A method and system for detecting and locating single-phase grounding faults in medium-voltage distribution networks

Abstract

This invention discloses a method and system for detecting and locating single-phase grounding faults in medium-voltage distribution networks. When no power electronic equipment is installed at the end of a critical busbar, harmonics are injected into the power electronic equipment during a single-phase grounding fault. The impedance of the monitoring points is calculated, and the impedance characteristics obtained from the measurements at three monitoring points are used to detect and locate single-phase grounding faults on critical busbars without power electronic equipment installed at the end. When power electronic equipment is installed at the end of a critical busbar, harmonics are injected into the existing power electronic equipment during a single-phase grounding fault, while harmonics of different frequencies are injected into the power electronic equipment at the end. The impedance of the monitoring points is calculated, and the impedance characteristics of the three monitoring points under a single-phase grounding fault on a critical busbar with power electronic equipment installed at the end are obtained. The impedance characteristics of the three monitoring points are used to detect and locate single-phase grounding faults on critical busbars with power electronic equipment installed at the end, thus achieving accurate and effective location of single-phase grounding faults.

Description

Technical Field

[0001] This invention belongs to the field of smart distribution network technology, specifically relating to a method and system for detecting and locating single-phase grounding faults in medium-voltage distribution networks. Background Technology

[0002] Power electronic equipment plays a key role in developing smart distribution network technology and building resilient distribution networks due to its advantages such as flexible control and fast response speed.

[0003] Because power electronic equipment has weak overcurrent tolerance to distribution network faults, a series of technologies based on hardware and control improvements of power electronic equipment have been proposed to limit overcurrent levels under distribution network faults and thus ensure the safe and reliable operation of power electronic equipment. Due to the application of fault ride-through technology in power electronic equipment, the current characteristics under fault conditions are altered, affecting the applicability of some traditional fault detection and location schemes: traditional current protection, including instantaneous overcurrent protection, time-limited instantaneous overcurrent protection, and overcurrent protection, requires parameter settings to adapt to the affected fault current characteristics; distance protection obtains impedance characteristics by measuring local voltage and current and locates faults through the linear relationship between impedance and distance, but the equivalent impedance of power electronic equipment is usually nonlinear, thus negatively impacting the results of distance protection. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method and system for detecting and locating single-phase grounding faults in medium-voltage distribution networks, which addresses the shortcomings of the prior art. This method and system solve the problem that traditional single-phase grounding fault detection and location schemes are not applicable in medium-voltage distribution networks when power electronic equipment is connected and fault crossing technology is applied.

[0005] The present invention adopts the following technical solution:

[0006] A method for detecting and locating single-phase grounding faults in medium-voltage distribution networks includes the following steps:

[0007] When no power electronic equipment is installed at the end of the critical busbar, harmonics are injected into the power electronic equipment when a single-phase ground fault occurs. The impedance of the monitoring point is calculated through the monitoring point. The detection and location of the single-phase ground fault of the critical busbar without power electronic equipment installed at the end is completed by measuring the impedance characteristics of the three monitoring points.

[0008] When power electronic equipment is installed at the end of a critical busbar, in the event of a single-phase ground fault, the original power electronic equipment is controlled to inject harmonics, while the power electronic equipment at the end is controlled to inject harmonics of different frequencies. The impedance of the monitoring points is calculated through the monitoring points to obtain the impedance characteristics of the three monitoring points under a single-phase ground fault of the critical busbar with power electronic equipment installed at the end. The detection and location of the single-phase ground fault of the critical busbar with power electronic equipment installed at the end are completed through the impedance characteristics of the three monitoring points.

[0009] Preferably, when no power electronic equipment is installed at the end of the critical busbar, the impedance of the monitoring point is calculated through the monitoring point when a single-phase ground fault occurs as follows:

[0010] Calculate the impedance at monitoring point 1 and detection point 3 to determine whether a single-phase ground fault occurs in zone I.

[0011] Calculate the impedance at monitoring point 1 and detection point 3 to determine whether a single-phase ground fault occurs in zone II.

[0012] Calculate the impedance at monitoring point 1, monitoring point 2, and detection point 3 to determine whether a single-phase ground fault occurs in zone III.

[0013] The impedance characteristics of three monitoring points were obtained under the condition of a single-phase ground fault on a key busbar with no power electronic equipment installed at the end.

[0014] Preferably, detecting whether a single-phase ground fault has occurred specifically involves:

[0015] Detect the DC bus voltage and common-mode voltage; perform DFT decomposition on the common-mode voltage and compare the power frequency component with the threshold to determine whether a single-phase ground fault has occurred.

[0016] Preferably, controlling the injection of harmonics into power electronic equipment specifically involves:

[0017] The reference value of the power frequency current is added to the reference value of the harmonic current to be injected, f1, to obtain the current reference value; the difference between the current reference value and the detected output current is calculated and passed through a proportional-resonant controller; the output of the proportional-resonant controller is added to the grid voltage feedforward and then pulse-width modulated to output the switching signal of the power electronic device.

[0018] Preferably, when determining whether a single-phase ground fault occurs in zone I, the impedances at monitoring point 1 and detection point 3 are calculated as follows:

[0019]

[0020] Z app3 =∞

[0021] Among them, Z app1 To measure the impedance at monitoring point 1, I fh Z represents the harmonic current at a single-phase grounding point. f For single-phase grounding impedance, I AMF1 To measure the current at monitoring point 1, Z I1 To measure the impedance from monitoring point 1 to the single-phase ground fault, I h For power electronic equipment to output harmonic current, Z I2 Z represents the impedance from the power grid to the single-phase ground fault. L For grounding impedance, Z app3Impedance was measured at monitoring point 3.

[0022] Preferably, when determining whether a single-phase ground fault occurs in zone II, the impedance at monitoring point 1 and detection point 3 is calculated as follows:

[0023]

[0024] Z app3 =∞

[0025] Among them, Z app1 To measure the impedance at monitoring point 1, I fh Z represents the harmonic current at a single-phase grounding point. f For single-phase grounding impedance, I AMF1 To measure the current at monitoring point 1, Z II1 To measure the impedance from monitoring point 1 to the single-phase ground fault, I h For power electronic equipment to output harmonic current, Z I For the line impedance in region I, Z L For grounding impedance, Z app3 Impedance was measured at monitoring point 3.

[0026] Preferably, when determining whether a single-phase ground fault occurs in zone III, the impedances at monitoring point 1, monitoring point 2, and detection point 3 are calculated as follows:

[0027]

[0028] Among them, Z app1 To measure the impedance at monitoring point 1, I fh Z represents the harmonic current at a single-phase grounding point. f For single-phase grounding impedance, I AMF1 To measure the current at monitoring point 1, I AMF3 To measure the current at monitoring point 3, Z III1 To measure the impedance from monitoring point 3 to the single-phase ground fault, I h For power electronic equipment to output harmonic current, Z I For the line impedance in region I, Z L For grounding impedance, Z app3 To measure the impedance at monitoring point 3, I AMF3 To measure the current at monitoring point 3, I AMF2 Measure the current at monitoring point 1.

[0029] Preferably, when power electronic equipment is installed at the end of the critical busbar, in the event of a single-phase ground fault, the existing power electronic equipment is controlled to inject harmonics, while the power electronic equipment at the end is controlled to inject harmonics of different frequencies. Specifically:

[0030] The reference value of the power frequency current is added to the reference value of the harmonic current to be injected, f1, to obtain the current reference value; the difference between the current reference value and the detected output current is calculated and passed through a proportional-resonant controller; the output of the proportional-resonant controller is added to the grid voltage feedforward and then pulse-width modulated to output the switching signal of the original power electronic equipment.

[0031] The reference value of the power frequency current is added to the reference value of the harmonic current to be injected, f2, to obtain the current reference value; the difference between the current reference value and the detected output current is calculated and passed through a proportional-resonant controller; the output of the proportional-resonant controller is added to the grid voltage feedforward and then pulse-width modulated to output the switching signal of the power electronic device at the end.

[0032] When the harmonic frequency injected by the existing power electronic equipment is much lower than the switching frequency and sampling frequency, the end power electronic equipment is equivalent to an open circuit at that frequency.

[0033] Preferably, the admittance of the terminal power electronic device is calculated as follows:

[0034]

[0035] Among them, i o Where e is the output current, e is the mains voltage, and T is the output current. d To control the delay, L f For filter inductor, H i For the transfer function of the current loop controller, u dc This refers to the magnitude of the DC voltage.

[0036] Secondly, embodiments of the present invention provide a single-phase grounding fault detection and location system for medium-voltage distribution networks, comprising:

[0037] The first positioning module, when no power electronic equipment is installed at the end of the critical busbar, controls the power electronic equipment to inject harmonics when a single-phase ground fault occurs, calculates the impedance of the monitoring point through the monitoring point, and completes the detection and positioning of the single-phase ground fault of the critical busbar without power electronic equipment installed at the end through the impedance characteristics measured by the three monitoring points.

[0038] The second positioning module, when power electronic equipment is installed at the end of the critical busbar, controls the original power electronic equipment to inject harmonics and simultaneously controls the power electronic equipment at the end to inject harmonics of different frequencies when a single-phase ground fault occurs; calculates the impedance of the monitoring points to obtain the impedance characteristics of the three monitoring points under a single-phase ground fault on the critical busbar with power electronic equipment installed at the end; and completes the detection and positioning of the single-phase ground fault on the critical busbar with power electronic equipment installed at the end by using the impedance characteristics of the three monitoring points.

[0039] Thirdly, a computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-described method for detecting and locating single-phase grounding faults in medium-voltage distribution networks.

[0040] Fourthly, embodiments of the present invention provide a computer-readable storage medium including a computer program, which, when executed by a processor, implements the steps of the above-described method for detecting and locating single-phase grounding faults in medium-voltage distribution networks.

[0041] Compared with the prior art, the present invention has at least the following beneficial effects:

[0042] A method for detecting and locating single-phase grounding faults in medium-voltage distribution networks is proposed. This method offers a simple and rapid detection scheme for single-phase grounding faults in medium-voltage distribution networks containing power electronic converters. It further categorizes faults based on whether power electronic equipment is installed at the terminal. For different scenarios, fault areas, and fault distances, a method for detecting and locating single-phase grounding faults in medium-voltage distribution networks containing power electronic equipment is proposed, which involves actively injecting harmonics through the power electronic equipment. This method accurately and effectively locates single-phase grounding faults by actively injecting harmonics and measuring the impedance at different monitoring points. It is adaptable to medium-voltage distribution networks with power electronic equipment and avoids the impact of power electronic equipment fault ride-through technology.

[0043] Furthermore, when no power electronic equipment is installed at the end of the critical busbar, in the event of a single-phase ground fault, if the fault occurs in different zones of the system, the calculated impedances at the three monitoring points exhibit distinct and discriminative characteristics. By calculating the impedances at the three monitoring points, the zone where the single-phase ground fault occurred can be easily and effectively determined through impedance characteristics.

[0044] Furthermore, by detecting the common-mode voltage of the DC bus and performing DFT decomposition on the common-mode voltage, and comparing the power frequency component with a threshold, it is possible to effectively, quickly, and reliably determine whether a single-phase ground fault has occurred in the system, and use this as the basis for subsequent impedance measurements.

[0045] Furthermore, if only the fundamental impedance of the three monitoring points is measured, this fundamental impedance measurement is not nearly linear with the fault zone and fault distance, and lacks distinguishability. By controlling the power electronic equipment to inject harmonics, the impedance of the three measurement points can be distinguished when power electronic equipment is installed on the critical bus and when a single-phase grounding fault occurs in different zones, thereby determining whether a single-phase grounding fault has occurred and its location.

[0046] Furthermore, when power electronic equipment is installed at the end of the critical busbar, when a fault occurs, different frequency harmonics are injected through the two converters, so that the converters are equivalent to an open circuit state at different harmonic frequencies. In this case, the installation of power electronic equipment at the end of the critical busbar is equivalent to the aforementioned case where no power electronic equipment is installed at the end of the critical busbar. Then, the impedance can be measured at three monitoring points to determine whether a single-phase ground fault has occurred and the location of the single-phase ground fault.

[0047] It is understandable that the beneficial effects of the second aspect mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here.

[0048] In summary, this invention proposes a simple and rapid single-phase grounding fault detection scheme for medium-voltage distribution networks with power electronic converters. It further categorizes the detection based on whether power electronic equipment is installed at the terminal. For different scenarios, fault areas, and fault distances, it proposes a method for detecting and locating single-phase grounding faults in medium-voltage distribution networks with power electronic equipment by actively injecting harmonics. This method accurately and effectively locates single-phase grounding faults by actively injecting harmonics and measuring the impedance at different monitoring points. It is adaptable to medium-voltage distribution networks with power electronic equipment and avoids the impact of power electronic equipment fault ride-through technology.

[0049] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0050] Figure 1 Logic diagram for single-phase grounding fault detection and location of critical busbars without power electronic equipment installation at the end;

[0051] Figure 2 A logic diagram for detecting and locating single-phase grounding faults on critical busbars where power electronic equipment is installed at the end.

[0052] Figure 3 The circuit diagrams for a single-phase ground fault are shown below, where (a) is the equivalent circuit diagram and (b) is the logic diagram.

[0053] Figure 4 Diagram of harmonic injection control strategy for power electronic equipment;

[0054] Figure 5 This is a block diagram of the inner current loop of a power electronic device using PQ control.

[0055] Figure 6 The circuit diagram is shown when a single-phase ground fault occurs in zone I, where (a) is a circuit diagram and (b) is a sequence network diagram.

[0056] Figure 7The circuit diagram is shown when a single-phase ground fault occurs in zone II, where (a) is a circuit schematic diagram and (b) is a sequence network diagram.

[0057] Figure 8 The circuit diagram is shown when a single-phase ground fault occurs in zone III, where (a) is a circuit schematic diagram and (b) is a sequence network diagram.

[0058] Figure 9 Schematic diagram of a power electronics system installed at the end;

[0059] Figure 10 A schematic diagram of a computer device provided in an embodiment of the present invention;

[0060] Figure 11 This is a block diagram of an electronic device according to an embodiment of the present invention. Detailed Implementation

[0061] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0062] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0063] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0064] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this invention generally indicates that the preceding and following objects have an "or" relationship.

[0065] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0066] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0067] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0068] This invention provides a method for detecting and locating single-phase grounding faults in medium-voltage distribution networks. Compared with existing technologies, this invention addresses the problem of insufficient applicability of traditional single-phase grounding fault detection schemes due to the influence of power electronic equipment control on the current characteristics under fault conditions. By controlling the output harmonics of the converter and calculating the impedance of the three monitoring points under fault conditions, this invention can accurately and effectively determine whether a single-phase grounding fault has occurred and determine the location of the fault. It can adapt to the influence of power electronics connected in medium-voltage distribution networks on fault characteristics and has the advantages of being simple, easy to implement, accurate, and reliable.

[0069] Please see Figure 1 The present invention provides a method for detecting and locating single-phase grounding faults in medium-voltage distribution networks, comprising the following steps:

[0070] S1. Determine whether power electronic equipment is installed at the end of the critical busbar. If no power electronic equipment is installed at the end, proceed to step S2. If it is installed, proceed to step S6.

[0071] S2. Check for a single-phase ground fault; if... Figure 3 As shown in (a), in a medium-voltage distribution network where the neutral point is ungrounded or grounded through a high-resistance circuit, when a single-phase ground fault occurs, the three-phase line voltage remains unchanged while the common-mode voltage increases; the specific detection steps are as follows: Figure 3 As shown in (b);

[0072] S201. Detect DC bus voltage and common-mode voltage;

[0073] S202. Perform DFT decomposition on the common-mode voltage and compare the power frequency component with the threshold to determine whether a single-phase ground fault has occurred.

[0074] S3, Controls the injection of harmonics into power electronic equipment;

[0075] Please see Figure 4 The specific control strategy steps are as follows:

[0076] S301. After determining that a ground fault has occurred through step S1, the power frequency current reference value and the harmonic current reference value to be injected (f1) are added together to obtain the current reference value.

[0077] S302. The difference between the current reference value and the detected output current is calculated and passed through a proportional-resonant (PR) controller.

[0078] S303: Add the output of the PR controller to the grid voltage feedforward and output the switching signal of the power electronic equipment after pulse width modulation.

[0079] S4. Calculate the impedance of the monitoring point to locate the fault;

[0080] Please see Figure 6 , Figure 7 and Figure 8 The specific steps are as follows:

[0081] S401. Determine whether a single-phase ground fault occurred in zone I, such as... Figure 6 (a) is a circuit diagram of a single-phase ground fault occurring in zone I. Figure 6 (b) is its three-sequence equivalent circuit diagram; its impedance at monitoring point 1 and detection point 3 is calculated as follows:

[0082]

[0083] Z app3 =∞ (2)

[0084] Among them, Z app1 To measure the impedance at monitoring point 1, I fh Z represents the harmonic current at a single-phase grounding point. f For single-phase grounding impedance, I AMF1 To measure the current at monitoring point 1, Z I1 The impedance from monitoring point 1 to the single-phase ground fault location (within area I), I h For power electronic equipment to output harmonic current, Z I2 Z represents the impedance from the power grid to the single-phase ground fault location (within region I). LFor grounding impedance, Z app3 Measure the impedance at monitoring point 3;

[0085] S402. Determine whether a single-phase ground fault occurred in zone II, such as... Figure 7 (a) is a circuit diagram of a single-phase ground fault occurring in zone II. Figure 7 (b) is its three-sequence equivalent circuit diagram; its impedance at monitoring point 1 and detection point 3 is calculated as follows:

[0086]

[0087] Z app3 =∞ (4)

[0088] Among them, Z app1 To measure the impedance at monitoring point 1, I fh Z represents the harmonic current at a single-phase grounding point. f For single-phase grounding impedance, I AMF1 To measure the current at monitoring point 1, Z II1 To measure the impedance from monitoring point 1 to the single-phase ground fault, I h For power electronic equipment to output harmonic current, Z I For the line impedance in region I, Z L For grounding impedance, Z app3 Measure the impedance at monitoring point 3;

[0089] S403. Determine whether a single-phase ground fault occurred in zone III, such as... Figure 8 (a) is a circuit diagram of a single-phase ground fault occurring in zone III. Figure 8 (b) is its three-sequence equivalent circuit diagram; its impedance calculations at monitoring points 1, 2, and 3 are as follows:

[0090]

[0091]

[0092] Among them, Z app1 To measure the impedance at monitoring point 1, I fh Z represents the harmonic current at a single-phase grounding point. f For single-phase grounding impedance, I AMF1 To measure the current at monitoring point 1, I AMF3 To measure the current at monitoring point 3, Z III1 To measure the impedance from monitoring point 3 to the single-phase ground fault, I h For power electronic equipment to output harmonic current, Z I For the line impedance in region I, Z L For grounding impedance, Z app3 To measure the impedance at monitoring point 3, I AMF3To measure the current at monitoring point 3, I AMF2 Measure the current at monitoring point 1;

[0093] The impedance characteristics of the three monitoring points under the condition of a single-phase grounding fault on the key busbar with no power electronic equipment installed at the end are obtained from steps S401 to S403.

[0094] S5. By measuring the impedance characteristics at three monitoring points, the detection and location of a single-phase grounding fault on a critical busbar without power electronic equipment installed at the end are completed, and the process ends. The complete process logic is as follows: Figure 1 As shown;

[0095] S6. When power electronic equipment is installed at the end, check whether a single-phase grounding fault has occurred. The specific steps are the same as in step S2.

[0096] S7. The original power electronic device is referred to as power electronic device 1, and the terminal power electronic device is referred to as power electronic device 2. Power electronic device 1 is controlled to inject harmonics, while power electronic device 2 is controlled to inject harmonics of different frequencies.

[0097] Please see Figure 9 The specific steps are as follows:

[0098] S701. Control the power electronic device 1 to inject harmonics, the steps are the same as S3;

[0099] S702, Specific Control Strategy Framework for Terminal Power Electronic Equipment 2 Figure 5 As shown, its admittance is calculated as follows:

[0100]

[0101] Among them, i o Where e is the output current, e is the mains voltage, and T is the output current. d To control the delay, L f For filter inductor, H i For the transfer function of the current loop controller, u dc This refers to the magnitude of the DC voltage.

[0102] When the harmonic frequency injected by power electronic device 1 is much lower than the switching frequency and sampling frequency, power electronic device 2 can be equivalent to an open circuit at that frequency. When power electronic device 2 with PQ control is connected, the analysis process after a single-phase grounding fault is the same as the detection and location steps for a single-phase grounding fault on a key bus without power electronic device installation at the end.

[0103] S703. After determining that a ground fault has occurred through S6, the reference value of the power frequency current is added to the reference value of the harmonic current to be injected (f2) (the frequency of this harmonic current is not equal to the frequency of the harmonic current injected in step S701 (f1)) as the current reference value.

[0104] S704. The difference between the current reference value and the detected output current is calculated and passed through a proportional-resonant (PR) controller.

[0105] S705 adds the output of the PR controller to the grid voltage feedforward and outputs the switching signal of the power electronic device after pulse width modulation.

[0106] S8. By calculating the impedance of the monitoring points, the fault can be located, and the impedance characteristics of the three monitoring points under a single-phase grounding fault on the key busbar where power electronic equipment is installed at the end are obtained.

[0107] S9. Using the impedance characteristics obtained from the three monitoring points, the detection and location of a single-phase grounding fault on the critical busbar of the power electronic equipment installed at the end are completed, thus concluding the process. The complete workflow is as follows: Figure 2 As shown.

[0108] Those skilled in the art will understand that various aspects of the present invention can be implemented as systems, methods, or program products. Therefore, various aspects of the present invention can be specifically implemented in the following forms: a completely hardware implementation, a completely software implementation (including firmware, microcode, etc.), or a combination of hardware and software aspects, collectively referred to herein as a "circuit," "module," or "platform."

[0109] In another embodiment of the present invention, a single-phase grounding fault detection and location system for medium-voltage distribution networks is provided. This system can be used to implement the above-mentioned single-phase grounding fault detection and location method for medium-voltage distribution networks. Specifically, the single-phase grounding fault detection and location system for medium-voltage distribution networks includes a first location module and a second location module.

[0110] The first positioning module, when no power electronic equipment is installed at the end of the critical busbar, controls the power electronic equipment to inject harmonics when a single-phase ground fault occurs. It calculates the impedance of the monitoring point through the monitoring point and completes the detection and positioning of the single-phase ground fault of the critical busbar without power electronic equipment installed at the end through the impedance characteristics measured by the three monitoring points.

[0111] The second positioning module, when power electronic equipment is installed at the end of the critical busbar, controls the original power electronic equipment to inject harmonics and simultaneously controls the power electronic equipment at the end to inject harmonics of different frequencies when a single-phase ground fault occurs; calculates the impedance of the monitoring points to obtain the impedance characteristics of the three monitoring points under a single-phase ground fault on the critical busbar with power electronic equipment installed at the end; and completes the detection and positioning of the single-phase ground fault on the critical busbar with power electronic equipment installed at the end by using the impedance characteristics of the three monitoring points.

[0112] In another embodiment of the present invention, a terminal device is provided, comprising a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions to achieve a corresponding method flow or corresponding function. The processor described in this embodiment of the present invention can be used in the operation of a method for detecting and locating single-phase grounding faults in medium-voltage distribution networks, including:

[0113] When no power electronic equipment is installed at the end of the critical busbar, harmonics are injected into the power electronic equipment when a single-phase ground fault occurs. The impedance of the monitoring point is calculated through the monitoring point. The detection and location of the single-phase ground fault of the critical busbar without power electronic equipment installed at the end is completed by measuring the impedance characteristics of the three monitoring points.

[0114] When power electronic equipment is installed at the end of a critical busbar, in the event of a single-phase ground fault, the original power electronic equipment is controlled to inject harmonics, while the power electronic equipment at the end is controlled to inject harmonics of different frequencies. The impedance of the monitoring points is calculated through the monitoring points to obtain the impedance characteristics of the three monitoring points under a single-phase ground fault of the critical busbar with power electronic equipment installed at the end. The detection and location of the single-phase ground fault of the critical busbar with power electronic equipment installed at the end are completed through the impedance characteristics of the three monitoring points.

[0115] In another embodiment of the present invention, a storage medium is provided, specifically a computer-readable storage medium (Memory), which is a memory device in a terminal device for storing programs and data. It is understood that the computer-readable storage medium here can include both built-in storage media in the terminal device and extended storage media supported by the terminal device; it can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, the storage space also stores one or more instructions suitable for loading and execution by a processor, which can be one or more computer programs (including program code). It should be noted that more specific examples (a non-exhaustive list) of the computer-readable storage medium include: an electrical connection having one or more wires, a portable disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0116] Computer-readable storage media also include data signals propagated in baseband or as part of a carrier wave, carrying readable program code. Such propagated data signals can take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. A readable storage medium can also be any readable medium other than a readable storage medium that can send, propagate, or transmit a program for use by or in connection with an instruction execution system, apparatus, or device. The program code contained on the readable storage medium can be transmitted using any suitable medium, including but not limited to wireless, wired, optical fiber, RF, etc., or any suitable combination thereof.

[0117] Program code for performing the operations of this invention can be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java and C++, and conventional procedural programming languages ​​such as C or similar languages. The program code can execute entirely on the user's computing device, partially on the user's device, as a standalone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server. In cases involving remote computing devices, the remote computing device can be connected to the user's computing device via any type of network, including a local area network (LAN) or a wide area network (WAN), or it can be connected to an external computing device (e.g., via the Internet using an Internet service provider).

[0118] One or more instructions stored in a computer-readable storage medium can be loaded and executed by a processor to implement the corresponding steps of the method for detecting and locating single-phase grounding faults in medium-voltage distribution networks in the above embodiments; one or more instructions in the computer-readable storage medium are loaded and executed by the processor to perform the following steps:

[0119] When no power electronic equipment is installed at the end of the critical busbar, harmonics are injected into the power electronic equipment when a single-phase ground fault occurs. The impedance of the monitoring point is calculated through the monitoring point. The detection and location of the single-phase ground fault of the critical busbar without power electronic equipment installed at the end is completed by measuring the impedance characteristics of the three monitoring points.

[0120] When power electronic equipment is installed at the end of a critical busbar, in the event of a single-phase ground fault, the original power electronic equipment is controlled to inject harmonics, while the power electronic equipment at the end is controlled to inject harmonics of different frequencies. The impedance of the monitoring points is calculated through the monitoring points to obtain the impedance characteristics of the three monitoring points under a single-phase ground fault of the critical busbar with power electronic equipment installed at the end. The detection and location of the single-phase ground fault of the critical busbar with power electronic equipment installed at the end are completed through the impedance characteristics of the three monitoring points.

[0121] Please see Figure 10 The terminal device is a computer device. In this embodiment, the computer device 60 includes a processor 61, a memory 62, and a computer program 63 stored in the memory 62 and executable on the processor 61. When executed by the processor 61, the computer program 63 implements the fluid composition calculation method in the reservoir stimulation wellbore of this embodiment. To avoid repetition, these details are not elaborated here. Alternatively, when executed by the processor 61, the computer program 63 implements the functions of each model / unit in the fluid composition calculation system in the reservoir stimulation wellbore of this embodiment. To avoid repetition, these details are not elaborated here.

[0122] Computer device 60 can be a desktop computer, laptop, handheld computer, cloud server, or other computing device. Computer device 60 may include, but is not limited to, a processor 61 and a memory 62. Those skilled in the art will understand that... Figure 10 This is merely an example of computer device 60 and does not constitute a limitation on computer device 60. It may include more or fewer components than shown, or combine certain components, or different components. For example, computer device may also include input / output devices, network access devices, buses, etc.

[0123] The processor 61 may be a central processing unit (CPU), or other general-purpose processors, CPUs, graphics processing units (GPUs), digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, quantum computing-based data processing logic units, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0124] The memory 62 can be an internal storage unit of the computer device 60, such as a hard disk or RAM of the computer device 60. The memory 62 can also be an external storage device of the computer device 60, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc. equipped on the computer device 60.

[0125] Furthermore, the memory 62 may include both internal storage units of the computer device 60 and external storage devices. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 can also be used to temporarily store data that has been output or will be output.

[0126] Any references to memory, databases, or other media used in the embodiments provided in this application may include at least one of non-volatile and volatile memory. Non-volatile memory may include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory may include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM may be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0127] The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0128] Please see Figure 11 The terminal device 600 is an electronic device, which takes the form of a general-purpose computing device. The components of the electronic device may include, but are not limited to: at least one processing unit 610, at least one storage unit 620, a bus 630 connecting different platform components (including storage unit 620 and processing unit 610), a display unit 640, etc.

[0129] The storage unit stores program code, which can be executed by the processing unit 610 to perform the steps described in the method section of this specification according to various exemplary embodiments of the present invention. For example, the processing unit 610 can perform actions such as... Figure 1 The steps are shown in the figure.

[0130] Storage unit 620 may include a readable medium in the form of a volatile storage unit, such as random access memory (RAM) 6201 and / or cache memory 6202, and may further include a read-only memory (ROM) 6203.

[0131] Storage unit 620 may also include a program / utility 6204 having a set (at least one) program module 6205, such program module 6205 including but not limited to: operating system, one or more application programs, other program modules and program data, each or some combination of these examples may include an implementation of a network environment.

[0132] Bus 630 can represent one or more of several types of bus structures, including a memory cell bus or memory cell controller, a peripheral bus, a graphics acceleration port, a processing unit, or a local bus using any of the multiple bus structures.

[0133] Electronic device 600 can also communicate with one or more external devices 700 (e.g., keyboard, pointing device, Bluetooth device, etc.), and with one or more devices that enable a user to interact with electronic device 600, and / or with any device that enables electronic device 600 to communicate with one or more other computing devices (e.g., router, modem, etc.). This communication can be performed via input / output (I / O) interface 650. Furthermore, electronic device 600 can also communicate with one or more networks (e.g., local area network (LAN), wide area network (WAN), and / or public networks, such as the Internet) via network adapter 660. Network adapter 660 can communicate with other modules of electronic device 600 via bus 630. It should be understood that, although not shown in the figures, other hardware and / or software modules can be used in conjunction with electronic device 600, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage platforms.

[0134] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0135] The impedance measurement data (unit: ohms) of each monitoring point in the system under different fault areas and different fault distances are as follows:

[0136] When no power electronic equipment is installed at the end:

[0137] Table 1. Measured impedance of monitoring point 1 under fault conditions in Zone I.

[0138] Distance (pu) <![CDATA[Z f =1]]> Zf = 10 <![CDATA[Z f =40]]> 0.2 0.200 0.204 0.224 0.5 0.496 0.552 0.548 0.8 0.816 0.808 0.856

[0139] Please refer to Table 1. Under different grounding impedances and fault distances in different zones, the measured impedance at monitoring point 1 is not affected by the grounding impedance and is linear with the fault distance. By measuring the impedance at monitoring point 1, the fault in zone I can be accurately located.

[0140] Table 2. Measured impedance of monitoring point 1 under fault conditions in Zone II.

[0141] Distance (pu) <![CDATA[Z f =1]]> Zf = 10 <![CDATA[Z f =40]]> 0.2 0.206 0.200 0.180 0.5 0.512 0.496 0.480 0.8 0.824 0.808 0.805

[0142] Please refer to Table 2. Under different grounding impedances and fault distances in different zones, the measured impedance at monitoring point 1 is not affected by the grounding impedance and is linear with the fault distance. By measuring the impedance at monitoring point 1, the fault in zone II can be accurately located.

[0143] Table 3. Measured impedance of monitoring point 3 under fault conditions in Zone III.

[0144] Distance (pu) <![CDATA[Z f =1]]> Zf = 10 <![CDATA[Z f =40]]> 0.2 1.08 9.92 39.2 0.5 1.20 10.1 39.2 0.8 1.42 10.0 39.6

[0145] Please refer to Table 3. Under different grounding impedances and fault distances in different zones, when a single-phase ground fault occurs in zone III, the measured impedance at monitoring point 3 is affected by both the fault distance and the grounding impedance, and is linear with the ground fault. By measuring the impedance at monitoring point 3, the fault in zone III can be accurately located.

[0146] When power electronic equipment is installed at the end:

[0147] Table 4. Measured impedance (300Hz) at monitoring point 3 under fault conditions in Zone III.

[0148] Distance (pu) <![CDATA[Z f =1]]> <![CDATA[Z f =10]]> <![CDATA[Z f =40]]> 0.2 0.320 0.312 0.328 0.5 0.784 0.776 0.768 0.8 1.26 1.23 1.24

[0149] Please refer to Table 4. Under different grounding impedances and fault distances in different zones, when a single-phase grounding fault occurs in zone III, the harmonic impedance measured at monitoring point 3 is not affected by the grounding impedance and has a linear relationship with the fault distance. By measuring the impedance at monitoring point 3, the fault in zone III can be accurately located.

[0150] In summary, this invention provides a method and system for detecting and locating single-phase grounding faults in medium-voltage distribution networks. Addressing the problem of insufficient applicability of traditional single-phase grounding fault detection schemes due to the influence of power electronic equipment control on current characteristics under fault conditions, this invention, by controlling the converter output harmonics and calculating the impedance of three monitoring points under fault conditions, can accurately and effectively determine whether a single-phase grounding fault has occurred and pinpoint its location. It can adapt to the influence of power electronics connected to medium-voltage distribution networks on fault characteristics. This fault detection and location method has the advantages of being simple, easy to implement, accurate, and reliable.

[0151] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0152] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0153] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this invention can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0154] In the embodiments provided by this invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0155] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0156] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0157] If the integrated module / unit is implemented as 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, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content included in the computer-readable medium can be appropriately added or removed according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electrical carrier signals and telecommunication signals.

[0158] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0159] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0160] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0161] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for detecting and locating single-phase grounding faults in medium-voltage distribution networks, characterized in that, Includes the following steps: When no power electronic equipment is installed at the end of the critical busbar, harmonics are injected into the power electronic equipment when a single-phase ground fault occurs. The impedance of the monitoring point is calculated through the monitoring point. The detection and location of the single-phase ground fault of the critical busbar without power electronic equipment installed at the end is completed by measuring the impedance characteristics of the three monitoring points. The specific steps for detecting whether a single-phase ground fault has occurred are as follows: Detect the DC bus voltage and common-mode voltage; perform DFT decomposition on the common-mode voltage and compare the power frequency component with a threshold to determine whether a single-phase ground fault has occurred; When PQ-controlled power electronic equipment is installed at the end of a critical busbar, in the event of a single-phase ground fault, the existing power electronic equipment injects harmonics while the terminal power electronic equipment injects harmonics at different frequencies. When the harmonic frequency injected by the existing power electronic equipment is much lower than the switching frequency and sampling frequency, the terminal power electronic equipment is equivalent to an open circuit at that frequency. The admittance of the terminal power electronic equipment is calculated as follows: in, i o For output current, e This is the grid voltage. T d To control latency, L f For filter inductors, H i For the current loop controller transfer function, u dc The magnitude of the DC voltage; when PQ-controlled power electronic equipment is connected, the analysis process after a single-phase grounding fault is the same as the detection and location steps for a single-phase grounding fault on a critical busbar without power electronic equipment installed at the end. The impedance of the monitoring point is calculated through the monitoring point to obtain the impedance characteristics of the three monitoring points under a single-phase grounding fault on a critical busbar with power electronic equipment installed at the end. The three monitoring points and zones are as follows: a load access point is set between the power supply and the power electronic equipment; zone I is set between the power supply and the load access point; zone II is set between the load access point and the existing power electronic equipment; and zone III is set between the loads and the load access points. The first monitoring point is set on the side of zone I closest to the load access point; the second monitoring point is set on the side of zone II closest to the load access point; and the third monitoring point is set between zone III and the load access point. The detection and location of single-phase grounding faults on key busbars of terminal-installed power electronic equipment are achieved by using the impedance characteristics of three monitoring points. To determine whether a single-phase ground fault occurred in zone I, the impedances at monitoring point 1 and detection point 3 are calculated as follows: in, Z app1 To measure the impedance at monitoring point 1, I fh This refers to the harmonic current at the single-phase grounding point. Z f For single-phase grounding impedance, I AMF1 To measure the current at monitoring point 1, Z I1 The impedance from monitoring point 1 to the single-phase ground fault is the magnitude. I h To output harmonic current for power electronic equipment, Z I2 The impedance from the power grid to the single-phase ground fault is... Z L For grounding impedance, Z app3 Measure the impedance at monitoring point 3; To determine whether a single-phase ground fault occurred in zone II, the impedances at monitoring point 1 and monitoring point 3 are calculated as follows: in, Z app1 To measure the impedance at monitoring point 1, I fh This refers to the harmonic current at the single-phase grounding point. Z f For single-phase grounding impedance, I AMF1 To measure the current at monitoring point 1, Z II1 The impedance from monitoring point 1 to the single-phase ground fault is the magnitude. I h To output harmonic current for power electronic equipment, Z I For the line impedance in region I, Z L For grounding impedance, Z app3 Measure the impedance at monitoring point 3; To determine whether a single-phase ground fault occurred in zone III, the impedances at monitoring points 1, 2, and 3 are calculated as follows: in, Z app1 To measure the impedance at monitoring point 1, I fh This refers to the harmonic current at the single-phase grounding point. Z f For single-phase grounding impedance, I AMF1 To measure the current at monitoring point 1, I AMF3 To measure the current at monitoring point 3, Z III1 To measure the impedance from monitoring point 3 to the single-phase ground fault, I h To output harmonic current for power electronic equipment, Z I For the line impedance in region I, Z L For grounding impedance, Z app3 To measure the impedance at monitoring point 3, I AMF3 To measure the current at monitoring point 3, I AMF2 Measure the current at monitoring point 1.

2. The method for detecting and locating single-phase grounding faults in medium-voltage distribution networks according to claim 1, characterized in that, Controlling the injection of harmonics into power electronic equipment specifically involves: The reference value of the power frequency current is added to the reference value of the harmonic current to be injected, f1, to obtain the current reference value; The difference between the current reference value and the detected output current is calculated and then processed by a proportional-resonant controller. The output of the proportional-resonant controller is added to the grid voltage feedforward and then pulse-width modulated to output the switching signal of the power electronic device.

3. The method for detecting and locating single-phase grounding faults in medium-voltage distribution networks according to claim 1, characterized in that, When power electronic equipment is installed at the end of a critical busbar, in the event of a single-phase ground fault, the existing power electronic equipment is controlled to inject harmonics, while the power electronic equipment at the end is controlled to inject harmonics of different frequencies. Specifically: The reference value of the power frequency current is added to the reference value of the harmonic current to be injected, f1, to obtain the current reference value; The difference between the current reference value and the detected output current is calculated and then processed by a proportional-resonant controller. The output of the proportional-resonant controller is added to the grid voltage feedforward and then pulse-width modulated to output the switching signal of the original power electronic equipment. The reference value of the power frequency current is added to the reference value of the harmonic current to be injected, f2, to obtain the current reference value; The difference between the current reference value and the detected output current is calculated and then processed by a proportional-resonant controller. The output of the proportional-resonant controller is added to the grid voltage feedforward and then pulse-width modulated to output the switching signal of the power electronic device at the end.

4. A single-phase grounding fault detection and location system for medium-voltage distribution networks, characterized in that, include: The first positioning module, when no power electronic equipment is installed at the end of the critical busbar, controls the power electronic equipment to inject harmonics when a single-phase ground fault occurs, calculates the impedance of the monitoring point through the monitoring point, and completes the detection and positioning of the single-phase ground fault of the critical busbar without power electronic equipment installed at the end through the impedance characteristics measured by the three monitoring points. The specific steps for detecting whether a single-phase ground fault has occurred are as follows: Detect the DC bus voltage and common-mode voltage; perform DFT decomposition on the common-mode voltage and compare the power frequency component with a threshold to determine whether a single-phase ground fault has occurred; The second positioning module, when power electronic equipment is installed at the end of the critical busbar, controls the original power electronic equipment to inject harmonics and controls the power electronic equipment at the end to inject harmonics of different frequencies when a single-phase ground fault occurs. When the harmonic frequency injected by the existing power electronic equipment is much lower than the switching frequency and sampling frequency, the terminal power electronic equipment is equivalent to an open circuit at that frequency; the admittance of the terminal power electronic equipment is calculated as follows: in, i o For output current, e This is the grid voltage. T d To control latency, L f For filter inductors, H i For the current loop controller transfer function, u dc The magnitude of the DC voltage; when PQ-controlled power electronic equipment is connected, the analysis process after a single-phase grounding fault is the same as the detection and location steps for a single-phase grounding fault on a critical busbar without power electronic equipment installed at the end. The impedance of the monitoring point is calculated through the monitoring point to obtain the impedance characteristics of the three monitoring points under a single-phase grounding fault on a critical busbar with power electronic equipment installed at the end. The three monitoring points and zones are as follows: a load access point is set between the power supply and the power electronic equipment; zone I is set between the power supply and the load access point; zone II is set between the load access point and the existing power electronic equipment; and zone III is set between the loads and the load access points. The first monitoring point is set on the side of zone I closest to the load access point; the second monitoring point is set on the side of zone II closest to the load access point; and the third monitoring point is set between zone III and the load access point. The detection and location of single-phase grounding faults on key busbars of terminal-installed power electronic equipment are achieved by using the impedance characteristics of three monitoring points. To determine whether a single-phase ground fault occurred in zone I, the impedances at monitoring point 1 and detection point 3 are calculated as follows: in, Z app1 To measure the impedance at monitoring point 1, I fh This refers to the harmonic current at the single-phase grounding point. Z f For single-phase grounding impedance, I AMF1 To measure the current at monitoring point 1, Z I1 The impedance from monitoring point 1 to the single-phase ground fault is the magnitude. I h To output harmonic current for power electronic equipment, Z I2 The impedance from the power grid to the single-phase ground fault is... Z L For grounding impedance, Z app3 Measure the impedance at monitoring point 3; To determine whether a single-phase ground fault occurred in zone II, the impedances at monitoring point 1 and monitoring point 3 are calculated as follows: in, Z app1 To measure the impedance at monitoring point 1, I fh This refers to the harmonic current at the single-phase grounding point. Z f For single-phase grounding impedance, I AMF1 To measure the current at monitoring point 1, Z II1 The impedance from monitoring point 1 to the single-phase ground fault is the magnitude. I h To output harmonic current for power electronic equipment, Z I For the line impedance in region I, Z L For grounding impedance, Z app3 Measure the impedance at monitoring point 3; To determine whether a single-phase ground fault occurred in zone III, the impedances at monitoring points 1, 2, and 3 are calculated as follows: in, Z app1 To measure the impedance at monitoring point 1, I fh This refers to the harmonic current at the single-phase grounding point. Z f For single-phase grounding impedance, I AMF1 To measure the current at monitoring point 1, I AMF3 To measure the current at monitoring point 3, Z III1 To measure the impedance from monitoring point 3 to the single-phase ground fault, I h To output harmonic current for power electronic equipment, Z I For the line impedance in region I, Z L For grounding impedance, Z app3 To measure the impedance at monitoring point 3, I AMF3 To measure the current at monitoring point 3, I AMF2 Measure the current at monitoring point 1.

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