A method for analyzing wind farm induced subsynchronous oscillation and evolution law

Abstract

A wind farm induced sub-synchronous oscillation and evolution rule analysis method, comprising: according to the topology and physical parameters of the wind turbine, a single-machine multi-physical coupling model containing an aerodynamic system, a mechanical system, an electrical system and a control system is established, the propagation path and frequency coupling characteristics of the equivalent wind speed low-frequency oscillation caused by the wind shear effect and the tower shadow effect to the electric energy oscillation are revealed;According to the physical state and spatial layout among different wind turbines, a wind farm aggregation model is established;The multi-machine disturbance coupling modeling is completed by combining the single-machine model and the aggregation model, and the evolution rule of single-machine sub-synchronous oscillation to wind farm sub-synchronous oscillation and its time domain and frequency domain characteristics are obtained.The present application provides technical support for the identification and prevention and control of new energy grid oscillation type, and can be used to ensure the safe and stable operation of power grid.

Description

Technical Field

[0001] This invention relates to the field of wind power generation technology, and in particular to a method for analyzing the subsynchronous oscillations induced by wind farms and their evolution. Background Technology

[0002] Compared to traditional synchronous generator sets, wind turbines exhibit different dynamic response characteristics. Disturbances propagate and couple among multiple turbines, significantly impacting system operating characteristics and easily inducing novel power system stability problems such as subsynchronous oscillations. Therefore, conducting analysis on the subsynchronous oscillations and their evolution in wind farms, and clarifying their oscillation mechanisms, is of significant engineering importance for ensuring the safe and stable operation of power systems.

[0003] Regarding the oscillation problem of wind turbines, existing methods often focus on the interactive stability between wind turbines and the power grid based on impedance matching. However, due to the intermittent and fluctuating characteristics of wind energy, as well as the multiple effects of wind turbine tower shadows and wind shear, the primary energy of the wind power system, i.e., the equivalent wind energy, oscillates, thus affecting the operating characteristics of the wind power generation system and causing oscillations in the output power of the wind turbines. This oscillating power can be transmitted to the power grid, inducing power system oscillations and affecting its safe operation.

[0004] Existing methods primarily focus on the oscillation mechanisms, transmission characteristics, and impacts on power systems of individual wind turbines. However, at the site level, when a wind farm as a whole feeds power into the grid, the subsynchronous oscillation characteristics differ from those of a single turbine, leading to coupling and evolution among multiple turbines. This difference stems from factors such as the interactions between multiple turbines within the wind farm. Therefore, compared to a single-turbine perspective, analyzing the evolution of multi-turbine disturbances and the mechanisms of induced subsynchronous oscillations from the perspective of the entire wind farm is more aligned with engineering practice and has greater guiding significance for revealing the oscillation mechanisms of large-scale wind power grid-connected systems and developing effective suppression strategies.

[0005] It should be noted that the information disclosed in the background section above is only for understanding the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] The main objective of this invention is to overcome the deficiencies in the aforementioned background technology and provide a method for analyzing the subsynchronous oscillations induced by wind farms and their evolution.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for analyzing the subsynchronous oscillations induced by wind farms and their evolution, comprising the following steps: S1: Based on the topology and physical parameters of wind turbine units in a wind farm, a multi-physics coupling model of the wind turbine unit system is established. The model includes an aerodynamic system, a mechanical system, an electrical system, and a control system. It is used to reveal the subsynchronous oscillations induced by aerodynamic characteristics and to obtain the formation principle and propagation law characteristics of low-frequency disturbances from wind energy to electrical energy in a single unit system. Among them, considering the wind shear effect and the tower shadow effect, the equivalent wind speed at the input wind turbine blade is composed of the hub height wind speed, the wind shear effect equivalent wind speed, and the tower shadow effect equivalent wind speed. The equivalent wind speed oscillates with three times the blade rotation frequency as the fundamental frequency. The oscillation of the equivalent wind speed causes the wind power input to the wind turbine to generate subsynchronous oscillations at the same frequency. S2: Based on the physical state and interrelationships between different wind turbine units, establish a wind farm aggregation model that includes multiple wind turbine units; S3: Combining the multi-physics coupling model of the wind turbine system with the wind farm aggregation model, complete the disturbance coupling modeling between multiple wind turbines, determine the evolution law from wind turbine subsynchronous oscillation to wind farm subsynchronous oscillation, analyze the formation mechanism of wind farm subsynchronous oscillation, and obtain its time domain and frequency domain characteristics.

[0008] A computer program product includes a computer program that, when executed by a processor, implements the method for analyzing the subsynchronous oscillations induced by wind farms and their evolution.

[0009] This invention addresses the shortcomings of existing wind power subsynchronous oscillation analyses, which generally neglect aerodynamic-induced oscillations and are often limited to a single-unit perspective, lacking an understanding of the evolution patterns at the farm level. It proposes a method for analyzing wind farm-induced subsynchronous oscillations and their evolution. Based on the topology and parameters of the wind turbine, this method constructs a multi-physics coupled single-unit model encompassing aerodynamic, mechanical, electrical, and control systems. This reveals the complete propagation path of wind power oscillations towards mechanical power oscillations, electromagnetic power oscillations, and ultimately grid power oscillations, as well as the frequency coupling characteristics within the "wind-electricity" energy channel. This solves the problems of limited modeling dimensions and insufficient analytical accuracy in existing methods, significantly improving the completeness and reliability of wind turbine oscillation characteristic analysis. Furthermore, considering the differences in operating conditions and spatial layout among different wind turbines, a wind farm aggregation model is established. Through multi-turbine disturbance coupling modeling, the evolution pattern from single-unit subsynchronous oscillations to wind farm subsynchronous oscillations is revealed. In particular, when all turbines in a wind farm operate at the same speed and their blade angles are equidistantly distributed, only the components with harmonic orders that are integer multiples of the number of turbines are retained in the subsynchronous oscillation of the wind farm's output power. The remaining components cancel each other out, and the amplitude of the retained components is equal to the direct sum of the output amplitudes of each turbine. This pattern clearly depicts the process by which the weak oscillations of a single turbine (which have low amplitude and low frequency and are often overlooked in the past) evolve into non-negligible farm-level oscillations after being superimposed on the wind farm, providing a new technical approach for subsequent oscillation analysis and suppression. This invention not only makes up for the shortcomings of the single-turbine perspective in analyzing the characteristics of farm-level oscillations, but also effectively supplements the existing types of oscillations in the new energy power grid, providing strong technical support for risk prevention and control, safe operation, and safe and stable operation of the power grid in the context of wind farm subsynchronous oscillations.

[0010] Compared with the prior art, the innovative contributions and outstanding advantages of this invention are mainly reflected in the following aspects: 1. A method for analyzing the subsynchronous oscillations induced by wind farms and their evolution is proposed. The method considers the influence of oscillations induced by wind energy and the mechanical parts of wind turbines on wind farms, and analyzes the resulting subsynchronous oscillations in the power system. This method can provide reliable technical support for risk prevention and safe operation of subsynchronous oscillations in wind farms. 2. A wind turbine model with coupled aerodynamic, mechanical, electrical and control systems was constructed, describing the propagation path from wind power oscillation to grid-connected power oscillation. The impact of wind power oscillation and mechanical system coupling on grid performance was fully considered, solving the problems of single modeling dimension and insufficient analysis accuracy in existing technologies, and improving the completeness and reliability of wind turbine oscillation characteristic analysis. 3. Simultaneously considering the models of wind turbine units and wind farms, it can reveal the actual operating characteristics and interaction relationships under the coupling effect of multiple units, make up for the deficiency in the analysis of the oscillation characteristics of the site from the perspective of a single unit, and reflect the evolution law and propagation characteristics of the transformation from wind turbine-induced subsynchronous oscillation to wind farm subsynchronous oscillation.

[0011] Other beneficial effects of the embodiments of the present invention will be further described below. Attached Figure Description

[0012] Figure 1 This is a flowchart of the method for analyzing the subsynchronous oscillations induced by wind farms and their evolution in an embodiment of the present invention.

[0013] Figure 2 This is a schematic diagram of the input wind speed oscillation in an embodiment of the present invention.

[0014] Figure 3 This is a schematic diagram of the power oscillation propagation path according to an embodiment of the present invention.

[0015] Figure 4 This is a schematic diagram of the wind turbine model established in the embodiment of the present invention.

[0016] Figure 5 This is a transfer function block diagram of the power oscillation propagation characteristics of a wind turbine generator according to an embodiment of the present invention.

[0017] Figure 6 This is a Bode plot of the transfer function of the wind turbine power oscillation propagation characteristics according to an embodiment of the present invention.

[0018] Figure 7 This is a schematic diagram of a wind farm according to an embodiment of the present invention.

[0019] Figure 8 This is a schematic diagram of the operating area of ​​the wind turbine unit according to an embodiment of the present invention.

[0020] Figure 9 This is a schematic diagram of the wind farm output power waveform according to an embodiment of the present invention.

[0021] Figure 10 This is a schematic diagram of the wind farm output current waveform according to an embodiment of the present invention. Detailed Implementation

[0022] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention.

[0023] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0024] Traditional methods for analyzing subsynchronous oscillations in wind farms often focus on the interactive stability between wind turbines and the power grid based on impedance matching, and are mainly limited to the study of the oscillation mechanism and transmission characteristics of a single wind turbine. However, due to the intermittent and fluctuating nature of wind energy, coupled with the multiple influences of the tower shadow effect and wind shear effect of wind turbines, the primary energy of wind turbines, i.e., the equivalent wind energy, itself exhibits low-frequency oscillations. This oscillation power can propagate to the power grid through mechanical and electrical systems, inducing subsynchronous oscillations in the power system. Existing technologies generally neglect the oscillations induced by aerodynamic characteristics and fail to consider the coupling and evolution laws between multiple units from the perspective of the entire wind farm. This results in a lack of effective analytical methods for the evolution, propagation laws, and time-domain and frequency-domain characteristics of subsynchronous oscillations caused by aerodynamic characteristics and affected by the operating states (such as speed range and blade angle) of different wind turbines in the wind farm.

[0025] This invention aims to address the aforementioned shortcomings by proposing a method for analyzing the subsynchronous oscillations induced by wind farms and their evolution. Based on the topology and physical parameters of wind turbines, this method constructs a multi-physics coupled single-machine model encompassing aerodynamic, mechanical, electrical, and control systems. This model reveals the complete propagation path and frequency coupling characteristics from wind power oscillations to mechanical power oscillations, electromagnetic power oscillations, and finally grid power oscillations. Furthermore, based on the physical states and interrelationships among different wind turbines, a wind farm aggregation model is established. Through multi-machine disturbance coupling modeling, the evolution law from single-machine subsynchronous oscillations to wind farm subsynchronous oscillations is revealed. Thus, a model for the propagation and evolution of power subsynchronous oscillations in wind farms is constructed, solving the problems of unclear evolution laws and lack of analytical methods for the transformation from wind turbine subsynchronous oscillations to grid subsynchronous oscillations in wind farms. Specifically, when all turbines in a wind farm operate at the same speed and their blade angles are equidistantly distributed, only the components with harmonic orders that are integer multiples of the number of turbines are retained in the subsynchronous oscillations of the wind farm's output power. The remaining components cancel each other out, and the amplitude of the retained components is equal to the direct sum of the output amplitudes of each turbine. This pattern clearly depicts how the aerodynamic oscillations, which are originally low in amplitude and frequency and are often ignored in a single unit, evolve into a non-negligible site-level oscillation after being superimposed on the wind farm. This provides reliable technical support for risk prevention and control of subsynchronous oscillations in wind farms and for the safe and stable operation of the power grid. It also makes up for the lack of analysis of site-level oscillation characteristics from the perspective of a single unit.

[0026] For details, please refer to [link / reference]. Figures 1 to 10 This invention provides a method for analyzing the subsynchronous oscillations induced by wind farms and their evolution, comprising the following steps: Step S1: Based on the topology and physical parameters of the wind turbines in the wind farm, establish a multi-physics coupling model of the wind turbine system, such as... Figure 1 As shown; the model includes an aerodynamic system, a mechanical system, an electrical system, and a control system, used to reveal the subsynchronous oscillations induced by aerodynamic characteristics, and to obtain the formation principle and propagation law characteristics of low-frequency disturbances from wind energy to electrical energy in a single-machine system.

[0027] In some embodiments, such as Figure 2 As shown, the subsynchronous oscillation induced by aerodynamic characteristics in step S1 is generated in the following way: considering the wind shear effect and the tower shadow effect, the equivalent wind speed at the input wind turbine blade is composed of the hub height wind speed, the wind shear effect equivalent wind speed and the tower shadow effect equivalent wind speed superimposed. This equivalent wind speed oscillates with three times the blade rotation frequency as the fundamental frequency. According to the functional relationship between wind speed and wind power, the oscillation of the equivalent wind speed causes the wind power input to the wind turbine to generate subsynchronous oscillations at the same frequency, and the wind power is proportional to the cube of the equivalent wind speed.

[0028] In some embodiments, the propagation characteristics described in step S1 are quantitatively characterized by establishing the transfer function of the wind turbine (as an example, the power transfer path of the subsynchronous oscillation can be referred to). Figure 3 The transfer function takes the input wind power oscillation as the input and the output grid power oscillation as the output. This transfer function describes the propagation path of the subsynchronous oscillation between the mechanical system, the control system and the electrical system, as well as the coupling closed-loop relationship between the subsystems.

[0029] In some embodiments, see Figure 5 The structure of the transfer function includes: The mechanical system module includes a first adder, a first transfer function, a second adder, and a shaft transfer function connected in series. The first adder is used to subtract one internal shaft feedback signal from the input wind power oscillation, and the first transfer function is used to convert the output of the first adder into mechanical power oscillation. The second adder is used to subtract the electromagnetic power oscillation fed back from the electrical system from the mechanical power oscillation, and the shaft transfer function is used to convert the output of the second adder into rotational speed oscillation, thus exhibiting oscillation characteristics in the mechanical power. The control system module receives the speed oscillation, compares it with a reference speed, and then sequentially passes it through a speed control transfer function, a current control transfer function, and a modulation transfer function before outputting the oscillation to the electrical system. Figure 4 and Figure 5 ); The electrical system module receives mechanical power oscillations through the control system and converts them into stator power oscillations and rotor power oscillations respectively. The two signals are combined to output grid power oscillations. At the same time, the stator-side and rotor-side power oscillations are generated by electromagnetic power oscillations, which are fed back to the second adder of the mechanical system module to form a mechanical-electrical coupling closed loop. Figure 6 The Bode plot of the transfer function is further shown, demonstrating that the oscillation can propagate effectively within the main frequency range of the subsynchronous oscillation.

[0030] Step S2: Based on the physical states and interrelationships between different wind turbine units, establish a wind farm aggregation model containing multiple wind turbine units. As an example, Figure 7 This illustrates one method of constructing a wind farm.

[0031] In some embodiments, the establishment of the wind farm aggregation model in step S2 is based on the operating conditions and spatial layout relationships of the wind turbine units, wherein the operating conditions include the speed range of each unit (e.g., Figure 8 (as shown) and blade angle, the spatial layout relationship includes the interconnection of each unit through transmission lines; when each wind turbine has the same rotational speed, the power subsynchronous oscillation of each unit has the same oscillation frequency.

[0032] Step S3: Combining the multi-physics coupling model of the wind turbine system with the wind farm aggregation model, complete the disturbance coupling modeling between multiple wind turbines, reveal the evolution law from wind turbine subsynchronous oscillation to wind farm subsynchronous oscillation, analyze the formation mechanism of wind farm subsynchronous oscillation, and obtain its time domain and frequency domain characteristics.

[0033] In some embodiments, the disclosure of the evolution law in step S3 includes: when the rotational speed of each wind turbine in the wind farm is the same and the blade angles are equidistantly distributed, in the subsynchronous oscillation of the wind farm output power, only the oscillation component whose harmonic order is an integer multiple of the number of wind turbines is retained, the other harmonic components cancel each other out, and the amplitude of the retained oscillation component is equal to the direct sum of the output amplitudes of each wind turbine.

[0034] In some embodiments, the time-domain and frequency-domain features further include: the fundamental frequency of the subsynchronous oscillation in the wind farm output power increases with the increase of the number of wind turbine units participating in the oscillation; at the same time, an oscillation frequency component symmetrical about the power frequency is generated in the grid current, that is, the current oscillation frequency is equal to the difference between the power frequency and the power oscillation frequency and the sum of the power frequency and the power oscillation frequency.

[0035] In some embodiments, the method further includes a simulation verification step based on a wind farm aggregation model: in a wind farm with identical wind turbines, the relevant operating parameters of the turbines are set according to the established aggregation model, and the time-domain and frequency-domain waveforms of the wind farm output power and grid current are obtained through simulation to verify the propagation and evolution characteristics of subsynchronous oscillations in the wind farm. For details, please refer to... Figure 9 and Figure 10 The output power and grid current waveforms are shown as an example.

[0036] In some embodiments, the method is applicable to wind turbines with different topologies, including doubly fed wind turbines or permanent magnet direct-drive wind turbines; the output lines of each wind turbine in the wind farm are eventually converged and connected to the external power grid to realize the superposition and evolution of subsynchronous power oscillations.

[0037] This invention proposes a method for analyzing the subsynchronous oscillations induced by wind farms and their evolution. It incorporates low-frequency oscillations induced by aerodynamic characteristics (tower shadow effect, wind shear effect) into the analysis system of wind farm subsynchronous oscillations, constructing a multi-physics coupling and transfer model from wind energy to the power grid. Furthermore, it establishes a wind farm aggregation model, revealing the evolution law from single-unit subsynchronous oscillations to wind farm subsynchronous oscillations. When wind turbine speeds are the same and blade angles are equidistantly distributed, only oscillation components with harmonic orders that are integer multiples of the number of turbines are retained in the wind farm output power; the remaining components cancel each other out, and the amplitude of the retained component is the sum of the output amplitudes of all turbines. This method overcomes the limitations of traditional single-unit impedance matching analysis and provides a new technical path for the identification and prevention of oscillation types in new energy power grids.

[0038] The following further describes the implementation, working principle, and advantages of specific embodiments of the present invention.

[0039] A method for analyzing the subsynchronous oscillations induced by wind farms and their evolution laws includes the following main steps: First, based on the topology and parameters of the wind turbine, a single wind turbine model is established, incorporating an aerodynamic system, mechanical system, electrical system (including generators and power electronic converters), and control system. This model reveals the generation mechanism of subsynchronous oscillations under the coupling of the aerodynamic and mechanical systems, the "wind-electricity" propagation characteristics of wind energy—mechanical energy—electromagnetic energy—power electronic conversion—grid in the energy transmission channel, and the frequency coupling law of the grid. Second, based on the physical states of different wind turbines, a wind farm aggregation model is established. Third, combining the wind turbine model and the wind farm aggregation model, disturbance coupling modeling among multiple wind turbines is completed, revealing the evolution law from wind turbine subsynchronous oscillations to wind farm subsynchronous oscillations, analyzing the formation mechanism of wind farm subsynchronous oscillations, and obtaining its time-domain and frequency-domain characteristics.

[0040] like Figure 1 As shown, the specific process of analyzing the subsynchronous oscillations induced by wind farms and their evolution includes the following steps: Step S1: Based on the topology and physical parameters of the wind turbine units in the wind farm, establish a multi-physics coupling model of the wind turbine unit system, reveal the subsynchronous oscillation induced by aerodynamic characteristics, and obtain the formation principle and propagation law characteristics of low-frequency disturbances from wind energy to electrical energy in a single unit system. Step S2: Based on the physical state and interrelationships between different wind turbine units, establish a wind farm aggregation model that includes multiple wind turbine units; Step S3: Combining the wind farm model and the multi-machine disturbance coupling model, reveal the evolution law of the wind farm from single-machine subsynchronous oscillation to wind farm subsynchronous oscillation and the time-domain and frequency-domain characteristics of this subsynchronous oscillation.

[0041] In step S1, such as Figure 2 As shown, when the external wind speed remains constant or fluctuates at low frequencies, aerodynamic characteristics indicate that, influenced by wind shear and tower shadow effects, the wind speed input to the wind turbine blades will oscillate with a fundamental frequency of three times the blade rotation frequency (3-period, 3p). This manifests as a subsynchronous oscillation induced by aerodynamic characteristics, expressed as follows: in, The equivalent wind speed that actually blows through the wind turbine blades. Wind speed at wheel hub height The equivalent wind speed due to wind shear effect. The equivalent wind speed for the tower shadow effect.

[0042] Based on the relationship between wind speed and wind energy power Subsynchronous oscillations are reflected in the wind power input to the wind turbine at the same frequency. That is, the oscillation of the input wind speed causes oscillations in the input mechanical power. This oscillation has a fundamental frequency of 3p and is accompanied by multiple harmonic components, belonging to a type of subsynchronous oscillation caused by forced oscillation. In the physical structure of wind turbine units, such as... Figure 3 As shown, the wind power oscillation of the input system In the mechanical system of a wind turbine, this is converted into mechanical power oscillation. In the electrical system, this is successively converted into electromagnetic power oscillation. With stator power oscillation Rotor power oscillation Ultimately, this merges into an output power oscillation. And it spreads to the external power grid.

[0043] Taking a doubly-fed induction generator (DFIG) as an example, when power oscillation occurs, the 3p frequency, which serves as the fundamental frequency, can reach 1.2 Hz, accompanied by multiple harmonic components, among which the 3p frequency is the most significant. n The frequency of the secondary harmonic is 3. np, i.e., 1.2 n Hz.

[0044] To quantify the characteristics of power oscillation propagation in wind turbine generators, this invention establishes a model of a doubly-fed induction generator (DFIG) wind turbine generator, comprising four parts: aerodynamic system, mechanical system, electrical system (including generator and power electronic converter, etc.), and control system. Figure 4 As shown.

[0045] Based on the actual physical parameters and control parameters of the wind turbine, combined with Figure 4 The model can be used to establish the transfer function control block diagram of the wind turbine in the power oscillation propagation, such as Figure 5 As shown, the power oscillation propagation characteristics can be expressed as follows: in, Transfer function for wind turbine model. Figure 5 The specific structure of this transfer function is shown. Its input is wind power oscillation, and its output is output power oscillation. This transfer function demonstrates the transmission path characteristics of power oscillations induced by aerodynamic properties within the mechanical-electromagnetic-power electronic-grid system.

[0046] Bode plot of transfer function as follows Figure 6 As shown, the amplitude-frequency curve approaches 0dB in the low-frequency range of no more than 10Hz, which means that within the main frequency range where the power subsynchronous oscillation occurs, the subsynchronous oscillation can be effectively propagated into the external power grid.

[0047] In step S2, the wind farm contains multiple wind turbines, which are interconnected via transmission lines to transmit wind energy to the power system. The specific construction method of the wind farm is as follows: Figure 7 As shown.

[0048] The magnitude of the fundamental frequency of the subsynchronous power oscillation, i.e., the 3p frequency, is directly related to the turbine's rotational speed. The operating range of the wind turbine is as follows: Figure 8 As shown, when the parameters of each unit are the same, the different wind turbines in the wind farm all have the same rotational speed, and therefore the power output of each unit has the same subsynchronous oscillation frequency. A wind farm aggregation model can be established under these conditions, containing... m In the subsynchronous oscillation of power output from the wind farm to the power grid by the typhoon turbine generator, the first n The expression for the second harmonic is: in, The blade rotation frequency, For the first i The blade angle of a typhoon turbine. For the power oscillation propagation characteristics in the firstn The initial phase angle of the subharmonic components.

[0049] Under this model, if the blade angles of each wind turbine are equidistantly distributed, then the expression for the subsynchronous oscillation of wind farm power is: The above formula shows that when the harmonic order of the subsynchronous power oscillation is an integer multiple of the number of wind turbine units, the oscillation amplitude of the harmonic component in the output power of the wind farm is equal to the direct sum of the output amplitudes of each wind turbine unit; conversely, when the harmonic order of the subsynchronous power oscillation is not an integer multiple of the number of wind turbine units, they cancel each other out, and the output power of the wind farm does not include the oscillation component.

[0050] In step S3, when power oscillations occur in a wind farm containing four identical wind turbines, simulations are performed on the PLECS platform according to the established model, where the 3p frequency of the oscillation is 1.2Hz. The time-domain and frequency-domain waveforms of the output power are as follows: Figure 9 As shown in the diagram, in this doubly-fed induction generator (DFIG) wind turbine, the fundamental frequency of the single-unit power oscillation is 1.2 Hz, while the fundamental frequency of the wind farm's output power oscillation is 4.8 Hz. This means that only subsynchronous oscillations with harmonic orders that are integer multiples of the number of wind turbine units appear in the output power spectrum, revealing the propagation and evolution characteristics of subsynchronous oscillations in the wind farm. If more turbine units participate in the oscillation, the fundamental frequency of the wind farm's output power oscillation will be even higher. For example, when 20 turbine units oscillate simultaneously, the fundamental frequency of the wind farm's oscillation will reach 24 Hz.

[0051] When subsynchronous power oscillations occur, the grid current will also oscillate. Taking the A-phase grid current as an example, the expression for its oscillation component is: in, This is the secondary synchronous oscillation frequency in the power range. This represents the current oscillation amplitude of the corresponding component.

[0052] When there are 4 wind turbines in a wind farm, the time-domain and frequency-domain waveforms of the grid current are as follows: Figure 10 As shown, compared with the oscillation in the output power waveform, the oscillation in the grid current has a symmetrical characteristic about the power frequency of 50 Hz. Taking the fundamental frequencies of 4.8 Hz and 24 Hz in the power oscillation as examples, the corresponding oscillation frequencies in the current are 50 ± 4.8 Hz and 50 ± 24 Hz, demonstrating the evolution law and frequency coupling characteristics of the subsynchronous oscillation of the wind turbine to the subsynchronous oscillation of the wind farm.

[0053] The present invention provides a novel subsynchronous oscillation mode for wind farms, which is used to analyze the subsynchronous oscillations induced by wind farms and their evolution. This provides technical support for the identification and control of oscillation types in new energy power grids and can be used to ensure the safe and stable operation of the power grid.

[0054] Alternative embodiments The wind turbine topologies used differ (e.g., doubly-fed induction generators are replaced with permanent magnet turbines); the connection methods of different wind turbines in the wind farm also differ. In all different wind turbine topologies, the wind energy input is received by a blade mechanism containing blades, thus allowing the establishment of the wind turbine model in this invention. This means that subsynchronous oscillations caused by aerodynamic characteristics will occur in the wind turbine. Furthermore, different wind farms may have different wiring methods, but as long as the lines of different wind turbines are ultimately converged and connected to the external power grid, the power subsynchronous oscillation superposition process in this invention can be achieved.

[0055] In summary, this invention, by constructing a multi-physics coupled model of wind turbines encompassing aerodynamic, mechanical, electrical, and control systems, reveals the complete propagation path and frequency coupling characteristics of equivalent wind speed low-frequency oscillations towards wind power oscillations, mechanical power oscillations, electromagnetic power oscillations, and ultimately grid power oscillations. Furthermore, based on the operating conditions and spatial layout of the wind turbines, a wind farm aggregation model is established. Through multi-turbine disturbance coupling modeling, the evolution law from single-turbine subsynchronous oscillations to wind farm subsynchronous oscillations is obtained. Specifically, when all turbines in the wind farm operate at the same speed and their blade angles are equidistantly distributed, only oscillation components with harmonic orders that are integer multiples of the number of turbines are retained in the wind farm's output power. The remaining components cancel each other out, and the amplitude of the retained components is the sum of the output amplitudes of all turbines. Simultaneously, the fundamental frequency of the output power oscillation increases with the number of participating turbines, while the grid current generates an oscillation frequency component symmetrical about the power frequency. This invention breaks through the limitations of traditional single-unit impedance matching analysis and solves the shortcomings of existing technologies that ignore aerodynamic oscillations and the evolution law at the station level. It provides a new technical path and reliable support for risk prevention and control, safe operation of wind farm subsynchronous oscillations, and identification and suppression of oscillation types in new energy power grids.

[0056] This invention also provides a storage medium for storing a computer program, which, when executed, performs at least the methods described above.

[0057] This invention also provides a control device, including a processor and a storage medium for storing a computer program; wherein the processor executes the computer program by performing at least the method described above.

[0058] This invention also provides a processor that executes a computer program, at least performing the methods described above.

[0059] The storage medium can be implemented by any type of non-volatile storage device, or a combination thereof. The non-volatile memory can be read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic random access memory (FRAM), flash memory, magnetic surface memory, optical disc or CD-ROM; magnetic surface memory can be disk storage or magnetic tape storage. The storage media described in the embodiments of this invention are intended to include, but are not limited to, these and any other suitable types of memory.

[0060] In the several embodiments provided by this invention, it should be understood that the disclosed systems and methods can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods, such as: multiple units or components can be combined, or integrated into another system, or some features can be ignored or not executed. In addition, the coupling or direct coupling or communication connection between the various components shown or discussed can be through some interfaces, and the indirect coupling or communication connection between devices or units can be electrical, mechanical, or other forms.

[0061] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the units may be selected to achieve the purpose of this embodiment according to actual needs.

[0062] In addition, in the various embodiments of the present invention, each functional unit can be integrated into one processing unit, or each unit can be a separate unit, or two or more units can be integrated into one unit; the integrated unit can be implemented in hardware or in the form of hardware plus software functional units.

[0063] Those skilled in the art will understand that all or part of the steps of the above method embodiments can be implemented by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When the program is executed, it performs the steps of the above method embodiments. The aforementioned storage medium includes various media capable of storing program code, such as mobile storage devices, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0064] Alternatively, if the integrated units of this invention are implemented as software functional modules and sold or used as independent products, they can also be stored in a computer-readable storage medium. Based on this understanding, the technical solutions of the embodiments of this invention, or the parts that contribute to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as mobile storage devices, ROM, RAM, magnetic disks, or optical disks.

[0065] The methods disclosed in the several method embodiments provided by this invention can be arbitrarily combined without conflict to obtain new method embodiments.

[0066] The features disclosed in the several product embodiments provided by this invention can be arbitrarily combined without conflict to obtain new product embodiments.

[0067] The features disclosed in the several method or device embodiments provided by the present invention can be arbitrarily combined without conflict to obtain new method or device embodiments.

[0068] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various equivalent substitutions or obvious modifications can be made without departing from the concept of the present invention, and all such modifications, achieving the same performance or application, should be considered within the scope of protection of the present invention.

Claims

1. A method for analyzing the subsynchronous oscillations induced by wind farms and their evolution, characterized in that, Includes the following steps: S1: Based on the topology and physical parameters of wind turbine units in a wind farm, a multi-physics coupling model of the wind turbine unit system is established. The model includes an aerodynamic system, a mechanical system, an electrical system, and a control system. It is used to reveal the subsynchronous oscillations induced by aerodynamic characteristics and to obtain the formation principle and propagation law characteristics of low-frequency disturbances from wind energy to electrical energy in a single unit system. Among them, considering the wind shear effect and the tower shadow effect, the equivalent wind speed at the input wind turbine blade is composed of the hub height wind speed, the wind shear effect equivalent wind speed, and the tower shadow effect equivalent wind speed. The equivalent wind speed oscillates with three times the blade rotation frequency as the fundamental frequency. The oscillation of the equivalent wind speed causes the wind power input to the wind turbine to generate subsynchronous oscillations at the same frequency. The propagation law characteristics described in step S1 are quantitatively characterized by establishing a transfer function for the wind turbine: the input wind power oscillation is used as the input of the transfer function, and the output grid power oscillation is used as the output of the transfer function. This transfer function describes the propagation path of the subsynchronous oscillation between the mechanical system, the control system and the electrical system, as well as the coupling closed-loop relationship between each subsystem. S2: Based on the physical state and interrelationships between different wind turbine units, establish a wind farm aggregation model that includes multiple wind turbine units; S3: Combining the multi-physics coupling model of the wind turbine system with the wind farm aggregation model, complete the disturbance coupling modeling between multiple wind turbines, determine the evolution law from wind turbine subsynchronous oscillation to wind farm subsynchronous oscillation, analyze the formation mechanism of wind farm subsynchronous oscillation, and obtain its time domain and frequency domain characteristics.

2. The method for analyzing the subsynchronous oscillations induced by wind farms and their evolution as described in claim 1, characterized in that, In step S1, the wind power is proportional to the cube of the equivalent wind speed.

3. The method for analyzing the subsynchronous oscillations induced by wind farms and their evolution as described in claim 1, characterized in that, The structure of the transfer function includes: The mechanical system module includes a first adder, a first transfer function, a second adder, and a shaft transfer function connected in series. The first adder is used to subtract one internal shaft feedback signal from the input wind power oscillation, and the first transfer function is used to convert the output of the first adder into mechanical power oscillation. The second adder is used to subtract the electromagnetic power oscillation fed back from the electrical system from the mechanical power oscillation, and the shaft transfer function is used to convert the output of the second adder into rotational speed oscillation, thus exhibiting oscillation characteristics in the mechanical power. The control system module receives the speed oscillation, compares it with a reference speed, and then outputs the oscillation to the electrical system via a speed control transfer function, a current control transfer function, and a modulation transfer function. The electrical system module receives mechanical power oscillations through the control system and converts them into stator power oscillations and rotor power oscillations respectively. The two signals are combined to output grid power oscillations. At the same time, the stator-side and rotor-side power oscillations are generated by electromagnetic power oscillations, which are fed back to the second adder of the mechanical system module to form a mechanical-electrical coupling closed loop.

4. The method for analyzing the subsynchronous oscillations induced by wind farms and their evolution as described in claim 1, characterized in that, The establishment of the wind farm aggregation model in step S2 is based on the operating conditions and spatial layout relationship of the wind turbine units. The operating conditions include the speed range and blade angle of each unit, and the spatial layout relationship includes the interconnection of each unit through transmission lines. When each wind turbine unit has the same speed, the power subsynchronous oscillation of each unit has the same oscillation frequency.

5. The method for analyzing the subsynchronous oscillations induced by wind farms and their evolution as described in claim 1, characterized in that, The evolution law described in step S3 includes: when the rotational speed of each wind turbine in the wind farm is the same and the blade angles are equidistantly distributed, in the subsynchronous oscillation of the wind farm's output power, only the oscillation component whose harmonic order is an integer multiple of the number of wind turbines is retained, the other harmonic components cancel each other out, and the amplitude of the retained oscillation component is equal to the direct sum of the output amplitudes of each wind turbine.

6. The method for analyzing the subsynchronous oscillations induced by wind farms and their evolution as described in claim 5, characterized in that, The time-domain and frequency-domain characteristics also include: the fundamental frequency of the subsynchronous oscillation in the wind farm output power increases with the increase of the number of wind turbine units participating in the oscillation; at the same time, the grid current generates an oscillation frequency component symmetrical about the power frequency, that is, the current oscillation frequency is equal to the difference between the power frequency and the power oscillation frequency and the sum of the power frequency and the power oscillation frequency.

7. The method for analyzing the subsynchronous oscillations induced by wind farms and their evolution as described in claim 1, characterized in that, The method also includes a simulation verification step based on a wind farm aggregation model: in a wind farm with the same wind turbine units, the relevant parameters of the unit operation are set according to the established aggregation model, and the time-domain waveforms and frequency-domain waveforms of the wind farm output power and grid current are obtained through simulation, thereby verifying the propagation and evolution characteristics of subsynchronous oscillations in the wind farm.

8. The method for analyzing the subsynchronous oscillations induced by wind farms and their evolution as described in claim 1, characterized in that, The method is used for wind turbines with different topologies, including doubly fed wind turbines or permanent magnet direct-drive wind turbines; the output lines of each wind turbine in the wind farm are eventually converged and connected to the external power grid to realize the superposition and evolution of subsynchronous power oscillations.

9. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by the processor, it implements the method for analyzing the subsynchronous oscillations induced by wind farms and their evolution as described in any one of claims 1 to 8.

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