Voltage-fed permanent-magnet stepper motor control via position-only feedback

A robust adaptive nonlinear dynamic controller is designed to achieve practical stabilisation for position tracking error of a voltage-fed permanent-magnet stepper motor. The control design is an output-feedback design that utilises only rotor position measurements. Rotor velocity and stator phase currents are not available for feedback. Furthermore, the only motor parameter that is required to be known is the time constant of the electrical subsystem. Adaptations are utilised so that no other knowledge of motor parameters is required. The proposed controller is a fourth-order dynamic compensator and is robust to load torques, friction, cogging forces and other disturbances satisfying certain bounds. Practical stabilisation of the tracking error is achieved with global boundedness of all closed-loop signals. Furthermore, under the condition that the torque disturbances are locally linearly bounded by a function of rotor position, the designed controller achieves asymptotic stabilisation of the rotor position. These results can also be extended to other classes of motors.