A safety risk analysis method for equipment speed fluctuation characteristics during low voltage ride-through

Abstract

The present invention discloses a safety risk analysis method for the speed fluctuation characteristics of equipment during low voltage ride-through, which relates to the technical field of wind turbine stability analysis, and includes the following steps: S1, constructing a mathematical model of the wind turbine; S2, constructing a state space equation using the mathematical model of the wind turbine; S3, establishing a characteristic root distribution diagram of the state space equation, and performing a safety risk analysis on the low-frequency fluctuation and high-frequency fluctuation of the state variables of the wind turbine during low voltage ride-through according to the imaginary value and the real value of the characteristic root in the distribution diagram. The present invention can effectively analyze the influence of the pitch angle controller parameters and the transmission chain parameters on the speed fluctuation characteristics during fault ride-through, and provide strong data support for reducing the fluctuation of the rotor speed, suppressing the fluctuation range of the speed and improving the speed recovery speed.

Description

Technical Field

[0001] The present invention relates to the technical field of wind turbine stability analysis, and more specifically to a safety risk analysis method for equipment speed fluctuation characteristics during a low voltage ride-through period. Background Art

[0002] In order to maintain the safety and stability of the power system, wind turbines need to have the ability to ride through faults. However, the active power of wind turbines will change significantly during fault ride-through, causing large fluctuations in the rotor speed and long-term oscillations.

[0003] The low voltage ride-through capability of wind turbines is an important evaluation indicator for evaluating the safe and stable operation of power systems with high wind power penetration. During low voltage ride-through, wind turbines need to maintain operation and provide reactive power support to the power grid until the fault is cleared. However, when maintaining operation, wind turbines need to reduce mechanical load stress by delaying the active power recovery time. Therefore, during low voltage ride-through, the energy accumulated in the rotor due to the inability to be transmitted to the power grid will cause speed fluctuations, affecting the safe and stable operation of wind turbines. The existing wind turbine pitch angle control strategy has a poor transient control effect on this fluctuation. The sharp fluctuations in the pitch angle position caused by speed fluctuations will affect the mechanical load. With the long-term accumulation of load and fatigue damage, it may even cause malicious events such as tower collapse, seriously affecting the safe operation of wind farms.

[0004] Therefore, it is urgent to propose a safety risk analysis method for the speed fluctuation characteristics of equipment during the low voltage ride-through period to provide strong data support for reducing the fluctuation of the rotor speed, suppressing the fluctuation range of the speed and improving the speed recovery speed. Summary of the invention

[0005] In order to overcome the defects existing in the above-mentioned prior art, the present invention discloses a safety risk analysis method for the speed fluctuation characteristics of equipment during low voltage ride-through. The present invention constructs a characteristic root distribution diagram of the state space equation for analyzing the rotor speed fluctuation characteristics during low voltage ride-through of wind turbines according to factors such as the rotor speed movement process, transmission chain torque, pitch angle control, and fault ride-through control. The fluctuation characteristics of the rotor speed are theoretically analyzed, and the influence of the pitch angle controller parameters and the transmission chain parameters on the speed fluctuation characteristics during fault ride-through can be effectively analyzed, so as to provide strong data support for reducing the fluctuation of the rotor speed, suppressing the fluctuation range of the speed and improving the speed recovery speed.

[0006] In order to achieve the above objectives, the technical solution adopted by the present invention is:

[0007] A safety risk analysis method for the speed fluctuation characteristics of equipment during low voltage ride-through period includes the following steps:

[0008] 1. Construction of mathematical model of wind turbine

[0009] S1. Constructing a mathematical model of a wind turbine generator set, wherein the mathematical model of the wind turbine generator set includes an aerodynamic model, a pitch angle control model, a fault ride-through control model and a transmission chain model;

[0010] In the present invention, the aerodynamic model is used to describe the wind energy capture dynamics of the wind turbine; the pitch angle control model is used to maintain the stable speed of the wind turbine; the fault ride-through control model is used for the wind turbine to achieve low voltage ride-through; and the transmission chain model is used to describe the speed change of the wind turbine.

[0011] (1) Aerodynamic model

[0012] Preferably, in step S1, the aerodynamic model includes the mechanical power captured by the wind wheel , the mechanical power captured by the wind wheel for:

[0013] ;

[0014] In the formula, is the circumference of a circle, is the air density, is the radius of the wind rotor blade, is the wind speed, is the wind energy utilization coefficient, is the tip speed ratio, is the blade pitch angle;

[0015] Among them, the tip speed ratio for:

[0016] ;

[0017] In the formula, is the radius of the wind rotor blade, is the wind speed, is the angular velocity of the wind wheel;

[0018] Among them, the wind energy utilization coefficient The efficiency of converting wind kinetic energy into mechanical energy is expressed as:

[0019] ;

[0020] In the formula, is the intermediate variable, is the tip speed ratio, is the blade pitch angle.

[0021] (2) Pitch angle control model

[0022] Preferably, in step S1, the pitch angle control model is:

[0023] ;

[0024] In the formula, is the generator speed, is the rated speed, is the blade pitch angle, is the pitch angle command reference value, and are the proportional and integral coefficients of the pitch angle controller, is the time constant of the pitch mechanism, Represents the total differential symbol.

[0025] (3) Fault ride-through control model

[0026] Preferably, in step S1, the fault ride-through control model is modeled using an active output model, wherein the active power recovery rate of the active output model is determined by actual control parameters of the wind turbine generator set fault ride-through.

[0027] In the present invention, according to the requirements of GB / T 36995-2018 "Test Procedure for Fault Voltage Ride-Through Capability of Wind Turbine Generator Sets", when the voltage at the grid-connected point of the wind turbine set is between 1.3pu and 0.2pu, the wind turbine set is required to operate continuously without disconnecting from the grid. Taking low voltage fault ride-through control as an example, when a low voltage fault occurs at the grid-connected point of the wind turbine set, due to the reactive power priority control principle of the wind turbine set, the electromagnetic power output of the wind turbine set will drop sharply; after the fault is cleared, its active power will be restored to the output level before the fault at a certain fixed slope; it is modeled with an active output model, wherein the active power recovery rate is determined by the actual control parameters of the wind turbine set fault ride-through.

[0028] (4) Transmission chain model

[0029] Preferably, in step S1, the transmission chain model includes a two-mass block model including a transmission shaft, and the transmission chain dynamics equation of the transmission chain model is:

[0030] ;

[0031] In the formula, the top variable represents the differential of the dependent variable, and are the inertia constants of the wind wheel and the generator, is the angular velocity of the transmission chain, is the wind rotor rotation angular velocity, is the generator speed, , , are the torques of the wind wheel, generator and transmission chain respectively, is the equivalent damping constant of the transmission chain, is the equivalent stiffness of the transmission chain, is the angular displacement of the transmission chain, is the gearbox transmission ratio.

[0032] 2. State Space Equation Construction

[0033] S2, constructing state space equations using mathematical models of wind turbines;

[0034] Preferably, step S2 comprises the following steps:

[0035] S21, setting the wind rotor rotation angular velocity and generator speed in differential form of relevant variables in the transmission chain model to incremental form;

[0036] Preferably, step S21 includes:

[0037] ;

[0038] In the formula, Indicates the increment of the related variable, the top of the variable represents the differential of the dependent variable, is the wind rotor rotation angular velocity, is the generator speed; and are the inertia constants of the wind wheel and the generator, , , are the torques of the wind wheel, generator and transmission chain respectively, is the gearbox transmission ratio.

[0039] S22, combining the mechanical power captured by the wind wheel in the aerodynamic model, obtaining the torque of the wind wheel, and setting the torque of the wind wheel to an incremental form;

[0040] Preferably, in step S22, the torque of the wind wheel for:

[0041] ;

[0042] In the formula, is the circumference of a circle, is the air density, is the radius of the wind rotor blade, is the wind speed, is the wind energy utilization coefficient, is the angular velocity of the wind wheel;

[0043] The torque of the wind wheel in incremental form is:

[0044] ;

[0045] In the formula, represents the increment of the relevant variable, represents the partial differential symbol, is the wind rotor rotation angular velocity, is the torque of the wind wheel, is the blade pitch angle;

[0046] Among them, according to the torque of the wind wheel , derive the torque of the wind wheel The derivatives of the rotation speed and pitch angle are:

[0047] ;

[0048] In the formula, the subscript represents the initial value of the relevant variable, is the wind energy utilization coefficient, is the wind rotor rotation angular velocity, is the torque of the wind wheel, is the blade pitch angle, is the gearbox transmission ratio, is the mechanical power coefficient, expressed as:

[0049] ;

[0050] in, is the circumference of a circle, is the air density, is the radius of the wind rotor blade, is the wind speed.

[0051] S23, establishing a relationship model between the torque and electromagnetic power of the wind turbine generator and the generator speed, and setting the relationship model to an incremental form;

[0052] Preferably, the relationship model in step S23 is:

[0053] ;

[0054] The relational model in incremental form is:

[0055] ;

[0056] In the formula, Indicates the increment of the relevant variable, subscript represents the initial value of the relevant variable, is the torque of the generator, is the electromagnetic power, is the generator speed.

[0057] S24, combining the incremental transmission chain model in step S21, the incremental wind rotor torque in step S22, and the incremental relationship model in step S23 to obtain the differential incremental form of the related variables of the wind rotor rotation angular velocity and the generator speed;

[0058] Preferably, the differential increment form of the relevant variables of the wind rotor rotation angular velocity and the generator speed in step S24 is:

[0059] ;

[0060] In the formula, Indicates the increment of the related variable, the top of the variable Denotes the differential of the relevant variable, subscript represents the initial value of the relevant variable, represents the partial differential symbol, is the electromagnetic power, is the wind rotor rotation angular velocity, is the generator speed, is the blade pitch angle, and are the inertia constants of the wind wheel and the generator, , are the torques of the wind wheel and the transmission chain respectively, is the gearbox transmission ratio.

[0061] S25, setting the pitch angle control model to an incremental form, and further setting the differential incremental form of the relevant variables for obtaining the blade pitch angle and the pitch angle command reference value;

[0062] Preferably, in step S25, the incremental pitch angle control model is:

[0063] ;

[0064] In the formula, represents the increment of the relevant variable, is the generator speed, is the blade pitch angle, is the pitch angle command reference value, and are the proportional and integral coefficients of the pitch angle controller, is the time constant of the pitch mechanism;

[0065] The differential increment form of the relevant variables of the blade pitch angle and the pitch angle command reference value is:

[0066] ;

[0067] In the formula, Indicates the increment of the related variable, the top of the variable Denotes the differential of the relevant variable, subscript represents the initial value of the relevant variable, is the generator speed, is the blade pitch angle, is the pitch angle command reference value, and are the proportional and integral coefficients of the pitch angle controller, is the time constant of the pitch mechanism, is the electromagnetic power, is the inertia constant of the generator, is the torque of the transmission chain, is the gearbox transmission ratio.

[0068] S26, setting the transmission chain torque of the transmission chain dynamics equation in the transmission chain model to a differential increment form of a related variable;

[0069] Preferably, the differential increment form of the relevant variable of the transmission chain torque in step S26 is:

[0070] ;

[0071] In the formula, Indicates the increment of the related variable, the top of the variable represents the differential of the dependent variable, is the generator speed, is the wind rotor rotation angular velocity, is the torque of the transmission chain, is the equivalent damping constant of the transmission chain, is the equivalent stiffness of the transmission chain, is the gearbox transmission ratio.

[0072] S27. Construct the state space equation using the rotor rotation angular velocity and generator speed in the differential increment form of the relevant variables in step S24, the blade pitch angle and pitch angle command reference value in the differential increment form of the relevant variables in step S25, and the transmission chain torque in the differential increment form of the relevant variables in step S26.

[0073] Preferably, in step S27, the state space equation is:

[0074] ;

[0075] In the formula, the top variable represents the differential of the dependent variable, is the state variable, is the system matrix, is the control matrix, are the control quantities, respectively expressed as:

[0076] ;

[0077] ;

[0078] ;

[0079] ;

[0080] ;

[0081] ;

[0082] In the formula, Indicates the increment of the relevant variable, subscript represents the initial value of the relevant variable, Indicates the partial differential symbol, superscript represents the transpose of a matrix, and are the inertia constants of the wind wheel and the generator, is the generator speed, is the wind rotor rotation angular velocity, , are the torques of the wind wheel and the transmission chain respectively, is the equivalent damping constant of the transmission chain, is the equivalent stiffness of the transmission chain, is the gearbox transmission ratio, is the blade pitch angle, is the pitch angle command reference value, and are the proportional and integral coefficients of the pitch angle controller, is the time constant of the pitch mechanism, is the electromagnetic power, , , They are the intermediate variables of the system matrix with 5 rows and 1 column, 5 rows and 2 columns, and 5 rows and 5 columns respectively.

[0083] In the present invention, the fault ride-through control model of step S1 is mainly used to adjust the target power of the wind turbine generator set. This achieves low wear and is a fixed value, which is omitted during the linearization of the S2 step, leaving only the additional power instruction .

[0084] 3. Establishment of characteristic root distribution map

[0085] S3. Establish a characteristic root distribution diagram of the state space equation, and perform safety risk analysis on the low-frequency and high-frequency fluctuations of the state variables of the wind turbine during the low voltage ride-through period based on the imaginary and real values ​​of the characteristic roots in the distribution diagram.

[0086] Preferably, in step S3, the state variables of the wind turbine generator set include rotational speed and transmission chain torque.

[0087] Beneficial effects of the present invention:

[0088] The present invention constructs a characteristic root distribution diagram of a state-space equation for analyzing the fluctuation characteristics of the rotor speed during low voltage ride-through of a wind turbine according to factors such as the rotor speed motion process, the transmission chain torque, the pitch angle control, and the fault ride-through control, and conducts a theoretical analysis of the fluctuation characteristics of the rotor speed. It can effectively analyze the influence of the pitch angle controller parameters and the transmission chain parameters on the speed fluctuation characteristics during fault ride-through, and provide strong data support for reducing the fluctuation of the rotor speed, suppressing the fluctuation range of the speed, and improving the speed recovery speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0089] Figure 1 This is a flow chart of the safety risk analysis method for the speed fluctuation characteristics of equipment during low voltage ride-through period;

[0090] Figure 2 This is the active output diagram of wind turbines during low voltage ride-through;

[0091] Figure 3 This is the speed fluctuation diagram during low voltage ride-through;

[0092] Figure 4 It is the characteristic root distribution diagram of the system under traditional control;

[0093] Figure 5 For different scale parameters K p The characteristic root distribution diagram of the lower system;

[0094] Figure 6 for Figure 5 The enlarged area in

[0095] Figure 7 For different integral parameters K i The characteristic root distribution diagram of the lower system;

[0096] Figure 8 for Figure 7 The enlarged area in

[0097] Fig. 9 is the equivalent damping constant D of different transmission chains s The distribution diagram of the characteristic roots of the lower system;

[0098] Fig.10 for Fig. 9 Magnified area in . DETAILED DESCRIPTION

[0099] The concept, specific structure and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments and drawings to fully understand the purpose, characteristics and effects of the present invention.

[0100] Example 1

[0101] A safety risk analysis method for the speed fluctuation characteristics of equipment during low voltage ride-through period, such as Figure 1 As shown, the following steps are included:

[0102] S1. Constructing a mathematical model of a wind turbine generator set, wherein the mathematical model of the wind turbine generator set includes an aerodynamic model, a pitch angle control model, a fault ride-through control model and a transmission chain model;

[0103] S2, constructing state space equations using mathematical models of wind turbines;

[0104] S3. Establish a characteristic root distribution diagram of the state space equation, and conduct a safety risk analysis on the low-frequency and high-frequency fluctuations of the state variables of the wind turbine during the low voltage ride-through period based on the imaginary and real values ​​of the characteristic roots in the distribution diagram.

[0105] Example 2

[0106] This embodiment further elaborates on step S1 based on embodiment 1. The aerodynamic model, pitch angle control model, fault ride-through control model and transmission chain model in step S1 are as follows:

[0107] 1. Aerodynamic model

[0108] In step S1, the aerodynamic model includes the mechanical power captured by the wind wheel. , the mechanical power captured by the wind wheel for:

[0109] ;

[0110] In the formula, is the circumference of a circle, is the air density, is the radius of the wind rotor blade, is the wind speed, is the wind energy utilization coefficient, is the tip speed ratio, is the blade pitch angle;

[0111] Among them, the tip speed ratio for:

[0112] ;

[0113] In the formula, is the radius of the wind rotor blade, is the wind speed, is the angular velocity of the wind wheel;

[0114] Among them, the wind energy utilization coefficient The efficiency of converting wind kinetic energy into mechanical energy is expressed as:

[0115] ;

[0116] In the formula, is the intermediate variable, is the tip speed ratio, is the blade pitch angle.

[0117] 2. Pitch angle control model

[0118] In step S1, the pitch angle control model is:

[0119] ;

[0120] In the formula, is the generator speed, is the rated speed, is the blade pitch angle, is the pitch angle command reference value, and are the proportional and integral coefficients of the pitch angle controller, is the time constant of the pitch mechanism, Represents the total differential symbol.

[0121] 3. Fault ride-through control model

[0122] According to the requirements of GB / T 36995-2018 "Test Procedure for Fault Voltage Ride-Through Capability of Wind Turbine Generators", when the voltage at the wind turbine grid connection point is between 1.3pu and 0.2pu, the wind turbine is required to operate continuously without disconnecting from the grid. Taking low voltage fault ride-through control as an example, when a low voltage fault occurs at the wind turbine grid connection point, due to the reactive power priority control principle of the wind turbine, the electromagnetic power output of the wind turbine will drop sharply; after the fault is cleared, its active power will recover to the output level before the fault at a certain fixed slope; it is modeled with an active output model, in which the active power recovery rate is determined by the actual control parameters of the wind turbine fault ride-through; Figure 2 The active power output model shown is used to model it, where the active power recovery rate is determined by the actual control parameters of the wind turbine fault ride-through.

[0123] 4. Transmission chain model

[0124] During the fault ride-through period, Figure 3As shown, the speed of the wind turbine will fluctuate greatly, including low-frequency fluctuations and high-frequency fluctuations. For high-frequency fluctuations, they are caused by the torque fluctuations of the transmission shaft. If the damping of the transmission shaft is low during the low-voltage fault ride-through, it will not only enhance the amplitude of the high-frequency fluctuations of the speed, but also cause the torque of the transmission shaft to fluctuate greatly, endangering the safety and stability of the wind turbine during the fault ride-through. Existing research on transmission chain models mainly includes single-mass block, two-mass block, three-mass block, six-mass block and multi-mass block models. Generally, the analysis of the speed mostly adopts a single-mass module, but the single-mass module cannot reflect the characteristics of the transmission shaft and cannot show the high-frequency fluctuation characteristics of the speed. Therefore, a two-mass block model containing the transmission shaft is used. At this time, the dynamic equation of the transmission chain is:

[0125] ;

[0126] In the formula, the top variable represents the differential of the dependent variable, and are the inertia constants of the wind wheel and the generator, is the angular velocity of the transmission chain, is the wind rotor rotation angular velocity, is the generator speed, , , are the torques of the wind wheel, generator and transmission chain respectively, is the equivalent damping constant of the transmission chain, is the equivalent stiffness of the transmission chain, is the angular displacement of the transmission chain, is the gearbox transmission ratio.

[0127] Example 3

[0128] This embodiment further describes step S2 based on embodiment 2. Step S2 includes the following steps:

[0129] S21. Set the wind rotor rotation angular velocity and generator speed in differential form of the relevant variables in the transmission chain model to incremental form:

[0130] ;

[0131] In the formula, Indicates the increment of the related variable, the top of the variable represents the differential of the dependent variable, is the wind rotor rotation angular velocity, is the generator speed; and are the inertia constants of the wind wheel and the generator, , , are the torques of the wind wheel, generator and transmission chain respectively, is the gearbox transmission ratio.

[0132] S22, combining the mechanical power captured by the wind wheel in the aerodynamic model, obtaining the torque of the wind wheel, and setting the torque of the wind wheel to an incremental form;

[0133] In step S22, the torque of the wind wheel for:

[0134] ;

[0135] In the formula, is the circumference of a circle, is the air density, is the radius of the wind rotor blade, is the wind speed, is the wind energy utilization coefficient, is the angular velocity of the wind wheel;

[0136] The torque of the wind wheel in incremental form is:

[0137] ;

[0138] In the formula, represents the increment of the relevant variable, represents the partial differential symbol, is the wind rotor rotation angular velocity, is the torque of the wind wheel, is the blade pitch angle;

[0139] Among them, according to the torque of the wind wheel , derive the torque of the wind wheel The derivatives of the rotation speed and pitch angle are:

[0140] ;

[0141] In the formula, the subscript represents the initial value of the relevant variable, is the wind energy utilization coefficient, is the wind rotor rotation angular velocity, is the torque of the wind wheel, is the blade pitch angle, is the gearbox transmission ratio, is the mechanical power coefficient, expressed as:

[0142] ;

[0143] in, is the circumference of a circle, is the air density, is the radius of the wind rotor blade, is the wind speed.

[0144] S23, establishing a relationship model between the torque and electromagnetic power of the wind turbine generator and the generator speed, and setting the relationship model to an incremental form;

[0145] The relational model in step S23 is:

[0146] ;

[0147] The relational model in incremental form is:

[0148] ;

[0149] In the formula, Indicates the increment of the relevant variable, subscript represents the initial value of the relevant variable, is the torque of the generator, is the electromagnetic power, is the generator speed.

[0150] S24, integrating the incremental transmission chain model in step S21, the incremental wind wheel torque in step S22, and the incremental relationship model in step S23, to obtain the differential incremental form of the related variables of the wind wheel rotation angular velocity and the generator speed:

[0151] ;

[0152] In the formula, Indicates the increment of the related variable, the top of the variable Denotes the differential of the relevant variable, subscript represents the initial value of the relevant variable, represents the partial differential symbol, is the electromagnetic power, is the wind rotor rotation angular velocity, is the generator speed, is the blade pitch angle, and are the inertia constants of the wind wheel and the generator, , are the torques of the wind wheel and the transmission chain respectively, is the gearbox transmission ratio.

[0153] S25, setting the pitch angle control model to an incremental form, and further setting the differential incremental form of the relevant variables for obtaining the blade pitch angle and the pitch angle command reference value;

[0154] In step S25, the incremental pitch angle control model is:

[0155] ;

[0156] In the formula, represents the increment of the relevant variable, is the generator speed, is the blade pitch angle, is the pitch angle command reference value, and are the proportional and integral coefficients of the pitch angle controller, is the time constant of the pitch mechanism;

[0157] The differential increment form of the relevant variables of the blade pitch angle and the pitch angle command reference value is:

[0158] ;

[0159] In the formula, Indicates the increment of the related variable, the top of the variable Denotes the differential of the relevant variable, subscript represents the initial value of the relevant variable, is the generator speed, is the blade pitch angle, is the pitch angle command reference value, and are the proportional and integral coefficients of the pitch angle controller, is the time constant of the pitch mechanism, is the electromagnetic power, is the inertia constant of the generator, is the torque of the transmission chain, is the gearbox transmission ratio.

[0160] S26. Set the transmission chain torque of the transmission chain dynamics equation in the transmission chain model to the differential increment form of the relevant variable:

[0161] ;

[0162] In the formula, Indicates the increment of the related variable, the top of the variable represents the differential of the dependent variable, is the generator speed, is the wind rotor rotation angular velocity, is the torque of the transmission chain, is the equivalent damping constant of the transmission chain, is the equivalent stiffness of the transmission chain, is the gearbox transmission ratio.

[0163] S27. Construct the state space equation using the wind rotor rotation angular velocity and generator speed in the differential increment form of the relevant variables in step S24, the blade pitch angle and pitch angle command reference value in the differential increment form of the relevant variables in step S25, and the transmission chain torque in the differential increment form of the relevant variables in step S26.

[0164] In step S27, the state space equation is:

[0165] ;

[0166] In the formula, the top variable represents the differential of the dependent variable, is the state variable, is the system matrix, is the control matrix, are the control quantities, respectively expressed as:

[0167] ;

[0168] ;

[0169] ;

[0170] ;

[0171] ;

[0172] ;

[0173] In the formula, Indicates the increment of the relevant variable, subscript represents the initial value of the relevant variable, Indicates the partial differential symbol, superscript represents the transpose of a matrix, and are the inertia constants of the wind wheel and the generator, is the generator speed, is the wind rotor rotation angular velocity, , are the torques of the wind wheel and the transmission chain respectively, is the equivalent damping constant of the transmission chain, is the equivalent stiffness of the transmission chain, is the gearbox transmission ratio, is the blade pitch angle, is the pitch angle command reference value, and are the proportional and integral coefficients of the pitch angle controller, is the time constant of the pitch mechanism, is the electromagnetic power, , , They are the intermediate variables of the system matrix with 5 rows and 1 column, 5 rows and 2 columns, and 5 rows and 5 columns respectively.

[0174] Example 4

[0175] This embodiment further elaborates step S3 on the basis of embodiment 3. In step S3, a characteristic root distribution diagram of the state space equation is established, and low-frequency fluctuations and high-frequency fluctuations of state variables such as the speed and transmission chain torque of the wind turbine are analyzed according to the values ​​of the imaginary part and the real part of the characteristic root in the distribution diagram.

[0176] The characteristic roots of this state space equation are Figure 4 As shown, it can be found that the system has two pairs of conjugate complex roots close to the imaginary axis, namely λ 1,2 =-0.1146±j2.6235, λ 3,4 =-0.6220±j0.3086. It can be found that for the first pair of conjugate complex roots, the imaginary part has a higher value, corresponding to the high-frequency fluctuations of state variables such as the speed and transmission chain torque of the wind turbine, and the real part has a lower value. If the oscillation decays to 5% of the initial value as the sign of the end of the transient process, the transient process will last for about 26.14 seconds, the damping ratio is 0.0436, and the fluctuation suppression capability is extremely poor. For the second pair of conjugate complex roots, the imaginary part has a lower value, corresponding to the low-frequency fluctuations of state variables such as the speed and transmission chain torque of the wind turbine, the real part has a higher value, the transient process will last for about 4.82 seconds, the damping ratio is 0.8958, and the fluctuation suppression capability is relatively good. Therefore, when a disturbance occurs, the state variables such as the speed and transmission chain torque of the wind turbine will fluctuate, and the recovery and stability time is long.

[0177] In order to further analyze the influence of pitch angle control and transmission chain on speed fluctuation characteristics, characteristic root analysis is carried out based on the constructed state space equation.

[0178] like Figure 5 and Figure 6 As shown in the figure, it is the characteristic root distribution diagram of the pitch angle control proportional parameter increasing from 50 to 100 by 10. It can be found that with the increase of the proportional parameter, λ 1,2 It moves along the imaginary axis, and the imaginary part continues to increase, which means that the fluctuation frequency increases and the damping ratio decreases, which worsens the high-frequency fluctuation characteristics of state variables such as speed and transmission chain torque. 3,4 It moves close to the real axis and the real part keeps decreasing, which means the fluctuation frequency decreases and the damping ratio increases, thus improving the low-frequency fluctuation characteristics.

[0179] like Figure 7 and Figure 8As shown in the figure, it is the characteristic root distribution diagram of the pitch angle control integral parameter increasing from 30 to 100 by 10. It can be found that with the increase of the integral parameter, λ 1,2 The system moves along the imaginary axis and is eventually greater than 0, causing the system to enter an unstable state from a stable state. This means that after the disturbance occurs, the system fluctuations will continue to diverge, seriously deteriorating the system stability. 3,4 Moving away from the real axis and the imaginary axis, both the real and imaginary parts increase, the fluctuation attenuation speed increases, but the fluctuation frequency increases.

[0180] like Fig. 9 and Fig.10 As shown in the figure, the characteristic root distribution diagram of the transmission chain equivalent damping constant increases from 1.2 to 3 by 0.1. It can be found that with the increase of the equivalent damping constant, λ 1,2 It keeps moving away from the imaginary axis, and the imaginary part keeps decreasing, which means that the fluctuation frequency is reduced and the damping ratio is improved, which improves the high-frequency fluctuation characteristics of state variables such as speed and transmission chain torque. 3,4 Similar to the case of the proportional parameter, the low-frequency fluctuation characteristics are improved.

[0181] In summary, under the traditional control mode, when the wind turbine is in low voltage fault ride-through, the state variables such as speed and transmission chain torque will fluctuate for a long time. Increasing the proportional and integral parameters of the pitch angle control has a certain improvement effect on the low-frequency fluctuation characteristics of the speed, but it will worsen the high-frequency fluctuation characteristics. Too large integral parameters may even cause the system to become unstable. Increasing the equivalent damping constant of the transmission chain can improve the low-frequency and high-frequency fluctuation characteristics of the speed at the same time, but the improvement of the low-frequency fluctuation characteristics is limited.

[0182] The present invention constructs a characteristic root distribution diagram of a state-space equation for analyzing the fluctuation characteristics of the rotor speed during low voltage ride-through of a wind turbine according to factors such as the rotor speed motion process, the transmission chain torque, the pitch angle control, and the fault ride-through control, and conducts a theoretical analysis of the fluctuation characteristics of the rotor speed. It can effectively analyze the influence of the pitch angle controller parameters and the transmission chain parameters on the speed fluctuation characteristics during fault ride-through, and provide strong data support for reducing the fluctuation of the rotor speed, suppressing the fluctuation range of the speed, and improving the speed recovery speed.

[0183] The above is a specific description of the implementation mode of the present invention, but the present invention is not limited to the described embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention, and these equivalents or substitutions are all included in the scope defined by the claims of the present invention.

Claims

1. A safety risk analysis method for the speed fluctuation characteristics of equipment during low voltage ride-through, characterized in that: The following steps are involved: S1. Constructing a mathematical model of a wind turbine generator set, wherein the mathematical model of the wind turbine generator set includes an aerodynamic model, a pitch angle control model, a fault ride-through control model and a transmission chain model; S2. Constructing a state space equation using a mathematical model of a wind turbine generator system, including the following steps: S21, setting the wind rotor rotation angular velocity and generator speed in differential form of relevant variables in the transmission chain model to incremental form; S22, combining the mechanical power captured by the wind wheel in the aerodynamic model, obtaining the torque of the wind wheel, and setting the torque of the wind wheel to an incremental form; S23, establishing a relationship model between the torque and electromagnetic power of the wind turbine generator and the generator speed, and setting the relationship model to an incremental form; S24, combining the incremental transmission chain model in step S21, the incremental wind rotor torque in step S22, and the incremental relationship model in step S23 to obtain the differential incremental form of the related variables of the wind rotor rotation angular velocity and the generator speed; S25, setting the pitch angle control model to an incremental form, and further setting the differential incremental form of the relevant variables for obtaining the blade pitch angle and the pitch angle command reference value; S26, setting the transmission chain torque of the transmission chain dynamics equation in the transmission chain model to a differential increment form of a related variable; S27, constructing a state space equation using the rotor rotation angular velocity and generator speed in the differential increment form of the relevant variables in step S24, the blade pitch angle and pitch angle command reference value in the differential increment form of the relevant variables in step S25, and the transmission chain torque in the differential increment form of the relevant variables in step S26; S3. Establish a characteristic root distribution diagram of the state space equation, and perform safety risk analysis on the low-frequency and high-frequency fluctuations of the state variables of the wind turbine during the low voltage ride-through period based on the imaginary and real values ​​of the characteristic roots in the distribution diagram.

2. A safety risk analysis method for the speed fluctuation characteristics of equipment during low voltage ride-through period as claimed in claim 1, characterized in that: In step S1, the aerodynamic model includes the mechanical power captured by the wind wheel. , the mechanical power captured by the wind wheel for: ； In the formula, is the circumference of a circle, is the air density, is the radius of the wind rotor blade, is the wind speed, is the wind energy utilization coefficient, is the tip speed ratio, is the blade pitch angle; Among them, the tip speed ratio for: ； In the formula, is the radius of the wind rotor blade, is the wind speed, is the angular velocity of the wind wheel; Among them, the wind energy utilization coefficient The efficiency of converting wind kinetic energy into mechanical energy is expressed as: ； In the formula, is the intermediate variable, is the tip speed ratio, is the blade pitch angle.

3. A safety risk analysis method for the speed fluctuation characteristics of equipment during low voltage ride-through period as claimed in claim 1, characterized in that: In step S1, the pitch angle control model is: ； In the formula, is the generator speed, is the rated speed, is the blade pitch angle, is the pitch angle command reference value, and are the proportional and integral coefficients of the pitch angle controller, is the time constant of the pitch mechanism, Represents the total differential symbol.

4. A safety risk analysis method for the speed fluctuation characteristics of equipment during low voltage ride-through period as claimed in claim 1, characterized in that: In step S1, the transmission chain model includes a two-mass block model including a transmission shaft, and the transmission chain dynamics equation of the transmission chain model is: ； In the formula, the variable at the top represents the differential of the dependent variable, and are the inertia constants of the wind wheel and the generator, is the angular velocity of the transmission chain, is the wind rotor rotation angular velocity, is the generator speed, , , are the torques of the wind wheel, generator and transmission chain respectively, is the equivalent damping constant of the transmission chain, is the equivalent stiffness of the transmission chain, is the angular displacement of the transmission chain, is the gearbox transmission ratio.

5. The method for analyzing the safety risk of the equipment speed fluctuation characteristics during the low voltage ride-through period according to claim 1 is characterized in that: Step S21 includes: ； In the formula, Indicates the increment of the related variable, the top of the variable represents the differential of the dependent variable, is the wind rotor rotation angular velocity, is the generator speed; and are the inertia constants of the wind wheel and the generator, , , are the torques of the wind wheel, generator and transmission chain respectively, is the gearbox transmission ratio; In step S22, the torque of the wind wheel for: ； In the formula, is the circumference of a circle, is the air density, is the radius of the wind rotor blade, is the wind speed, is the wind energy utilization coefficient, is the angular velocity of the wind wheel; The torque of the wind wheel in incremental form is: ； In the formula, represents the increment of the relevant variable, represents the partial differential symbol, is the wind rotor rotation angular velocity, is the torque of the wind wheel, is the blade pitch angle; According to the torque of the wind wheel, , derive the torque of the wind wheel The derivatives of the rotation speed and pitch angle are: ； In the formula, the subscript represents the initial value of the relevant variable, is the wind energy utilization coefficient, is the wind rotor rotation angular velocity, is the torque of the wind wheel, is the blade pitch angle, is the gearbox transmission ratio, is the mechanical power coefficient, expressed as: ； in, is the circumference of a circle, is the air density, is the radius of the wind rotor blade, is the wind speed; The relational model in step S23 is: ； The relational model in incremental form is: ； In the formula, Indicates the increment of the relevant variable, subscript represents the initial value of the relevant variable, is the torque of the generator, is the electromagnetic power, is the generator speed.

6. A safety risk analysis method for the speed fluctuation characteristics of equipment during low voltage ride-through period as claimed in claim 1, characterized in that: The differential increment form of the relevant variables of the wind rotor rotation angular velocity and the generator speed in step S24 is: ； In the formula, Indicates the increment of the related variable, the top of the variable Denotes the differential of the relevant variable, subscript represents the initial value of the relevant variable, represents the partial differential symbol, is the electromagnetic power, is the wind rotor rotation angular velocity, is the generator speed, is the blade pitch angle, and are the inertia constants of the wind wheel and the generator, , are the torques of the wind wheel and the transmission chain respectively, is the gearbox transmission ratio.

7. The method for analyzing the safety risk of the speed fluctuation characteristics of equipment during low voltage ride-through period according to claim 1, characterized in that: In step S25, the incremental pitch angle control model is: ； In the formula, represents the increment of the relevant variable, is the generator speed, is the blade pitch angle, is the pitch angle command reference value, and are the proportional and integral coefficients of the pitch angle controller, is the time constant of the pitch mechanism; The differential increment form of the relevant variables of the blade pitch angle and the pitch angle command reference value is: ； In the formula, Indicates the increment of the related variable, the top of the variable Denotes the differential of the relevant variable, subscript represents the initial value of the relevant variable, is the generator speed, is the blade pitch angle, is the pitch angle command reference value, and are the proportional and integral coefficients of the pitch angle controller, is the time constant of the pitch mechanism, is the electromagnetic power, is the inertia constant of the generator, is the torque of the transmission chain, is the gearbox transmission ratio.

8. The method for analyzing the safety risk of the speed fluctuation characteristics of equipment during low voltage ride-through period according to claim 1, characterized in that: The differential increment form of the relevant variable of the transmission chain torque in step S26 is: ； In the formula, Indicates the increment of the related variable, the top of the variable represents the differential of the dependent variable, is the generator speed, is the wind rotor rotation angular velocity, is the torque of the transmission chain, is the equivalent damping constant of the transmission chain, is the equivalent stiffness of the transmission chain, is the gearbox transmission ratio.

9. A safety risk analysis method for the speed fluctuation characteristics of equipment during low voltage ride-through period as claimed in claim 1, characterized in that: In step S27, the state space equation is: ； In the formula, the variable at the top represents the differential of the dependent variable, is the state variable, is the system matrix, is the control matrix, are the control quantities, respectively expressed as: ； ； ； ； ； ； In the formula, Indicates the increment of the relevant variable, subscript represents the initial value of the relevant variable, Indicates the partial differential symbol, superscript represents the transpose of a matrix, and are the inertia constants of the wind wheel and the generator, is the generator speed, is the wind rotor rotation angular velocity, , are the torques of the wind wheel and the transmission chain respectively, is the equivalent damping constant of the transmission chain, is the equivalent stiffness of the transmission chain, is the gearbox transmission ratio, is the blade pitch angle, is the pitch angle command reference value, and are the proportional and integral coefficients of the pitch angle controller, is the time constant of the pitch mechanism, is the electromagnetic power, , , They are the intermediate variables of the system matrix with 5 rows and 1 column, 5 rows and 2 columns, and 5 rows and 5 columns respectively.

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