Direct-current interconnected power grid secondary frequency modulation method and system considering same-frequency control

Abstract

The invention discloses a direct current interconnected power grid secondary frequency modulation method and system considering same-frequency control, and relates to the field of power system operation control, and the method comprises the steps: building a same-frequency control model of a direct current line based on the actual measurement parameters of the direct current line; based on the same-frequency control model, establishing a state-space equation of secondary frequency modulation control of the direct-current interconnected power grid, and performing discretization processing; based on the discretized state-space equation, establishing a secondary frequency modulation online optimization model based on model predictive control; solving the optimization model on line to obtain secondary frequency modulation instructions of the power grids at the sending end and the receiving end; according to the method, accurate modeling of the power interaction characteristic and the direct-current power response characteristic of the interconnected power grid can be realized, so that control resources and direct-current power control in power grid partitions at the two ends can be coordinated, and the secondary frequency modulation control effect is improved.

Description

Technical Field

[0001] The present invention relates to the field of power system operation control, and in particular to a method and system for secondary frequency regulation of a DC interconnected power grid considering same-frequency control. Background Art

[0002] In the context of asynchronous DC interconnection, the frequencies of the various sub-regional power grids are decoupled, resulting in a reduction in the rotational inertia of the grid within the sub-region and a weakening of its frequency regulation capability. This phenomenon is more pronounced in the weaker grid structure of the sending-end grid, creating a particularly serious frequency security issue. To achieve mutual power support between asynchronous sub-regional power grids and enhance the frequency support capability of the interconnected grid, additional control strategies are required for DC lines. These strategies modify the transmission power setpoint based on frequency measurements at both ends to achieve cross-regional power support.

[0003] Among them, co-frequency control is a type of DC control strategy. This control method collects the frequency difference between the two ends and generates a power increment through PI control to simulate the cross-region power support of the AC line. It can achieve near-synchronous operation of the DC power grids at both ends, thereby improving the overall anti-disturbance capability of the interconnected power grid. However, under this control mode, the frequencies of the sending and receiving power grids are deeply coupled, which also brings new challenges to the secondary frequency control of the interconnected power grid. The existing secondary frequency control mode does not consider the power interaction behavior of the two end power grids under the DC co-frequency control strategy. It cannot achieve the mutual coordination of the control resources of each zone and the DC power regulation, which is not conducive to the safe and economic operation of the interconnected power grid. Summary of the Invention

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

[0005] Therefore, the technical problem solved by the present invention is: how to overcome the problem of poor frequency regulation effect caused by the failure to coordinate the control resources of the power grids at both ends and the DC power regulation in the existing secondary frequency regulation method under the DC co-frequency control strategy.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] In a first aspect, an embodiment of the present invention provides a method for secondary frequency regulation of a DC interconnected power grid considering co-frequency control, comprising:

[0008] Based on the measured parameters of the DC line, a frequency synchronization control model of the DC line is established;

[0009] The control model collects the frequency difference of the power grid at both ends, generates power increment through PI control, and simulates the power support of the AC line, which is expressed as:

[0010]

[0011] Where, ΔP dcis the transmission power increment of the DC line under the same frequency control strategy; Δf s is the frequency deviation of the sending-end grid, Δf r is the frequency deviation of the receiving power grid; T dc represents the time constant of the DC control dynamic link, s is the Laplace operator; K P and K I is the PI control parameter, K P is the proportional control parameter, K I is the integral control parameter;

[0012] Based on the same-frequency control model, the state space equation of the secondary frequency regulation control of the DC interconnected power grid is established and discretized.

[0013] Based on the discretized state space equation, an online optimization model of quadratic frequency modulation based on model predictive control is established;

[0014] The optimization model is solved online to obtain secondary frequency regulation instructions of the sending-end and receiving-end power grids.

[0015] As a preferred solution for the secondary frequency regulation method of the DC interconnected power grid considering co-frequency control, wherein:

[0016] The state space equation comprehensively considers the frequency response characteristics of the power grids at both ends and the power response characteristics of the DC line, and is expressed as:

[0017]

[0018] Where x(t) represents the state vector, represents the first-order derivative of the state vector x(t) with respect to time t; u(t) represents the control input vector, and w(t) represents the disturbance vector; represents the state matrix, represents the control input matrix, represents the perturbation input matrix.

[0019] As a preferred solution for the secondary frequency regulation method of the DC interconnected power grid considering co-frequency control, wherein:

[0020] The discretization process includes:

[0021] Assume the control period is T c , based on the zero-order hold method, the state space equation in the discrete time domain is obtained as follows:

[0022] x n+1 =Ax n +B u u n +B w w n

[0023] Where x n ,u n , w n They represent the state vector, control input vector, and disturbance vector in discrete time domain, respectively, x n+1 Indicates the state vector at the next moment, i.e., moment n+1, relative to the current time index n in the discrete time domain; n represents the time index in the discrete time domain; A, B u , B w They represent the state matrix, control input matrix, and disturbance input matrix in the discrete time domain respectively.

[0024] As a preferred solution for the secondary frequency regulation method of the DC interconnected power grid considering co-frequency control, wherein:

[0025] The establishment of a quadratic frequency modulation online optimization model based on model predictive control based on the discretized state space equation includes:

[0026] The optimization model aims to minimize the regional control error and regulation cost of the power grid at both ends, and the constraints include state space equations, state variable constraints, and control variable constraints.

[0027] As a preferred solution for the secondary frequency regulation method of the DC interconnected power grid considering co-frequency control, wherein:

[0028] The online solving of the optimization model to obtain the secondary frequency regulation instructions of the sending-end and receiving-end power grids includes:

[0029] Parameter initialization: Measure the state values of the sending and receiving power grids and DC lines to construct the initial state vector x0; input the future N p The perturbation power vector of the step

[0030] The initial state vector x0 includes the frequency deviation of the sending and receiving power grids, the synchronous machine valve opening increment, the output power increment, and the integral control increment and transmission power increment of the DC line.

[0031] As a preferred solution for the secondary frequency regulation method of the DC interconnected power grid considering co-frequency control, wherein:

[0032] The online solving of the optimization model to obtain secondary frequency regulation instructions of the sending-end and receiving-end power grids further includes:

[0033] Solve the optimization model: the optimization variables include the future N c The control input vector of the step and future N p The predicted state vector of the step

[0034] As a preferred solution for the secondary frequency regulation method of the DC interconnected power grid considering co-frequency control, wherein:

[0035] The online solving of the optimization model to obtain secondary frequency regulation instructions of the sending-end and receiving-end power grids further includes:

[0036] Apply the optimization results: Take out the elements of the control input vector u0 of the first step in the optimization results Control resources sent to the sending and receiving power grids, and They represent the sending-end and receiving-end power grid control instructions respectively.

[0037] In a second aspect, an embodiment of the present invention provides a DC interconnected power grid secondary frequency regulation system considering co-frequency control, including:

[0038] A co-frequency control model building module is used to build a co-frequency control model for the DC line based on the measured parameters of the DC line;

[0039] The state equation establishment module is used to establish the state space equation of the secondary frequency regulation control of the DC interconnected power grid based on the same frequency control model and perform discretization processing;

[0040] The optimization model building module is used to build an online optimization model for quadratic frequency modulation based on model predictive control based on the discretized state space equation;

[0041] The frequency regulation instruction acquisition module is used to solve the optimization model online to obtain the secondary frequency regulation instructions of the sending-end and receiving-end power grids.

[0042] In a third aspect, an embodiment of the present invention provides a computing device, including:

[0043] memory and processor;

[0044] The memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions. When the one or more programs are executed by the one or more processors, the one or more processors implement the secondary frequency regulation method for a DC interconnected power grid considering co-frequency control as described in any embodiment of the present invention.

[0045] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the secondary frequency modulation method of a DC interconnected power grid considering co-frequency control.

[0046] Beneficial effects of the present invention: The secondary frequency regulation method of the DC interconnected power grid established by the present invention takes into account the same-frequency control strategy of the DC line. The control strategy collects the frequency difference of the power grids at both ends and generates a power increment through PI control to simulate the cross-regional power support behavior of the AC line, thereby realizing the approximate synchronous operation of the DC power grids at both ends; the present invention combines the frequency regulation models of the sending-end and receiving-end power grids and the power control model of the DC line to establish a state space equation and perform discretization processing, which can realize accurate modeling of the power interaction characteristics of the interconnected power grid and the power regulation characteristics of the DC line, and provide a model basis for online optimization control; the present invention performs secondary frequency regulation control based on model predictive control technology, and the goal of the online optimization model is to minimize the regional control error and regulation cost of the power grids at both ends. The constraints include state equations, state variable constraints and control variable constraints. By solving the optimization model online, the optimal secondary frequency regulation control of the DC interconnected power grid can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0048] Figure 1 This is an overall flow chart of the secondary frequency modulation method for a DC interconnected power grid considering co-frequency control according to the present invention. DETAILED DESCRIPTION

[0049] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, the following detailed description of the specific embodiments of the present invention is given in conjunction with the accompanying drawings. It is obvious that the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in this field without creative work should fall within the scope of protection of the present invention.

[0050] Example 1, with reference to Figure 1 , which is the first embodiment of the present invention, provides a method for secondary frequency regulation of a DC interconnected power grid considering co-frequency control, comprising:

[0051] S1: Based on the measured parameters of the DC line, a frequency synchronization control model of the DC line is established;

[0052] S2: Based on the same-frequency control model, the state space equation of the secondary frequency regulation control of the DC interconnected power grid is established and discretized;

[0053] S3: Based on the discretized state space equation, an online optimization model for quadratic frequency modulation based on model predictive control is established;

[0054] S4: Solve the optimization model online to obtain secondary frequency regulation instructions for the sending-end and receiving-end power grids.

[0055] It should be noted that compared with traditional control methods, the method proposed in this embodiment combines the sending-end and receiving-end power grid frequency regulation models and the DC line power control model to establish state-space equations, which can achieve accurate modeling of the power interaction characteristics and DC power response characteristics of the interconnected power grid. Therefore, it is possible to coordinate the control resources and DC power control within the power grid partitions at both ends, thereby improving the secondary frequency regulation control effect.

[0056] Example 2, reference Figure 1 , which is an embodiment of the present invention, provides a method for secondary frequency regulation of a DC interconnected power grid considering co-frequency control based on the previous embodiment, including:

[0057] In the embodiment of the present application, in the above step S1, establishing a co-frequency control model of the DC line based on the measured parameters of the DC line includes:

[0058] The control model collects the frequency difference of the power grid at both ends, generates power increment through PI control, and simulates the power support of the AC line, which is expressed as:

[0059]

[0060] Where ΔP dc is the transmission power increment of the DC line under the same frequency control strategy; Δf s is the frequency deviation of the sending-end grid, Δf r is the frequency deviation of the receiving power grid; T dc represents the time constant of the DC control dynamic link, s is the Laplace operator; K P and K I is the PI control parameter, K P is the proportional control parameter, K I is the integral control parameter.

[0061] It should be noted that DC synchronous frequency control requires that the frequency difference between the power grids at both ends be used to generate a DC power increment through the PI link to eliminate the frequency difference between the power grids at both ends and achieve approximately synchronous operation of the power grids at both ends.

[0062] It should be noted that generating DC power increments through PI control can enable DC lines to have frequency coupling characteristics similar to AC lines, thereby enhancing cross-regional frequency support capabilities; dynamically adjusting power based on the frequency difference between the two ends can eliminate frequency deviations of the sending / receiving power grids and improve the frequency stability of the interconnected system.

[0063] In the embodiment of the present application, in the above step S2, based on the same frequency control model, the state space equation of the DC interconnected power grid secondary frequency regulation control is established and discretized, including:

[0064] The state space equation comprehensively considers the frequency response characteristics of the power grids at both ends and the power response characteristics of the DC line, and is expressed as:

[0065]

[0066] Where x(t) represents the state vector, represents the first-order derivative of the state vector x(t) with respect to time t; y(t) represents the control input vector, and w(t) represents the disturbance vector. represents the state matrix, represents the control input matrix, represents the perturbation input matrix.

[0067] It should be noted that the above variables all belong to the continuous time domain (t). For the convenience of subsequent expression, (t) is omitted. The composition of each vector is as follows:

[0068]

[0069] In the formula, the state vector x can be decomposed into x s , x r , x dc The three parts represent the state quantities of the sending-end power grid, the receiving-end power grid, and the DC line respectively.

[0070] It should be noted that for the two-end power grid, the secondary frequency regulation model adopts the classic second-order dynamic model, which includes three state quantities: frequency deviation, synchronous machine valve opening increment, and output power increment. s , Δf r Respectively represent the frequency deviation of the sending and receiving power grids; Respectively represent the increment of the synchronous machine valve opening at the sending end and the receiving end of the power grid; Represents the output power increment of the synchronous machine at the sending and receiving end of the power grid. The state variables of the DC line include the output increment of the integral link and the transmission power increment ΔP dc The control input vector u contains the secondary frequency control instructions of the sending and receiving power grids. The disturbance vector w contains the load power variation of the sending and receiving power grids The superscript T indicates the transpose of a matrix or vector.

[0071] For the state matrix Its components are as follows:

[0072]

[0073]

[0074] Where, It can be decomposed into 9 sub-matrices, corresponding to the sending-end grid variables, receiving-end grid variables, and DC line variables. s , H r Respectively represent the moment of inertia of the sending and receiving power grids; D s , D r Respectively represent the load damping coefficients of the sending and receiving power grids; R s , R r They represent the synchronous machine droop control coefficients of the sending-end and receiving-end power grids respectively; Respectively represent the time constants of the speed regulators of the sending and receiving power grids; represent the turbine time constants of the sending and receiving power grids respectively; They represent the turbine proportional coefficients of the sending and receiving power grids respectively, and 0 represents the zero matrix.

[0075] For the control input matrix Its components are as follows:

[0076]

[0077] Where, Can be decomposed into The three parts correspond to the sending-end grid variables, the receiving-end grid variables, and the DC line variables respectively.

[0078] For the perturbation input matrix Its components are as follows:

[0079]

[0080] Where, Can be decomposed into The three parts correspond to the sending-end grid variables, the receiving-end grid variables, and the DC line variables respectively.

[0081] It should be noted that under the DC frequency synchronization control strategy, the power response characteristics of a DC line are similar to those of an AC line, with the transmission power increment varying based on the real-time frequency difference between the two ends. Similar to AC lines, the DC line transmission power should be controlled as close to the reference power base point as possible, with the transmission power increment kept as close to zero as possible.

[0082] Therefore, the area control error (ACE) of the sending and receiving power grids is defined as follows:

[0083] ACE s =β s Δfs +ΔP dc (9a)

[0084] ACE r =β r Δf r -ΔP dc (9b)

[0085] Where, ACE s , ACE r are the regional control errors of the sending and receiving power grids respectively; β s , β r are the power-frequency response coefficients of the sending and receiving power grids, respectively, and are defined as follows:

[0086]

[0087] At the same time, define the ACE of the power grid at both the sending and receiving ends as the output variable y:

[0088] y=[ACE s ACE r ] T (11)

[0089] Furthermore, discretization of the state space equations involves:

[0090] Since secondary frequency modulation usually operates in discrete mode, the dispatch control center starts, calculates and completes the issuance of instructions in a fixed cycle. Let the control cycle be T c , based on the zero-order hold method, the state space equation in the discrete time domain can be obtained as follows:

[0091] x n+1 =Ax n +B u u n +B w w n (12)

[0092] Where x n ,u n , w n They represent the state vector, control input vector, and disturbance vector in discrete time domain, respectively, x n+1 Indicates the state vector at the next moment, i.e., time n+1, relative to the current time index n in the discrete time domain; n represents the time index in the discrete time domain. A, B u , B w They represent the state matrix, control input matrix, and disturbance input matrix in the discrete time domain, respectively. Their calculation formulas are as follows:

[0093]

[0094] Where I represents the identity matrix, Representation matrix The inverse matrix of the three discrete time domain matrices can be obtained through matrix exponential operations.

[0095] It should be noted that the integration of the frequency modulation characteristics of the sending / receiving ends and the DC power response can fully characterize the dynamic coupling relationship of the interconnected power grid; converting the continuous model into a discrete form through the zero-order hold method can match the periodic scheduling requirements of the digital control system.

[0096] In the embodiment of the present application, in the above step S3, based on the discretized state space equation, establishing the quadratic frequency modulation online optimization model based on model predictive control includes:

[0097] The optimization model objective is to minimize the regional control error and regulation cost of the power grid at both ends, and the constraints include state space equations, state variable constraints and control variable constraints;

[0098] Model predictive control is an online optimization problem that can be modeled as an optimization model as follows:

[0099]

[0100] st:x n+1 =Ax n +B u u n +B w w n (15)

[0101]

[0102] In the formula, the objective function J consists of two parts, the first part is the control effect, and the second part is the control cost. are the corresponding cost matrices. p is the number of prediction steps in model predictive control, N c is the number of control steps in model predictive control. Constraint (15) is the system state space equation; constraints (16a) and (16b) are the frequency constraints of the sending and receiving power grids, respectively; constraints (17a) and (17b) are the output power increment constraints of the sending and receiving power grids, respectively; constraints (18a) and (18b) are the integral control constraints and transmission power constraints of the DC line, respectively; constraints (19a) and (19b) are the output power ramp constraints of the sending and receiving power grids, respectively; constraints (20a) and (20b) are the control input constraints of the sending and receiving power grids, respectively. (x) n Represents the system state / control quantity x at step n. Respectively represent the maximum frequency deviation allowed by the sending and receiving power grids; Respectively represent the lower limits of the output power increment of the sending-end and receiving-end power grids; Respectively represent the upper limit of the output power increment of the sending-end and receiving-end power grids; Respectively represent the upper and lower limits of DC line integral control; Respectively represent the upper and lower limits of the DC line transmission power increment; Rd s , Rd r Respectively represent the downward climbing limit of the output power increment of the sending end and the receiving end grid; Ru s , Ru r Respectively represent the upward climbing limit of the output power increment of the sending-end and receiving-end power grids; Respectively represent the lower limits of the control instructions of the sending-end and receiving-end power grids; They represent the upper limits of the control instructions of the sending and receiving power grids respectively.

[0103] It should be noted that by simultaneously minimizing the area control error (ACE) and the frequency regulation cost through the objective function, the partition resources and DC power regulation can be coordinated; embedding constraints such as frequency, power limit and ramp rate can prevent equipment overload or regulation instructions from exceeding the limit.

[0104] In the embodiment of the present application, in the above step S4, solving the optimization model online to obtain the secondary frequency regulation instructions of the sending-end and receiving-end power grids includes:

[0105] The secondary frequency regulation of the DC interconnected grid uses model predictive control technology, which is an online optimization control technology performed in the rolling time domain. In each control cycle, the control algorithm includes the following steps:

[0106] Parameter initialization: Measure the state values of the sending and receiving power grids and DC lines to construct the initial state vector x0; input the future N p The perturbation power vector of the step

[0107] The initial state vector x0 contains the frequency deviation of the sending and receiving power grids, the synchronous machine valve opening increment, the output power increment, and the integral control increment and transmission power increment of the DC line. It is collected locally and uploaded to the dispatch control center. Model predictive control requires the future N p The load power change prediction of the sending and receiving power grids can be obtained through ultra-short-term power forecasting.

[0108] Solving the optimization model: It should be noted that the optimization model is essentially a quadratic programming problem, and the optimization variables include the future N c The control input vector of the step and future N p The predicted state vector of the step The optimization model can be solved by calling a commercial solver (such as Gurobi, Cplex, etc.).

[0109] Apply the optimization results: Take out the elements of the control input vector u0 of the first step in the optimization results (representing the control instructions of the sending and receiving power grids respectively) are control resources issued to the sending and receiving power grids.

[0110] It should be noted that the secondary frequency modulation method proposed in this embodiment utilizes model predictive control technology, an online optimization control technique operating in the receding time domain. Within each control cycle, predictive calculations and state corrections are performed based on the latest measured data. Each calculation includes control instructions for multiple future steps, but only the calculated control instructions for the first step are applied. This control method performs startup calculations with a fixed control cycle, repeatedly initializing parameters, solving the optimization model, and applying the optimization results.

[0111] It should also be noted that based on rolling optimization of real-time measurement data, prediction errors can be dynamically corrected to improve control robustness; calling efficient solvers (such as Gurobi) to implement millisecond-level instruction calculations can meet the real-time control needs of the power system.

[0112] Example 3. The above is a schematic scheme of the secondary frequency regulation method for a DC interconnected power grid considering co-frequency control according to this embodiment. It should be noted that the technical scheme of the secondary frequency regulation system for a DC interconnected power grid considering co-frequency control and the technical scheme of the secondary frequency regulation method for a DC interconnected power grid considering co-frequency control are based on the same concept. For details not described in detail in the technical scheme of the secondary frequency regulation system for a DC interconnected power grid considering co-frequency control in this embodiment, please refer to the description of the technical scheme of the secondary frequency regulation method for a DC interconnected power grid considering co-frequency control.

[0113] This embodiment further provides a system for a DC interconnected power grid secondary frequency regulation method based on consideration of co-frequency control, including:

[0114] A co-frequency control model building module is used to build a co-frequency control model for the DC line based on the measured parameters of the DC line;

[0115] The state equation establishment module is used to establish the state space equation of the secondary frequency regulation control of the DC interconnected power grid based on the same frequency control model and perform discretization processing;

[0116] The optimization model building module is used to build an online optimization model for quadratic frequency modulation based on model predictive control based on the discretized state space equation;

[0117] The frequency regulation instruction acquisition module is used to solve the optimization model online to obtain the secondary frequency regulation instructions of the sending-end and receiving-end power grids.

[0118] This embodiment further provides a computing device applicable to a method for secondary frequency regulation of a DC interconnected power grid considering co-frequency control, including:

[0119] Memory and processor; the memory is used to store computer-executable instructions, and the processor is used to execute computer-executable instructions to implement the secondary frequency modulation method of the DC interconnected power grid considering the same frequency control as proposed in the above embodiment.

[0120] This embodiment further provides a storage medium having a computer program stored thereon. When the program is executed by a processor, the secondary frequency regulation method for a DC interconnected power grid considering co-frequency control proposed in the above embodiment is implemented.

[0121] The storage medium proposed in this embodiment and the secondary frequency modulation method for the DC interconnected power grid considering co-frequency control proposed in the above embodiment belong to the same inventive concept. For technical details not fully described in this embodiment, please refer to the above embodiment, and this embodiment has the same beneficial effects as the above embodiment.

[0122] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for secondary frequency modulation of a DC interconnected power grid considering co-frequency control, characterized in that: include: Based on the measured parameters of the DC line, a frequency synchronization control model of the DC line is established; The control model collects the frequency difference of the power grid at both ends, generates power increment through PI control, and simulates the power support of the AC line, which is expressed as: Where ΔP dc is the transmission power increment of the DC line under the same frequency control strategy; Δf s is the frequency deviation of the sending-end power grid, Δf r is the frequency deviation of the receiving power grid; T dc represents the time constant of the DC control dynamic link, s is the Laplace operator; K P and K I is the PI control parameter, K P is the proportional control parameter, K I is the integral control parameter; Based on the same-frequency control model, the state space equation of the secondary frequency regulation control of the DC interconnected power grid is established and discretized. Based on the discretized state space equation, an online optimization model of quadratic frequency modulation based on model predictive control is established; The optimization model is solved online to obtain secondary frequency regulation instructions of the sending-end and receiving-end power grids.

2. The method for secondary frequency modulation of a DC interconnected power grid considering frequency co-control according to claim 1, characterized in that: The state space equation comprehensively considers the frequency response characteristics of the power grids at both ends and the power response characteristics of the DC line, and is expressed as: Where x(t) represents the state vector, represents the first-order derivative of the state vector x(t) with respect to time t; u(t) represents the control input vector, and w(t) represents the disturbance vector; represents the state matrix, represents the control input matrix, represents the perturbation input matrix.

3. The method for secondary frequency modulation of a DC interconnected power grid considering frequency co-control according to claim 2, characterized in that: The discretization process includes: Assume the control period is T c , based on the zero-order hold method, the state space equation in the discrete time domain is obtained as follows: x n+1 =Ax n +B u u n +B w w n Where x n ,u n , w n They represent the state vector, control input vector, and disturbance vector in discrete time domain, respectively, x n+1 Indicates the state vector at the next moment, i.e., moment n+1, relative to the current time index n in the discrete time domain; n represents the time index in the discrete time domain; A, B u , B w They represent the state matrix, control input matrix, and disturbance input matrix in the discrete time domain respectively.

4. The method for secondary frequency modulation of a DC interconnected power grid considering frequency co-control according to claim 3, characterized in that: The establishment of a quadratic frequency modulation online optimization model based on model predictive control based on the discretized state space equation includes: The optimization model aims to minimize the regional control error and regulation cost of the power grid at both ends, and the constraints include state space equations, state variable constraints, and control variable constraints.

5. The method for secondary frequency modulation of a DC interconnected power grid considering frequency co-control according to claim 4, characterized in that: The online solving of the optimization model to obtain the secondary frequency regulation instructions of the sending-end and receiving-end power grids includes: Parameter initialization: Measure the state values of the sending and receiving power grids and DC lines to construct the initial state vector x0; input the future N p The perturbation power vector of the step The initial state vector x0 includes the frequency deviation of the sending and receiving power grids, the synchronous machine valve opening increment, the output power increment, and the integral control increment and transmission power increment of the DC line.

6. The method for secondary frequency modulation of a DC interconnected power grid considering frequency co-control according to claim 5, characterized in that: The online solving of the optimization model to obtain secondary frequency regulation instructions of the sending-end and receiving-end power grids further includes: Solve the optimization model: the optimization variables include the future N c The control input vector of the step and future N p The predicted state vector of the step 7. The method for secondary frequency modulation of a DC interconnected power grid considering frequency co-control according to claim 6, characterized in that: The online solving of the optimization model to obtain secondary frequency regulation instructions of the sending-end and receiving-end power grids further includes: Apply the optimization results: Take out the elements of the control input vector u0 of the first step in the optimization results Control resources sent to the sending and receiving power grids, and They represent the sending-end and receiving-end power grid control instructions respectively.

8. A DC interconnected power grid secondary frequency modulation system considering co-frequency control, applying the method according to any one of claims 1 to 7, characterized in that: include: A co-frequency control model building module is used to build a co-frequency control model for the DC line based on the measured parameters of the DC line; The state equation establishment module is used to establish the state space equation of the secondary frequency regulation control of the DC interconnected power grid based on the same frequency control model and perform discretization processing; The optimization model building module is used to build an online optimization model for quadratic frequency modulation based on model predictive control based on the discretized state space equation; The frequency regulation instruction acquisition module is used to solve the optimization model online to obtain the secondary frequency regulation instructions of the sending-end and receiving-end power grids.

9. A computing device comprising: memory and processor; The memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions. When the computer-executable instructions are executed by the processor, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium storing computer-executable instructions, wherein the computer-executable instructions, when executed by a processor, implement the steps of the method according to any one of claims 1 to 7.

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