Using Output-Feedback Disturbance Observer to Enhance Disturbance Suppression of PID Controllers for DC-Motor Trajectory Tracking Systems

Abstract

During trajectory tracking, a Proportional-Integral-Derivative (PID) control system for DC motors may exhibit unacceptably large tracking errors when exposed to severe, sudden time-varying disturbance torques.  To address this, a PIDA (Proportional-Integral-Derivative-Acceleration) controller is constructed by augmenting the existing PID controller with an auxiliary controller that estimates and compensates for the disturbance torque directly in the time domain.  The auxiliary controller is derived from an output-feedback disturbance observer, which does not require the disturbance torque to be a polynomial in time, as is usually assumed in existing proposals.  The controller design procedure is simple and could be applied without invoking disturbance observers.  It updates the existing PID gains according to the motor parameters and introduces acceleration feedback.  For practical situations in which equivalent mass moment of inertia is time-varying, a convenient setup is given to facilitate asserting input-to-state stability for the PIDA control system.  Using preliminary recommended values for three design parameters, results from analyses, simulations, and experiments confirm that the tracking error of the PIDA controller is typically 50% of that of the PID controller.  For demanding situations in which sufficient power for driving the motor is available, the tracking error could be decreased much further by tuning the design parameters.  Usually, this can be completed quickly because their influences on the system response are clearly stated.