Instantaneous Rotational Speed Measurement of Wind Turbine Blades using a Marker-Tracking Method

Rotational speed of wind turbine blades is an important parameter reflecting the operating and structural health conditions of wind turbines. Traditionally, the rotor speed is measured using inertial measuring units (IMUs). The biggest issue with IMUs is that the measurements drift over time and require constant calibration. This paper presents a direct way of measuring the instantaneous rotational speed of wind turbine blades using a camera and a marker-tracking method. The proposed measurement method is assessed by conducting a series of simulation experiments under different conditions - fixed speed, stepped varying speed, and linear varying speed. Results demonstrate that when using a camera with a frame rate of 30 fps (frames per second), the marker-tracking method yields a relative error within ±0.5% at the speed between 5 to 30 rpm (revolutions per minute). Compared to the image-correlation method, the marker-tracking method provides better results in terms of accuracy and reaction time, especially under varying speed conditions.