The Research On Control Strategy Of Parallel Cascade Delay Process

In industrial process control,complex or more advanced control systems are required due to some special requirements in the production process.The cascade control system is a common and complex control system,which is widely used in chemical processing industry to control temperature,flow and pressure.Cascade control system can be divided into series cascade control and parallel cascade control according to the structure of the controlled process.At present,most of the cascade control introduced in the literature is series cascade control,while parallel cascade control is rarely mentioned.This paper studies the existing problems in parallel cascade control system.The main contents include the following three aspects:(1)For the tuning of controller parameters in parallel cascade delay process,the maximum sensitivity internal mode PID tuning method is applied to the parallel cascade control system.The method determines the adjustable parameters of the controller according to a given sensitivity index,and overcomes the blindness of trying to continuously select parameters by experience.(2)For the first-order inertia time-delay process,a two-degree-of-freedom internal model control strategy is studied.This method can decouple the set-point tracking characteristic and disturbance rejection characteristic of the system,and the effectiveness of the strategy is verified by simulation.(3)For the unstable time-delay and integral time-delay process,a twodegree-of-freedom Smith predictor control strategy is studied.The purpose of weakening the process time lag is achieved by introducing a Smith predictor into the main loop.And the main loop adopts a two-degree-of-freedom control structure,which enables the control system to have good set-point tracking characteristics and disturbance rejection characteristics at the same time.