CN116706853A - New energy source line protection method and system through flexible direct delivery system - Google Patents
New energy source line protection method and system through flexible direct delivery system Download PDFInfo
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Classifications
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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
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/001—Methods to deal with contingencies, e.g. abnormalities, faults or failures
- H02J3/0012—Contingency detection
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/001—Methods to deal with contingencies, e.g. abnormalities, faults or failures
- H02J3/00125—Transmission line or load transient problems, e.g. overvoltage, resonance or self-excitation of inductive loads
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- Power Engineering (AREA)
- Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)
Abstract
The application relates to a method and a system for protecting a new energy source by a soft and straight delivery system line, belongs to the technical field of relay protection of power systems, and solves the problems that in the prior art, the new energy source is unreliable to operate by the soft and straight delivery system line protection, and protection misoperation and refusal operation are easy to occur. The method comprises collecting new energy after failure, sending out voltage and current at two sides of line via flexible direct delivery system, and extracting frequency omega of high frequency component f Voltage and current at that time; based on the two sides of the feeding line, the frequency of the high-frequency component is omega f The voltage and current at the time of obtaining omega in the frequency of the high-frequency component f The high-frequency inductance difference coefficients at the two sides of the sending-out line; according to the frequency of the high frequency componentThe rate is omega f When the high-frequency inductance difference coefficients and fault identification criteria at the two sides of the sending line are used, determining whether an in-area fault of the sending line occurs or not; if yes, the protection action of the sending-out line is started.
Description
Technical Field
The application relates to the technical field of relay protection of power systems, in particular to a line protection method and system for a new energy source through flexible direct delivery system.
Background
The wind power flexible direct delivery technology is used as an effective path for solving the problem of unbalanced wind energy and load distribution in China, has wide development prospect, and has great influence on the safety and stability of a power grid due to the fact that whether the wind power flexible direct delivery technology runs reliably or not. The wind field short-circuit current transient process is subjected to double constraint of electromagnetic physics and nonlinear control, and the short-circuit current amplitude is reduced due to the limitation of the overcurrent tolerance capability of power electronic equipment. Therefore, how to realize the reliable operation of the wind power flexible direct delivery system, and prevent the occurrence of protection misoperation and refusal operation has important practical significance for the safe operation of an actual system.
The transient protection mainly utilizes the fault transient characteristics to construct protection criteria, so that the protection time can be shortened to a greater extent, and therefore, the transient protection becomes one of main research directions of the current outgoing line protection. Transient protection can be divided into three main categories: transient traveling wave protection, single-ended transient based protection, and double-ended transient based protection. Transient traveling wave protection mainly constructs a protection criterion by transient traveling waves generated by line faults, namely fault components of the traveling waves. Traveling wave protection typically determines the fault direction by comparing the initial traveling wave voltage to current polarity relationship or by using forward traveling wave to reverse traveling wave amplitude ratio. However, the traveling wave head signal has short time, high acquisition difficulty, easy interference of the wave head signal and certain limitation. The protection based on the single-ended transient quantity utilizes the transient component of the fault to reflect the transient process of the fault, has short action time and ultra-high speed action performance, and requires a processor to have higher sampling rate. But for different types of faults, protection based on single-ended transient cannot be accurately identified. The protection scheme is formed by comparing the double-end transient state information based on the double-end transient state quantity, the action speed is high, different types of faults can be identified, the transition resistance and the noise resistance are high, but double-end electric quantity interaction is usually required, and the requirement on the synchronization rate of the data acquisition device is high.
Therefore, the existing new energy is unreliable in line protection operation through the flexible direct delivery system, and protection misoperation and refusal operation are easy to occur.
Disclosure of Invention
In view of the above analysis, the embodiment of the application aims to provide a method and a system for protecting a new energy source by a soft and straight delivery system line, which are used for solving the problems that the existing new energy source is unreliable to operate by the soft and straight delivery system line protection and is easy to cause protection misoperation and refusal operation.
In one aspect, an embodiment of the present application provides a method for protecting a new energy line through a flexible direct delivery system, including:
collecting new energy after fault occurrence, sending out voltage and current at two sides of the line by a flexible direct-current sending system, and further extracting the frequency omega of the high-frequency component f Voltage and current at that time;
based on the two sides of the feeding line, the frequency of the high-frequency component is omega f The voltage and current at the time of obtaining omega in the frequency of the high-frequency component f The high-frequency inductance difference coefficients at the two sides of the sending-out line;
according to the frequency omega of the high frequency component f When the high-frequency inductance difference coefficients and fault identification criteria at the two sides of the sending line are used, determining whether an in-area fault of the sending line occurs or not; if yes, the protection action of the sending-out line is started.
Further, one side of the wind power plant of the sending-out line is an M side, and one side of the flexible straight system is an N side; the high frequency inductance difference coefficient at both sides of the outgoing line is obtained by:
obtaining the frequency omega of the high-frequency component in the fault transient process according to the system structure and fault analysis of the side of the sending line M, N f The equivalent total impedance of the wind power plant and the equivalent impedance of the MMC converter at the time of the wind power plant are obtained, and the frequency of the high-frequency component at the side of the transmitting line M, N is omega f Inductance calculation value at the time;
on the basis of the feeding line M, N side, the frequency of the high-frequency component is omega f The voltage and current at this time are obtained to give ω as the high frequency component frequency of the transmission line M, N side f Inductance measurement at time;
on the basis of the feeding line M, N side, the frequency of the high-frequency component is omega f Inductance calculation and inductance sensing at the timeThe magnitude of the high frequency component is omega on the side of the delivery line M, N f The high frequency inductance difference coefficient.
Further, the feeding line M, N side has a high frequency component frequency of ω f The high frequency inductance difference coefficients at the time are respectively expressed as:
in the formula ,Sm (ω f )、S n (ω f ) Respectively show that the high frequency component frequency at the side of the transmission line M, N is omega f The high-frequency inductance difference coefficient at the time of failure is H, which represents the sampling point number in one period after failure occurs, L fm,h (ω f )、L fn,h (ω f ) Respectively represent that the high frequency component frequency of the transmission line M, N side at the h sampling point is omega f Inductance measurement at the time, L DFIG (ω f )、L mmc (ω f ) Respectively show that the high frequency component frequency at the side of the transmission line M, N is omega f Inductance calculation at that time.
Further, the frequency of the high-frequency component is omega f The fault identification criteria include:
in the formula ,Sset (ω f ) Indicating that the frequency of the high-frequency component is omega f A time action threshold value;
if S m (ω f) and Sn (ω f ) If the fault identification criteria are met, judging that the faults in the line area are sent out; otherwise, judging that the fault outside the transmission line area is sent out.
Further, if it is determined that the outgoing line is out of line, then
If S m (ω f ) If the fault recognition criterion is not met, judging that the back side system of the bus on the M side of the sending line fails;
if S n (ω f ) And if the fault identification criterion is not met, judging that the back side system of the N side bus of the sending line fails.
Further, the frequency ω of the high-frequency component is obtained by f Action threshold S at that time set (ω f )：
Let the percentage of fault locations on the outgoing line be denoted as a; wherein, the value range of a is 0-100%;
by changing the value of a in the following formula, a motion threshold value set S is obtained s a et ：
wherein ,
in the formula ,Sset,a (ω f ) Indicating a failure position percentage of a high frequency component frequency omega on the side of the delivery line M, N f Action threshold value at the time, L fm,h′ (ω f ) Indicating that the feeding line M side is at an arbitrary sampling point h' and the frequency of the high-frequency component is omega f Inductance measurement at time;
selecting action threshold value setAs a maximum or minimum value at the high frequency component frequency omega f Action threshold S at that time set (ω f )。
Further, the high frequency component has a frequency omega f Take the value ofThe +.>
wherein ,
ω m ＝{ω f |f'(ω f )＝0,f”(ω) f ＜0}
f(ω f )＝(L mmc (ω f )-L DFIG (ω f )) 2
in the formula, max () means taking the maximum value.
Further, the feeding line M has a high frequency component of ω f Inductance calculated value L at the time DFIG (ω f ) Expressed as:
in the formula ,c9 、c 7 、c 5 、c 3 、c 1 、d 8 、d 6 、d 4 、d 2 、d 0 The constant calculated from the element parameters on the side of the feeding line M is shown.
Further, the transmission line N side has a high frequency component frequency of ω f Inductance calculated value L at the time mmc (ω f ) Expressed as:
in the formula ,a7 、a 5 、a 3 、a 1 、b 6 、b 4 、b 2 、b 0 The constant calculated from the parameters of each element on the side of the transmission line N is shown.
On the other hand, the embodiment of the application provides a new energy source line protection system through a flexible direct delivery system, which comprises the following components:
the data acquisition module is used for acquiring the voltage and the current of the two sides of the line sent out by the new energy source through the flexible direct-current external transmission system after the fault occurs, and further extractingAt a high frequency component frequency of omega f Voltage and current at that time;
a high-frequency inductance difference coefficient module for providing omega-frequency components on both sides of the feeding line f The voltage and current at the time of obtaining omega in the frequency of the high-frequency component f The high-frequency inductance difference coefficients at the two sides of the sending-out line;
a fault recognition module for recognizing the frequency omega of the high-frequency component f When the high-frequency inductance difference coefficients and fault identification criteria at the two sides of the sending line are used, determining whether an in-area fault of the sending line occurs or not;
and the action protection module is used for starting the protection action of the sending out line if the fault occurs in the area of the sending out line.
Compared with the prior art, the application has at least the following beneficial effects:
the application provides a line protection method and a line protection system for a new energy through a flexible direct delivery system, which acquire data after faults occur to obtain data under high-frequency component frequency, further obtain a high-frequency inductance difference coefficient, and accurately identify faults inside and outside a zone by fault identification criteria, wherein only the two sides of the line are required to transmit judging results of fault directions instead of electrical quantity information, so that the requirement on data synchronism is lower, and the problem that the new energy is incorrectly acted through the line protection of the flexible direct delivery system is well solved; the high-resistance fault-tolerant resistor has strong tolerance to fault resistance and high sensitivity to high-resistance faults at the tail end of a line.
In the application, the technical schemes can be mutually combined to realize more preferable combination schemes. Additional features and advantages of the application will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the application. The objectives and other advantages of the application may be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the application, like reference numerals being used to refer to like parts throughout the several views.
Fig. 1 is a flow chart of a line protection method of a flexible direct delivery system for new energy provided in embodiment 1 of the present application;
FIG. 2 is a schematic diagram of a wind power output flexible-direct system provided in embodiment 1 of the present application;
fig. 3 is a topology of an MMC converter station provided in embodiment 1 of the present application;
fig. 4 is a schematic diagram of an MMC ac side short-circuit fault complex frequency domain arithmetic circuit provided in embodiment 1 of the present application;
fig. 5 is a fault equivalent model of an MMC converter provided in embodiment 1 of the present application;
FIG. 6 is a schematic diagram of a doubly-fed wind farm according to embodiment 1 of the present application;
FIG. 7 is an equivalent model of a single doubly-fed wind machine provided in embodiment 1 of the present application;
FIG. 8 is a model of a doubly-fed wind farm in embodiment 1 of the present application;
FIG. 9 is an equivalent model of a doubly-fed wind farm provided in embodiment 1 of the present application;
FIG. 10 is an equivalent frequency domain model of the delivery line fault system provided in embodiment 1 of the present application;
FIG. 11 is a fault component network at the time of an intra-zone fault provided in embodiment 1 of the present application;
FIG. 12 is a fault component network at the time of an out-of-zone fault provided in embodiment 1 of the present application;
FIG. 13 is a fault component network at the time of an out-of-zone fault provided in embodiment 1 of the present application;
FIGS. 14 (a) and (b) are the coefficients of difference in high frequency inductance at the M, N side protection installation in the case of a phase A single phase earth fault in the zone provided in example 3 of the present application, respectively;
FIGS. 14 (c) and (d) are the coefficients of difference in the high frequency inductance at the M, N side protection installation at the time of the BC two-phase interphase fault in the zone provided in example 3 of the present application, respectively;
FIGS. 14 (e) and (f) are the high frequency inductance difference coefficients of the side protection installation at M, N in the case of ABC three-phase failure in the area provided in example 3 of the present application, respectively;
FIGS. 15 (a) and (b) are the coefficients of difference in the high frequency inductance at the M, N side protection installation at the time of inter-phase failure of the intra-zone BC provided in example 3 of the present application, respectively;
FIGS. 16 (a) and (b) are the differential coefficients of the high-frequency inductance at the side M, N protection installation when the three phases of the back side outlet of the M-side bus provided in embodiment 3 of the present application are grounded;
fig. 17 (a) and (b) are the high frequency inductance difference coefficients of the protection installation on the M, N side at 50% MMC monopole ground fault on the soft dc line provided in example 3 of the present application.
Detailed Description
The following detailed description of preferred embodiments of the application is made in connection with the accompanying drawings, which form a part hereof, and together with the description of the embodiments of the application, are used to explain the principles of the application and are not intended to limit the scope of the application.
Example 1
The application discloses a line protection method of a new energy source through a flexible direct delivery system, which is shown in fig. 1 and comprises the following steps:
s1, collecting new energy after faults occur, sending out voltage and current on two sides of a line through a flexible direct-current external transmission system, and further extracting the frequency omega of a high-frequency component f Voltage and current at that time.
Specifically, current and voltage are collected by using transformers at protection installation positions on two sides of a sending line, and the current and voltage are extracted at the frequency omega of a high-frequency component by using the prior art f Voltage and current at that time.
S2, based on the two sides of the sending line, the frequency of the high-frequency component is omega f The voltage and current at the time of obtaining omega in the frequency of the high-frequency component f The high-frequency inductance difference coefficients at the two sides of the sending-out line;
in the implementation, in step S2, one side of the wind farm of the sending-out line is an M side, and one side of the flexible straightening system is an N side; the high frequency inductance difference coefficient at both sides of the outgoing line is obtained by:
obtaining the frequency omega of the high-frequency component in the fault transient process according to the system structure and fault analysis of the side of the sending line M, N f Equivalent total impedance of wind farm at the timeEquivalent impedance with MMC converter to obtain transmission line M, N with omega frequency component f Inductance calculation value at the time;
on the basis of the feeding line M, N side, the frequency of the high-frequency component is omega f The voltage and current at this time are obtained to give ω as the high frequency component frequency of the transmission line M, N side f Inductance measurement at time;
on the basis of the feeding line M, N side, the frequency of the high-frequency component is omega f The inductance calculated value and the inductance measured value at the time of the time are obtained to obtain the frequency omega of the high frequency component on the side of the transmitting line M, N f The high frequency inductance difference coefficient.
In practice, the transmitting line M, N side has a high frequency component frequency of ω f The high frequency inductance difference coefficients at the time are respectively expressed as:
in the formula ,Sm (ω f )、S n (ω f ) Respectively show that the high frequency component frequency at the side of the transmission line M, N is omega f The high-frequency inductance difference coefficient at the time of failure is H, which represents the sampling point number in one period after failure occurs, L fm,h (ω f )、L fn,h (ω f ) Respectively represent that the high frequency component frequency of the transmission line M, N side at the h sampling point is omega f Inductance measurement at the time, L DFIG (ω f )、L mmc (ω f ) Respectively show that the high frequency component frequency at the side of the transmission line M, N is omega f Inductance calculation at that time.
Specifically, the feeding line M has a high frequency component frequency of ω f Inductance calculated value L at the time DFIG (ω f ) Expressed as:
in the formula ,c9 、c 7 、c 5 、c 3 、c 1 、d 8 、d 6 、d 4 、d 2 、d 0 The constant calculated from the element parameters on the side of the feeding line M is shown.
Specifically, the transmission line N has a high frequency component frequency of ω f Inductance calculated value L at the time mmc (ω f ) Expressed as:
in the formula ,a7 、a 5 、a 3 、a 1 、b 6 、b 4 、b 2 、b 0 The constant calculated from the parameters of each element on the side of the transmission line N is shown.
S3, according to the frequency omega of the high-frequency component f When the high-frequency inductance difference coefficients and fault identification criteria at the two sides of the sending line are used, determining whether an in-area fault of the sending line occurs or not; if yes, the protection action of the sending-out line is started.
In practice, the frequency of the high-frequency component is omega f The fault identification criteria include:
in the formula ,Sset (ω f ) Indicating that the frequency of the high-frequency component is omega f A time action threshold value;
if S m (ω f) and Sn (ω f ) If the fault identification criteria are met, judging that the faults in the line area are sent out; otherwise, judging that the fault outside the transmission line area is sent out.
Specifically, if it is determined that the outgoing line is out of line, then
If S m (ω f ) If the fault recognition criterion is not met, judging that the back side system of the bus on the M side of the sending line fails;
if S n (ω f ) If the failure recognition criterion is not satisfied, it is determined that the back side system of the N-side bus of the outgoing lineThe system fails.
Specifically, the frequency ω of the high-frequency component is obtained by f Action threshold S at that time set (ω f )：
Let the percentage of fault locations on the outgoing line be denoted as a; wherein, the value range of a is 0-100%;
by changing the value of a in the following formula, a motion threshold value set is obtained
wherein ,
in the formula ,Sset,a (ω f ) Indicating a failure position percentage of a high frequency component frequency omega on the side of the delivery line M, N f Action threshold value at the time, L fm,h′ (ω f ) Indicating that the feeding line M side is at an arbitrary sampling point h' and the frequency of the high-frequency component is omega f Inductance measurement at time;
selecting action threshold value setAs a maximum or minimum value at the high frequency component frequency omega f Action threshold S at that time set (ω f )。
Preferably, the high frequency component has a frequency omega f Take the value ofThe +.>
wherein ,
ω m ＝{ω f |f'(ω f )＝0,f”(ω) f ＜0}
f(ω f )＝(L mmc (ω f )-L DFIG (ω f )) 2
in the formula, max () means taking the maximum value.
In order to facilitate the technical personnel in the art to better understand the forming process of the scheme in this embodiment, taking the wind power transmission and receiving flexible direct system shown in fig. 2 and the topological structure of the MMC converter station shown in fig. 3 as an example, the working principle of the line protection method of the flexible direct transmission system for new energy provided in this embodiment is described as follows:
fig. 3 is a structural diagram of an MMC converter in the wind power transmission receiving flexible direct system shown in fig. 2. In FIG. 3, U dc Is a soft direct side direct current voltage, i va Is the A-phase current of the alternating current side of the converter, u va Is the A phase port voltage of the converter, i pa 、i na The current of upper bridge arm and lower bridge arm of the phase A of the converter are respectively L 0 Is the inductance of a bridge arm of the converter, R 0 Is the equivalent resistance of a bridge arm of the converter, L s For the ac side inductance of the converter, SM denotes the submodule on the bridge arm, n 1 Indicating the number of sub-modules on the upper or lower leg of each phase.
Assuming that a short-circuit fault occurs at the ac side outlet, laplace is converted to the complex frequency domain, and a fault complex frequency domain arithmetic circuit at the time of ac side fault is obtained, as shown in fig. 4. In the figure, L sa I is the A-phase alternating current side inductance of the converter va (0) For the initial value of A-phase current of AC side of converter, n pa 、n na The input quantity of the sub-modules of the upper bridge arm and the lower bridge arm of the A phase of the alternating current side of the converter is respectively n pa (0)、n na (0) Respectively inputting initial values of quantity of sub-modules of an upper bridge arm and a lower bridge arm of an A phase of an alternating current side of the converter, C 0 For bridge arm submodule capacitance, i pa (0)、i na (0) Respectively the A phase of the alternating current side of the converterInitial value of upper bridge arm and lower bridge arm current, i va (0) Is the initial value of A-phase current of the alternating current side of the converter, U c Corresponding voltages for the individual submodules.
As can be seen from fig. 4, taking phase a as an example, the relationship between the voltage and current of the upper and lower arms on the ac side of the inverter is obtained:
u sa (s)+sL sa i va (s)＝u va (s)+L sa i va (0) (1)
i pa (s)＝i va (s)+i na (s) (4)
where s represents the Laplacian, u sa (s) represents the converter phase a port output voltage.
It should be noted that the inclusion of the suffix(s) to the parameters in the formula in this embodiment is expressed in the complex frequency domain.
The combined type (1) to (4) can be obtained:
wherein N represents the sum of the total sub-modules of the upper bridge arm and the lower bridge arm.
The MMC converter adopts the recent level to approach modulation, then there are:
in the formula ,uva * The reference value of the A-phase port voltage of the converter is represented and is output through a control link; round (x) represents taking the largest integer smaller than x.
Combined type (1) - (7), the calculation is as follows:
according to equation (8), an equivalent model of the phase a port voltage and the short-circuit current of the MMC converter when the ac line fails can be obtained, as shown in fig. 5:
u va (s)＝U mmc (s)-i va (s)Z mmc (s) (9)
in the formula ,Ummc (s) represents the equivalent voltage source, Z of the MMC converter in the fault transient process under the complex frequency domain mmc (s) represents equivalent impedance of the MMC converter in the fault transient process under the complex frequency domain, and the expressions are respectively as follows:
the doubly-fed wind power plant in the embodiment is composed of a plurality of doubly-fed wind power units, each unit in the wind power plant is connected to a collecting bus of the wind power plant through a current collecting circuit, and is boosted by a main transformer of the wind power plant and then sent out, and the structure of the doubly-fed wind power plant is shown in fig. 6.
To obtain a detailed wind field short-circuit current expression, a relation between the short-circuit current and the port voltage of a single fan when a short-circuit fault occurs needs to be deduced.
The voltage and flux linkage equation of a single DFIG in a wind field under the dq coordinate system are as follows:
wherein ,ω＝ω1 -ω r 。
in the formula ,ω1 Represents the synchronous angular velocity, ω represents the synchronous angular velocity ω 1 With rotor angular velocity omega r A difference between; l (L) m 、L s 、L r Respectively represents equivalent excitation inductance, stator inductance and rotor inductance, u sd 、u sq Respectively represent d and q components of stator voltage of doubly-fed generator, u rd 、u rq Respectively representing d and q components, i of the doubly-fed generator rotor voltage sd 、i sq Respectively representing d and q components, i of stator current of doubly-fed generator rd 、i rq Respectively representing d and q components, ψ, of doubly-fed generator rotor current sd 、ψ sq Respectively represent d and q components of doubly-fed generator stator flux, ψ rd 、ψ rq Respectively representing d and q components of doubly-fed generator rotor flux, R s Represents the stator side resistance, R r Representing the rotor side resistance.
Considering the time scale of the control link, the outer loop control can be ignored in the fault transient process, a given reference value is continuously output, and only the doubly-fed fan current loop control link is considered:
wherein ,
in the formula ,d and q axis reference values, i, respectively representing doubly-fed generator rotor voltages rdref 、i rqref Respectively represent d and q axis reference values, k of rotor current p 、k i Representing the rotor-side scaling factor and integration factor of the doubly-fed generator, respectively.
And (3) combining (12) - (15) to obtain the relational expression of the port voltage and the short-circuit current when the single fan has short-circuit fault:
wherein ,
α 1 ＝L r +R r τ s +k p τ s (17)
α 2 ＝R r +k i τ s +k p (18)
in the formula ,Usd 、U sq Respectively representing d and q axis components, i of fan port voltage s0d 、i s0q Respectively represent d-axis component and q-axis component of network side current caused by voltage drop of fan port ss1d 、i ss1q Respectively representing d-axis component and q-axis component of first network-side current caused by network-side converter control, i sr1d 、i sr1q Respectively representing first net side current d and q axis components caused by rotor side inverter control; i.e ss2d 、i ss2q Respectively representing d-axis and q-axis components of a second network-side current caused by control of a network-side converter, and a time constant tau in a time domain s ' attenuation; i.e ss3d 、i ss3q Respectively representing d-axis and q-axis components of a third network-side current caused by control of the network-side converter, and a time constant tau in a time domain r ' attenuation; i.e sr2d 、i sr2q Respectively representing the d-axis and q-axis components of the second net-side current caused by the control of the rotor-side converter, and the time constant L in the time domain r τ s '/α 1 Attenuation; i.e sr3d 、i sr3q i sr3d Respectively representing d-axis and q-axis components of a third net-side current caused by rotor-side inverter control, and a time constant L in a time domain r τ s '/α 2 Attenuation.
In equation (16), each short-circuit current fault component is expressed as:
/>
/>
wherein ,
α 3 ＝(R r +k p )ω 1 τ s +ωL r (1-σ) (35)
where k represents the voltage drop degree, u s0 And representing the voltage of the port of the wind turbine generator set before the fault.
When the power grid fails, the phase angle of the voltage jumps. At this point, the PLL control system cannot perfectly track the grid phase angle, i.e. the output reference value will deviate from the actual grid phase angle. Consider phase-locked loop dynamic errors, i.e., using the actual phase-locked loop output phase angle instead of the synchronous speed in calculating the short-circuit current, as shown in the following equation:
in the formula ,kpll-p 、k pll-i Respectively representing the proportional coefficient and the integral coefficient of the phase-locked loop control link.
And (3) combining the equation (16) and the equation (37), and applying park transformation to obtain a fault current and port voltage relational expression under the abc three-phase coordinate system.
I g (s)＝U g (s)/Z g +I μ (s) (38)
in the formula ,Ig Represents the feed-out current of the doubly-fed fan, U g Represents the port voltage of the doubly-fed fan, Z g Representing equivalent impedance of doubly-fed fan, I μ And the equivalent current in the doubly-fed wind turbine caused by a control link during faults is represented, and the value of the equivalent current is irrelevant to the port voltage.
From analysis, it can be known that the current fault component of the doubly-fed fan consists of a fault component caused by the drop of the port voltage and a fault component determined by the control link (represented as a current source), and an equivalent model of a single doubly-fed fan can be obtained, as shown in fig. 7. According to the wind farm structure shown in fig. 6, a model of a doubly fed wind farm can be obtained, as shown in fig. 8. In the figure, R i For the line resistance value of the current collecting wire where the ith fan is located, i=1, 2, … and n, wherein n represents the total number of fans; l (L) i The line reactance value of the electric collecting wire where the ith fan is positioned is U M For PCC grid-connected point voltage, I m To send out line current L T Is the reactance value of the main transformer of the wind field, U m Z is used for sending out the bus voltage at the wind field side of the line gi Is equivalent impedance of the ith doubly-fed fan, I μi The equivalent current of the ith doubly-fed fan caused by a control link during faults.
It should be noted that the collector wires are in one-to-one correspondence with the doubly fed fans.
For the doubly-fed wind field model shown in fig. 8, there are:
wherein ,
I m ＝I g1 +I g2 +…+I gn (40)
in the formula ,Ugi Representing the port voltage of the ith fan; i gi Indicating the i-th doubly-fed fan feed-out current.
Combined type (38) to (40) can be obtained:
in the formula ,Ll Represents the reactance of the line, R l Representing the line resistance.
The simplified wind field equivalent model can be obtained by analysis of the formula (41), as shown in fig. 9:
as can be seen from the figure 9 of the drawings,
in the formula ,UDFIG Represents the equivalent current source of the wind power plant, Z DFIG Representing the equivalent total impedance of the wind farm.
The wind field complex frequency domain model and the soft dc converter complex frequency domain model at the time of the line fault are obtained by the above analysis, so that a system model can be obtained as shown in fig. 10.
When the outgoing line fails, s=jω is calculated according to equation (11) f Substitution (11) of the frequency ω of the high-frequency component f Coefficient items of the same times can obtain impedance expression Z of the MMC converter mmc (ω f ) The method comprises the following steps:
in the formula ,a7 、a 6 、a 5 、a 4 、a 3 、a 2 、a 1 、b 6 、b 4 、b 2 B 0 For each element parameter according to the N side of the sending lineThe calculated constant, a 7 、a 6 、b 6 Are all greater than zero, i.e., are obtained on the basis of formula (11).
Its inductance expression L mmc (ω f ) The method comprises the following steps:
from (45), the frequency band omega of the MMC converter station when the fault equivalent impedance is inductive and capacitive can be obtained mmcL 、ω mmcC The method comprises the following steps of:
in the formula ,ω1.1 、ω 1.2 、ω 1.3 、ω 1.4 Is a as 7 ω 7 +a 5 ω 5 +…+a 1 Non-negative solution of ω=0; omega 2.1 、ω 2.2 、ω 2.3 Is a as 6 ω 6 +a 4 ω 4 +…+a 0 Non-negative solution of=0.
When the outgoing line fails, s=jω is calculated according to equation (43) f Substituting formula (43), extracting coefficient items with the same frequency of omega to obtain an equivalent total impedance expression Z of the wind field DFIG (ω f ) The method comprises the following steps:
in the formula ,c9 、c 8 、c 7 、c 6 、c 5 、c 4 、c 3 、c 2 、c 1 、c 0 、d 8 、d 7 、d 6 、d 5 、d 4 、d 3 、d 2 、d 1 、d 0 C, a constant calculated according to the parameters of each element on the side of the delivery line M 9 、c 8 、d 8 Are all greater than zero, i.e. obtainable according to equation (43).
Its inductance expression L DFIG (ω f ) The method comprises the following steps:
from (49), the frequency band omega when the wind field failure equivalent impedance is inductive and capacitive can be obtained DFIGC 、ω DFIGL The method comprises the following steps of:
in the formula ,ω3.1 、ω 3.2 、ω 3.3 、ω 3.4 C is 9 ω 9 +c 7 ω 7 +c 5 ω 5 +…+c 1 Non-negative solution of ω=0; omega 4.1 、ω 4.2 、ω 4.3 C is 8 ω 8 +c 6 ω 6 +c 4 ω 4 +…+c 0 Non-negative solution of=0.
As can be seen from the equations (46) and (50), the maximum value of the range of the wind field and the flexible-straight induction band is positive infinity, and the range of the capacitive band is limited, so that the induction band is wider than the information of the capacitive band, and the available voltage and current information of different frequency bands is more. As can be seen from the combination of the equation (50) and the equation (51), the maximum value of the frequency band of the larger transient component is positive infinity, so that the overlapping area of the inductive frequency band and the frequency band of the larger transient component is larger, and therefore, in the embodiment, the appropriate frequency harmonic is selected, and the protection principle is constructed by utilizing the fault component network composed of the transient model exhibiting the resistance.
It can be understood that in the embodiment, a wind turbine generator fault transient frequency domain model and an MMC converter fault transient frequency domain model are established based on wind turbine generator and soft direct current converter electrical parameters and control links, and characteristic frequency bands of the wind turbine generator and the MMC converter are accurately analyzed;
when a fault occurs in the outgoing line area, the fault component network of the wind field flexible straight outgoing system is shown in FIG. 11, in which Z DFIG Is wind field transient equivalent impedance; z is Z mmc Is MMC transient equivalent impedance; z is Z mn To send out line impedance; a is the fault location percentage; r is R f Is a transition resistance.
As can be seen from fig. 11, the voltage and current on the feeding line M side have the following relationship:
in the formula ,I′m 、I′ n Current measurements at the protective mounting on the side of the delivery line M, N are shown, respectively; u's' m 、U′ n The voltage measurements at the protection installation on the side of the outgoing line M, N are shown, respectively.
Thus, an inductance measurement value expression L on the send-out line M side is defined fm The method comprises the following steps:
in the formula ,RDFIG And Im represents an imaginary part, which is a fault equivalent resistance of the wind power plant.
Defining inductance measurement value expression L on N side of transmission line fn The method comprises the following steps:
in the formula ,Rmmc Is the fault equivalent resistance of the MMC converter station, L mmc And the fault equivalent reactance of the MMC converter station.
When a fault occurs in the outgoing line area, there are:
in the formula ,aLmn (ω f ) To send out the difference between the measured value and the calculated value of the inductance on the M side of the line, (1-a) L mn (ω f ) To send the difference between the measured value and the calculated value of the inductance on the N side of the line, the value is correlated with the fault location a.
When a fault occurs outside the M side area of the delivery line, taking the fault of the back side outlet of the M side bus as an example, the fault component network of the wind field flexible direct delivery system is shown in fig. 12.
As can be seen from fig. 12, the voltage and current on the transmission line M side have the following relationship:
in the formula ,If For passing through the resistor R f Fault current to ground.
When an out-of-zone fault occurs on the send-out line M side, there are:
when the back side outlet of the bus on the M side of the sending line fails, the measured value of the inductance on the M side of the sending line deviates from the calculated value, the difference value is large, the measured value of the inductance on the N side of the sending line approaches to the calculated value, and the difference value is small.
When a fault occurs outside the N-side area of the outgoing line, taking an example of a fault occurring at the back side outlet of the N-side bus of the outgoing line, a fault component network of the wind field flexible direct outgoing system is shown in fig. 13.
As can be seen from fig. 13, the voltage and current on the transmission line M side have the following relationship:
in the formula ,If Fault current flowing to the ground point through the transition resistor Rf.
When a fault occurs outside the N-side area of the outgoing line, there are:
when the back side outlet of the bus on the N side of the sending line fails, the measured value of the inductance on the N side of the sending line deviates from the calculated value, the difference value is large, the measured value of the inductance on the M side of the sending line approaches to the calculated value, and the difference value is small.
According to the analysis, when faults occur in the outgoing line area, the inductance measured values protected on the two sides of the line are consistent with the calculated values, and the theoretical error is 0. When an out-of-zone fault occurs on the back side system of the outgoing line bus, the inductance measured value of the bus side protection does not accord with the actual value, and the difference is large.
Therefore, the failure recognition is performed by the high-frequency inductance difference coefficient on the side of the send-out line M, N, and the two-side high-frequency inductance difference coefficient is expressed as:
in the formula ,Sm (ω f )、S n (ω f ) Respectively show that the high frequency component frequency at the side of the transmission line M, N is omega f The high-frequency inductance difference coefficient at the time of failure is H, which represents the sampling point number in one period after failure occurs, L fm,h (ω f )、L fn,h (ω f ) Respectively show that the transmission line M, N side is at the h sampling point and the high-frequency component frequency is omega f Inductance measurement at the time, L DFIG (ω f )、L mmc (ω f ) Respectively show that the high frequency component frequency at the side of the transmission line M, N is omega f Inductance calculation at that time.
The inductance measurement value of the transmitting line M, N is calculated according to the M, N side voltage and current data; l (L) mmc Calculated by the formula (45), L DFIG Calculated from equation (49).
In summary, the configurable fault identification criteria include:
in the formula ,Sset (ω f ) Indicating that the frequency of the high-frequency component is omega f A time action threshold value;
if S m (ω f) and Sn (ω f ) If the fault identification criteria are met, judging that the faults in the line area are sent out; otherwise, judging that the fault outside the sending line area exists; wherein,
if S m (ω f ) If the fault recognition criterion is not met, judging that the back side system of the bus on the M side of the sending line fails;
if S n (ω f ) And if the fault identification criterion is not met, judging that the back side system of the N side bus of the sending line fails.
Further, the action threshold is determined by the following derivation:
when a fault occurs in the outgoing line area, the value of the fault identification criterion on the outgoing line M, N side is as follows:
the maximum possible fault recognition criteria when faults occur in the outgoing line area are:
when a fault occurs outside the area of the delivery line M, the following steps are included:
when a fault occurs outside the N side area of the sending line, the following steps are included:
from the analysis of equations (63) and (64), when a fault occurs outside the outgoing line area, the protection criterion on one side is close to 0, and the value of the protection criterion on the other side is larger.
When faults occur outside the line area, the fault identification criterion value of the side with the larger fault identification criterion value is as follows:
let the possible maximum value S of fault recognition criterion of the district in max The protection criterion value Sex of the side with larger out-of-zone fault protection criterion value is larger than the action threshold value.
Therefore, according to the fault identification criterion values in and out of the area, determining the action threshold value by the following modes:
let the percentage of fault locations on the outgoing line be denoted as a; wherein, the value range of a is 0-100%;
by changing the value of a in the following formula, a motion threshold value set is obtained
wherein ,
in the formula ,Sset,a (ω f ) Indicating a failure position percentage of a high frequency component frequency omega on the side of the delivery line M, N f Action threshold value at the time, L fm,h′ (ω f ) Indicating that the feeding line M side is at an arbitrary sampling point h' and the frequency of the high-frequency component is omega f Inductance measurement at time;
selecting action threshold value setAs a maximum or minimum value at the high frequency component frequency omega f Action threshold S at that time set (ω f )。
It should be noted that, fault identification can be realized by selecting the maximum value or the minimum value, and whether the maximum value or the minimum value is selected as an action threshold value can be determined according to specific requirements, namely, the determination is performed by weighing the requirements of fault identification inside and outside the area; the maximum value is selected as an action threshold value, so that the fault identification coverage in the area is more comprehensive; and if the minimum value is selected as the action threshold value, the out-of-zone fault identification coverage is more comprehensive.
Alternatively, L can also be obtained by mn (ω f )：
in the formula ,Lfm,h′ (ω f ) Indicating that the transmitting line N side is at an arbitrary sampling point h' and the frequency of the high-frequency component is omega f Inductance measurement at that time.
According to the analysis, the value in the fault recognition criterion is related to the selected high-frequency component frequency, and in the embodiment, when faults exist inside and outside the area, the difference of the fault recognition criterion is the maximum value, and the provided protection method has better effect, and the value of the high-frequency component frequency is determined by the following method:
construction of a function f (omega) of the protection criterion with respect to the frequency of the high-frequency component f )：
f(ω f )＝(L mmc (ω f )-L DFIG (ω f )) 2 (68)
Meanwhile, the selected high-frequency component frequency meets the requirement of the wind field and the flexible straight model for presenting the sensibility, so that the function in the formula (62) is analyzed, and each maximum value point is taken as follows:
ω m ＝{ω f |f'(ω f )＝0,f”(ω) f ＜0} (69)
calculate comparative ω m The magnitude of each high-frequency component frequency in the set is selected to be the maximum value in the setAs a high-frequency component frequency value, i.e.
In the formula, max () means taking the maximum value.
Illustratively, the selection is made taking into account various factors
It will be appreciated that the high frequency component frequency is valued asThe fault identification criterion difference can be maximized when faults exist inside and outside the area, and the protection method in the embodiment has better effect.
Preferably, in this embodiment, the actually selected action threshold may be slightly larger than the result calculated by equation (66) in consideration of the influence of factors such as measurement error and noise drying.
More preferably, the operation threshold value is set to 500 in the present embodiment.
Compared with the prior art, the line protection method of the new energy through the flexible direct delivery system, provided by the embodiment, acquires data under high-frequency component frequency by collecting data after faults occur, further obtains high-frequency inductance difference coefficients, and then identifies faults in and out of a region, accurately identifies faults inside and outside the region, only needs judging results of fault directions transmitted by two sides of a line instead of electrical quantity information, has lower requirement on data synchronism, and well solves the problem that the new energy is incorrectly protected through the flexible direct delivery system line; the high-resistance fault-tolerant resistor has strong tolerance to fault resistance and high sensitivity to high-resistance faults at the tail end of a line.
Example 2
An embodiment 2 of the present application provides a line protection system for a new energy via a flexible direct delivery system, including:
the data acquisition module is used for acquiring the voltage and the current of the two sides of the line sent out by the new energy source through the flexible direct-current external transmission system after the fault occurs, and further extracting the frequency omega of the high-frequency component f Voltage and current at that time;
a high-frequency inductance difference coefficient module for providing omega-frequency components on both sides of the feeding line f The voltage and current at the time of obtaining omega in the frequency of the high-frequency component f The high-frequency inductance difference coefficients at the two sides of the sending-out line;
a fault recognition module for recognizing the frequency omega of the high-frequency component f When the high-frequency inductance difference coefficients and fault identification criteria at the two sides of the sending line are used, determining whether an in-area fault of the sending line occurs or not;
and the action protection module is used for starting the protection action of the sending out line if the fault occurs in the area of the sending out line.
The specific implementation process of the embodiment of the present application may be referred to the above method embodiment, and this embodiment is not described herein.
Since the principle of the embodiment is the same as that of the embodiment of the method, the system also has the corresponding technical effects of the embodiment of the method.
Example 3
To verify the correctness of the embodiments 1 and 2 of the present application, the present embodiment performs experimental verification on the schemes in the above embodiments. The system structure diagram adopted in the embodiment is shown in fig. 2, and main parameters of the wind field flexible straight delivery system are shown in table 1. Selection of ω in simulation verification f ＝950Hz。
TABLE 1 Main parameters of wind field Flexible direct delivery System
Scenario 1 set in this embodiment is: setting the high-frequency inductance difference coefficient S of the protection installation position on the side of the delivery line M, N under the conditions of 0-300 omega of transition resistance when the A-phase grounding fault, the BC two-phase interphase fault and the ABC three-phase fault occur at 50% of the delivery line area m 、S n As shown in fig. 14. Wherein, fault Resistance represents the transition Resistance.
As can be seen from fig. 14 (a), 14 (b), 14 (c), 14 (d), 14 (e) and 14 (f), under different fault types, S m and Sn The faults are all smaller than the action threshold value, and the faults are identified as faults of the collecting lines in the area. As can be seen from fig. 14 (a) and 14 (b), when a phase a ground fault occurs, S m At t=1.5 ms, the transition resistance is 300 Ω, which takes a maximum value of 22.55806; s is S n At t=1.1 ms the transition resistance 300 Ω is taken to be a maximum value of 24.46. As can be seen from FIGS. 14 (c) and 14 (d), S m A maximum value of 23.58 is reached at t=3.4 ms transition resistance 75Ω; s is S n At t=1.7 ms, the transition resistance 300 Ω is at a maximum value of 22.62. As can be seen from FIGS. 14 (e) and 14 (f), S m At t=1.8 ms, the transition resistance 0Ω is at a maximum value of 23.00; s is S n At t=1.1 ms, the transition resistance 0Ω is at a maximum value of 25.21. Due to S m and Sn The maximum values of (a) are smaller than the action threshold value, and satisfy S m <S set ,S n <S set So that all of the above types of faults can be identified as intra-zone faults.
According to the analysis, when faults of different transition resistances occur in the outgoing line, the method provided by the embodiment can accurately identify faults in the area, and has strong high resistance tolerance.
Scenario 2 set in this implementation is: the BC two-phase grounding faults are respectively generated at different positions in the sending-out line area, the transition resistance is 150Ω, and the high-frequency inductance difference coefficient S of the protection installation position at the side of the sending-out line M, N under the fault condition m 、S n As shown in fig. 15.
As can be seen from fig. 15 (a) and 15 (b), when a BC two-phase ground fault occurs, S m At t=9.9 ms, the maximum value is reached at the time of line end failure of the outgoing line, which is 74.1; s is S n The maximum value is taken at the time of t=3.6 ms of the fault of the first section of the outgoing line, which is 77.52, due to S m and Sn The maximum values of (a) are smaller than the action threshold value, and satisfy S m <S set ,S n <S set So that all of the above types of faults can be identified as intra-zone faults.
According to the analysis, the method provided by the embodiment can accurately judge faults in the area when faults at different positions of the line are sent out, and has higher sensitivity when high-resistance faults occur at the tail end of the line.
Scene 3 set in this embodiment is: let f in FIG. 2 2 At the position, the outlet on the back side of the M-side bus generates three-phase ground faults, and the change range of the transition resistance is 0-300 omega. High-frequency inductance difference coefficient S of the delivery line M, N side protection installation part under fault condition m 、S n As shown in fig. 16.
As can be seen from fig. 16 (a) and 16 (b), when the back side outlet of the M-side bus bar has a ground fault, S m The value of (2) is always higher than the action threshold value, and the minimum value is obtained when t=9.6 ms and the transition resistance is 300 omega, and the value is 4280; s is S n The value of (2) is always lower than the operation threshold, and the minimum value is taken at t=3.5 ms and the transition resistance is 0Ω, which is 13.67. Because of S m >S set ,S n <S set And judging that the fault is out of the area, and protecting the fault from action.
According to the analysis, when faults passing through different transition resistances occur outside the wind field side area of the sending line, the method provided by the application can accurately judge the faults outside the area and prevent protection misoperation.
Scene 4 set in this embodiment is: let f in FIG. 2 3 The fault of different transition resistances occurs in 50% of the soft direct current circuit, and the change range of the transition resistance is 0-300 omega. High frequency inductance difference at the delivery line M, N side protection installation in the event of such a faultCoefficient S m 、S n As shown in fig. 17.
As can be seen from fig. 17 (a) and 17 (b), when 50% of the soft dc line fails, S m The value of (2) is always lower than the action threshold value, and the maximum value is obtained when t=10.0 ms and the transition resistance 225 omega is 7.07; s is S n The value of (2) is always higher than the operation threshold, and at t=9.0 ms, the transition resistance 300 Ω assumes a minimum value of 3137.87. Because of S m <S set ,S n >S set And judging that the fault is out of the area, and protecting the fault from action.
According to the analysis, the method provided by the embodiment can accurately judge the fault to be out of the area when the soft direct current circuit goes through different transition resistance faults, prevents protection misoperation, and has strong high resistance tolerance.
Those skilled in the art will appreciate that all or part of the flow of the methods of the embodiments described above may be accomplished by way of a computer program to instruct associated hardware, where the program may be stored on a computer readable storage medium. Wherein the computer readable storage medium is a magnetic disk, an optical disk, a read-only memory or a random access memory, etc.
The present application is not limited to the above-mentioned embodiments, and any changes or substitutions that can be easily understood by those skilled in the art within the technical scope of the present application are intended to be included in the scope of the present application.
Claims (10)
1. A new energy line protection method through a flexible direct delivery system is characterized by comprising the following steps:
collecting new energy after fault occurrence, sending out voltage and current at two sides of the line by a flexible direct-current sending system, and further extracting the frequency omega of the high-frequency component f Voltage and current at that time;
based on the two sides of the feeding line, the frequency of the high-frequency component is omega f The voltage and current at the time of obtaining omega in the frequency of the high-frequency component f The high frequency inductance difference at the two sides of the sending lineCoefficients;
according to the frequency omega of the high frequency component f When the high-frequency inductance difference coefficients and fault identification criteria at the two sides of the sending line are used, determining whether an in-area fault of the sending line occurs or not; if yes, the protection action of the sending-out line is started.
2. The method for protecting the new energy source line through the flexible direct delivery system according to claim 1, wherein one side of a wind power plant of the delivery line is an M side, and one side of the flexible direct delivery system is an N side; the high frequency inductance difference coefficient at both sides of the outgoing line is obtained by:
obtaining the frequency omega of the high-frequency component in the fault transient process according to the system structure and fault analysis of the side of the sending line M, N f The equivalent total impedance of the wind power plant and the equivalent impedance of the MMC converter at the time of the wind power plant are obtained, and the frequency of the high-frequency component at the side of the transmitting line M, N is omega f Inductance calculation value at the time;
on the basis of the feeding line M, N side, the frequency of the high-frequency component is omega f The voltage and current at this time are obtained to give ω as the high frequency component frequency of the transmission line M, N side f Inductance measurement at time;
on the basis of the feeding line M, N side, the frequency of the high-frequency component is omega f The inductance calculated value and the inductance measured value at the time of the time are obtained to obtain the frequency omega of the high frequency component on the side of the transmitting line M, N f The high frequency inductance difference coefficient.
3. The line protection method of a new energy source through-flexible direct delivery system according to claim 2, wherein the delivery line M, N side has a high frequency component frequency of ω f The high frequency inductance difference coefficients at the time are respectively expressed as:
in the formula ,Sm (ω f )、S n (ω f ) Respectively show that the high frequency component frequency at the side of the transmission line M, N is omega f When (1)The high-frequency inductance difference coefficient, H represents the sampling point number in one period after the fault occurs, L fm,h (ω f )、L fn,h (ω f ) Respectively represent that the high frequency component frequency of the transmission line M, N side at the h sampling point is omega f Inductance measurement at the time, L DFIG (ω f )、L mmc (ω f ) Respectively show that the high frequency component frequency at the side of the transmission line M, N is omega f Inductance calculation at that time.
4. The line protection method of a new energy source through flexible direct delivery system according to claim 3, wherein the frequency of the high-frequency component is ω f The fault identification criteria include:
in the formula ,Sset (ω f ) Indicating that the frequency of the high-frequency component is omega f A time action threshold value;
if S m (ω f) and Sn (ω f ) If the fault identification criteria are met, judging that the faults in the line area are sent out; otherwise, judging that the fault outside the transmission line area is sent out.
5. The method according to claim 4, wherein if it is determined that the outgoing line is out of zone fault, then
If S m (ω f ) If the fault recognition criterion is not met, judging that the back side system of the bus on the M side of the sending line fails;
if S n (ω f ) And if the fault identification criterion is not met, judging that the back side system of the N side bus of the sending line fails.
6. The line protection method of a new energy source through a flexible direct delivery system according to claim 4, wherein the frequency of the high frequency component is ω is obtained by f Action threshold in timeValue S set (ω f )：
Let the percentage of fault locations on the outgoing line be denoted as a; wherein, the value range of a is 0-100%;
by changing the value of a in the following formula, a motion threshold value set is obtained
wherein ,
in the formula ,Sset,a (ω f ) Indicating a failure position percentage of a high frequency component frequency omega on the side of the delivery line M, N f Action threshold value at the time, L fm,h′ (ω f ) Indicating that the feeding line M side is at an arbitrary sampling point h' and the frequency of the high-frequency component is omega f Inductance measurement at time;
selecting action threshold value setAs a maximum or minimum value at the high frequency component frequency omega f Action threshold S at that time set (ω f )。
7. The line protection method of a new energy source through-flexible direct delivery system according to claim 4, wherein the high-frequency component frequency ω f Take the value ofThe +.>
wherein ,
ω m ＝{ω f |f'(ω f )＝0,f”(ω) f ＜0}
f(ω f )＝(L mmc (ω f )-L DFIG (ω f )) 2
in the formula, max () means taking the maximum value.
8. The line protection method of a new energy source through-flexible direct delivery system according to claim 7, wherein the delivery line M side has a frequency ω of high frequency component f Inductance calculated value L at the time DFIG (ω f ) Expressed as:
in the formula ,c9 、c 7 、c 5 、c 3 、c 1 、d 8 、d 6 、d 4 、d 2 、d 0 The constant calculated from the element parameters on the side of the feeding line M is shown.
9. The line protection method of a new energy source through-flexible direct delivery system according to claim 7, wherein the delivery line N side has a frequency ω of high frequency component f Inductance calculated value L at the time mmc (ω f ) Expressed as:
in the formula ,a7 、a 5 、a 3 、a 1 、b 6 、b 4 、b 2 、b 0 The constant calculated from the parameters of each element on the side of the transmission line N is shown.
10. A new energy line protection system of a flexible direct delivery system is characterized by comprising:
the data acquisition module is used for acquiring the voltage and the current of the two sides of the line sent out by the new energy source through the flexible direct-current external transmission system after the fault occurs, and further extracting the frequency omega of the high-frequency component f Voltage and current at that time;
a high-frequency inductance difference coefficient module for providing omega-frequency components on both sides of the feeding line f The voltage and current at the time of obtaining omega in the frequency of the high-frequency component f The high-frequency inductance difference coefficients at the two sides of the sending-out line;
a fault recognition module for recognizing the frequency omega of the high-frequency component f When the high-frequency inductance difference coefficients and fault identification criteria at the two sides of the sending line are used, determining whether an in-area fault of the sending line occurs or not;
and the action protection module is used for starting the protection action of the sending out line if the fault occurs in the area of the sending out line.
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