Control of active power reserve in a wind-farm

Abstract

A method and system of active power reserve regulation in a wind farm with a communication network having a plurality of wind turbines that provide an active power reserve in order to support eventual power grid contingencies and to deliver an increase of power in case it is needed.

1 . A method of active power reserve regulation in a wind farm having a plurality of wind turbines and a communication network, the method comprising:
 determining an active power reserve setpoint indicating a target value of a total active power reserve for the wind farm;   determining a first subset of wind-turbines of the plurality of wind turbines and operating the first subset of wind turbines without an external command of power output limitation as an estimation of the maximum active power available in the wind farm; and   determining, a second subset of wind-turbines of the plurality of wind-turbines, and operating the second subset of wind turbines to achieve the active power reserve setpoint by using an external command of power output limitation.   
     
     
         2 . The method of  claim 1 , wherein the active power reserve setpoint is determined by a wind-farm active power reserve controller by using an economic profit optimization algorithm. 
     
     
         3 . The method of  claim 1 , wherein the active power reserve setpoint is determined by a wind-farm active power reserve controller based on grid frequency control. 
     
     
         4 . The method of  claim 1 , wherein the active power reserve setpoint is received from outside of the wind farm by communication means. 
     
     
         5 . The method of  claim 1 , wherein the active power reserve setpoint is determined in absolute units or as a percentage of active power output from the wind farm. 
     
     
         6 . The method of  claim 1 , the method further comprising operating a controlled load using an amount of active power produced by the wind farm less than or equal to the total active power reserve, said amount of active power used by the controlled load being part of the active power reserve. 
     
     
         7 . The method of  claim 6 , wherein an active power reserve achieved by the second subset of wind turbines (Sp_PwtsRes) is the difference between the total active power reserve and the active power used to operate the controlled load (AV_P CL ). 
     
     
         8 . The method of  claim 1 , wherein the second subset of wind-turbines are operated so as to be limited to a percentage of each of their respective rated active power outputs within a specified range limit. 
     
     
         9 . The method of  claim 1 , wherein the number of wind-turbines determined for the first and second subsets of wind turbines is determined based on the active power reserve setpoint. 
     
     
         10 . The method of  claim 1 , wherein the number of wind-turbines determined for the second subset of wind turbines is varied based on a difference between an actual value of the total active power reserve of the wind farm and the target value of the total active power reserve in the wind farm. 
     
     
         11 . The method of  claim 10 , wherein the variation of wind-turbines in the second subset of wind turbines is based on a ratio between a mean active power output from the first subset of wind turbines and a mean active power output from the second subset of wind turbines. 
     
     
         12 . The method of  claim 11 , wherein the ratio is maintained between an upper threshold and a lower threshold. 
     
     
         13 . The method of  claim 1  further comprising:
 calculating an error (ε_Pres) between the active power reserve setpoint (Sp_Pwtsres) to be achieved by the second subset of wind turbines and an estimated active power reserve of the wind turbines (est_PwtsRes);   using the error ε_Pres to generate a percentage of maximum rated power, limiting the percentage of maximum rated power and keeping it within a lower and an upper value.   
     
     
         14 . The method of  claim 13 , wherein the error (ε_Pres) is input to at least one of a PID controller, a higher order transfer function, a lead-lag controller and standard non linear blocks. 
     
     
         15 . The method of  claim 13 , wherein the estimated active power reserve (est_PwtsRes) is based on a comparison between the active power generated by the first subset of wind turbines and the second subset of wind turbines. 
     
     
         16 . A system of active power reserve regulation in a wind farm having a plurality of wind turbines, comprising:
 a wind-farm controller which interacts with the plurality of wind turbines to manage a reserve of active power using active power limitation commands;   an active power wind-turbine controller in each of the plurality of wind-turbines, wherein each active power wind turbine controller is configured to limit a maximum amount of active power generated by a corresponding one of the plurality of wind turbines according to the active power limitation commands received from the wind-farm active power reserve controller.   
     
     
         17 . The system of  claim 16 , further comprising a controlled load which receives active power from the wind-turbines, said active power being part of the active power reserve. 
     
     
         18 . The system of  claim 17  wherein the controlled load is used as an electric load or as electrical energy storage. 
     
     
         19 . The system of  claim 17  wherein the controlled load is an electrolyzer, a flywheel, or other type of energy storage device. 
     
     
         20 . The system of  claim 16 , wherein the active power reserve wind-farm controller transmits an active reserve mode command to the plurality of wind-turbines so that the first subset of wind turbines operate with no external power output limitations and the second subset of wind-turbines operate at less than a maximum active power output, according to the active power limitation command received from the wind farm controller, to contribute to the total reserve of active power in the wind-farm. 
     
     
         21 . The system of  claim 17 , wherein the active power reserve wind-farm controller determines an actual power consumption of the controlled load and determines an active power limitation command for the second subset of wind turbines based on the actual power consumption of the controlled load and the active power reserve setpoint. 
     
     
         22 . The system of  claim 20 , wherein the first subset of wind-turbines, in response to the active power reserve mode command, operate with no constraints related to the wind farm active power reserve controller, and maintain said maximum active power output unless additional constraints unrelated to the reserve of active power limit the active power output. 
     
     
         23 . The system of  claim 20 , wherein the second subset of wind-turbines, in response to the active power limitation command, do not exceed a commanded percentage of their rated active power. 
     
     
         24 . The system of  claim 20 , wherein a number of wind-turbines in the second subset of wind turbines is varied based on a difference between an actual value of the total reserve of active power in the wind farm and a target value of the total reserve of active power in the wind farm. 
     
     
         25 . The system of  claim 24  wherein the second subset of wind turbines is varied based on the active power reserve setpoint. 
     
     
         26 . The system of  claim 24 , wherein the second subset of wind turbines is varied based on a ratio between a mean active power output from the first subset of wind turbines and a mean active power output from the second subset of wind turbines. 
     
     
         27 . The system of  claim 26 , wherein the ratio is maintained between an upper threshold and a lower threshold. 
     
     
         28 . A method of active power reserve regulation in a wind farm having a plurality of wind turbines and a communication network, the method comprising:
 operating a controlled load to generate an active power reserve from power generated by the plurality of wind turbines.   
     
     
         29 . The method of  claim 28 , wherein the power to operate the controlled load is varied dynamically. 
     
     
         30 . The method of  claim 28 , wherein the power to operate the controlled load is maintained constant. 
     
     
         31 . A system of active power reserve regulation in a wind farm having a plurality of wind turbines, comprising:
 a controlled load to generate an active power reserve.   
     
     
         32 . The system of  claim 31 , wherein the controlled load is one or more different loads. 
     
     
         33 . The system of  claim 31 , wherein the controlled load is used as an electric load or as an energy storage device. 
     
     
         34 . The system of  claim 31 , wherein the controlled load is an electrolyzer, a flywheel, or other type of energy storage device.