CN113937826B - Double-fed fan self-adaptive frequency modulation control system and method based on critical oscillation wind speed - Google Patents
Double-fed fan self-adaptive frequency modulation control system and method based on critical oscillation wind speed Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/48—Controlling the sharing of the in-phase component
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
- H02J3/241—The oscillation concerning frequency
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
- H02P9/007—Control circuits for doubly fed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/28—The renewable source being wind energy
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P2101/00—Special adaptation of control arrangements for generators
- H02P2101/15—Special adaptation of control arrangements for generators for wind-driven turbines
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Abstract
The invention discloses a doubly-fed wind turbine self-adaptive frequency modulation control system and method based on critical oscillation wind speed, wherein a doubly-fed wind turbine DFIG 1 Adaptive switching of a virtual synchronous generator and a droop control strategy is utilized to adapt to frequency modulation requirements at different running wind speeds; specifically, a small signal model of the fan system under virtual synchronous control is established according to control parameters of the system, critical oscillation wind speed of the system is calculated, and the actual running wind speed and the critical oscillation wind speed of the system are compared to reasonably switch between virtual synchronous machine control and droop control. The self-adaptive frequency modulation control system and method for the doubly-fed wind turbine based on the critical oscillation wind speed are beneficial to the doubly-fed wind turbine to adapt to different wind speeds, and the frequency modulation effect is improved on the premise of reducing the risk of system oscillation instability.
Description
Technical Field
The invention relates to the technical field of power generation system control, in particular to a doubly-fed wind turbine self-adaptive frequency modulation control system and method based on critical oscillation wind speed.
Background
With the large-scale incorporation of high-proportion renewable energy sources, the influence of the access of large-scale wind turbines on the transient characteristics of the system is paid attention to. At present, in order to obtain the maximum energy utilization rate, various types of grid-connected converters of wind turbines adopt a power regulation mode independent of a power grid, so that the power control of the converters is decoupled from the frequency of the power grid, and the doubly-fed wind power generator (Doubly fed Induction Generator, DFIG) becomes a main stream type of a wind power generation market due to the advantages of high wind energy conversion efficiency, simplicity in grid connection, low cost and the like. At present, in order to obtain the maximum energy utilization rate, various wind turbine grid-connected converters adopt a power regulation mode independent of a power grid, so that the coupling relation between the rotating speed of a rotor and the frequency of a system is not generated, the rotational inertia of a fan is zero, and the frequency modulation capability of the system can be obviously weakened by large-scale wind power connection. The wind power active participation system frequency adjustment is a necessary choice for ensuring the safe and stable operation of the power system after large-scale grid connection of wind power. In order to simplify the calculation analysis, the control of the fan mostly considers the operation mode when the wind speed is constant in modeling, and the actual critical oscillation wind speed is continuously changed along with the fluctuation of the wind speed. At different operating wind speeds, different frequency modulation control strategies behave differently in terms of frequency stability and output power oscillations. Aiming at different influences of the running state of the fan on frequency modulation characteristics of different controls, a proper frequency modulation controller is selected according to the critical oscillation wind speed, so that the frequency modulation capability and stability of a fan system are improved. Therefore, it is necessary to provide a doubly-fed wind turbine multi-mode adaptive frequency modulation control method based on critical oscillation wind speed.
Disclosure of Invention
The invention aims to provide a doubly-fed wind machine self-adaptive frequency modulation control system and method based on critical oscillation wind speed, which are used for reasonably switching between virtual synchronous generator control and droop control based on the magnitude relation between actual operation wind speed and critical oscillation wind speed by detecting the operation state of a system, and improving the inertial response and power supporting capacity of a wind machine system on the premise of avoiding system oscillation instability and fully ensuring system stability.
In order to achieve the above object, the present invention provides the following solutions:
a doubly-fed wind machine self-adaptive frequency modulation control system based on critical oscillation wind speed comprises: synchronous generator G 1 Synchronous generator G 2 DFIG of doubly-fed wind turbine generator 1 Grid-connected inverter and transformer T 1 Transformer T 2 Transformer T 3 Load L 1 Load L 2 Load L 3 Bus bar B1, bus bar B2, bus bar B3, bus bar B4, impedance B 1 Impedance b 2 And impedance b 3 Synchronous generator G 1 Through a transformer T 1 Connected to bus B1 via impedance B 1 Connected to bus B4, synchronous generator G 2 Through a transformer T 2 Connected to bus B2 via impedance B 2 Connected to bus B4, doubly-fed wind generator DFIG 1 Sequentially pass through a grid-connected inverter and a transformer T 3 Connected to bus B3 via impedance B 3 Connected to bus B4, load L 1 And load L 3 Direct accessBus B4, load L 2 The direct access bus B1 is connected with a conversion controller, wherein virtual synchronization and droop self-adaptive switching control strategy based on critical oscillation wind speed is adopted in the conversion controller, so that control of a doubly-fed wind turbine grid-connected inverter is realized, and the doubly-fed wind turbine DFIG is realized 1 Adaptive switching of the virtual synchronous generator and droop control strategy is utilized to accommodate frequency modulation requirements at different operating wind speeds.
The invention also provides a doubly-fed wind machine self-adaptive frequency modulation control method based on the critical oscillation wind speed, which is applied to the doubly-fed wind machine self-adaptive frequency modulation control system based on the critical oscillation wind speed, and comprises the following steps:
s1, establishing a fan system small signal model comprising doubly-fed fan prime motor control and virtual synchronous generator control, and converting the fan system small signal model into a state space matrix form;
s2, calculating critical oscillation wind speed according to control system parameters by using the state space matrix of the fan system obtained in the S1;
s3, detecting the power grid frequency omega of the control system in real time by using a phase-locked loop technology m ；
S4, judging the grid frequency deviation delta omega at the grid connection point of the rotor converter at the DFIG1 side of the doubly-fed wind turbine generator m Whether or not the allowable fluctuation range Δω is exceeded 0 The method comprises the steps of carrying out a first treatment on the surface of the If yes, executing the step S3, and if not, executing the step S1;
s5, detecting the running wind speed v of the control system in real time w Dynamically identifying the running state of the doubly-fed wind generator DFIG 1;
s6, judging the running wind speed v w Whether or not it is greater than the critical oscillation wind speed v ov If yes, executing the step S7, and if not, executing the step S8;
s7, switching a strategy of the virtual synchronous generator to control the doubly-fed fan to participate in system frequency adjustment;
s8, controlling the doubly-fed fan to participate in system frequency adjustment by switching the droop strategy;
s9, performing frequency modulation control by utilizing the control strategy selected in the step S7 or the step S8, and judging whether the power grid frequency of the control system is recovered; if not, returning to the step S3, and if yes, ending the frequency modulation control.
Further, in the step S1, a fan system small signal model including a doubly-fed fan prime mover control and a virtual synchronous generator control is established and converted into a state space matrix form, which specifically includes:
virtual inertia control is introduced into a doubly-fed fan control algorithm based on a synchronous generator set rotor motion equation, and disturbance on the power grid side, omega, is not considered g For the angular frequency measurement of the system, a large deviation exists due to the limitation of the phase-locked loop technology, and the angular frequency reference value omega is generally used ref Instead, let the angular frequency measurement of the system change by an amount Δω g =0, resulting in a fan system small signal model:
due to Deltaomega m =sΔθ, the above formula is sorted into a higher order differential equation of Δθ:
s 4 Δθ+a 1 s 3 Δθ+a 2 s 2 Δθ+a 3 sΔθ+a 4 Δθ＝0
wherein ：
arranging the small signal model into a state space matrix form:
wherein ,
the state variable x is:
since the disturbance on the grid side is not considered, the input u=0, b=0;
wherein ,Kω Is a frequency droop control coefficient; j and D are virtual inertia coefficient and damping coefficient respectively; lambda (lambda) opt Is the optimal tip speed ratio; r is the radius of the wind wheel; h is the inherent inertia time constant of the doubly-fed wind turbine generator; k (k) pv The ratio coefficient is the rotation speed controller; k (k) iv Integrating the coefficient for the rotating speed controller; e is the output voltage of VSG; u is the grid voltage; θ is the impedance angle, Z is the system impedance; v w0 Is the steady state operating point wind speed.
Further, the step S2 of calculating the critical oscillation wind speed according to the control system parameters by using the state space matrix of the fan system obtained in the step S1 specifically includes:
by solving the characteristic root of a high-order differential equation of a small signal model of the fan system, taking the wind speed corresponding to the characteristic root with the imaginary part being zero as the critical oscillation wind speed v ov The formula is:
according to the parameters of the control system, calculating and obtaining the critical oscillation wind speed v by using a formula ov And taking the comparison condition of the monitored real-time wind speed and the critical oscillation wind speed as the basis of the frequency modulation control mode selection of the doubly-fed wind turbine.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects: according to the doubly-fed wind machine self-adaptive frequency modulation control system and method based on the critical oscillation wind speed, a small signal model containing wind speed variation is established according to a doubly-fed wind machine virtual synchronous control schematic diagram, the small signal model is converted into a state space matrix form, the critical oscillation wind speed is calculated, the frequency modulation capacity is exerted to the greatest extent in order to avoid system oscillation instability, and the frequency modulation strategy is reasonably switched in virtual synchronous generator control and droop control according to the magnitude relation between the critical oscillation wind speed and the running wind speed; the invention is beneficial to the double-fed wind turbine generator to adapt to different wind speeds, and improves the frequency modulation capability and the power supporting capability of the double-fed wind turbine generator on the premise of reducing the risk of system oscillation instability.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a simulation topology structure diagram of a doubly-fed wind turbine adaptive frequency modulation control system based on critical oscillation wind speed in an embodiment of the invention;
FIG. 2 is a flow chart of a doubly-fed wind machine adaptive frequency modulation control method based on critical oscillation wind speed according to an embodiment of the present invention;
FIG. 3a is a schematic diagram of a droop control of a doubly-fed wind turbine according to an embodiment of the present invention;
FIG. 3b is a schematic diagram of a doubly-fed wind turbine virtual synchronous generator control according to an embodiment of the present invention;
FIG. 4 is a graph of maximum power tracking control operation of a doubly-fed wind turbine generator according to an embodiment of the invention;
FIG. 5 is a diagram of a control small signal model of a doubly-fed wind turbine virtual synchronous generator according to an embodiment of the present invention;
FIG. 6a is a trace of a characteristic root of a VSG control system when wind speeds take different values according to an embodiment of the present invention;
FIG. 6b is a graph showing the root trajectories of the droop control system according to the embodiment of the present invention for wind speeds at different values;
FIG. 7 is a schematic diagram of adaptive frequency modulation control of a doubly-fed wind turbine based on critical oscillation wind speed in accordance with an embodiment of the present invention;
FIG. 8a is a graph showing frequency variation versus different control modes below a critical wind speed according to an embodiment of the present invention;
FIG. 8b is a graph showing the output power variation versus the critical wind speed for different control modes according to the embodiment of the present invention;
FIG. 9a is a graph showing the frequency variation of different control modes above the critical wind speed according to the embodiment of the present invention;
FIG. 9b is a graph showing the output power variation versus the critical wind speed in different control modes according to the embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention aims to provide a doubly-fed wind machine self-adaptive frequency modulation control system and method based on critical oscillation wind speed, which are used for reasonably switching between virtual synchronous generator control and droop control based on the magnitude relation between actual operation wind speed and critical oscillation wind speed by detecting the operation state of a system, and improving the inertial response and power supporting capacity of a wind machine system on the premise of avoiding system oscillation instability and fully ensuring system stability.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
As shown in FIG. 1, the doubly-fed wind machine adaptive frequency modulation control system based on critical oscillation wind speed provided by the invention comprises a synchronous generator G 1 Synchronous generator G 2 DFIG of doubly-fed wind turbine generator 1 Grid-connected inverter and transformer T 1 Transformer T 2 Transformer T 3 Load L 1 Load L 2 Load L 3 Bus bar B1, bus bar B2, bus bar B3, bus bar B4, impedance B 1 Impedance b 2 And impedance b 3 Synchronous generator G 1 Through a transformer T 1 Connected to bus B1 via impedance B 1 Connected to bus B4, synchronous generator G 2 Through a transformer T 2 Connected to bus B2 via impedance B 2 Connected to bus B4, doubly-fed wind generator DFIG 1 Sequentially pass through a grid-connected inverter and a transformer T 3 Connected to bus B3 via impedance B 3 Connected to bus B4, load L 1 And load L 3 Directly connected with bus B4 and load L 2 The direct access bus B1 is connected with a conversion controller, wherein virtual synchronization and droop self-adaptive switching control strategy based on critical oscillation wind speed is adopted in the conversion controller, so that control of a doubly-fed wind turbine grid-connected inverter is realized, and the doubly-fed wind turbine DFIG is realized 1 Adaptive switching of the virtual synchronous generator and droop control strategy is utilized to accommodate frequency modulation requirements at different operating wind speeds.
As shown in fig. 2, the invention further provides a doubly-fed wind machine adaptive frequency modulation control method based on critical oscillation wind speed, which is applied to the doubly-fed wind machine adaptive frequency modulation control system based on critical oscillation wind speed, and comprises the following steps:
s1, establishing a fan system small signal model comprising doubly-fed fan prime motor control and virtual synchronous generator control, and converting the fan system small signal model into a state space matrix form;
s2, calculating critical oscillation wind speed according to control system parameters by using the state space matrix of the fan system obtained in the S1;
s3, detecting the power grid frequency omega of the control system in real time by using a phase-locked loop technology m ；
S4, judging the grid frequency deviation delta omega at the grid connection point of the rotor converter at the DFIG1 side of the doubly-fed wind turbine generator m Whether or not the allowable fluctuation range Δω is exceeded 0 The method comprises the steps of carrying out a first treatment on the surface of the If yes, executing the step S3, and if not, executing the step S1;
s5, detecting the running wind speed v of the control system in real time w Dynamically identifying the running state of the doubly-fed wind generator DFIG 1;
s6, judging the running wind speed v w Whether or not it is greater than the critical oscillation wind speed v ov If yes, executing the step S7, and if not, executing the step S8;
s7, switching a strategy of the virtual synchronous generator to control the doubly-fed fan to participate in system frequency adjustment;
s8, controlling the doubly-fed fan to participate in system frequency adjustment by switching the droop strategy;
s9, performing frequency modulation control by utilizing the control strategy selected in the step S7 or the step S8, and judging whether the power grid frequency of the control system is recovered; if not, returning to the step S3, and if yes, ending the frequency modulation control.
FIG. 3a is a schematic diagram of a doubly-fed wind turbine droop control according to an embodiment of the present invention. The active-frequency control equation is obtained according to the basic principle of droop control:
P ref -K p (ω-ω ref )＝P m (1)
FIG. 3b is a schematic diagram of a doubly-fed wind turbine virtual synchronous generator control according to an embodiment of the present invention. Virtual inertia control is introduced into a doubly-fed fan control algorithm based on a synchronous generator set rotor motion equation, and an active-frequency control equation of a doubly-fed fan virtual synchronous generator can be obtained:
take j=j×ω m, wherein ωg For the angular frequency measurement of the system, a large deviation exists due to the limitation of the phase-locked loop technology, and the angular frequency reference value omega is generally used ref Instead of.
The above method can be simplified into:
wherein ,Pref And P e Respectively an active power reference value and an output power; j and D are virtual inertia coefficient and damping coefficient, omega m The angular frequency is output for the system.
FIG. 4 is a graph showing maximum power tracking control operation of a doubly-fed wind turbine according to an embodiment of the present invention, with a rotor speed range of typically 0.7 pu. Ltoreq.ω r Less than or equal to 1.2pu, dividing the operation interval: 1) Low wind speed region, curve AB, rotor speed is minimum ω min The method comprises the steps of carrying out a first treatment on the surface of the 2) Middle wind speed region, curve BC, wind energy conversion efficiency coefficient C P Optimally, the wind speed is positively correlated with the rotor speed; 3) High wind speed region, curveCD, rotor speed reaches maximum value omega max When the wind speed is increased and the rotating speed of the rotor is kept constant and the maximum power tracking control is adopted by the fan, the kinetic energy of the wind wheel of the fan at the initial moment of system frequency change can be expressed as:
in the formula ,JD Is the rotational inertia omega of the fan r0 The initial rotation speed of the fan.
In the stage of providing power for the fan, the rotating speed of the fan is omega r0 Reduced to omega r1 The active power support provided by releasing the kinetic energy of the wind wheel in the process can be calculated according to the change value of the rotating speed, and is as follows:
for a doubly-fed asynchronous wind generator, the minimum value of the rotational speed of the wind wheel is generally 0.7pu, so that the power support limit provided by releasing the kinetic energy of the wind wheel at the fan is not all initial kinetic energy, and the kinetic energy release limit can be calculated according to the lower rotational speed limit of the doubly-fed fan, and is as follows:
in the formula ,ΔEDmax For maximum releasable kinetic energy, ω min Is the lower rotation speed limit.
Maximum energy of frequency modulation can be participated in by fans in different wind speed intervals:
in the low wind speed region, ΔE Dmax When the speed is 0, the fan system is unstable due to too low rotating speed caused by excessive kinetic energy release; in the high wind speed region, the rotating speed of the fan reaches the maximum value and is kept constant,the available capacity reaches the maximum, if the actual released kinetic energy of the system is larger than the maximum releasable kinetic energy in the interval, the system is unstable, namely the control parameter is unreasonable to set at any wind speed. Based on the analysis, the invention establishes a small signal model controlled by the doubly-fed fan virtual synchronous generator in a middle output area, namely a maximum power tracking area.
Fig. 5 is a diagram of a doubly-fed fan virtual synchronous generator control small signal model, taking a maximum power tracking interval as an example, and assuming that the fan is operated at an optimal operating point before disturbance, the system is in a balanced state:
P in0 ＝P e0 ＝k opt ω r0 3 (8)
in the formula ,Pin0 For steady-state input of mechanical power, P e0 To steady-state output electromagnetic power, k opt The maximum power tracking coefficient.
The influence of the change of the rotating speed and the running state of the pitch angle of the fan on the input mechanical power is not considered, and the wind speed is not changed during disturbance, namely the change quantity delta P of the input mechanical power in =0. The change amount of the active power reference value can be known according to the small signal model as follows:
in the formula ,ΔPref 、ΔP e The variation of the reference power and the output power are respectively, H represents the inherent inertia time constant k of the mechanical system of the doubly-fed fan pv 、k iv The proportion and integral coefficient omega of the rotating speed controller are respectively r0 The rotor speed is the stable operating point before disturbance.
Wherein the corresponding relation between wind speed and rotating speed is as follows:
in the formula ,λopt For optimum tip speed ratio v w0 For stabilizing the wind speed of the working point, R is the radius of the wind wheel.
The electromagnetic power controlled by the virtual synchronous generator is as follows:
the VSG output power is converted into a small signal model:
obtaining a small signal model of the virtual synchronous generator according to a control equation of the virtual synchronous generator in the formula (3):
ΔP ref -ΔP e ＝JΔω m +(D+K ω )Δω m (13)
substituting the formulas (9), (10) and (12) into the formula (13) to obtain the product:
due to Deltaomega m =sΔθ, the above equation can be formulated as a higher order differential equation for Δθ:
s 4 Δθ+a 1 s 3 Δθ+a 2 s 2 Δθ+a 3 sΔθ+a 4 Δθ＝0 (15)
wherein ,
the small signal model is organized into the form of a state space expression:
wherein ,
the state variable x is:
since the disturbance on the grid side is not considered, the input u=0, b=0.
As shown in fig. 6, it can be known from the system characteristic root trace that the stability of the doubly-fed fan system controlled by the VSG is affected by the wind speed at the initial operating point, and the system characteristic value appears in a conjugate way, namely:
λ＝σ+jω (17)
the real part of the eigenvalue is negative and represents the ringing, and the real part is positive and represents the diverging ringing. From the system characteristic root track, it can be found that the characteristic value lambda varies with the wind speed 3,4 The real part of the characteristic value is a constant negative value, and the pair of characteristic values correspond to a damping oscillation mode; and the eigenvalue lambda 1,2 The real part of the system is changed from a positive value to a negative value along with the increase of wind speed, the oscillation mode is changed, and the divergent oscillation is changed to the damping oscillation, so that the influence on the stability of the system is mainly exerted.
The characteristic equation of the small signal model is solved to obtain:
when v w ＝v ov The time system is characterized by the following conjugated characteristic roots:
the frequency of oscillation corresponding to the set of conjugate eigenvalues is:
the damping ratio is defined as:
damping ratio characterizes the damping of oscillations, a damping ratio of 0 indicates that the system is in a critical steady state at this wind speed. v ov Can be seen as the critical wind speed for virtual synchronous generator control. As can be seen from the system characteristic root trace of FIG. 6a, the control parameters are fixed, when v w ≤v ov When the system is in the right half plane of s, a group of conjugate eigenvalues of the system are positioned, the output power of the doubly-fed fan system oscillates, and the instability risk exists; as the wind speed increases, the system characteristic value gradually moves to the left half plane of s, when v w >v ov The characteristic values of the virtual synchronous generator control system are all positioned on the left half plane of s, the oscillation is attenuated, and the system can be kept stable.
As can be seen from the root track of the droop control in FIG. 6b, the characteristic value of the droop control system is always positioned on the left half plane of s within the range of 7m/s-13m/s of the set wind speed, and the characteristic root track of the system is gradually far away from the virtual axis along with the increase of the wind speed, so that the system stability is enhanced. By comparing the system characteristic root tracks of the virtual synchronous generator control and the droop control, the introduction of the inertia link enables the virtual synchronous generator control to be easier to generate output power oscillation, and particularly, the system has the risk of instability at low wind speed, so that the stability of the droop control is better at low wind speed.
Fig. 7 is a schematic diagram of a doubly-fed wind turbine adaptive frequency modulation control based on a critical oscillation wind speed, and the main control function implementation process of the DFIG adaptive frequency modulation control strategy based on the critical oscillation wind speed is as follows: 1) And detecting the synchronous angular frequency change of the system through a phase-locked loop, tracking the running state of the system, and identifying the frequency change condition of the system. When the frequency deviation of the system is smaller than or equal to the dead zone frequency, the wind turbine generator does not participate in system frequency adjustment, and the wind turbine generator operates according to the most power tracking mode; and when the system frequency deviation is larger than the dead zone, starting a multi-mode frequency modulation control strategy of the wind turbine. 2) And dynamically monitoring the running wind speed, and determining a frequency modulation control mode to be selected through a wind speed evaluation function.
The system running state evaluation function is as follows:
the wind speed state evaluation function is:
the embodiment of the invention builds a wind Power plant grid-connected simulation system based on a DIGSILENT/Power factor simulation platform, wherein the simulation system comprises 2 synchronous generators (G) with the capacities of 150MW and 400MW respectively 1 、G 2 ) A doubly-fed wind generator DFIG of 100 multiplied by 2MW 1 Load L with capacities of 100MW, 120MW and 90MW, respectively 1 、L 2 、L 3 DFIG of doubly-fed wind turbine generator 1 The grid is incorporated by bus bar 3.
The adaptability of the invention and the traditional single control strategy to different running wind speeds, namely the frequency modulation capability and the system stability of the doubly-fed fan system of different frequency modulation control methods under different wind speeds are verified by setting the following two simulation schemes under the wind speeds, which shows that the invention reasonably switches between the virtual synchronous generator control and the sagging control according to the comparison of the running wind speed and the critical oscillation wind speed, and improves the inertial response and the power supporting capability of the fan system on the premise of avoiding the system oscillation instability and fully ensuring the system stability.
Setting the simulated wind speed to 8m/s and 10m/s, and enabling the simulation system to load L at 90s 1 The burst was 10%, and no additional control, droop control and VSG control were used, respectively.
8a and 8b, at a wind speed of 8m/s, the system suddenly increases the load, and the lowest point 48.81Hz of the frequency drop of the fan system without additional control is provided; when the wind speed is 8m/s, the frequency deviation of the sagging control system reaches the maximum value of 0.76Hz after the load suddenly increases for 1.98 s; the frequency deviation of the fan system controlled by VSG reaches the maximum value of 0.75Hz after the load is suddenly increased for 2.24 s. And the output power of the fan system controlled by the VSG has obvious fluctuation. When the wind speed is lower than the critical wind speed, VSG control is adopted to achieve similar frequency drop lifting effect with the sagging control system, output power fluctuation of VSG control is obvious, and the risk of oscillation instability exists, so that the frequency modulation effect achieved by adopting sagging control is better when the wind speed is lower than the critical wind speed.
As shown in fig. 9a and 9b, when the wind speed is 10m/s, the system suddenly increases the load, the system without additional frequency control is reduced to 48.81Hz at 91.58s frequency, a certain frequency modulation effect can be achieved by adopting both droop control and VSG control, and compared with adopting droop control, when adopting VSG control, the time for the system frequency to fall to the lowest point is increased from 1.99s to 4.68s, and the frequency maximum falling amount is reduced from 0.72Hz to 0.67Hz. When the wind speed is higher than the critical wind speed, the VSG control reduces the system frequency drop amount compared with the droop control, increases the time for the frequency to drop to the lowest point, obviously improves the frequency modulation effect, and has little difference in output power change, so that the VSG control is better when the wind speed is higher than the critical wind speed. Therefore, the system and the method can ensure the stability of the system and improve the power supporting capacity and the frequency modulation stability by reasonably switching the frequency modulation control strategy according to the running wind speed of the fan.
The invention considers the relation between the change of the running wind speed and the critical oscillation wind speed, reasonably switches the frequency modulation control strategy, and can adapt to different running wind speeds compared with single VSG control and sagging control, when the wind speed is higher, the virtual synchronous generator control is adopted, the frequency modulation capability can be fully exerted, the frequency modulation effect is greatly improved, when the wind speed is lower, the sagging control is adopted, the possibility of oscillation instability of the system can be reduced, and the stable running of the system is ensured.
Compared with the traditional control method, the system and the method for controlling the self-adaptive frequency modulation of the doubly-fed wind turbine based on the critical oscillation wind speed establish a small signal model for virtual synchronous control according to control parameters of the system, calculate the critical oscillation wind speed of the system, and reasonably switch between virtual synchronous machine control and sagging control by comparing the actual running wind speed and the critical oscillation wind speed of the system, thereby realizing the stability of the system running under low wind speed and fully playing the frequency modulation potential and the power supporting capability of the system under high wind speed. The invention can effectively reduce the risks of power oscillation and instability of the virtual synchronous machine control fan system at lower wind speeds and the problem of insufficient power support of the sagging control system at higher wind speeds. The invention provides a double-fed fan multi-mode self-adaptive frequency modulation control strategy based on critical oscillation wind speed, which utilizes the adjustability of the frequency modulation control strategy of a wind turbine generator, reasonably switches the frequency modulation control strategy according to the wind speed of the fan operation, enhances the stability of the fan system operation, and improves the power supporting capacity and the frequency modulation stability of the system.
The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to assist in understanding the methods of the present invention and the core ideas thereof; also, it is within the scope of the present invention to be modified by those of ordinary skill in the art in light of the present teachings. In view of the foregoing, this description should not be construed as limiting the invention.
Claims (2)
1. A doubly-fed wind machine self-adaptive frequency modulation control method based on critical oscillation wind speed is characterized by comprising the following steps:
s1, establishing a fan system small signal model comprising doubly-fed fan prime motor control and virtual synchronous generator control, and converting the fan system small signal model into a state space matrix form;
s2, calculating critical oscillation wind speed according to control system parameters by using the state space matrix of the fan system obtained in the S1;
s3, detecting the power grid frequency omega of the control system in real time by using a phase-locked loop technology m ；
S4, judging the grid frequency deviation delta omega at the grid connection point of the rotor converter at the DFIG1 side of the doubly-fed wind turbine generator m Whether or not the allowable fluctuation range Δω is exceeded 0 The method comprises the steps of carrying out a first treatment on the surface of the If yes, executing step S5, and if not, executing step S1;
s5, detecting the running wind speed v of the control system in real time w Dynamically identifying the running state of the doubly-fed wind generator DFIG 1;
s6, judging the running wind speed v w Whether or not it is greater than the critical oscillation wind speed v ov If yes, executing the step S7, and if not, executing the step S8;
s7, switching a strategy of the virtual synchronous generator to control the doubly-fed fan to participate in system frequency adjustment;
s8, controlling the doubly-fed fan to participate in system frequency adjustment by switching the droop strategy;
s9, performing frequency modulation control by utilizing the control strategy selected in the step S7 or the step S8, and judging whether the power grid frequency of the control system is recovered; if not, returning to execute the step S3, and if so, ending the frequency modulation control;
in the step S1, a fan system small signal model including doubly-fed fan prime mover control and virtual synchronous generator control is established and converted into a state space matrix form, which specifically includes:
virtual inertia control is introduced into a doubly-fed fan control algorithm based on a synchronous generator set rotor motion equation, and disturbance on the power grid side, omega, is not considered g For the angular frequency measurement of the system, the angular frequency reference value omega is used because of deviation caused by the limitation of phase-locked loop technology ref Instead, let the angular frequency measurement of the system change by an amount Δω g =0, resulting in a fan system small signal model:
due to Deltaomega m =sΔθ, the above formula is sorted into a higher order differential equation of Δθ:
s 4 Δθ+a 1 s 3 Δθ+a 2 s 2 Δθ+a 3 sΔθ+a 4 Δθ＝0
wherein ：
arranging the small signal model into a state space matrix form:
wherein ,
the state variable x is:
since the disturbance on the grid side is not considered, the input quantity u=0 and b=0;
wherein ,Kω Is a frequency droop control coefficient; j and D are virtual inertia coefficient and damping coefficient respectively; lambda (lambda) opt Is the optimal tip speed ratio; r is the radius of the wind wheel; h is the inherent inertia time constant of the doubly-fed wind turbine generator; k (k) pv The ratio coefficient is the rotation speed controller; k (k) iv Integrating the coefficient for the rotating speed controller; e is the output voltage of VSG; u is the grid voltage; θ is the impedance angle, Z is the system impedance; v w0 Is the steady state operating point wind speed.
2. The method for controlling adaptive frequency modulation of a doubly-fed wind turbine based on critical oscillation wind speed according to claim 1, wherein the step S2 is performed by using the state space matrix of the wind turbine system obtained in the step S1, and calculating the critical oscillation wind speed according to the control system parameters, and specifically comprises:
by solving the characteristic root of a high-order differential equation of a small signal model of the fan system, taking the wind speed corresponding to the characteristic root with the imaginary part being zero as the critical oscillation wind speed v ov The formula is:
according to the parameters of the control system, calculating and obtaining the critical oscillation wind speed v by using a formula ov And taking the comparison condition of the monitored real-time running wind speed and the critical oscillation wind speed as the basis of the frequency modulation control mode selection of the doubly-fed wind turbine.
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| CN110460098A (en) * | 2019-08-28 | 2019-11-15 | 华北电力大学（保定） | The double mass shafting stable control methods of wind energy conversion system based on virtual mass block |
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