Branch energy transient stability evaluation method, device and equipment of grid-following type fan grid-connected system and storage medium

Abstract

The invention provides a branch energy transient stability evaluation method, device and equipment of a network following type fan grid-connected system and a storage medium. Relates to the technical field of wind power generation. The method comprises the following steps: constructing a branch energy function of the following-network type fan grid-connected system based on mathematical characteristics of a phase-locked loop and voltage distribution characteristics in a network; and according to the branch energy function, determining a branch stability discrimination index BSCGFLWT of the grid-following type fan grid-connected system, after a fault occurs, if the branch BSCGFLWT is equal to 0, the transient state of the system is unstable, and if the branch BSCGFLWT is not equal to 0, the transient state of the system is stable. According to the method, the four-machine two-area simulation model containing the following net type fan is constructed on the DIgSILENT / PowerFactory platform, and the effectiveness of the stability index of the proposed system is verified.

Description

Technical Field

[0001] The present application relates to the field of wind power generation technology, and in particular to a method, device, equipment and storage medium for evaluating the transient stability of branch energy in a grid-connected wind turbine system. Background Art

[0002] With the rapid increase in the proportion of renewable energy generation, transient stability issues caused by grid-connected wind turbines connected via power electronic converters are becoming increasingly prominent. Traditional power system transient stability analysis is primarily based on the electromechanical transient model of synchronous generators, using methods such as power angle trajectories and transient energy functions to assess system stability. However, grid-connected wind turbines exhibit characteristics such as lack of inertia, fast control response, and limited fault ride-through capability. The dynamic processes of their grid-connected systems exhibit multi-timescale coupling. Traditional energy assessment metrics based on the dominant synchronous generator mode struggle to accurately characterize the transient stability boundaries of wind turbine grid-connected systems. Existing research has primarily focused on converter-level control strategy optimization or system-level voltage / frequency stability analysis, but there remains a theoretical gap in quantitative transient stability assessment at the branch energy level. In particular, when a wind turbine grid-connected system is subjected to a fault, the spatiotemporal distribution characteristics of the grid branch energy are significantly distorted. Conventional energy flow calculation methods cannot effectively capture the modulation effect of converter dynamics on branch energy, resulting in deviations in stability margin assessments of critical transmission sections. There is an urgent need to build a branch energy transient stability assessment system that adapts to the dynamic characteristics of power electronic equipment to solve the problem of system stability judgment in an environment with a high proportion of new energy grid connection. Summary of the Invention

[0003] The present application provides a method, apparatus, equipment and storage medium for evaluating the transient stability of branch energy of a grid-connected wind turbine system, aiming to solve the problem of transient stability judgment in a new scenario of a grid-connected wind turbine system. By combining the mathematical characteristics of a phase-locked loop and the voltage distribution characteristics in a network, a branch energy function of a grid-connected wind turbine system is constructed. According to the distribution characteristics of branch energy under different system stability conditions, key factors of system stability contained in the branch are extracted, and a system stability index based on branch information is constructed. A four-machine, two-zone simulation model containing grid-connected wind turbines is constructed on the DIgSILENT / PowerFactory platform, and the effectiveness of the proposed system stability index is verified.

[0004] In a first aspect, the present application provides a method for evaluating the transient stability of branch energy in a grid-connected wind turbine system, comprising:

[0005] Based on the mathematical characteristics of the phase-locked loop and the voltage distribution characteristics in the network, the branch energy function of the grid-connected wind turbine system is constructed;

[0006] According to the branch energy function, the branch stability judgment index BSC of the grid-connected wind turbine system is determined. GFLWT , after the fault occurs, if there is a branch BSCGFLWT = 0, the system transient instability occurs, the branch BSC GFLWT ≠0, the system is transiently stable.

[0007] In one possible design, based on the mathematical properties of the phase-locked loop and the voltage distribution characteristics in the network, a branch energy function for the grid-connected wind turbine system is constructed, including:

[0008] Based on the set assumptions, the equivalent motion equation of the grid-type fan is established;

[0009] Based on the equivalent motion equation of the grid-type fan, an energy function is constructed;

[0010] Based on the infinite system of grid-connected wind turbines, the paper expands to the multi-machine system and obtains the state space expression of the grid-connected wind turbine multi-machine system.

[0011] Based on the state space expression of the grid-connected wind turbine multi-machine system and the energy function, a branch energy function of the grid-connected wind turbine system is constructed. The branch energy function includes the energy function of the entire system and the transient energy function of the multi-machine system.

[0012] In a possible design, the set assumptions include:

[0013] Ignore the transient process of mechanical rotor and PWM in the grid-following direct-drive fan;

[0014] Assume that the DC voltage is stable and ignore the dynamic characteristics of the rotor-side converter;

[0015] Ignoring the current loop dynamics, using unity power factor control, there is a q-axis reference current of 0;

[0016] The voltage loop control parameters are regarded as constants, and the voltage control loop dynamics are not considered in the transient stability analysis of grid-following wind turbines.

[0017] Based on the set assumptions, the equivalent motion equation of the grid-type fan is established, including:

[0018] Based on the set assumptions, a mathematical model of a grid-connected wind turbine system is constructed. The phase-locked loop control structure of the mathematical model of the grid-connected wind turbine system is expressed as follows:

[0019] θ pll =∫(K i ∫U 1,q dt+K p U 1,q )dt+∫ω N dt

[0020] Where: U 1,q is the q-axis component of the voltage at U1, K pis the phase-locked loop proportional coefficient, K i is the phase-locked loop integral coefficient, ω N is the system rated angular frequency, θ pll is the phase-locked loop output phase angle, t is the time;

[0021] According to the distribution law of the q-axis component of the voltage at each node on the branch and the phase-locked loop control structure, an equivalent motion equation of the grid-following wind turbine is established;

[0022] The distribution law of the q-axis component of the voltage at each node on the branch is:

[0023]

[0024] Where: ω pll The rotation speed of the reference system generated by the grid-following wind turbine control system, L 12 , L 13 , L 14 are the line inductances from node 1 to nodes 2, 3, and 4, θ2, θ3, and θ4 are the voltage phase angles at nodes 2, 3, and 4, respectively. is the power factor angle. Under unity power factor control, θ 12 ,θ 13 ,θ 14 is the impedance angle of lines 1-2, 1-3, and 1-4, θ 12 =θ 12 =θ 14 =90°; the q-axis component of the line current is I g is a constant value, δ is the difference between the phase angle of the phase-locked loop output and the voltage phase angle at infinity;

[0025] The equivalent motion equation of the grid-type fan is expressed as:

[0026]

[0027] Where: U1, U2, U3, and U4 are the voltages of nodes 2, 3, and 4 respectively.

[0028] In one possible design, the grid-connected infinite system of wind turbines is expanded to a multi-machine system, and the state space expression of the grid-connected infinite system of wind turbines is obtained as follows:

[0029]

[0030] Where: V is the total energy of the system, V KE is the system kinetic energy, V PE is the transient potential energy of the system, V D is the system damping energy, σ k is the phase angle difference of line k, σk,s is the phase angle difference of line k in the system stable state, M is the equivalent inertia time constant, P k (δ) is the equivalent electromagnetic power, P k,s is the steady-state equivalent power value, D is the damping coefficient of the grid-type fan, U j,q For U j The q-axis component of the voltage at 1j is the line inductance from node 1 to node j, U j is the voltage at node j, u is the branch phase angle difference, k is the line number, and t0 is the moment when the system is in steady state.

[0031] In one possible design, based on the state space expression of the grid-connected wind turbine multi-machine system and the energy function, a branch energy function of the grid-connected wind turbine system is constructed, including:

[0032] Based on the state space expression of the grid-connected wind turbine multi-machine system and the energy function, according to the equilibrium point (α s ,0), establish the energy function of the whole system:

[0033]

[0034] Where: is the kinetic energy function, W(α,α s ) is the potential energy function, where is the damping energy function, V(α,ω g ) is the total energy of the system, is the transpose of the generator angular velocity vector, M g is the equivalent inertia time constant matrix, ω g is the generator angular velocity vector, α s is the steady-state phase angle of the node voltage relative to the reference point, α is the phase angle of the node voltage relative to the reference point, D is the generator damping coefficient matrix, f(α s ) is the steady-state value of the equivalent active power of each branch, and f(α) is the equivalent active power of each branch;

[0035] Taking the branch phase angle difference at the moment of fault removal as the reference point, the transient energy function of the multi-machine system is constructed as follows:

[0036]

[0037] Where: V is the total energy of the system, i is the generator number, m is the total number of GFL-PMSG, M i is the equivalent inertia time constant of the i-th generator, ω i is the angular frequency of the i-th generator, D i is the damping coefficient of the i-th generator.

[0038] In one possible design, the branch stability judgment index BSC of the grid-connected wind turbine system is determined by the following formula: GFLWT :

[0039]

[0040] Where: V' PEK (t a ,t b )=V PEK (t a ,t b ) / (1-K p l 1j I g ) is the form of eliminating the internal parameters of the mesh type fan, K p is the phase-locked loop proportional coefficient, l 1j is the line inductance from node 1 to node j, V PEK (t a ,t b ) is the branch k in (t a ,t b ) time, the change in branch potential energy, U j,q (t b ) is t b The voltage at node j at the moment is in the q-axis component, U j,q (t0) is the q-axis component of the voltage at node j at time t0.

[0041] In a possible design, the branch stability judgment index is used to judge the change trend of the branch angle difference, with the initial flow direction of branch k as the positive direction, in (t a ,t b ) exists at all times When Δω k (t)<0, if BSC GFLWT <0, then [P k (t)-P k,s ]<0,; when Δω k (t)>0, if BSC GFLWT >0, then [P k (t)-P k,s ]>0, where represents the derivative of the potential energy of branch k, Δω k (t) represents the angular frequency difference of the potential energy of branch k, P k (t) is the equivalent power corresponding to branch k at time t, P k,s It represents the equivalent power corresponding to the stable moment of branch k.

[0042] In a second aspect, the present application provides a branch energy transient stability assessment device for a grid-connected wind turbine system, the device comprising:

[0043] A function construction module is configured to construct a branch energy function of a grid-connected wind turbine system based on mathematical characteristics of a phase-locked loop and voltage distribution characteristics in a network;

[0044] The index evaluation module is configured to determine the branch stability judgment index BSC of the grid-connected wind turbine system based on the branch energy function. GFLWT , after the fault occurs, if there is a branch BSC GFLWT = 0, the system transient instability occurs, the branch BSC GFLWT ≠0, the system is transiently stable.

[0045] In a third aspect, an embodiment of the present application provides an electronic device comprising: at least one processor and a memory; the memory stores computer-executable instructions; the at least one processor executes the computer-executable instructions stored in the memory, so that the at least one processor executes the branch energy transient stability assessment method of the grid-connected wind turbine system as described in the first aspect and various possible designs of the first aspect.

[0046] In a fourth aspect, an embodiment of the present application provides a computer-readable storage medium, in which computer execution instructions are stored. When a processor executes the computer execution instructions, the branch energy transient stability assessment method of the grid-connected wind turbine system as described in the first aspect and various possible designs of the first aspect is implemented.

[0047] In a fifth aspect, an embodiment of the present application provides a computer program product, including a computer program. When the computer program is executed by a processor, it implements the branch energy transient stability assessment method of the grid-connected wind turbine system as described in the first aspect and various possible designs of the first aspect.

[0048] The method, device, equipment, and storage medium for evaluating branch energy transient stability of a grid-connected wind turbine system provided by this application have at least the following beneficial effects:

[0049] 1) This application constructs a branch energy model under a grid-connected wind turbine system, completing the branch energy model system.

[0050] 2) The branch energy transient stability evaluation index of the grid-connected wind turbine system proposed in this application can determine the weak links of the system through network variables, and then determine the system stability, which has the advantages of being simple and easy to obtain.

[0051] 3) The case analysis shows that the branch energy transient stability assessment index of the grid-connected wind turbine system proposed in this application does not require the calculation of critical energy and can quantify the system stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0053] Figure 1 A flow chart of a method for evaluating branch energy transient stability of a grid-connected wind turbine system provided in an embodiment of the present application;

[0054] Figure 2 A topological diagram of the GFLWT grid-connected infinite system provided in an embodiment of the present application;

[0055] Figure 3 A flow chart for constructing a branch energy function of a grid-connected wind turbine system provided in an embodiment of the present application;

[0056] Figure 4 The transient energy curves of each branch under stable and unstable conditions of the GFLWT grid-connected infinite system according to the embodiment of the present application are shown in FIG. (a) is a transient energy change curve of each branch under stable conditions; (b) is a transient energy change curve of each branch under unstable conditions;

[0057] Figure 5 This is a diagram of a 4-machine 2-zone system under GFLWT access according to an embodiment of the present application:

[0058] Figure 6 The transient energy curves of each branch in the GFLWT access 4-machine 2-zone system under stable and unstable conditions in the embodiment of the present application are shown in FIG. (a) is a transient energy change curve of each branch under stable conditions; and (b) is a transient energy change curve of each branch under unstable conditions.

[0059] Figure 7 This is a structural diagram of the branch energy transient stability assessment device of the grid-connected wind turbine system provided in an embodiment of the present application.

[0060] The above drawings illustrate specific embodiments of the present application, which will be described in more detail below. These drawings and the textual description are not intended to limit the scope of the present application in any way, but rather to illustrate the concepts of the present application to those skilled in the art by reference to specific embodiments. DETAILED DESCRIPTION

[0061] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.

[0062] In the technical solution of this application, the collection, storage, use, processing, transmission, provision and disclosure of information such as financial data or user data involved comply with the provisions of relevant laws and regulations and do not violate public order and good morals.

[0063] It should be noted that in the embodiments of the present application, certain software, components, models and other existing solutions in the industry may be mentioned. They should be regarded as exemplary. Their purpose is only to illustrate the feasibility of implementing the technical solution of the present application, but it does not mean that the applicant has or will necessarily use the solution.

[0064] The following specific embodiments describe in detail the technical solution of the present application and how the technical solution of the present application solves the above-mentioned technical problems. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0065] The present application embodiment provides a method for evaluating the transient stability of branch energy in a grid-connected wind turbine system. Figure 1 As shown, it is a flow chart of a method for evaluating transient stability of branch energy of a grid-connected wind turbine system provided by an embodiment of the present application. The method for evaluating transient stability of branch energy of a grid-connected wind turbine system includes the following steps S100-S200.

[0066] S100: Based on the mathematical characteristics of the phase-locked loop and the voltage distribution characteristics in the network, a branch energy function of the grid-connected wind turbine system is constructed.

[0067] In some embodiments, as Figure 2 As shown in FIG, the topological structure diagram of the GFLWT grid-connected infinite system provided by the embodiment of the present application. Based on the GFLWT grid-connected infinite system, as shown in FIG. Figure 3 As shown in Figure 2, the branch energy function of the grid-connected wind turbine system is constructed through the following steps:

[0068] S101: Based on the set assumptions, an equivalent motion equation of the grid-type fan is established.

[0069] In this embodiment, in order to accurately describe the transient characteristics of the phase-locked loop, based on the above analysis, the following assumptions are proposed for the grid-connected direct-drive wind turbine system:

[0070] 1) Ignore the transient process of the mechanical rotor and PWM in the grid-following direct-drive fan;

[0071] 2) Assuming that the DC voltage is stable, the dynamic characteristics of the rotor-side converter are ignored;

[0072] 3) Ignore the current loop dynamics, adopt unity power factor control, and have a q-axis reference current of 0;

[0073] 4) The voltage loop control parameters are regarded as constants, and the voltage control loop dynamics are not considered in the transient stability analysis of grid-following wind turbines;

[0074] Based on the above assumptions, a mathematical model of the grid-connected wind turbine system is constructed, and the phase-locked loop control structure can be obtained:

[0075] θ pll =∫(K i ∫U 1,q dt+K p U 1,q )dt+∫ω N dt

[0076] Where: U 1,q is the q-axis component of the voltage at U1, where K p is the phase-locked loop proportional coefficient, K i is the phase-locked loop integral coefficient, ω N is the system rated angular frequency, θ pll is the phase-locked loop output phase angle.

[0077] The distribution law of the q-axis component of the voltage at each node on the branch is:

[0078]

[0079] Where: ω pll The rotation speed of the reference system generated by the grid-following wind turbine control system, L 12 , L 13 , L 14 are the line inductances from node 1 to nodes 2, 3, and 4, θ2, θ3, and θ4 are the voltage phase angles at nodes 2, 3, and 4, respectively. is the power factor angle. Under unity power factor control, θ 12 ,θ 13 ,θ 14 is the impedance angle of lines 1-2, 1-3, and 1-4. Since the line resistance is ignored, θ 12 =θ 12 =θ 14 =90°; the q-axis component of the line current is Ignoring the current loop dynamics, assuming I gis a constant, and δ is the difference between the phase angle of the phase-locked loop output and the voltage phase angle at infinity.

[0080] Combined with the above formula, the equivalent motion equation of the grid-type fan can be expressed as:

[0081]

[0082] Where: U1, U2, U3, and U4 are the voltages of nodes 2, 3, and 4 respectively.

[0083] S102: Construct an energy function based on the equivalent motion equation of the grid-type fan.

[0084] In this embodiment, the energy function is constructed by constructing the equivalent motion equation of the grid-type fan:

[0085]

[0086] Where: V is the total energy of the system, V KE is the system kinetic energy, V PE is the transient potential energy of the system, V D is the system damping energy, σ k is the phase angle difference of line k, σ k,s is the phase angle difference of line k in the system stable state, M is the equivalent inertia time constant, P k (δ) is the equivalent electromagnetic power, P k,s is the steady-state equivalent power value, D is the damping coefficient of the grid-type fan, U j,q For U j The q-axis component of the voltage at 1j is the line inductance from node 1 to node j.

[0087] S103: Based on the infinite grid-connected wind turbine system, the system is expanded to a multi-machine system, and a state space expression of the grid-connected wind turbine multi-machine system is obtained.

[0088] In this embodiment, the grid-connected infinite system of wind turbines is expanded to a multi-machine system based on the grid-connected infinite system, and the state space expression of the grid-connected multi-machine system of wind turbines is obtained:

[0089]

[0090] Where M is the equivalent inertia time constant matrix, ω g is the angular velocity vector of the grid-following fan, T g is the identity matrix, U j,q (α) / (1-K p l 1j I g ) is the equivalent electromagnetic power of each branch, ω N l 1j Ig / (1-K p l 1j I g ) is the steady-state equivalent power value of each branch, and D is the damping coefficient matrix of the grid-type fan.

[0091] S104: Based on the state space expression of the grid-connected wind turbine multi-machine system and the energy function, construct a branch energy function of the grid-connected wind turbine system, wherein the branch energy function includes the energy function of the entire system and the transient energy function of the multi-machine system.

[0092] In this embodiment, it is assumed that there is an equilibrium point (α s ,0), relative to this equilibrium point, the energy function of the whole system is established:

[0093]

[0094] Where: is the kinetic energy function, W(α,α s ) is the potential energy function, where is the damping energy function, V(α,ω g ) is the total energy of the system, is the transpose of the generator angular velocity vector, M g is the equivalent inertia time constant matrix, ω g is the generator angular velocity vector, α s is the steady-state phase angle of the node voltage relative to the reference point, α is the phase angle of the node voltage relative to the reference point, D is the generator damping coefficient matrix, f(α s ) is the steady-state value of the equivalent active power of each branch, and f(α) is the equivalent active power of each branch;

[0095] Taking the branch phase angle difference at the moment of fault removal as the reference point, the transient energy function of the multi-machine system is constructed as follows:

[0096]

[0097] Where: V is the total energy of the system, i is the generator number, m is the total number of GFL-PMSG, M i is the equivalent inertia time constant of the i-th generator, ω i is the angular frequency of the i-th generator, D i is the damping coefficient of the i-th generator.

[0098] Taking into account the impact of synchronous machine grid connection, the multi-machine system can be expressed as:

[0099]

[0100] Where: is the synchronous kinetic energy function in the system, is the kinetic energy function of the synchronous machine in the system.

[0101] S200: Determine the branch stability judgment index BSC of the grid-connected wind turbine system based on the branch energy function GFLWT , after the fault occurs, if there is a branch BSC GFLWT = 0, the system transient instability occurs, the branch BSC GFLWT ≠0, the system is transiently stable.

[0102] like Figure 4 As shown in the figure, when the system is stable, the transient potential energy of each branch fluctuates within a certain bounded range. Specifically, the transient potential energy of branch 2-3 fluctuates significantly more than that of branches 1-2 and 3-4. Once the system becomes unstable, the transient potential energy of branch 2-3 continues to decline and is no longer confined to a bounded range, while the transient potential energy of branches 1-2 and 3-4 remains within a bounded range. This indicates that the subsystem consisting of branches 1-2 and 3-4 is internally stable, but the instability of branch 2-3 connecting these two subsystems causes the two subsystems to lose synchronization, leading to instability of the entire system.

[0103] In other words, within the network distribution, the potential energy of branches exhibits a certain regularity. When the system is stable, the potential energy of all branches varies within a bounded range, and the critical cut set contributes more to the potential energy than other branches. As the system stability gradually deteriorates, the tendency of the system potential energy to concentrate towards the critical cut set becomes increasingly apparent. In the event of system instability, the critical cut set potential energy may even decrease monotonically.

[0104] When the system is unstable, the difference between the equivalent electromagnetic power and the equivalent power steady-state value is 0; when the system is stable, the difference between the equivalent electromagnetic power and the equivalent power steady-state value is not 0. According to the above change characteristics, the branch stability judgment index BSC of the grid-connected wind turbine system is obtained. GFLWT (Grid-Following Wind Turbine Branch Stability Criterion, BSC GFLWT ), defined as:

[0105]

[0106] Where: V' PEK (t a ,t b )=V PEK (t a ,t b ) / (1-K p l 1j I g) is the form of eliminating the internal parameters of the mesh type fan, P k (t b ) is the branch k at t b The equivalent power corresponding to the moment, P k,s is the equivalent power corresponding to the stable moment of branch k, V PEK (t a ,t b ) is the branch k in (t a ,t b ) time, the change in branch potential energy U j,q (t b ) is t b The voltage at node j at the moment is in the q-axis component, U j,q (t0) is the q-axis component of the voltage at node j at time t0.

[0107] BSC GFLWT It can determine the changing trend of the branch angle difference. Assuming the initial flow direction of branch k is positive, in (t a ,t b ) exists at all times That is [P k (t)-P k,s ]Δω k (t)>0. Then when Δω k When (t)<0, there exists [P k (t)-P k,s ]<0,BSC GFLWT <0; when Δω k When (t)>0, there exists [P k (t)-P k,s ]>0,BSC GFLWT >0; among them, represents the derivative of the potential energy of branch k, Δω k (t) represents the angular frequency difference of the potential energy of branch k, P k (t) is the equivalent power corresponding to branch k at time t, P k,s It represents the equivalent power corresponding to the stable moment of branch k.

[0108] The following embodiment of the present application will verify the effectiveness of the proposed system stability index by using four machines and two zones containing grid-type wind turbines.

[0109] like Figure 5 As shown in the figure, the effectiveness of the proposed indicators is verified in a 4-machine 2-zone system with GFLWT access.

[0110] The embodiment of the present application proposes BSC GFLWTThis not only quantitatively analyzes system stability but also assesses the impact of each branch and cut set on the system's transient stability and identifies weak links in the network. The verification process includes steps 1 through 3.

[0111] Step 1: Based on branch parameters and branch variables, combined with the phase-locked loop structure characteristics and branch voltage distribution characteristics, the energy function of the grid-connected wind turbine system is constructed.

[0112] Step 2: Calculate the BSC of each branch of the system based on wide-area measurement information GFLWT , by comparing the size of SGPBI of each branch, the weak link of the system can be determined.

[0113] Step 3: If there is a branch BSC after the fault occurs GFLWT = 0, the system transient instability occurs, the branch BSC GFLWT ≠0, the system is transiently stable.

[0114] Figure 6 In the example, when the system is stable, the transient potential energy of each branch fluctuates within a bounded range. Among them, the transient potential energy of branches 8-9a(b) and 7-8a(b) varies more than that of the other branches. Once the system becomes unstable, the transient potential energy of branches 8-9a(b) and 7-8a(b) continues to decrease and is no longer confined to the bounded range, while the transient potential energy of the other branches remains within the bounded range. This indicates that the cut set formed by branches 8-9a(b) and 7-8a(b) is the weak link in the system. The instability of this cut set causes the two subsystems to lose synchronization, leading to the instability of the entire system.

[0115] Table 1 Stable branch BSC GFLWT Calculated value

[0116]

[0117] As can be seen from Table 1, when the system is stable, the BSCs of branches 8-9a(b) and 7-8a(b) GFLWT The calculated value is smaller than that of the other branches, and the corresponding stability is also worse. The cut set it constitutes is the weak link of the system.

[0118] Table 2 Unstable lower branch BSC GFLWT Calculated value

[0119]

[0120] It can be seen from Table 2 that when the system is unstable, branches 8-9a(b) and 7-8a(b) are the weak links of the system, and their BSC GFLWT The calculated value is 0. The indicator proposed in this application can determine the stability of the system.

[0121] The present application also provides a branch energy transient stability assessment device for a grid-connected wind turbine system. Figure 7 As shown, the branch energy transient stability assessment device of the grid-connected wind turbine system includes:

[0122] The function construction module 701 is configured to construct a branch energy function of the grid-connected wind turbine system based on the mathematical characteristics of the phase-locked loop and the voltage distribution characteristics in the network;

[0123] The index evaluation module 702 is configured to determine the branch stability judgment index BSC of the grid-connected wind turbine system based on the branch energy function. GFLWT , after the fault occurs, if there is a branch BSC GFLWT = 0, the system transient instability occurs, the branch BSC GFLWT ≠0, the system is transiently stable.

[0124] In some embodiments, the function building block is further configured to:

[0125] Based on the set assumptions, the equivalent motion equation of the grid-type fan is established;

[0126] Based on the equivalent motion equation of the grid-type fan, an energy function is constructed;

[0127] Based on the infinite system of grid-connected wind turbines, the paper expands to the multi-machine system and obtains the state space expression of the grid-connected wind turbine multi-machine system.

[0128] Based on the state space expression of the grid-connected wind turbine multi-machine system and the energy function, a branch energy function of the grid-connected wind turbine system is constructed. The branch energy function includes the energy function of the entire system and the transient energy function of the multi-machine system.

[0129] In some embodiments, the set assumptions include:

[0130] Ignore the transient process of mechanical rotor and PWM in the grid-following direct-drive fan;

[0131] Assume that the DC voltage is stable and ignore the dynamic characteristics of the rotor-side converter;

[0132] Ignoring the current loop dynamics, using unity power factor control, there is a q-axis reference current of 0;

[0133] The voltage loop control parameters are regarded as constants, and the voltage control loop dynamics are not considered in the transient stability analysis of grid-following wind turbines.

[0134] The function building block is further configured to:

[0135] Based on the set assumptions, a mathematical model of a grid-connected wind turbine system is constructed. The phase-locked loop control structure of the mathematical model of the grid-connected wind turbine system is expressed as follows:

[0136] θ pll =∫(K i ∫U 1,q dt+K p U 1,q )dt+∫ω N dt

[0137] Where: U 1,q is the q-axis component of the voltage at U1, K p is the phase-locked loop proportional coefficient, K i is the phase-locked loop integral coefficient, ω N is the system rated angular frequency, θ pll is the phase-locked loop output phase angle, t is the time;

[0138] According to the distribution law of the q-axis component of the voltage at each node on the branch and the phase-locked loop control structure, an equivalent motion equation of the grid-following wind turbine is established;

[0139] The distribution law of the q-axis component of the voltage at each node on the branch is:

[0140]

[0141] Where: ω pll The rotation speed of the reference system generated by the grid-following wind turbine control system, L 12 , L 13 , L 14 are the line inductances from node 1 to nodes 2, 3, and 4, θ2, θ3, and θ4 are the voltage phase angles at nodes 2, 3, and 4, respectively. is the power factor angle. Under unity power factor control, θ 12 ,θ 13 ,θ 14 is the impedance angle of lines 1-2, 1-3, and 1-4, θ 12 =θ 12 =θ 14 =90°; the q-axis component of the line current is I g is a constant value, δ is the difference between the phase angle of the phase-locked loop output and the voltage phase angle at infinity;

[0142] The equivalent motion equation of the grid-type fan is expressed as:

[0143]

[0144] Where: U1, U2, U3, and U4 are the voltages of nodes 2, 3, and 4 respectively.

[0145] In some embodiments, the function building module is further configured to expand the grid-connected wind turbine infinite system to a multi-machine system, and the state space expression of the grid-connected wind turbine multi-machine system is obtained as follows:

[0146]

[0147] Where: V is the total energy of the system, V KE is the system kinetic energy, V PE is the transient potential energy of the system, V D is the system damping energy, σ k is the phase angle difference of line k, σ k,s is the phase angle difference of line k in the system stable state, M is the equivalent inertia time constant, P k (δ) is the equivalent electromagnetic power, P k,s is the steady-state equivalent power value, D is the damping coefficient of the grid-type fan, U j,q For U j The q-axis component of the voltage at 1j is the line inductance from node 1 to node j, U j is the voltage at node j, u is the branch phase angle difference, k is the line number, and t0 is the time when the system is in steady state;

[0148] In some embodiments, the function building block is further configured to:

[0149] Based on the state space expression of the grid-connected wind turbine multi-machine system and the energy function, according to the equilibrium point (α s ,0), establish the energy function of the whole system:

[0150]

[0151] Where: is the kinetic energy function, W(α,α s ) is the potential energy function, where is the damping energy function, V(α,ω g ) is the total energy of the system, is the transpose of the generator angular velocity vector, M g is the equivalent inertia time constant matrix, ω g is the generator angular velocity vector, α s is the steady-state phase angle of the node voltage relative to the reference point, α is the phase angle of the node voltage relative to the reference point, D is the generator damping coefficient matrix, f(α s ) is the steady-state value of the equivalent active power of each branch, and f(β) is the equivalent active power of each branch;

[0152] Taking the branch phase angle difference at the moment of fault removal as the reference point, the transient energy function of the multi-machine system is constructed as follows:

[0153]

[0154] Where: V is the total energy of the system, i is the generator number, m is the total number of GFL-PMSG, M i is the equivalent inertia time constant of the i-th generator, ω i is the angular frequency of the i-th generator, D i is the damping coefficient of the i-th generator.

[0155] In some embodiments, the index evaluation module is further configured to determine the branch stability judgment index BSC of the grid-connected wind turbine system by the following formula: GFLWT :

[0156]

[0157] Where: V' PEK (t a ,t b )=V PEK (t a ,t b ) / (1-K p l 1j I g ) is the form of eliminating the internal parameters of the mesh type fan, K p is the phase-locked loop proportional coefficient, l 1j is the line inductance from node 1 to node j, V PEK (t a ,t b ) is the branch k in (t a ,t b ) time, the change in branch potential energy, U j,q (t b ) is t b The voltage at node j at the moment is in the q-axis component, U j,q (t0) is the q-axis component of the voltage at node j at time t0.

[0158] In some embodiments, the branch stability judgment index is used to judge the change trend of the branch angle difference, taking the initial flow direction of branch k as the positive direction, in (t a ,t b ) exists at all times When Δω k (t)<0, if BSC GFLWT <0, then [P k (t)-P k,s ]<0,; when Δω k(t)>0, if BSC GFLWT >0, then [P k (t)-P k,s ]>0, where represents the derivative of the potential energy of branch k, Δω k (t) represents the angular frequency difference of the potential energy of branch k, P k (t) is the equivalent power corresponding to branch k at time t, P k,s It represents the equivalent power corresponding to the stable moment of branch k.

[0159] An embodiment of the present application provides an electronic device, which may include a processor and a memory, wherein the processor and the memory can communicate with each other; illustratively, the processor and the memory communicate with each other via a communication bus.

[0160] The processor executes the computer-executable instructions stored in the memory, so that the processor implements the solutions in the above embodiments. The processor can be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it can also be a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0161] The communication bus can be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus. System buses can be categorized as address buses, data buses, and control buses. Transceivers enable communication between the database access device and other computers (e.g., clients, read-write libraries, and read-only libraries). Memory may include random access memory (RAM) or non-volatile memory.

[0162] The electronic device provided in the embodiment of the present application may be the terminal device of the above embodiment.

[0163] An embodiment of the present application also provides a computer-readable storage medium, which stores computer instructions. When the computer instructions are executed on a computer, the computer executes the technical solution of the branch energy transient stability assessment method of the grid-connected wind turbine system according to the above embodiment.

[0164] An embodiment of the present application also provides a computer program product, which includes a computer program stored in a computer-readable storage medium. At least one processor can read the computer program from the computer-readable storage medium. When at least one processor executes the computer program, it can implement the technical solution of the branch energy transient stability assessment method of the grid-connected wind turbine system in the above embodiment.

[0165] In the several embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of modules is only a logical function division. In actual implementation, there may be other division methods, such as multiple modules can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interface, device or module, which can be electrical, mechanical or other forms.

[0166] Modules described as separate components may or may not be physically separate, and components shown as modules may or may not be physical units, that is, they may be located in one place or distributed across multiple network elements. Some or all of these modules may be selected to implement the solution of this embodiment based on actual needs.

[0167] In addition, the functional modules in the various embodiments of the present application may be integrated into a single processing unit, or each module may exist physically separately, or two or more modules may be integrated into a single unit. The above-mentioned modules may be implemented in the form of hardware or hardware plus software functional units.

[0168] The above-mentioned integrated module implemented in the form of a software functional module can be stored in a computer-readable storage medium. The above-mentioned software functional module is stored in a storage medium and includes a number of instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) or a processor to perform some steps of the methods of various embodiments of the present application.

[0169] It should be understood that the processor may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSP), or application-specific integrated circuits (ASICs). A general-purpose processor may be a microprocessor or any conventional processor. The steps of the method disclosed in the present invention may be directly implemented by a hardware processor or implemented by a combination of hardware and software modules in the processor.

[0170] The memory may include a high-speed RAM memory, and may also include non-volatile storage NVM, such as at least one disk memory, and may also be a USB flash drive, a mobile hard disk, a read-only memory, a magnetic disk or an optical disk.

[0171] The bus can be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus. Buses can be divided into address buses, data buses, and control buses.

[0172] The storage medium may be implemented by any type of volatile or non-volatile memory device, or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk. The storage medium may be any available medium that can be accessed by a general-purpose or special-purpose computer.

[0173] An exemplary storage medium is coupled to a processor so that the processor can read information from the storage medium and write information to the storage medium. Of course, the storage medium can also be an integral part of the processor. The processor and the storage medium can be located in an application specific integrated circuit (ASIC). Of course, the processor and the storage medium can also exist as discrete components in an electronic control unit or a main control device.

[0174] Those skilled in the art will appreciate that all or part of the steps in the above-described method embodiments can be implemented using hardware associated with program instructions. The aforementioned program can be stored in a computer-readable storage medium. When executed, the program performs the steps of the above-described method embodiments. The aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks.

[0175] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for evaluating the transient stability of branch energy in a grid-connected wind turbine system, characterized in that: The method comprises: Based on the mathematical characteristics of the phase-locked loop and the voltage distribution characteristics in the network, the branch energy function of the grid-connected wind turbine system is constructed; According to the branch energy function, the branch stability judgment index BSC of the grid-connected wind turbine system is determined. GFLWT , after the fault occurs, if there is a branch BSC GFLWT = 0, the system transient instability occurs, the branch BSC GFLWT ≠0, the system is transiently stable.

2. The method for evaluating branch energy transient stability of a grid-connected wind turbine system according to claim 1, characterized in that: Based on the mathematical characteristics of the phase-locked loop and the voltage distribution characteristics in the network, the branch energy function of the grid-connected wind turbine system is constructed, including: Based on the set assumptions, the equivalent motion equation of the grid-type fan is established; Based on the equivalent motion equation of the grid-type fan, an energy function is constructed; Based on the infinite system of grid-connected wind turbines, the paper expands to the multi-machine system and obtains the state space expression of the grid-connected wind turbine multi-machine system. Based on the state space expression of the grid-connected wind turbine multi-machine system and the energy function, a branch energy function of the grid-connected wind turbine system is constructed. The branch energy function includes the energy function of the entire system and the transient energy function of the multi-machine system.

3. The method for evaluating branch energy transient stability of a grid-connected wind turbine system according to claim 2, characterized in that: The assumptions set include: Ignore the transient process of mechanical rotor and PWM in the grid-following direct-drive fan; Assume that the DC voltage is stable and ignore the dynamic characteristics of the rotor-side converter; Ignoring the current loop dynamics, using unity power factor control, there is a q-axis reference current of 0; The voltage loop control parameters are regarded as constants, and the voltage control loop dynamics are not considered in the transient stability analysis of grid-following wind turbines. Based on the set assumptions, the equivalent motion equation of the grid-type fan is established, including: Based on the set assumptions, a mathematical model of a grid-connected wind turbine system is constructed. The phase-locked loop control structure of the mathematical model of the grid-connected wind turbine system is expressed as follows: θ pll =∫(K i ∫U 1,q dt+K p U 1,q )dt+∫ω N dt Where: U 1,q is the q-axis component of the voltage at U1, K p is the phase-locked loop proportional coefficient, K i is the phase-locked loop integral coefficient, ω N is the system rated angular frequency, θ pll is the phase-locked loop output phase angle, t is the time; According to the distribution law of the q-axis component of the voltage at each node on the branch and the phase-locked loop control structure, an equivalent motion equation of the grid-following wind turbine is established; The distribution law of the q-axis component of the voltage at each node on the branch is: Where: ω pll The rotation speed of the reference system generated by the grid-following wind turbine control system, L 12 , L 13 , L 14 are the line inductances from node 1 to nodes 2, 3, and 4, θ2, θ3, and θ4 are the voltage phase angles at nodes 2, 3, and 4, respectively. is the power factor angle. Under unity power factor control, θ 12 ,θ 13 ,θ 14 is the impedance angle of lines 1-2, 1-3, and 1-4, θ 12 =θ 12 =θ 14 =90°; the q-axis component of the line current is I g is a constant value, δ is the difference between the phase angle of the phase-locked loop output and the voltage phase angle at infinity; The equivalent motion equation of the grid-type fan is expressed as: Where: U1, U2, U3, and U4 are the voltages of nodes 2, 3, and 4 respectively.

4. The method for evaluating branch energy transient stability of a grid-connected wind turbine system according to claim 3 is characterized in that: Based on the infinite grid-connected wind turbine system, the state space expression of the infinite grid-connected wind turbine system is expanded to the multi-machine system: Where: V is the total energy of the system, V KE is the system kinetic energy, V PE is the transient potential energy of the system, V D is the system damping energy, σ k is the phase angle difference of line k, σ k,s is the phase angle difference of line k in the system stable state, M is the equivalent inertia time constant, P k (δ) is the equivalent electromagnetic power, P k,s is the steady-state equivalent power value, D is the damping coefficient of the grid-type fan, U j,q For U j The q-axis component of the voltage at 1j is the line inductance from node 1 to node j, U j is the voltage at node j, u is the branch phase angle difference, k is the line number, and t0 is the moment when the system is in steady state.

5. The method for evaluating branch energy transient stability of a grid-connected wind turbine system according to claim 4, characterized in that: Based on the state space expression of the grid-connected wind turbine multi-machine system and the energy function, a branch energy function of the grid-connected wind turbine system is constructed, including: Based on the state space expression of the grid-connected wind turbine multi-machine system and the energy function, according to the equilibrium point (α s ,0), establish the energy function of the whole system: Where: is the kinetic energy function, W(α,α s ) is the potential energy function, where is the damping energy function, V(α,ω g ) is the total energy of the system, is the transpose of the generator angular velocity vector, M g is the equivalent inertia time constant matrix, ω g is the generator angular velocity vector, α s is the steady-state phase angle of the node voltage relative to the reference point, α is the phase angle of the node voltage relative to the reference point, D is the generator damping coefficient matrix, f(α s ) is the steady-state value of the equivalent active power of each branch, and f(α) is the equivalent active power of each branch; Taking the branch phase angle difference at the moment of fault removal as the reference point, the transient energy function of the multi-machine system is constructed as follows: Where: V is the total energy of the system, i is the generator number, m is the total number of GFL-PMSG, M i is the equivalent inertia time constant of the i-th generator, ω i is the angular frequency of the i-th generator, D i is the damping coefficient of the i-th generator.

6. The method for evaluating branch energy transient stability of a grid-connected wind turbine system according to claim 1, characterized in that: The branch stability judgment index BSC of the grid-connected wind turbine system is determined by the following formula GFLWT : Where: V' PEK (t a ,t b )=V PEK (t a ,t b ) / (1-K p l 1j I g ) is the form of eliminating the internal parameters of the mesh type fan, K p is the phase-locked loop proportional coefficient, l 1j is the line inductance from node 1 to node j, V PEK (t a ,t b ) is the branch k at (t a ,t b ) time, U j,q (t b ) is t b The voltage at node j at the moment is in the q-axis component, U j,q (t0) is the q-axis component of the voltage at node j at time t0.

7. The method for evaluating branch energy transient stability of a grid-connected wind turbine system according to claim 1, characterized in that: The branch stability judgment index is used to judge the change trend of the branch angle difference. The initial flow direction of branch k is taken as the positive direction. a ,t b ) exists at all times When Δω k (t)<0, if BSC GFLWT <0, then [P k (t)-P k,s ]<0,; when Δω k (t)>0, if BSC GFLWT >0, then [P k (t)-P k,s ]>0, where represents the derivative of the potential energy of branch k, Δω k (t) represents the angular frequency difference of the potential energy of branch k, P k (t) is the equivalent power corresponding to branch k at time t, P k,s It represents the equivalent power corresponding to the stable moment of branch k.

8. A branch energy transient stability assessment device for a grid-connected wind turbine system, characterized in that: The device comprises: A function construction module is configured to construct a branch energy function of a grid-connected wind turbine system based on mathematical characteristics of a phase-locked loop and voltage distribution characteristics in a network; The index evaluation module is configured to determine the branch stability judgment index BSC of the grid-connected wind turbine system based on the branch energy function. GFLWT , after the fault occurs, if there is a branch BSC GFLWT = 0, the system transient instability occurs, the branch BSC GFLWT ≠0, the system is transiently stable.

9. An electronic device, characterized in that: include: a processor, and a memory communicatively connected to the processor; The memory stores computer-executable instructions; The processor executes the computer-executable instructions stored in the memory to implement the branch energy transient stability assessment method of the grid-connected wind turbine system according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that The computer-readable storage medium stores computer-executable instructions, which, when executed by a processor, are used to implement the branch energy transient stability assessment method for a grid-connected wind turbine system according to any one of claims 1 to 7.

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