Robust nonlinear damping backstepping with augmented observer for position control of permanent magnet stepper motors

We innovate an approach to position control, a robust nonlinear damping backstepping with augmented observer for position control of permanent magnet stepper motors (PMSMs). The proposed method requires only position feedback and nominal value of Km over JL among PMSM parameters. We propose new 3rd order single-input single-output PMSM dynamics that consist of position, velocity, and acceleration using a commutation scheme. Instead of separated phase A and B current dynamics, the actual torque dynamics are proposed. The external disturbance, acceleration dynamic, and uncertainty of Km over JL are regarded as a disturbance. In order to estimate the position, the velocity, the accleration, and the disturbance, an augmented observer is designed. A nonlinear damping backstepping is developed to suppress a position tracking error increased as the estimation error of the disturbance is increased. This approach simplifies the design process such that the control algorithm is suitable for real time control. The performance of the proposed method was validated via experiments.