A coupled pendulum mapping model for grid-connected converters and its transient trajectory characterization method

Abstract

The present invention discloses a coupled pendulum mapping model of a grid-connected converter and a transient trajectory characterization method thereof. The present invention aims at transient stability analysis of grid-connected multi-grid converters, maps the power-frequency model of a traditional grid-connected converter to a classical coupled pendulum model, and characterizes the transient trajectory of the state quantity of the grid-connected converter after disturbance through the dynamic motion equation of the coupled pendulum, thereby analyzing the transient stability of the multi-grid-connected converter under large disturbance. The method compares the control model of the grid-connected converter with the motion model of the mechanical pendulum system, innovatively transforms the grid-connected transient stability problem of the grid-connected converter into the motion stability problem of the mechanical system, thereby avoiding the construction of complex Lyapunov functions, and at the same time, the analysis method of the coupled pendulum system can be used in electrical systems, providing new ideas for stability analysis of electrical systems.

Description

Technical Field

[0001] The invention belongs to the field of grid-connected control of multi-grid converters, and in particular relates to a coupled pendulum mapping model of a grid converter and a transient trajectory characterization method thereof. Background Art

[0002] The access of distributed renewable energy to the grid has become an inevitable trend. However, the access of a large number of intermittent and random distributed power sources to the grid has greatly increased the complexity and difficulty of control of the grid, and has had a significant impact on the safe, reliable and economic operation of the grid. How to ensure the orderly, safe, stable and flexible grid connection of renewable energy has become a major scientific issue in the field of energy and electricity.

[0003] Compared with traditional energy, new energy is usually connected to the grid through grid-connected converters. Grid-connected converters often adopt the grid-following mode, that is, they use phase-locked loops to achieve synchronous operation. Studies have shown that the stability of this operation mode is poor in weak grid scenarios. To this end, the academic community has proposed a grid-connected control mode for converters. In this mode, the converter can not only provide voltage support, but also provide necessary inertia support, so it has received widespread attention. When a high proportion of distributed new energy is connected to the grid through a grid-connected converter, its frequency coupling mechanism causes interactions between the grid and the converter and between the converters, causing various oscillation problems in the system. Especially under weak grid conditions, this interaction is more obvious, and the system is more likely to become unstable.

[0004] In recent years, researchers at home and abroad have conducted in-depth research on the transient stability of grid-connected converters under large disturbance transient events such as short-circuit faults, low voltage ride-through, and grid-on and off-grid switching. They mainly use Lyapunov function method, phase plane analysis method and equal area rule, etc. These analysis methods better reveal the oscillation mechanism of multi-machine parallel systems in specific scenarios and increase the stability of parallel operation of the system. However, the traditional method of constructing Lyapunov functions is difficult to apply to large disturbance stability analysis of multi-machine systems, and it is impossible to quantitatively characterize the phase trajectory operation characteristics of the system under large disturbance conditions. Therefore, the present invention proposes a coupled pendulum mapping model of a grid-connected converter and a transient trajectory characterization method thereof, which is suitable for the transient characteristics characterization of multi-grid converter parallel systems. Summary of the invention

[0005] The purpose of the present invention is to analyze the transient stability of multi-grid converters when a multi-grid converter parallel system encounters a large disturbance, map the power-frequency model of the traditional grid converter to the classic coupled pendulum model, and characterize the transient trajectory of the state quantity of the grid converter after the disturbance through the dynamic motion equation of the coupled pendulum, so as to analyze the transient stability of the multi-grid converter under large disturbance. This method compares the control model of the grid converter with the motion model of the mechanical pendulum system, innovatively transforms the grid-connected transient stability problem of the grid converter into the motion stability problem of the mechanical system, thereby avoiding the construction of complex Lyapunov functions, and at the same time, the analysis method of the coupled pendulum system can be used in the electrical system, providing a new idea for the stability analysis of the electrical system.

[0006] To achieve the above object, the present invention provides a coupled pendulum mapping model of a grid-connected converter and a transient trajectory characterization method thereof, which comprises the following steps:

[0007] Step S1, establishing a single grid-connected converter power frequency control model, specifically as follows:

[0008] Step S1.1, establish the main circuit structure of the grid-forming converter: a three-phase DC-AC converter circuit, with an LC filter connected in series at the converter outlet, is the filter inductor, is the filter capacitor, is the parasitic resistance of the filter inductor, is the parasitic resistance of the filter capacitor;

[0009] Step S1.2, establish the power-frequency control link of the grid-forming converter: including the active-frequency outer loop and the voltage-current inner loop; its control process is: first, collect the voltage and current at the port of the grid-forming converter, calculate its output active and reactive power, and the active-frequency outer loop generates the voltage-current loop reference voltage amplitude and phase through the power-frequency control model according to the output power; then, the voltage-current loop generates the inductor current reference value through the PI controller according to the deviation between the voltage reference value and the actual value, and the current inner loop generates the PWM modulation signal through the PI controller; finally, the grid-forming control is realized after PWM control, and the established power-frequency control model is as follows:

[0010] (1)

[0011] In the formula, To construct the internal virtual power angle of the grid converter, the internal virtual frequency And the frequency of the grid connection point The difference determines To construct the virtual inertia of the network converter, is the damping coefficient, is the droop coefficient; is the grid converter voltage amplitude reference value, is the voltage amplitude at the grid connection point; To construct the virtual impedance of the grid converter, It is the external virtual torque of the grid converter.

[0012] Step S2, establishing a single pendulum mapping model of a single grid-connected converter power-frequency model; starting from the grid-connected converter power-frequency model structure, establishing a mapping relationship between the converter model and the single pendulum model, as shown in the following formula:

[0013] (2)

[0014] In the above mapping relationship, the converter model is the power-frequency control model of equation (1), and the parameters of the simple pendulum mapping model are is the angle between the pendulum center of mass coordinate system and the vertical axis, , are the gravity acceleration of the pendulum's center of mass and the length of the pendulum line, , are the damping coefficient and non-conservative torque of the simple pendulum respectively. The parameters of the simple pendulum mapping model are derived through the above mapping relationship as follows:

[0015] (3)

[0016] In the formula, is the mass of the single pendulum center of mass. Through mapping, the transient stability problem of a single grid-connected converter is transformed into the stability problem of a mechanical pendulum system. When the entire mapping pendulum system is stable in the coordinate system or rotates at a uniform angular velocity, the power angle and frequency of the grid-connected converter are stable. From the mapping model, it can be seen that the period of the small-angle undamped free oscillation under zero excitation is , large angle undamped oscillation period , is the elliptic integral of the first kind, is the modulus of the elliptic function and is determined by the energy of the undamped oscillation of the system.

[0017] Step S3, establishing a coupled pendulum mapping model of a multi-grid converter parallel system, specifically as follows:

[0018] Step S3.1, calculation of nonlinear stability domain of grid-connected converter parallel system based on TS multi-model method: First, construct the full time domain dynamic model of the parallel system ,in, is the system state variable, is a nonlinear transfer matrix, whose internal elements contain the key time-invariant parameters of the system , including The related nonlinear terms are trigonometric functions, is the system input matrix, is the system excitation vector, , Secondly, the TS multi-model method is used to investigate the nonlinear transfer matrix The number of nonlinear terms in is , then the original nonlinear model can be equivalent to The state matrix of each linear model is ,

[0019] , and then determine whether the following nonlinear inequality equation has a solution:

[0020] (4)

[0021] in, is the feasible solution matrix. If there is a feasible solution, continue to increase the range of the stable domain and recalculate the above formula until there is no solution. The corresponding matrix That is, the nonlinear stability domain of the converter parallel system at this steady-state operating point is depicted, which is expressed as , That is, the multi-grid converter system is in state The stability domain below.

[0022] Step S3.2, parameter fitting of the single pendulum equivalent model of the parallel system based on the stable domain: First, a nonlinear single pendulum equivalent model of the parallel system is constructed and written as: The second-order differential equation of is defined as , C is the damping coefficient of the equivalent simple pendulum, D is a quantity related to the length of the cycloid of the equivalent simple pendulum, is the external non-conservative torque vector. Secondly, according to the above stable domain calculation method, the original time domain model is calculated in the key parameters and Nonlinear stability region under excitation , and the simple pendulum equivalent model in , Nonlinear stability region under the action , mapping the stability domains of the two to Phase plane, calculate the area of ​​the elliptic curve enclosed by the phase trajectory and , compare the two areas to see if they are approximately the same, if not, find a new area Until the same;

[0023] Step S3.3, coupled pendulum mapping model of multi-grid converter parallel system: Finally, the equivalent single pendulum model in step S3.2 is regarded as the power-frequency model of the grid-connected point of the parallel system. The single pendulum mapping model of each single grid converter in the system is connected to the equivalent single pendulum model to form the coupled pendulum model of the entire parallel system, as shown in the following formula:

[0024] (5)

[0025] Among them, the equivalent model of the parallel system single pendulum is the above second-order differential equation, is the angle between the parallel system grid-connected equivalent pendulum and the vertical axis, For the parallel system The angle between the coordinate system of the center of mass of a simple pendulum and the vertical axis is It is The length of the cycloid of a simple pendulum, , Respectively Damping coefficient and non-conservative torque of a simple pendulum.

[0026] Step S4, establishing a transient trajectory characterization method for a multi-grid converter parallel system, specifically as follows:

[0027] According to the coupled pendulum topology, the equivalent mass of the pendulum ball, and the length of the pendulum line, the Hamiltonian of the following system is constructed:

[0028] (6)

[0029] In the formula, is the kinetic energy of the parallel system, is the system potential energy, the Hamiltonian , Corresponding to the first The angle between the pendulum and the vertical axis is The corresponding first-order derivative is, is the total number of grid-connected converters in the system, For the The first derivative of the angle between a simple pendulum and the vertical axis, , With The equivalent mass and length of a simple pendulum are related to With Impedance and gravitational field of grid-connected converters According to the second kind of Lagrange equation, the Hamiltonian Differentiating the equation yields the following second-order nonlinear differential equation in matrix form:

[0030] (7)

[0031] in, is the angle vector between the simple pendulum in the system and the vertical axis, , , are their first and second order derivatives respectively, is the potential energy coefficient matrix, and is the coefficient matrix of the kinetic energy part, is the damping part coefficient matrix, is the external non-conservative torque vector, and equation (7) can be written as of the form, where , is the angular velocity of each pendulum in the system relative to the vertical axis, , is the time, given the initial value of the coupled pendulum system and the external non-conservative torque vector , according to the formula We can depict the The phase plane trajectory is also the transient trajectory of the multi-grid converter parallel system.

[0032] An electronic device comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the program, a coupled pendulum mapping model of a grid-connected converter and a transient trajectory characterization method thereof are implemented.

[0033] A computer-readable storage medium stores computer instructions, which, when executed by a processor, implement a coupled pendulum mapping model of a grid-connected converter and a transient trajectory characterization method thereof.

[0034] The present invention proposes a coupled pendulum mapping model of a grid-connected converter and a transient trajectory characterization method thereof for a multi-grid-connected converter parallel system. The determination of the stability of a traditional power system requires the construction of a Lyapunov function. However, Lyapunov only provides a theoretical proof, and it is extremely difficult to actually calculate the function solution of a system. In particular, when the number of system state variables is large, it is basically impossible to give a numerical solution of the Lyapunov function. To this end, this method maps the power-frequency model of the traditional grid-connected converter to the classical coupled pendulum model, and characterizes the transient trajectory of the state quantity of the grid-connected converter after the disturbance through the dynamic motion equation of the coupled pendulum, thereby analyzing the transient stability of the multi-grid-connected converter under large disturbances, avoiding the construction of complex Lyapunov functions, and simplifying the difficulty of stability analysis of the electrical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a flow chart of the present invention;

[0036] Figure 2 This is the coupled pendulum mapping diagram of the grid-connected converter. DETAILED DESCRIPTION

[0037] The present invention will be described in detail below with reference to the accompanying drawings.

[0038] Embodiment: A coupled pendulum mapping model of a grid-connected converter and a transient trajectory characterization method thereof, the process is as follows Figure 1 As shown, the specific steps include:

[0039] Step S1, establishing a power frequency control model of a single grid-connected converter;

[0040] Step S1.1, establish the main circuit structure of the grid-forming converter: a three-phase DC-AC converter circuit, with an LC filter connected in series at the converter outlet, is the filter inductor, is the filter capacitor, is the parasitic resistance of the filter inductor, is the parasitic resistance of the filter capacitor;

[0041] Step S1.2, establish the power-frequency control link of the grid-forming converter: including the active-frequency outer loop and the voltage-current inner loop; its control process is: first, collect the voltage and current at the port of the grid-forming converter, calculate its output active and reactive power, and the active-frequency outer loop generates the voltage-current loop reference voltage amplitude and phase through the power-frequency control model according to the output power; then, the voltage-current loop generates the inductor current reference value through the PI controller according to the deviation between the voltage reference value and the actual value, and the current inner loop generates the PWM modulation signal through the PI controller; finally, the grid-forming control is realized after PWM control, and the established power-frequency control model is as follows:

[0042] (1)

[0043] In the formula, To construct the internal virtual power angle of the grid converter, the internal virtual frequency And the frequency of the grid connection point The difference determines To construct the virtual inertia of the network converter, is the damping coefficient, is the droop coefficient; is the grid converter voltage amplitude reference value, is the voltage amplitude at the grid connection point; To construct the virtual impedance of the grid converter, It is the external virtual torque of the grid converter.

[0044] Step S2, establishing a simple pendulum mapping model of a single grid-connected converter power-frequency model;

[0045] In order to transform the large disturbance stability problem of the electrical system into the stability problem of the mechanical system, starting from the power-frequency model structure of the grid-connected converter, the mapping relationship between the converter model and the simple pendulum model is established as follows:

[0046] (2)

[0047] In the above mapping relationship, the converter model is the power-frequency control model of equation (1), and the parameters of the simple pendulum mapping model are is the angle between the pendulum center of mass coordinate system and the vertical axis, , are the gravity acceleration of the pendulum's center of mass and the length of the pendulum line, , are the damping coefficient and non-conservative torque of the simple pendulum respectively. The parameters of the simple pendulum mapping model are derived through the above mapping relationship as follows:

[0048] (3)

[0049] In the formula, is the mass of the single pendulum center of mass. Through mapping, the transient stability problem of a single grid-connected converter is transformed into the stability problem of a mechanical pendulum system. When the entire mapping pendulum system is stable in the coordinate system or rotates at a uniform angular velocity, the power angle and frequency of the grid-connected converter are stable. From the mapping model, it can be seen that the period of the small-angle undamped free oscillation under zero excitation is , large angle undamped oscillation period , is the elliptic integral of the first kind, is the modulus of the elliptic function, which is determined by the energy of the undamped oscillation of the system. The accuracy of the model can also be verified by comparing it with the zero-excitation oscillation period of the original grid-connected converter.

[0050] Step S3, establishing a coupled pendulum mapping model of a multi-grid converter parallel system;

[0051] In order to analyze the transient stability of multi-grid converters in parallel operation, based on the single pendulum mapping model of the single-grid converter mentioned above, an equivalent single pendulum model of the parallel system is first established. On this basis, a coupled pendulum mapping model of the multi-grid converter parallel system is constructed to provide a model basis for the subsequent transient trajectory characterization method.

[0052] Step S3.1, calculation of nonlinear stability domain of grid-connected converter parallel system based on TS multi-model method: First, construct the full time domain dynamic model of the parallel system ,in, is the system state variable, is a nonlinear transfer matrix, whose internal elements contain the key time-invariant parameters of the system , including The related nonlinear terms are trigonometric functions, is the system input matrix, is the system excitation vector, , Secondly, the TS multi-model method is used to investigate the nonlinear transfer matrix The number of nonlinear terms in is , then the original nonlinear model can be equivalent to The state matrix of each linear model is ,

[0053] , and then determine whether the following nonlinear inequality equation has a solution:

[0054] (4)

[0055] in, is the feasible solution matrix. If there is a feasible solution, continue to increase the range of the stable domain and recalculate the above formula until there is no solution. The corresponding matrix That is, the nonlinear stability domain of the converter parallel system at this steady-state operating point is depicted, which is expressed as , That is, the multi-grid converter system is in state The stability domain below.

[0056] Step S3.2, parameter fitting of the single pendulum equivalent model of the parallel system based on the stable domain: First, a nonlinear single pendulum equivalent model of the parallel system is constructed and written as: The second-order differential equation of is defined as , C is the damping coefficient of the equivalent simple pendulum, D is a quantity related to the length of the cycloid of the equivalent simple pendulum, is the external non-conservative torque vector. Secondly, according to the above stable domain calculation method, the original time domain model is calculated in the key parameters and Nonlinear stability region under excitation , and the simple pendulum equivalent model in , Nonlinear stability region under the action , mapping the stability domains of the two to Phase plane, calculate the area of ​​the elliptic curve enclosed by the phase trajectory and , compare the two areas to see if they are approximately the same, if not, find a new area Until the same;

[0057] Step S3.3, coupled pendulum mapping model of multi-grid converter parallel system: Finally, the equivalent single pendulum model in step S3.2 is regarded as the power-frequency model of the grid-connected point of the parallel system. The single pendulum mapping model of each single grid converter in the system is connected to the equivalent single pendulum model to form the coupled pendulum model of the entire parallel system, as shown in the following formula:

[0058] (5)

[0059] Among them, the equivalent model of the parallel system single pendulum is the above second-order differential equation, is the angle between the parallel system grid-connected equivalent pendulum and the vertical axis, For the parallel system The angle between the coordinate system of the center of mass of a simple pendulum and the vertical axis is It is The length of the cycloid of a simple pendulum, , Respectively The damping coefficient and non-conservative torque of a single pendulum. The coupled pendulum mapping block diagram is as follows Figure 2 As shown in the figure, a single grid-connected converter is mapped to a single pendulum. The length and mass of the pendulum are determined by the converter control parameters, as shown in formula (3). When multiple grid-connected converters are operated in parallel, the parallel system as a whole can be equivalent to a single pendulum. The length and mass of the pendulum are determined by the overall parameters of the multi-converter system. The mapped pendulums of each converter inside are connected to the equivalent pendulum.

[0060] Step S4, establishing a transient trajectory characterization method for a multi-grid converter parallel system;

[0061] Based on the mapping coupled pendulum form of the multi-machine parallel system of the above-mentioned grid-connected converter, in order to obtain the transient power-frequency trajectory curve of the multi-machine parallel system, it is proposed to describe the relationship between the power angle and the frequency under the Hamiltonian system. According to the coupled pendulum topology, the equivalent mass of the pendulum ball, and the length of the cycloid, the Hamiltonian of the following system is constructed:

[0062] (6)

[0063] In the formula, is the kinetic energy of the parallel system, is the system potential energy, the Hamiltonian , Corresponding to the first The angle between the pendulum and the vertical axis is The corresponding first-order derivative is, is the total number of grid-connected converters in the system, For the The first derivative of the angle between a simple pendulum and the vertical axis, , With The equivalent mass and length of a simple pendulum are related to With Impedance and gravitational field of grid-connected converters According to the second kind of Lagrange equation, the Hamiltonian Differentiating the equation yields the following second-order nonlinear differential equation in matrix form:

[0064] (7)

[0065] in, is the angle vector between the simple pendulum in the system and the vertical axis, , , are their first and second order derivatives respectively, is the potential energy coefficient matrix, and is the coefficient matrix of the kinetic energy part, is the coefficient matrix of the damping part, is the external non-conservative torque vector, and equation (7) can be written as of the form, where , is the angular velocity of each pendulum in the system relative to the vertical axis, , is the time, given the initial value of the coupled pendulum system and the external non-conservative torque vector , according to the formula We can depict the The phase plane trajectory is also the transient trajectory of the multi-grid converter parallel system.

[0066] It should be noted that the above embodiments are not intended to limit the protection scope of the present invention, and equivalent changes or substitutions made on the basis of the above technical solutions all fall within the protection scope of the claims of the present invention.

Claims

1. A coupled pendulum mapping model of a grid-connected converter and a transient trajectory characterization method thereof, characterized in that: The steps include: Step S1, establishing a single grid-connected converter power frequency control model, Step S2, establishing a single pendulum mapping model of a single grid-connected converter power-frequency model, Step S3, establishing a coupled pendulum mapping model for a multi-grid converter parallel system, Step S4, establishing a transient trajectory characterization method for a multi-grid converter parallel system, Among them, step S1 is to establish a single grid-connected converter power frequency control model, which is specifically as follows: Step S1.1, establish the main circuit structure of the grid-connected converter: a three-phase DC-AC converter circuit, with an LC filter connected in series at the converter outlet, L f is the filter inductor, C f is the filter capacitor, R f1 is the parasitic resistance of the filter inductor, R f2 is the parasitic resistance of the filter capacitor; Step S1.2, establish the power-frequency control link of the grid-forming converter: including the active-frequency outer loop and the voltage-current inner loop; its control process is: first, collect the voltage and current at the port of the grid-forming converter, calculate its output active and reactive power, and the active-frequency outer loop generates the voltage-current loop reference voltage amplitude and phase through the power-frequency control model according to the output power; then, the voltage-current loop generates the inductor current reference value through the PI controller according to the deviation between the voltage reference value and the actual value, and the current inner loop generates the PWM modulation signal through the PI controller; finally, the grid-forming control is realized after PWM control, and the established power-frequency control model is as follows: Where δ is the virtual power angle inside the grid-connected converter, which is determined by its internal virtual frequency ω and the grid-connected point frequency ω. n The difference is determined by J being the virtual inertia of the grid converter, ξ being the damping coefficient, and k f is the droop coefficient; E is the voltage amplitude reference value of the grid converter, U pcc is the voltage amplitude at the grid connection point; X v is the virtual impedance of the grid converter, M set It is the external virtual torque of the grid converter; Step S2, establishing a single pendulum mapping model of a single grid-connected converter power-frequency model; starting from the grid-connected converter power-frequency model structure, establishing a mapping relationship between the converter model and the single pendulum model, as shown in the following formula: In the above mapping relationship, the converter model is the power-frequency control model of formula (1), and the single pendulum mapping model parameter δ eq is the angle between the pendulum center of mass coordinate system and the vertical axis, g, l eq are the gravity acceleration of the center of mass of the pendulum and the length of the pendulum line, α and β are the damping coefficient and non-conservative torque of the pendulum, respectively. The parameters of the pendulum mapping model are derived from the above mapping relationship as follows: In the formula, m eq is the mass of the single pendulum center of mass. Through mapping, the transient stability problem of a single grid-connected converter is transformed into the stability problem of a mechanical pendulum system. When the entire mapping pendulum system is stable in the coordinate system or rotates at a uniform angular velocity, the power angle and frequency of the grid-connected converter are stable. From the mapping model, it can be seen that the period T of the small-angle undamped free oscillation under zero excitation is eq =2πsqrt(l eq / g), large angle undamped oscillation period T eq =4K(q), K is the first kind of elliptic integral, q is the modulus of the elliptic function, which is determined by the energy of the undamped oscillation of the system; Step S3, establishing a coupled pendulum mapping model of a multi-grid converter parallel system, specifically as follows: Step S3.1, calculation of nonlinear stability domain of grid-connected converter parallel system based on TS multi-model method: First, construct the full time domain dynamic model of the parallel system Among them, x is the system state variable, A is the nonlinear transfer matrix, and its internal elements contain the key time-invariant parameters μ of the system. or =[J,ξ,X v , k f ], including the nonlinear trigonometric function related to x, B is the system input matrix, U is the system excitation vector, U = [ω n , U pcc , M set ], and then, the TS multi-model method is used to examine the number of nonlinear terms in the nonlinear transfer matrix A. If it is r, then the original nonlinear model is equivalent to 2 r A combination of linear time-invariant models, the state matrix of each linear model is A j , j = 1, 2, ..., 2 r , and then determine whether the following nonlinear inequality equation has a solution: Where M is the feasible solution matrix. If there is a feasible solution, continue to increase the range of the stable domain and recalculate the above formula until there is no solution. The corresponding matrix M b The nonlinear stability domain of the converter parallel system at the steady-state operating point is characterized, which is expressed as V(x)=x T M b x, V(x) is the stability domain of the multi-grid converter system in state x, Step S3.2, parameter fitting of the single pendulum equivalent model of the parallel system based on the stable domain: First, a nonlinear single pendulum equivalent model of the parallel system is constructed and written as: The second-order differential equation is defined as μ eq =[C, D], C is the damping coefficient of the equivalent simple pendulum, D is the quantity related to the length of the equivalent simple pendulum, f is the external non-conservative torque vector, and then, according to the above stability domain calculation method, the original time domain model is calculated in the key parameter μ or and U0=[ω n , U pcc ,0] nonlinear stability region V under excitation or (0), and the simple pendulum equivalent model in μ eq , nonlinear stability region V under U0 eq (0), map the stability domains of the two onto the δ-ω phase plane, and calculate the elliptic curve area S enclosed by the phase trajectory respectively. or With S eq , compare whether the two areas are approximately the same, if not, find μ again eq Until the same; Step S3.3, coupled pendulum mapping model of multi-grid converter parallel system: Finally, the equivalent single pendulum model in step S3.2 is regarded as the power-frequency model of the grid-connected point of the parallel system. The single pendulum mapping model of each single grid converter in the system is connected to the equivalent single pendulum model to form the coupled pendulum model of the entire parallel system, as shown in the following formula: Among them, the equivalent model of the parallel system single pendulum is the above second-order differential equation, δ eq_1 is the angle between the parallel system grid-connected equivalent pendulum and the vertical axis, δ eq_i is the angle between the coordinate system of the center of mass of the i-th simple pendulum in the parallel system and the vertical axis, l eq_i is the length of the cycloid of the i-th simple pendulum, α i , β i are the damping coefficient and non-conservative moment of the ith pendulum, Step S4, establishing a transient trajectory characterization method for a multi-grid converter parallel system, specifically as follows: According to the coupled pendulum topology, the equivalent mass of the pendulum ball, and the length of the pendulum line, the Hamiltonian of the following system is constructed: In the formula, T is the kinetic energy of the parallel system, V is the potential energy of the system, Hamiltonian H = T + V, δ eq_j , j = 1, ..., n corresponds to the angle between the jth simple pendulum in the parallel system and the vertical axis, is the corresponding first-order derivative, n is the total number of grid-connected converters in the system, is the first derivative of the angle between the i-th simple pendulum and the vertical axis, G i 、N 1i It is related to the equivalent mass and length of the i-th simple pendulum, P i It is related to the impedance of the grid-connected point of the i-th grid-connected converter and the gravitational field g. According to the second-kind Lagrange equation, the Hamiltonian H is differentiated to obtain the second-order nonlinear differential equation in the following matrix form: Among them, δ is the angle vector between the simple pendulum in the system and the vertical axis, δ=[δ eq_1 , δ eq_2 , ..., δ eq_n ] T , are their first-order and second-order derivatives respectively, P is the potential energy coefficient matrix, G and N are the kinetic energy coefficient matrices, ξ is the damping coefficient matrix, and f is the external non-conservative torque vector. Equation (7) can be written as The form of , where y = [δ, ω] T , ω is the angular velocity of each simple pendulum in the system relative to the vertical axis, t is the time, given the initial value of the coupled pendulum system y0 = [δ0, ω0 ] T And the external non-conservative torque vector f, according to the formula The δ-ω phase plane trajectory of each simple pendulum can be depicted, which is also the transient trajectory of the multi-grid converter parallel system.

2. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, a coupled pendulum mapping model of a grid-connected converter and a transient trajectory characterization method thereof are implemented as described in claim 1.

3. A computer-readable storage medium having computer instructions stored thereon, characterized in that: When the computer instruction is executed by the processor, a coupled pendulum mapping model of a grid-connected converter and a transient trajectory characterization method thereof are implemented as described in claim 1.

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