A virtual synchronous vibration suppression bandwidth control method

Abstract

The present invention provides a virtual synchronous vibration suppression bandwidth control method, comprising: obtaining motor parameters for a grid-connected variable-speed wind turbine; calculating initial stiffness values ​​based on the motor parameters; introducing the cubic stiffness of the shaft system based on the initial stiffness values ​​to establish a nonlinear coupling motion model for the grid-connected variable-speed wind turbine; calculating the nonlinear virtual stiffness of the controller using the optimal bandwidth theory based on the initial stiffness values; and determining a nonlinear virtual coupling controller for the variable-speed wind turbine based on the nonlinear virtual stiffness. This method effectively expands the virtual synchronous vibration suppression bandwidth of wind turbines, avoids resonance risks, and improves the grid-connected active support performance for suppressing power oscillations and frequency variations.

Description

Technical Field

[0001] The present invention relates to the technical field of friendly grid-connected control of new energy power systems, and in particular to a virtual synchronous vibration suppression bandwidth control method. Background Art

[0002] In new power systems, the high proportion of power electronic equipment enhances system control potential, but also leads to complex and diverse power oscillation types. Virtual synchronous generators, based on maximum wind and solar power tracking control, enable renewable energy generators to respond to dynamic system changes. However, before the widespread deployment of large-scale wind and photovoltaic power plants, a comprehensive assessment of the operational risks of virtual synchronous control technology is urgently needed. The introduction of additional control inevitably alters the system's oscillation modes. Furthermore, the narrow bandwidth easily creates new resonance points. Virtual synchronous control is unable to adapt to complex oscillation types, which is a pressing issue that needs to be addressed before the deployment of virtual synchronous generators in new power systems. Currently, the shaft coupling between wind turbines and synchronous generators in virtual synchronous operation requires further development. To address the resonance issues associated with virtual synchronous operation, the potential for flexible and controllable shaft coupling between wind turbines and synchronous generators needs to be explored. Nonlinear cubic shaft coupling can be used to eliminate resonance points and expand the bandwidth of wind turbines' ability to suppress system power oscillations, effectively avoiding the risk of additional resonances. This will be key to its suitability for efficient power oscillation suppression in new power systems. Summary of the Invention

[0003] In view of the above problems, the present invention is proposed to provide a virtual synchronous vibration suppression bandwidth control method that overcomes the above problems or at least partially solves the above problems.

[0004] According to one aspect of the present invention, a virtual synchronous vibration suppression bandwidth control method is provided, the control method comprising:

[0005] Obtain the motor parameters of the variable speed wind turbine connected to the grid;

[0006] Calculating an initial stiffness value according to the motor parameters;

[0007] According to the initial stiffness value, the cubic stiffness of the shaft system is introduced to establish a nonlinear coupling motion model of the variable speed wind turbine connected to the grid;

[0008] Calculating the nonlinear virtual stiffness of the controller using the optimal bandwidth theory according to the initial stiffness value;

[0009] A nonlinear virtual coupling controller of the variable speed wind turbine generator set is determined according to the nonlinear virtual stiffness.

[0010] Optionally, the calculating the initial stiffness value according to the motor parameters specifically includes:

[0011] The initial stiffness parameter equations between the synchronous machine and the fan and the system are:

[0012]

[0013] Where k 10 、k 20 、k 30 are the initial stiffness of the generator G1, the wind turbine and the grid, and the initial stiffness between them; E0, E1, V2 are the grid-connected voltages of the generators G0, G1 and the wind turbine; B 10 、B 20 、B 12 are the generator G1, the fan and G0, and the susceptance between them; δ0 is the power angle of G0, δ1 is the power angle of G1, δ 10 is the power angle difference between generators G1 and G0; δ 20 is the power angle difference between the fan and G0.

[0014] Optionally, introducing the cubic stiffness of the shaft system according to the initial stiffness value to establish the nonlinear coupling motion model of the variable speed wind turbine connected to the grid specifically includes:

[0015] Select nonlinear cubic coupling to eliminate the resonance point and expand the bandwidth of the wind turbine's suppression of system power oscillations;

[0016] By utilizing the cubic stiffness coupling, the design contradiction between inertia and damping that is currently prevalent in virtual synchronous machines is coordinated and resolved;

[0017] If the cubic nonlinear coupling term between the fan and the synchronous machine is added, the coupling relationship between the two is ψ(δ1-δ2);

[0018] Set the sinusoidal disturbance signal ΔP = f m sinωt, where f m is the disturbance amplitude, w is the disturbance frequency, t is the disturbance time, and the wind turbine and synchronous machine power angle are replaced by variables: y1=δ1k 10 / f m , y2=(δ2-δ1)k 10 / f m ,have to

[0019]

[0020] Where λ 2 is the linear coupling stiffness of the system, v is the nonlinear cubic stiffness of the system, and the formula includes linear and nonlinear coupling terms; μ = J2 / J1 is the inertia ratio of the fan and synchronous machine;

[0021] Substitute the variables as follows: ω1=(k 10 / J1) 1 / 2 ;ω3=(k 30 / J2) 1 / 2; Ω=ω / ω1, the nonlinear coupling motion model of the doubly fed wind turbine connected to the grid is

[0022]

[0023] The nonlinear virtual coupling controller re-establishes the power coupling relationship between the wind turbine and the grid-connected synchronous generator.

[0024] Optionally, the calculating the nonlinear virtual stiffness of the controller by using the optimal bandwidth theory according to the initial stiffness value specifically includes:

[0025] The iterative method is used to analyze the bandwidth of wind turbines to suppress system oscillations. The initial oscillation amplitude of the synchronous machine is taken as the reference value, and the synchronous machine power angle amplitude is selected in the interval [-1,1] as the wind turbine oscillation suppression area. Let M = 1 + 1 / μ, Λ = μλ 2 , τ=ωt, the iterative form can be simplified to

[0026]

[0027]

[0028] Take the approximate value y1 for y1 and y2 (0) =b1sinτ,y2 (0) =b2sinτ;

[0029] Where b1 and b2 are the amplitude of the synchronous machine's power angle oscillation and the amplitude of the wind turbine's power angle difference during nonlinear coupling; y1 (0) ,y2 (0) are the initial values ​​of iteration respectively, then the initial differential equation y1 (1) ,y2 (1) for

[0030]

[0031]

[0032] Ignoring the influence of the nonlinear duration term in the above formula, that is, the coefficient of sinτ is 0, we get

[0033]

[0034]

[0035] The ratio of the system's oscillation amplitude to the excitation frequency Ω 2 If you want to compare the frequency range of fan oscillation suppression in nonlinear and linear conditions, select the optimal parameters of the two under the same oscillation suppression standard for comparison;

[0036] Extract the nonlinear coefficient of the above formula and let have to

[0037]

[0038] When b1 corresponds to the upper and lower limits of the oscillation suppression interval, the upper limit of the nonlinear coefficient is obtained. and lower limit Relational formula, that is

[0039]

[0040]

[0041] when When the derivative is 0, the corresponding nonlinear parameter has the largest oscillation suppression bandwidth. Ignoring the high-order terms of ω3, we get

[0042]

[0043] Where λ *2 represents the optimal λ under the maximum nonlinear bandwidth 2 ;

[0044] In order to determine the optimal value of the nonlinear stiffness v Substitute b1=0 into It turns out that when the synchronous machine power angle oscillation amplitude is the smallest, the corresponding for

[0045]

[0046] According to the change of oscillation frequency, select the optimal parameter and substitute it into λ *2 and In the paper, the oscillation suppression bandwidth under the nonlinear coupling of the wind turbine is obtained.

[0047] Optionally, determining the nonlinear virtual coupling controller of the variable-speed wind turbine generator set according to the nonlinear virtual stiffness specifically includes:

[0048] The controller includes a nonlinear virtual coupling link, an inertia damping link, a parameter calculation link, and a reactive voltage and vector limiting link;

[0049] The nonlinear virtual coupling link measures the initial power angle δ of the fan 20 and synchronous machine speed ω1, establish the power angle difference Δδ2-Δδ1 between the two generators, and input it into the inertia and damping links through the cubic term and linear additional relationship in the nonlinear coupling motion model;

[0050] The parameter calculation loop is calculated by inputting the initial power angle of the system, the inertia of the two generators J1 and J2, and the operating point frequency Ω of the initial system design, and the optimal linear stiffness coefficient λ *2 and the nonlinear stiffness coefficient v *, input to the nonlinear virtual coupling link;

[0051] The nonlinear virtual coupling controller is used for active power control. The inertia and damping links still use the rotor second-order equations, and a new virtual power angle δ2 of the wind turbine is generated according to the power change and the nonlinear coupling relationship.

[0052] Reactive power control loop measures voltage U meas and reference voltage U ref Perform traditional PI control to generate a new voltage reference value U r , δ2 and U r The two are transformed into a new voltage reference value through vector conversion, which is input to the rotor-side converter through the limiting link.

[0053] The present invention provides a virtual synchronous vibration suppression bandwidth control method, comprising: obtaining motor parameters for a grid-connected variable-speed wind turbine; calculating initial stiffness values ​​based on the motor parameters; introducing the cubic stiffness of the shaft system based on the initial stiffness values ​​to establish a nonlinear coupling motion model for the grid-connected variable-speed wind turbine; calculating the nonlinear virtual stiffness of the controller using the optimal bandwidth theory based on the initial stiffness values; and determining a nonlinear virtual coupling controller for the variable-speed wind turbine based on the nonlinear virtual stiffness. This method effectively expands the virtual synchronous vibration suppression bandwidth of wind turbines, avoids resonance risks, and improves the grid-connected active support performance for suppressing power oscillations and frequency variations.

[0054] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are specifically listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0056] Figure 1 A flow chart of a virtual synchronous vibration suppression bandwidth control method provided by an embodiment of the present invention;

[0057] Figure 2 This is an equivalent circuit diagram of a wind turbine virtual synchronous grid connection provided by an embodiment of the present invention;

[0058] Figure 3 The synchronous machine power angle amplitude under different coupling modes of the wind turbine provided by the embodiment of the present invention;

[0059] Figure 4 A comparison chart of the optimal oscillation suppression bandwidths for linear and nonlinear coupling provided in an embodiment of the present invention;

[0060] Figure 5 A structural diagram of a nonlinear virtual coupling controller for a doubly-fed wind turbine generator system provided by an embodiment of the present invention;

[0061] Figure 6 This is a diagram of the synchronous machine power response under different control conditions when a disturbance source is cut in, as provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0062] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0063] The terms "comprises" and "comprising" and any variations thereof in the description, embodiments, claims and drawings of the present invention are intended to cover non-exclusive inclusions, for example, including a series of steps or units.

[0064] The technical solution of the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0065] like Figure 1 As shown, a virtual synchronous vibration suppression bandwidth control method process includes the following steps:

[0066] Step S102: Calculating the initial stiffness value based on system parameters such as the fan, synchronous machine, and line;

[0067] Step S103: Introducing the cubic stiffness of the shaft system to establish a nonlinear coupling motion model for the grid-connected variable-speed wind turbine;

[0068] Step S104: designing the nonlinear virtual stiffness of the controller using the optimal bandwidth theory and the initial value;

[0069] Step S105: determining a nonlinear virtual coupling controller of the variable speed wind turbine generator system according to the virtual stiffness.

[0070] Figure 2 This is the equivalent circuit diagram of the virtual synchronous grid-connected wind turbine according to the embodiment of the present invention. Taking the double-fed wind turbine as an example, the grid-connected system of the variable speed wind turbine and the active power control structure of the virtual synchronous generator are shown as follows: Figure 2As shown in Figure 1, G1 is a synchronous generator set, which is connected to the double-fed wind turbine DFIG; G0 is used as a reference generator to simulate the power grid; DFIG adjusts the virtual rotor angle δ2 through the rotor-side converter to simulate the active response characteristics of the synchronous generator. The active output is expressed as P w , so it is regarded as a virtual synchronous machine, denoted as G2.

[0071] Under virtual synchronous control, the rotor angles of the wind turbine and synchronous generator change identically, eliminating dynamic power interaction between the units. Power from both the DFIG and G1 flows unidirectionally into the grid, G0. Wind turbines and synchronous generators have similar output power characteristics and exhibit synchronous oscillations. Wind turbines lack independent power angle control capabilities, limiting their power support potential to synchronous operation. Clearly, further improving wind turbine oscillation suppression requires greater independence in wind turbine power angle variation, creating a new power coupling between the shaft systems of the two types of units and increasing energy transfer paths.

[0072] Will Figure 2 The star network is transformed into a triangle network, and the electromagnetic power equations of the two are

[0073]

[0074] The initial stiffness parameter equations between the synchronous machine and the fan and the system can be expressed as follows

[0075]

[0076] Where k 10 、k 20 、k 30 are the initial stiffness of the generator G1, the wind turbine and the grid, and the initial stiffness between them; E0, E1, V2 are the grid-connected voltages of the generators G0, G1 and the wind turbine; B 10 、B 20 、B 12 are the generator G1, the fan and G0, and the susceptance between them; δ0 is the power angle of G0, δ1 is the power angle of G1, δ 10 is the power angle difference between generators G1 and G0; δ 20 is the power angle difference between the fan and G0.

[0077] When the fan has virtual inertia and damping, it can respond to system frequency changes and achieve power regulation with the synchronous machine. The second-order rotor equations of the two are as follows:

[0078]

[0079] Where ω0 is the system speed; D1 is the damping of the synchronous machine G1; J1 and J2 are the inertia of the synchronous machine G1 and the fan DFIG respectively; P m 、P mwis the mechanical power of G1 and DFIG.

[0080] When a disturbance occurs, the linearized small disturbance equation of formula (1) can be expressed as

[0081]

[0082] It can be seen from formula (4) that the coefficient k2 is the proportional coefficient of the power angle difference between the two generators. It can be defined as the coupling stiffness between the wind turbine and the synchronous machine, which represents the linkage relationship between the two generators.

[0083] For the wind turbine virtual synchronous grid-connected model, the small disturbance equation after linearization of Equation (2) can be expressed as

[0084]

[0085] Where Δδ1 and Δδ2 are the power angle changes of the synchronous machine G1 and the fan DFIG, respectively.

[0086] In order to reduce the additional resonance risk of the current wind turbine grid-connected support control, nonlinear cubic coupling is selected to eliminate the resonance point and expand the bandwidth of the wind turbine's suppression of system power oscillations. Using cubic stiffness coupling, the design contradiction between inertia and damping that is currently prevalent in virtual synchronous machines is coordinated and resolved. If the cubic nonlinear coupling term is added between the wind turbine and the synchronous machine, the coupling relationship between the two can be expressed as ψ(δ1-δ2). The sinusoidal disturbance signal ΔP=f is set in the system. m sinωt, where f m is the disturbance amplitude, w is the disturbance frequency, t is the disturbance time, and the wind turbine and synchronous machine power angle are replaced by variables: y1=δ1k 10 / f m , y2=(δ2-δ1)k 10 / f m , we can get

[0087]

[0088] Where λ 2 is the linear coupling stiffness of the system, and v is the nonlinear cubic stiffness of the system. The above formula includes linear and nonlinear coupling terms. μ = J2 / J1 is the inertia ratio of the fan and synchronous machine.

[0089] Substitute the variables as follows: ω1=(k 10 / J1) 1 / 2 ;ω3=(k 30 / J2) 1 / 2 ; Ω=ω / ω1; At this time, the nonlinear coupling motion model of the doubly fed wind turbine connected to the grid can be expressed as

[0090]

[0091] The nonlinear virtual coupling controller re-establishes the power coupling relationship between the wind turbine and the grid-connected synchronous generator. On the basis of ensuring the inertia and damping characteristics of the wind turbine, it further optimizes its oscillation suppression capability and expands the operating range of the wind turbine participating in power oscillation regulation.

[0092] Figure 3 The synchronous machine power angle oscillation amplitude a1 under the three coupling modes of linear and nonlinear cubic coupling and coherent virtual synchronous operation is as follows: Figure 3 As shown. Figure 3 It can be seen that when the wind turbine adopts the virtual synchronous machine model in formula (5) and establishes a linear coupling relationship with the system, if the wind turbine and the synchronous machine do not operate synchronously, the system contains two natural oscillation frequencies. 2 = 0.2 and 1.2, the synchronous generator's power angle oscillation has two resonance points, and the vibration amplitude increases significantly. During synchronous operation, the wind turbine and the synchronous machine have the same natural frequency, and the system still contains a resonance point. However, when the wind turbine establishes a nonlinear coupling relationship with the synchronous machine through the cubic nonlinearity in Equation (7), since the cubic coupling has no natural frequency, the resonance point caused by the natural frequency disappears, effectively avoiding the risk of induced oscillation of the virtual synchronous machine. In addition, compared with the linear coupling of the virtual synchronous machine, the power angle oscillation amplitude is also more significantly suppressed.

[0093] Figure 4 This is a comparison chart of the optimal oscillation suppression bandwidth for linear and nonlinear coupling in an embodiment of the present invention. An iterative method is used to analyze the bandwidth of wind turbine system oscillation suppression. The initial oscillation amplitude of the synchronous machine is used as the reference value, and the synchronous machine power angle amplitude is selected in the interval [-1, 1] as the wind turbine oscillation suppression region. Let M = 1 + 1 / μ, Λ = μλ. 2 , τ=ωt, its iterative form can be simplified to

[0094]

[0095] Take the approximate value y1 for y1 and y2 (0) =b1sinτ,y2 (0) =b2sinτ. Where b1 and b2 are the amplitude of the synchronous machine's power angle oscillation and the amplitude of the power angle difference with the wind turbine during nonlinear coupling; y1 (0) ,y2 (0) are the initial values ​​of iteration respectively, then the initial differential equation y1 (1) ,y2 (1) It can be expressed as

[0096]

[0097]

[0098] Ignoring the influence of the nonlinear duration term in Equation (9), that is, the coefficient of sinτ is 0, we can get

[0099]

[0100] From formula (10), we can know that the system's oscillation amplitude and excitation frequency ratio Ω 2 To compare the frequency range of fan oscillation suppression in nonlinear and linear conditions, it is necessary to select the optimal parameters of the two under the same oscillation suppression standard for comparison.

[0101] Extract the nonlinear coefficient of formula (10), let have to

[0102]

[0103] When b1 corresponds to the upper and lower limits of the oscillation suppression interval, the upper and lower limit relationship of the nonlinear coefficient can be obtained, that is,

[0104]

[0105]

[0106] when When the derivative is 0, the corresponding nonlinear parameter has the largest oscillation suppression bandwidth. Ignoring the high-order terms of ω3, we can get

[0107]

[0108] Where λ *2 represents the optimal λ under the maximum nonlinear bandwidth 2 At the same time, in order to determine the optimal value of the nonlinear stiffness v Substitute b1=0 into It can be obtained that when the synchronous machine power angle oscillation amplitude is the minimum, the corresponding as follows

[0109]

[0110] According to the change of oscillation frequency, select the optimal parameter and substitute it into λ *2 and In the paper, the oscillation suppression bandwidth under the nonlinear coupling of the wind turbine is obtained.

[0111] When ω3 2= 0.1, the width of power angle oscillation suppression is compared after optimal parameter design of linear and nonlinear coupling between the fan and the system synchronous machine. At the same design frequency, nonlinear coupling has a wider oscillation suppression bandwidth than linear coupling. However, both bandwidths are related to the magnitude of the fan's natural oscillation frequency ω3. As ω3 increases, the range of system oscillation suppression during nonlinear coupling decreases, while the oscillation suppression frequency during linear coupling increases. Therefore, for fans with larger virtual inertia J2, ω3 decreases relatively, and the nonlinear coupling method has a wider suppression frequency bandwidth.

[0112] Figure 5 This is a structural diagram of the nonlinear virtual coupling controller of the doubly-fed wind turbine according to an embodiment of the present invention. The controller mainly includes a nonlinear virtual coupling link, an inertia damping link, a parameter calculation link, and a reactive voltage and vector limit link. The nonlinear virtual coupling link measures the initial power angle δ of the wind turbine. 20 The power angle difference Δδ2-Δδ1 between the two generators is established by taking the cubic term and the linear additive relationship in equation (7) into account. The parameter calculation loop calculates the optimal linear stiffness coefficient λ by inputting the initial power angle of the system, the inertias J1 and J2 of the two generators, and the operating point frequency Ω of the initial system design using the design methods of equations (14) and (15). *2 and the nonlinear stiffness coefficient v * , which is input into the nonlinear virtual coupling link. The parameter calculation link ensures the optimal suppression bandwidth and oscillation suppression effect of the virtual coupling controller.

[0113] The proposed nonlinear virtual coupling controller is mainly aimed at active power control. The inertia and damping links still use the rotor second-order equations. The new virtual power angle δ2 of the wind turbine is generated according to the power change and the nonlinear coupling relationship. The reactive control loop measures the voltage U meas and reference voltage U ref Perform traditional PI control to generate a new voltage reference value U r , δ2 and U r The two are transformed into a new voltage reference value through vector conversion, which is input to the rotor side converter through the limiting link. Figure 5 As shown in the figure, the nonlinear virtual coupling controller re-establishes the power coupling relationship between the doubly fed wind turbine and the grid-connected synchronous generator. On the basis of ensuring the inertia and damping characteristics of the wind turbine, it further optimizes its oscillation suppression capability and expands the operating range of the wind turbine participating in power oscillation regulation.

[0114] IEEE 3-machine 9-node simulation system with high wind power penetration. The system includes a wind farm (100 x 2MWDFIG wind turbines) and three thermal power plants (G1, G2, and G3) with capacities of 300MW, 192MW, and 126MW respectively. The wind farm and thermal power plants are considered equivalent units. Load L A , L B , and L C The capacities are 185MW, 120MW, and 130MW respectively. The wind turbine DFIG is connected to the grid in parallel with generator G2 via busbar B7, resulting in a wind power penetration rate of approximately 32%.

[0115] Figure 6 This is the power response of the synchronous machine under different control when the disturbance source is cut in according to the embodiment of the present invention. In order to verify the accuracy of the theory and the oscillation suppression effect of the nonlinear virtual coupling control, the 2.0s Figure 6 The medium load LA generates a sinusoidal power oscillation with a frequency of 0.9Hz and an amplitude of 10MW. The disturbance is removed after 25s. The wind turbine adopts traditional maximum power tracking, virtual synchronization, nonlinear virtual coupling control and damping controller for comparison. The simulation results are shown in Figure 2. Figure 6 shown.

[0116] In order to observe the oscillation of the system, we use Figure 6 The envelope of the power oscillation amplitude in (a) represents the power oscillation variation, e.g. Figure 6 (b) shown. Figure 6 When the medium disturbance source was connected at 2.0s, the power of synchronous generator G2 experienced amplified oscillations when both maximum power and virtual synchronous control were used. The power oscillated from an initial 123MW to 187MW and 163MW, respectively. Synchronous resonance was observed in both control modes. Although the damping term in the virtual synchronous generator can somewhat suppress the oscillation amplitude, the system still oscillated violently. Introducing damping control into the wind turbine reduced the synchronous resonance amplitude to 141MW. While this improved the oscillation amplitude, damping control alone cannot guarantee the system's inertia characteristics. The coordination between virtual inertia and damping requires further discussion.

[0117] The nonlinear virtual coupling control method proposed in the present invention changes the inherent oscillation frequency characteristics of the fan by establishing a nonlinear coupling relationship between the fan and the synchronous machine. Figure 6 As shown in the figure, the system no longer experiences synchronous resonance, the oscillation amplitude is less than 2 MW, and the system quickly returns to a stable state within 2 s after the disturbance is removed. The nonlinear coupling significantly improves the system stability and oscillation suppression capability, while avoiding the risk of synchronous oscillation.

[0118] Beneficial effects: The present invention explores the potential for flexible and controllable shaft systems between wind turbines and synchronous machines by introducing a cubic nonlinear shaft coupling relationship between the wind turbine and the synchronous machine, and establishes a two-degree-of-freedom system motion model based on the nonlinear coupling of the unit. On this basis, the oscillation suppression bandwidth of the virtual synchronous machine is derived when the wind turbine and the synchronous machine are linearly and nonlinearly coupled, respectively. Combined with the optimal bandwidth theory, the controller parameters are optimized and a virtual synchronous vibration suppression bandwidth control method based on the nonlinear virtual coupling of the wind turbine is proposed. Compared with the traditional virtual synchronous machine, the proposed controller can expand the oscillation suppression bandwidth of the wind turbine and significantly improve its grid-connected support performance in suppressing power oscillations and frequency changes.

[0119] The above specific implementation methods further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific implementation methods of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A virtual synchronous vibration suppression bandwidth control method, characterized in that: The control method includes: Obtain the motor parameters of the variable speed wind turbine connected to the grid; The initial stiffness value is calculated based on the motor parameters, specifically: The initial stiffness parameter equations between the synchronous machine and the fan and the system are: Where k 10 、k 20 、k 30 are the initial stiffness of the generator G1, the wind turbine and the grid, and the initial stiffness between them; E0, E1, V2 are the grid-connected voltages of the generators G0, G1 and the wind turbine; B 10 、B 20 、B 12 are the generator G1, the fan and G0, and the susceptance between them; δ0 is the power angle of G0, δ1 is the power angle of G1, δ 10 is the power angle difference between generators G1 and G0; δ 20 is the power angle difference between the fan and G0; According to the initial stiffness value, the cubic stiffness of the shaft system is introduced to establish a nonlinear coupling motion model for the grid-connected variable-speed wind turbine generator set, specifically: Select nonlinear cubic coupling to eliminate the resonance point and expand the bandwidth of the wind turbine's suppression of system power oscillations; By utilizing the cubic stiffness coupling, the design contradiction between inertia and damping that is currently prevalent in virtual synchronous machines is coordinated and resolved; If the cubic nonlinear coupling term between the fan and the synchronous machine is added, the coupling relationship between the two is ψ(δ1-δ2); Set the sinusoidal disturbance signal ΔP = f m sinωt, where f m is the disturbance amplitude, w is the disturbance frequency, t is the disturbance time, and the wind turbine and synchronous machine power angle are replaced by variables: y1=δ1k 10 / f m , y2=(δ2-δ1)k 10 / f m ,have to Where λ 2 is the linear coupling stiffness of the system, v is the nonlinear cubic stiffness of the system, and the formula includes linear and nonlinear coupling terms; μ = J2 / J1 is the inertia ratio of the fan and synchronous machine; Substitute the variables as follows: ω1=(k 10 / J1) 1 / 2 ;ω3=(k 30 / J2) 1 / 2 ; Ω1=1 / ω1; Ω=ω / ω1, the nonlinear coupling motion model of the doubly fed wind turbine connected to the grid is The nonlinear virtual coupling controller re-establishes the power coupling relationship between the wind turbine and the grid-connected synchronous generator; Calculating the nonlinear virtual stiffness of the controller using the optimal bandwidth theory according to the initial stiffness value; A nonlinear virtual coupling controller of the variable speed wind turbine generator set is determined according to the nonlinear virtual stiffness.

2. A virtual synchronous vibration suppression bandwidth control method according to claim 1, characterized in that: The calculating of the nonlinear virtual stiffness of the controller by using the optimal bandwidth theory according to the initial stiffness value specifically includes: The iterative method is used to analyze the bandwidth of wind turbines to suppress system oscillations. The initial oscillation amplitude of the synchronous machine is taken as the reference value, and the synchronous machine power angle amplitude is selected in the interval [-1,1] as the wind turbine oscillation suppression area. Let M = 1 + 1 / μ, Λ = μλ 2 , τ=ωt, the iterative form can be simplified to Take the approximate value y1 for y1 and y2 (0) =b1sinτ,y2 (0) =b2sinτ; Where b1 and b2 are the amplitude of the synchronous machine's power angle oscillation and the amplitude of the wind turbine's power angle difference during nonlinear coupling; y1 (0) ,y2 (0) are the initial values ​​of iteration, then the initial differential equation y1 (1) ,y2 (1) for Ignoring the influence of the nonlinear duration term in the above formula, that is, the coefficient of sinτ is 0, we get The ratio of the system's oscillation amplitude to the excitation frequency Ω 2 If you want to compare the frequency range of fan oscillation suppression in nonlinear and linear conditions, select the optimal parameters of the two under the same oscillation suppression standard for comparison; Extract the nonlinear coefficient of the above formula and let have to When b1 corresponds to the upper and lower limits of the oscillation suppression interval, the upper limit of the nonlinear coefficient is obtained. and lower limit Relational, when When the derivative is 0, the corresponding nonlinear parameter has the largest oscillation suppression bandwidth. Ignoring the high-order terms of ω3, we get Where λ *2 represents the optimal λ under the maximum nonlinear bandwidth 2 ; In order to determine the optimal value of the nonlinear stiffness v Substitute b1=0 into It turns out that when the synchronous machine power angle oscillation amplitude is the smallest, the corresponding for According to the change of oscillation frequency, select the optimal parameter and substitute it into λ *2 and In the paper, the oscillation suppression bandwidth under the nonlinear coupling of the wind turbine is obtained.

3. A virtual synchronous vibration suppression bandwidth control method according to claim 2, characterized in that: Determining the nonlinear virtual coupling controller of the variable speed wind turbine generator set according to the nonlinear virtual stiffness specifically includes: The controller includes a nonlinear virtual coupling link, an inertia damping link, a parameter calculation link, and a reactive voltage and vector limiting link; The nonlinear virtual coupling link measures the initial power angle δ of the fan 20 and synchronous machine speed ω1, establish the power angle difference Δδ2-Δδ1 between the two generators, and input it into the inertia and damping links through the cubic term and linear additional relationship in the nonlinear coupling motion model; The parameter calculation loop is calculated by inputting the initial power angle of the system, the inertia of the two generators J1 and J2, and the operating point frequency Ω of the initial system design, and the optimal linear stiffness coefficient λ *2 and the nonlinear stiffness coefficient v * , input to the nonlinear virtual coupling link; The nonlinear virtual coupling controller is used for active power control. The inertia and damping links still use the rotor second-order equations, and a new virtual power angle δ2 of the wind turbine is generated according to the power change and the nonlinear coupling relationship. Reactive power control loop measures voltage U meas and reference voltage U ref Perform traditional PI control to generate a new voltage reference value U r , δ2 and U r The two are transformed into a new voltage reference value through vector conversion, which is input to the rotor-side converter through the limiting link.

Images