# US 11,905,927 B2 · Frequency content based monitoring of wind turbine blade pitch system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,905,927 B2 - Document ID: US11905927B2 - Status: Granted - Kind: B2 - Application number: 17/914,900 - Filed: 2021-04-12 - Published: 2023-04-27 - Granted: 2024-02-20 - Earliest claimed: 2020-04-30 - Assignees: Vestas Wind Systems A/S - Applicants: Vestas Wind Systems A/S - Inventors: Frank Møller Hansen - Web page: https://patentgrep.com/patent/US11905927B2 ## CPC - F03D 17/00: Monitoring or testing of wind motors, e.g. diagnostics (testing during commissioning of wind motors F03D13/30) - F03D 7/0224: {Adjusting blade pitch} - F05B 2270/328: Blade pitch angle - F05B 2270/331: Mechanical loads - 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 Systems, methods, and computer program products for monitoring a wind turbine (10). The system receives a signal (426) indicative of a pitch force being applied to a blade (20) of a wind turbine (10). The signal (426) is sampled to generate a discrete time-domain signal (426) including a plurality of pitch force samples. Samples are selected for analysis using a sampling window (326) that excludes samples obtained under operating conditions determined to be detrimental to obtaining good data. The selected samples are processed to generate a spectral density (150) of the signal (426), and the frequency content of the spectral density (150) analysed to determine the condition of one or more components of the wind turbine (10). If the analysis indicates that a component of the wind turbine (10) needs attention, the system generates an alarm. ## Claims ### Claim 1 A system for monitoring operation of a wind turbine including a rotor having a blade and rotates in a rotor plane having a plurality of sectors, the system comprising: one or more processors; and a memory coupled to the one or more processors and including program code that, when executed by the one or more processors, causes the system to: receive a time-domain signal indicative of a pitch force being applied to the blade; determine a first spectral density of the time-domain signal by sampling the time-domain signal to generate a discrete time-domain signal, selecting a plurality of samples from the discrete time-domain signal that are within a sampling window corresponding to a first period of time when the blade is in a selected sector of the plurality of sectors, and transforming the plurality of samples from a time-domain to a frequency-domain; determine a condition of the wind turbine based on a frequency content of the first spectral density; and in response to the condition being indicative of a problem with the wind turbine, generate an alarm signal. ### Claim 2 (depends on 1) The system according to claim 1, wherein the time-domain signal is indicative of a pressure of a fluid in a chamber of a hydraulic actuator of a pitch drive that controls a pitch of the blade. ### Claim 3 (depends on 1) The system according to claim 1, wherein the plurality of samples is selected so that each sample of the plurality of samples corresponds to a wind speed that is within a predetermined wind speed range or a rate of change in the wind speed that is within a predetermined rate of change in wind speed range. ### Claim 4 (depends on 1) The system according to claim 1, wherein the samples are selected so that each sample of the plurality of samples corresponds to a pitch position that is within a predetermined pitch position range or a rate of change in the pitch position that is within a predetermined rate of change in pitch position range. ### Claim 5 (depends on 1) The system according to claim 1, wherein the samples are selected so that each sample of the plurality of samples corresponds a power output of the wind turbine that is within a predetermined power output range or a rate of change in the power output of the wind turbine that is within a predetermined rate of change in power output range. ### Claim 6 (depends on 1) The system according to claim 1, wherein the samples are selected so that each sample of the plurality of samples corresponds to a load on the blade that is within a predetermined load range. ### Claim 7 (depends on 1) The system according to claim 1, wherein the program code causes the system to determine the condition of the wind turbine based on the frequency content of the first spectral density by: comparing the first spectral density to a second spectral density determined for the wind turbine during a second period of time when the wind turbine is known to have been operating normally. ### Claim 8 (depends on 1) The system according to claim 1, wherein the program code causes the system to determine the condition of the wind turbine based on the first spectral density by: defining at least one frequency bin covering a portion of the first spectral density; determining one or more of a maximum amplitude, a mean amplitude, and a minimum amplitude of the portion of the first spectral density covered by the at least one frequency bin; comparing the one or more of the maximum amplitude, the mean amplitude, and the minimum amplitude of the portion of the first spectral density to a respective alarm threshold; and triggering an alarm if the one or more of the maximum amplitude, the mean amplitude, and the minimum amplitude exceeds its respective alarm threshold. ### Claim 9 (depends on 8) The system according to claim 8, wherein the at least one frequency bin is one of a plurality of frequency bins each covering a different portion of the first spectral density, and the determining, comparing, and triggering steps are performed for each of the plurality of frequency bins. ### Claim 10 (depends on 1) The system according to claim 1, wherein the program code causes the system to determine the condition of the wind turbine based on the first spectral density by: defining at least one working-point having a frequency corresponding to a harmonic of a rotation of the rotor; determining one or more of a maximum amplitude, a mean amplitude, and a minimum amplitude for the at least one working-point; comparing the one or more of the maximum amplitude, the mean amplitude, and the minimum amplitude for the at least one working-point to a respective alarm threshold; and triggering an alarm if the one or more of the maximum amplitude, the mean amplitude, and the minimum amplitude of the at least one working-point exceeds the alarm threshold. ### Claim 11 (depends on 10) The system according to claim 10, wherein the at least one working-point is one of a plurality of working-points each corresponding to a different harmonic of the rotation of the rotor, and the determining, comparing, and triggering steps are performed for each of the plurality of working-points. ### Claim 12 (depends on 1) The system according to claim 1, wherein the program code further causes the system to: in response to the first spectral density including a frequency component having an amplitude above a resonance threshold, activate a resonance control algorithm that dampens resonances corresponding to the frequency component. ### Claim 13 A system for monitoring operation of a wind turbine including a rotor having a blade and that rotates in a rotor plane having a plurality of sectors, the system comprising: one or more processors; and a memory coupled to the one or more processors and including program code that, when executed by the one or more processors, causes the system to: receive a time-domain signal indicative of a pitch force being applied to the blade; determine a first spectral density of the time-domain signal by sampling the time-domain signal to generate a discrete time-domain signal, selecting a plurality of samples from the discrete time-domain signal that are within a sampling window, and transforming the plurality of samples from a time-domain to a frequency-domain; determine a condition of the wind turbine based on a frequency content of the first spectral density; and in response to the condition being indicative of a problem with the wind turbine, generate an alarm signal, wherein the sampling window is selected from: a first sampling window corresponding to a wind speed that is within a predetermined wind speed range or a rate of change in the wind speed that is within a predetermined rate of change in wind speed range; a second sampling window corresponding to a pitch position that is within a predetermined pitch position range or a rate of change in the pitch position that is within a predetermined rate of change in pitch position range; and a third sampling window corresponding to a power output of the wind turbine that is within a predetermined power output range or a rate of change in the power output of the wind turbine that is within a predetermined rate of change in power output range. ### Claim 14 A method for monitoring operation of a wind turbine including a rotor having a blade and that rotates in a rotor plane having a plurality of sectors, the method comprising: receiving a time-domain signal indicative of a pitch force being applied to the blade; determining a first spectral density of the time-domain signal by sampling the time-domain signal to generate a discrete time-domain signal, selecting a plurality of samples from the discrete time-domain signal that are within a sampling window corresponding to a first period of time when the blade is in a selected sector of the plurality of sectors, and transforming the plurality of samples from a time-domain to a frequency-domain; determining a condition of the wind turbine based on a frequency content of the first spectral density; and in response to the condition being indicative of a problem with the wind turbine, generating an alarm signal.