Additional stabilizer for suppressing low-frequency oscillation of doubly-fed fan and design method

Abstract

The invention discloses a design method of an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed fan, which comprises the following steps of: constructing an input end and an output end of the additional stabilizer, and designing a control link; performing closed-loop transfer function Bode diagram drawing on the original system, and determining a dominant oscillation frequency wd and a phase lag value theta h; performing parameter setting calculation on a phase compensation link in the control link; selecting an isolation link proportionality coefficient Ke of the additional stabilizer, a second-order band elimination filter quality coefficient xis of the additional stabilizer and an initial value of a resonance coefficient Ks; calculating a time length delta t required for disturbance suppression, and performing iterative calculation; and obtaining optimal parameters Ke, xis and Ks, and substituting the optimal parameters into expressions of the isolation link and the second-order band elimination filter. According to the additional stabilizer for suppressing the low-frequency oscillation of the doubly-fed fan and the design method, the low-frequency oscillation phenomenon of a doubly-fed fan grid-connected system can be effectively suppressed, and the small-disturbance stability of the system is effectively enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of renewable energy power generation, and more specifically, relates to an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine and a design method thereof. Background Art

[0002] In order to reduce the pressure of fossil energy, my country has proposed the goal of "carbon peak and carbon neutrality" and vigorously developed new energy power generation technology. my country's traditional power system, which is mainly based on thermal power, is turning to a new power system based on new energy. At present, the more mature technologies are mainly wind power generation and photovoltaic power generation. Among them, double-fed wind turbines, as the mainstream new energy power generation equipment, face many challenges in stability.

[0003] Doubly-fed wind turbines contain energy storage elements of different capacities. When disturbance events occur in the power system, they will show different response speeds, and the entire system will show multi-time scale characteristics. At the electromechanical scale, low-frequency oscillations often occur in doubly-fed wind turbines. Especially in the case of weak power grids, the system may change from low-frequency oscillations to divergent oscillations, which seriously threatens the safe and stable operation of the system. After many studies and analyses, it was found that it is mainly caused by shaft oscillations. As for the control link, the source of negative damping needs to be further identified. Therefore, the complex torque analysis method is generally used to identify the source of negative damping in doubly-fed wind turbines. Compared with the characteristic root analysis of the state space method, it has more physical meaning and a clearer mechanism description.

[0004] There are three main ideas for improving the low-frequency oscillation suppression strategy in the power system: the first is to improve the hardware structure of the equipment, and by adjusting the hardware configuration, the system stability can be improved; the second is to adjust the controller parameters of the equipment, and adjust the parameters without changing the hardware, without changing the structure of the equipment, and the cost is very low, but for systems with unclear instability mechanisms, strong nonlinearity, and strong coupling, the adjustment of parameters may not be completely applicable; the third is to improve the control strategy, and use the analysis idea of ​​the complex torque method to introduce a new branch to adjust the negative damping introduced by the original link to positive damping, thereby optimizing the damping characteristics of the system, further improving the small disturbance stability of the system, and effectively suppressing low-frequency oscillations. Therefore, the present invention introduces an additional stabilizer into the original system to suppress the low-frequency oscillation of the system and improve the disturbance stability of the system by designing an additional stabilizer and parameter setting. Summary of the invention

[0005] In view of the defects and improvement needs of the prior art, the present invention provides a

[0006] To achieve the above object, according to one aspect of the present invention, a method for designing an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine is provided, which is characterized by comprising:

[0007] S1, construct the input and output ends of the additional stabilizer and design the control link;

[0008] S2, draw the Bode diagram of the closed-loop transfer function of the original system and determine the dominant oscillation frequency w d And the phase lag value θ h ;

[0009] S3, performing parameter setting calculation on the phase compensation link in the control link;

[0010] S4, select the isolation link proportional coefficient K of the additional stabilizer e , the band-stop filter quality factor ξ of the additional stabilizer s And the resonance coefficient K s The initial value of

[0011] S5, calculating the time δt required for suppressing disturbances and performing iterative calculations; and

[0012] S6, obtain the optimal parameter K e ,ξ s and K s , and substitute it into the expressions of the isolation link and the second-order band-stop filter.

[0013] Preferably, the control link also includes an inverter, wherein the isolation link is connected to the input end, the isolation link, the phase compensation link, the band-stop filter and the inverter are cascaded in sequence, wherein the output end of the inverter is the output end of the additional stabilizer.

[0014] Preferably, the input end is a rotor speed change signal, and the output end is connected to a middle voltage change signal of the system.

[0015] Preferably, the dominant oscillation frequency w d is equal to the angular frequency of the original system Bode diagram at the phase jump, where the original system Bode diagram is at w d The phase lag value is θ h .

[0016] Preferably, the expression of the phase compensation link is as follows:

[0017]

[0018] The setting calculation formulas of parameter α and parameter T are as follows:

[0019]

[0020] Among them, the parameter α represents the proportional coefficient of the phase compensation link, and the parameter T represents the lag time constant of the phase compensation link.

[0021] Preferably, the expression of the isolation link is as follows:

[0022]

[0023] Among them, T w is the isolation link time constant, K e is the isolation link proportional coefficient.

[0024] Preferably, the expression of the band-stop filter is as follows:

[0025]

[0026] Among them, w s is the notch frequency, take ω s =ω d ,ξ s is the quality factor, K s is the resonance coefficient.

[0027] Preferably, verify the isolation link ratio coefficient K in the isolation link e , and update the isolation link proportional coefficient K according to the suppression result e .

[0028] Preferably, verifying the ξ in the band-stop filter s Quality factor, the resonance coefficient K s , and update the ξ according to the suppression result s Quality factor and the resonance coefficient K s .

[0029] The present invention also discloses an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine, characterized in that it includes the above-mentioned isolation link, phase compensation link, band-stop filter and inverter, wherein the isolation link, the phase compensation link, the band-stop filter and the inverter are cascaded in sequence.

[0030] In general, through the above technical solution conceived by the present invention, after the additional stabilizer is introduced into the system, the original system is transformed from the original low-frequency oscillation instability to small-disturbance stability.

[0031] The present invention proposes an additional stabilizer and a design method for suppressing low-frequency oscillation of a doubly-fed wind turbine, which can effectively suppress the low-frequency oscillation phenomenon of a doubly-fed wind turbine grid-connected system and effectively enhance the small-disturbance stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1It is a control block diagram of the electromechanical scale model of a doubly-fed wind turbine in the prior art;

[0033] Figure 2 A design diagram of an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine according to an embodiment of the present invention;

[0034] Figure 3 A flow chart of designing an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine according to an embodiment of the present invention;

[0035] Figure 4 A Bode diagram of a closed-loop transfer function of a system before an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine is introduced according to an embodiment of the present invention;

[0036] Figure 5 A time domain simulation comparison diagram of a system before and after an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine is provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] In the present invention, the terms "first", "second", etc. (if any) in the present invention and the accompanying drawings are used to distinguish similar objects but not necessarily to describe a specific order or sequence.

[0039] In the doubly-fed wind turbine grid-connected system, there is a low-frequency oscillation phenomenon. In the case of a weak power grid, the low-frequency oscillation may develop into a divergent oscillation phenomenon, thereby threatening the safe and stable operation of the power system. In order to suppress the low-frequency oscillation phenomenon of the doubly-fed wind turbine grid-connected system and ensure the stable and safe operation of the power system. The present invention discloses an additional stabilizer and a design method for suppressing the low-frequency oscillation of the doubly-fed wind turbine, which can suppress the low-frequency oscillation phenomenon by designing an additional stabilizer.

[0040] Figure 1 is the control block diagram of the electromechanical scale model of the doubly-fed wind turbine in the prior art, such as Figure 1 As shown in FIG. 1 , the existing control block diagram of the electromechanical scale model of the doubly fed wind turbine includes: a phase-locked loop link, a speed control link, a terminal voltage control link, and a rotor dynamic link. In an embodiment of the present invention, the rotor dynamic link adopts a single mass block model, P ref is a constant input mechanical power, P tis the electromagnetic output power, H is the known rotor inertia coefficient. Point A in the speed control link is the speed difference, which is the speed ω r and the speed reference value ω rref The difference between the speed difference and the rotor speed change signal is also called the rotor speed change signal. The speed control link is based on the speed difference (ω r -ω rref ) generates active current i rd ; The terminal voltage control link point B is the terminal voltage difference, that is, the terminal voltage U t With terminal voltage reference value U tref The difference between the terminal voltage and the terminal voltage is also called the terminal voltage change signal, and the terminal voltage control link is based on the terminal voltage difference (U t -U tref ) generates reactive current i rq The phase-locked loop collects the terminal voltage U t Projection u on the q axis tq =U t sin(θ t -θ pll ), to provide phase information θ pll , and transform the current in the dq coordinate system to the common coordinate system, and finally the control part generates the internal potential E s , and connected to the power grid.

[0041] Figure 2 A design diagram of an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine provided according to an embodiment of the present invention. Figure 2 Will combine Figure 1 Describe, such as Figure 2 As shown, the input end of the additional stabilizer is point A of the speed control link, and the output end is point B of the terminal voltage control link. The additional stabilizer is, from left to right, an isolation link, a phase compensation link, a second-order band-stop filter, and an inverter, which are cascaded in sequence. In the embodiment of the present invention, the expression of the isolation link is T w K is the time constant of the isolation link, which is generally given a value between 3 and 5. e is the isolation link proportional coefficient. In the embodiment of the present invention, K e Comprehensively consider the values ​​of various parameters of the actual system, and compare the oscillation suppression effect through repeated iterative calculations until the final isolation link proportional coefficient K is selected. e .

[0042] Furthermore, the expression of the phase compensation link is: The parameter α represents the proportional coefficient of the phase compensation link, and the parameter T represents the lag time constant of the phase compensation link. The expression of the second-order band-stop filter is: where w sis the notch frequency. In the low-frequency oscillation environment, the value range is between 0 and 1. For example, if w is selected s =w d ,ξ s is the quality factor, ranging from 1 to 5, K s is the resonance coefficient. In the embodiment of the present invention, K s Comprehensively consider the values ​​of various parameters of the actual system, and compare the oscillation suppression effect through repeated iterations until the final resonance coefficient K is selected. s .

[0043] Figure 3 A flow chart of designing an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine according to an embodiment of the present invention. Figure 3 Will combine Figure 2 and Figure 1 Describe, such as Figure 3 As shown in the figure, the design steps of the additional stabilizer for suppressing the low-frequency oscillation of the doubly fed wind turbine are as follows:

[0044] Step S1: Design the input end, output end and internal control link of the additional stabilizer. Specifically, the input end of the additional stabilizer is point A of the speed control link in the existing system, the output end is point B of the terminal voltage control link, and the internal control link is Figure 2 The isolation link, phase compensation link, second-order band-stop filter, and inverter cascade are shown;

[0045] Step S2: Draw the Bode diagram of the closed-loop transfer function of the original system to determine the dominant oscillation frequency w d and the phase lag value is θ h Specifically, the frequency at the phase jump of the Bode diagram of the closed-loop transfer function in the original system is the dominant oscillation frequency w d , the phase jump size of the closed-loop transfer function Bode diagram corresponds to the phase lag value θ h .

[0046] Step S3: Calculate and set parameters for the phase compensation link of the additional stabilizer. Specifically, the calculation formula for setting parameters for the phase compensation link is as follows:

[0047]

[0048] Among them, the dominant oscillation frequency w d and the phase lag value is θ h Acquired in step S2.

[0049] Step S4: Select the isolation link proportional coefficient K of the additional stabilizer e , quality factor ξ s And the resonance coefficient K s The initial value, specifically, Ke The value range is generally 1-10, s The value range is generally 1-5, K s The value range is generally 1-5, and the three parameters start from small to large.

[0050] Step S5: Calculate the time required to suppress disturbance δt and perform iterative calculation. Specifically, given a given disturbance condition, the disturbance time is recorded as t0, and the time when the waveform converges to a stable point is recorded as t c The time required from perturbation to convergence and stability is recorded as δt = t c -t0, optimize δt, isolate the link proportional coefficient K through repeated iterations e , quality factor ξ s , resonance coefficient K s Calculate the corresponding δt and obtain the final iterative parameter K e , ξ and K s The optimal solution of .

[0051] Step S6: Obtain the optimal parameter K e ,ξ s and K s , and substitute it into the expressions of the isolation link and the second-order band-stop filter. e ,ξ s and K s After substitution, the expression of the internal control link of the additional stabilizer is determined.

[0052] Figure 4 : is a Bode diagram of the closed-loop transfer function of the system before the additional stabilizer for suppressing the low-frequency oscillation of the doubly-fed wind turbine is introduced according to an embodiment of the present invention. Figure 4 As shown, the lag phase θ corresponding to the phase jump in the closed-loop transfer function Bode diagram is h , the dominant oscillation frequency w d =2πf d , where f d Indicates electrical frequency, unit is Hz; ω d Represents angular frequency in rad / s.

[0053] Figure 5 A time domain simulation comparison diagram of the system before and after the introduction of an additional stabilizer to suppress low-frequency oscillation of a doubly-fed wind turbine is provided according to an embodiment of the present invention. Figure 5 As shown in the figure, the introduction of the additional stabilizer disclosed in the present invention effectively suppresses the low-frequency oscillation instability of the doubly fed wind turbine and maintains safe and stable operation. pll is the phase-locked loop phase, variable ω r is the rotor speed, and the horizontal axis is time t.

[0054] In the existing double-fed wind turbine single-machine grid-connected system, the grid voltage drops with a small disturbance at 1 second. In the case of a weak grid, the system will experience low-frequency oscillation divergence and instability. According to the additional stabilizer and parameter setting calculation for suppressing the low-frequency oscillation of the double-fed wind turbine disclosed in the present invention, the additional stabilizer is introduced into the system, so that the original system changes from the original low-frequency oscillation instability to small disturbance stability.

[0055] In summary, the present invention proposes an additional stabilizer and a design method for suppressing low-frequency oscillation of a doubly-fed wind turbine, which can effectively suppress the low-frequency oscillation phenomenon of a doubly-fed wind turbine grid-connected system and effectively enhance the small-disturbance stability of the system.

[0056] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A design method for an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine, characterized in that: include: S1, construct the input and output ends of the additional stabilizer and design the control link; S2, draw the Bode diagram of the closed-loop transfer function of the original system and determine the dominant oscillation frequency w d And the phase lag value θ h ; S3, performing parameter setting calculation on the phase compensation link in the control link; S4, select the isolation link proportional coefficient K of the additional stabilizer e , the quality coefficient of the second-order band-stop filter of the additional stabilizer is ξ s And the resonance coefficient K s The initial value of S5, calculate the time δt required to suppress the disturbance and perform iterative calculation; as well as S6, obtain the optimal parameter K e ,ξ s and K s , and substitute it into the expressions of the isolation link and the second-order band-stop filter.

2. The design method of an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine according to claim 1 is characterized in that: The control link also includes an inverter, wherein the isolation link is connected to the input end, the isolation link, the phase compensation link, the band-stop filter and the inverter are cascaded in sequence, wherein the output end of the inverter is the output end of the additional stabilizer.

3. The design method of an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine according to claim 1, characterized in that: The input end is a rotor speed change signal, and the output end is connected to a middle voltage change signal of the system.

4. The design method of an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine according to claim 1, characterized in that: The dominant oscillation frequency w d is equal to the angular frequency of the original system Bode diagram at the phase jump, where the original system Bode diagram is at w d The phase lag value is θ h .

5. The design method of an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine according to claim 4, characterized in that: The expression of the phase compensation link is as follows: The setting calculation formulas of parameter α and parameter T are as follows: Among them, the parameter α represents the proportional coefficient of the phase compensation link, and the parameter T represents the lag time constant of the phase compensation link.

6. The design method of an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine according to claim 1, characterized in that: The expression of the isolation link is as follows: Among them, T w is the isolation link time constant, K e is the isolation link proportional coefficient.

7. The additional stabilizer design method for suppressing low-frequency oscillation of a doubly-fed wind turbine according to claim 2 is characterized in that: The expression of the second-order band-stop filter is as follows: Among them, w s is the notch frequency, take ω s =ω d ,ξ s is the quality factor, K s is the resonance coefficient.

8. The design method of an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine according to claim 6, characterized in that: Verify the isolation link ratio coefficient K in the isolation link e , and update the isolation link proportional coefficient K according to the suppression result e .

9. The design method of an additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine according to claim 7, characterized in that: Verify the second-order band-stop filter s Quality factor, the resonance coefficient K s , and according to the suppression result, update the ξ s Quality factor and the resonance coefficient K s .

10. An additional stabilizer for suppressing low-frequency oscillation of a doubly-fed wind turbine, characterized in that: It comprises the isolation link, phase compensation link, band stop filter and inverter in claims 1-9, wherein the isolation link, the phase compensation link, the band stop filter and the inverter are cascaded in sequence.

Images