Nonlinear position control with feedforward low pass filters in permanent magnet stepper motors

Since the previous position control methods for permanent magnet stepper motors (PMSMs) require states information, the methods was used to obtain the states with the observers and/or the sensors. In using observer case, the bandwidth of observer is determined by PMSM parameters. In using sensor case, since measured states have high frequency noises, low pass filters (LPFs) are used. However, using LPF resulted in phase lag. In this paper, we develop a nonlinear position control with feedforward low pass filters (FLPFs) to improve the position tracking performance in permanent magnet stepper motors (PMSMs). The proposed method consists of position controller and FLPFs. The position controller consists of a nonlinear torque modulation, a commutation scheme, and a Lyapunov-based controller (LBC). To generate the desired torque, nonlinear torque modulation is incorporated. Commutation scheme is developed to generate the desired currents. The LBC is designed in order to guarantee the desired currents. The FLPFs are developed to filter out high frequency noises of measured states and compensate for the phase lag caused by the LPFs. We prove the closed-loop stability using Lyapunov theory. Simulation results validate the effectiveness of the proposed method.