CN113820564A - Fault detection method suitable for source network load storage complex power grid - Google Patents
Fault detection method suitable for source network load storage complex power grid Download PDFInfo
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- CN113820564A CN113820564A CN202111119952.1A CN202111119952A CN113820564A CN 113820564 A CN113820564 A CN 113820564A CN 202111119952 A CN202111119952 A CN 202111119952A CN 113820564 A CN113820564 A CN 113820564A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/088—Aspects of digital computing
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
- Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
- Y04S10/00—Systems supporting electrical power generation, transmission or distribution
- Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
- Y04S10/52—Outage or fault management, e.g. fault detection or location
Abstract
The invention provides a fault detection method suitable for a source network load storage complex power grid. The method is simple and reliable in principle, is not influenced by transition resistance and line distributed capacitance, and provides technical support for safe and reliable operation of the power distribution network. In order to realize the invention, the invention adopts the following technical scheme: firstly, a measuring element carries out data acquisition and calculates current differential; judging whether a protection starting element is met or not according to the current variance; entering the next step when the threshold value is larger than the set threshold value, otherwise, returning the protection; calculating an inherent modal singular value entropy Kenyi coefficient and a current integral, and respectively carrying out fault identification and a fault pole selection program; the fault identification program identifies the fault type by using the entropy kini coefficient of the inherent modal singular value; if the entropy kini coefficient of the inherent modal singular value is larger than the threshold value, judging that the fault is in the region, and protecting to enter the next step; otherwise, judging the fault to be an out-of-area fault, and returning protection; and when the fault identification program and the fault pole selection simultaneously meet the conditions, sending an action signal to the fault pole.
Description
Technical Field
The invention relates to a fault detection method suitable for a source network load storage complex power grid, and belongs to the technical field of direct-current power distribution networks.
Background
Because the uncertainty of wind and light and other new energy power generation is large, the wind power generation amount is mainly concentrated in spring and winter seasons, the photovoltaic power generation amount is mainly concentrated in summer and autumn seasons and the like, and the randomness, volatility and intermittence of the new energy provide challenges for continuous and reliable power supply. Therefore, the existing research is difficult to meet the protection requirement of the novel double-high distribution network containing uncertain factors, and the research of a novel distribution network protection scheme under strong randomness influence factors is urgently needed to be developed. The direct current distribution network is one of the modes of distributed power supply and high-efficiency load absorption, but the access of high-density distributed power supply brings great challenges to the fault detection of the distribution network. Power electronic equipment contained in a direct-current power distribution network is susceptible to impact current, and a rapid fault detection scheme is urgently needed. In addition, the reliability of the traditional fault detection scheme is reduced by the influence factors such as line distributed capacitance, synchronization error and noise interference.
The power distribution network can accommodate a large number of distributed power supplies and direct current loads, utilization efficiency is improved, and equipment cost is reduced. Flexible control, higher electric energy quality and the like, so that the solar energy power generation system is deeply concerned at home and abroad. However, the fault detection scheme of the power distribution network still has more difficulties to influence the development of the power grid. The presence of a large number of power electronic devices makes a fault detection scheme necessary to identify faults within 5 ms. In addition, factors such as high-frequency distributed capacitance current, noise interference, synchronous errors and the like greatly reduce the reliability of the existing fault detection scheme. Therefore, a rapid and reliable fault detection scheme is urgently needed for a direct current distribution network containing a distributed power supply.
At present, fault detection schemes for power distribution networks with distributed power sources can be divided into three types: based on the electrical magnitude, based on the electrical differential, based on the fault distance.
The fault detection scheme based on the electric quantity amplitude mostly utilizes voltage, current and harmonic wave construction criteria. The invention provides a fault detection scheme based on voltage information, and realizes fault detection of a power distribution network by using inverse time limit characteristics.
In the invention, the criterion is constructed by utilizing harmonic wave quantity, and the rapidity of the scheme is ensured by utilizing the excess characteristic. However, the fault detection scheme based on the electrical quantity has the following problems: 1) faults in adjacent lines tend to cause malfunction in the line. 2) The setting value calculation lacks theoretical basis, and the reliability of the transition dependence simulation is reduced. 3) The presence of a distributed power source changes the rate of change of the electrical quantity, which in turn causes a rejection of the scheme.
The invention utilizes voltage differential to construct fault criterion and provides a fault detection scheme based on electrical quantity differential.
The invention discloses a constant value matching method for realizing voltage differential criterion.
The invention utilizes current differentiation to construct a fault criterion. Although the electrical quantity differentiation based scheme increases rapidity, it is only applicable in the fault initiation phase. In addition, the reliability is susceptible to noise interference such as fault resistance and lightning.
The invention provides a fault detection scheme based on fault distance, which utilizes the principle of traveling wave ranging or parameter identification ranging.
According to the invention, a distance-measuring type fault detection scheme is provided by using an R-L model, but a large number of voltage transformers are required. In fact, fault detection schemes based on fault distance all have the problems of low accuracy rate, high sampling rate requirement and the like.
The invention researches the current differential protection and the voltage differential protection, and utilizes the wavelet transformation coefficient and the differential of the current or the voltage to form a fault criterion.
The traveling wave protection, which is a single-ended protection, is fast in operation time and is not affected by distributed capacitance, but is susceptible to a large transition resistance.
The invention proposes a method for judging faults by using an injection signal technology, but the scheme relates to a control mode of a direct current system, and the engineering application of the scheme is to be discussed.
The invention provides differential protection for compensating distributed capacitance current, and the realization is more complex.
The invention utilizes the traveling wave to carry out pilot protection and utilizes the characteristic of the traveling wave to overcome the influence of distributed capacitance.
Disclosure of Invention
The invention aims to provide a fault detection method suitable for a source network charge storage complex power grid, and solves the problem that the protection of the existing direct-current power distribution network is easily influenced by distributed capacitance, fault resistance and noise interference.
In order to achieve the purpose, the invention is realized by the following technical scheme:
a fault detection method suitable for a source network load storage complex power grid comprises the following steps:
1) firstly, a measuring element carries out data acquisition and calculates current differential;
2) adopting di/dt as a protection starting element, and judging whether the protection starting element is met or not according to the current variance; entering the next step when the threshold value is larger than the set threshold value, otherwise, returning the protection;
3) calculating intrinsic mode singular value kini coefficient and current integral, and respectively carrying out fault identification and fault pole selection procedures;
4) the fault identification program identifies the fault type by using the inherent modal singular value kini coefficient; if the intrinsic mode singular value kini coefficient is larger than the threshold value, judging that the fault is in the area, and protecting to enter the next step; otherwise, judging the fault to be an out-of-area fault, and returning protection;
5) the fault pole selection process compares the absolute values of the positive and negative pole current integrals to obtain the criterion of fault pole selection as follows:
in the formula: | QpI and QnI represents the absolute value of the positive electrode current integral and the absolute value of the negative electrode current integral, kset1And kset2A threshold for selecting a pole for a fault; selecting a corresponding fault pole according to the criterion and sending an action signal;
6) and when the fault identification program and the fault pole selection simultaneously meet the conditions, sending an action signal to the fault pole, and ending the program.
Preferably, the calculation steps of the intrinsic mode singular value kini coefficient are as follows:
1) decomposing the signal by EMD method to obtain IMFs ((c)1(k),c2(k),…,cn(k) ) using IMF to construct a feature matrix, which is as follows:
wherein n is the IMF number of the signal, and K is the number of sampling points of the signal;
2) obtaining the singular value of the time sequence, decomposing the characteristic matrix according to the following formula,
A＝UΛVT
wherein U is [ U ]1,u2…,uN]∈RN×N，UTU＝I；VTV＝I,V＝[v1,v2,…,vM]∈RM×M。Λ∈RM×MIs [ diag { sigma ]1,σ2,…,σp}:0]The singular value of A of the matrix is obtained as sigma1,σ2,…,σp；
3) Calculating the size of the kini coefficient according to a natural mode singular value kini coefficient formula, wherein the calculation formula is as follows:
wherein the content of the first and second substances,
where H is the kini coefficient of the singular value of the natural mode,
is the ratio of the singular values of the eigenmodes, and σ is the sum of the singular values of the eigenmodes.
The invention has the advantages that: the invention aims to provide a novel protection principle, solves the problem that the protection of the existing direct-current power distribution network is easily influenced by distributed capacitance, fault resistance and noise interference, and improves the accuracy and reliability of fault detection.
Compared with the traditional single-ended protection principle based on the voltage amplitude and the change rate of the current-limiting reactor, the fault resistance capability of the protection principle of the invention is enhanced to 700 omega, and the problem that the time domain analysis protection principle is greatly influenced by high-resistance faults is solved. The method utilizes the inherent modal singular value kini coefficient to express the fault characteristic, so that the method has stronger anti-noise interference capability and solves the problem that the time domain analysis protection principle is greatly influenced by noise.
In addition, compared with the existing single-ended protection principle, the protection principle of the invention can be applied to a power distribution system with a plurality of boundary elements and has stronger adaptability.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention.
FIG. 1 is a schematic view of the flow structure of the present invention.
FIG. 2 is a DC distribution network model with distributed power supply according to 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 only a part of the embodiments of the present invention, and not all of the embodiments. 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.
The invention aims to provide a single-end protection principle based on an inherent modal singular value damping coefficient, aiming at the problem that the line protection principle is susceptible to high resistance faults. The method is simple and reliable in principle, is not influenced by transition resistance and line distributed capacitance, and provides technical support for safe and reliable operation of the power distribution network. In order to realize the invention, the invention adopts the following technical scheme:
1: firstly, the measuring element collects data and calculates the current differential.
2: substituting the current variance into equation (1) determines whether the protection start-up element is satisfied. And if the condition is met, entering the next step, otherwise, returning the protection.
Protection start criterion
The invention uses di/dt as a protective initiation element. Under normal operating conditions, the amount of current inrush is very small (power transfer is not a concern). When a dc system fails, its current must fluctuate and the current derivative must change. The threshold is set to a value slightly greater than zero to take into account the presence of harmonics during operation. When an increase or decrease in current occurs and a set threshold is exceeded, the current break or derivative initiates element action. Therefore, the starting criterion is set as follows:
di/dt＞kset (1)
3: and then, calculating intrinsic mode singular value kini coefficients and current integrals, respectively carrying the intrinsic mode singular value kini coefficients and the current integrals into a fault identification program and a fault pole selection program, and operating the two programs in parallel.
Protection identification criterion
The study model of this protocol is shown in figure 2. The model has two 5MW modular multilevel converters (CDSM-MMC), wherein the right-side MMC2 has a control mode of controlling active power, and the left-side MMC1 has a control voltage. In addition, distributed power supplies such as photovoltaic devices and energy storage devices are connected into a power distribution network system through an isolated full-bridge direct-current transformer.
The invention provides a single-ended protection principle based on an inherent modal singular value kini coefficient.
The method for defining and calculating the inherent modal singular value kini coefficient comprises the following steps:
assuming that there is a real matrix of N rows and M columns, the decomposition is performed according to equation (2), which is called singular value decomposition.
A＝UΛVT (2)
Wherein U is [ U ]1,u2…,uN]∈RN×N，UTU＝I；VTV＝I，V＝[v1,v2,…,vM]∈RM×M。Λ∈RM×MIs [ diag { sigma ]1,σ2,…,σp}:0]Transposed form of (1). So that the A singular value of the matrix is σ1,σ2,…,σp。
To obtain the singular values of the time series, a feature matrix thereof needs to be constructed. At present, the time series characteristic matrix is usually constructed by adopting a time delay embedding method. However, the embedding theorem has some defects, such as lack of prior knowledge of system dimension, and difficulty in determining the embedding dimension; the delay time is easily limited by noise and data length, increasing the difficulty of reconstructing the feature matrix. Therefore, the invention introduces the EMD method into the construction of the singular value decomposition characteristic matrix to solve the problem that the embedding dimension and the delay time are difficult to determine.
The EMD method is the core of Hilbert-Huang transformation, and IMF of signals can be obtained through the EMD method. The IMF reflects the inherent properties of the signal itself, with different IMFs containing different frequency components. Next, the process of building a feature matrix using IMF is discussed.
It is assumed that the signals are decomposed by EMD method to obtain IMFs ((c)1(k),c2(k),…,cn(k) ))). The initial feature matrix constructed using IMF is as follows:
where n is the IMF number of the signal. K is the number of sample points of the signal.
Referred to as natural modal anomaly. Assuming inherent singular values of the current signal as
Since different IMFs contain different frequency components, the natural modal singular values reflect the distribution of the frequency components in different frequency bands. The inherent modal singular value kini coefficient formula is as follows:
wherein the content of the first and second substances,
where H is the Keyny coefficient of the eigenmode singular values;
is the ratio of the singular values of the eigenmodes; σ is the sum of the eigenmode singular values. According to the definition and the calculation formula, the inherent modal singular value kini coefficient represents the disorder degree of the fault information. The more chaotic the fault information is, the larger the intrinsic mode singular value kini coefficient is.
When a fault occurs in a region, the current-limiting reactors are arranged on two sides of the line, so that the current-limiting reactors have large influence on transmission of traveling wave signals. When the fault occurs in the area, the wave of the initial line is transmitted to two sides. The forward and backward traveling waves can be measured at line measurement points M and N. Assuming that the wire is lossless, the time domain expression of the current limiting reactor reflection coefficient is:
in the formula: t is t0Is the time of arrival of the initial fault wave; l is the equivalent inductance of the current-limiting reactor; zCIs the line wave impedance. Obviously, the reflection coefficient of the current-limiting reactor is 1 at the initial moment of the fault, which shows that the current-limiting reactor has total reflection capacity to the traveling wave when the fault occurs in the area. In this case, the degree of disorder of the failure information is large. Therefore, the coefficient of the kini is large according to the singular value of the intrinsic mode at the time of the in-zone failure.
When an out-of-area fault occurs, the current-limiting reactor has a total reflection effect on the traveling wave signal at the initial stage of the fault. Therefore, in the case of an out-of-range fault, the degree of mixing of fault information is small, that is, the smaller the intrinsic mode singular value kini coefficient is.
4: and the fault identification program identifies the fault type by using the inherent modal singular value kini coefficient. If the intrinsic mode singular value kini coefficient is larger than the threshold value, judging that the fault is in the area, and protecting to enter the next step; otherwise, judging the fault to be an out-of-area fault, and returning protection. The criteria for protection identification are as follows:
5: the fault pole selection routine substitutes the current integral ratio into equation (7), selects the correct fault pole and signals the action.
And selecting a criterion for the fault pole.
The fault pole selection is an indispensable part in protection, and the absolute value of the current integral is used as a fault pole selection criterion. Because the integral absolute value of the current of the positive pole and the negative pole of the circuit represents the area enclosed by the current waveform and the coordinate axis, the areas of the positive pole and the negative pole are the same in a normal state. When a single-pole fault occurs, the current change of a fault pole is far larger than that of a healthy pole, which means that the area of the fault pole is increased and far larger than that of the healthy pole at the same moment; in bipolar failure, the positive and negative electrode area values are equal, i.e., the absolute values of the current integrals are equal. Therefore, the criterion for obtaining the fault pole selection by comparing the absolute values of the positive and negative pole current integrals is as follows:
in the formula: | QpI and QnI represents the absolute value of the positive electrode current integral and the absolute value of the negative electrode current integral, kset1And kset2The threshold value for selecting the pole for the fault needs to be set by considering factors such as high-resistance grounding, line coupling and the like.
6: and when the fault identification program and the fault pole selection simultaneously meet the conditions, sending an action signal to the fault pole, and ending the program.
Claims (2)
1. A fault detection method suitable for a source network load storage complex power grid is characterized by comprising the following steps:
1) firstly, a measuring element carries out data acquisition and calculates current differential;
2) adopting di/dt as a protection starting element, and judging whether the protection starting element is met or not according to the current variance; entering the next step when the threshold value is larger than the set threshold value, otherwise, returning the protection;
3) calculating intrinsic mode singular value kini coefficient and current integral, and respectively carrying out fault identification and fault pole selection procedures;
4) the fault identification program identifies the fault type by using the inherent modal singular value kini coefficient; if the intrinsic mode singular value kini coefficient is larger than the threshold value, judging that the fault is in the area, and protecting to enter the next step; otherwise, judging the fault to be an out-of-area fault, and returning protection;
5) the fault pole selection process compares the absolute values of the positive and negative pole current integrals to obtain the criterion of fault pole selection as follows:
in the formula: | QpI and QnI represents the absolute value of the positive electrode current integral and the absolute value of the negative electrode current integral, kset1And kset2A threshold for selecting a pole for a fault; selecting a corresponding fault pole according to the criterion and sending an action signal;
6) and when the fault identification program and the fault pole selection simultaneously meet the conditions, sending an action signal to the fault pole, and ending the program.
2. The fault detection method suitable for the source grid load-storage complex power grid according to claim 1, wherein the inherent modal singular value kini coefficient is calculated by the following steps:
1) decomposing the signal by EMD method to obtain IMFs ((c)1(k)，c2(k)，…，cn(k) ) using IMF to construct a feature matrix, which is as follows:
wherein n is the IMF number of the signal, and K is the number of sampling points of the signal;
2) obtaining the singular value of the time sequence, decomposing the characteristic matrix according to the following formula,
A＝UΛVT
wherein U is [ U ]1，u2…，uN]∈RN×N，UTU＝I；VTV＝I，V＝[v1，v2，…，vM]∈RM×M。Λ∈RM×MIs [ diag { sigma ]1，σ2，…，σp}：0]The singular value of A of the matrix is obtained as sigma1，σ2，…，σp；
3) Calculating the size of the kini coefficient according to a natural mode singular value kini coefficient formula, wherein the calculation formula is as follows:
wherein the content of the first and second substances,
where H is the kini coefficient of the singular value of the natural mode,
is the ratio of the singular values of the eigenmodes, and σ is the sum of the singular values of the eigenmodes.
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