Design of Networked Control Systems and Global Web-based Control Laboratory
This thesis mainly focuses on two Internet based control applications. One is a networked control system (NCS) where the control loop is closed through the network. The other is the Networked Control System Laboratory (NCSLab) which is a global web based remote experimentation platform. The contribution in the first part of the thesis relates to the networked predictive control (NPC) which was first introduced by Liu et al. (2004). In this method, the controller uses the model predictive approach to predict a future control sequence and send it to the plant in a network packet. The plant side receives this packet and then determine the appropriate control signal to apply to the actuator according to the time delay measurement. This method is innovative and works well in theory, but it has two deficiencies in practical applications. The first deficiency is that it needs synchronization between the controller and plant side to measure the individual forward and feedback channel time delays and this is very hard to achieve on the Internet. In this thesis, a round-trip NPC is proposed in which the predictive calculations and signal selections are based on the round-trip delay. The measurement of the round-tip delay is achieved using the plant side clock only, so that the need for synchronization is avoided. The second deficiency is that the mathematical model has to be accurately known. Otherwise the accuracy of the predictive calculation is affected, which may result in a degraded control performance. An event-driven NPC scheme is introduced to solve this problem. In this scheme, the selection of the appropriate control signal is not based on the time delay measurement but on the previous system output. This method can compensate for the effect of model uncertainty, which has been verified by both simulations and real-time experiments. Some experiments carried out on other NPC schemes are also reported on in this thesis. They are the NPC in state-space form and nonlinear NPC. These methods expand the use of NPC methodology. The second part of the thesis describes the design and implementation of the Networked Control System Laboratory. The NCSLab is based in the University of Glamorgan but its test rigs are diversely located in four Institutions from both the UK and China. In order to manage these test rigs from different places, a four layer structure (Central Server/Regional Server/Sub-Server/Test Rig) is adopted. The four layers are integrated into one system via the Internet. In order to deliver the remote experimentation to the users, a web-based user interface is designed. It provides great flexibility to the users such as remote monitoring, remote tuning and remote control algorithms. The implementation of the user interface (UI) heavily adopts the AJAX technology, so the remote experiments can be conducted inside the web browsers without installing special plug-ins. In order to show how the NCSLab works, two examples are given in the thesis.
Networked Digital Library of Theses and Dissertations