Dual-objective collaborative optimization method for inertia support and transient stability of doubly-fed wind turbine

Abstract

The application discloses a double-target cooperative optimization method for inertia support and transient stability of a doubly-fed fan, and the technical effect of accurately analyzing the dynamic evolution process of a virtual power angle under grid frequency drop is achieved by establishing a transient power angle model of the doubly-fed fan supported by inertia, overcoming the deep coupling effect between the dynamic behavior of a phase-locked loop under a small phase-locked loop bandwidth / damping ratio and the rotor internal potential response of the doubly-fed fan, and converting the dynamic evolution process into a point trajectory divided according to transient synchronous states. The transient stability boundary in the point trajectory is optimized and screened for a point trajectory with the maximum equivalent inertia, so that the inertia support capability of the doubly-fed fan can be optimized under the premise of transient synchronous stability, and the phase-locked loop parameters corresponding to the optimized point trajectory are used to realize the double-target cooperative optimization of the inertia support and the transient stability of the doubly-fed fan.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wind power grid connection technology, in particular to a double-target collaborative optimization method for inertia support and transient stability of a doubly-fed wind turbine. BACKGROUND

[0002] The doubly-fed wind turbine adopts a doubly-fed induction generator, which is directly connected to the power grid through the stator and connected to the power grid through the rotor via a converter, and is a device for realizing variable-speed constant-frequency power generation through the converter. When the doubly-fed wind turbine transmits power to the power grid or absorbs reactive power from the power grid through the converter, a phase-locked loop is needed to track the phase and frequency of the grid voltage in real time, and to provide a synchronous coordinate system for the control algorithm of the converter, such as vector control, to achieve consistency of voltage / current phase and frequency with the grid.

[0003] In the prior art, in order to maintain and improve the working stability of the doubly-fed wind turbine, inertia support and transient stability are often used as the benchmark. The inertia support requires the phase-locked loop to have high bandwidth and low damping ratio, but the transient stability requires the phase-locked loop to have low bandwidth and high damping ratio. Therefore, the compromise between the two targets is one of the necessary conditions for prompting the working stability of the doubly-fed wind turbine.

[0004] In the prior art, there is a power angle stability analysis method based on the equal area criterion for synchronous motors, which depends on the deterministic relationship between power angle and power and linearized dynamic characteristics. However, in the wind power grid connection system with a doubly-fed wind turbine, the influence of the phase-locked loop parameters on the transient stability boundary of the doubly-fed wind turbine is highly nonlinear, making it difficult for traditional methods to accurately depict the transient stability boundary, and making the parameter compatibility analysis in the double-target collaborative optimization process of inertia support and transient stability more complex.

[0005] The present application provides a double-target collaborative optimization method for inertia support and transient stability of a doubly-fed wind turbine to solve the above problems. SUMMARY

[0006] The present application aims to provide a double-target collaborative optimization method for inertia support and transient stability of a doubly-fed wind turbine to solve the problem that traditional methods are difficult to accurately depict the transient stability boundary, making the parameter compatibility analysis in the double-target collaborative optimization process of inertia support and transient stability complex.

[0007] The present application is achieved by the following technical solutions:

[0008] The double-target collaborative optimization method for inertia support and transient stability of a doubly-fed wind turbine comprises the following steps:

[0009] Step A1: The transient power angle of the doubly-fed wind turbine is obtained from the difference between the phase angle of the output of the phase-locked loop and the phase angle of the stator voltage in the three-phase stationary coordinate system, and the sum of the phase angle of the internal rotor potential in the dq synchronous rotating coordinate system of the phase-locked loop, and a transient power angle model supported by inertia is obtained after vector decomposition;

[0010] Step A2: In the grid voltage phase angle under different degrees of grid frequency disturbance, nested iteration is performed with the damping ratio as the outer loop and the bandwidth as the inner loop;

[0011] During the inner loop iteration process, the transient power angle model supported by inertia corresponding to the current grid voltage phase angle and under different phase-locked loop parameter groups: damping ratio and bandwidth is calculated, the power angle response curve is obtained, and the corresponding power angle change rate and its final value are calculated, the transient synchronous state is divided based on the final value of the power angle change rate, and the corresponding phase-locked loop parameter group is taken as a point trace, which is mapped to the phase-locked loop parameter plane to divide the transient stable region and the transient instability region;

[0012] Step A3: After the nested iteration is completed, the transient synchronous state corresponding to different phase-locked loop parameter groups is obtained according to different degrees of grid frequency disturbance, and the transient stability boundary is divided, the intersection of all transient stability boundaries is obtained in the phase-locked loop parameter plane to obtain the comprehensive transient stability boundary, and the equivalent inertia size corresponding to each point trace is calculated;

[0013] Step A4: In order to maximize the equivalent inertia, point trace optimization is performed on the comprehensive transient stability boundary, and the phase-locked loop parameters corresponding to the optimal point trace are obtained to realize the dual-objective collaborative optimization of inertia support and transient stability of the doubly-fed wind turbine.

[0014] Further, in step A1, the expression of the output phase angle θ pll of the phase-locked loop is:

[0015] ∫(V sq (K p,pll +K i,pll ∫dt)+ω g )dt=θ pll ;

[0016] In the formula, t represents time, V sq represents the q-axis component of the stator voltage V s of the doubly-fed wind turbine in the dq synchronous rotating coordinate system of the phase-locked loop, K p,pll represents the proportional parameter of the phase-locked loop, K i,pll represents the integral parameter of the phase-locked loop, and ω g represents the rated angular frequency.

[0017] Further, in step A1, the expression of the transient power angle δ of the doubly-fed wind turbine is as follows:

[0018] δ=θE,dq + θ err = θ E,dq + θ pll - θ s ;

[0019] wherein θ E,dq represents the phase angle of the rotor internal voltage E in the dq synchronous rotating coordinate system of the phase-locked loop, θ err represents the deviation angle of the phase-locked loop relative to the stator voltage V s , θ pll represents the output phase angle of the phase-locked loop, and θ s represents the phase angle of the stator voltage in the three-phase stationary coordinate system.

[0020] Further, in step A1, the expression of the transient power angle model supported by the inertia is obtained after vector decomposition as follows:

[0021]

[0022] wherein, is obtained after vector decomposition via the phase angle θ E,dq of the rotor internal voltage E in the dq synchronous rotating coordinate system of the phase-locked loop, wherein V sq represents the q-axis component of the stator voltage V s in the dq synchronous rotating coordinate system of the phase-locked loop, V sd represents the d-axis component of the stator voltage V s in the dq synchronous rotating coordinate system of the phase-locked loop, X s represents the stator reactance, I sd represents the d-axis component of the stator current in the dq synchronous rotating coordinate system of the phase-locked loop, and I sq represents the q-axis component of the stator current in the dq synchronous rotating coordinate system of the phase-locked loop.

[0023] wherein θ pll represents the output phase angle of the phase-locked loop.

[0024] wherein, is obtained after vector decomposition via the phase angle θ s of the stator voltage V s in the three-phase stationary coordinate system, wherein θ g represents the grid voltage phase angle, X g represents the grid reactance, and P s,ref represents the active power reference value.

[0025] Further, in the process of vector decomposition of the phase angle θ E,dq of the rotor internal voltage E in the dq synchronous rotating coordinate system of the phase-locked loop, the rotor internal voltage E is vector decomposed to obtain the following formula:

[0026] E = V s -jX s I s = jX m I r

[0027] In the formula, I s represents the stator current vector, I r represents the rotor current vector, X s represents the stator reactance of the doubly-fed wind turbine, X m represents the excitation reactance of the doubly-fed wind turbine, and j represents the imaginary unit.

[0028] Further, the rotor internal potential E is further decomposed into a d-axis component E d and a q-axis component E q in the dq synchronous rotating coordinate system of the phase-locked loop, to obtain the following formula:

[0029]

[0030] In the formula, V gm represents the grid voltage amplitude, θ g represents the grid voltage phase angle, and is used to represent the grid frequency disturbance amount.

[0031] In the formula, R g represents the grid resistance, X g represents the grid reactance, X s represents the stator reactance, I sd represents the d-axis component of the stator current in the dq synchronous rotating coordinate system of the phase-locked loop, I sq represents the q-axis component of the stator current in the dq synchronous rotating coordinate system of the phase-locked loop.

[0032] Further, in step A2, the value range of the grid voltage phase angle θ g under different degrees of grid frequency disturbance is: θ g ∈(0, 360°).

[0033] Further, in step A2, the specific nested iteration process includes the following steps:

[0034] Step B1: determining the scanning range of the bandwidth, determining the step size of the bandwidth, determining the scanning range of the damping ratio, and determining the step size of the damping ratio;

[0035] Step B2: determining the outer loop initial value of the damping ratio as the minimum value of the scanning range;

[0036] Step B3: determining the inner loop initial value of the bandwidth as the minimum value of the scanning range;

[0037] Step B4: calculating the steady-state working point of all electrical quantities and taking it as the initial value;​

[0038] Step B5: calculating the inertia-supported transient power angle model corresponding to the current grid voltage phase angle under different phase-locked loop parameter groups based on the obtained initial value;

[0039] Step B6: depicting the power angle response curve and obtaining the power angle change rate and the power angle change rate final value;

[0040] Step B7: establishing a transient stability criterion formula based on the power angle change rate final value to divide the transient synchronization state;

[0041] Step B8: realizing the inner loop bandwidth increment based on the determined step length;

[0042] Step B9: checking whether the bandwidth is greater than the maximum value of the scanning range, if yes, entering Step B9, otherwise, entering Step B4;

[0043] Step B10: realizing the outer loop damping ratio increment based on the determined step length;

[0044] Step B11: checking whether the damping ratio is greater than the maximum value of the scanning range, if yes, ending the iteration, otherwise, entering Step B3.

[0045] Further, in Step B6, the power angle change rate final value is expressed as: Wherein, δ represents the inertia-supported transient power angle model, and t represents time.

[0046] Further, in Step B7, the established transient stability criterion formula is as follows:

[0047]

[0048] When the limit of the obtained power angle change rate final value approaches 0, the phase-locked loop parameter group corresponding to the power angle change rate final value is mapped to the phase-locked loop parameter plane as a point trace, and the region is divided into a transient stable region;

[0049] When the limit of the obtained power angle change rate final value cannot approach 0, the phase-locked loop parameter group corresponding to the power angle change rate final value is mapped to the phase-locked loop parameter plane as a point trace, and the region is divided into a transient unstable region.

[0050] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0051] The application overcomes the deep coupling effect between the dynamic behavior of the phase-locked loop under a small phase-locked loop bandwidth / damping ratio and the response of the rotor internal potential of the doubly-fed wind turbine by establishing a transient power angle model of the doubly-fed wind turbine supported by inertia, achieves the technical effect of accurately analyzing the dynamic evolution process of the virtual power angle under the grid frequency drop, and converts the dynamic evolution process into a point diagram divided according to the transient synchronous state, optimizes and screens the point trace with the maximum equivalent inertia in the transient stability boundary of the point diagram, ensures that the inertia support capability of the doubly-fed wind turbine can be optimized under the premise of transient synchronous stability, and realizes the collaborative optimization of the doubly-fed wind turbine inertia support and transient stability by the phase-locked loop parameters corresponding to the optimal point trace, solves the problem that the traditional method is difficult to accurately depict the transient stability boundary, and solves the problem of complex parameter compatibility analysis in the process of collaborative optimization of the double targets of inertia support and transient stability. BRIEF DESCRIPTION OF DRAWINGS

[0052] In order to more clearly illustrate the technical scheme of the exemplary embodiments of the present application, the drawings needed in the embodiments will be briefly introduced as follows, and it should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope, and other related drawings can also be obtained by those skilled in the art without creative labor. In the drawings:

[0053] Figure 1 The flow chart of the double-target collaborative optimization method for the inertia support and transient stability of the doubly-fed wind turbine proposed in the embodiments of the present application;

[0054] Figure 2 The steady-state electrical vector diagram and the transient electrical vector diagram of the doubly-fed wind power grid-connected system proposed in the embodiments of the present application, wherein figure (a) is the steady-state electrical vector diagram of the doubly-fed wind power grid-connected system, and figure (b) is the transient electrical vector diagram of the doubly-fed wind power grid-connected system;

[0055] Figure 3 The equivalent circuit diagram of the doubly-fed wind power grid-connected system proposed in the embodiments of the present application;

[0056] Figure 4 The flow chart of the nested iteration process of the double-target collaborative optimization method for the inertia support and transient stability of the doubly-fed wind turbine proposed in the embodiments of the present application;

[0057] Figure 5 The three-dimensional schematic diagram of the equivalent inertia corresponding to each point trace proposed in the embodiments of the present application;

[0058] Figure 6 The projection diagram of each point trace in the phase-locked loop parameter plane proposed in the embodiments of the present application;

[0059] Figure 7The active power diagram of the double-fed wind turbine under the bandwidth of 5Hz and the damping ratio of 0.707 proposed by the embodiment of the application;

[0060] Figure 8 The power angle response curve diagram of the double-fed wind turbine under the bandwidth of 0.1Hz and the damping ratio of 0.707 proposed by the embodiment of the application;

[0061] Figure 9 The active power diagram of the double-fed wind turbine under the bandwidth of 0.1Hz and the damping ratio of 0.707 proposed by the embodiment of the application;

[0062] Figure 10 The power angle response curve diagram of the double-fed wind turbine under the bandwidth of 0.1Hz and the damping ratio of 0.707 proposed by the embodiment of the application;

[0063] Figure 11 The active power diagram of the double-fed wind turbine under the bandwidth of 0.5Hz and the damping ratio of 0.707 proposed by the embodiment of the application;

[0064] Figure 12 The power angle response curve diagram of the double-fed wind turbine under the bandwidth of 0.5Hz and the damping ratio of 0.707 proposed by the embodiment of the application. DETAILED DESCRIPTION

[0065] In order to make the purpose, technical scheme and advantages of the application clearer and more apparent, the application will be further described in detail below with reference to the embodiments and drawings, and the illustrative embodiments of the application and the description thereof are only used to explain the application, and do not limit the application.

[0066] The double-target collaborative optimization method for the inertia support and transient stability of the double-fed wind turbine, as shown in the embodiment of the application, Figure 1 includes the following steps:

[0067] Step A1: taking the difference between the output phase angle of the phase-locked loop and the phase angle of the stator voltage in the three-phase stationary coordinate system, and the sum of the phase angles of the rotor internal potential in the dq synchronous rotating coordinate system of the phase-locked loop as the transient power angle of the double-fed wind turbine, and obtaining the transient power angle model supported by the inertia after vector decomposition.

[0068] In the embodiment, Figure 2 The steady-state electrical vector diagram and the transient electrical vector diagram of the double-fed wind power grid-connected system composed of the double-fed wind turbine and the power grid connected thereto are shown, as shown in Fig. (a) in Figure 2 When in the steady state, the power angle of the double-fed wind turbine can be represented by the included angle between the rotor internal potential E and the stator voltage V s of the double-fed wind turbine, and can also be directly represented by the phase angle θ E,dq of the rotor internal potential E in the dq synchronous rotating coordinate system of the phase-locked loop, and at this time, the stator voltage V sPhase angle θ in a three-phase stationary coordinate system s The phase angle θ of the phase-locked loop output pll The angles are equal;

[0069] When in a transient state, that is, when there are varying degrees of grid frequency disturbances, the stator voltage V s The phase lags behind the phase of the phase-locked loop output phase angle, which is relative to the stator voltage V. s There is a deviation angle θ err Therefore, the power angle at this time is determined by the rotor internal electromotive force E at the d-axis of the phase-locked loop. q Phase angle θ in synchronous rotating coordinate system E,dq relative to the stator voltage V of the phase-locked loop s deviation angle θ err The sum of and represents the phase-locked loop relative to the stator voltage V. s deviation angle θ err The output phase angle θ of the phase-locked loop can be determined. pll The phase angle θ of the stator voltage in the three-phase stationary coordinate system s The difference is represented by the value of θ. Therefore, in the transient state, the transient power angle of the doubly-fed wind turbine is determined by the output phase angle θ of the phase-locked loop. pll The phase angle θ of the stator voltage in the three-phase stationary coordinate system s The difference between the two values, and the phase angle θ of the rotor internal potential in the dq synchronous rotating coordinate system of the phase-locked loop. E,dq The sum is represented by the vector decomposition, and a transient power angle model supported by inertia is obtained.

[0070] Specifically, the expression for the transient power angle δ of the doubly-fed wind turbine during the transient state is as follows:

[0071] δ=θ E,dq +θ err ;

[0072] In the formula, θ E,dq θ represents the phase angle of the rotor internal electromotive force E in the dq synchronous rotating coordinate system of the phase-locked loop. err This indicates the phase-locked loop relative to the stator voltage V. s The deviation angle.

[0073] In this embodiment, the output phase angle θ of the phase-locked loop pll The expression is:

[0074] ∫(V sq (K p,pll +K i,pll ∫dt)+ω g )dt=θ pll ;

[0075] In the formula, t represents time, and V sq V represents the stator voltage of the doubly fed wind turbine.s The q-axis component, K, in the dq synchronous rotating coordinate system of the phase-locked loop. p,pll K represents the proportional parameter of the phase-locked loop. i,pll ω represents the integral parameter of the phase-locked loop. g Indicates the rated angular frequency.

[0076] like Figure 2 As shown in Figure (b), during the transient state, when the phase-locked loop is relative to the stator voltage V... s deviation angle θ err Replace the output phase angle θ of the phase-locked loop pll The phase angle θ of the stator voltage in the three-phase stationary coordinate system s After expressing the difference, the expression for the transient power angle δ of the doubly-fed wind turbine is as follows:

[0077] δ=θ E,dq +θ err =θ E,dq +θ pll -θ s .

[0078] Furthermore, in this embodiment, the rotor internal potential E of the doubly-fed wind turbine also represents the internal excitation voltage vector of the doubly-fed wind turbine; therefore, the rotor internal potential E is vector-decomposed. According to the appendix... Figure 3 As shown, Figure 3 The equivalent circuit diagram of the doubly fed wind power grid-connected system proposed in this invention is shown. Since the current loop has a faster response speed than other control links, the dynamic change process of the current and the stator resistance are ignored when calculating the rotor internal potential E of the doubly fed wind turbine.

[0079] Therefore, after vector decomposition, the rotor internal electromotive force E is expressed as follows:

[0080] E = V s -jX s I s =jX m I r ;

[0081] In the formula, I s I represents the stator current vector. r X represents the rotor current vector. s X represents the stator reactance of a doubly-fed wind turbine. m This represents the excitation reactance of the doubly-fed wind turbine, where j is the imaginary unit.

[0082] Furthermore, the rotor internal electromotive force E of the doubly-fed wind turbine is expressed in the dq synchronous rotating coordinate system of the phase-locked loop as the d-axis component E. d , q Axial component E q Further decomposition yields the following formula:

[0083]

[0084] where V g represents grid voltage, V gm represents grid voltage amplitude, θ g represents grid voltage phase angle, used to characterize grid frequency disturbance amount;

[0085] where R g represents grid resistance, X g represents grid reactance, X s represents stator reactance, I sd represents d-axis component of stator current in dq synchronous rotating coordinate system of phase-locked loop, I sq represents q-axis component of stator current in dq synchronous rotating coordinate system of phase-locked loop.

[0086] Based on the above rotor internal voltage E after vector decomposition, the phase angle θ E,dq of rotor internal voltage E in dq synchronous rotating coordinate system of phase-locked loop is obtained as follows:

[0087]

[0088] where V sq represents stator voltage V s in dq synchronous rotating coordinate system of phase-locked loop, V sd represents stator voltage V s in dq synchronous rotating coordinate system of phase-locked loop.

[0089] According to the same steps above, the stator voltage V s in three-phase stationary coordinate system, θ s is obtained as follows:

[0090]

[0091] where θ g represents grid voltage phase angle, P s,ref represents active power reference value.

[0092] In summary, after vector decomposition, the expression of transient power angle supported by inertia is as follows:

[0093]

[0094] Step A2: in the grid voltage phase angle under different degrees of grid frequency disturbance, nested iteration is performed with damping ratio as outer loop and bandwidth as inner loop;

[0095] With the steady state working point of all electrical quantities as the initial value, the different phase-locked loop parameter groups: damping ratio and bandwidth, under the transient power angle model corresponding to the current grid voltage phase angle and supported by inertia, are obtained in the inner loop iteration process, the power angle response curve is obtained and the corresponding power angle change rate and its final value are calculated, the transient synchronous state is divided based on the final value of the power angle change rate, and the corresponding phase-locked loop parameter group is taken as a point trace, which is mapped to the phase-locked loop parameter plane to divide the transient stability region and the transient instability region.

[0096] In the embodiment, the value range of the grid voltage phase angle θ g under different degrees of grid frequency disturbance is: θ g ∈(0, 360°).

[0097] In the embodiment, the specific nested iteration process is as shown in Figure 4 , including the following steps:

[0098] Step B1: the scanning range of the bandwidth f BW is: f BW ∈[f min , f max ], the step size of the bandwidth f BW is Δf BW , the scanning range of the damping ratio ξ is: ξ∈[ξ min , ξ max ], and the step size of the damping ratio is Δξ.

[0099] Step B2: the outer loop initial value of the damping ratio ξ is: ξ=ξ min .

[0100] Step B3: the inner loop initial value of the bandwidth f BW is: f BW =f min .

[0101] Step B4: the steady state working point of all electrical quantities is calculated in combination with the current grid parameters, the doubly-fed wind turbine parameters and the controller parameters, and the steady state working point of all electrical quantities is taken as the initial value; in the embodiment, the steady state working point of the following electrical quantities is calculated, including but not limited to: the transient numerical solution of the stator active / reactive power, the stator voltage / current dq components, the rotor current dq components and the phase-locked loop output phase angle of the doubly-fed wind turbine and other state variables.

[0102] Step B5: the transient power angle model corresponding to the current grid voltage phase angle under different phase-locked loop parameter groups is calculated based on the obtained initial value.

[0103] Step B6: the power angle response curve is depicted, and the power angle change rate and the final value of the power angle change rate are calculated, and the final value of the power angle change rate is expressed as: wherein t represents time.

[0104] Step B7: Establishing transient stability criterion formula based on power angle change rate final value to divide transient synchronization state;

[0105] Specifically, the established transient stability criterion formula is as follows:

[0106]

[0107] When the limit of the obtained power angle change rate final value approaches 0, the phase-locked loop parameter group corresponding to the power angle change rate final value is mapped to the phase-locked loop parameter plane as a point trace, and the region is divided into a transient stability region;

[0108] When the limit of the obtained power angle change rate final value cannot approach 0, the phase-locked loop parameter group corresponding to the power angle change rate final value is mapped to the phase-locked loop parameter plane as a point trace, and the region is divided into a transient instability region.

[0109] In this embodiment, according to the power angle response curve of the doubly-fed wind turbine under grid frequency disturbance, if the doubly-fed wind turbine changes the power angle through the regulation of the phase-locked loop parameter group to respond to inertia and finally transits to the next stable working point, it indicates that the doubly-fed wind turbine controlled by the phase-locked loop parameter group can realize transient synchronization stability.

[0110] Step B8: Increment f BW of inner loop bandwidth by Δf BW BW ;

[0111] Step B9: Check whether f BW of bandwidth is greater than the maximum value f max of bandwidth, if yes, go to step B9, otherwise, go to step B4;

[0112] Step B10: Increment ξ = ξ + Δξ of outer loop damping ratio by Δξ;

[0113] Step B11: Check whether ξ of damping ratio is greater than the maximum value ξ max of damping ratio, if yes, end iteration, otherwise, go to step B3.

[0114] Step A3: After ending the nested iteration, divide according to different degrees of grid frequency disturbance to obtain transient synchronization states corresponding to different phase-locked loop parameter groups, and divide out transient stability boundaries, and obtain comprehensive transient stability boundaries by finding the intersection of all transient stability boundaries in the phase-locked loop parameter plane, and calculate the equivalent inertia size corresponding to each point trace.

[0115] ​Step A4: Point trajectory optimization is performed on the integrated transient stability boundary to maximize equivalent inertia, and the phase-locked loop parameters corresponding to the optimal point trajectory are obtained to realize the dual-target collaborative optimization of inertia support and transient stability for the doubly-fed wind turbine.

[0116] Specifically, the following is a specific example of the dual-target collaborative optimization method for inertia support and transient stability of the doubly-fed wind turbine proposed in this embodiment applied to the grid scenario of SCR=4, based on steps A1 to A4, as shown in Figure 5 The damping ratio ξ ∈ [0, 1], the bandwidth f BW The equivalent inertia of each point trajectory under the condition of damping ratio ξ ∈ [0, 1] and bandwidth f Figure 6 The equivalent inertia of each point trajectory under the condition of damping ratio ξ ∈ [0, 1] and bandwidth f

[0117] The grid frequency drops to 49Hz for 5s, and the damping ratio is kept at 0.707. The active power and power angle response curves of the doubly-fed wind turbine when the phase-locked loop bandwidth is 5Hz are shown in Figure 7 and Figure 8 Under the control of the conventional bandwidth phase-locked loop, the phase-locked loop tracks the voltage phase angle quickly, and the doubly-fed wind turbine cannot provide a large enough phase-locked deviation angle and internal potential phase angle to increase the inertia. Figure 7 and Figure 8 The doubly-fed wind turbine cannot increase active power to provide inertia support during the frequency disturbance, and the power angle quickly returns to the stable state. To enable the doubly-fed wind turbine to have inertia support capability when the frequency disturbance occurs, the phase-locked loop bandwidth is slowed down to 0.1Hz, and the active power and power angle response curves are shown in Figure 9 and Figure 10 As can be seen from the above, under the control of the low-bandwidth phase-locked loop, the doubly-fed wind turbine can significantly increase active power to provide inertia support for the system at the initial stage of the disturbance, but due to the low phase-locked bandwidth and slow speed, the phase-locked loop will not be able to synchronize with the AC grid after the doubly-fed wind turbine temporarily increases active power, and thereafter the power angle and active power will oscillate, and the doubly-fed wind turbine grid-connected system will lose transient synchronization stability.

[0118] According to Figure 6 It can be known that the intersection point of the maximum inertia contour line and the transient stability boundary line has a phase-locked loop bandwidth of about 0.42Hz and a damping ratio of about 0.65. To leave a certain transient stability margin, the phase-locked loop bandwidth is selected as 0.5Hz, and to ensure the balance between the response speed, overshoot and robustness of the transient power angle, the damping ratio is selected as the typical value 0.707 in engineering. The simulation results are shown in Figure 11 andFigure 12 As shown, the doubly-fed wind turbine has good inertia response ability at the bandwidth of 0.5 Hz, the active power can be increased by 10%, and the power angle can still return to the steady state after providing inertia support, thereby ensuring the transient stability performance of the system.

[0119] The present application overcomes the deep coupling effect between the dynamic behavior of the phase-locked loop under a small phase-locked loop bandwidth / damping ratio and the response of the rotor internal potential of the doubly-fed wind turbine by establishing a transient power angle model of the doubly-fed wind turbine supported by inertia, achieves the technical effect of accurately analyzing the dynamic evolution process of the virtual power angle under the grid frequency drop, and converts the dynamic evolution process into a point diagram divided according to the transient synchronous state, optimizes and screens the point trace with the maximum equivalent inertia in the transient stability boundary of the point diagram, ensures that the inertia support capability of the doubly-fed wind turbine can be optimal under the premise of transient synchronous stability, and realizes the collaborative optimization of the doubly-fed wind turbine inertia support and transient stability by using the phase-locked loop parameters corresponding to the optimal point trace.

[0120] The above specific embodiments further specifically describe the purposes, technical solutions and beneficial effects of the present application, and it should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application, and any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A dual-objective collaborative optimization method for inertia support and transient stability of a doubly-fed wind turbine, characterized in that, Comprising the following steps: Step A1: Taking the difference between the output phase angle of the phase-locked loop and the phase angle of the stator voltage in the three-phase stationary coordinate system, and the sum of the phase angle of the rotor internal potential in the dq synchronous rotating coordinate system of the phase-locked loop as the transient power angle of the doubly-fed wind turbine, and obtaining the transient power angle model supported by inertia after vector decomposition; Step A2: In the grid voltage phase angle under different degrees of grid frequency disturbance, nested iteration is carried out with damping ratio as outer loop and bandwidth as inner loop; In the process of inner loop iteration, the transient power angle model supported by inertia corresponding to the current grid voltage phase angle under different phase-locked loop parameter groups: damping ratio and bandwidth is calculated, the power angle response curve is obtained, and the corresponding power angle change rate and its final value are calculated, the transient synchronous state is divided based on the final value of the power angle change rate, and the corresponding phase-locked loop parameter group is taken as a point trace, which is mapped to the phase-locked loop parameter plane to divide the transient stable region and the transient instability region; Step A3: After the nested iteration is completed, the transient synchronous state corresponding to different phase-locked loop parameter groups is obtained according to different degrees of grid frequency disturbance, and the transient stability boundary is divided, the intersection of all transient stability boundaries is obtained in the phase-locked loop parameter plane to obtain the comprehensive transient stability boundary, and the equivalent inertia size corresponding to each point trace is calculated; Step A4: Taking the maximization of equivalent inertia as the goal, point trace optimization is carried out on the comprehensive transient stability boundary to obtain the phase-locked loop parameters corresponding to the optimal point trace to realize the double-objective collaborative optimization of inertia support and transient stability of the doubly-fed wind turbine; In step A1, the expression of the transient power angle model supported by inertia after vector decomposition is as follows: wherein via the phase angle Θ of the rotor internal voltage E in the dq synchronous rotating coordinate system of the phase locked loop E,dq after vector resolution, wherein V sq denotes the stator voltage V s in the q-axis component in the dq synchronous rotating coordinate system of the phase locked loop, V sd denotes the stator voltage V s in the d-axis component in the dq synchronous rotating coordinate system of the phase locked loop, X s denotes the stator reactance, I sd denotes the d-axis component of the stator current in the dq synchronous rotating coordinate system of the phase locked loop, I sq denotes the q-axis component of the stator current in the dq synchronous rotating coordinate system of the phase locked loop; In the formula, θ pll represents the output phase angle of the phase-locked loop; In the formula, The stator voltage V s The phase angle θ s After vector decomposition, wherein θ g The grid voltage phase angle is represented by X g The grid reactance is represented by P s,ref The active power reference value is represented by The phase angle Θ of the rotor internal voltage E in the dq synchronous rotating coordinate system of the phase-locked loop E,dq In the process of vector resolution, including vector resolution of the rotor internal voltage E, the following formula is obtained: E = V s -jX s I s = jX m I r ; where I s represents the stator current vector, I r represents the rotor current vector, X s represents the stator reactance of the doubly-fed wind turbine, X m represents the excitation reactance of the doubly-fed wind turbine, j represents the imaginary unit; Also included is the rotor internal potential E in the dq synchronous rotating coordinate system of the phase-locked loop, divided by the d-axis component E d、q axis component E q Further decomposition yields the following: wherein V gm denotes the grid voltage amplitude, θ g denotes the grid voltage phase angle, used to characterize the grid frequency disturbance amount; where R g represents the grid resistance, X g represents the grid reactance, X s represents the stator reactance, I sd represents the d-axis component of the stator current in the dq synchronous rotating coordinate system of the phase-locked loop, I sq represents the q-axis component of the stator current in the dq synchronous rotating coordinate system of the phase-locked loop.

2. The dual-objective collaborative optimization method for doubly-fed wind turbine inertia support and transient stability according to claim 1, characterized in that, In step Al, the output phase angle θ of the phase-locked loop pll is expressed by the equation: ∫(V sq (K p,pll +K i,pll ∫dt)+ω g )dt=θ pll ; where t represents time, V sq represents the stator voltage of the doubly-fed wind turbine s represents the q-axis component of the phase-locked loop in the dq synchronous rotating coordinate system, K p,pll represents the proportional parameter of the phase-locked loop, K i,pll represents the integral parameter of the phase-locked loop, ω g represents the rated angular frequency.

3. The dual-objective collaborative optimization method for doubly-fed wind turbine inertia support and transient stability according to claim 1, characterized in that, In step A1, the expression of the transient power angle δ of the doubly-fed wind turbine is as follows: δ = θ E,dq + θ err = θ E,dq + θ pll - θ s ; where θ E,dq represents the phase angle of the rotor internal voltage E in the dq synchronous rotating coordinate system of the phase-locked loop, θ err represents the deviation angle of the phase-locked loop relative to the stator voltage V s , θ pll represents the output phase angle of the phase-locked loop, θ s represents the phase angle of the stator voltage in the three-phase stationary coordinate system.

4. The dual-objective collaborative optimization method for doubly-fed wind turbine inertia support and transient stability according to claim 1, characterized in that, In step A2, the grid voltage phase angle θ under different degrees of grid frequency disturbances g The range of values ​​for θ is: g ∈(0,360°).

5. The dual-objective collaborative optimization method for doubly-fed wind turbine inertia support and transient stability according to claim 1, characterized in that, In step A2, the specific nested iteration process comprises the following steps: Step B1: Determine the scanning range of the bandwidth, determine the step size of the bandwidth, determine the scanning range of the damping ratio, and determine the step size of the damping ratio; Step B2: Determine the outer loop initial value of the damping ratio as the minimum value of the scanning range; Step B3: Determine the inner loop initial value of the bandwidth as the minimum value of the scanning range; Step B4: Calculate the steady-state working point of all electrical quantities, and take it as the initial value; Step B5: Calculate the transient power angle model supported by inertia corresponding to the current grid voltage phase angle under different phase-locked loop parameter groups based on the obtained initial value; Step B6: Draw the power angle response curve, and calculate the power angle change rate and the final value of the power angle change rate; Step B7: Based on the final value of the power angle change rate, establish a transient stability criterion formula to divide the transient synchronous state; Step B8: Based on the determined step size, increase the inner loop bandwidth; Step B9: Check whether the bandwidth is greater than the maximum value of the scanning range, if yes, go to step B9, otherwise, go to step B4; Step B10: Based on the determined step size, increase the outer loop damping ratio; Step B11: Check whether the damping ratio is greater than the maximum value of the scanning range, if yes, end the iteration, otherwise, go to step B3.

6. The dual-objective collaborative optimization method for doubly-fed wind turbine inertia support and transient stability according to claim 5, characterized in that, In step B6, the power angle rate of change final value is expressed as: where δ represents the transient power angle model supported by inertia, and t represents time.

7. The dual-objective collaborative optimization method for doubly-fed wind turbine inertia support and transient stability according to claim 6, characterized in that, In step B7, the established transient stability criterion formula is as follows: When the limit of the obtained terminal value of the power angle change rate approaches 0, the phase-locked loop parameter group corresponding to the terminal value of the power angle change rate is mapped to the phase-locked loop parameter plane as a point trace, and the region is divided into a transient stability region; When the limit of the obtained terminal value of the power angle change rate cannot approach 0, the phase-locked loop parameter group corresponding to the terminal value of the power angle change rate is mapped to the phase-locked loop parameter plane as a point trace, and the region is divided into a transient instability region.

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