Offshore wind power transmission system and its starting method, starting device and electronic equipment

Abstract

The present application relates to a system starting method. In view of the technical problem that the current starting and charging process of the offshore MMC cannot directly obtain energy from the onshore MMC, resulting in inconvenience in application, an offshore wind power transmission system and its starting method, starting device, and electronic equipment are provided. The grid-side VSC converter of the diesel generator is unlocked in the V / f control mode, and the sub-modules of the offshore MMC are charged by the diesel generator. After the control mode of the diesel generator is switched to the P / Q control mode, the active power and reactive power of the offshore MMC are controlled, and the diesel generator is used to provide the power required for starting the offshore MMC and some wind turbines. This can solve the problem that the offshore MMC cannot directly obtain energy from the onshore MMC due to the reverse cutoff of the DRU, reduce the voltage and current impact of the offshore wind power transmission system startup process, and enable the offshore wind power transmission system to start reliably and smoothly.

Description

Technical Field

[0001] The present application relates to a system startup method, and specifically to an offshore wind power transmission system and a startup method, a startup device, and electronic equipment thereof. Background Art

[0002] With the development of offshore wind power in a large scale and offshore, the solution based on the series connection of diode rectifier unit (DRU) and modular multilevel converter (MMC) has the characteristics of smaller size, lower weight and cost, and better economic benefits compared with the more widely used pure flexible direct current solution, and has therefore attracted widespread attention.

[0003] However, the offshore MMC is connected in series with the DRU. Due to the reverse cutoff characteristics of the offshore DRU, the startup and charging process of the offshore MMC cannot directly draw energy from the onshore MMC. Therefore, the conventional startup and charging method of the offshore MMC cannot be used directly, which brings many inconveniences in application. Summary of the invention

[0004] The present application aims to solve the technical problem that the startup and charging process of the current offshore MMC cannot directly obtain energy from the onshore MMC, resulting in inconvenience in application, and provides an offshore wind power transmission system and its startup method, startup device, and electronic equipment.

[0005] In order to achieve the above objectives, this application adopts the following technical solutions:

[0006] In a first aspect, the present application proposes a method for starting an offshore wind power transmission system, wherein the offshore wind power transmission system comprises a plurality of offshore wind farms, an offshore converter system, an onshore MMC and an AC power grid, wherein the plurality of offshore wind farms are connected in parallel to form an offshore AC bus; the offshore converter system comprises a diesel generator connected to the offshore AC bus, a filter circuit, a DRU connected in series and an offshore MMC; and comprises:

[0007] The submodules of the onshore MMC are charged through the AC power grid, and after the charging is completed, the onshore MMC is unlocked to establish the DC voltage of the offshore wind power transmission system to a first preset value;

[0008] The grid-side VSC converter of the diesel generator is unlocked in a V / f control mode, and the submodule of the offshore MMC is charged by the diesel generator. At the same time, the offshore AC bus voltage is established to a second preset value;

[0009] Controllable charging of the offshore MMC through a diesel generator;

[0010] The d-axis of the AC bus voltage on the offshore side is controlled by the active control loop of the offshore MMC, and the q-axis of the AC bus voltage on the offshore side is controlled by the reactive control loop of the offshore MMC;

[0011] Performing DC voltage balance control on the offshore MMC;

[0012] Switch the control mode of the diesel generator to the P / Q control mode, control the active power and reactive power of the diesel generator, and provide starting power for the converters of some wind turbines;

[0013] The offshore wind farm is gradually connected to the grid and the wind turbines are gradually started. At the same time, during the process of gradual connection to the grid and gradual start-up, the DRU is put into operation to complete the start-up of the offshore wind power transmission system.

[0014] Furthermore, before the grid-side VSC converter of the diesel generator is unlocked in the V / f control mode, the method further includes:

[0015] Unlock the diesel generator side converter and build up the DC voltage of the diesel generator side converter to the rated value.

[0016] Furthermore, the second preset value is greater than the voltage of the grid connection point of the offshore wind farm and less than the voltage of the grid connection point at which the DRU operates.

[0017] Further, the controlling of the d-axis of the offshore AC bus voltage by the offshore MMC active control loop and the controlling of the q-axis of the offshore AC bus voltage by the offshore MMC reactive control loop include:

[0018] The control system of the offshore MMC is enabled to lock the voltage and phase of the current offshore wind farm grid connection point to obtain a locked voltage value and a locked phase;

[0019] Set the AC voltage reference value to the locked voltage value and unlock it;

[0020] The d-axis of the AC bus voltage on the offshore side is controlled through the active control loop of the offshore MMC; wherein the d-axis voltage set value is the AC voltage reference value;

[0021] The q-axis of the AC bus voltage on the offshore side is controlled by the offshore MMC reactive power control loop; wherein the q-axis voltage set value is 0pu;

[0022] The control system phase angle of the offshore MMC is corrected according to the locked phase so that the offshore AC bus voltage reaches the AC voltage reference value.

[0023] Furthermore, the controllable charging of the offshore MMC by the diesel generator includes:

[0024] The offshore MMC is controlled and charged by the diesel generator until the voltage of the power module in the offshore MMC reaches 0.98pu;

[0025] The first preset value is 1pu;

[0026] The second preset value is 0.7 pu.

[0027] Furthermore, the DC voltage balance control on the offshore MMC includes:

[0028] If the DC port voltage of the offshore MMC is less than the DC port voltage reference value of the offshore MMC, the d-axis voltage given value is reduced;

[0029] If the DC port voltage of the offshore MMC is greater than the DC port voltage reference value of the offshore MMC, the d-axis voltage given value is increased;

[0030] The method for obtaining a given value of a d-axis voltage comprises:

[0031] According to the difference between the DC port voltage of the offshore MMC and the DC port voltage reference value of the offshore MMC, a regulation result is obtained through a PI regulator;

[0032] The d-axis voltage given value is obtained according to the sum of the adjustment result and the offshore MMC valve side voltage reference value.

[0033] Furthermore, the offshore wind farm is gradually connected to the grid and the wind turbines are gradually started. Meanwhile, during the process of gradual connection to the grid and gradual start-up, the DRU is put into operation, including:

[0034] Connect some offshore wind farms to the grid and start up some wind turbines;

[0035] Increase the power of some of the started wind turbines, and at the same time, control the voltage of the offshore MMC to increase the voltage of the offshore wind farm grid connection point to the DRU operation value;

[0036] The DC voltage balance controller in the offshore MMC controls the voltage at the offshore wind farm grid connection point, so that the power distribution between the DRU and the offshore MMC meets the preset requirements;

[0037] The remaining offshore wind farms are connected to the grid, and the number of filter groups required to be invested in the filter circuit is determined according to the active power of the offshore wind farm grid connection point.

[0038] In the second aspect, the present application proposes a starting device for an offshore wind power transmission system, wherein the offshore wind power transmission system includes multiple offshore wind farms, an offshore converter system, an onshore MMC and an AC power grid, wherein the multiple offshore wind farms are connected in parallel to form an offshore AC bus; the offshore converter system includes a diesel generator connected to the offshore AC bus, a filter circuit, a DRU connected in series and an offshore MMC; including:

[0039] The onshore MMC charging module is used to control the charging of the onshore MMC submodules through the AC power grid, unlock the onshore MMC after the charging is completed, and establish the DC voltage of the offshore wind power transmission system to a first preset value;

[0040] The offshore MMC charging module is used to control the grid-side VSC converter of the diesel generator to unlock in a V / f control mode, charge the submodules of the offshore MMC through the diesel generator, and at the same time, establish the offshore AC bus voltage to a second preset value;

[0041] The offshore MMC controllable charging module is used to control the offshore MMC to be charged in a controlled manner through a diesel generator;

[0042] The offshore MMC voltage control module is used to control the d-axis of the offshore AC bus voltage through the offshore MMC active control loop, and to control the q-axis of the offshore AC bus voltage through the offshore MMC reactive control loop;

[0043] An offshore MMC balancing control module, used for controlling the DC voltage balancing control of the offshore MMC;

[0044] A switching module is used to control the control mode of the diesel generator to switch to the P / Q control mode, control the active power and reactive power of the diesel generator, and provide starting power for the converters of some wind turbines;

[0045] The grid connection and DRU input module is used to control the gradual grid connection of the offshore wind farm and the gradual start-up of the wind turbines. At the same time, during the process of gradual grid connection and gradual start-up, the DRU is put into operation to complete the startup of the offshore wind power transmission system.

[0046] In a third aspect, the present application proposes an electronic device, comprising at least one memory and at least one processor; the memory stores an application, the processor calls the application stored in the memory, and the application is used to control the implementation of the above-mentioned offshore wind power transmission system startup method.

[0047] In a fourth aspect, the present application proposes an offshore wind power transmission system, which is started using the above-mentioned offshore wind power transmission system starting method.

[0048] Compared with the prior art, this application has the following beneficial effects:

[0049] The present application proposes a method for starting an offshore wind power transmission system, which effectively controls the voltage of multiple links during the startup process of the offshore wind power transmission system to ensure the startup effect. The grid-side VSC converter of the diesel generator is unlocked in the V / f control mode, and the submodule of the offshore MMC is charged by the diesel generator. After the control mode of the diesel generator is switched to the P / Q control mode, the active power and reactive power of the diesel generator are controlled, and the diesel generator is used to provide the power required for starting the offshore MMC and some wind turbines. This can solve the problem that the offshore MMC cannot directly obtain energy from the onshore MMC due to the reverse cutoff of the DRU, reduce the voltage and current impact during the startup process of the offshore wind power transmission system, and enable the offshore wind power transmission system to start reliably and smoothly.

[0050] The present application also proposes an offshore wind power transmission system starting device, an electronic device, and an offshore wind power transmission system, which have all the advantages of the above-mentioned offshore wind power transmission system starting method. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0052] Figure 1 Schematic diagram of a hybrid offshore wind power transmission system using DRU and MMC in series on the offshore side;

[0053] Figure 2 This is a first flow chart of a method for starting an offshore wind power transmission system in this application:

[0054] Figure 3 This is a second flow chart of a method for starting an offshore wind power transmission system according to the present application;

[0055] Figure 4 This is a schematic diagram of DC voltage balance control of the offshore MMC in an embodiment of the present application;

[0056] Figure 5 A schematic diagram of a starting device for an offshore wind power transmission system of the present application;

[0057] 1-Diesel generator, 2-Filter circuit, 3-Offshore converter system, 4-Onshore converter, 5-AC power grid. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0059] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0060] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0061] In the description of the embodiments of the present application, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the invented product is usually placed when used. It is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0062] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0063] In the description of the embodiments of the present application, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0064] DRU is an uncontrolled rectifier unit composed of diodes, which can convert AC power into DC power. When the AC voltage exceeds the conduction voltage of the diode, the diode starts to conduct, and the current flows from the anode to the cathode, realizing the rectification function. In the offshore wind power transmission system, DRU is usually used in series with MMC. DRU is mainly responsible for converting AC power into DC power, while MMC is responsible for providing stable AC voltage and realizing functions such as reactive power compensation and harmonic suppression of the system.

[0065] The structure of DRU itself is relatively simple and does not require complex control strategies. In addition, the loss of DRU is relatively low, which helps to improve the overall efficiency of the system. MMC itself is composed of multiple sub-modules in cascade, but in the series connection with DRU, the capacity of MMC can be designed to be relatively small, mainly used to provide the power, voltage and frequency support required for wind turbine startup, and to compensate for the harmonic current introduced by DRU. Therefore, compared with the large-capacity MMC in the pure flexible direct current solution, the volume and weight can also be effectively controlled.

[0066] Therefore, using DRU and MMC in series can give full play to the advantages of both, significantly reducing the volume and weight of the entire system compared to the pure flexible direct current solution. This is especially important for application scenarios such as offshore wind power that require long-distance transmission and have strict restrictions on equipment weight.

[0067] If the DRU and MMC are connected in series, the current must pass through the DRU and MMC in sequence. During the startup phase, the offshore MMC needs to establish a DC voltage and current to enter normal working conditions. However, due to the reverse cutoff characteristics of the DRU, when the offshore MMC attempts to obtain energy from the onshore MMC, if the voltage direction at both ends of the DRU is reversed at this time, the DRU will prevent the flow of current, resulting in the offshore MMC being unable to directly obtain energy.

[0068] In the Chinese invention patent with publication number CN116613822A, a method and device for starting an offshore wind power transmission system are disclosed. The method mainly includes: starting the onshore MMC, establishing the DC voltage of the offshore wind power transmission system to the rated DC voltage of the offshore MMC; after the DC voltage of the offshore wind power transmission system is stable, unlocking the offshore MMC, and establishing the AC bus voltage on the offshore side to the corresponding numerical range under the condition that the series diode is not started; after the AC bus voltage on the offshore side is stable, controlling the offshore wind power transmission system to boost to a preset range and the diode uncontrolled rectifier unit DRU is put into use. This invention patent provides a hybrid offshore wind power transmission system startup solution based on the use of DRU and MMC in series on the rectifier side, which solves the problem that the offshore MMC cannot directly draw energy from the onshore MMC due to the reverse cutoff of the series diode rectifier unit, reduces the voltage and current impact of the system startup process, and enables the system to start reliably and smoothly. However, this method adds a bypass switch of the auxiliary starting transformer and the diode rectifier unit, which requires more complex system coordination control.

[0069] Based on the above situation, the present application proposes an offshore wind power transmission system and its starting method, starting device, and electronic equipment, which are mainly used for a hybrid offshore wind power transmission system using DRU and MMC in series on the rectifier side. The present application is described in detail below in conjunction with embodiments and drawings.

[0070] like Figure 1 The figure shows a schematic diagram of a hybrid offshore wind power transmission system using DRU and MMC in series on the offshore side. It mainly includes multiple offshore wind farms ( Figure 1 A1 to An in the figure), diesel generator 1, filter circuit 2, offshore converter system 3, onshore converter 4 and AC power grid 5. Among them, multiple offshore wind farms are responsible for converting wind energy into electrical energy and generating AC power as the power source of the entire offshore wind power transmission system. The offshore converter system 3 mainly includes a diesel generator 1, a filter circuit 2, a DRU and an MMC. The DRU and the MMC are connected in series on the DC side. The DRU rectifies the AC power output by the offshore wind farm into DC power. The MMC can be started by an external power supply when the offshore wind power transmission system is shut down, and provide starting power for the offshore wind farm. The filter circuit 2 performs filtering processing. The diesel generator 1 is usually used as a black start power supply. When the offshore wind power transmission system is initially started or the main power grid fails, the diesel generator 1 can start quickly and provide necessary power. The onshore converter 4 inverts the received DC power into AC power and feeds it into the AC power grid 5. In fact, the onshore MMC can be used to realize the DC to AC inversion process. Figure 1 BRK1, BRK2, BRK11, BRKAC1 to BRKAC3 in the figure all represent circuit breakers.

[0071] like Figure 2As shown, it is a first flow chart of a method for starting an offshore wind power transmission system of the present application, which may include:

[0072] S101, charging the submodules of the onshore MMC through the AC power grid 5, unlocking the onshore MMC after the charging is completed, and establishing the DC voltage of the offshore wind power transmission system to a first preset value.

[0073] In practical applications, the AC power grid 5 performs uncontrolled charging and controllable charging on the submodules of the onshore MMC. When the capacitor voltages of all submodules in the onshore MMC reach a preset value and become stable, the charging process is considered complete.

[0074] It should be noted that the first preset value is a DC voltage target value set according to the design and operation requirements of the offshore wind power transmission system, which can ensure that the offshore wind power transmission system can operate stably and meet the power transmission requirements of the offshore wind power transmission system.

[0075] S102, unlocking the grid-side VSC converter of the diesel generator 1 in V / f control mode, charging the submodules of the offshore MMC through the diesel generator 1, and at the same time, establishing the offshore AC bus voltage to a second preset value.

[0076] It should be noted that the VSC converter (Voltage Source Converter) is a converter composed of devices with shutdown capabilities, which can monitor the grid status in real time, actively intervene in the grid operation, and remind operators when necessary. V / f control (Volt / Frequency Control) is the control of the voltage amplitude and frequency to maintain the voltage and frequency stability of the power system. In the grid-side VSC converter of the diesel generator 1, the V / f control mode adjusts the output voltage and frequency of the grid-side VSC converter to keep it consistent with the set reference value.

[0077] When the submodules of the offshore MMC are charged by the diesel generator 1, the diesel generator 1 is used as a power source to provide charging current to the submodules of the offshore MMC through the grid-side VSC converter that has been unlocked and entered into the V / f control mode.

[0078] S103, controllably charging the offshore MMC through a diesel generator.

[0079] S104, controlling the d-axis of the offshore AC bus voltage through the offshore MMC active control loop, and controlling the q-axis of the offshore AC bus voltage through the offshore MMC reactive control loop.

[0080] It should be noted that the AC voltage can be decomposed into two components, the d-axis and the q-axis, through Park transformation. The d-axis component is usually in phase with the voltage, while the q-axis component is perpendicular to the d-axis component. The d-axis component and the q-axis component of the AC bus voltage on the offshore side can be directly controlled.

[0081] S105, performing DC voltage balance control on the offshore MMC.

[0082] S106, switching the control mode of the diesel generator 1 to the P / Q control mode, controlling the active power and reactive power of the diesel generator 1, and providing starting power for the converters of some wind turbines.

[0083] It should be noted that in the P / Q control (Power / Reactive Power Control) mode, the active power and reactive power output by the diesel generator 1 can be controlled independently.

[0084] S107, gradually connecting the offshore wind farm to the grid and gradually starting the wind turbines. Meanwhile, during the process of gradually connecting to the grid and gradually starting, the DRU is put into operation to complete the startup of the offshore wind power transmission system.

[0085] like Figure 3 As shown, it is a second flow chart of a method for starting an offshore wind power transmission system of the present application, which may include:

[0086] S201 , starting the onshore MMC, and charging the submodules of the onshore MMC through the AC power grid 5 .

[0087] S202, after the charging in step S201 is completed, unlock the onshore MMC and steadily establish the DC voltage of the offshore wind power transmission system to 1pu.

[0088] S203, diesel generator 1 starts.

[0089] After the DC voltage of the offshore wind power transmission system is stably established to 1pu, close the five circuit breakers BRK1, BRK2, BRKAC1, BRKAC2 and BRKAC3, unlock the diesel generator 1 side converter first, and establish the DC voltage of the diesel generator 1 side converter to the rated value.

[0090] The grid-side VSC converter of diesel generator 1 is unlocked in V / f control mode, and the offshore AC bus voltage is established to 0.7pu while charging the submodules of the offshore MMC, and the diesel generator 1 is started. In actual applications, the offshore AC bus voltage is established to 0.7pu, which is usually greater than the voltage of the offshore wind farm grid connection point and less than the grid connection point voltage of the DRU operation.

[0091] S204, start the offshore side MMC.

[0092] First, the offshore MMC is controllably charged through the diesel generator 1, and the power module of the offshore MMC is gradually cut off at a certain rate until the power module voltage reaches 0.98pu, and the controllable charging is completed.

[0093] After the controllable charging is completed, the control system of the offshore MMC locks the voltage and phase of the current offshore wind farm grid connection point to obtain the locked voltage value and locked phase. Then the AC voltage reference value is set to the locked value and unlocked. The d-axis of the offshore AC bus voltage is controlled by the offshore MMC active control loop, and the d-axis voltage setting value is the AC voltage reference value. The q-axis of the offshore AC bus voltage is controlled by the offshore MMC reactive control loop, and the q-axis voltage setting value is 0pu. Finally, the phase angle of the control system of the offshore MMC is the phase angle corrected according to the locked phase, the offshore AC bus voltage reaches the reference value, and the startup of the offshore MMC is completed.

[0094] S205, DC voltage balance control of the MMC in series on the offshore side.

[0095] The AC current change process of the DRU during the phase change process is approximately linear, so the DC side voltage of the DRU composed of multiple units is for:

[0096]

[0097] in, is the number of 6-pulse DRUs, and the number of 12-pulse DRUs is 2, is the effective value of the fundamental line voltage when the valve side is open. is the power factor angle, is the commutation overlap angle.

[0098] Ignoring the effect of the commutation process, the DC side voltage of the DRU is The second term in the formula is 0, so:

[0099]

[0100] Active power of DRU P dc_DR It can be expressed as:

[0101]

[0102] in, It is the DC current at the outlet of the diode rectifier valve in the DRU.

[0103] Therefore, when the valve side of the DRU is open, the effective value of the fundamental line voltage is Less than / (1.35 ), the DRU does not transmit power. The active power of the DRU is proportional to the line voltage on the valve side of the DRU, that is, proportional to the line voltage at the grid connection point of the offshore wind farm.

[0104] If the proportion of active power of the offshore MMC is to be controlled, the DC voltage of the offshore MMC needs to be controlled. Therefore, the result of the DC voltage controller of the offshore MMC can be superimposed on the d-axis reference value of the offshore MMC. When the DC port voltage of the offshore MMC is less than the DC port voltage reference value of the offshore MMC, the d-axis reference value of the offshore MMC is reduced, thereby reducing the AC voltage at the grid connection point of the offshore wind farm, reducing the active power of the DRU, and increasing the active power of the offshore MMC, thereby achieving the purpose of increasing the DC voltage of the offshore MMC. Similarly, when the DC port voltage of the offshore MMC is greater than the DC port voltage reference value of the offshore MMC, the d-axis reference value of the offshore MMC is increased, thereby increasing the AC voltage at the grid connection point of the offshore wind farm, increasing the active power of the DRU, and reducing the active power of the offshore MMC, thereby achieving the purpose of reducing the DC voltage of the offshore MMC. d-axis voltage given value It can be expressed as:

[0105]

[0106] in, is the valve side voltage reference value of the offshore MMC, is the proportional coefficient of the DC voltage controller, is the integral coefficient of the DC voltage controller, is the DC port voltage of the offshore MMC, is the DC port voltage reference value of the offshore MMC, and s is a complex variable representing the frequency in the Laplace transform domain.

[0107] According to the above analysis, if Figure 4 The figure shows the DC voltage balance control schematic diagram of the offshore MMC. and DC port voltage reference value of MMC on the sea side The difference is passed through the PI regulator to obtain the adjustment result. Then, according to the adjustment result and the voltage reference value of the MMC valve side on the offshore side, The sum of the results is used to obtain the d-axis voltage given value .

[0108] S206, the control mode of diesel generator 1 is switched.

[0109] The grid-side VSC converter of diesel generator 1 exits the V / f control mode and switches to the P / Q control mode to control the active power and reactive power of diesel generator 1, provide power for the converter startup of a small number of wind turbines, and compensate for the operating losses of the offshore MMC.

[0110] S207, system voltage boost and DRU activation process.

[0111] First, some offshore wind farms are connected to the grid, and two wind turbines are started to generate power in preparation for the DRU to be put into operation. It should be noted that in this embodiment, two wind turbines are started because starting two wind turbines can meet the preparation for the DRU to be put into operation. In other embodiments of the present application, the number of wind turbines to be started can also be adjusted according to actual conditions.

[0112] After the two wind turbines are started, while the wind turbines increase their power, the offshore MMC performs voltage boost control to increase the voltage at the offshore wind farm grid connection point to the value at which the DRU is put into operation. The voltage at the offshore wind farm grid connection point is then controlled through the DC voltage balance controller, thereby controlling the power distribution between the DRU and the offshore MMC.

[0113] The remaining offshore wind farms are put into operation, and according to the size of the active power of the offshore wind farm grid connection point, the number of filter groups required to be put into use in the filter circuit 2 is determined, and the corresponding filter groups are automatically put into use, and finally the normal working mode is entered.

[0114] Based on the above offshore wind power transmission system startup method, Figure 5 As shown, the present application proposes an offshore wind power transmission system starting device, the offshore wind power transmission system includes multiple offshore wind farms, an offshore converter system 3, an onshore MMC and an AC power grid 5, multiple offshore wind farms are connected in parallel to form an offshore AC bus; the offshore converter system 3 includes a diesel generator 1 connected to the offshore AC bus, a filter circuit 2, a DRU connected in series and an offshore MMC; the offshore wind power transmission system starting device may include:

[0115] The onshore MMC charging module is used to control the charging of the onshore MMC submodules through the AC power grid 5, unlock the onshore MMC after the charging is completed, and establish the DC voltage of the offshore wind power transmission system to a first preset value;

[0116] The offshore MMC charging module is used to control the grid-side VSC converter of the diesel generator 1 to unlock in a V / f control mode, charge the submodules of the offshore MMC through the diesel generator 1, and at the same time, establish the offshore AC bus voltage to a second preset value;

[0117] The offshore MMC controllable charging module is used to control the controllable charging of the offshore MMC through the diesel generator 1;

[0118] The offshore MMC voltage control module is used to control the d-axis of the offshore AC bus voltage through the offshore MMC active control loop, and to control the q-axis of the offshore AC bus voltage through the offshore MMC reactive control loop;

[0119] An offshore MMC balancing control module, used for controlling the DC voltage balancing control of the offshore MMC;

[0120] A switching module is used to control the control mode of the diesel generator 1 to switch to the P / Q control mode, control the active power and reactive power of the diesel generator 1, and provide starting power for the converters of some wind turbines;

[0121] The grid connection and DRU input module is used to control the gradual grid connection of the offshore wind farm and the gradual start-up of the wind turbines. At the same time, during the process of gradual grid connection and gradual start-up, the DRU is put into operation to complete the startup of the offshore wind power transmission system.

[0122] It should be noted that in the several embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of each module is only a logical function division. There may be other division methods in actual implementation. For example, multiple modules can be combined or integrated into another device, or some features can be ignored or not executed. The module described as a separate component may or may not be physically separated. The component displayed as a module may be a physical unit or multiple physical units, that is, it may be located in one place, or it may be distributed in multiple different places. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment.

[0123] In addition, each module in each embodiment of the present invention may be integrated into a processing unit, each module may exist physically separately, or two or more modules may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of a software functional unit.

[0124] An embodiment of the present application provides an electronic device, which includes at least one memory and at least one processor; the memory stores an application, the processor calls the application stored in the memory, and the application is used to control and implement the above-mentioned offshore wind power transmission system startup method.

[0125] Another electronic device provided in the embodiment of the present application may also include: an input port connected to the processor, used to transmit multimodal data collected by an external acquisition device to the processor; and a display unit connected to the processor, used to display the processing results of the processor to the outside world; a communication module connected to the processor, used to realize the communication between the electronic device and the outside world. The display unit can be a display panel, a laser scanning display, etc.; the communication mode adopted by the communication module includes but is not limited to mobile high-definition link technology (HML), universal serial bus (USB), high-definition multimedia interface (HDMI), wireless connection (including wireless fidelity technology (WiFi), Bluetooth communication technology, low-power Bluetooth communication technology, and communication technology based on IEEE802.11s).

[0126] Furthermore, the present application also proposes an offshore wind power transmission system, which is started using the aforementioned offshore wind power transmission system starting method.

[0127] The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for starting an offshore wind power transmission system, the offshore wind power transmission system comprising a plurality of offshore wind farms, an offshore converter system (3), an onshore MMC and an AC power grid (5), wherein the plurality of offshore wind farms are connected in parallel to form an offshore AC bus; the offshore converter system (3) comprises a diesel generator (1) connected to the offshore AC bus, a filter circuit (2), a DRU connected in series and an offshore MMC; characterized in that: include: Charging the submodules of the onshore MMC through the AC power grid (5), unlocking the onshore MMC after charging is completed, and establishing the DC voltage of the offshore wind power transmission system to a first preset value; The grid-side VSC converter of the diesel generator (1) is unlocked in a V / f control mode, and the submodule of the offshore MMC is charged through the diesel generator (1), and at the same time, the offshore AC bus voltage is established to a second preset value; Controllable charging of the offshore MMC via a diesel generator (1); The d-axis of the AC bus voltage on the offshore side is controlled by the active power control loop of the offshore MMC, and the q-axis of the AC bus voltage on the offshore side is controlled by the reactive power control loop of the offshore MMC; The DC voltage balance control is performed on the offshore MMC: if the DC port voltage of the offshore MMC is less than the DC port voltage reference value of the offshore MMC, the d-axis voltage given value is reduced; if the DC port voltage of the offshore MMC is greater than the DC port voltage reference value of the offshore MMC, the d-axis voltage given value is increased; the method for obtaining the d-axis voltage given value comprises: obtaining a regulation result through a PI regulator according to the difference between the DC port voltage of the offshore MMC and the DC port voltage reference value of the offshore MMC; obtaining the d-axis voltage given value according to the sum of the regulation result and the offshore MMC valve side voltage reference value; Switching the control mode of the diesel generator (1) to a P / Q control mode, controlling the active power and reactive power of the diesel generator (1), and providing starting power for converters of some wind turbines; The offshore wind farm is gradually connected to the grid and the wind turbines are gradually started. At the same time, during the process of gradual connection to the grid and gradual start-up, the DRU is put into operation to complete the start-up of the offshore wind power transmission system.

2. The offshore wind power transmission system startup method according to claim 1, characterized in that: Before the grid-side VSC converter of the diesel generator (1) is unlocked in the V / f control mode, the method further comprises: Unlock the diesel generator (1) machine-side converter and build up the DC voltage of the diesel generator (1) machine-side converter to the rated value.

3. The offshore wind power transmission system startup method according to claim 2, characterized in that: The second preset value is greater than the voltage of the grid connection point of the offshore wind farm and less than the voltage of the grid connection point at which the DRU operates.

4. The offshore wind power transmission system startup method according to claim 3, characterized in that: The controlling of the d-axis of the offshore AC bus voltage by the offshore MMC active control loop and the controlling of the q-axis of the offshore AC bus voltage by the offshore MMC reactive control loop include: The control system of the offshore MMC is enabled to lock the voltage and phase of the current offshore wind farm grid connection point to obtain a locked voltage value and a locked phase; Set the AC voltage reference value to the locked voltage value and unlock it; The d-axis of the AC bus voltage on the offshore side is controlled through the active control loop of the offshore MMC; wherein the d-axis voltage set value is the AC voltage reference value; The q-axis of the AC bus voltage on the offshore side is controlled by the offshore MMC reactive power control loop; wherein the q-axis voltage set value is 0pu; The control system phase angle of the offshore MMC is corrected according to the locked phase so that the offshore AC bus voltage reaches the AC voltage reference value.

5. The offshore wind power transmission system startup method according to claim 4, characterized in that: The controllable charging of the offshore MMC by the diesel generator (1) comprises: The offshore MMC is controlled and charged by the diesel generator (1) until the voltage of the power module in the offshore MMC reaches 0.98 pu; The first preset value is 1pu; The second preset value is 0.7 pu.

6. The offshore wind power transmission system startup method according to claim 5, characterized in that: The offshore wind farm is gradually connected to the grid and the wind turbines are gradually started. Meanwhile, during the process of gradual connection to the grid and gradual start-up, the DRU is put into operation, including: Connect some offshore wind farms to the grid and start up some wind turbines; Increase the power of some of the started wind turbines, and at the same time, control the voltage of the offshore MMC to increase the voltage of the offshore wind farm grid connection point to the DRU operation value; The DC voltage balance controller in the offshore MMC controls the voltage at the offshore wind farm grid connection point, so that the power distribution between the DRU and the offshore MMC meets the preset requirements; The remaining offshore wind farms are connected to the grid, and the number of filter groups required to be invested in the filter circuit (2) is determined according to the active power of the offshore wind farm grid connection point.

7. A starting device for an offshore wind power transmission system, the offshore wind power transmission system comprising a plurality of offshore wind farms, an offshore converter system (3), an onshore MMC and an AC power grid (5), wherein the plurality of offshore wind farms are connected in parallel to form an offshore AC bus; the offshore converter system (3) comprises a diesel generator (1) connected to the offshore AC bus, a filter circuit (2), a DRU connected in series and an offshore MMC; characterized in that: include: An onshore MMC charging module is used to control the charging of the onshore MMC submodules through the AC power grid (5), unlock the onshore MMC after charging is completed, and establish the DC voltage of the offshore wind power transmission system to a first preset value; The offshore MMC charging module is used to control the grid-side VSC converter of the diesel generator (1) to be unlocked in a V / f control mode, to charge the submodules of the offshore MMC through the diesel generator (1), and at the same time, to establish the offshore AC bus voltage to a second preset value; The offshore MMC controllable charging module is used to control the offshore MMC to be controlled and charged via the diesel generator (1); The offshore MMC voltage control module is used to control the d-axis of the offshore AC bus voltage through the offshore MMC active control loop, and to control the q-axis of the offshore AC bus voltage through the offshore MMC reactive control loop; The offshore MMC balancing control module is used to control the DC voltage balancing control of the offshore MMC: if the DC port voltage of the offshore MMC is less than the DC port voltage reference value of the offshore MMC, the d-axis voltage given value is reduced; if the DC port voltage of the offshore MMC is greater than the DC port voltage reference value of the offshore MMC, the d-axis voltage given value is increased; the method for obtaining the d-axis voltage given value includes: obtaining a regulation result through a PI regulator according to the difference between the DC port voltage of the offshore MMC and the DC port voltage reference value of the offshore MMC; obtaining the d-axis voltage given value according to the sum of the regulation result and the offshore MMC valve side voltage reference value; A switching module, used to control the control mode of the diesel generator (1) to switch to a P / Q control mode, to control the active power and reactive power of the diesel generator (1), and to provide starting power for converters of some wind turbines; The grid connection and DRU input module is used to control the gradual grid connection of the offshore wind farm and the gradual start-up of the wind turbines. At the same time, during the process of gradual grid connection and gradual start-up, the DRU is put into operation to complete the startup of the offshore wind power transmission system.

8. An electronic device, characterized in that: The electronic device includes at least one memory and at least one processor; the memory stores an application, and the processor calls the application stored in the memory, and the application is used to control the offshore wind power transmission system startup method described in any one of claims 1-6.

9. An offshore wind power transmission system, characterized in that: The offshore wind power transmission system is started by using the offshore wind power transmission system starting method described in any one of claims 1 to 6.

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