A DC fault ride-through method and device for a renewable energy islanded DC transmission system

Abstract

This invention proposes a DC fault ride-through method and apparatus for a new energy islanded DC transmission system. The invention includes: in the event of a DC fault, controlling the receiving-end converter station to enter a zero DC current mode and the sending-end converter station to enter a zero DC voltage mode; the generation unit identifies the fault based on the AC frequency, switches to a load shedding mode, and engages an unloading circuit to dissipate surplus power; when the capacitor voltage of the sending-end converter station submodule drops to a preset threshold, it switches to the zero DC current mode, outputting a negative voltage to quickly suppress the DC current; after the fault is cleared and power is balanced, the converter station resumes normal operation, the generation unit ramps up power recovery, and unloading stops. This invention can quickly suppress faults, stabilize system operation, and achieve smooth recovery after a fault.

Description

Technical Field

[0001] This invention relates to the field of wind turbine power prediction technology, and in particular to a DC fault ride-through method and apparatus for a new energy islanded DC transmission system. Background Technology

[0002] As a key technology for large-scale renewable energy development, isolated DC transmission from renewable energy islands is widely used in remote areas such as deserts and Gobi. With the development of flexible DC transmission technology, systems based on modular multilevel converters have constructed a complete technical system covering power conversion, DC transmission, and frequency support through the coordinated operation of sending-end converter stations, receiving-end converter stations, and renewable energy generation units. Specifically, this system relies on the close coordination of converter topology control, grid synchronization mechanisms, and power balance strategies to achieve efficient long-distance power transmission.

[0003] However, existing DC fault ride-through methods, which directly employ centralized AC power dissipation devices or rely on communication commands for load shedding, do not achieve rapid, autonomous, and coordinated response between the power source and grid sides. Due to communication delays leading to lag in power regulation, or limitations imposed by the wind turbine's frequency response range and voltage regulation margin, surplus power cannot be dissipated in a timely manner during the initial stage of a fault, causing a sharp rise in the capacitor voltage of the sending-end converter. This may not only trigger overvoltage protection of submodules leading to system lockout, but also threaten equipment safety due to large power fluctuations, severely restricting the stable operation of the renewable energy base. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, the first objective of this invention is to propose a DC fault ride-through method for a new energy islanded DC transmission system.

[0006] Another objective of this invention is to provide a DC fault ride-through device for a new energy island DC transmission system.

[0007] The third objective of this invention is to provide a computer device.

[0008] A fourth objective of this invention is to provide a non-transitory computer-readable storage medium.

[0009] To achieve the above objectives, a first aspect of the present invention provides a DC fault ride-through method for a renewable energy islanded DC transmission system, comprising:

[0010] S1, when the sending-end converter station and the receiving-end converter station detect a DC fault, control the receiving-end converter station to enter the zero DC current mode and adjust the DC current to zero, and at the same time control the sending-end converter station to enter the zero DC voltage mode and adjust the DC voltage output to zero. S2, each power generation unit identifies the fault status based on the AC side frequency change, switches the generator-side converter to the load reduction operation mode and triggers the internal unloading circuit to work to dissipate the surplus power. S3, when the sending-end converter station detects that the average value of the submodule capacitor voltage has dropped and reached the preset overvoltage threshold, the DC control mode of the sending-end converter station is switched to the zero DC current mode, and the DC current is quickly suppressed to zero by outputting a negative DC voltage. S4, after the AC and DC power of the system is restored to balance and the fault is cleared, controls the sending-end converter station and the receiving-end converter station to return to normal working mode, and controls each power generation unit to restore active power output and stop the unloading circuit from working.

[0011] In one embodiment of the present invention, S1 includes: The DC controller of the receiving-end converter station switches to DC fault mode and performs proportional-integral control based on the deviation between the actual value of DC current and zero value to adjust the DC current to zero. The DC controller of the sending-end converter station switches to DC fault mode 1, directly controlling the DC internal potential output to zero, thereby regulating the DC voltage output to zero; The deviation between the actual value and the rated value of the capacitor voltage of the submodule at the sending end converter station is obtained, and the reference value of DC current is calculated by the proportional-integral controller. The current deviation is obtained by subtracting the DC current reference value from the actual DC current value, and the deviation is calculated by a proportional-integral controller. In DC fault mode 1, the calculation results of the deviation and feedforward DC voltage are ignored, and the DC internal potential of the sending-end converter station is forcibly set to zero value for output.

[0012] In one embodiment of the present invention, S2 includes: Each power generation unit monitors the actual value of the AC frequency in real time. When the actual value of the AC frequency deviates from the rated frequency, it is determined to be a fault state. The machine-side converter updates the AC power reference value to the reference value obtained by the maximum power point tracking control based on the wind turbine speed, minus the reference value generated by the frequency response control, thereby switching to the unloaded operation mode. At the same time, it triggers the full-capacity unloading circuit configured inside each power generation unit to conduct, converting the surplus electrical energy converted from rotor kinetic energy into heat energy for dissipation.

[0013] In one embodiment of the present invention, the reference value generated by the frequency response control is generated by subtracting the rated frequency from the actual AC frequency of the wind turbine, and then performing proportional control. The calculation formula is as follows:

[0014] in, The power reference value adjustment amount generated for frequency response control. This is the proportional control coefficient. This represents the actual AC frequency of the fan. This is the rated frequency.

[0015] In one embodiment of the present invention, S3 includes: The sending-end converter station calculates the rate of change of the average voltage of the submodule capacitor in real time. When the rate of change is detected to be negative and the average voltage of the submodule capacitor reaches the preset overvoltage threshold, the DC controller is switched from DC fault mode 1 to DC fault mode 2. In DC fault mode 2, the DC current reference value is set to zero. Based on the deviation between the zero value and the actual negative DC current value, the proportional controller calculates and processes the voltage through the limiting circuit to output a negative DC voltage to quickly control the DC current to zero.

[0016] In one embodiment of the present invention, the step of outputting a negative DC voltage after calculation by a proportional controller and processing by a limiting circuit includes: The current error signal is obtained by subtracting the negative actual value of the DC current from the zero DC current reference value. Multiply the current error signal by a scaling factor. A preliminary control level was obtained; The initial control quantity is subjected to amplitude limiting processing, and the upper limit is set to the rated value of DC voltage. The lower limit is ,in The ratio of the number of full-bridge submodules to the total number of modules in a hybrid modular multilevel converter is used as the DC internal potential output after limiting.

[0017] In one embodiment of the present invention, S4 includes: The receiving-end converter station controls the DC voltage to rise from zero to the rated value at a preset ramp rate in order to establish the DC voltage of the flexible DC system. Once the DC voltage has been established, the sending-end converter station switches back to normal mode and controls the AC voltage frequency to return to the rated frequency. After the DC voltage is established, each power generation unit controls the active power to gradually increase to the target value according to the preset ramp curve, and at the same time disconnects the internal unloading circuit to stop working.

[0018] To achieve the above objectives, a second aspect of the present invention provides a DC fault ride-through device for a new energy islanded DC transmission system, comprising: The fault detection and control module is used to control the receiving-end converter station to enter the zero DC current mode and adjust the DC current to zero when a DC fault is detected at the sending-end converter station and the receiving-end converter station, and at the same time control the sending-end converter station to enter the zero DC voltage mode and adjust the DC voltage output to zero. The power regulation module of the power generation unit is used to identify the fault status of each power generation unit based on the AC side frequency change, switch the generator-side converter to the load reduction operation mode and trigger the internal unloading circuit to work to dissipate the surplus power. The converter station overvoltage suppression module is used to switch the DC control mode of the sending-end converter station to zero DC current mode when the sending-end converter station detects that the average value of the submodule capacitor voltage has dropped and reached the preset overvoltage threshold. It then outputs a negative DC voltage to quickly suppress the DC current to zero. The system fault recovery module is used to control the sending-end converter station and receiving-end converter station to return to normal working mode after the AC and DC power of the system is restored to balance and the fault is cleared, and to control the ramp of each power generation unit to restore active power output and stop the unloading circuit from working.

[0019] The present invention discloses a DC fault ride-through method and apparatus for a new energy island DC transmission system. It does not require the configuration of a centralized energy consumption device and is not affected by communication delay. Through the coordinated control of the dual-sided converters of the wind turbine and the cooperation of the unloading circuit, it can realize the rapid local dissipation of surplus power, effectively suppress system overvoltage and reduce construction costs.

[0020] To achieve the above objectives, a third aspect of this application provides a computer device, including a processor and a memory; wherein the processor reads executable program code stored in the memory to run a program corresponding to the executable program code, for implementing a DC fault ride-through method for a new energy islanded DC transmission system as described in the first aspect embodiment.

[0021] To achieve the above objectives, the fourth aspect of this application proposes a non-transitory computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements a DC fault ride-through method for a new energy islanded DC transmission system as described in the first aspect embodiment.

[0022] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0023] Figure 1 This is a flowchart of a DC fault ride-through method for a new energy islanded DC transmission system according to an embodiment of the present invention; Figure 2 This is a structural diagram of a wind power-flexible DC grid-connected system according to an embodiment of the present invention; Figure 3 This is the DC fault ride-through implementation process according to an embodiment of the present invention; Figure 4 This is a block diagram of a fan control system according to an embodiment of the present invention; Figure 5 This is a control block diagram of a flexible DC transmission system according to an embodiment of the present invention; Figure 6 This is a structural diagram of a DC fault ride-through device for a new energy island DC transmission system according to an embodiment of the present invention; Figure 7 It is a computer device according to an embodiment of the present invention. Detailed Implementation

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] 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 should fall within the scope of protection of the present invention.

[0026] The following description, with reference to the accompanying drawings, illustrates a DC fault ride-through method and apparatus for a new energy islanded DC transmission system according to an embodiment of the present invention.

[0027] Figure 1 This is a flowchart of a DC fault ride-through method for a new energy islanded DC transmission system according to an embodiment of the present invention, as shown below. Figure 1 As shown, it includes: S1, when the sending-end converter station and the receiving-end converter station detect a DC fault, control the receiving-end converter station to enter the zero DC current mode and adjust the DC current to zero, and at the same time control the sending-end converter station to enter the zero DC voltage mode and adjust the DC voltage output to zero. S2, each power generation unit identifies the fault status based on the AC side frequency change, switches the generator-side converter to the load reduction operation mode and triggers the internal unloading circuit to work to dissipate the surplus power. S3, when the sending-end converter station detects that the average value of the submodule capacitor voltage has dropped and reached the preset overvoltage threshold, the DC control mode of the sending-end converter station is switched to the zero DC current mode, and the DC current is quickly suppressed to zero by outputting a negative DC voltage. S4, after the AC and DC power of the system is restored to balance and the fault is cleared, controls the sending-end converter station and the receiving-end converter station to return to normal working mode, and controls each power generation unit to restore active power output and stop the unloading circuit from working.

[0028] In one embodiment of the present invention, for such Figure 2 The illustrated renewable energy island is transmitted via a flexible DC transmission system. The wind turbines are equipped with full-capacity unloading circuits. The flexible DC converter station includes a sending-end converter station (WindFarm-side MMC, WFMMC) and a receiving-end converter station (Grid-side MMC, GSMMC). Both the WFMMC and GSMMC employ a hybrid MMC topology of half-bridge and full-bridge submodules. The fault ride-through process achieved by the control method proposed in this invention is as follows: Figure 3 As shown.

[0029] Specifically, the operating status of the wind power flexible DC system is monitored in real time. After the WFMMC and GSMMC detect a DC fault, the GSMMC's DC controller switches to DC fault mode (i.e., zero DC current mode), controlling the DC current to 0. The WFMMC's DC controller switches to DC fault mode 1 (i.e., zero DC voltage mode), directly outputting a DC voltage of 0. After each wind turbine detects a fault by measuring frequency changes, the turbine-side converter switches to load shedding mode, simultaneously triggering the unloading circuit inside each wind turbine. When the WFMMC detects that the rate of change of the average submodule capacitor voltage is negative and the average submodule capacitor voltage is 1.1 pu, the WFMMC DC controller switches to DC fault mode 2 (i.e., zero DC current mode), quickly controlling the DC current to 0 by outputting a negative DC voltage. After the above process, the AC and DC power at both ends of the WFMMC and GSMMC are balanced, and the system waits for fault recovery. When the system is ready to recover after a fault, both the WFMMC and GSMMC switch to normal operating mode, with the GSMMC controlling the DC voltage to rise from 0 to the rated value at a ramp rate. After the DC voltage of the flexible DC system is established, each wind turbine outputs active power on the ramp, and the unloading circuits all stop working.

[0030] Based on the above fault ride-through process, the control block diagrams of each converter in the wind power flexible DC system proposed in this invention are as follows: Figure 4 and Figure 5 As shown.

[0031] In one embodiment of the present invention, wind turbine control is divided into turbine-side converter control and grid-side converter control. The d-axis current reference value of the turbine-side converter controller... i sd The value is always 0. The outer loop of the q-axis is constant power control, based on the AC power reference value. P WT and actual value P WT By taking the difference and then applying proportional-integral control, the reference value of the q-axis current is obtained. i sq ,Right now:

[0032] AC power reference value in normal mode P WT Based on the current fan speed Ω m This is obtained from Maximum Power Point Tracking (MPPT) control. After a fault is detected, the AC power reference value... P WT Fan speed Ω m The reference value obtained by MPPT control is subtracted from the reference value generated by frequency response control. The reference value generated by frequency response control is obtained from the actual AC frequency of the fan. ω g Subtract the rated frequency ω N It is generated after proportional control, that is:

[0033] Based on the d-axis current reference value i sd and q-axis current reference value i sq By utilizing the inner current loop control, the d-axis and q-axis reference voltages of the machine-side converter are obtained. u sd , u sq Then, the coordinate system is transformed from the park coordinate system to the abc coordinate system, and the switching signal is obtained through PWM modulation.

[0034] Reference value of q-axis current of grid-side converter i fq The reactive power reference value is 2 / 3. Q WT Divide by the d-axis component of the grid-side AC voltage u fd d-axis current reference value i fdIt consists of two parts: one is the output generated by the constant DC voltage control circuit. i fd1 Secondly, the output of the additional frequency response control circuit. i fd2 ,Right now:

[0035] in, i fd1 The rated DC voltage of the fan u dcWN and actual value u dcW After taking the difference, it is obtained through proportional-integral control, that is:

[0036] i fd2 Then it is determined by the rated frequency of the wind farm. ω N Subtract the actual frequency ω g Generated after proportional-integral control, i.e.:

[0037] Therefore, the d-axis current reference value can be written in a combined form:

[0038] Based on the d-axis current reference value i fd and q-axis current reference value i fq By utilizing the inner current loop control, the d-axis and q-axis reference voltages of the grid-side converter are obtained. u fd , u fq Then, the coordinate system is transformed from the park coordinate system to the abc coordinate system, and the switching signal is obtained through PWM modulation.

[0039] In one embodiment of the present invention, the flexible DC transmission system control includes sending-end converter station control and receiving-end converter station control. The sending-end converter station controller includes an AC controller, a DC controller, and a circulating current controller.

[0040] AC controller: Energy stored in the capacitor by WFMMC W MMC2Subtract capacitor energy rating W MMCN Then, through a proportional controller, the frequency increment Δ is obtained. ω 2. Its expression can be written as:

[0041] The frequency addition Δ ω 2 plus rated frequency ω N Obtain AC voltage frequency ω 2. After passing through the integrator, the phase angle is obtained. θ 2. The expression is:

[0042] The AC voltage amplitude control of the converter is constant amplitude control, and the AC voltage reference value is... E MMC2 Set to the rated voltage at point PCC. U MMCN Voltage amplitude E MMC2 and phase angle θ 2. After passing through voltage and current dual closed-loop control, three-phase AC voltage is obtained. e a2 , e b2 , e c2 The output of the AC controller is the AC internal potential. e a2 , e b2 , e c2 .

[0043] DC Controller: The DC controller includes normal mode, DC fault mode 1, and DC fault mode 2. In normal mode, the rated capacitor voltage of the WFMMC submodule... u CN Subtract the actual value u C2 The DC current reference value is then obtained through a proportional-integral controller. i dc2 ,Right now:

[0044] DC current reference value i dc2 Subtract the actual value i dc2 The deviation is then obtained through a proportional-integral controller.

[0045]

[0046] DC voltage from feedforward quantity u dc2 Subtracting this deviation, we obtain the DC internal potential in normal mode. e dc2 :

[0047] Fault mode 1 is the zero DC voltage mode, DC internal potential e dc2 The direct output is 0. Fault mode 2 is the zero DC current mode, with a DC current reference value of 0, which is 0 minus the negative actual DC current value. i dc2 After passing through the proportional controller (proportional coefficient is...) k dc ), and then through the limiting process (the upper limit is ), u dcN The lower limit is (2 η 1) u dcN ,in u dcN This is the rated DC voltage. η (This is the ratio of the number of full-bridge submodules to the total number of modules in the hybrid MMC) e dc2 .

[0048] Circulating current controller: This part is the same as the existing circulating current controller in MMC, which converts the circulating current component... i cira2 , i cirb2 , i circ2 The suppression is 0, therefore it is not shown in detail in the diagram. The output is the internal potential of the circulating current. e cira2 and e cirb2 .

[0049] In one embodiment of the present invention, the receiving-end converter station controller includes an AC controller, a DC controller, and a circulating current controller. AC controller: Phase angle of the GSMMC. θ The voltage rating of the submodule capacitor is obtained by tracking the phase of the grid voltage using a phase-locked loop. u CN Subtract the actual value u C1 Then, after passing through a proportional-integral controller, the d-axis current reference value is obtained. i 1d:

[0050] q-axis current reference value i 1q for 2 / 3 of the reactive power reference value Q 1 divided by the d-axis component of the AC voltage u 1d Based on the d-axis current reference value i 1d and q-axis current reference value i 1q By utilizing the inner current loop control, the d-axis and q-axis reference voltages of the GSMMC are obtained. e d1 and e q1 After Park transformation, the output of the AC controller is obtained as the AC internal potential. e a1 , e b1 , e c1 .

[0051] DC Controller: The DC controller includes normal mode and DC fault mode. In normal mode, the actual value of the GSMMC DC voltage... u dc1 Subtract the rated value u dcN The DC current reference value is then obtained through a proportional-integral controller. i dc1 :

[0052] DC current reference value i dc1 Subtract the actual value i dc1 The deviation is then obtained through a proportional-integral controller:

[0053] Feedforward DC voltage u dc1 Subtracting this deviation, we obtain the DC internal potential in normal mode. e dc1 :

[0054] The DC fault mode is the zero DC current mode, which is the same as the DC fault mode 2 (zero DC current mode) of WFMMC, and the DC internal potential is obtained. e dc1 .

[0055] Circulating current controller: This part is the same as the circulating current controller in WFMMC, outputting the internal potential of the circulating current. e cira1 and e cirb1 .

[0056] The embodiments of this invention also have the following technical effects: The implementation process of DC fault ride-through in the wind power flexible DC system proposed in this invention is the timing coordination of fault ride-through between the wind turbine and the flexible DC system. The control block diagram of the wind turbine and flexible DC transmission system proposed in this invention is the control block diagram of the wind turbine machine-side converter, the wind turbine grid-side converter, WFMMC, and GSMMC. Both the wind turbine machine-side and grid-side converters are designed with frequency control response links, and the WFMMC DC fault control has two modes. Using the control method proposed in this invention, the wind turbine machine-side converter and the grid-side converter can simultaneously reduce power, which can improve the wind farm load shedding speed and efficiency, while reducing the requirements for the internal unloading circuit of the wind turbine, ultimately ensuring the safety and stability of the system during DC fault ride-through. No centralized energy dissipation device is required; DC fault ride-through can be achieved using the wind turbine's own unloading circuit, significantly reducing the system construction cost. There is no need to establish a communication channel between each wind turbine and the sending-end converter station, which can reduce the construction cost of the communication system and is not affected by communication delay.

[0057] To achieve the above embodiments, such as Figure 6 As shown, this embodiment also provides a DC fault ride-through device 10 for a new energy islanded DC transmission system, comprising: The fault detection and control module is used to control the receiving-end converter station to enter the zero DC current mode and adjust the DC current to zero when a DC fault is detected at the sending-end converter station and the receiving-end converter station, and at the same time control the sending-end converter station to enter the zero DC voltage mode and adjust the DC voltage output to zero. The power regulation module of the power generation unit is used to identify the fault status of each power generation unit based on the AC side frequency change, switch the generator-side converter to the load reduction operation mode and trigger the internal unloading circuit to work to dissipate the surplus power. The converter station overvoltage suppression module is used to switch the DC control mode of the sending-end converter station to zero DC current mode when the sending-end converter station detects that the average value of the submodule capacitor voltage has dropped and reached the preset overvoltage threshold. It then outputs a negative DC voltage to quickly suppress the DC current to zero. The system fault recovery module is used to control the sending-end converter station and receiving-end converter station to return to normal working mode after the AC and DC power of the system is restored to balance and the fault is cleared, and to control the ramp of each power generation unit to restore active power output and stop the unloading circuit from working.

[0058] This invention discloses a DC fault ride-through device for a new energy island DC transmission system. It does not require a centralized energy consumption device and is not affected by communication delays. Through the coordinated control of the dual-sided converters of the wind turbine and the cooperation of the unloading circuit, it can quickly dissipate surplus power locally, effectively suppress system overvoltage and reduce construction costs.

[0059] To implement the methods of the above embodiments, the present invention also provides a computer device, such as... Figure 7 As shown, the computer device 600 includes a memory 601 and a processor 602; wherein, the processor 602 reads the executable program code stored in the memory 601 to run a program corresponding to the executable program code, so as to implement the various steps of the DC fault ride-through method of a new energy island DC transmission system described above.

[0060] To implement the above embodiments, this application also proposes a non-transitory computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements a DC fault ride-through method for a new energy islanded DC transmission system as described in the foregoing embodiments.

[0061] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0062] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

Claims

1. A DC fault ride-through method for a renewable energy islanded DC transmission system, characterized in that, include: S1, when the sending-end converter station and the receiving-end converter station detect a DC fault, control the receiving-end converter station to enter the zero DC current mode and adjust the DC current to zero, and at the same time control the sending-end converter station to enter the zero DC voltage mode and adjust the DC voltage output to zero. S2, each power generation unit identifies the fault status based on the AC side frequency change, switches the generator-side converter to the load reduction operation mode and triggers the internal unloading circuit to work to dissipate the surplus power. S3, when the sending-end converter station detects that the average value of the submodule capacitor voltage has dropped and reached the preset overvoltage threshold, the DC control mode of the sending-end converter station is switched to the zero DC current mode, and the DC current is quickly suppressed to zero by outputting a negative DC voltage. S4, after the AC and DC power of the system is restored to balance and the fault is cleared, controls the sending-end converter station and the receiving-end converter station to return to normal working mode, and controls each power generation unit to restore active power output and stop the unloading circuit from working.

2. The method as described in claim 1, characterized in that, S1 includes: The DC controller of the receiving-end converter station switches to DC fault mode and performs proportional-integral control based on the deviation between the actual value of DC current and zero value to adjust the DC current to zero. The DC controller of the sending-end converter station switches to DC fault mode 1, directly controlling the DC internal potential output to zero, thereby regulating the DC voltage output to zero; The deviation between the actual value and the rated value of the capacitor voltage of the submodule at the sending end converter station is obtained, and the reference value of DC current is calculated by the proportional-integral controller. The current deviation is obtained by subtracting the DC current reference value from the actual DC current value, and the deviation is calculated by a proportional-integral controller. In DC fault mode 1, the calculation results of the deviation and feedforward DC voltage are ignored, and the DC internal potential of the sending-end converter station is forcibly set to zero value for output.

3. The method as described in claim 1, characterized in that, The S2 includes: Each power generation unit monitors the actual value of the AC frequency in real time. When the actual value of the AC frequency deviates from the rated frequency, it is determined to be a fault state. The machine-side converter updates the AC power reference value to the reference value obtained by the maximum power point tracking control based on the wind turbine speed, minus the reference value generated by the frequency response control, thereby switching to the unloaded operation mode. At the same time, it triggers the full-capacity unloading circuit configured inside each power generation unit to conduct, converting the surplus electrical energy converted from rotor kinetic energy into heat energy for dissipation.

4. The method as described in claim 3, characterized in that, The reference value generated by the frequency response control is produced by subtracting the rated frequency from the actual AC frequency of the wind turbine, and then proportionally controlling it. The calculation formula is as follows: in, The power reference value adjustment amount generated for frequency response control. This is the proportional control coefficient. This represents the actual AC frequency of the fan. This is the rated frequency.

5. The method as described in claim 1, characterized in that, The S3 includes: The sending-end converter station calculates the rate of change of the average voltage of the submodule capacitor in real time. When the rate of change is detected to be negative and the average voltage of the submodule capacitor reaches the preset overvoltage threshold, the DC controller is switched from DC fault mode 1 to DC fault mode 2. In DC fault mode 2, the DC current reference value is set to zero. Based on the deviation between the zero value and the actual negative DC current value, the proportional controller calculates and processes the voltage through the limiting circuit to output a negative DC voltage to quickly control the DC current to zero.

6. The method as described in claim 5, characterized in that, The negative DC voltage output after calculation by the proportional controller and processing by the limiting circuit includes: The current error signal is obtained by subtracting the negative actual value of the DC current from the zero DC current reference value. Multiply the current error signal by a scaling factor. A preliminary control level was obtained; The initial control quantity is subjected to amplitude limiting processing, and the upper limit is set to the rated value of DC voltage. The lower limit is ,in The ratio of the number of full-bridge submodules to the total number of modules in a hybrid modular multilevel converter is used as the DC internal potential output after limiting.

7. The method as described in claim 1, characterized in that, The S4 includes: The receiving-end converter station controls the DC voltage to rise from zero to the rated value at a preset ramp rate in order to establish the DC voltage of the flexible DC system. Once the DC voltage has been established, the sending-end converter station switches back to normal mode and controls the AC voltage frequency to return to the rated frequency. After the DC voltage is established, each power generation unit controls the active power to gradually increase to the target value according to the preset ramp curve, and at the same time disconnects the internal unloading circuit to stop working.

8. A DC fault ride-through device for a new energy islanded DC transmission system, characterized in that, include: The fault detection and control module is used to control the receiving-end converter station to enter the zero DC current mode and adjust the DC current to zero when a DC fault is detected at the sending-end converter station and the receiving-end converter station, and at the same time control the sending-end converter station to enter the zero DC voltage mode and adjust the DC voltage output to zero. The power regulation module of the power generation unit is used to identify the fault status of each power generation unit based on the AC side frequency change, switch the generator-side converter to the load reduction operation mode and trigger the internal unloading circuit to work to dissipate the surplus power. The converter station overvoltage suppression module is used to switch the DC control mode of the sending-end converter station to zero DC current mode when the sending-end converter station detects that the average value of the submodule capacitor voltage has dropped and reached the preset overvoltage threshold. It then outputs a negative DC voltage to quickly suppress the DC current to zero. The system fault recovery module is used to control the sending-end converter station and receiving-end converter station to return to normal working mode after the AC and DC power of the system is restored to balance and the fault is cleared, and to control the ramp of each power generation unit to restore active power output and stop the unloading circuit from working.

9. A computer device, characterized in that, Including processor and memory; The processor reads the executable program code stored in the memory to run the program corresponding to the executable program code, so as to implement the DC fault ride-through method of a new energy island DC transmission system as described in any one of claims 1-7.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements a DC fault ride-through method for a new energy islanded DC transmission system as described in any one of claims 1-7.

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