Robust control of permanent magnet stepper motors using only rotor position and velocity

In this paper, a robust adaptive nonlinear dynamic controller is designed to achieve practical stabilization for position tracking error of a voltage-fed permanent-magnet stepper motor. The control design is an output-feedback design that utilizes only rotor position and velocity measurements. Currents are not available for feedback. Adaptations are utilized so that no knowledge of motor parameters is required except for an upper and lower bound on the time constant of the electrical subsystem. Furthermore, these bounds are unnecessary under the assumption of sinusoidal flux distribution. The proposed controller has dynamic order three and is robust to load torques, cogging forces, and other disturbances satisfying certain bounds. The controller also guarantees asymptotic stabilization if the torque disturbances can be neglected and asymptotic set-point regulation in the sinusoidal flux distribution case. These results can also be extended to other classes of motors.