Double-fed fan broadband oscillation suppression method based on adaptive impedance remodeling

Abstract

The invention provides a double-fed fan broadband oscillation suppression method based on adaptive impedance remodeling, and the method comprises the steps: carrying out the optimization of an RSC current control link for the resonance suppression selection of a subsynchronous / supersynchronous frequency band, adding an adaptive virtual impedance controller, selecting a five-order Butterworth low-pass filter, and carrying out the adaptive improvement of the low-pass filter, the response characteristic in the passband can be adaptively increased along with the frequency, and the characteristic of adapting to the oscillation frequency change is realized; active damping control is added in a GSC current control link for resonance suppression selection of a middle frequency band, and parameter deviation and uncertainty of a controlled object are considered, so that an impedance remodeling effect on the GSC is not influenced by parameters of the converter, and phase compensation can be adaptively performed when the parameters of the converter change. Through frequency-band-division control, the negative damping characteristics of the DFIG in a sub / super-synchronous frequency band and a middle frequency band are improved, a grid-connected system of the DFIG can adapt to different power grid working conditions, and oscillation in a broadband range is effectively restrained.

Description

Technical Field

[0001] The present invention relates to the technical field of broadband oscillation of power systems, and in particular to a method for suppressing broadband oscillation of a doubly-fed wind turbine based on adaptive impedance reshaping. Background Art

[0002] As the penetration rate of new energy sources in new power systems continues to increase, power systems are characterized by a high degree of power electronics, the dynamic processes within the system are becoming increasingly complex, and the problem of power system oscillation stability is gradually becoming prominent. Different from traditional low-frequency oscillations and sub / supersynchronous oscillations, large-scale doubly-fed wind turbines (DFIG) access will cause the stability of power systems to present characteristics of wide frequency domain, strong time-varying and wide-area propagation. In addition, the complex control links of wind turbines lead to extremely complex dynamic interaction processes between them and the AC power grid, and the coupling effect is more obvious. This kind of wide-band oscillation with coupling characteristics has become a new oscillation form.

[0003] At present, broadband oscillation is defined as a periodic oscillation of electrical quantities caused by the interaction between power electronic equipment and the power grid, and a dynamic process in which the oscillation frequency varies from a few Hz to several thousand Hz. The main reason for the broadband oscillation is the dynamic interaction between a large number of heterogeneous power electronic equipment and the power grid, which is specifically manifested in the resonant broadband oscillation caused by the interaction between power electronic devices and series compensation and parallel compensation capacitors, and the medium and high frequency resonance caused by the interaction between the power electronic phase-locked loop and the weak power grid. According to the impedance stability theory, the operational stability of the grid-connected system depends on the phase margin of its output impedance and the grid impedance at the intersection of the amplitude. If the phase margin is insufficient at this time, the grid-connected voltage will produce harmonic resonance, deteriorating the grid stability and the operating performance of the wind power system, and even causing disconnection from the grid. Therefore, how to suppress the broadband oscillation of the double-fed wind turbine grid-connected becomes a key issue.

[0004] In the prior art, the means for suppressing broadband oscillation of wind turbines mainly include parameter optimization and adjustment and additional damping control. For parameter optimization and adjustment, broadband oscillation is prevented and controlled by optimizing control parameters. For example, a sensitivity analysis of the system is performed, and according to the analysis results, the dominant parameters affecting the stability of the system are the current loop, the proportional coefficient of the phase-locked loop, and the grid capacitance, and a parameter adjustment strategy is formulated. This type of means is mainly used to provide parameter design basis for converter manufacturers before wind turbines are connected to the grid. In addition, the process of parameter optimization may stimulate new oscillation modes or weaken the damping of other oscillation modes, which is also not conducive to system stability. Therefore, this method has certain limitations. For the additional damping control strategy, the converter is additionally controlled to improve the damping of the wind turbine. For example, the current feedback control of the improved band-stop filter is designed, and the voltage feedforward is added to the current loop control link to achieve impedance reshaping. Although the additional damping control method has the advantages of economy and flexibility, most of the existing control means cannot cope with the time-varying characteristics of broadband oscillations, and it is difficult to effectively improve the converter damping for a wider frequency band.

[0005] At present, there are difficulties in suppressing broadband oscillations due to the complex and changeable operating conditions of the power grid, and the fact that new energy stations usually transmit electricity over long distances through series or parallel compensation lines. Therefore, the impedance characteristics on the power grid side are highly time-varying, and most of the existing control methods usually have a narrow frequency band, making it difficult to effectively suppress them. Most of the current suppression strategies need to be designed for specific unit parameters and control structures, but the capacity, parameters, control structure, etc. of different wind turbines usually vary greatly, and when the unit parameters shift, the suppression effect will also weaken accordingly. Summary of the invention

[0006] In view of the technical problem that the suppression effect of existing wide-band oscillation suppression methods will be weakened when facing complex and changeable grid operating conditions and unit parameter deviations, the purpose of the present invention is to propose a wide-band oscillation suppression method for a doubly fed wind turbine based on adaptive impedance reshaping, so that the DFIG grid-connected system can adapt to different grid operating conditions and effectively suppress oscillations within a wide frequency range.

[0007] To achieve the above object, the present invention proposes a method for suppressing broadband oscillation of a doubly-fed wind turbine based on adaptive impedance reshaping, comprising the following steps:

[0008] Step 1: The three-phase current flowing into the stator port and the three-phase current flowing into the rotor winding are sampled by the current sensor and output, respectively denoted as i sa,sb,sc and i ra,rb,rc ; The grid-side filter inductor current is sampled by the current sensor and the output is recorded as i La,Lb,Lc , the three-phase voltage on the stator side is sampled by the voltage sensor and output, which is recorded as the three-phase stator voltage v sa,sb,sc ;

[0009] Step 2: According to the phase-locking angle θ PLL , the three-phase current i flowing into the stator port and the rotor winding is calculated by Park transformation sa,sb,sc 、i ra,rb,rc Current i in the dq rotating coordinate system sdq and i rdq , the grid-side filter inductor current in the dq rotating coordinate system i Ldq , and the three-phase stator voltage v sa,sb,sc The output voltage v in the dq rotating coordinate system sdq ;

[0010] Step 3: According to the dq axis rotor output current i rd 、i rq and d-axis stator output voltage v sd , through current decoupling control and stator voltage feedforward control, the machine-side dq axis modulation signal m is generated Rd 、m Rq ;

[0011] Step 4: According to the dq axis rotor output current i rd 、i rq After the adaptive virtual impedance controller selects the frequency and corrects the phase, the modulation correction signal △m is generated. d1 ,△m q1 , respectively superimposed on the machine side dq axis modulation signal m Rd 、m Rq The modified machine-side dq axis modulation signal is obtained

[0012] Step 5: According to the dq axis current i flowing into the stator port sd 、i sq , through current decoupling control, the grid-side dq axis modulation signal m is generated Gd 、m Gq ;

[0013] Step 6: According to the dq axis current i flowing into the stator port Ld 、i Lq After phase correction and noise isolation by the adaptive active damping controller, the modulation correction signal △m is generated d2 ,△m q2 , respectively superimposed on the grid-side dq axis modulation signal m Gd 、m Gq The modified network-side dq axis modulation signal is obtained

[0014] Step 7: According to the phase-locking angle θ PLL , the machine side dq axis modulation signal m Rd 、mRq and the network side dq axis modulation signal m Gd 、m Gq After the inverse Park transformation, the switching signals of the generator-side converter and the grid-side converter in the three-phase stationary coordinate system are obtained. By changing the converter outputs on the generator side and the grid side, the impedance of the DFIG sub / super synchronous frequency band and the intermediate frequency band are reshaped respectively.

[0015] In a further embodiment, in step 2, the phase-locking angle θ PLL The q-axis component of the grid-side voltage is obtained through the phase-locked loop transfer function and is expressed as:

[0016]

[0017] In the formula, k pp , k pi Respectively represent the proportional coefficient and integral coefficient of the phase-locked loop, v q Represents the q-axis component of the grid-side voltage.

[0018] In a further embodiment, in step 3, according to the dq axis rotor output current i rd 、i rq and d-axis stator output voltage v sd , through current decoupling control and stator voltage feedforward control, the machine-side dq axis modulation signal m is generated Rd 、m Rq ,include:

[0019] The machine-side dq axis modulation signal m is calculated according to the following method Rd 、m Rq :

[0020]

[0021] In the formula, They represent the ratio of the d-axis to the q-axis and the integral coefficient K of the machine-side current controller respectively. rd Denotes the decoupling gain coefficient, K f Represents the voltage feed-forward gain coefficient.

[0022] In a further embodiment, in step 4, the transfer function H of the adaptive virtual impedance controller is fa (s) is expressed as:

[0023]

[0024] In the formula, H f (s) is a fifth-order Butterworth low-pass filter, represents the normalized Laplacian operator, ω c represents the cut-off angular frequency, which is 2π×100rad / s; kf represents the virtual impedance coefficient;

[0025] Among them, a fifth-order Butterworth low-pass filter is selected as a virtual impedance controller, and the second-order differential link Z is constructed. sa =-s 2 As an adaptive impedance, the original virtual impedance controller can adaptively increase its gain as the frequency increases.

[0026] In a further embodiment, the amplitude-frequency characteristic of the adaptive virtual impedance controller in the sub- / super-synchronous frequency band increases linearly with increasing frequency, and the phase range is maintained at -50° to 50°, meeting the requirements of impedance reshaping target 1. In addition, in the adaptive virtual impedance controller, as the virtual impedance coefficient k f As increases, the amplitude-frequency characteristic of the adaptive virtual impedance controller increases accordingly, and has no effect on the phase-frequency characteristic.

[0027] In a further embodiment, in step 5, according to the dq axis current i flowing into the stator port sd 、i sq , through current decoupling control, the grid-side dq axis modulation signal m is generated Gd 、m Gq ,include:

[0028] The machine-side dq axis modulation signal m is calculated according to the following method Gd 、m Gq :

[0029]

[0030] In the formula, They represent the proportional and integral coefficients of the d-axis and q-axis of the grid-side current controller, respectively. d Represents the decoupling gain coefficient.

[0031] In a further embodiment, in step 6, the transfer function G of the adaptive active damping controller is m (s) is expressed as:

[0032]

[0033] Among them, G p (s) is a multi-order lead-lag correction controller, which is a phase compensation controller in the phase correction link and is expressed as:

[0034]

[0035] In the formula, K p represents the compensation gain, ω h ,ω lIt represents the upper and lower limits of the adjustment angular frequency, and n represents the controller order;

[0036] G p (s) The expression of the maximum adjustable phase angle is:

[0037]

[0038] Among them, G f (s) represents a second-order Chebyshev low-pass filter, which is used as a noise suppression controller in the noise isolation link and is expressed as:

[0039]

[0040] In the formula, K c represents the gain coefficient, s pi Represents the filter pole, i=1,2,s i =s i +jω i ; Both must satisfy the following expressions:

[0041]

[0042] In the formula, ω cut represents the filter cutoff frequency, and ε represents the fluctuation coefficient.

[0043] Therefore, in order to address the problems that the existing doubly-fed wind turbine broadband oscillation suppression strategy is difficult to work effectively when the grid operating conditions change, and the suppression effect will be weakened when the wind turbine capacity and control parameters shift, the present invention proposes a doubly-fed wind turbine broadband oscillation suppression method based on adaptive impedance reshaping. By designing RSC adaptive virtual impedance control and GSC adaptive active damping control, the DFIG impedance of the sub / super synchronous frequency band and the mid-frequency band are reshaped respectively.

[0044] In combination with the broadband oscillation suppression method of a doubly-fed wind turbine based on adaptive impedance reshaping of the above embodiment, by analyzing the impedance characteristic curve of DFIG in a wide frequency band, considering the main factors affecting the impedance characteristics of the doubly-fed wind turbine in each frequency band, the resonance suppression method for the sub / super synchronous frequency band is to transform the RSC current control link, add virtual impedance control, and adaptively improve the low-pass filter so that the response characteristics in the passband can change with the frequency, taking into account the variability of the grid operation conditions; for the resonance suppression method for the mid-frequency band, active damping control is added to the GSC current control link, taking into account the phase correction link and the noise isolation link, taking into account the parameter deviation of the controlled object. Through the frequency division control, the negative damping characteristics of DFIG in the sub / super synchronous frequency band and the mid-frequency band are significantly improved as a whole.

[0045] It can be seen from the above technical solutions of the present invention that, compared with the prior art, the present invention has the following significant advantages:

[0046] 1. RSC virtual impedance control takes into account the complexity and variability of power grid conditions. By adaptively improving the Butterworth low-pass filter, it avoids affecting the medium and high frequency bands, so that the response characteristics within the passband can be adaptively increased with the frequency, and has the characteristics of adapting to changes in oscillation frequency; at the same time, as the virtual impedance coefficient increases, the amplitude-frequency characteristics of the adaptive virtual impedance control also increase, and have no effect on the phase-frequency characteristics;

[0047] 2. GSC active damping control takes into account the parameter deviation and uncertainty of the controlled object, and its control effect is only related to the amplitude-frequency characteristics of the controller itself and K PWM Therefore, its impedance reshaping effect on GSC is not affected by the parameters of the converter itself. It can adaptively perform phase compensation when the converter parameters change and can adapt to the characteristics of different units.

[0048] It should be understood that all combinations of the aforementioned concepts and the additional concepts described in more detail below can be considered as part of the inventive subject matter of the present disclosure as long as such concepts are not mutually inconsistent. In addition, all combinations of the claimed subject matter are considered as part of the inventive subject matter of the present disclosure.

[0049] The foregoing and other aspects, embodiments and features of the present invention can be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the present invention, such as the features and / or beneficial effects of the exemplary embodiments, will be apparent from the following description or learned from the practice of the specific embodiments according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The accompanying drawings are not intended to be drawn to scale. In the accompanying drawings, each identical or nearly identical component shown in each figure may be represented by the same reference numeral. For clarity, not every component is labeled in each figure. Embodiments of various aspects of the present invention will now be described by way of example and with reference to the accompanying drawings.

[0051] Figure 1 Schematic diagram of the grid-side topology structure of a doubly-fed wind turbine according to an example of the present invention.

[0052] Figure 2 Schematic diagram of the topological structure of the doubly fed wind turbine side.

[0053] Figure 3 Schematic diagram of an RSC adaptive virtual impedance control structure according to an example of the present invention.

[0054] Figure 4 Schematic diagram of amplitude-frequency characteristics of an RSC adaptive virtual impedance controller according to an example of the present invention.

[0055] Figure 5 Schematic diagram of the GSC adaptive active damping control structure according to an example of the present invention.

[0056] Figure 6 The figure is a schematic diagram of the performance design of the second-order Chebyshev low-pass filter in the GSC adaptive active damping control according to an example of the present invention.

[0057] Figure 7 1 is a comparison diagram of impedance characteristics of DFIG sub / super synchronous frequency bands before and after the introduction of virtual impedance control according to an example of the present invention.

[0058] Figure 8 The figure is a comparison diagram of the impedance characteristics of the DFIG in the mid-frequency band before and after the active damping control is introduced according to an example of the present invention.

[0059] Fig. 9 Schematic diagram of the suppression effect of sub / super synchronous oscillation induced by series compensated lines according to the method of an example of the present invention, in which (a), (b) and (c) respectively represent the grid-connected point a-phase current, active power, electromagnetic torque waveform, FFT analysis results before reshaping and FFT analysis results after reshaping.

[0060] Fig.10 Schematic diagram of the suppression effect of sub / super synchronous oscillation caused by weak power grid according to the example method of the present invention, in which (a), (b), and (c) respectively represent the grid-connected point a-phase current, active power, electromagnetic torque waveform, FFT analysis results before reshaping, and FFT analysis results after reshaping.

[0061] Fig.11 This is a schematic diagram of the suppression effect of the medium-frequency oscillation caused by the grid-connected line through the method of an example of the present invention, in which (a), (b), and (c) respectively represent the a-phase current, active power, electromagnetic torque waveform of the grid-connected point, the FFT analysis results before reshaping, and the FFT analysis results after reshaping.

[0062] Fig.12 According to the method exemplified by the present invention, Fig.11 Based on , a schematic diagram of the adaptive active damping control effect when the rated power of the control object is different. DETAILED DESCRIPTION

[0063] In order to better understand the technical content of the present invention, specific embodiments are given and described as follows in conjunction with the accompanying drawings.

[0064] Various aspects of the present invention are described in this disclosure with reference to the accompanying drawings, in which many illustrative embodiments are shown. The embodiments of the present disclosure are not necessarily intended to include all aspects of the present invention. It should be understood that the various concepts and embodiments introduced above, as well as those described in more detail below, can be implemented in any of many ways, because the concepts and embodiments disclosed by the present invention are not limited to any implementation. In addition, some aspects disclosed by the present invention can be used alone or in any appropriate combination with other aspects disclosed by the present invention.

[0065] {Example 1}

[0066] Attached Figure 1 and attached Figure 2 They are the grid-side topology and machine-side topology of the doubly fed wind turbine, including the phase-locking angle θ PLL Acquisition, coordinate transformation of voltage and current, as well as voltage control and current control links.

[0067] According to an embodiment of the present invention, a method for suppressing broadband oscillation of a doubly-fed wind turbine based on adaptive impedance reshaping comprises the following steps:

[0068] Step 1: The three-phase current flowing into the stator port and the three-phase current flowing into the rotor winding are sampled by the current sensor and output, respectively denoted as i sa,sb,sc and i ra,rb,rc ; The grid-side filter inductor current is sampled by the current sensor and the output is recorded as i La,Lb,Lc , the three-phase voltage on the stator side is sampled by the voltage sensor and output, which is recorded as the three-phase stator voltage v sa,sb,sc ;

[0069] Step 2: According to the phase-locking angle θ PLL , the three-phase current i flowing into the stator port and the rotor winding is calculated by Park transformation sa,sb,sc 、i ra,rb,rc Current i in the dq rotating coordinate system sdq and i rdq , the grid-side filter inductor current in the dq rotating coordinate system i Ldq , and the three-phase stator voltage v sa,sb,sc The output voltage v in the dq rotating coordinate system sdq ;

[0070] Step 3: According to the dq axis rotor output current i rd 、i rq and d-axis stator output voltage v sd , through current decoupling control and stator voltage feedforward control, the machine-side dq axis modulation signal m is generated Rd 、m Rq ;

[0071] Step 4: According to the dq axis rotor output current i rd 、i rq After the adaptive virtual impedance controller selects the frequency and corrects the phase, the modulation correction signal △m is generated. d1 ,△m q1 , respectively superimposed on the machine side dq axis modulation signal m Rd 、m Rq The modified machine-side dq axis modulation signal is obtained

[0072] Step 5: According to the dq axis current i flowing into the stator port sd 、i sq , through current decoupling control, the grid-side dq axis modulation signal m is generated Gd 、m Gq ;

[0073] Step 6: According to the dq axis current i flowing into the stator port Ld 、i Lq After phase correction and noise isolation by the adaptive active damping controller, the modulation correction signal △m is generated d2 ,△m q2 , respectively superimposed on the grid-side dq axis modulation signal m Gd 、m Gq The modified network-side dq axis modulation signal is obtained

[0074] Step 7: According to the phase-locking angle θ PLL , the machine side dq axis modulation signal m Rd 、m Rq and the network side dq axis modulation signal m Gd 、m Gq After the inverse Park transformation, the switching signals of the generator-side converter and the grid-side converter in the three-phase stationary coordinate system are obtained. By changing the converter outputs on the generator side and the grid side, the impedance of the DFIG sub / super synchronous frequency band and the intermediate frequency band are reshaped respectively.

[0075] Combined with Figure 1 , 2 As shown, it will be attached Figure 1 The rotor winding and the attached Figure 2 The three-phase current flowing into the stator port is sampled by the current sensor and output, which are recorded as i sa,sb,sc and i ra,rb,rc ; The grid-side filter inductor current is sampled by the current sensor and the output is recorded as i La,Lb,Lc , will be attached Figure 1 The three-phase voltage on the stator side is sampled by the voltage sensor and output, which is recorded as the three-phase stator voltage v sa,sb,sc .

[0076] In step 2, the phase-locking angle θ PLL The q-axis component of the grid-side voltage is obtained through the phase-locked loop transfer function and is expressed as:

[0077]

[0078] The phase-locked loop output angle θ PLL The Park transformation matrix for angle reference is:

[0079]

[0080] In the formula, k pp , k pi Respectively represent the proportional coefficient and integral coefficient of the phase-locked loop, v q Represents the q-axis component of the grid-side voltage.

[0081] In a further embodiment, in step 3, according to the dq axis rotor output current i rd 、i rq and d-axis stator output voltage v sd , through current decoupling control and stator voltage feedforward control, the machine-side dq axis modulation signal m is generated Rd 、m Rq ,include:

[0082] The machine-side dq axis modulation signal m is calculated according to the following method Rd 、m Rq :

[0083]

[0084] In the formula, They represent the ratio of the d-axis to the q-axis and the integral coefficient K of the machine-side current controller respectively. rd Denotes the decoupling gain coefficient, K f Represents the voltage feed-forward gain coefficient.

[0085]

[0086] In a further embodiment, in step 4, Figure 3 As shown, the transfer function H of the aforementioned adaptive virtual impedance controller fa (s) is expressed as:

[0087]

[0088] In the formula, H f (s) is a fifth-order Butterworth low-pass filter, represents the normalized Laplacian operator, ω c represents the cut-off angular frequency, which is 2π×100rad / s; kf represents the virtual impedance coefficient;

[0089] Among them, the fifth-order Butterworth low-pass filter is selected as the virtual impedance controller to avoid affecting the mid- and high-frequency bands while ensuring sufficient gain in the sub / supersynchronous frequency bands.

[0090] Since the impedance amplitude of DFIG in the sub- / super-synchronous frequency band generally shows a trend of increasing with increasing frequency, while the gain of the low-pass filter in the passband range remains unchanged, it is necessary to improve the low-pass filter so that its response characteristics in the passband can increase adaptively with frequency. To this end, in an embodiment of the present invention, by constructing the second-order differential link Z sa =-s 2 As an adaptive impedance, the original virtual impedance controller can adaptively increase its gain as the frequency increases.

[0091] For phase correction, the two main control objectives of virtual impedance control are:

[0092] Goal 1: Control the impedance phase of DFIG to -90°~90°, and weaken its negative resistance characteristics as much as possible, corresponding to the first and fourth quadrants in the polar coordinate system;

[0093] Goal 2: Keep the DFIG impedance characteristic as inductive as possible, corresponding to the first and second quadrants in the polar coordinate system, and the overlap area between the two is Z DFIG The best adjustment target.

[0094] Considering that the grid-connected stability of DFIG should be ensured first, in the embodiment of the present invention, target 1 is set as the primary target of impedance reshaping.

[0095] By the attached Figure 4 It can be seen that compared with the traditional virtual impedance controller, the amplitude-frequency characteristic of the adaptive virtual impedance controller proposed in the present invention increases linearly with the increase of frequency in the sub- / super-synchronous frequency band, and the phase range is maintained at -50°~50°, so it can meet the impedance reshaping target 1 and significantly improve the DFIG grid-connected stability. At the same time, as the virtual impedance coefficient k f As increases, the amplitude-frequency characteristic of the adaptive virtual impedance controller increases accordingly, and has no effect on the phase-frequency characteristic.

[0096] In a further embodiment, in step 5, according to the dq axis current i flowing into the stator port sd 、i sq , through current decoupling control, the grid-side dq axis modulation signal m is generated Gd 、m Gq ,include:

[0097] The machine-side dq axis modulation signal m is calculated according to the following methodGd 、m Gq :

[0098]

[0099] In the formula, They represent the proportional and integral coefficients of the d-axis and q-axis of the grid-side current controller, respectively. d Represents the decoupling gain coefficient.

[0100] in,

[0101] In a further embodiment, in step 6, Figure 5 As shown, the transfer function G of the aforementioned adaptive active damping controller is m (s) is expressed as:

[0102]

[0103] Among them, G p (s) is a multi-order lead-lag correction controller, which is a phase compensation controller in the phase correction link and is expressed as:

[0104]

[0105] In the formula, K p represents the compensation gain, ω h ,ω l It represents the upper and lower limits of the adjustment angular frequency, and n represents the controller order;

[0106] G p (s) The expression of the maximum adjustable phase angle is:

[0107]

[0108] In the embodiment of the present invention, the upper and lower limits of the angular frequency are respectively set for the mid-frequency range as follows: l =2π×100rad / s,ω h =2π×1000rad / s.

[0109] The higher the controller order, the larger the adjustable phase range. However, too high an order will also make the controller design more difficult and not conducive to specific implementation. Therefore, in this embodiment, the controller order n=2 is selected, corresponding to It is 73°.

[0110] Combined with the transfer function design of the adaptive active damping controller in the above embodiment, as shown in FIG. Figure 6 As shown, G f(s) represents a second-order Chebyshev low-pass filter. Considering the specific operability, it is used as a noise suppression controller in the noise isolation link, which is expressed as:

[0111]

[0112] In the formula, K c represents the gain coefficient, s pi Represents the filter pole, i=1,2,s i =s i +jω i ; Both must satisfy the following expressions:

[0113]

[0114] In the formula, ω cut represents the filter cutoff frequency, and ε represents the fluctuation coefficient.

[0115] As an optional example, in step 6, for the noise isolation link, the filter cutoff angular frequency ω cut The value is 2π×1000rad / s.

[0116] In order to further determine the value of ε, Figure 5 It shows the fluctuation coefficient to the actual cut-off frequency f cut and passband ripple α max The actual cutoff frequency is the frequency corresponding to the amplitude -3dB. 2 The increase of f cut will continue to decrease, and α max will continue to increase, so there is a balance point between the two. 2 =0.24, the corresponding f cut =1070Hz,α max =1dB.

[0117] In a further embodiment, in step 7, the phase-locked loop output angle θ PLL The inverse Park transform equation for the angle reference is as follows:

[0118] m a =m d cosθ PLL -m q sinθ PLL

[0119]

[0120] {Example 2}

[0121] Combined with the method of the above embodiment, since the line series compensation capacitor is an important cause of the DFIG sub / super synchronous oscillation, the impedance reshaping performance of the DFIG in the scenario of grid-connected via series compensated lines is first analyzed. Based on the reshaped impedance model, the series compensation degree is 40%. The impedance characteristics of the DFIG sub / super synchronous frequency band before and after the introduction of virtual impedance control are shown in the attached figure. Figure 7 As shown in the figure, it can be seen that the adaptive virtual impedance control can significantly improve the negative damping characteristics of DFIG in the sub / supersynchronous frequency band, so that it can maintain a phase range of -90° to 90° in most frequency bands.

[0122] The line parallel compensation capacitor is one of the important reasons for the oscillation of DFIG in the mid-frequency band. The impedance reshaping effect of DFIG connected to the grid through the parallel compensation line is shown in the attached figure. Figure 8 As shown in Figure 2, it can be seen that adaptive active damping control can improve the negative resistance and capacitive characteristics of DFIG in the mid-frequency band and reshape the front Z DFIG With Z g Taking the intersection at 782 Hz as an example, the phase difference at the intersection is 172°. At this time, there is only 8° of phase margin, which poses a great risk of instability.

[0123] After the adaptive active damping control is reshaped, the phase difference at 782Hz is reduced to 101°, the phase margin is increased to 81°, and the oscillation risk is greatly reduced.

[0124] We further use Matlab / Simulink to conduct example simulation and combine the attached Figure 9-12 Further explanation of the technical solution provided by the above embodiment of the invention

[0125] Scenario 1: DFIG connected to the grid via series compensation line

[0126] Fig. 9 The effect of adaptive virtual impedance control on the suppression of sub / super synchronous oscillations caused by series compensated lines is shown. After the system puts in series compensation capacitors with a series compensation degree of 40% at 5s, the system grid-connected current, active power, and electromagnetic torque all oscillate and become unstable. At this time, the grid-connected current has a super synchronous oscillation coupled with a 29Hz subsynchronous oscillation and a 71Hz oscillation. After the adaptive virtual impedance control is put in at 6s, the oscillation of each electrical quantity gradually disappears. At 7s, the line series compensation degree becomes 50%, and the system can still remain stable at this time, indicating that the frequency oscillation suppression method proposed in the present invention can better adapt to different series compensation scenarios and has good adaptability.

[0127] Scenario 2: DFIG connected to weak power grid

[0128] Fig.10 The adaptive virtual impedance control shows the suppression effect on sub / super synchronous oscillation caused by weak grid. g=5.0mH inductive weak power grid, the system has 25 / 75Hz sub / super synchronous oscillation, after the virtual impedance control is put into use at 3s, the oscillation gradually disappears within 0.2s, and the system is stable. g When the impedance changes to 5.5 mH, the system can still maintain stable operation, indicating that the adaptive virtual impedance control proposed in the present invention also has good adaptability in weak power grid scenarios.

[0129] Scenario 3: DFIG is connected to the grid via the parallel and supplementary lines

[0130] Fig.11 It shows the suppressive effect of adaptive active damping control on medium-frequency oscillation caused by grid connection via parallel compensation line. Before remodeling, DFIG caused medium-frequency oscillation of about 116Hz due to grid connection via parallel compensation line (parallel compensation degree is 40%), and there was an oscillation coupling component of 216Hz. After adaptive active damping control was put into use at 2s, the oscillation was suppressed after about 0.2s, and the system was stable. At 3s, the parallel compensation degree became 45%, and it can be seen that no medium-frequency oscillation was caused at this time. The adaptive active damping control proposed in the present invention is adaptable to the oscillation frequency offset in the medium-frequency band.

[0131] Scenario 4: Different control objectives

[0132] Fig.12 It shows the effect of adaptive active damping control when the rated power of the control object is different. Based on scenario three, at the initial moment, due to the parallel compensation capacitor, the DFIG active power oscillates at a medium frequency. At 2s, the adaptive active damping controller is put into use, and the oscillation phenomenon of the three DFIGs with different rated powers is well suppressed. At 3s, the parallel compensation degree changes. At this time, the performance of impedance reshaping is consistent with the above analysis, which shows that when the control object changes, the frequency oscillation suppression method proposed in the present invention does not need to redesign the controller and has good adaptability to the control target.

[0133] The contents described in detail in this specification belong to the existing knowledge known to the professional and technical personnel in the field. Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Those with ordinary knowledge in the technical field to which the present invention belongs can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the definition of the claims.

Claims

1. A method for suppressing broadband oscillation of a doubly-fed wind turbine based on adaptive impedance reshaping, characterized in that: include: Step 1: The three-phase current flowing into the stator port and the three-phase current flowing into the rotor winding are sampled by the current sensor and output, respectively denoted as i sa,sb,sc and i ra,rb,rc ; The grid-side filter inductor current is sampled by the current sensor and the output is recorded as i La,Lb,Lc , the three-phase voltage on the stator side is sampled by the voltage sensor and output, which is recorded as the three-phase stator voltage v sa,sb,sc ; Step 2: According to the phase-locking angle θ PLL , the three-phase current i flowing into the stator port and the rotor winding is calculated by Park transformation sa,sb,sc 、i ra,rb,rc Current i in the dq rotating coordinate system sdq and i rdq , the grid-side filter inductor current in the dq rotating coordinate system i Ldq , and the three-phase stator voltage v sa,sb,sc The output voltage v in the dq rotating coordinate system sdq ; Step 3: According to the dq axis rotor output current i rd 、i rq and d-axis stator output voltage v sd , through current decoupling control and stator voltage feedforward control, the machine-side dq axis modulation signal m is generated Rd 、m Rq ; Step 4: According to the dq axis rotor output current i rd 、i rq After the adaptive virtual impedance controller selects the frequency and corrects the phase, the modulation correction signal △m is generated. d1 , △m q1 , respectively superimposed on the machine side dq axis modulation signal m Rd 、m Rq The modified machine-side dq axis modulation signal is obtained Step 5: According to the dq axis current i flowing into the stator port sd 、i sq , through current decoupling control, the grid-side dq axis modulation signal m is generated Gd 、m Gq ; Step 6: According to the dq axis current i flowing into the stator port Ld 、i Lq After phase correction and noise isolation by the adaptive active damping controller, the modulation correction signal △m is generated d2 , △m q2 , respectively superimposed on the grid-side dq axis modulation signal m Gd 、m Gq The modified network-side dq axis modulation signal is obtained Step 7: According to the phase-locking angle θ PLL , the machine side dq axis modulation signal m Rd 、m Rq and the network side dq axis modulation signal m Gd 、m Gq After the inverse Park transformation, the switching signals of the generator-side converter and the grid-side converter in the three-phase stationary coordinate system are obtained. By changing the converter outputs on the generator side and the grid side, the impedance of the DFIG sub / super synchronous frequency band and the intermediate frequency band are reshaped respectively.

2. The method for suppressing broadband oscillation of a doubly-fed wind turbine based on adaptive impedance reshaping according to claim 1 is characterized in that: In step 2, the phase-locking angle θ PLL The q-axis component of the grid-side voltage is obtained through the phase-locked loop transfer function and is expressed as: In the formula, k pp , k pi Respectively represent the proportional coefficient and integral coefficient of the phase-locked loop, v q Represents the q-axis component of the grid-side voltage.

3. The method for suppressing broadband oscillation of a doubly-fed wind turbine based on adaptive impedance reshaping according to claim 1, characterized in that: In step 3, according to the dq axis rotor output current i rd 、i rq and d-axis stator output voltage v sd , through current decoupling control and stator voltage feedforward control, the machine-side dq axis modulation signal m is generated Rd 、m Rq ,include: The machine-side dq axis modulation signal m is calculated according to the following method Rd 、m Rq : In the formula, They represent the ratio of the d-axis to the q-axis and the integral coefficient K of the machine-side current controller respectively. rd Denotes the decoupling gain coefficient, K f Represents the voltage feed-forward gain coefficient.

4. The method for suppressing broadband oscillation of a doubly-fed wind turbine based on adaptive impedance reshaping according to claim 1, characterized in that: In step 4, the transfer function H of the adaptive virtual impedance controller fa (s) is expressed as: In the formula, H f (s) is a fifth-order Butterworth low-pass filter, represents the normalized Laplacian operator, ω c represents the cut-off angular frequency, which is 2π×100rad / s; k f represents the virtual impedance coefficient; Among them, a fifth-order Butterworth low-pass filter is selected as a virtual impedance controller, and the second-order differential link Z is constructed. sa =-s 2 As an adaptive impedance, the original virtual impedance controller can adaptively increase its gain as the frequency increases.

5. The method for suppressing broadband oscillation of a doubly-fed wind turbine based on adaptive impedance reshaping according to claim 4 is characterized in that: The amplitude-frequency characteristic of the adaptive virtual impedance controller in the sub / super synchronous frequency band increases linearly with the increase of frequency, and the phase range is maintained at -50° to 50°, meeting the requirements of impedance reshaping target 1.

6. The method for suppressing broadband oscillation of a doubly-fed wind turbine based on adaptive impedance reshaping according to claim 4, characterized in that: In the adaptive virtual impedance controller, as the virtual impedance coefficient k f As increases, the amplitude-frequency characteristic of the adaptive virtual impedance controller increases accordingly, and has no effect on the phase-frequency characteristic.

7. The method for suppressing broadband oscillation of a doubly-fed wind turbine based on adaptive impedance reshaping according to claim 1, characterized in that: In step 5, according to the dq axis current i flowing into the stator port sd 、i sq , through current decoupling control, the grid-side dq axis modulation signal m is generated Gd 、m Gq ,include: The machine-side dq axis modulation signal m is calculated according to the following method Gd 、m Gq : In the formula, They represent the proportional and integral coefficients of the d-axis and q-axis of the grid-side current controller, respectively. d Represents the decoupling gain coefficient.

8. The method for suppressing broadband oscillation of a doubly-fed wind turbine based on adaptive impedance reshaping according to claim 1, characterized in that: In step 6, the transfer function G of the adaptive active damping controller is m (s) is expressed as: Among them, G p (s) is a multi-order lead-lag correction controller, which is a phase compensation controller in the phase correction link and is expressed as: In the formula, K p represents the compensation gain, ω h ,ω l It represents the upper and lower limits of the adjustment angular frequency, and n represents the controller order; G p (s) The expression of the maximum adjustable phase angle is: Among them, G f (s) represents a second-order Chebyshev low-pass filter, which is used as a noise suppression controller in the noise isolation link and is expressed as: In the formula, K c represents the gain coefficient, s pi Represents the filter pole, i=1,2,s i =s i +jω i ; Both must satisfy the following expressions: In the formula, ω cut represents the filter cutoff frequency, and ε represents the fluctuation coefficient.

9. The method for suppressing broadband oscillation of a doubly-fed wind turbine based on adaptive impedance reshaping according to claim 8, characterized in that: In step 6, for the phase correction link, the upper and lower limits of the adjustment angular frequency are respectively set to: ω l =2π×100rad / s,ω h =2π×1000rad / s; the controller order n is set to 2.

10. The method for suppressing broadband oscillation of a doubly-fed wind turbine based on adaptive impedance reshaping according to claim 8, characterized in that: In step 6, for the noise isolation link, the filter cutoff angular frequency ω cut The value is 2π×1000rad / s; ε 2 The value is 0.24.

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