A torque estimator-based control strategy for oil-well drill-string torsional vibrations active damping including an auto-tuning algorithm

Considerable compliance of the lengthy oil-well drill string combined with low tool inertia and stick–slip friction between the tool and the rock bed causes notable undesired torsional vibrations of the drill-string electrical drive. In order to attenuate the torsional vibrations and, thus, improve both the quality and the productivity of the drilling process, an automatically tuned active damping control strategy based on drill-string torque estimation is proposed in the paper. The core of the strategy includes a proportional-integral (PI) controller extended with estimator-based drill-string torque feedback loop. Furthermore, an appropriate algorithm that prevents drill-string back-spinning caused by the limited braking power of the power converter is presented. Finally, an auto-tuning algorithm is proposed, which is built around an adaptive Kalman filter-based estimator of drill-string drive natural frequencies. The drill-string control strategy is verified experimentally using a drill string hardware-in-the-loop setup under the laboratory conditions, as well as on an actual oil-drilling rig.

► Drill string compliance, low tool inertia, and friction cause torsional vibrations.
► Load torque estimator-based active-damping speed controller proposed.
► Drive back-spinning caused by motor torque braking limit analyzed and prevented.
► Kalman filter-based algorithm for overall control strategy auto-tuning proposed.
► Adaptive active-damping control strategy tested on HIL setup and in the field.