A method and device for determining the severity of a DC fault

Abstract

The present application provides a method and apparatus for determining the severity of a DC fault, relating to the field of power equipment maintenance. The method comprises: extracting corresponding low-frequency fault characteristic signals based on transient data of an AC / DC power transmission system; determining the equivalent electromagnetic power and equivalent power angle of the AC / DC power transmission system during the fault period based on the low-frequency fault characteristic signals; and determining the severity of the DC fault based on the equivalent electromagnetic power and equivalent power angle. The present application comprehensively considers the characteristics of the power angle in the AC / DC power transmission system, determines the severity of different DC faults, and intuitively compares the impact of different DC faults on the power grid.

Description

Technical Field

[0001] The present application relates to the field of power equipment maintenance, and specifically to a method and device for determining the severity of a DC fault. Background Art

[0002] High-voltage direct current (HVDC) transmission boasts significant advantages in long-distance, high-capacity power transmission. It is widely used in scenarios such as clean energy export and interregional interconnection, playing a vital role in optimizing resource utilization. Currently, many UHVDC projects are in operation. Due to the long distances and complex terrain along DC transmission lines, they are susceptible to natural factors such as lightning strikes and wind deflection, which can cause DC line failures and lead to converter valve lockout. Converter valves are subject to external circuit constraints and are prone to commutation failures when faced with disturbances such as malfunction of the rectifier-side trigger circuit and AC voltage fluctuations on the inverter side. These abnormal operating conditions pose significant challenges to the safe and stable operation of the transmission system.

[0003] To improve DC power supply reliability, restarting is often implemented after a DC line fault. After the converter valve fails to commutate initially, further attempts are typically allowed, with a lockout occurring only after a certain number of attempts and failures. However, in the current "strong DC, weak AC" grid structure, the impact of a DC restart strategy on the sending and receiving AC systems may exceed their carrying capacity, leading to AC system instability and a cascading failure. Furthermore, lockout after a DC commutation failure may exceed transient overvoltage limits. Therefore, it is crucial to determine the severity of different DC faults before a lockout occurs and select appropriate post-fault control and protection strategies accordingly to minimize the impact on the system and improve system stability.

[0004] Existing technologies calculate the system unbalanced energy impact caused by DC bipolar active power imbalance after different DC faults and calculate the difference in unbalanced energy. They also integrate the bipolar active power simulation curves during different fault periods to calculate the resulting system short-term fallback energy and then calculate the difference in system short-term fallback energy. By comprehensively considering the system energy imbalance and short-term fallback energy during the fault period, the energy difference to the system during the fault period is calculated, and a post-fault control and protection strategy is then formulated. However, existing technologies have the following drawbacks: First, it is difficult to intuitively compare the impact of different faults on the system. Second, when the system is weak and the DC power is high, the severity of the fault condition is difficult to determine due to the large amount of reactive power absorbed during a successful DC restart. Summary of the Invention

[0005] In response to the problems in the prior art, the present application provides a method and device for determining the severity of a DC fault, which can comprehensively consider the characteristics of the power angle in the AC / DC transmission system, judge the severity of different DC faults, and intuitively compare the impact of different DC faults on the power grid.

[0006] To solve the above technical problems, this application provides the following technical solutions:

[0007] In a first aspect, the present application provides a method for determining the severity of a DC fault, comprising:

[0008] Extracting corresponding low-frequency fault characteristic signals based on transient data of the AC / DC power transmission system; the transient data includes: the AC voltage, AC current and rotor angle of each generator;

[0009] Determining the equivalent electromagnetic power and equivalent power angle of the AC / DC power transmission system during the fault period according to the low-frequency fault characteristic signal;

[0010] The severity of the DC fault is determined according to the equivalent electromagnetic power and the equivalent power angle.

[0011] Furthermore, the method for determining the severity of a DC fault further includes:

[0012] Corresponding transient data is obtained according to the operating mode of the AC / DC power transmission system; the operating mode includes a full-start mode and a maintenance mode of the generator set.

[0013] Furthermore, determining the severity of the DC fault according to the equivalent electromagnetic power and the equivalent power angle includes:

[0014] Determining, based on the equivalent electromagnetic power and the equivalent power angle, the system kinetic energy generated by the AC / DC power transmission system when the AC / DC power transmission system adopts various restart strategies to restore the system after a fault;

[0015] The severity of the DC fault is determined based on the system kinetic energy.

[0016] Furthermore, determining the severity of the DC fault according to the equivalent electromagnetic power and the equivalent power angle includes:

[0017] generating a relationship curve graph between the equivalent electromagnetic power and the equivalent power angle;

[0018] The severity is determined according to the relationship curve graph.

[0019] Furthermore, the low-frequency fault characteristic signal includes: a voltage fault characteristic signal, a current fault characteristic signal, and a rotor angle fault characteristic signal; and determining the equivalent electromagnetic power and equivalent power angle of the AC / DC power transmission system during the fault period based on the low-frequency fault characteristic signal includes:

[0020] determining the active power of each generator during the system fault period according to the voltage fault characteristic signal and the current fault characteristic signal of each generator;

[0021] Determining the equivalent electromagnetic power of the AC / DC power transmission system during the fault period according to the inertia time constant of each generator and the active power of each generator during the system fault period;

[0022] The equivalent power angle of the AC / DC power transmission system during the fault period is determined according to the inertia time constant of each generator and the rotor angle fault characteristic signal.

[0023] Furthermore, the determining, based on the equivalent electromagnetic power and the equivalent power angle, the system kinetic energy generated by the AC / DC power transmission system when the AC / DC power transmission system adopts different restart strategies for system recovery after a fault, includes:

[0024] determining an electromagnetic power fault value according to the equivalent electromagnetic power;

[0025] The system kinetic energy is determined according to the mechanical input power of the prime mover, the electromagnetic power fault value, and the rotor angle of each generator.

[0026] Furthermore, determining the severity of the DC fault according to the system kinetic energy includes:

[0027] sorting the magnitude of system kinetic energy generated by the AC / DC power transmission system when the AC / DC power transmission system adopts different restart strategies for fault recovery after a fault;

[0028] The severity of the fault is determined based on the sorting results, and a corresponding policy set is generated.

[0029] In a second aspect, the present application provides a device for determining the severity of a DC fault, comprising:

[0030] A low-frequency feature extraction unit is used to extract corresponding low-frequency band fault feature signals based on transient data of the AC / DC power transmission system; the transient data includes: the terminal AC voltage, terminal AC current and rotor angle of each generator;

[0031] a power angle determination unit, configured to determine the equivalent electromagnetic power and equivalent angle of the AC / DC power transmission system during the fault period according to the low-frequency fault characteristic signal;

[0032] The severity determination unit is used to determine the severity of the DC fault according to the equivalent electromagnetic power and the equivalent power angle.

[0033] Furthermore, the device for determining the severity of a DC fault further includes:

[0034] The transient data acquisition unit is used to acquire corresponding transient data according to the operating mode of the AC / DC power transmission system; the operating mode includes the full startup mode and the maintenance mode of the generator set.

[0035] Furthermore, the severity determination unit includes:

[0036] a system kinetic energy determination module, configured to determine, based on the equivalent electromagnetic power and the equivalent power angle, the system kinetic energy generated by the AC / DC power transmission system when the AC / DC power transmission system adopts various restart strategies to restore the system after a fault;

[0037] The severity determination module is used to determine the severity of the DC fault according to the system kinetic energy.

[0038] Furthermore, the severity determination unit includes:

[0039] A relationship curve generating module, used for generating a relationship curve diagram between the equivalent electromagnetic power and the equivalent power angle;

[0040] The severity determination module is configured to determine the severity according to the relationship curve diagram.

[0041] Furthermore, the fault characteristic signal includes: a voltage fault characteristic signal, a current fault characteristic signal and a rotor angle fault characteristic signal; the power angle determination unit includes:

[0042] an active power determination module, configured to determine the active power of each generator during a system fault period based on the voltage fault characteristic signal and the current fault characteristic signal of each generator;

[0043] an electromagnetic power determination module, configured to determine the equivalent electromagnetic power of the AC / DC power transmission system during the fault period based on the inertia time constant of each generator and the active power of each generator during the system fault period;

[0044] A power angle determination module is used to determine the equivalent power angle of the AC / DC power transmission system during the fault period based on the inertia time constant of each generator and the rotor angle fault characteristic signal.

[0045] Furthermore, the system kinetic energy determination module includes:

[0046] a fault value determination module, configured to determine an electromagnetic power fault value according to the equivalent electromagnetic power;

[0047] The system kinetic energy determination module is used to determine the system kinetic energy according to the mechanical input power of the prime mover, the electromagnetic power fault value and the rotor angle of each generator.

[0048] Furthermore, the severity determination module includes:

[0049] a kinetic energy sorting module, configured to sort the magnitude of system kinetic energy generated by the AC / DC power transmission system when the AC / DC power transmission system adopts different restart strategies to recover from a fault;

[0050] The strategy set module is used to determine the severity of the fault according to the sorting result and generate a corresponding strategy set.

[0051] In a third aspect, the present application provides an electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the method for determining the severity of a DC fault when executing the program.

[0052] In a fourth aspect, the present application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method for determining the severity of a DC fault.

[0053] In a fifth aspect, the present application provides a computer program product, comprising a computer program / instruction, which, when executed by a processor, performs the steps of the method for determining the severity of a DC fault.

[0054] To address the problems in the prior art, the present application provides a method and device for determining the severity of a DC fault. These methods collect corresponding transient data based on the operating mode of the AC / DC power transmission system, extract corresponding fault characteristic signals, and then calculate the system power and power angle. Finally, the severity of the DC fault is determined based on the power and power angle. Furthermore, a relationship curve can be generated based on the power and power angle, and the severity of the DC fault can be determined from the relationship curve. The kinetic energy of the AC / DC power transmission system can also be calculated based on the power and power angle, and the severity of the DC fault can be ranked accordingly. This allows comparison of the impact of various DC faults and different restart strategies on the system. The calculation process is clear and does not require complex calculations, providing a basis for the subsequent formulation of reasonable control and protection strategies, thereby improving the operational stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 any creative work.

[0056] Figure 1 This is one of the flow charts of the method for determining the severity of a DC fault in an embodiment of the present application;

[0057] Figure 2This is a flow chart for determining electromagnetic power and power angle during a fault phase in an embodiment of the present application;

[0058] Figure 3 This is a flow chart for determining system kinetic energy in an embodiment of the present application;

[0059] Figure 4 This is a flow chart for determining the severity of a DC fault in an embodiment of the present application;

[0060] Figure 5 This is the second flow chart of the method for determining the severity of a DC fault in an embodiment of the present application;

[0061] Figure 6 This is one of the structural diagrams of the device for determining the severity of a DC fault in an embodiment of the present application;

[0062] Figure 7 This is a structural diagram of a power angle determination unit in an embodiment of the present application;

[0063] Figure 8 This is a structural diagram of a system kinetic energy determination module in an embodiment of the present application;

[0064] Figure 9 This is a structural diagram of the severity determination module in an embodiment of the present application;

[0065] Figure 10 This is a structural diagram of the severity determination module in an embodiment of the present application;

[0066] Figure 11 This is a structural diagram of a severity determination unit in an embodiment of the present application;

[0067] Figure 12 Schematic diagram of the power angle curve in the embodiment of the present application;

[0068] Figure 13 This is a schematic diagram of an equivalent system in an embodiment of the present application;

[0069] Figure 14 Schematic diagram showing comparison of curves before and after active power filtering of Strategy A in the embodiment of the present application;

[0070] Figure 15 This is a schematic diagram comparing the curves before and after active power filtering of Strategy B in the embodiment of this application;

[0071] Figure 16 This is a schematic diagram of the power angle curve of strategy A in the embodiment of this application;

[0072] Figure 17 This is a schematic diagram of the power angle curve of strategy B in the embodiment of this application;

[0073] Figure 18 A schematic structural diagram of an electronic device in an embodiment of the present application;

[0074] Figure 19 This is an overall flow chart of the method for determining the severity of a DC fault in an embodiment of the present application. DETAILED DESCRIPTION

[0075] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0076] In one embodiment, in order to comprehensively consider the characteristics of the power angle in the AC / DC power transmission system, determine the severity of different DC faults, and intuitively compare the impact of different DC faults on the power grid, see Figure 19 , the present application provides a method for determining the severity of a DC fault, comprising:

[0077] S001: Extracting corresponding low-frequency fault characteristic signals based on transient data of the AC / DC power transmission system; wherein the transient data includes: the AC voltage, AC current, and rotor angle of each generator on the AC side;

[0078] S002: Determine the equivalent electromagnetic power and equivalent power angle of the AC / DC power transmission system during the fault period based on the low-frequency fault characteristic signal; wherein the method for calculating the equivalent electromagnetic power and equivalent power angle is described in detail below;

[0079] S003: Determine the severity of the DC fault according to the equivalent electromagnetic power and the equivalent power angle.

[0080] Understandably, to prevent DC outages caused by DC line faults and overvoltages due to commutation failures and lockouts of converter valves, and to improve the DC operational reliability of AC / DC transmission systems, DC control and protection systems incorporate a DC line fault recovery sequence (DFRS) and set a maximum permissible number of commutation failures for the converter valves. However, when the restart mechanism is used after a DC line fault occurs, the energy accumulated during fault recovery can impact the AC / DC transmission system; different restart strategies have varying degrees of impact. Failure to restart or an excessive number of permissible commutation failures will directly impact the operating time of safety control devices in the AC / DC transmission system. Therefore, it is essential to determine the severity of different DC faults on the AC / DC transmission system in order to select an appropriate post-fault strategy.

[0081] It's important to note that the so-called "restart strategy" can be understood as follows: To ensure DC power supply reliability, a DC transmission system typically employs a restart strategy (similar to AC line reclosing) to restore the system after a DC line fault or multiple commutation failures in the converter valve occur. For example, in actual projects, UHVDC restart strategies include but are not limited to: DC unipolar double restart, DC bipolar single restart, and bipolar double restart.

[0082] The present embodiment selects a device with a lower sampling frequency and comprehensively considers the characteristics of the power angle to propose a screening method for distinguishing the severity of different DC faults. This method solves the problem of difficulty in intuitively comparing the impact of different DC faults on the power grid. The method mainly includes the following steps: determining the operating mode and performing data acquisition, extracting fault characteristic signals, calculating equivalent electromagnetic power and equivalent power angle, plotting power angle curves and / or calculating system kinetic energy, and determining the severity of the DC fault. This method overcomes the shortcomings of existing technologies, which make it difficult to compare the impact of various DC faults and different restart strategies on the system. Its judgment process is clear and does not require complex calculations. It provides a basis for formulating reasonable control and protection strategies, thereby improving system stability.

[0083] In an embodiment of the present application, the method for determining the severity of a DC fault provided by the present application can collect corresponding transient data according to the operating mode of the AC / DC power transmission system, extract the corresponding fault characteristic signal, and then calculate the system power and power angle, and finally determine the severity of the DC fault based on the power and power angle.

[0084] In another embodiment, see Figure 1 The method for determining the severity of a DC fault provided in this application includes:

[0085] S100: Acquire corresponding transient data according to the operating mode of the AC / DC power transmission system; the operating mode includes a full-start mode and a maintenance mode of the generator set;

[0086] S101: Extracting corresponding low-frequency fault characteristic signals based on transient data of the AC / DC power transmission system; the transient data includes: the AC voltage, AC current, and rotor angle of each generator on the AC side; specifically, using a synchronized phasor measurement unit (PMU) to collect fault data of the AC / DC power transmission system, using the angular velocity change of the generator as a protection triggering criterion to identify the time of fault occurrence; extracting corresponding low-frequency fault characteristic signals starting from the time of fault occurrence;

[0087] S102: Determine the equivalent electromagnetic power and equivalent power angle of the AC / DC power transmission system during the fault period according to the low-frequency fault characteristic signal;

[0088] S103: determining, based on the equivalent electromagnetic power and the equivalent power angle, system kinetic energy generated by the AC / DC power transmission system when the AC / DC power transmission system adopts different restart strategies for system recovery after a fault;

[0089] S104: Determine the severity of the DC fault according to the system kinetic energy.

[0090] Specifically, first, determine the operating mode of the AC / DC system and collect transient data. The operating mode of the AC / DC system requires determining the number of thermal power units in operation, their connection locations, and actual output, the output power of the DC and AC channels, and the reactive compensation parameters of the converter station. For example, the full-power-on mode of the generator sets: all thermal power units are turned on and operating at rated power, the DC operates at the maximum power, the AC channel is overloaded, and the converter station is overcompensated with a certain amount of capacitance. The maintenance mode: half of the thermal power units are turned on and the rest are under maintenance. The units operate at half of the rated power, the DC operates at the maximum power, the AC channel is lightly loaded, and the converter station is overcompensated with a certain amount of capacitance. Under a determined operating mode, data on the AC voltage, AC current, and rotor angle of each generator on the AC side of the UHV AC / DC system, as well as the rotor angle of the equivalent system, are collected during different DC faults and restart strategies.

[0091] Second, extract the low-frequency fault signal and calculate the electromagnetic power of each generator. Decompose the collected power signal into sub-band space to obtain a low-frequency range suitable for the signal (while retaining the original fault characteristics, minimize the sampling frequency). The embodiment of the present application uses a Butterworth low-pass filter to decompose the calculated generator outlet active power variable into sub-band space, filter out the interference of the high-frequency noise of the line itself, and the sampled signal is 0-200Hz.

[0092] Third, based on the equivalent electromagnetic power and equivalent power angle, the kinetic energy generated by the AC / DC transmission system when different restart strategies are used to restore the system after a fault can be determined. This step can be used to compare DC faults, such as a double commutation failure fault and a single-pole ground fault, to distinguish the impact of different faults on the AC / DC transmission system within the same timeframe. It can also be used to determine the impact of different restart strategies on the system after the same DC fault.

[0093] Fourth, determine the severity of the DC fault based on system kinetic energy. Some faults are transient, and a restart strategy can quickly restore the DC. By determining the severity of the fault and the impact of post-fault restart on the system, a screening set can be created to effectively guide post-fault safety and stability measures.

[0094] As can be seen from the above description, the method for determining the severity of a DC fault provided in this application can calculate the kinetic energy of the AC / DC transmission system based on the power and power angle, and rank the severity of the DC fault accordingly, thereby being able to compare the impact of various DC faults and different restart strategies on the system. The calculation process is clear and does not require complex calculations, providing a basis for the subsequent formulation of reasonable control and protection strategies, thereby improving the operational stability of the system.

[0095] In one embodiment, see Figure 2 The fault characteristic signal includes: a voltage fault characteristic signal, a current fault characteristic signal, and a rotor angle fault characteristic signal; determining the electromagnetic power and power angle of the AC / DC power transmission system during the fault period according to the fault characteristic signal includes:

[0096] S201: Determine the active power of each generator during the system fault period according to the voltage fault characteristic signal and the current fault characteristic signal of each generator;

[0097] S202: Determine the equivalent electromagnetic power of the AC / DC power transmission system during the fault period based on the inertia time constant of each generator and the active power of each generator during the system fault period;

[0098] S203: Determine an equivalent power angle of the AC / DC power transmission system during a fault period according to the inertia time constant of each generator and the rotor angle fault characteristic signal.

[0099] Understandably, see Figure 12 , the three-phase power supply is phase A, phase B, and phase C in sequence, where is the instantaneous voltage of phase A of the i-th generator, is the instantaneous current of phase A of the i-th generator.

[0100] The extended equal area method (EEAC) is used to calculate the equivalent electromagnetic power and equivalent power angle of AC / DC transmission systems. Specifically, the generator sets in the system are studied. The severely disturbed generator set is divided into S, and the remaining generator sets are divided into A. For example, if a UHV AC line fault occurs at the DC sending end, the UHV generator sets that are electrically close to the fault location (or within a three-level connection) are divided into the severe generator set S, and the DC receiving end generator sets are divided into A. It is assumed that the rotor angles of the generator sets in each generator set have no relative swing. The equivalent electrical output power and equivalent power angle are calculated as follows:

[0101]

[0102]

[0103]

[0104]

[0105] Where: P i and P j are the active power of each generator; δ i and δ j are the rotor angles of each generator; M i and M j are the inertia time constants of each generator; P and δ are the equivalent electromagnetic power and equivalent power angle of the equivalent system.

[0106] As can be seen from the above description, the method for determining the severity of a DC fault provided by this application can determine the electromagnetic power and power angle of the AC-DC power transmission system during the fault period according to the fault characteristic signal.

[0107] In one embodiment, referring to Figure 3 , when determining the system kinetic energy generated by the AC-DC power transmission system during fault recovery using different post-fault restart strategies according to the electromagnetic power and power angle of the AC-DC power transmission system during the fault period and the steady-state period respectively, it includes:

[0108] S301: Determine the electromagnetic power fault value according to the equivalent electromagnetic power;

[0109] S302: Determine the system kinetic energy according to the mechanical input power of the prime mover, the electromagnetic power fault value, and the rotor angles of each generator.

[0110] It can be understood that DC faults include but are not limited to single-pole grounding faults, two commutation failure faults, three commutation failure faults, etc. In steps S301 to S302, it is necessary to calculate the kinetic energy of the system during system recovery using different restart strategies after the same DC fault occurs. (For example, bipolar two full-voltage one-step voltage reduction restart, bipolar two full-voltage restart, single-pole two full-voltage one-step voltage reduction while blocking the restart function of the opposite pole, bipolar one restart, etc. strategies.)

[0111]

[0112] Where A1 is the kinetic energy of the equivalent system; P M is the mechanical input power of the prime mover in the equivalent system, per-unit value; P EMi is the peak value of the generator electromagnetic power, per-unit value; i is the time period serial number, i = 1 is the pre-fault steady-state stage (t < t0), i = 2 is the fault stage (t0 ~ t c ), i = 3 is the post-fault clearing stage (t > t c ); δ is the generator rotor angle, unit is rad. Among them, when calculating A1, only the fault stage (t0 ~ t c ) is considered.

[0113] As can be seen from the above description, the method for determining the severity of a DC fault provided in the present application can determine the system kinetic energy generated by the AC / DC transmission system when the AC / DC transmission system adopts different post-fault restart strategies for fault recovery based on the electromagnetic power and power angle of the AC / DC transmission system during the fault period and the steady-state period.

[0114] In one embodiment, see Figure 4 , the determining the severity of the DC fault according to the system kinetic energy includes:

[0115] S401: sorting the magnitude of system kinetic energy generated by the AC / DC power transmission system when the AC / DC power transmission system adopts different restart strategies for fault recovery after a fault;

[0116] S402: Determine the severity of the fault according to the ranking result and generate a corresponding policy set.

[0117] It can be understood that the system kinetic energy obtained under different DC faults and different restart strategies forms a set A={A1,A2…A n}. Sort the system kinetic energy under all faults from large to small. For example, A1>A2…A n , the greater the system kinetic energy, the greater the impact on the system, and thus the fault screening set is obtained.

[0118] It can be seen from the above description that the method for determining the severity of a DC fault provided in the present application can determine the severity of the DC fault according to the system kinetic energy.

[0119] In one embodiment, see Figure 5 , determining the severity of the DC fault according to the equivalent electromagnetic power and the equivalent power angle, including:

[0120] S501: generating a relationship curve diagram between the equivalent electromagnetic power and the equivalent power angle;

[0121] S502: Determine the severity according to the relationship curve graph.

[0122] Understandably, see Figure 12Steady state refers to the period before and after a fault, while the fault phase is transient. In normal operation, point a represents the normal generator operating point, corresponding to a power angle of δ0. In the fault phase, the power characteristic immediately drops to P2 after the fault. Due to rotor inertia, the rotor angle does not change suddenly, and the operating point immediately shifts from point a to point b. Furthermore, since the prime mover remains unchanged and is greater than the electromagnetic power, the generator rotor angle accelerates from operating point b to operating point c. If the fault is removed promptly, the generator's power characteristic shifts to P3, and the generator operating point suddenly shifts from point c to point e. The generator's electromagnetic power exceeds the prime mover's mechanical power, causing the rotor angle to decelerate. The larger the area of A1, the greater the impact on the system.

[0123] It can be seen from the above description that the method for determining the severity of a DC fault provided in the present application can determine the severity according to the relationship curve diagram.

[0124] In order to more clearly illustrate the method provided by this application, an example is given.

[0125] In simulation analysis, the feasibility of screening methods for determining the severity of different DC faults is generally discussed first. Then, based on the data obtained from the simulation, data processing is performed to rank the severity of different faults on the power grid, providing a theoretical reference for the power grid operation mode.

[0126] Based on the RTDS simulation platform, a real-world AC / DC combined transmission system (equivalent to the AC / DC transmission system in the embodiment of this application) is built. First, the AC system at the DC sending end is equivalent. The equivalent impedance at the sending end is X = 0.02313 pu. The equivalent system diagram is as follows: Figure 13 The AC system is connected to 12 thermal power units, six of which are connected to the 1050kV busbar and six to the 525kV busbar. The DC system uses a bipolar connection method, with layered connection at the receiving end. The rated DC voltage is ±800kV and the rated capacity is 10,000MW.

[0127] exist Figure 13 In the AC / DC system shown, the DC power is 4500 MW, the filter provides 1938 MVar reactive power, and nine thermal power units are in operation. A single-pole grounding fault occurs in the first section of the bipolar line 0.5 s after the fault occurs, lasting 100 ms. The method is verified using two faults: a successful bipolar full-voltage restart (Strategy A) and a successful bipolar full-voltage restart (Strategy B). The calculation method for other faults is the same.

[0128] Step 1: Determine the initial AC / DC operating mode: Start nine thermal power units, all operating at rated power: 4500 MW DC power, 1130 MW AC channel power, and 1938 MVar reactive power provided by the converter station capacitors. Collect transient data: Collect data on the machine-side AC voltage, machine-side AC current, and rotor angle of each of the nine units, as well as the rotor angle of the equivalent power grid.

[0129] Step 2: Low-pass filter the calculated generator active power. The embodiment of the present application uses a Butterworth low-pass filter to decompose the calculated generator output active power variable into sub-band space, filter out the interference of the high-frequency noise of the line itself, and the sampled signal is 0-200Hz. When using strategy A to restore the system, the waveforms before and after the active power filtering are as follows: Figure 14 When using strategy B to restore the system, the waveforms before and after active power filtering are as follows: Figure 15 As shown. Figure 14 and Figure 15 It can be seen that the main waveform features are retained after filtering.

[0130] Step 3: Calculate the equivalent electrical output power and equivalent power angle.

[0131] Step 4: Draw the power angle curve. Strategy A corresponds to Figure 16 , strategy B corresponds to Figure 17 .

[0132] Step 5: Calculate the system kinetic energy of the DC fault.

[0133] A1 策略A =358.5493

[0134] A1 策略B =213.9555

[0135] Step 6: Compare the system kinetic energy values of strategy A and strategy B, and sort them from large to small. The larger the value, the smaller the impact on the system, and obtain the final fault screening set.

[0136] 1) While retaining the original signal characteristics, the sampling frequency of the device is reduced, and a screening method for distinguishing the severity of different DC faults is proposed, which reduces the device procurement cost.

[0137] 2) The principle is simple and does not require complex calculations. It can intuitively give the impact of various fault conditions on the power grid and provide reference suggestions for actual power grid operation.

[0138] 3) It can calculate DC line faults and various restart strategies, as well as abnormal operation conditions such as commutation failure, and has a wide range of applications.

[0139] Based on the same inventive concept, the embodiments of the present application also provide a device for determining the severity of a DC fault, which can be used to implement the method described in the above embodiments, as described in the following embodiments. Since the principle of solving the problem by the device for determining the severity of a DC fault is similar to that of the method for determining the severity of a DC fault, the implementation of the device for determining the severity of a DC fault can refer to the implementation of the method based on software performance benchmark determination, and the repeated parts will not be repeated. As used below, the term "unit" or "module" can be a combination of software and / or hardware that implements a predetermined function. Although the system described in the following embodiments is preferably implemented in software, implementation in hardware, or a combination of software and hardware, is also possible and conceived.

[0140] In one embodiment, see Figure 6 In order to comprehensively consider the characteristics of the power angle in the AC / DC power transmission system, determine the severity of different DC faults, and intuitively compare the impact of different DC faults on the power grid, the present application provides a device for determining the severity of a DC fault, including: a low-frequency feature extraction unit 701, a power angle determination unit 702, and a severity determination unit 703.

[0141] The low-frequency feature extraction unit 701 is configured to extract corresponding low-frequency fault feature signals based on transient data of the AC / DC power transmission system; the transient data includes: the terminal AC voltage, terminal AC current, and rotor angle of each generator;

[0142] The power angle determination unit 702 is configured to determine the equivalent electromagnetic power and the equivalent angle of the AC / DC power transmission system during the fault period according to the low-frequency fault characteristic signal;

[0143] The severity determination unit 703 is configured to determine the severity of the DC fault according to the equivalent electromagnetic power and the equivalent power angle.

[0144] In one embodiment, the device for determining the severity of a DC fault further includes:

[0145] The transient data acquisition unit is used to acquire corresponding transient data according to the operating mode of the AC / DC power transmission system; the operating mode includes the full startup mode and the maintenance mode of the generator set.

[0146] In one embodiment, see Figure 11 The severity determination unit 703 includes: a system kinetic energy determination module 1101 and a severity determination module 1102.

[0147] A system kinetic energy determination module 1201 is configured to determine, based on the equivalent electromagnetic power and the equivalent power angle, the system kinetic energy generated by the AC / DC power transmission system when the AC / DC power transmission system adopts various restart strategies to restore the system after a fault;

[0148] The severity determination module 1202 is configured to determine the severity of the DC fault according to the system kinetic energy.

[0149] In one embodiment, see Figure 10 The severity determination unit 703 includes: a relationship curve generation module 1301 and a severity judgment module 1302.

[0150] A relationship curve generating module 1301 is used to generate a relationship curve diagram between the equivalent electromagnetic power and the equivalent power angle;

[0151] The severity determination module 1302 is configured to determine the severity according to the relationship curve diagram.

[0152] In one embodiment, see Figure 7 The fault characteristic signal includes: a voltage fault characteristic signal, a current fault characteristic signal and a rotor angle fault characteristic signal; the power angle determination unit 702 includes: an active power determination module 801, an electromagnetic power determination module 802 and a power angle determination module 803.

[0153] An active power determination module 801 is configured to determine the active power of each generator during a system fault period based on the voltage fault characteristic signal and the current fault characteristic signal of each generator;

[0154] The electromagnetic power determination module 802 is configured to determine the equivalent electromagnetic power of the AC / DC power transmission system during the fault period based on the inertia time constant of each generator and the active power of each generator during the system fault period;

[0155] The power angle determination module 803 is configured to determine the equivalent power angle of the AC / DC power transmission system during the fault period according to the inertia time constant of each generator and the rotor angle fault characteristic signal.

[0156] In one embodiment, see Figure 8 The system kinetic energy determination module 1201 includes: a fault value determination module 901 and a system kinetic energy determination module 902.

[0157] A fault value determination module 901 is configured to determine an electromagnetic power fault value based on the equivalent electromagnetic power;

[0158] The system kinetic energy determination module 902 is configured to determine the system kinetic energy according to the mechanical input power of the prime mover, the electromagnetic power fault value, and the rotor angle of each generator.

[0159] In one embodiment, see Figure 9 The severity determination module 1202 includes: a kinetic energy ranking module 1001 and a strategy set module 1002.

[0160] A kinetic energy ranking module 1001 is configured to rank the magnitude of system kinetic energy generated by the AC / DC power transmission system when the AC / DC power transmission system adopts different restart strategies for fault recovery after a fault;

[0161] The policy set module 1002 is used to determine the severity of the fault according to the sorting result and generate a corresponding policy set.

[0162] From a hardware perspective, in order to comprehensively consider the characteristics of the power angle in AC / DC power transmission systems, determine the severity of different DC faults, and intuitively compare the impact of different DC faults on the power grid, the present application provides an embodiment of an electronic device for implementing all or part of the method for determining the severity of a DC fault. The electronic device specifically includes the following:

[0163] A processor, a memory, a communications interface, and a bus; wherein the processor, memory, and communications interface communicate with each other via the bus; the communications interface is used to transmit information between the DC fault severity determination device and related devices such as core business systems, user terminals, and related databases; the logic controller can be a desktop computer, a tablet computer, a mobile terminal, etc., but this embodiment is not limited thereto. In this embodiment, the logic controller can be implemented with reference to the embodiments of the DC fault severity determination method and the DC fault severity determination device in the embodiments, the contents of which are incorporated herein and any repetitions are not repeated.

[0164] It is understandable that the user terminal may include a smart phone, a tablet electronic device, a network set-top box, a portable computer, a desktop computer, a personal digital assistant (PDA), a vehicle-mounted device, a smart wearable device, etc. Among them, the smart wearable device may include smart glasses, a smart watch, a smart bracelet, etc.

[0165] In practical applications, part of the method for determining the severity of a DC fault can be performed on the electronic device as described above, or all operations can be performed on the client device. The specific method can be selected based on the processing capabilities of the client device and the limitations of the user's usage scenario. This application does not impose any restrictions on this. If all operations are performed on the client device, the client device may also include a processor.

[0166] The client device may include a communication module (i.e., a communication unit) that can establish a communication connection with a remote server to implement data transmission with the server. The server may include a server on the task scheduling center side, and in other implementation scenarios, may also include a server on an intermediate platform, such as a server on a third-party server platform that has a communication link with the task scheduling center server. The server may include a single computer device, a server cluster consisting of multiple servers, or a server structure of a distributed device.

[0167] Figure 18 Schematic block diagram of the system structure of the electronic device 9600 according to an embodiment of the present application. Figure 18 As shown, the electronic device 9600 may include a central processing unit 9100 and a memory 9140; the memory 9140 is coupled to the central processing unit 9100. It is worth noting that the Figure 18 is exemplary; other types of structures may also be used to supplement or replace this structure to implement telecommunication functions or other functions.

[0168] In one embodiment, the function of determining the severity of a DC fault may be integrated into the central processing unit 9100. The central processing unit 9100 may be configured to perform the following control:

[0169] S001: Extracting corresponding low-frequency fault characteristic signals based on transient data of the AC / DC power transmission system; wherein the transient data includes: the AC voltage, AC current, and rotor angle of each generator on the AC side;

[0170] S002: Determine the equivalent electromagnetic power and equivalent power angle of the AC / DC power transmission system during the fault period based on the low-frequency fault characteristic signal; wherein the method for calculating the equivalent electromagnetic power and equivalent power angle is described in detail below;

[0171] S003: Determine the severity of the DC fault according to the equivalent electromagnetic power and the equivalent power angle.

[0172] In an embodiment of the present application, the method for determining the severity of a DC fault provided by the present application can collect corresponding transient data according to the operating mode of the AC / DC power transmission system, extract the corresponding fault characteristic signal, and then calculate the system power and power angle, and finally determine the severity of the DC fault based on the power and power angle.

[0173] In another embodiment, the device for determining the severity of a DC fault can be configured separately from the central processing unit 9100. For example, the device for determining the severity of a DC fault of the data composite transmission device can be configured as a chip connected to the central processing unit 9100, and the function of the method for determining the severity of a DC fault can be implemented under the control of the central processing unit.

[0174] like Figure 18 As shown, the electronic device 9600 may further include: a communication module 9110, an input unit 9120, an audio processor 9130, a display 9160, and a power supply 9170. It is worth noting that the electronic device 9600 does not necessarily have to include Figure 18 In addition, the electronic device 9600 may also include all components shown in Figure 18 For components not shown, reference may be made to the prior art.

[0175] like Figure 18 As shown, the central processing unit 9100 is sometimes also referred to as a controller or operation control, and may include a microprocessor or other processor device and / or logic device. The central processing unit 9100 receives input and controls the operation of various components of the electronic device 9600.

[0176] Memory 9140 can be, for example, one or more of a cache, flash memory, hard drive, removable media, volatile memory, non-volatile memory, or other suitable devices. It can store the aforementioned failure-related information and also store programs that execute the relevant information. The CPU 9100 can execute the programs stored in memory 9140 to implement information storage or processing.

[0177] The input unit 9120 provides input to the central processing unit 9100. The input unit 9120 may be, for example, a keypad or touch input device. The power supply 9170 is used to provide power to the electronic device 9600. The display 9160 is used to display objects such as images and text. The display may be, for example, an LCD display, but is not limited thereto.

[0178] The memory 9140 may be a solid-state memory, such as a read-only memory (ROM), a random access memory (RAM), or a SIM card. Alternatively, it may be a memory that retains information even when power is off, can be selectively erased, and is provided with more data. Examples of such memory are sometimes referred to as EPROMs. The memory 9140 may also be some other type of device. The memory 9140 includes a buffer memory 9141 (sometimes referred to as a buffer). The memory 9140 may include an application / function storage unit 9142 for storing application programs and function programs or processes for executing the operation of the electronic device 9600 by the central processing unit 9100.

[0179] The memory 9140 may also include a data storage unit 9143 for storing data, such as contacts, digital data, pictures, sounds, and / or any other data used by the electronic device. The driver storage unit 9144 of the memory 9140 may include various driver programs for the electronic device's communication functions and / or for executing other functions of the electronic device (such as messaging applications, address book applications, etc.).

[0180] The communication module 9110 is a transmitter / receiver 9110 that sends and receives signals via an antenna 9111. The communication module (transmitter / receiver) 9110 is coupled to the central processor 9100 to provide input signals and receive output signals, which may be the same as in a conventional mobile communication terminal.

[0181] Based on different communication technologies, multiple communication modules 9110 can be provided in the same electronic device, such as a cellular network module, a Bluetooth module, and / or a wireless local area network module. The communication module (transmitter / receiver) 9110 is also coupled to a speaker 9131 and a microphone 9132 via an audio processor 9130 to provide audio output via the speaker 9131 and receive audio input from the microphone 9132, thereby implementing common telecommunication functions. The audio processor 9130 may include any suitable buffer, decoder, amplifier, etc. In addition, the audio processor 9130 is also coupled to the central processing unit 9100, enabling local recording via the microphone 9132 and playback of stored audio via the speaker 9131.

[0182] Embodiments of the present application also provide a computer-readable storage medium capable of implementing all steps of the method for determining the severity of a DC fault in the above-mentioned embodiment, where the execution subject is a server or a client. The computer-readable storage medium stores a computer program. When the computer program is executed by a processor, the computer program implements all steps of the method for determining the severity of a DC fault in the above-mentioned embodiment, where the execution subject is a server or a client. For example, when the processor executes the computer program, the following steps are implemented:

[0183] S001: Extracting corresponding low-frequency fault characteristic signals based on transient data of the AC / DC power transmission system; wherein the transient data includes: the AC voltage, AC current, and rotor angle of each generator on the AC side;

[0184] S002: Determine the equivalent electromagnetic power and equivalent power angle of the AC / DC power transmission system during the fault period based on the low-frequency fault characteristic signal; wherein the method for calculating the equivalent electromagnetic power and equivalent power angle is described in detail below;

[0185] S003: Determine the severity of the DC fault according to the equivalent electromagnetic power and the equivalent power angle.

[0186] In an embodiment of the present application, the method for determining the severity of a DC fault provided by the present application can collect corresponding transient data according to the operating mode of the AC / DC power transmission system, extract the corresponding fault characteristic signal, and then calculate the system power and power angle, and finally determine the severity of the DC fault based on the power and power angle.

[0187] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, apparatus, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0188] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (apparatus), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as a combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0189] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0190] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0191] Specific embodiments are used in the present invention to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas. At the same time, for those skilled in the art, according to the ideas of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present invention.

Claims

1. A method for determining the severity of a DC fault, characterized in that: include: Extracting corresponding low-frequency fault characteristic signals based on transient data of the AC / DC power transmission system; wherein the low-frequency fault characteristic signals include: voltage fault characteristic signals, current fault characteristic signals, and rotor angle fault characteristic signals; the transient data include: generator-end AC voltage, generator-end AC current, and rotor angle of each generator; Determining the equivalent electromagnetic power and equivalent power angle of the AC / DC power transmission system during the fault period according to the low-frequency fault characteristic signal; determining the severity of the DC fault according to the equivalent electromagnetic power and the equivalent power angle; The determining of the severity of the DC fault based on the equivalent electromagnetic power and the equivalent power angle includes: determining, based on the equivalent electromagnetic power and the equivalent power angle, system kinetic energy generated by the AC / DC power transmission system when the AC / DC power transmission system adopts various restart strategies for system recovery after a fault; determining the severity of the DC fault based on the system kinetic energy; and sorting the system kinetic energy from large to small to obtain a fault screening set.

2. The method for determining the severity of a DC fault according to claim 1, wherein: Also includes: Acquiring corresponding transient data according to the operating mode of the AC / DC power transmission system; The operating modes include a full-start mode and an overhaul mode for the generator set.

3. The method for determining the severity of a DC fault according to claim 2, wherein: Determining the severity of the DC fault according to the equivalent electromagnetic power and the equivalent power angle includes: generating a relationship curve graph between the equivalent electromagnetic power and the equivalent power angle; The severity is determined according to the relationship curve graph.

4. The method for determining the severity of a DC fault according to claim 2, wherein: The determining, according to the low-frequency fault characteristic signal, the equivalent electromagnetic power and the equivalent power angle of the AC / DC power transmission system during the fault period includes: determining the active power of each generator during the system fault period according to the voltage fault characteristic signal and the current fault characteristic signal of each generator; Determining the equivalent electromagnetic power of the AC / DC power transmission system during the fault period according to the inertia time constant of each generator and the active power of each generator during the system fault period; The equivalent power angle of the AC / DC power transmission system during the fault period is determined according to the inertia time constant of each generator and the rotor angle fault characteristic signal.

5. The method for determining the severity of a DC fault according to claim 1, wherein: The determining, based on the equivalent electromagnetic power and the equivalent power angle, the system kinetic energy generated by the AC / DC power transmission system when the AC / DC power transmission system adopts various restart strategies to restore the system after a fault, includes: determining an electromagnetic power fault value according to the equivalent electromagnetic power; The system kinetic energy is determined according to the mechanical input power of the prime mover, the electromagnetic power fault value, and the rotor angle of each generator.

6. The method for determining the severity of a DC fault according to claim 1, wherein: Determining the severity of the DC fault according to the system kinetic energy includes: sorting the magnitude of system kinetic energy generated by the AC / DC power transmission system when the AC / DC power transmission system adopts various restart strategies to recover from a fault; The severity of the fault is determined based on the sorting results, and a corresponding policy set is generated.

7. A device for determining the severity of a DC fault, characterized in that: include: A low-frequency feature extraction unit is configured to extract corresponding low-frequency fault feature signals based on transient data of the AC / DC power transmission system; wherein the low-frequency fault feature signals include voltage fault feature signals, current fault feature signals, and rotor angle fault feature signals; and the transient data include the generator-end AC voltage, generator-end AC current, and rotor angle of each generator; a power angle determination unit, configured to determine the equivalent electromagnetic power and equivalent angle of the AC / DC power transmission system during the fault period according to the low-frequency fault characteristic signal; a severity determination unit, configured to determine the severity of a DC fault according to the equivalent electromagnetic power and the equivalent power angle; The severity determination unit includes: a system kinetic energy determination module, used to determine the system kinetic energy generated by the AC / DC power transmission system when the AC / DC power transmission system adopts various restart strategies to restore the system after a fault based on the equivalent electromagnetic power and the equivalent power angle; a severity determination module, used to determine the severity of the DC fault based on the system kinetic energy; wherein the system kinetic energy is sorted from large to small to obtain a fault screening set.

8. The device for determining the severity of a DC fault according to claim 7, characterized in that: Also includes: a transient data acquisition unit, configured to acquire corresponding transient data according to an operating mode of the AC / DC power transmission system; The operating modes include a full-start mode and an overhaul mode for the generator set.

9. The device for determining the severity of a DC fault according to claim 8, characterized in that: The severity determination unit includes: A relationship curve generating module, used for generating a relationship curve diagram between the equivalent electromagnetic power and the equivalent power angle; The severity determination module is configured to determine the severity according to the relationship curve diagram.

10. The device for determining the severity of a DC fault according to claim 8, characterized in that: The power angle determination unit includes: an active power determination module, configured to determine the active power of each generator during a system fault period based on the voltage fault characteristic signal and the current fault characteristic signal of each generator; an electromagnetic power determination module, configured to determine the equivalent electromagnetic power of the AC / DC power transmission system during the fault period based on the inertia time constant of each generator and the active power of each generator during the system fault period; A power angle determination module is used to determine the equivalent power angle of the AC / DC power transmission system during the fault period based on the inertia time constant of each generator and the rotor angle fault characteristic signal.

11. The device for determining the severity of a DC fault according to claim 7, characterized in that: The system kinetic energy determination module includes: a fault value determination module, configured to determine an electromagnetic power fault value according to the equivalent electromagnetic power; The system kinetic energy determination module is used to determine the system kinetic energy according to the mechanical input power of the prime mover, the electromagnetic power fault value and the rotor angle of each generator.

12. The device for determining the severity of a DC fault according to claim 7, wherein: The severity determination module includes: a kinetic energy ranking module, configured to rank the magnitude of the system kinetic energy generated by the AC / DC power transmission system when the AC / DC power transmission system adopts various restart strategies to perform fault recovery after a fault; The strategy set module is used to determine the severity of the fault according to the sorting result and generate a corresponding strategy set.

13. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the steps of the method for determining the severity of a DC fault according to any one of claims 1 to 6 are implemented.

14. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for determining the severity of a DC fault according to any one of claims 1 to 6 are implemented.

15. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instruction is executed by a processor, the steps of the method for determining the severity of a DC fault according to any one of claims 1 to 6 are implemented.

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