# US 2018/0320663 A1 · Control of a wind turbine during recovery after a grid fault > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2018/0320663 A1 - Document ID: US20180320663A1 - Status: Published application - Kind: A1 - Application number: 15/775,356 - Filed: 2016-11-17 - Published: 2018-11-08 - Earliest claimed: 2015-11-19 - Assignees: Vestas Wind Systems A/S - Applicants: Vestas Wind Systems A/S - Inventors: Martin Ansbjerg KJÆR; Kasper Zinck OSTERGAARD; Jan GRAUGAARD-JENSEN - Web page: https://patentgrep.com/patent/US20180320663A1 ## CPC - F03D 7/0284: {in relation to the state of the electric grid} - F03D 7/0224: {Adjusting blade pitch} - F05B 2270/10711: applying a low voltage ride through method - F05B 2270/309: Rate of change of parameters - F05B 2270/328: Blade pitch angle - F05B 2270/335: Output power or torque - Y02E 10/72: Wind turbines with rotation axis in wind direction - F03D: WIND MOTORS - F05B: INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G - Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION ## Abstract Embodiments of the present invention relate to control of a wind turbine during a recovery period after a grid fault. It is disclosed to operate a wind turbine during the recovery period to determine the actual pitch angle of the rotor blades and the actual wind speed, and based on that determining a desired pitch angle of the rotor blades, as well as a pitch ramp rate so that the actual pitch angle can be brought to match the desired pitch angle before the end of the recovery period. In embodiments, the steps performed in the recovery mode are repeated at intervals during the recovery period. ## Claims ### Claim 1 A method for controlling a wind turbine connected to a utility grid, wherein the wind turbine comprises rotor blades, the method comprising: detecting a fault of the utility grid; controlling one or more of the rotor blades in a fault mode; detecting a recovery of the utility grid; and controlling, during a recovery period, one or more of the rotor blades in a recovery mode, wherein the recovery mode comprises: determining an actual pitch angle of each of the rotor blades; determining an actual wind speed; determining a desired pitch angle of each of the rotor blades according to the actual wind speed; determining a pitch ramp rate of each of the rotor blades so that the actual pitch angles match the respective desired pitch angle before the end of the recovery period, and ramping the pitch angle of each of the rotor blades with the respective determined pitch ramp rate. ### Claim 2 (depends on 1) The method according to claim 1, wherein the steps performed in the recovery mode are repeated at intervals during the recovery period. ### Claim 3 (depends on 1) The method according to claim 1, wherein the wind turbine remains connected to the utility grid during the fault of the grid. ### Claim 4 (depends on 1) The method according to claim 1, wherein the desired pitch angle is a predefined aerodynamically optimal pitch angle. ### Claim 5 (depends on 1) The method according to claim 1, wherein the wind turbine during the recovery period is controlled by use of a power feedback control loop. ### Claim 6 (depends on 1) The method according to claim 1, wherein the wind turbine is controlled in partial load operation where the wind speed is below a rated wind speed for the wind turbine. ### Claim 7 (depends on 1) The method according to claim 1, further comprising: determining a desired output power of the wind turbine according to the actual wind speed; determining a ramp rate of the output power so that the output power matches the desired output power before an end of the recovery period, and ramping the output power with the determined ramp rate. ### Claim 8 (depends on 7) The method according to claim 7, wherein the ramp rate of the output power and the pitch ramp rate are aligned so that the output power reaches the desired output power at the same time the pitch angle reaches the desired pitch angle. ### Claim 9 A control system for a wind turbine, the control system comprises at least one processor for: detecting a fault of the utility grid; controlling one or more rotor blades in a fault mode; detecting a recovery of the utility grid; and controlling, during a recovery period, one or more of the rotor blades in a recovery mode, wherein the recovery mode comprises: determining an actual pitch angle of each of the rotor blades; determining an actual wind speed; determining a desired pitch angle of each of the rotor blades according to the actual wind speed; determining a pitch ramp rate of each of the rotor blades so that the actual pitch angle matches the respective desired pitch angle before an end of the recovery period, and ramping the pitch angle of each of the rotor blades with the respective determined pitch ramp rate. ### Claim 10 A wind turbine comprising a control system wherein the control system comprises at least one processor configured to perform an operation comprising: detecting a fault of the utility grid; controlling one or more rotor blades in a fault mode; detecting a recovery of the utility grid; and controlling, during a recovery period, one or more of the rotor blades in a recovery mode, wherein the recovery mode comprises: determining an actual pitch angle of each of the rotor blades; determining an actual wind speed; determining a desired pitch angle of each of the rotor blades according to the actual wind speed; determining a pitch ramp rate of each of the rotor blades so that the actual pitch angle matches the respective desired pitch angle before an end of the recovery period, and ramping the pitch angle of each of the rotor blades with the respective determined pitch ramp rate. ### Claim 11 (canceled) ### Claim 12 (depends on 10) The wind turbine according to claim 10, wherein the steps performed in the recovery mode are repeated at intervals during the recovery period. ### Claim 13 (depends on 10) The wind turbine according to claim 10, wherein the wind turbine remains connected to the utility grid during the fault of the grid. ### Claim 14 (depends on 10) The wind turbine according to claim 10, wherein the desired pitch angle is a predefined aerodynamically optimal pitch angle. ### Claim 15 (depends on 10) The wind turbine according to claim 10, wherein the wind turbine during the recovery period is controlled by use of a power feedback control loop. ### Claim 16 (depends on 10) The wind turbine according to claim 10, wherein the wind turbine is controlled in partial load operation where the wind speed is below a rated wind speed for the wind turbine. ### Claim 17 (depends on 10) The wind turbine according to claim 10, further comprising: determining a desired output power of the wind turbine according to the actual wind speed; determining a ramp rate of the output power so that the output power matches the desired output power before an end of the recovery period, and ramping the output power with the determined ramp rate. ### Claim 18 (depends on 17) The wind turbine according to claim 17, wherein the ramp rate of the output power and the pitch ramp rate are aligned so that the output power reaches the desired output power at the same time the pitch angle reaches the desired pitch angle. ### Claim 19 A computer program product comprising software code adapted to control a wind turbine when executed on a data processing system, the computer program product being adapted to control the wind turbine according to an operation comprising: entering a fault mode in response to detecting a fault of the utility grid; controlling one or more rotor blades of the wind turbine in the fault mode; detecting a recovery of the utility grid; and controlling, during a recovery period, one or more of the rotor blades in a recovery mode, wherein the recovery mode comprises: determining an actual pitch angle of each of the rotor blades; determining an actual wind speed; determining a desired pitch angle of each of the rotor blades according to the actual wind speed; determining a pitch ramp rate of each of the rotor blades so that the actual pitch angles match the respective desired pitch angle before the end of the recovery period, and ramping the pitch angle of each of the rotor blades with the respective determined pitch ramp rate. ### Claim 20 (depends on 19) The wind turbine according to claim 19, wherein the steps performed in the recovery mode are repeated at intervals during the recovery period. ### Claim 21 (depends on 19) The wind turbine according to claim 19, wherein the wind turbine remains connected to the utility grid during the fault of the grid.