Scale and Lag Effects on Control of Aerodynamic Power and Loads on a HAWT Rotor

P. J. Moriarty, A. J. Eggers, K. Chaney, W. E. Holley

Research output: Contribution to conferencePaperpeer-review

5 Scopus Citations


The effects of rotor scale and control system lag were examined for a variable-speed wind turbine. The scale study was performed on a teetered rotor with radii ranging between 22.5m and 33.75m. A 50% increase in radius more than doubled the rated power and annual energy capture. Using blade pitch to actively control fluctuating flatwise moments allowed for significant reductions in blade mass for a fixed fatigue life. A blade operated in closed-loop mode with a 33.75m radius weighed less than an open-loop blade with a 22.5m radius while maintaining the same fatigue life of 5×109 rotations.Actuator lag reduced the effectiveness of the control system. However, 50% reductions in blade mass were possible even when implementing a relatively slow actuator with a 1 sec. time constant. Other practical limits on blade mass may include fatigue from start/stop cycles, non-uniform turbulence, tower wake effects, and wind shear. The more aggressive control systems were found to have high control accelerations near 60 deg/s2, which may be excessive for realistic actuators. Two time lags were introduced into the control system when mean wind speed was estimated in a rapidly changing wind environment. Thefirst lag was the length oftime needed to determine mean wind speed, and therefore the mean control settings. The second was the frequency at which these mean control settings were changed. Preliminary results indicate that quickly changing the mean settings (every 10 seconds) and using a moderate length mean averaging time (60 seconds) resulted in the longest fatigue life. It wasdiscovered that large power fluctuations occurred during openloop operation which could cause sizeable damage to a realistic turbine generator. These fluctuations are reduced by one half or more when aerodynamic loads are actively controlled.

Original languageAmerican English
Number of pages9
StatePublished - 1 Nov 2001
Externally publishedYes
Event20th 2001 ASME Wind Energy Symposium - Reno, NV, United States
Duration: 11 Jan 200114 Jan 2001


Conference20th 2001 ASME Wind Energy Symposium
Country/TerritoryUnited States
CityReno, NV

Bibliographical note

Work performed by RANN Incorporated, Palo Alto, California

NREL Publication Number

  • NREL/CP-500-32340


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