Abstract:
The method for controlling a first wind energy turbine of a wind park comprising multiple wind energy turbines connected to the grid, in situations where the first energy turbine operates substantially at zero energy output level, comprises the steps of determining whether at least one of the other wind energy turbines of the wind park is operated above a predetermined energy output level, and if at least one of the other wind energy turbines of the wind park is operated above the predetermined energy output level, maintaining connection of the first wind energy turbine to the grid.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for controlling a wind energy turbine of a wind park comprising multiple wind energy turbines and, in particular, an optimized wind farm management with autonomous wind turbine control. 
     2. Related Prior Art 
     Wind turbines operating at lull wind conditions are exposed either to frequent switching operations or to higher energy consumptions due to the control of the wind energy turbine performed to the effect of keeping the turbine online and in rotation (motor operating mode). The reason for this behaviour is the aim of the turbine control system to gain as much energy from the wind as possible. The switches by which the generator of a wind energy turbine is connected and disconnected from the grid have a limited lifetime due to mechanical wear. At lull wind conditions, switching on and off the grid occurs more often and energy consumption will increase. Depending on wind speed characteristics, turbulences, controller structure, and parameter settings, the amount of switching operations per year varies considerably between different locations. If wind speed is often at cut-in and cut-out range, a high switching number will occur. Accordingly, maintenance and replacement of the switches have to be done after a certain switching number. Due to site-specific climate effects and turbulence intensities, the maintenance intervals can be rather small. In particular in off-shore applications, higher numbers of switching operations become economically questionable due to higher performance and replacement costs. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method for controlling a wind energy turbine of a wind park comprising multiple wind energy turbines, wherein the switching cycles can be reduced if the wind energy turbine to be controlled operates substantially at zero energy output level as e. g. in lull wind conditions. 
     In order to achieve the above object, the present invention provides for a method for controlling a first wind energy turbine of a wind park comprising multiple wind energy turbines connected to the grid, in situations where the first wind energy turbine operates substantially at zero energy output level, wherein the method comprises the steps of determining whether at least one of the other wind energy turbines of the wind park is operated above a predetermined energy output level, and if at least one of the other wind energy turbines of the wind park is operated above the predetermined energy output level, maintaining the connection of the first wind energy turbine to the grid. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     According to the invention, a wind energy turbine of a wind park is not automatically switched off if the wind energy turbine operates substantially at zero energy output level. Prior to switching off the wind energy turbine, it is first determined whether at least one of the other wind energy turbines of the wind park is operated above a predetermined energy output level. By means of this feature it is determined whether the whole wind park is operated at substantial zero energy output level or whether in an extreme situation it is merely the respective wind energy turbine which currently is operated substantially at zero energy output level. Accordingly, the other wind energy turbines of the wind part are used as sensors or detectors for detecting the current operating state of the wind park. If at least one of the other wind energy turbines of the wind park is operating above the predetermined energy output level, the wind energy turbine to be controlled is maintained connected to the grid i. e. is not automatically switched off for at least a predetermined time. 
     One aspect of the present invention is to deviate from optimal power curve settings for converting also small gusts at low wind speeds into rotational energy and, therefore allow the turbine to bridge longer negative gusts. Maintaining the wind energy turbine connected to the grid during e. g. a lull wind condition also means that this wind energy turbine is directly ready for producing electrical energy as soon as wind speed increases again. Accordingly, no time has to be spent for first switching on and running up the wind energy turbine. 
     Another aspect of the present invention is to supervise the turbine behaviour in close to zero power operation states and to make estimations on the upcoming wind condition to decide whether or not a reconnection to the grid is useful. Additionally, not only the turbine-integrated wind speed sensors can be used to decide whether a grid connection/disconnection should be performed but also the determined and observed turbine behaviour of neighbouring turbines in a wind park. For instance, if the wind energy turbine to be controlled is in the wake of another turbine, which in turn is operating at around zero energy output level, it can be useful to not connect the wind energy turbine located in the wake to the grid until the other turbine reaches a predetermined energy output level. 
     Accordingly, the idea of the present invention is to optimize the turbine behaviour at around zero energy output level conditions and, in particular, at lull wind conditions. By means of the invention the amount of switching cycles can be minimized. The optimization according to the invention is performed by means of individual controller settings of each of the wind energy turbines which will optimize energy production and switching cycles. 
     By means of the present invention an optimized operation and control of wind energy turbines below rated wind speeds are possible. Each turbine of a wind park uses the surrounding turbines, all turbines or the whole wind park as additional sensors. This allows to optimize the wind park operation based on the principles of cellular automat, self-organized systems, and distributed intelligence. Other aspects of the present invention relate to icing detection and load optimization within a wind park. 
     According to another embodiment of the present invention, the wind energy turbine to be controlled is disconnected from the grid if the majority of the wind energy turbines of the wind park operates substantially at zero energy level. As an alternative, if e. g. a group of wind energy turbines of the wind park spaced from the wind energy turbine to be controlled, operates above a predetermined energy output level, this could be a hint for an inhomogeneous current wind profile. In such a condition it would make sense to keep the wind energy turbine to be controlled connected to the grid since a homogeneous wind profile can be expected soon or, in other words, wind profile inhomogeneities will not last long. 
     On the other hand, if the wind energy turbine to be controlled is located within a group of wind energy turbines operating above a predetermined energy output level, this is an indication that the wind energy turbine to be controlled and currently operating substantially at zero energy output level has a certain defect, i. e. icing or other impairments or damages. 
     In another embodiment of the present invention the wind energy turbine to be controlled and operating substantially at zero energy output level is switched off if the current wind is blowing in a predetermined wind direction area so that results of the wind energy turbine to be controlled is located due to the topology of the surrounding area of the wind park in a wake. Accordingly, as mentioned above, if the wind energy turbine to be controlled is located in a wake of another wind energy turbine or of an obstacle (forest, building, hill or the like), maintaining connection of the respective wind energy turbine to the grid is not useful as long as the wind direction does not change. 
     The invention shows a new manner how to provide power generation and switching cycle reductions at e. g. low wind speeds. Energy to be provided to the grid is relevant. Due to that, according to the invention, the individual turbines of a wind park can be operated or switched on and off at different cut-in or cut-out wind speeds. 
     It is already known to collectively control all wind energy turbines in a wind park. However, the invention is clearly different from that known approach in that the invention relates to the control of individual turbines by individual controllers with individual parameter settings wherein all the turbines are connected to each other at their sensor levels in order to control each turbine individually depending on the behaviour of at least some of the other turbines of the wind park. The advantages of the invention are maximization of total power generation and failure effect decrease as compared to central wind farm managements. 
     Moreover, the invention can be used for optimizing control structures and parameter settings in the cut-in and cut-out areas of wind energy turbines. As wind conditions in different sites differ significantly from each other, also the turbine control behaviour will differ from good to bad, depending under what conditions the turbine is currently operated. Therefore, the present invention is also aimed at a self-learning controller concept adapted to optimize turbine behaviours according to local wind conditions.