Application of two alternative sliding-mode control approaches to DC servomotor position tracking

Simulation and experimental results are presented for angular position tracking, obtained when applying two different approaches to first-order sliding-mode control (SMC) and a classical positioning scheme to a permanent magnet DC motor with variable inertia and load-torque. The first tracking algorithm proposed is derived by following Slotine's general approach to SMC, and the second, which takes the various alternatives to angular speed control developed by Utkin as starting point, is designed by adopting his particular SMC approach. The former implies the use of pulse-width modulation, whereas its avoidance constitutes the very nature of the latter. The ways in which they deal with the problem of chattering are also very different from one another. The third positioning scheme considered is a classical structure comprising a P position controller cascaded to a PI speed regulator, also including speed command feedforward. To make the comparison fair, it is tuned analytically, through pole placement, to reach the highest bandwidth compatible with well-behaved response. It is demonstrated that any of the two SMC approaches is highly suitable as, in addition to the property of low sensitivity to parameter variations, they both confer a natural ability for tracking to the system.