Application of Robust-Adaptive Sliding Mode Control to the Speed Regulation of a Brushless AC Actuator System

In response to current trends in robotic systems, particularly those relevant to the area of actuators for use in rovers and space manipulators, researchers at Northeastern University have developed a precision prototype of a novel compact Brushless AC/gear-bearing actuator system in collaboration with the National Aeronautics and Space Administration’s Jet Propulsion Laboratory. As part of the preliminary investigations into the functional behavior and potential applications for this device, efforts have been made toward characterizing the open-loop behavior and realizing a control system to provide reliable closed-loop performance. To date, a preliminary open-loop model of the prototype has been developed and several active nonlinearities have been identified. As a first approach toward the closed-loop control of this system, a simplified linear model of the open-loop plant has been adopted which regards all nonlinearities and unidentified sources of error as unknown disturbances and parameter uncertainties. Under this paradigm, there is a clear need for a robust adaptive control scheme to handle both the resulting uncertainties and potential for variations during warm-up, break-in, and regular operational phases. The control technique known as Sliding Mode Control with Perturbation Estimation (SMCPE) is well suited to meet these needs, and is further capable of rejecting the ‘disturbances’ resulting from the model simplification. In this work, the nonlinear and simplified open-loop models are presented, as well as the relevant control theory and SMCPE controller design. Utilizing set-point regulation as a motivating example, results from numerical simulations and real-time control experiments are presented from which it is concluded that SMCPE provides both the desired robustness and disturbance rejection properties required to achieve satisfactory operation of the gear-bearing actuator in a closed-loop speed control mode.