A land station alternating current fault control method, system, device and medium

Abstract

The present application relates to the technical field of power systems, and discloses a kind of land station ac fault control method, system, equipment and medium, this method determines the ac voltage of land station flexible direct current variable network side according to ac fault flag bit, and by the basis of dq axis outer ring control and dq axis inner ring control in land station, introduce ac fault flag bit to identify whether land station is in ac fault period, so that in the period when land station is in ac fault, the second current reference value corresponding to the grid voltage amplitude during ac fault is used to modulate the reactive current of land station, also by the voltage modulation wave generated by the low-frequency component of the direct current of land station through filtering and damping coefficient operation to modulate the ac voltage of land station, realize the ac fault successful crossing of offshore wind power through the land station of flexible direct current grid-connected system, can reduce the risk of dc trip and wind turbine off-grid of wind farm, improve the safety and reliability of offshore wind power through flexible direct current grid-connected system.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to a method, system, device and medium for AC fault control at an onshore substation. Background Technology

[0002] In recent years, with the development of new energy power generation technology and power electronics technology, the technical solution of using flexible DC (Voltagesource converter based high-voltage direct current system, VSC-HVDC) to transmit large-scale, long-distance offshore wind power and connect it to the onshore power grid has been widely used. At present, dozens of offshore wind power grid-connected projects via flexible DC have been put into operation worldwide.

[0003] like Figure 1 The topology of the offshore wind power connected to the flexible DC grid, as shown, differs significantly from traditional two-terminal grid-connected flexible DC systems in its DC control functionality. Flexible DC systems typically require AC fault ride-through without DC tripping under various AC fault conditions. Current offshore wind power connected to the flexible DC grid struggles to effectively control AC faults at onshore stations. This can lead to a sharp increase in DC voltage caused by surplus power delivered from the wind farm, resulting in failed AC fault ride-through at the onshore station, or even serious consequences such as DC tripping and turbine disconnection from the grid. These issues compromise the safety and reliability of the offshore wind power connected to the flexible DC grid. Summary of the Invention

[0004] In view of this, the present invention provides a method, system, device and medium for AC fault control at onshore stations, which solves the technical problem that current offshore wind power connected to flexible DC grid systems cannot effectively control AC faults at onshore stations. This results in the surplus power delivered by the wind farm causing a sharp increase in DC voltage, leading to failure of AC fault ride-through at the onshore station, or even serious consequences such as DC tripping and wind turbine disconnection, affecting the safety and reliability of offshore wind power connected to flexible DC grid systems.

[0005] The first aspect of this invention provides a method for controlling AC faults at a land station, comprising:

[0006] The AC fault flag is determined based on the AC voltage on the flexible DC transformer side of the onshore station; wherein, the AC fault flag is used to indicate whether the onshore station is in the period of AC fault.

[0007] determine whether the land station is in the AC fault period according to the AC fault flag, when it is determined that the land station is in the AC fault period, then modulate the reactive current of the land station according to the first current reference value output by the dq-axis outer loop control of the land station and the second current reference value corresponding to the grid voltage amplitude during the AC fault period, to obtain a current modulation signal;

[0008] take the current modulation signal as the input of the dq-axis inner loop control of the land station, modulate the AC voltage of the land station according to the first voltage modulation wave output by the dq-axis inner loop control of the land station and the second voltage modulation wave generated by filtering and damping coefficient operation of the low-frequency component of the DC current of the land station, to obtain a voltage modulation wave signal.

[0009] Preferably, the AC fault flag is determined according to the AC voltage at the grid side of the land station, comprising:

[0010] normalizing the positive sequence voltage amplitude of the AC voltage at the grid side of the land station to obtain a positive sequence voltage amplitude normalized value of the AC voltage;

[0011] comparing the positive sequence voltage amplitude normalized value of the AC voltage with a preset amplitude threshold value;

[0012] when the positive sequence voltage amplitude normalized value of the AC voltage is greater than the preset amplitude threshold value, then determining the AC fault flag as a first AC fault flag, the first AC fault flag being used to indicate that the land station is not in the AC fault period;

[0013] when the positive sequence voltage amplitude normalized value of the AC voltage is not greater than the preset amplitude threshold value, then determining the AC fault flag as a second AC fault flag, the second AC fault flag being used to indicate that the land station is in the AC fault period.

[0014] Preferably, the reactive current of the land station is modulated according to the first current reference value output by the dq-axis outer loop control of the land station and the second current reference value corresponding to the grid voltage amplitude during the AC fault period, to obtain a current modulation signal, comprising:

[0015] the first current reference value output by the dq-axis outer loop control of the land station includes a d-axis current reference value and a q-axis current reference value;

[0016] the q-axis current reference value corresponding to the grid voltage amplitude during the AC fault period of the land station is determined according to a preset Urms-Iq curve;

[0017] The q-axis reactive current of the land station is modulated by the q-axis current reference value corresponding to the dq-axis outer loop control output of the land station and the grid voltage amplitude during the AC fault, to obtain a q-axis reactive current value;

[0018] A current modulation signal is determined according to the d-axis current reference value and the q-axis reactive current value.

[0019] Preferably, the first current reference value output by the dq-axis outer loop control of the land station comprises:

[0020] The DC voltage reference value of the land station is subtracted from the measured DC voltage value to obtain a DC voltage difference value;

[0021] The reactive power reference value of the land station is subtracted from the measured reactive power value to obtain a reactive power difference value;

[0022] The DC current superimposed difference value and the reactive current superimposed difference value are obtained by PI control of the DC voltage difference value and the reactive power difference value;

[0023] The d-axis current reference value and the q-axis current reference value are obtained by limiting the DC current superimposed difference value and the reactive current superimposed difference value through a limiting link.

[0024] Preferably, the voltage modulation wave signal is obtained by modulating the AC voltage of the land station with the current modulation signal as the input of the dq-axis inner loop control of the land station, and with the first voltage modulation wave output by the dq-axis inner loop control of the land station and the second voltage modulation wave generated by filtering the low-frequency component of the DC current of the land station and performing damping coefficient operation;

[0025] The first voltage modulation wave comprising the d-axis voltage reference value and the q-axis voltage reference value is output by the dq-axis inner loop control of the land station with the current modulation signal as the input of the dq-axis inner loop control of the land station;

[0026] The low-frequency filter component is obtained by filtering the low-frequency component of the DC current of the land station;

[0027] The second voltage modulation wave is obtained by multiplying the low-frequency filter component by a damping coefficient;

[0028] The d-axis voltage superimposed value is obtained by superimposing the second voltage modulation wave and the d-axis voltage reference value;

[0029] The three-phase voltage modulation signal is obtained by inverse Park operation of the d-axis voltage superimposed value and the q-axis voltage reference value;

[0030] The three-phase voltage modulation signal is used for modulation trigger control to obtain a voltage modulation wave signal.

[0031] Preferably, the current modulation signal comprises a d-axis current reference value and a q-axis reactive current value.

[0032] The current modulation signal is used as an input of dq-axis inner loop control of the onshore station, and a first voltage modulation wave is output by the dq-axis inner loop control of the onshore station, comprising:

[0033] The d-axis current reference value is subtracted from a d-axis current measured value to obtain a d-axis current difference value.

[0034] The q-axis reactive current value is subtracted from a q-axis current measured value to obtain a q-axis current difference value.

[0035] The d-axis current difference value and the q-axis current difference value are both subjected to PI control to obtain a d-axis current PI output value and a q-axis current PI output value.

[0036] The d-axis current PI output value is compensated by a q-axis voltage measured value and a d-axis current compensation value to obtain a d-axis voltage reference value, wherein the d-axis current compensation value is obtained by angle frequency compensation of the d-axis current measured value.

[0037] The q-axis current PI output value is compensated by a d-axis voltage measured value and a q-axis current compensation value to obtain a q-axis voltage reference value, wherein the q-axis current compensation value is obtained by angle frequency compensation of the q-axis current measured value.

[0038] Preferably, the method further comprises:

[0039] It is judged whether the DC voltage of the onshore station reaches an overvoltage threshold of a DC energy consumption device.

[0040] When the DC voltage of the onshore station reaches the overvoltage threshold of the DC energy consumption device, the DC energy consumption device is put into operation to consume surplus active power of the onshore station.

[0041] It is judged whether the DC voltage after the operation of the DC energy consumption device drops to a preset voltage threshold.

[0042] When it is judged that the DC voltage after the operation of the DC energy consumption device drops to the preset voltage threshold, the operation of the DC energy consumption device is cut off.

[0043] In a second aspect, the application further provides an onshore station AC fault control system, comprising:

[0044] A fault flag determination module is configured to determine an AC fault flag according to an AC voltage at a grid side of a converter transformer of the onshore station, wherein the AC fault flag is used to indicate whether the onshore station is in an AC fault period.

[0045] A current modulation module is configured to determine whether the onshore station is in the AC fault period according to the AC fault flag, and when it is determined that the onshore station is in the AC fault period, modulate a reactive current of the onshore station according to a first current reference value output by a dq-axis outer loop control of the onshore station and a second current reference value corresponding to a grid voltage amplitude in the AC fault period, to obtain a current modulation signal.

[0046] A voltage modulation module is configured to take the current modulation signal as an input of a dq-axis inner loop control of the onshore station, modulate an AC voltage of the onshore station according to a first voltage modulation wave output by the dq-axis inner loop control of the onshore station and a second voltage modulation wave generated by filtering and damping coefficient operation on a low-frequency component of a DC current of the onshore station, to obtain a voltage modulation wave signal.

[0047] In a third aspect, the present application further provides an electronic device, which comprises a memory and a processor, the memory stores a computer program, and the computer program is executed by the processor to make the processor execute the steps of the onshore station AC fault control method according to the first aspect.

[0048] In a fourth aspect, the present application further provides a computer readable storage medium, which stores a computer program, and the computer program is executed to implement the steps of the onshore station AC fault control method according to the first aspect.

[0049] As can be seen from the above technical solutions, the present application determines an AC fault flag according to an AC voltage at a grid side of a converter transformer of the onshore station, and identifies whether the onshore station is in an AC fault period by introducing the AC fault flag into dq-axis outer loop control and dq-axis inner loop control of the onshore station, so as to modulate a reactive current of the onshore station by a second current reference value corresponding to a grid voltage amplitude in the AC fault period when the onshore station is in the AC fault period, and modulate an AC voltage of the onshore station by a voltage modulation wave generated by filtering and damping coefficient operation on a low-frequency component of a DC current of the onshore station, so as to achieve the purpose of suppressing the low-frequency component at the DC side, solve the problem that the onshore station of the flexible DC grid-connected system of offshore wind power is difficult to effectively control in an AC fault period, realize successful AC fault ride-through of the onshore station of the flexible DC grid-connected system of offshore wind power, reduce the risk of DC tripping and wind turbine tripping of the wind farm, and improve the safety and reliability of the flexible DC grid-connected system of offshore wind power. BRIEF DESCRIPTION OF DRAWINGS

[0050] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced below. Obviously, the accompanying drawings in the following description only need to be some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0051] Figure 1 It is a topology schematic diagram of a double-ended offshore wind power flexible DC grid-connected system.

[0052] Figure 2 It is an application environment of a land station AC fault control method provided by the embodiment of the present application.

[0053] Figure 3 It is a flowchart of a land station AC fault control method provided by the embodiment of the present application.

[0054] Figure 4a It is a dq transformation process schematic diagram of a land station flexible DC transformer grid-side three-phase voltage.

[0055] Figure 4b It is a dq transformation process schematic diagram of a land station flexible DC transformer grid-side three-phase current.

[0056] Figure 5 It is an AC fault flag bit judgment logic schematic diagram.

[0057] Figure 6 It is a reactive current control logic schematic diagram.

[0058] Figure 7 It is a Urms-Iq curve control logic schematic diagram.

[0059] Figure 8 It is a DC oscillation suppression control logic schematic diagram.

[0060] Figure 9 It is a dq axis inner loop and modulation wave control logic schematic diagram.

[0061] Figure 10 It is a DC energy consumption switching control logic schematic diagram.

[0062] Figure 11 It is a structure schematic diagram of a land station AC fault control system provided by the embodiment of the present application.

[0063] Figure 12 It is a structure schematic diagram of an electronic device provided by the embodiment of the present application. DETAILED DESCRIPTION

[0064] In the following, the technical solutions in the embodiments of the present application will be described clearly and completely with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of the present application.

[0065] The land station AC fault control method provided by the embodiments of the present application can be applied to the application environment as shown in Figure 2 The land station AC system communicates with the server 102 through a network. The data storage system can store data required to be processed by the server 102. The data storage system can be integrated on the server 102, or placed on a cloud or other network server. The server 102 determines an AC fault flag bit according to the AC voltage at the grid side of the land station flexible AC / DC converter; the AC fault flag bit is used to indicate whether the land station is in an AC fault period; determines whether the land station is in the AC fault period according to the AC fault flag bit; when it is determined that the land station is in the AC fault period, modulates the reactive current of the land station according to a first current reference value output by dq-axis outer loop control of the land station and a second current reference value corresponding to the grid voltage amplitude during the AC fault period, to obtain a current modulation signal; takes the current modulation signal as the input of the dq-axis inner loop control of the land station, modulates the AC voltage of the land station according to a first voltage modulation wave output by the dq-axis inner loop control of the land station and a second voltage modulation wave generated by filtering and damping coefficient operation on the low-frequency component of the DC current of the land station, to obtain a voltage modulation wave signal. The server 102 can be a stand-alone physical server, a server cluster or a distributed system composed of multiple physical servers, or a cloud server providing cloud computing services.

[0066] As shown in Figure 3 The land station AC fault control method provided by the embodiments of the present application is described by taking the server 102 in Figure 2 as an example, which includes the following steps S1 to S3. Wherein:

[0067] Step S1, determine an AC fault flag bit according to the AC voltage at the grid side of the land station flexible AC / DC converter; the AC fault flag bit is used to indicate whether the land station is in an AC fault period.

[0068] The embodiments of the present application monitor the AC voltage at the grid side of the land station flexible AC / DC converter, determine whether the land station is in an AC fault period through the AC voltage at the grid side of the land station flexible AC / DC converter, and determine the AC fault flag bit.

[0069] Specifically, step S1, determining the AC fault flag based on the AC voltage on the onshore flexible DC transformer side, includes:

[0070] Step S101: Normalize the positive sequence voltage amplitude of the AC voltage on the flexible DC transformer side of the onshore station to obtain the per-unit value of the positive sequence voltage amplitude of the AC voltage.

[0071] Specifically, by collecting the three-phase AC voltage and current from the onshore flexible DC transformer network side, the three-phase AC voltage and current are decomposed into d- and q-axis values ​​respectively to obtain the three-phase AC d-axis voltage, three-phase AC q-axis voltage, three-phase AC d-axis current, and three-phase AC q-axis current, such as... Figures 4a-4b As shown. Then, by calculating the effective values ​​of the AC three-phase d-axis voltage and AC three-phase q-axis voltage, the per-unit value of the positive sequence voltage amplitude of the AC voltage is obtained.

[0072] Step S102: Compare the per-unit value of the positive sequence voltage amplitude of the AC voltage with the preset amplitude threshold.

[0073] Step S103: When the per-unit value of the positive sequence voltage amplitude of the AC voltage is greater than the preset amplitude threshold, the AC fault flag bit is determined to be the first AC fault flag bit. The first AC fault flag bit is used to indicate that the land station is not in an AC fault period.

[0074] Step S104: When the per-unit value of the positive sequence voltage amplitude of the AC voltage is not greater than the preset amplitude threshold, the AC fault flag bit is determined to be the second AC fault flag bit. The second AC fault flag bit is used to indicate that the land station is in the period of AC fault.

[0075] For example, such as Figure 5 The AC fault flag bit judgment logic shown is set with an amplitude threshold of 0.9pu. When the per-unit value of the positive sequence voltage amplitude of the AC voltage, Udrms, is greater than 0.9pu, it is determined that the onshore station is not in an AC fault period, and the AC fault flag bit ACfault is set to 0. When the per-unit value of the positive sequence voltage amplitude of the AC voltage, Udrms, is not greater than 0.9pu, it is determined that the onshore station is in an AC fault period, and the AC fault flag bit ACfault is set to 1.

[0076] Step S2: Determine whether the onshore station is in an AC fault period based on the AC fault flag bit. When it is determined that the onshore station is in an AC fault period, modulate the reactive current of the onshore station according to the first current reference value output by the outer loop control of the dq axis of the onshore station and the second current reference value corresponding to the grid voltage amplitude during the AC fault period to obtain a current modulation signal.

[0077] It can be understood that, on the basis of the dq-axis outer loop control of the land station, the application embodiment introduces an alternating current fault flag as a criterion for the reactive current control of the alternating current fault mode, and the specific control logic is as shown in Figure 6

[0078] When it is judged that the land station is not in the alternating current fault period, the reactive current of the land station is modulated according to the first current reference value output by the dq-axis outer loop control of the land station, and it is not necessary to adjust the reactive current according to the degree of alternating current voltage drop.

[0079] When it is judged that the land station is in the alternating current fault period, the reactive current of the land station is modulated according to the first current reference value output by the dq-axis outer loop control of the land station and the second current reference value corresponding to the grid voltage amplitude during the alternating current fault period, so as to provide reactive support for the recovery of the grid voltage.

[0080] Specifically, the modulation of the reactive current of the land station according to the first current reference value output by the dq-axis outer loop control of the land station and the second current reference value corresponding to the grid voltage amplitude during the alternating current fault period in step S2 includes:

[0081] In step S201, a first current reference value is output by the dq-axis outer loop control of the land station, and the first current reference value includes a d-axis current reference value and a q-axis current reference value.

[0082] As shown in Figure 6 , the first current reference value output by the dq-axis outer loop control of the land station includes:

[0083] In step S2011, a difference between a direct current voltage reference value Udcref of the land station and a direct current voltage measured value Udc is processed to obtain a direct current voltage difference.

[0084] In step S2012, a difference between a reactive power reference value and a reactive power measured value of the land station is processed to obtain a reactive power difference.

[0085] In step S2013, the direct current voltage difference and the reactive power difference are both subjected to PI control to obtain a direct current current superimposed difference and a reactive current superimposed difference.

[0086] The PI control includes a proportional link and an integral link, and the direct current voltage difference and the reactive power difference are both subjected to the proportional link and the integral link, so as to obtain the direct current current superimposed difference and the reactive current superimposed difference.

[0087] In step S2014, the direct current current superimposed difference and the reactive current superimposed difference are both subjected to amplitude limiting link to obtain a d-axis current reference value Idref and a q-axis current reference value Iqref0. ​

[0088] Step S202, determine the q-axis current reference value corresponding to the grid voltage amplitude during the AC fault according to the preset Urms-Iq curve.

[0089] As shown in Figure 7 , the reactive current will be controlled according to the AC voltage drop and the Urms-Iq curve designed according to the grid demand, and the q-axis current reference value Iqref1 corresponding to the grid voltage amplitude during the AC fault of the land station is obtained.

[0090] Wherein, the Urms-Iq curve is provided by different engineering designs, that is, a curve formed by providing reactive current corresponding to different voltage amplitudes, as shown in Figure 7 , with the decrease of voltage amplitude Urms, the required reactive current increases, and there is a maximum amplitude limit.

[0091] By inputting a voltage amplitude through the Urms-Iq curve, the current Iq value corresponding to the output voltage amplitude is found on the curve, which is used as the q-axis current reference value Iqref1.

[0092] Step S203, modulate the q-axis reactive current of the land station with the q-axis current reference value Iqref0 output by the dq-axis outer ring control and the q-axis current reference value Iqref1 corresponding to the grid voltage amplitude during the AC fault, to obtain the q-axis reactive current value Iqref.

[0093] Step S204, determine the current modulation signal according to the d-axis current reference value Idref and the q-axis reactive current value Iqref.

[0094] Wherein, the d-axis current reference value Idref and the q-axis reactive current value Iqref are input to the dq-axis inner ring control of the land station as the current modulation signal.

[0095] Step S3, take the current modulation signal as the input of the dq-axis inner ring control of the land station, modulate the AC voltage of the land station according to the first voltage modulation wave output by the dq-axis inner ring control of the land station and the second voltage modulation wave generated by filtering and damping coefficient operation of the low-frequency component of the DC current of the land station, to obtain the voltage modulation wave signal.

[0096] Wherein, when it is judged that the land station is not in the AC fault period, the current modulation signal is taken as the input of the dq-axis inner ring control of the land station, and the AC voltage of the land station is modulated according to the first voltage modulation wave output by the dq-axis inner ring control of the land station, without the need to suppress the low-frequency component on the DC side.

[0097] As shown in Figure 8As shown, when it is judged that the onshore station is in an AC fault period, through the configured DC oscillation suppression control function, by extracting the low-frequency component of the DC current, multiplying by a damping coefficient, generating a first voltage modulation wave Udref1 superimposed on the dq-axis inner loop control output, so as to achieve the purpose of suppressing the low-frequency component of the DC side, and by transmitting the voltage modulation wave signal to the converter of the onshore station for pulse modulation.

[0098] In the steady-state operation, the DC oscillation suppression control will effectively control the low-frequency oscillation of the DC side current and voltage. However, during the AC fault period of the onshore station, the DC energy consumption repeatedly switching process, if the DC oscillation suppression function is not exited, it will act together with the DC energy consumption switching on the fluctuation of the DC voltage, causing the DC system grid instability, therefore, when the onshore station AC fault flag is effective, the DC oscillation suppression function needs to be exited.

[0099] Among them, the damping coefficient is set according to the DC project, which can be taken as 0.1~0.5.

[0100] Specifically, as shown in Figure 9 The current modulation signal in step S3 is used as the input of the dq-axis inner loop control of the onshore station, and the first voltage modulation wave output by the dq-axis inner loop control of the onshore station is modulated according to the low-frequency component of the DC current of the onshore station, and the second voltage modulation wave generated by the filtering and damping coefficient operation, to obtain the voltage modulation wave signal, including:

[0101] Step S301, the current modulation signal Idref, Iqref is used as the input of the dq-axis inner loop control of the onshore station, and the first voltage modulation wave is output by the dq-axis inner loop control of the onshore station; The first voltage modulation wave includes d-axis voltage reference value Udref and q-axis voltage reference value Uqref;

[0102] Step S302, the low-frequency component of the DC current of the onshore station is filtered to obtain the low-frequency filtered component;

[0103] Step S303, multiply the low-frequency filtered component by the damping coefficient to obtain the second voltage modulation wave Udref1;

[0104] Step S304, superimpose the second voltage modulation wave Udref1 and the d-axis voltage reference value Udref to obtain the d-axis voltage superposition value;

[0105] Step S305, the d-axis voltage superposition value and the q-axis voltage reference value Uqref are subjected to inverse Park operation to obtain three-phase voltage modulation signals UAref, UBref, and UCref;

[0106] Step S306, modulate trigger control is carried out by using three-phase voltage modulation signal UAref, UBref, UCref, and voltage modulation wave signal is obtained.

[0107] In some embodiments, the current modulation signal includes a d-axis current reference value and a q-axis reactive current value;

[0108] In step S301, the current modulation signal is used as the input of the dq-axis inner loop control of the land station, and the first voltage modulation wave is output by the dq-axis inner loop control of the land station, including:

[0109] Step S3011, difference processing is carried out between the d-axis current reference value Idref and the d-axis current measured value Id, and the d-axis current difference value is obtained;

[0110] Step S3012, difference processing is carried out between the q-axis reactive current value Iqref and the q-axis current measured value Iq, and the q-axis current difference value is obtained;

[0111] Step S3013, PI control is carried out on the d-axis current difference value and the q-axis current difference value, and the d-axis current PI output value and the q-axis current PI output value are obtained;

[0112] Wherein, the PI control includes a proportional link and an integral link, and the d-axis current difference value and the q-axis current difference value are subjected to proportional link and integral link, so as to obtain the d-axis current PI output value and the q-axis current PI output value.

[0113] Step S3014, the d-axis voltage reference value Udref is obtained by compensating the d-axis current PI output value by using the q-axis voltage measured value Uq and the d-axis current compensation value, wherein the d-axis current compensation value is obtained by compensating the d-axis current measured value Id by the angular frequency wl.

[0114] Step S3015, the q-axis voltage reference value Uqref is obtained by compensating the q-axis current PI output value by using the d-axis voltage measured value Ud and the q-axis current compensation value, wherein the q-axis current compensation value is obtained by compensating the q-axis current measured value by the angular frequency wl.

[0115] It should be noted that, according to the AC fault flag bit determined according to the AC voltage at the grid side of the land station, and on the basis of the dq-axis outer loop control and the dq-axis inner loop control of the land station, the AC fault flag bit is introduced to identify whether the land station is in the AC fault period, so that the reactive current of the land station is modulated by the second current reference value corresponding to the grid voltage amplitude in the AC fault period, and the AC voltage of the land station is modulated by the voltage modulation wave generated by filtering and damping coefficient operation of the low-frequency component of the DC current of the land station, so as to achieve the purpose of suppressing the low-frequency component at the DC side, and solve the problem that the land station of the offshore wind power through the flexible DC grid connection system cannot be effectively controlled in the AC fault, realize the successful AC fault ride-through of the land station of the offshore wind power through the flexible DC grid connection system, reduce the risk of DC trip and wind turbine off-grid of the wind farm, and improve the safety and reliability of the offshore wind power through the flexible DC grid connection system.

[0116] In some embodiments, under a high-power and serious land station AC fault, the DC voltage will rise sharply because the power of the offshore station cannot be sent to the grid in time, and a DC energy consumption device needs to be configured at the DC side to absorb the excess active power by putting in the DC energy consumption device, thereby effectively reducing the DC voltage and avoiding overvoltage of the device and DC trip.

[0117] In some embodiments, the DC energy consumption device is configured to be put in when the DC voltage of the land station reaches the overvoltage threshold value of the DC energy consumption device, and the DC energy consumption device is removed when the DC voltage drops to the voltage threshold value of the DC energy consumption device. If the AC fault is not cleared, the DC voltage will continue to rise after the DC energy consumption device is removed, and the DC energy consumption device may be put in and removed repeatedly during the AC fault period, and the DC voltage will rise and drop repeatedly.

[0118] Specifically, the DC energy consumption device switching process further includes:

[0119] Step S401, determining whether the DC voltage of the land station reaches the overvoltage threshold value of the DC energy consumption device;

[0120] Step S402, when the DC voltage of the land station reaches the overvoltage threshold value of the DC energy consumption device, the DC energy consumption device is put in to consume the excess active power of the land station;

[0121] Step S403, determining whether the DC voltage after the DC energy consumption device is put in drops to the preset voltage threshold value;

[0122] Step S404, when the DC voltage after the DC energy consumption device is put in drops to the preset voltage threshold value, the DC energy consumption device is removed.

[0123] Exemplarily, as Figure 10 shown, when the DC voltage Udc of the onshore station reaches the overvoltage threshold value UdcH of the DC energy consumption input, the DC energy consumption input is input; when the DC voltage drops to the return threshold value UdcL, the DC energy consumption is cut off. If the AC fault is still not cleared, when the DC energy consumption is cut off, the DC voltage will continue to rise, and the DC energy consumption may still be input and cut off. During the AC fault, the DC voltage will present repeated rise and fall with the DC energy consumption switching.

[0124] It can be understood that, by cooperation of the DC energy consumption switching and the converter control of the onshore station, the onshore station AC fault successful crossing of the offshore wind power through the flexible DC grid-connected system can be realized, which provides a reference and guidance for the control system design of the offshore wind power flexible DC grid-connected project, and has the advantages of strong operability, simple and convenient implementation.

[0125] Based on the same inventive concept, the embodiment of the present application also provides an onshore station AC fault control system for realizing the onshore station AC fault control method.

[0126] The implementation scheme for solving the problem provided by the system is similar to the implementation scheme described in the above method, so the specific limitations in one or more onshore station AC fault control system embodiments provided below can be referred to the limitations of the onshore station AC fault control method in the above, which will not be described here.

[0127] As Figure 11 shown, the embodiment of the present application also provides an onshore station AC fault control system, which comprises:

[0128] The fault flag determination module 100 is configured to determine an AC fault flag bit according to the AC voltage of the grid side of the onshore station flexible DC converter; wherein the AC fault flag bit is used to indicate whether the onshore station is in an AC fault period;

[0129] The current modulation module 200 is configured to determine whether the onshore station is in an AC fault period according to the AC fault flag bit, and when it is determined that the onshore station is in an AC fault period, modulate the reactive current of the onshore station according to a first current reference value output by the dq-axis outer loop control of the onshore station and a second current reference value corresponding to the grid voltage amplitude during the AC fault period, to obtain a current modulation signal;

[0130] The voltage modulation module 300 is configured to take the current modulation signal as the input of the dq-axis inner loop control of the onshore station, modulate the AC voltage of the onshore station according to a first voltage modulation wave output by the dq-axis inner loop control of the onshore station and a second voltage modulation wave generated by filtering and damping coefficient operation of the low-frequency component of the DC current of the onshore station, to obtain a voltage modulation wave signal.

[0131] In some embodiments, the fault flag determination module 100 is configured to normalize the positive sequence voltage amplitude of the AC voltage at the grid side of the HVDC converter station to obtain a normalized positive sequence voltage amplitude of the AC voltage;

[0132] The normalized positive sequence voltage amplitude of the AC voltage is compared with a preset amplitude threshold value;

[0133] When the normalized positive sequence voltage amplitude of the AC voltage is greater than the preset amplitude threshold value, a first AC fault flag bit is determined, and the first AC fault flag bit is used to indicate that the HVDC converter station is not in an AC fault period;

[0134] When the normalized positive sequence voltage amplitude of the AC voltage is not greater than the preset amplitude threshold value, a second AC fault flag bit is determined, and the second AC fault flag bit is used to indicate that the HVDC converter station is in an AC fault period.

[0135] In some embodiments, the current modulation module 200 is configured to output a first current reference value through dq-axis outer loop control of the HVDC converter station, and the first current reference value includes a d-axis current reference value and a q-axis current reference value;

[0136] According to a preset Urms-Iq curve, a q-axis current reference value corresponding to a grid voltage amplitude during the AC fault period of the HVDC converter station is determined;

[0137] The q-axis current reference value output by the dq-axis outer loop control and the q-axis current reference value corresponding to the grid voltage amplitude during the AC fault period are used to modulate a q-axis reactive current of the HVDC converter station to obtain a q-axis reactive current value;

[0138] A current modulation signal is determined according to the d-axis current reference value and the q-axis reactive current value.

[0139] In some embodiments, the first current reference value is output through the dq-axis outer loop control of the HVDC converter station, including:

[0140] A DC voltage difference value is obtained by subtracting a DC voltage measured value from a DC voltage reference value of the HVDC converter station;

[0141] A reactive power difference value is obtained by subtracting a reactive power measured value from a reactive power reference value of the HVDC converter station;

[0142] The DC voltage difference value and the reactive power difference value are both subjected to PI control to obtain a DC current superimposed difference value and a reactive current superimposed difference value;

[0143] The DC current superimposed difference value and the reactive current superimposed difference value are both subjected to amplitude limiting through an amplitude limiting link to obtain the d-axis current reference value and the q-axis current reference value.

[0144] In some embodiments, the voltage modulation module 300 is configured to use the current modulation signal as an input of dq-axis inner loop control of the onshore station, output a first voltage modulation wave through the dq-axis inner loop control of the onshore station, and the first voltage modulation wave comprises a d-axis voltage reference value and a q-axis voltage reference value.

[0145] The low-frequency component of the direct current of the onshore station is filtered to obtain a low-frequency filtered component.

[0146] The low-frequency filtered component is multiplied by a damping coefficient to obtain a second voltage modulation wave.

[0147] The second voltage modulation wave is superimposed with the d-axis voltage reference value to obtain a d-axis voltage superimposed value.

[0148] The d-axis voltage superimposed value and the q-axis voltage reference value are subjected to inverse Park operation to obtain a three-phase voltage modulation signal.

[0149] The three-phase voltage modulation signal is used for modulation trigger control to obtain a voltage modulation wave signal.

[0150] In some embodiments, the current modulation signal comprises a d-axis current reference value and a q-axis reactive current value.

[0151] The current modulation signal is used as an input of dq-axis inner loop control of the onshore station, and a first voltage modulation wave is output through the dq-axis inner loop control of the onshore station, comprising:

[0152] The d-axis current reference value is subtracted from a measured d-axis current value to obtain a d-axis current difference value.

[0153] The q-axis reactive current value is subtracted from a measured q-axis current value to obtain a q-axis current difference value.

[0154] The d-axis current difference value and the q-axis current difference value are both subjected to PI control to obtain a d-axis current PI output value and a q-axis current PI output value.

[0155] The d-axis current PI output value is compensated by using a measured q-axis voltage value and a d-axis current compensation value to obtain a d-axis voltage reference value, wherein the d-axis current compensation value is obtained by angular frequency compensation on the measured d-axis current value.

[0156] The q-axis current PI output value is compensated by using a measured d-axis voltage value and a q-axis current compensation value to obtain a q-axis voltage reference value, wherein the q-axis current compensation value is obtained by angular frequency compensation on the measured q-axis current value.

[0157] In some embodiments, the system further comprises: a DC energy consumption switching module, configured to determine whether the DC voltage of the onshore station reaches a DC energy consumption device input overvoltage threshold; when the DC voltage of the onshore station reaches the DC energy consumption device input overvoltage threshold, the DC energy consumption device is input to consume the surplus active power of the onshore station; determine whether the DC voltage after the DC energy consumption device is input drops to a preset voltage threshold; when the DC voltage after the DC energy consumption device is input drops to the preset voltage threshold, the input of the DC energy consumption device is cut off.

[0158] As shown in Figure 12 The embodiments of the present application further provide an electronic device, the electronic device 10 comprises a memory 20 and a processor 30, the memory 20 stores a computer program, and the computer program is executed by the processor 30, so that the processor 30 executes the steps of the onshore station AC fault control method in any one of the above-mentioned embodiments.

[0159] The embodiments of the present application further provide a computer readable storage medium, which stores a computer program, and the computer program is executed to realize the steps of the onshore station AC fault control method in any one of the above-mentioned embodiments.

[0160] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the above-mentioned system, electronic device and computer storage medium can refer to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0161] It should be noted that the terms "first", "second" and the like in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or a chronological order. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the application described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not necessarily have to include all the steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0162] In several embodiments provided by the present application, it can be understood that each block in the flowchart or block diagram can represent a module, a segment or a portion of code which contains one or more executable instructions for implementing the specified logic function. It should also be noted that in some alternative implementations, the functions noted in the blocks can occur out of the order noted in the figure. For example, two blocks shown in succession may, in fact, be executed substantially concurrently or in the reverse order, depending on the functionality involved.

[0163] In several embodiments provided by the present application, it can be understood that the disclosed system, electronic device, computer storage medium and method can be implemented in other manners. For example, the described device embodiments are merely illustrative, and the division of units can be different from the embodiment. For example, the units can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections can be indirect couplings or communication connections through some interfaces, devices or units, and can be in electrical, mechanical or other forms.

[0164] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, i.e. may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the embodiment.

[0165] In addition, each functional unit in the various embodiments of the present application can be integrated into a processing unit, or each unit can be physically present separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in the form of hardware or in the form of a software functional unit.

[0166] The integrated unit, if implemented in the form of a software function unit and sold or used as an independent product, can be stored in a computer readable storage medium. Based on such understanding, the technical solutions of the present application or the entire or part of the technical solutions that essentially contribute to the prior art can be embodied in the form of a software product. The computer software product is stored in a storage medium, includes a plurality of instructions for executing all or part of the steps of the method described in various embodiments of the present application by a computer device (which can be a personal computer, a server, or a network device, etc.). The aforementioned storage medium includes: a U disk, a mobile hard disk, a read-only memory (English full name: Read-Only Memory, English abbreviation: ROM), a random access memory (English full name: Random Access Memory, English abbreviation: RAM), a magnetic disk or an optical disk, and various media that can store program codes.

[0167] The above embodiments are only used to illustrate the technical solutions of the present application, not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method of AC fault control for a land station, characterized by, The method comprises the steps of: determining an AC fault flag according to the AC voltage at the grid side of the converter transformer of the onshore station; wherein the AC fault flag is used to indicate whether the onshore station is in an AC fault period; judging whether the onshore station is in an AC fault period according to the AC fault flag; when it is judged that the onshore station is in an AC fault period, modulating the reactive current of the onshore station according to a first current reference value output by the dq-axis outer loop control of the onshore station and a second current reference value corresponding to the grid voltage amplitude during the AC fault period, to obtain a current modulation signal; using the current modulation signal as the input of the dq-axis inner loop control of the onshore station, modulating the AC voltage of the onshore station according to a first voltage modulation wave output by the dq-axis inner loop control of the onshore station and a second voltage modulation wave generated by filtering and damping coefficient operation of the low-frequency component of the DC current of the onshore station, to obtain a voltage modulation wave signal.

2. The land station AC fault control method of claim 1, wherein, The method of determining the AC fault flag according to the AC voltage at the grid side of the converter transformer of the onshore station comprises: normalizing the positive sequence voltage amplitude of the AC voltage at the grid side of the converter transformer of the onshore station to obtain the positive sequence voltage amplitude normalized value of the AC voltage; comparing the positive sequence voltage amplitude normalized value of the AC voltage with a preset amplitude threshold value; when the positive sequence voltage amplitude normalized value of the AC voltage is greater than the preset amplitude threshold value, determining the AC fault flag as a first AC fault flag, wherein the first AC fault flag is used to indicate that the onshore station is not in an AC fault period; when the positive sequence voltage amplitude normalized value of the AC voltage is not greater than the preset amplitude threshold value, determining the AC fault flag as a second AC fault flag, wherein the second AC fault flag is used to indicate that the onshore station is in an AC fault period.

3. The land station AC fault control method of claim 1, wherein, The method of modulating the reactive current of the onshore station according to the first current reference value output by the dq-axis outer loop control of the onshore station and the second current reference value corresponding to the grid voltage amplitude during the AC fault period to obtain a current modulation signal comprises: outputting the first current reference value by the dq-axis outer loop control of the onshore station, wherein the first current reference value comprises a d-axis current reference value and a q-axis current reference value; determining the q-axis current reference value corresponding to the grid voltage amplitude during the AC fault period according to a preset Urms-Iq curve; modulating the q-axis reactive current of the onshore station according to the q-axis current reference value output by the dq-axis outer loop control and the q-axis current reference value corresponding to the grid voltage amplitude during the AC fault period, to obtain a q-axis reactive current value; determining the current modulation signal according to the d-axis current reference value and the q-axis reactive current value.

4. The land station AC fault control method according to claim 3, characterized by, The method of outputting the first current reference value by the dq-axis outer loop control of the onshore station comprises: obtaining a DC voltage difference value by subtracting the DC voltage measured value from the DC voltage reference value of the onshore station; obtaining a reactive power difference value by subtracting the reactive power measured value from the reactive power reference value of the onshore station; The direct current voltage difference and the reactive power difference are both subjected to PI control to obtain a direct current superimposed difference and a reactive current superimposed difference; The direct current superimposed difference and the reactive current superimposed difference are both subjected to amplitude limiting to obtain a d-axis current reference value and a q-axis current reference value.

5. The land station AC fault control method of claim 1, wherein, The current modulation signal is taken as an input of dq-axis inner loop control of the land station, a first voltage modulation wave is output by the dq-axis inner loop control of the land station, and a second voltage modulation wave is generated by filtering and damping coefficient operation of a low-frequency component of a direct current of the land station, so as to modulate an alternating current voltage of the land station to obtain a voltage modulation wave signal, including: The current modulation signal is taken as an input of dq-axis inner loop control of the land station, a first voltage modulation wave is output by the dq-axis inner loop control of the land station, and a second voltage modulation wave is generated by filtering and damping coefficient operation of a low-frequency component of a direct current of the land station, so as to modulate an alternating current voltage of the land station to obtain a voltage modulation wave signal, including: The low-frequency component of the direct current of the land station is subjected to filtering to obtain a low-frequency filtered component; The low-frequency filtered component is multiplied by a damping coefficient to obtain a second voltage modulation wave; The d-axis voltage superimposed value and the q-axis voltage reference value are subjected to inverse Park operation to obtain a three-phase voltage modulation signal; The three-phase voltage modulation signal is used for modulation trigger control to obtain a voltage modulation wave signal. The current modulation signal includes a d-axis current reference value and a q-axis reactive current value; 6. The land station AC fault control method of claim 5, wherein, The current modulation signal is taken as an input of dq-axis inner loop control of the land station, a first voltage modulation wave is output by the dq-axis inner loop control of the land station, and a second voltage modulation wave is generated by filtering and damping coefficient operation of a low-frequency component of a direct current of the land station, so as to modulate an alternating current voltage of the land station to obtain a voltage modulation wave signal, including: The d-axis current reference value is subtracted from a d-axis current measured value to obtain a d-axis current difference value; The q-axis reactive current value is subtracted from a q-axis current measured value to obtain a q-axis current difference value; The d-axis current difference value and the q-axis current difference value are both subjected to PI control to obtain a d-axis current PI output value and a q-axis current PI output value; The d-axis current PI output value is compensated by a q-axis voltage measured value and a d-axis current compensation value to obtain a d-axis voltage reference value, wherein the d-axis current compensation value is obtained by angular frequency compensation of the d-axis current measured value; The q-axis current PI output value is compensated by a d-axis voltage measured value and a q-axis current compensation value to obtain a q-axis voltage reference value, wherein the q-axis current compensation value is obtained by angular frequency compensation of the q-axis current measured value. Further comprising:

7. The land station AC fault control method of claim 1, wherein, It is judged whether the direct current voltage of the land station reaches a overvoltage threshold of a direct current energy consumption device; When the direct current voltage of the land station reaches the overvoltage threshold of the direct current energy consumption device, the direct current energy consumption device is put into operation to consume surplus active power of the land station; It is judged whether the direct current voltage after the direct current energy consumption device is put into operation drops to a preset voltage threshold. ​ When it is judged that the DC voltage after the input of the DC energy consumption device drops to the preset voltage threshold, the input of the DC energy consumption device is cut off.

8. An AC fault control system for a land station, characterized by Comprise: The fault flag determination module is used for determining an AC fault flag bit according to the AC voltage at the grid side of the HVDC converter station; wherein the AC fault flag bit is used for indicating whether the HVDC converter station is in an AC fault period; The current modulation module is used for judging whether the HVDC converter station is in the AC fault period according to the AC fault flag bit; when it is judged that the HVDC converter station is in the AC fault period, the reactive current of the HVDC converter station is modulated according to a first current reference value output by the outer loop control of the dq axis of the HVDC converter station and a second current reference value corresponding to the grid voltage amplitude in the AC fault period, to obtain a current modulation signal; The voltage modulation module is used for taking the current modulation signal as the input of the inner loop control of the dq axis of the HVDC converter station, modulating the AC voltage of the HVDC converter station according to a first voltage modulation wave output by the inner loop control of the dq axis of the HVDC converter station and a second voltage modulation wave generated by filtering and damping coefficient operation of the low-frequency component of the DC current of the HVDC converter station, to obtain a voltage modulation wave signal.

9. An electronic device, comprising: The electronic device comprises a memory and a processor, the memory stores a computer program, and the computer program is executed by the processor to make the processor execute the steps of the AC fault control method of the HVDC converter station according to any one of claims 1-7.

10. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed to realize the steps of the AC fault control method of the HVDC converter station according to any one of claims 1-7.

Images