Method and system for processing DC voltage instability caused by RC DC voltage divider

Abstract

This application provides a method and system for handling DC voltage instability caused by a resistive-capacitive DC voltage divider. The method includes: acquiring the parameters of the resistive-capacitive DC voltage divider of the target MMC-HVDC system; inputting the parameters of the resistive-capacitive DC voltage divider into a pre-constructed voltage division ratio determination model to obtain the voltage division ratio between the positive terminal bus and the positive neutral point; determining whether the DC voltage of the target MMC-HVDC system is unstable based on the voltage division ratio between the positive terminal bus and the positive neutral point; if so, limiting the voltage division ratio between the positive terminal bus and the positive neutral point to complete the handling of DC voltage instability caused by the resistive-capacitive DC voltage divider. This application can handle DC-side bus voltage instability of MMC-HVDC systems caused by RCVD faults, and the response speed of voltage instability handling is high.

Description

Technical Field

[0001] This application relates to the field of power system technology, and in particular to a method and system for handling DC voltage instability caused by a resistive-capacitive DC voltage divider. Background Technology

[0002] Modular multilevel converter high-voltage direct current (MMC-HVDC) technology, as a highly efficient and controllable power transmission technology with flexible and high-precision regulation capabilities, provides an innovative technical path for the safe and stable operation of power systems and the improvement of overall energy efficiency. However, with the continuous expansion of the application scenarios and the gradual increase in the installed capacity of MMC-HVDC systems in power systems, the stability issues of its DC-side operation have gradually become prominent in engineering practice, facing many technical bottlenecks and application challenges.

[0003] The DC-side stability problem in MMC-HVDC systems poses a serious threat to the system and is influenced by numerous complex factors, making its research extremely challenging. Research methods generally fall into two categories: state-space methods and impedance analysis. To ensure stable system operation, various methods exist for analyzing and improving DC voltage stability, such as master-slave control, droop control strategies, and virtual synchronous generator control. However, most existing control strategies neglect the potential impact of secondary measurement equipment on system stability. Resistive Voltage Detector (RCD), a key DC voltage measurement device in MMC-HVDC systems, utilizes a mature and highly accurate resistive-capacitive voltage divider structure, primarily used for voltage measurement in the control and protection stages of MMC-HVDC systems. An RCVD failure leads to distorted measurement data, causing the control system to issue incorrect adjustment commands, resulting in DC voltage fluctuations and even system-wide cascading failures. As the RCVD failure worsens, the measured voltage continues to rise under the influence of the positive feedback loop, further amplifying DC voltage instability. Existing methods for optimizing RCVDs are mostly limited to improving the parameters of the equipment itself, or adopt empirical suppression strategies lacking system-level theoretical model support. No solution has yet been developed specifically for handling DC voltage instability caused by RC DC dividers. Therefore, there is an urgent need for a solution to address DC voltage instability caused by abnormal breakdown of RC DC dividers (RCVDs) in MMC-HVDC systems, achieving coordinated optimization of secondary equipment faults and primary control.

[0004] This section is intended to provide background or context for the embodiments of the invention set forth in the claims. The description herein is not an admission that it is prior art simply because it is included in this section. Summary of the Invention

[0005] To address at least one problem in the prior art, this application proposes a method and system for handling DC voltage instability caused by a resistive-capacitive DC voltage divider, which can handle the voltage instability of the MMC-HVDC DC side bus caused by RCVD faults, and has a high response speed for voltage instability handling.

[0006] To address the aforementioned technical problems, this application provides the following technical solution: In a first aspect, this application provides a method for handling DC voltage instability caused by a resistive-capacitive DC voltage divider, including: Collect parameters of the resistive-capacitive DC voltage divider of the target MMC-HVDC system; By inputting the parameters of the resistive-capacitive DC voltage divider into a pre-built voltage division ratio determination model, the voltage division ratio of the positive pole bus and the positive neutral point is obtained. Based on the voltage division ratio of the positive pole bus and the positive neutral point, determine whether the DC voltage of the target MMC-HVDC system is unstable. If so, limit the voltage division ratio of the positive pole bus and the positive neutral point to complete the DC voltage instability handling caused by the RC DC voltage divider.

[0007] In one embodiment, determining whether the DC voltage of the target MMC-HVDC system is unstable based on the voltage division ratio between the positive pole bus and the positive neutral point includes: Determine whether the voltage division ratio of the positive pole bus or the positive neutral point meets its corresponding preset instability condition. If so, determine that the DC voltage of the target MMC-HVDC system is unstable.

[0008] In one embodiment, determining whether the DC voltage of the target MMC-HVDC system is unstable based on the voltage division ratio between the positive pole bus and the positive neutral point further includes: If the voltage division ratio of the positive pole bus and the positive neutral point does not meet their corresponding preset instability conditions, then the DC voltage of the target MMC-HVDC system is determined to be unstable based on the instability identification parameters and the preset instability identification model. The instability identification parameters include at least one of the following: system internal control parameters, actual system electrical parameters, and the voltage division ratio of the positive pole bus and the positive neutral point. The preset instability identification model is obtained by training a batch of training samples and their corresponding labels based on a preset classification algorithm. Each training sample includes the historical voltage division ratio of the historical positive pole bus and the historical positive neutral point. The label is the DC voltage instability or DC voltage stability of the historical MMC-HVDC system.

[0009] In one embodiment, the step of limiting the voltage division ratio between the positive pole bus and the positive neutral point to handle DC voltage instability caused by the resistive-capacitive DC voltage divider includes: Determine whether the voltage division ratio of the positive electrode bus is less than the minimum allowable value of the first voltage division ratio. If so, adjust the voltage division ratio of the positive electrode bus to the minimum allowable value of the first voltage division ratio. Determine whether the voltage division ratio of the positive electrode busbar is greater than or equal to the minimum allowable value of the first voltage division ratio and less than or equal to the reference value of the voltage division ratio under the first ideal condition. If so, determine that the voltage division ratio of the positive electrode busbar remains unchanged. Determine whether the voltage division ratio of the positive electrode busbar is greater than the reference value of the voltage division ratio under the first ideal condition. If so, adjust the voltage division ratio of the positive electrode busbar to the reference value of the voltage division ratio under the first ideal condition. Determine whether the partial voltage ratio of the positive electrode neutral point is less than the minimum allowable value of the second partial voltage ratio. If so, adjust the partial voltage ratio of the positive electrode neutral point to the minimum allowable value of the second partial voltage ratio. Determine whether the partial voltage ratio of the positive electrode neutral point is greater than or equal to the minimum allowable value of the second partial voltage ratio and less than or equal to the reference value of the partial voltage ratio under the second ideal condition. If so, determine that the partial voltage ratio of the positive electrode neutral point remains unchanged. Determine whether the partial voltage ratio of the positive electrode neutral point is greater than the reference value of the partial voltage ratio under the second ideal condition. If so, adjust the partial voltage ratio of the positive electrode neutral point to the reference value of the partial voltage ratio under the second ideal condition.

[0010] In one embodiment, the parameters of the RC DC voltage divider include: the actual positive bus impedance, the actual positive neutral point impedance, and the significant frequency under specific operating conditions.

[0011] In one embodiment, before inputting the parameters of the resistive-capacitive DC voltage divider into a pre-built voltage division ratio determination model to obtain the voltage division ratio of the positive pole bus and the positive neutral point, the method further includes: An impedance analysis method was used to construct a model for determining the voltage division ratio.

[0012] Secondly, this application provides a DC voltage instability handling system caused by a resistive-capacitive DC voltage divider, comprising: The data acquisition device is used to acquire parameters of the resistive-capacitive DC voltage divider of the target MMC-HVDC system. The input device is used to input the parameters of the resistive-capacitive DC voltage divider into a pre-built voltage division ratio determination model to obtain the voltage division ratio of the positive pole bus and the positive neutral point; A limiting control device is used to determine whether the DC voltage of the target MMC-HVDC system is unstable based on the voltage division ratio between the positive pole bus and the positive neutral point. If so, the limiting control is applied to the voltage division ratio between the positive pole bus and the positive neutral point to complete the DC voltage instability handling caused by the RC DC voltage divider.

[0013] In one embodiment, the limiting control device includes: The judgment module is used to determine whether the voltage division ratio of the positive pole bus or the positive pole neutral point meets the corresponding preset instability condition. If so, the DC voltage of the target MMC-HVDC system is determined to be unstable.

[0014] Thirdly, this application provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the method for handling DC voltage instability caused by the resistive-capacitive DC voltage divider.

[0015] Fourthly, this application provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the method for handling DC voltage instability caused by a resistive-capacitive DC voltage divider.

[0016] As can be seen from the above technical solution, this application provides a method and system for handling DC voltage instability caused by a resistive-capacitive DC voltage divider. The method includes: acquiring the parameters of the resistive-capacitive DC voltage divider of the target MMC-HVDC system; inputting the resistive-capacitive DC voltage divider parameters into a pre-constructed voltage division ratio determination model to obtain the voltage division ratio between the positive terminal bus and the positive neutral point; based on the voltage division ratio between the positive terminal bus and the positive neutral point, determining whether the DC voltage of the target MMC-HVDC system is unstable; if so, limiting the voltage division ratio between the positive terminal bus and the positive neutral point to complete the handling of DC voltage instability caused by the resistive-capacitive DC voltage divider, thus enabling the handling of MMC-HVDC instability caused by RCVD faults. The HVDC DC-side bus voltage instability handling method boasts a high response speed. Specifically, it employs amplitude limiting control to confine the voltage division ratio within an ideal range, exhibiting a high response speed and essentially providing passive and protective voltage instability handling. An impedance analysis method is used to construct an impedance model of the MMC-HVDC DC side containing the RCVD. Combined with stability analysis and numerical experiments, the DC voltage positive feedback instability situation coupled with the RCVD and constant DC voltage control system is analyzed. A dynamic voltage division ratio adjustment strategy is proposed, which stabilizes the voltage at the reference value and suppresses abnormal voltage divergence by dynamically correcting the voltage division ratio. The physical meaning of the voltage division ratio determination model is clear, and the derivation is rigorous. The instability mechanism is verified by both experiments and waveform data, and the control strategy is highly targeted. It can be applied to voltage stability control under RCVD faults in MMC-HVDC projects, providing scientific and technological guidance for engineering and possessing significant theoretical value and practicality. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a first flowchart illustrating the method for handling DC voltage instability caused by a resistive-capacitive DC voltage divider in an embodiment of this application. Figure 2 This is a second flowchart illustrating the method for handling DC voltage instability caused by a resistive-capacitive DC voltage divider in the embodiments of this application. Figure 3 This is a schematic diagram of the main circuit structure of the MMC-HVDC in the application example of this application; Figure 4 This is a diagram of the constant DC voltage control structure in an application example of this application; Figure 5 The impedance Z of the positive pole bus varies with the RCVD voltage divider ratio in the application example of this application.dcP+ Bode plot; Figure 6 The neutral point impedance Z is the voltage divider ratio of the RCVD at the positive pole bus in the application example of this application. dcN+ Bode plot; Figure 7 The positive pole bus voltage when the RCVD voltage divider ratio changes at the pole bus in the application example of this application. U dcP1+ Electromagnetic transient simulation waveform diagram; Figure 8 The positive neutral point voltage at the pole bus changes when the RCVD voltage divider ratio changes in the application example of this application. U dcN1+ Electromagnetic transient simulation waveform diagram; Figure 9 When an RCVD fault occurs at the positive pole bus in the application example of this application. U dcP1+ Fault waveform; Figure 10 When an RCVD fault occurs at the positive pole bus in the application example of this application. U dcN1+ Fault waveform; Figure 11 The impedance Z of the front and rear pole buses in the limiting control example of this application. dcP+ Comparison chart; Figure 12 The neutral point impedance Z before and after the limiting control in the application example of this application is... dcN+ Comparison chart; Figure 13 This is an example of amplitude limiting control before and after application in this application. U dcP1+ Waveform diagram; Figure 14 This is an example of amplitude limiting control before and after application in this application. U dcN1+ Waveform diagram; Figure 15 This is a schematic block diagram of the DC voltage instability handling system caused by the RC DC voltage divider in the embodiments of this application; Figure 16 This is a schematic block diagram of the system configuration of an electronic device according to an embodiment of this application. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in 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 in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0019] As the core device for measuring DC bus voltage in MMC-HVDC systems, a failure in the RCVD (Resistive Voltage Divider) can lead to deviations in measurement data, causing the control system to issue incorrect adjustment commands, resulting in DC voltage fluctuations and even triggering system-wide cascading failures. Current optimization methods for RCVDs are mostly limited to improving the device's intrinsic parameters or employing empirical suppression strategies lacking system-level theoretical support. No strategy has yet been developed specifically for handling DC voltage instability caused by RC (Resistive Capacitive) DC voltage dividers. Therefore, how to address DC voltage instability caused by RC voltage dividers and achieve coordinated optimization between secondary equipment and primary control remains a pressing technical challenge. To address the aforementioned problems, this invention proposes a method and system for handling DC voltage instability caused by a resistive-capacitive DC voltage divider. To suppress DC voltage divergence caused by a single RCVD component failure, a voltage division ratio determination model for an MMC-HVDC system with an RCVD can be established, and a corresponding limiting control strategy can be designed to limit the RCVD voltage division ratio within a stable range, thereby suppressing abnormal voltage divergence. The DC-side impedance model (i.e., the pre-constructed voltage division ratio determination model) has a clear physical meaning and rigorous derivation, and the control strategy is highly targeted, which can be effectively applied to voltage stability control under RCVD failure scenarios in MMC-HVDC engineering.

[0020] As a key DC voltage measurement device in the MMC-HVDC system, the Resistor-Capacitor Diode (RCD) employs a mature and highly accurate resistor-capacitor (RC) voltage divider structure. It is primarily used for voltage measurement in the control and protection stages of the MMC-HVDC system. The RCVD's measurement signal provides input to the control unit of the MMC-HVDC system. When an RCVD at a different location on the DC bus fails, the voltage division ratio of the RCVD to the actual bus voltage increases. Due to the positive gain characteristic of the system's DC bus impedance, the measured voltage is consequently higher, leading to an increase in the pole bus voltage and the neutral point voltage, ultimately forming a positive feedback closed loop. As the RCVD failure worsens, the measured voltage continues to rise under the influence of the positive feedback loop, further amplifying DC voltage instability. This positive feedback mechanism clearly reveals the dynamic evolution and interaction mechanism of the impact of RCVD failures on the DC-side voltage.

[0021] The following examples illustrate this in detail.

[0022] To address the voltage instability on the DC side bus of the MMC-HVDC circuit caused by an RCVD fault, and to achieve a high response speed in voltage instability handling, this embodiment provides a DC voltage instability handling method induced by a RC DC voltage divider, where the execution entity is an RC DC voltage divider-based system. Figure 1 As shown, this method specifically includes the following: Step 1: Collect the parameters of the RC DC voltage divider of the target MMC-HVDC system.

[0023] Specifically, the parameters of the RC DC voltage divider may include: the actual positive bus impedance, the actual positive neutral point impedance, and the significant frequency under specific operating conditions.

[0024] Step 2: Input the parameters of the RC DC voltage divider into the pre-built voltage division ratio determination model to obtain the voltage division ratio of the positive pole bus and the positive neutral point.

[0025] Specifically, when the RCVD at the pole bus fails, the impedance exhibits a positive gain characteristic in the low-frequency range; when the RCVD at the neutral point fails, it affects the mid-to-high-frequency characteristics of the bus impedance. Therefore, the frequency range in which the RCVD affects the bus impedance differs significantly depending on its location on the bus. Furthermore, when the degree of RCVD damage varies, the amplitude and phase of the impedance resonance peak also differ accordingly. Based on the influence of RCVD faults on the significant frequencies of system impedance and their corresponding impedance amplitudes, the voltage division ratio can be calculated by establishing relevant equations. k 1+ or k 2+ Then, the damage status of the RCVD can be determined based on the characteristics of the change in the partial pressure ratio.

[0026] Step 3: Based on the voltage division ratio of the positive pole bus and the positive neutral point, determine whether the DC voltage of the target MMC-HVDC system is unstable. If so, limit the voltage division ratio of the positive pole bus and the positive neutral point to complete the DC voltage instability handling caused by the RC DC voltage divider.

[0027] like Figure 2 As shown, in one embodiment, step 3, determining whether the DC voltage of the target MMC-HVDC system is unstable based on the voltage division ratio between the positive pole bus and the positive neutral point, includes: Step 31: Determine whether the voltage division ratio of the positive pole bus or the positive neutral point meets the corresponding preset instability condition. If so, determine that the DC voltage of the target MMC-HVDC system is unstable.

[0028] Specifically, the preset instability condition for the voltage division ratio of the positive electrode bus can be: k1 =|k 1+ - k 1+0 |＞ K1, where k 1+0 K1 is the first threshold value, which is the preset reference value for the positive electrode bus voltage division ratio.

[0029] Specifically, the preset instability condition for the voltage division ratio of the positive electrode neutral point is: k2 =|k 2+ - k 2+0 |＞ K2, where, k 2+0 K2 is the preset reference value for the positive electrode neutral point voltage ratio, and K2 is the second threshold. The preset reference value for the positive electrode bus voltage ratio, the first threshold, the preset reference value for the positive electrode neutral point voltage ratio, and the second threshold can all be set according to actual conditions, and this application does not impose any restrictions on them.

[0030] To further improve the intelligence and reliability of determining whether DC voltage is unstable, such as Figure 2 As shown, in one embodiment, step 3, determining whether the DC voltage of the target MMC-HVDC system is unstable based on the voltage division ratio between the positive pole bus and the positive neutral point, further includes: Step 32: If the voltage division ratios of the positive pole bus and the positive neutral point do not meet their corresponding preset instability conditions, then determine whether the DC voltage of the target MMC-HVDC system is unstable based on the instability identification parameters and the preset instability identification model. The instability identification parameters include at least one of the following: system internal control parameters, actual system electrical parameters, and the voltage division ratios of the positive pole bus and the positive neutral point. The preset instability identification model is obtained by training a batch of training samples and their corresponding labels based on a preset classification algorithm. Each training sample includes the historical voltage division ratios of the historical positive pole bus and the historical positive neutral point. The label is the historical DC voltage instability or DC voltage stability of the MMC-HVDC system.

[0031] Specifically, the internal control parameters can be the control parameters of the inner and outer loop controllers, while the actual electrical parameters of the system are the parameters of the system components, such as inductors and capacitors. Both the internal control parameters and the actual electrical parameters of the system are constant values.

[0032] To improve the reliability of voltage division ratio limiting control, in one embodiment, step 3, which involves limiting the voltage division ratio between the positive pole bus and the positive neutral point to handle DC voltage instability caused by the RC DC voltage divider, includes: Step 331: Determine whether the voltage division ratio of the positive electrode bus is less than the minimum allowable value of the first voltage division ratio. If so, adjust the voltage division ratio of the positive electrode bus to the minimum allowable value of the first voltage division ratio.

[0033] Step 332: Determine whether the voltage division ratio of the positive electrode bus is greater than or equal to the minimum allowable value of the first voltage division ratio and less than or equal to the reference value of the voltage division ratio under the first ideal condition. If so, determine that the voltage division ratio of the positive electrode bus remains unchanged.

[0034] Step 333: Determine whether the voltage division ratio of the positive electrode bus is greater than the reference value of the voltage division ratio under the first ideal condition. If so, adjust the voltage division ratio of the positive electrode bus to the reference value of the voltage division ratio under the first ideal condition.

[0035] Step 334: Determine whether the partial voltage ratio of the positive electrode neutral point is less than the minimum allowable value of the second partial voltage ratio. If so, adjust the partial voltage ratio of the positive electrode neutral point to the minimum allowable value of the second partial voltage ratio.

[0036] Step 335: Determine whether the partial voltage ratio of the positive electrode neutral point is greater than or equal to the minimum allowable value of the second partial voltage ratio and less than or equal to the reference value of the partial voltage ratio under the second ideal condition. If so, determine that the partial voltage ratio of the positive electrode neutral point remains unchanged.

[0037] Step 336: Determine whether the partial voltage ratio of the positive electrode neutral point is greater than the reference value of the partial voltage ratio under the second ideal condition. If so, adjust the partial voltage ratio of the positive electrode neutral point to the reference value of the partial voltage ratio under the second ideal condition.

[0038] Specifically, the minimum allowable value of the first voltage division ratio, the reference value of the voltage division ratio under the first ideal condition, the minimum allowable value of the second voltage division ratio, and the reference value of the voltage division ratio under the second ideal condition can all be set according to the actual situation. Considering the influence of the voltage division ratio on the impedance characteristics, as a preferred option, the reference value of the voltage division ratio under the first and second ideal conditions is 1.

[0039] Specifically, the voltage division ratio between the positive electrode bus and the positive electrode neutral point can be used as a basis, combined with actual operating conditions, for targeted control and adjustment. A limiting control is adopted for the voltage division ratio of the RCVD to keep it within a stable range. After introducing limiting control, the voltage division ratio is corrected to a piecewise function.

[0040]

[0041] In the formulak 1+,2+Id This is the ideal reference value for the partial pressure ratio. k 1+,2+min This is the minimum allowable partial pressure ratio. k 1+,2+Re This is the actual value of the voltage division ratio. Considering the influence of the voltage division ratio on the impedance characteristics, this is the reference value of the voltage division ratio under ideal conditions. k 1+,2+Id =1.

[0042] To improve the reliability of constructing the voltage division ratio determination model, and thus improve the accuracy of subsequently applying the voltage division ratio determination model, in one embodiment, before step 2, the following steps are included: An impedance analysis method was used to construct a model for determining the voltage division ratio.

[0043] Specifically, the model for determining the partial pressure ratio can be:

[0044] in, This represents the DC-side positive pole bus impedance model. This represents the impedance model at the positive neutral point. For significant frequencies, The voltage division ratio of the positive pole busbar. The partial voltage ratio at the positive neutral point. The magnitude of the positive pole bus impedance at the stated significant frequency, Let be the amplitude of the positive neutral point impedance at the significant frequency.

[0045] U dcP1+ The positive DC side bus voltage of the fixed DC voltage station. U dcN1+ To determine the neutral point voltage of the DC voltage station, U dcP1+ RCVD partial voltage ratio k 1+ , U dcN1+ RCVD partial voltage ratio k 2+ The expressions are shown in formulas (1) and (2).

[0046] (1) (2) in, R iHO ( i =1,2) represents the high-voltage arm resistance. C iHO For high voltage arm capacitors,R iLO For low voltage arm resistors, C iLO For low-voltage arm capacitors, n 1+ and n 2+ These represent the number of RCVD high-voltage arm resistor-capacitor units that are operating normally. n 1+ , n 2+ =1,2,……, m , m (This is the total number of RCVD high-voltage arm resistor-capacitor units). Formulas (1) and (2) can be used to represent the voltage divider ratio model, that is, the ratio of the secondary side voltage to the primary side voltage of the voltage divider, which exists in the impedance model.

[0047] The steps for constructing the voltage division ratio determination model using impedance analysis may include: Obtain the voltage relationship on the AC side of the MMC-HVDC system. This AC side voltage relationship can be obtained from... Figure 3 and Figure 4 get: (3) In the formula, v s1j This indicates the voltage at the PCC point on the grid side. v j This indicates the grid-side voltage of the converter station. v sj L represents the AC power supply voltage, and L represents the grid-side inductance of the converter station. i j Indicates grid-side current. Z g This indicates AC impedance measurement. By performing an abc→dq coordinate transformation on formula (3), we obtain: (4) in, ,

[0048] In the formula, v s1dq+ , v dq+ and i dq+ In order v s1j , v j and i j The dq axis components.

[0049] Assuming the d-axis voltage is aligned with the PCC point voltage, then the following conditions are met. v s1q+ =0, therefore, the small-signal expression for the PCC point voltage of the MMC-HVDC system in the rotating coordinate system can be obtained as follows: (5) In the formula, v s1dq+ , v sd+ , v sq+ , i d+ and i q+ In order v s1dq+ , v sd+ , v sq+ , i d+ and i q+ small signal components, i sd0 , i sq0 , , In order i sd , i sq , , steady-state components, For AC side resistance, For AC side inductance.

[0050] Obtain the voltage relationship on the DC side of the MMC-HVDC system. This DC side voltage relationship can be obtained from... Figure 1 From the circuit relationship on the DC side, we can obtain: (6) In the formula, U dcP1+ , U dcN1+ , i dc+ They are respectively U dcP1+ , U dcN1+ ,i dc+ Small signal components. U dcP1+ , U dcN1+ , i dc+ The following represent, in sequence, the positive DC side bus voltage of the fixed DC voltage station, the neutral point voltage of the fixed DC voltage station, and the DC side current of the converter station. Indicates line inductance. This indicates the DC-side filter capacitor.

[0051] Combining formula (6) and the outer loop control relationship, we can obtain: (7) In the formula, i dref+ , i qref+ In order i dref+ , i qref+ small signal components, For the outer loop PI control of the DC voltage station.

[0052] Ignoring power loss, the small-signal expressions for the DC and AC sides are established as follows: (8) In the formula, v d+ , v q+ In order v d+ , v q+ small signal components, U dcP1+0 , U dcN1+0 , i dc+0 , i d+0 , i q+0 , v d+0、 v q+0 In order U dcP1+ , U dcN1+ , i dc+ , i d+ ,i q+ , v q+ , v d+ The steady-state component.

[0053] Combining equations (6) and (8), we get: (9) Combining formulas (4) and (5), we can obtain the small-signal expression for the converter station output voltage: (10) In the formula, , In order to represent v dq+ , Small signal components.

[0054] Substituting formula (10) into formula (9), we get: (11) Based on the inner loop current control relationship, we can obtain: (12) in: ,

[0055] s= jω 0= j 2π f 0

[0056] Combining formulas (5), (7), (11), and (12), we can obtain: (13) From this, the impedance of the positive pole bus can be obtained. The expression for the DC-side positive pole bus impedance model is as follows: (14) Combining equations (6) and (14), the impedance at the positive neutral point can be obtained. The expression for this is the positive neutral point impedance model: (15) From the above formulas (3) to (14), it can be seen that, and In reality, they are all with f 0. Significant frequency, voltage division ratio of the positive electrode busbar k 1+ The partial voltage ratio of the positive electrode neutral point k 2+The relevant models can all be expressed as the voltage division ratio of the positive pole bus at a significant frequency. k 1+ The partial voltage ratio of the positive electrode neutral point k 2+ For the model of variables, It can be represented as , It can be represented as .

[0057] Let significant frequency f 0 locations Z dcP+ and Z dcN+ The amplitudes are as follows: (16) According to the system small signal model Z dcP+ and Z dcN+ It can be represented as k 1+ and k 2+ Functions: (17) in α These are known parameters (control parameters, system parameters) in the system impedance.

[0058] Combining formulas (16) and (17), we can obtain the following: f The amplitude equation at 0: (18) Substituting the significant frequency, the amplitude of the positive pole bus impedance at the significant frequency, and the amplitude of the positive neutral point impedance into formula (18), the voltage division ratio of the positive pole bus can be obtained. k 1+ The partial voltage ratio of the positive electrode neutral point k 2+ .

[0059] To further illustrate this solution, this application provides an application example of a method for handling DC voltage instability caused by a resistive-capacitive DC voltage divider, as described in detail below: Step S101: Perform stability analysis on the DC bus impedance of MMC-HVDC under different fault conditions of RCVD based on the impedance model.

[0060] Taking an RCVD fault at the positive pole bus as an example, the Bode plots of the pole bus impedance and neutral point impedance when the RCVD voltage divider ratio at the positive pole bus changes are as follows: Figure 5 and Figure 6As shown, the blue curve represents the amplitude-frequency response of the impedance under ideal conditions.

[0061] When a fault occurs in the RCVD at the positive terminal bus, causing a change in its corresponding voltage division ratio, the impedance of the positive terminal bus... Z dcP+ and positive neutral point impedance Z dcN+ Bode plot as Figure 5 and Figure 6 As shown, the blue curve represents the ideal system condition. Z dcP+ The amplitude-frequency response. In Figure 5 In the middle, the fault curve and the ideal curve are in 10 -2 The phase difference within the Hz to 10Hz frequency range is approximately 360°, indicating that the two are in phase within this frequency band. Furthermore, Z dcP+ The amplitude of the fault curve is higher than that of the ideal curve, exhibiting positive gain characteristics.

[0062] exist Figure 6 In the process, although the amplitude difference between the fault curve and the ideal curve is small, RCVD faults still cause... Z dcN+ A noticeable spike appears near 40Hz, disrupting the [symbol / interference]. Z dcN+ Ideal impedance characteristics. Meanwhile, at 10... -2 RCVD faults cause problems in the frequency range of Hz to 10Hz. Z dcN+ This results in a significant phase shift, which in turn weakens system stability. In summary, due to the coupling between the RCVD and the DC voltage controller, an RCVD fault at the pole bus will also alter the amplitude-frequency characteristics of the neutral pole.

[0063] Step S102: Use PSCAD / EMTDC to build an electromagnetic transient simulation model including RCVD. Experimentally verify the proposed mechanism using on-site fault recordings.

[0064] An integrated electromagnetic transient simulation model combining MMC-HVDC, constant DC voltage control, and RCVD was established. The high-voltage arm of the RCVD at the pole bus is equivalent to 13 RC units. When an RCVD fault occurs at the positive pole bus... U dcP1+ and U dcN1+ The waveform is as follows Figure 7 and Figure 8 As shown. The yellow curve corresponds to the RCVD fault-free operating condition, at which point... U dcP1+ The amplitude is basically equal to the 500kV voltage reference value under ideal conditions; Figure 7 In the middle, whenn 1+ When the voltage is 10 (corresponding to the failure of the RC unit of the 3rd high-voltage arm), the waveform eventually converges, but the fluctuation amplitude increases significantly, reaching a maximum of about 600kV. n 1+ When the voltage reaches 7 (corresponding to the failure of the RC unit in section 6 of the high-voltage arm), the waveform amplitude further increases, approximately 1.8 times that under fault-free operating conditions. Figure 8 It is evident that damage to the RCVD at the pole bus can also lead to a decrease in neutral point voltage. U dcN1+ The waveform is distorted, which significantly affects the system's stability.

[0065] During converter station operation, the recorded waveform under RCVD fault at the positive pole bus is as follows: Figure 9 and Figure 10 As shown. Figure 9 Display: Positive bus voltage U dcP1+ The fault recordings exhibit oscillatory characteristics. As the severity of the RCVD fault intensifies, the oscillation amplitude envelope continues to rise, reaching 630kV at approximately 2.2s. Figure 10 In the middle, neutral point voltage U dcN1+ Irregular oscillations also occurred, with amplitudes fluctuating around ±400V, indicating that the system was in an unstable state.

[0066] Step S103: Solve for the voltage division ratio based on the frequency domain characteristics of the MMC-HVDC impedance under different fault conditions of RCVD.

[0067] When the RCVD voltage ratio at the pole bus changes, due to Z dcP+ and Z dcN+ The coupling effect between the two impedances simultaneously affects their amplitude-frequency characteristics. When the RCVD at the pole bus fails, it causes a positive gain in the impedance at low frequencies; when the RCVD at the neutral point fails, it affects the mid-to-high frequency characteristics of the bus impedance. Therefore, the frequency range at which the RCVD affects the bus impedance differs depending on where it fails. The degree of RCVD damage also affects the amplitude and phase of the impedance resonance peak. Based on the impact of RCVD faults on the significant frequencies of the system impedance and their corresponding impedance amplitudes, an equation can be established to inversely calculate the voltage division ratio. k 1+ or k 2+ The damage status of the RCVD can be determined based on the voltage divider ratio.

[0068] Step S104: Apply a limiting control strategy to the obtained voltage division ratio.

[0069] Based on the voltage divider ratio obtained in step S104, and combined with actual operating conditions, targeted control and adjustment are implemented. Amplitude limiting control is used for the voltage divider ratio of the RCVD to keep it within a stable range. After introducing amplitude limiting control, the voltage divider ratio is corrected to a piecewise function.

[0070] Step S105: Simulation experiment verification of the amplitude limiting control strategy.

[0071] The comparison between the bus impedance Bode plot after amplitude limiting control and the Bode plot under ideal conditions is as follows: Figure 11 and Figure 12 As shown. Figure 11 In the meantime, the amplitude and phase of the pole bus impedance are basically consistent with those under ideal conditions. Figure 12 In the figure, the phase of the neutral point impedance differs from that under ideal conditions by approximately 360°, indicating that they are in phase and their amplitudes are essentially identical. This demonstrates that the limiting control can constrain the voltage division ratio within the ideal range, thereby effectively suppressing the abnormal divergence of the DC-side bus voltage.

[0072] Figure 13 and Figure 14 When an RCVD fault occurs at the positive pole bus, limiting control is applied. U dcP1+ and U dcN1+ The waveform diagram. (From...) Figure 13 It can be seen that when the limiting control is applied at approximately 0.8 seconds, the voltage of the pole bus will be... U dcP1+ The waveform is close to the ideal amplitude, and the voltage waveform converges. Meanwhile, Figure 14 neutral point voltage U dcN1+ The waveform oscillation amplitude decreased significantly and eventually stabilized. This indicates that amplitude limiting control can effectively suppress the instability of the DC bus voltage caused by RCVD faults.

[0073] From a software perspective, to achieve high response speed in handling DC-side bus voltage instability caused by RCVD faults in the MMC-HVDC system, this application provides an embodiment of a DC voltage instability handling system for implementing all or part of the aforementioned DC voltage instability handling method, using a resistive-capacitive DC voltage divider. See [link to embodiment]. Figure 15 The DC voltage instability handling system specifically includes the following components: Acquisition device 10 is used to acquire parameters of the resistive-capacitive DC voltage divider of the target MMC-HVDC system; Input device 20 is used to input the parameters of the resistive-capacitive DC voltage divider into a pre-built voltage division ratio determination model to obtain the voltage division ratio of the positive pole bus and the positive neutral point; The limiting control device 30 is used to determine whether the DC voltage of the target MMC-HVDC system is unstable based on the voltage division ratio of the positive pole bus and the positive neutral point. If so, the limiting control is performed on the voltage division ratio of the positive pole bus and the positive neutral point to complete the DC voltage instability handling caused by the RC DC voltage divider.

[0074] In one embodiment, the limiting control device includes: The judgment module is used to determine whether the voltage division ratio of the positive pole bus or the positive pole neutral point meets the corresponding preset instability condition. If so, the DC voltage of the target MMC-HVDC system is determined to be unstable.

[0075] The embodiments of the DC voltage instability handling system caused by the RC DC voltage divider provided in this specification can be used to execute the processing flow of the embodiments of the above-described RC DC voltage divider-induced DC voltage instability handling method. Its functions will not be repeated here, but can be referred to the detailed description of the embodiments of the above-described RC DC voltage divider-induced DC voltage instability handling method.

[0076] From a hardware perspective, in order to achieve high response speed in handling DC voltage instability on the MMC-HVDC DC side bus caused by RCVD faults, this application provides an embodiment of an electronic device for implementing all or part of the DC voltage instability handling method caused by the aforementioned resistor-capacitor DC voltage divider. The electronic device specifically includes the following: The system comprises a processor, memory, a communications interface, and a bus; wherein the processor, memory, and communications interface communicate with each other via the bus; the communications interface is used to realize information transmission between the DC voltage instability handling system caused by the RC DC voltage divider and related devices such as user terminals; the electronic device can be a desktop computer, tablet computer, or mobile terminal, etc., and this embodiment is not limited to these. In this embodiment, the electronic device can be implemented with reference to the embodiments for implementing the DC voltage instability handling method caused by the RC DC voltage divider and the embodiments for implementing the DC voltage instability handling system caused by the RC DC voltage divider, the contents of which are incorporated herein, and repeated details will not be described again.

[0077] Figure 16 This is a schematic block diagram illustrating the system configuration of the electronic device 9600 according to an embodiment of this application. Figure 16 As shown, the electronic device 9600 may include a central processing unit 9100 and a memory 9140; the memory 9140 is coupled to the central processing unit 9100. It is worth noting that... Figure 16This is an example; other types of structures can also be used to supplement or replace this structure to achieve telecommunications functions or other functions.

[0078] In one or more embodiments of this application, the function for handling DC voltage instability caused by a resistive-capacitive DC voltage divider can be integrated into a central processing unit 9100. The central processing unit 9100 can be configured to perform the following control: Collect parameters of the resistive-capacitive DC voltage divider of the target MMC-HVDC system; By inputting the parameters of the resistive-capacitive DC voltage divider into a pre-built voltage division ratio determination model, the voltage division ratio of the positive pole bus and the positive neutral point is obtained. Based on the voltage division ratio of the positive pole bus and the positive neutral point, determine whether the DC voltage of the target MMC-HVDC system is unstable. If so, limit the voltage division ratio of the positive pole bus and the positive neutral point to complete the DC voltage instability handling caused by the RC DC voltage divider.

[0079] As can be seen from the above description, the electronic device provided in the embodiments of this application can realize the handling of voltage instability on the DC side bus of MMC-HVDC caused by RCVD fault, and the voltage instability handling has a high response speed.

[0080] In another embodiment, the DC voltage instability handling system caused by the RC DC voltage divider can be configured separately from the central processing unit 9100. For example, the DC voltage instability handling system caused by the RC DC voltage divider can be configured as a chip connected to the central processing unit 9100, and the DC voltage instability handling function caused by the RC DC voltage divider can be implemented through the control of the central processing unit.

[0081] It is worth noting that electronic device 9600 is not necessarily required to include it. Figure 16 All components shown; in addition, the electronic device 9600 may also include Figure 16 For components not shown, please refer to existing technologies.

[0082] like Figure 16 As shown, the central processing unit 9100, sometimes also referred to as a controller or operating control, may include a microprocessor or other processor device and / or logic device, which receives inputs and controls the operation of various components of the electronic device 9600.

[0083] The memory 9140 may be, for example, one or more of a cache, flash memory, hard drive, removable media, volatile memory, non-volatile memory, or other suitable devices. It may store the aforementioned failure-related information, and also store a program for executing that information. The central processing unit 9100 may execute the program stored in the memory 9140 to perform information storage or processing, etc.

[0084] The memory 9140 can be a solid-state memory, such as a read-only memory (ROM), random access memory (RAM), a SIM card, etc. It can also be a memory that retains information even when power is off, can be selectively erased, and contains more data; examples of this type of memory are sometimes referred to as EPROMs, etc. The memory 9140 can also be some other type of device.

[0085] As described above, the electronic device provided in the embodiments of this application can handle voltage instability on the DC side bus of MMC-HVDC caused by RCVD faults, and the voltage instability handling has a high response speed.

[0086] Embodiments of this application also provide a computer-readable storage medium capable of implementing all steps of the DC voltage instability handling method caused by the RC DC voltage divider in the above embodiments. The computer-readable storage medium stores a computer program that, when executed by a processor, implements all steps of the DC voltage instability handling method caused by the RC DC voltage divider in the above embodiments. For example, when the processor executes the computer program, it implements the following steps: Collect parameters of the resistive-capacitive DC voltage divider of the target MMC-HVDC system; By inputting the parameters of the resistive-capacitive DC voltage divider into a pre-built voltage division ratio determination model, the voltage division ratio of the positive pole bus and the positive neutral point is obtained. Based on the voltage division ratio of the positive pole bus and the positive neutral point, determine whether the DC voltage of the target MMC-HVDC system is unstable. If so, limit the voltage division ratio of the positive pole bus and the positive neutral point to complete the DC voltage instability handling caused by the RC DC voltage divider.

[0087] As can be seen from the above description, the computer-readable storage medium provided in the embodiments of this application can realize the handling of voltage instability on the DC side bus of MMC-HVDC caused by RCVD fault, and the voltage instability handling has a high response speed.

[0088] The various embodiments of the methods described in this application are presented in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on explaining the differences from other embodiments. Relevant details can be found in the descriptions of the method embodiments.

[0089] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application 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.

[0090] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. 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... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0091] 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.

[0092] 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.

[0093] This application uses specific embodiments to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for handling DC voltage instability caused by a resistive-capacitive DC voltage divider, characterized in that, include: Collect parameters of the resistive-capacitive DC voltage divider of the target MMC-HVDC system; By inputting the parameters of the resistive-capacitive DC voltage divider into a pre-built voltage division ratio determination model, the voltage division ratio of the positive pole bus and the positive neutral point is obtained. Based on the voltage division ratio of the positive pole bus and the positive neutral point, determine whether the DC voltage of the target MMC-HVDC system is unstable. If so, limit the voltage division ratio of the positive pole bus and the positive neutral point to complete the DC voltage instability handling caused by the RC DC voltage divider.

2. The method for handling DC voltage instability caused by a resistive-capacitive DC voltage divider according to claim 1, characterized in that, The determination of whether the DC voltage of the target MMC-HVDC system is unstable based on the voltage division ratio of the positive pole bus and the positive neutral point includes: Determine whether the voltage division ratio of the positive pole bus or the positive neutral point meets its corresponding preset instability condition. If so, determine that the DC voltage of the target MMC-HVDC system is unstable.

3. The method for handling DC voltage instability caused by a resistive-capacitive DC voltage divider according to claim 2, characterized in that, The method of determining whether the DC voltage of the target MMC-HVDC system is unstable based on the voltage division ratio between the positive pole bus and the positive neutral point further includes: If the voltage division ratio of the positive pole bus and the positive neutral point does not meet their corresponding preset instability conditions, then the DC voltage of the target MMC-HVDC system is determined to be unstable based on the instability identification parameters and the preset instability identification model. The instability identification parameters include at least one of the following: system internal control parameters, actual system electrical parameters, and the voltage division ratio of the positive pole bus and the positive neutral point. The preset instability identification model is obtained by training a batch of training samples and their corresponding labels based on a preset classification algorithm. Each training sample includes the historical voltage division ratio of the historical positive pole bus and the historical positive neutral point. The label is the DC voltage instability or DC voltage stability of the historical MMC-HVDC system.

4. The method for handling DC voltage instability caused by a resistive-capacitive DC voltage divider according to claim 1, characterized in that, The step of limiting the voltage division ratio between the positive pole bus and the positive neutral point to handle DC voltage instability caused by the resistive-capacitive DC voltage divider includes: Determine whether the voltage division ratio of the positive electrode bus is less than the minimum allowable value of the first voltage division ratio. If so, adjust the voltage division ratio of the positive electrode bus to the minimum allowable value of the first voltage division ratio. Determine whether the voltage division ratio of the positive electrode busbar is greater than or equal to the minimum allowable value of the first voltage division ratio and less than or equal to the reference value of the voltage division ratio under the first ideal condition. If so, determine that the voltage division ratio of the positive electrode busbar remains unchanged. Determine whether the voltage division ratio of the positive electrode busbar is greater than the reference value of the voltage division ratio under the first ideal condition. If so, adjust the voltage division ratio of the positive electrode busbar to the reference value of the voltage division ratio under the first ideal condition. Determine whether the partial voltage ratio of the positive electrode neutral point is less than the minimum allowable value of the second partial voltage ratio. If so, adjust the partial voltage ratio of the positive electrode neutral point to the minimum allowable value of the second partial voltage ratio. Determine whether the partial voltage ratio of the positive electrode neutral point is greater than or equal to the minimum allowable value of the second partial voltage ratio and less than or equal to the reference value of the partial voltage ratio under the second ideal condition. If so, determine that the partial voltage ratio of the positive electrode neutral point remains unchanged. Determine whether the partial voltage ratio of the positive electrode neutral point is greater than the reference value of the partial voltage ratio under the second ideal condition. If so, adjust the partial voltage ratio of the positive electrode neutral point to the reference value of the partial voltage ratio under the second ideal condition.

5. The method for handling DC voltage instability caused by a resistive-capacitive DC voltage divider according to claim 1, characterized in that, The parameters of the RC DC voltage divider include: the actual positive bus impedance, the actual positive neutral point impedance, and the significant frequency under specific operating conditions.

6. The method for handling DC voltage instability caused by a resistive-capacitive DC voltage divider according to claim 1, characterized in that, Before inputting the parameters of the resistive-capacitive DC voltage divider into a pre-built voltage division ratio determination model to obtain the voltage division ratio of the positive pole bus and the positive neutral point, the method further includes: An impedance analysis method was used to construct a model for determining the voltage division ratio.

7. A DC voltage instability handling system caused by a resistive-capacitive DC voltage divider, characterized in that, include: The data acquisition device is used to acquire parameters of the resistive-capacitive DC voltage divider of the target MMC-HVDC system. The input device is used to input the parameters of the resistive-capacitive DC voltage divider into a pre-built voltage division ratio determination model to obtain the voltage division ratio of the positive pole bus and the positive neutral point; A limiting control device is used to determine whether the DC voltage of the target MMC-HVDC system is unstable based on the voltage division ratio between the positive pole bus and the positive neutral point. If so, the limiting control is applied to the voltage division ratio between the positive pole bus and the positive neutral point to complete the DC voltage instability handling caused by the RC DC voltage divider.

8. The DC voltage instability handling system caused by the RC DC voltage divider according to claim 7, characterized in that, The limiting control device includes: The judgment module is used to determine whether the voltage division ratio of the positive pole bus or the positive pole neutral point meets the corresponding preset instability condition. If so, the DC voltage of the target MMC-HVDC system is determined to be unstable.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the method for handling DC voltage instability caused by the RC DC voltage divider as described in any one of claims 1 to 6.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the method for handling DC voltage instability caused by a resistive-capacitive DC voltage divider as described in any one of claims 1 to 6.

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