Microstepping With Nonlinear Torque Modulation for Permanent Magnet Stepper Motors

A new approach to position control based on microstepping with nonlinear torque modulation for permanent magnet stepper motors is studied. The proposed method comprises nonlinear torque modulation, a commutation scheme, and a nonlinear current tracking controller. To improve the position tracking performance of conventional microstepping, nonlinear torque modulation is incorporated. Commutation schemes implementing field-oriented control (FOC) and field weakening control (FWC) are developed to construct the desired current profile for torque generation without the use of direct-quadrature (DQ) transformation. The nonlinear controller is developed to guarantee the desired currents derived by the commutation scheme. Our study details the design of FOC and FWC methods based on a two-phase frame without DQ transformation. It is shown that the proposed commutation schemes of FOC and FWC are equivalent to microstepping, which has desired currents with time-varying amplitudes and electrical phase advance. The performances of the proposed methods are validated through simulations and experiments and compared with that of conventional microstepping.