Active shutdown method, device, system and electronic equipment of hybrid direct current transmission system

Abstract

The application provides a method, device, system and electronic equipment for actively shutting down a hybrid DC power transmission system. The method comprises: obtaining a set of power grid voltage coefficients of the hybrid DC power transmission system within a first preset time period; obtaining an effective value of an outlet end of a converter transformer on an AC side of a converter valve in a plurality of DC power transmission lines of a receiving end AC power grid at a first time, to obtain a first target effective value; determining an effective value of a controllable commutation converter valve at a second time according to the set of power grid voltage coefficients and the first target effective value, to obtain a second target effective value; obtaining a set of critical voltages of the hybrid DC power transmission system within a second preset time period; determining whether a commutation failure fault will occur in the controllable commutation DC power transmission line at the second time according to the set of critical voltages, the first target effective value and the second target effective value; and controlling the controllable commutation converter valve to shut down in the case that the commutation failure fault will occur in the controllable commutation DC power transmission line at the second time.

Description

Technical Field

[0001] This application relates to the field of power system control technology, and more specifically, to an active shutdown method, apparatus, system, and electronic equipment for a hybrid DC transmission system. Background Technology

[0002] Multi-infeed HVDC transmission systems are centralized energy processing systems at the load end. However, due to the semi-controlled nature of thyristors, the LCC can only control the switching on and requires commutation voltage from the AC grid for reliable switching off. When an AC fault causes an AC voltage drop, insufficient reverse voltage leads to re-conduction, resulting in commutation failure. With the formation of multi-infeed configurations, the strength of the receiving-end grid in existing multi-DC infeed systems is gradually weakening. Under fault conditions, multiple DC lines may fail to commutate simultaneously, resulting in significant power loss and seriously threatening the safe and stable operation of the power grid.

[0003] With the advancement of integrated gate-commutated thyristor (IGCT) technology, hybrid line commutated converters (HCCs) can be constructed by replacing thyristors with reverse-resistance IGCTs based on line commutated converter (LCC) technology. However, by using the traditional LCC control strategy, HCCs cannot effectively support AC grids in multi-infeed scenarios, which can easily lead to commutation failure and low operational reliability. Summary of the Invention

[0004] The main objective of this application is to provide an active shutdown method, apparatus, system, and electronic device for a hybrid DC transmission system, so as to at least solve the technical problem in the related art that the control strategy of a hybrid DC transmission system is difficult to resist commutation failure.

[0005] To achieve the above objectives, according to one aspect of this application, an active shutdown method for a hybrid DC transmission system is provided. The hybrid DC transmission system includes multiple DC transmission lines, each DC transmission line including a converter valve, and the multiple DC transmission lines include at least one controllable commutation DC transmission line, the controllable commutation DC transmission line including a controllable commutation converter valve. The method includes: acquiring a set of grid voltage coefficients of the hybrid DC transmission system within a first preset time period, the set of grid voltage coefficients representing the coupling degree of the AC-side outlet voltage of the converter transformers of the converter valves of the multiple sets of DC transmission lines in the receiving-end AC grid, each set of DC transmission lines having two DC transmission lines; acquiring the effective value of the AC-side outlet voltage of the converter transformers of the multiple sets of DC transmission lines in the receiving-end AC grid at a first moment, to obtain a first target effective value; Based at least on the set of grid voltage coefficients and the first target effective value, the effective value of the AC side outlet of the converter transformer of the controllable commutation converter valve at the second moment is determined, and the second target effective value is obtained. The second moment is after the first moment. The critical voltage set of the hybrid DC transmission system within a second preset time period is obtained. The critical voltage set includes the critical voltage values ​​of multiple DC transmission lines of the receiving-end AC grid that will experience commutation failure. Based on the critical voltage set, the first target effective value, and the second target effective value, it is determined whether the controllable commutation DC transmission line will experience a commutation failure fault at the second moment. If it is determined that the controllable commutation DC transmission line will experience a commutation failure fault at the second moment, the controllable commutation converter valve of the controllable commutation DC transmission line is controlled to close.

[0006] Optionally, obtaining the set of grid voltage coefficients of the hybrid DC transmission system within the first preset time period includes: obtaining multiple voltage interaction factors, wherein the multiple voltage interaction factors constitute the set of grid voltage coefficients, and the voltage interaction factors are used to characterize the degree of coupling of the output voltage of the converter transformer on the AC side of any two adjacent DC transmission lines of the receiving-end AC grid.

[0007] Optionally, obtaining multiple voltage interaction factors includes: obtaining the effective value of the output voltage of the converter transformer on the AC side of the converter valve in multiple DC transmission lines of the receiving-end AC power grid, to obtain multiple first effective voltage values; controlling the voltage drop at the bus of multiple DC transmission lines by a preset ratio, and obtaining multiple effective value changes of the output voltage of the converter transformer on the AC side of the converter valve in multiple DC transmission lines corresponding to the preset ratio; multiplying the effective value changes of each DC transmission line by a first preset coefficient to obtain multiple first product values; dividing the first product value of each DC transmission line by the first effective voltage value of its adjacent DC transmission line to obtain the voltage interaction factor of any two adjacent DC transmission lines.

[0008] Optionally, the multiple DC transmission lines further include multiple uncontrollable phase-commutated DC transmission lines. The first target effective value corresponding to the controllable phase-commutated DC transmission line is a controllable target effective value, and the first target effective value corresponding to the uncontrollable phase-commutated DC transmission line is an uncontrollable target effective value. The step of determining the effective value of the AC side outlet of the converter transformer of the controllable phase-commutated converter valve at a second moment, based at least on the set of grid voltage coefficients and the first target effective value, to obtain the second target effective value, includes: calculating the product of the uncontrollable target effective value of each of the uncontrollable phase-commutated DC transmission lines and the corresponding voltage interaction factor to obtain multiple second product values; summing the multiple second product values ​​to obtain a first sum value; and adding the result of multiplying the first sum value by a second preset coefficient to the controllable target effective value to obtain the second target effective value.

[0009] Optionally, obtaining the set of critical voltages of the hybrid DC transmission system within the second preset time period includes: obtaining the phase offset angle of the converter valve of each DC transmission line, the per-unit value of the commutation reactance of the converter valve, the first DC current before the commutation failure fault, the second DC current after the commutation failure fault, the turn-off angle before the commutation failure fault, and the critical turn-off angle; calculating the sum of the per-unit value, the cosine value of the target angle, and the cosine value of the critical turn-off angle of each DC transmission line to obtain multiple second summation values, wherein the target angle is the sum of the turn-off angle before the commutation failure fault and the phase offset angle. The summation is calculated as follows: the per-unit value of each DC transmission line is divided by the second summation value to obtain multiple first quotient values; the second DC current of each DC transmission line is divided by the first DC current to obtain multiple second quotient values; the first quotient values ​​of each DC transmission line are multiplied by the second quotient values ​​to obtain multiple third product values; the absolute value of the difference between the third product value of each DC transmission line and the third preset coefficient is calculated to obtain a first difference value; the multiple first differences are determined as the critical voltage values ​​for commutation failure of each DC transmission line; the multiple critical voltage values ​​constitute the critical voltage set.

[0010] Optionally, obtaining the phase offset angle of the converter valve of each of the DC transmission lines includes: obtaining the voltage drop value of the phase voltage of the multiple DC transmission lines during an asymmetrical fault; calculating the product of the voltage drop value of each DC transmission line and a fourth preset coefficient to obtain a fourth product value; calculating the absolute value of the difference between the fourth product value and a fifth preset coefficient to obtain a second difference value; dividing the voltage drop value by the second difference value to obtain a third quotient value; and the arctangent value of the third quotient value is the phase offset angle of the converter valve of each of the DC transmission lines.

[0011] Optionally, the first target effective value corresponding to the controllable commutated DC transmission line is a controllable target effective value. The step of determining whether the controllable commutated DC transmission line will experience a commutation failure fault at the second moment based on the critical voltage set, the first target effective value, and the second target effective value includes: calculating the absolute value of the difference between the controllable target effective value and the second target effective value as the voltage deviation; determining whether the voltage deviation is greater than the critical voltage value corresponding to the controllable commutated DC transmission line; if the voltage deviation is greater than the critical voltage value, determining that the controllable commutated DC transmission line will experience a commutation failure fault at the second moment; if the voltage deviation is less than or equal to the critical voltage value, determining that the controllable commutated DC transmission line has not experienced a commutation failure fault at the second moment.

[0012] According to another aspect of this application, an active shutdown device for a hybrid DC transmission system is provided. The hybrid DC transmission system includes multiple DC transmission lines, each DC transmission line including a converter valve, and the multiple DC transmission lines including at least one controllable phase-commutated DC transmission line. The converter valve of the controllable phase-commutated DC transmission line is a controllable phase-commutated converter valve. The active shutdown device includes: a first acquisition module, used to acquire a set of grid voltage coefficients of the hybrid DC transmission system within a first preset time period, the set of grid voltage coefficients representing the coupling degree of the AC-side outlet voltage of the converter transformers of the multiple sets of DC transmission lines in the receiving-end AC grid, each set of DC transmission lines having two DC transmission lines; and a second acquisition module, used to acquire the effective value of the AC-side outlet voltage of the converter transformers of the multiple sets of DC transmission lines in the receiving-end AC grid at a first moment, to obtain a first target value. The system comprises: a target effective value module, used to determine the effective value of the AC side outlet of the converter transformer of the controllable commutation converter valve at a second time moment, based at least on the set of grid voltage coefficients and the first target effective value, to obtain a second target effective value, wherein the second time moment is after the first time moment; and a control module, used to acquire the critical voltage set of the hybrid DC transmission system within a second preset time period, wherein the critical voltage set includes the critical voltage values ​​of multiple DC transmission lines of the receiving-end AC grid that would result in commutation failure, and based on the critical voltage set, the first target effective value, and the second target effective value, to determine whether the controllable commutation DC transmission line will experience a commutation failure fault at the second time moment, and, if it is determined that the controllable commutation DC transmission line will experience a commutation failure fault at the second time moment, to control the controllable commutation converter valve of the controllable commutation DC transmission line to close.

[0013] According to another aspect of this application, a hybrid DC transmission system is provided, comprising: multiple DC transmission lines, each DC transmission line including a converter valve, the multiple DC transmission lines including at least one controllable commutation DC transmission line, wherein the converter valve of the controllable commutation DC transmission line is a controllable commutation converter valve; and a controller, communicatively connected to the converter valves, and configured to execute an active shutdown method of the hybrid DC transmission system to control the multiple converter valves.

[0014] According to another aspect of this application, an electronic device is provided, comprising: one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include an active shutdown method for performing a hybrid DC transmission system.

[0015] Applying the technical solution of this application, the active shutdown method for a hybrid DC transmission system first obtains the set of grid voltage coefficients for the hybrid DC transmission system within a first preset time period. This allows for the prediction of voltage drops (voltage coupling) in the controllable commutation DC transmission lines caused by multi-source DC disturbances. At least based on the first target effective value of the AC side outlet of the converter transformer of the converter valves of multiple DC transmission lines in the receiving-end AC grid at the first moment, and the set of grid voltage coefficients, the AC side outlet of the converter transformer of the controllable commutation converter valves at the second moment after the first moment can be determined. The second target effective value at the side outlet is then matched with the critical voltage set to determine whether the controllable commutation converter valve will fail to shut off properly at the second moment, thus causing commutation failure. If it is determined that the controllable commutation DC transmission line will experience commutation failure at the second moment, the controllable commutation converter valve of the controllable commutation DC transmission line is controlled to shut off, forcing the valve to be commutated to shut off in advance, thus completing active commutation. This achieves the protection against commutation failure of HCC converter valve in multi-feed DC systems and solves the technical problem that the control strategy of hybrid DC transmission systems in related technologies is difficult to resist commutation failure. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0017] Figure 1 A hardware structure block diagram of a mobile terminal for performing an active shutdown method for a hybrid DC transmission system, according to an embodiment of this application, is shown.

[0018] Figure 2 A partial structural schematic diagram of a hybrid DC transmission system according to an embodiment of this application is shown;

[0019] Figure 3 A schematic flowchart of an active shutdown method for a hybrid DC transmission system according to an embodiment of this application is shown.

[0020] Figure 4 A schematic flowchart of another active shutdown method for a hybrid DC transmission system provided according to an embodiment of this application is shown.

[0021] Figure 5 A structural block diagram of an active shutdown device for a hybrid DC transmission system provided according to an embodiment of this application is shown.

[0022] The above figures include the following reference numerals:

[0023] 102. Processor; 104. Memory; 106. Transmission device; 108. Input / output device. Detailed Implementation

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0026] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0027] As described in the background section, if the HCC converter built in the existing multi-infeed high-voltage direct current transmission system adopts the traditional LCC control strategy, it cannot effectively support the AC grid in the multi-infeed scenario, which can easily lead to commutation failure and low operational reliability. The embodiments of this application provide an active shutdown method, device, system and electronic equipment for a hybrid direct current transmission system.

[0028] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0029] The methods and embodiments provided in this application can be executed on a mobile terminal, computer terminal, or similar computing device. Taking running on a mobile terminal as an example, Figure 1 This is a hardware structure block diagram of a mobile terminal for an active shutdown method of a hybrid DC transmission system according to an embodiment of this application. Figure 1 As shown, a mobile terminal may include one or more ( Figure 1Only one is shown in the diagram. A processor 102 (which may include, but is not limited to, a microprocessor MCU or a programmable logic device FPGA, etc.) and a memory 104 for storing data are also shown. The mobile terminal may further include a transmission device 106 for communication functions and an input / output device 108. Those skilled in the art will understand that... Figure 1 The structure shown is for illustrative purposes only and does not limit the structure of the mobile terminal described above. For example, the mobile terminal may also include components that are more... Figure 1 The more or fewer components shown, or having the same Figure 1 The different configurations shown.

[0030] The memory 104 can be used to store computer programs, such as application software programs and modules, like the computer program corresponding to the active shutdown method of the hybrid DC transmission system in this embodiment. The processor 102 executes various functional applications and data processing by running the computer program stored in the memory 104, thereby implementing the above-described method. The memory 104 may include high-speed random access memory and non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memory. In some instances, the memory 104 may further include memory remotely located relative to the processor 102, and these remote memories can be connected to the mobile terminal via a network. Examples of the aforementioned networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof. The transmission device 106 is used to receive or send data via a network. Specific examples of the aforementioned networks may include wireless networks provided by the mobile terminal's communication provider. In one example, the transmission device 106 includes a network interface controller (NIC), which can be connected to other network devices via a base station to communicate with the Internet. In one example, the transmission device 106 may be a radio frequency (RF) module, which is used to communicate with the Internet wirelessly.

[0031] This embodiment provides an active shutdown method for a hybrid DC transmission system that runs on a mobile terminal, computer terminal, or similar computing device. It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. Also, although a logical order is shown in the flowchart, in some cases, the steps shown or described may be executed in a different order than that shown here.

[0032] like Figure 2As shown, the hybrid DC transmission system includes multiple DC transmission lines, each DC transmission line includes a converter valve, and the multiple DC transmission lines include at least one controllable commutation DC transmission line. Figure 2 The first high-voltage direct current transmission line in the country (Line Commutated Converter High Voltage Direct Current, LCC-HVDC) is a controllable phase commutation direct current transmission line, which includes a controllable phase commutation converter valve (IGCT-HCC converter valve). Figure 3 This is a flowchart of an active shutdown method for a hybrid DC transmission system according to an embodiment of this application, wherein voltage coupling between AC and DC grids and voltage interaction between DC lines occur in the system. Figure 2 The structure shown is only a general illustration. For example... Figure 3 As shown, the method includes the following steps:

[0033] Step S1: Obtain the set of grid voltage coefficients of the hybrid DC transmission system within a first preset time period. The set of grid voltage coefficients represents the coupling degree of the AC side outlet voltage of the converter transformer of the converter valve of multiple DC transmission lines of the receiving AC grid. Each set of DC transmission lines has two DC transmission lines.

[0034] Optionally, obtaining the grid voltage coefficient set first requires acquiring system operating data. The first preset time period can be a periodic period such as a quarter or a year. The grid voltage coefficient set is established based on historical data, reflecting the mutual influence between DC transmission lines. Its purpose is to assess whether voltage coupling exists between multiple lines and to quantify the degree of this coupling. The grid voltage coefficient set is constructed by monitoring the receiving-end AC grid of the multi-infeed system and statistically analyzing the impact of voltage changes of different DC transmission lines during normal operation on the voltage of other lines. For example, in a multi-infeed system with four DC transmission lines, a 4×4 matrix coefficient set can be constructed. The off-diagonal elements of the matrix are the grid voltage coefficients, reflecting the degree of voltage coupling between each pair of DC transmission lines. The off-diagonal elements refer to the grid voltage coefficients between different DC transmission lines, such as line 1 and line 2, or line 1 and line 3. The grid voltage coefficient between the same line is 1. The closer the grid voltage coefficient is to 1, the greater the degree of voltage interaction coupling between the DC feed points of the two lines, and the higher the sensitivity to voltage fluctuations. By establishing a set of grid voltage coefficients, it is possible to accurately grasp the voltage interaction effects between various DC transmission lines in a multi-infeed hybrid DC transmission system, providing a quantitative basis for predicting commutation failures.

[0035] Step S2: Obtain the effective value of the AC side outlet of the converter transformer of the converter valve of multiple DC transmission lines of the receiving AC power grid at the first moment, and obtain the first target effective value.

[0036] Specifically, the instantaneous AC voltage at the inverter-side outlet of each DC transmission line in the receiving-end system is monitored in real time. Then, at a certain time point (e.g., the first sampling point per second), the effective value of these instantaneous values ​​is extracted as the first target effective value. This data reflects the instantaneous voltage status on the inverter side of the DC transmission line. All DC lines are monitored and recorded synchronously to ensure that the acquired data reflects the latest status, thereby improving the accuracy of predictions. The aforementioned first target effective value includes the effective value for both controllable commutation DC transmission lines and uncontrollable commutation DC transmission lines. Since AC voltage fluctuations directly affect the success of commutation, real-time monitoring and extraction of effective values ​​at key time points can quickly capture voltage change trends, providing an accurate data foundation for subsequent predictions. The aforementioned receiving-end system includes the receiving-end AC grid and the inverter stations of the DC transmission lines.

[0037] Step S3: Determine the effective value of the AC side outlet of the converter transformer of the controllable commutation valve at the second moment, based at least on the set of grid voltage coefficients and the first target effective value, and obtain the second target effective value. The second moment is after the first moment.

[0038] Specifically, by utilizing the set of grid voltage coefficients, the first target effective value obtained above, and a preset relational function, the effective value of the inverter-side AC voltage at the next moment (the second moment) can be predicted, thus obtaining the second target effective value. Compared to existing technologies where the HCC converter valve only designs its active shutdown strategy based on its own operating status detection signal, without considering the voltage interaction between DC transmission lines in multi-infeed scenarios, the HCC converter valve cannot fully utilize its ability to resist commutation failure, which is detrimental to the safe and stable operation of multi-infeed DC systems in scenarios with a high proportion of renewable energy penetration. The prediction process described in this application considers the voltage interaction between multiple DC transmission lines, enabling a more accurate assessment of the voltage state at future moments, thereby providing an early warning of the risk of commutation failure.

[0039] Step S4: Obtain the critical voltage set of the hybrid DC transmission system within a second preset time period. The critical voltage set includes the critical voltage values ​​of multiple DC transmission lines of the receiving-end AC grid that will experience commutation failure. Based on the critical voltage set, the first target effective value, and the second target effective value, determine whether the controllable commutation DC transmission line will experience a commutation failure fault at the second time. If it is determined that the controllable commutation DC transmission line will experience a commutation failure fault at the second time, control the controllable commutation converter valve of the controllable commutation DC transmission line to shut off.

[0040] Specifically, based on previously collected historical operating data of the receiving-end AC power grid under commutation failure fault conditions, the critical voltage values ​​for commutation failure of each DC transmission line under different conditions are determined. These multiple critical voltage values ​​constitute the critical voltage set of the multi-infeed hybrid DC transmission system. After predicting the second target effective value at the second moment, it is compared with the corresponding value in the critical voltage set. If the second target effective value is lower than the critical voltage value, it is determined that a commutation failure fault may occur at the second moment. The control strategy of the controllable commutation converter valve is immediately adjusted to actively shut it off to prevent commutation failure.

[0041] The active shutdown method for the hybrid DC transmission system in this embodiment first obtains the set of grid voltage coefficients for the hybrid DC transmission system within a first preset time period. This allows for the prediction of voltage drops (voltage coupling) in the controllable commutation DC transmission line caused by multi-source DC disturbances. At least based on the first target effective value of the AC side outlet of the converter transformer of the converter valve of multiple DC transmission lines in the receiving-end AC grid at the first moment and the set of grid voltage coefficients, the second target effective value of the AC side outlet of the converter transformer of the controllable commutation converter valve at the second moment after the first moment can be determined. Then, the second target effective value is matched with the critical voltage set to determine whether the controllable commutation converter valve will fail to shut off normally at the second moment, leading to commutation failure. If it is determined that the controllable commutation DC transmission line will experience commutation failure at the second moment, the controllable commutation converter valve of the controllable commutation DC transmission line is controlled to shut off, forcing the valve to be commutated to shut off in advance, completing active commutation. This achieves resistance to commutation failure of the HCC converter valve in a multi-infeed DC system, solving the technical problem in related technologies where the control strategy of the hybrid DC transmission system is difficult to resist commutation failure.

[0042] In the specific implementation process, step S1 above, obtaining the set of grid voltage coefficients of the hybrid DC transmission system within the first preset time period, can be achieved through the following steps:

[0043] Multiple voltage interaction factors are obtained, which constitute a set of grid voltage coefficients. The voltage interaction factors are used to characterize the coupling degree of the output voltage of the converter transformer on the AC side of any two adjacent DC transmission lines of the receiving-end AC grid.

[0044] By combining historical operating data of the receiving-end AC power grid under normal operating conditions, the voltage interaction effect between multiple DC transmission lines can be evaluated. The multi-infeed interaction factor (MIIF) can be used as a quantitative indicator. This indicator can describe the change in the terminal voltage of other DC transmission lines caused by voltage fluctuations on the inverter side of a certain DC transmission line in an AC power grid with multiple transmission feed points. It can also represent the coupling degree of the AC side outlet voltage of the converter transformer of any two adjacent DC transmission lines in the receiving-end AC power grid, and the sensitivity of voltage fluctuations between any two DC transmission lines. By measuring the degree of influence of voltage fluctuations on the inverter side of DC transmission line i on the inverter side voltage of line j, a set of voltage interaction factors is constructed to provide a basis for subsequent prediction of commutation failure, where i and j are two different labels from 1 to m.

[0045] The above set of grid voltage coefficients can be in the form of a grid voltage coefficient table, which can better identify the MIIF value between two DC transmission lines.

[0046] The steps for obtaining multiple voltage interaction factors described above include:

[0047] The effective values ​​of the output voltage on the AC side of the converter transformer of the converter valve in multiple DC transmission lines of the receiving-end AC power grid are obtained, resulting in multiple first effective voltage values; firstly, without... Figure 2 A three-phase reactor is installed between the busbar and the transformer on the LCC side to obtain the first effective voltage value of multiple DC transmission lines. .

[0048] The system controls the voltage drop at the busbars of multiple DC transmission lines by a preset ratio, and acquires multiple effective value changes in the output voltage of the converter transformers on the AC side of the converter valves in these DC transmission lines, corresponding to the preset ratio; [the system then continues with further details about the voltage drop and its implications.] Figure 2 A three-phase reactor is installed between the busbar and the transformer on the LCC side of the DC transmission line. The voltage drop at the busbar of the DC transmission line is reduced by a preset percentage (1%). The effective value changes of multiple DC transmission lines are then obtained. .

[0049] Multiply the effective value change of each DC transmission line by a first preset coefficient to obtain multiple first product values. Divide each first product value of a DC transmission line by the first effective voltage value of its adjacent DC transmission line to obtain the voltage interaction factor between any two adjacent DC transmission lines. The formula that expresses the above calculation process is the first formula:

[0050] ,

[0051] in, This represents the degree of coupling of the AC output voltage of the converter transformer of the converter valve between DC transmission line i and line j in the receiving AC power grid (voltage interaction factor between DC transmission line i and line j). This represents the change in the effective value of the AC side outlet voltage of the converter transformer of the converter valve in a multi-feed system's receiving-end AC grid DC transmission line j. This represents the effective voltage value of the AC side outlet voltage of the converter valve converter transformer of DC transmission line i in the receiving AC power grid before the three-phase symmetrical reactor is put into operation, where 100 is the aforementioned first preset coefficient. Combined with... Figure 2 The AC / DC hybrid system network structure has m DC lines and a receiving-end AC power grid. The above set of grid voltage coefficients can be in the form of a lookup table with dimensions m×m, denoted as the grid voltage coefficient table. The rows and columns of the table are indexed by the labels of the DC transmission lines. The off-diagonal elements in the table represent the MIIF value between any two lines. The diagonal position values ​​in the table are 1, and the remaining values ​​reflect the voltage interaction coupling between DC feed points. The closer to 1, the stronger the coupling effect.

[0052] When obtaining the voltage interaction factor, in addition to using the aforementioned fixed preset ratio (such as reducing the bus voltage by 1%) to test the voltage interaction effect, a dynamic testing method can also be used. This method automatically adjusts the voltage drop ratio according to the current operating state of the system to more accurately reflect the degree of voltage coupling under actual operating conditions. The specific steps are as follows:

[0053] Based on sensors and measuring devices installed at the busbar connection points, the operating parameters of the power grid are monitored and collected in real time, with a focus on the short-circuit ratio. These sensors include voltage sensors and current sensors, used to comprehensively understand the operating status of the AC power grid's current and voltage.

[0054] The short-circuit ratio (SCR) at the grid connection point is calculated based on the collected voltage, current, and grid cross-sectional data to assess the grid strength at the current node. The short-circuit ratio is calculated using the following formula, where... This represents the short-circuit ratio at the m-th DC transmission line. This indicates the rated voltage at the AC bus of the converter in this line. This represents the rated DC power of the m-th transmission line. It represents the equivalent impedance of an AC system.

[0055]

[0056] If the short-circuit ratio is below a preset threshold, a grid with a short-circuit ratio (SCR) > 2.5 is generally considered a strong grid, and one with an SCR < 2.5 is considered a weak grid. If the short-circuit ratio is below the preset threshold, the test voltage drop ratio should be adjusted. For example, the test voltage drop ratio can be increased from 1% to 2% to more sensitively test the voltage interaction factor, especially in the environment of multi-infeed hybrid DC transmission systems. This ratio adjustment should be automatically executed through a preset control system to adapt to real-time changes in the grid's operating status.

[0057] After dynamically adjusting the test voltage drop, the effective value change of the output voltage at the inverter side of all DC transmission lines is measured again. Using the ratio of the dynamically adjusted test voltage drop and the newly measured voltage change, combined with the original voltage reference value, the voltage interaction factor is recalculated using a preset calculation formula. The preset calculation formula includes the voltage before the test, the voltage change after the test, and the ratio of the test voltage drop to reflect the voltage interaction effect after dynamic adjustment.

[0058] The dynamically calculated voltage interaction factor is automatically updated in the power grid voltage coefficient table to reflect the interaction effects between lines under the current operating conditions.

[0059] The next part is the active shutdown triggering section, which combines real-time data monitoring. For Figure 2 The multi-infeed hybrid DC transmission system shown is represented by HCC-HVDC, which is DC transmission line 1, and the remaining m-1 lines are LCC-HVDC. At this point, commutation failure prediction and forced commutation triggering are deployed on line 1 using pole control and valve control, respectively.

[0060] like Figure 2 As shown, the multiple DC transmission lines also include multiple non-controllable phase-commutation DC transmission lines ( Figure 2 Only four lines are shown in the diagram: the second LCC-HVDC line, the third (Voltage Source Converter High Voltage Direct Current, VSC-HVDC) line, and the fourth LCC-HVDC line. The first target effective value for the controllable commutation DC transmission line is the controllable target effective value, while the first target effective value for the non-controllable commutation DC transmission line is the non-controllable target effective value. In step S3 of this application, at least based on the set of grid voltage coefficients and the first target effective value, the effective value of the AC side outlet of the converter transformer of the controllable commutation converter valve at the second moment is determined to obtain the second target effective value, including:

[0061] Calculate the product of the uncontrollable target effective value and the corresponding voltage interaction factor for each uncontrollable commutation DC transmission line to obtain multiple second product values; sum the multiple second product values ​​to obtain a first sum value; multiply the first sum value by a second preset coefficient and add the result to the controllable target effective value to obtain the second target effective value. In the commutation failure prediction and judgment, based on the real-time monitoring value (U1(k) to U) of the converter transformer AC side outlet of the controllable commutation converter valve of the controllable commutation DC transmission line at time k... m (k) The predicted line voltage amplitude (effective voltage value) of the controllable commutator valve at time k+1 can be represented by the second formula of the above calculation process:

[0062] ,

[0063] in, The voltage interaction factor between line i and line 1 in the set of grid voltage coefficients of a multi-infeed hybrid DC transmission system is represented by the grid voltage coefficient table, where i is the column. This represents the effective voltage value at time k of the AC side outlet of the converter transformer of the HCC converter valve in the receiving AC power grid. (i=2,…,m) represents the effective voltage value of the AC side outlet of the converter transformer of the other LCC converter valves of the receiving-end AC grid in the multi-feed system at time k; The effective voltage value predicted at time k+1 is the AC side outlet of the converter transformer of the HCC converter valve in the receiving AC power grid (the range between K+1 and K is on the order of microseconds, representing the voltage fluctuation of each DC line), and 1 / 100 is the second preset coefficient mentioned above.

[0064] The derivation of the second formula above can be summarized as follows:

[0065] In the prediction and judgment of commutation failure, the real-time monitoring value of the voltage at the AC side outlet of the converter transformer of the controllable commutation converter valve of the controllable commutation DC transmission line at time k (U1(k) to U...) is used. m (k) Predict the line voltage amplitude of DC line 1 at the next moment. According to the first formula, the influence of line i on the voltage fluctuation of line j in continuous time is given by the first sub-formula:

[0066] ,

[0067] in, This indicates the degree of coupling of the AC output voltage of the converter transformer of the converter valve between DC transmission line i and line j in the receiving AC power grid (voltage interaction factor between DC transmission line i and line j). This represents the effective voltage value at the AC output terminal of the converter transformer of DC transmission line i in the receiving-end AC power grid before the three-phase symmetrical reactor is switched on. By discretizing the above continuous expression, the coupling relationship expression of the voltage fluctuation amplitude between line i and line j can be obtained, as shown in the second sub-formula below:

[0068] ,

[0069] in, (i=2,…,m) represents the effective voltage value of the AC side outlet of the converter transformer of the converter valve of line i in the multi-feed system at time k. The voltage interaction factor between line i and line j in the set of grid voltage coefficients of a multi-infeed hybrid DC transmission system is represented. This represents the effective voltage value at the AC side outlet of the converter transformer of the converter valve of line j in the multi-feed system at time k. This represents the effective voltage value at the AC side outlet of the converter transformer of the converter valve of line j in the multi-feed system at time k+1.

[0070] By combining the voltage status information of multiple DC transmission lines within the receiving-end AC power grid, a predictive calculation expression can be established as the second formula.

[0071] Step S4 above, obtaining the critical voltage set of the hybrid DC transmission system within a second preset time period, includes:

[0072] The phase offset angle of the receiving-end converter valve, the per-unit value of the commutation reactance of the converter valve, the first DC current before the commutation failure, the second DC current after the commutation failure, the turn-off angle before the commutation failure, and the critical turn-off angle are obtained for each DC transmission line. These parameters together constitute the key factors for assessing the risk of commutation failure. By monitoring and calculating these parameters in real time, commutation failure can be predicted more effectively, control strategies can be optimized, and the impact of commutation failure on system operation can be avoided or mitigated.

[0073] In high-voltage direct current (HVDC) transmission systems, the aforementioned phase offset angle refers to the change in phase of the AC voltage on the inverter side relative to normal operating conditions. During commutation failure, the phase of the AC voltage may differ from that during normal operation. This phase change affects the commutation process, especially for thyristor-based LCC-HVDC systems and LCC-HVDC systems containing IGCTs. An increase in the phase offset angle may directly lead to commutation failure or exacerbate existing commutation failures. The per-unit value of the aforementioned commutation reactance is a dimensionless parameter used to quantify the impedance characteristics of the converter valve during commutation. It refers to the ratio of the converter valve's commutation reactance to a certain reference value of the system (usually rated voltage or rated current), and is a key indicator for evaluating commutation performance. A larger per-unit value of the commutation reactance means a more difficult commutation process, as a larger commutation reactance hinders the transfer of current from one valve to another, thus increasing the risk of commutation failure. The aforementioned first DC current represents the DC current value passing through the converter valve during normal system operation and is the basis for evaluating the system state before commutation failure. The second DC current mentioned above represents the DC current value through the converter valve under the influence of a fault. The turn-off angle mentioned above is the angle after the minimum inverter-side AC voltage required for the IGCT or thyristor to turn off during commutation, after it crosses zero. The critical turn-off angle mentioned above refers to the minimum turn-off angle at which the converter valve can successfully commutate under specific conditions. Once the actual turn-off angle approaches or falls below the critical turn-off angle, the risk of commutation failure increases significantly.

[0074] The per-unit value, the cosine of the target angle, and the cosine of the critical shut-off angle of each DC transmission line are calculated to obtain multiple second summation values. The target angle is the sum of the shut-off angle and the phase offset angle before the commutation failure fault. The per-unit value of each DC transmission line is divided by the second summation value to obtain multiple first quotient values. The second DC current of each DC transmission line is divided by the first DC current to obtain multiple second quotient values. The first quotient values ​​of each DC transmission line are multiplied by the second quotient values ​​to obtain multiple third product values. The absolute value of the difference between the third product value of each DC transmission line and the third preset coefficient is calculated to obtain the first difference value. The multiple first differences are determined as the critical voltage values ​​for commutation failure at the receiving end of each DC transmission line. The multiple critical voltage values ​​constitute the critical voltage set.

[0075] The formula that can represent the above calculation process is the third formula:

[0076] ,

[0077] in, This represents the critical voltage value at which commutation failure occurs in DC transmission line i of the receiving AC power grid. This represents the per-unit value of the commutation reactance of converter valve i in a DC transmission line. This is the DC current before the commutation failure fault of the DC line (the first DC current). This is the DC current (second DC current) after the commutation failure of the DC line. Indicates the shut-off angle before a commutation failure; This indicates the critical shut-off angle for DC transmission (for LCC-HVDC, the setting is approximately 7° to 8°). 1 represents the phase offset angle; 1 is the third preset coefficient mentioned above.

[0078] The aforementioned set of critical voltages can take the form of a critical voltage table, with a dimension of m×1 and the table header displaying the DC transmission line numbers 1 to m. The determination of critical voltage values ​​is based on the quantitative analysis of key parameters, including phase offset angle, per-unit commutation reactance, DC current variation, and turn-off angle. This allows the critical voltage table to better reflect the commutation failure threshold of DC lines under specific operating conditions, providing a scientific basis for decision-making in preventing commutation failures.

[0079] The steps described above for obtaining the phase offset angle of the converter valves of each DC transmission line include:

[0080] The voltage sag values ​​of multiple DC transmission lines under asymmetrical faults are obtained. The product of the sag value of each DC transmission line and a fourth preset coefficient is calculated to obtain the fourth product value. The absolute value of the difference between the fourth product value and the fifth preset coefficient is calculated to obtain the second difference value. The sag value is divided by the second difference to obtain the third quotient value. The arctangent of the third quotient value is the phase offset angle of the converter valve of each DC transmission line. Voltage sags under asymmetrical faults may lead to phase offsets, which directly affect the commutation conditions of DC lines, requiring sag value calculation. For symmetrical faults, the sag value can be set to 0. By calculating the phase offset angle, the impact of AC voltage sags on the commutation process of DC lines can be more accurately assessed, providing necessary parameters for the construction of critical voltage meters and further optimizing the prediction accuracy of commutation failure.

[0081] The fourth formula can express the above calculation process:

[0082] ,

[0083] in, This represents the phase voltage drop during an asymmetrical fault. The fourth preset coefficient is... The fifth preset coefficient is The calculation process described above splits the numerator in the fourth formula, and the second difference is... .

[0084] The first target effective value for a controllable commutated DC transmission line is the controllable target effective value. Step S4 involves determining, based on the critical voltage set, the first target effective value, and the second target effective value, whether the controllable commutated DC transmission line will experience a commutation failure fault at the second time point, including:

[0085] The absolute value of the difference between the effective value of the controllable target and the effective value of the second target is the voltage deviation; the voltage prediction value in the first formula above is used as the voltage deviation. Compared with the current value Perform deviation calculations and compare the voltage deviation with the coefficients in the first row of the multi-feed critical voltage table.

[0086] Determine whether the voltage deviation is greater than the critical voltage value corresponding to the controllable commutated DC transmission line. If the voltage deviation is greater than the critical voltage value, it is determined that the controllable commutated DC transmission line will experience a commutation failure fault at the second moment. If the voltage deviation is less than or equal to the critical voltage value, it is determined that the controllable commutated DC transmission line will not experience a commutation failure fault at the second moment.

[0087] In the above process, a deviation value higher than the coefficient indicates that the voltage drop exceeds the critical stability value, and a commutation failure fault will occur within the predicted time. At this time, a high-level signal is sent to the valve controller to trigger the HCC active shutdown action in the next commutation process. The HCC enters the forced commutation mode in advance, causing the valve to be commutated to shut down. A deviation value lower than the coefficient indicates that the voltage drop does not exceed the critical stability value, and a commutation failure fault may not occur within the predicted time. At this time, a low-level signal is sent to the valve controller. In the next commutation process, the commutation failure prediction result does not participate in the HCC operating mode judgment. The HCC converter valve operates in natural commutation mode or mixed commutation mode. At this time, the status signal that triggers the HCC active shutdown action comes from the valve's own operating status monitoring, such as the reverse of the commutation current change rate (di / dt) and the commutation overlap angle delay.

[0088] The active shutdown method for hybrid DC transmission systems proposed in this application, based on conventional active shutdown methods, incorporates a synergistic consideration of three factors: the multi-infeed voltage coefficient table, the uncontrollable target effective value of the inverter-side AC voltage of the LCC converter valve, and the multi-infeed critical voltage table. This overcomes the limitation of traditional HCCs relying solely on local signals, suppressing voltage coupling effects and reducing the risk of transient interference across DC lines through a global coordination strategy. Specifically, it can be described as follows: Figure 4As shown, a preset active shutdown time is set, and a time delay detection is performed. If the time delay detection shows that the active shutdown has not occurred by the preset active shutdown time, a pulse signal is triggered to control the HCC to actively shut down. The commutation current change rate di / dt is detected. If di / dt ≥ 0, it indicates a commutation abnormality, and a pulse signal is triggered to control the HCC to actively shut down. Based on the multi-feed voltage coefficient table and the uncontrollable target effective value of the inverter side AC voltage of the LCC converter valve, the second target effective value of the AC voltage on the inverter side of the HCC converter valve at the next moment is predicted. The difference between the second target effective value and the uncontrollable target effective value is taken as the absolute value to obtain the voltage deviation. The voltage deviation is then compared with the voltage critical value for commutation failure in the multi-feed critical voltage table. If the voltage deviation ≥ the voltage critical value, it indicates that the voltage drop exceeds the critical stability value, and a commutation failure fault will occur within the predicted time. A pulse signal is triggered to control the HCC to actively shut down, completing the commutation. Figure 4 In this context, OR stands for OR gate.

[0089] This application can also dynamically adjust the triggering conditions of the active shutdown strategy, especially voltage deviation, based on the system's current operating efficiency, the temperature state of the converter valve, and the actual load of the power grid. This adaptive mechanism not only ensures the flexibility of the strategy and its adaptability to various operating conditions, but also improves the system's stability, security, and energy transfer efficiency. The specific solution is as follows:

[0090] Step 1: Efficiency assessment and initial threshold setting.

[0091] Based on system operating data, including power transmission efficiency and the operating status of the converter valve, an operating efficiency assessment is performed. This is done by comparing the converter valve junction temperature and power transmission loss under rated operating conditions to determine the current operating status of the converter valve. When the operating efficiency is high, the aforementioned voltage deviation is reduced, for example, to 90% of the preset deviation value, so that it can respond quickly to slight voltage changes and prevent possible commutation failures.

[0092] Step 2: Temperature monitoring and threshold adjustment of the converter valve.

[0093] The temperature of the converter valve is monitored in real time by a temperature sensor. When the temperature of the converter valve rises to a preset warning value, the voltage deviation threshold is increased, for example, to 110% of the preset deviation value, thus relaxing the shutdown conditions. This adjustment aims to prevent the converter valve from overheating due to frequent active shutdowns at high temperatures, while also reducing unnecessary energy loss.

[0094] Step 3: Feedback on actual power grid load and dynamic adjustment of thresholds.

[0095] The system collects real-time data on the actual load of the power grid and combines this data with the predicted load and the aforementioned operating efficiency to dynamically adjust the voltage deviation. When the grid load is low, the voltage deviation is lowered to increase sensitivity to voltage changes; while during peak load periods or when the predicted load increases significantly, the voltage deviation is raised to avoid unnecessary active shutdowns that could cause system instability.

[0096] This application also provides an active shutdown device for a hybrid DC transmission system. It should be noted that the active shutdown device for a hybrid DC transmission system in this application can be used to execute the active shutdown method for a hybrid DC transmission system provided in this application. This device is used to implement the above embodiments and preferred embodiments; details already described will not be repeated. As used below, the term "module" can refer to a combination of software and / or hardware that performs a predetermined function. Although the device described in the following embodiments is preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0097] The active shutdown device for the hybrid DC transmission system provided in the embodiments of this application will be described below.

[0098] Figure 5 This is a schematic diagram of an active shutdown device for a hybrid DC transmission system according to an embodiment of this application. The hybrid DC transmission system includes multiple DC transmission lines, each DC transmission line including a converter valve, and the multiple DC transmission lines include at least one controllable commutated DC transmission line, which includes a controllable commutated converter valve, such as... Figure 5As shown, the device includes: a first acquisition module 10, used to acquire the set of grid voltage coefficients of the hybrid DC transmission system within a first preset time period, wherein the set of grid voltage coefficients represents the coupling degree of the AC-side outlet voltage of the converter transformers of multiple DC transmission lines of the receiving-end AC grid, and each set of DC transmission lines has two DC transmission lines; a second acquisition module 20, used to acquire the effective value of the AC-side outlet voltage of the converter transformers of the multiple DC transmission lines of the receiving-end AC grid at a first moment, thereby obtaining a first target effective value; and a determination module 30, used to determine the converter transformer of the controllable commutation converter valve based at least on the set of grid voltage coefficients and the first target effective value. The effective value of the AC side outlet at the second moment is used to obtain the second target effective value. The second moment is after the first moment. The control module 40 is used to obtain the critical voltage set of the hybrid DC transmission system within the second preset time period. The critical voltage set includes the critical voltage values ​​of multiple DC transmission lines of the receiving end AC grid that will fail to commutate. Based on the critical voltage set, the first target effective value and the second target effective value, it is determined whether the controllable commutation DC transmission line will fail to commutate at the second moment. If it is determined that the controllable commutation DC transmission line will fail to commutate at the second moment, the controllable commutation converter valve of the controllable commutation DC transmission line is turned off.

[0099] In one optional scheme, the first acquisition module includes a first sub-acquisition module, wherein the first sub-acquisition module is used to acquire multiple voltage interaction factors, the multiple voltage interaction factors constitute a set of grid voltage coefficients, and the voltage interaction factors are used to characterize the coupling degree of the output voltage of the converter transformer on the AC side of any two adjacent DC transmission lines of the receiving-end AC grid.

[0100] In one optional scheme, the first sub-acquisition module includes a first sub-acquisition unit, a first sub-control unit, and a first sub-determination unit. The first sub-acquisition module acquires the effective values ​​of the output voltages at the AC side of the converter transformers of the converter valves in multiple DC transmission lines of the receiving-end AC power grid, obtaining multiple first effective voltage values. The first sub-control unit controls the voltage drop at the busbars of the multiple DC transmission lines by a preset ratio and acquires multiple effective value changes in the output voltages at the AC side of the converter transformers of the converter valves in the multiple DC transmission lines corresponding to the preset ratio. The first sub-determination unit multiplies the effective value changes of each DC transmission line by a first preset coefficient to obtain multiple first product values, and divides the first product value of each DC transmission line by the first effective voltage value of its adjacent DC transmission line to obtain the voltage interaction factor between any two adjacent DC transmission lines.

[0101] In one optional scheme, multiple DC transmission lines include multiple uncontrolled commutated DC transmission lines, and the multiple DC transmission lines further include multiple uncontrolled commutated DC transmission lines. The first target effective value corresponding to the controllable commutated DC transmission line is the controllable target effective value, and the first target effective value corresponding to the uncontrolled commutated DC transmission line is the uncontrollable target effective value. The determination module includes a first sub-calculation module and a second sub-determination module. The first sub-calculation module is used to calculate the product of the uncontrollable target effective value of each uncontrolled commutated DC transmission line and the corresponding voltage interaction factor to obtain multiple second product values. The second sub-determination module is used to sum the multiple second product values ​​to obtain a first sum value, and add the result of multiplying the first sum value by a second preset coefficient to the controllable target effective value to obtain the second target effective value.

[0102] In one optional scheme, the control module includes a second sub-acquisition module, a second sub-calculation module, a third sub-determination module, and a third sub-calculation module. The second sub-acquisition module acquires the phase offset angle of the receiving-end converter valve, the per-unit value of the commutation reactance of the converter valve, the first DC current before the commutation failure fault, the second DC current after the commutation failure fault, the turn-off angle before the commutation failure fault, and the critical turn-off angle for each DC transmission line. The second sub-calculation module calculates the sum of the per-unit value, the cosine value of the target angle, and the cosine value of the critical turn-off angle for each DC transmission line, obtaining multiple second summations. The target angle is the sum of the turn-off angle and the phase offset angle before the commutation failure fault. The third sub-determination module divides the per-unit value of each DC transmission line by the second summation value to obtain multiple first quotients, divides the second DC current of each DC transmission line by the first DC current to obtain multiple second quotients, and multiplies the first quotients of each DC transmission line by the second quotients to obtain multiple third product values. The third sub-calculation module is used to calculate the absolute value of the difference between the third product value and the third preset coefficient of each DC transmission line to obtain the first difference value. Multiple first differences are determined as the critical voltage value at the receiving end of each DC transmission line when commutation failure occurs. Multiple critical voltage values ​​constitute a critical voltage set.

[0103] In one optional scheme, the second sub-acquisition module includes a first sub-acquisition unit and a first sub-determination unit. The first sub-acquisition unit is used to acquire the voltage drop values ​​of multiple DC transmission lines during asymmetrical faults. The first sub-determination unit is used to calculate the product of the voltage drop value of each DC transmission line and a fourth preset coefficient to obtain a fourth product value. The absolute value of the difference between the fourth product value and a fifth preset coefficient is calculated to obtain a second difference value. The voltage drop value is divided by the second difference value to obtain a third quotient value. The arctangent value of the third quotient value is the phase offset angle of the converter valve of each DC transmission line.

[0104] In one optional scheme, the first target effective value corresponding to the controllable commutated DC transmission line is the controllable target effective value. The control module includes a fourth sub-calculation module and a fourth sub-determination module. The fourth sub-calculation module is used to calculate the absolute value of the difference between the controllable target effective value and the second target effective value as the voltage deviation. The fourth sub-determination module is used to determine whether the voltage deviation is greater than the critical voltage value corresponding to the controllable commutated DC transmission line. If the voltage deviation is greater than the critical voltage value, it is determined that the controllable commutated DC transmission line will experience a commutation failure fault at the second moment. If the voltage deviation is less than or equal to the critical voltage value, it is determined that the controllable commutated DC transmission line will not experience a commutation failure fault at the second moment.

[0105] The active shutdown device of the hybrid DC transmission system includes a processor and a memory. The aforementioned first acquisition module and others are all stored as program units in the memory, and the processor executes the program units stored in the memory to achieve the corresponding functions. All of the above modules are located in the same processor; alternatively, the above modules may be located in different processors in any combination.

[0106] The processor contains a kernel, which retrieves the corresponding program unit from memory. One or more kernels can be configured, and adjusting kernel parameters can address the technical problem of control strategies in hybrid DC transmission systems being unable to withstand commutation failures.

[0107] The memory may include non-permanent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM, and the memory includes at least one memory chip.

[0108] This application provides a hybrid DC transmission system, including: multiple DC transmission lines, each DC transmission line including a converter valve, the multiple DC transmission lines including at least one controllable phase-commutated DC transmission line, the converter valve of the controllable phase-commutated DC transmission line being a controllable phase-commutated converter valve; and a controller, communicatively connected to the converter valves, for executing an active shutdown method of the hybrid DC transmission system to control the multiple converter valves.

[0109] This application provides a computer-readable storage medium including a stored program, wherein the program controls the device where the computer-readable storage medium is located to execute an active shutdown method for a hybrid DC transmission system when it is running.

[0110] Specifically, the active shutdown methods for hybrid DC transmission systems include:

[0111] Step S1: Obtain the set of grid voltage coefficients of the hybrid DC transmission system within a first preset time period. The set of grid voltage coefficients represents the coupling degree of the AC side outlet voltage of the converter transformer of the converter valve of multiple DC transmission lines of the receiving AC grid. Each set of DC transmission lines has two DC transmission lines.

[0112] Step S2: Obtain the effective value of the AC side outlet of the converter transformer of the converter valve of multiple DC transmission lines of the receiving AC power grid at the first moment, and obtain the first target effective value.

[0113] Step S3: Determine the effective value of the AC side outlet of the converter transformer of the controllable commutation valve at the second moment, based at least on the set of grid voltage coefficients and the first target effective value, and obtain the second target effective value. The second moment is after the first moment.

[0114] Step S4: Obtain the critical voltage set of the hybrid DC transmission system within a second preset time period. The critical voltage set includes the critical voltage values ​​of multiple DC transmission lines of the receiving-end AC grid that will experience commutation failure. Based on the critical voltage set, the first target effective value, and the second target effective value, determine whether the controllable commutation DC transmission line will experience a commutation failure fault at the second time. If it is determined that the controllable commutation DC transmission line will experience a commutation failure fault at the second time, control the controllable commutation converter valve of the controllable commutation DC transmission line to shut off.

[0115] This application provides a processor for running a program, wherein the program executes an active shutdown method for a hybrid DC transmission system.

[0116] Specifically, the active shutdown methods for hybrid DC transmission systems include:

[0117] Step S1: Obtain the set of grid voltage coefficients of the hybrid DC transmission system within a first preset time period. The set of grid voltage coefficients represents the coupling degree of the AC side outlet voltage of the converter transformer of the converter valve of multiple DC transmission lines of the receiving AC grid. Each set of DC transmission lines has two DC transmission lines.

[0118] Step S2: Obtain the effective value of the AC side outlet of the converter transformer of the converter valve of multiple DC transmission lines of the receiving AC power grid at the first moment, and obtain the first target effective value.

[0119] Step S3: Determine the effective value of the AC side outlet of the converter transformer of the controllable commutation valve at the second moment, based at least on the set of grid voltage coefficients and the first target effective value, and obtain the second target effective value. The second moment is after the first moment.

[0120] Step S4: Obtain the critical voltage set of the hybrid DC transmission system within a second preset time period. The critical voltage set includes the critical voltage values ​​of multiple DC transmission lines of the receiving-end AC grid that will experience commutation failure. Based on the critical voltage set, the first target effective value, and the second target effective value, determine whether the controllable commutation DC transmission line will experience a commutation failure fault at the second time. If it is determined that the controllable commutation DC transmission line will experience a commutation failure fault at the second time, control the controllable commutation converter valve of the controllable commutation DC transmission line to shut off.

[0121] This application provides an apparatus, including a processor, a memory, and a program stored in the memory and executable on the processor. When the processor executes the program, it performs at least the following steps: obtaining a set of grid voltage coefficients for a hybrid DC transmission system within a first preset time period, where the set of grid voltage coefficients represents the coupling degree of the AC-side outlet voltage of the converter transformers of multiple DC transmission lines in the receiving-end AC grid, each set of DC transmission lines having two DC transmission lines; obtaining the effective values ​​of the AC-side outlet voltages of the converter transformers of the multiple DC transmission lines in the receiving-end AC grid at a first moment, thus obtaining a first target effective value; and performing at least the following steps based on the set of grid voltage coefficients and the first target effective value. The effective value of the AC side outlet of the converter transformer of the controllable commutation converter valve is determined at a second moment, thus obtaining a second target effective value. The second moment is after the first moment. The critical voltage set of the hybrid DC transmission system within a second preset time period is obtained. This critical voltage set includes the critical voltage values ​​of multiple DC transmission lines in the receiving-end AC grid that would lead to commutation failure. Based on the critical voltage set, the first target effective value, and the second target effective value, it is determined whether the controllable commutation DC transmission line will experience a commutation failure at the second moment. If it is determined that the controllable commutation DC transmission line will experience a commutation failure at the second moment, the controllable commutation converter valve of the controllable commutation DC transmission line is shut off. The devices mentioned in this article can be servers, PCs, tablets, mobile phones, etc.

[0122] This application also provides a computer program product, which, when executed on a data processing device, is suitable for executing an initialization program having at least the following method steps: obtaining a set of grid voltage coefficients for a hybrid DC transmission system within a first preset time period, wherein the set of grid voltage coefficients represents the coupling degree of the AC-side outlet voltage of the converter transformers of multiple DC transmission lines in the receiving-end AC grid, each set of DC transmission lines having two DC transmission lines; obtaining the effective value of the AC-side outlet voltage of the converter transformers of the multiple DC transmission lines in the receiving-end AC grid at a first moment, obtaining a first target effective value; and determining a controllable... The effective value of the AC side outlet of the converter transformer of the commutation valve at the second moment is used to obtain the second target effective value. The second moment is after the first moment. The set of critical voltages of the hybrid DC transmission system within the second preset time period is obtained. The set of critical voltages includes the critical voltage values ​​of multiple DC transmission lines of the receiving-end AC grid that will fail to commutate. Based on the set of critical voltages, the first target effective value and the second target effective value, it is determined whether the controllable commutation DC transmission line will fail to commutate at the second moment. If it is determined that the controllable commutation DC transmission line will fail to commutate at the second moment, the controllable commutation converter valve of the controllable commutation DC transmission line is controlled to close.

[0123] Obviously, those skilled in the art should understand that the modules or steps of this application described above can be implemented using general-purpose computing devices. They can be centralized on a single computing device or distributed across a network of multiple computing devices. They can be implemented using computer-executable program code, and thus can be stored in a storage device for execution by a computing device. In some cases, the steps shown or described can be performed in a different order than those presented here, or they can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. Thus, this application is not limited to any particular combination of hardware and software.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0129] Memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, like read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0130] Computer-readable media include both permanent and non-permanent, removable and non-removable media that can store information by any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0131] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0132] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0133] As can be seen from the above description, the embodiments of this application achieve the following technical effects:

[0134] 1) The active shutdown method for the hybrid DC transmission system of this application firstly predicts the voltage drop (voltage coupling) in the controllable commutation DC transmission line caused by multi-source DC disturbances by obtaining the set of grid voltage coefficients of the hybrid DC transmission system within a first preset time period. At least based on the first target effective value of the AC side outlet of the converter transformer of the converter valve of multiple DC transmission lines in the receiving-end AC grid at the first moment and the set of grid voltage coefficients, the AC side outlet of the converter transformer of the controllable commutation converter valve at the second moment after the first moment can be determined. The second target effective value is then matched with the critical voltage set to determine whether the controllable commutation converter valve will fail to shut off properly at the second moment, thus causing commutation failure. If it is determined that the controllable commutation DC transmission line will experience commutation failure at the second moment, the controllable commutation converter valve of the controllable commutation DC transmission line is controlled to shut off, forcing the valve to be commutated to shut off in advance, thus completing active commutation. This achieves the protection against commutation failure of HCC converter valve in multi-infeed DC systems and solves the technical problem that the control strategy of hybrid DC transmission systems in related technologies is difficult to resist commutation failure.

[0135] 2) The active shutdown method for hybrid DC transmission systems in this application actively adjusts the shutdown timing of the IGCT by predicting grid voltage dips and the likelihood of commutation failures in real time. This avoids cascading commutation failures caused by grid voltage fluctuations or faults in nearby DC transmission lines, significantly improving system stability under weak grid conditions. Furthermore, it considers the voltage interaction effects between multiple DC transmission lines, overcoming the limitation of traditional HCCs relying solely on local signals. A global coordination strategy suppresses voltage coupling effects and reduces the risk of transient interference across DC lines.

[0136] 3) The active shutdown method for hybrid DC transmission systems in this application actively prevents commutation failure, reduces DC power transmission interruptions, ensures the continuous and stable operation of multi-infeed systems with a high proportion of new energy penetration, and avoids renewable energy curtailment caused by cascading failures. By integrating real-time parameter assessment of the receiving-end AC grid with dynamic threshold adjustment of the shutdown angle, it achieves advanced judgment of commutation failure risks, avoiding capacity waste caused by traditional fixed margin conservative control.

[0137] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An active shutdown method for a hybrid DC transmission system, the hybrid DC transmission system comprising multiple DC transmission lines, each DC transmission line comprising a converter valve, the multiple DC transmission lines including at least one controllable commutation DC transmission line, wherein the converter valve of the controllable commutation DC transmission line is a controllable commutation converter valve, characterized in that, include: Obtain the set of grid voltage coefficients of the hybrid DC transmission system within a first preset time period. The set of grid voltage coefficients represents the coupling degree of the AC side outlet voltage of the converter transformer of the converter valve of the multiple DC transmission lines of the receiving AC grid. Each set of DC transmission lines has two DC transmission lines. The effective value of the AC side outlet of the converter transformer of the converter valve of the multiple DC transmission lines of the receiving-end AC power grid at the first moment is obtained to obtain the first target effective value; Based at least on the set of grid voltage coefficients and the first target effective value, the effective value of the AC side outlet of the converter transformer of the controllable commutation valve at the second moment is determined, and the second target effective value is obtained. The second moment is after the first moment. Obtain the critical voltage set of the hybrid DC transmission system within a second preset time period. The critical voltage set includes the critical voltage values ​​of multiple DC transmission lines of the receiving-end AC grid that would cause commutation failure. Based on the critical voltage set, the first target effective value, and the second target effective value, determine whether the controllable commutation DC transmission line will experience a commutation failure at the second time. If it is determined that the controllable commutation DC transmission line will experience a commutation failure at the second time, control the controllable commutation converter valve of the controllable commutation DC transmission line to shut off.

2. The active shutdown method according to claim 1, characterized in that, The step of obtaining the set of grid voltage coefficients of the hybrid DC transmission system within the first preset time period includes: Multiple voltage interaction factors are obtained, and the multiple voltage interaction factors constitute the set of grid voltage coefficients. The voltage interaction factors are used to characterize the degree of coupling of the output voltage of the converter transformer on the AC side of any two adjacent DC transmission lines of the receiving-end AC grid.

3. The active shutdown method according to claim 2, characterized in that, The acquisition of multiple voltage interaction factors includes: The effective value of the output voltage of the converter transformer on the AC side of the converter valve in the multiple DC transmission lines of the receiving AC power grid is obtained to obtain multiple first effective voltage values; The voltage drop at the busbars of multiple DC transmission lines is controlled by a preset ratio, and multiple effective value changes of the output voltage of the AC side of the converter transformer of the converter valve in the multiple DC transmission lines corresponding to the preset ratio are obtained. The effective value change of each DC transmission line is multiplied by a first preset coefficient to obtain multiple first product values. The first product value of each DC transmission line is divided by the first effective voltage value of the adjacent DC transmission line to obtain the voltage interaction factor of any two adjacent DC transmission lines.

4. The active shutdown method according to claim 2, characterized in that, The multiple DC transmission lines also include multiple uncontrollable phase-commutated DC transmission lines. The first target effective value corresponding to the controllable phase-commutated DC transmission line is a controllable target effective value, and the first target effective value corresponding to the uncontrollable phase-commutated DC transmission line is an uncontrollable target effective value. The step of determining the effective value of the AC side outlet of the converter transformer of the controllable phase-commutated converter valve at a second moment, based at least on the set of grid voltage coefficients and the first target effective value, to obtain the second target effective value, includes: Calculate the product of the uncontrollable target effective value and the corresponding voltage interaction factor for each of the uncontrollable commutated DC transmission lines to obtain multiple second product values; The multiple second product values ​​are summed to obtain a first sum value. The result of multiplying the first sum value by a second preset coefficient is added to the controllable target effective value to obtain the second target effective value.

5. The active shutdown method according to claim 1, characterized in that, The step of obtaining the set of critical voltages of the hybrid DC transmission system within the second preset time period includes: The phase offset angle of the converter valve of each DC transmission line, the per-unit value of the commutation reactance of the converter valve, the first DC current before the commutation failure fault, the second DC current after the commutation failure fault, the turn-off angle and the critical turn-off angle before the commutation failure fault are obtained. The sum of the per-unit value, the cosine value of the target angle, and the cosine value of the critical shut-off angle for each DC transmission line is calculated to obtain multiple second sum values. The target angle is the sum of the shut-off angle before the commutation failure fault and the phase offset angle. Divide the per-unit value of each DC transmission line by the second summation value to obtain a plurality of first quotient values; divide the second DC current of each DC transmission line by the first DC current to obtain a plurality of second quotient values; and multiply the first quotient values ​​of each DC transmission line by the second quotient values ​​to obtain a plurality of third product values. The absolute value of the difference between the third product value and the third preset coefficient of each DC transmission line is calculated to obtain a plurality of first differences. Each first difference is a critical voltage value for commutation failure of each DC transmission line. The plurality of critical voltage values ​​constitute the critical voltage set.

6. The active shutdown method according to claim 5, characterized in that, The step of obtaining the phase offset angle of the converter valve of each of the DC transmission lines includes: Obtain the phase voltage drop values ​​of multiple DC transmission lines under asymmetrical fault conditions; Calculate the product of the drop value of each DC transmission line and the fourth preset coefficient to obtain the fourth product value. Calculate the absolute value of the difference between the fourth product value and the fifth preset coefficient to obtain the second difference value. Divide the drop value by the second difference value to obtain the third quotient value. The arctangent value of the third quotient value is the phase offset angle of the converter valve of each DC transmission line.

7. The active shutdown method according to claim 1, characterized in that, The first target effective value corresponding to the controllable commutation DC transmission line is a controllable target effective value. The step of determining whether the controllable commutation DC transmission line will experience a commutation failure fault at the second moment, based on the critical voltage set, the first target effective value, and the second target effective value, includes: The absolute value of the difference between the effective value of the controllable target and the effective value of the second target is the voltage deviation. If the voltage deviation is greater than the critical voltage value corresponding to the controllable commutation DC transmission line, and if the voltage deviation is greater than the critical voltage value, it is determined that the controllable commutation DC transmission line will experience a commutation failure fault at the second moment. If the voltage deviation is less than or equal to the critical voltage value, it is determined that the controllable commutation DC transmission line will not experience a commutation failure fault at the second moment.

8. An active shutdown device for a hybrid DC transmission system, the hybrid DC transmission system comprising multiple DC transmission lines, each DC transmission line comprising a converter valve, the multiple DC transmission lines including at least one controllable commutation DC transmission line, wherein the converter valve of the controllable commutation DC transmission line is a controllable commutation converter valve, characterized in that, The active shutdown device includes: The first acquisition module is used to acquire the set of grid voltage coefficients of the hybrid DC transmission system within a first preset time period. The set of grid voltage coefficients represents the coupling degree of the AC side outlet voltage of the converter transformer of the converter valve of the multiple DC transmission lines of the receiving AC grid. Each set of DC transmission lines has two DC transmission lines. The second acquisition module is used to acquire the effective value of the AC side outlet of the converter transformer of the converter valve of the multiple DC transmission lines of the receiving-end AC power grid at the first moment, and obtain the first target effective value. The determining module is used to determine the effective value of the AC side outlet of the converter transformer of the controllable commutation valve at a second time moment, based at least on the set of grid voltage coefficients and the first target effective value, so as to obtain the second target effective value, wherein the second time moment is after the first time moment; The control module is used to acquire the critical voltage set of the hybrid DC transmission system within a second preset time period. The critical voltage set includes the critical voltage values ​​of multiple DC transmission lines of the receiving-end AC grid that would cause commutation failure. Based on the critical voltage set, the first target effective value, and the second target effective value, the module determines whether the controllable commutation DC transmission line will experience a commutation failure at the second time. If it is determined that the controllable commutation DC transmission line will experience a commutation failure at the second time, the module controls the controllable commutation converter valve of the controllable commutation DC transmission line to shut off.

9. A hybrid DC transmission system, characterized in that, include: Multiple DC transmission lines, each of the DC transmission lines includes a converter valve, and the multiple DC transmission lines include at least one controllable phase-commutated DC transmission line, wherein the converter valve of the controllable phase-commutated DC transmission line is a controllable phase-commutated converter valve; A controller, communicatively connected to the converter valves, is used to execute the active shutdown method of the hybrid DC transmission system according to any one of claims 1 to 7 to control the plurality of converter valves.

10. An electronic device, characterized in that, include: One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs including an active shutdown method for performing a hybrid DC transmission system according to any one of claims 1 to 7.

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