Time domain model fault direction judgment method, directional element and system suitable for wind power access system

Abstract

A time-domain model fault direction judgment method, directional element, and system applicable to wind power access systems, which distinguish positive and reverse direction faults based on the relationship between the voltage and current derivative waveforms after resistor voltage compensation on one side of the line. Collect the three-phase voltage of the transmission line and select the fault phase using a low-voltage phase selection element; calculate the voltage and current of the fault circuit; calculate the voltage and current derivatives after resistor voltage compensation; use the time-domain waveform correlation formula to calculate the correlation coefficient of the voltage and current derivatives, and use the positive and negative correlation coefficients to determine the fault direction. This application uses a model identification method based on time-domain waveform correlation analysis to solve the problem that the traditional directional element constructed using fault components is not applicable to wind power systems based on the back-side system impedance. At the same time, this method can be implemented in the time domain to avoid the influence of high-order harmonics and current frequency deviation characteristics on the frequency domain extraction algorithm when the wind power system fails, which can effectively improve the safety of the wind power access system.

Description

Technical Field

[0001] The present invention relates to the field of relay protection, specifically to a fault directional element for connecting a wind turbine to a power grid, and more particularly to a directional element method for identifying forward and reverse faults based on a time domain model according to correlation coefficients of compensation voltage and current derivatives on one side of a line and a control system thereof. Background Art

[0002] The widespread application of power electronic components in new energy systems including wind power and photovoltaic power generation has brought severe challenges to the safe and stable operation of power grids. Directional elements, as the core elements of longitudinal directional protection, largely determine the performance of the entire protection. The existing technical document (Analysis of the adaptability of phase selection and directional elements in wind power access systems, Wang Chenqing et al., Automation of Electric Power Systems, 2016, (40)) analyzes the adaptability of traditional phase selection and directional elements in wind power access systems. Theoretical analysis shows that the traditional directional elements based on the fault component network require the stability of the impedance of each sequence of the back system. The phase of the positive sequence impedance of the wind power system will deviate from the inductive region with the control change, which makes the directional elements based on the phasor fault component and the directional elements based on the positive sequence fault component unsuitable for wind power grid-connected systems. The phase angles of the zero-sequence and negative-sequence impedances of the wind power system are basically stable in the inductive region. Therefore, the directional elements based on the negative-sequence fault component and the zero-sequence fault component do not have adaptability problems in wind power access systems, but will be limited by the fault type. The directional element based on the frequency domain extraction algorithm will have the problem of inaccurate phasor extraction under the influence of the high voltage harmonics and current frequency offset characteristics of the wind power system, which reduces the reliability and sensitivity of the directional element.

[0003] The essence of the model identification method is the change of network topology and parameters during faults. This method can transform the identification of unstable electrical quantity numbers into the identification of changes in the determined topology structure. It can not only eliminate the influence of capacitor current, but also has high sensitivity. Due to the frequency offset and high harmonic content of wind power access systems, the extraction of power frequency phasors will have a certain impact. Therefore, the protection principle based on the frequency domain cannot be well applied to wind power systems and should be considered for implementation in the time domain. Therefore, based on the idea of ​​model identification, a new principle of model identification directional elements using the time domain waveform correlation analysis method is proposed. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the present application provides a time domain model fault direction judgment method, a directional element method and a protection system suitable for wind power access systems. Under the fault direction judgment method of the present invention, the directional criterion for judging the fault direction is studied by using the correlation coefficient of the compensated voltage and current derivatives. The method element adopts the full amount of fault information and is not affected by the impedance characteristics of the wind power system. At the same time, the method is implemented in the time domain, which avoids the influence of high-order harmonics and current frequency deviation characteristics on the frequency domain extraction algorithm when the wind power system fails. The present invention is based on a new principle of identifying directional elements based on the time domain model of the correlation coefficient of the compensation voltage and current derivative on one side of the line. When a positive direction fault occurs, the correlation coefficient of the compensation voltage and current derivative is greater than zero; when a reverse direction fault occurs, the correlation coefficient of the compensation voltage and current derivative is less than zero. The correlation coefficient of voltage and current can be used to effectively distinguish positive direction faults and reverse direction faults.

[0005] This application adopts the following technical solutions:

[0006] In a first aspect, the present application discloses a single-ended time domain model fault direction determination method applicable to a wind power access system, characterized in that the method comprises the following steps:

[0007] Step 1: When a short circuit fault occurs in the line, a low voltage phase selection element is used to select the faulty phase;

[0008] Step 2, calculating the fault circuit voltage and the fault circuit current;

[0009] Step 3, calculating the equivalent resistance of the fault loop in the resistance-inductance model, and calculating the fault loop voltage after equivalent resistance voltage compensation, and the fault loop current derivative;

[0010] Step 4, calculate the correlation coefficient between the compensated fault circuit voltage and the fault circuit current derivative. When the correlation coefficient is greater than the positive correlation coefficient setting value, the short circuit fault is judged to be a positive direction fault; when the correlation coefficient is less than the negative correlation coefficient setting value, the short circuit fault is judged to be a negative direction fault.

[0011] More preferably,

[0012] In step 1, the fault phase is selected using a low voltage phase selection element:

[0013]

[0014] In the formula is the three-phase voltage, where u set It is the setting value of the low voltage phase selection element. When the voltage of a phase is lower than the setting value of the low voltage phase selection element, it is judged that a short circuit fault has occurred in this phase.

[0015] More preferably,

[0016] In step 2, when a single-phase short circuit fault occurs, the fault circuit voltage u is calculated according to the following formula: W and the fault circuit current i W :

[0017]

[0018] in, is the fault phase voltage, is the fault phase current, where u0 and i0 are zero-sequence voltage and zero-sequence current respectively;

[0019] When a phase-to-phase short circuit fault occurs, the fault circuit voltage u is calculated according to the following formula: W and the fault circuit current i W :

[0020]

[0021] is the fault phase voltage, is the fault phase current, is one of the three phases A, B, and C respectively, and Relative to Phase sequence first.

[0022] More preferably,

[0023] In step 3, according to the fault circuit voltage u W , fault circuit current i W And the fault current derivative i', the equivalent resistance R' of the fault circuit is calculated by the least squares method LF , assuming a forward fault occurs, according to the forward fault network topology, calculate the fault circuit voltage after equivalent resistance compensation when a forward fault occurs and the fault current derivative

[0024] More preferably,

[0025] Calculated according to step 3 and i', and use the following waveform correlation formula to calculate the correlation coefficient ρ(x,y);

[0026] The correlation coefficient formula is:

[0027]

[0028] Where ρ(x,y) is the correlation coefficient, x is the voltage after compensation y is the time domain curve of the first-order derivative i' of the current after compensation; N1 is the starting time of the data window; Nw is the data time window length.

[0029] More preferably,

[0030] The criterion for judging the short-circuit fault direction by the correlation coefficient is as follows:

[0031] If ρ(x,y)>ρ set , it is judged as a forward fault; if ρ(x,y)<-ρ set , it is judged as a reverse fault;

[0032] Among them, ρ(x,y) is the correlation coefficient, ρ set is the correlation coefficient setting value.

[0033] In a second aspect of the present application, a directional element of a single-ended time domain model applicable to a wind power access system using the aforementioned judgment method is disclosed, comprising a fault loop voltage and fault loop current calculation unit, a fault loop equivalent resistance calculation unit, and a fault direction judgment unit;

[0034] The fault loop voltage and fault loop current calculation unit calculates the loop voltage and the fault loop current after a line short circuit fault occurs;

[0035] The fault loop equivalent resistance calculation unit obtains the fault loop equivalent resistance in the calculated resistance-inductance model by fitting calculation, and calculates the fault loop voltage after equivalent resistance voltage compensation, and the fault loop current derivative;

[0036] The fault direction determination unit calculates the correlation coefficient between the compensated fault loop voltage and the fault loop current derivative, and identifies the fault direction according to the correlation coefficient calculation result.

[0037] More preferably,

[0038] The fault circuit equivalent resistance calculation unit calculates the fault circuit voltage u W , fault circuit current i W And the fault current derivative i', the equivalent resistance R' of the fault circuit is calculated by the least squares method LF ; Assuming a forward fault occurs, and based on the forward fault network topology, calculate the fault circuit voltage after equivalent resistance compensation when a forward fault occurs and the fault current derivative

[0039] More preferably,

[0040] The fault direction judgment unit calculates the correlation coefficient based on the compensated fault circuit voltage and the fault circuit current derivative obtained from the forward fault network topology diagram. When the correlation coefficient is greater than the positive correlation coefficient setting value, it is determined to be a forward fault; when the correlation coefficient is less than the negative correlation coefficient setting value, it is determined to be a reverse fault.

[0041] The third aspect of the present application discloses a time domain model fault direction protection system applicable to a wind power access system using the judgment method, comprising a three-phase voltage and current acquisition module, a low voltage phase selection module, a fault circuit voltage and current calculation module, and a correlation coefficient calculation and fault direction judgment module;

[0042] The three-phase voltage and current acquisition module uses a traveling wave voltage sensor and a current sensor to collect the three-phase voltage and current of the transmission line;

[0043] The low voltage phase selection module determines the fault phase according to the drop amplitude of the three-phase voltage;

[0044] The fault circuit voltage and current calculation module uses the parameter identification method to obtain the equivalent resistance of the fault circuit, and calculates the fault circuit voltage and the first-order derivative of the fault circuit current after resistance compensation;

[0045] The correlation coefficient calculation and fault direction determination module calculates the correlation coefficient using the fault circuit voltage and the first-order derivative of the fault circuit current after resistance compensation, and determines the fault direction according to the correlation coefficient. When the correlation coefficient is greater than the positive correlation coefficient setting value, it is determined to be a forward fault; when the correlation coefficient is less than the negative correlation coefficient setting value, it is determined to be a reverse fault.

[0046] More preferably,

[0047] The low voltage phase selection module uses low voltage phase selection elements to select the fault phase:

[0048]

[0049] In the formula is the three-phase voltage, where u set It is the setting value of the low voltage phase selection element. When the voltage of a phase is lower than the setting value of the low voltage phase selection element, it is judged that a short circuit fault has occurred in this phase.

[0050] More preferably,

[0051] The fault circuit equivalent resistance calculation unit calculates the fault circuit voltage u W , fault circuit current i W And the fault current derivative i', the equivalent resistance R' of the fault circuit is calculated by the least squares method LF; Assuming a forward fault occurs, and based on the forward fault network topology, calculate the fault circuit voltage after equivalent resistance compensation when a forward fault occurs and the fault current derivative

[0052] More preferably,

[0053] The fault direction judgment module calculates the correlation coefficient based on the compensated fault circuit voltage and the fault circuit current derivative obtained from the forward fault network topology diagram, and identifies the fault direction based on the correlation coefficient calculation result. The direction element correlation coefficient setting value ρ set Set to 0.2, when the correlation coefficient is greater than the set value ρ set It is judged as a forward fault; when the correlation coefficient is less than the negative setting value, it is judged as a reverse fault.

[0054] The present application also seeks to protect a terminal, including a processor and a storage medium; the characteristics of which are:

[0055] The storage medium is used to store instructions;

[0056] The processor is used to operate according to the instruction to execute the steps of the fault direction determination method according to the single-ended time domain model applicable to the wind power access system.

[0057] A computer-readable storage medium having a computer program stored thereon, characterized in that when the program is executed by a processor, the steps of the single-ended time domain model fault direction determination method applicable to a wind power access system are implemented.

[0058] Compared with the prior art, the present application provides a single-ended time domain model fault direction determination method, direction element and system applicable to a wind power access system, which has the following beneficial effects:

[0059] 1) The present invention uses full fault information and is not affected by the impedance characteristics of the wind power system;

[0060] 2) The principle of directional element identification based on the time domain full quantity model is simple, easy to implement, and has high reliability and sensitivity;

[0061] 3) The present invention adopts a time domain model identification method. Compared with the frequency domain model identification, this method avoids the influence of high-order harmonics and current frequency deviation characteristics when wind power is connected to the system on the frequency domain extraction algorithm. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 It is a flowchart of a method for identifying directional elements of a time domain model of a wind power access system in the present invention;

[0063] Figure 2 It is a simulation model of the wind farm access system in the present invention;

[0064] Figure 3 It is the relationship between the fault voltage and current derivative waveforms when the direct-drive wind turbine is connected to the system area and the BC forward fault occurs in the present invention;

[0065] Figure 4 It is the relationship between the fault voltage and current derivative waveforms when the direct-drive wind turbine in the present invention is connected to the system and a BC reverse fault occurs inside and outside the area. DETAILED DESCRIPTION

[0066] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0067] The present invention provides a time domain model fault direction judgment method applicable to a wind power access system. Figure 1 It can be seen that its specific contents include:

[0068] Step 1: Select the fault phase using the low voltage phase selection element:

[0069]

[0070] In the formula is the three-phase voltage, where u set It is the setting value of low voltage phase selection element.

[0071] Step 2: Determine the voltage and current of the selected fault circuit. For example, when phase A is grounded, u W =u A -u0,i W =i A -i0; when BC phase fault occurs, u W =u B -u C ,i W =i B -i C .

[0072] Among them, u A 、u B 、u C are the three-phase voltages, i A 、i B 、i C are the three-phase currents respectively, u0 and i0 are the zero-sequence voltage and zero-sequence current respectively.

[0073] Step 3: Use parameter identification protection idea to identify the voltage u W 、Current i W and the current derivative di W / dt, the equivalent resistance R' can be calculated by the least squares method LF , and calculate and i', assuming that a forward fault occurs, according to the forward fault network topology diagram, when a forward fault occurs,

[0074] Step 4: Calculate the value based on the formula in step 3 when a forward fault occurs. and i', step 4 uses the following waveform correlation formula, and the forward and reverse faults can be judged by whether the waveforms are positively correlated.

[0075] The correlation coefficient formula is

[0076]

[0077] Where ρ(x,y) is the correlation coefficient, x is the voltage after compensation y is the time domain curve of the first-order derivative i' of the current after compensation; N1 is the starting time of the data window; N w is the data time window length, which is 10ms. set , it is judged as a forward fault; if ρ(x,y)<-ρ set , it is judged as a reverse fault. set is the directional element setting value, which is also called the correlation coefficient setting value in this application and can be set by engineering and technical personnel according to the grid structure and protection requirements. The setting value is usually a decimal close to zero.

[0078] In a preferred embodiment of the present invention, it is set to 0.2.

[0079] The present application also claims protection for a directional element of a single-ended time domain model applicable to a wind power access system using the aforementioned judgment method, comprising a fault loop voltage and fault loop current calculation unit, a fault loop equivalent resistance calculation unit, and a fault direction judgment unit; characterized in that:

[0080] The fault loop voltage and fault loop current calculation unit calculates the loop voltage and the fault loop current after a line short circuit fault occurs.

[0081] The fault loop equivalent resistance calculation unit obtains the fault loop equivalent resistance in the calculated resistance-inductance model by fitting calculation, and calculates the fault loop voltage after equivalent resistance voltage compensation, and the fault loop current derivative;

[0082] The fault circuit equivalent resistance calculation unit calculates the fault circuit voltage uW , fault circuit current i W And the fault current derivative i', the equivalent resistance R' of the fault circuit is calculated by the least squares method LF ; Assuming a forward fault occurs, and based on the forward fault network topology, calculate the fault circuit voltage after equivalent resistance compensation when a forward fault occurs and the fault current derivative

[0083] The fault direction determination unit calculates the correlation coefficient between the compensated fault loop voltage and the fault loop current derivative, and identifies the fault direction according to the correlation coefficient calculation result.

[0084] The fault direction judgment unit calculates the correlation coefficient based on the compensated fault circuit voltage and the fault circuit current derivative obtained from the forward fault network topology diagram. When the correlation coefficient is greater than the set value ρ set It is judged as a forward fault; when the correlation coefficient is less than the negative setting value, it is judged as a reverse fault.

[0085] The present application also discloses a time domain model fault direction protection system applicable to a wind power access system using the aforementioned judgment method, including a three-phase voltage and current acquisition module, a low voltage phase selection module, a fault circuit voltage and current calculation module, and a correlation coefficient calculation and fault direction judgment module;

[0086] The three-phase voltage and current acquisition module uses traveling wave voltage sensors and current sensors to collect the three-phase voltage and current of the transmission line.

[0087] The low voltage phase selection module determines the fault phase according to the drop amplitude of the three-phase voltage;

[0088] The low voltage phase selection module uses low voltage phase selection elements to select the fault phase:

[0089]

[0090] In the formula is the three-phase voltage, where u set It is the setting value of the low voltage phase selection element. When the voltage of a phase is lower than the setting value of the low voltage phase selection element, it is judged that a short circuit fault has occurred in this phase.

[0091] The fault circuit voltage and current calculation module uses the parameter identification method to obtain the equivalent resistance of the fault circuit, and calculates the fault circuit voltage and the first-order derivative of the fault circuit current after resistance compensation;

[0092] The fault circuit equivalent resistance calculation unit calculates the fault circuit voltage u W , fault circuit current i WAnd the fault current derivative i', the equivalent resistance R' of the fault circuit is calculated by the least squares method LF ; Assuming a forward fault occurs, and based on the forward fault network topology, calculate the fault circuit voltage after equivalent resistance compensation when a forward fault occurs and the fault current derivative

[0093] The correlation coefficient calculation and fault direction determination module uses the fault circuit voltage and the first-order derivative of the fault circuit current after resistance compensation to calculate the correlation coefficient, and determines the fault direction according to the correlation coefficient. The direction element correlation coefficient setting value ρ set Set to 0.2, when the correlation coefficient is greater than the set value ρ set It is judged as a forward fault; when the correlation coefficient is less than the negative setting value, it is judged as a reverse fault.

[0094] The fault direction judgment unit calculates the correlation coefficient based on the compensated fault circuit voltage and the fault circuit current derivative obtained from the forward fault network topology diagram. When the correlation coefficient is greater than the set value ρ set It is judged as a forward fault; when the correlation coefficient is less than the negative setting value, it is judged as a reverse fault.

[0095] The verification example of the present invention is as follows: Figure 2 The wind power access system simulation model shown in the figure. The left side is a 49.5MW doubly-fed and direct-drive wind farm consisting of 33 wind turbines, which is connected to the conventional power system on the right through a 220kV interconnection line. The rotor-side control system of the doubly-fed wind turbine model is based on stator flux orientation and adopts PQ control mode; the grid-side control system is based on grid voltage orientation. The machine-side control system of the direct-drive wind turbine model adopts zero d-axis current control based on rotor magnetic field orientation, and the grid side is the same as the doubly-fed wind turbine model. During a fault, the doubly-fed wind turbine will automatically enter the Crowbar protection circuit when detecting DC overvoltage or rotor overcurrent. After 2 cycles, the Crowbar protection will be removed and reactive current will be injected according to the requirements of the grid; the direct-drive wind turbine will provide the corresponding reactive current according to the requirements of the grid, and at the same time limit the outlet short-circuit current to no more than 1.5 times the rated current.

[0096] like Figure 2 As shown, u G 、u W 、i G 、i W The voltage and current values ​​measured at the G and W protection installations are respectively. The line length is 120 km, the line positive sequence parameters are r1 = 0.053 Ω / km, l1 = 1.081 mH / km, c1 = 0.0132 uF / km; the line zero sequence parameters are r0 = 0.291 Ω / km, l0 = 2.74 mH / km, c0 = 0.0089 uF / km; the system impedance of the conventional power supply is ZG1 =2.43+j54.35Ω, Z G0 =1.1+j16.5Ω. Set the three positions of OF1, IF2 and IF3 to set the metallic fault and the grounding fault with transition resistance respectively. OF1 is located outside the wind power side area, IF2 is located at the midpoint of the line, IF3 is located at the system side outlet, and the sampling rate is set to 2.5kHz.

[0097] Figure 3 The relationship between the fault voltage and current derivative waveforms when the direct-drive wind turbine is connected to the BC fault inside and outside the system area is given. Figure 4 As shown in the figure, when a reverse BC fault occurs on the wind power side, the voltage and current on the wind power side conform to the negative resistance-inductance model, so the fault voltage and fault current derivative after resistance voltage compensation are completely negatively correlated. When a forward fault occurs, the voltage and current on the wind power side conform to the positive resistance-inductance model, so the fault voltage and fault current derivative after resistance voltage compensation are completely positively correlated.

[0098] Table 1 shows the simulation results of the doubly fed wind turbine and direct drive wind turbine connected to the system tie line when different types of faults occur at different fault locations. The data window in the correlation coefficient calculation is taken as the data within 10ms after the fault occurs.

[0099] Table 1 Simulation results of wind power access system tie line metallic fault

[0100]

[0101]

[0102] It can be seen from Table 1 that no matter whether it is a doubly-fed wind turbine or a direct-drive wind turbine connected to the system tie line, no matter what type of fault it is, when a reverse fault occurs on the wind power side, since the fault voltage and current conform to the negative resistance-inductance model, the conformity of the positive resistance-inductance model is close to -1, and it can be reliably determined as a reverse fault. When a positive fault occurs on the wind power side, since the fault voltage and current conform to the positive resistance-inductance model, the conformity of the positive resistance-inductance model is close to 1, and it can be reliably determined as a positive fault.

[0103] Table 2 lists the simulation results of the AG faults passing through different transition resistances at different fault locations of the DFIG and DDIG access system tie lines. The data window in the correlation coefficient calculation is taken as the data within 10ms after the fault occurs.

[0104] Table 2 Simulation results of wind power access system tie line phase A with different transition resistances

[0105]

[0106] It can be seen from Table 2 that no matter whether it is a doubly fed wind turbine or a direct-drive wind turbine connected to the system interconnection line, regardless of the size of the transition resistance, when a reverse fault occurs on the wind power side, since the fault voltage and current conform to the negative resistance inductance model, the positive resistance inductance model conformity is close to -1, and it can be reliably determined as a reverse fault. When a positive fault occurs on the wind power side, since the fault voltage and current conform to the positive resistance inductance model, the positive resistance inductance model conformity is close to 1, and it can be reliably determined as a positive fault. Based on the above simulation results, it can be seen that the directional element identified based on the time domain full quantity model can reliably distinguish positive and reverse faults, can tolerate high transition resistance, and has high sensitivity.

[0107] The present invention also discloses a time domain model identification direction element control system suitable for a wind power access system, comprising: a three-phase voltage and current acquisition module, a low voltage phase selection module, a fault circuit voltage and current calculation module, and a correlation coefficient calculation and fault direction determination module;

[0108] The three-phase voltage and current acquisition module uses a traveling wave voltage sensor and a current sensor to collect the three-phase voltage and current of the transmission line;

[0109] The low voltage phase selection module determines the fault phase according to the amplitude of the three-phase voltage;

[0110] The fault circuit voltage and current calculation module uses the parameter identification method to obtain the equivalent resistance and calculates the first-order derivatives of the voltage and current after resistance compensation;

[0111] The correlation coefficient calculation and fault direction determination module calculates the correlation coefficient using the first-order derivatives of the voltage and current after resistance compensation, and determines the fault direction based on the correlation coefficient. If the correlation coefficient is greater than zero, it is determined to be a positive direction fault; if the correlation coefficient is less than zero, it is determined to be a reverse direction fault.

[0112] The present invention proposes a new principle for identifying directional elements using a time domain model suitable for wind power access systems. The method utilizes the waveform relationship between the compensated voltage and current derivatives at one end of the line and uses time domain waveform correlation to identify positive and negative directional faults. The principle is calculated in the time domain and is therefore easy to implement, avoiding the influence of high-order harmonics and current frequency deviation characteristics during wind power system faults on the frequency domain extraction algorithm. It has high reliability and rapidity, and is therefore suitable for wind power access systems. Simulation results verify the effectiveness of the method.

[0113] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0114] A computer-readable storage medium may be a tangible device that can hold and store instructions used by an instruction execution device. A computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples of computer-readable storage media (a non-exhaustive list) include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure in a groove on which instructions are stored, and any suitable combination of the foregoing. As used herein, a computer-readable storage medium is not to be interpreted as a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted through a wire.

[0115] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0116] The computer program instructions for performing the operation of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-related instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages, such as Smalltalk, C++, etc., and conventional procedural programming languages, such as "C" language or similar programming languages. Computer-readable program instructions may be executed completely on a user's computer, partially on a user's computer, as an independent software package, partially on a user's computer, partially on a remote computer, or completely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., using an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), may be customized by utilizing the state information of the computer-readable program instructions, and the electronic circuit may execute the computer-readable program instructions, thereby realizing various aspects of the present disclosure.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A single-ended time domain model fault direction determination method applicable to wind power access system, characterized in that: The method comprises the following steps: Step 1: When a short circuit fault occurs in the line, a low voltage phase selection element is used to select the faulty phase; Step 2, calculating the fault circuit voltage and the fault circuit current; Step 3, calculating the equivalent resistance of the fault loop in the resistance-inductance model, and calculating the fault loop voltage after equivalent resistance voltage compensation, and the fault loop current derivative; Step 4, calculate the correlation coefficient between the compensated fault circuit voltage and the fault circuit current derivative. When the correlation coefficient is greater than the positive correlation coefficient setting value, the short circuit fault is judged to be a positive direction fault; when the correlation coefficient is less than the negative correlation coefficient setting value, the short circuit fault is judged to be a negative direction fault.

2. The single-ended time domain model fault direction determination method applicable to a wind power access system according to claim 1 is characterized in that: In step 1, the fault phase is selected using a low voltage phase selection element: In the formula is the three-phase voltage, where u set It is the setting value of the low voltage phase selection element. When the voltage of a phase is lower than the setting value of the low voltage phase selection element, it is judged that a short circuit fault has occurred in this phase.

3. The single-ended time domain model fault direction determination method applicable to a wind power access system according to claim 1 is characterized in that: In step 2, when a single-phase short circuit fault occurs, the fault circuit voltage u is calculated according to the following formula: W and the fault circuit current i W : in, is the fault phase voltage, is the fault phase current, where u0 and i0 are zero-sequence voltage and zero-sequence current respectively; When a phase-to-phase short circuit fault occurs, the fault circuit voltage u is calculated according to the following formula: W and the fault circuit current i W : is the fault phase voltage, is the fault phase current, is one of the three phases A, B, and C respectively, and Relative to Phase sequence first.

4. The single-ended time domain model fault direction determination method applicable to a wind power access system according to claim 1 or 3, characterized in that: In step 3, according to the fault circuit voltage u W , fault circuit current i W And the fault current derivative i', the equivalent resistance R' of the fault circuit is calculated by the least squares method LF , assuming a forward fault occurs, according to the forward fault network topology, calculate the fault circuit voltage after equivalent resistance compensation when a forward fault occurs and the fault current derivative 5. The single-ended time domain model fault direction determination method applicable to a wind power access system according to claim 4 is characterized in that: Calculated according to step 3 and i', and use the following waveform correlation formula to calculate the correlation coefficient ρ(x,y); The correlation coefficient formula is: Where ρ(x,y) is the correlation coefficient, x is the voltage after compensation y is the time domain curve of the first-order derivative i' of the current after compensation; N1 is the starting time of the data window; N w is the data time window length.

6. The single-ended time domain model fault direction determination method applicable to a wind power access system according to claim 1 or 5, characterized in that: The criterion for judging the short-circuit fault direction by the correlation coefficient is as follows: If ρ(x,y)>ρ set , it is judged as a forward fault; if ρ(x,y)<-ρ set , it is judged as a reverse fault; Among them, ρ(x,y) is the correlation coefficient, ρ set is the correlation coefficient setting value.

7. A directional element of a single-ended time domain model applicable to a wind power access system using the judgment method according to any one of claims 1 to 6, comprising a fault loop voltage and fault loop current calculation unit, a fault loop equivalent resistance calculation unit, and a fault direction judgment unit; characterized in that: The fault loop voltage and fault loop current calculation unit calculates the loop voltage and the fault loop current after a line short circuit fault occurs; The fault loop equivalent resistance calculation unit obtains the fault loop equivalent resistance in the calculated resistance-inductance model by fitting calculation, and calculates the fault loop voltage after equivalent resistance voltage compensation, and the fault loop current derivative; The fault direction determination unit calculates the correlation coefficient between the compensated fault loop voltage and the fault loop current derivative, and identifies the fault direction according to the correlation coefficient calculation result.

8. The directional element of the single-ended time domain model applicable to the wind power access system according to claim 7, characterized in that: The fault circuit equivalent resistance calculation unit calculates the fault circuit voltage u W , fault circuit current i W And the fault current derivative i', the equivalent resistance R' of the fault circuit is calculated by the least squares method LF ; Assuming a forward fault occurs, and based on the forward fault network topology, calculate the fault circuit voltage after equivalent resistance compensation when a forward fault occurs and the fault current derivative 9. The directional element of the single-ended time domain model applicable to the wind power access system according to claim 8, characterized in that: The fault direction judgment unit calculates the correlation coefficient based on the compensated fault circuit voltage and the fault circuit current derivative obtained from the forward fault network topology diagram. When the correlation coefficient is greater than the positive correlation coefficient setting value, it is determined to be a forward fault; when the correlation coefficient is less than the negative correlation coefficient setting value, it is determined to be a reverse fault.

10. A time domain model fault direction protection system for a wind power access system using the judgment method according to any one of claims 1 to 6, comprising a three-phase voltage and current acquisition module, a low voltage phase selection module, a fault circuit voltage and current calculation module, and a correlation coefficient calculation and fault direction judgment module; characterized in that: The three-phase voltage and current acquisition module uses a traveling wave voltage sensor and a current sensor to collect the three-phase voltage and current of the transmission line; The low voltage phase selection module determines the fault phase according to the drop amplitude of the three-phase voltage; The fault circuit voltage and current calculation module uses the parameter identification method to obtain the equivalent resistance of the fault circuit, and calculates the fault circuit voltage and the first-order derivative of the fault circuit current after resistance compensation; The correlation coefficient calculation and fault direction determination module calculates the correlation coefficient using the fault circuit voltage and the first-order derivative of the fault circuit current after resistance compensation, and determines the fault direction according to the correlation coefficient. When the correlation coefficient is greater than the positive correlation coefficient setting value, it is determined to be a forward fault; when the correlation coefficient is less than the negative correlation coefficient setting value, it is determined to be a reverse fault.

11. The time domain model fault direction protection system applicable to the wind power access system according to claim 10, characterized in that: The low voltage phase selection module uses low voltage phase selection elements to select the fault phase: In the formula is the three-phase voltage, where u set It is the setting value of the low voltage phase selection element. When the voltage of a phase is lower than the setting value of the low voltage phase selection element, it is judged that a short circuit fault has occurred in this phase.

12. The time domain model fault direction protection system applicable to the wind power access system according to claim 11, characterized in that: The fault circuit equivalent resistance calculation unit calculates the fault circuit voltage u W , fault circuit current i W And the fault current derivative i', the equivalent resistance R' of the fault circuit is calculated by the least squares method LF ; Assuming a forward fault occurs, and based on the forward fault network topology, calculate the fault circuit voltage after equivalent resistance compensation when a forward fault occurs and the fault current derivative 13. The time domain model fault direction protection system applicable to the wind power access system according to claim 12, characterized in that: The fault direction determination module calculates the correlation coefficient based on the compensated fault circuit voltage and the fault circuit current derivative obtained from the forward fault network topology diagram, and identifies the fault direction based on the correlation coefficient calculation result. The direction element correlation coefficient setting value ρ set Set to 0.2, when the correlation coefficient is greater than the set value ρ set It is judged as a forward fault; when the correlation coefficient is less than the negative setting value, it is judged as a reverse fault.

14. A terminal comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is used to operate according to the instruction to execute the steps of the single-ended time domain model fault direction determination method applicable to a wind power access system according to any one of claims 1 to 6.

15. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the single-ended time domain model fault direction determination method applicable to a wind power access system as described in any one of claims 1 to 6 are implemented.

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