Enhancing Position Tracking of Hybrid Stepper Motors Using Lyapunov-Based Current Controllers

This paper presents a vector control (VC) scheme with a position sensor designed for hybrid stepper motors (HSMs). The proposed scheme consists of three main components: a current tracking controller, a position controller, and a phase reference current generation algorithm. Based on the principle of optimal current control, the algorithm calculates the minimum target phase current required to generate the desired torque under transient conditions by evaluating the stator flux. This approach eliminates the need for coordinate transformations typically used in conventional vector control methods, as the current tracking is performed directly in the stator reference frame. A current controller in the stator reference frame is designed using the Lyapunov stability theory, featuring a simple structure with only one adjustable control parameter. Additionally, a nonlinear torque modulation algorithm is employed for position control. Closed-loop stability analysis demonstrates that the proposed scheme is robustly stable. Both simulation and experimental results confirm that the position tracking performance of the HSM is significantly improved under the proposed control scheme.