A virtual modal admittance-based direct-drive wind farm fault location method and system

Abstract

The application discloses a kind of direct-drive wind farm fault location method and system based on virtual module admittance, belong to the technical field of power system relay protection, solve the problem of poor accuracy of existing direct-drive wind farm fault location.The method comprises: collecting the bus voltage of outgoing line before and after the fault of direct-drive wind farm collection station, and the port voltage and port current of each power collection line after the fault;According to the port voltage and port current of each power collection line after the fault, the actual value of 1 module and 2 module admittance of the corresponding power collection line is obtained;According to the bus voltage of outgoing line before and after the fault, and the port voltage of each power collection line after the fault, the predicted value of 1 module and 2 module admittance of the corresponding power collection line is obtained;Based on the actual value and predicted value of the admittance of each power collection line, the fault criterion value of the corresponding power collection line is obtained to determine whether the corresponding power collection line has an internal fault, if so, the protection device of the corresponding power collection line acts.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection technology, and in particular to a method and system for locating faults in direct-drive wind farms based on virtual modal admittance. Background Technology

[0002] With the increasing integration of fluctuating renewable energy sources, the operation modes and dynamic processes of the source-end power grid are becoming more varied and complex. This leads to a gradual decrease in the characteristic differences between faulty and non-faulty electrical quantities, and even their overlap. It becomes difficult to simultaneously ensure both non-malfunctioning and non-failure-to-operate protection, significantly increasing the risk of a single equipment failure triggering a systemic accident across the entire grid. Traditional fault location methods and systems relying solely on independent information from the protected equipment face severe challenges. Direct-drive wind farms have abundant harmonic content at the source end, and the limited amplitude variation of short-circuit currents will reduce the sensitivity of the main protection system to minor faults such as transformer inter-turn short circuits and high-resistance grounding of lines. Since faults in the collection line belong to low-current grounding systems, traditional collection line protection faces problems such as weak fault signals and insufficient protection sensitivity. Simultaneously, the complex and variable operation modes of the source-end power grid and the random fluctuations in the output of wind farms and photovoltaic power plants will make it difficult to set backup protection settings, further highlighting the contradiction between protection selectivity and sensitivity, and resulting in both protection failure and malfunction risks.

[0003] The short-circuit current amplitude of direct-drive wind turbines is limited and the phase angle is controlled. After a voltage jump at the turbine terminals, the transient characteristics of the short-circuit current are significantly different from those of synchronous motors. The transient characteristics of wind turbine groups connected to the same collector line are affected by inter-turbine interactions, and the analytical accuracy of traditional single-unit aggregated wind farm group transient models is insufficient. The direct-drive wind farm topology is a series chain power supply, which is more complex than traditional AC transmission lines. Protection configurations need to consider coordination between upstream and downstream levels. The protection configuration of the collector line in a direct-drive wind farm is located near the collector bus port, and fuse protection devices are installed on the low-voltage side of the wind turbine transformer. Compared with traditional distribution network protection, the protection of the collector line in a direct-drive wind farm is difficult to achieve selective protection through coordination between upstream and downstream levels.

[0004] In recent years, scholars both domestically and internationally have conducted extensive research on the protection of wind farm collector lines. Existing collector lines are generally equipped with overcurrent protection to identify and clear phase-to-phase short circuits, and zero-sequence current protection to identify and clear ground faults. There are three overcurrent protection setting methods: The first is the maximum short-circuit current when a fault occurs on the low-voltage side of the first wind turbine transformer; this setting method satisfies the selectivity between collector line protection and transformer protection at the threshold level, but its sensitivity is poor, and the slow clearing speed can easily lead to an increase in the number of wind turbines disconnected from the grid, affecting wind farm stability. The second is the maximum short-circuit current when a fault occurs at the end of the collector line; this method has better selectivity, but cannot protect the entire length of the line, has poor sensitivity, and cannot quickly clear the fault, thus expanding the fault range. The third is a method with some sensitivity to faults in the minimum operating mode at the end of the collector line; this setting method can cover the entire length of the collector line, but due to the excessively long protection range, it is prone to non-selective maloperation when a fault occurs on the low-voltage side of the wind turbine transformer. Due to the wind farm transformer winding connection method, zero-sequence current protection has high sensitivity and protection range, but it cannot identify phase-to-phase faults.

[0005] Furthermore, traditional methods for fault location calculations mostly only consider fault information on the local line. In reality, fault currents from other collecting lines also feed into the protected collecting line, and the fault information is abundant. Since the fault currents from other collecting lines are not considered in the fault location calculation process, the accuracy of existing fault location methods has decreased. Summary of the Invention

[0006] Based on the above analysis, the embodiments of the present invention aim to provide a method and system for fault location in direct-drive wind farms based on virtual modal admittance, so as to improve the accuracy of fault location in direct-drive wind farms.

[0007] On one hand, this invention discloses a fault location method for direct-drive wind farms based on virtual modal admittance, comprising:

[0008] Collect the bus voltage of the outgoing lines before and after the fault of the direct-drive wind farm collection station, as well as the port voltage and port current of each collection line after the fault of the direct-drive wind farm collection station.

[0009] Based on the port voltage and port current of each collector line after a fault at the direct-drive wind farm collection station, the actual values ​​of the 1-mode and 2-mode admittances of the corresponding collector lines are obtained.

[0010] Based on the bus voltage of the transmission lines before and after the fault of the direct-drive wind farm collection station, and the port voltage of each collection line after the fault of the direct-drive wind farm collection station, the predicted values ​​of the 1-mode and 2-mode admittance of the corresponding collection lines are obtained.

[0011] Based on the actual values ​​of the 1-mode and 2-mode admittances and the predicted values ​​of the 1-mode and 2-mode admittances for each collector line, the fault criterion values ​​for the corresponding collector lines are obtained. Based on the fault criterion values ​​for each collector line, it is determined whether an intra-zone fault has occurred in the corresponding collector line. If so, the protection device of the corresponding collector line is activated.

[0012] Based on the above solution, the present invention also makes the following improvements:

[0013] Furthermore, for each collector line, the fault criterion value E is calculated according to the following formula. m :

[0014]

[0015] Among them, G M1 (s), G M2 (s) represent the predicted 1-mode and 2-mode admittance values ​​of the collector line at the s-th sampling point, respectively, G′ M1 (s), G′ M2 (s) represent the actual values ​​of the 1-mode and 2-mode admittances of the collector line at the s-th sampling point, respectively, and S is the total number of sampling points after the failure of the direct-drive wind farm collection station.

[0016] Furthermore, for each sampling point, the actual values ​​of the 1-mode and 2-mode admittances of the collector line are calculated according to the following formula:

[0017]

[0018]

[0019] Among them, G′ M1 This represents the actual value of the 1-mode admittance of the collector line, G′. M2 This represents the actual 2-mode admittance of the collector circuit; i a i b i c These represent the currents at the a, b, and c phase ports of the current collector at the current sampling point; u a u b u c These represent the voltages at the a, b, and c phase ports of the current collector at the current sampling point.

[0020] Furthermore, for each sampling point, the predicted values ​​of the 1-mode and 2-mode admittances of the nth collector line are calculated according to the following formula:

[0021]

[0022]

[0023] in,

[0024]

[0025]

[0026]

[0027]

[0028]

[0029]

[0030]

[0031] k pi k ii These are the proportional and integral coefficients of the current loop PI control, respectively; L is the inductance connected to the grid-side converter; I... max I represents the maximum output current of the direct-drive fan. N Z is the rated per-unit value of the output current of the direct-drive fan, where K is a constant and Z is the rated per-unit value of the output current. T z represents the equivalent reactance of the main transformer on the transmitting line. ln x represents the equivalent impedance of the nth collector line, where n ranges from 1 to N, and N represents the total number of collector lines; n This indicates the number of direct-drive fans on the nth collector line, and T represents the sampling period; These represent the bus voltage u of the output line instants before and after the fault time t0, respectively. m The measured value; i wn Let u be the port current of the nth collector line at the current sampling point. m i m These represent the bus voltage and bus current of the output line at the current sampling point, respectively; u M1,n u M2,n These represent the 1-mode voltage and 2-mode voltage of the port voltage of the nth collector line at the current sampling point, respectively.

[0032] Furthermore, based on the fault criterion value of each collector line, it is determined whether a fault has occurred within the area on the corresponding collector line, including:

[0033] For each collector line,

[0034] If E is satisfied m >E set This indicates that a fault has occurred within the current collector line, and the protection system has activated.

[0035] If E is satisfied m <E set This indicates that an external fault has occurred in the current collector line, and the protection is locked.

[0036] Among them, E set This represents the fault threshold value.

[0037] Furthermore, E set The value is 30.

[0038] On the other hand, the present invention also discloses a fault location system for direct-drive wind farms based on virtual modal admittance, comprising:

[0039] The data acquisition module is used to collect the bus voltage of the outgoing lines before and after the fault of the direct-drive wind farm collection station, as well as the port voltage and port current of each collection line after the fault of the direct-drive wind farm collection station.

[0040] The parameter calculation module is used to obtain the actual values ​​of the 1-mode and 2-mode admittances of the corresponding collector lines based on the port voltage and port current of each collector line after a fault in the direct-drive wind farm collection station; it is also used to obtain the predicted values ​​of the 1-mode and 2-mode admittances of the corresponding collector lines based on the bus voltage of the transmission lines before and after the fault in the direct-drive wind farm collection station, as well as the port voltage of each collector line after the fault in the direct-drive wind farm collection station.

[0041] The protection action module is used to obtain the fault criterion value of the corresponding collector line based on the actual value of the 1-mode and 2-mode admittance and the predicted value of the 1-mode and 2-mode admittance of each collector line respectively; and to determine whether the corresponding collector line has experienced an intra-zone fault based on the fault criterion value of each collector line. If so, the protection device of the corresponding collector line will operate.

[0042] Based on the above solution, the present invention also makes the following improvements:

[0043] Furthermore, for each collector line, the fault criterion value E is calculated according to the following formula. m :

[0044]

[0045] Among them, G M1 (s), G M2 (s) represent the predicted 1-mode and 2-mode admittance values ​​of the collector line at the s-th sampling point, respectively, G′ M1 (s), G′ M2 (s) represent the actual values ​​of the 1-mode and 2-mode admittances of the collector line at the s-th sampling point, respectively, and S is the total number of sampling points after the failure of the direct-drive wind farm collection station.

[0046] Furthermore, for each sampling point, the actual values ​​of the 1-mode and 2-mode admittances of the collector line are calculated according to the following formula:

[0047]

[0048]

[0049] Among them, G′ M1 This represents the actual value of the 1-mode admittance of the collector line, G′. M2 This represents the actual 2-mode admittance of the collector circuit; i a i b i c These represent the currents at the a, b, and c phase ports of the current collector at the current sampling point; u a u b u c These represent the voltages at the a, b, and c phase ports of the current collector at the current sampling point, respectively.

[0050] For each sampling point, the predicted 1-mode and 2-mode admittance values ​​of the nth collector line are calculated according to the following formula:

[0051]

[0052]

[0053] in,

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

[0061] k pi k ii These are the proportional and integral coefficients of the current loop PI control, respectively; L is the inductance connected to the grid-side converter; I... max I represents the maximum output current of the direct-drive fan. N Z is the rated per-unit value of the output current of the direct-drive fan, where K is a constant and Z is the rated per-unit value of the output current. T z represents the equivalent reactance of the main transformer on the transmitting line. ln x represents the equivalent impedance of the nth collector line, where n ranges from 1 to N, and N represents the total number of collector lines; n This indicates the number of direct-drive fans on the nth collector line, and T represents the sampling period; These represent the bus voltage u of the output line instants before and after the fault time t0, respectively. mThe measured value; i wn Let u be the port current of the nth collector line at the current sampling point. m i m These represent the bus voltage and bus current of the output line at the current sampling point, respectively; u M1,n u M2,n These represent the 1-mode voltage and 2-mode voltage of the port voltage of the nth collector line at the current sampling point, respectively.

[0062] Furthermore, based on the fault criterion value of each collector line, it is determined whether a fault has occurred within the area on the corresponding collector line, including:

[0063] For each collector line,

[0064] If E is satisfied m >E set This indicates that a fault has occurred within the current collector line, and the protection system has activated.

[0065] If E is satisfied m <E set This indicates that an external fault has occurred in the current collector line, and the protection is locked.

[0066] Among them, E set This represents the fault threshold value.

[0067] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0068] The present invention provides a fault location method for direct-drive wind farms based on virtual modal admittance. Based on the collected three-phase voltage and three-phase current at the bus end of each collector line, and the bus voltage of the transmitting line, the actual values ​​and predicted values ​​of the 1-mode and 2-mode admittances of each collector line are calculated. Then, based on these values, a fault criterion value for each collector line is obtained. Finally, the fault criterion value for each collector line is used to determine whether an intra-area fault has occurred. If so, the protection device of the corresponding collector line is activated. Therefore, by providing a criterion for the full fault construction after a fault, compared to a fault mutation criterion, the criterion remains valid as long as the fault exists, eliminating the need for fault-preserving logic. Thus, the present invention can accurately locate the collector line where a fault has occurred.

[0069] Meanwhile, since the method and system in this invention are based on the same technical principles, this system also possesses the technical effects corresponding to the above-mentioned method.

[0070] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0071] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0072] Figure 1 This is the wind field equivalent circuit diagram provided in Embodiment 1 of the present invention;

[0073] Figure 2 This is the equivalent circuit diagram of the wind farm when the collector line is faulty, provided in Embodiment 1 of the present invention;

[0074] Figure 3 This is a flowchart of the direct-drive wind farm fault location method based on virtual modal admittance provided in Embodiment 1 of the present invention;

[0075] Figure 4 This is a schematic diagram of the structure of the direct-drive wind farm fault location system based on virtual modal admittance provided in Embodiment 2 of the present invention;

[0076] Figure 5 This is a schematic diagram of the direct-drive wind turbine farm model structure provided in Embodiment 3 of the present invention;

[0077] Figure 6 This is the fault location judgment value provided in Embodiment 3 of the present invention when an AB phase fault with a transition resistance of 100Ω occurs at the location of the collector line from the collecting bus.

[0078] Figure 7 This is the fault location judgment value provided in Embodiment 3 of the present invention when an ABC phase fault with a transition resistance of 100Ω occurs at the location of the collector line from the collecting bus.

[0079] Figure 8 This is the fault location judgment value provided in Embodiment 3 of the present invention when a phase A grounding fault occurs on the AC system sending line side;

[0080] Figure 9 It is the fault location judgment value when a short fault occurs between phases BC on the AC system output line side, as provided in Embodiment 3 of the present invention. Detailed Implementation

[0081] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0082] Example 1

[0083] First, the formation principle of the direct-drive wind farm fault location method based on virtual modal admittance provided in Embodiment 1 is explained as follows:

[0084] Since the direct-drive fan is a full inverter power supply, the voltage equation at the fan terminal is expressed as follows:

[0085]

[0086] In the formula: u vd u vq These are the d-axis and q-axis components of the grid-side converter port voltage, respectively; i d i q These are the d-axis and q-axis components of the grid-side converter output current, respectively; u sd u sq ω represents the d-axis and q-axis components of the voltage at the direct-drive fan terminal, respectively; R and L represent the resistance and inductance connected to the grid-side converter, respectively; and ω represents the synchronous angular velocity.

[0087] Wind field equivalent circuit diagram as follows Figure 1 As shown, when a grid fault occurs, the direct-drive wind turbine directly disconnects the outer voltage loop. At this time, the reference value for the inner current loop can be given based on the voltage drop at the direct-drive wind turbine terminals. The calculation formula is as follows:

[0088]

[0089] in, These are the reference values ​​for the d-axis and q-axis components of the grid-side converter output current, respectively. max U is the maximum output current of the direct-drive fan, U is the amplitude of the fault voltage at the fan terminals, and I is the maximum output current of the direct-drive fan. N is the rated per-unit value of the output current of the direct-drive fan, which is generally 1; K is a constant, which is generally taken as 1.5 in engineering.

[0090] When the outer voltage loop is open, the reference value of the inner current loop is constant. Therefore, when analyzing transient currents, only the dynamic response process of the inner current loop is considered. Figure 1 The control structure of the inner current loop control of a direct-drive wind turbine shows that the current loop control equation is:

[0091]

[0092] In the formula: k pi k iiThese are the proportional and integral coefficients for the current loop PI control, respectively.

[0093] Substituting equation (2) into equation (3) and solving for the problem, and performing the dq transformation, we obtain the expression for the transient current in the synchronous rotating coordinate system as follows:

[0094]

[0095] In the formula: C1 and C2 are both attenuation coefficients, which are related to the control parameters and the operating conditions before the fault. The expressions for a1, b1, C1, and C2 are as follows:

[0096]

[0097] in, These represent the instants before and after the fault time t0 of the nth collector line, respectively. Reference value, This indicates the instant before the fault time t0 of the nth collector line. Reference value, These represent the bus voltage u of the output line instants before and after the fault time t0, respectively. m The measured value.

[0098] The equivalent circuit diagram of the wind farm when the collector line is faulty is as follows: Figure 2 As shown, when a fault occurs in the collector lines within a direct-drive wind farm, the wind farm's topology changes. Let's take a fault occurring on the collector line where the first wind turbine is located as an example (i.e....). Figure 2 (A fault occurs at point f). Assuming there is only one direct-drive fan on each collector line, the actual voltage equation for the direct-drive wind farm is:

[0099]

[0100] In the formula, u f The voltage at the fault point is given by u; k represents the fault location, with a value ranging from 0 to 1, indicating the proportion of the fault location to the total length of the current collector line; wn Let i be the port voltage of the nth collector line. wn Let u be the port current of the nth collector line. m i m These are the bus voltage and bus current of the transmitting line, respectively. T z represents the equivalent reactance of the main transformer on the transmitting line. ln This represents the equivalent impedance of the nth collector line, where N represents the total number of collector lines.

[0101] After transforming the system from the dq coordinate system to the three-phase coordinate system, the three-phase electrical quantities of the system are then subjected to phase-mode transformation. The calculation formula is as follows:

[0102]

[0103]

[0104] In the formula, θ is the angle by which the d-axis of the synchronously rotating coordinate system leads the a-axis. a F b F c F represents the electrical quantities of phase a, phase b, and phase c, respectively. d F q F1, F2, and F3 represent the electrical quantities of the d and q axes, respectively, and represent the decoupled 1-mode, 2-mode, and 0-mode electrical quantities, respectively.

[0105] Combining formulas (7) and (8), the general formula for expressing the mode current is obtained as follows:

[0106]

[0107] Combining formulas (4), (6), and (9), the expression for the modulus current of the faulty collector line, i.e., the first collector line, is obtained as follows:

[0108]

[0109]

[0110] i M0f =0 (10)

[0111] At this point, the expression for the virtual modulo admittance of the fault within the first collector line area is:

[0112]

[0113]

[0114] u M1 u M2 These represent the mode 1 voltage and mode 2 voltage of the current collector line port voltage, respectively.

[0115] Similar to the solution process for the first collector line, when a collector line is faulty, the expression for the modulo current of the remaining lines that are not faulty is as follows:

[0116]

[0117]

[0118] i M0 =0 (12)

[0119] For a collector line that has not experienced a fault, the expression for the modulo admittance is:

[0120]

[0121]

[0122] This shows that when a fault occurs in a collector line, there is a significant difference between the virtual modal admittance of the faulty line and the non-faulty line.

[0123] For a scenario where x direct-drive wind turbines are connected to a collector line, due to the short distances between the wind turbines within the wind farm, the lines between the turbines can be ignored for quick and convenient calculation of the virtual modulo admittance. The modulo admittance value is directly proportional to the modulo admittance value when a single wind turbine is connected to the collector line. In this case, when the collector line fails, the expression for the modulo admittance of the faulty line and the lines without faults is:

[0124]

[0125]

[0126]

[0127]

[0128] In the formula, x represents the number of direct-drive wind turbine generators on this set of wires.

[0129] Therefore, it is evident that when a fault occurs in the collector line, there is a significant difference between the virtual modulo admittance of the faulty line and the non-faulty line. Based on this, the protection criterion of this embodiment is constructed. The specific description is as follows:

[0130] This embodiment 1 provides a fault location method for direct-drive wind farms based on virtual modal admittance, the flowchart of which is as follows: Figure 3 As shown, it includes the following steps:

[0131] Step S1: Collect the bus voltage of the outgoing lines before and after the fault of the direct-drive wind farm collection station, as well as the port voltage and port current of each collection line after the fault of the direct-drive wind farm collection station.

[0132] Step S2: Based on the port voltage and port current of each collector line after a fault at the direct-drive wind farm collection station, obtain the actual values ​​of the 1-mode and 2-mode admittances of the corresponding collector lines.

[0133] Step S3: Based on the bus voltage of the transmission lines before and after the fault of the direct-drive wind farm collection station, and the port voltage of each collection line after the fault of the direct-drive wind farm collection station, obtain the predicted values ​​of the 1-mode and 2-mode admittance of the corresponding collection lines.

[0134] Step S4: Based on the actual values ​​of the 1-mode and 2-mode admittances and the predicted values ​​of the 1-mode and 2-mode admittances for each collector line, obtain the fault criterion value for the corresponding collector line; determine whether an intra-zone fault has occurred in the corresponding collector line based on the fault criterion value for each collector line; if so, the protection device of the corresponding collector line will operate.

[0135] It should be noted that steps S2 and S3 can be executed simultaneously, without any order. Step S4 can only be performed after the actual values ​​of the 1-mode and 2-mode admittances and the predicted values ​​of the 1-mode and 2-mode admittances for each collector line are obtained simultaneously.

[0136] In this embodiment, for each collector line, the fault criterion value E is calculated according to the following formula. m :

[0137]

[0138] Among them, G M1 (s), G M2 (s) represent the predicted 1-mode and 2-mode admittance values ​​of the collector line at the s-th sampling point, respectively, G′ M1 (s), G′ M2 (s) represent the actual values ​​of the 1-mode and 2-mode admittances of the collector line at the s-th sampling point, respectively, and S is the total number of sampling points after the failure of the direct-drive wind farm collection station.

[0139] Meanwhile, for each sampling point, the actual values ​​of the 1-mode and 2-mode admittances of the collector line are calculated according to the following formula:

[0140]

[0141]

[0142] Among them, G′ M1 This represents the actual value of the 1-mode admittance of the collector line, G′. M2 This represents the actual 2-mode admittance of the collector circuit; i a i b i c These represent the currents at the a, b, and c phase ports of the current collector at the current sampling point; u a u b u c These represent the voltages at the a, b, and c phase ports of the current collector at the current sampling point.

[0143] The predicted 1-mode and 2-mode admittance values ​​of the current collector line at each sampling point are obtained by discretizing formula (15), that is: for each sampling point, the predicted 1-mode and 2-mode admittance values ​​of the nth collector line are calculated according to the following formula:

[0144]

[0145]

[0146] in,

[0147]

[0148]

[0149]

[0150]

[0151]

[0152]

[0153]

[0154] k pi k ii These are the proportional and integral coefficients of the current loop PI control, respectively; L is the inductance connected to the grid-side converter; I... max I represents the maximum output current of the direct-drive fan. N Z is the rated per-unit value of the output current of the direct-drive fan, where K is a constant and Z is the rated per-unit value of the output current. T z represents the equivalent reactance of the main transformer on the transmitting line. ln x represents the equivalent impedance of the nth collector line, where n ranges from 1 to N, and N represents the total number of collector lines; n This indicates the number of direct-drive fans on the nth collector line, and T represents the sampling period; These represent the bus voltage u of the output line instants before and after the fault time t0, respectively. m The measured value; i wn Let u be the port current of the nth collector line at the current sampling point. m i m These represent the bus voltage and bus current of the output line at the current sampling point, respectively; u M1,n u M2,n These represent the 1-mode voltage and 2-mode voltage of the port voltage of the nth collector line at the current sampling point, respectively.

[0155] In this embodiment, determining whether a fault has occurred in the area for each collector line based on the fault criterion value includes: for each collector line, if E... m >E set If E is satisfied, it indicates that a fault has occurred within the current collector line area, and the protection system will activate; m <E setThis indicates that an external fault has occurred on the current collector line, and the protection is blocked; where E set This represents the fault threshold value. For example, E set The value is 30.

[0156] Example 2

[0157] Embodiment 2 of the present invention provides a fault location system for direct-drive wind farms based on virtual modal admittance, the structural schematic diagram of which is shown below. Figure 4 As shown, it includes:

[0158] The data acquisition module is used to collect the bus voltage of the outgoing lines before and after the fault of the direct-drive wind farm collection station, as well as the port voltage and port current of each collection line after the fault of the direct-drive wind farm collection station.

[0159] The parameter calculation module is used to obtain the actual values ​​of the 1-mode and 2-mode admittances of the corresponding collector lines based on the port voltage and port current of each collector line after a fault in the direct-drive wind farm collection station; it is also used to obtain the predicted values ​​of the 1-mode and 2-mode admittances of the corresponding collector lines based on the bus voltage of the transmission lines before and after the fault in the direct-drive wind farm collection station, as well as the port voltage of each collector line after the fault in the direct-drive wind farm collection station.

[0160] The protection action module is used to obtain the fault criterion value of the corresponding collector line based on the actual value of the 1-mode and 2-mode admittance and the predicted value of the 1-mode and 2-mode admittance of each collector line respectively; and to determine whether the corresponding collector line has experienced an intra-zone fault based on the fault criterion value of each collector line. If so, the protection device of the corresponding collector line will operate.

[0161] It should be noted that the system embodiments described above are based on the same principles and can be referenced from each other. Further details will not be repeated here.

[0162] Meanwhile, since both are based on the same principle, the system embodiment and the above method embodiment have the same technical effect.

[0163] Example 3

[0164] The correctness and rationality of the above system and method are verified through simulation. A 1.5MW direct-drive wind turbine generator model of a 148.5MW wind farm in a certain region was built in Matlab for verification. The model is as follows. Figure 5As shown, the wind farm consists of 100 wind turbine units with a rated power of 1.5MW, a rated frequency of 50Hz, a stator rated voltage of 690V, a stator resistance of 0.0054pu, a rotor resistance of 0.00607pu, a stator leakage inductance of 0.1pu, a rotor leakage inductance of 0.1lpu, a mutual inductance of 4.5pu, an inertial time constant of 0.5s, and a stator-rotor winding ratio of 0.3. The turbine radius is 40m, the rated wind speed is 12m / s, the optimal wind energy utilization factor is 0.28, and the air density is 1.225kg / m^3. The parameters of the collector line are consistent with those of the transmission line, which is 10.3km long, with parameters as follows: r1=0.55*10 -4 Ω / m, x1 = 1.265 * 10 -4 Ω / m, c1=500MΩ*m, r0=0.825*10 -3 Ω / m, x0 = 1.898 * 10 -4 Ω / m, c0=414MΩ*m. Transmitter Z T The parameters are: capacity 100MVA, transformation ratio 38.5kV / 345kV, impedance percentage 10%. The equivalent impedance of the AC system is Z. R1 =3.737+j47.442Ω.

[0165] Taking an AB-phase fault with a transition resistance of 100Ω and an ABC three-phase short circuit as examples, the fault location judgment value E is... m Each as Figure 6 and Figure 7 As shown. By Figure 6 and Figure 7 It can be seen that when an AB phase fault and an ABC three-phase short-circuit fault occur on the AC system's outgoing line side, with a transition resistance of 100Ω, E m If the minimum value is greater than the threshold value, it is determined to be a fault within the sending line area.

[0166] Depend on Figure 8 and Figure 9 It can be seen that when a phase A ground fault and a phase-to-phase short fault (B and C) occur on the AC system's outgoing line side, with a transition resistance of 100Ω, E m The maximum values ​​are all less than the threshold value, so it is determined to be a fault outside the collector area.

[0167] The computational examples based on the Matlab platform demonstrate that the system has the following characteristics:

[0168] (1) The criterion can continuously reflect the fault state without the need for additional hold logic. As long as the fault continues to exist, the fault location criterion will always be valid.

[0169] (2) It can adapt to various operating modes of the system and is not affected by transition impedance or fault location.

[0170] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0171] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware, and the program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0172] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A fault location method for direct-drive wind farms based on virtual modal admittance, characterized in that, include: Collect the bus voltage of the outgoing lines before and after the fault of the direct-drive wind farm collection station, as well as the port voltage and port current of each collection line after the fault of the direct-drive wind farm collection station. Based on the port voltage and port current of each collector line after a fault at the direct-drive wind farm collection station, the actual values ​​of the 1-mode and 2-mode admittances of the corresponding collector lines are obtained. Based on the bus voltage of the transmission lines before and after the fault of the direct-drive wind farm collection station, and the port voltage of each collection line after the fault of the direct-drive wind farm collection station, the predicted values ​​of the 1-mode and 2-mode admittance of the corresponding collection lines are obtained. Based on the actual values ​​of the 1-mode and 2-mode admittances and the predicted values ​​of the 1-mode and 2-mode admittances for each collector line, the fault criterion value for the corresponding collector line is obtained; based on the fault criterion value for each collector line, it is determined whether an intra-zone fault has occurred in the corresponding collector line; if so, the protection device of the corresponding collector line is activated. For each collector line, the fault criterion value is calculated according to the following formula. : (1) in, , They represent the first s The predicted 1-mode and 2-mode admittance values ​​of the collector line at each sampling point. , They represent the first s The actual values ​​of the 1-mode and 2-mode admittances of the collector at each sampling point. This represents the total number of sampling points after a failure at the direct-drive wind farm's collection station. For each sampling point, the actual values ​​of the 1-mode and 2-mode admittances of the collector line are calculated according to the following formula: (2) (3) in, This represents the actual value of the 1-mode admittance of the collector line. This represents the actual value of the 2-mode admittance of the collector line; , , These represent the current collector line at the current sampling point. a , b , c Phase port current; , , These represent the current collector line at the current sampling point. a , b , c Phase port voltage; For each sampling point, the first n The predicted 1-mode and 2-mode admittance values ​​of each collector line are calculated according to the following formula: (4) (5) in, ； , These are the proportional and integral coefficients for the current loop PI control, respectively. L The inductor connected to the grid-side converter, This represents the maximum output current of the direct-drive fan. This is the rated per-unit value of the output current of the direct-drive fan. K It is a constant. This represents the equivalent reactance of the main transformer on the transmission line. Indicates the first The equivalent impedance of the collector line, The value range is 1 to , Indicates the total number of collector lines; Indicates the first The number of direct-drive fans on the power line. Indicates the sampling period; , These represent the time of the fault. Bus voltage of the transmission line at the moment before and after The measured value; For the current sampling point, the first The port current of the collector line, , These are the bus voltage and bus current of the output line at the current sampling point, respectively. , These represent the current sampling point at the th sampling point. The port voltages of the collector line are the 1-mode voltage and the 2-mode voltage.

2. The method for fault location in direct-drive wind farms based on virtual modal admittance according to claim 1, characterized in that, Determine whether a fault has occurred in the area for each collector line based on the fault criterion value, including: For each collector line, If satisfied This indicates that a fault has occurred within the current collector line, and the protection system has activated. If satisfied This indicates that an external fault has occurred in the current collector line, and the protection is locked. in, This represents the fault threshold value.

3. The method for fault location in direct-drive wind farms based on virtual modal admittance according to claim 2, characterized in that, The value is 30.

4. A fault location system for direct-drive wind farms based on virtual modal admittance, characterized in that, include: The data acquisition module is used to collect the bus voltage of the outgoing lines before and after the fault of the direct-drive wind farm collection station, as well as the port voltage and port current of each collection line after the fault of the direct-drive wind farm collection station. The parameter calculation module is used to obtain the actual values ​​of the 1-mode and 2-mode admittances of each collector line based on the port voltage and port current of each collector line after a fault in the direct-drive wind farm collection station. It is also used to obtain the predicted 1-mode and 2-mode admittance values ​​of the corresponding collection lines based on the bus voltage of the transmission lines before and after the fault of the direct-drive wind farm collection station, and the port voltage of each collection line after the fault of the direct-drive wind farm collection station. The protection action module is used to obtain the fault criterion value of the corresponding collector line based on the actual value of the 1-mode and 2-mode admittance and the predicted value of the 1-mode and 2-mode admittance of each collector line respectively; and to determine whether the corresponding collector line has experienced an intra-zone fault based on the fault criterion value of each collector line. If so, the protection device of the corresponding collector line will be activated. For each collector line, the fault criterion value is calculated according to the following formula. : (6) in, , They represent the first s The predicted 1-mode and 2-mode admittance values ​​of the collector line at each sampling point. , They represent the first s The actual values ​​of the 1-mode and 2-mode admittances of the collector at each sampling point. This represents the total number of sampling points after a failure at the direct-drive wind farm's collection station. For each sampling point, the actual values ​​of the 1-mode and 2-mode admittances of the collector line are calculated according to the following formula: (7) (8) in, This represents the actual value of the 1-mode admittance of the collector line. This represents the actual value of the 2-mode admittance of the collector line; , , These represent the current collector line at the current sampling point. a , b , c Phase port current; , , These represent the current collector line at the current sampling point. a , b , c Phase port voltage; For each sampling point, the first n The predicted 1-mode and 2-mode admittance values ​​of each collector line are calculated according to the following formula: (9) (10) in, ； , These are the proportional and integral coefficients for the current loop PI control, respectively. L The inductor connected to the grid-side converter, This represents the maximum output current of the direct-drive fan. This is the rated per-unit value of the output current of the direct-drive fan. K It is a constant. This represents the equivalent reactance of the main transformer on the transmission line. Indicates the first The equivalent impedance of the collector line, The value range is 1 to , Indicates the total number of collector lines; Indicates the first The number of direct-drive fans on the power line. Indicates the sampling period; , These represent the time of the fault. Bus voltage of the transmission line at the moment before and after The measured value; For the current sampling point, the first The port current of the collector line, , These are the bus voltage and bus current of the output line at the current sampling point, respectively. , These represent the current sampling point at the th sampling point. The port voltages of the collector line are the 1-mode voltage and the 2-mode voltage.

5. The direct-drive wind farm fault location system based on virtual modal admittance according to claim 4, characterized in that, Determine whether a fault has occurred in the area for each collector line based on the fault criterion value, including: For each collector line, If satisfied This indicates that a fault has occurred within the current collector line, and the protection system has activated. If satisfied This indicates that an external fault has occurred in the current collector line, and the protection is locked. in, This represents the fault threshold value.

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