Method and System for Adding Resistance to the Drive Train of a Grid-Forming Doubly Fed Wind Turbine Based on Phase Angle Feedforward

Abstract

The present invention proposes a method and system for adding resistance to the drive train of a grid-forming doubly-fed wind turbine based on phase angle feedforward, including: obtaining the active power of the grid-forming doubly-fed wind turbine; after subtracting the obtained active power of the grid-forming doubly-fed wind turbine from the active power reference value, inputting it into a PI controller to obtain an output signal; adding the output signal to the reference value of the frequency in the virtual synchronous coordinate system to obtain the frequency in the virtual synchronous coordinate system; integrating the frequency in the virtual synchronous coordinate system to obtain an output value; multiplying the active power reference value of the grid-forming doubly-fed wind turbine by the control gain of the phase angle feedforward control to obtain a product result; adding the product result to the output value to obtain the angle in the virtual synchronous coordinate system, and obtaining the control quantity of the generator output voltage phase based on this angle.

Description

Technical Field

[0001] The present invention belongs to the technical field of doubly-fed wind turbine control, and particularly relates to a method and system for adding resistance to the drive train of a grid-forming doubly-fed wind turbine based on phase angle feedforward. Background Art

[0002] The statements in this section merely provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] Against the backdrop of the increasingly serious global energy shortage and environmental problems, wind power generation, as a clean and renewable energy form, has gradually become an important part of modern power systems. Doubly-fed induction generator sets occupy an important position in the global wind power generation market due to their relatively low energy conversion costs and high power generation efficiency, and are widely used in wind power generation systems.

[0004] A doubly-fed wind turbine unit is a complex system integrating pneumatic, mechanical, and electrical subsystems. Ensuring the electrical and mechanical safety of the doubly-fed wind turbine unit is crucial, which can not only guarantee the stable operation of the system and the long-term reliability of the equipment, but also improve power generation efficiency, reduce downtime and maintenance costs, while meeting safety and environmental requirements.

[0005] Grid-forming doubly-fed wind turbine units are a technology widely adopted in the current wind power industry. Currently, a large number of wind turbine units use a droop control strategy to enable the units to provide support for grid voltage and frequency during grid connection and achieve grid-forming control. At the same time, during the operation of the units, the torque acting on the gearbox will fluctuate greatly due to insufficient drive train damping, damaging the gearbox and affecting system safety. Therefore, virtual damping control is mostly used during the operation of wind turbine units to increase the drive train damping by simulating the effect of physical damping and ensure the safe operation of the units.

[0006] However, when the unit is connected to a weak grid, the active power response of a grid-forming doubly-fed wind turbine unit using droop control will exhibit a significant delay, resulting in a significant weakening of the virtual damping control effect and making it difficult to produce the same control effect as when applied to a grid-following wind turbine unit. At the same time, there is a coupling between the active power response and the grid-forming ability of a doubly-fed wind turbine unit, and existing controls are difficult to optimize both the active power response speed and the grid-forming ability under weak grid conditions. Summary of the Invention

[0007] To overcome the deficiencies of the above-mentioned prior art, the present invention provides a method for adding resistance to the drive train of a grid-forming doubly-fed wind turbine based on phase angle feedforward, which effectively reduces the delay of the active power response, improves the virtual damping control effect under weak grid conditions, and does not affect the grid-forming ability of the doubly-fed wind turbine unit.

[0008] To achieve the above object, one or more embodiments of the present invention provide the following technical solutions:

[0009] In a first aspect, a method for adding resistance to the drive train of a grid-forming doubly-fed wind turbine based on phase angle feedforward is disclosed, including:

[0010] Obtain the active power of the grid-forming doubly-fed wind turbine;

[0011] After subtracting the obtained active power of the grid-forming doubly-fed wind turbine from the active power reference value, input it into a PI controller to obtain an output signal;

[0012] Add the output signal to the reference value of the virtual synchronous coordinate system frequency to obtain the frequency of the virtual synchronous coordinate system;

[0013] Integrate the frequency of the virtual synchronous coordinate system to obtain an output value;

[0014] Multiply the active power reference value of the grid-forming doubly-fed wind turbine by the control gain of the phase angle feedforward control to obtain a product result;

[0015] Add the product result to the output value to obtain the angle of the virtual synchronous coordinate system, and based on this angle, obtain the control quantity of the generator output voltage phase;

[0016] Based on this control quantity, obtain the PWM modulation signal of the wind turbine converter, and use the PWM modulation signal to control the switching tubes of the converter of the wind turbine, and finally realize the control of the wind power generation unit to add resistance to the drive train.

[0017] As a further technical solution, the angle of the virtual synchronous coordinate system can be expressed as:

[0018]

[0019] where K PFF is the control gain of the phase angle feedforward control, f GFM is the frequency of the virtual synchronous coordinate system, and θ U is the phase of the output voltage of the wind turbine.

[0020] As a further technical solution, the transfer function of the method is:

[0021]

[0022] where G(s) is the forward transfer function of the active power control block diagram for phase adjustment ( Figure 1 ), and H(s) is the backward transfer function of the active power control block diagram for phase adjustment ( Figure 1 ).

[0023] In a second aspect, a system for adding resistance to the drive train of a grid-forming doubly-fed wind turbine based on phase angle feedforward is disclosed, including:

[0024] The active power acquisition module is configured to: acquire the active power of the grid-forming doubly-fed wind turbine;

[0025] The controller processing module is configured to: after subtracting the acquired active power of the grid-forming doubly-fed wind turbine from the active power reference value, input it into a PI controller to obtain an output signal;

[0026] Adding the output signal to the reference value of the virtual synchronous coordinate system frequency to obtain the frequency of the virtual synchronous coordinate system;

[0027] Integrating the frequency of the virtual synchronous coordinate system to obtain an output value;

[0028] Multiplying the active power reference value of the grid-forming doubly-fed wind turbine by the control gain of the phase angle feedforward control to obtain a product result;

[0029] Adding the product result to the output value to obtain the angle of the virtual synchronous coordinate system, and obtaining the control amount of the generator output voltage phase based on this angle;

[0030] The control module is configured to: based on this control amount, obtain the PWM modulation signal of the wind turbine converter, and use the PWM modulation signal to realize the control of the switching tubes of the converter of the wind turbine, and finally realize the control of the wind power generation set to complete the addition of resistance to the drive chain.

[0031] The above one or more technical solutions have the following beneficial effects:

[0032] The technical solution of the present invention directly feeds forward the active power reference value of the grid-forming doubly-fed wind turbine into the phase angle, avoiding the phase adjustment process dominated by the integral component. It speeds up the active response speed.

[0033] The overall controller of the technical solution of the present invention adopts an asymmetric control structure, breaking the coupling between the active power response and the grid-forming ability. On the basis of not affecting the grid-forming ability of the wind turbine, it effectively reduces the active power response delay and improves the virtual damping control effect under weak grid conditions.

[0034] The advantages of the additional aspects of the present invention will be partially given in the following description, partially will become obvious from the following description, or will be understood through the practice of the present invention. Description of the Drawings

[0035] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0036] Figure 1 Schematic diagram of the characteristic values corresponding to the characteristic equations under different grid strengths;

[0037] Figure 2 is the traditional control structure block diagram;

[0038] Figure 3 is the control structure block diagram proposed in the embodiment of the present invention;

[0039] Figure 4 is the corresponding eigenvalue diagram of the characteristic equation under different grid strengths after the phase angle feedforward control is adopted in the embodiment of the present invention;

[0040] Figure 5 is the specific implementation control block diagram of the traditional control scheme;

[0041] Figure 6 is the specific implementation control block diagram of the control scheme proposed in the embodiment of the present invention;

[0042] Figure 7 is the schematic diagram of the simulation conditions of Case 1;

[0043] Figure 8 is the schematic diagram of the grid-forming ability analysis; (a) Schematic diagram of the grid-forming ability analysis of the traditional control structure, (b) Schematic diagram of the grid-forming ability analysis of the proposed control structure;

[0044] Figure 9 is the schematic diagram of the simulation conditions of Case 2;

[0045] Figure 10 is the schematic diagram of the active power response delay analysis; (a) Schematic diagram of the active power response delay analysis of the traditional control structure, (b) Schematic diagram of the active power response delay analysis of the proposed control structure. Specific implementation manners

[0046] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0047] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention.

[0048] Without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0049] Embodiment 1

[0050] The double-mass model is used to illustrate that the virtual damping control effect of the grid-forming doubly-fed wind turbine under weak grid conditions will be weakened.

[0051] The double-mass model can accurately reflect the torsional dynamic characteristics of the drive train, and its motion equation is as follows:

[0052]

[0053] T s = K s (θ t - θ g ) + D s (ω t - ω g ) (2)

[0054] where J t , J g , ω t , ω g , θ t and θ g are the moments of inertia, angular velocities and angles of the wind turbine and the generator respectively. T t , T g , and T s are the aerodynamic torque, electromagnetic torque and shaft torque respectively. K s and D s are the equivalent stiffness and equivalent damping of the drive shaft respectively.

[0055] Substituting (2) into (1) gives

[0056] Δω g = -G shaft (s)ΔT g (3)

[0057] where

[0058]

[0059] where the addition of Δ represents the incremental model of each quantity. The characteristic equation of the further power transmission system can be expressed as

[0060] 1 + G shaft (s)G damp_1 (s) = 0 (5)

[0061] where G damp_1 (s) is the transfer function corresponding to ΔT g = G damp_1 (s)Δω g respectively.

[0062] The characteristic values corresponding to the characteristic equation under different grid strengths are as Figure 1 shown. It can be seen that the weakly damped mode of the system is controlled by a pair of conjugate characteristic values, corresponding to the vibration of the drive train shafting. As the grid strength decreases, the real part of the characteristic value gradually increases from -1.8 to -0.26, and the stability of the drive train deteriorates, i.e., the virtual damping control effect weakens.

[0063] The coupling analysis of grid connection control and active power response of a doubly-fed wind power generation mechanism is carried out for the technical solution of this embodiment:

[0064] The grid-forming ability is the ability of a wind turbine to keep the amplitude and phase of the internal voltage almost unchanged when external grid disturbances occur. In this patent, the ability of the internal voltage phase of a doubly-fed wind turbine set to be nearly unchanged is concerned. Figure 2 It is the active power control block diagram for phase adjustment. The nonlinear system is linearized at the point of common coupling.

[0065] The transfer function from ΔP ref (s) to ΔP(s) and the transfer function from Δθ E to Δθ U are as follows

[0066]

[0067] The transfer functions ΔP(s) / ΔP ref (s) and Δθ U / Δθ E are the same. The former represents that the active power response hopes for a fast response speed, and the latter represents that the grid-forming ability expects a slow response speed. However, no matter how G(s) is modified, it will affect both the active power response characteristics and the grid-forming ability under the traditional control structure. That is, accelerating the active power response will also lead to a weakening of the grid-forming ability, and the two cannot be optimized simultaneously.

[0068] In the above formula, P and P ref are the active power and the reference value of the active power respectively, and θ E and θ U are the phase of the grid voltage and the phase of the output voltage of the doubly-fed wind turbine set respectively. Adding Δ represents the incremental model of each quantity. The transfer functions ΔP(s) / ΔP ref (s) and Δθ U / Δθ E are the same. The former represents that the active power response hopes for a fast response speed, and the latter represents that the grid-forming ability expects a slow response speed. However, no matter how G(s) is modified, it will affect both the active power response characteristics and the grid-forming ability under the traditional control structure. That is, accelerating the active power response will also lead to a weakening of the grid-forming ability, and the two cannot be optimized simultaneously.

[0069] This embodiment discloses a method for adding resistance to the drive chain of a grid-forming doubly-fed wind turbine based on phase angle feedforward, including:

[0070] Directly feedforward P ref into the phase angle, avoiding the phase adjustment process dominated by the integral component. Accelerate the active power response speed. The phase angle formula in the virtual synchronous coordinate system is:

[0071]

[0072] Among them, K PFF is the control gain of the phase angle feedforward control, f GFM After further adopting the phase angle feedforward scheme for the frequency of the virtual synchronous coordinate system, the structure diagram of the phase angle feedforward control is as follows: Figure 3 shown.

[0073] The transfer function becomes:

[0074]

[0075] By adopting an asymmetric control structure, the coupling between active power response and grid-building capability is broken, which effectively reduces the active power response delay and improves the virtual damping control effect under weak grid conditions without affecting the grid-building capability of wind turbines.

[0076] After further adopting phase angle feedforward control, equation (5) becomes

[0077] 1+G shaft (s)G damp (s) = 0 (10) where G damp (s) is ΔT after phase angle feedforward g =G damp (s)Δω g The corresponding transfer function.

[0078] After adopting phase angle feedforward control, the corresponding characteristic values ​​of the characteristic equation under different power grid strengths are as follows: Figure 4 As shown in the figure, after adopting the proposed control scheme, the real part of the eigenvalue is reduced from -0.26 to -2.1. The stability of the transmission system is significantly improved.

[0079] Figure 5 , Figure 6 The specific implementation control block diagrams of the traditional scheme and the proposed scheme are given respectively. When the power grid fluctuates, the collected active power is subtracted from the active power reference value, and then input into the PI controller to obtain the output signal, which is further added to f0 (the reference value of the given virtual synchronous coordinate system frequency) to obtain f GFM (the frequency of the virtual synchronous coordinate system), further, f GFM The output value after integration is P ref With K PFF The product of is added to get θ U (θ U The phase of the wind turbine output voltage is obtained, and the control amount of the generator output voltage phase is further obtained, and the PWM modulation signal of the wind turbine converter is further obtained to realize the wind turbine control of the converter switch tube, and finally realize the control of the wind turbine.

[0080] Furthermore, two simulation cases were used to verify the proposed control structure and system effectiveness:

[0081] Case 1: Grid frequency drop. Verify that the phase angle feed-forward control scheme does not affect the grid-forming ability of the unit.

[0082] The simulation conditions are as Figure 7 shown. At t = 1 s, the external grid frequency drops from 50 Hz to 49.75 Hz. The analysis of grid-forming ability is as Figure 8 shown, where (a) is the schematic diagram of the grid-forming ability analysis of the traditional control structure, and (b) is the schematic diagram of the grid-forming ability analysis of the proposed control structure.

[0083] It can be seen that neither the steady-state active power support nor the active power support response speed is affected after the frequency drop. The phase angle feed-forward control does not affect the frequency support ability of the wind turbine generator, that is, the ability to maintain the phase almost unchanged in the grid-forming ability is maintained.

[0084] Case 2: A 10-ms phase jump is used to excite the torsional vibration of the drive train. Verify that the phase angle feed-forward control scheme can reduce the active power response delay and improve the virtual damping control effect under weak grid conditions. The simulation conditions are as Figure 9 shown. At t = 1 s, the phase of the external grid voltage jumps by 0.5 rad at 1 s and recovers at 1.01 s. Figure 10 is the schematic diagram of the active power response delay analysis, where (a) is the schematic diagram of the active power response delay analysis of the traditional control structure, and (b) is the schematic diagram of the active power response delay analysis of the proposed control structure.

[0085] It can be seen that under the traditional control structure, the vibration duration of the drive train exceeds 10 s, while when the proposed control structure is adopted, the vibration of the drive train is successfully suppressed within 2 s. It is verified that the proposed control scheme can improve the virtual damping control effect of the grid-forming doubly-fed wind turbine generator connected to a weak grid.

[0086] The technical solution of this embodiment analyzes the coupling mechanism of grid-forming control and active power response. Based on the analysis results of the electromechanical coupling characteristics, a phase angle feed-forward control method is proposed to break the coupling between the two, while improving the virtual damping control effect under weak grid conditions and maintaining its grid-forming ability.

[0087] Analysis of the coupling between grid-forming control and active power response of doubly-fed wind turbine generators.

[0088] The grid-forming ability is the ability of the wind turbine generator to keep the amplitude and phase of the internal voltage almost unchanged when external grid disturbances occur. In this embodiment, the ability of the doubly-fed wind turbine generator to keep the internal voltage phase almost unchanged is concerned. The nonlinear system is linearized at the point of common coupling.

[0089] The technical solution of this embodiment accelerates the active power response speed when the grid-forming doubly-fed wind turbine is connected to a weak grid, optimizes the dynamic response performance of the unit, and improves the virtual damping control effect.

[0090] The technical solution of this embodiment adopts an asymmetric control structure, breaking the coupling between the active power response and the grid-forming ability. While reducing the active response delay of the unit, it ensures that the steady-state active support and the active support response speed after frequency drop are hardly affected, maintaining the grid-forming ability of the unit.

[0091] Embodiment 2

[0092] The purpose of this embodiment is to provide a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, the steps of the above method are implemented.

[0093] Embodiment 3

[0094] The purpose of this embodiment is to provide a computer-readable storage medium.

[0095] A computer-readable storage medium, on which a computer program is stored. When the program is executed by a processor, the steps of the above method are executed.

[0096] Embodiment 4

[0097] The purpose of this embodiment is to provide a grid-forming doubly-fed wind turbine drive train damping system based on phase angle feedforward, including:

[0098] An active power acquisition module, configured to: acquire the active power of the grid-forming doubly-fed wind turbine;

[0099] A controller processing module, configured to: after subtracting the acquired active power of the grid-forming doubly-fed wind turbine from the active power reference value, input it into a PI controller to obtain an output signal;

[0100] Adding the output signal to the reference value of the virtual synchronous coordinate system frequency to obtain the frequency of the virtual synchronous coordinate system;

[0101] Integrating the frequency of the virtual synchronous coordinate system to obtain an output value;

[0102] Multiplying the active power reference value of the grid-forming doubly-fed wind turbine by the control gain of the phase angle feedforward control to obtain a product result;

[0103] Adding the product result to the output value to obtain the angle of the virtual synchronous coordinate system, and obtaining the control quantity of the generator output voltage phase based on this angle;

[0104] The control module is configured to: obtain the PWM modulation signal of the converter of the wind turbine based on the control quantity, and use the PWM modulation signal to control the switching tubes of the converter of the wind turbine, and finally realize the control of the wind turbine generator set to complete the addition of resistance to the drive train.

[0105] Embodiment 5

[0106] The purpose of this embodiment is to provide a computer program product containing instructions, which when running on a computer, enables the computer to execute the methods and functions involved in any one of the above embodiments.

[0107] The steps involved in the devices of the above embodiments correspond to those of Method Embodiment 1. For specific implementation manners, reference may be made to the relevant description part of Embodiment 1. The term "computer-readable storage medium" should be understood to include a single medium or multiple media containing one or more instruction sets; it should also be understood to include any medium that can store, encode, or carry an instruction set for execution by a processor and enable the processor to execute any method in the present invention.

[0108] Those skilled in the art should understand that the above-mentioned modules or steps of the present invention can be implemented by a general computer device. Optionally, they can be implemented by program codes executable by a computing device, so that they can be stored in a storage device for execution by the computing device, or they can be separately fabricated into individual integrated circuit modules, or multiple modules or steps among them can be fabricated into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0109] Although the specific implementation manners of the present invention have been described above in conjunction with the accompanying drawings, they are not limitations on the protection scope of the present invention. Those skilled in the art should understand that based on the technical solutions of the present invention, various modifications or deformations that can be made without creative efforts by those skilled in the art are still within the protection scope of the present invention.

Claims

1. A method for adding resistance to the drive train of a grid-forming doubly-fed wind turbine based on phase angle feedforward, characterized by comprising: Obtaining the active power of the grid-forming doubly-fed wind turbine; After subtracting the obtained active power of the grid-forming doubly-fed wind turbine from the active power reference value, inputting it into a PI controller to obtain an output signal; Adding the output signal to the reference value of the frequency in the virtual synchronous coordinate system to obtain the frequency in the virtual synchronous coordinate system; Integrating the frequency in the virtual synchronous coordinate system to obtain an output value; Multiplying the active power reference value of the grid-forming doubly-fed wind turbine by the control gain of the phase angle feedforward control to obtain a product result; Adding the product result to the output value to obtain the angle in the virtual synchronous coordinate system, and obtaining the control quantity of the generator output voltage phase based on this angle; Based on this control quantity, obtaining the PWM modulation signal of the wind turbine converter, and using the PWM modulation signal to realize the control of the switching tubes of the converter by the wind turbine, and finally realizing the control of the wind power generation set to complete the addition of resistance to the drive train.

2. The method for adding resistance to the drive train of a grid-forming doubly-fed wind turbine based on phase angle feedforward according to claim 1, characterized in that, The angle in the virtual synchronous coordinate system is: Among them, K PFF is the control gain of the phase angle feedforward control, f GFM is the frequency of the virtual synchronous coordinate system, θ U is the phase of the output voltage of the wind turbine, is the reference value of the active power.

3. The damping addition method for the drive train of the network-forming doubly-fed wind turbine based on phase angle feedforward according to claim 1, characterized in that The transfer function of the method is: Among them, is the increment of active power, is the forward transfer function of the active power control block diagram for phase adjustment, is the backward transfer function of the active power control block diagram for phase adjustment, K PFF is the control gain of the phase angle feedforward control, is the increment of the active power reference value, is the phase increment of the output voltage of the wind turbine, is the increment of the grid voltage phase.

4. The method for adding resistance to the drive train of a grid-forming doubly-fed wind turbine based on phase angle feedforward as claimed in claim 1, wherein The reference value of the frequency in the virtual synchronous coordinate system is a given value.

5. The damping system for the drive train of a grid-forming doubly-fed wind turbine based on phase angle feedforward is characterized in that, Including: An active power acquisition module configured to: obtain the active power of the grid-forming doubly-fed wind turbine; A controller processing module configured to: after subtracting the obtained active power of the grid-forming doubly-fed wind turbine from the active power reference value, inputting it into a PI controller to obtain an output signal; Adding the output signal to the reference value of the frequency in the virtual synchronous coordinate system to obtain the frequency in the virtual synchronous coordinate system; Integrating the frequency in the virtual synchronous coordinate system to obtain an output value; Multiplying the active power reference value of the grid-forming doubly-fed wind turbine by the control gain of the phase angle feedforward control to obtain a product result; Adding the product result to the output value to obtain the angle in the virtual synchronous coordinate system, and obtaining the control quantity of the generator output voltage phase based on this angle; A control module configured to: based on this control quantity, obtain the PWM modulation signal of the wind turbine converter, and use the PWM modulation signal to realize the control of the switching tubes of the converter by the wind turbine, and finally realize the control of the wind power generation set to complete the addition of resistance to the drive train.

6. The network-forming type doubly-fed fan drive chain damping system based on phase angle feedforward according to claim 5, characterized in that, The angle in the virtual synchronous coordinate system is: Among them, K PFF is the control gain of the phase angle feedforward control, f GFM is the frequency of the virtual synchronous coordinate system, θ U is the phase of the output voltage of the wind turbine, is the reference value of the active power.

7. The damping system for the drive train of a grid-forming doubly-fed wind turbine based on phase angle feedforward as claimed in claim 5, characterized in that, The transfer function of the system is: Among them, is the increment of active power, is the forward transfer function of the active power control block diagram for phase adjustment, is the backward transfer function of the active power control block diagram for phase adjustment, K PFF is the control gain of the phase angle feedforward control, is the increment of the active power reference value, is the phase increment of the output voltage of the wind turbine, is the increment of the grid voltage phase.

8. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the method according to any one of claims 1 to 4.

9. A computer device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that When the processor executes the program, it implements the steps of the method according to any one of the above claims 1-4.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it executes the steps of the method according to any one of the above claims 1-4.

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