# US 11,028,829 B2 · Controlling wind turbine based on rain drop size > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,028,829 B2 - Document ID: US11028829B2 - Status: Granted - Kind: B2 - Application number: 16/461,574 - Filed: 2017-11-17 - Published: 2019-12-05 - Granted: 2021-06-08 - Earliest claimed: 2016-11-18 - Assignees: MHI Vestas Offshore Wind A/S - Applicants: Mhi Vestas Offshore Wind A/S - Inventors: Hideyasu Fujioka - Web page: https://patentgrep.com/patent/US11028829B2 ## CPC - F03D 7/0276: {controlling rotor speed, e.g. variable speed} - F03D 1/00: Wind motors with rotation axis substantially parallel to the air flow entering the rotor (controlling thereof F03D7/02) - F03D 7/0224: {Adjusting blade pitch} - F03D 7/042: {by means of an electrical or electronic controller} - F03D 7/043: {characterised by the type of control logic} - F03D 17/00: Monitoring or testing of wind motors, e.g. diagnostics (testing during commissioning of wind motors F03D13/30) - F05B 2240/221: with horizontal axis - F05B 2260/70: Adjusting of angle of incidence or attack of rotating blades - F05B 2260/80: Diagnostics - F05B 2270/101: to control rotational speed (n) - F05B 2270/323: Air humidity - F05B 2270/804: Optical devices - G01F 22/00: Methods or apparatus for measuring volume of fluids or fluent solid material, not otherwise provided for - G01W 1/14: Rainfall or precipitation gauges (measuring volume in general G01F) - 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 - G01F: MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME - G01W: METEOROLOGY (radar, sonar, lidar or analogous systems, designed for meteorological use G01S13/95, G01S15/88, G01S17/95) - Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION ## Abstract There is presented a method (320) for controlling a wind turbine (100), wherein said wind turbine comprises a wind turbine rotor (102) with one or more blades (103), wherein the wind turbine has a rated angular rotation speed (214) of the wind turbine rotor, said method comprising providing (322) an estimated drop size (324) of rain drops impinging on the one or more blades, determining (326) whether an entry criterion for operation according to a reduced mode is fulfilled, wherein said determining is based at least partially on the estimated drop size (324), controlling (328) the wind turbine according to the reduced mode if the entry criterion is fulfilled, wherein in the reduced mode an angular rotation speed of the wind turbine rotor is limited below an angular rotation speed threshold (216), wherein the angular rotation speed threshold is smaller than the rated angular rotation speed of the wind turbine. ## Claims ### Claim 1 A method for controlling a wind turbine comprising a wind turbine rotor with one or more blades, wherein the wind turbine has a rated angular rotation speed of the wind turbine rotor; the method comprising: providing an estimated drop size of rain drops impinging on the one or more blades, determining whether an entry criterion for operation according to a reduced mode is fulfilled, wherein said determining is based at least partially on the estimated drop size, and controlling the wind turbine according to the reduced mode upon determining that the entry criterion is fulfilled, wherein in the reduced mode an angular rotation speed of the wind turbine rotor is limited below an angular rotation speed threshold, and wherein the angular rotation speed threshold is smaller than the rated angular rotation speed of the wind turbine. ### Claim 2 (depends on 1) The method according to claim 1, wherein the entry criterion is fulfilled upon determining the estimated drop size is above a predetermined drop size entry threshold. ### Claim 3 (depends on 1) The method according to claim 1, further comprising providing an estimated precipitation intensity of precipitation impinging on the wind turbine, wherein said determining is based at least partially on said estimated precipitation intensity. ### Claim 4 (depends on 3) The method according to claim 3, wherein the entry criterion is fulfilled upon determining at least one of: that the estimated drop size is above a predetermined drop size entry threshold, and that the estimated precipitation intensity is above a predetermined precipitation intensity entry threshold. ### Claim 5 (depends on 4) The method according to claim 4, wherein the predetermined drop size entry threshold is 1 mm. ### Claim 6 (depends on 4) The method according to claim 4, wherein the predetermined precipitation intensity entry threshold is 2.5 mm/hour. ### Claim 7 (depends on 1) The method according to claim 1, wherein the angular rotation speed threshold is less than 95% of the rated angular rotation speed. ### Claim 8 (depends on 1) The method according to claim 1, wherein providing an estimated drop size comprises estimating drop size with any one of: an optical rain gauge, an acoustic rain gauge, a disdrometer, and a laser drop-sizing gauge. ### Claim 9 (depends on 1) The method according to claim 1, further comprising: providing an estimated precipitation intensity of precipitation impinging on the wind turbine, providing an estimated rain drop terminal speed of rain drops impinging on the wind turbine, providing an estimated rain drop impact speed of rain drops impinging on the one or more blades, and providing an estimated rain drop impact angle of rain drops impinging on the one or more blades, wherein the entry criterion is fulfilled upon determining that an estimated incubation time is below a predetermined incubation time entry threshold, and wherein incubation time tic is determined according to a formula given as: tic∝−1Iα*Vtβ*(V*cos(θ))γ*dζ wherein: tic represents incubation time, I represents precipitation intensity (accumulated amount of rainfall per time), Vt represents rain drop terminal speed, V represents rain drop impact speed, θ represents rain drop impact angle, d represents rain drop diameter, α is a constant, β is a constant, γ is a constant, ζ is a constant. ### Claim 10 (depends on 9) The method according to claim 9, wherein providing an estimated precipitation intensity comprises estimating precipitation intensity with any one of: an optical rain gauge, an acoustic rain gauge, a disdrometer, and a laser drop-sizing gauge. ### Claim 11 (depends on 1) The method according to claim 1, further comprising: controlling the angular rotation speed according to the reduced mode due to the entry criterion having been fulfilled, subsequently providing a subsequently estimated drop size of rain drops impinging on the one or more blades, subsequently determining whether an exit criterion for discontinuing reduced mode operation is fulfilled, wherein said subsequently determining is based at least partially on the subsequently estimated drop size, and discontinuing controlling wind turbine according to the reduced mode upon determining that the exit criterion is fulfilled. ### Claim 12 (depends on 1) The method according to claim 1, wherein the wind turbine further comprises a pitch control system for controlling a pitch angle of the one or more blades; and wherein the method further comprises controlling the angular rotation speed by controlling the pitch angle of the one or more blades with the pitch control system. ### Claim 13 A computer program product comprising a non-transitory computer readable medium having instructions which, when executed by one or more processors cause a control system for a wind turbine having a rotor with one or more blades to perform an operation; wherein the wind turbine has a rated angular rotation speed of the rotor; wherein the operation comprises: providing an estimated drop size of rain drops impinging on the one or more blades, determining whether an entry criterion for operation according to a reduced mode is fulfilled, wherein said determining is based at least partially on the estimated drop size, and controlling the wind turbine according to the reduced mode upon determining that the entry criterion is fulfilled, wherein in the reduced mode an angular rotation speed of the rotor is limited below an angular rotation speed threshold, and wherein the angular rotation speed threshold is smaller than the rated angular rotation speed of the wind turbine. ### Claim 14 A wind turbine, comprising: a tower; a nacelle disposed on the tower; a rotor extending from the nacelle, the wind turbine has a rated angular rotation speed of the rotor; a plurality of blades disposed on an end of the nacelle; and a control system configured to: provide an estimated drop size of rain drops impinging on the plurality of blades, determine whether an entry criterion for operation according to a reduced mode is fulfilled, wherein said determining is based at least partially on the estimated drop size, and control the wind turbine according to the reduced mode upon determining that the entry criterion is fulfilled, wherein in the reduced mode an angular rotation speed of the rotor is limited below an angular rotation speed threshold, and wherein the angular rotation speed threshold is smaller than the rated angular rotation speed of the wind turbine. ### Claim 15 A method for controlling a wind turbine, wherein the wind turbine comprises a wind turbine rotor with one or more blades, wherein the wind turbine has a rated angular rotation speed of the wind turbine rotor; the method comprising: providing an estimated aerial particle size of aerial particles impinging on the one or more blades, determining whether an entry criterion for operation according to a reduced mode is fulfilled, wherein said determining is based at least partially on the estimated aerial particle size, and controlling the wind turbine according to the reduced mode upon determining that the entry criterion is fulfilled, wherein in the reduced mode an angular rotation speed of the wind turbine rotor is limited below an angular rotation speed threshold, wherein the angular rotation speed threshold is smaller than the rated angular rotation speed of the wind turbine.