Simplified torque modulated microstepping for position control of permanent magnet stepper motors

In previous methods designed based on field oriented (and/or weakening) control, high performance of current control is required for position control of permanent magnet (PM) stepper motors. This paper proposes a simplified torque modulated microstepping (STMMS) based on singular perturbation theory for position control of the PM stepper motors. Since a two phase frame PM stepper motor model involves slow and fast dynamics, singular perturbation theory is applied to improve the transient response and to reduce the ripple. The torque modulated microstepping method is applied with a simplified current tracking control law obtained from singular perturbed system analysis. Using applied conditions and stability proofs, we find that the proposed control design procedure is simplified. This eliminates the high-bandwidth control efforts for the current tracking required in the previous methods. Furthermore, the STMMS does not use current feedback for the current tracking. It is shown that high performance in the current tracking does not necessarily entail high performance in the position tracking. The proposed method was validated by simulation and experimental results. It is observed that the STMMS not only improved transient response but also reduced ripple in position control over the previous method. Furthermore, the STMMS used the input voltages less than the previous method does.