This paper presents a detailed mathematical model of a rotary steerable drilling system (RSS) that adopts hydro-electromechanical devices to generate bending torque in adjusting the toolface (TF). Key requirements of RSS are to adjust the TF promptly to track the TF command, to maintain the TF in presence of the external disturbances, and to do so during the drilling process. Accordingly, a controller with a fast response time and effective disturbance rejection capability is desired for the RSS. The complexity and non-linearities of the RSS creates additional challenges to the controller design. This paper describes a simple and effective controller scheme that is designed based on the analysis of the system’s dynamics model. By decoupling the disturbances, physical state feedback, and non-linearities, the RSS can be controlled by using a simple and effective proportional-integral-derivative (PID) controller with the desired performance. The simulation results show that the proposed controller is effective against the disturbance and the variations of the parameters.

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