A method and device for protecting a flexible low-frequency transmission system for sending out offshore wind power, a storage medium and an electronic device

Abstract

The present application relates to the technical field of power system relay protection, and particularly relates to a kind of offshore wind power through flexible low-frequency transmission system sending out line protection method, offshore wind farm is connected with modular multi-level matrix converter after being sent out by low-frequency through booster transformer, and is incorporated into large power grid after being frequency converted by M3C. When M3C of offshore wind farm fails, negative sequence current suppression and positive sequence current limiting strategy are adopted for fault ride-through, and relay protection devices are installed at both ends of low-frequency sending out line and communicate. The current sampling values before and after the fault on both sides of the line are reconstructed in phase space, and the difference between the permutation entropies is used to construct a protection scheme, which overcomes the problem of sensitivity reduction of traditional current differential protection for sending out line, reduces the amount of data interaction, and reduces the pressure of protection communication and the requirement of data synchronization. It is not affected by the control strategy of wind turbine and modular multi-level matrix converter at both ends of the line, fault ride-through mode, transition resistance and fault location, and has high reliability and good speed.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection technology, and in particular to a method, apparatus, storage medium and electronic device for protecting the outgoing lines of offshore wind power transmitted through a flexible low-frequency transmission system. Background Technology

[0002] With the development of wind power generation technology, large-capacity long-distance offshore wind power is the future trend of offshore wind power generation. Flexible frequency division transmission system has strong competitive potential in large-scale long-distance offshore wind power transmission scenarios and has gradually become one of the mainstream solutions for large-scale and efficient transmission of long-distance offshore wind power.

[0003] Since both ends of the low-frequency transmission line are power electronic devices, the fault characteristics of the low-frequency transmission line have changed fundamentally compared with the traditional power system based on synchronous machines. It exhibits non-traditional fault characteristics such as amplitude limitation and phase angle deviation. Traditional current differential protection faces severe challenges such as reduced sensitivity and possible failure of protection to operate in the fault zone. There is an urgent need to propose a new protection scheme to ensure the safe operation of the flexible low-frequency system. Summary of the Invention

[0004] This invention provides a protection method for the outgoing lines of offshore wind power transmitted through a flexible low-frequency transmission system, which can effectively solve the problems in the background art.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for protecting the outgoing lines of offshore wind power transmission systems via flexible low-frequency transmission systems includes the following steps:

[0007] Real-time acquisition of current data on both sides of the outgoing line of the flexible low-frequency power transmission system and calculation of current similarity; protection is activated when the current similarity meets the activation criterion.

[0008] Based on the current data from both sides of the transmission line of the flexible low-frequency power transmission system, a current sampling sequence I is constructed. X I Y and reference current sampling sequence

[0009] Phase spaces X and X' are constructed based on the current sampling sequence and the reference current sampling sequence. 0 and Y, Y 0 ;

[0010] The phase spaces X and X' are calculated using the protection devices on both sides of the transmission line of the flexible low-frequency power transmission system. 0 and Y, Y 0 The set of index values ​​Q, Q' corresponding to all phase point elements. 0 and W, W 0 ;

[0011] The arrangement entropy of the two phase spaces on the same side of the outgoing line of the flexible low-frequency power transmission system is calculated, and the ratio of the arrangement entropy on the same side is calculated.

[0012] The ratio of the arrangement entropy on both sides of the outgoing line of the flexible low-frequency power transmission system is transmitted to the other side, and fault identification and judgment are performed inside and outside the zone.

[0013] When the protection devices on both sides of the outgoing line of the flexible low-frequency transmission system determine that it is a single-phase ground fault, the protection devices will operate to disconnect the faulty phase; when it is determined to be a two-phase or three-phase fault, the protection devices will directly operate to disconnect all three phases.

[0014] Furthermore, the real-time acquisition of current data on both sides of the flexible low-frequency transmission line of the low-frequency transmission system and the calculation of current similarity, and the activation of protection when the current similarity meets the activation criterion, includes constructing current sampling sequences I on both sides respectively. k and I k-4m The similarity between the two current sampling sequences is calculated using the following formula:

[0015]

[0016] The protection activation criterion uses the following formula:

[0017] η(I k I k-4m )<η set ;

[0018] Where i(t) k ) for t k The instantaneous sampled value of the current at time t k (k∈N) represents the relative time value formed after the protection device's sampling initialization is completed, where k represents the sampling sequence number of the device. The sequence number is incremented by one for each sampling. η set The protection activation criterion setting value, m represents the number of data points in the data window corresponding to a quarter of a low-frequency cycle.

[0019] Furthermore, the protection device on the sending line side of the flexible low-frequency transmission system takes the current sampling time t. k As the reference time, the instantaneous current samples within the preceding quarter of a low-frequency cycle are used to form the current sampling sequence I. k ;

[0020] Simultaneously, the protection device on this side takes a low-frequency period before sampling (t). k -T l Using this as the reference time, and taking the instantaneous current samples from the preceding quarter of a low-frequency cycle to form the current sampling sequence I. k-4m ;

[0021] The number of data points in the data window corresponding to a quarter of a low-frequency cycle is m = 0.25f.s / f l , where f l f represents the current frequency in a low-frequency power transmission system. s T represents the sampling frequency. l T represents the current period of a low-frequency power transmission system. s Indicates the sampling period;

[0022] The protection device on the other side of the transmission line of the flexible low-frequency transmission system also constructs two current sampling sequences.

[0023] Furthermore, the current sampling sequence I is constructed based on the current data on both sides of the low-frequency transmission line. X I Y and reference current sampling sequence In this system, the protection devices on both sides of the outgoing line of the flexible low-frequency transmission system take the instantaneous current sampling values ​​within half a low-frequency cycle before the protection is activated to form the current sampling sequence I. X I Y Simultaneously, the instantaneous current sampling values ​​within the half-low-frequency cycle corresponding to the moment before the protection starts to the moment before the protection starts are taken to form a reference current sampling sequence. The details are as follows:

[0024]

[0025] Among them, I X I Y , All are 2m-dimensional row vectors.

[0026] Furthermore, the phase space X, X' is constructed based on the current sampling sequence and the reference current sampling sequence. 0 and Y, Y 0 Specifically, the phase space X and X' is constructed on both sides of the transmission line of the flexible low-frequency transmission system based on the current sampling sequence and the reference current sequence through the protection devices on both sides of the transmission line. 0 and Y, Y 0 The details are as follows:

[0027]

[0028]

[0029] Where τ is the delay factor, representing the index of the instantaneous current sample value shifted backward from the current sampling sequence, p = 2m - (n-1)τ, X, X 0 and Y, Y 0 Both are p×n matrices.

[0030] Furthermore, for the two phase spaces X and X on the same side of the outgoing line of the flexible low-frequency transmission system...0 The permutation entropy calculation includes the following steps:

[0031] Phase space X, X 0 any phase point They are respectively recorded as:

[0032]

[0033] According to X respectively i , The instantaneous sampled values ​​of the intermediate current are sorted in ascending order, and their corresponding sequence numbers are renumbered to obtain the phase space X, X'. 0 The set of index values ​​Q, Q' corresponding to all phase point elements. 0 ;

[0034] For the index value sequence set Q, Q 0 For identical phase point index value sequences, remove duplicate index value sequences to obtain a new set of index value sequences Q′ and Q′. 0 ;

[0035] Calculate the phase point index value sequences in the new phase point index value sequence set in the original index value sequence set Q, Q'. 0 The probability of occurrence in the phase space X and X' is used to obtain the phase space X and X''. 0 The permutation entropy.

[0036] Furthermore, phase space X, X 0 The set of index value sequences Q and Q' corresponding to all phase point elements in the set. 0 As shown below:

[0037]

[0038] Where, q ij , i x (t k-2m+i+(j-1)τ ), i x (t k-6m+i+(j-1)τ The index value of ), that is, the index value of the current sample at phase point X. i , All sampled values ​​are sorted in ascending order by their corresponding index numbers.

[0039] Furthermore, based on the index value sequence set, the arrangement entropy of the two phase spaces on the same side of the flexible low-frequency transmission line is calculated, and the ratio of the arrangement entropy on the same side is calculated. The phase spaces X and X' are calculated respectively using the following formula. 0 Permutation entropy:

[0040]

[0041]

[0042] Among them, the new index value sequence sets Q′ and Q′ 0 The probabilities of the occurrence of each phase point index value sequence are denoted as follows: and num(Q′), num(Q′) 0 ) represent the new set of phase point index value sequences Q′ and Q′, respectively. 0 The number of elements in the sequence set or the number of rows in the matrix, where 1 ≤ num(Q′) ≤ p and 1 ≤ num(Q′) ≤ p. 0 )≤p;

[0043] The sequence of phase point index values ​​Q′ i , In the original index value sequence set Q, Q 0 The number of times it appears in all row vector sequences

[0044] Furthermore, regarding the two phase spaces Y and Y on the other side of the flexible low-frequency transmission line, 0 The permutation entropy calculation includes the following steps:

[0045] Phase space Y, Y 0 The instantaneous current sampling values ​​at any phase point are sorted in ascending order, and the corresponding sequence numbers are renumbered. Furthermore, the index value sequence is deduplicated to obtain a new set of index value sequences W′ and W′. 0 ;

[0046] Calculate the probability of each phase point index value sequence appearing in the new phase point index value sequence set to obtain the permutation entropy of the phase space Y, and then calculate the phase space Y. 0 The probability of the occurrence of all different phase point index value sequences is used to obtain the phase space Y. 0 The permutation entropy.

[0047] The phase spaces Y and Y are calculated using the following formulas. 0 Permutation entropy:

[0048]

[0049]

[0050] Among them, the new index value sequence sets W′ and W′ 0 The probabilities of the occurrence of each phase point index value sequence are denoted as follows: num(W′), num(W′) 0 W' and W'' represent the new set of phase point index value sequences, respectively. 0 The number of elements in the sequence set or the number of rows in the matrix, where 1 ≤ num(W′) ≤ p and 1 ≤ num(W′) ≤ p.0 )≤p;

[0051] num(W i ')and The sequence of phase point index values ​​W i ′、 In the original index value sequence set W, W 0 The number of times it appears in all row vector sequences

[0052] Furthermore, the ratio of the arrangement entropy on both sides of the flexible low-frequency transmission line is transmitted to the other side via a communication channel, and fault identification is performed using the following formula:

[0053]

[0054] in: P represents the ratio of the arrangement entropy of the phase spaces constructed based on the sampled currents on both sides. E-set The setpoint for the entropy difference action is the permutation entropy difference.

[0055] A protection device for the outgoing line of an offshore wind power transmission system via a flexible low-frequency transmission system includes:

[0056] The data acquisition module is used to collect current data on both sides of the outgoing line of the flexible low-frequency power transmission system in real time.

[0057] The fault determination module is used to calculate the ratio of the arrangement entropy on both sides of the outgoing line of the flexible low-frequency power transmission system and to identify and determine faults inside and outside the zone.

[0058] The communication module is used to transmit the ratio of the arrangement entropy on both sides of the transmission line of the flexible low-frequency power transmission system to the other side;

[0059] The line protection module is used to disconnect the faulty phase when the fault determination module determines that it is a single-phase ground fault; when the fault determination module determines that it is a two-phase or three-phase fault, it directly disconnects the three phases through the relay protection devices at both ends of the low-frequency transmission line.

[0060] Furthermore, the line protection module also includes relay protection devices installed at both ends of the outgoing line of the flexible low-frequency power transmission system, and both relay protection devices are electrically connected to the fault determination module.

[0061] A computer-readable storage medium includes a stored program, wherein, when the program is executed, it controls the device containing the computer-readable storage medium to perform the above-described protection method for outgoing lines of offshore wind power via a flexible low-frequency transmission system.

[0062] An electronic device includes a memory and a processor, characterized in that the memory stores a computer program, and the processor is configured to execute the above-described method for protecting the outgoing lines of offshore wind power via a flexible low-frequency transmission system through the computer program.

[0063] The beneficial effects of this invention are as follows:

[0064] This invention proposes a protection method for outgoing lines of offshore wind power low-frequency transmission systems based on the current phase space arrangement entropy. The method reconstructs the phase space of the current sampling values ​​before and after the fault on both sides of the line, and constructs a protection scheme by utilizing the difference between their arrangement entropies. This overcomes the problem of decreased sensitivity of traditional current differential protection for outgoing lines of offshore wind power low-frequency transmission systems.

[0065] Compared to traditional current differential protection, this invention only exchanges the arrangement entropy ratio data of the sampled current phase space on each side, rather than the current quantity. This results in a small amount of data exchange, reducing the pressure on protection communication and the requirements for data synchronization. This method is unaffected by the control strategies of the wind turbines and modular multilevel matrix converters at both ends of the line, fault ride-through methods, transition resistance, and fault location. It boasts high reliability and fast response, making it suitable for the protection of outgoing lines in offshore wind power flexible low-frequency transmission systems, and possesses significant engineering application value. Attached Figure Description

[0066] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0067] Figure 1 This is a schematic diagram of the flexible low-frequency power transmission system for offshore wind power in this invention;

[0068] Figure 2 This is a schematic diagram of the process for protecting the outgoing line of a low-frequency offshore wind power transmission system according to the present invention.

[0069] Figure 3 This is a schematic diagram of the start criterion data sampling in this invention;

[0070] Figure 4 This is a schematic diagram of the sampling of the main criterion data in this invention. Detailed Implementation

[0071] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0072] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0073] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0074] This invention proposes a protection method for the outgoing lines of offshore wind power transmission systems via flexible low-frequency transmission systems, such as... Figure 1 The diagram shows a schematic of a flexible low-frequency transmission system for offshore wind power. The offshore wind farm's voltage is boosted by a step-up transformer and then connected to a Modular Multilevel Matrix Converter (M3C) via the flexible low-frequency transmission system's outgoing lines. After frequency conversion by the M3C, the voltage is connected to the main power grid. During M3C failures, the offshore wind farm employs negative-sequence current suppression and positive-sequence current limiting strategies for fault ride-through. Relay protection devices are installed at both ends of the flexible low-frequency transmission system's outgoing lines and are connected in communication.

[0075] The method for protecting the outgoing lines of offshore wind power through a flexible low-frequency transmission system disclosed in this invention includes the following steps:

[0076] Real-time acquisition of current data on both sides of the transmission line of the flexible low-frequency transmission system and calculation of current similarity; activation of protection when current similarity meets the activation criterion; construction of current sampling sequence I based on the current data on both sides of the transmission line of the flexible low-frequency transmission system. X I Y and reference current sampling sequence Phase spaces X and X' are constructed based on the current sampling sequence and the reference current sampling sequence. 0 and Y, Y 0 The phase space X and X' values ​​are calculated using the protection devices on both sides of the transmission line of the flexible low-frequency transmission system. 0 and Y, Y 0 The set of index values ​​Q, Q' corresponding to all phase point elements. 0 and W, W 0The arrangement entropy of the two phase spaces on the same side of the outgoing line of the flexible low-frequency transmission system is calculated, and the ratio of the arrangement entropy on the same side is calculated. The ratio of the arrangement entropy on both sides of the outgoing line of the flexible low-frequency transmission system is transmitted to the other side, and fault identification and judgment are performed inside and outside the zone. When the protection devices on both sides of the outgoing line of the flexible low-frequency transmission system determine that it is a single-phase ground fault, the protection devices will operate to disconnect the faulty phase. When it is determined to be a two-phase or three-phase fault, the three phases will be directly disconnected.

[0077] Specifically, the three-phase current is independently sampled in real time by current transformers on both sides of the transmission line of the flexible low-frequency transmission system. The current frequency of the low-frequency transmission system is f. l Hz, period T l =(1 / f l The sampling frequency is f. s Hz, sampling period is T s =(1 / f s The number of data points in the data window corresponding to a quarter of a low-frequency cycle is m = 0.25f. s / f l .

[0078] The protection device on the sending line side of the flexible low-frequency transmission system takes the current sampling time t. k As the reference time, the instantaneous current samples within the preceding quarter of a low-frequency cycle are used to form the current sampling sequence I. k Simultaneously, the protection device on this side takes a low-frequency period before sampling (t). k -T l Using this as the reference time, and taking the instantaneous current samples from the preceding quarter of a low-frequency cycle to form the current sampling sequence I. k-4m The protection device on the other side of the transmission line of the flexible low-frequency power transmission system also constructs two current sampling sequences.

[0079] Secondly, the real-time acquisition of current data on both sides of the flexible low-frequency transmission line of the low-frequency transmission system and the calculation of current similarity, and the activation of protection when the current similarity meets the activation criterion, includes constructing current sampling sequences I on both sides respectively. k and I k-4m Specifically, I k ={i(t) k-m+1 ), …, i(t) k-1 ), i(t k )}, I k-4m ={i(t) k-5m+1 ), …, i(t) k-4m-1 ), i(t k-4m The similarity between two current sampling sequences is calculated using the following formula:

[0080]

[0081] The protection activation criterion uses the following formula:

[0082] η(I k I k-4m )<η set ;

[0083] Where i(t) k ) for t k The instantaneous sampled value of the current at time t k (k∈N) represents the relative time value formed after the protection device sampling initialization is completed. If the initialization time t0=0, then t k =k·T s k represents the sampling sequence number of the device. The sequence number is incremented by one for each sampling. k and I k-4m Both current sampling sequences are m-dimensional row vectors, η set The activation criterion setting value for protection.

[0084] After the protection is activated, the current sampling sequence I is constructed based on the current data on both sides of the low-frequency output line. X I Y and reference current sampling sequence In this system, the protection devices on both sides of the outgoing line of the flexible low-frequency transmission system take the instantaneous current sampling values ​​within half a low-frequency cycle before the protection is activated to form the current sampling sequence I. X I Y Simultaneously, the instantaneous current sampling values ​​within the half-low-frequency cycle corresponding to the moment before the protection starts to the moment before the protection starts are taken to form a reference current sampling sequence. The details are as follows:

[0085]

[0086] Among them, I X I Y , All are 2m-dimensional row vectors.

[0087] The phase space X, X' is constructed based on the current sampling sequence and the reference current sampling sequence. 0 and Y, Y 0 Specifically, the phase space X and X' is constructed on both sides of the transmission line of the flexible low-frequency transmission system based on the current sampling sequence and the reference current sequence through the protection devices on both sides of the transmission line. 0 and Y, Y 0 The details are as follows:

[0088]

[0089] Where τ is the delay factor, representing the index of the instantaneous current sample value shifted backward from the current sampling sequence, p = 2m - (n-1)τ, X, X 0 and Y, Y 0 Both are p×n matrices.

[0090] For the two phase spaces X and X on the M3C side 0 The permutation entropy calculation includes the following steps:

[0091] Phase space X, X 0 Any phase point X i , (i∈N, 1≤i≤p) are respectively denoted as:

[0092]

[0093] According to X respectively i , The instantaneous sampled values ​​of the intermediate current are sorted in ascending order, and their corresponding sequence numbers are renumbered to obtain the phase space X, X'. 0 The set of index values ​​Q, Q' corresponding to all phase point elements. 0 The index value corresponding to the smallest sample value in the phase point is 1, and the index value corresponding to the largest sample value is n. For multiple sample values ​​of equal magnitude, the index value corresponding to the sample value sampled earlier is the smallest, and the index values ​​of the next sample values ​​are incremented by one.

[0094] Phase space X, X 0 The set of index value sequences Q and Q' corresponding to all phase point elements in the set. 0 As shown below:

[0095]

[0096] in, i x (t k-2m+i+(j-1)τ ), i x (t k-6m+i+(j-1)τ The index value of ), that is, the index value of the current sample at phase point X. i , All sampled values ​​are sorted in ascending order and their corresponding index numbers are q. ij ,

[0097] For the index value sequence set Q, Q 0 For identical phase point index value sequences, remove duplicate index value sequences to obtain a new set of index value sequences Q′ and Q′. 0 ; Calculate the phase point index value sequences in the new phase point index value sequence set in the original index value sequence set Q, Q 0 The probability of occurrence in the phase space X and X' is used to obtain the phase space X and X''.0 The permutation entropy.

[0098] Specifically, based on the index value sequence set, the permutation entropy of the two phase spaces on the same side of the outgoing line of the flexible low-frequency transmission system is calculated, and the ratio of the permutation entropy on the same side is calculated. The phase spaces X and X' are calculated respectively using the following formulas. 0 Permutation entropy:

[0099]

[0100]

[0101] Among them, the new index value sequence sets Q′ and Q′ 0 The probabilities of the occurrence of each phase point index value sequence are denoted as follows: num(Q′), num(Q′) 0 ) represent the new set of phase point index value sequences Q′ and Q′, respectively. 0 The number of elements in the sequence set or the number of rows in the matrix, where 1 ≤ num(Q′) ≤ p and 1 ≤ num(Q′) ≤ p. 0 )≤p;

[0102] num(Q i ')and The phase point index value sequence Q i ′、 In the original index value sequence set Q, Q 0 The number of times it appears in all row vector sequences

[0103] Similar to the M3C side, the wind farm side can also obtain the phase space Yi and Yi constructed from the current sampling sequence and the reference current sequence on that side. 0 The permutation entropy, specifically, for the two phase spaces Y and Y on the other side of the transmission line of the flexible low-frequency transmission system. 0 The permutation entropy calculation includes the following steps:

[0104] Phase space Y, Y 0 The instantaneous current sampling values ​​at any phase point are sorted in ascending order, and the corresponding sequence numbers are renumbered. Furthermore, the index value sequence is deduplicated to obtain a new set of index value sequences W′ and W′. 0 ;

[0105] Calculate the probability of each phase point index value sequence appearing in the new phase point index value sequence set to obtain the permutation entropy of the phase space Y, and then calculate the phase space Y. 0 The probability of the occurrence of all different phase point index value sequences is used to obtain the phase space Y. 0 The permutation entropy.

[0106] The phase spaces Y and Y are calculated using the following formulas.0 Permutation entropy:

[0107]

[0108] Among them, the new index value sequence sets W′ and W′ 0 The probabilities of the occurrence of each phase point index value sequence are denoted as follows: and num(W′), num(W′) 0 W' and W'' represent the new set of phase point index value sequences, respectively. 0 The number of elements in the sequence set or the number of rows in the matrix, where 1 ≤ num(W′) ≤ p and 1 ≤ num(W′) ≤ p. 0 )≤p;

[0109] num(W i ')and The sequence of phase point index values ​​W i ′、 In the original index value sequence set W, W 0 The number of times it appears in all row vector sequences

[0110] The ratio of the arrangement entropy on both sides of the outgoing line of the flexible low-frequency transmission system is transmitted to the other side through a communication channel, and fault identification is performed using the following formula:

[0111]

[0112] in: P represents the ratio of the arrangement entropy of the phase spaces constructed based on the sampled currents on both sides. E-set The setpoint for the entropy difference action is 0.2. When the absolute value of the difference between the calculated entropy ratios of the two sides exceeds the setpoint, it is considered that an intra-regional fault has occurred on the transmission line of the offshore wind power low-frequency transmission system.

[0113] As specific embodiments of the present invention, the following embodiments are only used to illustrate the technical solutions of the present invention more clearly, and should not be used to limit the scope of protection of the present invention.

[0114] like Figure 1 The diagram shows a schematic of a flexible low-frequency transmission system for offshore wind power. After being stepped up by a transformer, the offshore wind farm's power supply is connected to a Modular Multilevel Matrix Converter (M3C) via the flexible low-frequency transmission system's outgoing lines. The power is then converted by the M3C and connected to the main power grid. During M3C faults, the offshore wind farm employs negative-sequence current suppression and positive-sequence current limiting strategies for fault ride-through. Relay protection devices are installed at both ends of the flexible low-frequency transmission system's outgoing lines and are connected in communication.

[0115] A flowchart of a protection method for outgoing lines of offshore wind power low-frequency transmission systems based on current phase space arrangement entropy is shown below. Figure 2 As shown, the specific steps are as follows.

[0116] In a flexible low-frequency transmission system, current transformers on both sides of the outgoing line independently sample the three-phase current in real time. For a 20Hz low-frequency system, T l =50ms, f s =2000Hz, then T s =0.5ms, m=25.

[0117] like Figure 3 The diagram shows the start-up criterion current sampling data window. The protection devices on both sides of the line take the current sampling time t. k The instantaneous current samples within a quarter of a low-frequency cycle preceding the reference time constitute the current sampling sequence I. k And take a low-frequency period before the sampling time (t) k -T l The instantaneous current samples within a quarter of a low-frequency cycle preceding the reference time constitute the current sampling sequence I. k-100 There is: I k ={i(t) k-24 ), …, i(t) k-1 ), i(t k )}、I k-100 ={i(t) k-124 ), ..., (t k-101 ), i(t k-100 )},i(t k ) for t k The instantaneous sampled value of the current at time t k (k∈N) represents the relative time value formed after the protection device sampling initialization is completed. Assuming the initialization time is t0=0, then t k =k·T s k represents the sampling sequence number of the device; the sequence number is incremented by one for each sampling. k and I k-100 Both current sampling sequences are 25-dimensional row vectors. Independent comparison of protection starting elements on both sides of the line (I) k and I k-100 The similarity between these two current sampling sequences is calculated using the following algorithm:

[0118]

[0119] The criteria for initiating protection are:

[0120] η(I k I k-100 )<η set ;

[0121] Where: η set The activation criterion setting value for protection can be 0.8.

[0122] like Figure 4 The diagram shows a schematic of the protection criterion current sampling data window. After protection is initiated, the protection devices on both sides of the line take the instantaneous current sampling values ​​within half a low-frequency cycle before protection initiation to form the current sampling sequence I. X I Y Simultaneously, the instantaneous current sampling values ​​within the half-low-frequency cycle corresponding to the moment before the protection device starts to the moment before the start of the protection device are taken to form a reference current sampling sequence. I X I Y , Both are 50-dimensional row vectors, as follows:

[0123]

[0124] With each side protection device set to a delay factor τ = 5 and n = 5, p = 30 can be calculated. Correspondingly, the phase spaces X and X' constructed based on the current sampling sequence and the reference current sequence are... 0 and Y, Y 0 for:

[0125]

[0126]

[0127] X, X 0 and Y, Y 0 It is a 30×5 matrix.

[0128] M3C side respectively controls the two phase spaces X and X on this side. 0 Perform permutation entropy calculation.

[0129] For phase space matrices X and X, respectively 0 Each row vector (also called a phase point) X i , The instantaneous current samples in (i = 1, ..., 30) are renumbered according to their sequence numbers in ascending order of magnitude. The index of the smallest current sample at a phase point is 1, and the index of the largest sample is n. For multiple samples with equal magnitude, the sample with the earliest sampling time has the smallest index, and the indices of the next samples are incremented by one. This yields the phase spaces X, X', ..., X'. 0 The set of index values ​​Q, Q' corresponding to all phase point elements. 0 :

[0130]

[0131] Where: q ij , i x (t k-55+i+5j ), i x (t k-155+i+5j The index value of ), that is, the index value of the current sample at phase point X. i , All sampled values ​​are sorted in ascending order and their corresponding index numbers are q. ij ,

[0132] For example: X1 = [-2 0 4 2 -1], If X2 = [0 -2 -4 -2 3], then Q1 = [1 3 5 4 2]. Q2 = [4 2 1 3 5].

[0133] Assuming that the 30 phase points in phase space X generate 12 distinct index value sequences, the new set of index value sequences Q′ is a 12-row, 5-column matrix, Q′1 = [1 3 5 4 2], Q′2 = [4 2 1 3 5], num(Q′) = 12. Next, we calculate the probability of these 12 different index value sequences appearing.

[0134] For example, Q′ 0 If it appears 5 times in the index value sequence set, then Furthermore, the permutation entropy of phase space X can be obtained:

[0135]

[0136] Similarly, the phase space X can be calculated. 0 permutation entropy Similar to the M3C side, the wind farm side can also obtain the phase space Yi and Yi constructed from the current sampling sequence and the reference current sequence on that side. 0 permutation entropy

[0137] The ratio of the permutation entropy calculated on both sides is transmitted to the other side through a communication channel, and the difference in permutation entropy between the two sides is used for fault identification, as shown in the following formula:

[0138]

[0139] in: P represents the ratio of the arrangement entropy of the phase spaces constructed based on the sampled currents on both sides. E-set The setpoint for the permutation entropy difference action can be 0.2.

[0140] When the absolute value of the difference between the calculated entropy ratios of the two sides exceeds the set value, it is considered that an intra-regional fault has occurred on the transmission line of the offshore wind power low-frequency transmission system. When the protection devices on both sides determine that it is a single-phase ground fault, the protection devices will operate to disconnect the faulty phase. When it is determined to be a two-phase or three-phase fault, the protection devices will directly operate to disconnect all three phases.

[0141] This protection criterion data window only uses current data within half a low-frequency cycle and does not consider the delay of the communication channel. For a low-frequency system using 20Hz, the protection action time is 25ms.

[0142] This protection system only exchanges the ratio of the arrangement entropy of the phase space constructed from the sampled currents on each side. Compared to traditional current differential protection, which exchanges current sample data, the amount of data exchanged is reduced. Simultaneously, the ratio of the arrangement entropy of the phase space of the currents on each side reflects the change in the current sampled value within the first half of the low-frequency cycle data window and the current sampled value within the next half of the low-frequency cycle data window. Compared to traditional current differential protection, which requires differential current calculation using current data from both sides, the synchronization requirement for the current data on both sides is reduced.

[0143] This invention also discloses a protection device for the outgoing line of offshore wind power through a flexible low-frequency transmission system, comprising:

[0144] The data acquisition module is used to collect current data on both sides of the outgoing line of the flexible low-frequency power transmission system in real time.

[0145] The fault determination module is used to calculate the ratio of the arrangement entropy on both sides of the outgoing line of the flexible low-frequency power transmission system and to identify and determine faults inside and outside the zone.

[0146] The communication module is used to transmit the ratio of the arrangement entropy on both sides of the transmission line of the flexible low-frequency power transmission system to the other side;

[0147] The line protection module is used to disconnect the faulty phase when the fault determination module determines that it is a single-phase ground fault; when the fault determination module determines that it is a two-phase or three-phase fault, it directly disconnects the three phases through the relay protection devices at both ends of the low-frequency transmission line.

[0148] The line protection module also includes relay protection devices installed at both ends of the outgoing line of the flexible low-frequency power transmission system, and both relay protection devices are electrically connected to the fault determination module.

[0149] It is obvious to those skilled in the art that the modules or steps of the present invention described above can be implemented using general-purpose computing devices. They can be centralized on a single computing device or distributed across a network of multiple computing devices. They can be implemented using computer-executable program code, and thus can be stored in a storage device for execution by a computing device. In some cases, the steps shown or described can be performed in a different order than those described herein, or they can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. Thus, the present invention is not limited to any particular combination of hardware and software.

[0150] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0151] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0152] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0153] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0154] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0155] Memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0156] Computer-readable media includes both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic magnetic disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0157] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0158] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for protecting the outgoing lines of offshore wind power transmission systems via flexible low-frequency transmission systems, characterized in that, Includes the following steps: Real-time acquisition of current data on both sides of the outgoing line of the flexible low-frequency power transmission system and calculation of current similarity; protection is activated when the current similarity meets the activation criterion. Current sampling sequences were constructed based on current data from both sides of the transmission line of the flexible low-frequency power transmission system. , and reference current sampling sequence , ; Constructing a phase space based on the current sampling sequence and the reference current sampling sequence X , and Y , ; The phase space was calculated using the protection devices on both sides of the transmission line of the flexible low-frequency transmission system. X , and Y , The set of index values ​​corresponding to all phase point elements Q , and W , ; Based on the index value sequence set, the arrangement entropy of the two phase spaces on the same side of the outgoing line of the flexible low-frequency power transmission system is calculated, and the ratio of the arrangement entropy on the same side is calculated. The ratio of the arrangement entropy on both sides of the outgoing line of the flexible low-frequency power transmission system is transmitted to the other side, and fault identification and judgment are performed inside and outside the zone. When the protection devices on both sides of the outgoing line of the flexible low-frequency transmission system determine that it is a single-phase ground fault, the protection devices will operate to disconnect the faulty phase; when it is determined to be a two-phase or three-phase fault, the protection devices will directly operate to disconnect all three phases. The system involves real-time acquisition of current data from both sides of the outgoing line of the flexible low-frequency transmission system and calculation of current similarity. Protection is activated when the current similarity meets the activation criterion, including constructing current sampling sequences from both sides. and The similarity between the two current sampling sequences is calculated using the following formula: ； The protection activation criterion uses the following formula: ； in, for The instantaneous sampled value of the current at time t. This is the relative time value formed after the protection device's sampling initialization is completed. k represents the sampling sequence number of the device; the sequence number is incremented by one for each sampling. The protection activation criterion setting value, m represents the number of data points in the data window corresponding to a quarter of a low-frequency cycle; The current sampling sequence is constructed based on the current data from both sides of the transmission line of the flexible low-frequency power transmission system. , and reference current sampling sequence , In this system, the protection devices on both sides of the outgoing line of the flexible low-frequency transmission system take the instantaneous current sampling values ​​within half a low-frequency cycle before the protection is activated to form a current sampling sequence. , Simultaneously, the instantaneous current sampling values ​​within the half-low-frequency cycle corresponding to the moment before the protection starts to the moment before the protection starts are taken to form a reference current sampling sequence. , The details are as follows: ； ； in, , , , All are 2m-dimensional row vectors; The phase space is constructed based on the current sampling sequence and the reference current sampling sequence. X , and Y , Specifically, the phase space is constructed based on the current sampling sequence and the reference current sequence through the protection devices on both sides of the transmission line of the flexible low-frequency transmission system. X , and Y , The details are as follows: ； ； in, τ The delay factor represents the index of the instantaneous current sample value shifted backward from the current sampling sequence. p =2 m -( n -1) τ , X , and Y , All p × n Matrix; For the two phase spaces on the same side of the outgoing line of the flexible low-frequency transmission system X , The permutation entropy calculation includes the following steps: Phase space X , any phase point , They are respectively recorded as: ； According to , The instantaneous sampled values ​​of the intermediate current are sorted in ascending order, and their corresponding sequence numbers are renumbered to obtain the phase space. X , The set of index values ​​corresponding to all phase point elements Q , ,in, ; For the set of index values Q , For identical phase point index value sequences, remove duplicate index value sequences to obtain a new set of index value sequences. , ; Calculate the phase point index value sequences in the new phase point index value sequence set relative to the original index value sequence set. Q , The probability of occurrence in the phase space is obtained. X and The permutation entropy; For the two phase spaces on the other side of the transmission line of the flexible low-frequency transmission system Y , The permutation entropy calculation includes the following steps: Phase space Y , The instantaneous current sampling values ​​at any phase point are sorted in ascending order. The corresponding sequence numbers are then renumbered, and duplicate index value sequences are removed to obtain a new set of index value sequences. , ; Calculate the probability of each phase point index value sequence appearing in the new phase point index value sequence set to obtain the phase space. Y The permutation entropy, calculating the phase space The probability of the occurrence of all different phase point index value sequences is used to obtain the phase space. The permutation entropy; The phase space is calculated using the following formulas. Y , Permutation entropy: ； ； ； ； Among them, the new index value sequence set , The probabilities of the occurrence of each phase point index value sequence are denoted as follows: and , , These represent the new set of phase point index values. , The number of elements in the sequence set matrix or the number of rows in the sequence set matrix, and , ; and A sequence of phase point index values , In the original index value sequence set W , The number of times it appears in all row vector sequences , ; The ratio of the arrangement entropy on both sides of the outgoing line of the flexible low-frequency transmission system is transmitted to the other side through a communication channel, and fault identification is performed using the following formula: ； in: , These are the ratios of the arrangement entropy of the phase spaces constructed based on the sampled currents on both sides. The setpoint value for the entropy difference action is the permutation entropy difference.

2. The method for protecting the outgoing lines of offshore wind power through a flexible low-frequency transmission system according to claim 1, characterized in that, The protection device on the sending line side of the flexible low-frequency transmission system takes the current sampling time. As a reference time, the instantaneous current samples from the preceding quarter of a low-frequency cycle are used to construct the current sampling sequence. ; Simultaneously, the protection device on this side takes a low-frequency period before sampling. As a reference time, the instantaneous current samples from the preceding quarter of a low-frequency cycle are used to construct the current sampling sequence. ; Number of data points in a data window corresponding to a quarter of a low-frequency cycle ,in, This indicates the current frequency in a low-frequency power transmission system. Indicates the sampling frequency. Indicates the current cycle of a low-frequency power transmission system. Indicates the sampling period; The protection device on the other side of the transmission line of the flexible low-frequency transmission system also constructs two current sampling sequences.

3. The method for protecting the outgoing lines of offshore wind power through a flexible low-frequency transmission system according to claim 1, characterized in that, phase space X , The set of index values ​​corresponding to all phase point elements in the set. Q , As shown below: ； ； in, , They are respectively , The index value, that is, the index value corresponding to the current sample value at the phase point. , All sampled values ​​are sorted in ascending order by their corresponding index numbers. , .

4. The method for protecting the outgoing lines of offshore wind power through a flexible low-frequency transmission system according to claim 1, characterized in that, The arrangement entropy of the two phase spaces on the same side of the outgoing line of the flexible low-frequency transmission system is calculated based on the index value sequence set, and the ratio of the arrangement entropy on the same side is calculated. The phase spaces are calculated using the following formula. X , Permutation entropy: ； ； ； ； Among them, the new index value sequence set , The probabilities of the occurrence of each phase point index value sequence are denoted as follows: and , , These represent the new set of phase point index values. , The number of elements in the sequence set matrix or the number of rows in the sequence set matrix, and , ; and A sequence of phase point index values , In the original index value sequence set Q , The number of times it appears in all row vector sequences , .

5. A protection device for the outgoing line of an offshore wind power transmission system via a flexible low-frequency transmission system, characterized in that, The method for protecting the outgoing lines of offshore wind power through a flexible low-frequency transmission system as described in any one of claims 1 to 4 includes: The data acquisition module is used to collect current data on both sides of the outgoing line of the flexible low-frequency power transmission system in real time. The fault determination module is used to calculate the ratio of the arrangement entropy on both sides of the outgoing line of the flexible low-frequency power transmission system and to identify and determine faults inside and outside the zone. The communication module is used to transmit the ratio of the arrangement entropy on both sides of the transmission line of the flexible low-frequency power transmission system to the other side; The line protection module is used to disconnect the faulty phase when the fault determination module determines that it is a single-phase ground fault; when the fault determination module determines that it is a two-phase or three-phase fault, it directly disconnects the three phases through the relay protection devices at both ends of the low-frequency transmission line.

6. The protection device for the outgoing line of the offshore wind power transmission system via a flexible low-frequency transmission system according to claim 5, characterized in that, The line protection module also includes relay protection devices installed at both ends of the outgoing line of the flexible low-frequency power transmission system, and both relay protection devices are electrically connected to the fault determination module.

7. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored program, wherein, when the program is executed, it controls the device containing the computer-readable storage medium to perform the offshore wind power transmission line protection method according to any one of claims 1 to 4.

8. An electronic device comprising a memory and a processor, characterized in that, The memory stores a computer program, and the processor is configured to execute the offshore wind power transmission line protection method via any one of claims 1 to 4 through the computer program.

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