A method, device and storage medium for electromechanical transient simulation of LCC-VSC hybrid DC power grid

Abstract

The present invention discloses a method, device and storage medium for electromechanical transient simulation of a LCC-VSC hybrid DC power grid, the method comprising: constructing a dynamic model of a hybrid DC power grid according to the characteristics of dynamic components of the hybrid DC power grid and the network topology; constructing a differential equation group corresponding to the dynamic model of the hybrid DC power grid according to a preset simulation step size; constructing a Jacobian matrix according to the partial derivatives of the hybrid DC power grid state variables of the differential equation group; using the Newton-Raphson method to iteratively solve the differential equation group at the current simulation moment, continuously updating the variable elements in the differential equation group and the Jacobian matrix during the iteration process until convergence; obtaining the state variables of the hybrid DC power grid at the next simulation moment according to the solution results of the differential equation group at the current simulation moment. The present invention can improve the calculation accuracy and efficiency of electromechanical transient simulation of the LCC-VSC hybrid DC power grid as a whole, and meet the requirements of engineering applications.

Description

Technical Field

[0001] The present invention relates to an electromechanical transient simulation method, device and storage medium for an LCC-VSC hybrid DC power grid, and belongs to the technical field of power system automation. Background Art

[0002] Grid-commutated converter HVDC systems (LCC-HVDC) offer advantages such as large transmission capacity, low operating losses, and mature and reliable technology. However, they suffer from limitations such as inverter station commutation failure, inability to power weak AC systems, and the need for significant reactive power consumption during operation. Voltage-source converter HVDC systems (VSC-HVDC, with MMC-HVDC being the most widely used) offer advantages such as flexible control, small compensation and filtering capacity, no commutation failures, and ease of forming multi-terminal networks. However, they suffer from limitations such as low transmission capacity, high operating losses, and high construction costs. The construction of an LCC-VSC hybrid DC grid, using LCC-HVDC to achieve stable long-distance, high-capacity power transmission and VSC-HVDC to aggregate distributed renewable energy, will interconnect and integrate the two, complementing each other's strengths and becoming a highly promising form of DC grid development for the future.

[0003] Due to limitations in computing power and data parameters, electromechanical transient simulation, compared to electromagnetic transient simulation, is currently the primary method for analyzing the safety and stability of large power grids. Due to the rapid dynamic response of DC-side capacitors and inductors, AC / DC hybrid power grids exhibit significantly different response speeds. To balance computational efficiency and accuracy, the mainstream approach for electromechanical transient simulation of AC / DC hybrid power grids is to use a larger step size (h = 0.01s) for AC power grids and a smaller step size (h / 10 to h / 4) for DC power grids. Alternating iterative solutions are the current mainstream approach.

[0004] For simulation calculations within the DC grid, since the interface between the converter and the DC network contains nonlinear equations, the existing solution steps are as follows:

[0005] 1) Assume that the DC voltage U d Calculate the current I injected into the DC network by the converter d ;

[0006] 2) Solve the DC network differential equations according to Id and update U d ;

[0007] 3) Repeat step 1) and step 2) until U d The iteration error is less than the threshold.

[0008] That is, the existing method is to linearize the original equation and use a simple iterative method to alternately solve the dynamic equations on both sides of the interface. However, the handover error caused by the alternating iteration in a complex multi-terminal DC power grid may lead to slow convergence or even no convergence. Summary of the Invention

[0009] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method, device and storage medium for electromechanical transient simulation of an LCC-VSC hybrid DC power grid. The method solves the technical problem that when solving the nonlinear equations of the DC power grid in electromechanical transient simulation, the handover error caused by alternating iteration in a complex multi-terminal DC power grid may lead to slow convergence or even no convergence.

[0010] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0011] In a first aspect, the present invention provides a method for simulating electromechanical transients in an LCC-VSC hybrid DC power grid, the method comprising:

[0012] Construct a dynamic model of the hybrid DC grid based on the dynamic component characteristics and network topology of the hybrid DC grid;

[0013] Constructing a set of differential equations corresponding to the dynamic model of the hybrid DC grid according to a preset simulation step size;

[0014] Constructing the Jacobian matrix based on the partial derivatives of the hybrid DC grid state variables in the differential equations;

[0015] The Newton-Raphson method is used to iteratively solve the difference equations at the current simulation moment. During the iteration process, the variable elements in the difference equations and the Jacobian matrix are continuously updated until convergence;

[0016] According to the solution results of the differential equation group at the current simulation moment, the state variables of the hybrid DC power grid at the next simulation moment are obtained.

[0017] Furthermore, before constructing the dynamic model of the hybrid DC grid, a circuit equivalent transformation is performed on the hybrid DC grid.

[0018] Furthermore, the hybrid DC grid dynamic model includes a DC line dynamic model, an LCC converter DC side dynamic model, and a VSC converter DC side dynamic model.

[0019] Furthermore, the DC line dynamic model is described by equation (1):

[0020]

[0021] Among them, R i,j 、L i,j , I i,jare the equivalent resistance, equivalent inductance and current flowing through the DC line respectively; t represents time; V i 、V j are the DC voltages at nodes i and j at both ends of the DC line respectively; the positive direction of the DC line current flows from i to j, i<j;

[0022] The dynamic model of the DC side of the LCC converter is described by equations (2) to (4):

[0023]

[0024]

[0025]

[0026] Among them, U i is the DC side voltage of the LCC converter; L i is a smoothing reactor; X i is the equivalent impedance of the LCC converter; I i The current injected into the DC link by the LCC converter; C i , I c,i are the equivalent ground capacitance of node i and the current flowing through it; S i is the set of DC lines connected to node i; g i 、h i S i Current, head-end node, and end-end node of the DC line, g i <h i ; is the direction factor, if i=g i but otherwise

[0027] The dynamic model of the VSC converter DC side is described by equations (5) to (7):

[0028] V j I j =P j (5)

[0029]

[0030]

[0031] Where: C j , I c,j are the equivalent ground capacitance of node j and the current flowing through it; I j The current injected into the DC line by the VSC converter; S jis the set of DC lines connected to node j; g j 、h j S j Current, head-end node, and end-end node of the DC line, g j <h j ; is the direction factor, if j = g j ,but otherwise P j The power injected into the DC link by the VSC converter.

[0032] Furthermore, the difference equations include:

[0033] DC line difference equation:

[0034]

[0035] The differential equations of the DC side of the LCC converter are:

[0036]

[0037]

[0038]

[0039] The differential equations of the VSC converter DC side are:

[0040]

[0041]

[0042]

[0043] Where Δt is the preset time interval, n and n+1 represent time n and time n+1, respectively. The subscripts n and n+1 added to each parameter represent the value of the parameter at time n and time n+1, respectively.

[0044] Furthermore, the following method is used to sort rows and columns when constructing the Jacobian matrix:

[0045] The row order corresponds to the order of the differential equations, which are DC line differential equation (8), LCC converter DC side differential equation (9), LCC converter DC side differential equation (10), VSC converter DC side differential equation (13), LCC converter DC side differential equation (11), VSC converter DC side differential equation (14), VSC converter DC side differential equation (12);

[0046] The column sorting corresponds to the sorting of the hybrid DC grid state variables, which are the current flowing through the DC line, the DC voltage at the end node of the DC line connected to the LCC converter, the current in the ground capacitance branch of the DC line node, the current injected into the DC line by the LCC converter, the current injected into the DC line by the VSC converter, and the DC voltage at the end node of the DC line connected to the VSC converter.

[0047] Furthermore, the DC side voltage U i Use formula (15) to calculate:

[0048]

[0049] Where, E i is the AC voltage measured by the LCC converter, α i is the control trigger angle of the LCC converter.

[0050] In a second aspect, an electromechanical transient simulation device for an LCC-VSC hybrid DC power grid includes:

[0051] Dynamic model building unit: used to build a dynamic model of the hybrid DC grid according to the dynamic component characteristics and network topology of the hybrid DC grid;

[0052] A differential equation group construction unit: used for constructing a differential equation group corresponding to the hybrid DC grid dynamic model according to a preset simulation step size;

[0053] Jacobian matrix construction unit: used to construct the Jacobian matrix according to the partial derivatives of the hybrid DC grid state variables of the difference equation system;

[0054] Iterative solution unit: used to iteratively solve the differential equations at the current simulation moment using the Newton-Raphson method. During the iteration process, the variable elements in the differential equations and the Jacobian matrix are continuously updated until convergence;

[0055] Acquisition unit: used to obtain the state variables of the hybrid DC power grid at the next simulation moment based on the solution results of the differential equation group at the current simulation moment.

[0056] In a third aspect, the present invention further provides an electromechanical transient simulation device for an LCC-VSC hybrid DC power grid, comprising a processor and a storage medium;

[0057] The storage medium is used to store instructions;

[0058] The processor is configured to operate according to the instruction to execute the steps of the electromechanical transient simulation method for the LCC-VSC hybrid DC grid according to any one of the first aspects.

[0059] In a fourth aspect, the present invention further provides a computer-readable storage medium having a computer program stored thereon, characterized in that when the program is executed by a processor, the steps of the electromechanical transient simulation method of the LCC-VSC hybrid DC power grid described in any one of the first aspects are implemented.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] The electromechanical transient simulation method for an LCC-VSC hybrid DC power grid provided by the present invention uses the Newton-Raphson method to iteratively solve the differential equation group at the current simulation moment. During the iteration, the variable elements in the differential equation group and the Jacobian matrix are continuously updated, thereby improving convergence stability. Since the Jacobian matrix is ​​constructed and obtained based on the partial derivatives of the hybrid DC power grid state variables in the differential equation group, only a small number of matrix elements are variables. Therefore, only a small number of variable elements in the Jacobian matrix need to be updated during each iterative solution, which greatly reduces the amount of calculation. This can improve the calculation accuracy and efficiency of the electromechanical transient simulation of the LCC-VSC hybrid DC power grid as a whole, meeting the requirements of engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 This is a flow chart of a method for electromechanical transient simulation of an LCC-VSC hybrid DC power grid provided by an embodiment of the present invention;

[0063] Figure 2 is an equivalent circuit diagram of an LCC-VSC hybrid DC grid provided by an embodiment of the present invention;

[0064] Figure 3 This is a circuit diagram of an LCC-VSC three-terminal hybrid DC grid provided by an embodiment of the present invention;

[0065] Figure 4 is based on Figure 3 The circuit diagram provided constructs a sorted graph of the Jacobian matrix. DETAILED DESCRIPTION

[0066] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0067] Example 1:

[0068] See Figure 1 The embodiment of the present invention provides an electromechanical transient simulation method for an LCC-VSC hybrid DC power grid, which is used to simulate and obtain state variables of the hybrid DC power grid at the next simulation time. The method specifically includes the following steps:

[0069] Step A: constructing a dynamic model of the hybrid DC grid based on the dynamic component characteristics and network topology of the hybrid DC grid;

[0070] In the embodiment of the present invention, before constructing the dynamic model of the hybrid DC grid, the hybrid DC grid circuit can be equivalently transformed to divide the circuit structure into three parts: the DC side of the LCC converter, the DC line, and the DC side of the VSC converter. Figure 2 , which is an equivalent circuit diagram of a hybrid DC grid provided by an embodiment of the present invention. Corresponding dynamic models can be constructed for the DC side of the LCC converter, the DC line, and the DC side of the VSC converter.

[0071] like Figure 2 As shown, the dynamic model of the DC line can be described by equation (1):

[0072]

[0073] Among them, R i,j 、L i,j , I i,j are the equivalent resistance, equivalent inductance and current flowing through the DC line respectively; t represents time; V i 、V j are the DC voltages at nodes i and j at both ends of the DC line respectively. The positive direction of the DC line current flows from i to j.

[0074] The dynamic model of the DC side of the LCC converter can be described by equations (2) to (4):

[0075]

[0076]

[0077]

[0078] Among them, U i is the DC side voltage of the LCC converter; L i is a smoothing reactor; X i is the equivalent impedance of the LCC converter; I i The current injected into the DC link by the LCC converter; C i , I c,i are the equivalent ground capacitance of node i and the current flowing through it; S i is the set of DC lines connected to node i; g i 、h i S i Current, head-end node, and end-end node of the DC line, g i <h i ; is the direction factor, if i=g i but otherwise

[0079] The dynamic model of the DC side of the VSC converter can be described by equations (5) to (7):

[0080] V j I j =P j (5)

[0081]

[0082]

[0083] Where: C j , I c,j are the equivalent ground capacitance of node j and the current flowing through it; I j The current injected into the DC line by the VSC converter; S j is the set of DC lines connected to node j; g j 、h j S j Current, head-end node, and end-end node of the DC line, g j <h j ; is the direction factor, if j = g j ,but otherwise P j The power injected into the DC link by the VSC converter.

[0084] Step B: constructing a group of differential equations corresponding to the dynamic model of the hybrid DC grid according to a preset simulation step size;

[0085] The corresponding differential equations for the DC line dynamic model, the LCC converter DC side dynamic model, and the VSC converter DC side dynamic model include: the DC line differential equation, the LCC converter DC side differential equation, and the VSC converter DC side differential equation. This embodiment of the present invention uses an implicit trapezoidal integration method to convert the DC grid dynamic differential equation into a differential equation system, specifically including:

[0086] DC line difference equation:

[0087]

[0088] The differential equations of the DC side of the LCC converter are:

[0089]

[0090]

[0091]

[0092] The differential equations of the VSC converter DC side are:

[0093]

[0094]

[0095]

[0096] Where Δt is the preset time interval (i.e., simulation step size), n and n+1 represent time n and time n+1, respectively; the subscripts n and n+1 added to each parameter represent the value of the parameter corresponding to time n and time n+1, respectively.

[0097] Step C: constructing a Jacobian matrix based on the partial derivatives of the hybrid DC grid state variables of the differential equation system;

[0098] In vector calculus, the Jacobian matrix is ​​a matrix in which first-order partial derivatives are arranged in a certain way. Its determinant is called the Jacobian determinant. The importance of the Jacobian matrix lies in that it represents the optimal linear approximation of a differentiable equation to a given point. Therefore, the Jacobian matrix is ​​similar to the derivative of a multivariate function.

[0099] As an embodiment of the present invention, the following method can be used to perform row sorting and column sorting when constructing the Jacobian matrix:

[0100] The row order corresponds to the order of the differential equations, which are DC line differential equation (8), LCC converter DC side differential equation (9), LCC converter DC side differential equation (10), VSC converter DC side differential equation (13), LCC converter DC side differential equation (11), VSC converter DC side differential equation (14), VSC converter DC side differential equation (12);

[0101] The column sorting corresponds to the sorting of the hybrid DC grid state variables, which are the current flowing through the DC line, the DC voltage at the end node of the DC line connected to the LCC converter, the current in the ground capacitance branch of the DC line node, the current injected into the DC line by the LCC converter, the current injected into the DC line by the VSC converter, and the DC voltage at the end node of the DC line connected to the VSC converter.

[0102] like Figure 3 As shown in the figure, taking the LCC-VSC three-terminal hybrid DC grid as an example, the three-terminal hybrid DC grid includes a DC network, an LCC converter and two VSC converters; the DC network includes three DC lines, corresponding to three nodes, which can be recorded as nodes 1, 2, and 3 respectively, where node 1 is connected to the LCC converter, and nodes 2 and 3 are connected to the two VSC converters respectively. Figure 3 For the hybrid DC grid shown in Figure 1, the following methods can be used to sort the Jacobian matrix rows and columns:

[0103] The rows are sorted as:

[0104] Group 1: Rows (1) to (3) correspond to equation (8);

[0105] Group 2: Row (4) corresponds to equation (9);

[0106] Group 3: Rows (5) to (7) correspond to equations (10) and (13);

[0107] Group 4: Rows (8) to (10) correspond to equations (11) and (14);

[0108] Group 5: Rows (11) to (12) correspond to equation (12);

[0109] The columns are sorted as:

[0110] Group 1: Columns (1) to (3) correspond to DC line currents Partial derivatives;

[0111] Group 2: Column (4) corresponds to the DC voltage of the LCC converter Partial derivatives;

[0112] Group 3: Columns (5) to (7) correspond to the converter-to-ground capacitance branch current Partial derivatives;

[0113] Group 4: Column (8) corresponds to the DC network current injected by the LCC converter Partial derivatives;

[0114] Group 5: Columns (9) to (10) correspond to the VSC converters injecting DC network current Partial derivatives;

[0115] Group 6: Columns (11) to (12) correspond to the VSC converter DC point voltage Partial derivative.

[0116] It should be noted that the row ordering and column ordering described above are only a preferred ordering method of the Jacobian matrix in this embodiment. In the present invention, the Jacobian matrix can also be ordered in other ways.

[0117] like Figure 4 As shown, it is for Figure 3 The Jacobian matrix of the constructed three-terminal hybrid DC grid is: Figure 4 The middle box a shows the main diagonal elements of the Jacobian matrix, and the values ​​of the main diagonal elements are relatively large; except Figure 4 The matrix elements circled in box b Except for the variable, the rest of the matrix elements are constants.

[0118] Step D: Use the Newton-Raphson method to iteratively solve the difference equations at the current simulation moment. During the iteration process, the variable elements in the difference equations and the Jacobian matrix are continuously updated until convergence;

[0119] The Newton-Raphson method is a method for approximately solving equations in the real and complex domains. It uses the first few terms of the Taylor series of a function to find the roots of the equation. Its greatest advantage is that it has quadratic convergence near a single root of the equation.

[0120] It should be noted that the main diagonal elements of the Jacobian matrix generated by the sorting method in step C are relatively large; only the first calculation requires full matrix LU factorization; subsequent calculations only require updating some elements of the Jacobian matrix (such as Figure 4 The matrix element circled by box b in the lower right corner ) and its corresponding LU factor.

[0121] In this embodiment, the “next simulation time” can be understood as time n+1, time n is recorded as the current simulation time, and the time interval between time n+1 and time n is Δt.

[0122] Step E: According to the solution results of the differential equation group at the current simulation time, the state variables of the hybrid DC power grid at the next simulation time are obtained.

[0123] The electromechanical transient simulation method for an LCC-VSC hybrid DC power grid provided by the present invention uses the Newton-Raphson method to iteratively solve the differential equation group at the current simulation moment. During the iteration, the variable elements in the differential equation group and the Jacobian matrix are continuously updated, thereby improving convergence stability. Since the Jacobian matrix is ​​constructed and obtained based on the partial derivatives of the hybrid DC power grid state variables in the differential equation group, only a small number of matrix elements are variables. Therefore, only a small number of variable elements in the Jacobian matrix need to be updated during each iterative solution, which greatly reduces the amount of calculation. This can improve the calculation accuracy and efficiency of the electromechanical transient simulation of the LCC-VSC hybrid DC power grid as a whole, meeting the requirements of engineering applications.

[0124] Example 2:

[0125] An embodiment of the present invention provides an electromechanical transient simulation device for an LCC-VSC hybrid DC power grid, comprising:

[0126] Dynamic model building unit: used to build a dynamic model of the hybrid DC grid according to the dynamic component characteristics and network topology of the hybrid DC grid;

[0127] A differential equation group construction unit: used for constructing a differential equation group corresponding to the hybrid DC grid dynamic model according to a preset simulation step size;

[0128] Jacobian matrix construction unit: used to construct the Jacobian matrix according to the partial derivatives of the hybrid DC grid state variables of the difference equation system;

[0129] Iterative solution unit: used to iteratively solve the differential equations at the current simulation moment using the Newton-Raphson method. During the iteration process, the variable elements in the differential equations and the Jacobian matrix are continuously updated until convergence;

[0130] Acquisition unit: used to obtain the state variables of the hybrid DC power grid at the next simulation moment based on the solution results of the differential equation group at the current simulation moment.

[0131] The device provided in the embodiment of the present invention can be used to implement the simulation method described in the first embodiment. The specific implementation method of each unit in the device to realize the corresponding function can refer to the description of the corresponding part of the first embodiment.

[0132] Example 3:

[0133] An embodiment of the present invention further provides an electromechanical transient simulation device for an LCC-VSC hybrid DC power grid, comprising a processor and a storage medium;

[0134] The storage medium is used to store instructions;

[0135] The processor is configured to operate according to the instructions to execute the steps of the electromechanical transient simulation method of the LCC-VSC hybrid DC grid described in the first embodiment.

[0136] Example 4:

[0137] An embodiment of the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein when the program is executed by a processor, the program implements the steps of the electromechanical transient simulation method of the LCC-VSC hybrid DC power grid described in Example 1.

[0138] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0139] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0140] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0141] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 The steps for the function specified in one or more boxes.

[0142] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for simulating electromechanical transient state of a LCC-VSC hybrid DC power grid, characterized in that: The method comprises: Constructing a hybrid DC grid dynamic model according to the dynamic component characteristics of the hybrid DC grid and the network topology, wherein the hybrid DC grid dynamic model includes a DC line dynamic model, a DC side dynamic model of an LCC converter, and a DC side dynamic model of a VSC converter; Constructing a differential equation group corresponding to the hybrid DC power grid dynamic model according to a preset simulation step size, wherein the differential equation group includes a DC line differential equation, a DC side differential equation group of the LCC converter, and a DC side differential equation group of the VSC converter; According to the partial derivatives of the hybrid DC power grid state variables of the difference equation group, the Jacobian matrix is ​​constructed; The Newton-Raphson method is used to iteratively solve the differential equations at the current simulation time. During the iteration, the variable elements in the differential equations and the Jacobian matrix are continuously updated until convergence. According to the solution results of the differential equation group at the current simulation time, the state variables of the hybrid DC power grid at the next simulation time are obtained; The DC line dynamic model is described by equation (1): （1） in, , , are the equivalent resistance, equivalent inductance and current flowing through the DC line respectively; t represents time; , They are the nodes at both ends of the DC line. , The positive direction of the DC line current is determined by Flow direction , ; The dynamic model of the DC side of the LCC converter is described by equations (2) to (4): （2） （3） （4） in, is the DC side voltage of the LCC converter; It is a smoothing reactor; is the equivalent impedance of the LCC converter; The current injected into the DC line for the LCC converter; , Node Equivalent capacitance to ground and the current flowing through it; Same node A collection of connected DC lines; , g i 、h i They are The current, the first end node, and the terminal node of the DC line. ; is the direction factor, if but =1, otherwise =-1; The dynamic model of the VSC converter DC side is described by equations (5) to (7): （5） （6） （7） in: , are the equivalent capacitance to ground of node j and the current flowing through it; The current injected into the DC line for the VSC converter; is the set of DC lines connected to node j; , , They are The current, the first end node, and the terminal node of the DC line. ; is the direction factor, if ,but =1, otherwise =-1; The power injected into the DC link is fed into the VSC converter.

2. The electromechanical transient simulation method of the LCC-VSC hybrid DC power grid according to claim 1 is characterized in that: Before constructing the dynamic model of the hybrid DC grid, the hybrid DC grid is subjected to circuit equivalent transformation.

3. The electromechanical transient simulation method of the LCC-VSC hybrid DC power grid according to claim 1 is characterized in that: The difference equations include: DC line difference equation: （8） The differential equations of the DC side of the LCC converter are: （9） （10） （11） The differential equations of the VSC converter DC side are: （12） （13） （14） In the formula, is a preset time interval, n and n+1 represent time n and time n+1 respectively; each parameter is marked with n and n+1 to represent the value of the parameter corresponding to time n and time n+1 respectively.

4. The electromechanical transient simulation method of the LCC-VSC hybrid DC power grid according to claim 3 is characterized in that: The following method is used to sort rows and columns when constructing the Jacobian matrix: The row order corresponds to the order of the differential equation group, which is DC line differential equation (8), LCC converter DC side differential equation (9), LCC converter DC side differential equation (10), VSC converter DC side differential equation (13), LCC converter DC side differential equation (11), VSC converter DC side differential equation (14), VSC converter DC side differential equation (12); The column sorting corresponds to the sorting of the state variables of the hybrid DC grid, which are the current flowing through the DC line, the DC voltage of the end node on the side where the DC line is connected to the LCC converter, the current of the DC line node to ground capacitance branch, the current injected into the DC line by the LCC converter, the current injected into the DC line by the VSC converter, and the DC voltage of the end node on the side where the DC line is connected to the VSC converter.

5. The electromechanical transient simulation method of the LCC-VSC hybrid DC power grid according to claim 1 is characterized in that: LCC converter DC side voltage Use formula (15) to calculate: （15） In the formula, Measure the AC voltage of the LCC converter. is the control trigger angle of the LCC converter.

6. An electromechanical transient simulation device for a LCC-VSC hybrid DC power grid, characterized in that: include: A dynamic model building unit: used to build a hybrid DC grid dynamic model according to the dynamic component characteristics of the hybrid DC grid and the network topology, wherein the hybrid DC grid dynamic model includes a DC line dynamic model, a LCC converter DC side dynamic model and a VSC converter DC side dynamic model; A differential equation group construction unit: used to construct a differential equation group corresponding to the hybrid DC power grid dynamic model according to a preset simulation step size, wherein the differential equation group includes a DC line differential equation, a DC side differential equation group of the LCC converter, and a DC side differential equation group of the VSC converter; Jacobian matrix construction unit: used to construct the Jacobian matrix according to the partial derivatives of the hybrid DC power grid state variables of the difference equation group; Iterative solution unit: used to iteratively solve the differential equations at the current simulation time using the Newton-Raphson method. During the iteration process, the variable elements in the differential equations and the Jacobian matrix are continuously updated until convergence; Acquisition unit: used to obtain the state variables of the hybrid DC power grid at the next simulation moment according to the solution results of the differential equation group at the current simulation moment; The DC line dynamic model is described by equation (1): （1） in, , , are the equivalent resistance, equivalent inductance and current flowing through the DC line respectively; t represents time; , They are the nodes at both ends of the DC line. , The positive direction of the DC line current is determined by Flow direction , ; The dynamic model of the DC side of the LCC converter is described by equations (2) to (4): （2） （3） （4） in, is the DC side voltage of the LCC converter; It is a smoothing reactor; is the equivalent impedance of the LCC converter; The current injected into the DC line for the LCC converter; , Node Equivalent capacitance to ground and the current flowing through it; Same node A collection of connected DC lines; , g i 、h i They are The current, the first end node, and the terminal node of the DC line. ; is the direction factor, if but =1, otherwise =-1; The dynamic model of the VSC converter DC side is described by equations (5) to (7): （5） （6） （7） in: , are the equivalent capacitance to ground of node j and the current flowing through it; The current injected into the DC line for the VSC converter; is the set of DC lines connected to node j; , , They are The current, the first end node, and the terminal node of the DC line. ; is the direction factor, if ,but =1, otherwise =-1; The power injected into the DC link is fed into the VSC converter.

7. An electromechanical transient simulation device for a LCC-VSC hybrid DC power grid, characterized in that: including processor and storage medium; The storage medium is used to store instructions; the processor is used to operate according to the instructions to execute the steps of the method according to any one of claims 1 to 5.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method described in any one of claims 1 to 5 are implemented.

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