Performance evaluation of marker tracking method for rotational speed measurement of wind turbine blades

• A marker tracking method for rotational speed measurement of wind turbine blades. • A relative error mostly within ±0.5 % achieved under different test conditions. • Better performance in response time compared to correlation-based methods. Rotational speed is one of the most important operating parameters of wind turbines. It is not only related to the power output but also the operating status of mechanical parts. To measure the rotational speed of wind turbine blades, image processing methods demonstrate the advantages of non-contact measurement and low maintenance requirements. However, it is still challenging to achieve instantaneous rotational speed with high accuracy. In this paper, a new marker tracking method is proposed and implemented to measure the instantaneous rotational speed of wind turbine blades. Experiments were conducted on a wind turbine test rig with different camera settings, camera positions, and lighting conditions to assess the performance of the proposed method. Results show that the maker tracking method achieves a relative error mostly within ±0.5 % and a normalised standard deviation below 0.35 % with the typical speed range of wind turbine blades from 5 rpm to 30 rpm. Compared with the existing image correlation and frequency analysis method, the maker tracking method produces accurate measurement results and faster response.