Land station alternating current fault control method, system, equipment and medium

Abstract

The invention relates to the technical field of power systems, and discloses a land station alternating current fault control method, system, device and medium, the method comprises the following steps: determining an alternating current fault flag bit according to the alternating current voltage of a land station flexible direct current transformer network side, and on the basis of dq-axis outer ring control and dq-axis inner ring control of a land station, determining the alternating current fault flag bit according to the dq-axis outer ring control and the dq-axis inner ring control of the land station; an alternating current fault flag bit is introduced to identify whether the land station is in an alternating current fault period, so that when the land station is in the alternating current fault period, a second current reference value corresponding to the power grid voltage amplitude in the alternating current fault period is utilized to modulate the reactive current of the land station; the alternating current voltage of the onshore station is modulated through a voltage modulation wave generated by filtering and damping coefficient operation of the low-frequency component of the direct current of the onshore station, so that the onshore station alternating current fault successful crossing of offshore wind power through the flexible direct current grid-connected system is realized, and the risks of direct current tripping and wind power plant fan off-network can be reduced; and the safety and the reliability of offshore wind power passing through the flexible direct-current grid-connected system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a method, system, equipment and medium for controlling AC faults in a land station. Background Art

[0002] In recent years, with the development of new energy power generation technology and power electronics technology, the technical solution of using flexible direct current (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 flexible direct current grid-connected projects have been put into operation around the world.

[0003] like Figure 1 The topology of the offshore wind power grid-connected system via flexible direct current is shown in the figure. Compared with the traditional two-terminal flexible direct current, the offshore wind power grid-connected system via flexible direct current has a large difference in direct current control function. For flexible direct current, it is generally required to achieve AC fault ride-through and DC does not trip under various AC fault conditions. The current offshore wind power grid-connected system via flexible direct current is difficult to effectively control the AC fault of the onshore station, so that the surplus power sent by the wind farm will cause the DC voltage to rise sharply, resulting in the failure of AC fault ride-through at the onshore station, and even DC tripping and wind turbine disconnection and other serious consequences, affecting the safety and reliability of the offshore wind power grid-connected system via flexible direct current. Summary of the invention

[0004] In view of this, the present invention provides a method, system, equipment and medium for controlling AC faults of land stations, which solves the technical problem that the current offshore wind power flexible DC grid-connected system is difficult to effectively control AC faults of land stations, so that the surplus power delivered by the wind farm will cause the DC voltage to rise sharply, resulting in failure to cross the AC fault of the land station, and even serious consequences such as DC tripping and wind turbine disconnection, affecting the safety and reliability of the offshore wind power flexible DC grid-connected system.

[0005] A first aspect of the present invention provides a land station AC fault control method, comprising:

[0006] Determine an AC fault flag bit according to the AC voltage on the flexible DC transformer network side of the land station; wherein the AC fault flag bit is used to indicate whether the land station is in an AC fault period;

[0007] Determining whether the land station is in an AC fault period according to the AC fault flag bit, and when it is determined that the land station is in an AC fault period, modulating the reactive current of the land station according to a first current reference value output by a 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;

[0008] The current modulation signal is used as the input of the dq-axis inner loop 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 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 calculating the damping coefficient, so as to obtain a voltage modulation wave signal.

[0009] Preferably, the step of determining the AC fault flag bit according to the AC voltage on the flexible DC transformer network side of the land station includes:

[0010] The positive-sequence voltage amplitude of the AC voltage on the flexible DC transformer grid side of the onshore station is normalized to obtain the normalized value of the positive-sequence voltage amplitude of the AC voltage;

[0011] Comparing the per-unit value of the positive-sequence voltage amplitude of the AC voltage with a preset amplitude threshold;

[0012] 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 is determined to be a first AC fault flag, and the first AC fault flag is used to indicate that the land station is not in an AC fault period;

[0013] 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 is determined to be a second AC fault flag, and the second AC fault flag is used to indicate that the land station is in an AC fault period.

[0014] Preferably, the reactive current of the onshore station is modulated 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 to obtain the current modulation signal, including:

[0015] Outputting a first current reference value through the dq axis outer loop control of the land station, wherein the first current reference value includes a d axis current reference value and a q axis current reference value;

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

[0017] The q-axis reactive current of the onshore station is modulated by 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 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 outputting of the first current reference value through the dq axis outer loop control of the land station includes:

[0020] Performing a difference processing on the DC voltage reference value and the DC voltage measured value of the land station to obtain a DC voltage difference value;

[0021] Performing a difference processing on the reactive power reference value and the reactive power measured value of the land station to obtain a reactive power difference value;

[0022] The DC voltage difference and the reactive power difference are both subjected to PI control to obtain a DC current superposition difference and a reactive current superposition difference;

[0023] The DC current superposition difference and the reactive current superposition difference are both subjected to a limiting process through a limiting link to obtain a d-axis current reference value and a q-axis current reference value.

[0024] Preferably, the current modulation signal is used as the input of the dq axis inner loop 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 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 calculating the damping coefficient to obtain the voltage modulation wave signal, including:

[0025] The current modulation signal is used as an input of the dq axis inner loop control of the land station, and a first voltage modulation wave is output through the dq axis inner loop control of the land station; the first voltage modulation wave includes a d-axis voltage reference value and a q-axis voltage reference value;

[0026] Filtering the low-frequency component of the direct current of the land station to obtain a low-frequency filtered component;

[0027] Multiplying the low-frequency filter component by the damping coefficient to obtain a second voltage modulation wave;

[0028] superimposing the second voltage modulation wave with the d-axis voltage reference value to obtain a d-axis voltage superimposed value;

[0029] Performing an inverse Park operation on the d-axis voltage superposition value and the q-axis voltage reference value to obtain a three-phase voltage modulation signal;

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

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

[0032] The method of using the current modulation signal as an input of the dq axis inner loop control of the land station and outputting a first voltage modulation wave through the dq axis inner loop control of the land station comprises:

[0033] Performing a difference processing on the d-axis current reference value and the d-axis current measured value to obtain a d-axis current difference value;

[0034] Performing a difference processing on the q-axis reactive current value and the q-axis current measured value to obtain a q-axis current difference value;

[0035] Performing PI control on both the d-axis current difference and the q-axis current difference 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 using the q-axis voltage measured value and the 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;

[0037] The q-axis current PI output value is compensated using the d-axis voltage measured value and the 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.

[0038] Preferably, the method further comprises:

[0039] Determining whether the DC voltage of the land station reaches an overvoltage threshold for the DC energy consumption device to be put into operation;

[0040] When the DC voltage of the land station reaches the overvoltage threshold of the DC energy consumption device, the DC energy consumption device is activated to consume the surplus active power of the land station;

[0041] Determining whether the DC voltage after the DC energy consumption device is put into operation drops to a preset voltage threshold;

[0042] When it is determined that the DC voltage after the DC energy consumption device is put into operation drops to the preset voltage threshold, the DC energy consumption device is cut off from being put into operation.

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

[0044] A fault flag determination module is used to determine an AC fault flag according to the AC voltage on the flexible DC transformer network side of the land station; wherein the AC fault flag is used to indicate whether the land station is in an AC fault period;

[0045] a current modulation module, configured to determine whether the land station is in an AC fault period according to the AC fault flag bit, and when it is determined that the land station is in an AC fault period, modulate the reactive current of the land station according to a first current reference value output by the 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;

[0046] A voltage modulation module is used to use 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 the low-frequency component of the DC current of the land station and calculating the damping coefficient, so as to obtain a voltage modulation wave signal.

[0047] In a third aspect, the present invention further provides an electronic device, comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the land station AC fault control method as described in the first aspect.

[0048] In a fourth aspect, the present invention further provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed, implements the steps of the onshore station AC fault control method as described in the first aspect.

[0049] It can be seen from the above technical scheme that the present invention determines the AC fault flag according to the AC voltage on the flexible DC transformer grid side of the land station, and introduces the AC fault flag on the basis of the dq axis outer loop control and the dq axis inner loop control of the land station to identify whether the land station is in an AC fault period, so that when the land station is in an AC fault period, the reactive current of the land station is modulated by using the second current reference value corresponding to the grid voltage amplitude during 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 calculation 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 on the DC side, solve the problem that it is difficult for offshore wind power to effectively control the AC fault of the land station through the flexible DC grid-connected system, and realize the successful crossing of the AC fault of the land station of the offshore wind power through the flexible DC grid-connected system, which can reduce the risk of DC tripping and wind farm wind turbine disconnection, and improve the safety and reliability of the offshore wind power through the flexible DC grid-connected system. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

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

[0052] Figure 2 An application environment of a land station AC fault control method provided by an embodiment of the present invention;

[0053] Figure 3 A flow chart of a land station AC fault control method provided by an embodiment of the present invention;

[0054] Figure 4a It is a schematic diagram of the dq transformation process of the three-phase voltage on the grid side of the flexible DC transformer in the onshore station;

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

[0056] Figure 5 This is a logic diagram for judging the AC fault flag;

[0057] Figure 6 It is a logic diagram of reactive current control;

[0058] Figure 7 It is the schematic diagram of Urms-Iq curve control logic;

[0059] Figure 8 This is a logic diagram of DC oscillation suppression control;

[0060] Fig. 9 It is a schematic diagram of the dq axis inner loop and modulation wave control logic;

[0061] Fig.10 It is a logic diagram of DC energy consumption switching control;

[0062] Fig.11 A schematic diagram of the structure of an onshore station AC fault control system provided by an embodiment of the present invention;

[0063] Fig.12 A schematic diagram of the structure of an electronic device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0064] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0065] The onshore station AC fault control method provided in the embodiment of the present application can be applied to Figure 2 In the application environment shown. Among them, the AC system of the land station communicates with the server 102 through the network. The data storage system can store the data that the server 102 needs to process. The data storage system can be integrated on the server 102, or it can be placed on the cloud or other network servers. The server 102 determines the AC fault flag according to the AC voltage on the flexible DC transformer network side of the land station; wherein the AC fault flag is used to indicate whether the land station is in an AC fault period; according to the AC fault flag, it is judged whether the land station is in an AC fault period. When it is judged that the land station is in an AC 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 AC fault period to obtain a current modulation signal; the current modulation signal is used as the input of the dq axis inner loop 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 loop control of the land station and the second voltage modulation wave generated by filtering and damping coefficient calculation of the low-frequency component of the DC current of the land station to obtain a voltage modulation wave signal. The server 102 may be an independent physical server, or a server cluster or distributed system composed of multiple physical servers, or a cloud server providing cloud computing services.

[0066] like Figure 3 As shown, the embodiment of the present application provides a land station AC fault control method, which is applied to Figure 2 The server 102 in the example is used as an example to illustrate the method, which includes the following steps S1 to S3. Among them:

[0067] Step S1, determining an AC fault flag according to the AC voltage on the network side of the flexible DC transformer of the land station; wherein the AC fault flag is used to indicate whether the land station is in an AC fault period.

[0068] The embodiment of the present application monitors the AC voltage on the grid side of the flexible DC transformer of the land station, determines whether the land station is in an AC fault period through the AC voltage on the grid side of the flexible DC transformer of the land station, and determines the AC fault flag.

[0069] Specifically, the step S1 of determining the AC fault flag according to the AC voltage on the flexible DC transformer grid side of the land station includes:

[0070] Step S101, normalize the positive sequence voltage amplitude of the AC voltage on the flexible DC transformer grid side of the onshore station to obtain the normalized value of the positive sequence voltage amplitude of the AC voltage.

[0071] Among them, by collecting the AC three-phase voltage and AC three-phase current on the flexible DC transformer grid side of the onshore station, the AC three-phase voltage and AC three-phase current are decomposed into d and q axes respectively to obtain the AC three-phase d-axis voltage, AC three-phase q-axis voltage, AC three-phase d-axis current and AC three-phase q-axis current, such as Figure 4a~4b Then, by calculating the effective value of the AC three-phase d-axis voltage and the 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 a 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 is determined to be the first AC fault flag, and the first AC fault flag is used to indicate that the onshore 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 is determined to be the second AC fault flag, and the second AC fault flag is used to indicate that the onshore station is in an AC fault period.

[0075] For example, Figure 5 The AC fault flag judgment logic shown sets the amplitude threshold to 0.9pu. When the per-unit value Udrms of the positive-sequence voltage amplitude of the AC voltage is greater than 0.9pu, it is judged that the land station is not in the AC fault period, and the AC fault flag ACfault is set to 0; when the per-unit value Udrms of the positive-sequence voltage amplitude of the AC voltage is not greater than 0.9pu, it is judged that the land station is in the AC fault period, and the AC fault flag ACfault is set to 1.

[0076] Step S2, judging whether the land station is in an AC fault period according to the AC fault flag; when it is judged that the land station is in an AC fault period, modulating 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.

[0077] It can be understood that, based on the dq axis outer loop control of the onshore station, the embodiment of the present application introduces the reactive current control of the AC fault mode using the AC fault flag as a criterion. The specific control logic is as follows: Figure 6 shown.

[0078] When it is determined that the land station is not in an AC fault period, the reactive current of the land station can be modulated according to the first current reference value output by the dq axis outer loop control of the land station, without adjusting the reactive current according to the degree of AC voltage drop.

[0079] When it is determined that the onshore station is in an AC fault period, the reactive current of the onshore station is modulated 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, so as to provide reactive support for grid voltage recovery.

[0080] Specifically, in step S2, the reactive current of the onshore station is modulated 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 to obtain the current modulation signal, which includes:

[0081] Step S201: output a first current reference value through the dq axis outer loop control of the land station, where the first current reference value includes a d axis current reference value and a q axis current reference value.

[0082] like Figure 6 As shown, the first current reference value is output through the dq axis outer loop control of the land station, including:

[0083] Step S2011: perform a difference process on the DC voltage reference value Udcref of the land station and the DC voltage measured value Udc to obtain a DC voltage difference.

[0084] Step S2012: perform a difference process on the reactive power reference value and the reactive power measured value of the land station to obtain a reactive power difference value.

[0085] Step S2013: Perform PI control on both the DC voltage difference and the reactive power difference to obtain a DC current superposition difference and a reactive current superposition difference.

[0086] Among them, PI control includes a proportional link and an integral link, and the DC voltage difference and the reactive power difference are both subjected to the proportional link and the integral link to obtain the DC current superposition difference and the reactive current superposition difference.

[0087] Step S2014: The DC current superposition difference and the reactive current superposition difference are both subjected to a limiting process in a limiting link to obtain a d-axis current reference value Idref and a q-axis current reference value Iqref0.

[0088] Step S202: Determine a q-axis current reference value corresponding to the grid voltage amplitude of the onshore station during the AC fault period according to a preset Urms-Iq curve.

[0089] like Figure 7 As shown, the reactive current will be controlled according to the degree of 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 period of the onshore station is obtained.

[0090] Among them, the Urms-Iq curve is required to be provided by different engineering designs. Specifically, it is a curve formed by the reactive current provided under different voltage amplitudes, such as Figure 7 As shown in Figure 1, as the voltage amplitude Urms decreases, the required reactive current increases and has a maximum limit value.

[0091] Input a voltage amplitude through the Urms-Iq curve, and find the output current Iq value corresponding to the voltage amplitude from the curve as the q-axis current reference value Iqref1.

[0092] Step S203, modulate the q-axis reactive current of the onshore station by the q-axis current reference value Iqref0 output by the dq-axis outer loop 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 a current modulation signal according to the d-axis current reference value Idref and the q-axis reactive current value Iqref.

[0094] Among them, the d-axis current reference value Idref and the q-axis reactive current value Iqref are input into the dq-axis inner loop control of the onshore station as current modulation signals.

[0095] Step S3, using the current modulation signal as the input of the dq-axis inner loop control of the land station, modulating 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 calculation of the low-frequency component of the DC current of the land station, to obtain a voltage modulation wave signal.

[0096] Among them, when it is determined that the land station is not in an AC fault period, the current modulation signal is used as the input of the dq-axis inner loop 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 loop control of the land station, without suppressing the low-frequency component on the DC side.

[0097] like Figure 8As shown, when it is determined that the onshore station is in an AC fault period, the configured DC oscillation suppression control function extracts the low-frequency component of the DC current, multiplies it by the damping coefficient, and generates Udref1 which is superimposed on the first voltage modulation wave output by the dq axis inner loop control, thereby achieving the purpose of suppressing the low-frequency component on the DC side, and transmits the voltage modulation wave signal to the converter of the onshore station for pulse modulation.

[0098] In steady-state operation, DC oscillation suppression control will effectively control the low-frequency oscillation of the DC side current and voltage. However, during the AC fault of the land station, if the DC energy consumption is repeatedly switched on and off, the DC oscillation suppression function will act together with the DC energy consumption switching on and off to cause the fluctuation of the DC voltage, causing instability in the DC system grid. Therefore, it is necessary to exit the DC oscillation suppression function when the AC fault flag of the land station is valid.

[0099] The damping coefficient is set according to the DC project and can be between 0.1 and 0.5.

[0100] Specifically, if Fig. 9 As shown, in step S3, the current modulation signal is used as the input of the dq axis inner loop 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 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 calculating the damping coefficient to obtain the voltage modulation wave signal, including:

[0101] Step S301, using the current modulation signals Idref and Iqref as inputs of the dq axis inner loop control of the land station, and outputting a first voltage modulation wave through the dq axis inner loop control of the land station; the first voltage modulation wave includes a d-axis voltage reference value Udref and a q-axis voltage reference value Uqref;

[0102] Step S302, filtering the low-frequency component of the DC current of the land station to obtain a low-frequency filtered component;

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

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

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

[0106] Step S306: Use the three-phase voltage modulation signals UAref, UBref, and UCref to perform modulation trigger control to obtain a voltage modulation wave signal.

[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 through the dq axis inner loop control of the land station, including:

[0109] Step S3011, performing a difference process on the d-axis current reference value Idref and the d-axis current measured value Id to obtain a d-axis current difference value;

[0110] Step S3012, performing a difference process on the q-axis reactive current value Iqref and the q-axis current measured value Iq to obtain a q-axis current difference value;

[0111] Step S3013, performing PI control on both the d-axis current difference and the q-axis current difference to obtain a d-axis current PI output value and a q-axis current PI output value;

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

[0113] Step S3014, using the q-axis voltage measured value Uq and the d-axis current compensation value to compensate the d-axis current PI output value, to obtain a d-axis voltage reference value Udref; 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, using the d-axis voltage measured value Ud and the q-axis current compensation value to compensate the q-axis current PI output value to obtain the q-axis voltage reference value Uqref; 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 the embodiment of the present application determines the AC fault flag according to the AC voltage on the flexible DC transformer grid side of the onshore station, and introduces an AC fault flag on the basis of the dq axis outer loop control and the dq axis inner loop control of the onshore station to identify whether the onshore station is in an AC fault period. Therefore, when the onshore station is in an AC fault period, the reactive current of the onshore station is modulated using the second current reference value corresponding to the grid voltage amplitude during the AC fault period. The AC voltage of the onshore station is also modulated by a voltage modulation wave generated by filtering and damping coefficient calculation of the low-frequency component of the DC current of the onshore station, thereby achieving the purpose of suppressing the low-frequency component on the DC side, solving the problem that it is difficult for offshore wind power to effectively control the AC fault of the onshore station through the flexible DC grid-connected system, and achieving successful crossing of the AC fault of the onshore station through the flexible DC grid-connected system of offshore wind power, which can reduce the risk of DC tripping and wind farm wind turbine disconnection, and improve the safety and reliability of the offshore wind power through the flexible DC grid-connected system.

[0116] In some embodiments, in the case of a high-power and serious AC fault at the onshore station, the DC voltage will rise sharply because the power of the offshore station cannot be sent to the grid in time. It is necessary to configure DC energy-consuming equipment on the DC side to absorb the surplus active power by putting DC energy-consuming equipment into use, thereby effectively reducing the DC voltage and avoiding equipment overvoltage and DC tripping.

[0117] In some embodiments, the embodiments of the present application configure the DC energy consumption switching. When the DC voltage of the onshore station reaches the overvoltage setting value of the DC energy consumption, the DC energy consumption is switched on. When the DC voltage drops to the DC energy consumption cut-off setting value, the DC energy consumption is cut off. If the AC fault has not been cleared, the DC voltage will continue to rise after the DC energy consumption is cut off, and the DC energy consumption may still be switched on and off. During the AC fault, the DC voltage will show repeated increases and decreases as the DC energy consumption is switched on and off.

[0118] Specifically, the embodiment of the present application further includes:

[0119] Step S401, determining whether the DC voltage of the land station reaches the overvoltage threshold for the DC energy consumption device to be put into operation;

[0120] Step S402: When the DC voltage of the land station reaches the overvoltage threshold of the DC energy consumption device, the DC energy consumption device is activated to consume the surplus active power of the land station;

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

[0122] Step S404: when it is determined that the DC voltage after the DC energy consumption device is put into operation drops to a preset voltage threshold, the DC energy consumption device is turned off.

[0123] For example, Fig.10 As shown in the figure, when the DC voltage Udc of the onshore station reaches the overvoltage threshold value UdcH for DC energy consumption, the DC energy consumption is put into operation; when the DC voltage drops to the return threshold value UdcL, the DC energy consumption is cut off. If the AC fault is not cleared, after the DC energy consumption is cut off, the DC voltage will continue to rise, and the DC energy consumption may still be put into operation and cut off. During the AC fault period, the DC voltage will show repeated increases and decreases with the switching of the DC energy consumption.

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

[0125] Based on the same inventive concept, an embodiment of the present application further provides a land station AC fault control system for implementing the land station AC fault control method involved above.

[0126] The implementation solution for solving the problem provided by the system is similar to the implementation solution recorded in the above method, so the specific limitations in one or more land station AC fault control system embodiments provided below can refer to the limitations on the land station AC fault control method above, and will not be repeated here.

[0127] like Fig.11 As shown, the embodiment of the present application also provides a land station AC fault control system, including:

[0128] The fault flag determination module 100 is used to determine the AC fault flag according to the AC voltage on the flexible DC transformer network side of the land station; wherein the AC fault flag is used to indicate whether the land station is in an AC fault period;

[0129] The current modulation module 200 is used to determine whether the land station is in an AC fault period according to the AC fault flag bit. When it is determined that the land station is in an AC 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 AC fault period to obtain a current modulation signal;

[0130] The voltage modulation module 300 is used to use 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 calculation of the low-frequency component of the DC current of the land station, to obtain a voltage modulation wave signal.

[0131] In some embodiments, the fault sign determination module 100 is used to normalize the positive sequence voltage amplitude of the AC voltage on the flexible DC transformer grid side of the onshore station to obtain the normalized value of the positive sequence voltage amplitude of the AC voltage;

[0132] Comparing the per-unit value of the positive sequence voltage amplitude of the AC voltage with a preset amplitude threshold;

[0133] 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 is determined to be the first AC fault flag, and the first AC fault flag is used to indicate that the onshore station is not in an AC fault period;

[0134] 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 is determined to be the second AC fault flag, and the second AC fault flag is used to indicate that the onshore station is in an AC fault period.

[0135] In some embodiments, the current modulation module 200 is used to output a first current reference value through a 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;

[0136] Determine a q-axis current reference value corresponding to the grid voltage amplitude of the onshore station during the AC fault according to a preset Urms-Iq curve;

[0137] The q-axis reactive current of the onshore station is modulated by 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 to obtain the q-axis reactive current value;

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

[0139] In some embodiments, outputting a first current reference value through a dq axis outer loop control of the land station includes:

[0140] The DC voltage reference value of the land station and the DC voltage measured value are subjected to difference processing to obtain the DC voltage difference value;

[0141] The reactive power reference value of the land station and the reactive power measured value are subtracted to obtain the reactive power difference;

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

[0143] The DC current superposition difference and the reactive current superposition difference are both subjected to a limiting link for limiting processing to obtain a d-axis current reference value and a q-axis current reference value.

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

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

[0146] Multiplying the low-frequency filter component by the damping coefficient to obtain a second voltage modulation wave;

[0147] Superimposing the second voltage modulation wave with the d-axis voltage reference value to obtain a d-axis voltage superimposed value;

[0148] Perform an inverse Park operation on the d-axis voltage superposition value and the q-axis voltage reference value to obtain a three-phase voltage modulation signal;

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

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

[0151] 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 through the dq axis inner loop control of the land station, including:

[0152] Performing a difference process on the d-axis current reference value and the d-axis current measured value to obtain the d-axis current difference value;

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

[0154] The d-axis current difference and the q-axis current difference 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 the q-axis voltage measured value and the 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;

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

[0157] In some embodiments, the system also includes: a DC energy consumption switching module, which is used to determine whether the DC voltage of the land station reaches the overvoltage threshold of the DC energy consumption device; when the DC voltage of the land station reaches the overvoltage threshold of the DC energy consumption device, the DC energy consumption device is put into operation to consume the surplus active power of the land station; it is determined whether the DC voltage after the DC energy consumption device is put into operation drops to a preset voltage threshold; when it is determined that the DC voltage after the DC energy consumption device is put into operation drops to the preset voltage threshold, the DC energy consumption device is cut off.

[0158] like Fig.12 As shown, an embodiment of the present application further provides an electronic device, the electronic device 10 includes a memory 20 and a processor 30, the memory 20 stores a computer program, and when the computer program is executed by the processor 30, the processor 30 executes the steps of the land station AC fault control method in any of the above embodiments.

[0159] An embodiment of the present application further provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed, the steps of the land station AC fault control method in any of the above embodiments are implemented.

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

[0161] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0162] In several embodiments provided by the present invention, it is understood that each box in the flow chart or block diagram can represent a module, a program segment or a part of a code, and a part of a module, a program segment or a code includes one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in a different order from that marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved.

[0163] In the several embodiments provided by the present invention, it should be understood that the disclosed systems, electronic devices, computer storage media and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of units is only a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0164] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0165] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0166] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for executing all or part of the steps of the method described in each embodiment of the present invention through a computer device (which can be a personal computer, server, or network device, etc.). The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (full name in English: Read-Only Memory, English abbreviation: ROM), random access memory (full name in English: Random Access Memory, English abbreviation: RAM), disk or optical disk and other media that can store program codes.

[0167] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for controlling AC faults in a land station, characterized in that: include: Determine an AC fault flag bit according to the AC voltage on the flexible DC transformer network side of the land station; wherein the AC fault flag bit is used to indicate whether the land station is in an AC fault period; Determining whether the land station is in an AC fault period according to the AC fault flag bit, and when it is determined that the land station is in an AC fault period, modulating the reactive current of the land station according to a first current reference value output by a 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; The current modulation signal is used as the input of the dq-axis inner loop 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 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 calculating the damping coefficient, so as to obtain a voltage modulation wave signal.

2. The onshore station AC fault control method according to claim 1, characterized in that: The step of determining the AC fault flag bit according to the AC voltage on the flexible DC transformer grid side of the land station includes: The positive-sequence voltage amplitude of the AC voltage on the flexible DC transformer grid side of the onshore station is normalized to obtain the normalized value of the positive-sequence voltage amplitude of the AC voltage; Comparing the per-unit value of the positive-sequence voltage amplitude of the AC voltage with a preset amplitude threshold; 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 is determined to be a first AC fault flag, and the first AC fault flag is used to indicate that the land station is not in an AC fault period; 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 is determined to be a second AC fault flag, and the second AC fault flag is used to indicate that the land station is in an AC fault period.

3. The onshore station AC fault control method according to claim 1, characterized in that: 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 to obtain a current modulation signal includes: Outputting a first current reference value through the dq axis outer loop control of the land station, wherein the first current reference value includes a d axis current reference value and a q axis current reference value; Determining a q-axis current reference value corresponding to the grid voltage amplitude of the onshore station during the AC fault according to a preset Urms-Iq curve; The q-axis reactive current of the onshore station is modulated by 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 to obtain a q-axis reactive current value; A current modulation signal is determined according to the d-axis current reference value and the q-axis reactive current value.

4. The onshore station AC fault control method according to claim 3, characterized in that: The outputting of the first current reference value through the dq axis outer loop control of the land station includes: Performing a difference processing on the DC voltage reference value and the DC voltage measured value of the land station to obtain a DC voltage difference value; Performing a difference processing on the reactive power reference value and the reactive power measured value of the land station to obtain a reactive power difference value; The DC voltage difference and the reactive power difference are both subjected to PI control to obtain a DC current superposition difference and a reactive current superposition difference; The DC current superposition difference and the reactive current superposition difference are both subjected to a limiting process through a limiting link to obtain a d-axis current reference value and a q-axis current reference value.

5. The onshore station AC fault control method according to claim 1, characterized in that: The method uses 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 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 calculating the damping coefficient, to obtain a voltage modulation wave signal, including: The current modulation signal is used as an input of the dq axis inner loop control of the land station, and a first voltage modulation wave is output through the dq axis inner loop control of the land station; the first voltage modulation wave includes a d-axis voltage reference value and a q-axis voltage reference value; Filtering the low-frequency component of the direct current of the land station to obtain a low-frequency filtered component; Multiplying the low-frequency filter component by the damping coefficient to obtain a second voltage modulation wave; superimposing the second voltage modulation wave with the d-axis voltage reference value to obtain a d-axis voltage superimposed value; Performing an inverse Park operation on the d-axis voltage superposition value and the q-axis voltage reference value to obtain a three-phase voltage modulation signal; The three-phase voltage modulation signal is used to perform modulation trigger control to obtain a voltage modulation wave signal.

6. The onshore station AC fault control method according to claim 5, characterized in that: The current modulation signal includes a d-axis current reference value and a q-axis reactive current value; The method of using the current modulation signal as an input of the dq axis inner loop control of the land station and outputting a first voltage modulation wave through the dq axis inner loop control of the land station comprises: Performing a difference processing on the d-axis current reference value and the d-axis current measured value to obtain a d-axis current difference value; Performing a difference processing on the q-axis reactive current value and the q-axis current measured value to obtain a q-axis current difference value; Performing PI control on both the d-axis current difference and the q-axis current difference 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 using the q-axis voltage measured value and the 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 using the d-axis voltage measured value and the 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.

7. The onshore station AC fault control method according to claim 1, characterized in that: Also includes: Determining whether the DC voltage of the land station reaches an overvoltage threshold for the DC energy consumption device to be put into operation; When the DC voltage of the land station reaches the overvoltage threshold of the DC energy consumption device, the DC energy consumption device is activated to consume the surplus active power of the land station; Determining whether the DC voltage after the DC energy consumption device is put into operation drops to a preset voltage threshold; When it is determined that the DC voltage after the DC energy consumption device is put into operation drops to the preset voltage threshold, the DC energy consumption device is cut off from being put into operation.

8. An onshore station AC fault control system, characterized in that: include: A fault flag determination module is used to determine an AC fault flag according to the AC voltage on the flexible DC transformer network side of the land station; wherein the AC fault flag is used to indicate whether the land station is in an AC fault period; a current modulation module, configured to determine whether the land station is in an AC fault period according to the AC fault flag bit, and when it is determined that the land station is in an AC fault period, modulate the reactive current of the land station according to a first current reference value output by the 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; A voltage modulation module is used to use 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 the low-frequency component of the DC current of the land station and calculating the damping coefficient, so as to obtain a voltage modulation wave signal.

9. An electronic device, characterized in that: The electronic device includes a memory and a processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the processor executes the steps of the onshore station AC fault control method according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed, the steps of the onshore station AC fault control method according to any one of claims 1 to 7 are implemented.

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