Offshore wind power dc transmission system reactive power balance control method and system

Abstract

The application discloses a kind of offshore wind power DC transmission system reactive power balance control method and system, using the thought of feedforward control, using the strong coupling relationship of reactive power consumption and active input, by changing the reactive power output of wind turbine, the reactive power consumption of diode rectifier unit is dynamically compensated, the reactive power compensation capability of reactive power compensation device and wind turbine generator can be effectively combined, the reactive power balance of system is realized, and the stability of system is improved to ensure the normal transmission of electric energy.

Description

Technical Field

[0001] The present invention relates to an offshore wind power direct current transmission project, and in particular to a reactive power balance control method for an offshore wind power direct current transmission system. Background Art

[0002] In recent years, offshore wind farms have continued to grow in size, scale, and depth. Traditional AC transmission methods are unable to meet these demands, and DC transmission has gradually become the dominant method for offshore wind power transmission. Currently, the primary offshore wind power transmission method in engineering projects utilizes flexible DC transmission based on modular multilevel converters (MMCs). Flexible DC transmission systems offer passive operation capabilities and flexible control.

[0003] MMC converter stations are large and heavy, with complex topologies and control systems. As offshore wind farms move farther from shore, their construction difficulty, investment, and maintenance costs continue to rise. To address the economic viability of offshore MMC converter stations, an offshore wind power DC transmission system based on grid-type wind turbines and diode rectifier units is being adopted. Replacing MMC rectifier stations with offshore diode rectifier stations can significantly reduce project costs. However, due to the uncontrolled nature of diodes, they consume a significant amount of reactive power during the rectification process. Failure to compensate for this reactive power will affect the diode's commutation process, and thus the system's power transmission.

[0004] CN115632429A provides a reactive power control method and device for an offshore wind power low-frequency AC transmission system. The method determines the reactive power reference value required by the wind farm in combination with the power transmission characteristics of a diode rectifier, calculates the actual power margin of the wind turbines in each area, and obtains the reactive power instructions of the wind farms in different areas based on the actual power margin and the total reactive power reference value. The reactive power instructions are optimized and adjusted according to the reactive power threshold range allowed by the wind turbine converters in each area, and the adjusted reactive power instructions are sent to the wind turbines in the corresponding area, so that the wind turbines in each area perform reactive power control according to the received reactive power instructions. This scheme uses low-frequency AC transmission for offshore wind power, but the transmission distance and capacity of low-frequency transmission are limited. When the transmission capacity of offshore wind power reaches the GW level and the transmission distance exceeds 120km, the DC transmission scheme is the internationally recognized offshore wind power transmission solution. Therefore, the reactive power control method and device for the offshore wind power low-frequency AC transmission system proposed in CN115632429A cannot meet the needs of offshore wind power DC transmission.

[0005] Reducing the investment cost of DC transmission for offshore wind power is a critical issue for the future of offshore wind power. Compared to MMC devices, diode rectifiers offer advantages such as lower cost, smaller size, lighter weight, and higher reliability. Offshore DC transmission solutions based on diode rectifiers have the potential to reduce offshore converter station volume by 50%, platform load requirements by 40%, and total investment costs by 30%. However, due to the limited space and load-bearing capacity of offshore platforms, the capacity of AC filters is limited, and the reactive power compensation they provide is insufficient to meet the reactive power requirements of diode rectifiers. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a reactive power balance control method and system for an offshore wind power DC transmission system to compensate for the reactive power consumption of a diode rectifier unit in real time, in view of the deficiencies in the existing technology.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is: a reactive power balance control method for an offshore wind power DC transmission system, wherein the offshore wind power DC transmission system includes an offshore wind farm, an offshore diode rectifier station, a DC transmission line, an onshore MMC inverter station, and an onshore power grid connected in sequence; the offshore wind farm uses a permanent magnet direct-drive wind turbine generator set, and the unit equipment mainly includes an impeller, a synchronous generator, a machine-side converter, a grid-side converter, etc.; the offshore diode rectifier station includes an AC filter, a converter transformer, and a twelve-pulse diode rectifier unit connected in sequence; the method includes:

[0008] The reactive power margin ΔQ of offshore wind farm compensation is determined using the following formula: ΔQ = Q d -Q f ; Using the reactive power margin ΔQ to determine the reactive power command value Q of each wind turbine wi * ;Q d is the reactive power demand of the twelve-pulse diode rectifier unit, Q f is the reactive compensation capacity of the AC filter;

[0009] The reactive power command value Q wi * The deviation Q from the actual value of the wind turbine output reactive power wi * -Q wi After the PI controller, the AC voltage phase angle command value θ is generated * ;

[0010] byU fm * and phase angle command value θ * Get the AC voltage reference value U fabc , AC voltage reference value U fabcAfter abc-dq transformation, the d-axis reference voltage U is generated fd * and q-axis reference voltage U fq * ; d-axis reference voltage U fd * and the actual voltage U of the d-axis fd The difference U fd * -U fd After the PI controller, the inductor current d-axis command value i is generated. Ld * ;q-axis reference voltage U fq * The actual voltage U of the q axis fq The difference U fq * -U fq The PI controller generates the inductor current q-axis command value i Lq * ;;

[0011] Inductor current d-axis reference value i Ld * The actual value of the inductor current d axis i Ld The difference i Ld * -i Ld The modulation voltage command value u is generated through PI controller and decoupling control fd * , inductor current q-axis reference value i Lq * The actual value of the inductor current q axis i Lq The difference i Ld * -i Ld The modulation voltage command value u is generated through PI controller and decoupling control fd * ,i Lq * -i Lq The modulation voltage command value u is generated through PI controller and decoupling control fq * ;

[0012] u fd * and u fq * After dq-αβ conversion, an input signal is generated, and the input signal is modulated by SVPWM to generate a PWM signal that drives the grid-side converter switch to operate.

[0013] Among them, P dis the active power input of the twelve-pulse diode rectifier unit, is the power factor angle, P w is the active power output of the offshore wind farm.

[0014] Where μ = arccos(1-u k );u k is the short-circuit impedance of the converter transformer.

[0015] Reactive power command value Q wi * The calculation formula is: Among them, Q w =ΔQ,P wi * is the active power command value of the wind turbine, P w is the active power output of the offshore wind farm, is the power factor angle, and n is the number of wind turbines in the offshore wind farm.

[0016] The present invention also provides a reactive power balance control system for an offshore wind power DC transmission system, which comprises:

[0017] A memory for storing instructions; wherein the instructions are used to implement the reactive power balance control method for the offshore wind power direct current transmission system as described above;

[0018] A processor is configured to execute instructions in the memory.

[0019] The present invention also provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the reactive power balance control method for the offshore wind power DC transmission system as described above is implemented.

[0020] Compared with the prior art, the present invention has the following beneficial effects: the present invention can reasonably configure the reactive compensation device of the offshore rectifier station, fully utilize the reactive compensation capacity of the reactive compensation device, achieve optimal utilization of the equipment and minimize the investment cost of the equipment; the present invention adopts the idea of ​​feedforward control, utilizes the strong coupling relationship between reactive consumption and active input, and dynamically compensates the reactive consumption of the diode rectifier unit by changing the reactive power output of the wind turbine. It can effectively combine the reactive compensation capacity of the reactive compensation device and the wind turbine to achieve reactive power balance of the system, improve the stability of the system to ensure the normal transmission of electric energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a topological diagram of an offshore wind power DC transmission system based on grid-type wind turbines and diode rectifier units in one embodiment of the present invention.

[0022] The components in the figure are numbered as follows: 1 is the converter transformer, 2 is the twelve-pulse diode rectifier unit, 3 is the onshore MMC converter station, 4 is the onshore converter transformer, and 5 is the onshore AC power grid.

[0023] Figure 2 This is a schematic diagram of reactive power balance control principle of an offshore system in one embodiment of the present invention.

[0024] The components in the figure are numbered as follows: 6 is the impeller, 7 is the permanent magnet synchronous generator, 8 is the machine-side converter, 9 is the grid-side converter, 10 is the wind turbine grid-connected filter, and 11 is the wind turbine step-up transformer.

[0025] Figure 3 This is a control principle diagram of a grid-side converter for a grid-type wind turbine in one embodiment of the present invention. DETAILED DESCRIPTION

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0027] Example 1

[0028] like Figure 1 As shown, embodiment 1 of the present invention provides a reactive power balance control method for an offshore wind power DC transmission system based on a grid-type wind turbine and a diode rectifier unit, which is applied to the offshore wind power DC transmission system. The offshore wind power DC transmission system includes: an offshore wind farm, an offshore diode rectifier station, a DC transmission line, an onshore MMC converter station, and an onshore AC power grid. The offshore diode rectifier station includes an AC filter, a converter transformer, and a twelve-pulse diode rectifier unit. The reactive power balance control method of this embodiment includes:

[0029] A) According to the power characteristics of the diode rectifier unit, the active power P output by the wind farm is obtained w The reactive power Q consumed by the diode rectifier unit d The relationship between the active power of the wind turbine and the reactive power of the diode rectifier unit is established based on the relationship. The specific process is as follows:

[0030] A1) According to the short-circuit impedance of the converter transformer, calculate the commutation angle μ under rated operating conditions = arccos(1-u k ).

[0031] A2) Calculate the power factor angle The tangent value of

[0032] A3) Calculate the reactive power consumed by the diode rectifier unit

[0033] B) Research the configuration scheme and harmonic suppression scheme of the AC filter device, design the parameters of the AC filter, and determine the reactive power compensation capacity Q of the AC filter f . Further, the reactive power balance ΔQ of the offshore wind farm can be determined, ΔQ = Q d - Q f , and finally the reactive power instruction value Q wi * . The specific process is as follows:

[0034] B1) Analyze the characteristic harmonic orders of the 12-pulse rectifier station, mainly containing 11, 13, 23, and 25 orders. Select double-tuned filters to realize the AC filtering and reactive power compensation of the system, and use two sets of double-tuned filters as backup for each other, and set the tuning points at 12 and 24 orders.

[0035] B2) Set the reactive power compensation capacity Q f of the filter.

[0036] B3) Calculate the reactive power Q w that needs to be provided by the offshore wind farm d = Q f . Assuming that there are n grid-connected wind turbines, the required reactive power provided by each wind turbine is

[0037] C) Design the control strategy of the offshore wind farm back-to-back converter, and the control target of the machine-side converter is the DC bus voltage U dc of the back-to-back converter. w , and realize the decoupling of the active power P w and the reactive power Q f of the wind turbine. The control target of the grid-side converter is the output AC voltage U wi with stable amplitude and frequency, and the instruction values of the amplitude and frequency are obtained by the active power controller and the reactive power controller, respectively. Set the reactive power instruction value of the reactive power controller to Q * , which can realize dynamic compensation of the diode reactive power consumption and realize the reactive power balance of the system, as shown in Figure 2 , the specific process is as follows:

[0038] C1) Use the maximum power tracking controller to generate the active power instruction value P wi * of the grid-connected wind turbine. wi * - Pwi The AC voltage amplitude command value U is generated by the PI controller fm * According to the calculation result of step B), the reactive power command value is composed of the active power command P wi * Calculated, Get the deviation Q between the reactive power command value and the actual value of the wind turbine output reactive power wi * -Q wi The PI controller generates the AC voltage phase angle command value θ * .

[0039] C2) by U fm * and phase angle command value θ * The AC voltage reference value U can be obtained fabc , after abc-dq transformation, the d-axis reference voltage U is generated fd * and q-axis reference voltage U fq * d-axis reference voltage U fd * and the actual voltage U of the d-axis fd The difference U fd * -U fd The PI controller generates the inductor current d-axis command value i Ld * ;q-axis reference voltage U fq * The actual voltage U of the q axis fq The difference U fq * -U fq The PI controller generates the inductor current q-axis command value i Ld * .

[0040] C3) Inductor current d-axis reference value i Ld * The actual value of the inductor current d axis i Ld The difference i Ld * -i Ld After the PI controller and decoupling control (see Modeling and Simulation of Wind Power Generation System (Wind Power Generation Engineering Technology Series) [M]. Beijing: China Water Resources and Hydropower Press, 2015), the modulation voltage command value u is generated. fd * , inductor current q-axis reference value i Lq * The actual value of the inductor current q axis i Lq The difference iLq * -i Lq The modulation voltage command value u is generated through PI controller and decoupling control fq * .

[0041] C4)u fd * and u fq * After dq-αβ transformation, the control input signal of the SVPWM module is generated, and finally the SVPWM modulation is used to generate the PWM signal that drives the PWM converter switch to work.

[0042] The reactive power balance control method of an offshore wind power DC transmission system based on a grid-type wind turbine and a diode rectifier unit in an embodiment of the present invention can improve the stability and equipment utilization rate of the offshore wind power DC transmission system, achieve optimal utilization of electrical equipment and smooth transmission of system power.

[0043] Example 2

[0044] Embodiment 2 of the present invention provides a terminal device corresponding to the above-mentioned embodiment 1. The terminal device can be a processing device for a client, such as a mobile phone, a laptop computer, a tablet computer, a desktop computer, etc., to execute the method of the above-mentioned embodiment.

[0045] The terminal device of this embodiment includes a memory, a processor, and a computer program stored in the memory; the processor executes the computer program in the memory to implement the steps of the method in the above-mentioned embodiment 1.

[0046] In some implementations, the memory may be a high-speed random access memory (RAM), and may also include a non-volatile memory, such as at least one disk storage.

[0047] In other implementations, the processor may be a central processing unit (CPU), a digital signal processor (DSP), or other general-purpose processors, which are not limited here.

[0048] Example 3

[0049] Embodiment 3 of the present invention provides a computer-readable storage medium corresponding to the above-mentioned embodiment 1, on which a computer program / instruction is stored. When the computer program / instruction is executed by a processor, the steps of the method of the above-mentioned embodiment 1 are implemented.

[0050] Computer readable storage media can be tangible devices that hold and store instructions used by instruction execution devices. Computer readable storage media can be, for example, but not limited to, electronic storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any combination thereof.

[0051] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code. The scheme in the embodiment of the present application can be implemented in various computer languages, for example, object-oriented programming language Java and literal translation scripting language JavaScript, etc.

[0052] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0053] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0054] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0055] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A reactive power balance control method for an offshore wind power DC transmission system, wherein the offshore wind power DC transmission system comprises an offshore wind farm, an offshore diode rectifier station, a DC transmission line, an onshore MMC inverter station, and an onshore power grid connected in sequence; the offshore diode rectifier station comprises an AC filter, a converter transformer, and a twelve-pulse diode rectifier unit connected in sequence; the method is characterized in that: The method includes: The reactive power margin ΔQ of offshore wind farm compensation is determined using the following formula: ΔQ = Q d -Q f ; Using the reactive power margin ΔQ to determine the reactive power command value Q of each wind turbine wi * ;Q d is the reactive power demand of the twelve-pulse diode rectifier unit, Q f is the reactive compensation capacity of the AC filter; The reactive power command value Q wi * The deviation Q from the actual value of the wind turbine output reactive power wi * -Q wi After the PI controller, the AC voltage phase angle command value θ is generated * ; byU fm * and phase angle command value θ * Get the AC voltage reference value U fabc , AC voltage reference value U fabc After abc-dq transformation, the d-axis reference voltage U is generated fd * and q-axis reference voltage U fq * ; d-axis reference voltage U fd * and the actual voltage U of the d-axis fd The difference U fd * -U fd After the PI controller, the inductor current d-axis command value i is generated. Ld * ;q-axis reference voltage U fq * The actual voltage U of the q axis fq The difference U fq * -U fq The PI controller generates the inductor current q-axis command value i Lq * ; Inductor current d-axis reference value i Ld * The actual value of the inductor current d axis i Ld The difference i Ld * -i Ld The modulation voltage command value u is generated through PI controller and decoupling control fd * , inductor current q-axis reference value i Lq * The actual value of the inductor current q axis i Lq The difference i Lq * -i Lq The modulation voltage command value u is generated through PI controller and decoupling control fq * ; u fd * and u fq * After dq-αβ conversion, an input signal is generated, and the input signal is modulated by SVPWM to generate a PWM signal that drives the switch of the grid-side converter of the offshore wind farm.

2. The reactive power balance control method of the offshore wind power DC transmission system according to claim 1 is characterized in that: Among them, P d is the active power input of the twelve-pulse diode rectifier unit, is the power factor angle, P w is the active power output of the offshore wind farm.

3. The reactive power balance control method of the offshore wind power DC transmission system according to claim 2 is characterized in that: Where μ = arccos(1-u k );u k is the short-circuit impedance of the converter transformer.

4. The reactive power balance control method of an offshore wind power DC transmission system according to claim 1, characterized in that: Reactive power command value Q wi * The calculation formula is: Among them, Q w =ΔQ,P wi * is the active power command value of the wind turbine, P w is the active power output of the offshore wind farm, is the power factor angle, and n is the number of wind turbines in the offshore wind farm.

5. A reactive power balance control system for an offshore wind power DC transmission system, characterized in that: include: A memory for storing instructions; wherein the instructions are used to implement the reactive power balance control method for an offshore wind power direct current transmission system according to any one of claims 1 to 4; A processor is configured to execute instructions in the memory.

6. A computer-readable storage medium, characterized in that The computer-readable storage medium stores a computer program, and when the computer program is executed by the processor, the method for controlling reactive power balance of an offshore wind power direct current transmission system according to any one of claims 1 to 4 is implemented.

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