Research On Compensation Algorithm For Time Delays In Networked Control System

Networked Control System (NCS) is a special distributed feedback control system wherein the control loops are closed through real-time network. In the NCS, controller, sensor and actuator nodes exchange information through a shared network. Integrating computer technology, communication technology and control theory, NCS is an emerging technology and becoming future trend of modern industry. Although NCS has the advantages of resources share, reduced system cost, increased system agility and ease of system maintenances, network transfer causes the time delays and data package dropout. That not only makes it difficult to analyze the system, but also cannot apply conventional control theories to NCS directly.This paper studies the modeling of NCS first and presents the models of NCS in different conditions. Main discussion is based on the model in which time delay is less than one sample, data is transmitted in a single packet and there is no data package dropout.When the model is determined, the paper studies the effect on the control performance of NCS caused by time delays. The performance becomes worse when the delay increases, and the system will be unstable if the delay is big enough. In order to improve the control performance, a compensation algorithm for time delays based on time stamp is discussed. This algorithm can compensate only the time delays from sensor to controller. But the complete compensation for delays cannot be realized because the time from controller to actuator cannot be known exactly.Considering a random delay, this paper applies stochastic optimal control theory to NCS. An augmented system of NCS is firstly built up, and an optimal state feedback with Bellman dynamic programming is deduced. And some simulations are done to validate the effectiveness of this algorithm.Finally, we use Ethernet as an example to design a real-time simulation platform of NCS. This platform brings actual network into software simulation. It has the characteristics of NCS and is easy to realize. Experiments of round-trip delay measurement are done and control system simulations are achieved on this...