A net-type wind power diode rectifier direct current sending-out system and a control method thereof

Abstract

This invention relates to the field of offshore wind power DC transmission technology, and discloses a grid-connected wind power diode rectifier DC transmission system and its control method. The system includes a diode rectifier module, a black-start converter module, a bus voltage support module, and an onshore converter station. The black-start converter module dynamically adjusts the system's active power during the system startup phase after establishing the AC voltage of the offshore combiner bus based on an external AC power source. The bus voltage support module dynamically adjusts the system's reactive power after the offshore combiner bus voltage is established, maintaining the stability of the offshore combiner bus's AC voltage. This invention enables black-start and continuous energized operation of the offshore wind power diode rectifier transmission system without relying on grid-connected wind turbines, significantly improving the system's reliability and availability.

Description

Technical Field

[0001] This invention relates to the field of offshore wind power DC transmission technology, specifically to a grid-connected wind power diode rectifier DC transmission system and its control method. Background Technology

[0002] Long-distance offshore wind power transmission typically employs high-voltage direct current (HVDC) transmission technology. Offshore wind turbines generate electricity, which is collected via AC cables. Offshore converter stations then convert the AC power into DC power, which is transmitted to onshore converter stations via DC submarine cables. Currently, the converter valves in offshore wind power HVDC transmission projects all use the MMC (Multi-Chip Container Regulator) structure. However, MMC converter valves are expensive and bulky. To adapt to various application scenarios and reduce transmission costs, multiple collection and transmission topologies and networking schemes are commonly used, such as using diode-based unidirectional current-type uncontrolled rectifier converters at the sending end. Using diode-based unidirectional current-type uncontrolled rectifier converters at the sending end helps to achieve lightweight offshore platforms. However, diode-based uncontrolled rectifier valves lack the capability to construct offshore AC grids; therefore, offshore wind farms require grid-connected wind turbines.

[0003] However, existing pure diode check valves cannot transfer power from land to sea, making black start of offshore wind farms difficult. In the absence of wind, the entire offshore wind farm will be in a state of complete power loss and shutdown, making restarting difficult. Furthermore, grid-connected wind turbine technology is still in the research and development stage, with insufficient maturity. The control algorithm has not yet been standardized, and the hardware overload capacity and supporting energy storage requirements drive up costs. There is a lack of complete grid connection standards and operation and maintenance system, and the stability risks are prominent, which may lead to synchronous instability or oscillation. Summary of the Invention

[0004] In view of this, the present invention provides a grid-connected wind power diode rectifier DC transmission system and its control method to solve the problem that the black start of the existing offshore wind power diode rectifier DC transmission system must rely on the grid-connected wind turbine.

[0005] In a first aspect, the present invention provides a grid-connected wind power diode rectifier DC transmission system, comprising: a diode rectifier module, a black-start converter module, a bus voltage support module, and an onshore converter station, wherein the AC power output from the grid-connected wind turbine is collected to an offshore busbar via a medium-voltage AC cable; the AC side of the black-start converter module is connected to the offshore busbar, and the black-start converter module draws power from an external AC power source; the bus voltage support module is connected to the offshore busbar; the AC side of the diode rectifier module is connected to the offshore busbar, and the diode rectifier module… The positive terminal of the DC side is connected to the positive terminal of the onshore converter station via a positive DC submarine cable, and the negative terminal of the DC side of the diode rectifier module is connected to the negative terminal of the DC side of the onshore converter station via a negative DC submarine cable. The AC side of the onshore converter station is connected to the power grid. The black-start converter module is used to dynamically adjust the active power of the system after the AC voltage of the offshore combiner bus is established based on the external AC power supply during the system startup phase. The bus voltage support module is used to dynamically adjust the reactive power of the system after the voltage of the offshore combiner bus is established, so as to maintain the stability of the AC voltage of the offshore combiner bus.

[0006] The system provided by this invention solves the black-start problem of the inability of pure diode rectifier valves to build up voltage independently during the system startup phase by setting up a black-start converter module. After the bus voltage is established, a bus voltage support module takes over to maintain voltage stability, providing stable grid-connected voltage support for grid-connected wind turbines that lack grid-connection capabilities, thus breaking the technical limitation of traditional solutions that rely on grid-connected wind turbines. Through the coordinated operation of the black-start converter module dynamically adjusting active power after voltage establishment and the bus voltage support module dynamically adjusting reactive power, smooth conduction of the diode rectifier module and orderly grid connection of the wind turbines are achieved. Furthermore, during windless periods, the black-start converter module and the bus voltage support module work together to maintain bus energization, keeping the wind turbines in standby mode and avoiding the shutdown and restart problem caused by a complete power outage, significantly improving the system's operational reliability and availability.

[0007] In one alternative implementation, the diode rectifier module includes: a plurality of 12-pulse rectifier diode valves, wherein the DC side of each 12-pulse rectifier diode valve is connected in series.

[0008] In one optional implementation, the black-start converter module includes: a VSC converter, a diode rectifier, a first transformer, and a second transformer, wherein the DC side of the VSC converter is connected to the DC side of the diode rectifier, the AC side of the VSC converter is connected to the marine busbar through the first transformer, and the AC side of the diode rectifier is connected to an external AC power source through the second transformer.

[0009] In one alternative implementation, the bus voltage support module includes a grid-type SVG and a third transformer, wherein the grid-type SVG is connected to the offshore busbar via the third transformer.

[0010] Secondly, the present invention provides a control method for a grid-connected wind power diode rectifier DC transmission system, applicable to the system described in the first aspect or any corresponding embodiment. The method includes: controlling a black-start converter module to establish the AC voltage of the offshore combiner bus based on an external AC power source by simultaneously adjusting the active and reactive power of the system; when the AC voltage of the offshore combiner bus reaches a preset voltage, controlling the bus voltage support module to take over the reactive power regulation function of the black-start converter module to maintain the stability of the AC voltage of the offshore combiner bus; under the condition of stable AC voltage of the offshore combiner bus, controlling the black-start converter module to dynamically adjust the active power of the system after the grid-connected wind turbine is in standby mode, so that the diode rectifier module is turned on; when the diode rectifier module is turned on, controlling the grid-connected wind turbine to connect to the grid for power generation.

[0011] The method provided by this invention achieves orderly connection and stable operation of grid-connected wind turbines in diode rectifier DC transmission systems through a phased collaborative control strategy. During the startup phase, the black-start converter module is controlled to simultaneously regulate active and reactive power to establish the offshore bus voltage, solving the black-start problem where pure diode rectifier valves cannot autonomously build voltage. Once the bus voltage is established, the reactive power regulation function is smoothly transferred to the bus voltage support module, which maintains voltage stability and provides reliable grid-connected voltage support for grid-connected wind turbines that lack grid connection capabilities. Under stable voltage conditions, after the wind turbines are in standby mode, the black-start converter module gradually increases the active power output, allowing the diode rectifier module to smoothly conduct, avoiding current surges caused by direct grid connection. Finally, the wind turbines are controlled to connect to the grid in an orderly manner, achieving fully automated startup and operation of the system. This method not only makes technically mature grid-connected wind turbines applicable to diode rectifier transmission scenarios but also ensures a smooth transition in key stages such as black start, mode switching, and wind turbine grid connection, significantly improving the system's operational reliability and operability.

[0012] In one optional implementation, the process of controlling the bus voltage support module to take over the reactive power regulation function of the black-start converter module to maintain the stability of the AC voltage of the offshore bus includes: setting the current reactive power output value of the black-start converter module to the reactive power regulation target value of the bus voltage support module, so that the reactive power output of the black-start converter module gradually decreases to zero; switching the reactive power control of the bus voltage support module to a constant voltage amplitude control mode and setting the reactive power output of the black-start converter module to 0; switching the active power loop control of the bus voltage support module to an open-loop control mode and switching the active power loop control of the black-start converter module to a voltage following mode, so that the DC side voltage of the sub-modules in the bus voltage support module remains stable; the voltage following mode aims to stabilize the DC side voltage of the sub-modules.

[0013] In one optional implementation, when the active power loop control of the black-start converter module is switched to voltage follower mode, the active power value currently output by the black-start converter module is collected in real time, and this active power value is introduced into the active power loop control of the black-start converter module as a feedforward quantity.

[0014] In one optional implementation, after the grid-connected wind turbine is in standby mode, the process of controlling the black-start converter module to dynamically adjust the active power of the system to turn on the diode rectifier module includes: after the grid-connected wind turbine is started to standby mode, using the current active power output value of the black-start converter module as a power threshold; switching the reactive power control link of the bus voltage support module from the constant voltage amplitude control mode to the DC side average voltage feedback control mode of the sub-module to maintain the DC side voltage stability of the bus voltage support module; and based on the power threshold, gradually increasing the active power output of the black-start converter module until the diode rectifier module turns on.

[0015] In one optional implementation, the process of switching the reactive power control loop of the bus voltage support module from a constant voltage amplitude control mode to a DC-side average voltage feedback control mode of the sub-module to maintain the DC-side voltage stability of the bus voltage support module includes: acquiring the DC-side average voltage of the sub-module in real time and comparing the average voltage with a preset reference value; when the average voltage is greater than the reference value, controlling the bus voltage support module to increase the amplitude of its output voltage; when the average voltage is less than the reference value, controlling the bus voltage support module to decrease the amplitude of its output voltage.

[0016] In one optional implementation, the preset voltage is 95% of the diode rectifier module's turn-on voltage. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a composition diagram of a grid-connected wind power diode rectifier DC transmission system according to an embodiment of the present invention;

[0019] Figure 2 This is a detailed circuit diagram of a grid-connected wind power diode rectifier DC transmission system according to an embodiment of the present invention; Figure 3 This is a flowchart illustrating the control method of a grid-connected wind power diode rectifier DC transmission system according to an embodiment of the present invention. Figure 4 This is a schematic diagram of the first control strategy of the VSC converter according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the first control strategy for a network-type SVG according to an embodiment of the present invention; Figure 6 This is a schematic diagram of a second control strategy for a VSC converter according to an embodiment of the present invention; Figure 7 This is a schematic diagram of a second control strategy for a network-type SVG according to an embodiment of the present invention; Figure 8 This is a schematic diagram of a third control strategy for a VSC converter according to an embodiment of the present invention; Figure 9 This is a schematic diagram of a third control strategy for a network-type SVG according to an embodiment of the present invention; Figure 10 This is a schematic diagram of the fourth control strategy for a VSC converter according to an embodiment of the present invention; Figure 11 This is a schematic diagram of the fourth control strategy for a network-type SVG according to an embodiment of the present invention; Figure 12 This is a schematic diagram of the fifth control strategy for a VSC converter according to an embodiment of the present invention; Figure 13 This is a schematic diagram of the fifth control strategy for a network-type SVG according to an embodiment of the present invention; Figure 14 This is a diagram illustrating the composition of the control device for a grid-connected wind power diode rectifier DC transmission system according to an embodiment of the present invention. Figure 15 This is a schematic diagram of the hardware structure of an electronic device according to an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, 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.

[0021] It is understood that before using the technical solutions disclosed in the various embodiments of the present invention, users should be informed of the types, scope of use, and usage scenarios of the personal information involved in the present invention and their authorization should be obtained in accordance with relevant laws and regulations through appropriate means.

[0022] 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 one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0023] This embodiment provides a grid-connected wind power diode rectified DC power transmission system, such as... Figure 1 As shown, it includes: black start converter module 1, bus voltage support module 2, diode rectifier module 3 and onshore converter station 4.

[0024] Figure 1 In the middle, the AC power output of the grid-connected wind turbine is collected to the offshore busbar through a medium-voltage AC cable; the AC side of the black start converter module 1 is connected to the offshore busbar; the busbar voltage support module 2 is connected to the offshore busbar.

[0025] Specifically, Figure 1 In the process, the AC power generated by the grid-connected wind turbines is collected to the offshore busbar via medium-voltage AC cables, forming an AC collection network for the offshore wind farm. The AC side of the black start converter module 1 is connected to the offshore busbar, serving as the core power access point during the system startup phase; the busbar voltage support module 2 is also connected to the offshore busbar to provide continuous support after the voltage is established.

[0026] Figure 1 In this circuit, the AC side of diode rectifier module 3 is connected to the marine busbar, the positive DC side of diode rectifier module 3 is connected to the positive DC side of onshore converter station 4 via a positive DC submarine cable, and the negative DC side of diode rectifier module 3 is connected to the negative DC side of onshore converter station 4 via a negative DC submarine cable; the AC side of onshore converter station 4 is connected to the power grid.

[0027] Specifically, Figure 1 In this system, the diode rectifier module 3 and the onshore converter station 4 constitute a complete power transmission channel for offshore wind power DC transmission. This connection method employs a bipolar DC transmission structure, with positive and negative DC submarine cables corresponding to two polarity circuits, forming a symmetrical DC transmission system. The diode rectifier module 3, acting as the rectifier on the offshore side, converts the AC power from the offshore busbar into DC power; the onshore converter station 4, as the core converter equipment on the shore side, receives the DC power and prepares to invert it before connecting it to the grid. The positive and negative DC submarine cables, serving as the transmission medium connecting the offshore and onshore sides, provide bidirectional isolation and long-distance transmission.

[0028] Optionally, the onshore converter station adopts a half-bridge MMC topology; the diode rectifier module is an uncontrolled rectifier circuit based on diode devices.

[0029] Figure 1 In this system, the black-start converter module 1 draws power from an external AC power source. During system startup, after establishing the AC voltage of the offshore combiner bus based on the external AC power source, the black-start converter module 1 dynamically adjusts the system's active power. The bus voltage support module 2 dynamically adjusts the system's reactive power after the offshore combiner bus voltage is established, maintaining the stability of the offshore combiner bus's AC voltage.

[0030] Specifically, Figure 1 In the system startup phase, the black-start converter module 1 draws power from an external AC power source and injects active and reactive power into the offshore busbar through internal inverter control, realizing zero-start voltage boost and voltage establishment of the offshore AC busbar, thus solving the black-start problem that pure diode rectifier valves cannot build voltage independently. After the voltage of the offshore busbar is established, the black-start converter module 1 exits the voltage regulation role and takes on the task of dynamic regulation of active power.

[0031] Meanwhile, after the offshore bus voltage is established, bus voltage support module 2 takes over the reactive power regulation function. By dynamically adjusting the reactive power output, it maintains stable bus voltage, providing a stable grid-connected voltage environment for grid-connected wind turbines that lack grid-connection capabilities. The black-start converter module and bus voltage support module work together, with the black-start converter module building voltage and regulating active power, maintaining voltage stability with the bus voltage support module. This achieves a smooth transition from black start to normal operation, enabling grid-connected wind turbines that lack independent grid-connection capabilities to stably connect to the diode rectifier DC transmission system.

[0032] The system provided in this embodiment solves the black-start problem of the inability of pure diode rectifier valves to build up voltage independently by setting up a black-start converter module during the system startup phase. This is achieved by drawing power from an external AC power source to establish AC voltage on the offshore busbar. A busbar voltage support module maintains voltage stability after the busbar voltage is established, providing stable grid-connected voltage support for grid-connected wind turbines that lack grid-connection capabilities, thus breaking the technical limitation of traditional solutions that rely on grid-connected wind turbines. Through the coordinated operation of the black-start converter module dynamically adjusting active power after voltage establishment and the busbar voltage support module dynamically adjusting reactive power, smooth conduction of the diode rectifier module and orderly grid connection of the wind turbines are achieved. Furthermore, during windless periods, the black-start converter module and the busbar voltage support module work together to maintain busbar energization, keeping the wind turbines in standby mode and avoiding shutdown and restart issues caused by complete system power loss, significantly improving the system's operational reliability and availability.

[0033] In some alternative implementations, such as Figure 2 As shown, the diode rectifier module includes multiple 12-pulse rectifier diode valves 31, with the DC side of each 12-pulse rectifier diode valve 31 connected in series. The 12-pulse rectifier structure, through a combination of star and delta connections on the valve-side transformer, effectively eliminates characteristic harmonics such as the 5th and 7th orders, significantly reducing the harmonic content on the AC side and alleviating the filtering burden. The series connection of multiple valve groups on the DC side allows the DC voltage across each valve group to be accumulated, thereby meeting the voltage level requirements for high-voltage, high-capacity offshore wind power DC transmission.

[0034] Preferably, Figure 2 In the process, the diode rectifier module includes two 12-pulse rectifier diode valves 31. The marine busbar is connected to the two 12-pulse rectifier diode valves 31 through switches Brk3 and Brk4 and rectifier transformers T4 and T5 respectively.

[0035] In some alternative implementations, such as Figure 2 As shown, the black-start converter module includes: a VSC converter 11, a diode rectifier 12, a first transformer T1, and a second transformer T2. The DC side of the VSC converter 11 is connected to the DC side of the diode rectifier 12, and the AC side of the VSC converter 11 is connected to the marine busbar through the first transformer T1. The AC side of the diode rectifier 12 is connected to an external AC power supply through the second transformer T2.

[0036] Specifically, Figure 2In this system, VSC converter 11 is a voltage source converter (VSC), and diode rectifier 12 serves as the front-end uncontrolled rectifier unit, rectifying the AC power from the external AC power supply into DC power to establish a stable DC bus voltage for the subsequent VSC converter 11. VSC converter 11, as the back-end controllable inverter unit, injects active and reactive power into the marine bus via the first transformer T1 during system startup, based on this DC bus voltage, achieving zero-start voltage boost and voltage establishment of the AC bus. After the bus voltage is established, VSC converter 11 then undertakes the task of dynamic regulation of active power, gradually increasing the active power output in conjunction with the conduction control of diode rectifier module 3. Through the coordinated operation of this two-stage architecture, this module achieves both the black-start function of drawing power from the external AC power supply and the dual capability of continuing to participate in active power regulation after voltage establishment.

[0037] In some alternative implementations, such as Figure 2 As shown, the bus voltage support module 2 includes a grid-type SVG 21 and a third transformer T3, wherein the grid-type SVG 21 is connected to the marine busbar through the third transformer T3.

[0038] Specifically, Figure 2 In this system, the grid-connected SVG 21 is a Static Var Generator (SVG). After being stepped up by the third transformer T3, the SVG 21 connects to the offshore combiner bus via switch Brk5, undertaking the voltage support task during steady-state system operation. Employing a grid-connected control strategy, the SVG 21 can simulate the inertia and damping characteristics of a synchronous generator, autonomously establishing and maintaining a stable AC voltage amplitude and frequency, providing a reliable grid-connected voltage reference for grid-connected wind turbines that lack grid-connection capabilities. During system startup, the SVG 21 first establishes its own DC-side voltage through uncontrolled charging, then unlocks and gradually takes over reactive power regulation. After the bus voltage is established, it dynamically adjusts its reactive power output to quickly respond to voltage fluctuations on the offshore combiner bus, maintaining voltage stability within the rated range. The SVG 21 achieves voltage support through pure reactive power regulation, without relying on external communication or wind turbine participation, significantly improving the system's autonomous operation capability and disturbance rejection performance.

[0039] Specifically, Figure 2 In the process, the onshore converter station 4 is connected to the power grid via switch Brk2, transformer T6, and switch Brk1. Meanwhile, the offshore combiner bus is also connected to a filter, primarily used to filter out the 11th and 13th harmonics generated by the 12-pulse rectification.

[0040] This embodiment provides a control method for a grid-connected wind power diode rectifier DC transmission system, applicable to the system described in the above embodiment or any corresponding implementation, controlling the process from black start to normal operation of an offshore wind farm, such as... Figure 3 As shown, the method includes: Step S1: Control the black start converter module to establish the AC voltage of the marine busbar by simultaneously adjusting the active and reactive power of the system based on the external AC power supply.

[0041] Specifically, Figure 4 This is the control block diagram of the VSC converter at the current moment, where V dcfb V represents the average DC-side voltage value of the SVG submodule, used for DC voltage control. dcref The DC voltage reference value is the control target for the DC side voltage of the VSC; P vsc P represents the active power sample value of the VSC. vscfb The active power reference value for VSC is P, which is the control target for the active power of VSC. th The active power threshold, i.e., the VSC active power value recorded when the wind turbine is in standby mode, is used for subsequent conduction control; Q vscfb This is the reactive power reference value for the VSC, i.e., the sampled value of the reactive power actually output by the VSC; V 0vsc This is the initial reference value for the VSC voltage, i.e., the initial voltage setting value of VSC in VF control mode; V refvsc ω0 is the VSC voltage reference value, i.e., the control target for the VSC voltage amplitude; ω0 is the rated angular frequency; ω0 refvsc This is the VSC angular frequency reference value, i.e., the angular frequency reference value in VSC control.

[0042] Specifically, Figure 5 This is the control block diagram of the mesh-type SVG at the current moment, where V 0svg This is the initial reference value for the SVG voltage, i.e., the initial voltage setpoint of the SVG in constant voltage control mode; V 1svg This is the actual control value of the SVG voltage amplitude, i.e., the actual control value recorded during mode switching, used for smooth switching; ω refsvg This refers to the angular frequency reference value for SVG, i.e., the angular frequency reference value in SVG mesh control; V refsvg The SVG voltage reference value is the target value for controlling the SVG voltage amplitude; P svgfb Q is the reference value for the active power of the SVG, i.e., the control target for the active power of the SVG; vsc Q represents the reactive power sample value of VSC. svgfb This is the reference value for reactive power of the SVG, i.e., the control target for reactive power of the SVG.

[0043] Specifically, refer to Figure 4 and Figure 5 The specific control process of step S1 is as follows: (1) Close the switches Brk1 and Brk2 to unlock and start the onshore converter station, and establish the rated voltage of the DC side of the offshore diode rectifier valve. U dc .

[0044] (2) Close switches Brk3, Brk4, and Brk5. Then, the VSC converter is unlocked by VF control and starts to rise from zero until the voltage of the offshore bus reaches the preset voltage, which is 95% of the conduction voltage of the diode rectifier valve in the diode rectifier module.

[0045] (3) The grid-type SVG performs uncontrolled charging and then unlocks. Its control method adopts grid-type PQ control. Its reactive power reference command is set to 0, and its active power command adopts the sub-module voltage feedback control of the grid-type SVG. The main purpose is to keep the sub-module voltage of the grid-type SVG at the rated value.

[0046] Specifically, the control system activates the black-start converter module, enabling it to operate based on an external AC power supply. This module, through its internal VSC converter and employing a VF control strategy, simultaneously regulates the active and reactive power injected into the offshore bus. The injection of active power provides energy support to the bus, driving the voltage to rise from zero; the injection of reactive power is used for excitation, establishing and stabilizing the AC voltage amplitude of the bus. Through the coordinated regulation of both, the offshore bus voltage smoothly rises from zero to near the preset rated value, creating conditions for the subsequent activation of the bus voltage support module and grid connection of the wind turbine. This step utilizes the black-start converter module to simulate voltage source characteristics, solving the black-start problem where pure diode rectifier valves cannot autonomously build up voltage.

[0047] Step S2: When the AC voltage of the offshore busbar reaches the preset voltage, the control busbar voltage support module takes over the reactive power regulation function of the black start converter module to maintain the stability of the AC voltage of the offshore busbar.

[0048] The process by which the control bus voltage support module takes over the reactive power regulation function of the black-start converter module to maintain the stability of the AC voltage of the offshore bus includes: Step S21: Set the current reactive power output value of the black start converter module to the reactive power adjustment target value of the bus voltage support module, so that the reactive power output of the black start converter module gradually decreases to zero.

[0049] Specifically, refer to Figure 6 and Figure 7 After the SVG is running stably, record the active power value P output by the VSC at this time. vsc and reactive power value Q vscAt this point, the reactive power reference command of the SVG is set to Q. vsc At this point, the reactive power output of the VSC converter will gradually decrease to near zero.

[0050] Specifically, the current actual output Qvsc of the black-start converter module is assigned to the grid-type SVG as its reactive power reference value Qsvgfb. This serves as the target value for reactive power regulation, establishing a smooth transfer path for system reactive power. The grid-type SVG gradually takes over the reactive power regulation task from the offshore busbar, while simultaneously reducing the reactive power output of the VSC converter according to the control logic until its reactive power feedback value Qvsc drops to zero. This operation effectively avoids voltage fluctuations on the offshore busbar caused by sudden increases or decreases in reactive power, ensuring system voltage stability during the initial switching phase of reactive power regulation.

[0051] Step S22: Switch the reactive power control of the bus voltage support module to constant voltage amplitude control mode, and set the reactive power output of the black start converter module to 0.

[0052] Specifically, refer to Figure 8 and Figure 9 After the reactive power output of VSC drops to near zero, record the actual control value V of the voltage amplitude in SVG control at this time. 1svg Switch the VSC reactive power control command reference value to 0, and simultaneously switch the SVG reactive power control to constant voltage amplitude control. To reduce inrush current, the V in the SVG control... 0svg Change to V 1svg .

[0053] Specifically, after the initial transfer of reactive power is completed, the grid-type SVG of the bus voltage support module is switched to constant voltage control mode, using the grid-type SVG voltage reference value V. refsvg To anchor the voltage amplitude of the offshore combiner bus to the core control target, and at the same time, to adjust the Q of the VSC converter vscfb By setting it to zero, its reactive power output channel is completely shut down, and the reactive power regulation function is officially handed over, making the grid-type SVG the sole entity responsible for reactive power regulation and voltage support of the offshore busbar.

[0054] Step S23: Switch the active power loop control of the bus voltage support module to open-loop control mode, and switch the active power loop control of the black-start converter module to voltage follower mode, so that the DC-side voltage of the sub-modules within the bus voltage support module remains stable. Voltage follower mode aims to stabilize the DC-side voltage of the sub-modules. When switching the active power loop control of the black-start converter module to voltage follower mode, the current output active power value of the black-start converter module is collected in real time, and this active power value is introduced as a feedforward into the active power loop control of the black-start converter module.

[0055] Specifically, refer to Figure 10 and Figure 11 First, switch the active power loop control command of the SVG to open-loop control. Then, quickly switch the active power loop control command of the VSC to a feedback control strategy aimed at stabilizing the DC side voltage of the SVG single module. To avoid current surges, add the VSC active power sampling value P to this control loop. vsc It is a feedforward quantity.

[0056] Specifically, the P of the grid-type SVG in the bus voltage support module svgfb The control is set to open-loop control to eliminate the coupling interference of its active power regulation link to the offshore bus voltage, ensuring that the grid-type SVG focuses on reactive power regulation and voltage support; at the same time, the active power loop control of the VSC converter in the black-start converter module is switched to voltage follower mode, so that V dcfb For control reference, V dcref To control the target, real-time dynamic adjustments are made, and P is set at this time. vsc As a feedforward variable introduced into the control loop, it compensates for DC-side voltage variations in the grid-type SVG through precise active power regulation, thereby maintaining its DC-side voltage stability. This completes the smooth switching between VSC and SVG control modes.

[0057] Step S3: Under the condition that the AC voltage of the offshore busbar is stable, after the grid-connected wind turbine is in standby mode, control the black start converter module to dynamically adjust the active power of the system, so that the diode rectifier module is turned on.

[0058] After the grid-connected wind turbine unit is in standby mode, the process of controlling the black-start converter module to dynamically adjust the active power of the system, thereby turning on the diode rectifier module, includes: Step S31: After the grid-connected wind turbine is started to standby mode, the active power value output by the current black start converter module is used as the power threshold.

[0059] Specifically, after smoothly switching between VSC and SVG control modes based on the above steps, the offshore wind turbines are gradually started up, keeping all turbines in a standby state without generating electricity. After all turbines have completed their standby, the active power output of VSC is recorded as the active power threshold P. th .

[0060] Step S32: Switch the reactive power control loop of the bus voltage support module from the constant voltage amplitude control mode to the DC side average voltage feedback control mode of the sub-module in order to maintain the DC side voltage stability of the bus voltage support module.

[0061] For details, please refer to Figure 12 and Figure 13 The specific steps of step S32 are as follows: (1) Obtain the average DC voltage value of the submodule in real time and compare the average voltage value with the preset reference value.

[0062] Specifically, the DC-side voltage of the grid-type SVG submodule is acquired in real time to obtain V. dcfb Then, combine it with V dcref Real-time comparison calculations are performed to serve as the core basis for SVG output voltage amplitude control, establishing a precise numerical reference for subsequent closed-loop voltage amplitude adjustment, and ensuring that the triggering of control actions is always based on the deviation between the actual voltage and the target voltage.

[0063] (2) When the average voltage value is less than the reference value, the control bus voltage support module reduces the amplitude of its output voltage.

[0064] Specifically, when V dcfb Less than V dcref When the voltage amplitude control loop of the SVG is triggered, the downward adjustment command is triggered, which controls the grid-type SVG to reduce the amplitude of its output voltage. This adjustment action changes the voltage support of the SVG to the offshore busbar, thereby adjusting the voltage level of the DC side of the SVG submodule in the reverse direction, gradually reducing the deviation between the actual value and the reference value, and realizing the return of the DC side voltage to the reference value.

[0065] (3) When the average voltage value is greater than the reference value, the control bus voltage support module increases the amplitude of its output voltage.

[0066] Specifically, when V dcfb Greater than V dcref When the voltage amplitude control loop of the SVG is triggered, the upward adjustment command is activated, which controls the grid-type SVG to increase the amplitude of its output voltage. By increasing the voltage support strength of the SVG to the offshore busbar, the voltage state of the DC side of the SVG submodule is positively adjusted, gradually making up for the difference between the actual value and the reference value, so that the DC side voltage of the SVG submodule is stabilized within the preset reference value range.

[0067] Step S33: Based on the power threshold, control the active power output of the black-start converter module to gradually increase until the diode rectifier module is turned on.

[0068] Specifically, the VSC active power control command is switched to P at the same time. th And gradually increase P th The value is maintained until the 12-pulse diode rectifier is turned on, and then P is held. th The value remains unchanged until the 12-pulse diode rectifier valve is initially turned on.

[0069] Step S4: After the diode rectifier module is turned on, control the grid-connected wind turbine to generate electricity.

[0070] Specifically, during the conduction of the 12-pulse diode rectifier valve, the voltage of the offshore busbar remains essentially constant, at which point the offshore wind turbines gradually begin to connect to the grid and generate electricity. In the operating mode proposed in this embodiment, even if all offshore wind turbines shut down due to lack of wind, the offshore busbar can still be energized, waiting for the offshore wind turbines to restart and generate electricity.

[0071] The method provided in this embodiment achieves orderly connection and stable operation of grid-connected wind turbines in a diode rectifier DC transmission system through a phased collaborative control strategy. During the startup phase, the black-start converter module is controlled to simultaneously adjust active and reactive power to establish the offshore bus voltage, solving the black-start problem where pure diode rectifier valves cannot autonomously build voltage. Once the bus voltage is established, the reactive power regulation function is smoothly transferred to the bus voltage support module, which maintains voltage stability and provides reliable grid-connected voltage support for grid-connected wind turbines that lack grid connection capabilities. Under stable voltage conditions, after the wind turbines are in standby mode, the black-start converter module gradually increases the active power output, allowing the diode rectifier module to smoothly conduct, avoiding current surges caused by direct grid connection. Finally, the wind turbines are controlled to connect to the grid in an orderly manner, achieving fully automated startup and operation of the system. This method not only makes technically mature grid-connected wind turbines applicable to diode rectifier transmission scenarios but also ensures a smooth transition of the system in key stages such as black start, mode switching, and wind turbine grid connection, significantly improving the system's operational reliability and operability.

[0072] This embodiment also provides a control device for a grid-connected wind power diode rectifier DC transmission system. This device is used to implement the above embodiments and preferred embodiments, and details already described will not be repeated. As used below, the term "module" can refer to a combination of software and / or hardware that performs a predetermined function. Although the device described in the following embodiments is preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0073] This embodiment provides a control device for a grid-connected wind power diode rectifier DC transmission system, such as... Figure 14 As shown, it includes: The bus voltage building module 1401 is used to control the black start converter module to establish the AC voltage of the marine busbar based on the external AC power supply by simultaneously adjusting the active and reactive power of the system.

[0074] The reactive power switching module 1402 is used to control the bus voltage support module to take over the reactive power regulation function of the black start converter module when the AC voltage of the offshore bus reaches the preset voltage, so as to maintain the stability of the AC voltage of the offshore bus.

[0075] The rectifier turn-on module 1403 is used to control the active power of the black start converter module to dynamically adjust the system after the grid-connected wind turbine is in standby mode, under the condition that the AC voltage of the offshore busbar is stable, so that the diode rectifier module is turned on.

[0076] The wind turbine grid connection module 1404 is used to control the grid-connected wind turbine to generate electricity when the diode rectifier module is turned on.

[0077] The control device for the grid-connected wind power diode rectifier DC transmission system provided in this embodiment of the invention can execute the method provided in any embodiment of the invention, and has the corresponding functional modules and beneficial effects for executing the method. Further functional descriptions of the above modules and units are the same as in the corresponding embodiments described above, and will not be repeated here. Figure 15 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention.

[0078] The following is a detailed reference. Figure 15 The diagram illustrates a structural schematic suitable for implementing an electronic device according to embodiments of the present invention. The electronic device may include a processor (e.g., a central processing unit, graphics processor, etc.) 001, which can perform various appropriate actions and processes according to a program stored in read-only memory (ROM) 002 or a program loaded from memory 008 into random access memory (RAM) 003. The RAM 003 also stores various programs and data required for the operation of the electronic device. The processor 001, ROM 002, and RAM 003 are interconnected via bus 004. An input / output (I / O) interface 005 is also connected to bus 004.

[0079] Typically, the following devices can be connected to I / O interface 005: input devices 006 including, for example, touchscreens, touchpads, keyboards, mice, cameras, microphones, accelerometers, gyroscopes, etc.; output devices 007 including, for example, liquid crystal displays (LCDs), speakers, vibrators, etc.; memory devices 008 including, for example, magnetic tapes, hard disks, etc.; and communication devices 009. Communication device 009 allows electronic devices to exchange data via wireless or wired communication with other devices. Although Figure 15 Electronic devices with various devices are shown, but it should be understood that it is not required to implement or have all of the devices shown, and more or fewer devices may be implemented or have instead.

[0080] In particular, according to embodiments of the present invention, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments of the present invention include a computer program product comprising a computer program carried on a non-transitory computer-readable medium, the computer program containing program code for performing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network via communication device 009, or installed from memory 008, or installed from ROM 002. When the computer program is executed by processor 001, it performs the functions defined in the methods of the embodiments of the present invention.

[0081] Figure 15 The electronic device shown is merely an example and should not be construed as limiting the functionality and scope of use of the embodiments of the present invention.

[0082] This invention also provides a computer-readable storage medium. The methods described above according to embodiments of the invention can be implemented in hardware or firmware, or implemented as computer code that can be recorded on a storage medium, or implemented as computer code downloaded via a network and originally stored on a remote storage medium or a non-transitory machine-readable storage medium and then stored on a local storage medium. Thus, the methods described herein can be processed by software stored on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. The storage medium can be a magnetic disk, optical disk, read-only memory, random access memory, flash memory, hard disk, or solid-state drive, etc.; further, the storage medium can also include combinations of the above types of memory. It is understood that computers, processors, microprocessor controllers, or programmable hardware include storage components capable of storing or receiving software or computer code, which, when accessed and executed by the computer, processor, or hardware, implements the methods shown in the above embodiments.

[0083] A portion of this invention can be applied as a computer program product, such as computer program instructions, which, when executed by a computer, can invoke or provide the methods and / or technical solutions according to the invention through the operation of the computer. Those skilled in the art will understand that the forms in which computer program instructions exist in a computer-readable medium include, but are not limited to, source files, executable files, installation package files, etc. Correspondingly, the ways in which computer program instructions are executed by a computer include, but are not limited to: the computer directly executing the instructions, or the computer compiling the instructions and then executing the corresponding compiled program, or the computer reading and executing the instructions, or the computer reading and installing the instructions and then executing the corresponding installed program. Here, the computer-readable medium can be any available computer-readable storage medium or communication medium accessible to a computer.

[0084] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A grid-connected wind power diode rectifier DC transmission system, characterized in that, include: Diode rectifier modules, black-start converter modules, bus voltage support modules, and onshore converter stations, among which, The AC power output from the grid-connected wind turbine is collected into the offshore busbar via a medium-voltage AC cable; The AC side of the black-start converter module is connected to the marine busbar, and the black-start converter module draws power from an external AC power source. The bus voltage support module is connected to the marine busbar; The AC side of the diode rectifier module is connected to the marine busbar, the positive DC side of the diode rectifier module is connected to the positive DC side of the onshore converter station via a positive DC submarine cable, and the negative DC side of the diode rectifier module is connected to the negative DC side of the onshore converter station via a negative DC submarine cable. The AC side of the onshore converter station is connected to the power grid; The black-start converter module is used to dynamically adjust the active power of the system after establishing the AC voltage of the marine busbar based on the external AC power supply during the system startup phase. The bus voltage support module is used to dynamically adjust the reactive power of the system after the offshore bus voltage is established, so as to maintain the stability of the AC voltage of the offshore bus.

2. The system according to claim 1, characterized in that, The diode rectifier module includes: multiple 12-pulse rectifier diode valves, with the DC side of each 12-pulse rectifier diode valve connected in series.

3. The system according to claim 1, characterized in that, The black-start converter module includes: a VSC converter, a diode rectifier, a first transformer, and a second transformer, wherein... The DC side of the VSC converter is connected to the DC side of the diode rectifier, and the AC side of the VSC converter is connected to the marine busbar through the first transformer. The AC side of the diode rectifier is connected to the external AC power supply via the second transformer.

4. The system according to claim 1, characterized in that, The bus voltage support module includes: a grid-type SVG and a third transformer, wherein... The grid-type SVG is connected to the marine busbar via the third transformer.

5. A control method for a grid-connected wind power diode rectifier DC transmission system, characterized in that, Applied to the system according to any one of claims 1 to 4, the method comprises: The black-start converter module is controlled by an external AC power supply, and the AC voltage of the marine busbar is established by simultaneously adjusting the active and reactive power of the system. When the AC voltage of the offshore busbar reaches the preset voltage, the busbar voltage support module takes over the reactive power regulation function of the black start converter module to maintain the stability of the AC voltage of the offshore busbar. Under the condition that the AC voltage of the offshore busbar is stable, after the grid-connected wind turbine is in standby mode, the black-start converter module is controlled to dynamically adjust the active power of the system, so that the diode rectifier module is turned on. When the diode rectifier module is turned on, it controls the grid-connected wind turbine to generate electricity.

6. The method according to claim 5, characterized in that, The process by which the control bus voltage support module takes over the reactive power regulation function of the black-start converter module to maintain the stability of the AC voltage of the offshore bus includes: Set the current reactive power output value of the black-start converter module to the reactive power adjustment target value of the bus voltage support module, so that the reactive power output of the black-start converter module gradually decreases to zero. Switch the reactive power control of the bus voltage support module to constant voltage amplitude control mode, and set the reactive power output of the black start converter module to 0. The active loop control of the bus voltage support module is switched to open loop control mode, and the active loop control of the black start converter module is switched to voltage follower mode, so that the DC side voltage of the sub-modules in the bus voltage support module remains stable. The voltage follower mode aims to stabilize the DC-side voltage of the submodule.

7. The method according to claim 6, characterized in that, When the active power loop control of the black-start converter module is switched to voltage follower mode, the active power value currently output by the black-start converter module is collected in real time, and this active power value is introduced into the active power loop control of the black-start converter module as a feedforward quantity.

8. The method according to claim 6, characterized in that, After the grid-connected wind turbine unit is in standby mode, the process of controlling the black-start converter module to dynamically adjust the active power of the system, thereby turning on the diode rectifier module, includes: After the grid-connected wind turbine is started to standby mode, the active power value output by the black start converter module is used as the power threshold. The reactive power control loop of the bus voltage support module is switched from the constant voltage amplitude control mode to the DC side average voltage feedback control mode of the sub-module in order to maintain the DC side voltage stability of the bus voltage support module. Based on the power threshold, the active power output of the black-start converter module is gradually increased until the diode rectifier module is turned on.

9. The method according to claim 8, characterized in that, The process of switching the reactive power control loop of the bus voltage support module from the constant voltage amplitude control mode to the DC-side average voltage feedback control mode of the sub-module to maintain the DC-side voltage stability of the bus voltage support module includes: The average DC-side voltage of the submodule is acquired in real time, and the average voltage is compared with a preset reference value. When the average voltage is greater than the reference value, the bus voltage support module is controlled to increase the amplitude of its output voltage. When the average voltage is less than the reference value, the bus voltage support module is controlled to reduce the amplitude of its output voltage.

10. The method according to claim 5, characterized in that, The preset voltage is 95% of the turn-on voltage of the diode rectifier module.

Images