to the power supply side element unit is: x pv =[U dc ,i dk ,i qk ,i dg ,i qg ,u dcf ,u qcf ,x1,x2,x3,x4,x5,θ P ]; in gdq =[in dg ,in qg ]; Among them, x pv is the state variable column vector, u gdq is the terminal voltage column vector of the photovoltaic power generation unit, A pv , B pv , C pv are coefficient matrices; i gdq It is the current output by the photovoltaic power generation unit to the network.

9. A computer device comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the wide-band oscillation analysis method for a grid-connected photovoltaic grid-connected system according to any one of claims 1 to 8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method for analyzing wide-band oscillation of a grid-connected photovoltaic system according to any one of claims 1 to 8 is implemented.

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