A method for suppressing subsynchronous oscillation caused by grid-connected doubly-fed wind turbines via different series compensation capacitors

Abstract

The present invention discloses a method for suppressing subsynchronous oscillations caused by doubly-fed wind turbines connected to the grid via different series compensation capacitors. The present invention is based on the occurrence mechanism of subsynchronous oscillations caused by doubly-fed wind turbines connected to the grid via series compensation capacitors, uses the doubly-fed wind turbine rotor control equation as the underlying model, designs an extended state observer, and realizes real-time tracking and observation of subsynchronous components in the rotor converter. Afterwards, a DC isolation link and a proportional-phase shift link are designed to output and compensate for the influence of the subsynchronous component on the rotor output voltage, thereby effectively suppressing subsynchronous oscillations under different series compensation degrees. The control strategy proposed is compared with the additional damping control and the anti-disturbance control to suppress subsynchronous oscillations. The results show that the strategy can effectively suppress subsynchronous oscillations under different series compensation degrees, has strong adaptability, effectively improves the robustness of the system, and can provide an effective suppression method for subsynchronous oscillations generated by the grid connection of doubly-fed wind turbines.

Description

Technical Field

[0001] The present invention relates to a method and system for suppressing subsynchronous oscillation caused by grid connection of a doubly-fed wind turbine via different series compensation capacitors, and belongs to the field of new energy grid connection. Background Art

[0002] The subsynchronous oscillation problem caused by the dynamic interaction between the doubly-fed wind turbine converter control and the fixed series compensation capacitor of the line has brought severe challenges to the stable operation of the doubly-fed wind turbine grid-connected system. Compared with traditional subsynchronous oscillations, the oscillation frequency of SSCI has significant time-varying characteristics. At the same time, the generation of SSCI is unrelated to the torsional vibration of the wind turbine shaft system, has a faster oscillation divergence speed, and will cause a large number of units to be disconnected from the grid, seriously restricting the large-scale grid-connected consumption of wind energy. Therefore, designing a control strategy that can dynamically track the changes in series compensation and effectively suppress subsynchronous oscillations at different oscillation frequencies is the key to meeting the needs of subsynchronous oscillation suppression in the power grid. Summary of the invention

[0003] The present invention provides a method and system for suppressing subsynchronous oscillation caused by a doubly-fed wind turbine connected to the grid via different series compensation capacitors, so as to suppress the subsynchronous oscillation problem caused by the doubly-fed wind turbine via the series compensation capacitors.

[0004] The technical solution of the present invention is: a method for suppressing subsynchronous oscillation caused by grid-connection of a doubly-fed wind turbine via different series compensation capacitors, comprising:

[0005] Step S1, based on the doubly-fed wind turbine rotor current control equation, an extended state observer is designed to track and estimate the subsynchronous resonant current in the rotor converter in real time;

[0006] Step S2, designing a DC isolation link to filter out the DC amount contained in the subsynchronous resonant current output by the extended state observer;

[0007] Step S3, designing a proportional phase shifting link, shifting the subsynchronous component by 180 degrees to compensate for the subsynchronous disturbance component existing in the rotor converter, maintaining the output voltage of the wind turbine rotor, and avoiding the generation of new subsynchronous resonant current;

[0008] Step S4, adding the subsynchronous oscillation suppression mechanism of the doubly fed wind turbine subsynchronous oscillation damping controller based on expanded state observation to the inner loop control of the rotor converter: wherein the doubly fed wind turbine subsynchronous oscillation damping controller based on expanded state observation includes an expanded state observer, a DC isolation link, and a proportional phase shift link.

[0009] Also includes:

[0010] Step S5: using the Hurwitz criterion, evaluating the stability of the subsynchronous oscillation damping controller of the doubly-fed wind turbine based on extended state observation.

[0011] Based on the doubly-fed wind turbine rotor current control equation, an extended state observer is designed, as follows:

[0012] The doubly-fed wind turbine rotor current control equation is obtained by phase shifting:

[0013]

[0014] Where: i rd 、i rq are the d-axis and q-axis components of the rotor current respectively; u rd 、u rq are the d-axis and q-axis components of the rotor voltage respectively; R r is the rotor resistance; L r is the rotor self-inductance; ω sl is the slip electrical angular velocity; σ=1-L m 2 / (L r L s ) is the leakage inductance coefficient of the fan, L s is the stator inductance; L m is the stator mutual inductance; ψ s is the stator flux;

[0015] According to the doubly-fed wind turbine rotor current control equation, the resistance voltage drop (R r i rd ) / (σL r )、(R r i rq ) / (σL r ), the coupling term ω sl i rq ,ω sl ((L m ψ s ) / (σL r L s )), and subsynchronous components Considered as the total disturbance component f of the doubly fed wind turbine d 、f q ; At this time, the doubly fed wind turbine rotor current control equation is restated as:

[0016]

[0017] Where: b = 1 / (σL r );

[0018] Taking the d-axis current control equation of the doubly-fed wind turbine rotor as an example, f d The real-time action of (x1, t) is expanded to a new state variable x2, that is, x2 = f d (x1(t),t), and recorded as At this time, the d-axis current control equation of the doubly fed wind turbine rotor is expressed as:

[0019]

[0020] In the formula: x1 is the system state variable; y is the input;

[0021] The d-axis expansion state observer of the doubly fed wind turbine rotor is obtained as:

[0022]

[0023] Where: ε is the error; z1 is the estimated value of the system state variable; z2 is the estimated value of the total disturbance of the system; α1 and α2 are nonlinear factors; β 01 , β 02 is the output error gain coefficient; fal is the error feedback piecewise function, and its specific algorithm is expressed as:

[0024]

[0025] Where: sign is the sign function, ξ is the length of the linear segment in the fal function; α refers to α1 and α2;

[0026] Similarly, the q-axis expansion state observer of the doubly fed wind turbine rotor can be obtained as:

[0027]

[0028] The designed d- and q-axis extended state observer of the doubly-fed wind turbine can track and estimate the subsynchronous oscillation component entering the rotor converter when subsynchronous oscillation occurs in the system.

[0029] The DC isolation link is expressed by a DC isolation link transfer function. The DC isolation link transfer function G ld (s) is specifically expressed as:

[0030]

[0031] Where: T ld is the DC isolation time constant, and s is a complex parameter.

[0032] The proportional phase shift link is expressed by a proportional phase shift link transfer function. The proportional phase shift link transfer function G ks (s) is specifically expressed as:

[0033]

[0034] Where: k is the gain coefficient, T ks is the time constant of the proportional phase shifter.

[0035] The subsynchronous oscillation suppression mechanism of the doubly-fed wind turbine subsynchronous oscillation damping controller based on extended state observation is added to the rotor converter inner loop control, including:

[0036] The doubly-fed fan rotor voltage control equation is:

[0037]

[0038] When an SSCI accident occurs, there is a subsynchronous component in the rotor converter. At this time, the offsets of the d-axis current and q-axis current of the doubly fed wind turbine rotor caused by SSCI are Δi rd and Δi rq , when SSCI occurs, the d-axis and q-axis components u' of the rotor voltage of the doubly fed wind turbine are rd 、u' rq It is expressed as:

[0039]

[0040] Let the subsynchronous component of the d-axis and q-axis components of the rotor voltage be Δu rd , Δu rq , which is expressed as follows:

[0041]

[0042] By introducing additional damping control based on the extended state observer on the rotor d-axis and q-axis, the extended state observer can rd , Δu rq Real-time tracking observation is performed, and the d-axis and q-axis components of the rotor voltage after the DC isolation link and the proportional-phase shift link are expressed as:

[0043]

[0044] The DC isolation link G ld Filter out the DC amount, proportional-phase shift link G ks Shifting its phase by 180°, we get rd , Δu rq The reverse control signal is used to compensate the doubly fed wind turbine system. The d-axis and q-axis components of the rotor voltage of the doubly fed wind turbine system after the doubly fed wind turbine system is configured with a subsynchronous oscillation damping controller based on extended state observation are:

[0045]

[0046] Where: u rd 、u rq are the d-axis and q-axis components of the rotor voltage respectively; i rd 、i rq are the d-axis and q-axis components of the rotor current respectively; R r is the rotor resistance; L r is the rotor self-inductance; ω sl is the slip electrical angular velocity; σ=1-Lm 2 / (L r L s ) is the leakage inductance coefficient of the fan, L s is the stator inductance; L m is the stator mutual inductance; ψ s is the stator flux.

[0047] The Hurwitz criterion is used to evaluate the stability of the subsynchronous oscillation damping controller of the doubly fed wind turbine based on the extended state observation, as follows:

[0048] The evaluation methods of the d-axis expanded state observer and the q-axis expanded state observer are the same. Taking the d-axis expanded state observer as an example, the expression of the d-axis expanded state observer can be sorted out as follows:

[0049]

[0050] Where: ε is the error; z1 is the estimated value of the system state variable; z2 is the estimated value of the total disturbance of the system; α1 and α2 are nonlinear factors; β 01 , β 02 is the output error gain coefficient; fal is the error feedback piecewise function, ξ is the length of the linear segment in the fal function; u rd is the d-axis component of the rotor voltage; b=1 / (σL r );

[0051] The extended state observer is a rd is the input, z1 and z2 are the outputs of the dual-input dual-output system, let ω α1 , The above formula can be restated as:

[0052]

[0053] The transfer function matrix of the above formula can be calculated:

[0054]

[0055] ω α Refers to ω α1 ,ω α2 , the specific algorithm formula is:

[0056]

[0057] Open-loop transfer function G of subsynchronous oscillation damping controller for doubly-fed wind turbine based on extended state observation ssd for:

[0058] G ssd =G eso Gks G ld

[0059] Where: G eso , G ks , G ld They are the transfer functions of the extended state observer, the proportional-phase shift link, and the DC isolation link;

[0060] By calculating the open-loop transfer function of the subsynchronous oscillation damping controller of the doubly fed wind turbine based on the extended state observation, the characteristic equation of the subsynchronous oscillation damping controller of the doubly fed wind turbine based on the extended state observation is obtained:

[0061] T ks T ld s 4 +(T ks +T ld +β 01 ω α1 T ks T ld )s 3 +(1+β 01 ω α1 T ks +β 01 ω α1 T ld +β 02 ω α2 T ks T ld )s 2 +(β 01 ω α1 +β 02 ω α2 T ks +β 02 ω α2 T ld )s+β 02 ω α2 =0

[0062] Where: T ld is the DC isolation time constant, s is a complex parameter; T ks is the time constant of the proportional phase shift link;

[0063] Write the Hurwitz polynomial in terms of the characteristic equation:

[0064]

[0065] Where: a0 = β 02 ω α2 ; a1=β 01 ω α1 +β 02 ω α2 T ks+β 02 ω α2 T ld ; a2=1+β 01 ω α1 T ks +β 01 ω α1 T ld +β 02 ω α2 T ks T ld ; a3 = β 01 ω α1 T ks T ld +T ks +T ld ; a4 = T ks T ld .

[0066] A subsynchronous oscillation suppression system applicable to a doubly-fed wind turbine connected to the grid via different series compensation capacitors comprises:

[0067] The first design module is used to design an extended state observer based on the doubly-fed wind turbine rotor current control equation to track and estimate the subsynchronous resonant current in the rotor converter in real time;

[0068] The second design module is used to design a DC isolation link to filter out the DC amount contained in the subsynchronous resonant current output by the extended state observer;

[0069] The third design module is used to design a proportional phase shift link, which compensates for the subsynchronous disturbance component existing in the rotor converter after shifting the subsynchronous component by 180 degrees, maintains the output voltage of the wind turbine rotor, and avoids the generation of new subsynchronous resonant current;

[0070] The subsynchronous oscillation suppression mechanism analysis module is used to add the subsynchronous oscillation suppression mechanism of the doubly fed wind turbine subsynchronous oscillation damping controller based on expanded state observation to the inner loop control of the rotor converter: wherein, the doubly fed wind turbine subsynchronous oscillation damping controller based on expanded state observation includes an expanded state observer, a DC isolation link, and a proportional phase shift link.

[0071] Also includes:

[0072] The evaluation module is used to evaluate the stability of the subsynchronous oscillation damping controller of a doubly-fed wind turbine based on extended state observation using the Hurwitz criterion.

[0073] The beneficial effects of the present invention are as follows: the present invention is based on the occurrence mechanism of subsynchronous oscillation caused by grid-connected doubly-fed wind turbines through series compensation capacitors, and uses the doubly-fed wind turbine rotor control equation as the underlying model to design an extended state observer to achieve real-time tracking and observation of subsynchronous components in the rotor converter. Afterwards, a DC isolation link and a proportional-phase shift link are designed to output and compensate for the influence of the subsynchronous component on the rotor output voltage, thereby effectively suppressing subsynchronous oscillations under different series compensation degrees. The control strategy proposed is compared with additional damping control and self-disturbance rejection control to show the suppressive effect on subsynchronous oscillations. The results show that the strategy can effectively suppress subsynchronous oscillations under different series compensation degrees, has strong adaptability, effectively improves the robustness of the system, and can provide an effective suppression method for subsynchronous oscillations generated by grid-connected doubly-fed wind turbines. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 is a flow chart of the method of the present invention;

[0075] Figure 2 It is a specific configuration diagram of the method of the present invention;

[0076] Figure 3 It is a simulation system diagram of the method of the present invention;

[0077] Figure 4 The transfer function phase-frequency characteristics of the DC isolation link and the proportional-phase shift link and the current spectrum analysis under different series compensation degrees;

[0078] Figure 5 ω α The relationship curve with the change of error ε;

[0079] Figure 6 It is the system operation status under different series compensation degree, different wind speed and different control parameters;

[0080] Figure 7 The suppression effect comparison of three suppression methods under different series compensation degrees;

[0081] Figure 8 Comparison of the suppression effects of the three suppression methods at different wind speeds;

[0082] Fig. 9 Comparison of the inhibition effects of three inhibition methods under different control parameters. DETAILED DESCRIPTION

[0083] The invention is further described below in conjunction with the accompanying drawings and embodiments, but the content of the invention is not limited to the scope of the embodiments.

[0084] Example 1: Figure 1-9 As shown, a method for suppressing subsynchronous oscillation caused by grid-connecting a doubly-fed wind turbine via different series compensation capacitors comprises:

[0085] Step S1, designing an extended state observer based on the doubly-fed wind turbine rotor current control equation; tracking and estimating the subsynchronous resonant current in the rotor converter in real time;

[0086] Step S2, designing a DC isolation link to filter out the DC amount contained in the subsynchronous resonant current output by the extended state observer;

[0087] Step S3, designing a proportional phase shifting link, shifting the subsynchronous component by 180 degrees to compensate for the subsynchronous disturbance component existing in the rotor converter, maintaining the output voltage of the wind turbine rotor, and avoiding the generation of new subsynchronous resonant current;

[0088] Step S4, adding the subsynchronous oscillation suppression mechanism of the doubly-fed wind turbine subsynchronous oscillation damping controller based on extended state observation to the inner loop control of the rotor converter: wherein the doubly-fed wind turbine subsynchronous oscillation damping controller based on extended state observation includes an extended state observer ESO, a DC isolation link, and a proportional phase shift link;

[0089] Furthermore, the method may be arranged to further include: step S5, using the Hurwitz criterion to evaluate the stability of the subsynchronous oscillation damping controller of the doubly-fed wind turbine based on extended state observation.

[0090] Furthermore, the doubly-fed wind turbine rotor current control equation can be set to design an extended state observer, as follows:

[0091] The doubly-fed wind turbine rotor current control equation is obtained by phase shifting:

[0092]

[0093] Where: i rd 、i rq are the d-axis and q-axis components of the rotor current respectively; u rd 、u rq are the d-axis and q-axis components of the rotor voltage respectively; R r is the rotor resistance; L r is the rotor self-inductance; ω sl is the slip electrical angular velocity; σ=1-L m 2 / (L r L s ) is the leakage inductance coefficient of the fan, L s is the stator inductance; L m is the stator mutual inductance; ψ s is the stator flux;

[0094] According to the doubly-fed wind turbine rotor current control equation, the resistance voltage drop (R r i rd ) / (σL r )、(Rr i rq ) / (σL r ), the coupling term ω sl i rq ,ω sl ((L m ψ s ) / (σL r L s )), and subsynchronous components Considered as the total disturbance component f of the doubly fed wind turbine d 、f q ; At this time, the doubly fed wind turbine rotor current control equation is restated as:

[0095]

[0096] Where: b = 1 / (σL r ); i rd 、i rq The derivative of

[0097] Taking the d-axis current control equation of the doubly-fed wind turbine rotor as an example, f d The real-time action of (x1, t) is expanded to a new state variable x2, that is, x2 = f d (x1(t),t), and recorded as At this time, the d-axis current control equation of the doubly fed wind turbine rotor is expressed as:

[0098]

[0099] In the formula: x1 is the system state variable; y is the input;

[0100] According to the above formula, the d-axis expansion state observer of the doubly fed wind turbine rotor is obtained as:

[0101]

[0102] Where: ε is the error; z1 is the estimated amount of the system state variable; z2 is the estimated amount of the total disturbance of the system; α1 and α2 are nonlinear factors, and the present invention takes α1=0.5 and α2=0.25 respectively; β 01 , β 02 is the output error gain coefficient; fal is the error feedback piecewise function, and its specific algorithm is expressed as:

[0103]

[0104] Where: sign is the sign function, ξ is the length of the linear segment in the fal function, which is taken as 0.005 in the present invention; α refers to α1 and α2;

[0105] Similarly, the q-axis expansion state observer of the doubly fed wind turbine rotor can be obtained as:

[0106]

[0107] The designed d- and q-axis extended state observer of the doubly-fed wind turbine can track and estimate the subsynchronous oscillation component entering the rotor converter when subsynchronous oscillation occurs in the system.

[0108] Furthermore, the DC isolation link can be set to be expressed by a DC isolation link transfer function, where the DC isolation link transfer function G ld (s) is specifically expressed as:

[0109]

[0110] Where: T ld is the DC isolation time constant, and s is a complex parameter.

[0111] The total disturbance z2 of the rotor converter output by the extended state observer contains DC flow, which has no phase problem. If z2 is directly used to compensate the system, the compensated DC flow will be superimposed on the original DC flow of the system, which will weaken the controller's suppression effect on SSCI. Therefore, the DC isolation link is designed to filter out the DC flow in the total disturbance z2.

[0112] Furthermore, the proportional phase shift link can be set to be expressed by a proportional phase shift link transfer function, where the proportional phase shift link transfer function G ks (s) is specifically expressed as:

[0113]

[0114] Where: k is the gain coefficient, T ks is the time constant of the proportional phase shifter.

[0115] Assume that the phase of the subsynchronous oscillation after the DC isolation link is 0 after filtering. At this time, the proportional phase shift link is designed to control the phase of the compensation signal z2 to be in the second and third quadrants, which can improve the system damping, reduce the voltage change caused by the subsynchronous oscillation SSCI, and achieve effective suppression of SSCI. The closer the phase of z2 is to 180°, the more significant the suppression effect on SSCI. The transfer function of the DC isolation link and the proportional-phase shift link can be expressed as G ld G ks , by drawing G ld G ks Phase-frequency characteristics. At the same time, the spectrum analysis of the current under different series compensation degrees is performed, such as Figure 4As shown. It can be seen that when the series compensation degree changes, the subsynchronous oscillation frequency generated by the system changes accordingly. The introduced proportional-phase shift link can produce a phase shift of nearly 180° for the subsynchronous oscillation components under different series compensation degrees, making the positive damping close to the maximum, and meeting the phase shift requirements of the subsynchronous oscillation frequency under different series compensation degrees.

[0116] Furthermore, the subsynchronous oscillation suppression mechanism of adding the subsynchronous oscillation damping controller of the doubly-fed wind turbine based on extended state observation to the inner loop control of the rotor converter can be set, including:

[0117] The doubly-fed fan rotor voltage control equation is:

[0118]

[0119] When an SSCI accident occurs, there is a subsynchronous component in the rotor converter. At this time, the offsets of the d-axis current and q-axis current of the doubly fed wind turbine rotor caused by SSCI are Δi rd and Δi rq , when SSCI occurs, the d-axis and q-axis components u' of the rotor voltage of the doubly fed wind turbine are rd 、u' rq It is expressed as:

[0120]

[0121] Let the subsynchronous component of the d-axis and q-axis components of the rotor voltage be Δu rd , Δu rq , which is expressed as follows:

[0122]

[0123] By introducing additional damping control based on the extended state observer on the rotor d-axis and q-axis, the extended state observer can rd , Δu rq Real-time tracking observation is performed, and the d-axis and q-axis components of the rotor voltage after the DC isolation link and the proportional-phase shift link are expressed as:

[0124]

[0125] The DC isolation link G ld Filter out the DC amount, proportional-phase shift link G ks Shifting its phase by 180°, we get rd , Δu rq The reverse control signal is used to compensate the doubly fed wind turbine system. The d-axis and q-axis components of the rotor voltage of the doubly fed wind turbine system after the doubly fed wind turbine system is configured with a subsynchronous oscillation damping controller based on extended state observation are:

[0126]

[0127] By introducing a subsynchronous oscillation damping controller for a doubly fed wind turbine based on extended state observation into the inner loop control of the wind turbine's rotor converter, the real-time tracking, estimation and compensation of the subsynchronous component in the rotor converter can be effectively achieved, so that the rotor output voltage does not contain subsynchronous components, avoiding the generation of new subsynchronous resonant currents, blocking the spread of subsynchronous oscillations, and effectively suppressing SSCI.

[0128] Furthermore, the Hurwitz criterion can be set to evaluate the stability of the subsynchronous oscillation damping controller of the doubly fed wind turbine based on the extended state observation, including:

[0129] The operation of the doubly-fed wind turbine is easily disturbed by external environmental factors and has strong randomness and volatility. At this time, if the designed controller lacks sufficient stability, it will not only fail to effectively suppress the occurrence of subsynchronous oscillations, but will also deteriorate the stable operation ability of the system. Therefore, it is particularly important to study the stability of the controller.

[0130] The evaluation methods of the d-axis expanded state observer and the q-axis expanded state observer are the same. Taking the d-axis expanded state observer as an example, the expression of the d-axis expanded state observer can be sorted out as follows:

[0131]

[0132] The extended state observer is a rd is the input, z1 and z2 are the outputs of the dual-input dual-output system, let ω α1 , ω α2 , the above formula can be restated as:

[0133]

[0134] The transfer function matrix of the above formula can be calculated:

[0135]

[0136] ω α ω α1 ,ω α2 , the specific algorithm formula is:

[0137]

[0138] By drawing ω α The relationship curve with the change of error ε is as follows: Figure 5 As shown. It can be seen that ω α As the error ε increases, it approaches 0, and when the error ε is 0, ω α There is an upper limit, namely ωα The perturbation range of is determined. At this time, the time-varying gain that is independent of the error ε can be used to replace β 01 ω α1 , β 02 ω α2 Therefore, the extended state observer represented in the present invention can be understood as a linear extended state observer, that is, the stability thereof can be studied by using a transfer function.

[0139] Open-loop transfer function G of subsynchronous oscillation damping controller for doubly-fed wind turbine based on extended state observation ssd for:

[0140] G ssd =G eso G ks G ld

[0141] Where: G eso , G ks , G ld They are the transfer functions of the extended state observer, the proportional-phase shift link, and the DC isolation link;

[0142] By calculating the open-loop transfer function of the subsynchronous oscillation damping controller of the doubly fed wind turbine based on the extended state observation, the characteristic equation of the subsynchronous oscillation damping controller of the doubly fed wind turbine based on the extended state observation is obtained:

[0143] T ks T ld s 4 +(T ks +T ld +β 01 ω α1 T ks T ld )s 3 +(1+β 01 ω α1 T ks +β 01 ω α1 T ld +β 02 ω α2 T ks T ld )s 2 +(β 01 ω α1 +β 02 ω α2 T ks +β 02 ω α2 T ld )s+β 02 ω α2 =0

[0144] Write the Hurwitz polynomial in terms of the characteristic equation:

[0145]

[0146] Where: a0 = β 02 ω α2 ; a1=β 01 ω α1 +β 02 ω α2 T ks +β 02 ω α2 T ld ; a2=1+β 01 ω α1 T ks +β 01 ω α1 T ld +β 02 ω α2 T ks T ld ; a3 = β 01 ω α1 T ks T ld +T ks +T ld ; a4 = T ks T ld .

[0147] The control parameter β of the present invention 01 , β 02 , T ks , T ld are greater than 0, by drawing ω α Curve graphs, such as Figure 5 As shown. It can be seen that ω α1 >0,ω α2 >0, so it can be seen that all the co-factors in the Hurwitz polynomial are greater than 0. According to the Hurwitz criterion, the damping controller based on extended state observation meets the stability requirements.

[0148] In order to demonstrate the implementation effect of the present invention, a simulation platform is built based on MATLAB / Simulink. Figure 3 The simulation model of the double-fed wind farm connected to the grid via the series compensation line is shown. The system includes 90 1.5MW double-fed wind turbines, which are stepped up by the machine-side transformer T1 (0.575kV / 35kV) and the line transformer T2 (35kV / 220kV), and then the long-distance transmission of electric energy is realized through the 300km series compensation transmission line. The simulation results are as follows:

[0149] When the controller is not added, the influence of the change of series compensation degree k on SSCI is studied. The wind speed of the wind farm is set to be constant at 10m / s. At t=5s, series compensation capacitors with series compensation degrees of 40%, 50%, and 60% are respectively added to the line. The simulation results of wind farm power curves under different k values ​​are shown in Figure 2. Figure 6 (a) shown.

[0150] It is assumed that the series compensation capacitor with a series compensation degree of 20% is put into use at t=5s. At t=7s, the wind speed of the wind farm changes from the initial value of 10m / s to 12m / s, 8m / s and 6m / s respectively. The simulation results of the wind turbine power curve and current spectrum under different wind speed changes are shown in the figure below. Figure 6 (b) as shown.

[0151] Keep the series compensation at 40% and design K p The initial value of 0.6 was changed to 1.5 and 0.2 respectively, with different K p The fan power curve and current spectrum simulation results are as follows: Figure 6 (c) as shown.

[0152] The results show that changes in series compensation, wind speed, and rotor inner ring proportional coefficient will all affect subsynchronous oscillations, and the greater the series compensation, the greater the wind speed, and the larger the inner ring proportional coefficient, the worse the system stability will be.

[0153] Figure 7 When the series compensation is 40%, 50% and 60% respectively, the suppression effect of the suppression method ESSDC of the present invention is compared with two traditional suppression methods, namely, Supplementary Sub-synchronous Damping Controller SSDC and Active Disturbance Rejection Control (ADRC), wherein SSDC is set at 40% series compensation; Figure 8 The suppression effect of the suppression method of the present invention is compared with two traditional suppression methods, namely, additional damping control and active disturbance rejection control, when the wind speed drops from 10m / s to 8m / s and 6m / s respectively; Fig. 9 When the proportional coefficient of the rotor inner ring is 0.6 and 1.5 respectively, the suppression effect of the suppression method of the present invention is compared with that of two traditional suppression methods, namely additional damping control and active disturbance rejection control. The results show that the present invention can effectively suppress the occurrence of subsynchronous oscillations when the system series compensation degree changes, the wind speed changes, and the rotor inner ring changes, and compared with traditional suppression methods, the present invention has advantages in oscillation convergence time and the degree of stability after oscillation convergence.

[0154] Embodiment 2: According to another aspect of the embodiment of the present invention, a subsynchronous oscillation suppression system applicable to a doubly-fed wind turbine connected to the grid via different series compensation capacitors is provided, comprising:

[0155] The first design module is used to design an extended state observer based on the doubly-fed wind turbine rotor current control equation to track and estimate the subsynchronous resonant current in the rotor converter in real time;

[0156] The second design module is used to design a DC isolation link to filter out the DC amount contained in the subsynchronous resonant current output by the extended state observer;

[0157] The third design module is used to design a proportional phase shift link, which compensates for the subsynchronous disturbance component existing in the rotor converter after shifting the subsynchronous component by 180 degrees, maintains the output voltage of the wind turbine rotor, and avoids the generation of new subsynchronous resonant current;

[0158] The subsynchronous oscillation suppression mechanism analysis module is used to add the subsynchronous oscillation suppression mechanism of the doubly fed wind turbine subsynchronous oscillation damping controller based on expanded state observation to the inner loop control of the rotor converter: wherein, the doubly fed wind turbine subsynchronous oscillation damping controller based on expanded state observation includes an expanded state observer, a DC isolation link, and a proportional phase shift link.

[0159] Also includes:

[0160] The evaluation module is used to evaluate the stability of the subsynchronous oscillation damping controller of a doubly-fed wind turbine based on extended state observation using the Hurwitz criterion.

[0161] It should be noted that the above-mentioned modules can be implemented by software or hardware. For example, for the latter, it can be implemented in the following ways: the above-mentioned modules can be located in the same processor; and / or the above-mentioned modules are located in different processors in any combination.

[0162] The specific implementation modes of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for suppressing subsynchronous oscillation caused by grid-connecting a doubly-fed wind turbine via different series compensation capacitors, characterized in that: include: Step S1, based on the doubly-fed wind turbine rotor current control equation, an extended state observer is designed to track and estimate the subsynchronous resonant current in the rotor converter in real time; Step S2, designing a DC isolation link to filter out the DC amount contained in the subsynchronous resonant current output by the extended state observer; Step S3, designing a proportional phase shifting link, shifting the subsynchronous component by 180 degrees to compensate for the subsynchronous disturbance component existing in the rotor converter, maintaining the output voltage of the wind turbine rotor, and avoiding the generation of new subsynchronous resonant current; Step S4, adding the subsynchronous oscillation suppression mechanism of the doubly fed wind turbine subsynchronous oscillation damping controller based on expanded state observation to the inner loop control of the rotor converter: wherein the doubly fed wind turbine subsynchronous oscillation damping controller based on expanded state observation includes an expanded state observer, a DC isolation link, and a proportional phase shift link.

2. The method for suppressing subsynchronous oscillation caused by grid-connection of a doubly-fed wind turbine via different series compensation capacitors according to claim 1 is characterized in that: Also includes: Step S5: using the Hurwitz criterion, evaluating the stability of the subsynchronous oscillation damping controller of the doubly-fed wind turbine based on extended state observation.

3. The method for suppressing subsynchronous oscillation caused by grid-connection of a doubly-fed wind turbine via different series compensation capacitors according to claim 2 is characterized in that: Based on the doubly-fed wind turbine rotor current control equation, an extended state observer is designed, as follows: The doubly-fed wind turbine rotor current control equation is rearranged by shifting terms: Where: i rd 、i rq are the d-axis and q-axis components of the rotor current respectively; u rd 、u rq are the d-axis and q-axis components of the rotor voltage respectively; R r is the rotor resistance; L r is the rotor self-inductance; ω sl is the slip electrical angular velocity; σ=1-L m 2 / (L r L s ) is the leakage inductance coefficient of the fan, L s is the stator inductance; L m is the stator mutual inductance; ψ s is the stator flux; According to the doubly-fed wind turbine rotor current control equation, the resistance voltage drop (R r i rd ) / (σL r )、(R r i rq ) / (σL r ), the coupling term ω sl i rq ,ω sl ((L m ψ s ) / (σL r L s )), and subsynchronous components Considered as the total disturbance component f of the doubly fed wind turbine d 、f q ; At this time, the doubly fed wind turbine rotor current control equation is restated as: Where: b = 1 / (σL r ); Taking the d-axis current control equation of the doubly-fed wind turbine rotor as an example, f d The real-time action of (x1, t) is expanded to a new state variable x2, that is, x2 = f d (x1(t),t), and recorded as At this time, the d-axis current control equation of the doubly fed wind turbine rotor is expressed as: Where: x1 is the system state variable; y is the input; The d-axis expansion state observer of the doubly fed wind turbine rotor is obtained as: Where: ε is the error; z1 is the estimated value of the system state variable; z2 is the estimated value of the total disturbance of the system; α1 and α2 are nonlinear factors; β 01 , β 02 is the output error gain coefficient; fal is the error feedback piecewise function, and its specific algorithm is expressed as: Where: sign is the sign function, ξ is the length of the linear segment in the fal function; α refers to α1 and α2; Similarly, the q-axis expansion state observer of the doubly fed wind turbine rotor can be obtained as: The designed d- and q-axis extended state observer of the doubly-fed wind turbine can track and estimate the subsynchronous oscillation component entering the rotor converter when subsynchronous oscillation occurs in the system.

4. The method for suppressing subsynchronous oscillation caused by grid connection of a doubly-fed wind turbine via different series compensation capacitors according to claim 3 is characterized in that: The DC isolation link is expressed by a DC isolation link transfer function. The DC isolation link transfer function G ld (s) is specifically expressed as: Where: T ld is the DC isolation time constant, and s is a complex parameter.

5. The method for suppressing subsynchronous oscillation caused by grid connection of a doubly-fed wind turbine via different series compensation capacitors according to claim 4 is characterized in that: The proportional phase shift link is expressed by a proportional phase shift link transfer function. The proportional phase shift link transfer function G ks (s) is specifically expressed as: Where: k is the gain coefficient, T ks is the time constant of the proportional phase shifter.

6. The method for suppressing subsynchronous oscillation caused by grid connection of a doubly-fed wind turbine via different series compensation capacitors according to claim 5 is characterized in that: The subsynchronous oscillation suppression mechanism of the doubly-fed wind turbine subsynchronous oscillation damping controller based on extended state observation is added to the rotor converter inner loop control, including: The doubly-fed fan rotor voltage control equation is: When an SSCI accident occurs, there is a subsynchronous component in the rotor converter. At this time, the offsets of the d-axis current and q-axis current of the doubly fed wind turbine rotor caused by SSCI are Δi rd and Δi rq , when SSCI occurs, the d-axis and q-axis components u of the rotor voltage of the doubly fed wind turbine are r ' d 、u r ' q It is expressed as: Let the subsynchronous component of the d-axis and q-axis components of the rotor voltage be Δu rd , Δu rq , which is expressed as follows: By introducing additional damping control based on the extended state observer on the d-axis and q-axis of the rotor, the extended state observer can rd , Δu rq Real-time tracking observation is performed, and the d-axis and q-axis components of the rotor voltage after the DC isolation link and the proportional-phase shift link are expressed as: The DC isolation link G ld Filter out the DC amount, proportional-phase shift link G ks Shifting its phase by 180°, we get rd , Δu rq The reverse control signal is used to compensate the doubly fed wind turbine system. The d-axis and q-axis components of the rotor voltage of the doubly fed wind turbine system after the doubly fed wind turbine system is configured with a subsynchronous oscillation damping controller based on extended state observation are: Where: u rd 、u rq are the d-axis and q-axis components of the rotor voltage respectively; i rd 、i rq are the d-axis and q-axis components of the rotor current respectively; R r is the rotor resistance; L r is the rotor self-inductance; ω sl is the slip electrical angular velocity; σ=1-L m 2 / (L r L s ) is the leakage inductance coefficient of the fan, L s is the stator inductance; L m is the stator mutual inductance; ψ s is the stator flux.

7. The method for suppressing subsynchronous oscillation caused by grid connection of a doubly-fed wind turbine via different series compensation capacitors according to claim 5 is characterized in that: The Hurwitz criterion is used to evaluate the stability of the subsynchronous oscillation damping controller of the doubly fed wind turbine based on the extended state observation, as follows: The evaluation methods of the d-axis expanded state observer and the q-axis expanded state observer are the same. Taking the d-axis expanded state observer as an example, the expression of the d-axis expanded state observer can be sorted out as follows: Where: ε is the error; z1 is the estimated value of the system state variable; z2 is the estimated value of the total disturbance of the system; α1 and α2 are nonlinear factors; β 01 , β 02 is the output error gain coefficient; fal is the error feedback piecewise function, ξ is the length of the linear segment in the fal function; u rd is the d-axis component of the rotor voltage; b=1 / (σL r ); The extended state observer is a rd is the input, z1 and z2 are the outputs of the dual-input dual-output system, let ω α1 , ω α2 , the above formula can be restated as: The transfer function matrix of the above formula can be calculated: ω α Refers to ω α1 ,ω α2 , the specific algorithm formula is: Open-loop transfer function G of subsynchronous oscillation damping controller for doubly-fed wind turbine based on extended state observation ssd for: G ssd =G eso G ks G ld Where: G eso , G ks , G ld They are the transfer functions of the extended state observer, the proportional-phase shift link, and the DC isolation link; By calculating the open-loop transfer function of the subsynchronous oscillation damping controller of the doubly fed wind turbine based on the extended state observation, the characteristic equation of the subsynchronous oscillation damping controller of the doubly fed wind turbine based on the extended state observation is obtained: T ks T ld s 4 +(T ks +T ld +b 01 oh α1 T ks T ld )s 3 +(1+β 01 oh α1 T ks +b 01 oh α1 T ld +b 02 oh α2 T ks T ld )s 2 +(β 01 oh α1 +b 02 oh α2 T ks +b 02 oh α2 T ld )s+β 02 oh α2 =0 Where: T ld is the DC isolation time constant, s is a complex parameter; T ks is the time constant of the proportional phase shift link; Write the Hurwitz polynomial in terms of the characteristic equation: where: a0 = β 02 ω α2 ; a1 = β 01 ω α1 + β 02 ω α2 T ks + β 02 ω α2 T ld ; a2 = 1 + β 01 ω α1 T ks + β 01 ω α1 T ld + β 02 ω α 2T ks T ld ; a3 = β 01 ω α1 T ks T ld + T ks + T ld ; a4 = T ks T ld .

8. A subsynchronous oscillation suppression system suitable for doubly-fed wind turbines connected to the grid via different series compensation capacitors, characterized in that: include: The first design module is used to design an extended state observer based on the doubly-fed wind turbine rotor current control equation to track and estimate the subsynchronous resonant current in the rotor converter in real time; The second design module is used to design a DC isolation link to filter out the DC amount contained in the subsynchronous resonant current output by the extended state observer; The third design module is used to design a proportional phase shift link, which compensates for the subsynchronous disturbance component existing in the rotor converter after shifting the subsynchronous component by 180 degrees, maintains the output voltage of the wind turbine rotor, and avoids the generation of new subsynchronous resonant current; The subsynchronous oscillation suppression mechanism analysis module is used to add the subsynchronous oscillation suppression mechanism of the doubly fed wind turbine subsynchronous oscillation damping controller based on expanded state observation to the inner loop control of the rotor converter: wherein, the doubly fed wind turbine subsynchronous oscillation damping controller based on expanded state observation includes an expanded state observer, a DC isolation link, and a proportional phase shift link.

9. The subsynchronous oscillation suppression system for a doubly-fed wind turbine connected to the grid via different series compensation capacitors according to claim 8 is characterized in that: Also includes: The evaluation module is used to evaluate the stability of the subsynchronous oscillation damping controller of a doubly-fed wind turbine based on extended state observation using the Hurwitz criterion.

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