Offshore wind power low-frequency alternating current sending-out system and starting method thereof

Abstract

According to the offshore wind power low-frequency alternating current sending-out system and the starting method thereof, a small-capacity energy storage device is arranged on the direct current side of a current converter of a small number of offshore wind turbine units, so that the small-capacity energy storage device becomes an energy storage fan and has the self-starting capacity, and the energy storage device assists starting of a mechanical part and a machine side current converter of the wind turbine units; in the process that the alternating voltage of the wind power plant linearly rises, one energy storage fan is made to maintain active power balance of the offshore wind power plant, the output active power of other energy storage fans is controlled to be zero, and active circulation among the energy storage fans is avoided; all energy storage fans are controlled to output active power, so that the alternating voltage amplitude of the offshore wind plant is close to a rated value.

Description

Technical Field

[0001] The present invention relates to offshore wind turbine start-up technology, and in particular to an offshore wind power low-frequency alternating current transmission system and a start-up method thereof. Background Art

[0002] Large-scale and high-quality development of the wind power industry is an important strategic choice for implementing the "dual carbon" goals and tasks. Wind power generation is one of the main energy sources for building a new power system. With the continuous development of wind power generation technology, the scale of wind farms continues to expand and gradually expand to deep sea areas.

[0003] At present, offshore wind power mainly adopts flexible direct current transmission system transmission scheme, relying on offshore converter stations to provide AC voltage support. The weight and volume of offshore converter station equipment are large, and the cost of adopting direct current transmission technology is high. In recent years, some scholars have proposed a technical solution for low-frequency AC transmission of offshore wind farms based on DRU (Diode Rectifier Unit). The wind turbine converter adopts a grid-type control strategy to construct low-frequency AC voltage, increases the length of AC submarine cables, and places offshore converter stations on land, which can greatly reduce construction costs. It has high research value and good application prospects.

[0004] During the black start process of an offshore wind farm, the black start power supply needs to first establish the AC voltage of the offshore wind farm, but the DRU is uncontrollable and has unidirectional current flow, so it cannot be used as the black start power supply of the offshore wind farm. In existing literature, the AC voltage establishment method using diesel generators as black start power supplies does not consider the case of connecting to DRUs, and the synchronous operation capability of diesel engines and grid-type wind turbine converters during the subsequent startup process needs to be studied. The solution of configuring large-capacity auxiliary converters and centralized energy storage will reduce the economic advantages of low-frequency AC transmission. Summary of the invention

[0005] Based on this, the present invention proposes an offshore wind power low-frequency AC transmission system and a starting method thereof, and a small-capacity energy storage device is arranged on the DC side of the converter of a small number of offshore wind turbines to make them into energy storage wind turbines, which jointly establish the AC voltage of the low-frequency AC system.

[0006] In a first aspect, the present invention proposes an offshore wind power low-frequency AC transmission system, comprising an offshore wind farm, an AC cable, an onshore converter station and an AC power grid, wherein the offshore wind farm comprises a wind turbine and a step-up transformer, and the wind turbine is connected to the AC power grid through the step-up transformer; a first side of the onshore converter station is connected to the AC power grid through a low-frequency AC bus, and a second side is connected to an onshore AC system;

[0007] Among them, energy storage devices are provided on the DC side of the converters of several wind turbines in the offshore wind farm, and the several wind turbines constitute energy storage wind turbines in the offshore wind farm.

[0008] Furthermore, the onshore converter station also includes a low-frequency side converter transformer, a diode rectifier unit, a modular multilevel converter, an AC side converter transformer, a reactive power compensation device, and an AC filter;

[0009] The low-frequency side converter transformer, reactive power compensation device, and AC filter are connected in parallel at the low-frequency AC bus, the AC side of the diode rectifier unit is connected to the low-frequency side converter transformer, the DC side of the diode rectifier unit is connected to the DC side of the modular multilevel converter, and the AC side of the modular multilevel converter is connected to the onshore AC system through the AC side converter transformer.

[0010] In a second aspect, the present invention provides a method for starting an offshore wind power low-frequency AC transmission system, comprising:

[0011] Start the energy storage devices of several wind turbines to start the energy storage wind turbines;

[0012] Only one energy storage wind turbine is controlled to output active power, which is recorded as a power balancing wind turbine. The d-axis voltage of the grid-connected point of the grid-side converter of the power balancing wind turbine is calculated, so that the AC voltage of the offshore wind farm rises linearly to the initial voltage value.

[0013] After the AC voltage rises linearly to the initial voltage value, all energy storage fans are controlled to output active power.

[0014] Furthermore, before the AC voltage of the offshore wind farm rises linearly to the initial voltage value, the voltage reference value of the d-axis voltage at the grid connection point of the grid-side converter of the power balancing wind turbine is calculated as follows:

[0015]

[0016] Where t is time, v u is the rate of increase of the AC voltage amplitude;

[0017] The reference value of the d-axis voltage at the grid connection point of the grid-side converter of other energy storage wind turbines except the power balancing wind turbine is calculated as follows:

[0018]

[0019] Among them, s is the Laplace operator, t is time, v u is the rate of increase of the AC voltage amplitude, P j (j=2,3,…,n) is the actual value of the active power of the energy storage fan, k p and k i They are the proportional parameter and integral parameter of the active power controller respectively, and n represents the number of energy storage wind turbines in the offshore wind farm.

[0020] Furthermore, after the AC voltage rises linearly to the initial voltage value, the voltage reference value of the d-axis voltage at the grid connection point of the energy storage wind turbine is calculated as follows:

[0021]

[0022] Among them, s is the Laplace operator, u f0 is the initial value of the AC voltage, P i * and P i is the active power reference value and actual active power value of the i-th energy storage wind turbine, k pa and k ia are the proportional and integral parameters of the active power controller respectively;

[0023] The active power reference value of the energy storage fan is calculated as follows:

[0024]

[0025] Among them, V dcDRU is the DRU DC voltage, U g is the voltage amplitude at the low-frequency AC bus, T DRU and X T are the transformation ratio and leakage reactance of the DRU converter respectively, and n is the number of energy storage wind turbines.

[0026] Furthermore, after the AC voltage rises linearly to the initial voltage value, the active power reference value of the energy storage wind turbine meets the following conditions:

[0027] (1) Voltage amplitude U at the low-frequency AC bus of the onshore converter station g Greater than 0.95pu

[0028] (2) The active power reference value of the energy storage fan is less than the capacity of the energy storage fan.

[0029] Further, starting the energy storage devices of several wind turbines to start the energy storage wind turbines includes:

[0030] Starting the energy storage device to charge the DC capacitor of the fan converter of the energy storage fan;

[0031] Start the mechanical part of the energy storage fan and establish the AC voltage of the machine-side converter of the energy storage fan;

[0032] The generator-side converter is unlocked according to the AC voltage of the generator-side converter, the DC voltage of the wind turbine converter is controlled to its rated value, and the energy storage device is locked;

[0033] Control the grid-side converters of all energy storage wind turbines to unlock, and calculate the phase reference value of the grid-side converter and the d-axis voltage reference value of the grid connection point.

[0034] Furthermore, the phase reference value of the grid-side converter of the energy storage wind turbine is calculated as follows:

[0035]

[0036] Among them, s is the Laplace operator, ω base is the reference value of voltage frequency, ω 0 is the initial value of the voltage frequency, K G and K T are the proportional and time parameters of the first-order inertial controller, Q i (i=1,2,…,n) is the actual value of reactive power of the energy storage fan, Q i * is the reactive power reference value of the energy storage fan. All energy storage fans take the same proportional parameter K G and reactive power reference value Q i * , so that the reactive power is evenly distributed among the energy storage wind turbines.

[0037] In a third aspect, the present invention provides a starting device for an offshore wind power low-frequency AC transmission system, comprising:

[0038] Energy storage wind turbine starting module, used to start the energy storage devices of several wind turbines to start the energy storage wind turbines;

[0039] The energy storage fan output control module is used to perform the following processes:

[0040] Only one energy storage wind turbine is controlled to output active power, which is recorded as a power balancing wind turbine. The d-axis voltage of the grid-connected point of the grid-side converter of the power balancing wind turbine is calculated, so that the AC voltage of the offshore wind farm rises linearly to the initial voltage value.

[0041] After the AC voltage rises linearly to the initial voltage value, all energy storage fans are controlled to output active power.

[0042] In a fourth aspect, the present invention provides an electronic device comprising a memory storing computer executable instructions and a processor, wherein when the computer executable instructions are executed by the processor, the device executes each step of the offshore wind power low-frequency AC transmission system startup method provided in the second aspect.

[0043] In a fifth aspect, the present invention provides a readable storage medium storing a computer executable program, which, when executed, can implement the various steps of the offshore wind power low-frequency AC transmission system startup method provided in the second aspect.

[0044] It can be seen from the above technical solutions that the present invention has the following beneficial effects:

[0045] The present invention proposes an offshore wind power low-frequency AC transmission system and a starting method thereof. A small-capacity energy storage device is arranged on the DC side of the converter of a small number of offshore wind turbines to make them energy storage wind turbines with self-starting capability. The energy storage device assists the mechanical part of the wind turbines and the machine-side converter in starting. In the process of linear increase of the AC voltage of the wind farm, one energy storage wind turbine is controlled to maintain the active power balance of the offshore wind farm, and the output active power of other energy storage wind turbines is controlled to be zero to avoid active circulation between the energy storage wind turbines. When the AC voltage of the wind farm rises linearly to the initial value, all energy storage wind turbines are controlled to output active power, and the diode rectifier unit of the onshore converter station is further turned on, so that the AC voltage amplitude of the offshore wind farm reaches the rated value, so that the energy storage wind turbines jointly establish the AC voltage of the low-frequency AC system. Since only a small number of wind turbines need to be provided with energy storage devices, the energy storage capacity is small and the system construction cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0047] Figure 1 This is a structural diagram of an offshore wind power low-frequency AC transmission system provided by an embodiment of the present invention;

[0048] Figure 2 This is a flow chart of an implementation method of a method for starting an offshore wind power low-frequency AC transmission system provided by an embodiment of the present invention;

[0049] Figure 3 It is a waveform diagram of the effective value of the AC voltage of the AC busbar on the offshore wind farm side in the test system of the offshore wind power low-frequency AC transmission system startup method provided by the embodiment of the present invention;

[0050] Figure 4 It is a curve diagram of the AC voltage frequency variation of the AC busbar on the offshore wind farm side in the test system of the offshore wind power low-frequency AC transmission system startup method provided by the embodiment of the present invention;

[0051] Figure 5 It is a curve diagram of the DC voltage variation of the wind turbine converter in the test system of the offshore wind power low-frequency AC transmission system startup method provided by the embodiment of the present invention;

[0052] Figure 6 It is a curve diagram of active power variation of an energy storage wind turbine in a test system of a method for starting an offshore wind power low-frequency AC transmission system provided by an embodiment of the present invention;

[0053] Figure 7 It is a reactive power variation curve diagram of the energy storage wind turbine in the test system of the offshore wind power low-frequency AC transmission system startup method provided by the embodiment of the present invention;

[0054] Figure 8 This is a structural diagram of a starting device for an offshore wind power low-frequency AC transmission system provided by an embodiment of the present invention;

[0055] Fig. 9 This is a diagram of the electronic device architecture provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0056] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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 creative work are within the scope of protection of the present invention.

[0057] See also Figure 1 An embodiment of the present invention provides an offshore wind power low-frequency AC transmission system, including an offshore wind farm, an AC cable, an onshore converter station and an AC power grid. The offshore wind farm includes a wind turbine and a step-up transformer. The wind turbine is connected to the AC power grid through the step-up transformer; the first side of the onshore converter station is connected to the AC power grid through a low-frequency AC bus, and the second side is connected to the onshore AC system, wherein the DC side of the converter of several wind turbines in the offshore wind farm is provided with an energy storage device, and the several wind turbines constitute energy storage wind turbines in the offshore wind farm.

[0058] In a further embodiment, the onshore converter station further includes a low-frequency side converter transformer, a diode rectifier unit (DRU), a modular multilevel converter (MMC), an AC side converter transformer, a reactive power compensation device, and an AC filter;

[0059] The low-frequency side converter transformer, reactive power compensation device, and AC filter are connected in parallel at the low-frequency AC bus, the AC side of the diode rectifier unit is connected to the low-frequency side converter transformer, the DC side of the diode rectifier unit is connected to the DC side of the modular multilevel converter, and the AC side of the modular multilevel converter is connected to the onshore AC system through the AC side converter transformer.

[0060] Specifically, Figure 1 As shown, wind turbines are connected in series through collector lines to obtain multiple wind turbine strings and connected to AC bus 1. AC bus 1 is connected to onshore AC bus 2 through an AC submarine cable line via a step-up transformer. The reactive compensation device and the AC filter are connected in parallel to onshore AC bus 2. The onshore converter station converts the non-industrial frequency voltage into industrial frequency voltage through DRU rectification and MMC inversion, and finally connects to the onshore AC system.

[0061] In the above-mentioned embodiment of the present invention, an energy storage device is arranged on the DC side of the converter of several wind turbines in an offshore wind farm, with the purpose of assisting the start-up of the mechanical part and the machine-side converter of the wind turbine, so that these wind turbines have self-starting capability. All energy storage wind turbines will start first and establish the AC voltage of the offshore wind farm, preparing for the subsequent start-up of other wind turbines.

[0062] participate Figure 2 One embodiment of the present invention provides a method for starting the offshore wind power low-frequency AC transmission system illustrated in the above embodiment, comprising the following steps:

[0063] Step S210: Start the energy storage devices of several wind turbines to start the energy storage wind turbines.

[0064] In this step, the starting steps of the energy storage fan include:

[0065] Step S211. Start the energy storage device to charge the DC capacitor of the fan converter of the energy storage fan;

[0066] Step S212: starting the mechanical part of the energy storage fan to establish an AC voltage of the machine-side converter of the energy storage fan;

[0067] Step S213. Control the generator-side converter to unlock according to the AC voltage of the generator-side converter, control the DC voltage of the fan converter to its rated value, and lock the energy storage device;

[0068] Step S214: Control the grid-side converters of all energy storage wind turbines to unlock, and calculate the phase reference value of the grid-side converter and the d-axis voltage reference value of the grid connection point.

[0069] Among them, the phase reference value of the grid-side converter of the energy storage wind turbine is calculated as follows:

[0070]

[0071] Among them, s is the Laplace operator, ω base is the reference value of voltage frequency, ω 0 is the initial value of the voltage frequency, K G and K T are the proportional and time parameters of the first-order inertial controller, Q i (i=1,2,…,n) is the actual value of reactive power of the energy storage fan, Q i * is the reactive power reference value of the energy storage fan. All energy storage fans take the same proportional parameter K G and reactive power reference value Q i * , so that the reactive power is evenly distributed among the energy storage wind turbines.

[0072] Step S220. Control only one energy storage wind turbine to output active power, recorded as the power balancing wind turbine, calculate the grid-connected point d-axis voltage of the grid-side converter of the power balancing wind turbine, and make the AC voltage of the offshore wind farm rise linearly to the initial voltage value.

[0073] In this step, the q-axis voltage reference value of the grid-connected point of the grid-side converter of the energy storage wind turbine is set to 0, and a storage wind turbine is randomly selected as a balancing node for power balancing. The active power output of other storage wind turbines is controlled to be 0 to avoid active circulation between wind turbines. For low-frequency AC systems connected to DRUs, the amplitude of the AC voltage needs to be controlled during the establishment of the system AC voltage, and the active power of the wind turbine is strongly related to the voltage amplitude. Therefore, the system can be controlled by controlling the d-axis voltage at the wind turbine grid-connected point. The purpose of controlling the AC voltage amplitude is to make the AC voltage rise linearly to achieve the effect of zero-starting voltage boost. In addition, the voltage amplitude can be close to the rated value after the AC voltage is established.

[0074] Specifically, before the AC voltage of the offshore wind farm rises linearly to the initial voltage value, the voltage reference value of the d-axis voltage at the grid connection point of the grid-side converter of the energy storage wind turbine selected as the power balancing wind turbine is calculated as follows:

[0075]

[0076] Where t is time, v u is the rate of increase of the AC voltage amplitude;

[0077] The reference value of the d-axis voltage at the grid connection point of the grid-side converter of other energy storage wind turbines except the power balancing wind turbine is calculated as follows:

[0078]

[0079] Among them, s is the Laplace operator, t is time, v u is the rate of increase of the AC voltage amplitude, P j (j=2,3,…,n) is the actual value of the active power of the energy storage fan, k p and k i They are the proportional parameter and integral parameter of the active power controller respectively, and n represents the number of energy storage wind turbines in the offshore wind farm.

[0080] In this step, the d-axis voltage of the energy storage wind turbine grid connection point is controlled to make the AC voltage amplitude rise linearly, and one of the energy storage wind turbines is controlled to output active power to balance the active power. At the same time, the active power of other energy storage wind turbines is controlled to be 0 to avoid active circulating current during the AC voltage increase process.

[0081] Step S230: After the AC voltage rises linearly to the initial voltage value, all energy storage fans are controlled to output active power.

[0082] Specifically, when the AC voltage amplitude of the system rises linearly to the initial value u f0 After that, the d-axis voltage at the grid connection point of the energy storage wind turbine is calculated, and all energy storage wind turbines are controlled to generate active power, so that the DRU of the onshore converter station is turned on, and the AC voltage of the offshore wind farm is increased to close to its rated value.

[0083] After the AC voltage rises linearly to the initial voltage value, the voltage reference value of the d-axis voltage at the grid connection point of the energy storage wind turbine is calculated as follows:

[0084]

[0085] Among them, s is the Laplace operator, u f0 is the initial value of the AC voltage, P i * and P i is the active power reference value and actual active power value of the i-th energy storage wind turbine, k pa and k ia are the proportional and integral parameters of the active power controller respectively;

[0086] The active power reference value of the energy storage fan is calculated as follows:

[0087]

[0088] Among them, V dcDRU is the DRU DC voltage, U g is the voltage amplitude at the low-frequency AC bus, T DRU and X T are the transformation ratio and leakage reactance of the DRU converter respectively, and n is the number of energy storage wind turbines.

[0089] The active power reference value of the energy storage fan meets the following conditions:

[0090] (1) Voltage amplitude U at the low-frequency AC bus of the onshore converter station g Greater than 0.95pu

[0091] (2) The active power reference value of the energy storage fan is less than the capacity of the energy storage fan.

[0092] The above embodiments describe a method for starting an offshore wind power low-frequency AC transmission system. A small-capacity energy storage device is set on the DC side of the converter of a small number of offshore wind turbines to make them energy storage wind turbines with self-starting capability. The energy storage device assists the mechanical part of the wind turbine and the machine-side converter in starting. During the linear increase of the AC voltage of the wind farm, one energy storage wind turbine is controlled to maintain the active power balance of the offshore wind farm, and the output active power of other energy storage wind turbines is controlled to zero to avoid active circulation between the energy storage wind turbines. When the AC voltage of the wind farm rises linearly to the initial value, all energy storage wind turbines are controlled to output active power, and the diode rectifier unit of the onshore converter station is further turned on. The AC voltage amplitude of the offshore wind farm reaches the rated value, so that the energy storage wind turbines jointly establish the AC voltage of the low-frequency AC system.

[0093] The method for starting the offshore wind power low-frequency AC transmission system proposed by the present invention is further illustrated below by a specific simulation example.

[0094] by Figure 1 Taking the system architecture shown as an example, this embodiment adopts a test system including three energy storage wind turbines for simulation verification, each of which has a capacity of 10MW, a system rated frequency of 20Hz, and a rated voltage of 66kV at AC bus 1.

[0095] At t=0.0s, the energy storage devices in all energy storage wind turbines are unlocked to charge the DC capacitors of the wind turbine converters, and the DC voltage increases linearly from 0 to 1.0pu at a rate of 0.5pu / s. At t=1.0s, the mechanical parts of all energy storage wind turbines are unlocked. At t=1.5s, the machine-side converters of all energy storage wind turbines are unlocked, and the DC voltage is controlled to be 1.0pu. At t=2.0s, the grid-side converters of all energy storage wind turbines are unlocked, and the voltage amplitude of the offshore wind farm is controlled to increase linearly from zero to 0.85pu at a rate of 0.21pu / s. Among them, wind turbine 1 is responsible for the active power balance of the offshore wind farm, and wind turbines 2 and 3 are controlled to output active power of 0 during this process. At t=6.0s, the active power output of all energy storage wind turbines is controlled to 2MW.

[0096] like Figure 3 As shown, it illustrates the voltage waveform at the AC bus 1 in the system. It can be seen from the figure that after t=2.0s, the effective value of the AC voltage at the AC bus 1 rises linearly to 52.8kV. After time t=6.0s, the energy storage fan increases the active power, and the effective value of the AC voltage at the AC bus 1 rises to 63.9kV, achieving the effect of controlling the voltage amplitude close to the rated value.

[0097] Figure 4The variation curve of the AC voltage frequency at the AC bus 1 in the test system is shown. It can be seen that during the AC voltage establishment process after time t=2.0s, the AC voltage frequency is maintained near the rated frequency of 20Hz. Figure 5 The curve of the DC voltage change of the wind turbine converter in the test system is shown. It can be seen that after the energy storage device charges the DC capacitor, the machine-side converter starts smoothly and controls the DC voltage to the rated value. Figure 6 The change curve of the active power of the energy storage fan in the test system is illustrated. It can be seen that during the linear increase of the AC voltage amplitude between time t=2s~6s, the active power output by fan 1 is greater than zero, while the active power of fans 2 and 3 is equal to zero, avoiding the active circulation between the energy storage fans. Figure 7 The variation curve of reactive power of energy storage fans in the test system is shown. It can be seen that the reactive power of all energy storage fans is basically equal during the establishment of AC voltage, thus achieving reactive power equalization.

[0098] The above disclosed embodiment describes in detail a method for starting an offshore wind power low-frequency AC transmission system. The above disclosed method can be implemented using various forms of equipment. Therefore, the present invention also discloses a device corresponding to the above method. A specific embodiment is given below for detailed description.

[0099] like Figure 8 As shown, one embodiment of the present invention provides a starting device for an offshore wind power low-frequency AC transmission system, comprising:

[0100] The energy storage wind turbine starting module 802 is used to start the energy storage devices of several wind turbines to start the energy storage wind turbines;

[0101] The energy storage fan output control module 804 is used to perform the following process:

[0102] Only one energy storage wind turbine is controlled to output active power, which is recorded as a power balancing wind turbine. The d-axis voltage of the grid-connected point of the grid-side converter of the power balancing wind turbine is calculated, so that the AC voltage of the offshore wind farm rises linearly to the initial voltage value.

[0103] After the AC voltage rises linearly to the initial voltage value, all energy storage fans are controlled to output active power.

[0104] The implementation principle and technical effects of the device provided in the embodiments of the present application are the same as those of the aforementioned method embodiments. For the sake of brief description, for matters not mentioned in the device embodiment, reference may be made to the corresponding contents in the aforementioned method embodiments.

[0105] The methods and related devices mentioned in the above embodiments are described with reference to the method flow charts and / or structural diagrams provided in the embodiments of the present application. Specifically, each process and / or block in the method flow charts and / or structural diagrams, as well as the combination of processes and / or blocks in the flow charts and / or block diagrams, 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 generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the process in the process. Figure 1 Schematic diagram of one or more processes and / or structures Figure 1 These computer program instructions can also be stored in a computer-readable memory that can guide a computer or other programmable data processing device to work in a specific way, so that the instructions stored in the computer-readable memory produce a product including an instruction device, which implements the functions specified in the process. Figure 1 Schematic diagram of one or more processes and / or structures Figure 1 These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable device provide for implementing the process in the process. Figure 1 A flow or multiple flows and / or structures illustrate the steps of the functions specified in one block or multiple blocks.

[0106] The following embodiments are described by taking the method applied to a computer device as an example. It can be understood that the computer device can be any device with computing and processing functions, and can be but not limited to a server or a personal laptop computer, etc. In one embodiment, the computer device can be an application server, and the application server can be a server for running an application to be tested.

[0107] See also Fig. 9 , which shows a hardware block diagram of an electronic device, the electronic device is intended to represent various forms of digital computers, such as laptop computers, desktop computers, workstations, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. The electronic device can also represent various forms of mobile devices, such as personal digital processing, cellular phones, smart phones, wearable devices, and other similar computing devices. The components shown herein, their connections and relationships, and their functions are merely examples and are not intended to limit the implementation of the present application described and / or required herein.

[0108] like Fig. 9As shown, the electronic device includes: at least one processor 1, at least one communication interface 2, at least one memory 3 and at least one communication bus 4;

[0109] In the embodiment of the present application, the number of the processor 1, the communication interface 2, the memory 3, and the communication bus 4 is at least one, and the processor 1, the communication interface 2, and the memory 3 communicate with each other through the communication bus 4;

[0110] The processor 1 may be a central processing unit CPU, or an application-specific integrated circuit ASIC (Application Specific Integrated Circuit), or one or more integrated circuits configured to implement the embodiments of the present invention, etc.;

[0111] The memory 3 may include a high-speed RAM memory, and may also include a non-volatile memory (non-volatile memory), etc., such as at least one disk memory;

[0112] The memory stores a program, and the processor can call the program stored in the memory, and the program is used to: implement various processing flows of the aforementioned offshore wind power low-frequency AC transmission system startup solution.

[0113] An embodiment of the present invention also provides a readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the various processing flows of the offshore wind power low-frequency AC transmission system startup scheme provided in the above embodiment and / or any possible implementation method in combination with the embodiment are implemented.

[0114] The above-mentioned embodiments have described the present invention in particular detail with respect to possible scenarios, and those skilled in the art will recognize that the present invention can be practiced through other embodiments. The specific naming of components, the capitalization of terms, attributes, data structures, or any other programming or structural aspects are not mandatory or important, and the mechanisms or features of the present invention may have different names, forms, or procedures. The system may be implemented by a combination of hardware and software (as described), entirely by hardware elements, or entirely by software elements. The specific division of functions between the various system components described herein is exemplary only and not mandatory; on the contrary, the functions performed by a single system component may be performed by multiple components, or the functions performed by multiple components may be performed by a single component.

[0115] Those skilled in the art should understand that the various steps of the above disclosed method can be implemented by a general computing device, they can be concentrated on a single computing device, or distributed on a network composed of multiple computing devices, optionally, they can be implemented with program codes executable by the computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. Thus, the embodiments of the present invention are not limited to any specific combination of hardware and software.

[0116] These computing device executable programs (also referred to as programs, software, software applications, or code) include machine instructions for programmable processors, and these computing programs can be implemented using high-level procedural and / or object-oriented programming languages, and / or assembly / machine languages. As used herein, the terms "machine-readable medium" and "computer-readable medium" refer to any computer program product, device, and / or device (e.g., disk, optical disk, memory, programmable logic device (PLD)) for providing machine instructions and / or data to a programmable processor, including a machine-readable medium that receives machine instructions as a machine-readable signal. The term "machine-readable signal" refers to any signal for providing machine instructions and / or data to a programmable processor.

[0117] Certain aspects of the present invention include process steps and instructions described herein in the form of algorithms. It should be noted that the process steps and instructions of the present invention can be implemented in software, firmware and / or hardware, and when implemented by software, it can be downloaded, stored on different platforms used by various operating systems and operated from the platforms.

[0118] Those skilled in the art will understand that the structures shown in the accompanying drawings are merely block diagrams of partial structures related to the scheme of the present application, and do not constitute a limitation on the terminal device to which the scheme of the present application is applied. The specific terminal device may include more or fewer components than shown in the figures, or combine certain components, or have a different arrangement of components.

[0119] Some embodiments may be described using "coupled" and "connected" and their derivatives. It should be understood that these terms are not intended to be synonymous with each other. For example, some embodiments may be described using the word "connected" to indicate that two or more elements are in direct physical or electrical contact with each other. In another example, some embodiments may be described using the word "coupled" to indicate that two or more elements are in direct physical or electrical contact with each other. However, the term "coupled" may also mean that two or more elements are not in direct contact with each other, but still cooperate or interact with each other. The embodiments are not limited to this context.

[0120] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "possible design" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0121] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0122] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An offshore wind power low-frequency AC transmission system, characterized in that: It comprises an offshore wind farm, an AC cable, an onshore converter station and an AC power grid, wherein the offshore wind farm comprises a wind turbine and a step-up transformer, wherein the wind turbine is connected to the AC power grid through the step-up transformer, wherein a first side of the onshore converter station is connected to the AC power grid through a low-frequency AC bus, and a second side is connected to an onshore AC system; The DC side of the converter of several wind turbines in the offshore wind farm is provided with an energy storage device, and the several wind turbines constitute energy storage wind turbines in the offshore wind farm.

2. The system according to claim 1, characterized in that The onshore converter station also includes a low-frequency side converter transformer, a diode rectifier unit, a modular multi-level converter, an AC side converter transformer, a reactive power compensation device, and an AC filter; The low-frequency side converter transformer, reactive power compensation device, and AC filter are connected in parallel at the low-frequency AC bus, the AC side of the diode rectifier unit is connected to the low-frequency side converter transformer, the DC side of the diode rectifier unit is connected to the DC side of the modular multilevel converter, and the AC side of the modular multilevel converter is connected to the onshore AC system through the AC side converter transformer.

3. A method for starting an offshore wind power low-frequency AC transmission system, characterized in that: include: Start the energy storage devices of several wind turbines to start the energy storage wind turbines; Control only one energy storage wind turbine to output active power, which is recorded as a power balancing wind turbine, and calculate the d-axis voltage of the grid-connected point of the grid-side converter of the power balancing wind turbine, so that the AC voltage of the offshore wind farm rises linearly to the initial voltage value; After the AC voltage linearly rises to an initial voltage value, all energy storage fans are controlled to output active power.

4. The method according to claim 3, characterized in that Before the AC voltage of the offshore wind farm rises linearly to the initial voltage value, the voltage reference value of the d-axis voltage at the grid connection point of the grid-side converter of the power balancing wind turbine is calculated as follows: Where t is time, v u is the rate of increase of the AC voltage amplitude; The grid-connected point d-axis voltage reference value of the grid-side converter of other energy storage wind turbines except the power balancing wind turbine is calculated as follows: Among them, s is the Laplace operator, t is time, v u is the rate of increase of the AC voltage amplitude, P j (j=2,3,…,n) is the actual value of the active power of the energy storage fan, k p and k i They are the proportional parameter and integral parameter of the active power controller respectively, and n represents the number of energy storage wind turbines in the offshore wind farm.

5. The method according to claim 3, characterized in that: After the AC voltage rises linearly to the initial voltage value, the voltage reference value of the d-axis voltage at the grid connection point of the energy storage wind turbine is calculated as follows: Among them, s is the Laplace operator, u f0 is the initial value of the AC voltage, P i * and P i is the active power reference value and actual active power value of the i-th energy storage wind turbine, k pa and k ia are the proportional and integral parameters of the active power controller respectively; The active power reference value of the energy storage fan is calculated as follows: Among them, V dcDRU is the DRU DC voltage, U g is the voltage amplitude at the low-frequency AC bus, T DRU and X T are the transformation ratio and leakage reactance of the DRU converter respectively, and n is the number of energy storage wind turbines.

6. The method according to claim 5, characterized in that After the AC voltage rises linearly to the initial voltage value, the active power reference value of the energy storage fan meets the following conditions: (1) Voltage amplitude U at the low-frequency AC bus of the onshore converter station g Greater than 0.95pu (2) The active power reference value of the energy storage fan is less than the capacity of the energy storage fan.

7. The method according to claim 3, characterized in that The method of starting the energy storage devices of several wind turbines to start the energy storage wind turbines comprises: Starting the energy storage device to charge the DC capacitor of the fan converter of the energy storage fan; Start the mechanical part of the energy storage fan and establish the AC voltage of the machine-side converter of the energy storage fan; According to the AC voltage of the machine-side converter, the machine-side converter is unlocked, the DC voltage of the fan converter is controlled to be the rated value, and the energy storage device is locked; Control the grid-side converters of all energy storage wind turbines to unlock, and calculate the phase reference value of the grid-side converter and the d-axis voltage reference value of the grid connection point.

8. A starting device for an offshore wind power low-frequency AC transmission system, characterized in that: include: Energy storage wind turbine starting module, used to start the energy storage devices of several wind turbines to start the energy storage wind turbines; The energy storage fan output control module is used to perform the following processes: Only one energy storage wind turbine is controlled to output active power, which is recorded as a power balancing wind turbine. The d-axis voltage of the grid-connected point of the grid-side converter of the power balancing wind turbine is calculated, so that the AC voltage of the offshore wind farm rises linearly to the initial voltage value. After the AC voltage rises linearly to the initial voltage value, all energy storage fans are controlled to output active power.

9. An electronic device, characterized in that: It comprises a memory storing computer executable instructions and a processor. When the computer executable instructions are executed by the processor, the device executes the offshore wind power low-frequency AC transmission system startup method as described in any one of claims 3 to 7.

10. A readable storage medium, characterized in that: A computer executable program is stored, and when the program is executed, the offshore wind power low-frequency AC transmission system startup method as described in any one of claims 3 to 7 can be implemented.

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