CN108825434A - Blower variable-pitch optimization method based on the control of wind wheel kinetic energy smooth power - Google Patents

Abstract

The invention discloses a wind turbine pitch optimization method based on wind rotor kinetic energy smooth power control. Aiming at the problem of frequent wind turbine pitch change under high wind speed conditions, the method realizes smooth output power based on wind rotor kinetic energy buffering, Make full use of the kinetic energy buffering/releasing effect of the large moment of inertia wind wheel at any pitch angle to realize the speed range control of the fan at any pitch angle; the variable speed adjustment is used in conjunction with the variable pitch adjustment, and the variable speed adjustment is smooth from small amplitude to high For wind power fluctuations caused by frequency wind speed fluctuations, the pitch adjustment should respond to large-value, low-frequency wind speed changes. The present invention effectively reduces the amplitude and frequency of the pitch-changing action while not enlarging the influence of power fluctuations on the grid frequency, reduces the fatigue degree and blade load of the pitch-changing servo mechanism, and prolongs the life of the fan.

Description

Wind turbine pitch optimization method based on smooth power control of wind rotor kinetic energy

technical field

The invention belongs to the field of wind turbine control, and in particular relates to a wind turbine pitch optimization method based on wind rotor kinetic energy smooth power control.

Background technique

The output of wind turbines has significant intermittent and random fluctuation characteristics. With its large-scale and high penetration rate connected to the grid, the large fluctuations in wind power power from seconds to minutes will make the power system face more severe frequency stability problems. For this reason, wind turbines abandon the traditional maximization of wind energy capture and switch to smooth power control, which has become one of the effective ways to relieve the pressure of frequency regulation on the power grid.

At present, the methods for smoothing the output of wind turbines can be mainly divided into two categories: the smooth power method relying on external energy storage and the method relying on wind turbine control. For the former, although the energy buffer of energy storage equipment can effectively alleviate the fluctuation of wind power, it also greatly increases the cost of power generation and the difficulty of operation and maintenance of wind farms. Therefore, considering that the wind rotor with large moment of inertia can also be used as an energy buffer, the method of wind turbine control has become a current research hotspot.

Power smoothing based on wind turbine control mainly includes priority pitch angle control and priority speed control. The former changes the input aerodynamic power by adjusting the pitch angle, and its too frequent pitch angle action inevitably increases the fatigue of the pitch servo mechanism and the blade load. In contrast, the priority speed control not only realizes the smooth output of wind power by alternately accumulating and releasing the kinetic energy of the wind rotor, but also effectively reduces the amount of action of the pitch angle. This will be beneficial for engineering applications of smooth power control.

However, studies have found that wind turbines with smooth power control often accelerate to rated speed easily due to the use of rotor acceleration to buffer kinetic energy. Reaching the upper limit of the speed not only invalidates the kinetic energy buffering of the wind rotor, but also shifts the focus of wind turbine control to constant speed control that only relies on pitch adjustment. At this time, the fan still needs frequent and large amount of pitch angle adjustments to avoid overspeeding of the fan, which will also increase the fatigue and blade load of the pitch servo mechanism. The reason is that existing power smoothing methods are limited to the independent application of variable speed control and pitch control, resulting in that only the wind rotor with a pitch angle of zero degrees is used as a kinetic energy buffer.

Contents of the invention

The purpose of the present invention is to provide a wind turbine pitch optimization method based on wind rotor kinetic energy smooth power control, by using the wind rotor at any pitch angle as a kinetic energy buffer, variable speed adjustment and pitch adjustment are carried out alternately, to a great extent On the other hand, the action range and frequency of the pitch angle are reduced, and the action pressure and blade load of the pitch servo mechanism are reduced.

The technical solution to realize the object of the present invention is: a method for optimizing wind turbine pitch based on smooth power control of wind rotor kinetic energy, comprising the following steps:

Step 1. Obtain the structural parameters and aerodynamic parameters of the fan. The structural parameters include the blade radius R of the fan, the rated speed ω _rate , the aerodynamic parameters include the air density ρ, the optimal tip speed ratio λ _opt and the maximum wind energy utilization coefficient C _pmax ;

Step 2. Determine the speed range [ω _lim.l ,ω _lim.u ] based on the smooth power control method of the wind rotor kinetic energy;

Step 3. Select the pitch angle control mode according to the rotational speed signal ω _r . When ω _lim.l ≤ ω _r ≤ ω _lim.u , select mode 1: constant pitch angle mode, and go to step 6; otherwise, go to step 4;

Step 4. Select the pitch angle control mode according to the rotational speed signal ω _r . When ω _r > ω _lim.u , select mode 2: increase the pitch angle mode and go to step 6; otherwise, go to step 5;

Step 5. Select the pitch angle control mode according to the rotational speed signal ω _r , when ω _r <ω _lim.l , select mode 3: down-regulate the pitch angle mode, and enter step 6;

Step 6. Obtain the reference pitch angle command β _ref .

Compared with the prior art, the present invention has the remarkable advantages as follows: 1) the present invention proposes a wind turbine pitch optimization method based on wind rotor kinetic energy smooth power control, which solves the problem of frequent pitch change in the existing method under high wind speed wind conditions 2) The present invention discloses the steps of the wind turbine pitch optimization method based on wind rotor kinetic energy smooth power control, by using any pitch angle (zero degree and non-zero degree) wind rotor as a kinetic energy buffer, it can ensure that the power does not expand While reducing the impact of fluctuations on the frequency of the grid, the amplitude and frequency of the pitch angle action are greatly reduced, and the action pressure and blade load of the pitch servo mechanism are reduced.

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Description of drawings

Fig. 1 is a flow chart of the wind turbine pitch optimization method based on wind rotor kinetic energy smooth power control of the present invention.

Fig. 2 (a)～Fig. 2 (c) are the experimental results of the effectiveness verification of the present invention, wherein Fig. 2 (a) is the wind speed sequence, rotating speed, paddle of fan simulator under the proposed method of the present invention and existing method Pitch angle and power curve figure, Fig. 2 (b) is the comparison diagram of the moment magnitude that the proposed method of the present invention and existing method cause to blade root when changing pitch, Fig. 2 (c) is the proposed method of the present invention and existing The frequency fluctuation comparison diagram of the fan output power introduced into the grid under the method.

Detailed ways

Referring to Fig. 1, a wind turbine pitch optimization method based on smooth power control of wind rotor kinetic energy includes the following steps:

Step 1. Obtain the structural parameters and aerodynamic parameters of the fan. The structural parameters include the blade radius R of the fan, the rated speed ω _rate , the aerodynamic parameters include the air density ρ, the optimal tip speed ratio λ _opt and the maximum wind energy utilization coefficient C _pmax ;

Step 2. Determine the speed range [ω _lim.l ,ω _lim.u ] based on the wind rotor kinetic energy smoothing power control method;

Step 3. Select the pitch angle control mode according to the rotational speed signal ω _r . When ω _lim.l ≤ ω _r ≤ ω _lim.u , select mode 1: constant pitch angle mode, and go to step 6; otherwise, go to step 4;

Step 4. Select the pitch angle control mode according to the rotational speed signal ω _r . When ω _r > ω _lim.u , select mode 2: increase the pitch angle mode and go to step 6; otherwise, go to step 5;

Step 5. Select the pitch angle control mode according to the rotational speed signal ω _r . When ω _r <ω _lim.l , select mode 3: lower pitch angle mode, and enter step 6;

Step 6. Obtain the reference pitch angle command β _ref .

Further, the specific determination method of the smooth power control method based on the kinetic energy of the wind rotor and the speed range [ω _lim.l ,ω _lim.u ] in step 2 is as follows:

The smoothing of fan output power based on the kinetic energy of the wind rotor is realized by the kinetic energy buffering function of the wind rotor. When the wind speed increases, the fan rotates faster and stores kinetic energy. When the wind speed decreases, the fan speed slows down, releasing kinetic energy. Its essence is to smooth the wind rotor speed ω _r , and the smoothed reference speed ω _ref is specifically calculated as follows:

The fan operates in the maximum power point tracking control mode, and its maximum output power P _max is

P _max ＝ T _e ω _opt

Among them, T _e is the electromagnetic torque, ω _opt is the optimal speed.

The average value of the maximum output power of the fan in period T for

Among them, t represents the current time, and T represents the period.

The kinetic energy E of the wind wheel is defined as

Among them, J _g represents the moment of inertia of the generator, J _ω represents the moment of inertia of the wind rotor, and J _g +J _ω represents the equivalent moment of inertia of the wind turbine.

The smoothed rotor reference speed ω _ref is calculated as

Among them, △P represents the maximum output power P _max and the average value of the maximum output power period T The difference, E represents the kinetic energy of the wind wheel.

In order to avoid fan instability due to too low speed, set the lower limit of the fan speed range ω _lim.l for stable operation. In the present invention, the lower limit value of the rotational speed range is set as ω _lim.l =0.7ω _rate , and the upper limit value of the rotational speed range is set as ω _lim.u =ω _rate .

Further, the specific form of the constant pitch angle mode in step 3:

When ω _lim.l ≤ω _r ≤ω _lim.u , the pitch angle of the fan remains unchanged, and the output power of the fan is smoothed by making full use of the kinetic energy buffering effect of the wind rotor at any pitch angle.

Further, the specific form of the up-adjustment pitch angle mode in step 4:

When ω _r >ω _lim.u , in order to prevent the wind rotor speed from exceeding the rated speed, the wind energy capture coefficient is reduced by increasing the pitch angle, thereby reducing the wind rotor speed. The given form of the pitch angle is:

β _ref ＝K _uP (ω _r -ω _lim.u )+K _uI ∫(ω _r -ω _lim.u )dt

Among them, K _uP and K _uI are the proportional coefficient and integral coefficient in the process of increasing the pitch angle, respectively.

Further, the specific form of the down-regulation pitch angle mode in step 5:

When ω _r <ω _lim.l , in order to prevent the wind rotor from shutting down due to too low speed, the wind energy capture coefficient is increased by reducing the pitch angle, thereby increasing the wind rotor speed. The given form of the pitch angle is:

β _ref ＝K _lP (ω _r -ω _lim.l )+K _lI ∫(ω _r -ω _lim.l )dt

Among them, K _lP and K _lI are the proportional coefficient and integral coefficient in the process of lowering the pitch angle, respectively

Below in conjunction with embodiment the present invention is described in further detail:

Example

The open source professional wind turbine simulation software FAST (Fatigue, Aerodynamics, Structures, and Turbulence) provided by the US National Renewable Energy Laboratory (NREL) is used to simulate the control effect. The wind turbine model adopts the 600kW CART3 test model developed by NREL, and the specific parameters are shown in Table 1.

Table 1 Main parameters of NREL 600kW CART3 wind turbine

Taking the wind rotor speed ω _r as input, the output torque command and the pitch angle command β _ref , and then send the two commands to the generator and the pitch servo mechanism respectively.

The realization of the smooth power control method based on the kinetic energy of the wind rotor and the speed range of the pitch optimization method are determined as follows:

The fan operates in the maximum power point tracking control mode, and its maximum output power P _max is

P _max ＝ T _e ω _opt

Among them, T _e is the electromagnetic torque, ω _opt is the optimal speed.

The average value of the maximum output power of the fan in the cycle T for

Among them, t represents the current time, and T represents the period.

The kinetic energy E of the wind wheel is defined as

Among them, J _g represents the moment of inertia of the generator, J _ω represents the moment of inertia of the wind rotor, and J _g +J _ω represents the equivalent moment of inertia of the wind turbine.

The smoothed rotor reference speed ω _ref is calculated as

Among them, △P represents the maximum output power P _max and the average value of the maximum output power period T The difference, E represents the kinetic energy of the wind wheel.

The speed range of the fan pitch optimization method based on the smooth power control of the wind rotor kinetic energy is determined as follows:

In order to avoid fan instability due to too low speed, the lower limit of the fan speed range ω _lim.l should be set for stable operation of the fan. Usually, the lower limit value of the rotational speed range is set as ω _lim.l =0.7ω _rate , and the upper limit value of the rotational speed range is set as ω _lim.u =ω _rate .

In the formula, proportional coefficients K _uP , K _lP and integral coefficients K _uI , K _lI are constant parameters.

Then, the operation mode of the fan is determined according to the change of the rotational speed. The specific flow chart is shown in Figure 1.

Mode 1: When ω _r > ω _lim.u , the fan is in the stage of increasing the pitch angle;

Mode 2: When ω _r <ω _lim.l , the fan is in the stage of pitch angle reduction;

Mode 3: When ω _lim.l ≤ω _r ≤ω _lim.u , the pitch angle of the fan remains unchanged, and the output power of the fan is smoothed by making full use of the kinetic energy buffering effect of the wind rotor at any pitch angle.

Finally, the present invention is verified experimentally through the fan simulator platform. A 600s turbulent wind speed sequence is selected to conduct experiments on the existing method and the improved method proposed by the present invention respectively, and the experimental results are shown in Fig. 2(a) to Fig. 2(c). Curve in Fig. 2 (a) is wind speed sequence, rotating speed, pitch angle and power signal respectively, and solid straight line in the rotating speed figure is the upper limit of the rotational speed of setting, and dotted straight line is the lower limit of rotational speed of setting, and the rotational speed of the proposed method of the present invention runs The range is wider than the existing method, and the pitch angle is kept constant for a long time, and the pitch frequency is lower than the existing method. Fig. 2 (b) shows that the method proposed by the present invention and the existing method compare the moment magnitude caused to the blade root when pitching, and it can be seen that the load on the blade root of the proposed method in the present invention is lower than that of the existing method. Figure 2(c) shows the influence of the output power fluctuations of the two methods on the grid frequency after they are introduced into the grid model. The dotted line at ±0.2 Hz is the maximum frequency deviation allowed by the grid. It can be seen that the two methods affect the grid frequency The impact is within its allowable range.

The above experimental results show that adopting the wind turbine pitch optimization method based on wind rotor kinetic energy smooth power control proposed by the present invention can effectively reduce the amplitude and frequency of the pitch angle action, further verifying the effectiveness and effectiveness of the improved method proposed by the present invention. practicality.

Claims (4)

1. a kind of blower variable-pitch optimization method based on the control of wind wheel kinetic energy smooth power, which is characterized in that include the following steps：

Step 1, structural parameters, the aerodynamic parameter for obtaining blower, structural parameters include the blade radius R of blower, rated speed ω_rate, aerodynamic parameter includes atmospheric density ρ, optimal tip speed ratio λ_optAnd maximal wind-energy usage factor C_pmax；

Step 2, the smooth power control method based on wind wheel kinetic energy, determine revolving speed section [ω_lim.l,ω_lim.u]；

Step 3, according to tach signal ω_rAward setting mode is selected, ω is worked as_lim.l≤ω_r≤ω_lim.uWhen, selection mode 1： Constant propeller pitch angle mode, enters step 6, otherwise, enters step 4；

Step 4, according to tach signal ω_rAward setting mode is selected, ω is worked as_r> ω_lim.uWhen, selection mode 2：Raise pitch Angle mould formula enters step 6, otherwise, enters step 5；

Step 5, according to tach signal ω_rAward setting mode is selected, ω is worked as_r<ω_lim.lWhen, selection mode 3：Lower propeller pitch angle Mode enters step 6；

Step 6 is obtained with reference to propeller pitch angle instruction β_ref。

2. the blower variable-pitch optimization method according to claim 1 based on the control of wind wheel kinetic energy smooth power, feature exist In determining revolving speed section [ω based on the smooth power control method of wind wheel kinetic energy in step 2_lim.l,ω_lim.u] detailed process For：

To wind speed round ω_rCarry out smooth, smoothed out reference rotation velocity ω_refSpecific calculating is as follows：

Fan operation is under MPPT maximum power point tracking control mode, peak power output P_maxFor

P_max=T_eω_opt

Wherein, T_eIt is electromagnetic torque, ω_optIt is optimized rotating speed；

Average value of the blower peak power output in cycle TFor

Wherein, t indicates current time, and T indicates the period.

The kinetic energy E of wind wheel is defined as

Wherein, J_gIndicate the rotary inertia of generator, J_ωIndicate the rotary inertia of wind wheel, J_g+J_ωIndicate that blower Equivalent Rotational is used Amount；

Smoothed out wind wheel reference rotation velocity ω_refIt is calculated as

Wherein, △ P indicates peak power output P_maxWith average value in peak power output cycle TDifference, E indicates that wind wheel is dynamic Energy；

The revolving speed interval limit value ω of blower stable operation is set_lim.l=0.7 ω_rate, the upper limit value ω in revolving speed section_lim.u= ω_rate。

3. the blower variable-pitch optimization method according to claim 1 based on the control of wind wheel kinetic energy smooth power, feature exist In the concrete form of up-regulation propeller pitch angle mode in step 4：

Work as ω_r> ω_lim.uWhen, Wind energy extraction coefficient is reduced by up-regulation propeller pitch angle, so that wind speed round is reduced, propeller pitch angle Given form is：

β_ref=K_uP(ω_r-ω_lim.u)+K_uI∫(ω_r-ω_lim.u)dt

Wherein, K_uP、K_uIRespectively raise the proportionality coefficient and integral coefficient during propeller pitch angle.

4. the blower variable-pitch optimization method according to claim 1 based on the control of wind wheel kinetic energy smooth power, feature exist In the concrete form of downward propeller pitch angle mode in step 5：

Work as ω_r<ω_lim.lWhen, increase Wind energy extraction coefficient by lowering propeller pitch angle, so that wind speed round is promoted, propeller pitch angle Given form is：

β_ref=K_lP(ω_r-ω_lim.l)+K_lI∫(ω_r-ω_lim.l)dt

Wherein, K_lP、K_lIRespectively lower the proportionality coefficient and integral coefficient during propeller pitch angle.