Network construction type and network following type hybrid wind power plant-network frequency response modeling method

Abstract

The invention relates to the technical field of frequency response between a network construction type wind power plant, a network following type wind power plant and a power grid, in particular to a network construction type and network following type hybrid wind power plant-network frequency response modeling method. The method comprises the following steps: S1, establishing a synchronous generator frequency response model according to an electric quantity parameter of a dominant synchronous generator in a power system, a difference adjustment coefficient of a synchronous generator speed regulator, a time constant and a load-damping constant of the power system; s2, calculating the grid following type wind power access proportion eta 1 according to the capacity of the grid following type wind turbine generator in the wind power plant; therefore, the method has the advantages that the frequency response interaction mechanism between the network construction type wind turbine generator and the power grid as well as between the network following type wind turbine generator and the power grid can be elaborated, the frequency stability analysis of a large power grid system is facilitated, and the technical problems that after the network construction type wind turbine generator is merged into the power grid, the frequency response modeling of the power system is difficult, and the quantitative evaluation is difficult are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of frequency response between a grid-building type wind farm, a grid-following type wind farm and a power grid, and in particular to a grid-building type and grid-following type hybrid wind farm-grid frequency response modeling method. Background Art

[0002] In the face of the challenges of global climate change, the "dual carbon" goal of "carbon peak in 2030 and carbon neutrality in 2060" was proposed at the United Nations General Assembly in 2020. New energy power sources are gradually replacing conventional thermal power and will soon become the main power source for the power system.

[0003] At present, conventional energy is connected to the power grid through synchronous generators. The electromagnetic and electromechanical physical properties of synchronous generators determine the frequency and voltage source properties of the power grid. In contrast, the grid-connected characteristics of new energy sources such as wind energy and solar energy are mainly determined by the control characteristics of power electronic converters. At present, wind turbines generally adopt the "grid-following" control method, which requires the synchronous generators in the power grid to operate in a master-slave mode, and lack the ability to support the voltage and transient process of the power grid. It can be seen that building a power system dominated by new energy is not just a simple replacement of traditional thermal power energy by new energy, but must also be able to assume the obligation to establish the voltage of the power system and maintain the real-time energy balance of the system. The "grid-building" wind turbine proposed to address the shortcomings of the "grid-building" wind turbine is currently generally considered to be an effective method for building a new energy-dominated power system. With the implementation and promotion of the application of grid-building wind turbines, most of the current wind farms are in the form of mixed grid-building wind farms and grid-building wind farms. In view of the continuous increase in wind power penetration rate and the continuous decrease in system equivalent inertia worldwide, the "grid-building" control of wind turbines is considered to be an effective way to build a new energy-dominated power system, and is showing a trend of gradually replacing traditional "grid-following" wind turbines.

[0004] However, with the deepening of research on the control of grid-connected wind turbines, there is currently no specific modeling method that can effectively describe the entire process of field-grid frequency response between the wind farm and the power grid after the grid-connected wind turbines are connected to the grid, nor can it accurately explain the frequency response interaction mechanism between the grid-connected wind farm, the grid-following wind farm and the power grid when the grid-connected wind farm and the grid-following wind farm are mixed and connected to the grid.

[0005] The patent document (publication number: CN114977270B) discloses a self-synchronous voltage source full-power conversion wind turbine control system, including: a startup control module for realizing flexible grid-connected startup control without impact current; a steady-state control module for realizing voltage source control in the non-fault state of the power grid; a transient control module for realizing voltage source control in the fault state of the power grid; a transient-stable switching module for realizing seamless switching between steady-state operation mode and transient operation mode; an asymmetric current control module for realizing negative sequence current control under an asymmetric power grid; a harmonic current control module for realizing harmonic current control under a power grid containing background harmonics; a power grid impedance adaptive control module for realizing power grid impedance adaptive control under different short-circuit ratio power grid access scenarios. The invention can realize startup operation, steady-state operation and transient operation control, as well as high-performance stable control in the scenario where the unit is connected to an asymmetric power grid containing background harmonics and a wide range of impedance changes. However, the patent does not analyze the small signal model of the grid-forming wind turbine, and it is impossible to perform stability analysis on the control method.

[0006] The patent document (publication number: CN111396247B) discloses a voltage source wind turbine control method and system considering load and speed constraints. The method and system consider load and speed constraints, including a voltage source converter, a shaft load optimization control loop, a speed optimization control loop and a variable speed pitch control. The voltage source converter outputs f to the shaft load optimization control loop, outputs ΔTf, Pg and ωg to the speed optimization control loop, the variable speed pitch control outputs Tgrd to the speed optimization control loop, the speed optimization control loop outputs Tgrd to an adder, and simultaneously outputs ωg to the shaft load optimization control loop and the variable speed pitch control loop. The shaft load optimization control loop outputs TBd to the adder, and the adder outputs Tgd to the voltage source converter. This invention solves the problem of active power coordination between the main control system and the converter of the voltage source wind turbine, avoiding speed overspeed or underspeed faults; and reducing the load impact of the transmission chain shaft system of the voltage source wind turbine under the grid frequency disturbance condition. Although the invention performs small signal modeling for the aerodynamic part of the grid-forming wind turbine, it does not perform small signal modeling for the active power loop, and cannot perform stability analysis. Summary of the invention

[0007] The purpose of the present invention is to provide a grid-forming and grid-following hybrid wind farm-grid frequency response modeling method, which can explain the frequency response interaction mechanism between grid-forming wind turbines, grid-following wind turbines and the power grid, and is convenient for frequency stability analysis of large power grid systems. It solves the technical problems of difficulty in frequency response modeling and quantitative evaluation of the power system after the grid-forming wind turbines are connected to the power grid.

[0008] To achieve the above object, the present invention provides the following technical solution: a method for modeling the frequency response of a hybrid wind farm-grid of a grid-building type and a grid-following type, comprising the following steps:

[0009] S1: A frequency response model of synchronous generators is established based on the electrical quantity parameters of the dominant synchronous generators in the power system, the regulation coefficient and time constant of the synchronous generator speed regulator, and the load-damping constant of the power system;

[0010] S2: According to the capacity of the grid-connected wind turbines in the wind farm, the grid-connected wind power access ratio η1 is calculated, and the synchronous generator frequency response model in S1 is equivalently transformed according to the access ratio η1 to establish a grid-connected double-fed wind farm-grid frequency response model;

[0011] S3: According to the control strategy of the doubly-fed grid-connected wind turbine, small signal models of the wind turbine shaft system, MPPT link, active power control and electromagnetic power calculation are established respectively, and the frequency response model of the doubly-fed grid-connected wind turbine is integrated and established;

[0012] S4: According to the capacity of the grid-connected wind turbines in the wind farm, the grid-connected wind power access ratio η2 is calculated, and the frequency response model of the double-fed grid-connected wind turbines in S3 is equivalently transformed according to the access ratio η2, and finally added to the grid-following double-fed wind farm-grid frequency response model in S2 to establish a grid-connected and grid-following hybrid wind farm-grid frequency response model;

[0013] S5: Equivalently simplify the grid-forming and grid-following hybrid wind farm-grid frequency response model obtained in S4;

[0014] S6: Perform stability verification in the simplified frequency response model to verify the changes in system parameters and the impact of different degrees of load switching on the system frequency response.

[0015] Preferably, the synchronous generator frequency response model in step S1 includes electrical quantity parameters of the synchronous generator, the adjustment coefficient of the synchronous generator speed regulator, the time constant and the load-damping constant of the power system, which can be expressed as a closed-loop transfer function from the system load small signal change -ΔPL to the grid frequency small signal change Δωsg.

[0016] Preferably, the grid-connected wind power access ratio η1 is calculated in step S2, and an equivalent transformation is performed on the synchronous generator frequency response model in step S1 according to the grid-connected wind power access ratio η1 to establish a grid-connected double-fed wind farm-grid frequency response model.

[0017] Preferably, the grid-type wind turbine shaft system and MPPT link model in step S3 use a transfer function method to represent the change relationship from the small signal change ΔTt of the wind turbine aerodynamic torque to the small signal change ΔTe* of the given value of the electromagnetic torque.

[0018] Preferably, the active power control and electromagnetic power calculation model in step S3 uses a transfer function method to represent the change relationship from the small signal change ΔTe* of the given value of the electromagnetic torque to the small signal change ΔPe of the electromagnetic power of the wind turbine.

[0019] Preferably, the shaft system and MPPT link models of the grid-type wind turbine generator set and the active power control and electromagnetic power calculation models are combined to construct a frequency response model of the doubly-fed grid-type wind turbine generator set.

[0020] Preferably, the calculation of the grid-connected wind power access ratio η2 in step S4 is performed according to the grid-connected wind power access ratio η2, and an equivalent transformation is performed on the basis of the frequency response model of the doubly-fed grid-connected wind turbine unit and the grid-following doubly-fed wind farm-grid frequency response model to establish a grid-connected and grid-following hybrid wind farm-grid frequency response model.

[0021] Preferably, in step S5, based on the equivalent transformation principle, the grid-building type and grid-following type hybrid wind farm-grid frequency response model is equivalently simplified, and a simplified version of the grid-building type and grid-following type hybrid wind farm-grid frequency response model is established to facilitate power system stability analysis.

[0022] Preferably, step S6 includes quantitative analysis and verification of changes in system parameters and the impact of different degrees of load shedding on system frequency response, so as to achieve an accurate description of the frequency response of grid-building and grid-following hybrid wind farms.

[0023] Preferably, the calculation formula of η1 in step S2 is as follows:

[0024]

[0025] Where S WT _following and S SG They represent the installed capacity of grid-connected wind turbines and synchronous generators respectively.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention can explain the frequency response interaction mechanism between grid-building wind farms, grid-following wind farms and power grids, accurately depict the whole process of frequency response in the power system of mixed grid-building wind farms and networking wind farms, facilitate quantitative analysis of the influence of system parameters on frequency response effects, and facilitate frequency stability analysis of large power grid systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The modeling method flow chart of the present invention;

[0029] Figure 2 It is a schematic diagram of the frequency response model of the existing synchronous generator;

[0030] Figure 3 It is a schematic diagram of the grid-following double-fed wind farm-grid frequency response model;

[0031] Figure 4 It is a schematic diagram of the shaft system and MPPT link model of the grid-type wind turbine;

[0032] Figure 5 It is a schematic diagram of the active power control and electromagnetic power calculation model of the grid-type wind turbine;

[0033] Figure 6 It is a schematic diagram of the frequency response model of the doubly-fed grid-connected wind turbine;

[0034] Figure 7 It is a schematic diagram of the grid-building type and grid-following type hybrid wind farm-grid frequency response model;

[0035] Figure 8 This is a schematic diagram of the simplified model process for the frequency response of a doubly-fed grid-connected wind turbine;

[0036] Fig. 9 It is a schematic diagram of the grid-building type and grid-following type hybrid wind farm-grid frequency response model;

[0037] Fig.10 To simplify the schematic diagram of the post-grid type and grid-following type hybrid wind farm-grid frequency response model;

[0038] Fig.11 This is a schematic diagram of a doubly-fed wind farm;

[0039] Fig.12 It is a comparison chart of RTDS simulation results and frequency response model analysis results of the present invention. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] See also Figure 1-Figure 12 As shown, the present invention provides a technical solution:

[0042] A method for modeling the frequency response of a hybrid wind farm-grid of a grid-building type and a grid-following type comprises the following steps:

[0043] S1: A frequency response model of synchronous generators is established based on the electrical quantity parameters of the dominant synchronous generators in the power system, the regulation coefficient and time constant of the synchronous generator speed regulator, and the load-damping constant of the power system;

[0044] S2: According to the capacity of the grid-connected wind turbines in the wind farm, the grid-connected wind power access ratio η1 is calculated, and the synchronous generator frequency response model in S1 is equivalently transformed according to the access ratio η1 to establish a grid-connected double-fed wind farm-grid frequency response model;

[0045] S3: According to the control strategy of the doubly-fed grid-connected wind turbine, small signal models of the wind turbine shaft system, MPPT link, active power control and electromagnetic power calculation are established respectively, and the frequency response model of the doubly-fed grid-connected wind turbine is integrated and established;

[0046] S4: According to the capacity of the grid-connected wind turbines in the wind farm, the grid-connected wind power access ratio η2 is calculated, and the frequency response model of the double-fed grid-connected wind turbines in S3 is equivalently transformed according to the access ratio η2, and finally added to the grid-following double-fed wind farm-grid frequency response model in S2 to establish a grid-connected and grid-following hybrid wind farm-grid frequency response model;

[0047] S5: Equivalently simplify the grid-forming and grid-following hybrid wind farm-grid frequency response model obtained in S4;

[0048] S6: Perform stability verification in the simplified frequency response model to verify the changes in system parameters and the impact of different degrees of load switching on the system frequency response.

[0049] The synchronous generator frequency response model in step S1 includes the electrical quantity parameters of the synchronous generator, the adjustment coefficient of the synchronous generator speed regulator, the time constant and the load-damping constant of the power system, which can be expressed as a closed-loop transfer function from the system load small signal change -ΔPL to the grid frequency small signal change Δωsg.

[0050] The grid-connected wind power access ratio η1 is calculated in step S2, and an equivalent transformation is performed on the synchronous generator frequency response model in step S1 according to the grid-connected wind power access ratio η1 to establish a grid-connected double-fed wind farm-grid frequency response model.

[0051] The grid-type wind turbine shaft system and MPPT link model in step S3 uses a transfer function method to represent the change relationship from the small signal change ΔTt of the wind turbine aerodynamic torque to the small signal change ΔTe* of the given value of the electromagnetic torque.

[0052] The active power control and electromagnetic power calculation model in step S3 uses a transfer function method to represent the change relationship from the small signal change ΔTe* of the given value of the electromagnetic torque to the small signal change ΔPe of the electromagnetic power of the wind turbine.

[0053] The shaft system and MPPT link models of the grid-connected wind turbine set as well as the active power control and electromagnetic power calculation models are combined to construct a frequency response model of the doubly-fed grid-connected wind turbine set.

[0054] The grid-connected wind power access ratio η2 is calculated in step S4, and an equivalent transformation is performed on the basis of the double-fed grid-connected wind turbine frequency response model and the grid-following double-fed wind farm-grid frequency response model according to the grid-connected wind power access ratio η2, so as to establish a grid-connected and grid-following hybrid wind farm-grid frequency response model.

[0055] In step S5, based on the equivalent transformation principle, the grid-building type and grid-following type hybrid wind farm-grid frequency response model is equivalently simplified, and a simplified version of the grid-building type and grid-following type hybrid wind farm-grid frequency response model is established to facilitate power system stability analysis.

[0056] Step S6 includes quantitative analysis and verification of changes in system parameters and the impact of different degrees of load shedding on system frequency response, so as to achieve an accurate description of the frequency response of grid-building and grid-following hybrid wind farms.

[0057] The calculation formula of η1 in step S2 is as follows:

[0058]

[0059] Where S WT _following and S SG They represent the installed capacity of grid-connected wind turbines and synchronous generators respectively.

[0060] Specifically, the frequency response model of the synchronous generator in S1 is as follows: Figure 2As shown, the load small signal change -ΔPL of the system is subtracted from the small signal change ΔPsgm of the input motive force of the synchronous machine to obtain the load power difference ΔPcal, and ΔPcal is input into the forward channel transfer function 1 / 2Hsgs+D that characterizes the synchronous generator rotor motion equation and the system damping effect to obtain the grid frequency small signal change Δωsg, where Hsg represents the inertia constant of the synchronous generator and D represents the load-damping constant. Δωsg is passed through the feedback channel transfer function (1+sT2) / R(1+sT1)(1+sT3) that characterizes the synchronous generator differential control and the speed regulator to obtain the small signal change ΔPsgm of the input motive force of the synchronous machine, where R represents the differential control coefficient of the synchronous generator, and T1, T2, and T3 respectively represent the time constants related to the speed regulator system, thereby forming a complete closed-loop transfer function, which is the existing synchronous generator frequency response model.

[0061] Specifically, the grid-fed double-fed wind farm-grid frequency response model in S2 is as follows: Figure 3 As shown in the figure, in order to reflect the frequency response effect of the grid-following double-fed wind farm, the difference ΔPcal between the system load small signal change -ΔPL and the small signal change ΔPsgm of the synchronous machine input original power is first divided by (1-η1) and then input into the transfer function 1 / 2Hsgs+D to obtain the grid frequency small signal change Δωsg, where η1 represents the grid-following wind power access ratio, and the calculation formula is as follows:

[0062]

[0063] Among them, SWT_following and SSG represent the installed capacity of grid-following wind turbines and synchronous generators, respectively.

[0064] The small signal change of the grid frequency Δωsg is input into the feedback channel transfer function and multiplied by (1-η1). The result is the small signal change of the synchronous machine input motive force ΔPsgm, thus forming a complete closed-loop transfer function. This closed-loop transfer function is the grid-following doubly-fed wind farm-grid frequency response model.

[0065] Specifically, establishing the frequency response model of the doubly-fed grid-connected wind turbine in S3 includes the following steps:

[0066] S31: Establishment of the axis system and MPPT link model of grid-type wind turbines

[0067] like Figure 4As shown in the figure, the purpose of establishing the grid-type wind turbine shaft system and MPPT link model is to obtain the transfer function of the small signal change ΔTe* of the given value of the electromagnetic torque of the rotor side converter. Specifically, in the grid-type wind turbine shaft system model, the difference between the small signal change ΔTt of the wind turbine aerodynamic torque and the small signal change ΔTe of the electromagnetic torque is output as the small signal change Δωr of the generator speed after passing through the transfer function 1 / 2Hts that characterizes the generator rotor motion equation, where Ht represents the moment of inertia of the generator rotor. It represents the partial differential result of aerodynamic torque Tt with respect to speed ωr, Multiplying it by the small signal change Δωr of the generator speed can give the small signal change ΔTt of the wind turbine aerodynamic torque.

[0068] In the MPPT link model of the grid-type wind turbine, the small signal change ΔTe* of the electromagnetic torque given value and the small signal change Δωr of the generator speed satisfy the following relationship:

[0069] ΔT e * =2k opt ω r0 Δω r (2)

[0070] Among them, kopt represents the maximum power utilization factor of the wind turbine, and ωr0 represents the generator speed at the steady-state point.

[0071] S32: Establish active power control and electromagnetic power calculation model of grid-connected wind turbines

[0072] like Figure 5 As shown in the figure, the purpose of establishing the active control and electromagnetic power calculation model of the grid-type wind turbine is to obtain the transfer function of the electromagnetic power small signal ΔPe of the doubly fed grid-type wind turbine. Specifically, in the grid-type active control small signal model, the small signal change ΔTe* of the electromagnetic torque given value is subtracted from the small signal change ΔTe of the electromagnetic torque actual value to obtain the torque difference ΔTe_ref, and the difference between the small signal change Δωvsg of the virtual synchronous angular velocity and the small signal change Δωsg of the grid frequency is multiplied by the virtual inertia coefficient Dvsg to obtain the virtual inertia deviation ΔD; the difference between the torque difference ΔTe_ref and the virtual inertia deviation ΔD is input into the integrator 1 / 2Hvsgs to obtain the small signal change Δωvsg of the virtual synchronous angular velocity, Hvsg represents the virtual inertia coefficient, and the difference between the small signal change Δωvsg of the virtual synchronous angular velocity and the small signal change Δωsg of the grid frequency is input into the integrator ωb / s to obtain the small signal change Δδvsg of the equivalent power angle.

[0073] In the electromagnetic power calculation model of the grid-type wind turbine, the small signal change of the equivalent power angle Δδvsg is multiplied by the power-power angle coefficient kPδ to obtain the small signal change of the electromagnetic power of the wind turbine ΔPe. ΔPe is divided by the generator speed ωr0 representing the steady-state point to obtain the small signal change of the electromagnetic torque ΔTe.

[0074] S33: Combined establishment of frequency response model of doubly-fed grid-connected wind turbines

[0075] The output of step S31 is used as the input of step S32 (both are: small signal change ΔTe* of the given value of electromagnetic torque), and the small signal change ΔTe of the electromagnetic torque in step S32 is used as the input of step S31 to form a closed-loop transfer function, and the frequency response model of the doubly-fed grid-connected wind turbine is established by combination, such as Figure 6 shown.

[0076] Specifically, the grid-connected and grid-following hybrid wind farm-grid frequency response model in S4 is as follows: Figure 7 As shown, the output result ΔP of the frequency response model of the doubly-fed grid-connected wind turbine in step S3 is e Multiplying it by the grid-connected wind power ratio η2, we can get the small signal change of electromagnetic power ΔP of the double-fed grid-connected wind farm. e_WT , where η2 represents the proportion of grid-connected wind power, and the calculation formula is as follows:

[0077]

[0078] Among them, SWT_forming and SSG represent the installed capacity of grid-forming wind turbines and synchronous generators, respectively.

[0079] The sum of ΔPe_WT and the system load change - ΔPL minus the change in the synchronous machine input motive force ΔPsgm is obtained to obtain the load power difference ΔPcal. Substituting this into the calculation, the grid frequency change Δωsg can be obtained.

[0080] So far, the modeling of the grid-building type and grid-following type hybrid wind farm-grid frequency response has been completed. The grid-building type and grid-following type hybrid wind farm-grid frequency response model is as follows: Figure 7 shown.

[0081] Specifically, the simplification of the grid-connected and grid-following hybrid wind farm-grid frequency response models in S5 includes the following two steps:

[0082] S51: Based on the equivalent transformation principle, the frequency response model of the doubly-fed grid-connected wind turbine is simplified

[0083] The small signal change of the grid frequency Δωsg is extracted as the signal input, and the small signal change of the electromagnetic power of the wind turbine is taken as the signal output. Based on the transfer function equivalent transformation principle, the frequency response model of the doubly fed grid-connected wind turbine is simplified. The schematic diagram is shown in the figure. Figure 8 shown.

[0084] Figure 8 In the equation, the relationship between ΔPe and Δωsg can be expressed by the following transfer function:

[0085]

[0086] The meanings of the variables in the above formula are as follows:

[0087]

[0088] S52: Based on the principle of equivalent transformation, the grid-connected and grid-following hybrid wind farm-grid frequency response models are simplified.

[0089] Substitute the simplified frequency response model of the doubly-fed grid-connected wind turbine generator set equivalently simplified in step S51 into Figure 7 The grid-connected and grid-following hybrid wind farm-grid frequency response model shown in the figure is as follows: Fig. 9 The grid-connected and grid-following hybrid wind farm-grid frequency response models are shown.

[0090] Based on the principle of equivalent transformation, Fig. 9 The transfer function represented by is transformed equivalently, and finally the following is sorted out: Fig.10 The simplified grid-connected and grid-following hybrid wind farm-grid frequency response model shown.

[0091] The simplified grid-type and grid-following hybrid wind farm-grid frequency response models can be accurately characterized by a simple closed-loop transfer function, in which the forward channel transfer function 1 / (2Hsgs+D)(1-η1) includes the influence of the equivalent inertia and static damping of the hybrid wind farm on the frequency response results.

[0092] The simplified feedback channel transfer function includes the influence of the dynamic damping of the hybrid wind farm on the frequency response results. The input of the feedback channel transfer function is the small signal change of the grid frequency Δωsg, and the output is the small signal change of the hybrid wind farm equivalent power feedback ΔPdel. ΔPdel and Δωsg satisfy the following relationship:

[0093]

[0094] Specifically, in step S6, Fig.10Stability verification is performed in the simplified frequency response model shown, including but not limited to verifying the changes in system parameters and the impact of different degrees of load shedding on the frequency response of the hybrid wind farm system, and quantitative analysis and verification of power system stability.

[0095] A system simulation model of a hybrid grid-connected wind farm with grid-connected and grid-following wind farms is built in the RTDS real-time digital simulator. The wind farm system structure is as follows: Fig.11 As shown, the total capacity of the grid-type wind turbine is 20MVA, the total capacity of the grid-following wind turbine is 80MVA, and the relevant parameters of the doubly-fed wind turbine are shown in Tables 1 and 2.

[0096] Table 1 Wind turbine parameters

[0097]

[0098] Table 2 Electrical parameters of doubly-fed wind turbine

[0099]

[0100] In order to verify the correctness of the frequency response model proposed in this patent, the system is put into temporary load at the 4th second of operation, and the operation results in the RTDS real-time digital simulator are compared with the analytical results based on the frequency response model of this patent. The comparison results are as follows: Fig.12 shown.

[0101] The small signal variation of electromagnetic torque ΔTe, electromagnetic power ΔPe, generator speed Δωr and virtual synchronous angular velocity Δωvsg of grid-type wind turbines are selected as the main objects for comparison and verification. Fig.12 It can be seen that when the system is temporarily loaded, the electromagnetic torque and electromagnetic power of the grid-type wind turbine both show an obvious inertia response process. The increase in electromagnetic power leads to torque imbalance, which causes the wind turbine speed to drop and further release the rotor kinetic energy. The analytical results of the grid-type and grid-following hybrid wind farm-grid frequency response model based on this patent and the simulation results of RTDS show a high degree of consistency, which fully demonstrates the correctness of this frequency response model.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for modeling the frequency response of a hybrid wind farm of a grid-building type and a grid-following type, characterized by: The following steps are involved: S1: A frequency response model of synchronous generators is established based on the electrical quantity parameters of the dominant synchronous generators in the power system, the regulation coefficient and time constant of the synchronous generator speed regulator, and the load-damping constant of the power system; S2: According to the capacity of the grid-connected wind turbines in the wind farm, the grid-connected wind power access ratio η1 is calculated, and the synchronous generator frequency response model in S1 is equivalently transformed according to the access ratio η1 to establish a grid-connected double-fed wind farm-grid frequency response model; S3: According to the control strategy of the doubly-fed grid-connected wind turbine, small signal models of the wind turbine shaft system, MPPT link, active power control and electromagnetic power calculation are established respectively, and the frequency response model of the doubly-fed grid-connected wind turbine is integrated and established; S4: According to the capacity of the grid-connected wind turbines in the wind farm, the grid-connected wind power access ratio η2 is calculated, and the frequency response model of the double-fed grid-connected wind turbines in S3 is equivalently transformed according to the access ratio η2, and finally added to the grid-following double-fed wind farm-grid frequency response model in S2 to establish a grid-connected and grid-following hybrid wind farm-grid frequency response model; S5: Equivalently simplify the grid-forming and grid-following hybrid wind farm-grid frequency response model obtained in S4; S6: Perform stability verification in the simplified frequency response model to verify the changes in system parameters and the impact of different degrees of load switching on the system frequency response.

2. A grid-building and grid-following hybrid wind farm-grid frequency response modeling method according to claim 1, characterized in that: The synchronous generator frequency response model in step S1 includes the electrical quantity parameters of the synchronous generator, the adjustment coefficient of the synchronous generator speed regulator, the time constant and the load-damping constant of the power system, which can be expressed as a closed-loop transfer function from the system load small signal change -ΔPL to the grid frequency small signal change Δωsg.

3. A grid-building and grid-following hybrid wind farm-grid frequency response modeling method according to claim 1, characterized in that: The grid-connected wind power access ratio η1 is calculated in step S2, and an equivalent transformation is performed on the synchronous generator frequency response model in step S1 according to the grid-connected wind power access ratio η1 to establish a grid-connected double-fed wind farm-grid frequency response model.

4. A grid-building and grid-following hybrid wind farm-grid frequency response modeling method according to claim 1, characterized in that: The grid-type wind turbine shaft system and MPPT link model in step S3 uses a transfer function method to represent the change relationship from the small signal change ΔTt of the wind turbine aerodynamic torque to the small signal change ΔTe* of the given value of the electromagnetic torque.

5. A grid-building and grid-following hybrid wind farm-grid frequency response modeling method according to claim 4, characterized in that: The active power control and electromagnetic power calculation model in step S3 uses a transfer function method to represent the change relationship from the small signal change ΔTe* of the given value of the electromagnetic torque to the small signal change ΔPe of the electromagnetic power of the wind turbine.

6. A grid-building and grid-following hybrid wind farm-grid frequency response modeling method according to claim 5, characterized in that: The shaft system and MPPT link models of the grid-connected wind turbine set as well as the active power control and electromagnetic power calculation models are combined to construct a frequency response model of the doubly-fed grid-connected wind turbine set.

7. A method for modeling the frequency response of a hybrid wind farm-grid of a grid-building type and a grid-following type according to any one of claims 1, 3, and 6, characterized in that: The grid-connected wind power access ratio η2 is calculated in step S4, and an equivalent transformation is performed on the basis of the double-fed grid-connected wind turbine frequency response model and the grid-following double-fed wind farm-grid frequency response model according to the grid-connected wind power access ratio η2, so as to establish a grid-connected and grid-following hybrid wind farm-grid frequency response model.

8. A grid-building and grid-following hybrid wind farm-grid frequency response modeling method according to claim 7, characterized in that: In step S5, based on the equivalent transformation principle, the grid-building type and grid-following type hybrid wind farm-grid frequency response model is equivalently simplified, and a simplified version of the grid-building type and grid-following type hybrid wind farm-grid frequency response model is established to facilitate power system stability analysis.

9. A grid-building and grid-following hybrid wind farm-grid frequency response modeling method according to claim 1, characterized in that: Step S6 includes quantitative analysis and verification of changes in system parameters and the impact of different degrees of load shedding on system frequency response, so as to achieve an accurate description of the frequency response of grid-building and grid-following hybrid wind farms.

10. A grid-building and grid-following hybrid wind farm-grid frequency response modeling method according to claim 1, characterized in that: The calculation formula of η1 in step S2 is as follows: Where S WT _following and S SG They represent the installed capacity of grid-connected wind turbines and synchronous generators respectively.

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