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Microstepping with nonlinear torque modulation for position tracking control in permanent magnet stepper motors

A new approach to position control based on microstepping with nonlinear torque modulation in permanent magnet stepper motors is explored in this paper. The proposed method consists of nonlinear torque modulation, a commutation scheme, and a nonlinear current tracking controller. Previous microstepping control methods that guarantee the desired currents have relatively large position tracking errors due to their mechanical dynamics. A method of nonlinear torque modulation is designed to solve this problem. We propose a commutation scheme that is equivalent to microstepping in which the desired currents have time-varying amplitudes with π over 2 electrical phase advance. The nonlinear controller in the electrical dynamics is developed to guarantee the desired current derived by the commutation scheme. The proposed control method is in the form of field oriented control (FOC) even though direct quadrature transformation so that the zero direct current is kept to maximize the torque. Thus, the efficiency of the energy consumption of the proposed method is better those that of previous microstepping control methods for guarantees of the desired currents. The performance of the proposed position control method was validated through simulations.