Yaw control for floating wind turbines

Activity: Examinations and supervisionSupervisor activities

Description

This MSc thesis deals with the development of a representative yaw controller and its implementation to both bottom-fixed and floating wind turbine simulations. This yaw con- troller approach includes two operating modes that make use of moving averages of the misalignment error to determine the commencement and the completion of the yawing sequence. Two different averaging filters are compared, while a feature to account for small direction changes that can last for long time periods is developed (second operat- ing mode). The defined controller is evaluated against simple direction changes, where the time windows are examined with respect to the response of the yaw sequence. The yaw controller is then used in bottom-fixed and floating simulations to capture the response of the IEA 15MW RWT in varying wind speed and direction conditions. Mea- surements from a met mast are obtained and 1 hour samples are selected based on high standard deviation of the wind direction, representing a realistic wind input.
The response of the implemented control system showed that it can effectively align the rotor with the mean wind direction, eliminating the yaw offset. The selection of the time windows in the averaging filter is therefore considered sufficient with respect to not triggering a yaw action too early and not overshooting after reaching zero yaw error. A comparison between the bottom-fixed and floating simulations revealed higher moments in the tower-base for the floating application. The difference is attributed to the platform’s motion, which increases the gravitational moment-arm around the tower-base position. Blade moments are found identical, while yaw-bearing moments showed minor differences, mainly in the pitch direction, showing that the yaw movement of the rotor is not inducing higher yaw-loads in the floating case. The floating simulations also revealed that the tuning of the default pitch controller is insufficient for the floating case, leading to pitch instability above rated wind speeds. An analysis of different potential settings resulted in a new tuning that alleviates the instability, although making the controller slower and introducing uncertainty in the results obtained.
PeriodJan 2023Jun 2023
ExamineeCharalampos Themistokleous
Examination held at
Degree of RecognitionNational

Keywords

  • Floating wind turbines
  • wind turbine loads
  • yaw controller
  • IEA 15 MW