Open-loop Unstable Control Of Delay Systems

This paper summarizes the present research situation on open-loop unstable systems with time delay and several new control algorithms are proposed for unstable systems with time delay.Firstly, a set point weighted PID control method based on fuzzy logic is proposed for unstable system with time delay. The set-point weight of the proportional part of the PID controller is adjusted online by a two-dimensional fuzzy logic controller with error, error derivative as its inputs, so that the system has a better target tracking characteristic.Secondly, IMC-PID controller design methods for unstable systems with time delay are given first. Thus, a simple approach to get parameters of PI-PD controller from parameters of a PID controller is introduced. This method simplifies the problem of selecting the four tuning parameters of PI-PD controller, improves the command tracking performance.Finally, an adaptive IMC-PID control method based on neural network, combining neural network with IMC-PID control method, is proposed for first-order unstable process with time delay. The parameters of IMC-PID controller are tuned online through the neural network self-learning function, which improves the effects of changes of controlled object parameters on the performance of system and enhances the system robustness and adaptive ability.Theoretical analysis and simulation results for unstable systems with time delay show the validity of these control methods.