Wind turbine

Abstract

A method of controlling a wind turbine having a rotor and a generator for producing power, the wind turbine being designed for a nominal load, the method comprising the steps of: determining a current load acting on at least a part of the wind turbine; calculating a load error, the load error representing the difference between the nominal load and the current load; controlling the wind turbine based on the load error; wherein the step of controlling the wind turbine comprises altering a parameter of the wind turbine so that the power or torque produced by the generator is altered.

1 . A method of controlling a wind turbine having a rotor and a generator for producing power, the wind turbine being designed for a nominal load, the method comprising the steps of:
 determining a current load acting on at least a part of the wind turbine;   calculating a load error, the load error representing a difference between the nominal load and the current load;   controlling the wind turbine based on the load error;   wherein the step of controlling the wind turbine comprises altering a parameter of the wind turbine so that the power or torque produced by the generator is altered.   
     
     
         2 . A method of controlling a wind turbine according to  claim 1 , wherein if the current load is higher than the nominal load, the power produced by the generator is decreased such that the current load is equal to or lower than the nominal load. 
     
     
         3 . A method of controlling a wind turbine according to  claim 1 , wherein if the current load is lower than the nominal load, the power produced by the generator is increased. 
     
     
         4 . A method according to  claim 3 , wherein the power produced by the generator is increased until the current load is equal to the nominal load. 
     
     
         5 . A method according to  claim 1 , wherein the parameter of the wind turbine to be altered is at least one of:
 a pitch angle of one or more rotor blades;   the speed of revolution of the rotor; and   a power reference of the generator.   
     
     
         6 . A method according to  claim 5 , wherein the parameter of the wind turbine to be altered is selected based on the load error. 
     
     
         7 . A method according to  claim 1 , wherein the wind turbine is designed for a plurality of nominal loads, each of the plurality of nominal loads being associated with a different component of the wind turbine; the method further comprising the steps of:
 determining a plurality of current loads, each of the plurality of current loads acting on the different components of the wind turbine which are associated with at least one of the nominal loads;   calculating a plurality load errors for each of the plurality of current loads, each load error representing the difference between the nominal load and the associated current load; and   controlling the wind turbine based on the plurality of load errors;   wherein the step of controlling the wind turbine comprises altering a parameter of the wind turbine so that the power produced by the generator is altered.   
     
     
         8 . A method of controlling a wind turbine according to  claim 1 , wherein the wind turbine is erected on a location, the method further comprising the steps of:
 defining a plurality of sectors each specifying a range of wind directions towards the wind turbine;   defining, for each sector, an expected wind load from the specified directions and a sector control strategy which is based on a predetermined comparison between the expected wind load and the nominal load;   determining a current wind direction;   before controlling the wind turbine based on the load error, controlling the wind turbine in accordance with the sector control strategy defined for the sector to which the current wind direction corresponds; and then   controlling the wind turbine based on the load error.   
     
     
         9 . A method of controlling a wind turbine according to  claim 1 , wherein the wind turbine is erected on a location, the method further comprising the steps of:
 defining a plurality of sectors each specifying a range of wind directions towards the wind turbine;   defining, for each sector, an expected wind load from the specified directions and a sector control strategy which is based on a predetermined comparison between the expected wind load and the nominal load;   determining a current wind direction; and   after the step of controlling the wind turbine based on the load error, controlling the wind turbine in accordance with the sector control strategy defined for the sector to which the current wind direction corresponds.   
     
     
         10 . A method according to  claim 9 , wherein the step of defining for each sector an expected wind load comprises the step of:
 determining the current loads acting on at least a part of the wind turbine over a period of time for each sector, and calculating the expected wind load for each sector based on accumulated values of the current loads over the period of time.   
     
     
         11 . A method according to  claim 9 , wherein the step of controlling the wind turbine in accordance with the sector control strategy defined for the sector to which the current wind direction corresponds comprises the step of:
 selecting one control strategy from a plurality of control strategies defined for each sector, wherein the selection is based on the expected wind load.   
     
     
         12 . A method according to  claim 9 , wherein each sector control strategy is defined based on an expected wind load from wind from the corresponding sector of wind directions towards the turbine for a specific geographical location. 
     
     
         13 . A method according to  claim 9 , wherein a given power output of the wind turbine as a function of wind speed is defined for a range of wind speeds, the given power output as a function of wind speed being the same for all sectors; and the sector control strategy for each sector controls the wind turbine such that the power output of the wind turbine is either:
 below the given power output for a given wind speed; or   equal to the given power output for a given wind speed; or   above the given power output for a given wind speed.   
     
     
         14 . A control system for a wind turbine having a rotor and a generator for producing power, the wind turbine being designed for a nominal load, the control system having a control structure adapted to:
 determine a current load acting on at least a part of the wind turbine;   calculate a load error, the load error representing a difference between the nominal load and the current load;   control the wind turbine based on the load error by altering a parameter of the wind turbine so that the power or torque produced by the generator is altered.   
     
     
         15 . A control system according to  claim 14 , wherein the control system is adapted to carry out the method according to  claim 1 . 
     
     
         16 . A wind turbine for converting between wind energy and electrical energy, the wind turbine comprising a control system according to  claim 14 .