Abstract
In this paper, a current-error-based iterative learning controller (ILC) with a nonlinear controller is proposed to improve the position-tracking performance in permanent-magnet (PM) stepper motors. Our proposed method comprises a current-error-based ILC for mechanical dynamics and a nonlinear controller for current dynamics. A nonlinear controller using a variable structure is designed to obtain the field-oriented control. This nonlinear controller can cause the PM stepper motor become a single-input single-output linear system after finite time. The add-on-type ILC with proportional–integral control is designed to improve the position-tracking performance as the systems repeatedly perform the same operation. To increase the rate of error convergence, the current-error-based ILC is designed using the plant inversion method. The condition that the error converges to zero is mathematically derived. Thus, the proposed method can reduce the position-tracking error as the systems repeatedly perform the same operation. Furthermore, the proposed method can be easily plugged into the pre-designed controller. The performance of our proposed method was evaluated via simulations. In simulations, it is observed that the proposed method reduces the position-tracking error compared to the previous methods.
Highlights
Permanent-magnet (PM) stepper motors have been widely used for positioning applications owing to their power density, high efficiency, durability, high torque-to-inertia ratio, and the absence of rotor winding in industrial applications such as antennae, lasers, video cameras, rotary tables, wrapping machines, and robots [1,2]
As the microstepping-based control method with the current controller only considered the electrical dynamics in the PM stepper motor, a position-tracking error during the nonzero velocity period cannot be avoided [4]
A simple and effective position and velocity controller was proposed for field-weakening control (FWC) of PM stepper motors [6]
Summary
Permanent-magnet (PM) stepper motors have been widely used for positioning applications owing to their power density, high efficiency, durability, high torque-to-inertia ratio, and the absence of rotor winding in industrial applications such as antennae, lasers, video cameras, rotary tables, wrapping machines, and robots [1,2]. As the microstepping-based control method with the current controller only considered the electrical dynamics in the PM stepper motor, a position-tracking error during the nonzero velocity period cannot be avoided [4]. Various control methods have been developed to improve the position/velocity control performance in PM stepper motors [5,6,7,8,9,10,11,12]. An enhanced nonlinear damping controller was proposed to reduce the position-tracking error [10]. A current-error-based ILC with a nonlinear controller is proposed to improve the position-tracking performance of the PM stepper motors. The proposed method can reduce the position-tracking error as the systems repeatedly perform the same operation.
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