Patent Publication Number: US-2013241209-A1

Title: Method and arrangement for operating a wind turbine taking into account power losses

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of European Patent Office application No. 12159727.2 EP filed Mar. 15, 2012, which is incorporated by reference herein in its entirety. 
     FIELD OF INVENTION 
     The present application is related to a method and to an arrangement for operating, such as a convertor of, a wind turbine, wherein power loss of at least one energy consuming wind turbine component and also mechanical losses or friction of a drive train and/or electronic losses of a converter associated with switching, is taken into account to adjust the power output of the wind turbine. 
     BACKGROUND OF INVENTION 
     At an output terminal of the wind turbine electrical power is output and fed to a utility grid. In order to operate the wind turbine optimally, the output power is controlled by a wind turbine controller. The controller, according to a conventional wind turbine, assumes a fixed relation between the power at different locations from the wind turbine rotor to the output terminal of the wind turbine. 
     It has been observed that conventional methods are not able in every situation to operate the wind turbine such that maximal power output is ensured, while mechanical and/or electronic loads are in acceptable limits or are reduced. 
     There may be a need for a method and for an arrangement for operating, such as a converter of, a wind turbine wherein the wind turbine is operated optimally regarding power production and regarding mechanical and/or electronic loads that the components of the wind turbine are subjected to. 
     SUMMARY OF INVENTION 
     This need may be satisfied by the subject matter of the independent claims. The dependent claims specify embodiments of the present application. 
     According to an embodiment of the present application it is provided a method for operating of a wind turbine having a rotor and a wind turbine output terminal connected to a utility grid (or to a wind farm grid or via a wind farm transformer to the utility grid), the method comprising: obtaining an input signal related to an action output of the wind turbine available at a location between the rotor and the wind turbine output terminal; estimating a power related quantity from the input signal; controlling the wind turbine based on the input signal and the estimated power related quantity, wherein the wind turbine has a wind turbine converter having a converter output terminal upstream of the wind turbine output terminal, wherein the estimated power related quantity comprises estimating a power difference of power associated with the action output available at the location and output power at the converter output terminal, and wherein the controlling the wind turbine comprises controlling the wind turbine based on the input signal and the estimated power difference. 
     Operating the wind turbine may comprise supplying one or more control signals to one or more components of the wind turbine. One or more control signals may be supplied to a converter of the wind turbine, such as to an AC-DC-AC converter of the wind turbine. The AC-DC-AC converter may be adapted to convert a variable frequency AC voltage (or power stream) via converting to a DC power stream to a fixed frequency AC voltage (or power stream), having a frequency of 50 Hz or 60 Hz. The converter may comprise one or more power electronic transistors, such as isolated gate bipolar transistors (IGBTs). The transistors may be controlled at respective gates by pulse width modulation signals, which in a fast manner and repetitively switch on and off the plural transistors. The power output of the wind turbine, which is output at an output terminal of the converter may be controlled. 
     The control signal or control signals supplied to the converter may comprise one or more reference signals, such as a voltage reference signal, a power reference signal, a torque reference signal or the like. Based on (at least one of) these reference signals a processor of the converter may derive the corresponding pulse width with modulation signal(s) which are then supplied to the respective transistors comprised within the converter. 
     Further, operating the wind turbine may comprise supplying one or more control signals to actuators of the wind turbine, such as actuators for adjusting the rotor blade pitch angles. 
     The method may operate the wind turbine such that for given external conditions, such as wind speed, a maximal power production is ensured, while the load on components of the wind turbine is maintained in acceptable limits. 
     Obtaining the rotational speed signal may comprise measuring the rotational speed of the rotor, of the generator or of any mechanical shaft in between the rotor and the generator. The rotational speed signal may be indicative also of a rotational speed of the generator. 
     The intended mechanical rotor power refers to the mechanical power the rotor is intended to deliver, such as to optimize the operation of the rotor regarding maximal power output and keeping the mechanical load within acceptable limits. A relation between the rotational speed of the rotor (or generator) and the intended mechanical rotor power may be provided such as in the form of one or more curves or one or more tables. To a given obtained rotational speed of the rotor (or generator) an intended mechanical rotor power may be associated. For the given rotational speed of the rotor the associated intended mechanical rotor power represents the mechanical rotor power for which the optimal operation condition is met. The optimal relation between the rotational speed of the rotor and the intended mechanical rotor power in a variable-speed operation of a wind turbine may be constant for constant environmental conditions, such as constant air density, constant temperature, but may vary for example for varying air density or varying temperature. The relation (also referred to as speed-power curve or speed-power relation) may depend on the configuration and constitution of the wind turbine. 
     In the variable-speed operation the turbine may be controlled in order to maximize its power production, by running the aerodynamics optimally. Hence, an optimal tip-speed ratio should be ensured, i.e. an optimal rotational speed for a given wind speed, which is controlled using the speed-power curve lookup table. 
     In the constant-speed region and constant-power region, the control objective is not to maximize power production but to keep control of loads and acoustic noise, and (in the constant-speed region) produce as much power as possible while keeping the other constraints. 
     In contrast to the embodiment of the present application, in a conventional system, a fixed relationship between a rotational speed of the rotor and an intended electrical power output may have been used, based on which the wind turbine may have been controlled. 
     In an operating wind turbine, in which the rotor rotates by wind impacting on one or more rotor blades, the mechanical rotor power is transferred via a transmission line to provide an electrical power output at the output terminal of the wind turbine. The transmission line may include a drive train, a generator, a converter. During the transferring of the mechanical rotor power to the electrical power output a power loss may occur which may be due to individual power losses and individual power consumptions of different components or processes of the transmission line. The power loss will cause a reduction of the power associated with the mechanical rotor power such that the electrical power output corresponds to a lower power than the actual mechanical rotor power of the rotor. 
     In a conventional system the power loss may have been considered, but the power loss may have been assumed to be constant or a function of (such as proportional, linear, nonlinear, affine) the mechanical rotor power. In a conventional system it may have been assumed that the electrical power output may be derived by the product of an efficiency and the mechanical rotor power. The controlling the wind turbine based on the intended mechanical rotor power and the estimated power loss may improve the efficiency of the wind turbine, while at the same time the mechanical load does not exceed predetermined thresholds. 
     For estimating the power related quantity (such as the power loss) the operational state of at least one energy consuming wind turbine component may be taken into account such that the power loss may depend on the operational state of the energy consuming wind turbine component. It may be taken into account, whether the energy consuming wind turbine component is consuming energy or is not consuming energy. If the energy consuming wind turbine component is consuming energy, the power loss will be larger compared to the case, when the energy consuming wind turbine component is not consuming energy. The estimated power loss may vary with time due to switching on or off one or more energy consuming wind turbine components. Thus, also the wind turbine may be controlled in a varying manner, such that for example reference values supplied to the wind turbine more to a converter of the wind turbine, may vary in dependence of the operational state of the energy consuming wind turbine component. 
     According to an embodiment of the present application wherein the obtaining the input signal comprises: obtaining a first input signal related to an action output of the wind turbine available at a first location, wherein the first location is between the rotor and the converter output terminal; obtaining a second input signal related to an action output of the wind turbine available at a second location, wherein the second location is between the converter output terminal and the wind turbine output terminal, wherein the estimating the power difference comprises: estimating a first power reduction associated to transferring the action output available at the first location to the converter output terminal; estimating a second power reduction associated to a consumption of energy by a wind turbine component connected at the converter output terminal; and wherein the controlling the converter comprises: controlling the converter based on the first input signal and/or the second input signal and the first estimated power reduction and/or the second estimated power reduction, wherein for estimating the second power reduction an operational state of at least one energy consuming wind turbine component is taken into account. 
     The energy consuming wind turbine component may for example comprise one or more fans for cooling components of the wind turbine, one or more heaters for heating some components of the wind turbine, such as oil of the drive train or a rotor blade for de-icing, one or more actuators, such as an actuator for actuating the rotor blades in order to adjust the rotor blade pitch angle or a yawing actuator in order to rotate a nacelle of the wind turbine around a vertical axis. 
     According to an embodiment of the present application during the method the operational state changes from a high energy consuming state to a low energy consuming state or vice versa. For example, if a fan which is running is turned off the operational state of the fan may change from a high energy consuming state to a low energy consuming state. Further, when a fan which is running at a high fan speed is switched to a state, in which the fan rotates with a lower fan speed, the fan may change from a high energy consuming state to a low energy consuming state. Further, switching a running heater off may change the state of the heater from a high energy consuming state to a low energy consuming state. 
     Taking into account and responding to the different levels of energy consumption by the energy consuming wind turbine component may improve the operation of the wind turbine regarding power improvement or optimization and load optimization. 
     According to an embodiment of the present application the method for operating the wind turbine further comprises obtaining an operational state signal indicative of the operational state of the energy consuming wind turbine component, wherein the estimating the second power reduction is further based on the operational state signal. 
     Obtaining the operational state signal may comprise supplying a state signal from the energy consuming wind turbine component to a controller of the wind turbine, wherein the state signal may be an electrical and/or optical signal or a wireless signal. The operational state signal (or more than one signal, such as a plurality of operational state signals indicating operational states of a plurality of energy consuming wind turbine components) may be supplied to the wind turbine controller which may process the plural state signal in order to estimate individual energy consumption of the plural energy consuming wind turbine components. The power loss associated with the energy consuming wind turbine components may then be estimated taking into account a sum of the individual power consumptions. 
     The estimating the power loss may be improved, also improving the controlling the wind turbine. 
     According to an embodiment of the present application the operational state signal is one of a binary signal and a signal varying, with the energy consumed by the energy consuming wind turbine component. When the operational state signal is a binary signal the binary signal may be multiplied with a predetermined (average) energy consumption or power consumption of the energy consuming wind turbine component. The operational state signal may be multiplied with a constant to derive the energy consumption or power consumption of the respective energy consuming wind turbine component. The method may be simplified. 
     According to an embodiment of the present application between the rotor and the converter at least one wind turbine component is arranged including at least one of a drive train, mechanically connected to the rotor, an electrical generator, mechanically connected to the drive train, a AC-DC-AC converter, electrically connected to the generator, wherein the estimating the first power reduction (such as representing a power loss) comprises estimating a component power loss associated with at least one wind turbine component arranged between the rotor and the converter output terminal. 
     The drive train may comprise a gear box, one or more bearings and all kinds of frictional losses. The drive train may be mechanically connected between the rotor at which plural rotor blades are connected and a generator of the wind turbine. The generator may be an induction generator having a stator with plural coils and a rotating permanent magnet generator rotor. Each of the wind turbine components between the rotor and the converter (these wind turbine components forming the transmission line) may contribute individually according to a degree to the power loss. The individual contributions may be estimated by a specific physical/mathematical model of the respective wind turbine component. The individual power loss of the wind turbine component is also referred to as component power loss. The individual component power losses may be estimated or derived or computed from a model of the respective wind turbine component. Estimation of the power loss may be made more accurate and, when used by the wind turbine controller, operation can be optimized/improved. 
     One or more energy consuming wind turbine components including the energy consuming wind turbine component, the energy consuming wind turbine components including at least one of a fan, a heater, an actuator may be electrically connected to (an output terminal of) the converter. Their power consumption may contribute (such as a sum) to the second power reduction. 
     According to an embodiment of the present application the estimating the first power reduction comprises estimating a component power loss according to loss_component=constant*(T_componenent−T_surrounding), wherein loss_component is the power loss of the component, constant is a constant, T_component is the temperature of the component, and T_surrounding is the temperature of the surrounding of the component. 
     According to an embodiment the estimating the first power reduction comprises estimating a generator power loss associated with the generator which estimated generator power loss depends on a temperature of the generator. 
     Also taking into account the temperature of the generator for estimating the generator power loss may improve the accuracy of the estimated generator power loss. Further, estimating other component power losses may comprise taking into account the temperature of the respective wind turbine component. 
     The power loss may increase with increasing temperature of the respective wind turbine component. The generator power loss may comprise a term which may be proportional to a square of a generator current times a constant times the generator temperature. Estimating the power loss may be improved. 
     According to an embodiment of the present application the generator power loss is estimated using the relation as an example: 
       loss_generator= c 0+ I   2 *( c 1* T+c 2), 
     wherein 
     loss_generator is the power loss associated with the generator; 
     c0, c1, c2 are constants; 
     I is the electrical current flowing through the generator; and 
     T is the generator temperature. 
     A more detailed physical model is employed which may ensure an even higher accuracy of the estimated generator power loss. 
     According to an embodiment of the present application controlling the converter comprises deriving a reference signal, such as indicative of the reference power, reference torque and/or reference voltage, based on the input signal, such as the first input signal and/or the second input signal and the estimated power difference, such as the first power reduction and/or the second power reduction; and supplying the reference signal to the converter. 
     A conventional AC-DC-AC converter of a wind turbine may be adapted to be supplied with a reference power, reference torque and/or reference voltage based on which the converter derives pulse width modulation signal(s) and delivers these pulse width modulation signals to gates of plural transistors comprised within the converter. A simple manner of controlling the power output of the wind turbine and thus controlling the operation of the wind turbine is enabled. 
     According to an embodiment of the present application the reference signal (such as reference power, reference torque and/or reference voltage) is derived based on a difference between an intended mechanical rotor power and the first estimated power reduction and/or wherein the reference signal is derived based on a sum between an power output at the wind turbine output terminal and the estimated second power reduction. 
     Thus, a predetermined speed-power curve or graph or table may be used indicating the dependency or relationship between the rotational speed of the rotor (or generator) and the mechanical rotor power. 
     The speed-power (or speed-torque) curve may be only applied during variable-speed operation (i.e. for lower wind speeds, i.e. before reaching constant-speed and constant-power operation). As an example Variable-speed operation may comprise wind speed up to 8 m/s; Constant-speed operation may comprise wind speed between 8 and 11 m/s; Constant-power operation comprises wind speed 11 to 25 m/s. 
     Having derived the intended mechanical rotor power of the rotor for a given rotational speed of the rotor the estimated power loss of the transmission line and energy consuming components are subtracted from the intended mechanical rotor power. Then, this value (being a power reference) is send to the converter. Considering the power losses, this will result that the intended mechanical rotor power is achieved by making the converter power reference as function of the current power losses. 
     According to an embodiment of the present application the reference signal is further based on a wind speed. The method may still be improved. 
     According to an embodiment of the present application the controlling the wind turbine further comprises supplying a blade pitch signal to an actuator for adjusting a blade pitch angle of a rotor blade connected to the rotor. In a region of relatively high wind speed the blade pitch of the rotor blade may be adjusted in order to maintain a constant power output, such as a nominal power output and a constant rotor speed, such as a nominal rotor speed. 
     According to an embodiment of the present application the method comprises operating the wind turbine subsequently in at least one of a first mode, in which the wind speed is in a first (wind speed) interval (or region) and in which the rotational speed is below a rated (or nominal) rotational speed and in which the intended rotor power is below a rated (or nominal) rotor power, a second mode, in which the wind speed is in a second (wind speed) interval comprising higher wind speed than the first interval, and in which the rotational speed is at the rated rotational speed, and in which the intended rotor power is below the rated rotor power, and a third mode, in which the wind speed is in a third (wind speed) interval, comprising higher wind speed than the second interval, and in which the intended rotor power is at the rated rotor power. 
     A simple three mode operational scheme for operating the wind turbine may be provided. Optimal power production of wind turbines at below rated power (rated power output at the wind turbine output terminal) may depend on the ability to apply an optimal pitch angle (the pitch angle is the angle between the blade chord line and the rotor plane of rotation) and track the optimal rotor tip-speed ratio (the ratio of rotor shaft speed to effective wind speed) at below rated rotational speed (of the rotor or the generator). The method may accomplish this by setting a predetermined pitch angle and a generator (or converter) reference power or reference torque or reference voltage, to balance the rotor by aerodynamic torque. Below the rated power the pitch angle may be typically fixed in the variable rotor speed region (within the first wind speed interval) and the power (or torque or voltage) reference may be set as a function of the rotational speed (of the rotor or the generator) (or the wind speed). 
     In the second wind speed interval, below rated power in the constant rotor speed region the pitch angle may be changed as a function of the power, torque, or wind speed, while the power (or torque or voltage) reference may be adjusted in order to maintain the desired rotational speed. 
     Within the third wind speed region, i.e. in the third mode, at rated power the torque/power may be maintained, while the pitch angle may be adjusted (such as varied) to maintain the rated rotational speed. 
     A save and effective and efficient operation of the wind turbine may be ensured. 
     According to an embodiment of the present application the pitch angle is fixed during the first mode, wherein the pitch angle is changed based on the intended rotor power and wind speed during the second mode, wherein the pitch angle is further adjusted to maintain the rated rotor power during the third mode. A save and efficient operation of the wind turbine may be ensured. 
     It should be understood that features individually or in any combination disclosed, described, explained or provided for a method for operating a wind turbine may also be applied to an arrangement for operating a wind turbine according to an embodiment of the present application and vice versa. 
     According to an embodiment of the present application it is provided an arrangement for operating of a wind turbine having a rotor, a wind turbine converter and a wind turbine output terminal connected to a utility grid, the converter having a converter output terminal upstream of the wind turbine output terminal, the arrangement comprising: an input terminal for obtaining an input signal related to an action output of the wind turbine available at a location between the rotor and the wind turbine output terminal; a processor adapted to estimate a power difference of power associated with the action output available at the location and output power at the converter output terminal; and to control the converter based on the input signal and the estimated power difference. 
     The arrangement may be or may not be comprised within a wind turbine controller. The arrangement may be associated with the individual wind turbine. Alternatively, the arrangement may be comprised within a wind park controller controlling a plurality of wind turbines. The processor or the arrangement may further comprise an electronic storage for storing for example configuration values, calibration curves or tables, such as a relationship between rotational speed of the rotor and the intended mechanical rotor power. 
     Further, different kinds of calibration curves may be stored within the storage of the arrangement. These calibration curves or calibration values may be used for deriving the intended mechanical rotor power and/or for estimating the power loss. Estimating the power loss may also involve receiving one or more state signals from one or more wind turbine components. Controlling the wind turbine may involve supplying one or more reference signals to a converter of the wind turbine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present application are now described with reference to the accompanying drawings. The application is not limited to the disclosed or illustrated embodiments. The aspects defined above and further aspects of the present application are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The application will be described in more detail hereinafter with reference to examples of embodiment but to which the application is not limited. 
         FIG. 1  schematically illustrates a wind turbine comprising an arrangement for operating the wind turbine according to an embodiment of the present application performing a method for operating the wind turbine according to an embodiment of the present application; and 
         FIG. 2  illustrates graphs for illustrating a method for operating the wind turbine illustrated in  FIG. 1  according to an embodiment of the present application. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
       FIG. 1  illustrates a wind turbine  100  comprising an arrangement  101  for operating the wind turbine according to an embodiment of the present application. The wind turbine comprises a rotor  103  at which one or more (not illustrated) rotor blades are connected. 
     The rotor  103  outputs mechanical rotor power  104  and is mechanically connected to a drive train  105  which may for example comprise a gear box, one or more bearing and one or more shafts to which the gear box is mechanically connected. A secondary rotor shaft  106  transfers rotational energy or power to a generator  107  which is adapted to convert the mechanical energy to electrical energy output at an output terminal  109 . The electric energy or power is received by a converter  111 , which is in the illustrated embodiment a AC-DC-AC converter for converting a variable fixed AC energy stream received from the generator  107  to a fixed frequency AC energy stream  114  output at an output terminal  115  of the converter  111  which may correspond to the output terminal  117  of the wind turbine  100 . The energy stream  114 , such as a portion  113 , is supplied to the utility grid  119  for supplying the electric energy to one or more consumers. The power  113  supplied to the grid  119  is measured by signal  140  and supplied to the controller  101 . 
     The wind turbine  100  comprises energy consuming wind turbine components  121 ,  123  and  125 , for example. The component  121  may for example be a fan, the component  123  may be a heater and the component  125  may be an actuator, for example. More or less energy consuming components may be comprised within the wind turbine  100 . The energy consuming components  121 ,  123 ,  125  receive electric energy or power from the output power  114  at output terminal  115  of the converter via the power lines  127 . Power  129  is supplied to the component  121 , power  131  is supplied to the component  123  and power  133  is supplied to the component  125 . These power portions  129 ,  131 ,  133  are subtracted from the power stream  114  output at the output terminal  115  of the converter  111 , such that the power stream  113  delivered to the grid  119  is the power stream  114  reduced by the power portions  129 ,  131  and  133  (in sum being related to a second power reduction). 
     However, the mechanical rotor power  104  output by the rotor  103  does not equal to the power output stream  114  output by the converter  111 , but is higher than the electric output stream  114 . The power output stream  114  output by the converter is smaller than the mechanical rotor power  104  output by the rotor  103  due to power losses within the transmission line comprising the drive train  105 , the generator  107  and the converter  111  and due to power consumptions by wind turbine components  121 ,  123 ,  125 . 
     For controlling the wind turbine  100  the arrangement  101  is provided which may carry out a method according to an embodiment of the present application. The arrangement  101  receives state signals  135  from the energy consuming components  121 ,  123  and  125  in order to obtain information of the operational state of the components  121 ,  123 ,  125 . The state signals  135  may indicate whether the components  121 ,  123 ,  125  consume energy or not or may even indicate how much energy the components  121 ,  123 ,  125  consume or how much power these components consume. The arrangement  101  receives the state signals at input terminals  137 . 
     Further, the arrangement  101  receives at input terminal  102  a rotational speed signal  139  (and/or  138 ) from the rotor  103  (and/or the generator  107 ). Alternatively or additionally the rotational speed signal  139  (or another rotation speed signal) may be obtained from the generator  107 . Further, the arrangement  101  comprises a storage, such as an electronic storage, such as a data base, storing or including one or more calibration curves, reference values, reference tables or calibration tables, such as a speed-power relationship, such as a table or a curve relating the rotational speed of the rotor (or the generator) to the intended mechanical rotor power  104  of the rotor  103 , in order to operate the wind turbine in an effective way, at the same time meeting load limits of mechanical and/or electronic components of the wind turbine. 
     Alternatively to a relationship between the rotational speed of the rotor  103  and the intended mechanical rotor power  104  the arrangement  101  may comprise curves, such as those illustrated in  FIG. 2 . 
     In the graphs  201 ,  203 ,  205  of  FIG. 2  the abscissa  207  indicates the wind speed in m/s. The ordinate  209  of the graph  201  indicates the generator speed of the generator, thus the rotational speed signal  138 . 
     As an example, the rotational speed signal  138  may indicate that the generator speed (curve  210 ) is at about 1200 rpm as indicated by reference sign  211  in the graph  201  in  FIG. 2 . To this rotational speed  211  of the generator an intended mechanical rotor power  213  is associated. This associated intended mechanical rotor power  213  may be obtained by drawing a vertical line from the point  212  in the upper graph  201  in  FIG. 2  to the lower graph  205  in  FIG. 2  which indicates by a curve  215  the relationship between wind speed and intended mechanical rotor power ( 104  in  FIG. 1 ) which is denoted at the ordinate  217 . By drawing a vertical line from the point  212  (having as Y-coordinate the measured generator speed  211 ) the point  219  at the curve  215  is intersected, which has as a Y-coordinate the intended mechanical rotor power  213 . 
     From this intended mechanical rotor power  213  an estimated first power reduction ΔP 1  is subtracted in order to derive a reference power  221  which is then supplied to the converter  111 , as is apparent from  FIG. 1 . The electric output power  114  (power_out) is derived from the mechanical rotor power  104  (power_rotor) according to the following equation: 
       power_out=power_rotor−loss_drive_train−loss_generator−loss_converter−own_consumption.
 
     Own_consumption may be obtained by the following relationship: 
     
       
         
           
             own_consumption 
             = 
             
               
                 fan 
                  
                 
                     
                 
                  
                 1 
                  
                 _power 
                 * 
                 fan 
                  
                 
                     
                 
                  
                 1 
                  
                 _isOn 
               
               + 
               
                 fan 
                  
                 
                     
                 
                  
                 2 
                  
                 _power 
                 * 
                 fan 
                  
                 
                     
                 
                  
                 2 
                  
                 _isOn 
               
               + 
               
                 heaeter 
                  
                 
                     
                 
                  
                 1 
                  
                 _power 
                 * 
                 heater 
                  
                 
                     
                 
                  
                 1 
                  
                 _isOn 
               
               + 
               
                 heaeter 
                  
                 
                     
                 
                  
                 2 
                  
                 _power 
                 * 
                 heater 
                  
                 
                     
                 
                  
                 2 
                  
                 _isOn 
               
               + 
               
                 actuator 
                  
                 
                     
                 
                  
                 1 
                  
                 _power 
                 * 
                 actuator 
                  
                 
                     
                 
                  
                 1 
                  
                 _isOn 
               
               + 
               
                 actuator 
                  
                 
                     
                 
                  
                 2 
                  
                 _power 
                 * 
                 actuator 
                  
                 
                     
                 
                  
                 2 
                  
                 _isOn 
               
               + 
               … 
               + 
               standby_consumption 
             
           
         
       
     
     wherein XXX_isOn are binary quantities or may also be real numbers between 0 and 1, for example, reflection the relative amount of energy/power consumption relative to a maximal power consumption. 
     Graph  203  indicates the rotor pitch angle  216  according to an embodiment. 
     The method performed by the arrangement  101  is adapted to operate the wind turbine in a first wind interval  223 , a second wind interval  225  and a third wind interval  227 . The second wind interval  225  comprises wind speeds which are higher than the wind speeds comprised in the first wind interval  223  and the third wind interval  227  comprises wind speeds which are higher than the wind speeds in the second wind speed interval  225 . 
     In the first wind interval  223  the generator speed is below the rated or nominal generator speed  229 . In the wind interval  225  and  227  the wind turbine is operated at the nominal generator speed  229 . In the first wind speed interval  223  and also the second wind speed interval  225  the intended mechanical rotor power  215  is below the nominal mechanical rotor power  231  and increases from zero to the nominal mechanical rotor power which is indicated with reference sign  231 . In the third wind speed interval  227  the mechanical rotor power stays at the nominal mechanical rotor power  231 . In the graph  201  the generator speed is indicated by curve  210 . 
     In the first wind speed interval  223  (from about 3-9 m/s) the objective may be to maximize the power production. This is done following a speed-power curve, i.e. the controller  101  sends a power (or torque) reference to the converter  111  as a function of the measured rotational speed  210  of the generator (i.e. the generator speed  210 ) or the rotational speed of the rotor. Using the proposed method according to the embodiment of the present application the power reference  221  will be the rotor power  213  reduced by the power loss ΔP. The efficiency of the rotor may be optimized and thus the turbine may be optimized regarding power output. 
     In the third wind speed interval  227  (from 10 m/s to higher wind speeds) the objective may be to limit the power production to maintain the power production at the rated power  231 . Limitation of the power production may be performed to reduce loads of the wind turbine components. In this region  227  the power limit may be the power at any of the components. In the third wind interval  227  the component that limits the power output may e.g. a gear box, such as a gear box included in the drive train  105  in  FIG. 1 . According to an embodiment the power at the gearbox is used as a limiting factor of not the grid connection point (such as output terminal  117 ). 
     The method according to an embodiment of the present application performed by the controller or arrangement  101  according to an embodiment of the present application may produce more power in the wind speed interval  223 . A conventional controller may assume a certain (fixed) loss and own consumption of the turbine, but turning a fan on, heater, deicing system on, will change the own consumption of the wind turbine (for example by the components  121 ,  123 ,  125  illustrated in  FIG. 1 ), which may directly impact the counter-torque applied to the rotor  103  (since the converter  111  will have to deliver this extra power), which is sub-optimal. 
     The method according to an embodiment of the present application produces more power in the third wind speed interval  227  and/or it reduces turbine loading in this interval. A conventional controller may have a fixed rated power in the third wind speed interval  227  and has to assume certain component power consumption and losses. However, by evaluating the real consumption of power and estimate the losses the following features may be achieved: 
     Increase of output power in the third region  227  for low power consumption; this may result in performance increase. 
     Decrease output power in the third wind speed interval for high power consumption in order to not overload mechanical and/or electrical components. 
     The generator power loss (loss_generator) may be estimated using the following relation: 
       loss_generator= c 0+ I   2 *( c 1* T+c 2), 
     wherein 
     loss_generator is the power loss associated with the generator; 
     c0, c1, c2 are constants; 
     I is the electrical current flowing through the generator; and 
     T is the generator temperature. 
     The estimation of the generator power loss takes also into account the generator temperature T. 
     Embodiments of the present application may result in smaller loads. In contrast, a conventional controller reacts on changes in the turbines own power consumption which may result in unnecessary control action and increased loading. 
     The new arrangement and new method according to embodiments of the present application may improve the insight in the turbine performance. Further, the efficiency of components and the own power consumption (of the wind turbine) may be related to the ambient temperature or operating temperature of the respective component. By having temperature depending controller settings the operation may be at least partially optimized. Some turbines may use torque control instead of power control or voltage control, wherein this control function may also be performed by the method according to an embodiment of the present application. 
     It should be noted that the term “comprising” does not exclude other elements or steps and “a” or “an” does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.