Active damping control method and system for direct-drive wind turbine adapted to weak grid

Abstract

The application provides a direct-drive wind turbine active damping control method suitable for extremely weak power grids, comprising: a first oscillation stability improvement control strategy of a grid-side converter of a direct-drive wind turbine, and a second oscillation stability improvement control strategy of a machine-side converter; the first oscillation stability improvement control strategy is to apply d-axis and q-axis current components to corresponding voltage channels after damping compensation through the combination of a high-pass filter and a virtual impedance link; meanwhile, the q-axis current components are cross-compensated to the d-axis voltage channel after passing through a band-stop filter and a virtual impedance link; the second oscillation stability improvement control strategy is to apply d-axis and q-axis current components to corresponding voltage channels after damping compensation through the combination of a band-stop filter and a virtual impedance link. Through the grid-side converter control strategy and the machine-side converter control strategy, the oscillation stability of the direct-drive wind turbine is improved under the condition of extremely weak power grids, and the dynamic performance is not affected.

Description

Technical Field

[0001] This application relates to the field of new energy power generation technology, specifically to an active damping control method and system for direct-drive wind turbines adapted to extremely weak power grids. Background Technology

[0002] As the world's reliance on renewable energy deepens, new power systems are gradually replacing traditional ones. Wind power, a key component of renewable energy, is seeing its installed capacity and grid connection rate continuously increase. However, with the rapid expansion of wind power systems, the challenges to their stable operation are becoming increasingly prominent, especially under extremely weak grid conditions. Direct-drive wind turbines, as an important component of wind power systems, directly affect the operational efficiency and safety of the entire system due to their oscillation stability.

[0003] In strong grid environments, traditional control strategies can effectively maintain the stable operation of wind turbines. Patent CN121124177A discloses a virtual damping control method and system for wind power grid-side converters. It first uses a frequency-locked loop to precisely track the oscillation signal in the q-axis current, extracting the oscillation amplitude and frequency in real time. Then, the oscillation amplitude is used as the input to a PI controller to dynamically calculate the optimal virtual resistance value. Through adaptive virtual damping control, the wind power grid-side converter can automatically adapt to complex operating conditions such as grid topology changes and equipment switching, significantly improving the stability of wind farm grid connection under weak grid conditions. However, under extremely weak grid conditions with a short-circuit ratio less than 2, power electronic equipment using existing control strategies will be severely affected, leading to system oscillation instability. Currently, research on improving the oscillation stability of wind turbines mainly focuses on weak grid conditions with short-circuit ratios of 1.5 to 3.0, primarily relying on adding active damping to the grid-side converter to suppress oscillations. However, the applicability of existing methods in extremely weak grid environments with even lower short-circuit ratios is debatable. Summary of the Invention

[0004] In view of one of the deficiencies in the prior art, the purpose of this application is to provide an active damping control method for direct-drive wind turbines that is adapted to extremely weak power grids.

[0005] The first aspect of this application provides an active damping control method for direct-drive wind turbines adapted to extremely weak power grids, comprising implementing the following two control strategies: The first oscillation stability improvement control strategy for grid-side converter of direct-drive wind turbine and the second oscillation stability improvement control strategy for generator-side converter of direct-drive wind turbine; The first oscillation stability enhancement control strategy involves applying damped compensation to the d-axis and q-axis current components and then applying them to the corresponding voltage channels through a combination of a high-pass filter and a virtual impedance circuit. Simultaneously, the q-axis current component is cross-compensated to the d-axis voltage channel after passing through a band-stop filter and a virtual impedance circuit. The second oscillation stability enhancement control strategy is to apply damping compensation to the d-axis and q-axis current components and then apply them to the corresponding voltage channels by combining a band-stop filter with a virtual impedance element.

[0006] Optionally, the first oscillation stability improvement control strategy includes: Obtain the d-axis current component and q-axis current component of the grid-side converter of the direct-drive wind turbine; The d-axis current component of the grid-side converter of the direct-drive wind turbine is applied to the output voltage of the inner loop regulator of the d-axis current through a high-pass filter and a virtual impedance link. The q-axis current component of the grid-side converter of the direct-drive wind turbine is applied to the output voltage of the q-axis current inner loop regulator through the high-pass filter and the virtual impedance link. The q-axis current component of the grid-side converter of the direct-drive wind turbine is applied to the output voltage of the d-axis current inner loop regulator through the band-stop filter and the virtual impedance link, thereby increasing the oscillation stability of the grid-side converter.

[0007] Optionally, the step of applying the d-axis current component of the grid-side converter of the direct-drive wind turbine to the output voltage of the d-axis current inner loop regulator through a high-pass filter and a virtual impedance link specifically involves: ; In the formula, u c dref This represents the d-axis component of the converter output voltage. k ipd and k iid These are the proportional and integral coefficients of the current inner-loop PI control, respectively. This is the reference value for the current output of the outer loop control; I c d This represents the d-axis component of the alternating current. oh 0 represents the fundamental angular frequency; L f For filtering inductors; u gd The voltage measurement at the point of common coupling is expressed as the d-axis component. G vd This refers to a high-pass filter and virtual impedance element on the d-axis. Among them, the d-axis high-pass filter and the virtual impedance element The expression is: ; In the formula, R vd For virtual resistance, L vd For virtual inductance, R vd + sL vd For virtual impedance, sT vd / (1+ sT vd ) is a high-pass filter. T vd =1 / f vd , f vd This is the cutoff frequency of the high-pass filter; s For the Laplace operator.

[0008] Optionally, the step of applying the q-axis current component of the direct-drive wind turbine grid-side converter to the output voltage of the q-axis current inner loop regulator through the high-pass filter and the virtual impedance link specifically involves: ; In the formula, u c qref This represents the q-axis component of the converter output voltage. k ipq and k iiq These are the proportional and integral coefficients of the current inner-loop PI control, respectively. This is the reference value for the current output of the outer loop control; I c q This represents the q-axis component of the alternating current. oh 0 represents the fundamental angular frequency; L f For filtering inductors; u gq The voltage measurement at the point of common coupling is expressed as the q-axis component. G vq This refers to a high-pass filter and virtual impedance element on the q-axis. Among them, the q-axis high-pass filter and the virtual impedance element The expression is: ; In the formula, R vq For virtual resistance,L vq For virtual inductance, R vq + sL vq For virtual impedance, sT vq / (1+ sT vq ) is a high-pass filter. T vq =1 / f vq ，f vq This is the cutoff frequency of the high-pass filter; For the Laplace operator.

[0009] Optionally, the step of applying the q-axis current component of the direct-drive wind turbine grid-side converter to the output voltage of the d-axis current inner loop regulator through the band-stop filter and the virtual impedance link specifically involves: ; In the formula, u c dref This refers to the output voltage of the current loop regulator; k ipd and k iid These are the proportional and integral coefficients of the current inner-loop PI control, respectively. This is the reference value for the current output of the outer loop control; I c q This represents the q-axis component of the alternating current. oh 0 represents the fundamental angular frequency; L f For filtering inductors; I c d This represents the d-axis component of the alternating current. u gq The voltage measurement at the point of common coupling is expressed as the q-axis component. G vq For high-pass filters and virtual impedance circuits; G vdq For cross-term band-stop filters and virtual impedance circuits; Among them, the cross-term band-stop filter and the virtual impedance element G vdq The expression is: ; In the formula, R vdq For virtual resistance, Lvdq For virtual inductance, R vdq + sL vdq For virtual impedance, (s 2 + oh 2 ndq ) / (s 2 +2 x dq oh ndq s+ oh 2 ndq () is a band-stop filter. oh ndq For the center frequency, x dq For the damping ratio, 2 x dq oh ndq For bandwidth.

[0010] Optionally, the second oscillation stability improvement control strategy includes: The d-axis current component of the direct-drive wind turbine generator's 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 direct-drive wind turbine generator is applied to the output voltage of the q-axis current inner loop regulator through a band-stop filter and a virtual impedance link, thereby increasing the oscillation stability of the generator.

[0011] Optionally, the step of applying the d-axis current component of the direct-drive wind turbine generator's 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 specifically involves: ; In the formula, This is the reference value for the current output of the outer loop control; I c md Let represent the d-component of the alternating current. u c mref For the converter output voltage at d The components of the axis; k impd and k imid These are the proportional and integral coefficients of the current inner-loop PI control, respectively. L m For the rotor inductance on the machine side, oh m The fundamental angular frequency; Gvmd For the band-stop filter and virtual impedance element on the d-axis of the machine side; Among them, the band-stop filter and virtual impedance link on the d-axis of the machine side G vmd The expression is: ; In the formula, R vmd For virtual resistance, L vmd For virtual inductance, R vmd + sL vmd For virtual impedance, (s 2 + oh 2 nd ) / (s 2 +2 x d oh nd s+ oh 2 nd () is a band-stop filter. oh nd For the center frequency, x d For the damping ratio, 2 x d oh nd For bandwidth.

[0012] Optionally, the step of applying the q-axis current component of the direct-drive wind turbine generator to the output voltage of the q-axis current inner loop regulator through a band-stop filter and a virtual impedance link on the q-axis side specifically involves: ; In the formula, This is the reference value for the current output of the outer loop control. I c mq For alternating current in q Components of the axis, u c mref This represents the q-axis component of the converter output voltage. k impq and k imiq These are the proportional and integral coefficients of the inner loop PI control, respectively, and the rotor inductance on the machine side is... L m , oh m The fundamental angular frequency; Gvmq This refers to the band-stop filter and virtual impedance element on the machine-side q-axis. Among them, the band-stop filter and virtual impedance element on the machine-side q-axis G vmq The expression is: ; In the formula, R vmq For virtual resistance, L vmq For virtual inductance, R vmq + sL vmq For virtual impedance, ( s 2 + oh 2 nq ) / ( s 2 +2 x q oh nq s + oh 2 nq () is a band-stop filter. oh nq For the center frequency, x q For the damping ratio, 2 x q oh nq For bandwidth.

[0013] Optionally, the direct-drive wind turbine includes: a grid-side converter, a turbine-side converter, and a wind turbine. The grid-side converter of the direct-drive wind turbine adopts a dual closed-loop vector control structure with constant DC voltage and reactive power outer loop and current inner loop. The machine-side converter of the direct-drive wind turbine adopts constant speed outer loop control and current inner loop control.

[0014] A second aspect of this application provides an active damping control system for direct-drive wind turbines adapted to extremely weak power grids, comprising: The grid-side converter control module is used to implement the first oscillation stability improvement control strategy in the controller of the grid-side converter to improve the oscillation stability of the direct-drive wind turbine under extremely weak grid conditions. The machine-side converter control module is used to implement a second stability enhancement control strategy in the controller of the machine-side converter to further improve the oscillation stability of the direct-drive wind turbine. The first oscillation stability enhancement control strategy involves applying damped compensation to the d-axis and q-axis current components and then applying them to the corresponding voltage channels through a combination of a high-pass filter and a virtual impedance circuit. Simultaneously, the q-axis current component is cross-compensated to the d-axis voltage channel after passing through a band-stop filter and a virtual impedance circuit. The second oscillation stability enhancement control strategy is to apply damping compensation to the d-axis and q-axis current components and then apply them to the corresponding voltage channels by combining a band-stop filter with a virtual impedance element.

[0015] This application provides an active damping control method for direct-drive wind turbines adapted to extremely weak power grids. It combines a first oscillation stability enhancement control strategy for the grid-side converter of the direct-drive wind turbine with a second oscillation stability enhancement control strategy for the machine-side converter. Through a combination of a high-pass filter and a virtual impedance link, the d-axis and q-axis current components are damped and compensated before being applied to the corresponding voltage channels. The q-axis current component is also cross-compensated to the d-axis voltage channel after passing through a band-stop filter and a virtual impedance link, thus increasing the oscillation stability of the grid-side converter. Furthermore, the combination of a band-stop filter and a virtual impedance link further enhances the oscillation stability of the machine-side converter, improving the stable operation capability of the wind turbine in harsh power grid environments. This provides strong support for the safe and reliable operation of the wind power generation system without affecting its dynamic performance, and allows the wind turbine to maintain stability during fault ride-through.

[0016] Other technical effects resulting from the additional features will be further illustrated in the corresponding embodiments. Attached Figure Description

[0017] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 The flowchart illustrates an active damping control method for a direct-drive wind turbine adapted to an extremely weak power grid, according to an exemplary embodiment. Figure 2 This is a flowchart illustrating an active damping control method for a direct-drive wind turbine adapted to an extremely weak power grid, according to an exemplary embodiment. Figure 3 This is a block diagram illustrating a direct-drive wind turbine stability control system adapted to an extremely weak power grid, according to an exemplary embodiment. Figure 4Figure 1 shows the active and reactive power simulation waveforms of a direct-drive wind turbine generator with a short-circuit ratio of 1.1 in an extremely weak power grid according to an exemplary embodiment. Figure 2 shows the power waveform without any stabilization control strategy, Figure 3 shows the power waveform with only the turbine-side converter stabilization control strategy applied, Figure 4 shows the power waveform with only the grid-side converter stabilization control strategy applied, and Figure 5 shows the power waveform with the active damping control method for direct-drive wind turbine generators proposed in this application. Detailed Implementation

[0018] 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, and these all fall within the protection scope of the present application. Parts not described in detail in the following embodiments can be implemented using existing technology.

[0019] In existing technologies, under strong power grid conditions, traditional control strategies can effectively maintain the stable operation of wind turbine generators. However, under extremely weak power grid conditions with a short-circuit ratio of less than 2, power electronic equipment using existing control strategies is severely affected, leading to system oscillations and instability. Based on these problems, this application provides an active damping control method for direct-drive wind turbine generators adapted to extremely weak power grids to address these issues.

[0020] Reference Figure 1 As shown in one embodiment of this application, an active damping control method for direct-drive wind turbines adapted to extremely weak power grids includes executing two control strategies: a first oscillation stability improvement control strategy for the grid-side converter of the direct-drive wind turbine and a second oscillation stability improvement control strategy for the generator-side converter of the direct-drive wind turbine. The first oscillation stability enhancement control strategy involves applying damped compensation to the d-axis and q-axis current components to the corresponding voltage channels through a combination of a high-pass filter and a virtual impedance circuit. Simultaneously, the q-axis current component is cross-compensated to the d-axis voltage channel after passing through a band-stop filter and a virtual impedance circuit. The second oscillation stability enhancement control strategy involves applying damped compensation to the d-axis and q-axis current components to the corresponding voltage channels through a combination of a band-stop filter and a virtual impedance circuit.

[0021] It should be noted that the extremely weak power grid environment in this application is a power grid environment with a short-circuit ratio of not less than 1.1. The first oscillation stability improvement control strategy and the second oscillation stability improvement control are executed independently on the grid side and the machine side, respectively. They can be executed simultaneously or at different times.

[0022] Specifically, in the grid-side converter's inner current loop, the acquired d-axis and q-axis current components are processed by a combination of a high-pass filter and a virtual impedance link. The processed signals are then injected into the corresponding d-axis and q-axis voltage control channels. Simultaneously, the q-axis current component is passed through another set of band-stop filters and virtual impedance links before being cross-injected into the d-axis voltage channel. This actively introduces an additional damping term into the control loop, dynamically increasing virtual resistance and inductance in a specific system frequency band (high-frequency oscillation band), thus enhancing the damping capability for high-frequency oscillations. Meanwhile, in the machine-side converter, its d-axis and q-axis current components are processed by a combination of a band-stop filter and a virtual impedance link. The results are then applied to their respective inner current loop voltage outputs. The center frequency of the band-stop filter is set to the system's potential resonant frequency point. This allows the band-stop filter to extract the oscillating current component in this frequency band, and the virtual impedance link generates a compensation voltage with an opposite phase to the oscillation component. This actively cancels and dampens the oscillation at this specific frequency in the original control loop.

[0023] The embodiments described above, targeting the grid-side converter, can effectively suppress broadband oscillations (especially sub / supersynchronous oscillations) caused by the interaction between the grid-side converter and the weak grid under extremely weak grid conditions (such as a short-circuit ratio as low as 1.1), significantly improving the power stability at the grid connection point. Furthermore, due to the characteristics of the high-pass filter, it does not affect the steady-state and dynamic performance near the power frequency, ensuring the continuous and stable operation of the wind turbine during fault ride-through. Combined with the strategy of the turbine-side converter, it can effectively suppress narrowband, specific-frequency resonances or oscillations (such as shaft torsional vibration, coupling between the turbine-side controller and the grid side) excited within the direct-drive wind turbine unit under extremely weak grid conditions, preventing turbine-side instability from propagating to the entire system, improving the unit's own operational stability, and providing better internal conditions for grid-side stable control by stabilizing the turbine side. The two work together to ensure the global stability and power generation continuity of the wind turbine under extreme grid environments.

[0024] Reference Figure 2 As shown, in some specific embodiments of this application, the first oscillation stability improvement control strategy includes: Obtain the d-axis current component and q-axis current component of the grid-side converter of the direct-drive wind turbine; S100. The d-axis current component of the grid-side converter of the direct-drive wind turbine is applied to the output voltage of the inner loop regulator of the d-axis current through a high-pass filter and a virtual impedance link. S200: The q-axis current component of the grid-side converter of the direct-drive wind turbine is applied to the output voltage of the q-axis current inner loop regulator through a high-pass filter and a virtual impedance link; S300: The q-axis current component of the grid-side converter of the direct-drive wind turbine is applied to the output voltage of the d-axis current inner loop regulator through a band-stop filter and a virtual impedance link, thereby increasing the oscillation stability of the grid-side converter.

[0025] Specifically, firstly, the d-axis and q-axis current components of the grid-side converter of the direct-drive wind turbine are acquired in real time in the synchronous rotating coordinate system through the current detection unit to ensure the real-time performance and accuracy of the current signal. Then, for the d-axis current component, the oscillation component is filtered out using a high-pass filter, and then impedance is adjusted through a virtual impedance circuit. The processed current component is then applied to the output voltage of the d-axis current inner loop regulator, forming the first layer of damping compensation. Simultaneously, the q-axis current component is processed by the same high-pass filter and virtual impedance circuit before being applied to the output voltage of the q-axis current inner loop regulator, forming the second layer of damping compensation. Finally, the q-axis current component is optimized again by a band-stop filter and virtual impedance circuit before being applied across channels to the output voltage of the d-axis current inner loop regulator, constructing the third layer of cross-damping compensation. Through the coordinated action of these three channels, the oscillation stability of the grid-side converter is improved and controlled.

[0026] The embodiments described above in this application, through the collaborative design of a high-pass filter and a virtual impedance link, screen harmonic components of specific frequencies, and improve the system damping characteristics under extremely weak power grids (short-circuit ratio ≥ 1.1) by simulating the equivalent impedance of the power grid using virtual impedance. The triple damping compensation covers the oscillation suppression requirements of the d-axis and q-axis currents of the grid-side converter, solving the problem that a single damping strategy is difficult to cope with multi-frequency oscillations under extremely weak power grids. At the same time, damping compensation is performed in the inner current loop without changing the original dual closed-loop control architecture of the grid-side converter, ensuring the oscillation suppression effect and without sacrificing the dynamic response speed of the unit. This ensures that the wind turbine can maintain stability during normal operation and fault ride-through in extremely weak power grids, and improves the adaptability and operational reliability of direct-drive wind turbines in complex power grid environments.

[0027] Reference Figure 3 As shown in (a) in the figure, the control loop is constructed based on the power grid synchronous rotating coordinate system. and The input is the current command, and the feedback is the actual d-axis and q-axis current during operation. I c d and I c q ; H i (s) is the PI controller for the inner current loop; oh 0 L f This is a decoupling step for dq; G vd(s) represents the high-pass filter element and virtual impedance element along the d-axis; G vq (s) represents the high-pass filter element and virtual impedance element on the q-axis; G vdq (s) represents the high-pass filter stage and virtual impedance stage of the cross term; u c dref This represents the d-axis component of the converter output voltage. u c qref This represents the q-axis component of the converter output voltage. u gd and u gq It is a voltage feedforward quantity; Current commands on the d-axis and q-axis and For input, and the actual current of feedback. I d c , I q c After comparison, it passes through the PI controller. H i (s) is adjusted; through oh 0 L f The project achieves dynamic decoupling between the d and q axes and introduces a combination of high-pass filtering and virtual impedance in each channel. G vd (s), G vq (s) and the band-stop filter stage and virtual impedance stage of the cross term G vdq (s) is used to improve grid-side stability. The converter modulation voltage signal is ultimately generated. u c dref and u c qref And add grid voltage feedforward. u gd , u gq .

[0028] In some specific embodiments of this application, the d-axis current component of the direct-drive wind turbine grid-side converter is applied to the output voltage of the d-axis current inner loop regulator through a high-pass filter and a virtual impedance link, specifically as follows: ; In the formula, u cdref This represents the d-axis component of the converter output voltage. k ipd and k iid These are the proportional and integral coefficients of the current inner-loop PI control, respectively. This is the reference value for the current output of the outer loop control; I c d This represents the d-axis component of the alternating current. oh 0 represents the fundamental angular frequency; L f For filtering inductors; u gq The voltage measurement at the point of common coupling is expressed as the d-axis component. G vd This refers to a high-pass filter and virtual impedance element on the d-axis. Among them, the high-pass filter and the virtual impedance element G vd The expression is: ; In the formula, R vd For virtual resistance, L vd For virtual inductance, R vd + sL vd For virtual impedance, sT vd / (1+ sT vd ) is a high-pass filter. T vd =1 / f vd , f vd This is the cutoff frequency of the high-pass filter; For the Laplace operator.

[0029] In some specific embodiments of this application, the q-axis current component of the grid-side converter of the direct-drive wind turbine is applied to the output voltage of the q-axis current inner loop regulator through a high-pass filter and a virtual impedance link, specifically as follows: ; In the formula, u c qref This represents the q-axis component of the converter output voltage. k ipd and k iid These are the proportional and integral coefficients of the current inner-loop PI control, respectively. This is the reference value for the current output of the outer loop control; I c q This represents the q-axis component of the alternating current. oh 0 represents the fundamental angular frequency; L f For filtering inductors; u gq The voltage measurement at the point of common coupling is expressed as the q-axis component. G vq This refers to a high-pass filter and virtual impedance element on the q-axis. Among them, the high-pass filter and virtual impedance element on the q-axis The expression is: ; In the formula, R vq For virtual resistance, L vq For virtual inductance, R vq + sL vq For virtual impedance, sT vq / (1+ sT vq ) is a high-pass filter. T vq =1 / f vq ，f vq This is the cutoff frequency of the high-pass filter; For the Laplace operator.

[0030] It should be noted that the cutoff frequency of the high-pass filter... f vq Choose the frequency of the low-frequency oscillation that occurs in the synchronous machine. In principle, the larger the virtual resistance and virtual inductance of the virtual impedance, the more stable the system; however, their upper limits are limited by the converter's modulation index.

[0031] Method for determining the lower limit of virtual impedance parameters: When designing virtual impedance parameters, the Nyquist curve of the full-power wind turbine interconnection system with the AC grid is plotted according to the Nyquist stability criterion, and its phase margin is equal to the set threshold (such as 30°), thereby obtaining the lower limit of virtual resistance and virtual inductance in virtual impedance.

[0032] In some specific embodiments of this application, the q-axis current component of the direct-drive wind turbine grid-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, specifically as follows: ; In the formula, u c dref k is the output voltage of the current loop regulator. ipd and k iid These are the proportional and integral coefficients of the current inner-loop PI control, respectively. This is the reference value for the current output of the outer loop control; I c d This represents the d-axis component of the alternating current. oh 0 represents the fundamental angular frequency; L f For filtering inductors; I c q This represents the q-axis component of the alternating current. u gd The voltage measurement at the point of common coupling is expressed as the d-axis component. G vd This refers to the high-pass filter and virtual impedance element on the d-axis. G vdq For cross-term band-stop filters and virtual impedance circuits; Among them, the cross-term band-stop filter and the virtual impedance element The expression is: ; In the formula, R vdq For virtual resistance, L vdq For virtual inductance, R vdq + sL vdq For virtual impedance, (s 2 + oh 2 ndq ) / (s 2 +2 x dq oh ndq s+ oh 2 ndq () is a band-stop filter. oh ndq For the center frequency, x dq For the damping ratio, 2 x dq oh ndq For bandwidth.

[0033] Specifically, appropriate high-pass filters and virtual impedance circuits are determined as needed. The d-axis and q-axis current components of the grid-side converter are acquired through current sensors or current measurement circuits. The acquired d-axis current components are filtered by a high-pass filter to remove harmonic components of a specified frequency. Then, the filtered d-axis current components are impedance-adjusted through a virtual impedance circuit to obtain the 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 voltage of the d-axis and q-axis current inner loop regulator is calculated and used as the control command for the grid-side converter to achieve precise control of the grid-side converter.

[0034] In the above embodiments of this application, the output voltage of the inner loop regulator of the d-axis and q-axis current of the grid-side converter is improved by using a high-pass filter and a virtual impedance circuit. The high-pass filter can accurately filter out oscillation components; the virtual impedance circuit 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, by using the high-pass filter and the virtual impedance circuit, the d-axis and q-axis current components are filtered and impedance adjusted to achieve precise control of the current output and improve the response speed and accuracy of current control.

[0035] In some specific embodiments of this application, the second oscillation stability enhancement control strategy includes: S400: The d-axis current component of the direct-drive 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. S500 applies the q-axis current component of the direct-drive wind turbine generator's 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, thereby increasing the oscillation stability of the machine-side converter.

[0036] Specifically, for the machine-side converter, the d-axis and q-axis current components of the direct-drive wind turbine machine-side converter in the synchronous rotating coordinate system are collected by a current sensing module to ensure accurate acquisition of the current signal. For the d-axis current component, a band-stop filter is first used to target and filter out specific frequency harmonic components that cause oscillations under extremely weak grid conditions. Then, impedance matching adjustment is performed through a virtual impedance circuit containing virtual resistance and virtual inductance. The processed d-axis current component is applied to the output voltage of the d-axis current inner loop regulator to form the first damping compensation. At the same time, the same band-stop filtering and virtual impedance adjustment process is performed on the q-axis current component. The processed q-axis current component is applied to the output voltage of the q-axis current inner loop regulator to construct the second damping compensation. The oscillation stability improvement control of the machine-side converter is completed through dual-channel synchronous action.

[0037] The embodiments described above employ a collaborative method combining a band-stop filter and a virtual impedance link. The band-stop filter can precisely suppress specific frequency oscillations of the generator-side converter under extremely weak power grid conditions, avoiding interference with the fundamental frequency current signal. The virtual impedance link optimizes the output impedance characteristics of the generator-side converter through a combination of virtual resistance and inductance, enhancing the impedance matching degree with the extremely weak power grid and effectively suppressing the current oscillation amplitude. Dual-channel damping compensates for the oscillation suppression requirements of the d-axis and q-axis currents of the grid-side converter. Simultaneously, local optimization is performed only in the inner current loop without changing the original constant-speed outer loop control architecture of the generator-side converter. This significantly improves oscillation stability without affecting the unit's speed regulation accuracy and dynamic response performance, ensuring that the direct-drive wind turbine can operate stably and maintain good power generation efficiency under extremely weak power grid conditions. It can also maintain stable generator-side current during fault ride-through, expanding the applicable power grid scenarios for the unit.

[0038] Reference Figure 3 As shown in (b) in the figure, the control loop is constructed based on the power grid synchronous rotating coordinate system. and The input is the current command, and the feedback is the actual d-axis and q-axis current during operation. I c md and I c mq ; H mi (s) is the PI controller for the inner current loop; oh 0 L f This is a decoupling step for dq; G vmd (s) represents the band-stop filter element and the virtual impedance element along the d-axis; G vmq (s) represents the band-stop filter element and the virtual impedance element on the q-axis.

[0039] Current commands on the d-axis and q-axis and For input, and the actual current of feedback. I c md , I c mq After comparison, it passes through the PI controller. H mi (s) is adjusted; through oh m L m The project achieves dynamic decoupling between the d and q axes, with band-stop filter components and virtual impedance components for the d and q axes, respectively. G vmd (s) and Gvmq (s) to improve machine-side stability.

[0040] In some specific embodiments of this application, the d-axis current component of the direct-drive wind turbine generator is applied to the output voltage of the d-axis current inner loop regulator through a band-stop filter and a virtual impedance link, specifically as follows: ; In the formula, This is the reference value for the current output of the outer loop control; I c md Let represent the d-component of the alternating current. u c mdref For the converter output voltage at d The components of the axis; k impd and k imid These are the proportional and integral coefficients of the current inner-loop PI control, respectively. L m For the rotor inductance on the machine side, oh m The fundamental angular frequency; G vmd For the machine-side d-axis band-stop filter and virtual impedance element; Among them, the band-stop filter and virtual impedance element on the machine-side d-axis G vmd The expression is: ; In the formula, R vmd For virtual resistance, L vmd For virtual inductance, R vmd + sL vmd For virtual impedance, (s 2 + oh 2 nd ) / (s 2 +2 x d oh nd s+ oh 2 nd () is a band-stop filter. oh nd For the center frequency, x d For the damping ratio, 2 x d ohnd For bandwidth.

[0041] In some specific embodiments of this application, the q-axis current component of the direct-drive wind turbine generator is applied to the output voltage of the q-axis current inner loop regulator through a band-stop filter and a virtual impedance link, specifically as follows: ; In the formula, This is the reference value for the current output of the outer loop control. I c mq For alternating current in q Components of the axis, u c mqref For the converter output voltage at q Components of the axis, k impq and k imiq These are the proportional and integral coefficients of the inner loop PI control, respectively, and the rotor inductance on the machine side is... L m , oh m The fundamental angular frequency; G vmq This refers to the band-stop filter and virtual impedance element on the machine-side q-axis. Among them, the machine-side q-axis band-stop filter and virtual impedance element G vmq The expression is: ; In the formula, R vmq For virtual resistance, L vmq For virtual inductance, R vmq + sL vmq For virtual impedance, ( s 2 + oh 2 nq ) / ( s 2 +2 x q oh nq s + oh 2 nq () is a band-stop filter. oh nq For the center frequency, x q For the damping ratio, 2 x q oh nq For bandwidth.

[0042] In some specific embodiments of this application, the direct-drive wind turbine includes: a grid-side converter, a machine-side converter, and a wind turbine; the grid-side converter of the direct-drive wind turbine adopts a dual closed-loop vector control structure with constant DC voltage and reactive power outer loop and current inner loop; the machine-side converter of the direct-drive wind turbine adopts constant speed outer loop control and current inner loop control.

[0043] The embodiments described above in this application, through the basic control strategy of the grid-side converter, employ a dual closed-loop vector control structure with a constant DC voltage outer loop and a current inner loop to achieve precise control of DC voltage and current, ensuring stable operation of the wind turbine under extremely weak grid conditions. Simultaneously, combined with the basic control strategy of the turbine-side converter, a constant speed outer loop control and a current inner loop control are adopted to achieve precise control of the wind turbine speed and current, ensuring that the wind turbine operates at the optimal speed, improving power generation efficiency and power quality, and further enhancing the stability of the wind turbine in extremely weak grid environments.

[0044] Based on the same concept, in another specific embodiment of the application, an active damping control system for direct-drive wind turbines adapted to extremely weak power grids is provided, used to implement the active damping control method for direct-drive wind turbines adapted to extremely weak power grids in any of the above embodiments, specifically including: The grid-side converter control module is used to implement a first oscillation stability enhancement control strategy in the controller of the grid-side converter to improve the oscillation stability of the direct-drive wind turbine under extremely weak grid conditions; the machine-side converter control module is used to implement a second stability enhancement control strategy in the controller of the machine-side converter to further improve the oscillation stability of the direct-drive wind turbine.

[0045] The first oscillation stability enhancement control strategy involves applying damped compensation to the d-axis and q-axis current components to the corresponding voltage channels through a combination of a high-pass filter and a virtual impedance circuit. Simultaneously, the q-axis current component is cross-compensated to the d-axis voltage channel after passing through a band-stop filter and a virtual impedance circuit. The second oscillation stability enhancement control strategy involves applying damped compensation to the d-axis and q-axis current components to the corresponding voltage channels through a combination of a band-stop filter and a virtual impedance circuit.

[0046] This application achieves basic operation through the basic control modules of the grid-side and turbine-side converters. Simultaneously, it implements stability control strategies in the current inner loop through the grid-side converter stability control module and the turbine-side converter stability control module, thereby improving the operational stability of the wind turbine under extremely weak grid conditions. During execution, the first oscillation stability enhancement control strategy and the second stability enhancement control strategy are executed in parallel. The system first ensures the normal operation of the grid-side and turbine-side converters through the basic converter control module. Subsequently, the grid-side and turbine-side converter stability control modules perform fine-tuning for the grid and turbine sides respectively, achieving stable control under extremely weak grid conditions.

[0047] Furthermore, it also has a converter control module for implementing basic converter control; the d-axis current component of the grid-side converter is applied to the output voltage of the d-axis current inner loop regulator through a high-pass filter and a virtual impedance link; the q-axis current component of the grid-side converter of the direct-drive wind turbine is applied to the output voltage of the q-axis current inner loop regulator through a high-pass filter and a virtual impedance link; and the q-axis current component of the grid-side converter of the direct-drive wind turbine is applied to the output voltage of the d-axis current inner loop regulator through a band-stop filter and a virtual impedance link.

[0048] In extremely weak grid environments, to enhance system damping characteristics, a high-pass filter and a virtual impedance element are introduced into the inner current loop of the grid-side converter. Specifically, the d-axis current component of the grid-side converter of the direct-drive wind turbine is processed by a high-pass filter and a virtual impedance element before being applied to the output voltage of the d-axis current inner loop regulator; the q-axis current component is processed by a high-pass filter and a virtual impedance element before being applied to the output voltage of the q-axis current inner loop regulator. Simultaneously, the q-axis current component is processed by a band-stop filter and a virtual impedance element before being applied to the output voltage of the d-axis current inner loop regulator, thus constructing a d–q cross-damping channel to achieve precise control of the grid-side converter current. By setting a high-pass filter in the control structure of the grid-side converter, harmonic components of specific frequencies are filtered out; at the same time, the virtual impedance element in the control structure enhances the system's damping characteristics and suppresses system oscillations. By relying on the high-pass filter and virtual impedance element in the control structure, the d-axis and q-axis current components are precisely controlled, realizing the precise adjustment of voltage and power on the grid side of the full-power wind turbine in the grid environment (including extremely weak grid scenarios), thus improving the stability of the wind turbine.

[0049] Specifically, the d-axis current component of the direct-drive wind turbine generator's 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, and the q-axis current component of the direct-drive wind turbine generator's 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.

[0050] In extremely weak grid environments, the d-axis and q-axis current components of the full-power wind turbine generator's generator-side converter are filtered by band-stop filters to remove harmonic components of specific frequencies, and then impedance is regulated by virtual impedance. The regulated current components are then applied to the output voltage of the d-axis and q-axis current inner loop regulators, achieving precise control of the generator-side converter current.

[0051] By setting a band-stop filter in the turbine-side converter, 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 are precisely adjusted in an extremely weak grid environment, thereby improving the stability of the wind turbine.

[0052] The preferred features in the above embodiments can be used individually in any embodiment, or in any combination thereof, provided they do not conflict with each other. Furthermore, parts not described in detail in the embodiments can be implemented using existing technologies.

[0053] The following examples and comparative examples will be used to further illustrate this application in order to better understand the above-mentioned technical solutions. It should be understood that the following are only some examples and are not intended to limit this application.

[0054] Example: The key parameters of the simulation system are set as follows: rated capacity of the unit is 4MW; rated DC bus voltage is 1.12kV; AC side line voltage is 0.69kV. The main parameters of the generator-side permanent magnet synchronous generator (PMSG) are: stator resistance... R m The synchronous reactance is 46.1mΩ. L R It is 17.2 mH, and the number of pole pairs is... n P It is 32. Near the rated wind speed, the rotor angular velocity is approximately... oh R The permanent magnet flux is 2 rad / s. P r The value is 8.4. The main circuit parameters of the grid-side converter (GSC) include: filter inductor. L f is 30μH, DC support capacitor C dc The parameters of the PI regulator used in the control system of the 32640μF generator-side and grid-side converter are shown in Table 1.

[0055] Table 1. Control system parameters for direct-drive wind turbine generator sets: Table 1: DD-WTGS Control System Parameters

[0056] Under an extremely weak power grid with a grid strength of 1.01, Figure 4 (a) Without any additional measures, wind turbines using traditional grid-connected control cannot operate stably. Figure 4 (b) Only the suppression measures on the generator side are implemented. Simply increasing generator-side stability cannot make the system operate stably under extremely weak power grid conditions. Figure 4 (c) Only grid-side suppression measures are implemented, and simply increasing grid-side stability cannot enable the system to operate stably under extremely weak power grid conditions. Figure 4 (d) To implement all active damping control methods, the system can operate stably under extremely weak power grid conditions after this measure is implemented.

[0057] The foregoing has described some specific embodiments of this application. It should be understood that this application is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the substantive content of this application. The above-described preferred features can be used in any combination without conflict.

Claims

1. An active damping control method for direct-drive wind turbines adapted to extremely weak power grids, characterized in that, This includes implementing the following two control strategies: The first oscillation stability improvement control strategy for grid-side converter of direct-drive wind turbine and the second oscillation stability improvement control strategy for generator-side converter of direct-drive wind turbine; The first oscillation stability enhancement control strategy involves applying damped compensation to the d-axis and q-axis current components and then applying them to the corresponding voltage channels through a combination of a high-pass filter and a virtual impedance circuit. Simultaneously, the q-axis current component is cross-compensated to the d-axis voltage channel after passing through a band-stop filter and a virtual impedance circuit. The second oscillation stability enhancement control strategy is to apply damping compensation to the d-axis and q-axis current components and then apply them to the corresponding voltage channels by combining a band-stop filter with a virtual impedance element.

2. The active damping control method for direct-drive wind turbines adapted to extremely weak power grids according to claim 1, characterized in that, The first oscillation stability improvement control strategy for the grid-side converter of the direct-drive wind turbine includes: Obtain the d-axis current component and q-axis current component of the grid-side converter of the direct-drive wind turbine; The d-axis current component of the grid-side converter of the direct-drive wind turbine is applied to the output voltage of the inner loop regulator of the d-axis current through a high-pass filter and a virtual impedance link. The q-axis current component of the grid-side converter of the direct-drive wind turbine is applied to the output voltage of the q-axis current inner loop regulator through the high-pass filter and the virtual impedance link. The q-axis current component of the grid-side converter of the direct-drive wind turbine is applied to the output voltage of the d-axis current inner loop regulator through the band-stop filter and the virtual impedance link, thereby increasing the oscillation stability of the grid-side converter.

3. The active damping control method for direct-drive wind turbines adapted to extremely weak power grids according to claim 2, characterized in that, The process of applying the d-axis current component of the grid-side converter of the direct-drive wind turbine to the output voltage of the d-axis current inner loop regulator through a high-pass filter and a virtual impedance link is as follows: ； In the formula, u c dref This represents the d-axis component of the converter output voltage. k ipd and k iid These are the proportional and integral coefficients of the current inner-loop PI control, respectively. This is the reference value for the current output of the outer loop control; I c d This represents the d-axis component of the alternating current. ω 0 represents the fundamental angular frequency; L f For filtering inductors; u gd The voltage measurement at the point of common coupling is expressed as the d-axis component. G vd This refers to the high-pass filter and virtual impedance element on the d-axis. Among them, the d-axis high-pass filter and the virtual impedance element The expression is: ； In the formula, R vd For virtual resistance, L vd For virtual inductance, R vd + sL vd For virtual impedance, sT vd / (1+ sT vd () is a high-pass filter. T vd =1 / f vd , f vd This is the cutoff frequency of the high-pass filter; For the Laplace operator.

4. The active damping control method for direct-drive wind turbines adapted to extremely weak power grids according to claim 2, characterized in that, The process of applying the q-axis current component of the grid-side converter of the direct-drive wind turbine to the output voltage of the q-axis current inner loop regulator through the high-pass filter and the virtual impedance link is as follows: ； In the formula, u c qref This represents the q-axis component of the converter output voltage. k ipd and k iid These are the proportional and integral coefficients of the current inner-loop PI control, respectively. This is the reference value for the current output of the outer loop control; I c q This represents the q-axis component of the alternating current. ω 0 represents the fundamental angular frequency; L f For filtering inductors; u gq The voltage measurement at the point of common coupling is expressed as the q-axis component. G vq This refers to a high-pass filter and virtual impedance element on the q-axis. Among them, the high-pass filter and virtual impedance element on the q-axis The expression is: ； In the formula, R vq For virtual resistance, L vq For virtual inductance, R vq + sL vq For virtual impedance, sT vq / (1+ sT vq () is a high-pass filter. T vq =1 / f vq , f vq This is the cutoff frequency of the high-pass filter; s For the Laplace operator.

5. The active damping control method for direct-drive wind turbines adapted to extremely weak power grids according to claim 2, characterized in that, Specifically, the process of applying the q-axis current component of the direct-drive wind turbine grid-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 as follows: ； In the formula, u c dref This refers to the output voltage of the current loop regulator; k ipd and k iid These are the proportional and integral coefficients of the current inner-loop PI control, respectively. This is the reference value for the current output of the outer loop control; I c d This represents the d-axis component of the alternating current. ω 0 represents the fundamental angular frequency; L f For filtering inductors; I c q Represents the q-axis component of the alternating current; u gd The voltage measurement at the point of common coupling is expressed as the d-axis component. G vd This refers to the high-pass filter and virtual impedance element on the d-axis. G vdq For cross-term band-stop filters and virtual impedance elements; Among them, the band-stop filter and virtual impedance element on the cross term G vdq The expression is: ； In the formula, R vdq For virtual resistance, L vdq For virtual inductance, R vdq + sL vdq For virtual impedance, (s 2 + ω 2 ndq ) / (s 2 +2 ξ dq ω ndq s+ ω 2 ndq () is a band-stop filter. ω ndq For the center frequency, ξ dq For the damping ratio, 2 ξ dq ω ndq For bandwidth.

6. The active damping control method for direct-drive wind turbines adapted to extremely weak power grids according to claim 1, characterized in that, The second oscillation stability enhancement control strategy for the direct-drive wind turbine generator side converter includes: The d-axis current component of the direct-drive wind turbine generator's 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 direct-drive wind turbine generator is applied to the output voltage of the q-axis current inner loop regulator through a band-stop filter and a virtual impedance link, thereby increasing the oscillation stability of the generator.

7. The active damping control method for direct-drive wind turbines adapted to extremely weak power grids according to claim 6, characterized in that, The process of applying the d-axis current component of the direct-drive wind turbine generator's 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 is the reference value for the current output of the outer loop control; I c md Let represent the d-axis component of the alternating current. u c mdref This represents the d-axis component of the converter output voltage. k impd and k imid These are the proportional and integral coefficients of the current inner-loop PI control, respectively. L m For the rotor inductance on the machine side, ω m The fundamental angular frequency; G vmd This consists of a machine-side d-axis band-stop filter and a virtual impedance circuit. Among them, the machine-side d-axis band-stop filter and virtual impedance link G vmd The expression is: ； In the formula, R vmd For virtual resistance, L vmd For virtual inductance, R vmd + sL vmd For virtual impedance, (s 2 + ω 2 nd ) / (s 2 +2 ξ d ω nd s+ ω 2 nd () is a band-stop filter. ω nd For the center frequency, ξ d For the damping ratio, 2 ξ d ω nd For bandwidth.

8. The active damping control method for direct-drive wind turbines adapted to extremely weak power grids according to claim 6, characterized in that, The process of applying the q-axis current component of the direct-drive wind turbine generator to the output voltage of the q-axis current inner loop regulator through a generator-side q-axis band-stop filter and a virtual impedance link is as follows: ； In the formula, This is the reference value for the current output of the outer loop control. I c mq For alternating current in q Components of the axis, u c mqref For the converter output voltage at q Components of the axis, k impq and k imiq These are 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; G vmq This consists of a machine-side q-axis band-stop filter and a virtual impedance circuit. Among them, the machine-side q-axis band-stop filter and virtual impedance element G vmq The expression is: ； In the formula, R vmq For virtual resistance, L vmq For virtual inductance, R vmq + sL vmq For virtual impedance, ( s 2 + ω 2 nq ) / ( s 2 +2 ξ q ω nq s + ω 2 nq () is a band-stop filter. ω nq For the center frequency, ξ q For the damping ratio, 2 ξ q ω nq For bandwidth.

9. The active damping control method for direct-drive wind turbines adapted to extremely weak power grids according to claim 1, characterized in that, The direct-drive wind turbine includes: a grid-side converter, a turbine-side converter, and a wind turbine. The grid-side converter of the direct-drive wind turbine adopts a dual closed-loop vector control structure with constant DC voltage and reactive power outer loop and current inner loop. The machine-side converter of the direct-drive wind turbine adopts constant speed outer loop control and current inner loop control.

10. An active damping control system for direct-drive wind turbines adapted to extremely weak power grids, used to implement the active damping control method for direct-drive wind turbines adapted to extremely weak power grids as described in any one of claims 1-9, characterized in that, include: The grid-side converter control module is used to implement the first oscillation stability improvement control strategy in the controller of the grid-side converter to improve the oscillation stability of the direct-drive wind turbine under extremely weak grid conditions. The machine-side converter control module is used to implement a second stability enhancement control strategy in the controller of the machine-side converter to further improve the oscillation stability of the direct-drive wind turbine. The first oscillation stability enhancement control strategy involves applying damped compensation to the d-axis and q-axis current components and then applying them to the corresponding voltage channels through a combination of a high-pass filter and a virtual impedance circuit. Simultaneously, the q-axis current component is cross-compensated to the d-axis voltage channel after passing through a band-stop filter and a virtual impedance circuit. The second oscillation stability enhancement control strategy is to apply damping compensation to the d-axis and q-axis current components and then apply them to the corresponding voltage channels by combining a band-stop filter with a virtual impedance element.

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