Using Disturbance Observer for Disturbance Rejection of DC Motor Trajectory Control Systems without Current Feedback

Abstract

We employ the concept of disturbance observer to obtain an auxiliary linear controller that can be augmented to existing linear controllers for the primary purpose of disturbance rejection in DC motor trajectory control systems. Our development is all in state space and does not require feedback of current in motor coils. Uncertain time-varying parameters in the system matrix and the input matrix are allowed, and a simple sufficient condition for asserting robust input-to-state stability of the resulting control system is provided. It appears in numerical simulations that the proposed auxiliary control can reduce magnitude of tracking error and output oscillation due to persistent high-frequency disturbance by approximately 40%. Primarily, it achieves this by reacting quickly to changes in disturbance, not by increasing magnitude of the control signal. This allows its application in existing control systems without need to enlarge capacity of the associated amplifiers.