Fault ride-through method of flexible direct current power transmission system containing wind power integration and related products

Abstract

The invention discloses a fault ride-through method of a flexible DC power transmission system containing wind power access and related products, and the method comprises the steps: carrying out the equivalence of a receiving-end power grid when the AC fault of the receiving-end power grid occurs, and obtaining the fault equivalence parameter of the receiving-end power grid based on the real-time collected electric quantity of a wind power grid-connected point; according to the equivalent parameters, constructing a first transmission model of the power of the flexible direct current receiving end converter station and the voltage of the wind power grid-connected point, and a second transmission model of the power of the flexible direct current receiving end converter station and the frequency change rate of the receiving end power grid; based on the first transfer model and the second transfer model, taking the minimization of the voltage deviation of the wind power grid-connected point and the minimization of the frequency change rate of the receiving-end power grid as targets to construct a fault ride-through control model; and solving the fault ride-through control model to obtain a current control reference value of the flexible DC receiving end converter station, so as to control the flexible DC power transmission system based on the current control reference value. By adopting the embodiment of the invention, the phenomenon of off-network operation of the fan during the fault period can be avoided.

Description

Technical Field

[0001] This application relates to the field of fault ride-through technology for flexible DC transmission systems, and in particular to fault ride-through methods and related products for flexible DC transmission systems with wind power integration. Background Technology

[0002] In current power systems, the large-scale integration of renewable energy units and flexible DC transmission systems has become a key characteristic of the new power grid. While the high penetration rate of renewable energy generation increases the proportion of clean energy, it also exacerbates the risk of wind turbines disconnecting from the grid during grid faults. When the voltage at the wind power grid connection point drops below the critical value due to an AC fault, its protection system trips the turbine to prevent equipment damage. Under existing AC faults, wind turbines utilize low-voltage ride-through technology to restore voltage through reactive current injection. However, if the voltage drop is too deep, the wind turbine itself cannot support its grid connection point voltage. Simultaneously, the rapid change in the receiving-end grid frequency (i.e., system frequency) under AC faults may exceed the frequency tolerance range of the wind turbine, further triggering frequency protection and causing the wind turbine to trip. Therefore, under AC faults, the low-voltage ride-through control strategy relying solely on the wind turbine itself cannot simultaneously meet the safety threshold requirements for both voltage and frequency. Meanwhile, as a critical power regulation unit in the power grid, the flexible DC transmission system's control methods and the low-voltage ride-through control of renewable energy units have not yet formed effective synergy under AC faults, failing to fully leverage the flexible DC transmission system's support capability for safe system operation.

[0003] Current technical solutions for fault ride-through in flexible DC transmission systems with wind power integration mainly focus on the independent optimization of single equipment. They typically only study a single objective, such as the voltage at the wind power grid connection point or the frequency of the receiving-end grid. At the same time, existing research also ignores the dynamic interaction between wind turbines and adjacent flexible DC transmission systems. The research is limited to a single-machine control framework and has not built a collaborative optimization model between wind turbines and flexible DC transmission systems, resulting in insufficient adaptability of single equipment parameters under system-level fault scenarios.

[0004] In summary, existing research on fault ride-through in flexible DC transmission systems with wind power integration suffers from several drawbacks. Firstly, if wind turbine fault ride-through control only supports the wind turbine grid connection voltage, the active power imbalance during AC faults will exacerbate the frequency change rate of the receiving-end grid, causing it to exceed the protection threshold and trigger grid disconnection. Secondly, the dynamic coupling relationship between the power of the flexible DC transmission system and the wind turbine grid connection voltage versus the receiving-end grid frequency lacks effective modeling, failing to fully leverage the system's ability to collaboratively support both. Therefore, a collaborative control method that considers both the wind turbine grid connection voltage and the receiving-end grid frequency is urgently needed to prevent wind turbine disconnection during AC grid faults. Summary of the Invention

[0005] This application provides a fault ride-through method and related products for a flexible DC transmission system with wind power access, in order to solve the problem that the control target in the prior art only considers voltage or frequency and the control means lack systematic coordination.

[0006] To achieve the above objectives, embodiments of this application provide a fault ride-through method for a flexible DC transmission system with wind power integration, comprising:

[0007] When an AC fault occurs in the receiving-end power grid, the receiving-end power grid is equivalently evaluated, and the equivalent parameters of the receiving-end power grid fault are obtained based on the real-time collected electrical quantities at the wind power grid connection point.

[0008] Based on the equivalent parameters, a first transfer model of the power of the flexible DC receiving-end converter station and the voltage of the wind power grid connection point are constructed, and a second transfer model of the power of the flexible DC receiving-end converter station and the frequency change rate of the receiving-end grid is constructed.

[0009] Based on the first and second transmission models, a fault ride-through control model is constructed with the objectives of minimizing the voltage deviation at the wind power grid connection point and minimizing the frequency change rate of the receiving-end power grid.

[0010] The fault ride-through control model is solved to obtain the current control reference value of the flexible DC receiving-end converter station, and the flexible DC transmission system is controlled based on the current control reference value.

[0011] As an improvement to the above scheme, the method of obtaining equivalent parameters of grid faults at the receiving end based on real-time collected electrical quantities at the wind power grid connection point includes:

[0012] The equivalent impedance and equivalent potential of the receiving-end power grid fault are obtained from the following formulas:

[0013]

[0014] Among them, ZE X is the equivalent impedance of the receiving-end power grid fault; j is the imaginary unit; X L X is the equivalent reactance of the receiving-end power grid under normal operating conditions; T For transformer reactance; e E e is the equivalent potential of the receiving-end grid fault; S R is the voltage vector under normal operating conditions of the receiving-end power grid. f X f These are the virtual transition resistance and virtual transition reactance, respectively, for the effects of an equivalent AC short circuit.

[0015]

[0016] Among them, I f.d I represents the d-axis current flowing into the receiving-end grid from the wind power grid connection point under grid fault conditions. f.q U is the q-axis current flowing into the receiving-end grid from the wind power grid connection point under grid fault conditions. PCC.d U represents the d-axis voltage component at the wind power grid connection point. PCC.q E represents the q-axis voltage component at the wind power grid connection point. S.d E represents the d-axis voltage component of the receiving-end grid's normal operating voltage. S.q This represents the q-axis voltage component of the grid voltage under normal operating conditions at the receiving end.

[0017] As an improvement to the above scheme, the first transmission model is specifically as follows:

[0018] U PCC =f(P rec Q rec )

[0019] Among them, U PCC f(P) represents the voltage amplitude at the wind power grid connection point. rec Q rec ) for U PCC Regarding the output active power P of the flexible DC receiving-end converter station rec The output reactive power Q of the flexible DC receiving-end converter station rec The function is established as follows:

[0020]

[0021] Among them, E E G represents the equivalent potential amplitude of a fault in the receiving-end power grid. E This refers to the conductance between the voltage at the wind power grid connection point and the equivalent potential of a fault in the receiving-end power grid. Re() represents the real part operation, Z E B is the equivalent impedance of the receiving-end power grid fault; E This refers to the susceptance between the voltage at the wind power grid connection point and the equivalent potential of a fault in the receiving-end power grid. Im() represents the imaginary part operation; θ WE I represents the phase difference between the voltage at the wind power grid connection point and the equivalent electromotive force of the fault in the receiving-end power grid. wf.d I is the output d-axis current of the wind turbine. wf.q The output q-axis current of the wind turbine is as follows:

[0022]

[0023] Where K is the reactive current coefficient; U PCC.N I represents the rated voltage amplitude at the wind power grid connection point. wf.N I is the rated output current of the wind turbine generator set. max This is the AC current limiting value.

[0024] As an improvement to the above scheme, the second transfer model is specifically as follows:

[0025]

[0026] Where d is the differential, f is the receiving-end grid frequency; t is the duration of the AC fault; ΔP rec ΔP represents the change in output active power of the flexible DC receiving-end converter station. wf ΔP represents the change in the output active power of the wind turbine generator. im ρ is the system unbalanced active power at the moment of failure; D is the system load damping constant; ρ is the wind turbine permeability; H is the system inertial time constant; and τ is the time integral variable.

[0027] As an improvement to the above scheme, the objective function of the fault ride-through control model is specifically:

[0028]

[0029] Wherein, F1 is the objective function with the voltage deviation at the wind power grid connection point as the optimization objective; F2 is the objective function with the frequency change rate of the receiving-end grid as the optimization objective; U PCC U represents the voltage amplitude at the wind power grid connection point. PCC.N d is the rated voltage amplitude at the wind power grid connection point; f is the differential; t is the receiving-end grid frequency; and t is the duration of the AC fault.

[0030] As an improvement to the above scheme, the constraints of the fault ride-through control model include:

[0031] The node voltage and current constraints are:

[0032] U PCC.min ≤U PCC ≤U PCC.max

[0033] U E.min ≤UE ≤U E.max

[0034] I f.min ≤I f ≤I f.max

[0035] Among them, U PCC.max U is the upper limit of the voltage amplitude at the wind power grid connection point. PCC.min U is the lower limit of the voltage amplitude at the wind power grid connection point; E.max U is the upper limit of the potential within the fault location point. E.min I is the lower limit of the internal potential at the fault location point; f.max I is the upper limit of the current flowing into the receiving-end power grid from the wind power grid connection point. f.min This is the lower limit of the current flowing into the receiving-end power grid at the wind power grid connection point;

[0036] The line current carrying capacity constraint is:

[0037] |S WE |≤S WE.max

[0038] Among them, S WE S represents the apparent power flowing into the receiving-end power grid from the wind power grid connection point. WE.max The maximum allowable flow rate;

[0039] DC voltage constraints in flexible DC transmission systems:

[0040]

[0041] Among them, P rec P represents the output active power of the flexible DC receiving-end converter station. dc For the DC output power of the flexible DC sending-end converter station, U dc.N K is the rated DC voltage of the DC line. U C is the maximum allowable voltage coefficient. eq For DC circuits, the DC capacitor is U. dc.0 This refers to the DC voltage of the DC line during normal operation.

[0042] Frequency constraints of the receiving end power grid:

[0043] f0-Δf max ≤f≤f0+Δf max

[0044]

[0045] Where f0 is the rated operating frequency of the receiving-end power grid; Δf max denoted as the maximum permissible frequency deviation; f is the receiving-end grid frequency; μ is the maximum permissible frequency change rate of the wind turbine without disconnecting from the grid.

[0046] Optionally, solving the fault ride-through control model to obtain the current control reference value for the flexible DC receiving-end converter station includes:

[0047] Gene encoding and population initialization: The active current control parameters and reactive current control reference values ​​of the flexible DC receiving-end converter station are encoded into a two-dimensional array, and an initial population that satisfies the constraints of the fault ride-through control model is randomly generated; wherein, each individual in the initial population represents a set of current control reference value combinations that satisfy the constraints of the fault ride-through control model.

[0048] Non-dominated ranking and front partitioning: Based on the objective function of the fault-crossing control model, individuals are non-dominated and ranked. The condition for individual i to dominate individual j is defined as follows:

[0049] and

[0050] Where F1(i) is the objective function with the voltage deviation at the wind power grid connection point as the optimization objective, and F2(i) is the objective function with the frequency change rate of the receiving-end grid as the optimization objective;

[0051] The population is divided into multiple fronts based on non-dominance relationships, where front 1 contains all solutions that are not dominated by other individuals;

[0052] Crowding Calculation and Diversity Maintenance: Within the same frontier, selection is performed based on the relationship between crowding in descending order to maintain population diversity. Crowding is defined as:

[0053]

[0054] Where: d i F represents the crowding level of individual i; k (p i+1 F represents the function value of the first individual after i in the objective function sorting; k (p i-1 F represents the function value of the first individual preceding i in the objective function sorting; k,max F represents the maximum value of the objective function. k,min This represents the minimum value of the objective function;

[0055] Genetic operations and offspring generation: Based on sorting from front to back, individuals with crowding greater than a preset threshold are selected for crossover to generate new offspring individuals. A simulated binary crossover operation is used.

[0056]

[0057] Among them, c 1,k p is the value of the kth gene in offspring individual 1;1,k p 2,k These are the values ​​of the k-th gene in parent individual 1 and individual 2, respectively; γ k The cross-distribution factor; u k η is a random number uniformly distributed within the interval [0,1]. c The cross-distribution index;

[0058] Elite retention and iterative optimization: merge the parent and offspring populations, re-execute non-dominated sorting and crowding calculation to select the top N optimal individuals, and repeat the iteration until the objective function of the fault crossing control model converges;

[0059] Optimal parameter decision: Select the optimal combination of current control reference values ​​from the Pareto frontier, which combines the voltage deviation at the wind power grid connection point and the frequency change rate of the receiving-end grid.

[0060] To achieve the above objectives, embodiments of this application also provide a fault ride-through system for a flexible DC transmission system with wind power integration, including...

[0061] The equivalent module is used to perform equivalent assessment on the receiving-end power grid when an AC fault occurs, and to obtain the equivalent parameters of the receiving-end power grid fault based on the real-time collected electrical quantities at the wind power grid connection point.

[0062] The first construction module is used to construct a first transfer model of the power of the flexible DC receiving-end converter station and the voltage of the wind power grid connection point, and a second transfer model of the power of the flexible DC receiving-end converter station and the frequency change rate of the receiving-end power grid, based on the equivalent parameters.

[0063] The second construction module is used to construct a fault ride-through control model based on the first transmission model and the second transmission model, with the objectives of minimizing the voltage deviation at the wind power grid connection point and minimizing the frequency change rate of the receiving-end power grid.

[0064] The control module is used to solve the fault ride-through control model to obtain the current control reference value of the flexible DC receiving-end converter station, so as to control the flexible DC transmission system based on the current control reference value.

[0065] To achieve the above objectives, this application also provides a fault ride-through device for a flexible DC transmission system with wind power access, including a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. When the processor executes the computer program, it implements the fault ride-through method for a flexible DC transmission system with wind power access as described above.

[0066] To achieve the above objectives, embodiments of this application also provide a computer-readable storage medium, the computer-readable storage medium including a stored computer program; wherein, when the computer program is executed, it controls the device where the computer-readable storage medium is located to perform the fault ride-through method of the flexible DC transmission system with wind power access as described above.

[0067] Compared with existing technologies, the present application provides a fault ride-through and related products for a flexible DC transmission system. When an AC fault occurs in the receiving-end grid, the receiving-end grid is equivalently evaluated, and equivalent fault parameters are obtained based on real-time collected electrical quantities at the wind power grid connection point. Based on these equivalent parameters, a first transfer model is constructed between the power of the flexible DC receiving-end converter station and the voltage at the wind power grid connection point, and a second transfer model is constructed between the power of the flexible DC receiving-end converter station and the frequency change rate of the receiving-end grid. Based on the first and second transfer models, a fault ride-through control model is constructed with the objectives of minimizing the voltage deviation at the wind power grid connection point and minimizing the frequency change rate of the receiving-end grid. The fault ride-through control model is solved to obtain a current control reference value for the flexible DC receiving-end converter station. The flexible DC transmission system is then controlled based on this current control reference value. Therefore, this application embodiment achieves coordinated control of the dual objectives of minimizing voltage deviation and suppressing the frequency change rate of the receiving-end grid by establishing a transfer model (including the first transfer model and the second transfer model) between the power of the flexible DC receiving-end converter station and the voltage at the wind power grid connection point and the frequency change rate of the receiving-end grid, effectively avoiding the phenomenon of wind turbine disconnection during faults. Attached Figure Description

[0068] Figure 1 This is a flowchart of a fault ride-through method for a flexible DC transmission system with wind power access, provided in an embodiment of this application.

[0069] Figure 2 This is a structural block diagram of a standard test system for building a mainnet model, provided in an embodiment of this application.

[0070] Figure 3 This is a structural block diagram of a power grid model based on the equivalent electrical quantities at the wind power grid connection point, provided in the embodiments of this application.

[0071] Figure 4 This is a structural block diagram of a fault ride-through system of a flexible DC transmission system with wind power access provided in an embodiment of this application;

[0072] Figure 5 This is a structural block diagram of a fault ride-through device for a flexible DC transmission system with wind power access, provided in an embodiment of this application. Detailed Implementation

[0073] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0074] In the description of this application, the sequence numbers of the following processes do not imply a specific order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application. The terms "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design scheme described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design schemes.

[0075] See Figure 1 , Figure 1 This is a flowchart illustrating a fault ride-through method for a flexible DC transmission system with wind power integration, provided in an embodiment of this application. The fault ride-through method for the flexible DC transmission system with wind power integration includes:

[0076] S1. When an AC fault occurs in the receiving-end power grid, the receiving-end power grid is equivalently evaluated, and the equivalent parameters of the receiving-end power grid fault are obtained based on the real-time collected electrical quantities at the wind power grid connection point.

[0077] S2. Based on the equivalent parameters, construct a first transfer model of the power of the flexible DC receiving-end converter station and the voltage of the wind power grid connection point, and a second transfer model of the power of the flexible DC receiving-end converter station and the frequency change rate of the receiving-end power grid.

[0078] S3. Based on the first transmission model and the second transmission model, a fault ride-through control model is constructed with the objectives of minimizing the voltage deviation at the wind power grid connection point and minimizing the frequency change rate of the receiving-end power grid.

[0079] S4. Solve the fault ride-through control model to obtain the current control reference value of the flexible DC receiving-end converter station, and control the flexible DC transmission system based on the current control reference value.

[0080] In specific implementation, in step S1, some electrical parameter measuring instruments such as power analyzers and power quality analyzers can be used to measure parameters such as voltage, current, active power, and reactive power in real time at the ports of the flexible DC system, the wind turbine ports, and the wind power grid connection points; for example, a resistive voltage divider or an isolated voltage sensor can be used to collect the DC bus voltage of the flexible DC system. There are no specific limitations on this in the field.

[0081] In specific implementation, in step S1, in order to obtain the relationship between the power of the flexible DC receiving-end converter station under fault conditions and the voltage at the wind power grid connection point and the system rate of change, it is necessary to perform equivalent calculations on the faulted power grid. The equivalent calculation methods include:

[0082] Based on the active current, reactive current, and dq-axis voltage components at the wind power grid connection point, AC faults occurring within the receiving-end grid are equivalent to virtual impedances at the wind power grid connection point. Using the transformer reactance equivalent parameters and the grid voltage vector phase difference, the equivalent impedance and equivalent potential of the receiving-end grid fault are derived.

[0083] Specifically, the equivalent impedance and equivalent potential of the receiving-end grid fault are obtained according to the following formulas:

[0084]

[0085] Among them, Z E X is the equivalent impedance of the receiving-end power grid fault; j is the imaginary unit; X L X is the equivalent reactance of the receiving-end power grid under normal operating conditions; T For transformer reactance; e E e is the equivalent potential of the receiving-end grid fault; S R is the voltage vector under normal operating conditions of the receiving-end power grid. f 、X f These are the virtual transition resistance and virtual transition reactance, respectively, for the effects of an equivalent AC short circuit.

[0086]

[0087] Among them, I f.d I represents the d-axis current flowing into the receiving-end grid from the wind power grid connection point under grid fault conditions. f.q U is the q-axis current flowing into the receiving-end grid from the wind power grid connection point under grid fault conditions. PCC.d U represents the d-axis voltage component at the wind power grid connection point. PCC.q E represents the q-axis voltage component at the wind power grid connection point. S.d E represents the d-axis voltage component of the receiving-end grid's normal operating voltage. S.q This represents the q-axis voltage component of the receiving-end power grid under normal operating conditions.

[0088] In an optional embodiment, the first transfer model in step S2 is specifically:

[0089] U PCC =f(P rec Q rec )

[0090] Among them, U PCC f(P) represents the voltage amplitude at the wind power grid connection point. rec Qrec ) for U PCC Regarding the output active power P of the flexible DC receiving-end converter station rec The output reactive power Q of the flexible DC receiving-end converter station rec The function is established as follows:

[0091]

[0092] Among them, E E G represents the equivalent potential amplitude of a fault in the receiving-end power grid. E This refers to the conductance between the voltage at the wind power grid connection point and the equivalent potential of a fault in the receiving-end power grid. Re() represents the real part operation, Z E B is the equivalent impedance of the receiving-end power grid fault; E This refers to the susceptance between the voltage at the wind power grid connection point and the equivalent potential of a fault in the receiving-end power grid. Im() represents the imaginary part operation; θ WE I represents the phase difference between the voltage at the wind power grid connection point and the equivalent electromotive force of the fault in the receiving-end power grid. wf.d I is the output d-axis current of the wind turbine. wf.q The output q-axis current of the wind turbine is as follows:

[0093]

[0094] Where K is the reactive current coefficient; U PCC.N I represents the rated voltage amplitude at the wind power grid connection point. wf.N I is the rated output current of the wind turbine generator set. max This is the AC current limiting value.

[0095] In this embodiment of the application, a first transfer model between the power of the flexible DC receiving-end converter station and the voltage at the wind power grid connection point is determined through the following steps:

[0096] Based on the power flow relationship of the power grid, the functional relationships between the output active power of the flexible DC receiving-end converter station, the voltage amplitude at the wind power grid connection point, and the output current amplitude of the wind turbine are derived:

[0097]

[0098] Based on the low-voltage control equations of the wind turbine under fault conditions, the relationship between the dq-axis components of the wind turbine's output current and the voltage amplitude at the wind power grid connection point is derived:

[0099]

[0100] The first transitive model is obtained as follows:

[0101] U PCC =f(P rec Qrec )

[0102] Among them, U PCC f(P) represents the voltage amplitude at the wind power grid connection point. rec Q rec ) for U PCC Regarding the output active power P of the flexible DC receiving-end converter station rec The output reactive power Q of the flexible DC receiving-end converter station rec The function.

[0103] In an optional embodiment, the second transfer model in step S2 is specifically:

[0104]

[0105] Where d is the differential, f is the receiving-end grid frequency; t is the duration of the AC fault; ΔP rec ΔP represents the change in output active power of the flexible DC receiving-end converter station. wf ΔP represents the change in the output active power of the wind turbine generator. im ρ is the system unbalanced active power at the moment of failure; D is the system load damping constant; ρ is the wind turbine permeability; H is the system inertial time constant; and τ is the time integral variable.

[0106] In this embodiment of the application, a second transfer model for the active power and frequency change rate of the flexible DC receiving-end converter station is determined by combining the equivalent impedance and equivalent potential of the receiving-end grid fault with the equivalent impedance and equivalent potential of the receiving-end grid fault through the following steps:

[0107] Based on the power flow equations, determine the impact of active power variations at the flexible DC receiving-end converter station on the active power of the wind turbine generators:

[0108]

[0109] In the formula, P wf ΔP represents the output active power of the wind turbine under normal operating conditions. wf P represents the change in the output active power of the wind turbine generator. rec The output active power of the flexible DC receiving-end converter station; ΔP rec U represents the change in output active power of the flexible DC receiving-end converter station; PCC E represents the voltage amplitude at the wind power grid connection point. E G represents the equivalent potential amplitude of a fault in the receiving-end power grid. E θ is the conductance between the voltage at the wind power grid connection point and the equivalent potential of the fault in the receiving-end grid; WE B is the phase difference between the voltage at the wind power grid connection point and the equivalent electromotive force of the fault in the receiving-end power grid. E Q is the susceptance between the voltage at the wind power grid connection point and the equivalent potential of a fault in the receiving-end grid; wfΔQ represents the reactive power output of the wind turbine under normal operating conditions. wf Q represents the change in reactive power output of the wind turbine generator. rec The output reactive power of the flexible DC receiving-end converter station; ΔQ rec This represents the change in output reactive power at the receiving end of the flexible DC converter station.

[0110] Based on the receiving-end power grid frequency response model, the frequency shift of the system caused by changes in the power of the flexible DC receiving-end converter station and the power of the wind turbine generators is quantified. The receiving-end power grid frequency response model is as follows:

[0111]

[0112] In the formula, ρ represents the wind turbine penetration rate, specifically the proportion of wind turbine installed capacity in a region to the total installed capacity of the power system in that region; ΔP im denoted as Δf, where Δf is the system unbalanced active power at the instant of the fault; H is the system inertial time constant; D is the system load damping constant; f is the receiving-end grid frequency; and Δf is the frequency deviation of the receiving-end grid under the fault.

[0113] Based on the receiving-end power grid frequency response model, the expression for Δf in the time domain is:

[0114]

[0115] In the formula, t is the duration of the fault.

[0116] Furthermore, after eliminating Δf, the second transfer model is obtained as follows:

[0117]

[0118] Where d is the differential, f is the receiving-end grid frequency; t is the duration of the AC fault; ΔP rec ΔP represents the change in output active power of the flexible DC receiving-end converter station. wf ΔP represents the change in the output active power of the wind turbine generator. im ρ is the system unbalanced active power at the moment of failure; D is the system load damping constant; ρ is the wind turbine permeability; H is the system inertial time constant; and τ is the time integral variable.

[0119] In an optional embodiment, the objective function of the fault ride-through control model in step S3 is specifically:

[0120]

[0121] Wherein, F1 is the objective function with the voltage deviation at the wind power grid connection point as the optimization objective; F2 is the objective function with the frequency change rate of the receiving-end grid as the optimization objective; U PCC U represents the voltage amplitude at the wind power grid connection point.PCC.N d is the rated voltage amplitude at the wind power grid connection point; f is the differential; t is the receiving-end grid frequency; and t is the duration of the AC fault.

[0122] In this embodiment, the objective function of the fault ride-through control model considers the impact of power adjustment at the receiving-end converter station of the flexible DC transmission line on the voltage at the wind power grid connection point and the frequency of the receiving-end grid, avoiding wind turbine disconnection caused by excessive voltage deviation at the wind power grid connection point or excessive frequency change rate of the receiving-end grid. It is established as follows:

[0123] To avoid wind turbine disconnection under fault conditions, the voltage deviation at the wind power grid connection point and the frequency change rate of the receiving-end grid should be minimized. Therefore, a dual objective function is constructed by using the first transfer model of the power of the flexible DC receiving-end converter station and the voltage at the wind power grid connection point, and the second transfer model of the power of the flexible DC receiving-end converter station and the frequency change rate of the receiving-end grid.

[0124] In an optional embodiment, the constraints of the fault ride-through control model in step S3 include:

[0125] The node voltage and current constraints are:

[0126] U PCC.min ≤U PCC ≤U PCC.max

[0127] U E.min ≤U E ≤U E.max

[0128] I f.min ≤I f ≤I f.max

[0129] Among them, U PCC.max U is the upper limit of the voltage amplitude at the wind power grid connection point. PCC.min U is the lower limit of the voltage amplitude at the wind power grid connection point; E.max U is the upper limit of the potential within the fault location point. E.min I is the lower limit of the internal potential at the fault location point; f.max I is the upper limit of the current flowing into the receiving-end power grid from the wind power grid connection point. f.min This is the lower limit of the current flowing into the receiving-end power grid at the wind power grid connection point;

[0130] The line current carrying capacity constraint is:

[0131] |S WE |≤S WE.max

[0132] Among them, S WE S represents the apparent power flowing into the receiving-end power grid from the wind power grid connection point. WE.max The maximum allowable flow rate;

[0133] DC voltage constraints in flexible DC transmission systems:

[0134]

[0135] Among them, P rec P represents the output active power of the flexible DC receiving-end converter station. dc For the DC output power of the flexible DC sending-end converter station, U dc.N K is the rated DC voltage of the DC line. U C is the maximum allowable voltage coefficient. eq For DC circuits, the DC capacitor is U. dc.0 This refers to the DC voltage of the DC line during normal operation.

[0136] Frequency constraints of the receiving end power grid:

[0137] f0-Δf max ≤f≤f0+Δf max

[0138]

[0139] Where f0 is the rated operating frequency of the receiving-end power grid; Δf max denoted as the maximum permissible frequency deviation; f is the receiving-end grid frequency; μ is the maximum permissible frequency change rate of the wind turbine without disconnecting from the grid.

[0140] It is worth noting that existing technologies neglect key constraints such as line current carrying capacity, DC voltage safety threshold, and wind turbine frequency tolerance range. This application integrates node voltage and current constraints, line current carrying capacity constraints, DC voltage constraints, and frequency change rate constraints to construct a fault ride-through control model, ensuring that the control strategy achieves optimal adjustment while meeting the power grid's safe operation boundaries, thus balancing equipment safety and system safety.

[0141] This application's embodiments consider the maximum allowable AC current and DC voltage constraints when determining the power of the flexible DC receiving-end converter station, which can prevent equipment damage due to overcurrent or overvoltage, extend the service life of the equipment, and reduce maintenance costs. By reasonably determining the current reference value of the flexible DC receiving-end converter station, it ensures that the flexible DC converter station can meet the AC current and DC voltage constraints during operation, and also ensures that critical wind turbine units will not disconnect from the grid due to excessive frequency variation of the receiving-end grid and excessive voltage deviation of the wind turbine units.

[0142] In specific implementation, step S5 involves solving the fault ride-through control model using the NSGA-II multi-objective genetic algorithm. The solution process includes:

[0143] The active current control parameters and reactive current control reference values ​​of the flexible DC receiving-end converter station are encoded as two-dimensional array individuals. The optimization performance of each two-dimensional array individual under the objective function of the fault ride-through control model is compared. The two-dimensional array individuals are then subjected to genetic screening to generate a non-dominated sorting selection front solution set. The optimal two-dimensional array is selected from the Pareto front through a congestion mechanism. This two-dimensional array corresponds to the optimal active current control parameters and reactive current control reference values.

[0144] Specifically, gene encoding and population initialization: the active current control parameters and reactive current control reference values ​​of the flexible DC receiving-end converter station are encoded into a two-dimensional array, and an initial population that satisfies the constraints of the fault ride-through control model is randomly generated; wherein, each individual in the initial population represents a set of current control reference value combinations that satisfy the constraints of the fault ride-through control model.

[0145] Non-dominated ranking and front partitioning: Based on the objective function of the fault-crossing control model, individuals are non-dominated and ranked. The condition for individual i to dominate individual j is defined as follows:

[0146] and

[0147] Where F1(i) is the objective function with the voltage deviation at the wind power grid connection point as the optimization objective, and F2(i) is the objective function with the frequency change rate of the receiving-end grid as the optimization objective;

[0148] The population is divided into multiple fronts based on non-dominance relationships, where front 1 contains all solutions that are not dominated by other individuals;

[0149] Crowding Calculation and Diversity Maintenance: Within the same frontier, selection is performed based on the relationship between crowding in descending order to maintain population diversity. Crowding is defined as:

[0150]

[0151] Where: d i F represents the crowding level of individual i; k (p i+1 F represents the function value of the first individual after i in the objective function sorting; k (p i-1 F represents the function value of the first individual preceding i in the objective function sorting; k,max F represents the maximum value of the objective function. k,min This represents the minimum value of the objective function;

[0152] Genetic operations and offspring generation: Based on sorting from front to back, individuals with crowding greater than a preset threshold are selected for crossover to generate new offspring individuals. A simulated binary crossover operation is used.

[0153]

[0154] Among them, c 1,k p is the value of the kth gene in offspring individual 1; 1,k p 2,k These are the values ​​of the k-th gene in parent individual 1 and individual 2, respectively; γ k The cross-distribution factor; u k η is a random number uniformly distributed within the interval [0,1]. c The cross-distribution index;

[0155] Elite retention and iterative optimization: merge the parent and offspring populations, re-execute non-dominated sorting and crowding calculation to select the top N optimal individuals, and repeat the iteration until the objective function of the fault crossing control model converges;

[0156] Optimal parameter decision: Select the optimal combination of current control reference values ​​from the Pareto frontier, which combines the voltage deviation at the wind power grid connection point and the frequency change rate of the receiving-end grid.

[0157] It is worth noting that existing fault ride-through technologies for new energy sources at inverter interfaces mainly employ methods such as additional energy storage, supercapacitors, or load shedding, which suffer from high costs, complex operation and maintenance, or inapplicability of the underlying principles. This application uses the NSGA-II multi-objective genetic algorithm to quickly generate optimal control parameters that balance dynamic performance and safety constraints, without increasing costs and with a faster fault response speed.

[0158] In this embodiment, a simulation model is built in MATLAB / Simulink to verify the correctness and effectiveness of the theoretical analysis and the embodiments of this application. The embodiment constructs a mainnet model based on an improved IEEE 39-bus standard test system, as follows: Figure 2 The main grid transmission voltage is 345kV, and the distribution network voltages are 138kV and 35kV. This model includes 39 nodes, 10 synchronous generators, 19 load branches, and multiple transmission lines. Specific parameters are as follows: Traditional thermal and hydropower are distributed at nodes 31, 32, 33, and 35-39, with a rated voltage of 22kV, stepped up to 345kV for grid connection, and a total installed capacity of 6.2GW. The flexible DC receiving-end converter station is connected at node 34, with a DC side voltage of ±320kV. Node 34 is the connection point for a new energy wind farm, with a rated capacity of 300MW, connected to node 34 via a 35kV collector line. The total load of load nodes 3, 4, 7, and 8 is 6.15GW, with a power factor ranging from 0.85 to 0.95.

[0159] For complex main grid models, the equivalent method proposed in this application simplifies the flexible DC receiving-end converter station and the power grid outside the wind farm into an equivalent impedance network, such as... Figure 3 U dc C is the DC voltage of the DC line. eq P is the DC capacitor of a DC circuit. rec Q represents the output active power of the flexible DC receiving-end converter station. rec U represents the output reactive power of the flexible DC receiving-end converter station; j is the imaginary unit; U rec X is the output voltage of the flexible DC receiving-end converter station; T For transformer reactance; U PCC Z represents the voltage amplitude at the wind power grid connection point. E e is the equivalent impedance of the receiving-end power grid fault; E I is the equivalent potential of the receiving-end grid fault; wf This is the output current of the wind turbine.

[0160] Table 1. Contribution of the power front 1 of the flexible DC receiving-end converter station to the objective function.

[0161]

[0162]

[0163] Table 2. Contribution of the power front 2 of the flexible DC receiving-end converter station to the objective function.

[0164]

[0165] As shown in Tables 1 and 2, the voltage deviation at the wind power grid connection point and the frequency change rate of the receiving-end grid exhibit significant differences under different frontiers. In Frontier 1 of Table 1, when the active power of the flexible DC transmission is 150MW and the reactive power is 80MVar, the voltage deviation is 0.8% and the frequency change rate is 0.14Hz / s. However, in Frontier 2 of Table 2, when the active power of the flexible DC transmission is 180MW and the reactive power is 60MVar, the voltage deviation rises to 1.5% and the frequency change rate is 0.14Hz / s. Comparing the two sets of data, the first set of parameters in Frontier 1 is significantly better than the first set of parameters in Frontier 2 in terms of voltage deviation, while the frequency dynamic response index is the same. This indicates that the first set of solutions in Frontier 1 completely dominates the first set of solutions in Frontier 2 in multi-objective optimization. For any set of solutions in Frontier 2, a better dominant solution can be found in Frontier 1, demonstrating that the solutions in Frontier 1 have performance advantages under the voltage and frequency optimization objectives.

[0166] Analysis of the solution set characteristics within the same frontier reveals that the voltage deviation and frequency change rate exhibit an inverse trade-off relationship between the two data sets (150MW / 80MVar and 170MW / 70MVar) in frontier 1. The voltage deviation of the 170MW / 70MVar combination is slightly higher at 1.0%, but the frequency change rate is lower at 0.12Hz / s. There is no dominance relationship between solutions within the same frontier; that is, no single solution can be superior to other solutions simultaneously in terms of both voltage and frequency objectives. Therefore, it is necessary to combine congestion ranking to find the optimal solution within frontier 1.

[0167] Table 3 Ranking of Congestion at the Power Front of Flexible DC Receiving-End Converter Stations

[0168]

[0169]

[0170] Table 3 shows the congestion ranking of different parameter combinations in Pareto front 1. The congestion value of parameter combination 3, with 170MW of active power and 70MVar of reactive power in the flexible DC system, is 1.5, and is marked as the optimal solution due to its sparse distribution in the Pareto front. The congestion mechanism effectively maintains the diversity of the population, avoids the algorithm getting trapped in local optima, and ensures that the solution set covers a wider optimization space. By comprehensively evaluating the congestion and the contribution of the objective function, parameter combination number 3 is finally selected as the optimal control strategy, achieving dual optimization of voltage deviation of 0.8% and frequency change rate of 0.15Hz / s.

[0171] Table 4 Comparison of wind power grid connection point voltage deviation and receiving-end grid frequency change rate before and after optimization.

[0172]

[0173] Table 4 shows that before optimization, the voltage deviation at the wind power grid connection point was as high as 3.5%, and the frequency change rate of the receiving-end grid was 0.50 Hz / s, far exceeding the safety threshold for wind turbines not disconnecting from the grid. After optimization, the voltage deviation was reduced to 0.8%, and the frequency change rate was only 0.15 Hz / s, significantly improving system stability. This result verifies the effectiveness of the embodiments of this application in suppressing voltage sags and frequency fluctuations, and solves the problem of wind turbine disconnection caused by excessively rapid changes in voltage and frequency at the wind power grid connection point under low voltage ride-through control in traditional flexible DC transmission systems.

[0174] See Figure 4 , Figure 4 This is a structural block diagram of a fault ride-through system 10 for a flexible DC transmission system with wind power integration, provided in an embodiment of this application. The fault ride-through system 10 for the flexible DC transmission system with wind power integration includes:

[0175] The equivalent module is used to perform equivalent assessment on the receiving-end power grid when an AC fault occurs, and to obtain the equivalent parameters of the receiving-end power grid fault based on the real-time collected electrical quantities at the wind power grid connection point.

[0176] The first construction module is used to construct a first transfer model of the power of the flexible DC receiving-end converter station and the voltage of the wind power grid connection point, and a second transfer model of the power of the flexible DC receiving-end converter station and the frequency change rate of the receiving-end power grid, based on the equivalent parameters.

[0177] The second construction module is used to construct a fault ride-through control model based on the first transmission model and the second transmission model, with the objectives of minimizing the voltage deviation at the wind power grid connection point and minimizing the frequency change rate of the receiving-end power grid.

[0178] The control module is used to solve the fault ride-through control model to obtain the current control reference value of the flexible DC receiving-end converter station, so as to control the flexible DC transmission system based on the current control reference value.

[0179] Optionally, obtaining the equivalent parameters of the receiving-end grid fault based on the real-time collected electrical quantities at the wind power grid connection point includes:

[0180] The equivalent impedance and equivalent potential of the receiving-end power grid fault are obtained from the following formulas:

[0181]

[0182] Among them, Z E X is the equivalent impedance of the receiving-end power grid fault; j is the imaginary unit; X L X is the equivalent reactance of the receiving-end power grid under normal operating conditions; T For transformer reactance; e E e is the equivalent potential of the receiving-end grid fault; S R is the voltage vector under normal operating conditions of the receiving-end power grid. f X f These are the virtual transition resistance and virtual transition reactance, respectively, for the effects of an equivalent AC short circuit.

[0183]

[0184] Among them, I f.d I represents the d-axis current flowing into the receiving-end grid from the wind power grid connection point under grid fault conditions. f.q U is the q-axis current flowing into the receiving-end grid from the wind power grid connection point under grid fault conditions. PCC.d U represents the d-axis voltage component at the wind power grid connection point. PCC.q E represents the q-axis voltage component at the wind power grid connection point. S.d E represents the d-axis voltage component of the receiving-end grid's normal operating voltage. S.qThis represents the q-axis voltage component of the receiving-end power grid under normal operating conditions.

[0185] Optionally, the first transfer model is specifically:

[0186] U PCC =f(P rec Q rec )

[0187] Among them, U PCC f(P) represents the voltage amplitude at the wind power grid connection point. rec Q rec ) for U PCC Regarding the output active power P of the flexible DC receiving-end converter station rec The output reactive power Q of the flexible DC receiving-end converter station rec The function is established as follows:

[0188]

[0189] Among them, E E G represents the equivalent potential amplitude of a fault in the receiving-end power grid. E This refers to the conductance between the voltage at the wind power grid connection point and the equivalent potential of a fault in the receiving-end power grid. Re() represents the real part operation, Z E B is the equivalent impedance of the receiving-end power grid fault; E This refers to the susceptance between the voltage at the wind power grid connection point and the equivalent potential of a fault in the receiving-end power grid. Im() represents the imaginary part operation; θ WE I represents the phase difference between the voltage at the wind power grid connection point and the equivalent electromotive force of the fault in the receiving-end power grid. wf.d I is the output d-axis current of the wind turbine. wf.q The output q-axis current of the wind turbine is as follows:

[0190]

[0191] Where K is the reactive current coefficient; U PCC.N I represents the rated voltage amplitude at the wind power grid connection point. wf.N I is the rated output current of the wind turbine generator set. max This is the AC current limiting value.

[0192] Optionally, the second transfer model is specifically:

[0193]

[0194] Where d is the differential, f is the receiving-end grid frequency; t is the duration of the AC fault; ΔP rec ΔP represents the change in output active power of the flexible DC receiving-end converter station. wfΔP represents the change in the output active power of the wind turbine generator. im ρ is the system unbalanced active power at the moment of failure; D is the system load damping constant; ρ is the wind turbine permeability; H is the system inertial time constant; and τ is the time integral variable.

[0195] Optionally, the objective function of the fault ride-through control model is specifically:

[0196]

[0197] Wherein, F1 is the objective function with the voltage deviation at the wind power grid connection point as the optimization objective; F2 is the objective function with the frequency change rate of the receiving-end grid as the optimization objective; U PCC U represents the voltage amplitude at the wind power grid connection point. PCc.N d is the rated voltage amplitude at the wind power grid connection point; f is the differential; t is the receiving-end grid frequency; and t is the duration of the AC fault.

[0198] Optionally, the constraints of the fault ride-through control model include:

[0199] The node voltage and current constraints are:

[0200] U PCC.min ≤U PCC ≤U PCC.max

[0201] U E.min ≤U E ≤U E.max

[0202] I f.min ≤I f ≤I f.max

[0203] Among them, U PCC.max U is the upper limit of the voltage amplitude at the wind power grid connection point. PCC.min U is the lower limit of the voltage amplitude at the wind power grid connection point; E.max U is the upper limit of the potential within the fault location point. E.min I is the lower limit of the internal potential at the fault location point; f.max I is the upper limit of the current flowing into the receiving-end power grid from the wind power grid connection point. f.min This is the lower limit of the current flowing into the receiving-end power grid at the wind power grid connection point;

[0204] The line current carrying capacity constraint is:

[0205] |S WE |≤S WE.max

[0206] Among them, S WE S represents the apparent power flowing into the receiving-end power grid from the wind power grid connection point. wE.maxThe maximum allowable flow rate;

[0207] DC voltage constraints in flexible DC transmission systems:

[0208]

[0209] Among them, P rec P represents the output active power of the flexible DC receiving-end converter station. dc For the DC output power of the flexible DC sending-end converter station, U dc.N K is the rated DC voltage of the DC line. U C is the maximum allowable voltage coefficient. eq For DC circuits, the DC capacitor is U. dc.0 This refers to the DC voltage of the DC line during normal operation.

[0210] Frequency constraints of the receiving end power grid:

[0211] f0-Δf max ≤f≤f0+Δf max

[0212]

[0213] Where f0 is the rated operating frequency of the receiving-end power grid; Δf max denoted as the maximum permissible frequency deviation; f is the receiving-end grid frequency; μ is the maximum permissible frequency change rate of the wind turbine without disconnecting from the grid.

[0214] Optionally, solving the fault ride-through control model to obtain the current control reference value for the flexible DC receiving-end converter station includes:

[0215] Gene encoding and population initialization: The active current control parameters and reactive current control reference values ​​of the flexible DC receiving-end converter station are encoded into a two-dimensional array, and an initial population that satisfies the constraints of the fault ride-through control model is randomly generated; wherein, each individual in the initial population represents a set of current control reference value combinations that satisfy the constraints of the fault ride-through control model.

[0216] Non-dominated ranking and front partitioning: Based on the objective function of the fault-crossing control model, individuals are non-dominated and ranked. The condition for individual i to dominate individual j is defined as follows:

[0217] and

[0218] Where F1(i) is the objective function with the voltage deviation at the wind power grid connection point as the optimization objective, and F2(i) is the objective function with the frequency change rate of the receiving-end grid as the optimization objective;

[0219] The population is divided into multiple fronts based on non-dominance relationships, where front 1 contains all solutions that are not dominated by other individuals;

[0220] Crowding Calculation and Diversity Maintenance: Within the same frontier, selection is performed based on the relationship between crowding in descending order to maintain population diversity. Crowding is defined as:

[0221]

[0222] Where: d i F represents the crowding level of individual i; k (p i+1 F represents the function value of the first individual after i in the objective function sorting; k (p i-1 F represents the function value of the first individual preceding i in the objective function sorting; k,max F represents the maximum value of the objective function. k,min This represents the minimum value of the objective function;

[0223] Genetic operations and offspring generation: Based on sorting from front to back, individuals with crowding greater than a preset threshold are selected for crossover to generate new offspring individuals. A simulated binary crossover operation is used.

[0224]

[0225] Among them, c 1,k p is the value of the kth gene in offspring individual 1; 1,k p 2,k These are the values ​​of the k-th gene in parent individual 1 and individual 2, respectively; γ k The cross-distribution factor; u k η is a random number uniformly distributed within the interval [0,1]. c The cross-distribution index;

[0226] Elite retention and iterative optimization: merge the parent and offspring populations, re-execute non-dominated sorting and crowding calculation to select the top N optimal individuals, and repeat the iteration until the objective function of the fault crossing control model converges;

[0227] Optimal parameter decision: Select the optimal combination of current control reference values ​​from the Pareto frontier, which combines the voltage deviation at the wind power grid connection point and the frequency change rate of the receiving-end grid.

[0228] It is worth noting that the working process of each module in the fault ride-through system 10 of the flexible DC transmission system with wind power access described in the embodiments of this application can refer to the fault ride-through working process of the flexible DC transmission system with wind power access described in the above embodiments, and will not be repeated here.

[0229] This application provides a fault ride-through system 10 for a flexible DC transmission system with wind power access. When an AC fault occurs in the receiving-end grid, the system performs an equivalent assessment of the receiving-end grid, obtaining equivalent fault parameters based on real-time collected electrical quantities at the wind power grid connection point. Based on these equivalent parameters, a first transfer model is constructed between the power of the flexible DC receiving-end converter station and the voltage at the wind power grid connection point, and a second transfer model is constructed between the power of the flexible DC receiving-end converter station and the frequency change rate of the receiving-end grid. Based on the first and second transfer models, a fault ride-through control model is constructed with the objectives of minimizing the voltage deviation at the wind power grid connection point and minimizing the frequency change rate of the receiving-end grid. The fault ride-through control model is solved to obtain a current control reference value for the flexible DC receiving-end converter station. The flexible DC transmission system is then controlled based on this current control reference value. Therefore, this application embodiment achieves coordinated control of the dual objectives of minimizing voltage deviation and suppressing the frequency change rate of the receiving-end grid by establishing a transfer model (including the first transfer model and the second transfer model) between the power of the flexible DC receiving-end converter station and the voltage at the wind power grid connection point and the frequency change rate of the receiving-end grid, effectively avoiding the phenomenon of wind turbine disconnection during faults.

[0230] Furthermore, this application also provides a computer-readable storage medium, which includes a stored computer program; wherein, when the computer program is executed, it controls the device where the computer-readable storage medium is located to perform the fault ride-through method of a flexible DC transmission system with wind power access as described in any of the above embodiments.

[0231] Furthermore, this application also provides a computer program product, including a computer program / instruction, which, when executed by a processor, implements the fault ride-through method for a flexible DC transmission system with wind power access as described in any of the above embodiments.

[0232] See Figure 5 , Figure 5 This is a structural block diagram of a fault ride-through device 20 for a flexible DC transmission system with wind power access, provided in an embodiment of this application. The fault ride-through device 20 includes a processor 21, a memory 22, and a computer program stored in the memory 22 and executable on the processor 21. When the processor 21 executes the computer program, it implements the steps in the aforementioned embodiments of the fault ride-through method for a flexible DC transmission system with wind power access. Alternatively, when the processor 21 executes the computer program, it implements the functions of each module / unit in the aforementioned device embodiments.

[0233] For example, the computer program may be divided into one or more modules / units, which are stored in the memory 22 and executed by the processor 21 to complete this application. The one or more modules / units may be a series of computer program instruction segments capable of performing specific functions, which describe the execution process of the computer program in the fault ride-through device 20 of the flexible DC transmission system with wind power access.

[0234] The fault ride-through device 20 of the flexible DC transmission system with wind power access may include, but is not limited to, a processor 21 and a memory 22. Those skilled in the art will understand that the schematic diagram is merely an example of the fault ride-through device 20 of the flexible DC transmission system with wind power access and does not constitute a limitation on the fault ride-through device 20. It may include more or fewer components than illustrated, or combine certain components, or use different components. For example, the fault ride-through device 20 of the flexible DC transmission system with wind power access may also include input / output devices, network access devices, buses, etc.

[0235] The processor 21 can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor. The processor 21 is the control center of the fault ride-through device 20 of the flexible DC transmission system with wind power access, connecting various parts of the fault ride-through device 20 of the flexible DC transmission system with wind power access through various interfaces and lines.

[0236] The memory 22 can be used to store the computer programs and / or modules. The processor 21 implements various functions of the fault ride-through device 20 of the flexible DC transmission system with wind power access by running or executing the computer programs and / or modules stored in the memory 22 and calling the data stored in the memory 22. The memory 22 may mainly include a program storage area and a data storage area. The program storage area may store the operating system, at least one application program required for a function (such as sound playback function, image playback function, etc.), etc.; the data storage area may store data created according to the use of the mobile phone (such as audio data, phonebook, etc.). In addition, the memory 22 may include high-speed random access memory, and may also include non-volatile memory, such as hard disk, memory, plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, at least one disk storage device, flash memory device, or other volatile solid-state storage device.

[0237] The fault ride-through device 20 of the flexible DC transmission system with wind power access, if implemented as a software functional unit and sold or used as an independent product, can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by the processor 21, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0238] It should be noted that the device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Furthermore, in the accompanying drawings of the device embodiments provided in this application, the connection relationships between modules indicate that they have communication connections, which can be specifically implemented as one or more communication buses or signal lines. Those skilled in the art can understand and implement this without any creative effort.

[0239] The above description is the preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. A fault ride-through method for a flexible DC transmission system with wind power integration, characterized in that, include: When an AC fault occurs in the receiving-end power grid, the receiving-end power grid is equivalently evaluated, and the equivalent parameters of the receiving-end power grid fault are obtained based on the real-time collected electrical quantities at the wind power grid connection point. Based on the equivalent parameters, a first transfer model of the power of the flexible DC receiving-end converter station and the voltage of the wind power grid connection point are constructed, and a second transfer model of the power of the flexible DC receiving-end converter station and the frequency change rate of the receiving-end grid is constructed. Based on the first and second transmission models, a fault ride-through control model is constructed with the objectives of minimizing the voltage deviation at the wind power grid connection point and minimizing the frequency change rate of the receiving-end power grid. The fault ride-through control model is solved to obtain the current control reference value of the flexible DC receiving-end converter station, and the flexible DC transmission system is controlled based on the current control reference value.

2. The fault ride-through method for a flexible DC transmission system with wind power integration as described in claim 1, characterized in that, The method of obtaining equivalent parameters of grid faults at the receiving end based on real-time collected electrical quantities at the wind power grid connection point includes: The equivalent impedance and equivalent potential of the receiving-end power grid fault are obtained from the following formulas: Among them, Z E X is the equivalent impedance of the receiving-end power grid fault; j is the imaginary unit; X L X is the equivalent reactance of the receiving-end power grid under normal operating conditions; T For transformer reactance; e E e is the equivalent potential of the receiving-end grid fault; S R is the voltage vector under normal operating conditions of the receiving-end power grid. f X f These are the virtual transition resistance and virtual transition reactance, respectively, for the effects of an equivalent AC short circuit. Among them, I f.d I represents the d-axis current flowing into the receiving-end grid from the wind power grid connection point under grid fault conditions. f.q U is the q-axis current flowing into the receiving-end grid from the wind power grid connection point under grid fault conditions. PCC.d U represents the d-axis voltage component at the wind power grid connection point. PCC.q E represents the q-axis voltage component at the wind power grid connection point. S.d E represents the d-axis voltage component of the receiving-end grid's normal operating voltage. S.q This represents the q-axis voltage component of the receiving-end power grid under normal operating conditions.

3. The fault ride-through method for a flexible DC transmission system with wind power integration as described in claim 1, characterized in that, The first transmission model is specifically as follows: U PCC =f(P rec ,Q rec ) Among them, U PCC f(P) represents the voltage amplitude at the wind power grid connection point. rec Q rec ) for U PCC Regarding the output active power P of the flexible DC receiving-end converter station rec The output reactive power Q of the flexible DC receiving-end converter station rec The function is established as follows: Among them, E E G represents the equivalent potential amplitude of a fault in the receiving-end power grid. E This refers to the conductance between the voltage at the wind power grid connection point and the equivalent potential of a fault in the receiving-end power grid. Re() represents the real part operation, Z E B is the equivalent impedance of the receiving-end power grid fault; E This refers to the susceptance between the voltage at the wind power grid connection point and the equivalent potential of a fault in the receiving-end power grid. Im() represents the imaginary part operation; θ WE I represents the phase difference between the voltage at the wind power grid connection point and the equivalent electromotive force of the fault in the receiving-end power grid. wf.d I is the output d-axis current of the wind turbine. wf.q The output q-axis current of the wind turbine is as follows: Where K is the reactive current coefficient; U PCC.N I represents the rated voltage amplitude at the wind power grid connection point. wf.N I is the rated output current of the wind turbine generator set. max This is the AC current limiting value.

4. The fault ride-through method for a flexible DC transmission system with wind power integration as described in claim 1, characterized in that, The second transfer model is as follows: Where d is the differential, f is the receiving-end grid frequency; t is the duration of the AC fault; ΔP rec ΔP represents the change in output active power of the flexible DC receiving-end converter station. wf ΔP represents the change in the output active power of the wind turbine generator. im ρ is the system unbalanced active power at the moment of failure; D is the system load damping constant; ρ is the wind turbine permeability; H is the system inertial time constant; and τ is the time integral variable.

5. The fault ride-through method for a flexible DC transmission system with wind power integration as described in claim 1, characterized in that, The objective function of the fault ride-through control model is specifically: Wherein, F1 is the objective function with the voltage deviation at the wind power grid connection point as the optimization objective; F2 is the objective function with the frequency change rate of the receiving-end grid as the optimization objective; U PCC U represents the voltage amplitude at the wind power grid connection point. PCC.N d is the rated voltage amplitude at the wind power grid connection point; f is the differential; t is the receiving-end grid frequency; and t is the duration of the AC fault.

6. The fault ride-through method for a flexible DC transmission system with wind power integration as described in claim 5, characterized in that, The constraints of the fault ride-through control model include: The node voltage and current constraints are: IN PCC.min ≤U PCC ≤U PCC.max IN E.min ≤U E ≤U E.max I f.min ≤I f ≤I f.max Among them, U PCC.max U is the upper limit of the voltage amplitude at the wind power grid connection point. PCC.min U is the lower limit of the voltage amplitude at the wind power grid connection point; E.max U is the upper limit of the potential within the fault location point. E.min I is the lower limit of the internal potential at the fault location point; f.max I is the upper limit of the current flowing into the receiving-end power grid from the wind power grid connection point. f.min This is the lower limit of the current flowing into the receiving-end power grid at the wind power grid connection point; The line current carrying capacity constraint is: |S WE |≤S WE.max Among them, S WE S represents the apparent power flowing into the receiving-end power grid from the wind power grid connection point. WE.max The maximum allowable flow rate; DC voltage constraints in flexible DC transmission systems: Among them, P rec P represents the output active power of the flexible DC receiving-end converter station. dc For the DC output power of the flexible DC sending-end converter station, U dc.N K is the rated DC voltage of the DC line. U C is the maximum allowable voltage coefficient. eq For DC circuits, the DC capacitor is U. dc.0 This refers to the DC voltage of the DC line during normal operation. Frequency constraints of the receiving end power grid: f0-Δf max ≤f≤f0+Δf max Where f0 is the rated operating frequency of the receiving-end power grid; Δf max denoted as the maximum permissible frequency deviation; f is the receiving-end grid frequency; μ is the maximum permissible frequency change rate of the wind turbine without disconnecting from the grid.

7. The fault ride-through method for a flexible DC transmission system with wind power integration as described in claim 1, characterized in that, Solving the fault ride-through control model to obtain the current control reference value for the flexible DC receiving-end converter station includes: Gene encoding and population initialization: The active current control parameters and reactive current control reference values ​​of the flexible DC receiving-end converter station are encoded into a two-dimensional array, and an initial population that satisfies the constraints of the fault ride-through control model is randomly generated; wherein, each individual in the initial population represents a set of current control reference value combinations that satisfy the constraints of the fault ride-through control model. Non-dominated ranking and front partitioning: Based on the objective function of the fault-crossing control model, individuals are non-dominated and ranked. The condition for individual i to dominate individual j is defined as follows: and Where F1(i) is the objective function with the voltage deviation at the wind power grid connection point as the optimization objective, and F2(i) is the objective function with the frequency change rate of the receiving-end grid as the optimization objective; The population is divided into multiple fronts based on non-dominance relationships, where front 1 contains all solutions that are not dominated by other individuals; Crowding Calculation and Diversity Maintenance: Within the same frontier, selection is performed based on the relationship between crowding in descending order to maintain population diversity. Crowding is defined as: Where: d i F represents the crowding level of individual i; k (p i+1 F represents the function value of the first individual after i in the objective function sorting; k (p i-1 F represents the function value of the first individual preceding i in the objective function sorting; k,max F represents the maximum value of the objective function. k,min This represents the minimum value of the objective function; Genetic operations and offspring generation: Based on sorting from front to back, individuals with crowding greater than a preset threshold are selected for crossover to generate new offspring individuals. A simulated binary crossover operation is used. Among them, c 1,k p is the value of the kth gene in offspring individual 1; 1,k p 2,k These are the values ​​of the k-th gene in parent individual 1 and individual 2, respectively; γ k The cross-distribution factor; u k η is a random number uniformly distributed within the interval [0,1]. c The cross-distribution index; Elite retention and iterative optimization: merge the parent and offspring populations, re-execute non-dominated sorting and crowding calculation to select the top N optimal individuals, and repeat the iteration until the objective function of the fault crossing control model converges; Optimal parameter decision: Select the optimal combination of current control reference values ​​from the Pareto frontier, which combines the voltage deviation at the wind power grid connection point and the frequency change rate of the receiving-end grid.

8. A fault ride-through system for a flexible DC transmission system with wind power access, characterized in that, include: The equivalent module is used to perform equivalent assessment on the receiving-end power grid when an AC fault occurs, and to obtain the equivalent parameters of the receiving-end power grid fault based on the real-time collected electrical quantities at the wind power grid connection point. The first construction module is used to construct a first transfer model of the power of the flexible DC receiving-end converter station and the voltage of the wind power grid connection point, and a second transfer model of the power of the flexible DC receiving-end converter station and the frequency change rate of the receiving-end power grid, based on the equivalent parameters. The second construction module is used to construct a fault ride-through control model based on the first transmission model and the second transmission model, with the objectives of minimizing the voltage deviation at the wind power grid connection point and minimizing the frequency change rate of the receiving-end power grid. The control module is used to solve the fault ride-through control model to obtain the current control reference value of the flexible DC receiving-end converter station, so as to control the flexible DC transmission system based on the current control reference value.

9. A fault ride-through device for a flexible DC transmission system with wind power access, characterized in that, The system includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein the processor, when executing the computer program, implements the fault ride-through method for a flexible DC transmission system with wind power access as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored computer program; wherein, when the computer program is executed, it controls the device where the computer-readable storage medium is located to perform the fault ride-through method for a flexible DC transmission system with wind power access as described in any one of claims 1 to 7.

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