Rapid frequency support control method and device for offshore wind power uncontrolled rectification sending-out system

Abstract

The invention discloses a rapid frequency support control method and device for an offshore wind power uncontrolled rectification sending-out system, and the method comprises the steps: obtaining the frequency of a receiving-end AC power grid, and obtaining an improved receiving-end converter DC bus voltage instruction value based on the frequency information when the frequency change of the receiving-end AC power grid is detected; on the basis of the instruction value, the direct current bus voltage of the receiving end converter is regulated and controlled, so that the direct current bus voltage of the receiving end converter tracks the direct current bus voltage reference value of the receiving end converter, and the amplitude change of the alternating current voltage of the offshore wind field is caused; based on the change of the AC voltage amplitude of the offshore wind field, constructing a power outer ring of the active power-voltage amplitude and the reactive power-voltage phase angle of the similar synchronous machine, determining the terminal voltage reference value of the offshore wind turbine, regulating and controlling the terminal voltage of the offshore wind turbine, enabling the terminal voltage of the wind turbine to track the terminal voltage reference value, and controlling the active output of the offshore wind field. According to the invention, the inertia supporting capability of the offshore wind power uncontrolled rectification sending-out system to the receiving end power grid is improved.

Description

Technical Field

[0001] The present application relates to the research field of offshore wind power generation technology, and specifically to a method and device for rapid frequency support control of an offshore wind power uncontrolled rectifier transmission system. Background Art

[0002] With the rapid development of offshore wind power, wind energy development in coastal areas has reached saturation, and offshore wind power is gradually moving into deep-sea areas. To ensure the reliable transmission of deep-sea wind power, high-voltage direct current (HVDC) transmission systems have become the preferred choice. Among them, HVDC transmission systems based on uncontrolled rectifier units (DRUs) have attracted considerable attention in offshore wind power development due to their high reliability and low cost.

[0003] However, HVDC decouples the sending-end offshore wind turbines from the receiving-end AC grid, resulting in the offshore wind turbines being unable to directly obtain the frequency information of the receiving-end AC grid, and thus unable to provide inertia response as when the offshore wind turbines are AC-connected to the grid.

[0004] To enable offshore wind turbines to participate in receiving-end AC grid frequency support, existing methods often use communications to transmit receiving-end AC grid frequency information directly to the offshore wind turbines, which then adjust their output power accordingly to respond to inertia. However, communication equipment not only increases system costs but also presents reliability and latency issues. To address these issues, Chi Yongning et al. adjusted the DC bus voltage of the receiving-end converter based on the receiving-end AC grid frequency. The sending-end converter then adjusted the AC grid frequency of the offshore wind farm based on the DC bus voltage. This mapped the receiving-end AC grid frequency changes to the offshore grid frequency changes. The offshore wind turbines only need to obtain the offshore grid frequency information to provide frequency support.

[0005] However, for DRU-HVDC, its sending-end converter DRU relies on natural commutation to achieve rectification. Therefore, it cannot regulate the offshore AC grid like a flexible DC transmission system and transmit the receiving-end AC grid frequency information coupled with the DC bus voltage. H. Xiao et al. adjusted the receiving-end converter DC bus voltage based on the frequency difference, while the offshore wind turbine directly collected the DC bus voltage of the sending-end DRU to obtain the receiving-end AC grid frequency information and adjust the active power reference value of the offshore wind turbine. Although this method eliminates the need for communication equipment between the sending and receiving ends, the DC bus voltage information still needs to be transmitted through multiple levels such as the sending-end communication unit, the wind farm group communication unit, the station controller, the collector switch, and the wind turbine master control, resulting in a certain delay. In addition, the offshore wind turbine under uncontrolled rectification needs to adopt a network control strategy, which has a slow power adjustment speed and is difficult to meet the needs of the receiving-end AC grid for fast frequency support.

[0006] Therefore, how to avoid dependence on communication and external information and improve the power response capability of offshore wind turbines is the key to achieving frequency support for the receiving AC power grid by offshore wind farms under uncontrolled rectifier transmission. Summary of the Invention

[0007] In view of this, embodiments of the present application provide a method and device for rapid frequency support control of an uncontrolled rectifier transmission system for offshore wind power. This method regulates the DC bus voltage of the receiving-end converter based on frequency changes of the receiving-end AC grid, thereby affecting the voltage amplitude of the sending-end AC grid. By constructing a synchronous-type active power-voltage amplitude control loop, the offshore wind turbine's power is regulated in response to frequency changes of the receiving-end AC grid. This method, without requiring additional communication, coordinates the DC bus capacitor energy of the receiving-end converter and the frequency modulation energy of the offshore wind turbine, improving the inertia response and frequency support capabilities of the offshore wind power uncontrolled rectifier transmission system to the onshore grid.

[0008] According to a first aspect of an embodiment of the present application, a method for rapid frequency support control of an offshore wind power uncontrolled rectifier transmission system is provided, comprising: Acquiring the receiving-end AC grid frequency, and when detecting a frequency change of the receiving-end AC grid, obtaining an improved receiving-end converter DC bus voltage command value based on the frequency information; Based on the receiving-end converter DC bus voltage command value, regulating the receiving-end converter DC bus voltage so that the receiving-end converter DC bus voltage tracks the receiving-end converter DC bus voltage reference value, thereby causing the AC voltage amplitude of the offshore wind farm to change; Based on the changes in AC voltage amplitude in offshore wind farms, a power outer loop of active power-voltage amplitude and reactive power-voltage phase angle similar to synchronous machines is constructed to determine the terminal voltage reference value of offshore wind turbines. According to the terminal voltage reference value, the terminal voltage of the offshore wind turbine is regulated so that the terminal voltage of the offshore wind turbine tracks the terminal voltage reference value, thereby controlling the active power output of the offshore wind farm.

[0009] Optionally, obtaining an improved DC bus voltage command value of the receiving-end converter based on the frequency information includes: Obtaining the receiving-end AC grid frequency, and if a frequency change of the receiving-end AC grid is detected, performing an improved calculation of the receiving-end converter DC bus voltage command value; Calculating the difference between the receiving-end AC grid frequency and the rated frequency of the receiving-end AC grid to obtain the receiving-end AC grid frequency difference; According to the receiving-end AC grid frequency difference, multiplying it by the frequency droop control coefficient, to obtain the receiving-end converter DC bus voltage droop adjustment amount; performing differential processing on the receiving-end AC power grid frequency to obtain a frequency change rate of the receiving-end AC power grid; According to the receiving-end AC grid frequency change rate, multiplying it by the frequency inertia control coefficient, obtains the receiving-end converter DC bus voltage inertia adjustment amount; According to the receiving-end converter DC bus voltage droop adjustment amount and the inertia adjustment amount, they are added to the receiving-end converter rated DC bus voltage command value to obtain an improved receiving-end converter DC bus voltage command value.

[0010] Optionally, based on the receiving-end converter DC bus voltage command value, regulating the receiving-end converter DC bus voltage so that the receiving-end converter DC bus voltage tracks the receiving-end converter DC bus voltage reference value, thereby causing the AC voltage amplitude of the offshore wind farm to change, includes: According to the DC bus voltage command value of the receiving converter, the difference between it and the actual value of the DC bus voltage of the receiving converter is calculated and sent to the DC bus voltage controller of the receiving converter based on proportional integral PI control, and its output is used as the grid-connected current of the receiving converter. d Reference values ​​of axis components; Set the receiving end converter grid-connected current q Reference values ​​of axis components; Calculate the grid-connected current of the receiving-end converter d 、 q The reference value of the axis component and the grid-connected current of the receiving converter d 、 q The difference between the actual value of the axis component is sent to the receiving-end converter current controller based on PI control to obtain the receiving-end converter modulation voltage d 、 q Axis component; According to the receiving end converter modulation voltage d 、 q The axis component is obtained by coordinate transformation and pulse width modulation to obtain a corresponding switching signal, which is applied to the receiving-end converter, so that the DC bus voltage of the receiving-end converter tracks the DC bus voltage reference value of the receiving-end converter, thereby causing the AC voltage amplitude of the offshore wind farm to change.

[0011] Optionally, based on the change in AC voltage amplitude of the offshore wind farm, a power outer loop of active power-voltage amplitude and reactive power-voltage phase angle of a quasi-synchronous machine is constructed to determine a terminal voltage reference value of the offshore wind turbine, including: Based on the changes in the AC voltage amplitude of the offshore wind farm and referring to the active power-frequency response characteristics of the synchronous machine, a synchronous machine-like active power-voltage amplitude control loop is constructed to obtain the terminal voltage amplitude reference value of the offshore wind turbine; According to the offshore wind farm, a droop-based reactive power-voltage phase angle control loop is constructed to obtain the terminal voltage phase angle reference value and coordinate transformation angle of the offshore wind turbines to achieve synchronous operation and reactive power equalization of the wind turbines in the offshore wind farm; A terminal voltage reference value of the offshore wind turbine is determined according to a terminal voltage amplitude reference value and a terminal voltage phase angle reference value of the offshore wind turbine.

[0012] According to a second aspect of an embodiment of the present application, a rapid frequency support control device for an offshore wind power uncontrolled rectifier transmission system is provided, comprising: The receiving-end converter instruction construction module is used to obtain the receiving-end AC grid frequency and, when detecting a frequency change of the receiving-end AC grid, obtain an improved receiving-end converter DC bus voltage instruction value based on the frequency information; a receiving-end converter control module, configured to regulate the receiving-end converter DC bus voltage based on the receiving-end converter DC bus voltage command value, so that the receiving-end converter DC bus voltage tracks the receiving-end converter DC bus voltage reference value, thereby causing the AC voltage amplitude of the offshore wind farm to change; The offshore wind turbine power control module is used to build a synchronous machine-like power outer loop of active power-voltage amplitude and reactive power-voltage phase angle based on the change of AC voltage amplitude in the offshore wind farm, and determine the terminal voltage reference value of the offshore wind turbine; The offshore wind turbine voltage control module is used to regulate the offshore wind turbine terminal voltage according to the terminal voltage reference value, so that the offshore wind turbine terminal voltage tracks the terminal voltage reference value and controls the active power output of the offshore wind farm.

[0013] According to a third aspect of the embodiments of the present application, there is provided an electronic device, including: one or more processors; a memory for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the method as described in the first aspect.

[0014] According to a fourth aspect of an embodiment of the present application, a computer-readable storage medium is provided, on which computer instructions are stored. When the instructions are executed by a processor, the steps of the method described in the first aspect are implemented.

[0015] The technical solutions provided by the embodiments of the present application may have the following beneficial effects: As can be seen from the above embodiments, the method of the present invention does not require communication, and uses the DC bus voltage to couple the receiving-end AC grid frequency information and the sending-end AC grid voltage amplitude information, thereby improving system reliability. The present invention constructs a synchronous machine-like active power-voltage amplitude control loop to simulate the characteristics of the synchronous machine, and the inertia response is faster. The present invention enhances frequency support by coordinating the DC bus capacitor energy of the receiving-end converter and the frequency modulation energy of the offshore wind turbine, integrating the two types of frequency modulation resources. The present invention provides ideas for improving the rapid frequency support capability of similar uncontrolled rectifier transmission systems.

[0016] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0018] Figure 1 The present invention is a flow chart showing a method for fast frequency support control of an offshore wind power uncontrolled rectification and transmission system according to an exemplary embodiment.

[0019] Figure 2 The figure is a structural diagram of an offshore wind power uncontrolled rectification and transmission system according to an exemplary embodiment.

[0020] Figure 3 The figure is a control structure diagram of a fast frequency support method for an offshore wind power uncontrolled rectification and transmission system according to an exemplary embodiment.

[0021] Figure 4 The simulation results of the AC grid frequency at the receiving end using the traditional strategy and the proposed strategy when a 300MW load is suddenly added to the AC grid at the receiving end.

[0022] Figure 5 The simulation results of the AC grid frequency at the sending end using the traditional strategy and the proposed strategy when a 300MW load is suddenly added to the AC grid at the receiving end.

[0023] Figure 6 The simulation results of the AC grid amplitude at the sending-end offshore wind farm using the traditional strategy and the proposed strategy when a sudden 300MW load is added to the AC grid at the receiving end.

[0024] Figure 7 The DRU active power simulation results of the traditional strategy and the proposed strategy when a 300MW load is suddenly added to the receiving AC grid.

[0025] Figure 8 The DRU reactive power simulation results of the traditional strategy and the proposed strategy when a 300MW load is suddenly added to the receiving AC grid.

[0026] Figure 9 Figure 2 shows the HVDC DC current simulation results of the traditional strategy and the proposed strategy when a 300MW load is suddenly added to the receiving AC grid.

[0027] Figure 10 The simulation results of the DC bus voltage of the receiving-end converter for the traditional strategy and the proposed strategy when a 300MW load is suddenly added to the receiving-end AC grid.

[0028] Figure 11The simulation results of the active power of the receiving-end converter of the traditional strategy and the proposed strategy when a 300MW load is suddenly added to the receiving-end AC grid.

[0029] Figure 12 The simulation results of the active power of offshore wind turbines using the traditional strategy and the proposed strategy when a 300MW load is suddenly added to the receiving AC grid.

[0030] Figure 13 The reactive power simulation results of offshore wind turbines using the traditional strategy and the proposed strategy when a 300MW load is suddenly added to the receiving AC grid.

[0031] Figure 14 The simulation results of the AC grid frequency at the receiving end using the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly reduces its load by 300MW.

[0032] Figure 15 The simulation results of the AC grid frequency at the sending end using the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly drops 300MW.

[0033] Figure 16 The simulation results of AC grid amplitude at the sending-end offshore wind farm using the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly drops 300MW.

[0034] Figure 17 The DRU active power simulation results of the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly reduces by 300MW.

[0035] Figure 18 The DRU reactive power simulation results of the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly reduces by 300MW.

[0036] Figure 19 Figure 2 shows the HVDC DC current simulation results of the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly reduces its load by 300MW.

[0037] Figure 20 The simulation results of the DC bus voltage of the receiving-end converter for the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly reduces its load by 300MW.

[0038] Figure 21 The following figure shows the simulation results of the active power of the receiving-end converter of the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly reduces the load by 300MW.

[0039] Figure 22 The following is the simulation result of the active power of offshore wind turbines using the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly reduces the load by 300MW. Figure 23The following is the simulation result of reactive power of offshore wind turbines using traditional strategy and proposed strategy when the AC grid at the receiving end suddenly reduces 300MW load.

[0040] Figure 24 The present invention is a block diagram of a fast frequency support control device for an offshore wind power uncontrolled rectification and transmission system according to an exemplary embodiment. DETAILED DESCRIPTION

[0041] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.

[0042] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. As used in this application and the appended claims, the singular forms "a," "an," "the," and "the" are intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0043] It should be understood that although the terms first, second, third, etc. may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from each other. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0044] In order to describe the present invention in more detail, the present invention will be further described below with reference to the accompanying drawings and specific implementation examples.

[0045] Figure 1 This is a flow chart showing a method for fast frequency support control of an offshore wind power uncontrolled rectifier transmission system according to an exemplary embodiment. Figure 1 As shown, the method may include the following steps: S1: Acquire the receiving-end AC grid frequency. When a frequency change of the receiving-end AC grid is detected, obtain an improved receiving-end converter DC bus voltage command value based on the frequency information. This step includes the following sub-steps: S11: If a frequency change of the AC power grid at the receiving end is detected based on the frequency of the AC power grid at the receiving end, a difference between the frequency of the AC power grid at the receiving end and the rated frequency of the AC power grid at the receiving end is calculated to obtain a frequency difference of the AC power grid at the receiving end; Specifically, taking a 1000MW offshore wind power uncontrolled rectification transmission system as an example, its main structure diagram is as follows: Figure 2 The offshore wind farm consists of three clustered wind turbines (330MW, 330MW, and 340MW, respectively). These are connected to a DRU-HVDC system with a rated capacity of 1000MW and a rated DC voltage of ±320kV via a 690V / 66kV step-up transformer and a 66kV / 258kV / 258kV DRU converter transformer. The system is then connected to the onshore grid via a 330kV / 230kV step-down transformer. The onshore grid consists of a single synchronous generator with an installed capacity of 2000MW and a constant load of 2000MW.

[0046] Collect the three-phase grid voltage of the receiving AC grid U re , obtain the receiving end AC grid frequency through the phase-locked loop f re . Compare it with the rated frequency of the receiving AC grid f 0, and obtain the AC grid frequency difference Δ at the receiving end f ,for: (1) S12: multiplying the receiving-end AC grid frequency difference by a frequency droop control coefficient to obtain a receiving-end converter DC bus voltage droop adjustment amount; Specifically, according to the receiving end AC grid frequency difference Δ f , DC bus voltage droop adjustment value of the receiving end converter for: (2) in, k D is the DC bus voltage frequency droop control coefficient of the receiving-end converter.

[0047] S13: performing differential processing on the receiving-end AC grid frequency to obtain a frequency change rate of the receiving-end AC grid; Specifically, the receiving end AC grid frequency is calculated f re The differential value of the receiving end AC grid frequency change rate is obtained df / dt ; S14: multiplying the receiving-end AC grid frequency change rate by the frequency inertia control coefficient to obtain a receiving-end converter DC bus voltage inertia adjustment value; Specifically, according to the receiving end AC grid frequency change rate df / dt , DC bus voltage inertia adjustment of the receiving converter for: (3) in, k I is the DC bus voltage frequency inertia control coefficient of the receiving-end converter.

[0048] S15: adding the DC bus voltage droop adjustment amount and the inertia adjustment amount of the receiving-end converter to the rated DC bus voltage command value of the receiving-end converter to obtain an improved DC bus voltage command value of the receiving-end converter under the fast frequency support control method; Specifically, according to the DC bus voltage droop adjustment amount of the receiving-end converter and inertia adjustment , compare the two with the rated DC bus voltage command value of the receiving converter Add together to obtain the improved DC bus voltage command value of the receiving converter under the fast frequency support control method. ,for: (4) Through this step, the receiving-end AC grid frequency information is converted into the receiving-end converter DC bus voltage reference value, providing guidance for the receiving-end converter regulation and providing relevant information for the rapid frequency support of offshore wind turbines.

[0049] S2: Based on the DC bus voltage command value of the receiving-end converter, regulating the DC bus voltage of the receiving-end converter, so that the DC bus voltage of the receiving-end converter tracks the DC bus voltage reference value of the receiving-end converter, thereby causing the AC voltage amplitude of the offshore wind farm to change; Specifically, according to the DC bus voltage command value of the receiving end converter , calculate its difference with the actual value of the DC bus voltage of the receiving converter The difference is sent to the DC bus voltage controller of the receiving converter based on proportional integral (PI) control, and its output is used as the grid-connected current of the receiving converter. d Reference values ​​of axis components ,Right now: (4) in, k preVdc 、 k ireVdc are the proportional and integral coefficients of the DC bus voltage loop of the receiving-end converter.

[0050] In addition, the grid-connected current of the receiving converter is generally set q Reference values ​​of axis components for: (5) Calculate the grid-connected current of the receiving-end converter d 、 q Reference values ​​of axis components 、 Grid-connected current of the receiving converter d 、 q Actual value of the axis component 、 The difference is sent to the receiving-end converter current controller based on PI control to obtain the receiving-end converter modulation voltage d 、 q Axis component 、 : (6) (7) in, k preI 、 k ireI are the proportional and integral coefficients of the current loop of the receiving-end converter; According to the receiving end converter modulation voltage d 、 q The axis component is obtained by coordinate transformation and pulse width modulation (PWM) to obtain a corresponding switching signal, which is applied to the receiving-end converter to make the DC bus voltage of the receiving-end converter track the DC bus voltage reference value of the receiving-end converter.

[0051] According to the HVDC DC line topology, the DC bus voltage of the DRU at the sending end can be obtained as and the receiving-end converter DC bus voltage The relationship is: (8) in, I dc is the HVDC direct current, R dc 、 I dc is the equivalent resistance and inductance of the HVDC line; Due to the regulation of the DC bus voltage of the receiving converter, the actual value of the DC bus voltage of the receiving converter is equal to its reference value, and then the DC bus voltage of the sending DRU is Also changes accordingly.

[0052] According to the topology and commutation characteristics of the sending-end DRU and considering the dynamic characteristics of the converter transformer inductance, the AC voltage amplitude of the sending-end offshore wind farm can be obtained: and the DC bus voltage of the DRU at the sending end The relationship is: (9) in, is the AC voltage frequency of the offshore wind farm at the sending end, T DR 、 L DR is the transformation ratio and inductance of the DRU converter transformer; Sending-end DRU DC bus voltage Changes in the AC voltage amplitude at the sending end of the offshore wind farm change.

[0053] Through this step, the actual value of the DC bus voltage of the receiving-end converter contains the receiving-end AC grid frequency information. After passing through physical links such as the HVDC DC line and DRU commutation, it causes the AC voltage amplitude of the sending-end offshore wind farm to change. The receiving-end AC grid frequency information can be mapped without the need for a communication line.

[0054] S3: Based on the changes in the AC voltage amplitude of the offshore wind farm, a power outer loop of active power-voltage amplitude and reactive power-voltage phase angle of a synchronous machine is constructed to determine the terminal voltage reference value of the offshore wind turbine; S31: Based on the change of the AC voltage amplitude of the offshore wind farm and referring to the active power-frequency response characteristics of the synchronous machine, a synchronous machine-like active power-voltage amplitude control loop is constructed to obtain a terminal voltage amplitude reference value of the offshore wind turbine; Specifically, in order for offshore wind turbines to autonomously respond to changes in the AC voltage amplitude of the offshore wind farm and adjust their power output, they need to exhibit synchronous-like characteristics. Referring to the synchronous machine's active power-frequency response characteristics, the synchronous-like active power-voltage amplitude response characteristics can be obtained: (10) in, 、 is the reference value and rated value of the terminal voltage amplitude of the offshore wind turbine, 、 The reference value and actual value of the active power output of the offshore wind turbine, J 、 D is the moment of inertia and damping coefficient of the offshore wind turbine; According to the active power-voltage amplitude response characteristics of the quasi-synchronous machine, the active power-voltage amplitude control loop of the quasi-synchronous machine is constructed to obtain the terminal voltage amplitude reference value of the offshore wind turbine. : (11) Through this step, the external characteristics of the offshore wind turbine are simulated as a quasi-synchronous machine with active power and voltage amplitude correlation, providing a control basis for achieving inertia support for the offshore wind turbine.

[0055] S32: Based on the offshore wind farm, a droop-based reactive power-voltage phase angle control loop is constructed to obtain a terminal voltage phase angle reference value and a coordinate transformation angle of the offshore wind turbine, so as to achieve synchronous operation and reactive power equalization of the offshore wind turbines in the offshore wind farm; Specifically, for offshore wind farms that are sent out through uncontrolled rectification, the reactive power output by the offshore wind turbines is proportional to the AC voltage frequency of the sending-end offshore wind farm. In view of this, droop control is used to achieve equal distribution of the reactive power of offshore wind turbines, thereby achieving synchronous operation of each wind turbine in the offshore wind farm. By constructing a droop-based reactive power-voltage phase angle control loop, the terminal voltage frequency reference value of the offshore wind turbine is obtained. : (12) in, is the terminal voltage frequency rating of the offshore wind turbine, 、 The reference value and actual value of the reactive power output of the offshore wind turbine, k G 、 k T The proportional coefficient and time coefficient for offshore wind turbine droop control; The terminal voltage frequency reference value of the offshore wind turbine By integrating, we can obtain the terminal voltage phase angle reference value and coordinate transformation angle of the offshore wind turbine: (13) in, ω base is the reference value of angular frequency.

[0056] Through this step, the offshore wind turbines evenly distribute the reactive power required by the offshore wind farm and obtain coordinate change angle information, providing a control basis for the offshore wind turbines to achieve self-synchronous operation.

[0057] S33: determining a terminal voltage reference value of the offshore wind turbine according to a terminal voltage amplitude reference value and a terminal voltage phase angle reference value of the offshore wind turbine; Specifically, the offshore wind turbine control system coordinate system is oriented to the reactive power-voltage phase angle control loop to obtain the offshore wind turbine terminal voltage phase angle reference value, and then the offshore wind turbine terminal voltage can be obtained. d 、 q Axis component reference value 、 : (14) (15) Through this step, the voltage at the offshore wind turbine terminal is obtained using the known information. d 、q The axis component reference value provides accurate information for offshore wind turbine terminal voltage control.

[0058] S4: regulating the terminal voltage of the offshore wind turbine according to the terminal voltage reference value, so that the terminal voltage of the offshore wind turbine tracks the terminal voltage reference value, thereby controlling the active power output of the offshore wind farm; Specifically, according to the terminal voltage of the offshore wind turbine d 、 q Axis component reference value 、 , respectively calculate the voltage at the offshore wind turbine terminal d 、 q Actual value of axis component 、 The difference is sent to the offshore wind turbine voltage controller based on PI control, and its output is used as the offshore wind turbine grid-connected current d 、 q Reference values ​​of axis components 、 ,Right now: (16) (17) in, k pgU 、 k igU are the proportional and integral coefficients of the offshore wind turbine voltage loop; According to the offshore wind turbine grid-connected current d 、 q Reference values ​​of axis components 、 Grid-connected current for offshore wind turbines d 、 q Actual value of the axis component 、 The difference is sent to the offshore wind turbine current controller based on PI control to obtain the offshore wind turbine modulation voltage d 、 q Axis component 、 : (18) (19) in, k pgI 、 k igI are the proportional and integral coefficients of the offshore wind turbine current loop; According to the offshore wind turbine voltage modulation d 、 qThe axis component is transformed into a coordinate system and pulse width modulation (PWM) to obtain the corresponding switching signal, which is applied to the grid-side converter of the offshore wind turbine.

[0059] In addition, the machine-side converter of the offshore wind turbine adopts the existing conventional DC bus voltage-current dual closed-loop control structure, which will not be described here.

[0060] Through this step, the terminal voltage of the offshore wind turbine tracks the terminal voltage reference value obtained by the power loop, thereby controlling the power output of the offshore wind farm and achieving rapid frequency support for the receiving-end AC power grid.

[0061] According to the example, the control structure diagram of the fast frequency support method for the offshore wind power uncontrolled rectifier transmission system is as follows: Figure 3 shown.

[0062] Figure 4 The simulation results of the AC grid frequency at the receiving end using the traditional strategy and the proposed strategy when a 300MW load is suddenly added to the AC grid at the receiving end. Figure 5 The simulation results of the AC grid frequency at the sending end using the traditional strategy and the proposed strategy when a 300MW load is suddenly added to the AC grid at the receiving end. Figure 6 The simulation results of the AC grid amplitude at the sending-end offshore wind farm using the traditional strategy and the proposed strategy when a sudden 300MW load is added to the AC grid at the receiving end. Figure 7 The DRU active power simulation results of the traditional strategy and the proposed strategy when a 300MW load is suddenly added to the receiving AC grid. Figure 8 The DRU reactive power simulation results of the traditional strategy and the proposed strategy when a 300MW load is suddenly added to the receiving AC grid. Figure 9 Figure 2 shows the HVDC DC current simulation results of the traditional strategy and the proposed strategy when a 300MW load is suddenly added to the receiving AC grid. Figure 10 The simulation results of the DC bus voltage of the receiving-end converter for the traditional strategy and the proposed strategy when a 300MW load is suddenly added to the receiving-end AC grid. Figure 11 The simulation results of the active power of the receiving-end converter of the traditional strategy and the proposed strategy when a 300MW load is suddenly added to the receiving-end AC grid. Figure 12 The simulation results of the active power of offshore wind turbines using the traditional strategy and the proposed strategy when a 300MW load is suddenly added to the receiving AC grid. Figure 13 The following is the simulation result of reactive power of offshore wind turbines using traditional strategy and proposed strategy when the AC grid at the receiving end suddenly adds 300MW load. Figure 4-13It can be seen that when using the traditional control strategy, the offshore wind turbine does not respond to frequency changes in the sending AC grid, and the power transmitted to the sending AC grid through the DRU-HVDC remains almost unchanged. At this time, the sending AC grid frequency drops to a minimum of 49.8Hz. However, when using the proposed control strategy, the receiving-end converter regulates its DC bus voltage based on the receiving AC grid frequency information, and the AC voltage amplitude of the sending offshore wind farm naturally changes accordingly. The offshore wind turbine adjusts its power output through the constructed active power-voltage amplitude control loop, delivering more active power to the receiving AC grid within 500ms, raising the minimum receiving AC grid frequency to 49.86Hz.

[0063] Figure 14 The simulation results of the AC grid frequency at the receiving end using the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly reduces its load by 300MW. Figure 15 The simulation results of the AC grid frequency at the sending end using the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly drops 300MW. Figure 16 The simulation results of AC grid amplitude at the sending-end offshore wind farm using the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly drops 300MW. Figure 17 The DRU active power simulation results of the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly reduces by 300MW. Figure 18 The DRU reactive power simulation results of the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly reduces by 300MW. Figure 19 Figure 2 shows the HVDC DC current simulation results of the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly reduces its load by 300MW. Figure 20 The simulation results of the DC bus voltage of the receiving-end converter for the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly reduces its load by 300MW. Figure 21 The following figure shows the simulation results of the active power of the receiving-end converter of the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly reduces the load by 300MW. Figure 22 The simulation results of the active power of offshore wind turbines using the traditional strategy and the proposed strategy when the AC grid at the receiving end suddenly reduces its load by 300MW. Figure 23 The following is the simulation result of reactive power of offshore wind turbines using traditional strategy and proposed strategy when the AC grid at the receiving end suddenly reduces 300MW load. Figure 14-23 It can be seen that when the AC grid load suddenly decreases at the receiving end, the receiving AC grid frequency rises to 50.22 Hz using the traditional strategy. However, when the proposed control strategy is used, the offshore wind turbine responds to the AC grid frequency change by reducing its output power, slowing the rate of increase in the AC grid frequency, and reducing the maximum value of the AC grid frequency to 50.18 Hz. This shows that the proposed control strategy has excellent rapid frequency support capabilities under different frequency change conditions.

[0064] In summary, the present invention proposes a method for rapid frequency support control of an offshore wind power uncontrolled rectifier transmission system. The innovation of this method lies in that the DC bus voltage of the receiving-end converter is regulated according to the frequency change of the receiving-end AC grid, thereby affecting the voltage amplitude of the sending-end AC grid. By constructing a synchronous machine-like active power-voltage amplitude control loop, the power regulation of the offshore wind turbine is achieved to respond to the frequency change of the receiving-end AC grid. This method does not require additional communication, and coordinates the DC bus capacitor energy of the receiving-end converter and the frequency modulation energy of the offshore wind turbine, thereby improving the inertia response and frequency support capability of the offshore wind power uncontrolled rectifier transmission system to the onshore power grid. The present invention provides ideas for improving the rapid frequency support capability of similar uncontrolled rectifier transmission systems.

[0065] Corresponding to the aforementioned embodiment of the rapid frequency support control method for an offshore wind power uncontrolled rectification and transmission system, the present application also provides an embodiment of a rapid frequency support control device for an offshore wind power uncontrolled rectification and transmission system.

[0066] Figure 24 This is a block diagram of a fast frequency support control device for an offshore wind power uncontrolled rectification transmission system according to an exemplary embodiment. Figure 24 , the device comprises: The receiving-end converter instruction construction module 1 is used to obtain the receiving-end AC grid frequency and, when detecting a frequency change of the receiving-end AC grid, obtain an improved receiving-end converter DC bus voltage instruction value based on the frequency information; The receiving-end converter control module 2 is configured to regulate the receiving-end converter DC bus voltage based on the receiving-end converter DC bus voltage command value, so that the receiving-end converter DC bus voltage tracks the receiving-end converter DC bus voltage reference value, thereby causing the AC voltage amplitude of the offshore wind farm to change; The offshore wind turbine power control module 3 is used to build a synchronous machine-like power outer loop of active power-voltage amplitude and reactive power-voltage phase angle based on the change of the AC voltage amplitude of the offshore wind farm, and determine the terminal voltage reference value of the offshore wind turbine; The offshore wind turbine voltage control module 4 is used to regulate the offshore wind turbine terminal voltage according to the terminal voltage reference value, so that the offshore wind turbine terminal voltage tracks the terminal voltage reference value, thereby controlling the active power output of the offshore wind farm.

[0067] Regarding the apparatus in the above embodiment, the specific manner in which each module performs operations has been described in detail in the embodiment of the method, and will not be elaborated here.

[0068] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can be referred to the partial description of the method embodiments. The device embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the present application scheme. A person of ordinary skill in the art can understand and implement it without paying any creative work.

[0069] Correspondingly, the present application also provides an electronic device, including: one or more processors; a memory for storing one or more programs; when the one or more programs are executed by the one or more processors, the one or more processors implement the above-mentioned rapid frequency support control method for the offshore wind power uncontrolled rectifier transmission system.

[0070] Accordingly, the present application also provides a computer-readable storage medium having computer instructions stored thereon, which, when executed by a processor, implement the above-mentioned method for rapid frequency support control of an offshore wind power uncontrolled rectifier transmission system.

[0071] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the contents disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present application that follow the general principles of the present application and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered merely as exemplary, and the true scope and spirit of the present application are indicated by the claims.

[0072] It should be understood that the present application is not limited to the exact structures described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A fast frequency support control method for an offshore wind power uncontrolled rectifier transmission system, characterized in that: include: Acquiring the receiving-end AC grid frequency, and when detecting a frequency change of the receiving-end AC grid, obtaining an improved receiving-end converter DC bus voltage command value based on the frequency information; Based on the receiving-end converter DC bus voltage command value, regulating the receiving-end converter DC bus voltage so that the receiving-end converter DC bus voltage tracks the receiving-end converter DC bus voltage reference value, thereby causing the AC voltage amplitude of the offshore wind farm to change; Based on the changes in AC voltage amplitude in offshore wind farms, a power outer loop of active power-voltage amplitude and reactive power-voltage phase angle similar to synchronous machines is constructed to determine the terminal voltage reference value of offshore wind turbines. According to the terminal voltage reference value, the terminal voltage of the offshore wind turbine is regulated so that the terminal voltage of the offshore wind turbine tracks the terminal voltage reference value, thereby controlling the active power output of the offshore wind farm.

2. The method according to claim 1, characterized in that Based on the frequency information, an improved DC bus voltage command value of the receiving-end converter is obtained, including: Calculating the difference between the receiving-end AC grid frequency and the rated frequency of the receiving-end AC grid to obtain the receiving-end AC grid frequency difference; According to the receiving-end AC grid frequency difference, multiplying it by the frequency droop control coefficient, to obtain the receiving-end converter DC bus voltage droop adjustment amount; performing differential processing on the receiving-end AC power grid frequency to obtain a frequency change rate of the receiving-end AC power grid; According to the receiving-end AC grid frequency change rate, multiplying it by the frequency inertia control coefficient, obtains the receiving-end converter DC bus voltage inertia adjustment amount; According to the receiving-end converter DC bus voltage droop adjustment amount and the inertia adjustment amount, they are added to the receiving-end converter rated DC bus voltage command value to obtain an improved receiving-end converter DC bus voltage command value.

3. The method according to claim 1, characterized in that Based on the receiving-end converter DC bus voltage command value, regulating the receiving-end converter DC bus voltage so that the receiving-end converter DC bus voltage tracks the receiving-end converter DC bus voltage reference value, thereby causing the AC voltage amplitude of the offshore wind farm to change, including: According to the DC bus voltage command value of the receiving converter, the difference between it and the actual value of the DC bus voltage of the receiving converter is calculated and sent to the DC bus voltage controller of the receiving converter based on proportional integral PI control, and its output is used as the grid-connected current of the receiving converter. d Reference values ​​of axis components; Set the receiving end converter grid-connected current q Reference values ​​of axis components; Calculate the grid-connected current of the receiving-end converter d 、 q The reference value of the axis component and the grid-connected current of the receiving converter d 、 q The difference between the actual value of the axis component is sent to the receiving-end converter current controller based on PI control to obtain the receiving-end converter modulation voltage d 、 q Axis component; According to the receiving end converter modulation voltage d 、 q The axis component is obtained by coordinate transformation and pulse width modulation to obtain a corresponding switching signal, which is applied to the receiving-end converter, so that the DC bus voltage of the receiving-end converter tracks the DC bus voltage reference value of the receiving-end converter, thereby causing the AC voltage amplitude of the offshore wind farm to change.

4. The method according to claim 1, wherein Based on the changes in AC voltage amplitude in offshore wind farms, a power outer loop of active power-voltage amplitude and reactive power-voltage phase angle similar to synchronous machines is constructed to determine the terminal voltage reference value of offshore wind turbines, including: Based on the changes in the AC voltage amplitude of the offshore wind farm and referring to the active power-frequency response characteristics of the synchronous machine, a synchronous machine-like active power-voltage amplitude control loop is constructed to obtain the terminal voltage amplitude reference value of the offshore wind turbine; According to the offshore wind farm, a droop-based reactive power-voltage phase angle control loop is constructed to obtain the terminal voltage phase angle reference value and coordinate transformation angle of the offshore wind turbines to achieve synchronous operation and reactive power equalization of the offshore wind turbines in the offshore wind farm; A terminal voltage reference value of the offshore wind turbine is determined according to a terminal voltage amplitude reference value and a terminal voltage phase angle reference value of the offshore wind turbine.

5. A fast frequency support control device for an offshore wind power uncontrolled rectifier transmission system, characterized in that: include: The receiving-end converter instruction construction module is used to obtain the receiving-end AC grid frequency and, when detecting a frequency change of the receiving-end AC grid, obtain an improved receiving-end converter DC bus voltage instruction value based on the frequency information; a receiving-end converter control module, configured to regulate the receiving-end converter DC bus voltage based on the receiving-end converter DC bus voltage command value, so that the receiving-end converter DC bus voltage tracks the receiving-end converter DC bus voltage reference value, thereby causing the AC voltage amplitude of the offshore wind farm to change; The offshore wind turbine power control module is used to build a synchronous machine-like power outer loop of active power-voltage amplitude and reactive power-voltage phase angle based on the change of AC voltage amplitude in the offshore wind farm, and determine the terminal voltage reference value of the offshore wind turbine; The offshore wind turbine voltage control module is used to regulate the offshore wind turbine terminal voltage according to the terminal voltage reference value, so that the offshore wind turbine terminal voltage tracks the terminal voltage reference value and controls the active power output of the offshore wind farm.

6. An electronic device, characterized in that: include: one or more processors; a memory for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the method according to any one of claims 1 to 5.

7. A computer-readable storage medium having computer instructions stored thereon, characterized in that: When the instruction is executed by a processor, the steps of the method according to any one of claims 1 to 5 are implemented.

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