Short-circuit fault current suppression method and device of flexible direct-current power grid, computer equipment and storage medium

Abstract

The invention relates to a short-circuit fault current suppression method and device for a flexible DC power grid, computer equipment and a storage medium. The method comprises the steps of obtaining change data of direct current and a preset first current limiting parameter under the condition that the flexible direct current power grid has a short-circuit fault; according to the change data of the direct current and the first current limiting parameter, determining a first input proportion of a converter sub-module; according to the first input proportion, the input state of the converter sub-module in the first suppression stage is controlled; obtaining a current amplitude corresponding to the first input proportion and a preset second current limiting parameter; the second current limiting parameter is determined according to a limiting condition of a direct current peak value; determining a second input proportion of the converter sub-module according to the current amplitude and a second current limiting parameter; and according to the second input proportion, controlling the input state of the converter sub-module in the second suppression stage so as to complete suppression of the short-circuit fault current. And the fault current can be quickly and effectively suppressed at low cost.

Description

Technical Field

[0001] This application relates to the field of flexible DC power transmission technology, and in particular to a method, apparatus, computer equipment, and storage medium for suppressing short-circuit fault current in a flexible DC power grid. Background Technology

[0002] Flexible DC grids, based on modular multilevel converters (MMCs), are a core technology supporting renewable energy grid connection and long-distance power transmission. However, their low damping and low inertia characteristics cause short-circuit fault currents to surge to dangerous peak values ​​within milliseconds, seriously threatening equipment safety. Currently, the mainstream half-bridge MMC is widely used due to its simple structure and low losses, but it cannot independently isolate faults and relies on high-cost DC circuit breakers (DCCBs). Taking the Zhangbei ±500kV project as an example, the cost of DCCBs accounts for as much as two-thirds of the total cost of converter valves, significantly restricting the system's economic efficiency.

[0003] Existing fault current limiting technologies are divided into two categories: physical and control-based. Physical technologies achieve current limiting by improving the topology (such as hybrid MMC), multi-port DCCB, or superconducting current limiters; control-based technologies rely on strategy optimization (such as virtual reactance, adaptive control, and bridge arm voltage regulation), and have the advantages of low cost and fast response.

[0004] However, during implementation, the applicant discovered that the relevant technology has at least one drawback: it cannot suppress fault current quickly and effectively at low cost. Summary of the Invention

[0005] Based on this, the purpose of this application is to at least solve one of the above-mentioned technical defects, especially the technical defect that the prior art cannot suppress fault current quickly and effectively at low cost. This application provides a method, device, computer equipment and storage medium for suppressing short-circuit fault current in a flexible DC power grid.

[0006] In a first aspect, this application provides a method for suppressing short-circuit fault current in a flexible DC power grid, the method comprising:

[0007] In the event of a short-circuit fault in a flexible DC power grid, acquire data on changes in DC current and preset first current-limiting parameters;

[0008] Based on the DC current change data and the first current limiting parameter, determine the first activation ratio of the converter submodule;

[0009] According to the first input ratio, the input state of the converter submodule is controlled in the first suppression stage; and the current amplitude corresponding to the first input ratio and the preset second current limiting parameter are obtained; the second current limiting parameter is determined according to the limiting condition of the DC current peak value.

[0010] The second activation ratio of the converter submodule is determined based on the current amplitude and the second current limiting parameter.

[0011] According to the second input ratio, the input state of the converter submodule in the second suppression stage is controlled to suppress the short-circuit fault current.

[0012] In one embodiment, the method further includes:

[0013] Send a command to zero the d-axis current to the dq decoupling controller;

[0014] Upon receiving the fault clearing signal, a d-axis current recovery command is sent to the dq decoupling controller;

[0015] The dq decoupling controller is used to set the d-axis current to zero according to the d-axis current zeroing command, or to restore the current to a preset d-axis current reference value according to the d-axis current recovery command.

[0016] In one embodiment, the first input ratio is determined according to the following expression:

[0017]

[0018] in, As the first proportion of investment, This is the first current limiting parameter. This is data on the change of direct current.

[0019] In one embodiment, the second input ratio is determined according to the following expression:

[0020]

[0021] in, As the second largest proportion of investment, This is the rated value of DC current. This is the initial fault current. This represents the current amplitude.

[0022] In one embodiment, the method further includes:

[0023] Obtain the system equivalent inductance and DC voltage of the flexible DC power grid;

[0024] Using a pre-built current limiting parameter optimization model, the optimized first current limiting parameter is obtained based on the first input ratio, the system equivalent inductance, and the DC voltage; the optimized first current limiting parameter is used as the preset first current limiting parameter for the next short-circuit fault.

[0025] In one embodiment, the first current limiting parameter is optimized using the following expression:

[0026]

[0027] in, As the first proportion of investment, DC voltage This is the system's equivalent inductance.

[0028] In one embodiment, the value range of the second current limiting parameter is [0,1].

[0029] Secondly, this application provides a short-circuit fault current suppression device for a flexible DC power grid, the device comprising:

[0030] The first-stage parameter module is used to acquire DC current change data and preset first current limiting parameters in the event of a short-circuit fault in the flexible DC grid.

[0031] The first phase determines the module, which is used to determine the first activation ratio of the converter sub-module based on the DC current change data and the first current limiting parameter;

[0032] The second-stage parameter module is used to control the activation state of the converter submodule in the first suppression stage according to the first activation ratio; and to obtain the current amplitude corresponding to the first activation ratio and the preset second current limiting parameter; the second current limiting parameter is determined according to the limiting condition of the DC current peak value.

[0033] The second phase determination module is used to determine the second activation ratio of the converter submodule based on the current amplitude and the second current limiting parameter.

[0034] The fault current suppression module is used to control the activation state of the converter submodule in the second suppression stage according to the second activation ratio, so as to suppress the short-circuit fault current.

[0035] Thirdly, this application provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the above-described method.

[0036] Fourthly, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the above-described method.

[0037] As can be seen from the above technical solutions, the embodiments of this application have the following advantages:

[0038] The method, apparatus, computer equipment, and storage medium for suppressing short-circuit fault current in flexible DC grids provided in this application can effectively suppress the rate of current rise and peak value in the early stage of the fault by dynamically adjusting the commissioning ratio of converter sub-modules in stages when a short-circuit fault occurs in the flexible DC grid. This also allows for rapid current recovery after the fault is cleared, thereby suppressing the fault current quickly and effectively at low cost. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 A flowchart illustrating a short-circuit fault current suppression method for a flexible DC power grid provided in this application embodiment;

[0041] Figure 2 A flowchart illustrating a short-circuit fault current suppression method for a flexible DC power grid provided in this application embodiment;

[0042] Figure 3 A schematic diagram of an MMC control structure with an auxiliary suppression element provided in an embodiment of this application;

[0043] Figure 4 A flowchart illustrating a step for optimizing current limiting parameters provided in an embodiment of this application;

[0044] Figure 5 A schematic diagram of a short-circuit fault current suppression device for a flexible DC power grid provided in this application embodiment;

[0045] Figure 6 This is a schematic diagram of the internal structure of a computer device provided in an embodiment of this application. Detailed Implementation

[0046] 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 skilled in the art without creative effort are within the scope of protection of this application.

[0047] Flexible DC grids, based on modular multilevel converters (MMCs), are a key technology for flexible DC transmission, addressing renewable energy grid integration, efficient power transmission, and improved grid stability. They are widely used in new energy grid integration, large-capacity long-distance power transmission, and DC distribution networks. However, due to the low damping and inertia of flexible DC grids, when a short-circuit fault occurs, the fault current can rapidly increase to an extremely high peak value within milliseconds, potentially severely jeopardizing the safe operation of the system's electrical equipment.

[0048] Among current technologies, half-bridge MMCs are widely used in flexible DC transmission projects due to their advantages such as simple structure, low loss, and ease of implementation. However, because they cannot isolate faulty lines through blocking, fault current limiting usually relies on high-cost DC circuit breakers (DCCBs) for line isolation. Taking a ±500kV flexible DC project in a certain area as an example, the total cost of DCCBs in this project accounts for two-thirds of the total cost of converter valves. This not only increases the construction cost of the system but also limits the economics of the flexible DC grid.

[0049] Therefore, how to quickly and effectively suppress fault current when a fault occurs, while reducing the overall cost of the system, has become an important challenge for the development of flexible DC grid technology.

[0050] Existing fault current limiting technologies for flexible DC power grids are mainly divided into two categories: physical current limiting measures and control-type current limiting measures.

[0051] 1) Physical flow restriction measures

[0052] An improved converter topology was proposed: based on a hybrid half-bridge MMC, fault current transfer and blocking were achieved by adding transfer branches to the converter arms. However, this method requires additional hardware modifications, increasing system complexity and cost.

[0053] Using current-limiting devices: A multi-port DC circuit breaker was designed with thyristor devices in the main current-limiting circuit, which has current-limiting capability and low conduction loss. However, DC circuit breaker technology is still immature and expensive.

[0054] Superconducting current limiter: Applying a saturated iron core type superconducting current limiter to a flexible DC grid can significantly limit the peak short-circuit current, but it is almost ineffective for steady-state short-circuit current.

[0055] While these physical current limiting measures do limit fault current to some extent, they typically introduce additional hardware costs and engineering complexity, and may also negatively impact system stability.

[0056] 2) Control-type flow restriction measures

[0057] Control-type current limiting measures limit fault current by optimizing system control strategies, offering advantages such as rapid response and no additional hardware costs.

[0058] The current limiting method based on virtual reactance can effectively suppress fault current by increasing virtual reactance, but its debugging is complicated when applied to actual engineering.

[0059] The adaptive current limiting control using a half-bridge MMC achieves current limiting by dynamically adjusting the number of converter sub-modules, but the specific selection process for the current limiting parameters is rather cumbersome.

[0060] An active current limiting strategy based on bridge arm voltage control is adopted, which limits the current by adjusting the DC and AC components of the bridge arm voltage. However, this strategy will affect the AC output voltage and may cause overcurrent in the bridge arm.

[0061] Although control-type current limiting measures are low-cost and flexible, existing methods still have the following shortcomings: lack of clear guidance on the selection of current limiting parameters; inability to simultaneously consider the rapid current suppression after a fault and the current balance during the recovery phase; and some methods may cause AC side current distortion, affecting system stability.

[0062] In summary, the applicant has found that related technologies at least suffer from the problem of failing to suppress fault current quickly and effectively at low cost. Based on this, this application provides a method, apparatus, computer device, and storage medium for suppressing short-circuit fault current in a flexible DC power grid. By dynamically adjusting the commissioning ratio of converter submodules in stages during a short-circuit fault in the flexible DC power grid, the initial current rise rate and peak value can be effectively suppressed. This also allows for rapid current recovery after the fault is cleared, thereby enabling rapid and effective suppression of fault current at low cost.

[0063] In one exemplary embodiment, Figure 1 A flowchart illustrating a short-circuit fault current suppression method for a flexible DC power grid provided in this application embodiment is shown below. Figure 1 As shown, a short-circuit fault current suppression method for a flexible DC power grid is provided. The method is illustrated using a terminal as an example. It is understood that this method can also be applied to a server, or to a system including both a terminal and a server, and is implemented through interaction between the terminal and the server. The terminal can be, but is not limited to, various personal computers, laptops, smartphones, and tablets. The server can be a standalone physical server, a server cluster or distributed system composed of multiple physical servers, or a cloud server providing cloud computing services. In this embodiment, the method includes the following steps S101 to S105: Wherein:

[0064] S101. In the event of a short-circuit fault in the flexible DC grid, acquire the change data of DC current and the preset first current limiting parameter.

[0065] The DC current change data refers to the rate of change of current over time when a fault occurs. This data can be acquired in real time by a current sensor and calculated using a differentiating circuit or a digital signal processor. It is used to characterize the rate of rise of the fault current. The first current limiting parameter is a pre-set proportional coefficient, which can be calculated from the system's equivalent inductance and DC voltage. It is used to adjust the relationship between the submodule's activation speed and the rate of change of current.

[0066] S102. Based on the DC current change data and the first current limiting parameter, determine the first activation ratio of the converter submodule.

[0067] The first activation ratio refers to the conduction ratio of the converter submodule, which can be achieved by adjusting the duty cycle of the trigger pulse of the insulated gate bipolar transistor (IGBT). This is used to form a dynamic equivalent impedance in the early stages of a fault.

[0068] S103. According to the first input ratio, control the input state of the converter submodule in the first suppression stage; and obtain the current amplitude corresponding to the first input ratio and the preset second current limiting parameter; the second current limiting parameter is determined according to the limiting condition of the DC current peak value.

[0069] The second current limiting parameter is set according to the maximum allowable peak current of the system, specifically within the range of 1.2-1.5 times the rated current value, to prevent the current from exceeding the equipment's tolerance limit.

[0070] S104. Determine the second activation ratio of the converter submodule based on the current amplitude and the second current limiting parameter.

[0071] The calculation of the second input ratio takes into account both the initial fault current and the real-time current amplitude. Specifically, it can be dynamically adjusted by the proportional-integral controller to ensure precise control during the current peak stage.

[0072] S105. According to the second input ratio, control the input state of the converter submodule in the second suppression stage to suppress the short-circuit fault current.

[0073] For example, when a short-circuit fault is detected in the DC line, current monitoring can be initiated immediately. The differential current signal is acquired via a high-speed sampling circuit, and combined with pre-acquired and stored first current-limiting parameters, the initial engagement ratio of the converter submodule can be calculated in real time. For instance, when the current change rate reaches 500 A / ms, the control unit adjusts the submodule engagement ratio to 60%, increasing the converter's equivalent inductance to slow the current rise. After entering the peak current phase, the system can switch to a second control mode, dynamically adjusting the submodule engagement ratio based on the current amplitude and a preset safety threshold. For example, when the current amplitude reaches 130% of the rated value, the engagement ratio is adjusted to 75%, providing additional damping to suppress current oscillations. The entire process is implemented through a hierarchical control architecture, with the lower-level controller executing the submodule switching operation and the upper-level controller performing parameter calculations and mode switching.

[0074] Optionally, this embodiment may include an adaptive suppression controller comprising a two-stage suppression mechanism: the first stage is based on the current change rate calculation, and the first input ratio K1 is dynamically adjusted using formula (1):

[0075] (1);

[0076] k a This is the first current limiting parameter. This is the rated value for DC current.

[0077] The second stage can be based on the current amplitude suppression strategy, and further current limiting can be achieved through the calculation of formula (2) to adjust the second input ratio K2.

[0078] (2);

[0079] Where, k b I is the second current limiting parameter. dcN I is the rated DC current, and I0 is the initial fault current.

[0080] When a fault is detected, the switching ratio K1 is controlled by calculating the rate of change of DC current in real time to initially limit the fault current. Subsequently, the switching ratio K2 is calculated based on the actual amplitude of the fault current to further reduce the peak value of the DC current.

[0081] In this way, the number of sub-modules in operation can be adjusted through the converter's control module, thereby reducing the converter's DC output voltage.

[0082] In practical applications, a phased dynamic adjustment mechanism is used to prioritize suppressing the rate of current change in the early stages of a fault and to focus on controlling the current amplitude during peak periods, thus achieving a dual protection effect. Compared to physical solutions that require modifications to the converter topology, this method directly utilizes the switching control functions of existing submodules without the need for additional hardware. Compared to a single control strategy that relies solely on virtual reactance, this solution achieves a balance between control response speed and system stability through parameter correlation design.

[0083] In this embodiment, the upgrade can be achieved through software algorithms, significantly reducing system modification costs while maintaining the continuous controllability of the converter during faults. By employing a phased control strategy, a rapid response is ensured in the initial stage of a fault, thereby enabling rapid and effective suppression of fault currents at low cost.

[0084] like Figure 2 As shown, Figure 2 This application provides a schematic diagram of an adaptive current limiting controller, which includes: an input DC current signal module, a current change rate calculation module, a limiting module, and a control signal output module. The calculation results can be applied in real-time to the sub-module control of the converter through series connection between the modules.

[0085] Where Idc: DC current; d / dt: current change rate calculation module (used to calculate the rate of change of DC current in real time, providing a basis for the first-stage current limiting strategy). dcN : Rated DC current (mentioned in formulas (1) and (2), used as the benchmark value for judging current amplitude). I0 is the initial fault current (mentioned in the formula, the initial current value when the fault occurs). K1, K2: The activation ratio of the converter submodule (K1 is the activation ratio based on the current change rate in the first stage, and K2 is the activation ratio based on the current amplitude in the second stage). Protection signal switching: The signal switching module after fault detection (used to trigger the start of the current limiting strategy). |x| is the limiting module (may be used to perform absolute value calculation on the current change rate or amplitude). N / D is the ratio calculation module that can be "rated value / actual value" (used to combine the rated value and the actual current value for parameter adjustment). "*" indicates the multiplication operation module (used to calculate the activation ratios K1 and K2 according to the formula).

[0086] In one exemplary embodiment, the method further includes:

[0087] Send a command to zero the d-axis current to the dq decoupling controller;

[0088] Upon receiving the fault clearing signal, a d-axis current recovery command is sent to the dq decoupling controller.

[0089] The dq decoupling controller is used to set the d-axis current to zero according to the d-axis current zeroing command, or to restore the current to a preset d-axis current reference value according to the d-axis current recovery command.

[0090] The dq decoupling controller refers to a device that achieves current decoupling control based on a synchronous rotating coordinate system. For example, a coordinate transformation algorithm can be used to convert three-phase AC current into d-axis and q-axis components, and power control can be achieved by independently adjusting the d-axis and q-axis currents. The d-axis current zeroing command refers to a control signal that instantaneously returns the d-axis current component to zero. For example, this can be achieved by adjusting the current loop reference value, used to quickly eliminate active power fluctuations during faults. The fault clearing signal refers to a trigger signal generated after a short-circuit fault is detected as isolated or eliminated. For example, this can be achieved using voltage recovery detection or circuit breaker status feedback. The d-axis current recovery command refers to a control command that reconstructs the current with a preset d-axis current reference value as the target. For example, a ramp function or exponential curve can be used to generate a reference trajectory to avoid secondary impacts caused by sudden current changes.

[0091] For example, upon detecting a short-circuit fault, the control center immediately generates a d-axis current zero-reset command and transmits it to the dq decoupling controller, causing the d-axis current component to return to zero within the control cycle, thereby cutting off the active power injected by the converter to the fault point. At this time, the q-axis current still maintains its reactive power regulation function, ensuring AC system voltage support. After the protection device clears the fault, it receives the fault clearing signal through the communication interface, and the control center generates a d-axis current recovery command, gradually increasing the current to the rated level based on a preset d-axis current reference value. A gradual adjustment strategy is adopted during the recovery process to ensure a smooth DC current reconstruction process and avoid equipment overstress or system oscillation caused by abrupt current changes.

[0092] Optionally, in order to further reduce the impact of AC side current on DC side, the auxiliary suppression circuit reduces power exchange and suppresses bridge arm current overstress by briefly zeroing the d-axis current reference value.

[0093] An auxiliary suppression circuit can be added to the control structure of the MMC. After a fault occurs, the controller can set the d-axis current reference value to zero to reduce the active power injected into the AC system. The formula for the active power injected into the AC system after a fault is:

[0094] (3);

[0095] in, Let be the voltage along the d-axis at time t. Let be the current along the d-axis at time t.

[0096] After setting the d-axis current reference value to zero, the formula for the peak AC current output by the system is as follows:

[0097] (4);

[0098] Where Q is the reactive power and U is the amplitude of the fundamental phase voltage on the MMC valve side.

[0099] In this way, without involving the removal of any physical components, the current limiting effect is equivalent to cutting off the active power connection path between the AC system and the DC system from the perspective of energy flow and circuit behavior, thus achieving a similar effect to "cutting off".

[0100] In practical applications, the power feed can be reduced to a minimum within milliseconds through the rapid dynamic response of the control system.

[0101] like Figure 3 As shown, Figure 3 A schematic diagram of an MMC control structure with an auxiliary suppression stage is provided for an embodiment of this application. The modular multilevel converter (MMC) control structure includes:

[0102] u diff,d u diff,q q represents the voltage difference between the d-axis and q-axis. P represents active power (the active power injected into the AC system; the auxiliary suppression circuit limits current by controlling the active power), and Q represents reactive power. max This represents the maximum q-axis current (which can be the maximum limit for reactive current, used to constrain the arm current). d,max i is the maximum current along the d-axis. q,max Qref is the maximum q-axis current, and Pref is the reactive power reference value. Pref is the active power reference value.

[0103] In practical applications, by controlling the d-axis current state in stages, it is possible to force it to zero during a fault to block energy feed. During the recovery period, a reference value tracking mode is adopted, which not only optimizes the dynamic response speed of fault suppression but also maintains the transient stability of the system and avoids the parameter conflict problem in a single control mode.

[0104] In this embodiment, the above technical solution can quickly cut off the converter's energy output path in the early stage of a fault, effectively suppress the rise rate of the short-circuit current, and at the same time ensure a smooth electromagnetic transient transition during the system reconstruction process through a controlled recovery mechanism. Thus, the fault current can be suppressed quickly and effectively at low cost, and the current can be effectively restored.

[0105] In one exemplary embodiment, the first input ratio is determined according to the following expression:

[0106] (1);

[0107] in, As the first proportion of investment, This is the first current limiting parameter. This is data on the change of direct current;

[0108] For example, during the fault current rise phase, the activation ratio of the converter submodule is dynamically calculated by real-time monitoring of the differential value of the DC current and combining it with a preset current limiting coefficient. When the rate of change of current increases, the expression... The item will increase significantly, leading to a higher proportion of investment. The inductance is reduced, at which point the equivalent inductance of the converter increases to suppress the rate of current rise. This formula uses mathematical constraints to ensure that the switching ratio is always within the range of 0 to 1, avoiding AC side current distortion caused by overmodulation. For example, when the rate of change of fault current exceeds a preset threshold, the switching ratio can be automatically adjusted to the lower limit, forcing the converter into a fully inductive switching state.

[0109] In practical applications, by establishing a linear relationship between the current derivative and the input ratio, real-time tracking and active suppression of the upward trend of fault current are achieved, ensuring response speed while avoiding the risk of system oscillation caused by parameter over-adjustment.

[0110] In this embodiment, the equivalent inductance of the converter can be precisely adjusted according to the dynamic characteristics of the fault current, which can quickly suppress the current rise rate in the early stage of the fault. At the same time, the system is kept in a safe range through mathematical constraint mechanism, so that the fault current can be suppressed quickly and effectively at low cost.

[0111] In one exemplary embodiment, the second input ratio is determined according to the following expression:

[0112] (2);

[0113] in, As the second largest proportion of investment, This is the rated value of DC current. This is the initial fault current. This represents the current amplitude.

[0114] For example, in the second suppression stage, after the current amplitude is acquired, a difference calculation is performed with the initial fault current, and a dynamic adjustment factor is constructed by combining this difference with the rated DC current. The second current-limiting parameter is pre-set according to the system's requirement to limit the current peak value. By multiplying the dynamic adjustment factor by the second current-limiting parameter, the second activation ratio of the converter submodule is obtained. This ratio is limited to the range of 0 to 1 to ensure that the number of converter submodules in operation does not exceed their physical capacity limit. By adjusting the second activation ratio in real time, the equivalent impedance of the converter submodule is dynamically changed, thereby suppressing further increases in the short-circuit fault current.

[0115] In practical applications, by introducing the dynamic difference calculation between the initial fault current and the current amplitude, combined with the reference constraint of the rated current, the second input ratio can be automatically adjusted according to the actual current state, which can suppress the current peak while avoiding system instability caused by excessive input of sub-modules.

[0116] In this embodiment, the commissioning ratio of the converter submodule can be precisely controlled in the second suppression stage, effectively suppressing the rising trend of short-circuit fault current, while avoiding current oscillation or equipment overload problems caused by improper commissioning ratio. Thus, fault current can be suppressed quickly and effectively at low cost.

[0117] In one exemplary embodiment, Figure 4 A flowchart illustrating a step for optimizing current limiting parameters is provided in an embodiment of this application, as shown below. Figure 4 As shown, it is possible to Figure 1 Based on this, a further exemplary description of short-circuit fault current suppression in flexible DC power grids is provided, wherein the method may further include:

[0118] S401. Obtain the system equivalent inductance and DC voltage of the flexible DC power grid;

[0119] S402. Using a pre-built current limiting parameter optimization model, based on the first input ratio, the system equivalent inductance, and the DC voltage, the optimized first current limiting parameter is obtained; the optimized first current limiting parameter is used as the preset first current limiting parameter for the next short-circuit fault.

[0120] The system equivalent inductance refers to the equivalent inductance parameter of the power grid under fault conditions. This can be achieved, for example, by real-time monitoring of the power grid topology or offline calculation of power grid parameters, reflecting the dynamic relationship between the rate of change of fault current and voltage. The DC voltage refers to the voltage parameter on the DC side of the converter during a fault. This can be achieved, for example, by collecting the DC bus voltage using a voltage sensor, and it directly affects the upward trend of the fault current. The current-limiting parameter optimization model refers to a mathematical relationship constructed based on the circuit's dynamic equations. For example, it can be implemented using linear regression or parameter fitting methods, used to dynamically adjust the current-limiting parameters according to the current fault stage's operational ratio and system parameters, thereby adapting to the current-limiting requirements under different operating conditions.

[0121] For example, when a short-circuit fault occurs, the system's equivalent inductance and DC voltage can be obtained through real-time monitoring or historical data retrieval. Based on the current initial input ratio and system parameters, the current-limiting parameter optimization model calculates the optimized initial current-limiting parameters using a preset mathematical formula. The optimized parameters are stored in the control system and can be used as preset values ​​for the next fault occurrence, thereby achieving dynamic self-adjustment of the current-limiting parameters. This process requires no additional hardware; parameter optimization can be completed solely through the control algorithm.

[0122] By optimizing the current limiting parameters online, the first current limiting parameter can adapt to changes in the equivalent inductance of the power grid and the DC voltage. For example, after system expansion or operation mode switching, the applicability of the current limiting parameter can still be guaranteed, thereby improving the response speed and accuracy of subsequent fault suppression.

[0123] In this embodiment, by feeding back the operating data of the current fault stage to the parameter optimization model, the current limiting parameters can be automatically corrected, avoiding repeated manual debugging and improving the reliability and maintenance efficiency of subsequent fault suppression. Thus, fault current can be suppressed quickly and effectively at low cost.

[0124] In an exemplary embodiment, the first current limiting parameter is optimized using the following expression:

[0125] (5);

[0126] in, As the first proportion of investment, DC voltage This is the system's equivalent inductance.

[0127] For example, after obtaining the system's equivalent inductance and DC voltage, the first input ratio is substituted into the optimization expression, establishing a direct correlation between the current-limiting parameter and the system's operating state through mathematical relationships. When the DC voltage increases or the equivalent inductance decreases, the expression automatically increases the current-limiting parameter value, thereby accelerating the input and adjustment speed of the converter submodule; conversely, it decreases the current-limiting parameter value to avoid excessive suppression. This dynamic optimization mechanism allows the first current-limiting parameter to adapt to changes in grid operating conditions in real time, without relying on manual experience to preset fixed values, effectively solving the problem of lack of systematic basis for parameter design in traditional control-type current-limiting strategies.

[0128] In this embodiment, the current limiting intensity can be automatically adjusted according to real-time system parameters, quickly suppressing the current rise rate in the early stage of a fault, and maintaining a stable current limiting effect during the fault duration. This significantly improves the fault ride-through capability and equipment safety margin of the flexible DC grid, and is achieved entirely through control algorithm optimization without increasing any hardware costs. Thus, fault current can be suppressed quickly and effectively at low cost.

[0129] In one exemplary embodiment, the value range of the second current limiting parameter is [0,1].

[0130] For example, in the second suppression phase, the activation ratio of the converter submodule is determined by the current amplitude and the second current limiting parameter. When the DC current amplitude is detected to exceed a preset threshold, the second current limiting parameter is activated and participates in the activation ratio calculation. By constraining the parameter value range to between 0 and 1, the abrupt change in the activation state of the submodule can be effectively limited.

[0131] By clearly defining the range of values ​​for the second current limiting parameter, a direct link between parameter selection and safe system operation is established, ensuring that fault current is effectively suppressed and avoiding equipment overvoltage or power oscillation problems caused by improper parameter settings.

[0132] In this embodiment, the current limiting action of the second suppression stage is always kept within a safe and controllable range by constraining the parameter value range, thereby suppressing the fault current quickly and effectively at low cost.

[0133] In some specific implementations, the DC current-based suppression strategy involves the selection of two parameters, namely ka and kb. ka is the suppression parameter based on the rate of change of current in the first segment; its selection should consider both achieving good current suppression and avoiding large fluctuations during normal operation. A first-order Taylor expansion and derivative of equation (6) are performed, taking into account R under metallic fault conditions. eq Much smaller than L eq The simplified current change rate is shown in equation (7).

[0134] (6);

[0135] (7);

[0136] U in equation (7) dc Replace with K1U dc Substituting this into the K1 expression, the current change rate of the first stage suppression circuit is shown in equation (8).

[0137] (8);

[0138] Substituting equation (8) into the expression for K1 in equation (1), we can obtain k a Represented as:

[0139] (5);

[0140] The value of K2 in the second stage can be calculated from equation (2). K2 is the correlation between the fixed coefficient kb in the first term and the current amplitude in the second term. The product of the two values ​​ensures that the value is always less than 1 during the fault period and gradually decreases as the fault develops, thus achieving adaptive current suppression; kb only needs to be selected according to the requirements for the peak DC current, and its value range is [0,1].

[0141] Among the above-mentioned methods for suppressing short-circuit fault current in flexible DC grids, a composite current suppression strategy based on two-stage adaptive control and power exchange-assisted control is proposed. This strategy can quickly limit the peak fault current when a short-circuit fault occurs in the flexible DC grid, while optimizing the current balance during the system recovery phase.

[0142] The first-stage current limiting strategy based on the rate of change of DC current (Formula (1)) initially limits the growth of fault current by adjusting the commissioning ratio K1 of the converter submodule in real time. The second-stage current limiting strategy based on the amplitude of DC current (Formula (2)) further suppresses the peak fault current by dynamically calculating the commissioning ratio K2. In this way, the speed and effectiveness of fault current suppression are improved. Clear principles for selecting current limiting parameters are provided, making the strategy highly operable in engineering.

[0143] After a fault occurs, the d-axis reference current value of the converter is temporarily set to zero (Equations (3) and (4)) to reduce the power feed into the AC system and suppress the overstress phenomenon of the arm current. In this way, the peak current of the AC side and the degree of arm current distortion are effectively reduced. This improves the dynamic recovery performance after fault clearance and enhances the stability of the system.

[0144] In the composite current limiting strategy, the adaptive control loops of the first and second stages are organically combined with the auxiliary suppression loops to form a unified fault current control logic. Based on the development characteristics of the fault current, the current limiting strategy is dynamically switched, and the selection of parameters ka and kb is optimized. In this way, while reducing hardware costs, the peak values ​​of DC line current, DC bus current, and bridge arm current are significantly reduced. A flexible and scalable current limiting solution is provided, suitable for various flexible DC grid scenarios.

[0145] By adjusting the submodule allocation ratio of the half-bridge MMC, dual suppression of DC-side current and bridge arm current is achieved. Combined with existing MMC control systems, the implementation path is simplified, improving engineering applicability. This reduces the technical requirements for the breaking current of the DC circuit breaker, significantly improving the system's economy and feasibility.

[0146] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0147] The following describes the short-circuit fault current suppression device for flexible DC power grids provided in the embodiments of this application. The short-circuit fault current suppression device for flexible DC power grids has the same inventive concept as the short-circuit fault current suppression method for flexible DC power grids described above. The solution to the problem provided by this device is similar to the solution described in the above method. Therefore, the specific limitations of one or more embodiments of the short-circuit fault current suppression device for flexible DC power grids provided below can be referred to the limitations of the short-circuit fault current suppression method for flexible DC power grids described above. The short-circuit fault current suppression device for flexible DC power grids described below and the short-circuit fault current suppression method for flexible DC power grids described above can be referred to each other, and will not be repeated here.

[0148] In one exemplary embodiment, Figure 5 A schematic diagram of a short-circuit fault current suppression device for a flexible DC power grid provided in this application embodiment is shown below. Figure 5 As shown, the short-circuit fault current suppression device 50 of the flexible DC power grid includes: a first-stage parameter module 510, a first-stage determination module 520, a second-stage parameter module 530, a second-stage determination module 540, and a second-stage determination module 5400, wherein:

[0149] The first-stage parameter module 510 is used to acquire DC current change data and preset first current limiting parameters in the event of a short-circuit fault in the flexible DC grid.

[0150] The first phase determines module 520, which is used to determine the first activation ratio of the converter submodule based on the DC current change data and the first current limiting parameter.

[0151] The second-stage parameter module 530 is used to control the activation state of the converter submodule in the first suppression stage according to the first activation ratio; and to obtain the current amplitude corresponding to the first activation ratio and the preset second current limiting parameter; the second current limiting parameter is determined according to the limiting condition of the DC current peak value.

[0152] The second phase determines module 540, which is used to determine the second activation ratio of the converter submodule based on the current amplitude and the second current limiting parameter.

[0153] The fault current suppression module 550 is used to control the activation state of the converter submodule in the second suppression stage according to the second activation ratio, so as to suppress the short-circuit fault current.

[0154] In an exemplary embodiment, the fault current suppression module 550 is used to send a d-axis current zeroing command to the dq decoupling controller; upon receiving a fault clearing signal, it sends a d-axis current recovery command to the dq decoupling controller. The dq decoupling controller is used to zero the d-axis current according to the d-axis current zeroing command, or to restore the current to a preset d-axis current reference value according to the d-axis current recovery command.

[0155] In one exemplary embodiment, the first input ratio is determined according to the following expression:

[0156]

[0157] in, As the first proportion of investment, This is the first current limiting parameter. This is data on the change of direct current;

[0158] In one exemplary embodiment, the second input ratio is determined according to the following expression:

[0159]

[0160] in, As the second largest proportion of investment, This is the rated value of DC current. This is the initial fault current. This represents the current amplitude.

[0161] In one exemplary embodiment, the fault current suppression module 550 is used to obtain the system equivalent inductance and DC voltage of the flexible DC grid;

[0162] Using a pre-built current limiting parameter optimization model, the optimized first current limiting parameter is obtained based on the first input ratio, the system equivalent inductance, and the DC voltage; the optimized first current limiting parameter is used as the preset first current limiting parameter for the next short-circuit fault.

[0163] In an exemplary embodiment, the first current limiting parameter is optimized using the following expression:

[0164]

[0165] in, As the first proportion of investment, DC voltage This is the system's equivalent inductance.

[0166] In one exemplary embodiment, the value range of the second current limiting parameter is [0,1].

[0167] In one exemplary embodiment, this application also provides a computer-readable storage medium storing a computer program that, when executed by one or more processors, causes the one or more processors to perform the steps of any of the short-circuit fault current suppression methods for flexible DC power grids described in the above embodiments.

[0168] In one exemplary embodiment, this application also provides a computer device storing a computer program in which computer-readable instructions, when executed by one or more processors, cause the one or more processors to perform the steps of any of the above embodiments of the short-circuit fault current suppression method for a flexible DC power grid.

[0169] In one exemplary embodiment, this application also provides a computer program product, including a computer program that, when executed by a processor, implements the steps of any of the above embodiments of the short-circuit fault current suppression method for a flexible DC power grid.

[0170] Indicatively, such as Figure 6 As shown, Figure 6 This is a schematic diagram of the internal structure of a computer device 600 provided in an embodiment of this application. The computer device 600 can be provided as a server. (Refer to...) Figure 6 The computer device 600 includes a processing component 602, which further includes one or more processors, and memory resources represented by memory 601 for storing instructions, such as application programs, that can be executed by the processing component 602. The application programs stored in memory 601 may include one or more modules, each corresponding to a set of instructions. Furthermore, the processing component 602 is configured to execute instructions to perform the short-circuit fault current suppression method for a flexible DC power grid according to any of the above embodiments.

[0171] The computer device 600 may also include a power supply component 603 configured to perform power management of the computer device 600, a wired or wireless network interface 604 configured to connect the computer device 600 to a network, and an input / output (I / O) interface 605. The computer device 600 may operate on an operating system stored in memory 601, such as Windows Server™, Mac OS X™, Unix™, Linux™, Free BSD™, or similar.

[0172] Those skilled in the art will understand that Figure 6 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0173] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0174] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can be referred to each other.

[0175] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for suppressing short-circuit fault current in a flexible DC power grid, characterized in that, The method includes: In the event of a short-circuit fault in a flexible DC power grid, acquire data on changes in DC current and preset first current-limiting parameters; Based on the DC current change data and the first current limiting parameter, the first commissioning ratio of the converter submodule is determined; According to the first input ratio, the input state of the converter submodule is controlled in the first suppression stage; and the current amplitude corresponding to the first input ratio and the preset second current limiting parameter are obtained; the second current limiting parameter is determined according to the limiting condition of the DC current peak value; Based on the current amplitude and the second current limiting parameter, determine the second activation ratio of the converter submodule; According to the second input ratio, the input state of the converter submodule in the second suppression stage is controlled to suppress the short-circuit fault current.

2. The method according to claim 1, characterized in that, The method further includes: Send a command to zero the d-axis current to the dq decoupling controller; Upon receiving the fault clearing signal, a d-axis current recovery command is sent to the dq decoupling controller; The dq decoupling controller is used to set the d-axis current to zero according to the d-axis current zeroing command, or to restore the current with a preset d-axis current reference value according to the d-axis current recovery command.

3. The method according to claim 1, characterized in that, The first input ratio is determined according to the following expression: in, As the first proportion of investment, This is the first current limiting parameter. This is data on the change of direct current.

4. The method according to claim 1, characterized in that, The second input ratio is determined according to the following expression: in, As the second largest proportion of investment, This is the rated value of DC current. This is the initial fault current. This represents the current amplitude.

5. The method according to claim 1, characterized in that, The method further includes: Obtain the system equivalent inductance and DC voltage of the flexible DC power grid; Using a pre-built current limiting parameter optimization model, the optimized first current limiting parameter is obtained based on the first input ratio, the system equivalent inductance, and the DC voltage; the optimized first current limiting parameter is used as the preset first current limiting parameter for the next short-circuit fault.

6. The method according to claim 5, characterized in that, The first rate limiting parameter is optimized using the following expression: in, As the first proportion of investment, DC voltage This is the system's equivalent inductance.

7. The method according to claim 1, characterized in that, The value range of the second current limiting parameter is [0,1].

8. A short-circuit fault current suppression device for a flexible DC power grid, characterized in that, The device includes: The first-stage parameter module is used to acquire DC current change data and preset first current limiting parameters in the event of a short-circuit fault in the flexible DC grid. The first-stage determination module is used to determine the first input ratio of the converter submodule based on the change data of the DC current and the first current limiting parameter. The second-stage parameter module is used to control the activation state of the converter submodule in the first suppression stage according to the first activation ratio; and to obtain the current amplitude corresponding to the first activation ratio and the preset second current limiting parameter; the second current limiting parameter is determined according to the limiting condition of the DC current peak value. The second-stage determination module is used to determine the second activation ratio of the converter submodule based on the current amplitude and the second current limiting parameter. The fault current suppression module is used to control the activation state of the converter submodule in the second suppression stage according to the second activation ratio, so as to suppress the short-circuit fault current.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 7.

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