Virtual resistance subsynchronous oscillation control method and system for variable-speed operating condition of doubly-fed wind turbine

Abstract

The application discloses a kind of doubly-fed fan variable-speed condition virtual resistance subsynchronous oscillation control method and system, comprising: the difference between the stator current complex vector reference value and stator current complex vector measurement is input to stator current controller, and the output of stator current controller is added to decoupling item to obtain rotor voltage modulation signal;Desired virtual resistance is obtained by frequency and winding reduction through calculation on rotor side;Based on the desired virtual resistance on rotor side, the rotor subsynchronous voltage modulation signal is calculated;Rotor subsynchronous voltage modulation signal is used as adjustment amount, and the adjustment amount is added to rotor voltage modulation signal, to obtain updated rotor voltage modulation signal.The application can realize the safe and stable operation of doubly-fed fan in full wind speed working range.

Description

Technical Field

[0001] This invention relates to the field of grid connection of wind turbine generators, and specifically to a virtual resistance subsynchronous oscillation control method and system for doubly fed wind turbines under variable wind speed conditions. Background Technology

[0002] Doubly fed induction generators (DFIGs) are widely used in wind power systems due to their mature technology and high cost-effectiveness. However, actual engineering operation shows that the oscillation characteristics of DFIGs are closely related to wind speed. When operating at low wind speeds, the interaction between the DFIG and the series compensation line will lead to frequent subsynchronous oscillation accidents, which seriously restricts the safe absorption of wind power and hinders the development of a new type of power system based on new energy sources in the future.

[0003] To address the grid-connected oscillation problem of doubly-fed induction generator (DFIG) wind turbines, existing research has proposed several effective oscillation control methods, including additional damping devices, virtual impedance control, and adaptive intelligent control. However, additional damping devices significantly increase system investment and power generation costs. Virtual impedance control can be implemented in software, is convenient and simple to implement, but is mostly designed based on one or more specific operating points, making it difficult to meet the grid-connected stability requirements of wind turbines under varying wind speeds. While adaptive intelligent control can improve the adaptability of wind turbines to some extent, the controller design is complex and heavily reliant on a large amount of operational data, limiting its practicality. Therefore, to solve the grid-connected oscillation problem of DFIG wind turbines, a virtual resistance subsynchronous oscillation control method and system for DFIG wind turbines under varying wind speeds is needed, capable of achieving safe and stable operation of DFIG wind turbines across the entire wind speed range. Summary of the Invention

[0004] In view of this, the purpose of this invention is to overcome the defects in the prior art and provide a virtual resistance subsynchronous oscillation control method and system for doubly fed wind turbines under variable wind speed conditions, which can realize the safe and stable operation of doubly fed wind turbines in the full wind speed range.

[0005] The virtual resistance subsynchronous oscillation control method for doubly-fed induction generator (DFIG) under variable wind speed conditions of the present invention includes the following steps:

[0006] S1. Input the difference between the stator current complex vector reference value and the stator current complex vector measured value to the stator current controller, and add the output of the stator current controller to the decoupling term to obtain the rotor voltage modulation signal;

[0007] S2. Calculate the desired virtual resistance on the rotor side by adjusting for frequency and winding;

[0008] S3. Based on the expected virtual resistance on the rotor side, the rotor subsynchronous voltage modulation signal is calculated;

[0009] S4. The rotor subsynchronous voltage modulation signal is used as an adjustment amount, and the adjustment amount is added to the rotor voltage modulation signal to obtain the updated rotor voltage modulation signal.

[0010] Furthermore, the decoupling term K is determined according to the following formula. sd :

[0011] K sd =ω s (L s L r / L m -L m );

[0012] Where, ω s L is the slip frequency of the doubly fed wind turbine. s L r and L m These are the stator winding leakage inductance, rotor winding leakage inductance, and motor magnetizing inductance, respectively.

[0013] Furthermore, the desired virtual resistance R on the rotor side is determined according to the following formula. dr (v w ):

[0014] R dr (v w )=|σ p (s) / k e 2 |R vp (v w );

[0015] Where, σ p (s) represents the disturbance slip rate of the induction motor, k e R is the ratio of the number of turns in the stator winding to the number of turns in the rotor winding. vp (v w ) represents the desired virtual resistance on the stator side, v w This indicates the real-time wind speed.

[0016] Furthermore, the disturbance slip σ of the induction motor is determined according to the following formula. p (s):

[0017] σ p (s)=(s-jω r ) / s;

[0018] Where, ω r This represents the electrical angular frequency of the rotor winding, where s is the complex frequency and j is the imaginary unit.

[0019] Furthermore, the desired virtual resistance R on the stator side is determined according to the following formula. vp (v w ):

[0020] R vp (v w )=m·|R DFIG (v w )|;

[0021] Where m is a multiple; R DFIG (v w The resistance is a negative resistance that varies with wind speed.

[0022]

[0023] v in Indicates the cut-in wind speed, v cov This indicates the maximum switching wind speed when the fan is running at a constant speed, v rated Re represents the rated wind speed; Re[·] represents taking the real part of a complex number, Z DFIG (v w ,f c ) represents the bivariate impedance of the doubly fed fan at wind speed and frequency, f c The frequency of the intersection of the amplitudes of the wind turbine impedance and the grid impedance in the subsynchronous frequency band, v w This represents the real-time wind speed, and a, b, and c are all fitting coefficients.

[0024] Furthermore, the amplitude intersection frequency f is determined according to the following formula. c :

[0025] |Z DFIG (v w ,f c )|-|Z g (f c )|=0;

[0026] Among them, Z g (f c () represents the power grid impedance.

[0027] Furthermore, the rotor subsynchronous voltage modulation signal U is determined according to the following formula. rm_sub :

[0028]

[0029] Where, ω c1 This indicates that the bandpass filter removes the 50Hz cutoff angular frequency from the mains frequency. ω c2 The cutoff angular frequency for suppressing switching noise is represented by s, where s is a complex frequency, and I sdq This is the measured value of the stator current complex vector.

[0030] Furthermore, ω is determined according to the following formula. c1 and ω c2 :

[0031] ω c1 =2π×f c1 rad / s, ω c2 =2π×f c2 rad / s;

[0032] Among them, f c1 and f c2 All are cutoff frequencies.

[0033] A virtual resistance subsynchronous oscillation control system for a doubly fed wind turbine operating under variable wind speed conditions includes a stator current control module, a desired virtual resistance solution module, and a virtual resistance control module.

[0034] The stator current control module is used to input the difference between the stator current complex vector reference value and the stator current complex vector measured value to the stator current controller, and add the output of the stator current controller to the decoupling term to obtain the rotor voltage modulation signal;

[0035] The desired virtual resistance solving module is used to obtain the desired virtual resistance on the rotor side and calculate the rotor subsynchronous voltage modulation signal.

[0036] The virtual resistance control module is used to add the rotor subsynchronous voltage modulation signal and the rotor voltage modulation signal to obtain the updated rotor voltage modulation signal.

[0037] Furthermore, the desired virtual resistance R on the rotor side is determined according to the following formula. dr (v w ):

[0038] R dr (v w )=|σ p (s) / k e 2 |R vp (v w );

[0039] Where, σ p (s) represents the disturbance slip rate of the induction motor, k e R is the ratio of the number of turns in the stator winding to the number of turns in the rotor winding. vp (v w ) represents the desired virtual resistance on the stator side, v w This indicates the real-time wind speed.

[0040] The beneficial effects of this invention are as follows: The virtual resistance subsynchronous oscillation control method and system for doubly-fed induction generator (DFIG) under variable wind speed conditions disclosed in this invention introduces wind speed information into the current control of the rotor-side converter and introduces wind speed-related fitting impedance components into the current controller, thereby offsetting the negative resistance effect that induces oscillation under variable wind speed conditions. This overcomes the limitations of existing virtual impedance control technology applied to variable wind speed conditions, enabling safe and stable operation of the DFIG across the entire wind speed operating range without the need for additional damping equipment. It is simple to implement and easy to operate. Attached Figure Description

[0041] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0042] Figure 1 This is a schematic diagram of the control method of the present invention;

[0043] Figure 2 This is a schematic diagram of the control principle of the present invention. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings, as shown in the figures:

[0045] The virtual resistance subsynchronous oscillation control method for doubly-fed induction generator (DFIG) under variable wind speed conditions of the present invention includes the following steps:

[0046] S1. The stator current complex vector reference value I sdq_ref Compared with the complex vector measurement value of stator current I sdq The difference between I sdq_ref -I sdq The input is sent to the stator current controller, and the output of the stator current controller is connected to the decoupling term K. sd The two signals are added together to obtain the rotor voltage modulation signal; among them, the stator current complex vector reference value I is set according to the power generation requirements. sdq_ref The stator current controller adopts the existing stator current proportional-integral controller H. si (s), H si (s)=k p +k i / s,k p k i These are the proportional coefficient and integral coefficient, respectively, and s is the complex frequency;

[0047] S2. During actual operation, measure the current wind speed information and obtain the desired virtual resistance R on the stator side based on the fitting function. vp (v w Then, the desired virtual resistance R on the rotor side is calculated using frequency and winding conversion. dr (v w );

[0048] S3. After filtering out the fundamental frequency component and switching noise harmonic components in the stator current using a bandpass filter, the oscillation component in the stator current is obtained. Then, the oscillation component is multiplied by the desired virtual resistance R on the rotor side. dr (v w The calculated rotor subsynchronous voltage modulation signal can then be output.

[0049] S4. The rotor subsynchronous voltage modulation signal is used as an adjustment amount, and the adjustment amount is added to the rotor voltage modulation signal to obtain an updated rotor voltage modulation signal. The updated rotor voltage modulation signal eliminates harmonic components, thereby offsetting the negative resistance effect of oscillation induced by the doubly fed fan under variable wind speed conditions, and realizing the safe and stable operation of the doubly fed fan in the full wind speed range.

[0050] In this embodiment, the decoupling term K is determined according to the following formula. sd :

[0051] K sd =ω s (L s L r / L m -L m );

[0052] Where, ω s L is the slip frequency of the doubly fed wind turbine. s L r and L m These are the stator winding leakage inductance, rotor winding leakage inductance, and motor magnetizing inductance, respectively.

[0053] The desired virtual resistance R on the rotor side is determined using the following formula. dr (v w ):

[0054] R dr (v w )=|σ p (s) / k e 2 |R vp (v w );

[0055] Where, σ p (s) represents the disturbance slip rate of the induction motor, k e R is the ratio of the number of turns in the stator winding to the number of turns in the rotor winding. vp (v w ) represents the desired virtual resistance on the stator side, v w This indicates the real-time wind speed.

[0056] The disturbance slip σ of the induction motor is determined using the following formula. p (s):

[0057] σ p (s)=(s-jω r ) / s;

[0058] Where, ω r This represents the electrical angular frequency of the rotor winding, where s is the complex frequency and j is the imaginary unit.

[0059] Based on offsetting the negative resistance effect, and considering a positive resistance margin of one times the negative resistance value, the expected virtual resistance on the stator side can be obtained. The expected virtual resistance R on the stator side is determined according to the following formula. vp (v w ):

[0060] R vp (v w )=m·|R DFIG (v w )|;

[0061] Among them, R DFIG (v w ) represents the negative resistance that varies with wind speed, and m is a multiple, with values ​​ranging from [1.2, 2.0].

[0062]

[0063] v in Indicates the cut-in wind speed, v cov This indicates the maximum switching wind speed when the fan is running at a constant speed, v rated Re represents the rated wind speed; Re[·] represents taking the real part of a complex number, Z DFIG (v w ,f c ) represents the bivariate impedance of the doubly fed fan at wind speed and frequency, f c The frequency of the intersection of the amplitudes of the wind turbine impedance and the grid impedance in the subsynchronous frequency band, v w Let represent the real-time wind speed, and a, b, and c be fitting coefficients. A bivariate impedance model of the doubly-fed induction generator (DFIG) wind speed-frequency can be established using existing technology to obtain the bivariate impedance Z of the DFIG wind speed-frequency. DFIG (v w ,f c );

[0064] When the doubly fed wind turbine is operating at v in and v cov In the constant speed mode, the minimum negative resistance {Re[Z] is taken. DFIG (v w ,f c )]} min ;

[0065] When running in v cov and v ratedIn the maximum power point tracking (MPPT) mode, the negative resistance is highly sensitive to wind speed changes. Therefore, a polynomial is used to fit the variation of negative resistance with wind speed, where a, b, and c are the coefficients of the polynomial fitting function. The process for calculating the fitting coefficients is as follows: import the wind speed dataset and the negative resistance dataset from the MPPT mode into Matlab's Curve Fitting Tool, select polynomial as the fitting function type, and the fitting coefficients a, b, and c will be automatically calculated.

[0066] The amplitude intersection frequency f is determined using the following formula. c :

[0067] |Z DFIG (v w ,f c )|-|Z g (f c )|=0;

[0068] Among them, Z g (f c () represents the power grid impedance.

[0069] Similarly, a series of intersection frequencies at different wind speeds can be obtained, and thus the negative resistance R of the doubly-fed induction generator's dual-element impedance at the intersection frequencies, varying with wind speed, can be calculated. DFIG (v w ).

[0070] The rotor subsynchronous voltage modulation signal U is determined according to the following formula. rm_sub :

[0071]

[0072] Where, ω c1 This indicates that the bandpass filter removes the 50Hz cutoff angular frequency from the mains frequency. ω c2 The cutoff angular frequency for suppressing switching noise is represented by s, where s is a complex frequency.

[0073] Since the 50Hz fundamental frequency component in the stationary coordinate system is transformed into a DC component in the dq coordinate system, ω can be determined using the following formula. c1 and ω c2 :

[0074] ω c1 =2π×f c1 rad / s, ω c2 =2π×f c2 rad / s;

[0075] Among them, f c1 and f c2These are all cutoff frequencies. Generally, f is chosen. c1 <10Hz, f c2 <300Hz.

[0076] This invention also relates to a virtual resistance subsynchronous oscillation control system for doubly fed wind turbines under variable wind speed conditions. The system corresponds to the above-mentioned virtual resistance subsynchronous oscillation control method for doubly fed wind turbines under variable wind speed conditions and can be understood as a system that implements the above method. The system includes a stator current control module, a desired virtual resistance solution module, and a virtual resistance control module.

[0077] The stator current control module is used to input the difference between the stator current complex vector reference value and the stator current complex vector measured value to the stator current controller, and add the output of the stator current controller to the decoupling term to obtain the rotor voltage modulation signal;

[0078] The desired virtual resistance solving module is used to obtain the desired virtual resistance on the rotor side and calculate the rotor subsynchronous voltage modulation signal.

[0079] The virtual resistance control module is used to add the rotor subsynchronous voltage modulation signal and the rotor voltage modulation signal to obtain the updated rotor voltage modulation signal.

[0080] The virtual resistance subsynchronous oscillation control method and system provided by this invention, by introducing wind speed information, calculates the expected virtual resistance of the wind turbine in real time at the current wind speed, thus offsetting the negative resistance effect induced by oscillation under varying wind speed conditions. This enables the safe and stable operation of the doubly-fed induction generator (DFIG) wind turbine across the entire wind speed range. No additional damping equipment is required, and there is no need to sample the rotor current, making it simple to implement and easy to operate.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A virtual resistance subsynchronous oscillation control method for a doubly-fed induction generator (DFIG) under variable wind speed conditions, characterized in that: Includes the following steps: S1. Input the difference between the stator current complex vector reference value and the stator current complex vector measured value to the stator current controller, and add the output of the stator current controller to the decoupling term to obtain the rotor voltage modulation signal; S2. During actual operation, measure the current wind speed information and obtain the desired virtual resistance on the stator side based on the fitting function. The desired virtual resistance on the rotor side is calculated by adjusting the frequency and winding. The desired virtual resistance on the stator side is determined using the following formula. : ； in, Multiples; The negative resistance varies with wind speed; ； Indicates the cut-in wind speed. This indicates the maximum switching wind speed when the fan is running at a constant speed. Indicates the rated wind speed; This indicates taking the real part of a complex number. For the doubly fed fan, the wind speed frequency is a two-element impedance. The frequency of the intersection of the amplitudes of the wind turbine impedance and the grid impedance in the subsynchronous frequency band, v w Indicates real-time wind speed. All are fitting coefficients; S3. Based on the expected virtual resistance on the rotor side, the rotor subsynchronous voltage modulation signal is calculated; S4. Use the rotor subsynchronous voltage modulation signal as an adjustment amount, and add the adjustment amount to the rotor voltage modulation signal to obtain the updated rotor voltage modulation signal.

2. The virtual resistance subsynchronous oscillation control method for doubly fed wind turbines under variable wind speed conditions according to claim 1, characterized in that: The decoupling term K is determined according to the following formula. sd : K sd =ω s (L s L r / L m -L m ); Where, ω s L is the slip frequency of the doubly fed wind turbine. s L r and L m These are the stator winding leakage inductance, rotor winding leakage inductance, and motor magnetizing inductance, respectively.

3. The virtual resistance subsynchronous oscillation control method for doubly fed wind turbines under variable wind speed conditions according to claim 1, characterized in that: The desired virtual resistance R on the rotor side is determined using the following formula. dr (v w ): R dr (v w )=|σ p (s) / k e 2 |R vp (v w ); Where, σ p (s) represents the disturbance slip rate of the induction motor, k e R is the ratio of the number of turns in the stator winding to the number of turns in the rotor winding. vp (v w ) represents the desired virtual resistance on the stator side, v w This indicates the real-time wind speed.

4. The virtual resistance subsynchronous oscillation control method for doubly fed wind turbines under variable wind speed conditions according to claim 3, characterized in that: The disturbance slip σ of the induction motor is determined using the following formula. p (s): σ p (s)=(s-jω r ) / s. Where, ω r This represents the electrical angular frequency of the rotor winding, where s is the complex frequency and j is the imaginary unit.

5. The virtual resistance subsynchronous oscillation control method for doubly-fed fan under variable wind speed conditions according to claim 1, characterized in that: The amplitude intersection frequency is determined using the following formula. : ； in, This represents the power grid impedance.

6. The virtual resistance subsynchronous oscillation control method for doubly fed wind turbines under variable wind speed conditions according to claim 3, characterized in that: The rotor subsynchronous voltage modulation signal is determined according to the following formula. : ； Where, ω c1 This indicates that the bandpass filter removes the 50Hz cutoff angular frequency from the mains frequency. ω c2 The cutoff angular frequency for suppressing switching noise is represented by s, where s is a complex frequency, and I sdq This is the measured value of the stator current complex vector.

7. The virtual resistance subsynchronous oscillation control method for doubly fed wind turbines under variable wind speed conditions according to claim 6, characterized in that: ω is determined according to the following formula. c1 and ω c2 : oh c1 =2π×f c1 rad / s, ω c2 =2π×f c2 rad / s; Among them, f c1 and f c2 All are cutoff frequencies.

8. A virtual resistance subsynchronous oscillation control system for a doubly-fed induction generator (DFIG) under variable wind speed conditions, implementing the virtual resistance subsynchronous oscillation control method for DFIGs under variable wind speed conditions as described in any one of claims 1-7, characterized in that: It includes a stator current control module, a desired virtual resistance calculation module, and a virtual resistance control module; The stator current control module is used to input the difference between the stator current complex vector reference value and the stator current complex vector measured value to the stator current controller, and add the output of the stator current controller to the decoupling term to obtain the rotor voltage modulation signal; The desired virtual resistance solving module is used to obtain the desired virtual resistance on the rotor side and calculate the rotor subsynchronous voltage modulation signal. The virtual resistance control module is used to add the rotor subsynchronous voltage modulation signal and the rotor voltage modulation signal to obtain the updated rotor voltage modulation signal.

9. The virtual resistance subsynchronous oscillation control system for doubly fed wind turbines under variable wind speed conditions according to claim 8, characterized in that: The desired virtual resistance R on the rotor side is determined using the following formula. dr (v w ): R dr (v w )=|σ p (s) / k e 2 |R vp (v w ); Where, σ p (s) represents the disturbance slip rate of the induction motor, k e R is the ratio of the number of turns in the stator winding to the number of turns in the rotor winding. vp (v w ) represents the desired virtual resistance on the stator side, v w This indicates the real-time wind speed.

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