Sensorless Rotor Velocity Tracking Controller for the Permanent Magnet
Stepper Motor


In this paper, we present a sensorless rotor velocity tracking controller for the full order, nonlinear dynamic model of the permanent magent stepper motor. We design a volatge control strategy in conjunction with an open-loop position estimation scheme that achieves global exponential rotor velocity/phase current tracking and only requires phase current measurements. Experimental results are included to demonstrate the efficacy of the proposed algorithm.

Research Objective:

Our objective is to design a sensorless, singularity free controller for the full-order, nonlinear dynamic model of a stepper motor, to obtain rotor velocity tracking.The control algorithm does require measurement of stator currents, however, to estimate the rotor position and velocity.


The overall control strategy is formulated at the voltage level, the physical input to an electric motor. However, as characteristic of the integrator backstepping approach, intermediate or embedded control signals are formulated. The integrator backstepping approach will require that a control signal is generated for the output subsytem, i.e., the rotor velocity in the mechanical subsytem. Next, this control signal is propagated back through the connected subsystems, the electrical subsystems, until a controller is formulated for the system inputs, the input voltages.Following this approach, we develop a desired torque trajectory for the mechanical subsystem. Specifically, this trajectory would ensure rotor velocity tracking if applied directly to the mechanical subsystem. Subsequently, we design the desired phase current trajectories to ensure that the desired torque is delivered to the mechanical subsystem. The stator voltage control inputs are then designed to guarantee that phase current tracking is achieved. Lastly, a Lyapunov-like stability analysis is performed to examine the stability of the overall closed-loop system.

Some Experimental Results:

Select and click to view some of the experimental plots:


For more information concerning this research, please refer to the following publication:

A. Behal, M. Feemster, D. M. Dawson, and A. Mangal, "Sensorless Rotor Velocity Tracking Controller for the Permanent Magnet Stepper Motor'', Proc. of the IEEE Conference on Control Applications, Anchorage, AK, pp. 150-155, September 2000.