Nonlinear Adaptive Control of a Permanent Magnet Stepper Motor

This paper considers adaptive position control of a permanent magnet (PM) stepper motor using exact linearization via static state-feedback. Physical outputs are chosen in such a way that the resulting closed-loop system is linearized and decoupled. The objective of the adaptive controller for a PM stepper motor is to achieve output tracking between the motor outputs and prescribed reference signals in presence of parameter uncertainties. This will be achieved by incorporating a parameter identification scheme in the nonlinear state-feedback control law. Simulation results are presented and discussed. INTRODUCTION Stepper motors are electromechanical devices that convert input digital pulses into an output analog motion. Permanent magnet stepper motors are simple, low cost, and reliable motors compared with the widely used de motors. Moreover, compared with other control systems, a control system using a .stepper motor has the advantages that no feedback is normally required for either position or speed control and the position error is non-cumulative. However, the performance of a PM stepper motor is limited using open-loop drive. For instance a stepper motor driven in the open-loop mode may fail to follow a pulse command when the pulse train frequency is too high or the inertial load is too heavy. Also, the motor performance tends to be oscillatory in the open-loop mode. The performance of a stepper motor can be improved to a great extent by employing either position or velocity feedback. Closed-loop control of a PM stepper motor is advantageous over open-loop control not only in that the step failure never occurs but also the dynamic behavior is much quicker and smoother [1].