Offshore wind power alternating current sending-out system resonance suppression method and system based on Fermat fuzzy

Abstract

The invention relates to an offshore wind power alternating current sending-out system resonance suppression method and system based on Fermat fuzzy, and the method comprises the steps: building an impedance model, and obtaining a coupling relation between a variable and a grid-connected point current in an offshore wind power alternating current submarine cable sending-out system based on the impedance model; obtaining the form of the uncertain factors influencing the resonance of the offshore wind turbine AC submarine cable sending-out system based on the coupling relationship, and quantifying the uncertain factors by using Fermat fuzzy; and generating a resonance suppression strategy of the offshore wind turbine alternating current submarine cable sending-out system based on the quantized uncertain factors. Compared with the prior art, the method introduces the Fermat fuzzy theory for the resonance problem of the offshore wind power alternating current sending-out system, comprehensively depicts the influence of inherent complex uncertainty of offshore wind power on the resonance of the offshore wind power, and generates a resonance suppression strategy considering uncertain factors. The stability and the reliability of the offshore wind turbine alternating current submarine cable sending-out system are improved.

Description

Technical Field

[0001] The present invention relates to the field of offshore wind power analysis, and in particular to a method and system for suppressing resonance of an offshore wind power AC transmission system based on Fermat fuzzy. Background Art

[0002] Due to the complexity of the marine environment and the inherent uncertainty of offshore wind power, especially the interactive coupling effect with the AC transmission system, the grid connection of offshore wind power faces huge challenges, bringing great pressure to the safe and stable operation of the power system. When the offshore wind speed drops to calm or light wind, overcurrent events may occur in the wind farm, thus triggering high-frequency series resonance accidents, resulting in large-area tripping of the wind turbine yaw system and failure to achieve self-recovery, causing serious economic losses. Therefore, in order to effectively reduce the safety risks brought by offshore wind farm resonance accidents, it is necessary to introduce scientific control strategies to suppress the resonance phenomenon of the AC transmission system caused by the complex uncertainty of offshore wind power, so as to ensure the safe and stable operation of the system. In the prior art, offline simulation is often used or a dynamic model is established for resonance analysis of wind turbines. For offshore wind power, the resonance mechanism analysis generally includes theoretical analysis and simulation based on the system model and simulation reproduction of real accidents. For example, a frequency-domain analysis method based on an impedance model is used to study the high-frequency resonance problem of the offshore wind farm collector grid; a frequency scan combined with harmonic power flow analysis is used to analyze the causes of offshore wind farm resonance accidents; the resonance overvoltage problem of an offshore wind farm in Zhejiang is analyzed through theoretical calculation, simulation reproduction and analysis. Specifically, as in the Chinese patent application 《CN117498301A》, it provides a method for analyzing the specific frequency of offshore wind power resonance by using the resonance point movement method, calculating the equivalent parameters of offshore wind power, and building a harmonic resonance simulation analysis model for offshore wind farm resonance analysis. It can be seen that at present, most of the resonance analysis of offshore wind power focuses on discussing the influence of internal factors of the offshore wind power system on resonance. However, in actual offshore wind farms, in addition to its internal factors, there are other factors that will also affect its resonance. Therefore, the existing resonance suppression methods for offshore wind farms cannot comprehensively and objectively conduct resonance analysis, resulting in poor effects of the generated resonance suppression strategies.

[0003] Therefore, it is a technical problem to be solved to provide a resonance suppression method for offshore wind power that is comprehensive and can effectively suppress resonance. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a method and system for suppressing resonance of an offshore wind power AC transmission system based on Fermat fuzzy, comprehensively considering the influence of inherent uncertain factors of offshore wind power such as offshore wind speed fluctuation, failure rate of offshore AC transmission equipment and change of operation characteristic parameters on offshore wind power resonance, and realizing the suppression of offshore wind power AC transmission system resonance by setting parameter intervals based on Fermat fuzzy.

[0005] The object of the present invention can be achieved by the following technical solutions:

[0006] According to the first aspect of the present invention, a resonance suppression method for an offshore wind power AC transmission system based on Fermat fuzzy is provided. The method includes:

[0007] Construct an impedance model, and based on the impedance model, obtain the coupling relationship between variables and the grid connection point current in the offshore wind turbine AC submarine cable transmission system; the variables include the equivalent controlled current source of the offshore permanent magnet direct drive wind turbine, the equivalent impedance of the offshore wind power AC transmission system, and the equivalent impedance of the non-ideal power grid;

[0008] Based on the coupling relationship, obtain the form of the influence of uncertain factors on the resonance of the offshore wind turbine AC submarine cable transmission system, and use Fermat fuzzy to quantify the uncertain factors; the uncertain factors include the offshore wind speed and the failure rate of the offshore wind power AC transmission system;

[0009] Generate a resonance suppression strategy for the offshore wind turbine AC submarine cable transmission system based on the quantified uncertain factors.

[0010] As a preferred technical solution, the expression of the coupling relationship is:

[0011]

[0012] Where, I WT is the equivalent controlled current source of the offshore permanent magnet direct drive wind turbine, Z sys is the equivalent impedance of the offshore wind power AC transmission system, Z G is the equivalent impedance of the non-ideal power grid, U G is the equivalent voltage of the power grid, and I a is the grid connection point current of the system.

[0013] As a preferred technical solution, the method for obtaining the form of the influence of uncertain factors on the resonance of the offshore wind turbine AC submarine cable transmission system is: obtain the equivalent impedance of the offshore wind power AC transmission system, and its expression is,

[0014]

[0015] Where, G PLL represents the phase-locked loop transfer function; G represents the auxiliary function; E d0 represents the d-axis component of the steady-state grid connection point voltage; X, N, H, W, T, and K are all auxiliary functions; P g0 represents the active power output of the converter on the wind turbine side in the offshore wind turbine AC submarine cable transmission system, and is affected by the failure rate of the offshore wind power AC transmission system.

[0016] As a preferred technical solution, the method for calculating the active power output of the converter on the fan side in the AC submarine cable transmission system of the offshore wind turbine is as follows:

[0017] P g0 =-k2P tur / S b ,

[0018] where k2 represents the conversion efficiency of the active power between the converter on the fan side and the DC bus considering the failure rate of the AC transmission system of offshore wind power; P tur represents the active power output of the permanent magnet synchronous generator and is affected by the offshore wind speed; S b represents the base capacity of the AC submarine cable transmission system of the offshore wind turbine.

[0019] As a preferred technical solution, the expression for calculating the active power output of the permanent magnet synchronous generator is:

[0020]

[0021] where R tur represents the radius of the fan blade; ρ represents the air density; v cut-in represents the cut-in wind speed; v cut-out represents the cut-out wind speed; v rated represents the rated wind speed; P rate represents the rated power of the fan; C p represents the wind energy utilization coefficient; v represents the offshore wind speed.

[0022] As a preferred technical solution, the method for generating the resonance suppression strategy of the AC submarine cable transmission system of the offshore wind turbine is as follows:

[0023] Obtain the historical data of the uncertainty factors and construct the interval-valued Fermat fuzzy numbers of the uncertainty factors based on the historical data;

[0024] Calculate the interval Fermat score function values of each uncertainty factor based on the interval-valued Fermat fuzzy numbers;

[0025] Tune the active power output of the permanent magnet synchronous generator and the active power transmitted by the converter on the fan side in the AC submarine cable transmission system of the offshore wind turbine based on the interval Fermat score function values;

[0026] Tune the active power output of the permanent magnet synchronous generator and the converter on the fan side based on the tuned offshore wind speed, calculate the grid connection point current of the AC submarine cable transmission system of the offshore wind turbine, draw the impedance frequency characteristic curve, and obtain the interval range of the control parameters of the converter on the fan side of the wind turbine group based on the impedance frequency characteristic curve;

[0027] Generate a resonance suppression strategy based on the set active power output and the control parameter range of the wind turbine side converter of the wind turbine unit.

[0028] As a preferred technical solution, the method for constructing the interval-valued Fermat fuzzy number of the uncertainty factor is as follows:

[0029] Obtain the historical data of the offshore wind speed, and construct the interval-valued Fermat fuzzy number of the offshore wind speed based on the historical data of the offshore wind speed;

[0030] Obtain the historical data of the failure rate of the offshore wind power AC transmission system, and generate the historical data of the conversion efficiency of the active power between the machine side wind turbine side converter and the DC bus based on the historical data of the failure rate of the offshore wind power AC transmission system. Its expression is: k2 = mk n , where m represents the historical data of the failure rate of the offshore wind power AC transmission system; k n represents the rated conversion efficiency;

[0031] Construct the interval-valued Fermat fuzzy number of the failure rate of the offshore wind power AC transmission system based on the historical data of the conversion efficiency of the active power between the machine side wind turbine side converter and the DC bus.

[0032] As a preferred technical solution, the expression of the interval Fermat score function is:

[0033]

[0034] Among them, represents the upper and lower limits of the membership degree interval of the interval-valued Fermat fuzzy number of the uncertainty factor t; represents the upper and lower limits of the non-membership degree interval of the Fermat fuzzy number of the uncertainty factor t.

[0035] As a preferred technical solution, the method for setting the active power output of the permanent magnet synchronous generator and the wind turbine side converter includes:

[0036] Use the interval Fermat score function to convert the offshore wind speed and the conversion efficiency of the active power between the wind turbine side converter and the DC bus;

[0037] Based on the converted offshore wind speed, set the active power output of the permanent magnet synchronous generator;

[0038] Based on the converted conversion efficiency of the active power between the wind turbine side converter and the DC bus, set the active power output of the wind turbine side converter.

[0039] According to the second aspect of the present invention, a resonance analysis system for an offshore wind power AC transmission system based on Fermat fuzzy is provided. The system is used to implement the method as described above.

[0040] Compared with the prior art, the present invention takes into account the inherent uncertainties of offshore wind power, such as the offshore wind speed and the failure rate of the offshore wind power AC transmission system, in the consideration of offshore wind power resonance, and uses Fermat fuzzy to comprehensively quantify the impact of uncertainties on offshore wind power resonance; uses interval-valued Fermat fuzzy sets to describe uncertain information such as the output power fluctuation of offshore wind power, equipment failure rate, and the change of the parameters of the wind turbine side converter, so as to quantify the impact of uncertainties on offshore wind power resonance, and intuitively reflects the coupling relationship between the uncertainties and the electrical quantities of the offshore wind power transmission system; and based on the quantified uncertainties, data rectification is carried out on the electrical quantities, and according to the rectified data, the impedance frequency characteristic curve of the offshore wind power AC transmission system is drawn, and the interval range of the control parameters of the grid-side converter of the wind turbine is determined, effectively reducing the possibility of resonance caused by the inherent complex uncertainties of offshore wind power, and significantly improving the stability and reliability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is the method flow chart of the present invention;

[0042] Figure 2 is the schematic diagram of the offshore wind power AC submarine cable transmission system of the present invention;

[0043] Figure 3 is the simplified circuit diagram of the impedance model of the offshore wind power AC submarine cable transmission system of the present invention;

[0044] Figure 4 is the schematic diagram of the change of the impedance amplitude of the offshore permanent magnet direct drive wind turbine when the active power output changes according to the present invention;

[0045] Figure 5 is the schematic diagram of the phase change of the offshore permanent magnet direct drive wind turbine when the active power output changes according to the present invention;

[0046] Figure 6 is the flow chart of generating the resonance suppression strategy according to the present invention;

[0047] Figure 7 is the schematic diagram of the calculated value of the interval Fermat fuzzy score function according to the present invention;

[0048] Figure 8 is the impedance frequency characteristic curve diagram of the impedance amplitude of the offshore permanent magnet direct drive wind turbine changing with the current inner loop parameters according to the present invention;

[0049] Figure 9 is the impedance frequency characteristic curve diagram of the phase of the offshore permanent magnet direct drive wind turbine changing with the current inner loop parameters according to the present invention;

[0050] Figure 10 is the impedance frequency characteristic curve diagram of the impedance amplitude of the offshore permanent magnet direct drive wind turbine changing with the phase-locked loop parameters according to the present invention;

[0051] Figure 11 It is the impedance frequency characteristic curve diagram of the phase of the offshore permanent magnet direct drive wind turbine of the present invention varying with the PLL parameters;

[0052] Figure 12 It is the schematic diagram for selecting measurement points in the simulation verification experiment of the present invention;

[0053] Figure 13 It is the current waveform diagram of the measurement points under different scenario controls of the current inner loop of the present invention;

[0054] Figure 14 It is the current waveform diagram of the measurement points under different scenario controls of the PLL of the present invention. Specific implementation manners

[0055] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0056] The details of one or more embodiments of the present application are presented in the following drawings and description to make other features, objectives, and advantages of the present application more concise and understandable.

[0057] In order to analyze the resonance disturbance transfer mechanism between the inherent complex uncertainties of offshore wind power and the AC submarine cable transmission system and formulate resonance strategies in this embodiment, a resonance suppression method based on Fermat fuzzy theory and comprehensively considering uncertain factors such as the fluctuation of offshore wind speed, the failure rate of offshore AC transmission equipment, and the change of operating characteristic parameters of the converter on the wind turbine side is proposed. Its process is as Figure 1 shown and includes:

[0058] S1. Construct an impedance model, and based on the impedance model, obtain the coupling relationship between the variables and the grid-connected point current in the offshore wind turbine AC submarine cable transmission system, where the variables include the equivalent controlled current source of the offshore permanent magnet direct drive wind turbine, the equivalent impedance of the offshore wind power AC transmission system, and the equivalent impedance of the non-ideal power grid.

[0059] Specifically, build as Figure 2The time-domain simulation model of the offshore wind power AC transmission system shown. This time-domain simulation model includes a wind turbine, a permanent magnet synchronous generator, a converter on the wind turbine side and its control system, a filter circuit, a transformer, a submarine cable, etc. It can be seen that the converter of the offshore permanent magnet direct drive wind turbine adopts a double closed-loop vector control strategy. The converter on the machine side has a speed loop and a current loop, and the converter on the grid side has a voltage loop and a current loop. The electric energy output by the wind turbine is stepped up and connected to the grid through a submarine cable. If offshore wind power resonance analysis is required, impedance modeling of the wind turbine and the submarine cable needs to be carried out first. Through Thevenin's theorem, the impedance of the offshore permanent magnet direct drive wind turbine and the impedance of the submarine cable are equivalent to a controlled current source and the system impedance, then this system can be simplified to Figure 3 the circuit shown.

[0060] Based on Figure 3 the circuit shown, analyze the coupling relationship between the grid connection point current and the above variables, and the following relationship can be obtained:

[0061]

[0062] where, I WT is the equivalent controlled current source of the offshore permanent magnet direct drive wind turbine, Z sys is the equivalent impedance of the offshore wind power AC transmission system, Z G is the equivalent impedance of the non-ideal grid, U G is the equivalent voltage of the grid, and I a is the grid connection point current of the system.

[0063] S2. Based on the coupling relationship, obtain the form of the influence of uncertain factors on the resonance of the offshore wind turbine AC submarine cable transmission system, and use Fermat fuzzy quantification for uncertain factors. Among them, the uncertain factors include offshore wind speed and the failure rate of the offshore wind power AC transmission system.

[0064] The particularity of the environment where offshore wind power is located leads to its complex uncertainty. These uncertainties make the AC submarine cable transmission system show multiple coupling characteristics, increasing the risk of offshore wind power resonance. For example: 1) The offshore wind speed fluctuates frequently, directly affecting the actual active power of the permanent magnet direct drive wind turbine, and then affecting the system equivalent impedance; 2) The marine environment is harsh, and conditions such as high humidity and high salt fog increase the equipment failure rate. For example, the salt accumulation on the wind turbine blades reduces the wind energy utilization coefficient and the submarine cable is corroded, affecting the capacitance parameters, etc. The equipment failure rate of the offshore wind power AC transmission system directly affects the active power output of the converter on the wind turbine side, and then affects the equivalent impedance of the offshore wind power AC transmission system, thus affecting the occurrence of system resonance; 3) The high capacitance to ground of the AC submarine cable has an amplifying effect on high-frequency harmonics, further increasing the resonance risk; 4) The uncertainty of the control parameters of the converter of the offshore permanent magnet direct drive wind turbine will also affect the occurrence of system resonance phenomena.

[0065] Specifically, the method for obtaining the resonance form of the AC submarine cable transmission system of offshore wind turbines affected by uncertainties includes:

[0066] S21. Obtain the equivalent impedance of the offshore wind power AC transmission system, and its expression is

[0067]

[0068] G PLL represents the transfer function of the phase-locked loop, and F PLL (s) represents the transfer function of the PI controller of the phase-locked loop, and G represents the auxiliary function, and F I (s) represents the transfer function of the PI controller of the current inner loop, and K PP represents the proportional gain coefficient of the phase-locked loop; T ip represents the integral time constant of the phase-locked loop; E0 represents the steady-state value of the grid connection point voltage; s represents the impedance modeling in the s-domain; ω b represents the reference angular frequency in radians; L1 represents the value of the filter inductor at the outlet of the wind turbine side converter; k represents the output voltage gain of the grid side converter; U dc0 represents the steady-state DC voltage; k gi represents the proportional gain coefficient of the PI controller of the current inner loop; T gi represents the integral time constant of the PI controller of the current inner loop; E d0 represents the d-axis component of the steady-state grid connection point voltage; X, N, H, W, T, and K are all auxiliary functions; P g0 represents the active power output of the wind turbine side converter in the AC submarine cable transmission system of offshore wind turbines, and is affected by the failure rate of the AC transmission system of offshore wind power.

[0069] S22. Obtain the influence form of the failure rate of the offshore wind power AC transmission system on the active power output of the wind turbine side converter, which is

[0070] P g0 =-k2P tur / S b ,

[0071] where k2 represents the conversion efficiency of the active power between the wind turbine side converter and the DC bus considering the failure rate of the offshore wind power AC transmission system; P tur represents the active power output of the permanent magnet synchronous generator, and is affected by the offshore wind speed; S b represents the base capacity of the AC submarine cable transmission system of offshore wind turbines.

[0072] S23. Obtain the influence form of the offshore wind speed on the active power output of the permanent magnet synchronous generator as

[0073]

[0074] Among them, R tur represents the radius of the wind turbine blade; ρ represents the air density; v cut-in represents the cut-in wind speed; v cut-out represents the cut-out wind speed; v rated represents the rated wind speed; P rate represents the rated power of the wind turbine; C p represents the wind energy utilization coefficient; v represents the offshore wind speed.

[0075] It can be seen that the active power output of the system, the failure rate of the offshore wind power AC transmission equipment, and the equivalent impedance of the AC submarine cable transmission system interact and couple with each other, thereby affecting the occurrence of resonance in the offshore wind power AC transmission system. The failure rate of the offshore wind power AC transmission equipment directly acts on the active power output of the system. Therefore, when the active power output changes, the influence of the active power output and the failure rate of the offshore wind power AC transmission equipment on the system resonance can be obtained, as shown in Figure 4 and Figure 5 shown

[0076] S3. Generate a resonance suppression strategy for the offshore wind turbine AC submarine cable transmission system based on the quantified uncertain factors. The process is as shown in Figure 6 shown, including:

[0077] S31. Obtain the historical data of the uncertainty factors, and construct the interval-valued Fermat fuzzy numbers of the uncertainty factors based on the historical data.

[0078] Specifically, the definition of the Fermat fuzzy set is as follows:

[0079]

[0080] In the formula, represents the upper and lower limits of the membership degree interval of x ∈ X, represents the upper and lower limits of the non-membership degree interval of x ∈ X. The membership degree function μF(x) represents that the object x belongs to the acceptance domain, the non-membership degree function vF(x) represents that the object x belongs to the rejection domain, and the hesitation degree πF(x) represents that the object x belongs to the boundary domain.

[0081] S311. Obtain the historical data of the offshore wind speed, and construct the interval-valued Fermat fuzzy numbers of the offshore wind speed based on the historical data of the offshore wind speed.

[0082] In this embodiment, the offshore wind speed directly acts on the actual active power obtained by the offshore permanent magnet direct drive unit and affects the occurrence of system resonance. Therefore, the interval Fermat fuzzy number represents the uncertainty interval range of the offshore wind speed.

[0083] S312. The failure of the offshore wind power AC transmission equipment causes fluctuations in the active power output by the offshore wind power AC transmission system. In this embodiment, to simplify the analysis process, the power transmission efficiency is used to indirectly reflect the equipment failure rate of the offshore wind power AC transmission system. Specifically, historical data on the failure rate of the offshore wind power AC transmission system is obtained, and historical data on the conversion efficiency of the active power between the machine-side converter and the DC bus is generated based on the historical data on the failure rate of the offshore wind power AC transmission system. Its expression is: k2 = mk n , where m represents the historical data on the failure rate of the offshore wind power AC transmission system; k n represents the rated conversion efficiency.

[0084] S313. Based on the historical data on the conversion efficiency of the active power between the machine-side converter and the DC bus, an interval-valued Fermat fuzzy number of the failure rate of the offshore wind power AC transmission system is constructed.

[0085] Construct an interval Fermat fuzzy number of the power transmission efficiency k where represents the upper and lower limits of the membership degree interval of the failure condition of the offshore wind power AC transmission equipment in the uncertain factors, represents the upper and lower limits of the non-membership degree interval of the failure condition of the offshore wind power AC transmission equipment in the uncertain factors.

[0086] S32. Calculate the interval Fermat score function value of each uncertainty factor based on the interval-valued Fermat fuzzy number. Specifically, the expression of the interval Fermat score function is:

[0087]

[0088] where, represents the upper and lower limits of the membership degree interval of the interval Fermat fuzzy number of the uncertainty factor t; represents the upper and lower limits of the non-membership degree interval of the Fermat fuzzy number of the uncertainty factor t; and N(τ) ∈ [0, 2]. If the value of N(τ) is larger, the value of the interval-valued Fermat fuzzy number τ is larger, and the influence of this uncertainty factor on resonance is greater.

[0089] The result is as Figure 7 shown, where "·" represents the value after the interval Fermat fuzzy score function calculation of the offshore wind speed, and "*" represents the value after the interval Fermat fuzzy score function calculation of the failure rate of the offshore wind power AC transmission equipment.

[0090] S33. Based on the interval Fermat score function, the active power output of the permanent magnet synchronous generator and the active power output transmitted by the machine-side converter in the offshore wind turbine AC submarine cable transmission system are adjusted.

[0091] S331. Convert the offshore wind speed and the conversion efficiency of the active power between the wind turbine side converter and the DC bus using the interval Fermat score function to obtain v F and k 2F .

[0092] S332. Set the active power output of the permanent magnet synchronous generator based on the converted offshore wind speed. From step S23, the form of the active power output of the permanent magnet synchronous generator is known. Substitute the converted offshore wind speed v F into the expression provided in step S23 to achieve the setting of the active power output of the permanent magnet synchronous generator. The expression is:

[0093]

[0094] R tur represents the radius of the wind turbine blade; ρ represents the air density; v cut-in represents the cut-in wind speed; v cut-out represents the cut-out wind speed; v rated represents the rated wind speed; P rate represents the rated power of the wind turbine; C pF represents the wind energy utilization coefficient; v F represents the converted offshore wind speed.

[0095] S333. Set the active power output transmitted by the wind turbine side converter based on the converted conversion efficiency of the active power between the wind turbine side converter and the DC bus. From step S22, the form of the active power output of the wind turbine side converter is known. Substitute the converted conversion efficiency k of the active power between the wind turbine side converter and the DC bus 2F into the expression provided in step S22 to achieve the setting of the active power output transmitted by the wind turbine side converter. The expression is:

[0096] P g0F =-k 2F P turF / S b ,

[0097] where S b is the base capacity of the system, k 2F is the conversion efficiency of the active power between the machine side converter and the DC bus considering the failure rate after being transformed by the interval-valued Fermat fuzzy score function, and P turF represents the set active power output of the permanent magnet synchronous generator.

[0098] S34. Set the active power outputs of the permanent magnet synchronous generator and the wind turbine side converter based on the set offshore wind speed, calculate the grid connection point current of the AC submarine cable transmission system of the offshore wind turbine, and draw the impedance frequency characteristic curve. Obtain the interval range of the control parameters of the wind turbine side converter of the wind turbine group based on the impedance frequency characteristic curve.

[0099] Specifically, based on the calibrated offshore wind speed, the active power outputs of the permanent magnet synchronous generator and the wind turbine side converter are calibrated, and the expression for calculating the grid connection point current of the AC submarine cable transmission system of the offshore wind turbine is as follows:

[0100]

[0101] Among them, Z sysF (s) is the equivalent impedance of the converted AC transmission system of the offshore wind power, I WT (s) represents the equivalent controlled current source of the offshore permanent magnet direct drive wind turbine, Z G (s) represents the equivalent impedance of the non-ideal power grid, U G (s) represents the equivalent voltage of the power grid.

[0102] Since the change of the current inner loop of the converter and the proportional gain coefficient of the phase-locked loop will affect the impedance characteristics of the offshore wind turbine, the risk of system resonance is increased. Reasonable constraints are imposed on the current inner loop of the converter and the phase-locked loop parameters, and the impedance frequency characteristic curves of the current inner loop parameters are plotted as shown in Figures 8 - 9 and the impedance frequency characteristic curve of the phase-locked loop parameters is shown in Figures 10 - 11 as shown.

[0103] Specifically, from Figures 8 - 9 it can be obtained that when the proportional gain coefficient of the current inner loop is less than 0.1, the impedance characteristics of the offshore permanent magnet direct drive wind turbine change in the low frequency band, increasing the probability of system resonance. Therefore, in order to suppress the occurrence of system resonance, the proportional gain coefficient of the current inner loop needs to be controlled within 0.1, and finally the interval range of the proportional gain coefficient of the current inner loop is (0.1, 0.833). From Figures 10 - 11 it can be seen that when the proportional gain coefficient of the phase-locked loop is less than 10, the impedance phase of the wind turbine fluctuates violently, which is not conducive to system stability. Therefore, the proportional gain coefficient of the phase-locked loop should be greater than 10. Considering that the damping ratio of the phase-locked loop is mostly around 0.7, the upper limit of the interval of the proportional gain coefficient of the phase-locked loop is determined to be 54, and finally the interval range of the proportional gain coefficient of the phase-locked loop is (10, 54).

[0104] S35. Generate a resonance suppression strategy based on the calibrated active power output and the interval range of the control parameters of the wind turbine side converter of the wind turbine unit.

[0105] To verify the feasibility of the method provided above, select as shown in Figure 12Measurements are taken at the measurement points shown. Due to the relatively large capacitance of the AC submarine cable to the ground, it has an amplifying effect on the high-frequency harmonics generated by the power electronic devices in the AC transmission system of offshore wind power. Therefore, the high-frequency resonance phenomenon in the AC transmission system of offshore wind power is mainly related to the AC submarine cable. And in this embodiment, the generated resonance suppression strategy is to limit the values of the control parameters of the converter, which has a small impact on high-frequency resonance and a large impact on the sub-supersynchronous resonance and low-frequency resonance of the system. In order to highlight the role of the converter control parameters in the simulation process and weaken the influence of the AC submarine cable on the high-frequency resonance of the system, the front end of the cable is selected as the measurement point. As a result, we can obtain Figures 13 to 14 , where Figure 13 is the current waveform diagram of the measurement point under different scenarios of the current inner loop control. The green line is the current waveform of the measurement point when the rated parameters of the current inner loop are used for control, and the red line is the current waveform of the measurement point when the method provided in this embodiment is used for control. It can be seen that the current amplitude range ratio when using the method provided in this embodiment for control is 3.95% smaller than that when using the rated parameters for control, indicating that the method of this embodiment can effectively reduce the resonance amplitude to a certain extent and mitigate the resonance hazard for the control of the interval parameters of the current inner loop. Figure 14 is the current waveform diagram of the measurement point under different scenarios of the loop control. The blue curve is the current waveform diagram when the phase-locked loop uses the rated parameters for control, and the orange curve is the current waveform diagram when the phase-locked loop uses the method provided in this embodiment for control. The current amplitude range ratio when using the method provided in this embodiment for control is 2.57% smaller than that when using the rated parameters for control, which proves that the method of this embodiment can effectively reduce the resonance amplitude to a certain extent and mitigate the resonance hazard for the control of the interval parameters of the phase-locked loop.

[0106] In summary, it can be seen that the method provided in this embodiment is feasible and can effectively suppress the resonance occurrence in the AC transmission system of offshore wind power.

[0107] This embodiment also provides a resonance analysis system for the AC transmission system of offshore wind power based on Fermat fuzzy. This system is used to implement the above method. Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working process described can refer to the corresponding process in the foregoing method embodiment and will not be elaborated here.

[0108] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A resonance suppression method for offshore wind power AC transmission system based on Fermat fuzzy, characterized in that: The method includes: Construct an impedance model, and obtain the coupling relationship between variables and the grid connection point current in the offshore wind turbine AC submarine cable transmission system based on the impedance model; the variables include an equivalent controlled current source of an offshore permanent magnet direct-drive wind turbine, an equivalent impedance of the offshore wind power AC transmission system, and an equivalent impedance of a non-ideal power grid; Based on the coupling relationship, the form of the uncertainty factors affecting the resonance of the AC submarine cable transmission system of the offshore wind turbine is obtained, and the uncertainty factors are quantified by Fermat fuzzy; the uncertainty factors include offshore wind speed and failure rate of the offshore wind power AC transmission system; Based on the quantified uncertainties, a resonance suppression strategy for the AC submarine cable transmission system of offshore wind turbines is generated.

2. According to claim 1, a Fermat fuzzy-based method for suppressing resonance of an offshore wind power AC transmission system is characterized in that: The expression of the coupling relationship is: Among them, I WT is the equivalent controlled current source of the offshore permanent magnet direct-drive wind turbine, Z sys is the equivalent impedance of the offshore wind power AC transmission system, Z G is the equivalent impedance of the non-ideal power grid, U G is the grid equivalent voltage, I a is the system grid-connected point current.

3. A resonance suppression method for an offshore wind power AC transmission system based on Fermat fuzzy according to claim 2, characterized in that: The method for obtaining the form in which uncertain factors affect the resonance of the offshore wind turbine AC cable transmission system is: obtaining the equivalent impedance of the offshore wind power AC transmission system, and its expression is: Among them, G PLL represents the phase-locked loop transfer function; G represents the auxiliary function; E d0 represents the d-axis component of the steady-state grid-connected point voltage; X, N, H, W, T and K are all auxiliary functions; P g0 It represents the active output of the wind turbine-side converter in the offshore wind turbine AC submarine cable transmission system and is affected by the failure rate of the offshore wind power AC transmission system.

4. A resonance suppression method for an offshore wind power AC transmission system based on Fermat fuzzy according to claim 3, characterized in that: The method for calculating the active output of the wind turbine side converter in the offshore wind turbine AC cable delivery system is: P g0 =-k2P tur / S b , Wherein, k2 represents the conversion efficiency of active power between the wind turbine side converter and the DC bus considering the failure rate of the offshore wind power AC transmission system; P tur Represents the active output of the permanent magnet synchronous generator and is affected by the offshore wind speed; S b Represents the benchmark capacity of the AC submarine cable delivery system for offshore wind turbines.

5. A resonance suppression method for an offshore wind power AC transmission system based on Fermat fuzzy according to claim 4, characterized in that: The active output of the permanent magnet synchronous generator is calculated as follows: Among them, R tur represents the fan blade radius; ρ represents the air density; v cut-in Indicates the cut-in wind speed; v cut-out Indicates the cut-out wind speed; v rated Indicates rated wind speed; P rate Indicates the rated power of the fan; C p represents the wind energy utilization coefficient; v represents the wind speed at sea.

6. The resonance suppression method of an offshore wind power AC transmission system based on Fermat fuzzy according to claim 1 is characterized in that: The method for generating a resonance suppression strategy for an AC submarine cable delivery system for an offshore wind turbine is: Acquire historical data of the uncertainty factor, and construct an interval-valued Fermat fuzzy number of the uncertainty factor based on the historical data; Calculate the interval Fermat score function value of each uncertainty factor based on the interval-valued Fermat fuzzy number; Based on the interval Fermat score function value, the active output of the permanent magnet synchronous generator in the AC submarine cable delivery system of the offshore wind turbine and the active output transmitted by the wind turbine side converter are adjusted; Based on the active output of the permanent magnet synchronous generator and the wind turbine side converter after the offshore wind speed setting, the grid connection point current of the offshore wind turbine AC submarine cable transmission system is calculated, and the impedance frequency characteristic curve is drawn. Based on the impedance frequency characteristic curve, the control parameter range of the wind turbine side converter of the wind turbine group is obtained; A resonance suppression strategy is generated based on the adjusted active power output and the control parameter range of the wind turbine-side converter of the wind turbine group.

7. A resonance suppression method for an offshore wind power AC transmission system based on Fermat fuzzy according to claim 6, characterized in that: The method for constructing interval-valued Fermat fuzzy numbers of uncertainty factors is: Acquire historical offshore wind speed data, and construct an interval-valued Fermat fuzzy number of offshore wind speed based on the historical offshore wind speed data; Obtain the historical data of the failure rate of the offshore wind power AC transmission system, and generate the historical data of the conversion efficiency of the active power on the wind turbine side converter and the DC bus based on the historical data of the failure rate of the offshore wind power AC transmission system, and the expression is: k2 = mk n , where m represents the historical data of failure rate of offshore wind power AC transmission system; k n Indicates the rated conversion efficiency; Based on the historical data of conversion efficiency between the wind turbine-side converter and the active power on the DC bus, an interval-valued Fermat fuzzy number of the failure rate of the offshore wind power AC transmission system is constructed.

8. A resonance suppression method for an offshore wind power AC transmission system based on Fermat fuzzy according to claim 6, characterized in that: The interval Fermat score function expression is: in, The upper and lower limits of the membership interval of the interval Fermat fuzzy number representing the uncertainty factor t; The upper and lower limits of the non-membership interval of the Fermat fuzzy number representing the uncertainty factor t.

9. A resonance suppression method for an offshore wind power AC transmission system based on Fermat fuzzy according to claim 6, characterized in that: The method for setting the active output of the permanent magnet synchronous generator and the wind turbine side converter includes: The interval Fermat score function is used to convert the offshore wind speed and the conversion efficiency of the active power on the wind turbine side converter and the DC bus; The active output of the permanent magnet synchronous generator is adjusted based on the converted offshore wind speed; The active output of the wind turbine side converter is adjusted based on the conversion efficiency between the converted active power on the wind turbine side converter and the DC bus.

10. A resonance analysis system for offshore wind power AC transmission system based on Fermat fuzzy, characterized in that: The system is used to implement the method according to any one of claims 1 to 9.

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