KR101370542B1 - Method for controling mppt using wind speed estimation of wind power generation system - Google Patents

Abstract

The present invention relates to an MPPT control method through estimating wind speed of a wind power generation system which comprises the steps: (a) deriving a rotational energy of a blade; (b) deriving a tip speed ratio from the rotational energy of the blade; (c) deriving a pitch angle and the tip speed ratio of an efficiency coefficient as a non-linear function and approximating the derived non-linear function to be a third degree polynomial; (d) deriving the sum of a squared error; (e) deriving the sum of the squared error as a fourth degree polynomial; and (f) estimating current wind speed by deriving a solution to the third degree polynomial. [Reference numerals] (AA) Start; (BB) End; (S10) Deriving a rotational energy of a blade; (S20) Deriving a tip speed ratio from the rotational energy of the blade; (S30) Deriving as a non-linear function through [Equation 3] and approximating the derived non-linear function to be a third degree polynomial through [Equation 4]; (S40) Deriving the sum of a squared error relative to the [Equation 3] and the [Equation 4] through [Equation 5]; (S50) Deriving the derived sum of the squared error as a fourth degree polynomial such as [Equation 6]; (S60) Estimating current wind speed by deriving a solution to the third degree polynomial through [Equation 7]

Description

MFP control system using wind speed estimation of wind power generation system and its method {METHOD FOR CONTROLING MPPT USING WIND SPEED ESTIMATION OF WIND POWER GENERATION SYSTEM}

The present invention relates to a method for controlling MPPT through wind speed estimation of a wind power generation system. More specifically, polynomial approximation of a blade efficiency curve estimates wind speed based on blade output power, angular velocity and pitch angle, and maximizes the estimated wind speed. The present invention relates to a technology for providing maximum power point tracking (MPPT) by deriving a rotational speed of a blade having efficiency.

Wind power generation is a kind of renewable energy, developed by many countries as the most realistic alternative energy to date. Research and investment in wind power generation will continue as it is the only renewable energy source with a price competitiveness over coal / nuclear power. In particular, the current trend is to focus on offshore wind power generation rather than onshore wind power generation.

Although it is a short history except for primitive windmills, wind power is divided into several types depending on blade shape, generator type, and MPPT method.

The shape of the blade is the current horizontal axis and it is known to have the highest efficiency when it has three blades. The generator is mainly used Doubly Fed Induction Generator (DFIG), but the efficiency is higher and the technical / price aspect of the grid-connected converter is higher. As improvements improve the use of PMSGs.

Except for the special use, the main structure of the wind power generation system is almost uniform. However, various methods are still used in the control method of controlling the speed of the blade.

In general, a wind turbine has a rotation speed having a maximum generating power according to the wind speed, which is given as a function of the wind speed and the characteristics of the blade. If you use anemometer, you can easily find out the optimum rotational speed by using this function, but because of the inaccuracy and the unit cost of the anemometer, to find out the optimum rotational speed without using the anemometer, you can use the maximum power point tracking (MPPT). You have to go through the process.

P & O method, Optimal TSR method and PSF method are mainly used for MPPT control. First, the P & O method is to change the blade speed in the direction of increasing the generated power by analyzing the difference in generated power when the blade speed is changed.

In this method, the main issue is how much speed should be changed and how to determine the steady state. In addition, in the back-to-back system, since the measurement of the generated power is made at the system side, not at the generator side, it has the advantage that the actual generated power is controlled to the maximum.

On the other hand, the Optimal TSR method has a disadvantage in that the wind speed must be measured by comparing the actual TSR with the optimal TSR of the blade, and it is necessary to know the optimal TSR of the blade. The PSR method has the disadvantage of knowing the maximum output curve by controlling the speed by comparing the maximum output curve and the actual generated power at a certain angular velocity when the maximum output curve of the blade is known, and how much the speed is changed by comparing the outputs. Is the point.

Korean Patent No. 10-830518 (Method of estimating wind speed of a wind turbine) discloses a technique of estimating wind speed through a support vector regression algorithm in a controller of a wind turbine.

However, the wind speed estimation using the above-described support vector regression algorithm has a limitation in that it is impossible to determine the optimum rotational speed at a time, and thus it takes a relatively long time for the generator to reach the optimum rotational speed.

In addition, there is a problem that the wind speed is constantly changing and as a result it is not always operating at the optimum rotation speed.

In addition, when estimating the wind speed without using the anemometer, a control method of a form that continuously changes in the direction of increasing output power by adding or subtracting wind speed, such as P & O (Perturbation & Observation) method, follows. However, this method takes a long time to control the system at the optimum rotational speed and there is a problem that it cannot always follow the maximum power point because the wind speed also changes continuously.

The present invention has been made to solve the above problems, and the object of the present invention is to estimate the wind speed based on the blade output power, the angular velocity and the pitch angle by polynomial approximation of the blade efficiency curve.

In addition, the present invention is to provide a maximum power point tracking (MPPT) by controlling the rotation of the blade by deriving the rotational speed of the blade having the maximum efficiency based on the estimated wind speed.

의 피치각

과 주속비

를 [수학식 3]을 통해 비선형함수로 도출하고, 도출한 비선형함수를 [수학식 4]를 통해 3차 다항식으로 근사하는 (c) 단계; [수학식 3]과 [수학식 4]에 대한 오차의 제곱의 합을 [수학식 5]를 통해 도출하는 (d) 단계; 오차의 제곱의 합을 4차 행렬식으로 도출하는 (e) 단계; 및 [수학식 4]를 [수학식 1]에 대입하여 [수학식 7]을 도출하고, [수학식 7]로부터 3차 방정식의 해를 도출하여 현재 풍속을 추정하는 (f) 단계;를 포함한다.MPPT control method by estimating the wind speed of the wind power generation system according to the present invention for achieving the technical problem, (a) deriving the rotational energy of the blade; (B) deriving a main speed ratio from rotational energy of the blade; Efficiency factor

Pitch angle

And speed ratio

(C) deriving a nonlinear function through Equation 3 and approximating the derived nonlinear function to a third order polynomial through Equation 4; (D) deriving through Equation 5 the sum of squared errors of Equations 3 and 4; (E) deriving a sum of squares of errors into a fourth order determinant; And (f) substituting [Equation 4] into [Equation 1] to derive [Equation 7] and deriving a solution of a cubic equation from [Equation 7] to estimate the current wind speed. do.

[Equation 1]

&Quot; (3) "

&Quot; (4) "

&Quot; (5) "

&Quot; (7) "

에 대한 함수는, 주속비(Tip Speed Ratio: TSR)

와, 블레이드 피치각

로 구성되며, 풍속은

이고, 회전속도의 비율은

이며, 블레이드 날개의 경사각도는

이다.Here, the wind speed is a constant that is unknown because anemometer is not used, and the efficiency factor of the blade

The function for, Tip Speed Ratio (TSR)

With blade pitch angle

And wind speed

And the rate of rotation is

The angle of inclination of the blade wing is

to be.

According to the present invention as described above, the blade efficiency curve is approximated by a polynomial to estimate the wind speed based on the blade output power, the angular velocity and the pitch angle.

In addition, according to the present invention, by controlling the rotation of the blade by deriving the rotational speed of the blade having the maximum efficiency based on the estimated wind speed, there is an effect of providing the maximum power point tracking (MPPT).

1 is a graph showing the peripheral speed ratio of the MPPT control method through the wind speed estimation of the wind power generation system according to the present invention.
2 is a diagram of deriving the coefficient by solving the inverse matrix of Equation 6 of the MPPT control method through the wind speed estimation of the wind power generation system according to the present invention, comparing the approximation curve and the actual curve.
Figure 3 is a flow chart illustrating a MPPT control method through the wind speed estimation of the wind power generation system according to the present invention.
Figure 4 is a flow chart illustrating a process after step S60 of the MPPT control method through the wind speed estimation of the wind power generation system according to the present invention.

Specific features and advantages of the present invention will become more apparent from the following detailed description based on the accompanying drawings. Prior to this, terms and words used in the present specification and claims are to be interpreted in accordance with the technical idea of the present invention based on the principle that the inventor can properly define the concept of the term in order to explain his invention in the best way. It should be interpreted in terms of meaning and concept. It is to be noted that the detailed description of known functions and constructions related to the present invention is omitted when it is determined that the gist of the present invention may be unnecessarily blurred.

First, wind power converts the kinetic energy of the wind from the blade (blade) to the rotational energy, and converts it into electrical energy through the generator. At this time, the rotational speed of the generator is controlled to convert the kinetic energy of the wind into the rotational energy of the blade as much as possible.

Equation 1 below is a formula for deriving the rotational energy of the blade.

[Equation 1]

에 대한 함수는, 주속비(Tip Speed Ratio: TSR)

와, 블레이드 피치각

로 구성된다.Here, the wind speed is a constant that is unknown because anemometer is not used, and the efficiency factor of the blade

The function for, Tip Speed Ratio (TSR)

With blade pitch angle

.

는 하기의 [수학식 2]와 같은 비선형적 함수형태를 갖으며, 이 효율함수의 인자로는 풍속

과, 회전속도의 비율

과, 블레이드 날개의 경사각도

를 포함한다.Circumferential speed ratio in [Equation 1] above

Has a nonlinear function form as shown in Equation 2 below.

Ratio of rotation speed

And tilt angle of blade wing

.

&Quot; (2) "

를 측정해서 회전속도

를 항상 위 비율에 맞게 변화시켜주어야 한다. 1 is a graph representing [Equation 2]. The horizontal axis represents the main speed ratio, and the vertical axis represents the efficiency. Wind speeds due to maximum efficiency at specific speed ratios (8.1 for this blade)

Rotational speed by measuring

Should always be changed to the above ratio.

At this time, if the output of the blade is known and the efficiency coefficient is approximated by the polynomial, it can be transformed into a single-variable equation having only the wind speed as an unknown.

에서 피치각을 0도로 고정시킨다고 가정하는 경우, 아래의 [수학식 3]과 같이 효율계수는 TSR만의 비선형함수로 도출할 수 있고, 이를 다항식으로 근사할 경우, 다항식의 차수를 결정해야하며 근사의 적합도와 프로세서의 연산량을 고려하여 [수학식 4]와 같이 3차 다항식으로 근사할 수 있다.Also, efficiency factor

If we assume that the pitch angle is fixed at 0 degrees, the efficiency coefficient can be derived as a nonlinear function of TSR only, as shown in [Equation 3] below. Considering the goodness of fit and the amount of computation of the processor can be approximated to the third order polynomial as shown in [Equation 4].

&Quot; (3) "

&Quot; (4) "

At this time, in order to approximate, first, an approximation error that is a difference between Equations 3 and 4 must be derived, and the error must be minimized in the entire area of the actual speed ratio. In order to establish this equation, the sum of squared errors is derived as shown in [Equation 5].

&Quot; (5) "

Since the sum of squared errors should be '0' when differentiating each coefficient of the approximation equation, four equations can be made with four approximation coefficients. It can be expressed as

&Quot; (6) "

Coefficients are derived by solving the inverse of the matrix, and the approximation curve is compared with the actual curve as shown in FIG. 2.

In addition, when [Equation 4] is substituted into [Equation 1], it is arranged as shown in [Equation 7], and when it is arranged for wind speed, it is derived as shown in [Equation 8]. By solving the cubic equation for, we can find the wind speed.

This equation has three solutions, but the second root is the actual solution. This equation can be used to predict the current wind speed, so that the optimum rotation speed command can be obtained in the same way as using the anemometer.

&Quot; (7) "

&Quot; (8) "

Hereinafter, the MPPT control method through the wind speed estimation of the wind power generation system according to the present invention with reference to Figure 3 as follows.

First, the rotational energy of the blade is derived through [Equation 1] (S10).

[Equation 1]

에 대한 함수는, 주속비(Tip Speed Ratio: TSR)

와, 블레이드 피치각

로 구성된다.
Here, the wind speed is a constant that is unknown because anemometer is not used, and the efficiency factor of the blade

The function for, Tip Speed Ratio (TSR)

With blade pitch angle

.

Subsequently, the peripheral speed ratio is derived from the rotational energy of the blade through [Equation 2] (S20).

&Quot; (2) "

이고, 회전속도의 비율은

이며, 블레이드 날개의 경사각도는

이다.
Where wind speed is

And the rate of rotation is

The angle of inclination of the blade wing is

to be.

의 피치각

과 주속비

를 [수학식 3]을 통해 비선형함수로 도출하고, 도출한 비선형함수를 [수학식 4]를 통해 3차 다항식으로 근사한다(S30).Followed by the efficiency factor

Pitch angle

And speed ratio

Is derived as a nonlinear function through [Equation 3], and the derived nonlinear function is approximated as a third order polynomial through [Equation 4] (S30).

&Quot; (3) "

&Quot; (4) "

Subsequently, the sum of the squares of the errors with respect to [Equation 3] and [Equation 4] is derived through [Equation 5] (S40).

&Quot; (5) "

Subsequently, the sum of squares of the obtained errors is derived as a fourth order determinant as shown in [Equation 6] (S50).

&Quot; (6) "

Substituting [Equation 4], which is the polynomial equation of the efficiency coefficient curve, into [Equation 1] to derive [Equation 7], and derive the solution of the cubic equation from [Equation 7] to estimate the current wind speed. (S60).

&Quot; (7) "

Meanwhile, referring to FIG. 4, the process after step S60 of the MPPT control method through the wind speed estimation of the wind power generation system according to the present invention is as follows.

After step S60, a maximum output point tracking (MPPT) value is calculated by deriving a solution (second root) of the third equation of [Equation 8] obtained by arranging the wind speeds estimated by Equation (7). (S70).

While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. It will be appreciated by those skilled in the art that numerous changes and modifications may be made without departing from the invention. And all such modifications and changes as fall within the scope of the present invention are therefore to be regarded as being within the scope of the present invention.

Claims (5)

In the MPPT control method through the wind speed estimation of the wind power generation system,
(a) deriving rotational energy of the blade;
(b) deriving a peripheral speed ratio from the rotational energy of the blade;
(c) efficiency factor

Pitch angle

And speed ratio

Deriving a nonlinear function through [Equation 3] and approximating the derived nonlinear function to the third order polynomial through [Equation 4];
(d) deriving the sum of squared errors of Equations 3 and 4 through Equation 5;
(e) deriving a sum of squares of the errors as a fourth order determinant; And
(f) substituting [Equation 4] into [Equation 1] to derive [Equation 7], and deriving a solution of a cubic equation from [Equation 7] to estimate the current wind speed. MPPT control method through the wind speed estimation of the wind power generation system, characterized in that.
[Equation 1]

&Quot; (3) "

&Quot; (4) "

&Quot; (5) "

&Quot; (7) "

Here, the wind speed is a constant that is unknown because anemometer is not used, and the efficiency factor of the blade

The function for, Tip Speed Ratio (TSR)

With blade pitch angle

And wind speed

And the rate of rotation is

The angle of inclination of the blade wing is

to be.
The method of claim 1,
The step (a)
[Equation 1] MPPT control method through the wind speed estimation of the wind power generation system, characterized in that to derive the rotational energy of the blade.
[Equation 1]

Here, the wind speed is a constant that is unknown because anemometer is not used, and the efficiency factor of the blade

The function for, Tip Speed Ratio (TSR)

With blade pitch angle

.
The method of claim 1,
The step (b)
[Equation 2] MPPT control method by estimating the wind speed of the wind power generation system, characterized in that derived from the rotational speed of the blade energy.
&Quot; (2) "

Where wind speed is

And the rate of rotation is

The angle of inclination of the blade wing is

to be.
The method of claim 1,
The step (e)
MPPT control method by estimating the wind speed of the wind power generation system, characterized in that the sum of the squares of the error is derived by the fourth order matrix as shown in [Equation 6].
&Quot; (6) "

Where the speed ratio is

The efficiency factor of the blade is

to be.
The method of claim 1,
After the step (f)
(g) [Equation 7] is summarized as [Equation 8],
And calculating a maximum output point tracking (MPPT) value by deriving a solution to the cubic equation of Equation (8).
&Quot; (8) "

Where wind speed is

And the rate of rotation is

The angle of inclination of the blade wing is

to be.

Images