DC fault ride-through method and system for wind farms via DC transmission systems

Abstract

This invention relates to the field of power system technology and discloses a DC fault ride-through method and system for a wind farm through a DC transmission system. This method rapidly responds to DC faults in the wind farm's DC transmission system by switching the operating modes of the wind turbine and the receiving-end converter station, thereby reducing the DC current of the wind turbine and the receiving-end converter station to below a preset current safety lower limit threshold. This allows the line to be mechanically switched off by the fault current, thus rapidly reducing the DC fault current in the early stages of the fault and preventing the fault current from becoming too large and damaging the system. It also eliminates the need for additional complex DC-side protection devices, relying on the wind turbine control system itself to achieve a rapid decrease in fault current. Combined with the rapid mechanical switch to disconnect the circuit, this reduces the complexity and maintenance cost of the system, quickly restores the system to stable operation, and reduces the downtime of the wind turbine system.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to a DC fault ride-through method and system for a wind farm via a DC transmission system. Background Technology

[0002] Wind power, as a green energy source, has developed rapidly in recent years, and its power conversion and transmission technologies have become a research hotspot both domestically and internationally. Currently, large-scale long-distance wind power transmission in engineering mainly adopts flexible DC transmission based on modular multilevel converters (MMCs). However, the converters in flexible DC transmission systems are large in size, heavy in weight, and have high construction costs. To improve the economy and reliability of long-distance DC transmission of wind power from large wind farms, some scholars have proposed a scheme of DC transmission via diode rectifiers (DRs).

[0003] To meet the economic requirements of long-distance transmission of ultra-large-scale wind power, current projects typically use overhead DC lines to transmit power to load centers. However, overhead lines are more prone to short-circuit faults than cables. Figure 1 As shown, for a system where wind power is transmitted via DC through a DR, if a DC fault occurs, the DR lacks control capabilities and cannot clear the fault current on its own. 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 the DC transmission system of a wind farm, the fault clearing and recovery time is relatively 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 method and system for DC fault ride-through of a wind farm through a DC transmission system, which solves the technical problem that 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.

[0006] The first aspect of this invention provides a DC fault ride-through method for a wind farm via a DC transmission system, applied to such a system; the wind farm via DC transmission system includes wind turbines and a receiving-end converter station; the wind turbines are 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; the method includes:

[0007] The system monitors the operation status of the wind farm's DC transmission system in real time. If a DC fault is detected in the operation mode, the system controls both the wind turbine and the receiving-end converter station to switch from the first operation mode to the second operation mode and performs unloading operations on the wind turbine.

[0008] 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.

[0009] In the second operating mode, the DC current of the wind turbine and the receiving-end converter station are 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 when the line is cut off by the mechanical switch;

[0010] After disconnecting the DC-side fault line of the wind turbine and the receiving-end converter station 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 operating mode, 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 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. 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 turbine-side converter;

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

[0015] The first d-axis current difference is obtained by subtracting the reference value of the d-axis component of the rotor current of the machine-side converter from the actual value of the d-axis current.

[0016] The first d-axis current difference is input to the proportional-integral controller, which outputs the first d-axis current deviation.

[0017] The reference value of the first d-axis voltage component is obtained by subtracting the first d-axis current deviation from the preset first feedforward value; wherein, the first feedforward value is obtained based on the rotor electric angular velocity, stator and rotor inductance, and rotor current q-axis component.

[0018] The first voltage component difference is obtained by subtracting the actual value of the first DC voltage of the fan from the rated value of the first DC voltage.

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

[0020] The first q-axis current difference value is obtained by subtracting the reference value of the first current q-axis component from the actual value of the current q-axis component.

[0021] The deviation of the first q-axis current difference is obtained by inputting the first q-axis current difference into the proportional-integral controller.

[0022] The reference value of the first q-axis voltage component is obtained by summing the deviation of the first q-axis current difference with the preset second feedforward value.

[0023] The first port three-phase voltage reference value of the machine-side converter is obtained by performing Park transformation on the first d-axis voltage component reference value and the first q-axis voltage component reference value. Then, the first port three-phase voltage reference value is processed by PWM modulation to obtain the switching 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 operating mode is as follows:

[0026] By applying the actual rotational speed of the fan to maximum power point tracking control, a reference value for the fan power is obtained.

[0027] The difference in fan power is obtained by subtracting the reference value and the actual value of fan power.

[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 summing the wind turbine power difference deviation with a preset third feedforward value; wherein the third feedforward value is obtained based on the grid-side phase voltage rating.

[0030] Based on the wind turbine voltage amplitude and the actual wind turbine voltage amplitude, the first d-axis current reference value of the turbine-side converter in the first operating mode is obtained;

[0031] The first q-axis voltage difference is obtained by performing a subtraction operation between the reference value of the first q-axis voltage and the actual value of the first q-axis voltage of the grid-side converter.

[0032] The first q-axis voltage difference is input to the proportional-integral controller, which outputs the first q-axis current reference value.

[0033] By using the first d-axis current reference value and the first q-axis current reference value for current closed-loop control, the first d-axis voltage component reference value and the first q-axis voltage component reference value of the machine-side converter in the first operating mode are obtained.

[0034] By performing Park transformation on the first d-axis voltage component reference value and the first q-axis voltage component reference value, the port three-phase voltage reference value of the machine-side converter in the first operating mode is obtained. Then, the first port three-phase voltage reference value is processed by PWM modulation to obtain the switching modulation signal of the machine-side converter in the first operating mode.

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

[0036] The reference value of the second d-axis current of the machine-side converter in the second operating mode is determined by the current safety lower limit threshold.

[0037] By using the second d-axis current reference value and the first q-axis current reference value for current closed-loop control, the second d-axis voltage component reference value and the second q-axis voltage component reference value of the machine-side converter in the second operating mode are obtained.

[0038] By performing Park transformation on the second d-axis voltage component reference value and the second q-axis voltage component reference value, the three-phase voltage reference value of the third port of the machine-side converter in the second operating mode is obtained. Then, the three-phase voltage reference value of the third port is processed by PWM modulation to obtain the switching 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 as follows:

[0041] The difference between the rated value of the submodule capacitor voltage and the actual value of the submodule capacitor voltage of the AC controller is obtained by subtracting the value of the submodule capacitor voltage.

[0042] The third d-axis current reference value is obtained by inputting the capacitor voltage difference of the submodule into the proportional-integral controller.

[0043] The difference value of the third d-axis current is obtained by subtracting the reference value of the third d-axis current from the actual value of the third d-axis current.

[0044] The deviation of the third d-axis current difference is obtained by passing the third d-axis current difference through a proportional-integral controller.

[0045] The third d-axis voltage reference value is obtained by subtracting the deviation of the third d-axis current difference from the preset fourth feedforward value; wherein, the fourth feedforward value is obtained based on the frequency, transformer inductance, bridge arm inductance and grid-side d-axis voltage.

[0046] The second q-axis current difference value is obtained by subtracting the reference value of the second q-axis current and the actual value of the second q-axis current of the AC controller.

[0047] The deviation of the second q-axis current difference is obtained by inputting the second q-axis current difference into the proportional-integral controller.

[0048] The second q-axis voltage reference value is obtained by subtracting the deviation of the second q-axis current difference from the preset fifth feedforward value.

[0049] The AC internal potential of the AC controller is obtained by performing Park transformation on 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 operating mode is as follows:

[0052] The second DC voltage difference value is obtained by subtracting the actual value of the second DC voltage and the rated value of the second DC voltage from the DC controller.

[0053] The first DC current deviation is obtained by inputting the second DC voltage difference into the proportional-integral controller.

[0054] The first DC internal potential of the DC controller in the first operating mode is obtained by subtracting the first DC current deviation from the preset sixth feedforward quantity.

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

[0056] The DC current difference is obtained by subtracting the DC current reference value of the DC controller from the negative actual DC current 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 circuit to obtain the second DC internal potential of the DC controller in the second operating mode.

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

[0059] The control process of the circulating controller is as follows:

[0060] The circulating current component of the circulating current controller is suppressed to zero to obtain the circulating current internal potential of the circulating current controller.

[0061] Secondly, the present invention provides a DC fault ride-through system for a wind farm via a DC transmission system, 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 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; the system includes:

[0062] The mode switching module 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 both the wind turbine and the receiving-end converter station to switch from the first operation mode to the second operation mode, and perform unloading operation on the wind turbine.

[0063] 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.

[0064] The fault ride-through module is used to 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 in the second operating mode; the current safety lower limit threshold is used to characterize the DC current threshold when the line is disconnected by the mechanical switch.

[0065] The fault recovery module is used to control the receiving-end converter station to switch back to the first operating mode after disconnecting the DC side fault line of 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] Thirdly, the present invention provides an electronic device, the electronic device including a memory and a processor, the memory storing a computer program, the computer program being executed by the processor causing the processor to perform the steps of the DC fault ride-through method for a wind farm via a DC transmission system as described in the first aspect.

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

[0068] As can be seen from the above technical solutions, this invention rapidly responds to DC faults in the wind farm's DC transmission system. By switching the operating modes of the wind turbine and the receiving-end converter station, the DC current of the wind turbine and the receiving-end converter station is reduced to below a preset safe current lower limit threshold, so that the fault current is mechanically cut off by the line. This rapidly reduces the DC fault current in the early stages of the fault, preventing the fault current from becoming too large and damaging the system. It also eliminates the need for additional complex DC-side protection devices. The rapid reduction of the fault current is achieved by relying on the wind turbine control system itself, and the circuit is disconnected in conjunction with the fast mechanical switch, reducing the complexity and maintenance costs of the system. After the fault, the AC system remains connected, 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, minimizing the impact of DC faults on the system, and ensuring the safe and stable operation of the system. Attached Figure Description

[0069] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0070] Figure 1 This is a schematic diagram of the structure of a wind farm DC transmission system provided in an embodiment of the present invention;

[0071] Figure 2 A diagram illustrating the application environment of the DC fault ride-through method for wind farms via DC transmission systems provided in this embodiment of the invention.

[0072] Figure 3 This is a schematic diagram of the topology of a hybrid MMC provided in an embodiment of the present invention;

[0073] Figure 4 A flowchart of a DC fault ride-through method for a wind farm via a DC transmission system is provided in an embodiment of the present invention;

[0074] Figure 5 This is a control block diagram of a fan provided in an embodiment of the present invention;

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

[0076] Figure 7 This is a schematic diagram of the structure of a DC fault ride-through system for a wind farm via a DC transmission system, provided in an embodiment of the present invention.

[0077] Figure 8This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0078] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0079] Currently, to meet the economic requirements of long-distance transmission of ultra-large-scale wind power, projects typically use overhead DC lines to transmit power to load centers. However, overhead lines are more prone to short-circuit faults than cables. For example... Figure 1 As shown, for a system where wind power is transmitted via DC through a DR, if a DC fault occurs, the DR lacks control capabilities and cannot clear the fault current on its own. 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] Currently, when a short circuit or fault occurs on the DC side, a Direct Current Circuit Breaker (DCCB) can quickly isolate the faulty line. However, DCCBs are expensive, significantly increasing system costs. Furthermore, the structure and control of DCCBs are complex, and their reliability in practical use requires further research. While tripping an Alternating Current Circuit Breaker (ACB) can also clear DC faults, the fault clearing and recovery times are long, which is detrimental to the safe and stable operation of the system and may lead to power outages. Therefore, DCCBs can only be used in end-to-end DC transmission systems.

[0081] In view of this, the DC fault ride-through method for wind farms via DC transmission systems provided in this application can be applied to, for example... Figure 2The application environment shown is illustrated. Terminal 101 communicates with server 102 via a network. A data storage system can store the data that server 102 needs to process. The data storage system can be integrated onto server 102, or it can be located in the cloud or on another network server. Terminal 101 or server 102 monitors the real-time operating status of the wind farm's DC transmission system. Upon detecting a DC fault in the operating mode, it controls both the wind turbine and the receiving-end converter station to switch from a first operating mode to a second operating mode and performs unloading operations on the wind turbine. The first operating mode controls the reference power output of the wind turbine and the receiving-end converter station under normal operating conditions, while the second operating mode controls fault ride-through of the wind turbine and the receiving-end converter station under DC fault conditions. In the second operating mode, the DC current of both the wind turbine and the receiving-end converter station is reduced to below a preset safe current lower limit threshold. This safe current lower limit threshold characterizes the DC current threshold at which the line is mechanically disconnected. After the faulty DC line of the wind turbine and the receiving-end converter station is disconnected 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.

[0082] Terminal 101 can be, but is not limited to, various personal computers, laptops, smartphones, and tablets.

[0083] Server 102 can be a standalone physical server, a server cluster or distributed system consisting of multiple physical servers, or a cloud server that provides cloud computing services.

[0084] This application provides a DC fault ride-through method for a wind farm via a DC transmission system, applicable 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 such Figure 1The illustrated wind power DC transmission system uses diode rectification. Wind power is collected via AC to the Point of Common Coupling (PCC) bus, rectified by a DR (Diode Rectifier), and then transmitted to the receiving end via a long-distance overhead DC line. The receiving-end converter employs a Multi-Mechanical Converter (MMC) to prevent commutation failure and enhance support for the receiving-end grid. Since the DR cannot provide a stable AC voltage, the converters of each wind turbine need to adopt a grid-based control strategy to collectively support the AC voltage and frequency of the sending-end islanded system and achieve synchronous operation. Each wind turbine is equipped with a rated capacity load shedding circuit. The MMC uses a hybrid MMC topology consisting of half-bridge submodules (HBSM) and full-bridge submodules (FBSM) to achieve DC fault clearing, such as... Figure 3 The topology of the hybrid MMC is shown.

[0086] like Figure 4 As shown in the embodiment of this application, a DC fault ride-through method for a wind farm via a DC transmission system is provided. The method includes:

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

[0088] 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, while 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.

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

[0090] The hybrid MMC and fan clear DC faults in the second operating mode.

[0091] Understandably, when a DC short-circuit fault occurs in the DC transmission system of a wind farm, the DC voltage drops rapidly to 0. Since both the MMC and the wind turbine discharge to the short-circuit point, the DC current will rise rapidly. If no measures are taken, it will lead to damage to the switching devices. Therefore, switching to the second operating mode is to quickly clear the DC fault.

[0092] Step S2: In the second operating mode, control the DC current of the wind turbine and the receiving-end converter station to be reduced to below the preset current safety lower limit threshold; the current safety lower limit threshold is used to characterize the DC current threshold when the line is mechanically cut off.

[0093] In a typical 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 a preset current safety lower limit threshold. The receiving-end converter station is also controlled to actively output a negative DC voltage and the DC current of the receiving-end converter station is reduced to below a preset current safety lower limit threshold.

[0094] Understandably, based on the characteristics of diode uncontrolled rectification, the wind turbine side can quickly reduce the AC current by actively regulating the AC controller, which can rapidly reduce the DC fault current in the early stages of a fault and prevent the fault current from becoming too large and causing damage to the system.

[0095] For example, the grid-side converter controlling the wind turbine actively reduces the AC current, causing the DC current to drop rapidly to near zero. This allows the wind turbine's DC current to decrease quickly to a level where it can be interrupted by a high-speed mechanical switch. Simultaneously, the receiving-end converter station actively outputs a negative DC voltage, forcing the DC fault current to drop to zero. This allows the receiving-end converter station's DC current to decrease rapidly to a level where it can be interrupted by a high-speed mechanical switch (HSS), thus quickly clearing the DC fault. During this process, the high-speed mechanical switch's interruption time is extremely short, minimizing the impact of the DC fault on the system. After this process, the fault currents on both the MMC and DR DC sides are cleared, awaiting fault recovery. At this point, the high-speed mechanical switch activates, disconnecting the faulty line. After disconnecting the faulty line, the system enters the fault recovery phase.

[0096] Step S3: After disconnecting the faulty DC-side line between the wind turbine and the receiving-end converter station via a mechanical switch, control the receiving-end converter station to switch back to the first operating mode, then control the wind turbine to switch back to the first operating mode, and stop the unloading operation of the wind turbine.

[0097] It should be noted that when the system is preparing to recover after a fault, the receiving-end converter station switches back to the first operating mode, and the ramp restores the DC voltage to the rated value. This establishes the DC voltage, and then the wind turbine is switched back to the first operating mode and the unloading operation of the wind turbine is stopped. At this time, the wind farm resumes normal operation through the DC transmission system and continues to realize the long-distance transmission of wind power.

[0098] It should be noted that the embodiments of this application respond quickly to DC faults in the DC transmission system of the wind farm. By switching the operating modes of the wind turbine and the receiving-end converter station, the DC current of the wind turbine and the receiving-end converter station is reduced to below a preset safe current lower limit threshold, so that the fault current is cut off by the mechanical switch. This quickly reduces the DC fault current in the early stage of the fault, avoiding damage to the system caused by the continuous excessive fault current. It also eliminates the need for additional complex DC-side protection devices. The fault current is rapidly reduced by relying on the wind turbine control system itself. The circuit is disconnected in conjunction with the fast mechanical switch, which reduces the complexity of the system and the maintenance cost. The AC system remains connected after the fault, and the normal operation mode can be directly restored after the fault is cleared, quickly restoring the stable operation of the system and reducing the downtime of the wind turbine system. This minimizes the impact of DC faults on the system and ensures the safe and stable operation of the system.

[0099] Meanwhile, the entire process does not require the use of DC circuit breakers, reducing system costs and avoiding the complexity of DC circuit breaker structure and control, thus improving system reliability and stability.

[0100] In wind turbine control, wind turbines include machine-side converters (MSC) and grid-side converters (GSC).

[0101] The control process of the machine-side converter is as follows:

[0102] Step S201: Obtain the first d-axis current difference by subtracting the reference value of the rotor current d-axis component and the actual value of the d-axis current from the reference value of the rotor current d-axis component of the machine-side converter.

[0103] Step S202: Input the first d-axis current difference into the proportional-integral controller and output the first d-axis current deviation.

[0104] Step S203: Obtain the reference value of the first d-axis voltage component by subtracting the first d-axis current deviation from the preset first feedforward quantity; wherein, the first feedforward quantity is obtained based on the rotor electric angular velocity, stator and rotor inductance, and rotor current q-axis component.

[0105] Step S204: Obtain the first voltage component difference by subtracting the actual value of the first DC voltage of the fan from the rated value of the first DC voltage;

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

[0107] Step S206: Obtain the first q-axis current difference by subtracting the reference value of the first current q-axis component from the actual value of the current q-axis component;

[0108] Step S207: Input the first q-axis current difference into the proportional-integral controller to obtain the deviation of the first q-axis current difference;

[0109] Step S208: By summing the first q-axis current difference deviation with the preset second feedforward, the reference value of the first q-axis voltage component is obtained;

[0110] Step S209: The first port three-phase voltage reference value of the machine-side converter is obtained by passing the first d-axis voltage component reference value and the first q-axis voltage component reference value through Park transformation. Then, the first port three-phase voltage reference value is processed by PWM modulation to obtain the switching modulation signal of the machine-side converter.

[0111] The control process of the grid-side converter in the first operating mode is as follows:

[0112] Step S211: Obtain the fan power reference value by using the actual fan speed value through maximum power point tracking control;

[0113] Step S212: Obtain the fan power difference by subtracting the fan power reference value from the actual fan power value;

[0114] Step S213: After inputting the fan power difference into the proportional-integral controller, the fan power difference deviation is obtained;

[0115] Step S214: The wind turbine voltage amplitude is obtained by summing the wind turbine power difference deviation with the preset third feedforward quantity; wherein, the third feedforward quantity is obtained based on the grid-side phase voltage rated value.

[0116] Step S215: Based on the fan voltage amplitude and the actual fan voltage amplitude, obtain the first d-axis current reference value of the generator-side converter in the first operating mode;

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

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

[0119] Step S218: By using the first d-axis current reference value and the first q-axis current reference value for current closed-loop control, the reference values ​​of the first d-axis voltage component and the first q-axis voltage component of the machine-side converter in the first operating mode are obtained.

[0120] Step S219: By performing Park transformation on the first d-axis voltage component reference value and the first q-axis voltage component reference value, the port three-phase voltage reference value of the machine-side converter in the first operating mode is obtained. Then, the first port three-phase voltage reference value is processed by PWM modulation to obtain the switching modulation signal of the machine-side converter in the first operating mode.

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

[0122] Step S221: Determine the reference value of the second d-axis current of the machine-side converter in the second operating mode by using the current safety lower limit threshold.

[0123] Step S222: By using the second d-axis current reference value and the first q-axis current reference value for current closed-loop control, the reference values ​​of the second d-axis voltage component and the second q-axis voltage component of the machine-side converter in the second operating mode are obtained.

[0124] Step S223: By transforming the second d-axis voltage component reference value and the second q-axis voltage component reference value, the three-phase voltage reference value of the third port of the machine-side converter in the second operating mode is obtained. Then, the three-phase voltage reference value of the third port is processed by PWM modulation to obtain the switching modulation signal of the machine-side converter in the second operating mode.

[0125] For example, such as Figure 5 As shown, the d-axis current control of the wind turbine's machine-side converter is the same as the conventional method, and the reference value i for the d-axis component of the rotor current is... * sd The value is 0, and the reference value of the d-axis component of the rotor current is i. * sd Compared with the actual value of d-axis current i sd Subtracting the two values ​​and passing them through a proportional-integral controller, we obtain the deviation. This deviation is then subtracted from the feedforward (ω). e L s i sq , where ω e It is the rotor electrical angular velocity, L s It is the stator and rotor inductance, i sq The d-axis voltage reference value e is obtained from the q-axis component of the rotor current. * sd .

[0126] Actual value of DC voltage of the fan u dcW With the rated value u dcWN Subtracting the values ​​and passing them through a proportional-integral controller, we obtain the reference value i for the q-axis component of the rotor current. * sq Reference value i for the q-axis component of rotor current. * sq The actual value of the q-axis component of the rotor current isq Subtracting the two values ​​and passing them through a proportional-integral controller yields the deviation. This deviation is then added to the feedforward (ω). e ψ f + ω e L s i sd , where ψ f (This is the magnetic 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 reference values ​​of the three-phase voltage at the converter port are obtained, and then the switching modulation signal is obtained through PWM.

[0127] The grid-side converter of the wind turbine adopts grid-type control. The frequency ω of the converter output voltage. g The frequency ω of the converter output voltage is obtained through reactive power control. g Integrating yields the phase θ g Phase θ g Used to convert grid-side AC voltage u g and alternating current i g Perform the Park transform to obtain the input u of the grid-side converter. gd u gq i gd i gq This serves as the input to the controller. Additionally, after current inner-loop control, e is obtained. * gd and e * gq It also needs to undergo Park transformation to obtain the three-phase reference voltage, and then perform PWM modulation to obtain the switching signal. Phase θ g It is the phase angle required for the Park transformation.

[0128] For d-axis control of the grid-side converter, the reference value i for the d-axis current is... * gd Under normal circumstances, it is obtained according to the first operating mode; under fault conditions, 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 Compared with the actual power value P WTThe difference is then passed through a proportional-integral controller to obtain the deviation, which is then added to the feedforward quantity U. gN (Rated phase voltage on the grid side) yields the voltage amplitude U. m U m d-axis voltage u gd Reference value. U m with u gd Subtracting the values ​​and then passing them through a proportional-integral controller yields the reference value i of the d-axis current in Mode 1. * gd .

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

[0131] For 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 The reference value i of the q-axis current is then obtained through a proportional-integral controller. * gq Get i * gd and i * gq Then, the d-axis component reference value e of the converter output voltage is obtained through current closed-loop control. * gd and q-axis component reference value e * gq Finally, e * gd and e * gq The reference values ​​of the three-phase voltage at the converter port are obtained through Park transformation, and then the switching modulation signal is obtained through PWM.

[0132] Understandably, the turbine-side converter and 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 turbine-side converter, precise control of the d-axis and q-axis components of the rotor current enables regulation of the wind turbine power and stabilization of the DC voltage. In the control of the grid-side converter, a grid-based control strategy achieves precise control of the frequency and phase of the converter output voltage, thereby ensuring a stable connection between the wind turbine and the power grid.

[0133] Furthermore, during DC fault ride-through, the grid-side converters of the wind turbines need to switch according to the system's operating status. In normal operation mode, the grid-side converters are controlled according to the maximum power point tracking strategy to maximize the wind farm's output power. However, in the event of a DC fault, a rapid switch to fault ride-through mode is required. This involves controlling the DC current of the wind turbines and the receiving-end converter station to reduce it below a preset safe current lower limit threshold, thereby quickly clearing the DC fault.

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

[0135] The control process of the AC controller is as follows:

[0136] Step S231: Obtain the submodule capacitor voltage difference value by subtracting the rated value of the submodule capacitor voltage and the actual value of the submodule capacitor voltage of the AC controller.

[0137] Step S232: Input the voltage difference of the submodule capacitors into the proportional-integral controller to obtain the reference value of the third d-axis current;

[0138] Step S233: Obtain the third d-axis current difference by subtracting the reference value of the third d-axis current from the actual value of the third d-axis current.

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

[0140] Step S235: The third d-axis voltage reference value is obtained by subtracting the deviation of the third d-axis current difference from the preset fourth feedforward value; wherein, the fourth feedforward value is obtained based on the frequency, transformer inductance, bridge arm inductance and grid-side d-axis voltage.

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

[0142] Step S237: Input the second q-axis current difference to the proportional-integral controller to obtain the deviation of the second q-axis current difference;

[0143] Step S238: Obtain the second q-axis voltage reference value by subtracting the second q-axis current difference deviation from the preset fifth feedforward value;

[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 operating mode is as follows:

[0146] Step S241: Obtain the second DC voltage difference value by performing a difference operation on the actual value of the second DC voltage and the rated value of the second DC voltage of the DC controller;

[0147] Step S242: The first DC current deviation is obtained by inputting the second DC voltage difference into the proportional-integral controller;

[0148] Step S243: By subtracting the first DC current deviation from the preset sixth feedforward quantity, the first DC internal potential of the DC controller in the first operating mode is obtained.

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

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

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

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

[0153] For example, such as 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. The rated voltage u of the submodule capacitor is also shown. CN Subtract the actual value u C Then, after passing through a 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 The error is then obtained by passing the proportional-integral controller. The feedforward quantity ω0(L) T +L s / 2)i q +u d (where ω0 is the frequency, L) T For transformer inductance, L s For the bridge arm inductance, u d Subtracting this deviation from the grid-side d-axis voltage yields 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 The error is then obtained by passing it through a proportional-integral controller. (Feedforward quantity) (where u) q Subtracting this deviation from the q-axis voltage on the grid side yields 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: During normal operation, the DC controller operates in the first mode, and the actual value of the MMC DC voltage is u. dc Subtract the rated value u dcN The DC current reference value i is then obtained through a proportional-integral controller. * dc DC current reference value i * dc Subtract the actual value i dc The deviation is then obtained through a proportional-integral controller. The feedforward DC voltage u dc Subtracting this deviation, we obtain 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, and the actual negative DC current value is 0 minus the actual negative DC current value. After passing through the proportional controller, and then through the limiting stage (the upper limit is u), dcN The lower limit is , where u dcN e is obtained by considering the DC voltage rating and η as the proportion of the number of full-bridge submodules in the hybrid MMC to the total number of modules. dc .

[0156] The control process of the circulating current controller is the same as that of the existing MMC circulating current controller, which controls the circulating current component i. cira i cirb i circ The suppression is 0, and the internal potential of the output circulating current is e. cira and e cirb .

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

[0158] Understandably, during the DC fault ride-through process of the wind farm's DC transmission system, the various controllers at the receiving-end converter station work together to achieve a rapid response and effective ride-through of the DC fault. The AC controller maintains the stable operation of the converter by precisely controlling the capacitor voltage of the submodules.

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

[0160] During the generation of reference voltage and control signals, 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 reference voltage values ​​for the six bridge arms. These values ​​are then modulated to obtain the control signals for each submodule of the receiving-end MMC. This process enables precise control of the converter output voltage and current, ensuring a stable connection and power transmission between the wind farm and the power grid.

[0161] Based on the same inventive concept, this application also provides a DC fault ride-through system for a wind farm through a DC transmission system for implementing the DC fault ride-through method of the wind farm through a DC transmission system mentioned above.

[0162] The solution provided by this system is similar to the solution described in the above method. Therefore, the specific limitations of the one or more wind farm DC fault ride-through system embodiments provided below can be found in the limitations of the DC fault ride-through method of wind farm DC transmission system described above, and will not be repeated here.

[0163] like Figure 7As shown, this application provides a DC fault ride-through system for a wind farm via a DC transmission system, applied to a wind farm via a DC transmission system; the wind farm via a DC transmission system includes wind turbines and a receiving-end converter station; the wind turbines are 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; this system includes:

[0164] The mode switching module 100 is used to monitor 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 mode, it controls both the wind turbine and the receiving-end converter station to switch from the first operating mode to the second operating mode, and performs unloading operation on the wind turbine.

[0165] 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.

[0166] The fault ride-through module 200 is used in the second operating mode to control the DC current of the wind turbine and the receiving-end converter station to be reduced to below the preset current safety lower limit threshold; the current safety lower limit threshold is used to characterize the DC current threshold when the line is mechanically disconnected.

[0167] The fault recovery module 300 is used to control the receiving-end converter station to switch back to the first operating mode after disconnecting the DC side fault line of 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 operating mode and stop the unloading operation of the wind turbine.

[0168] In some embodiments, the fault-crossing 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. 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 turbine-side converter;

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

[0172] The first d-axis current difference is obtained by subtracting the reference value of the d-axis component of the rotor current of the machine-side converter from the actual value of the d-axis current.

[0173] The first d-axis current difference is input to the proportional-integral controller, which outputs the first d-axis current deviation.

[0174] The reference value of the first d-axis voltage component is obtained by subtracting the first d-axis current deviation from the preset first feedforward value; wherein, the first feedforward value is obtained based on the rotor electric angular velocity, stator and rotor inductance, and rotor current q-axis component.

[0175] The difference of the first voltage component is obtained by subtracting the actual value of the first DC voltage of the fan from the rated value of the first DC voltage.

[0176] The reference value of the first current q-axis component is obtained by passing the difference of the first voltage component through a proportional-integral controller.

[0177] The first q-axis current difference value is obtained by subtracting the reference value of the first current q-axis component from the actual value of the current q-axis component.

[0178] The deviation of the first q-axis current difference is obtained by inputting the first q-axis current difference into the proportional-integral controller.

[0179] The reference value of the first q-axis voltage component is obtained by summing the deviation of the first q-axis current difference with the preset second feedforward value.

[0180] By performing Park transformation on the first d-axis voltage component reference value and the first q-axis voltage component reference value, the first port three-phase voltage reference value of the machine-side converter is obtained. Then, the first port three-phase voltage reference value is processed by PWM modulation to obtain the switching 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 operating mode is as follows:

[0183] By using the actual speed of the fan and maximum power point tracking control, a reference value for the fan power is obtained.

[0184] The difference in fan power is obtained by subtracting the reference value and the actual value of fan power.

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

[0186] The wind turbine voltage amplitude is obtained by summing the wind turbine power difference deviation with the preset third feedforward value; whereby the third feedforward value is obtained based on the grid-side phase voltage rating.

[0187] Based on the wind turbine voltage amplitude and the actual wind turbine voltage amplitude, the reference value of the first d-axis current of the turbine-side converter in the first operating mode is obtained;

[0188] The first q-axis voltage difference is obtained by performing a subtraction operation between the reference value and the actual value of the first q-axis voltage of the grid-side converter.

[0189] The first q-axis voltage difference is input to the proportional-integral controller, which outputs the first q-axis current reference value.

[0190] By using the first d-axis current reference value and the first q-axis current reference value for current closed-loop control, the reference values ​​of the first d-axis voltage component and the first q-axis voltage component of the machine-side converter in the first operating mode are obtained.

[0191] By performing Park transformation on the first d-axis voltage component reference value and the first q-axis voltage component reference value, the port three-phase voltage reference value of the machine-side converter in the first operating mode is obtained. Then, the first port three-phase voltage reference value is processed by PWM modulation to obtain the switching modulation signal of the machine-side converter in the first operating mode.

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

[0193] The reference value of the second d-axis current of the machine-side converter in the second operating mode is determined by the current safety lower limit threshold.

[0194] By using the second d-axis current reference value and the first q-axis current reference value for current closed-loop control, the second d-axis voltage component reference value and the second q-axis voltage component reference value of the machine-side converter in the second operating mode are obtained.

[0195] By transforming the second d-axis voltage component reference value and the second q-axis voltage component reference value, the three-phase voltage reference value of the third port of the machine-side converter in the second operating mode is obtained. Then, the three-phase voltage reference value of the third port is processed by PWM modulation to obtain the switching 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 as follows:

[0198] The difference between the rated value of the submodule capacitor voltage and the actual value of the submodule capacitor voltage of the AC controller is obtained by subtracting the value of the submodule capacitor voltage.

[0199] The third d-axis current reference value is obtained by inputting the capacitor voltage difference of the submodule into the proportional-integral controller;

[0200] The difference between the reference value and the actual value of the third d-axis current is obtained by subtracting the reference value and the actual value of the third d-axis current.

[0201] The deviation of the third d-axis current difference is obtained by passing the third d-axis current difference through a proportional-integral controller.

[0202] The third d-axis voltage reference value is obtained by subtracting the deviation of the third d-axis current difference from the preset fourth feedforward value; the fourth feedforward value is obtained based on the frequency, transformer inductance, bridge arm inductance and grid-side d-axis voltage.

[0203] The difference value of the second q-axis current is obtained by subtracting the reference value of the second q-axis current and the actual value of the second q-axis current of the AC controller.

[0204] The deviation of the second q-axis current difference is obtained by inputting the second q-axis current difference into the proportional-integral controller.

[0205] The second q-axis voltage reference value is obtained by subtracting the deviation of the second q-axis current difference from the preset fifth feedforward value.

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

[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 as follows:

[0209] The difference between the actual value and the rated value of the second DC voltage of the DC controller is used to obtain the second DC voltage difference value.

[0210] The first DC current deviation is obtained by inputting the second DC voltage difference into the proportional-integral controller.

[0211] The first DC internal potential of the DC controller in the first operating mode is obtained by subtracting the first DC current deviation from the preset sixth feedforward quantity.

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

[0213] The DC current difference is obtained by subtracting the DC current reference value of the DC controller from the negative actual DC current value; where the DC current reference value is zero.

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

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

[0216] The control process of the circulating current controller is as follows:

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

[0218] like Figure 8 As shown, this application provides an electronic device 10, which includes a memory 20 and a processor 30. The memory 20 stores a computer program. When the computer program is executed by the processor 30, the processor 30 performs the steps of the DC fault ride-through method of the wind farm through the DC transmission system as described in the above embodiment.

[0219] This application provides a computer-readable storage medium storing a computer program thereon, which, when executed, implements the steps of the virtual impedance control parameter optimization method as described in the above embodiments.

[0220] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, electronic devices, and computer storage media described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0221] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0222] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0223] In the embodiments provided by this 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 merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between devices or units through some interfaces, and may be electrical, mechanical, or other forms.

[0224] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0225] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0226] If the integrated unit is implemented as 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, in essence, 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. This computer software product is stored in a storage medium and includes several instructions for executing all or part of the steps of the methods described in the various embodiments of the present invention through a computer device (which may be a personal computer, a server, or a network device, etc.). The aforementioned storage medium includes: USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, optical disks, and other media capable of storing program code.

[0227] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for DC fault ride-through of a wind farm via a DC transmission system, characterized in that, The method is applied to a wind farm DC transmission system; the wind farm DC transmission system includes wind turbines and a receiving-end converter station; the wind turbines are 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; the method includes: The system monitors the operation status of the wind farm's DC transmission system in real time. If a DC fault is detected in the operation status, the system controls both the wind turbine and the receiving-end converter station to switch from the first operation mode to the second operation mode and performs unloading operations on the wind turbine. 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 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 when the line is cut off by the mechanical switch; After disconnecting the faulty DC-side line between the wind turbine and the receiving-end converter station 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. The receiving-end converter station includes a DC controller; The control process of the DC controller in the first operating mode is as follows: The second DC voltage difference value is obtained by subtracting the actual value of the second DC voltage and the rated value of the second DC voltage from the DC controller. The first DC current deviation is obtained by inputting the second DC voltage difference into the proportional-integral controller. The first DC internal potential of the DC controller in the first operating mode is obtained by subtracting the first DC current deviation from the preset sixth feedforward quantity. The control process of the DC controller in the second operating mode is as follows: The DC current difference is obtained by subtracting the DC current reference value of the DC controller from the negative actual DC current value; wherein the DC current reference value is zero. The DC current difference is passed through a proportional controller and then through a limiting circuit to obtain the second DC internal potential of the DC controller in the second operating mode.

2. The DC fault ride-through method for wind farms via DC transmission systems according to claim 1, characterized in that, In the second operating mode, 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 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. 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 for wind farms via DC transmission systems according to claim 1, characterized in that, The wind turbine includes a machine-side converter; The control process of the machine-side converter is as follows: The first d-axis current difference value is obtained by subtracting the reference value of the d-axis component of the rotor current of the machine-side converter from the actual value of the d-axis current. The first d-axis current difference is input to the proportional-integral controller, which outputs the first d-axis current deviation. The reference value of the first d-axis voltage component is obtained by subtracting the first d-axis current deviation from the preset first feedforward value; wherein, the first feedforward value is obtained based on the rotor electric angular velocity, stator and rotor inductance, and rotor current q-axis component. The first voltage component difference is obtained by subtracting the actual value of the first DC voltage of the fan from the rated value of the first DC voltage. The reference value of the first current q-axis component is obtained by passing the first voltage component difference through a proportional-integral controller; The first q-axis current difference value is obtained by subtracting the reference value of the first current q-axis component from the actual value of the current q-axis component. The deviation of the first q-axis current difference is obtained by inputting the first q-axis current difference into the proportional-integral controller. The reference value of the first q-axis voltage component is obtained by summing the deviation of the first q-axis current difference with the preset second feedforward value. The first port three-phase voltage reference value of the machine-side converter is obtained by performing Park transformation on the first d-axis voltage component reference value and the first q-axis voltage component reference value. Then, the first port three-phase voltage reference value is processed by PWM modulation to obtain the switching modulation signal of the machine-side converter.

4. The DC fault ride-through method for wind farms via DC transmission systems 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 operating mode is as follows: By applying the actual rotational speed of the fan to maximum power point tracking control, a reference value for the fan power is obtained. The difference in fan power is obtained by subtracting the reference value and the actual value of fan power. 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 summing the wind turbine power difference deviation with a preset third feedforward value; wherein the third feedforward value is obtained based on the grid-side phase voltage rating. Based on the aforementioned wind turbine voltage amplitude and the actual wind turbine voltage amplitude, the first d-axis current reference value of the turbine-side converter in the first operating mode is obtained; The first q-axis voltage difference is obtained by performing a subtraction operation between the reference value of the first q-axis voltage and the actual value of the first q-axis voltage of the grid-side converter. The first q-axis voltage difference is input to the proportional-integral controller, which outputs the first q-axis current reference value. By using the first d-axis current reference value and the first q-axis current reference value for current closed-loop control, the first d-axis voltage component reference value and the first q-axis voltage component reference value of the machine-side converter in the first operating mode are obtained. By performing Park transformation on the first d-axis voltage component reference value and the first q-axis voltage component reference value, the port three-phase voltage reference value of the machine-side converter in the first operating mode is obtained. Then, the first port three-phase voltage reference value is processed by PWM modulation to obtain the switching modulation signal of the machine-side converter in the first operating mode. The control process of the grid-side converter in the second operating mode is as follows: The reference value of the second d-axis current of the machine-side converter in the second operating mode is determined by the current safety lower limit threshold. By using the second d-axis current reference value and the first q-axis current reference value for current closed-loop control, the second d-axis voltage component reference value and the second q-axis voltage component reference value of the machine-side converter in the second operating mode are obtained. By performing Park transformation on the second d-axis voltage component reference value and the second q-axis voltage component reference value, the three-phase voltage reference value of the third port of the machine-side converter in the second operating mode is obtained. Then, the three-phase voltage reference value of the third port is processed by PWM modulation to obtain the switching modulation signal of the machine-side converter in the second operating mode.

5. The DC fault ride-through method for wind farms via DC transmission systems according to claim 1, characterized in that, The receiving-end converter station includes an AC controller; The control process of the AC controller is as follows: The difference between the rated value of the submodule capacitor voltage and the actual value of the submodule capacitor voltage of the AC controller is obtained by subtracting the value of the submodule capacitor voltage. The third d-axis current reference value is obtained by inputting the capacitor voltage difference of the submodule into the proportional-integral controller. The difference value of the third d-axis current is obtained by subtracting the reference value of the third d-axis current from the actual value of the third d-axis current. The deviation of the third d-axis current difference is obtained by passing the third d-axis current difference through a proportional-integral controller. The third d-axis voltage reference value is obtained by subtracting the deviation of the third d-axis current difference from the preset fourth feedforward value; wherein, the fourth feedforward value is obtained based on the frequency, transformer inductance, bridge arm inductance and grid-side d-axis voltage. The second q-axis current difference value is obtained by subtracting the reference value of the second q-axis current and the actual value of the second q-axis current of the AC controller. The deviation of the second q-axis current difference is obtained by inputting the second q-axis current difference into the proportional-integral controller. The second q-axis voltage reference value is obtained by subtracting the deviation of the second q-axis current difference from the preset fifth feedforward value. The AC internal potential of the AC controller is obtained by performing Park transformation on the third d-axis voltage reference value and the second q-axis voltage reference value.

6. The DC fault ride-through method for wind farms via DC transmission systems according to claim 1, characterized in that, The receiving-end converter station includes a circulating controller; The control process of the circulating controller is as follows: The circulating current component of the circulating current controller is suppressed to zero to obtain the circulating current internal potential of the circulating current controller.

7. A DC fault ride-through system for a wind farm via a DC transmission system, characterized in that, This system is applied to a wind farm DC transmission system; the wind farm DC transmission system includes wind turbines and a receiving-end converter station; the wind turbines are connected to the receiving-end converter station via a common coupling point and a diode rectifier; a mechanical switch is provided on the line between the diode rectifier and the receiving-end converter station; the system includes: The mode switching module is used to monitor 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 status, control both the wind turbine and the receiving-end converter station to switch from the first operating mode to the second operating mode, and perform unloading operation on the wind turbine. 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. The fault ride-through module is used to 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 in the second operating mode; the current safety lower limit threshold is used to characterize the DC current threshold when the line is disconnected by the mechanical switch. The fault recovery module is used to control the receiving-end converter station to switch back to the first operating mode after disconnecting the DC side fault line of 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. The receiving-end converter station includes a DC controller; The control process of the DC controller in the first operating mode is as follows: The second DC voltage difference value is obtained by subtracting the actual value of the second DC voltage and the rated value of the second DC voltage from the DC controller. The first DC current deviation is obtained by inputting the second DC voltage difference into the proportional-integral controller. The first DC internal potential of the DC controller in the first operating mode is obtained by subtracting the first DC current deviation from the preset sixth feedforward quantity. The control process of the DC controller in the second operating mode is as follows: The DC current difference is obtained by subtracting the DC current reference value of the DC controller from the negative actual DC current value; wherein the DC current reference value is zero. The DC current difference is passed through a proportional controller and then through a limiting circuit to obtain the second DC internal potential of the DC controller in the second operating mode.

8. An electronic device, characterized in that, The electronic device includes a memory and a processor. The memory stores a computer program. When the computer program is executed by the processor, the processor performs the steps of the DC fault ride-through method for a wind farm via a DC transmission system as described in any one of claims 1-6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed, it implements the steps of the DC fault ride-through method for wind farms via DC transmission systems as described in any one of claims 1-6.

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