Research On Two-degree-of-freedom PID Control Algorithm For Industrial Process

Proportional-integral-derivative(PID)control has been applied widely in automatic control fields since it possesses many merits to satisfy most control requirements in practice.However,due to the fact that large time delays exist in the production processes,which complicates the relevant controller regulation.Hence,there are challenges for the pure PID control strategies.It is known that the ensemble control performance of the general controller may be unsatisfactory,so that it is difficult to achieve the accurate control in industrial process control.The goals of the two-degree-of-freedom(2-DOF)control are to optimize the performance indexes of set-point tracking and disturbance rejection simultaneously by using different independent controllers and obtain the desired control effects.At present,the proposed 2-DOF control method still has many problems to be solved in terms of controller structure,parameter tuning and control performance.Based on such backgrounds,it is necessary to develop the modified 2-DOF control approach in which the aforementioned issues are settled.This paper studies the analytical design method of 2-DOF-PID controller for representative processes in the field of industrial control.The designed controller has simple structure and convenient parameter setting,and the superior set-point tracking and disturbance rejection performance can be gained simultaneously by adjusting two parameters.The effectiveness of the proposed algorithm is verified through simulations.The detailed work of this paper can be divided into three parts;The first part studies the design of a 2-DOF internal model PID(2-DOF-IMC-PID)controller.For the stable time-delay process,the influence of the interaction between control loops is regarded as the interference to the loop,then the controller is deigned by combining the 2-DOF structure with the internal model control(IMC)theory.Meanwhile,the all-pole approximation method is employed for the time-delay,and different parameter tuning methods are adopted for different processes to reduce the calculation amount.The simulation results show that the set-point tracking and disturbance rejection performance are both satisfying for the proposed approach.The second part is the design of a unified 2-DOF control structure for the representative unstable first-order time-delay system in chemical processes.The designed controller is consist of an internal stabilization controller,a set-point feedforward controller and a feedback controller.The structure of the controller is simple,and the acceptable control performance is also achieved for the unstable processes.The third part is the research of a 2-DOF Smith predictive control method by improving the Smith control structure and synthesizing the IMC theory.The set-point tracking and disturbance rejection are decoupled in the proposed scheme,and better control performance is acquired The developed algorithm is simple and convenient in parameter tuning.