CN114002550B - Direct-current power distribution network ground fault line selection method and system - Google Patents
Direct-current power distribution network ground fault line selection method and system Download PDFInfo
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Abstract
The invention discloses a direct-current power distribution network ground fault line selection method and system, which utilize a bus voltage unbalance criterionStarting MMC additional control, and injecting a detection signal; acquiring the positive current and the negative current of the head end of each feeder line by delaying delta t; filtering the anode current and the cathode current at the head end of each feeder line, and setting the center frequency f mp Obtaining the positive and negative currents of the head ends of the feeder lines after filtering for detecting the characteristic frequency of the signal; obtaining zero mode current of each feeder line from the positive and negative electrode current at the head end of each filtered feeder line, carrying out normalization processing, and summing to obtain reference current; calculating waveform correlation by using the normalized feeder zero-mode currents and the reference current one by one, and determining a fault line and a healthy line by fault discrimination according to the Pearson correlation coefficient to complete the line selection of the direct-current power distribution network ground fault; the method effectively enhances the fault characteristics, avoids the installation of additional devices, and has the characteristics of high sensitivity and no need of double-end communication.
Description
Technical Field
The invention belongs to the technical field of power distribution network fault identification, and particularly relates to a direct-current power distribution network ground fault line selection method and system.
Background
With the rapid development of power electronic technology and the wide application thereof in power systems, direct current power distribution networks are widely researched due to the fact that new energy access is easy to achieve and the quality of electric energy is convenient to improve. The main topological structure of the direct current distribution network comprises a radial structure, a two-end hand-pulling structure and a ring structure, wherein the radial structure becomes the most common structure in the engineering practice developed at present due to the advantages of low investment cost and the like.
The medium-voltage direct-current power distribution network mostly adopts a pseudo-bipolar structure, and adopts a direct-current side grounding mode through a clamping resistor, wherein the grounding mode is to continuously operate for a period of time with faults when a distribution feeder line has a single-pole grounding fault, so that the power supply reliability is improved, but the fault current is very small in the clamping resistor grounding mode, so that the fault characteristics are difficult to observe, and the fault feeder line is difficult to accurately and reliably identify.
The existing research aiming at identifying the single-pole grounding fault of the direct-current power distribution network can be divided into: passive detection and active probing. The passive detection method is based on fault characteristics provided by a converter parallel capacitor of a fault transient state or a line distributed capacitor current to identify faults, and because the inertia of a direct current power distribution system is low, the fault transient state duration is generally hundreds of microseconds to several milliseconds, fault transient state information is used for identifying the faults, and high requirements are provided for the performance of a measurement and protection device. The active detection method is dependent on a specific injection device or limited by a specific network topology, and there is little systematic research on the monopole ground fault line selection of the MMC-based flexible direct-current power distribution network. The existing method is low in sensitivity and poor in reliability, and the traditional ground fault line selection method of the alternating current low-current grounding system is difficult to refer to in a flexible direct current power distribution network containing a large number of distributed power sources and energy storage equipment, so that a new flexible direct current power distribution network single-pole ground fault identification method needs to be researched urgently.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a method and a system for selecting a line of a direct current power distribution network ground fault, aiming at the defects in the prior art, wherein the existing MMC of the direct current power distribution network is utilized to actively inject a detection signal to enhance the fault characteristics, the sensitivity is improved by identifying a fault feeder line according to the difference of the detection signal between a fault line and a sound line, and the transient fault judgment is realized through a multiple injection strategy.
The invention adopts the following technical scheme:
a direct current distribution network earth fault line selection method utilizes a bus voltage unbalance criterion to start MMC additional control and injects detection signals; acquiring the positive current and the negative current of the head end of each feeder line by delaying delta t; filtering the positive current and the negative current at the head end of each feeder line, and selecting the center frequency f of the filter mp Obtaining the positive and negative currents of the head ends of the feeder lines after filtering for detecting the characteristic frequency of the signal; obtaining zero-mode current of each feeder line by using the positive and negative currents at the head end of each feeder line after filtering, performing normalization processing by dividing all sampling values of the zero-mode current in the data window by the maximum value in the sampling values, and summing the zero-mode feeder line currents after the normalization processing to obtain reference current; and introducing a Pearson correlation coefficient, solving the waveform correlation by using the normalized feeder zero-mode current and the reference current one by one, and judging the fault according to the Pearson correlation coefficient to determine a fault line and a healthy line so as to complete the ground fault line selection of the direct-current power distribution network.
Specifically, the bus voltage imbalance criterion is as follows:
|v dcP +v dcN |＞0.2v dcB
wherein v is dcP 、v dcN Respectively positive and negative DC bus line to ground voltage amplitude v dcB Is a rated DC voltage.
Specifically, the additional MMC control function is:
wherein u is in For the detection signal injected into MMC, k in For detecting signal injection coefficient, omega in For the angular frequency of the injected probe signal, t is the time,
is the initial phase of the injected probe signal.
Specifically, the detection signal ω in The frequency of (a) is selected according to:
wherein, ω is MMClim In order to limit the frequency of the response speed of the MMC,
the system impedance resonance frequency is solved for the incoming parameters.
In particular, each feeder has a zero-mode current i dci0 The calculation is as follows:
wherein, ω is in For injecting a characteristic frequency, i, of the probe signal dciP (ω in )、i dciN (ω in ) Respectively the positive and negative currents of the feeder line.
In particular, the reference current i Lref The method specifically comprises the following steps:
wherein i dci0-nm A normalized zero-mode current value seen by the head end of line i within the length of the data window is calculated.
Specifically, each feeder has a zero-mode current value i dci0 And a reference zero-mode current value i base Pearson's correlation coefficient between
The calculation is as follows:
wherein, cov (i) Lref (ω in ),i dci0-nm (ω in ) Is the covariance between the two currents,
respectively the standard deviation, omega, of the zero-mode current reference value and the zero-mode current value of the feeder line in Is the characteristic frequency of the injected probe signal.
Specifically, the correlation coefficient calculated when only the ith line is present
When the current value is less than the setting value, determining that the ith line has a single-pole grounding fault, and the rest lines are sound lines, and when all the calculated correlation coefficients are greater or less than the setting value>
When the voltage values are all larger than the setting value, further judging whether the bus voltage is balanced, if the voltage values are | v |, determining whether the bus voltage is balanced dcP +v dcN |＞0.2v dcB The output result is the bus fault if | v dcP +v dcN |≤0.2v dcB The output result is a transient fault, v dcP 、v dcN Positive and negative dc bus-line to ground voltage amplitude, v, respectively dcB Is a rated DC voltage.
Further, the fault determination specifically includes:
wherein, k is a setting value,
for a Pearson correlation coefficient, omega, for calculating a normalized zero-mode current value at the head end of a line i within the length of the data window and a feeder zero-mode current reference value in Is the characteristic frequency of the injected probe signal.
Another technical solution of the present invention is a dc distribution network ground fault line selection system, including:
the injection module starts MMC additional control by utilizing a bus voltage unbalance criterion and injects a detection signal;
the measuring module is used for delaying delta t to collect the positive electrode current and the negative electrode current at the head end of each feeder line;
the filtering module is used for filtering the positive current and the negative current of the head end of each feeder line acquired by the measuring module and selecting the central frequency f of the filter mp Obtaining the positive and negative currents of the head ends of the feeder lines after filtering for detecting the characteristic frequency of the signal;
the transformation module is used for solving the zero-mode current of each feeder line by using the positive and negative currents at the head end of each feeder line after filtering by the filtering module, performing normalization processing by dividing all sampling values of the zero-mode current in the data window by the maximum value in the sampling values, and summing the zero-mode feeder line currents after the normalization processing to obtain a reference current;
and the line selection module introduces a Pearson correlation coefficient, obtains waveform correlation by using the feeder zero-mode current subjected to normalization processing of the conversion module and the obtained reference current one by one, and determines a fault line and a healthy line by fault discrimination according to the Pearson correlation coefficient to complete ground fault line selection of the direct-current power distribution network.
Compared with the prior art, the invention at least has the following beneficial effects:
the invention relates to a direct current distribution network ground fault line selection method, in particular to a direct current distribution network ground fault line selection method utilizing correlation of injection signals and response signal waveforms thereof, wherein detection signals are actively injected by utilizing the existing MMC of a direct current distribution network, so that the fault characteristics are enhanced; the fault feeder line is identified according to the difference of the fault line and the sound line to the detection signal, so that the sensitivity is improved; the long-time injection strategy can reduce the requirements on the sampling rate of the measurement and protection device; and the multiple injection strategy realizes the transient fault judgment.
Further, when a single-pole ground fault occurs, the voltage to ground of the fault pole falls to 0 rapidly, the absolute value of the voltage to ground of the non-fault pole rises to twice of the rated voltage, and the voltage to ground of the positive pole and the negative pole are seriously unbalanced. Therefore, the voltage unbalance protection criterion which is generally configured in the direct-current power distribution network protection is used as the starting condition for active injection additional control and subsequent fault judgment, and the method has the advantages of high sensitivity and high rapidness.
Furthermore, after the detection signal injection additional control strategy is started, the detection signal is injected by using a preset additional control function, and an injection coefficient is obtained by using a PI link, so that the detection signal with high-quality waveform can be stably injected.
Furthermore, since the influence of factors such as line propagation delay and device measurement delay from the injection of the detection signal to the reliable detection exists, the additional control strategy needs to be started and then a certain delay is required to ensure that the detection signal is stably injected.
Furthermore, considering the restriction on the response speed of the MMC and the restriction on the resonance frequency of the system impedance, an ideal detection signal characteristic frequency is obtained, and the frequency is set as the injected characteristic frequency, so that the most obvious response characteristic difference can be realized on the premise of meeting the performance restriction of equipment so as to facilitate sensitive detection.
Furthermore, after the reference current is set, each outgoing line can calculate the correlation coefficient according to the self zero-mode current and the reference current, and further can detect the single-pole ground fault.
Furthermore, for the condition that only one line has a single-pole ground fault, the correlation coefficient of the pearson line with the fault is very small, and the correlation coefficient of the sound line is very large, so that the detection of the fault line can be reliably and sensitively realized through the pearson correlation coefficient.
Further, the single-pole ground fault branch breaks the symmetry of the original direct current distribution network, so that the direction of the zero-mode current measured from the head end of the healthy line is opposite to that of the zero-mode current measured from the head end of the fault line. Based on this difference, a faulty feeder can be reliably identified; if no feeder line is judged as a fault line, the bus fault or transient fault is considered, if the bus fault is judged as the bus fault, the bus voltage is seriously unbalanced, if the bus fault is the transient fault, the bus voltage is restored to a rated value, the voltage is basically balanced, and therefore the two fault conditions can be identified according to the voltage unbalance criterion.
Furthermore, on the basis of fault analysis, setting corresponding identification criteria, calculating normalized zero-mode current, comparing the normalized zero-mode current with a reference value of the zero-mode current, and solving a Pearson correlation coefficient to further identify faults.
In conclusion, the fault characteristics are enhanced by injecting detection signals based on the MMC, the fault line is identified based on the feeder line zero-mode current characteristics, the method has bus fault identification and permanent fault discrimination capabilities, and simulation results show that the method can reliably identify the single-pole grounding fault occurring at any position of the bus or each feeder line under the transition resistance of 500 ohms, and has the advantages of high sensitivity, strong reliability, no need of double-end communication and low requirement on the sampling rate of a measurement and protection device.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Drawings
FIG. 1 is a schematic diagram of the probe injection principle of the present invention, wherein (a) is a schematic diagram of a power grid for probe injection, and (b) is an MMC controller that accounts for additional control strategies for probe injection;
FIG. 2 is a topological structure diagram of a radial +/-10 kV flexible direct-current power grid of the invention;
FIG. 3 is a flow chart of the fault identification of the present invention;
FIG. 4 is a diagram of a zero-mode current waveform simulation result of a feeder terminal positive fault according to the present invention;
FIG. 5 is a diagram of a simulation result of a bus fault zero-mode current waveform of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, it should be understood that the terms "comprises" and/or "comprising" indicate the presence of the stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It is also to be understood that the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the specification of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
It should be further understood that the term "and/or" as used in this specification and the appended claims refers to any and all possible combinations of one or more of the associated listed items and includes such combinations.
Various structural schematics according to the disclosed embodiments of the invention are shown in the drawings. The figures are not drawn to scale, wherein certain details are exaggerated and possibly omitted for clarity of presentation. The shapes of various regions, layers and their relative sizes and positional relationships shown in the drawings are merely exemplary, and deviations may occur in practice due to manufacturing tolerances or technical limitations, and a person skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions, according to actual needs.
The invention provides a direct current power distribution network ground fault line selection method, which is characterized in that detection signal injection is realized by applying MMC additional control, a Pearson correlation coefficient is introduced by combining the response characteristic of a fault network to a detection signal, and a fault line is identified on the basis that the Pearson correlation coefficient of a fault feeder zero-mode current and zero-mode current reference value is-1 and the Pearson correlation coefficient of a healthy feeder zero-mode current and zero-mode current reference value is 1.
Referring to fig. 3, the method for selecting a line of a ground fault of a dc power distribution network according to the present invention, which uses the waveform correlation of an injection signal and a response signal thereof to implement the line selection of the fault, includes the following steps:
s1, starting MMC additional control by using a bus voltage unbalance criterion to realize the injection of a detection signal, as shown in figure 1;
the bus voltage imbalance criterion is as follows:
|v dcP +v dcN |＞0.2v dcB (1)
the additional control function is as follows:
wherein v is dcB Representing the rated DC voltage, k in And determining the amplitude of the injection signal for detecting the injection coefficient of the signal, wherein the injection coefficient is obtained by setting a PI link.
S2, after the additional control strategy of the step S1 is started for a certain time delay delta t, collecting positive and negative electrode currents at the head ends of all the feeder lines in the graph 1 (a), and recording as i dciP 、i dciN And i represents the ith feeder line;
the delay delta t is required to ensure that the detection signal is stably injected, the value is more than 10ms, and the value of the method is 20ms.
FIG. 1 (b) shows a typical MMC converter control strategy, which includes outer loop power control and inner loop current control, wherein during normal operation, the switch is at 0 position, and when a probing signal needs to be injected, a reference voltage u is superimposed on the input modulation signal ctrl The injection of the probe signal can be achieved when the switch is at u ctrl Location.
S3, filtering the positive and negative currents collected at the head ends of the feeder lines in the step S2 by adopting a band-pass filter, and setting the central frequency f mp Obtaining the positive and negative electrode currents i of the head end of each feeder line after filtering for detecting the characteristic frequency of the signal dciP ’、i dciN ’；
Frequency of probe signal (omega) in ) The basic principle of selection is as follows:
response characteristic differences are made most significant for more sensitive detection while meeting injection device performance constraints, accounting for device performance limitations and line impedance characteristic constraints.
The frequency of the detection signal is selected according to the following conditions:
wherein, ω is MMClim In order to limit the frequency of the response speed of the MMC,
solving the system impedance resonance frequency for the introduced parameters;
s4, based on the positive and negative electrode currents filtered in the step S3, obtaining zero-mode currents of the feeder line one by one, and performing normalization; summing the normalized zero-mode feeder current to obtain a feeder zero-mode current reference value i base ；
The zero mode current of each feeder line is obtained one by one as follows:
wherein i dci0 For a calculation of the value of the zero-mode current, omega, seen by the head end of the line i within the length of the data window in For injecting a characteristic frequency, i, of the probe signal dciP (ω in )、i dciN (ω in ) Respectively a positive electrode current and a negative electrode current of the feeder line.
Feeder zero-mode current reference value i Lref The method specifically comprises the following steps:
wherein i Lref For a reference value of zero-mode current of a long inner feeder of a calculation data window i dci0-nm A normalized zero-mode current value seen by the head-end of line i within the calculated data window length is calculated.
Normalization is as follows:
wherein i dci0-nm (k) Sample point value of kth normalized zero-mode current in data window i dci0 (k) Sample point value for the kth zero-mode current in the data window, max (i) dci0 ) Is the maximum value of the sample points within the data window.
S5, introducing a Pearson correlation coefficient, and utilizing the normalized feeder zero-mode current i obtained in the step S4 dci0 Each with a reference current i base Calculating waveform correlation, dividing all sampling values of zero-mode current in a data window by the maximum value in the sampling values to carry out normalization processing, and carrying out fault judgment according to a Pearson correlation coefficient to determine a fault line and a healthy line;
zero mode current value i of each feeder dci0 And a reference zero-mode current value i base The pearson correlation coefficient between them is calculated as follows:
wherein the content of the first and second substances,
pearson correlation coefficient, cov (i) for a normalized zero-mode current value at the beginning of line i within the length of a calculation data window and a zero-mode current reference value of the feeder Lref (ω in ),i dci0-nm (ω in ) Is the covariance between the two currents,
is the standard deviation, omega, of the zero-mode current reference value and the zero-mode current value of the feeder line respectively in Is the characteristic frequency of the injected probe signal.
The fault discrimination specifically comprises the following steps:
wherein k is a reliability coefficient,
for a Pearson correlation coefficient, omega, for calculating a normalized zero-mode current value at the head end of a line i within the length of the data window and a feeder zero-mode current reference value in Is the characteristic frequency of the injected probe signal.
S6, if the fault of the ith feeder line is identified in the step S5, outputting a result, and finishing the operation; if the calculation result of any feeder line does not satisfy the formula (4), performing step S7;
s7, judging according to the bus voltage unbalance criterion again, if the bus voltage unbalance criterion is met, outputting a result that the bus fault occurs, and ending the operation; if the bus voltage unbalance criterion is not met, the output result is an instantaneous fault, and the operation is ended.
In another embodiment of the present invention, a dc power distribution network ground fault line selection system is provided, where the system can be used to implement the dc power distribution network ground fault line selection method, and specifically, the dc power distribution network ground fault line selection system includes an injection module, a measurement module, a filtering module, a transformation module, and a line selection module.
The injection module starts MMC additional control by utilizing a bus voltage unbalance criterion and injects a detection signal;
the measuring module is used for delaying delta t to collect the positive current and the negative current of the head end of each feeder line;
the filtering module is used for filtering the positive current and the negative current of the head end of each feeder line acquired by the measuring module and selecting the central frequency f of the filter mp Obtaining the positive and negative currents of the head ends of the feeder lines after filtering for detecting the characteristic frequency of the signal;
the transformation module is used for solving the zero-mode current of each feeder line by utilizing the positive and negative currents at the head end of each feeder line after filtering by the filtering module, performing normalization processing by dividing all sampling values of the zero-mode current in the data window by the maximum value in the sampling values, and summing the zero-mode feeder line currents after the normalization processing to obtain a reference current;
and the line selection module introduces a Pearson correlation coefficient, obtains waveform correlation by using the zero-mode current of the feeder line subjected to normalization processing of the transformation module and the obtained reference current one by one, and determines a fault line and a healthy line according to fault discrimination by using the Pearson correlation coefficient so as to complete ground fault line selection of the direct-current power distribution network.
In yet another embodiment of the present invention, a terminal device is provided that includes a processor and a memory for storing a computer program comprising program instructions, the processor being configured to execute the program instructions stored by the computer storage medium. The Processor may be a Central Processing Unit (CPU), or may be other general purpose Processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), an off-the-shelf Programmable gate array (FPGA) or other Programmable logic device, a discrete gate or transistor logic device, a discrete hardware component, etc., which is a computing core and a control core of the terminal, and is adapted to implement one or more instructions, and is specifically adapted to load and execute one or more instructions to implement a corresponding method flow or a corresponding function; the processor provided by the embodiment of the invention can be used for the operation of the direct current distribution network ground fault line selection method, and comprises the following steps:
starting MMC additional control by utilizing a bus voltage unbalance criterion, and injecting a detection signal; acquiring the positive electrode current and the negative electrode current of the head end of each feeder line by delaying delta t; filtering the positive current and the negative current at the head end of each feeder line, and selecting the center frequency f of the filter mp Obtaining the positive and negative currents of the head ends of the feeder lines after filtering for detecting the characteristic frequency of the signal; obtaining zero-mode current of each feeder line by using the positive and negative currents at the head end of each feeder line after filtering, performing normalization processing by dividing all sampling values of the zero-mode current in the data window by the maximum value in the sampling values, and summing the zero-mode feeder line currents after the normalization processing to obtain reference current; introducing a Pearson correlation coefficient, calculating waveform correlation by using the normalized zero-mode current of the feeder line and the reference current one by one, and performing correlation according to the Pearson correlation coefficientAnd (4) determining a fault line and a healthy line by fault discrimination to complete the earth fault line selection of the direct-current power distribution network.
In still another embodiment of the present invention, the present invention further provides a storage medium, specifically a computer-readable storage medium (Memory), which is a Memory device in the terminal device and is used for storing programs and data. It is understood that the computer readable storage medium herein may include a built-in storage medium in the terminal device, and may also include an extended storage medium supported by the terminal device. The computer-readable storage medium provides a storage space storing an operating system of the terminal. Also, one or more instructions, which may be one or more computer programs (including program code), are stored in the memory space and are adapted to be loaded and executed by the processor. It should be noted that the computer-readable storage medium may be a high-speed RAM memory, or may be a non-volatile memory (non-volatile memory), such as at least one disk memory.
The processor can load and execute one or more instructions stored in the computer readable storage medium to realize the corresponding steps of the method for selecting the line of the direct current distribution network ground fault in the embodiment; one or more instructions in the computer-readable storage medium are loaded by the processor and perform the steps of:
starting MMC additional control by utilizing a bus voltage unbalance criterion, and injecting a detection signal; acquiring the positive current and the negative current of the head end of each feeder line by delaying delta t; filtering the positive current and the negative current at the head end of each feeder line, and selecting the center frequency f of the filter mp Obtaining the positive and negative currents of the head ends of the feeder lines after filtering for detecting the characteristic frequency of the signal; obtaining zero-mode current of each feeder line by using the positive and negative currents at the head end of each feeder line after filtering, performing normalization processing by dividing all sampling values of the zero-mode current in the data window by the maximum value in the sampling values, and summing the zero-mode feeder line currents after the normalization processing to obtain reference current; introducing a Pearson correlation coefficient, and solving the zero-mode current of the feeder line and the reference current one by utilizing the normalized zero-mode currentAnd (4) taking waveform correlation, and carrying out fault judgment according to the Pearson correlation coefficient to determine a fault line and a healthy line so as to complete the ground fault line selection of the direct-current power distribution network.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Simulation verification
Referring to fig. 2, a radiation-type flexible dc power distribution network model is built by using PSCAD/EMTDC. The high-voltage side of the converter transformer adopts a star connection method of direct grounding, the valve side adopts a triangle connection method to avoid third harmonic invasion, the MMC outer ring control strategy adopts constant direct current voltage control and constant reactive power control, wherein Load1 (4 MW) simulates a relatively long-distance constant power Load, a circuit L2 simulates photovoltaic power generation (photovoltaic, PV) is connected with a grid through a DC/DC converter, and the Load is provided with a constant resistance Load of Load2 (800 ohm), load3 (267 ohm) simulates a constant resistance Load, and Load4 (1 MW) simulates a relatively short-distance constant power Load.
1. Feeder line fault
Taking the occurrence of positive pole metal grounding fault at the end of the line L1 as an example, the simulation result is shown in fig. 4, a 120Hz voltage detection signal is injected, the obtained zero mode current response is shown in fig. 4, the zero mode current pearson correlation coefficient of the feeder line L1 is near-1, and the healthy lines L2 to L4 are all near-1.
In addition, different fault positions are set, the judgment result is shown in the table 1, and the table shows that the fault feeder line can be reliably identified.
Table 1 feeder fault simulation results
2. Bus fault
The simulation result of the metallic ground fault occurring when the positive dc bus was installed is shown in fig. 5. As can be seen from fig. 5, when a bus fault occurs, all calculated values of the correlation coefficients of the zero-mode currents of the feeder lines are all close to 1, and the bus fault can be identified further according to a voltage imbalance criterion.
The simulation result proves the effectiveness of the invention, the invention can reliably identify the fault line/bus under the condition of 500 omega transition resistance, has certain transition resistance performance, can still correctly identify the fault under the interference of 40dB white noise, has certain noise resistance performance, adopts the fault steady-state detection signal to identify the fault, and has low requirements on the sampling rate of the detection and protection equipment.
In summary, the direct current distribution network ground fault line selection method and system provided by the invention have the advantages that the fault characteristics are enhanced by injecting the detection signals based on the MMC, the fault line is identified based on the feeder line zero-mode current characteristics, the method has the bus fault identification and permanent fault discrimination capabilities, and simulation results show that the method can reliably identify the single-pole ground fault occurring at any position of the bus or each feeder line under the 500 ohm transition resistance, and has the advantages of high sensitivity, strong reliability, no need of double-end communication, and low requirement on the sampling rate of a measurement and protection device.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and so forth) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention should not be limited thereby, and any modification made on the basis of the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.
Claims (4)
1. A direct current distribution network ground fault line selection method is characterized in that a bus voltage unbalance criterion is used for starting MMC additional control, and a detection signal is injected; acquiring the positive current and the negative current of the head end of each feeder line by delaying delta t; filtering the positive current and the negative current at the head end of each feeder line, and selecting the center frequency f of the filter mp Obtaining the positive and negative currents of the head ends of the feeder lines after filtering for detecting the characteristic frequency of the signal; obtaining zero-mode current of each feeder line by using the positive and negative currents at the head end of each feeder line after filtering, carrying out normalization processing, and summing the zero-mode feeder line currents after the normalization processing to obtain reference current; introducing a Pearson correlation coefficient, solving waveform correlation by using the normalized feeder zero-mode current and the reference current one by one, carrying out fault discrimination according to the Pearson correlation coefficient to determine a fault line and a healthy line, completing the ground fault line selection of the direct-current power distribution network, and obtaining the correlation coefficient when only the ith line is calculated
When the current value is less than the setting value, determining that the ith line has a single-pole grounding fault, and the rest lines are sound lines, and when all the calculated correlation coefficients are greater or less than the setting value>
When the voltage values are all larger than the setting value, further judging whether the bus voltage is balanced, if the voltage values are | v |, determining whether the bus voltage is balanced dcP +v dcN |＞0.2v dcB The output result is the bus fault if | v dcP +v dcN |≤0.2v dcB The output result is a transient fault, v dcP 、v dcN Positive and negative dc bus-line to ground voltage amplitude, v, respectively dcB For the direct current rated voltage, the fault discrimination specifically comprises the following steps:
wherein k is a setting value,
for a Pearson correlation coefficient, omega, for calculating a normalized zero-mode current value at the head end of a line i within the length of the data window and a feeder zero-mode current reference value in Is the characteristic frequency of the injected detection signal;
zero mode current i of each feeder dci0 The calculation is as follows:
wherein, ω is in For injecting a characteristic frequency, i, of the probe signal dciP (ω in )、i dciN (ω in ) Respectively the positive and negative currents of the feeder line;
normalization is as follows:
wherein i dci0-nm (k) Sample point value of kth normalized zero-mode current in data window i dci0 (k) The sample point value for the kth zero-mode current in the data window, max (i) dci0 ) The maximum value of the sampling points in the data window is obtained;
reference current i Lref The method specifically comprises the following steps:
wherein i dci0-nm Calculating a normalized zero-mode current value seen by the head end of the line i in the length of a data window, wherein n is the number of feeder lines;
zero mode current value i of each feeder dci0 Pearson correlation coefficient with reference zero mode current value
Is calculated asThe following:
wherein, cov (i) Lref (ω in ),i dci0-nm (ω in ) Is the covariance between the two currents,
respectively the standard deviation, omega, of the zero-mode current reference value and the zero-mode current value of the feeder line in Is the characteristic frequency of the injected probe signal.
2. The method of claim 1, wherein the additional control of the MMC is a function of:
wherein u is in For the probe signal injected into MMC, k in For detecting the signal injection coefficient, omega in To inject the angular frequency of the probe signal, t is time,
is the initial phase of the injected probe signal.
3. Method according to claim 1, characterized in that the signal ω is detected in The frequency selection basis of (2) is:
wherein, ω is MMClim In order to limit the frequency of the response speed of the MMC,
finding parameters for inliningThe system impedance resonance frequency of the solution.
4. The utility model provides a direct current distribution network ground fault route selection system which characterized in that includes:
the injection module starts MMC additional control by utilizing a bus voltage unbalance criterion and injects a detection signal;
the measuring module is used for delaying delta t to collect the positive current and the negative current of the head end of each feeder line;
the filtering module is used for filtering the positive current and the negative current of the head end of each feeder line acquired by the measuring module and selecting the central frequency f of the filter mp Obtaining the positive and negative currents of the head ends of the feeder lines after filtering for detecting the characteristic frequency of the signal;
the transformation module is used for solving the zero-mode current of each feeder line by using the positive and negative currents at the head end of each feeder line after filtering by the filtering module, performing normalization processing by dividing all sampling values of the zero-mode current in the data window by the maximum value in the sampling values, and summing the zero-mode feeder line currents after the normalization processing to obtain a reference current;
the line selection module introduces a Pearson correlation coefficient, obtains waveform correlation by using the feeder zero-mode current subjected to normalization processing of the conversion module and the obtained reference current one by one, determines a fault line and a healthy line by fault discrimination according to the Pearson correlation coefficient, completes direct-current power distribution network ground fault line selection, and obtains the correlation coefficient when only the ith line is calculated
When the current value is less than the setting value, determining that the ith line has a single-pole grounding fault, and the rest lines are sound lines, and when all the calculated correlation coefficients are greater or less than the setting value>
When the voltage values are all larger than the setting value, further judging whether the bus voltage is balanced, if the voltage values are | v |, determining whether the bus voltage is balanced dcP +v dcN |＞0.2v dcB The output result is the bus fault if | v dcP +v dcN |≤0.2v dcB The output result is instantaneousTime of flight fault, v dcP 、v dcN Respectively positive and negative DC bus line to ground voltage amplitude v dcB For the direct current rated voltage, the fault judgment specifically comprises the following steps:
wherein k is a setting value,
for a Pearson correlation coefficient, omega, for calculating a normalized zero-mode current value at the head end of a line i within the length of the data window and a feeder zero-mode current reference value in Is the characteristic frequency of the injected detection signal;
zero mode current i of each feeder dci0 The calculation is as follows:
wherein, ω is in For injecting a characteristic frequency, i, of the probe signal dciP (ω in )、i dciN (ω in ) Respectively the positive and negative currents of the feeder line;
normalization is as follows:
wherein i dci0-nm (k) Sample point value of kth normalized zero-mode current in data window i dci0 (k) The sample point value for the kth zero-mode current in the data window, max (i) dci0 ) The maximum value of the sampling point in the data window;
reference current i Lref The method specifically comprises the following steps:
wherein i dci0-nm Calculating a normalized zero-mode current value seen by the head end of the line i in the length of a data window, wherein n is the number of feeder lines;
zero-mode current value i of each feeder dci0 Pearson correlation coefficient between reference zero-mode current value and reference
The calculation is as follows:
wherein, cov (i) Lref (ω in ),i dci0-nm (ω in ) Is the covariance between the two currents,
is the standard deviation, omega, of the zero-mode current reference value and the zero-mode current value of the feeder line respectively in Is the characteristic frequency of the injected probe signal. />
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