New energy grid-connected system transient stability evaluation method based on normal type

Abstract

The invention discloses a new energy grid-connected system transient stability evaluation method based on a normal type, and relates to the technical field of stable operation of a power system, and the method comprises the steps: building a full-order model of a new energy equipment grid-connected system, and dividing fast and slow variables according to the time constant of each state variable; performing perturbation on the full-order model based on a singular perturbation method to obtain a singular perturbation system, and obtaining a simplified model of the new energy equipment grid-connected system based on the singular perturbation system; performing linear and nonlinear transformation on the simplified model based on a regular method to obtain stability manifold estimation near a dominant unstable equilibrium point of the system, and further obtaining stability domain boundary estimation; and the transient stability of the system is judged by comparing the fault trajectory after the fault is removed with the stability domain boundary estimation. According to the method, the full-process automation from system modeling to stability judgment is realized, the accuracy and efficiency of evaluation are improved, and the complexity and nonlinear characteristics of the new energy equipment grid-connected system can be effectively processed.

Description

Technical Field

[0001] The present invention relates to the technical field of stable operation of electric power systems, and in particular to a transient stability assessment method for a new energy grid-connected system based on a regular type. Background Art

[0002] With the large-scale access of high-proportion new energy equipment to the power grid, the new power system with high proportion of renewable energy and high proportion of power electronic equipment as the main features will gradually replace the power system dominated by synchronous machines, and the composition structure and operation form of the power system have undergone tremendous changes. Most power electronic converters adopt complex multi-time scale sequential switching control and have poor overcurrent capacity. They need to be equipped with nonlinear control links such as hardware protection circuits, controller switching and saturation limiting, which leads to the characteristics of strong nonlinearity, strong coupling and unclear leading links in the new power system. This makes the control of new energy equipment strongly coupled with the transient process of the system at different time scales, and the grid-connected stability of the equipment is strongly related to the transient stability of the system. Under faults, it is easy to cause a large-scale chain reaction, the transient process is complex, and the instability characteristics are difficult to identify. In recent years, new theoretical methods are urgently needed to determine the stability of power systems containing new energy equipment. At present, the stability judgment of new power systems under large disturbances can be mainly divided into two categories: the first category is to analyze the transient stability of the grid-connected system of new energy equipment under large disturbances based on numerical simulation. The second category is to simplify the grid-connected system of new energy equipment into a phase-locked loop grid-connected system, and then perform transient stability evaluation based on direct methods such as energy functions.

[0003] At present, the stability judgment of new power systems under large disturbances can be mainly divided into two categories: the first category is to analyze the transient stability of the grid-connected system of new energy equipment under large disturbances based on numerical simulation, but this type of method lacks the corresponding physical mechanism explanation, and has large amount of calculation, slow speed and low efficiency; the second category is to simplify the grid-connected system of new energy equipment into a phase-locked loop grid-connected system, and then perform transient stability evaluation based on direct methods such as energy function, but this type of method greatly simplifies the new energy equipment and has poor accuracy. Summary of the invention

[0004] In view of the above-mentioned problems, the present invention is proposed.

[0005] Therefore, the technical problem solved by the present invention is: How to provide a transient stability assessment method for a new energy grid-connected system based on a regular type to solve the problems that the existing technology lacks corresponding physical mechanism explanations and has large calculation complexity, slow speed, low efficiency, and greatly simplifies new energy equipment and has poor accuracy?

[0006] To solve the above technical problems, the present invention provides the following technical solutions: establish a full-order model of a new energy equipment grid-connected system, and divide fast and slow variables according to the time constants of each state variable; perturb the full-order model based on a singular perturbation method to obtain a singular perturbation system, and obtain a simplified model of the new energy equipment grid-connected system based on the singular perturbation system; perform linear and nonlinear transformations on the simplified model based on a normal method to obtain a stable manifold estimate near the dominant unstable equilibrium point of the new energy equipment grid-connected system, and then obtain a stable domain boundary estimate; and judge the transient stability of the new energy equipment grid-connected system by comparing the fault trajectory after fault removal with the stable domain boundary estimate.

[0007] As a preferred solution of the transient stability assessment method of the new energy grid-connected system based on the regular type described in the present invention, the full-order system is perturbed based on the singular perturbation method to obtain a singular perturbation system, which is expressed as:

[0008]

[0009] Where X is a slow variable, Y is a fast variable, ε is a perturbation parameter, 0<ε<<1, and when the perturbation parameter ε=0, we get the slow subsystem:

[0010]

[0011] The obtained slow subsystem is used as a simplified model of the new energy equipment grid-connected system.

[0012] As a preferred solution of the transient stability assessment method of the new energy grid-connected system based on the regular type described in the present invention, wherein: the simplified model is linearly and nonlinearly transformed based on the regular type method to obtain a stable manifold estimate near the dominant unstable equilibrium point of the new energy equipment grid-connected system, and then obtain a stable domain boundary estimate, including: obtaining the Jacobian matrix A and the Hessian matrix B of the simplified model at the dominant unstable equilibrium point of the new energy equipment grid-connected system 1-n Based on the normal method, the characteristic root λ of the grid-connected renewable energy equipment system at the dominant unstable equilibrium point is obtained. 1-5 , and obtain the Jordan standard form matrix J r ; The Jordan standard matrix J r The structure is represented as:

[0013]

[0014] Among them, λ 1-n is the characteristic root of the system, α and β are the real and imaginary parts of a pair of conjugate characteristic roots respectively. The Jordan standard form matrix J r It is obtained by linearly transforming the Jacobian matrix A:

[0015] Jr =U -1 AU;

[0016] Where U is the transformation matrix, and the column vectors of U are the eigenvectors or generalized eigenvectors of A; U -1 is the inverse matrix of U,

[0017] Based on the Hessian matrix B 1-n Obtain the nonlinear influence C of the i-th state variable in W space i :

[0018]

[0019] V=U -1 ;

[0020] Among them, V (i,j) It is the i,jth element of matrix V; matrix V is the inverse matrix of transformation matrix U.

[0021] Then transform the system in X space to W space, expressed as:

[0022]

[0023] Among them, w1,w2,w3,...,w n Indicates w i , w i is the i-th subvector of the state variable vector; express is the i-th subvector w of the state variable vector i The time derivative of T C1w,w T C2w,...,w T C n w means w T C i w, w T C i w is the nonlinear interaction between state variables, T is the transpose; n is the number of state variable subvectors; C1, C2, ..., C n Represents C i , C i is the nonlinear influence of the i-th state variable.

[0024] Then transform the system in W space to Z space, and the nonlinear transformation equation is:

[0025]

[0026] Among them, z1,z2,z3,...,z n Indicates z i , zi is the i-th subvector of the new state variable vector in Z space; y1,y2,...,y n Represents y i ,y i is the linear combination of the state variable vectors in W space, representing the linear transformation from W space to Z space; D1,D2,...,D n Indicates D i , each D i represents an n×n matrix; y T D i y represents the part of nonlinear transformation, y T is the transpose of y.

[0027] As a preferred solution of the transient stability assessment method of the new energy grid-connected system based on the regular type described in the present invention, wherein: the simplified model is linearly and nonlinearly transformed based on the regular type method to obtain a stable manifold estimate near the dominant unstable equilibrium point of the new energy equipment grid-connected system, and then obtain a stable domain boundary estimate, and further includes:

[0028] Obtain the transformation matrix D from W space to Z space 1-n , as shown below:

[0029]

[0030] Then the estimation of the boundary of the stable region is obtained, and the expression is: z1=0.

[0031] As a preferred solution of the transient stability assessment method of the new energy grid-connected system based on the regular type described in the present invention, wherein: the transient stability of the new energy equipment grid-connected system is judged by comparing the fault trajectory after the fault is removed with the stability domain boundary estimate, including mapping the system state quantity to the Z space to obtain the initial value z1(0) at the time of fault removal t=0; if z1(0)<0, dynamic analysis is performed; if z1(0)≥0, the new energy equipment grid-connected system is directly determined to be unstable.

[0032] The dynamic analysis includes the following steps: performing trajectory sampling, specifically, if z1(0)<0, collecting N system state samples at a fixed interval Δt in the time interval [0, T] to form a state sequence {X(t i )}, i = 0, 1, ..., N-1, and N = T / Δt+1; {X(t i )} is mapped to Z space, and the sequence {z1(t i )}:

[0033] {z1(t i )}={z1(t0),z1(t1),z1(t2),...,z1(tN-1 )};

[0034] Among them, t i is the i-th sampling moment, and N is the total number of sampling points.

[0035] Calculate the stability index S:

[0036]

[0037] Among them, τ is the time constant; z1(t) is a continuous time function, representing the continuous change of the system state over time.

[0038] Fit z1(t) = Pe -μt +L, where μ is the attenuation coefficient, and C and L are fitting constants.

[0039] Calculate the stability margin:

[0040] M = -L;

[0041] When S<-Ω and M<-Ω, the grid-connected system of the new energy equipment is determined to be stable; when S>Ω and M>Ω, the grid-connected system of the new energy equipment is determined to be unstable; when |S|≤Ω or |M|≤Ω, the grid-connected system of the new energy equipment is determined to be in a critical stable state; Ω is a preset threshold.

[0042] As a preferred solution of the transient stability assessment method of the new energy grid-connected system based on the regular type described in the present invention, the new energy equipment grid-connected system includes power electronic devices with different energy storage capabilities and a multi-time scale control structure corresponding to each energy storage element.

[0043] To further solve the above technical problems, the present invention provides the following technical solutions: a transient stability assessment system for a new energy grid-connected system based on a regular type, comprising: a full-order modeling module, used to establish a full-order model of a new energy equipment grid-connected system, and divide fast and slow variables according to the time constants of each state variable; a simplified model generation module, used to perturb the full-order model based on a singular perturbation method to obtain a singular perturbation system, and obtain a simplified model of the new energy equipment grid-connected system based on the singular perturbation system; a stable domain estimation module, used to perform linear and nonlinear transformations on the simplified model based on a regular type method, obtain an estimate of the stable manifold near the dominant unstable equilibrium point of the new energy equipment grid-connected system, and then obtain an estimate of the stable domain boundary; a transient stability judgment module, used to judge the transient stability of the new energy equipment grid-connected system by comparing the fault trajectory after fault removal with the stable domain boundary estimate.

[0044] A computer device includes a memory and a processor, wherein the memory stores a computer program, and is characterized in that when the processor executes the computer program, the steps of the transient stability assessment method of a new energy grid-connected system based on a regular type are implemented as described above.

[0045] A computer-readable storage medium having a computer program stored thereon, characterized in that when the computer program is executed by a processor, the steps of the transient stability assessment method of a new energy grid-connected system based on a regular type are implemented as described above.

[0046] Beneficial effects of the present invention: The present invention is based on the theory that the stable manifold of the system at the unstable equilibrium point constitutes the boundary of the stable domain of the system. It uses the relevant knowledge of nonlinear dynamics, obtains the estimation of the stable boundary of the system through the singular perturbation method and the normal form method, and judges the stability of the system in combination with the fault trajectory. Compared with the time domain simulation method, the present invention can quickly and accurately judge the stability of the system, and has a strong theoretical basis, revealing the instability mechanism of the system. Compared with direct methods such as energy functions, the present invention avoids the construction of complex energy functions, and is more superior in simplifying models, grasps the dominant instability characteristics of the system, and has higher accuracy and speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0048] Figure 1 An overall flow chart of a transient stability assessment method for a new energy grid-connected system based on a regular type is provided in accordance with an embodiment of the present invention.

[0049] Figure 2 It is a simulation verification diagram of the original model and the simplified model of the transient stability assessment method of the new energy grid-connected system based on the regular type of the present invention.

[0050] Figure 3 It is a phase output waveform diagram of the system under different fault removal times of the transient stability assessment method of the new energy grid-connected system based on the regular type of the present invention. DETAILED DESCRIPTION

[0051] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0052] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0053] Example 1

[0054] Reference Figure 1 to Figure 3 , which is an embodiment of the present invention, provides a transient stability assessment method for a new energy grid-connected system based on a regular type, comprising:

[0055] S1: Establish a full-order model of the grid-connected system of new energy equipment, and divide the fast and slow variables according to the time constants of each state variable.

[0056] Specifically, there are power electronic devices with different energy storage capabilities inside the grid-connected system of new energy equipment, as well as multi-time scale control structures corresponding to each energy storage element. Therefore, the state space equation is written from the two aspects of energy storage element dynamics and multi-time scale control. Furthermore, the time constants of each state quantity in the state space equation are obtained, and fast and slow variables are divided, where the slow variable is represented by X and the fast variable is represented by Y, which together constitute the full-order model:

[0057]

[0058] S2: Based on the singular perturbation method, the full-order model is perturbed to obtain a singular perturbation system, and based on the singular perturbation system, a simplified model of the grid-connected system for new energy equipment is obtained.

[0059] Specifically, the singular perturbation method is used to separate the fast and slow subsystems of the new energy equipment grid-connected system, and the original system is decomposed into a slow subsystem dominated by the electromechanical time scale, that is, a simplified model of the new energy equipment grid-connected system (electromechanical time scale). According to the singular perturbation theory, the simplified model of the new energy equipment grid-connected system (electromechanical time scale) is used to represent the transient stability of the original system.

[0060] Specifically, based on the singular perturbation method, the full-order system is perturbed to obtain the singular perturbation system:

[0061]

[0062] Among them, X is the slow variable, Y is the fast variable, and ε is the perturbation parameter. Let the perturbation parameter ε = 0, and we get the slow subsystem:

[0063]

[0064] The obtained slow subsystem is used as a simplified model of the grid-connected system for new energy equipment.

[0065] For the simplified electromechanical time scale model of the new energy equipment grid-connected system, the Jacobian matrix A and Hessian matrix B of the simplified model are obtained at the dominant unstable equilibrium point of the new energy equipment grid-connected system through the linearization method. 1-n Based on the normal method, the characteristic root λ of the grid-connected renewable energy equipment system at the dominant unstable equilibrium point is obtained. 1-5 , and obtain the Jordan standard form matrix J r .

[0066] S3: Based on the normal form method, the simplified model is transformed linearly and nonlinearly to obtain the stable manifold estimate near the dominant unstable equilibrium point of the new energy equipment grid-connected system, and then the boundary estimate of the stable domain is obtained.

[0067] Specifically, the Jacobian matrix A and Hessian matrix B of the simplified model are obtained at the dominant unstable equilibrium point of the new energy equipment grid-connected system. 1-n .

[0068] Jordan standard matrix J r It is obtained by linearly transforming the Jacobian matrix A:

[0069] J r =U -1 AU;

[0070] Where U is the transformation matrix, and the column vectors of U are the eigenvectors or generalized eigenvectors of A; U -1 is the inverse matrix of U.

[0071] Based on the normal form method, the characteristic root λ of the grid-connected renewable energy equipment system at the dominant unstable equilibrium point is obtained. 1-5 , and obtain the Jordan standard form matrix J r ; Jordan standard matrix J r The structure is represented as:

[0072]

[0073] Among them, λ 1-n is the characteristic root of the system, α and β are the real and imaginary parts of a pair of conjugate characteristic roots respectively.

[0074] Based on the Hessian matrix B 1-nObtain the nonlinear influence C of the i-th state variable in W space i :

[0075]

[0076] V=U -1 ;

[0077] Among them, V (i,j) It is the i,jth element of matrix V; matrix V is the inverse matrix of transformation matrix U.

[0078] Then transform the system in X space to W space, expressed as:

[0079]

[0080] Among them, w1,w2,w3,...,w n Indicates w i , w i is the i-th sub-vector of the state variable vector. In the new energy equipment grid-connected system, it represents specific physical quantities, such as the rotor angular velocity and angle of the generator, the stator current of the generator, the DC bus voltage, the grid-side current, the state variables of the control system, etc. express is the i-th subvector w of the state variable vector i The time derivative of , which represents the rate of change of the corresponding state variable over time. n Represents C i , C i is the nonlinear influence of the i-th state variable; in the grid-connected system of new energy equipment, these nonlinear terms may come from: the nonlinear characteristics of the generator (such as saturation effect), the nonlinear characteristics of power electronic equipment (such as switching characteristics), the nonlinear part of the control system (such as dead zone, saturation limit, etc.), etc. T C1w,w T C2w,...,w T C n w means w T C i w, w T C i w is the nonlinear interaction between state variables, and T is the transposition. n is the number of subvectors of system state variables, reflecting the complexity of the system. In the grid-connected system of new energy equipment, the value of n depends on the level of detail of the model and the number of physical processes considered.

[0081] Then transform the system in W space to Z space, and the nonlinear transformation equation is:

[0082]

[0083] Among them, z1,z2,z3,...,z n Indicates z i , z i is the i-th subvector of the new state variable vector in Z space; y1,y2,...,y n Represents y i ,y i is the linear combination of the state variable vectors in W space, representing the linear transformation from W space to Z space; D1,D2,...,D n Indicates D i , each D i represents an n×n matrix; y T D i y represents the part of nonlinear transformation, y T is the transpose of y.

[0084] Obtain the transformation matrix D from W space to Z space 1-n , as shown below:

[0085] according to

[0086] Then the system stability boundary estimate z1=0 is obtained.

[0087] The formal method includes the following steps:

[0088] First, solve the dominant unstable equilibrium point of the system according to the state equation; then calculate the system Jacobian matrix and Hessian matrix to perform linear and nonlinear transformations on the nonlinear differential equations, transform the nonlinear differential equations into a set of linear differential equations, and the stable and unstable manifolds of the nonlinear system at a certain equilibrium point are correspondingly transformed into the stable and unstable subspaces of the linear system; then obtain the local stable and unstable manifolds through inverse transformation, and finally estimate the stable manifold (i.e., the boundary of the stable domain) at the dominant unstable equilibrium point of the system, z1=0.

[0089] S4: Determine the transient stability of the grid-connected system with new energy equipment by comparing the fault trajectory after fault removal with the estimated boundary of the stability region.

[0090] If the fault trajectory is within the stable domain, the grid-connected system of the new energy equipment is stable. If the fault trajectory is outside the stable domain, the grid-connected system of the new energy equipment is unstable.

[0091] At the fault removal time t=0, the system state quantity is mapped to the Z space to obtain the initial value z1(0); if z1(0)<0, a dynamic analysis is performed; if z1(0)≥0, the grid-connected system of the new energy equipment is directly determined to be unstable;

[0092] Dynamic analysis includes the following steps:

[0093] Trajectory sampling is performed. Specifically, if z1(0)<0, N system state samples are collected at a fixed interval Δt in the time interval [0, T] to form a state sequence {X(t i )}, i=0,1,...,N-1, and N=T / Δt+1;

[0094] {X(t i )} is mapped to Z space, and the sequence {z1(t i )}:

[0095] {z1(t i )}={z1(t0),z1(t1),z1(t2),...,z1(t N-1 )};

[0096] Among them, t i is the i-th sampling moment, N is the total number of sampling points;

[0097] Calculate the stability index S:

[0098]

[0099] Among them, τ is the time constant; z1(t) is a continuous time function, representing the continuous change of the system state over time;

[0100] Fit z1(t) = Pe -μt +L, where μ is the attenuation coefficient, C and L are fitting constants;

[0101] Calculate the stability margin:

[0102] M = -L;

[0103] When S<-Ω and M<-Ω, the grid-connected system of new energy equipment is determined to be stable;

[0104] When S>Ω and M>Ω, the grid-connected system of new energy equipment is determined to be unstable;

[0105] When |S|≤Ω or |M|≤Ω, the new energy equipment grid-connected system is determined to be in a critical stable state;

[0106] Where Ω is the preset threshold.

[0107] Preferably, S4 introduces a stability index S. The calculation of the stability index S takes into account z1(t) and its derivative, which not only reflects the degree of deviation of the system state, but also includes the trend information of the system state change. This comprehensive consideration makes the stability assessment more comprehensive and accurate. The stability margin M is introduced, and the long-term stability trend of the system is predicted by fitting z1(t) and calculating M=-L. Therefore, the present invention can combine the instantaneous state with the long-term trend, thereby improving the reliability of stability judgment. In addition, S4 adopts a dual-index judgment mechanism: combining S and M for judgment, which takes into account both the instantaneous state of the system and the long-term trend, avoiding the one-sidedness that may be caused by a single indicator. Compared with the traditional method based only on energy function, this method can more accurately reflect the complex dynamic characteristics of the grid-connected system of new energy equipment. Finally, the critical stable state judgment is introduced: when |S|≤Ω or |M|≤Ω, the system is judged to be in a critical stable state. This innovation provides a more detailed state division for system operation, which is conducive to taking preventive measures in time and improving the safety and reliability of the system.

[0108] In summary, the present invention proposes a transient stability assessment method for a new energy grid-connected system based on a normal type based on singular perturbation and normal type nonlinear methods. The method takes the stable manifold of the system at the unstable equilibrium point as the theoretical basis, and uses the relevant knowledge of nonlinear dynamics to obtain the estimation of the stable boundary of the system through the singular perturbation method and the normal type method, and judges the stability of the system in combination with the fault trajectory. Compared with the time domain simulation method, the present invention can quickly and accurately judge the stability of the system, and has a strong theoretical basis, revealing the instability mechanism of the system. Compared with direct methods such as energy functions, the present invention avoids the construction of complex energy functions, and is more superior in simplifying models, grasps the dominant instability characteristics of the system, and has higher accuracy and speed.

[0109] Example 2

[0110] As an embodiment of the present invention, a transient stability assessment system for a new energy grid-connected system based on a regular type is provided, including: a full-order modeling module, used to establish a full-order model of a new energy equipment grid-connected system, and divide fast and slow variables according to the time constants of various state variables; a simplified model generation module, used to perturb the full-order model based on a singular perturbation method to obtain a singular perturbation system, and obtain a simplified model of the new energy equipment grid-connected system based on the singular perturbation system; a stable domain estimation module, used to perform linear and nonlinear transformations on the simplified model based on a regular type method, obtain a stable manifold estimate near a dominant unstable equilibrium point of the new energy equipment grid-connected system, and then obtain a stable domain boundary estimate; a transient stability judgment module, used to judge the transient stability of the new energy equipment grid-connected system by comparing the fault trajectory after fault removal with the stable domain boundary estimate.

[0111] Example 3

[0112] It is an embodiment of the present invention, which is different from the previous embodiment in that:

[0113] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program codes.

[0114] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0115] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or, if necessary, processing in another suitable manner, and then stored in a computer memory.

[0116] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0117] Example 4

[0118] As an embodiment of the present invention, a transient stability assessment method for a new energy grid-connected system based on a regular type is provided. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through economic benefit calculation and simulation experiments.

[0119] The embodiment of the present invention adopts a direct-drive wind turbine grid-connected system. At 0.1s, the grid voltage drops and the fault is not cleared. The phase output diagram of the original system and the simplified model is as follows: Figure 2 As shown in the figure, the fit between the two is good, which verifies the correctness of the simplified model obtained by singular perturbation.

[0120] At 0.1s, the grid voltage drops, and the fault is cleared at 0.29s and 0.30s respectively. The phase output diagram of the system is shown in Figure 3 When the fault is removed at 0.29s, z1=-0.2167<0, the system is stable, corresponding to Figure 3 The black solid line in the figure; when the fault is removed at 0.30s, z1=0.5443>0, the system becomes unstable, corresponding to Figure 3 The red dotted line in FIG. The method for evaluating the stability of a new energy equipment grid-connected system proposed by the present invention can effectively determine the stability of the system.

[0121] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A transient stability assessment method for a new energy grid-connected system based on a regular model, characterized in that: include: Establish a full-order model of the grid-connected system of new energy equipment, and divide the fast and slow variables according to the time constants of each state variable; The full-order model is perturbed based on a singular perturbation method to obtain a singular perturbation system, and a simplified model of a new energy equipment grid-connected system is obtained based on the singular perturbation system; Based on the normal form method, the simplified model is linearly and nonlinearly transformed to obtain a stable manifold estimate near the dominant unstable equilibrium point of the new energy equipment grid-connected system, and then obtain a stable domain boundary estimate; By comparing the fault trajectory after fault removal with the stability region boundary estimate, the transient stability of the new energy equipment grid-connected system is determined.

2. The transient stability assessment method for a new energy grid-connected system based on a regular type as claimed in claim 1, characterized in that: Establish a full-order model of the grid-connected system of new energy equipment, and divide the fast and slow variables into the following according to the time constants of each state variable: Based on power electronic devices and control structures, state space equations are written from two aspects: dynamics of energy storage elements and multi-time scale control; Obtain the time constant of each state variable in the state space equation, divide the fast and slow variables, where the slow variable is represented by X and the fast variable is represented by Y, to form a full-order model:

3. The transient stability assessment method for a new energy grid-connected system based on a regular type as claimed in claim 2, characterized in that: Based on the singular perturbation method, the full-order system is perturbed to obtain the singular perturbation system, which is expressed as: Among them, X is the slow variable, Y is the fast variable; ε is the perturbation parameter; 0<ε<<1; let the perturbation parameter ε=0, and the slow subsystem is obtained: The obtained slow subsystem is used as a simplified model of the new energy equipment grid-connected system.

4. The transient stability assessment method for a new energy grid-connected system based on a regular type as claimed in claim 3, characterized in that: The method based on the normal form is used to perform linear and nonlinear transformation on the simplified model to obtain a stable manifold estimate near the dominant unstable equilibrium point of the new energy equipment grid-connected system, and then obtain a stable domain boundary estimate, including: The Jacobian matrix A and Hessian matrix B of the simplified model are obtained at the dominant unstable equilibrium point of the new energy equipment grid-connected system. 1-n ; Based on the normal form method, the characteristic root λ of the grid-connected renewable energy equipment system at the dominant unstable equilibrium point is obtained. 1-5 , and obtain the Jordan standard form matrix J r ; The Jordan standard matrix J r The structure is represented as: Among them, λ 1-n is the characteristic root of the system, α and β are the real and imaginary parts of a pair of conjugate characteristic roots respectively; The Jordan standard matrix J r It is obtained by linearly transforming the Jacobian matrix A: I r =U -1 AT; Where U is the transformation matrix, and the column vectors of U are the eigenvectors or generalized eigenvectors of A; U -1 is the inverse matrix of U; Based on the Hessian matrix B 1-n Obtain the nonlinear influence C of the i-th state variable in W space i : V=U -1 ; Among them, V (i,j) is the i,jth element of matrix V; matrix V is the inverse matrix of transformation matrix U; Then transform the system in X space to W space, expressed as: Among them, w1,w2,w3,...,w n Indicates w i , w i is the i-th subvector of the state variable vector; express is the i-th subvector w of the state variable vector i The time derivative of T C1w,w T C2w,...,w T C n w means w T C i w, w T C i w is the nonlinear interaction between state variables, T is the transpose; n is the number of state variable subvectors; C1, C2, ..., C n Represents C i , C i is the nonlinear influence of the i-th state variable; Then transform the system in W space to Z space, and the nonlinear transformation equation is: Among them, z1,z2,z3,...,z n Indicates z i , z i is the i-th subvector of the new state variable vector in Z space; y1,y2,...,y n Represents y i ,y i is the linear combination of the state variable vectors in W space, representing the linear transformation from W space to Z space; D1,D2,...,D n Indicates D i , each D i represents an n×n matrix; y T D i y represents the part of nonlinear transformation, y T is the transpose of y.

5. The transient stability assessment method for a new energy grid-connected system based on a regular type as claimed in claim 4, characterized in that: The method of performing linear and nonlinear transformation on the simplified model based on the normal form method to obtain a stable manifold estimate near the dominant unstable equilibrium point of the new energy equipment grid-connected system, and then obtaining a stable domain boundary estimate, further includes: Obtain the transformation matrix D from W space to Z space 1-n , as shown below: Then the estimation of the boundary of the stable region is obtained, and the expression is: z1=0.

6. The transient stability assessment method for a new energy grid-connected system based on a regular type as claimed in claim 5, characterized in that: By comparing the fault trajectory after the fault removal with the estimated boundary of the stability region, the transient stability of the grid-connected system of the new energy equipment is judged, including mapping the system state quantity to the Z space to obtain the initial value z1(0) at the time of fault removal t=0; if z1(0)<0, a dynamic analysis is performed; if z1(0)≥0, the grid-connected system of the new energy equipment is directly judged to be unstable; The dynamic analysis includes the following steps: Trajectory sampling is performed. Specifically, if z1(0)<0, N system state samples are collected at a fixed interval Δt in the time interval [0, T] to form a state sequence {X(t i )}, i=0, 1,..., N-1, and N=T / Δt+1; {X(t i )} is mapped to Z space, and the sequence {z1(t i )}: {z1(t i )}={z1(t0),z1(t1),z1(t2),…,z1(t N-1 )}; Among them, t i is the i-th sampling moment, N is the total number of sampling points; Calculate the stability index S: Among them, τ is the time constant; z1(t) is a continuous time function, representing the continuous change of the system state over time; Fit z1(t) = Pe -μt +L, where μ is the attenuation coefficient, C and L are fitting constants; Calculate the stability margin: M = -L; When S<-Ω and M<-Ω, the grid-connected system of new energy equipment is determined to be stable; When S>Ω and M>Ω, the grid-connected system of new energy equipment is determined to be unstable; When |S|≤Ω or |M|≤Ω, the new energy equipment grid-connected system is determined to be in a critical stable state; Where Ω is the preset threshold.

7. The transient stability assessment method for a new energy grid-connected system based on a regular type as claimed in claim 6, characterized in that: The new energy equipment grid-connected system includes power electronic devices with different energy storage capabilities and a multi-time scale control structure corresponding to each energy storage element.

8. A system using the transient stability assessment method for a new energy grid-connected system based on a regular type as described in any one of claims 1 to 7, characterized in that: include: Full-order modeling module, used to establish a full-order model of the grid-connected system of new energy equipment, and divide fast and slow variables according to the time constants of each state variable; A simplified model generation module is used to perturb the full-order model based on the singular perturbation method to obtain a singular perturbation system, and to obtain a simplified model of the grid-connected system of new energy equipment based on the singular perturbation system; The stability domain estimation module is used to perform linear and nonlinear transformations on the simplified model based on the normal form method to obtain the stable manifold estimation near the dominant unstable equilibrium point of the new energy equipment grid-connected system, and then obtain the stability domain boundary estimation; The transient stability judgment module is used to judge the transient stability of the grid-connected system of new energy equipment by comparing the fault trajectory after fault removal with the estimated boundary of the stability domain.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the transient stability assessment method for a new energy grid-connected system based on a regular type are implemented as described in any one of claims 1 to 7.

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 steps of the transient stability assessment method for a new energy grid-connected system based on a regular type are implemented as described in any one of claims 1 to 7.

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