A method and terminal for analyzing and calculating short-circuit current of offshore wind farms under three-phase faults

Abstract

The present invention discloses a method and terminal for analyzing and calculating short-circuit current in offshore wind farms under three-phase faults. Based on the control strategy of a single wind turbine, an output current model for the corresponding direct-drive wind turbine during low voltage ride-through is established. A node admittance matrix from the wind farm to the fault point is constructed based on the wind farm's internal impedance parameters and the equivalent impedance from the fault point to the wind farm's PCC point. The output current of each wind turbine under normal operating conditions is obtained as the initial value for current iteration, and the terminal voltage and output short-circuit current of each wind turbine are iteratively calculated. The short-circuit current output from the offshore wind farm to the power grid is calculated. By using the established output current model and node admittance matrix during low voltage ride-through, the short-circuit current output from the wind farm to the power grid is analyzed and calculated iteratively. This method has a faster computation speed than existing simulation calculation methods and can meet the needs of relay protection engineering in the case of large-scale wind farms.

Description

Technical Field

[0001] The present invention relates to the field of electric field safety technology, and in particular to a method and terminal for analyzing and calculating short-circuit current in an offshore wind farm under a three-phase fault. Background Art

[0002] As the installed capacity of offshore wind farms continues to increase, the challenges they bring to the safe and stable operation of the current power grid are becoming increasingly apparent. Since the low-voltage ride-through current calculation method after large-scale offshore wind power is connected to the grid is the basis for analyzing whether the existing relay protection devices can meet the needs of offshore wind power, the relevant low-voltage ride-through current calculation method is receiving more and more attention.

[0003] Currently, when calculating the low voltage ride-through current for direct-drive wind farms, they are generally considered to be equivalent direct-drive wind turbines. However, in reality, the capacity and number of wind turbines in offshore wind farms, as well as the cables used in wind farms, differ significantly from those in onshore wind farms. This results in significant differences in the transient characteristics during low voltage ride-through compared to onshore wind farms. Therefore, traditional current calculation methods cannot guarantee sufficient accuracy when calculating and analyzing the low voltage ride-through current for offshore wind farms.

[0004] Specifically, current research on control strategies for direct-drive wind turbines during low voltage ride-through is mainly based on the simulation of electromechanical or electromagnetic transients. By establishing a time-domain dynamic model of the electromechanical or electromagnetic transients of the wind turbine, a time-domain simulation of the transients after the fault is performed, and then the waveform of the output current is analyzed. The sensitivity of this type of method is limited by the model, and when the wind farm is large, the calculation time is long and the analysis efficiency is low, which cannot meet the needs of relay protection engineering. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method and terminal for analyzing and calculating short-circuit current of offshore wind farms under three-phase faults, which can quickly calculate the short-circuit current output by the wind farm to the power grid to meet the needs of relay protection engineering.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A method for analyzing and calculating short-circuit current of an offshore wind farm under a three-phase fault, comprising the steps of:

[0008] S1. Based on the control strategy of a single wind turbine, establish the output current model of the corresponding direct-drive wind turbine during the low voltage ride-through period;

[0009] S2. Obtain the internal impedance parameters of the wind farm and the equivalent impedance from the fault point to the PCC point of the wind farm, and construct a node admittance matrix from the wind farm to the fault point based on the internal impedance parameters of the wind farm and the equivalent impedance from the fault point to the PCC point of the wind farm;

[0010] S3. Obtain the output current of each wind turbine under normal operating conditions as the initial value of current iteration, and iteratively calculate the terminal voltage and output short-circuit current of each wind turbine according to the output current model and node admittance matrix during low voltage ride-through;

[0011] S4. Calculate the sum of the output short-circuit currents of each wind turbine generator set as the short-circuit current output by the offshore wind farm to the system.

[0012] In order to solve the above technical problems, another technical solution adopted by the present invention is:

[0013] A terminal for analyzing and calculating short-circuit current of an offshore wind farm under a three-phase fault, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the following steps when executing the computer program:

[0014] S1. Based on the control strategy of a single wind turbine, establish the output current model of the corresponding direct-drive wind turbine during the low voltage ride-through period;

[0015] S2. Obtain the internal impedance parameters of the wind farm and the equivalent impedance from the fault point to the PCC point of the wind farm, and construct a node admittance matrix from the wind farm to the fault point based on the internal impedance parameters of the wind farm and the equivalent impedance from the fault point to the PCC point of the wind farm;

[0016] S3. Obtain the output current of each wind turbine under normal operating conditions as the initial value of current iteration, and iteratively calculate the terminal voltage and output short-circuit current of each wind turbine according to the output current model and node admittance matrix during low voltage ride-through;

[0017] S4. Calculate the sum of the output short-circuit currents of each wind turbine generator set as the short-circuit current output by the offshore wind farm to the system.

[0018] The beneficial effects of the present invention are: a method and terminal for analyzing and calculating the short-circuit current of an offshore wind farm under a three-phase fault, which analyzes and calculates the short-circuit current output by the wind farm to the power grid in an iterative manner by establishing an output current model and a node admittance matrix during low voltage ride-through. Compared with the existing simulation calculation method, it has a faster calculation speed and can meet the needs of relay protection engineering in the case of large-scale wind farms. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of a flow chart of a method for analyzing and calculating short-circuit current of an offshore wind farm under a three-phase fault according to an embodiment of the present invention;

[0020] Figure 2 A flow diagram of a method for analyzing and calculating short-circuit current in an offshore wind farm under a three-phase fault according to an embodiment of the present invention;

[0021] Figure 3 A schematic diagram of low voltage ride-through capability requirements for a wind turbine generator system according to an embodiment of the present invention;

[0022] Figure 4 This is a schematic diagram of the topology of an offshore wind farm involved in an embodiment of the present invention;

[0023] Figure 5 Schematic diagram of an iterative process in short-circuit current calculation according to an embodiment of the present invention;

[0024] Figure 6 A comparison diagram of the short-circuit currents of the BPA simulation and the calculation method involved in the embodiment of the present invention;

[0025] Figure 7 A comparison diagram of short-circuit currents between partial unit removal and no unit removal according to an embodiment of the present invention;

[0026] Figure 8 The present invention is a schematic structural diagram of a terminal for analyzing and calculating short-circuit current in an offshore wind farm under three-phase fault conditions according to an embodiment of the present invention.

[0027] Description of labels:

[0028] 1. A terminal for analyzing and calculating short-circuit current of an offshore wind farm under three-phase fault conditions; 2. A processor; 3. A memory. DETAILED DESCRIPTION

[0029] To illustrate the technical content, achieved objectives and effects of the present invention in detail, the following description is given in conjunction with the embodiments and accompanying drawings.

[0030] Please refer to Figures 1 to 7 A method for analyzing and calculating short-circuit current of an offshore wind farm under a three-phase fault condition comprises the following steps:

[0031] S1. Based on the control strategy of a single wind turbine, establish the output current model of the corresponding direct-drive wind turbine during the low voltage ride-through period;

[0032] S2. Obtain the internal impedance parameters of the wind farm and the equivalent impedance from the fault point to the PCC point of the wind farm, and construct a node admittance matrix from the wind farm to the fault point based on the internal impedance parameters of the wind farm and the equivalent impedance from the fault point to the PCC point of the wind farm;

[0033] S3. Obtain the output current of each wind turbine under normal operating conditions as the initial value of current iteration, and iteratively calculate the terminal voltage and output short-circuit current of each wind turbine according to the output current model and node admittance matrix during low voltage ride-through;

[0034] S4. Calculate the sum of the output short-circuit currents of each wind turbine generator set as the short-circuit current output by the offshore wind farm to the system.

[0035] From the above description, it can be seen that the beneficial effects of the present invention are: a method and terminal for analyzing and calculating the short-circuit current of an offshore wind farm under a three-phase fault, which analyzes and calculates the short-circuit current output by the wind farm to the power grid in an iterative manner by establishing an output current model and a node admittance matrix during low voltage ride-through. Compared with the existing simulation calculation method, it has a faster calculation speed and can meet the needs of relay protection engineering in the case of large-scale wind farms.

[0036] Furthermore, the control strategy of the single motor is specifically a reactive power control priority strategy;

[0037] The output current model during the low voltage ride-through period is as follows:

[0038]

[0039] Where, ψ t is the phase angle of the wind turbine terminal voltage, U t is the modulus of the wind turbine terminal voltage, I max is the per-unit value of the inverter current limit, θ t The phase angle of the wind turbine output current leading the voltage.

[0040] From the above description, it can be seen that a specific solution of the output current model during low voltage ride-through is given.

[0041] Furthermore, the step S3 specifically includes:

[0042] S31, obtain the output current of each wind turbine under normal working conditions as the initial value of current iteration, calculate the voltage of each node according to the initial value of current iteration, and filter out the column vector U of the terminal voltage of each wind turbine t∑ (1) ;

[0043] S32, according to the arrangement order of the fans, use the terminal voltage of the j-th fan in turn The output current model during low voltage ride-through is used to calculate the output current of the jth unit. Form the output current column vector I of each wind turbine ∑ (n) ;

[0044] S33, output current column vector I ∑ (n) Substitute into the node voltage equation to obtain the column vector U containing the terminal voltage of each unit t∑ (n+1) ;

[0045] Repeat the iterative execution of steps S32-S33 until ||U t∑ (n+1) -U t∑ (n) ||≤10 -6 Or after the number of executions reaches the preset iteration limit, the output current column vector I is output ∑ (n) The various elements are used as the output short-circuit current of each wind turbine set.

[0046] From the above description, it can be seen that the output short-circuit current of each wind turbine group is iteratively calculated.

[0047] Furthermore, the nodes of the node admittance matrix include the wind turbine input node and the contact node, and the maximum dimension of the node admittance matrix is ​​the node admittance matrix Y M It is generated by combining the line parameters inside the wind farm with the equivalent impedance from the fault point to the PCC point of the wind farm when all wind turbines are working. It is expressed as follows:

[0048]

[0049] In the formula, the fan input nodes are numbered from #1 to #m, and the connection nodes are numbered from &1 to &n; Y ## Represents the admittance matrix between the fan input points; Y && represents the admittance matrix between the connection nodes; Y #& With Y &# Represents the mutual admittance matrix between the wind turbine input node and the connection node.

[0050] From the above description, it can be seen that the establishment of the maximum dimension node admittance matrix is ​​achieved.

[0051] Furthermore, when the #i typhoon is shut down, the following steps are implemented:

[0052] A1. Locate the self-admittance position of the input node of the #i wind turbine;

[0053] A2. Eliminate the row and column where the self-admittance is located;

[0054] A3. Locate the self-admittance position of the contact node &j that is electrically connected to the #i wind turbine;

[0055] A4. The self-admittance of the connection node minus the self-admittance of the fan input node is the new self-admittance of the connection node.

[0056] From the above description, it can be seen that the modification of the node admittance matrix is ​​realized when the #i typhoon is shut down.

[0057] Please refer to Figure 8A terminal for analyzing and calculating short-circuit current of an offshore wind farm under a three-phase fault condition includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the following steps are implemented:

[0058] S1. Based on the control strategy of a single wind turbine, establish the output current model of the corresponding direct-drive wind turbine during the low voltage ride-through period;

[0059] S2. Obtain the internal impedance parameters of the wind farm and the equivalent impedance from the fault point to the PCC point of the wind farm, and construct a node admittance matrix from the wind farm to the fault point based on the internal impedance parameters of the wind farm and the equivalent impedance from the fault point to the PCC point of the wind farm;

[0060] S3. Obtain the output current of each wind turbine under normal operating conditions as the initial value of current iteration, and iteratively calculate the terminal voltage and output short-circuit current of each wind turbine according to the output current model and node admittance matrix during low voltage ride-through;

[0061] S4. Calculate the sum of the output short-circuit currents of each wind turbine generator set as the short-circuit current output by the offshore wind farm to the system.

[0062] From the above description, it can be seen that the beneficial effects of the present invention are: a method and terminal for analyzing and calculating the short-circuit current of an offshore wind farm under a three-phase fault, which analyzes and calculates the short-circuit current output by the wind farm to the power grid in an iterative manner by establishing an output current model and a node admittance matrix during low voltage ride-through. Compared with the existing simulation calculation method, it has a faster calculation speed and can meet the needs of relay protection engineering in the case of large-scale wind farms.

[0063] Furthermore, the control strategy of the single motor is specifically a reactive power control priority strategy;

[0064] The output current model during the low voltage ride-through period is as follows:

[0065]

[0066] Where, ψ t is the phase angle of the wind turbine terminal voltage, U t is the modulus of the wind turbine terminal voltage, I max is the per-unit value of the inverter current limit, θ t The phase angle of the wind turbine output current leading the voltage.

[0067] From the above description, it can be seen that a specific solution of the output current model during low voltage ride-through is given.

[0068] Furthermore, the step S3 specifically includes:

[0069] S31, obtain the output current of each wind turbine under normal working conditions as the initial value of current iteration, calculate the voltage of each node according to the initial value of current iteration, and filter out the column vector U of the terminal voltage of each wind turbine t∑ (1) ;

[0070] S32, according to the arrangement order of the fans, use the terminal voltage of the j-th fan in turn The output current model during low voltage ride-through is used to calculate the output current of the jth unit. Form the output current column vector I of each wind turbine ∑ (n) ;

[0071] S33, output current column vector I ∑ (n) Substitute into the node voltage equation to obtain the column vector U containing the terminal voltage of each unit t∑ (n+1) ;

[0072] Repeat the iterative execution of steps S32-S33 until ||U t∑ (n+1) -U t∑ (n) ||≤10 -6 Or after the number of executions reaches the preset iteration limit, the output current column vector I is output ∑ (n) The various elements are used as the output short-circuit current of each wind turbine set.

[0073] From the above description, it can be seen that the output short-circuit current of each wind turbine group is iteratively calculated.

[0074] Furthermore, the nodes of the node admittance matrix include the wind turbine input node and the contact node, and the maximum dimension of the node admittance matrix is ​​the node admittance matrix Y M It is generated by combining the line parameters inside the wind farm with the equivalent impedance from the fault point to the PCC point of the wind farm when all wind turbines are working. It is expressed as follows:

[0075]

[0076] In the formula, the fan input nodes are numbered from #1 to #m, and the connection nodes are numbered from &1 to &n; Y ## Represents the admittance matrix between the fan input points; Y && represents the admittance matrix between the connection nodes; Y #& With Y &# Represents the mutual admittance matrix between the wind turbine input node and the connection node.

[0077] From the above description, it can be seen that the establishment of the maximum dimension node admittance matrix is ​​achieved.

[0078] Furthermore, when the #i typhoon is shut down, the following steps are implemented:

[0079] A1. Locate the self-admittance position of the input node of the #i wind turbine;

[0080] A2. Eliminate the row and column where the self-admittance is located;

[0081] A3. Locate the self-admittance position of the contact node &j that is electrically connected to the #i wind turbine;

[0082] A4. The self-admittance of the connection node minus the self-admittance of the fan input node is the new self-admittance of the connection node.

[0083] From the above description, it can be seen that the modification of the node admittance matrix is ​​realized when the #i typhoon is shut down.

[0084] The present invention is used for short-circuit current analysis and calculation of large-scale wind farms, and is particularly suitable for short-circuit current analysis and calculation of offshore wind farms.

[0085] Please refer to Figures 1 to 7 , embodiment 1 of the present invention is:

[0086] A method for analyzing and calculating short-circuit current of an offshore wind farm under a three-phase fault, comprising the following steps:

[0087] S1. Based on the control strategy of a single wind turbine, establish the output current model of the corresponding direct-drive wind turbine during the low voltage ride-through period.

[0088] In this embodiment, please refer to Figure 3 , Figure 3 The low voltage ride-through capability requirement for wind turbines specified in the existing technology "GB / T19963.1-2021 Technical Regulations for Wind Farm Connection to Power System" requires that when a short circuit fault occurs in the power system, causing the wind turbine voltage to drop below 20% of the nominal voltage, the wind turbine should be disconnected immediately; if the wind farm grid connection point voltage U t When the voltage drops to 20% of the nominal voltage, the wind turbines in the wind farm should be guaranteed to operate continuously for 625ms without disconnecting from the grid. During this period, reactive current injection I q ≥1.05I N If the grid voltage drops to 20%-90% of the nominal voltage, the wind turbine's continuous operation time without disconnecting from the grid increases from 625ms to 2s. During this period, the reactive current increment responds to the change in grid voltage as follows:

[0089] I q ≥K*(0.9-U t )*I N ;

[0090] Where K represents the dynamic reactive current proportional coefficient of the wind farm. If the grid voltage drops below 20%, the wind turbine is allowed to be disconnected from the grid, and no reactive current requirements are made at this time. If the grid voltage drops to 90%-100%, the wind farm is required to maintain the active and reactive current control strategy during normal operation. t Indicates the per-unit value of the wind turbine generator output voltage, I N Indicates the rated current of the wind turbine.

[0091] When the reactive power control priority strategy is adopted, taking the direct-drive wind turbine as an example, when the wind turbine is not disconnected, the target value of the reactive current component of the wind turbine I qref The calculation formula is as follows:

[0092]

[0093] In the formula, the wind farm dynamic reactive power ratio K is taken as 1.5, I qref It represents the reference value of reactive current component, and I1 represents the current injected into the grid by the wind turbine before the fault.

[0094] The short-circuit current reactive component reference value I qref , calculate the short-circuit current active component limit I dref.max for:

[0095]

[0096] Where K lim is the inverter current limit. In this embodiment, its value is 1.1-1.2. The active component reference value I dref and the active component limit per unit value I dref.max Compare, if I dref ≥I dref.max , it means that the inverter current limit is reached. If I dref dref.max , it means that the inverter current limit is not reached. At this time:

[0097]

[0098] Where P represents the per-unit value of the active power output by the wind turbine under normal operating conditions.

[0099] Among them, the active component reference value I dref The calculation formula is:

[0100]

[0101] At this time, the wind turbine terminal voltage Its active current I dref , reactive current I qref ​And the wind turbine output current The relationship is as follows:

[0102]

[0103] Where, ψ t is the phase angle of the wind turbine terminal voltage, U t is the modulus of the wind turbine terminal voltage; I max =K lim I N , which means the per-unit value of the inverter current limit; θ t The phase angle of the wind turbine output current leading the voltage.

[0104] S2. Obtain the internal impedance parameters of the wind farm and the equivalent impedance from the fault point to the PCC point of the wind farm, and construct a node admittance matrix from the wind farm to the fault point based on the internal impedance parameters of the wind farm and the equivalent impedance from the fault point to the PCC point of the wind farm.

[0105] Specifically, the internal impedance parameters of the wind farm and the equivalent impedance from the fault point to the PCC (point of common coupling) of the wind farm are obtained from the distributed energy management system.

[0106] The wind farm's distributed energy management system collects and controls the active and reactive power output of each wind turbine in the wind farm. The adjustment range changes in real time with the equipment's operating status, wind speed, and the grid's operating conditions. Therefore, based on the information provided by the distributed energy management system, the disconnection status of each wind turbine in the wind farm can be determined. Simulation software can then be used to obtain the output current of each wind turbine under normal operating conditions, which serves as the initial value for current iteration.

[0107] Please refer to Figure 4 Given the wind farm topology, it is known that the node admittance matrix generated when all wind turbines are working is the largest. Therefore, in this context, the line parameters within the wind farm and the equivalent impedance from the fault point to the wind farm PCC point are combined to generate the maximum-dimensional node admittance matrix. The nodes are divided into two parts: wind turbine input nodes and contact nodes. The maximum-dimensional node admittance matrix Y M The expression is as follows:

[0108]

[0109] In the formula, the fan input nodes are numbered from #1 to #m, and the connection nodes are numbered from &1 to &n; Y ## Represents the admittance matrix between the fan input points; Y && represents the admittance matrix between the connection nodes; Y #& With Y &#Represents the mutual admittance matrix between the wind turbine input node and the connection node.

[0110] In the subsequent use, Y can be adjusted according to the fan disconnection information provided by EMS. M Considering that wind turbines are usually only electrically connected to one connection node, when the #i wind turbine is in the off state, the node admittance matrix can be modified as follows:

[0111] A1. Locate the self-admittance position of the input node of the #i wind turbine;

[0112] A2. Eliminate the row and column where the self-admittance is located;

[0113] A3. Locate the self-admittance position of the contact node &j that is electrically connected to the #i wind turbine;

[0114] A4. The self-admittance of the connection node minus the self-admittance of the wind turbine input node is the new self-admittance of the connection node;

[0115] The modified node admittance matrix Y' is as follows:

[0116]

[0117] S3. Obtain the output current of each wind turbine under normal operating conditions as the initial value of current iteration, and iteratively calculate the terminal voltage and output short-circuit current of each wind turbine according to the output current model and node admittance matrix during low voltage ride-through.

[0118] When the voltage at the wind farm's grid connection point is known, the node voltage equation cannot be solved directly due to the coupling between wind turbines and the nonlinear relationship between wind turbine terminal voltage and output current. Therefore, an iterative method is required for calculation.

[0119] Please refer to Figure 5 , step S3 specifically includes:

[0120] S31, obtain the output current of each wind turbine under normal working conditions as the initial value of current iteration, calculate the voltage of each node according to the initial value of current iteration, and filter out the column vector U of the terminal voltage of each wind turbine t∑ (1) .

[0121] In this embodiment, the output current of each wind turbine generator set under normal operating conditions is obtained as the current iteration initial value column vector I ∑ (0) , the voltage U of each node in the wind farm is obtained from the node voltage equation ∑ (1) And filter out the column vector U containing the terminal voltage of each wind turbine t∑ (1), the column vector U of the terminal voltage of each wind turbine t∑ (1) As shown below:

[0122]

[0123] Among them, for a network with n nodes, the mathematical model of the node voltage equation can be expressed as follows:

[0124] I = Y * U;

[0125] Where Y is the node admittance matrix.

[0126] S32, according to the arrangement order of the fans, use the terminal voltage of the j-th fan in turn The output current model during low voltage ride-through is used to calculate the output current of the jth unit. Form the output current column vector I of each wind turbine ∑ (n) .

[0127] S33, output current column vector I ∑ (n) Substitute into the node voltage equation to obtain the column vector U containing the terminal voltage of each unit t∑ (n+1) .

[0128] Repeat the iterative execution of steps S32-S33 until ||U t∑ (n+1) -U t∑ (n) ||≤10 -6 Or after the number of executions reaches the preset iteration limit, the output current column vector I is output ∑ (n) The various elements are used as the output short-circuit current of each wind turbine set.

[0129] If||U t∑ (n+1) -U t∑ (n) ||≤10 -6 At this time, the terminal voltage of each unit reaches the convergence value and meets the error requirements at the same time, and exits the loop. If ||U ∑ (n) -U ∑ (n-1) ||>10 -6 , it is considered that convergence has not yet occurred and the n+1th iteration needs to be continued until the iteration converges or the number of iterations exceeds the upper limit Max of the loop iteration number, and the loop is exited.

[0130] The result of the last cycle is the terminal voltage column vector U of each wind turbine in the wind farm. t∑And the output short-circuit current column vector I t∑ The final result.

[0131] S4. Calculate the sum of the output short-circuit currents of each wind turbine generator set as the short-circuit current output by the offshore wind farm to the system.

[0132] That is, the total short-circuit current output by the offshore wind farm to the grid can be calculated by the following formula:

[0133]

[0134] Where m is the number of wind turbines, I t∑.i Represents the short-circuit current output by the i-th wind turbine.

[0135] This embodiment is verified by Matlab calculation, and the simulation parameters of each wind turbine in the wind farm are typical parameters. The reliability of this method can be verified by comparing the simulation results of a detailed wind farm in BPA (simulation software developed by Bonneville Power Administration) and the calculation method described in this patent. The fault scenario is set with the line between the wind farm grid connection point and the infinite power grid. The output of each unit in the wind farm is 1MW, and the voltage drop at the grid connection point is set to 0.5-0.8pu. Figure 6 From the simulation results shown, it can be seen that the simulation results of this method are basically consistent with the simulation results of BPA software.

[0136] The reliability of this method is verified by increasing the cut-off voltage of some wind turbines in the case of partial cut-off of wind farm units. The fault scenario is set to the cut-off voltage of wind turbine units #1, #2, and #3 in the wind farm to be 0.4 pu. Figure 7 The simulation results shown in the figure show that the calculation results of this method can provide some data for the setting and selection of relay protection devices in the scenario of partial unit disconnection.

[0137] Please refer to Figure 8 , the second embodiment of the present invention is:

[0138] A terminal 1 for analyzing and calculating short-circuit current of an offshore wind farm under three-phase fault conditions includes a memory 3, a processor 2, and a computer program stored in the memory 3 and executable on the processor 2. When the processor 2 executes the computer program, the steps of the above-mentioned embodiment 1 are implemented.

[0139] In summary, the present invention provides a method and terminal for analyzing and calculating the short-circuit current of an offshore wind farm under a three-phase fault. By establishing an output current model and a node admittance matrix during low voltage ride-through, the short-circuit current output by the wind farm to the power grid is analyzed and calculated in an iterative manner. Compared with the existing simulation calculation method, it has a faster calculation speed and can meet the needs of relay protection engineering in the case of large-scale wind farms.

[0140] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's description and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for analyzing and calculating short-circuit current of an offshore wind farm under three-phase fault, characterized in that: Including steps: S1. Based on the control strategy of a single wind turbine, establish the output current model of the corresponding direct-drive wind turbine during the low voltage ride-through period; S2. Obtain the internal impedance parameters of the wind farm and the equivalent impedance from the fault point to the PCC point of the wind farm, and construct a node admittance matrix from the wind farm to the fault point based on the internal impedance parameters of the wind farm and the equivalent impedance from the fault point to the PCC point of the wind farm; S3. Obtain the output current of each wind turbine under normal operating conditions as the initial value of current iteration, and iteratively calculate the terminal voltage and output short-circuit current of each wind turbine according to the output current model and node admittance matrix during low voltage ride-through; S4. Calculate the sum of the output short-circuit currents of each wind turbine as the short-circuit current output by the offshore wind farm to the system; The control strategy of the single wind turbine is specifically a reactive power control priority strategy; The output current model during the low voltage ride-through period is as follows: ； Where, is the phase angle of the wind turbine terminal voltage, is the modulus of the wind turbine terminal voltage, is the per-unit value of the inverter current limit, The phase angle of the wind turbine output current leading the voltage; The nodes of the node admittance matrix include the wind turbine input node and the contact node, and the maximum dimension of the node admittance matrix is ​​the node admittance matrix It is generated by combining the line parameters inside the wind farm with the equivalent impedance from the fault point to the PCC point of the wind farm when all wind turbines are working. It is expressed as follows: ； Where, the number range of wind turbine input nodes is #1 to #m, and the number range of connecting nodes is &1 to &n; Represents the admittance matrix between wind turbine input nodes; Represents the admittance matrix between the connection nodes; and Represents the mutual admittance matrix between the wind turbine input node and the connection node.

2. The method for analyzing and calculating short-circuit current of an offshore wind farm under a three-phase fault according to claim 1, characterized in that: The step S3 specifically includes: S31, obtain the output current of each wind turbine under normal working conditions as the initial value of current iteration, calculate the voltage of each node according to the initial value of current iteration, and filter out the column vector of the terminal voltage of each wind turbine ; S32, according to the arrangement order of the fans, use the terminal voltage of the j-th fan in turn The output current model during low voltage ride-through is used to calculate the output current of the jth unit. , forming the output current column vector of each wind turbine ; S33, output current column vector Substitute into the node voltage equation to obtain the column vector containing the terminal voltage of each unit ; Repeat steps S32-S33 until Or output the output current column vector after the execution number reaches the preset iteration limit The various elements are used as the output short-circuit current of each wind turbine set.

3. The method for analyzing and calculating short-circuit current of an offshore wind farm under a three-phase fault according to claim 1, characterized in that: When the #i typhoon is shut down, the following steps are implemented: A1. Locate the self-admittance position of the input node of the #i wind turbine; A2. Eliminate the row and column where the self-admittance is located; A3. Locate the self-admittance position of the contact node &j that is electrically connected to the #i wind turbine; A4. The self-admittance of the connection node minus the self-admittance of the fan input node is the new self-admittance of the connection node.

4. A terminal for analyzing and calculating short-circuit current of an offshore wind farm under a three-phase fault, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the following steps are implemented: S1. Based on the control strategy of a single wind turbine, establish the output current model of the corresponding direct-drive wind turbine during the low voltage ride-through period; S2. Obtain the internal impedance parameters of the wind farm and the equivalent impedance from the fault point to the PCC point of the wind farm, and construct a node admittance matrix from the wind farm to the fault point based on the internal impedance parameters of the wind farm and the equivalent impedance from the fault point to the PCC point of the wind farm; S3. Obtain the output current of each wind turbine under normal operating conditions as the initial value of current iteration, and iteratively calculate the terminal voltage and output short-circuit current of each wind turbine according to the output current model and node admittance matrix during low voltage ride-through; S4. Calculate the sum of the output short-circuit currents of each wind turbine as the short-circuit current output by the offshore wind farm to the system; The control strategy of the single wind turbine is specifically a reactive power control priority strategy; The output current model during the low voltage ride-through period is as follows: ； Where, is the phase angle of the wind turbine terminal voltage, is the modulus of the wind turbine terminal voltage, is the per-unit value of the inverter current limit, The phase angle of the wind turbine output current leading the voltage; The nodes of the node admittance matrix include the wind turbine input node and the contact node, and the maximum dimension of the node admittance matrix is ​​the node admittance matrix It is generated by combining the line parameters inside the wind farm with the equivalent impedance from the fault point to the PCC point of the wind farm when all wind turbines are working. It is expressed as follows: ； Where, the number range of wind turbine input nodes is #1 to #m, and the number range of connecting nodes is &1 to &n; Represents the admittance matrix between wind turbine input nodes; Represents the admittance matrix between the connection nodes; and Represents the mutual admittance matrix between the wind turbine input node and the connection node.

5. The offshore wind farm short-circuit current analysis and calculation terminal under three-phase fault according to claim 4, characterized in that: The step S3 specifically includes: S31, obtain the output current of each wind turbine under normal working conditions as the initial value of current iteration, calculate the voltage of each node according to the initial value of current iteration, and filter out the column vector of the terminal voltage of each wind turbine ; S32, according to the arrangement order of the fans, use the terminal voltage of the j-th fan in turn The output current model during low voltage ride-through is used to calculate the output current of the jth unit. , forming the output current column vector of each wind turbine ; S33, output current column vector Substitute into the node voltage equation to obtain the column vector containing the terminal voltage of each unit ; Repeat steps S32-S33 until Or output the output current column vector after the execution number reaches the preset iteration limit The various elements are used as the output short-circuit current of each wind turbine set.

6. The offshore wind farm short-circuit current analysis and calculation terminal under three-phase fault according to claim 4, characterized in that: When the #i typhoon is shut down, the following steps are implemented: A1. Locate the self-admittance position of the input node of the #i wind turbine; A2. Eliminate the row and column where the self-admittance is located; A3. Locate the self-admittance position of the contact node &j that is electrically connected to the #i wind turbine; A4. The self-admittance of the connection node minus the self-admittance of the fan input node is the new self-admittance of the connection node.

Images