A differentiated blocking control method and device for a converter station of a marine wind power flexible direct current power transmission system

Abstract

The embodiment of the present specification provides a kind of offshore wind power flexible DC transmission system converter station's differentiated blocking control method and device, wherein the method comprises: real-time monitoring the operating state data of each bridge arm of the offshore converter station and the land converter station;When it is determined that any bridge arm of the offshore converter station occurs bridge arm abnormality, only the target bridge arm that occurs the bridge arm abnormality is executed blocking, the remaining bridge arm of the offshore converter station maintains operation;When it is determined that any bridge arm of the land converter station occurs bridge arm abnormality, all bridge arms of the land converter station are executed blocking.The technical effect that overvoltage level of offshore converter station and land converter station can be inhibited simultaneously is realized, thereby the insulation level requirement of key equipment of converter station is reasonably reduced, and the floor area of valve hall is reduced, simultaneously, without adding primary equipment, engineering implementation is convenient.

Description

Technical Field

[0001] The embodiments in this specification relate to the field of power electronics technology, and in particular to a differentiated interlocking control method and device for a converter station of an offshore wind power flexible DC transmission system. Background Technology

[0002] As offshore wind power development gradually extends into deeper waters, flexible DC transmission technology has become the mainstream technology for large-scale offshore wind power transmission due to its advantages such as transmission distance not being limited by AC cable charging current and the ability to achieve independent control of active and reactive power. Offshore wind power transmission systems via flexible DC typically consist of three main components: an offshore converter station, a DC submarine cable, and an onshore converter station. The offshore converter station, located on an offshore platform, is responsible for converting the AC power output from the wind farm into DC power for transmission. The onshore converter station, located at the onshore grid connection point, is responsible for inverting the DC power back into AC power and connecting it to the grid. Each converter station internally adopts a modular multilevel converter topology, containing a three-phase six-arm structure. Each arm consists of multiple series-connected submodules, which typically consist of a half-bridge or full-bridge topology and DC capacitors.

[0003] During the operation of flexible DC transmission systems, converter stations may experience abnormal increases in arm current due to AC-side faults, DC-side faults, or internal faults in the converter valves. To protect the converter valves and system safety, existing technologies typically employ arm current rate-of-change protection. When the current rate of change of a particular arm exceeds a preset protection setting, a blocking operation is triggered to cut off the fault current. Currently, the arm blocking control of converter stations in offshore wind power flexible DC transmission systems generally adopts a unified strategy: regardless of whether the converter station is offshore or onshore, when the current rate of change of a particular arm in any converter station reaches the protection setting, all six arms of that converter station are simultaneously blocked.

[0004] However, the aforementioned unified interlocking strategy has significant shortcomings in actual operation. Due to the fundamental difference in power transmission roles between offshore and onshore converter stations, the voltage of the converter valve submodule capacitors in an offshore converter station, as the power output end, is primarily determined by the station's own control strategy and interlocking method. In contrast, the voltage of the converter valve submodule capacitors in an onshore converter station, as the power receiving end, is affected not only by its own control strategy and interlocking method but also by the continuous charging effect of the power transmitted from the offshore converter station. Using the same interlocking strategy cannot effectively suppress the interlocking overvoltages at both converter stations simultaneously. Specifically, using full-arm interlocking in an offshore converter station leads to too many submodule capacitors being connected to the converter circuit simultaneously, causing higher inter-terminal overvoltages. Conversely, if a split-arm interlocking strategy is used in an onshore converter station, the overall interlocking time is prolonged, and the submodule capacitors are continuously charged during the interlocking process, ultimately resulting in a higher overvoltage level when all are interlocked. These overvoltage problems directly lead to higher insulation requirements for critical equipment in the converter station, resulting in a larger valve hall footprint, which is particularly unfavorable for scenarios with limited space on offshore platforms.

[0005] Therefore, a technical solution is needed that can configure differentiated blocking strategies according to the type of converter station, so as to simultaneously suppress post-fault blocking overvoltages in both offshore and onshore converter stations, thereby reducing the insulation design requirements and footprint of the converter stations. Summary of the Invention

[0006] In view of this, embodiments of this specification provide a differentiated interlocking control method for converter stations of offshore wind power flexible DC transmission systems. One or more embodiments of this specification also relate to a differentiated interlocking control device for converter stations of offshore wind power flexible DC transmission systems, to address the technical deficiencies existing in the prior art.

[0007] According to a first aspect of the embodiments of this specification, a differentiated interlocking control method for a converter station in an offshore wind power flexible DC transmission system is provided, wherein the offshore wind power flexible DC transmission system includes an offshore converter station and an onshore converter station, and the method includes: Real-time monitoring of the operational status data of each bridge arm of the offshore converter station and the onshore converter station; When it is determined that any arm of the offshore converter station has an abnormality, only the target arm with the abnormality is locked, while the other arms of the offshore converter station remain in operation. When any arm of the onshore converter station is determined to be abnormal, all arms of the onshore converter station are locked.

[0008] It should be noted that, based on the aforementioned operational status data, the corresponding interlocking responses are triggered independently for each of the two scenarios.

[0009] In one possible implementation, the real-time monitoring of the operating status data of each arm of the offshore converter station and the onshore converter station includes: acquiring the arm current change rate of each arm; comparing the arm current change rate with a preset protection setting; when the arm current change rate of any arm is greater than or equal to the preset protection setting, determining that the arm has an arm abnormality, and identifying the corresponding arm as the target arm.

[0010] In one possible implementation, the preset protection settings for the offshore converter station are configured independently of the preset protection settings for the onshore converter station.

[0011] In one possible implementation, the locking operation is performed only on the target bridge arm where the bridge arm anomaly occurs, which includes sending a locking command to each submodule within the target bridge arm.

[0012] In one possible implementation, the method further includes: when the absolute value of the current of any arm in the offshore converter station or the onshore converter station exceeds the valve-controlled overcurrent protection setting, triggering the valve-controlled overcurrent protection action of the corresponding converter station, and cooperating with the target arm lockout or full arm lockout to protect the converter valve.

[0013] In one possible implementation, the fault type that causes the bridge arm abnormality includes at least one of the following: converter transformer grid-side fault, converter transformer valve-side fault, or DC submarine cable fault.

[0014] In one possible implementation, each bridge arm comprises 200 to 500 sub-modules.

[0015] In one possible implementation, the DC voltage level of the flexible DC transmission system is ±200kV to ±800kV.

[0016] According to a second aspect of the embodiments of this specification, a differentiated interlocking control device is provided for a converter station of an offshore wind power flexible DC transmission system, the offshore wind power flexible DC transmission system including an offshore converter station and an onshore converter station, comprising: The data acquisition module is configured to monitor the operating status data of each bridge arm of each converter station in real time, and determine whether the bridge arm of the converter station has an abnormality based on the operating status data. The differentiated blocking decision module is configured to select a blocking strategy based on the type of converter station where the bridge arm anomaly occurs: if it is the offshore converter station, a partial blocking command is output, and only the target bridge arm where the bridge arm anomaly occurs is blocked, while the other bridge arms remain in operation; if it is the onshore converter station, a full bridge arm blocking command is output, and all bridge arms are blocked. The locking execution module is connected to the differentiated locking decision module and is configured to receive the partial locking command or the full bridge arm locking command and execute the corresponding locking operation.

[0017] In one possible implementation, the data acquisition module includes: A current sensor is configured to collect current sampling values ​​from each bridge arm; A differential calculation unit, connected to the current sensor, is configured to perform differential calculations on the current sampled value to obtain the bridge arm current change rate. The comparison unit, connected to the differential calculation unit, is configured to compare the rate of change of the bridge arm current with a preset protection setting, and output a bridge arm abnormal signal when the rate of change of the bridge arm current is greater than or equal to the preset protection setting.

[0018] One embodiment of this specification achieves the following beneficial effects: Because the offshore converter station employs a partial blocking strategy that only blocks the target bridge arm, the number of sub-modules connected to the converter circuit when the converter valve is blocked is significantly reduced, and the voltage fluctuation amplitude between the converter valve terminals is consequently reduced, effectively suppressing the overvoltage level of the offshore converter station. Because the onshore converter station employs a strategy that triggers simultaneous blocking of all bridge arms upon any bridge arm anomaly, the time interval from the occurrence of a bridge arm anomaly to the completion of blocking of all bridge arms is significantly shortened, effectively controlling the continuous charging increase of the sub-module capacitor voltage during this period, thus significantly reducing the overvoltage level when all bridge arms of the onshore converter station are blocked. The synergistic effect of these two strategies allows for the simultaneous suppression of overvoltage levels in both offshore and onshore converter stations, thereby reasonably reducing the insulation level requirements of key equipment in the converter station and reducing the valve hall footprint. This invention does not require additional primary equipment; the above effects can be achieved through differentiated configuration of secondary control and protection strategies, making engineering implementation convenient. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the submodule status before and after the converter valve is locked after a fault in a certain bridge arm in a converter station in the existing technology; Figure 2 This is a flowchart of a differentiated interlocking control method for a converter station of an offshore wind power flexible DC transmission system, provided in one embodiment of this specification. Figure 3 This is a flowchart of the offshore converter station arm interlocking control method provided in one embodiment of the present specification for a differentiated interlocking control method of an offshore wind power flexible DC transmission system converter station; Figure 4 This is a flowchart of the onshore converter station arm interlocking control method of a differentiated interlocking control method for a converter station of an offshore wind power flexible DC transmission system, provided in one embodiment of this specification. Figure 5This is a comparison diagram of overvoltage waveforms between converter valve terminals in an embodiment of this specification for an offshore converter station; Figure 6 This is a comparison diagram of overvoltage waveforms between converter valve terminals in an onshore converter station provided in one embodiment of this specification. Detailed Implementation

[0020] Many specific details are set forth in the following description to provide a full understanding of this specification. However, this specification can be implemented in many other ways than those described herein, and those skilled in the art can make similar extensions without departing from the spirit of this specification. Therefore, this specification is not limited to the specific implementations disclosed below.

[0021] The terminology used in one or more embodiments of this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the one or more embodiments of this specification. The singular forms “a” and “the” as used in one or more embodiments of this specification and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in one or more embodiments of this specification refers to and includes any or all possible combinations of one or more associated listed items.

[0022] It should be understood that although the terms first, second, etc., may be used to describe various information in one or more embodiments of this specification, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, first may also be referred to as second without departing from the scope of one or more embodiments of this specification, and similarly, second may also be referred to as first. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to a determination."

[0023] In existing technologies, converter stations in offshore wind power flexible DC transmission systems generally adopt a unified arm blocking control strategy. When the electrical operating parameters of one arm in any converter station trigger protection conditions, all six arms of that converter station are synchronously blocked. The design logic of this strategy stems from the need for rapid interruption of fault current, that is, by maximizing the blocking range to ensure that the fault current is quickly suppressed, thereby protecting the converter valves and system safety.

[0024] The reason for this lies in the fact that the strategy fails to consider the fundamental differences in the power transmission roles of offshore and onshore converter stations, and the resulting differences in the formation mechanisms of submodule capacitor voltages. As the power transmitting end, the voltage of the submodule capacitors in the converter valves of an offshore converter station is primarily determined by its own control strategy and blocking method. The number of submodules connected to the converter circuit after blocking directly determines the magnitude of the voltage fluctuation between the converter valve terminals. As the power receiving end, the voltage of the submodule capacitors in the converter valves of an onshore converter station is not only affected by its own control strategy and blocking method, but also continuously charged by the power transmitted from the offshore converter station. The cumulative capacitor voltage at the moment of blocking directly determines the final overvoltage level.

[0025] The root cause of this deficiency lies in the fact that existing blocking methods are designed with the goal of quickly interrupting fault current, without considering how to suppress post-fault blocking overvoltage. While full-arm blocking can quickly interrupt fault current, it leads to too many submodule capacitors being connected to the circuit simultaneously in offshore converter stations, causing higher inter-terminal overvoltages. While split-arm blocking can reduce the number of connected submodules, it prolongs the overall blocking time of onshore converter stations, and the submodule capacitor voltage continues to rise during the step-by-step blocking process, ultimately resulting in a higher overvoltage level when all modules are blocked.

[0026] like Figure 1 As shown, before the converter valve locks out after the fault occurs ( Figure 1 (a) During operation, the submodules in each arm of the converter valve are in the engaged or bypassed state according to the normal modulation strategy, with current flowing through both the upper and lower arms, and the capacitor voltage of each submodule is at the rated operating level. When the full arm interlocking action is triggered ( Figure 1 (b) In this configuration, all IGBTs in all submodules of all bridge arms are turned off, and the bridge arm current freewheels through the anti-parallel diodes of each submodule. This freewheeling path forces all submodule capacitors to be connected in series in the converter circuit. Under these conditions, the voltage between the converter valve terminals is the sum of the voltages of all submodule capacitors within the bridge arm, which is much higher than the voltage between the bridge arm terminals during normal operation, resulting in a high overvoltage across the converter valve. This overvoltage places higher demands on the insulation level of the converter equipment, correspondingly increasing the footprint of the valve hall, which is particularly disadvantageous for offshore converter stations with limited platform space. Furthermore, if the same blocking method is adopted for onshore converter stations as for offshore converter stations, the overvoltage formation characteristics of the two converter stations differ, and the aforementioned unified strategy cannot simultaneously address the overvoltage suppression effect of both converter stations.

[0027] Therefore, the technical problem faced by the existing technology is that the unified bridge arm blocking control scheme adopted by the offshore converter station and the onshore converter station in the offshore wind power flexible DC transmission system cannot effectively suppress the blocking overvoltage after the fault of the converter stations at both ends. This results in higher insulation level requirements for the key equipment of the converter station, a larger valve hall area, and increased equipment investment costs.

[0028] In view of this, there is a need for a technical solution that can configure differentiated blocking according to the type of converter station, so as to simultaneously suppress the blocking overvoltage after a fault in both offshore and onshore converter stations, and reduce the insulation design requirements and footprint of the converter station.

[0029] This specification provides a differentiated interlocking control method and apparatus for converter stations in offshore wind power flexible DC transmission systems to address the aforementioned technical problems. By configuring differentiated arm interlocking conditions based on the role of the converter station in the power transmission system, and adapting to the different submodule capacitor voltage formation mechanisms at both converter stations, it simultaneously reduces the post-fault interlocking overvoltage level at both converter stations without increasing hardware investment. Detailed descriptions are provided in the following embodiments.

[0030] See Figure 2 , Figure 2 A flowchart illustrating a differentiated interlocking control method for a converter station in an offshore wind power flexible DC transmission system according to an embodiment of this specification is shown. The offshore wind power flexible DC transmission system includes an offshore converter station and an onshore converter station. In the scenario described in this specification, the DC voltage level of the flexible DC transmission system can be ±200kV to ±800kV. In some embodiments, the DC voltage level can be selected as ±400kV to ±600kV, achieving a good balance between transmission capacity and engineering feasibility. In at least one embodiment, the DC voltage level can be ±500kV. The method specifically includes the following steps.

[0031] Step 101: Monitor the operational status data of each bridge arm of the offshore converter station and the onshore converter station in real time; Real-time monitoring of the operating status data of each bridge arm in each converter station is used to obtain the electrical operating parameters of the bridge arm and provide input for anomaly detection. The operating status data may include at least one of the parameters such as bridge arm current, bridge arm voltage, and bridge arm temperature. In one or more embodiments, the operating status data includes at least the bridge arm current. By performing differential or derivative operations on the bridge arm current, the rate of change of the bridge arm current is obtained and used to determine whether an anomaly has occurred in the bridge arm.

[0032] By monitoring the operational status data of each bridge arm in real time, this method can promptly detect bridge arm anomalies, avoiding missed or false diagnoses and providing accurate trigger signals for the subsequent execution of differentiated blocking strategies. Because the monitoring granularity is refined to the individual bridge arm, compared to a unified assessment of the entire converter station, it can more accurately locate the source of the anomaly and reduce unnecessary blocking operations.

[0033] In one or more embodiments, monitoring the operating status data of each bridge arm may include: acquiring the bridge arm current change rate of each bridge arm; comparing the bridge arm current change rate with a preset protection setting; when the bridge arm current change rate of any bridge arm is greater than or equal to the preset protection setting, determining that the bridge arm has an abnormality, and identifying the corresponding bridge arm as the target bridge arm. By introducing the bridge arm current change rate as a specific abnormality judgment indicator, compared with the method of only monitoring the current amplitude, the current change rate can reflect the transient change trend of the current, and can detect the abnormal upward trend in the early stage of the fault, thereby providing an earlier triggering opportunity for the differentiated blocking strategy. Because the triggering opportunity is earlier, the blocking operation can be executed before the overvoltage has accumulated sufficiently, further enhancing the overvoltage suppression effect. In some embodiments, the bridge arm current change rate can be obtained by performing differential operations on the current sampling values ​​of each bridge arm. Differential operations can directly reflect the transient change trend of the current, and have a faster response speed than differential or filtering methods, which helps to detect the abnormal upward trend of the bridge arm current in a timely manner. In practical implementation, both offshore and onshore converter stations typically include six bridge arms, divided into three phases, with each phase consisting of an upper bridge arm and a lower bridge arm. Local interlocking in offshore converter stations is executed independently of each phase. The three-phase, six-bridge-arm structure is the standard topology for modular multilevel converters. The independent execution of local interlocking across phases means that an abnormality in one phase's bridge arm will not affect the normal operation of other phases, improving system redundancy and reliability.

[0034] For example, the six bridge arms are divided into phases A, B, and C. The upper and lower bridge arms of each phase are connected in series between the DC positive line and the AC connection point. The partial blocking is executed independently between each phase, which means that when a bridge arm of phase A is blocked due to an abnormality, the bridge arms of phases B and C are not affected and can still maintain normal operation.

[0035] In one or more embodiments, the preset protection settings for offshore converter stations and onshore converter stations can be configured independently. Since the rated current, fault current rise rate, and other operating parameters differ between offshore and onshore converter stations, independently configuring the protection settings allows the anomaly detection conditions at both ends to be adapted to their respective operating characteristics, avoiding either a setting that is too lenient leading to missed detections or too strict leading to false detections, thereby improving protection sensitivity.

[0036] Based on the monitoring results of step 101, and according to the type of converter station where the bridge arm anomaly occurred, the following two parallel blocking processing branches are triggered independently: When it is determined that any of the bridge arms of the offshore converter station has an abnormality, step 102 is executed; When it is determined that any arm of the onshore converter station has an abnormality, step 103 is executed.

[0037] The two branch conditions mentioned above are independent of each other and can be triggered individually, or they can be triggered simultaneously when bridge arm anomalies occur at both the offshore and onshore converter stations, without interfering with each other.

[0038] Step 102 (Offshore Converter Station Branch): When it is determined that any arm of the offshore converter station has an abnormality, only the target arm with the abnormality is locked, and the other arms of the offshore converter station continue to operate. By locking only the target bridge arm, this method reduces the number of submodules connected to the converter circuit after fault locking, thereby reducing the voltage fluctuation amplitude between converter valve terminals in offshore converter stations and thus reducing overvoltage levels. Since the submodule capacitor voltage in offshore converter stations is mainly determined by their own control strategies and locking methods, reducing the number of connected submodules directly reduces the total capacitor voltage, achieving overvoltage suppression. In one or more embodiments, each bridge arm may include 200 to 500 submodules. If the number of submodules in each bridge arm is less than 200, the submodule capacitor voltage is high, increasing the voltage load on individual devices and potentially affecting system reliability; if the number of submodules in each bridge arm is more than 500, the control system complexity and cost increase significantly, and additional control delays may be introduced. In some embodiments, each bridge arm may optionally include 300 to 400 submodules, achieving a better balance between system reliability and control complexity. In at least one embodiment, each bridge arm may include 500 submodules.

[0039] Reference Figure 3 In one or more embodiments, the step of locking only the target bridge arm where the bridge arm anomaly occurs includes sending a locking command to each submodule within the target bridge arm. By sending locking commands only to the target bridge arm, erroneous operations affecting normal bridge arms are avoided, maintaining partial operational capability of the offshore converter station while ensuring accurate execution of the local locking. In some embodiments, the submodule may include at least one of a half-bridge submodule or a full-bridge submodule. In some embodiments, after locking the target bridge arm, monitoring of the remaining bridge arms of the offshore converter station continues, and when any of the remaining bridge arms experiences a bridge arm anomaly, locking is performed on that bridge arm. Through continuous monitoring, subsequent anomalies in other bridge arms after local locking can be detected in a timely manner, and additional locking can be added, preventing the spread of faults after a single bridge arm locking and improving the overall system safety.

[0040] Step 103 (Onshore Converter Station Branch): When it is determined that any bridge arm of the onshore converter station has an abnormality, all bridge arms of the onshore converter station are locked.

[0041] By synchronously locking all bridge arms, this method cuts off the fault current loop in one go, preventing the submodule capacitor voltage from continuously rising during the step-by-step locking process. This reduces the cumulative capacitor voltage at the moment of full-arm locking of the onshore converter station, thereby lowering the overvoltage level. Since the submodule capacitor voltage of the onshore converter station has been continuously charged by the offshore converter station before locking, synchronous locking of all bridge arms can prevent the capacitor voltage from continuing to accumulate during the locking process.

[0042] It should be noted that steps 102 and 103 are two independent condition-triggered branches, which are triggered independently by the abnormal events of the bridge arms of the offshore converter station and the onshore converter station, respectively. There is no sequential dependency between the two, and they can be executed separately or simultaneously depending on the actual fault occurrence.

[0043] Reference Figure 4 In one or more embodiments, locking all bridge arms of the onshore converter station may include: synchronously sending lockout commands to the submodules of all six bridge arms of the onshore converter station. By synchronously sending the lockout commands, delays in locking some bridge arms due to timing differences are avoided, preventing the capacitor voltage from continuing to rise within the timing difference and ensuring that the fault circuit is disconnected in one go.

[0044] In summary, the partial blocking strategy of offshore converter stations reduces overvoltage by decreasing the number of connected submodules, while the full-bridge arm blocking strategy of onshore converter stations reduces overvoltage by preventing the continuous accumulation of capacitor voltage. The two strategies are adapted to the different capacitor voltage formation mechanisms of the two converter stations, forming differentiated overvoltage suppression schemes.

[0045] The method may further include: Step 104: When the absolute value of the current in any arm of the offshore converter station or the onshore converter station exceeds the valve-controlled overcurrent protection setting, the valve-controlled overcurrent protection action of the corresponding converter station is triggered, which works in conjunction with the target arm lockout or the full arm lockout to protect the converter valve.

[0046] Valve-controlled overcurrent protection, acting as backup protection, works in conjunction with arm current rate of change protection to prevent system risks caused by the failure of a single protection, thus improving the overall safety of the converter valve. In conjunction with the overall technical solution of the differentiated interlocking control method described in steps 101 to 103 above, the introduction of valve-controlled overcurrent protection as an auxiliary protection means expands the protection system of the differentiated interlocking strategy from a single protection to a multi-protection synergy. Arm current rate of change protection, as the primary protection, can respond quickly in the early stages of a fault, triggering the differentiated interlocking strategy; valve-controlled overcurrent protection, as backup protection, provides a second layer of protection when the interlocking protection fails to act in time or the fault current continues to increase. The two protections work together to form a dual protection system with rapid response and deep protection, further improving the safety of the converter valve under fault conditions.

[0047] In one or more embodiments, the fault types that trigger the bridge arm anomaly include at least one of a converter transformer grid-side fault, a converter transformer valve-side fault, or a DC submarine cable fault. Grid-side faults are typically caused by AC grid disturbances, with the fault current transmitted to the converter valve bridge arm via the converter transformer; valve-side faults occur between the converter transformer and the converter valve, with the fault current acting directly on the bridge arm; DC submarine cable faults occur on the DC side, with the fault current transmitted through the DC line. All three fault types result in rapid changes in the bridge arm current, triggering bridge arm current change rate protection, and subsequently initiating a differentiated blocking strategy.

[0048] Corresponding to the above method embodiments, according to a second aspect of the embodiments of this specification, a differentiated interlocking control device for a converter station of an offshore wind power flexible DC transmission system is provided, the offshore wind power flexible DC transmission system including an offshore converter station and an onshore converter station, comprising: The data acquisition module is configured to monitor the operating status data of each bridge arm of each converter station in real time, and determine whether the bridge arm of the converter station has an abnormality based on the operating status data. The differentiated blocking decision module is configured to select a blocking strategy based on the type of converter station where the bridge arm anomaly occurs: if it is the offshore converter station, a partial blocking command is output, and only the target bridge arm where the bridge arm anomaly occurs is blocked, while the other bridge arms remain in operation; if it is the onshore converter station, a full bridge arm blocking command is output, and all bridge arms are blocked. The locking execution module is connected to the differentiated locking decision module and is configured to receive the partial locking command or the full bridge arm locking command and execute the corresponding locking operation.

[0049] In one or more embodiments, the data acquisition module includes: A current sensor is configured to collect current sampling values ​​from each bridge arm; A differential calculation unit, connected to the current sensor, is configured to perform differential calculations on the current sampled value to obtain the bridge arm current change rate. The comparison unit, connected to the differential calculation unit, is configured to compare the rate of change of the bridge arm current with a preset protection setting, and output a bridge arm abnormal signal when the rate of change of the bridge arm current is greater than or equal to the preset protection setting.

[0050] The following example, using the application of a differentiated interlocking control method for a converter station of a flexible DC transmission system for offshore wind power provided in this specification in a certain offshore wind power transmission system, further illustrates the method.

[0051] (1) Application scenarios and implementation plans: A simulation verification was conducted for an offshore wind power transmission system with a DC voltage of ±500kV, each bridge arm comprising 500 sub-modules, and each sub-module having an average voltage of 2kV. Three schemes were compared: a segmented bridge arm blocking strategy for the offshore converter station, a full-bridge arm blocking strategy for the onshore converter station (hereinafter referred to as Scheme 1), a full-bridge arm blocking strategy for both the offshore and onshore converter stations (hereinafter referred to as Scheme 2), and a segmented bridge arm blocking strategy for both the offshore and onshore converter stations (hereinafter referred to as Scheme 3). Under these three blocking schemes, simulation analysis was performed on typical faults that are prone to occur in the converter station.

[0052] (2) Fault settings: Faults were set at different locations, including the converter transformer grid side, converter transformer valve side, bridge arm reactor valve side, DC pole line, and DC submarine cable, with fault times set to 3.15s, 3.16s...3.17s, and the overvoltage level after the fault was analyzed.

[0053] (3) Simulation results: like Figure 5 As shown, the waveforms of the overvoltage between the upper and lower arm converter valves of the offshore converter station differ in Schemes 1, 2, and 3. When Schemes 1 and 3 are adopted, the overvoltage between the upper and lower arm converter valves of the offshore converter station is approximately 1945kV; when Scheme 2 is adopted, the overvoltage between the upper and lower arm converter valves of the offshore converter station is approximately 1989kV. When the offshore converter station adopts a segmented arm blocking strategy, the overvoltage between the converter valves can be reduced by approximately 44kV compared to a full-arm blocking strategy.

[0054] The mechanism behind these differences lies in the fact that, as the power output end, the voltage of the converter valve submodule capacitors in an offshore converter station is primarily determined by the station's own control strategy and interlocking method. When Scheme 2 (full-arm interlocking) is used, all six arm submodules engage simultaneously, resulting in a large number of submodule capacitors being connected to the converter circuit at the same time. This leads to a significant voltage fluctuation between the converter valve terminals and a higher overvoltage level. When Scheme 1 or Scheme 3 (partial arm interlocking) is used, only the target arm experiencing an anomaly is interlocked, while the remaining arms maintain normal operation. This reduces the number of submodules connected to the converter circuit, correspondingly lowering the voltage fluctuation between the converter valve terminals and thus reducing the overvoltage level.

[0055] like Figure 6 As shown, the waveforms of the overvoltage between the upper and lower arm converter valves of the onshore converter station differ in Schemes 1, 2, and 3. When Schemes 1 and 2 are adopted, the overvoltage between the upper and lower arm converter valves of the onshore converter station is approximately 2100kV; when Scheme 3 is adopted, the overvoltage between the upper and lower arm converter valves of the onshore converter station is approximately 2350kV. When the onshore converter station adopts a full-arm blocking strategy, the overvoltage between the converter valves can be reduced by approximately 250kV compared to a split-arm blocking strategy.

[0056] The mechanism behind this difference lies in the fact that, as the power receiving end, the onshore converter station's converter valve submodule capacitor voltage is continuously charged by the power transmitted from the offshore converter station before the lockout. When Scheme 3 (partial arm lockout) is adopted, after the first locked arm is taken out of operation, the unlocked arms will continue to receive power from the offshore converter station, causing their submodule capacitor voltage to continuously rise during the lockout waiting period, resulting in a higher overvoltage level when all arms are locked out. When Scheme 1 or Scheme 2 (full arm lockout) is adopted, all arms are locked out at the same time or within a very short time window, cutting off the power transmission path from the offshore converter station to the onshore converter station in one go. This eliminates the continuous accumulation of capacitor voltage during the partial lockout process, minimizing the accumulated capacitor voltage at the moment of full arm lockout, thereby reducing the overvoltage level.

[0057] Further analysis reveals that while Scheme 2 (using full-arm blocking at both ends) can reduce the overvoltage of the onshore converter station, it leads to an increase in the overvoltage of the offshore converter station (1989kV). Scheme 3 (using partial-arm blocking at both ends) can reduce the overvoltage of the offshore converter station, but it leads to a significant increase in the overvoltage of the onshore converter station (2350kV). Only Scheme 1 (partial-arm blocking at the offshore station and full-arm blocking at the onshore station) can simultaneously address the overvoltage at both ends, maintaining the overvoltage of the offshore converter station at 1945kV and the overvoltage of the onshore converter station at 2100kV, thus achieving an overall reduction in overvoltage levels.

[0058] In summary, in the embodiments described above in this specification, Scheme 1, which employs a split-arm blocking strategy for offshore converter stations and a full-arm blocking strategy for onshore converter stations, can simultaneously reduce the overvoltage levels between the converter valve terminals of both offshore and onshore converter stations. This scheme eliminates the need for additional primary equipment; overvoltage suppression can be achieved solely through differentiated configurations of secondary control and protection strategies, thereby reducing the insulation design requirements for critical equipment in the converter station.

[0059] The foregoing has described specific embodiments of this specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in a different order than that shown in the embodiments and may still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require the specific or sequential order shown to achieve the desired result. In some embodiments, multitasking and parallel processing are possible or may be advantageous.

[0060] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that the embodiments in this specification are not limited to the described order of actions, because according to the embodiments in this specification, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in this specification are all preferred embodiments, and the actions and modules involved are not necessarily essential to the embodiments in this specification.

[0061] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0062] The preferred embodiments disclosed above are merely illustrative of this specification. The optional embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the embodiments described herein. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the embodiments, thereby enabling those skilled in the art to better understand and utilize this specification. This specification is limited only by the claims and their full scope and equivalents.

Claims

1. A differentiated interlocking control method for a converter station in an offshore wind power flexible DC transmission system, wherein the offshore wind power flexible DC transmission system includes an offshore converter station and an onshore converter station, characterized in that, The method includes: Real-time monitoring of the operational status data of each bridge arm of the offshore converter station and the onshore converter station; When it is determined that any arm of the offshore converter station has an abnormality, only the target arm with the abnormality is locked, while the other arms of the offshore converter station remain in operation. When any arm of the onshore converter station is determined to be abnormal, all arms of the onshore converter station are locked.

2. The method according to claim 1, characterized in that, The real-time monitoring data of the operating status of each bridge arm of the offshore converter station and the onshore converter station includes: Obtain the rate of change of bridge arm current for each bridge arm; The rate of change of the bridge arm current is compared with a preset protection setting. When the rate of change of the bridge arm current of any bridge arm is greater than or equal to the preset protection setting, it is determined that the bridge arm has an abnormality, and the corresponding bridge arm is identified as the target bridge arm.

3. The method according to claim 2, characterized in that, The preset protection settings for the offshore converter station are configured independently of those for the onshore converter station.

4. The method according to claim 1, characterized in that, The method of locking only for the target bridge arm where the bridge arm anomaly occurs includes: Send a locking command to each submodule within the target bridge arm.

5. The method according to claim 1, characterized in that, The method further includes: When the absolute value of the current in any arm of the offshore or onshore converter station exceeds the valve-controlled overcurrent protection setting, the valve-controlled overcurrent protection action of the corresponding converter station is triggered, which works in conjunction with the target arm lockout or full arm lockout to protect the converter valve.

6. The method according to claim 1, characterized in that, The fault types that cause the bridge arm abnormality include at least one of the following: converter transformer grid-side fault, converter transformer valve-side fault, or DC submarine cable fault.

7. The method according to claim 1, characterized in that, Each bridge arm comprises 200 to 500 sub-modules.

8. The method according to claim 1, characterized in that, The DC voltage level of the flexible DC transmission system is ±200kV to ±800kV.

9. A differentiated interlocking control device for a converter station in an offshore wind power flexible DC transmission system, wherein the offshore wind power flexible DC transmission system includes an offshore converter station and an onshore converter station, characterized in that, include: The data acquisition module is configured to monitor the operating status data of each bridge arm of each converter station in real time, and determine whether the bridge arm of the converter station has an abnormality based on the operating status data. The differentiated blocking decision module is configured to select a blocking strategy based on the type of converter station where the bridge arm anomaly occurs: if it is the offshore converter station, a partial blocking command is output, and only the target bridge arm where the bridge arm anomaly occurs is blocked, while the other bridge arms remain in operation; if it is the onshore converter station, a full bridge arm blocking command is output, and all bridge arms are blocked. The locking execution module is connected to the differentiated locking decision module and is configured to receive the partial locking command or the full bridge arm locking command and execute the corresponding locking operation.

10. The differentiated interlocking control device according to claim 9, characterized in that, The data acquisition module includes: A current sensor is configured to collect current sampling values ​​from each bridge arm; A differential calculation unit, connected to the current sensor, is configured to perform differential calculations on the current sampled value to obtain the bridge arm current change rate. The comparison unit, connected to the differential calculation unit, is configured to compare the rate of change of the bridge arm current with a preset protection setting, and output a bridge arm abnormal signal when the rate of change of the bridge arm current is greater than or equal to the preset protection setting.

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