A wind farm oscillation suppression system and oscillation suppression method

Abstract

The present application relates to the technical field of oscillation suppression, and particularly to a wind farm oscillation suppression system and an oscillation suppression method. The output end of a PMSG wind turbine generator is connected with a grid-side converter and a step-up transformer, and is connected to a bus section with a voltage level of 35kV through the step-up transformer; a static var generator adopts a double closed-loop control structure; the bus section is stepped up to 220kV at the high-voltage side to be connected to a power grid; a wide-frequency oscillation damping controller is integrated in an inner-loop current control circuit and injects a compensation signal into a q-axis current reference value. The present application compresses a complex wind farm full-order model to a low-dimensional reduced-order model with about 65 orders. On the premise of completely retaining main dynamic characteristics such as a key oscillation mode at 20-30Hz, the model greatly reduces the calculation dimension and resource consumption, and embeds a wide-frequency oscillation damping controller with adjustable frequency response, so that the damping ratio of a target oscillation mode is increased from 0.02 to 0.19. The newly-added oscillation suppression function will not interfere with the basic power control of the wind turbine, and the low-frequency regulation of the wind turbine will not mis-trigger the intermediate-frequency oscillation.

Description

Technical Field

[0001] This invention relates to the field of oscillation suppression technology, and in particular to a wind farm oscillation suppression system and method. Background Technology

[0002] With the increasing penetration rate of wind power, wind power systems based on traditional control architectures are facing new stability challenges in actual grid-connected operation. Especially under specific operating conditions, when the number of wind turbines in operation in the wind farm is small, the active power output of the units is at a low level, or the SVG outputs a large amount of inductive reactive power, the system is prone to broadband oscillations in the range of 20Hz to 30Hz.

[0003] Studies have shown that the root cause of such oscillations lies in the complex negative damping coupling generated in the mid-frequency band between the rapid current inner loop dynamics of the SVG and the control dynamics of the grid-side converter of the wind turbine. This coupling makes the system prone to instability under disturbances, manifesting as periodic and severe fluctuations in the SVG output current and the wind farm output power. In severe cases, it can trigger the operation of protection devices, causing equipment to disconnect from the grid and threatening the operational safety of the entire wind farm.

[0004] Therefore, there is a need for a method that can effectively solve the problem of high-dimensional system modeling and analysis, and provide a wind farm oscillation suppression system and method that can accurately identify and actively suppress mid-frequency oscillations and is easy to deploy and implement on existing equipment, so as to fundamentally improve the grid-connected stable operation capability of PMSG wind farms containing SVG. Summary of the Invention

[0005] Therefore, the technical problem to be solved by this invention is that a complex negative damping coupling occurs in the mid-frequency band between the fast current inner loop dynamics of the SVG and the control dynamics of the grid-side converter of the wind turbine. This makes the system prone to instability under disturbances, resulting in periodic and severe fluctuations in the SVG output current and the wind farm output power. In severe cases, this can trigger the protection device to operate, causing the equipment to disconnect from the grid and threatening the operational safety of the entire wind farm.

[0006] The above-mentioned technical problems are solved by the following technical solution: This invention proposes a wind farm oscillation suppression system, which includes, The output of the PMSG wind turbine is connected in sequence to the grid-side converter and the step-up transformer, and then connected to the 35kV collector bus section through the step-up transformer. The AC side of the static var generator is connected in parallel to the end of the collector bus section, and the static var generator adopts a dual closed-loop control structure. The high-voltage side of the collector bus section is stepped up to 220kV to connect to the power grid; A wideband oscillation damping controller is integrated into the inner loop current control circuit of the static var generator, injecting a compensation signal into the q-axis current reference value of the static var generator.

[0007] In a preferred embodiment of the wind farm oscillation suppression system described in this invention: The control structure of the static var generator also includes an outer loop voltage controller, an inner loop dq current PI regulator, a phase-locked loop, and a feedback channel; The outer loop of the static var generator is a constant voltage control mode, and the inner loop is a current regulator in the dq coordinate system. The static var generator adopts a transfer function compensation structure with double zeros and double poles.

[0008] In a preferred embodiment of the wind farm oscillation suppression system described in this invention: The input signal of the wideband oscillation damping controller is at least one of the following: the bus voltage measurement signal at the grid connection point of the static var generator, the rate of change of active power, or the bus current signal. The input signal, after being bandpass filtered, is superimposed on the main path of the current inner loop controller of the static var generator to form a disturbance suppression channel; The operating frequency band of the wideband oscillation damping controller is set between 20Hz and 30Hz to suppress system oscillations within the frequency band.

[0009] An oscillation suppression method includes the aforementioned wind farm oscillation suppression system, and, Step S1: Establish a reduced-order model including the PMSG wind turbine, static var generator, and collector network; Step S2: Based on the reduced-order model, identify the low-damped oscillation modes in the 20Hz to 30Hz frequency band of the system; Step S3: Based on the identification results, the parameters of the wideband oscillation damping controller integrated in the static var generator control loop are tuned.

[0010] In a preferred embodiment of the oscillation suppression method of the present invention: In step S1, Linearized sub-models of the PMSG wind turbine, static var generator, and collector network are established respectively. The structural aggregation method is used to merge similar state variables in multiple PMSG wind turbine sub-models to form a centralized PMSG subsystem model; The centralized PMSG subsystem model, SVG device submodel, and collector network submodel are interconnected to construct a reduced-order model.

[0011] In a preferred embodiment of the oscillation suppression method of the present invention: In the structural aggregation method process, Linearize the converter control loop, motor equations, and voltage control loop of the PMSG wind turbine; State variables describing the same physical processes and control functions in multiple PMSG wind turbine units are merged into an equivalent lumped state variable.

[0012] In a preferred embodiment of the oscillation suppression method of the present invention: In step S2, Eigenvalue analysis is performed on the reduced-order model to extract all oscillation modes of the system. The degree of participation of each state variable in a specific mode is calculated, thereby determining the dominant state variable and dominant control loop of the low-damped oscillation mode in the 20Hz to 30Hz frequency band.

[0013] In a preferred embodiment of the oscillation suppression method of the present invention: In step S3, Tuning of the parameters in the transfer function of the wideband oscillation damping controller; The operating frequency band of the wideband oscillation damping controller is configured to be 20Hz to 30Hz, while the adjustment frequency band of the PMSG wind turbine controller is configured to be 5Hz to 15Hz, so as to achieve coordinated decoupling control of the two in the frequency domain.

[0014] The beneficial effects of this invention are as follows: it compresses a complex wind farm full-order model containing dozens of devices into a low-dimensional reduced-order model of approximately 65th order. While fully preserving key dynamic features such as the 20-30Hz critical oscillation mode, the model significantly reduces computational dimensionality and resource consumption. An adjustable-frequency broadband oscillation damping controller is embedded, increasing the damping ratio of the target oscillation mode from 0.02 to 0.19, and reducing the amplitude of SVG output power fluctuations by approximately 70%, achieving targeted management of specific mid-frequency oscillations. The newly added oscillation suppression function does not interfere with the basic power control of the wind turbine itself, and the low-frequency regulation of the wind turbine will not inadvertently trigger mid-frequency oscillations. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments of the present invention will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention.

[0016] Figure 1 A connection framework diagram of the wind farm oscillation suppression system in this invention is shown.

[0017] Figure 2 The diagram shows a spatial modeling block diagram of the reduced-order model of the wind farm oscillation suppression system in this invention.

[0018] Figure 3 A block diagram of the static var generator control structure of the wind farm oscillation suppression system in this invention is shown.

[0019] Figure 4 A block diagram of the phase-locked loop structure of the wind farm oscillation suppression system in this invention is shown.

[0020] Figure 5 A flowchart of the oscillation suppression method corresponding to the wind farm oscillation suppression system of the present invention is shown. Detailed Implementation

[0021] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0022] The terminology used in this invention refers to those general terms currently widely used in the art in consideration of the functionality of the invention; however, these terms may vary according to the intent of those skilled in the art, precedent, or new techniques. Furthermore, specific terms may be chosen independently, and in such cases, their detailed meanings will be described in the detailed description of the invention. Therefore, the terminology used in this specification should not be construed as simple names, but rather based on the meaning of the terms and the overall description of the invention.

[0023] Reference Figures 1-4 This embodiment provides a wind farm oscillation suppression system.

[0024] Multiple PMSG wind turbine units 1 constitute a power generation unit. The output of each PMSG wind turbine unit 1 is first connected to the grid-side converter GSC, and then connected to the power collection system inside the wind farm via a step-up transformer 2. In this embodiment, the power collection system adopts a 35kV power collection bus section 3. Multiple wind turbines and their corresponding step-up transformers 2 can be connected in parallel to the same 35kV power collection bus section 3.

[0025] To achieve dynamic reactive power support and voltage regulation, a static var generator (SVA) device 4 is connected in parallel at the end of the 35kV collector bus section 3. The AC side of the SVA device 4 is connected to the bus to filter harmonics and limit short-circuit current. The wind farm contains multiple 35kV collector bus sections 3, which are connected in parallel via a busbar. The collected electricity is stepped up to 220kV by the main transformer and finally connected to the regional power grid.

[0026] The static var generator device 4 adopts a dual closed-loop vector control structure, including an outer loop voltage controller 41, an inner loop dq current PI regulator 42, a phase-locked loop 43, and a feedback channel 44. In this embodiment, the outer loop voltage controller 41 is set to a constant AC voltage control mode, which is used to calculate the inner loop current reference value based on the deviation between the grid voltage command and the feedback value.

[0027] The inner-loop dq current PI regulator 42 operates in a synchronously rotating dq coordinate system determined by the phase-locked loop 43. It receives the current reference value from the outer loop and achieves rapid and accurate tracking of the reactive component of the d-axis current and the active component of the q-axis current through PI regulation. The feedback channel 44 can be used to acquire signals such as the output voltage and current of the SVG AC side for use in the static var generator device 4.

[0028] To specifically suppress mid-frequency oscillations in the 20Hz to 30Hz frequency band, this embodiment integrates a wideband oscillation damping controller 5 in the inner loop current control circuit of the reactive power generator device 4. The input signal of the wideband oscillation damping controller 5 can be selected as an electrical quantity that can effectively reflect the oscillation state of the system, such as at least one of the bus voltage measurement signal of the collector bus section 3, the active power change rate output by the reactive power generator device 4, or the bus current signal flowing through the connected reactor. The filtered signal is sent to the core compensator of the wideband oscillation damping controller 5.

[0029] The core of the wideband oscillation damping controller 5 is a compensator with frequency shaping function, and its transfer function adopts a double-zero, double-pole form: In the function, K is the gain coefficient, T1 to T4 are zero-pole constants, and the frequency parameters are set through modal sensitivity analysis to achieve a negative phase gain around 23Hz. By using appropriate parameters in the function, the wideband oscillation damping controller 5 can generate the required phase and amplitude response within the target operating frequency band of 20Hz to 30Hz. This allows the output compensation signal to accurately cancel the harmful coupling caused by the SVG and wind turbine in this frequency band, transforming the system behavior from positive feedback to damping enhancement.

[0030] By embedding a wideband oscillation damping controller 5 with a specific frequency response in the inner loop control of the reactive power generator device 4, the 20Hz to 30Hz mid-frequency oscillation mode that threatens the stability of the system can be directly and effectively suppressed.

[0031] As one embodiment provided, such as Figures 1-5 , The core of the method involved in this embodiment is to establish an accurate and efficient reduced-order system model, identify key oscillation modes, and design precise parameters for the wideband oscillation damping controller 5 accordingly, thereby effectively improving the system stability.

[0032] Step S1 involves establishing a reduced-order model of the system, creating linearized small-signal state-space models for each major component. A sub-model is established for PMSG wind turbine unit 1, including linearizing the key dynamic aspects of each turbine. The establishment of the PMSG wind turbine sub-model 1 requires linearizing the key dynamic components of each turbine. The acquisition of the static var generator (SVM) sub-model 4 is primarily achieved through linearizing the control system of SVM 4, encompassing the dynamic equations of the outer-loop voltage controller 41, the inner-loop dq current PI regulator 42, and the phase-locked loop 43. Furthermore, the process requires pre-embedding the transfer function structure of the wideband oscillation damping controller 5 into the q-axis current control path.

[0033] The establishment of the six sub-models of the collector network requires that grid-side components such as the 35kV collector bus section 3, the busbar and the main transformer be modeled as an equivalent coupled reactance network composed of resistors and inductors.

[0034] Next, structural aggregation is performed. Since the multiple PMSG wind turbine units 1 in the wind farm are highly similar in structure, parameters, and control strategies, this method uses structural aggregation to simplify the wind turbine model. Specifically, for all wind turbine sub-models established in step 1, the state variables describing the same physical processes and control functions are merged, and through equivalent transformation, the originally scattered multiple similar state variables are aggregated into one or a group of equivalent centralized state variables.

[0035] The aggregated centralized PMSG subsystem model, the complete reactive power generator four-sub-model, and the collector network six-sub-model are interconnected according to their electrical connections, ultimately forming a complete, low-dimensional system-level reduced-order model. This step significantly reduces the total order of the model from over 200 to approximately 65, greatly alleviating the computational burden while maintaining the accuracy of the main electromechanical oscillation modes.

[0036] The core process of step 2 is to identify low-damped oscillation modes. After obtaining a manageable reduced-order model in step 1, system stability mode analysis is required to identify the target oscillations that need to be suppressed.

[0037] Perform eigenvalue analysis on the reduced-order model obtained in step S1. Calculate all eigenvalues ​​of the system state matrix. Each complex eigenvalue λ = σ ± jω corresponds to an oscillation mode of the system, where the imaginary part ω represents the oscillation frequency, and the real part σ is related to the damping ratio ζ, expressed as ζ = -σ / |λ|. A negative real part, i.e., positive damping, indicates attenuation, and a positive real part, i.e., negative damping, indicates divergence.

[0038] Next, participation factor analysis and mode determination were performed. Among all modes, modes with frequencies in the range of 20Hz to 30Hz were selected. Then, for these modes in the target frequency band, the participation factors of each state variable were calculated.

[0039] The participation factor quantitatively characterizes the degree of "participation" or influence of a certain state variable on the dynamic behavior of a mode. Through analysis, it is possible to determine which state variables are involved. In this scheme, the q-axis current state of the static var generator 4 and the specific bus voltage state dominate the oscillation mode, thereby tracing back to its dominant control loop. This step clarifies the source and mechanism of the oscillation, providing direction for targeted control.

[0040] Step 3 involves controller parameter tuning and collaborative design. Based on the precise information identified in step S2, the wideband oscillation damping controller 5 is finalized and optimized at the system level.

[0041] First, the damping controller parameters are tuned. Based on the identified target oscillation mode, ensuring sufficient damping, the parameters in the transfer function of the broadband oscillation damping controller 5 are tuned. To ensure that the newly added damping controller does not interfere with the existing controller of the wind turbine and that each performs its own function, frequency band planning was carried out. The effective operating frequency band of the broadband oscillation damping controller 5 was strictly configured and optimized within 20Hz to 30Hz, so that it could focus on suppressing mid-frequency oscillations.

[0042] Meanwhile, the core power and voltage regulation bandwidth of the grid-side converter controller of PMSG wind turbine unit 1 is limited to a lower frequency band of 5Hz to 15Hz, mainly undertaking the tasks of power point tracking and low-frequency stability. This frequency domain collaborative decoupling control design, based on the difference in participation factors of the two controllers for different modes, effectively avoids conflicts between control loops and improves the robustness of the overall system.

[0043] Simulation results from a reduced-order model using full-modal simulation show that, under weakly damped conditions, the natural oscillation frequency is precisely concentrated around 23Hz. Therefore, locking the wideband oscillation damping controller 5 at 20-30Hz can cover this fault center. If the control frequency of the PMSG wind turbine 1 extends to 20Hz, frequency domain overlap interference will occur. Therefore, setting the frequency of the PMSG wind turbine 1 to 5-15Hz can create an isolation band between it and the wideband oscillation damping controller 5, avoiding mutual interference.

[0044] Finally, it should be noted that the methods and devices described in detail above are merely embodiments, and those skilled in the art can modify these embodiments in different ways as long as they do not depart from the scope of the present invention.

Claims

1. A wind farm oscillation suppression system, characterized in that: include, The output end of the PMSG wind turbine (1) is connected to the grid-side converter and the step-up transformer (2) in sequence, and is connected to the collector bus section (3) with a voltage level of 35kV through the step-up transformer (2). The AC side of the static var generator (4) is connected in parallel to the end of the collector bus section (3), and the static var generator (4) adopts a double closed-loop control structure. The high voltage side of the collector bus section (3) is stepped up to 220kV to connect to the power grid; The wideband oscillation damping controller (5) is integrated into the inner loop current control circuit of the static var generator (4) and injects a compensation signal into the q-axis current reference value of the static var generator (4).

2. The wind farm oscillation suppression system according to claim 1, characterized in that: The control structure of the static var generator (4) also includes an outer loop voltage controller (41), an inner loop dq current PI regulator (42), a phase-locked loop (43), and a feedback channel (44). The static var generator (4) has a constant voltage control mode in the outer loop and a current regulator in the dq coordinate system in the inner loop. The static var generator (4) adopts a transfer function compensation structure in the form of double zero and double pole.

3. The wind farm oscillation suppression system according to claim 1 or 2, characterized in that: The input signal of the wideband oscillation damping controller (5) is at least one of the following: the bus voltage measurement signal at the grid connection point of the static var generator (4), the rate of change of active power, or the bus current signal. The input signal, after being filtered by a bandpass filter, is superimposed on the main path of the current inner loop controller of the static var generator (4) to form a disturbance suppression channel; The operating frequency band of the wideband oscillation damping controller (5) is set to 20Hz to 30Hz to suppress system oscillations within the frequency band.

4. An oscillation suppression method, characterized in that: Including the wind farm oscillation suppression system as described in claim 3, and, Step S1: Establish a reduced-order model including PMSG wind turbine (1), static var generator (4) and collector network (6); Step S2: Based on the reduced-order model, identify the low-damped oscillation modes in the 20Hz to 30Hz frequency band of the system; Step S3: Based on the identification results, the parameters of the wideband oscillation damping controller (5) integrated in the control loop of the static var generator (4) are tuned.

5. The oscillation suppression method according to claim 4, characterized in that: In step S1, Linearized sub-models of PMSG wind turbine (1), static var generator (4) and collector network (6) are established respectively; The structural aggregation method is used to merge similar state variables in multiple PMSG wind turbine (1) sub-models to form a centralized PMSG subsystem model; The centralized PMSG subsystem model, the SVG device (4) submodel, and the collector network (6) submodel are interconnected to construct a reduced-order model.

6. The oscillation suppression method according to claim 5, characterized in that: In the structural aggregation method process, Linearize the converter control loop, motor equations and voltage control loop of the PMSG wind turbine (1); The state variables describing the same physical processes and control functions in multiple PMSG wind turbine units (1) are merged into an equivalent lumped state variable.

7. The oscillation suppression method according to claim 6, characterized in that: In step S2, Eigenvalue analysis is performed on the reduced-order model to extract all oscillation modes of the system. The degree of participation of each state variable in a specific mode is calculated, thereby determining the dominant state variable and dominant control loop of the low-damped oscillation mode in the 20Hz to 30Hz frequency band.

8. The oscillation suppression method according to claim 7, characterized in that: In step S3, The parameters in the transfer function of the wideband oscillation damping controller (5) are tuned; The operating frequency band of the wideband oscillation damping controller (5) is configured to be 20Hz to 30Hz, while the controller adjustment frequency band of the PMSG wind turbine (1) is configured to be 5Hz to 15Hz, so as to achieve coordinated decoupling control of the two in the frequency domain.

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