Transient overvoltage suppression method and device after direct current commutation failure

Abstract

The invention discloses a transient overvoltage suppression method and a transient overvoltage suppression device after a direct current commutation failure, which are used for solving the technical problem that in the prior art, after the direct current commutation failure occurs, low-pass reactive power withdrawal of a near-region power grid and network type equipment is not timely in the process that the power grid voltage is converted from low to high. The method is applied to a wind power direct-current delivery system, the wind power direct-current delivery system comprises a wind power plant and a direct-current converter station, and when a direct-current fault occurs in the system, whether the distance between the wind power plant and the direct-current converter station is smaller than a preset distance threshold value or not is judged; if yes, judging whether the direct current fault is a direct current commutation failure fault or not by adopting an inter-station signal cooperation judgment strategy; if not, judging whether the direct-current fault is a direct-current commutation failure fault or not by adopting a fan characteristic judgment strategy; and when the judgment result is the direct current commutation failure fault, generating a commutation failure signal, and based on the commutation failure signal, performing fan reactive withdrawal according to a reactive withdrawal control strategy.

Description

Technical Field

[0001] The present invention relates to the technical field of power system control, and in particular to a method for suppressing transient overvoltage after a DC commutation failure, a device for suppressing transient overvoltage after a DC commutation failure, an electronic device and a storage medium. Background Art

[0002] With the increasing demand for electricity in my country and the large-scale access to renewable energy, new energy generation technologies represented by wind power have developed rapidly. However, when large-scale wind power is transmitted via grid-commutated high-voltage direct current (LCC-HVDC) transmission (hereinafter referred to as wind power transmission system via DC), it is susceptible to DC system failures. When DC fails to lock and commutation fails, the reactive power balance between the converter station and the wind farm is broken. A large amount of surplus reactive power flows into the DC sending system, causing transient overvoltage in the DC sending system, and even exceeding the voltage range for stable operation of the wind turbine. Once this happens, it is easy to cause wind turbines to be disconnected from the grid and chain reactions, which in turn leads to system collapse, seriously threatening the safe and stable operation of the system.

[0003] Existing wind turbines are basically equipped with complete high and low voltage ride-through control strategies. In addition, reactive power compensation devices such as SVG (Static Var Generator) are generally installed in the station to improve the voltage stability of the wind farm.

[0004] However, in the case of a DC commutation failure, since the transient voltage of the power grid at the sending end presents a "first low and then high" characteristic, the reactive power generated by the wind turbine through low-through control in the low-voltage stage is difficult to withdraw in time. After the transient voltage recovers, the wind turbine will increase the transient peak voltage, thereby worsening the transient voltage. The connected SVG will also affect the transient overvoltage at the wind turbine end. At present, it is not ruled out that the SVG in the station also has the above risks, resulting in restrictions on the reactive compensation configuration. Therefore, it is very necessary to adjust and optimize the transient characteristics of grid-connected power electronic equipment including DC near-field wind turbines and supporting SVG in wind power collection stations to curb the risks brought about by further increases in transient overvoltages. Summary of the invention

[0005] The present invention provides a method for suppressing transient overvoltage after a DC commutation failure, a device for suppressing transient overvoltage after a DC commutation failure, an electronic device and a storage medium, which are used to solve or partially solve the technical problem in the existing related technology that after a DC commutation failure occurs, the low-voltage reactive power of the nearby power grid and the grid-following equipment is not withdrawn in time during the process of the power grid voltage changing from low to high.

[0006] The present invention provides a method for suppressing transient overvoltage after a DC commutation failure, which is applied to a wind power transmission system via DC. The wind power transmission system via DC includes a wind farm and a DC converter station. The method includes:

[0007] When a DC fault occurs in the system, determining whether the distance between the wind farm and the DC converter station is less than a preset distance threshold;

[0008] If yes, then the inter-station signal coordinated determination strategy is adopted to determine whether the DC fault is a DC commutation failure fault;

[0009] If not, a fan characteristic determination strategy is adopted to determine whether the DC fault is a DC commutation failure fault;

[0010] When the judgment result is a DC commutation failure fault, a commutation failure signal is generated, and based on the commutation failure signal, reactive power withdrawal of the wind turbine is performed according to a reactive power withdrawal control strategy.

[0011] Optionally, the adopting of an inter-station signal coordinated determination strategy to determine whether the DC fault is a DC commutation failure fault includes:

[0012] Obtaining the DC side current of the DC converter station and the terminal voltage of the wind turbine in the wind farm;

[0013] Determining whether the DC side current is greater than a DC overcurrent detection threshold, and generating an overcurrent detection signal;

[0014] If the signal value of the overcurrent detection signal is 1, a DC overcurrent fault occurs in the DC converter station;

[0015] If the signal value of the overcurrent detection signal is 0, no DC overcurrent fault occurs in the DC converter station;

[0016] Determine whether the terminal voltage is lower than a preset low breakdown voltage threshold, and generate a low breakdown control signal;

[0017] If the signal value of the low wear control signal is 1, the fan is in a low wear operation mode;

[0018] If the signal value of the low-breakthrough control signal is not 1, the fan is not in the low-breakthrough operation mode; the low-breakthrough operation mode indicates that the terminal voltage is lower than the preset low-breakthrough voltage threshold;

[0019] If the signal value of the overcurrent detection signal is 1, and / or the signal value of the low-through control signal is 1, and the signal value after the AND operation based on the overcurrent detection signal and the low-through control signal is 1, then the DC fault is determined to be a DC commutation failure fault.

[0020] Optionally, the adopting of a fan characteristic determination strategy to determine whether the DC fault is a DC commutation failure fault includes:

[0021] Obtaining the terminal voltage of the wind turbine in the wind farm;

[0022] When the terminal voltage is lower than the preset low voltage threshold, firstly perform three-phase voltage symmetry detection on the DC fault, then perform voltage amplitude detection, and then perform voltage drop change rate analysis;

[0023] On the basis that the machine-end voltage is lower than a preset low-breakdown voltage threshold, when the DC fault is a three-phase symmetrical fault, and the voltage amplitude after the fault meets the preset fault condition, and the voltage drop after the fault is a gradual process, it is determined that the DC fault is a DC commutation failure fault.

[0024] Optionally, when the terminal voltage is lower than a preset low-breakdown voltage threshold, firstly performing a three-phase voltage symmetry detection on the DC fault, then performing a voltage amplitude detection, and then performing a voltage drop change rate analysis, including:

[0025] When the terminal voltage is lower than the preset low breakdown voltage threshold:

[0026] The DC fault is symmetrically detected by three-phase voltage symmetry detection to obtain a symmetrical fault detection result; the symmetrical fault detection result is that the DC fault is a three-phase symmetrical fault, or an asymmetrical fault; the three-phase symmetrical fault includes a three-phase ground short circuit fault and a DC commutation failure fault;

[0027] Performing voltage fault detection on the three-phase symmetrical fault by voltage amplitude detection;

[0028] When the post-fault voltage amplitude of the three-phase symmetrical fault is greater than a preset fault voltage threshold, the DC fault is preliminarily determined to be a DC commutation failure fault;

[0029] When the post-fault voltage amplitude of the three-phase symmetrical fault is less than or equal to a preset fault voltage threshold, the DC fault is preliminarily determined to be a three-phase ground short circuit fault;

[0030] Performing voltage drop change rate analysis on the three-phase symmetrical fault to perform secondary judgment on the DC fault;

[0031] When the post-fault voltage drop of the three-phase symmetrical fault is a step-type process, the DC fault is finally determined to be a three-phase ground short circuit fault;

[0032] When the post-fault voltage drop of the three-phase symmetrical fault is a gradual process, and the post-fault voltage amplitude is greater than a preset fault voltage threshold, the DC fault is finally determined to be a DC commutation failure fault.

[0033] Optionally, the step of performing reactive power withdrawal of the wind turbine according to a reactive power withdrawal control strategy based on the commutation failure signal includes:

[0034] generating a reactive power withdrawal signal according to the commutation failure signal;

[0035] When the distance between the wind farm and the DC converter station is less than a preset distance threshold, based on the reactive power withdrawal signal, after a first setting delay, the wind turbines in the wind farm are controlled to exit the low-throughput operation mode and switch to the steady-state operation mode to achieve reactive power withdrawal of the wind turbines;

[0036] When the distance between the wind farm and the DC converter station is greater than or equal to a preset distance threshold, based on the reactive power withdrawal signal, after a second setting delay, the wind turbines in the wind farm are controlled to exit the low-throughput operation mode and switch to the steady-state operation mode to achieve reactive power withdrawal of the wind turbines.

[0037] Optionally, the first setting delay is obtained by subtracting the peak current time and the inter-station signal communication delay from the delay time constant; the second setting delay is obtained by subtracting the peak current time from the delay time constant; wherein the delay time constant is the duration of the low voltage process of the nearby power grid after a DC commutation failure occurs; the peak current time is the time for the DC side current to climb to the DC overcurrent detection threshold after a DC commutation failure occurs; and the inter-station signal communication delay is the communication time required for the DC converter station to send an overcurrent detection signal to the wind farm.

[0038] Optionally, the determining whether the distance between the wind farm and the DC converter station is less than a preset distance threshold comprises:

[0039] Obtaining an inter-station signal communication delay between the wind farm and the DC converter station;

[0040] If the inter-station signal communication delay is less than the preset maximum signal delay, it is determined that the distance between the wind farm and the DC converter station is less than a preset distance threshold;

[0041] If the inter-station signal communication delay is greater than or equal to a preset maximum signal delay, it is determined that the distance between the wind farm and the DC converter station is greater than or equal to a preset distance threshold.

[0042] The present invention also provides a transient overvoltage suppression device after a DC commutation failure, which is applied to a wind power transmission system via DC. The wind power transmission system via DC includes a wind farm and a DC converter station. The device includes:

[0043] The inter-station distance judgment module is used to judge whether the distance between the wind farm and the DC converter station is less than a preset distance threshold when a DC fault occurs in the system;

[0044] A first DC commutation failure fault judgment module, configured to use an inter-station signal coordinated judgment strategy to judge whether the DC fault is a DC commutation failure fault;

[0045] A second DC commutation failure fault judgment module is used to use a fan characteristic judgment strategy to judge whether the DC fault is a DC commutation failure fault;

[0046] The wind turbine reactive power withdrawal module is used to generate a commutation failure signal when the judgment result is a DC commutation failure fault, and based on the commutation failure signal, perform reactive power withdrawal of the wind turbine according to a reactive power withdrawal control strategy.

[0047] The present invention also provides an electronic device, the device comprising a processor and a memory:

[0048] The memory is used to store program code and transmit the program code to the processor;

[0049] The processor is used to execute the method for suppressing transient overvoltage after DC commutation failure as described in any one of the above items according to the instructions in the program code.

[0050] The present invention also provides a computer-readable storage medium, wherein the computer-readable storage medium is used to store program code, and the program code is used to execute the method for suppressing transient overvoltage after DC commutation failure as described in any of the above items.

[0051] It can be seen from the above technical solutions that the present invention has the following advantages:

[0052] A method for suppressing transient overvoltage after a DC commutation failure is provided. The method is applied to a wind power transmission system via DC, and the wind power transmission system via DC includes a wind farm and a DC converter station. When a DC fault occurs in the system, it is determined whether the distance between the wind farm and the DC converter station is less than a preset distance threshold; if so, an inter-station signal coordination judgment strategy is adopted to determine whether the DC fault is a DC commutation failure fault; if not, a fan characteristic judgment strategy is adopted to determine whether the DC fault is a DC commutation failure fault; when the judgment result is a DC commutation failure fault, a commutation failure signal is generated, and based on the commutation failure signal, the fan reactive power is withdrawn according to the reactive power withdrawal control strategy. Thus, the distance between the wind farm and the DC converter station is comprehensively considered, and based on the two different situations of faster / slower communication, the inter-station signal coordination judgment strategy and the fan characteristic judgment strategy are respectively given to determine the DC commutation failure fault, and after the DC commutation failure, the fan reactive power is withdrawn based on the reactive power withdrawal control strategy, thereby suppressing the transient overvoltage after the DC commutation failure fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0054] Figure 1 It is a structural schematic diagram of a wind power direct current transmission system;

[0055] Figure 2 A flow chart of the steps of a method for suppressing transient overvoltage after a DC commutation failure;

[0056] Figure 3 A logic framework diagram of a transient overvoltage suppression strategy after a DC commutation failure;

[0057] Figure 4 It is a logical framework diagram of a reactive power withdrawal prediction control strategy based on inter-station communication between wind farms and DC converter stations;

[0058] Figure 5 It is a logical framework diagram of a reactive power withdrawal prediction control strategy based on the terminal voltage characteristics of a wind turbine;

[0059] Figure 6 A schematic diagram of voltage and current space vectors of a grid-side converter;

[0060] Figure 7 A schematic diagram of the change of the controllable area of ​​the grid-side converter after a DC commutation failure;

[0061] Figure 8 A comparison diagram of grid transient voltage before and after an improved control strategy is adopted;

[0062] Fig. 9 The present invention is a structural block diagram of a transient overvoltage suppression device after a DC commutation failure. DETAILED DESCRIPTION

[0063] The embodiments of the present invention provide a method for suppressing transient overvoltage after a DC commutation failure, a device for suppressing transient overvoltage after a DC commutation failure, an electronic device and a storage medium, which are used to solve or partially solve the technical problem in the existing related technology that after a DC commutation failure occurs, the low-voltage reactive power of the nearby power grid and the grid-following equipment is not withdrawn in time during the process of the power grid voltage changing from low to high.

[0064] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0065] As an example, existing wind turbines are basically equipped with complete high and low voltage ride-through control strategies. In addition, reactive power compensation devices such as SVG are generally installed in the station to improve the voltage stability of the wind farm.

[0066] However, in the case of a DC commutation failure, since the transient voltage of the power grid at the sending end presents a "first low and then high" characteristic, the reactive power generated by the wind turbine through low-through control in the low-voltage stage is difficult to withdraw in time. After the transient voltage recovers, the wind turbine will increase the transient peak voltage, thereby worsening the transient voltage. The connected SVG will also affect the transient overvoltage at the wind turbine end. At present, it is not ruled out that the SVG in the station also has the above risks, resulting in restrictions on the reactive compensation configuration. Therefore, it is very necessary to adjust and optimize the transient characteristics of grid-connected power electronic equipment including DC near-field wind turbines and supporting SVG in wind power collection stations to curb the risks brought about by further increases in transient overvoltages.

[0067] Therefore, one of the core invention points of the embodiments of the present invention is: for a large-scale wind power grid-connected system composed of a generator set, an ultra-high voltage direct current transmission valve group, a new energy grid-connected equipment and active load, in order to suppress the transient overvoltage of the transmission-end power grid after a commutation failure occurs in the ultra-high voltage direct current system, a transient overvoltage suppression method based on wind turbine reactive power withdrawal predictive control is proposed.

[0068] On the one hand, taking into account the distance between the wind farm and the DC converter station, based on the two different situations of faster / slower communication, the inter-station signal coordination judgment strategy and the wind turbine characteristic judgment strategy are respectively given to judge the DC commutation failure fault. After the DC commutation failure, by locating the time of the DC commutation failure fault and judging the optimal interval of the wind turbine reactive power withdrawal by actual setting, the wind turbine reactive power withdrawal is realized based on the reactive power withdrawal control strategy, so as to realize the early withdrawal of the low-through reactive power of the grid-following power electronic equipment before the voltage changes from low to high, thereby effectively suppressing the transient overvoltage after the DC commutation failure fault, suppressing the wind turbine from disconnecting from the grid during the transient process, and improving the stability of the power grid operation.

[0069] On the other hand, the factors affecting the transient reactive power response characteristics of the fan and the stable operation limit of the equipment are fully considered, and the change in the fan terminal voltage after the DC commutation failure occurs and the influence of the improved control strategy designed by the present invention on the stable operation limit of the fan are analyzed. Thus, it is verified that the transient overvoltage can be suppressed without affecting the normal operation of the fan, and the method involved will not bring side effects. In view of the gap in existing research in this field, the technical solution proposed by the present invention has a certain reference and guiding role in subsequent related work.

[0070] To assist understanding, refer to Figure 1 , showing a schematic diagram of the structure of a wind power transmission system via direct current provided by an embodiment of the present invention. Wherein, for the sake of simplicity, the wind power transmission system via direct current includes at least a wind farm and a direct current converter station. The direct current converter station is used to convert alternating current (AC) into direct current (DC) or convert direct current into alternating current. The wind farm contains multiple wind turbines (i.e., wind turbines) for converting wind energy into electrical energy.

[0071] Reference Figure 2 , shows a flowchart of the steps of a method for suppressing transient overvoltage after a DC commutation failure provided by an embodiment of the present invention. The method is applied to the wind power DC transmission system as described above, and the method may specifically include the following steps:

[0072] Step 201, when a DC fault occurs in the system, determining whether the distance between the wind farm and the DC converter station is less than a preset distance threshold;

[0073] In order to make those skilled in the art better understand, the following will be combined with Figure 3 The technical solution of the present invention is introduced. Figure 3 The figure shows a logic framework diagram of a transient overvoltage suppression strategy after a DC commutation failure, that is, a wind turbine reactive power withdrawal prediction control strategy logic block diagram.

[0074] Figure 3 middle, is the effective value of the single-phase voltage at the wind turbine end; , They are the d-axis and q-axis components of the wind turbine terminal voltage respectively; , They are the d-axis and q-axis components of the wind turbine output current respectively; is the maximum operating current of the converter; is the rated output current of the wind turbine; is the delay time constant.

[0075] Simply put, this control strategy is attached to the outer loop control mode judgment logic, and realizes the reactive power withdrawal of the wind turbine by forcibly setting the judgment logic to 0 in the characteristic mode (that is, forcibly switching the wind turbine from the low-power operation mode to the steady-state operation mode through logical control).

[0076] based on Figure 3 The given control logic first analyzes several possible situations that may occur in the system:

[0077] When the DC is operating normally, or locked, the values ​​of the two input channels of the reactive power withdrawal prediction controller are both 0. The reactive power withdrawal prediction control output signal is 1. At this time, the judgment logic of the entire outer loop control mode is consistent with the judgment logic output of the wind turbine terminal voltage.

[0078] When a ground short circuit fault occurs in the DC transmission grid, causing the grid voltage to drop, the reactive power withdrawal prediction controller low-throughput signal input channel value is 1. However, the DC commutation failure prediction command signal is still 0. At this time, the reactive power withdrawal prediction control output signal is 1. The wind turbine outer ring enters the conventional low-throughput control mode, and the wind turbine provides reactive power support to the grid until the fault ends.

[0079] When a DC commutation failure occurs, assuming that the commutation failure judgment instruction can provide a signal input to the fan controller at the same time when the DC fault occurs, the signal values ​​of the two input channels of the reactive power withdrawal prediction controller are both 1. The reactive power withdrawal prediction controller receives the commutation failure judgment signal and After milliseconds, the output signal changes from 1 to 0. At this time, the entire outer loop control judgment logic is forced to 0, and the fan achieves reactive power withdrawal. When the fan is determined to exit the low-throughput control operation mode, the reactive power withdrawal controller also exits operation. After that, the fan can be normally switched to the high-throughput control operation mode.

[0080] Through the above analysis, it can be found that the wind turbine can achieve early prediction of reactive power withdrawal, which depends on the reading of the commutation failure signal and the accurate prediction of the duration of the low voltage process in the nearby power grid after the DC commutation failure occurs (the duration is corresponding actual physical meaning).

[0081] To prove the feasibility of the technical solution of the present invention, the following is given by setting The feasibility analysis is carried out to predict the duration of low voltage process in nearby power grid after DC commutation failure occurs.

[0082] After a DC commutation failure occurs, the duration of the low voltage process of the AC system at the sending end is relatively fixed. It is generally 80~100ms (unit: milliseconds). And this duration is almost only affected by the characteristics of the DC converter valve group itself, and has nothing to do with other components in the power grid. Therefore, after a DC commutation failure occurs, it is feasible to take a fixed time to predict the change of the grid voltage.

[0083] Based on the actual situation, The setting of specific values ​​has certain requirements on accuracy. If the value is set too large, the wind turbine reactive power will not be withdrawn in time, which will limit the effect of transient overvoltage suppression. If the value is set too small, the wind turbine reactive power will be withdrawn prematurely during the low voltage stage, further aggravating the grid voltage drop.

[0084] Generally speaking, after a DC commutation failure causes the voltage of the power grid near the sending end to drop, the voltage can still be maintained above 0.4pu (higher than the 0.2pu required by the relevant standards). The setting value of can be less than the time taken for the voltage to rise and cross zero after the actual fault. The present invention believes that, considering the delay of the inner loop response process, it is recommended to It is set to about 40ms. The setting of the value needs to be debugged in combination with the on-site conditions.

[0085] Based on the above analysis, the embodiment of the present invention comprehensively considers the distance between the wind farm and the DC converter station, and proposes different judgment methods for DC commutation failure faults from two perspectives: directly obtaining the commutation failure signal through signal communication with the nearby DC converter station (when the distance is relatively close) and judging the commutation failure based on the wind turbine itself after the fault (when the distance is relatively far).

[0086] To judge the distance between the two, first obtain the inter-station signal communication delay between the wind farm and the DC converter station. If the inter-station signal communication delay is less than the preset maximum signal delay, it is determined that the distance between the wind farm and the DC converter station is less than the preset distance threshold. At this time, the first judgment method is used. If the inter-station signal communication delay is greater than or equal to the preset maximum signal delay, it is determined that the distance between the wind farm and the DC converter station is greater than or equal to the preset distance threshold. At this time, the second judgment method is used.

[0087] The distance is usually determined according to the specific project. The channel transmission rate is related to the properties of the transmission medium. For example, the transmission rate in an optical fiber is the optical signal, that is, the speed of light. At this time, the transmission rate is multiplied by the transmission time (that is, the signal communication delay between stations), which is the distance.

[0088] Step 202: If yes, then use the inter-station signal coordination determination strategy to determine whether the DC fault is a DC commutation failure fault;

[0089] Reference Figure 4 , a logical framework diagram of a reactive power withdrawal prediction control strategy based on inter-station communication between wind farm and DC converter station is given. At this time, the wind farm is close to the DC converter station.

[0090] Figure 4 middle, is the DC side current of the DC transmission system; It is the DC over-current detection judgment threshold; The time required for channel transmission, that is, the signal communication delay between stations. The time required for channel transmission must be less than the preset maximum signal delay ( ). Otherwise, the strategy is not available.

[0091] At this time, since the signal communication delay between the two stations is relatively short, the signal within the DC converter station can be directly sent to the fan controller to realize the commutation failure judgment.

[0092] Since the DC commutation failure occurs at the DC receiving converter station, the fault detection device can only be installed in the receiving converter station. However, it is difficult to achieve rapid information transmission between the sending and receiving stations. .

[0093] Therefore, the embodiment of the present invention adopts a strategy of coordinated control of the overcurrent detection signal in the DC sending end station and the low-throughput control signal of the nearby wind turbine generator set, and realizes the determination of the DC commutation failure fault by simultaneously judging the indicators of the DC system overcurrent and the AC side low voltage (the above two indicators will be met at the same time only after the DC system has a commutation failure fault).

[0094] Combined with the above content, in the specific implementation, the inter-station signal coordination judgment strategy is adopted to judge whether the DC fault is a DC commutation failure fault, which can be:

[0095] Get the DC side current of the DC converter station and the terminal voltage of the wind turbines in the wind farm ;

[0096] Determine the DC side current Is it greater than the DC overcurrent detection threshold? , and generate an over-current detection signal;

[0097] If the signal value of the overcurrent detection signal is 1, a DC overcurrent fault occurs in the DC converter station;

[0098] If the signal value of the overcurrent detection signal is 0, no DC overcurrent fault occurs in the DC converter station;

[0099] Determine the terminal voltage Is it lower than the preset low voltage threshold? , and generate a low wear control signal;

[0100] If the signal value of the low penetration control signal is 1, the fan is in the low penetration operation mode;

[0101] If the signal value of the low-through control signal is not 1, the fan is not in the low-through operation mode; the low-through operation mode indicates that the terminal voltage is lower than the preset low-through voltage threshold;

[0102] If the signal value of the overcurrent detection signal is 1, and / or the signal value of the low-through control signal is 1, and the signal value after the AND operation based on the overcurrent detection signal and the low-through control signal is 1, the DC fault is determined to be a DC commutation failure fault.

[0103] Step 203: if not, then adopt the fan characteristic determination strategy to determine whether the DC fault is a DC commutation failure fault;

[0104] Reference Figure 5 , showing a logical framework diagram of a reactive power withdrawal prediction control strategy based on wind turbine terminal voltage characteristics.

[0105] At this time, the wind farm is far away from the DC converter station. The signal communication delay between the two stations does not meet Due to the relationship, communication is slow. Therefore, the DC commutation failure can only be determined by the wind turbine itself according to the terminal voltage characteristics.

[0106] The commutation failure determination method based on the wind turbine terminal voltage characteristics needs to focus on distinguishing the difference between the low voltage process after the DC commutation failure and the low voltage process after the ground short circuit occurs in the nearby AC power grid. The following is a judgment of the system DC fault from the shallow to the deep from three perspectives to improve the reliability of DC commutation failure fault identification.

[0107] (1) Considering that the DC commutation failure fault itself is a three-phase symmetrical fault, the three-phase voltage symmetry detection is used to eliminate the common asymmetric faults such as the single-phase grounding fault in the AC system.

[0108] (2) Considering the severity of the three-phase ground short circuit fault, the voltage amplitude detection is used to distinguish it from the DC commutation failure fault. Generally, a fault with a grid voltage amplitude higher than 0.4pu after the fault is judged as a DC commutation failure fault, otherwise it is a three-phase ground short circuit fault.

[0109] (3) Considering that the grid voltage drops gradually after a DC commutation failure, and the grid voltage drops in a step-like process after a three-phase short circuit grounding fault, the two faults can be distinguished by the voltage drop change rate. Generally, when |du / dt| satisfies the threshold value between 1p.u. / s and 30p.u. / s, it is judged that the system has a DC commutation failure.

[0110] By combining the voltage change rate judgment and the voltage amplitude judgment, it can be determined that when a three-phase symmetrical fault occurs in the system, the DC fault must be a DC commutation failure fault.

[0111] It can be understood that the first method is used to determine whether the fault itself is three-phase symmetrical, that is, the symmetry of the commutation failure. Secondly, the absolute value of the voltage amplitude and the voltage drop change rate are used to jointly determine whether they meet the amplitude and rate requirements of the commutation failure, and perform an AND operation. Finally, when all the above three meet the requirements, it can be finally determined whether the fault is a DC commutation failure fault.

[0112] Combined with the above content, the fan characteristic determination strategy is used to determine whether the DC fault is a DC commutation failure fault, which can be:

[0113] Obtain the terminal voltage of wind turbines in wind farms ;

[0114] When the terminal voltage Below the preset low breakdown voltage threshold When a DC fault occurs, first perform a three-phase voltage symmetry test, then perform a voltage amplitude test, and then perform a voltage drop change rate analysis;

[0115] Voltage at the machine end Below the preset low breakdown voltage threshold On this basis, when the DC fault is a three-phase symmetrical fault, and the voltage amplitude after the fault meets the preset fault condition (that is, the grid voltage amplitude after the fault is higher than 0.4pu), and the voltage drop after the fault is a gradual process, the DC fault is determined to be a DC commutation failure fault.

[0116] Furthermore, when the terminal voltage is lower than the preset low-breakthrough voltage threshold, the three-phase voltage symmetry detection is first performed on the DC fault, and then the voltage amplitude detection is performed, and then the voltage drop change rate analysis is performed, which can be specifically:

[0117] When the terminal voltage Below the preset low breakdown voltage threshold hour:

[0118] A symmetrical fault detection is performed on the DC fault through three-phase voltage symmetry detection to obtain a symmetrical fault detection result; the symmetrical fault detection result is that the DC fault is a three-phase symmetrical fault, or an asymmetrical fault; the three-phase symmetrical fault includes a three-phase grounding short circuit fault and a DC commutation failure fault;

[0119] Voltage fault detection is performed on three-phase symmetrical faults through voltage amplitude detection;

[0120] When the post-fault voltage amplitude of the three-phase symmetrical fault is greater than the preset fault voltage threshold, the DC fault is preliminarily judged as a DC commutation failure fault;

[0121] When the post-fault voltage amplitude of the three-phase symmetrical fault is less than or equal to the preset fault voltage threshold, the DC fault is preliminarily judged as a three-phase ground short circuit fault;

[0122] Analyze the voltage drop change rate of three-phase symmetrical faults to make a secondary judgment on DC faults;

[0123] When the post-fault voltage drop of a three-phase symmetrical fault is a step-like process, the DC fault is ultimately determined to be a three-phase ground short-circuit fault;

[0124] When the post-fault voltage drop of a three-phase symmetrical fault is a gradual process and the post-fault voltage amplitude is greater than a preset fault voltage threshold, the DC fault is ultimately determined to be a DC commutation failure fault.

[0125] In particular, the above-mentioned method of fault determination based on the wind turbine's own characteristics is more susceptible to the grid environment than the fault determination method based on communication between the wind farm and the DC converter station. When the AC grid is weak, the voltage amplitude may fall below the threshold after the commutation failure, causing the controller to refuse to operate. However, this method is relatively easy to implement and is not limited by the distance between the wind farm and the DC converter station.

[0126] Step 204: When the judgment result is a DC commutation failure fault, a commutation failure signal is generated, and based on the commutation failure signal, reactive power withdrawal of the wind turbine is performed according to a reactive power withdrawal control strategy.

[0127] When reactive power withdrawal is performed based on the communication fault judgment method between the wind farm and the DC converter station, the time when the wind farm receives the DC overcurrent command is not consistent with the actual time when the DC commutation failure occurs.

[0128] On the one hand, there is a delay in the communication between the DC converter station and the nearby wind farm station. On the other hand, the DC line current after the fault Climb to It takes a certain amount of time, which can be recorded as the peak current time (This value can be measured in practice). For the former, the actual delay time of inter-station communication should be taken into consideration. , the delay time constant of the wind turbine reactive power withdrawal prediction controller For the latter, the delay time constant needs to be The setting part will be appropriately The value of is reduced. That is, the final delay after setting in this way is .

[0129] When the wind turbine uses its own characteristics to determine the fault mode and perform reactive power withdrawal, although there is no need to consider the inter-station communication delay, the peak current time still needs to be considered. , to The final delay after adjustment in this way is .

[0130] Combined with the above content, in the specific implementation, based on the commutation failure signal, the wind turbine reactive power is withdrawn according to the reactive power withdrawal control strategy, which can be:

[0131] Generate reactive power withdrawal signal according to commutation failure signal;

[0132] When the distance between the wind farm and the DC converter station is less than the preset distance threshold, based on the reactive power withdrawal signal, the wind turbines in the wind farm are controlled to exit the low-power operation mode after the first setting delay and switch to the steady-state operation mode to achieve reactive power withdrawal of the wind turbines;

[0133] When the distance between the wind farm and the DC converter station is greater than or equal to the preset distance threshold, based on the reactive power withdrawal signal, the wind turbines in the wind farm are controlled to exit the low-throughput operation mode after the second setting delay and switch to the steady-state operation mode to achieve reactive power withdrawal of the wind turbines.

[0134] The first setting delay is obtained by subtracting the peak current time and the inter-station signal communication delay from the delay time constant; the second setting delay is obtained by subtracting the peak current time from the delay time constant; wherein, the delay time constant is the duration of the low voltage process of the nearby power grid after the DC commutation failure occurs; the peak current time is the time it takes for the DC side current to climb to the DC overcurrent detection threshold after the DC commutation failure occurs; the inter-station signal communication delay is the communication time required for the DC converter station to send an overcurrent detection signal to the wind farm.

[0135] Furthermore, in order to study the influence of the wind turbine terminal voltage change and the improved control strategy designed in the embodiment of the present invention on the wind turbine stable operation limit, the following analysis is carried out:

[0136] Figure 6 A schematic diagram of the voltage and current space vector of a grid-side converter is shown. Figure 7 A schematic diagram showing the change of the controllable area of ​​a grid-side converter after a DC commutation failure is shown.

[0137] In the dq coordinate system, the relationship between the wind turbine grid-side converter outlet voltage and the AC grid voltage satisfies the following formula:

[0138]

[0139] In the formula, , They are the d-axis and q-axis components of the grid voltage respectively; is the line resistance of the grid-side converter; is the line inductance of the grid-side converter; is the grid synchronization electrical angle.

[0140] Generally, since the line resistance of the grid-side converter is much smaller than the inductance value, the voltage drop on the resistance can be ignored. In this case, the above formula can be simplified to:

[0141]

[0142] In order to keep the system in a stable operating state, the grid-side converter of the wind turbine needs to be constrained by its own modulation ratio and maximum operating current.

[0143] Since the current wind turbine grid-side converter generally adopts PWM (Pulse Width Modulation) control, according to the existing voltage space vector modulation theory, in order to avoid overmodulation, the modulation ratio m must meet the following requirements:

[0144]

[0145] is the DC bus voltage; generally, m is 2.

[0146] The inverter itself is limited by hardware, and the operating current has an upper limit :

[0147]

[0148] Combining the above equations and inequality equations, the grid-side converter voltage and current space vector diagram under stable operation constraints can be obtained as follows: Figure 6 .

[0149] in, Figure 6 The shaded area in the middle is the controllable area of ​​the grid-side converter that satisfies the stable operation constraints of the wind turbine. The following will analyze the impact of the DC commutation failure and the use of reactive power prediction withdrawal control on the stable operation of the wind turbine.

[0150] After the DC commutation failure, the voltage of the nearby power grid shows a "first drop and then rise" characteristic, corresponding to Figure 6The center of the maximum current limit circle in the figure moves first to the left and then to the right along the d axis. Under the condition that the radius of the two circles does not change, the controllable area of ​​the fan will first increase and then decrease. Figure 7 shown.

[0151] Depend on Figure 7 It can be seen that the increase of the terminal voltage of the fan is not conducive to the function of the high-throughput controller of the fan. At this time, the maximum modulation ratio limit of the converter will become the main factor restricting the increase of the operating voltage and current of the fan. The reduction of the terminal voltage of the fan will lead to an increase in the controllable area of ​​the fan. This is conducive to the better functioning of the low-throughput controller. Moreover, the reactive current withdrawal control proposed by the present invention will also not cause the operating voltage and current of the fan to deviate from the operating limit.

[0152] For example, refer to Figure 8 , a comparison diagram of the transient peak overvoltage of the nearby power grid after a DC commutation failure fault based on the improved control strategy proposed in the present invention is given on an electromagnetic transient simulation experimental platform.

[0153] in, Figure 8 (a) in the figure is the transient overvoltage suppression for the commutation bus voltage at the sending end. Its horizontal axis is time, and its vertical axis is the commutation bus voltage at the sending end (AC voltage). Figure 8 (b) in the figure is the transient overvoltage suppression for the bus voltage at the wind turbine end. Its horizontal axis is time, and its vertical axis is the bus voltage at the wind turbine end (AC voltage).

[0154] Combination Figure 8 It can be found that the improved control strategy for wind turbines based on reactive power withdrawal prediction control proposed in the embodiment of the present invention can suppress the voltage of the nearby power grid after a fault and suppress the peak voltage rise. The suppression effect is best near the wind turbine end bus. As the electrical distance from the wind turbine end bus increases, the suppression effect weakens.

[0155] It should be noted that, in order to enable those skilled in the art to better distinguish data of the same type but with different actual meanings, some technical features are distinguished by the first and the second in the embodiments of the present invention. The first and the second are only used for data distinction and have no other special meanings. It can be understood that the present invention is not limited to this.

[0156] In an embodiment of the present invention, a transient overvoltage suppression method based on wind turbine reactive power withdrawal predictive control is proposed. On the one hand, the distance between the wind farm and the DC converter station is comprehensively considered, and based on the two different situations of faster / slower communication, the signal coordination judgment strategy between the stations and the wind turbine characteristic judgment strategy are respectively given to determine the DC commutation failure fault. After the DC commutation failure, by locating the time when the DC commutation failure fault occurs, and judging the optimal interval of the wind turbine reactive power withdrawal by actual setting, the wind turbine reactive power withdrawal is realized based on the reactive power withdrawal control strategy, so as to realize the low-through reactive power of the grid-following power electronic equipment to withdraw in advance before the voltage changes from low to high, thereby effectively suppressing the transient overvoltage after the DC commutation failure fault, suppressing the wind turbine from being disconnected from the grid during the transient process, and improving the stability of the power grid operation. On the other hand, the influencing factors of the transient reactive power response characteristics of the wind turbine and the stable operation limit of the equipment are fully considered, and the wind turbine terminal voltage change after the DC commutation failure fault and the influence of the improved control strategy designed by the present invention on the stable operation limit of the wind turbine are analyzed. Thereby verifying that the transient overvoltage is suppressed without affecting the normal operation of the wind turbine.

[0157] Reference Fig. 9 , shows a structural block diagram of a transient overvoltage suppression device after a DC commutation failure provided by an embodiment of the present invention, the device is applied to a wind power transmission system via DC, the wind power transmission system via DC includes a wind farm and a DC converter station, the device may specifically include:

[0158] The inter-station distance judgment module 901 is used to judge whether the distance between the wind farm and the DC converter station is less than a preset distance threshold when a DC fault occurs in the system;

[0159] A first DC commutation failure fault judgment module 902, configured to use an inter-station signal coordinated judgment strategy to judge whether the DC fault is a DC commutation failure fault;

[0160] A second DC commutation failure fault judgment module 903 is used to use a fan characteristic judgment strategy to judge whether the DC fault is a DC commutation failure fault;

[0161] The wind turbine reactive power withdrawal module 904 is used to generate a commutation failure signal when the judgment result is a DC commutation failure fault, and based on the commutation failure signal, perform reactive power withdrawal of the wind turbine according to a reactive power withdrawal control strategy.

[0162] In an optional embodiment, the first DC commutation failure fault judgment module 902 includes:

[0163] A data acquisition module, used to acquire the DC side current of the DC converter station and the terminal voltage of the wind turbine in the wind farm;

[0164] An overcurrent detection module, used to determine whether the DC side current is greater than a DC overcurrent detection threshold and generate an overcurrent detection signal;

[0165] If the signal value of the overcurrent detection signal is 1, a DC overcurrent fault occurs in the DC converter station;

[0166] If the signal value of the overcurrent detection signal is 0, no DC overcurrent fault occurs in the DC converter station;

[0167] A low-breakthrough judging module, used to judge whether the terminal voltage is lower than a preset low-breakthrough voltage threshold and generate a low-breakthrough control signal;

[0168] If the signal value of the low wear control signal is 1, the fan is in a low wear operation mode;

[0169] If the signal value of the low-breakthrough control signal is not 1, the fan is not in the low-breakthrough operation mode; the low-breakthrough operation mode indicates that the terminal voltage is lower than the preset low-breakthrough voltage threshold;

[0170] The first DC commutation failure fault determination module is used to determine that the DC fault is a DC commutation failure fault when the signal value of the overcurrent detection signal is 1 and / or the signal value of the low-throw control signal is 1, and the signal value after the AND operation based on the overcurrent detection signal and the low-throw control signal is 1.

[0171] In an optional embodiment, the second DC commutation failure fault judgment module 903 includes:

[0172] A machine-end voltage acquisition module, used to acquire the machine-end voltage of the wind turbine in the wind farm;

[0173] A fault analysis module is used to first perform a three-phase voltage symmetry detection on the DC fault, then perform a voltage amplitude detection, and then perform a voltage drop change rate analysis when the machine-end voltage is lower than a preset low-breakdown voltage threshold;

[0174] The second DC commutation failure fault judgment module is used to judge that the DC fault is a DC commutation failure fault on the basis that the generator terminal voltage is lower than a preset low-breakdown voltage threshold, when the DC fault is a three-phase symmetrical fault, the voltage amplitude after the fault meets the preset fault condition, and the voltage drop after the fault is a gradual process.

[0175] In an optional embodiment, the fault analysis module includes:

[0176] A three-phase symmetric detection module is used to perform symmetric detection on the DC fault by detecting the symmetry of the three-phase voltage to obtain a symmetric fault detection result; the symmetric fault detection result is that the DC fault is a three-phase symmetric fault, or an asymmetric fault; the three-phase symmetric fault includes a three-phase ground short circuit fault and a DC commutation failure fault;

[0177] A voltage fault detection module, used for performing voltage fault detection on the three-phase symmetrical fault by voltage amplitude detection;

[0178] A DC commutation failure fault preliminary judgment module is used to preliminarily judge the DC fault as a DC commutation failure fault when the post-fault voltage amplitude of the three-phase symmetrical fault is greater than a preset fault voltage threshold;

[0179] A three-phase ground short circuit fault preliminary determination module, used for preliminarily determining the DC fault as a three-phase ground short circuit fault when the post-fault voltage amplitude of the three-phase symmetrical fault is less than or equal to a preset fault voltage threshold;

[0180] A voltage drop change rate analysis module is used to perform voltage drop change rate analysis on the three-phase symmetrical fault to make a secondary judgment on the DC fault;

[0181] A three-phase ground short circuit fault final determination module, used for finally determining that the DC fault is a three-phase ground short circuit fault when the post-fault voltage drop of the three-phase symmetrical fault is a step-type process;

[0182] The DC commutation failure fault final judgment module is used to finally judge that the DC fault is a DC commutation failure fault when the post-fault voltage drop of the three-phase symmetrical fault is a gradual process and the post-fault voltage amplitude is greater than a preset fault voltage threshold.

[0183] In an optional embodiment, the wind turbine reactive power withdrawal module 904 includes:

[0184] A reactive power withdrawal signal generating module, used for generating a reactive power withdrawal signal according to the commutation failure signal;

[0185] A first wind turbine reactive power withdrawal submodule is used for controlling the wind turbines in the wind farm to exit the low-throughput operation mode and switch to the steady-state operation mode after a first setting delay based on the reactive power withdrawal signal when the distance between the wind farm and the DC converter station is less than a preset distance threshold, so as to realize reactive power withdrawal of the wind turbines;

[0186] The second wind turbine reactive power withdrawal submodule is used to control the wind turbines in the wind farm to exit the low-throughput operation mode and switch to the steady-state operation mode after a second setting delay based on the reactive power withdrawal signal when the distance between the wind farm and the DC converter station is greater than or equal to a preset distance threshold, so as to achieve reactive power withdrawal of the wind turbines.

[0187] In an optional embodiment, the first setting delay is obtained by subtracting the peak current time and the inter-station signal communication delay from the delay time constant; the second setting delay is obtained by subtracting the peak current time from the delay time constant; wherein the delay time constant is the duration of the low voltage process of the nearby power grid after a DC commutation failure occurs; the peak current time is the time for the DC side current to climb to the DC overcurrent detection threshold after a DC commutation failure occurs; and the inter-station signal communication delay is the communication time required for the DC converter station to send an overcurrent detection signal to the wind farm.

[0188] In an optional embodiment, the inter-station distance determination module 901 includes:

[0189] An inter-station signal communication delay acquisition module, used to acquire the inter-station signal communication delay between the wind farm and the DC converter station;

[0190] A first inter-station distance judgment submodule, configured to determine that the distance between the wind farm and the DC converter station is less than a preset distance threshold when the inter-station signal communication delay is less than a preset maximum signal delay;

[0191] The first inter-station distance judgment submodule is used to determine that the distance between the wind farm and the DC converter station is greater than or equal to a preset distance threshold when the inter-station signal communication delay is greater than or equal to a preset maximum signal delay.

[0192] As for the device embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the aforementioned method embodiment.

[0193] An embodiment of the present invention further provides an electronic device, the device comprising a processor and a memory:

[0194] The memory is used to store the program code and transmit the program code to the processor;

[0195] The processor is used to execute the method for suppressing transient overvoltage after DC commutation failure according to any embodiment of the present invention according to the instructions in the program code.

[0196] An embodiment of the present invention further provides a computer-readable storage medium, which is used to store program code, and the program code is used to execute the method for suppressing transient overvoltage after DC commutation failure of any embodiment of the present invention.

[0197] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0198] In the several embodiments provided by the present invention, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0199] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0200] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0201] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk, etc., various media that can store program codes.

[0202] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for suppressing transient overvoltage after DC commutation failure, characterized in that: Applied to a wind power transmission system via direct current, the wind power transmission system via direct current includes a wind farm and a direct current converter station, the method includes: When a DC fault occurs in the system, determining whether the distance between the wind farm and the DC converter station is less than a preset distance threshold; If yes, then the inter-station signal coordinated determination strategy is adopted to determine whether the DC fault is a DC commutation failure fault; If not, a fan characteristic determination strategy is adopted to determine whether the DC fault is a DC commutation failure fault; When the judgment result is a DC commutation failure fault, a commutation failure signal is generated, and based on the commutation failure signal, reactive power withdrawal of the wind turbine is performed according to a reactive power withdrawal control strategy.

2. The transient overvoltage suppression method according to claim 1, characterized in that: The adopting of the inter-station signal coordinated determination strategy to determine whether the DC fault is a DC commutation failure fault includes: Obtaining the DC side current of the DC converter station and the terminal voltage of the wind turbine in the wind farm; Determining whether the DC side current is greater than a DC overcurrent detection threshold, and generating an overcurrent detection signal; If the signal value of the overcurrent detection signal is 1, a DC overcurrent fault occurs in the DC converter station; If the signal value of the overcurrent detection signal is 0, no DC overcurrent fault occurs in the DC converter station; Determine whether the terminal voltage is lower than a preset low breakdown voltage threshold, and generate a low breakdown control signal; If the signal value of the low wear control signal is 1, the fan is in a low wear operation mode; If the signal value of the low-breakthrough control signal is not 1, the fan is not in the low-breakthrough operation mode; the low-breakthrough operation mode indicates that the terminal voltage is lower than the preset low-breakthrough voltage threshold; If the signal value of the overcurrent detection signal is 1, and / or the signal value of the low-throw control signal is 1, and the signal value after the AND operation based on the overcurrent detection signal and the low-throw control signal is 1, then the DC fault is determined to be a DC commutation failure fault.

3. The transient overvoltage suppression method according to claim 1, characterized in that: The adopting of the fan characteristic determination strategy to determine whether the DC fault is a DC commutation failure fault includes: Obtaining the terminal voltage of the wind turbine in the wind farm; When the terminal voltage is lower than the preset low voltage threshold, firstly perform three-phase voltage symmetry detection on the DC fault, then perform voltage amplitude detection, and then perform voltage drop change rate analysis; On the basis that the machine-end voltage is lower than the preset low-breakdown voltage threshold, when the DC fault is a three-phase symmetrical fault, and the voltage amplitude after the fault meets the preset fault condition, and the voltage drop after the fault is a gradual process, it is determined that the DC fault is a DC commutation failure fault.

4. The transient overvoltage suppression method according to claim 3, characterized in that: When the terminal voltage is lower than the preset low voltage threshold, firstly perform three-phase voltage symmetry detection on the DC fault, then perform voltage amplitude detection, and then perform voltage drop change rate analysis, including: When the terminal voltage is lower than the preset low breakdown voltage threshold: The DC fault is symmetrically detected by three-phase voltage symmetry detection to obtain a symmetrical fault detection result; the symmetrical fault detection result is that the DC fault is a three-phase symmetrical fault, or an asymmetrical fault; the three-phase symmetrical fault includes a three-phase ground short circuit fault and a DC commutation failure fault; Performing voltage fault detection on the three-phase symmetrical fault by voltage amplitude detection; When the post-fault voltage amplitude of the three-phase symmetrical fault is greater than a preset fault voltage threshold, the DC fault is preliminarily determined to be a DC commutation failure fault; When the post-fault voltage amplitude of the three-phase symmetrical fault is less than or equal to a preset fault voltage threshold, the DC fault is preliminarily determined to be a three-phase ground short circuit fault; Performing voltage drop change rate analysis on the three-phase symmetrical fault to perform secondary judgment on the DC fault; When the post-fault voltage drop of the three-phase symmetrical fault is a step-type process, the DC fault is finally determined to be a three-phase ground short circuit fault; When the post-fault voltage drop of the three-phase symmetrical fault is a gradual process, and the post-fault voltage amplitude is greater than a preset fault voltage threshold, the DC fault is finally determined to be a DC commutation failure fault.

5. The transient overvoltage suppression method according to claim 1, characterized in that: Based on the commutation failure signal, the wind turbine reactive power withdrawal is performed according to the reactive power withdrawal control strategy, including: generating a reactive power withdrawal signal according to the commutation failure signal; When the distance between the wind farm and the DC converter station is less than a preset distance threshold, based on the reactive power withdrawal signal, after a first setting delay, the wind turbines in the wind farm are controlled to exit the low-throughput operation mode and switch to the steady-state operation mode to achieve reactive power withdrawal of the wind turbines; When the distance between the wind farm and the DC converter station is greater than or equal to a preset distance threshold, based on the reactive power withdrawal signal, after a second setting delay, the wind turbines in the wind farm are controlled to exit the low-throughput operation mode and switch to the steady-state operation mode to achieve reactive power withdrawal of the wind turbines.

6. The transient overvoltage suppression method according to claim 5, characterized in that: The first setting delay is obtained by subtracting the peak current time and the inter-station signal communication delay from the delay time constant; the second setting delay is obtained by subtracting the peak current time from the delay time constant; wherein the delay time constant is the duration of the low voltage process of the nearby power grid after a DC commutation failure occurs; the peak current time is the time for the DC side current to climb to the DC overcurrent detection threshold after a DC commutation failure occurs; and the inter-station signal communication delay is the communication time required for the DC converter station to send an overcurrent detection signal to the wind farm.

7. The transient overvoltage suppression method according to any one of claims 1 to 6, characterized in that: The determining whether the distance between the wind farm and the DC converter station is less than a preset distance threshold comprises: Obtaining an inter-station signal communication delay between the wind farm and the DC converter station; If the inter-station signal communication delay is less than the preset maximum signal delay, it is determined that the distance between the wind farm and the DC converter station is less than a preset distance threshold; If the inter-station signal communication delay is greater than or equal to a preset maximum signal delay, it is determined that the distance between the wind farm and the DC converter station is greater than or equal to a preset distance threshold.

8. A device for suppressing transient overvoltage after DC commutation failure, characterized in that: Applicable to a wind power transmission system via direct current, the wind power transmission system via direct current includes a wind farm and a direct current converter station, and the device includes: The inter-station distance judgment module is used to judge whether the distance between the wind farm and the DC converter station is less than a preset distance threshold when a DC fault occurs in the system; A first DC commutation failure fault judgment module, configured to use an inter-station signal coordinated judgment strategy to judge whether the DC fault is a DC commutation failure fault; A second DC commutation failure fault judgment module is used to use a fan characteristic judgment strategy to judge whether the DC fault is a DC commutation failure fault; The wind turbine reactive power withdrawal module is used to generate a commutation failure signal when the judgment result is a DC commutation failure fault, and based on the commutation failure signal, perform reactive power withdrawal of the wind turbine according to a reactive power withdrawal control strategy.

9. An electronic device, characterized in that: The device comprises a processor and a memory: The memory is used to store program code and transmit the program code to the processor; The processor is used to execute the method for suppressing transient overvoltage after DC commutation failure according to any one of claims 1-7 according to the instructions in the program code.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium is used to store program codes, and the program codes are used to execute the method for suppressing transient overvoltage after DC commutation failure as described in any one of claims 1 to 7.

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