Index evaluation method and system for evaluating fault ride-through capability of direct-current fault current limiter

Abstract

The invention belongs to the field of fault analysis, and discloses an index evaluation method and system for evaluating the fault ride-through capability of a direct-current fault current limiter, and the method comprises the steps: uniformly presetting bipolar short-circuit fault points in a target flexible direct-current power transmission system model, and determining a fault analysis time interval; the fault response processes under the two working conditions that the current limiter is connected and the current limiter is not connected are kept consistent on the time scale, so that a unified analysis basis is provided for comparison and evaluation among different working conditions; according to the method, bipolar short-circuit fault simulation is carried out under the same fault condition, and the state quantity of the system is obtained, so that the influence of the short-circuit fault on the voltage, current and power of the system can be completely described under the two conditions of a current limiter and a non-current limiter, and information loss caused by evaluation only depending on a single electrical quantity is avoided.

Description

Technical Field

[0001] This invention belongs to the field of fault analysis, specifically relating to an evaluation method and system for assessing the fault ride-through capability of DC fault current limiters. Background Technology

[0002] With the rapid development of flexible DC transmission technology, operational flexible DC transmission projects now account for nearly half of the total transmission capacity globally, and their transmission capacity and voltage levels continue to improve. While this trend significantly enhances the grid's inter-regional transmission capacity and the level of renewable energy absorption, it also presents DC systems with more severe safety challenges under fault conditions.

[0003] In high-capacity, strongly coupled flexible DC systems, DC-side short-circuit faults are characterized by rapid development and high peak values. Actual operation and simulation studies show that some DC short-circuit currents can rapidly rise to a dangerous peak value within approximately 10–15 ms, severely impacting converter valves, DC buses, cables, and other primary equipment, significantly reducing the system's safety margin, and even triggering cascading failures. Therefore, it is urgent to introduce effective DC fault suppression measures to limit the amplitude and rise rate of short-circuit current and mitigate the impact of faults on the power grid.

[0004] Fault current limiters (FCLs) are considered an important technical approach to improve the safety and fault ride-through capability of DC systems due to their ability to quickly intervene in the early stages of a fault and suppress the development of short-circuit current. However, existing research mainly focuses on the topology of flexible DC transmission systems centered on modular multilevel converters (MMCs). Related work is mostly from the perspective of converter body protection or local electrical quantity response, and systematic research on introducing DC current limiters to improve system-level fault ride-through characteristics is still relatively insufficient.

[0005] Furthermore, existing studies often focus on single response indicators, such as changes in DC voltage, current, or power, in performance evaluation, lacking a unified and comprehensive evaluation framework for the overall system operation under the coupling of multiple indicators. Especially under DC short-circuit fault conditions, the system's energy balance is rapidly disrupted, and its evolution process and recovery capability have a critical impact on the system's safe operation. However, these impacts have not yet been incorporated into a unified evaluation system, making it difficult for current analyses to fully reflect the actual impact of DC faults on the fault ride-through characteristics of flexible DC transmission systems. Summary of the Invention

[0006] The purpose of this invention is to overcome the problem of lacking a comprehensive evaluation method that can simultaneously reflect the degree of disruption of voltage, current, power and energy balance, and to provide an index evaluation method and system for evaluating the fault ride-through capability of DC fault current limiters.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an index evaluation method for assessing the fault ride-through capability of a DC fault current limiter, comprising the following steps: Bipolar short-circuit fault points are preset in the target flexible DC transmission system model to obtain the fault analysis time interval; The target flexible DC transmission system model is simulated under two operating conditions: with and without a current limiter, to obtain the state variables of the target flexible DC transmission system model. Based on the state variables and fault analysis time interval of the target flexible DC transmission system model, the time cumulative effect index of each electrical quantity in the target flexible DC transmission system model is obtained under two operating conditions: with and without a current limiter. The time cumulative effect index of each electrical quantity in the target flexible DC transmission system model is normalized to obtain the fault ride-through coefficient; The fault ride-through capability of the DC fault current limiter in the target flexible DC transmission system model is evaluated based on the fault ride-through coefficient.

[0008] A further improvement of this invention is that the fault analysis time interval includes the moment when the DC fault occurs and the moment when the DC fault ends.

[0009] A further improvement of the present invention is that the state variables of the target flexible DC transmission system model include the instantaneous values ​​of short-circuit current, fault voltage and power curve when the current limiter is connected during the fault duration, and the instantaneous values ​​of short-circuit current, fault voltage and power curve when the current limiter is not connected.

[0010] A further improvement of this invention is that, when the target flexible DC transmission system model is connected to a current limiter, the specific method for simulating bipolar short-circuit faults is as follows: Start the bipolar short-circuit fault simulation and send fault information; When the current limiter reaches the fault trigger point, the current limiter enters the adaptive current limiting state. Determine whether the current is overcurrent after being limited by the current limiter; If no overcurrent occurs, record the duration of the fault, as well as the instantaneous values ​​of the short-circuit current, fault voltage, and power curve when the current limiter is connected. If an overcurrent occurs, connect the circuit breaker to DC return, turn on the thyristor inside the current limiter, and record the duration of the fault, as well as the instantaneous values ​​of the short-circuit current, fault voltage, and power curve connected to the current limiter during the fault duration.

[0011] A further improvement of this invention lies in the following method for obtaining the time cumulative effect index of each electrical quantity in the target flexible DC transmission system model under two operating conditions: with and without a current limiter, based on the state variables and fault analysis time interval of the target flexible DC transmission system model: Obtain the state variables and fault analysis time interval of the target flexible DC transmission system model; By integrating the state variables over the fault analysis time interval, the time cumulative effect index of each electrical quantity in the target flexible DC transmission system model is obtained under two operating conditions: with and without a current limiter.

[0012] A further improvement of this invention lies in the method of normalizing the time cumulative effect index of each electrical quantity in the target flexible DC transmission system model to obtain the fault ride-through coefficient, as follows: The time cumulative effect index of each electrical quantity in the target flexible DC transmission system model under two operating conditions is obtained, and the integral of the time cumulative effect index is normalized. Obtain the current, voltage, and power data from the normalized time cumulative effect index, and calculate the ratio of the current, voltage, and power data connected to the current limiter to the current, voltage, and power data not connected to the current limiter. The fault ride-through coefficient is obtained by performing an equal-weighted average of the comparison values. The fault ride-through coefficient ranges from 0 to 1.

[0013] A further improvement of this invention lies in the following specific method for evaluating the fault ride-through capability of the DC fault current limiter in the target flexible DC transmission system model based on the fault ride-through coefficient: Obtain the fault ride-through coefficient. The closer the fault ride-through coefficient is to the lower limit, the more significant the overall effect of the current limiter in suppressing short-circuit current, maintaining fault voltage level, and promoting power recovery. When the fault ride-through factor approaches its upper limit, it indicates that the current limiter has a limited overall effect on suppressing short-circuit current, maintaining fault voltage levels, and promoting power recovery.

[0014] Secondly, the present invention provides an index evaluation system for evaluating the fault ride-through capability of a DC fault current limiter, comprising: The fault pre-setting module is used to pre-set bipolar short-circuit fault points in the target flexible DC transmission system model to obtain the fault analysis time interval; The simulation module is used to simulate bipolar short-circuit faults in the target flexible DC transmission system model under two operating conditions: with and without a current limiter, to obtain the state variables of the target flexible DC transmission system model. The index acquisition module is used to obtain the time cumulative effect index of each electrical quantity in the target flexible DC transmission system model under two operating conditions: with and without a current limiter, based on the state variables and fault analysis time interval of the target flexible DC transmission system model. The data processing module is used to normalize the time cumulative effect index of each electrical quantity in the target flexible DC transmission system model to obtain the fault ride-through coefficient. The capability assessment module is used to assess the fault ride-through capability of the DC fault current limiter in the target flexible DC transmission system model based on the fault ride-through coefficient.

[0015] Thirdly, the present invention provides an electronic 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 an index evaluation method for evaluating the fault ride-through capability of a DC fault current limiter.

[0016] Fourthly, the present invention provides a storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of an index evaluation method for evaluating the fault ride-through capability of a DC fault current limiter.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention, by uniformly pre-setting bipolar short-circuit fault points and defining the fault analysis time interval in the target flexible DC transmission system model, ensures that the fault response process remains consistent in time scale under both current-limited and current-limit-free operating conditions, thus providing a unified analytical basis for comparative evaluation between different operating conditions. Furthermore, this invention performs bipolar short-circuit fault simulations under the same fault conditions and obtains system state variables, enabling the impact of short-circuit faults on system voltage, current, and power to be fully characterized in both current-limited and current-limit-free scenarios, avoiding information gaps caused by relying solely on a single electrical quantity for evaluation. Finally, by combining system state variables with the fault analysis time interval, this invention constructs a time-cumulative effect index for each electrical quantity during the fault duration, ensuring that the evaluation process reflects not only voltage, current, and power, but also other electrical quantities. The transient change amplitudes of current and power can also reflect the cumulative time impact of short-circuit faults on the system's energy distribution and energy balance. This invention normalizes the time cumulative effect indicators of various electrical quantities and forms a fault ride-through coefficient, enabling current, voltage, and power to be comprehensively measured under the same dimension and evaluation scale, thereby achieving a unified and quantitative description of multiple electrical responses. Finally, the fault ride-through capability of the DC fault current limiter is evaluated through the fault ride-through coefficient, allowing the comprehensive role of the current limiter in suppressing short-circuit current, maintaining fault voltage levels, and improving power response and energy recovery to be intuitively reflected by a single indicator. This overcomes the problem in the prior art of lacking a comprehensive evaluation method that can simultaneously reflect the degree of disruption of voltage, current, power, and energy balance. Attached Figure Description

[0018] Figure 1 This is a flowchart of the present invention; Figure 2 This is a system diagram of the present invention; Figure 3 A schematic diagram of a simulation model of a five-terminal flexible DC transmission system; Figure 4 This is a simulation model diagram of a DC fault current limiter. Figure 5 This is a simulation flowchart; Figure 6 The waveform diagram of fault point 1 at station S1 during operation; Figure 7 The waveform diagram of fault point 2 at station S1 during operation; Figure 8 The waveform diagram of fault point 3 at station S1 during operation; Figure 9 This is a system diagram of Embodiment 7 of the present invention; Detailed Implementation To further understand the content of this invention, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments are merely illustrative and not limiting of the invention.

[0019] Example 1: See Figure 1 An evaluation method for assessing the fault ride-through capability of a DC fault current limiter includes the following steps: S1. Pre-set bipolar short-circuit fault points in the target flexible DC transmission system model to obtain the fault analysis time interval.

[0020] S2 enables bipolar short-circuit fault simulation of the target flexible DC transmission system model under two operating conditions: with and without a current limiter, to obtain the state variables of the target flexible DC transmission system model.

[0021] S3. Based on the state variables and fault analysis time interval of the target flexible DC transmission system model, the time cumulative effect index of each electrical quantity in the target flexible DC transmission system model is obtained under two operating conditions: with and without a current limiter.

[0022] S4. Normalize the time cumulative effect index of each electrical quantity in the target flexible DC transmission system model to obtain the fault ride-through coefficient.

[0023] S5, evaluate the fault ride-through capability of the DC fault current limiter in the target flexible DC transmission system model based on the fault ride-through coefficient.

[0024] Example 2: See Figure 2 An evaluation system for assessing the fault ride-through capability of DC fault current limiters includes: The fault pre-setting module is used to pre-set bipolar short-circuit fault points in the target flexible DC transmission system model to obtain the fault analysis time interval.

[0025] The simulation module is used to simulate bipolar short-circuit faults in the target flexible DC transmission system model under two operating conditions: with and without a current limiter, to obtain the state variables of the target flexible DC transmission system model.

[0026] The index acquisition module is used to obtain the time cumulative effect index of each electrical quantity in the target flexible DC transmission system model under two operating conditions: with and without a current limiter, based on the state variables and fault analysis time interval of the target flexible DC transmission system model.

[0027] The data processing module is used to normalize the time cumulative effect index of each electrical quantity in the target flexible DC transmission system model to obtain the fault ride-through coefficient.

[0028] The capability assessment module is used to assess the fault ride-through capability of the DC fault current limiter in the target flexible DC transmission system model based on the fault ride-through coefficient.

[0029] Example 3: This embodiment is used to quantitatively evaluate the suppression and recovery effect of DC fault current limiters on DC-side short-circuit faults in flexible DC transmission systems. The specific method is as follows: Step one involves pre-setting a bipolar short-circuit fault point in the target flexible DC transmission system model, and defining a unified fault analysis time interval using the DC fault occurrence and termination times as boundaries. By clearly defining the fault analysis time interval, the fault response process under different operating conditions has a consistent time scale, which helps ensure the comparability and consistency of subsequent evaluation results.

[0030] Step two involves simulating bipolar short-circuit faults in the target flexible DC transmission system model under both conditions: with and without a current limiter. During the simulation, the state variables of the target flexible DC transmission system model are acquired during the fault duration. These state variables include the instantaneous values ​​of the short-circuit current, fault voltage, and power curves when the current limiter is connected, and the instantaneous values ​​of the short-circuit current, fault voltage, and power curves when the current limiter is not connected. By simultaneously collecting state variables under both current-limited and current-free conditions, a complete data foundation is provided for subsequently constructing comparative evaluation indicators, thereby accurately reflecting the regulatory role of the current limiter in the system's fault response.

[0031] Under the condition of connecting the current limiter, the bipolar short-circuit fault simulation is performed according to the following procedure: The bipolar short-circuit fault simulation is started and fault information is sent. The current limiter enters an adaptive current-limiting state after the fault triggering time. During this process, it is determined whether the current after current limiting by the current limiter is excessive. If no overcurrent occurs, the instantaneous values ​​of the short-circuit current, fault voltage, and power curves during the fault duration and when the current limiter is connected are recorded. If an overcurrent occurs, the circuit breaker is connected to the DC circuit, turning on the thyristor inside the current limiter, and the instantaneous values ​​of the short-circuit current, fault voltage, and power curves after connecting the current limiter are recorded during the fault duration. Through the above settings, the current limiter can be accurately modeled under different fault severity levels, thereby improving the adaptability to actual engineering conditions and the reliability of the simulation results.

[0032] Step three: After collecting the state variables under both operating conditions, the time cumulative effect indices of each electrical quantity in the target flexible DC transmission system model are obtained based on the state variables and the fault analysis time interval. Specifically, the short-circuit current, fault voltage, and power state variables are integrated over time within the fault analysis time interval to obtain the time cumulative effect indices of each electrical quantity under the two operating conditions: with and without a current limiter. By introducing the time cumulative effect indices, not only can the transient response amplitude of the fault be reflected, but the duration of the fault's impact on the system can also be characterized, thus providing a more comprehensive description of the destructive impact of short-circuit faults on the system's operating state.

[0033] Step four involves normalizing the time-cumulative effect indices of each electrical quantity in the target flexible DC transmission system model to obtain the fault ride-through coefficient. Specifically, the time-cumulative effect indices of each electrical quantity under two operating conditions are obtained, and their integrals are normalized. After normalization, the ratios of current, voltage, and power data connected to the current limiter to those not connected to the current limiter are calculated. These ratios are then weighted equally to obtain the fault ride-through coefficient, which ranges from 0 to 1. This weighted averaging method ensures that current, voltage, and power have equal weight in the evaluation system, thus avoiding bias from a single electrical quantity and enhancing the comprehensiveness and objectivity of the indicators.

[0034] Step 5: Evaluate the fault ride-through capability of the DC fault current limiter in the target flexible DC transmission system model based on the fault ride-through coefficient. When the fault ride-through coefficient is closer to the lower limit, it indicates that the current limiter has a more significant overall effect on suppressing short-circuit current, maintaining fault voltage levels, and promoting power recovery; conversely, when the fault ride-through coefficient is closer to the upper limit, it indicates that the current limiter's role in suppressing short-circuit current, maintaining fault voltage levels, and promoting power recovery is more limited.

[0035] This embodiment can quantitatively reflect the effect of the DC fault current limiter on the fault ride-through capability of the flexible DC transmission system with unified and intuitive numerical indicators.

[0036] Example 4: This embodiment constructs a fault ride-through technical index—the Fault Ride-Through Capability Index (FRTCI)—that comprehensively considers short-circuit current, fault voltage, and power sag response performance. This index is used to analyze the impact of hybrid DC fault current limiters on the fault ride-through capability of flexible DC transmission systems. The specific method is as follows: Step 1: Pre-determine a bipolar short-circuit fault point in the target flexible DC transmission system model, and set the DC fault occurrence time as the starting point. When the DC fault ends or the system returns to stability As a boundary, a unified fault analysis time interval is defined. By unifying the fault analysis time interval, the consistency of system fault response data on the time scale under different operating conditions is ensured, providing a basis for subsequent indicator calculation and comparative analysis.

[0037] Step two involves simulating or testing a bipolar short-circuit fault in the target flexible DC transmission system model under two conditions: with and without a hybrid DC fault current limiter. System state variables are collected during the fault duration. These state variables include the short-circuit current when the current limiter is connected. Fault voltage when connected to current limiter Instantaneous power curve values ​​when connected to the current limiter and the short-circuit current when no current limiter is connected. Fault voltage when no current limiter is connected Instantaneous power curve values ​​when no current limiter is connected By acquiring complete fault response status quantities under two operating conditions, a one-to-one correspondence is established between the system operating states before and after the current limiter intervention.

[0038] See Figure 5When the current limiter is connected, the bipolar short-circuit fault simulation follows this procedure: The bipolar short-circuit fault simulation is initiated and fault information is sent; the current limiter enters adaptive current limiting mode after the fault triggering time; it is determined whether overcurrent occurs after the current limiter has limited the current; if no overcurrent occurs, the instantaneous values ​​of the short-circuit current, fault voltage, and power curve when the current limiter is connected during the fault duration are directly recorded; if an overcurrent occurs, the circuit breaker is connected to the DC circuit, causing the thyristor inside the current limiter to conduct, suppressing the development of the short-circuit current through energy dissipation, and the instantaneous values ​​of the short-circuit current, fault voltage, and power curve after the current limiter is connected during the fault duration are recorded. This procedure accurately reflects the actual operating state of the hybrid DC fault current limiter under different fault severity levels.

[0039] Step 3: After collecting the state variables under both operating conditions, construct time-cumulative effect indices for each electrical quantity based on the state variables and the fault analysis time interval. Specifically, short-circuit current, fault voltage, and power state variables are respectively included in the fault analysis time interval. Integrating over time, we get:

[0040]

[0041] in, This represents the integral value of the short-circuit current, fault voltage, or power during the fault duration after the current limiter is connected. This represents the integral value of the short-circuit current, fault voltage, or power during the fault duration when no current limiter is connected. They represent currents respectively. ,Voltage and power By introducing the time cumulative effect index, the evaluation process not only considers the instantaneous amplitude of the fault, but also reflects the time cumulative effect of the short-circuit fault on the system.

[0042] Based on this, the time cumulative effect index of each electrical quantity is normalized to construct the fault ride-through coefficient (FRTCI), which is defined as follows:

[0043]

[0044] The range of values ​​for the fault ride-through coefficient (FRTCI) is as follows: By applying an equal-weighted average to the time-cumulative effect indicators of current, voltage, and power, each electrical quantity is given equal importance in the evaluation system, thus avoiding the dominance of a single indicator in the evaluation results.

[0045] From a physical perspective, state quantities and It can reflect the transient impact of short-circuit faults on the system in real time under both current-limited and current-free operating conditions, and the corresponding integral quantity and This characterizes the time-cumulative effect of the short-circuit fault on the system current, voltage, and power. Through the analysis of... and By calculating the ratio and further constructing the FRTCI, a comprehensive and intuitive quantitative assessment of the impact of the current limiter on the system's fault ride-through capability can be achieved. This indicator only requires simulation or experimental calculation until the system returns to stability, and is independent of the current limiter's structure, converter station topology, and control methods at each end, making it highly applicable.

[0046] Finally, the fault ride-through capability of the DC fault current limiter in the target flexible DC transmission system model was evaluated based on the fault ride-through coefficient (FRTCI): when the FRTCI value is closer to 0, it indicates that the hybrid DC fault current limiter has a more significant comprehensive effect in suppressing short-circuit current, maintaining fault voltage level, and promoting power recovery; when the FRTCI value is closer to 1, it indicates that the current limiter has a more limited effect on improving the fault ride-through capability of the flexible DC transmission system.

[0047] Example 5: Building such Figure 3 The simulation model of a five-terminal flexible DC transmission system shown has three typical fault points (reverse near end, forward near end, and forward far end) set up for simulation with and without a hybrid DC fault current limiter. Five converter stations operate simultaneously in the system; station S1 operates in inverter mode, and the other four stations operate in rectification mode. Station S1 is directly connected to station S2, and the DC line branches off in two directions after reaching station S2, connecting to stations S5 and S3. Station S5 is directly connected to station S4. Each converter station outlet is equipped with a circuit breaker, and the current limiter is installed between the circuit breaker and the converter station. The simulation parameters of the model are shown in Table 1.

[0048] Table 1 Line Parameter Table

[0049] Simulation model of DC fault current limiter as follows Figure 4 As shown, current flows into port A and out port B, and Ty corresponds to the IGBT's trigger signal. The surge arrester is connected in parallel with the IGBT and diode, and is equivalent to a large resistor in the simulation. In the model, =0.05H, =0.03H, =3Ω, =2Ω. After the fault occurs, current flows through and Current limiting begins. When the DC circuit breaker (DCCB) receives a protection signal and the surge arrester is activated, Ty is triggered, and the IGBT turns on. and Continuing current in and Dissipation in the middle.

[0050] At the start of the simulation, all five stations maintained steady-state operation. A permanent bipolar ground fault occurred at the DC-side inlet of station S1 at t=0.5s. The DC fault current limiter initiated current limiting. Six ms after the fault, the DCCB received a protection signal and switched the surge arrester to the line. The thyristor of the DC fault current limiter turned on to dissipate energy. The simulation calculation process is as follows: Figure 3 As shown.

[0051] In the simulation, the hybrid DC fault current limiter is installed 20m from the converter station outlet, and bipolar short-circuit faults are set at fault point 1 (backward near end), fault point 2 (forward near end), and fault point 3 (forward far end) of the current limiter.

[0052] See also Figure 6 Under fault point 1 (facing away from the near end), the fault operation waveform of station S1 is shown in the figure. The figure presents the power, current, and voltage response curves for two operating conditions: with and without the hybrid DC fault current limiter connected. Figure 6 (a) It can be seen that, compared with the condition without the current limiter, the power drop during the fault period is reduced, the power recovery speed is accelerated, and the power oscillation is significantly weakened after the current limiter is connected. Figure 6 (b) It can be seen that without the current limiter, the DC-side short-circuit current increases rapidly after the fault occurs, with a high peak value and large oscillation amplitude; however, after connecting the hybrid DC fault current limiter, the rise slope and peak value of the short-circuit current are significantly reduced, and the current oscillation amplitude is significantly reduced, indicating that the current limiter can effectively suppress the rapid development of the short-circuit current. Figure 6 (c) It can be seen that when the current limiter is not connected, the DC voltage drops sharply and the oscillation lasts for a long time; after the current limiter is connected, the minimum DC voltage rises significantly, the voltage oscillation amplitude decreases, and the voltage recovery process is more stable.

[0053] See Figure 7 Under fault point 2 (positive near end) conditions, the fault operation waveform of station S1 is shown in the figure, which presents the power, current, and voltage response curves for two operating conditions: with and without the hybrid DC fault current limiter connected. Figure 7 (a) It can be seen that, compared with the condition without the current limiter, the power drop during the fault period is significantly reduced, the power decay rate is accelerated, the power oscillation is significantly weakened, and the system power recovery characteristics are significantly improved after the current limiter is connected. Figure 7(b) It can be seen that without the current limiter, the DC-side short-circuit current rises rapidly after the fault occurs, with a significantly larger peak value; however, after the hybrid DC fault current limiter is connected, the rise rate and peak value of the short-circuit current are significantly reduced, and the current is suppressed and falls back within a short time, indicating that the current limiter can quickly intervene and effectively limit the development of the short-circuit current under positive near-end fault conditions. Figure 7 (c) It can be seen that when the current limiter is not connected, the DC voltage drops sharply and the oscillation amplitude is large; after the current limiter is connected, the minimum DC voltage rises significantly, the voltage oscillation amplitude decreases, and the voltage recovery process is more stable, which shows that the current limiter provides good support for the DC voltage.

[0054] See Figure 8 Under fault point 3 (positive remote end) conditions, the fault operation waveform of station S1 is shown in the figure, which presents the power, current, and voltage response curves for two operating conditions: with and without the hybrid DC fault current limiter connected. Figure 8 (a) It can be seen that after connecting the current limiter, the power drop during the fault is significantly smaller than that without the current limiter, the power attenuation and recovery process is smoother, and the system power surge is effectively mitigated. Figure 8 (b) It can be seen that without the current limiter, the DC-side short-circuit current continues to rise after the fault occurs, with a high peak value; however, after the hybrid DC fault current limiter is connected, the rise rate of the short-circuit current decreases significantly, the peak current decreases significantly, and it falls back in a short time, indicating that even under forward far-end fault conditions, the current limiter can still effectively suppress the development of the short-circuit current. Figure 8 (c) It can be seen that when the current limiter is not connected, the DC voltage drops sharply and is accompanied by obvious oscillations. After the current limiter is connected, the minimum DC voltage rises, the voltage oscillation amplitude decreases, and the voltage recovery process is more stable. However, compared with the positive near-end fault, the voltage improvement is weaker.

[0055] The current, voltage, and power data during the fault period were extracted, and the FRTCI values ​​at each fault point were calculated as shown in Table 2. Table 2 Calculation Table of Fault Crossing Index for Station S1

[0056] As shown in Table 2, after installing the current limiter, the FRTCI values ​​at the three fault points were all less than 65%. Comparing the FRTCI values ​​at different fault locations, it can be seen that the current limiter works best at the near-side of the fault location, and has the best effect on improving fault ride capability. As the distance between the fault location and the current limiter increases, the FRTCI value gradually increases, and the effect of the current limiter decreases, which is in line with objective laws.

[0057] Example 6: See Figure 9 The present invention also provides an electronic device 100 for evaluating the index assessment method for evaluating the fault ride-through capability of a DC fault current limiter; the electronic device 100 includes a memory 101, at least one processor 102, a computer program 103 stored in the memory 101 and executable on the at least one processor 102, and at least one communication bus 104.

[0058] The memory 101 can be used to store the computer program 103. The processor 102 implements the steps of the evaluation method for assessing the fault ride-through capability of a DC fault current limiter as described in Embodiment 1 by running or executing the computer program stored in the memory 101 and calling the data stored in the memory 101. The memory 101 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 electronic device 100 (such as audio data), etc. In addition, the memory 101 may 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 non-volatile solid-state storage device.

[0059] The at least one processor 102 may 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 processor 102 may be a microprocessor or any conventional processor. The processor 102 is the control center of the electronic device 100, connecting various parts of the electronic device 100 via various interfaces and lines.

[0060] The memory 101 in the electronic device 100 stores multiple instructions to implement an evaluation method for assessing the fault ride-through capability of a DC fault current limiter, and the processor 102 can execute the multiple instructions to achieve the following: Bipolar short-circuit fault points are preset in the target flexible DC transmission system model to obtain the fault analysis time interval; The target flexible DC transmission system model is simulated under two operating conditions: with and without a current limiter, to obtain the state variables of the target flexible DC transmission system model. Based on the state variables and fault analysis time interval of the target flexible DC transmission system model, the time cumulative effect index of each electrical quantity in the target flexible DC transmission system model is obtained under two operating conditions: with and without a current limiter. The time cumulative effect index of each electrical quantity in the target flexible DC transmission system model is normalized to obtain the fault ride-through coefficient; The fault ride-through capability of the DC fault current limiter in the target flexible DC transmission system model is evaluated based on the fault ride-through coefficient.

[0061] Example 7: If the modules / units integrated in the electronic device 100 are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of 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 a processor, 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, and a read-only memory (ROM).

[0062] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0063] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0064] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0065] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for evaluating the fault ride-through capability of a DC fault current limiter, characterized in that, Includes the following steps: Bipolar short-circuit fault points are preset in the target flexible DC transmission system model to obtain the fault analysis time interval; The target flexible DC transmission system model is simulated under two operating conditions: with and without a current limiter, to obtain the state variables of the target flexible DC transmission system model. Based on the state variables and fault analysis time interval of the target flexible DC transmission system model, the time cumulative effect index of each electrical quantity in the target flexible DC transmission system model is obtained under two operating conditions: with and without a current limiter. The time cumulative effect index of each electrical quantity in the target flexible DC transmission system model is normalized to obtain the fault ride-through coefficient; The fault ride-through capability of the DC fault current limiter in the target flexible DC transmission system model is evaluated based on the fault ride-through coefficient.

2. The evaluation method for assessing the fault ride-through capability of a DC fault current limiter according to claim 1, characterized in that, The fault analysis time interval includes the moment when the DC fault occurs and the moment when the DC fault ends.

3. The evaluation method for assessing the fault ride-through capability of a DC fault current limiter according to claim 1, characterized in that, The state variables of the target flexible DC transmission system model include the instantaneous values ​​of short-circuit current, fault voltage, and power curves when the current limiter is connected during the fault duration, and the instantaneous values ​​of short-circuit current, fault voltage, and power curves when the current limiter is not connected.

4. The evaluation method for assessing the fault ride-through capability of a DC fault current limiter according to claim 1, characterized in that, The specific method for simulating bipolar short-circuit faults when the target flexible DC transmission system model is connected to a current limiter is as follows: Start the bipolar short-circuit fault simulation and send fault information; When the current limiter reaches the fault trigger point, the current limiter enters the adaptive current limiting state. Determine whether the current is overcurrent after being limited by the current limiter; If no overcurrent occurs, record the duration of the fault, as well as the instantaneous values ​​of the short-circuit current, fault voltage, and power curve when the current limiter is connected. If an overcurrent occurs, connect the circuit breaker to DC return, turn on the thyristor inside the current limiter, and record the duration of the fault, as well as the instantaneous values ​​of the short-circuit current, fault voltage, and power curve connected to the current limiter during the fault duration.

5. The evaluation method for assessing the fault ride-through capability of a DC fault current limiter according to claim 1, characterized in that, Based on the state variables and fault analysis time interval of the target flexible DC transmission system model, the specific method for obtaining the time cumulative effect index of each electrical quantity in the target flexible DC transmission system model under two operating conditions—with and without a current limiter—is as follows: Obtain the state variables and fault analysis time interval of the target flexible DC transmission system model; By integrating the state variables over the fault analysis time interval, the time cumulative effect index of each electrical quantity in the target flexible DC transmission system model is obtained under two operating conditions: with and without a current limiter.

6. The evaluation method for assessing the fault ride-through capability of a DC fault current limiter according to claim 1, characterized in that, The specific method for normalizing the time cumulative effect indices of various electrical quantities in the target flexible DC transmission system model to obtain the fault ride-through coefficient is as follows: The time cumulative effect index of each electrical quantity in the target flexible DC transmission system model under two operating conditions is obtained, and the integral of the time cumulative effect index is normalized. Obtain the current, voltage, and power data from the normalized time cumulative effect index, and calculate the ratio of the current, voltage, and power data connected to the current limiter to the current, voltage, and power data not connected to the current limiter. The fault ride-through coefficient is obtained by performing an equal-weighted average of the comparison values. The fault ride-through coefficient ranges from 0 to 1.

7. The evaluation method for assessing the fault ride-through capability of a DC fault current limiter according to claim 1, characterized in that, The specific method for evaluating the fault ride-through capability of the DC fault current limiter in the target flexible DC transmission system model based on the fault ride-through coefficient is as follows: Obtain the fault ride-through coefficient. The closer the fault ride-through coefficient is to the lower limit, the more significant the overall effect of the current limiter in suppressing short-circuit current, maintaining fault voltage level, and promoting power recovery. When the fault ride-through factor approaches its upper limit, it indicates that the current limiter has a limited overall effect on suppressing short-circuit current, maintaining fault voltage levels, and promoting power recovery.

8. An index evaluation system for assessing the fault ride-through capability of a DC fault current limiter, characterized in that, include: The fault pre-setting module is used to pre-set bipolar short-circuit fault points in the target flexible DC transmission system model to obtain the fault analysis time interval; The simulation module is used to simulate bipolar short-circuit faults in the target flexible DC transmission system model under two operating conditions: with and without a current limiter, to obtain the state variables of the target flexible DC transmission system model. The index acquisition module is used to obtain the time cumulative effect index of each electrical quantity in the target flexible DC transmission system model under two operating conditions: with and without a current limiter, based on the state variables and fault analysis time interval of the target flexible DC transmission system model. The data processing module is used to normalize the time cumulative effect index of each electrical quantity in the target flexible DC transmission system model to obtain the fault ride-through coefficient. The capability assessment module is used to assess the fault ride-through capability of the DC fault current limiter in the target flexible DC transmission system model based on the fault ride-through coefficient.

9. An electronic 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 index evaluation method for evaluating the fault ride-through capability of a DC fault current limiter as described in any one of claims 1 to 7.

10. A storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the index evaluation method for evaluating the fault ride-through capability of a DC fault current limiter as described in any one of claims 1 to 7.

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