Modeling And Controller Design For NCS Over IP Network

Networked control systems (NCS) are distributed control systems which have sensors, actuators, and controllers interconnected by communication networks. NCS is an integrated area of traditional control technology and information technology; it obtained increasing attentions in recent years due to its cost effective and flexible applications. However, the change of communication architecture from point-to-point to this common-bus approach introduces different forms of time-delay uncertainty in the closed-loop system dynamics. Network induced time-delay degrades the NCS control performance and destabilize the system, which makes the system analysis and controller design more difficult and challenging.This thesis proposes a dynamic model to describe time delay and package dropping of data transmitting in NCS based on IP networks. Then the round trip time is introduced to estimate the varying network-induced delay in NCS; based on the estimation, a novel adaptive Smith compensator is proposed to overcome the impact of varying time delay in NCS.The main contents of this thesis are as follows:1. Introduce the concept of Networked Control Systems, and then review the main research results in stability analysis, modeling and controller design in NCS.2. Proposes a dynamic model to describe the time-delay and packets-dropping during data transmission in a NCS. Based on the model, this paper demonstrates the open-loop and close-loop characteristics of a single-input-single-output NCS with a regular PID controller under different network loads.3. Round trip time is introduced to estimate the varying network-induceddelay in NCS and a novel adaptive Smith compensator is presented. Simulation results show that PID controller with the adaptive Smith compensator can overcome the negative impacts of long time delay and the dropped package, the closed-loop system has better performance and robustness than queuing methodology and traditional PID controllers.