CN100409562C - Control method for tracking maximum power point of wind electric power generation - Google Patents

Abstract

The special point is the twin closed loop method for controlling rotary speed and power mutual independently. The control process includes 3 steps: during the original state, executes the power signal feedback control against the fan according to the original max power curve; during the smaller change of wind speed, executes mountain climbing method for controlling optimal power; via the rotary speed disturbance, obtains the max output power under the recent wind speed and the corresponding generator rotary speed. Then according to the original max power curve and the new added data points, obtains modified max power curve. During the larger change of wind speed, executes the power signal feedback control according to the mortified new max power curve. This method adapts the rapid change of the wind speed and is independent from the functions of the wind field and the fan. It can restrain the system disturb near the max power point effectively.

Description

Control method for tracking maximum power point of wind electric power generation

Technical field:

The present invention relates to control method for tracking maximum power point of wind electric power generation.More specifically say so and be applied in maximum power point-tracing control method in the variable-speed constant-frequency wind power generation system.

Background technology:

Three kinds of methods that conventional maximal power tracing (MPPT) control is adopted in the variable-speed constant-frequency wind power generation system are to be respectively tip speed ratio control method, power signal FEEDBACK CONTROL and climbing method optimizing control.

Tip speed ratio control method is to adjust by the mechanical structure to wind wheel, make wind wheel catch maximum power, mainly depend on the tip speed ratio and the wind speed curve of blower fan, control the angle that facings the wind of blade by the change pulp grinder structure of control wind wheel, thereby make the tip speed ratio of wind wheel under this state reach maximum.This control method is to the performance parameter sensitivity of wind wheel, and need accurately measure wind speed, therefore is of limited application.

Power signal FEEDBACK CONTROL and climbing method optimizing control all belongs to electric control method, by the control of wind generator system grid-connected converter to motor, thereby reaches the purpose of Maximum Power Output.The power signal FEEDBACK CONTROL is according to blower fan maximum power curve, and control blower fan power output makes it follow the maximum power curve under different rotating speeds.This method can adapt to change of wind velocity preferably, but to the fan parameter sensitivity, and there is error in the maximum power curve, thus the precision of the power tracking that has the greatest impact, and because different type of machines parameter difference, thereby its adaptability is relatively poor.Climbing method optimizing control is to adopt rotating speed disturbance control method, according to the power ratio before and after the rotation speed change, thus the size and Orientation of definite rotating speed disturbance.But the method can not be applicable to the quick variation of blower fan, because when wind speed changes, cause the variation of wind speed round, therefore a part of wind energy is stored in the impeller, so can not reflect the variable quantity of wind energy fully to the measurement of output of a generator, therefore cause the inaccurate of power control, and because the rotating speed disturbance causes near the vibration of the system of maximum power point.

Summary of the invention:

The present invention is for avoiding above-mentioned existing in prior technology weak point, a kind of any characteristic that does not rely on wind field and blower fan is provided, the quick variation of wind speed can be adapted to, near the control method for tracking maximum power point of wind electric power generation of the system disturbance of maximum power point can be effectively suppressed.

The technical scheme that technical solution problem of the present invention is adopted is:

Control method for tracking maximum power point of wind electric power generation of the present invention is provided with each other the independently two closed loop control methods of rotating speed and power, and control procedure is divided into three phases:

Under a, the initial condition,, obtain original maximum power curve, according to described original maximum power curve blower fan is carried out the power signal FEEDBACK CONTROL when moving for the first time according to the original power characteristic of blower fan;

B, wind speed change hour, adopt climbing method power control method for improving, obtain peak power output under the current wind speed and corresponding generator speed by the rotating speed disturbance, according to original maximum power curve and initiate data point, the maximum power curve is revised, new data point of every acquisition is revised in real time to curve in running, thereby obtains revised maximum power curve;

When c, wind speed change greatly,, system is adopted the power signal FEEDBACK CONTROL according to revised up-to-date power curve.

The characteristics of the inventive method are that variable step control method is adopted in the rotating speed disturbance in the stage b, and when the size of rotating speed disturbance medium speed instruction changed according to different wind speed, output of a generator changed and the ratio k i of rotation speed change determines

$k_i<\frac{\left|\mathrm{\&Delta;\&omega;}\right|}{\left|\mathrm{\&Delta;P}\right|}$

In the formula: k _iBe ratio, Δ ω is an incremental speed, and Δ P is a power increment;

The judgement of the direction of rotary speed instruction is provided by following table

Rule of judgment:	ΔP(k)＞0	ΔP(k)＜0
			Δω(k-1)＝0	Δω(k)＞0	Δω(k)＜0
Δω(k-1)＞0	Δω(k)＞0	Δω(k)＜0
			Δω(k-1)＜0	Δω(k)＜0	Δω(k)＞0

In the table: Δ ω (k-1), Δ ω (k)＜0 be for rotating speed subtracts instruction, Δ ω (k-1), and Δ ω (k)＞0 increases instruction for rotating speed.

Compared with the prior art, beneficial effect of the present invention is embodied in:

The present invention combines with the control method of climbing the mountain with the power signal FEEDBACK CONTROL, changes when very fast at wind speed, adopts the power signal FEEDBACK CONTROL, according to the maximum power curve, blower fan is carried out power control; And change when slow at wind speed, adopt climbing method control, and carry out on-line study, the maximum power curve of blower fan is upgraded.Make the system acquisition maximal wind-energy according to the different control method of the different choice of wind regime, and make system's power output maximum.The inventive method does not rely on any characteristic of wind field and blower fan, has accelerated the trace performance that system changes wind speed, can guarantee the accuracy of tracking results simultaneously.

Description of drawings:

Fig. 1 is the inventive method schematic diagram.

Fig. 2 is maximum power curve fit of the present invention.

Fig. 3 is climbing method power optimizing control principle figure of the present invention.

Fig. 4 is a control method flow chart of the present invention.

By the following examples, and in conjunction with the accompanying drawings the present invention is further described.

Embodiment:

The present embodiment setting is two closed loop control methods of rotating speed and power independently each other, and control procedure is divided into three phases:

Under a, the initial condition,, obtain original maximum power curve, according to described original maximum power curve blower fan is carried out the power signal FEEDBACK CONTROL when moving for the first time according to the original power characteristic of blower fan;

B, wind speed change hour, adopt climbing method power control method for improving, obtain peak power output under the current wind speed and corresponding generator speed by the rotating speed disturbance, according to original maximum power curve and initiate data point, the maximum power curve is revised, new data point of every acquisition is revised in real time to curve in running, thereby obtains revised maximum power curve;

When c, wind speed change greatly,, system is adopted the power signal FEEDBACK CONTROL according to revised up-to-date power curve.

Setting about the power signal feedback:

As shown in Figure 1, in power ring, promptly control switch is in 1 position.When wind speed increases, wind wheel is caught power to be increased, but the transient speed of blower fan does not change the then machine torque of blower fan increase, because the control action of the power ring of generator, its output electromagnetic power is constant, and rotating speed do not change, so the electromagnetism resistive torque of generator is constant, therefore cause the rising of system's rotating speed, by inquiry maximum power curve,, make it to reach maximum then by the power output of power ring control generator.

In the process according to the maximum power curve controlled, the accuracy of its power output control mainly depends on the order of accuarcy of maximum power curve.Owing to fan operation can if directly design or the test data that provides according to blower fan manufacturer controlled, can not guarantee the accuracy of blower fan in running because various losses cause curve error.Therefore present embodiment design curve fitting method is come online in real time correction maximum power curve, makes it to keep optimum state.

According to the least-squares estimation of parameter in curve fit and the empirical equation, in real time curve is carried out match.

When system runs on maximum power point, catch formula according to the wind generator system wind energy:

$P_{m\max }=\frac{1}{2}\mathrm{\&rho;\&pi;}{r}_m^2{C}_{p\max }{\left(\frac{r_m}{{\mathrm{\&lambda;}}_{\mathrm{opt}}}\right)}^3\&CenterDot;{\mathrm{\&omega;}}^3$

In the formula: P _MmaxBe the blower fan Maximum Power Output, ρ is an atmospheric density, is similar to think constant, r _mBe blower fan wind wheel radius, C _PmaxBe maximal wind-energy usage factor, λ _OptBe optimum tip speed ratio, the ω generator speed;

If: $k=\frac{1}{2}\mathrm{\&rho;\&pi;}{r}_m^2{C}_{p\max }{\left(\frac{R}{{\mathrm{\&lambda;}}_{\mathrm{opt}}}\right)}^3$ Be worth constantly, so system's power output is directly proportional with the cube method of rotating speed.At this moment: make z=ω ³, then formula (1) can be converted into:

P＝k·z (2)

Provide n on P～ω curve to measured value (z ₁, P ₁), (i=1,2 ..., n), and then the numerical value of definite parameter k;

Carry out curve fit by least square method:

$Q=\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{(P_i-k\&CenterDot;z_i)}^2---\left(3\right)$

For making Q reach maximum, then should satisfy $\&PartialD;Q/\&PartialD;k=0,$ Push away:

$k=\frac{\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{P}_i\&CenterDot;z}{\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{z}^2}---\left(4\right)$

Thereby acquisition blower fan power output and generator speed relational expression: $P=k\&CenterDot;{\mathrm{\&omega;}}^3=\frac{\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{P}_i\&CenterDot;z}{\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{z}^2}\&CenterDot;{\mathrm{\&omega;}}^3$

Therefore in system's running, can by when wind speed is steady to the search of maximum power point, and then original maximum power curve a upgraded, thereby guarantee accuracy when blower fan adopts the power signal FEEDBACK CONTROL, revise back maximum power curve and intend b as shown in Figure 2.

The climbing method control method

Referring to Fig. 3, at wind speed v ₁Down, system stable operation is in the A point, and generator speed is ω ₁, the Maximum Power Output P of system _AWind speed becomes v ₂, because impeller inertia, rotating speed can not change immediately, still is ω ₁, this moment, system ran on the B point, and power output is P _B

$T_L-T_e=J\&CenterDot;\frac{\mathrm{d\&omega;}}{\mathrm{dt}}---\left(5\right)$

By equation of motion (5) as can be known, because the blower fan machine torque increases, must cause the generator electromagnetic torque to increase by the speed ring adjusting, output of a generator increases, and the MPPT controller provides incremental speed, and control system is quickened operation.Blower fan carries out the power optimizing along B-C-D, and generator then quickens operation along A-D.Rotating speed reaches ω ₂The time, power output reaches maximum P _DIn like manner analyze the wind speed decreased situation.

When control, consider, when carrying out the rotating speed disturbance, regulate its output instantaneous power and reduce, therefore when power is sampled comparison, can judge whether der Geschwindigkeitkreis reaches stable earlier according to formula (6) by der Geschwindigkeitkreis.

|ω-ω _ref|≤σ (6)

The rotating speed disturbance can be adopted the method for disturbance of fixed step size rotating speed or the disturbance of variable step rotating speed.Because the fixed step size disturbance is vibrated system near maximum power point, and tracking speed is slower, therefore in order effectively to suppress system vibration and the rapidity that guarantees to follow the trail of, this paper adopts the rotating speed disturbance control method of variable step.When its step sizes can change according to different wind speed, output of a generator changed and the ratio of rotation speed change is determined, as the formula (7).

$k_1<\frac{\left|\mathrm{\&Delta;\&omega;}\right|}{\left|\mathrm{\&Delta;P}\right|}---\left(7\right)$

The rotary speed instruction direction can be judged by table 1.

Table 1 rotary speed instruction direction is judged

Rule of judgment:	ΔP(k)＞0	ΔP(k)＜0
			Δω(k-1)＝0	Δω(k)＞0	Δω(k)＜0
Δω(k-1)＞0	Δω(k)＞0	Δω(k)＜0
			Δω(k-1)＜0	Δω(k)＜0	Δω(k)＞0

Wherein: Δ ω (k-1), Δ ω (k)＜0 be for rotating speed subtracts instruction, Δ ω (k-1), and Δ ω (k)＞0 increases instruction for rotating speed.

Because being changed to of rotary speed instruction is discrete, so power output can only be near maximum.Therefore in the time of between variable power is less than a certain given area, provide, can think to reach maximum power that keep incremental speed this moment is 0 by formula (8).

|ΔP|＝|P(k)-P(k-1)|≤P _σ (8)

Choosing of control method

For the switching of the different control methods in the control procedure, the variation that causes the blower fan machine torque that can change according to wind speed, thereby the variation of generator rotor current torque component.Therefore by judging the rate of change of generator rotor current torque component, can whether stablize wind speed and judge.

If the rate of change of torque component is in the rotor current:

$\mathrm{\&Lambda;}=\frac{\mathrm{\&Delta;}{I}_q}{\mathrm{\&Delta;t}}---\left(9\right)$

According to formula (9), give certain value σ, as Λ 〉=σ, think that wind speed changes, therefore adopt the power signal feedback, follow the tracks of the maximum power curve, system is controlled.When Λ≤σ, think that wind speed is steady, adopt climbing method optimizing control, it is carried out the rotating speed disturbance, seek the peak power output value point under this wind speed, and the maximum power curve is revised.The method is indifferent to its air speed value, as long as wind speed is stable.

Concrete control flow in the present embodiment as shown in Figure 4

To torque current sampling n time, be averaged and judge the wind speed stable case, if wind speed is stable, then adopt der Geschwindigkeitkreis to control, by sampling to power, carry out MPPT maximum power point tracking, then the maximum power curve is carried out match, if judge the wind speed instability, then adopt power ring to control, current rotating speed is sampled, tabling look-up by the maximum power curve obtains optimal power output, thereby compare with power feedback signal, control then.

Claims (3)

1. a control method for tracking maximum power point of wind electric power generation is provided with each other the independently two closed loop control methods of rotating speed and power, and control procedure is divided into three phases:

Under a, the initial condition,, obtain original maximum power curve, according to described original maximum power curve blower fan is carried out the power signal FEEDBACK CONTROL when moving for the first time according to the original power characteristic of blower fan;

B, wind speed change hour, adopt climbing method power control method for improving, obtain peak power output under the current wind speed and corresponding generator speed by the rotating speed disturbance, according to original maximum power curve and initiate data point, the maximum power curve is revised, new data point of every acquisition is revised in real time to curve in running, thereby obtains revised maximum power curve;

When c, wind speed change greatly,, system is adopted the power signal FEEDBACK CONTROL according to revised up-to-date power curve;

It is characterized in that the rotating speed disturbance employing variable step control method in the described stage b, when the size of rotating speed disturbance medium speed instruction changed according to different wind speed, output of a generator changed and the ratio k i of rotation speed change determines

$k_1<\frac{\left|\mathrm{\&Delta;\&omega;}\right|}{\left|\mathrm{\&Delta;P}\right|}$

In the formula: k _iBe ratio, Δ ω is an incremental speed, and Δ P is a power increment;

The judgement of the direction of rotary speed instruction is provided by following table

Rule of judgment: ΔP(k)＞0 ΔP(k)＜0 Δω(k-1)＝0 Δω(k)＞0 Δω(k)＜0 Δω(k-1)＞0 Δω(k)＞0 Δω(k)＜0 Δω(k-1)＜0 Δω(k)＜0 Δω(k)＞0

In the table: Δ ω (k-1), Δ ω (k)＜0 be for rotating speed subtracts instruction, Δ ω (k-1), and Δ ω (k)＞0 increases instruction for rotating speed.

2. control method according to claim 1 is characterized in that described curve is revised in real time is the curve-fitting method that adopts least square method to estimate, when system runs on maximum power point, catches formula according to the wind generator system wind energy:

$P_{m\max }=\frac{1}{2}{\mathrm{\&rho;\&pi;r}}_m^2{C}_{p\max }{\left(\frac{r_m}{{\mathrm{\&lambda;}}_{\mathrm{opt}}}\right)}^3\&CenterDot;{\mathrm{\&omega;}}^3$

In the formula: P _MmaxBe the blower fan Maximum Power Output, ρ is an atmospheric density, is similar to think constant, r _mBe blower fan wind wheel radius, C _PmaxBe maximal wind-energy usage factor, λ _OptBe optimum tip speed ratio, the ω generator speed;

Obtain blower fan power output and generator speed relational expression by least square method:

$P=k\&CenterDot;{\mathrm{\&omega;}}^3=\frac{\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{P}_i\&CenterDot;z}{\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{z}^2}\&CenterDot;{\mathrm{\&omega;}}^3.$

3. control method according to claim 1 is characterized in that the size of the rate of change by judging the generator rotor current torque component is judged the change of wind velocity size.

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