Research ArticleA novel double loop control model design for chemical unstable processes

•A novel double loop control model is developed for chemical unstable processes.•Inner loop is to stabilize integrating the unstable process and transform the original process to first-order plus pure dead-time dynamic stable process.•Outer loop is to enhance the performance of set point response.•Disturbance controller can enhance the performance of disturbance response.•Three controllers are separately design in the improved scheme.

In this manuscript, based on Smith predictor control scheme for unstable process in industry, an improved double loop control model is proposed for chemical unstable processes. Inner loop is to stabilize integrating the unstable process and transform the original process to first-order plus pure dead-time dynamic stable process. Outer loop is to enhance the performance of set point response. Disturbance controller is designed to enhance the performance of disturbance response. The improved control system is simple with exact physical meaning. The characteristic equation is easy to realize stabilization. Three controllers are separately design in the improved scheme. It is easy to design each controller and good control performance for the respective closed-loop transfer function separately. The robust stability of the proposed control scheme is analyzed. Finally, case studies illustrate that the improved method can give better system performance than existing design methods.