A method and apparatus for evaluating the equivalent inertia of an offshore wind power flexible direct transmission system.

Abstract

This invention belongs to the field of power and discloses a method and apparatus for evaluating the equivalent inertia of an offshore wind power flexible DC transmission system. The method includes: establishing a small-signal model of the flexible DC transmission system based on its control topology; establishing a small-signal model of the generator-side converter based on its control topology, and establishing a small-signal model of the offshore wind farm based on the generator-side converter's small-signal model and the grid-side converter's control topology; analogizing the response of the flexible DC transmission system to the rotor motion equation of a synchronous machine and the response of the offshore wind farm to the primary frequency regulation process of a synchronous machine, and characterizing the system's quasi-synchronous characteristics in the form of the rotor motion equation of a synchronous machine to establish a quasi-synchronous support model for the offshore wind power flexible DC transmission system; and calculating the equivalent inertia transfer function of the offshore wind power flexible DC transmission system based on the quasi-synchronous support model.

Description

Technical Field

[0001] This invention belongs to the field of power, and in particular relates to a method and apparatus for evaluating the equivalent inertia of an offshore wind power flexible direct transmission system. Background Technology

[0002] With the increasing sophistication of near-shore resource development, the development and utilization of offshore wind power resources are receiving more and more attention, and more and more wind farms are shifting to deep-sea and offshore areas. Flexible DC transmission technology has advantages such as independent reactive power control, low commutation failure rate, and the ability to achieve black start, making it the best choice for offshore wind power transmission. The receiving-end converters of offshore wind power flexible DC transmission systems typically adopt phase-locked synchronization and are primarily positioned as "grid followers," lacking the ability to support the inertia of the receiving-end grid. As the transmission capacity of offshore wind power flexible DC transmission systems continues to increase, the equivalent inertia of the receiving-end grid also continuously decreases. When the system's inertia level falls below a certain level, some common disturbances (such as synchronous generator disconnection) can cause severe fluctuations in system frequency, leading to serious consequences.

[0003] In related technologies, to improve the equivalent inertia of offshore wind power flexible DC transmission systems and enhance the stability of the receiving-end grid, a DC capacitor inertial support strategy is typically adopted. This strategy utilizes the charging and discharging of DC capacitors to absorb / release active power, thereby providing a certain amount of inertial support. However, to maintain system stability, the DC capacitor cannot experience excessive fluctuations, thus the inertial support provided by this method is quite limited. Furthermore, there is a converter station remote communication strategy aimed at frequency regulation of offshore wind power, but this strategy involves many components, resulting in significant delays and an inability to promptly transmit information such as frequency changes, making it relatively outdated. More importantly, these two methods only technically answer the question of "how to enable the system to have inertial support capabilities," failing to clarify the specific mechanism of inertia formation and lacking consideration for multi-device coupled systems like offshore wind power flexible DC transmission systems. Summary of the Invention

[0004] In view of this, the present invention discloses an equivalent inertia assessment method and apparatus for offshore wind power flexible direct transmission systems, which can solve the shortcomings of related technologies.

[0005] To achieve the above objectives, the present invention discloses the following technical solution:

[0006] According to a first aspect of the present invention, an equivalent inertia assessment method for an offshore wind power flexible DC transmission system is proposed, applicable to such a system. The offshore wind power flexible DC transmission system includes an offshore wind farm and a flexible DC transmission system. The offshore wind farm includes a turbine-side converter and a grid-side converter, and the flexible DC transmission system includes a receiving-end converter and a sending-end converter. The method includes:

[0007] A small-signal model of the flexible DC transmission system is established based on the control topology of the flexible DC transmission system.

[0008] A small-signal model of the generator-side converter is established based on the control topology of the generator-side converter of the offshore wind farm, and a small-signal model of the offshore wind farm is established based on the small-signal model of the generator-side converter and the control topology of the grid-side converter of the offshore wind farm.

[0009] The response of the flexible DC transmission system is analogous to the rotor motion equation of a synchronous machine, and the response of the offshore wind farm is analogous to the primary frequency regulation process of a synchronous machine. The system's quasi-synchronous characteristics are characterized in the form of the rotor motion equation of the synchronous machine, so as to establish a quasi-synchronous support model for the offshore wind power flexible DC transmission system.

[0010] The equivalent inertia transfer function of the offshore wind power flexible direct transmission system is calculated based on the synchronous support model of the offshore wind power flexible direct transmission system.

[0011] According to a second aspect of the present invention, an equivalent inertia assessment device for an offshore wind power flexible direct transmission system is provided, the device comprising:

[0012] First building block: Establish a small-signal model of the flexible DC transmission system based on the control topology of the flexible DC transmission system;

[0013] The second building unit: Based on the control topology of the generator-side converter of the offshore wind farm, a small-signal model of the generator-side converter is established, and based on the small-signal model of the generator-side converter and the control topology of the grid-side converter of the offshore wind farm, a small-signal model of the offshore wind farm is established.

[0014] Analogy Unit: The response of the flexible DC transmission system is analogous to the rotor motion equation of a synchronous machine, and the response of the offshore wind farm is analogous to the primary frequency regulation process of a synchronous machine. The system's quasi-synchronous characteristics are characterized in the form of the rotor motion equation of the synchronous machine, so as to establish a quasi-synchronous support model for the offshore wind power flexible DC transmission system.

[0015] Calculation Unit: Calculates the equivalent inertia transfer function of the offshore wind power flexible direct transmission system based on the synchronous support model of the offshore wind power flexible direct transmission system.

[0016] According to a third aspect of the present invention, an electronic device is provided, comprising:

[0017] processor;

[0018] a memory for storing processor-executable instructions;

[0019] The processor implements the steps of the method as described in the first aspect by running the executable instructions.

[0020] According to a fourth aspect of the invention, a computer-readable storage medium is provided having computer instructions stored thereon that, when executed by a processor, implement the steps of the method as described in the first aspect.

[0021] As can be seen from the above technical solutions, the equivalent inertia evaluation method disclosed in this invention is as follows:

[0022] On the one hand, small-signal models of the flexible DC transmission system and the offshore wind farm were established respectively. Combining these models, a near-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 near-synchronous characteristics of the system were explored. On the other hand, based on the near-synchronous support model of the offshore wind power flexible DC transmission system, the transfer functions of the partial inertia 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 respectively. 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. Attached Figure Description

[0023] Figure 1 This is an exemplary embodiment of an architecture diagram of an offshore wind power flexible direct transmission system;

[0024] Figure 2 This is a flowchart of an exemplary embodiment of a method for evaluating the equivalent inertia of an offshore wind power flexible direct transmission system;

[0025] Figure 3 This is a schematic diagram of the grid-connected operation of an offshore wind power flexible DC transmission system provided in an exemplary embodiment;

[0026] 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 in an exemplary embodiment;

[0027] Figure 5 This is a schematic diagram of a small-signal model of a turbine-side converter in an offshore wind farm, provided as an exemplary embodiment.

[0028] Figure 6 This is a schematic diagram of a small-signal model of an offshore wind farm provided in an exemplary embodiment;

[0029] Figure 7 This is a schematic diagram of a small-signal model of an offshore wind power flexible direct transmission system provided in an exemplary embodiment;

[0030] Figure 8 This is a schematic diagram of a near-synchronous support model of an offshore wind power flexible direct transmission system provided in an exemplary embodiment;

[0031] Figure 9This is a schematic structural diagram of a device provided in an exemplary embodiment;

[0032] Figure 10 This is a block diagram of an equivalent inertia assessment device for an offshore wind power flexible direct transmission system, provided in an exemplary embodiment. Detailed Implementation

[0033] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with one or more embodiments of the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of one or more embodiments of the present invention as detailed in the appended claims.

[0034] It should be noted that the steps of the corresponding methods in other embodiments are not necessarily performed in the order shown and described in this invention. In some other embodiments, the methods may include more or fewer steps than those described in this invention. Furthermore, a single step described in this invention may be broken down into multiple steps in other embodiments; and multiple steps described in this invention may be combined into a single step in other embodiments.

[0035] To further illustrate the present invention, the following embodiments are provided:

[0036] With the increasing sophistication of near-shore resource development, the development and utilization of offshore wind power resources are receiving more and more attention, and more and more wind farms are shifting to deep-sea and offshore areas. Flexible DC transmission technology has advantages such as independent reactive power control, low commutation failure rate, and the ability to achieve black start, making it the best choice for offshore wind power transmission. The receiving-end converters of offshore wind power flexible DC transmission systems typically adopt phase-locked synchronization and are primarily positioned as "grid followers," lacking the ability to support the inertia of the receiving-end grid. As the transmission capacity of offshore wind power flexible DC transmission systems continues to increase, the equivalent inertia of the receiving-end grid also continuously decreases. When the system's inertia level falls below a certain level, some common disturbances (such as synchronous generator disconnection) can cause severe fluctuations in system frequency, leading to serious consequences.

[0037] In related technologies, to improve the equivalent inertia of offshore wind power flexible DC transmission systems and enhance the stability of the receiving-end grid, a DC capacitor inertial support strategy is typically adopted. This strategy utilizes the charging and discharging of DC capacitors to absorb / release active power, thereby providing a certain amount of inertial support. However, to maintain system stability, the DC capacitor cannot experience excessive fluctuations, thus the inertial support provided by this method is quite limited. Furthermore, there is a converter station remote communication strategy aimed at frequency regulation of offshore wind power, but this strategy involves many components, resulting in significant delays and an inability to promptly transmit information such as frequency changes, making it relatively outdated. More importantly, these two methods only technically answer the question of "how to enable the system to have inertial support capabilities," failing to clarify the specific mechanism of inertia formation and lacking consideration for multi-device coupled systems like offshore wind power flexible DC transmission systems.

[0038] To address the shortcomings in related technologies, this invention proposes an equivalent inertia assessment method for offshore wind power flexible direct transmission systems.

[0039] Figure 1 This is an exemplary embodiment of an offshore wind power flexible direct transmission system architecture diagram. (See diagram below.) 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 turbine-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.

[0040] 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 frequency control to control the frequency and AC voltage of the offshore AC grid so that the offshore wind farm can achieve voltage following. The grid-side converter 12 is similar to the receiving-end converter 21 and uses constant DC voltage control; the generator-side converter 11 uses speed control to control the output active power.

[0041] Figure 2 This is a flowchart illustrating an exemplary embodiment of a method for evaluating the equivalent inertia of an offshore wind power flexible direct transmission system. For example... Figure 2 As shown, the method may include the following steps:

[0042] Step 201: Establish a small-signal model of the flexible DC transmission system based on the control topology of the flexible DC transmission system;

[0043] Step 202: Establish a small-signal model of the generator-side converter based on the control topology of the generator-side converter of the offshore wind farm, and establish a small-signal model of the offshore wind farm based on the small-signal model of the generator-side converter and the control topology of the grid-side converter of the offshore wind farm.

[0044] Step 203: The response of the flexible DC transmission system is compared with the rotor motion equation of a synchronous machine, and the response of the offshore wind farm is compared with the primary frequency regulation process of a synchronous machine. The synchronous characteristics of the system are characterized in the form of the rotor motion equation of the synchronous machine, so as to establish a synchronous support model for the offshore wind power flexible DC transmission system.

[0045] Step 204: Calculate the equivalent inertia transfer function of the offshore wind power flexible direct transmission system based on the synchronous support model of the offshore wind power flexible direct transmission system.

[0046] In this embodiment, on the one hand, small-signal models of the flexible DC transmission system and the offshore wind farm were established respectively. Combining these models, a near-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 near-synchronous characteristics of the system were explored. On the other hand, based on the near-synchronous support model of the offshore wind power flexible DC transmission system, the transfer functions of the partial inertia 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 respectively. 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.

[0047] In one embodiment, such as Figure 3 As shown, the small-signal model of the flexible DC transmission system includes: a DC voltage control loop with additional inertia control, a phase-locked loop, a small-signal expression for the terminal voltage, a small-signal expression for the internal potential amplitude and power control angle, and a small-signal expression for the active power at the internal potential.

[0048] Linearizing the DC voltage dynamic process, the DC voltage control loop, and the additional inertia control loop of the receiving-end converter, we have:

[0049] ;

[0050] in, s Here, Δ represents the small-signal quantity of the variable, and the subscript 0 indicates the steady-state value of the variable. P m For the input power of the receiving-end converter, P e For the output power of the receiving-end converter, C It is a DC capacitor. U dc This is the DC line voltage. k p_dc , k i_dc These are the proportional and integral coefficients of the DC voltage PI regulator, respectively. U dcref This is the reference voltage for the DC line. idref This is the reference value for the d-axis component of the output current of the receiving-end converter. U dc * This is the actual reference voltage value for the DC line. f 1 represents the receiving-end grid frequency measured by the receiving-end converter's phase-locked loop. f ref The rated frequency of the receiving-end power grid. K 1 represents the droop coefficient of the receiving-end converter.

[0051] The DC voltage control loop with additional inertia control obtained after merging is as follows:

[0052] ;

[0053] The phase-locked loop component is:

[0054] ;

[0055] The small-signal expression for the terminal voltage is:

[0056] ;

[0057] The small-signal expressions for the internal potential amplitude and power control angle are:

[0058] ;

[0059] The small-signal expression for the active power at the internal potential is:

[0060] ;

[0061] in, s Here, Δ represents the small-signal quantity of the variable, and the subscript 0 indicates the steady-state value of the variable. k p_dc , k i_dc These are the proportional and integral coefficients of the DC voltage PI regulator, respectively. P m For the input power of the receiving-end converter, P e For the output power of the receiving-end converter, C It is a DC capacitor. U dc This is the DC line voltage. K 1 represents the droop factor of the receiving-end converter. k p_pll This is the proportional gain of the phase-locked loop. k i_pll The integral coefficients of the phase-locked loop are... U t Terminal voltage,U td The terminal voltage component along the d-axis in the phase-locked coordinate system. U tq The terminal voltage component along the q-axis in the phase-locked loop coordinate system. θ t For the terminal voltage phase, θ pll To obtain the reference phase for the phase-locked loop, E Internal potential, E d The d-axis component is the internal potential phase-locked coordinate system. E q The q-axis component in the phase-locked coordinate system. X f For filter reactance, I d The d-axis component of the output current of the receiving-end converter. I q This refers to the q-axis component of the output current of the receiving-end converter. θ ctrl This represents the power control angle of the internal potential in the phase-locked loop coordinate system. θ t For the terminal voltage phase, θ E The phase of the internal potential, P e The active power output of the receiving-end converter.

[0062] In one embodiment, such as 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 offshore wind farms, only the small-signal model of the machine-side converter needs to be analyzed separately.

[0063] Considering the control characteristics of the machine-side converter, a small-signal model of the machine-side converter is established, including: speed control, virtual inertia control, small-signal expression of output power of permanent magnet direct-drive wind turbine, and rotor motion equation of direct-drive wind turbine.

[0064] The speed control mechanism is as follows:

[0065] ;

[0066] The virtual inertia control is as follows:

[0067] ;

[0068] The small-signal expression for the output power of the permanent magnet direct-drive fan is:

[0069] ;

[0070] The equation of motion for the direct-drive fan rotor is:

[0071] ;

[0072] in, s Here, Δ represents the small-signal quantity of the variable, and the subscript 0 indicates the steady-state value of the variable. i qref This is the reference value for the q-axis component of the current. k p_ω This is the proportional coefficient of the speed controller. k i_ω The integral coefficient of the speed controller. ω rer This is the actual reference rotor speed for the direct-drive fan. ω rref This is the reference speed for the direct-drive fan. K 3 represents the virtual inertia control coefficient. T f The time constant of the low-pass filter. θ pll To obtain the reference phase for the phase-locked loop, P w This refers to the output power of the direct-drive fan. ω r The rotor speed is Ψ f For rotor flux linkage, i sq The stator phase current q-axis component, P in This is the input power for the direct-drive fan. J This represents the rotational inertia of the direct-drive fan.

[0073] Taking into account the speed control, virtual inertia control, small-signal expression of output power of permanent magnet direct-drive wind turbine, and rotor motion equation of direct-drive wind turbine, the small-signal model of the turbine-side converter of offshore wind farm can be obtained as follows: Figure 5 As shown.

[0074] Furthermore, the method also includes: simplifying the small-signal model of the machine-side converter to:

[0075] ;

[0076] Where K(s) is represented as:

[0077] ;

[0078] ;

[0079] in, kp_ω This is the proportional coefficient of the speed controller. k i_ω This is the integral coefficient of the speed controller.

[0080] In one embodiment, considering that the transient response of the grid-side converter in an offshore wind farm is similar to that of the receiving-end converter under conventional control, and referring to the small-signal model of a flexible DC transmission system, combined with the small-signal model of the machine-side converter and the control topology of the grid-side converter in an offshore wind farm, a small-signal model of the offshore wind farm can be obtained, such as... Figure 6 As shown.

[0081] Simplifying the small-signal model of the offshore wind farm, we can obtain the following small-signal model:

[0082] ;

[0083] ;

[0084] Where s is the Laplace operator, Δ represents the small-signal quantity of the variable, the 0 subscript represents the steady-state value of the variable, and P e_OWF This refers to the output power of the grid-side converter in an offshore wind farm.

[0085] In one embodiment, a quasi-synchronous support model for the offshore wind power flexible DC transmission system is established based on the small-signal model of the flexible DC transmission system and the small-signal model of the offshore wind farm, characterizing the quasi-synchronous characteristics of the system. Figure 3 In the offshore wind power flexible DC 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 impact on the system's inertial response; therefore, the sending-end converter is not considered in the modeling. According to... Figure 3 The schematic diagram of the offshore wind power DC transmission system shown above indicates that when K1 = 1 / K2, the frequencies at both ends can be considered to be consistent on the electromechanical time scale, i.e., f1 = f2. Therefore, the transient process of the offshore wind power DC transmission system under frequency disturbance of the receiving end grid can be described as follows:

[0086] 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 capacitors of the receiving-end converter submodules will release or absorb a certain amount of energy to dampen the change in grid frequency. From an electromechanical time scale perspective, 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 its speed control reference value to increase or decrease its output active power P. e_OWF .

[0087] Combining the small-signal model of the flexible DC transmission system and the small-signal model of the offshore wind farm, a small-signal model of the offshore wind power flexible DC transmission system is obtained, such as... Figure 7As shown. Considering that the response of the flexible DC transmission system is analogous to the rotor motion equation of a synchronous machine, and the response of the offshore wind farm is analogous to the primary frequency regulation process of a synchronous machine, a quasi-synchronous support model for the offshore wind power flexible DC transmission system is obtained, as follows. Figure 8 As shown, the deviation of the output active power is:

[0088] ;

[0089] The small-signal expression for the internal potential phase of the frequency modulation process is:

[0090] ;

[0091] The synchronous characteristics of the system are characterized by the equation of motion of the rotor of the synchronous machine, and a synchronous support model for the offshore wind power flexible direct transmission system is established as follows:

[0092] ;

[0093] The expressions for each item are as follows:

[0094] ;

[0095] .

[0096] In one embodiment, the step of calculating the equivalent inertia transfer function of the offshore wind power flexible direct transmission system based on the synchronous support model of the offshore wind power flexible direct transmission system includes: calculating the partial inertia transfer functions of the flexible DC transmission system and the offshore wind farm, and the equivalent inertia transfer function of the complete offshore wind power flexible direct transmission system, based on the synchronous support model of the offshore wind power flexible direct transmission system.

[0097] Specifically, neglecting the damping coefficient, the synchronous machine rotor motion equation is expressed as:

[0098] ;

[0099] Analogous to the rotor motion equation of a synchronous machine, and based on the aforementioned synchronous support model for the flexible DC transmission system for offshore wind power, the transfer functions of the partial inertia of the flexible DC transmission system and the offshore wind farm, as well as the transfer function of the equivalent inertia of the complete flexible DC transmission system for offshore wind power, are calculated as follows:

[0100] ;

[0101] Among them, J HVDC (s) is the partial inertia transfer function of the flexible DC transmission system, J OWF (s) is the partial 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 transmission system, K OWF(s) represents the potential phase θ within the offshore wind farm. E_OWF Phase θ of the phase-locked loop reference pll The relationship between them is as follows:

[0102] .

[0103] Figure 9 This is a schematic structural diagram of a device provided in an exemplary embodiment. Please refer to... Figure 9 At the hardware level, the device includes a processor 902, an internal bus 904, a network interface 906, memory 908, and non-volatile memory 910, and may also include other hardware required for its functions. One or more embodiments of the present invention can be implemented in software, for example, the processor 902 reads the corresponding computer program from the non-volatile memory 910 into memory 908 and then runs 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 hardware and software, etc. That is to say, the execution subject of the following processing flow is not limited to each logic unit, but can also be hardware or logic devices.

[0104] Please refer to Figure 10 An equivalent inertia assessment device for offshore wind power flexible direct transmission systems can be applied to, for example... Figure 10 The device shown, in order to implement the technical solution of the present invention, includes:

[0105] The first building unit 1001 is used to establish a small-signal model of the flexible DC transmission system based on the control topology of the flexible DC transmission system;

[0106] The second building unit 1002 is used to establish a small-signal model of the generator-side converter based on the control topology of the generator-side converter of the offshore wind farm, and to establish a small-signal model of the offshore wind farm based on the small-signal model of the generator-side converter and the control topology of the grid-side converter of the offshore wind farm.

[0107] Analogy unit 1003 is used to compare the response of the flexible DC transmission system with the rotor motion equation of a synchronous machine and the response of the offshore wind farm with the primary frequency regulation process of a synchronous machine, and to characterize the system's quasi-synchronous characteristics in the form of the rotor motion equation of the synchronous machine, so as to establish a quasi-synchronous support model for the offshore wind power flexible DC transmission system.

[0108] The calculation unit 1004 is used to calculate the equivalent inertia transfer function of the offshore wind power flexible direct transmission system based on the synchronous support model of the offshore wind power flexible direct transmission system.

[0109] Optionally, the small-signal model of the flexible DC transmission system includes: a DC voltage control loop with additional inertia control, a phase-locked loop, a small-signal expression for the terminal voltage, a small-signal expression for the internal potential amplitude and power control angle, and a small-signal expression for the active power at the internal potential.

[0110] The DC voltage control loop for the additional inertia control is as follows:

[0111] ;

[0112] The phase-locked loop component is:

[0113] ;

[0114] The small-signal expression for the terminal voltage is:

[0115] ;

[0116] The small-signal expressions for the internal potential amplitude and power control angle are:

[0117] ;

[0118] The small-signal expression for the active power at the internal potential is:

[0119] ;

[0120] in, s Here, Δ represents the small-signal quantity of the variable, and the subscript 0 indicates the steady-state value of the variable. k p_dc , k i_dc These are the proportional and integral coefficients of the DC voltage PI regulator, respectively. P m For the input power of the receiving-end converter, P e For the output power of the receiving-end converter, C It is a DC capacitor. U dc This is the DC line voltage. K 1 represents the droop factor of the receiving-end converter. k p_pll This is the proportional gain of the phase-locked loop. k i_pll The integral coefficients of the phase-locked loop are... U t Terminal voltage, U td The terminal voltage component along the d-axis in the phase-locked coordinate system. U tq The terminal voltage component along the q-axis in the phase-locked loop coordinate system. θt For the terminal voltage phase, θ pll To obtain the reference phase for the phase-locked loop, E Internal potential, E d The d-axis component is the internal potential phase-locked coordinate system. E q The q-axis component in the phase-locked coordinate system. X f For filter reactance, I d The d-axis component of the output current of the receiving-end converter. I q This refers to the q-axis component of the output current of the receiving-end converter. θ ctrl This represents the power control angle of the internal potential in the phase-locked loop coordinate system. θ t For the terminal voltage phase, θ E The phase of the internal potential, P e The active power output of the receiving-end converter.

[0121] Optionally, the small-signal model of the machine-side converter includes: speed control loop, virtual inertia control, small-signal expression of output power of permanent magnet direct-drive wind turbine, and rotor motion equation of direct-drive wind turbine;

[0122] The speed control mechanism is as follows:

[0123] ;

[0124] The virtual inertia control is as follows:

[0125] ;

[0126] The small-signal expression for the output power of the permanent magnet direct-drive fan is:

[0127] ;

[0128] The equation of motion for the direct-drive fan rotor is:

[0129] ;

[0130] in, s Here, Δ represents the small-signal quantity of the variable, and the subscript 0 indicates the steady-state value of the variable. i qref This is the reference value for the q-axis component of the current. k p_ω This is the proportional coefficient of the speed controller. k i_ωThe integral coefficient of the speed controller. ω rer This is the actual reference rotor speed for the direct-drive fan. ω rref This is the reference speed for the direct-drive fan. K 3 represents the virtual inertia control coefficient. T f The time constant of the low-pass filter. θ pll To obtain the reference phase for the phase-locked loop, P w This refers to the output power of the direct-drive fan. ω r The rotor speed, Ψ f For rotor flux linkage, i sq The stator phase current q-axis component, P in This is the input power for the direct-drive fan. J This represents the rotational inertia of the direct-drive fan.

[0131] Optionally, the device further includes:

[0132] Simplification unit 1005 is used to simplify the small-signal model of the machine-side converter to:

[0133] ;

[0134] Where K(s) is represented as:

[0135] ;

[0136] ;

[0137] in, k p_ω This is the proportional coefficient of the speed controller. k i_ω This is the integral coefficient of the speed controller.

[0138] Optionally, the small-signal model for the offshore wind farm is:

[0139] ;

[0140] ;

[0141] Where s is the Laplace operator, Δ represents the small-signal quantity of the variable, the 0 subscript represents the steady-state value of the variable, and P e_OWF This refers to the output power of the grid-side converter in an offshore wind farm.

[0142] Optional,

[0143] The deviation of the active power output during the frequency modulation process is:

[0144] ;

[0145] The small-signal expression for the internal potential phase of the frequency modulation process is:

[0146] ;

[0147] The synchronous support model for the offshore wind power flexible direct transmission system is as follows:

[0148] ;

[0149] The expressions for each item are as follows:

[0150] ;

[0151] .

[0152] Optionally, the computing unit 1004 is specifically used for:

[0153] Based on the aforementioned synchronous support model for the offshore wind power flexible DC transmission system, the transfer functions of the partial inertia 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, are calculated as follows:

[0154] ;

[0155] Among them, J HVDC (s) is the partial inertia transfer function of the flexible DC transmission system, J OWF (s) is the partial 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 transmission system, K OWF (s) represents the potential phase θ within the offshore wind farm. E_OWF Phase θ of the phase-locked loop reference pll The relationship between them is as follows:

[0156] .

[0157] The systems, devices, modules, or units described in the above embodiments can be implemented by computer chips or entities, or by products with certain functions. A typical implementation device is a computer, which can take the form of a personal computer, laptop computer, cellular phone, camera phone, smartphone, personal digital assistant, media player, navigation device, email sending and receiving device, game console, tablet computer, wearable device, or any combination of these devices.

[0158] In a typical configuration, a computer includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0159] Memory may include non-persistent storage in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0160] Computer-readable media, including both permanent and non-permanent, removable and non-removable media, can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, 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, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, disk storage, quantum memory, graphene-based storage media or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0161] For any computer-readable medium (or computer-readable storage medium) as described above or otherwise, computer instructions may be stored thereon, which, when executed by a processor, implement one or more of the above embodiments, thereby realizing the technical solution of the present invention.

[0162] The present invention also proposes a computer program that, when executed by a processor, implements one or more of the embodiments described above, thereby realizing the technical solution of the present invention. This computer program may be specifically recorded on the above-described or other computer-readable media, and the present invention does not impose any limitations on this.

[0163] 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.

[0164] The foregoing has described specific embodiments of the invention. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps described in the claims may be performed in a different order than that shown in the embodiments and may still achieve the desired results. Furthermore, the processes depicted in the drawings do not necessarily require the specific or sequential order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0165] The terminology used in one or more embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” used in one or more embodiments of the invention and in the appended claims are also 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 includes any or all possible combinations of one or more associated listed items.

[0166] 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 one another. For example, first information may also be referred to as second information without departing from the scope of one or more embodiments of the present invention, 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 "when," "when," or "in response to a determination."

[0167] The above description is merely a preferred embodiment of one or more embodiments of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments of the present invention should be included within the protection scope 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 transmission system, characterized in that, An application is made to an offshore wind power flexible DC transmission system, wherein the offshore wind power flexible DC transmission system includes an offshore wind farm and a flexible DC transmission system, the offshore wind farm includes a turbine-side converter and a grid-side converter, and the flexible DC transmission system includes a receiving-end converter and a sending-end converter; the method includes: A small-signal model of the flexible DC transmission system is established based on the control topology of the flexible DC transmission system. The small-signal model of the flexible DC transmission system includes: a DC voltage control loop with additional inertia control, a phase-locked loop, a small-signal expression for the terminal voltage, a small-signal expression for the internal potential amplitude and power control angle, and a small-signal expression for the active power at the internal potential. The DC voltage control loop for the additional inertia control is as follows: ； The phase-locked loop component is: ； The small-signal expression for the terminal voltage is: ； The small-signal expressions for the internal potential amplitude and power control angle are: ； The small-signal expression for the active power at the internal potential is: ； in, s Here, Δ represents the small-signal quantity of the variable, and the subscript 0 indicates the steady-state value of the variable. k p_dc , k i_dc These are the proportional and integral coefficients of the DC voltage PI regulator, respectively. P m For the input power of the receiving-end converter, P e For the output power of the receiving-end converter, C It is a DC capacitor. U dc This is the DC line voltage. K 1 represents the droop factor of the receiving-end converter. k p_pll This is the proportional gain of the phase-locked loop. k i_pll The integral coefficients of the phase-locked loop are... U t Terminal voltage, U td The terminal voltage component along the d-axis in the phase-locked coordinate system. U tq The terminal voltage component along the q-axis in the phase-locked loop coordinate system. θ t For the terminal voltage phase, θ pll To obtain the reference phase for the phase-locked loop, E Internal potential, E d The d-axis component is the internal potential phase-locked coordinate system. E q The q-axis component in the phase-locked coordinate system. X f For filter reactance, I d The d-axis component of the output current of the receiving-end converter. I q This refers to the q-axis component of the output current of the receiving-end converter. θ ctrl This represents the power control angle of the internal potential in the phase-locked loop coordinate system. θ t For the terminal voltage phase, θ E The phase of the internal potential, P e The active power output of the receiving-end converter; A small-signal model of the generator-side converter is established based on the control topology of the generator-side converter of the offshore wind farm, and a small-signal model of the offshore wind farm is established based on the small-signal model of the generator-side converter and the control topology of the grid-side converter of the offshore wind farm. The response of the flexible DC transmission system is analogous to the rotor motion equation of a synchronous machine, and the response of the offshore wind farm is analogous to the primary frequency regulation process of a synchronous machine. The system's quasi-synchronous characteristics are characterized in the form of the rotor motion equation of the synchronous machine, so as to establish a quasi-synchronous support model for the offshore wind power flexible DC transmission system. The equivalent inertia transfer function of the offshore wind power flexible direct transmission system is calculated based on the synchronous support model of the offshore wind power flexible direct transmission system.

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

3. The method according to claim 2, characterized in that, The method further includes: The small-signal model of the machine-side converter is simplified as follows: ； Where K(s) is represented as: ； ； in, k p_ω This is the proportional coefficient of the speed controller. k i_ω This is the integral coefficient of the speed controller.

4. The method according to claim 3, characterized in that, The small-signal model for offshore wind farms is as follows: ； ； Where s is the Laplace operator, Δ represents the small-signal quantity of the variable, the 0 subscript represents the steady-state value of the variable, and P e_OWF This refers to the output power of the grid-side converter in an offshore wind farm.

5. The method according to claim 4, characterized in that, The deviation of the active power output during the frequency modulation process is: ； The small-signal expression for the internal potential phase of the frequency modulation process is: ； The synchronous support model for the offshore wind power flexible direct transmission system is as follows: ； The expressions for each item are as follows: ； 。 6. The method according to claim 5, characterized in that, The calculation of the equivalent inertia transfer function of the offshore wind power flexible direct transmission system based on the synchronous support model of the offshore wind power flexible direct transmission system includes: Based on the aforementioned synchronous support model for the offshore wind power flexible DC transmission system, the transfer functions of the partial inertia 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, are calculated as follows: ； Among them, J HVDC (s) is the partial inertia transfer function of the flexible DC transmission system, J OWF (s) is the partial 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 transmission system, K OWF (s) represents the potential phase θ within the offshore wind farm. E_OWF Phase θ of the phase-locked loop reference pll The relationship between them is as follows: 。 7. An equivalent inertia assessment device for an offshore wind power flexible direct transmission system, characterized in that, The device includes: First construction unit: Establish a small-signal model of the flexible DC transmission system based on the control topology of the flexible DC transmission system; the small-signal model of the flexible DC transmission system includes: DC voltage control loop with additional inertia control, phase-locked loop loop, small-signal expression of terminal voltage, small-signal expression of internal potential amplitude and power control angle, and small-signal expression of active power at internal potential. The DC voltage control loop for the additional inertia control is as follows: ； The phase-locked loop component is: ； The small-signal expression for the terminal voltage is: ； The small-signal expressions for the internal potential amplitude and power control angle are: ； The small-signal expression for the active power at the internal potential is: ； in, s Here, Δ represents the small-signal quantity of the variable, and the subscript 0 indicates the steady-state value of the variable. k p_dc , k i_dc These are the proportional and integral coefficients of the DC voltage PI regulator, respectively. P m For the input power of the receiving-end converter, P e For the output power of the receiving-end converter, C It is a DC capacitor. U dc This is the DC line voltage. K 1 represents the droop factor of the receiving-end converter. k p_pll This is the proportional gain of the phase-locked loop. k i_pll The integral coefficients of the phase-locked loop are... U t Terminal voltage, U td The terminal voltage component along the d-axis in the phase-locked coordinate system. U tq The terminal voltage component along the q-axis in the phase-locked loop coordinate system. θ t For the terminal voltage phase, θ pll To obtain the reference phase for the phase-locked loop, E Internal potential, E d The d-axis component is the internal potential phase-locked coordinate system. E q The q-axis component in the phase-locked coordinate system. X f For filter reactance, I d The d-axis component of the output current of the receiving-end converter. I q This refers to the q-axis component of the output current of the receiving-end converter. θ ctrl This represents the power control angle of the internal potential in the phase-locked loop coordinate system. θ t For the terminal voltage phase, θ E The phase of the internal potential, P e The active power output of the receiving-end converter; The second building unit: Based on the control topology of the generator-side converter of the offshore wind farm, a small-signal model of the generator-side converter is established, and based on the small-signal model of the generator-side converter and the control topology of the grid-side converter of the offshore wind farm, a small-signal model of the offshore wind farm is established. Analogy Unit: The receiving-end converter of the flexible DC transmission system is analogous to the rotor motion equation of a synchronous machine, and the response of the offshore wind farm is analogous to the primary frequency regulation process of a synchronous machine. The system's quasi-synchronous characteristics are characterized in the form of the rotor motion equation of the synchronous machine, so as to establish a quasi-synchronous support model for the offshore wind power flexible DC transmission system. Calculation unit: Calculates the equivalent inertia transfer function of the offshore wind power flexible direct transmission system based on the synchronous support model of the offshore wind power flexible direct transmission system.

8. An electronic device, characterized in that, include: processor; Memory used to store processor-executable instructions; The processor implements the steps of the method as described in any one of claims 1-6 by running the executable instructions.

9. A computer-readable storage medium storing computer instructions thereon, characterized in that, When executed by the processor, this instruction implements the steps of the method as described in any one of claims 1-6.

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