CONTROL METHOD, CONTROL DEVICE AND WIND FARM SYSTEM FOR WIND TURBINE FREQUENCY SUPPORT

Abstract

A control method, a control device and a wind farm system for a wind turbine frequency support are provided. The control method includes the following: calculating a comprehensive inertia power value by using a wind farm frequency modulation capability level coefficient when a frequency accident occurs in the wind farm; obtaining a real-time rotational speed of each wind turbine to calculate a state factor that changes in real time, where each wind turbine adjusts a state reference power value of its own by exchanging the state factor with a neighboring wind turbine; and determining instantaneous stator power of each wind turbine by using a MPPT part corresponding to the rotational speed, the comprehensive inertia power value, and the state reference power value, so as to control each wind turbine to perform frequency support until a predetermined frequency support time is reached.

Claims

1. A control method for a wind turbine frequency support, comprising: S1: obtaining an initial rotational speed .sub.r,i0 and a minimum rotational speed limit .sub.r,min of each wind turbine in a wind farm in real time to calculate a wind farm frequency modulation capability level coefficient k.sub.c; S2: when a frequency accident occurs in the wind farm, adaptively adjusting a droop coefficient k.sub.wdr,i and an inertia coefficient k.sub.win,i according to the wind farm frequency modulation capability level coefficient k.sub.c corresponding to a moment fb when each wind turbine fails to calculate a comprehensive inertia power value P.sub.w,i(t) and obtaining a real-time rotational speed .sub.r,i of each wind turbine to calculate a state factor C; that changes in real time, wherein each wind turbine adjusts a state reference power value P.sub.c,i(t) of its own by exchanging the state factor with a neighboring wind turbine; and S3: determining instantaneous stator power P.sub.si of each wind turbine by using a MPPT part corresponding to the rotational speed, the comprehensive inertia power value P.sub.w,i(t), and the state reference power value P.sub.c,i(t), so as to control each wind turbine to perform frequency support until a predetermined frequency support time t is reached.

2. The control method for the wind turbine frequency support according to claim 1, wherein S1 comprises: calculating the wind farm frequency modulation capability level coefficient $k_c=\frac{.Math.{}_{r,i0}^2-{}_{r,\min }^2}{.Math.{}_{\mathrm{ref},i}^2-{}_{r,\min }^2}$ by using the initial rotational speed .sub.r,i0 and the minimum rotational speed limit .sub.r,min of each wind turbine in the wind farm, wherein .sub.ref,i is a wind turbine rotational speed under a predetermined wind farm state.

3. The control method for the wind turbine frequency support according to claim 1, wherein S2 comprises: S2: when a frequency accident occurs in the wind farm, adaptively adjusting the droop coefficient k.sub.wdr,i and the inertia coefficient k.sub.win,i according to the wind farm frequency modulation capability level coefficient k.sub.c corresponding to the moment fb when each wind turbine fails and calculating the comprehensive inertia power value P.sub.w,i(t) through the formula $P_{w,i}\left(t\right)=k_{\mathrm{wdr},i}f+k_{\mathrm{win},i}\frac{\mathrm{df}}{\mathrm{dt}},$ wherein f and df/dt represent a system frequency deviation and a frequency change rate respectively; and S22: obtaining the real-time rotational speed @r,i of each wind turbine to calculate the state factor C; that changes in real time, wherein each wind turbine adjusts the state reference power value P.sub.c,i(t) of its own by exchanging the state factor with a neighboring wind turbine.

4. The control method for the wind turbine frequency support according to claim 3, wherein S22 comprises: calculating the state factor C that changes in real time of an i.sup.th wind turbine through the formula $C_i=\frac{{}_{r,i0}^2-{}_{r,i}^2}{{}_{r,i0}^2-{}_{r,\min }^2};$ and calculating the state reference power value P.sub.c,i(t) of the i.sup.th wind turbine through the formula $P_{c,i}\left(t\right)=k_{P,i}\underset{j=i-1}{\overset{i+1}{.Math.}}\left(c_j-c_i\right)+k_{I,i}\underset{j=i-1}{\overset{i+1}{.Math.}}\left(c_j-c_i\right),$ wherein k.sub.P,i and k.sub.I,i represents a proportion and an integral coefficient of a state difference between adjacent wind turbines, and C.sub.j is the state factor corresponding to the neighboring wind turbine of the i.sup.th wind turbine.

5. The control method for the wind turbine frequency support according to claim 1, wherein S3 comprises: determining the instantaneous stator power P.sub.si of the i.sup.th wind turbine by using P.sub.si=k.sub.opt.sub.w,i.sup.2+P.sub.c,i(t)+P.sub.c,i(t), so as to control each wind turbine to perform frequency support until the predetermined frequency support time t is reached, wherein k.sub.opt.sub.r,i.sup.2 represents the MPPT part corresponding to the rotational speed, and k.sub.opt represents an optimal coefficient in a maximum power point tracking curve equation.

6. The control method for the wind turbine frequency support according to claim 5, wherein 10st20s.

7. A control device for a wind turbine frequency support, comprising: an acquisition module, configured to obtain an initial rotational speed .sub.r,i0 and a minimum rotational speed limit .sub.r,min of each wind turbine in a wind farm in real time to calculate a wind farm frequency modulation capability level coefficient k.sub.c; a calculation module configured to, when a frequency accident occurs in the wind farm, adaptively adjust a droop coefficient k.sub.wdr,i and an inertia coefficient k.sub.win,i according to the wind farm frequency modulation capability level coefficient k.sub.c corresponding to a moment fb when each wind turbine fails to calculate a comprehensive inertia power value P.sub.w,i(t) and obtain a real-time rotational speed .sub.r,i of each wind turbine to calculate a state factor C; that changes in real time, wherein each wind turbine adjusts a state reference power value P.sub.c,i(t) of its own by exchanging the state factor with a neighboring wind turbine; and a support module, configured to determine instantaneous stator power P.sub.si of each wind turbine by using a MPPT part corresponding to the rotational speed, the comprehensive inertia power value P.sub.w,i(t), and the state reference power value P.sub.c,i(t), so as to control each wind turbine to perform frequency support until a predetermined frequency support time t is reached.

8. A wind farm system comprising a memory and a processor, wherein the memory stores a computer program, and the processor implement the steps of the control method according to claim 1 when executing the computer program.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 is a schematic diagram of a control method for a wind turbine frequency support according to an embodiment of the disclosure.

[0034] FIG. 2 is a diagram of control state switching of the wind turbine frequency support according to an embodiment of the disclosure.

[0035] FIG. 3 is a schematic diagram of a wind farm grid-connected four-generator and two-zone system according to an embodiment of the disclosure.

[0036] FIG. 4 is a schematic diagram of a communication link of the wind farm according to an embodiment of the disclosure.

[0037] FIG. 5 is a line chart illustrating system frequency changes with time when using different control strategies of wind turbine frequency support under the condition of disturbance of a sudden load increase of 900 MW according to an embodiment of the disclosure.

DESCRIPTION OF THE EMBODIMENTS

[0038] In order to make the objectives, technical solutions, and advantages of the disclosure clearer and more comprehensible, the disclosure is further described in detail with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein serve to explain the invention merely and are not used to limit the invention. In addition, the technical features involved in the various embodiments of the invention described below can be combined with each other as long as the technical features do not conflict with each other.

[0039] As shown in FIG. 1, the disclosure provides a control method for a wind turbine frequency support, and the control method includes the following: [0040] In S1, an initial rotational speed .sub.r,i0 and a minimum rotational speed limit .sub.r,min of each wind turbine in a wind farm are obtained in real time to calculate a wind farm frequency modulation capability level coefficient k.sub.c; [0041] In S2, when a frequency accident occurs in the wind farm, a droop coefficient k.sub.wdr,i and an inertia coefficient k.sub.win,i are adaptively adjusted according to the wind farm frequency modulation capability level coefficient k.sub.c corresponding to a moment fb when each wind turbine fails to calculate a comprehensive inertia power value P.sub.w,i(t), and a real-time rotational speed .sub.r,i of each wind turbine is obtained to calculate a state factor C; that changes in real time. Each wind turbine adjusts a state reference power value P.sub.c,i(t) of its own by exchanging the state factor with a neighboring wind turbine; [0042] In S3, instantaneous stator power P.sub.si of each wind turbine is determined by using a MPPT part corresponding to the rotational speed, the comprehensive inertia power value P.sub.w,i(t), and the state reference power value P.sub.c,i(t), so as to control each wind turbine to perform frequency support until a predetermined frequency support time t is reached.

[0043] To be specific, the main idea of the disclosure is to add the state reference power value carrying the state factor to a power reference value of each wind turbine in the wind farm. The state factors C.sub.i are exchanged between adjacent wind turbines, and further, the wind turbines all adopt adaptive frequency modulation coefficients, so that the output of the wind turbines is adjusted according to their states and the frequency modulation capability of the wind farm. In this way, the system frequency performance is improved, and unreasonable power distribution that causes the wind turbines to operate unsafely is prevented from occurring.

[0044] In one of the embodiments, S1 includes the following. A controller obtains the minimum rotational speed limit .sub.r,min of each wind turbine WT.sub.i and the initial rotational speed .sub.r,i0 of each wind turbine in the wind farm in real time and calculates the wind farm frequency modulation capability level coefficient

[00006]$k_c=\frac{.Math.{}_{r,i0}^2-{}_{r,\min }^2}{.Math.{}_{\mathrm{ref},i}^2-{}_{r,\min }^2}$

through the rotational speed of each wind turbine in a rolling manner, where .sub.ref,i is the rotational speed of each wind turbine under a predetermined wind farm state.

[0045] In one of the embodiments, S2 includes the following: when a frequency accident occurs in the wind farm, the wind turbine frequency modulation coefficients k.sub.wdr,i and k.sub.win,i are adaptively adjusted according to the wind farm frequency modulation capability level coefficient k.sub.c at the moment. In a time period t.sub.b to t.sub.b+t, the comprehensive inertia power value P.sub.w,i(t) of the leading wind turbine satisfies

[00007]$P_{w,i}\left(t\right)=k_{\mathrm{wdr},i}f+k_{\mathrm{win},i}\frac{\mathrm{df}}{\mathrm{dt}}.$

The droop coefficient k.sub.wdr,i and the inertia coefficient k.sub.win,i change with the frequency modulation capability of the wind farm according to the formulas k.sub.wdr,i=k.sub.wdr0,ik.sub.c and k.sub.wdr,i=k.sub.wdr0,ik.sub.c, where k.sub.wdr0,i represents the base droop coefficient, and k.sub.wdr0,i represents the base inertia coefficient. By setting the relationship between the power of the leading wind turbine and the change of system frequency in this way, the adaptive frequency support of the leading wind turbine to the degree of system frequency changes can be achieved. It should be noted that these are only preferred implementation of the embodiments of the disclosure and shall not be understood as the sole limitation of the disclosure. In some other embodiments of the disclosure, the droop/inertia link of the leading wind turbine may also be eliminated.

[0046] In one of the embodiments, the state reference power value is expressed as:

[00008]$P_{c,i}\left(t\right)=k_{P,i}\underset{j=i-1}{\overset{i+1}{.Math.}}\left(c_j-c_i\right)+k_{I,i}\underset{j=i-1}{\overset{i+1}{.Math.}}\left(c_j-c_i\right),$

where C.sub.i represents the state factor, and its expression is

[00009]$C_i=\frac{{}_{r,i0}^2-{}_{r,i}^2}{{}_{r,i0}^2-{}_{r,\min }^2},$

which represents the deviation of the wind turbine output from the initial state.

[0047] In one of the embodiments, the wind farm is an onshore wind farm. Taking into account the effect of increasing a lowest frequency point of an onshore alternating current system and the safety of the wind turbines, a value range of frequency support time specifically is 10st20s in the disclosure, and optionally t=11.5s in this embodiment.

[0048] In one of the embodiments, before a wind turbine frequency is supported and after the wind turbine rotational speed is restored, a torque of each wind turbine WT.sub.i is controlled, so that the instantaneous stator power P.sub.si and the rotational speed .sub.r,i satisfy P.sub.si=k.sub.opt.sub.r,i.sup.2, where k.sub.opt represents an optimal coefficient in a maximum power point tracking curve equation. Therefore, based on the control method for the wind turbine frequency support provided by this embodiment, the state of an offshore wind farm may be divided into three states as shown in FIG. 2: a maximum power point tracking state, a frequency support state, and a rotational speed recovery state. Herein, in the maximum power point tracking state, the instantaneous stator power P.sub.si and rotational speed .sub.r,i of the wind turbine satisfy P.sub.si=k.sub.opt.sub.r,i.sup.2. In the frequency support state, an instantaneous stator power reference value P.sub.si of the wind turbine satisfies a constraint relationship of P.sub.si=k.sub.opt.sub.r,i.sup.2+P.sub.w,i(t)+P.sub.c,i(t). In the rotational speed recovery state, P.sub.si=k.sub.opt.sub.r,i.sup.2+P.sub.r,i(t), where .sub.r,i(t) represents additional power of a wind turbine rotational speed recovery stage.

[0049] The specific expression of the constraint relationship between the instantaneous stator power P.sub.si and rotational speed .sub.r,i of the wind turbine under different states is:

[00010]$P_{\mathrm{si}}=\{\begin{array}{cc}{k}_{\mathrm{opt}}{}_{r,i}^2& t<t_b\\ k_{\mathrm{opt}}{}_{r,i}^2+P_{w,i}\left(t\right)L_i+P_{c,i}\left(t\right)& t_{b}t{t}_b+t\\ k_{\mathrm{opt}}{}_{r,i}^2+P_{r,i}\left(t\right)& t{t}_b+t\end{array},$ [0050] where P.sub.r,i(t) represents the additional power of the wind turbine rotational speed recovery stage.

[0051] In general, in this embodiment, by adding a correction term to the power reference value of each wind turbine, the state reference power value

[00011]$P_{c,i}\left(t\right)=k_{P,i}\underset{j=i-1}{\overset{i+1}{.Math.}}\left(c_j-c_i\right)+k_{I,i}\underset{j=i-1}{\overset{i+1}{.Math.}}\left(c_j-c_i\right),$

where C.sub.i represents the state factor and its expression is

[00012]$C_i=\frac{{}_{r,i0}^2-{}_{r,i}^2}{{}_{r,i0}^2-{}_{r,\min }^2},$

represents the deviation of the wind turbine output relative to the initial state. The state factors C.sub.i are exchanged between adjacent wind turbines, so that the output of the wind turbines can be adjusted according to their states, the frequency modulation capability of the wind farm is fully utilized, and frequency performance is improved. In this way, unreasonable power distribution that causes the wind turbines to operate unsafely is prevented from occurring.

[0052] The beneficial effects achieved by the disclosure are further described in the following paragraphs together with a specific application scenario.

[0053] FIG. 3 shows a four-generator and two-zone power system including one wind farm, where WT.sub.1 to WT.sub.15 represent the fifteen wind turbines in the onshore wind farm, and G.sub.1 to G.sub.4 represent the four generators in the system. The information exchange between among the wind turbines in the wind farm is shown in FIG. 4. In the case of disturbance of a sudden load increase of 900 MW, the control provided by the disclosure, the frequency support control (centralized control) provided by the related art, and the wind turbine not participating in the frequency support control are adopted, and the system frequency changes with time is as shown in FIG. 5. Obviously, the lowest point of frequency may be increased by adopting the control provided by the disclosure.

[0054] According to another aspect of the disclosure, a control device for a wind turbine frequency support is provided, and the control device includes: [0055] An acquisition module is configured to obtain an initial rotational speed .sub.r,i0 and a minimum rotational speed limit .sub.r,min of each wind turbine in a wind farm in real time to calculate a wind farm frequency modulation capability level coefficient k.sub.c; [0056] A calculation module is configured to, when a frequency accident occurs in the wind farm, adaptively adjust a droop coefficient k.sub.wdr,i and an inertia coefficient k.sub.win,i according to the wind farm frequency modulation capability level coefficient k.sub.c corresponding to a moment fb when each wind turbine fails to calculate a comprehensive inertia power value P.sub.w,i(t) and obtain a real-time rotational speed .sub.r,i of each wind turbine to calculate a state factor C.sub.i that changes in real time. Each wind turbine adjusts a state reference power value P.sub.c,i(t) of its own by exchanging the state factor with a neighboring wind turbine; [0057] A support module is configured to determine instantaneous stator power P.sub.si of each wind turbine by using a MPPT part corresponding to the rotational speed, the comprehensive inertia power value P.sub.w,i(t), and the state reference power value P.sub.c,i(t), so as to control each wind turbine to perform frequency support until a predetermined frequency support time t is reached.

[0058] In this embodiment, specific implementation of each of the modules may be found with reference to the description of the abovementioned method, and description thereof is not repeated herein.

[0059] According to another aspect of the disclosure, a wind farm system for a wind turbine frequency support is provided, and the system includes a memory and a processor. The memory stores a computer program, and the processor implements the steps of the abovementioned method when executing the computer program.

[0060] The wind farm system in this embodiment includes a plurality of wind turbines, and the abovementioned control device for wind turbine frequency support is installed in each of the wind turbines.

[0061] A person having ordinary skill in the art shall understand that embodiments of the disclosure may be provided as methods, systems, or computer program products. Accordingly, the disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment that combines software and hardware aspects. Further, the disclosure may take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to a disk memory, a CD-ROM, an optical storage device, etc.) having computer-usable program code embodied therein.

[0062] A person having ordinary skill in the art should be able to easily understand that the above description is only preferred embodiments of the disclosure and is not intended to limit the disclosure. Any modifications, equivalent replacements, and modifications made without departing from the spirit and principles of the disclosure should fall within the protection scope of the disclosure.