Abstract:
A wind power plant, a wind power plant controller and a method of controlling a wind power plant are provided. The method includes a) preparing a telegram comprising wind turbine controlling data for one of the plurality of wind turbines of the wind power plant; b) sending the telegram to the wind turbine upon completion of the telegram; and c) successively repeating steps a) and b) for each of the remaining wind turbines. An initial response time of the wind power plant is shortened; thus, initial response time requirements of the wind power plant specified by grid codes may be fulfilled more easily.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/183,573, filed Jun. 3, 2009, and also claims priority under 35 U.S.C. §119(a) to Danish Patent Application No. PA 2009 00690, filed Jun. 3, 2009. The content of each of these documents is incorporated herein by reference in its entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to a wind power plant, a wind power plant controller and a method of controlling a wind power plant. 
     BACKGROUND 
     A wind power plant usually has a plurality of wind turbines for converting wind energy to electricity. To supply electricity to the electricity end users, the wind power plant is connected to a power grid. However, before the wind power plant can be connected to a power grid, the wind power plant has to meet the requirements of electrical performance of the wind power plant specified by grid codes. One requirement is an initial response time of the wind power plant. Generally, the wind power plant has a wind power plant controller which monitors a power grid voltage and compares the power grid voltage with an external setpoint. A difference between the actual power grid voltage and the external setpoint (e.g. an error signal) is used to calculate a command for reactive power production for the wind power plant. This command is sent from the wind power plant controller to the individual wind turbines which in turn will respond (e.g. produce more or less power in order to adjust the power grid voltage) upon receiving the command. The error signal may be caused by a change in the actual power grid voltage or a change in the external setpoint. The initial response time of the wind power plant is to be understood as the time period starting upon detection of a change in the power grid voltage or a change in the external setpoint and ending as soon as the first wind turbine of the plurality of wind turbines of the wind power plant responds (as soon as response is detected). 
     For example, as shown in a graph  500  of  FIG. 5 , the British grid code requires an initial response time of not more than 200 ms. That is, the first wind turbine of the wind power plant is required to respond at a time of not more than 200 ms after the time a change in the power grid voltage or a change in the external setpoint takes place, based on the reception of respective control data. The remaining wind turbines of the wind power plant subsequently respond, also based on respective control data. The British grid code requires that, after 1 s, the reactive power production of the wind power plant must be greater than 95% of the required response  502  (e.g. reactive power production). 
     Generally, control data is sent to a wind turbine only after information about all wind turbines has been collected, the collected information has been processed and the control data for all the wind turbines has been prepared to be sent out. Therefore, the total time for collecting the information about the wind turbines, processing the collected information and generating the control data for all the wind turbines might not meet the requirement of the initial response time specified by the grid codes. 
     Hence, one objective of the present invention is to avoid the above-mentioned problems. 
     SUMMARY 
     According to an embodiment, a method of controlling a wind power plant comprising a plurality of wind turbines is provided. The method includes: a) preparing a telegram comprising wind turbine controlling data for one of the plurality of wind turbines of the wind power plant; b) sending the telegram to the wind turbine upon completion of the telegram; and c) successively repeating steps a) and b) for each of the remaining wind turbines. One effect of this embodiment is that the initial response time of the wind power plant is shortened; thus, initial response time requirements of the wind power plant specified by grid codes may be fulfilled more easily. 
     According to an embodiment, the wind turbine controlling data includes wind turbine setpoint controlling data. 
     According to an embodiment, the wind turbine setpoint controlling data includes any one of a group consisting of reactive power production setpoint controlling data and active power production setpoint controlling data. 
     According to an embodiment, step a) is carried out after having collected status information about the wind turbine. Step a) may be carried out in dependence on the collected status information. 
     According to an embodiment, the status information collected from the respective wind turbines includes current power output, possible future power output and operating conditions of the respective wind turbines. 
     According to an embodiment, the telegrams are sent to the respective wind turbines via a wind power plant network. 
     According to an embodiment, the number of wind turbines of the wind power plant is more than 20. 
     According to an embodiment, steps a) to c) are carried out on a regular time interval basis ranging between 10 ms and 100 ms. 
     According to an embodiment, steps a) to c) are carried out on a regular time interval basis ranging between 50 ms and 100 ms. 
     According to an embodiment, a wind power plant controller is provided. The wind power plant controller is configured to a) prepare a telegram comprising wind turbine controlling data for one of a plurality of wind turbines of a wind power plant; b) send the telegram to the wind turbine upon completion of the telegram; and c) successively repeat steps a) and b) for each of the remaining wind turbines. One effect of this embodiment is that the initial response time of the wind power plant is shortened; thus, initial response time requirements of the wind power plant specified by grid codes may be fulfilled more easily. 
     According to an embodiment, a wind power plant is provided. The wind power plant includes a plurality of wind turbines; and a wind power plant controller configured to a) prepare a telegram comprising wind turbine controlling data for one of the plurality of wind turbines of the wind power plant; b) send the telegram to the wind turbine upon completion of the telegram; and c) successively repeat steps a) and b) for each of the remaining wind turbines. One effect of this embodiment is that the initial response time of the wind power plant is shortened; thus, initial response time requirements of the wind power plant specified by grid codes may be fulfilled more easily. 
     According to an embodiment, each wind turbine includes a controller configured to receive the telegram from the wind power plant controller and to send status information about the wind turbine to the wind power plant controller. 
     According to an embodiment, the wind turbine controlling data includes wind turbine setpoint controlling data. 
     According to an embodiment, the wind turbine setpoint controlling data includes any one of a group consisting of reactive power production setpoint controlling data and active power production setpoint controlling data. 
     According to an embodiment, the status information of the respective wind turbines includes current power output, possible future power output and operating conditions of the respective wind turbines. 
     According to an embodiment, the wind power plant further includes a wind power plant network coupled between the plurality of wind turbines and the wind power plant controller. 
     According to an embodiment, the wind power plant network is configured to transmit the telegrams from the wind power plant controller to the plurality of wind turbines and to transmit the status information of the plurality of wind turbines to the wind power plant controller. 
     According to an embodiment, the wind power plant controller is implemented on a Programmable Logic Controller (PLC). 
     According to an embodiment, the wind power plant controller includes communication modules configured to send the telegrams to the respective wind turbines. 
     According to an embodiment, the number of wind turbines of the wind power plant is more than 20. 
     According to an embodiment, steps a) to c) are carried out on a regular time interval basis ranging between 10 ms and 100 ms. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the invention are described with reference to the following drawings, in which: 
         FIG. 1  illustrates a common setup of a conventional wind turbine. 
         FIG. 2  shows a schematic diagram of a wind power plant according to an embodiment of the present invention. 
         FIG. 3   a  shows a conventional sequence of preparation and transmission of telegrams. 
         FIG. 3   b  shows a sequence of preparation and transmission of telegrams according to an embodiment of the present invention. 
         FIG. 4  shows a flowchart of an embodiment of controlling a wind power plant according to the present invention. 
         FIG. 5  shows a graph illustrating a requirement of an initial response time of a wind power plant specified by the British grid code. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of a wind power plant, a wind power plant controller and a method of controlling a wind power plant in accordance with the present invention will be described in detail below with reference to the accompanying figures. It will be appreciated that the exemplary embodiments described below can be modified in various aspects without changing the essence of the invention. 
       FIG. 1  illustrates a common setup of a conventional wind turbine  100 . The wind turbine  100  is mounted on a base  102 . The wind turbine  100  includes a tower  104  having a number of towers sections, such as tower rings. A wind turbine nacelle  106  is placed on top of the tower  104 . The wind turbine rotor includes a hub  108  and at least one rotor blade  110 , e.g. three rotor blades  110 . The rotor blades  110  are connected to the hub  108  which in turn is connected to the nacelle  106  through a low speed shaft which extends out of the front of the nacelle  106 . 
       FIG. 2  shows a schematic diagram of a wind power plant  200  (also known as “wind farm” or “wind park”) according to an embodiment of the present invention. In  FIG. 2 , the wind power plant  200  includes a plurality of wind turbines  100 . The number of wind turbines  100  of the wind power plant  200  can be more than  20 . However, it is to be understood that the term “wind power plant” in the sense of the present invention may also include the case of at least two wind turbines. 
     In one embodiment, each wind turbine  100  of the wind power plant  200  may include a controller  202  located within the wind turbine  100 , e.g. in the tower  104  or in the nacelle  106 . Alternatively, the controller  202  may be located outside the wind turbine  100 . The controller  202  of each wind turbine  100  is configured to receive a telegram and to send status information about the respective wind turbine  100 . The controller  202  may also be configured to control all functions of the respective wind turbine  100 . Alternatively, each wind turbine  100  may include a separate controller  202  configured to control all functions of the respective wind turbine  100 . 
     The wind power plant  200  includes a wind power plant controller (PPC)  204 . The wind power plant controller  204  may for example be implemented on a Programmable Logic Controller (PLC). The wind power plant  200  includes a plurality of communication modules  206 . The communication modules  206  may be EWEB modules. However, also other communication modules may be used. The communication modules  206  are integrated into the wind power plant controller  204 . 
     The wind power plant  200  also includes a wind power plant (WPP) network  208 . The WPP network  208  is coupled between the wind turbines  100  and the wind power plant controller  204  via control lines  210 . 
     In the wind power plant  200 , all the wind turbines  100  can communicate with the wind power plant controller  204  through the WPP network  208 . For example, the wind turbines  100  may be configured to send status information about the wind turbines  100  to the wind power plant controller  204  via the WPP network  208  using the respective controllers  202 . The status information about the wind turbines  100  may be sent to the wind power plant controller  204  only upon request by the wind power plant controller  204 . Alternatively, the status information about the wind turbines  100  may be sent to the wind power plant controller  204  at a regular time interval basis. For example, a possible time interval range may be about 10 ms to about 100 ms. 
     In one embodiment, the status information sent from the wind turbines  100  to the wind power plant controller  204  indicates if the respective wind turbines  100  are in an operating mode, are tripped or are starting up. The status information may for example include current power output and/or possible future power output of the respective wind turbines. The possible power outputs of the respective wind turbines generally depend on the wind speed. The status information may also include general operating conditions of the respective wind turbines  100 , e.g. temperature of e.g. a motor of the wind turbine  100 , grid voltage, etc. 
     The wind power plant controller  204  in response controls the wind turbines  100  via the WPP network  208 . The wind power plant controller  204  may also control components such as switchgears, motors, etc in the wind turbines  100 . After receiving the status information about the wind turbines  100 , the wind power plant controller  204  prepares a telegram for each wind turbine  100  comprising corresponding wind turbine controlling data based on the status information received from the respective wind turbine  100 , and sends each telegram to the corresponding wind turbine  100  via the WPP network  208 . The wind power plant controller  204  may be configured to prepare a telegram for a chosen wind turbine  100  of the wind power plant  200  and to send the telegram to the chosen wind turbine  100  upon completion of the telegram. The wind power plant controller  204  may be configured to successively repeat the same process for each of the remaining wind turbines  100 . That is, the next telegram is prepared after having sent out the previous telegram. The wind power plant controller  204  may work based on a discrete time sampled system. It is understood that in a discrete time sampled system, a continuous signal is being read at a fixed time interval (Ts). The value of the continuous signal is represented by its instantaneous value at the respective time instants Ts, 2 Ts, 3 Ts, 4 Ts, . . . , KTs. The instantaneous values of the continuous signal at the respective time instants Ts, 2 Ts, 3 Ts, 4 Ts, . . . , KTs is named sample nos. 1, 2, 3, 4, . . . , K respectively. That is, the wind power plant controller  204  can start to prepare the telegram for a chosen wind turbine N+1 while the telegram for a previous chosen wind turbine N is being sent by the communication modules  206 . More generally, while the communication modules are handling the sending of telegrams which have been prepared based on power plant controller sample #K, the power plant controller may itself start calculating the setpoints for power plant controller sample #K+1. 
     The wind power plant controller  204  prepares and sends one telegram to each wind turbine  100 . In another embodiment, the wind power plant controller  204  may prepare and send more than one telegram to each wind turbine  100 . The control information included within the telegrams may be the same for all telegrams. Alternatively, control data may differ from telegram to telegram, i.e. each wind turbine may receive individual control data. 
     The telegram for each wind turbine  100  can be sent out on a regular time interval basis ranging between about every 10 ms to about 100 ms. The telegram for each wind turbine  100  may be sent to the respective wind turbines  100  by the communication modules  206  which control the sending process. In the event that the wind power plant  200  has a large number of wind turbines  100 , each communication module  206  is configured to send the telegrams to a respective group of wind turbines  100  in the wind power plant  200 . For example, if the wind power plant  200  has twenty-four wind turbines  100  and three communication modules  206 , the twenty-four wind turbines  100  may be equally distributed among the three communication modules such that each communication module  206  controls telegram communication between the wind power plant controller  204  and a respective group of e.g. eight wind turbines of the wind power plant  200 . 
     It is understood that it is not necessary to distribute the number of wind turbines  100  equally among the number of communication modules  206 . Some communication modules  206  may be configured to send the telegram to a larger number of wind turbines  100  than other communication modules  206 . The number of wind turbines  100  for each communication module  206  may be manually adjusted by a user, or may be automatically determined by a software program. 
     The telegrams sent from the wind power plant controller  204  to the respective wind turbines  100  may be data packets/concatenation of data packets. The data packets/concatenation of data packets may be sent using Ethernet IP network technology. However, also other network technology types may be used for sending the data packets. In one embodiment, the wind turbine controlling data of the telegram includes wind turbine setpoint controlling data. The wind turbine setpoint controlling data can include reactive power production setpoint controlling data only, active power production setpoint controlling data only, or both reactive power production setpoint controlling data and active power production setpoint controlling data. 
     The respective controllers  202  of the wind turbines  100  are also configured to receive telegrams from the wind power plant controller  204 . Upon receiving the telegrams, the wind turbines  100  may adjust the existing reactive power production setpoint and the existing active power production setpoint based on the reactive power production setpoint controlling data and the active power production setpoint controlling data in the telegrams, if the existing reactive power production setpoint and the existing active power production setpoint of the wind turbines  100  are different from the reactive power production setpoint controlling data and the active power production setpoint controlling data in the telegrams. It is to be understood that generally the wind turbines  100  should be in an operating mode before the wind turbines  100  can respond to controlling data like the reactive power production setpoint controlling data and the active power production setpoint controlling data in the telegrams. 
       FIG. 3   a  shows a conventional sequence  302  of preparation and transmission of telegrams by the wind power plant controller  204 . Based on the conventional sequence  302 , the wind power plant controller  204  prepares all telegrams for all wind turbines  100  to be controlled in a time interval t 1  and sends the telegrams to the respective wind turbines  100  in a time interval t 2  after all telegrams have been prepared and are ready to be sent out. The total time taken to prepare and to send all the telegrams is T total . 
     A wind power plant using the conventional sequence  302  shown in  FIG. 3   a  may not meet the requirements of the grid codes relating to an initial response time of the wind power plant. The initial response time of the wind power plant using the conventional sequence  302  may be a sum of the time taken to prepare all telegrams (i.e. t 1 ), the time taken to send out the first telegram (i.e. t 3 ) and the time taken for a first wind turbine receiving the first telegram to respond to the control information included within the first telegram. To meet the requirement of the grid codes, the number of wind turbines of the wind power plant may have to be reduced to achieve a faster initial response time. However, higher costs may be incurred if another wind power plant needs to be set up to meet the electricity demand. 
       FIG. 3   b  shows a sequence  304  of preparation and transmission of telegrams by the wind power plant controller  204  according to an embodiment of the present invention. Using the sequence  304  shown in  FIG. 3   b , the wind power plant controller  204  prepares a telegram including wind turbine controlling data for a first wind turbine  100  in a time interval t a  and sends the telegram to the wind turbine  100  at time T 1  upon completion of the telegram. The first wind turbine  100  to receive a telegram is determined by the communication modules  206  and can be changed using a software program. More generally, the order based on which the plurality of wind turbines receive the telegrams can be changed using a software program. The wind power plant controller  204  then proceeds to prepare a telegram for a second wind turbine  100  after sending the telegram for the first wind turbine  100 . The telegram for the second wind turbine  100  is sent out at time T 2  upon completion of the telegram. This process continues until all the wind turbines  100  in the wind power plant  200  receive the respective telegrams. This process is carried out on a regular time interval basis ranging between about 10 ms and about 100 ms. 
     As shown in  FIG. 3   b , the time interval taken for preparing the telegrams for each wind turbine  100  is the same (e.g. t a  for each wind turbine  100 ). However, depending on the individual control information included within each telegram, the time interval taken for preparing the telegrams may differ from telegram to telegram. The telegrams are successively sent out at time T 1 , T 2 , . . . , T 16  respectively. 
     Comparing  FIGS. 3   a  and  3   b , the total time taken for the sequence shown in  FIG. 3   b  to prepare and to send all the telegrams is about the same as the total time taken for the conventional sequence  302  shown in  FIG. 3   a . Therefore, using the sequence  304  shown in  FIG. 3   b  does not result in a total processing time which is longer, as compared to using the conventional sequence  302  shown in  FIG. 3   a . 
     Further, using the sequence shown in  FIG. 3   b  can minimize initial control delay (i.e. initial response time) of the wind power plant  200  and thus achieving a faster response time, since the telegram for the first wind turbine  100  is sent as soon as it is ready. The initial response time of the wind power plant  200  using the sequence  304  may be a sum of the time taken to prepare and send the first telegram (i.e. T 1 ) and the time taken for a first wind turbine  100  to respond to the control information included within the first telegram. Comparing the initial response time of the conventional sequence  302  and the initial response time of the sequence  304 , the wind power plant  200  using the sequence  304  has a faster initial response time. 
     In addition, with e.g. eight wind turbines  100  on each communication module  206  and using the sequence  304 , the first wind turbine  100  of each communication  206  may receive the telegram after about 3 to 5 ms after having started preparing the telegram for the first wind turbine, and the last wind turbine  100  of each communication  206  may receive the telegram after about 25 to 30 ms after having started preparing the telegram for the first wind turbine. Thus, according to one embodiment, the initial response time of the wind power plant  200  may be regarded as a sum of the following time periods: one sample period of the wind power plant controller  204  for calculating new setpoint controlling data included with the telegram for the first wind turbine  100 , the time taken for the first wind turbine  100  to receive the telegram (e.g. about 3 to 5 ms) and a communication delay of the first wind turbine  100  to respond to the setpoint controlling data included within the received telegram. Therefore, the wind power plant  200  having a large number of wind turbines  100  can still meet the requirement of the grid codes relating to an initial response time of the wind power plant  200 . 
     In one embodiment, it may be possible for the wind power plant  200  to use a sequence which is a combination of the conventional sequence  302  and the sequence  304 . Assuming that for example six wind turbines  100  of the wind power plant  200  can achieve the required response  502  shown in  FIG. 5 , the telegrams for six wind turbines  100  of the wind power plant  200  can first be prepared and sent using the sequence  304 , and the telegrams for the remaining wind turbines  100  of the wind power plant  200  can then be prepared and sent using the conventional sequence  302 . More generally, according to one embodiment, the wind power plant controller  204  may determine how many wind turbines  100  are necessary to be controlled according to embodiments of the present invention in order to achieve the required response. Then, these wind turbines  100  may be controlled accordingly (using the sequence  304 ). All remaining wind turbines may be controlled using the conventional sequence  302 . 
       FIG. 4  show a flowchart  400  of an embodiment of controlling a wind power plant according to the present invention. At  402 , a process of successively preparing and sending a telegram to each of the plurality of wind turbines of the wind power plant starts. At  404 , a telegram having wind turbine controlling data for one of the plurality of wind turbines of the wind power plant is prepared. At  406 , the telegram is sent to the wind turbine upon completion of the telegram. At  408 , it is checked if there is any remaining wind turbine to which a corresponding telegram has not been sent. If there is, a telegram comprising wind turbine controlling data is prepared for the remaining wind turbine at  404 , and the telegram is sent to the remaining wind turbine upon completion of the telegram at  406 . This iterative process is successively repeated for each of the remaining wind turbines. If all wind turbines of the wind power plant have received a corresponding telegram, the process ends at  410 . 
     While embodiments of the invention have been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.