Double-fed fan subsynchronous oscillation suppression system

Abstract

The invention discloses a double-fed fan subsynchronous oscillation suppression system. Comprising four control loops, namely a doubly-fed fan rotor rotating speed output feedback control loop, a doubly-fed fan stator reactive output current output feedback control loop, a doubly-fed fan grid side converter reactive output current output feedback control loop and a doubly-fed fan back-to-back converter direct current link capacitor voltage output feedback control loop. Four output variables are utilized to form four feedback control channels, and each control channel is provided with a cascade high-gain observer and an output feedback controller. According to the method, subsynchronous oscillation disturbance caused by series compensation line grid connection of the doubly-fed fan can be effectively suppressed, and the method has very high robustness on system operation working conditions and system parameters. The method can be widely applied to the field of stability control of power systems.

Description

Technical Field

[0001] The present invention relates to the field of power system stability control, and particularly to a subsynchronous oscillation suppression system for doubly-fed induction generators (DFIGs). Background Art

[0002] In recent years, the wind power industry in China has developed rapidly. However, the areas with rich wind resources in China are relatively far from the areas with concentrated power loads. Therefore, in engineering, a series capacitor compensation scheme is usually adopted to improve the long-distance power transmission capacity of the line. However, when a wind farm composed of DFIGs is connected to the power grid through a line with a high compensation level, the interaction between the DFIGs and the series compensated line will cause subsynchronous oscillation of the line current and voltage. And as the oscillation diverges, it will eventually lead to the disconnection of the wind turbines, affecting the safe and stable operation of the power system. Current research believes that this subsynchronous oscillation is an electrical resonance, originating from the line LC resonance and then enhanced by the control loop of the machine side converter of the DFIG. The factors affecting the characteristics of subsynchronous oscillation mainly include wind speed, the number of wind turbines, and the degree of line compensation.

[0003] Currently, the common measures to suppress subsynchronous oscillation mainly fall into two categories: One is to install flexible AC transmission system (FACTS) devices on the grid side. However, this strategy cannot solve the subsynchronous oscillation problem at the source, and in addition, installing FACTS devices will increase the equipment operation cost; The other is to optimize or change the control loop of the DFIG converter. This strategy mainly includes optimizing the control parameters of the DFIG converter and adding an additional damping controller. However, due to the limitation of the steady-state operation requirements of the wind turbines, the range of modification of optimizing the controller parameters is limited, and it cannot solve the subsynchronous oscillation problem of DFIGs under different operating conditions. Adding an additional damping controller to the original control loop of the DFIG converter can improve the damping level of the wind turbines in a wide frequency band. However, this method is overly dependent on the system model and parameters. Due to factors such as the nonlinearity and time-variability of the power system and the random uncertainty of the operating state of the wind turbine generator sets, it is difficult to accurately model the system. Therefore, the method of adding an additional damping controller has low robustness. Summary of the Invention

[0004] To solve at least one of the technical problems existing in the prior art to a certain extent, an object of the present invention is to provide a subsynchronous oscillation suppression system for DFIGs based on a cascaded high-gain observer.

[0005] To achieve the above object, the technical solution provided by the present invention is as follows:

[0006] A subsynchronous oscillation suppression system for DFIGs includes four control loops:

[0007] A feedback control loop for the rotor speed output of the DFIG based on a three-stage cascaded high-gain state disturbance observer, whose input signal is the rotor speed deviation of the DFIG The output signal is the d-axis control voltage u of the rotor side converter of the doubly-fed wind turbine dr ;

[0008] The output feedback control loop of the reactive power output current of the stator of the doubly-fed wind turbine based on a second-order high-gain state disturbance observer, and its input signal is the deviation of the reactive power output current of the stator of the doubly-fed wind turbine The output signal is the q-axis control voltage u of the rotor side converter of the doubly-fed wind turbine qr ;

[0009] The output feedback control loop of the reactive power output current of the grid side converter of the doubly-fed wind turbine based on a second-order high-gain state disturbance observer, and its input signal is the deviation of the reactive power output current of the grid side converter of the doubly-fed wind turbine The output signal is the q-axis control voltage u of the grid side converter of the doubly-fed wind turbine qg ;

[0010] The output feedback control loop of the DC link capacitor voltage of the back-to-back converter of the doubly-fed wind turbine based on a third-order cascaded high-gain state disturbance observer, and its input signal is the deviation of the DC link capacitor voltage of the back-to-back converter of the doubly-fed wind turbine The output signal is the d-axis control voltage u of the grid side converter of the feed wind turbine dg .

[0011] Furthermore, the control system includes four control input signals, which are respectively the deviation of the rotor speed of the doubly-fed wind turbine The deviation of the reactive power output current of the stator of the doubly-fed wind turbine The deviation of the reactive power output current of the grid side converter of the doubly-fed wind turbine The deviation of the DC link capacitor voltage of the back-to-back converter of the doubly-fed wind turbine

[0012] The control system includes four control output signals, which are respectively the d-axis control voltage u of the rotor side converter of the doubly-fed wind turbine dr , the q-axis control voltage u qr ; The q-axis control voltage u of the grid side converter of the doubly-fed wind turbine qg , the d-axis control voltage u dg ;

[0013] The above four control output signals and control input signals respectively correspond to four feedback control channels

[0014] Furthermore, the subsynchronous oscillation suppression system of the doubly-fed wind turbine is designed in the following way

[0015] Using the output feedback linearization theory, the multi-input multi-output doubly-fed wind turbine system is decomposed into four single-input single-output subsystems

[0016] In each single-input single-output subsystem, a virtual state is introduced to represent the modeling error of the system and the external disturbance of the system;

[0017] For each subsystem, a cascaded high-gain state disturbance observer is designed to estimate the state and disturbance of the system, where the disturbance signal includes a subsynchronous oscillation disturbance signal;

[0018] An output feedback controller is designed using the estimated system state and disturbance to suppress the system disturbance and maintain the stable operation of the system.

[0019] Furthermore, the expression of the cascaded high-gain state disturbance observer is:

[0020]

[0021] where ξ j (j = 1, 2,..., ρ + 1) are the state variables of the cascaded high-gain observer, ρ is the order of the system, ε is the high-gain parameter of the cascaded high-gain observer, β j (j = 1, 2,…, ρ + 1) are the design parameters of the cascaded high-gain observer, is the estimated system state, u is the control signal of the system, τ0 is a positive constant, and y is the control signal of the system.

[0022] Furthermore, the rotor speed output feedback control loop of the doubly-fed wind turbine based on the third-order cascaded high-gain state disturbance observer uses the estimated value of the third-order cascaded high-gain state disturbance observer to generate the d-axis control voltage u dr of the grid-side converter of the doubly-fed wind turbine. The expression of the third-order cascaded high-gain state disturbance observer is:

[0023]

[0024] where ξ 11 , ξ 12 and ξ 13 are the state variables of the third-order cascaded high-gain state disturbance observer in the rotor speed output feedback control loop of the doubly-fed wind turbine, respectively. β 11 , β 12 and β 13 are the design parameters of the third-order cascaded high-gain state disturbance observer, respectively. τ1 is a positive constant, ε1 is the high-gain parameter of the third-order cascaded high-gain state disturbance observer, and y1 is the rotor speed deviation of the doubly-fed wind turbine, that is, y1 = ω r -ω r_ref , is the state variable estimated for ξ 12 .

[0025] Further, in the output feedback control loop of the stator reactive output current of the doubly-fed wind turbine based on the second-order high-gain state disturbance observer, the estimated value of the second-order cascaded high-gain state disturbance observer is used to generate the q-axis control voltage u of the machine-side converter of the doubly-fed wind turbine qr , and the expression of the second-order cascaded high-gain state disturbance observer is:

[0026]

[0027] where ξ 21 and ξ 22 are respectively the state variables of the second-order high-gain state disturbance observer in the output feedback control loop of the stator reactive output current of the doubly-fed wind turbine, β 21 and β 22 are respectively the design parameters of the second-order high-gain state disturbance observer, τ2 is a positive constant, ε2 is the high-gain parameter of the second-order high-gain state disturbance observer, y2 is the deviation of the stator reactive output current of the doubly-fed wind turbine, that is, y2 = i qr -i qr_ref .

[0028] Further, in the output feedback control loop of the DC-link capacitor voltage of the back-to-back converter of the doubly-fed wind turbine based on the third-order cascaded high-gain state disturbance observer, the estimated value of the third-order cascaded high-gain state disturbance observer is used to generate the d-axis control voltage u of the grid-side converter of the doubly-fed wind turbine dg , and the expression of the third-order cascaded high-gain state disturbance observer is:

[0029]

[0030] where ξ 31 , ξ 32 and ξ 33 are respectively the state variables of the third-order cascaded high-gain state disturbance observer in the output feedback control loop of the DC-link capacitor voltage of the back-to-back converter of the doubly-fed wind turbine, β 31 , β 32 and β 33 are respectively the design parameters of the third-order cascaded high-gain state disturbance observer, τ3 is a positive constant, ε3 is the high-gain parameter of the third-order cascaded high-gain state disturbance observer, y3 is the deviation of the DC-link capacitor voltage of the back-to-back converter of the feed wind turbine, that is, y3 = U dc -U dc_ref , is the state variable estimated for ξ 32 .

[0031] Further, in the output feedback control loop of the reactive output current of the grid-side converter of the doubly-fed wind turbine based on the second-order high-gain state disturbance observer, the q-axis control voltage u of the grid-side converter of the doubly-fed wind turbine is generated by using the estimated value of the second-order cascaded high-gain state disturbance observer. qg The expression of the second-order cascaded high-gain state disturbance observer is as follows:

[0032]

[0033] In the formula, ξ 41 and ξ 42 are respectively the state variables of the second-order high-gain state disturbance observer in the output feedback control loop of the reactive output current of the grid-side converter of the doubly-fed wind turbine, β 41 and β 42 are respectively the design parameters of the second-order high-gain state disturbance observer, τ4 is a positive constant, ε4 is the high-gain parameter of the second-order high-gain state disturbance observer, and y4 is the deviation of the reactive output current of the stator of the doubly-fed wind turbine, that is, y4 = i qg -i qg_ref .

[0034] Compared with the existing methods, the present invention has the following advantages and beneficial effects:

[0035] (1) The present invention does not rely on the accurate model and parameters of the system and has robustness to the uncertainty of system parameters.

[0036] (2) The present invention realizes the complete decoupling of the control loop of the doubly-fed wind turbine converter and can well avoid the power coupling oscillation of the doubly-fed wind turbine.

[0037] (3) The present invention can well estimate the subsynchronous oscillation disturbance signal of the doubly-fed wind turbine and effectively suppress it, and can still achieve a good suppression effect when the operating conditions of the unit change, and has robustness to external disturbances of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following introduces the drawings of the related technical solutions in the embodiments of the present invention or the prior art. It should be understood that the drawings introduced below are only for conveniently and clearly expressing some embodiments of the technical solutions in the present invention, and those skilled in the art can obtain other drawings according to these drawings without creative efforts.

[0039] Figure 1 FIG. is a schematic structural diagram of a subsynchronous oscillation suppression system for a doubly-fed wind turbine based on a cascaded high-gain observer proposed in an embodiment of the present invention;

[0040] Figure 2It is the composition diagram of the subsynchronous oscillation suppression system for a doubly-fed wind turbine based on a cascaded high-gain observer proposed in the embodiments of the present invention;

[0041] Figure 3 It is the layout schematic diagram of a test power system with a doubly-fed wind turbine in the embodiments of the present invention;

[0042] Figure 4 It is the simulation result diagram when the doubly-fed wind turbine operates under the conditions of a transmission line series compensation degree of 40% and a wind speed of 12 m / s in the embodiments of the present invention; among them, Figure 4 (a) is the output active power output curve of the doubly-fed wind turbine, Figure 4 (b) is the output reactive power output curve of the doubly-fed wind turbine, Figure 4 (c) is the d-axis control voltage u dr curve of the machine-side converter of the doubly-fed wind turbine, Figure 4 (d) is the q-axis control voltage u qr curve of the machine-side converter of the doubly-fed wind turbine;

[0043] Figure 5 It is the simulation result diagram when the doubly-fed wind turbine operates under the conditions of a transmission line series compensation degree of 80% and a wind speed of 12 m / s in the embodiments of the present invention; among them, Figure 5 (a) is the output active power output curve of the doubly-fed wind turbine, Figure 5 (b) is the output reactive power output curve of the doubly-fed wind turbine, Figure 5 (c) is the d-axis control voltage U dr curve of the machine-side converter of the doubly-fed wind turbine, Figure 5 (d) is the q-axis control voltage u qr curve of the machine-side converter of the doubly-fed wind turbine;

[0044] Figure 6 It is the simulation result diagram when the doubly-fed wind turbine operates under the conditions of a transmission line series compensation degree of 40% and a wind speed of 9 m / s in the embodiments of the present invention; among them, Figure 6 (a) is the output active power output curve of the doubly-fed wind turbine, Figure 6 (b) is the output reactive power output curve of the doubly-fed wind turbine, Figure 6 (c) is the d-axis control voltage u dr curve of the machine-side converter of the doubly-fed wind turbine, Figure 6 (d) is the q-axis control voltage u qr curve of the machine-side converter of the doubly-fed wind turbine. Specific embodiments

[0045] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where like or similar reference numerals denote like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as a limitation to the present invention. For the step numbers in the following embodiments, they are only set for the convenience of explanation and illustration, and no limitation is imposed on the order between the steps. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0046] In the description of the present invention, it should be understood that for the orientation description, such as the orientation or positional relationship indicated by up, down, front, back, left, right, etc., is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0047] In the description of the present invention, the meaning of several is one or more, the meaning of multiple is more than two, understand greater than, less than, exceeding, etc. as not including the recited number, and understand above, below, within, etc. as including the recited number. If the first and second are described only for the purpose of distinguishing technical features, they should not be construed as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence relationship of the indicated technical features.

[0048] In the description of the present invention, unless otherwise clearly defined, words such as set, install, connect, etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meaning of the above words in the present invention in combination with the specific content of the technical solution.

[0049] Aiming at the shortcomings and deficiencies of the prior art, the present invention proposes a double-fed wind turbine subsynchronous oscillation suppression system based on a cascaded high-gain observer. The present invention fully considers the subsynchronous oscillation suppression effect under the change of the operating conditions of the double-fed wind turbine, and can still effectively suppress the subsynchronous oscillation under the change of the unit operating mode, enhancing the robustness of the double-fed wind turbine to external disturbances.

[0050] As Figure 1 and Figure 2As shown in the figure, this embodiment provides a control system for a sub-synchronous oscillation suppression method of a doubly-fed wind turbine based on a cascaded high-gain observer, including four control loops, namely: an output feedback control loop for the rotor speed of the doubly-fed wind turbine based on a third-order cascaded high-gain state disturbance observer, an output feedback control loop for the reactive power output current of the stator of the doubly-fed wind turbine based on a second-order high-gain state disturbance observer, an output feedback control loop for the reactive power output current of the grid-side converter of the doubly-fed wind turbine based on a second-order high-gain state disturbance observer, and an output feedback control loop for the DC-link capacitor voltage of the back-to-back converter of the doubly-fed wind turbine based on a third-order cascaded high-gain state disturbance observer.

[0051] In the appendix Figure 1 and Figure 2 the following are the definitions of the parameters: w1 is the deviation of the rotor speed of the doubly-fed wind turbine, that is, w1 = ω r - ω r_ref where ω r is the rotor speed of the doubly-fed wind turbine, and ω r_ref is the reference value of the rotor speed of the doubly-fed wind turbine; v1 is the deviation of the reactive power output current of the stator of the doubly-fed wind turbine, that is, v1 = i qr - i qr_ref where i qr is the q-axis component of the rotor current, and i qr_ref is the reference value of the q-axis component of the rotor current; λ1 is the deviation of the reactive power output current of the grid-side converter of the doubly-fed wind turbine, that is, λ1 = i qg - i qg_ref where i qg is the q-axis component of the current of the grid-side converter of the doubly-fed wind turbine, and i qg_ref is the reference value of the q-axis component of the current of the grid-side converter of the doubly-fed wind turbine; η1 is the deviation of the DC-link capacitor voltage of the back-to-back converter of the doubly-fed wind turbine, that is, η1 = U dc - U dc_ref where U dc is the DC-link capacitor voltage of the back-to-back converter of the doubly-fed wind turbine, and U dc_ref is the reference value of the DC-link capacitor voltage of the back-to-back converter of the doubly-fed wind turbine. and are the estimated values of the third-order cascaded high-gain state disturbance observer in the output feedback control loop for the rotor speed of the doubly-fed wind turbine, and are the estimated values of the second-order cascaded high-gain state disturbance observer in the output feedback control loop for the reactive power output current of the stator of the doubly-fed wind turbine, and are the estimated values of the second-order cascaded high-gain state disturbance observer in the output feedback control loop for the reactive power output current of the stator of the doubly-fed wind turbine, and is the estimated value of the third-order cascaded high-gain state disturbance observer in the DC-link capacitor voltage output feedback control loop of the back-to-back converter of the doubly-fed wind turbine. u1 and u dr The d-axis control voltage of the machine-side converter of the doubly-fed wind turbine, i.e., u1 = u dr , u2 and u qr The q-axis control voltage of the machine-side converter of the doubly-fed wind turbine, i.e., u2 = u qr , u3 and u dg The d-axis control voltage of the grid-side converter of the doubly-fed wind turbine, i.e., u3 = u dg , u4 and u qg The q-axis control voltage of the grid-side converter of the doubly-fed wind turbine, i.e., u4 = u qg .

[0052] Specifically, the output variables of the doubly-fed wind turbine are selected as the generator rotor speed, the reactive output current of the machine-side converter of the doubly-fed wind turbine, the reactive output current of the grid-side converter of the doubly-fed wind turbine, and the DC capacitor terminal voltage of the back-to-back converter of the doubly-fed wind turbine. Four feedback control channels are formed by using the four output variables, and a cascaded high-gain observer and an output feedback controller are designed for each control channel. Its working principle is: the cascaded high-gain state disturbance observer is used to estimate the system disturbance including the subsynchronous oscillation disturbance, and the output feedback controller uses the observed system disturbance signal to suppress the subsynchronous oscillation and control the system stability. The system of this embodiment can effectively suppress the subsynchronous oscillation disturbance caused by the doubly-fed wind turbine connected to the grid through a series-compensated line, and has strong robustness to the operating conditions and system parameters of the system operation.

[0053] To test the performance of the present invention in suppressing subsynchronous oscillation, a simulation study was carried out in the test power system (PSCAD) as Figure 3 shown.

[0054] As Figure 3 shown, the test power system in which the doubly-fed wind farm is connected to the grid through a series-compensated line is laid out, and the doubly-fed wind farm is equivalent to an equivalent wind turbine. The parameters of the doubly-fed wind turbine are selected as: base frequency 50 Hz, base voltage 3.6 kV, base capacity 4.16 MVA, stator resistance 0.0079 p.u., stator inductance 4.4794 p.u., rotor resistance 0.025 p.u., rotor inductance 4.8 p.u., mutual inductance between stator and rotor 4.4 p.u., DC-link capacitor of the back-to-back converter 0.016 F, DC-link capacitor voltage of the back-to-back converter 3600 V. Attached Figure 3 In, the definitions of each parameter are as follows: C2 is the line-to-ground capacitance of the 35 kV line, L2 is the inductance of the 35 kV line, R2 is the inductance of the 35 kV line, L1 is the inductance of the 220 kV line, R1 is the resistance of the 220 kV line, L T3$L_{T3}$ is the leakage inductance of transformer T3, and $C1$ is the series capacitor of the 220 kV line. The line parameters are selected as follows: $L2 = 0.01 H$, $R2 = 0.5 \Omega$, $L1 = 0.026526 H$, and $R1 = 1.6667 \Omega$.

[0055] To evaluate the performance of the present invention in suppressing subsynchronous oscillations, the simulation results of a test system with vector control (VC) are presented for comparison. The parameters of VC are selected as follows: $K$ p1 $= 1$, $T$ i1 $= 5$, $K$ p2 $= 0.8$, $T$ i2 $= 10$, $K$ p3 $= 2$, $T$ i3 $= 5$, $K$ p4 $= 0.8$, $T$ i4 $= 10$, $K$ p5 $= 1$, $T$ i5 $= 5$, $K$ p6 $= 0.8$, $T$ i6 $= 10$, $K$ p7 $= 0.8$, $T$ i7 $= 10$. The parameters of the present invention are selected as follows: $\varepsilon1 = \varepsilon2 = \varepsilon3 = \varepsilon4 = 0.001$, $\beta$ 11 $= 3$, $\beta$ 12 $= 3$, $\beta$ 13 $= 1$, $\beta$ 21 $= 2$, $\beta$ 22 $= 1$, $\beta$ 31 $= 3$, $\beta$ 32 $= 3$, $\beta$ 33 $= 1$, $\beta$ 41 $= 2$, $\beta$ 42 $= 1$, $\tau1 = -1200$, $\tau2 = 5000$, $\tau3 = -10000$, $\tau4 = -1000$, $k$ 11 $= 625$, $k$ 12 $= 50$, $k$ 21 $= 1000$, $k$ 31 $= 6400$, $k$ 32 $= 160$, $k$ 41 $= 1100$. As Figure 4 (a)- Figure 4 (d) shows, combining the simulation results obtained for the grid-connected system of a doubly-fed induction generator with series compensation under the present invention (CHGSPOC) and VC control when the wind speed is 12 m / s and the series compensation degree of the line is 40%. Among them, Figure 4 (a) and Figure 4 (b) the red line is for the doubly-fed induction generator equipped with VC, and the gray line is for the system dynamics of the doubly-fed induction generator using CHGSPOC. Figure 4 (c) and Figure 4 (d) are the four control output signals of the doubly-fed induction generator using CHGSPOC, and the series compensation capacitor is switched in at $t = 2 s$. AsFigure 4 (a) and Figure 4 As shown in (b), after the series compensation capacitor is put into operation, the active power and reactive power output of the DFIG controlled by VC both exhibit subsynchronous oscillation phenomena. However, no subsynchronous oscillation phenomena are observed in the active power and reactive power output of the DFIG controlled by CHGSPOC. As Figure 4 (c) and Figure 4 As shown in (d), the control output signals u dr and u qr of the output feedback control loop of the DFIG rotor speed with a three - stage cascaded high - gain state disturbance observer and the output feedback control loop of the DFIG stator reactive current output with a second - order high - gain state disturbance observer equipped on the rotor side of the DFIG successfully estimate the subsynchronous oscillation disturbance signal and effectively suppress it.

[0056] As Figure 5 (a) - Figure 5 As shown in (d), combining the simulation results obtained when the DFIG is connected to the grid through a series - compensated line under CHGSPOC and VC control at a wind speed of 12 m / s and a series compensation degree of 80%. Among them, Figure 5 (a) and Figure 5 In (b), the red line is for the DFIG equipped with VC, and the gray line is for the system dynamics of the DFIG using CHGSPOC. Figure 5 (c) and Figure 5 In (d) are the four control output signals of the DFIG using CHGSPOC, and the series compensation capacitor is put into operation at t = 2 s. As Figure 5 (a) and Figure 5 As shown in (b), after the series compensation capacitor is increased, the active power and reactive power output of the DFIG controlled by VC both exhibit subsynchronous oscillation phenomena, and Figure 4 (a) and Figure 4 compared with (a) and (b), the system becomes unstable faster. However, the DFIG controlled by CHGSPOC can still well suppress subsynchronous oscillation. As Figure 5 (c) and Figure 5 As shown in (d), the control output signals u dr and u qr still successfully estimate the subsynchronous oscillation disturbance signal and effectively suppress it.

[0057] As Figure 6 (a) - Figure 6As shown in (d), combined with the simulation results obtained by the grid-connected system of a doubly-fed wind turbine via a series-compensated line under CHGSPOC and VC control when the line wind speed is 9 m / s and the series compensation degree is 40%, where Figure 6 (a) and Figure 6 (b), the red line is the doubly-fed wind turbine equipped with VC, and the gray line is the system dynamics of the doubly-fed wind turbine using CHGSPOC. Figure 6 (c) and Figure 6 (d) show the four control output signals of the doubly-fed wind turbine using CHGSPOC, and the series compensation capacitor is switched in at t = 2 s. As Figure 6 (a) and Figure 6 (b) show, after the wind speed of the doubly-fed wind turbine decreases when it is switched in, both the active power and reactive power output of the doubly-fed wind turbine controlled by VC exhibit subsynchronous oscillation phenomena, and Figure 4 (a) and Figure 4 (b) show that the system becomes unstable faster. However, the doubly-fed wind turbine controlled by CHGSPOC can still effectively suppress subsynchronous oscillation. As Figure 6 (c) and Figure 6 (d) show, the control output signals u dr and u qr of the output feedback control loop of the rotor speed of the doubly-fed wind turbine equipped with a three-stage cascaded high-gain state disturbance observer and the output feedback control loop of the stator reactive output current of the doubly-fed wind turbine based on a second-order high-gain state disturbance observer can still successfully estimate the subsynchronous oscillation disturbance signal and effectively suppress it.

[0058] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0059] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable those of ordinary skill in the art to understand the content of the present invention and implement it accordingly. It should not be used to limit the protection scope of the present invention. Any other changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A subsynchronous oscillation suppression system for a doubly-fed wind turbine, characterized in that, It includes four control loops: The rotor speed output feedback control loop of the doubly-fed wind turbine based on a three-stage cascaded high-gain state disturbance observer has the rotor speed deviation of the doubly-fed wind turbine as its input signal and the d-axis control voltage U of the grid-side converter of the doubly-fed wind turbine as its output signal dr ; Output feedback control loop of stator reactive output current of doubly-fed wind turbine based on second-order high-gain state disturbance observer, whose input signal is the deviation of stator reactive output current of doubly-fed wind turbine The output signal is the q-axis control voltage U of the machine-side converter of the doubly-fed wind turbine qr ; Output feedback control loop for reactive output current of grid-side converter of doubly-fed wind turbine based on second-order high-gain state disturbance observer, whose input signal is the deviation of reactive output current of grid-side converter of doubly-fed wind turbine The output signal is the q-axis control voltage U of the grid-side converter of the doubly-fed wind turbine qg ; The output feedback control loop of the DC-link capacitor voltage of the back-to-back converter of the doubly-fed wind turbine based on a three-stage cascaded high-gain state disturbance observer has the deviation of the DC-link capacitor voltage of the back-to-back converter of the doubly-fed wind turbine as its input signal and the d-axis control voltage u of the grid-side converter of the feed wind turbine as its output signal dg .

2. The sub-synchronous oscillation suppression system for a doubly-fed wind turbine according to claim 1, characterized in that The sub-synchronous oscillation suppression system of the doubly-fed wind turbine is designed in the following way: Using the output feedback linearization theory, the multi-input multi-output doubly-fed wind turbine system is decomposed into four single-input single-output subsystems; A virtual state is introduced into each single-input single-output subsystem to represent the modeling error of the system and the external disturbance of the system; A cascaded high-gain state disturbance observer is designed for each subsystem to estimate the state and disturbance of the system; An output feedback controller is designed using the estimated system state and disturbance to suppress the system disturbance and maintain the stable operation of the system.

3. The sub-synchronous oscillation suppression system for a doubly-fed wind turbine according to claim 2, characterized in that, The expression of the cascaded high-gain state disturbance observer is: where ξ j (j = 1, 2, ..., ρ + 1) are the state variables of the cascaded high-gain observer, ρ is the system order, ε is the high-gain parameter of the cascaded high-gain observer, β j (j = 1, 2, …, ρ + 1) are the design parameters of the cascaded high-gain observer, is the estimated system state, U is the control signal of the system, τ0 is a positive constant, and y is the system output signal.

4. A subsynchronous oscillation suppression system for a doubly-fed wind turbine according to claim 1 or 2, characterized in that, The rotor speed output feedback control loop of the doubly-fed wind turbine based on the three-stage cascaded high-gain state disturbance observer uses the estimated value of the three-stage cascaded high-gain state disturbance observer to generate the d-axis control voltage u of the machine-side converter of the doubly-fed wind turbine dr , and the expression of the three-stage cascaded high-gain state disturbance observer is as follows: where ξ 11 , ξ 12 and ξ 13 are the state variables of the third-order cascaded high-gain state disturbance observer in the rotor speed output feedback control loop of the doubly-fed wind turbine, β 11 , β 12 and β 13 are the design parameters of the third-order cascaded high-gain state disturbance observer respectively, τ1 is a positive constant, ε1 is the high-gain parameter of the third-order cascaded high-gain state disturbance observer, y1 is the rotor speed deviation of the doubly-fed wind turbine, is the state variable estimated for ξ 12 .

5. A subsynchronous oscillation suppression system for a doubly-fed wind turbine according to claim 1 or 2, characterized in that, The output feedback control loop of the stator reactive output current of the doubly-fed wind turbine based on the second-order high-gain state disturbance observer generates the q-axis control voltage u of the machine-side converter of the doubly-fed wind turbine by using the estimated value of the second-order cascaded high-gain state disturbance observer qr , and the expression of the second-order cascaded high-gain state disturbance observer is as follows: where ξ 21 and ξ 22 are state variables of the second-order high-gain state disturbance observer in the output feedback control loop of the stator reactive power output current of the doubly-fed wind turbine, β 21 and β 22 are design parameters of the second-order high-gain state disturbance observer respectively, τ2 is a positive constant, ε2 is the high-gain parameter of the second-order high-gain state disturbance observer, and y2 is the deviation of the stator reactive power output current of the doubly-fed wind turbine.

6. A sub-synchronous oscillation suppression system for a doubly-fed wind turbine according to claim 1 or 2, characterized in that The DC-link capacitor voltage output feedback control loop of the back-to-back converter of the doubly-fed wind turbine based on the three-stage cascaded high-gain state disturbance observer uses the estimated value of the three-stage cascaded high-gain state disturbance observer to generate the d-axis control voltage u of the grid-side converter of the doubly-fed wind turbine dg , and the expression of the three-stage cascaded high-gain state disturbance observer is as follows: where ξ 31 , ξ 32 and ξ 33 are the state variables of the third-order cascaded high-gain state disturbance observer in the DC-link capacitor voltage output feedback control loop of the back-to-back converter of the doubly-fed wind turbine, β 31 , β 32 and β 33 are the design parameters of the third-order cascaded high-gain state disturbance observer respectively, τ3 is a positive constant, ε3 is the high-gain parameter of the third-order cascaded high-gain state disturbance observer, y3 is the DC-link capacitor voltage deviation of the back-to-back converter of the feed wind turbine, is the state variable estimated for ξ 32 .

7. A subsynchronous oscillation suppression system for a doubly-fed wind turbine according to claim 1 or 2, characterized in that, The output feedback control loop of the reactive output current of the grid-side converter of the doubly-fed wind turbine based on the second-order high-gain state disturbance observer uses the estimated value of the second-order cascaded high-gain state disturbance observer to generate the q-axis control voltage u of the grid-side converter of the doubly-fed wind turbine qg , and the expression of the second-order cascaded high-gain state disturbance observer is as follows: where ξ 41 and ξ 42 are the state variables of the second-order high-gain state disturbance observer in the output feedback control loop of the reactive power output current of the grid-side converter of the doubly-fed wind turbine, β 41 and β 42 are the design parameters of the second-order high-gain state disturbance observer respectively, τ4 is a positive constant, ε4 is the high-gain parameter of the second-order high-gain state disturbance observer, and y4 is the deviation of the reactive power output current of the stator of the doubly-fed wind turbine.

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