Direct-current fault ride-through method and system for wind power plant through direct-current sending-out system

Abstract

The invention relates to the technical field of electric power systems, and discloses a direct current fault ride-through method and system for a wind power plant through a direct current sending-out system, and the method comprises the steps: rapidly responding to a direct current fault of the wind power plant through the direct current sending-out system, and switching the operation modes of a fan and a receiving end converter station; the direct current of the fan and the receiving end converter station is controlled to be reduced to be below the preset current safety lower limit threshold value, so that the fault current of the line is cut off by the mechanical switch, the direct current fault current is quickly reduced at the initial stage of the fault, and the damage to the system caused by continuously overlarge fault current is avoided; according to the utility model, the fault current can be rapidly reduced by depending on the fan control system, and the fan control system is matched with the rapid mechanical switch to disconnect the loop, so that the complexity and the maintenance cost of the system are reduced, the stable operation of the system is rapidly recovered, and the downtime of the fan system is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a method and system for riding through a direct current fault in a wind farm via a direct current transmission system. Background Art

[0002] As a green energy source, wind power has developed rapidly in recent years, and its power conversion and transmission technology has become a hot topic of research at home and abroad. At present, the large-scale long-distance transmission of wind power in engineering mainly adopts flexible direct current transmission based on modular multilevel converter (MMC). However, the converter in the flexible direct current transmission system is large in size, heavy in weight, and has high construction cost. In order to improve the economy and reliability of long-distance direct current transmission of wind power from large wind farms, some scholars have proposed a solution of direct current transmission through a diode rectifier (DR).

[0003] In order to meet the economic needs of large-scale long-distance transmission of wind power, current projects usually use DC overhead lines to transmit it to the load center. However, overhead lines are more prone to short circuit failures than cables. Figure 1 As shown in the figure, for a system where wind power is transmitted via DR DC, if a DC fault occurs, the DR cannot clear the fault current by itself due to its lack of control capability. In order to prevent the DC fault current from rising rapidly and damaging the converter, effective measures need to be taken to clear the DC fault as soon as possible.

[0004] Currently, when a DC fault occurs in a wind farm through a DC transmission system, the fault clearing and post-fault recovery time is long, which is not conducive to the safe and stable operation of the system. Summary of the invention

[0005] In view of this, the present invention provides a DC fault ride-through method and system for a wind farm via a DC transmission system, which solves the technical problem that when a DC fault occurs in a wind farm via a DC transmission system, the fault clearing and post-fault recovery time is long, which is not conducive to the safe and stable operation of the system.

[0006] A first aspect of the present invention provides a DC fault ride-through method for a wind farm via a DC transmission system, which is applied to a wind farm via a DC transmission system; the wind farm via a DC transmission system comprises a wind turbine and a receiving-end converter station; the wind turbine is connected to the receiving-end converter station via a common coupling point and a diode rectifier, and a mechanical switch is provided on the line between the diode rectifier and the receiving-end converter station, and the method comprises:

[0007] real-time monitoring of the operation status of the wind farm through the DC transmission system, and when a DC fault is detected in the operation mode, controlling the wind turbine and the receiving-end converter station to switch from the first operation mode to the second operation mode, and performing load unloading operation on the wind turbine;

[0008] The first operation mode is used to control the reference power output of the wind turbine and the receiving-end converter station under normal operation, and the second operation mode is used to control the fault ride-through of the wind turbine and the receiving-end converter station under DC fault operation;

[0009] In the second operation mode, the DC current of the wind turbine and the receiving-end converter station are respectively controlled to be reduced to below a preset current safety lower limit threshold; the current safety lower limit threshold is used to represent the DC current threshold at which the line is cut off by the mechanical switch;

[0010] After the DC side fault line between the wind turbine and the receiving-end converter station is cut off by the mechanical switch, the receiving-end converter station is controlled to switch back to the first operating mode, and then the wind turbine is controlled to switch back to the first operating mode, and the unloading operation of the wind turbine is stopped.

[0011] Optionally, in the second operation mode, respectively controlling the DC current of the wind turbine and the receiving-end converter station to decrease to below a preset current safety lower limit threshold value includes:

[0012] In the second operating mode, the grid-side converter of the wind turbine is controlled to reduce the AC current, and the DC current of the grid-side converter of the wind turbine is reduced to below the preset current safety lower limit threshold, and the receiving-end converter station is controlled to actively output a negative DC voltage, and the DC current of the receiving-end converter station is reduced to below the preset current safety lower limit threshold.

[0013] Optionally, the wind turbine includes a machine-side converter;

[0014] The control process of the machine-side converter is as follows:

[0015] Obtain a first d-axis current difference by performing a difference operation between a reference value of a d-axis component of the rotor current of the machine-side converter and an actual value of the d-axis current;

[0016] The first d-axis current difference is input into a proportional-integral controller, and a first d-axis current deviation is output;

[0017] A first d-axis voltage component reference value is obtained by performing a difference operation between the first d-axis current deviation and a preset first feedforward amount; wherein the first feedforward amount is obtained according to the rotor electrical angular velocity, the stator-rotor inductance and the rotor current q-axis component;

[0018] A first voltage component difference is obtained by performing a difference operation between the first DC voltage actual value and the first DC voltage rated value of the fan;

[0019] Obtaining a first current q-axis component reference value by passing the first voltage component difference through a proportional-integral controller;

[0020] Obtaining a first q-axis current difference by performing a difference operation between the first current q-axis component reference value and the current q-axis component actual value;

[0021] The first q-axis current difference is input into a proportional-integral controller to obtain a first q-axis current difference deviation;

[0022] Obtaining a first q-axis voltage component reference value by adding the first q-axis current difference deviation amount and a preset second feedforward amount;

[0023] The first d-axis voltage component reference value and the first q-axis voltage component reference value are subjected to park transformation to obtain the first port three-phase voltage reference value of the machine-side converter, and then the first port three-phase voltage reference value is processed by PWM modulation to obtain the switch modulation signal of the machine-side converter.

[0024] Optionally, the wind turbine includes a grid-side converter;

[0025] The control process of the grid-side converter in the first operation mode is as follows:

[0026] The actual speed value of the fan is subjected to maximum power point tracking control to obtain a fan power reference value;

[0027] By performing a difference operation between the fan power reference value and the fan power actual value, a fan power difference value is obtained;

[0028] After the fan power difference is input into the proportional-integral controller, the fan power difference deviation is obtained;

[0029] The wind turbine voltage amplitude is obtained by adding the wind turbine power difference deviation amount and a preset third feedforward amount; wherein the third feedforward amount is obtained according to the grid-side phase voltage rated value;

[0030] Obtaining a first d-axis current reference value of the machine-side converter in the first operating mode according to the wind turbine voltage amplitude and the wind turbine actual voltage amplitude;

[0031] Performing a difference operation on the first q-axis voltage reference value and the first q-axis voltage actual value of the grid-side converter to obtain a first q-axis voltage difference value;

[0032] The first q-axis voltage difference is input into a proportional-integral controller, and a first q-axis current reference value is output;

[0033] Obtaining a first d-axis voltage component reference value and a first q-axis voltage component reference value of the generator-side converter in the first operating mode through current closed-loop control of the first d-axis current reference value and the first q-axis current reference value;

[0034] Obtain a port three-phase voltage reference value of the machine-side converter in the first operating mode by performing park transformation on the first d-axis voltage component reference value and the first q-axis voltage component reference value, and then obtain a switch modulation signal of the machine-side converter in the first operating mode by performing PWM modulation processing on the first port three-phase voltage reference value;

[0035] The control process of the grid-side converter in the second operation mode is as follows:

[0036] Determining a second d-axis current reference value of the generator-side converter in the second operating mode by using the current safety lower limit threshold;

[0037] Obtaining a second d-axis voltage component reference value and a second q-axis voltage component reference value of the generator-side converter in the second operating mode through current closed-loop control of the second d-axis current reference value and the first q-axis current reference value;

[0038] The second d-axis voltage component reference value and the second q-axis voltage component reference value are subjected to park transformation to obtain the three-phase voltage reference value of the third port of the machine-side converter in the second operating mode, and then the three-phase voltage reference value of the third port is processed by PWM modulation to obtain the switch modulation signal of the machine-side converter in the second operating mode.

[0039] Optionally, the receiving-end converter station includes an AC controller;

[0040] The control process of the AC controller is:

[0041] The rated value of the submodule capacitor voltage of the AC controller and the actual value of the submodule capacitor voltage are processed to obtain the submodule capacitor voltage difference;

[0042] The voltage difference of the capacitor of the submodule is input into the proportional-integral controller to obtain a third d-axis current reference value;

[0043] Obtain a third d-axis current difference by performing a difference operation between the third d-axis current reference value and the third d-axis current actual value;

[0044] The third d-axis current difference is passed through a proportional-integral controller to obtain a third d-axis current difference deviation;

[0045] The third d-axis voltage reference value is obtained by performing a difference process on the third d-axis current difference deviation amount and a preset fourth feedforward amount; wherein the fourth feedforward amount is obtained according to the frequency, the transformer inductance, the bridge arm inductance and the grid-side d-axis voltage;

[0046] A second q-axis current difference is obtained by performing a difference operation on a second q-axis current reference value of the AC controller and a second q-axis current actual value;

[0047] The second q-axis current difference is input into a proportional-integral controller to obtain a second q-axis current difference deviation;

[0048] Obtaining a second q-axis voltage reference value by performing a difference operation on the second q-axis current difference deviation amount and a preset fifth feedforward amount;

[0049] The AC internal potential of the AC controller is obtained by park transforming the third d-axis voltage reference value and the second q-axis voltage reference value.

[0050] Optionally, the receiving-end converter station includes a DC controller;

[0051] The control process of the DC controller in the first operation mode is:

[0052] A second DC voltage difference is obtained by performing a difference operation between a second DC voltage actual value and a second DC voltage rated value of the DC controller;

[0053] The second DC voltage difference is input into a proportional-integral controller to obtain a first DC current deviation;

[0054] Obtaining a first DC internal potential of the DC controller in a first operating mode by performing a difference operation between the first DC current deviation and a preset sixth feedforward value;

[0055] The control process of the DC controller in the second operation mode is as follows:

[0056] Performing a difference operation on the DC current reference value of the DC controller and the negative DC current actual value to obtain a DC current difference value; wherein the DC current reference value is zero;

[0057] The DC current difference is passed through a proportional controller and then through a limiting link to obtain a second DC internal potential of the DC controller in a second operating mode.

[0058] Optionally, the receiving-end converter station includes a circulating current controller;

[0059] The control process of the circulation controller is:

[0060] The circulating current internal potential of the circulating current controller is obtained by suppressing the circulating current component of the circulating current controller to zero.

[0061] In a second aspect, the present invention provides a DC fault ride-through system for a wind farm via a DC transmission system, which is applied to a wind farm via a DC transmission system; the wind farm via a DC transmission system comprises a wind turbine and a receiving-end converter station; the wind turbine is connected to the receiving-end converter station via a common coupling point and a diode rectifier, and a mechanical switch is provided on the line between the diode rectifier and the receiving-end converter station, and the system comprises:

[0062] A mode switching module is used to monitor the operating state of the wind farm through the DC transmission system in real time, and when a DC fault is detected in the operating state, control the wind turbine and the receiving-end converter station to switch from the first operating mode to the second operating mode, and perform load unloading operation on the wind turbine;

[0063] The first operation mode is used to control the reference power output of the wind turbine and the receiving-end converter station under normal operation, and the second operation mode is used to control the fault ride-through of the wind turbine and the receiving-end converter station under DC fault operation;

[0064] A fault ride-through module, used for controlling the DC current of the wind turbine and the receiving-end converter station to be reduced to below a preset current safety lower limit threshold value respectively in the second operation mode; the current safety lower limit threshold value is used to represent the DC current threshold value at which the line is cut off by the mechanical switch;

[0065] A fault recovery module is used to control the receiving-end converter station to switch back to the first operating mode after cutting off the DC side fault line between the wind turbine and the receiving-end converter station through the mechanical switch, and then control the wind turbine to switch back to the first operating mode and stop the unloading operation of the wind turbine.

[0066] In a third aspect, the present invention 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 DC fault ride-through method of a wind farm through a DC transmission system as described in the first aspect.

[0067] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed, implements the steps of the method for DC fault ride-through of a wind farm via a DC transmission system as described in the first aspect.

[0068] It can be seen from the above technical solutions that the present invention responds quickly to a DC fault in the DC transmission system of the wind farm, and switches the operation modes of the wind turbine and the receiving-end converter station, so that the DC currents of the wind turbine and the receiving-end converter station are respectively controlled to be reduced to below the preset current safety lower limit threshold, so that the line is cut off from the fault current by the mechanical switch, thereby quickly reducing the DC fault current in the early stage of the fault, avoiding damage to the system caused by the continuous excessive fault current, and no additional complex DC side protection device is required. The fault current is quickly reduced by relying on the wind turbine control system itself, and the loop is disconnected in cooperation with the fast mechanical switch, thereby reducing the complexity and maintenance cost of the system. After the fault, the AC system remains connected, and the normal operation mode can be directly restored after the fault is cleared, so that the system can be quickly restored to stable operation, reducing the downtime of the wind turbine system, minimizing the impact of the DC fault on the system, and ensuring the safe and stable operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] 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.

[0070] Figure 1 A schematic diagram of the structure of a direct current transmission system for a wind farm provided by an embodiment of the present invention;

[0071] Figure 2 A diagram of the application environment of the DC fault ride-through method of a wind farm through a DC transmission system provided by an embodiment of the present invention;

[0072] Figure 3 A schematic diagram of the topological structure of a hybrid MMC provided in an embodiment of the present invention;

[0073] Figure 4 A flow chart of a method for riding through a DC fault in a wind farm through a DC transmission system provided by an embodiment of the present invention;

[0074] Figure 5 A control block diagram of a fan provided by an embodiment of the present invention;

[0075] Figure 6 A control block diagram of a receiving-end converter provided in an embodiment of the present invention;

[0076] Figure 7 A schematic structural diagram of a DC fault ride-through system for a wind farm via a DC transmission system provided by an embodiment of the present invention;

[0077] Figure 8A schematic diagram of the structure of an electronic device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0078] 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.

[0079] At present, in order to meet the economic needs of large-scale long-distance transmission of wind power, current projects usually use DC overhead lines to transmit to the load center. However, overhead lines are more prone to short circuit failures than cables. Figure 1 As shown in the figure, for a system where wind power is transmitted via DR DC, if a DC fault occurs, the DR cannot clear the fault current by itself due to its lack of control capability. In order to prevent the DC fault current from rising rapidly and damaging the converter, effective measures need to be taken to clear the DC fault as soon as possible.

[0080] At present, when a short circuit or fault occurs on the DC side, a DC circuit breaker (DCCB) can be used to quickly isolate the faulty line. However, the cost of DC circuit breakers is high, which will significantly increase the system cost. At the same time, the structure and control of DC circuit breakers are complex, and the reliability of actual use still needs further research. At the same time, if the DC fault can be cleared by tripping the AC current circuit breaker (Alternating Current Circuit Breaker), however, the fault clearing and post-fault recovery time is long, which is not conducive to the safe and stable operation of the system, and may also cause polar power transmission interruption. It can only be used in end-to-end DC transmission systems.

[0081] In view of this, the DC fault ride-through method of a wind farm through a DC transmission system provided in the embodiment of the present application can be applied to Figure 2In the application environment shown, the terminal 101 communicates with the server 102 via a network. The data storage system can store data that the server 102 needs to process. The data storage system can be integrated on the server 102, or placed on the cloud or other network servers. The terminal 101 or the server 102 monitors the operating status of the wind farm through the DC transmission system in real time, and when a DC fault is detected in the operating state, controls the wind turbine and the receiving-end converter station to switch from the first operating mode to the second operating mode, and performs a load shedding operation on the wind turbine; wherein the first operating mode is used to control the reference power output of the wind turbine and the receiving-end converter station under normal operation, and the second operating mode is used to control the fault ride-through of the wind turbine and the receiving-end converter station under DC fault operation; in the second operating mode, the DC current of the wind turbine and the receiving-end converter station are respectively controlled to be reduced to below a preset current safety lower limit threshold; the current safety lower limit threshold is used to characterize the DC current threshold at which the line is cut off by a mechanical switch; after the DC side fault line of the wind turbine and the receiving-end converter station is cut off by a mechanical switch, the receiving-end converter station is controlled to switch back to the first operating mode, and then the wind turbine is controlled to switch back to the first operating mode, and the load shedding operation of the wind turbine is stopped.

[0082] The terminal 101 may be, but is not limited to, various personal computers, laptop computers, smart phones, tablet computers, and the like.

[0083] 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 that provides cloud computing services.

[0084] An embodiment of the present application provides a DC fault ride-through method for a wind farm via a DC transmission system, which is applied to a wind farm via a DC transmission system; the wind farm via a DC transmission system includes a wind turbine and a receiving-end converter station; the wind turbine is connected to the receiving-end converter station through a common coupling point and a diode rectifier, and a mechanical switch is provided on the line between the diode rectifier and the receiving-end converter station.

[0085] Among them, for Figure 1The wind power shown in the figure is a DC transmission system with diode rectification. The wind power is collected to the Point of Common Coupling (PCC) bus through AC, and then sent to the receiving end through long-distance DC overhead lines after DR rectification. The receiving end converter adopts MMC to avoid commutation failure and improve the support capacity for the receiving end power grid. Since DR cannot provide stable AC voltage, the converter of each wind turbine needs to adopt a grid-type control strategy to jointly support the AC voltage and frequency of the sending end island system and achieve synchronous operation. The wind turbine is equipped with a rated capacity unloading circuit. MMC adopts a hybrid MMC topology composed of a half-bridge submodule (HBSM) and a full-bridge submodule (FBSM) to achieve DC fault clearing, such as Figure 3 The topology of the hybrid MMC is shown.

[0086] like Figure 4 As shown, an embodiment of the present application provides a method for riding through a DC fault in a wind farm through a DC transmission system, the method comprising:

[0087] Step S1, real-time monitoring of the operating status of the wind farm through the DC transmission system, and when a DC fault is detected in the operating mode, control the wind turbine and the receiving-end converter station to switch from the first operating mode to the second operating mode, and perform load unloading operation on the wind turbine.

[0088] The first operation mode is used to control the reference power output of the wind turbine and the receiving-end converter station under normal operation, and the second operation mode is used to control the fault ride-through of the wind turbine and the receiving-end converter station under DC fault operation.

[0089] The hybrid MMC provides a stable DC voltage in the first operating mode, and the wind turbine controls active power in the first operating mode, and outputs the active power obtained by Maximum Power Point Tracking (MPPT) to the DC system normally.

[0090] The hybrid MMC and the fans clear the DC fault in the second operation mode.

[0091] It is understandable that after a DC short circuit fault occurs in the DC transmission system of a wind farm, the DC voltage quickly drops to 0. Since both the MMC and the wind turbine will discharge to the short circuit point, the DC current will rise rapidly. If no measures are taken, the switching devices will be damaged. Therefore, switching to the second operating mode is to quickly clear the DC fault.

[0092] Step S2: in the second operation mode, respectively control the DC current of the wind turbine and the receiving-end converter station to be reduced to below a preset current safety lower limit threshold; the current safety lower limit threshold is used to represent the DC current threshold at which the line is cut off by the mechanical switch.

[0093] In a general example, in the second operating mode, the grid-side converter of the wind turbine is controlled to reduce the AC current, and the DC current of the grid-side converter of the wind turbine is reduced to below the preset current safety lower limit threshold, and the receiving-end converter station is controlled to actively output a negative DC voltage, and the DC current of the receiving-end converter station is reduced to below the preset current safety lower limit threshold.

[0094] It is understandable that based on the characteristics of uncontrolled rectification of diodes, the wind turbine side can quickly reduce the AC current by actively adjusting the AC controller, which can quickly reduce the DC fault current at the early stage of the fault and avoid damage to the system caused by excessive fault current.

[0095] Exemplarily, the grid-side converter of the wind turbine is controlled to actively reduce the AC current, so that the DC current drops rapidly to near 0, so that the DC current of the wind turbine can drop rapidly to the extent that the DC current can be cut off by a fast mechanical switch. And the receiving-end converter station is made to actively output a negative DC voltage, forcing the DC fault current to drop to 0, so that the DC current of the receiving-end converter station can drop rapidly to the extent that the DC current can be cut off by a fast mechanical switch (High Speed ​​Switch, HSS), so as to complete the rapid clearing of the DC fault. In this process, the cutting time of the fast mechanical switch is extremely short, which can minimize the impact of the DC fault on the system. After the above process, the fault currents on the DC sides of MMC and DR are cleared, waiting for the fault to be restored. At this time, the fast mechanical switch is actuated to cut off the fault line. After the fault line is cut off, the system enters the fault recovery stage.

[0096] Step S3: After the DC side fault line between the wind turbine and the receiving-end converter station is cut off by the mechanical switch, the receiving-end converter station is controlled to switch back to the first operation mode, and then the wind turbine is controlled to switch back to the first operation mode, and the unloading operation of the wind turbine is stopped.

[0097] It should be noted that when the system is ready to recover after a fault, the receiving end converter station switches back to the first operation mode and ramps back the DC voltage to the rated value. Thus, the DC voltage is established, and then the wind turbine is controlled to switch back to the first operation mode and stop the unloading operation of the wind turbine. At this time, the wind farm resumes normal operation through the DC transmission system and continues to realize long-distance transmission of wind power.

[0098] It should be noted that the embodiment of the present application responds quickly to a DC fault in the wind farm through the DC transmission system, and switches the operating modes of the wind turbine and the receiving-end converter station, so that the DC currents that control the wind turbine and the receiving-end converter station are reduced to below the preset current safety lower limit threshold, so that the line is cut off from the fault current by a mechanical switch, thereby quickly reducing the DC fault current in the early stage of the fault to avoid damage to the system caused by a continuous excessive fault current. There is no need to add additional complex DC side protection devices, and the fault current is quickly reduced by relying on the wind turbine control system itself, and the loop is disconnected in cooperation with a fast mechanical switch, thereby reducing the complexity and maintenance cost of the system. The AC system remains connected after the fault, and the normal operating mode can be directly restored after the fault is cleared, quickly restoring the system to stable operation, reducing the downtime of the wind turbine system, and minimizing the impact of the DC fault on the system, ensuring the safe and stable operation of the system.

[0099] At the same time, the entire process does not require the use of a DC circuit breaker, which reduces system costs, avoids the complexity of the DC circuit breaker structure and control, and improves the reliability and stability of the system.

[0100] Among them, in the wind turbine control, the wind turbine includes a machine-side converter (MSC) and a grid-side converter (GSC).

[0101] Among them, the control process of the machine-side converter is:

[0102] Step S201, performing a difference operation between a reference value of a rotor current d-axis component of a machine-side converter and an actual value of a d-axis current to obtain a first d-axis current difference;

[0103] Step S202, inputting the first d-axis current difference into a proportional-integral controller, and outputting a first d-axis current deviation;

[0104] Step S203, obtaining a first d-axis voltage component reference value by performing a difference operation between the first d-axis current deviation and a preset first feedforward amount; wherein the first feedforward amount is obtained according to the rotor electrical angular velocity, the stator-rotor inductance and the rotor current q-axis component;

[0105] Step S204, performing a difference operation between the first DC voltage actual value and the first DC voltage rated value of the fan to obtain a first voltage component difference;

[0106] Step S205, obtaining a first current q-axis component reference value by passing the first voltage component difference through a proportional-integral controller;

[0107] Step S206, obtaining a first q-axis current difference by performing a difference operation between the first current q-axis component reference value and the current q-axis component actual value;

[0108] Step S207, inputting the first q-axis current difference into a proportional-integral controller to obtain a first q-axis current difference deviation;

[0109] Step S208, obtaining a first q-axis voltage component reference value by adding the first q-axis current difference deviation amount and a preset second feedforward amount;

[0110] Step S209, obtain the three-phase voltage reference value of the first port of the machine-side converter by Park transformation of the first d-axis voltage component reference value and the first q-axis voltage component reference value, and then obtain the switch modulation signal of the machine-side converter by PWM modulation processing of the three-phase voltage reference value of the first port.

[0111] Among them, the control process of the grid-side converter in the first operation mode is:

[0112] Step S211, obtaining a fan power reference value by performing maximum power point tracking control on the actual fan speed value;

[0113] Step S212, performing a difference operation between the fan power reference value and the fan power actual value to obtain a fan power difference value;

[0114] Step S213, after the fan power difference is input into the proportional integral controller, the fan power difference deviation is obtained;

[0115] Step S214, obtaining the wind turbine voltage amplitude by adding the wind turbine power difference deviation amount and the preset third feedforward amount; wherein the third feedforward amount is obtained according to the grid-side phase voltage rated value;

[0116] Step S215, obtaining a first d-axis current reference value of the machine-side converter in the first operating mode according to the wind turbine voltage amplitude and the wind turbine actual voltage amplitude;

[0117] Step S216, performing a difference operation on the first q-axis voltage reference value and the first q-axis voltage actual value of the grid-side converter to obtain a first q-axis voltage difference value;

[0118] Step S217, input the first q-axis voltage difference into a proportional-integral controller, and output a first q-axis current reference value;

[0119] Step S218, obtaining a first d-axis voltage component reference value and a first q-axis voltage component reference value of the generator-side converter in the first operating mode through current closed-loop control using the first d-axis current reference value and the first q-axis current reference value;

[0120] Step S219, obtaining a port three-phase voltage reference value of the machine-side converter in the first operating mode by performing park transformation on the first d-axis voltage component reference value and the first q-axis voltage component reference value, and then performing PWM modulation processing on the first port three-phase voltage reference value to obtain a switch modulation signal of the machine-side converter in the first operating mode;

[0121] The control process of the grid-side converter in the second operation mode is as follows:

[0122] Step S221, determining a second d-axis current reference value of the generator-side converter in the second operating mode by using a current safety lower limit threshold;

[0123] Step S222: obtaining a second d-axis voltage component reference value and a second q-axis voltage component reference value of the generator-side converter in the second operation mode through current closed-loop control using the second d-axis current reference value and the first q-axis current reference value;

[0124] Step S223, obtain the three-phase voltage reference value of the third port of the machine-side converter in the second operating mode by Park transformation of the second d-axis voltage component reference value and the second q-axis voltage component reference value, and then obtain the switch modulation signal of the machine-side converter in the second operating mode by PWM modulation processing of the three-phase voltage reference value of the third port.

[0125] For example, Figure 5 As shown in the figure, the d-axis current control of the fan side converter is the same as the conventional method, and the d-axis component reference value of the rotor current i * sd is 0, the rotor current d-axis component reference value i * sd The actual value of the d-axis current i sd Subtract the feedforward amount (ω e L s i sq , where ω e is the rotor electrical angular velocity, L s is the stator and rotor inductance, i sq is the q-axis component of the rotor current) to obtain the d-axis voltage reference value e * sd .

[0126] Actual value of fan DC voltage u dcW With the rated value u dcWN Subtract and pass through the proportional integral controller to obtain the rotor current q-axis component reference value i * sq The reference value of the rotor current q-axis component i * sq The actual value of the q-axis component of the rotor current isq Subtract, and pass through the proportional integral controller to get the deviation. This deviation plus the feedforward (ω e ψ f + ω e L s i sd , where ψ f is the flux linkage) to obtain the q-axis voltage reference value e * sq Finally, the d-axis voltage reference value e * sd and q-axis voltage reference value e * sq After park transformation, the three-phase voltage reference value of the converter port is obtained, and then the switch modulation signal is obtained through PWM.

[0127] The grid-side converter of the wind turbine adopts grid-type control. The frequency of the converter output voltage ω g Through reactive power control, the frequency of the converter output voltage ω g Integrate to get the phase θ g Phase θ g Used to convert the grid-side AC voltage u g and the alternating current i g Perform park transformation to obtain the input quantity u of the grid-side converter gd 、u gq 、i gd 、i gq , as the input of the controller. In addition, after the current inner loop control, e * gd and e * gq , it is also necessary to go through park transformation to get the three-phase reference voltage, and then perform PWM modulation to get the switching signal. Phase θ g is the phase angle required for the park transformation.

[0128] For the d-axis control of the grid-side converter, the reference value of the d-axis current i * gd Under normal circumstances, it is obtained according to the first operating mode, and under fault circumstances, it is obtained according to the second operating mode.

[0129] In the first operating mode, the actual value of the fan speed ω m After Maximum Power Point Tracking (MPPT) control, the wind turbine power reference value P is obtained. * WT . Fan power reference value P * WT The actual power value P WTSubtract and pass through the proportional integral controller to get the deviation, which is added to the feedforward value U gN (grid side phase voltage rated value) to obtain the voltage amplitude U m , U m is the d-axis voltage u gd Reference value of U m with u gd Subtract and then pass through the proportional integral controller to obtain the reference value i of the d-axis current in mode 1 * gd .

[0130] In the second operating mode, i gd_lower is the reference value i of the d-axis current in the second operating mode * gd ,i gd_lower It is a safe lower limit of active current (such as 0.1pu) designed according to specific working conditions, so that the DC current can drop quickly to the extent that the DC current can be cut off by a fast mechanical switch.

[0131] For the q-axis control of the grid-side converter, the q-axis voltage reference value u * gq 0, 0 minus the actual value of the q-axis voltage u gq Then the reference value i of the q-axis current is obtained through the proportional-integral controller. * gq . Get i * gd and i * gq After that, the d-axis component reference value e of the converter output voltage is obtained through current closed-loop control. * gd and the q-axis component reference value e * gq Finally, e * gd and e * gq The three-phase voltage reference value of the converter port is obtained through park transformation, and then the switch modulation signal is obtained through PWM.

[0132] It can be understood that the machine-side converter and the grid-side converter of the wind turbine achieve rapid response and fault clearing in the event of a DC fault through coordinated control. In the control of the machine-side converter, the adjustment of the wind turbine power and the stability of the DC voltage are achieved through the precise control of the d-axis component and q-axis component of the rotor current. In the control of the grid-side converter, the precise control of the frequency and phase of the converter output voltage is achieved through the grid-type control strategy, thereby ensuring a stable connection between the wind turbine and the grid.

[0133] In addition, during the DC fault ride-through process, the grid-side converter of the wind turbine also needs to be switched according to the operating status of the system. In the normal operation mode, the grid-side converters are controlled according to the maximum power point tracking strategy to maximize the output power of the wind farm. In the case of a DC fault, it is necessary to quickly switch to the fault ride-through mode to quickly clear the DC fault by controlling the DC current of the wind turbine and the receiving converter station to be reduced to below the preset current safety lower limit threshold.

[0134] In some embodiments, the receiving end converter station includes an AC controller, a DC controller and a circulating current controller;

[0135] Among them, the control process of the AC controller is:

[0136] Step S231, performing difference processing between the rated value of the submodule capacitor voltage of the AC controller and the actual value of the submodule capacitor voltage to obtain the submodule capacitor voltage difference;

[0137] Step S232, input the submodule capacitor voltage difference into the proportional-integral controller to obtain a third d-axis current reference value;

[0138] Step S233, obtaining a third d-axis current difference by performing a difference operation between the third d-axis current reference value and the third d-axis current actual value;

[0139] Step S234, obtaining a third d-axis current difference deviation by passing the third d-axis current difference through a proportional-integral controller;

[0140] Step S235, obtaining a third d-axis voltage reference value by performing difference processing on the third d-axis current difference deviation amount and a preset fourth feedforward amount; wherein the fourth feedforward amount is obtained according to the frequency, transformer inductance, bridge arm inductance and grid-side d-axis voltage;

[0141] Step S236, performing a difference operation between the second q-axis current reference value of the AC controller and the second q-axis current actual value to obtain a second q-axis current difference value;

[0142] Step S237, input the second q-axis current difference into the proportional-integral controller to obtain the second q-axis current difference deviation;

[0143] Step S238, obtaining a second q-axis voltage reference value by performing a difference operation on the second q-axis current difference deviation amount and a preset fifth feedforward amount;

[0144] Step S239: Obtain the AC internal potential of the AC controller by performing Park transformation on the third d-axis voltage reference value and the second q-axis voltage reference value.

[0145] The control process of the DC controller in the first operation mode is as follows:

[0146] Step S241, performing a difference operation between a second DC voltage actual value and a second DC voltage rated value of the DC controller to obtain a second DC voltage difference value;

[0147] Step S242, inputting the second DC voltage difference into a proportional-integral controller to obtain a first DC current deviation;

[0148] Step S243, obtaining a first DC internal potential of the DC controller in the first operating mode by performing a difference operation between the first DC current deviation and a preset sixth feedforward value;

[0149] The control process of the DC controller in the second operating mode is:

[0150] Step S251, performing a difference operation on a DC current reference value of a DC controller and a negative DC current actual value to obtain a DC current difference value; wherein the DC current reference value is zero;

[0151] Step S252: The DC current difference passes through a proportional controller and then a limiting link to obtain a second DC internal potential of the DC controller in a second operating mode.

[0152] The control process of the circulating current controller is as follows: suppressing the circulating current component of the circulating current controller to zero to obtain the circulating current internal potential of the circulating current controller.

[0153] For example, Figure 6 As shown, the phase angle θ of the AC controller: MMC is obtained by tracking the grid voltage phase through a phase-locked loop. Submodule capacitor voltage rating u CN Subtract the actual value u C , and then through the proportional integral controller, the d-axis current reference value i is obtained * d . d-axis current reference value i * d Subtract the actual value of the d-axis current i d , and then through the proportional integral controller, the deviation is obtained. Feedforward ω0(L T +L s / 2)i q +u d (where ω0 is the frequency, L T is the transformer inductance, L s is the bridge arm inductance, u d = (the grid-side d-axis voltage) minus the deviation to obtain the d-axis voltage reference value e d . q-axis current reference value i * q for / 3 reactive power reference value Q * acDivide by the actual value of the d-axis voltage u d ,i * q Subtract the actual value of the q-axis current i q , and then through the proportional integral controller, the deviation is obtained. Feedforward (where u q = (q-axis voltage on the grid side) minus the deviation to obtain the q-axis voltage reference value e q .e d and e q After park transformation, the output of the AC controller is the AC internal potential e a, e b , e c .

[0154] The control process of the DC controller is as follows: the DC controller is in the first operating mode during normal operation, and the actual value of the MMC DC voltage u dc Subtract the rated value u dcN , and then the DC current reference value i is obtained through the proportional integral controller * dc . DC current reference value i * dc Subtract the actual value i dc , and then the deviation is obtained through the proportional integral controller. Feedforward DC voltage u dc Subtracting this deviation, we get the DC internal potential e dc .

[0155] After a fault, the DC controller switches to the second operating mode, namely zero DC current control, where the DC current reference value is 0, which is 0 minus the negative DC current actual value. , through the proportional controller, and then through the limit link (the upper limit is u dcN , the lower limit is , where u dcN is the DC voltage rating, η is the ratio of the number of full-bridge sub-modules to the total number of modules in the hybrid MMC) and then we get e dc .

[0156] The control process of the circulation controller is the same as that of the existing MMC circulation controller. cira , i cirb ,i circ Suppressed to 0, the output circulating current potential e cira and e cirb .

[0157] The reference voltage and control signal generation process is to convert e a , e b , e c , e dc , ecira , e cirb Converted into six bridge arm voltage reference values ​​u * ap , u * an , u * bp , u * bn , u * cp , u * cn , where the subscripts p and n represent the upper bridge arm and the lower bridge arm respectively. Then, the control signals of each submodule of the receiving MMC are obtained through modulation.

[0158] It is understandable that during the DC fault ride-through process of the wind farm through the DC transmission system, the various controllers of the receiving-end converter station work together to achieve rapid response and effective ride-through of the DC fault. The AC controller maintains the stable operation of the converter by accurately controlling the submodule capacitor voltage.

[0159] The DC controller adjusts the DC current reference value according to the difference between the actual value and the rated value of the DC voltage, thus achieving precise control of the DC voltage. In the event of a DC fault, the DC controller can quickly switch to the fault ride-through mode, and quickly clear the DC fault by controlling the DC current to be lowered below the safety lower limit. The circulating current controller is responsible for suppressing the circulating current component, reducing the impact of the circulating current on the system, and improving the stability and efficiency of the system.

[0160] In the process of generating reference voltage and control signal, the AC internal potential of the AC controller, the DC internal potential of the DC controller and the circulating current internal potential of the circulating current controller are converted into six bridge arm voltage reference values, and then modulated to obtain the control signals of each submodule of the receiving end MMC. This process realizes the precise control of the output voltage and current of the converter, ensuring the stable connection and power transmission between the wind farm and the power grid.

[0161] Based on the same inventive concept, an embodiment of the present application further provides a DC fault ride-through system of a wind farm via a DC transmission system for implementing the DC fault ride-through method of a wind farm via a DC transmission system as mentioned above.

[0162] The implementation solution to the problem provided by the system is similar to the implementation solution recorded in the above method. Therefore, the specific limitations in the DC fault ride-through system embodiments of one or more wind farms via a DC transmission system provided below can be referred to the limitations on the DC fault ride-through method of a wind farm via a DC transmission system in the above text, and will not be repeated here.

[0163] like Figure 7As shown, the embodiment of the present application provides a DC fault ride-through system of a wind farm via a DC transmission system, which is applied to the wind farm via a DC transmission system; the wind farm via a DC transmission system includes a wind turbine and a receiving-end converter station; the wind turbine is connected to the receiving-end converter station through a common coupling point and a diode rectifier, and a mechanical switch is provided on the line between the diode rectifier and the receiving-end converter station. The system includes:

[0164] The mode switching module 100 is used to monitor the operation status of the wind farm through the DC transmission system in real time, and when a DC fault is detected in the operation mode, control the wind turbine and the receiving end converter station to switch from the first operation mode to the second operation mode, and perform load unloading operation on the wind turbine;

[0165] The first operation mode is used to control the reference power output of the wind turbine and the receiving-end converter station under normal operation, and the second operation mode is used to control the fault ride-through of the wind turbine and the receiving-end converter station under DC fault operation;

[0166] The fault ride-through module 200 is used to control the DC current of the wind turbine and the receiving-end converter station to be lower than a preset current safety lower limit threshold value in the second operation mode; the current safety lower limit threshold value is used to represent the DC current threshold value at which the line is cut off by the mechanical switch;

[0167] The fault recovery module 300 is used to control the receiving end converter station to switch back to the first operation mode after cutting off the DC side fault line between the wind turbine and the receiving end converter station through a mechanical switch, and then control the wind turbine to switch back to the first operation mode and stop the unloading operation of the wind turbine.

[0168] In some embodiments, the fault ride-through module 200 is configured to:

[0169] In the second operating mode, the grid-side converter of the wind turbine is controlled to reduce the AC current, and the DC current of the grid-side converter of the wind turbine is reduced to below the preset current safety lower limit threshold, and the receiving-end converter station is controlled to actively output a negative DC voltage, and the DC current of the receiving-end converter station is reduced to below the preset current safety lower limit threshold.

[0170] In some embodiments, the wind turbine includes a machine-side converter;

[0171] The control process of the machine-side converter is as follows:

[0172] A first d-axis current difference is obtained by performing a difference operation between a reference value of a rotor current d-axis component of the machine-side converter and an actual value of the d-axis current;

[0173] The first d-axis current difference is input into the proportional-integral controller, and the first d-axis current deviation is output;

[0174] A first d-axis voltage component reference value is obtained by performing a difference operation between the first d-axis current deviation and a preset first feedforward amount; wherein the first feedforward amount is obtained according to the rotor electrical angular velocity, the stator-rotor inductance and the rotor current q-axis component;

[0175] A first voltage component difference is obtained by performing a difference operation between a first DC voltage actual value and a first DC voltage rated value of the fan;

[0176] Obtaining a first current q-axis component reference value by passing the first voltage component difference through a proportional-integral controller;

[0177] By performing a difference operation between a first current q-axis component reference value and an actual current q-axis component value, a first q-axis current difference value is obtained;

[0178] The first q-axis current difference is input into a proportional-integral controller to obtain a first q-axis current difference deviation;

[0179] Obtaining a first q-axis voltage component reference value by adding a first q-axis current difference deviation amount and a preset second feedforward amount;

[0180] The first d-axis voltage component reference value and the first q-axis voltage component reference value are subjected to park transformation to obtain the first port three-phase voltage reference value of the machine-side converter, and then the first port three-phase voltage reference value is processed by PWM modulation to obtain the switch modulation signal of the machine-side converter.

[0181] In some embodiments, the wind turbine includes a grid-side converter;

[0182] The control process of the grid-side converter in the first operation mode is as follows:

[0183] The actual speed value of the fan is controlled by the maximum power point tracking to obtain the fan power reference value;

[0184] The fan power difference is obtained by performing a difference operation between the fan power reference value and the fan power actual value;

[0185] After the fan power difference is input into the proportional-integral controller, the fan power difference deviation is obtained;

[0186] The wind turbine voltage amplitude is obtained by adding the wind turbine power difference deviation and the preset third feedforward quantity; wherein the third feedforward quantity is obtained according to the grid-side phase voltage rated value;

[0187] Obtaining a first d-axis current reference value of the machine-side converter in the first operating mode according to the wind turbine voltage amplitude and the wind turbine actual voltage amplitude;

[0188] Performing a difference operation on a first q-axis voltage reference value and a first q-axis voltage actual value of the grid-side converter to obtain a first q-axis voltage difference value;

[0189] The proportional-integral controller is inputted through the first q-axis voltage difference value, and the first q-axis current reference value is outputted;

[0190] Obtaining a first d-axis voltage component reference value and a first q-axis voltage component reference value of the machine-side converter in the first operating mode through current closed-loop control using the first d-axis current reference value and the first q-axis current reference value;

[0191] Obtain a port three-phase voltage reference value of the machine-side converter in the first operating mode by performing park transformation on the first d-axis voltage component reference value and the first q-axis voltage component reference value, and then obtain a switch modulation signal of the machine-side converter in the first operating mode by performing PWM modulation processing on the first port three-phase voltage reference value;

[0192] The control process of the grid-side converter in the second operation mode is as follows:

[0193] Determine a second d-axis current reference value of the machine-side converter in the second operating mode by using a current safety lower limit threshold;

[0194] Obtaining a second d-axis voltage component reference value and a second q-axis voltage component reference value of the machine-side converter in the second operating mode through current closed-loop control of the second d-axis current reference value and the first q-axis current reference value;

[0195] The second d-axis voltage component reference value and the second q-axis voltage component reference value are park transformed to obtain the three-phase voltage reference value of the third port of the machine-side converter in the second operating mode, and then the three-phase voltage reference value of the third port is processed by PWM modulation to obtain the switch modulation signal of the machine-side converter in the second operating mode.

[0196] In some embodiments, the receiving end converter station includes an AC controller;

[0197] The control process of the AC controller is:

[0198] The submodule capacitor voltage difference is obtained by performing difference processing on the submodule capacitor voltage rated value and the submodule capacitor voltage actual value of the AC controller;

[0199] The voltage difference of the capacitor of the submodule is input into the proportional-integral controller to obtain the third d-axis current reference value;

[0200] A third d-axis current difference value is obtained by performing a difference operation between the third d-axis current reference value and the third d-axis current actual value;

[0201] The third d-axis current difference is passed through a proportional-integral controller to obtain a third d-axis current difference deviation;

[0202] The third d-axis voltage reference value is obtained by performing a difference process on the third d-axis current difference deviation amount and the preset fourth feedforward amount; wherein the fourth feedforward amount is obtained according to the frequency, the transformer inductance, the bridge arm inductance and the grid-side d-axis voltage;

[0203] A second q-axis current difference is obtained by performing a difference operation on a second q-axis current reference value of the AC controller and an actual value of the second q-axis current;

[0204] The second q-axis current difference is input into the proportional-integral controller to obtain the second q-axis current difference deviation;

[0205] The second q-axis voltage reference value is obtained by performing a difference operation on the second q-axis current difference deviation amount and a preset fifth feedforward amount;

[0206] The AC internal potential of the AC controller is obtained by park transforming the third d-axis voltage reference value and the second q-axis voltage reference value.

[0207] In some embodiments, the receiving end converter station includes a DC controller;

[0208] The control process of the DC controller in the first operating mode is:

[0209] A second DC voltage difference is obtained by performing a difference operation between a second DC voltage actual value and a second DC voltage rated value of the DC controller;

[0210] The second DC voltage difference is input into a proportional-integral controller to obtain a first DC current deviation;

[0211] By performing a difference operation between the first DC current deviation and a preset sixth feedforward quantity, a first DC internal potential of the DC controller in the first operating mode is obtained;

[0212] The control process of the DC controller in the second operating mode is:

[0213] Performing a difference operation on the DC current reference value of the DC controller and the negative DC current actual value to obtain a DC current difference value; wherein the DC current reference value is zero;

[0214] The DC current difference passes through a proportional controller and then a limiting link to obtain a second DC internal potential of the DC controller in a second operating mode.

[0215] In some embodiments, the receiving end converter station includes a circulating current controller;

[0216] The control process of the circulation controller is:

[0217] The circulating current component of the circulating current controller is suppressed to zero, thereby obtaining the circulating current internal potential of the circulating current controller.

[0218] like Figure 8 As shown, an embodiment of the present application 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 DC fault ride-through method of the wind farm through the DC transmission system in the above embodiment.

[0219] An embodiment of the present application provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed, the steps of the virtual impedance control parameter optimization method in the above embodiment are implemented.

[0220] 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.

[0221] 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.

[0222] It should be understood that, although the various steps in the flowcharts involved in the above-mentioned embodiments are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps does not have a strict order restriction, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above-mentioned embodiments can include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0223] 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 the units is only a logical function division. There may be other division methods in actual implementation, such as 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.

[0224] 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.

[0225] 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.

[0226] 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.

[0227] 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 riding through a DC fault in a wind farm through a DC transmission system, characterized in that: Applied to a wind farm DC transmission system; the wind farm DC transmission system comprises a wind turbine and a receiving-end converter station; the wind turbine is connected to the receiving-end converter station via a common coupling point and a diode rectifier, and a mechanical switch is provided on the line between the diode rectifier and the receiving-end converter station, and the method comprises: real-time monitoring of the operation status of the wind farm through the DC transmission system, and when a DC fault is detected in the operation mode, controlling the wind turbine and the receiving-end converter station to switch from the first operation mode to the second operation mode, and performing load unloading operation on the wind turbine; The first operation mode is used to control the reference power output of the wind turbine and the receiving-end converter station under normal operation, and the second operation mode is used to control the fault ride-through of the wind turbine and the receiving-end converter station under DC fault operation; In the second operation mode, the DC current of the wind turbine and the receiving-end converter station are respectively controlled to be reduced to below a preset current safety lower limit threshold; the current safety lower limit threshold is used to represent the DC current threshold at which the line is cut off by the mechanical switch; After the DC side fault line between the wind turbine and the receiving-end converter station is cut off by the mechanical switch, the receiving-end converter station is controlled to switch back to the first operating mode, and then the wind turbine is controlled to switch back to the first operating mode, and the unloading operation of the wind turbine is stopped.

2. The DC fault ride-through method of a wind farm via a DC transmission system according to claim 1, characterized in that: In the second operation mode, respectively controlling the DC current of the wind turbine and the receiving-end converter station to be reduced to below a preset current safety lower limit threshold value includes: In the second operating mode, the grid-side converter of the wind turbine is controlled to reduce the AC current, and the DC current of the grid-side converter of the wind turbine is reduced to below the preset current safety lower limit threshold, and the receiving-end converter station is controlled to actively output a negative DC voltage, and the DC current of the receiving-end converter station is reduced to below the preset current safety lower limit threshold.

3. The DC fault ride-through method of a wind farm via a DC transmission system according to claim 1, characterized in that: The wind turbine comprises a machine-side converter; The control process of the machine-side converter is as follows: Obtain a first d-axis current difference by performing a difference operation between a reference value of a d-axis component of the rotor current of the machine-side converter and an actual value of the d-axis current; The first d-axis current difference is input into a proportional-integral controller, and a first d-axis current deviation is output; A first d-axis voltage component reference value is obtained by performing a difference operation between the first d-axis current deviation and a preset first feedforward amount; wherein the first feedforward amount is obtained according to the rotor electrical angular velocity, the stator-rotor inductance and the rotor current q-axis component; A first voltage component difference is obtained by performing a difference operation between the first DC voltage actual value and the first DC voltage rated value of the fan; Obtaining a first current q-axis component reference value by passing the first voltage component difference through a proportional-integral controller; Obtaining a first q-axis current difference by performing a difference operation between the first current q-axis component reference value and the current q-axis component actual value; The first q-axis current difference is input into a proportional-integral controller to obtain a first q-axis current difference deviation; Obtaining a first q-axis voltage component reference value by adding the first q-axis current difference deviation amount and a preset second feedforward amount; The first d-axis voltage component reference value and the first q-axis voltage component reference value are subjected to park transformation to obtain the first port three-phase voltage reference value of the machine-side converter, and then the first port three-phase voltage reference value is processed by PWM modulation to obtain the switch modulation signal of the machine-side converter.

4. The method for DC fault ride-through of a wind farm via a DC transmission system according to claim 1, characterized in that: The wind turbine includes a grid-side converter; The control process of the grid-side converter in the first operation mode is as follows: The actual speed value of the fan is subjected to maximum power point tracking control to obtain a fan power reference value; By performing a difference operation between the fan power reference value and the fan power actual value, a fan power difference value is obtained; After the fan power difference is input into the proportional-integral controller, the fan power difference deviation is obtained; The wind turbine voltage amplitude is obtained by adding the wind turbine power difference deviation amount and a preset third feedforward amount; wherein the third feedforward amount is obtained according to the grid-side phase voltage rated value; Obtaining a first d-axis current reference value of the machine-side converter in the first operating mode according to the wind turbine voltage amplitude and the wind turbine actual voltage amplitude; Performing a difference operation on the first q-axis voltage reference value and the first q-axis voltage actual value of the grid-side converter to obtain a first q-axis voltage difference value; The first q-axis voltage difference is input into a proportional-integral controller, and a first q-axis current reference value is output; Obtaining a first d-axis voltage component reference value and a first q-axis voltage component reference value of the generator-side converter in the first operating mode through current closed-loop control of the first d-axis current reference value and the first q-axis current reference value; Obtain a port three-phase voltage reference value of the machine-side converter in the first operating mode by performing park transformation on the first d-axis voltage component reference value and the first q-axis voltage component reference value, and then obtain a switch modulation signal of the machine-side converter in the first operating mode by performing PWM modulation processing on the first port three-phase voltage reference value; The control process of the grid-side converter in the second operation mode is as follows: Determining a second d-axis current reference value of the generator-side converter in the second operating mode by using the current safety lower limit threshold; Obtaining a second d-axis voltage component reference value and a second q-axis voltage component reference value of the generator-side converter in the second operating mode through current closed-loop control of the second d-axis current reference value and the first q-axis current reference value; The second d-axis voltage component reference value and the second q-axis voltage component reference value are subjected to park transformation to obtain the three-phase voltage reference value of the third port of the machine-side converter in the second operating mode, and then the three-phase voltage reference value of the third port is processed by PWM modulation to obtain the switch modulation signal of the machine-side converter in the second operating mode.

5. The method for DC fault ride-through of a wind farm via a DC transmission system according to claim 1, characterized in that: The receiving-end converter station includes an AC controller; The control process of the AC controller is: The rated value of the submodule capacitor voltage of the AC controller and the actual value of the submodule capacitor voltage are processed to obtain the submodule capacitor voltage difference; The voltage difference of the capacitor of the submodule is input into the proportional-integral controller to obtain a third d-axis current reference value; Obtaining a third d-axis current difference by performing a difference operation between the third d-axis current reference value and the third d-axis current actual value; The third d-axis current difference is passed through a proportional-integral controller to obtain a third d-axis current difference deviation; The third d-axis voltage reference value is obtained by performing a difference process on the third d-axis current difference deviation and a preset fourth feedforward value; wherein the fourth feedforward value is obtained according to the frequency, the transformer inductance, the bridge arm inductance and the grid-side d-axis voltage; A second q-axis current difference is obtained by performing a difference operation on a second q-axis current reference value of the AC controller and a second q-axis current actual value; The second q-axis current difference is input into a proportional-integral controller to obtain a second q-axis current difference deviation; Obtaining a second q-axis voltage reference value by performing a difference operation on the second q-axis current difference deviation amount and a preset fifth feedforward amount; The AC internal potential of the AC controller is obtained by park transforming the third d-axis voltage reference value and the second q-axis voltage reference value.

6. The DC fault ride-through method of a wind farm via a DC transmission system according to claim 1, characterized in that: The receiving-end converter station includes a DC controller; The control process of the DC controller in the first operation mode is as follows: A second DC voltage difference is obtained by performing a difference operation between a second DC voltage actual value and a second DC voltage rated value of the DC controller; The second DC voltage difference is input into a proportional-integral controller to obtain a first DC current deviation; Obtaining a first DC internal potential of the DC controller in a first operating mode by performing a difference operation between the first DC current deviation and a preset sixth feedforward value; The control process of the DC controller in the second operation mode is as follows: Performing a difference operation on the DC current reference value of the DC controller and the negative DC current actual value to obtain a DC current difference value; wherein the DC current reference value is zero; The DC current difference is passed through a proportional controller and then through a limiting link to obtain a second DC internal potential of the DC controller in a second operating mode.

7. The method for DC fault ride-through of a wind farm via a DC transmission system according to claim 1, characterized in that: The receiving-end converter station includes a circulating current controller; The control process of the circulation controller is: The circulating current internal potential of the circulating current controller is obtained by suppressing the circulating current component of the circulating current controller to zero.

8. A DC fault ride-through system for a wind farm via a DC transmission system, characterized in that: Applicable to a wind farm DC transmission system; the wind farm DC transmission system includes a wind turbine and a receiving-end converter station; the wind turbine is connected to the receiving-end converter station through a common coupling point and a diode rectifier, and a mechanical switch is provided on the line between the diode rectifier and the receiving-end converter station. The system includes: A mode switching module is used to monitor the operating state of the wind farm through the DC transmission system in real time, and when a DC fault is detected in the operating state, control the wind turbine and the receiving-end converter station to switch from the first operating mode to the second operating mode, and perform load unloading operation on the wind turbine; The first operation mode is used to control the reference power output of the wind turbine and the receiving-end converter station under normal operation, and the second operation mode is used to control the fault ride-through of the wind turbine and the receiving-end converter station under DC fault operation; A fault ride-through module, used for controlling the DC current of the wind turbine and the receiving-end converter station to be reduced to below a preset current safety lower limit threshold value respectively in the second operation mode; the current safety lower limit threshold value is used to represent the DC current threshold value at which the line is cut off by the mechanical switch; A fault recovery module is used to control the receiving-end converter station to switch back to the first operating mode after cutting off the DC side fault line between the wind turbine and the receiving-end converter station through the mechanical switch, and then control the wind turbine to switch back to the first operating mode and stop the unloading operation of the wind turbine.

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 DC fault ride-through method of a wind farm through a DC transmission system as described in 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 method for riding through a DC fault of a wind farm through a DC transmission system as described in any one of claims 1 to 7 are implemented.

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