Nonlinear Gain Position Control Using Only Position Feedback for Permanent Magnet Stepper Motors

Abstract

This paper proposes a robust nonlinear position control for permanent magnet (PM) stepper motors. We develop new single-input single-output (SISO) model that consists of position, velocity, and acceleration using a commutation scheme to lump a system function and a external disturbance into a disturbance. An augmented observer (AOB) is designed to estimate the position, velocity, acceleration, and disturbance. Because the disturbance refers to external disturbance, acceleration dynamics, and parameter uncertainties, it is difficult to accurately estimate disturbance without the high observer gain. It may result in the degradation of the position tracking performance. The nonlinear controller is then developed using backstepping to suppress the position tracking error using the input-to-state stability (ISS) property. The key innovation of the proposed method is the design of the nonlinear gain to suppress the position tracking error according to the disturbance estimation error. Thus the use of the high observer gain to accurately estimate the disturbance can be avoided. The proposed control algorithm was experimentally verified using the PM stepper motor control system and can be easily implemented in real-time using position measurements only.