Parameter optimization method and device for flexible direct current networking system

Abstract

This application proposes a parameter optimization method and apparatus for a flexible DC-DC grid system. The method includes: determining the equivalent grid strength of the AC grid based on grid parameter information of the AC grid served by the flexible DC-DC grid system; obtaining the parameter constraints and small-disturbance stability constraints of the flexible DC-DC grid system; determining the converter station's maximum transmission power based on the equivalent grid strength of the AC grid and the parameter constraints of the flexible DC-DC grid system; and determining the optimal set of main circuit correlation parameters and system control parameters when the flexible DC-DC grid system reaches the converter station's maximum transmission power based on a preset parameter optimization algorithm, within the parameter range defined by the parameter constraints and small-disturbance stability constraints. This technical solution improves the dynamic response capability of the flexible DC-DC grid system and provides effective protection for the safe operation of the AC grid.

Description

[Technical field]

[0001] The present application relates to the field of distributed deployment technology, and in particular to a parameter optimization method and device for a flexible direct current networking system. [Background technology]

[0002] By simulating the rotor equation of the synchronous generator, the grid-forming control can actively construct the voltage frequency and provide inertia support for the AC system, which is beneficial to improving the stability of the power system under weak power grids and improving the active support capacity of new energy. Therefore, the flexible direct current grid-forming system using grid-forming control has obvious advantages in solving the problem of new energy consumption under weak power grids.

[0003] However, the actual operation capability of the flexible DC network system is affected by both its steady-state operation characteristics and small disturbance stability. Specifically, the steady-state operation characteristics determine the physical operation limit that the flexible DC network system can achieve in theory. However, whether the flexible DC network system can reach its physical limit in actual operation or whether it can have good operation stability under extreme conditions is not only related to the selection of the main circuit parameters and grid characteristics of the flexible DC network system, but also to the selection of the control parameters of the flexible DC network system. In other words, the selection of the main circuit parameters and control parameters of the flexible DC network system directly affects the small disturbance stability of the system.

[0004] In the current research on parameter setting of flexible DC grid systems, only the parameters of the current loop PI parameters are often set for a single control link, without involving the optimization setting of the global control parameters under the influence of multiple control parameter coupling. This will cause the parameter setting of the flexible DC grid system to be unable to match its actual application requirements, affecting the energy efficiency of the AC power grid served by the flexible DC grid system.

[0005] Therefore, how to comprehensively and accurately set the main circuit-related parameters and system control parameters for the flexible DC network system has become a technical problem that needs to be solved urgently. [Summary of the invention]

[0006] The embodiments of the present application provide a parameter optimization method and device for a flexible DC networking system, aiming to solve the technical problem that the parameter setting method of the flexible DC networking system in the related art lacks comprehensiveness and accuracy.

[0007] In a first aspect, an embodiment of the present application provides a parameter optimization method for a flexible direct current networking system, comprising:

[0008] Based on the grid parameter information of the AC grid served by the flexible DC grid system, determining the equivalent grid strength of the AC grid, wherein the equivalent grid strength is used to reflect the voltage stability of the AC grid when reactive power is injected;

[0009] Obtaining parameter constraints of the flexible DC networking system and obtaining small disturbance stability constraints of the flexible DC networking system, wherein the parameter constraints are used to reflect the rules that the main circuit associated parameters and system control parameters of the flexible DC networking system match when the flexible DC networking system provides effective services to the AC power grid, and the small disturbance stability constraints are used to reflect the rules that the flexible DC networking system matches to maintain stable operation when facing disturbances;

[0010] Based on the equivalent grid strength of the AC grid and the parameter constraints of the flexible DC network system, determining the converter station limit transmission power of the flexible DC network system;

[0011] Based on a preset parameter optimization algorithm, the optimal solution set of the main circuit associated parameters and system control parameters of the flexible DC network system when the flexible DC network system reaches the limit transmission power of the converter station is determined within the parameter range defined by the parameter constraints and the small interference stability constraints.

[0012] In one embodiment of the present application, optionally, the method further includes:

[0013] Determine whether all optimal solutions in the optimal solution set are within the corresponding preset safety range;

[0014] If all optimal solutions in the optimal solution set are within the corresponding preset safety range, the optimal solution set is determined to be a valid candidate parameter;

[0015] If at least one optimal solution in the optimal solution set is not within the corresponding preset safety range, the optimal solution set is determined to be an invalid candidate parameter, and the parameter range limited by the corresponding parameter constraint condition is adjusted based on the at least one optimal solution, and the process returns to the step of determining the maximum transmission power of the converter station of the flexible DC network system.

[0016] In one embodiment of the present application, optionally, determining the equivalent grid strength of the AC grid based on grid parameter information of the AC grid served by the flexible DC networking system includes:

[0017] Determine the equivalent impedance of the AC power grid connected in series with an equivalent infinite power source, where:

[0018] Z g =R g +jX g ,

[0019] Z g is the equivalent impedance of the infinite power source in series, R g and X g are the equivalent resistance and equivalent reactance connected in series with the equivalent infinite power source, respectively, and j is an imaginary unit;

[0020] Based on the equivalent impedance of the equivalent infinite power source connected in series, the rated DC power of the converter station of the AC power grid and the rated AC voltage amplitude of the common connection point in the AC power grid, the equivalent AC power grid short-circuit ratio of the AC power grid is determined as the equivalent power grid strength of the AC power grid, wherein:

[0021]

[0022] SCR is the equivalent AC grid short-circuit ratio of the AC grid, P dc is the rated DC power of the converter station of the AC power grid, U s is the rated AC voltage amplitude of the common connection point in the AC power grid.

[0023] In one embodiment of the present application, optionally, the obtaining of parameter constraints of the flexible direct current networking system includes:

[0024] Obtain the power flow solvable constraint conditions of the flexible direct current grid system, the grid connection point bus voltage constraint conditions, the voltage modulation ratio constraint conditions, the current constraint conditions, the transmission capacity and voltage level constraint conditions, the capacitor voltage fluctuation constraint conditions, the double frequency circulating current limit constraint conditions and the circulating current resonance constraint conditions, wherein:

[0025] The power flow solvability constraint condition is:

[0026]

[0027] P is the active power output by the converter station, Q is the reactive power output by the converter station, and U g is the equivalent voltage of the AC grid, R g is the equivalent resistance of the AC power grid connected in series with an equivalent infinite power source, X g The equivalent reactance connected in series with the equivalent infinite power source of the AC power grid;

[0028] The grid connection point bus voltage constraint condition is:

[0029] U smin ≤U s ≤U smax ,

[0030] U s The rated AC voltage amplitude of the common connection point in the AC power grid is used to reflect the bus voltage at the grid connection point, U smin is the minimum value allowed by the bus voltage at the grid connection point, U smax The maximum value allowed for the bus voltage at the grid connection point;

[0031] The voltage modulation ratio constraint condition is:

[0032]

[0033] M is the MMC modulation ratio, U dc is the MMC DC voltage;

[0034] The current constraint condition is:

[0035]

[0036] j is the imaginary unit, I sN is the rated current of the MMC AC side;

[0037] The transmission capacity and voltage level constraints are:

[0038] S dc =αU dc I pa ,

[0039] S dc is the DC transmission power, I pa is the upper bridge arm current of phase a, and α is the second predetermined coefficient;

[0040] The capacitor voltage fluctuation constraint condition is:

[0041]

[0042] C0 is the MMC submodule capacitance, N is the number of MMC submodules, ε is the operating fluctuation range of the capacitor voltage, U c0 is the MMC submodule capacitor voltage, ω is the system frequency;

[0043] The double frequency circulating current restriction constraint condition is:

[0044]

[0045] L is the MMC bridge arm inductance, U N is the rated voltage, γ is the allowable fluctuation range of the double frequency circulating current, I dc is the MMC DC current;

[0046] The ring current resonance constraint condition is:

[0047]

[0048] ω res is the resonant angular frequency of the circulating current resonance.

[0049] In one embodiment of the present application, optionally, obtaining a small interference stability constraint condition of the flexible direct current networking system includes:

[0050] Obtain a small interference analysis model of the flexible DC networking system, wherein the small interference analysis model reflects the correlation between the sum of the state variable and the interference input variable of the flexible DC networking system and the system state change level of the flexible DC networking system in unit time, and the small interference analysis model is:

[0051]

[0052] Wherein, Δx is the increment of n state variables in the flexible direct current networking system, Δu is the increment of m input variables, A is an n×n order state matrix, and B is an n×m order input matrix;

[0053] Based on the small disturbance analysis model, the small disturbance stability constraint condition of the flexible DC networking system is determined as follows:

[0054]

[0055] Among them, rank(A) refers to the rank of matrix A, λ i is the i-th characteristic root of the flexible DC network system, Re(λ i ) refers to finding λ i The real part of .

[0056] In one embodiment of the present application, optionally, determining the converter station limit transmission power of the flexible DC network system based on the equivalent grid strength of the AC grid and the parameter constraint condition of the flexible DC network system includes:

[0057] Within the optional parameter range of the flexible DC network system defined by the power flow solubility constraint, the grid connection point bus voltage constraint, the voltage modulation ratio constraint, and the current constraint, determine the converter station limit transmission power of the flexible DC network system when the AC power grid reaches the equivalent power grid strength.

[0058] In one embodiment of the present application, optionally, the optimal solution set of main circuit associated parameters and system control parameters of the flexible DC network system when reaching the limit transmission power of the converter station is determined within the parameter range defined by the parameter constraint condition and the small interference stability constraint condition based on a preset parameter optimization algorithm, including:

[0059] Based on a preset parameter optimization algorithm, determine the optimal solution set of the main circuit associated parameters and system control parameters of the flexible DC network system that satisfies the current constraint condition, the transmission capacity and voltage level constraint condition, the capacitor voltage fluctuation constraint condition, the double frequency circulating current limit constraint condition and the circulating current resonance constraint condition, satisfies the small interference stability constraint condition, and enables the flexible DC network system to reach the converter station limit transmission power and the minimum MMC DC voltage, wherein:

[0060] The preset parameter optimization algorithm is a particle swarm optimization algorithm, a genetic algorithm or an ant colony algorithm.

[0061] In a second aspect, an embodiment of the present application provides a parameter optimization device for a flexible direct current networking system, including:

[0062] An equivalent grid strength determination unit, used to determine the equivalent grid strength of the AC grid served by the flexible DC grid system based on grid parameter information of the AC grid, wherein the equivalent grid strength is used to reflect the voltage stability of the AC grid when reactive power is injected;

[0063] A constraint determination unit, used for obtaining parameter constraints of the flexible DC networking system and obtaining small disturbance stability constraints of the flexible DC networking system, wherein the parameter constraints are used to reflect the rules that the main circuit associated parameters and system control parameters of the flexible DC networking system match when the flexible DC networking system provides effective services to the AC power grid, and the small disturbance stability constraints are used to reflect the rules that the flexible DC networking system matches to maintain stable operation when facing disturbances;

[0064] A limit transmission power determination unit, configured to determine the limit transmission power of a converter station of the flexible DC network system based on the equivalent grid strength of the AC grid and the parameter constraints of the flexible DC network system;

[0065] The optimal solution determination unit is used to determine the optimal solution set of the main circuit associated parameters and system control parameters of the flexible DC network system when the maximum transmission power of the converter station is reached within the parameter range defined by the parameter constraint condition and the small interference stability constraint condition based on a preset parameter optimization algorithm.

[0066] In one embodiment of the present application, optionally, the device further includes:

[0067] An optimal solution rationality judgment unit, used to judge whether all optimal solutions in the optimal solution set are within a corresponding preset safety range;

[0068] A first execution unit, configured to determine that the optimal solution set is a valid candidate parameter if all optimal solutions in the optimal solution set are within a corresponding preset safety range;

[0069] The second execution unit is used to determine that the optimal solution set is an invalid candidate parameter if at least one optimal solution in the optimal solution set is not within the corresponding preset safety range, and adjust the parameter range limited by the corresponding parameter constraint condition based on the at least one optimal solution, and return to the step of determining the maximum transmission power of the converter station of the flexible direct current network system.

[0070] In one embodiment of the present application, optionally, the equivalent grid strength determination unit is used to: determine the equivalent impedance of the equivalent infinite power source in series of the AC grid, wherein:

[0071] Z g =R g +jX g ,

[0072] Z g is the equivalent impedance of the infinite power source in series, R g and X g are the equivalent resistance and equivalent reactance connected in series with the equivalent infinite power source, respectively, and j is an imaginary unit; based on the equivalent impedance connected in series with the equivalent infinite power source, the rated DC power of the converter station of the AC power grid, and the rated AC voltage amplitude of the common connection point in the AC power grid, the equivalent AC power grid short-circuit ratio of the AC power grid is determined as the equivalent power grid strength of the AC power grid, wherein,

[0073]

[0074] SCR is the equivalent AC grid short-circuit ratio of the AC grid, P dc is the rated DC power of the converter station of the AC power grid, U s is the rated AC voltage amplitude of the common connection point in the AC power grid.

[0075] In one embodiment of the present application, optionally, the constraint condition determination unit includes:

[0076] The first acquisition unit is used to obtain the power flow solvable constraint conditions of the flexible direct current grid system, the grid connection point bus voltage constraint conditions, the voltage modulation ratio constraint conditions, the current constraint conditions, the transmission capacity and voltage level constraint conditions, the capacitor voltage fluctuation constraint conditions, the double frequency circulating current limit constraint conditions and the circulating current resonance constraint conditions, wherein:

[0077] The power flow solvability constraint condition is:

[0078]

[0079] P is the active power output by the converter station, Q is the reactive power output by the converter station, and U g is the equivalent voltage of the AC grid, R g is the equivalent resistance of the AC power grid connected in series with an equivalent infinite power source, X g The equivalent reactance connected in series with the equivalent infinite power source of the AC power grid;

[0080] The voltage modulation ratio constraint condition is:

[0081]

[0082] M is the MMC modulation ratio, U dc is the MMC DC voltage;

[0083] The current constraint condition is:

[0084]

[0085] j is the imaginary unit, I sN is the rated current of the MMC AC side;

[0086] The transmission capacity and voltage level constraints are:

[0087] S dc =αU dc I pa ,

[0088] S dc is the DC transmission power, I pa is the upper bridge arm current of phase a, and α is the second predetermined coefficient;

[0089] The capacitor voltage fluctuation constraint condition is:

[0090]

[0091] C0 is the MMC submodule capacitance, N is the number of MMC submodules, ε is the operating fluctuation range of the capacitor voltage, U c0 is the MMC submodule capacitor voltage, ω is the system frequency;

[0092] The double frequency circulating current restriction constraint condition is:

[0093]

[0094] L is the MMC bridge arm inductance, U N is the rated voltage, γ is the allowable fluctuation range of the double frequency circulating current, I dc is the MMC DC current;

[0095] The ring current resonance constraint condition is:

[0096]

[0097] ω res is the resonant angular frequency of the circulating current resonance.

[0098] In one embodiment of the present application, optionally, the constraint condition determination unit includes:

[0099] The second acquisition unit is used to acquire a small interference analysis model of the flexible DC networking system, wherein the small interference analysis model reflects the correlation between the sum of the state variable and the interference input variable of the flexible DC networking system and the system state change level of the flexible DC networking system in unit time, and the small interference analysis model is:

[0100]

[0101] Wherein, Δx is the increment of n state variables in the flexible direct current networking system, Δu is the increment of m input variables, A is an n×n order state matrix, and B is an n×m order input matrix;

[0102] Based on the small disturbance analysis model, the small disturbance stability constraint condition of the flexible DC networking system is determined as follows:

[0103]

[0104] Among them, rank(A) refers to the rank of matrix A, λ i is the i-th characteristic root of the flexible DC network system, Re(λ i ) refers to finding λ i The real part of .

[0105] In one embodiment of the present application, optionally, the limit transmission power determination unit is used to determine the limit transmission power of the converter station of the flexible DC network system when the AC power grid reaches the equivalent grid strength within the optional parameter range of the flexible DC network system defined by the power flow solvability constraint condition, the grid connection point bus voltage constraint condition, the voltage modulation ratio constraint condition, and the current constraint condition.

[0106] In one embodiment of the present application, optionally, the optimal solution determination unit is used to: determine, based on a preset parameter optimization algorithm, an optimal solution set of main circuit associated parameters and system control parameters of the flexible DC network system that satisfies the current constraint condition, the transmission capacity and voltage level constraint condition, the capacitor voltage fluctuation constraint condition, the double frequency circulating current limit constraint condition and the circulating current resonance constraint condition, satisfies the small interference stability constraint condition, and enables the flexible DC network system to reach the converter station's limit transmission power and the minimum MMC DC voltage, wherein the preset parameter optimization algorithm is a particle swarm optimization algorithm, a genetic algorithm, or an ant colony algorithm.

[0107] In a third aspect, an embodiment of the present application provides a computer device, comprising: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are configured to execute the method described in the first aspect above.

[0108] In a fourth aspect, an embodiment of the present application provides a computer-readable storage medium storing computer-executable instructions, wherein the computer-executable instructions are used to execute the method described in the first aspect above.

[0109] The above technical solution aims at the technical problem that the parameter setting method of the flexible DC network system in the related technology lacks comprehensiveness and accuracy. For the flexible DC network system, on the basis of meeting the AC power grid strength limit for MMC transmission power, combined with the parameter constraints of the main circuit and the small interference stability constraints of the flexible DC network system itself, a preset parameter optimization algorithm is used to determine the optimal solution set of the main circuit associated parameters and system control parameters of the flexible DC network system. The parameters determined in this way can not only realize the transmission limit power of the converter station, but also meet the actual operation requirements of the flexible DC network system and the AC power grid in multiple dimensions, improve the dynamic response capability of the flexible DC network system, and provide effective guarantee for the safe operation of the AC power grid.

Brief Description of the Drawings

[0110] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0111] Figure 1 A flow chart of a parameter optimization method for a flexible direct current networking system according to an embodiment of the present application is shown;

[0112] Figure 2 A main circuit structure diagram of a flexible direct current networking system according to an embodiment of the present application is shown;

[0113] Figure 3 A schematic diagram of a control system and a sampling delay link of a meshed MMC converter station according to an embodiment of the present application is shown;

[0114] Figure 4 A schematic diagram showing the transmission power range of a converter station of a flexible DC network system according to an embodiment of the present application is shown;

[0115] Figure 5 A block diagram of a computer device according to an embodiment of the present application is shown;

[0116] Figure 6 A block diagram of a computer device according to another embodiment of the present application is shown. [Specific implementation method]

[0117] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0118] Figure 1 A flow chart of a parameter optimization method for a flexible direct current networking system according to an embodiment of the present application is shown.

[0119] like Figure 1 As shown, the process of the parameter optimization method for a flexible direct current networking system according to an embodiment of the present application includes:

[0120] Step 102: Determine the equivalent grid strength of the AC grid based on grid parameter information of the AC grid served by the flexible DC grid system.

[0121] The principle of the flexible DC grid system is to transmit high-voltage DC power based on voltage source converters, which can supply power to passive networks. It can be said that the flexible DC grid system is equivalent to a controllable dam in the AC power grid, which can accurately control the direction and size of the power flow in the AC power grid in a tolerant and inclusive manner. Figure 2 The main circuit structure diagram of the flexible direct current network system according to an embodiment of the present application is shown. Figure 2 As shown, on the AC side, the converter station passes through the equivalent impedance Z s =R s +jL s Connected to PCC (Point of Common Coupling), and then connected to the AC power grid. s , Q s They represent the active power and reactive power transmitted from the flexible DC grid connection point to the AC system. The Thevenin equivalent of the AC grid is an infinite voltage source connected in series with an equivalent impedance Z g =R g +jL g In the form of g is the grid voltage, U s is the voltage at the PCC point on the AC side, U v is the AC output voltage of the converter.

[0122] like Figure 2 As shown on the right, the flexible DC grid system regards the receiving-end converter station adopting the fixed active power control strategy as a controlled current source. dc is the DC current flowing into the converter, C dc is the equivalent capacitance on the DC side. At this time, the controlled current source current I dc2 It can be calculated by the following formula:

[0123]

[0124] Among them, P ref is the active reference value of the receiving converter station, U dcm is the actual value of DC voltage.

[0125] Based on the above circuit structure, the control system and sampling delay link of the network-type MMC converter station are as follows: Figure 3 As shown in the figure, the control system of the grid-type MMC converter station includes three parts: phase generation link, voltage-current dual closed-loop control link and circulating current suppression control link. The control parameters involved in the optimization include: the active power-frequency droop coefficient m of the phase generation link f , inertia time constant T j , damping coefficient D, DC voltage control PI controller parameter K pdc With K idc , AC voltage outer loop d-axis PI controller parameter K p1 With K i1 , q-axis PI controller parameter K p2 With K i2 , current inner loop d-axis PI controller parameter K p3 With K i3 , q-axis PI controller parameter K p4 With K i4 , PI controller parameter K of the circulation suppression link pcir With K icir .

[0126] The equivalent grid strength is used to reflect the voltage stability of the AC grid when reactive power is injected. The voltage stability of the AC grid when reactive power is injected is an important condition that affects the level of interaction between the AC grid and the flexible DC grid system. Therefore, when setting the parameters required for the flexible DC grid system, the voltage stability of the AC grid when reactive power is injected needs to be considered.

[0127] In a possible design, the voltage stability of the AC grid when reactive power is injected can be converted and quantified into a value of the equivalent grid strength of the AC grid to facilitate subsequent calculations.

[0128] In a possible design, the grid parameter information of the AC power grid includes: the equivalent resistance and equivalent reactance of the equivalent infinite power source in series, the rated DC power of the converter station of the AC power grid, and the rated AC voltage amplitude of the common connection point in the AC power grid.

[0129] Specifically, the equivalent impedance of the equivalent infinite power source in series with the AC power grid can be determined first, that is, Z g =R g +jXg , where Z g is the equivalent impedance of the infinite power source in series, R g and X g are respectively the equivalent resistance and equivalent reactance connected in series with the equivalent infinite power source, and j is an imaginary unit.

[0130] Next, based on the equivalent impedance of the equivalent infinite power source connected in series, the rated DC power of the converter station of the AC power grid and the rated AC voltage amplitude of the common connection point in the AC power grid, the equivalent AC power grid short-circuit ratio of the AC power grid is determined, wherein:

[0131]

[0132] SCR is the equivalent AC grid short-circuit ratio of the AC grid, P dc is the rated DC power of the converter station of the AC power grid, U s is the rated AC voltage amplitude of the common connection point in the AC power grid.

[0133] In one possible design, SCR = 3, and the AC system impedance angle

[0134] At this point, the equivalent AC grid short-circuit ratio of the AC grid can be determined as the equivalent grid strength of the AC grid, which is used to reflect the voltage stability of the AC grid when reactive power is injected into it.

[0135] Step 104: Obtain parameter constraints of the flexible DC networking system, and obtain small interference stability constraints of the flexible DC networking system.

[0136] Among them, the parameter constraints are used to reflect the matching rules of the main circuit-related parameters and system control parameters of the flexible DC network system when the flexible DC network system provides effective services to the AC power grid, including but not limited to the power flow solubility constraints of the flexible DC network system, the bus voltage constraints of the grid connection point, the voltage modulation ratio constraints, the current constraints, the transmission capacity and voltage level constraints, the capacitor voltage fluctuation constraints, the double frequency circulating current limit constraints and the circulating current resonance constraints, and any other constraints involving the main circuit-related parameters and system control parameters of the flexible DC network system. It can be known that the main circuit-related parameters and system control parameters of the flexible DC network system include the parameters described in the following formulas.

[0137] Optionally, the power flow solvable constraint condition is:

[0138]

[0139] P is the active power output by the converter station, Q is the reactive power output by the converter station, and Ug is the equivalent voltage of the AC grid, R g is the equivalent resistance of the AC power grid connected in series with an equivalent infinite power source, X g The equivalent reactance connected in series with the equivalent infinite power source of the AC power grid;

[0140] Optionally, the grid connection point bus voltage constraint condition is:

[0141] U smin ≤U s ≤U smax ,

[0142] U s The rated AC voltage amplitude of the common connection point in the AC power grid is used to reflect the bus voltage at the grid connection point, U smin is the minimum value allowed by the bus voltage at the grid connection point, U smax is the maximum value allowed for the grid-connected point bus voltage. This condition defines the upper and lower limits of the grid-connected point bus voltage, that is, the setting value of the grid-connected point bus voltage obtained in the optimal solution set must be within U smin and U smax between.

[0143] Optionally, the voltage modulation ratio constraint condition is:

[0144]

[0145] M is the MMC modulation ratio, U dc is the MMC DC voltage. This constraint condition defines the relationship between the MMC modulation ratio, the MMC DC voltage and the grid-connected bus voltage. In other words, the MMC modulation ratio, the MMC DC voltage and the grid-connected bus voltage in the optimal solution set must satisfy the above inequality.

[0146] Optionally, the current constraint condition is:

[0147]

[0148] j is the imaginary unit, I sN is the rated current of the MMC AC side. The above constraints define the relationship between the active power and reactive power output by the converter station, the rated current of the MMC AC side, and the bus voltage at the grid connection point. In other words, the optimal solution set must satisfy these defined relationships.

[0149] Optionally, the transmission capacity and voltage level constraints are:

[0150] S dc =αU dc I pa ,

[0151] S dc is the transmission capacity, I pa is the upper arm current of phase a, and α is the second predetermined coefficient; the above constraints limit the relationship between the transmission capacity and the upper arm current of phase a and the MMC voltage level. In other words, the optimal solution set must satisfy these limited relationships.

[0152] Optionally, the capacitor voltage fluctuation constraint condition is:

[0153]

[0154] C0 is the MMC submodule capacitance, N is the number of MMC submodules, and ε is the operating fluctuation range of the capacitor voltage.

[0155] In one possible design, ε is 10%.

[0156] In another possible design, ε is less than 10%.

[0157] U c0 is the MMC submodule capacitor voltage, and ω is the system frequency. This constraint condition limits the relationship between the MMC modulation ratio, system frequency, MMC submodule capacitor voltage, and the operating fluctuation range of the MMC submodule capacitor and capacitor voltage under the premise of considering the number of MMC submodules. In other words, the optimal solution set must satisfy this limited relationship.

[0158] Optionally, the double frequency circulating current restriction constraint condition is:

[0159]

[0160] L is the MMC bridge arm inductance, U N is the rated voltage, γ is the allowable fluctuation range of the double frequency circulating current, I dc is the MMC DC current. Similarly, this constraint defines L, U N、 U dc , U c0 ,I dc , ω and γ, that is, the final optimal solution set must satisfy this restricted relationship.

[0161] The ring current resonance constraint condition is:

[0162]

[0163] Among them, ω resis the resonant angular frequency during the circulating current resonance. This constraint condition limits the calculation method of the resonant angular frequency during the circulating current resonance, and in this calculation method, the resonant angular frequency during the circulating current resonance is calculated by the number of MMC sub-modules, the MMC bridge arm inductance, and the MMC sub-module capacitance, which is restricted by the system frequency. In other words, this constraint condition actually limits the relationship between the number of MMC sub-modules, the MMC bridge arm inductance, the MMC sub-module capacitance and the system frequency. Therefore, in the final optimal solution set, the relationship between the number of MMC sub-modules, the MMC bridge arm inductance, the MMC sub-module capacitance and the system frequency must satisfy the above inequality.

[0164] Among them, small interference stability refers to the flexible DC networking system maintaining stable operation when facing some small disturbances, and the small interference stability constraint condition is used to reflect the rules matched by the flexible DC networking system to maintain stable operation when facing disturbances.

[0165] Specifically, a small interference analysis model of the flexible DC networking system can be constructed.

[0166] The small interference analysis model reflects the correlation between the sum of the state variable and the interference input variable of the flexible DC networking system and the level of system state change of the flexible DC networking system in unit time. The small interference analysis model is:

[0167]

[0168] Among them, Δx is the increment of n state variables in the flexible DC networking system, Δu is the increment of m input variables, A is an n×n order state matrix, and B is an n×m order input matrix. Among them, the m input variables refer to the m small disturbances to which the flexible DC networking system is subjected, and the n state variables refer to the system state of the flexible DC networking system that changes after being affected by the m small disturbances. On this basis, when A and B are known matrices, the stability of the system can be estimated after knowing the increments of m input variables and n state variables. It can be understood that matrix A reflects the stability level of the flexible DC networking system after being subjected to m small disturbances.

[0169] Next, based on the small disturbance analysis model, the small disturbance stability constraint condition of the flexible DC networking system is determined as follows:

[0170]

[0171] Among them, rank(A) refers to the rank of matrix A, λ i is the i-th characteristic root of the flexible DC network system, Re(λ i ) refers to finding λ i The real part of .

[0172] Since the matrix A reflects the stability level of the flexible DC network system after m small disturbances, the rank of the matrix A can be obtained, and the size of the real part of the characteristic root can be limited within the range of the number of characteristic roots with the rank as the upper limit. In other words, the flexible DC network system can maintain system stability under small disturbances only when the real part of each characteristic root within the range of the number of characteristic roots with the rank as the upper limit is negative.

[0173] Step 106: Determine the maximum transmission power of the converter station of the flexible DC network system based on the equivalent grid strength of the AC grid and the parameter constraints of the flexible DC network system.

[0174] That is to say, the converter station limit transmission power of the flexible DC network system is subject to the equivalent grid strength and the parameter ranges defined in the parameter constraints. When solving the optimal solution set of the parameters of the flexible DC network system, after the optimal solution set is used in the flexible DC network system, the converter station transmission power of the flexible DC network system should reach the converter station limit transmission power.

[0175] In a possible design, the maximum transmission power of the converter station of the flexible DC network system can be determined when the AC power grid reaches the equivalent power grid strength within the optional parameter range of the flexible DC network system defined by the power flow solubility constraint, the grid connection point bus voltage constraint, the voltage modulation ratio constraint, and the current constraint.

[0176] In a possible design, under the combined effect of the voltage upper limit constraint, voltage lower limit constraint brought about by the grid connection point bus voltage constraint condition and the voltage modulation ratio constraint condition, as well as the power flow solvability constraint condition and the current constraint condition, when the AC power grid reaches the equivalent power grid strength, the transmission power distribution of the converter station of the flexible DC network system is as follows: Figure 4 shown.

[0177] Optionally, the maximum value of the converter station transmission power of the flexible DC network system can be solved by any algorithm such as particle swarm optimization algorithm, genetic algorithm or ant colony algorithm as the converter station limit transmission power.

[0178] Step 108, based on a preset parameter optimization algorithm, determine the optimal solution set of the main circuit associated parameters and system control parameters of the flexible DC network system when the limit transmission power of the converter station is reached within the parameter range defined by the parameter constraint condition and the small interference stability constraint condition, as the optimal solution set.

[0179] The preset parameter optimization algorithm is a particle swarm optimization algorithm, a genetic algorithm or an ant colony algorithm. In actual calculations, no matter which algorithm is used, multiple iterations can be performed. After reaching the maximum number of iterations, the optimal solution set with main circuit associated parameters and system control parameters is output as an optional parameter setting content. Of course, the optimal solution set can be one set of main circuit associated parameters and system control parameters, or multiple sets.

[0180] Optionally, based on a preset parameter optimization algorithm, an optimal solution set of main circuit associated parameters and system control parameters of the flexible DC network system that satisfies the current constraint, the transmission capacity and voltage level constraint, the capacitor voltage fluctuation constraint, the double frequency circulating current limit constraint and the circulating current resonance constraint, satisfies the small interference stability constraint, and enables the flexible DC network system to reach the converter station's maximum transmission power and the minimum MMC DC voltage can be determined.

[0181] Specifically, a particle swarm optimization algorithm, a genetic algorithm or an ant colony algorithm can be used to find a set of parameters that can enable the flexible DC network system to reach the converter station limit transmission power and the minimum MMC DC voltage within the current constraint conditions, the transmission capacity and voltage level constraint conditions, the capacitor voltage fluctuation constraint conditions, the double frequency circulating current limit constraint conditions and the circulating current resonance constraint conditions, and satisfy the small interference stability constraint conditions. Under this set of parameters, the system performance of the flexible DC network system is optimal. The optimization objectives of the preset parameter optimization algorithm are as follows:

[0182]

[0183] f1 and f2 are the optimization targets of the preset parameter optimization algorithm, f1 indicates that the MMC DC voltage is the lowest, and f2 indicates that the system performance is the best.

[0184] In addition, after each optimal solution set is determined, the feasibility of the optimal solution set is verified. Specifically, it is determined whether all optimal solutions in the optimal solution set are within the corresponding preset safety range.

[0185] Since numerical deviation may occur in the actual iteration process, the parameter values ​​in the obtained optimal solution set may deviate from the parameter range defined by the parameter constraint condition and the small disturbance stability constraint condition. At this point, the obtained optimal solution set can be tested based on the parameter constraint condition and the parameter range defined by the small disturbance stability constraint condition.

[0186] If all optimal solutions in the optimal solution set are within the corresponding preset safety range, the optimal solution set is determined to be a valid candidate parameter.

[0187] If at least one optimal solution in the optimal solution set is not within the corresponding preset safety range, the optimal solution set is determined to be an invalid candidate parameter, and the parameter range limited by the corresponding parameter constraint condition is adjusted based on the at least one optimal solution, and the process returns to the step of determining the converter station limit transmission power of the flexible direct current network system, recalculates the converter station limit transmission power based on the adjusted parameter constraint condition, and re-executes the preset parameter optimization algorithm to obtain the next set of optimal solution combinations.

[0188] The above technical solution, for the flexible DC network system, on the basis of meeting the AC power grid strength limit for MMC transmission power, combined with the parameter constraints of the main circuit and the small interference stability constraints of the flexible DC network system itself, adopts a preset parameter optimization algorithm to determine the optimal solution set of the main circuit associated parameters and system control parameters of the flexible DC network system. The parameters thus determined can not only achieve the transmission limit power of the converter station, but also meet the actual operation requirements of the flexible DC network system and the AC power grid in multiple dimensions, improve the dynamic response capability of the flexible DC network system, and provide effective guarantee for the safe operation of the AC power grid.

[0189] The embodiment of the present application provides a parameter optimization device for a flexible direct current networking system, including:

[0190] An equivalent grid strength determination unit, used to determine the equivalent grid strength of the AC grid served by the flexible DC grid system based on grid parameter information of the AC grid, wherein the equivalent grid strength is used to reflect the voltage stability of the AC grid when reactive power is injected;

[0191] A constraint determination unit, used for obtaining parameter constraints of the flexible DC networking system and obtaining small disturbance stability constraints of the flexible DC networking system, wherein the parameter constraints are used to reflect the rules that the main circuit associated parameters and system control parameters of the flexible DC networking system match when the flexible DC networking system provides effective services to the AC power grid, and the small disturbance stability constraints are used to reflect the rules that the flexible DC networking system matches to maintain stable operation when facing disturbances;

[0192] A limit transmission power determination unit, configured to determine the limit transmission power of a converter station of the flexible DC network system based on the equivalent grid strength of the AC grid and the parameter constraints of the flexible DC network system;

[0193] The optimal solution determination unit is used to determine, based on a preset parameter optimization algorithm, the optimal solution set of the main circuit associated parameters and the system control parameters of the flexible DC network system when the flexible DC network system reaches the limit transmission power of the converter station within the parameter range defined by the parameter constraint condition and the small interference stability constraint condition, as the optimal solution set.

[0194] In one embodiment of the present application, optionally, the device further includes:

[0195] An optimal solution rationality judgment unit, used to judge whether all optimal solutions in the optimal solution set are within a corresponding preset safety range;

[0196] A first execution unit, configured to determine that the optimal solution set is a valid candidate parameter if all optimal solutions in the optimal solution set are within a corresponding preset safety range;

[0197] The second execution unit is used to determine that the optimal solution set is an invalid candidate parameter if at least one optimal solution in the optimal solution set is not within the corresponding preset safety range, and adjust the parameter range limited by the corresponding parameter constraint condition based on the at least one optimal solution, and return to the step of determining the maximum transmission power of the converter station of the flexible direct current network system.

[0198] In one embodiment of the present application, optionally, the equivalent grid strength determination unit is used to: determine the equivalent impedance of the equivalent infinite power source in series of the AC grid, wherein:

[0199] Z g =R g +jX g ,

[0200] Z g is the equivalent impedance of the infinite power source in series, R g and X g are the equivalent resistance and equivalent reactance connected in series with the equivalent infinite power source, respectively, and j is an imaginary unit; based on the equivalent impedance connected in series with the equivalent infinite power source, the rated DC power of the converter station of the AC power grid, and the rated AC voltage amplitude of the common connection point in the AC power grid, the equivalent AC power grid short-circuit ratio of the AC power grid is determined as the equivalent power grid strength of the AC power grid, wherein,

[0201]

[0202] SCR is the equivalent AC grid short-circuit ratio of the AC grid, P dc is the rated DC power of the converter station of the AC power grid, U s is the rated AC voltage amplitude of the common connection point in the AC power grid.

[0203] In one embodiment of the present application, optionally, the constraint condition determination unit includes:

[0204] The first acquisition unit is used to obtain the power flow solvable constraint conditions of the flexible direct current grid system, the grid connection point bus voltage constraint conditions, the voltage modulation ratio constraint conditions, the current constraint conditions, the transmission capacity and voltage level constraint conditions, the capacitor voltage fluctuation constraint conditions, the double frequency circulating current limit constraint conditions and the circulating current resonance constraint conditions, wherein:

[0205] The power flow solvability constraint condition is:

[0206]

[0207] P is the active power output by the converter station, Q is the reactive power output by the converter station, and U g is the equivalent voltage of the AC grid, R g is the equivalent resistance of the AC power grid connected in series with an equivalent infinite power source, X g The equivalent reactance connected in series with the equivalent infinite power source of the AC power grid;

[0208] The grid connection point bus voltage constraint condition is:

[0209] U smin ≤U s ≤U smax ,

[0210] U s The rated AC voltage amplitude of the common connection point in the AC power grid is used to reflect the bus voltage at the grid connection point, U smin is the minimum value allowed by the bus voltage at the grid connection point, U smax The maximum value allowed for the bus voltage at the grid connection point;

[0211] The voltage modulation ratio constraint condition is:

[0212]

[0213] M is the MMC modulation ratio, U dc is the MMC DC voltage;

[0214] The current constraint condition is:

[0215]

[0216] j is the imaginary unit, I sN is the rated current of the MMC AC side;

[0217] The transmission capacity and voltage level constraints are:

[0218] S dc =αU dc I pa ,

[0219] Sdc is the DC transmission power, I pa is the upper bridge arm current of phase a, and α is the second predetermined coefficient;

[0220] The capacitor voltage fluctuation constraint condition is:

[0221]

[0222] C0 is the MMC submodule capacitance, N is the number of MMC submodules, ε is the operating fluctuation range of the capacitor voltage, U c0 is the MMC submodule capacitor voltage, ω is the system frequency;

[0223] The double frequency circulating current restriction constraint condition is:

[0224]

[0225] L is the MMC bridge arm inductance, U N is the rated voltage, γ is the allowable fluctuation range of the double frequency circulating current, I dc is the MMC DC current;

[0226] The ring current resonance constraint condition is:

[0227]

[0228] ω res is the resonant angular frequency of the circulating current resonance.

[0229] In one embodiment of the present application, optionally, the constraint condition determination unit includes:

[0230] The second acquisition unit is used to acquire a small interference analysis model of the flexible DC networking system, wherein the small interference analysis model reflects the correlation between the sum of the state variable and the interference input variable of the flexible DC networking system and the system state change level of the flexible DC networking system in unit time, and the small interference analysis model is:

[0231]

[0232] Wherein, Δx is the increment of n state variables in the flexible DC networking system, Δu is the increment of m input variables, A is an n×n order state matrix, and B is an n×m order input matrix; based on the small interference analysis model, the small interference stability constraint condition of the flexible DC networking system is determined as follows:

[0233]

[0234] Among them, rank(A) refers to the rank of matrix A, λ i is the i-th characteristic root of the flexible DC network system, Re(λi ) refers to finding λ i The real part of .

[0235] In one embodiment of the present application, optionally, the limit transmission power determination unit is used to determine the limit transmission power of the converter station of the flexible DC network system when the AC power grid reaches the equivalent grid strength within the optional parameter range of the flexible DC network system defined by the power flow solvability constraint condition, the grid connection point bus voltage constraint condition, the voltage modulation ratio constraint condition, and the current constraint condition.

[0236] In one embodiment of the present application, optionally, the optimal solution determination unit is used to: determine, based on a preset parameter optimization algorithm, an optimal solution set of main circuit associated parameters and system control parameters of the flexible DC network system that satisfies the current constraint condition, the transmission capacity and voltage level constraint condition, the capacitor voltage fluctuation constraint condition, the double frequency circulating current limit constraint condition and the circulating current resonance constraint condition, satisfies the small interference stability constraint condition, and enables the flexible DC network system to reach the converter station's limit transmission power and the minimum MMC DC voltage, wherein the preset parameter optimization algorithm is a particle swarm optimization algorithm, a genetic algorithm, or an ant colony algorithm.

[0237] The device uses any one of the solutions described in the above embodiments, and therefore has all the above technical effects, which will not be repeated here.

[0238] In addition, in one embodiment, the present application provides a computer device, which may be a server, and its internal structure diagram may be as follows: Figure 5 As shown. The computer device includes a processor, a memory, a network interface and a database connected via a system bus. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile and / or volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The network interface of the computer device is used to communicate with an external client via a network connection. When the computer program is executed by the processor, the method described in any of the above embodiments can be implemented.

[0239] In one embodiment, the present application further provides a computer device, which may be a client, and its internal structure diagram may be as follows: Figure 6As shown. The computer device includes a processor, a memory, a network interface, a display screen and an input device connected via a system bus. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The network interface of the computer device is used to communicate with an external server via a network connection. When the computer program is executed by the processor, the method described in any of the above embodiments can be implemented.

[0240] Any of the above-mentioned computer devices in the embodiments of the present application may exist in various forms, including but not limited to:

[0241] (1) Mobile communication devices: These devices are characterized by having mobile communication functions and their main purpose is to provide voice and data communications. These terminals include: smart phones (such as iPhone), multimedia phones, functional phones, and low-end phones.

[0242] (2) Ultra-mobile personal computer devices: These devices fall into the category of personal computers, have computing and processing capabilities, and generally also have mobile Internet access features. These terminals include: PDA, MID and UMPC devices, such as iPad.

[0243] (3) Portable entertainment devices: These devices can display and play multimedia content. They include audio and video players (such as iPods), handheld game consoles, e-books, as well as smart toys, wearable devices, and portable car navigation devices.

[0244] (4) Server: A device that provides computing services. The server consists of a processor, hard disk, memory, system bus, etc. The server is similar to a general computer architecture, but because it needs to provide highly reliable services, it has higher requirements in terms of processing power, stability, reliability, security, scalability, and manageability.

[0245] (5) Other electronic devices with data interaction functions.

[0246] In addition, an embodiment of the present application provides a computer-readable storage medium storing computer-executable instructions, wherein the computer-executable instructions are used to perform the following steps:

[0247] Based on the grid parameter information of the AC grid served by the flexible DC grid system, determining the equivalent grid strength of the AC grid, wherein the equivalent grid strength is used to reflect the voltage stability of the AC grid when reactive power is injected;

[0248] Obtaining parameter constraints of the flexible DC networking system and obtaining small disturbance stability constraints of the flexible DC networking system, wherein the parameter constraints are used to reflect the rules that the main circuit associated parameters and system control parameters of the flexible DC networking system match when the flexible DC networking system provides effective services to the AC power grid, and the small disturbance stability constraints are used to reflect the rules that the flexible DC networking system matches to maintain stable operation when facing disturbances;

[0249] Based on the equivalent grid strength of the AC grid and the parameter constraints of the flexible DC network system, determining the converter station limit transmission power of the flexible DC network system;

[0250] Based on a preset parameter optimization algorithm, the optimal solution set of the main circuit associated parameters and system control parameters of the flexible DC network system when the flexible DC network system reaches the limit transmission power of the converter station is determined within the parameter range defined by the parameter constraints and the small interference stability constraints.

[0251] It should be noted that the above functions or steps that can be implemented by the computer-readable storage medium or computer device can refer to the relevant description in the aforementioned method embodiment. To avoid repetition, they will not be described one by one here.

[0252] The technical solution of the present application is described in detail above in combination with the accompanying drawings. The technical solution of the present application is aimed at the flexible DC networking system. On the basis of satisfying the MMC transmission power limit of the AC power grid strength, combined with the parameter constraints of the main circuit and the small interference stability constraints of the flexible DC networking system itself, a preset parameter optimization algorithm is used to determine the optimal solution set of the main circuit associated parameters and system control parameters of the flexible DC networking system. The parameters determined in this way can not only realize the transmission limit power of the converter station, but also meet the actual operation requirements of the flexible DC networking system and the AC power grid in multiple dimensions, improve the dynamic response capability of the flexible DC networking system, and provide effective guarantee for the safe operation of the AC power grid.

[0253] The word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrases "if it is determined" or "if (stated condition or event) is detected" may be interpreted as "when it is determined" or "in response to determining" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)", depending on the context.

[0254] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0255] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0256] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of hardware plus software functional units.

[0257] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. As an illustration and not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

[0258] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A parameter optimization method for a flexible DC network system, characterized in that: include: Based on the grid parameter information of the AC grid served by the flexible DC grid system, determining the equivalent grid strength of the AC grid, wherein the equivalent grid strength is used to reflect the voltage stability of the AC grid when reactive power is injected; Obtaining parameter constraints of the flexible DC networking system and obtaining small disturbance stability constraints of the flexible DC networking system, wherein the parameter constraints are used to reflect the rules that the main circuit associated parameters and system control parameters of the flexible DC networking system match when the flexible DC networking system provides effective services to the AC power grid, and the small disturbance stability constraints are used to reflect the rules that the flexible DC networking system matches to maintain stable operation when facing disturbances; Based on the equivalent grid strength of the AC grid and the parameter constraints of the flexible DC network system, determining the converter station limit transmission power of the flexible DC network system; Based on a preset parameter optimization algorithm, the optimal solution set of the main circuit associated parameters and system control parameters of the flexible DC network system when the flexible DC network system reaches the limit transmission power of the converter station is determined within the parameter range defined by the parameter constraints and the small interference stability constraints.

2. The method according to claim 1, characterized in that: Also includes: Determine whether all optimal solutions in the optimal solution set are within the corresponding preset safety range; If all optimal solutions in the optimal solution set are within the corresponding preset safety range, the optimal solution set is determined to be a valid candidate parameter; If at least one optimal solution in the optimal solution set is not within the corresponding preset safety range, the optimal solution set is determined to be an invalid candidate parameter, and the parameter range limited by the corresponding parameter constraint condition is adjusted based on the at least one optimal solution, and the process returns to the step of determining the maximum transmission power of the converter station of the flexible DC network system.

3. The method according to claim 1, characterized in that The determining the equivalent grid strength of the AC grid based on the grid parameter information of the AC grid served by the flexible DC networking system includes: Determine the equivalent impedance of the AC power grid connected in series with an equivalent infinite power source, where: Z g =R g +jX g , Z g is the equivalent impedance of the infinite power source in series, R g and X g are the equivalent resistance and equivalent reactance connected in series with the equivalent infinite power source, respectively, and j is an imaginary unit; Based on the equivalent impedance of the equivalent infinite power source connected in series, the rated DC power of the converter station of the AC power grid and the rated AC voltage amplitude of the common connection point in the AC power grid, the equivalent AC power grid short-circuit ratio of the AC power grid is determined as the equivalent power grid strength of the AC power grid, wherein: SCR is the equivalent AC grid short-circuit ratio of the AC grid, P dc is the rated DC power of the converter station of the AC power grid, U s is the rated AC voltage amplitude of the common connection point in the AC power grid.

4. The method according to any one of claims 1 to 3, characterized in that The obtaining of the parameter constraint conditions of the flexible direct current networking system includes: Obtain the power flow solvable constraint conditions of the flexible direct current grid system, the grid connection point bus voltage constraint conditions, the voltage modulation ratio constraint conditions, the current constraint conditions, the transmission capacity and voltage level constraint conditions, the capacitor voltage fluctuation constraint conditions, the double frequency circulating current limit constraint conditions and the circulating current resonance constraint conditions, wherein: The power flow solvability constraint condition is: P is the active power output by the converter station, Q is the reactive power output by the converter station, and U g is the equivalent voltage of the AC grid, R g is the equivalent resistance of the AC power grid connected in series with an equivalent infinite power source, X g The equivalent reactance connected in series with the equivalent infinite power source of the AC power grid; The grid connection point bus voltage constraint condition is: IN smin ≤U s ≤U smax , U s The rated AC voltage amplitude of the common connection point in the AC power grid is used to reflect the bus voltage at the grid connection point, U smin is the minimum value allowed by the bus voltage at the grid connection point, U smax The maximum value allowed for the bus voltage at the grid connection point; The voltage modulation ratio constraint condition is: M is the MMC modulation ratio, U dc is the MMC DC voltage; The current constraint condition is: j is the imaginary unit, I sN is the rated current of the MMC AC side; The transmission capacity and voltage level constraints are: S dc =αU dc I pa , S dc is the DC transmission power, I pa is the upper bridge arm current of phase a, and α is the second predetermined coefficient; The capacitor voltage fluctuation constraint condition is: C0 is the MMC submodule capacitance, N is the number of MMC submodules, ε is the operating fluctuation range of the capacitor voltage, U c0 is the MMC submodule capacitor voltage, ω is the system frequency; The double frequency circulating current restriction constraint condition is: L is the MMC bridge arm inductance, U N is the rated voltage, γ is the allowable fluctuation range of the double frequency circulating current, I dc is the MMC DC current; The ring current resonance constraint condition is: ω res is the resonant angular frequency of the circulating current resonance.

5. The method according to claim 4, characterized in that Obtaining the small interference stability constraint condition of the flexible DC networking system, including: Obtain a small interference analysis model of the flexible DC networking system, wherein the small interference analysis model reflects the correlation between the sum of the state variable and the interference input variable of the flexible DC networking system and the system state change level of the flexible DC networking system in unit time, and the small interference analysis model is: Wherein, Δx is the increment of n state variables in the flexible direct current networking system, Δu is the increment of m input variables, A is an n×n order state matrix, and B is an n×m order input matrix; Based on the small disturbance analysis model, the small disturbance stability constraint condition of the flexible DC networking system is determined as follows: Among them, rank(A) refers to the rank of matrix A, λ i is the i-th characteristic root of the flexible DC network system, Re(λ i ) refers to finding λ i The real part of .

6. The method according to claim 5, characterized in that The determining the converter station limit transmission power of the flexible DC networking system based on the equivalent grid strength of the AC grid and the parameter constraint condition of the flexible DC networking system includes: Within the optional parameter range of the flexible DC network system defined by the power flow solubility constraint, the grid connection point bus voltage constraint, the voltage modulation ratio constraint, and the current constraint, determine the converter station limit transmission power of the flexible DC network system when the AC power grid reaches the equivalent power grid strength.

7. The method according to claim 1, characterized in that The method of determining the optimal solution set of main circuit associated parameters and system control parameters of the flexible DC network system when the flexible DC network system reaches the limit transmission power of the converter station based on the preset parameter optimization algorithm within the parameter range defined by the parameter constraint condition and the small interference stability constraint condition includes: Based on a preset parameter optimization algorithm, determine the optimal solution set of the main circuit associated parameters and system control parameters of the flexible DC network system that satisfies the current constraint condition, the transmission capacity and voltage level constraint condition, the capacitor voltage fluctuation constraint condition, the double frequency circulating current limit constraint condition and the circulating current resonance constraint condition, satisfies the small interference stability constraint condition, and enables the flexible DC network system to reach the converter station limit transmission power and the minimum MMC DC voltage, wherein: The preset parameter optimization algorithm is a particle swarm optimization algorithm, a genetic algorithm or an ant colony algorithm.

8. A parameter optimization device for a flexible DC network system, characterized in that: include: An equivalent grid strength determination unit, used to determine the equivalent grid strength of the AC grid served by the flexible DC grid system based on grid parameter information of the AC grid, wherein the equivalent grid strength is used to reflect the voltage stability of the AC grid when reactive power is injected; A constraint determination unit, used for obtaining parameter constraints of the flexible DC networking system and obtaining small disturbance stability constraints of the flexible DC networking system, wherein the parameter constraints are used to reflect the rules that the main circuit associated parameters and system control parameters of the flexible DC networking system match when the flexible DC networking system provides effective services to the AC power grid, and the small disturbance stability constraints are used to reflect the rules that the flexible DC networking system matches to maintain stable operation when facing disturbances; A limit transmission power determination unit, configured to determine the limit transmission power of a converter station of the flexible DC network system based on the equivalent grid strength of the AC grid and the parameter constraints of the flexible DC network system; The optimal solution determination unit is used to determine the optimal solution set of the main circuit associated parameters and system control parameters of the flexible DC network system when the maximum transmission power of the converter station is reached within the parameter range defined by the parameter constraint condition and the small interference stability constraint condition based on a preset parameter optimization algorithm.

9. A computer device, characterized in that: include: at least one processor; and, a memory communicatively coupled to the at least one processor; The memory stores instructions executable by the at least one processor, wherein the instructions are configured to execute the method according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that: Computer executable instructions are stored, and the computer executable instructions are used to execute the method according to any one of claims 1 to 7.

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