Series auxiliary device-based network construction transformation method and system for network-following type wind power plant

Abstract

The invention belongs to the technical field of power system new energy grid connection, and provides a grid-following type wind power plant grid construction transformation method and system based on a series auxiliary device, a plurality of fans in a grid-following type wind power plant run in a grid-following type, and a plurality of fan sets are connected in parallel and collected at a common connection point after being boosted by a transformer. Performing net construction type transformation through a series auxiliary device; the series auxiliary device adopts a unified power flow controller for centralized network construction type transformation, and at least comprises a parallel side converter and a series side converter; based on the common connection point, a plurality of wind generator sets in the distributed following grid type wind power plant are connected in parallel and collected, and the impedance of a power transmission line is adjusted through the series side converter so as to remodel the port of the wind power plant. And the parallel side converter adopts network construction type control to adjust the power of the network-following wind power plant within a stable range so as to complete centralized network construction type transformation of the network-following wind power plant.

Description

Technical Field

[0001] This invention belongs to the field of new energy grid connection technology in power systems, specifically relating to a method and system for grid-connected wind farm transformation based on series auxiliary devices. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] With the energy transition, the wind power industry has developed rapidly, becoming the third largest power source after thermal power and hydropower. Currently, in practical engineering, most wind turbine converters adopt grid-connected control. However, with the large-scale grid connection of new energy units, the grid strength and system inertia are constantly decreasing, posing a significant challenge to the stable operation of grid-connected new energy units. Grid-based control, on the other hand, dynamically constructs an autonomous synchronous grid by simulating synchronous generators, exhibiting voltage source characteristics similar to synchronous generators, and can spontaneously provide active support to the grid under disturbance conditions. Wind farms should participate in power system peak shaving, frequency regulation, and active power control to achieve continuous and smooth power regulation; therefore, the grid-based operation of wind farms or clusters as a whole is more in line with the grid connection requirements of the new power system. Therefore, the grid-based transformation of existing grid-connected wind farms to exhibit grid-based characteristics is of significant research importance.

[0004] Currently, there are two main methods for grid-connected wind farms: grid-connected modification of each wind turbine converter, and adding hardware auxiliary devices to make the wind farm as a whole exhibit grid-connected characteristics.

[0005] Existing grid-based control strategies mainly include droop control, virtual synchronization control, power synchronization control, and matching control. Time-domain simulation can be used to compare the impact of the system's equivalent impedance on grid-connected and grid-connected wind turbines, demonstrating that grid-connected doubly-fed induction generators have better voltage stability under weak grid conditions. Some scholars have proposed a droop grid-connected strategy for flux linkage-controlled doubly-fed induction generators, which effectively improves the unit's damping characteristics. However, existing grid-connected control schemes are suitable for grid-connected retrofitting of each wind turbine converter, which has disadvantages such as large engineering workload, complex construction, and high retrofitting costs.

[0006] For existing grid-connected wind farms, grid-connected devices can be added to make the overall structure exhibit grid-connected characteristics. This method has advantages such as simple construction, centralized equipment for easy maintenance, and low cost. Grid-connected energy storage can simulate synchronous generators, exhibiting voltage source characteristics and possessing frequency and voltage regulation capabilities. However, it has disadvantages such as safety risks and capacity limitations during long-term operation. Grid-connected static var generators can be used to achieve adaptive voltage regulation of the grid and dynamic reactive power support under emergency fault conditions. However, parallel static var generators need to absorb active power from the grid to maintain their stability during operation and cannot adjust dynamic damping.

[0007] The grid-based transformation of existing grid-connected wind farms requires the grid-based transformation of each wind turbine converter, which involves a large amount of work, complex construction, and high transformation costs. Furthermore, the centralized grid-based transformation of grid-connected wind farms has disadvantages such as absorbing active power and being unable to adjust dynamic damping. Currently, there is a lack of suitable solutions. Summary of the Invention

[0008] To address the aforementioned issues, this invention proposes a method and system for grid-connected wind farm transformation based on a series auxiliary device. This method utilizes a series auxiliary device to achieve centralized grid-connected wind farm transformation. Based on the series-side virtual impedance control of a Unified Power Flow Controller (UPFC), the equivalent grid impedance at the wind farm port is reshaped, improving the line's power transmission capacity. Simultaneously, this invention's centralized grid-connected control based on UPFC solves the problems of complex construction and high cost in traditional grid-connected wind farm transformation, as well as the power consumption and inability to adjust dynamic damping issues of existing parallel centralized grid-connected devices, thereby improving the dynamic performance and stability of grid-connected wind farms.

[0009] According to some embodiments, the first aspect of the present invention provides a method for modifying the grid structure of a grid-connected wind farm based on a series auxiliary device, which adopts the following technical solution: A method for grid-connected wind farm transformation based on series auxiliary devices is disclosed. In this method, several wind turbines in the grid-connected wind farm operate in a grid-connected configuration. After being stepped up by a transformer, the turbines are connected in parallel at the Point of Common Coupling (PCC) and then the grid-connected configuration is transformed using series auxiliary devices. The series auxiliary devices employ a unified power flow controller for centralized grid-connected transformation and include at least parallel-side converters and series-side converters. Based on the common connection point, several wind turbines in the distributed grid-connected wind farm are connected in parallel and aggregated. The transmission line impedance is adjusted by the series-side converter to reshape the wind farm port. The parallel-side converter adopts grid-type control to regulate the power of the grid-connected wind farm within a stable range to complete the centralized grid-connected wind farm transformation.

[0010] As a further technical limitation, when the grid-connected wind turbines are stepped up by a transformer and connected in parallel at the AC bus common connection point, the parallel-side converter provides frequency and voltage to the grid-connected wind turbine units using synchronous AC power, by increasing... V dc - f Droop control maintains the stability of DC voltage, enabling power exchange between the parallel and series sides; when the active power of the grid-connected wind turbine changes, the output power and frequency of the wind turbine change accordingly.

[0011] Furthermore, the aforementioned V dc - f The control equation for droop control is: ;in, This represents the droop factor between DC voltage and frequency. and These represent the angular velocity and rated angular velocity of the parallel-side power grid, respectively. and These represent the actual measured value and the reference value of the system's DC voltage, respectively.

[0012] As a further technical limitation, the parallel-side converter adopts a dual closed-loop control of AC voltage loop and current loop, wherein the outer loop is the AC voltage loop and the inner loop is the current loop; based on the three-phase voltage and three-phase current of the grid-connected wind farm after the transformer is stepped up, the obtained three-phase voltage and three-phase current are compared with the reference three-phase voltage and reference three-phase current respectively, and the voltage control signal of the parallel converter in the abc three-phase coordinate system is obtained through inverse Park coordinate transformation. The trigger pulse of the controller switch is generated by modulation to obtain a stable AC voltage and frequency.

[0013] As a further technical limitation, the series-side converter uses a three-loop virtual impedance control consisting of an outer impedance loop, an outer voltage loop, and an inner current loop to adjust the transmission line impedance.

[0014] As a further technical limitation, the parallel-side converter is connected to the common coupling point via a transformer and then connected in parallel with the transmission line; one end of the series-side converter is connected to the parallel-side converter, and the other end is connected in series with the transmission line and then connected to the AC power grid.

[0015] According to some embodiments, the second aspect of the present invention provides a grid-connected wind farm grid-connected retrofit system based on a series auxiliary device, which adopts the following technical solution: A grid-connected wind farm conversion system based on a series auxiliary device is disclosed. In the grid-connected wind farm, several wind turbines operate in a grid-connected manner. After being stepped up by a transformer, the wind turbines are connected in parallel and converged at a common junction point. The system is then converted to a grid-connected configuration using a series auxiliary device. The series auxiliary device is a unified power flow controller for centralized grid-connected conversion and includes at least a parallel-side converter and a series-side converter. The aggregation module is configured to connect and aggregate several wind turbine units in a distributed grid-connected wind farm in parallel based on the common connection point. The modification module is configured to adjust the transmission line impedance through the series-side converter to reshape the wind farm port, and the parallel-side converter adopts grid-type control to adjust the power of the grid-connected wind farm within a stable range to complete the centralized grid-connected wind farm modification.

[0016] According to some embodiments, a third aspect of the present invention provides a computer-readable storage medium, employing the following technical solution: A computer-readable storage medium having a program stored thereon, which, when executed by a processor, implements the steps in the grid-type transformation method for wind farms based on series auxiliary devices as described in the first aspect of the present invention.

[0017] According to some embodiments, the fourth aspect of the present invention provides an electronic device, which adopts the following technical solution: An electronic device includes a memory, a processor, and a program stored in the memory and running on the processor. When the processor executes the program, it implements the steps in the grid-type transformation method for wind farms based on series auxiliary devices as described in the first aspect of the present invention.

[0018] According to some embodiments, the fifth aspect of the present invention provides a computer program product, which adopts the following technical solution: A computer program product includes software code, wherein the program in the software code performs the steps in the grid-type transformation method for wind farms based on series auxiliary devices as described in the first aspect of the present invention.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes a series auxiliary device to perform centralized grid-connected wind farm retrofitting, solving the problems of complex construction and high cost associated with traditional grid-connected wind farm retrofitting. It also addresses the power consumption issues of traditional parallel-connected devices (such as static var generators and energy storage converters) during operation, enabling grid-connected wind turbines to better achieve grid connection capabilities and promoting stable system operation. Furthermore, by combining UPFC series-side virtual impedance control, the equivalent grid impedance at the wind farm port is reshaped, improving the line's power transmission capacity. Simultaneously, it solves the problem of traditional centralized grid-connected wind farm retrofitting's inability to adjust dynamic damping in weak grid and long-distance wind power transmission scenarios, enhancing the system's dynamic performance and stability. Attached Figure Description

[0020] The accompanying drawings, which form part of this embodiment, are used to provide a further understanding of this embodiment. The illustrative embodiments and their descriptions are used to explain this embodiment and do not constitute an improper limitation of this embodiment.

[0021] Figure 1 This is a flowchart of the grid-type wind farm modification method based on series auxiliary devices in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the grid-type wind farm modification based on a series auxiliary device in Embodiment 1 of the present invention; Figure 3 This is a circuit topology diagram of the parallel-side converter in Embodiment 1 of the present invention; Figure 4(a) is a schematic diagram of a two-terminal power supply system model with series compensation in Embodiment 1 of the present invention; Figure 4(b) is a vector diagram in Embodiment 1 of the present invention without series compensation; Figure 4(c) is a vector diagram with series compensation in Embodiment 1 of the present invention; Figure 5 This is a block diagram of the AC voltage amplitude control of the parallel-side converter in Embodiment 1 of the present invention; Figure 6 The series-side converter in Embodiment 1 of the present invention V dc -f Droop control block diagram; Figure 7 This is a control block diagram of the series-side converter in Embodiment 1 of the present invention; Figure 8 This is a structural block diagram of the grid-type wind farm transformation system based on a series auxiliary device in Embodiment 2 of the present invention. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0024] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0025] In this invention, terms such as "upper," "lower," "left," "right," "front," "back," "vertical," "horizontal," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only to facilitate the description of the structural relationships of the various components or elements of this invention and do not specifically refer to any component or element in this invention. They should not be construed as limiting the invention.

[0026] In this invention, terms such as "fixed connection," "connected," and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this invention based on the specific circumstances, and they should not be construed as limitations on the invention.

[0027] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0028] Example 1 Embodiment 1 of the present invention introduces a method for modifying the grid structure of a grid-connected wind farm based on a series auxiliary device.

[0029] like Figure 1 The method shown is a grid-type wind farm transformation method based on a series auxiliary device. In the grid-type wind farm, several wind turbines are all operating in a grid-type configuration. After the several wind turbine units are stepped up by a transformer, they are connected in parallel and gathered at a common junction point. Then, the grid-type transformation is carried out through a series auxiliary device. The series auxiliary device adopts a unified power flow controller for centralized grid-type transformation and includes at least a parallel-side converter and a series-side converter. Based on the common connection point, several wind turbines in the distributed grid-connected wind farm are connected in parallel and aggregated. The transmission line impedance is adjusted by the series-side converter to reshape the wind farm port. The parallel-side converter adopts grid-type control to regulate the power of the grid-connected wind farm within a stable range to complete the centralized grid-connected wind farm transformation.

[0030] In this embodiment, all wind turbines maintain grid-connected operation. After being stepped up by a transformer, they are connected in parallel at a common junction point. The grid is then constructed using a series auxiliary device before being connected to the grid. This avoids the power consumption problem of traditional parallel devices and the complex and costly grid-connected wind farm transformation. At the same time, virtual impedance control is adopted on the UPFC series side to reshape the equivalent grid impedance of the wind farm port according to different control objectives, so that the system can achieve high controllability, improve the power transmission capacity of the line, effectively dampen system power oscillation, and have stronger dynamic performance and stability.

[0031] The core function of UPFC (Upstream Power Controller) is power flow control, which relies on the injected voltage of its series section. Its implementation exhibits characteristics of a series-connected device, and with appropriate control methods, it can regulate the bus voltage. A schematic diagram of the grid-connected wind farm centralized grid transformation based on a series auxiliary device in this embodiment is shown below. Figure 2 As shown, the parallel-side converter 1 of the UPFC is connected to the PCC via a transformer and then connected in parallel with the transmission line; the series-side converter 2 is connected to the PCC at one end via a transformer and to the AC power grid at the other end via a transmission line; the DC capacitor provides a channel for active power transmission for the two back-to-back connected converters. The active power loss in the entire UPFC structure is very limited and can usually be ignored in theoretical analysis.

[0032] This embodiment transfers the responsibility of distributed grid construction from individual wind turbines to the PCC (Power Grid Connector) where multiple turbines are connected in parallel. The parallel side of the UPFC (Power Grid Connector) provides centralized grid support for the entire wind farm, and the series side of the UPFC adjusts the line impedance to reshape the equivalent grid impedance at the wind farm port. This solves the stability problem of grid-connected wind turbine systems in weak grid scenarios and realizes centralized grid construction transformation.

[0033] The basic circuit topology of the parallel-side converter of UPFC is as follows: Figure 3 As shown, v 1i ( i =a,b,c) represents the three-phase phase voltages. R sh and L sh These represent the equivalent internal resistance of the converter on the parallel side and the line inductance on the parallel side, respectively. v shi ( i=a,b,c) represents the output voltage of the parallel-side converter. i shi ( i =a,b,c) represents the three-phase currents of the parallel-side converter. V dc This refers to the DC-side capacitor voltage. When the grid-connected wind turbine is stepped up by a transformer and connected in parallel to the AC bus PCC, the UPFC parallel-side converter uses a constant current... Vf After control, it acts as a synchronous AC power source, providing stable frequency and voltage to the wind farm. This is especially beneficial in weak grid environments where frequency and voltage regulation is more flexible, enabling grid-connected wind turbines to better achieve their grid connection capabilities and promoting stable system operation. Simultaneously, therefore, when using a fixed-frequency AC power source... Vf On the basis of, add V dc - f Droop control to maintain DC voltage V dc Stability allows for better power exchange between the parallel and series sides. When the system's active power changes, the corresponding frequency changes, causing the wind turbine to increase or decrease its power output, thus maintaining system stability.

[0034] The basic circuit topology of the series-side converter is similar to that of the parallel-side converter, but a suitable control strategy can reshape the equivalent grid impedance at the wind farm port. Figure 4(a) shows a two-terminal power system model with series compensation, where the line reactance is... X The area within the dashed box represents the series compensation capacitor. C , resistance is X c And the voltage at the beginning is equal to the voltage at the end. V s = V r = V Without series compensation, the corresponding voltage and current phasor diagrams are shown in Figure 4(b), and the active power output of the first-end power supply is... P s reactive power Q s And the active power transmitted through the line to the power source at the end of the line. P r reactive power Q r for (1) (2) (3) There are series capacitors CThe corresponding voltage and current phasor diagrams after compensation are shown in Figure 4(c). The equivalent reactance of the transmission line is... (4) in, k For series compensation degree, it is defined as (5) From equations (1) to (5), it can be seen that the active power and inductive reactive power transmitted to the end of the line after series capacitor compensation are: (6) (7) Therefore, series compensation can improve the transmission power of transmission lines and change the line voltage and current. The strength and stability of the power grid largely depend on the physical impedance of the lines. In the traditional wind turbine grid connection process, the line impedance is usually fixed and difficult to change. Especially in weak grids and high renewable energy penetration scenarios, the interaction between power electronic equipment and grid impedance can easily cause broadband oscillations. However, the UPFC series side adopts virtual impedance control, which actively adds or subtracts a virtual impedance component that can be adjusted in real time based on the physical line impedance according to control requirements. This improves the line's power transmission capacity, effectively dampens system power oscillations, and increases system stability.

[0035] like Figure 5 The control block diagram of the parallel-side converter shown is illustrated. The UPFC parallel-side converter employs dual closed-loop control, with an outer loop for AC voltage and an inner loop for current. The input is the primary voltage of the parallel transformer. v sh1 and current i sh1 Three-phase voltage v sh1 The voltage amplitude after the transformer is obtained by dq transformation. U sd and U sq , respectively with the set reference voltage U sdref and U sqref After comparison, the d-axis and q-axis reference currents are obtained through PI control. i sdref and i sqref The input three-phase current i sh1 After being transformed by a transformer and then subjected to dq transformation, the result is obtained. i sd and i sq , and reference current i sdref andi sqref After decoupling via a current regulator, the voltage control signal of the parallel converter in the abc three-phase coordinate system is obtained through inverse Park coordinate transformation. Then, the trigger pulse of the controller switch is generated by modulation. The main function of the parallel side is to provide grid support for the grid-connected wind turbines gathered at the PCC, establish stable AC voltage and frequency, and realize the centralized grid-connected transformation of traditional grid-connected wind farms.

[0036] like Figure 6 As shown, for the DC side of the converter, the following is adopted: V dc - f Droop control. The control equation is shown in equation (8): (8) in, This represents the droop factor between DC voltage and frequency. and These represent the angular velocity and rated angular velocity of the parallel-side power grid, respectively, 100π rad / s. and These represent the actual measured value and the reference value of the system's DC voltage, respectively. and It typically remains constant during operation. When the parallel-side converter senses a change in DC voltage, it immediately... V dc - f The frequency of the wind turbine is controlled and adjusted to transmit the active power demand information of the power grid to the frequency signal on the parallel side of the UPFC. Upon sensing the frequency change, the wind turbine with frequency regulation capability immediately adjusts its active power output to provide power support. When the system's input and output active power reach balance again, the system's AC frequency returns to normal, eliminating DC voltage deviation. The system stabilizes and enters a new stable operating state, providing a channel for power transmission between the parallel and series sides and reducing power consumption. This control method can change the active power output of the wind turbine without relying on a communication system, avoiding many drawbacks caused by the unreliability and transmission delay of communication signals.

[0037] like Figure 7 The control block diagram of the series-side converter shown depicts a three-loop virtual impedance control system. The outermost loop is the impedance outer loop, followed by the voltage outer loop and the current inner loop. Different control requirements are addressed in various scenarios, such as improving the equivalent short-circuit ratio, suppressing subsynchronous oscillations, and improving transmission efficiency in weak power grids, thereby obtaining the desired impedance value. After system planning, the impedance of the transmission line is essentially fixed and difficult to change; therefore, the known line impedance is used... Z line and the series side impedance reference value obtained based on the control target. Zse The voltage is fed into the voltage calculation module for calculation, and the AC reference voltage on the series side can be obtained. As shown in equation (9), where and They are respectively Figure 1 The AC voltage at the PCC and the power grid is shown.

[0038] (9) AC voltage referenced on the series side After dq transformation, we get U sedr and U seqr The values ​​are then compared with the actual values ​​and fed into the voltage outer loop and current inner loop. Series-side control can reshape the equivalent grid impedance at the wind farm port through different control objectives, improve the line's power transmission capacity, and achieve objectives such as increasing the equivalent short-circuit ratio and adjusting dynamic damping, thus exhibiting stronger dynamic performance and stability.

[0039] This embodiment utilizes a series auxiliary device to perform centralized grid-connected wind farm retrofitting, solving the problems of complex construction and high cost associated with traditional grid-connected wind farm retrofitting. It also addresses the power consumption issues of traditional parallel-connected devices (such as static var generators and energy storage converters) during operation, enabling grid-connected wind turbines to better achieve grid connection capabilities and promoting stable system operation. Combined with UPFC series-side virtual impedance control, the equivalent grid impedance at the wind farm port is reshaped, improving the line's power transmission capacity. Furthermore, it solves the problem of traditional centralized grid-connected wind farm retrofitting's inability to adjust dynamic damping in weak grid and long-distance wind power transmission scenarios, enhancing the system's dynamic performance and stability.

[0040] Example 2 Embodiment 2 of the present invention introduces a grid-type wind farm transformation system based on a series auxiliary device.

[0041] like Figure 8 The system shown is a grid-type wind farm transformation system based on a series auxiliary device. In a grid-type wind farm, several wind turbines operate in a grid-connected manner. After being stepped up by a transformer, the wind turbines are connected in parallel and converged at a common junction point. Then, the grid-type transformation is carried out through a series auxiliary device. The series auxiliary device adopts a unified power flow controller for centralized grid-type transformation and includes at least a parallel-side converter and a series-side converter. The aggregation module is configured to connect and aggregate several wind turbine units in a distributed grid-connected wind farm in parallel based on the common connection point. The modification module is configured to adjust the transmission line impedance through the series-side converter to reshape the wind farm port, and the parallel-side converter adopts grid-type control to adjust the power of the grid-connected wind farm within a stable range to complete the centralized grid-connected wind farm modification.

[0042] The detailed steps are the same as those provided in Example 1 for the grid-type wind farm modification method based on series auxiliary devices, and will not be repeated here.

[0043] Example 3 Embodiment 3 of the present invention provides a computer-readable storage medium.

[0044] A computer-readable storage medium having a program stored thereon, which, when executed by a processor, implements the steps in the grid-type transformation method for wind farms based on series auxiliary devices as described in Embodiment 1 of the present invention.

[0045] The detailed steps are the same as those provided in Example 1 for the grid-type wind farm modification method based on series auxiliary devices, and will not be repeated here.

[0046] Example 4 Embodiment 4 of the present invention provides an electronic device.

[0047] An electronic device includes a memory, a processor, and a program stored in the memory and running on the processor. When the processor executes the program, it implements the steps in the grid-type transformation method for wind farms based on series auxiliary devices as described in Embodiment 1 of the present invention.

[0048] The detailed steps are the same as those provided in Example 1 for the grid-type wind farm modification method based on series auxiliary devices, and will not be repeated here.

[0049] Example 5 Embodiment 5 of the present invention provides a computer program product.

[0050] A computer program product includes software code, wherein the program in the software code performs the steps in the grid-type wind farm transformation method based on series auxiliary devices as described in Embodiment 1 of the present invention.

[0051] The detailed steps are the same as those provided in Example 1 for the grid-type wind farm modification method based on series auxiliary devices, and will not be repeated here.

[0052] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take 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.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0053] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations 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, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0054] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0055] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0056] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0057] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

[0058] The above description is merely a preferred embodiment of this practice and is not intended to limit the scope of this practice. Various modifications and variations can be made to this practice by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this practice should be included within the protection scope of this practice.

Claims

1. A grid-type modification method for a string-assisted onshore wind farm, characterized by, The wind turbines in the wind farm are all operated in the grid-following mode, and the wind turbines are connected in parallel at the common connection point after being boosted by the transformer and then are reformed by the series auxiliary device; the series auxiliary device adopts the unified power flow controller for the centralized grid-forming reform, and at least includes the parallel side converter and the series side converter; The wind turbines in the wind farm are connected in parallel at the common connection point, and the transmission line impedance is adjusted by the series side converter to reshape the wind farm port, and the power of the wind farm is regulated in the stable range by the parallel side converter to complete the centralized grid-forming reform of the wind farm.

2. A grid connection type retrofit method for a netted wind farm based on a series auxiliary device according to claim 1, characterized in that, When the grid-following wind turbine is connected in parallel to the AC bus common connection point after being boosted by a transformer, the parallel side converter provides frequency and voltage for the grid-following wind turbine with a synchronous AC power source, and through increasing V dc - f Droop control, maintaining the stability of the DC voltage, enabling power exchange between the parallel side and the series side; when the active power of the grid-following wind turbine changes, the output power and frequency of the wind turbine change accordingly.

3. A grid connection type modification method of a netted wind farm based on a series auxiliary device according to claim 2, characterized in that, The V dc - f The control equation of droop control is ; wherein, represents the droop coefficient between DC voltage and frequency, and respectively represent the parallel side grid angular velocity and the rated angular velocity, and respectively represent the actual measured value and the reference value of the system DC voltage.

4. The grid connection type modification method of a netted wind farm based on a series auxiliary device according to claim 1, characterized by, The parallel side converter adopts the double-loop control of the AC voltage loop and the current loop, wherein the outer loop is the AC voltage loop, and the inner loop is the current loop; the obtained three-phase voltage and three-phase current are compared with the reference three-phase voltage and three-phase current, the voltage control signal of the parallel converter in the abc three-phase coordinate system is obtained by the inverse Park coordinate transformation, the trigger pulse of the controller switch is generated by the modulation, and the stable AC voltage and frequency are obtained.

5. The grid connection type modification method of a netted wind farm based on a series auxiliary device according to claim 1, characterized in that, The series side converter adopts the three-loop virtual impedance control of the impedance outer loop, the voltage outer loop and the current inner loop to adjust the transmission line impedance.

6. The grid connection type modification method of a netted wind farm based on a series auxiliary device according to claim 1, characterized in that, The parallel side converter is connected with the common connection point through the transformer and then is connected in parallel with the transmission line; one end of the series side converter is connected with the parallel side converter, and the other end is connected with the AC grid in series with the transmission line.

7. A grid-type modification system for a string-assisted onshore wind farm, characterized by The wind turbines in the wind farm are all operated in the grid-following mode, and the wind turbines are connected in parallel at the common connection point after being boosted by the transformer and then are reformed by the series auxiliary device; the series auxiliary device adopts the unified power flow controller for the centralized grid-forming reform, and at least includes the parallel side converter and the series side converter; The wind turbines in the wind farm are connected in parallel at the common connection point, and the transmission line impedance is adjusted by the series side converter to reshape the wind farm port, and the power of the wind farm is regulated in the stable range by the parallel side converter to complete the centralized grid-forming reform of the wind farm. The program is executed by the processor to realize the steps of the grid-forming reform method of the wind farm in the grid-following mode based on the series auxiliary device.

8. A computer-readable storage medium having stored thereon a computer program, characterized in that, The processor executes the program to realize the steps of the grid-forming reform method of the wind farm in the grid-following mode based on the series auxiliary device.

9. An electronic device comprising a memory, a processor, and a computer program stored on the memory and running on the processor, characterized in that, The program in the software code executes the steps of the grid-forming reform method of the wind farm in the grid-following mode based on the series auxiliary device.

10. A computer program product comprising software code, characterized in that, ​

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