CN114928031A - Double-fed wind power alternating current circuit pilot protection system and protection method based on singular entropy - Google Patents

Double-fed wind power alternating current circuit pilot protection system and protection method based on singular entropy Download PDF

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CN114928031A
CN114928031A CN202210618457.3A CN202210618457A CN114928031A CN 114928031 A CN114928031 A CN 114928031A CN 202210618457 A CN202210618457 A CN 202210618457A CN 114928031 A CN114928031 A CN 114928031A
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current
singular
wind power
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breaker
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段建东
赵宇航
杨威
路文超
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Xian University of Technology
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/26—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents
    • H02H3/28—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at two spaced portions of a single system, e.g. at opposite ends of one line, at input and output of apparatus
    • H02H3/30—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at two spaced portions of a single system, e.g. at opposite ends of one line, at input and output of apparatus using pilot wires or other signalling channel
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/261—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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Abstract

The invention discloses a double-fed wind power alternating current circuit pilot protection method based on singular entropy, which comprises the steps of respectively collecting current values at a first circuit breaker and a tail circuit breaker on a circuit through a first current transformer and a tail current transformer, and respectively inputting the measured current values into a programmable processor a and a programmable processor b through the first current transformer and the tail current transformer; calculating the current singular entropies of the two ends by using the current data of each phase of the first and the tail end circuit breakers, and if the difference value H of the current singular entropies of the two ends is obtained through calculation d Is greater than the setting value H set Then the zone fault, breaker action, first and last breaker tripping circuit break, such as H obtained by calculation d Is less than H set If the fault is an out-of-range fault, continuing to sample current data; and the circuit is broken by tripping the first and the tail end circuit breakers, so that the longitudinal protection of the double-fed wind power alternating current circuit is completed. The invention solves the problem that the double-fed wind power alternating current sending-out line system protection method of the connected MMC converter station can not adapt to the complex fault characteristicsThe double-end power electronic power supply has high practicability.

Description

Double-fed wind power alternating current circuit pilot protection system and protection method based on singular entropy
Technical Field
The invention belongs to the technical field of power grid relays, and particularly relates to a double-fed wind power alternating current circuit pilot protection system method based on singular entropy and a protection method of the system.
Background
Energy is the most fundamental driving force for economic growth throughout the world. Wind energy in various new energy sources is a permanent local energy source and has the characteristics of cleanness, safety, abundance and the like. In the development of renewable energy in the world nowadays, wind power generation is a new energy power generation form which has the most mature technology except for water energy and has the most large-scale development and utilization, and increasingly receives attention from the world. The double-fed wind driven generator occupies most proportion of the installed wind power capacity due to the superiority of the double-fed wind driven generator. The investment of more and more double-fed wind power projects and the capacity of wind power plants are continuously increased. However, in China, wind energy is unevenly distributed, east-west difference is large, a wind energy construction base is far away from a power load center, and in order to improve transmission efficiency and reduce loss, the flexible direct current transmission technology based on the modular multilevel converter is widely applied to double-fed wind power transmission. Compared with the traditional direct current transmission, the direct current transmission converter has the characteristics of independent control of active power and reactive power, low switching loss, strong fault tolerance capability, strong fault ride-through capability and the like, has the characteristics of low manufacturing cost, low loss, flexible operation, low harmonic content, suitability for passive system power transmission and the like, and is the high-voltage direct current transmission converter which meets the wind power transmission requirement at present most. However, the flexible direct-current transmission system also brings challenges to traditional relay protection, damage caused when a wind power plant fails is also increased seriously, and challenges are brought to stability and safety of a power grid.
The relay protection is used as a first defense line for safe and stable operation of a power grid, and the relay protection undertakes the tasks of quickly and reliably identifying and effectively isolating faults when the faults occur, so that the relay protection has important significance for restraining further deterioration of the operation condition of a system and ensuring efficient and stable transmission and utilization of electric energy. For a double-fed wind power alternating current sending system of an associated MMC converter station, the double-fed wind power alternating current sending system comprises a large number of power electronic devices, fault characteristics of a double-fed wind power sending line are complex, a phase angle of fault current is often influenced by a control strategy, and the traditional protection principle designed based on current phase difference faces the problems of performance reduction and even incorrect action. Therefore, the wind power access MMC-HVDC brings great challenges to the traditional relay protection scheme in the aspects of reliability and sensitivity.
At present, a double-fed wind power plant can be divided into three sections through an MMC-HVDC grid-connected output line, the first section is an alternating current transmission line of the double-fed wind power plant connected to a wind field side MMC converter station, namely the double-fed wind power alternating current output line of an associated MMC converter station, the second section is a direct current transmission line of the wind field side MMC converter station connected to a grid side MMC converter station, and the third section is an alternating current transmission line of the grid side converter station connected to a public power grid. For a first section of alternating current sending-out circuit, one end of the first section of alternating current sending-out circuit is a wind power supply, the other end of the first section of alternating current sending-out circuit is an MMC power supply, and both ends of the first section of alternating current sending-out circuit are power electronic power supplies. Therefore, under the working scene of a double-fed wind power alternating current sending circuit of an associated MMC converter station, a new pilot protection scheme is provided.
Disclosure of Invention
The invention aims to provide a double-fed wind power alternating current circuit pilot protection method based on singular entropy, and solves the problem that a double-fed wind power alternating current sending circuit protection method for an associated MMC converter station in the prior art cannot adapt to complex fault characteristics of a double-end power electronic power supply circuit.
The first technical scheme adopted by the invention is as follows: double-fed wind-powered electricity generation alternating current circuit pilot protection system based on singular entropy: the system comprises a doubly-fed wind generator, a bus A and a bus B, wherein the bus A is connected with the bus B through a circuit, the bus A is connected with the doubly-fed wind generator through a step-down transformer, and the bus B is connected with an MMC converter station through a step-up transformer;
a head end breaker and a head end current transformer for detecting the current value of the head end breaker are arranged at an outlet of the A bus, the head end breaker is connected with an action controller a, and the head end current transformer and the action controller a are both connected with a programmable processor a; and a tail end breaker and a tail end current transformer for detecting the current value of the tail end breaker are arranged at the inlet of the bus B, wherein the tail end breaker is connected with the action controller B, and the tail end current transformer and the action controller B are both connected with the programmable processor B.
The second technical scheme adopted by the invention is as follows: the double-fed wind power alternating current circuit pilot protection method based on the singular entropy is implemented according to the following steps:
step 1, respectively acquiring current values of a head-end breaker and a tail-end breaker on a circuit through a head-end current transformer and a tail-end current transformer, inputting the measured current value into a programmable processor a through the head-end current transformer, and inputting the measured current value into a programmable processor b through the tail-end current transformer;
step 2, obtaining current data of each phase of the head-end circuit breaker and the tail-end circuit breaker by utilizing the step 1, calculating current singular entropies at two ends, and if the difference value H of the current singular entropies at two ends is obtained through calculation d Greater than setting value H set The circuit breaker acts, and the head end circuit breaker and the tail end circuit breaker trip out to break the circuit; e.g. calculated H d Is less than H set If the fault is an out-of-range fault, continuing to sample current data;
step 1, simulating different types of faults of the power distribution network through a PSCAD simulation experiment, and importing the obtained fault current data into an MATLAB program.
The calculation method of the singular entropy of the current at the two ends in the step 2 comprises the following steps:
Figure BDA0003675161760000031
Figure BDA0003675161760000032
p n the proportion of the nth singular value in the whole singular value spectrum is taken as the proportion of the nth singular value in the whole singular value spectrum; at the same time, p n Also represents the proportion of the nth mode in the configurable mode matrix A in all modes;
the pattern matrix A can be constructed as shown in equation (3):
Figure BDA0003675161760000033
wherein the content of the first and second substances,
Figure BDA0003675161760000034
selecting 10ms as a time window, selecting a sampling frequency of 5kHz, and selecting a sampling point number N of 100 in one time window to obtain 100 discrete current signals, wherein the embedding dimension M is 5; the delay constant r is 1, and if M is (c-1) × r +1, the matrix a is a matrix with M rows and M columns;
for the current sampling signal i (t) ═ i in step 1 1 ,i 2 ,...i N The specific method of singular entropy decomposition is as follows:
singular value decomposition is carried out on a mode matrix formed by a one-dimensional array formed by one-phase discrete current sampling signals, and the formula (4) is as follows:
Figure BDA0003675161760000041
in the formula, U and V are orthogonal matrices in left and right directions, respectively, and are expressed in a column vector form, that is, U ═ U { (U) } 1 ,u 2 ,...u m }，V＝{v 1 ,v 2 ,...v m },S＝diag(s 1 ,s 2 ,...s m ) (ii) a Carrying out singular entropy calculation of the current signal i (t) by substituting S into (1) and (2);
the diagonal elements of S are arranged from small to large to obtain a one-dimensional array sigma n Will σ n By bringing into formula (2) to obtain p n Then p is added n Substituting the formula (1) to obtain the singular entropy H of the current signal i (t) S Therefore, the singular entropies of the DFIG side and the MMC side can be respectively calculated as shown in the following formula (6):
Figure BDA0003675161760000042
in the formula (I), the compound is shown in the specification,
H DFIG the singular entropy value of the current at the installation position of the DFIG side head end circuit breaker
H MMC -singular entropy value of the current at the installation of the MMC side end circuit breaker
In conclusion, the pilot protection criterion of the double-fed wind power alternating current sending line of the MMC converter station can be constructed as follows:
H d >H set (6)
H d ＝100(H DFIG -H MMC ) (7)。
step 2 setting value H set Is 15.
The double-fed wind power alternating current output line protection system and the system pilot protection method for the MMC converter station have the beneficial effects that the problem that the double-fed wind power alternating current output line protection method for the MMC converter station cannot adapt to the complex fault characteristics of a double-end power electronic power supply line in the prior art is solved. Singular entropy calculation is adopted to represent the complex situation of the current at two ends of the protected line, and the difference of the complexity of the two ends effectively distinguishes the internal fault and the external fault, so that the protection reliability is improved.
Drawings
FIG. 1 is a circuit diagram of a double-fed wind power alternating current circuit pilot protection system based on singular entropy;
FIG. 2 is a flow chart of current signal singular entropy extraction in the double-fed wind power alternating current line pilot protection method based on singular entropy;
FIG. 3 is a schematic diagram of current waveforms at two ends of a fault phase line in the double-fed wind power alternating current line pilot protection method based on singular entropy;
FIG. 4 is a schematic diagram of singular entropy of currents at two ends of a fault phase line in the double-fed wind power alternating current line pilot protection method based on the singular entropy;
FIG. 5 is a flow chart of a double-fed wind power alternating current circuit pilot protection method based on singular entropy of the invention;
fig. 6 is a schematic diagram of the influence of different fault types on the protection scheme in the double-fed wind power alternating current circuit pilot protection method based on the singular entropy.
In the figure, 1, a double-fed wind power generator, 2, a double-fed wind power transmission end circuit, 3, a step-down transformer, 4, an A bus, 5, a head-end circuit breaker, 6, a head-end current transformer, 7, a circuit, 8, a programmable processor a, 9, an action controller a, 10, a tail-end circuit breaker B, 11, a tail-end current transformer, 12, a programmable processor B, 13, an action controller B, 14, a B bus, 15, a step-up transformer, 16, an MMC converter station side circuit and 17, an MMC converter station.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The double-fed wind power alternating current sending line protection system of the connected MMC converter station takes the following circuit as an example for explanation: as shown in fig. 1, the double-fed wind driven generator comprises a double-fed wind driven generator 1, an a bus 4 and a B bus 14, wherein the a bus 4 is connected with the B bus 14 through a line 7, the a bus 4 is connected with the double-fed wind driven generator 1 through a step-down transformer 3, and the B bus 14 is connected with an MMC converter station 17 through a step-up transformer 15 and an MMC converter station side line;
a head-end circuit breaker 5 and a head-end current transformer 6 for detecting the current value of the head-end circuit breaker are arranged at an outlet of the A bus 4, the head-end circuit breaker 5 is connected with an action controller a9, and the head-end current transformer 6 and the action controller a9 are both connected with a programmable processor a 8; at the inlet of the B bus 14, there are provided a terminal breaker 10 and a terminal current transformer 11 for detecting a current value at the terminal breaker, wherein the terminal breaker 10 is connected to a motion controller B13, and the terminal current transformer 11 and the motion controller B13 are connected to a programmable processor B12.
The pilot protection method of the double-fed wind power alternating current output line protection system connected with the MMC converter station is implemented according to the following steps as shown in figure 2:
step 1, respectively acquiring current values of a head-end breaker 5 and a tail-end breaker 10 on a circuit through a head-end current transformer 6 and a tail-end current transformer 7, inputting the measured current values into a programmable processor a8 through the head-end current transformer 6, and inputting the measured current values into a programmable processor b12 through a tail-end current transformer 11;
step 1 is specifically carried out as follows: and simulating different types of faults of a doubly-fed wind power alternating current circuit system of the connected MMC converter station through a PSCAD simulation experiment, and importing fault current data into an MATLAB program.
Step 2, obtaining current data of each phase of the head-end breaker 5 and the tail-end breaker 10 by utilizing the step 1, calculating current singular entropies at two ends, and if the difference value H of the current singular entropies at two ends is obtained through calculation d Greater than setting value H set If the fault is an internal fault, the circuit breaker acts, and the head-end circuit breaker 5 and the tail-end circuit breaker 10 trip to break the line; e.g. calculated H d Is less than H set If the fault is an out-of-range fault, continuing to sample current data;
the singular entropy calculation method in the step 2 comprises the following steps:
the calculation method of the singular entropy of the current at the two ends in the step 2 comprises the following steps:
Figure BDA0003675161760000061
Figure BDA0003675161760000062
p n the proportion of the nth singular value in the whole singular value spectrum is taken as the weight of the nth singular value; at the same time, p n Also represents the proportion of the nth mode in the configurable mode matrix A in all modes;
the pattern matrix A can be constructed as shown in equation (3):
Figure BDA0003675161760000071
wherein the content of the first and second substances,
Figure BDA0003675161760000072
selecting 10ms as a time window, selecting a sampling frequency of 5kHz, and selecting a sampling point number N of 100 in one time window to obtain 100 discrete current signals, wherein the embedding dimension M is 5; the delay constant r is 1, and if M is equal to (c-1) × r +1, the matrix a is a matrix with M rows and M columns;
for the current sampling signal i (t) ═ i in step 1 1 ,i 2 ,...i N The specific method of singular entropy decomposition is as follows:
performing singular value decomposition on a mode matrix formed by a one-dimensional array formed by one-phase discrete current sampling signals, wherein the mode matrix is represented by formula (4):
Figure BDA0003675161760000073
equation (4) is the singular value decomposition of the matrix A, in which U and V are left and right orthogonal matrices respectively and expressed in the form of column vectors, and each column vector in U is defined as U n I.e. U ═ U 1 ,u 2 ,...u m }，u n Namely, the left singular vector of the matrix A; v is a right orthogonal matrix, and each column vector in V is defined as V n ，V＝{v 1 ,v 2 ,...v m }v n I.e. the right singular vector of the matrix a, the diagonal matrix S ═ diag (S) 1 ,s 2 ,...s m )，s m Namely singular values of the matrix A; carrying out singular entropy calculation on the current signal i (t) by substituting S into (1) and (2);
the diagonal elements of S are arranged from small to large to obtain a one-dimensional array sigma n Will σ n Substitution into formula (2) to obtain p n Then p is added n Substituting the formula (1) to obtain the singular entropy H of the current signal i (t) S Therefore, the singular entropies of the DFIG side and the MMC side can be respectively calculated as shown in the following formula (5):
Figure BDA0003675161760000074
in the formula (I), the compound is shown in the specification,
H DFIG the singular entropy value of the current at the installation position of the DFIG side head end circuit breaker
H MMC -singular entropy value of current at installation of MMC side end circuit breaker
In conclusion, the pilot protection criterion of the doubly-fed wind power alternating current sending line of the MMC converter station can be constructed as follows:
H d >H set (6)
H d ＝100(H DFIG -H MMC ) (7)。
the advantage of the singular entropy algorithm is that: the key part of the singular entropy algorithm is singular value decomposition, the singular value decomposition is widely applied to numerical linear algebraic processing due to good stability, and compared with other signal processing methods, the singular entropy algorithm has unique advantages, no phase drift exists in the processing result, and the waveform distortion rate is low. The singular entropy substantially represents the uncertainty of each component of the time domain signal after singular value decomposition. From a complexity point of view, the singular entropy reflects the extrinsic representation of the complexity of the signal components over time. The simpler the signal, the more concentrated the energy is in a few components, the lower its singular entropy value. That is, the energy distribution of a signal with a complex component is relatively dispersed, and its singular entropy must be larger than that of a signal with a simple component. When a fault occurs, the difference of the components of fault current provided by power supplies at two ends of the line is researched, namely theoretically, when the power transmission line has an external fault, the singular entropies at the protection installation positions at the two ends of the line are almost equal, and when the internal fault occurs, the singular entropies at the two ends of the line have larger difference. The singular entropy can correctly reflect the characteristic that the signal characteristics of the power system are different when the power system breaks down under any condition, and is very suitable for extracting the fault signal characteristics when the line breaks down.
Examples
When a three-phase fault occurs in a double-fed wind power alternating current sending line system of an associated MMC converter station and the fault occurs in 2 seconds, the waveform of the phase A current is shown in figure 3.
Singular entropy calculation is performed on the currents before and after the fault, and the singular entropy of the short-circuit current provided by the power supplies at the two ends can be obtained as shown in fig. 4. As can be seen from fig. 4, the magnitude relationship between the singular entropies of the currents at the two ends of the line is very different between before and after the fault. Before a fault occurs, the difference value between currents at two ends of a line is small, and singular entropies are almost consistent; the difference between the singular entropies of the currents at the two ends of the line after a fault is significantly greater than before the fault.
Constructing a pilot protection criterion of a double-fed wind power alternating current sending line of an associated MMC converter station:
H d >H set (6)
H d ＝100(H DFIG -H MMC ) (7)
in the formula
H DFIG -singular entropy value of current at installation of DFIG side head end circuit breaker
H MMC -singular entropy value of current at installation of MMC side end circuit breaker
For easy observation and analysis, the difference is multiplied by a factor of 100 to obtain H d 。H set The maximum transmission error of the current sensor is considered to be 10% and a certain margin is reserved for the threshold value, namely the maximum transmission error is certainly larger than the maximum value of the line when the line has an out-of-area fault and is smaller than the minimum value of the transmission line when the line has an in-area fault, and the protection device is ensured not to reject and malfunction. After a large number of simulation tests and comprehensive consideration, H set Take 15. The protection scheme flow diagram is shown in fig. 5.
Verifying different fault types and fault positions
The specific process is as follows:
(1) at the midpoint of the line, under Crowbar input, a three-phase short circuit, an AB two-phase ground short circuit, an AB interphase short circuit, and an a-phase ground short circuit are respectively set, it is verified whether the proposed protection scheme can operate correctly, and the simulation result of performing the protection scheme on the a-phase is shown in fig. 6. As can be seen from fig. 6, the protection proposed herein operates reliably and with high sensitivity for different fault types.
(2) Under the condition that a Crowbar circuit of the double-fed fan is not put into different control strategies and the Crowbar circuit is put into different control strategies, multiple groups of simulation are carried out under different fault types of a protected circuit, the fault types are set to be a three-phase short circuit, a two-phase grounding short circuit, an interphase short circuit and a single-phase grounding short circuit, and whether the provided protection scheme can act correctly or not is verified. The simulation results are shown in table 1.
TABLE 1
Figure BDA0003675161760000091
Figure BDA0003675161760000101
From table 1, it can be seen that the protection scheme is not affected by the control strategy of the doubly-fed wind turbine under various fault types, can correctly act, and has high sensitivity. However, in the test process, it is found that different positions of the fault occur may affect the protection action value, so that it is necessary to simulate different positions of the fault occur and verify the performance of the proposed protection scheme.
(3) And performing multiple groups of simulation at different positions in the protected line, setting the fault types to be three-phase short circuit, AB two-phase grounding short circuit, AB inter-phase short circuit and A-phase grounding short circuit by taking the A phase as an example at the positions with the distances of 0%, 25%, 50%, 75% and 100%, and testing the performance of the protection scheme. The simulation results are shown in table 2.
TABLE 2
Figure BDA0003675161760000102
Figure BDA0003675161760000111
As can be seen from table 2, the protection scheme can protect the full length of the line well under various fault types. And the difference of the protection action values at each position of the line is not large, which indicates that the fault occurrence position has little influence on the protection.
The pilot protection method of the double-fed wind power alternating current output line system of the MMC converter station utilizes pilot protection aiming at the DFIG MMC system, has simple and quick calculation process, starts from the entropy angle, utilizes the singular entropy to calculate the complexity of fault current at two ends, constructs a novel pilot protection scheme, can adapt to various fault conditions at a lower sampling rate, and meets the requirements on reliability and sensitivity under different fault types and fault positions. The problem that a double-fed wind power alternating current sending-out line system protection method for an associated MMC converter station in the prior art cannot adapt to a double-end power electronic power supply with complex fault characteristics is solved, and the practicability is high; and the method is favorable for reliable judgment and fault removal of faults.

Claims (5)

1. The double-fed wind power alternating current circuit pilot protection system based on the singular entropy is characterized by comprising a double-fed wind power generator (1), an A bus (4) and a B bus (14), wherein the A bus (4) is connected with the B bus (14) through a circuit (7), the A bus (4) is connected with the double-fed wind power generator (1) through a step-down transformer (3), and the B bus (14) is connected with an MMC converter station (17) through a step-up transformer (15);
a head-end circuit breaker (5) and a head-end current transformer (6) for detecting the current value of the head-end circuit breaker are arranged at an outlet of the A bus (4), the head-end circuit breaker (5) is connected with an action controller a (9), and the head-end current transformer (6) and the action controller a (9) are both connected with a programmable processor a (8); and a tail end breaker (10) and a tail end current transformer (11) for detecting the current value at the tail end breaker are arranged at the inlet of the B bus (14), wherein the tail end breaker (10) is connected with a motion controller B (13), and the tail end current transformer (11) and the motion controller B (13) are both connected with a programmable processor B (12).
2. The double-fed wind power alternating current circuit pilot protection method based on the singular entropy of claim 1 is specifically implemented according to the following steps:
step 1, respectively acquiring current values of a head-end breaker (5) and a tail-end breaker (10) on a circuit through a head-end current transformer (6) and a tail-end current transformer (7), inputting the measured current value into a programmable processor a (8) through the head-end current transformer (6), and inputting the measured current value into a programmable processor b (12) through a tail-end current transformer (11);
step 2, obtaining current data of each phase of the head-end breaker (5) and the tail-end breaker (10) by utilizing the step 1, calculating current singular entropies at two ends, and if the difference value H of the current singular entropies at two ends is obtained through calculation d Greater than setting value H set It is an intra-area fault, cutThe route device acts, and the head end breaker (5) and the tail end breaker (10) trip to break the line; e.g. calculated H d Is less than H set The current data sampling continues for an out-of-range fault.
3. The double-fed wind power alternating current line pilot protection method based on the singular entropy as claimed in claim 2, wherein in step 1, different types of faults occurring in the power distribution network are simulated through a PSCAD simulation experiment, and obtained fault current data are imported into an MATLAB program.
4. The singular entropy-based doubly-fed wind power alternating current line pilot protection method according to claim 2, wherein the calculation method of the singular entropy of the current at the two ends in the step 2 is as follows:
Figure FDA0003675161750000021
Figure FDA0003675161750000022
p n the proportion of the nth singular value in the whole singular value spectrum is taken as the proportion of the nth singular value in the whole singular value spectrum; at the same time, p n Also represents the proportion of the nth mode in the configurable mode matrix A in all modes;
the mode matrix A can be constructed as shown in equation (3):
Figure FDA0003675161750000023
wherein, the first and the second end of the pipe are connected with each other,
Figure FDA0003675161750000024
selecting 10ms as a time window, selecting a sampling frequency of 5kHz, and selecting the number N of sampling points as 100 in one time window to obtain 100 discrete current signals, wherein the embedding dimension M is 5; the delay constant r is 1, and if M is (c-1) × r +1, the matrix a is a matrix with M rows and M columns;
for the current sampling signal i (t) ═ i in step 1 1 ,i 2 ,...i N The specific method of singular entropy decomposition is as follows:
singular value decomposition is carried out on a mode matrix formed by a one-dimensional array formed by one-phase discrete current sampling signals, and the formula (4) is as follows:
Figure FDA0003675161750000025
in the formula, U and V are orthogonal matrices in left and right directions, respectively, and are expressed in the form of column vectors, i.e., U ═ U 1 ,u 2 ,...u m }，V＝{v 1 ,v 2 ,...v m },S＝diag(s 1 ,s 2 ,...s m ) (ii) a Carrying out singular entropy calculation of the current signal i (t) by substituting S into (1) and (2);
the diagonal elements of S are arranged from small to large to obtain a one-dimensional array sigma n Will σ n By bringing into formula (2) to obtain p n Then p is added n Substituting the formula (1) to obtain the singular entropy H of the current signal i (t) S Therefore, the singular entropies of the DFIG side and the MMC side can be respectively calculated as shown in the following formula (5):
Figure FDA0003675161750000031
in the formula (I), the compound is shown in the specification,
H DFIG -singular entropy value of current at installation of DFIG side head end circuit breaker
H MMC -singular entropy value of the current at the installation of the MMC side end circuit breaker
In summary, a pilot protection criterion of a doubly-fed wind power ac outgoing line of an associated MMC converter station may be constructed:
H d >H set (6)
H d ＝100(H DFIG -H MMC ) (7)。
5. the singular entropy-based doubly-fed wind power alternating current line pilot protection method according to claim 2, wherein the setting value H in the step 2 set Is 15.
CN202210618457.3A 2022-06-01 2022-06-01 Double-fed wind power alternating current circuit pilot protection system and protection method based on singular entropy Pending CN114928031A (en)

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