Flexible composite arc extinguishing method for ground fault in distribution network adapting to structure and load changes

Abstract

The present invention relates to a flexible composite arc extinguishing method for grounding faults in a distribution network that is adaptable to changes in structure and load. A single-phase cascaded H-bridge converter is used as an arc extinguishing device, which is hung between the neutral point of the grounding transformer and the earth. Through a parallel voltage and current double closed-loop control method, the system zero-sequence voltage is regulated to the negative value of the fault phase power supply voltage, and at the same time, the fault phase current of the fault feeder is regulated to be equal to the fault phase load current of the fault feeder. According to the characteristic that the load current of the fault feeder is the same as the positive sequence component in the three-phase current, a method for calculating the fault phase load current of the fault feeder is proposed. Coordinate transformation and filter are used to extract the positive sequence component in the three-phase current of the fault feeder in real time, and then the fault phase load current of the fault feeder is obtained through inverse coordinate transformation. The present invention solves the problems that the existing flexible arc extinguishing method is greatly affected by line impedance voltage drop, ground parameter measurement accuracy and load current changes.

Description

Technical Field

[0001] The invention belongs to the technical field of power system operation and maintenance, fault processing and arc extinguishing of single-phase grounding fault in power grid, and in particular relates to a flexible composite arc extinguishing method for grounding fault in distribution network adapting to structure and load changes. Background Art

[0002] As the link closest to the power load in the power system, the distribution network has a complex line structure and poor operating conditions. Single-phase grounding faults caused by tree branches scraping overhead lines, cable damage discharge, and insulator flashover often occur. Direct grounding operation will cause frequent line tripping. To ensure power supply reliability, the direct grounding method can be changed to an ungrounded method. However, with the expansion of the distribution network, the arc of a single-phase grounding fault cannot be extinguished in time, resulting in arc overvoltage and threatening system insulation. At present, the most commonly used arc extinguishing method is to achieve it through neutral point grounding through an arc extinguishing coil. The arc extinguishing coil mainly compensates for the capacitive current of the distribution network, limits the fault current value, and makes the arc easy to extinguish. The arc extinguishing coil quickly adjusts the inductance of the arc extinguishing coil to compensate for the fundamental capacitive reactive component in the fault current. It cannot compensate for the fundamental active component and harmonic component of the fault current. With the growth of distribution network lines, the laying of overhead lines, and the extensive use of nonlinear devices such as power electronics, the fundamental active component and harmonic component of the single-phase ground fault current in the distribution network have also increased. The arc extinguishing coil that only compensates for the fundamental reactive component of the fault current can no longer meet the arc extinguishing requirements. The arc extinguishing coil achieves arc extinguishing by compensating for the fault current, which uses the current arc extinguishing principle. The principle of the voltage arc extinguishing method is to suppress the recovery speed and amplitude of the fault phase voltage, directly control the fault voltage to a lower value, and thus prevent the arc from reigniting. The products that apply this arc extinguishing principle mainly include arc extinguishing cabinets. However, the impact on the power grid during its switching process is large, and it is easy to cause ferromagnetic resonance.

[0003] With the development and maturity of power electronics technology, conditions have been provided for the application of power electronics technology in arc extinguishing of distribution network faults, and flexible arc extinguishing technology has emerged. However, flexible arc extinguishing technology is different from traditional arc extinguishing technology. It requires a given control target. According to the different control objects, it is divided into flexible voltage arc extinguishing method and flexible current arc extinguishing method. Flexible voltage and current arc extinguishing methods aim to control the voltage and current at the fault point to zero respectively. However, the voltage and current at the fault point cannot be measured directly. The bus voltage is often used instead of the fault point voltage, and the fault point current is estimated by the ground parameters. This method causes errors in the given control target. When the distribution network structure and load change, the arc extinguishing effect may be seriously affected. The flexible voltage arc extinguishing method may even increase the current at the fault point when a low-resistance grounding fault occurs at the end of a heavy-loaded line. Therefore, it is of great significance to study flexible arc extinguishing methods that are not affected by changes in the distribution network structure and load. Summary of the invention

[0004] The purpose of the present invention is to make up for the gaps and deficiencies in the prior art, and to provide a flexible composite arc extinguishing method for grounding faults in a distribution network that adapts to changes in structure and load, using a single-phase cascade H-bridge converter as an arc extinguishing device, which is hung between the neutral point of the grounding transformer and the earth. A parallel voltage and current dual closed-loop control method is proposed, and the system zero-sequence voltage is regulated to the negative value of the fault phase power supply voltage, and the fault phase current of the fault feeder is regulated to be equal to the fault phase load current of the fault feeder. According to the characteristics that the fault feeder load current and the positive sequence component in the three-phase current of the fault feeder are the same, the positive sequence component in the three-phase current of the fault feeder is extracted in real time by using coordinate transformation and filter, and then the fault feeder load current is obtained by inverse coordinate transformation. Both the voltage and current closed-loop controllers do not involve ground parameter measurement and play a major role in high-resistance and low-resistance grounding faults, respectively, solving the problems that the flexible voltage arc extinguishing method is greatly affected by the line impedance voltage drop and is easy to fail in metallic grounding faults, and the flexible current arc extinguishing method is greatly affected by the ground parameter measurement and has poor arc extinguishing effect in high-resistance grounding faults. The proposed arc extinguishing method is not restricted by the change of ground transition resistance and can adapt to the changes of distribution network operating parameters and load current.

[0005] To achieve the above-mentioned purpose, the technical scheme of the present invention is: a flexible composite arc extinguishing method for grounding faults in distribution networks that adapts to changes in structure and load, adopts a single-phase cascaded H-bridge multi-level converter as an arc extinguishing device, and is connected to the distribution network via a grounding transformer; through a parallel voltage and current double closed-loop control method, the system zero-sequence voltage is regulated to a negative value of the fault phase power supply voltage, and at the same time, the fault phase current of the fault feeder is regulated to be equal to the fault phase load current of the fault feeder; based on the characteristic that the fault phase load current of the fault feeder is the same as the positive sequence component in the three-phase current, a method for calculating the fault phase load current of the fault feeder is proposed; coordinate transformation and filter are used to extract the positive sequence component in the three-phase current of the fault feeder in real time, and then the fault phase load current of the fault feeder is obtained through inverse coordinate transformation.

[0006] In one embodiment of the present invention, the given reference values ​​of the voltage closed-loop controller and the current closed-loop controller in the parallel voltage and current dual closed-loop control method are respectively the negative value of the fault phase power supply voltage and the fault phase load current of the fault feeder, and the outputs of the voltage controller and the current controller and the neutral point voltage are superimposed as the final control target of the arc extinguishing device.

[0007] In one embodiment of the present invention, the coordinate transformation and filter are used to extract the positive sequence component in the three-phase current of the fault feeder in real time, and then the fault phase load current of the fault feeder is obtained through inverse coordinate transformation, that is: the three-phase current of the fault feeder is transformed from the abc coordinate system to the dq0 coordinate system through coordinate transformation, and then the DC component in the dq axis is extracted through a low-pass filter, and the 0 axis is set to zero, and then the positive sequence component in the three-phase current of the fault feeder in the abc coordinate system is obtained after the dq0-abc inverse transformation, that is, the fault phase load current of the fault feeder is obtained.

[0008] In one embodiment of the present invention, the method is specifically implemented in the following steps:

[0009] Step S1, connecting a single-phase cascaded H-bridge multilevel converter to a distribution network via a grounding transformer, wherein one end of the single-phase cascaded H-bridge multilevel converter is connected to the neutral point of the grounding transformer, and the other end is connected to the ground;

[0010] Step S2: During normal operation, real-time detection of the three-phase voltage at the distribution network bus, the neutral point voltage of the grounding transformer, and the current of each phase of each feeder of the distribution network;

[0011] Step S3: after a ground fault occurs, the power supply voltage phase of the fault phase is calculated using the power supply voltage amplitude and the neutral point voltage amplitude and phase, the fault phase is selected by phase comparison, and then the faulty feeder is selected by an artificial intelligence algorithm;

[0012] Step S4: Calculate the fault phase power supply voltage e by using the fault phase voltage and the neutral point voltage f ; Extract the three-phase current i of the fault feeder through coordinate transformation, filter and coordinate inverse transformation n The load current i nL ;

[0013] Step S5: Control the single-phase cascaded H-bridge multilevel converter to inject current into the neutral point of the distribution network to control the neutral point voltage to be the negative value of the fault phase power supply voltage -e f , and control the fault phase current i of the fault feeder at the same time nf The fault phase load current i nfL Equal, suppressing the voltage and current at the fault point and achieving flexible arc extinguishing.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. The present invention combines the flexible voltage arc extinguishing method and the flexible current arc extinguishing method, and integrates the advantages of the two flexible arc extinguishing methods, and has a good arc extinguishing effect in both high-resistance and low-resistance grounding faults. It solves the problems that the flexible voltage arc extinguishing method is easy to fail in the case of metallic grounding faults, and may increase the fault point current when a low-resistance grounding fault occurs at the end of a heavy-loaded line; the flexible current arc extinguishing method has a poor arc extinguishing effect in the case of a high-resistance grounding fault.

[0016] 2. The flexible current arc extinguishing method of the present invention is realized by regulating the phase current of the fault feeder, without measuring the system ground parameters. The arc extinguishing effect is not affected by the measurement of the system ground parameters, and can adapt to changes in the distribution network structure. In addition, the given reference value of the phase current of the fault feeder is extracted in real time through coordinate changes and filters, which can adapt to changes in load current. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a control block diagram of an embodiment of the present invention;

[0018] Figure 2 A schematic diagram of a power distribution network according to an embodiment of the present invention;

[0019] Figure 3 It is a schematic diagram of a simulation model of a flexible arc extinguishing method for ground fault in a distribution network according to a simulation example of the first embodiment of the present invention;

[0020] Figure 4 This is a waveform diagram of arc extinguishing results when a high-resistance 3000Ω resistor is grounded in a simulation example of the first embodiment of the present invention;

[0021] Figure 5 This is a waveform diagram of arc extinguishing results when metallic grounding is performed in a simulation example of the first embodiment of the present invention;

[0022] Figure 6 This is a waveform diagram of arc extinguishing results when a low-resistance grounding fault occurs at the end of a heavy-load line in a simulation example of the first embodiment of the present invention;

[0023] Figure 7 This is a waveform diagram of arc extinguishing results when load changes in a simulation example of the first embodiment of the present invention;

[0024] Figure 8 This is a waveform diagram of arc extinguishing results when the distribution network structure changes in a simulation example of the first embodiment of the present invention. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings.

[0026] The invention discloses a flexible composite arc extinguishing method for grounding fault of distribution network which is adaptable to structure and load changes. The method adopts a single-phase cascaded H-bridge multi-level converter as an arc extinguishing device and is connected to the distribution network via a grounding transformer. The system zero-sequence voltage is regulated to be a negative value of the fault phase power supply voltage by a parallel voltage and current double closed-loop control method, and the fault phase current of the fault feeder is regulated to be equal to the fault phase load current of the fault feeder at the same time. According to the characteristic that the fault phase load current of the fault feeder is the same as the positive sequence component in the three-phase current, a calculation method for the fault phase load current of the fault feeder is proposed. The positive sequence component in the three-phase current of the fault feeder is extracted in real time by using coordinate transformation and a filter, and the fault phase load current of the fault feeder is obtained by inverse coordinate transformation.

[0027] The following are specific implementation examples of the present invention.

[0028] like Figure 1As shown, this embodiment provides a flexible composite arc extinguishing method for grounding faults in a distribution network that is adaptable to changes in structure and load. A single-phase cascaded H-bridge converter is used as an arc extinguishing device and is connected to the distribution network via a grounding transformer. Through a parallel voltage and current dual closed-loop control method, the system zero-sequence voltage is regulated to the negative value of the fault phase power supply voltage, and at the same time, the fault phase current of the fault feeder is regulated to be equal to the fault phase load current of the fault feeder. According to the characteristic that the load current of the fault feeder is the same as the positive sequence component in the three-phase current, a method for calculating the fault phase load current of the fault feeder is proposed. Coordinate transformation and filter are used to extract the positive sequence component in the three-phase current of the fault feeder in real time, and then the fault phase load current of the fault feeder is obtained through inverse coordinate transformation. Specifically, the following steps are included:

[0029] Step S1, connecting a single-phase cascaded H-bridge multilevel converter to a distribution network via a grounding transformer, wherein one end of the single-phase cascaded H-bridge converter is connected to the neutral point of the grounding transformer, and the other end is connected to the ground;

[0030] Step S2: During normal operation, real-time detection of the three-phase voltage at the distribution network bus, the neutral point voltage of the grounding transformer, and the current of each phase of each feeder of the distribution network;

[0031] Step S3: after a ground fault occurs, the power supply voltage phase of the fault phase is calculated using the power supply voltage amplitude and the neutral point voltage amplitude and phase, the fault phase is selected by phase comparison, and then the faulty feeder is selected by an artificial intelligence algorithm;

[0032] Step S4: Calculate the fault phase power supply voltage e by using the fault phase voltage and the neutral point voltage f ; Extract the three-phase current i of the fault feeder through coordinate transformation, filter and coordinate inverse transformation n The load current i nL .

[0033] Step S5: Control the single-phase cascaded H-bridge converter to inject current into the neutral point of the distribution network to control the neutral point voltage to be the negative value of the fault phase power supply voltage -e f , and control the fault phase current i of the fault feeder at the same time nf The fault phase load current i nfL Suppress the voltage and current at the fault point and achieve flexible arc extinguishing.

[0034] Preferably, in the parallel voltage and current dual closed-loop control method, the given reference values ​​of the voltage closed-loop controller and the current closed-loop controller are respectively the negative value of the fault phase power supply voltage and the fault phase load current of the fault feeder, and the outputs of the voltage controller and the current controller and the neutral point voltage are superimposed as the final control target of the arc extinguishing device.

[0035] Preferably, the method for calculating the fault phase load current of the fault feeder uses coordinate transformation to transform the three-phase current of the fault feeder from the abc coordinate system to the dq0 coordinate system, and then uses a low-pass filter to extract the DC component in the dq axis, and sets the 0 axis to zero, and then obtains the positive sequence component of the three-phase current of the fault feeder in the abc coordinate system after dq0-abc inverse transformation, that is, the load current.

[0036] The technical solution of this embodiment is described in detail from the perspective of principle as follows:

[0037] 1. Principle of flexible voltage arc extinguishing

[0038] The schematic diagram of the distribution network structure with cascaded H-bridge converter is as follows: Figure 2 As shown. According to Kirchhoff's voltage law (KVL), we can get

[0039] U0+E A +I na Z Z -U f =0 (1)

[0040] Line impedance Z Z It is generally difficult to obtain and is often omitted. The zero-sequence voltage is controlled to be the fault phase power supply voltage, that is,

[0041] U0=-E A (2)

[0042] At this time, the residual pressure at the fault point is

[0043] U fδ_U =I na Z Z (3)

[0044] The residual current at the fault point is

[0045]

[0046] If the fault phase current and line impedance of the fault feeder are small, the residual voltage at the fault point is small. Otherwise, the residual voltage at the fault point is large. If the ground fault resistance is large, the residual current at the fault point is small. If the ground fault resistance is small, the current at the fault point is large.

[0047] 2. Principle of flexible phase current arc extinguishing

[0048] Most of the existing flexible current arc extinguishing uses zero-sequence current or ground current as the control object, but it is necessary to measure the ground parameters. The present invention proposes to use phase current as the control object, and the specific principle is as follows.

[0049] After the ground fault occurs and before the flexible arc extinguishing, the fault phase current of the fault feeder is the superposition of the fault phase-to-ground current of the fault feeder, the ground fault point current and the load current of the fault feeder, while the non-fault phase current of the fault feeder is the superposition of the non-fault phase-to-ground current of the fault feeder and the load current.

[0050]

[0051] If the fault phase current of the fault feeder is controlled to be the sum of the fault phase load current of the fault feeder and the fault phase ground current of the fault feeder, that is,

[0052] I na =I nag +I naL (6)

[0053] Then the fault branch current will be suppressed to zero. Usually I nag is very small and can be ignored. Then formula (6) can be approximated as

[0054] I na ≈I naL (7)

[0055] At this time, the residual current at the fault point is

[0056] I fδ_I =I nag (8)

[0057] According to Ohm's law, the residual voltage at the fault point is

[0058] U fδ_I =I fδ_I R f =I nag R f (9)

[0059] In the formula, I nag The value is very small, so the fault phase current I na The fault phase load current I of the fault feeder is regulated naL , the current at the fault point can be suppressed to a smaller value.

[0060] 3. Flexible voltage and current composite arc extinguishing principle

[0061] If the flexible voltage arc extinguishing method and the flexible current arc extinguishing method are superimposed, then from equations (3) and (9), the residual voltage at the fault point is:

[0062] U fδ =U fδ_I +U fδ_U =I nag R f +I na Z Z (10)

[0063] From equations (4) and (9), we can get the residual current at the fault point as

[0064]

[0065] In the case of low-resistance grounding fault, the current control loop plays a major role, and in the case of high-resistance grounding fault, the voltage control loop plays a major role. Then the residual voltage and residual current at the fault point in the case of low-resistance grounding fault are approximately equal to the residual voltage and residual current at the fault point when the flexible current arc extinguishing method is used, that is, respectively

[0066] U fδ ≈U fδ_I =I nag R f (12)

[0067] I fδ ≈U fδ_I =I nag (13)

[0068] Low resistance ground fault R f Smaller, and I nag It is also very small, so the residual pressure and residual current at the fault point are small.

[0069] The residual voltage and residual current at the fault point during a high-resistance grounding fault are approximately equal to the residual voltage and residual current at the fault point when the flexible voltage arc extinguishing method is used, that is,

[0070] U fδ ≈U fδ_U =I nag Z Z (14)

[0071]

[0072] Typical line impedance drop I na Z Z Small, generally less than 7% E A , so the residual voltage at the fault point is small. When there is a high-resistance ground fault, R f If it is very large, the residual current at the fault point will also be small.

[0073] Therefore, the flexible voltage-current composite arc extinguishing method can suppress the voltage and current at the fault point to a smaller value under different grounding resistance fault conditions.

[0074] 4. Method for obtaining the fault phase load current of the fault feeder

[0075] From formula (7), we can know that the fault phase current I na The load current I of the fault phase of the fault feeder needs to be controlled naLSince most 10 / 0.4kV distribution transformers are Δ / Y connected, the ground current of the distribution line only flows in the 10kV side network and will not be transmitted to the 0.4kV side. The distribution line phase current consists of two parts: load current and ground current. Therefore, after the load current in the distribution line phase current is transformed by the abc-dq0 coordinate system, it is the DC component of the dq axis in the dq0 coordinate system. It can be obtained after filtering with a low-pass filter, and then the load current can be extracted from the distribution line phase current by the dq0-abc inverse transformation. The specific steps are: transform the three-phase current of the fault feeder to the dq0 coordinate system through the Parker transformation, that is

[0076]

[0077] In the formula, i ni1 (i=A, B, C) are the positive sequence components of the load current of phases A, B, and C respectively, i ni2 (i=A, B, C) are the negative sequence components of the load current of phases A, B, and C respectively, i ni0 (i=A, B, C) are the zero-sequence components of the A, B, and C phase load currents respectively. The fundamental positive sequence active and reactive components in the three-phase current are DC quantities on the d-axis and q-axis respectively. The fundamental positive sequence active and reactive components can be extracted from the d-axis and q-axis components respectively by using a low-pass filter, and then the three-phase fundamental positive sequence current in the abc coordinate system can be obtained by dq-abc inverse transformation, that is,

[0078]

[0079] The fault feeder load current and the positive sequence component of the fault feeder three-phase current are the same.

[0080]

[0081] In order to allow those skilled in the art to better understand the technical solution of the present invention, the present invention is further introduced below in conjunction with a simulation example.

[0082] Use PSCAD / EMTDC software to build Figure 3 The simulation model of a distribution network with four feeders is shown. The Bergeron model is used for the distribution lines.

[0083] right Figure 3 The distribution network shown in the figure has a fault point set at fault point 1 (Fault1). The simulation results for a high-resistance 3000Ω grounding resistance fault and a 10Ω grounding fault are as follows: Figure 4-5 As shown. Figure 4 and Figure 5It can be seen that no matter it is a high-resistance grounding fault or a low-resistance grounding fault, the proposed flexible arc extinguishing method can effectively suppress the voltage and current at the fault point, and the effect is better than using the flexible voltage arc extinguishing method or the flexible current arc extinguishing method alone.

[0084] right Figure 3 In the distribution network shown in the figure, the fault point is set at fault point 2 (Fault2), the ground fault resistance is 5Ω, a low-resistance ground fault occurs at the end of the heavy-load line, the load current of the fault feeder changes, and the distribution network structure changes (ground parameter changes or line switching). The simulation results are as follows Figure 6 to Figure 8 As shown. Figure 6 It can be seen that when a low-resistance grounding fault occurs at the end of a heavy-loaded line, the flexible voltage arc extinguishing method increases the fault point current, and the proposed flexible composite arc extinguishing method compensates the fault point current to a smaller value. Figure 7 It can be seen that when the load current of the fault feeder changes, the arc extinguishing effect of the proposed flexible composite arc extinguishing method is little affected by the load current change. Figure 8 It can be seen that during the ground fault arc extinguishing period, the arc extinguishing effect of the proposed new composite arc extinguishing method is not affected after the feeder 3 is shut down. It is verified that the proposed new composite arc extinguishing method can adapt to different ground fault resistances, load currents and distribution network structure changes.

[0085] This embodiment uses a parallel voltage and current dual closed-loop control method to adjust the system zero-sequence voltage to the negative value of the fault phase power supply voltage, and at the same time adjusts the fault phase current of the fault feeder to be equal to the fault phase load current of the fault feeder. The flexible voltage arc extinguishing principle and the flexible current arc extinguishing principle are combined into the same flexible arc extinguishing device, giving full play to the advantages of the flexible voltage arc extinguishing method in high-resistance grounding faults and the flexible current arc extinguishing method in low-resistance grounding faults. The flexible composite arc extinguishing method can adapt to different grounding resistance faults, solving the problems that the flexible voltage arc extinguishing method is greatly affected by the line impedance voltage drop and is easy to fail in metallic grounding faults; the flexible current arc extinguishing method has poor arc extinguishing effect in high-resistance grounding faults. The positive sequence component in the three-phase current of the fault feeder is extracted in real time by coordinate transformation and filter, and then the load current of the fault feeder is obtained by inverse coordinate transformation. The flexible composite arc extinguishing method can adapt to changes in load current. The current closed-loop controller does not involve ground parameter measurement, which solves the problem that the flexible current arc extinguishing method is greatly affected by ground parameter measurement. The flexible composite arc extinguishing method can adapt to changes in distribution network structure (ground parameters).

[0086] This patent application is not limited to the above-mentioned optimal implementation mode. Anyone can derive other forms of flexible voltage and current composite arc extinguishing methods for single-phase grounding faults in distribution networks under the inspiration of this patent application. All equal changes and modifications made within the scope of the patent application of the present invention should fall within the scope of this patent.

Claims

1. A flexible composite arc extinguishing method for ground fault in distribution network adapting to structure and load changes, characterized in that: A single-phase cascaded H-bridge multilevel converter is used as an arc extinguishing device and connected to the distribution network through a grounding transformer. Through a parallel voltage and current double closed-loop control method, the system zero-sequence voltage is regulated to the negative value of the fault phase power supply voltage, and at the same time, the fault phase current of the fault feeder is regulated to be equal to the fault phase load current of the fault feeder. According to the characteristic that the fault phase load current of the fault feeder is the same as the positive sequence component in the three-phase current, a method for calculating the fault phase load current of the fault feeder is proposed; the positive sequence component in the three-phase current of the fault feeder is extracted in real time by using coordinate transformation and filter, and then the fault phase load current of the fault feeder is obtained by inverse coordinate transformation; in the parallel voltage and current dual closed-loop control method, the given reference values ​​of the voltage closed-loop controller and the current closed-loop controller are respectively the negative value of the fault phase power supply voltage and the fault phase load current of the fault feeder, and the output of the voltage controller and the current controller and the neutral point voltage are superimposed as the final control target of the arc extinguishing device; the coordinate transformation and filter are used to extract the positive sequence component in the three-phase current of the fault feeder in real time, and then the fault phase load current of the fault feeder is obtained by inverse coordinate transformation, that is: the three-phase current of the fault feeder is transformed from the abc coordinate system to the dq0 coordinate system by using coordinate transformation, and then the DC component in the dq axis is extracted by using a low-pass filter, and the 0 axis is set to zero, and then the positive sequence component in the three-phase current of the fault feeder in the abc coordinate system is obtained after the dq0-abc inverse transformation, that is, the fault phase load current of the fault feeder is obtained; the specific implementation steps of the method are as follows: Step S1, connecting a single-phase cascaded H-bridge multilevel converter to a distribution network via a grounding transformer, wherein one end of the single-phase cascaded H-bridge multilevel converter is connected to the neutral point of the grounding transformer, and the other end is connected to the ground; Step S2: During normal operation, real-time detection of the three-phase voltage at the distribution network bus, the neutral point voltage of the grounding transformer, and the current of each phase of each feeder of the distribution network; Step S3: after a ground fault occurs, the power supply voltage phase of the fault phase is calculated using the power supply voltage amplitude and the neutral point voltage amplitude and phase, the fault phase is selected by phase comparison, and then the faulty feeder is selected by an artificial intelligence algorithm; Step S4: Calculate the fault phase power supply voltage by using the fault phase voltage and the neutral point voltage ; Extract the three-phase current of the fault feeder through coordinate transformation, filter and coordinate inverse transformation The load current in ; Step S5: Control the single-phase cascaded H-bridge multilevel converter to inject current into the neutral point of the distribution network to control the neutral point voltage to be the negative value of the fault phase power supply voltage. , while controlling the fault phase current of the fault feeder The fault phase load current of the fault feeder Equal, suppressing the voltage and current at the fault point and achieving flexible arc extinguishing.

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