Double-end hybrid converter type offshore wind power direct current sending-out system and control method, equipment and medium thereof

Abstract

The invention belongs to the technical field of direct-current power transmission, and discloses a double-end hybrid converter type offshore wind power direct-current sending-out system, a control method thereof, equipment and a medium, so as to solve the problems of economy and stability of an existing system. The system comprises an offshore wind power plant, an alternating current collection network, an offshore converter station, a direct current submarine cable, an onshore converter station and an onshore alternating current power grid which are electrically connected in sequence, the offshore wind power plant adopts a net-following type fan; a current converter of the offshore converter station is a flexible diode rectifier which is formed by connecting the diode rectifier and a full-bridge modular multilevel converter serving as a first FBMMC in series on the direct current side and connecting the diode rectifier and the full-bridge modular multilevel converter in parallel on the alternating current side, and a voltage / frequency control mode is executed. A current converter of the land converter station is a flexible power grid commutation current converter, is formed by connecting a 12-pulse power grid commutation current converter and a full-bridge modular multi-level current converter serving as a second FBMMC in series on the direct current side and connecting the 12-pulse power grid commutation current converter and the full-bridge modular multi-level current converter in parallel on the alternating current side, and executes a direct current voltage / reactive power control mode.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of direct current transmission, and particularly relates to a double-ended hybrid converter type far-sea wind power direct current transmission system, a control method, equipment and a medium thereof. BACKGROUND

[0002] For a flexible direct current transmission system of far-sea wind power, the converter is the electrical equipment with the largest space size and the largest weight proportion in the offshore platform, and the cost of which directly affects the engineering economy. The widely used offshore converter topology is a modular multi-level converter (MMC). In actual engineering, in order to meet the capacity demand of gigawatt-level wind power transmission, a large number of sub-modules need to be integrated into the MMC, resulting in a large volume of offshore converter platform, a significant increase in weight, and high construction and installation costs. This situation restricts the economy of large-scale development of offshore wind power and is difficult to meet the requirements of cost control.

[0003] To alleviate the above problems, the prior art proposes an offshore wind power direct current transmission scheme based on a hybrid converter, such as a topology combining a diode rectifier and a partial capacity modular multi-level converter, to reduce the equipment complexity, volume and cost of the offshore converter station. However, this method mainly focuses on the lightening and economy of the offshore converter station, and pays insufficient attention to the topology selection and cost optimization of the onshore converter station when connecting to larger capacity wind power. On the land side, to increase the grid-connected capacity, a full capacity modular multi-level converter is usually selected and expanded by modules to achieve capacity expansion. Although this method is mature in technology, it also faces the problems of high equipment cost, large occupied area and poor economy.

[0004] In addition, in the existing hybrid converter system, the diode rectifier and the modular multi-level converter mixed topology used by the sending end cannot achieve complete voltage source characteristics due to the control strategy. Specifically, the hybrid converter cannot independently control the amplitude and frequency of the alternating current side voltage, that is, it cannot realize the complete voltage / frequency (V / f) control function required by the grid connection standard. The lack of this control capability makes it difficult for the system to support the stable operation of grid-connected wind turbines. V / f

[0005] In summary, the existing far-sea wind power direct current transmission system faces the volume, weight and cost pressure caused by the large capacity modular multi-level converter on the offshore side, the economic constraints caused by the capacity expansion of the full capacity modular multi-level converter on the onshore side, and the inability of the sending end hybrid converter to realize stable network construction due to insufficient control capability. SUMMARY

[0006] ​Based on the above-mentioned shortcomings and deficiencies existing in the prior art, one of the purposes of the present application is to at least solve one or more of the above-mentioned problems existing in the prior art, in other words, one of the purposes of the present application is to provide a double-ended hybrid converter type far-sea wind power DC transmission system and a control method, equipment and medium thereof which meet one or more of the aforementioned needs, so as to reduce the construction cost and platform scale of the offshore converter station, improve the expansion economy of the onshore converter station, realize complete and independent control of the voltage amplitude and frequency of the AC power grid by the sending-end converter, and thus enhance the overall operation stability of the system.

[0007] In order to achieve the above-mentioned purposes of the application, the following technical solutions are adopted in the present application:

[0008] In a first aspect, the present application provides a double-ended hybrid converter type far-sea wind power DC transmission system, comprising: a far-sea wind farm, an AC collection network, an offshore converter station, a DC submarine cable, an onshore converter station and an onshore AC power grid which are electrically connected in sequence; The offshore wind farm adopts a grid-following type wind turbine; The converter of the offshore converter station is a flexible diode rectifier FDR; The flexible diode rectifier FDR is composed of a diode rectifier DR and a full-bridge modular multilevel converter as a first FBMMC which are connected in series at the DC side and in parallel at the AC side, and performs a voltage / frequency V / f control mode; The converter of the onshore converter station is a flexible grid commutated converter FLCC; The flexible grid commutated converter FLCC is composed of a 12-pulse grid commutated converter LCC and a full-bridge modular multilevel converter as a second FBMMC which are connected in series at the DC side and in parallel at the AC side, and performs a DC voltage / reactive power U dc / Q control mode.

[0009] As a preferred scheme, the first FBMMC and the second FBMMC are both composed of full-bridge submodules.

[0010] As a preferred scheme, when the flexible grid commutated converter FLCC performs the DC voltage / reactive power U dc / Q control mode, the 12-pulse grid commutated converter LCC operates at a constant firing angle.

[0011] As a preferred scheme, the value of the firing angle ranges from 140° to 160°.

[0012] In a second aspect, the present application provides a control method for controlling the system as described in the first aspect, comprising a marine converter station control process and a land converter station control process: The marine converter station control comprises V / f control performed on the flexible diode rectifier FDR, the land converter station control comprises V / f control performed on the flexible line commutated converter FLCC, and the control processes are realized cooperatively through a first control path and a second control path. The land converter station control step comprises U dc / Q control performed on the flexible line commutated converter FLCC, and the control processes are realized cooperatively through a first control path and a second control path. U dc / Q The control is realized cooperatively through a third control path and a fourth control path.

[0013] As a preferred solution, the first control path performs the following operations: generating a first DC port current reference value through a first voltage outer loop proportional integral PI regulator according to the deviation between the reference value and the measured value of the d-axis component of the grid-side voltage of the FDR; The second control path performs the following operations: generating a grid-side current d-axis component reference value of the first FBMMC through a first capacitor voltage loop PI regulator according to the deviation between the reference value and the measured value of the sum average of the bridge arm capacitor voltages of the first FBMMC; generating a q-axis component reference value of the grid-side current of the first FBMMC through a first voltage q-axis loop PI regulator according to the deviation between the reference value and the measured value of the q-axis component of the grid-side voltage of the FDR; generating a valve-side voltage reference value of the first FBMMC through a first current tracking controller according to the reference value and the measured value of the d-axis and q-axis components of the grid-side current of the first FBMMC; modulating the bridge arm voltage of the first FBMMC through a first FBMMC three-degree-of-freedom controller based on the first DC port current reference value, the grid-side current d-axis component reference value of the first FBMMC, and the q-axis component reference value of the grid-side current of the first FBMMC, to realize stable control of the voltage amplitude and frequency of the AC side bus of the FDR; As a preferred solution, the third control path performs the following operations: generating a second DC port current reference value through a second voltage outer loop PI regulator according to the deviation between the reference value and the measured value of the DC voltage of the FLCC; The fourth control path performs the following operations: a reference value of a sum of bridge arm capacitor voltages of the second FBMMC and a measured value of the sum of bridge arm capacitor voltages of the second FBMMC, a d-axis component reference value of a grid-side current of the second FBMMC is generated through a second capacitor voltage loop PI regulator according to a deviation between the reference value and the measured value; a q-axis component reference value of a grid-side current of the second FBMMC is generated through a second reactive power loop PI regulator according to a deviation between a reference value of reactive power of the FLCC and a measured value of the reactive power of the FLCC; based on the second DC port current reference value, the d-axis component reference value of the grid-side current of the second FBMMC, and the q-axis component reference value of the grid-side current of the second FBMMC, a bridge arm voltage of the second FBMMC is modulated through a second FBMMC three-degree-of-freedom controller to achieve stable control of DC voltage and adjustment of reactive power at the grid connection point.

[0014] In a third aspect, the present application provides an electronic device, which comprises a memory, a processor, and a computer program, and the computer program, when executed by the processor, implements the control method according to the second aspect.

[0015] In a fourth aspect, the present application provides a computer-readable storage medium, which stores a computer program, and the computer program, when executed by a processor, implements the control method according to the second aspect.

[0016] Compared with the prior art, the present application has the following beneficial effects: 1. The double-ended hybrid converter system proposed in the present application uses a low-cost FDR at sea and an economic FLCC on land, thereby greatly reducing the investment in key equipment and losses compared with the full-flexible solution while ensuring performance. The system as a whole has better economic efficiency and can better meet the requirements of the marketization and parity development of offshore wind power.

[0017] 2. In the present application, the offshore FDR adopts V f network control, and the active power is mainly transmitted by the diode rectifier, while the parallel full-bridge modular multilevel converter only needs about 15% of the total capacity of the system to complete voltage construction and reactive power compensation. This significantly reduces the size and weight of the offshore converter station, making it easier to arrange on the space-limited offshore platform and reducing the construction difficulty and cost of offshore engineering.

[0018] 3. In the present application, the onshore FLCC combines the mature and reliable grid commutated converter with the flexible and controllable full-bridge modular multilevel converter. The LCC is responsible for main power transmission, while the FBMMC is mainly responsible for DC voltage stabilization and reactive power adjustment. This combination effectively controls the overall construction cost of the converter station while realizing large-capacity wind power grid connection.

[0019] ​Further or more detailed advantageous effects will be described in the specific embodiments in conjunction with specific examples. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0021] Figure 1 is a topological structure schematic diagram of the double-ended hybrid converter type far sea wind power DC transmission system described in embodiment one of the present application.

[0022] Figure 2 is a framework schematic diagram of the offshore converter station control described in embodiment two of the present application.

[0023] Figure 3 is a framework schematic diagram of the land converter station control described in embodiment two of the present application.

[0024] Figure 4 is a structure diagram of the electronic device provided by the embodiment of the present application.

[0025] Corresponding reference signs in the drawings include: 400, electronic device; 401, processor; 402, communication bus; 403, user interface; 404, network interface; 405, memory. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application.

[0027] In the following description, a plurality of embodiments of the present application are provided, and different embodiments can be replaced or combined, so the present application can also be considered to include all possible combinations of the same and / or different embodiments described. Thus, if one embodiment includes features A, B, C, and another embodiment includes features B, D, the present application should also be considered to include embodiments including one or more of all other possible combinations of A, B, C, and D, even if the embodiment is not explicitly described in the following content.

[0028] The following description provides examples, and does not limit the scope, applicability, or examples set forth in the claims. Alterations can be made to the elements’ functions and arrangements described, without departing from the scope of the inventive concept. Various examples can omit, substitute, or add various procedures or components as appropriate. For example, the described methods can be performed in an order different than described, and various steps can be added, omitted, or combined. Also, features described with respect to some examples can be combined in other examples.

[0029] In order to better understand the embodiments of the present application, the application scenarios thereof are described before the specific embodiments of the present application are explained in detail.

[0030] The double-ended hybrid converter type far-sea wind power DC transmission system and the control method thereof described in the embodiments of the present application are applied to the field of large-scale and long-distance offshore wind power grid connection, and are particularly suitable for scenarios with long distance from shore (usually more than 80 kilometers) and large transmission capacity (up to hundreds of megawatts to gigawatt level). In these scenarios, the application of the double-ended hybrid converter type far-sea wind power DC transmission system and the control method thereof aims to solve the problem of efficient and reliable transmission of far-sea wind power, build stable operation support for offshore weak grid / passive network, improve the flexibility and friendliness of land grid access, enhance the system fault ride-through and recovery capability, and optimize the economic efficiency and technical compatibility of the system.

[0031] The flexible diode rectifier, diode rectifier, full-bridge modular multilevel converter, voltage / frequency V / f control mode, flexible grid commutation converter, DC voltage / reactive power U dc / Q control mode are simply explained as follows: Flexible diode rectifier (FDR): in the context of the present application, it is composed of a diode rectifier DR and a full-bridge modular multilevel converter in series at the DC side and in parallel at the AC side. This structure utilizes the DR to realize efficient and low-cost rectification of most of the power, while the parallel FBMMC provides voltage support, harmonic compensation and control freedom, so that the originally uncontrollable DR system can perform active control strategies such as voltage / frequency V / f control mode, thereby building a stable AC grid for offshore wind farms.

[0032] Diode rectifier (DR): a kind of uncontrollable rectifier circuit composed of diodes. It has simple structure, low cost, high reliability and small loss, but cannot independently control the AC side voltage and frequency, and needs a stable AC voltage source to work normally.

[0033] Full-Bridge Modular Multilevel Converter (FBMMC): A high-voltage and high-capacity converter topology composed of cascaded full-bridge submodules. Each full-bridge submodule contains four fully controlled switching devices (such as IGBT) and one DC energy storage capacitor. This topology has the advantages of multiple output voltage levels, good harmonic performance, independent control of active and reactive power, and the ability to block DC fault current (with DC fault self-clearing capability).

[0034] Voltage / Frequency V / f Control Mode: A grid-forming control strategy. The control objective is to maintain the voltage amplitude (V) and frequency (f) of the converter's AC side common connection point constant at the given reference value. When applied to offshore FDR, this mode enables it to provide a voltage and frequency stable AC grid for the connected offshore wind farm, just like a synchronous generator, supporting the operation of grid-connected wind turbines.

[0035] Flexible Line-Commutated Converter (FLCC): In the context of this invention, it is composed of a traditional 12-pulse line-commutated converter (LCC) and a full-bridge modular multilevel converter (FBMMC) connected in series on the DC side and in parallel on the AC side. This structure combines the economic advantages of LCC's high-voltage and large-capacity, low-loss, and FBMMC's fast and flexible control capability, enabling the entire converter to perform advanced controls such as DC voltage / reactive power U dc / Q control mode, etc.

[0036] DC Voltage / Reactive Power U dc / Q Control Mode: A grid-forming control strategy. The control objective is to maintain the voltage amplitude (V) and frequency (f) of the converter's AC side common connection point constant at the given reference value. When applied to offshore FDR, this mode enables it to provide a voltage and frequency stable AC grid for the connected offshore wind farm, just like a synchronous generator, supporting the operation of grid-connected wind turbines.

[0037] Example One: This embodiment provides a double-ended hybrid converter type long-distance offshore wind power DC transmission system, whose topology is as follows Figure 1As shown, the system is composed of offshore wind farm, AC collection network, offshore converter station, DC submarine cable, onshore converter station and onshore AC grid connected in sequence. The offshore wind farm adopts the grid-following wind turbine, and the output AC power is collected by the AC collection network and then transmitted to the offshore converter station.

[0038] The converter of the offshore converter station adopts flexible diode rectifier (FDR), whose topology structure is composed of diode rectifier (DR) and first full-bridge modular multilevel converter (FBMMC) in series at DC side and in parallel at AC side, and performs voltage / frequency V / f control mode. The first FBMMC is composed of multiple full-bridge sub-modules (FBSM). In the FDR, the DR undertakes the main power transmission function, and the first FBMMC realizes reactive power compensation and AC side voltage construction for the DR with small capacity.

[0039] The converter of the onshore converter station adopts flexible line commutated converter (FLCC), whose topology structure is composed of 12-pulse line commutated converter (LCC) and second full-bridge modular multilevel converter (FBMMC) in series at DC side and in parallel at AC side. The second FBMMC is also composed of multiple full-bridge sub-modules and performs DC voltage / reactive power U dc / Q control mode. In the FLCC, the LCC undertakes the main power inversion function, and the second FBMMC realizes reactive power compensation and DC voltage support for the LCC with small capacity. When the flexible line commutated converter FLCC performs the DC voltage / reactive power Udc / Q control mode, the 12-pulse line commutated converter LCC operates with constant trigger angle, and the value range of the trigger angle is [140°, 160°].

[0040] The offshore converter station and the onshore converter station are connected through the DC submarine cable to form a DC transmission link. The power generated by the offshore wind farm is converted into DC power by the FDR, transmitted to the land through the DC submarine cable, and then inverted into power frequency AC power by the FLCC and fed into the onshore AC grid.

[0041] This system combines high-power, low-cost, and structurally simple converters (DRs) and liquid capacitors (LCCs) with smaller-capacity but more flexible-controlling fair-metal converters (FBMMCs), achieving lightweight and economical converter stations on the offshore side and cost optimization for large-capacity grid connection on the onshore side. Simultaneously, through specific control methods for FDRs and FLCCs, it achieves complete autonomous control of AC voltage amplitude and frequency at the sending end, as well as stable regulation of DC voltage and reactive power at the receiving end.

[0042] Example 2: This embodiment provides a control method for controlling the system described in Embodiment 1, including a control process for an offshore converter station and a control process for an onshore converter station, as detailed below: The control of the offshore converter station aims to maintain the stability of voltage amplitude and frequency in the AC collection network of the offshore wind farm, and executes the flexible diode rectifier (FDR). V / f Control. The control is achieved collaboratively through a first control path and a second control path; specific steps and corresponding signal flows can be found in [reference needed]. Figure 2 The control block diagram shown.

[0043] It should be noted that the following is in conjunction with the appendix. Figure 2 The main variable symbols used in the operational instructions of the control block diagram shown are defined as follows: Explanation of superscript and subscript: "Represents the reference value of the variable," "The measured value of the variable," "and" "Refers to the variables in Coordinates Axial components and Axial components; It is the AC three-phase voltage at the common coupling point of the FDR. and They are respectively The reference amplitude and phase angle, for angular frequency, and for of Quantity; This refers to the grid-side current of the MMC. and for of Quantity; This refers to the measured grid-side voltage value of the FBMMC; and for of Quantity; The valve-side voltage of the FBMMC. and for of Quantity; The DC voltage of the FBMMC section; This is the average value of the sum of the capacitor voltages of the FBMMC bridge arms; The equivalent inductance of FDR; This refers to the DC port current. As an intermediate variable, and For the bridge arm voltage of FBMMC, "and" "These represent the upper arm and the lower arm, respectively."

[0044] The first control path performs the following operations: Voltage outer loop control: Obtain the three-phase voltage measurement values ​​at the AC side common coupling point (PCC) of the FDR. Given a reference value for the amplitude of the AC bus voltage of the FDR. and phase reference value Based on phase reference value ,Will conduct Coordinate transformation to obtain its Shaft component measurement value .Will Shaft voltage reference value (and and (Related) and measured values The comparison results in a deviation signal that is input to the first voltage outer loop proportional-integral (PI) regulator. The output of this PI regulator serves as a reference value for the first DC port current. .

[0045] The second control path performs the following operations: Measure the average sum of the voltages across the bridge arms of the first FBMMC. Given a reference value and The resulting deviation signal is input to the first capacitor voltage loop PI regulator after comparison. The output of this regulator serves as the grid-side current of the first FBMMC. Axis component reference value .

[0046] The grid-side voltage of the FDR Axis component reference value (Usually set to 0) and its measured value The comparison generates a deviation signal which is then input to the first voltage. PI regulator. The output of this regulator is the reference value of the d-axis component of the first FBMMC grid-side current .

[0047] The first FBMMC three-degree-of-freedom controller performs the following operations: Current inner loop and intermediate variable generation: measure the actual DC port current . Compare the first DC port current reference value with its measured value , and input the resulting deviation signal into the first current inner loop PI regulator for processing. Add the processing result to 0.5 times the DC voltage measurement value of the first FBMMC to generate the reference value of the first intermediate variable .

[0048] Current tracking control: measure the grid-side current and grid-side voltage of the first FBMMC, and perform abc / dq transformation based on the phase reference value to obtain its d-axis component measurement value , , , . Compare the current reference value , with the measured value , , and generate the d-axis component reference value , and of the first FBMMC valve-side voltage through the first current tracking controller (combined with grid voltage feedforward and coupling term compensation).

[0049] Valve-side voltage synthesis and bridge arm modulation: perform dq / abc coordinate inverse transformation on and to obtain the valve-side three-phase voltage reference value of the first FBMMC. Based on the reference value generated by the first control path and the reference value generated by this path, synthesize the bridge arm voltage reference signal and of the first FBMMC through a modulation algorithm (such as the nearest level approximation modulation NLM or carrier phase shift PWM). The modulation system synthesizes and ​​​Generate trigger pulse signals for all switching devices in the first FBMMC to control the voltage amplitude of the AC bus of the FDR. With frequency (Depend on Stable control (determined by the rate of change).

[0050] The control process for the onshore converter station includes executing the flexible grid phase converter (FLCC). U dc / Q The control aims to maintain stable DC transmission voltage and regulate reactive power at the grid connection point. This control is achieved collaboratively through a third and fourth control path; specific steps and corresponding signal flows can be found in the appendix. Figure 3 The control block diagram shown.

[0051] It should be noted that the following is in conjunction with the appendix. Figure 3 The main variable symbols used in the operational instructions of the control block diagram shown are defined as follows: Explanation of superscript and subscript: "Represents the reference value of the variable," "The measured value of the variable," "and" "Refers to the variables in Coordinates Axial components and Axial components; It is the AC three-phase voltage at the FLCC point of common connection (PCC). for phase angle, for angular frequency, and for of Quantity; For the grid-side current of FBMMC, and for of Quantity; The grid-side voltage of the FBMMC. and for of Quantity; The valve-side voltage of the FBMMC. and for of Quantity; The DC voltage of the FBMMC section; is the average of the FBMMC bridge leg capacitor voltages; is the reactive power of the FLCC; is the equivalent inductance of the FLCC; is the DC port current; is an intermediate variable; and is the FBMMC bridge leg voltage, and denote the upper and lower bridge legs, respectively.

[0052] The third control path performs the following operations: DC voltage outer loop control: measure the DC voltage of the FLCC . Compare the DC voltage reference value with , and input the resulting error signal into a second voltage outer loop PI regulator. The output of this PI regulator serves as the second DC port current reference value .

[0053] The fourth control path performs the following operations: capacitor voltage and reactive power outer loop control: capacitor voltage loop: measure the average of the FBMMC bridge leg capacitor voltages . Compare the given reference value with , and input the resulting error signal into a second capacitor voltage loop PI regulator. The output of this regulator serves as the axis component reference value of the FBMMC grid-side current.

[0054] reactive power loop: measure the reactive power exchanged between the FLCC and the land AC grid . Compare the reactive power reference value with , and input the resulting error signal into a second reactive loop PI regulator. The output of this regulator serves as the axis component reference value of the FBMMC grid-side current.

[0055] The second FBMMC three-degree-of-freedom controller performs the following operations: current inner loop and intermediate variable generation: measure the actual DC port current . Compare the second DC port current reference value with its measured value The deviation signal is input to a second current inner loop PI regulator for processing. The processing result is compared with 0.5 times the DC voltage measurement value of the second FBMMC The addition generates a second intermediate variable The reference value i .

[0056] Grid voltage phase synchronization: using a phase-locked loop (PLL) to obtain the voltage phase of the land AC grid PCC point to which the FLCC is connected in real time , providing a reference phase for all subsequent grid voltage orientation-based coordinate transformations.

[0057] Current tracking control: measuring the grid-side current and grid-side voltage of the second FBMMC, and performing abc / dq transformation based on the grid voltage phase obtained by the phase-locked loop to obtain its axis component measurement value 、 、 、 . Compare the current reference value 、 with the measurement value 、 , and generate the axis component reference value and of the valve-side voltage of the second FBMMC through the second current tracking controller (combined with grid voltage feedforward 、 and coupling term compensation).

[0058] Valve-side voltage synthesis and bridge arm modulation: perform dq / abc coordinate inverse transformation on and to obtain the valve-side three-phase voltage reference value of the second FBMMC. Based on the reference value generated by the third control path and the reference value generated by this path, synthesize the bridge arm voltage reference signal and of the second FBMMC through a modulation algorithm (such as nearest level approximation modulation NLM or carrier phase shift PWM). The modulation system generates trigger pulse signals for all full-bridge sub-module switching devices in the second FBMMC according to and .

[0059] LCC fixed trigger angle control: at the same time, for the 12-pulse grid commutated converter (LCC) part in the FLCC, fixed trigger angle control is adopted, i.e. fixing the trigger angle of the LCC is a constant value In one preferred embodiment of the present embodiment, the trigger angle is in the range of [140°, 160°]. The modulation system independently generates trigger pulse signals for all thyristors in the LCC according to the constant

[0060] Through the above-mentioned coordinated execution of the offshore (sea) V / f control) and onshore (land) U dc / Q control) converter station control processes, the system realizes stable transmission of far-sea wind power through high-voltage direct current, in which the offshore converter station builds a stable AC voltage and frequency reference for the grid-connected wind turbine, and the onshore converter station ensures the stability of the DC transmission voltage and has flexible reactive power regulation capability. Figure 2 and attached Figure 3 clearly show the complete processing flow and interaction of each control path signal in the offshore and onshore converter station control.

[0061] Embodiment three: As shown in Figure 4 , the present embodiment provides an electronic device, which can include at least one processor, at least one network interface, a user interface, a memory and at least one communication bus.

[0062] The communication bus can be used to realize the connection and communication of the above-mentioned components.

[0063] The user interface can include a key, and the optional user interface can further include a standard wired interface, a wireless interface.

[0064] The network interface can include but is not limited to a Bluetooth module, an NFC module, a Wi-Fi module, etc.

[0065] ​The processor may include one or more processing cores. It connects various parts of the electronic device via various interfaces and lines, executing instructions, programs, code sets, or instruction sets stored in memory, and accessing data stored in memory to perform various functions and process data. Optionally, the processor can be implemented using at least one hardware form of DSP, FPGA, or PLA. The processor may integrate one or more of the following: CPU, GPU, and modem. The CPU primarily handles the operating system, user interface, and applications; the GPU is responsible for rendering and drawing the content required for display; and the modem handles wireless communication. It is understood that the modem may also be implemented as a separate chip without being integrated into the processor.

[0066] The memory may include RAM or ROM. Optionally, the memory may include a non-transitory computer-readable medium. The memory can be used to store instructions, programs, code, code sets, or instruction sets. The memory may include a program storage area and a data storage area, wherein the program storage area may store instructions for implementing an operating system, instructions for at least one function (such as touch function, sound playback function, image playback function, etc.), instructions for implementing the above-described method embodiments, etc.; the data storage area may store data involved in the above-described method embodiments, etc. Optionally, the memory may also be at least one storage device located remotely from the aforementioned processor. The memory, as a computer storage medium, may include an operating system, a network communication module, a user interface module, and a control application program. The processor can be used to call the control application program stored in the memory and execute the steps of the control methods mentioned in the foregoing embodiments.

[0067] Example 4: This embodiment provides a computer-readable storage medium storing instructions that, when executed on a computer or processor, cause the computer or processor to perform the above-described instructions. Figures 2-3 One or more steps in the illustrated embodiment. If the constituent modules of the above-described electronic device are implemented as software functional units and sold or used as independent products, they can be stored in the computer-readable storage medium.

[0068] In the above embodiments, all or part of the methods can be implemented by software, hardware, firmware, or any combination thereof. When implemented by software, all or part of the methods can be implemented in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of the present specification are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices. The computer instructions can be stored in a computer-readable storage medium or transmitted by the computer-readable storage medium. The computer instructions can be transmitted from one website, computer, server or data center to another website, computer, server or data center by wire (such as coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (such as infrared, wireless, microwave, etc.). The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server, data center, etc. that includes one or more available media sets. The available media can be a magnetic medium (for example, a floppy disk, a hard disk, a magnetic tape), an optical medium (for example, a digital versatile disc (DVD)), or a semiconductor medium (for example, a solid state disk (SSD)) and the like.

[0069] A person of ordinary skill in the art can understand that all or part of the processes in the above-mentioned second embodiment method can be implemented by instructing the relevant hardware through a computer program, which can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of the above-mentioned embodiments of each method. The aforementioned storage medium includes ROM, RAM, magnetic or optical discs, and various media that can store program codes. In the case of no conflict, the technical features in the embodiments and the implementation schemes can be combined arbitrarily.

[0070] It should be noted that for the above-mentioned method embodiments, in order to simply describe, they are all expressed as a series of action combinations, but those skilled in the art should know that the present application is not limited by the described action sequence, because according to the present application, some steps can be performed in other order or simultaneously. Secondly, those skilled in the art should know that the embodiments described in the specification all belong to preferred embodiments, and the actions and modules involved are not necessarily necessary for the present application.

[0071] In the above embodiments, the description of each embodiment has its own focus, and the parts not described in detail in a certain embodiment can be referred to the related description of other embodiments.

[0072] The above merely illustrates the embodiments of the present application, and cannot be used to limit the scope of the present application. Any equivalent changes and modifications made according to the teachings of the present application shall fall within the scope of the present application. Any further embodiments of the present application will be readily apparent to those skilled in the art in view of the disclosure herein. The present application is intended to cover any variations, uses or adaptive changes of the present application falling within the generic principles of the present application and including common knowledge or conventional technical means in the art not recited in the present application. The scope of the present application is defined by the claims and their equivalents, and the embodiments and examples are merely illustrative and not restrictive.

Claims

1. A long distance wind power DC transmission system with a double-ended hybrid converter, characterized in that, The offshore wind farm, the AC collection network, the offshore converter station, the DC submarine cable, the onshore converter station and the onshore AC power grid are sequentially electrically connected. The offshore wind farm adopts wind turbines of the following-net type. The converter of the offshore converter station is a flexible diode rectifier (FDR). The converter of the onshore converter station is a flexible line-commutated converter (FLCC). The flexible diode rectifier FDR is composed of a diode rectifier DR and a full-bridge modular multilevel converter as a first FBMMC in series at the DC side and in parallel at the AC side, and performs voltage / frequency V / f control mode; 2. The double-ended hybrid converter type far-sea wind power DC transmission system according to claim 1, wherein: the first FBMMC and the second FBMMC are both composed of full-bridge sub-modules. The flexible line commutated converter FLCC is composed of a 12-pulse line commutated converter LCC in series at the DC side and in parallel at the AC side with a full-bridge modular multilevel converter as a second FBMMC and performs DC voltage / reactive power U dc / Q Control mode.

3. The double-ended hybrid converter type far-sea wind power DC transmission system according to claim 2, wherein: the first FBMMC and the second FBMMC are both composed of full-bridge sub-modules.

4. The double-ended hybrid converter type far-sea wind power DC transmission system according to claim 3, wherein: the trigger angle is in the range of [140°, 160°]. The offshore converter station control process and the onshore converter station control process are included. The flexible line commutated converter FLCC performs the DC voltage / reactive power U dc / Q In control mode, the 12-pulse line commutated converter LCC is operated with constant firing angle.

6. The control method according to claim 5, wherein: the first control path performs the following operations: a first DC port current reference value is generated by a first voltage outer loop proportional-integral (PI) regulator according to the deviation between the reference value and the measured value of the d-axis component of the grid-side voltage of the FDR; 5. A control method for controlling the system according to any one of claims 1 to 4, characterized in that, the second control path performs the following operations: The offshore converter station control comprises a control of the flexible diode rectifier FDR V / f control, the V / f control process is realized in cooperation by a first control path and a second control path; The land converter station control step includes executing control on the flexible grid line-commutated converter (FLCC) U dc / Q control, the U dc / Q The control is realized in cooperation through a third control path and a fourth control path. a d-axis component reference value of the grid-side current of the first FBMMC is generated by a first capacitor voltage loop PI regulator according to the deviation between the reference value and the measured value of the average value of the bridge arm capacitor voltage of the first FBMMC; a q-axis component reference value of the grid-side current of the first FBMMC is generated by a first voltage q-axis loop PI regulator according to the deviation between the reference value and the measured value of the q-axis component of the grid-side voltage of the FDR; a valve-side voltage reference value of the first FBMMC is generated by a first current tracking controller according to the reference values and the measured values of the d-axis and q-axis components of the grid-side current of the first FBMMC; the bridge arm voltage of the first FBMMC is modulated by a first FBMMC three-degree-of-freedom controller based on the first DC port current reference value, the d-axis component reference value of the grid-side current of the first FBMMC and the q-axis component reference value of the grid-side current of the first FBMMC, so as to realize stable control of the voltage amplitude and frequency of the AC side bus of the FDR.

7. The control method according to claim 6, wherein: the third control path performs the following operations: a second DC port current reference value is generated by a second voltage outer loop PI regulator according to the deviation between the reference value and the measured value of the DC voltage of the FLCC; the fourth control path performs the following operations: a d-axis component reference value of the grid-side current of the second FBMMC is generated by a second capacitor voltage loop PI regulator according to the deviation between the reference value and the measured value of the average value of the bridge arm capacitor voltage of the second FBMMC; a q-axis component reference value of the grid-side current of the second FBMMC is generated by a second reactive power loop PI regulator according to the deviation between the reference value and the measured value of the reactive power of the FLCC; ​ ​ ​ ​ ​ Based on the second DC port current reference value, a d-axis component reference value of the second FBMMC grid-side current and a q-axis component reference value of the second FBMMC grid-side current, a bridge arm voltage of the second FBMMC is modulated through a second FBMMC three-freedom controller to realize stable control of the DC voltage and adjustment of the grid point reactive power.

8. A computer device comprising a memory, a processor and a computer program, characterized in that The computer program, when executed by a processor, implements the control method of any one of claims 5-7.

9. A computer readable storage medium having stored thereon a computer program, characterized in that, The computer program, when executed by a processor, implements the control method of any one of claims 5-7.

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