15 Nov 2023
 | 15 Nov 2023
Status: this preprint is currently under review for the journal WES.

Brief communication: Real-time estimation of optimal tip-speed ratio for controlling wind turbines with degraded blades

Devesh Kumar and Mario Rotea

Abstract. Rotor performance is adversely affected by wear and tear of blade surfaces caused, for example, by rain, snow, icing, dirt, bugs, ageing, etc. Blade surface degradation changes the aerodynamic properties of the rotor, which in turn changes the optimal tip-speed ratio (TSR) and the corresponding maximum power coefficient. Below rated wind speed, if a turbine continues to operate at the manufacturer designed optimal TSR, the rotor power could decrease more than necessary unless the optimal TSR is corrected to compensate for blade degradation or other off-design conditions. Re-tuning the tip-speed ratio in these off-design conditions can lead to an improvement in energy capture. In this work, we describe a real-time algorithm to re-tune the tip-speed ratio to its optimal, but unknown, value under blade degradation. The algorithm uses power measurements only and a Log-of-Power Proportional-Integral Extremum Seeking Control (LP-PIESC) strategy to re-tune the TSR. The value of this algorithm is demonstrated using it to command the TSR set-point required by a generator speed control loop that maximizes power generated below rated wind speeds. Comparison of this solution with a baseline controller that uses the optimal TSR for a rotor with clean blades demonstrates improvements in energy capture between 0.5 % and 3.4 %, depending on the severity of blade degradation and the wind conditions. These results are obtained using the OpenFAST simulation tool, the NREL 5-MW reference turbine and the Reference Open-Source Controller developed by the US National Renewable Energy Laboratory.

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Devesh Kumar and Mario Rotea

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wes-2023-144', Anonymous Referee #1, 23 Nov 2023
  • RC2: 'Comment on wes-2023-144', Anonymous Referee #2, 06 Dec 2023
  • AC1: 'Comment on wes-2023-144', Mario Rotea, 19 Jan 2024
Devesh Kumar and Mario Rotea
Devesh Kumar and Mario Rotea


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Short summary
The performance of a wind turbine is affected by blade surface degradation due to wear and tear, dirt, bugs, icing. As blades degrade, optimal operating points such as the tip-speed ratio (TSR) can change. Re-tuning the TSR to its new optimal value can lead to recovery of energy losses under blade degradation. In this work, we utilize a real-time gradient-based algorithm to retune the TSR to its new unknown optimal value under blade degradation and demonstrate energy gains using simulations.