A discrete-time composite switching control scheme for performance improvement in servo systems

This paper presents a composite switching control (CSC) scheme in discrete-time domain for fast and precise set-point tracking in double-integrator servo systems subject to unknown disturbance. The idea here is to combine the proximate time-optimal servomechanism (PTOS) and the composite nonlinear feedback (CNF) control, using the output position as the only measurable information for feedback. The PTOS is responsible for fast targeting in servo systems when the tracking error is large, while the CNF is to ensure a smooth settling. A reduced-order extended state observer is adopted to estimate the speed signal for feedback and the disturbance for compensation. The proposed control scheme was applied to a permanent magnet synchronous motor (PMSM) position servo system. Simulation and experimental results verify that the proposed control scheme is effective in improving the tracking performance for a wide range of target set-points.