Abstract:
The present invention relates to a method for operating a wind turbine with the steps: detection of the values of predetermined operating parameters by means of suitable sensors, detection of at least one predetermined initial condition, comparison of the detected values to stored values of the operating parameters. The invention further relates to a wind turbine for implementing the method. Therefore, the object of the present invention is, to be able to adapt the operation of a wind turbine to changes using a method of the type named above, such that when the detected parameter values deviate from the stored parameter values, as a function of the initial condition, either the stored parameter values are adapted to the detected parameter values or the operation of the wind turbine is influenced as a function of the detected parameter values. In this way, the invention is based on the knowledge that, from a pragmatic view, the formation of ice on a rotor blade is also a (temporary, meteorologically-related) change to the rotor blade shape. From this it follows that the formation of ice on the rotor blades always leads to a change of the aerodynamic profile and thus to a negative effect of the output of the wind turbine. However, deviations from this shape and thus deviations in the magnitude of the generated output also result just from manufacturing-dependent deviations of the rotor blades from the predetermined optimum shape and from gradual soiling of the rotor blades during operation.

Description:
TECHNICAL FIELD 
     The present invention relates to a method for operating a wind turbine with the steps: detecting the values of predetermined operating parameters by means of suitable sensors, detecting at least one predetermined initial condition, and comparing the detected values to stored values of operating parameters. The invention further relates to a wind turbine for realizing the method. 
     Here, the term “parameter” or “operating parameter” is used in the sense of a directly detected parameter, but also in the sense of a parameter value derived from a detected value. 
     BACKGROUND INFORMATION 
     Wind turbines have already been manufactured for some time in such quantities that it is quite acceptable to talk about series production. In the end, however, each wind turbine is definitely unique, because deviations from optimum settings also occur in series production. As is known, this is definitely not a phenomenon of series production of just wind turbines. Instead, in many areas of daily life there are default values and an acceptable tolerance range, within which deviations from the predetermined values are acceptable and not problematic. 
     Because the rotor blades of wind turbines are produced with an extraordinarily high percentage of manual labor and reach considerable dimensions, each individual rotor blade is unique. Thus, a wind turbine with three rotor blades already has three unique blades on its rotor. Therefore, a rotor of one wind turbine is not like any other and even the exchange of one rotor blade changes the entire rotor, within the tolerance range. 
     Accordingly, the operating behavior of each wind turbine also differs from that of all other wind turbines; even when these are of the same type. Even if the deviations lie within the permissible tolerance range, they can nevertheless still lead to power losses. 
     Wind turbines and especially their parts mounted outside in the area of the gondola, such as the rotor, but also the anemometer, are subject to the risk of icing, especially in winter. Icing of the anemometer can easily lead to measurement errors, which in turn result in unsuitable control of the wind turbine. 
     Icing of the rotor involves the risk that persons and things in the area of the wind turbine could be injured or damaged due to falling ice. When rotor blades are covered with ice, it cannot be predicted when or how much ice will fall, and the wind turbine must be stopped, in particular, due to icing of the rotor blades, in order to prevent endangering the area. 
     In the state of the art, various approaches have become known to prevent this problem. Thus, e.g., heated anemometers are available. The heaters of these anemometers should prevent icing. However, such a heater is not complete protection against icing of the anemometer, because, on one hand, the heater could fail and, on the other hand, even a functional heater cannot prevent the formation of ice to arbitrarily low temperatures. 
     Various designs have also become known for the rotor blades. For example, rotor blades can be heated in order to prevent any formation of ice. However, for large wind turbines with correspondingly large rotor blades, the power consumption needed is considerable. From DE 195 28 862 A1, a system is known in which the turbine is stopped after there is icing and then the rotor blades are heated in order to eliminate the icing of the rotor blades, with power use optimized as much as possible. However, the detection of icing in the state of the art is frequently realized through the detection of an unbalanced rotor, which results when the rotor drops a part of the already-formed ice. 
     However, the first time ice falls already represents a danger to the area; with increasing size of the rotor blades their mass also increases, so the fall of relatively small amounts of ice does not lead to a detectable imbalance, and reliable detection of ice formation is difficult. 
     BRIEF SUMMARY OF THE INVENTION 
     Therefore, the object of the present invention is to be able to adapt the operation of a wind turbine to changes. This object is achieved for the method of the type named above such that when the detected parameter values deviate from the stored parameter values as a function of the initial conditions, either the stored parameter values are adapted to the detected parameter values or the operation of the wind turbine is influenced as a function of the detected parameter values. 
     The invention is based on the knowledge that, from a pragmatic view, the formation of ice on a rotor blade also represents a (temporary, meteorologically-related) change of the rotor blade shape, with the result that the formation of ice on the rotor blades of a wind turbine always leads to a change of the aerodynamic profile and thus to a negative effect on the output of the wind turbine. However, manufacturing-dependent deviations of the rotor blades from the predetermined optimum shape and gradual soiling of the rotor blades during operation also lead to deviations from this shape and thus deviations in terms of the generated output. 
     Now, if predetermined operating parameters, such as wind speed, angle of attack of the rotor blades, and generated output are detected, these can be compared to values stored in the wind turbine. Under consideration of the initial condition of the outside temperature, from which it can be derived whether icing can occur at all, now either the values stored in the wind turbine can be adapted to the actual situation or the operation of the turbine is influenced accordingly. 
     The initial condition of the outside temperature can be monitored with a temperature sensor. If the outside temperature is 2° C. or higher, then icing can be reliably ruled out and deviation of the values is consequently reliably not traced back to icing, but instead to deviations as a result of tolerances, e.g., in the rotor blade profile. If the temperature falls below 2° C., icing can no longer be reliably ruled out. Consequently, if the parameter values change, icing cannot be ruled out and therefore the operation of the turbine is influenced, e.g., the turbine is stopped. 
     In order to be able to adapt the parameter values stored in the turbine to continuous changes to the turbine and not to lead to an erroneous detection of ice formation, the parameter values stored in the turbine can be adapted accordingly for (repeated) appearance of deviations. In order to adapt these parameter values, a difference between the stored parameter value and the detected parameter value is determined and, according to this difference, the values of the stored parameter can be changed with a predetermined weight. This weight can be, e.g., a fraction of the amount of the difference, so that a one-time change does not lead to a significant change to the stored parameter values. 
     The values of the parameters and/or the initial condition can be detected during a time period that can be preset, e.g., 60 s, and/or during a preset number of measurement cycles, in order to reduce the influence of random single events. 
     Because the wind turbine is controlled with different parameters as a function of the wind speed, the parameters used preferably vary as a function of a second initial condition. Below the wind speed at which the turbine generates nominal output, the turbine is controlled by the generated output and is dependent on, among other things, the wind speed. Accordingly, the wind speed can be determined from the generated output. When the nominal wind speed is reached and exceeded, the turbine always generates the nominal output. In this range, the turbine is controlled by changing the angle of attack of the rotor blades. Accordingly, a wind speed can be allocated to the angle of attack of the rotor blades. Consequently, as a function of reaching the nominal output as an initial condition, the parameter can change between the generated output and rotor blade angle of attack. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       An embodiment of the invention is explained in more detail below with reference to the figures. Shown are: 
         FIG. 1 , a flow chart of the method according to the invention; 
         FIG. 2 , a flow chart of an alternative embodiment of the method; 
         FIG. 3 , an example of a predetermined standard characteristic line and characteristic lines determined by measurements; and 
         FIG. 4 , a representation for illustrating the change of the stored parameter values. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of techniques for operating a wind turbine are described herein. In the following description, numerous specific details are given to provide a thorough understanding of embodiments. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The individual steps are designated with reference symbols in the flow chart shown in  FIG. 1 . Step  10  is the beginning of the flow chart. In Step  11 , it is tested whether this is the first startup of this wind turbine. The branch extending downwards symbolizes the answer “yes” and the branch extending to the right symbolizes the answer “no.” If this is the first startup of the turbine, then in Step  12 , typical standard values are recorded in a memory. If this is not the first startup, this Step  12  is skipped. 
     In Step  13 , the generated output P actual , the rotor blade angle of attack α, and the wind speed v W  are detected. In Step  14 , it is tested whether the generated output P actual  is the nominal output P N . If this is the case, the process continues via the bottom branch to Step  15 . There, the rotor blade angle of attack α is selected as the parameter. If the generated output is not the nominal output, i.e., if it is less than the nominal output, the right branch is used and the process continues with Step  16 , where the generated output P actual  is selected as the parameter. In the subsequent Step  19 , it is tested whether the outside temperature u is at least 2° C. If this is the case, the process continues via the bottom branch to Step  20 . 
     The detection of the outside temperature u can be realized by means of a thermometer. Naturally, there can also be another thermometer, optionally at a different location, wherein the temperatures detected by these thermometers can be checked with one another for plausibility. 
     In Step  20 , depending on the parameter determined in Steps  14 ,  15 , and  16 , blade angle of attack α or generated output P actual , the associated wind speed v K  is determined from the data stored in the wind turbine. Then this wind speed v K  is compared to the detected wind speed v W . In Step  21 , it is tested whether the detected wind speed deviates from the stored wind speed. If this is the case, the process continues via the bottom branch, and in Step  22 , a new value is defined for the stored parameter value and stored in the wind turbine. 
     This new value is multiplied by a factor of 0.05 as a weighting factor and added to the previous value, taking its sign into account. If a smaller value is produced, then 1/20 of the difference from the previously stored value is subtracted; if a higher value is produced, 1/20 of the difference is added to this value. After this newly determined value has been stored, the generated output P actual , the rotor blade angle of attack α and the wind speed v W  are detected again and the process is executed again beginning at Step  13 . 
     Naturally, the weighting factor can also assume any other suitable value. Here, it is easy to see that for a larger weighting factor, the stored values are adapted to the detected values more quickly than for a smaller weighting factor. 
     The weighting factor can also be changed, e.g., as a function of the magnitude of the difference between the detected value and the stored value. The greater the difference, the smaller the weighting factor can be, in order to reduce the influence, e.g., due to a large difference, or vice versa. 
     Alternatively, a weighting factor can be eliminated. Instead, the stored values can be adapted to the detected values independently or in steps dependent on the differences with predetermined amounts. Thus, the adaptation can always be realized with a value w, or for a predetermined first range of the difference amount, a first predetermined value w 1  is used, and for a predetermined second range of the difference amount, a predetermined second value w 2  is used, and for a third range, a value w 3 , etc. 
     If the value determined in Step  20  does not deviate at all or not significantly from the stored value, the process continues from Step  21  via the right branch and Step  22  is bypassed. Accordingly, this Step  22  can be spared and thus the load on the processor that is used is reduced. 
     In Step  19 , if it is determined that the temperature is not at least 2° C., icing of the rotor blades can no longer be reliably ruled out. Accordingly, the process branches via the side branch to Step  23 . In Step  23 , in turn, according to the detected parameters, the wind speed v W  allocated to the stored parameter value is determined. 
     In Step  24 , it is tested whether (under consideration of a tolerance range) the wind speed v K  determined from the stored parameter values agrees with the detected wind speed v W . If this is the case, the process returns via the side branch to Step  13  and the process continues, in turn, with the detection of the generated output P actual , the rotor blade angle of attack α, and the wind speed v W . 
     In Step  24 , when it is recognized that the detected wind speed v W  does not agree with the wind speed v K  determined from the stored values, in Step  25  it is tested whether the detected wind speed v W  is smaller than the wind speed v K  determined from the parameter values. 
     If this is the case, the process continues via the bottom branch and, in Step  26 , anemometer icing is assumed, because it results from the output generated by the turbine or from the blade angle of attack that the wind speed must be higher than that detected by the anemometer. 
     If the detected wind speed v W  is not smaller than the wind speed v K  determined from the stored parameter values, the process continues via the side branch and Step  27 . 
     Because it is known from Step  24  that the detected wind speed v W  is not equal to the wind speed determined from the stored parameter values v K , and because the detected wind speed v W  is also not smaller than the wind speed v K  determined from the stored parameter values, it must therefore be greater. However, for this greater wind speed, if a smaller output is generated or a smaller rotor blade angle of attack is detected, it necessarily follows that the aerodynamic behavior of the rotor blades is changed. Because it is known from Step  19  that the temperature lies below 2° C., icing of the rotor blades cannot be ruled out. Accordingly, in Step  27  icing of the rotor blades is now assumed. 
     Both icing of the anemometer assumed in Step  26  and also icing of the rotor blades assumed in Step  27  lead to stoppage of the turbine in Step  28 . Thus, risk to the surroundings is reliably ruled out in each case. 
     The entire process then ends in Step  29 . 
     In the flow chart shown in  FIG. 2 , the individual steps are designated with reference symbols. Step  10  is the beginning of the flow chart. In Step  11 , it is tested whether it is the first startup of this wind turbine. The branch extending downwards symbolizes the answer “yes” and the branch extending to the right symbolizes the answer “no.” If it is the first startup, then typical turbine standard values are recorded in a memory in Step  12 . If it is not the first startup, Step  12  is skipped. 
     In Step  13 , the generated output P actual , the rotor blade angle of attack α, and the wind speed v W  are detected. In Step  14 , it is tested whether the generated output P actual  is the nominal output P N . If this is the case, the process continues via the bottom branch to Step  15 . There, the rotor blade angle of attack α is selected as the parameter. If the generated output is not the nominal output, it is consequently smaller than the nominal output, the right branch is used and the process continues with Step  16 , where the generated output P actual  is selected as the parameter. 
     Accordingly, in Step  17 , the stored wind speed v K  allocated to the parameter selected in Step  15  or Step  16  is determined. A tolerance range with a width that can be preset is allocated to this wind speed v K . This width can vary, e.g., as a function of the installation site of the wind turbine. 
     At installation sites with higher risk to the surroundings, e.g., in the vicinity of buildings, a quick reaction by the controller of the wind turbine to deviations of the stored values can be realized through a tight tolerance range. For this tight tolerance range, empirical values of ±0.5 m/s to ±2 m/s, preferably ±1.2 m/s have been determined. For areas with lower risks, a range of ±1 m/s to ±3 m/s, preferably +2 m/s is given as useful. 
     In Step  18 , it is tested whether the detected wind speed v W , under consideration of the tolerance range, agrees with the wind speed v K  determined from the stored values. If this is the case, the process continues via the right branch from Step  18  and returns to Step  13 . There, the wind speed v W , the rotor blade angle of attack α, and the generated output P actual  are detected again. 
     If the detected wind speed v W  does not agree with the stored wind speed v K  (naturally, in turn, under consideration of the tolerance range), the process continues in Step  18  through the bottom branch to Step  19 . 
     In Step  19 , it is tested whether the outside temperature u equals at least 2° C. If this is the case, the process continues via the bottom branch to Step  20 . 
     In Step  20 , the associated wind speed v K  is determined from the data stored in the wind turbine and also the difference values as a function of the parameters blade angle of attack α or generated output P actual  determined in Steps  14 ,  15 , and  16 . In Step  22 , a new value is defined for the stored parameter value and stored in the wind turbine. 
     This new value is multiplied by a factor of 0.05 as a weighting factor and added to the previous value, taking its sign into account. If a smaller value is produced, then 1/20 of the difference of the previously stored value is subtracted; if a higher value is produced, then 1/20 of the difference is added to this value. After this newly-determined value is stored, the generated output P actual , the rotor blade angle of attack α, and the wind speed v W  are detected again and the process is executed again starting at Step  13 . 
     Naturally, the remarks made in the description about  FIG. 1  also apply here for the weighting factor. 
     In Step  19 , if it is determined that the temperature is not at least 2° C., then icing of the rotor blades can no longer be reliably ruled out. Accordingly, the process continues via the side branch to Step  25 . 
     In Step  25 , it is tested whether the detected wind speed v W  is smaller than the wind speed v K  determined from the parameter values. 
     If this is the case, the process continues via the bottom branch, and in Step  26 , anemometer icing is assumed, because it results from the output P actual  generated by the turbine or from the blade angle of attack α that the wind speed must be higher than that detected by the anemometer. 
     If the detected wind speed v W  is not smaller than the wind speed v K  determined from the stored parameter values, the process continues via the side branch and in Step  25 . 
     Because it is known from Step  24  that the detected wind speed v W  is not equal to the wind speed v K  determined from the stored parameter values, and because the detected wind speed v W  also is not smaller than the wind speed v K  determined from the stored parameter values, this must therefore be larger. However, if a smaller output is generated or a smaller rotor blade angle of attack is detected for this larger wind speed, it necessarily follows that the aerodynamic behavior of the rotor blades has changed. Because it is known from Step  19  that the temperature lies below 2° C., icing of the rotor blades cannot be ruled out. Accordingly, in Step  27 , icing of the rotor blades is assumed. 
     Both icing of the anemometer assumed in Step  26  and icing of the rotor blades assumed in Step  27  lead in Step  28  to stoppage of the turbine. Thus, risk to the surroundings is reliably ruled out in each case. 
     The entire process then ends in Step  29 . 
       FIG. 3  shows a representation with three characteristic lines. The wind speed v W  is given on the abscissa of the coordinate system. Here, the wind speed v W  is the parameter relevant up to the nominal wind speed v N , at which the wind turbine reaches its nominal output; above this wind speed v N , the rotor blade angle of attack α is the relevant parameter. However, for reasons of clarity, this is not shown in the figure. 
     The output P is recorded on the ordinate. The nominal output P N  is indicated. 
     Let the continuous line be the example for the standard parameter values stored in the wind turbine at the first startup. The dashed line designates a first characteristic line specific to the turbine formed by adapting the stored standard values to the detected values, and the dash-dot line represents a second example of a characteristic line specific to the turbine, also formed by adapting the stored standard values to the detected values. Naturally, only one characteristic line specific to the turbine can apply to one wind turbine. 
     The first dashed characteristic line running below the continuous characteristic line already gives a hint that the output actually generated by the turbine lies below the output seen in the standard parameters. In contrast, the second, dash-dot characteristic line represents higher outputs in the range up to the nominal wind speed v N . 
     Below the nominal wind speed v N , the parameter P actual  is used. From the dashed characteristic line it follows that the output P 1  is generated at a detected wind speed v 2 . From the (continuous) standard characteristic line, a wind speed v 1 , is given for the output P 1 , which lies below the detected wind speed v 2 . The wind speed v 2  detected at the output P 1  is thus greater than the wind speed v 1  determined from the stored values. At a temperature below 2° C., according to the invention, the wind turbine would be turned off under the assumption of rotor blade icing. 
     At a temperature of at least 2° C., the difference Δv=v 2 −v 1  would be formed. As a correction value, Δv/20 is added to the stored value and recorded in the memory instead of the previous value. Because the difference Δv has a positive sign, the stored value is shifted in the direction of larger values, thus in the direction v 2  with 1/20 of the amount of the difference. 
     The dash-dot line shows a deviation in the opposite direction. At the output P 1 , a wind speed v 3  is detected which is smaller than the wind speed v 1  determined from the standard characteristic line. The difference v 3 −v 1  produces, in turn, Δv, and Δv/20 is added as the correction value to the stored value. However, in this case, because the difference Δv is negative, a value with a negative sign is accordingly added to the stored value, consequently Δv/20 is subtracted. Thus, here the stored value is also adapted with 1/20 of the difference, taking into account the sign, thus in the direction towards v 3 . 
     If the nominal output is reached, thus the nominal wind speed v N  is reached or exceeded, then the generated output P actual  is no longer detected as the parameter, but instead, the angle of attack α of the rotor blades is detected as the parameter. The further process corresponds to that explained above. From the detected rotor blade angle of attack α, the allocated wind speed is determined by means of the standard characteristic line (continuous characteristic line). This is compared to the detected wind speed. Here, if differences are produced, these processes are as described above. 
       FIG. 4  is an enlarged representation of a section of the characteristic lines shown in  FIG. 3  in a range below the nominal wind speed v N . In this  FIG. 4 , the wind speeds are recorded as in  FIG. 3 . 
     Through the enlarged representation, the difference can be seen more easily. The reference wind speed is the wind speed v 1  determined from the stored values. This is subtracted from the detected wind speed v 2 , v 3 . Accordingly, Δv is produced. For the difference v 2 −v 1 , Δv has a positive sign. For the difference v 3 −v 1 , however, Δv has a negative sign. 
     To prevent too great an influence of these deviations on the stored values, the difference is weighted with a preset factor. In the present case, let this factor be 0.05. 
     To adapt the stored values to the individual wind turbine, the weighted difference, here, Δv/20, is added to the stored value v 1  or icing is assumed for the appearance of a difference at an outside temperature below 2° C. and the operation of the wind turbine is stopped. 
     In order not to have to react to every arbitrarily small deviation Δv, a tolerance range can be provided. This is designated in the figure with −T for the lower limit and +T for the upper limit. For deviations Δv in the tolerance range, the turbine continues to operate or the values stored in the wind turbine are not changed. Obviously, the tolerance range can apply, e.g., only for the operational control of the wind turbine. Then, the stored values are adapted even for small changes, but the turbine still continues to operate even at temperatures below 2° C. 
     According to the installation site of the individual wind turbine, the values for the tolerance range can be set individually. Where a tolerance of ±2 m/s is sufficient for one installation site, a tolerance range of ±1.2 m/s is necessary for a different installation site of the same turbine type. 
     At a wind speed v 1 , of 10 m/s, an upper limit of 11.2 m/s and a lower limit of 8.8 m/s are given for ±1.2 m/s as the tolerance. Within this range from 8.8 m/s to 11.2 m/s, the parameters can be adapted, for example, but the turbine continues to operate at low outside temperatures. 
     In the figure, let v 1 , equal 10 M/s, v 2  equal 12 m/s, and v 3  lie at 8.5 m/s. Thus, Δv=v 2 −v 1 =2 m/s. The adaptation of the stored value is realized with 1/20, thus, in this example, 0.1 m/s. Because the sign is positive, v 1  changes accordingly to 10.1 m/s. 
     For a difference Δv=v 3 −v 1  a value of 8.5 m/s−10 m/s=−1.5 m/s is produced. The adaptation of v 1 , is realized, in turn, with Δv/20, thus −0.075 m/s. Therefore, v 1 , is changed to 9.925 m/s. 
     The weighting factor determines how fast the stored values are adapted to the detected values. The greater this factor, the faster the adaptation. 
     However, the detection of the values also has an affect. Typically, in the area of the wind turbines, especially environmental values, such as temperature or wind speed, are not determined from a single measurement, but instead from a plurality of measurement cycles, e.g., 30, or detected over a predetermined time period, e.g., 60 s. The values are then derived from these results, e.g., as arithmetic or geometric means. 
     All of the above U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, are incorporated herein by reference, in their entirety. 
     The above description of illustrated embodiments, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments and examples are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention and can be made without deviating from the spirit and scope of the invention. 
     These and other modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.