Power distribution network grounding fault active positioning method based on flexible regulation of grid-connected converter

Abstract

The application provides a power distribution network grounding fault active positioning method based on flexible regulation of grid-connected converters, comprising: obtaining a fault node ground current; determining an arc extinguishing current injected by a grid-connected converter based on the fault node ground current; determining a fourth bridge arm switch signal of the grid-connected converter based on the arc extinguishing current; collecting an electrical state parameter of a regulated power distribution network; and determining a fault point distance from a bus position based on the electrical state parameter of the power distribution network. The method provided in the application realizes accurate positioning by using the inherent characteristics of the effectively suppressed fault point voltage after regulation. Compared with existing fault positioning methods, the method realizes accurate positioning of the grounding fault without relying on the time when the fault occurs and expensive measurement units, and does not cause power quality and arc reignition problems.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of single-phase grounding fault support of distribution network, and particularly relates to a distribution network grounding fault active positioning method based on flexible regulation of grid-connected converters. BACKGROUND

[0002] The distribution network is deeply connected to user terminals, and the running environment is complex and random faults occur frequently. Single phase-to-ground fault (SPG) accounts for nearly 70%, which seriously threatens the safe and reliable operation of the distribution network. According to the nature of the fault, SPG fault can be divided into transient fault and permanent fault. For transient fault, the arc can be extinguished by using the dynamic compensation capability of the arc extinguishing device. For permanent fault, accurate fault location is needed to identify the fault location, and then artificial intervention is used to realize fault isolation and rapid removal. Therefore, safe arc extinction and accurate positioning during SPG fault are of great significance.

[0003] Existing fault positioning methods can be divided into passive positioning method and active positioning method. The passive fault positioning method mainly constructs the positioning criterion according to the voltage or current signals before and after the fault. The zero sequence impedance positioning method proposed is based on the time domain voltage and current signals to calculate the zero sequence impedance between the fault point and the bus to realize positioning. However, the voltage and current signals are weak in high resistance grounding fault, and the fault positioning accuracy is difficult to guarantee. Traveling wave is caused by voltage mutation at the fault point, and is not affected by the system operation mode, which can effectively overcome the positioning difficulty of high resistance grounding fault. Based on this, single-ended measurement, double-ended measurement and network positioning traveling wave positioning methods are proposed. However, accurate measurement of traveling wave requires widely arranging detection units with high-frequency sampling and time synchronization capability at key nodes, which is costly. In addition, when the fault occurs at the voltage zero crossing point or its vicinity, the traveling wave will not exist or the amplitude will be very small, which reduces the fault positioning accuracy. To solve the above problems, the active positioning method of reusing power electronic equipment for fault positioning has attracted widespread attention. The low-frequency voltage type positioning method is proposed, which uses flexible interconnected devices to actively inject positive sequence low-frequency voltage signals during fault steady state, and is not affected by the fault occurrence time and fault transition resistance. However, the injected harmonic signals reduce the power quality of the distribution network. In order to avoid the problem of power quality, the zero sequence phase difference positioning method is proposed, which actively reduces the regulated current of the grid-connected converter to construct the zero sequence component change, and uses the phase difference between the zero sequence voltage and the zero sequence current to realize fault positioning. However, actively reducing the regulated current will increase the fault current, which has the risk of arc burning. Therefore, the economic and reliable active fault positioning method needs further research. SUMMARY

[0004] The application provides a distribution network grounding fault active positioning method based on flexible regulation of grid-connected converters.

[0005] The application provides a distribution network grounding fault active positioning method based on flexible regulation of grid-connected converters, which comprises the following technical solutions.

[0006] Obtaining the fault node-to-ground current;

[0007] Based on the fault node-to-ground current, the arc-extinguishing current injected by the grid-connected converter is determined.

[0008] Based on the arc-extinguishing current, the switch signal of the fourth bridge arm of the grid-connected converter is determined.

[0009] Collecting the electrical state parameters of the regulated distribution network;

[0010] Based on the electrical state parameters of the distribution network, the distance between the fault point and the busbar is determined.

[0011] Optionally, the determination process of the fault node-to-ground current comprises the following steps.

[0012] Collecting the core electrical state parameters of the distribution network before and after the fault phase fails;

[0013] Based on the core electrical state parameters of the distribution network before and after the fault phase fails, the fault node-to-ground current is determined.

[0014] Optionally, the core electrical state parameters of the distribution network before and after the fault phase fails comprise the busbar current before the fault, the grid phase voltage before the fault, the neutral point voltage before the fault, the busbar current after the fault, the grid phase voltage after the fault and the neutral point voltage after the fault, and the electrical state parameters of the regulated distribution network comprise the regulated neutral point voltage, the regulated grid phase voltage, the fault phase feeder current and the unit line impedance of the fault feeder.

[0015] Optionally, the determination of the fault node-to-ground current based on the core electrical state parameters of the distribution network before and after the fault phase fails comprises the following steps.

[0016] Based on the core electrical state parameters of the distribution network before and after the fault phase fails, the fault phase load current is determined.

[0017] Based on the fault phase load current, the fault node-to-ground current is determined.

[0018] Optionally, the determination of the fault node-to-ground current based on the fault phase load current comprises the following steps.

[0019] Based on the busbar current after the fault and the fault phase load current, the fault node-to-ground current is determined.

[0020] Optionally, the arc-extinguishing current injected by the grid-connected converter is determined based on the fault node-to-ground current, including:

[0021] The fault node-to-ground current is input into a first adaptive voltage loop to obtain an adaptive virtual voltage;

[0022] The voltage outer loop error quantity is obtained based on the adaptive virtual voltage, the post-fault grid phase voltage and the real-time collected neutral point voltage;

[0023] The voltage outer loop error quantity is input into a second adaptive voltage loop to obtain the arc-extinguishing current injected by the grid-connected converter.

[0024] Optionally, the switch signal of the fourth bridge arm of the grid-connected converter is determined based on the arc-extinguishing current, including:

[0025] The injected zero-sequence current is obtained;

[0026] The current inner loop error quantity is obtained based on the arc-extinguishing current and the zero-sequence current;

[0027] The current inner loop error quantity is input into a third adaptive voltage loop to determine a modulation signal compensation quantity;

[0028] The modulation signal is generated based on the modulation signal compensation quantity and the post-fault grid phase voltage;

[0029] The switch signal of the fourth bridge arm of the grid-connected converter is determined based on the modulation signal.

[0030] Optionally, the switch signal includes an NPC unit switch signal and a CHB switch signal, and the switch signal of the fourth bridge arm of the grid-connected converter is determined based on the modulation signal, including:

[0031] The NPC unit switch signal is determined by performing modulation processing on the modulation signal using a nearest level approximation modulation;

[0032] The CHB unit switch signal is determined by performing modulation processing on the modulation signal using a carrier phase-shifted modulation.

[0033] Optionally, the fault point distance from the bus position is determined based on the power distribution network electrical state parameters, including:

[0034] The feeder impedance is determined based on the regulated neutral point voltage, the fault phase feeder current and the regulated grid phase voltage;

[0035] The fault point distance from the bus position is determined based on the feeder impedance and the unit line impedance of the fault feeder.

[0036] The application has the following beneficial effects:

[0037] The method proposed in this application achieves precise location by utilizing the inherent characteristic that the fault point voltage is effectively suppressed after regulation. Compared with existing fault location methods, this method achieves precise location of ground faults without relying on the time of fault occurrence or expensive measurement units, and does not cause power quality or arc reignition problems. Attached Figure Description

[0038] Figure 1 Equivalent circuit diagram of a distribution network including a grid-connected converter provided in the embodiments of this application;

[0039] Figure 2 This is a flowchart illustrating the active location method for grounding faults in distribution networks based on flexible control of grid-connected converters provided in this application embodiment.

[0040] Figure 3 This is a schematic diagram of the process of generating a grid-connected converter modulation signal provided in an embodiment of this application; Figure 3 (a) is a schematic diagram of the calculation process of the fault node to ground current provided in the embodiment of this application; Figure 3 (b) is a flowchart of the control loop for generating the modulated signal provided in an embodiment of this application; Figure 3 (c) is a schematic diagram of the modulation section provided in the embodiments of this application. Detailed Implementation

[0041] To facilitate understanding by those skilled in the art, the present application will be further described below in conjunction with embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present application.

[0042] Since this application achieves fault location by injecting arc-suppressing current into the grid-connected converter when a ground fault occurs in the distribution network, therefore, it is combined with, for example... Figure 1 The equivalent circuit of the distribution network including the grid-connected converter shown below provides a brief explanation of the ground fault arc suppression principle of this application:

[0043] Figure 1 middle, , and These represent the system's equivalent ground current, load current, and bus current, respectively. It is the virtual impedance of the grid-connected converter; , These represent the phase voltage of the power grid and the voltage to ground, respectively. and These represent the feeder impedance, ground admittance, and fault transition conductance, respectively. This refers to the phase voltage of the mains power supply.

[0044] Now, let's assume the fault occurs in phase A. Near the node, Kirchhoff's current law is written for the fault node, and the fault node's current to ground is... is:

[0045] (1)

[0046] wherein, is the fault current.

[0047] When , the equivalent-to-ground current of the fault phase can be expressed as:

[0048] (2)

[0049] wherein, is the fault transition resistance.

[0050] At this time, the fault node-to-ground current can be further expressed as:

[0051] (3)

[0052] As can be seen from equation (1) and equation (3), the fault node-to-ground current can be calculated by using the bus current of the fault phase and the load current, and then the fault node-to-ground current is controlled to 0, so as to completely compensate the fundamental component and harmonic component of the fault current.

[0053] At this time, the control target corresponding to the complete compensation of the fault current can be generated by closed-loop control:

[0054] (4)

[0055] (5)

[0056] wherein: is the real-time collected neutral point voltage, , , and are the proportional coefficient, the resonance coefficient, the resonance frequency and the cut-off frequency of the PR controller, respectively; is the adaptive virtual voltage, wherein .

[0057] After adding the adaptive virtual voltage, the fault current can be expressed as:

[0058] (6)

[0059] Based on the above, the calculation process of the fault node-to-ground current can be obtained as follows:

[0060] According to Kirchhoff's current law, the bus current before the fault satisfies:

[0061] (7)

[0062] (8)

[0063] wherein: , and denote the pre-fault neutral voltage, the line-to-ground current and the line-to-ground admittance, respectively.

[0064] If , Otherwise, the pre-fault neutral voltage satisfies:

[0065] (9)

[0066] At the moment of SPG fault, the load current remains unchanged, then the post-fault bus current can be expressed as:

[0067] (10)

[0068] wherein: and denote the post-fault neutral voltage and the line-to-ground current, respectively.

[0069] Combining equation (7) and equation (10), the bus current variation can be expressed as:

[0070] (11)

[0071] Combining equation (7), equation (9) and equation (11), the load current of the fault phase can be expressed as:

[0072] (12) After the SPG fault is regulated, the real-time load current

[0073] can be determined by detecting the bus current variation:

[0074] (13)

[0075] wherein: and are the bus current at the moment of fault and the variation, respectively, is the bus current in the time period after the moment of fault.

[0076] ​Therefore, in combination with formula (1), formula (12) and formula (13), the fault node-to-ground current can be accurately obtained by detecting the bus current, the neutral point voltage and the grid phase voltage, thereby providing a real-time feedback value for the full compensation active arc extinguishing method of the grounding fault current.

[0077] According to the above, in order to solve the problems raised in the background art, as shown in Figure 2 , the application proposes a distribution network grounding fault active positioning method based on flexible regulation of grid-connected converters, comprising:

[0078] Step S201: obtaining the fault node-to-ground current;

[0079] The fault node-to-ground current of the application is calculated in the manner as shown in Figure 3 (b), and the specific process is as follows:

[0080] First, the core electrical state parameters of the distribution network before and after the fault phase occurs are collected, including the bus voltage before the fault , the bus current before the fault , the grid phase voltage before the fault , the bus current after the fault , the grid phase voltage after the fault and the neutral point voltage after the fault , and then the above collected data is substituted into formula (12), so that the fault phase load current is obtained.

[0081] Further, the above collected bus current after the fault and the fault phase load current are substituted into formula (1), so that the fault node-to-ground current is obtained.

[0082] It should be noted that , and the grid phase voltage after the fault and the grid phase voltage before the fault are equal.

[0083] Step S202: determining the arc extinguishing current injected by the grid-connected converter based on the fault node-to-ground current;

[0084] As shown in Figure 3 (a), the fault node-to-ground current is input into the first voltage adaptive voltage loop PR to obtain the adaptive virtual voltage , and then the adaptive virtual voltage and the grid phase voltage after the fault are added, and then the real-time collected neutral point voltage is subtracted.The voltage outer loop error quantity is obtained The voltage outer loop error quantity is obtained The second adaptive voltage loop PR is input to obtain the arc extinguishing current injected by the grid-connected converter .

[0085] Step S203: based on the arc extinguishing current, determine the switching signal of the fourth bridge arm of the grid-connected converter;

[0086] The arc extinguishing current is further injected as a zero sequence current reference value, and the injected zero sequence current is obtained The arc extinguishing current and the zero sequence current are subtracted to obtain the current inner loop error quantity The current inner loop error quantity is input to the third adaptive voltage loop to obtain the modulation signal compensation quantity The modulation signal compensation quantity is added to the post-fault phase grid voltage to generate the modulation signal The modulation signal is used to determine the switching signal of the fourth bridge arm of the grid-connected converter.

[0087] The switching signal of the present application includes the NPC unit (neutral point clamped unit) switching signal and the CHB unit (cascaded H-bridge module) switching signal of the fourth bridge arm of the grid-connected converter, as shown in Figure 3 (c), and the specific process of determining the switching signal of the fourth bridge arm of the grid-connected converter according to the modulation signal is as follows:

[0088] The modulation signal is modulated by using the nearest level modulation (NLM) to determine the NPC unit switching signal The modulation signal is modulated by using the carrier phase shifted modulation (CPS) to determine the CHB unit switching signal .

[0089] The above-mentioned regulated switching signal is used for accurate regulation.

[0090] Step S204: collect the regulated power distribution network electrical state parameters;

[0091] After regulation, the regulated power distribution network electrical state parameters are collected, that is, the regulated power distribution network electrical state parameters include the regulated neutral point voltage ​, regulating the phase voltage of the power grid , the fault phase feeder current , and the unit line impedance .

[0092] Step S205: determining the fault point distance from the bus position based on the power distribution network electrical state parameters.

[0093] When the grounding fault current full compensation active arc extinguishing method is adopted, the SPG fault point voltage can be effectively suppressed to 0. At this time, the line impedance voltage of the fault feeder can be expressed as:

[0094] (14)

[0095] In the formula: , is the regulated neutral point voltage and the fault feeder current;

[0096] According to formula (15), the fault point distance from the bus position can be expressed as:

[0097] (15)

[0098] In the formula: is the unit line impedance of the fault feeder.

[0099] For a determined line type, the unit line impedance is also determined. Therefore, the feeder impedance Z can be calculated according to the regulated neutral point voltage , the regulated phase voltage of the power grid , and the fault phase feeder current , and then the fault point distance from the bus position can be calculated according to the feeder impedance Z and the unit line impedance of the fault feeder, realizing accurate positioning of the SPG fault, improving the efficiency of artificial line patrol, and promoting the rapid removal of permanent grounding faults.

[0100] As described above, the method proposed in the present application realizes accurate positioning by utilizing the inherent characteristics that the fault point voltage is effectively suppressed after regulation. Compared with existing fault positioning methods, the method realizes accurate positioning of the grounding fault without relying on the time when the fault occurs and expensive measurement units, and does not cause problems of power quality and arc reignition.

[0101] The above embodiments are preferred implementation schemes of the present application, and in addition to this, the present application can also be implemented in other ways, and any obvious replacement without departing from the technical solution concept of the present application is within the protection scope of the present application.

[0102] In order to make the improvement of the present application more convenient for those skilled in the art to understand, some drawings and descriptions of the present application have been simplified, and some other elements have also been omitted in the present application file for the sake of clarity, and those skilled in the art should realize that these omitted elements can also constitute the content of the present application.

Claims

1. A method for active location of grounding faults in distribution networks based on flexible control of grid-connected converters, characterized in that, include: Collect core electrical status parameters of the distribution network before and after the faulty phase occurs; Based on the core electrical state parameters of the distribution network before and after the faulty phase, the ground current of the fault node is determined; the core electrical state parameters of the distribution network before and after the faulty phase include the bus current before the fault, the phase voltage of the grid before the fault, the neutral point voltage before the fault, the bus current after the fault, the phase voltage of the grid after the fault, and the neutral point voltage after the fault. Based on the ground current of the fault node, the arc suppression current injected by the grid-connected converter is determined. Based on the arc suppression current, determine the switching signal of the fourth bridge arm of the grid-connected converter; Collect and regulate the electrical status parameters of the distribution network after control. Based on the electrical status parameters of the distribution network, the distance of the fault point from the busbar is determined; The determination of the arc-suppression current injected by the grid-connected converter based on the ground current of the fault node includes: The ground current of the fault node is input into the first adaptive voltage loop to obtain the adaptive virtual voltage; Based on the adaptive virtual voltage, the post-fault grid phase voltage, and the real-time collected neutral point voltage, the voltage outer loop error is obtained. The voltage outer loop error is input into the second adaptive voltage loop to obtain the arc suppression current injected by the grid-connected converter.

2. The active location method for grounding faults in distribution networks based on flexible control of grid-connected converters according to claim 1, characterized in that, The regulated electrical state parameters of the distribution network include the regulated neutral point voltage, the regulated phase voltage of the grid, the faulty phase feeder current, and the unit line impedance of the faulty feeder.

3. The active location method for grounding faults in distribution networks based on flexible control of grid-connected converters according to claim 2, characterized in that, The determination of the ground current of the fault node based on the core electrical state parameters of the distribution network before and after the fault phase occurs includes: Based on the core electrical state parameters of the distribution network before and after the fault phase occurs, the load current of the fault phase is determined. Based on the load current of the faulted phase, the ground current of the faulted node is determined.

4. The active location method for grounding faults in distribution networks based on flexible control of grid-connected converters according to claim 3, characterized in that, The step of determining the fault node-to-ground current based on the fault phase load current includes: The ground current of the fault node is determined based on the bus current and the load current of the faulted phase after the fault.

5. The active location method for grounding faults in distribution networks based on flexible control of grid-connected converters according to claim 1, characterized in that, Based on the arc-suppression current, the switching signal of the fourth arm of the grid-connected converter is determined, including: Obtain the injected zero-sequence current; Based on the arc-suppression current and the zero-sequence current, the inner loop error of the current is obtained; The current inner loop error is input into the third adaptive voltage loop to determine the modulation signal compensation amount. A modulation signal is generated based on the modulation signal compensation amount and the phase voltage of the power grid after the fault. Based on the modulation signal, the switching signal of the fourth bridge arm of the grid-connected converter is determined.

6. The active location method for grounding faults in distribution networks based on flexible control of grid-connected converters according to claim 5, characterized in that, The switching signals include NPC unit switching signals and CHB switching signals. Determining the switching signal of the fourth arm of the grid-connected converter based on the modulation signals includes: The nearest-level approximation modulation is used to modulate the modulation signal to determine the NPC unit switching signal; The modulation signal is modulated using carrier phase-shift modulation to determine the CHB unit switching signal.

7. The active location method for grounding faults in distribution networks based on flexible control of grid-connected converters according to claim 2, characterized in that, Determining the distance of the fault point from the busbar based on the electrical state parameters of the distribution network includes: The feeder impedance is determined based on the regulated neutral point voltage, the fault phase feeder current, and the regulated grid phase voltage. Based on the feeder impedance and the unit line impedance of the faulty feeder, the distance of the fault point from the busbar is determined.

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