Power tracking method and system for network-forming type wind turbine generator

Abstract

The invention discloses a power tracking method and system for a network construction type wind turbine generator, and the method comprises the steps: 1) inputting control parameters of a virtual synchronous generator, and building a mathematical model of the virtual synchronous generator; the model comprises dynamic characteristics; 2) obtaining a power expression and a power increment expression of the virtual synchronous generator according to the dynamic characteristics of the virtual synchronous generator; 3) obtaining a plurality of virtual synchronous generator space state equations and space state discretization equations according to the dynamic characteristics of the virtual synchronous generator and the power expression and the power increment expression of the virtual synchronous generator; and 4) obtaining a power prediction expression of the virtual synchronous generator according to the power increment expression of the virtual synchronous generator, and constructing and solving a power tracking performance optimization problem of the constructed network type wind turbine generator in combination with the power prediction expression and the discretized space state equations of the plurality of virtual synchronous generators. The method has the advantages of improving the power tracking performance and the like.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of wind power, and in particular to a power tracking method and system for a grid-connected wind turbine generator set. Background Art

[0002] Compared with the conventional grid-connected control mode of current wind power, voltage source grid control reflects substantial innovation and breakthrough in methods and characteristics, which is very consistent with the role positioning and grid-connected requirements of new power systems for new energy, and has important research significance and value. During the operation of grid-connected wind turbines under the virtual synchronous generator (VSG) control strategy, they follow the synchronous rotation equation with a virtual inertia ring and present a unique virtual swing equation characteristic. However, in actual operation, the existence of this virtual swing equation causes the power output to not respond instantly to the power reference signal, but to have a certain lag.

[0003] For grid-type wind turbines, this power output lag not only affects the instant power regulation capability of the unit, but also poses a potential threat to the stable operation of the entire power system. In the power system, stability is a crucial consideration. It not only affects the normal operation of the system, but also directly affects the safety and reliability of the entire power grid. Therefore, when dealing with the problem of actual power lag of the grid-type wind turbines, the stability requirements of the system must be fully considered.

[0004] Furthermore, as a key link in regulating the power output of the unit, the power response rate of the grid control has a decisive influence on the overall performance of the system. However, under current technical conditions, the power response of the grid control is often slow, which to a certain extent limits the system's ability to quickly adjust to power fluctuations. In order to optimize the performance of the grid-connected units and improve the overall stability of the system, future research should focus on how to improve the power response speed of the grid control to more effectively deal with the problem of actual power lagging behind the given power. Summary of the invention

[0005] In view of the technical problems existing in the prior art, the present invention provides a power tracking method and system for a grid-connected wind turbine generator set which improves the power tracking performance.

[0006] In order to solve the above technical problems, the technical solution proposed by the present invention is: A power tracking method for a grid-type wind turbine generator system, comprising the steps of: 1) Inputting control parameters of the virtual synchronous generator and establishing a mathematical model of the virtual synchronous generator; wherein the mathematical model of the virtual synchronous generator includes the dynamic characteristics of the virtual synchronous generator; 2) According to the dynamic characteristics of the virtual synchronous generator obtained in step 1), the frequency ω of the virtual synchronous generator is obtained.ν , phase angle δ and voltage amplitude E of the virtual synchronous generator power expression and power increment expression; 3) According to the dynamic characteristics of the virtual synchronous generator obtained in step 1) and the power expression and power increment expression of the virtual synchronous generator obtained in step 2), the inertia J is obtained. ν , Damping D ν and droop coefficient K q A single virtual synchronous generator spatial state equation is input, and then multiple virtual synchronous generator spatial state equations and spatial state discretization equations are obtained; 4) Based on the power increment expression of the virtual synchronous generator obtained in step 2), the power prediction expression of the virtual synchronous generator is obtained. Combining the power prediction expression and the discretized spatial state equations of multiple virtual synchronous generators obtained in step 3), the power tracking performance optimization problem of the grid-type wind turbine is constructed and solved.

[0007] Preferably, the dynamic characteristic expression of the virtual synchronous generator in step 1) is: (1) (2) (3) where δ is the phase angle of the virtual synchronous generator, and represents the virtual synchronous generator frequency and the grid frequency, E is the voltage amplitude of the virtual synchronous generator, is the initial value of the grid voltage; , , , They are active power reference value, active power, reactive power reference value and reactive power; It's inertia. is the damping, It is the droop coefficient of the reactive voltage loop droop control loop.

[0008] Preferably, the power expression of the virtual synchronous generator in step 2) is: (4) Among them, R g and X g Represents line resistance and impedance respectively, U g is the grid voltage.

[0009] Preferably, the power increment expression of the virtual synchronous generator in step 2) is: (5) in, are the virtual synchronous generator active power increment coefficients, and are the phase angle increment and voltage amplitude increment respectively.

[0010] Preferably, in step 3), the spatial state equation of a single virtual synchronous generator is: (6) in, , is the number of virtual synchronous generators; are the increments of frequency, phase angle, voltage amplitude, inertia, damping and droop coefficient of the i-th virtual synchronous generator respectively; , are the increments of the reference values ​​of inertia, damping and droop coefficient of the i-th virtual synchronous generator respectively; are the state equation coefficients respectively.

[0011] Preferably, in step 3), the spatial state equations of the multiple virtual synchronous generators are: (7) in, They are A collection of .

[0012] Preferably, in step 3), the spatial state discretization equations of the multiple virtual synchronous generators are: (8) in, , , , is the sampling time; represents the state at the kth moment, and k+1 represents the state at the next moment.

[0013] Preferably, in step 4), the power prediction expression of the virtual synchronous generator is: (9) in, is the initial value of active power of the i-th virtual synchronous generator; and are all the active power increment coefficients of the i-th virtual synchronous generator; are the voltage amplitude increment and phase angle increment of the i-th virtual synchronous generator, ; is the number of virtual synchronous generators; is the predicted number of steps; represents the state at the kth moment, and k+1 represents the state at the next moment.

[0014] Preferably, in step 4), the main cost function of the power tracking performance optimization problem of the grid-type wind turbine is for: (10) in, is the power prediction value of the i-th virtual synchronous generator, is the power reference value of the i-th virtual synchronous generator, ; is the number of predicted steps, is the number of VSGs.

[0015] The present invention also discloses a power tracking system for a grid-type wind turbine generator set, comprising a memory and a processor connected to each other, wherein a computer program is stored in the memory, and when the computer program is run by the processor, the steps of the method described above are executed.

[0016] Compared with the prior art, the advantages of the present invention are: The present invention establishes a mathematical model of VSG (including VSG dynamic characteristics, power and its increment, single and multiple spatial state equations) by inputting multiple control parameters of VSG, and obtains a power prediction model of a virtual synchronous generator group that takes into account changes in VSG inertia, damping and droop coefficient. The power tracking performance improvement problem of a grid-type wind turbine is constructed in combination with the above model, including cost function, parameter fluctuation limit and parameter constraint. By solving this problem, multiple VSG control parameters (inertia, damping and droop coefficient of VSG) are coordinated and adjusted to enable VSG to obtain better power tracking performance, that is, the power output of VSG can always better track the power reference value, thereby improving power utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The figure is a flow chart of a power tracking method in an embodiment of the present invention.

[0018] Figure 2 Schematic diagram of the step power response of the present invention; wherein (a) is a schematic diagram of time-VSG power; (b) is a schematic diagram of time-inertia; (c) is a schematic diagram of time-damping; and (d) is a schematic diagram of time-droop coefficient.

[0019] Figure 3 Schematic diagram of the ramp power response of the present invention; (a) is a schematic diagram of time-VSG power; (b) is a schematic diagram of time-inertia; (c) is a schematic diagram of time-damping; and (d) is a schematic diagram of time-droop coefficient.

[0020] Figure 4Schematic diagram of random power response of 5 VSGs of the present invention; (a) is a schematic diagram of time-VSG power; (b) is a schematic diagram of time-inertia; (c) is a schematic diagram of time-damping; and (d) is a schematic diagram of time-droop coefficient.

[0021] Figure 5 Schematic diagram of power error comparison under random power response of the present invention; (a) is a schematic diagram of time-accumulated power error; (b) is a schematic diagram of power error ratio under time-pu parameter condition.

[0022] Figure 6 This is a topological diagram of a single wind turbine generator set in the present invention. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0024] like Figure 1 As shown, the power tracking method of a grid-type wind turbine provided by an embodiment of the present invention comprises the steps of: 1) Input multiple control parameters of virtual synchronous generator (VSG) and establish the mathematical model of VSG; The control parameters input to the VSG include the inertia J ν , Damping D ν and the droop coefficient K of the QU loop q ; The mathematical model of VSG includes the dynamic characteristics of VSG; the dynamic characteristics of VSG include VSG frequency ω ν , expressions for VSG phase angle δ and VSG voltage amplitude E; 2) According to the dynamic characteristics of VSG, the VSG frequency ω is obtained ν , the power expression and power increment expression of VSG including phase angle δ and voltage amplitude E; 3) According to the dynamic characteristics of VSG in step 1) and the power expression and power increment expression of VSG in step 2), the inertia J is obtained. ν , Damping D ν and droop coefficient K q The single VSG spatial state equation is input, and then the spatial state equations of multiple VSGs and the discretized spatial state equations are obtained; 4) According to the power increment expression of VSG in step 2), the power prediction expression of VSG is obtained. Combining the power prediction expression and the discretized spatial state equations of multiple VSGs in step 3), the power tracking performance improvement problem of grid-type wind turbines is constructed and solved, and the VSG parameters are optimized to reduce the error between the VSG power and the reference power.

[0025] In step 1), a dynamic characteristic expression of VSG is established by inputting multiple control parameters of VSG; wherein the dynamic characteristic expression is: (1) (2) (3) where δ is the VSG phase angle, and represents the VSG frequency and the grid frequency, E is the VSG voltage amplitude, is the initial value of the grid voltage; , , , They are active power reference value, active power, reactive power reference value and reactive power. It's inertia. is the damping, It is the droop coefficient of the reactive voltage loop droop control (QU) loop.

[0026] In step 2), include the VSG frequency ω ν The VSG power expression including the phase angle δ and the voltage amplitude E is: (4) Among them, R g and X g Represents line resistance and impedance respectively, U g is the grid voltage.

[0027] In step 2), and are related to δ and E, so they can be expressed linearly with the increments of δ and E The increment and The increment The expression is: (5) in, is the VSG active power increment coefficient; is the VSG reactive power increment coefficient; Specifically, , , The subscript i represents the i-th VSG, and the subscript 0 represents the initial value of each calculation. and are the phase angle increment and voltage amplitude increment respectively.

[0028] In step 3), according to equations (1) to (5), we can get ν, Damping D ν and droop coefficient K q The single VSG space state equation for input is: (6) in, , N VSG is the number of VSG; are the increments of frequency, phase angle, voltage amplitude, inertia, damping and droop coefficient of the i-th VSG respectively; are the increments of the reference values ​​of inertia, damping and droop coefficient of the i-th VSG respectively; in, is the state equation coefficient, specifically: in, , , ; in, ; ; ; ; ; ; in, are the initial values ​​of damping, inertia, and droop coefficient of the i-th VSG, respectively; is the rated power; is the initial value of the frequency of the i-th VSG; are the active power, active power reference value, reactive power and reactive power reference value of the i-th VSG respectively; is the increment coefficient of active power and reactive power of the ith VSG; Delay time for controlling parameter changes.

[0029] In step 3), based on equation (6), the multiple VSG spatial state equations are obtained as follows: (7) in, They are respectively A collection of ;Specifically, , , , , .

[0030] In step 3), based on equation (7), the discretized spatial state equations of multiple VSGs are obtained as follows: (8) in, , , , is the sampling time; represents the state at the kth moment, and k+1 represents the state at the next moment.

[0031] In step 4), the VSG power prediction expression based on formula (5) is: (9) in, is the initial value of active power of the ith VSG, are the active power increment coefficients of the ith VSG, are the increments of the voltage amplitude and phase angle of the i-th VSG, ; is the number of prediction steps.

[0032] In step 4), the power tracking performance improvement problem of grid-connected wind turbines is constructed based on equations (8)-(9), with the goal of minimizing power deviation. The main cost function of the power tracking performance improvement problem can be written in the form of quadratic programming: (10) in, is the power prediction value of the i-th VSG, is the power reference value of the i-th VSG, ; is the number of predicted steps, is the number of VSGs.

[0033] Considering the inertia J ν , Damping D ν , droop coefficient K q The parameters fluctuate. The parameter fluctuations of the power tracking performance improvement problem of the constructed grid-type wind turbine should be limited to: (11) in, are the reference value increments of inertia, damping and droop coefficient of the i-th VSG respectively; Inertia J ν , Damping D ν , droop coefficient K q The weight coefficient of .

[0034] Considering the inertia J ν , Damping D ν , droop coefficient K q The parameter values ​​are limited. The parameter constraints for the power tracking performance improvement problem of the constructed grid-type wind turbine are: (12) (13) (14) in, Inertia J ν Minimum and maximum values; The damping D ν Minimum and maximum values; They are the droop coefficient K q Minimum and maximum values.

[0035] By solving the problem of improving the power tracking performance of quadratic grid-type wind turbines such as equations (12) to (14), the inertia, damping and droop coefficients of multiple VSGs can be optimized simultaneously, reducing the error between the VSG power and the power reference, thereby better tracking the power command and enhancing the VSG power tracking performance.

[0036] The present invention establishes a mathematical model of VSG (including VSG dynamic characteristics, power and its increment, single and multiple spatial state equations) by inputting multiple control parameters of VSG, and obtains a power prediction model of a virtual synchronous generator group that takes into account changes in VSG inertia, damping and droop coefficient. The power tracking performance improvement problem of a grid-type wind turbine is constructed in combination with the above model, including cost function, parameter fluctuation limit and parameter constraint. By solving this problem, multiple VSG control parameters (inertia, damping and droop coefficient of VSG) are coordinated and adjusted to enable VSG to obtain better power tracking performance, that is, the power output of VSG can always better track the power reference value, thereby improving power utilization.

[0037] Compared with the adaptive inertial damping control and fixed parameter control methods, the present invention only needs to change fewer parameters to obtain better power tracking performance, thereby reducing overshoot and power oscillation.

[0038] In order to verify the effectiveness of the present invention, five VSGs (the topology of a single wind turbine is as follows) are connected in parallel. Figure 6 As shown in the figure, the power grid is connected to the first VSG node through a transformer. There is a transmission line between the power grid and the first VSG node, and there are also transmission lines between each VSG node. The comparison working condition is selected under the rated parameters (pu parameters) after 5 VSGs in parallel are connected to the power grid through a transformer, and the working condition response of one VSG. The rated parameters are obtained by adjusting the parameters according to the empirical values. After the adjustment, the stable operation of multiple units is ensured, so as to serve as the benchmark parameters for parameter optimization.

[0039] The power response of VSG under step and ramp commands is as follows: Figure 2 and Figure 3 As shown, compared Figure 2(a) and Figure 3 As shown in (a), the VSG can better track the power reference under step and ramp commands through the present invention. The case of pu parameter shows that the inertia J v and damping D v Limited help with VSG power tracking. Figure 2 and Figure 3 The results in J show that the present invention can be v and D v Better power tracking performance is achieved with less fluctuation.

[0040] The results of VSG under random power response are as follows Figure 4 and Figure 5 As shown, Figure 4 The results in Figure 2 and Figure 3 The results are consistent with those in the v , Damping D v and droop coefficient K q After slight adjustments to improve power tracking, this demonstrates the adaptability of the proposed method. The same power reference value is also given for the comparative case. The cumulative power error between the sum of the five VSG powers and the power reference value is shown in Figure 5 As shown in (a), the error ratio is calculated with the cumulative power error of the PU condition as the denominator, as shown in Figure 5 Compared with the pu parameter, the proposed method reduces the cumulative power error of random power by about 7.36% within 300s.

[0041] The present invention also discloses a power tracking system for a grid-type wind turbine generator set, comprising a memory and a processor connected to each other, wherein a computer program is stored on the memory, and when the computer program is executed by the processor, the steps of the method described above are executed. The tracking system of the present invention corresponds to the tracking method described above, and also has the advantages of the tracking method described above.

[0042] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A power tracking method for a grid-type wind turbine generator system, characterized in that: Includes steps: 1) Inputting control parameters of the virtual synchronous generator and establishing a mathematical model of the virtual synchronous generator; wherein the mathematical model of the virtual synchronous generator includes the dynamic characteristics of the virtual synchronous generator; 2) According to the dynamic characteristics of the virtual synchronous generator obtained in step 1), the frequency ω of the virtual synchronous generator is obtained. ν , phase angle δ and voltage amplitude E of the virtual synchronous generator power expression and power increment expression; 3) According to the dynamic characteristics of the virtual synchronous generator obtained in step 1) and the power expression and power increment expression of the virtual synchronous generator obtained in step 2), the inertia J is obtained. ν , Damping D ν and droop coefficient K q A single virtual synchronous generator spatial state equation is input, and then multiple virtual synchronous generator spatial state equations and spatial state discretization equations are obtained; 4) Based on the power increment expression of the virtual synchronous generator obtained in step 2), the power prediction expression of the virtual synchronous generator is obtained. Combining the power prediction expression and the discretized spatial state equations of multiple virtual synchronous generators obtained in step 3), the power tracking performance optimization problem of the grid-type wind turbine is constructed and solved.

2. The power tracking method of a grid-type wind turbine generator set according to claim 1, characterized in that: The dynamic characteristic expression of the virtual synchronous generator in step 1) is: （1） （2） （3） where δ is the phase angle of the virtual synchronous generator, and represents the virtual synchronous generator frequency and the grid frequency, E is the voltage amplitude of the virtual synchronous generator, is the initial value of the grid voltage; , , , They are active power reference value, active power, reactive power reference value and reactive power; It's inertia. is the damping, It is the droop coefficient of the reactive voltage loop droop control loop.

3. The power tracking method of a grid-type wind turbine generator set according to claim 2, characterized in that: The power expression of the virtual synchronous generator in step 2) is: （4） Among them, R g and X g Represents line resistance and impedance respectively, U g is the grid voltage.

4. The power tracking method of a grid-type wind turbine generator set according to claim 3, characterized in that: The power increment expression of the virtual synchronous generator in step 2) is: （5） in, are the virtual synchronous generator active power increment coefficients, and are the phase angle increment and voltage amplitude increment respectively.

5. The power tracking method of a grid-type wind turbine generator system according to any one of claims 1 to 4, characterized in that: In step 3), the spatial state equation of a single virtual synchronous generator is: （6） in, , is the number of virtual synchronous generators; are the increments of frequency, phase angle, voltage amplitude, inertia, damping and droop coefficient of the i-th virtual synchronous generator respectively; ; are the increments of the reference values ​​of inertia, damping and droop coefficient of the i-th virtual synchronous generator respectively; are the state equation coefficients respectively.

6. The power tracking method of a grid-type wind turbine generator set according to claim 5, characterized in that: In step 3), the spatial state equations of multiple virtual synchronous generators are: （7） in, They are A collection of .

7. The power tracking method of a grid-type wind turbine generator set according to claim 6, characterized in that: In step 3), the spatial state discretization equations of multiple virtual synchronous generators are: （8） in, , , , is the sampling time; represents the state at the kth moment, and k+1 represents the state at the next moment.

8. The power tracking method of a grid-connected wind turbine generator system according to any one of claims 1 to 4, characterized in that: In step 4), the power prediction expression of the virtual synchronous generator is: （9） in, is the initial value of active power of the i-th virtual synchronous generator; and are all the active power increment coefficients of the i-th virtual synchronous generator; are the voltage amplitude increment and phase angle increment of the i-th virtual synchronous generator, ; is the number of virtual synchronous generators; is the predicted number of steps; represents the state at the kth moment, and k+1 represents the state at the next moment.

9. The power tracking method of a grid-type wind turbine generator set according to claim 8, characterized in that: In step 4), the main cost function of the power tracking performance optimization problem of grid-connected wind turbines is for: （10） in, is the power prediction value of the i-th virtual synchronous generator, is the power reference value of the i-th virtual synchronous generator, ; is the number of predicted steps, is the number of VSGs.

10. A power tracking system for a grid-type wind turbine generator system, comprising a memory and a processor connected to each other, wherein a computer program is stored in the memory, characterized in that: When the computer program is executed by a processor, the computer program performs the steps of the method according to any one of claims 1 to 9.

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