Design of a new nonlinear predictive PI controller for cascaded control system applications

Abstract

An alternative to traditional feedback control for two subsystems interacting sequentially, cascade control can boost a control system's performance, especially in the face of disturbances. However, the cascade control technique may not provide an adequate performance to track a set point if the outer loop's time delay is significant. A new predictive proportional-integral (PPI) controller is proposed in this paper to counteract and anticipate the time delay of the outer primary process. By combining the best cascade control and predictive control capabilities, the closed-loop performance can significantly be enhanced by superior disturbance rejection. To achieve higher performance than is possible with linear control, in which the gain of the master-slave controller is fixed regardless of the error signal's magnitude, we investigate the use of nonlinear predictive cascade control. Two examples are provided to show how the suggested controller can be applied and how its structure is an improvement over the status quo in terms of controlling delayed systems. Measurement noise is less of an issue with the new structure compared to the old cascade control scheme. The performance, robustness and effectiveness of the suggested controller for set-point tracking under the influence of a load disturbance have been validated in this research.