Nonlinear Adaptive Speed Tracking Control for Sensorless Permanent Magnet Step Motors

Assuming that only stator currents and voltages are available for feedback, a nonlinear output feedback adaptive speed tracking control strategy is proposed for a permanent magnet step motor with unknown load torque. It relies on three new theoretical results: the "s-alignment" and "c-alignment" procedures, in which the motor is forced to reach certain known equilibrium points, and an output feedback controller which guarantees uniform asymptotic speed tracking for every initial condition belonging to an explicitly computed domain of attraction. Global exponential convergence is achieved in the case of known load torque. Numerical simulation results show the effectiveness of the proposed solution.