A small signal model construction method of a wind power and light heat integrated power generation system

Abstract

The application discloses a kind of wind power photo-thermal integrated power generation system small signal model construction methods, comprising the following steps: constructing the time domain small signal model of photo-thermal generator unit;According to the time domain small signal model of photo-thermal generator unit, the frequency domain small signal model of photo-thermal generator unit is established;The time domain small signal model of permanent magnet direct drive wind turbine is constructed;According to the time domain small signal model of permanent magnet direct drive wind turbine, the frequency domain small signal model of permanent magnet direct drive wind turbine is established;Equivalent current source frequency domain small signal model and equivalent power grid frequency domain small signal model are constructed;Establish the small signal model of wind power photo-thermal integrated power generation system.The application can better reflect the dynamic of wind power photo-thermal integrated power generation system, modeling process is relatively simple, suitable for large-scale wind power photo-thermal integrated power generation system grid-connected stability analysis, using system small signal model to judge system stability, can be judged according to system parameter relationship, concise and clear, help to solve the electromagnetic oscillation problem of photo-thermal power station.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power system modeling, and particularly relates to a small signal model construction method for a wind power and solar thermal integrated power generation system. BACKGROUND

[0002] New energy power generation is increasingly becoming a development trend of power systems, and various forms of new energy power generation are rapidly developing, among which, wind power generation and solar thermal power generation are important forms of new energy power generation.

[0003] Wind power generation and solar thermal power generation both have the characteristic of large occupation area, and therefore, with the continuous increase of the installed capacity of the two, it is inevitable that solar thermal power stations and wind power bases will be connected to the same or adjacent grid points to form a wind power and solar thermal integrated power generation system.

[0004] However, wind power generation and solar thermal power generation each have different characteristics, which bring some problems to the integrated power generation system. The single-machine capacity of solar thermal units is small, and the number is large, and unreasonable setting of the parameters of the excitation controller can cause electromagnetic oscillation in the solar thermal power station; large-scale power electronic converters in the wind power base can bring negative damping characteristics to the wind power and solar thermal integrated power generation system, causing the strength of the power grid to decrease, and further aggravating the electromagnetic oscillation of the solar thermal power station.

[0005] To solve the above problems, it is necessary to first study and analyze the above electromagnetic oscillation phenomenon, and analyze the stability of the wind power and solar thermal integrated power generation system.

[0006] However, the research on the above electromagnetic oscillation problem in the wind power and solar thermal integrated power generation system is still blank, because the current research mainly aims at new energy power generation systems connected to converters, and lacks analysis of the stability of the wind power and solar thermal integrated power generation system. SUMMARY

[0007] The purpose of the present application is to provide a small signal model construction method for a wind power and solar thermal integrated power generation system, which establishes a small signal model including solar thermal units, permanent magnet direct drive wind turbine units, equivalent current source simulated wind turbine units and an equivalent power grid, uses relevant parameters of the small signal model to judge the stability of the wind power and solar thermal integrated power generation system, and solves the above problem of analyzing the stability of the wind power and solar thermal integrated power generation system. The small signal model is based on the linear approximation principle, linearizes the nonlinear circuit near a specific operating point (bias point), and uses a linear matrix to approximately describe the dynamic behavior of the circuit. In the small signal model, all nonlinear elements in the circuit are regarded as linear single-ended gain elements, and the gain parameters of voltage and current are used for description. This model can effectively analyze the frequency response, signal gain and other parameters of the circuit.

[0008] To achieve the above purpose, the present application provides the following technical solutions:

[0009] A small signal model construction method of a wind power and solar thermal power integrated power generation system, comprising the following specific steps:

[0010] 11) Constructing a small signal model of a solar thermal power generating unit, specifically, the solar thermal power generating unit comprises an excitation subsystem and a synchronous generator subsystem. First, a time domain small signal model of each subsystem is established according to the differential equation of the subsystem; then, a frequency domain small signal model of the solar thermal power generating unit is established according to the time domain small signal model of the subsystem.

[0011] 12) Constructing a small signal model of a permanent magnet direct-driven wind power generating unit, wherein the permanent magnet direct-driven wind power generating unit comprises a wind turbine blade subsystem, a permanent magnet synchronous generator subsystem and a back-to-back converter subsystem; the back-to-back converter subsystem comprises a machine-side converter and a grid-side converter. First, a time domain small signal model of each subsystem is established according to the differential equation of the subsystem; then, a frequency domain small signal model of the permanent magnet direct-driven wind power generating unit is established according to the time domain small signal model of the subsystem.

[0012] 13) Constructing a frequency domain small signal model of an equivalent current source and a frequency domain small signal model of an equivalent grid, the equivalent current source is used to simulate N-1 wind turbines, N is the number of wind power generating units in a wind power base. The equivalent current source is modeled as a controlled current source, and the control quantity of the controlled current source is the current fed into the grid by the permanent magnet direct-driven wind power generating unit. The equivalent grid is modeled as an ideal voltage source.

[0013] 14) Based on the frequency domain small signal model of the solar thermal power generating unit, the frequency domain small signal model of the permanent magnet direct-driven wind power generating unit, the frequency domain small signal model of the equivalent current source and the frequency domain small signal model of the equivalent grid, a small signal model of the wind power and solar thermal power integrated power generation system is established.

[0014] Further, the step 11) comprises the following specific steps:

[0015] 111) Constructing a time domain small signal model of the excitation subsystem of the solar thermal power generating unit.

[0016] 112) Constructing a time domain small signal model of the synchronous generator subsystem of the solar thermal power generating unit.

[0017] 113) Constructing a time domain small signal model of the solar thermal power generating unit and deriving a transfer function block diagram of the solar thermal power generating unit.

[0018] 114) Deriving a frequency domain small signal model of the solar thermal power generating unit according to the transfer function block diagram of the solar thermal power generating unit.

[0019] Further, the step 12) comprises the following specific steps:

[0020] 121) Establishing a time domain small signal model of the wind turbine blade subsystem of the permanent magnet direct-driven wind power generating unit.

[0021] 122) Establish the time-domain small-signal model of the permanent magnet synchronous machine subsystem of the permanent magnet direct-driven wind turbine.

[0022] 123) Establish the time-domain small-signal model of the machine-side converter. Since the transient dynamics of the machine-side converter is much faster than the electromagnetic dynamics and mechanical dynamics of the permanent magnet synchronous machine, the dynamics of the converter can be ignored.

[0023] 124) Ignore the resistance of the DC link between the machine-side converter and the grid-side converter, only consider the filter capacitance on the DC link, and do not consider the active power loss of the converter, to establish the time-domain small-signal model of the DC link.

[0024] 125) Establish the time-domain small-signal model of the grid-side converter. Like the machine-side converter, the transient dynamics of the grid-side converter is also much faster than the electromagnetic dynamics and mechanical dynamics of the permanent magnet synchronous machine. Therefore, the dynamics of the converter can be ignored.

[0025] 126) According to the time-domain small-signal models established in steps 121)-125) above, establish the transfer function block diagram of the wind turbine.

[0026] 127) According to the transfer function block diagram of the wind turbine, derive the frequency-domain small-signal model of the permanent magnet direct-driven wind turbine:

[0027] Further, in step 13), the equivalent current source simulates the output current of N-1 wind turbines, and the external output power characteristic is the same as the wind turbine mathematical model in step S12). The equivalent grid is modeled as an ideal voltage source, and the voltage fluctuation is 0.

[0028] Further, the final small-signal model of the wind-solar-thermal integrated power generation system established in step 14) is as follows:

[0029]

[0030] In the formula, X qΣ = X t + X q , X dΣ = X t + X d , X' dΣ = X t + X' d ;

[0031] ΔP t1 is the synchronous electromagnetic power of the solar-thermal power generation unit, V b is the voltage of the ideal voltage source, X t is the reactance value of the transmission line between the solar-thermal power generation unit and the ideal voltage source, and X' dis the direct axis transient reactance of the synchronous generator, V td and V tq are the d-axis and q-axis components of the terminal voltage of the CTP, respectively, and the subscript 0 indicates the value of the corresponding variable at the steady state operating point of the system;

[0032] K A is the gain of the automatic voltage regulator in the CTP, T A is the time constant of the automatic voltage regulator, V t is the terminal voltage of the CTP; E q is the quadrature axis transient electromotive force of the synchronous generator in the CTP, T d0 is the time constant of the field winding; δ is the angular displacement of the synchronous generator relative to the synchronous reference axis, ω is the rotational speed of the synchronous generator, X d , X q are the self-inductances of the windings with the corresponding subscript;

[0033] is the q-axis output stator current of the permanent magnet synchronous generator in the WTG, R s is the resistance of the stator winding, is the q-axis inductance, ψ pm is the permanent magnet flux, n p is the number of magnetic pole pairs, and N is the number of WTGs in the wind power base.

[0034] Further, according to the small signal model of the wind power and CTP integrated power system established in step 14), through Bode plot analysis, an equivalent small signal model with the smallest difference between the Bode amplitude curve and the Bode phase curve of the original expression is obtained, as shown in the following formula:

[0035]

[0036] In the formula, the variables with the subscript “, e” are all equivalent parameters after equivalent;

[0037] Let s = jω, substitute into the above formula ΔP t1 , and the imaginary part expression is Since , then that is, corresponding to Δω, the frequency characteristic of the system is obtained, D a that is, the system damping coefficient corresponding to the frequency ω;

[0038] ΔP t1 = K a Δδ + D a Δω

[0039]

[0040] Further, the system damping coefficient D aThe expression can be simplified as:

[0041]

[0042] From the above formula, the absolute value of D a increases with the decrease of frequency, when K 5,e becomes negative, the damping coefficient D a of the system is negative, at this time, the system appears low frequency oscillation.

[0043] The application also provides a wind power and solar thermal integrated power generation system stability judgment method, comprising:

[0044] 1) establishing a small signal model of the wind power and solar thermal integrated power generation system.

[0045] 2) judging the stability of the wind power and solar thermal integrated power generation system according to the small signal model of the wind power and solar thermal integrated power generation system.

[0046] Further, in the step 2), the stability of the wind power and solar thermal integrated power generation system is judged according to the system damping coefficient, if the system damping coefficient is negative, it is judged that the system appears low frequency oscillation.

[0047] The application also provides a wind power and solar thermal integrated power generation system stability judgment system, comprising:

[0048] a model module containing a small signal model of the wind power and solar thermal integrated power generation system;

[0049] a judgment module judging the stability of the wind power and solar thermal integrated power generation system according to the small signal model of the wind power and solar thermal integrated power generation system.

[0050] Further, the model module comprises:

[0051] a solar thermal power generating unit submodule containing a frequency domain small signal model of the solar thermal power generating unit;

[0052] a permanent magnet direct drive wind power generating unit submodule containing a frequency domain small signal model of the permanent magnet direct drive wind power generating unit;

[0053] an equivalent current source and equivalent grid submodule containing a frequency domain small signal model of the equivalent current source and a frequency domain small signal model of the equivalent grid.

[0054] The application also provides a wind power and solar thermal integrated power generation system stability judgment device, comprising:

[0055] a memory;

[0056] Processor, for calling the computer execution program of the above-mentioned wind power and light heat integrated power generation system stability judgment method from the memory, execution: establish the small signal model of wind power and light heat integrated power generation system;According to the small signal model of wind power and light heat integrated power generation system, judge the stability of wind power and light heat integrated power generation system.

[0057] Compared with the prior art, the beneficial effects of the present application are:

[0058] The present application establishes the small signal model of wind power and light heat integrated power generation system, which can better reflect the dynamic of wind power and light heat integrated power generation system, and the modeling process is relatively simple, suitable for grid-connected stability analysis of large-scale wind power and light heat integrated power generation system, using the small signal model of the system to judge the stability of the system, which can be judged according to the relationship between system parameters, simple and clear, and helpful to solve the electromagnetic oscillation problem of light heat power station. BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 It is a flowchart of a wind power and light heat integrated power generation system small signal model construction method provided by the present application.

[0060] Figure 2 It is a flowchart of a wind power and light heat integrated power generation system stability judgment method provided by the present application.

[0061] Figure 3 It is a transfer function block diagram of a light heat power generating unit provided by the present application.

[0062] Figure 4 It is a transfer function block diagram of a wind power unit provided by the present application. DETAILED DESCRIPTION

[0063] The present application will be further described in detail below by means of the drawings and specific embodiments.

[0064] As shown in Figure 1 A wind power and light heat integrated power generation system small signal model construction method, comprising the following steps:

[0065] 11) Construct the small signal model of light heat power generating unit, specifically, the light heat power generating unit includes excitation subsystem and synchronous generator subsystem. First, the time domain small signal model of each subsystem is established according to the differential equation of the subsystem; then, the frequency domain small signal model of light heat power generating unit is established according to the time domain small signal model of the subsystem.

[0066] 12) Constructing the small signal model of the permanent magnet direct-driven wind turbine, which includes the wind turbine blade subsystem, the permanent magnet synchronous generator subsystem and the back-to-back converter subsystem. The back-to-back converter subsystem includes the machine-side converter and the grid-side converter. Firstly, the time-domain small signal model of each subsystem is established according to the differential equation of the subsystem. Then, the frequency-domain small signal model of the permanent magnet direct-driven wind turbine is established according to the time-domain small signal model of the subsystem.

[0067] 13) Constructing the frequency-domain small signal model of the equivalent current source and the frequency-domain small signal model of the equivalent grid. The equivalent current source is used to simulate N-1 wind turbines, N being the number of wind turbines in the wind power base. The equivalent current source is modeled as a controlled current source, and the control quantity of the controlled current source is the current fed into the grid by the permanent magnet direct-driven wind turbine. The equivalent grid is modeled as an ideal voltage source.

[0068] 14) Based on the frequency-domain small signal model of the solar-thermal generator, the frequency-domain small signal model of the permanent magnet direct-driven wind turbine, the frequency-domain small signal model of the equivalent current source and the frequency-domain small signal model of the equivalent grid, the small signal model of the solar-thermal and wind power integrated system is established.

[0069] Further, the step 11) includes the following specific steps:

[0070] 111) Constructing the time-domain small signal model of the excitation subsystem of the solar-thermal generator. The generator excitation voltage E fd is divided into two parts: one part is the constant excitation voltage E fd0 , and the other part is the output voltage E fd ' of the automatic voltage regulator. The established time-domain small signal model of the excitation subsystem is as follows:

[0071] ΔE fd = ΔE fd0 + ΔE′ fd

[0072]

[0073] In the formula, K A is the gain of the automatic voltage regulator, T A is the time constant of the automatic voltage regulator, V t is the generator terminal voltage, and V ref is the generator terminal voltage reference value.

[0074] 112) Constructing the time-domain small signal model of the synchronous generator subsystem of the solar-thermal generator. The established time-domain small signal model of the synchronous generator subsystem is as follows:

[0075]

[0076] In the formula, ψd , ψ q , ψ f is the flux linkage of the winding corresponding to the subscript, I d , I q , I f is the current of the winding corresponding to the subscript; E q ' is the quadrature axis transient electromotive force of the synchronous generator; E q is the no-load electromotive force; T d0 ' is the time constant of the excitation winding; M is the rotor inertia constant; D is the damping coefficient; δ is the angular displacement of the synchronous generator relative to the synchronous reference axis; ω0 is the synchronous speed; T m and T t are the mechanical torque and electromagnetic torque of the synchronous generator rotor respectively; ω is the speed of the synchronous generator; X d 、X q 、X f are the self-reactances of the windings corresponding to the subscripts; and assuming that the mutual reactances between coaxial windings are equal, that is, X ad is the mutual reactance between the d-axis windings.

[0077] At this time, the active power P output by the generator t The linearized expression of can be expressed as:

[0078] ΔP t =K1Δδ+K2ΔE' q ;

[0079] Where, V b is the voltage of the ideal voltage source, X′ dΣ =X t +X′ d , X qΣ =X t +X q , X t is the reactance of the transmission line between the CST generator and the ideal voltage source, X′ d is the direct-axis transient reactance, δ is the synchronous generator power angle, and the quantities with subscript 0 represent the values ​​of the corresponding variables at the steady-state operating point of the system.

[0080] 113) Construct a time domain small signal model of the CSP generator set and derive the transfer function block diagram of the CSP generator set. Figure 3 As shown. Among them, Δω is the speed of the synchronous generator, ΔP t1 is the synchronous electromagnetic power, ΔP t Output power for the generator.

[0081]

[0082] X dΣ= X t + X d Here, V td and V tq are the d-axis and q-axis components of the generator terminal voltage, respectively, and the subscript 0 indicates the value of the corresponding variable at the steady-state operating point of the system.

[0083] 114) The frequency-domain small-signal model of the CTPP system is derived from the transfer function block diagram of the CTPP system. Specifically, from the transfer function block diagram, the synchronous electromagnetic power ΔP t1 related to the power angle Δδ and the synchronous generator speed Δω is:

[0084]

[0085] Further, the step 12) comprises the following specific steps:

[0086] 121) The time-domain small-signal model of the wind turbine blade subsystem of the PMSG wind turbine is established. The specific model is as follows:

[0087]

[0088] In the formula, ω is the mechanical angular speed of the PMSM, J C is the combined inertia of the wind turbine blade and the PMSM, P m is the mechanical power captured by the blade, P e is the electrical power of the PMSM, ρ is the air density, r is the radius of the turbine blade, W s is the wind speed faced by the wind turbine.

[0089] 122) The time-domain small-signal model of the PMSM subsystem of the PMSG wind turbine is established. The specific model is as follows:

[0090]

[0091] In the formula, is the q-axis output stator current of the PMSM, is the q-axis output stator voltage, R s is the stator winding resistance, is the q-axis inductance, ψ pm is the permanent magnet flux, n p is the number of magnetic pole pairs.

[0092] 123) The time-domain small-signal model of the machine-side converter is established. Since the instantaneous dynamics of the machine-side converter are much faster than the electromagnetic dynamics and the mechanical dynamics of the PMSM, the dynamics of the converter can be ignored. The time-domain small-signal model of the machine-side converter is as follows:

[0093]

[0094] wherein, is an introduced intermediate variable, K PP and K IP are q-axis outer loop controller parameters.

[0095] 124) Neglect the resistance of DC link between machine side converter and grid side converter, only consider the filter capacitor C dc , without considering the active power loss of the converter, the time domain small signal model of DC link is established as follows:

[0096]

[0097] wherein, V dc is DC link voltage, P gsc is the output power of grid side converter (GSC).

[0098] 125) Establish the time domain small signal model of grid side converter. As same as machine side converter, the transient dynamics of grid side converter is also much faster than the electromagnetic dynamics and mechanical dynamics of permanent magnet synchronous machine. Therefore, the dynamics of converter can be neglected. The time domain small signal model of grid side converter is as follows:

[0099]

[0100] wherein, is an introduced intermediate variable, is the d-axis component of grid side converter output current, K PV and K IV are q-axis outer loop controller parameters.

[0101] 126) According to the time domain small signal model established in steps 121)-125) above, the transfer function model of wind turbine is established, and the transfer function block diagram is shown in Figure 4 wherein, is the grid side converter output voltage.

[0102] 127) According to the transfer function block diagram of wind turbine, the synchronous electromagnetic power ΔP e related to Δδ and Δω is:

[0103]

[0104] wherein, s is a complex variable generated by Laplace transform.

[0105] Further, the step 13) comprises the following specific steps:

[0106] 131) The equivalent current source simulates N-1 wind turbine output current, whose external output power characteristics are the same as the wind turbine mathematical model in step S12). The equivalent grid is modeled as an ideal voltage source, whose voltage fluctuation Δu g is 0. The frequency domain small signal model of the equivalent current source and the frequency domain small signal model of the equivalent grid are as follows:

[0107]

[0108] In the two expressions of the step 131), the upper expression is the frequency domain small signal model of the equivalent current source, and the lower expression is the frequency domain small signal model of the equivalent grid.

[0109] Further, the step 14) comprises the following specific steps:

[0110] 141) The small signal model of the wind power and optical thermal integrated power generation system is established as follows:

[0111]

[0112] Further, the step 2) in judging the stability of the wind power and optical thermal integrated power generation system, according to the model established in step 141), through Bode diagram analysis, the equivalent small signal model with the smallest difference between the Bode amplitude curve of the original expression and the Bode phase curve of the original expression is obtained, as shown in the following expression:

[0113]

[0114] In the expression, the parameters with subscript “e” are all equivalent parameters after equivalence.

[0115] Let s = jω, substitute into ΔP t1 , and the imaginary part expression is Since , that is, corresponding to Δω, the following is obtained:

[0116] ΔP t1 = K a Δδ+D a Δω

[0117]

[0118] D a that is, the system damping coefficient corresponding to the frequency ω. In the above expression of D a , the denominator is always positive regardless of the case, and the sign of D a depends on the numerator, while K 2,e , K A,e , and ω 0,e are all positive, so the positive and negative of D a is determined by K 5,e . K5,e K can be called damping factor, with the increase of delta, K 5,e becomes negative, at this time D a is negative.When K A,e is large, T A,e is small enough, the above formula can be simplified as:

[0119]

[0120] From the above formula, the absolute value of D a increases with the decrease of frequency, when K 5,e becomes negative, the damping coefficient D a of the system is negative, at this time, the system appears low frequency oscillation.

[0121] The application also provides a wind power and solar thermal integrated power generation system stability judgment method, as shown in the figure, comprising: Figure 2

[0122] 1) a small signal model of the wind power and solar thermal integrated power generation system is established.

[0123] 2) according to the small signal model of the wind power and solar thermal integrated power generation system, the stability of the wind power and solar thermal integrated power generation system is judged.

[0124] The application also provides a wind power and solar thermal integrated power generation system stability judgment system, comprising:

[0125] a model module containing a small signal model of the wind power and solar thermal integrated power generation system;

[0126] a judgment module for judging the stability of the wind power and solar thermal integrated power generation system according to the small signal model of the wind power and solar thermal integrated power generation system.

[0127] Further, the model module comprises:

[0128] a solar thermal power generating unit submodule containing a frequency domain small signal model of the solar thermal power generating unit;

[0129] a permanent magnet direct drive wind turbine unit submodule containing a frequency domain small signal model of the permanent magnet direct drive wind turbine unit;

[0130] an equivalent current source and equivalent grid submodule containing a frequency domain small signal model of the equivalent current source and a frequency domain small signal model of the equivalent grid.

[0131] The application also provides a wind power and solar thermal integrated power generation system stability judgment device, comprising:

[0132] a memory;

[0133] ​Processor, for calling the computer program of the wind power and solar heat integrated power generation system stability judging method from the memory, executing: establishing the small signal model of the wind power and solar heat integrated power generation system; judging the stability of the wind power and solar heat integrated power generation system according to the small signal model of the wind power and solar heat integrated power generation system.

[0134] The above examples are only examples for clearly illustrating the present application, but not limitation to the embodiments. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, all the embodiments cannot be enumerated, and the obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for constructing a small signal model of a wind power and solar thermal integrated power generation system, characterized in that: Comprise the following specific steps: 11) constructing a time domain small signal model of the photo-thermal generator set, and establishing a frequency domain small signal model of the photo-thermal generator set according to the time domain small signal model of the photo-thermal generator set; 12) constructing a time domain small signal model of the permanent magnet direct drive wind turbine generator set, and establishing a frequency domain small signal model of the permanent magnet direct drive wind turbine generator set according to the time domain small signal model of the permanent magnet direct drive wind turbine generator set; 13) constructing a frequency domain small signal model of the equivalent current source and a frequency domain small signal model of the equivalent power grid; 14) based on the frequency domain small signal model of the photo-thermal generator set, the frequency domain small signal model of the permanent magnet direct drive wind turbine generator set, the frequency domain small signal model of the equivalent current source and the frequency domain small signal model of the equivalent power grid, establishing a small signal model of the wind power photo-thermal integrated power generation system; The photo-thermal generator set and the permanent magnet direct drive wind turbine generator set respectively comprise different subsystems, and a time domain small signal model of each subsystem is established according to a differential equation corresponding to the subsystem; and a frequency domain small signal model of the photo-thermal generator set and a frequency domain small signal model of the permanent magnet direct drive wind turbine generator set are respectively established according to the time domain small signal model of each subsystem; The photo-thermal generator set comprises an excitation subsystem and a synchronous generator subsystem; the permanent magnet direct drive wind turbine generator set comprises a fan blade subsystem, a permanent magnet synchronous generator subsystem and a back-to-back converter subsystem; and the back-to-back converter subsystem comprises a machine-side converter and a grid-side converter; The small signal model of the wind power photo-thermal integrated power generation system is as follows: wherein X qΣ = X t + X q , X dΣ = X t + X d , X' dΣ = X t + X' d ; ΔP t1 V is the synchronous electromagnetic power of the photovoltaic generator b V is the voltage of the ideal voltage source t X' is the reactance value of the transmission line between the photovoltaic generator and the ideal voltage source d Xd is the direct-axis transient reactance td and V tq Vd0 and Vq0 are the d-axis and q-axis components of the photovoltaic generator terminal voltage, respectively, and the subscript 0 indicates the value of the corresponding variable at the steady-state operating point of the system K A T is the gain of the automatic voltage regulator in the photovoltaic generator set A T is the time constant of the automatic voltage regulator t E is the terminal voltage of the photovoltaic generator q E is the transient quadrature-axis electromotive force of the synchronous generator of the photovoltaic generator set d0 T is the time constant of the excitation winding δ is the angular displacement of the synchronous generator with respect to a synchronous reference axis, ω is the synchronous generator rotational speed, X d , X q are the self-inductances of the windings corresponding to the subscript, respectively; is the q-axis output stator current of the permanent magnet synchronous motor in the wind turbine, R s is the stator winding resistance, is the q-axis inductance, ψ pm is the permanent magnet flux, n p is the number of magnetic poles, N is the number of wind turbines in the wind power base.

2. The method according to claim 1, wherein the method is characterized in that: The equivalent current source is modeled as a controlled current source, and the control quantity of the controlled current source is the current fed into the power grid by the permanent magnet direct drive wind turbine generator set; and the equivalent power grid is modeled as an ideal voltage source.

3. The method according to claim 1, wherein the method is characterized in that: According to the small signal model of the wind power photo-thermal integrated power generation system, through Bode diagram analysis, an equivalent small signal model with the smallest difference from the Bode amplitude curve and the Bode phase curve of the original expression is obtained, as shown in the following formula: In the formula, the quantities with subscript "e" are all parameters after equivalence; Let s = jω, substitute into the above equation ΔP t1 where the imaginary part is expressed as Since Then That is, corresponding to Δω, the frequency characteristic of the system, D a That is, the system damping coefficient corresponding to the frequency ω; ΔP t1 = K a Δδ+D a Δω; 4. The method according to claim 3, wherein the method is characterized in that: The system damping coefficient D a The expression for D simplifies to:

5. A wind power and solar thermal integrated power generation system stability determination method, characterized by, Comprise the following steps: 1) establishing the small signal model of the wind power photo-thermal integrated power generation system as claimed in claim 3 or 4; 2) judging the stability of the wind power photo-thermal integrated power generation system according to the small signal model of the wind power photo-thermal integrated power generation system; In the step 2), the stability of the wind power photo-thermal integrated power generation system is judged according to the system damping coefficient, and if the system damping coefficient is negative, it is judged that low-frequency oscillation occurs in the system.

6. The wind power and solar thermal integrated power system stability determination system is applied to the wind power and solar thermal integrated power system stability determination method of claim 5, characterized in that, Comprise: a model module containing the small signal model of the wind power photo-thermal integrated power generation system; a judging module for judging the stability of the wind power photo-thermal integrated power generation system according to the small signal model of the wind power photo-thermal integrated power generation system; The model module comprises: a photo-thermal generator set submodule containing the frequency domain small signal model of the photo-thermal generator set; a permanent magnet direct drive wind turbine generator set submodule containing the frequency domain small signal model of the permanent magnet direct drive wind turbine generator set; an equivalent current source and equivalent power grid submodule containing the frequency domain small signal model of the equivalent current source and the frequency domain small signal model of the equivalent power grid.

7. A device for determining the stability of a wind power and solar thermal integrated power generation system, characterized in that: Comprise: a memory; Processor, for calling the computer program of the wind power and solar heat integrated power generation system stability judging method of claim 5 from the memory, executing: establishing the small signal model of the wind power and solar heat integrated power generation system; judging the stability of the wind power and solar heat integrated power generation system according to the small signal model of the wind power and solar heat integrated power generation system.

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