Method and device for improving stability of doubly-fed fan
By modeling the doubly fed wind turbine grid-connected system and adding signal processing units and filter parameters, the problem of insufficient stability of the doubly fed wind turbine under low short-circuit ratio weak power grid is solved, and the stability of the system under small and large disturbances is improved.
Patent Information
- Application Number
- CN202510886756.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-30
- Publication Date
- 2025-09-09
AI Technical Summary
How to balance the stability of small and large disturbances and reduce the risk of broadband oscillation and transient out-of-step failure in the doubly fed wind power system, especially in a weak power grid environment with low short-circuit ratio. Existing technologies are difficult to effectively improve the stability of doubly fed wind turbines.
By modeling the doubly fed wind turbine grid-connected system under an ideal power grid, the closed-loop transfer function and closed-loop error function of the phase-locked loop are determined, the error response under underdamping and overdamping conditions is calculated, and the negative impact of the phase-locked loop parameters under a low short-circuit ratio weak power grid is obtained. Signal processing units and filter parameters are added under the ideal power grid, including feedforward paths and high-pass filter matrices, and virtual impedance is designed to improve system stability.
It effectively improves the stability of the doubly-fed wind turbine grid-connected system, reduces the risk of broadband oscillation and transient out-of-step faults, and takes into account the stability requirements under small and large disturbances.
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Figure CN120613780A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of new energy power generation, and in particular to a method and device for improving the stability of a doubly-fed wind turbine. Background Art
[0002] Compared to the environmental pollution caused by traditional fossil fuels like coal, oil, and natural gas, clean energy sources like wind, solar, biomass, and tidal energy offer promising prospects. Wind and solar energy are widely distributed and flexible, allowing for local development and utilization, while excess electricity can be distributed through the power grid. These energy sources offer excellent economic benefits and broad development prospects.
[0003] In recent years, the installed capacity of wind power generation systems has continued to increase. Doubly fed wind turbines have the advantages of small size, light weight, low cost, and no risk of permanent magnet demagnetization. They are still the mainstream model of onshore wind power and have the largest market share.
[0004] With the increasing penetration of new energy, the high proportion of renewable energy and power electronic equipment has significantly impacted the steady-state and transient characteristics of the power system. Wind power resources and power loads are distributed inversely, and wind turbines are mostly connected to the end of the grid. Therefore, weak grids with low short-circuit ratios are the primary form of wind power integration, and grid impedance is not negligible. Therefore, it is crucial to balance stability under both small and large disturbances and mitigate the risk of broadband oscillations and transient out-of-step faults in doubly-fed wind power systems. Summary of the Invention
[0005] In view of the above problems, the present invention provides a method and device for improving the stability of a doubly-fed wind turbine, so as to at least solve the problems existing in the related art.
[0006] In a first aspect, an embodiment of the present invention provides a method for improving the stability of a doubly-fed wind turbine, which is applied to a doubly-fed wind turbine grid-connected system, wherein the doubly-fed wind turbine in the doubly-fed wind turbine grid-connected system adopts a phase-locked loop design. The method for improving the stability of the doubly-fed wind turbine includes: The doubly-fed wind turbine grid-connected system is modeled under an ideal power grid to determine the closed-loop transfer function and closed-loop error function of the phase-locked loop. Calculating error responses of phase step and frequency step of the doubly-fed wind turbine grid-connected system under underdamping and overdamping conditions based on the closed-loop transfer function and the closed-loop error function; Obtaining the negative impact of preset phase-locked loop parameters on the stability of the doubly fed wind turbine grid-connected system under a low short-circuit ratio weak power grid; Based on the error response and negative impact, a signal processing unit is added to the doubly fed wind turbine grid-connected system under an ideal power grid, and filter parameters of the doubly fed wind turbine grid-connected system are set to stabilize the doubly fed wind turbine grid-connected system.
[0007] In some embodiments, the expressions of the closed-loop transfer function and the closed-loop error function include:
[0008]
[0009] in, is the cutoff frequency, is the damping ratio, and are the proportional and integral gains of the phase-locked loop respectively.
[0010] In some embodiments, the expressions of the error responses of the phase step and the frequency step of the doubly-fed wind turbine grid-connected system under underdamping conditions include:
[0011]
[0012] in, is the cutoff frequency, is the damping ratio.
[0013] In some embodiments, the expressions for the error responses of the phase step and the frequency step of the doubly-fed wind turbine grid-connected system under overdamping conditions include:
[0014]
[0015] in, is the cutoff frequency, is the damping ratio, P1 and P2 are the poles of the closed-loop error function, which is expressed as follows:
[0016] in, is the cutoff frequency, is the damping ratio, is the proportional gain of the phase-locked loop, is the integral gain of the phase-locked loop.
[0017] In some embodiments, the proportional gain of the phase-locked loop and the integral gain of the phase-locked loop satisfy the following relationship:
[0018] in, is the proportional gain of the phase-locked loop, is the integral gain of the phase-locked loop.
[0019] In some embodiments, the adding of a signal processing unit to the doubly-fed wind turbine grid-connected system under an ideal power grid based on the error response and negative impact includes: Based on the error response and negative impact, a feedforward path and a high-pass filter matrix are added to the doubly-fed wind turbine grid-connected system under an ideal power grid; or Based on the error response and negative impact, a virtual impedance is added to the doubly-fed wind turbine grid-connected system under an ideal power grid.
[0020] In some embodiments, the adding of a signal processing unit to the doubly-fed wind turbine grid-connected system under an ideal power grid based on the error response and negative impact further includes: Based on the error response and negative impact, a third-order high-pass filter is added to the doubly-fed wind turbine grid-connected system under an ideal power grid.
[0021] In some embodiments, the expression of the virtual impedance includes:
[0022] in, is the proportional gain of the phase-locked loop and is the integral gain of the phase-locked loop, is the proportional gain of the power loop, is the integral gain of the power loop, is the high-pass filter matrix.
[0023] In some embodiments, the high-pass filter matrix adopts a third-order Butterworth high-pass filter, and its expression includes:
[0024] in, is the cutoff frequency.
[0025] In a second aspect, an embodiment of the present invention provides a device for improving the stability of a doubly-fed wind turbine, which is applied to a doubly-fed wind turbine grid-connected system, wherein the doubly-fed wind turbine in the doubly-fed wind turbine grid-connected system adopts a phase-locked loop design, and the device includes: A modeling module is used to model the doubly-fed wind turbine grid-connected system under an ideal power grid to determine the closed-loop transfer function and closed-loop error function of the phase-locked loop; A calculation module, configured to calculate error responses of phase steps and frequency steps of the doubly-fed wind turbine grid-connected system under underdamping and overdamping conditions based on the closed-loop transfer function and the closed-loop error function; An acquisition module, configured to acquire the negative impact of preset phase-locked loop parameters on the stability of the doubly-fed wind turbine grid-connected system under a low short-circuit ratio weak power grid; A stabilization module is used to add a signal processing unit to the doubly fed wind turbine grid-connected system under an ideal power grid based on the error response and negative impact, and set the filter parameters of the doubly fed wind turbine grid-connected system to stabilize the doubly fed wind turbine grid-connected system.
[0026] A method and device for improving the stability of a doubly fed wind turbine provided by an embodiment of the present invention are applied to a doubly fed wind turbine grid-connected system, wherein the doubly fed wind turbine in the doubly fed wind turbine grid-connected system adopts a phase-locked loop design. In the method for improving the stability of the doubly fed wind turbine, the doubly fed wind turbine grid-connected system is modeled under an ideal power grid to determine the closed-loop transfer function and closed-loop error function of the phase-locked loop, and the error response of the phase step and frequency step of the doubly fed wind turbine grid-connected system under underdamping and overdamping conditions is calculated based on the closed-loop transfer function and the closed-loop error function; the negative impact of preset phase-locked loop parameters on the stability of the doubly fed wind turbine grid-connected system under a low short-circuit ratio weak power grid is obtained, and a signal processing unit is added to the doubly fed wind turbine grid-connected system under the ideal power grid based on the error response and the negative impact, and the filter parameters of the doubly fed wind turbine grid-connected system are set to stabilize the doubly fed wind turbine grid-connected system and take into account both small disturbance and large disturbance stability.
[0027] It should be understood that the content described in this section is not intended to identify the key or important features of the embodiments of the present invention, nor is it intended to limit the scope of the present invention. Other features of the present invention will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Hereinafter, the present invention will be described in more detail based on embodiments with reference to the accompanying drawings.
[0029] Figure 1 A schematic flow chart of a method for improving the stability of a doubly-fed wind turbine proposed in one embodiment of the present invention is shown; Figure 2 A simplified schematic diagram of a frequency band in a DFIG system of an exemplary virtual impedance proposed in one embodiment of the present invention is shown; Figure 3 FIG2 shows an exemplary virtual impedance equivalent schematic diagram proposed in an embodiment of the present invention; Figure 4 FIG2 shows a schematic diagram of an exemplary virtual impedance control in the dq domain proposed in one embodiment of the present invention; Figure 5 A schematic structural diagram of a doubly-fed wind turbine stability improvement device proposed in one embodiment of the present invention is shown. DETAILED DESCRIPTION
[0030] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.
[0031] In related technologies, with the continuous improvement of the penetration rate of new energy, a high proportion of renewable energy and a high proportion of power electronic equipment have significantly affected the steady-state and transient characteristics of the power system. Due to the inverse distribution of wind power resources and power loads, most wind turbines are connected to the end of the power grid. Therefore, low short-circuit ratio weak power grids have become the main form of wind power grid connection, and the grid impedance cannot be ignored.
[0032] To address the above issues, the applicant has proposed a method and apparatus for improving the stability of a doubly-fed wind turbine, as provided in the embodiments of the present invention. This method balances stability under both small and large disturbances, reducing the risk of broadband oscillations and transient out-of-step faults in the doubly-fed wind power system. The method is described in detail in subsequent embodiments.
[0033] The following describes the application scenarios of the method for improving the stability of a doubly-fed wind turbine provided by an embodiment of the present invention: See also Figure 1 , Figure 1 FIG. 1 is a flow chart of a method for improving the stability of a doubly-fed wind turbine provided in an embodiment of the present invention. In this embodiment, the method for improving the stability of a doubly-fed wind turbine can be applied to the following situations: Figure 5 In the doubly-fed wind turbine stability improvement device 300 shown in FIG. Figure 1 The process shown is described in detail and is applied to a doubly-fed wind turbine grid-connected system, wherein the doubly-fed wind turbine in the doubly-fed wind turbine grid-connected system adopts a phase-locked loop design. A method for improving the stability of the doubly-fed wind turbine may include S110 to S140.
[0034] S110: Model the doubly-fed wind turbine grid-connected system under an ideal power grid to determine the closed-loop transfer function and closed-loop error function of the phase-locked loop.
[0035] In some embodiments, the closed-loop transfer function of the phase-locked loop is and the closed-loop error function They can be expressed as:
[0036]
[0037] in, is the cutoff frequency, is the damping ratio, and are the proportional and integral gains of the phase-locked loop respectively.
[0038] Modeling studies have shown that the closed-loop transfer function has two poles at the origin, allowing the doubly-fed wind turbine grid-connected system to accurately track the phase signal of the ramp input. Furthermore, the phase-locked loop (PLL) exhibits low-pass filter properties, thus suppressing detection errors caused by noise and higher harmonics.
[0039] S120: Calculating error responses of a phase step and a frequency step of the doubly-fed wind turbine grid-connected system under underdamping and overdamping conditions based on the closed-loop transfer function and the closed-loop error function.
[0040] The expressions for the error responses of the phase step and frequency step of the doubly-fed wind turbine grid-connected system under underdamping conditions include:
[0041]
[0042] in, is the cutoff frequency, is the damping ratio.
[0043] The expressions for the error responses of the phase step and frequency step of the doubly-fed wind turbine grid-connected system under overdamping conditions include:
[0044]
[0045] in, is the cutoff frequency, is the damping ratio, P1 and P2 are the poles of the closed-loop error function, and its expression is:
[0046] in, is the cutoff frequency, is the damping ratio, is the proportional gain of the phase-locked loop, is the integral gain of the phase-locked loop.
[0047] Research in control theory has shown that pole location plays a decisive role in the response of a doubly-fed wind turbine grid-connected system. The larger the negative real part of the pole, the faster the transient response; the larger the imaginary part, the greater the system overshoot. For phase steps, overdamping results in faster system response. This is because the slow pole P2 is located near the origin and can be offset by the zero at the origin, making the fast pole P1 the dominant pole. For frequency steps, underdamping results in faster system response. This is because the lack of a zero at the origin prevents the slow pole P2 from being offset, making it the dominant pole. However, as the damping ratio decreases, the system overshoot increases.
[0048] Therefore, in this application, under an ideal power grid, the doubly fed wind turbine grid-connected system is designed to be critically damped to take into account both fast response speed and reasonable overshoot. At this time, the proportional gain and integral gain of the phase-locked loop satisfy the following relationship.
[0049]
[0050] in, is the proportional gain of the phase-locked loop, is the integral gain of the phase-locked loop.
[0051] S130: Obtaining the negative impact of preset phase-locked loop parameters on the stability of the doubly-fed wind turbine grid-connected system under a low short-circuit ratio weak power grid condition.
[0052] S140: Based on the error response and the negative impact, a signal processing unit is added to the doubly fed wind turbine grid-connected system under the ideal power grid, and filter parameters of the doubly fed wind turbine grid-connected system are set to stabilize the doubly fed wind turbine grid-connected system.
[0053] In the embodiment of the present application, a feedforward path and a high-pass filter matrix are added to the doubly-fed wind turbine grid-connected system under an ideal power grid based on the error response and negative impact.
[0054] Among them, see Figure 2 As shown, the present application considers the idea of improving stability by adding a feedforward path to offset the negative impact of the matrix.
[0055] Since the stator voltage It is the electrical component, while the stator voltage measured in reality is generally the control component. Therefore, it is necessary to introduce the conversion matrix between the stator voltage electrical component and the control component , as shown below:
[0056] in, is the open-loop transfer function of the phase-locked loop, is the stator voltage.
[0057] Considering that the fundamental frequency impedance of the DFIG system is closely related to the steady-state operating point, the introduced feedforward path is not expected to affect the 50Hz amplitude-frequency and phase-frequency characteristics. This application further optimizes it by adding a high-pass filter matrix. To facilitate the determination of the order, the feedforward point can be moved after the current controller matrix.
[0058] Therefore, see Figure 2 and Figure 3 , this application will Figure 2 Convert to Figure 3Specifically, by adding a feedforward path consisting of a phase compensation link and a filter, it can also be equivalent to a virtual impedance that can offset the negative impact of the rotor current Park transformation. The specific expression of the virtual impedance under positive sequence is as follows:
[0059] in, is the proportional gain of the phase-locked loop and is the integral gain of the phase-locked loop, is the proportional gain of the power loop, is the integral gain of the power loop, is the high-pass filter matrix.
[0060] In the embodiment of the present application, considering that the phase compensation link has three 50Hz poles, which will affect the impedance characteristics of the fundamental frequency, the present application improves it by introducing a third-order high-pass filter.
[0061] In some embodiments, the present application selects a third-order Butterworth high-pass filter, which should be designed to be as high as possible to minimize its impact on the impedance characteristics near the fundamental frequency.
[0062] The third-order Butterworth high-pass filter expression includes:
[0063] in, is the cutoff frequency.
[0064] In this application, it is considered that the phase compensation link is a low-pass link. This is because the phase-locked loop loses its effect at high frequencies, and the added phase compensation link also no longer has gain at high frequencies.
[0065] After the improved application is connected in series with a high-pass filter, the resulting virtual impedance exhibits a bandpass characteristic, meaning it only works in the frequency band where phase margin compensation is required. While the current tracking transfer function G remains unchanged after the virtual impedance is added, the impedance characteristics around the fundamental frequency will still change because the filter's cutoff frequency cannot be too large, which is equivalent to affecting the voltage perturbation transfer function in automatic control principles.
[0066] In this application, the above virtual impedance structure and parameter design are all in the phase sequence domain, but in a specific implementation, the virtual impedance proposed in this application should act on the dq domain. According to the conversion formula between the dq domain and the phase sequence domain, the virtual impedance control block diagram in the dq domain can be obtained. For details, see Figure 4 .
[0067] In summary, the present invention provides a method and device for improving the stability of a doubly fed wind turbine. Under an ideal power grid, the phase-locked loop closed-loop transfer function and closed-loop error function of the doubly fed wind turbine are designed. Based on the obtained phase-locked loop closed-loop transfer function and closed-loop error function, the error response of the phase step and frequency step under the underdamped and overdamped conditions of the system is obtained, and the influence of the phase-locked loop parameters on the system stability under the weak power grid is analyzed. In the design of the phase-locked loop of the doubly fed wind turbine under the ideal power grid, a feedforward path is added to offset the phase-locked loop. To eliminate the negative impact of the matrix, a third-order high-pass filter is introduced and the system filter parameters are designed to improve the stability of the system.
[0068] See also Figure 5 , Figure 5 This is a structural block diagram of an intelligent deduplication device for image data based on a digital camera provided by the present invention, which is applied to a mobile terminal connected to a digital camera, including: a modeling module 310, a calculation module 320, an acquisition module 330 and a stabilization module 340, wherein: A modeling module 310 is used to model the doubly-fed wind turbine grid-connected system under an ideal power grid to determine a closed-loop transfer function and a closed-loop error function of a phase-locked loop; A calculation module 320 is configured to calculate error responses of phase steps and frequency steps of the doubly-fed wind turbine grid-connected system under underdamping and overdamping conditions based on a closed-loop transfer function and a closed-loop error function; An acquisition module 330 is used to obtain the negative impact of preset phase-locked loop parameters on the stability of the doubly-fed wind turbine grid-connected system under a low short-circuit ratio weak power grid; The stabilization module 340 is used to add a signal processing unit to the doubly fed wind turbine grid-connected system under the ideal power grid based on the error response and negative impact, and set the filter parameters of the doubly fed wind turbine grid-connected system to stabilize the doubly fed wind turbine grid-connected system.
[0069] It should be noted that the device embodiment of the present invention corresponds to the aforementioned method embodiment. The specific principles in the device embodiment can be found in the contents of the aforementioned method embodiment, which will not be repeated here.
[0070] In several embodiments provided in this embodiment, the coupling between modules may be electrical, mechanical or other forms of coupling.
[0071] In addition, the functional modules in various embodiments of the present invention may be integrated into a single processing module, or each module may exist physically separately, or two or more modules may be integrated into a single module. The aforementioned integrated modules may be implemented in the form of hardware or software functional modules.
[0072] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not drive the essence of the corresponding technical solutions away from the spirit and scope of the technical solutions of the various embodiments of the present invention.
Claims
1. A method for improving the stability of a doubly-fed wind turbine, characterized in that: Applied to a doubly-fed wind turbine grid-connected system, wherein the doubly-fed wind turbine in the doubly-fed wind turbine grid-connected system adopts a phase-locked loop design, and the doubly-fed wind turbine stability improvement method includes: The doubly-fed wind turbine grid-connected system is modeled under an ideal power grid to determine the closed-loop transfer function and closed-loop error function of the phase-locked loop. Calculating error responses of phase step and frequency step of the doubly-fed wind turbine grid-connected system under underdamping and overdamping conditions based on the closed-loop transfer function and the closed-loop error function; Obtaining the negative impact of preset phase-locked loop parameters on the stability of the doubly fed wind turbine grid-connected system under a low short-circuit ratio weak power grid; Based on the error response and negative impact, a signal processing unit is added to the doubly fed wind turbine grid-connected system under an ideal power grid, and filter parameters of the doubly fed wind turbine grid-connected system are set to stabilize the doubly fed wind turbine grid-connected system.
2. The method for improving the stability of a doubly-fed wind turbine according to claim 1, characterized in that: The expressions of the closed-loop transfer function and the closed-loop error function include: in, is the cutoff frequency, is the damping ratio, and are the proportional and integral gains of the phase-locked loop respectively.
3. The method for improving the stability of a doubly-fed wind turbine according to claim 2, characterized in that: The expressions of the error responses of the phase step and frequency step of the doubly-fed wind turbine grid-connected system under underdamping conditions include: in, is the cutoff frequency, is the damping ratio.
4. The method for improving the stability of a doubly-fed wind turbine according to claim 2, characterized in that: The expressions of the error responses of the phase step and frequency step of the doubly-fed wind turbine grid-connected system under the overdamping condition include: in, is the cutoff frequency, is the damping ratio, P1 and P2 are the poles of the closed-loop error function, which is expressed as follows: in, is the cutoff frequency, is the damping ratio, is the proportional gain of the phase-locked loop, is the integral gain of the phase-locked loop.
5. The method for improving the stability of a doubly-fed wind turbine according to claim 5, characterized in that: The proportional gain of the phase-locked loop and the integral gain of the phase-locked loop satisfy the following relationship: in, is the proportional gain of the phase-locked loop, is the integral gain of the phase-locked loop.
6. The method for improving the stability of a doubly-fed wind turbine according to claim 1, characterized in that: The method of adding a signal processing unit to the doubly-fed wind turbine grid-connected system under an ideal power grid based on the error response and negative impact includes: Based on the error response and negative impact, a feedforward path and a high-pass filter matrix are added to the doubly-fed wind turbine grid-connected system under an ideal power grid; or Based on the error response and negative impact, a virtual impedance is added to the doubly-fed wind turbine grid-connected system under an ideal power grid.
7. The method for improving the stability of a doubly-fed wind turbine according to claim 1, characterized in that: The signal processing unit is added to the double-fed wind turbine grid-connected system under the ideal power grid based on the error response and negative impact, and further includes: Based on the error response and negative impact, a third-order high-pass filter is added to the doubly-fed wind turbine grid-connected system under an ideal power grid.
8. The method for improving the stability of a doubly-fed wind turbine according to claim 6, characterized in that: The expression of the virtual impedance includes: in, is the proportional gain of the phase-locked loop and is the integral gain of the phase-locked loop, is the proportional gain of the power loop, is the integral gain of the power loop, is the high-pass filter matrix.
9. The method for improving the stability of a doubly-fed wind turbine according to claim 8, characterized in that: The high-pass filter matrix adopts a third-order Butterworth high-pass filter, and its expression includes: in, is the cutoff frequency.
10. A device for improving the stability of a doubly-fed wind turbine, characterized in that: Applicable to a doubly-fed wind turbine grid-connected system, wherein the doubly-fed wind turbine in the doubly-fed wind turbine grid-connected system adopts a phase-locked loop design, and the device includes: A modeling module is used to model the doubly-fed wind turbine grid-connected system under an ideal power grid to determine the closed-loop transfer function and closed-loop error function of the phase-locked loop; A calculation module, configured to calculate error responses of phase steps and frequency steps of the doubly-fed wind turbine grid-connected system under underdamping and overdamping conditions based on the closed-loop transfer function and the closed-loop error function; An acquisition module, configured to acquire the negative impact of preset phase-locked loop parameters on the stability of the doubly-fed wind turbine grid-connected system under a low short-circuit ratio weak power grid; A stabilization module is used to add a signal processing unit to the doubly fed wind turbine grid-connected system under an ideal power grid based on the error response and negative impact, and set the filter parameters of the doubly fed wind turbine grid-connected system to stabilize the doubly fed wind turbine grid-connected system.