System and a method for optimal yaw control

Abstract

The present invention relates to a system and a method for optimal yaw control of a wind turbine, comprising a tower carrying a rotatable nacelle rotated by a yaw motor, which nacelle comprises at least one generator connected by a shaft to a rotor, comprising one or more wings, which nacelle further comprises means for detecting wind direction and wind velocity, which system performs measurement and storing data related to power production, wind velocity and wind direction. The object of this invention is to optimize the yaw position of a nacelle to the wind direction. The object can be fulfilled by power production measured in a positive direction to actual yaw position is accumulated in a first storages related to measured wind direction and that power production measured in a negative direction to actual yaw position is accumulated in a second storages related to measured wind direction. By this system the power production of the wind turbine is optimized by self-calibrating yaw control.

Claims

1. A system adapted for optimal yaw control of a wind turbine, comprising: a tower carrying a rotatable nacelle rotated by a yaw motor, wherein the nacelle comprises at least one generator connected by a shaft to a rotor, comprising one or more wings, said nacelle further comprises a sensor for detecting wind direction and wind velocity, the system performs measurement and stores data related to power production of the wind turbine, wind velocity and wind direction, wherein power production of the wind turbine measured in a positive direction to actual yaw position, generating a positive yaw error, is accumulated in a first storage and power production of the wind turbine measured in a negative direction to actual yaw position, generating a negative yaw error, is accumulated in a second storage, whereby data related to power production in positive and negative yaw errors is accumulated during a defined time period that is longer than 24 hours, wherein the system calculates an effect of the rotor (Cp) which is defined as:
Cp=P/(½*A*Rho*V.sup.3); where P is generated power, V is wind speed, Rho is air density, and A is rotor area; wherein the system is adapted to provide the positive and negative yaw error and effect of the rotor (Cp) to a yaw correction algorithm, wherein the yaw correction algorithm utilizes the effect of the rotor (Cp) and comparison of power production accumulated for positive and negative yaw errors to generate a power difference signal (Perr), wherein the system is further adapted to transmit the power difference signal (Perr) to a PI controller which performs integration of the signal (Perr) and generates and communicates a yaw offset set point to a yaw controller, and wherein the yaw controller communicates the yaw offset setpoint to the wind turbine and controls the wind turbine yaw using the yaw offset setpoint.

2. The system according to claim 1, wherein the wind turbine is adapted to communicate a yaw signal (γ) representing the actual yaw position of the wind turbine back to the yaw controller, which yaw signal (γ) is communicated further back to the yaw correction algorithm.

3. The system according to claim 2, wherein the yaw correction algorithm is adapted to receive input (P) from the actual power production of the wind turbine.

4. A method for self-calibrating yaw control of the wind turbine system of claim 1 comprising the following steps of operation: a) measuring power production of a wind turbine for positive and negative yaw errors, b) performing accumulation of data representing measured power production for positive and negative yaw errors, c) performing the accumulation of data in at least a defined time period which is longer than 24 hours, d) calculating an effect of the rotor (Cp) using generated power, wind speed, air density, and rotor area of the turbine, e) using the accumulated data of power production in the positive and negative yaw error direction and effect of the rotor (Cp) to estimate a power difference (Perr), f) generating a yaw offset set point based on the power difference (Perr), g) controlling the wind turbine yaw using the yaw offset setpoint.

Description

DESCRIPTION OF THE DRAWING

(1) FIG. 1 discloses theoretical power generation as function of yaw misalignment.

(2) FIG. 2 discloses a block diagram overview of the Yaw Alignment Correction algorithm.

(3) FIG. 3 discloses the method to use this information in order to estimate a power difference.

DETAILED DESCRIPTION OF THE INVENTION

(4) Since the wind is a varying energy resource, it is necessary to track the wind direction with a turbine rotor in order to optimize the power intake. This is done by letting a yaw motor rotate the turbine nacelle according to a yaw sensor (wind vane) by a yawing algorithm. The wind vane and the airflow around the rotor and the nacelle is often offset from the true wind direction, leading to a general drop in power, as illustrated in FIG. 1. The potential in AEP of correcting the yaw offset is up to several percentages, thus being a strong argument for inventing an automatic correction algorithm. The invention described in this document includes a yaw controller which tracks a specific power-optimal yaw set point.

(5) FIG. 1: The blue line is theoretical power 24 as function of yaw misalignment. The yaw measurement is offset by 5°, leading to a power optimal yaw marked by γδ 46. As indicated by arrows, the actual wind direction will have some fluctuations from the point where the yaw adjustment is fixed for a period. Wind direction will change plus and minus to the defined direction. For this patent application we have realized that yaw misalignment often happens simply because the measurement of the wind direction is performed in a rather primitive way, for example by a wind vane placed on the top of a nacelle. Turbulence or shadow effects can change the wind direction and the rotating rotor can have some influence on the actual wind direction. Also the actual shape of the nacelle can have some influence on the actual wind direction. By continuous measurement of actual produced power of a wind turbine, which often takes place, it is possible to perform a correlation to the measured wind direction. In the pending application, this performed an accumulation of power production plus/minus in relation to the yaw position. It is probably necessary to measure the power production for a rather long time in order to have a reliably better adjustment of the yaw position.

(6) FIG. 2: Block diagram overview of the Yaw Alignment Correction algorithm 40. An algorithm calculates a power error P.sub.err 42 used by a PI controller 44. This, in turn, gives a yaw offset setpoint γγ 46 which is tracked by a yaw controller 48. γ: yaw error measurement 50, P: power measurement 24. FIG. 2, which describe how the parts interface to the turbine 4. During normal operation the wind direction 20 changes stochastically, leading to a variation in yaw error γ 46 and power P 24. Hereby, a more or less continuous yaw correction algorithm is operating. This yaw correction algorithm is probably also a module where the accumulation of power production takes place. At least there is a power input to that module. After a defined delay, communication of the Perr 42 to the PI controller 44 will probably start. This PI controller will perform integration of the signal that is received, so that any quick response in the pen signal 42 will be very much delayed. The output from the PI controller is the yaw correction signal 46, which is transmitted into the yaw controller 48. This yaw controller 48 generates a commanding signal 50 to the wind turbine and forces the wind turbine to change its yaw direction. The actual yaw signal 54 is transmitted back to the yaw controller 48 and back to the yaw correction algorithm 40. That way, a continuous adjustment of the yaw signal can be performed, even when the yaw controller 40 has performed with a relatively long time delay, which could be more than 24 hours. In order to get reliable data it is possible to change the yaw direction of the nacelle into a more correct position and hereby maybe increase the yield of power up to 5 percent.

(7) FIG. 3 describes the method to use this information in order to estimate a power difference, P.sub.err, which indicates an imbalance between positive- and negative yaw error. Feeding P.sub.err to a PI controller it is then possible to track zero imbalances by minimizing P.sub.err. The output of the PI controller is the yaw offset setpoint γδ, which is used as the set point for the yaw controller. Thereby the yaw controller becomes self-calibrating in order to maximize the power output: The average power to the left 26 and right 32 of the yaw offset γδ 46 is estimated with sufficient filtering. The difference, P.sub.err 42 indicates whether it is possible to increase the power output by moving the yaw offset set point 46. At FIG. 3 it is clearly indicated that there is a difference in power production between 26 and 32. Therefore this figure indicates that a yaw correction in the correct direction of the PI 26 probably could give a better yield.

(8) It is possible by this patent application to increase the power production of a wind turbine in any place where a wind turbine is operating. The optimization of the production seems to be effective for medium wind maybe starting from 5 metres per second and ending at approximately 15 metres per second. At very low wind velocities it is probably possible to increase the yield but it is very difficult to measure the positive effect. Above 15 metres per second, wind mills are starting maximal production and other regulation means, such as pitch control or maybe stall control will reduce the production, so the method of self-adjustment of the yaw has only minimal effect. But measured over a year, it is a fact that between 5 and 15 metres per second is where most of the power production is performed by nearly all wind turbines. Therefore, the effect of the pending application, which has shown that it is possible to increase the power production maybe up to 5 percent, could be very important, not only at single operating wind mills but probably also at wind farms at land or wind farms at sea. In wind farms every single wind turbine will optimize its yaw position according to the actual wind situation. In that way different shadowing effects are maybe compensated in a highly effective way.

LIST OF NUMBERS

(9) System 2

(10) wind turbine 4

(11) tower 6

(12) nacelle 8

(13) generator 10

(14) shaft 12

(15) rotor 14

(16) wings 16

(17) means for detecting wind direction 18,20

(18) wind velocity 22

(19) power production 24

(20) power production measured in a positive direction 26

(21) yaw position 28

(22) first storages 30

(23) power production measured in a negative direction 32

(24) second storages 34

(25) defined time period 36

(26) yaw correction, algorithm 40

(27) signal Perr 42

(28) PI controller 44

(29) yaw offset set point γδ 46

(30) yaw controller 48

(31) yaw correction signals 50

(32) a yaw signal γ 54