Receiving-end alternating-current fault ride-through method and apparatus for power transmission system, and device and storage medium

Abstract

A receiving-end alternating-current fault ride-through method and apparatus for a power transmission system, and a device and a storage medium. The method comprises: when a fault occurs in a receiving-end power grid (50), acquiring a fault category of the receiving-end power grid (201); if the fault category indicates that a first fault has occurred, reducing to a target voltage a first direct-current voltage output by a receiving-end converter station (40) to a direct-current line (30) (202); and when a second direct-current voltage output by a transmitting-end converter station (20) to the direct-current line is less than a first preset voltage, reducing, from an initial current to a target current, a direct current output by the transmitting-end converter station to the direct-current line, so that a direct-current power transmission system realizes fault ride-through (203). By means of the method, system overvoltage can be prevented, and the transmitting-end converter station senses, in a timely manner, the first fault that has occurred in the receiving-end power grid, and adjusts the current on a direct-current side in a timely manner, thereby preventing further deterioration of the fault; and the whole process does not rely on inter-station communication, and thus there is no impact of a long delay caused by a long-distance direct-current line, so that the safety stability is relatively high, and a fault ride-through requirement can be well met.

Description

AC fault ride-through method, device, equipment and storage medium for receiving end of power transmission system Technical Field

[0001] The present application relates to the field of direct current (DC) transmission technology, and in particular to a method, apparatus, device, and storage medium for riding through an AC fault at a receiving end of a transmission system. Background Art

[0002] A DC transmission system primarily consists of a sequentially connected sending grid, a sending converter station, a DC line, a receiving converter station, and a receiving grid. During long-distance DC transmission through this system, if a severe AC fault occurs in the receiving grid, the long-distance DC line creates a communication delay between stations, making it difficult for the sending converter station to receive fault information before the DC system overvoltages. Consequently, the sending converter station continues to inject power into the DC transmission system, causing the DC system voltage to exceed safety limits in a short period of time. This can cause the receiving converter station to overvoltage and shut down, halting power transmission.

[0003] To ensure reliable ride-through of AC faults at the receiving end of long-distance DC transmission systems, a common approach is to deploy DC energy dissipation devices during the fault period to dissipate excess energy on the DC line. However, this increases system cost and complexity. Another common approach is for the receiving converter station to transmit fault information to the sending converter station via high-latency inter-station communication after a fault occurs. This allows the sending converter station to take appropriate power reduction measures after receiving the fault information.

[0004] However, due to the high delay in inter-station communication caused by long-distance DC lines, the DC system is very likely to have tripped due to overvoltage at this time, and cannot meet the normal fault ride-through requirements, which is not conducive to the safe and stable operation of the system.

[0005] Summary of the Invention

[0006] Purpose of the invention: An embodiment of the present application provides a method for riding through an AC fault at the receiving end of a power transmission system, aiming to overcome the technical problem that the prior art relies on inter-station communication and cannot meet the fault riding requirements; another purpose of an embodiment of the present application is to provide an AC fault riding device at the receiving end of a power transmission system; the third purpose of the present application is to provide an electronic device; the fourth purpose of the present application is to provide a computer-readable storage medium.

[0007] Technical Solution: A method for riding through an AC fault at the receiving end of a power transmission system, as described in an embodiment of the present application, is applied to a DC transmission system. The DC transmission system includes a sending-end converter station, a DC line, a receiving-end converter station, and a receiving-end power grid connected in sequence. The method includes:

[0008] When a fault occurs in the receiving-end power grid, obtaining a fault type of the receiving-end power grid;

[0009] If the fault type indicates that a first fault has occurred, reducing the first DC voltage output by the receiving-end converter station to the DC line to a target voltage;

[0010] When the second DC voltage output by the sending-end converter station to the DC line is less than the first preset voltage, the DC current output by the sending-end converter station to the DC line is reduced from an initial current to a target current, so that the DC power transmission system can achieve fault ride-through.

[0011] In some embodiments, the method further comprises:

[0012] When the fault of the receiving-end power grid is eliminated, restoring the first DC voltage from the target voltage to a rated DC voltage;

[0013] In a case where the second DC voltage is greater than a second preset voltage, the DC current is restored from the target current to the initial current, and the second preset voltage is greater than the first preset voltage.

[0014] In some embodiments, after the step of reducing the DC current output by the sending-end converter station to the DC line from an initial current to a target current, the method further includes:

[0015] Obtaining a three-phase AC voltage output by the receiving-end converter station to the receiving-end power grid;

[0016] obtaining a three-phase positive sequence voltage and a three-phase negative sequence voltage based on the three-phase AC voltage;

[0017] When the three-phase positive sequence voltage is equal to the rated AC voltage and the three-phase negative sequence voltage is equal to zero, it is determined that the fault of the receiving-end power grid is eliminated.

[0018] In some embodiments, restoring the first DC voltage from the target voltage to a rated DC voltage includes:

[0019] The first DC voltage is restored from the target voltage to the rated DC voltage according to a first preset rate v1, wherein the value of the first preset rate v1 is equal to the product of the first adjustment coefficient θ1 and the rated DC voltage, and satisfies: 0.04≤θ1≤0.06.

[0020] In some embodiments, restoring the DC current from the target current to the initial current includes:

[0021] The DC current is restored from the target current to the initial current according to a second preset rate v2, wherein the value of the second preset rate v2 is equal to the product of the second adjustment coefficient θ2 and the rated DC current, and satisfies: 0.01≤θ2≤0.03.

[0022] In some embodiments, the method further comprises:

[0023] If the fault category indicates a second fault, then when the second DC voltage exceeds a third preset voltage, the DC current is adjusted so that the DC power transmission system achieves fault ride-through, and the fault severity of the first fault is higher than the fault severity of the second fault.

[0024] In some embodiments, when the second DC voltage exceeds a third preset voltage, adjusting the DC current includes:

[0025] If the second DC voltage exceeds the third preset voltage and is less than or equal to a fourth preset voltage, adjusting the DC current based on a change in the second DC voltage, wherein the change in the DC current is opposite to the change in the second DC voltage;

[0026] If the second DC voltage exceeds the fourth preset voltage, the DC current is reduced to the target current.

[0027] In some embodiments, the method further comprises:

[0028] When the second DC voltage is less than or equal to the third preset voltage, the DC current is maintained unchanged.

[0029] In some embodiments, obtaining the fault type of the receiving-end power grid includes:

[0030] Obtaining a three-phase AC voltage output by the receiving-end converter station to the receiving-end power grid;

[0031] obtaining a three-phase positive sequence voltage and a three-phase negative sequence voltage based on the three-phase AC voltage;

[0032] When the three-phase positive sequence voltage is less than a fifth preset voltage and the three-phase negative sequence voltage is less than a sixth preset voltage, it is determined that the fault type of the receiving-end power grid is the first fault.

[0033] In some embodiments, reducing the first DC voltage output by the receiving-end converter station to the DC line to a target voltage includes:

[0034] The first DC voltage is reduced to the target voltage according to a third preset rate v3, wherein the value of the third preset rate v3 is equal to the product of the third adjustment coefficient θ3 and the rated DC voltage, and satisfies: 0.5≤θ3≤0.7.

[0035] In some embodiments, the target voltage and the target current are both zero.

[0036] Accordingly, an AC fault ride-through device at a receiving end of a power transmission system according to an embodiment of the present application is applied to a DC power transmission system, wherein the DC power transmission system includes a sending-end converter station, a DC line, a receiving-end converter station, and a receiving-end power grid connected in sequence. The device includes:

[0037] a fault type determination module, configured to obtain the fault type of the receiving-end power grid when a fault occurs in the receiving-end power grid;

[0038] a voltage regulating module, configured to reduce the first DC voltage output by the receiving-end converter station to the DC line to a target voltage if the fault type indicates the occurrence of a first fault;

[0039] The first current regulating module is configured to reduce the DC current output by the sending-end converter station to the DC line from an initial current to a target current when the second DC voltage output by the sending-end converter station to the DC line is less than a first preset voltage, so as to enable the DC transmission system to achieve fault ride-through.

[0040] Accordingly, an electronic device described in an embodiment of the present application includes a memory, a processor, and a computer program stored on the memory and runnable on the processor. When the processor executes the computer program, the steps of the AC fault crossing method at the receiving end of the power transmission system as described above are implemented.

[0041] Accordingly, a computer-readable storage medium described in an embodiment of the present application stores a computer program thereon, and when the computer program is executed by a processor, the steps of the above-mentioned method for riding through an AC fault at the receiving end of a power transmission system are implemented.

[0042] Beneficial effect: Compared with the prior art, the transmission system receiving-end AC fault ride-through method, apparatus, equipment and storage medium of the embodiments of the present application, the transmission system receiving-end AC fault ride-through method includes obtaining the fault type of the receiving-end power grid when a fault occurs in the receiving-end power grid, and if the fault type indicates a first fault, reducing the first DC voltage output by the receiving-end converter station to the DC line to a target voltage, and when the second DC voltage output by the sending-end converter station to the DC line is less than a first preset voltage, reducing the DC current output by the sending-end converter station to the DC line from the initial current to the target current, so that the DC transmission system can achieve fault ride-through. The receiving-end AC fault ride-through method of the transmission system forcibly reduces the first DC voltage on the DC side of the receiving-end converter station to a target voltage when a first fault occurs, thereby preventing overvoltage in the DC transmission system. Since the second DC voltage on the DC side of the sending-end converter station will decrease along with the first DC voltage, the sending-end converter station can promptly sense the first fault in the receiving-end power grid and adjust the DC side current in a timely manner to avoid further deterioration of the fault. The entire process does not rely on inter-station communication, and thus does not suffer from the high latency impact of long-distance DC lines. Power can be adjusted in a timely manner for receiving-end AC faults, and the method has high safety and stability, can better meet fault ride-through requirements, and has high engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0044] FIG1 is a schematic structural diagram of a DC power transmission system according to an embodiment of the present application;

[0045] FIG2 is a schematic diagram of the overall process of the AC fault ride-through method at the receiving end of the power transmission system according to an embodiment of the present application;

[0046] 3 is a schematic structural diagram of an AC fault ride-through device at a receiving end of a power transmission system according to an embodiment of the present application;

[0047] FIG4 is a schematic structural diagram of an electronic device according to an embodiment of the present application.

[0048] Reference numerals: 10 - sending-end power grid; 20 - sending-end converter station; 30 - DC line; 40 - receiving-end converter station; 50 - receiving-end power grid; 301 - fault type determination module; 302 - voltage regulation module; 303 - first current regulation module; 304 - second current regulation module. DETAILED DESCRIPTION

[0049] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0050] It should be understood that although the terms first, second, etc. may be used herein to describe various components, these components should not be limited by these terms. These terms are used to distinguish one component from another. Thus, the first component discussed below could be referred to as the second component without departing from the teachings of the present invention. As used herein, the term "and / or" includes any one and all combinations of one or more of the associated listed items.

[0051] Those skilled in the art will appreciate that the drawings are merely schematic diagrams of exemplary embodiments and may not be to scale. The modules or processes in the drawings are not necessarily required to implement the present application and therefore cannot be used to limit the scope of protection of the present application.

[0052] Please refer to Figure 1, which illustrates the structure of a DC transmission system according to an embodiment of the present application. The DC transmission system according to an embodiment of the present application includes a sending-end power grid 10, a sending-end converter station 20, a DC line 30, a receiving-end converter station 40, and a receiving-end power grid 50, which are connected in sequence. The sending-end power grid 10 may include power generation facilities such as fossil energy power stations and new energy power stations. The AC power generated by the power generation facilities is rectified by the sending-end converter station 20 and converted into DC power. The DC power is then transmitted to the receiving-end converter station 40 via the DC line 30 between the sending-end converter station 20 and the receiving-end converter station 40. The receiving-end converter station 40 inverts the received DC power into AC power and transmits it to the receiving-end power grid 50. In some examples, the sending-end converter station 20 can be a thyristor-based LCC (Line Commutated Converter) valve or a thyristor-based MMC (Modular Multilevel Converter) valve. The number of valves per pole can be one or multiple valve groups connected in series. The receiving-end converter station 40 can be a thyristor-based LCC valve or a thyristor-based MMC valve. The number of valves per pole can be one or multiple valve groups connected in series.

[0053] During long-distance DC power transmission via a DC transmission system, when a severe AC fault occurs in the receiving-end power grid 50, the long-distance DC line 30 generates high-latency inter-station communication delays, making it difficult for the sending-end converter station 20 to obtain fault information from the receiving-end converter station 40 before the DC transmission system overvoltages. Consequently, the sending-end converter station 20 continues to inject power into the DC transmission system, causing the DC transmission system voltage to exceed safety limits in a short period of time. This causes the receiving-end converter station 40 to overvoltage-lock and halt power transmission. To ensure reliable transmission of AC faults at the receiving end of a long-distance DC transmission system, a common approach is to activate DC energy dissipation devices during the fault period to consume excess energy on the DC line 30. However, this increases system cost and complexity. Another common approach is for the receiving-end converter station 40 to transmit fault information to the sending-end converter station 20 via high-latency inter-station communication after a fault occurs, so that the sending-end converter station 20 can take appropriate power reduction measures after receiving the fault information. However, due to the high delay of the long-distance DC line 30, the DC system is highly likely to have tripped due to overvoltage at this time, and cannot meet the normal fault ride-through requirements, which is not conducive to the safe and stable operation of the system.

[0054] In view of this, an embodiment of the present application provides a method for riding through an AC fault at the receiving end of a power transmission system, which is applied to a DC power transmission system. When a serious fault occurs in the receiving-end power grid, the DC side voltage of the receiving-end converter station 40 is forced to be reduced, so that the DC side voltage of the sending-end converter station 20 is reduced accordingly, so that the sending-end converter station 20 can sense the fault in time and perform corresponding power adjustment, thereby solving at least part of the above-mentioned technical problems.

[0055] Please refer to FIG2 , which illustrates the overall process of the AC fault ride-through method at the receiving end of the power transmission system according to an embodiment of the present application. The AC fault ride-through method at the receiving end of the power transmission system includes the following steps:

[0056] Step 201: When a fault occurs in the receiving-end power grid 50 , obtain the fault type of the receiving-end power grid 50 .

[0057] A fault in the receiving-end grid 50 typically indicates a receiving-end AC fault. This fault can be a metallic or non-metallic single-phase ground fault, a two-phase short circuit fault, a two-phase short-circuit ground fault, or a three-phase short circuit fault. After a receiving-end AC fault occurs, the power delivered by the receiving-end converter station 40 to the receiving-end grid 50 is limited. If the sending-end converter station 20 continues to inject power into the DC transmission system, this will result in excess power on the DC side. The more severe the receiving-end fault, the faster it develops, the greater the excess power on the DC side, and the more likely it is to cause an overvoltage trip.

[0058] In some embodiments, the fault type of the receiving-end power grid 50 may be obtained by the following steps:

[0059] Step 1: Obtain the three-phase AC voltage output by the receiving-end converter station 40 to the receiving-end power grid 50.

[0060] Step 2: Obtain three-phase positive sequence voltage and three-phase negative sequence voltage based on the three-phase AC voltage.

[0061] Step three: when the three-phase positive sequence voltage is less than the fifth preset voltage and the three-phase negative sequence voltage is less than the sixth preset voltage, determine that the fault type of the receiving-end power grid 50 is the first fault.

[0062] Among them, the first fault is used to characterize a serious fault with a high fault severity. In practice, the three-phase metal short circuit fault is the most serious and the fault develops the fastest. It needs to be quickly identified and a corresponding fault crossing strategy should be adopted. One of the discrimination conditions selected in the embodiment of the present application is that if the three-phase positive sequence voltage on the AC side of the receiving end converter station 40 is less than the fifth preset voltage, one of the conditions is met. Since the three-phase metal short circuit is a symmetrical fault, other single-phase grounding, two-phase short circuit, and two-phase grounding faults are asymmetrical faults. Therefore, the three-phase negative sequence voltage on the AC side of the receiving end converter station 40 can be selected as another discrimination condition. If the three-phase negative sequence voltage is less than the sixth preset voltage, the other condition is met. In this way, if a three-phase metal short circuit fault is identified, it is determined that a serious fault has occurred in the receiving end power grid 50. If other types of faults are identified, it is determined that a non-serious fault has occurred in the receiving end power grid 50.

[0063] Specifically, the unit of the fifth preset voltage V5 is kilovolt (kV), and the fifth preset voltage V5 is the product of the fifth voltage coefficient δ5 and the three-phase positive sequence voltage rated value V 正 In some examples, the fifth voltage coefficient δ5 ranges from 0.2 to 0.4. For example, the fifth voltage coefficient δ5 ranges from 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, and 0.40, or any two of the range values.

[0064] Specifically, the unit of the sixth preset voltage V6 is kilovolt (kV), and the sixth preset voltage V6 is the sixth voltage coefficient δ6 and the three-phase negative sequence voltage rated value V 负In some examples, the sixth voltage coefficient δ6 ranges from 0.04 to 0.06. For example, the sixth voltage coefficient δ6 ranges from any one of or any two of 0.040, 0.041, 0.042, 0.043, 0.044, 0.045, 0.046, 0.047, 0.048, 0.049, 0.050, 0.051, 0.052, 0.053, 0.054, 0.055, 0.056, 0.057, 0.058, 0.059, and 0.060.

[0065] Step 202: If the fault type indicates that a first fault has occurred, the first DC voltage outputted by the receiving-end converter station 40 to the DC line 30 is reduced to a target voltage.

[0066] In some examples, the target voltage is zero.

[0067] In some embodiments, the first DC voltage can be reduced to the target voltage according to a third preset rate v3. Specifically, the unit of the third preset rate v3 is kV / ms (kilovolts / millisecond), and the value of the third preset rate v3 is the third adjustment coefficient θ3 and the rated DC voltage V DC In some examples, the third adjustment coefficient θ3 ranges from 0.5 to 0.7. For example, the third adjustment coefficient θ3 ranges from 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, and 0.70, or any two of these ranges. In this way, the stability of the long-distance direct current transmission system during the adjustment process can be ensured.

[0068] Specifically, the first DC voltage can be adjusted by adjusting a first voltage instruction. The first voltage instruction is used to instruct the receiving-end converter station 40 to output a corresponding DC voltage to the DC line 30. By adjusting the DC voltage value carried in the first voltage instruction to zero, the first DC voltage can be controlled to drop to zero.

[0069] Through the above approach, when the receiving-end AC fault reaches a critical level, the receiving-end grid 50 experiences a three-phase metallic short circuit, rendering the receiving-end converter station 40 virtually unable to transmit power, causing the DC voltage to rise rapidly. Therefore, the DC-side voltage of the receiving-end converter station 40 is reduced to zero at a third predetermined rate v3 via the first voltage command. This prevents DC overvoltage while also allowing the sending-end converter station 20 to quickly detect the critical AC fault in the receiving-end grid 50. This eliminates the need for inter-station communication, resulting in shorter latency and higher efficiency.

[0070] Step 203: When the second DC voltage outputted by the sending-end converter station 20 to the DC line 30 is less than the first preset voltage, the DC current outputted by the sending-end converter station 20 to the DC line 30 is reduced from the initial current to the target current, so that the DC transmission system can achieve fault ride-through.

[0071] In some examples, the target current is zero.

[0072] Specifically, the initial current is the normal current in a fault-free state. The DC current outputted by the sending-end converter station 20 to the DC line 30 can be adjusted by adjusting the current command. The current command instructs the sending-end converter station 20 to output a corresponding DC current to the DC line 30. By adjusting the DC current value carried in the current command to zero, the DC current can be controlled to zero.

[0073] Specifically, the unit of the first preset voltage V1 is kilovolt (kV), and the first preset voltage V1 is the product of the first voltage coefficient δ1 and the rated DC voltage V DC In some examples, the value range of the first voltage coefficient δ1 is 0.7 to 0.9. For example, the value of the first voltage coefficient δ1 is 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, or any two of the range values.

[0074] In the above manner, when the AC fault at the receiving end is severe, the second DC voltage output by the sending-end converter station 20 to the DC line 30 is correspondingly reduced by reducing the DC side voltage of the receiving-end converter station 40. When the second DC voltage is less than the first preset voltage, the DC current is reduced to zero, and no electric energy is injected into the DC transmission system, thereby preventing the fault from further deteriorating.

[0075] In some embodiments, after executing step 203, the method of the embodiment of the present application may further include the following steps:

[0076] Step 1: Obtain the three-phase AC voltage output by the receiving-end converter station 40 to the receiving-end power grid 50.

[0077] Step 2: Obtain three-phase positive sequence voltage and three-phase negative sequence voltage based on the three-phase AC voltage.

[0078] Step three: when the three-phase positive sequence voltage is equal to the rated AC voltage and the three-phase negative sequence voltage is equal to zero, it is determined that the fault of the receiving-end power grid 50 is eliminated.

[0079] It is understandable that after the receiving-end AC fault is eliminated, the voltage of the receiving-end grid 50 returns to normal. Under normal conditions, the three-phase positive-sequence voltage is at the rated AC voltage, and there is no three-phase negative-sequence voltage.

[0080] Step 4: When the fault of the receiving-end grid 50 is eliminated, the first DC voltage is restored from the target voltage to the rated DC voltage.

[0081] In some embodiments, the first DC voltage can be restored from the target voltage to the rated DC voltage at a first preset rate v1. Specifically, the unit of the first preset rate v1 is kV / ms (kilovolts / millisecond), and the value of the first preset rate v1 is the first adjustment coefficient θ1 and the rated DC voltage V DC In some examples, the value range of the first adjustment coefficient θ1 is 0.04 to 0.06. For example, the value of the first adjustment coefficient θ1 is 0.040, 0.041, 0.042, 0.043, 0.044, 0.045, 0.046, 0.047, 0.048, 0.049, 0.050, 0.051, 0.052, 0.053, 0.054, 0.055, 0.056, 0.057, 0.058, 0.059, and 0.060, or any two of the range values.

[0082] Step 5: When the second DC voltage is greater than a second preset voltage, the DC current is restored from the target current to the initial current, wherein the second preset voltage is greater than the first preset voltage.

[0083] Specifically, the unit of the second preset voltage V2 is kilovolt (kV), and the second preset voltage V2 is the product of the second voltage coefficient δ2 and the rated DC voltage V DC In some examples, the second voltage coefficient δ2 ranges from 0.8 to 0.9. For example, the second voltage coefficient δ2 ranges from any one of 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, and 0.90, or any two of these ranges.

[0084] In some embodiments, the DC current can be restored from the target current to the initial current at a second preset rate v2. Specifically, the unit of the second preset rate v2 is A / ms (ampere / millisecond), and the value of the second preset rate v2 is the second adjustment coefficient θ2 and the rated DC current I DCIn some examples, the second adjustment coefficient θ2 ranges from 0.01 to 0.03. For example, the second adjustment coefficient θ2 ranges from 0.010, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, 0.020, 0.021, 0.022, 0.023, 0.024, 0.025, 0.026, 0.027, 0.028, 0.029, and 0.030, or any two of these ranges. This ensures the stability of the long-distance direct current transmission system during the adjustment process.

[0085] It is understandable that when the voltage on the DC side of the receiving-end converter station 40 is about to reach the rated value, the voltage on the DC side of the sending-end converter station 20 may be greater than the second preset voltage, and the sending-end converter station 20 may restore the initial current before the fault.

[0086] Through the above method, after the AC fault at the receiving end is eliminated, the system restores the DC voltage and DC current, that is, the DC voltage multiplied by the DC current equals the transmission power, which means that the power transmission state before the fault can be restored, and the voltage of the receiving-end power grid 50 returns to normal. The entire fault ride-through process will not cause overvoltage lockout.

[0087] In some embodiments, after executing step 201, if the fault type indicates that a second fault has occurred, the AC fault ride-through method at the receiving end of the power transmission system according to the embodiment of the present application continues to execute the following steps:

[0088] Step 204: If the fault type indicates that a second fault has occurred, then when the second DC voltage exceeds a third preset voltage, the DC current is adjusted to enable the DC power transmission system to achieve fault ride-through.

[0089] The severity of the first fault is higher than the severity of the second fault. For example, the second fault may be an asymmetric fault such as a single-phase ground fault, a two-phase short circuit, or a two-phase ground fault. It is understood that when the receiving-end AC fault is a non-critical fault, the fault progresses relatively slowly, and the excess energy in the DC line 30 is within the controllable range of the DC transmission system. Therefore, when the sending-end converter station 20 senses that the DC side voltage is too high, it can reduce the DC current based on the preset overvoltage and current limiting logic to reduce the energy injected into the DC transmission system.

[0090] In some embodiments, the DC current can be adjusted by the following steps:

[0091] Step 1: When the second DC voltage is less than or equal to the third preset voltage, the DC current is maintained unchanged.

[0092] Specifically, the unit of the third preset voltage V3 is kilovolt (kV), and the third preset voltage V3 is the product of the third voltage coefficient δ3 and the rated DC voltage V DC In some examples, the third voltage coefficient δ3 has a value of 1.05.

[0093] Specifically, the DC current can be maintained constant by maintaining the original current instruction constant.

[0094] Step 2: If the second DC voltage exceeds the third preset voltage and is less than or equal to the fourth preset voltage, adjusting the DC current based on the change of the second DC voltage, wherein the change of the DC current is opposite to the change of the second DC voltage.

[0095] In other words, the DC current decreases as the second DC voltage increases, and increases as the second DC voltage decreases. In this way, the DC current can be adjusted in real time based on the change in the second DC voltage, thereby adjusting the power injected into the DC transmission system in real time.

[0096] Specifically, the unit of the fourth preset voltage V4 is kilovolt (kV), and the fourth preset voltage V4 is the product of the fourth voltage coefficient δ4 and the rated DC voltage V DC In some examples, the fourth voltage coefficient δ4 has a value of 1.15.

[0097] Step three: if the second DC voltage exceeds the fourth preset voltage, the DC current is reduced to the target current.

[0098] In some examples, the target current is zero.

[0099] That is to say, even if the receiving-end power grid 50 is in a non-serious fault state, the fault severity can be further divided. The sending-end converter station 20 specifically judges the fault severity of the receiving-end power grid 50 based on the second DC voltage. If the second DC voltage is less than or equal to the third preset voltage, the current instruction on the DC side of the sending-end converter station 20 remains unchanged. At this time, it is determined that the fault severity of the receiving-end power grid 50 is relatively minor, and there is no need to adjust the DC current instruction. If the second DC voltage is greater than the fourth preset voltage, the current instruction on the DC side of the sending-end converter station 20 is set to 0. At this time, the system determines that the fault severity of the receiving-end power grid 50 is relatively serious, and the DC current instruction is directly set to the minimum value 0. If the second DC voltage is between the third preset voltage and the fourth preset voltage, for example, at the rated DC voltage V DC At this time, the current instruction on the DC side of the sending-end converter station 20 decreases as the second DC voltage increases, or increases as the second DC voltage decreases.

[0100] It is understood that the AC fault ride-through method for the receiving end of the transmission system in the embodiments of the present application specifies a control strategy based on the severity of the AC fault at the receiving end. For non-critical faults in the long-distance DC transmission system, an overvoltage current limiting strategy is adopted to limit the DC current command based on the severity of the overvoltage, achieving successful fault ride-through and ensuring maximum power delivery capacity. For critical faults in the long-distance DC transmission system, the DC voltage command at the receiving-end converter station 40 is quickly reduced to zero, thereby preventing overvoltage in the DC transmission system. This also enables the sending-end converter station 20 to promptly detect the critical fault in the receiving-end power grid 50 and set the current command to zero, preventing further deterioration of the fault. These different ride-through methods, adapted for varying degrees of AC fault severity at the receiving end, do not rely on inter-station communication and do not require DC energy-consuming devices. They eliminate the high inter-station communication latency associated with long-distance DC lines, while reducing the cost of the long-distance DC transmission system. The fault ride-through method is simple and reliable, with a low risk of malfunction, and possesses high engineering application value.

[0101] Accordingly, an embodiment of the present application further provides an AC fault ride-through device for a receiving end of a power transmission system. Please refer to FIG3 , which illustrates a structural diagram of the AC fault ride-through device for a receiving end of a power transmission system according to an embodiment of the present application. The AC fault ride-through device for a receiving end of a power transmission system provided in an embodiment of the present application is applied to a DC power transmission system. The DC power transmission system includes a sending-end converter station 20, a DC line 30, a receiving-end converter station 40, and a receiving-end power grid 50, which are sequentially connected. The device includes:

[0102] The fault type determination module 301 is configured to obtain the fault type of the receiving-end power grid 50 when a fault occurs in the receiving-end power grid 50 .

[0103] The voltage regulating module 302 is configured to reduce the first DC voltage outputted by the receiving-end converter station 40 to the DC line 30 to a target voltage if the fault type indicates that a first fault has occurred.

[0104] The first current regulating module 303 is configured to reduce the DC current outputted from the sending-end converter station 20 to the DC line 30 from an initial current to a target current when the second DC voltage outputted from the sending-end converter station 20 to the DC line 30 is less than a first preset voltage, so as to enable the DC transmission system to achieve fault ride-through.

[0105] In some embodiments, the voltage regulating module 302 is further configured to restore the first DC voltage from the target voltage to the rated DC voltage when the fault of the receiving-end power grid 50 is eliminated.

[0106] The first current regulating module 303 is further configured to restore the DC current from the target current to the initial current when the second DC voltage is greater than a second preset voltage, and the second preset voltage is greater than the first preset voltage.

[0107] In some embodiments, the apparatus further includes a fault status detection module, the fault status detection module being configured to:

[0108] The three-phase AC voltage outputted by the receiving-end converter station 40 to the receiving-end power grid 50 is obtained.

[0109] A three-phase positive sequence voltage and a three-phase negative sequence voltage are obtained based on the three-phase AC voltage.

[0110] When the three-phase positive sequence voltage is equal to the rated AC voltage and the three-phase negative sequence voltage is equal to zero, it is determined that the fault of the receiving-end power grid 50 is eliminated.

[0111] In some embodiments, the voltage regulation module 302 is specifically configured to:

[0112] The first DC voltage is restored from the target voltage to the rated DC voltage according to a first preset rate v1, wherein the value of the first preset rate v1 is equal to the product of the first adjustment coefficient θ1 and the rated DC voltage, and satisfies: 0.04≤θ1≤0.06.

[0113] In some embodiments, the first current regulating module 303 is specifically configured to:

[0114] According to the second preset rate v2, the DC current is restored from the target current to the initial current, wherein the value of the second preset rate v2 is equal to the product of the second adjustment coefficient θ2 and the rated DC current, and satisfies: 0.01≤θ2≤0.03.

[0115] In some embodiments, the apparatus further comprises:

[0116] The second current regulating module 304 is configured to regulate the DC current if the fault type indicates a second fault occurs, and when the second DC voltage exceeds a third preset voltage, so that the DC transmission system can achieve fault ride-through, and the fault severity of the first fault is higher than the fault severity of the second fault.

[0117] In some embodiments, the second current regulating module 304 is specifically configured to:

[0118] If the second DC voltage exceeds the third preset voltage and is less than or equal to the fourth preset voltage, the DC current is adjusted based on the change of the second DC voltage, and the change of the DC current is opposite to the change of the second DC voltage.

[0119] If the second DC voltage exceeds the fourth preset voltage, the DC current is reduced to a target current.

[0120] In some embodiments, the second current regulating module 304 is further configured to:

[0121] When the second DC voltage is less than or equal to the third preset voltage, the DC current is maintained unchanged.

[0122] In some embodiments, the fault type determination module 301 is specifically configured to:

[0123] The three-phase AC voltage outputted by the receiving-end converter station 40 to the receiving-end power grid 50 is obtained.

[0124] A three-phase positive sequence voltage and a three-phase negative sequence voltage are obtained based on the three-phase AC voltage.

[0125] When the three-phase positive sequence voltage is less than the fifth preset voltage and the three-phase negative sequence voltage is less than the sixth preset voltage, it is determined that the fault type of the receiving-end power grid 50 is the first fault.

[0126] In some embodiments, the voltage regulation module 302 is specifically configured to:

[0127] The first DC voltage is reduced to a target voltage according to a third preset rate v3, wherein the value of the third preset rate v3 is equal to the product of the third adjustment coefficient θ3 and the rated DC voltage, and satisfies: 0.5≤θ3≤0.7.

[0128] In some embodiments, the target voltage and the target current are both zero.

[0129] It can be understood that the AC fault ride-through device at the receiving end of the transmission system forces the first DC voltage on the DC side of the receiving-end converter station 40 to be reduced to the target voltage when the first fault occurs, thereby preventing overvoltage in the DC transmission system. Since the second DC voltage on the DC side of the sending-end converter station 20 will decrease along with the first DC voltage, the sending-end converter station 20 can promptly sense the first fault in the receiving-end power grid 50 and then promptly adjust the DC side current to avoid further deterioration of the fault. The entire process does not rely on inter-station communication, and thus there is no high latency effect caused by long-distance DC lines. Power adjustment can be made in a timely manner for receiving-end AC faults, and the system has high safety and stability, can better meet the fault ride-through requirements, and has high engineering application value.

[0130] Accordingly, an embodiment of the present application further provides an electronic device. Please refer to Figure 4, which illustrates a block diagram of the electronic device according to an embodiment of the present application. The electronic device includes a memory, a processor, and a computer program stored in the memory and executable by the processor. When the processor executes the computer program, the steps of the above-described method for riding through an AC fault at the receiving end of a power transmission system are implemented. Since the above description of the method for riding through an AC fault at the receiving end of a power transmission system is detailed, it will not be repeated here.

[0131] Accordingly, embodiments of the present application further provide a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the aforementioned method for riding through an AC fault at the receiving end of a power transmission system. Since the aforementioned method for riding through an AC fault at the receiving end of a power transmission system has been described in detail above, it will not be further described here.

[0132] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0133] The above is a detailed introduction to the AC fault ride-through method, device, equipment and storage medium for the receiving end of the transmission system provided in the embodiments of the present application, and specific examples are used to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the technical solution and core idea of ​​the present application; ordinary technicians in this field should understand that: they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not cause the essence of the corresponding technical solution to deviate from the scope of the technical solution of the embodiments of the present application.

Claims

1. A method for riding through an AC fault at a receiving end of a power transmission system, characterized in that: Applied to a direct current transmission system, the direct current transmission system comprises a sending-end converter station, a direct current line, a receiving-end converter station and a receiving-end power grid connected in sequence, the method comprises: When a fault occurs in the receiving-end power grid, obtaining a fault type of the receiving-end power grid; If the fault type indicates that a first fault has occurred, reducing the first DC voltage output by the receiving-end converter station to the DC line to a target voltage; When the second DC voltage output by the sending-end converter station to the DC line is less than the first preset voltage, the DC current output by the sending-end converter station to the DC line is reduced from an initial current to a target current so that the DC power transmission system can achieve fault ride-through.

2. The AC fault ride-through method for a power transmission system receiving end according to claim 1, characterized in that: The method further comprises: When the fault of the receiving-end power grid is eliminated, restoring the first DC voltage from the target voltage to a rated DC voltage; In a case where the second DC voltage is greater than a second preset voltage, the DC current is restored from the target current to the initial current, and the second preset voltage is greater than the first preset voltage.

3. The AC fault ride-through method for a power transmission system receiving end according to claim 2, characterized in that: After the step of reducing the DC current outputted by the sending-end converter station to the DC line from an initial current to a target current, the method further comprises: Acquiring the three-phase AC voltage output by the receiving-end converter station to the receiving-end power grid; Acquire a three-phase positive sequence voltage and a three-phase negative sequence voltage based on the three-phase AC voltage; When the three-phase positive sequence voltage is equal to the rated AC voltage and the three-phase negative sequence voltage is equal to zero, it is determined that the fault of the receiving-end power grid is eliminated.

4. The AC fault ride-through method for a power transmission system receiving end according to claim 2, characterized in that: Restoring the first DC voltage from the target voltage to a rated DC voltage includes: The first DC voltage is restored from the target voltage to the rated DC voltage according to a first preset rate v1, wherein the value of the first preset rate v1 is equal to the product of the first adjustment coefficient θ1 and the rated DC voltage, satisfying: 0.04≤θ1≤0.

06.

5. The AC fault ride-through method for a power transmission system receiving end according to claim 2, characterized in that: Restoring the direct current from the target current to the initial current includes: According to a second preset rate v2, the DC current is restored from the target current to the initial current, wherein the value of the second preset rate v2 is equal to the product of the second adjustment coefficient θ2 and the rated DC current, satisfying: 0.01≤θ2≤0.

03.

6. The AC fault ride-through method for a power transmission system receiving end according to claim 1, characterized in that: The method further comprises: If the fault category indicates that a second fault has occurred, then when the second DC voltage exceeds a third preset voltage, the DC current is adjusted so that the DC power transmission system can achieve fault ride-through, and the fault severity of the first fault is higher than the fault severity of the second fault.

7. The AC fault ride-through method for a power transmission system receiving end according to claim 6, characterized in that: When the second DC voltage exceeds a third preset voltage, adjusting the DC current includes: If the second DC voltage exceeds the third preset voltage and is less than or equal to a fourth preset voltage, adjusting the DC current based on a change in the second DC voltage, the change in the DC current being opposite to the change in the second DC voltage; If the second DC voltage exceeds the fourth preset voltage, the DC current is reduced to the target current.

8. The AC fault ride-through method for a power transmission system receiving end according to claim 6, characterized in that: The method further comprises: When the second DC voltage is less than or equal to the third preset voltage, the DC current is maintained unchanged.

9. The AC fault ride-through method for a power transmission system receiving end according to claim 1, characterized in that: Obtaining the fault type of the receiving-end power grid includes: Acquiring the three-phase AC voltage output by the receiving-end converter station to the receiving-end power grid; Acquire a three-phase positive sequence voltage and a three-phase negative sequence voltage based on the three-phase AC voltage; When the three-phase positive-sequence voltage is less than the fifth preset voltage and the three-phase negative-sequence voltage is less than the sixth preset voltage, it is determined that the fault type of the receiving-end power grid is the first fault.

10. The AC fault ride-through method for a power transmission system receiving end according to claim 1, characterized in that: Reducing the first DC voltage output by the receiving-end converter station to the DC line to a target voltage includes: According to a third preset rate v3, the first DC voltage is reduced to the target voltage, wherein The value of the third preset rate v3 is equal to the product of the third adjustment coefficient θ3 and the rated DC voltage, and satisfies: 0.5≤θ3≤0.

7.

11. The AC fault ride-through method for a power transmission system receiving end according to any one of claims 1 to 10, characterized in that: The target voltage and the target current are both zero.

12. An AC fault ride-through device at the receiving end of a power transmission system, characterized in that: Applied to a direct current transmission system, the direct current transmission system comprises a sending-end converter station, a direct current line, a receiving-end converter station and a receiving-end power grid connected in sequence, the device comprises: A fault category determination module, used for obtaining the fault category of the receiving-end power grid when a fault occurs in the receiving-end power grid; a voltage regulating module, configured to reduce a first DC voltage output by the receiving-end converter station to the DC line to a target voltage if the fault type indicates that a first fault has occurred; The first current regulating module is used to reduce the DC current output by the sending-end converter station to the DC line from an initial current to a target current when the second DC voltage output by the sending-end converter station to the DC line is less than a first preset voltage, so as to enable the DC power transmission system to achieve fault ride-through.

13. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the steps of the method for riding through an AC fault at the receiving end of a power transmission system according to any one of claims 1 to 11 are implemented.

14. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for riding through an AC fault at a receiving end of a power transmission system according to any one of claims 1 to 11 are implemented.

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