Flexible DC power grid fault area identification method based on traveling wave dispersion coefficient

Abstract

The invention discloses a flexible DC power grid fault area identification method based on a traveling wave dispersion coefficient, and the method comprises the following steps: constructing a general expression of a line mode voltage first traveling wave according to a mathematical model of the line mode voltage first traveling wave of an internal fault and an external fault on a DC line in a flexible DC power grid; constructing a fault area identification criterion based on the mathematical model; and for a direct current line to be diagnosed, collecting a line mode voltage first traveling wave through a protection device, fitting the line mode voltage first traveling wave by using an LM algorithm according to the general expression, obtaining a # imgabs0 # value from the fitted general expression, and substituting the # imgabs1 # value into the fault area identification criterion to identify an internal fault or an external fault. According to the method, the problem of insufficient applicability of a single-ended protection scheme based on a line boundary in a boundary-free power grid structure is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible direct current transmission protection, and in particular relates to a method for identifying a fault area in a flexible direct current grid based on a traveling wave dispersion coefficient. Background Art

[0002] As global energy and environmental challenges become increasingly severe, the trend is toward adjusting the energy mix through the development of renewable energy sources such as wind power and photovoltaics, thereby transitioning from traditional fossil fuels to clean and renewable energy. As energy transformation and the power revolution continue to advance, traditional power systems are no longer able to meet the demands for fast, efficient, and intelligent power transmission and distribution. Therefore, a new, safer, more reliable, efficient, intelligent, and environmentally friendly power system is needed to leverage the leading role of renewable energy in the green and low-carbon energy transition.

[0003] Flexible DC grids are an effective solution for achieving smooth integration, reliable transmission, flexible consumption, and optimized allocation of large-scale renewable energy. While boasting numerous technical advantages and promising development potential, flexible DC transmission technology also faces numerous key technical challenges. Due to the low damping characteristic of DC grids, after a fault occurs on the DC side, the submodule capacitance of the near-end converter station will rapidly discharge toward the fault point, causing fault currents to reach tens of kiloamperes within a few milliseconds. This can potentially cause the near-end converter valves to lock and irreversible damage to the power electronic components of the system's main equipment. Traveling wave protection, with its superior performance, is unaffected by factors such as line capacitance, current transformer saturation, system impedance, and system oscillations. It is an ideal protection principle for long-distance ultra-high / ultra-high voltage (UHV) transmission lines, including long-distance DC transmission lines. Furthermore, traveling wave protection effectively utilizes the earliest fault information to reach the protection installation. Theoretically, traveling wave protection offers one of the fastest operating speeds of all protection principles. Therefore, researching new traveling wave protection principles for DC transmission lines and improving line protection performance are crucial for ensuring the safe and stable operation of HVDC transmission systems.

[0004] Compared to distributing current-limiting reactors at both ends of a line, centralizing current-limiting reactors at the converter station exit in a multi-terminal flexible DC grid can reduce construction costs and improve economic efficiency. However, traditional single-ended protection schemes rely on current-limiting inductors at both ends of the line. When the current-limiting inductors are concentrated at the converter station exit, single-ended protection schemes based on time and frequency domains fail to distinguish transient quantities in the fault area, making them difficult to apply.

[0005] Chinese patent publication number CN113572139A discloses a single-ended fault protection method and device for flexible DC transmission lines. The method includes: obtaining voltage and current signals at the positive and negative poles of the line, and determining voltage and current fault components based on the steady-state voltage and current signals; constructing a protection activation criterion based on the DC line voltage mutation; calculating the fault voltage reverse wave and its high-frequency component based on the DC transmission line wave impedance, voltage fault component, and current fault component, and then calculating the time-domain energy value of the fault voltage reverse wave within a preset integration window; and constructing an in-zone and out-of-zone fault identification criterion based on the time-domain energy value of the fault voltage reverse wave. When a strong current-limiting inductor is present at either end of the line, the current-limiting inductor changes the propagation characteristics of the reverse wave, including propagation speed and waveform variation. In the method described in this invention, the time domain energy value of the fault voltage reverse wave is an important basis for judging the fault area, and the time domain energy value of the fault voltage reverse wave is related to the amplitude, frequency characteristics, etc. of the reverse wave. If the current limiting inductor causes the propagation characteristics of the reverse wave to change, it may cause irregular attenuation of the reverse wave energy, thereby affecting the accuracy of fault judgment. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for identifying fault areas in a flexible DC grid based on the traveling wave dispersion coefficient, so as to solve the problem of insufficient applicability of single-ended protection schemes based on line boundaries in a "boundaryless" grid structure.

[0007] The technical solutions of the present invention are as follows: In one aspect, the present invention provides a method for identifying a fault area in a flexible DC grid based on a traveling wave dispersion coefficient, comprising the following steps: According to the mathematical model of the first wave of line-mode voltage under internal and external faults on DC lines in flexible DC grid, the general expression of the first wave of line-mode voltage is constructed:

[0008] Where, It is the first wave of line mode voltage under internal fault or external fault on DC line; is a custom symbol obtained by fitting the first wave of the line mode voltage using the LM algorithm; For time; The fault area identification criterion is constructed based on the mathematical model:

[0009]

[0010] Where, is the fault threshold within the area; is the out-of-zone fault threshold; is the exponential coefficient related to the dispersion coefficient of the line mode component; For the DC line to be diagnosed, the first wave of the line mode voltage is collected through the protection device, and the first wave of the line mode voltage is fitted using the LM algorithm according to the general expression, and the value, will The value is substituted into the fault area identification criterion to identify the fault within the area or the fault outside the area.

[0011] Preferably, the construction process of the general expression is specifically as follows: First, by considering the influence of line dispersion on traveling waves, the mathematical models of the first traveling wave of the line mode voltage measured at the protection device when an internal fault occurs and an external fault occurs are calculated respectively:

[0012] Where, is the transfer function of the first wave of line mode voltage on the transmission line, is the propagation distance of the traveling wave, is the propagation speed of the line mode traveling wave, is a complex frequency domain variable, is the line mode component attenuation coefficient, is the line mode component dispersion coefficient, To characterize the traveling wave transmission delay; Based on the mathematical model of the first wave of the line-mode voltage, ignoring the traveling wave delay and considering the attenuation and dispersion of the first wave of the line-mode voltage during the line propagation process, the fault in the DC line occurrence area is calculated. The expression of the first wave of the line-mode voltage is:

[0013] Where, It is the first wave of the line mode voltage measured by the protection device when a fault occurs in the DC line; is the constant term of the expression of the first wave of line mode voltage when there is a fault in the zone; It is the sum of the equivalent inductance of the converter station on the DC side and the inductance of the current-limiting reactor; is the wave impedance of the DC line; Based on the mathematical model of the first wave of the line-mode voltage, ignoring the traveling wave delay and considering the attenuation and dispersion of the first wave of the line-mode voltage during the line propagation process, the expression of the first wave of the line-mode voltage measured by the protection device when an out-of-zone fault occurs on the DC line is calculated as follows:

[0014] Where, It is the first wave of the line mode voltage measured by the protection device when an out-of-zone fault occurs on the DC line; It is the first constant term of the expression of the first wave of line mode voltage when there is an out-of-zone fault; is the second constant term of the expression of the first wave of line mode voltage when there is an out-of-zone fault; Based on the influence of the wave head change time of the first wave of the line mode voltage, when an out-of-zone fault occurs on the DC line, the parameter The second term is ignored, and the expression of the first wave of the line mode voltage is simplified to:

[0015] The general expression is constructed based on the expression of the first row wave of the line mode voltage measured by the protection device when an internal fault or an external fault occurs on the DC line.

[0016] Preferably, the parameters and The calculation formula is as follows:

[0017] Where, is the equivalent inductance of the commutation station on the DC side; is the inductance of the current limiting reactor; For time; is the line mode voltage traveling wave at the fault point.

[0018] Preferably, the parameters The calculation formula is as follows:

[0019] Where, is the equivalent inductance of the commutation station on the DC side; is the inductance of the current limiting reactor; For time; is the line mode voltage traveling wave at the fault point.

[0020] Preferably, the reasoning process of the fault area identification criterion is specifically as follows: Since the traveling wave transmission distance when a fault occurs within the area is shorter than the traveling wave transmission distance when a fault occurs outside the area, the magnitude of the attenuation coefficient can be determined as follows based on the magnitude of the system parameters:

[0021] Where, is the fault traveling wave transmission distance within the area, is the traveling wave transmission distance of the out-of-zone fault; The fault area is identified by comparing the exponential coefficient related to the dispersion coefficient in the double exponential decay function. Let it be the larger component of the exponential coefficient:

[0022] pass The value is compared with the preset in-zone fault threshold and out-zone fault threshold to identify the fault area:

[0023] Where, is the fault threshold within the area; is the out-of-zone fault threshold.

[0024] On the other hand, the present invention provides a flexible DC grid fault area identification system based on traveling wave dispersion coefficient, comprising an inference module, a criterion construction module and a fault identification module; An inference module is used to construct a general expression for the first wave of the line-mode voltage based on a mathematical model of the first wave of the line-mode voltage under internal and external faults on the DC line in the flexible DC grid; A criterion construction module, used for constructing a fault area identification criterion based on the mathematical model; The fault identification module is used to collect the first wave of the line mode voltage through the protection device for the DC line to be diagnosed, fit the first wave of the line mode voltage using the LM algorithm according to the general expression, and obtain value, will The value is substituted into the fault area identification criterion to identify the fault within the area or the fault outside the area.

[0025] On the other hand, the present invention also provides an electronic device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the method for identifying a fault area in a flexible DC grid based on a traveling wave dispersion coefficient as described in any embodiment of the present invention is implemented.

[0026] On the other hand, the present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method for identifying a fault area in a flexible DC grid based on a traveling wave dispersion coefficient as described in any embodiment of the present invention.

[0027] Compared with the prior art, the present invention has the following technical effects: The present invention provides a method for identifying fault areas in a flexible direct current (DC) power grid based on traveling wave dispersion coefficient. The method derives analytical expressions for the first traveling wave of the line-mode voltage for intra-region faults and forward out-of-region faults through the traveling wave dispersion phenomenon. By analyzing the order of magnitude of system parameters, it is proved that the analytical expressions for the first traveling wave of the line-mode voltage for both types of faults conform to the characteristics of a double-exponential attenuation function, and that the exponential coefficient related to the dispersion coefficient in the function is greater within the region than outside the region. Based on this, a protection scheme for identifying fault areas using the attenuation coefficient is proposed, which solves the problem that single-terminal protection schemes based on line boundaries are difficult to apply when current-limiting reactors are centrally configured at the outlet of a multi-terminal flexible DC power grid converter station. This ensures the safe and stable operation of the flexible DC transmission system and helps build a new power system with stronger new energy absorption capabilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is an overall flow chart of the method for identifying fault areas in a flexible DC grid based on traveling wave dispersion coefficient according to the present invention; Figure 2 Schematic diagram of a flexible direct current transmission system constructed according to an embodiment of the present invention; Figure 3 Schematic diagram of the overhead line tower structure used in an embodiment of the present invention; Figure 4 This is a comparison diagram of the simulation value and expression curve of the first wave of the line mode voltage during an intra-zone fault according to the present invention; Figure 5 This is a comparison diagram of the simulation value and expression curve of the first wave of the line mode voltage when there is an out-of-zone fault as described in the present invention. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in combination with specific embodiments of the present application and with reference to the accompanying drawings.

[0030] Example 1 This embodiment provides a method for identifying fault areas in a flexible DC grid based on traveling wave dispersion coefficient. Figure 1 As shown, the following steps are included: An intra-zone fault refers to a fault that occurs within the protection range of a protection device, while an extra-zone fault refers to a fault that occurs outside the protection range of a protection device. Based on the mathematical model of the first wave of the line-mode voltage under intra-zone and extra-zone faults on a DC line in a flexible DC grid, a general expression for the first wave of the line-mode voltage is constructed:

[0031] Where, It is the first wave of line mode voltage under internal fault or external fault on DC line; It is a custom symbol, and its specific value is obtained by fitting the first wave of the line mode voltage using the LM algorithm; For time.

[0032] As a preferred implementation of this embodiment, the construction process of the general expression is specifically as follows: First, by considering the influence of line dispersion on traveling waves, the mathematical models of the first traveling wave of the line mode voltage measured at the protection device when an internal fault occurs and an external fault occurs are calculated respectively:

[0033] Where, is the transfer function of the first wave of line mode voltage on the transmission line, is the propagation distance of the traveling wave, is the propagation speed of the line mode traveling wave, is a complex frequency domain variable; is the attenuation coefficient of the line mode component, is the line mode component dispersion coefficient, To characterize the traveling wave transmission delay.

[0034] Based on the mathematical model of the first wave of the line-mode voltage, ignoring the traveling wave delay and considering the attenuation and dispersion of the first wave of the line-mode voltage during the line propagation process, the fault in the DC line occurrence area is calculated. The expression of the first wave of the line-mode voltage is:

[0035] Where, It is the first wave of the line mode voltage measured by the protection device when a fault occurs in the DC line; is the constant term of the expression of the first wave of line mode voltage when there is a fault in the zone; It is the sum of the equivalent inductance of the converter station on the DC side and the inductance of the current-limiting reactor; is the wave impedance of the DC line.

[0036] See Figure 4 As shown in the figure, there is a comparison between the simulation value and expression curve of the first wave of the line mode voltage when the fault occurs in the zone. There is an error between the simulation value and the theoretical analysis, but it is within the allowable range. Therefore, the expression of the first wave of the line mode voltage when the fault occurs in the zone can accurately describe the voltage change when the fault occurs in the zone.

[0037] As a preferred implementation of this embodiment, the parameters and The calculation formula is as follows:

[0038] Where, is the equivalent inductance of the commutation station on the DC side; is the inductance of the current limiting reactor; For time; is the line mode voltage traveling wave at the fault point.

[0039] Based on the mathematical model of the first wave of the line-mode voltage, ignoring the traveling wave delay and considering the attenuation and dispersion of the first wave of the line-mode voltage during the line propagation process, the expression of the first wave of the line-mode voltage measured by the protection device when an out-of-zone fault occurs on the DC line is calculated as follows:

[0040] Where, It is the first wave of the line mode voltage measured by the protection device when an out-of-zone fault occurs on the DC line; It is the first constant term of the expression of the first wave of line mode voltage when there is an out-of-zone fault; It is the second constant term in the expression of the first wave of line mode voltage in case of out-of-zone fault.

[0041] The parameters and The calculation formula is as follows:

[0042] Where, is the equivalent inductance of the commutation station on the DC side; is the inductance of the current limiting reactor; For time; is the line mode voltage traveling wave at the fault point.

[0043] Based on the influence of the wave head change time of the first wave of the line mode voltage, when an out-of-zone fault occurs on the DC line, the parameter Specifically, substitute the magnitude of the system parameters into and In The order of magnitude is 10 3 , The order of magnitude is 10 5 .but Time also needs to be considered The change time of the first wave of the line mode voltage is usually in the order of tens of microseconds, so the time The order of magnitude is 10 -5 Consider the time After the impact of The order of magnitude is 10 0 Therefore, the second term in the expression of the first wave of the line-mode voltage under out-of-zone fault can be ignored compared with the first term. The expression of the first wave of the line-mode voltage is simplified to:

[0044] See Figure 5 As shown in the figure, there is a comparison between the simulation value and expression curve of the first wave of the line mode voltage when the fault occurs outside the zone. There is an error between the simulation value and the theoretical analysis, but it is within the allowable range. Therefore, the expression of the first wave of the line mode voltage when the fault occurs outside the zone can accurately describe the voltage change when the fault occurs outside the zone.

[0045] The general expression is constructed based on the expression of the first row wave of the line mode voltage measured by the protection device when an internal fault or an external fault occurs on the DC line.

[0046] As a preferred implementation of this embodiment, the parameters The calculation formula is as follows:

[0047] Where, is the equivalent inductance of the commutation station on the DC side; is the inductance of the current limiting reactor; For time; is the line mode voltage traveling wave at the fault point.

[0048] The fault area identification criterion is constructed based on the mathematical model:

[0049]

[0050] Where, is the fault threshold within the area; is the out-of-zone fault threshold; is the exponential coefficient related to the dispersion coefficient of the line mode component.

[0051] As a preferred implementation of this embodiment, the reasoning process of the fault area identification criterion is specifically as follows: Since the traveling wave transmission distance when a fault occurs within the area is shorter than that when a fault occurs outside the area, and the attenuation coefficient related to the dispersion coefficient in the expression of the first traveling wave of the line mode voltage is related to the distance, the relationship between the attenuation coefficients in the expressions of the first traveling wave of the line mode voltage is as follows:

[0052] Where, is the fault traveling wave transmission distance within the area, is the traveling wave transmission distance of the out-of-zone fault.

[0053] Therefore, the attenuation coefficient related to the dispersion coefficient in the expression of the first traveling wave of the line mode voltage is a transient quantity that characterizes the fault distance and is inversely proportional to the fault distance. The fault areas can be distinguished by comparing the magnitude of the attenuation coefficient.

[0054] Substituting the order of magnitude of the system parameters, we can see that the attenuation coefficient related to the dispersion coefficient is on the order of 10 6 , the attenuation coefficient related to the system parameters is on the order of 10 3 , the relationship between the two attenuation coefficients in the expression of the first wave of the line mode voltage is as follows:

[0055] Therefore, the attenuation coefficient related to the dispersion coefficient can be obtained by comparing the attenuation coefficient in the expression of the first-row wave of the line-mode voltage.

[0056] In summary, the fault area identification criterion is divided into two steps. First, the attenuation coefficient related to the dispersion coefficient is obtained by comparing the attenuation coefficient in the expression of the first wave of the line mode voltage. Then, the fault area is distinguished by comparing the attenuation coefficient.

[0057] The relationship between the attenuation coefficients is as follows:

[0058] The fault area is identified by comparing the exponential coefficient related to the dispersion coefficient in the double exponential decay function. Let it be the larger component of the exponential coefficient:

[0059] According to the above analysis, The value is inversely proportional to the fault distance. The value is compared with the preset in-zone fault threshold and out-zone fault threshold to identify the fault area:

[0060] Where, is the fault threshold within the area; is the fault threshold outside the zone. Considering that the attenuation coefficient related to the dispersion coefficient in the first wave expression of the line mode voltage is similar when the remote fault occurs in the zone and the local fault occurs in the zone, and the transition resistance will affect the In order to avoid malfunction of protection, in actual application, The transition resistance of 200 is generated at 80% of the lines in the area. Attenuation coefficient in case of ground fault, The transition resistance of 200 is generated at 20% of the line outside the area. Attenuation factor in case of ground fault.

[0061] For the DC line to be diagnosed, the first wave of the line mode voltage is collected through the protection device, and the first wave of the line mode voltage is fitted using the LM algorithm according to the general expression, and the value, will The value is substituted into the fault area identification criterion to identify the fault within the area or the fault outside the area.

[0062] To verify the effectiveness and superiority of the method provided in this embodiment, some specific cases are provided below: Establish as attached Figure 2 The electromagnetic transient simulation model of the ±400kV flexible DC grid is shown in Figure 1, where the capacity of MMC1 and MMC3 is 2400MW, the capacity of MMC2 and MMC4 is 1600MW, the rated voltage of the transformer grid valve is 220kV, the current limiting reactor is 200mH, and the line length is 500km. Figure 3 For the tower structure shown, the DC line adopts a frequency response model and the protection sampling frequency is 200kHz.

[0063] Taking the protection device R1 as an example, the transition resistance is set to 0 at 50km, 100km, 200km, and 300km away from the protection device on line L1. and 200 In case of single-pole ground fault in the area, the transition resistance is set to 0 at 600km, 700km and 800km away from the protection device on line L2. and 200 The attenuation coefficient of the out-of-area single-pole ground fault is fitted As shown in Table 1.

[0064] Table 1 Attenuation coefficients at different fault distances

[0065] According to the simulation results in Table 1, the protection method proposed in this embodiment can complete the identification of most protection areas and has good ability to withstand transition resistance.

[0066] Establish as attached Figure 2 The electromagnetic transient simulation model of the ±400 kV flexible DC grid is shown. 30 dB Gaussian white noise is added to the sampled signal to verify the impact of noise interference on the proposed protection scheme. The fitted attenuation coefficient As shown in Table 2.

[0067] Table 2 Attenuation coefficient after adding white noise

[0068] According to the simulation results in Table 2, the addition of white noise will affect the attenuation coefficient. However, by setting an appropriate fault area distinction threshold, the identification of most protection areas can still be completed. Therefore, the identification method proposed in this embodiment has good noise resistance.

[0069] Example 2 Accordingly, this embodiment provides a flexible DC grid fault area identification system based on traveling wave dispersion coefficient. The system is used to implement the flexible DC grid fault area identification method based on traveling wave dispersion coefficient as described in Example 1 of the present invention, including an inference module, a judgment construction module, and a fault identification module. An inference module is used to construct a general expression for the first wave of the line-mode voltage based on a mathematical model of the first wave of the line-mode voltage under internal and external faults on the DC line in the flexible DC grid; A criterion construction module, used for constructing a fault area identification criterion based on the mathematical model; The fault identification module is used to collect the first wave of the line mode voltage through the protection device for the DC line to be diagnosed, fit the first wave of the line mode voltage using the LM algorithm according to the general expression, and obtain value, will The value is substituted into the fault area identification criterion to identify the fault within the area or the fault outside the area.

[0070] Example 3 This embodiment provides an electronic device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the method for identifying a fault area in a flexible DC grid based on a traveling wave dispersion coefficient as described in Embodiment 1 of the present invention is implemented.

[0071] Example 4 This embodiment provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the method for identifying a fault area in a flexible DC grid based on a traveling wave dispersion coefficient as described in the first embodiment of the present invention is implemented.

[0072] In the embodiments of the present application, "at least one" refers to one or more, and "more" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent the existence of A alone, the existence of A and B at the same time, and the existence of B alone. Among them, A and B can be singular or plural. The character " / " generally indicates that the previous and next associated objects are in an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b and c can represent: a, b, c, a and b, a and c, b and c or a and b and c, where a, b, c can be single or multiple.

[0073] Those skilled in the art will appreciate that the various units and algorithm steps described in the embodiments disclosed herein can be implemented using a combination of electronic hardware, computer software, and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0074] Those skilled in the art will 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.

[0075] In the several embodiments provided in this application, if any function 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 this application, or the part that contributes to the prior art, or the 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 and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of this application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (Read-Only Memory; hereinafter referred to as: ROM), random access memory (Random Access Memory; hereinafter referred to as: RAM), magnetic disk or optical disk, and other media that can store program code.

[0076] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention's description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for identifying fault areas in a flexible DC grid based on traveling wave dispersion coefficient, characterized in that: The following steps are involved: According to the mathematical model of the first wave of line-mode voltage under internal and external faults on DC lines in flexible DC grid, the general expression of the first wave of line-mode voltage is constructed: Where, It is the first wave of line mode voltage under internal fault or external fault on DC line; is a custom symbol obtained by fitting the first wave of the line mode voltage using the LM algorithm; For time; The fault area identification criterion is constructed based on the mathematical model: Where, is the fault threshold within the area; is the out-of-zone fault threshold; is the exponential coefficient related to the dispersion coefficient of the line mode component; For the DC line to be diagnosed, the first wave of the line mode voltage is collected through the protection device, and the first wave of the line mode voltage is fitted using the LM algorithm according to the general expression, and the value, will The value is substituted into the fault area identification criterion to identify the fault within the area or the fault outside the area.

2. The method for identifying fault areas in a flexible DC grid based on traveling wave dispersion coefficient according to claim 1, characterized in that: The construction process of the general expression is specifically as follows: First, by considering the influence of line dispersion on traveling waves, the mathematical models of the first traveling wave of the line mode voltage measured at the protection device when an internal fault occurs and an external fault occurs are calculated respectively: Where, is the transfer function of the first wave of line mode voltage on the transmission line, is the propagation distance of the traveling wave, is the propagation speed of the line mode traveling wave, is a complex frequency domain variable, is the line mode component attenuation coefficient, is the line mode component dispersion coefficient, To characterize the traveling wave transmission delay; Based on the mathematical model of the first wave of the line-mode voltage, ignoring the traveling wave delay and considering the attenuation and dispersion of the first wave of the line-mode voltage during the line propagation process, the fault in the DC line occurrence area is calculated. The expression of the first wave of the line-mode voltage is: Where, It is the first wave of the line mode voltage measured by the protection device when a fault occurs in the DC line; is the constant term of the expression of the first wave of line mode voltage when there is a fault in the zone; It is the sum of the equivalent inductance of the converter station on the DC side and the inductance of the current-limiting reactor; is the wave impedance of the DC line; Based on the mathematical model of the first wave of the line-mode voltage, ignoring the traveling wave delay and considering the attenuation and dispersion of the first wave of the line-mode voltage during the line propagation process, the expression of the first wave of the line-mode voltage measured by the protection device when an out-of-zone fault occurs on the DC line is calculated as follows: Where, It is the first wave of the line mode voltage measured by the protection device when an out-of-zone fault occurs on the DC line; It is the first constant term of the expression of the first wave of line mode voltage when there is an out-of-zone fault; is the second constant term of the expression of the first wave of line mode voltage when there is an out-of-zone fault; Based on the influence of the wave head change time of the first wave of the line mode voltage, when an out-of-zone fault occurs on the DC line, the parameter The second term is ignored, and the expression of the first wave of the line mode voltage is simplified to: The general expression is constructed based on the expression of the first row wave of the line mode voltage measured by the protection device when an internal fault or an external fault occurs on the DC line.

3. The method for identifying fault areas in a flexible DC grid based on traveling wave dispersion coefficient according to claim 2, characterized in that: parameter and The calculation formula is as follows: Where, is the equivalent inductance of the commutation station on the DC side; is the inductance of the current limiting reactor; For time; is the line mode voltage traveling wave at the fault point.

4. The method for identifying fault areas in a flexible DC grid based on traveling wave dispersion coefficient according to claim 2, characterized in that: parameter The calculation formula is as follows: Where, is the equivalent inductance of the commutation station on the DC side; is the inductance of the current limiting reactor; For time; is the line mode voltage traveling wave at the fault point.

5. The method for identifying fault areas in a flexible DC grid based on traveling wave dispersion coefficient according to claim 2, characterized in that: The reasoning process of the fault area identification criterion is specifically as follows: Since the traveling wave transmission distance when a fault occurs within the area is shorter than the traveling wave transmission distance when a fault occurs outside the area, the magnitude of the attenuation coefficient can be determined as follows based on the magnitude of the system parameters: Where, is the fault traveling wave transmission distance within the area, is the traveling wave transmission distance of the out-of-zone fault; The fault area is identified by comparing the exponential coefficient related to the dispersion coefficient in the double exponential decay function. Let it be the larger component of the exponential coefficient: pass The value is compared with the preset in-zone fault threshold and out-zone fault threshold to identify the fault area: Where, is the fault threshold within the area; is the out-of-zone fault threshold.

6. A flexible DC grid fault area identification system based on traveling wave dispersion coefficient, characterized in that: The system is used to implement the flexible DC grid fault area identification method based on traveling wave dispersion coefficient according to any one of claims 1 to 5, comprising an inference module, a criterion construction module and a fault identification module; An inference module is used to construct a general expression for the first wave of the line-mode voltage based on a mathematical model of the first wave of the line-mode voltage under internal and external faults on the DC line in the flexible DC grid; A criterion construction module, used for constructing a fault area identification criterion based on the mathematical model; The fault identification module is used to collect the first wave of the line mode voltage through the protection device for the DC line to be diagnosed, fit the first wave of the line mode voltage using the LM algorithm according to the general expression, and obtain value, will The value is substituted into the fault area identification criterion to identify the fault within the area or the fault outside the area.

7. An electronic device, comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the method for identifying a fault area in a flexible DC grid based on a traveling wave dispersion coefficient according to any one of claims 1 to 5 is implemented.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method for identifying a fault area in a flexible direct current grid based on a traveling wave dispersion coefficient according to any one of claims 1 to 5 is implemented.

Images