A weak grid full power wind turbine stability control method and system

Abstract

The application provides a kind of extremely weak power grid full-power wind turbine stable control method, comprising: control the grid-side converter of full-power wind turbine, by additional reactive power synchronization process in the phase-locked loop of grid-side converter, execute grid-side stable control strategy;Control the machine-side converter of full-power wind turbine, by band-stop filter and virtual impedance link to the output voltage of d-axis and q-axis current inner loop regulator of machine-side converter is improved, execute machine-side stable control strategy.The application can significantly improve the stability of grid-connected full-power wind turbine through the above control method, ensure that full-power wind turbine is stably operated under the condition that short-circuit ratio is not less than 1.1 in extremely weak power grid.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy power generation, in particular, to a full-power wind turbine generator stable control method and system for an extremely weak power grid. BACKGROUND

[0002] Under the background of global energy structure transformation, the installed capacity of wind power generation is rapidly growing worldwide, becoming a key force to combat climate change and achieve energy sustainable development goals. However, as the wind power penetration rate continues to rise, especially when wind power is connected to an extremely weak power grid area with a weak power grid structure and low short-circuit ratio, a series of technical problems gradually emerge. The interaction between wind turbine generators and the power grid under an extremely weak power grid becomes more complex, which can easily cause sub / super-synchronous oscillation and other stability problems, and even lead to wind turbine generator disconnection, posing a threat to the safe and stable operation of the power grid. Therefore, how to improve the stability of full-power wind turbine generators under an extremely weak power grid has become a technical difficulty in the current wind power technology field. Existing stability improvement strategies suppress sub / super-synchronous oscillation by applying an active damping control link in the grid-side converter of the full-power wind turbine generator. However, the existing method cannot guarantee the stable operation of the full-power wind turbine generator under the condition of an extremely weak power grid with a short-circuit ratio not lower than 1.1. SUMMARY

[0003] In view of the defects in the prior art, the purpose of the present application is to provide a full-power wind turbine generator stable control method and system for an extremely weak power grid, which can significantly improve the stable operation capability of the full-power wind turbine generator under the condition of an extremely weak power grid, and provide a strong guarantee for the safe and reliable operation of the wind power generation system.

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

[0005] controlling the grid-side converter of the full-power wind turbine generator by adding a reactive power synchronization process in the phase-locked loop of the grid-side converter to execute a grid-side stability control strategy;

[0006] controlling the machine-side converter of the full-power wind turbine generator by improving the output voltage of the d-axis and q-axis current inner loop regulator of the machine-side converter through a band-stop filter and a virtual impedance link to execute a machine-side stability control strategy.

[0007] Further, the execution of the grid-side stability control strategy by adding a reactive power synchronization process in the phase-locked loop of the grid-side converter comprises:

[0008] obtaining a reference value of the reactive power and an actual value of the reactive power in the reactive power synchronization process;

[0009] obtaining a difference value by subtracting the actual value of the reactive power from the reference value of the reactive power.

[0010] inputting the difference into a proportional or proportional-integral controller to output an angular frequency variation;

[0011] superimposing the angular frequency variation on the angular frequency output by the phase-locked loop;

[0012] outputting a synchronization phase angle of the phase-locked loop through an integral element of the integrator.

[0013] Further, in the step of inputting the difference into a proportional or proportional-integral controller to output an angular frequency variation, a proportional-integral (PI) controller is selected.

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

[0015]

[0016] where θ represents the synchronization phase angle output by the phase-locked loop; Q Gref represents a reference value of the reactive power; Q G represents an actual value of the reactive power; represents a component of an alternating current voltage at a point of common coupling in the q-axis, and the superscript "c" represents a component in a control coordinate system; k ppll and k ipll respectively represent proportional and integral coefficients of the PI controller of the phase-locked loop, k pHSC and k iHSC respectively represent proportional and integral coefficients of the PI controller of the reactive power loop, ω0 is a base frequency angular frequency, and 1 / s represents an integral element.

[0017] Further, the step of improving the output voltage of the inner loop regulator of the d-axis and q-axis current of the machine-side converter through a band-stop filter and a virtual impedance element includes:

[0018] 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 element;

[0019] 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 element.

[0020] Further, an 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 element is:

[0021]

[0022] In the expression, I represents a current reference value output by an outer loop control, 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 respectively represent the proportional and integral coefficients of the current inner loop PI control, and L m , ω m is the base frequency, represents the component of the alternating current on the q-axis;

[0023] wherein the band-stop filter and the virtual impedance element G vmd is expressed as:

[0024]

[0025] wherein R vmd represents a virtual resistance, L vmd represents a virtual inductance, R vmd +sL vmd represents a 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 a center frequency, ξ d represents a damping ratio, and 2ξ d ω nd represents a bandwidth, and s represents a complex frequency variable of Laplace transform.

[0026] Further, the expression of 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 element is:

[0027]

[0028] wherein, represents a current reference value output by the outer loop control, 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 respectively represent the proportional and integral coefficients of the current inner loop PI control, and L m , ω m is the base frequency, and s represents a complex frequency variable of Laplace transform, represents the component of the alternating current on the d-axis;

[0029] The band-stop filter and the virtual impedance element G vmq The expression of the band-stop filter is:

[0030]

[0031] In the expression, R vmq represents a virtual resistance, L vmq represents a virtual inductance, R vmq +sL vmq represents a 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 a center frequency, ξ q represents a damping ratio, and 2ξ q ω nq represents a bandwidth.

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

[0033] The grid-side converter stability control module is configured to control a grid-side converter of the full-power wind turbine generator, and to execute a grid-side stability control strategy by adding a reactive power synchronization process in a phase-locked loop of the grid-side converter.

[0034] The machine-side converter stability control module is configured to control a machine-side converter of the full-power wind turbine generator, and to execute a machine-side stability control strategy by improving an output voltage of a d-axis and q-axis current inner loop regulator of the machine-side converter through a band-stop filter and a virtual impedance element.

[0035] Further, a converter basic control module is further included, and the converter basic control module is configured to implement basic control of the grid-side converter and the machine-side converter.

[0036] The basic control of the grid-side converter and the machine-side converter comprises:

[0037] The basic control of the grid-side converter adopts a double-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 stability control strategy implemented in the phase-locked loop of the grid-side converter is that a reactive power synchronous link is added in the phase-locked loop of the grid-side converter, a difference between a reactive power reference value and an actual reactive power value is obtained, an angular frequency variation is output after a proportional or proportional-integral controller, the angular frequency variation is superimposed on an angular frequency output by the phase-locked loop, and then a synchronous phase angle is output by an integrator.

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

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

[0042] The application enhances the stability of the wind turbine in a weak power grid environment, effectively deals with voltage fluctuation and frequency deviation caused by insufficient power grid strength, and ensures that the wind turbine can still operate stably in an extremely weak power grid environment with a short-circuit ratio not less than 1.1. BRIEF DESCRIPTION OF DRAWINGS

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

[0044] Figure 1 A flow chart of a full-power wind turbine stability control method for an extremely weak power grid in an embodiment of the application.

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

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

[0047] In the figures, (a) is a power waveform diagram without any stability control strategy, (b) is a power waveform diagram with only the grid-side converter stability control strategy, (c) is a power waveform diagram with only the machine-side converter stability control strategy, and (d) is a power waveform diagram with the full-power wind turbine stability control method. Detailed Implementation

[0048] The present application will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application. These all fall within the protection scope of the present application.

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

[0050] S2. Control the generator-side converter of the full-power wind turbine unit, improve the output voltage of the inner loop regulator of the d-axis and q-axis current of the generator-side converter through the band-stop filter and virtual impedance link, and execute the generator-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] This application improves the stability of wind turbines in weak grid environments by adding a reactive power synchronization process to the phase-locked loop of the grid-side converter and using a band-stop filter and virtual impedance circuit to improve the output voltage of the d-axis and q-axis current inner loop regulators of the turbine-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. This effectively addresses the voltage fluctuations and frequency offset problems caused by insufficient grid strength and ensures that the wind turbine can still operate stably in extremely weak grid environments with a short-circuit ratio of not less than 1.1.

[0053] The grid-side converter of the grid-connected full-power wind turbine uses a phase-locked loop (PLL) to detect the phase of the grid connection point voltage, using the grid connection point voltage as the PLL input. This is primarily suitable for strong grid environments. However, in weak grid environments, the PLL of the grid-connected full-power wind turbine will deteriorate its control performance and is prone to subsynchronous / supersynchronous oscillations. This application significantly improves the oscillation stability of the grid-connected full-power wind turbine, ensuring stable operation of the full-power wind turbine under extremely weak grid conditions.

[0054] Specifically, first, when the grid environment in which the full-power wind turbine generator is located is an extremely weak grid environment, that is, the short-circuit ratio is not less than 1.1, then, the grid-side converter is controlled, the grid-side stability control strategy is executed, the oscillation stability of the grid-side converter is improved by adding a reactive power synchronization process in the phase-locked loop, and the machine-side converter is controlled, the output voltage of the d-axis and q-axis current inner loop regulator of the machine-side converter is improved by introducing a band-stop filter and a virtual impedance link, so as to increase the oscillation stability of the machine-side converter, so that the full-power wind turbine generator can stably operate under the condition of extremely low grid short-circuit ratio by using the stability control method of the application, and the problem that the general full-power wind turbine generator cannot operate under the extremely weak grid is solved.

[0055] In some specific embodiments, under the condition of extremely weak grid with a short-circuit ratio of 1.1, in order to execute the grid-side stability control strategy by adding a reactive power synchronization process in the phase-locked loop of the grid-side converter, the following steps are included: obtaining a reference value of reactive power and an actual value of reactive power in the reactive power synchronization process; obtaining a difference value by subtracting the actual value of reactive power from the reference value of reactive power; inputting the difference value 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 a synchronous phase angle of the phase-locked loop through an integration link of an integrator.

[0056] By adding a reactive power synchronization process in the phase-locked loop of the grid-side converter under the condition of extremely weak grid with a short-circuit ratio of 1.1, the application can effectively improve the grid-side stability control, calculate the angular frequency change corresponding to the difference value by comparing the reference value and the actual value of reactive power and using a proportional or proportional-integral controller, superimpose the angular frequency change on the original angular frequency output by the phase-locked loop, and finally obtain an accurate synchronous phase angle through the integrator, so as to realize accurate control and synchronization of the grid reactive power and enhance the stability of the grid under extremely weak conditions.

[0057] When controlling, first, according to the operating state and load demand of the grid, the reference value of reactive power and the actual value of reactive power in the current grid are set; the reference value of reactive power is compared with the actual value to obtain a difference value. The difference value reflects the imbalance between supply and demand of the reactive power in the current grid. Then, the calculated difference value is input into a 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 value, then the angular frequency change output by the controller is superimposed on the original angular frequency output by the phase-locked loop, the angular frequency of the phase-locked loop is adjusted, the adjusted angular frequency is integrated by the integrator to output the synchronous phase angle of the phase-locked loop, and the phase and amplitude of the output voltage and current are adjusted to realize accurate control of the reactive power.

[0058] ReferenceFigure 2 As shown, the net-side stability control link, specifically, the difference value is input into a proportional or proportional-integral controller, and the output is the angular frequency variation.

[0059] Among them, the proportional controller mainly adjusts 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 considers the cumulative effect of the difference, realizes 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 synchronous phase angle through the integrator is:

[0061]

[0062] Among them, θ represents the synchronous phase angle output by the phase-locked loop; Q Gref represents the reference value of the reactive power; Q G represents the actual value of the reactive power; represents the component of the point of common coupling alternating voltage in 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 respectively represent the proportional and integral coefficients of the reactive power ring PI controller, ω0 is the base frequency 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 regulator of the machine-side converter through the band-stop filter and the virtual impedance link, it 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 the band-stop filter and the 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 only the oscillation frequency works, without causing other oscillation stability problems.

[0066] The virtual resistance and virtual inductance of the virtual impedance should be as large as possible in principle, but the upper limit value is limited by the modulation degree of the converter.

[0067] Virtual impedance parameter lower limit value determination method: when designing the virtual impedance parameter, according to the Nyquist stability criterion, draw the Nyquist curve of the full-power wind turbine and the alternating current grid interconnection system, so that the phase margin is equal to the set threshold (such as 30°), thereby obtaining the lower limit value of the 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 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 harmonic components in 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 oscillation, and improve the overall stability of the system; finally, the d-axis and q-axis current components are filtered and impedance-regulated through the band-stop filter and the virtual impedance link to achieve accurate 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, the d-axis and q-axis current components of the machine-side converter are obtained through a current sensor or a current measurement circuit, the obtained d-axis current component is filtered through a band-stop filter to remove harmonic components of a specified frequency, then the filtered d-axis current component is impedance-regulated through a virtual impedance link to obtain a regulated d-axis current component, and the output voltage of the d-axis and q-axis current inner loop regulators is calculated according to the regulated d-axis and q-axis current components and the control algorithm of the current inner loop regulator, serving as the control instruction of the machine-side converter to achieve accurate control of the machine-side converter.

[0071] Referring to Figure 2 Specifically, 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 a band-stop filter and a virtual impedance link, the expression is as follows:

[0072]

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

[0074] The expression of the band-stop filter and the virtual impedance link G vmd is as follows:

[0075]

[0076] where R vmd represents a virtual resistance, L vmd represents a virtual inductance, R vmd +sL vmd represents a 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 a center frequency, ξ d represents a damping ratio, 2ξ d ω nd represents a bandwidth, and s represents a complex frequency variable of Laplace transform.

[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 a band-stop filter and a virtual impedance link, the expression is:

[0078]

[0079] where I represents a current reference value output by the outer loop control, represents a q-axis component of the alternating current, represents a q-axis component of the converter output voltage, k impq and k imiq respectively represent proportional and integral coefficients of the current inner loop PI control, the machine-side rotor inductance is L m , ω m is a fundamental angular frequency, s represents a complex frequency variable of Laplace transform, represents a d-axis component of the alternating current.

[0080] where the expression of the band-stop filter and the virtual impedance link G vmq :

[0081]

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

[0083] As Figure 3 shown in the waveform diagram after the experiment, the running effect of the application in the extremely weak power grid environment, wherein, Figure 3 (a) is the power waveform diagram without any stability control strategy, at this time the system is rapidly oscillating instability under the extremely weak power grid condition, Figure 3 (b) is the power waveform diagram when only the grid-side converter stability control strategy is applied, at this time the system oscillation instability speed slows down, but still exists oscillation instability, Figure 3 (c) is the power waveform diagram when only the machine-side converter stability control strategy is applied, at this time the system oscillation amplitude divergence speed slows down, the stability is improved to a certain extent, but still exists oscillation instability, Figure 3 (d) is the power waveform diagram when the full-power wind turbine stability control method of the application is adopted, under the extremely weak power grid condition, the system is stable.

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

[0085] The grid-side converter stability control module is used to control the grid-side converter of the full-power wind turbine, and executes 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 stability control module is used to control the machine-side converter of the full-power wind turbine, and executes the machine-side stability control strategy by improving the output voltage of the d-axis and q-axis current inner loop regulator of the machine-side converter through a band-stop filter and a virtual impedance link.

[0086] The application realizes basic operation through the basic control modules of the grid-side and machine-side converters, and improves the running stability of the wind turbine under the extremely weak power grid condition by implementing the stability control strategy in the phase-locked loop of the grid-side converter stability control module and the current inner loop of the machine-side converter stability control module. During the execution process, the system first ensures the normal operation of the grid-side converter and the machine-side converter through the converter basic control module, and then finely adjusts 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 stability control under the extremely weak power grid environment.

[0087] In some possible embodiments, the converter basic control module is configured to implement basic control of the grid-side converter and the machine-side converter; the basic control of the grid-side converter comprises: adopting a double closed-loop vector control structure of a constant DC voltage outer loop and a current inner loop; the basic control of the machine-side converter comprises: adopting a constant speed outer loop control and a current inner loop control.

[0088] Through the basic control strategy of the grid-side converter, the double closed-loop vector control structure of the constant DC voltage outer loop and the current inner loop is adopted to realize accurate control of the DC voltage and the current, ensure stable operation of the wind turbine under the condition of the extremely weak power grid, and, in combination with the basic control strategy of the machine-side converter, the constant speed outer loop control and the current inner loop control are adopted to realize accurate control of the speed of the wind turbine and the current, ensure operation of the wind turbine at the optimal speed, improve power generation efficiency and power quality, and further improve the stability of the wind turbine under the condition of the extremely weak power grid.

[0089] Specifically, the stable control strategy implemented in the phase-locked loop of the grid-side converter is that a reactive power synchronous link is added in the phase-locked loop of the grid-side converter, a difference between a reactive power reference value and an actual value of the reactive power is calculated, an angular frequency variation is output after a proportional or proportional-integral controller, the angular frequency variation is superimposed on an angular frequency output by the phase-locked loop, and then a synchronous phase angle is output by an integrator.

[0090] In the operation process, first, the system calculates a difference between the reactive power reference value and the actual value in real time in the extremely weak power grid environment, which reflects an imbalance between supply and demand of the reactive power of the full-power wind turbine in the current power grid; then, the difference is input into a proportional-integral (PI) controller to calculate an angular frequency variation that needs to be adjusted; then, the angular frequency variation 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 by the integrator to output the synchronous phase angle of the phase-locked loop, which is used for accurate control of the grid-side converter.

[0091] Through the above setting, the stability of the grid-side converter under the condition of the extremely weak power grid is improved, the synchronous operation between the grid-side converter and the power grid is ensured by monitoring and controlling the reactive power and controlling the phase-locked loop, the overall performance and reliability of the system are improved, and the stability of the full-power wind turbine in the extremely weak power grid environment is improved.

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

[0093] In the extremely weak environment, the d-axis and q-axis current components of the full-power wind turbine generator side converter are filtered by the band-stop filter and the virtual impedance link respectively, the harmonic components of specific frequency are removed, and the adjusted current components are applied to the output voltage of the d-axis and q-axis current inner loop regulator, so as to realize the accurate control of the current of the side converter.

[0094] The harmonic components in the current are effectively suppressed by setting the band-stop filter in the side converter, and the quality of the current waveform is improved, and the damping characteristics of the system are enhanced by setting the virtual impedance link, and the system oscillation is suppressed, the d-axis and q-axis current components are controlled by the band-stop filter and the virtual impedance link, the accurate regulation of the speed and power of the full-power wind turbine generator in the extremely weak environment is realized, and the stability of the wind turbine generator is improved.

[0095] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the above specific embodiments, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application. The above preferred features can be used in combination in the case of not conflicting with each other.

Claims

1. A method for stable control of a full-power wind turbine generator in an extremely weak power grid, characterized in that, include: To control the grid-side converter of a full-power wind turbine, a grid-side stability control strategy is implemented by adding a reactive power synchronization process to the phase-locked loop of the grid-side converter. The generator-side converter of the full-power wind turbine is controlled by improving the output voltage of the inner loop regulator of the d-axis and q-axis current of the generator-side converter through a band-stop filter and a virtual impedance link, thereby implementing a generator-side stability control strategy. The grid-side stability control strategy is implemented by adding a reactive power synchronization process to the phase-locked loop of the grid-side converter, including: Obtain the reference value and the actual value of reactive power during the reactive power synchronization process; The difference is obtained by subtracting the reference value of reactive power from the actual value of reactive power. The difference is input into a proportional or proportional-integral controller, which outputs the change in angular frequency. The change in angular frequency is superimposed on the angular frequency output by the phase-locked loop; The synchronization phase angle of the phase-locked loop is output through the integrator's integration stage; The method of inputting the difference value into a proportional or proportional-integral controller and outputting the change in angular frequency is to select a proportional-integral (PI) controller that inputs the difference value. The formula for outputting the synchronization phase angle through the integrator is: Where θ represents the synchronization phase angle of the phase-locked loop output; Q Gref A reference value representing reactive power; Q G The actual value representing reactive power; This represents the q-axis component of the AC voltage at the point of common coupling; the superscript "c" indicates the component in the control coordinate system. ppll and k ipll These represent the proportional and integral coefficients of the phase-locked loop PI controller, respectively, k pHSC and k iHSC These 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 element.

2. The method for stable control of a full-power wind turbine generator in an extremely weak power grid according to claim 1, characterized in that, The improvement of the output voltage of the d-axis and q-axis current inner loop regulator of the machine-side converter through a band-stop filter and a virtual impedance circuit includes: 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.

3. The method for stable control of a full-power wind turbine generator in an extremely weak power grid according to claim 2, 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 a band-stop filter and a virtual impedance link is as follows: In the formula, This represents the reference current value of the outer loop control output. This represents the component of the alternating current along the d-axis. k represents the d-axis component of the converter output voltage. impd and k imid These represent the proportional and integral coefficients of the inner loop PI control, respectively, and the rotor inductance on the machine side is L. m ω m The fundamental angular frequency, Represents the q-axis component of the alternating current; Among them, the band-stop filter and the virtual impedance link G vmd The expression is: In the formula, R vmd L represents virtual resistance. 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 ξ represents the center frequency. d Represents the damping ratio, 2ξ d ω nd represents the bandwidth; s represents the complex frequency variable of the Laplace transform.

4. The method for stable control of a full-power wind turbine generator in an extremely weak power grid according to claim 2, 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 a band-stop filter and a virtual impedance link is as follows: In the formula, This represents the reference current value of the outer loop control output. This represents the q-axis component of the alternating current. k represents the q-axis component of the converter output voltage. impq and k imiq These represent the proportional and integral coefficients of the inner loop PI control, respectively, and the rotor inductance on the machine side is L. m ω m Let be the fundamental angular frequency, and s represent the complex frequency variable of the Laplace transform. Represents the component of alternating current on the d-axis; Among them, the band-stop filter and the virtual impedance link G vmq The expression: In the formula, R vmq L represents virtual resistance. 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 ξ represents the center frequency. q Represents the damping ratio, 2ξ q ω nq represents the bandwidth, and s represents the complex frequency variable of the Laplace transform.

5. A system for a full-power wind turbine stability control method for an extremely weak power grid according to any one of claims 1-4, characterized in that, include: Grid-side converter stability control module and generator-side converter stability control module; The grid-side converter stability control module is used to control the grid-side converter of the full-power wind turbine. It executes the grid-side stability control strategy by adding a reactive power synchronization process to the phase-locked loop of the grid-side converter. The machine-side converter stability control module is used to control the machine-side converter of the full-power wind turbine. It improves the output voltage of the inner loop regulator of the d-axis and q-axis current of the machine-side converter through a band-stop filter and a virtual impedance link, and executes the machine-side stability control strategy.

6. A full-power wind turbine stability control system for an extremely weak power grid according to claim 5, characterized in that, It also includes a converter basic control module, which is used to implement basic control of the grid-side converter and the machine-side converter; The basic control of the grid-side converter and the machine-side converter includes: The basic control of the grid-side converter 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 adopts constant speed outer loop control and current inner loop control.

7. A full-power wind turbine stability control system for an extremely weak power grid according to claim 5, characterized in that, The stability control strategy implemented in the phase-locked loop of the grid-side converter is as follows: a reactive power synchronization link is added to the phase-locked loop of the grid-side converter. The difference between the reactive power reference value and the actual reactive power value is calculated, and the change in angular frequency is output after passing through a proportional or proportional-integral controller. This change is then superimposed on the angular frequency output by the phase-locked loop, and finally, the synchronization phase angle is output through an integrator. The stability control strategy implemented in the inner current loop of the generator-side converter is as follows: the d-axis current component of the full-power wind turbine generator-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 full-power wind turbine generator-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.

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