The Research On The Control System With Time Delay

In the industrial process, there is a widespread phenomenon of time-delay. Due to the existence of time-delay, the plants with time delays can not reflect the disturbance of the system in time, which results in significant overshoot, makes the control system unstable, and adjusts too long. For the design and control of the system it brings great difficulties. Therefore, In the industry control area, the control process with time-delay has always been an important subject to study.Commonly,using the ratio of the time delay 0 and time constant T to estimate the influence of the time delay.whenθ/T < 0.3 ,called common process with time delay;whenθ/T > 0.5 ,called process with a long time delay. Here , the general control methods are hard to work, a variety of compensation methods or advanced control methods should be used to reduce or compensate for the disadvantage effects because of time delay.The traditional control methods,such as:PID, self-tuning control method, can not make the satisfying control effect.Since 50's,when Smith predictive control has been proposed, there have been a large number of research results for time delay, which are typical algorithm including PID algorithm, Dahlin algorithm and internal model control algorithm, as well as intelligent control algorithm including fuzzy control, neural networks, etc. Although the majority of control algorithms have better effect in simulation, there are more difficulties in actual industry.This paper mainly discussed control method for time delay,and compared four kinds of improved Smith.Secondly,doing research on the internal model control with good robustness and good anti-jamming ability.For the unstable process with time delay in industry, This paper also introduced an improved internal model control(IMC)method.For the time delay of the plant,discussing four kinds of approximation method,such as: first-order Pade approximation, second-order Pade approximation, second-order non-symmetric Pade approximation and all-pole approximation, and compared them both in open-loop and closed-loop .using the all-pole approximation in IMC-PID formula.Combination of tradtional control method and fuzzy method to approach time-delay system, study the adaptive fuzzy PID control and fuzzy-Smith control methods with an integral part. In order to avoid the unstability or oscillation.