Extremum seeking-based control method for maximum output tracking of a wind turbine generator

Abstract

The present invention discloses an extremum seeking-based control method for maximum output tracking of a wind turbine generator, mainly comprising three steps of first closed-loop feedback, second closed-loop feedback, and third closed-loop feedback. The method for resisting mechanical fatigue of a double-fed variable speed constant frequency wind turbine generator by controlling mechanical torque while capturing maximum wind energy provided in the present invention is applied to a double-fed variable speed constant frequency wind turbine system by improving the control based on sliding mode extremum seeking with the following effects that, with regard to the maximum wind energy tracking effect, the rotating speed can be quickly adjusted to keep the tip speed ratio as its optimum value after the wind speed changes, so that the wind energy utilization coefficient is restored to the maximum value.

Claims

1. An extremum seeking-based control method for maximum output tracking of a wind turbine generator, wherein the method is a sliding mode extremum seeking-based control method for realizing maximum output tracking of the wind turbine generator, and the method comprises: first step: comparing an active power p.sub.s output by a double-fed motor and a present power reference value p.sub.s,ref, delivering a difference to a sign function when the $\mathrm{sgn}\left(\mathrm{.Math.}\right):a=\mathrm{sgn}\left(\mathrm{.Math.}\right)=\{\begin{array}{cc}1,& \mathrm{.Math.}>0\\ 0,& \mathrm{.Math.}=0\\ -1,& \mathrm{.Math.}<0\end{array},$ when the sign function sgn() changes, delivering a constant u to a module U.sub.0/s by calculating $\frac{U_o}{t}.Math.u,$ wherein U.sub.0 is a rated voltage of the double-fed motor, and t is time, then obtaining a reference value of rotating speed .sub.r,ref, and comparing the reference value of rotating speed .sub.r,ref with a real-time value of rotating speed .sub.r, processing a difference of the .sub.r,ref and the .sub.r in a PI proportional differential step to obtain a standard rotor quadrature axis component $.Math.\frac{{}_{r,\mathrm{ref}}}{t}.Math.=i_{\mathrm{qr}}^{*},$ and then further comparing with a preset value i.sub.qr to determine an upper limit *.sub.r of variations to the real-time value of rotating speed .sub.r; second step: when the sign function sgn() in the first step changes, the constant u is compared with a preset value after being magnified by a factor of Z.sub.0, processing a difference in a 1/s step to obtain a new power reference value p.sub.s,ref, then repeating the first step and obtaining a new upper limit *.sub.r; third step: converting the upper limit *.sub.r into a mechanical torque variation T.sub.m, and in turn limiting T.sub.m within (0, T*.sub.m), and T*.sub.m being a maximum variation of mechanical torque; and forth step: adjusting a rotating speed of the wind turbine generator based on the maximum variation of mechanical torque T*.sub.m.

2. The sliding mode extremum seeking-based control method for maximum output tracking of a wind turbine generator of claim 1, wherein the first step forms a first closed-loop feedback, and wherein the first closed-loop feedback comprises a WCES image module, comparison of the active power p.sub.s and the power reference value p.sub.s,ref, the sign function sgn() and the U.sub.0/s module.

3. The sliding mode extremum seeking-based control method for maximum output tracking of a wind turbine generator of claim 1, wherein the second step forms a second closed-loop feedback, and wherein the second closed-loop feedback comprises the sign function sgn(), the magnifying module Z.sub.0, the preset value comparison step and the 1/s step.

4. The sliding mode extremum seeking-based control method for maximum output tracking of a wind turbine generator of claim 1, wherein the third step forms a third closed-loop feedback, and wherein the third closed-loop feedback comprises a comparison step of .sub.r and the reference value, a PI proportional differential step, and a comparison step of i.sub.qr and a preset value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a structure diagram of an extremum seeking-based control method for maximum output tracking of a wind turbine generator provided in an embodiment of the present invention.

DETAILED DESCRIPTION

(2) For better understanding of the purpose, technical solution and advantage of the present invention, the invention is further illustrated in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only for explanation and not for limiting the scope of the present invention.

(3) The inventive embodiment provides an extremum seeking-based control method for maximum output tracking of a wind turbine generator, comprising the following steps:

(4) First closed-loop feedback for generating a feedback value of an output active power p.sub.s; The specific signaling process comprises comparing the active power p.sub.s output by a double-fed motor and a power reference value p.sub.s,ref, delivering the difference to a sign function sgn(), producing a sliding mode action when sgn() changes, delivering the information to a module v.sub.0/s after multiplying by a constant u, thus obtaining a reference value .sub.r,ref of the rotating speed, and obtaining the active power p.sub.s according to a WCES image and feeding the active power p.sub.s back to the power reference value p.sub.s,ref, thereby forming power closed-loop feedback;

(5) Second closed-loop feedback for generating a feedback closed-loop system of the difference between an output value and a reference value; The specific signaling process comprises comparing the sign function sgn() with a preset value after being magnified by a factor of Z.sub.0, processing the difference in a 1/s step to obtain a power reference value p.sub.s,ref, comparing the power reference value p.sub.s,ref with the active power p.sub.s to obtain the difference , and then delivering the difference to the sign function sgn() to form a feedback closed-loop system;

(6) Third closed-loop feedback for implementing control of rate of change of .sub.r and in turn for limiting T.sub.m within (0, T*.sub.m). The specific implementation method comprises comparing the active power p.sub.s with the power reference value p.sub.s,ref to obtain the difference , then delivering the difference to the sign function sgn(); on one hand, comparing the sign function sgn() with a preset value after being magnified by a factor of Z.sub.0, processing the difference in a 1/s step to obtain the power reference value p.sub.s,ref, and further comparing with the active power p.sub.s to form closed-loop feedback; and on the other hand, magnifying the sign function sgn() by a factor of U to obtain U.sub.0/s, and thus obtaining the reference value .sub.r,ref of the rotating speed, comparing .sub.r,ref with .sub.r, processing the difference in a PI proportional differential step to obtain a standard rotor quadrature axis component

(7) $.Math.\frac{{}_{r,\mathrm{ref}}}{t}.Math.=i_{\mathrm{qr}}^{*},$
and then further comparing with a preset value i.sub.qr to determine a reasonable upper limit *.sub.r, thereby implementing control of the rate of change of .sub.r and in turn limiting T.sub.m within (0, T*.sub.m).

(8) As a preferred solution of the inventive embodiment, the first closed-loop feedback mainly consists of a WCES image module, comparison of the active power p.sub.s and the power reference value p.sub.s,ref, the sign function sgn() and a v.sub.0/s module.

(9) As a preferred solution of the inventive embodiment, the second closed-loop feedback mainly consists of the sign function sgn(), a magnifying module Z.sub.0, a preset value comparison step and a 1/s step.

(10) As a preferred solution of the inventive embodiment, the third closed-loop feedback mainly consists of a comparison step of .sub.r and the reference value, a PI proportional differential step, and a comparison step of i.sub.qr and the preset value.

(11) Referring to FIG. 1, the extremum seeking-based control method for maximum output tracking of a wind turbine generator of the inventive embodiment is further described in detail below.

(12) As shown in FIG. 1, the principle of the extremum seeking-based control method for maximum output tracking of a wind turbine generator of the present invention is that the structure diagram mainly consists of double closed-loop feedback.

(13) First closed-loop feedback, for generating a feedback value of an output active power p.sub.s, comprising a WCES image module, comparison of the active power p.sub.s and the power reference value p.sub.s,ref, the sign function sgn() and a v.sub.0/s module; the specific signaling process comprises comparing the active power p.sub.s output by a double-fed motor and a power reference value p.sub.s,ref, delivering the difference to a sign function sgn(), producing a sliding mode action when sgn() changes, delivering the information to a module v.sub.0/s after multiplying by a constant u, thus obtaining a reference value .sub.r,ref of the rotating speed, and obtaining the active power p.sub.s according to a WCES image and feeding the active power p.sub.s back to the power reference value p.sub.s,ref, thereby forming power closed-loop feedback;

(14) Second closed-loop feedback, for generating a feedback closed-loop system of the difference between an output value and a reference value, comprising the sign function sgn(), a magnifying module Z.sub.0, a preset value comparison step and a 1/s step; The specific signaling process comprises comparing the sign function sgn() with a preset value after being magnified by a factor of Z.sub.0, processing the difference in a 1/s step to obtain a power reference value p.sub.s,ref, comparing the power reference value p.sub.s,ref with the active power p.sub.s to obtain the difference , and then delivering the difference to the sign function sgn() to form a feedback closed-loop system;

(15) The present invention further comprises a comparison step of .sub.r and the reference value, a PI proportional differential step, and a comparison step of i.sub.qr and the preset value for implementing control of rate of change of .sub.r and in turn for limiting T.sub.m within (0, T*.sub.m). The specific implementation method comprises comparing the active power p.sub.s with the power reference value p.sub.s,ref to obtain the difference , then delivering the difference to the sign function sgn(); on one hand, comparing the sign function sgn() with a preset value after being magnified by a factor of Z.sub.0, processing the difference in a 1/s step to obtain the power reference value p.sub.s,ref, and further comparing with the active power p.sub.s to form closed-loop feedback; and on the other hand, magnifying the sign function sgn() by a factor of U to obtain U.sub.0/s, and thus obtaining the reference value .sub.r,ref of the rotating speed, comparing .sub.r,ref with .sub.r, processing the difference in a PI proportional differential step to obtain a standard rotor quadrature axis component

(16) $.Math.\frac{{}_{r,\mathrm{ref}}}{t}.Math.=i_{\mathrm{qr}}^{*},$
and then further comparing with a preset value i.sub.qr to determine a reasonable upper limit *.sub.r, thereby implementing control of the rate of change of .sub.r and in turn limiting T.sub.m within (0, T*.sub.m).

(17) The above are only the preferred embodiments of the present invention and not intended to limit the present invention. Any modifications, equivalent replacements, improvements and the like within the spirit and principle of the present invention shall fall within the scope of protection of the present invention.