Offshore wind power DR-mmc parallel dc transmission system control method and device

Abstract

The application provides a kind of offshore wind power DR-MMC parallel DC transmission system control method and device method comprising: obtaining the relevant parameters of wind farm, MMC and DR transmission;Calculate the active power reference value of DR, when the actual active power of wind farm transmission is less than the rated transmission power of DR, the active power reference value of DR is the actual active power of wind farm transmission, otherwise it is the rated transmission power of DR;Through the active power reference value of DR and actual active power, combined with the amplitude actual value of AC grid bus voltage reaches the active power of MMC transmission when DR input voltage threshold, calculate the amplitude reference value of AC grid bus voltage, to obtain the reference value of MMC modulation voltage, and generate corresponding control pulse to realize the active power control of system.Compared with prior art, it can make MMC transmit less active power, thereby reducing the required capacity to ensure stable operation of system and improve system efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of offshore wind power direct current transmission, and in particular to a control method, device, terminal equipment and computer-readable storage medium for an offshore wind power DR-MMC parallel direct current transmission system. Background Art

[0002] Offshore wind power has the advantages of high average wind speed and small wind speed fluctuation, and has therefore become the focus of large-scale offshore wind power development in the future. With the increase in wind power grid connection capacity and distance, DC transmission has gradually become the preferred method for offshore wind power transmission. Among them, since the commonly used offshore wind power DC transmission method often uses diode rectification transmission, this method is low-cost and highly scalable, but it cannot provide voltage and frequency support for the offshore AC side grid. The transmission method of voltage source type converter valve rectification can achieve passive control, which has high voltage quality. However, considering the large size and weight of the offshore circulation platform, there are disadvantages such as difficulty in transportation and high cost. Therefore, the technical solution of hybrid DC transmission of offshore wind power through parallel connection of diode rectifier unit (DR) and modular multilevel converter (MMC) can effectively combine the advantages of both, and realize black start of offshore wind power without auxiliary equipment and flexible power transmission.

[0003] In the existing technology of large-scale offshore wind power DR-MMC parallel DC transmission, a droop coefficient is usually added to the control link to distribute power between the MMC and DR, where the MMC and DR each transmit a certain proportion of active power. However, this control method requires the MMC to transmit a certain amount of active power, so the capacity of the MMC cannot be reduced, which in turn has certain economic cost requirements and also affects the overall working efficiency of the DC transmission system. Summary of the Invention

[0004] The present invention provides a control method, apparatus, terminal device, and computer-readable storage medium for an offshore wind power DR-MMC parallel DC transmission system, enabling a modular multilevel converter to transmit as little active power as possible to reduce the capacity of the modular multilevel converter, thereby solving the technical problem of how to further improve the overall operating efficiency of the DC transmission system.

[0005] In order to solve the above technical problems, an embodiment of the present invention provides a control method for an offshore wind power DR-MMC parallel DC transmission system, comprising:

[0006] Obtaining the actual active power transmitted by the wind farm, the active power transmitted by the modular multilevel converter, the actual active power transmitted by the diode rectifier unit, and the actual value of the AC grid bus voltage amplitude at the common connection point of the modular multilevel converter and the diode rectifier unit in the offshore AC grid;

[0007] According to the actual active power transmitted by the wind farm and in combination with the rated transmission power of the diode rectifier unit, an active power reference value of the diode rectifier unit is obtained. Specifically, when the actual active power transmitted by the wind farm is less than the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the actual active power transmitted by the wind farm; when the actual active power transmitted by the wind farm is greater than or equal to the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the rated transmission power of the diode rectifier unit;

[0008] Calculating the AC grid bus voltage amplitude reference value by using the active power reference value and actual active power of the diode rectifier unit, combined with the active power transmitted by the modular multilevel converter when the actual value of the AC grid bus voltage amplitude reaches the input voltage threshold of the diode rectifier unit;

[0009] The reference value of the modulation voltage of the modular multilevel converter is calculated by using the reference value and actual value of the AC grid bus voltage amplitude, and a corresponding control pulse is generated to achieve active power control of the offshore wind power DR-MMC parallel DC transmission system.

[0010] As a preferred solution, the active power reference value and actual active power of the diode rectifier unit are combined with the active power transmitted by the modular multilevel converter when the actual value of the AC grid bus voltage amplitude reaches the input voltage threshold of the diode rectifier unit to calculate the AC grid bus voltage amplitude reference value, specifically as follows:

[0011] The AC grid bus voltage amplitude reference value is calculated according to the following formula

[0012]

[0013] Among them, E dc represents the DC side voltage rating of the modular multilevel converter, n is the number of diode 6 pulsating rectifier bridges, k is the transformation ratio of the converter transformer of the diode rectifier unit, P0 represents the active power transmitted by the modular multilevel converter when the actual value of the AC grid bus voltage amplitude reaches the input voltage threshold of the diode rectifier unit, ΔU DR Represents the difference between the initial bus voltage reference value and the diode rectifier unit input voltage threshold, KP and K I are the proportional parameter and integral parameter of the active power proportional-integral controller, s is the Laplace operator, and P DR They represent the reference value and actual value of the active power transmitted by the diode rectifier unit, and P1 represents the active power transmitted by the modular multilevel converter.

[0014] As a preferred solution, the reference value of the modulation voltage of the modular multilevel converter is calculated by using the reference value and actual value of the AC grid bus voltage amplitude, specifically:

[0015] According to the AC grid bus voltage amplitude reference value and actual value, a d-axis voltage reference value of the differential-mode voltage of the modular multilevel converter bridge arm is calculated, thereby obtaining a voltage reference value of the modulation voltage of the modular multilevel converter bridge arm in the abc stationary coordinate system.

[0016] As a preferred solution, the generation of corresponding control pulses to achieve active power control of the offshore wind power DR-MMC parallel DC transmission system is specifically as follows:

[0017] Based on the voltage reference value of the modulation voltage of the bridge arm of the modular multilevel converter in the abc stationary coordinate system, a nearest level modulation strategy and a capacitor voltage balancing strategy are used to generate control pulses for the insulated gate bipolar transistors in each bridge arm submodule of the modular multilevel converter, thereby achieving active power control of the offshore wind power DR-MMC parallel DC transmission system.

[0018] As a preferred solution, the d-axis voltage reference value of the differential-mode voltage of the bridge arm of the modular multilevel converter is calculated according to the AC grid bus voltage amplitude reference value and actual value, specifically:

[0019] The d-axis voltage reference value of the bridge arm differential mode voltage of the modular multilevel converter is calculated according to the following formula:

[0020] Among them, E dc Represents the DC side voltage rating of the modular multilevel converter, K PV and K IV Represent the proportional parameter and integral parameter of the voltage controller, U l is the actual value of the AC grid bus voltage amplitude.

[0021] As a preferred solution, the voltage reference value of the modulation voltage of the bridge arm of the modular multilevel converter in the abc stationary coordinate system is obtained as follows:

[0022] The voltage reference value of the modulation voltage of the bridge arm of the modular multilevel converter in the abc stationary coordinate system is calculated by the following formula:

[0023]

[0024] in, represents the a-axis voltage reference value of the modulation voltage of the bridge arm of the modular multilevel converter in the abc stationary coordinate system, represents the b-axis voltage reference value of the modulation voltage of the bridge arm of the modular multilevel converter in the abc stationary coordinate system, represents the c-axis voltage reference value of the modulation voltage of the bridge arm of the modular multilevel converter in the abc stationary coordinate system, and θ is the phase reference value of the modular multilevel converter.

[0025] As a preferred solution, the actual value of the active power transmitted by the diode rectifier unit is obtained according to the following formula:

[0026] P DR =1.35nkU1I DR ;

[0027] Among them, P DR is the actual value of the active power transmitted by the diode rectifier unit, U l is the actual value of the AC grid bus voltage amplitude, I DR is the DC current value output by the diode rectifier unit.

[0028] Accordingly, an embodiment of the present invention further provides a control device for an offshore wind power DR-MMC parallel DC transmission system, comprising an acquisition module, a first calculation module, a second calculation module and a control module; wherein,

[0029] The acquisition module is used to acquire the actual active power transmitted by the wind farm, the active power transmitted by the modular multilevel converter, the actual active power transmitted by the diode rectifier unit, and the actual value of the AC grid bus voltage amplitude at the common connection point between the modular multilevel converter and the diode rectifier unit in the offshore AC grid;

[0030] The first calculation module is configured to obtain an active power reference value of the diode rectifier unit based on the actual active power transmitted by the wind farm and the rated transmission power of the diode rectifier unit. Specifically, when the actual active power transmitted by the wind farm is less than the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the actual active power transmitted by the wind farm; when the actual active power transmitted by the wind farm is greater than or equal to the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the rated transmission power of the diode rectifier unit.

[0031] The second calculation module is configured to calculate the AC grid bus voltage amplitude reference value by using the active power reference value and actual active power of the diode rectifier unit and the active power transmitted by the modular multilevel converter when the actual value of the AC grid bus voltage amplitude reaches the input voltage threshold of the diode rectifier unit;

[0032] The control module is used to calculate the reference value of the modulation voltage of the modular multilevel converter based on the reference value and actual value of the AC grid bus voltage amplitude, and generate corresponding control pulses to achieve active power control of the offshore wind power DR-MMC parallel DC transmission system.

[0033] Correspondingly, an embodiment of the present invention also provides a terminal device, including a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. When the processor executes the computer program, it implements the control method of the offshore wind power DR-MMC parallel DC transmission system.

[0034] Correspondingly, an embodiment of the present invention also provides a computer-readable storage medium, which includes a stored computer program, wherein when the computer program is running, the device where the computer-readable storage medium is located is controlled to execute the control method of the offshore wind power DR-MMC parallel DC transmission system.

[0035] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0036] An embodiment of the present invention provides a control method, device, terminal equipment and computer-readable storage medium for an offshore wind power DR-MMC parallel DC transmission system. The control method includes: obtaining the actual active power transmitted by the wind farm, the active power transmitted by the modular multilevel converter, the actual active power transmitted by the diode rectifier unit and the actual value of the AC grid bus voltage amplitude at the common connection point between the modular multilevel converter and the diode rectifier unit in the offshore AC grid; according to the actual active power transmitted by the wind farm and the rated transmission power of the diode rectifier unit, obtaining the active power reference value of the diode rectifier unit. Specifically: when the actual active power transmitted by the wind farm is less than the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the rated transmission power of the diode rectifier unit. The actual active power transmitted by the wind farm. When the actual active power transmitted by the wind farm is greater than or equal to the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the rated transmission power of the diode rectifier unit; the AC grid bus voltage amplitude reference value is calculated based on the active power reference value and actual active power of the diode rectifier unit, combined with the active power transmitted by the modular multilevel converter when the actual value of the AC grid bus voltage amplitude reaches the input voltage threshold of the diode rectifier unit; the reference value of the modular multilevel converter modulation voltage is calculated based on the AC grid bus voltage amplitude reference value and actual value, and corresponding control pulses are generated to achieve active power control of the offshore wind power DR-MMC parallel DC transmission system. In implementing the embodiment of the present application, when the actual active power transmitted by the wind farm is less than the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the active power transmitted by the wind farm, that is, the remaining active power is transmitted by the modular multilevel converter. When the actual active power transmitted by the wind farm is greater than or equal to the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the rated power. Compared with the existing technology, the modular multilevel converter can transmit less active power, thereby reducing the required modular multilevel converter capacity, thereby reducing the weight and volume of the offshore converter station, making the offshore converter platform lightweight while ensuring stable operation, and improving the overall working efficiency of the DC transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 : A flow chart of an embodiment of a control method for an offshore wind power DR-MMC parallel DC transmission system provided by the present invention.

[0038] Figure 2 : A schematic diagram of simulation waveforms of an embodiment of the power of each device after a large-scale wind farm is connected to the grid provided by the present invention.

[0039] Figure 3: A structural schematic diagram of an embodiment of a control device for an offshore wind power DR-MMC parallel DC transmission system provided by the present invention. DETAILED DESCRIPTION

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0041] Embodiment one:

[0042] Please refer to Figure 1 , Figure 1 A control method for an offshore wind power DR-MMC parallel DC transmission system provided in an embodiment of the present invention includes steps S1 to S4; wherein,

[0043] DR stands for diode rectifier unit, and MMC stands for modular multilevel converter. This embodiment is primarily targeted at offshore wind farm DR-MMC parallel DC transmission systems for wind farm clusters of 1000MW and above. During system startup, the modular multilevel converter primarily provides voltage and reactive power support for the wind farm. During normal operation of the wind farm, most of the active power generated by the wind farm is transmitted through the diode rectifier unit, while the modular multilevel converter only serves to balance reactive power and ensure voltage quality. Regarding the control method of this embodiment:

[0044] Step S1: obtaining the actual active power transmitted by the wind farm, the active power transmitted by the modular multilevel converter, the actual active power transmitted by the diode rectifier unit, and the actual value of the AC grid bus voltage amplitude at the common connection point between the modular multilevel converter and the diode rectifier unit in the offshore AC grid.

[0045] Step S2: obtaining an active power reference value of the diode rectifier unit based on the actual active power delivered by the wind farm and the rated transmission power of the diode rectifier unit. Specifically, when the actual active power delivered by the wind farm is less than the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the actual active power delivered by the wind farm; when the actual active power delivered by the wind farm is greater than or equal to the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the rated transmission power of the diode rectifier unit.

[0046] Step S3: Calculate the AC grid bus voltage amplitude reference value by using the active power reference value and actual active power of the diode rectifier unit and the active power transmitted by the modular multilevel converter when the actual value of the AC grid bus voltage amplitude reaches the input voltage threshold of the diode rectifier unit.

[0047] Step S4: Calculate the reference value of the modulation voltage of the modular multilevel converter by using the reference value and actual value of the AC grid bus voltage amplitude, and generate corresponding control pulses to achieve active power control of the offshore wind power DR-MMC parallel DC transmission system.

[0048] In this embodiment, for the above step S2, the active power reference value of the diode rectifier unit is obtained based on the actual active power transmitted by the wind farm and the rated transmission power of the diode rectifier unit. Specifically, it is calculated according to the following formula:

[0049]

[0050]

[0051] Among them, S1 is the switching function, P DR,base Represents the rated transmission power of the diode rectifier unit, P WF Represents the actual active power generated by the wind farm.

[0052] Furthermore, in step S3 above, the active power reference value and actual active power of the diode rectifier unit are combined with the active power transmitted by the modular multilevel converter when the actual value of the AC grid bus voltage amplitude reaches the input voltage threshold of the diode rectifier unit to calculate the AC grid bus voltage amplitude reference value, specifically:

[0053] The AC grid bus voltage amplitude reference value is calculated according to the following formula

[0054]

[0055] Among them, E dc represents the DC side voltage rating of the modular multilevel converter, n is the number of diode 6 pulsating rectifier bridges, k is the transformation ratio of the converter transformer of the diode rectifier unit, P0 represents the active power transmitted by the modular multilevel converter when the actual value of the AC grid bus voltage amplitude reaches the input voltage threshold of the diode rectifier unit, ΔU DR Represents the difference between the initial bus voltage reference value and the diode rectifier unit input voltage threshold, K P and K Iare the proportional parameter and integral parameter of the active power proportional-integral controller, s is the Laplace operator, and P DR They represent the reference value and actual value of the active power transmitted by the diode rectifier unit, and P1 represents the active power transmitted by the modular multilevel converter.

[0056] According to Kirchhoff's voltage law and current law, the actual value of the active power transmitted by the diode rectifier unit can be obtained according to the following formula:

[0057] P DR =1.35nkU1I DR ;

[0058] Among them, P DR is the actual value of the active power transmitted by the diode rectifier unit, U l is the actual value of the AC grid bus voltage amplitude, I DR The DC current value output by the diode rectifier unit is 0.001V. As described above, the power delivered by the diode rectifier unit is linearly related to the AC bus voltage amplitude, so the power delivered by the diode rectifier unit can be controlled by the bus voltage amplitude at the common connection point.

[0059] As a preferred implementation of this embodiment, in step S4, the reference value of the modulation voltage of the modular multilevel converter is calculated by using the reference value and actual value of the AC grid bus voltage amplitude, specifically:

[0060] A d-axis voltage reference value of the differential-mode voltage of the modular multilevel converter bridge arm is calculated based on the AC power grid bus voltage amplitude reference value and the actual value, thereby obtaining a voltage reference value of the modulation voltage of the modular multilevel converter bridge arm in the abc stationary coordinate system. The voltage reference value of the modulation voltage of the modular multilevel converter bridge arm in the abc stationary coordinate system includes an a-axis voltage reference value, a b-axis voltage reference value, and a c-axis voltage reference value.

[0061] The d-axis voltage reference value of the bridge arm differential mode voltage of the modular multilevel converter Calculate according to the following formula:

[0062]

[0063] Among them, E dc Represents the DC side voltage rating of the modular multilevel converter, K PV and K IV Represent the proportional parameter and integral parameter of the voltage controller, U l is the actual value of the AC grid bus voltage amplitude.

[0064] The step of obtaining a voltage reference value of the modulation voltage of the bridge arm of the modular multilevel converter in the abc stationary coordinate system is as follows:

[0065] The voltage reference value of the modulation voltage of the bridge arm of the modular multilevel converter in the abc stationary coordinate system is calculated by the following formula:

[0066]

[0067] in, represents the a-axis voltage reference value of the modulation voltage of the bridge arm of the modular multilevel converter in the abc stationary coordinate system, represents the b-axis voltage reference value of the modulation voltage of the bridge arm of the modular multilevel converter in the abc stationary coordinate system, represents the c-axis voltage reference value of the modulation voltage of the modular multilevel converter bridge arm in the abc stationary coordinate system, and θ is the phase reference value of the modular multilevel converter. Furthermore, based on the voltage reference value of the modulation voltage of the modular multilevel converter bridge arm in the abc stationary coordinate system obtained by the above calculation, a nearest level modulation strategy and a capacitor voltage balancing strategy can be utilized to generate control pulses for the insulated gate bipolar transistors (IGBTs) in each bridge arm submodule of the offshore modular multilevel converter. These control pulses are used to control the wind power DR-MMC parallel DC transmission system. System control includes, but is not limited to, island control.

[0068] Furthermore, with respect to the control method of the above-mentioned offshore wind power DR-MMC parallel DC transmission system, this embodiment simulates a large-scale offshore wind power double-terminal MMC-DR parallel DC system. The simulation waveform diagram is shown in FIG. Figure 2 The wind farm cluster of this system includes three wind farms: H1, H2, and H3. The rated output power of wind farm H1 is 400MW, the rated output power of wind farm H2 is also 400MW, and the rated output power of wind farm H3 is 200MW.

[0069] Each wind farm uses direct-drive wind turbines with a single unit capacity of 2MW. At t = 0.2s, the offshore modular multilevel converter established the AC voltage of the offshore AC grid. At t = 0.3s, the wind turbines in wind farm H1 started and connected to the grid when the closing conditions were met. At t = 1s, the wind turbines in wind farm H2 started and connected to the grid. At t = 2s, the wind turbines in wind farm H3 connected to the grid, completing the grid connection of all wind turbines.

[0070] The modular multilevel converter uses 125 half-bridge submodules with a rated capacity of 450MVA. The diode rectifier unit uses a 12-pulse rectifier bridge with a rated power of 800MW. The system's baseline capacity is 800MW. It can be determined that when the active power generated by the wind farm is less than 800MW, the active power transmitted by the diode rectifier unit always remains consistent with the power generated by the wind farm. When the active power generated by the wind farm exceeds 800MW, the modular multilevel converter transmits the remaining power. After all wind farms are connected to the grid, the diode rectifier unit transmits 800MW of power and the modular multilevel converter transmits 200MW of power, allowing the system to smoothly transmit active power. In summary, this demonstrates that the control method provided in this embodiment can enable the modular multilevel converter to transmit less active power than in the prior art, thereby reducing the required modular multilevel converter capacity.

[0071] Accordingly, refer to Figure 3 The embodiment of the present invention further provides a control device for an offshore wind power DR-MMC parallel DC transmission system, comprising an acquisition module 101, a first calculation module 102, a second calculation module 103 and a control module 104; wherein,

[0072] The acquisition module 101 is configured to acquire the actual active power transmitted by the wind farm, the active power transmitted by the modular multilevel converter, the actual active power transmitted by the diode rectifier unit, and the actual value of the AC grid bus voltage amplitude at the common connection point between the modular multilevel converter and the diode rectifier unit in the offshore AC grid;

[0073] The first calculation module 102 is configured to obtain an active power reference value of the diode rectifier unit based on the actual active power delivered by the wind farm and the rated transmission power of the diode rectifier unit. Specifically, when the actual active power delivered by the wind farm is less than the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the actual active power delivered by the wind farm; when the actual active power delivered by the wind farm is greater than or equal to the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the rated transmission power of the diode rectifier unit.

[0074] The second calculation module 103 is configured to calculate the AC grid bus voltage amplitude reference value by using the active power reference value and actual active power of the diode rectifier unit and the active power transmitted by the modular multilevel converter when the actual value of the AC grid bus voltage amplitude reaches the input voltage threshold of the diode rectifier unit;

[0075] The control module 104 is configured to calculate a reference value of the modulation voltage of the modular multilevel converter based on the reference value and actual value of the AC grid bus voltage amplitude, and generate corresponding control pulses to achieve active power control of the offshore wind power DR-MMC parallel DC transmission system.

[0076] Correspondingly, an embodiment of the present invention also provides a terminal device, including a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. When the processor executes the computer program, it implements the control method of the offshore wind power DR-MMC parallel DC transmission system.

[0077] The processor may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor, etc. The processor is the control center of the terminal, connecting various parts of the entire terminal using various interfaces and lines.

[0078] The memory can be used to store the computer program, and the processor realizes various functions of the terminal by running or executing the computer program stored in the memory and calling the data stored in the memory. The memory can mainly include a program storage area and a data storage area, wherein the program storage area can store an operating system, at least one application required for a function (such as a sound playback function, an image playback function, etc.); the data storage area can store data created according to the use of the mobile phone (such as audio data, a phone book, etc.). In addition, the memory can include a high-speed random access memory and can also include a non-volatile memory, such as a hard disk, a memory, a plug-in hard disk, a smart memory card (SmartMedia Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), at least one disk storage device, a flash memory device, or other volatile solid-state storage device.

[0079] Correspondingly, an embodiment of the present invention also provides a computer-readable storage medium, which includes a stored computer program, wherein when the computer program is running, the device where the computer-readable storage medium is located is controlled to execute the control method of the offshore wind power DR-MMC parallel DC transmission system.

[0080] Wherein, if the module integrated in the control device of the offshore wind power DR-MMC parallel DC transmission system is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, it can implement the steps of the above-mentioned various method embodiments. Wherein, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device that can carry the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal and software distribution medium, etc.

[0081] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0082] An embodiment of the present invention provides a control method, device, terminal equipment and computer-readable storage medium for an offshore wind power DR-MMC parallel DC transmission system. The control method includes: obtaining the actual active power transmitted by the wind farm, the active power transmitted by the modular multilevel converter, the actual active power transmitted by the diode rectifier unit and the actual value of the AC grid bus voltage amplitude at the common connection point between the modular multilevel converter and the diode rectifier unit in the offshore AC grid; according to the actual active power transmitted by the wind farm and the rated transmission power of the diode rectifier unit, obtaining the active power reference value of the diode rectifier unit. Specifically: when the actual active power transmitted by the wind farm is less than the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the rated transmission power of the diode rectifier unit. The actual active power transmitted by the wind farm. When the actual active power transmitted by the wind farm is greater than or equal to the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the rated transmission power of the diode rectifier unit; the AC grid bus voltage amplitude reference value is calculated based on the active power reference value and actual active power of the diode rectifier unit, combined with the active power transmitted by the modular multilevel converter when the actual value of the AC grid bus voltage amplitude reaches the input voltage threshold of the diode rectifier unit; the reference value of the modular multilevel converter modulation voltage is calculated based on the AC grid bus voltage amplitude reference value and actual value, and corresponding control pulses are generated to achieve active power control of the offshore wind power DR-MMC parallel DC transmission system. In implementing the embodiment of the present application, when the actual active power transmitted by the wind farm is less than the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the active power transmitted by the wind farm, that is, the remaining active power is transmitted by the modular multilevel converter. When the actual active power transmitted by the wind farm is greater than or equal to the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the rated power. Compared with the existing technology, the modular multilevel converter can transmit less active power, thereby reducing the required modular multilevel converter capacity, thereby reducing the weight and volume of the offshore converter station, making the offshore converter platform lightweight while ensuring stable operation, and improving the overall working efficiency of the DC transmission system.

[0083] The specific embodiments described above further illustrate the objectives, technical solutions, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A control method for an offshore wind power DR-MMC parallel DC transmission system, characterized in that: include: Obtaining the actual active power transmitted by the wind farm, the active power transmitted by the modular multilevel converter, the actual active power transmitted by the diode rectifier unit, and the actual value of the AC grid bus voltage amplitude at the common connection point of the modular multilevel converter and the diode rectifier unit in the offshore AC grid; According to the actual active power transmitted by the wind farm and in combination with the rated transmission power of the diode rectifier unit, an active power reference value of the diode rectifier unit is obtained. Specifically, when the actual active power transmitted by the wind farm is less than the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the actual active power transmitted by the wind farm; when the actual active power transmitted by the wind farm is greater than or equal to the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the rated transmission power of the diode rectifier unit; Calculating the AC grid bus voltage amplitude reference value by using the active power reference value and actual active power of the diode rectifier unit, combined with the active power transmitted by the modular multilevel converter when the actual value of the AC grid bus voltage amplitude reaches the input voltage threshold of the diode rectifier unit; Calculating a reference value of the modulation voltage of the modular multilevel converter using the reference value and actual value of the AC grid bus voltage amplitude, and generating corresponding control pulses to achieve active power control of the offshore wind power DR-MMC parallel DC transmission system; The active power reference value and actual active power of the diode rectifier unit are combined with the active power transmitted by the modular multilevel converter when the actual value of the AC grid bus voltage amplitude reaches the input voltage threshold of the diode rectifier unit to calculate the AC grid bus voltage amplitude reference value, specifically: The AC grid bus voltage amplitude reference value is calculated according to the following formula : ； Among them, E dc represents the DC side voltage rating of the modular multilevel converter, n is the number of diode 6 pulsating rectifier bridges, k is the transformation ratio of the converter transformer of the diode rectifier unit, P0 represents the active power transmitted by the modular multilevel converter when the actual value of the AC grid bus voltage amplitude reaches the input voltage threshold of the diode rectifier unit, Represents the difference between the initial bus voltage reference value and the diode rectifier unit input voltage threshold, K P and K I are the proportional parameter and integral parameter of the active power proportional-integral controller, s is the Laplace operator, and They represent the reference value and actual value of the active power transmitted by the diode rectifier unit, and P1 represents the active power transmitted by the modular multilevel converter.

2. The control method of the offshore wind power DR-MMC parallel DC transmission system according to claim 1, characterized in that: The reference value of the modulation voltage of the modular multilevel converter is calculated by using the reference value and actual value of the AC grid bus voltage amplitude, specifically: According to the AC grid bus voltage amplitude reference value and actual value, a d-axis voltage reference value of the differential-mode voltage of the modular multilevel converter bridge arm is calculated, thereby obtaining a voltage reference value of the modulation voltage of the modular multilevel converter bridge arm in the abc stationary coordinate system.

3. The control method of the offshore wind power DR-MMC parallel DC transmission system according to claim 2, characterized in that: The generating of corresponding control pulses to realize active power control of the offshore wind power DR-MMC parallel DC transmission system is specifically as follows: Based on the voltage reference value of the modulation voltage of the bridge arm of the modular multilevel converter in the abc stationary coordinate system, a nearest level modulation strategy and a capacitor voltage balancing strategy are used to generate control pulses for the insulated gate bipolar transistors in each bridge arm submodule of the modular multilevel converter, thereby achieving active power control of the offshore wind power DR-MMC parallel DC transmission system.

4. The control method of the offshore wind power DR-MMC parallel DC transmission system according to claim 2, characterized in that: The d-axis voltage reference value of the bridge arm differential mode voltage of the modular multilevel converter is calculated according to the AC grid bus voltage amplitude reference value and actual value, specifically: The d-axis voltage reference value of the bridge arm differential mode voltage of the modular multilevel converter is calculated according to the following formula: : ； in, Represents the DC side voltage rating of the modular multilevel converter, K PV and K IV Represent the proportional parameter and integral parameter of the voltage controller, U l is the actual value of the AC grid bus voltage amplitude.

5. The control method of the offshore wind power DR-MMC parallel DC transmission system according to claim 4, characterized in that: The step of obtaining a voltage reference value of the modulation voltage of the bridge arm of the modular multilevel converter in the abc stationary coordinate system is as follows: The voltage reference value of the modulation voltage of the bridge arm of the modular multilevel converter in the abc stationary coordinate system is calculated by the following formula: ； in, represents the a-axis voltage reference value of the modulation voltage of the bridge arm of the modular multilevel converter in the abc stationary coordinate system, represents the b-axis voltage reference value of the modulation voltage of the bridge arm of the modular multilevel converter in the abc stationary coordinate system, represents the c-axis voltage reference value of the modulation voltage of the bridge arm of the modular multilevel converter in the abc stationary coordinate system, is the phase reference value of the modular multilevel converter.

6. The control method of the offshore wind power DR-MMC parallel DC transmission system according to claim 1, characterized in that: The actual value of the active power transmitted by the diode rectifier unit is obtained according to the following formula: ； Among them, P DR is the actual value of the active power transmitted by the diode rectifier unit, U l is the actual value of the AC grid bus voltage amplitude, I DR is the DC current value output by the diode rectifier unit.

7. A control device for an offshore wind power DR-MMC parallel DC transmission system, characterized in that: It includes an acquisition module, a first calculation module, a second calculation module and a control module; wherein, The acquisition module is used to acquire the actual active power transmitted by the wind farm, the active power transmitted by the modular multilevel converter, the actual active power transmitted by the diode rectifier unit, and the actual value of the AC grid bus voltage amplitude at the common connection point between the modular multilevel converter and the diode rectifier unit in the offshore AC grid; The first calculation module is configured to obtain an active power reference value of the diode rectifier unit based on the actual active power transmitted by the wind farm and the rated transmission power of the diode rectifier unit. Specifically, when the actual active power transmitted by the wind farm is less than the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the actual active power transmitted by the wind farm; when the actual active power transmitted by the wind farm is greater than or equal to the rated transmission power of the diode rectifier unit, the active power reference value of the diode rectifier unit is the rated transmission power of the diode rectifier unit. The second calculation module is configured to calculate the AC grid bus voltage amplitude reference value by using the active power reference value and actual active power of the diode rectifier unit and the active power transmitted by the modular multilevel converter when the actual value of the AC grid bus voltage amplitude reaches the input voltage threshold of the diode rectifier unit; The control module is configured to calculate a reference value of the modulation voltage of the modular multilevel converter based on the reference value and actual value of the AC grid bus voltage amplitude, and generate corresponding control pulses to achieve active power control of the offshore wind power DR-MMC parallel DC transmission system; The second calculation module calculates the AC grid bus voltage amplitude reference value by using the active power reference value and actual active power of the diode rectifier unit, combined with the active power transmitted by the modular multilevel converter when the actual value of the AC grid bus voltage amplitude reaches the input voltage threshold of the diode rectifier unit, specifically: The second calculation module calculates the AC grid bus voltage amplitude reference value according to the following formula: : ； Among them, E dc represents the DC side voltage rating of the modular multilevel converter, n is the number of diode 6 pulsating rectifier bridges, k is the transformation ratio of the converter transformer of the diode rectifier unit, P0 represents the active power transmitted by the modular multilevel converter when the actual value of the AC grid bus voltage amplitude reaches the input voltage threshold of the diode rectifier unit, Represents the difference between the initial bus voltage reference value and the diode rectifier unit input voltage threshold, K P and K I are the proportional parameter and integral parameter of the active power proportional-integral controller, s is the Laplace operator, and They represent the reference value and actual value of the active power transmitted by the diode rectifier unit, and P1 represents the active power transmitted by the modular multilevel converter.

8. A terminal device, characterized in that: The invention comprises a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein when the processor executes the computer program, the control method of the offshore wind power DR-MMC parallel DC transmission system according to any one of claims 1 to 6 is implemented.

9. A computer-readable storage medium, characterized in that The computer-readable storage medium includes a stored computer program, wherein, when the computer program is running, the device where the computer-readable storage medium is located is controlled to execute a control method for an offshore wind power DR-MMC parallel DC transmission system according to any one of claims 1 to 6.

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