Equivalent inertia evaluation method and device for offshore wind power flexible direct output system

Abstract

The invention belongs to the field of electric power, and discloses an equivalent inertia evaluation method and device for an offshore wind power flexible direct-current transmission system, and the method comprises the steps: building a small-signal model of the flexible direct-current transmission system according to the control topology of the flexible direct-current transmission system; establishing a machine-side converter small-signal model according to the control topology of the machine-side converter of the offshore wind plant, and establishing an offshore wind plant small-signal model according to the machine-side converter small-signal model and the control topology of the network-side converter of the offshore wind plant; the flexible direct current power transmission system responds to an analog synchronous machine rotor motion equation, the offshore wind power plant responds to a primary frequency modulation process of an analog synchronous machine, and system class synchronization characteristics are described in the form of the synchronous machine rotor motion equation, so that an offshore wind power flexible direct output system class synchronization supporting model is established; and calculating an equivalent inertia transfer function of the offshore wind power flexible direct output system according to the synchronous support model of the offshore wind power flexible direct output system.

Description

Technical Field

[0001] The present invention belongs to the field of electric power, and in particular relates to an equivalent inertia evaluation method and device for an offshore wind power flexible direct current transmission system. Background Art

[0002] With the increasing development of offshore resources, the development and utilization of offshore wind power resources has received increasing attention, and more and more wind farms are being relocated to deep and offshore areas. Flexible DC transmission technology offers advantages such as independent reactive power control, susceptibility to commutation failures, and the ability to achieve black starts, making it an optimal choice for offshore wind power transmission. The receiving-end converters of offshore wind power flexible DC transmission systems typically use phase-locked synchronization and are primarily designed for "grid following." They lack the ability to support the inertia of the receiving grid. As the transmission capacity of offshore wind power flexible DC transmission systems continues to increase, the equivalent inertia of the receiving grid continues to decrease. When the system inertia level falls below a certain level, common disturbances (such as synchronous generator disconnection) can cause drastic fluctuations in the system frequency, resulting in serious consequences.

[0003] In related technologies, in order to increase the equivalent inertia of the offshore wind power flexible direct current transmission system and improve the stability of the receiving power grid, a DC capacitor inertia support strategy is usually adopted, which uses the charging and discharging of DC capacitors to absorb / release active power, thereby providing a certain amount of inertia support. However, in order to maintain system stability, the DC capacitor is not allowed to fluctuate too much, so the inertia support provided by this method is quite limited. In addition, there is also a remote communication strategy for converter stations aimed at frequency regulation of offshore wind power, but this strategy has many links, resulting in a large delay, and it cannot transmit information such as frequency changes in a timely manner, which is relatively backward. More importantly, these two methods only technically answer the question of "how to make the system have inertia support capabilities" and cannot clarify the specific mechanism of inertia formation. At the same time, they lack consideration of multi-device coupling systems such as offshore wind power flexible direct current transmission systems. Summary of the Invention

[0004] In view of this, the present invention discloses an equivalent inertia evaluation method and device for an offshore wind power flexible direct current transmission system, which can solve the deficiencies in the related art.

[0005] To achieve the above purpose, the present invention discloses the following technical solutions: According to a first aspect of the present invention, an equivalent inertia assessment method for an offshore wind power flexible direct current transmission system is proposed. The method is applied to the offshore wind power flexible direct current transmission system, wherein the offshore wind power flexible direct current transmission system includes an offshore wind farm and a flexible direct current transmission system, wherein the offshore wind farm includes a generator-side converter and a grid-side converter, and the flexible direct current transmission system includes a receiving-end converter and a sending-end converter. The method comprises: Establishing a small signal model of the flexible direct current transmission system according to the control topology of the flexible direct current transmission system; Establishing a small-signal model of a machine-side converter according to the control topology of the machine-side converter of the offshore wind farm, and establishing a small-signal model of an offshore wind farm according to the small-signal model of the machine-side converter and the control topology of the grid-side converter of the offshore wind farm; The response of the flexible direct current transmission system is analogized to the synchronous machine rotor motion equation, and the response of the offshore wind farm is analogized to the synchronous machine primary frequency modulation process. The system-like synchronization characteristics are characterized in the form of the synchronous machine rotor motion equation to establish a synchronous support model for the offshore wind power flexible direct current transmission system. The equivalent inertia transfer function of the offshore wind power flexible direct current transmission system is calculated based on the synchronous support model of the offshore wind power flexible direct current transmission system.

[0006] According to a second aspect of the present invention, an equivalent inertia evaluation device for an offshore wind power flexible direct current transmission system is proposed, the device comprising: The first construction unit: establishing a small signal model of the flexible DC transmission system according to the control topology of the flexible DC transmission system; The second construction unit: establishes a small signal model of the generator-side converter according to the control topology of the generator-side converter of the offshore wind farm, and establishes a small signal model of the offshore wind farm according to the small signal model of the generator-side converter and the control topology of the grid-side converter of the offshore wind farm; Analogy unit: The response of the flexible direct current transmission system is analogized to the synchronous machine rotor motion equation, and the response of the offshore wind farm is analogized to the synchronous machine primary frequency modulation process. The system-like synchronization characteristics are characterized in the form of the synchronous machine rotor motion equation to establish a synchronous support model for the offshore wind power flexible direct current transmission system. Calculation unit: Calculates the equivalent inertia transfer function of the offshore wind power flexible direct current transmission system according to the synchronous support model of the offshore wind power flexible direct current transmission system.

[0007] According to a third aspect of the present invention, an electronic device is provided, comprising: processor; a memory for storing processor-executable instructions; The processor implements the steps of the method described in the first aspect by running the executable instructions.

[0008] According to a fourth aspect of the present invention, 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.

[0009] It can be seen from the above technical solutions that the equivalent inertia evaluation method disclosed in the present invention: On the one hand, a small-signal model of the Flexible DC transmission system and a small-signal model of the offshore wind farm were established. Combining these models, a quasi-synchronous support model for the offshore wind power Flexible DC transmission system was established. The transmission mechanism and path of transient support power in the system were analyzed, and the quasi-synchronous characteristics of the system were explored. On the other hand, based on the quasi-synchronous support model for the offshore wind power Flexible DC transmission system, the inertia transfer functions of the Flexible DC transmission system and the offshore wind farm, as well as the transfer function of the equivalent inertia of the complete offshore wind power Flexible DC transmission system, were calculated. This accurately evaluated the equivalent inertia of the offshore wind power DC transmission system, providing important theoretical basis and technical support for optimizing the active support control effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is an architectural diagram of an offshore wind power flexible direct current transmission system provided by an exemplary embodiment; Figure 2 This is a flow chart of an equivalent inertia evaluation method for an offshore wind power flexible direct current transmission system provided by an exemplary embodiment; Figure 3 This is a schematic diagram of a grid-connected operation of an offshore wind power flexible direct current transmission system provided by an exemplary embodiment; Figure 4 This is a schematic diagram of a small signal model of a receiving-end converter of an offshore wind power DC transmission system provided by an exemplary embodiment; Figure 5 This is a schematic diagram of a small signal model of a machine-side converter of an offshore wind farm provided by an exemplary embodiment; Figure 6 is a schematic diagram of a small signal model of an offshore wind farm provided by an exemplary embodiment; Figure 7 This is a schematic diagram of a small signal model of an offshore wind power flexible direct current transmission system provided by an exemplary embodiment; Figure 8 This is a schematic diagram of a quasi-synchronous support model of an offshore wind power flexible direct current transmission system provided by an exemplary embodiment; Figure 9 is a schematic structural diagram of a device provided by an exemplary embodiment; Figure 10 It is a block diagram of an equivalent inertia evaluation device for an offshore wind power flexible direct current transmission system provided by an exemplary embodiment. DETAILED DESCRIPTION

[0011] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, like numbers in different figures represent like or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all possible implementations consistent with one or more embodiments of the present invention. Rather, they are merely examples of apparatuses and methods consistent with certain aspects of one or more embodiments of the present invention, as detailed in the appended claims.

[0012] It should be noted that in other embodiments, the steps of the corresponding method are not necessarily performed in the order shown and described in the present invention. In some other embodiments, the method may include more or fewer steps than those described in the present invention. In addition, a single step described in the present invention may be broken down into multiple steps for description in other embodiments, and multiple steps described in the present invention may be combined into a single step for description in other embodiments.

[0013] To further illustrate the present invention, the following examples are provided: With the increasing development of offshore resources, the development and utilization of offshore wind power resources has received increasing attention, and more and more wind farms are being relocated to deep and offshore areas. Flexible DC transmission technology offers advantages such as independent reactive power control, susceptibility to commutation failures, and the ability to achieve black starts, making it an optimal choice for offshore wind power transmission. The receiving-end converters of offshore wind power flexible DC transmission systems typically use phase-locked synchronization and are primarily designed for "grid following." They lack the ability to support the inertia of the receiving grid. As the transmission capacity of offshore wind power flexible DC transmission systems continues to increase, the equivalent inertia of the receiving grid continues to decrease. When the system inertia level falls below a certain level, common disturbances (such as synchronous generator disconnection) can cause drastic fluctuations in the system frequency, resulting in serious consequences.

[0014] In related technologies, in order to increase the equivalent inertia of the offshore wind power flexible direct current transmission system and improve the stability of the receiving power grid, a DC capacitor inertia support strategy is usually adopted, which uses the charging and discharging of DC capacitors to absorb / release active power, thereby providing a certain amount of inertia support. However, in order to maintain system stability, the DC capacitor is not allowed to fluctuate too much, so the inertia support provided by this method is quite limited. In addition, there is also a remote communication strategy for converter stations aimed at frequency regulation of offshore wind power, but this strategy has many links, resulting in a large delay, and it cannot transmit information such as frequency changes in a timely manner, which is relatively backward. More importantly, these two methods only technically answer the question of "how to make the system have inertia support capabilities" and cannot clarify the specific mechanism of inertia formation. At the same time, they lack consideration of multi-device coupling systems such as offshore wind power flexible direct current transmission systems.

[0015] In order to solve the deficiencies in the related art, the present invention proposes an equivalent inertia evaluation method for an offshore wind power flexible direct current transmission system.

[0016] Figure 1 This is an architectural diagram of an offshore wind power flexible direct current transmission system provided by an exemplary embodiment. Figure 1 As shown, the system includes: an offshore wind farm 10 and a flexible DC transmission system 20. The offshore wind farm 10 includes a generator-side converter 11 and a grid-side converter 12, and the flexible DC transmission system 20 includes a receiving-end converter 21 and a sending-end converter 22.

[0017] The receiving-end converter 21 uses constant DC voltage control to maintain a stable DC bus voltage. The sending-end converter 22 uses constant amplitude and frequency control to control the frequency and AC voltage of the offshore AC grid, enabling voltage tracking in the offshore wind farm. Similar to the receiving-end converter 21, the grid-side converter 12 uses constant DC voltage control. The generator-side converter 11 uses speed control to control the output active power.

[0018] Figure 2 This is a flowchart of an equivalent inertia evaluation method for an offshore wind power flexible direct current transmission system provided by an exemplary embodiment. Figure 2 As shown, the method may include the following steps: Step 201: establishing a small signal model of the flexible direct current transmission system according to the control topology of the flexible direct current transmission system; Step 202: establishing a small-signal model of a generator-side converter according to the control topology of the generator-side converter of the offshore wind farm, and establishing a small-signal model of the offshore wind farm according to the small-signal model of the generator-side converter and the control topology of the grid-side converter of the offshore wind farm; Step 203: Analogize the response of the flexible direct current transmission system to the synchronous machine rotor motion equation, and analogize the response of the offshore wind farm to the synchronous machine primary frequency modulation process, and characterize the system-like synchronization characteristics in the form of the synchronous machine rotor motion equation to establish a synchronous support model for the offshore wind power flexible direct current transmission system; Step 204: Calculate the equivalent inertia transfer function of the offshore wind power flexible direct current transmission system according to the offshore wind power flexible direct current transmission system-like synchronous support model.

[0019] In this embodiment, a small-signal model of the Flexible DC transmission system and a small-signal model of the offshore wind farm were established. Combining these models, a quasi-synchronous support model for the offshore wind power Flexible DC transmission system was established. The transmission mechanism and path of transient support power within the system were analyzed, and the quasi-synchronous characteristics of the system were explored. Furthermore, based on the quasi-synchronous support model for the offshore wind power Flexible DC transmission system, the partial inertia transfer functions of the Flexible DC transmission system and the offshore wind farm, as well as the transfer function of the equivalent inertia of the complete offshore wind power Flexible DC transmission system, were calculated. This accurately assessed the equivalent inertia of the offshore wind power DC transmission system, providing important theoretical basis and technical support for optimizing active support control.

[0020] In one embodiment, if Figure 3 As shown, the small signal model of the flexible DC transmission system includes: a DC voltage control link with additional inertia control, a phase-locked loop link, a terminal voltage small signal expression, an internal potential amplitude and power control angle small signal expression, and an active power small signal expression at the internal potential.

[0021] The DC voltage dynamic process, DC voltage control link, and receiving-end converter additional inertia control link are linearized as follows: ; in, s is the Laplace operator, Δ represents the small signal value of the variable, and the subscript 0 represents the steady-state value of the variable. P m is the input power of the receiving converter, P e is the output power of the receiving converter, C is the DC capacitance, U dc is the DC line voltage, k p_dc 、 k i_dc are the proportional and integral coefficients of the DC voltage PI regulator respectively, U dcref is the DC line reference voltage, i dref is the reference value of the d-axis component of the output current of the receiving converter, U dc * is the actual reference voltage of the DC line, f 1 is the receiving-end grid frequency measured by the receiving-end converter phase-locked loop, f ref is the rated frequency of the receiving power grid, K 1 is the droop coefficient of the receiving-end converter.

[0022] After merging, the DC voltage control link of the additional inertia control is: ; The phase-locked loop link is: ; The terminal voltage small signal expression is: ; The internal potential amplitude and power control angle small signal expressions are: ; The small signal expression of active power at the internal potential is: ; in, s is the Laplace operator, Δ represents the small signal value of the variable, and the subscript 0 represents the steady-state value of the variable. k p_dc 、 k i_dc are the proportional and integral coefficients of the DC voltage PI regulator respectively, P m is the input power of the receiving converter, P e is the output power of the receiving converter, C is the DC capacitance, U dc is the DC line voltage, K 1 is the droop coefficient of the receiving-end converter, k p_pll is the phase-locked loop proportional coefficient, k i_pll is the phase-locked loop integral coefficient, U t is the terminal voltage, U td is the d-axis component of the terminal voltage in the phase-locked coordinate system, U tq is the q-axis component of the terminal voltage in the phase-locked coordinate system, θ t is the terminal voltage phase, θ pll Measure the reference phase for the phase-locked loop, E is the internal potential, E d is the d-axis component in the internal potential phase-locked coordinate system, E q is the q-axis component in the phase-locked coordinate system, X f is the filter reactance, I d is the d-axis component of the output current of the receiving converter, I q is the q-axis component of the output current of the receiving-end converter, θ ctrl is the power control angle of the internal potential in the phase-locked loop coordinate system, θ t is the terminal voltage phase, θ E is the internal potential phase, P e Output active power to the receiving converter.

[0023] In one embodiment, if Figure 4 As shown, Figure 4 This is a schematic diagram of the small signal model of the receiving-end converter of the offshore wind power DC transmission system. Considering that the transient response of the grid-side converter of the offshore wind farm is similar to that of the receiving-end converter under conventional control, for the offshore wind farm, only the small signal model of the generator-side converter needs to be additionally analyzed.

[0024] Considering the control characteristics of the generator-side converter, a small-signal model of the generator-side converter is established, including: speed control link, virtual inertia control, small-signal expression of the permanent magnet direct-drive wind turbine output power, and the direct-drive wind turbine rotor motion equation; The speed control link is: ; The virtual inertia control is: ; The output power small signal expression of the permanent magnet direct drive fan is: ; The direct-drive fan rotor motion equation is: ; in, s is the Laplace operator, Δ represents the small signal value of the variable, and the subscript 0 represents the steady-state value of the variable. i qref is the reference value of the current q-axis component, k p_ω is the proportional coefficient of the speed controller, k i_ω is the integral coefficient of the speed controller, ω rer is the actual reference rotor speed of the direct-drive wind turbine, ω rref is the reference speed of the direct drive fan, K 3 is the virtual inertia control coefficient, T f is the low-pass filter time constant, θ pll Measure the reference phase for the phase-locked loop, P w is the output power of the direct drive fan, ω r is the rotor speed, Ψ f is the rotor flux, i sq is the q-axis component of the stator phase current, P in Input power for direct drive wind turbine, J is the moment of inertia of the direct-drive fan.

[0025] Taking into account the speed control link, virtual inertia control, small signal expression of permanent magnet direct-drive wind turbine output power, and direct-drive wind turbine rotor motion equation, the small signal model of the offshore wind farm machine-side converter can be obtained as follows: Figure 5 shown.

[0026] Furthermore, the method further includes: simplifying the small signal model of the generator-side converter to: ; Where K(s) is expressed as: ; ; in, k p_ω is the proportional coefficient of the speed controller, k i_ω is the integral coefficient of the speed controller.

[0027] In one embodiment, considering that the transient response of the grid-side converter of an offshore wind farm is similar to that of the receiving-end converter under conventional control, a small signal model of the offshore wind farm can be obtained by referring to the small signal model of the flexible DC transmission system and combining the small signal model of the generator-side converter with the control topology of the grid-side converter of the offshore wind farm, as shown in FIG. Figure 6 shown.

[0028] By simplifying the small signal model of the offshore wind farm, the small signal model of the offshore wind farm can be obtained as follows: ; ; Where s is the Laplace operator, Δ represents the small signal value of the variable, the subscript 0 represents the steady-state value of the variable, and P e_OWF Output power to the grid-side converter of the offshore wind farm.

[0029] In one embodiment, based on the flexible direct current transmission system small signal model and the offshore wind farm small signal model, an offshore wind power flexible direct current transmission system type synchronous support model is established to characterize the system type synchronous characteristics. Figure 3In the offshore wind power flexible direct current transmission system, the AC / DC power at the sending end is equal, the DC capacitor at the sending end is merged into the receiving end, and the sending end converter has almost no effect on the inertia response of the system, so the sending end converter modeling is not considered. Figure 3 The grid-connected operation diagram of the offshore wind power flexible direct current transmission system shown in the figure shows that when K1=1 / K2, the frequencies at both ends can be considered to be consistent on the electromechanical time scale, that is, f1=f2. Therefore, the transient process of the offshore wind power direct current transmission system under the condition of frequency disturbance of the receiving end grid can be described as follows: When a frequency disturbance occurs in the receiving-end power grid, the receiving-end converter will first change its DC voltage control reference value. Therefore, the capacitor of the receiving-end converter submodule will release or absorb a certain amount of energy to damp the change of the grid frequency. From the perspective of electromechanical time scale, the receiving-end frequency f1 and the sending-end frequency f2 change almost simultaneously. Under the virtual inertia control of the wind turbine, the wind turbine will change the speed control reference value to increase or decrease its output active power P. e_OWF .

[0030] Combining the small signal model of the flexible direct current transmission system and the small signal model of the offshore wind farm, the small signal model of the offshore wind power flexible direct current transmission system is obtained, as shown in Figure 7 As shown. Considering that the response of the flexible DC transmission system is analogous to the synchronous machine rotor motion equation, and the response of the offshore wind farm is analogous to the synchronous machine primary frequency regulation process, the synchronous support model of the offshore wind power flexible DC transmission system is obtained, as shown in Figure 8 As shown, the deviation of the output active power is: ; The small signal expression of the internal potential phase in the frequency modulation process is: ; The synchronous characteristics of the system are described in the form of synchronous machine rotor motion equations, and the synchronous support model of the offshore wind power flexible direct current transmission system is established as follows: ; The expressions are: ; .

[0031] In one embodiment, the calculation of the equivalent inertia transfer function of the offshore wind power flexible direct current transmission system based on the offshore wind power flexible direct current transmission system-like synchronous support model includes: according to the offshore wind power flexible direct current transmission system-like synchronous support model, respectively calculating the partial inertia transfer functions of the flexible direct current transmission system and the offshore wind farm and the transfer function of the equivalent inertia of the complete offshore wind power flexible direct current transmission system.

[0032] Specifically, ignoring the damping coefficient, the synchronous machine rotor motion equation is expressed as: ; By analogy with the synchronous machine rotor motion equation, according to the synchronous support model of the offshore wind power flexible direct current transmission system, the partial inertia transfer functions of the flexible direct current transmission system and the offshore wind farm and the transfer function of the equivalent inertia of the complete offshore wind power flexible direct current transmission system are calculated as follows: ; Among them, J HVDC (s) is the inertia transfer function of the flexible DC transmission system, J OWF (s) is the inertia transfer function of the offshore wind farm, J total (s) is the equivalent inertia transfer function of the complete offshore wind power flexible direct current transmission system, K OWF (s) is the potential phase θ in the offshore wind farm E_OWF Phase locked with reference phase θ pll The relationship between them is: .

[0033] Figure 9 This is a schematic structural diagram of a device provided by an exemplary embodiment. Figure 9 At the hardware level, the device includes a processor 902, an internal bus 904, a network interface 906, a memory 908, and a non-volatile memory 910. Of course, it may also include hardware required for other functions. One or more embodiments of the present invention can be implemented based on software, such as the processor 902 reading the corresponding computer program from the non-volatile memory 910 into the memory 908 and then running it. Of course, in addition to software implementation, one or more embodiments of the present invention do not exclude other implementation methods, such as logic devices or a combination of software and hardware, etc., that is, the execution subject of the following processing flow is not limited to each logic unit, but can also be hardware or logic devices.

[0034] Please refer to Figure 10 , an equivalent inertia evaluation device for offshore wind power flexible direct current transmission system can be applied to Figure 10 In the device shown, to implement the technical solution of the present invention, the device includes: The first building unit 1001 is configured to establish a small signal model of the flexible direct current transmission system according to the control topology of the flexible direct current transmission system; A second construction unit 1002 is configured to establish a small-signal model of a generator-side converter according to a control topology of the generator-side converter of the offshore wind farm, and to establish a small-signal model of the offshore wind farm according to the small-signal model of the generator-side converter and the control topology of the grid-side converter of the offshore wind farm; The analogy unit 1003 is used to analogize the response of the flexible direct current transmission system to the synchronous machine rotor motion equation, and the response of the offshore wind farm to the synchronous machine primary frequency modulation process, and to characterize the system-like synchronization characteristics in the form of the synchronous machine rotor motion equation, so as to establish a synchronous support model for the offshore wind power flexible direct current transmission system; The calculation unit 1004 is used to calculate the equivalent inertia transfer function of the offshore wind power flexible direct current transmission system according to the synchronous support model of the offshore wind power flexible direct current transmission system.

[0035] Optionally, the small signal model of the flexible DC transmission system includes: a DC voltage control link with additional inertia control, a phase-locked loop link, a terminal voltage small signal expression, an internal potential amplitude and power control angle small signal expression, and an active power small signal expression at the internal potential; The DC voltage control link of the additional inertia control is: ; The phase-locked loop link is: ; The terminal voltage small signal expression is: ; The internal potential amplitude and power control angle small signal expressions are: ; The small signal expression of active power at the internal potential is: ; in, s is the Laplace operator, Δ represents the small signal value of the variable, and the subscript 0 represents the steady-state value of the variable. k p_dc 、 k i_dc are the proportional and integral coefficients of the DC voltage PI regulator respectively, P m is the input power of the receiving converter, P e is the output power of the receiving converter, C is the DC capacitance, U dc is the DC line voltage, K 1 is the droop coefficient of the receiving-end converter, k p_pll is the phase-locked loop proportional coefficient, k i_pll is the phase-locked loop integral coefficient, U t is the terminal voltage, U td is the d-axis component of the terminal voltage in the phase-locked coordinate system, Utq is the q-axis component of the terminal voltage in the phase-locked coordinate system, θ t is the terminal voltage phase, θ pll Measure the reference phase for the phase-locked loop, E is the internal potential, E d is the d-axis component in the internal potential phase-locked coordinate system, E q is the q-axis component in the phase-locked coordinate system, X f is the filter reactance, I d is the d-axis component of the output current of the receiving converter, I q is the q-axis component of the output current of the receiving-end converter, θ ctrl is the power control angle of the internal potential in the phase-locked loop coordinate system, θ t is the terminal voltage phase, θ E is the internal potential phase, P e Output active power to the receiving converter.

[0036] Optionally, the small signal model of the machine-side converter includes: a speed control link, a virtual inertia control, a small signal expression of the output power of the permanent magnet direct-drive wind turbine, and a direct-drive wind turbine rotor motion equation; The speed control link is: ; The virtual inertia control is: ; The output power small signal expression of the permanent magnet direct drive fan is: ; The direct-drive fan rotor motion equation is: ; in, s is the Laplace operator, Δ represents the small signal value of the variable, and the subscript 0 represents the steady-state value of the variable. i qref is the reference value of the current q-axis component, k p_ω is the proportional coefficient of the speed controller, k i_ω is the integral coefficient of the speed controller, ω rer is the actual reference rotor speed of the direct-drive wind turbine, ω rrefis the reference speed of the direct drive fan, K 3 is the virtual inertia control coefficient, T f is the low-pass filter time constant, θ pll Measure the reference phase for the phase-locked loop, P w is the output power of the direct drive fan, ω r is the rotor speed, Ψ f is the rotor flux, i sq is the q-axis component of the stator phase current, P in Input power for direct drive wind turbine, J is the moment of inertia of the direct-drive fan.

[0037] Optionally, the device further includes: The simplification unit 1005 is configured to simplify the generator-side converter small signal model to: ; Where K(s) is expressed as: ; ; in, k p_ω is the proportional coefficient of the speed controller, k i_ω is the integral coefficient of the speed controller.

[0038] Optionally, the offshore wind farm small signal model is: ; ; Where s is the Laplace operator, Δ represents the small signal value of the variable, the subscript 0 represents the steady-state value of the variable, and P e_OWF Output power to the grid-side converter of the offshore wind farm.

[0039] Optional, The deviation of the active power output during the frequency modulation process is: ; The small signal expression of the internal potential phase in the frequency modulation process is: ; The synchronous support model of the offshore wind power flexible direct current transmission system is: ; The expressions are: ; .

[0040] Optionally, the calculation unit 1004 is specifically configured to: According to the synchronous support model of the offshore wind power flexible direct current transmission system, the inertia transfer functions of the flexible direct current transmission system and the offshore wind farm and the transfer function of the equivalent inertia of the complete offshore wind power flexible direct current transmission system are calculated respectively as follows: ; Among them, J HVDC (s) is the inertia transfer function of the flexible DC transmission system, J OWF (s) is the inertia transfer function of the offshore wind farm, J total (s) is the equivalent inertia transfer function of the complete offshore wind power flexible direct current transmission system, K OWF (s) is the potential phase θ in the offshore wind farm E_OWF Phase locked with reference phase θ pll The relationship between them is: .

[0041] The systems, devices, modules, or units described in the above embodiments may be implemented by computer chips or entities, or by products having certain functions. A typical implementation device is a computer, which may be in the form of a personal computer, laptop computer, cellular phone, camera phone, smartphone, personal digital assistant, media player, navigation device, email transceiver, game console, tablet computer, wearable device, or any combination of these devices.

[0042] In a typical configuration, a computer includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0043] Memory may include non-permanent storage in a computer-readable medium, in the form of random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of a computer-readable medium.

[0044] Computer-readable media include permanent and non-permanent, removable and non-removable media that can be implemented by any method or technology to store information. Information can be computer-readable instructions, data structures, program modules, or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical storage, magnetic cassettes, magnetic disk storage, quantum memory, graphene-based storage media or other magnetic storage devices, or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined herein, computer-readable media does not include transitory computer-readable media such as modulated data signals and carrier waves.

[0045] For the computer-readable medium (or computer-readable storage medium) as described above or in any other form, computer instructions may be stored thereon, which, when executed by a processor, implement one or more of the above-mentioned embodiments, thereby realizing the technical solution of the present invention.

[0046] The present invention further provides a computer program that, when executed by a processor, implements one or more of the aforementioned embodiments, thereby realizing the technical solution of the present invention. The computer program may be recorded on the aforementioned or any other form of computer-readable medium, and the present invention is not limited thereto.

[0047] It should also be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, commodity, or apparatus that includes a series of elements includes not only those elements but also other elements not explicitly listed, or includes elements inherent to such process, method, commodity, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of other identical elements in the process, method, commodity, or apparatus that includes the element.

[0048] The foregoing description describes specific embodiments of the present invention. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims can be performed in an order different from that described in the embodiments and still achieve the desired results. Furthermore, the processes depicted in the accompanying drawings do not necessarily require the specific order shown or the sequential order to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0049] The terms used in one or more embodiments of the present invention are for the purpose of describing specific embodiments only and are not intended to limit one or more embodiments of the present invention. The singular forms "a", "an", "the" and "the" used in one or more embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0050] It should be understood that although the terms first, second, third, etc. may be used to describe various information in one or more embodiments of the present invention, 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 one or more embodiments of the present invention, 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."

[0051] The above description is merely a preferred embodiment of one or more embodiments of the present invention and is not intended to limit one or more embodiments of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of the present invention shall be included in the scope of protection of one or more embodiments of the present invention.

Claims

1. A method for evaluating the equivalent inertia of an offshore wind power flexible direct current transmission system, characterized in that: The method is applied to an offshore wind power flexible direct current transmission system, the offshore wind power flexible direct current transmission system including an offshore wind farm and a flexible direct current transmission system, the offshore wind farm including a machine-side converter and a grid-side converter, and the flexible direct current transmission system including a receiving-end converter and a sending-end converter; the method includes: Establishing a small signal model of the flexible direct current transmission system according to the control topology of the flexible direct current transmission system; Establishing a small-signal model of a machine-side converter according to the control topology of the machine-side converter of the offshore wind farm, and establishing a small-signal model of an offshore wind farm according to the small-signal model of the machine-side converter and the control topology of the grid-side converter of the offshore wind farm; The response of the flexible direct current transmission system is analogized to the synchronous machine rotor motion equation, and the response of the offshore wind farm is analogized to the synchronous machine primary frequency modulation process. The system-like synchronization characteristics are characterized in the form of the synchronous machine rotor motion equation to establish a synchronous support model for the offshore wind power flexible direct current transmission system. The equivalent inertia transfer function of the offshore wind power flexible direct current transmission system is calculated based on the synchronous support model of the offshore wind power flexible direct current transmission system.

2. The method according to claim 1, characterized in that The small signal model of the flexible DC transmission system includes: a DC voltage control link with additional inertia control, a phase-locked loop link, a terminal voltage small signal expression, an internal potential amplitude and power control angle small signal expression, and an active power small signal expression at the internal potential; The DC voltage control link of the additional inertia control is: ； The phase-locked loop link is: ； The terminal voltage small signal expression is: ； The internal potential amplitude and power control angle small signal expressions are: ； The small signal expression of active power at the internal potential is: ； in, s is the Laplace operator, Δ represents the small signal value of the variable, and the subscript 0 represents the steady-state value of the variable. k p_dc 、 k i_dc are the proportional and integral coefficients of the DC voltage PI regulator respectively, P m is the input power of the receiving converter, P e is the output power of the receiving converter, C is the DC capacitance, U dc is the DC line voltage, K 1 is the droop coefficient of the receiving-end converter, k p_pll is the phase-locked loop proportional coefficient, k i_pll is the phase-locked loop integral coefficient, U t is the terminal voltage, U td is the d-axis component of the terminal voltage in the phase-locked coordinate system, U tq is the q-axis component of the terminal voltage in the phase-locked coordinate system, θ t is the terminal voltage phase, θ pll Measure the reference phase for the phase-locked loop, E is the internal potential, E d is the d-axis component in the internal potential phase-locked coordinate system, E q is the q-axis component in the phase-locked coordinate system, X f is the filter reactance, I d is the d-axis component of the output current of the receiving converter, I q is the q-axis component of the output current of the receiving converter, θ ctrl is the power control angle of the internal potential in the phase-locked loop coordinate system, θ t is the terminal voltage phase, θ E is the internal potential phase, P e Output active power to the receiving end converter.

3. The method according to claim 1, characterized in that The small signal model of the machine-side converter includes: a speed control link, a virtual inertia control, a small signal expression of the output power of the permanent magnet direct-drive wind turbine, and a direct-drive wind turbine rotor motion equation; The speed control link is: ； The virtual inertia control is: ； The output power small signal expression of the permanent magnet direct drive fan is: ； The direct-drive fan rotor motion equation is: ； in, s is the Laplace operator, Δ represents the small signal value of the variable, and the subscript 0 represents the steady-state value of the variable. i qref is the reference value of the current q-axis component, k p_ω is the proportional coefficient of the speed controller, k i_ω is the integral coefficient of the speed controller, ω rer is the actual reference rotor speed of the direct-drive wind turbine, ω rref is the reference speed of the direct drive fan, K 3 is the virtual inertia control coefficient, T f is the low-pass filter time constant, θ pll Measure the reference phase for the phase-locked loop, P w is the output power of the direct drive fan, ω r is the rotor speed, Ψ f is the rotor flux, i sq is the q-axis component of the stator phase current, P in Input power for direct drive wind turbine, J is the moment of inertia of the direct-drive fan.

4. The method according to claim 3, characterized in that The method further comprises: The small signal model of the generator-side converter is simplified as follows: ； Where K(s) is expressed as: ； ； in, k p_ω is the proportional coefficient of the speed controller, k i_ω is the integral coefficient of the speed controller.

5. The method according to claim 4, characterized in that The small signal model of the offshore wind farm is: ； ； Where s is the Laplace operator, Δ represents the small signal value of the variable, the subscript 0 represents the steady-state value of the variable, and P e_OWF Output power to the grid-side converter of the offshore wind farm.

6. The method according to claim 5, characterized in that The deviation of the active power output during the frequency modulation process is: ； The small signal expression of the internal potential phase in the frequency modulation process is: ； The synchronous support model of the offshore wind power flexible direct current transmission system is: ； The expressions are: ； 。 7. The method according to claim 6, characterized in that The calculating the equivalent inertia transfer function of the offshore wind power flexible direct current transmission system according to the offshore wind power flexible direct current transmission system synchronous support model includes: According to the synchronous support model of the offshore wind power flexible direct current transmission system, the inertia transfer functions of the flexible direct current transmission system and the offshore wind farm and the transfer function of the equivalent inertia of the complete offshore wind power flexible direct current transmission system are calculated respectively as follows: ； Among them, J HVDC (s) is the inertia transfer function of the flexible DC transmission system, J OWF (s) is the inertia transfer function of the offshore wind farm, J total (s) is the equivalent inertia transfer function of the complete offshore wind power flexible direct current transmission system, K OWF (s) is the potential phase θ in the offshore wind farm E_OWF Phase locked with reference phase θ pll The relationship between them is: 。 8. An equivalent inertia evaluation device for an offshore wind power flexible direct current transmission system, characterized in that: The device comprises: The first construction unit: establishing a small signal model of the flexible DC transmission system according to the control topology of the flexible DC transmission system; The second construction unit: establishes a small signal model of the generator-side converter according to the control topology of the generator-side converter of the offshore wind farm, and establishes a small signal model of the offshore wind farm according to the small signal model of the generator-side converter and the control topology of the grid-side converter of the offshore wind farm; Analogy unit: The receiving-end converter of the flexible direct current transmission system is analogized to the synchronous machine rotor motion equation, and the offshore wind farm response is analogized to the synchronous machine primary frequency modulation process. The system's quasi-synchronous characteristics are characterized in the form of the synchronous machine rotor motion equation to establish a quasi-synchronous support model for the offshore wind power flexible direct current transmission system. Calculation unit: Calculates the equivalent inertia transfer function of the offshore wind power flexible direct current transmission system according to the synchronous support model of the offshore wind power flexible direct current transmission system.

9. An electronic device, characterized in that: include: processor; a memory for storing processor-executable instructions; The processor implements the steps of the method according to any one of claims 1 to 7 by running the executable instructions.

10. 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 7 are implemented.

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