Predictor-based disturbance rejection control for sampled systems with input delay

To cope with input delay involved with many industrial system operations, a predictor-based disturbance rejection control (PDRC) scheme is proposed in discrete-time domain for sampling implementation, which can be generally applied for open-loop stable, integrating and unstable processes. An extended state observer (ESO) is introduced to estimate not only the deterministic system state but also the generalized disturbance composed of system uncertainties and external disturbance, based on a filtered Smith predictor to estimate the delay-free output response. Correspondingly, by specifying the desired poles of ESO and the closed-loop control system, the ESO gain vector and the PDRC controller are analytically derived. A notable merit is that there is a single tuning parameter in the proposed ESO, output predictor, and the PDRC controller, which can be monotonically tuned to achieve a good trade-off between the prediction (or control) performance and its robustness. A sufficient robust stability condition of the closed-loop system is established in terms of linear matrix inequality (LMI). An illustrative example from the literature along with an application to the temperature control system for a crystallization reactor is used to demonstrate the effectiveness and advantage of the proposed control method.