Transmitting end alternating current fault ride-through method and device, equipment and storage medium

Abstract

The embodiment of the invention discloses a sending end alternating current fault ride-through method and device, equipment and a storage medium, the method is applied to a receiving end hybrid cascade type extra-high voltage direct current transmission system, and the method comprises the following steps: when a sending end converter station has an alternating current fault, controlling a sending end LCC to be switched to a fixed minimum firing angle control mode; determining the fault handling capacity of the receiving-end high-pressure valve group LCC according to the voltage reduction reference value and the controllable voltage regulation range of the receiving-end high-pressure valve group LCC; if the fault handling capacity of the receiving-end high-pressure valve group LCC is sufficient to handle the current fault, the receiving-end high-pressure valve group LCC is controlled to be switched to a constant direct current control mode, so that the receiving-end high-pressure valve group LCC undertakes all voltage reduction tasks; and if the current fault is not enough to cope with the current fault, controlling the receiving-end MMC to be switched to a voltage-power collaborative voltage reduction mode, so that the receiving-end MMC undertakes all voltage reduction tasks and performs power redistribution during the fault period. According to the mode, uninterrupted operation of the system during the fault period can be quickly realized, and the reliability and stability of the power transmission system during the abnormal working condition period are improved.

Description

Technical Field

[0001] This invention relates to the field of ultra-high voltage direct current transmission technology, and in particular to a method, apparatus, equipment and storage medium for AC fault ride-through at the sending end. Background Technology

[0002] The receiving-end converter station of the power transmission system adopts a hybrid cascaded DC transmission technology that combines traditional grid-commutated converters (LCCs) and modular multilevel converters (MMCs), and has been successfully put into operation.

[0003] During an AC fault at the sending end of a hybrid cascaded UHVDC transmission system, the DC voltage at the sending-end converter station will adaptively decrease following the effective value of the PCC AC voltage, and the DC voltage difference between the sending and receiving ends will continuously decrease. When the sending-end output DC voltage is lower than the receiving-end DC voltage, it will lead to power transmission interruption at the sending end and power flow reversal between the receiving-end MMC converters, seriously affecting the safe and stable operation of the transmission system. Therefore, how to design corresponding sending-end and receiving-end coordinated fault ride-through strategies to maintain uninterrupted system operation and ensure the safe and stable operation of the transmission system during an AC fault at the sending end is an urgent problem to be solved. Summary of the Invention

[0004] The main objective of this invention is to provide a method, apparatus, device, and storage medium for AC fault ride-through at the sending end, which can solve the problem that the prior art lacks a coordinated fault ride-through strategy between the sending and receiving ends during an AC fault at the sending end, which seriously affects the safe and stable operation of the power transmission system.

[0005] To achieve the above objectives, the first aspect of the present invention provides a sending-end AC fault ride-through method, the method being applied to a receiving-end hybrid cascaded ultra-high voltage direct current (UHVDC) transmission system. The UHVDC transmission system includes a sending-end converter station and a receiving-end hybrid cascaded converter station. The sending-end converter station includes a sending-end LCC; the receiving-end hybrid cascaded converter station includes a receiving-end high-voltage valve group LCC and a receiving-end MMC. The output terminal of the sending-end LCC is electrically connected to the input terminal of the receiving-end high-voltage valve group LCC; the output terminal of the receiving-end high-voltage valve group LCC is electrically connected to the input terminal of the receiving-end MMC. The method includes: When an AC fault occurs at the sending-end converter station, the sending-end LCC is controlled to switch to the fixed minimum firing angle control mode. The fault response capability of the receiving-end high-pressure valve group LCC is determined by comparing the predetermined pressure reduction reference value with the controllable pressure adjustment range of the receiving-end high-pressure valve group LCC. If the fault response capability of the receiving-end high-pressure valve group LCC is sufficient to handle the current fault, then control the receiving-end high-pressure valve group LCC to switch to constant DC control mode so that the receiving-end high-pressure valve group LCC undertakes all the voltage reduction tasks. If the fault response capability of the receiving-end high-pressure valve group LCC is insufficient to handle the current fault, then the receiving-end MMC is controlled to switch to voltage-power coordinated buck mode so that the receiving-end MMC can undertake all bucking tasks.

[0006] To achieve the above objectives, a second aspect of the present invention provides a sending-end AC fault ride-through device, which is applied to a receiving-end hybrid cascaded ultra-high voltage direct current (UHVDC) transmission system. The UHVDC transmission system includes a sending-end converter station and a receiving-end hybrid cascaded converter station. The sending-end converter station includes a sending-end LCC; the receiving-end hybrid cascaded converter station includes a receiving-end high-voltage valve group LCC and a receiving-end MMC. The output terminal of the sending-end LCC is electrically connected to the input terminal of the receiving-end high-voltage valve group LCC; the output terminal of the receiving-end high-voltage valve group LCC is electrically connected to the input terminal of the receiving-end MMC. The device includes: Sending-end control module: used to control the sending-end LCC to switch to the fixed minimum firing angle control mode when an AC fault occurs in the sending-end converter station; Receiving-end control module: This module compares a predetermined step-down reference value with the controllable voltage regulation range of the receiving-end high-pressure valve group LCC to determine the fault response capability of the receiving-end high-pressure valve group LCC. If the fault response capability of the receiving-end high-pressure valve group LCC is sufficient to handle the current fault, the module controls the receiving-end high-pressure valve group LCC to switch to a constant DC control mode, allowing the receiving-end high-pressure valve group LCC to undertake all step-down tasks. If the fault response capability of the receiving-end high-pressure valve group LCC is insufficient to handle the current fault, the module controls the receiving-end MMC to switch to a voltage-power coordinated step-down mode, allowing the receiving-end MMC to undertake all step-down tasks.

[0007] To achieve the above objectives, a third aspect of the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform the steps of the method shown in the first aspect.

[0008] To achieve the above objectives, a fourth aspect of the present invention provides a computer device including a memory and a processor, the memory storing a computer program that, when executed by the processor, causes the processor to perform the steps of the method shown in the first aspect.

[0009] The embodiments of the present invention have the following beneficial effects: This invention provides a method for AC fault ride-through at the sending end, applied to a hybrid cascaded ultra-high voltage direct current (UHVDC) transmission system at the receiving end. The UHVDC transmission system includes a sending-end converter station and a hybrid cascaded converter station at the receiving end. The sending-end converter station includes a sending-end LCC (Limited Control Center); the receiving-end hybrid cascaded converter station includes a receiving-end high-voltage valve group (LCC) and a receiving-end MMC (Mechanical Management Center). The output terminal of the sending-end LCC is electrically connected to the input terminal of the receiving-end high-voltage valve group (LCC); the output terminal of the receiving-end high-voltage valve group (LCC) is electrically connected to the input terminal of the receiving-end MMC. The method includes: when an AC fault occurs at the sending-end converter station, controlling the sending-end LCC... Switch to the fixed minimum firing angle control mode; compare the pre-determined step-down reference value with the controllable voltage adjustment range of the receiving-end high-voltage valve group LCC to determine the fault response capability of the receiving-end high-voltage valve group LCC; if the fault response capability of the receiving-end high-voltage valve group LCC is sufficient to handle the current fault, then control the receiving-end high-voltage valve group LCC to switch to the fixed DC control mode so that the receiving-end high-voltage valve group LCC undertakes all the step-down tasks; if the fault response capability of the receiving-end high-voltage valve group LCC is insufficient to handle the current fault, then control the receiving-end MMC to switch to the voltage-power coordinated step-down mode so that the receiving-end MMC undertakes all the step-down tasks.

[0010] By switching the LCC at the sending end to a fixed minimum firing angle control, voltage drops are compensated to the maximum extent. At the same time, the receiving end flexibly selects either the LCC fixed DC control mode or the MMC voltage-power coordinated step-down mode to undertake all the step-down tasks based on the comparison between the step-down requirements and the LCC voltage regulation range. This ensures real-time matching of DC voltages at the sending and receiving ends, fundamentally avoiding power transmission interruption at the sending end and power flow reversal between the MMCs at the receiving end, and significantly improving the operational safety during system failures. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] in: Figure 1 This is a schematic diagram of the main wiring of a hybrid cascaded ultra-high voltage direct current transmission system at the receiving end, according to an embodiment of the present invention. Figure 2 This is a flowchart of a method for AC fault ride-through at the sending end in an embodiment of the present invention; Figure 3 This is another flowchart of a method for overcoming AC faults at the sending end in an embodiment of the present invention; Figure 4This is a schematic diagram of an adaptive buck operation strategy for a receiving-end MMC in an embodiment of the present invention; Figure 5 This is a schematic diagram of an adaptive power adjustment strategy for a receiver-side MMC in an embodiment of the present invention; Figure 6 This is a structural block diagram of a transmitting-end AC fault ride-through device according to an embodiment of the present invention; Figure 7 This is a structural block diagram of a computer device in an embodiment of the present invention. Detailed Implementation

[0013] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] Please see Figure 1 , Figure 1 This is a schematic diagram of the main wiring of a hybrid cascaded ultra-high voltage direct current transmission system at the receiving end, as described in an embodiment of the present invention. Figure 1 The ultra-high voltage direct current (UHVDC) transmission system shown includes a sending-end converter station and a receiving-end hybrid cascaded converter station. The sending-end converter station includes a sending-end LCC (Line Commutated Converter); the receiving-end hybrid cascaded converter station includes a receiving-end high-voltage valve group LCC and a receiving-end MMC (Modular Multilevel Converter). The output of the sending-end LCC is electrically connected to the input of the receiving-end high-voltage valve group LCC; the output of the receiving-end high-voltage valve group LCC is electrically connected to the input of the receiving-end MMC. The receiving-end MMC includes a master station MMC and multiple slave station MMCs.

[0015] Please see Figure 2 , Figure 2 This is a flowchart of a sending-end AC fault ride-through method according to an embodiment of the present invention. This method is a sending-end AC fault ride-through strategy applicable to receiving-end hybrid cascaded UHVDC transmission systems, such as... Figure 2 The method shown is applied to, for example Figure 1 The method for the ultra-high voltage direct current transmission system of the receiving end hybrid cascade type shown includes: 201. When an AC fault occurs at the sending-end converter station, control the sending-end LCC to switch to the fixed minimum firing angle control mode; It should be noted that the application scenario of this patent is "AC fault occurring at the sending end". When an AC fault occurs at the sending end, the sending end LCC switches to the fixed minimum firing angle control mode in real time. This fixed minimum firing angle control mode compensates for the drop in the effective value of the AC voltage at the grid coupling point (PCC) to the greatest extent possible, thus ensuring the DC voltage value at the sending end.

[0016] In order to realize the fault traversal strategy of the sending and receiving ends, the further execution step 202 determines the control mode of the receiving end.

[0017] 202. Based on the predetermined pressure reduction reference value and the controllable pressure adjustment range of the receiving end high pressure valve group LCC, determine the fault response capability of the receiving end high pressure valve group LCC; Furthermore, based on a comparison between the predetermined pressure reduction reference value and the controllable pressure adjustment range of the receiving-end high-pressure valve group LCC, the fault response capability of the receiving-end high-pressure valve group LCC is determined. If the fault response capability of the receiving-end high-pressure valve group LCC is sufficient to handle the current fault, then step 203 is executed to control the receiving-end high-pressure valve group LCC to undertake all pressure reduction tasks; if the fault response capability of the receiving-end high-pressure valve group LCC is insufficient to handle the current fault, then step 204 is executed to control the receiving-end MMC to undertake all pressure reduction tasks.

[0018] Among them, the switching criterion for the receiving end segmented coordinated voltage reduction strategy is: when an AC fault occurs at the sending end, a voltage reduction reference value that meets the power transmission requirements can be obtained in advance. By comparing the preset voltage reduction reference value with the controllable pressure regulation range of the receiving end high-pressure valve group LCC, the receiving end fault ride-through strategy can be determined.

[0019] Setting the step-down reference value to meet the power continuity requirements: To match the adjustment value of the inverter-side DC voltage with the drop value of the rectifier-side DC voltage, after an AC fault at the sending end, the MMC DC voltage should be set as follows: ; In the formula, This is the reference value for reduced pressure; This represents the amplitude of the AC bus voltage after the fault. The trigger angle is set to 5°. For converter transformer turns ratio; The steady-state operating value of the DC current is used to calculate the adjustment value of the DC voltage on the inverter side; This is the equivalent reactance of the converter transformer; The resistance of the DC line is denoted by . The AC bus voltage amplitude is collected, and the adjustment value of the DC voltage on the inverter side is calculated according to the above formula. Then, it is transmitted to the receiving end via inter-station communication.

[0020] Among them, the receiving-end high-pressure valve group LCC has a significant voltage reduction capability and can operate in the state of 0 output voltage. The voltage regulation range is considered to be from 0 to the steady-state rated voltage. That is, the controllable voltage regulation range of the receiving-end high-pressure valve group LCC can be: [0, steady-state rated voltage].

[0021] The step of determining the fault response capability of the receiving-end high-pressure valve group LCC by comparing a predetermined pressure drop reference value with the controllable pressure adjustment range of the receiving-end high-pressure valve group LCC includes: if the pressure drop reference value is within the controllable pressure adjustment range of the receiving-end high-pressure valve group LCC (for example, the pressure drop reference value is less than the controllable pressure adjustment range of the receiving-end high-pressure valve group LCC), then the fault response capability of the receiving-end high-pressure valve group LCC is determined to be sufficient to cope with the current fault, and step 203 is executed; if the pressure drop reference value exceeds the controllable pressure adjustment range of the receiving-end high-pressure valve group LCC (for example, the pressure drop reference value is greater than or equal to the controllable pressure adjustment range of the receiving-end high-pressure valve group LCC), then the fault response capability of the receiving-end high-pressure valve group LCC is determined to be insufficient to cope with the current fault, and step 204 is executed.

[0022] 203. If the fault response capability of the receiving end high-pressure valve group LCC is sufficient to cope with the current fault, then control the receiving end high-pressure valve group LCC to switch to constant DC control mode so that the receiving end high-pressure valve group LCC undertakes all voltage reduction tasks. 204. If the fault response capability of the receiving-end high-pressure valve group LCC is insufficient to cope with the current fault, then control the receiving-end MMC to switch to voltage-power coordinated buck mode so that the receiving-end MMC can undertake all buck tasks.

[0023] Furthermore, the specific switching method of the sending-end AC fault ride-through strategy for the receiving-end hybrid cascaded UHVDC transmission system is as follows: 1) If the preset voltage reduction reference value is within the controllable voltage regulation range of the receiving-end high-voltage valve group LCC, the receiving-end high-voltage valve group LCC switches to the constant DC control mode for rapid quantitative voltage reduction and to undertake the task of stabilizing the DC current of the system, while the receiving-end low-voltage valve group MMC continues to maintain the steady-state operation control mode. 2) If the preset voltage reduction value exceeds the controllable voltage regulation range of the receiving-end high-voltage valve group LCC, the receiving-end MMC switches to the voltage-power coordinated voltage reduction mode so that the receiving-end MMC undertakes all voltage reduction tasks. At this time, the "receiving-end high-voltage valve group LCC" is in an equivalent short-circuit state, and the DC output voltage is approximately 0kV.

[0024] Among them, the "steady-state operation control mode" includes: the receiving end low-voltage valve group master station MMC1 continues to maintain the constant DC voltage control mode, and the receiving end low-voltage valve group slave stations MMC2 and MMC3 continue to maintain the constant active power control mode. It should be noted that the constant minimum firing angle control mode, constant DC control mode and constant active power control mode are mature control methods in the field of DC transmission, and will not be elaborated here.

[0025] In one feasible implementation, the receiving-end MMC includes a master MMC (MMC station 1) and multiple slave MMCs (MMC station 2 and MMC station 3). Controlling the receiving-end MMC to switch to a voltage-power coordinated buck mode includes: controlling the master MMC to activate an adaptive voltage adjustment strategy; and controlling the slave MMCs to activate an adaptive power adjustment strategy. Specifically, switching the receiving-end MMC to the voltage-power coordinated buck mode involves: the receiving-end MMC activating an adaptive voltage adjustment strategy to quantitatively reduce its output DC voltage and undertake part of the buck reduction task; simultaneously, adaptive power adjustment strategies are activated among the cascaded MMCs to ensure reasonable power distribution during fault periods.

[0026] Please see Figure 3 , Figure 3 This is another flowchart of a sending-end AC fault traversal method according to an embodiment of the present invention, as follows: Figure 3 The AC fault ride-through strategy of the receiving-end hybrid cascaded UHVDC transmission system includes: when an AC fault occurs at the sending end of the receiving-end hybrid cascaded UHVDC transmission system, the sending-end LCC is switched to the fixed minimum firing angle control mode; then it is determined whether "the voltage reduction value required for freewheeling is less than the voltage regulation range of the receiving-end high-pressure valve group LCC"; if it is less than (Y), the receiving-end high-pressure valve group LCC is switched to the fixed DC control mode, and the receiving-end low-pressure valve group MMC continues to maintain the steady-state operation mode; if it is not less than (N), the receiving-end high-pressure valve group LCC is switched to the fixed advanced firing angle control mode, and the receiving-end low-pressure valve group MMC adopts an adaptive voltage adjustment strategy and an adaptive power adjustment strategy.

[0027] Furthermore, this adaptive voltage adjustment strategy includes: the outer loop reference value of the main station MMC (MMC1) voltage. U dcref From the rated value U dcN The voltage reduction reference value is switched to achieve active quantitative voltage reduction; the current inner loop reference value of the master station MMC is locked to a steady-state value to ensure that the transmission power does not decrease sharply during the voltage reduction period and to prevent power flow reversal.

[0028] Please see Figure 4 , Figure 4 This is a schematic diagram of an adaptive buck operation strategy for the receiving-end MMC in an embodiment of the present invention, illustrating the adaptive buck operation strategy of the faulty receiving-end MMC1. Figure 4 In the control strategy shown: The steady-state rated value of the DC voltage output from the main station; The minimum step-down limit for MMC (determined by the converter's own configuration); for and The difference; The measured current value of MMC1 at the time of the fault; the reference value of DC current of MMC1 during the fault period. Taking the steady-state value achieves reduced-voltage operation and avoids a significant reduction in the power that the main station MMC1 can allocate, thereby reducing the probability of power back transmission.

[0029] Furthermore, the adaptive power adjustment strategy includes: when the voltage drop of the master station MMC causes the output voltage of the slave station MMC to decrease... U dc Below safety limit U dcmin At that time, the passive power compensation circuit is activated: the active power compensation value is generated by the PI controller using the current deviation of the slave station MMC as input. Dynamically correct power reference value This enables automatic load balancing among cascaded slave MMCs.

[0030] Please see Figure 5 , Figure 5 This is a schematic diagram of an adaptive power adjustment strategy for a receiving-end MMC in an embodiment of the present invention, specifically illustrating a dynamic active power adjustment strategy for slave MMC2 and MMC3. Figure 5 middle: This is the actual DC current value for MMC2 or MMC3. The measured DC voltage at the direct output of MMC2 or MMC3; The lower limit of voltage drop allowed by MMC2 or MMC3; This is the active power reference compensation value; The active power reference value is the steady-state value of MMC2 or MMC3. As shown in the figure, the DC current reference value of the slave station's MMC2 or MMC3 is automatically taken as the steady-state value. This dynamic active power adjustment strategy works in coordination with the adaptive step-down control of the master station's MMC1 to achieve the purpose of dynamic power allocation and adaptive step-down of MMC1, MMC2, and MMC3.

[0031] In the appendix Figure 5 Under the control architecture, during normal system operation, the DC current and active power reference values ​​at the outputs of MMC2 and MMC3 are in a steady state. During fault ride-through, the master station MMC performs active quantitative voltage reduction, and the DC side voltage of the slave station MMC2 decreases accordingly. When its output DC voltage falls below the steady-state allowable lower limit, MMC2 automatically engages the active power adaptive adjustment strategy, that is, it generates active power reference compensation values ​​for MMC2 and MMC3 through PI control based on the DC current deviation.

[0032] This invention discloses a sending-end AC fault ride-through strategy for a receiving-end hybrid cascaded UHVDC transmission system, comprising: when an AC fault occurs at the sending end of the receiving-end hybrid cascaded UHVDC transmission system, the sending-end LCC adaptively switches to a fixed minimum firing angle control to maximize compensation for the DC output voltage drop of the sending-end LCC; to continue power transmission during the fault, a segmented collaborative voltage reduction strategy is adopted between the receiving-end hybrid cascaded converters, including: when the required voltage reduction value for follow-through is within the controllable voltage regulation range of the receiving-end high-voltage valve group LCC, the receiving-end high-voltage valve group LCC will prioritize the use of its large voltage reduction capability to quickly and quantitatively reduce voltage for follow-through and maintain stable power transmission of the system during the fault using a constant current control method; when the required voltage reduction value at the receiving end exceeds the controllable voltage regulation range of the receiving-end high-voltage valve group LCC, the receiving-end MMC will adaptively reduce its output DC voltage value to undertake part of the voltage reduction task, and will simultaneously adaptively adjust the power distribution value between the cascaded MMCs. The AC fault ride-through strategy proposed in this invention can quickly achieve uninterrupted operation of the system during faults, thereby improving the reliability and stability of the power transmission system during abnormal operating conditions.

[0033] This invention provides a method for AC fault ride-through at the sending end. By switching the LCC at the sending end to a fixed minimum firing angle control, the voltage drop is compensated to the maximum extent. At the same time, the receiving end flexibly selects either the LCC fixed DC control mode or the MMC voltage-power coordinated step-down mode to undertake the entire step-down task based on the comparison between the step-down requirements and the LCC voltage regulation range. This ensures real-time matching of DC voltages at the sending and receiving ends, fundamentally avoiding power transmission interruption at the sending end and power flow reversal between the MMCs at the receiving end, and significantly improving the operational safety of the system during faults.

[0034] Please see Figure 6 , Figure 6 This is a structural block diagram of a transmitting-end AC fault ride-through device according to an embodiment of the present invention, such as... Figure 6 The apparatus shown includes: The device is applied to a hybrid cascaded ultra-high voltage direct current (UHVDC) transmission system at the receiving end. The UHVDC transmission system includes a sending-end converter station and a hybrid cascaded converter station at the receiving end. The sending-end converter station includes a sending-end LCC (Limited Channel Control Unit); the receiving-end hybrid cascaded converter station includes a receiving-end high-voltage valve group (LCC) and a receiving-end MMC (Medium-voltage Control Unit). The output terminal of the sending-end LCC is electrically connected to the input terminal of the receiving-end high-voltage valve group (LCC); the output terminal of the receiving-end high-voltage valve group (LCC) is electrically connected to the input terminal of the receiving-end MMC. The device includes: Sending-end control module 601: used to control the sending-end LCC to switch to the fixed minimum firing angle control mode when an AC fault occurs in the sending-end converter station; The receiving-end control module 602 is used to compare a predetermined step-down reference value with the controllable voltage adjustment range of the receiving-end high-pressure valve group LCC to determine the fault response capability of the receiving-end high-pressure valve group LCC. If the fault response capability of the receiving-end high-pressure valve group LCC is sufficient to handle the current fault, the receiving-end high-pressure valve group LCC is controlled to switch to a constant DC control mode so that the receiving-end high-pressure valve group LCC undertakes all the step-down tasks. If the fault response capability of the receiving-end high-pressure valve group LCC is insufficient to handle the current fault, the receiving-end MMC is controlled to switch to a voltage-power coordinated step-down mode so that the receiving-end MMC undertakes all the step-down tasks.

[0035] It should be noted that, Figure 6 The contents of each module in the device shown are... Figure 2 The steps in the method shown are similar, and will not be repeated here to avoid repetition. For details, please refer to [reference needed]. Figure 2 The content of each step in the method shown.

[0036] This invention provides a sending-end AC fault ride-through device. By switching the sending-end LCC to a fixed minimum firing angle, it maximizes compensation for voltage drops. Simultaneously, the receiving end flexibly selects either the LCC fixed DC control mode or the MMC voltage-power coordinated step-down mode to undertake all the step-down tasks based on the comparison between the step-down requirements and the LCC voltage regulation range. This ensures real-time matching of DC voltages between the sending and receiving ends, fundamentally avoiding power transmission interruption at the sending end and power flow reversal between the receiving end MMCs, and significantly improving the operational safety during system faults.

[0037] Figure 7 An internal structural diagram of a computer device in one embodiment is shown. This computer device can specifically be a terminal or a server. Figure 7 As shown, the computer device includes a processor, memory, and a network interface connected via a system bus. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system and may also store a computer program, which, when executed by the processor, causes the processor to perform the aforementioned methods. The internal memory may also store a computer program, which, when executed by the processor, causes the processor to perform the aforementioned methods. Those skilled in the art will understand that… Figure 7 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0038] In one embodiment, a computer device is provided, including a memory and a processor, the memory storing a computer program that, when executed by the processor, causes the processor to perform actions such as... Figure 2 or Figure 3 The steps of the method shown.

[0039] In one embodiment, a computer-readable storage medium is provided storing a computer program that, when executed by a processor, causes the processor to perform the following actions: Figure 2 or Figure 3 The steps of the method shown.

[0040] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments described above. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and RAMbus dynamic RAM (RDRAM), etc.

[0041] 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.

[0042] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for traversing AC faults at the sending end, characterized in that, The method is applied to a hybrid cascaded ultra-high voltage direct current (UHVDC) transmission system at the receiving end. The UHVDC transmission system includes a sending-end converter station and a hybrid cascaded converter station at the receiving end. The sending-end converter station includes a sending-end LCC (Limited Control Center); the receiving-end hybrid cascaded converter station includes a receiving-end high-voltage valve group (LCC) and a receiving-end MMC (Medium-voltage Control Center). The output terminal of the sending-end LCC is electrically connected to the input terminal of the receiving-end high-voltage valve group (LCC). The output terminal of the receiving-end high-pressure valve group LCC is electrically connected to the input terminal of the receiving-end MMC; The method includes: When an AC fault occurs at the sending-end converter station, the sending-end LCC is controlled to switch to the fixed minimum firing angle control mode. The fault response capability of the receiving-end high-pressure valve group LCC is determined by comparing the predetermined pressure reduction reference value with the controllable pressure adjustment range of the receiving-end high-pressure valve group LCC. If the fault response capability of the receiving-end high-pressure valve group LCC is sufficient to handle the current fault, then control the receiving-end high-pressure valve group LCC to switch to constant DC control mode so that the receiving-end high-pressure valve group LCC undertakes all the voltage reduction tasks. If the fault response capability of the receiving-end high-pressure valve group LCC is insufficient to handle the current fault, then the receiving-end MMC is controlled to switch to voltage-power coordinated buck mode so that the receiving-end MMC can undertake all bucking tasks.

2. The method according to claim 1, characterized in that, The receiving-end MMC includes a master MMC and multiple slave MMCs. Controlling the receiving-end MMC to switch to a voltage-power coordinated buck mode includes: The master station MMC is controlled to implement an adaptive voltage adjustment strategy; Control the slave station MMC to implement an adaptive power adjustment strategy.

3. The method according to claim 2, characterized in that, The adaptive voltage adjustment strategy includes: The voltage outer loop reference value of the master station MMC is switched from the rated value to the step-down reference value to achieve active quantitative step-down; the current inner loop reference value of the master station MMC is locked to the steady-state value to ensure that the transmission power does not decrease sharply during step-down and to prevent power flow reversal.

4. The method according to claim 2, characterized in that, The adaptive power adjustment strategy includes: When the voltage drop of the master station MMC causes the output voltage of the slave station MMC to fall below the safety limit, the power compensation circuit is passively activated: the current deviation of the slave station MMC is used as input to generate an active power compensation value through a PI controller, dynamically correcting the power reference value, and realizing automatic load balancing among cascaded slave station MMCs.

5. The method according to claim 1, characterized in that, The reference value for blood pressure reduction is determined using the following mathematical expression: ； In the formula, This is the reference value for reduced pressure; This represents the AC bus voltage amplitude after the fault. For trigger angle; For converter transformer turns ratio; This represents the steady-state operating value of the DC current. This refers to the equivalent reactance of the converter transformer. The resistance of the DC line.

6. The method according to claim 1, characterized in that, The step of determining the fault response capability of the receiving-end high-pressure valve group LCC by comparing a predetermined pressure reduction reference value with the controllable pressure adjustment range of the receiving-end high-pressure valve group LCC includes: If the pressure drop reference value is within the controllable pressure adjustment range of the receiving end high pressure valve group LCC, then it is determined that the fault response capability of the receiving end high pressure valve group LCC is sufficient to cope with the current fault. If the pressure drop reference value exceeds the controllable pressure adjustment range of the receiving end high pressure valve group LCC, then it is determined that the fault response capability of the receiving end high pressure valve group LCC is insufficient to cope with the current fault.

7. The method according to claim 1, characterized in that, The controllable voltage regulation range of the receiving-end high-pressure valve group LCC is: [0, steady-state rated voltage].

8. A sending-end AC fault ride-through device, characterized in that, The device is applied to a hybrid cascaded ultra-high voltage direct current (UHVDC) transmission system at the receiving end. The UHVDC transmission system includes a sending-end converter station and a hybrid cascaded converter station at the receiving end. The sending-end converter station includes a sending-end LCC (Limited Control Center); the receiving-end hybrid cascaded converter station includes a receiving-end high-voltage valve group LCC (Limited Control Center) and a receiving-end MMC (Medium-voltage Control Center). The output terminal of the sending-end LCC is electrically connected to the input terminal of the receiving-end high-voltage valve group LCC. The output terminal of the receiving-end high-pressure valve group LCC is electrically connected to the input terminal of the receiving-end MMC; The device includes: Sending-end control module: used to control the sending-end LCC to switch to the fixed minimum firing angle control mode when an AC fault occurs in the sending-end converter station; Receiving-end control module: This module compares a predetermined step-down reference value with the controllable voltage regulation range of the receiving-end high-pressure valve group LCC to determine the fault response capability of the receiving-end high-pressure valve group LCC. If the fault response capability of the receiving-end high-pressure valve group LCC is sufficient to handle the current fault, the module controls the receiving-end high-pressure valve group LCC to switch to a constant DC control mode, allowing the receiving-end high-pressure valve group LCC to undertake all step-down tasks. If the fault response capability of the receiving-end high-pressure valve group LCC is insufficient to handle the current fault, the module controls the receiving-end MMC to switch to a voltage-power coordinated step-down mode, allowing the receiving-end MMC to undertake all step-down tasks.

9. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it causes the processor to perform the steps of the method as described in any one of claims 1 to 7.

10. A computer device, comprising a memory and a processor, characterized in that, The memory stores a computer program that, when executed by the processor, causes the processor to perform the steps of the method as described in any one of claims 1 to 7.

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