Stable control method and system for full-power wind turbine generator of extremely weak power grid

Abstract

The invention provides a stability control method for a full-power wind turbine generator of an extremely weak power grid, which comprises the following steps: controlling a grid-side converter of the full-power wind turbine generator, and executing a grid-side stability control strategy by adding a reactive power synchronization process in a phase-locked loop of the grid-side converter; and controlling a machine-side converter of the full-power wind turbine generator, improving output voltages of a d-axis current inner loop regulator and a q-axis current inner loop regulator of the machine-side converter through a band elimination filter and a virtual impedance link, and executing a machine-side stable control strategy. By means of the control method, the stability of the following grid type full-power wind turbine generator can be remarkably improved, and it is guaranteed that the full-power wind turbine generator stably operates under the extremely weak power grid condition that the short-circuit ratio is not lower than 1.1.

Description

Technical Field

[0001] The present application relates to the field of renewable energy power generation technology, and in particular to a method and system for stabilizing control of a full-power wind turbine generator set in an extremely weak power grid. Background Art

[0002] Against the backdrop of global energy structure transformation, the installed capacity of wind power has grown rapidly around the world, becoming a key force in addressing climate change and achieving energy sustainable development goals. However, with the continuous increase in wind power penetration, a series of technical difficulties have gradually emerged, especially when wind power is connected to extremely weak grid areas with relatively weak grid structures and low short-circuit ratios. The interaction between wind turbines and the grid under extremely weak grids becomes more complicated, which can easily lead to stability problems such as sub- / super-synchronous oscillations. In severe cases, it may even cause wind turbines to be disconnected from the grid, posing a threat to the safe and stable operation of the grid. Therefore, how to improve the stability of full-power wind turbines under extremely weak grids has become a technical difficulty in the current field of wind power technology. The existing stability improvement strategy suppresses sub- / super-synchronous oscillations by applying an active damping control link in the grid-side converter of the full-power wind turbine. However, the existing method is difficult to ensure the stable operation of full-power wind turbines under extremely weak grid conditions with a short-circuit ratio of not less than 1.1. Summary of the invention

[0003] In view of the defects in the prior art, the purpose of this application is to provide a method and system for stable control of full-power wind turbines in extremely weak power grids, which can significantly improve the stable operation capability of full-power wind turbines in extremely weak power grid conditions and provide strong guarantee for the safe and reliable operation of wind power generation systems.

[0004] In one aspect of the present application, a method for stabilizing a full-power wind turbine generator system in an extremely weak power grid is provided, comprising:

[0005] Control the grid-side converter of the full-power wind turbine and implement the grid-side stability control strategy by adding a reactive power synchronization process in the phase-locked loop of the grid-side converter;

[0006] The machine-side converter of the full-power wind turbine is controlled, the output voltage of the d-axis and q-axis current inner loop regulator of the machine-side converter is improved through the band-stop filter and the virtual impedance link, and the machine-side stability control strategy is implemented.

[0007] Furthermore, the grid-side stability control strategy is executed by adding a reactive power synchronization process in the phase-locked loop of the grid-side converter, including:

[0008] Obtaining a reference value of reactive power and an actual value of reactive power during reactive power synchronization;

[0009] Subtracting the reference value of the reactive power from the actual value of the reactive power to obtain a difference;

[0010] Input the difference into a proportional or proportional-integral controller and output the angular frequency change;

[0011] Superimposing the angular frequency variation onto the angular frequency output by the phase-locked loop;

[0012] The synchronous phase angle of the phase-locked loop is output through the integral link of the integrator.

[0013] Further, the difference is input into a proportional or proportional-integral controller, and in the output angular frequency change, the difference is selected to be input into a proportional-integral (PI) controller.

[0014] Furthermore, the formula for outputting the synchronization phase angle through the integrator is:

[0015]

[0016] Where, θ represents the synchronous phase angle of the phase-locked loop output; Q Gref Represents the reference value of reactive power; Q G Represents the actual value of reactive power; represents the component of the AC voltage at the common connection point on the q axis, and the superscript "c" represents the component in the control coordinate system; k ppll and k ipll Respectively represent the proportional and integral coefficients of the phase-locked loop PI controller, k pHSC and k iHSC They represent the proportional and integral coefficients of the reactive power loop PI controller respectively, ω0 is the fundamental angular frequency, and 1 / s represents the integral link.

[0017] Furthermore, the output voltage of the d-axis and q-axis current inner loop regulators of the machine-side converter is improved by using a band-stop filter and a virtual impedance link, including:

[0018] The d-axis current component of the machine-side converter is applied to the output voltage of the d-axis current inner loop regulator through a band-stop filter and a virtual impedance link;

[0019] The q-axis current component of the machine-side converter is applied to the output voltage of the q-axis current inner loop regulator through a band-stop filter and a virtual impedance link.

[0020] Furthermore, the expression for applying the d-axis current component of the machine-side converter to the output voltage of the d-axis current inner loop regulator through the band-stop filter and the virtual impedance link is:

[0021]

[0022] In the formula, Represents the current reference value of the outer loop control output, represents the component of the alternating current on the d-axis, represents the component of the converter output voltage on the d-axis, k impd and k imid They represent the proportional and integral coefficients of the current inner loop PI control respectively, and the rotor inductance on the machine side is L m ,ω m is the fundamental angular frequency;

[0023] Among them, the band-stop filter and the virtual impedance link G vmd The expression is:

[0024]

[0025] In the formula, R vmd Represents virtual resistance, L vmd Represents virtual inductance, R vmd +sL vmd represents virtual impedance, (s 2 +ω 2 nd ) / (s 2 +2ξ d ω nd s+ω 2 nd ) represents a band-stop filter, ω nd represents the center frequency, ξ d represents the damping ratio, 2ξ d ω nd Represents bandwidth.

[0026] Furthermore, the expression for applying the q-axis current component of the machine-side converter to the output voltage of the q-axis current inner loop regulator through the band-stop filter and the virtual impedance link is:

[0027]

[0028] In the formula, Represents the current reference value of the outer loop control output, represents the component of the AC current on the q axis, represents the component of the converter output voltage on the q axis, k impq and k imiq They represent the proportional and integral coefficients of the current inner loop PI control respectively, and the rotor inductance on the machine side is L m ,ω m is the fundamental angular frequency;

[0029] Among them, the band-stop filter and the virtual impedance link G vmq The expression is:

[0030]

[0031] In the formula, R vmq Represents virtual resistance, L vmq Represents virtual inductance, R vmq +sL vmq represents virtual impedance, (s 2 +ω 2 nq ) / (s 2 +2ξ q ω nq s+ω 2 nq ) represents a band-stop filter, ω nq represents the center frequency, ξ q represents the damping ratio, 2ξ q ω nq Represents bandwidth.

[0032] A second aspect of the present application provides a full-power wind turbine stability control system for an extremely weak power grid, comprising: a grid-side converter, a machine-side converter, a converter basic control module, a grid-side converter stability control module, and a machine-side converter stability control module;

[0033] The converter basic control module is used to implement basic control of the grid-side converter and the generator-side converter;

[0034] The grid-side converter stability control module is used to implement a stability control strategy in a phase-locked loop of the grid-side converter;

[0035] The machine-side converter stability control module is used to implement a stability control strategy in the current inner loop of the machine-side converter.

[0036] Furthermore, the basic control of the grid-side converter and the generator-side converter includes:

[0037] The basic control of the grid-side converter adopts a double closed-loop vector control structure with a constant DC voltage outer loop and a current inner loop;

[0038] The basic control of the machine-side converter adopts a constant speed outer loop control and a current inner loop control.

[0039] Further, the stable control strategy implemented in the phase-locked loop of the grid-side converter is to add a reactive power synchronization link in the phase-locked loop of the grid-side converter, make a difference between the reactive power reference value and the reactive power actual value, output the angular frequency change after passing through a proportional or proportional-integral controller, superimpose it on the angular frequency output by the phase-locked loop, and then output the synchronous phase angle through an integrator;

[0040] The stable control strategy implemented in the current inner loop of the machine-side converter is to apply the d-axis current component of the machine-side converter of the full-power wind turbine to the output voltage of the d-axis current inner loop regulator through a band-stop filter and a virtual impedance link; and to apply the q-axis current component of the machine-side converter of the full-power wind turbine to the output voltage of the q-axis current inner loop regulator through a band-stop filter and a virtual impedance link.

[0041] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0042] The present application improves the output voltage of the d-axis and q-axis current inner loop regulators of the machine-side converter by adding a reactive power synchronization process in the phase-locked loop of the grid-side converter when the wind turbine is connected to an extremely weak grid area with a relatively weak grid structure and a low short-circuit ratio, and uses a band-stop filter and a virtual impedance link to enhance the stability of the wind turbine in a weak grid environment, effectively deal with the voltage fluctuation and frequency deviation problems caused by insufficient grid strength, and ensure that the wind turbine can still operate stably in an extremely weak grid environment with a short-circuit ratio of not less than 1.1. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Other features, objects and advantages of the present application will become more apparent by reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0044] Figure 1 This is a flow chart of a method for stabilizing control of a full-power wind turbine in an extremely weak power grid in one embodiment of the present application.

[0045] Figure 2 This is a block diagram of a full-power wind turbine stability control system for an extremely weak power grid in one embodiment of the present application.

[0046] Figure 3 This is a simulation waveform diagram of active and reactive power of a full-power wind turbine in an extremely weak power grid with a short-circuit ratio of 1.1 in one embodiment of the present application.

[0047] Among them, Figure (a) is a power waveform diagram when no stability control strategy is applied, Figure (b) is a power waveform diagram when only the grid-side converter stability control strategy is applied, Figure (c) is a power waveform diagram when only the machine-side converter stability control strategy is applied, and Figure (d) is a power waveform diagram when the full-power wind turbine stability control method proposed in the present invention is adopted. DETAILED DESCRIPTION

[0048] The present application is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements can also be made without departing from the concept of the present application. These all belong to the protection scope of the present application.

[0049] Reference Figure 1 As shown, a method for stabilizing a full-power wind turbine in an extremely weak power grid according to an embodiment of the present application includes: S1, controlling a grid-side converter of the full-power wind turbine, and executing a grid-side stabilization control strategy by adding a reactive power synchronization process in a phase-locked loop of the grid-side converter.

[0050] S2, controls the machine-side converter of the full-power wind turbine, improves the output voltage of the d-axis and q-axis current inner loop regulator of the machine-side converter through the band-stop filter and the virtual impedance link, and executes the machine-side stability control strategy.

[0051] Among them, the extremely weak power grid environment is a power grid environment with a short circuit ratio of not less than 1.1.

[0052] The present application improves the output voltage of the d-axis and q-axis current inner loop regulators of the machine-side converter by adding a reactive power synchronization process in the phase-locked loop of the grid-side converter when the wind turbine is connected to an extremely weak grid area with a relatively weak grid structure and a low short-circuit ratio, and uses a band-stop filter and a virtual impedance link to enhance the stability of the wind turbine in a weak grid environment, effectively deal with the voltage fluctuation and frequency deviation problems caused by insufficient grid strength, and ensure that the wind turbine can still operate stably in an extremely weak grid environment with a short-circuit ratio of not less than 1.1.

[0053] Among them, the grid-side converter of the full-power wind turbine with grid connection adopts a phase-locked loop to detect the phase of the grid connection point voltage, and uses the voltage of the grid connection point as the input of the phase-locked loop, which is mainly suitable for strong grid environments. In weak grid environments, the phase-locked loop of the full-power wind turbine with grid connection will deteriorate the control performance and easily cause sub- / super-synchronous oscillation problems. This application significantly improves the oscillation stability of the full-power wind turbine with grid connection, ensuring the stable operation of the full-power wind turbine under extremely weak grid conditions.

[0054] Specifically, first, when the power grid environment in which the grid-following full-power wind turbine is located is an extremely weak power grid environment, that is, the short-circuit ratio is not less than 1.1, then, the grid-side converter is controlled and the grid-side stability control strategy is executed. By adding a reactive power synchronization process in the phase-locked loop, the oscillation stability of the grid-side converter is improved. At the same time, the machine-side converter is controlled, and the output voltage of the d-axis and q-axis current inner loop regulators of the machine-side converter is improved by introducing a band-stop filter and a virtual impedance link, thereby increasing the oscillation stability of the machine-side converter. By investing the stable control method of the present application in the grid-following full-power wind turbine, the grid-following full-power wind turbine can operate stably under extremely low grid short-circuit ratio conditions, thereby solving the problem that general grid-following full-power wind turbines cannot operate under extremely weak power grids.

[0055] In some specific embodiments, under extremely weak grid conditions with a short-circuit ratio of 1.1, in order to execute a grid-side stability control strategy by adding a reactive power synchronization process in the phase-locked loop of the grid-side converter, the strategy includes: obtaining a reference value of reactive power and an actual value of reactive power in the reactive power synchronization process; subtracting the reference value of reactive power from the actual value of reactive power to obtain a difference; inputting the difference into a proportional or proportional-integral controller to output an angular frequency change; superimposing the angular frequency change on the angular frequency output by the phase-locked loop; and outputting the synchronous phase angle of the phase-locked loop through the integral link of the integrator.

[0056] The present application can effectively improve the grid-side stability control by adding a reactive power synchronization process in the phase-locked loop of the grid-side converter under extremely weak grid conditions with a short-circuit ratio of 1.1. By acquiring and comparing the reference value and actual value of the reactive power, the angular frequency change corresponding to the difference is calculated using a proportional or proportional-integral controller and superimposed on the original angular frequency output of the phase-locked loop. Finally, an accurate synchronization phase angle is obtained through an integrator, thereby achieving precise control and synchronization of the reactive power of the grid and enhancing the stability of the grid under extremely weak conditions.

[0057] When controlling, first, according to the operating status of the power grid and the load demand, the reference value of reactive power and the actual value of reactive power in the current power grid are set; the reference value of reactive power is compared with the actual value to obtain the difference. Among them, the difference reflects the imbalance between the supply and demand of reactive power in the current power grid. Then the calculated difference is input into the proportional (P) or proportional integral (PI) controller. The controller calculates the angular frequency change that needs to be adjusted according to the size and direction of the difference. Then the angular frequency change output by the controller is superimposed on the angular frequency originally output by the phase-locked loop, and the angular frequency of the phase-locked loop is adjusted. The adjusted angular frequency is integrated through the integrator, and the synchronous phase angle of the phase-locked loop is output. By adjusting the phase and amplitude of the output voltage and current, precise control of reactive power is achieved.

[0058] Reference Figure 2 As shown, in the grid-side stability control link, specifically, the difference is input into a proportional or proportional-integral controller to output an angular frequency change.

[0059] Among them, the proportional controller is mainly adjusted according to the current difference, and there is a steady-state static difference between the reference value and the actual value, while the proportional-integral controller takes into account the cumulative effect of the difference to achieve smoother control, and there is no steady-state static difference between the reference value and the actual value.

[0060] In some specific embodiments, the formula for outputting the synchronization phase angle through the integrator is:

[0061]

[0062] Where, θ represents the synchronous phase angle of the phase-locked loop output; Q Gref Represents the reference value of reactive power; Q G Represents the actual value of reactive power; represents the component of the AC voltage at the common connection point on the q axis, and the superscript "c" represents the component in the control coordinate system; k ppll and k ipll Respectively represent the proportional and integral coefficients of the phase-locked loop PI controller, k pHSC and k iHSC They represent the proportional and integral coefficients of the reactive power loop PI controller respectively, ω0 is the fundamental angular frequency, and 1 / s represents the integral link.

[0063] In some possible specific embodiments, in order to improve the output voltage of the d-axis and q-axis current inner loop regulators of the machine-side converter through the band-stop filter and the virtual impedance link, the method includes:

[0064] The d-axis current component of the machine-side converter is applied to the output voltage of the d-axis current inner loop regulator through a band-stop filter and a virtual impedance link.

[0065] The center frequency of the band-stop filter should be selected as the oscillation frequency of the system, and the damping ratio should be selected as 0.1, so that the bandwidth of the band-stop filter is small and it only works on the oscillation frequency without causing other oscillation stability problems.

[0066] In principle, the larger the virtual resistance and virtual inductance of the virtual impedance, the more stable the system, but their upper limit is limited by the modulation degree of the converter.

[0067] Method for determining the lower limit of virtual impedance parameters: When designing virtual impedance parameters, the Nyquist curve of the interconnection system of full-power wind turbines and AC power grid is drawn according to the Nyquist stability criterion, so that its phase margin is equal to the set threshold (such as 30°), thereby obtaining the lower limit of virtual resistance and virtual inductance in the virtual impedance.

[0068] The q-axis current component of the machine-side converter is applied to the output voltage of the q-axis current inner loop regulator through a band-stop filter and a virtual impedance link.

[0069] The present application improves the output voltage of the d-axis and q-axis current inner-loop regulators of the machine-side converter through a band-stop filter and a virtual impedance link, wherein the band-stop filter can suppress the harmonic components within a specified frequency range and reduce the harmonic content in the current waveform; the virtual impedance link can simulate the actual impedance in the power grid, improve the damping characteristics of the system, suppress system oscillations, and improve the overall stability of the system. Finally, the d-axis and q-axis current components are filtered and impedance adjusted through the band-stop filter and the virtual impedance link, so as to achieve precise control of the current output and improve the response speed and accuracy of the current control.

[0070] Specifically, appropriate band-stop filters and virtual impedance links are determined as needed, and the d-axis and q-axis current components of the machine-side converter are obtained through current sensors or current measurement circuits. The obtained d-axis current components are filtered through band-stop filters to remove harmonic components of specified frequencies. The filtered d-axis current components are then impedance-adjusted through a virtual impedance link to obtain adjusted d-axis current components. Based on the adjusted d-axis and q-axis current components and the control algorithm of the current inner-loop regulator, the output voltages of the d-axis and q-axis current inner-loop regulators are calculated and obtained as control instructions for the machine-side converter to achieve precise control of the machine-side converter.

[0071] Reference Figure 2 As shown, specifically, in order to apply the d-axis current component of the machine-side converter to the output voltage of the d-axis current inner loop regulator through the band-stop filter and the virtual impedance link, the expression is:

[0072]

[0073] In the formula, Represents the current reference value of the outer loop control output, represents the component of the alternating current on the d-axis, represents the component of the converter output voltage on the d-axis, k impd and k imid They represent the proportional and integral coefficients of the current inner loop PI control respectively, and the rotor inductance on the machine side is L m ,ω m is the fundamental angular frequency.

[0074] Among them, the band-stop filter and the virtual impedance link G vmd The expression is:

[0075]

[0076] In the formula, Rvmd Represents virtual resistance, L vmd Represents virtual inductance, R vmd +sL vmd represents virtual impedance, (s 2 +ω 2 nd ) / (s 2 +2ξ d ω nd s+ω 2 nd ) represents a band-stop filter, ω nd represents the center frequency, ξ d represents the damping ratio, 2ξ d ω nd Represents bandwidth.

[0077] Specifically, in order to apply the q-axis current component of the machine-side converter to the output voltage of the q-axis current inner loop regulator through the band-stop filter and the virtual impedance link, the expression is:

[0078]

[0079] In the formula, Represents the current reference value of the outer loop control output, represents the component of the AC current on the q axis, represents the component of the converter output voltage on the q axis, k impq and k imiq They represent the proportional and integral coefficients of the current inner loop PI control respectively, and the rotor inductance on the machine side is L m ,ω m is the fundamental angular frequency.

[0080] Among them, the band-stop filter and the virtual impedance link G vmq The expression is:

[0081]

[0082] In the formula, R vmq Represents virtual resistance, L vmq Represents virtual inductance, R vmq +sL vmq represents virtual impedance, (s 2 +ω 2 nq ) / (s 2 +2ξ q ω nq s+ω 2 nq ) represents a band-stop filter, ω nq represents the center frequency, ξ q represents the damping ratio, 2ξ q ωnq Represents bandwidth.

[0083] like Figure 3 As shown in the waveform diagram after the experiment, the operating effect of the present application in an extremely weak power grid environment is reflected, among which, Figure 3 (a) is the power waveform without any stabilization control strategy. At this time, the system oscillates rapidly and becomes unstable under extremely weak grid conditions. Figure 3 (b) is the power waveform when only the grid-side converter stability control strategy is applied. At this time, the system oscillation instability speed slows down, but oscillation instability still exists. Figure 3 (c) is the power waveform when only the stable control strategy of the machine-side converter is applied. At this time, the divergence speed of the system oscillation amplitude slows down and the stability is improved to a certain extent, but oscillation instability still exists. Figure 3 (d) is a power waveform diagram when the full-power wind turbine stability control method proposed in the present invention is adopted. Under extremely weak power grid conditions, the system is stable.

[0084] The second aspect of the present application provides a full-power wind turbine stability control system for an extremely weak power grid, comprising: a grid-side converter, a machine-side converter, a converter basic control module, a grid-side converter stability control module and a machine-side converter stability control module.

[0085] The basic control module of the converter is used to implement the basic control of the grid-side converter and the machine-side converter; the stable control module of the grid-side converter is used to implement the stable control strategy in the phase-locked loop of the grid-side converter; the stable control module of the machine-side converter is used to implement the stable control strategy in the current inner loop of the machine-side converter.

[0086] This application realizes basic operation through the basic control modules of the grid-side and machine-side converters, and implements stable control strategies in the phase-locked loop through the grid-side converter stability control module and the current inner loop through the machine-side converter stability control module to improve the system's operating stability of wind turbines under extremely weak grid conditions. During the execution process, the system first ensures the normal operation of the grid-side converter and the machine-side converter through the basic converter control module, and then fine-tunes the grid-side and machine-side through the grid-side converter stability control module and the machine-side converter stability control module, respectively, to achieve the purpose of stable control in an extremely weak grid environment.

[0087] In some possible specific embodiments, the basic control of the grid-side converter and the machine-side converter includes: the basic control of the grid-side converter, which adopts a dual closed-loop vector control structure with a constant DC voltage outer loop and a current inner loop; the basic control of the machine-side converter, which adopts a constant speed outer loop control and a current inner loop control.

[0088] Through the basic control strategy of the grid-side converter, a dual closed-loop vector control structure with a fixed DC voltage outer loop and a current inner loop is adopted to achieve precise control of the DC voltage and current, ensuring the stable operation of the wind turbine under extremely weak grid conditions. At the same time, combined with the basic control strategy of the machine-side converter, a fixed speed outer loop control and a current inner loop control are adopted to achieve precise control of the speed and current of the wind turbine, ensuring that the wind turbine operates at the optimal speed, improving the power generation efficiency and power quality, and further improving the stability of the wind turbine in an extremely weak grid environment.

[0089] Specifically, the stable control strategy implemented in the phase-locked loop of the grid-side converter is to add a reactive power synchronization link in the phase-locked loop of the grid-side converter, make a difference between the reactive power reference value and the actual reactive power value, output the angular frequency change after passing through a proportional or proportional-integral controller, superimpose it on the angular frequency output by the phase-locked loop, and then output the synchronous phase angle through an integrator.

[0090] During operation, first, the system calculates the difference between the reference value and the actual value of reactive power in real time in an extremely weak power grid environment, which is used to reflect the imbalance between the supply and demand of reactive power of full-power wind turbines in the current power grid; then, the difference is input into the proportional integral (PI) controller to calculate the angular frequency change that needs to be adjusted; then, the angular frequency change output by the controller is superimposed on the angular frequency originally output by the phase-locked loop to adjust the angular frequency of the phase-locked loop; finally, the adjusted angular frequency is integrated through an integrator to output the synchronous phase angle of the phase-locked loop for precise control of the grid-side converter.

[0091] Through the above settings, the stability of the grid-side converter under extremely weak grid conditions is improved. By monitoring and controlling reactive power and controlling the phase-locked loop, the synchronous operation between the grid-side converter and the grid is ensured, thereby improving the overall performance and reliability of the system and improving the stability of full-power wind turbines in extremely weak power environments.

[0092] Specifically, the stable control strategy implemented in the current inner loop of the machine-side converter is to apply the d-axis current component of the machine-side converter of the full-power wind turbine to the output voltage of the d-axis current inner loop regulator through a band-stop filter and a virtual impedance link; and to apply the q-axis current component of the machine-side converter of the full-power wind turbine to the output voltage of the q-axis current inner loop regulator through a band-stop filter and a virtual impedance link.

[0093] In the extremely weak point environment, in the current inner loop of the machine-side converter, by introducing a band-stop filter and a virtual impedance link, the d-axis and q-axis current components of the machine-side converter of the full-power wind turbine are filtered by band-stop filters respectively to remove harmonic components of specific frequencies, and impedance adjustment is performed through a virtual impedance link. The adjusted current components are applied to the output voltage of the d-axis and q-axis current inner loop regulators to achieve precise control of the machine-side converter current.

[0094] By setting a band-stop filter in the machine-side converter, the harmonic components in the current are effectively suppressed and the current waveform quality is improved. At the same time, setting a virtual impedance link enhances the damping characteristics of the system and suppresses system oscillation. By controlling the d-axis and q-axis current components through the band-stop filter and the virtual impedance link, the speed and power of the full-power wind turbine can be accurately adjusted in an extremely weak electrical environment, thereby improving the stability of the wind turbine.

[0095] The above describes the specific embodiments of the present application. It should be understood that the present application is not limited to the above specific embodiments, and those skilled in the art can make various modifications or variations within the scope of the claims, which does not affect the substantive content of the present application. The above preferred features can be used in any combination without conflicting with each other.

Claims

1. A method for stabilizing the control of a full-power wind turbine in an extremely weak power grid, characterized in that: include: Control the grid-side converter of the full-power wind turbine and implement the grid-side stability control strategy by adding a reactive power synchronization process in the phase-locked loop of the grid-side converter; The machine-side converter of the full-power wind turbine is controlled, the output voltage of the d-axis and q-axis current inner loop regulator of the machine-side converter is improved through the band-stop filter and the virtual impedance link, and the machine-side stability control strategy is implemented.

2. The method for stabilizing a full-power wind turbine generator system in an extremely weak power grid according to claim 1, characterized in that: The grid-side stability control strategy is executed by adding a reactive power synchronization process in the phase-locked loop of the grid-side converter, including: Obtaining a reference value of reactive power and an actual value of reactive power during reactive power synchronization; Subtracting the reference value of the reactive power from the actual value of the reactive power to obtain a difference; Input the difference into a proportional or proportional-integral controller and output the angular frequency change; Superimposing the angular frequency variation onto the angular frequency output by the phase-locked loop; The synchronous phase angle of the phase-locked loop is output through the integral link of the integrator.

3. The method for stabilizing a full-power wind turbine generator set in an extremely weak power grid according to claim 2, characterized in that: The difference is input into a proportional or proportional-integral controller, and in the output angular frequency change, the difference is selected to be input into a proportional-integral (PI) controller.

4. The method for stabilizing a full-power wind turbine generator set in an extremely weak power grid according to claim 2, characterized in that: The formula for outputting the synchronous phase angle through the integrator is: Where, θ represents the synchronous phase angle of the phase-locked loop output; Q Gref Represents the reference value of reactive power; Q G Represents the actual value of reactive power; represents the component of the AC voltage at the common connection point on the q axis, and the superscript "c" represents the component in the control coordinate system; k ppll and k ipll Respectively represent the proportional and integral coefficients of the phase-locked loop PI controller, k pHSC and k iHSC They represent the proportional and integral coefficients of the reactive power loop PI controller respectively, ω0 is the fundamental angular frequency, and 1 / s represents the integral link.

5. The method for stabilizing a full-power wind turbine generator system in an extremely weak power grid according to claim 1, characterized in that: The output voltage of the d-axis and q-axis current inner loop regulators of the machine-side converter is improved by using a band-stop filter and a virtual impedance link, including: The d-axis current component of the machine-side converter is applied to the output voltage of the d-axis current inner loop regulator through a band-stop filter and a virtual impedance link; The q-axis current component of the machine-side converter is applied to the output voltage of the q-axis current inner loop regulator through a band-stop filter and a virtual impedance link.

6. A method for stabilizing a full-power wind turbine generator system in an extremely weak power grid according to claim 5, characterized in that: The expression for applying the d-axis current component of the machine-side converter to the output voltage of the d-axis current inner loop regulator through the band-stop filter and the virtual impedance link is: In the formula, Represents the current reference value of the outer loop control output, represents the component of the alternating current on the d-axis, represents the component of the converter output voltage on the d-axis, k impd and k imid They represent the proportional and integral coefficients of the current inner loop PI control respectively, and the rotor inductance on the machine side is L m ,ω m is the fundamental angular frequency; Among them, the band-stop filter and the virtual impedance link G vmd The expression is: In the formula, R vmd Represents virtual resistance, L vmd Represents virtual inductance, R vmd +sL vmd represents virtual impedance, (s 2 +ω 2 nd ) / (s 2 +2ξ d ω nd s+ω 2 nd ) represents a band-stop filter, ω nd represents the center frequency, ξ d represents the damping ratio, 2ξ d ω nd Represents bandwidth.

7. A method for stabilizing a full-power wind turbine generator set in an extremely weak power grid according to claim 5, characterized in that: The expression for applying the q-axis current component of the machine-side converter to the output voltage of the q-axis current inner loop regulator through the band-stop filter and the virtual impedance link is: In the formula, Represents the current reference value of the outer loop control output, represents the component of the alternating current on the q axis, represents the component of the converter output voltage on the q axis, k impq and k imiq They represent the proportional and integral coefficients of the current inner loop PI control respectively, and the rotor inductance on the machine side is L m ,ω m is the fundamental angular frequency; Among them, the band-stop filter and the virtual impedance link G vmq The expression is: In the formula, R vmq Represents virtual resistance, L vmq Represents virtual inductance, R vmq +sL vmq represents virtual impedance, (s 2 +ω 2 nq ) / (s 2 +2ξ q ω nq s+ω 2 nq ) represents a band-stop filter, ω nq represents the center frequency, ξ q represents the damping ratio, 2ξ q ω nq Represents bandwidth.

8. A full-power wind turbine stability control system for an extremely weak power grid, characterized in that: include: Grid-side converter, machine-side converter, converter basic control module, grid-side converter stability control module and machine-side converter stability control module; The converter basic control module is used to implement basic control of the grid-side converter and the generator-side converter; The grid-side converter stability control module is used to implement a stability control strategy in a phase-locked loop of the grid-side converter; The machine-side converter stability control module is used to implement a stability control strategy in the current inner loop of the machine-side converter.

9. A full-power wind turbine stability control system for an extremely weak power grid according to claim 8, characterized in that: The basic control of the grid-side converter and the generator-side converter includes: The basic control of the grid-side converter adopts a double closed-loop vector control structure with a constant DC voltage outer loop and a current inner loop; The basic control of the machine-side converter adopts a constant speed outer loop control and a current inner loop control.

10. A full-power wind turbine stability control system for an extremely weak power grid according to claim 8, characterized in that: The stable control strategy implemented in the phase-locked loop of the grid-side converter is to add a reactive power synchronization link in the phase-locked loop of the grid-side converter, make a difference between the reactive power reference value and the reactive power actual value, output the angular frequency change after passing through a proportional or proportional-integral controller, superimpose it on the angular frequency output by the phase-locked loop, and then output the synchronous phase angle through an integrator; The stable control strategy implemented in the current inner loop of the machine-side converter is to apply the d-axis current component of the machine-side converter of the full-power wind turbine to the output voltage of the d-axis current inner loop regulator through a band-stop filter and a virtual impedance link; and to apply the q-axis current component of the machine-side converter of the full-power wind turbine to the output voltage of the q-axis current inner loop regulator through a band-stop filter and a virtual impedance link.

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