Single-step auto-tuning of external active damping control strategy for a drill-string speed-controlled electrical drive

This paper presents a single-step automatic tuning procedure and an estimator of key parameters of the drill-string system used in deep drilling applications. It is aimed at precise tuning of an external vibration suppression system based on speed control loop of the drilling electrical drive tuned for "stiff" motor-side speed control (the so-called speed source behavior), and the external drill-string torque feedback used for torsional vibration active damping. The automatic tuning procedure is carried out for the case when the drill-string and drill-bit are hoisted from the bottom of the well and the drilling electrical drive briefly enters the limit cycle oscillatory behavior under stiff speed control. The proposed auto-tuning system features a suitable control-oriented process model of the torsional oscillator and a modified-mixer phase detector phase locked-loop equipped with adaptive second-order generalized integrator (band-pass filter) for the extraction of key features of the drive resonance mode. The overall control system design relies on the so-called damping optimum criterion which guarantees a desired level of closed-loop system damping. The functionality of the proposed adaptive control system with automatic tuning of the control strategy has been systematically verified by means of comprehensive simulations, and the effectiveness of the drill-string parameter estimator has also been confirmed using the previously recorded field data to illustrate its robustness in the presence of realistic measurement noise.