Fault section location method for active distribution network based on mathematical morphology polarity

Abstract

The present invention proposes a method for locating a fault section of an active distribution network based on mathematical morphology polarity, and relates to the technical field of fault locating of distribution networks. The present invention includes: when the measured current of any phase in the feeder terminal meets the fault detection criterion, it is considered that a fault may occur, and enters a fault location process based on mathematical morphology polarity, and executes: the feeder terminal selects a suitable morphological M value according to the number of fault phases; the measured current waveform is filtered using a mathematical morphology algorithm; after filtering, the fault current mutation amount is calculated using a full-cycle subtraction method; the peak value of the fault current mutation amount waveform is extracted using a mathematical morphology algorithm, and the polarity of the peak value is determined; the terminal devices at both ends of the protected section mutually transmit the polarity of the mathematical morphology peak value; and the polarity of the mathematical morphology peak value at both ends is considered to be a fault section if both are regular. The present invention is not affected by the fault characteristics of distributed power supply, and can better adapt to the complex fault characteristics of active distribution networks.

Description

Technical Field

[0001] The invention belongs to the technical field of fault section positioning in a distribution network, and in particular relates to a fault section positioning method for an active distribution network based on mathematical morphology polarity. Background Art

[0002] With the acceleration of the construction of new power systems, a large number of distributed power sources, mainly distributed photovoltaics, are connected to the distribution network on site, upgrading the traditional distribution network to an active distribution network. When a fault occurs in the traditional distribution network, overcurrent protection and local feeder automation are generally used to locate the fault section. However, the traditional fault section location method will be difficult to apply in the active distribution network. First, the access of a large number of distributed power sources upgrades the traditional single-power radial power supply network to an active network with multiple power supplies and multiple terminals. The distributed power source can still supply power after the line outlet circuit breaker is opened, and the logic of "power failure opening and power on" of the local feeder automation is no longer applicable; secondly, the fault characteristics of distributed power sources are extremely complex, and the fault responses of different types of distributed power sources vary greatly, resulting in the inability to adjust and coordinate conventional overcurrent protection, and it is difficult to use it in active distribution networks with high penetration rates of distributed power sources. Therefore, it is urgent to study the fault section location method applicable to active distribution networks.

[0003] The prior art proposes a method for locating the fault section of an active distribution network based on adaptive directional current protection. First, directional protection elements are installed at each switch, and then the constant value of the current protection is adaptively adjusted according to the output of the distributed power source. This type of method takes into account the external absorption and auxiliary enhancement of distributed power sources, and can better adapt to the fault characteristics of active distribution networks than traditional overcurrent protection methods. However, in actual distribution networks, there are many distributed power sources that do not have measurement conditions, and the fault location method based on adaptive directional current protection is not applicable enough in this scenario.

[0004] The prior art proposes a centralized fault section location method based on wide-area protection of the master station. After a fault occurs, the distribution master station first collects multi-point information located at different protection installations, and then the master station locates the fault section based on the wide-area information using artificial intelligence, nonlinear programming, state estimation and other means. The advantage of this method is that it can comprehensively utilize all the information in the distribution system and can adapt to the complex fault characteristics of the active distribution network. However, the centralized fault section location method has the disadvantages of being completely dependent on the master station, having a long judgment time, and having poor interpretation of the fault characteristics of distributed power sources.

[0005] The prior art proposes a method for locating the distributed fault section of an active distribution network based on longitudinal current differential protection, which introduces the longitudinal differential protection that has been maturely applied in high-voltage lines into the protection of active distribution networks. This type of method is based on Kirchhoff's current law, has strong interpretability, and has extremely high reliability when all distributed power sources are connected by busbars / ring mains cabinets. However, with the increase in the penetration rate of distributed power sources in active distribution networks, some distributed power sources may be connected to the grid in the form of T-connection inside the line. At this time, the prerequisite for applying current differential protection is destroyed, and the effect of fault section locating is difficult to guarantee.

[0006] The existing fault section location method of active distribution network is easily affected by factors such as distributed power generation fault characteristics, penetration rate and access location. There is no fault section location method that is not affected by distributed power generation access and has strong interpretability. Summary of the invention

[0007] In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides a method for locating fault sections of active distribution networks based on mathematical morphology polarity. The method uses a mathematical morphology algorithm to extract the peak polarity in the fault current mutation waveform, and then comprehensively compares the peak polarity at both ends of the line to locate the fault section. It is not affected by the fault characteristics of distributed power sources and can better adapt to the complex fault characteristics of active distribution networks.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A first aspect of the present invention provides a method for locating a fault section of an active distribution network based on mathematical morphology polarity, comprising:

[0010] Configure feeder terminals at both ends of the protected section to measure local three-phase current data in real time;

[0011] When the measured current of any phase detected by the feeder terminal meets the fault detection criterion, it is considered that a fault may occur and the fault location process based on mathematical morphology polarity is started;

[0012] After entering the fault location process, the feeder terminal selects the corresponding morphological M value according to the number of fault phases. The morphological M value is the length of the structural element in the mathematical morphological algorithm.

[0013] According to the M value, a structural element of corresponding length is constructed, and the measured current waveform is filtered by using the structural element to perform an open-close-close-open median filtering algorithm;

[0014] After filtering is completed, the fault current mutation amount is calculated using the full-cycle subtraction method;

[0015] The peak value of the fault current mutation waveform is extracted using mathematical morphology algorithm, and the polarity of the peak value is determined;

[0016] The polarity of the mathematical morphology peak value of mutual transmission between the feeder terminals at both ends of the protected section;

[0017] Whether the section is a fault section is determined based on the polarity of the mathematical morphology peaks at both ends.

[0018] Furthermore, when the feeder terminal detects that the measured current of any phase meets the fault detection criterion, it is considered that a fault may occur and enters the fault location process based on mathematical morphology polarity. The fault detection criterion adopts the phase current mutation amount criterion. The fault detection criterion is as follows:

[0019] ,

[0020] In the formula, i φ ( k )express φ Phase current in the k The sampling value of the sampling point, N is the number of sampling points at the feeder terminal within one power frequency cycle, K S is the fault detection threshold coefficient, I N is the rated current amplitude.

[0021] Furthermore, the feeder terminal selects the corresponding morphological M value according to the number of fault phases:

[0022] Since the grounding point has a relatively large transition resistance when an asymmetric fault occurs, a larger M value is required to ensure the effect of mathematical morphology processing; when a symmetric fault occurs, the short-circuit current is large, and a smaller M value is required to ensure the effect of mathematical morphology processing; by judging whether the fault is symmetrical, the corresponding M value is selected. When the number of phases in the three-phase current that meets the fault detection criterion is 3, the first M value is selected, otherwise the second M value is selected. The first M value is smaller than the second M value. The first M value and the second M value are determined according to hardware conditions and site environment.

[0023] Furthermore, an open-close-close-open median filtering algorithm in mathematical morphology is selected to filter the measured current waveform, including:

[0024] For filtering, assume that the input signal is f (n), the structural element is g (m), the dilation and erosion operators are as follows:

[0025] ,

[0026] ,

[0027] In the formula, Df , Dg are the domains of input signal and structural element respectively;

[0028] The opening operator is obtained by combining the expansion and corrosion operators ( ) and the closing operator ( ), as follows:

[0029] ,

[0030] ,

[0031] The open-close-close-open median filter is realized by combining the open and close operators, as shown below:

[0032] ,

[0033] in, For input signal f (n) The result after open-close-close-open median filtering.

[0034] Furthermore, when the peak value of the fault current mutation waveform is extracted by using the mathematical morphology algorithm and the polarity of the peak value is determined, the top hat operator and the bottom hat operator in mathematical morphology are combined to form a mathematical morphology peak detection algorithm to process the fault current mutation. When the first peak value obtained after processing is positive, the polarity is considered to be positive, and when the first peak value is negative, the polarity is considered to be negative; wherein, the morphological peak detection algorithm is as follows:

[0035] ,

[0036] in, is the peak value.

[0037] Furthermore, the fault current mutation in the full cycle subtraction method The current sampling value at the current moment minus the current sampling value one cycle ago is obtained:

[0038] ,

[0039] In the formula, express Phase current in the The sampling value of the sampling point, is the number of sampling points at the feeder terminal within one power frequency cycle.

[0040] Furthermore, whether the section is a fault section is determined according to the polarities of the mathematical morphology peaks at both ends. If the polarities at both ends are positive, it is considered to be a fault section.

[0041] The second aspect of the present invention provides a method for locating a feeder terminal in a fault section of an active distribution network based on mathematical morphology polarity, comprising: at least one processing unit, the processing unit, a storage unit, a collection unit and a communication unit being interconnected through a bus unit, the storage unit storing a computer program, and when the computer program is executed by the processing unit, the method for locating a fault section of an active distribution network based on mathematical morphology polarity is implemented.

[0042] The above technical solution has the following beneficial effects:

[0043] The present invention uses the polarity of the first peak in the current mutation waveform to judge the fault section, and can complete the judgment within 5ms after the fault occurs. At this time, the fault control strategy of the distributed power supply has not responded. Therefore, this method is not affected by the fault characteristics, penetration rate and access location factors of the distributed power supply.

[0044] The present invention utilizes mathematical morphology filtering and peak detection algorithm to extract peak features in the fault current waveform mutation quantity, is not affected by measurement noise and has strong peak extraction capability, can still correctly extract peak polarity when the short-circuit current is small, and has strong resistance to transition resistance.

[0045] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0047] Figure 1 It is a schematic diagram of the configuration and simulation model of the active distribution network feeder terminal according to an embodiment of the present invention;

[0048] Figure 2 Schematic diagram of the mathematical morphological filtering effect of an embodiment of the present invention; wherein (a) is a schematic diagram of a current waveform with a signal-to-noise ratio of 30 dB after superimposed noise in an embodiment of the present invention, and (a) and (b) are aligned on the time axis; (b) is a schematic diagram of a current waveform after morphological filtering of (a) in an embodiment of the present invention; (c) is a schematic diagram of a current waveform with a signal-to-noise ratio of 20 dB after superimposed noise in an embodiment of the present invention, and (c) and (d) are aligned on the time axis; (d) is a schematic diagram of a current waveform after morphological filtering of (c) in an embodiment of the present invention;

[0049] Figure 3Schematic diagram of the peak detection effect of mathematical morphology according to an embodiment of the present invention; wherein (a) is a schematic diagram of the current mutation waveform according to an embodiment of the present invention, and (a) and (b) are aligned in time axis; (b) is a schematic diagram of the current mathematical morphology polarity according to an embodiment of the present invention;

[0050] Figure 4 This is a schematic diagram of the polarity distribution of the first wave of the sudden change amount of fault current in the active power distribution network according to an embodiment of the present invention;

[0051] Figure 5 Schematic diagram of the processing result of the fault section B1B2 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the current mutation waveform of the fault section B1B2 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the fault section B1B2 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention;

[0052] Figure 6 Schematic diagram of the processing result of the non-fault section B2B3 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the waveform of the current mutation amount of the non-fault section B2B3 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the non-fault section B2B3 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention;

[0053] Figure 7 Schematic diagram of the processing result of the non-fault section B3B4 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the waveform of the current mutation amount of the non-fault section B3B4 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the non-fault section B3B4 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention;

[0054] Figure 8 Schematic diagram of the processing result of the non-fault section B1B5 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the waveform of the current mutation amount of the non-fault section B1B5 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the non-fault section B1B5 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention;

[0055] Fig. 9Schematic diagram of the processing result of the non-fault section B5B6 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the waveform of the current mutation amount of the non-fault section B5B6 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the non-fault section B5B6 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention;

[0056] Fig.10 Schematic diagram of the processing result of the non-fault section B6B7 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the waveform of the current mutation amount of the non-fault section B6B7 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the non-fault section B6B7 when a three-phase short circuit fault occurs at point f1 in the simulation model of the embodiment of the present invention;

[0057] Fig.11 Schematic diagram of the processing result of the non-fault section B1B2 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the current mutation waveform of the non-fault section B1B2 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the non-fault section B1B2 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention;

[0058] Fig.12 Schematic diagram of the processing result of the non-fault section B2B3 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the waveform of the current mutation amount of the non-fault section B2B3 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the non-fault section B2B3 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention;

[0059] Fig.13 It is a schematic diagram of the processing result of the fault section B3B4 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the waveform of the current mutation amount of the fault section B3B4 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the fault section B3B4 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention;

[0060] Fig.14Schematic diagram of the processing result of the non-fault section B1B5 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the waveform of the current mutation amount of the non-fault section B1B5 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the non-fault section B1B5 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention;

[0061] Fig.15 Schematic diagram of the processing result of the non-fault section B5B6 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the waveform of the current mutation amount of the non-fault section B5B6 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the non-fault section B5B6 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention;

[0062] Fig.16 Schematic diagram of the processing result of the non-fault section B6B7 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the waveform of the current mutation amount of the non-fault section B6B7 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the non-fault section B6B7 when a two-phase short circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention;

[0063] Fig.17 Schematic diagram of the processing result of the non-fault section B1B2 when a two-phase grounding fault occurs at point f5 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the current mutation waveform of the non-fault section B1B2 when a two-phase grounding fault occurs at point f5 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the non-fault section B1B2 when a two-phase grounding fault occurs at point f5 in the simulation model of the embodiment of the present invention;

[0064] Fig.18 Schematic diagram of the processing result of the non-fault section B2B3 when a two-phase grounding fault occurs at point f5 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the waveform of the current mutation amount of the non-fault section B2B3 when a two-phase grounding fault occurs at point f5 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the non-fault section B2B3 when a two-phase grounding fault occurs at point f5 in the simulation model of the embodiment of the present invention;

[0065] Fig.19Schematic diagram of the processing result of the non-fault section B3B4 when a two-phase grounding fault occurs at point f5 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the waveform of the current mutation amount of the non-fault section B3B4 when a two-phase grounding fault occurs at point f5 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the non-fault section B3B4 when a two-phase grounding fault occurs at point f5 in the simulation model of the embodiment of the present invention;

[0066] Fig. 20 Schematic diagram of the processing result of the non-fault section B1B5 when a two-phase grounding fault occurs at point f5 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the waveform of the current mutation amount of the non-fault section B1B5 when a two-phase grounding fault occurs at point f5 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the non-fault section B1B5 when a two-phase grounding fault occurs at point f5 in the simulation model of the embodiment of the present invention;

[0067] Fig.21 Schematic diagram of the processing result of the fault section B5B6 when a two-phase grounding fault occurs at point f5 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the waveform of the current mutation amount of the fault section B5B6 when a two-phase grounding fault occurs at point f5 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the fault section B5B6 when a two-phase grounding fault occurs at point f5 in the simulation model of the embodiment of the present invention;

[0068] Fig. 22 Schematic diagram of the processing result of the non-fault section B6B7 when a two-phase grounding fault occurs at point f5 in the simulation model of the embodiment of the present invention; wherein (a) is a schematic diagram of the waveform of the current mutation amount of the non-fault section B6B7 when a two-phase grounding fault occurs at point f5 in the simulation model of the embodiment of the present invention, and the time axes of (a) and (b) are aligned; (b) is a schematic diagram of the mathematical morphological polarity of the current in the non-fault section B6B7 when a two-phase short-circuit fault occurs at point f3 in the simulation model of the embodiment of the present invention;

[0069] Fig.23 It is an overall flow chart of the method for locating fault section of active distribution network based on mathematical morphology polarity according to an embodiment of the present invention;

[0070] Fig.24 Schematic diagram of a feeder terminal according to an embodiment of the present invention. DETAILED DESCRIPTION

[0071] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0072] It should be noted that the terms used herein are for describing specific embodiments only and are not intended to be limiting of exemplary embodiments according to the present invention.

[0073] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0074] Based on the description of the background technology, Figure 1 Taking the active distribution network topology shown in the figure as an example, the limitations of the traditional distribution network fault section location method after the distributed power generation is connected are described.

[0075] When a fault occurs in a traditional distribution network, overcurrent protection and local feeder automation are generally used to locate the faulty section. The circuit breaker / recloser at the substation exit and the section switch in the line operate in a preset logical sequence to isolate the faulty section.

[0076] Without considering the access of distributed power generation, Figure 1 Take the fault at point f3 as an example to illustrate: after the fault, the terminal device at the outlet R1 of the substation first detects the overcurrent and controls the circuit breaker at this position to trip. The section switches at R3 and R5 in feeder 1 trip due to the loss of voltage. Since traditional feeder automation only sets protection and section switches at the head end of each section, R2, R4, and R6 are ignored; after a period of time, the circuit breaker at R1 is closed for the first time, and the subsequent section switches are closed in sequence according to the order of incoming calls. After the section switch at R3 is closed, the upstream switch state remains unchanged because no fault occurs in the section where it is located. After the section switch at R5 is closed, due to the fault in the section where it is located, the section switch at R5 and its upstream section switches (section switches at R1 and R3) are tripped again, and the B3B4 section where R5 is located is recorded as the faulty section; finally, the upstream section switch of the faulty section is closed again to isolate the faulty section and restore power supply to the non-faulty section.

[0077] The above-mentioned fault section location method based on overcurrent protection and local feeder automation has a good effect in traditional distribution networks, but it is difficult to apply to active distribution networks. Figure 1Taking the distribution network topology shown in the figure as an example, after a fault occurs and the outlet circuit breaker is opened, the logic of "power failure opening, power supply closing" of the local feeder automation fails because the distributed power source can still supply power to the grid during the low voltage ride-through period. In the distribution network with a low penetration rate of distributed power sources, in order to ensure the effectiveness of the traditional fault section location method, the distributed power source is usually directly shut down after the feeder fault, but this approach exerts the support capacity of the distributed power source for the grid. In addition, when the penetration rate of distributed power sources in the active distribution network is high, directly cutting off all distributed power sources will affect the stability of the power system. Therefore, the fault section location method based on overcurrent protection and local feeder automation in the traditional distribution network cannot be applied to the active distribution network with high penetration rate distributed power sources.

[0078] The overall idea proposed by the present invention is:

[0079] The present invention first configures feeder terminals at both ends of a protected section to measure local three-phase current data in real time; when the measured current of any phase in the feeder terminal meets the fault detection criterion, it is considered that a fault may occur and enters a fault location process based on mathematical morphology polarity; after entering the fault location process, the feeder terminal selects a corresponding morphological M value according to the number of fault phases, and the morphological M value is the length of a structural element in a mathematical morphology algorithm; the measured current waveform is filtered using a mathematical morphology algorithm; after filtering, the fault current mutation amount is calculated using a full-cycle subtraction method; the peak value of the fault current mutation amount waveform is extracted using a mathematical morphology algorithm, and the polarity of the peak value is determined; the terminal devices at both ends of the protected section mutually transmit the polarity of the mathematical morphology peak value; whether the section is a fault section is determined according to the polarity of the mathematical morphology peak values ​​at both ends, and if the polarities at both ends are positive, it is considered to be a fault section.

[0080] Embodiment 1

[0081] See also Fig.23 As shown, this embodiment discloses a method for locating a fault section of an active distribution network based on mathematical morphology polarity, which specifically includes the following steps:

[0082] Step 1: Configure feeder terminals at both ends of the protected section. The feeder terminals measure the local three-phase current data in real time.

[0083] Step 2: When the measured current of any phase in the feeder terminal meets the fault detection criterion, it is considered that a fault may have occurred and the fault location process based on mathematical morphology polarity is entered.

[0084] Specifically, in order to reduce the amount of calculation and ensure the normal execution of other monitoring functions when the system is operating normally, the terminal is set not to enter the fault location process when it is operating normally. Only when the measured current of any phase meets the fault detection criterion, the fault location process based on mathematical morphology polarity is entered. The fault detection criterion adopts the phase current mutation criterion. For each phase current, the fault detection criterion is as follows:

[0085] ,

[0086] In the formula, i φ ( k )express φ Phase current in the k The sampling value of the sampling point, N is the number of sampling points at the feeder terminal within one power frequency cycle, K S is the fault detection threshold coefficient, I N is the rated current amplitude.

[0087] Step 3: After entering the fault location process based on mathematical morphology polarity, the feeder terminal selects the corresponding morphology M value according to the number of fault phases, and the morphology M value is the length of the structural element in the mathematical morphology algorithm.

[0088] Specifically, the morphological M value is the length of the structural element in the mathematical morphological algorithm, which is directly related to the processing effect of the subsequent morphological filtering algorithm and the morphological peak detection algorithm. Since the grounding point may have a relatively large transition resistance when an asymmetric fault occurs, a larger M value is required to ensure the effect of the mathematical morphological processing; while when a symmetrical fault (three-phase short circuit) occurs, the short-circuit current is large, and only a smaller M value is required to ensure the effect of the mathematical morphological processing. Therefore, this step selects the corresponding M value by judging whether the fault is symmetrical. When the number of fault phases (the number of phases in the three-phase current that meet the fault detection criteria) is 3, a smaller first M value is selected, otherwise a larger second M value is selected. The first M value is smaller than the second M value, and the first M value and the second M value are determined according to the hardware conditions and the on-site environment.

[0089] Step 4: Construct a structural element of corresponding length according to the M value, and use the structural element to perform an open-close-close-open median filtering algorithm in the mathematical morphology algorithm to filter the measured current waveform.

[0090] Specifically, the process of filtering the measured current waveform using the digital open-close-close-open median filtering algorithm includes:

[0091] Due to the complex electromagnetic environment at the feeder terminal installation site, there is a certain amount of noise in the measured current waveform. In order to ensure that the subsequent mathematical morphology peak detection algorithm can effectively extract the true peak characteristics of the current mutation waveform, the measured current waveform needs to be filtered first. Morphological filtering can be achieved through the combination of mathematical morphology basic operators. This application selects the open-close-close-open median filtering algorithm with the best filtering effect to filter the measured current waveform.

[0092] The basic principle of mathematical morphology is to select structural elements to move in the input signal, and extract the required features in the neighborhood of each sampling point of the signal through the interaction between the two. The most basic operator in mathematical morphology is dilation ( ) and corrosion ( ). Assume the input signal is f (n), the structural element is g (m), the dilation and erosion operators are as follows:

[0093] ,

[0094] ,

[0095] In the formula, Df , Dg are the domains of the input signal and the structure element, respectively.

[0096] By combining the expansion and erosion operators, we can get the opening operator ( ) and the closing operator ( ) Two advanced operators, as shown below:

[0097] ,

[0098] ,

[0099] The open-close-close-open median filter is realized by combining the open and close operators, as shown below:

[0100] .

[0101] The processing effect of the open-close-close-open median filter algorithm is as follows Figure 2 As shown in (a), (b), (c), and (d), it can be seen that the greater the noise and the lower the signal-to-noise ratio, the more glitches there are in the current waveform. However, after morphological filtering, the current waveform can remain monotonous on both sides of the peak, thereby ensuring that the subsequent algorithm can effectively extract the peak polarity of the waveform.

[0102] Step 5: Calculate the fault current mutation using the full-cycle phase subtraction method. The current sampling value at the current moment minus the current sampling value one cycle ago is obtained:

[0103] ,

[0104] In the formula, express Phase current in the The sampling value of the sampling point, is the number of sampling points at the feeder terminal within one power frequency cycle.

[0105] When a fault occurs in an active distribution network, the fault wave propagates along the line to both sides. For the fault section, the first fault wave detected by the feeder terminals on both sides is positive, and the polarity of the first peak in the current mutation waveform is positive; for the non-fault section, the first fault wave detected by the proximal feeder terminal is reverse, and the polarity of the first peak in the current mutation waveform is negative, while the first fault wave detected by the distal feeder terminal is positive, and the polarity of the first peak in the current mutation waveform is positive. Based on this feature, it can be determined whether it is a fault section, so it is necessary to calculate the fault current mutation.

[0106] Step 6: Use mathematical morphology algorithm to extract the peak value of the fault current mutation waveform and determine the polarity of the peak value.

[0107] Specifically, the morphological peak detection operator is formed by adding the top hat operator and the bottom hat operator in mathematical morphology, as shown below:

[0108] ,

[0109] The mathematical morphology peak detection algorithm is used to process the fault phase current mutation waveform at both ends of the line in a fault case. The effect is as follows: Figure 3 As shown. Figure 3 In (a), I1a and I2a are the original current mutation waveforms on both sides of the fault section. Figure 3 In (b), I1am and I2am are the waveforms on both sides after being processed by the mathematical morphological peak detection algorithm, and time 0 is the time when the fault occurs. It can be seen from the figure that only the peak information in the original waveform is retained in the processed waveform, and the peak polarity is the same as the original waveform. The peak polarities corresponding to the peak and trough in the original waveform are positive and negative respectively. Therefore, the peak polarity obtained by the morphological peak detection algorithm can reflect the peak polarity of the original current mutation.

[0110] Step 7: The terminal devices at both ends of the protected section mutually transmit the polarity of the first peak extracted by the mathematical morphology peak detection algorithm. When the first peak obtained after processing is positive, the polarity is considered positive, and when the first peak is negative, the polarity is considered negative.

[0111] Step 8: Determine whether the section is a fault section based on the polarity of the mathematical morphology peaks at both ends. If the polarities at both ends are positive, it is considered to be a fault section.

[0112] Specifically, when a fault occurs in the active distribution network, the fault wave propagates along the line to both sides. For the fault section, the first fault wave detected by the feeder terminals on both sides is positive, and the polarity of the first peak in the current mutation waveform is positive; for the non-fault section, the first fault wave detected by the proximal feeder terminal is reverse, and the polarity of the first peak in the current mutation waveform is negative, while the first fault wave detected by the distal feeder terminal is positive, and the polarity of the first peak in the current mutation waveform is positive. Figure 1 Take the fault at point f2 as an example. At this time, the fault current mutation waveform detected by each terminal in feeder 1 is as follows: Figure 4 As shown. It can be seen that for the fault section B2B3, the polarity of the first peak in the fault current mutation waveform on both sides is positive; for the non-fault sections B1B2 and B3B4, the polarity of the first peak in the near-end fault current mutation waveform is negative and the polarity of the first peak in the near-end fault current mutation waveform is positive. From the analysis in step 6, it can be seen that the peak polarity obtained by the morphological peak detection algorithm can reflect the peak polarity of the original fault current mutation. Therefore, it can be judged whether the section is a fault section based on the mathematical morphological peak polarity of the fault current mutation at both ends. If the polarity at both ends is positive, it is considered to be a fault section.

[0113] Verification Example

[0114] Use PSCAD / EMTDC simulation software to build topological structures such as Figure 1 The active distribution network simulation model shown in the figure sets faults in different positions of the line, exports the fault recording data obtained by simulation, and uses MATLAB software to write a mathematical morphology algorithm to verify the active distribution network fault section location method based on mathematical morphology polarity proposed by the present invention. The sampling frequency of the PSCAD / EMTDC simulation model is 100kHz, and the first M value and the second M value of the mathematical morphology filtering and peak detection in the MATLAB algorithm are 9 and 11 respectively.

[0115] 1) Simulation model

[0116] The voltage level of the distribution network is 10 kV, and the neutral point grounding method is the most commonly used ungrounded method in my country's distribution network. Figure 1 In the figure, symbol B represents busbar; symbol L represents load, and the specific parameters are shown in Table 1.

[0117] Table 1 Load parameters

[0118]

[0119] Figure 1 In the figure, the symbol R represents the feeder terminal, which can collect the current information at the corresponding load switch; the symbol DG represents the distributed power source, where DG1 and DG3 are photovoltaic power sources with rated power of 4 MW and 1 MW respectively, simulating the inverter distributed power source, and DG2 and DG4 are diesel generators with rated power of 2 MW, simulating the synchronous distributed power source; the symbol f represents the fault point, where points f1 and f2 are located at the midpoint of the line segment, points f3 and f6 are located 10 meters from the beginning of the line segment, points f4 are located 10 meters from the end of the line segment, and points f5 are located 250 meters from the beginning of the line segment. The positive sequence impedance and zero sequence impedance of the distribution line are 0.27 + j0.352 (Ω / km) and 0.42 + j3.618 (Ω / km), respectively, and the line length between each two adjacent busbars is 2 km.

[0120] 2) Simulation verification

[0121] In a distribution network with non-effective grounding at the neutral point, the short-circuit current of a single-phase grounding fault is very small, and the system can operate with the fault for a period of time. Usually, a separate fault line selection / location method is used. Therefore, this fault location method is mainly aimed at three-phase short circuit, two-phase short circuit and two-phase grounding fault.

[0122] a) Verification of the effectiveness of fault section location based on mathematical morphology polarity during three-phase short circuit:

[0123] In order to verify the effectiveness of the fault section location method based on mathematical morphology polarity in three-phase short circuit, Figure 1 The three-phase short-circuit faults are set at points f1-f6 of the simulation model shown in the figure. The mathematical morphology algorithm is used to calculate the R1-R 12 The fault current mutation measured at the position is processed, and the first peak value of the obtained current mutation waveform is recorded in Table 2.

[0124] Table 2 Morphological peaks at each terminal when three-phase short circuit occurs at different positions

[0125]

[0126] It can be seen from Table 2 that: when a fault occurs at point f1, the morphological polarities of the feeder terminals R1 and R2 on both sides of the fault section B1B2 are both positive, and the morphological polarities of the feeder terminals on both sides of the non-fault sections B2B3, B3B4, B1B5, B5B6, and B6B7 are one positive and one negative. The fault section location method based on mathematical morphological polarity can correctly locate the fault section as B1B2; when a fault occurs at point f2, the morphological polarities of the feeder terminals R3 and R4 on both sides of the fault section B2B3 are both positive, and the morphological polarities of the feeder terminals on both sides of the non-fault sections B1B2, B3B4, B1B5, B5B6, and B6B7 are one positive and one negative. The fault section location method based on mathematical morphological polarity can correctly locate the fault section as B2B3; when a fault occurs at point f3, The morphological polarities of feeder terminals R5 and R6 on both sides of the fault section B3B4 are both positive, and the morphological polarities of feeder terminals on both sides of non-fault sections B1B2, B2B3, B1B5, B5B6, and B6B7 are one positive and one negative. The fault section location method based on mathematical morphological polarity can correctly locate the fault section as B3B4; when a fault occurs at point f4, the morphological polarities of feeder terminals R7 and R8 on both sides of the fault section B1B5 are both positive, and the morphological polarities of feeder terminals on both sides of non-fault sections B1B2, B2B3, B3B4, B5B6, and B6B7 are one positive and one negative. The fault section location method based on mathematical morphological polarity can correctly locate the fault section as B1B5; when a fault occurs at point f5, the morphological polarities of feeder terminals R9 and R10 on both sides of the fault section B5B6 are both positive, and the morphological polarities of feeder terminals on both sides of non-fault sections B1B2, B2B3, B3B4, B5B6, and B6B7 are one positive and one negative. 10 The morphological polarity of the feeder terminals on both sides of the non-fault sections B1B2, B2B3, B3B4, B1B5, and B6B7 is one positive and one negative. The fault section location method based on mathematical morphological polarity can correctly locate the fault section as B5B6. When a fault occurs at point f6, the feeder terminals R on both sides of the fault section B6B7 11 , R 12 The morphological polarities of the feeder terminals on both sides of the non-fault sections B1B2, B2B3, B3B4, B1B5, and B5B6 are all positive, one positive and one negative. The fault section location method based on mathematical morphological polarity can correctly locate the fault section as B6B7.

[0127] The fault sections in all fault cases can be correctly identified by the positioning method based on mathematical morphology polarity, and the non-fault sections will not be misjudged as fault sections. Among them, when a three-phase short circuit fault occurs at point f1, the original current mutation waveform at each terminal and the current peak polarity obtained after processing by the mathematical morphology algorithm are as follows: Figure 5 (a) (b) Figure 6 (a) (b) Figure 7 (a) (b) Figure 8 (a) (b) Fig. 9 (a) (b) and Fig.10 As shown in (a) and (b). Figure 5 It can be seen from (a) and (b) that the first peak of the terminal current mutation occurs within 5ms, at which time the fault control strategy of the distributed power supply has not responded. Therefore, this method is not affected by the type of distributed power supply and the control strategy.

[0128] b) Verification of the effectiveness of fault section location based on mathematical morphology polarity during two-phase short circuit:

[0129] In order to verify the effectiveness of the fault section location method based on mathematical morphology polarity in two-phase short circuit, Figure 1 The f1-f6 points of the simulation model shown in the figure are respectively set with two-phase short-circuit faults, and the mathematical morphology algorithm is used to calculate the R1-R 12 The fault current mutation measured at the position is processed, and the first peak value of the obtained current mutation waveform is recorded in Table 3.

[0130] Table 3 Morphological peak values ​​at each terminal when two-phase short circuit occurs at different positions

[0131]

[0132] It can be seen from Table 3 that, through the positioning method based on mathematical morphology polarity, the fault sections in all fault cases have the situation that the morphological peak polarity on both sides is positive, and can be correctly judged as the fault section; while the non-fault sections have the morphological peak polarity on both sides as one positive and one negative, and will not be misjudged as the fault section. Among them, when a two-phase short circuit fault occurs at point f3, the original current mutation waveform at each terminal and the current peak polarity obtained after processing by the mathematical morphology algorithm are as follows Fig.11 (a) (b) Fig.12 (a) (b) Fig.13 (a) (b) Fig.14 (a) (b) Fig.15 (a) (b) Fig.16 As shown in (a) and (b).

[0133] c) Verification of the effectiveness of fault section location based on mathematical morphology polarity when two phases are grounded:

[0134] In order to verify the effectiveness of the fault section location method based on mathematical morphology polarity when two phases are grounded, Figure 1 The f1-f6 points of the simulation model shown in the figure are set with two-phase grounding faults respectively, and the mathematical morphology algorithm is used to calculate the R1-R 12 The fault current mutation measured at the position is processed, and the first peak value of the obtained current mutation waveform is recorded in Table 4.

[0135] Table 4 Morphological peak values ​​at each terminal when two-phase grounding occurs at different locations

[0136]

[0137] It can be seen from Table 4 that, through the positioning method based on mathematical morphology polarity, the fault sections in all fault cases have positive morphology peak polarities on both sides, and can be correctly judged as fault sections; while the non-fault sections have one positive and one negative morphology peak polarities on both sides, and will not be misjudged as fault sections. Among them, when a two-phase grounding fault occurs at point f5, the original current mutation waveform at each terminal and the peak polarity obtained after processing by the mathematical morphology algorithm are as follows Fig.17 (a) (b) Fig.18 (a) (b) Fig.19 (a) (b) Fig. 20 (a) (b) Fig.21 (a) (b) Fig. 22 As shown in (a) and (b).

[0138] d) Verification of the effectiveness of fault section location based on mathematical morphology polarity when there is a transition resistance fault:

[0139] In order to verify the effectiveness of the fault section location method based on mathematical morphology polarity when the fault point contains different transition resistances, Figure 1 The f5 point of the simulation model shown in the figure sets the transition resistance value (R f ) Different two-phase grounding faults are analyzed by using mathematical morphology algorithm for each fault case R1-R 12 The fault current mutation measured at is processed, and the first peak value of the obtained current mutation waveform is recorded in Table 5.

[0140] Table 5: The morphological peak values ​​at each terminal when two phases with different transition resistances are grounded at point f5

[0141]

[0142] It can be seen from Table 5 that as the transition resistance increases, the amplitude of the morphological peak at different terminals will decrease, but its polarity still satisfies that both sides of the fault section are positive and both sides of the non-fault section are positive and negative. Therefore, the positioning method based on mathematical morphology polarity can still correctly determine the fault section and is not affected by the transition resistance.

[0143] The simulation results based on PSCAD show that the active distribution network fault section location method based on mathematical morphology polarity proposed in the present invention can correctly judge different types of faults occurring in different locations, and the judgment time does not exceed 5ms (less than the response time of the distributed power supply fault control strategy). It can be applied to active distribution networks with complex fault characteristics after the access of high-penetration distributed power supplies, and can still correctly locate the fault section when the fault point contains a large transition resistance.

[0144] Embodiment 2

[0145] like Fig.24 As shown, the present invention provides a feeder terminal for locating a fault section of an active distribution network based on mathematical morphology polarity, which is used for the active distribution network fault section locating based on mathematical morphology polarity, comprising: at least one processing unit, the processing unit, the storage unit, the acquisition unit and the communication unit are interconnected through a bus unit, the feeder terminals at both ends of the protected section are connected through the communication unit, the storage unit of each feeder terminal stores a computer program, and when the computer program is executed by the processing unit, the active distribution network fault section locating method based on mathematical morphology polarity is implemented, comprising: configuring feeder terminals at both ends of the protected section, and measuring local three-phase current data in real time;

[0146] When the measured current of any phase detected by the feeder terminal meets the fault detection criterion, it is considered that a fault may occur and the fault location process based on mathematical morphology polarity is started;

[0147] After entering the fault location process, the feeder terminal selects the corresponding morphological M value according to the number of fault phases. The morphological M value is the length of the structural element in the mathematical morphological algorithm.

[0148] According to the M value, a structural element of corresponding length is constructed to filter the measured current waveform using a mathematical morphological algorithm;

[0149] After filtering is completed, the fault current mutation amount is calculated using the full-cycle subtraction method;

[0150] The peak value of the fault current mutation waveform is extracted using mathematical morphology algorithm, and the polarity of the peak value is determined;

[0151] The polarity of the mathematical morphology peak value of mutual transmission between the feeder terminals at both ends of the protected section;

[0152] Whether the section is a fault section is determined based on the polarity of the mathematical morphology peaks at both ends. If the polarities at both ends are positive, it is considered to be a fault section.

[0153] Those skilled in the art should understand that the modules or steps of the present invention described above can be implemented by a general-purpose computer device, or alternatively, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0154] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A method for locating fault sections of active distribution networks based on mathematical morphology polarity, characterized in that: include: Configure feeder terminals at both ends of the protected section to measure local three-phase current data in real time; When the measured current of any phase detected by the feeder terminal meets the fault detection criterion, it is considered that a fault may occur and the fault location process based on mathematical morphology polarity is started; After entering the fault location process, the feeder terminal selects the corresponding morphological M value according to the number of fault phases. The morphological M value is the length of the structural element in the mathematical morphological algorithm; wherein, the feeder terminal selects the corresponding morphological M value according to the number of fault phases, including: since the grounding point has a relatively large transition resistance when an asymmetric fault occurs, a larger M value is required to ensure the effect of the mathematical morphological processing; and when a symmetrical fault occurs, the short-circuit current is large, and a smaller M value is required to ensure the effect of the mathematical morphological processing; the corresponding M value is selected by judging whether the fault is symmetrical, and the first M value is selected when the number of phases in the three-phase current that meets the fault detection criterion is 3, otherwise the second M value is selected, and the first M value is less than the second M value, and the first M value and the second M value are determined according to the hardware conditions and the on-site environment; According to the M value, a structural element of corresponding length is constructed, and the measured current waveform is filtered by using the structural element to perform an open-close-close-open median filtering algorithm; After filtering is completed, the fault current mutation amount is calculated using the full-cycle subtraction method; the fault current mutation amount in the full-cycle subtraction method The current sampling value at the current moment minus the current sampling value one cycle ago is obtained: , where express Phase current in the The sampling value of the sampling point, is the number of sampling points at the feeder terminal within one power frequency cycle; The peak value of the fault current mutation waveform is extracted using mathematical morphology algorithm, and the polarity of the peak value is determined; The polarity of the mathematical morphology peak value of mutual transmission between the feeder terminals at both ends of the protected section; Determine whether the section is a fault section based on the polarity of the mathematical morphology peaks at both ends: Determine whether the section is a fault section based on the polarity of the mathematical morphology peaks at both ends. If the polarities at both ends are positive, it is considered to be a fault section.

2. The method for locating fault sections of active distribution networks based on mathematical morphology polarity as claimed in claim 1, characterized in that: When the measured current of any phase detected by the feeder terminal meets the fault detection criterion, it is considered that a fault may occur and the fault location process based on mathematical morphology polarity is entered. The fault detection criterion adopts the phase current mutation criterion. The fault detection criterion is as follows: ， In the formula, i φ ( k )express φ Phase current in the k The sampling value of the sampling point, N is the number of sampling points at the feeder terminal within one power frequency cycle, K S is the fault detection threshold coefficient, I N is the rated current amplitude.

3. The method for locating fault sections of active distribution networks based on mathematical morphology polarity as claimed in claim 1, characterized in that: The open-close-close-open median filter algorithm in mathematical morphology is selected to filter the measured current waveform, including: For filtering, assume that the input signal is f (n), the structural element is g (m), the dilation and erosion operators are as follows: ， ， In the formula, Df , Dg are the domains of input signal and structural element respectively; The opening operator is obtained by combining the expansion and corrosion operators ( ) and the closing operator ( ), as follows: ， ， The open-close-close-open median filter is realized by combining the open and close operators, as shown below: ， in, For input signal f (n) The result after open-close-close-open median filtering.

4. The method for locating fault sections of active distribution networks based on mathematical morphology polarity as claimed in claim 1, characterized in that: When the peak value of the fault current mutation waveform is extracted by the mathematical morphology algorithm and the polarity of the peak value is determined, the top hat operator and the bottom hat operator in mathematical morphology are combined to form a mathematical morphology peak detection algorithm to process the fault current mutation. When the first peak value obtained after processing is positive, the polarity is considered to be positive, and when the first peak value is negative, the polarity is considered to be negative; wherein, the morphological peak detection algorithm is as follows: ， in, is the peak value.

5. A method for locating feeder terminals in fault sections of an active distribution network based on mathematical morphology polarity, characterized in that it comprises: At least one processing unit, the processing unit, the storage unit, the collection unit and the communication unit are interconnected through a bus unit, the storage unit stores a computer program, and when the computer program is executed by the processing unit, the method for locating the fault section of the active distribution network based on mathematical morphology polarity as described in any one of claims 1-4 is implemented.

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