Nonlinear motion control of servo-systems actuated by permanent-magnet stepper motors: analysis, dynamics, and control

Permanent-magnet stepper motors have begun to displace direct current motors in servo-systems and direct drives. The principle of operation of stepper motors is simple, and high-precision state-of-the-art servos are equipped with an incremental encoder because the frequency of the applied voltage must be adjusted with the rotor position. Conventional open loop servo-systems actuated by permanent-magnet motors do not ensure microstepping capabilities, and microstepping features can be achieved through the use of nonlinear robust control laws. We tackle the problem of synthesizing the nonlinear controllers to guarantee the robust tracking and disturbance rejection by applying the Lyapunov-based design framework and admissibility concept. Nonquadratic Lyapunov candidates are used, and nonlinear state and error feedback ensure robustness, tracking, and disturbance attenuation. Analytical and experimental results are reported to validate the explored methodology, and microstepping tracking capabilities have been ensured by a nonlinear controller